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

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.