Potassium and Boron Co-Doping of g-C3N4 Tuned CO2 Reduction Mechanism for Enhanced Photocatalytic Performance: A First-Principles Investigation

Graphitic phase carbon nitride (g-C₃N₄, abbreviated as CN) can be used as a photocatalyst to reduce the concentration of atmospheric carbon dioxide. However, there is still potential for improvement in the small band gap and carrier migration properties of intrinsic materials. K-B co-doped CN (KBCN) was investigated as a promising photocatalyst for carbon dioxide reduction via the Density Functional Theory (DFT) method. The electronic and optical properties of CN and KBCN indicate that doping K and B can improve the catalytic performance of CN by promoting charge migration and separation. In terms of the Gibbs free energy change, the CO₂ reduction reaction catalysed by KBCN results in CH₃OH, and its optimal pathway is CO₂ → *CO₂ → *COOH → CO → *OCH → HCHO → *OCH₃ → CH₃OH. Compared with CN, the doping elements K and B shift the rate-determining step from CO₂ → *CO₂ to *CO₂ → *COOH. The K and B elements co-doping tuned the charge distribution between the catalyst and the adsorbate and reduced the Gibbs free energy of the rate-determining step from 1.571 to 0.861 eV, suggesting that the CO₂ reduction activity of KBCN is superior to that of CN. Our work provides useful insights for the design of metallic-nonmetallic co-doped CN for photocatalytic CO₂ reduction (CO₂PR) reactions.