Research progress in graphene based single atom catalysts in recent years

The wide application of single atom catalysts(SAC) has become an important research topic recently. Due to the highest atomic efficiency and high selectivity of the transition metal center single atom, the single atom catalyst combines the advantages of heterogeneous and homogeneous catalysts, and further makes up the gap between them with its unique characteristics. Among many SACs, carbon-loaded SAC has attracted particular attention in electrocatalysis due to the high conductivity of graphite skeleton, which can accelerate electron transfer in the reaction process. However, large-scale synthesis of such highly loaded metal nitrogen doped single atom catalysts (SACs) with carbon supports is challenging because of the need to balance loading and dispersion of single atoms at high temperatures. Previously, few strategies have been reported for the preparation of nitrogen-doped graphene-supported single-atom catalysts in different electrocatalytic reactions, such as oxygen evolution (OER)，oxygen reduction (ORR), hydrogen evolution (HER), nitrogen reduction (NRR) and carbon dioxide reduction (CO2RR). As a result, this review screens the metal-center atoms of single-atom catalysts from three aspects of thermodynamic stability, catalytic activity and product selectivity from a unified perspective, and reviews the efficient and economical synthesis of metal nitrogen doped single atom catalysts M-N-C-SAC, which provides better insights into existing techniques and, enable new opportunities for future advances.