Role of Surface Hydrogen Coverage in C–C Coupling\nProcess for CO<sub>2</sub> Electroreduction on Ni-Based Catalysts

Research\ninto electrochemical CO<sub>2</sub> reduction reaction\n(CO<sub>2</sub>RR) toward multicarbon products has long been dominated\nby the investigation of Cu-based catalyst system. Yet, several recent\nstudies have documented competitive catalytic performance on Ni-based\nalloys and compounds, which can trigger C–C coupling for producing\nlong-chain hydrocarbons. To develop an in-depth understanding of how\nNi-based catalysts carry out C–C coupling, here we present\na comparative study of Ni metal and Ni<sub>3</sub>Ga via density functional\ntheory calculations. Inspiringly, unlike Ni metal where the distribution\nof hydrogen adsorbates on the surface is found irregular during CO<sub>2</sub>RR, Ni<sub>3</sub>Ga exhibits a perfectly ordered distribution\npattern of surface hydrogen at a low coverage when CO<sub>2</sub> is\nreduced into intermediates ready for C–C coupling. This difference\nin adsorbate coverage leads to scenarios in which neighboring CO<sub>2</sub>RR intermediates on Ni metal tend to be separated by a large\ndistance, whereas they can be accommodated much closer on Ni<sub>3</sub>Ga surface, thus creating the opportunity for the coupling reaction.\nThis mechanistic insight finds support from previous experimental\nreports, and can establish surface hydrogen coverage as a nonnegligible\nfactor for C–C coupling on Ni-based catalysts.