Unveiling a Two-Electron Reaction Pathway for Electrocatalytic CO ₂ Reduction on Boron-Doped Diamonds: A First-Principles Calculation

Converting excessive CO₂ molecules into formic acid (HCOOH) as a liquid fuel and hydrogen storage carrier using a sustainable electrochemical method has received enormous attentions. However, the reaction mechanism during this two-electron reaction pathway is still controversial. Inspired by the high selectivity toward HCOOH on the boron-doped diamond (BDD) electrode, this work calculates the adsorption of the CO₂ molecule and first two-electron reaction pathway on BDD with different B doping configurations by the density functional theory method. The results show that CO₂ molecules are more readily adsorbed on the surface B doping sites with charge transfer between B-O bonding. And the total overpotential of the first two-electron reaction pathway displays a Volcano relationship with the Gibbs energy of the *CO₂-*COOH step. The partially sp²-C hybridized (111) (2 × 1) configuration exhibits the lowest overpotential of 0.81 eV and the best CO₂ reduction performance toward the HCOOH product. Furthermore, the dynamic kinetics of the *CO₂-*COOH step is investigated by the climbing image-nudged elastic band method under the external electric field. The negative electric field of -0.4 eV/Å promotes the adsorption of CO₂ and *H but inhibits the migration of *H with an energy barrier of 4.34 eV. This work elucidates the decision factor of high selectivity toward the HCOOH product on the BDD electrode and provides a comprehensive understanding of two-electron reaction pathway mechanisms.