Recent advances in skin waste heat energy harvesting wearable flexible thermo-electric and moist-electric devices

The miniaturization, portability, and reduction in power consumption of wearable devices have greatly facilitated significant advancements in the field of wearable human energy harvesting systems. Human metabolism results in waste heat production and dissipation to the surroundings via skin radiation, convection, and evaporation. Wearable flexible thermo-electric and moist-electric devices uses skin waste heat harvesting to convert thermal energy into electricity without user involvement. The principle and structure of the device is simple and pollution free with great application potential in generating power supply. Skin waste heat can be dissipated in the forms of both sensible and latent heat. Wearable thermo-electric generators (WTEGs) collects sensible heat, and wearable moist-electric generators (WMEGs) collects latent heat. This paper reviews the mechanism behind the generator of WTEG and WMEG, as well as state-of-the-art research progress made in material properties and structural design of thermoelectric devices. The performance optimization and design of wearable, flexible thermoelectric devices for skin waste heat harvesting at the material and device levels are studied, followed by a breakdown on the fibers and fabrics used in the foundation for future development of WTEG and WMEG's. The research findings provides valuable insight on the future development of WTEG and WMEG's, providing integration into wearable applications for health and physiological monitoring and disease diagnosis.