The Asymmetrical Fe-O-Se Bonds in FeO(SeO) 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 FeO(SeO)/FeC@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 FeO(SeO) crystal phase of FeO(SeO)/FeC@NC, and the Fe-O-Se bonds could obviously enhance ORR and OER catalytic performance of FeO(SeO)/FeC@NC. Density functional theoretical calculations (DFT) confirmed that the FeO(SeO) in FeO(SeO)/FeC@NC had a higher d-band center of Fe atom and a lower p-orbital coupling degree with its own lattice O atom than FeO, which leads to Fe site of FeO(SeO) being more likely to adsorb external oxygen intermediates. The Fe-O-Se bonds in FeO(SeO) results in the modification of coordination environment of Fe atoms and optimizes the adsorption energy of Fe site for oxygen intermediates. Compared with FeO/FeC@NC, the FeO(SeO)/FeC@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 in a 1.0 M KOH electrolyte. The peak power density and specific capacity of FeO(SeO)/FeC@NC-based ZABs are higher than those of Pt/C+RuO-ZABs. The above results demonstrate that the asymmetrical Fe-O-Se bonds in FeO(SeO) plays a key role in improving the bifunctional catalytic activities of ORR/OER for ZABs.