Cyclic voltammetry reaction order approach

Cyclic voltammetry was carried out in the presence of penta- and hexacyano-ferrate complexes in order to probe the homogeneity and conductivity of the TRPyPz/CuTSPc films (125), (Fig. 36). When the potentials are scanned from 0.40 to 1.2 V in the presence of [Fe (CN)6] and [Fe CN)5(NH3)] complexes, no electrochemical response was observed at their normal redox potentials (i.e., 0.42 and 0.33 V), respectively. However, a rather sharp and intense anodic peak appears at the onset of the broad oxidation wave, 0.70 V. The current intensity of this electrochemical process is proportional to the square root of the scan rate, as expected for a diffusion-controlled oxidation reaction at the modified electrode surface. The results are consistent with an electrochemical process mediated by the porphyrazine film, which act as a physical barrier for the approach of the cyanoferrate complexes from the glassy carbon electrode surface. 

Typical steady-state tip and substrate current approach curves for the oxidation of different concentrations of ArCT are shown in Figure 23. A general observation is that as the concentration of ArCT increases, the tip and substrate currents—at a particular distance—decrease, due to the second-order nature of the follow-up chemical reaction. The experimental approach curves are shown alongside theoretically derived curves for a spread of normalized rate constants, K2, from which it can be seen that there is reasonable agreement between the observed and predicted trends. From measurements of both feedback currents, for all three ArCT concentrations investigated, and collection efficiencies, for the lowest two concentrations, a radical dimerization rate constant of 1.2 ( 0.3) X 10s M 1 s 1 was determined (5), which was in reasonable agreement with that determined earlier using fast scan cyclic voltammetry (36). 

Of the three SECM modes that can be used to study electrode reaction mechanisms—the TG/SC, feedback, and SG/TC modes—the former is the most powerful for measuring rapid kinetics. With this approach, fast followup and sandwiched chemical reactions can be characterized under steady-state conditions, which are difficult to study even with rapid transient techniques such as fast scan cyclic voltammetry or double potential step chronoamperometry, where extensive corrections for background currents are often mandatory (44). At present, first- and second-order rate constants up to 105 s 1 and 1010 M 1 s, respectively, should be measurable with SECM. The development of smaller tip and substrate electrodes that can be placed closer together should facilitate the detection and characterization of electrogenerated species with submirosecond lifetimes. In this context, the introduction of a fabrication procedure for spherical UMEs with diameters... 

The redox reactions for supported BLMs containing vinylferrocene as an electron mediator have been investigated using cyclic voltammetry. The results have shown the following, (i) Ferrocene can be very easily immobilized in the lipid bilayer on the surface of a metallic wire (s-BLM) system. This demonstrates that the s-BLM system offers a novel approach to electrode modification by simple immobilization of compounds within BLM. (ii) Ferrocene in a BLM increases the sensitivity to the potassium ferri/ferrocyanide ion by about two orders of magnitude in comparison to that of the platinum electrode [79]. 

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