Electrodes solid

In hydrodynamic voltammetry the solution is stirred either by using a magnetic stir bar or by rotating the electrode. Because the solution is stirred, a dropping mercury electrode cannot be used and is replaced with a solid electrode. Both linear potential scans or potential pulses can be applied. 

Wang, J. Sensitive Electroanalysis Using Solid Electrodes, /. Chem. Educ. 1982, 59, 691-692. 

Conventional batteries consist of a liquid electrolyte separating two solid electrodes. In the Na/S battery this is inverted a solid electrolyte separates two liquid electrodes a ceramic tube made from the solid electrolyte sodium /5-alumina (p. 249) separates an inner pool of molten. sodium (mp 98°) from an outer bath of molten sulfur (mp 119°) and allows Na" " ions to pass through. The whole system is sealed and is encased in a stainless steel canister which also serves as the sulfur-electrode current collector. Within the battery, the current is passed by Na+ ions which pass through the solid electrolyte and react with the sulfur. The cell reaction can be written formally as... 

A quite different approach was introduced in the early 1980s [44-46], in which a dense solid electrode is fabricated which has a composite microstructure in which particles of the reactant phase are finely dispersed within a solid, electronically conducting matrix in which the electroactive species is also mobile. There is thus a large internal reactant/mixed-conductor matrix interfacial area. The electroactive species is transported through the solid matrix to this interfacial region, where it undergoes the chemical part of the electrode reaction. Since the matrix material is also an electronic conductor, it can also act as the electrode s current collector. The electrochemical part of the reaction takes place on the outer surface of the composite electrode. 

Some further important aspects for the design of solid electrolytes and solid electrodes for battery-type applications are the following ... 

The difference between the various pulse voltammetric techniques is the excitation waveform and the current sampling regime. With both normal-pulse and differential-pulse voltammetry, one potential pulse is applied for each drop of mercury when the DME is used. (Both techniques can also be used at solid electrodes.) By controlling the drop time (with a mechanical knocker), the pulse is synchronized with the maximum growth of the mercury drop. At this point, near the end of the drop lifetime, the faradaic current reaches its maximum value, while the contribution of the charging current is minimal (based on the time dependence of the components). 

About 20 amalgam-forming metals, including Pb, Sn, Cu, Zn, Cd, Bi, Sb, Tl, Ga, In and Mn, are easily measurable by stripping strategies (ASV and PSA) based on cathodic deposition onto mercury electrodes. Additional metals, such as Se, Hg, Ag, Te and As are measurable at bare solid electrodes such as carbon or gold. 

The limited anodic potential range of mercury electrodes has precluded their utility for monitoring oxidizable compounds. Accordingly, solid electrodes with extended anodic potential windows have attracted considerable analytical interest. Of the many different solid materials that can be used as working electrodes, the most often used are carbon, platinum, and gold. Silver, nickel, and copper can also be used for specific applications. A monograph by Adams (17) is highly recommended for a detailed description of solid-electrode electrochemistry. 

S.2.2 Carbon Electrodes Solid electrodes based on carbon are currently in widespread use in electroanalysis, primarily because of their broad potential window, low background current, rich surface chemistry, low cost, chemical inertness, and suitability for various sensing and detection applications. In contrast, electron-transfer rates observed at carbon surfaces are often slower than those observed at metal electrodes. The electron-transfer reactivity is strongly affected by the origin... 

R.N. Adams, Electrochemistry at Solid Electrodes, Marcel Dekker, New York, 1969. 

Sodium-silicate glass, 151 Sol-gel films, 120, 173 Solid electrodes, 110 Solid state devices, 160 Solvents, 102 Speciation, 84 Spectroelectrochenristry, 40 Spherical electrode, 6, 8, 9, 61 Square-wave voltammetry, 72, 92 Staircase voltammetry, 74 Standard potential, 3 Standard rate constant, 12, 18 Stripping analysis, 75, 79, 110 Supporting electrolyte, 102 Surface-active agents, 79... 

While the method based on the surface tension measurement has been established since the pioneering work of Gouy, conceptual and experimental problems arise with solid electrodes, whose surfaces cannot... 

There have been many attempts to apply the surface tension (y, E curve) method to solid electrodes, and various experimental approaches... 

The estimation of the working surface area of solid electrodes is a difficult matter owing to irregularities at a submicroscopic level.10 15 20 24 32 63 64 67 68 73 74 218-224 Depending on the irregularity-to-probe size ratio, either the entire surface or only a fraction of it is accessible to a particular measurement. Only when the size of the molecule or ion used as a probe particle is smaller than the smallest surface irregularity... 

Various in situ and ex situ methods have been used to determine the real surface area of solid electrodes. Each method10,15 32 67,73 74 218 is applicable to a limited number of electrochemical systems so that a universal method of surface area measurement is not available at present. On the other hand, a number of methods used in electrochemistry are not well founded from a physical point of view, and some of them are definitely questionable. In situ and ex situ methods used in electrochemistry have been recently reviewed by Trasatti and Petrii.73 A number of methods are listed in Table 3. 

M) were typically used for such a comparison to eliminate the influence of possible differences in the inner-layer capacities. However, C of different solid metals, as well as of liquid Ga, In(Ga), and Tl(Ga) alloys have shown such a large variation that this approach can hardly be considered as appropriate. It should be noted that the error in C, which for solid electrodes is much higher than for liquid electrodes, increases with the decrease ofcei further, as shown later (Section II.2 (iv)), the effects of surface crystallographic inhomogeneity also prove especially appreciable.24 67 74... 

Substantial contributions to the interpretation of the experimental data for solid electrodes have been made by Leilas et al.m m and by Valette and Hamelin.67 Both approaches are based on the same model the... 

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