Progresses and insights of thermoelectrochemical devices for low-grade heat harvesting: From mechanisms, materials to devices

Low-grade heat (<100 degrees C), as a typical and ubiquitous wasted energy, exhibits widely in nature, industrial activity, and our daily life. However, tremendous amount of heat energy is still not harvested efficiently due to the lack of effective and sustainable technologies. Therefore, the development of thermoelectrochemical devices with characteristics such as giant thermopower, cost effectiveness, good scalability and multi-functionality for heat-to-electricity conversion should be a top priority at present. However, there is great challenges to simultaneously achieve high power density and energy conversion efficiency as well as the integration with energy storage devices. Till now, a lot of works have been contributed to counter above-mentioned problems by the design of electrode materials, the optimization of electrolyte, and the assembly of devices. To accelerate the application of the thermoelectrochemical systems, this review exclusively summarizes the recent progresses of typical thermoelectrochemical devices containing thermodiffusion based devices, thermogalvanic based devices, and thermoextraction based devices from materials to devices, and discusses the energy conversion-storage mechanisms. We also give insights into the relationship between microstructures and performances of devices. Moreover, we present the key challenges and potential perspectives in future works about high value-added conversion and storage of low-grade heat.