(5a) Probing the Role of Interfacial Cation Concentration in Modulating CO? Reduction Kinetics

Electrochemical CO₂ reduction (CO₂R) offers a promising route for storing intermittent renewable energy in chemical bonds. While catalyst composition and active site structure influence performance, the local microenvironment—particularly electrolyte cations—also plays a significant role. Despite extensive studies, the mechanisms by which cations affect catalytic activity remain debated. Existing models often conflict and struggle to generalize across systems, especially when extending insights from simple alkali cations to the design of cationic ionomers or binders for practical electrolyzers. Thus, a unified framework describing cation effects in electrocatalysis is needed.

Our recent work shows that in a range of polar aprotic electrolytes, CO₂R rates on a polycrystalline silver (pC-Ag) electrode vary markedly with alkylammonium cation size. We attribute these changes to variations in the metal–cation distance [Ag–C⁺(Å)], governed by alkyl chain length, which modulates the interfacial electric field, alters the reaction energetics of the CO₂ activation step, and consequently tunes the reaction rate. However, these promoting effects may not arise solely from electrode–cation separation. In fact, changes in cation size may also influence other electrical double-layer (EDL) properties, complicating mechanistic interpretation. To address this, we now employed a class of functionalized organic cations to systematically control and vary interfacial cation concentration at the electrified interface of silver catalyst. From a series of kinetic, spectroscopic, and computational measurements in aprotic media, we propose a physical model to clarify how cation identity influences electrocatalysis. Beyond deepening our understanding of the role of electrochemical microenvironments in electrocatalysis, this work offers new strategies for designing selective and efficient electrochemical devices critical for decarbonizing the fuels and chemicals industries.