A simple method for the preparation of a nickel selenide and cobalt selenide mixed catalyst to enhance bifunctional oxygen activity for Zn–air batteries

Developing a low-cost, simple, and efficient method to prepare excellent bifunctional electrocatalysts toward the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is critical in rechargeable zinc–air batteries. Non-stoichiometric M(0.85)Se (M = Ni or Co) nanoparticles are synthesized and modified on nitrogen-doped hollow carbon sphere (NHCS). The NHCS loaded Ni(0.85)Se (Ni(0.85)Se-NHCS) with rich Ni(3+) presents higher OER activity, whereas the NHCS-loaded Co(0.85)Se (Co(0.85)Se-NHCS) with abundant Co(2+) displays better ORR activity, respectively. When Co(0.85)Se-NHCS is mixed with Ni(0.85)Se-NHCS in a mass ratio of 1 : 1, the resulting mixture (Ni(0.85)Se/Co(0.85)Se-NHCS-2) shows better ORR and OER dual catalytic functions than a single selenide. Moreover, zinc–air batteries equipped with Ni(0.85)Se/Co(0.85)Se-NHCS-2 as the oxygen electrode catalyst exhibit excellent charge and discharge performance as well as improved stability over precious metals. This work has developed a simple and effective method to prepare excellent bifunctional electrocatalysts for ORR and OER, which is beneficial for the practical large-scale application of zinc–air batteries.