Hollow structured Zn0.76Co0.24S–Co9S8 composite with two-phase synergistic effect as bifunctional catalysts

It is of great significance to develop efficient and inexpensive oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) bifunctional catalysts for the current energy crisis. But this is still a long-term and formidable challenge. In this work, a two-phase synergistic effect between transition metal sulfides is applied in the design of ORR/OER bifunctional catalysts. Co-based zeolite imidazolate framework (MOF) is used as a precursor to prepare the hollow Co 9 S 8 through vulcanization and heat treatment. At the same time, the phase transformation occurs to form some Zn 0.76 Co 0.24 S on surface during the heat treatment due to the Zn-polydopamine coating. The hollow structure Zn 0.76 Co 0.24 S–Co 9 S 8 composite has been verified and promotes the diffusion of reactants and products, and the interaction between two phases greatly promotes the catalytic reactions . The coating of Zn-polydopamine forms uniform carbon layer on surface, enhancing the conductivity of Zn 0.76 Co 0.24 S–Co 9 S 8 composite. The Zn 0.76 Co 0.24 S–Co 9 S 8 composite shows much better performance of ORR and OER compared to any of them. The overpotential of OER at a current density of 10 mA/cm 2 is 330 mV, and the half-wave potential of ORR is 0.83 V. Additionally, the Zn 0.76 Co 0.24 S–Co 9 S 8 composite displays better cyclic stability. The synergistic effect of Zn 0.76 Co 0.24 S and Co 9 S 8 can be considered as the foremost factor for the improvement of catalyst performance, which provides new possibilities for the development of non-precious metal bifunctional catalysts.