| Abstract Scope |
Electrode potential is a thermodynamic control variable of electrochemical interfaces, complementing temperature, pressure, and composition in determining the equilibrium interfacial state. Using constant-potential, explicit-water ab initio molecular dynamics and grand-canonical analysis on an absolute electrochemical scale, we construct potential-dependent interfacial phase diagrams for two contrasting metal–water systems. For passivating Al(111), grand-canonical free energies of 22 solvated metastable configurations define a convex hull with voltage-driven stability transitions among a clean surface, an ordered passivating oxide, and a disordered oxide at anodic potentials. For catalytic Pt(111), potential selects hydrogen-rich and water-rich interfacial states with distinct wettability and charge-transfer response. Across both systems, electrode potential determines the preferred atomic structure and response mechanism, establishing the thermodynamic basis for passivation, oxide evolution, corrosion resistance, and catalytic behavior. These phase diagrams extend interface thermodynamics to operating electrochemical conditions and provide a unified framework for predicting interfacial structure, stability, and function. |