The regulation of the bifunctional electrocatalytic activity of transition metal atoms embedded in a biphenylene network by the asymmetric nitrogen coordination environment

The development of sustainable energy is currently of paramount importance, and electrocatalytic technology serves as a critical foundation for building a sustainable energy system. Extensive efforts have been devoted to finding effective non-noble metal-based catalysts as a substitute for noble metal-based materials. Single-atom catalysts (SACs) were formally proposed in 2011 and have been widely studied due to their high atomic utilization efficiency. In this work, we employ Biphenylene network (BPN) as a substrate and systematically investigate the ORR (oxygen reduction reaction) and OER (oxygen evolution reaction) electrocatalytic performance of transition metal-embedded BPN under asymmetric nitrogen coordination (TMN_x-BPN, where TM = Mn, Fe, Co; x = 1, 2, 3) using density functional theory (DFT). The results demonstrate that the FeN₃-BPN catalyst exhibits the lowest overpotentials for both ORR and OER, at 0.30 V and 0.38 V, respectively. The volcano plot reveals that the Fe atom's adsorption strength for oxygen-containing reaction intermediates is neither too strong nor too weak, and this moderate adsorption strength is more conducive to the reaction process. Furthermore, we compare the electronic structure properties of the FeN₃-BPN catalyst with those of the Fe-BPN catalyst to explore the origin of the catalytic activity of FeN₃-BPN. Analyses such as crystal orbital Hamilton population (COHP) and density of states (DOS) indicate that the FeN₃-BPN system facilitates the desorption of *OH, thereby enhancing ORR/OER catalytic performance. This study provides insights into the development of high-performance ORR/OER electrocatalysts and offers guidance for discovering efficient non-noble metal-based alternatives to noble metal-based catalysts.