Theoretical study on the mechanism of electroreduction of nitrite to ammonia on Co-based dual-atom catalysts: the key role of electron transfer

The revised abstract (191 words) is below: The electrocatalytic reduction of nitrite (NO₂RR) to ammonia is of great significance for the nitrogen cycle and environmental remediation. Here, density functional theory is employed to investigate the catalytic performance of Co-based dual-atom catalysts anchored on 2D N-doped graphene (Co-M/CN₆, M = Mn, Fe, Ni, Cu, Zn) for NO₂RR, aiming to reveal the underlying reasons affecting the catalytic efficiency of eNO2RR. Results show that CoFe electrocatalyst exhibited excellent NO₂RR activity, with the energy barriers of the rate determining steps (ΔGRDS) as low as 0.58 eV. The introduction of Fe accelerates the charge transfer between reaction intermediates and active sites by regulating the electronic structure of the catalyst, significantly reducing the reaction energy barrier. The selectivity for NO₂RR is discussed by comparing the ΔGRDS of HER with the ΔGRDS of NO2RR. It is also found that the CoFe catalysts can effectively inhibit the competitive HER. By using multiple descriptors (pCOHP, d-band center, electron localization function (ELF), free energy of *NO₂ adsorption (ΔG*NO₂), Bader charge transfer, charge density difference) to analyze electronic and energetic factors, it is further revealed that the promoting effects of Fe are closely related to the electron transfer ability.