Steric effect induces CO electroreduction to CH4 on Cu‒Au alloy catalyst

The electrocatalytic reduction of carbon monoxide (CO) has been driving substantial research efforts in developing new catalysts and structures, among which the bimetallic component catalysts feature both functional diversity and high-density of active sites. In this work, we demonstrate that the fine tuning of adjacent bimetallic sites can allow to select different reaction pathways toward C1 or C2+ products in electroreduction of CO. Cu and Cu‒Au alloy catalysts with different atomic ratios were fabricated and investigated for appropriate molecular distances. The pure Cu catalyst was found to be active for electroreducing CO to C2H4, as the adjacent Cu sites were beneficial for adsorbing multiple CO molecules and subsequent C‒C coupling. On the other hand, the alloying of Cu with Au introduced steric hindrance and larger intermolecular distance between adjacent adsorbed *CO intermediates, thus leading to a decrease of C2H4 selectivity but enhanced CH4 pathway. Our work revealed the importance of spacings between active sites for CO electroreduction, which can benefit the catalyst design to further improve activities and selectivities in electrocatalytic CO reduction.