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Comparison of V[sub 2]O[sub 5] Xerogels Prepared by the Vanadate and Alkoxide Routes Using X-Ray Absorption and other Methods

2003; Institute of Physics; Volume: 150; Issue: 6 Linguagem: Inglês

10.1149/1.1571534

1945-7111

Gregory P. Holland, Fritz Huguenin, Roberto M. Torresi, Daniel A. Buttry,

Gas Sensing Nanomaterials and Sensors

X-ray absorption near edge spectroscopy (XANES), Brunauer-Emmett-Teller surface area, Fourier transform infrared (FTIR), and thermogravimetric analysis were used to characterize two xerogels of prepared using the vanadate hydrolysis (i.e., the material) or the vanadyl tris(isopropoxide) hydrolysis (i.e., the material) synthetic routes. XANES spectra were obtained and analyzed for samples at varying degrees of lithiation that were either bathed in 0.5 M carbonate (PC) supporting electrolyte (i.e., in situ) or from which the solvent had been removed by treatment under high vacuum (i.e., ex situ), as judged by FTIR analysis. The pre-edge, main edge, and edge resonance peak intensities were examined to track the symmetry around the vanadium center. The results for the in situ samples made by both synthetic routes showed that the local symmetry around vanadium did not change significantly for x values ranging from 0 to 0.98, where x represents the degree of reduction in the formulation For the ex situ samples, substantial distortion was observed on going from either the hydrated or PC-swollen states to states in which solvent was absent. Further, the XANES spectrum for an unlithiated ex situ material showed very substantial distortion around vanadium compared to the material, presumably due to the rapidity of polymerization in the alkoxide synthetic procedure. The galvanostatic intermittent titration technique was used to obtain the apparent diffusion coefficient in both materials, revealing diffusion in the material that appeared to be more than two orders of magnitude faster than in the material. The origin of that observation is discussed. © 2003 The Electrochemical Society. All rights reserved.