(277h) Characterization of the Gas Phase Hydrolysis of Sodium Borohydride

Hydrogen storage is vital to the implementation of fuel cell technology and development of appropriate storage strategies represents a challenge that must be overcome. The gravimetric and volumetric capacities of sodium borohydride combined with its relatively low cost make it a prominent near-term candidate for hydrogen storage. The traditional hydrolysis of sodium borohydride with liquid water has been extensively studied and the reaction and its kinetic limitations are well documented in literature. Although thermodynamically favored, aqueous hydrolysis does not proceed to completion even in excess water due to the formation of alkaline byproducts that inhibit the reaction. Therefore an acid catalyst is required to lower the pH and increase the hydrogen yield. In addition, the hydride must be stored in a caustic solution to prevent premature reaction.

Alternatively, the gas phase hydrolysis of solid chemical hydrides has the potential to provide a safe and efficient hydrogen storage system that overcomes the current obstacles in the aqueous phase reaction. High yields of hydrogen have been obtained using pure steam with no acid catalyst. Evidently, the gas phase reaction pathway differs significantly from that of the liquid phase reaction. This finding suggests a hydrogen production scheme where the hydride is stored in its dry form, eliminating the caustic solution and its associated weight from the system. This paper investigates the steam hydrolysis reaction in order to determine the reaction pathway and evaluate the gas/solid hydride concept as a hydrogen storage media for automotive and portable power applications. In order to accomplish these goals, a suite of analytical techniques has been employed to detect and characterize byproducts and intermediates of the hydrolysis reaction.

This poster specifically focuses on two techniques that can be used to characterize the unreacted borohydride, hydrolysis products and reaction intermediates. ¹¹B Nuclear Magnetic Resonance (NMR) is employed to observe and identify boron-containing constituents in both the solid products and the condensed unreacted vapor from the steam hydrolysis reaction. An iodine titration quantifies the amount unreacted hydride for the determination of the theoretical yield of hydrogen via hydrolysis. These analytical techniques, used in parallel with reaction rate measurements and physical observations, provide insight into the reaction pathway. This understanding will help to optimize hydrogen yield and generation rates while minimizing excess water and system weight.