Switching CO₂ Electroreduction Selectivity Between C₁ and C₂ Hydrocarbons on Cu Gas-Diffusion Electrodes

Regulating the selectivity toward a target hydrocarbon product is still the focus of CO₂ electroreduction. Here, we discover that the original surface Cu species in Cu gas-diffusion electrodes plays a more important role than the surface roughness, local pH, and facet in governing the selectivity toward C₁ or C₂ hydrocarbons. The selectivity toward C₂H₄ progressively increases, while CH₄ decreases steadily upon lowering the Cu oxidation species fraction. At a relatively low electrodeposition voltage of 1.5 V, the Cu gas-diffusion electrode with the highest Cu^δ+/Cu⁰ ratio favors the pathways of ^*CO hydrogenation to form CH₄ with maximum Faradaic efficiency of 65.4% and partial current density of 228 mA cm⁻² at −0.83 V vs RHE. At 2.0 V, the Cu gas-diffusion electrode with the lowest Cu^δ+/Cu⁰ ratio prefers C–C coupling to form C₂₊ products with Faradaic efficiency topping 80.1% at −0.75 V vs RHE, where the Faradaic efficiency of C₂H₄ accounts for 46.4% and the partial current density of C₂H₄ achieves 279 mA cm⁻². This work demonstrates that the selectivity from CH₄ to C₂H₄ is switchable by tuning surface Cu species composition of Cu gas-diffusion electrodes.