Potentially Wearable Thermo-Electrochemical Cells for Body Heat Harvesting: From Mechanism, Materials, Strategies to Applications

Wearable electronics are becoming one of the key technologies in health care applications including health monitoring, data acquisitions, and real-time diagnosis. The commercialization of next-generation devices has been stymied by the lack of ultrathin, flexible, and reliable power sources. Wearable thermo-electrochemical cells (TECs), which can convert body heat to electricity via an electrochemical process, are showing great promise as power sources for such wearable systems. TECs harvest orders of magnitude more voltage per temperature difference (Seebeck coefficient (1–34 mV K⁻¹)) when compared to the more common thermoelectric generators (Seebeck coefficient ≈tens or hundreds of µV K⁻¹). However, there still remain great challenges for TECs progressing towards wearable applications. This review summarizes the recent development of potentially wearable TECs with promise for body-heat harvesting, with a specific focus on flexible electrode materials, solid-state electrolytes, device fabrication, and strategies toward applications. It also clarifies the challenges and gives some future direction to enhance future investigations on high-performance wearable TECs for practical and self-powered wearable devices.