Alkali Metal Cations Induce Pseudo-outer-sphere Oxygen Reduction Reaction Mechanism in Electrolyte-Catalyst Synergy.

Abstract

Alkali metal cations (AMCs) are known to play pivotal roles in modulating electrocatalytic systems, significantly affecting the oxygen reduction reaction (ORR). While their macroscopic effects are well recognized, the molecular-level interactions of AMCs at the electrochemical interface remain poorly understood. Here, using constant-potential ab initio molecular dynamics simulations, we uncover that AMCs (Li+, Na+, and K+) act as molecular switches that trigger a pseudo-outer-sphere ORR mechanism. In this mechanism, surface-adsorbed water molecules serve as dynamic bridges that simultaneously mediate interfacial electron transfer and proton transport. As a result, the reactive zone extends beyond the catalyst surface, overcoming the spatial constraints of traditional inner-sphere pathways. Crucially, H2O2 is generated directly within the outer Helmholtz plane via reduction of AMC-O2 complexes, effectively bypassing the catalyst surface and avoiding over-reduction. This results in significantly enhanced selectivity and production efficiency. Our results demonstrate that AMCs activate interfacial coupling to unlock alternative reaction pathways, while concurrently elucidating the critical yet often overlooked role of solute molecules in governing electrocatalytic behavior. This work establishes a framework for the understanding of electrolyte-catalyst coupling and provides principles for designing next-generation electrochemical systems.