Protic ionic liquid-based thermoelectrochemical cells for the harvesting of waste heat.

Abstract

The ability to efficiently harvest heat as a source of sustainable energy would make a significant contribution to reducing our current reliance on fossil fuels. Waste heat sources, such as those produced in industrial processes or through geothermal activity, are extensive, often continuous, and at present severely underutilised. Thermoelectrochemical cells offer an alternative design to the traditional semiconductor-based thermoelectric devices and offer thepromise of continuous and cheap operation at moderate temperatures, low maintenance and with no carbon emissions. They utilise two electrodes, held at different temperatures, separated by an electrolyte containing a redox couple. It is the temperature dependence of the electrochemical redox potential that generates the potential difference across the device as a result of the appliedtemperature difference. The magnitude of this redox potential temperature dependence is given by the Seebeck coefficient, S_e. Until recently, research into thermoelectrochemical cells had primarily focused on aqueous media, predominantly with the Fe(CN)6^3-/4- redox couple.[1] However, the good thermal and electrochemical stability, non-volatility and non-flammability ofmany ionic liquids make them promising alternative electrolytes for these devices. The use of ionic liquid (IL) electrolytes offers potential advantages that include increased thermoelectrochemical device efficiencies and lifetimes and the ability to utilise low temperature (often “waste”) heat sources in the 100 – 200 °C temperature range.[2] Here we discuss our research into the use of the Fe(CN)6^3-/4- redox couple in protic IL electrolytes, with different amounts of added water, in a thermoelectrochemical device with platinum and single walled carbon nanotube (SWNT) electrodes.