Phase and morphology engineering of porous cobalt-copper sulfide as a bifunctional oxygen electrode for rechargeable Zn-air batteries

Developing efficient electrocatalysts for the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) is crucial for various sustainable energy devices such as rechargeable Zn-air batteries. Phase engineering has been proven to effectively tune the active-site electronic structure and thus improve the activity of electrocatalysts. However, phase transition usually induces morphology transformation, and the influence of realistic morphological feature change on the activity of electrocatalysts has seldom been considered. Herein, we present a facile thermal annealing strategy to transform cobalt-copper oxide nanosheets (Co₂Cu₁-ONS) into nanoparticle-stacked porous sulfide nanonetworks (Co₂Cu₁-S). Density functional theory (DFT) and dynamic DFT calculations confirm that the S thermal annealing process could bring about higher intrinsic activity of active sites and faster mass transfer of reactants, which endow Co₂Cu₁-S with remarkably higher OER/ORR catalytic performance than that of Co₂Cu₁-ONS and Co₃S₄. Its potential gap between the potential for an OER current density of 10.0 mA cm⁻²and the ORR half-wave potential is as low as 0.74 V. The Co₂Cu₁-S is then employed as an air electrode for a rechargeable Zn-air battery, which exhibits a peak power density of 0.195 W cm⁻², high specific capacity of 815.3 mA h g⁻¹, and robust stability (up to 80 h).