Mechanisms of reversible hydrogen storage in NaBH4 through NdF3 addition

Abstract

In this work, a reversible hydrogen storage composite, 3NaBH₄/NdF₃, has been prepared using a mechanical milling method. The de-/rehydrogenation properties as well as the mechanisms of reversible hydrogen sorption in the composite were carefully investigated. Based on the pressure–temperature–composition measurements, the de-/rehydrogenation enthalpies of the 3NaBH₄/NdF₃ composite are determined to be 86.4 kJ mol⁻¹ H₂ and −13.2 kJ mol⁻¹ H₂, respectively. The onset dehydriding temperature of the composite is determined to be 413 °C in 0.1 MPa Ar atmosphere and can be as low as 80 °C under vacuum conditions. Analyses revealed that NdB₆, Nd₂H₅ and NaF were formed after the decomposition of the composite, which can be hydrogenated to produce NaBH₄ and NaNdF₄. The formation of NaNdF₄ instead of NdF₃ in the hydrogenated products is believed to be responsible for the reduced hydrogen storage capacity, while the intermediate formation of B, Nd and NdB₄ during dehydrogenation accounts for the asymmetric hydriding/dehydriding behaviors in the 3NaBH₄/NdF₃ composite.