Thermogalvanic (or thermoelectrochemical) systems can convert a temperature difference into an electrical current, by exploiting the entropy change associated with a redox process. The Seebeck coefficient is a key parameter in this process, as is the overall power density. Initially this project investigated establishing the apparatus to efficiently and effectively measure the Seebeck coefficient and power density of thermogalvanic cells using hermitically sealed CR2032 battery casings. Subsequently the ferri/ferrocyanide system (known Seebeck coefficient of -1.4 mV K-1) was investigated at platinum electrodes, and for the first time at stainless steel electrodes. Subsequently the iodide/triiodide redox couple was investigated under the same conditions at platinum and stainless steel electrodes. Dilute iodine was found to display a poor Seebeck coefficient of +0.26 mV K-1 at platinum electrodes and a very significant Seebeck coefficient of +2.1 mV K-1 at stainless steel electrodes. The stainless steel system was investigated in more detail and found change over time, and under optimal conditions an apparent Seebeck coefficient of +13.6 mV K-1 could be achieved; the highest value ever reported. This is demonstrated to be due to a combination of the iodide/triiodide thermogalvanic redox couple and thermogalvanic iodine-induced corrosion of the stainless steel. Analysis of the corrosion, thermogalvanic corrosion, metal surfaces and electrolyte composition was performed. 9Preliminary experiments confirmed that the extraordinary performance was not due to the composition of the electrolyte, but instead the interaction of the electrolyte with the stainless steel surface. The promising performance of ionic liquids as replacement electrolytes was also noted.
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