Facilitating Oxygen Redox on Manganese Oxide Nanosheets by Tuning Active Species and Oxygen Defects for Zinc-Air Batteries

Bifunctional oxygen catalyst is an important component in the cathode for rechargeable zinc-air batteries. MnO₂ catalysts have aroused intense interests owing to their promising activity for oxygen reduction reaction (ORR), which, however, is still not comparable to precious metal catalysts. To improve the ORR catalysis and meet the requirement for a bifunctional oxygen catalyst, MnO₂ nanosheets are modified with Co, Ni or Fe via a facile solution-based method. Among the modified samples, Co−MnO₂ presents improved catalysis for both ORR and oxygen evolution reaction (OER). The modification introduces additional active sites for OER and induced more oxygen defects to further facilitate the ORR. Zn-air batteries with the Co−MnO₂ air cathode showed a higher peak power density of 167 mW cm⁻², a lower potential gap of 0.75 V and a higher round-trip efficiency of 63 % (5 mA cm⁻²) compared to MnO₂ without modification. Good cycling stability of the battery is also achieved. The proper amount of cobalt species in the MnO₂ is vital for achieving a balance between high performance and durable cycling.