Thermodynamic study on the solubility of NaBH4 and NaBO2 in NaOH solutions

Extensive research has been performed for on-board hydrogen generation, such as pyrolysis of metal hydrides (e.g. LiH, MgH), hydrogen storages in adsorption materials (e.g. carbon nanotubes and graphites), compressed hydrogen tanks and the hydrolysis of chemical hydrides. Among these methods, the hydrolysis of NaBH has attracted great attention due to the high stability of its alkaline solution and the relatively high energy density, with further advantages such as moderate temperature range (from -5°C to 100°C) requirement, non-flammable, no side reactions or other volatile products, high purity H output. The H energy density contained by the system is fully depend on the solubility of the complicated solution contains reactant, product and the solution stabiliser. In this work, an approach based on thermodynamic equilibrium was proposed to model the relationship between the solubility of an electrolyte and temperature, and the effect of another component on its solubility. The relationship was then applied to NaBH and NaBO aqueous solutions, and the effect of introduction of NaOH on their solubility after deriving their solubility from phase diagrams. The data has been shown in good agreement with the proposed model.