Towards a viable hydrogen storage system for transportation application

Hydrogen energy may provide the means to an environmentally friendly future. One of the problems related to its application for transportation is “on-board” storage. Hydrogen storage in solids has long been recognized as one of the most practical approaches for this purpose. The H-capacity in interstitial hydrides of most metals and alloys is limited to below 2.5% by weight and this is unsatisfactory for on-board transportation applications. Magnesium hydride is an exception with hydrogen capacity of ∼ 8.2 wt.%, however, its operating temperature, above 350 ° C, is too high for practical use. Sodium alanate (NaAlH4) absorbs hydrogen up to 5.6 wt.% theoretically; however, its reaction kinetics and partial reversibility do not completely meet the new target for transportation application. Recently Chen et al. [1] reported that (Li3N+2H2⇔LiNH2+2LiH) provides a storage material with a possible high capacity, up to 11.5 wt.%, although this material is still too stable to meet the operating pressure/temperature requirement. Here we report a new approach to destabilize lithium imide system by partial substitution of lithium by magnesium in the (LiNH2+LiH⇔Li2NH+H2) system with a minimal capacity loss. This Mg-substituted material can reversibly absorb 5.2 wt.% hydrogen at pressure of 30 bar at 200 ° C. This is a very promising material for on-board hydrogen storage applications. It is interesting to observe that the starting material (2LiNH2+MgH2) converts to (Mg(NH2)2+2LiH) after a desorption/re-absorption cycle.