An analysis of the cell theory

It goes something like this:

An analysis of the cell theory

Potential as a function of time for anodic stripping voltammetry Three-electrode setup: Voltammetry is the study of current as a function of applied potential. The potential is varied arbitrarily either step by step or continuously, and the actual current value is measured as the dependent variable.

The shape of the curves depends on the speed of potential variation nature of driving force and on whether the solution is stirred or quiescent mass transfer.

Voltammetry - Wikipedia

Most experiments control the potential volts of an electrode in contact with the analyte while measuring the resulting current amperes. The working electrodewhich makes contact with the analyte, must apply the desired potential in a controlled way and facilitate the transfer of charge to and from the analyte.

A second electrode acts as the other half of the cell. This second electrode must have a known potential with which to gauge the potential of the working electrode, furthermore it must balance the charge added or removed by the working electrode.

While this is a viable setup, it has a number of shortcomings. Most significantly, it is extremely difficult for an electrode to maintain a constant potential while passing current to counter redox events at the working electrode. To solve this problem, the roles of supplying electrons and providing a reference potential are divided between two separate electrodes.

The reference electrode is a half cell with a known reduction potential. Its only role is to act as reference in measuring and controlling the working electrode's potential and at no point does it pass any current.

The auxiliary electrode passes all the current needed to balance the current observed at the working electrode. To achieve this current, the auxiliary will often swing to extreme potentials at the edges of the solvent windowwhere it oxidizes or reduces the solvent or supporting electrolyte.

These electrodes, the workingreferenceand auxiliary make up the modern three electrode system. There are many systems which have more electrodes, but their design principles are generally the same as the three electrode system.

For example, the rotating ring-disk electrode has two distinct and separate working electrodes, a disk and a ring, which can be used to scan or hold potentials independently of each other.

An analysis of the cell theory

Both of these electrodes are balanced by a single reference and auxiliary combination for an overall four electrode design. More complicated experiments may add working electrodes as required and at times reference or auxiliary electrodes. In practice it can be important to have a working electrode with known dimensions and surface characteristics.

An analysis of the cell theory

As a result, it is common to clean and polish working electrodes regularly. The auxiliary electrode can be almost anything as long as it doesn't react with the bulk of the analyte solution and conducts well.

It is or was? The reference is the most complex of the three electrodes; there are a variety of standards used and it is worth investigating elsewhere.

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