Hydrogen Storage Materials for Mobile and Stationary Applications: Current State of the Art

One of the limitations to the widespread use of hydrogen as an energy carrier is its storage in a safe and compact form. Herein, recent developments in effective high-capacity hydrogen storage materials are reviewed, with a special emphasis on light compounds, including those based on organic porous structures, boron, nitrogen, and aluminum. These elements and their related compounds hold the promise of high, reversible, and practical hydrogen storage capacity for mobile applications, including vehicles and portable power equipment, but also for the large scale and distributed storage of energy for stationary applications. Current understanding of the fundamental principles that govern the interaction of hydrogen with these light compounds is summarized, as well as basic strategies to meet practical targets of hydrogen uptake and release. The limitation of these strategies and current understanding is also discussed and new directions proposed.

Solid-Solid heterogeneous catalysis: the role of potassium in promoting the dehydrogenation of the Mg(NH(2))(2)/2 LiH composite

Considerable efforts have been devoted to the catalytic modification of hydrogen storage materials. The K-modified Mg(NH2 )2 /2 LiH composite is a typical model for such studies. In this work, we analyze the origin of the kinetic barrier in the first step of the dehydrogenation and investigate how K catalyzes this heterogeneous solid-state reaction. Our results indicate that the interface reaction of Mg(NH2 )2 and LiH is the main source of the kinetic barrier at the early stage of the dehydrogenation for the intensively ball-milled Mg(NH2 )2 /2 LiH sample. K can effectively activate Mg(NH2 )2 as well as promote LiH to participate in the dehydrogenation. Three K species of KH, K2 Mg(NH2 )4 , and Li3 K(NH2 )4 likely transform circularly in the dehydrogenation (KH↔K2 Mg(NH2 )4 ↔KLi3 (NH2 )4 ), which creates a more energy-favorable pathway and thus leads to the overall kinetic enhancement. This catalytic role of K in the amide/hydride system is different from the conventional catalysis of transition metals in the alanate system.

Hydrogen sorption from the Mg(NH2)2-KH system and synthesis of an amide-imide complex of KMg(NH)(NH2)

The interaction between KH and Mg(NH(2))(2) is investigated. Results from temperature-programmed desorption measurements on samples of [Mg(NH(2))(2)][KH](x) (x=0.5, 1.0, and 2.0) indicated that dehydrogenation from [Mg(NH(2))(2)][KH] occurred through a two-step reaction with an onset temperature as low as 60 °C. Accompanied by hydrogen release, K(2)Mg(NH(2))(4) and MgNH successively developed at lower temperatures, whereas KMg(NH)(NH(2)) developed at higher temperatures. However, when dehydrogenation was conducted under isothermal and near-equilibrium conditions, a single-step reaction that led to the formation of KMg(NH)(NH(2)) was observed. KMg(NH)(NH(2)) is a new amide-imide complex. The synthesis of KMg(NH)(NH(2)) can be achieved either by dehydrogenation of the [Mg(NH(2))(2)][KH] mixture or by thermal decomposition of the [K(2)Mg(NH(2))(4)][Mg(NH(2))(2)] mixture.