Specific Features of Certain Reference Electrodes

For aqueous hydrogen electrodes, the potentiometric data are now available in both sub- and supercritical regions, up to 723 K and 275 bar [48]. However, their use as the high-temperature reference systems involves numerous complications. 

Among reliable systems for high-temperature measurements, gaseous (first of all, oxygen) electrodes based on solid electrolytes of the yttria-stabilized zirconia (YSZ) type can be recommended, which are always applied in the electrochemical cells with solid electrolytes. Gaseous electrodes based on Pt or carbon are also widely used in high-temperature melts, especially 

There are lots of systems, especially for electroplating and electrosynthesis, in which electrodes of the first kind can be used, without any liquid junctions (the example is liquid A1 in AlFs-containing melts). More universal systems for melts of various kinds are a chlorine electrode in equimolar NaCl + KCl melt and Ag/Ag+ electrodes with the range of Ag concentrations (0.01-10 mM) corresponding to usual solubility values. Reference electrodes of the second kind can hardly be used in melts because of the high solubility of the majority of inorganic solids. 

When studying nonaqueous systems by means of galvanic cells with aqueous or mixed reference electrodes, we cannot avoid liquid/liquid junctions and estimate the corresponding potential drop from any realistic model. In protic nonaqueous media (alcohols, dioxane, acetone, etc.), a hydrogen electrode can be used it is also suitable for some aqueous/aprotic mixtures. However, the io values for the hydrogen reaction are much lower as compared with purely aqueous solutions. When studies are carried out in nonaqueous media, in order to avoid liquid/liquid junction preference should be given to the reference electrodes in the same solvent as the electrode of interest. 

In aprotic (as well as in protic and mixed) media, the two reference systems of choice are ferrocene/ferrocenium and bis (biphenil) chromium (I/O). The pen-tamethylcyclopentadienyl analog of the former was recently shown to yield higher performance [49, 50]. Among other typical electrodes, Ag/AgN03 should be mentioned. We can also mention special reference systems suitable for certain solvents, such as amalgam electrodes based 

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An exhaustive consideration of the specific features of various reference electrodes (fabrication, reproducibility and stabiKty, modes of applicability, effects of impiulties, necessary corrections) can be found in Refs. [36, 51-54]. Nowadays, certain new findings in this field are possible because of the novel approaches to immobilization of redox centers on the electrode surfaces. 

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