Density functional theory study of the sulfur/oxygen doped CoN4-graphene electrocatalyst for oxygen reduction reaction

It has been found that hetematoms doped transition metal-nitrogen embedded carbon materials are potential candidates for high-efficient oxygen reduction reaction (ORR) catalysts. Herein, the four-electron ORR mechanism and activity of CoN4, CoN4Sx, and CoN4Ox (x = 1-4) have been investigated theoretically. The results indicate that sulfur (5) doping can effectively enhance ORR activity of CoN4, but oxygen (O) doping cannot. Specifically, due to the weakened *OH binding, the overpotential of CoN4Sx(x = 1-3) is decreased by about 100 mV compared with that of CoN4. Especially, the ORR overpotential of CoN4S1 is as small as 0.25 V. However, for almost all CoN4Ox, the O doping could make the binding strength of *OH be strengthened, leading to high ORR overpotential. The electronic structure analysis of CoN4S1 reveals that due to the activation of nitrogen atoms after S doping and the tuned energy gap of pristine CoN4, its ORR activity is enhanced.