Two-Electron Electrochemical Reduction of CO<sub>2</sub> on B-Doped Ni–N–C Catalysts: A First-Principles Study
Arifin Luthfi Maulana, Adhitya Gandaryus Saputro, Yusuf Prasetyo, Muhammad Haris Mahyuddin, Muhammad Iqbal, Hadi Teguh Yudistira, I Gede Wenten, Hermawan Kresno Dipojono
Abstract
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.