A Comparison of Ammonia Borane Dehydrogenation Methods for Proton-Exchange-Membrane Fuel Cell Vehicles: Hydrogen Yield and Ammonia Formation and Its Removal

Current promising methods to release hydrogen from ammonia borane (NH3BH3, AB; 19.6 wt % H-2) 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 degrees C (13.5 wt % H-2, 1 mol % NH3) and thermolysis in bmimCl with 3 wt % moisture at 110 degrees C (13 wt % H-2, 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.