A Mixed Ion-Electron Thermoelectric Generator with an Activated Carbon Ionogel for Heat Harvesting from Fluctuated and Steady Temperature Gradients

Ionic thermoelectric (iTE) materials hold great potential for efficient heat-to-electricity conversion due to their exceptionally high thermopower. However, they can harvest only intermittent heat, and no power is generated under steady temperature gradient. In this study, we present a mixed ion-electron thermoelectric generator (MTEG) that can continuously generate electricity under not only fluctuated temperature but also steady temperature gradient. The active material is an ionogel embedded with activated carbon (AC) particles. It is a mixed ion-electron conductor as the ionic liquid is an ion conductor while the AC particles can form conductive networks for electron transport. The TE performance under steady temperature gradient is like that of the conventional thermoelectric generators (TEGs) with electronic materials. The MTEGs under the temperature gradient of 3 K can supply an output voltage of more than 7.9 mV·K^-1 to the external load of 25 kΩ, which is higher than that of the best electronic TE materials by 1-2 orders in magnitude. The TE behavior of the MTEGs is ascribed to the synergistic contributions of the Soret effect of the ions and hole tunneling through the AC networks.