Figure 7 The output voltage and current of the organohydrogelthermocell during deformation: (a) The voltage-time (blue) and current-time (red)curves of the organohydrogelthermocell being repeatedly pressed when Tc = 20 °C and Th = 30 °C. (b) The voltage-time (blue) and current-time (red)curves of the organohydrogelthermocell being repeatedly pressed when Tc = −20 °C and Th = 20 °C. (c) A photograph of the organohydrogel thermocell being pressed on an ice surface of −20 °C. Reproduced with permission from Gao et al. Copyright 2021, Wiley-VCH.[48] (d) Thermogravimetric characterization of BC, BC-TGC, and BC-TGC with different LiBr weight fractions. (e) Schematic of TGC used as smart windows. (f) The corresponding voltage and temperature-time diagram of (e). Reproduced with permission from Yin et al. Copyright 2023, Elsevier.[97]
Gelatin, a polypeptide polymer, contains numerous polar groups such as -COOH, -NH2, and -OH; thus, it exhibits strong polarization ability under the action of an electric field.[49–51] Using this property, Chen et al. developed a gelatin-based device that achieved a considerable thermoelectric conversion effect by combining alkali metal salts with iron-based reduction couples.[52]This device demonstrated the ability to effectively harness energy from body heat and achieved a high thermoelectric energy of 17.0 mV K–1. It was noticed that the ion transport in gelatin occurred by the thermal diffusion of KCl, NaCl, and KNO3. Additionally, the thermoelectric effect was increased by the presence of [\({Fe(CN)}_{6}^{4-}\)/\({Fe(CN)}_{6}^{3-}\)]. This enhancement enables wearable devices, utilizing body heat energy as a heat source, to obtain a thermoelectric effect of 2 V and a maximum ΔT power of 12.8 J m–2.