Efficient Oxygen Electrocatalyst for Zn–Air Batteries: Carbon Dots and Co₉S₈ Nanoparticles in a N,S-Codoped Carbon Matrix

Non-noble metal-based bifunctional electrocatalysts for both oxygen reduction reactions (ORRs) and oxygen evolution reactions (OERs) are an essential component of high-performance rechargeable Zn-air batteries (ZABs). Herein, we report a novel and simple method for preparing Co₉S₈ nanoparticles embedded in N and S codoped carbon materials with aid of carbon dots (CDs). CDs play a key role in distributing Co₉S₈ nanoparticles in the matrix uniformly and enhancing the specific surface area and the electric conductivity simultaneously. The obtained Co₉S₈/CD@NSC exhibits an excellent ORR and OER bifunctional catalytic activity and a great long-term durability, with a half-wave potential of 0.84 V versus reversible hydrogen electrode (RHE) for the ORR and a low potential of 1.62 V versus RHE at 10 mA cm^-2, which outperform the popular Pt/C and RuO₂ commercial catalysts. Moreover, the Co₉S₈/CD@NSC catalyst also displays a superior activity and cycling stability as a cathode material in ZABs, which is far better than Pt/C + RuO₂ mixture catalysts. Such a ZAB shows a low charge/discharge voltage gap of 0.62 V and great cycling stability over 125 h at 10 mA cm^-2.