High-efficient OER/ORR bifunctional electrocatalysts based on hexagonal boron nitride enabled by co-doping of transition metal and carbon

The construction of highly active earth-abundant electrocatalysts, which hold bifunctional oxygen reduction and evolution reactions simultaneously, is of great importance for inexpensive and high-performance electrochemical energy devices, yet still challenging. Here, we demonstrate that the inert hexagonal boron nitride (h-BN) can accommodate single atomic 3d transition metal (TM) sites by co-doping of carbon atoms as high-performance bifunctional electrocatalysts for oxygen evolution reaction (OER) and oxygen reduction reaction (ORR). The TM atoms including Fe, Co, and Ni have been anchored with either four or two substituting carbon atoms forming TM–C₄–BN and TM–C₂N₂–BN structures, in which the latter exhibits higher structural stability and stronger adsorption in response to the oxygen-containing intermediates such as OH^*, O^*, and OOH^* in the reaction pathways. The optimal OER/ORR bifunctional catalyst is determined to be Co–C₂N₂–BN, showing η^OER of 0.42 V and η^ORR of 0.26 V. Especially, its excellent ORR catalytic activity can be compared to that of well-known Pt(111) surface. It exhibits high thermodynamic stability and most favorable binding strength toward OER/ORR intermediates. The density functional theory calculations of the charge transfer and redistribution reveal the origin of the excellent catalytic activity in Co–C₂N₂–BN. This work provides a promising and feasible solution in searching for high-performance non-precious bifunctional oxygen electrocatalysts.