Advanced Energy Materials and Devices for Low-Grade Heat Harvesting and Flexible Thermal Sensing

With the recent advance of the internet of things, wearable technology, and soft robotics, there is a great interest to develop low-cost energy harvesting devices for converting low-grade heat into electricity and flexible sensors for artificial thermal sensation. In this talk, I will share our recent research efforts in these directions through exploring three effects: (1) thermoelectric effect; (2) thermogalvanic effect; and (3) thermodiffusion effect. Specifically, we developed flexible micro thermoelectric generators (TEGs) with high power density and light weight by integrating pulsed electroplating with microfabrication processes. Compared to traditional electron-based thermoelectric materials, redox couples and ionic thermoelectric (iTE) materials using ions as charge carriers can achieve much larger thermopowers typically on the order of mV/K. Recently, we report polarized electrolytes consisting of I⁻/I₃⁻ redox couple, methylcellulose (MC), and KCl with ultrahigh thermopowers of -8.18 mV/K for n-type and 9.62 mV/K for p-type. Thermoresponsive MC enables polarization switching from n-type to p-type above the gelation temperature, while the giant thermopowers mainly come from the thermogalvanic effect of the I⁻/I₃⁻ redox couple enhanced synergistically by MC and KCl. We also developed an iTE hydrogel with a thermopower of 24.17 mV/K and flexible thermal sensor arrays for human-machine interaction.