Ultralow-Cost magnetocaloric compound for Cryogenic Cooling

TL;DR

This paper introduces FeCl₂, an ultralow-cost ionic compound exhibiting significant magnetocaloric effects suitable for cryogenic hydrogen liquefaction, offering a promising, cost-effective alternative to rare-earth materials.

Contribution

The study reports on FeCl₂ as a new, low-cost magnetocaloric material with high entropy change and temperature shift capabilities, suitable for large-scale hydrogen liquefaction.

Findings

FeCl₂ shows both inverse and conventional magnetocaloric effects.

The entropy change reaches 18.6 J/kg/K near 20 K at 5 T.

Adiabatic temperature change is about 3.6 K at 5 T.

Abstract

Cost-effective materials are essential for large-scale deployment. The emerging magnetocaloric hydrogen liquefaction technology could transform the liquid hydrogen industry due to its potential in achieving higher efficiency. Most studies of the cryogenic magnetocaloric effect (MCE) have focused on resource-critical rare-earth-based compounds. Here we report on an ionic magnetocaloric compound FeCl$_2$ which is based on ultralow-cost elements, as a candidate working material for hydrogen liquefaction. FeCl$_2$ shows both inverse and conventional MCE. From 0 to 1.5 T, the inverse effect yields a positive magnetic entropy change ($\Delta S_T$) of about 5 J/kg/K near 20 K, then declines toward zero at higher fields. In contrast, the conventional (negative) response strengthens with field. The $\Delta S_T$ reaches 18.6 J/kg/K near 20 K in magnetic fields of 5 T. This value exceeds most light rare-earth-based compounds and approaches that of heavy rare-earth-based compounds. In magnetic fields of 5 T, the adiabatic temperature change reaches about 3.6 K. The large $\Delta S_T$, along with the low cost of the elements in FeCl$_2$, are prerequisites for inexpensive industrial-scale production, giving the prospect of a practical magnetocaloric candidate for hydrogen liquefaction in the 20 $\sim$ 77 K temperature window.