Topological and Electron-Transfer Properties of the 2-Thiobarbituric Acid Adlayer on Polycrystalline Gold Electrodes
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- 作者：Eduardo Mé ; ndez ; Michael Wö ; rner ; Carol Lages ; Marí ; a F. Cerdá
- 刊名：Langmuir
- 出版年：2008
- 出版时间：May 6, 2008
- 年：2008
- 卷：24
- 期：9
- 页码：5146 - 5154
- 全文大小：149K
- 年卷期：v.24,no.9(May 6, 2008)
- ISSN：1520-5827
文摘
The voltammetric behavior of [Ru(NH3)6]3+ on bare gold and that on 2-thiobarbituric acid (TBA)-modified goldsurfaces are almost identical, with formal rate constants for the electron-transfer process of 0.25 and 0.21 cm s-1,respectively. A detailed analysis of the modified surface allowed us to establish that this behavior is due to (i) a highsurface coverage of 0.67, (ii) a low adsorption resistance that minimizes the potential drop across the TBA monolayer,(iii) the enhanced hydrophilic character of the modified surface compared with that of bare gold, and (iv) a low decayconstant for the electronic coupling of the TBA adlayer that minimizes the tunneling barrier for the electron transfer.The electron-transfer process from Au and Au
TBA electrodes to the soluble [Ru(NH3)6]3+/2+ redox couple can beexplained according to the multistate model under the Landau-Zener formalism in the nonadiabatic regime that wasrecently proposed (Feldberg, S. W.; Sutin, N. Chem. Phys. 2006, 324, 216-225). The behavior of soluble[Ru(NH3)6]3+ changes from semi-infinite linear diffusion on Au to finite-length bounded on AuTBA, in agreementwith a surface dimension of 2.17 for the TBA adlayer with a bidimensional underlying gold surface. This value forthe surface dimension was determined by two essentially different electrochemical techniques with different sensingcapabilities: cyclic voltammetry and electrochemical impedance spectroscopy. The estimated dielectric constant ofthe adlayer (around 37) and the low potential drop across the monolayer suggest the formation of a "mirror" patternof water molecules in the diffusion layer, which explains this result.
TBA electrodes to the soluble [Ru(NH3)6]3+/2+ redox couple can beexplained according to the multistate model under the Landau-Zener formalism in the nonadiabatic regime that wasrecently proposed (Feldberg, S. W.; Sutin, N. Chem. Phys. 2006, 324, 216-225). The behavior of soluble[Ru(NH3)6]3+ changes from semi-infinite linear diffusion on Au to finite-length bounded on AuTBA, in agreementwith a surface dimension of 2.17 for the TBA adlayer with a bidimensional underlying gold surface. This value forthe surface dimension was determined by two essentially different electrochemical techniques with different sensingcapabilities: cyclic voltammetry and electrochemical impedance spectroscopy. The estimated dielectric constant ofthe adlayer (around 37) and the low potential drop across the monolayer suggest the formation of a "mirror" patternof water molecules in the diffusion layer, which explains this result.