Theoretical study of transition metals supported on g-C3N4 as electrochemical catalysts for CO2 reduction to CH3OH and CH4

Electrochemical CO2 reduction has become a promising technology to address the globally accelerating CO2 emissions and produce value-add chemicals and liquid fuels. In this work, transition metals supported on graphitic carbon nitride (M/g-C3N4, M = Fe, Co, Ni) as catalysts applied in electrochemical CO2 reduction to CH3OH and CH4 is investigated by density functional theory (DFT) calculations. From Ni/g-C3N4, Fe/g-C3N4 to Co/g-C3N4, the interaction between CO2 and catalysts is found to be gradually enhanced, especially for the adsorption of CO2 on Co/g-C3N4, which is a typical chemical interaction. Fe/g-C3N4 and Co/g-C3N4 prefer to produce CH4 with limiting potentials of 0.67 V and 0.81 V, while Ni/g-C3N4 tends to produce CH3OH. Moreover, the electrolyte environment has little influence on the limiting potential of Fe/g-C3N4 and Ni/g-C3N4. Given the superior performance of M/g-C3N4, g-C3N4 shows great potential as the platform to support transition metal for CO2 reduction system. These insights can be used to guide the synthesis of highly active CO2 reduction catalysts from nonprecious metals.