A Material Study on Magnetocaloric Liquefaction of Hydrogen

Magnetic cooling is a refrigeration technique that is based on the so-called magnetocaloric effect, the change of temperature caused by a magnetic field [1]. It can be utilized to construct environmentally friendly cooling devices, air conditioners, and heat pumps [2]. Originally, magnetic cooling was used to achieve ultra-low temperatures by adiabatic demagnetization of magnetic salts. Recently, low temperatures have once again become the focus of attention as an area of application for magnetocaloric cooling namely for hydrogen liquefaction [3,4].<br/><br/>Hydrogen is light, energy dense and clean. If produced from sustainable resources, it represents the ultimate energy carrier for many of our needs. Liquid hydrogen has more than twice the energy density of the gas at 700 bars. What is more, it can be transported in conventional, unpressurised dewars. However, conventional liquefaction means we use 40 % of the energy content of the gas we are compressing, just to liquefy it! Magnetocaloric materials enable an alternative and more efficient approach. A large number of compounds are already known that show magnetocaloric effects in the desired temperature range and new candidates are constantly being added. In this work, we would like to discuss our current progress for the creation of a materials library for cryogenic applications. The basis for this is our characterization infrastructure for materials research at the Dresden High Magnetic Field Laboratory in static and pulsed fields. With this, we want to able to understand these materials in order to further optimize the magnetic-cooling performance near the boiling temperature of hydrogen.<br/><br/>[1] T. Gottschall et al., Adv. Energy Mater. 9, 1901322 (2019).<br/>[2] D. Benke et al., Appl. Phys. Lett. 119, 203901 (2021).<br/>[3] X. Tang et al., Nat. Comm. 13, 1817 (2022).<br/>[4] W. Liu et al., Appl. Mater. Today 29, 101624 (2022).