Spent alkaline battery-derived manganese oxides as efficient oxygen electrocatalysts for Zn–air batteries

Abstract

Manganese oxides were derived from spent commercial AA-type alkaline Zn–MnO₂ batteries (ZMBs) via a facile route and applied as effective oxygen electrocatalysts for Zn–air batteries (ZABs). After leaching in dilute acid and annealing in air at mild temperature, the cathode dismantled from the battery discharged to 0.8 V is converted from γ-MnO₂ into ε-MnO₂, which features abundant defects, a porous structure and a high surface area and shows high activity in catalyzing the oxygen reduction/evolution reaction (ORR/OER). Remarkably, the recycled manganese oxide from one ZMB is estimated to sustain 1000 coin-type ZABs, which could potentially deliver a total capacity of 675 A h and an energy of 810 W h. Additionally, a rechargeable ZAB assembled with the recycled ε-MnO₂ exhibits a considerable charge–discharge voltage separation of 0.65 V at 2 mA cm⁻². Furthermore, we show that the hydrothermally prepared α-MnO₂ serves initially as a cathode in a ZMB and directly functions as an efficient air electrode in a ZAB at its discharged states. This study offers a unique way to synthesize active manganese oxide electrocatalysts and a promising strategy to recycle spent batteries.