X-ray adsorption spectroscopy studies of the local atomic and electronic structure of iron incorporated into electrodeposited hydrous nickel oxide films
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 edge 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.
- Research Organization:
- Argonne National Lab., IL (US)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- W-31109-ENG-38
- OSTI ID:
- 20075914
- Journal Information:
- Journal of Physical Chemistry B: Materials, Surfaces, Interfaces, amp Biophysical, Vol. 104, Issue 18; Other Information: PBD: 11 May 2000; ISSN 1089-5647
- Country of Publication:
- United States
- Language:
- English
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