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in Wiley Online Library (wileyonlinelibrary.com).Ammonia borane (AB) is a promising hydrogen storage material as it contains 19.6 wt % hydrogen. In this article, our recently developed hydrothermolysis approach to release hydrogen is studied over a wide range of AB concentrations (6-88 wt %), at pressure 14.7 and 200 psia, and temperature 85-135 C. It is shown that with increasing AB concentration up to 77 wt %, the H 2 yield increases, and that the role of thermolysis, when compared with hydrolysis, increases. The maximum hydrogen storage capacity, obtained at 77 wt % AB and T reactor $ 85 C along with rapid kinetics, was 11.6 and 14.3 wt % at pressure 14.7 and 200 psia, respectively. To our knowledge, on a material basis, the AB hydrothermolysis process is the first one to provide such high hydrogen yield values at near PEM fuel cell operating temperatures without use of catalyst, and thus is promising for use in fuel cell-based vehicle applications.

Among chemical hydrides, ammonia borane (AB) is of interest as a hydrogen storage material due to its high hydrogen capacity (19.6 wt %). In this paper, our recently developed hydrothermolysis process was investigated over a wide range of AB weight percentages (wt %) in water, pressures, and heating rates. It was found that hydrogen yield and thermal characteristics were influenced by these operating conditions. Ammonia generation was also observed during AB hydrothermolysis, where 14−53% of AB was converted to NH3 depending on the reaction conditions. It is remarkable that some AB (2−4%) was converted to NH3, which must be removed for use in proton exchange membrane (PEM) fuel cells, even by neat thermolysis. It was also found that during the hydrothermolysis reaction at T reactor of 85 °C, the T sample can exceed 500 °C, where AB can be completely decomposed to boron nitride (BN). The 11B NMR characterization of hydrothermolysis products showed compounds with B−O and B−N bonds. This paper suggests directions for future research to identify optimal conditions, where the hydrothermolysis process provides the best balance between H2 yield and undesirable products, for PEM fuel cell vehicle applications.

Current promising methods to release hydrogen from ammonia borane (NH3BH3, AB; 19.6 wt % H2) including neat thermolysis, thermolysis in ionic liquid bmimCl with or without proton sponge, thermolysis with nano-BN and hydrothermolysis, were investigated for hydrogen yield and ammonia formation. It was found that even trace moisture influences AB dehydrogenation significantly. The hydrothermolysis at 85 °C (13.5 wt % H2, 1 mol % NH3) and thermolysis in bmimCl with 3 wt % moisture at 110 °C (13 wt % H2, 0.2 mol % NH3) methods were found to be the most promising. Since the target for a proton exchange membrane (PEM) fuel cell is an ammonia concentration less than 0.1 ppm, different purification methods were evaluated. Using experiments and simulations, the proposed ammonia removal method, involving absorption in water followed by adsorption on carbon, was optimized and tested. This study demonstrates that, with high hydrogen yield and an effective method to remove ammonia and borazine, AB dehydrogenation is an attractive approach to generate hydrogen for PEM fuel cell vehicle applications.

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