Rapid preparation of a self-adhesive PAA ionic hydrogel using lignin sulfonate–Al3+ composite systems for flexible moisture-electric generators

Abstract

Hydrogels have great potential in flexible moisture-induced electricity generators (MEGs) due to their excellent water-capturing capability and ionic conductivity. However, conventional hydrogels face challenges of prolonged heating for preparation, the use of toxic crosslinkers, and poor mechanical properties. Herein, we used lignin sulfonate (LS)–Al³⁺ composite systems to rapidly prepare a polyacrylic acid (PAA) ionic hydrogel for harvesting electrical energy from atmospheric moisture. The semiquinone radicals from ammonium persulfate (APS) oxidized LS could rapidly trigger the polymerization of acrylic acid monomers into PAA polymer chains. Then, the green crosslinker Al³⁺ ions could crosslink the polymer chains into hydrogels via ionic interaction within a few minutes at room temperature. The excellent mechanical and adhesion properties allowed hydrogels to be very easily assembled into a low-cost, flexible, and efficient hydrogel-based moisture-electric generator (HMEG). When exposed to moisture, thanks to the synergies of asymmetric moisture adsorption and ion migration, a single HMEG device could generate an open-circuit voltage of ∼550 mV and a short-circuit current density of ∼3.28 μA cm⁻² in the ambient environment (26 °C and 55% relative humidity). The HMEG also exhibited excellent output stability under mechanical deformation, long-time output durability, and all-weather workability. This work provides new insights into the development of self-powered portable wearable electronic devices from hydrogels.