Growth restriction of Co₃O₄ nanoparticles by α-MnO₂ nanorods as air cathode catalyst for rechargeable aluminum-air battery

Obstacles to the efficient operation of rechargeable aluminum-air batteries include slow oxygen reduction reaction (ORR), slow kinetics, and large overpotential of oxygen evolution reactions (OER). An effective solution is to develop a new bifunctional electrocatalyst that is effective for both the ORR/OER processes. In this study, we prepared the α-MnO₂/Co₃O₄ bifunctional composite catalyst by the in situ generation of Co₃O₄ nanoparticles on α-MnO₂ nanorods. ORR/OER catalytic activity and structures of the prepared catalysts have been investigated systematically. Compared with single-component α-MnO₂ nanorods and Co₃O₄ particles catalyst, the α-MnO₂/Co₃O₄ composite catalyst possesses the smallest average pore diameter (11.84 nm), and the largest specific surface area (41.34 m² g⁻¹), which is due to the restriction of the growth of Co₃O₄ particles by α-MnO₂ nanorods. Besides, during the ORR process, the α-MnO₂/Co₃O₄ composite catalyst shows the most positive onset potential of 0.833 V, the most positive half-wave potential of 0.760 V, and the biggest limiting current density of 3.881 mA cm⁻². Meanwhile, during the OER process, the composite catalyst exhibits the lowest onset potential of 1.630 V, the lowest overpotential of 554 mV, and the biggest limiting current density of 24.590 mA cm⁻². Furthermore, the α-MnO₂/Co₃O₄-assembled aluminum-air battery (AAB) delivers the best cycling performance. Our work provides an idea for optimizing the bifunctional catalyst with high ORR/OER activity and low cost used in secondary AAB. Highlights: A novel α-MnO₂/Co₃O₄ bifunctional composite catalyst was prepared successfully. The α-MnO₂/Co₃O₄ composite catalyst was applied in a rechargeable Al-air battery. The α-MnO₂/Co₃O₄ exhibited better ORR/OER catalytic activity than α-MnO₂ and Co₃O₄. The Al-air battery using α-MnO₂/Co₃O₄ catalyst showed excellent cycling performances. Novelty Statement: This is our original work. Neither the entire paper nor any part of its content has been published or has been accepted elsewhere. It is not being submitted to any other journal.