Shaping the electrode–electrolyte interface: Alkali cations drive HER, OER, and ORR

Electrochemical processes such as the oxygen evolution reaction (OER), the hydrogen evolution reaction (HER), and the oxygen reduction reaction (ORR) are fundamental to emerging clean energy technologies, including water electrolyzers, fuel cells, and metal–air batteries. While catalysts based on noble metals or transition metals have been extensively investigated, recent work reveals that alkali metal cations (Li + , Na + , K + , Rb + , Cs + ) play a pivotal role in modulating reaction mechanisms and performance. Once considered passive species, these cations actively reshape the electric double layer, alter hydration environments, and adjust the adsorption energies of key intermediates. In HER, the size and hydration energy of the cation determine whether water dissociation or proton transfer is enhanced, leading to variable trends. Smaller cations such as Li + often excel on reactive metals like Pt by stabilizing essential intermediates, whereas larger cations (K + , Cs + ) can facilitate water splitting on metals like Au and Ag. In OER, due to sluggish kinetics, larger cations frequently lower overpotentials by promoting structural and electronic changes in oxide-based or noble-metal catalysts. Moreover, doping or intercalating alkali cations into layered oxides, perovskites, or transition metal phosphides can introduce lattice vacancies, maintain higher valence states, and enhance metal–oxygen bond covalency, and thus enhancing catalytic performance. In ORR, which underpins fuel cells and metal–air batteries, alkali cations tune oxygenated intermediate adsorption or desorption, shifting both current densities and product selectivity. Overall, these observations highlight how a deep understanding of cation–catalyst interactions can lead to highly optimized and sustainable electrocatalytic processes. • Reviews alkali-cation effects on HER, OER, and ORR performance. • Links cation size and hydration to EDL and interfacial kinetics. • Compares cation-driven trends in fuel cells and electrolyzers. • Summarizes mechanistic insights from experiments and theory. • Outlines design rules for sustainable electrolyte engineering.