Lithium Ion-Enabled Rapid Fabrication of Hygroscopic Hydrogels for Portable Water Supply and Seed Germination

Lithium ions (Li+) were found to be effective in triggering the polymerization and cross-linking of vinyl monomers in the presence of adipate dihydrazide, resulting in rapid preparation of hygroscopic hydrogels. No external energy supply, cross-linkers, or oxygen-scavenging steps were needed. Experimental and computational results reveal that Li+ coordination elevates the electrostatic potential at nitrogen atoms, which facilitates oxidation of adipate dihydrazide to generate free radicals and activate polymerization. Additionally, the high hydration free energy of Li+ can cause an effective spatial confinement to polymer segments, leading to formation of a compact polymer network; thus, a hydrogel was rapidly obtained. The polymers in the hydrogel network displayed ultrahigh molecular weights and exceptional monodispersity, contributing to the outstanding mechanical performance of the hydrogel. Specifically, it exhibited a toughness of 30.19 MJ/m3, outperforming most of its counterparts with comparable elongations (3036%). Attributed to the hygroscopic and conductive properties of lithium salts, the as-prepared hydrogel was fabricated into a sensitive humidity sensor by leveraging its resistance and capacitance variations, and it was also demonstrated to be a promising material for portable water supply, facilitating seed germination in water-scarce regions.