Pulsed electrochemistry: A pathway to enhanced electrocatalysis and sustainable electrosynthesis

Wei Chen; Yuanqing He; Yuqin Zou; Shuangyin Wang

doi:10.1360/nso/20240047

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Volume 3 / No 6 (2024)

Natl Sci Open, 3 6 (2024) 20240047

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Special Topic: Key Materials for Carbon Neutrality

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Review

Issue		Natl Sci Open Volume 3, Number 6, 2024 Special Topic: Key Materials for Carbon Neutrality


Article Number		20240047
Number of page(s)		37
Section		Materials Science
DOI		https://doi.org/10.1360/nso/20240047
Published online		28 October 2024

National Science Open 3: 20240047, 2024

REVIEW

Pulsed electrochemistry: A pathway to enhanced electrocatalysis and sustainable electrosynthesis

Wei Chen, Yuanqing He, Yuqin Zou^* and Shuangyin Wang^*

State Key Laboratory of Chem/Bio-Sensing and Chemometrics, College of Chemistry and Chemical Engineering, Hunan University, Changsha 410000, China

^* Corresponding authors (emails: yuqin_zou@hnu.edu.cn (Yuqin Zou); shuangyinwang@hnu.edu.cn (Shuangyin Wang))

Received: 5 September 2024
Revised: 19 October 2024
Accepted: 24 October 2024

Abstract

This review delves into pulsed electrochemistry, a new technique that is becoming an essential tool in the field of electrocatalysis and electrosynthesis. Unlike traditional potentiostatic methods, pulsed electrochemical approaches provide dynamic control over catalytic reactions, leading to better selectivity, efficiency, and stability across a range of applications. We examine the underlying theory of pulsed electrocatalysis and explore how waveform characteristics, potential, and pulse time affect catalytic processes. The review pays special attention to its application in key areas such as organic electrosynthesis, CO₂ reduction reactions, and water splitting, explaining how pulsed techniques improve reaction conditions to boost yields and selectivity. Meanwhile, we focus on the technique’s impact on catalyst surface modulation, managing local interface environments, and addressing issues like catalyst deactivation and mass transfer limitations. Ultimately, this review highlights the transformative potential of pulsed electrochemistry in driving various electrocatalysis and electrosynthesis applications and sets the stage for future exploration and optimization of these electrochemistry systems.

Key words: electrocatalysis and electrosynthesis / pulsed electrochemical / local interface environments / mass transfer limitations

© The Author(s) 2024. Published by Science Press and EDP Sciences.

This is an Open Access article distributed under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

INTRODUCTION

As science and technology evolve, the material wealth of modern human society has greatly increased, primarily due to the extensive production of modern chemical entities such as fuels, fertilizers, plastics, paints, and pharmaceuticals [1,2]. It is important to note that around 80% of global energy needs are met by fossil fuels [1]. This reliance on non-renewable resources extends to the materials used in industrial production, which are mainly derived from fossil fuel-based refining processes [3]. However, this dependence is unsustainable due to the finite nature of fossil fuels, their high energy demands, and their negative impact on the environment [4–6]. Therefore, it is crucial to develop renewable energy alternatives and sustainable feedstocks for diversified production. In recent years, there has been a shift towards green and sustainable industrial production frameworks, which have received significant attention and undergone considerable development. In the emerging energy production models, several renewable energy sources exist, such as tidal, solar, wind, and hydroelectric power. A wide range of raw materials such as water, biomass, recycled waste, and atmospheric gases like CO₂ and N₂, are being utilized to create renewable products and reduce dependence on fossil fuels [1,2,7–9].

Electrocatalysis and electrosynthesis are considered to be environmentally friendly and sustainable methods for producing valuable fuels and chemicals. These methods have gained significant attention in recent years. Electrochemical technology allows for the creation and transformation of chemical substances through the production of highly reactive free radicals or intermediates, which can be achieved by adjusting electrochemical potential under mild conditions [10,11]. This approach has significant potential to modulate oxidation-reduction reactions and could replace or modify traditional fossil fuel refineries [2]. Although there has been progress made in electrocatalysis, its transition from a theoretical concept to an industrial application presents significant technical challenges. These challenges include achieving low over-potentials, high current densities (more than 100 mA·cm⁻²), high product selectivity, and Faradaic efficiency greater than 90%. Additionally, it is crucial to ensure that the stability performance is robust and lasts for more than 100 hours [12]. Research primarily concentrates on developing innovative electrocatalysts, optimizing reactor structure, and adjusting the microenvironment for better electrocatalytic performance [12–14]. Extensive research is being conducted to devise high-performance catalysts that are crucial in influencing electrocatalytic efficiency. The researchers are basing their work on the classical Sabatier principle of heterogeneous catalysis, and utilizing advanced characterization techniques and theoretical analyses to tailor the geometrical and electronic structures of electrocatalysts for optimal performance [15–17]. Despite advancements in electrocatalysts, their effectiveness remains below optimal due to several issues such as instability, complex design and preparation processes, and limited catalytic activity. Since electrocatalytic reactions happen at the interface between the catalyst and the electrolyte, the microenvironment at this interface plays a critical role. Therefore, significant research has been conducted to adjust this microenvironment, such as modulating interfacial pH, charge distribution, and mass transport [14,18–21]. Controlling these variables is challenging due to their complex mechanisms of action, which require further investigation.

In an electrocatalytic reaction, the potential or current applied, along with the catalyst and reaction medium, plays a crucial role. Currently, most electrochemical processes use a constant potential or current electrocatalyst (CE) to enable chemical transformations [22,23]. In these systems, the potential or current is usually kept constant at a specific value during the CE process, which is customized for the specific electrochemical reaction being targeted. However, electrocatalysis is a dynamic process that involves fluctuations in substrate concentration, intermediates, adsorption species, and the physical and chemical states of the catalysts [18,24]. The electrocatalytic process can become unpredictable due to various variables, which can ultimately reduce the reaction’s stability and catalytic efficiency. However, using pulsed potential or alternating current electrocatalysis (PE) can help regulate electrolytic parameters, resulting in a significant improvement in catalytic performance [25–28]. This straightforward yet effective method shows great potential in advancing electrocatalytic systems.

Pulsed electrocatalysis technology, initially introduced by Bowden and Rideal in 1928, aimed at measuring the actual surface area of electrode materials [29]. By 1933, Butler and Armstrong had expanded pulse durations into the sub-millisecond domain, employing this technique for kinetic measurements [30]. Following these developments, the pulse techniques played an important role in the electrochemical kinetics studies with the introduction of the dropping mercury electrode [31]. In the past, researchers were curious about the pulsed electrocatalysis phenomena and decided to explore the use of alternating current in the electrolysis of organic compounds. In the 1930s, Shipley and colleagues [32] conducted studies to compare the results of direct current electrolysis versus alternating current electrolysis on various organic substances. However, the findings were inconclusive and the yields were slightly lower than those achieved with direct current electrolysis. Over time, as technology advanced, the scope of pulse technology applications expanded to include chemical composition analysis [33,34], sensing [35,36], biomedical applications [37,38], and electrodeposition [39–41]. Unlike constant current or potential electrolysis, pulsed electrocatalysis, characterized by intermittent energy supply, induces unique electrochemical behaviors. Therefore, research on pulsed electrolysis is becoming increasingly hot recently (Figure 1).

Figure 1

Summary of pulsed electrocatalysis-related literature publications and citations in recent years. Data from Web of Science as of September 2024.

In this review, we explore the key factors involved in the pulsed process and their impact on electrocatalysis (as shown in Figure 2). These factors primarily pertain to the catalyst and its immediate surface environment, which includes changes in valence state and surface morphology, deposition or dissolution of the catalyst, fluctuations in surface pH, modifications to the electrical double layer (EDL), changes in the diffusion layer’s species, adsorption and desorption dynamics of intermediates on the catalyst surface, as well as limitations in species mass transfer. These factors offer opportunities for the regulation and refinement of electrocatalytic reactions. Consequently, pulsed technology has gained significant attention in the fields of electrocatalysis and electrosynthesis, including organic electrosynthesis [22,42–45], water electrolysis [27,46,47], carbon dioxide reduction (CO₂RR) [19,25,48], nitrogen reduction (NRR) [26,49–51], oxygen reduction (ORR) [52–55], and the element extraction and contaminant mitigation [5,28,56,57]. This paper provides a comprehensive review of recent literature on pulsed processes, categorizing and identifying gaps in their application. It concludes by discussing the challenges and potential advancements in pulsed electrocatalysis.

Figure 2

Schematic illustration of the application of pulsed electrochemistry for enhancing electrocatalysis and sustainable electrosynthesis.

PULSED ELECTROCATALYSIS (PE) PROCESS

Pulsed electrocatalysis is different from constant potential or current methods. In pulsed electrocatalysis, the potential or current fluctuates periodically, providing various parameters to adjust the pulse profile. As catalytic reactions depend on time and potential, these adjustments can have a significant impact on catalytic activity. This section focuses on the application of pulse parameters and their effects on catalytic processes.

Waveforms of pulsed electrocatalysis

In implementing pulse electrolysis, selecting an appropriate pulse waveform is pivotal, determined by the pulse’s potential or current and its period or frequency. Typically, the pulse profile manifests in four primary forms prevalent in power electronics circuits, including sinusoidal-shaped, sawtooth, triangular, and square pulses (Figure 3a) [58].

Figure 3

(a) Demonstration of the different current waveforms. (b) The maximal ripple factor of different current waveforms. (c) Hydrogen generation efficiency as a function of amplitude. j_DC is the mean current density (offset), and f is the frequency of the waveform. (d) Hydrogen generation efficiency as a function of frequency at different ripple factors. The graph represents the results obtained with square waveform. (Reproduced from Ref. [58]. Copyright©2017, Springer Nature Limited).

Presently, sinusoidal pulses are primarily utilized in impedance studies of electrocatalytic processes, sawtooth pulses in examining potential increment effects on reaction kinetics, and triangular pulses for analyzing potential change rates on reaction kinetics due to their linear increase and decrease regions [5,59,60]. Square wave pulses, due to their simplicity and control, are predominantly used in pulsed catalytic reactions, particularly for potential pulses. This preference stems from the ease of ensuring catalytic reaction selectivity and controlling the entire process, alongside elucidating reaction mechanisms. Additionally, square wave pulses generate smaller capacitive currents and are more manageable and reproducible during experiments [5]. While the impact of varying waveforms on catalytic reactions remains underexplored, the focus has predominantly been on the implications of pulse potential or current, duration, and frequency on catalytic efficiency.

Dobo et al. [58] use the amplitude-dependent ripple factor (r) instead of amplitude as a parameter for different pulse waveforms. The r_max represents the maximal ripple factor of each waveform, as shown in Figure 3b. They demonstrated that any deviation from steady direct current (DC) causes efficiency loss, the efficiency loss of unsteady DC (pulse current) depends on three main factors: ripple factor, frequency, and mean current density (Figure 3c and d). The square waveform shows the lowest H₂ hydrogen generation efficiency due to its highest ripple factor compared to triangle, sine or sawtooth waveforms. Also, the authors state that hydrogen production efficiency can be improved by increasing the frequency or decreasing the current density for the same ripple factor. Similarly, Wang et al. [52] found that square waveform electrolysis has lower H₂O₂ production yields and higher energy consumption than triangle or sine waveform electrolysis. However, the authors did not further investigate the mechanism of the effect of these three pulse waveforms on electrocatalysis. Studies on the mechanism of the effect of different waveforms on the pulsed electrolysis process are still very limited and insufficiently in-depth, and need to be further investigated and improved.

Potential of pulsed electrocatalysis

The selection of potential is a paramount factor in electrocatalytic processes, applicable to both constant and pulsed electrocatalysis. A typical square wave pulsed electrocatalytic waveform generally comprises an anodic and a cathodic pulse potential. The anodic potential, typically more positive, is not necessarily related to redox processes and serves as the working potential in electrocatalytic oxidation reactions. Conversely, in reduction reactions, the cathodic potential functions as the working potential. For instance, in water electrolysis, the oxidation potential must surpass 1.23 V_RHE, whereas for CO₂RR (Copper as the catalyst), the reduction potential typically hovers around −0.8 V_RHE.

However, in practical research, selecting potentials is a multifaceted consideration involving electrolytic properties like selectivity, Faraday efficiency, and catalyst stability. Engelbrecht et al. [61] for example, assessed the Faraday efficiencies of various CO₂RR products at different reduction potentials, finding that a reduction potential of −1.6 V vs Ag/AgCl could significantly suppress hydrogen precipitation while yielding a maximum FE_C2H4≈23%. Similarly, the anodic potential in pulsed electrocatalytic CO₂RR is vital for controlling Cu(Ⅰ) production, a key species in multi-carbon product generation. Arán-Ais et al. [62] determined that Cu(Ⅰ) content on the catalyst surface rises with increasing oxidation potential, with the final choice of anodic pulse potential being contingent upon the properties of carbon dioxide reduction.

In essence, the selection of potential in research involves considering changes in the catalyst, regulation of surface pH, EDL charging and discharging, diffusion layer substance movement, and surface species adsorption and desorption. These factors collectively exert substantial influence on the catalytic reaction, necessitating a thorough evaluation of different elements in potential selection.

Pulse time parameters of pulsed electrocatalysis

Pulsed electrocatalysis aims to catalyze reactions in non-equilibrium states, influenced not just by the applied potential but also by pulse time parameters like period, frequency, and duty cycle [5]. In cases where pulse time is prolonged, the electrolysis approaches the behavior of constant potential/current methods.

A typical CO₂RR reduction current is used to delineate phases within a pulse cycle. Potential shifts lead to a significant non-Faradaic current from EDL charging and discharging. This current declines exponentially as the bilayer stabilizes [11]. The EDL’s behavior, shaped by catalyst characteristics, electrolyte composition, and applied potential, affects the ion distribution on the surface, impacting the microenvironment and the catalytic reaction. Typically, bilayer reorganization completes in milliseconds. In the second stage, as non-Faraday currents diminish, Faraday currents signaling redox reactions begin, initially not kinetically limited but eventually reaching a steady state influenced by mass transfer and catalyst changes [11]. Based on this, Shimizu et al. [63] found that when electrolyzing water using the ultra-short pulse voltage method, the limiting mechanism for the entire reaction is the rate of electron transfer rather than the diffusion-limiting mechanism in conventional water electrolysis. This is due to the fact that rapid potential changes do not allow the formation of a stable double electric layer and diffusion layer on the electrode surface. Similar conclusions were obtained when wang et al. [52] used pulsed potentials for the oxygen reduction reaction to obtain H₂O₂. However, Dobo et al. [64] demonstrated that lower electrolysis frequencies and higher amplitudes increase the rate of gas production from electrolyzed water. Over extended periods, Faraday currents decrease due to catalyst alterations (like degradation or deactivation) and substrate depletion. This process is similar to anodic pulses. Optimal pulse timing is often chosen in the intermediate region to balance efficient electrolysis and avoid rapid degradation or inefficiency from too brief or prolonged pulses, respectively.

In conclusion, selecting appropriate pulsed electrocatalytic parameters is vital. The relationship between electrocatalytic performance and pulse characteristics like profile, duration, and potential is crucial, guiding future research in pulsed electrocatalysis.

APPLICATIONS FOR PULSED ELECTROCATALYSIS

Organic electrosynthesis

Organic electrocatalytic synthesis (OES) is termed as “green synthesis” for its comparative advantages over traditional methods, including higher selectivity, reduced side reactions, better energy efficiency, and less use of toxic substances [42,44,65–67]. Despite these benefits, OES faces challenges like limited mass transfer, electrode passivation, low current densities, and complex reaction pathways [68,69]. To address these issues, pulsed electrocatalysis has emerged as a viable approach to address these issues, notably by preventing catalyst deactivation and refreshing the local interface environment, thereby enhancing the performance of organic electrocatalysis [11,12].

The stability of the catalyst

In organic electrocatalysis, catalyst deactivation typically stems from toxic substance accumulation, irreversible catalyst changes, and degradation by organic reactants. Schotten et al. [70] generated a Cu(I)–NHC complex in a two-electrode system, using copper as a sacrificial electrode. However, with potentiostatic, unreacted metal cations accumulate at the cathode, leading to short-circuiting after prolonged electrolysis. To address this, pulsed-potential electrolysis was introduced, ensuring balanced electrolysis of copper electrodes and avoiding dendrite formation. This method increased electrolytic current density and prolonged system stability (Figure 4a). Ehrenberg et al. [71] used a similar strategy to prevent catalyst surface passivation, maintaining stable long-term catalysis.

Figure 4

(a) Considerations for altered mass transfer. A: normal reaction dependent on mass transport (blue M); B: switch avoids mass transport by forming intermediates on both electrodes; C: reverse reaction of copper cation possible (Reproduced from Ref. [70]. Copyright©2021, RSC Pub). (b) EPC for sorbitol conversion. Current density traces of EPC with a total of 4,000 cycles at 100 mV/s. The red arrows indicate the scan direction. Yellow arrows indicate the trend of current density curves throughout. (c) Product selectivity and K/A by EPC and the average of SS runs (Reproduced from Ref. [72]. Copyright©2021, National Academy of Science of the United States of America). (d) Scheme illustrating the catalyst in situ reactivation by applying the potential pulse program (E_high and E_low) (Reproduced from Ref. [73]. Copyright 2020, RSC Pub). (e) The proposed mechanism of asymmetric-waveform alternating current-promoted silver catalysis for C–H phosphorylation (Reproduced from Ref. [45]. Copyright©2022, Springer Nature Limited).

Noble metals like Pt, Pd, and Au are highly active in the electro-oxidation of alcohols, but their oxidation leads to rapid deactivation. Kim et al. [72] applied continuous voltage cycling for sorbic alcohol electro-oxidation with Pt/C, enhancing both the efficiency and selectivity of ketoses-to-aldoses significantly over potentiostatic methods (Figure 4b). Successive cycling of potentials enables Pt to catalyze reactions in a non-equilibrium state (Pt-O_ads), with positive potential sweeps electro-oxidation of sorbitol and rapid sweeps back reducing Pt to its pristine state. This approach not only significantly improves the electrooxidation efficiency and the catalyst stability, but also increases the selectivity of ketoses-to-aldoses ratio over sixfold compared to potentiostatic electrolysis (Figure 4c). This work also provides a new idea for the electrocatalytic oxidation of noble metals. Similarly, Martin-Yerga et al. [73] introduced a pulsed potential program that is a relatively lower potential was applied (between −0.1 and −0.22 V vs Hg/HgO, 60 s) to regenerate the Pd catalyst from PdO_x which originates in a high potential of 0.5 V vs Hg/HgO for 5 s (Figure 4d). This method exhibits higher current density and better catalytic stability than a conventional potentiostatic method. A similar phenomenon was observed in the electrocatalytic oxidation of benzyl alcohol with an Au-based catalyst by Li et al. [74]. Therefore, the authors adopted a periodic switch potential to avoid deactivation of Au by over-oxidation to AuO_x and achieved stable benzyl alcohol oxidative coupling for hydrogen production over a long period.

It is worth mentioning that deactivation of catalysts is not only due to changes in the structure of the catalyst itself (oxidized or change in morphology), but can also originate from the adsorption of toxic species, resulting in the absence of active sites. Typically, Pt catalysts have strong adsorption properties for CO, and if not removed in time, the adsorbed CO will occupy a large number of active sites of Pt leading to catalyst deactivation. As early as 1978, Adzic et al. [75] found that periodic removal of toxic species from the surface of Pt-based catalysts during formic acid oxidation experiments using a pulsed electrocatalytic process allowed regeneration of the catalysts. The fact that the poison spices can be removed only at a high potential. Therefore, Wang et al. [76] applied a high potential of 1.18 V_NHE for the oxidation of poison spices to form CO₂. Then, a lower potential (0.4 or 0.6 V_NHE) was applied for the methanol oxidation reaction. The results show that, compared to potentiostatic electrolysis, pulse electrolysis increases the average current density at potentials of 0.4 and 0.6 V_NHE by a staggering three and five orders of magnitude, respectively. Similarly, Román et al. [77] proposed a sinusoidal potential modulation method to remove adsorbed CO by the fast potential-dependent OH adsorption/desorption kinetics on Pt. The results show that a 30-fold increase in the oxidizing activity of formic acid relative to potentiostatic electrolysis can be reached when this sinusoidal potential is applied.

Transition metal ion-mediated electrocatalytic reactions have always been an important part of organic electrochemical synthesis, mainly because high-valent metal ions are key catalysts for C–H/X–H cross-coupling reactions [78,79]. However, the deposition of metal ions at the cathode when catalytic reactions are carried out using a direct current (DC) has been an important issue that has been troubling researchers. Zeng et al. [45] conduct the silver-catalyzed C–H phosphorylation combined with an asymmetric-waveform alternating current (AC) electrolysis. As shown in Figure 4e, the silver catalyst is regenerated in situ by redox at the same electrode, which could prevent the continuous reduction of silver ions at the cathode. The authors extended a large number of substrates to generate the corresponding phosphite derivatives, including alkynes, alkenes, and (hetero)arenes, and the results all showed that the yields of AC electrocatalysis were all better than those of DC electrocatalysis. Furthermore, the authors note that this strategy can also be used for Pd- and Cu-catalyzed C-H functionalization modifications.

Release of mass transfer limitations

Mass transfer limitation is a common phenomenon in electrocatalytic processes, not only for some reactions with three-phase systems involving gases, such as CO₂RR, NRR, ORR, etc., but also for reactions with only two-phase interfaces, this phenomenon also limits the efficiency of the electrocatalytic reaction to a great extent.

Figure 5 summarizes pulsed electrolysis specific effects on mass transfer for different reactions. The impact of pulsed electrolysis on the mass transfer of the different reactions focuses on four main areas, including update of the substrate, diffusion of intermediate spices/products, diffusion control of surface ions and facile bubble removal. Among these, the update of the substrate is the main effect of pulsed electrolysis on the catalytic reaction, because the continuous depletion of substrate by constant-potential electrolysis leads to a decrease in the concentration of substrate on the surface of the catalyst, whereas pulsed electrolysis normally provides diffusion time for the substrate, thus facilitating the timely renewal of the substrate [11,26,28,53,80,81]. For organic electrocatalysis, the timely diffusion of intermediate species or products is important, especially for paired electrolysis, where the slow mass transfer process between the two electrode intermediate species greatly limits the efficiency of the reaction [82]. Pulsed electrocatalysis enables short-lived intermediate species to undergo reduction and oxidation reactions at the same electrode so that the intermediate species do not need to be transferred between the two electrolytic solutions, which is the main reason why many researchers have used this property of pulsed electrocatalysis to improve the efficiency of organic electrocatalysis [42,70]. In particular, pulsed electrocatalysis promotes rapid mass transfer of hydrogen and oxygen bubbles during water electrolysis through a pumping effect [46]. Overall, pulsed electrocatalysis can facilitate the electrocatalytic mass transfer process in different ways. The focus of each author is different in different research work, and Figure 5 only summarizes the parts of specific effects that have been investigated, so these positive effects may also exist at the same time. Furthermore, the mechanism of the effect of pulsed electrocatalysis on the electrocatalytic reaction has not been thoroughly investigated and there is still a great deal of work that needs to be done.

Figure 5

The summarized of pulsed electrolysis specific effects on mass transfer for different reactions. OES: organic electrosynthesis, WER: water electrolysis reaction, CO₂RR: carbon dioxide reduction reaction, NRR: nitrogen reduction reaction, ORR: oxygen reduction reaction, EECM: element extraction and contaminant mitigation. These summary data were derived from the relevant research papers cited in this review.

The largest organic electrosynthesis synthesis process currently in industry is the electrocatalytic acrylonitrile reduction dimerization to adiponitrile, which is the main precursor for the production of Nylon 6,6 [68]. However, during this catalytic reaction, high current densities lead to the generation of propionitrile, the main by-product of the process. High current densities lead to a low concentration of the reaction substrate (acrylonitrile) on the surface of the electrode, which results in an over-reduced product rather than a dimerization product. Meanwhile, when the low density was applied, another by-product of 1,3,6-tricyanohexane was favored with high acrylonitrile concentration in the EDL. This contradiction between high current density as well as product selectivity is difficult to realize under conventional potentiostatic conditions. Therefore, the pulsed electrocatalyst combined with an AI-enhanced approach was introduced to control and optimize the composition of the EDL [68]. As shown in Figure 6a, the applied pulsed potential can effectively alleviate mass transfer limitations and increase the substrate concentration in the EDL, which in turn improves the product selectivity. Meanwhile, the charging and discharging of the EDL also leads to the redistribution of charged particles on the catalyst surface, which also has a profound effect on the catalytic reaction. After further optimization of the conditions, the authors finally obtained a 325% and 50% increase in product selectivity and production rate, which is the largest performance improvement in the 50 years since the reaction was reported, and provides a general model for other organic-electrochemical reactions.

Figure 6

(a) The graph on the left shows a DPA potential waveform. The graphical representations in the center and right describe the effects that cathodic and resting potentials, respectively (Reproduced from Ref. [68]. Copyright©2019, National Academy of Science of the United States of America). (b) Comparison of conventional and pulsed chiral electrosynthesis (Reproduced from Ref. [66]. Copyright©2017, Springer Nature Limited). (c) Alternating current electrolysis for organic electrosynthesis: Trifluoromethylation of (Hetero)arenes. (Reproduced from Ref. [22]. Copyright©2020, American Chemical Society).

The synthesis of chiral molecules has always been the most important research topic in chemistry, and the design and synthesis of chiral metal catalysts are of great significance for the electrocatalytic synthesis of chiral molecules. The main reason for the correspondence selectivity of chiral metal catalysts is the large number of chiral-encoded mesoporous inside the catalyst [83]. However, such materials do not improve the selectivity of chiral products significantly, and the main problem is that there is no chiral information on the outer surface of such chiral materials. Wattanakit et al. [66] introduced pulse electrolysis to suppress nonchiral electrosynthesis on the outer surface of the catalyst. As shown in Figure 6b, during the resting time of pulsed potential progress, the precursor of achiral acetophenone diffuses inside the porous structure of the catalyst while adsorbing in the chambers with a chiral structure. After the chamber of the chiral multi-hollow catalyst is filled with precursors, a pulsed potential is applied to reduce the adsorbed precursors in an enantioselective manner by hydrogenation. When the applied potential is disconnected (open circuit), the obtained chiral product diffuses into solution, while the reaction precursor re-enters and fills the catalyst chiral chamber. This pulsed electrocatalytic method cannot directly prevent the diastereoselective reduction of the substrate on the outer surface of the catalyst, but since the porous inner surface area of the catalyst is 2–3 orders of magnitude larger than the outer surface area, the reduction interference on the outer surface can be completely suppressed, and the final product obtained has an enantioselectivity of more than 90%. This strategy of pulsed electrocatalysis combined with chiral-imprinted catalysts provides a feasible solution for the synthesis of chiral compounds with promising applications.

In organic electrosynthesis reactions, one electrode is generally used for the conversion of the target product, while the other electrode is used for the redox conversion of the sacrificial species. To fully utilize the other half of the electrode, scientists came up with the concept of paired electrolysis. Paired electrolysis allows two electrodes to simultaneously carry out two desirable different half-reactions in the same reactor [84]. However, during paired electrolysis, the intermediates need to be transferred from one electrode to another, which requires good stability of the intermediates, especially for some short-lived intermediates, and this inter-electrode mass transfer can lead to a large number of intermediates being lost, which results in low yield. Based on this, Rodrigo et al. [22] proposed an alternating current electrolysis method to realize oxidation and reduction reactions on the same electrode. The intermediates produced at the electrode surface in this way do not have to migrate to another electrode but react directly on the same electrode surface to obtain the target product. The authors select the trifluoromethylation of (hetero)arenes as the model reaction to validate the idea proposed above. The results of electrolysis show that utilizing pulses for this reaction gives 84% yield, whereas conventional electrostatic potential electrolysis gives only 13% yield under the same conditions (Figure 6c). Thus, pulsed electrocatalysis provides a solution to the problem of intermediate mass-transfer limitations and instability in pairwise electrolysis, which also promotes the further development of organic electrosynthesis.

Preventing over-oxidation/reduction

It is an unavoidable problem that over-oxidation/reduction of reagents in the conventional electrocatalysis process (with constant current or potential). When applied constant current electrocatalyst, as the reaction proceeds, a higher potential may be required to maintain the same current, which can cause some side reactions to occur, which in turn leads to a decrease in catalytic efficiency and selectivity [42]. Even under potentiostatic conditions, side reactions cannot be avoided, mainly because the redox potentials of different species may be relatively close to each other in an electrolytic system. Lucky et al. [85] found that the adsorbed butane can be transforms to adsorbed CH_x fragments under oxidizing potentials. However, at this oxidation potential the intermediate species are also susceptible to further oxidation to adsorbed carbon monoxide (Figure 7a), hence the low selectivity of the methane product when constant potential electrolysis is performed. Based on this, the authors modulated the adsorption and desorption behavior and oxidation kinetics of specific intermediate adsorbed species by pulsed potentials, ultimately obtaining product selectivity an order of magnitude higher than those of constant potential electrolysis. This is a classic case of preventing over-oxidation of intermediate species by pulsed potential electrocatalysis.

Figure 7

(a) Potential programme for the repeated generation and desorption of methane from butane adsorbed at 0.3 V for 15 min. Inset: Methane generation is hypothesized to occur through two steps. The fragmentation potential (E₁) was varied between 0.4 and 0.7 V. E₂, desorption potential; t₁, time of fragmentation step; t₂, time of desorption step. (Reproduced from Ref. [85]. Copyright©2024, Springer Nature Limited). (b) Results of constant current electrolysis in a divided cell. Conditions: divided cell; Pt/Pt (1.0 cm² each); 10 mA; 1/2 (0.5 mmol each), CH₃CN (10 mL), TBABF₄ (0.3 M), rt. (Reproduced from Ref. [87]. Copyright©2020, Wiley-VCH GmbH). (c) Chemoselective electrosynthesis using rapid alternating polarity. (Reproduced from Ref. [44]. Copyright©2021, American Chemical Society). (d) Schematic of the pathways of pulsed electrocatalytic oxidation of glycerol. GLY: glycerol, GLAD: glyceraldehyde, GLA: glyceric acid, TA: tartronic acid, GA: glycolic acid. (Reproduced from Ref. [88]. Copyright©2024, The Author(s)).

Selective manipulation of specific ground functional groups in organic synthesis has been very challenging. Different functional groups have certain potential dependence in the electrocatalytic process due to different systems or catalysts. However, for large organic molecules with many reactive groups, this potential dependence also fails to obtain highly selective products [86]. Kawamata et al. [44] introduced a rapid alternating polarity (rAP) strategy for chemoselective carbonyl reduction. Experimental results show that this catalytic strategy of rAP selectively reduces the more reactive carbonyl groups, resulting in high selectivity, whereas only complex mixtures are obtained when electrolysis is carried out with direct current (Figure 7c). Sattler et al. [87] attempted to synthesize asymmetric disulfides (3) using two symmetric sulfides (1 and 2) via sulfur bond decomposition reaction using direct current (Figure 7b). However, during electrolysis for long durations of time, this can lead to over-oxidation of the disulfide compounds at the anode and over-reduction at the cathode and can result in a black precipitate, which also leads to a significant decrease in the yield of the target product 3. When the alternating current was applied, the over-oxidation/reduction of the disulfide compounds was significantly suppressed, and the selectivity of product 3 remained stable at about 57%. Similarly, to prevent excessive oxidation of glycerol on the surface of the Pt catalyst, which led to a decrease in the selectivity of the C3 product, Chen et al. [88] utilized the strategy of pulsed electrocatalysis, which inhibited the breakage of the C–C bond, resulting in high selectivity to obtain the glyceric acid product (81%) (Figure 7d).

It was found that the selectivity and yield of Ni-catalyzed amination, esterification, and etherification reactions can be improved by using alternating current (AC) electrolysis compared to direct current (DC) electrolysis [89]. In a nickel catalytic cycle for cross-coupling reactions with AC, the Ni(Ⅱ) was firstly reduced to Ni(0) and then oxidative addition of aryl halide to formed Ni(Ⅱ). Then, the Ni(Ⅱ) further ligand exchange with a nucleophile and oxidation to Ni(Ⅲ) by anodic current. Eventually, the cross-coupling product was obtained by reductive elimination (Figure 7c). However, when the constant current or voltage was applied, the products obtained were usually dominated by diaryl coupling products rather than cross-coupled products. The relatively high selectivity of AC electrocatalysis for the cross-coupling products is mainly due to the prevention of over-reduction of [NiLn(Ar)(Nu)] to Ni(Ⅰ), while oxidation and reduction at the same electrode also reduce the loss of intermediates.

As one of the oldest C-C coupled electrochemical reactions, the Kolbe reaction, its study is severely limited by its limited substrate range and dependence on precious metals. Hioki et al. [43] recently found that the Kolbe reaction can be realized using pulsed electrocatalysis with reticulated vitreous carbon as an electrode and a large number of substrate extensions. Pulsed electrocatalysis can significantly improve the reactivity and the selectivity of the reaction compared to DC electrocatalysis. At the same time, the authors found that this reactivity largely originated from the difference in local pH on the electrode surface. When this reaction is carried out with the direct current, the catalyst surface pH becomes acidic, known as electrogenerated acid, when the substrate reacts in a neutral molecular form. Whereas, when a pulsed current is applied, the electrode surface pH is to the bulk phase (alkaline), at which point the substrate is oxidized mainly in the deprotonated (salt) form, which protects the other groups on the substrate molecule, thus increasing selectivity and reactivity. Therefore, pulsed electrocatalysis can improve the reaction rate, selectivity, and catalytic stability of organic electrosynthesis, which is attributed to the modulation of the catalyst surface, the protection of unstable intermediates, and the alleviation of mass transfer limitations.

CO₂RR

With growing concerns about climate change and carbon dioxide emissions, scientists are finding it feasible to use electrochemical methods to fix carbon dioxide. Among the many catalysts for carbon dioxide reduction, Copper is one of the few metal catalysts that could yield the C₂₊ product, due to its optimal intermediate binding energy, especially for CO intermediates [11,90]. However, an undesirable electrolytic environment, poor catalyst stability, limitation of mass transfer, and unsatisfied selectivity have severely limited its application [5,91]. Recently, a large number of studies have focused on improving catalytic efficiency and selectivity of CO₂RR, such as the design of catalysts [92–96], the selection of electrolytes and electrodes [97–99], the optimum of CO₂RR pathways [98,100] and the electrolytic cells [90,101]. Although these studies have improved the catalytic efficiency and the selectivity of CO₂RR, there are still many limitations to be addressed. Unlike complex catalyst design and pretreatment methods, pulsed electrocatalysis provides a simpler and more convenient way to improve the CO₂RR performance. This is because pulsed electrocatalysis can modulate the structure of the catalyst and the surface microenvironment of the catalytic reaction by simply changing the pulse profile.

Regulation of catalyst surface structure

The excellent performance of the catalyst is crucial for commercial applications of CO₂RR, mainly including high current density and product selectivity, as well as the stability for long-term operation [102,103]. However, catalyst stability has not received enough attention relative to catalyst reactivity and selectivity. The catalyst stability problems are prevalent in CO₂RR, especially the Cu-based catalysts. The main causes of Cu-based catalyst deactivation during CO₂RR include poisoning by experimental impurities or product intermediates and surface reconstruction of the catalyst [5,24,48,104]. In an earlier study, researchers found that when CO₂RR was performed with a Cu catalyst with a potentiostatic process, a carbon layer formed on the surface of the catalyst, which led to the deactivation of the Cu catalyst [105]. It was suggested that the formation of carbon layers may originate from side reactions of CO₂RR [93] or from intermediate species that produce hydrocarbon products [106]. To prevent the deactivation of the Cu catalyst, the researchers employed anodic pulsing to reverse the deposition of the carbon layer on the catalyst surface [107–109]. Further studies showed that the main reason for anodic pulsing to prevent catalyst deactivation is the formation of Cu₂O, and the dissolution and re-deposition of Cu prevents the adsorption of carbon layers on the catalyst surface [110].

The change and reconstruction of the surface structure is another major reason for the deactivation of Cu catalysts, especially for catalysts with well-defined nanostructures [111]. However, the reconfiguration of Cu catalysts is prevalent during potentiostatic CO₂RR, which makes it difficult to maintain the stability of Cu catalysts for a long period [111–113]. Therefore, a large number of researchers have devoted themselves to using pulsed electrocatalysis to stabilize or modulate the surface structure (including the oxidized copper spices and surface morphology) of catalysts to improve the stability as well as the catalytic performance of catalysts [25,48,62,102]. Arán-Ais et al. [62] optimized the selectivity of the C₂₊ products by controlling the parameters of the pulse potential to regulate the defect structure and the ratio of Cu(Ⅰ) species of the Cu catalyst surface. As shown in Figures 8a–c, the pulsed electrolysis causes a large number of defects on the Cu (100) surface to form a regular particle morphology, while potentiostatic electrocatalysis leads to the healing of the surface defect morphology, which in turn affects the selectivity and catalyst stability. Meanwhile, by comparing the surface structure of the CO₂RR product with that of the Cu catalyst, the authors found that the percentage of Cu(Ⅰ) on the catalyst surface correlates strongly with the generation of ethanol, while the degree of surface defects is closely related to the generation of ethylene. Similarly, Timoshenko et al. [25] utilized the advanced operando X-ray to investigate the complex interactions between a (reversible) oxide formation and their catalytic performance in cubic copper nanocatalysts. They found that the Faraday efficiency of pulsed electrocatalysis to obtain ethanol was twice as high as that using potentiostatic electrocatalysis when a balance of metallic copper and its oxide spices was reached on the catalyst surface. At the same time, they established a right-angle coordinate system in terms of the oxidation and reduction times of pulse catalysis to visualize the changes of the catalyst under different pulse conditions and its effect on the product selectivity (Figure 8d). For copper nanoparticle catalysts, agglomeration of catalyst particles is also an important cause of catalyst deactivation. As shown in Figure 8e, to prevent the aggregation of Cu-based catalysts, two pulsed catalytic strategies were proposed by Zhang et al. [48] which not only significantly improved the catalytic performance of CO₂RR, but also achieved ultra-long stable catalytic times of 300 h for the catalysts, whereas the traditional potentiostatic electrocatalysis had a stability time of less than 1 h. Similarly, Timoshenko et al. [114] found that the pulsed catalytic strategies enable controlled fragmentation of the copper catalysts and partial regeneration of monatomic catalytic sites. The morphology of these different catalysts exhibits unique functions for the CO₂RR (Figure 8f–h).

Figure 8

Atomic force microscopy images of a Cu (100) electrode after different surface treatments and reaction settings. (a) Constant potential of −1.0 V versus RHE; Pulsed electrolysis: (b) E_a= 0.6 V, E_c= −1.0 V, t_a=t_c= 1 s. (c) The surface from panel (b) after a subsequent hour of potentiostatic electrolysis at −1.0 V versus RHE. (Reproduced from Ref. [62]. Copyright©2020, Springer Nature Limited). (d) Schematic depiction of the catalyst structure and composition during a cathodic pulse extracted from XAS and XRD data. (Reproduced from Ref. [25]. Copyright©2022, Springer Nature Limited). (e) Design and performance of ALPS-1, ALPS-2, and potentiostatic methods for Cu₃(DMPz)₃ Catalyst (Reproduced from Ref. [48]. Copyright©2023, American Chemical Society). (f) Faradaic efficiencies of the reaction products under static CO₂RR at −1.35 V and under pulsed CO₂RR with E_c = − 1.35 V, E_a = 0.44 V, Δt_a = 30 s and different Δt_c values (30, 10, and 1 s). (g) Corresponding selectivity for H₂ and the main gaseous CO₂RR products as a function of Δt_c. Inset: calculated concentrations of Cu within cationic single site species (x_SAC), small Cu clusters (x_S), and large Cu nanoparticles (x_L). Shaded regions indicated as (i), (ii), and (iii) mark three distinct regimes with different selectivity trends, and dominated by different Cu species, as indicated in (h) (Reproduced from Ref. [114]. Copyright©2024, Springer Nature Limited).

In addition to the surface morphology, the valence modulation of copper catalysts is very important in electrocatalytic processes, which is mainly because different valence states have a significant effect on the catalytic performance of CO₂RR. In particular, under traditional potentiostatic conditions, the copper catalyst remains essentially at Cu⁰, whereas a large number of studies have shown that high-valence copper is more favorable for the generation of C₂₊ products [102,115–118]. This is mainly due to the ability of high-valence copper to increase the coverage of CO while preventing its further protonation, which provides the necessary conditions for the C-C coupling during CO₂RR [119,120]. Therefore, most of the work on CO₂RR in Cu catalysts utilizes the pulsed potential strategy with the main objective of modulating the valence state of Cu and thus improving the selectivity and Faradic efficiency of CO₂RR.

Arán-Ais et al. [62] used quasi in situ Auger electron spectroscopy to monitor the change in the valence state of the Cu catalyst during pulsed electrocatalytic CO₂RR. The Cu⁺ was formed during the anodic pulse and its content increases with increasing anodic potential (from 0 to 0.8 V_RHE). When transferred to a cathodic pulse at −1 V_RHE, a certain amount of Cu⁺ can still be detected. Meanwhile, higher ethanol selectivity was observed when the proportion of the Cu⁺ spices on the Cu catalyst was higher (Figure 9d). However, the valence of copper catalysts is very sensitive to the reaction environment and potential, and it poses a great challenge for the detection of oxide species on the surface of copper catalysts, which requires time-resolved in situ and operando detection experiments. Therefore, Timoshenko et al. [25] used the time-resolved XAS and XRD to characterize the catalyst transformations during each pulse cycle of the PE process. As shown in Figures 9a–c, different Cu spices (including the Cu⁰, Cu⁺, and Cu²⁺) on the catalyst are in excellent quantitative agreement with the waveforms of pulse potentials. At the same time, it can be seen that the curves of the oxidation and reduction processes show strong asymmetry. When an anodic pulse time of 10–20 s is applied, the catalyst reaches its stable oxidized state, but the cathodic pulse time is only 1–2 s, and the oxidized spices are completely removed. The results of the XRD analysis have the same pattern. Similarly, Lin et al. [116] utilized the operando time-resolved XAS to track the evolution of Cu spices during the CO₂RR process. The results show that the application of pulse potential can maintain the ratio of Cu⁰ and Cu⁺ on the catalyst surface unchanged, while the ratio of Cu⁺ on the catalyst surface gradually decreases when CO₂RR is carried out by utilizing potentiostatic (Figures 9d–i). Product analysis also showed that the presence of Cu⁺ also favored ethanol production. Accordingly, the authors also propose a carbonyl stabilization mechanism, suggesting that the boundary OH spices could prevent further protonation of the terminal oxygen site, thus facilitating the generation of C₂₊ products.

Figure 9

(a) LCA-XANES analysis results (grey open circles) for averaged data for NCs under CO₂RR with pulse lengths Δt_a=Δt_c= 10 s, E_c=−1.0 V and E_a= 0.6 V. (b) Evolution of the Cu (311) Bragg peak parameters. (c) Evolution of the Cu₂O-like Bragg peak parameters during the anodic pulse. (Reproduced from Ref. [25]. Copyright©2022, Springer Nature Limited). (d) Time-resolved variations using Redox Shuttle (R.S.) of Cu species in CuO_x and the corresponding electrochemical responses during CO₂RR at −0.75 V and (e) the corresponding time-resolved EXAFS spectra without phase-correction of CuO_x under CO₂RR. (f) Time-resolved variations using chronoamperometry (CA) of Cu species in CuO_x and the corresponding electrochemical responses during CO₂RR at −0.75 V and (g) the corresponding time-resolved EXAFS spectra without phase-correction of CuO_x under CO₂RR. Quantification of time-resolved chemical composition information extracted from operando Quick Cu XAS for CuO_x under eCO₂RR using redox shuttle (h) and conventional chronoamperometry (i) (Reproduced from Ref. [116]. Copyright©2020, Springer Nature Limited).

Modulation of the surface microenvironment

In addition to reconfiguring the surface structure of the catalyst, pulsed potential electrocatalysis can also affect the performance of CO₂RR through the modulation of the surface microenvironment, such as the adsorption/desorption of surface species, EDL, distribution of electrolyte ions, interfacial pH [11,121]. This microenvironmental regulation is crucial for the path selection and Faraday efficiency of CO₂RR which is inaccessible with potentiostatic conditions. Compared to static potential, Li et al. [121] found that pulsed electrolysis can lead to the enrichment of cations on the catalyst surface, which can significantly affect the ratio of C1 and C2 products for CO₂RR.

For electrocatalytic CO₂RR with multiphase interfaces, the adsorption/desorption of species on the catalyst surface can directly affect the catalytic reaction pathway. Kimura et al. [122] used a multi-species Langmuir isotherm model with the support of in situ XPS to explore how pulse potential affects CO₂RR by modulating the adsorption/desorption of surface species. They suggested that the pulsed anodic potential could disrupt the Helmholtz plane and displace H_ads with OH_ads resulting in a higher local pH of the catalyst surface. Meanwhile, the surface adsorbent of OH_ads can prevent the CO_bridge formation that could deactivate the Cu surface. All these findings demonstrated that pulsed electrocatalysis can improve the CO₂RR performance by inhibiting HER and preventing catalyst poisoning. Similarly, Bui et al. [123] developed a time-dependent continuum model for CO₂RR with pulsed potential electrolysis. It was shown that pulsed anodic potential favors higher pH and concentrations of CO₂ on the Cu electrode surface and minimizes the production of C₁ and H₂, which leads to an increase in the Faraday efficiency of the C₂₊ products.

However, the use of computer simulation cannot fully reflect the situation under actual working conditions, especially for complex multiphase electrocatalytic systems. Therefore, a fast time-resolved in situ Raman spectroscopic method was developed by Li et al. for dynamic detection of the major intermediate species (CO_ads) changes during pulsed electrocatalytic CO₂RR [124]. In the pulsed electrocatalytic reduction of carbon dioxide, when an anodic pulse potential was applied, the CO_ads concentration on the catalyst surface at the cathodic reduction potential was significantly higher than that under the static condition (Figure 10a). Meanwhile, the CO_ads concentration varies periodically with pulse potentials. The authors attribute this periodic variation mainly to the changes in the Cu_xO/Cu ratio of the Cu catalyst surface. In addition to the ability of pulsed electrocatalysis to modulate the surface microenvironment, the use of ionic polymers to modify the catalyst surface is also a viable approach. Recently, Kim et al. [19] combined pulsed electrocatalysis with ionomer coating to modulate the catalyst surface microenvironment, both of which enhanced the local CO₂/H₂O and pH. In this study, two different coatings of cation-exchange ionomer (CEI, Nafion) and anion-exchange ionomer (AEI, Sustainion) were adopted. As shown in Figure 10c, each ionomer layer has its individual effects regardless of their stacking order. The AEI membrane favors the increase in CO₂/H₂O ratio because of its high CO₂ solubility. In contrast, the CEI membrane favors the increase in local pH due to the trapping of OH⁻ produced during the reduction process, and meantime preventing bicarbonate, which has a buffering effect, from entering the local microenvironment of the catalyst. Moreover, the application of the pulse potential leads to a further increase in the pH and CO₂/H₂O ratio of the catalyst surface, resulting in higher C₂₊ FE and lower H₂ FE. The selectivity of the C₂ product was increased by 250% (90% C₂₊ FE and 4% H₂ FE) compared to potentiostatic electrolysis over bare Cu.

Figure 10

(a) Dynamic transformation of CO_ads on Cu surface during static (Right) and pulsed CO₂RR (Left) at indicated time ranges at E_c = −0.60 V (Reproduced from Ref. [124]. Copyright©2023, American Chemical Society). (b) Experimental faradic efficiency for pulsed- and constant-potential CO₂RR in thick and thin boundary layers (Reproduced from Ref. [127]. Copyright©2018, Wiley-VCH GmbH). (c) Schematic depiction of enhanced CO₂RR using ionomers (Reproduced from Ref. [19]. Copyright©2021, Springer Nature Limited).

Facilitation of mass transfer

In pulsed electrocatalysis, the tailoring of the surface microenvironment is not only from the redistribution of charged particles caused by the electric field action but also the modulation of the adsorption/desorption behavior originating from the catalyst structure changes (as discussed above). For multiphase electrocatalytic reactions, however, mass transfer at the electrode interface is critical due to its ability to affect the overall reaction rate. Especially for CO₂, a relatively low solubility species, rapid substrate consumption can lead to significant concentration polarization on the electrode surface [11]. In contrast to conventional static electrolysis, in pulsed electrocatalytic CO₂RR, CO₂ can be replenished during the anodic ‘‘off’’ pulse. There exists an optimal anodic ‘‘off’’ pulse duration, which is largely dependent on the CO₂ replenishment rate, and too long “off’’ time will affect the overall electrolysis efficiency. The effect of this replenishing effect on the CO₂RR performance was evaluated using experiments combined with simulations by Kim et al. [125].

In general, mass transfer limitations exist mainly in the boundary layer with a thickness of 100 μm. It has been shown in the literature that the CO₂ in the boundary layer can be fully replenished when the anodic ‘‘off’’ pulse duration reaches 5–10 s [125,126]. Therefore, too short a pulse duration has a limited contribution to the mass transfer limitation of CO₂ at the catalyst surface [122,127,128]. To reduce the time to replenish the boundary layer CO₂ concentration, reducing the thickness of the boundary layer is a feasible approach. The results show that when the boundary layer thickness is reduced to 50 μm, the anodic pulse time needs only 50 ms to realize the CO₂ concentration at the electrode surface close to the system concentration [126]. Based on this, Kimura et al. [127] used a high-speed rotating (1000 r/min) planar electrode to investigate whether pulsed electrolysis affects product selectivity solely through enhanced mass transfer. As shown in Figure 10b, the methane selectivity of pulse electrolysis for CO₂RR was significantly higher than that of static electrolysis, with or without stirring. This suggests that the effect of pulsed electrolysis on mass transfer is unable to explain the trend of increased product selectivity. Therefore, pulsed potentials alleviate the mass transfer limitations of the carbon dioxide reduction reaction process. Still, the overall catalytic efficiency improvement stems from many reasons, including but not limited to local pH, the change of over-potential, reconstruction of catalyst, and adsorption/desorption of intermediate species.

Water splitting

Water electrocatalysis is a successful case of electrocatalysis in industrial applications, which consists of two main reactions, the two-electron process of hydrogen evolution reaction (HER) on the cathode, and the four-electron process of oxygen evolution reaction (OER) on the anode. In the conventional potentiostatic water electrolysis process, the slow kinetics of the OER and the multi-step electron-coupled proton transfer process result in an unsatisfactory efficiency of the overall water electrolysis process. Some early literature suggests that pulse electrolysis is a more efficient way of water splitting [63,129,130]. With a deeper understanding of pulse electrolysis of water, the impact of pulse potential on the efficiency of water electrolysis is mainly focused on two aspects, including an increase in the concentration of reactants on the electrode surface [47,63,131–133], and promotes the elimination of gas bubbles and enhances mass transfer [46,134–136].

During pulse electrolysis of water, when the pulse potential is applied to the surface of the electrode, a rapid electron transfer occurs between the adsorbed water and the electrode, and at the same time, a charge accumulates on the surface of the electrode to form an EDL [29]. The EDL on the electrode surface can directly affect the distribution of species in the diffusion layer, and in the process of potentiostatic electrolysis, the active species in the diffusion layer on the electrode surface are rapidly consumed as electrolysis proceeds, leading to the emergence of a concentrated polarization on the electrode surface, which seriously affects the electrolysis efficiency. Shimizu et al. [63] proposed the use of the ultra-short pulsed power supply circuit for water electrolysis. This pulsed power supply provides an inductive pulse of 300 ns width, which is below the build-up time (3 μs) of the diffusion layer. Thus, electrons can be transferred quickly from the electrode surface to hydrogen ions or water instead of forming a steady diffusion layer, thus increasing the efficiency of hydrogen production. At the same time, such a short pulse time also reduces the electron loss during the charging and discharging of the EDL [29,63]. Similarly, Vincent et al. [47] investigated the thickness of the diffusion layer at different pulse frequencies, and the results showed that the thickness of the diffusion layer on the electrode surface gradually decreases with the increase of the pulse frequency, which in turn reduces the mass transfer limitations in the electrolysis process. The diffusion layer on the catalyst surface is also affected by the convection of the electrolyte on the electrode surface. de Radigues et al. [131] investigated the effects of forced convection, 3D structured electrodes, and pulse potential on the performance of Ni-catalyzed water electrolysis. It was found that the contribution of the 3D structured electrodes to the current density mainly originated from their higher active area, while forced convection did not significantly enhance the performance of the 2D electrodes. However, by combining 3D electrodes, forced convection, and pulsed potential, the current for water electrolysis can be increased by a factor of 5 compared to electrolysis with 2D electrodes at a potentiostatic under natural convection conditions.

Since the main products of water electrolysis are H₂ and O₂, the diffusion rate of the gas also affects the mass transfer process at the electrode surface. Lin et al. [135] investigated the effects of magnetic field and pulse potential on the motion of bubbles during water electrolysis and mass transfer. The experimental results show that the addition of a magnetic field can change the direction of convection of the electrolyte, thus affecting the motion of the bubbles while the current density was increased by 15%. The application of the pulse potential increases the transient current at the electrode surface, which accelerates the bubble detachment from the electrode surface as well as the electrolyte mass transfer rate, and also alleviates the polarization of the diffusion layer. All these phenomena favored the electrolysis efficiency, and the current density increased by 680 mA·cm⁻² under optimal conditions. Demir et al. [46] also showed that the application of pulsed potentials has a pumping effect that promotes the diffusion of hydrogen and oxygen bubbles. At the same time, the rapid diffusion of oxygen can also reduce the corrosive effect on the anode electrode and maintain the stability of the anode electrode. Moreover, the authors demonstrated that the reduction in mass transfer losses can result in a 20–25% reduction in energy consumption for water electrolysis.

These results show that the improved performance of pulsed electrolyzed water is mainly due to the modulation of the diffusion layer on the electrode surface, reducing the mass transfer limit, promoting the diffusion of hydrogen and oxygen by the pulse potential, and demonstrating the potential of the PE method as an alternative to the conventional CE method for water splitting. However, there is still a lack of systematic and comprehensive research on the mechanism of pulse electrolysis of water, therefore, pulse electrolysis of water to replace the existing industrial electrolysis of water process lacks sufficient theoretical support.

Contaminant removal and element extraction

Since industrialization, the development of industry, rapid population growth, and over-consumption have led to more and more serious environmental problems, including water pollution, which hurts all living things [5,137]. At the same time, due to the scarcity of freshwater resources, the purification and treatment of polluted water have become particularly important. The main pollutants in water are metal ions, organic matter, dyes, and others [5].

Electrochemical oxidation technology is a technology of anode catalysis to produce hydroxyl radical (·OH) or other active groups to oxidize organic pollutants in wastewater. This technique is seen as the most efficient way to remove pollution from wastewater, mainly due to its environmental friendliness, easy operation, and minimal chemical consumption [5,138]. Compared with the traditional DC-driven electrochemical oxidation technology, pulsed electrocatalytic oxidation has many advantages, including low energy consumption, high selectivity, and efficiency, long catalyst life, short treatment time, and low sludge deposition [5]. Currently, many wastewater treatment technologies require high-voltage pulses (25–40 kV) due to rapid mass transfer as well as faster kinetics [139,140]. However, this high-voltage pulse cannot significantly reduce energy consumption. Therefore, low-pressure pulse (20–30 V) electrocatalytic oxidation is a popular wastewater treatment technology.

General anodic electrochemical oxidation of wastewater treatment is an indirect oxidation process mediated by hydroxyl radicals, but the hydroxyl radicals have a very short lifetime, while the oxidation of organic matter and OER compete with each other as a reaction [141,142]. When oxidative electrolysis is carried out with a potentiostatic, the organic matter on the catalyst surface is rapidly consumed, and a stable diffusion layer is formed at the same time. If the organic matter does not reach the surface of the catalyst in time to react with the hydroxyl radicals, the hydroxyl radicals that are constantly being formed are consumed through the competitive reaction (OER) [12,143]. In the pulsed electrolysis mode, the resting time of the pulse allows the organic to diffuse towards the anode, replenishing the organic that was consumed during the anodic pulse, thus eliminating the concentration polarization on the anodic surface. This can increase the utilization of hydroxyl radicals, the degradation rate of pollutants and reduce energy consumption [12]. Wei et al. [143] utilized a pulsed process to degrade phenol contaminants with 53% lower energy consumption than constant current degradation when achieving the same degradation goal. Similarly, when Pei et al. [144] utilized a pulsed process for the treatment of phenol in wastewater, they found that the oxidation rate constant for phenol in the pulsed mode (1.48 h⁻¹) was 52.5% higher than in the DC mode (0.97 h⁻¹), while the energy consumption was 57.1% lower. Diao et al. [145] used a pulsed current to remove malachite green dye from wastewater using lead dioxide as an anode. At a current density of 30 mA, a duty cycle of 0.6 for the pulsed current, and a pulse frequency of 10 Hz, 99.6% of malachite green could be removed. Compared with direct current oxidation, this method produces more hydroxyl radicals and reduces the occurrence of side reactions, as well as reduces energy consumption.

In addition to organic pollutants, heavy metal ion pollution is also a major contributor to water and soil pollution. Zhou et al. [57] utilized a triboelectric nanogenerator to provide a pulsed power supply for the removal of hexavalent chromium ions Cr(Ⅵ) from wastewater. The authors used Fe as the anode and carbon rods as the cathode. During electrolysis, Fe²⁺ generated from iron oxidation at the anode reduces Cr(Ⅵ) to Cr(Ⅲ), while the cathode reduces Cr(Ⅵ) directly to Cr(Ⅲ). Compared with traditional DC methods, pulse electrochemical methods show better utilization of Fe²⁺, lower electrode passivation, and more energy efficiency. Removal of heavy metal contamination from soil is more complicated compared to heavy metal contamination in water. Xu et al. [146] presented a recirculating soil cleaning device for asymmetric electrochemical pulsed filtration devices. The authors first cleaned the heavy metal-contaminated soil using a solution containing EDTA, and then the complex solution formed by the metal and EDTA was used for selective removal of heavy metals by pulsed electrolysis. As shown in Figure 11a, when the anode pulse of 5 V was applied, the negatively charged metal-EDTA complexes were quickly adsorbed on the electrode surface. Then, a bias of −10 V was applied, and the heavy metal cations were reduced to zero-valent particles. Meanwhile, due to the loss of affinity for neutral ions, the EDTA anions return to the solution. Nutrient metal ions in the soil (Na⁺, Mg²⁺, etc.), however, cannot be removed by this filtration system, mainly due to their relatively low reduction potential. This filtration system does not produce secondary contamination because the EDTA solution is recyclable.

Figure 11

(a) The waveform of the applied bias and the physical process in the AACE filtration (Reproduced from Ref. [146]. Copyright©2019, Springer Nature Limited). Schematics of physicochemical and HW-ACE extraction. (b) In physicochemical adsorption systems, Coulomb repulsion can cause incoming ions to be rejected by the adsorbed charged ions. (c) Competition between uranyl ions and other cations reduces the adsorption of uranyl ions and results in the blocking of active sites. (d) Physical processes in HW-ACE extraction (Reproduced from Ref. [28]. Copyright©2017, Springer Nature Limited).

The uranium content in seawater is enormous, but the extraction of uranium from seawater is a challenging endeavor due to its low content (∼3 ppb, 3 μg·L⁻¹) [147]. For traditional physicochemical adsorption, if positively charged ions are adsorbed on the surface, Coulomb repulsion will occur to other surrounding ions with the same charge (Figure 11b), and at the same time, other charged ions will compete with uranium ions for adsorption, occupying a large number of adsorption sites (Figure 11c). Therefore, Liu et al. [28] reported a half-wave rectified alternating current electrochemical (HW-ACE) method for extracting uranium from seawater. As shown in Figure 11d, the random distribution of ions in solution when no voltage is applied. When a bias is applied, positively charged particles migrate toward the negative electrode to form a stable EDL. The uranyl ions are further reduced to neutral uranium particles UO₂ and deposited on the electrode surface. Positively charged ions that have collected on the surface of the negative electrode and have not been deposited will diffuse back into the solution after the bias is removed. As the number of pulse cycles increases, uranium particles continue to accumulate on the electrode surface, while other cations in the water do not occupy the adsorption sites on the electrode surface. This uranium extraction method has a ninefold increase in extraction capacity over conventional physicochemical adsorption, and the kinetics of adsorption is four times faster. Overall, pulsed potential has great potential for contaminant removal and elemental extraction. This mainly stems from its unique role in making full use of reactive radicals, regulating the EDL and the diffusion layer, reducing the concentration polarization, and modulating the adsorption/desorption of charged ions.

Electrochemical nitrogen fixation and ORR

Electrochemical nitrogen fixation has been recognized as a sustainable and promising method for the production of NH₃ and HNO₃ [50]. Due to the very stable N≡N triple bond (945 kJ·mol⁻¹) and low solubility of nitrogen, the Faraday efficiency and the yield rate of electrochemical nitrogen fixation with CE is low. Even so, a great deal of work has been devoted to electrochemical nitrogen fixation. However, there are few works about the pulsed electrolysis for nitrogen fixation. Recently, some works on pulsed electrocatalysis for electrochemical NRR, NO₃RR, and NOR are given below.

Guo et al. [50] developed an iron-loaded single-atom Janus electrocatalyst on titanium dioxide combined with PE for bipolar nitrogen fixation in a two-electrode system, including anodic NOR production of HNO₃ and cathodic NRR production of NH₃ (Figure 12a). The authors found that, compared to CE, the use of PE can inhibit the generation of two intermediates (including *OOH and *H) which are mainly used for the water splitting process, and also promote the non-electrochemical step of N₂ activation. At a voltage of 3.5 V, the final yields reached 7055.81 μmol·h⁻¹·g⁻¹_cat. (NOR) and 12868.33 μmol·h⁻¹·g⁻¹_cat. (NRR), respectively. Corresponding Faraday efficiency was 44.94 and 7.8 times higher than those catalyzed with a CE under the same conditions.

Figure 12

(a) Schematic diagram of NOR and NRR process at the anode and cathode chamber by pulsed electrocatalysis (Reproduced from Ref. [50]. Copyright©2023, Wiley-VCH GmbH). Schematic of reaction pathways with CE and PE. (b) Profile of applied potentials for CE. (c) Reaction mechanism of the NO₃RR with CE at E_L and E_H. (d) Profile of the applied potential for PE. (e) Reaction pathways of the NO₃RR through the tandem NO₂⁻ accumulation-conversion process with PE (Reproduced from Ref. [26]. Copyright©2023, American Chemical Society). (f) In situ Raman spectra of RuIn₃/C under −0.1 V and then +0.6 V in 0.1 M KOH + 10 mM NO₃⁻ solution with 3 cycles. (g) Schematic illustration for the effect of pulsed voltage on the mass transport of different species (Reproduced from Ref. [49]. Copyright©2023, Springer Nature Limited).

Unlike N₂, it is easier to produce NH₃ using NO₃⁻ (NO₃RR), mainly due to the lower dissociation energy (204 kJ·mol⁻¹) of the N–O bond and much higher solubility in water [148]. The NO₃RR process has a slow kinetic rate because it involves nine proton and eight electron transfers, which requires a sufficiently high overpotential [26]. However, when applied with a conventional CE process (Figure 12b and c), high over-potentials result in the occurrence of the competing reaction HER and occupy more active sites of the catalyst, leading to a decrease in overall Faraday efficiency. At a lower over-potential, the adsorbed *H content on the catalyst surface is insufficient to convert NO₂⁻ to NH₃, which leads to the accumulation of the intermediate species NO₂⁻ on the catalyst surface. To solve this issue, Li et al. [26] proposed a pulsed potential process for producing NH₃ by cascading the NO₂⁻ intermediates accumulation-conversion (Figure 12d and e). When applied the low potential, NO₂⁻ intermediate was obtained with fast reaction kinetics and accumulated on the surface of the catalyst. Then, the concentrated NO₂⁻ can be rapidly converted to NH₄⁺ at high potential. Meanwhile, HER can be suppressed effectively due to the highly concentrated NO₂⁻ leading to a prioritization of the NO₂⁻-to-NH₄⁺ step over H₂O-to-H₂, thermodynamically and kinetically. This method is 22% more energy efficient and offers a 28% increase in yield compared to potentiostatic electrolysis. Bu et al. [149] introduced the pulse potential that enables the Cu catalyst to maintain a rich Cu/Cu₂O interface, proving to be highly reaction active for NO₃RR [150]. Since NO₃⁻ is negatively charged, there is a limited distribution on the electrode surface when a reduction reaction is performed, which largely limits the reduction of nitrate with low concentration. Huang et al. [49] significantly optimized the adsorption configuration of key *NO intermediate and increased the local concentration of NO₃⁻ using the pulsed potential approach (Figure 12f and g). The results showed that at a NO₃⁻ concentration of 10 mM, the conversion rate and Faraday efficiency were 96.4% and 97.6%, respectively, with a yield of 2.7 mmol·h⁻¹·g_ru⁻¹, which were significantly higher than that of the potentiostatic test.

In addition to NO₃RR, there are currently two interesting works to use the pulsed electrocatalytic process for C-N coupling. One work by Gerke et al. [151] to synthesize urea from CO₂ and NO₃⁻ found that nitrate mass transport can be enhanced by pulsed potential electrolysis. The authors attribute this to the disruption of the EDL structure by pulsed potentials, causing mutual attraction and repulsion between differently charged spices and electrodes. Another work by He et al. [51] to synthesize arylamines from nitrite and arylboronic acids found that the anodic pulses can oxidize Cu to Cu(Ⅱ) in situ for catalytic C-N coupling. Meanwhile, the rapid polarity change also increases the concentration of NH₃, ArB(OH)₃⁻, and Cu(II) near the electrolytic surface, which further enhances the overall reaction efficiency.

There are few studies on the use of PE for ORR, only a group of Gao et al. have reported on this, and their work is briefly summarized below [52–55]. In their work, the ORR electrolysis experiments were carried out using square wave pulse potential with carbon-based materials as catalysts. Firstly, they found that the discharge of EDL favors the desorption of *OOH and absorption of O₂. Meanwhile, the rest time of PE helps species such as H⁺ and O₂ to diffuse to the electrode surface in time to alleviate the phenomenon of concentration polarization and also facilitates the timely diffusion of the generated H₂O₂ into the electrolyte to reduce the unnecessary H₂O₂ electroreduction process [55]. Then, the authors found that the pulse potential can dynamically activate the defective structures on the catalyst surface and maintain the catalyst’s stabilization. The *O₂ to get protons is a spontaneous process at a positive pulse potential, which is conducive to the rapid generation of H₂O₂ [54]. In another work, they found that pulsed potentials can stimulate cationic effects to activate C-*OOH and lower the energy barrier of the overall ORR reaction [53]. In conclusion, the work of Ding et al. focuses on the modulation of the ORR reaction surface microenvironment, species adsorption and desorption, mass transfer processes, and catalysts by pulsed electrocatalysis, and provides some new insights into the ORR mechanism in pulsed electrocatalysis.

CONCLUSIONS AND PERSPECTIVES

Pulsed electrocatalysis is receiving more and more attention as a developing versatile and powerful catalytic tool. We briefly introduce the simple knowledge of pulsed electrocatalysis and also summarize the new applications of pulsed electrocatalysis in different electrocatalysis and electrosynthesis fields (Table 1). By analyzing the examples of different applications, it is found that pulsed electrocatalysis is a powerful and versatile technique for modulating the factors at the surface interface during the catalytic reaction process, such as the surface remodeling of the catalyst, the adsorption and detachment of intermediate species on the surface, the structure of the EDL, the microenvironment of the surface, and the diffusion of water, ions, and species in the diffusive layer, among others. The activity, selectivity, or stability of the catalytic reaction can be improved by these modulatory effects, which cannot be achieved by potentiostatic catalysis.

Table 1

Summary of the effect of pulsed electrocatalysis on different catalytic reactions

The types of catalysts mainly studied in pulsed electrocatalysis are still limited, mainly focusing on Cu-based catalysts and noble metal catalysts. Cu-based catalysts are mainly applied to CO₂RR because Cu is one of the few metal catalysts that can produce multi-carbon products, and at the same time, the valence state of Cu is multivariate in the catalytic process, and its valence state can be well dynamically regulated by pulsed electrocatalysis. Precious metals are also widely used as highly active catalysts, but poisoning and deactivation can easily occur when oxidation reactions are carried out with precious metals, which is expected to be solved by pulsed electrocatalysis. In general, pulsed electrocatalysis has three main effects on the catalyst, the first being the dynamic regulation of the valence or coordination environment of the catalyst to achieve specific catalytic demands. The second is to control the dissolution and deposition of the catalyst to improve the stability and activity of the catalyst. The third point is to achieve adsorption and desorption of different species by regulating the changes in the potential applied to the catalyst surface, which in turn modulates the reaction path of the catalytic process.

Although pulsed electrocatalysis has achieved some elegant research results so far and has shown us the amazing potential in the field of electrocatalysis and electrosynthesis, the research on pulsed electrocatalysis is still in its infancy, and a large number of challenges and directions that merit further research and development.

Currently, pulse electrocatalysis is most studied for CO₂RR, however, the study of its mechanism is still not systematic enough, and the whole mechanism of the effect of pulse electrocatalysis on CO₂RR has not been agreed upon. For other aspects of the application is limited, there is still a lot of application space to be explored.

Although several studies have pointed out the role of pulsed electrocatalysis in the modulation of factors at the catalyst surface interface, the changes in these factors are usually simultaneous. Therefore, the interactions of these mechanisms and the mechanism of their influence on the catalytic reaction are still unclear and require further studies.

Both the catalyst and the surface interface environment are in different states under working and non-working conditions, especially for pulsed electrocatalysis. Thus, a large number of in situ characterization techniques are necessary, which help to monitor the changes of catalyst or surface interface factors in real-time during pulsed electrocatalysis, and at the same time deepen the understanding of the whole reaction mechanism.

Due to the rapid transformation of different factors in the pulsed electrocatalytic process, even high-time-resolved in situ techniques cannot be monitored in real-time, especially for those reactions with large pulse frequencies. Therefore, computerized finite element simulation and analysis techniques combined with experimental results also play an indispensable role in the understanding of the pulsed electrocatalytic process.

A large number of studies have focused on the effect of square-wave pulses on the catalytic reaction, and few studies have been conducted on pulsed electrocatalysis with other waveforms, which is a direction that needs to be further investigated.

For the optimization of pulse parameters, the current study mainly uses the one-factor method, however, there are many process parameters for pulsed electrocatalysis, so a large number of optimization experiments are needed. This can be achieved by machine learning to optimize the system, avoiding high-throughput experiments and improving experimental efficiency.

Funding

This work was supported by the National Key R&D Program of China (2022YFA1504200), and the Provincial Natural Science Foundation of Hunan (2021JC0008, 2021JJ20024 and 2021RC3054).

Author contributions

W.C. drafted the manuscript with the assistance of Y.Q.H. under the direction of Y.Q.Z. and S.Y.W. All co-authors discussed and commented on the manuscript.

Conflict of interest

The authors declare no conflict of interest.

References

Seh ZW, Kibsgaard J, Dickens CF, et al. Combining theory and experiment in electrocatalysis: Insights into materials design. Science 2017; 355: eaad4998. [Article] [CrossRef] [PubMed] [Google Scholar]
Tang C, Zheng Y, Jaroniec M, et al. Electrocatalytic refinery for sustainable production of fuels and chemicals. Angew Chem Int Ed 2021; 60: 19572-19590. [Article] [CrossRef] [PubMed] [Google Scholar]
Malik B, Vijaya Sankar K, Aziz SKT, et al. Uncovering the change in catalytic activity during electro-oxidation of urea: Answering overisolation of the relaxation phenomenon. J Phys Chem C 2021; 125: 23126-23132. [Article] [CrossRef] [Google Scholar]
Chu S, Cui Y, Liu N. The path towards sustainable energy. Nat Mater 2017; 16: 16-22. [Article] [CrossRef] [Google Scholar]
Masaud ZLiu GRoseng LE et al. Progress on pulsed electrocatalysis for sustainable energy and environmental applications. Chem Eng J 2023; 475: 145882. [NASA ADS] [CrossRef] [Google Scholar]
Jiang R, Wang H, Liu L, et al. Recent progress of Rh-based three-way catalysts. Smart Molecules 2024; 2: 20240004 [CrossRef] [Google Scholar]
Akhade SA, Singh N, Gutiérrez OY, et al. Electrocatalytic hydrogenation of biomass-derived organics: A review. Chem Rev 2020; 120: 11370-11419. [Article] [CrossRef] [PubMed] [Google Scholar]
Chen Z, Liao Y, Chen S. Facile synthesis of platinum-copper aerogels for the oxygen reduction reaction. Energy Mater 2022; 2: 200033. [Article] [CrossRef] [Google Scholar]
Jin B, Gao J, Zhang Y, et al. Deprotonated of layered double hydroxides during electrocatalytic water oxidation for multi‐cations intercalation. Smart Molecules 2024; 2: e20230026. [Article] [CrossRef] [Google Scholar]
Novaes LFT, Liu J, Shen Y, et al. Electrocatalysis as an enabling technology for organic synthesis. Chem Soc Rev 2021; 50: 7941-8002. [Article] [CrossRef] [PubMed] [Google Scholar]
Casebolt R, Levine K, Suntivich J, et al. Pulse check: Potential opportunities in pulsed electrochemical CO₂ reduction. Joule 2021; 5: 1987-2026. [Article] [CrossRef] [Google Scholar]
Wang J, Zhou W, Li J, et al. Recent advances and performance enhancement mechanisms of pulsed electrocatalysis. Acta Chim Sin 2022; 80: 1555-1568. [Article] [CrossRef] [Google Scholar]
Yang Y, Yang Y, Pei Z, et al. Recent progress of carbon-supported single-atom catalysts for energy conversion and storage. Matter 2020; 3: 1442-1476. [Article] [CrossRef] [Google Scholar]
Liu Y, Yang Z, Zou Y, et al. Interfacial micro‐environment of electrocatalysis and its applications for organic electro‐oxidation reaction. Small 2023; 20: 2306488. [Article] [Google Scholar]
Medford AJ, Vojvodic A, Hummelshøj JS, et al. From the Sabatier principle to a predictive theory of transition-metal heterogeneous catalysis. J Catal 2015; 328: 36-42. [Article] [CrossRef] [Google Scholar]
An Z, Zhang Z, Huang Z, et al. Pt1 enhanced C-H activation synergistic with Pt_n catalysis for glycerol cascade oxidation to glyceric acid. Nat Commun 2022; 13: 5467. [Article] [CrossRef] [MathSciNet] [PubMed] [Google Scholar]
Wang B, Zhang F. Main descriptors to correlate structures with the performances of electrocatalysts. Angew Chem Int Ed 2022; 61: e202111026. [Article] [CrossRef] [Google Scholar]
Wang PY, Zhou JF, Chen H, et al. Activation of H₂ O tailored by interfacial electronic states at a nanoscale interface for enhanced electrocatalytic hydrogen evolution. JACS Au 2022; 2: 1457-1471. [Article] [CrossRef] [PubMed] [Google Scholar]
Kim C, Bui JC, Luo X, et al. Tailored catalyst microenvironments for CO₂ electroreduction to multicarbon products on copper using bilayer ionomer coatings. Nat Energy 2021; 6: 1026-1034. [Article] [CrossRef] [Google Scholar]
Xie C, Niu Z, Kim D, et al. Surface and interface control in nanoparticle catalysis. Chem Rev 2020; 120: 1184-1249 [CrossRef] [PubMed] [Google Scholar]
Li P, Jiang Y, Hu Y, et al. Hydrogen bond network connectivity in the electric double layer dominates the kinetic pH effect in hydrogen electrocatalysis on Pt. Nat Catal 2022; 5: 900-911. [Article] [CrossRef] [Google Scholar]
Rodrigo S, Um C, Mixdorf JC, et al. Alternating current electrolysis for organic electrosynthesis: Trifluoromethylation of (hetero)arenes. Org Lett 2020; 22: 6719-6723. [Article] [CrossRef] [PubMed] [Google Scholar]
Yan M, Kawamata Y, Baran PS. Synthetic organic electrochemical methods since 2000: On the verge of a renaissance. Chem Rev 2017; 117: 13230-13319. [Article] [CrossRef] [PubMed] [Google Scholar]
Amirbeigiarab R, Tian J, Herzog A, et al. Atomic-scale surface restructuring of copper electrodes under CO₂ electroreduction conditions. Nat Catal 2023; 6: 837-846. [Article] [CrossRef] [Google Scholar]
Timoshenko J, Bergmann A, Rettenmaier C, et al. Steering the structure and selectivity of CO₂ electroreduction catalysts by potential pulses. Nat Catal 2022; 5: 259-267. [Article] [CrossRef] [Google Scholar]
Li P, Li R, Liu Y, et al. Pulsed nitrate-to-ammonia electroreduction facilitated by tandem catalysis of nitrite intermediates. J Am Chem Soc 2023; 145: 6471-6479. [Article] [CrossRef] [PubMed] [Google Scholar]
Nong HN, Falling LJ, Bergmann A, et al. Key role of chemistry versus bias in electrocatalytic oxygen evolution. Nature 2020; 587: 408-413. [Article] [NASA ADS] [CrossRef] [PubMed] [Google Scholar]
Liu C, Hsu PC, Xie J, et al. A half-wave rectified alternating current electrochemical method for uranium extraction from seawater. Nat Energy 2017; 2: 17007. [Article] [CrossRef] [Google Scholar]
Liu T, Wang J, Yang X, et al. A review of pulse electrolysis for efficient energy conversion and chemical production. J Energy Chem 2021; 59: 69-82. [Article] [NASA ADS] [CrossRef] [Google Scholar]
Butler JAV, Armstrong G. The kinetics of electrode processes. Part II.—Reversible reduction and oxidation processes. Proc R Soc Lond A Math Phys Sci 1933; 139: 406-416 [NASA ADS] [Google Scholar]
Viswanathan K, Cheh HY. Mass transfer aspects of electrolysis by periodic currents. J Electrochem Soc 1979; 126: 398-401. [Article] [NASA ADS] [CrossRef] [Google Scholar]
Shipley JW, Rogers MT. The electrolysis of some organic compounds with alternating current. Can J Res 1939; 17b: 147-158. [Article] [CrossRef] [Google Scholar]
García CD, Henry CS. Coupling capillary electrophoresis and pulsed electrochemical detection. Electroanalysis 2005; 17: 1125-1131 [CrossRef] [Google Scholar]
Fedorowski J, LaCourse WR. A review of pulsed electrochemical detection following liquid chromatography and capillary electrophoresis. Anal Chim Acta 2015; 861: 1-11. [Article] [NASA ADS] [CrossRef] [PubMed] [Google Scholar]
Karaman C, Karaman O, Yola BB, et al. A novel electrochemical aflatoxin B1 immunosensor based on gold nanoparticle-decorated porous graphene nanoribbon and Ag nanocube-incorporated MoS₂ nanosheets. New J Chem 2021; 45: 11222-11233. [Article] [CrossRef] [MathSciNet] [Google Scholar]
Xu G, Jarjes ZA, Desprez V, et al. Sensitive, selective, disposable electrochemical dopamine sensor based on PEDOT-modified laser scribed graphene. Biosens Bioelectron 2018; 107: 184-191. [Article] [CrossRef] [PubMed] [Google Scholar]
Davalos R, Huang Y, Rubinsky BE. Electroporation: Bio-electrochemical mass transfer at the nano scale. Microscale Thermophys Eng 2000; 4: 147-159. [Article] [CrossRef] [Google Scholar]
Sadik MM, Yu M, Zheng M, et al. Scaling relationship and optimization of double-pulse electroporation. Biophys J 2014; 106: 801-812. [Article] [NASA ADS] [CrossRef] [PubMed] [Google Scholar]
Jadhav HS, Kalubarme RS, Ahn SJ, et al. Effects of duty cycle on properties of CIGS thin films fabricated by pulse-reverse electrodeposition technique. Appl Surf Sci 2013; 268: 391-396. [Article] [CrossRef] [Google Scholar]
Seetharaman S, Balaji R, Ramya K, et al. Electrochemical behaviour of nickel-based electrodes for oxygen evolution reaction in alkaline water electrolysis. Ionics 2014; 20: 713-720. [Article] [CrossRef] [Google Scholar]
Puippe JC, Ibl N. Influence of charge and discharge of electric double layer in pulse plating. J Appl Electrochem 1980; 10: 775-784. [Article] [Google Scholar]
Rodrigo S, Gunasekera D, Mahajan JP, et al. Alternating current electrolysis for organic synthesis. Curr Opin Electrochem 2021; 28: 100712. [Article] [CrossRef] [Google Scholar]
Hioki Y, Costantini M, Griffin J, et al. Overcoming the limitations of Kolbe coupling with waveform-controlled electrosynthesis. Science 2023; 380: 81-87. [Article] [NASA ADS] [CrossRef] [PubMed] [Google Scholar]
Kawamata Y, Hayashi K, Carlson E, et al. Chemoselective electrosynthesis using rapid alternating polarity. J Am Chem Soc 2021; 143: 16580-16588. [Article] [NASA ADS] [CrossRef] [PubMed] [Google Scholar]
Zeng L, Jiao Y, Yan W, et al. Asymmetric-waveform alternating current-promoted silver catalysis for C–H phosphorylation. Nat Synth 2023; 2: 172-181. [Article] [NASA ADS] [CrossRef] [Google Scholar]
Demir N, Kaya MF, Albawabiji MS. Effect of pulse potential on alkaline water electrolysis performance. Int J Hydrogen Energy 2018; 43: 17013-17020. [Article] [NASA ADS] [CrossRef] [Google Scholar]
Vincent I, Choi B, Nakoji M, et al. Pulsed current water splitting electrochemical cycle for hydrogen production. Int J Hydrogen Energy 2018; 43: 10240-10248. [Article] [CrossRef] [Google Scholar]
Zhang XD, Liu T, Liu C, et al. Asymmetric low-frequency pulsed strategy enables ultralong CO₂ reduction stability and controllable product selectivity. J Am Chem Soc 2023; 145: 2195-2206. [Article] [NASA ADS] [CrossRef] [PubMed] [Google Scholar]
Huang Y, He C, Cheng C, et al. Pulsed electroreduction of low-concentration nitrate to ammonia. Nat Commun 2023; 14: 7368. [Article] [NASA ADS] [CrossRef] [PubMed] [Google Scholar]
Guo M, Fang L, Zhang L, et al. Pulsed electrocatalysis enabling high overall nitrogen fixation performance for atomically dispersed Fe on TiO₂. Angew Chem 2023; 135: e202217635. [Article] [CrossRef] [Google Scholar]
He M, Wu Y, Li R, et al. Aqueous pulsed electrochemistry promotes C−N bond formation via a one-pot cascade approach. Nat Commun 2023; 14: 5088. [Article] [NASA ADS] [CrossRef] [PubMed] [Google Scholar]
Wang J, Zhou W, Li J, et al. Insights into the effects of pulsed parameters on H₂O₂ synthesis by two-electron oxygen reduction under pulsed electrocatalysis. Electrochem Commun 2023; 146: 107414. [Article] [CrossRef] [Google Scholar]
Ding Y, Zhou W, Li J, et al. Revealing the in situ dynamic regulation of the interfacial microenvironment induced by pulsed electrocatalysis in the oxygen reduction reaction. ACS Energy Lett 2023; 8: 3122-3130. [Article] [CrossRef] [Google Scholar]
Ding Y, Xie L, Zhou W, et al. Pulsed electrocatalysis enables the stabilization and activation of carbon-based catalysts towards H₂O₂ production. Appl Catal B-Environ 2022; 316: 121688. [Article] [NASA ADS] [CrossRef] [Google Scholar]
Ding Y, Zhou W, Xie L, et al. Pulsed electrocatalysis enables an efficient 2-electron oxygen reduction reaction for H₂ O₂ production. J Mater Chem A 2021; 9: 15948-15954. [Article] [CrossRef] [Google Scholar]
Jiani L, Zhicheng X, Hao X, et al. Pulsed electrochemical oxidation of acid red G and crystal violet by PbO₂ anode. J Environ Chem Eng 2020; 8: 103773. [Article] [CrossRef] [Google Scholar]
Zhou L, Liu D, Li S, et al. Effective removing of hexavalent chromium from wasted water by triboelectric nanogenerator driven self-powered electrochemical system—Why pulsed DC is better than continuous DC? Nano Energy 2019; 64: 103915 [CrossRef] [Google Scholar]
Dobó Z, Palotás ÁB. Impact of the current fluctuation on the efficiency of alkaline water electrolysis. Int J Hydrogen Energy 2017; 42: 5649-5656 [CrossRef] [Google Scholar]
Polatides C, Dortsiou M, Kyriacou G. Electrochemical removal of nitrate ion from aqueous solution by pulsing potential electrolysis. Electrochim Acta 2005; 50: 5237-5241. [Article] [CrossRef] [Google Scholar]
Karimi S, Foulkes FR. Pulse electrodeposition of platinum catalyst using different pulse current waveforms. Electrochem Commun 2012; 19: 17-20. [Article] [CrossRef] [Google Scholar]
Engelbrecht A, Uhlig C, Stark O, et al. On the electrochemical CO₂ reduction at copper sheet electrodes with enhanced long-term stability by pulsed electrolysis. J Electrochem Soc 2018; 165: 3059-3068 [Google Scholar]
Arán-Ais RM, Scholten F, Kunze S, et al. The role of in situ generated morphological motifs and Cu(I) species in C₂₊ product selectivity during CO₂ pulsed electroreduction. Nat Energy 2020; 5: 317-325 [CrossRef] [Google Scholar]
Shimizu N, Hotta S, Sekiya T, et al. A novel method of hydrogen generation by water electrolysis using an ultra-short-pulse power supply. J Appl Electrochem 2006; 36: 419-423. [Article] [Google Scholar]
Dobó Z, Palotas A. Impact of the voltage fluctuation of the power supply on the efficiency of alkaline water electrolysis. Int J Hydrogen Energy 2016; 41: 11849-11856 [CrossRef] [Google Scholar]
Xiong P, Xu HC. Chemistry with electrochemically generated N-centered radicals. Acc Chem Res 2019; 52: 3339-3350. [Article] [CrossRef] [PubMed] [Google Scholar]
Wattanakit C, Yutthalekha T, Asssavapanumat S, et al. Pulsed electroconversion for highly selective enantiomer synthesis. Nat Commun 2017; 8: 2087. [Article] [CrossRef] [PubMed] [Google Scholar]
Lee B, Naito H, Nagao M, et al. Alternating-current electrolysis for the production of phenol from benzene. Angew Chem Int Ed 2012; 51: 6961-6965. [Article] [CrossRef] [PubMed] [Google Scholar]
Blanco DE, Lee B, Modestino MA. Optimizing organic electrosynthesis through controlled voltage dosing and artificial intelligence. Proc Natl Acad Sci USA 2019; 116: 17683-17689. [Article] [NASA ADS] [CrossRef] [PubMed] [Google Scholar]
Blanco DE, Modestino MA. Organic electrosynthesis for sustainable chemical manufacturing. Trends Chem 2019; 1: 8-10. [Article] [CrossRef] [Google Scholar]
Schotten C, Taylor CJ, Bourne RA, et al. Alternating polarity for enhanced electrochemical synthesis. React Chem Eng 2021; 6: 147-151. [Article] [CrossRef] [Google Scholar]
Vehrenberg J, Vepsäläinen M, Macedo DS, et al. Steady-state electrochemical synthesis of HKUST-1 with polarity reversal. Microporous Mesoporous Mater 2020; 303: 110218. [Article] [NASA ADS] [CrossRef] [Google Scholar]
Kim D, Zhou C, Zhang M, et al. Voltage cycling process for the electroconversion of biomass-derived polyols. Proc Natl Acad Sci USA 2021; 118: e2113382118. [Article] [CrossRef] [PubMed] [Google Scholar]
Martín-Yerga D, Yu X, Terekhina I, et al. In situ catalyst reactivation for enhancing alcohol electro-oxidation and coupled hydrogen generation. Chem Commun 2020; 56: 4011-4014 [CrossRef] [PubMed] [Google Scholar]
Li Z, Yan Y, Xu SM, et al. Alcohols electrooxidation coupled with H₂ production at high current densities promoted by a cooperative catalyst. Nat Commun 2022; 13: 147. [Article] [CrossRef] [PubMed] [Google Scholar]
Adžić RR, Popov KI, Pamić MA. Acceleration of electrocatalytic reactions by pulsation of potential: Oxidation of formic acid on Pt and Pt/Pb_ads electrodes. Electrochim Acta 1978; 23: 1191-1196. [Article] [CrossRef] [Google Scholar]
Wang SR, Fedkiw PS. Pulsed-potential oxidation of methanol: I. Smooth platinum electrode with and without tin surface modification. J Electrochem Soc 1992; 139: 2519-2525. [Article] [CrossRef] [Google Scholar]
Román AM, Spivey TD, Medlin JW, et al. Accelerating electro-oxidation turnover rates via potential-modulated stimulation of electrocatalytic activity. Ind Eng Chem Res 2020; 59: 19999-20010 [CrossRef] [Google Scholar]
Saint-Denis TG, Zhu RY, Chen G, et al. Enantioselective C(sp³ )‒H bond activation by chiral transition metal catalysts. Science 2018; 359: eaao4798. [Article] [CrossRef] [PubMed] [Google Scholar]
Hickman AJ, Sanford MS. High-valent organometallic copper and palladium in catalysis. Nature 2012; 484: 177-185. [Article] [NASA ADS] [CrossRef] [PubMed] [Google Scholar]
Atkins AP, Chaturvedi AK, Tate JA, et al. Pulsed electrolysis: Enhancing primary benzylic C(sp³ )–H nucleophilic fluorination. Org Chem Front 2024; 11: 802-808. [Article] [CrossRef] [PubMed] [Google Scholar]
Monk N, Watson S. Review of pulsed power for efficient hydrogen production. Int J Hydrogen Energy 2016; 41: 7782-7791. [Article] [NASA ADS] [CrossRef] [Google Scholar]
Ma Y, Yao X, Zhang L, et al. Direct arylation of α‐amino C(sp³ )-H bonds by convergent paired electrolysis. Angew Chem Int Ed 2019; 58: 16548-16552. [Article] [Google Scholar]
Yutthalekha T, Wattanakit C, Lapeyre V, et al. Asymmetric synthesis using chiral-encoded metal. Nat Commun 2016; 7: 12678. [Article] [CrossRef] [PubMed] [Google Scholar]
Hilt G. Basic strategies and types of applications in organic electrochemistry. ChemElectroChem 2020; 7: 395-405 [CrossRef] [Google Scholar]
Lucky C, Jiang S, Shih CR, et al. Understanding the interplay between electrocatalytic C(sp3)‒C(sp3) fragmentation and oxygenation reactions. Nat Catal 2024; 7: 1021-1031. [Article] [CrossRef] [Google Scholar]
Brix AC, Krysiak OA, Cechanaviciutè IA, et al. Oxidative depolymerisation of Kraft lignin: From fabrication of multi‐metal‐modified electrodes for vanillin electrogeneration via pulse electrolysis to high‐throughput screening of multi‐metal composites. ChemElectroChem 2024; 11: e202300483. [Article] [CrossRef] [PubMed] [Google Scholar]
Sattler LE, Otten CJ, Hilt G. Alternating current electrolysis for the electrocatalytic synthesis of mixed disulfide via sulfur–sulfur bond metathesis towards dynamic disulfide libraries. Chem-Eur J 2020; 26: 3129-3136 [CrossRef] [PubMed] [Google Scholar]
Chen W, Zhang L, Xu L, et al. Pulse potential mediated selectivity for the electrocatalytic oxidation of glycerol to glyceric acid. Nat Commun 2024; 15: 2420. [Article] [Google Scholar]
Bortnikov EO, Semenov SN. Coupling of alternating current to transition-metal catalysis: Examples of nickel-catalyzed cross-coupling. J Org Chem 2021; 86: 782-793 [CrossRef] [PubMed] [Google Scholar]
Nitopi S, Bertheussen E, Scott SB, et al. Progress and perspectives of electrochemical CO₂ reduction on copper in aqueous electrolyte. Chem Rev 2019; 119: 7610-7672. [Article] [CrossRef] [PubMed] [Google Scholar]
Kuhl KP, Cave ER, Abram DN, et al. New insights into the electrochemical reduction of carbon dioxide on metallic copper surfaces. Energy Environ Sci 2012; 5: 7050-7059. [Article] [CrossRef] [Google Scholar]
Nguyen TP, Tuan Nguyen DM, Tran DL, et al. MXenes: Applications in electrocatalytic, photocatalytic hydrogen evolution reaction and CO₂ reduction. Mol Catal 2020; 486: 110850. [Article] [CrossRef] [Google Scholar]
Zhou Y, Martín AJ, Dattila F, et al. Long-chain hydrocarbons by CO₂ electroreduction using polarized nickel catalysts. Nat Catal 2022; 5: 545-554. [Article] [CrossRef] [Google Scholar]
Tang C, Gong P, Xiao T, et al. Direct electrosynthesis of 52% concentrated CO on silver’s twin boundary. Nat Commun 2021; 12: 2139. [Article] [NASA ADS] [CrossRef] [PubMed] [Google Scholar]
Zhou H, Chen Z, López AV, et al. Engineering the Cu/Mo₂CTx (MXene) interface to drive CO₂ hydrogenation to methanol. Nat Catal 2021; 4: 860-871. [Article] [CrossRef] [Google Scholar]
Lu D, Fu X, Guo D, et al. Challenges and opportunities in 2D high-entropy alloy electrocatalysts for sustainable energy conversion. SusMat 2023; 3: 730-748. [Article] [CrossRef] [MathSciNet] [Google Scholar]
Möller T, Ngo Thanh T, Wang X, et al. The product selectivity zones in gas diffusion electrodes during the electrocatalytic reduction of CO₂. Energy Environ Sci 2021; 14: 5995-6006. [Article] [CrossRef] [Google Scholar]
Liu H, Xia J, Zhang N, et al. Solid–liquid phase transition induced electrocatalytic switching from hydrogen evolution to highly selective CO₂ reduction. Nat Catal 2021; 4: 202-211. [Article] [CrossRef] [Google Scholar]
Wang D, Mao J, Zhang C, et al. Modulating microenvironments to enhance CO₂ electroreduction performance. eScience 2023; 3: 100119. [Article] [CrossRef] [Google Scholar]
Guo Y, He X, Su Y, et al. Machine-learning-guided discovery and optimization of additives in preparing Cu catalysts for CO₂ reduction. J Am Chem Soc 2021; 143: 5755-5762. [Article] [NASA ADS] [CrossRef] [PubMed] [Google Scholar]
Ma W, He X, Wang W, et al. Electrocatalytic reduction of CO₂ and CO to multi-carbon compounds over Cu-based catalysts. Chem Soc Rev 2021; 50: 12897-12914. [Article] [CrossRef] [PubMed] [Google Scholar]
Popović S, Smiljanić M, Jovanovič P, et al. Stability and degradation mechanisms of copper‐based catalysts for electrochemical CO₂ reduction. Angew Chem Int Ed 2020; 59: 14736-14746. [Article] [CrossRef] [PubMed] [Google Scholar]
Haas T, Krause R, Weber R, et al. Technical photosynthesis involving CO₂ electrolysis and fermentation. Nat Catal 2018; 1: 32-39. [Article] [CrossRef] [Google Scholar]
Yang Y, Louisia S, Yu S, et al. Operando studies reveal active Cu nanograins for CO₂ electroreduction. Nature 2023; 614: 262-269. [Article] [CrossRef] [PubMed] [Google Scholar]
DeWulf DW, Jin T, Bard AJ. Electrochemical and surface studies of carbon dioxide reduction to methane and ethylene at copper electrodes in aqueous solutions. J Electrochem Soc 1989; 136: 1686-1691. [Article] [NASA ADS] [CrossRef] [Google Scholar]
Xie JF, Huang YX, Li WW, et al. Efficient electrochemical CO₂ reduction on a unique chrysanthemum-like Cu nanoflower electrode and direct observation of carbon deposite. Electrochim Acta 2014; 139: 137-144. [Article] [CrossRef] [Google Scholar]
Nogami G, Itagaki H, Shiratsuchi R. Pulsed electroreduction of CO₂ on copper electrodes‐II. J Electrochem Soc 1994; 141: 1138-1142. [Article] [CrossRef] [Google Scholar]
Wasmus S, Cattaneo E, Vielstich W. Reduction of carbon dioxide to methane and ethene—An on-line MS study with rotating electrodes. Electrochim Acta 1990; 35: 771-775. [Article] [CrossRef] [Google Scholar]
Shiratsuchi R, Aikoh Y, Nogami G. Pulsed electroreduction of CO₂ on copper electrodes. J Electrochem Soc 1993; 140: 3479-3482. [Article] [NASA ADS] [CrossRef] [Google Scholar]
Lee J, Tak Y. Electrocatalytic activity of Cu electrode in electroreduction of CO₂. Electrochim Acta 2001; 46: 3015-3022. [Article] [CrossRef] [Google Scholar]
Gao D, Arán-Ais RM, Jeon HS, et al. Rational catalyst and electrolyte design for CO₂ electroreduction towards multicarbon products. Nat Catal 2019; 2: 198-210. [Article] [CrossRef] [Google Scholar]
Jung H, Lee SY, Lee CW, et al. Electrochemical fragmentation of Cu₂ O nanoparticles enhancing selective C–C coupling from CO₂ reduction reaction. J Am Chem Soc 2019; 141: 4624-4633. [Article] [CrossRef] [PubMed] [Google Scholar]
Grosse P, Gao D, Scholten F, et al. Dynamic changes in the structure, chemical state and catalytic selectivity of Cu nanocubes during CO₂ electroreduction: Size and support effects. Angew Chem Int Ed 2018; 57: 6192-6197. [Article] [CrossRef] [PubMed] [Google Scholar]
Timoshenko J, Rettenmaier C, Hursán D, et al. Reversible metal cluster formation on nitrogen-doped carbon controlling electrocatalyst particle size with subnanometer accuracy. Nat Commun 2024; 15: 6111. [Article] [NASA ADS] [CrossRef] [PubMed] [Google Scholar]
Jouny M, Luc W, Jiao F. General techno-economic analysis of CO₂ electrolysis systems. Ind Eng Chem Res 2018; 57: 2165-2177. [Article] [CrossRef] [Google Scholar]
Lin SC, Chang CC, Chiu SY, et al. Operando time-resolved X-ray absorption spectroscopy reveals the chemical nature enabling highly selective CO₂ reduction. Nat Commun 2020; 11: 3525. [Article] [CrossRef] [PubMed] [Google Scholar]
Mistry H, Varela AS, Bonifacio CS, et al. Highly selective plasma-activated copper catalysts for carbon dioxide reduction to ethylene. Nat Commun 2016; 7: 12123. [Article] [CrossRef] [Google Scholar]
Li CW, Ciston J, Kanan MW. Electroreduction of carbon monoxide to liquid fuel on oxide-derived nanocrystalline copper. Nature 2014; 508: 504-507. [Article] [NASA ADS] [CrossRef] [PubMed] [Google Scholar]
Yano J, Morita T, Shimano K, et al. Selective ethylene formation by pulse-mode electrochemical reduction of carbon dioxide using copper and copper-oxide electrodes. J Solid State Electrochem 2007; 11: 554-557. [Article] [CrossRef] [Google Scholar]
Liu C, Hedström S, Stenlid JH, et al. Amorphous, periodic model of a copper electrocatalyst with subsurface oxygen for enhanced CO coverage and dimerization. J Phys Chem C 2019; 123: 4961-4968. [Article] [CrossRef] [Google Scholar]
Li Z, Wang L, Sun L, et al. Dynamic cation enrichment during pulsed CO₂ electrolysis and the cation-promoted multicarbon formation. J Am Chem Soc 2024; 146: 23901-23908. [Article] [NASA ADS] [CrossRef] [PubMed] [Google Scholar]
Kimura KW, Casebolt R, Cimada DaSilva J, et al. Selective electrochemical CO₂ reduction during pulsed potential stems from dynamic interface. ACS Catal 2020; 10: 8632-8639. [Article] [CrossRef] [Google Scholar]
Bui JC, Kim C, Weber AZ, et al. Dynamic boundary layer simulation of pulsed CO₂ electrolysis on a copper catalyst. ACS Energy Lett 2021; 6: 1181-1188 [Google Scholar]
Li Z, Wang L, Wang T, et al. Steering the dynamics of reaction intermediates and catalyst surface during electrochemical pulsed CO₂ reduction for enhanced C₂₊ selectivity. J Am Chem Soc 2023; 145: 20655-20664. [Article] [CrossRef] [PubMed] [Google Scholar]
Kim C, Weng LC, Bell AT. Impact of pulsed electrochemical reduction of CO₂ on the formation of C₂₊ products over Cu. ACS Catal 2020; 10: 12403-12413. [Article] [CrossRef] [Google Scholar]
Gupta N, Gattrell M, MacDougall B. Calculation for the cathode surface concentrations in the electrochemical reduction of CO₂ in KHCO₃ solutions. J Appl Electrochem 2006; 36: 161-172. [Article] [Google Scholar]
Kimura KW, Fritz KE, Kim J, et al. Controlled selectivity of CO₂ reduction on copper by pulsing the electrochemical potential. ChemSusChem 2018; 11: 1781-1786. [Article] [NASA ADS] [CrossRef] [PubMed] [Google Scholar]
Kumar B, Brian JP, Atla V, et al. Controlling the product syngas H₂ :CO ratio through pulsed-bias electrochemical reduction of CO₂ on copper. ACS Catal 2016; 6: 4739-4745. [Article] [CrossRef] [Google Scholar]
Jasem SM, Tseung ACC. A potentiostatic pulse study of oxygen evolution on teflon‐bonded nickel‐cobalt oxide electrodes. J Electrochem Soc 1979; 126: 1353-1360. [Article] [CrossRef] [Google Scholar]
Shaaban AH. Water electrolysis and pulsed direct current. J Electrochem Soc 1993; 140: 2863 [NASA ADS] [CrossRef] [Google Scholar]
de Radiguès Q, Thunis G, Proost J. On the use of 3-D electrodes and pulsed voltage for the process intensification of alkaline water electrolysis. Int J Hydrogen Energy 2019; 44: 29432-29440 [CrossRef] [Google Scholar]
Vanags M, Kleperis J, Bajars G. Electrolyses model development for metal/electrolyte interface: Testing with microrespiration sensors. Int J Hydrogen Energy 2011; 36: 1316-1320. [Article] [CrossRef] [Google Scholar]
Hristova D, Betova I, Tzvetkoff T. An electrochemical and analytical characterization of surface films on AISI 316 as electrode material for pulse electrolysis of water. Int J Hydrogen Energy 2013; 38: 8232-8243. [Article] [CrossRef] [Google Scholar]
Khosla NK, Venkatachalam S, Somasundaran P. Pulsed electrogeneration of bubbles for electroflotation. J Appl Electrochem 1991; 21: 986-990. [Article] [Google Scholar]
Lin MY, Hourng LW. Effects of magnetic field and pulse potential on hydrogen production via water electrolysis. Int J Energy Res 2014; 38: 106-116. [Article] [NASA ADS] [CrossRef] [Google Scholar]
Yang F, Kim MJ, Brown M, et al. Alkaline water electrolysis at 25 A cm⁻² with a microfibrous flow-through electrode. Adv Energy Mater 2020; 10: 2001174. [Article] [CrossRef] [Google Scholar]
Chong MN, Jin B, Chow CWK, et al. Recent developments in photocatalytic water treatment technology: A review. Water Res 2010; 44: 2997-3027. [Article] [CrossRef] [PubMed] [Google Scholar]
Lan J, Sun Y, Huang P, et al. Using electrolytic manganese residue to prepare novel nanocomposite catalysts for efficient degradation of Azo dyes in fenton-like processes. Chemosphere 2020; 252: 126487. [Article] [NASA ADS] [CrossRef] [PubMed] [Google Scholar]
Sharma AK, Locke BR, Arce P, et al. A preliminary study of pulsed streamer corona discharge for the degradation of phenol in aqueous solutions. Hazard Waste Hazard Mater 1993; 10: 209-219. [Article] [CrossRef] [Google Scholar]
Chen YS, Zhang XS, Dai YC, et al. Pulsed high-voltage discharge plasma for degradation of phenol in aqueous solution. Separation Purification Tech 2004; 34: 5-12. [Article] [CrossRef] [Google Scholar]
Zhu X, Tong M, Shi S, et al. Essential explanation of the strong mineralization performance of boron-doped diamond electrodes. Environ Sci Technol 2008; 42: 4914-4920. [Article] [CrossRef] [PubMed] [Google Scholar]
Chen X, Gao F, Chen G. Comparison of Ti/BDD and Ti/SnO₂–Sb₂O₅ electrodes for pollutant oxidation. J Appl Electrochem 2005; 35: 185-191. [Article] [Google Scholar]
Wei J, Zhu X, Ni J. Electrochemical oxidation of phenol at boron-doped diamond electrode in pulse current mode. Electrochim Acta 2011; 56: 5310-5315. [Article] [CrossRef] [Google Scholar]
Pei S, You S, Zhang J. Application of pulsed electrochemistry to enhanced water decontamination. ACS EST Eng 2021; 1: 1502-1508. [Article] [CrossRef] [Google Scholar]
Diao Y, Wei F, Zhang L, et al. The electrochemical degradation of malachite green with lead dioxide electrodes by pulse current oxidation methods. Int J Environ Anal Chem 2020; 102: 1126-1140. [Article] [Google Scholar]
Xu J, Liu C, Hsu PC, et al. Remediation of heavy metal contaminated soil by asymmetrical alternating current electrochemistry. Nat Commun 2019; 10: 2440. [Article] [CrossRef] [PubMed] [Google Scholar]
Tabushi I, Kobuke Y, Nishiya T. Extraction of uranium from seawater by polymer-bound macrocyclic hexaketone. Nature 1979; 280: 665-666. [Article] [NASA ADS] [CrossRef] [Google Scholar]
Chen GF, Yuan Y, Jiang H, et al. Electrochemical reduction of nitrate to ammonia via direct eight-electron transfer using a copper–molecular solid catalyst. Nat Energy 2020; 5: 605-613. [Article] [NASA ADS] [CrossRef] [Google Scholar]
Bu Y, Wang C, Zhang W, et al. Electrical pulse‐driven periodic self‐repair of Cu‐Ni tandem catalyst for efficient ammonia synthesis from nitrate. Angew Chem Int Ed 2023; 62: e202217337. [Article] [CrossRef] [PubMed] [Google Scholar]
Wang Y, Zhou W, Jia R, et al. Unveiling the activity origin of a copper‐based electrocatalyst for selective nitrate reduction to ammonia. Angew Chem Int Ed 2020; 59: 5350-5354. [Article] [NASA ADS] [CrossRef] [PubMed] [Google Scholar]
Gerke CSKlenk MZapol P et al. Pulsed-potential electrolysis enhances electrochemical C–N coupling by reorienting interfacial ions. ACS Catal 2023; 13: 1454014547. [CrossRef] [Google Scholar]

All Tables

Table 1

Summary of the effect of pulsed electrocatalysis on different catalytic reactions

In the text

All Figures

	Figure 1 Summary of pulsed electrocatalysis-related literature publications and citations in recent years. Data from Web of Science as of September 2024.
In the text

	Figure 2 Schematic illustration of the application of pulsed electrochemistry for enhancing electrocatalysis and sustainable electrosynthesis.
In the text

Figure 3

(a) Demonstration of the different current waveforms. (b) The maximal ripple factor of different current waveforms. (c) Hydrogen generation efficiency as a function of amplitude. j_DC is the mean current density (offset), and f is the frequency of the waveform. (d) Hydrogen generation efficiency as a function of frequency at different ripple factors. The graph represents the results obtained with square waveform. (Reproduced from Ref. [58]. Copyright©2017, Springer Nature Limited).

In the text

Figure 4

(a) Considerations for altered mass transfer. A: normal reaction dependent on mass transport (blue M); B: switch avoids mass transport by forming intermediates on both electrodes; C: reverse reaction of copper cation possible (Reproduced from Ref. [70]. Copyright©2021, RSC Pub). (b) EPC for sorbitol conversion. Current density traces of EPC with a total of 4,000 cycles at 100 mV/s. The red arrows indicate the scan direction. Yellow arrows indicate the trend of current density curves throughout. (c) Product selectivity and K/A by EPC and the average of SS runs (Reproduced from Ref. [72]. Copyright©2021, National Academy of Science of the United States of America). (d) Scheme illustrating the catalyst in situ reactivation by applying the potential pulse program (E_high and E_low) (Reproduced from Ref. [73]. Copyright 2020, RSC Pub). (e) The proposed mechanism of asymmetric-waveform alternating current-promoted silver catalysis for C–H phosphorylation (Reproduced from Ref. [45]. Copyright©2022, Springer Nature Limited).

In the text

Figure 5

The summarized of pulsed electrolysis specific effects on mass transfer for different reactions. OES: organic electrosynthesis, WER: water electrolysis reaction, CO₂RR: carbon dioxide reduction reaction, NRR: nitrogen reduction reaction, ORR: oxygen reduction reaction, EECM: element extraction and contaminant mitigation. These summary data were derived from the relevant research papers cited in this review.

In the text

Figure 6

(a) The graph on the left shows a DPA potential waveform. The graphical representations in the center and right describe the effects that cathodic and resting potentials, respectively (Reproduced from Ref. [68]. Copyright©2019, National Academy of Science of the United States of America). (b) Comparison of conventional and pulsed chiral electrosynthesis (Reproduced from Ref. [66]. Copyright©2017, Springer Nature Limited). (c) Alternating current electrolysis for organic electrosynthesis: Trifluoromethylation of (Hetero)arenes. (Reproduced from Ref. [22]. Copyright©2020, American Chemical Society).

In the text

Figure 7

(a) Potential programme for the repeated generation and desorption of methane from butane adsorbed at 0.3 V for 15 min. Inset: Methane generation is hypothesized to occur through two steps. The fragmentation potential (E₁) was varied between 0.4 and 0.7 V. E₂, desorption potential; t₁, time of fragmentation step; t₂, time of desorption step. (Reproduced from Ref. [85]. Copyright©2024, Springer Nature Limited). (b) Results of constant current electrolysis in a divided cell. Conditions: divided cell; Pt/Pt (1.0 cm² each); 10 mA; 1/2 (0.5 mmol each), CH₃CN (10 mL), TBABF₄ (0.3 M), rt. (Reproduced from Ref. [87]. Copyright©2020, Wiley-VCH GmbH). (c) Chemoselective electrosynthesis using rapid alternating polarity. (Reproduced from Ref. [44]. Copyright©2021, American Chemical Society). (d) Schematic of the pathways of pulsed electrocatalytic oxidation of glycerol. GLY: glycerol, GLAD: glyceraldehyde, GLA: glyceric acid, TA: tartronic acid, GA: glycolic acid. (Reproduced from Ref. [88]. Copyright©2024, The Author(s)).

In the text

Figure 8

Atomic force microscopy images of a Cu (100) electrode after different surface treatments and reaction settings. (a) Constant potential of −1.0 V versus RHE; Pulsed electrolysis: (b) E_a= 0.6 V, E_c= −1.0 V, t_a=t_c= 1 s. (c) The surface from panel (b) after a subsequent hour of potentiostatic electrolysis at −1.0 V versus RHE. (Reproduced from Ref. [62]. Copyright©2020, Springer Nature Limited). (d) Schematic depiction of the catalyst structure and composition during a cathodic pulse extracted from XAS and XRD data. (Reproduced from Ref. [25]. Copyright©2022, Springer Nature Limited). (e) Design and performance of ALPS-1, ALPS-2, and potentiostatic methods for Cu₃(DMPz)₃ Catalyst (Reproduced from Ref. [48]. Copyright©2023, American Chemical Society). (f) Faradaic efficiencies of the reaction products under static CO₂RR at −1.35 V and under pulsed CO₂RR with E_c = − 1.35 V, E_a = 0.44 V, Δt_a = 30 s and different Δt_c values (30, 10, and 1 s). (g) Corresponding selectivity for H₂ and the main gaseous CO₂RR products as a function of Δt_c. Inset: calculated concentrations of Cu within cationic single site species (x_SAC), small Cu clusters (x_S), and large Cu nanoparticles (x_L). Shaded regions indicated as (i), (ii), and (iii) mark three distinct regimes with different selectivity trends, and dominated by different Cu species, as indicated in (h) (Reproduced from Ref. [114]. Copyright©2024, Springer Nature Limited).

In the text

Figure 9

(a) LCA-XANES analysis results (grey open circles) for averaged data for NCs under CO₂RR with pulse lengths Δt_a=Δt_c= 10 s, E_c=−1.0 V and E_a= 0.6 V. (b) Evolution of the Cu (311) Bragg peak parameters. (c) Evolution of the Cu₂O-like Bragg peak parameters during the anodic pulse. (Reproduced from Ref. [25]. Copyright©2022, Springer Nature Limited). (d) Time-resolved variations using Redox Shuttle (R.S.) of Cu species in CuO_x and the corresponding electrochemical responses during CO₂RR at −0.75 V and (e) the corresponding time-resolved EXAFS spectra without phase-correction of CuO_x under CO₂RR. (f) Time-resolved variations using chronoamperometry (CA) of Cu species in CuO_x and the corresponding electrochemical responses during CO₂RR at −0.75 V and (g) the corresponding time-resolved EXAFS spectra without phase-correction of CuO_x under CO₂RR. Quantification of time-resolved chemical composition information extracted from operando Quick Cu XAS for CuO_x under eCO₂RR using redox shuttle (h) and conventional chronoamperometry (i) (Reproduced from Ref. [116]. Copyright©2020, Springer Nature Limited).

In the text

Figure 10

(a) Dynamic transformation of CO_ads on Cu surface during static (Right) and pulsed CO₂RR (Left) at indicated time ranges at E_c = −0.60 V (Reproduced from Ref. [124]. Copyright©2023, American Chemical Society). (b) Experimental faradic efficiency for pulsed- and constant-potential CO₂RR in thick and thin boundary layers (Reproduced from Ref. [127]. Copyright©2018, Wiley-VCH GmbH). (c) Schematic depiction of enhanced CO₂RR using ionomers (Reproduced from Ref. [19]. Copyright©2021, Springer Nature Limited).

In the text

Figure 11

(a) The waveform of the applied bias and the physical process in the AACE filtration (Reproduced from Ref. [146]. Copyright©2019, Springer Nature Limited). Schematics of physicochemical and HW-ACE extraction. (b) In physicochemical adsorption systems, Coulomb repulsion can cause incoming ions to be rejected by the adsorbed charged ions. (c) Competition between uranyl ions and other cations reduces the adsorption of uranyl ions and results in the blocking of active sites. (d) Physical processes in HW-ACE extraction (Reproduced from Ref. [28]. Copyright©2017, Springer Nature Limited).

In the text

Figure 12

(a) Schematic diagram of NOR and NRR process at the anode and cathode chamber by pulsed electrocatalysis (Reproduced from Ref. [50]. Copyright©2023, Wiley-VCH GmbH). Schematic of reaction pathways with CE and PE. (b) Profile of applied potentials for CE. (c) Reaction mechanism of the NO₃RR with CE at E_L and E_H. (d) Profile of the applied potential for PE. (e) Reaction pathways of the NO₃RR through the tandem NO₂⁻ accumulation-conversion process with PE (Reproduced from Ref. [26]. Copyright©2023, American Chemical Society). (f) In situ Raman spectra of RuIn₃/C under −0.1 V and then +0.6 V in 0.1 M KOH + 10 mM NO₃⁻ solution with 3 cycles. (g) Schematic illustration for the effect of pulsed voltage on the mass transport of different species (Reproduced from Ref. [49]. Copyright©2023, Springer Nature Limited).

In the text

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Pulsed electrochemistry: A pathway to enhanced electrocatalysis and sustainable electrosynthesis

INTRODUCTION

PULSED ELECTROCATALYSIS (PE) PROCESS

Waveforms of pulsed electrocatalysis

Potential of pulsed electrocatalysis

Pulse time parameters of pulsed electrocatalysis

APPLICATIONS FOR PULSED ELECTROCATALYSIS

Organic electrosynthesis

The stability of the catalyst

Release of mass transfer limitations

Preventing over-oxidation/reduction

CO2RR

Regulation of catalyst surface structure

Modulation of the surface microenvironment

Facilitation of mass transfer

Water splitting

Contaminant removal and element extraction

Electrochemical nitrogen fixation and ORR

CONCLUSIONS AND PERSPECTIVES

Funding

Author contributions

Conflict of interest

References

All Tables

All Figures

CO₂RR