Electroreduction of CO to 2.8 A cm⁻2 C2+ Products: Maximizing Efficiency with Minimalist Electrode Design Featuring a Mesopore‐Rich Hydrophobic Copper Catalyst Layer

This work shows how hydrophobicity and porosity can be incorporated into copper catalyst layers (CLs) for the efficient electroreduction of CO (CORR) in a flow cell. Oxide‐derived (OD) Cu catalysts are synthesized using K+ and Cs+ as templates, termed respectively as OD‐Cu‐K and OD‐Cu‐Cs. CLs, assembled from OD‐Cu‐K and OD‐Cu‐Cs, exhibit enhanced CORR performance compared to “unmodified” OD‐Cu CL. OD‐Cu‐Cs can notably reduce CO to C2+ products with Faradaic efficiencies (FE) as high as 96% (or 4% FE H2). During CO electrolysis at −3000 mA cm−2 (−0.73 V vs reversible hydrogen electrode), C2+ products and the alcohols are formed with respective current densities of −2804 and −1205 mA cm−2. The mesopores in the OD‐Cu‐Cs CL act as barriers against electrolyte flooding. Contact angle measurements confirm the CL's hydrophobicity ranking: OD‐Cu‐Cs > OD‐Cu‐K > OD‐Cu. The enhanced hydrophobicity of a catalyst is proposed to allow more triple‐phase (CO‐electrolyte‐catalyst) interfaces to be available for CORR. This study shows how the pore size‐hydrophobicity relationship can be harvested to guide the design of a less‐is‐more Cu electrode, which can attain high CORR current density and selectivity, without the additional use of hydrophobic polytetrafluoroethylene particles or dopants, such as Ag. A hydrophobic copper catalyst layer, created solely by the presence of numerous mesopores, is developed. This simple, but highly effective design slows down the penetration of the electrolyte, thus avoiding electrode flooding. Consequently, the catalyst layer can reduce CO to C2+ products with a partial current density (jC2+) up to −2.8 A cm−2.