Biopolymeric hydrogel electrolytes obtained by using natural polysaccharide-poly(itaconic acid-co-2-hydroxyethyl methacrylate) in deep eutectic solvents for rechargeable Zn-air batteries

Rechargeable Zn-air batteries (ZABs) are safe energy storage systems, making them attractive for different applications, while their attractiveness can be boosted by adding natural constituents for eco-friendly disposal. In this work, biopolymeric hydrogels (biohydrogels) were synthesized using deep eutectic solvents (DESs), poly(itaconic acid) (PIA), and polysaccharides cross-linked with 2-hydroxyethyl methacrylate (HEMA). Three biohydrogels were studied, one based on alginate from Sargassum (PIA-ALG), another on inulin from Dahlia tubers (PIA-INU), and the third on dextran from Leuconostoc spp. (PIA-DEX), chosen due to their eco-friendly, cost-effective, and excellent water retention properties. Among these, PIA-INU presents pH-dependent water swelling absorption and an amorphous structure, both beneficial properties in applying biohydrogels as bioelectrolytes. These biohydrogels were then tested in a ZAB by mixing them with 6 M KOH solutions, displaying low internal resistances (below 7 & omega; cm(2)). The ZAB assembled with 3 wt% of PIA-INU showed the best performance. It presented an open circuit voltage of 1.44 V, a current density of 112 mA cm(-2)@0.6 V, and a maximum power density of 62 mW cm(-2). Additionally, it presented high rechargeability, being functional for more than 1600 cycles. According to post-mortem analyses, the long life of the battery can be attributed to the ability of this biohydrogel to decrease zinc issues such as shape changes and passivation.