engleski

Working electrodes

In electrochemistry an electrode is an electronic conductor in the contact with an ionic conductor. The electronic conductor can be a metal, or a semiconductor, or a mixed electronic and ionic conductor. The ionic conductor is usually an electrolyte solution ; however, solid electrolytes and ionic melts can be used as well. The term “electrode” is also used in a technical sense, meaning the electronic conductor only. If not specified otherwise, this meaning of the term “electrode” is the subject of the present chapter. In the simplest case the electrode is a metallic conductor immersed in an electrolyte solution. At the surface of the electrode, dissolved electroactive ions change their charges by exchanging one or more electrons with the conductor. In this electrochemical reaction both the reduced and oxidized ions remain in solution, while the conductor is chemically inert and serves only as a source and sink of electrons. The technical term “electrode” usually also includes all mechanical parts supporting the conductor (e.g.: a rotating disk electrode, or a static mercury drop electrode). Furthermore, it includes all chemical and physical modifications of the conductor, or its surface (e.g.: a mercury film electrode, an enzyme electrode, a carbon paste electrode, etc.). However, this term does not cover the electrolyte solution and the ionic part of a double layer at the electrode/solution interface. Ion-selective electrodes, which are used in potentiometry, will not be considered in this chapter. Theoretical and practical aspects of electrodes are covered in various books and reviews. Electrodes for voltammetry are usually made of solid or liquid metals, or from carbon. Less frequently, metal oxides or polymers are used. The primary metallic conductor may be covered with a thin film of a secondary conductor (e.g.: mercury, or oxides and polymers), or a monolayer of covalently bound foreign atoms or molecules such as thiols on gold substrate. These are called chemically modified electrodes. The chemical preparation of the electrode surface can be performed either before the measurement, in a separate procedure, or in situ, as an integral part of the analytical protocol.

working electrodes

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