Large-scale defect-engineering tailored tri-doped graphene as a metal-free bifunctional catalyst for superior electrocatalytic oxygen reaction in rechargeable Zn-air battery

N, S and P tri-doped graphene (NSP-Gra) is successfully large-scale fabricated via a defect assisted in-situ pyrolysis strategy. NSP-Gra displays highly efficient metal-free bifunctional ORR/OER electrocatalyst in rechargeable Zn-air battery, ascribing to the fast charge transport capability and rich active sites introduced by multi-heteroatom dopants. [Display omitted] •Tri-doped graphene is fabricated via ball-milling induced defect assisted in-situ pyrolysis strategy.•The structural defect is greatly advantageous for effective doping of heteroatoms.•The carbon based metal free catalyst shows a superior catalytic activity toward ORR and OER.•Zn-air battery equipped with metal-free cathode demonstrates high power density of 225 mW cm−2.•Enhanced catalytic activity is ascribed to rich active sites introduced by multi-heteroatom dopants. Controllable tailoring the microstructure of carbon based metal-free catalysts offers a promising avenue for boosting the bifunctional performance of oxygen electrode, but a big challenge owing to the sluggish kinetics of ORR and OER. Herein, a wet ball-milling induced defect assisted in-situ pyrolysis strategy is designed to fabricate N, S and P tri-doped graphene (NSP-Gra). The structural defect of graphene, generated by strong mechanical shear forces during ball-milling, is greatly advantageous for effective doping of the heteroatoms. The NSP-Gra shows a superior bifunctional catalytic activity toward ORR and low operating potential of 1.50 V at 10 mA cm−2 for OER in 6.0 M KOH. Excitingly, the Zn-air battery equipped with NSP-Gra as cathode demonstrates a power density up to 225 mW cm−2, and long charge-discharge cycling stability. The enhanced electrochemical performance of NSP-Gra can be ascribed to the fast charge transport capability and rich active sites introduced by multi-heteroatom dopants.