Potential Range, Choice

Choice of an appropriate reference electrode remains an enigma for non-corrosion-aware personnel-although commercially available polarisation-resistance probes can be adapted. An interesting aspect concerns localised corrosion in that, for some materials, localised corrosion only occurs within characteristic potential ranges. 

Electrochemical measurements are commonly carried out in a medium that consists of solvent containing a supporting electrolyte. The choice of the solvent is dictated primarily by the solubility of the analyte and its redox activity, and by solvent properties such as the electrical conductivity, electrochemical activity, and chemical reactivity. The solvent should not react with the analyte (or products) and should not undergo electrochemical reactions over a wide potential range. 

Before mentioning some more literature data on non-aqueous voltammetry, we suggest on the basis of our previous discussions that the choice of the experimental conditions used in the techniques must be a compromise between a sufficient solubility of the analyte in the solution, an ample redox potential range of the solvent, a suitable type of indicator electrode and adequate conductance of the solution with supporting electrolyte added. In this connection Fig. 4.20 may be a useful guide. 

The choice of new complexes was guided by some simple considerations. The overall eel efficiency of any compound is the product of the photoluminescence quantum yield and the efficiency of excited state formation. This latter parameter is difficult to evaluate. It may be very small depending on many factors. An irreversible decomposition of the primary redox pair can compete with back electron transfer. This back electron transfer could favor the formation of ground state products even if excited state formation is energy sufficient (13,14,38,39). Taking into account these possibilities we selected complexes which show an intense photoluminescence (0 > 0.01) in order to increase the probability for detection of eel. In addition, the choice of suitable complexes was also based on the expectation that reduction and oxidation would occur in an appropriate potential range. 

The guiding criterion for the choice of a working electrode is that it must be made of a redox-inert material, at least in the potential range of interest. 

Choice of electrode materials depends usually on potential range in the solvent being studied and available purity. In the case of hydrodynamic electrodes, we also have to consider carefully the ease of machining in order to conform to the shapes and forms required by the theoretical equations. 

The choice of an electrode material depends to a great extent on the useful potential range of the electrode in the particular solvent employed and the qualities and purity of the material. The usable potential range is limited by one or more of the following factors ... 

Electrolysis can occur only at the boundary between an electrode and a medium that conducts the electric current, and the nature of the solvent is important for the course of electrolytic reactions. Such factors as proton activity, usable potential range, dielectric constant, ability to dissolve electrolytes and substrates, ion pair formation, accessible temperature range, vapor pressure, viscosity, toxicity, and price must be taken into consideration when the choice of solvent is made. 

Electrochemical polymerization is often used to prepare redox active polymer films on electrode surfaces (27). This technique has the advantage that a wide variety of conducting substrates can be used, and that film thickness can be directly controlled by the electrochemical potential scan rate, the potential range, polymerization time, and the choice of monomer concentration and electrolyte solution. 

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