International Journal of Hydrogen Energy, Vol.32, No.18, 4723-4730, 2007
Minimizing water utilization in hydrolysis of sodium borohydride: The role of sodium metaborate hydrates
Keywords:hydrogen can be obtained from hydrolysis of chemical hydrides;making this an interesting option for hydrogen storage. The gravimetric;and volumetric energy densities attainable from hydrolysis of chemical hydrides depend in large measure on the amount of water required;for the process. The steam hydrolysis of sodium borohydride produces hydrated metaborate byproducts in which the degree of hydration of;the metaborate is closely tied to the amount of water in the reaction. Experimental characterization of these sodium metaborate byproducts;indicates that the primary byproduct of steam hydrolysis is NaBO2 center dot 2H(2)O under a variety of reaction conditions. A group contribution method;is used to estimate the heats and free energies of formation of a variety of hydrated metaborates. This information will be useful in establishing;the preferred (stable) hydration state of the byproducts;and in distinguishing these from metastable products.;(c) 2007 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.