Synergistic improvement of Seebeck coefficient and power density of an aqueous thermocell using natural convection for low-grade heat utilization

Abstract

As a cutting-edge heat-to-electricity technology, thermocells possess the advantages of large Seebeck coefficient, low cost and high scalability, indicating a great prospect in low-grade heat recovery. Previous studies about thermocells focus on the electrode materials and electrolytes, but the internal heat and mass transfer mechanisms are less considered, especially the effects of natural convection on the performance of aqueous thermocells. The purpose of this study is to explore the influence of natural convection on the performance of aqueous thermocells. Firstly, a fundamental test bench for aqueous ferricyanide/ferrocyanide ([Fe(CN)6]3−/4-) thermocells using Pt as electrodes is designed and established. Based on the self-developed test bench, then the performance of thermocells related to electrode orientation θ are experimentally investigated under typical thermal boundary conditions, including the constant electrode temperature, and constant heating and cooling temperature. The experimental results under constant electrode temperature show that natural convection can significantly reduce the internal resistance of thermocells. The thermocell obtains the largest |Se| of 1.75 mV/K at θ = 90°, which is 19.9% higher than that of θ = 0°. Meanwhile, the thermocell achieves the maximum power density of 0.211 W/m2 at θ = 135°, which is 744% higher than that of θ = 0°. In addition, by combining the experimental results under constant heating and cooling temperature, it can be observed that natural convection can also sharply reduce the thermal resistance and then lead to a smaller temperature difference of two electrodes. Overall, natural convection has trade-off effects on internal resistance and thermal resistance, and the proper use of natural convection can succeed in prominent improvement of Seebeck coefficient and power density for thermocells.