A bifunctional catalyst of CoO/NBC composite for high-performance rechargeable flexible zinc-air battery

Rechargeable flexible zinc-air batteries (ZABs) represent a promising energy-supply device for wearable electronics due to their low cost, safety and high energy density, but their electrochemical performance often suffers from the sluggish reaction kinetics of air electrode and poor moisture-retention ability of polymer electrolytes. Here, we report a type of high-performance rechargeable flexible ZABs endowed by an efficient bifunctional catalyst for air electrode and a high moisture-retention hydrogel electrolyte. The designed nitrogen-boron co-doped carbon nanotube arrays loaded with cobalt oxide nanoparticles (CoO/NBC) with abundant catalytic active sites and oriented structure provide its excellent electrochemical catalytic activities for both oxygen reduction reaction and oxygen evolution reaction. Based on the bifunctional catalyst of CoO/NBC, the developed rechargeable ZABs exhibit a high open-circuit voltage of 1.44 V and a high energy density of 920.0 Wh kg^-1, which are superior than commercial Pt/C + RuO₂ and most reported non-precious metal catalysts. Furthermore, a trehalose modified polyacrylamide hydrogel electrolytes (trehalose/PAAm) with high moisture-retention has been synthesized to construct flexible ZABs, which not only exhibit outstanding electrochemical performance (1.39 V and 824.8 Wh kg^-1), but also show excellent stability even after 400 charge/discharge cycles or being bent to any angle.