Electrolysis auxiliary electrode

In the controlled (constant) potential method the procedure starts and continues to work with the limiting current iu but as the ion concentration and hence its i, decreases exponentially with time, the course of the electrolysis slows down quickly and its completion lags behind therefore, one often prefers the application of a constant current. Suppose that we want to oxidize Fe(II) we consider Fig. 3.78 and apply across a Pt electrode (WE) and an auxiliary electrode (AE) an anodic current, -1, of nearly the half-wave current this means that the anodic potential (vs. an RE) starts at nearly the half-wave potential, Ei, of Fe(II) - Fe(III) (= 0.770 V), but increases with time, while the anodic wave height diminishes linearly and halfway to completion the electrolysis falls below - / after that moment the potential will suddenly increase until it attains the decomposition potential (nearly 2.4 V) of H20 -> 02. The way to prevent this from happening is to add previously a small amount of a so-called redox buffer, i.e., a reversible oxidant such as Ce(IV) with a standard... 

The working electrode is kept at zero potential by connecting it to the virtual ground of the electronics. A counter electrode CE (auxiliary electrode ae) is used to regulate the potential difference between the reference electrode and the working electrode, necessary for electrolysis of the analyte. 

Pairs of platinum plate (2x5 cm) were set in a cell with 1 mm spacing as the working and the auxiliary electrode (Figure 2). Reference electrode was Ag/AgCl. The solution (50 ml) of phenol (0.005 mol) and electrolyte (0.01 mol) such as tetraethylammonium bromide and tetraethylammonium perchrolate was kept under nitrogen atmosphere in the cell. The electrolysis was carried out with constant potential or current density (10 mA/cm2) which was supplied by a potentiogalva-... 

Controlled-potential electrolysis is conducted in a three-electrode cell in which the potential of the working electrode is measured with respect to a reference electrode to which negligible current flows. Current flows between the working and auxiliary electrodes. 

Another important feature of the cell is that the positions of R and W must remain fixed to avoid changes in the resistance. Furthermore, W should have a small surface to insure that the extent of electrolysis during the experiments has a negligible effect on the solution composition. When this is the case, separate compartments for the working and auxiliary electrodes is an unnecessary complication. 

Figure 22.8 Schematic representation of an electrolysis cell (three-electrode construction W = working electrode AUX = auxiliary electrode R = reference electrode Q = coulometer D = diaphragm, if necessary CS = current source A = amperometer V = voltmeter).

An electrochemical detector is destructive. It requires (1) a working electrode (where oxidation or reduction takes place), (2) an auxiliary electrode, and (3) a reference electrode (to regulate voltage and compensate for changes in background conductivity of the eluent). When an active substance flows into the electrochemical cell and a potential difference is applied between the working and reference electrodes, the electrolysis of the analyte yields a current (detector signal) that is a function of the applied potential. The three steps in the process are ... 

The electrodes for BE methods are important for efficient electrolysis. The working and auxiliary electrodes are required to electrolyze much more of the sample in these BE techniques. The working and auxiliary electrodes... 

Figure 15 H-cell for bulk electrolysis showing the working and auxiliary electrodes, reference electrode, bubbler, porous glass frit, solvent, electrolyte, and analyte...

The setup for this experiment is indicated in the block diagram of Fig. 1. The working-electrode compartment and the auxiliary-electrode compartments are physically separated (by a frit or other such device) to avoid unwanted mixing of cathode- and anode-electrolysis products. During the experiment either the electrolysis current, i, the... 

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