Development of an on-board H2 storage and recovery system based on lithium borohydride.

PDFTech ReportHydrogen storagepH valueCatalystsHydrogen fuelsLithium compoundsFuel cellsElectrochemical processesUnited StatesYoungstown State University. Center for Transportation and Materials EngineeringLinkous, Clovis A.Youngstown State University. Dept. of ChemistryUniversity Transportation Centers Program (U.S.)US Transportation CollectionAlkali metal borohydrides based on sodium and lithium, NaBH4 and LiBH4, have been evaluated as a potential hydrogen storage and recovery system for on-board vehicle use. The borohydride salts could be dissolved in water, followed by a hydrolytic reaction evolving hydrogen gas, H2. It was found that pH of the aqueous solution, temperature, concentration of the borohydride salt, and exposure to catalytic surfaces all played a role in the rate of H2 evolution. The solution pH alone could vary the gas evolution rate over several orders of magnitude. However, without addition of external reagents, the solution left to itself would quickly rise into the pH 10-11 range and level out, due to the buffering capacity of the boric acid product. Therefore, it was decided to exclude secondary reagents and let the pH stay near the buffered value, and use other variables to control gas evolution rate. Varying temperature from ambient to 80 oC enabled a four-fold increase in reaction rate, enabling an effective means of control. Inserting plastic substrates bearing painted films of organic pigment catalysts such as pyranthrenedione into the borohydride solution could enhance gas evolution rates up to 40%. Better design of the mixing chamber could greatly improve this effect. In general, LiBH4 and NaBH4 evolved H2 at the same rate, but the lithium salt had a tendency to generate an initial surge upon contact with solution that could make it potentially problematic when mixing at high rates in tight spaces. As a proof of concept, a remote controlled, 1/10th scale monster truck was obtained and modified to run off of a proton-exchange membrane fuel cell supplied with H2 from a borohydride generator