Two-Electron Electrochemical Reduction of CO₂ on B-Doped Ni–N–C Catalysts: A First-Principles Study

We evaluate the electrocatalytic activity of graphene-supported NiN 4 active center in facilitating two-electron CO 2 electrochemical reduction into CO and HCOOH, as well as the competing hydrogen evolution reaction. NiN 4 center is found to be more stable in zigzag-edge and armchair-edge proximity of graphene, confirming experimental evidence. In an attempt to reduce the CO 2 reduction overpotential, we construct a neighboring-site environment of NiN 4 center and BN substitutional defect. B-doped structures are found to be capable of reducing the CO 2 reduction energy barrier through direct (HCOOH pathway) or indirect (CO pathway) participation in facilitating CO 2 reduction-related key intermediates. In most Ni sites, the presence of adjacent BN site is also discovered to change the product selectivity from CO to HCOOH. Our result predicts that B-doped NiN 4 sites on the interior side (NiN 4 BN-G) and on the armchair-edge side of tilted orientation (t-NiN 4 BN-AGNR) are HCOOH-selective. Although the rest of zigzag-edge and armchair-edge sites have a tendency to selectively produce CO and HCOOH, respectively, the undesirable hydrogen evolution reaction is found to be more dominant and therefore obscuring the potential. Our result demonstrates that the hydrogen evolution reaction is most likely to occur on top of a neighboring C atom instead of on the Ni center, in contrast to the commonly understood mechanism. To ultimately suppress the activity of the hydrogen evolution reaction, we predict that an effective electrocatalyst optimization cannot be realized by only selecting the best metal center and dopant pair but also by altering the neighbor’s electronic structure.