Voltammograms, monolayer

The following two pictures (Figure 6.2-8a and b) were acquired at h-500 mV and at -I-450 mV vs. Cu/Cu and show that at h-450 mV vs. Cu/Cu monolayer high Cu clusters nucleate at the steps between different Au terraces. Thus, the pair of shoulders in the cyclic voltammogram is correlated with this surface process. 

F. la-c. Cyclic voltammograms of dissolved and stance confined ferrcx ne in a< tonitrile/0.1 M TBAP. a. 4 X 10 M dissolved ferrocene at Pt. b. 4-ferrocenyl-phenylacetamid monolayer bound to Pt (ref. ). c. Poly-vinylferrocene dip coated on Pt,r = 1 x lO raolcm. Straight arrows indicate diffusional events. Curved arrows electron transfer events (from ref. ). 

FIG. 26 Cyclic voltammograms of 40 monolayers of Langmuir-Schaefer films of cytochrome P450SCC on indium-tin oxide glass plate (ITO) in 10 mM phosphate buffer at a scan rate of 20 mV/s between 0.4 and —0.4 V vs. Ag/AgCl. LS films on ITO worked as the working electrode, platinum as the counter, and Ag/AgCl as the reference electrode. Cholesterol dissolved in X-triton 100 was added 50 p.1 at a time (1) with cholesterol, (2) 50 p.1 of cholesterol, (3) 100 p.1 cholesterol, and (4) 150 p.1 of cholesterol. 

Figure 9. Cyclic voltammogram of Fe-TsPc adsorbed on Vulcan XC-72 at monolayer coverages. This measurement was obtained with the material In the form of a thin porous coating. Scan rate 50 mV s. Other conditions are the same as those In caption of Fig. 6.

The additivity principle was well obeyed on adding the voltammograms of the two redox couples involved even though the initially reduced platinum surface had become covered by a small number of underpotential-deposited mercury monolayers. With an initially anodized platinum disk the catalytic rates were much smaller, although the decrease was less if the Hg(I) solution had been added to the reaction vessel before the Ce(lV) solution. The reason was partial reduction by Hg(l) of the ox-ide/hydroxide layer, so partly converting the surface to the reduced state on which catalysis was greater. 

In an ideal case the electroactive mediator is attached in a monolayer coverage to a flat surface. The immobilized redox couple shows a significantly different electrochemical behaviour in comparison with that transported to the electrode by diffusion from the electrolyte. For instance, the reversible charge transfer reaction of an immobilized mediator is characterized by a symmetrical cyclic voltammogram ( pc - Epa = 0 jpa = —jpc= /p ) depicted in Fig. 5.31. The peak current density, p, is directly proportional to the potential sweep rate, v ... 

Fig. 5.31 Cyclic voltammogram of a chemically modified electrode with a monolayer of a reversible mediator. The shaded area corresponds to the charge Q...

Why do we believe that a Cu monolayer is inserted between SAM and gold substrate The 2D-deposit grows and dissolves extremely slowly. Another indication is that the 2D deposit is very stable and shows no displacement by the scanning tip. Cu clusters on top of an alkanethiol-SAM would be only weakly bound and should be easily pushed away by the tip at higher tunnel currents, very much like metal clusters on a hydrogen-terminated Si(lll) surface, which for that very reason are difficult to image by STM (or AFM [122]). And finally, the cyclic voltammograms (Fig. 33) point to the formation of a buried monolayer . 

Figure 27b shows typical voltammograms of monolayers of three PBI derivatives on Au (111). The two reduction peaks merge into a single broad peak, due to specific solvent-PBI interactions, as well as the possibility of incorporating cations of the supporting electrolyte into the charged PBI adlayers. The peak-to-peak... 

The cyclic voltammogram for a silver electrode in 0.1M LiC104 acetonitrile solution is shown in Figure 1 (curve a). At a potential of -1.5 V, cathodic current due to the reduction of Li+ ions commences. The upd of lithium has been reported previously by Kolb et al. for positive potential sweeps after substantial lithium reduction (i) however, due to the reactivity of the metallic lithium with impurities in solution, the adsorbed layer formed on the negative potential sweep is not as stable as other upd monolayers (i). An additional cathodic wave due to the reduction of lithium is observed at approximately -2.5V, and on the return sweep the lack of an anodic wave is indicative of the reactivity of the chemisorbed atoms. 

Mixed monolayers. An electrode coated with a mixed monolayer of ClsSH and C18bpyMe2+ exhibits a surface redox wave assignable to the reduction of the bipyridinium to the radical cation (Figure 1) (in all 3 figures the cyclic voltammograms at 0.1 V/s (solid line), 1 V/s (dashed line) and 10 V/s (dotted line) are plotted with the current axis scaled in proportion to the scan rate). A second reduction wave at -0.9 V (not shown) is obscured by increasing background currents. The electrochemical parameters for the surface... 

Further experiments with the coated electrode suggests that the surfactant bipyridiniums are mobile within the mercaptan monolayer. If the electrode is transferred to a fresh electrolyte, the coverage (measured at 0.1 V/s) greatly diminishes. Likewise rinsing the coated electrode with a stream of pure water between cyclic voltammograms removes most of the electroactive bipyridiniums. 

Figure 1. Cyclic voltammograms of a mixed monolayer of ClsSH + (ciebpyMe)Cl2.

Figure 3. Cyclic voltammograms of CiebpyMe2 adsorbed from solution on a gold electrode coated with a CieSH monolayer.

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