Improving Seebeck Coefficient of Thermogalvanic Cells Using Polyelectrolytes

Thermogalvanic cells, also known as thermoelectrochemical cells or simply as thermocells, have recently attracted a lot of attention because of their immense potential in converting low-grade thermal energy to electricity. The thermal temperature coefficient of electrode potential (α) in a thermogalvanic cell is directly proportional to the change in entropy (ΔS) of the redox reaction in the cell through the relation (α = ∂E/∂T = ΔS/nF), where E is the cell potential, T the temperature, n the number of electrons involved in the reaction, and F the Faraday’s constant. Although the nature of effects are different, α is often referred to as the Seebeck coefficient. In an ideal thermogalvanic cell, one therefore prefers to employ a redox couple exhibiting the largest α. Therefore, in the current study we discuss an alternate method to enhance ΔS for the electron transfer process. Thus, by coupling a redox process to solution phase complexation, we show that there is marked increase in both the change in entropy and the resulting α. While the change in entropy was calculated using quantum-chemical methods, α was experimentally measured for a Cu/Cu²⁺ thermogalvanic cell. The results indicate that a complexation of the Cu²⁺ species with a dissolved polymer, such as poly(acrylic acid) (PAA) or ethylenediaminetetraacetic acid (EDTA), dramatically improve α by up to 75%. We believe, that this novel approach to enhance α, would prove to be useful in the development of thermodynamically more efficient thermogalvanic cells.