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Measurement of apparent diffusion coefficients within ultrathin Nafion Langmuir-Schaefer films: Comparison of a novel scanning electrochemical microscopy approach with cyclic voltammetry
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Bertoncello, Paolo, Ciani, Ilenia, Li, Fei and Unwin, Patrick R. (2006) Measurement of apparent diffusion coefficients within ultrathin Nafion Langmuir-Schaefer films: Comparison of a novel scanning electrochemical microscopy approach with cyclic voltammetry. LANGMUIR, 22 (25). pp. 10380-10388. doi:10.1021/la061214i ISSN 0743-7463.
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Official URL: http://dx.doi.org/10.1021/la061214i
Abstract
The use of scanning electrochemical microscopy (SECM) to evaluate the apparent diffusion coefficient, Dapp, of redox-active species in ultrathin Nafion films is described. In this technique, an ultramicroelectrode (UME) tip, positioned close to a film on a macroscopic electrode, is used to oxidize (or reduce) a species in bulk solution, causing the tip-generated oxidant (reductant) to diffuse to the film/solution interface. The oxidation ( reduction) of film-confined species regenerates the reductant (oxidant) in solution, leading to feedback to the UME. A numerical model is developed that allows Dapp to be determined. For these studies, ultrathin films of Nafion were prepared using the Langmuir-Schaefer (LS) technique and loaded with an electroactive species, either the ferrocene derivative ferrocenyltrimethylammonium cation, FA(+), or tris(2,2(')- bipyridyl) ruthenium(II), Ru(bpy)(3)(2+). The morphology and the thickness of the Nafion LS films (1.5 +/- 0.2 nm per layer deposited) were evaluated using atomic force microscopy (AFM). For comparison with the SECM measurements, cyclic voltammetry (CV) was employed to evaluate the concentration of electroactive species within the Nation LS films and to determine Dapp. The latter was found to be essentially invariant with film thickness, but the value for Ru(bpy)(3)(2+) was 1 order of magnitude larger than for FA(+). CV and SECM measurements yield different values of D-app, and the underlying reasons are discussed. In general, the D-app values for these films are considerably smaller than for recast Nafion films, which can be attributed to the compactness of Nafion LS films. Nonetheless, the ultrathin nature of the films leads to fast response times, and we thus expect that these modified electrodes could find applications in sensing, electroanalysis, and electrocatalysis.
| Item Type: | Journal Article | ||||
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| Subjects: | Q Science > QD Chemistry T Technology > TA Engineering (General). Civil engineering (General) |
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| Journal or Publication Title: | LANGMUIR | ||||
| Publisher: | AMER CHEMICAL SOC | ||||
| ISSN: | 0743-7463 | ||||
| Official Date: | 5 December 2006 | ||||
| Dates: |
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| Volume: | 22 | ||||
| Number: | 25 | ||||
| Number of Pages: | 9 | ||||
| Page Range: | pp. 10380-10388 | ||||
| DOI: | 10.1021/la061214i | ||||
| Publication Status: | Published |
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