Synergetic contribution of nitrogen and fluorine species in porous carbons as metal-free and bifunctional oxygen electrocatalysts for zinc–air batteries

High-efficient bifunctional catalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are critical to the practical application of zinc–air batteries. Herein, a comprehensive investigation on the synergetic contribution of nitrogen (N) and fluorine (F) species in porous carbon for ORR/OER catalyses is firstly conducted. The metal-free N, F co-doped porous carbon (NFPC) possesses appealing catalytic activities in zinc–air batteries and is superior to many other catalysts. Combined with the careful exploration of N and F dopants, seventeen optimized carbon cluster structures with all possible co-doping of N and F species are considered for density functional theory calculations. It can be inferred that the F doping with graphitic and pyridinic N triggers active paramagnetic centers. The co-doping of covalent F and graphitic N especially gives the lowest free energy barrier for both ORR/OER, which could account for the notable performance of NFPC catalysts in zinc–air batteries.