Enhancing hydrogen permeation barrier performance of ErCo₂ magnetic refrigeration material via surface oxide layer...

The ErCo₂ intermetallic compound exhibits a significant magnetocaloric effect at approximately 32 K and has potential applications as a magnetic refrigeration material for hydrogen liquefaction. However, exposure to a hydrogen atmosphere may lead to hydride formation, which weakens the magnetocaloric effect. Thus, preventing hydrogen permeation into ErCo₂ is crucial. Herein, we enhance the hydrogen permeation barrier (HPB) performance of ErCo₂ particles by using electroless Cu plating followed by oxidation treatment to form a CuO layer with a thickness of a few micrometers. In experiments, ErCo₂ particles, with a　1.5- to 5-µm-thick CuO surface layer, exhibited a large magnetic entropy change of 24 J kg⁻¹ K⁻¹ even after exposure to a H₂ atmosphere at 1.27 MPa and 296 K for 7 d. Experimental analyses and first-principles calculations revealed the potential of CuO as an HPB material for magnetic refrigeration.