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.