Online Quizzes for CliffsNotes Chemistry QuickReview, 2nd Edition Electrode Potential The potential difference, which is measured in volts vdepends upon the particular substances constituting the electrodes.
Does the auxiliary electrode need to be isolated from the working electrode? Most electrochemical cells I've seen have only 2 electrodes. Why do I need 3 electrodes for cyclic voltammetry and related techniques? All electrochemical cells require at least two electrodes, since the potential of a given electrode can only be measured relative to another electrode, the potential of which must be constant a reference electrode.
In potentiometric measurements such as measurement of pHthere is no current through the cell, and these two electrodes are sufficient. It should be noted that many pH and ion-selective electrodes used in potentiometric measurements are combination electrodes — both electrodes are contained within the same body.
However, in a cyclic voltammetry experiment, an external potential is applied to the cell, and the current response is measured. Better potential control is achieved using a potentiostat and a 3-electrode system, in which the potential of one electrode the working electrode is controlled relative to the reference electrodeand the Electrochemistry electrode potential passes between the working electrode and the third electrode the auxiliary electrode.
What are the requirements for a working electrode materialand which material should I choose? A working electrode acts as a source or sink of electrons for exchange with molecules in the interfacial region the solution adjacent to the electrode surfaceand must be an electronic conductor.
It must also be electrochemically inert i. Commonly used working electrode materials for cyclic voltammetry include platinum, gold, mercuryand glassy carbon. The choice of material depends upon the potential window required e. The rate of electron transfer can vary considerably from one material to another, even for the same analyte, due to, for example, catalytic interactions between the analyte and active species on the electrode surface.
Is there a difference between glassy carbon and pyrolytic graphite?
Glassy carbon is an amorphous form of carbon, whereas pyrolytic graphite has a more ordered structure, with distinct planes — the basal plane and the edge plane. The edge plane is considerably more conductive than the basal plane. Glassy carbon is mechanically more durable than pyrolytic graphite.
Do I need to clean the surface of the working electrode between experiments, and, if so, how? If material adsorbs to the surface of a working electrode, then the current response will degrade and the electrode surface needs to be cleaned. Such adsorption occurs more readily for some analytes than for others, and hence the required cleaning frequency varies.
In many cases, the only cleaning required is light polishing with a fine material such as 1 mm diamond, or 0. A few drops of polish are placed on a polishing pad brown Texmet for alumina, and white nylon for diamondand the electrode is held vertically and the polish rubbed on in a figure-eight pattern for a period of 30 seconds to a few minutes, depending upon the condition of the electrode surface.
After polishing, the electrode surface is rinsed thoroughly with water for alumina or methanol for diamondand allowed to air dry. Electrodes polished with alumina may also need to be sonicated in distilled water for a few minutes to remove any residual alumina particles. The choice of polish depends upon the analyte and the electrode; use the polishing method that gives the best results i.In-line mountings are ideal for replacing existing threaded electrodes.
They are useful in piping systems where flow can be shut off for electrode maintenance and where flow rates match the application’s needs; for example, turbulent flow is needed in self-cleaning applications.
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Electrode Potential The potential difference, which is measured in volts (v), depends upon the particular substances constituting the electrodes. For any electric cell, the total potential is the sum of those produced by the reactions at the two electrodes.
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