Novel Hybrid Electronic-Ionic-Type Thermoelectric Device with Enhanced Performance by Using Steel Wool and [Fe(CN) ₆ ] ^4– /[Fe(CN) ₆ ] ^3– Ion Solution

The utilization of low-quality thermal energy is one of the most important ways to alleviate energy-related problems. Thermoelectric conversion materials or devices can convert thermal energy directly into electrical energy in the presence of a temperature difference, which is an effective way to utilize low-quality thermal energy. In this study, a hybrid electronic-ionic-type thermoelectric device (K-E@SW/EDTA-F) was prepared by combining a surface-modified electronic-type thermoelectric material (steel wool, i.e., SW) with an ionic-type thermal galvanic cell. The redox pair of the ionic-type thermal galvanic cell (referred to as EDTA-[Fe(CN)6]4–/[Fe(CN)6]3–, i.e., EDTA-F) consists of an [Fe(CN)6]4–/[Fe(CN)6]3– redox pair containing ethylenediaminetetraacetic acid disodium salt (EDTA-2Na). The surface of the SW was pretreated with γ-aminopropyltriethoxysilane (KH550) and ethyl acetate (EAC) (referred to as K-E@SW). The results show that the optimized Seebeck coefficient of K-E@SW/EDTA-F is significantly enhanced compared with those of purely electronic-type thermoelectric material (SW) and a purely ionic-type thermal galvanic cell (EDTA-F). Thanks to the high electrical conductivity of SW, the electrical conductivity of K-E@SW/EDTA-F can reach 690 times relative to that of EDTA-F. When SW is modified with 1 g of EAC and the concentrations of [Fe(CN)6]4– and [Fe(CN)6]3– were both 0.45 mol L–1, an optimized Seebeck coefficient of −19.0 mV K–1 could be obtained for K-E@SW/EDTA-F. Its ZT value was 8.9 × 10–3, which was 2.39 × 105 times higher than that of SW. Combining electronic-type thermoelectric material with an ionic-type thermal galvanic cell results in better thermoelectric performance, which provides a new idea for the construction of a high-performance thermoelectric conversion system.