Fluxional Coordination-Driven Reversible Metal–Support Bonding in Dual-Atom Electrocatalysts for HER

Abstract

Dual-atom catalysts (DACs) are emerging as promising candidates for electrocatalytic energy conversion, yet the role of metal coordination geometry in governing catalytic function remains unexplored. Despite their promising catalytic performance, the stability of DACs and the role of the coordination environment under operating conditions remain poorly understood. Therefore, we use ab initio molecular dynamics (AIMD) and slow-growth free-energy simulations to understand how the coordination environment of Pt in an Fe-phthalocyanine (Fe-Pc)-based Fe–Pt DAC dictates hydrogen evolution reaction (HER) activity and structural stability. The focus of the study has been on the role of coordinative unsaturation, the reversible metal–support bonding, interfacial synergy with the Volmer step, and kinetic vs thermodynamic active sites. We demonstrate that a three-coordinated Pt site (2N, 1C) significantly outperforms its four-coordinated counterpart, reducing the free-energy barrier for hydrogen adsorption from 2.08 eV to a kinetically accessible 0.75 eV. AIMD simulations with explicit acidic electrolyte (1 M H2SO4) reveal that the three-coordinated Pt site undergoes reversible structural reorganization during catalysis, including breaking and reforming a Pt–N bond while adsorbing two water molecules. Unexpectedly, while charge-density analysis initially suggested Fe as the more electron-rich center, free-energy simulations identified Pt as the kinetically favored active site for HER. By explicitly modeling the acidic electrolyte, we capture the cooperative dynamics of H2SO4 dissociation and H+ hydration. This reveals how the dual-metal environment facilitates a cooperative Volmer step through synchronized water orientation and proton transfer. This work shows that the catalytic superiority of DACs arises from the synergistic interplay among coordination flexibility, reversible metal–support bonding, and cooperative dual-metal functionality for HER.