A bio-inspired Co₃O₄-polypyrrole-graphene complex as an efficient oxygen reduction catalyst in one-step ball milling

The development of non-precious metal-based electrocatalysts has attracted much research attention because of their high oxygen reduction reaction (ORR) activities, low cost, and good durability. By one-step in-situ ball milling of graphite, pyrrole, and cobalt salt without resorting to high-temperature annealing, we developed a general and facile strategy to synthesize bio-inspired cobalt oxide and polypyrrole coupled with a graphene nanosheet (Co₃O₄-PPy/GN) complex. Herein, the exfoliation of graphite and polymerization of pyrrole occurred simultaneously during the ball milling process. Meanwhile, the Co₃O₄ and Co-N_x ORR active sites were generated from the oxidized cobalt ion, cobalt-PPy, and the newly exfoliated graphene nanosheets via strong π–π stacking interactions. The resultant Co₃O₄-PPy/GN catalysts showed efficient electrocatalytic performances for ORRs in an alkaline medium with a positive onset and reduction potentials of -0.102 and -0.196 V (vs. Ag/AgCl), as well as a high diffusion-limited current density (4.471 mA·cm^-2), which was comparable to that of a Pt/C catalyst (4.941 mA·cm^-2). Compared to Pt/C, Co₃O₄-PPy/GN catalysts displayed better long-term stability, methanol tolerance, and anti-CO-poisoning effects, which are of great significance for the design and development of advanced non-precious metal electrocatalysts.