Cation-Dependent Interfacial Properties Determine the Activity of Pt(111) Electrodes in Alkaline Media.

Energy conversion and storage technologies require optimal electrode-electrolyte interfaces to drive electrocatalytic reactions. However, the impact of interfacial phenomena on the catalytic activity remains debated. This study investigates the role of alkali metal cations in interfacial properties and correlates them with electrocatalytic activities toward several energy-related reactions in alkaline media using model Pt(111) single crystal electrodes. Through electrochemical impedance spectroscopy and laser-induced current transient techniques, interfacial parameters, such as the double layer capacitance, the potential of the capacitance minimum, and the potential of maximum entropy (pme), are determined. The latter exhibit a linear dependence on cation hydration energies. Notably, two distinct pmes are observed at the Pt(111)-alkaline electrolyte interfaces, attributed to water dipole reorientation. Correlating pme with reaction activities reveals that interfacial entropy is a robust and general descriptor of electrocatalytic reaction kinetics. Particularly, electrocatalytic activity improves as the pme aligns more closely with the thermodynamic equilibrium potential of the respective reaction, providing a solid framework for optimizing interfacial microenvironments to enhance electrocatalytic performance.