Cobalt ion intercalated MnO₂/C as air cathode catalyst for rechargeable aluminum–air battery

Overcoming the self-corrosion and surface passivation of aluminum anode, and the slow kinetics of cathodic electrochemical reactions are of great significance for the practical application of aluminum–air battery. In this study, we replaced the traditional aqueous electrolyte with AlCl₃-urea ionic liquid electrolyte, and prepared Co–MnO₂/C catalysts as cathode catalyst. Structures and electrocatalytic activity of the x % Co–MnO₂/C (x is the mole percent of Co to Mn, x = 0, 10, 20, 30, 40 and 50) catalysts have been investigated systematically. After Co ions intercalation, the specific surface area of the catalyst increased and average pore diameter decreased. The unique interaction between Co ions and MnO₂ led to an increase in the catalytic activity of the catalyst in the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) compared with MnO₂/C. In particular, 40% Co–MnO₂/C showed the largest specific surface area (154.25 m² g⁻¹) and the smallest average pore diameter (6.47 nm). It showed the most positive half-wave potential (0.727 V vs. RHE) and the biggest limiting current density (4.744 mA cm⁻²) in ORR process, and also exhibited the lowest onset potential (1.593 V) and the biggest limit current density (15.177 mA cm⁻²) in OER process. Furthermore, aluminum–air battery assembled with 40% Co–MnO₂/C demonstrated excellent reversible charge and discharge performance, which had an average discharge voltage of 1.5 V and an average charge voltage of 2 V during 30 cycles at a limited battery capacity of 375 mAh g⁻¹. Our results reveal the possibility of designing a rechargeable aluminum-air battery working at ambient conditions based on the Co–MnO₂/C air cathode catalyst for the first time. Our work opens up a new way to achieve the rechargeability of aluminum-air batteries, and our highly active electrocatalytic materials can be used in a wider range of electrochemical energy applications.