Morphologically controlled Co3O4 nanodisks as practical bi-functional catalyst for rechargeable zinc–air battery applications

• Co3O4 nanodisks with surface porosity are synthesized using polyvinylpyrrolidone.
• Co3O4 nanodisks as bi-functional catalysts are active towards both ORR and OER.
• The morphological control enhances the rechargeable zinc-air battery performance.
• The enhanced performance is due to superior charge transfer and mass diffusion.
• Co3O4 nanodisks outperform commercial Pt/C highlighting its practicality.

The morphological control of Co3O4 by polyvinylpyrrolidone during precipitation reaction has resulted in the formation of two-dimensional nanodisks with surface porosity. As a bi-functional catalyst, Co3O4 nanodisks are active towards both the oxygen reduction and evolution reactions. The electrocatalytic activity is evaluated by preparing air electrodes for rechargeable zinc–air batteries utilizing ambient air to emphasize practicality. The galvanodynamic charge and discharge behaviors are far superior than Co3O4 nanoparticle counterparts particularly at high applied current densities. Electrochemical impedance spectroscopy reveals that Co3O4 nanodisk electrode results in significantly less internal, solid-electrolyte interface, and charge transfer resistances which lead to highly efficient electrochemical reactions. Superior rechargeability has also been confirmed where virtually no voltage drops are observed over 60 pulse cycles. The practicality of Co3O4 nanodisks is highlighted by demonstrating comparable discharge voltages and greatly outperforming charge voltages with excellent electrochemical stability than commercial Pt/C catalyst.