Insights into the Influence of Local Microenvironment and Surface Dynamics on C2H4 Selectivity over Cu(100) Single-Crystal Electrode

Electrochemical reduction of CO2 (eCO2RR) for C2H4 production over Cu presents a promising approach for mitigating greenhouse gas emissions while producing fuels and value-added chemical feedstocks. Understanding the eCO2RR mechanism and identifying the factors that can affect its selectivity are essential for the design of effective electrochemical systems. However, the polycrystalline Cu substrates/particles used in most literature make it challenging to investigate the influence of a single factor. Herein, single-crystalline foils exposing the (100) surface are prepared and employed to explore the underlying mechanism of the selectivity switch between C2H4 and CH4. Evolution in the microenvironment, especially the local pH and CO2 concentration, is speculated to be the main cause of the observed selectivity change from C2H4 to CH4 over Cu(100). Considering this conjecture, a pulsed potential strategy is used to finely modulate the local pH of the electrochemical system via tuning the anodic pulse width. Based on the results of simulations for local pH evolution and operando Raman measurements, the local pH effect and chemical states on the Cu surface are responsible for the pulse-enhanced C2H4 selectivity and the volcano-shaped dependence of C2H4/CH4 on pulse width. The highest C2H4 Faradaic efficiency (FE) reaches 51.75%, with the maximum C2 selectivity of 65.5%. This work may provide insights into the modulation of product selectivity in electrocatalytic systems, not just limited to eCO2RR.