Compact fuel cell system utilizing a combination of hydrogen storage materials for optimized performance.

Abstract

Abstractn entirely new class of light-weight reversible hydrides was recently discovered (the Tidoped alanates)[lI. These NaAIH,-based materials have demonstrated reversible hydrogen storage capacities of up to 5 wt%, nearly 4 times the gravimetrically density of commercial metal hydrides. For this reason, they have been considered a breakthrough for hydrogen storage in fuel cell vehicles. This project is the first to publish the use of alanates for the generation of electrical power and the first demonstration of a hydride-fueled elevatedtemperature PEM Fuel Cell. Because the kinetics of hydrogen uptake and release by the alanate improves with elevated temperatures, novel concepts were tested for the purpose of developing a highly efficient stand-alone power system. A major focus of this work was on the modeling, design, construction and testing of an integrated fuel cell stack and hydrogen storage system that eliminates the need of complicated heat transfer systems and media. After extensive modeling efforts, a proof-of-concept system was built that employs an integrated fuel cell stack and hydride beds that balancing the generation of fuel cell waste heat with the endothermic release of hydrogen from the alanates. Our demonstration unit was capable of greater than one hour of operation on a single charge of hydrogen from the integrated 173 gram alanate bed. In addition, composite hydride materials with synergistic reaction heats were evaluated and tested to enhance the operational performance of the alanates. The composites provide a unique opportunity to utilize the heat produced from hydriding classic metal hydrides to improve both absorption and desorption rates of the alanates. A particular focus of the mixed storage materials work was to balance the thermodynamics and kinetics of the hydrides for start-up conditions. Modeling of the sorption properties proved invaluable in evaluating the optimum composition of hydrides. The modeling efforts were followed by full validation by experimental measurements. This project successfully completed the proof-of-concept goals and generated a powerful set of tools for optimizing the complete power-generation system. It has also created a new direction for hydrogen power generation as well the potential for new R&D based on this work.

High temperature proton exchange membranes based on polybenzimidazoles for fuel cells

“…In this case there is a much better match with the HT-PEMFC than with a conventional PEMFC. A simple system of a 6 cell PBI stack thermally integrated with an alanate tank was made at Sandia National Laboratory [257].…”