Thermoelectric ionogel for low-grade heat harvesting

Low-grade waste heat (below 100°C) is widely generated throughout industrial or geothermal processes and is a particularly important source of energy that can potentially be harvested for power generation. Specifically, the fast developments in the area of Internet-of-Things (IoT), wearable electronics, and e-skins have stimulated the emerging demand for gel-state thermoelectric devices with high thermopower and power density. In this chapter, a systematical introduction to thermoelectric ionogel is reviewed from three aspects. First, the fundamental principles of ionic thermoelectric systems are introduced with a focus on thermodiffusion cells and thermogalvanic cells. Then, recent developments in the thermoelectric ionogel design optimization and applications are summarized, including gelation process, electrode materials, and integration of devices. At last, the challenges and some future ways to improve the performance of thermoelectric ionogel for low-grade heat harvesting are discussed.