Facile Generation of a Stable Bi-Functional Mixed Phase Fe₃O₄/Fe-N₄ Electrocatalyst for Rechargeable Zinc-Air Battery

Abstract

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) and the oxygen evolution reaction(OER). Here, we report a simple and effective route to introduce nitrogen functionalities coordinated with Fe to generate ORR active Fe-N4 species. Fe-N-C catalytic sites are known to play an active role toward ORR; however, the higher oxidation state of Fe has been speculated to be good for OER. This method generates a mixture of ORR active and OER active phases. The superior ORR activity of the catalyst, prepared by annealing at 800°C consists of the mixed phases of Fe-N4, Fe3O4, and Fe3C. The oxygen bifunctional activity measured in terms of ΔE value (1.06 V) makes it suitable for the cathode of aqueous zinc-air battery. The catalyst remains stable for approximately 63 hours of continuous charging-discharging cycles with a high specific capacity of 689 mAh g-1 with a constant charge-discharge voltage gap.

Understanding the evolution of catalytically active multi-metal sites in a bifunctional high-entropy alloy electrocatalyst for zinc–air battery application

“…The presence of zinc ions in the electrolyte as an additive facilitates the replenishment of zinc at the anode during charging by maintaining a reserve of zincate ions. 50,56 However, as confirmed by the XPS survey spectra and high-resolution zinc 2p spectra, zinc was found to be incorporated at the CCMNF catalyst either by substituting for the leached metal sites or by replacing them. In either case, the electrocatalytic activity of CCMNF was diminished by the structural and electronic defects brought by unrequited zinc incorporation.…”

“…A higher ECSA implies more participation of the catalyst surface in the redox reactions, thus availing better performance. To gain insights into the electrocatalytic activity at the catalyst's surface, its ECSA was evaluated by the double-layer capacitance method 50 since ECSA is directly related to double-layer capacitance ( C dl ). Cyclic voltammetry scans were run in non-faradaic regions at different scan rates as shown in Fig.…”

“…The active electrocatalyst material was coated as ink/paste on the carbon paper. The electrolyte is typically a highly concentrated alkali to achieve excellent conductivity, with a salt of zinc added to maintain uninterrupted redeposition of zinc 50 from the electrolyte to the anode. The discharging polarization curves of the CCMNF catalyst, as shown in Fig.…”