Machine learning force field molecular dynamics simulation of interfacial reactions on platinum in concentrated aqueous electrolytes

Abstract

Aqueous lithium-ion batteries provide a promising route toward safe and sustainable energy storage, yet their energy density is constrained by the narrow electrochemical stability window of aqueous electrolytes. Although high salt concentrations can kinetically extend the cathodic limit of the electrolyte via anion-derived interphases, this effect depends strongly on the electrode material and is absent on platinum. To elucidate the interfacial reaction mechanisms behind the absence of cathodic-limit extension on platinum, we performed molecular dynamics simulations based on a machine learning force field, combining near first-principles accuracy with large-scale configurational sampling. The simulations reveal a dominant pathway for anion decomposition on a hydrogen-covered platinum surface under cathodic conditions, mediated by adsorbed hydrogen (H*). However, this pathway directly competes with hydrogen evolution via the Tafel step (2H* → H2) at comparable activation barriers, suppressing the formation of stable anion-derived interphases and the extension of the cathodic limit. These findings reveal interfacial H* coverage as a key factor governing electrode-dependent cathodic stabilization in concentrated aqueous electrolytes.