PNNL

Abstract

Ammonia borane (AB) is a very attractive hydrogen storage material with a high gravimetric (196 gm/ H2 kg-1) and volumetric density (145 gm/ H2 liter-1) of hydrogen. Hydrogen release from AB in solution, catalyzed with acids and or metal catalysts, have impressive rates [1-5] however these dissolved AB systems will have difficulty meeting the long term DOE targets if they can not be stabilized in concentrated form [6]. One alternative is neat AB (solid or liquid) releasing >2 equivalents of H2 shows promise to meet the long-term DOE targets if the rates of hydrogen release are sufficient at moderate temperatures. Ammonia borane, formed by a dative bond between the non-bonding electron pair of ammonia with the empty p-orbital of borane (H3N?BH3) is a molecular crystal formed by a hydrogen bonding network of dihydrogen bonds. Amorphous powder can be compressed into a pellet of comparable density to the crystal packing density (0.74 gm/cc). Support for this work was provided through the DOE center of Excellence for Chemical Hydrogen Storage of the Hydrogen Program at the U.S. Department of Energy. Pacific Northwest National Laboratory is operated by Battelle for the U.S. Department of Energy.