Electrolytes power thermocell to generate electrical energy

Researchers at Monash University, working under the Australian Research Council (ARC) Centre of Excellence for Electromaterials Science (ACES), have developed an ionic liquid-based thermocell which provides a source of electricity from the harvesting of waste heat.

The project was led by Australian Laureate Fellow Professor Doug MacFarlane and PhD student Theodore Abraham, with the results published in Energy and Environmental Science. The team’s thermocell device, featuring a “cheap and flexible design”, according to Professor MacFarlane, was found to generate high power outputs yet no carbon emissions.

Professor MacFarlane said the breakthrough included the development of an ionic liquid-based redox electrolyte. As noted in the research paper, “The unique physical properties of ionic liquids offer ideal characteristics for their use as electrolytes in thermoelectrochemical cells, particularly for applications involving thermal energy available at temperatures in the 100-200°C range.”

Abraham described the thermocell as containing two platinum disc electrodes, separated by an insert which contains “a little reservoir where we can inject our electrolyte”. One of the electrodes is heated, which keeps both electrodes at different temperatures and thus generates a temperature difference across the liquid electrolyte. The thermal energy generated from this temperature difference can then be converted into electrical energy.

Professor MacFarlane says the device can “work at elevated temperatures typical of important heat sources, as opposed to water-based systems, which cannot operate at temperatures above 100°C”. Abraham suggested that such areas might include hot water pipes and exhaust pipes in cars. Another suggestion is the generation of electricity from low-grade steam in coal-fired power stations at temperatures around 130°C, implemented by having the steam pass over the outer surface of the hot electrode to keep it hot while the other electrode is air- or water-cooled.

Abraham noted that the device is not a standalone energy generation technique but it will improve efficiency where a system is “going to be at a high temperature whether this device is there or not, and just add a little bit more electrical conversion into the process”. This means it will harness “energy that is already readily out there … otherwise lost to surroundings”, he said.

Abraham’s supervisor, Dr Jenny Pringle of Deakin University, said the system is “generating more electrical energy than any previous power cell in this temperature range”.