Abstract
About 25 years ago, Bogdanovic and Schwickardi (B. Bogdanovic, M. Schwickardi: J. Alloys Compd. 1–9, 253 (1997) discovered the catalyzed release of hydrogen from NaAlH4. This discovery stimulated a vast research effort on light hydrides as hydrogen storage materials, in particular boron hydrogen compounds. Mg(BH4)2, with a hydrogen content of 14.9 wt %, has been extensively studied, and recent results shed new light on intermediate species formed during dehydrogenation. The chemistry of B3H8−, which is an important intermediate between BH4− and B12H122−, is presented in detail. The discovery of high ionic conductivity in the high-temperature phases of LiBH4 and Na2B12H12 opened a new research direction. The high chemical and electrochemical stability of closo-hydroborates has stimulated new research for their applications in batteries. Very recently, an all-solid-state 4 V Na battery prototype using a Na4(CB11H12)2(B12H12) solid electrolyte has been demonstrated. In this review, we present the current knowledge of possible reaction pathways involved in the successive hydrogen release reactions from BH4− to B12H122−, and a discussion of relevant necessary properties for high-ionic-conduction materials.
Highlights
Molecules 2021, 26, 7425. https://Boron hydrogen compounds have been intensively studied for almost a century since the pioneering studies of A
The dehydrogenation reactions of metal borohydrides lead to hydrogen, metal and boron, or metal borides
The controlled dehydrogenation of a borohydride salt can be used to safely prepare new closo- and nido- hydroborate salts for potential battery applications [30] without using toxic boranes such as B10 H14, which were used for the synthesis of this large boron species [31]
Summary
Boron hydrogen compounds have been intensively studied for almost a century since the pioneering studies of A. Boron hydrogen compounds are energetic materials and were considered as rocket or jet fuels [2]; the toxicity of boranes has prevented their extended use. The dehydrogenation reactions of metal borohydrides lead to hydrogen, metal and boron, or metal borides. In this reaction process, intermediate species are formed, compounds with closo-hydroborate anion B12 H12 2− [23,24]. The controlled dehydrogenation of a borohydride salt can be used to safely prepare new closo- and nido- hydroborate salts for potential battery applications [30] without using toxic boranes such as B10 H14 , which were used for the synthesis of this large boron species [31].
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