Hydrogen Evolution on Electrode-Supported Ptn Clusters: Ensemble of Hydride States Governs the Size Dependent Reactivity

We report the size-dependent activity and stability of supported Pt-1,Pt-4,Pt-7,Pt-8 for electrocatalytic hydrogen evolution reaction, and show that clusters outperform polycrystalline Pt in activity, with size-dependent stability. To understand the size effects, we use DFT calculations to study the structural fluxionality under varying potentials. We show that the clusters can reshape under H coverage and populate an ensemble of states with diverse stoichiometry, structure, and thus reactivity. Both experiment and theory suggest that electrocatalytic species are hydridic states of the clusters (2 H/Pt). An ensemble-based kinetic model reproduces the experimental activity trend and reveals the role of metastable states. The stability trend is rationalized by chemical bonding analysis. Our joint study demonstrates the potential- and adsorbate-coverage-dependent fluxionality of subnano clusters of different sizes and offers a systematic modeling strategy to tackle the complexities.

Automated summary

We studied the size-dependent activity and stability of supported Pt-1, Pt-4, Pt-7, and Pt-8 for electrocatalytic hydrogen evolution reaction and found that clusters have higher activity than polycrystalline Pt, along with size-dependent stability. DFT calculations were used to understand the size effects by studying the structural fluxionality under different potentials. Our research showed that the clusters can reshape under H coverage, leading to a diverse ensemble of states with varying stoichiometry, structure, and reactivity. Both experimental and theoretical results suggest that the electrocatalytic species are hydridic states of the clusters (2 H/Pt). An ensemble-based kinetic model reproduced the experimental activity trend and highlighted the role of metastable states. The stability trend was rationalized through chemical bonding analysis. Our joint study showcases the potential- and adsorbate-coverage-dependent fluxionality of subnano clusters of different sizes and provides a systematic modeling strategy to tackle the complexities.