Theoretical Study on the Nitrogen Reduction Reaction (NRR) on Cu Oxide-Based Electrocatalysts

Abstract

Inspired by the excellent carrier concentration and escalated catalytic activity of CuO, the reduction of N₂ to NH₃ was studied using density functional theory. Concentrating on the most stable CuO(111) surface orientation, different surface terminations as well as defective surfaces were considered. Analyzing the free energies involved in nitrogen reduction reaction (NRR) across different pathways based on the associative Heyrovský mechanism highlights the reconstructed Cu-terminated and O-defective surfaces to be the prospective ones, with *NNH formation free energies of 1.41 and 1.45 eV, significantly lower than 2.58 eV observed for the pristine surface. However, the preferential mechanism on the reconstructed surface is characterized by endergonic hydrogenation steps, whereas for the O-defective surface, all steps are downhill and exergonic. Subsequently, the negative free energy for the desorption of NH₃ from the O-defective surface discloses the availability of catalytic sites for further NRR. In addition, the reconstructed surface possessing multifarious coordinatively unsaturated Cu atoms succumbs to irreversible structural variations, unlike the O-defective surface, which has well-defined active centers. Moreover, Bader charge and charge density difference analyses showcase extensive hybridization between the Cu–3d and N–2p states on the O-defective surface. Further, the highest ICOHP value of −15.15 recorded for the O-defective surface displayed a significant activation of the N≡N triple bond in N₂, which corroborates the enhanced catalytic activity of the O-deficient surface.