(Co,Mn)3O4-doped carbon nanotube composite as a bifunctional electrocatalyst for aluminum–air batteries

Aluminum–air batteries (AABs) with high energy density and environment-friendly features are a potential candidate for future energy-storage devices. However, their practical application has been seriously hampered by a variety of inevitable factors, such as cathodic slow reaction kinetics and anodic self-corrosion. In order to address the above challenges, a bifunctional electrocatalyst with satisfactory ORR and OER catalytic activity and stability has yet to be developed. Herein, a (Co,Mn)3O4-doped carbon nanotube composite was designed and synthesized as an advanced cathode catalyst for AABs. The results revealed that (Co,Mn)3O4 with closely-intertwined carbon nanotubes and nitrogen-doped graphene (NG) was successfully prepared. In an alkaline environment, (Co,Mn)3O4/NG could catalyze the ORR and OER more efficaciously and durably than monometallic Co3O4/NG and Mn3O4/NG catalysts. (Co,Mn)3O4/NG demonstrated a half-wave potential of 0.831 V, which was equivalent to that of commercial Pt/C, and an Ej of 1.72 V, which was comparable to that of commercial IrO2. The improvements in the ORR and OER performances were closely related to the heightened synergistic effects between cobalt and manganese, coupled with the conductivity of carbon nanotubes and graphene. Furthermore, the (Co,Mn)3O4/NG catalyst applied to the battery-stacked cathodes of AABs showed a peak power density of 147 mW cm−2, a discharge voltage of 1.34 V at a current density of 50 mA cm−2, and long-term stability.