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U.S. Gov Lab Researchers Test Rare-Earth Free Polymer that could Revolutionize Refrigeration

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Highlights

  • Oak Ridge National Laboratory researchers discovered a rare-earth-free layered coordination polymer with a giant magnetocaloric effect at liquid hydrogen temperatures.
  • The study demonstrates a potential breakthrough in developing alternative materials for magnetic refrigeration with strong magnetic field response.
  • The research aims to disrupt current rare-earth material extraction and processing by exploring sustainable and cost-effective cooling technology alternatives.

Researchers from Oak Ridge National Laboratory (opens in a new tab) led by Mengya Li (opens in a new tab), a battery R&D scientist and Ilias Belkarouak (opens in a new tab), Corporate Fellow, Head of Electrification and colleagues recently led a study published in the journal Nature Communications (opens in a new tab).  The final output involved  a rare-earth-free layered coordination polymer, Co4(OH)6(SO4)2[enH2], exhibiting a giant magnetocaloric effect at liquid hydrogen temperatures.  Why is this significant?  Because the investigation fits in a trajectory of those seeking to find alternatives to rare-earth materials.  This would be a topic of pursuit to disrupt the current approach of extraction and mining, separation and processing and the overall supply chain which today is dominated by the People’s Republic of China.

So what is the magnetocaloric effect? The materials temperature could change in reaction to a changing magnetic field raises intriguing questions for the scientists collaborating on this study at Oak Ridge National Laboratory and Advanced Photon Source, Argonne National Laboratory (opens in a new tab), Lemont, IL.

Overview

Studied for use in refrigeration, especially energy-efficient cooling systems, magnetocaloric materials typically depend on rare-earth elements. But of course to find, extract and process rare-earth elements, not to mention the supply chain dynamics, including severe environmental degradation,  raises lots of concern and a desire to find alternatives.

Enter the key driver of this study: to find superior magnetocaloric effects less any requirement to include rare-earth elements.   This is where the promising candidate that is Co4(OH)6(SO4)2[enH2] polymer comes in. Based on a set of unique structural properties andmagnetic behavior,  research to date suggests layered coordination polymers may enable significant magnetic interactions. This could mean that they would be conducive for magnetocaloric applications.

What are the magnetic properties of the polymer under study?  Could there be pragmatic applications in refrigeration in the future?

The Investigation

The U.S. government employed scientists at Oak Ridge National Laboratory and Argonne National Laboratory had to design a series of tailored experimental techniques to get to the question as to the magnetocaloric properties of the layered coordination polymer Co4(OH)6(SO4)2[enH2].

Synthesizing the polymer via a hydrothermal method the team sought to develop a formation of high-quality single crystals reports (opens in a new tab) Dr. Noopur Jain, PhD (opens in a new tab) at AZO Materials (opens in a new tab).

Jain reviewed the paper reporting that the investigators characterized the output crystals based on use of a  single-crystal X-ray diffraction (SCXRD) to both clarify their structural arrangement as well as confirm the coordination environment of the metal ions.  The rest of the study methodology can be reviewed at the journal Batteries & Supercaps (opens in a new tab) or at AZO Materials.

Outcomes

The study team writes in the paper that Co4(OH)6(SO4)2[enH2] exhibits a significant magnetocaloric effect, with a maximum magnetic entropy change (ΔSM) observed at low temperatures.  Finding that the final product’s ΔSM values reached up to -15.3 J kg-1 K-1 for magnetic field changes of 5 T, indicating its strong response to magnetic fields, the authors also analyzed temperature dependence of magnetization.  They report a device transition at approximately 10.2K, observing a lambda-like peak in heat capacity was observed, reports Dr. Jain.

The authors observed what they suspect is a robust magnetocaloric response given the peak changed to higher temperatures with greater magnetic field strength.

Final Takeaway

This highly experimental study demonstrates the ability to develop through other means a rare-earth-free layered coordination polymer Co4(OH)6(SO4)2[enH2] demonstrating robust magnetocaloric effect at liquid hydrogen temperatures. The promise?  Could this approach pave the way to alternatives for magnetic refrigeration applications?

According to Dr. Jain, an accomplished science reporter based in the city of New Delhi, India,

“The comprehensive characterization of its magnetic and structural properties reveals a material that performs well under varying magnetic fields but also aligns with the growing demand for sustainable and cost-effective cooling solutions.”

Advancing the understanding of magnetocaloric materials, the study output directs attention to research centering on layered coordination polymers. How to optimize the synthesis while investigating  the material’s scalability attributes seem next on the research horizon.  While there is a lot of research to do, the authors imply this direction could certainly be transformative in the refrigeration field, as well as in energy efficiency.

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