Bifunctional porous Co-doped NiO nanoflowers electrocatalysts for rechargeable zinc-air batteries

Abstract Zinc-air batteries (ZnABs) represent one of the most promising options to power next-generation electric vehicles owing to their high theoretical energy density and reliable safety. However, their further development and application is hampered due to the lack of high-efficiency bifunctional air electrocatalysts. Herein, porous Co-doped NiO nanoflowers (Co-NiO NFs) with outstanding electrocatalytic activity and stability toward oxygen evolution reaction (ORR) and oxygen reduction reaction (OER) is reported for the first time, including a positive half-wave potential (0.79 V) for ORR and a small overpotential (1.53 V at 10 mA cm−2) for OER. Firstly, the synergistic effect between the sound two-dimensional (2D) hexagonal framework and numerous nanopores inside the nanosheets offers an available surface for O2 adsorption/diffusion, and a large effective electrochemical active surface area for exploring and utilizing more active sites. Secondly, Co dopants can effectively increase the conductivity of pristine NiO nanoflowers (NFs) and simultaneously enhances the intrinsic ORR and OER activity. Notably, the liquid ZnABs with engineered Co-NiO NFs electrode exhibits a high discharge peak power density of 93 mW cm−2, a satisfactory specific capacity of 830 mA h g-1 at the current density of 5 mA cm−2, together with excellent cycling stability of 110 h at 2 mA cm−2. Additionally, the corresponding all-solid-state ZnABs assembled with Co-NiO NFs shows a long durability with the stable charge-discharge cycles of 6 h and good flexible nature.