New research published in Joule suggests that a more efficient and environmentally friendly form of refrigeration might soon be available. This novel technology is based on thermogalvanic cells that produce a cooling effect through a reversible electrochemical reaction.
Thermogalvanic refrigeration is cheaper and more environmentally friendly than other cooling methods because it requires a far lower energy input, and its scalability means that it could be used for various applications—from wearable cooling devices to industrial-grade scenarios.
“Thermogalvanic technology is on its way to our lives, either in the form of clean electricity or low-power cooling, and both research and commercial communities should be paying attention,” said senior author Jiangjiang Duan of Huazhong University of Science and Technology in Wuhan, China.
Thermogalvanic cells use the heat of reversible electrochemical reactions to create electrical power. In theory, reversing this process—applying an external electrical current to drive electrochemical reactions—generates cooling power.
Previous studies have shown that thermogalvanic cells have a limited potential to produce cooling power. Duan’s team dramatically increased this potential by optimising the chemicals used in the technology.
“While previous studies mostly focus on original system design and numerical simulation, we report a rational and universal design strategy of thermogalvanic electrolytes, enabling a record-high cooling performance that is potentially available for practical application,” said Duan.
The cooling thermodynamic cells are based on electrochemical redox reactions involving dissolved iron ions. In one reaction phase, iron ions lose an electron and absorb heat (Fe3+ → Fe2+); in the other phase, they gain an electron and release heat (Fe2+ → Fe3+). The power produced by the first reaction cools the surrounding electrolyte solution, and a heat sink removes the heat produced by the first reaction.
The researchers improved the hydrogalvanic cell’s cooling power by tweaking the solutes and solvents used in the electrolyte solution. They used a hydrated iron salt containing perchlorate, which helped the iron ions dissolve and dissociate more freely than other previously tested iron-containing salts, such as ferricyanide. By dissolving the iron salts in a solvent containing nitriles rather than pure water, the researchers improved the hydrogalvanic cell’s cooling power by 70 per cent.
The optimised system cooled the surrounding electrolyte by 1.42 K, a significant improvement over the 0.1 K cooling capacity reported by previously published thermogalvanic systems.
The team plans to continue optimising their system’s design and investigating potential commercial applications.
“Though our advanced electrolyte is commercially viable, further efforts in the system-level design, scalability, and stability are required to promote the practical application of this technology,” said Duan. “In the future, we aim to continuously improve the thermogalvanic cooling performance by exploring novel mechanisms and advanced materials. We are also attempting to develop diverse refrigerator prototypes for potential application scenarios and are seeking to collaborate with innovation companies to promote the commercialisation of thermogalvanic technologies.”