A bifunctional electrocatalyst α-MnO2-LaNiO3/carbon nanotube composite for rechargeable zinc–air batteries

Abstract

Development of highly active, non-precious, electrochemical catalysts is needed to optimize rechargeable zinc–air battery electrodes. Herein, we fabricate a bifunctional electrocatalyst α-MnO₂-LaNiO₃/carbon nanotube (CNTs) composite to improve the activity of the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). CNTs are used to support the bifunctional catalysts in one integrated material. The chemical and physical characterization of the bifunctional catalyst is performed by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), and scanning electron microscopy (SEM). The electrochemical properties of the bifunctional catalyst tested by a rotating disc electrode system revealed enhanced catalytic activity toward both the ORR and OER. A four-electron reduction pathway contributes to the ORR process at different rotation speeds indicating an effective catalytic activity. A rechargeable zinc–air battery using the bifunctional catalyst achieved a maximum power density of 55.1 mW cm⁻², and its voltage polarization showed a 1.4% decrease in discharge and a 4.8% increase in charge after 75 charge–discharge (C–D) cycles. The charge transfer resistance for the ORR and OER catalyzed by the bifunctional catalyst increased from 1.24 to 4.68 Ω after 75 C–D cycles. The bifunctional electrocatalysts show satisfactory performance in an electrically rechargeable zinc–air battery.