Reaction paths between LiNH2 and LiH with effects of nitrides

The solid-state reaction between LiNH2 and LiH potentially offers an effective route for hydrogen storage if it can be tailored to meet all the requirements for practical applications. To date, there still exists large uncertainty on the mechanism of the reaction-whether it is mediated by a transient NH3 or directly between LiNH2 and LiH. In an effort to clarify this issue and improve the reactivity, the effects of selected nitrides were investigated here by temperature-programmed desorption, X-ray diffraction, in-situ infrared analysis, and hydrogen titration. The results show that the reaction of LiNH2 with LiH below 300 degrees C is a heterogeneous solid-state reaction controlled by Li+ diffusion from LiH to LiNH2 across the interface. At the LiNH2/LiH interface, an ammonium ion Li2NH2+ and a penta-coordinated nitrogen Li2NH3 could be the intermediate states leading to the production of hydrogen and the formation of lithium imide. In addition, it is identified that BN is an efficient "catalyst" that improves Li+ diffusion and hence the kinetics of the reaction between LiNH2 and LiH. Hydrogen is fully released within 7 h at 200 degrees C with BN addition, rather than several days without the modification.