Bifunctional Bimetallic Biomass-Derived Electrocatalyst Materials for Usage as Air Electrode Catalysts in Rechargeable Zinc–Air Batteries

Rechargeable zinc–air batteries (RZAB) have so far required expensive precious metal electrocatalysts for efficient operation. Herein, a series of cost-efficient electrocatalysts is prepared by ionothermal carbonization of rapeseed press cake, followed by iron, nickel, and nitrogen doping with varying iron-to-nickel ratios. These materials exhibit excellent bifunctional electrocatalytic activity for both the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), even at low relative nickel content, comparable to that of commercial 50:25:25 PtRu/C. When used as air electrode catalysts in RZABs, the materials show high maximum power density (up to Pmax = 179 mW cm–2) which was improved by ball-milling (up to Pmax = 205 mW cm–2). During long-term cycling at practically relevant areal capacities, the RZAB shows stable performance for at least 65 h. Additionally, the effects of catalyst loading and ionomer as a binder in the catalyst layer on the RZAB performance are studied. This work provides a feasible approach for the production of highly active bifunctional electrocatalysts for air electrodes of RZABs.