A new magnetocaloric ionic liquid for safe refrigeration

The magnetocaloric effect describes the change in temperature of a magnetic substance in response to the application or removal of a magnetic field. Its discovery, attributed to the German physicist Emil Warburg, dates back to 1881. For some materials, this effect is large enough to be concretely exploited in refrigerating systems. In this case, the thermodynamic cycle of compression/expansion of the refrigerant gas used in conventional cooling systems is replaced by a thermomagnetic cycle of magnetization/demagnetization of an MMC which plays the role of refrigerant. This potentially more flexible, less dangerous and less polluting alternative to conventional cold production technologies is attracting growing interest fueled by increasingly high-performance materials and a better understanding of their behavior.

In addition to their intrinsic thermodynamic properties, the efficiency of MMCs in refrigerating systems is essentially based on their good contact with the surfaces of the heat exchangers. Since most MMCs are often friable solids, this contact must be ensured by means of “thermal greases” in which the MMCs are diluted. In terms of performance, the ideal would however be to be able to avoid the preparation of mixtures and use pure MMCs.

To answer this problem, a team of chemists and physicists from the Institutes of Chemistry of Strasbourg and the Institute of Physics and Chemistry of Materials of Strasbourg (CNRS/University of Strasbourg) propose to exploit the chemistry of magnetic metal complexes and the exceptional properties of Ionic liquids (ILs). They thus prepared a complex of gadolinium(III) (Gd) which constitutes the first magnetocaloric LI. This “2 in 1” formulation combines the magnetocaloric effect of Gd with the improved thermal contact of a liquid/glass compared to solid MMCs to achieve unparalleled properties.

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