Floatable Liquid Metal Porous Hydrogel With Hydrogen Production for Flexible Sensor and Energy Harvesting

Liquid metal (LM) micro/nano droplets, when used as initiators, fillers, and cross-linkers, are desirable for enhancing toughness, self-healing, and sensing properties of LM hydrogels. Despite recent progress in designing multifunctional LM hydrogel, porous LM hydrogel is not widely reported. In this study, porous LM hydrogel is fabricated by sonicating bulk LM into carboxymethyl chitosan (CMCS) solution (> 2 wt.%). A high-density polymeric network forms by a cross-linked structure through metal ions (i.e., Ga³⁺) produced from sonication with bifunctional groups (i.e., carboxyl and amino groups) of CMCS, hydrogen bonding, and electrostatic interactions. Without additional initiators or cross-linkers, LM hydrogels with different gelation times are obtained by adjusting the ratio of LM/CMCS, thereby enabling additive manufacturing. Owing to the reaction of gallium and its oxides with water, hydrogen gas is produced, leading to the formation of numerous pores within the hydrogel. The floatable hydrogel expand its volume to ≈1.5 times of its original size, reducing its density to float on water. This innovative LM hydrogel serves as flexible sensors with high sensitivity and as a solar-thermal-electrical generator by leveraging the LM's photo-thermal conversion properties, which not only extends the fundamental knowledge of floatable LM hydrogels, but also demonstrate its potential for versatile applications.