Improved Thermal Gradients in Diffuser-/Nozzle-Shaped Thermally Driven Electrochemical Cells for Enhanced Output Power Density

Abstract

Efficiently transforming thermal energy into electricity through inexpensive and ecofriendly devices can address energy shortage while reducing global warming. Thermally driven electrochemical cells (TECs) convert thermal gradient (ΔT) into open-circuit voltage (V_oc) through reduction–oxidation (redox) reactions. For TECs, it is essential to maintain the integrity of thermal disequilibrium throughout energy transformation. However, the natural convection occurring in TEC electrolytes reduces ΔT, thus adversely affecting output power. It is necessary to design and fabricate TECs that are capable of providing and maintaining higher thermal gradients. This paper demonstrates that higher ΔT can be achieved by fabricating TECs in nozzle- and diffuser-shaped geometries rather than traditional cylindrical-shaped formations. We experimentally compared the performance of our proposed designs: (a) nozzle-shaped TECs (n-TECs) and (b) diffuser-shaped TECs (d-TECs) against the traditional cylindrical-shaped TECs (c-TECs). We found that variations in mechanical features of the cell structures completely change heat flow across the cells. According to our observations, c-TECs attain ΔT of only 3.9 °C once placed between temperature source (90 °C) and sink (28 °C), representing a very high thermal flow across the cell. On the contrary, n-TECs and d-TECs significantly resisted the thermal leakage, consequently attaining higher ΔT of 4.8 and 8.6 °C, respectively. The higher ΔT in d-TECs resulted in power density of 5.8 mWm⁻² which is 83% higher than the traditional c-TECs.