Rational synthesis of bifunctional electrocatalysts with high performance and strong durability is highly demanded rechargeable metal-air battery. In this work, ZIF-derived Co9S8/C coated with conductive graphene nanosheet (Co9S8/GN) was synthesized by a simple solvothermal method and formed a stable double-carbon structure. As expected, the prepared Co9S8/GN catalyst exhibits a high catalytic activity (ΔE: 0.88 V) and long-term durability toward both oxygen reduction reaction and oxygen evolution reaction (ORR and OER), which is even superior to the Pt/C + Ir/C mixture (0.91 V). In addition, the Zn-air battery with the Co9S8/GN catalyst showed higher power density (186 mW cm-2) and more stable charge-discharge cycling performances (2000 cycles) than the Pt/C + Ir/C (118 mW cm-2). Based on these analysis results, the favorable catalytic performance of ORR/OER should be illustrated by the following reasons: (i) large specific surface area and unique mesoporous structure, providing abundant active sites; (ii) good conductivity, accelerating the electrons transfer; and (iii) the unique stable "double-carbon" structures (metal-S-C-C), preventing the agglomeration of metal sulfide, building new quick transfer pathway, and forming the strong electron coupling ability and synergistic effect.
Keywords: Co9S8/graphene; ZIF-67; Zn−air battery; bifunctional catalyst; double carbon.