Theoretical Studies on the Nitrogen Reduction Reaction (NRR) on Cu−Oxide Based Electrocatalysts

Inspired by the excellent carrier concentration and escalated catalytic activity of CuO, the reduction of N2 to NH3 was modelled via density functional theory calculations. 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 espied for the pristine surface. However, the preferential mechanism on the reconstructed surface is characterised 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 charges and charge density difference plots showcase extensive hybridization between the Cu−3d and N−2p states in the O-defective surface. Further, the highest ICOHP value of −15.15 eV recorded for the O-defective surface displayed a significant activation of the N≡N in N2, which corroborates the enhanced catalytic activity of the O-deficient surface.