Design and integration of binder-free MnO2 nanotube arrays on carbon cloth as efficient cathodes for Mg-air batteries

Abstract

Magnesium-air batteries are considered promising next-generation energy storage systems due to their high specific energy density and environmental benefits. However, the sluggish kinetics of the oxygen reduction reaction (ORR) at the cathode significantly limits their practical applications. In this study, we successfully fabricated MnO₂ nanotube arrays (MnO₂-NTA) grown in situ on a carbon cloth (CC) substrate using a hydrochloric acid-assisted hydrothermal method. The resulting MnO₂-NTA@CC electrode demonstrated excellent electrocatalytic performance and stability for ORR, with an initial potential of approximately − 0.15 V and a half-wave potential around − 0.3 V. Furthermore, the electrode exhibited a diffusion-limited current density of 5.0 mA/cm² at a rotation speed of 2000 rpm and maintained a loss of less than 0.015 V in the half-wave potentials after 10000 CV cycles, indicating outstanding durability. Theoretical calculations revealed that the MnO₂ (200) surface efficiently catalyzes oxygen reduction via a four-electron pathway, with the *OOH to *O transition being the rate-determining step. This excellent catalytic activity can be attributed to the unique hollow nanotube architecture, providing abundant active sites and enhancing electron and oxygen transport. Additionally, the integrated MnO₂-NTA@CC structure eliminates the need for binders and functions as a gas diffusion layer, simplifying the electrode preparation process and reducing manufacturing costs. When directly employed as the cathode in magnesium-air batteries, the MnO₂-NTA@CC electrode achieved a stable open-circuit voltage of 1.5 V and a peak power density of 14.91 mW/cm². These results demonstrate that the MnO₂-NTA@CC electrode is a promising candidate for high-performance magnesium-air batteries and provide valuable insights into the design of efficient air electrodes for future energy storage systems.