Computational study of transition metal single-atom catalysts supported on nitrogenated carbon nanotubes for electrocatalytic nitrogen reduction

Developing efficient and stable catalysts for the electrocatalytic N2 reduction reaction (NRR) shows promise in nitrogen fixation. Here, we proposed active and stable single-atom catalysts (SACs) toward NRR, where transition metals are anchored on nitrogenated carbon nanotubes (NCNTs). Among the screened nine common transition metals (Ti, V, Cr, Mn, Fe, Mo, Ru, Rh, and Ag) on (4, 4) NCNTs, we found Mo-NCNT possesses the most excellent NRR catalytic activity and selectivity with a low overpotential of 0.29 V. Then, the NRR performance of Mo-NCNT was further engineered by controlling the nanotube diameter, where the lowest overpotential is 0.18 V at a diameter of 9.6 Å. In addition, we found a linear scaling relation between *NNH and *NH2 on the studied catalysts with the exception of (2, 2) and (3, 3) Mo-NCNTs, owing to their extremely unstable structures. We attribute the outstanding NRR performance of Mo-NCNT to the moderate adsorption of N2 due to the slightly low d-band center of Mo, and the charge donating and accepting capacity of NCNTs. This work has provided a deeper insight into designing high-efficiency and stable NRR SACs supported by NCNTs.