Pollen-derived porous carbon decorated with cobalt/iron sulfides hybrids as cathode catalyst for flexible all-solid-state rechargeable Zn-air battery
Developing flexible all-solid-state rechargeable Zn-air batteries (FS-ZABs) for wearable applications faces challenges from the balance between performance and flexibility of battery, efficient cathode catalyst and reasonable electrode construction design are key factors. Herein, a low-cost pollen derived N, S co-doped porous carbon decorated with Co9S8/Fe3S4 nanoparticles hybrids (Co-Fe-S@NSRPC) has been synthesized. Owing to the active Co9S8/Fe3S4 nanoparticles, N, S co-doping, and large specific area of the pollen derived porous carbon matrix, the Co-Fe-S@NSRPC composite displays an excellent bifunctional catalytic activity with a small potential gap (ΔE=0.80 V) between the half-wave potential for ORR (0.80 V) and the potential at 10 mA cm-2 for OER (1.60V), and endows a liquid Zn-air battery with a high power density of 138 mW·cm-2, larger specific capacity of 891 mAh g-1 and stable rechargeability up to 331 cycles. Based on the Co-Fe-S@NSRPC cathode catalyst, a 2D coplanar FS-ZAB has been fabricated with specially designed parallel narrow strip electrodes alternately arrayed on the polyacrylamide polyacrylic acid copolymer hydrogel solid electrolyte. The presented FS-ZAB exhibits excellent battery performance with a high open-circuit-voltage (1.415 V), competitive peak power density (78 mW cm-2), large specific capacity (785 mAh g-1) and stable rechargeability (150 cycles), offers robust flexibility to maintain stable charge/discharge capacity under different bending deformations, and provides convenient coplanar integrability to realize parallel or series connection of multiple cells in a relatively small area.