F‑Doped\nNickel Cobalt Oxide-Carbon Composite\nElectrocatalysts Paired with Mechanically Robust Anion-Conducting\nChitosan Membranes for Flexible and Rechargeable Zinc–Air Batteries

High-performing,\ncost-effective electrocatalysts and anion-conducting\npolymer electrolyte membranes are essential for realizing commercially\naffordable zinc–air batteries (ZABs). In this context, the\npresent work deals with the development of a bifunctional electrocatalyst\nand an anion-exchange quasi-solid-state electrolyte membrane (based\non quaternary ammonium group-grafted chitosan) for demonstrating flexible\nand rechargeable ZABs. The electrocatalyst composed of NiCoO<sub>2</sub> nanoparticles supported on a carbon framework showcased substantial\nadvancements in its ability to catalyze both oxygen reduction and\nevolution reactions (ORR and OER) due to the heteroatom doping by\nfluorine. For instance, the optimized electrocatalyst (F-NCO-ADC-600)\nexhibited an onset potential of 0.96 V vs RHE with a half-wave potential\nof 0.83 V vs RHE for ORR, a comparable performance with the state-of-the-art\nPt/C (1.0 and 0.86 V vs RHE, respectively). On a similar note, the\nsame catalyst also displayed an overpotential of 340 mV vs RHE for\nOER at a current density of 20 mA cm<sup>–2</sup>, close to\nthat of a standard RuO<sub>2</sub> catalyst (337 mV vs RHE). In the\ncontext of polymer electrolytes, the quaternary ammonium-group-grafted\nchitosan membrane depicted superior ionic conductivity, liquid electrolyte\nuptake, and mechanical properties, thereby proving to be an efficient\nanion-conducting polymer electrolyte membrane. The realistic application\nof the developed electrocatalyst and the polymer electrolyte membrane\nis demonstrated in the ZAB prototypes. The assembled rechargeable\nZAB (RZAB) delivered a power density of 207 mW cm<sup>–2</sup> and maintained high-rate capability and cycling stability, notably\nin a flexible configuration (f-RZABs). Thus, this work provides a\nstrategy for the rational design of anion-exchange membranes and bifunctional\nelectrocatalysts for f-RZABs.