Hybridization of carbon nanotube tissue and MnO₂ as a generic advanced air cathode in metal–air batteries

This paper presents the utilization of hybrid carbon nano-tube (CNT) – manganese dioxide (MnO₂) tissues as air electrodes in nonaqueous aluminum- and lithium-based battery systems. The CNT tissues are impregnated with α-manganese dioxide nanoparticles via a straightforward binder-free ultrasonic treatment, thereby enabling an improved oxygen reduction reaction (ORR) catalytic activity. Half-cell potentiodynamic measurements along with full-cell discharge evaluations of Li- and Al-based battery systems are reported. Higher discharge potentials and capacities were obtained from generic and advanced hybrid CNT–MnO₂ air cathodes. The discharge products obtained on the air cathode surface were studied using high-resolution scanning electron microscopy. Their chemical compositions were evaluated using elemental mapping energy-dispersive X-ray spectroscopy. We complemented our analysis with density functional theory calculations of oxygen adsorption on MnO₂ and graphene. The modifications obtained for the discharge products in both systems, along with their improved distribution within the cathode surface, supported longer discharge processes without clogging the O₂ penetration pathways at the air cathode. The stability of the α-MnO₂ catalyst was studied using X-ray photoelectron spectroscopy and electron paramagnetic resonance spectroscopy, thereby indicating the ongoing formation of an outer MnF₂ shell layer, which affected the α-MnO₂ functionality, as an efficient ORR catalyst.