Coordination engineering on novel 2D pentagonal NiN2 for bifunctional oxygen electrocatalysts

For renewable and environment-friendly green energy, it is crucial to look for prominent bifunctional oxygen electrocatalysts. Herein, by doping a single transition metal (TM) or non-metal atom into the two-dimensional NiN2 to regulate the coordination environment, the electrocatalytic performance is comprehensively studied based on the density functional theory (DFT). By which, we found that catalytic activity could be significantly improved. Specifically, the Co/VNi-NiN2 and C3/VN3-NiN2 systems possess low overpotentials for oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) (ηOER = 0.38, 0.30 V and ηORR = 0.37, 0.37 V), separately, displaying outstanding bifunctional catalytic activity. The electronic structures of the catalyst system have been investigated to explain the origin of high OER and ORR activities. In addition, this research confirms that the electronegativity of the TM atoms, the d-band center (εd), and the quantity of d-orbital electrons are reliable descriptors for these TM/VNi-NiN2 systems. Thus, this study can serve as guidance for the development of more effective oxygen-catalyzed bifunctional electrocatalysts.