Effects of BaTiO3 Addition on Polymer Solid Electrolytes for Ge-Sensitized Thermal Cells (Supporting Information)

Semiconductor-sensitized thermal cells (STCs) represent an innovative technology designed to convert waste heat into electrical energy. The operational mechanism relies on the thermal excitation of charge carriers within the semiconductor, which subsequently drives electrochemical redox reactions in the electrolyte. Previous research has demonstrated the successful operation of Ge-sensitized thermal cells (Ge-STCs) using solid electrolytes composed of polyethylene glycol (PEG1540) and copper ions. While PEG1540 ensures structural stability at the operating temperature of 40 °C, its power output remains lower than that of liquid-electrolytes systems. To address this, we focused on the incorporation of BaTiO3 (BTO, barium titanate) fillers, which have been reported to promote ion dissociation and enhance the ionic conductivity in all-solid-state lithium-ion batteries. This study is the first to investigate the addition of BTO to a polymer solid electrolyte in a Ge-STC for improving power output. The experimental results revealed that the inclusion of BTO significantly enhanced the electrochemical properties, achieving an ionic conductivity of 2.8 × 10−4 S/cm. Most notably, the Ge-STC featuring the BTO-dispersed electrolyte yielded a current density more than twice as high as previously reported values for BTO-free systems. These findings demonstrate that the synergistic effect between the dielectric BTO fillers and the polymer matrix is a highly effective strategy for improving the performance of solid-state STCs.