A bilayer hydrogel device: Coupling ion migration and water phase-change for low-grade heat-driven self-circulating energy supply

Abstract Wearable flexible electronics show great potential in health monitoring and motion sensing, but conventional ion gradient generators have discontinuous power output due to reliance on external high-grade heat for ion gradient reconstruction. To solve this, we designed a bilayer composite hydrogel device based on PAMPS (poly(2-acrylamido-2-methylpropane sulfonic acid)) and PDMAPS (poly ([2-(methacryloyloxy) ethyl] dimethyl-(3-sulfopropyl) ammonium hydroxide)). It establishes an “ion diffusion power generation-water phase-change heat storage” coupling mechanism driven by low-grade body heat for a self-circulating energy supply. The PAD (PAMPS and PDMAPS) hydrogel device produces an open-circuit voltage of 225 mV and a short-circuit current density of 2.4 μA cm −2 in a saturated swollen state. When ion migration reaches equilibrium, it captures 36 °C body surface heat, triggering water phase change to store energy (heat storage density: 2495 J g −1 ) and regenerate ion gradients. At 36 °C during regeneration, reverse ion migration generates 1 μA cm −2 current, forming a “power generation-heat storage-regeneration” cycle. This study breaks the dependence on external high-grade energy. By coupling ion migration and phase-change energy storage inherent in the material, it enables efficient low-grade heat utilization and continuous power output, offering a new model for self-powered wearable electronics.