One-step in situ biosynthesis fabrication of double-network hydrogel electrolytes with satisfactory water retention capacity and excellent electrical conductivity for Zn-air batteries

•The BC-PVA composite hydrogel was successfully prepared by a one-step in situ biosynthesis method.•Benefiting from the double-network, the BC-PVA hydrogel had excellent water retention and electrical conductivity capacity.•The sandwich-type ZABs based on BC-PVA exhibited excellent electrochemical performance.