Regulation of the Coordination Structures of Transition Metals on Nitrogen-Doped Carbon Nanotubes for Electrochemical CO2 Reduction.

The electrochemical carbon dioxide reduction reaction (CO2RR) has been extensively studied due to its potential to reduce the globally accelerating CO2 emission and produce value-added chemicals and fuels. Despite great efforts to optimize the catalyst activity and selectivity, the development of robust design criteria for screening the catalysts and understanding the role of water and potassium for CO2 activation poses a significant challenge. Herein, a rapid method for screening single-atom catalysts (SACs) possessing different coordination structures toward the CO2RR process to form CO, namely, a metal atom supported on nitrogen-doped carbon nanotubes (M@CNT, M@1N_CNT, M@2N_CNT, and M@3N_CNT), was established using large-scale density functional theory computations. Adopting the free energy of *CO2 and *OH as screening descriptors, Fe@CNT, Cu@1N_CNT, Pd@2N_CNT, and Ni@3N_CNT were found to exhibit high activity for CO in the gas phase with the overpotential values of 0.22, 0.11, 0.13, and 0.05 V, respectively. Water and potassium present on the surface of the active sites can accelerate the activation of CO2 relative to the gas phase. Ni@3N_CNT shows the highest activity and selectivity in the environment having four water and one potassium. Particularly, the least absolute shrinkage and selection operator regression study revealed that the CO2 adsorption is intrinsically governed by the number of electrons lost by the metal atom in the three N-doped systems, which can be correlated to the distance of the metal atom from the plane of the coordination atom in the M@CNT system. Besides, the study proposes equations for the calculation of the free energy of CO2 adsorption. The current work not only advances the exploration of highly active SACs for the heterogeneous electrocatalytic systems for CO2RR but also highlights the significance of water and potassium in the aqueous solution.