The Asymmetrical Fe-O-Se Bonds in Fe2O(SeO3)2 Boosting Bifunctional Oxygen Electrocatalytic Performance for Zinc-Air Battery.

Zinc-air batteries (ZABs) have the advantages of high energy density and rich zinc raw materials. It is a low-cost, green and sustainable energy storage device. At present, one of the key technologies that hinder the large-scale application of ZABs is the design and fabrication oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) bifunctional catalysts with excellent performance, especially the non-platinum-based catalysts. Here N-doped carbon-coated Fe-based selenium oxide catalyst Fe₂O(SeO₃)₂/Fe₃C@NC with high performance has been fabricated by a one-step pyrolysis and then the electrochemical oxidization. The experimental results confirmed that the existence of Fe-O-Se bonds in Fe₂O(SeO₃)₂ crystal phase of Fe₂O(SeO₃)₂/Fe₃C@NC, and the Fe-O-Se bonds could obviously enhance ORR and OER catalytic performance of Fe₂O(SeO₃)₂/Fe₃C@NC. Density functional theoretical calculations (DFT) confirmed that the Fe₂O(SeO₃)₂ in Fe₂O(SeO₃)₂/Fe₃C@NC had a higher d-band center of Fe atom and a lower p-orbital coupling degree with its own lattice O atom than Fe₂O₃, which leads to Fe site of Fe₂O(SeO₃)₂ being more likely to adsorb external oxygen intermediates. The Fe-O-Se bonds in Fe₂O(SeO₃)₂ results in the modification of coordination environment of Fe atoms and optimizes the adsorption energy of Fe site for oxygen intermediates. Compared with Fe₂O₃/Fe₃C@NC, the Fe₂O(SeO₃)₂/Fe₃C@NC showed the obvious enhancements of ORR/OER catalytic activities with a half-wave potential of 0.91 V for ORR in 0.1 M KOH electrolyte and a low overpotential of 345 mV for OER at 10 mA cm^-2 in a 1.0 M KOH electrolyte. The peak power density and specific capacity of Fe₂O(SeO₃)₂/Fe₃C@NC-based ZABs are higher than those of Pt/C+RuO₂-ZABs. The above results demonstrate that the asymmetrical Fe-O-Se bonds in Fe₂O(SeO₃)₂ plays a key role in improving the bifunctional catalytic activities of ORR/OER for ZABs.