Wood-derived integrated air electrode with Co–N sites for rechargeable zinc-air batteries

The sluggish reaction kinetics in oxygen reduction reaction (ORR) is one of the bottlenecks in next generation energy conversion systems. The integrated design strategy based on simultaneously constructing active sites and forming porous carbon network will address this concern by facilitating charge exchange, mass transfer and electron transportation. In this article, a three-dimensional integrated air electrode (Co–N@ACS) containing Co–N sites and hierarchically porous carbon is fabricated via growth of Co-doped ZIF-8 in activated wood substrate and synchronous pyrolysis. The optimized integrated air electrodes exhibit ultrahigh ORR activity (E_1/2 = 0.86 V). Co–N sites provide outstanding ORR activity, and hierarchically porous structures facilitate oxygen diffusion and electrolyte penetration. Aqueous zinc-air battery assembled with Co–N@ACS possesses open-circuit voltage of 1.46 V, peak power density of 155 mW·cm^-2 and long-term stability of 540 cycles (180 h). Solid-state zinc-air battery assembled with Co–N@ACS shows open-circuit voltage up to 1.36 V and low charge-discharge voltage gap (0.8 V). This design strategy paves the way for the conversion of wood biomass to integrated air electrodes and catalytically active carbon for next generation energy storage and conversion devices.