New Methods to Generate Hydrogen from Boron Compounds and Water for Fuel-Cell Applications
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Sodium borohydride (SBH; NABH4) and ammonia borane (AB; NH3BH3) contain 10.8 and 19.6 wt% H2, respectively, and are promising hydrogen storage materials for PEM fuel cell power systems. To release hydrogen from these compounds, thermolysis, catalytic hydrolysis, exothermic reactions with solid oxidizers or heat generated by additional reactive mixtures have been employed. All the current methods, however, have disadvantages which decrease the efficiency of hydrogen storage systems. In this work, we report new approaches to release hydrogen from SBH or AB, and simultaneously from water, which do not require any catalyst and provide relatively high hydrogen yield and environmentally benign byproducts. One such approach involves metal/water combustion reactions, which provide heat for SBH or AB dehydrogenation and release additional hydrogen from water. The second approach thermally activates AB hydrolysis in aqueous AB solutions and slurries under modest inert gas pressure. The third approach involves AB thermolysis alone, with effective reaction heat management. The investigations include digital video recording, pressure monitoring, thermocouple measurements, gas chromatography, mass spectrometry, powder XRD analysis, NMR spectroscopy and isotopic (deuterium) labeling. The results show that the proposed methods are promising for hydrogen storage involving SBH or AB. The combustion-based methods could be used in compact power sources for portable electronic devices, while AB hydrothermolysis or thermolysis are attractive for vehicle transportation applications.