Complex chemical hydrides are a means to store hydrogen in the solid state near ambient temperatures and pressures. Hydrolysis of hydrides has the potential to provide high gravimetric and volumetric energy densities if water consumption can be minimized. At low temperatures (110-140 degrees C), the product of NaBH4 hydrolysis is NaBO2 center dot 2H(2)O (dihydrate), consuming 2 mol of unutilized water. The objective of this work was to conduct water vapor hydrolysis of NaBH4 at elevated pressure and temperature above 150 degrees C. It was hypothesized that this would yield a solid borate with decreased water bound in the crystal structure. A series of batch reactions were conducted to verify the hypothesis. Experimental characterization of the sodium metaborate byproducts indicated that the primary product of water vapor hydrolysis was NaBO2 center dot 1/3H(2)O (hemihydrate) under a variety of reaction conditions. For the most cases, the conversion of NaBH4 approached 100%. Copyright (C) 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.