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 similar to 8.2 wt.%, however, its operating temperature, above 350 degrees 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 + 2H(2) <-> 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 + H-2) system with a minimal capacity loss. This Mg-substituted material can reversibly absorb 5.2 wt.% hydrogen at pressure of 30 bar at 200 degrees C. This is a very promising material for on-board hydrogen storage applications. It is interesting to observe that the starting material (2LiNH(2) + MgH2) converts to (Mg(NH2)(2) + 2UH) after a desorption/re-absorption cycle. (c) 2005 Elsevier B.V. All rights reserved.