Investigation On Hydrogen Storage Properties Of Lithium Amide/Aluminum Hydrides Composites

Hydrogen energy is considered as one of the ideal clear energy. The largest challenge for ultilization of hydrogen at large scall is to find hydrogen storage solutions that at the same time are safe, compact, light, reversible, and cheap. Recently, hydrogen storage in metal hydrides has attracted much attention because of their high gravimetric and volumetric hydrogen strorage capacity.The Li-Al-N-H systems (included LiAlH4/2LiNH2 and LiNH2/xAlH3(x=1,2)) were chosen to be the objects of this work. The hydrogen desorption and absorption properties of the above mentioned Li-Al-N-H systems were studied by means of P-C-T (Pressure-Composition-Temperature) measurements. The dehydrogenation/ re-hydrogenation mechenisms were studied by means of X-ray diffraction (XRD), Differential scanning calorimetry (DSC), Mass spectrum (MS) and Fourier transform infrared spectrophotometer (FTIR) analysis. The effects of doping catalysts on the above mentioned Li-Al-N-H systems were also discussed. Experimental results showed that the addition of LiNH2 can efficiently decrease the onset desorption temperature both of LiAlH4 and AIH3.Experimental results showed the dehydrogenation process of LiAlH4/2LiNH2 composite was a three-step reaction, and Li3AIN2 was finally formed after releasing 8.65 wt.% hydrogen. Furthermore, the derived Li3AlN2 can be re-hydrogenated to LiNH2, AlN and LiH under conditions of 10 MPa H2 and 400℃, and 5.0 wt% hydrogen can be reversibly stored by Li3AlN2. The dehydrogenation/re-hydrogenation mechanism of LiAlH4/2LiNH2 composite was also discussed.The AIH3 samples used in this investigation were freshly synthesized through the chemical reaction of LiAIH4 with AICl3 in diethyl ether solution. The dehydrogenation/re-hydrogenation properties of AlH3/LiNH2 at a molar ratio of 1:1 mechanically ball-milled were investigated. DSC and XRD analysis indicate that the dehydrogenation is a two-step process:AIH3 decomposes to metallic A1 and H2, then, metallic A1 reacts with LiNH2. About 8.47 wt.% hydrogen is released after heating to 500℃, and Li3AlN2, AlN, Al are the final products. The fully dehydrogenated composites can absorb around 2.0 wt.% hydrogen upon heating to 400℃under 10 MPa hydrogen atmospheres.For AlH3/2LiNH2 composite, the experimental results indicate that NH3 is detected during the decomposition process, and the desorption mechanism is similar with that of AlH3/LiNH2 system. The fully dehydrogenated composites (Li3AIN2 and AlN) can absorb around 3.3 wt.% hydrogen upon heating to 400℃under 10 MPa hydrogen atmospheres.