Flag electrode

A noteworthy advance in the design of solution STMs was achieved by Lev et. al. (Lev, 0. Fan, F-R.F. Bard, A.J. J. Electroanal. Chem.. submitted) by including a Pt "flag" electrode in the STM of Fan et. al. (Fan, F-R.F. Bard, A.J. Anal. Chem.. submitted). A battery between the sample and this flag electrode, which remains poised at the rest potential of the solution, enables the sample to be biased away from the rest potential independently of the tip to sample bias. 

The electrode potential of such a solution-phase system is best followed with an inert electrode such as platinum or gold. An inert electrode is so called because it is not involved in the redox reaction except as a probe of the electrode potential E. An inert electrode is also called a passive electrode, flag electrode or indicator electrode. 

Appleby and Nicholson 173, 174) report the rate laws obtained at flag electrodes that are consistent with the reduction of hyperoxide and peroxide anions, respectively. 

Outer alumina jacket 6. Catalyst in gas inlet 7. Alumina crucible 8. Reference electrode gas outlet 9. Silicon rubber stops 10. Glass lid 11. Flag electrode. CE Counter electrode. 

A cell of this design was employed in studies of microcrystal solids attached to a platinum flag electrode [608]. The measured ESR spectrum of electrochem-ically reduced 7,7, 8,8 -tetracyanoquinodimethane was in perfect agreement with the respective spectrum of the chemically prepared compound and the simulated spectrum. 

Fig.l Schematic representations of various masking techniques and sample configurations, (a) Flag electrode (b) wire loop electrode (c) sample painted with protective coating (d) sample mounted in epoxy or other metallographic mount. The wires for electrical... 

A wide range of cells can be used for corrosion experiments. As mentioned, the selection of the cell is connected to the form of the sample and the masking scheme. It is often possible to simply immerse a sample into a beaker. Fig. 1. The water line can be managed with a flag electrode, or by masking the sample to expose only a submerged area. 

Chronopotentiometry is an important molten salt technique because it can be used with electrodes of relatively large areas, such as simple flag electrodes without an insulating seal By using current-reversal chronopotentiometry, preliminary diagnostic work to determine whether the electrode reaction product is soluble or insoluble, and whether the electrode reaction is reversible or irreversible has proven to be convenient, especially for coitplex reactions such as the reduction of chromate (30). The important... 

FIG. 3—(a) Wire loop configuration for electrochemical testing, (b) flag electrode configuration for electrochemical testing. 

Electrochemical Techniques. Cyclic Voltammetry (CV) was performed on most of the poly(3-methylthiophene) anion sensor electrodes. Cyclic voltammetry provided the electrochemical characterization and evaluation of the post treatment of the modified electrodes. The potential of the platinum electrodes (Model MF-1012, BAS Inc.), with or without modifying film of poly(3-methylthiophene) was controlled relative to an Ag/AgCl reference electrode (BioanaJytical Systems Inc., West Lafayette, IN). The auxiliaiy electrode was a platinum flag electrode or in the case of the FIA experiments a stainless steel block electrode (BAS, West Lafayette, IN). 

The electrode Is formed by taking a platinum flag electrode and electroplating a fine deposit of platinum black from a solution containing a soluble platinum compound. 

As counter electrodes again, any of the above materials are suited, with for instance Pt coil or flag electrodes frequently used for electrochemical characterization studies, and Cu electrodes usable when the Cu Cu reaction is used at the counter electrode. As discussed at some length in Chapter 2, a 3-electrode mode is used in most electrochemical work, while a 2-electrode mode finds use in bulk syntheses or emulation of electrochromic or other end-use devices. 

Figure 7.21. Voltammograms recorded for Ceo film (16.6 nmol of Ceo on an approx. 1 cm Pt flag electrode) in 0.05 M Zn(bpy)3(Pp6)2 solution in acetonitrile, (a) Steady state voltammograms at 50 mV/s (b) first scan recorded at 50 mV/s after recording a voltammogram at 1 mV/s with the film from (a) (c) the next scan at 50 mV/s recorded after (b).

Figure 7.23. Effect of the reversal potential on the shape of voltammograms recorded for C6o films in 0.05 M Cd(bpy)3(PF6)2 solution in acetonitrile (a) 30 nanomoles of Ceo on approx. 1 cm Pt flag electrode scan rate 50 mV/s 5 = 200 /rA. Cathodic reversal potential changed. (bHg) 16.6 nmol of Cgo on approx. 1 cm Pt flag electrode in the presence of 0.64 M bipyridine scan rate, 20 mV/s S=100/iA. Cathodic (bHf) and anodic (g) reversal potentials changed.

Figure 7.34. (a) Voltammograms (first and second scan) recorded for film (approx. 22 nmol on approx. 1 cm Pt flag electrode) in 0.1 M TBAPFe solution after the electrochemical reduction and reoxidation of the film in 0.05 M Cd(bpy)3(Pp6)2 solution (see text). First scan, solid line second scan, broken line. Scan rate, 50 mV/s. 5=500 / A except for the portion of the first anodic scan between —0.1 V and -H 2.0 V, for which S was 20 /xA in order to detect any metallic Cd oxidation, (b) Voltammogram recorded for 1.7 mM Cd(bpy)3(Pp6)2 in 0.1 M TBAPp6 using the same electrode as in (a). Scan rate, 50 mV/s S = 500 fiA. Solid and broken lines represent scans performed in differential potential ranges. 

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