2011
DOI: 10.1039/c0cp01472a
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X-Ray spectroscopy of electrochemically deposited iridium oxide films: detection of multiple sites through structural disorder

Abstract: We report the results of X-ray absorption spectroscopy studies on electrochemically deposited iridium oxide films. The emphasis of the study is the correlation of X-ray derived structural data with electrochemically controlled charge state. Data were acquired for films subject to redox cycling in neutral and alkaline aqueous media. In both cases, cyclic voltammetric responses show two redox couples, coulometrically of roughly equal magnitude. Assays of the iridium population (based on the iridium L(3) absorpti… Show more

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Cited by 76 publications
(90 citation statements)
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“…Fast changes of the Ir partial oxidation state as a function of potential are well-known for electrochemically formed iridium oxide films 30 and for sputtered iridium oxide films 31 in the potential range below OER onset and are generally interpreted in terms of proton insertion/extraction into/from the bulk of the iridium oxide film. However, this proton intercalation process is suppressed for thermally prepared crystalline iridium oxides as used in our study, which is in good agreement with our observation of a constant electron density at Ir centers at potentials below OER onset.…”
Section: Resultsmentioning
confidence: 99%
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“…Fast changes of the Ir partial oxidation state as a function of potential are well-known for electrochemically formed iridium oxide films 30 and for sputtered iridium oxide films 31 in the potential range below OER onset and are generally interpreted in terms of proton insertion/extraction into/from the bulk of the iridium oxide film. However, this proton intercalation process is suppressed for thermally prepared crystalline iridium oxides as used in our study, which is in good agreement with our observation of a constant electron density at Ir centers at potentials below OER onset.…”
Section: Resultsmentioning
confidence: 99%
“…The intensity of the white line peak is generally interpreted as a measure of the number of vacant Ir dstates and thus of the Ir partial oxidation state (charge density around Ir centers). [30][31][32] Therefore, an increase of the white line peak intensity is an indication of the removal of electronic charge from the Ir sites with increasing potentials starting at the onset of OER.…”
Section: Resultsmentioning
confidence: 99%
“…In fact, our in situ study is the first that has attempted to observe directly the oxidation states of Ru and Ir during electrocatalysis under OER conditions: previous mechanistic studies of ruthenium and iridium oxides have inferred changes in oxidation state indirectly from electrochemical data, [3] and earlier in situ XAFS studies used lower applied potentials. [9,15] Our results reveal that in mixed ruthenium-iridium oxides both metals can contribute to the electrocatalytic activity and, indeed, show a cooperative effect that is compositiondependent. By this observation we have confirmed directly that the pyrochlore materials are atomically well-mixed phases and offer greater activity than a commercially available benchmark material.…”
Section: And D)mentioning
confidence: 87%
“…[12] They suggested that for oxide Pb 2 (Pb,Ir) 2 O 7Àd the displacement of surface hydroxide ions, linked to Pb, by superoxide anions maintains the octahedral coordination, but allows oxygen evolution by the Ir 4+ /Ir 5+ couple through exchange of surface "O À " species. Recent work on iridium oxide films has used X-ray spectroscopy to examine local structure under moderate electrochemical potential and revealed the possibility of multiple Ir sites contributing to redox activity [15] and surface reactivity, [16] whereas for IrO x dispersed in solution the oxidation of Ir to the + 7 state has been proposed in water oxidation under basic conditions from conventional electrochemical measurements. [17] Our new in situ data are therefore more consistent with the Ir 4+ /Ir 5+ model of Goodenough and co-workers, rather than with models that involve the oxidation of the precious metals to higher oxidation states than + 5.…”
Section: And D)mentioning
confidence: 99%
“…However, the deconvolution of Ir 4f region is more complex due to presence of a series of Ir oxides. Since it has been proved that the L 3 edge shift of octahedral Pt-O bonding is 0.7 eV per formal charge and it could be promoted to other noble elements [38][39][40], in the case of only oxygen to be the ligand, the Ir 4f 7/2 region is deconvoluted into three peaks : 60.8 to 61.2 eV for Ir (0), 61.8 to 62.3 eV for IrO 2 [Ir(IV)], and 62.7 to 63.3 eV for IrO x [mostly Ir(VI)], respectively, and the bonding energies of 4f 5/2 region are about 2.98 eV higher [36,41].…”
Section: Structure and Composition Characterization Of Ir-pd Alloy Namentioning
confidence: 99%