Novel XAS Techniques for Probing Fuel Cells and Batteries

Dynamics of Reactive Species and Reactant-Induced Reconstruction of Pt Clusters in Pt/Al2O3Catalysts

“…22,27−42 Most of the analyses are based on subtracting the Pt L 3 -edge spectrum of the catalyst in the absence of adsorbed hydrogen (μ(Pt)) from those in the presence of adsorbed hydrogen (μ(Pt−H)), also known as the ΔXANES approach. 43 The resulting difference spectra Δμ = μ(Pt−H)−μ(Pt) contain several features that have been ascribed to specific geometry of the adsorption site on the basis of DFT calculations, although bridged (twofold coordinated) and hollow (threefold coordinated) sites cannot be distinguished. 18,32,35 On the basis of the ΔXANES approach, Koningsberger's group proposed a three-site model for hydrogen adsorption on small Pt particles (coordination number N Pt−Pt < 6.5).…”

“…Part of the difficulty is associated with the intrinsic complexity of nanosized noble metal clusters. − In the last decades a large amount of experimental evidence demonstrated that the Pt clusters undergo electronic and morphological reconstruction as a function of the support, of the adsorbate, and of the reaction temperature. ,− Pt L 3 -edge XAS spectroscopy (in both XANES and EXAFS regions) has been one of the main techniques employed to investigate the structural and electronic changes experienced by nanometric Pt particles supported on different materials in the presence of hydrogen. As far as the XANES region is concerned, it has been observed that H 2 adsorption on small Pt particles causes dramatic changes in the spectra: the “white line” intensity decreases and the spectra broaden to higher energy as hydrogen is added. ,− ,− There have been many efforts to interpret these effects, which are due to both electronic and geometric phenomena. ,− Most of the analyses are based on subtracting the Pt L 3 -edge spectrum of the catalyst in the absence of adsorbed hydrogen (μ­(Pt)) from those in the presence of adsorbed hydrogen (μ­(Pt–H)), also known as the ΔXANES approach . The resulting difference spectra Δμ = μ­(Pt–H)−μ­(Pt) contain several features that have been ascribed to specific geometry of the adsorption site on the basis of DFT calculations, although bridged (twofold coordinated) and hollow (threefold coordinated) sites cannot be distinguished. ,, On the basis of the ΔXANES approach, Koningsberger’s group proposed a three-site model for hydrogen adsorption on small Pt particles (coordination number N Pt–Pt < 6.5) .…”

New Features Observed in Self-Absorption-Corrected X-ray Fluorescence Spectra for Ni Complexes with Uncertainties

“…Previous investigations of these distortions in fluorescence spectra of XAFS required knowledge of the sample stoichiometry or the energy dependence of the absorption coefficients, or making a series of measurements at multiple angles . Major surveys and developments have been made in this area by many researchers in pure and applied chemistry, , biological and medical science, and earth sciences and engineering. , …”