Preparation, characterization and modification of magnesium hydride for enhanced solid-state hydrogen storage properties

Magnesium-magnesium hydride (Mg-MgH2) system has attracted attention worldwide recently because of its simple hydrogenation-dehydrogenation process, the cost-effectiveness of the raw materials, and relatively high hydrogen storage capacity compared to the other metal-metal hydride systems. The present study deals with the optimization of the process parameters for the synthesis of magnesium hydride (MgH2) in sizable quantities using commercial-grade magnesium powder, characterization with respect to hydrogen storage capacity, by thermal dehydrogenation and pH-controlled aqueous hydrolysis. The thermal hydrogenation-dehydrogenation and mild acidified aqueous dehydrogenation behaviour of MgH2 were studied systematically to compare the decomposition kinetics and storage capacity. The superior catalytic effect of V2O5 on decreasing the onsetdehydrogenation temperature of MgH2 is demonstrated. The MgH2-5 wt. % mesoporous V2O5 sample starts releasing hydrogen at 220 degrees C, which is substantially less than the as-synthesized un-catalysed MgH2 under identical conditions which starts releasing hydrogen at 430 degrees C. The dehydrogenated MgH2-5wt. %V2O5 could be completely re-hydrogenated at 150 degrees C. Hydrolysis of as-synthesized MgH2 was demonstrated using an aqueous solution using tartaric acid and the dehydrogenation behaviour was co-related with the pH of the solution. More than 90% hydrogen yield was achieved by the hydrolysis of MgH2 in a tartaric acid solution of pH-4. Based on the result, a hydrogen gas dispenser using solid-state magnesium hydride as a hydrogen source is proposed for laboratory applications for the supply of ultra-pure hydrogen for various reactions and crystal growth experiments.