Rechargeable Zinc–Air Batteries with Seawater Electrolyte and Cranberry Bean Shell-Derived Carbon Electrocatalyst

Zinc–air batteries with seawater electrolyte utilize abundant and cheap resources. However, it requires an electrocatalyst with high bifunctional activity in seawater. In this work, a carbon electrocatalyst is obtained via one-step pyrolysis of the shell waste of cranberry beans. During the oxygen reduction reaction (ORR) in seawater electrolyte, the cranberry bean shell-derived carbon catalyst exhibits an ORR onset potential of 0.69 V vs RHE and an ORR saturating current density of 2.93 mA cm–2, which are promising compared to the ORR performance of Pt/C in seawater electrolyte (0.78 V vs RHE and 3.15 mA cm–2). During OER (oxygen evolution reaction) in seawater electrolyte, the carbon catalyst shows an overpotential of 582 mV at 5 mA cm–2, 35 mV smaller than the commercial Ir/C catalyst (617 mV). Furthermore, when the catalyst is applied to the zinc–air battery with seawater electrolyte, the cell is able to exhibit discharge and charge voltages of 0.93 and 2.2 V, respectively, which are stable for more than 120 cycles of the cycling test. This work highlights the fabrication of metal–air batteries with cost-effective and sustainable resources.