Researchers at the University of Groningen have developed a more energy-efficient cooling method called magnetocaloric cooling. This technique uses magnets to cool down a substance to -253°C, cold enough to liquefy hydrogen.
With the global commitments towards carbon neutrality, industries are growing their interest in using hydrogen on a large scale. To use hydrogen at industrial levels, it has to be liquified. However, cooling it down to minus 253°C or 20°K requires energy-consuming cooling technology.
The study, published in Nature Communications, says that this magnetic refrigeration could reduce the associated energy and economic cost of hydrogen liquefaction.
This method involves using magnetocaloric materials – that heat up on exposure to the magnetic field. The external magnetic field causes atoms in a substance to magnetically align in a ferromagnetic state, which raises the temperature.
The heat is then transferred to the heat sink to reduce the temperature. Then, the magnetic field is turned off which causes atoms to lose their magnetic alignment.
This causes the material to cool down. With enough temperature gradient, magnetocaloric materials can be used to cool other things as well.
“We show that the excellent magnetocaloric properties can be attributed to a second-order ferromagnetic phase transition,” says the study.
Upper right: an external magnetic field is applied and causes the material to enter the magnetically ordered (ferromagnetic) state, with a consequent rise in temperature to T+ΔT.
Lower right: heat is transferred away from the material to reduce its temperature back to T.
Lower left: the magnetic field is removed and causes the material to lose its magnetic order, returning to the paramagnetic state and decreasing the temperature to T-ΔT. Heat can now be removed from the substance to be cooled (hydrogen), raising the temperature of the magnetocaloric material back to T (upper left)
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The team used magnetocaloric materials to cool down to 20°K, which is enough to produce liquid hydrogen. Researchers have already used this method but with rare-earth elements. However, the mining of rare elements consumes a lot of energy, which adds to environmental causes.
To improve the environmental friendliness of this cooling technology, researchers are developing magnetocaloric materials comprised of earth-abundant elements.
The lead author Graeme Blake says, “Our material, or a future variant of it, could probably reduce the cost and improve the environmental friendliness of this cooling technology.“
“We expect that there is still room for improving the magnetocaloric properties, for instance by incorporating transition metals with larger magnetic moments.“
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Journal Reference
- Levinsky, J. J., Beckmann, B., Gottschall, T., Koch, D., Ahmadi, M., Gutfleisch, O., & Blake, G. R. (2024). Giant magnetocaloric effect in a rare-earth-free layered coordination polymer at liquid hydrogen temperatures. Nature Communications, 15(1), 1-9. DOI: 10.1038/s41467-024-52837-x
