Hydrogen storage materials: present scenarios and future directions

Solid–Solid Heterogeneous Catalysis: The Role of Potassium in Promoting the Dehydrogenation of the Mg(NH2)2/2 LiH Composite

“…In contrast, KH can easily react with Mg(NH 2 ) 2 to release hydrogen at a temperature as low as 60 8C, which is very close to the onset temperature of hydrogen desorption from the post-milled 1 Mg(NH 2 ) 2 / 1.9 LiH/0.1 KH sample. In addition, interaction between KH and Li 2 Mg 2 (NH) 3 was also found to occur at higher temperatures than that of KH and Mg(NH 2 ) 2 ( Figure S1). Thus, it is highly possible that KH firstly reacts with Mg(NH 2 ) 2 to be functional.…”

“…Consistent results were also found in the corresponding IR spectra (Figure 5 c). The absorbances at 3196 and 3162 cm À1 in the heat-treated sample were a result of the NÀH stretches of Li 2 Mg 2 (NH) 3 . [41] The other peaks were also identified ( Figure 5 c).…”

“…The interaction of Li 3 K(NH 2 ) 4 and MgNH results in the formation of Li 2 Mg 2 (NH) 3 and LiNH 2 (the products of the first step of the dehydrogenation of the Mg(NH 2 ) 2 /2 LiH system) together is, KH$K 2 Mg(NH 2 ) 4 $KLi 3 (NH 2 ) 4 . This agrees with the XAFS results reported earlier, [29] which showed that KÀH and KÀN components coexist in the material during the dehydrogenation process.…”

“…If dehydrogenation is performed under the conditions of some hydrogen background pressure rather than under vacuum, more KH can be observed at a hydrogen content of 1.4 H ( Figure S7). This implies that the reaction in Equation (5) may be the main step that determines the overall rate of the reaction in Equation (3). Moreover, from the circular pathway of K in the dehydrogenation, it could be deduced that K may not stay fixed but likely moves around to some degree in the sample to interact with other reacting species.…”

“…A number of mechanistic investigations have been conducted, which have controversial interpretations. [3,6] One of the proposals is the ammonia-mediated mechanism, in which Mg(NH 2 ) 2 decomposes firstly to NH 3 and MgNH, and then NH 3 reacts with LiH to produce hydrogen. [14,[16][17][18][19] The kinetic barrier in those processes should be mainly from the self-decomposition of Mg(NH 2 ) 2 as NH 3 can react with LiH rapidly.…”