Hydrogen desorption/absorption properties of Li–Ca–N–H system

Hydrogen storage properties of two ball-milled composites of Ca(NH2)2 + 2LiH and CaH2 + 2LiNH2 were investigated as a series of searching studies of high performance hydrogen storage materials. About 4.5 mass% hydrogen is desorbed from about 100 °C and the thermal desorption profiles show a peak around 200 and 220 °C for the composites of CaH2 + 2LiNH2 and Ca(NH2)2 + 2LiH, respectively, under a helium flow at 5 °C/min heating rate without any NH3 emission within our experimental accuracy. The powder X-ray diffraction and infrared absorption spectroscopy indicated that the dehydrogenated states of both composites form “an unknown imide phase” after heating up to 400 °C, while the dehydrogenated states after heating up to 200 °C in vacuum are the mixed phases of Li2NH and CaNH. The rehydrogenated state for the ball-milled composite of CaH2 + 2LiNH2 is transformed into the composite of Ca(NH2)2 and 2LiH by repeating the dehydrogenation and rehydrogenation cycles at 180–200 °C.