Ionocaloric Cooling Could Transform Refrigeration

Ionocaloric cooling is an emerging approach to reducing temperatures that could replace established refrigeration techniques with a process that is safer and less damaging to the planet.

Conventional refrigeration units remove heat from an enclosed area using a fluid. As this fluid evaporates into a gas, it takes in heat; it then travels through a sealed pipe, where it condenses into a liquid again.

Although this method works well, several commonly used refrigerants 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.

In a method introduced in 2023, researchers at Lawrence Berkeley National Laboratory and the University of California, Berkeley, used the energy absorbed or released when a material changes phase - such as solid ice becoming liquid water.

Heating a block of ice causes it to melt. Less obvious is that the melting process draws heat from the surrounding area, thereby cooling it.

Ice can also be made to melt without raising its temperature by adding charged particles, known as ions. Spreading salt on roads to stop ice forming is a familiar real-world example. The ionocaloric cycle similarly 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."

Ionocaloric cycle efficiency and environmental potential

The researchers modelled the ionocaloric cycle to demonstrate that it could rival - or potentially exceed - the efficiency of refrigerants currently in use. An electric current passing through the system would move its ions, altering the material’s melting point and, in turn, its temperature.

The team also carried out 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 made using carbon dioxide as an input. As a result, the system might be not only GWP [global warming potential] zero, but GWP negative.

During the experiment, applying less than one volt of charge produced a temperature change of 25 degrees Celsius (45 degrees Fahrenheit), surpassing 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."

The vapour-compression systems now used for refrigeration depend on gases with high GWP, including a range of 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. Ionocaloric cooling could have an important role in achieving that reduction.

Moving from laboratory research to practical systems

The next task for the researchers is to take the technology beyond the laboratory, creating commercial systems that can be scaled up without problems. In time, such systems might provide heating as well as cooling.

Current studies are testing various salts to identify the combinations that most effectively remove heat from a space. In 2025, an international research team published findings on a highly efficient version that used nitrate-based salts, recycled through electric fields and membranes.

This is precisely the direction that Prasher and his colleagues expected their work to take.

"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.