Three-dimensional nanoflower-like transition metal sulfide heterostructures (Co9S8/Co1-xS /WS2) as efficient bifunctional oxygen electrocatalysts for Zn-air batteries

•A nanoflower-like bifunctional oxygen electrocatalyst (Co9S8/Co1-xS/WS2) comprising a combination of nanosheets, and its unique morphology effectively prevented metal agglomeration.•Owing to the abundant s vacancies in Co9S8/Co1-xS/WS2 and the synergistic effect between Co9S8, Co1-xS, and WS2, the catalyst structure was optimized for good oxygen electrocatalytic performance.•Co9S8/Co1-xS/WS2 was applied to ZABs, which exhibited high specific capacity, excellent energy density, and improved stability compared to commercial noble metal catalysts. The charging and discharging processes of rechargeable Zn-air batteries (ZABs) require the use of precious metal catalysts (Pt and RuO2) that are expensive. Therefore, preparing efficient, stable, and affordable metal bifunctional oxygen electrocatalysts compatible with both the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is crucial. Herein, a nanoflower-like Co9S8/Co1-xS/WS2 bifunctional oxygen electrocatalyst with a layered structure has been prepared. The cobalt sulfide serves as the main active site and the synergistic interaction between the multi-components modulates the electronic structure of the active site and generates abundant S vacancies, thereby effectively improving the bifunctional oxygen electrocatalytic performance. The electrocatalytic activity of the prepared catalyst for ORR/OER is close to that of commercial noble metal catalysts. When Co9S8/Co1-xS/WS2 is used as the cathode material in Zn-air batteries, the batteries exhibit high specific capacity (822.6 mAh gZn−1), excellent energy density (958.9 Wh kgZn−1), as well as a battery charge/discharge cycling time that was twice that of the commercial catalyst PtC+RuO2. A typical 3D nanoflower structure promotes the ORR/OER mass transfer kinetics of Co9S8/Co1-xS/WS2. The introduction of WS2 increases the number of S vacancies and optimizes the adsorption energy of Co9S8/Co1-xS on oxygen adsorption intermediates, resulting in a good electrocatalytic performance and efficient ZABs. [Display omitted]