Role of Surface Hydrogen Coverage in C–C Coupling Process for CO₂ Electroreduction on Ni-Based Catalysts

Research into electrochemical CO2 reduction reaction (CO2RR) toward multicarbon products has long been dominated by the investigation of Cu-based catalyst system. Yet, several recent studies have documented competitive catalytic performance on Ni-based alloys and compounds, which can trigger C–C coupling for producing long-chain hydrocarbons. To develop an in-depth understanding of how Ni-based catalysts carry out C–C coupling, here we present a comparative study of Ni metal and Ni3Ga via density functional theory calculations. Inspiringly, unlike Ni metal where the distribution of hydrogen adsorbates on the surface is found irregular during CO2RR, Ni3Ga exhibits a perfectly ordered distribution pattern of surface hydrogen at a low coverage when CO2 is reduced into intermediates ready for C–C coupling. This difference in adsorbate coverage leads to scenarios in which neighboring CO2RR intermediates on Ni metal tend to be separated by a large distance, whereas they can be accommodated much closer on Ni3Ga surface, thus creating the opportunity for the coupling reaction. This mechanistic insight finds support from previous experimental reports, and can establish surface hydrogen coverage as a nonnegligible factor for C–C coupling on Ni-based catalysts.