Mixed Ion‐Electron Thermoelectric Generators With Ionogels Blended With MXene Continuously Harvesting Heat Under Both Steady and Fluctuated Temperature Gradients

ABSTRACT Harvesting waste heat into electricity by thermoelectric (TE) conversion is of great significance for sustainable development. However, this still poses a significant challenge because of the inherent limitations of conventional TE materials. Ionic thermoelectric materials are very promising alternatives owing to their extremely high thermopower. They are used in ionic thermoelectric capacitors (ITECs). However, ITECs are limited to harvesting intermittent heat, since no electricity can be generated under a steady temperature gradient due to the inability of ions to transfer across the electrodes to the external circuit. In this work, we report a mixed ion‐electron thermoelectric generator (MTEG) that enables heat‐to‐electricity conversion under steady and fluctuating temperature gradients. It is made of an ionogel blended with two‐dimensional MXene nanosheets, which is a mixed ion‐electron conductor. Under a steady temperature gradient, the MTEGs provide a stable output voltage and exhibit TE behavior comparable to that of conventional thermoelectric generators employing electronic TE materials. The MTEGs can exhibit a thermopower of 4.77 mV K ⁻¹ , and they can continuously supply electricity for a very long time. The MTEG operates through a combination of electron tunneling between MXene nanosheets and the ionic Soret effect.