Combined TEM-EDX and XAFS studies of Ti-doped sodium alanate
Combined TEM-EDX and XAFS studies of Ti-doped sodium alanate
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DOI：
10.1039/b403657n
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发表时间：
2004-08
影响因子：
3.3
通讯作者：
M. Felderhoff;K. Klementiev;W. Grünert;B. Spliethoff;B. Tesche;J. B. V. Colbe;B. Bogdanovic;M. Härtel;André Pommerin;F. Schüth;C. Weidenthaler
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文献类型：
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作者：
M. Felderhoff;K. Klementiev;W. Grünert;B. Spliethoff;B. Tesche;J. B. V. Colbe;B. Bogdanovic;M. Härtel;André Pommerin;F. Schüth;C. Weidenthaler
在研究掺杂丙酸钠作为储氢材料的背景下，采用四丁酸钛（Ti(OBun)4）、胶体钛纳米颗粒（Ti*）或TiCl3作为掺杂剂，对掺杂丙酸钠进行了TEM-EDX研究和XAFS测量相结合的研究。结果表明，湿法脱氢Ti(OBun)4掺杂的NaAlH4由结晶Al和无定形NaH相组成。EDX分析的惊人结果是，在每种情况下，ti掺杂剂都只存在于Al相中。另一方面，通过球磨掺杂Ti*或ticl3的脱氢NaAlH4是一种非晶材料，Al相和NaH相之间的边界扩散，钛在Al相中的分布高度均匀。使用球磨掺杂方法和Ti*纳米颗粒作为掺杂剂，可能是Ti*掺杂材料具有出色动力学的原因（B. Bogdanovic， M. Felderhoff， S. Kaskel， A. Pommerin， K. Schlichte和F. Schuth, ad . Mater）。， 2003,15, 1012；M. Fichtner， O. Fuhr， O. Kircher和J. Rothe，纳米技术，2003,14,778)。结合TEM-EDX和之前对储氢材料的XRD研究，讨论了储氢和再充氢反应的过程。掺ti的NaAlH4在掺杂、几次和100次脱氢化和再氢化循环后的Ti-EXAFS和XANES光谱非常接近。显然，在Ti掺杂后，形成了一个零价Ti，在循环试验过程中几乎保持不变。XAFS光谱表明，Ti在Al相中大量原子分散，即形成Al - Ti合金，从而证实了先前的假设（V. P. Balema， J. W. Wiench， K. W. M. Dennis， M. Pruski和V. K. Pecharsky， J. Alloys Compd.）。植物学报，2001,329,108；E. H. Majzoub和K. J. Gross， J.合金公司。， 2003, 356-357, 363)。
In context of investigations of doped sodium alanate as a hydrogen storage material, an investigation combining a TEM-EDX study and XAFS measurements has been carried out on doped sodium alanate, using titanium tetrabutylate (Ti(OBun)4), colloidal titanium nanoparticles (Ti*) or TiCl3 as doping agents. It was found that the dehydrogenated wet-chemically Ti(OBun)4 doped NaAlH4 consists of a crystalline Al and an amorphous NaH phase. The striking result of EDX analyses is that in each case the Ti-dopant is found to be present only in the Al phase. On the other hand, dehydrogenated NaAlH4 doped with Ti* or TiCl3via ball milling is an amorphous material, with diffuse boundaries between Al and NaH phases and a highly uniform distribution of titanium in the Al-phase. Both the use of the ball milling doping method and of Ti* nanoparticles as dopants, are probable reasons for the outstanding kinetics of the Ti* doped material (B. Bogdanovic, M. Felderhoff, S. Kaskel, A. Pommerin, K. Schlichte and F. Schuth, Adv. Mater., 2003, 15, 1012; M. Fichtner, O. Fuhr, O. Kircher and J. Rothe, Nanotechnology, 2003, 14, 778). The course of hydrogen dis- and recharging reactions is discussed in light of the present TEM-EDX and the preceding XRD investigations of storage materials. Ti-EXAFS and XANES spectra of Ti-doped NaAlH4 after the doping, after several, and after 100 de- and rehydrogenation cycles are very close to each other. Apparently, after the Ti-doping, a zerovalent Ti species is formed which remains almost unchanged in the course of the cycle test. The XAFS spectra indicate that Ti is largely atomically dispersed in the Al phase, i.e. forms an Al–Ti alloy, thus confirming the earlier hypothesis (V. P. Balema, J. W. Wiench, K. W. M. Dennis, M. Pruski and V. K. Pecharsky, J. Alloys Compd., 2001, 329, 108; E. H. Majzoub and K. J. Gross, J. Alloys Compd., 2003, 356–357, 363) on this matter.