X-ray Absorption Spectroscopy Studies of the Local Atomic and Electronic Structure of Iron Incorporated into Electrodeposited Hydrous Nickel Oxide Films
| Autor: | C. A. Melendres, Mahalingam Balasubramanian, S. M. Mini |
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| Rok vydání: | 2000 |
| Předmět: | |
| Zdroj: | The Journal of Physical Chemistry B. 104:4300-4306 |
| ISSN: | 1520-5207 1520-6106 |
| DOI: | 10.1021/jp9921710 |
| Popis: | The authors have utilized X-ray absorption fine structure (XAFS) spectroscopy to investigate the local atomic and electronic structure of iron incorporated into electrodeposited nickel hydroxide films. It was found that cathodic codeposition from a solution containing Fe(II) and Ni(II) ions results in iron occupying Ni lattice sites in {alpha}-Ni(OH){sub 2}. The X-ray absorption near edge structure (XANES) shows that Fe is present as Fe(III) ions in the cathodically codeposited film. Analysis of the extended X-ray absorption fine structure (EXAFS) shows that Fe is coordinated to oxygen at {approximately}2.00 {angstrom} and to Ni at {approximately}3.11 {angstrom}. This Fe-O bond length is smaller than the Fe(II)-O bond distance found in Fe(OH){sub 2} ({approximately}2.10 {angstrom}) but is in good agreement with the average Fe(III)-O bond distance found in FeOOH ({alpha}, {gamma}). The Fe-Ni bond distance is in agreement with that of the Ni(II)-Ni(II) bond distance found in {alpha}-Ni(OH){sub 2}. Moreover, the radial structure function (RSF) around Fe shows a distinct peak at {approximately}5.8 {angstrom}, which is a fingerprint of the brucite ({alpha}-Ni(OH){sub 2}) structure. On anodic oxidation of the codeposited film in KOH, the workers found that the Fe ions occupied Ni lattice sites in {gamma}-NiOOH. The XANES shows that the Fe edgemore » shifts to higher energy values, indicating an increase in the oxidation state of Fe on charging. Analysis of the EXAFS data shows that Fe is coordinated to oxygen at {approximately}1.94 {angstrom} and to Ni at {approximately}2.84 {angstrom}. The latter value is in good agreement with the Ni(IV)-Ni(IV) bond length found in {gamma}-NiOOH. The RSF around Fe in the oxidized film shows a distinct peak at {approximately}5.4 {angstrom}, just as in the RSF of Ni in {gamma}-NiOOH. The Fe-O bond distance of {approximately}1.94 {angstrom} is in good agreement with the Fe(IV)-O bond distance found in SrFeO{sub 3}. The results strongly suggest that the Fe ions in the oxidized film are nominally tetravalent but with the Fe-O bond possessing a high degree of covalency.« less |
| Databáze: | OpenAIRE |
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