(378e) Mitigating Strategies for Reactive Solids-Based Hydrogen Storage Systems

Solid-state materials such as metal hydrides and complex hydrides have been shown to be viable candidates for on-board hydrogen storage systems.  However, some complex metal hydrides such as sodium alanate (NaAlH₄) in the powder form, exhibit unfavorable exothermic reactions when exposed to air or water.  Mitigating this reactivity and its associated risks in the event of inadvertent exposure (e.g., tank rupture during a vehicular collision) is an important step for achieving widespread use and public acceptance of these technologies.

Several types of accident scenarios, exposures, and mitigating methods have been investigated in the past.  This paper focuses on a specific scenario and mitigating strategy: exposure of the reactive solid to oxygen, and the effect of an active material-polymer composite mixture on its exothermic behavior.

Sodium alanate is selected as the representative of reactive solid hydrogen storage materials that exhibit unfavorable exothermicity, and is the “active material,” although the mitigation methods developed are applicable to other similar materials.  Previously, we reported on the use and effectiveness of polystyrene polymers synthesized (polymerized) along with the active material to create a composite[1].  This paper presents our work on other polymers using the same methodology, comparing their effectiveness to the active material alone and to the previous work with polystyrene.  Additive effectiveness is measured by the amount of heat released during controlled exposure to oxygen.  Measurements are done both before and after subjecting the composite material to representative operating conditions of adsorption/desorption cycling, to understand the impacts (if any) of operating conditions on the stability and effectiveness of the composite material.  SEM imagery is also used as a tool to better understand the method of mitigation and reasons for degradation (if any) of the composite.  Additional tests were performed to investigate the impact of exposing the hydride (both in powder and powder compact forms) to vehicle fluids and road sprays and also to assess the sensitivity of the mitigated material to mechanical impact.