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

The charging and discharging processes of rechargeable Zn-air batteries (ZABs) require the use of precious metal catalysts (Pt and RuO 2 ) 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 Co 9 S 8 /Co 1-x S/WS 2 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 Co 9 S 8 /Co 1-x S/WS 2 is used as the cathode material in Zn-air batteries, the batteries exhibit high specific capacity (822.6 mAh g Zn −1 ), excellent energy density (958.9 Wh kg Zn −1 ), as well as a battery charge/discharge cycling time that was twice that of the commercial catalyst PtC+RuO 2 .