Microenvironment Tailoring for Electrocatalytic CO₂ Reduction: Effects of Interfacial Structure on Controlling Activity and Selectivity

The performance of the electrocatalytic CO₂ reduction reaction (CO₂RR) is highly dependent on the microenvironment around the cathode. Despite efforts to optimize the microenvironment by modifying nanostructured catalysts or microporous gas diffusion electrodes, their inherent disorder presents a significant challenge to understanding how interfacial structure arrangement within the electrode governs the microenvironment for CO₂RR. This knowledge gap limits fundamental understanding of CO₂RR while also hindering efforts to enhance CO₂RR selectivity and activity. In this work, we investigate this knowledge gap using a tunable system featuring superhydrophobic hierarchical Cu nanowire arrays with microgrooves (NAMs). Adjusting the NAM structure tunes multiple synergistic effects in the microenvironment, which include stabilization of the microwetting state, confinement of CO*, improvement to local CO₂ concentration, and modulation of the local pH. Notably, using mass transport modeling, we quantify the role of the gas-liquid-solid interface in boosting local CO₂ concentrations within several microns of the interface itself. Leveraging these effects, we elucidate how CO* and H* competitively occupy active sites, influencing reaction pathways toward multicarbon products based on tuning the microenvironment. Consequently, we provide new insights into why the optimized configuration significantly increased CO₂RR activity by 690% (as normalized by electrochemical active surface area), C₂₊ product selectivity by 72%, and Faradaic efficiency by 36%, compared to CO₂RR with hydrophobic Cu foil. Based on these insights, our findings unlock new opportunities to engineer the CO₂RR microenvironment through the rational organization of hierarchical interface materials in gas diffusion electrodes toward improved CO₂RR selectivity and activity. © 2025 The Authors. Published by American Chemical Society.