Thermo-osmotic ionogel enabled high-efficiency harvesting of low-grade heat

Abstract

Low efficiency in recovering low-grade heat remains unresolved despite decades of attempts. In this research, we designed and fabricated a novel thermo-osmotic ionogel (TOI) composite to recover low-grade heat to generate electric power through a thermo-induced ion gradient and selective ion diffusion. The TOI composite was assembled with a crystalline ionogel (polymer-confined LiNO₃–3H₂O) film, ion selective membrane, and hydrogel film. With a 90 °C heat supply, the single TOI composite produced a high open-circuit voltage of 0.52 V, a differential thermal voltage of ∼26 mV K⁻¹, a peak power density of 0.4 W m⁻², and a ground-breaking peak energy conversion efficiency of 11.17%. Eight pieces of such a TOI composite were connected in series, demonstrating an open-circuit voltage of 3.25 volts. Such a TOI system was also demonstrated to harvest body temperature for powering a LED, opening numerous opportunities in powering wearable devices.