Cation-Gated Interfacial Electrocatalysis: Mechanisms and Effects of Alkali and Alkaline Earth Metal Cations

Abstract Electrolyte cations, long considered inert charge-balancing species, are now recognized as active regulators of electrocatalytic interfaces. This review systematically examines alkali metal cations (Li+, Na+, K+, Rb+, Cs+) and alkaline earth metal cations (Mg2+, Ca2+, Sr2+, Ba2+) in five key reactions: hydrogen evolution/oxidation, oxygen evolution, oxygen reduction, carbon dioxide reduction, and nitrate reduction. We demonstrate that cation effects are reaction-specific, governed by electric double layer structure, interfacial electric fields, local pH, water networks, and intermediate stabilization. Alkali metal cations mainly regulate reactant access, proton transfer, pathway selection, and stability through electric-field modulation, solvation restructuring, intermediate stabilization, and, over longer timescales, catalyst-surface evolution. Hydration characteristics dictate their behavior: weakly hydrated large cations (K+, Rb+, Cs+) enhance local electric fields and stabilize polar intermediates in CO2RR, while strongly hydrated small cations (Li+, Na+) support water dissociation and proton transfer in HER/HOR. Alkaline earth metal cations exhibit chemically coupled interfacial regulation due to higher charge density, stronger hydration, and greater Lewis acidity. These divalent cations facilitate reactions through local pH buffering, water rearrangement, and intermediate stabilization, yet their hydrolysis and precipitation tendencies risk active site blockage and catalyst deactivation, particularly in real electrolytes like seawater and wastewater. By mapping diverse microscopic cation effects onto these five catalytic functions, this review provides a cross-reaction framework for rationalizing apparently contradictory cation trends and identifying the dominant interfacial bottleneck under different conditions. Finally, we highlight future directions in operando characterization, multiscale modeling, multi-ion systems, and electrolyte-catalyst co-design for efficient, selective, and stable electrocatalysis.