Catalytic hydrolysis of hydrazine borane for chemical hydrogen storage: Highly efficient and fast hydrogen generation system at room temperature

Abstract

There has been rapidly growing interest for materials suitable to store hydrogen in solid state for transportation of hydrogen that requires materials with high volumetric and gravimetric storage capacity. B-N compounds such as ammonia-triborane, ammonia-borane and amine-borane adducts are well suited for this purpose due to their light weight, high gravimetric hydrogen storage capacity and inclination for bearing protic (N-H) and hydridic (B-H) hydrogens. In addition to them, more recent study [26] has showed that hydrazine borane with a gravimetric hydrogen storage capacity of 15.4% wt needs to be considered as another B-N compound that can be used for the storage of hydrogen. Herein we report for the first time, metal catalyzed hydrolysis of hydrazine borane (N 2H 4BH 3, HB) under air at room temperature. Among the catalyst systems tested, rhodium(III) chloride was found to provide the highest catalytic activity in this reaction. In the presence of rhodium(III) chloride, the aqueous solution of hydrazine borane undergoes fast hydrolysis to release nearly 3.0 equivalent of H 2 at room temperature with previously unprecedented H 2 generation rate TOF = 12000 h −1. More importantly, it was found that in the catalytic hydrolysis of hydrazine borane the reaction between hydrazine borane and water proceeds almost in stoichiometric proportion indicating that the efficient hydrogen generation can be achieved even from the highly concentrated solution of hydrazine borane or in the solid state when water added to the solid hydrazine borane. This finding is crucial especially for on-board application of the existing system. The work reported here also includes ( i) finding the solubility of hydrazine borane plus its stability against self-hydrolysis in water, ( ii) the definition of reaction stoichiometry and the identification of reaction products for the catalytic hydrolysis of hydrazine borane, ( iii) the collection of wealthy kinetic data to demonstrate the effect of substrate and catalyst concentrations on the hydrogen generation rate and to determine the rate law for the catalytic hydrolysis of hydrazine borane, ( iv) the investigation of the effect of temperature on the rate of hydrogen generation and determination of activation parameters ( E a, ΔH #, and ΔS #) for the catalytic hydrolysis of hydrazine borane.