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

Abstract

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.