Decoding Hydrogen-Affinity-Controlled Surface State Evolution in Sn-Based Single-Atom Alloys for CO2 Electroreduction

The catalytic role of heteroatom dopants in Sn-based electrocatalysts remains elusive because the dynamic evolution of surface states under electrochemical conditions is rarely considered. Herein, density functional theory calculations combined with pH-dependent microkinetic simulations reveal that hydrogen affinity governs the evolution of catalytic surface states in Sn-based single-atom alloys (SAAs) during electrochemical CO2 reduction to formate. We demonstrate that hydrogen preferentially occupies either dopant or neighboring Sn sites depending on the electronic structure of the dopant and identify simple electronic descriptors based on the dopant d-band and p-band centers that enable the screening of preferential H adsorption sites. Surface Pourbaix analysis further reveals that Sn-based SAAs tend to evolve into nearly monolayer hydrogen-covered surfaces under practical CO2RR conditions, indicating that the catalytic performance should be evaluated on reconstructed rather than pristine surfaces. By incorporating dipole-field interactions, explicit potential of zero charge, and pH-dependent electric-field effects into microkinetic modeling, a predictive pH-dependent activity volcano is established, showing excellent agreement with experimental benchmarking. The resulting framework identifies promising catalysts with distinct pH-dependent activity windows and, more importantly, establishes hydrogen affinity as a fundamental descriptor governing surface-state evolution and thereby influencing catalytic performance, providing a general strategy for the rational design of p-block-metal-based electrocatalysts.