Structure preferred spinel ferrite on polypyrrole derived N-doped carbon nanofibers as bifunctional electrocatalyst for Zn-air battery

Abstract The exploration of noble metal free bifunctional oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) electrocatalysts is very important for Zn-air batteries (ZABs). Spinel ferrites are famous bifunctional ORR/OER electrocatalysts. Herein, to further improve their ORR and OER activities, we anchor CoFe₂O₄ on N-doped carbon nanofibers (NCNF) derived from polypyrrole (PPy) and obtain CoFe₂O₄ loaded NCNF (CoFe2O4@NCNF). In its structure, CoFe₂O₄ particles with small size distribute evenly on NCNF. The combination of CoFe₂O₄ and NCNF generates excellent ORR activity with typical four-electron character in both alkaline and neutral electrolyte. In OER, the activity of CoFe2O4@NCNF is also excellent. To explore the superior ORR and OER activities of CoFe2O4@NCNF over other spinel ferrites, theoretical calculation was employed. A rechargeable ZAB is constructed with CoFe2O4@NCNF as cathode material. The specific capacity and energy density of this ZAB reach 807.4 mA·h·g⁻ ¹ and 963.6 Wh·kg⁻ ¹ at 10 mA·cm⁻ ², respectively. ZAB can keep stable after continuous charge/discharge test for 120 h. This work not only provides an efficient and low cost cathode material for ZABs, but also clarifies the structure-activity relationship in ORR/OER for spinel ferrites.