Electrochemical catalytic mechanism of single transition metal atom embedded BC₃ monolayer for oxygen reduction and evolution reactions

The graphene embedded with single transition metal (TM) atom shows great potential to replace precious metals as the electrochemical catalyst of fuel cells and metal-air batteries. However, the electrochemical catalytic mechanism of single TM atom supported on other substrates is less well understood. Herein, a density functional theory calculation of single 3d TM atom embedded on two-dimensional BC₃ as an active site for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is performed. The electronic structure analysis reveals that the hybridized antibonding orbitals formed by TM-3d and O-2p orbitals possess lower energy level and higher occupancy, weakening the interaction between OH and TM, further determines the catalytic activity of TM-N₄ active site. Among all considered active sites, the Fe-N₄ and Mn-N₄ sites show the best ORR catalytic performance while Co-N₄ site shows the best OER catalytic performance. Finally, an adsorption factor is put forward via the coordination environment around TM atom to provide a guidance on the exploration of new high-performance single atom catalysts family.