(283f) Hydrogen Liberated by Sodium Borohydride Hydrolysis: Kinetics and Material Properties in the Limited Water Regime

Sodium borohydride is being commercialized to provide hydrogen storage for portable fuel cells. Prior kinetic studies have focused on catalytic hydrolysis of dilute aqueous solutions at room temperature. Kinetic models for both homogeneous acid catalysts and heterogeneous solid catalysts have previously been proposed. We have developed an alternative pathway allowing the reaction of solid NaBH4 with water vapor. In this approach, the hydride deliquesces to form a concentrated liquid phase that reacts to evolve hydrogen at temperatures near the boiling point of water. Hydrated solid borate byproducts are also formed. Characterization of both liquid phase kinetics as well as BH4 and BO2 solid phase is essential. This work reports kinetics of non-catalyzed sodium borohydride hydrolysis in highly concentrated solutions measured with a novel in-situ 11B NMR technique. To further characterize the solid reactants and products, in-situ Raman spectroscopy was implemented. The experimental work was complemented by first-principles density functional theory calculations to gain insight into possible reaction pathways for NaBH4 solutions. Both constant temperature and constant energy first-principles molecular dynamics simulations have been used to characterize the reactivity of NaBH4 under various conditions.