In Situ Synchronized SERS‐SEIRAS Unveils Cation‐Regulated Interfacial Water and Intermediates in the Oxygen Reduction Reaction

ABSTRACT Interfacial water plays a crucial yet poorly understood role in the alkaline oxygen reduction reaction (ORR) by modulating the adsorption of oxygen intermediates and mediating proton‐coupled electron transfer (PCET). However, the lack of techniques to dynamically correlate interfacial water with adsorbed intermediates makes it difficult to elucidate the mechanism governing the evolution of intermediate species. Here, we report a synchronized, site‐consistent SERS–SEIRAS platform that tracks interfacial water and surface‐adsorbed species (OOH ad and OH ad ) in real time during cation‐dependent ORR. Our results show that decreasing cation hydration energy induces the formation of an interfacial water layer with weak hydrogen bonding, low orientation constraints, and high dynamic flexibility, which diminishes its interactions with OOH ad and OH ad . This structure enhances water and oxygen transport and weakens OH ad solvation, thereby reducing OH ad coverage and accelerating the final PCET step. Our results reveal how cations reshape the interfacial hydrogen‐bond network to control ORR kinetics. More broadly, this work demonstrates the power of multi‐spectroscopic coupling for probing dynamic electrocatalytic interfaces and offers a strategy for improving catalyst performance via electrolyte and interface engineering.