Counter electrode choice

A further argument for the choice of the cathode material may be the catalytic activity for hydrogenation reactions. Vice versa, this is also important if the cathode is the counter electrode - usually evolving hydrogen - where hydrogenation reactions are undesired. 

This kind of source has the advantages of the fixed chemical potential of sodium, good contact between liquid sodium and the solid electrolyte, and no additional electronic conducting electrode is needed as the counter electrode (C) to connect with the external electric circuit. In practice, elemental sodium is too active, and a very tight seal is required to prevent sodium vapor from migrating and reacting chemically with CO and in the sink vapor phase. Consequently, the system setup becomes more complex. The choice of the source in the current study is a combination of Na COj, CO and O2 gas phase, and an inert Pt counter... 

Where Na is number of moles of A transformed. The counter electrode reaction must be chosen carefully in undivided cells to prevent reaction with the target product. The use of a sacrificial counter electrode may be satisfactory. The ideal solution is a paired electrosynthesis, i.e., when both cathodic and anodic processes are of interest. In most electrolyses, oxygen, which is electroactive, is a poison and must be removed by bubbling an inert gas through the solution or by vacuum techniques. When the electrolysis is complete, the product must be recovered. Obviously, there is no problem when the product precipitates or electrocrystallizes. The work-up of the solution may be facilitated by an appropriate choice of the experimental conditions. In... 

The counter-electrode chosen should be as large as possible and made up of a material that is resistant to the electrolyte used. For sodium hydroxide, a good choice is stainless steel or nickel. As the counter-electrode is generally used with anodic polarisation, one should be aware that some electrochemical dissolution will take place. If the electrode surface is very large, current densities will remain small and therefore limit anodic dissolution of the electrode material. The geometry of the counter-electrode should be such that the inter-electrode resistance will remain constant during machining. This resistance should also... 

The choice of a suitable counter-electrode for a successful EW is not easy since only a few compounds fulfil the desired operational requirements which call for an uncommon combination of electrochemical and optical properties. The most promising, and, thus far, the mostly used materials are indium tin oxide, nickel oxide, iridium oxide and cobalt oxide among the inorganic ECMs, and polyaniline (PANI) among the organic ECMs. The electrochromic properties of indium tin oxide and PANI have been described in Chapter 7. Therefore, here attention will be mainly focused on transition metal oxide counter-electrodes. 

To measure S, the somewhat severe geometrical constraints which obtain for R and a are relaxed. Enderby and co-workers have used the cell shown in Figure 7.17, but many variations both in choice of cell material and electrode configuration are possible (see, for example, Davies (1969)). The idea of separating the counter electrode material from the liquid (which may be chemically highly reactive) by a thin sheet of refractory material was first suggested by Cusack et al (1964). 

Layers can also be analyzed by SSMS, usually in the point-to-plane geometry and with movement of the plane sample [127]. The achievable resolution is limited, though, to 10-100 pm lateral and approximately 1 pm depth resolution [104], and is influenced by the choice of the counter electrode shape [105]. 

As noted above, the counter electrode should not impose any characteristics on the measured data, and in consequence it should have a large area compared to the working electrode. Moreover, as also noted above, its shape and position are important since these determine whether the working electrode is an equi-potential surface, and consequently it is preferable to avoid a separator in the cell. This requires the choice of clean counter electrode chemistry. 

The material of choice for the sensor s electrodes can be different for each function. The RE needs to establish a stable potential. The counter electrode, CE, or auxiliary electrode should be able to catalyze its half-cell reaction over an extended period. In addition, of course, the SE should be the ideal catalyst for its sensing reaction and be selective for it (Chang et al. 1993 Stetter and Li 2008). All of the electrodes need to be stable, manufacturable, and good interfaces for the electrochemistry. 

Multiple choice What counter electrode does this lab use ... 

Consider a three-electrode electrochemical cell comprising an electrolyte solution of metal ions with a bulk concentration c, an inert, ideally polarizable working electrode, a counter electrode and a reference electrode with a fixed potential Eref. The whole system is kept at a constant temperature T. For the sake of convenience, we select a reference electrode made of the bulk metal M whose ions are present in the solution. The only requirement that we have to meet for the purpose is the bulk metal M to have a stable and reversible equilibrium potential JE x(c). That being the case. Ere/ = Ej(c) and any external potential E which we apply to the working electrode polarizes it directly to the electrochemical overpotential t] = EJ/f) - E, which is a measurable quantity with a clear physical significance. Certainly we can use any other reference electrode with a fixed potential Ere/ and this is what we should do if the bulk metal M has no reversible potential in the particular experimental system or if this potential is not known. However, then the external potential E will polarize the working electrode to the overpotential rjre/ = Ere/ - E, which relates to rj according to //re/ = // + AEref where AEre/= Ere/- Eao(c). Namely the difference Ere/-EJ/S) is which we eliminate with the special choice of our reference electrode. 

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