(566f) Thermal Diffusion in Thermogalvanic Cells Containing Polymer Electrolyte

According to annual energy flow diagrams from Lawrence Livermore National Lab, over half the energy produced in the United States is lost as waste heat. Much is low-grade heat that cannot readily be recovered by traditional thermodynamic cycles. Thermogalvanic cells are a potential solution to recovering low-grade waste heat. In contrast to thermoelectric devices that require high temperature gradients to generate power in semiconductor devices, thermogalvanic cells are like batteries that are powered by temperature gradients. Solid polymer-electrolyte-based cells could provide a flexible method to convert low-grade waste heat into electricity. Thermal diffusion, also known as the Soret Effect, is an important process in thermogalvanic cells. The temperature gradient induces a concentration gradient in the electrolyte. Theoretical prediction of the magnitude and direction of thermal diffusion is not possible despite a thermodynamic theory for small temperature gradients and a force-based theory derived for thermophoresis of colloidal particles. The missing link to understanding this phenomena may lie in a novel and interesting system that spans the gap between small molecule mixtures and colloidal dispersions, namely polymer electrolytes. We have measured thermal diffusion in a dry polymer electrolyte using two innovative approaches designed specifically for solid systems. The first approach measures the electrochemical potential of a thermogalvanic cell subjected to different thermal gradients. At steady-state, the electrochemical potential is directly related to the concentration gradient in the polymer electrolyte. We have also conducted transient current-voltage measurements of the thermogalvanic cell to determine the power that can be produced by the temperature gradient. These measurements will be corroborated with a second method based on spectroscopic measurement of concentration gradients in polymer electrolyte exposed to different temperature gradients. The results will be analyzed using a transport model based on irreversible thermodynamics in order to better understand the phenomena underlying thermal diffusion.