Potassium octahydridotriborate: diverse polymorphism in a potential hydrogen storage material and potassium ion conductor. Issue 24 (29th May 2019)

• Record Type: Journal Article
• Authors: Grinderslev, Jakob B.; Møller, Kasper T.; Yan, Yigang; Chen, Xi-Meng; Li, Yongtao; Li, Hai-Wen; Zhou, Wei; Skibsted, Jørgen; Chen, Xuenian; Jensen, Torben R.
• Is Part Of: Dalton transactions. Volume 48:Issue 24(2019)
• Page Start: 8872
• Page End: 8881
• Publication Date: 2019-05-29
• Subjects: Chemistry, Inorganic -- Periodicals; Chemistry, Physical and theoretical -- Periodicals; Chemistry, Inorganic -- Periodicals; 546.05
• DOI: 10.1039/c9dt00742c
• Languages: English
• ISSNs: 1477-9226

Abstract

Abstract : Hydrogen storage properties and polymorphism in KB3 H8 . The order–disorder polymorphic transition results in disordered B3 H8 − anions, facilitating cation mobility. Abstract : Octahydridoborate, i.e. [B3 H8 ] − containing compounds, have recently attracted interest for hydrogen storage. In the present study, the structural, hydrogen storage, and ion conductivity properties of KB3 H8 have been systematically investigated. Two distinct polymorphic transitions are identified for KB3 H8 from a monoclinic (α) to an orthorhombic (α′) structure at 15 °C via a second-order transition and eventually to a cubic (β) structure at 30 °C by a first-order transition. The β-polymorph of KB3 H8 displays a high degree of disorder of the [B3 H8 ] − anion, which facilitates increased cation mobility, reaching a K + conductivity of ∼10 −7 S cm −1 above 100 °C. β-KB3 H8 starts to release hydrogen at ∼160 °C, simultaneously with the release of B5 H9 and trace amounts of B2 H6 . KBH4 and K3 (BH4 )(B12 H12 ) are identified as crystalline decomposition products above 200 °C, and the formation of a KBH4 deficient structure of K3− x (BH4 )1− x (B12 H12 ) is observed at elevated temperature. The hydrogen-uptake properties of a KB3 H8 –2KH composite have been examined under 380 bar H2, resulting in the formation of KBH4 at T ≥ 150 °C along with higher metal hydridoborates, i.e. K2 B9 H9, K2 B10 H10, and K2 B12 H12 .