Recently, self-powered health monitoring systems using a wearable thermoelectric generator (WTEG) have been rapidly developed since no battery is needed for continuous signal monitoring, and there is no need to worry about battery leakage. However, the existing materials and devices have limitations in rigid form factors and small-scale manufacturing. Moreover, the conventional bulky WTEG is not compatible with soft and deformable tissues, including human skins or internal organs. These limitations restrict the WTEG from stabilizing the thermoelectric gradient that is necessary to harvest the maximum body heat and generate valuable electrical energy. This paper summarizes recent advances in soft, flexible materials and device designs to overcome the existing challenges. Specifically, we discuss various organic and inorganic thermoelectric materials with their properties for manufacturing flexible devices. In addition, this review discusses energy budgets required for effective integration of WTEGs with wearable biomedical systems, which is the main contribution of this article compared to previous articles. Lastly, the key challenges of the existing WTEGs are discussed, followed by describing future perspectives for self-powered health monitoring systems.

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This study focuses on development of Nickel–Yttira Stabilized Zirconia (Ni/YSZ) based anode material by solid-state synthesis using polyvinyl alcohol (PVA) in varying weight concentrations (3 wt.% and 6 wt.%) both as a binder and as a pore-former. Scanning electron microscopy and X-ray diffraction based structural and morphological analyses were performed and the synthesis of a homogeneous NiO/YSZ phase was confirmed after sintering at 1 000 °C. Microscopic study investigating effects of PVA concentration upon pore density in pellets pressed under the same conditions was conducted. Thermo-gravimetric/differential thermal analysis of the powders pre-dried at around 120 °C was carried out up to 1 000 °C to investigate the phase change and the thermal decomposition behavior. Findings on reduction of NiO/YSZ in a mixed atmosphere of H2/Ar at 550 °C are also discussed in detail. The results demonstrated that areal porosity of 12 % and 24 % was achieved with 3 wt.% and 6 wt.% of PVA, respectively.

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