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

The performance of the electrocatalytic CO reduction reaction (CORR) 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 CORR. This knowledge gap limits fundamental understanding of CORR while also hindering efforts to enhance CORR 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 CO 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 CO 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 CORR activity by 690% (as normalized by electrochemical active surface area), C product selectivity by 72%, and Faradaic efficiency by 36%, compared to CORR with hydrophobic Cu foil. Based on these insights, our findings unlock new opportunities to engineer the CORR microenvironment through the rational organization of hierarchical interface materials in gas diffusion electrodes toward improved CORR selectivity and activity.