NOVELTY - A hydrogen storage material for providing hydrogen to a hydrogen-consuming device from a vessel of predetermined capacity, initially comprises a particulate mixture of sodium aluminum tetrahydride, aluminum, and a metal-containing catalyst, where the aluminum content is predetermined for a prescribed hydrogenation reaction time in the vessel to reach a hydrogen-restored level with a desired catalyst composition and content. The storage material being composed for cycling between a hydrogen-containing condition and a hydrogen-depleted condition.    USE - For providing hydrogen to a hydrogen-consuming device from a vessel of predetermined capacity (claimed).    ADVANTAGE - The presence of the aluminum particles intimately mixed with the other material particles markedly improves the thermal conductivity of the hydrogen storage mixture. Consequently, the volume of alanate content relative to overall system volume (including heat exchangers, valves, piping) increases overall system gravimetric and volumetric storage efficiencies. The material result in an optimized system for using sodium alanate as a hydrogen storage medium on-board automobiles. It increases both volumetric and gravimetric system energy densities that are the two most important parameters for on-board hydrogen storage systems.    DETAILED DESCRIPTION - An INDEPENDENT CLAIM is included for method of operating a hydrogen storage system for delivery of hydrogen to a hydrogen-using device, involving: adding a predetermined quantity of a hydrogen-containing particulate mixture to a hydrogen storage vessel; heating the particulate mixture in the storage vessel, upon a demand for hydrogen for the hydrogen-using device, to a hydrogen-release temperature to release hydrogen for delivery to the hydrogen-using device and to successively form Na3AlH6 and then NaH and Al; and when the hydrogen content of the particulate mixture reaches a hydrogen-depleted level, adding hydrogen under pressure to the hydrogen-depleted particulate mixture in the vessel while cooling the particulate mixture to facilitate reaction of hydrogen with NaH, Al, and Na3AlH6 to re-form NaAlH4 in the particulate mixture to a hydrogen-restored level for the particulate mixture. The particulate mixture comprises sodium aluminum tetrahydride, aluminum, and a metal-containing catalyst. The aluminum content of the added particulate mixture is predetermined for a prescribed reaction time to reach the hydrogen-restored level with desired catalyst content.