Engineering the electronic structure of Fe-N/C catalyst via fluorine self-doping for enhanced oxygen reduction reaction in liquid and all-solid-state Zn-air batteries

Heteroatom doping is considered as an effective approach that manipulates the local bonding environment to improve the electroactivity of Fe-N/C catalysts. Herein, the oxidation polymerization-pyrolysis approach is applied to fabricate the uniformly F-doped porous Fe-N/C catalysts (F-FeNC) through utilizing 4-fluoroaniline as a "self-doping" precursor with N and F elements simultaneously. The synergistic effect between ligand trapping and long-range interaction of F atoms provides high density of Fe-Nx active sites. The F-FeNC catalyst demonstrates superior ORR performance in alkaline media with a positive half-wave potential (E1/2) of 0.82 V, low H2O2 yield of -3.4% and rapid 4e- transfer process. The liquid-state Zn-air battery (ZAB) assembled with FFeNC catalyst as air cathode delivers excellent rate capability, power density (141 mW cm-2), specific capacity (760 mAh g-1) and long-term cycle durability over 120 h. Moreover, the as-assembled all-solid-state ZAB shows excellent cycle stability at 0 degrees -180 degrees bending conditions, revealing great prospects in flexible electronic device applications. Engineering the electronic structure of active sites via F self-doping provides an insightful route for designing multi-heteroatom doped Fe-N/C catalysts.