A Mixed Ion/Electron Thermoelectric Generator with Ultrahigh Steady Thermopower by Exploring Both the Hole Tunneling and Ion Accumulations

Ionic thermoelectric (TE) materials are promising candidate for efficient heat harvesting mainly because they can have a thermopower higher than the electronic TE materials by 2–3 orders in magnitude. However, they cannot be directly exploited in conventional thermoelectric generators (TEGs) since ions cannot transport across the electrodes into the external circuit, and they cannot be used to harvest heat under steady temperature gradient. Here, a mixed ion/electron thermoelectric generator (MTEG) is reported that can continuously generate electricity under not only temperature fluctuation but also steady temperature gradient. It is consisted of a layer of an ionogel added with reduced graphene oxide (rGO). The ionic liquid is an ionic conductor, while rGO is an electronic conductor. The MTEG can supply a constant output voltage to the external load under steady temperature gradient, and the behavior is similar to that of the conventional TEGs, particularly when the external resistance is relatively high. The thermopower can be more than 7.0 mV K⁻¹, higher than the Seebeck coefficient of the best electronic TE materials by 1–2 orders in magnitude. The operation mechanism is attributed to the hole tunneling across the rGO sheets and the high thermopower due to the Soret effect of the ions.