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This is a basic content about the types of working electrodes used for electrochemical measurement, their uses, and selection methods, for beginners in electrochemical measurement.

The topics are listed below:

3. Usually used working electrodes & features

Laboratory Of Research & Development, BAS Inc.
Professor Noriyuki Watanabe

Contrasting to aqueous electrolyte solution, in non-proton organic solvent, platinum electrode can be used in a wide potential range without any proton adsorption desorption and hydrogen evolution reaction occurring. It is necessary to be considered in advance, when high concentration of chloride ions are contained in aqueous solution, dissolution of platinum metal is occurred, due to the formation of chloroplatinic acid ion at high oxidation potential.

Same as platinum, gold is commonly used electrode material. The difference is that gold does not have any proton adsorption-desorption waves, and the over-potential for proton reduction to hydrogen formation is much higher than platinum, therefore the potential window of gold in aqueous solution is wider than platinum in reductive direction. Similar to platinum, in aqueous electrolyte solution containing high concentration of chloride ions may cause the gold metal dissolution due to the formation of gold chloride acid ion at high oxidation potential. Because the surface of gold can be easily chemical modified by the thiol compounds, it has been used for the purpose of many research fields.

Carbon which is usually used electrode material same as gold and platinum, has many types. Such as graphite, pyrolytic graphite, highly oriented pyrolytic graphite (HOPG), glassy carbon and boron-doped diamond electrodes etc. Glassy carbon is the most commonly used electrode material among them. Significant progress regarding the carbon electrode surface analysis and chemical modification is expected to explain in detail in the next future article.

Metallic mercury is liquid state at room temperature, accumulated mercury may drop down through the capillary by gravity, and it is used as repeatedly dropping microelectrode (dropping mercury electrode) in most cases. It is also frequently used as a stationary suspension electrode (hanging mercury electrode). This is the classic polarography.
Mercury is a pioneer electrode by which the electrochemical reduction analysis methods being developed up to today. Mercury electrode surface is smooth up to atomic level, and it is possible to prepare a high surface reproducibility electrode. Since the over-potential for the reduction of hydrogen ions is large, it is utilized for many heavy metal (Pb, Tl, In, Cd, Sn, Zn, Ni, Cu, Mn, Fe, Co, Sb, Mg, Ca, Sr, W, etc.)ions reductive detection. Mercury can not be used in oxidation area, due to the oxidative dissolution of mercury itself. Gold electrode surface coated with mercury is amalgam electrode, on which the heavy metals ions can be detected in high sensitivity using anodic stripping voltammetry. However, from the viewpoint of environmental pollution, mercury environmental standards are extremely strict and difficult for mercury use in Japan.

The typical working electrodes generally used in electrochemical measurements are described above and it is of course be able to use other types of electrodes for special purpose. In corrosion research field, iron electrode is used for polarization measurement of Tafel plot, a nickel electrode and a nickel titanium alloy electrode are used for selective detection of carbohydrate in alkaline solution etc. examples are not shortage in the enumeration. The point is any materials can be used as working electrode in proper applications according to the research purpose.
last modified 2021/03/29