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Evolution of an Oxygen Near-Edge X-ray Absorption Fine Structure Transition in the Upper Hubbard Band in alpha-Fe2O3 upon Electrochemical Oxidation

Bora, Debajeet K. and Braun, Artur and Erat, Selma and Ariffin, Ahmad K. and Loehnert, Romy and Sivula, Kevin and Toepfer, Joerg and Graetzel, Michael and Manzke, Recardo and Graule, Thomas and Constable, Edwin C.. (2011) Evolution of an Oxygen Near-Edge X-ray Absorption Fine Structure Transition in the Upper Hubbard Band in alpha-Fe2O3 upon Electrochemical Oxidation. Journal of Physical Chemistry C, 115 (13). pp. 5619-5625.

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Official URL: http://edoc.unibas.ch/dok/A6056205

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Abstract

Electrochemical oxidation of hematite (alpha-Fe2O3) nanoparticulate films at 600 mV vs Ag+/AgCl in KOH electrolyte forms a species at the hematite surface which causes a new transition in the upper Hubbard band between the Fe(3d)-O(2p) state region and the Fe(4sp)-O(2p) region, as evidenced by oxygen near-edge X-ray absorption fine structure (NEXAFS) spectra. The electrochemical origin of this transition suggests that it is related to a surface state. This transition, not previously observed for pristine alpha-Fe2O3, is at about the same X-ray energy as that of 196 Si-doped Si: Fe2O3. The occurrence of this state coincides with the onset of an oxidative dark current wave at around 535-mV a potential range where the tunneling exchange current has been previously reported to increase by 3 orders of magnitude with the valence band and the transfer coefficient by a factor of 10. Oxidation to only 200 mV does not form such an extra NE.XAFS feature, suggesting that a critical electrochemical potential between 200 and 600 mV is necessary to change the electronic structure of the iron oxide at the surface. A decrease of the surface roughness, as suggested by visual inspection, profilometry, and X-ray reflectivity, points to faceting as the potential structural origin of the surface state.
Faculties and Departments:05 Faculty of Science > Departement Chemie > Chemie > Anorganische Chemie (Constable)
UniBasel Contributors:Constable, Edwin Charles
Item Type:Article, refereed
Article Subtype:Research Article
Publisher:American Chemical Society
ISSN:1932-7447
e-ISSN:1932-7455
Note:Publication type according to Uni Basel Research Database: Journal article
Identification Number:
Last Modified:08 May 2017 07:18
Deposited On:01 Feb 2013 08:40

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