Liquid hydrogen serves as an ideal carrier for energy storage and transportation, boasting a significant energy storage capacity of 120 MJ/kg; more than twice that of most traditional fuels. However, conventional liquefaction by compression methods delivers efficiencies of less than 30%. Modelling, based on bench-scale studies, has shown that magnetic refrigeration techniques have high potential for substantial improvements in conversion efficiency [1].
Recent research in refrigeration technologies has revealed that magnetic cooling at cryogenic temperatures holds promise for use in liquefying and transporting gases such as helium and hydrogen at low temperatures, [2-5]. These technologies show potential for reduced energy costs to liquefy gases, enhanced efficiency of the liquefaction process, reduced gas boil-off during transportation, and thus, potential use over a wide range of scalable applications.
Materials exhibiting a giant magnetocaloric effect (MCE) are promising candidates for magnetic refrigeration. Research mainly focuses on investigating magnetic materials with a giant MCE at room temperature [6]. On the other hand, magnetic cooling technology based on MCE has also been effective at temperatures below 30K [3, 4]. However, existing magnetocaloric materials exhibit large entropy changes over a limited temperature range, require high magnetic field sources and contain rare-earth elements.
Another important consideration in hydrogen liquefaction is its composition: hydrogen exists as a mixture of spin isomers, namely ortho- and para-H2, with a ratio of 75:25 under normal conditions. The liquefaction process involves cooling hydrogen from room temperature to 20 K. While hydrogen predominantly consists of ortho-hydrogen (o-H2) at ambient conditions, with para-hydrogen (p-H2) at a lower concentration, this balance shifts towards para-H2 as the temperature decreases during liquefaction. However, the conversion process is hindered by slow kinetics. This presents a challenge for transporting liquid hydrogen, as the conversion reaction releases heat and can result in excessive boil-off during storage. Industrial processes utilize catalysts to accelerate this conversion and mitigate vaporization losses. Without catalytic assistance, surplus o-H2 may undergo spontaneous conversion to p-H2, releasing significant heat in the process. In specific cases, both magnetic cooling and catalytic conversion of the ortho-para transition may be addressed by a specific material family (e.g., metal alloys, and intermetallics).
This project aims to advance the design and operation of hydrogen liquefaction facilities by developing and implementing innovative magnetic refrigeration systems that integrate novel hybrid materials with magnetocaloric (MC) and/or ortho-para(O-P) conversion properties. Through the project, new hybrid materials will be developed that can showcase both an efficient MCE and/or a catalytic O-P conversion of H2.
Partners: Queensland University of Technology, The State of Queensland acting through the Department of State Development and Infrastructure, The University of Western Australia
Project Leader: Dr. Mahboobeh Shahbazi
Duration: 36 months