Ionocaloric Cooling Could Offer a Safer Way to Chill Things

Meet ionocaloric cooling, an emerging approach to reducing temperatures that could replace current cooling techniques with a process that is safer and kinder to the planet.

Conventional refrigeration systems remove heat from an area using a fluid. As the fluid evaporates into a gas, it takes in heat, before travelling through sealed tubing and condensing back into a liquid.

Although this method works well, several refrigerants commonly used are especially harmful to the environment.

How ionocaloric cooling changes temperature

A material can, however, be made to take in and release thermal energy in more than one way.

A technique revealed in 2023 by scientists at Lawrence Berkeley National Laboratory and the University of California, Berkeley, exploits the energy absorbed or released when a material undergoes a phase change - such as solid ice becoming liquid water.

Heat a block of ice and it melts. Less obvious is that this melting process draws heat from the surrounding environment, thereby cooling it.

Ice can also be made to melt without raising its temperature by introducing charged particles, known as ions. Spreading salt on roads to stop ice forming is a familiar example. The ionocaloric cycle likewise uses salt to alter a fluid’s phase and cool the space around it.

"The landscape of refrigerants is an unsolved problem," said mechanical engineer Drew Lilley from the Lawrence Berkeley National Laboratory in California.

"No one has successfully developed an alternative solution that makes stuff cold, works efficiently, is safe, and doesn't hurt the environment. We think the ionocaloric cycle has the potential to meet all those goals if realized appropriately."

The researchers used a model of the ionocaloric cycle to demonstrate that it could potentially rival, or even outperform, the efficiency of refrigerants used today. An electric current passing through the system would shift its ions, altering the material’s melting point and therefore its temperature.

Ionocaloric cycle efficiency and environmental potential

The group also conducted experiments with a salt containing iodine and sodium to melt ethylene carbonate. This widely used organic solvent also features in lithium-ion batteries and is manufactured using carbon dioxide as an input. As a result, the system could be not only GWP [global warming potential] zero, but GWP negative.

In the experiment, applying less than a single volt of charge produced a temperature change of 25 degrees Celsius (45 degrees Fahrenheit), exceeding the results achieved so far by other caloric technologies.

"There are three things we're trying to balance: the GWP of the refrigerant, energy efficiency, and the cost of the equipment itself," said mechanical engineer Ravi Prasher from the Lawrence Berkeley National Laboratory.

"From the first try, our data looks very promising on all three of these aspects."

Today’s vapour-compression refrigeration systems depend on gases with high GWP, including various hydrofluorocarbons (HFCs).

Nations that joined the Kigali Amendment have pledged to cut HFC production and consumption by at least 80 percent during the next 25 years - and ionocaloric cooling could have an important role in achieving that reduction.

From laboratory tests to commercial cooling systems

The next task for the researchers is to move the technology beyond the laboratory into practical, commercially usable systems that can be scaled up smoothly. In time, the systems may be applied to heating as well as cooling.

Researchers are continuing to test different salts to identify the combinations most effective at removing heat from a space. In 2025, an international research team reported results from a highly efficient version that used nitrate-based salts, recycled through electric fields and membranes.

This is precisely the development that Prasher and his colleagues expected their work to encourage.

"We have this brand-new thermodynamic cycle and framework that brings together elements from different fields, and we've shown that it can work," said Prasher.

"Now, it's time for experimentation to test different combinations of materials and techniques to meet the engineering challenges."

The research was published in Science.

An earlier version of this article was published in January 2023.