Facile Generation of a Stable Bi-Functional Mixed Phase Fe3O4/Fe-N-4 Electrocatalyst for Rechargeable Zinc-Air Battery

The successful commercialization of rechargeable zinc-air batteries requires an inexpensive and stable bifunctional oxygen electrocatalyst which can efficiently facilitate both the oxygen reduction reaction (ORR) as well as oxygen evolution reaction (OER). In this paper, we are reporting a simple and effective route to introduce nitrogen functionalities coordinated with Fe to generate ORR active Fe-N-4 species. Fe-N-C catalytic sites are known to play an active role towards ORR; however, the higher oxidation state of Fe has been speculated to be good for OER. This method generates a mixture of numerous ORR active and OER active phases. The superior ORR activity of the catalyst, prepared by annealing at 800 degrees C consists of the mixed phases of Fe-N-4,N- Fe3O4, and Fe3C. The oxygen bifunctional activity measured in terms of Delta E value (1.06 V) makes it suitable for the cathode of an aqueous zinc-air battery. The catalyst remains stable for approximately 63 h of continuous charging-discharging cycles with a high specific capacity of 689 mAh g(-1) with a constant charge-discharge voltage gap.