Non-hazardous and fully recyclable ionic thermoelectrics for sustainable human–machine interfaces

Thermoelectric (TE) materials directly convert temperature gradients into electrical potential. However, conventional rigid TE materials are limited by poor mechanical compliance, potential toxicity, and non-recyclability. Here, we present an ionic TE hydrogel that addresses these challenges through high stretchability, full recyclability, and non-toxic composition. The hydrogel can be recycled through an environmentally friendly process that generates no hazardous byproducts. Our material exhibits exceptional mechanical stretchability with 1400% strain capacity, 98% optical transparency, high electrical conductivity (1.9 mS cm^-1), and a Seebeck coefficient (-1.05 mV/K). When encapsulated in recyclable polyurethane, the resulting devices enable stable dual-mode sensing through both TE and triboelectric mechanisms, allowing simultaneous temperature and pressure detection without complex signal processing. The devices maintain 96% of their electrical performance even after recycling and self-healing cycles. This innovative hydrogel design strategy aligns with circular economy principles for environment-friendly human-machine interface applications.