Membrane-controlled CO2 electrocatalysts with switchable C2 product selectivity and high faradaic efficiency for ethanol

Bimetallic Cu materials are promising CO2 reduction electrocatalysts for the formation of valuable multicarbon products. We describe membrane-modified Ag–Cu electrocatalysts that convert CO2 to C2 products with high selectivity. While traditional Ag–Cu catalysts generate ethylene (C2H4) as the main product, we demonstrate that product selectivity can be switched to ethanol (C2H5OH) by introducing a proton-permeable fluoropolymer. By optimizing the catalyst composition, voltage, and membrane thickness and identity, we develop a catalyst that generates C2H5OH with up to 72% faradaic efficiency, making it the most selective Ag–Cu catalyst for C2H5OH reported. Lastly, we discuss a detailed chemical mechanism that explains how the hydrophobicity of the membrane overlayer enables catalysts with switchable C2 product selectivity.