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

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 -MnO2 into epsilon-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 epsilon-MnO2 exhibits a considerable charge-discharge voltage separation of 0.65 V at 2 mA cm(-2). Furthermore, we show that the hydrothermally prepared -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.