The Roles of Ions in Electrochemical Interface for Electrocatalysis

While ions in electrolytes have traditionally been regarded as background components in electrocatalysis, emerging evidence shows they actively shape catalytic outcomes by influencing interfacial properties and reaction pathways. This Perspective introduces a unified classification of ion roles as promoter, inhibitor, and spectator to systematically describe how both cations and anions affect electrocatalytic activity, selectivity, and stability across diverse reactions. This framework enables a cross-reaction comparison of ionic effects, moving beyond reaction- or ion-specific categorizations. Based on a wide range of experimental and computational studies, we illustrate how ions engage in specific interactions with intermediates, alter electric fields and local pH, or passively reside without exerting significant impact. By identifying the mechanistic principles underlying these roles, we emphasize the necessity of context-dependent understanding of ion roles and offer a roadmap for strategically leveraging ionic interactions in the rational design of next-generation electrochemical interfaces.