For centuries, nature is the source of inspiration to mankind in various aspects including materials, processes, concepts, and so on [1]. In particular, bio-inspired electrocatalysts and devices have played pivotal roles in energy conversion and storage reactions [2]. Vesicles, a hollow structure constructed from dual layers of amphiphilic lipids with both hydrophilic head and hydrophobic tail, are playing vital roles in material transport and other biological processes (Figure 1a) [3]. While exposed to water, the interaction between the hydrophobic tail and the solvent should be minimized to reduce surface tension, giving the driving force toward formation of vesicles. Taking inspiration from natural vesicles, artificial vesicles and micelles were synthesized using amphiphilic block copolymers as soft templates and hollow/mesoporous metal-based catalysts mimicking the natural vesicle morphology could be fabricated [4]. Despite the fruitful achievements, current synthetic strategies were limited to mainly metal oxides. Synthesis of all-metallic vesicles has remained a great challenge and was seldom reported in literature.

Figure 1 Schematic drawing of the formation mechanism for (a) bio-vesicles and (b) RhRu nanovesicles. (c) TEM image of a typical RhRu nanovesicle. (d) Mass and specific hydrogen oxidation reaction activity of RhRu nanovesicles/C, RhRu nanosheets/C, Rh/C, and Pt/C. (e) Catalyst durability evaluation of RhRu nanovesicles/C, RhRu nanosheets/C, Rh/C, and Pt/C in H2-saturated 0.1 M KOH at an overpotential of 100 mV vs. reversible hydrogen electrode. (f) Polarization and power density curves of H2-O2 HEMFCs with RhRu nanovesicles/C and commercial Pt/C.

In a recent study, Zhang et al. has utilized interfacial strains as the driving force to curl ultrathin nanosheets, presenting an unconventional wet-chemistry strategy for synthesis of nature-mimicking all-metallic nanovesicles (Figure 1b) [5]. Rh nanosheets were formed at the initial stage, followed by deposition of Ru atoms onto the surface of Rh nanosheets, generating the RhRu alloy overlayer. The lattice mismatch between the two layers generates the interfacial strain force, and bending of nanosheets occurred to relieve such a strain force, giving rise to the desired nanovesicle structure. On the basis of transmission electron microscopy (TEM) image (Figure 1c), the as-prepared RhRu hollow nanovesicles have high size uniformity and a mean diameter of 89.5 nm, while the vesicle shell was constructed with several layers and each layer was 1.1 nm in thickness.

Owing to its unique vesicular morphology and the associated compressive strain on exposed Rh surface, this RhRu nanovesicle/C catalyst has demonstrated superior performance for hydrogen oxidation reaction. When evaluated using standard rotating disk electrode (RDE) conditions, this RhRu nanovesicle/C catalyst has demonstrated a high mass activity of 7.52 A mg_(Rh+Ru)⁻¹ at an overpotential of 50 mV, which is 3.40 times higher than that of RhRu nanosheets/C and 24.19 times higher than that of commercial Pt/C (Figure 1d). More importantly, this RhRu nanovesicles/C catalyst has shown remarkable stability with only 16% deactivation after a continuous testing of 2000 s at 100 mV overpotential (Figure 1e). Moreover, the catalyst was evaluated with H₂-O₂ hydroxide exchange membrane fuel cell (HEMFC) using membrane electrode assembly (Figure 1f). The peak power density achieved using RhRu nanovesicle/C catalyst was 1.62 W cm⁻², which is much higher than that of commercial Pt/C catalyst (1.18 W cm⁻²).

In summary, the work by Zhang et al. demonstrates a novel strategy of utilizing interfacial strain force for the fabrication of hollow all-metallic RhRu vesicles with significantly enhanced HOR activity and durability, surpassing both its nanosheet counterpart and commercial Pt/C catalysts. This synthetic strategy has shed light on morphological manipulation of all-metallic catalysts, and we believe it has great potential to be adapted with other metal compositions toward broader catalytic applications.

References

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

All Figures

Figure 1 Schematic drawing of the formation mechanism for (a) bio-vesicles and (b) RhRu nanovesicles. (c) TEM image of a typical RhRu nanovesicle. (d) Mass and specific hydrogen oxidation reaction activity of RhRu nanovesicles/C, RhRu nanosheets/C, Rh/C, and Pt/C. (e) Catalyst durability evaluation of RhRu nanovesicles/C, RhRu nanosheets/C, Rh/C, and Pt/C in H2-saturated 0.1 M KOH at an overpotential of 100 mV vs. reversible hydrogen electrode. (f) Polarization and power density curves of H2-O2 HEMFCs with RhRu nanovesicles/C and commercial Pt/C.

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