Electrochemical CO2 Reduction to C1 Products on Single Nickel/Cobalt/Iron-Doped Graphitic Carbon Nitride: A DFT Study

Electrocatalytic CO2 reduction reaction (CRR) is one of the most promising strategies to convert greenhouse gases to energy sources. Herein, the CRR was applied towards making C-1 products (CO, HCOOH, CH3OH, and CH4) on g-C3N4 frameworks with single Ni, Co, and Fe introduction; this process was investigated by density functional theory. The structures of the electrocatalysts, CO2 adsorption configurations, and CO2 reduction mechanisms were systematically studied. Results showed that the single Ni, Co, and Fe located from the corner of the g-C3N4 cavity to the center. Analyses of the adsorption configurations and electronic structures suggested that CO2 could be chemically adsorbed on Co-C3N4 and Fe-C3N4, but physically adsorbed on Ni-C3N4. The H-2 evolution reaction (HER), as a suppression of CRR, was investigated, and results showed that Ni-C3N4, Co-C3N4, and Fe-C3N4 exhibited more CRR selectivity than HER. CRR proceeded via COOH and OCHO as initial protonation intermediates on Ni-C3N4 and Co/Fe-C3N4, respectively, which resulted in different C-1 products along quite different reaction pathways. Compared with Ni-C3N4 and Fe-C3N4, Co-C3N4 had more favorable CRR activity and selectivity for CH3OH production with unique rate-limiting steps and lower limiting potential.