Interconnected Hollow Porous Polyacrylonitrile-Based Electrolyte Membrane for a Quasi-Solid-State Flexible Zinc-Air Battery with Ultralong Lifetime.

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Quasi-solid-state flexible zinc-air batteries (FZABs) have received enormous attention due to their low cost and high safety. However, the constraints in lifetime resulting from the lack of stable quasi-solid-state electrolyte membranes and efficient bifunctional electrocatalysts toward oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) hinder the large-scale manufacture and commercialization of FZABs to power electric devices. Herein, a polyacrylonitrile (PAN)-based membrane (HPPANP) fabricated via facile coaxial electrospinning, water dissolution, lyophilization, and KOH preimmersion method was utilized as the quasi-solid-state electrolyte membrane. The interconnected hollow porous structure based on PAN nanofibers endows HPPANP with outstanding electrolyte-uptake/retention capabilities for high ionic conductivity and nanolevel wetted electrolyte/anode interface for uniform Zn dissolution/deposition, thus prolonging the lifespan of the FZABs. In addition, the in situ alkaline hydrolysis of KOH solution supplies HPPANP with abundant oxygen-containing groups, which also improves its ionic conductivity. Additionally, we synthesized a Co/N-doped hollow carbon sphere (CoN-CS) electrocatalyst that exhibits superior ORR and OER electrocatalytic activities with a low potential difference (ΔE) of 0.73 V. Such favorable ORR and OER performances can be mainly attributed to the hierarchical hollow micro/nanostructures with abundant active sites, long-term stability, and favorable electron/ion diffusion pathway. As a result, the assembled FZAB equipped with the CoN-CS catalyst and HPPANP displays high power density (123.8 mW cm-2) and preferable long-term cycling performance (more than 50 h at 3 mA cm-2).