Tuning oxygen vacancies in spinel nanosheets for binder-free oxygen cathodes with superior catalytic activity in zinc-air batteries

As a promising energy storage technology, zinc-air battery (ZAB) has attracted much attention because of its safety, cleanliness, and potential high efficiency. However, slow kinetics of the oxygen evolution and reduction reactions (OER and ORR) on air cathode significantly limit the battery performance. Herein, a facile two-step tuning strategy is investigated to convert NiCoLDH to oxygen vacancy-rich NiCo2O4 nanosheet (R–NiCo2O4-x/CC). With carefully controlled air annealing and NaBH4 treatment processes, the optimal R–NiCo2O4-x/CC exhibits enhanced OER and ORR activities compared with NiCo2O4/CC counterpart. Liquid and quasi-solid-state ZABs based on the binder-free R–NiCo2O4-x/CC electrode demonstrate power density and cycling stability that surpass the reference RuO2+Pt/C/CC catalyst with open-circuit voltage and peak power density of 1.486 and 1.39 V, and 88.6 and 38.6 mW cm−2, respectively. This study provides a new approach toward high-performance catalysts for ZABs using an oxygen vacancy engineering strategy under mild conditions.