Combustion-assisted hydrolysis of sodium borohydride for hydrogen generation

Hydrolysis of sodium borohydride, usually with a precious metal catalyst, is a promising method for hydrogen generation in fuel cell applications. We introduce sodium borohydride/metal/water mixtures where the parallel highly exothermic reaction of the metal (aluminum or magnesium) with water assists hydrolysis of sodium borohydride, eliminating the need of catalyst. Upon ignition, such mixtures exhibit self-sustained propagation of combustion wave with simultaneous release of hydrogen stored in sodium borohydride and water. We report mixture ingredients and sodium borohydride/metal mass ratios required for stable generation of hydrogen, with ∼7wt% yield. Because of difficult Al ignition, only nanoscale Al powders can be used, but they contain less active metal. For Mg, coarse (10–50μm) powders provide high efficiency, and the same hydrogen yield as more expensive nanoscale aluminum.