Ternary nitrides for hydrogen storage: Li–B–N, Li–Al–N and Li–Ga–N systems

This paper reports an investigation of hydrogen storage performance of ternary nitrides based on lithium and the Group 13 elements boron, aluminum and gallium. These were prepared by ball milling Li3N together with the appropriate Group 13 nitride—BN, AlN or GaN. Powder X-ray diffraction of the products revealed that the ternary nitrides obtained are not the known Li3BN2, Li3AlN2 and Li3GaN2 phases. At 260 °C and 30 bar hydrogen pressure, the Li–Al–N ternary system initially absorbed 3.7 wt.% hydrogen, although this is not fully reversible. We observed, for the first time, hydrogen uptake by a pristine ternary nitride of Li and Al synthesized from the binary nitrides of the metals. While the Li–Ga–N ternary system also stored a significant amount of hydrogen, the storage capacity for the Li–B–N system was near zero. The hydrogenation reaction is believed to be similar to that of Li3N, and the enthalpies of hydrogen absorption for Li–Al–N and Li–Ga–N provide evidence that AlN and GaN, as well as the ball milling process, play a significant role in altering the thermodynamics of Li3N.