Solid state synthesis, structural characterization and ionic conductivity of bimetallic alkali-metal yttrium borohydrides MY(BH4)4 (M = Li and Na)

Elsa Roedern*, Young-Su Lee, Morten Brix Ley, Kiho Park, Young Whan Cho, Jørgen Skibsted, Torben René Jensen

*Corresponding author for this work

Research output: Contribution to journal/Conference contribution in journal/Contribution to newspaperJournal articleResearchpeer-review

Abstract

Two bimetallic borohydrides, lithium yttrium tetraborohydride, LiY(BH 4) 4, and sodium yttrium tetraborohydride, NaY(BH 4) 4, have been synthesized by thermal treatment and quenching of ball-milled precursors. LiY(BH 4) 4 crystallizes in the space group P42c and NaY(BH 4) 4 in C222 1 and the compounds are isostructural to LiSc(BH 4) 4 and NaSc(BH 4) 4, respectively. Both LiY(BH 4) 4 and NaY(BH 4) 4 are built from the complex anions of [Y(BH 4) 4] -. The unit cell volumes per formula unit of the bimetallic compounds LiY(BH 4) 4 and NaY(BH 4) 4 are significantly larger compared to those of the constituent components (14% and 7.5% unit cell expansion, respectively), which may contribute to the mobility of the Li + and Na + cations. The ionic conductivities of LiY(BH 4) 4 and NaY(BH 4) 4 at room temperature, measured by impedance spectroscopy, are σ = 1.26 × 10 -6 and 6.92 × 10 -7 S cm -1 respectively, and are improved compared to those of the precursors. DFT calculations were used to optimize the structures and identify a possible mechanism for the Na ion mobility. In addition, they provide the basis for assignment of the 11B NMR parameters determined by 11B MAS NMR for the two boron sites in NaY(BH 4) 4.

Original languageEnglish
JournalJournal of Materials Chemistry A
Volume4
Issue22
Pages (from-to)8793-8802
Number of pages10
ISSN2050-7488
DOIs
Publication statusPublished - 2016

Keywords

  • HYDROGEN-STORAGE MATERIALS
  • DENSITY-FUNCTIONAL THEORY
  • AUGMENTED-WAVE METHOD
  • X-RAY-DIFFRACTION
  • B-11 MAS-NMR
  • THERMAL-PROPERTIES
  • Y(BH4)(3)
  • DECOMPOSITION
  • LIBH4
  • LISC(BH4)(4)

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