DFT investigation into efficient transition metal single-atom catalysts supported on N-doped graphene for nitrate reduction reactions

The electrochemical conversion of nitrate (NO3−), an environmental pollutant, into ammonia (NH3), a hydrogen energy carrier, is attracting attention as a promising alternative to the conventional Haber–Bosch process. Single-atom catalysts (SACs) based on N-doped graphene (NDG) have shown excellent efficiency for the nitrate reduction reaction (NO3RR). However, a fundamental understanding of the effect of the arrangement and number of N atoms on the NO3RR has not yet been achieved. Herein, we designed various 3d, 4d, and 5d transition metal (TM)-SAC/NDG systems and proposed specific patterns and quantities of N doping to develop highly stable and efficient candidate catalysts for the NO3RR. The activities of the screened TM-SACs (e.g., Ru- and Ir-SACs/NDG) were investigated by analyzing the density of states and excess Bader charges, and the stabilities of the catalysts were evaluated based on nanocluster formation energies and ab initio molecular dynamic (AIMD) simulations.