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.
Keywords: Lithium nitride; Mechanochemical synthesis; Hydrogen storage
Fig. 1. XRD patterns for Li–B–N milled for 6, 12, 18, 24 and 48 h. The XRD patterns for the starting materials Li3N and BN are also shown.
Fig. 2. XRD patterns for Li–Al–N milled for 18 and 48 h. The XRD patterns for the starting materials Li3N and AlN are also shown.
Fig. 3. XRD patterns for Li–Ga–N milled for 18 and 48 h. The XRD patterns for the starting materials Li3N and GaN are also shown.
Fig. 4. Hydrogen absorption–desorption isotherms at 195 and 260 °C for Li–Al–N.
Fig. 5. Hydrogen absorption–desorption isotherms at 195 °C for Li–Ga–N.
Fig. 6. Hydrogen absorption–desorption isotherms at 195 °C for Li–B–N.
Fig. 7. 1H MAS NMR spectra of hydrogenated Li–B–N, Li–Al–N and Li–Ga–N.
Fig. 8. Hydrogen absorption kinetic curves for Li–Al–N and Li–Ga–N over a series of temperatures from 160 to 295 °C.
Fig. 9. DSC plots of hydrogen absorption by Li–B–N, Li–Al–N and Li–Ga.