Topic
XANES
About: XANES is a research topic. Over the lifetime, 7737 publications have been published within this topic receiving 188032 citations.
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TL;DR: In this article, the change in valence states of Ni, Co and Mn of Li[Ni0.17Li0.2Co0.07Mn0.56]O2 during charge-discharge was examined in detail using in situ X-ray absorption spectroscopy (XAS).
168 citations
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TL;DR: Direct specific adsorption of bisulfate anions in H2SO4 is spectroscopically seen in both the EXAFS and XANES data and is seen to impede oxygen adsorbed consistent with previous reports.
Abstract: The adsorption of atomic oxygen and hydroxide on a platinum electrode in 0.1 M HClO4 or H2SO4 electrolytes was studied in situ with Pt L(2,3) X-ray absorption spectroscopy (EXAFS and XANES). The Pt L3 edge absorption data, mu, were collected at room temperature in transmission mode on beamline X-11A at the National Synchrotron Light Source using a custom built cell. The Pt electrode was formed of highly dispersed 1.5-3 nm particles supported on carbon. A novel difference procedure (delta mu = mu(O[H]/Pt) - mu(Pt)) utilizing the L3 XANES spectra at different applied voltages was used to isolate the effects of O[H] (O or OH) adsorption in the XANES spectra. The Deltamu results are compared with results obtained from real-space full-multiple scattering calculations utilizing the FEFF8 code on model clusters. The experimental results, when compared with theoretical calculations, allow the adsorption site to be identified. At low coverages OH adsorbs primarily in 1-fold coordinated atop sites. As the coverage increases, O binds in the bridge/fcc sites, and at still higher coverages above 1.05 V RHE, O adsorbs into a higher coordinated n-fold or subsurface site, which is thought to be the result of Pt-O site exchange and oxide formation. These results are similar to those found in the gas phase. Direct specific adsorption of bisulfate anions in H2SO4 is spectroscopically seen in both the EXAFS and XANES data and is seen to impede oxygen adsorption consistent with previous reports.
167 citations
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TL;DR: In this paper, the authors reported femtosecond time-resolved X-ray absorption near-edge spectroscopy (XANES) measurements of a spin-crossover system, iron(II) tris(2,2′-bipyridine) in water.
Abstract: X-ray free electron lasers (XFELs) deliver short (<100 fs) and intense (∼1012 photons) pulses of hard X-rays, making them excellent sources for time-resolved studies. Here we show that, despite the inherent instabilities of current (SASE based) XFELs, they can be used for measuring high-quality X-ray absorption data and we report femtosecond time-resolved X-ray absorption near-edge spectroscopy (XANES) measurements of a spin-crossover system, iron(II) tris(2,2′-bipyridine) in water. The data indicate that the low-spin to high-spin transition can be modeled by single-exponential kinetics convoluted with the overall time resolution. The resulting time constant is ∼160 fs.
167 citations
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TL;DR: In this paper, high-resolution x-ray photoelectron spectroscopy (XPS) and near-edge X-ray absorption-fine structure (NEXAFS) measurements were carried out on sub-monolayer bi-isonicotinic acid rutile TiO2(110).
Abstract: Bi-isonicotinic acid ~2,28-bipyridine–4,48-dicarboxylic acid! is the ligand of several organometallic
dyes, used in photoelectrochemical applications. Therefore the atomic scale understanding of the
bonding of this molecule to rutile TiO2(110) should give insight into the crucial dye–surface
interaction. High resolution x-ray photoelectron spectroscopy ~XPS!, near edge x-ray absorption
fine structure ~NEXAFS!, and periodic intermediate neglect of differential overlap ~INDO!
calculations were carried out on submonolayer bi-isonicotinic acid rutile TiO2(110). Data from
multilayers is also presented to support the submonolayer results. For a multilayer, XPS shows that
the carboxyl groups remain in the ~pristine! protonated form, and NEXAFS show that the molecular
plane is tilted by 57° with respect to the surface normal. For the submonolayer, the molecule bonds
to the rutile TiO2(110) surface via both deprotonated carboxyl groups, with a tilt angle of 25°, and
additionally an azimuthal orientation of 44° with respect to the @001# crystallographic direction. The
adsorbant system was also investigated by quantum mechanical calculations using a periodic INDO
model. The most stable theoretical adsorption geometry involves a twist around the molecular axis,
such that the pyridine rings are tilted in opposite directions. Both oxygen atoms of each carboxyl
group are bonded to five-fold coordinated Ti atoms ~2M-bidentate!, in excellent agreement with the
experimental results.
167 citations
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TL;DR: In this article, the Ti valence and coordination in Ti-activated sodium alanate was explored using X-ray absorption near edge spectroscopy (XANES) and the Ti K-edge onset was established based on a set of standards.
Abstract: Ti K-edge x-ray absorption near edge spectroscopy (XANES) was used to explore the Ti valence and coordination in Ti-activated sodium alanate. An empirical relationship was established between the Ti valence and the Ti K-edge onset based on a set of standards. This relationship was used to estimate oxidation states of the titanium catalyst in 2 mol% and 4 mol% Ti-doped NaAlH4. These results demonstrate that the formal titanium valence is zero in doped sodium alanate and nearly invariant during hydrogen cycling. A qualitative comparison of the edge fine structure suggests that the Ti is present on the surface in the form of amorphous TiAl3.
166 citations