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Title: Reactivity enhancement of oxide skins in reversible Ti-doped NaAlH{sub 4}

The reversibility of hydrogen sorption in complex hydrides has only been shown unambiguously for NaAlH{sub 4} doped with transition metal compounds. Despite a multitude of investigations of the effect of the added catalyst on the hydrogen sorption kinetics of NaAlH{sub 4}, the mechanism of catalysis remains elusive so far. Following the decomposition of TiCl{sub 3}-doped NaAlH{sub 4} by in-situ X-ray photoelectron spectroscopy (XPS), we link the chemical state of the dopant with those of the hydride and decomposition products. Titanium and aluminium change their oxidation states during cycling. The change of the formal oxidation state of Al from III to zero is partly due to the chemical reaction from NaAlH{sub 4} to Al. Furthermore, aluminium oxide is formed (Al{sub 2}O{sub 3}), which coexists with titanium oxide (Ti{sub 2}O{sub 3}). The interplay of metallic and oxidized Ti with the oxide skin might explain the effectiveness of Ti and similar dopants (Ce, Zr…)
Authors:
;  [1] ;  [2] ;  [1] ;  [3]
  1. Laboratory for Hydrogen and Energy, Swiss Federal Laboratories for Materials Science and Technology, Überlandstrasse 129, CH-8600 Dübendorf (Switzerland)
  2. Laboratory for Nanoscale Materials Science, Swiss Federal Laboratories for Materials Science and Technology, Überlandstrasse 129, CH-8600 Dübendorf (Switzerland)
  3. (EPFL), Institut des Sciences et Ingénierie Chimiques, CH-1015 Lausanne (Switzerland)
Publication Date:
OSTI Identifier:
22420209
Resource Type:
Journal Article
Resource Relation:
Journal Name: AIP Advances; Journal Volume: 4; Journal Issue: 12; Other Information: (c) 2014 Author(s); Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; ALUMINIUM; ALUMINIUM HYDRIDES; ALUMINIUM OXIDES; CATALYSIS; CATALYSTS; CHEMICAL STATE; DECOMPOSITION; DOPED MATERIALS; HYDROGEN; KINETICS; SORPTION; TITANIUM; TITANIUM CHLORIDES; TITANIUM OXIDES; X-RAY PHOTOELECTRON SPECTROSCOPY