F-Doped Co-N-C Catalysts for Enhancing the Oxygen Reduction Reaction in Zn-Air Batteries

Zn-air battery is a promising next-generation energy storage device. Its performance, however, is limited by a high overpotential resulted from the slow kinetics of the cathodic oxygen reduction reaction (ORR). This study reports a simple strategy for preparation of a fluorine-doped Co-N-C composite as highly efficient electrocatalyst for ORR. The C@PVI-(TPFC)Co-800 catalyst was prepared by pyrolysis of F-containing Co-corrole that was assembled on PVI-functionalized carbon black through the axial imidazole coordination (PVI=polyvinylimidazole, TPFC=5,10,15-triperfluorophenyl-21H, 22H-corrole). The C@PVI-(TPFC)Co-800 catalyst exhibited much more positive ORR half-wave potential (E-1/2=0.88 V vs. RHE) than its counterpart C@PVI-(TPC)Co-800 (E-1/2=0.82 V, TPC=5,10,15-triphenyl-21H, 22H-corrole) without F-doping in 0.1 M KOH electrolyte. C@PVI-(TPFC)Co-800 also achieved a greater kinetic current density and enhanced durability in alkaline media. In addition, a Zn-air battery with C@PVI-(TPFC)Co-800 loaded at the cathode delivered much higher peak power density (P-max=141 mW/cm(2)) and open-circuit voltage (OCV=1.45 V) over the C@PVI-(TPC)Co-800 counterpart (P-max=110 mW/cm(2), OCV=1.39 V) and the commercial 20 % Pt/C (P-max=119 mW/cm(2), OCV=1.42 V) as well. The promoted catalyst performance for ORR was attributed to the increased specific surface area, more defects generated, and reduced electron density distribution around the Co metal center after F-doping.