Linking Electric Double Layer Formation to Electrocatalytic Activity

Electric double layers form at electrode–electrolyte interfaces and often play defining roles in governing electrochemical reaction rates and selectivity. While double layer formation has remained an active area of research for more than a century, most frameworks used to predict electric double layer properties, such as local ion concentrations, potential gradients, and reactant chemical potentials, remain rooted in classical Gouy–Chapman–Stern theory, which neglects ion–ion interactions and assumes nonreactive interfaces. Yet, recent findings from the surface forces and electrocatalysis communities have highlighted how the emergence of ion–ion interactions fundamentally alters electric double layer formation mechanisms and interface properties. Notably, recent studies with ionic liquids show that ionic correlations and clustering can substantially alter reaction rates and selectivity, especially in concentrated electrolytes. Further, emerging studies suggest that electric double layer structures and dynamics significantly change at potentials where electrocatalytic reactions occur. Here, we provide our perspective on how ion–ion interactions can impact electric double layer properties and contribute to modulating electrocatalytic systems, especially under conditions where high ion concentrations and large applied potentials cause deviations from classical electrolyte theory. We also summarize growing questions and opportunities to further explore how electrochemical reactions can drastically alter electric double layer properties. We conclude with a perspective on how these findings open the door to using electrocatalytic reactions to study electric double layer formation and achieve electrochemical conversion by engineering electrode–electrolyte interfaces.