We evaluate the electrocatalytic activity of graphene-supported NiN4 active center in facilitating two-electron CO2 electrochemical reduction into CO and HCOOH, as well as the competing hydrogen evolution reaction. NiN4 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 CO2 reduction overpotential, we construct a neighboring-site environment of NiN4 center and BN substitutional defect. B-doped structures are found to be capable of reducing the CO2 reduction energy barrier through direct (HCOOH pathway) or indirect (CO pathway) participation in facilitating CO2 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 NiN4 sites on the interior side (NiN4BN-G) and on the armchair-edge side of tilted orientation (t-NiN4BN-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.

We try to use small size Ni cluster supported on graphitic material as an alternative for CO 2 hydrogenation catalyst. As an initial step, we study the ability of the supported Ni 4 cluster to interact with CO 2 molecule by means of density functional theory-based calculations. We find that strong CO2 adsorption can only be formed on top of the Ni 4 cluster site. Due to the strong Ni 4-CO 2 interaction, the CO 2 molecule is always adsorbed with a bidentate adsorption configuration on the Ni 4 cluster. The graphene surface and Ni 4-graphene interface cannot accommodate CO 2 chemisorption due to the weak graphene-CO 2 interaction.