Study on decomposition process of NaAlH4 by in-situ TEM

Abstract

In-situ transmission electron microscopy (TEM) has been performed to observe decomposition process of sodium alanate (NaAlH 4 ) in this work. NaAlH 4 was ground in a glove box under inert gas, and then it was transferred into microscope without exposed to air by Plastic Bag Method. The results of in-situ electron beam diffraction showed that NaAlH 4 decomposed to Na 3 AlH 6 + Al, and NaH + Al during heated up to 150, 200°C, respectively. Moreover, we obtained the result of high resolution (HR) TEM images about the decomposition of NaAlH 4 by high voltage electron microscopy (HVEM) of 1250 keV. It showed that the porous structures appeared with increase of temperature. This should be from structural defects and/or cavities due to volume change of the phases. It was also shown that Na 3 AlH 6 and Al particles with the grain size of several ten nm were irregularly distributed near the pores.

Regeneration of sodium alanate studied by powder in situ neutron and synchrotron X-ray diffraction

“…Sodium alanate (NaAlH 4 ) has arguably become the leading model for complex metal hydride-based hydrogen storage materials since the pioneering work by Bogdanović and Schwickardi. 1 The demonstration that the addition of selected titanium compounds to NaAlH 4 results in enhanced kinetics of reversible hydrogen storage under moderate conditions in the solid state has instigated a host of publications regarding the optimised cycling of this material (employing a variety of additives), [2][3][4][5][6][7][8][9][10][11][12][13] the mechanism involved in the reversible hydrogenation processes [14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29] and the adaption of the method to other complex metal hydrides. [30][31][32][33][34] The factor that has inhibited the commercialisation of NaAlH 4 for automobile applications is the unfavourable theoretical hydrogen capacity of 5.6 wt%, 35 but the incorporation of this material into composites containing materials with higher hydrogen capacity has recently gained much attention.…”

“…The decomposition pathway of NaAlH 4 (with and without additives) has been determined to occur in two discrete steps by a number of in situ powder X-ray diffraction (PXD), 16,39 TEM, 25,40 and NMR spectroscopy 41 studies. The rst step is the decomposition of NaAlH 4 to Na 3 AlH 6 releasing $3.8 wt% H 2 , followed by the decomposition of Na 3 AlH 6 to NaH releasing a further 1.8 wt% H 2 (eqn (1) and ( 2)).…”

Rational Design of Nanosized Light Elements for Hydrogen Storage: Classes, Synthesis, Characterization, and Properties

“…Consequently it is possible that decomposition, aggregation and rearrangement can occur. This is typically the case with borohydrides, alanates [219] and even MgH 2 . [220] An additional major limitation of TEM is the requirement of high vacuum condition for examination, and the result does not necessarily correspond to the real properties of the material under hydrogen cycling.…”

Reactivity enhancement of oxide skins in reversible Ti-doped NaAlH4

“…9,29,30 The temperatures for hydrogen desorption are significantly reduced by the addition of a few mol. % of Ti catalyst.…”