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 <i>operando</i> 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.