Metal-doped sodium aluminium hydrides as potential new hydrogen storage materials

Exploration of the Nature of Active Ti Species in Metallic Ti-Doped NaAlH4

“…40 While the formation of hexahydride from the NaH/Al mixture and further reconstruction of tetrahydride is possible, it requires high H pressure and temperature conditions. 5 Therefore, NaH and Na 3 -AlH 6 should play critical roles in the formation of the Al-H bond. With the presence of a Ti catalyst, the operation temperature and pressure conditions in the rehydriding process can be markedly reduced.…”

“…In the case of the hydrides doped with Ti halides, it is believed and also experimentally shown that the high-valance Ti n+ is rapidly reduced to Ti 0 via the highly exothermic reaction between the host hydrides and dopant precursors. 2,5,17 Thus formed, Ti 0 has achieved an atomic-level dispersion in the hydride matrix that is much more favorable than that obtained by mechanically milling the hydrides with metallic Ti powder. As a result, the thermodynamically favorable formation of Ti hydride(s) during the doping and/or subsequent hydriding processes should be further kinetically facilitated.…”

“…One is that the surface-localized species consisting of titanium metal or Al-Ti alloy acts as an active catalyst and is present in the hydride matrix in an X-ray amorphous form. 2,5,[16][17][18][19][20][21][22][23] This hypothesis was partially supported by the observed H 2 evolution during the doping process, X-ray absorption and electron microscopy studies of the doped hydride at various states, 2,5,[16][17][18][19][20][21][22] and also by theoretical calculation. 23 Alternatively, on the basis of the observation that lattice parameters of NaAlH 4 changed upon Ti doping, Sun et al proposed that Ti cations with variable valence were incorporated into the host lattice and substituted for Na + .…”

“…2 This finding offers a clear potential to achieve >5 wt % hydrogen storage at a moderate temperature condition and thus quickly stimulates worldwide interest in developing catalytically enhanced TiNaAlH 4 and other related light metal complex hydrides as practical hydrogen storage media. [3][4][5][6][7][8][9][10][11][12][13][14][15] The hydrogen storage performance of the Ti-NaAlH 4 system at moderate temperature range is dominated by the catalytic enhancement arising upon doping with Ti catalyst. So far, however, the catalytic mechanism and even the nature of active Ti species have not been firmly established.…”

Structural study of ball-milled sodium alanate under high pressure

“…These favorable characteristics, particularly the reversibility of NaAlH 4 as a hydrogen storage media, were reported first by Bogdanovich et al [1] and was immediately followed by extensive study of related complex metal hydrides by a number of researchers [2][3][4][5][6]. Reversibility and enhanced desorption kinetics were clearly demonstrated for NaAlH 4 when doped with titanium and other transition metals [1][2][3][4][5]. Phase transitions and crystal structure modifications have been studied during the thermal decomposition of NaAlH 4 [7,8].…”