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High energy density hydrogen storage is a critical technology requirement in a hydrogen-based energy infrastructure. Although there are no current storage methods that meet desired energy density goals for vehicular hydrogen storage, complex metal hydride based systems are among the most promising. These materials form compounds with hydrogen under appropriate conditions and release hydrogen by thermal decomposition. The complex hydride, sodium alanate, is particularly useful due to its favorable reversibility. Thermal properties characterization of sodium alanate has been performed at Sandia National Laboratories to gain a detailed understanding of how complex hydrides will behave in a storage system. Thermal properties were investigated using the thermal probe method (ASTM D5334). Custom test hardware was designed and built to accommodate the complex decomposition and recombination of sodium alanate. Thermal conductivity and thermal wall resistance were determined by utilizing analytical and numerical data analysis methods. The thermal conductivity of sodium alanate was found to vary by more than 90% with changes in phase composition and hydrogen gas pressures between 1 and 100 atm. The quality of thermal contact between the alanate and the vessel wall was characterized numerically for various pressures and phase compositions. The contact resistance is high for all states, indicating poor contact between the material and the vessel wall.

Publisher Summary Efficient hydrogen storage is a significant challenge inhibiting the use of hydrogen as a primary energy carrier. In general, three main categories of energy storage applications require the use of energy-dense hydrogen storage materials; transportation, portable auxiliary power, and personal electronics. Each of these applications requires relatively high energy and power density capability. This chapter focuses on the automotive applications as these will likely have the most extensive impact on consumer-scale energy storage technologies. Automotive systems are arguably the most challenging energy storage application since the low cost and high performance of current fossil fuel technologies cause consumers to expect similarly plentiful energy and power from new transportation technologies. For automotive systems, current hydrogen storage technologies (liquid and compressed gas) fall short in terms of energy density and cost and do not provide a clear path for efficiency improvement and the resulting increase in energy density. Hydrogen storage technologies that are efficient, low cost, and robust must be developed to enable the use of hydrogen fuel in transportation applications. Solid-state hydrogen storage solutions are theoretically able to store more hydrogen per unit volume than liquid or solid storage systems. Given this potential for high energy density reversible hydrogen storage, significant effort has been applied to develop storage solutions based on this technology.