All-Solid Germanium-Sensitized Thermal Cells with Polyethylene Glycol 1540-Based Electrolytes

The semiconductor-sensitized thermal cell (STC) is an innovative technology that utilizes waste heat. The STC generates electricity when the thermally excited charges of the semiconductors cause redox reactions in the electrolyte. Another key feature of the STC is that after the discharge is completed, the ions in the electrolyte diffuse and can be discharged again. Thus far, the germanium-STC (Ge-STC), whose electrolytes are composed of polyethylene glycol (PEG) 600 and copper ions, exhibited clear discharge and recovery. However, the PEG600-based electrolyte has a liquid phase at over 21 °C; thus, electrolyte leakage is a concern. In this study, the PEG1540-based electrolyte, which has a larger molecular weight than the PEG600-based electrolyte and is solid below ∼45 °C, was used; the STC with the PEG1540-based electrolyte in the solid state discharged and recovered successfully at 40 °C. This is the first electrolyte that enables repeated discharge in the STCs using solid electrolytes. The PEG1540-based solid electrolyte with a stable output expands the STCs’ application fields.