Stabilization of ammonium borohydride in solid solutions of NH4BH4–MBH4 (M = K, Rb, Cs). Issue 46 (8th November 2022)

• Record Type: Journal Article
• Authors: Grinderslev, Jakob B.; Jensen, Torben R.
• Is Part Of: Dalton transactions. Volume 51:Issue 46(2022)
• Page Start: 17762
• Page End: 17771
• Publication Date: 2022-11-08
• Subjects: Chemistry, Inorganic -- Periodicals; Chemistry, Physical and theoretical -- Periodicals; Chemistry, Inorganic -- Periodicals; 546.05
• DOI: 10.1039/d2dt03173f
• Languages: English
• ISSNs: 1477-9226

Abstract

Abstract : Ammonium borohydride, an extremely hydrogen rich material, is stabilized in solid solutions with alkali metal borohydrides, NH4 BH4 –MBH4 (M = K, Rb, Cs). Here we report the synthesis, crystal structures and thermal behaviors of these solid solutions. Abstract : Ammonium borohydride, NH4 BH4, has the highest gravimetric and volumetric hydrogen density among known inorganic compounds and a fascinating rock salt type crystal structure composed of H disordered tetrahedral complexes, NH4 + and BH4 −, which are interlinked by a dense network of dihydrogen bonds. Here we report the synthesis, structure and properties of solid solutions in the binary systems, NH4 BH4 –MBH4 (M = K, Rb, Cs), which are investigated by in situ synchrotron radiation powder X-ray diffraction and thermal and photographic analysis. Full solubility and formation of (NH4 ) x M1− x BH4, is observed upon cryo-mechanochemical treatment. The solid solutions stabilize NH4 BH4 from T ∼68 to ∼96 °C, alter the decomposition pathway and suppress the fierce decomposition of NH4 BH4 . However, for increased amounts of NH4 BH4 in the solid solutions, the decomposition gradually shows more resemblance to that of pristine ammonium borohydride, and the thermal stability of the solid solutions appears to decrease down the group of the alkali metal ions, i.e. decreasing from K +, Rb + and to Cs + .