Synergistic cation-facet effects boost alkaline hydrogen evolution kinetics on stepped Pt surfaces

Understanding how electrolyte-catalyst interactions govern reaction kinetics is crucial for advancing electrocatalytic hydrogen production. Here, we elucidate the atomic-scale synergy between alkali cations and platinum surface structure in accelerating the alkaline hydrogen evolution reaction (HER) through combined constant-potential density functional theory and ab initio molecular dynamics simulations. Our simulations demonstrate that stepped Pt(311) surfaces uniquely stabilize Na⁺ cations through formation of a Pt-H₂O-Na⁺(H₂O)ₓ adduct at step edges, positioning cations 2.3 Å closer to the surface than on Pt(111) terraces. This proximity creates a stronger interfacial electric field that polarizes adjacent water molecules, inducing partial O-H bond dissociation and lowering the Volmer step activation energy by 0.14 eV - threefold greater than the reduction observed on Pt(111). The stark facet dependence arises from fundamental differences in ion-surface coordination, with Pt(111) maintaining distant cation solvation that minimally perturbs HER kinetics. These findings establish cation-facet cooperativity as a key design principle, showing how atomic-scale control of both surface geometry and the electrochemical double layer can overcome intrinsic kinetic limitations of alkaline HER catalysis.