Synchrotron x-ray absorption spectroscopy (XAS) for understanding dopant effects in Ti-doped NaAlH4

Tabbetha A. Dobbins, Roland Tittsworth, Scott A. Speakman, Joachim Schneibel

Research output: Chapter in Book/Report/Conference proceedingConference contribution

2 Scopus citations

Abstract

We report studies concerning the time frame for catalytic reactions between NaAlH4 (sodium alanate) and TiCl3 during high energy milling. Spectral features in x-ray absorption spectra were analyzed for samples milled for various times (0 minutes, 1 minute, 5 minutes, 25 minutes, and 125 minutes). A structural transition from Ti3+ to Ti0 is observed within the first 5 minutes of milling. The Ti0 structure persists for samples milled for times longer than 5 minutes - even after those samples underwent a subsequent single hydrogen desorption/absorption cycle. Samples milled for less than 5 minutes retain Ti3+. For samples milled for 1 minute, the Ti-K edge position shifts from Ti3+ to Ti0 after a single desorption/absorption cycle. However, the first coordination sphere around the Ti0 absorber occurs at longer distances for 1 minute milled sample. These results hint at the formation of Ti0 pure metallic clusters upon desorption/adsorption cycling of 1 minute milled sample. Previously reported x-ray absorption spectroscopy studies have demonstrated the structural transition from Ti3+ (in TiCl 3) to Ti0 (determined to be TiAl3 found at the surface of the alanate powder). Aluminum deficiency on the NaAlH4 lattice is responsible for controlling hydrogen absorption capacity. These time-resolved spectroscopy studies suggest the possibility for controlling aluminum deficiency, while still maintaining titanium activation of the alanate powder, by manipulating the coordination environment of the titanium dopant during the first five minutes of high energy milling. Specifically, a possible approach to mitigating aluminum deficiency during doping would be to introduce an alternative species to which the to Ti3+ catalyst would form a metallic bond after the TiCl3 has attached at the surface of the sodium alanate powder and before the Ti3+ forms the TiAl3 intermetallic species.

Original languageEnglish (US)
Title of host publicationAdvanced Materials for Energy Conversion III - A Symposium in Honor of Drs. Gary Sandrock, Louis Schlapbach and Seijirau Suda for Lifetime Achievements in Metal Hydride Research and Development
Pages263-270
Number of pages8
StatePublished - May 23 2006
Event2006 TMS Annual Meeting - San Antonio, TX, United States
Duration: Mar 12 2006Mar 16 2006

Publication series

NameTMS Annual Meeting
Volume2006

Other

Other2006 TMS Annual Meeting
CountryUnited States
CitySan Antonio, TX
Period3/12/063/16/06

All Science Journal Classification (ASJC) codes

  • Condensed Matter Physics
  • Mechanics of Materials
  • Metals and Alloys

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