Metal Oxide Additives Incorporated Hydrogen Storage Systems: Formation of In Situ Catalysts and Mechanistic Understanding

Abstract

Hydrogen storage is a critical bottleneck to hydrogen economy. Presently none of the solid-state hydrogen storage materials (metal hydrides) reaches the capacity vs performance target (6.5 wt.% at 85 °C/5-12 bar, 1500 cycles) for the commercialization of light duty H2 fuel cell vehicles. A few reversible hydrogen storage materials (e.g. MgH2, LiBH4/MgH2 composite) possess adequate capacity, but their performance needs to be improved significantly. Metal oxide additives improve the hydrogen storage performance of metal hydrides, but the additive-hydride reaction mechanism remains not well understood. In this context, the present chapter discusses how various metal oxide additives interact with metal hydrides and facilitate the low temperature de/ab-sorption of hydrogen. The metal oxide additives may either directly catalyze the reaction without making any chemical changes or they catalyze indirectly by making active in situ products. In this chapter, various oxides and hydride combinations of the latter category are analyzed, and factors governing the improved hydrogen ab-/desorption performance are highlighted.