Energy–entropy competition in cation–hydroxyl interactions at the liquid water–Pt(111) interface

Abstract

Electrochemical reaction rates are sensitive to interactions between electrolyte cations and adsorbed reaction intermediates, e.g., cation–*OH interactions in the oxygen reduction reaction on platinum. Here, we calculate the free energy interaction between adsorbed *OH and K⁺/Li⁺ situated at the liquid water–Pt(111) interface using ab initio molecular dynamics (AIMD) and metadynamics. Li⁺ stabilizes *OH by 0.1 ± 0.1 eV and K⁺ destabilizes *OH by 0.1 ± 0.1 eV, in qualitative agreement with experimental cyclic voltammogram (CV) measurements. In contrast, the internal energy of *OH is stabilized by 0.3 eV and 0.4 eV for Li⁺ and K⁺, respectively. This demonstrates that entropy significantly destabilizes cation–*OH interactions and is vital in order to understand even the relative influence of cations at interfaces.