Anomalous Enhancement of the Electrocatalytic Hydrogen Evolution Reaction in AuPt Nanoclusters

Energy- and resource-efficient electrocatalytic water splitting is of paramount importance to enable hydrogen production. The best bulk catalyst for the hydrogen evolution reaction (HER), platinum, is one of the scarcest elements on Earth. The use of nanoclusters significantly reduces the amount of raw material required for HER, while nanoalloying further enhances performance by modulating hydrogen adsorption. However, the interplay between the atomic structure and HER performance in alloyed nanoclusters remains unclear. In this study, we report an anomalous HER enhancement at low and intermediate Au contents in monodisperse AuPt nanoclusters immobilized on carbon nanotubes. This enhancement is driven by the segregation of Au atoms toward the nanocluster surface and a synergistic effect, whereby the ability of surface Pt atoms to bind hydrogen is increased in the presence of adjacent Au atoms. This enhancement is noteworthy and “anomalous”, given that the overall hydrogen adsorption activity significantly decreases for pure Au nanoclusters compared to pure Pt nanoclusters. We rationalize these observations by combining extensive experimental characterization data with detailed atomistic simulations based on purpose-built machine learning interatomic potential and Markov-chain Monte Carlo simulations with variable chemical potential. The agreement between simulation and experiment allows us to develop a mechanistic understanding of the atomic-scale processes underlying the enhanced HER activity.