Sodium Borohydride, Its Hydrolysis and its Use as a Reducing Agent and in the Generation of Hydrogen¹

Abstract

Sodium borohydride reacts slowly with water ultimately to liberate 4 moles of hydrogen per mole of the compound at room temperature, or 2.4 1. per gram. The reaction is greatly accelerated by rise of temperature or by the addition of acidic substances, for which latter purpose boric oxide is convenient and effective when the objective is the generation of hydrogen. Particularly striking is the catalytic effect of certain metal salts, especially that of eobalt(II) chloride. Thus pellets of sodium borohydride containing only 5% of the cobalt salt react as rapidly as those containing 10 times that amount of boric oxide. The effect of the cobalt salt is ascribed to the catalytic action of a material of empirical composition, Co2B, which is formed in the initial stages o'f the reaction.

Recent Progress in Metal Borohydrides for Hydrogen Storage

“…Reproduced with permission from reference 3. First-principles calculations of the electronic structures of M(BH 4 ) n show that they are nonmetallic and have relatively large energy gaps of 1.8 4 ) n have been used as "one-way" hydrogen sources that release the hydrogen on contact with water (via hydrolysis) [9][10][11]. Because the hydrolysis reaction is highly irreversible, such materials are certainly not candidates for reversible hydrogen storage.…”

Structure and Properties of NaBH4·2H2O and NaBH4

“…[4] Although the reactions with water are usually fast, the reaction kinetics under practical conditions is rather slow, thus suggesting the use of expensive catalysts. [5] Catalytically accelerated NaBH 4 hydrolysis for the generation of hydrogen has been studied since the 1950s, [6] and it is now under intensive investigation, [5] leading to a number of recent applications. [7] However, until now, there is no experimental structural information on intermediate phases or reaction pathways in the NaBH 4 + H 2 O system.…”

Cobalt boride catalysts for hydrogen generation from alkaline NaBH4 solution

“…In the 1950s, Schlesinger et al [7] had first found that cobalt chloride could accelerate the decomposition of NaBH 4 in water. It is interesting that cobalt chlorides react with NaBH 4 , release H 2 and produce precipitate as byproduct; and the precipitate can help getting much faster hydrogen generation rates in the succeeding hydrogen generation reactions.…”