Working Electrode Surface Area

Electrolytic efficiency (represented by analyte peak current) and noise as a function of the working electrode surface area is shown in Figure 3-7. 

Signal and noise as a function of working electrode surface area... 

Cells are classified according to how the working electrode is positioned relative to the flow stream. There are three major configurations tubular, thin layer, and wall jet. The tubular cell (open or packed) with its greater working electrode surface area is used for coulometric detection. The thin layer and wall jet designs are used for amperometric detector cells. In thin layer cells, the eluent flow is in the same plane as... 

N being the number of modules and S the working electrode surface area in m. The factors a and a depend on electrode materials and the materials... 

The value of Eff is affected by many experimental conditions other than the electrolyte and anode materials. The experimental conditions include such factors as the cell configuration, electrode orientation, electrode surface area, working electrode substrate, charge-discharge currents, charge quantity, and amount of electrolyte. 

Similar to the experiments carried out at palladium electrodes and described in Chapter3, the concentration of electrolyte (c), the electrode surface area (A) and the distance between the electrodes (d) will be studied as a function of type of textile structure. In this work, three structures will be studied knitted, woven and non-woven textile structures, all obtained from stainless-steel fibres. To complete the data of this work, palladium sheets will also be inserted in the study as a fourth set of electrodes. Therefore, for palladium electrodes, the work described in section 9.2 will actually be repeated here in order to have a direct comparison between results obtained with palladium electrodes and textile electrodes. Of course, correlation with the data obtained in section 9.2 will be verified. 

The microelectrode is a class of working electrodes that has increased in popularity since the 1980s and is used mainly by electroanalytical chemists. These electrodes have improved time resolution for electrochemical reactions, and can function in higher resistance solutions. Diffusion is treated as hemispherical as the electrode surface area is more like a point than a plane as is the case with macroelectrodes. Typically microelectrodes are difficult to construct and have cross sections on the order of 5 J,m. 

Spectroelectrochemistry has become a valued technique coupling spectroscopy and electrochemistry. Spectroelectrochemistry is a bulk electrochemical technique and as such many of the cell requirements discussed above that pertain to BE apply for spectroelectrochemistry. Often concentrations for spectroelectrochemistry are much lower than most electrochemical techniques due to the spectroscopic absorbance requirements. The bulk solution must still be oxi-dized/reduced in spectroelectrochemistry. Large surface area working and auxiliary electrodes are employed as in the bulk methods described above. Cells designed with optically transparent electrodes like thin films of Sn02 or In203 or optically transparent mesh electrodes are employed, otherwise the electrode must be manually removed to record spectra. Optically transparent electrodes can be constructed such that the solution volume to electrode surface area ratio is very small making the BE occm rapidly. 

Auxiliary electrode placement is not usually a problem with small electrodes and low currents, as in voltammetric experiments, but it is of critical importance in bulk electrolysis cells. With large electrodes and an asymmetrically placed auxiliary electrode, the solution resistance is different between the auxiliary and different parts of the working electrode. The varying iR drops along the different current paths produce a nonuniform potential across the working electrode surface, as shown in Figure 11.2.3, and as a consequence there is a nonuniform current density on the working electrode surface. These effects can cause undesired side reactions or ineffective use of the total electrode area. 

---