Developing non-precious-metal bifunctional oxygen reduction and evolution reaction (ORR/OER) catalysts is a major task for promoting the reaction efficiency of Zn-air batteries. Co-based catalysts have been regarded as promising ORR and OER catalysts owing to the multivalence characteristic of cobalt element. Herein, the synthesis of Co nanoislands rooted on Co-N-C nanosheets supported by carbon felts (Co/Co-N-C) is reported. Co nanosheets rooted on the carbon felt derived from electrodeposition are applied as the self-template and cobalt source. The synergistic effect of metal Co islands with OER activity and Co-N-C nanosheets with superior ORR performance leads to good bifuctional catalytic performances. Wavelet transform extended X-ray absorption fine spectroscopy and X-ray photoelectron spectroscopy certify the formation of Co (mainly Co0 ) and the Co-N-C (mainly Co2+ and Co3+ ) structure. As the air-cathode, the assembled aqueous Zn-air battery exhibits a small charge-discharge voltage gap (0.82 V@10 mA cm-2 ) and high power density of 132 mW cm-2 , outperforming the commercial Pt/C catalyst. Additionally, the cable flexible rechargeable Zn-air battery exhibits excellent bendable and durability. Density functional theory calculation is combined with operando X-ray absorption spectroscopy to further elucidate the active sites of oxygen reactions at the Co/Co-N-C cathode in Zn-air battery.
Keywords: Co nanoislands; Co-N-C nanosheets; Zn-air batteries; flexible batteries; operando XAFS.
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