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 C₁ 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 C₁ 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.