Modified layered oxides curves

Figure 8.4 shows the importance of the coordination mode around the metal ion for the electrochemical properties of the layer. In Fig. 8.4 the mediation of the Fe(II)/(III) oxidation is studied by using a rotating disk electrode. Initially a thin film of [Ru(bipy)2(PVP)5Cl] is used and with this coating the current potential curve I is obtained (see Fig. 8.4b). On photolysis of the coating and formation of the aquocomplex (according to Reaction 5) curve II is obtained. Rotating disk behavior very clearly shows that the redox potential of the modifying layer is of prime importance to the electrochemical properties of the modified electrode.

In the final experiment to be presented h, we modified the oxide layer by HF attack and studied the effect of this treatment on the photoluminescence properties of the sample. The results are summarized in Fig. 5. We started fijom an already passivated sample whose PL spectrum is given by the black solid curve peaking at approximately 775 nm or 1.6 eV. Then the sample was... 

For the same reason, Ru(OOOl) modihcation by Pt monolayer islands results in a pronounced promotion of the CO oxidation reaction at potentials above 0.55 V, which on unmodified Ru(OOOl) electrodes proceeds only with very low reaction rates. The onset potential for the CO oxidation reaction, however, is not measurably affected by the presence of the Pt islands, indicating that they do not modify the inherent reactivity of the O/OH adlayer on the Ru sites adjacent to the Pt islands. At potentials between the onset potential and a bending point in the j-E curves, COad oxidation proceeds mainly by dissociative H2O formation/ OHad formation at the interface between the Ru(OOOl) substrate and Pt islands, and subsequent reaction between OHad and COad- The Pt islands promote homo-lytic H2O dissociation, and thus accelerate the reaction. At potentials anodic of the bending point, where the current increases steeply, H2O adsorption/OHad formation and COad oxidation are proposed to proceed on the Pt monolayer islands. The lower onset potential for CO oxidation in the presence of second-layer Pt islands compared with monolayer island-modified Ru(OOOl) is assigned to the stronger bonding of a double-layer Pt film (more facile OHad formation). 

The SAM consists of a mixture of octadecyl mercaptan (OM) and two short chain disulfides, which form -S-CH2-CH2-CH2-COO" and -S-CH2-CH2-NH3+ on the surface. The short chain, charged modifiers may provide defects, or pockets, in the OM layer where the enzyme may adsorb through electrostatic interactions. At oxidizing potentials, the electrode generates a catalytic current at densities up to about 10 pA/cm when exposed to fructose solution. The enzyme electrode exhibits a response time well under a minute and the calibration curve is linear at fructose concentrations up to 0.8 mM. The biosensor prototype exhibits low susceptibility to positive interference by ascorbic acid indicating that this construct could be useful for fructose analysis of citrus fruit juice. 

The best corrosion protection is achieved by the electrolysis process, as can be seen, for example, by comparing the material consumption per unit area on the five materials investigated in accordance with Figures 40 and 41. From the current density/potential curves plotted, it was found that the protective action by the electrolysis process is based on inhibition of the cathodic part reaction. This is evidently caused by incorporation of aluminium hydroxide into the surface layers which form. This has the effect of a significantly lower conductivity of the surface layer compared with the surface layers otherwise formed from zinc oxide. The studies also showed that the modified zinc layers tested, without the electrolysis method, show a distinctly poorer corrosion behaviour than standard galvanisation according to DIN EN 10240. 

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