Quasi-reference electrode platinum

Conducting properties can also be achieved by reduction of the neutral state. An example is the poly(dibutoxyphenylenevinylene). A platinum electrode coated with polymer in acetonitrile showed the transition between neutral and oxidized state at -r 1V versus a platinum quasi reference electrode and the transition between neutral and reduced state at-1.8 V. The cyclic voltaimnogram is shown in Figure 11.22b as an example to determine characteristic semiconductor properties from cyclic voltammograms. The reduced state has received much less attention than the oxidized state. 

Quantum mechanical calculations electrochemical promotion, 267 with copper clusters, 268 with platinum clusters, 268 Quasi-reference electrodes, 118... 

If the three-electrode instrument is equipped with an iR-drop compensator, most of the iT-drop caused by the solution resistance can be eliminated. However, in order to minimize the effect of the iT-drop, a Fuggin capillary can be attached to the reference electrode with its tip placed close to the indicator electrode. Moreover, for a solution of extremely high resistance, it is effective to use a quasi-reference electrode of a platinum wire (Fig. 8.1(a)) or a dual-reference electrode (Fig. 8.1(b)), instead of the conventional reference electrode [12]. 

The reference electrode recommended for use in the AlCl3-NaCl melt is the A1(III)/A1 couple that is obtained by placing an aluminum wire in a tube containing NaCl(satd) melt (49.8-50.2 mol% AlCl3-NaCl at 175°C). The reference electrode tube is terminated at one end with a Pyrex frit [26] or a thin Pyrex membrane [27]. A platinum wire quasi-reference electrode is used by some researchers [28]. 

The electrochemical window of pure molten cryolite has not been expressly stated, but a voltammogram of purified cryolite recorded at a graphite working electrode exhibits very little residual current over the range of potentials extending from 0.4 to -1.9 V vs. a nickel wire quasi-reference electrode [7]. Physical property data for molten cryolite and phase equilibria for the AlF3-NaF melt system have been summarized [31,32]. The extremely high temperature of cryolite places severe constraints on the materials that can be used for cells. Platinum and boron nitride are the materials of choice. 

Accordingly, much voltammetry in non-aqueous solvents has been conducted using a pseudo -reference electrode (alternatively labelled a quasi -reference electrode) constituting, quite simply, a metal wire, most often silver or platinum. It is then expected (hoped) that the potential of the wire remains constant throughout the voltammetric experiment. This may be a realistic hope if, as Bard and Faulkner [32] point out, the composition of the bulk solution is essentially constant during the period of experimentation, as may be realized during voltammetric studies but certainly not in electrosynthetic work. 

The regenerated ionic liquid phase was investigated dectrochemically to determine its quality. Cyclic voltammetry was performed using a rotating platinum disk electrode (500 rpm), a platinum counter electrode and a platinum wire as (quasi ) reference electrode placed closed to the rotating disk. 

Quasi-reference electrodes such as platinum or silver wires or mercury pools are sometimes used in voltammetric experiments, particularly transient experiments. The advantage is low electrical resistance, but... 

Quasi-reference electrodes can be employed in situations where the high reproducibility of potential is not necessary, such as in many voltammetric analysis experiments. Mercury pools (referred to above) or silver wires in aqueous halide media are examples. Platinum wires can also be used. The advantage of wires, apart from their small size, is in reducing the uncompensated resistance in resistive media, relative to conventional reference electrodes. 

Both SRET and SVET perform potentiometric measurements with micrometer-sized quasi-reference electrodes (typically platinum micro-cones electrochemically coated with platinum black) held precisely above the sample surface. So far these commercial instruments have not been designed to accommodate ion-selective microelectrodes. However, some groups have reported the use of home-made instruments to probe the concentration of specific ions (see Sec. V.B). 

Choice of reference electrodes is one of the most important points in electrochemical measurements in ILs. The reference electrodes are required to show stable electrode potentials, which are usually determined by an equilibrium between reversible redox couples. The redox reaction between silver and silver cation, Ag/Ag(I), is often used as the redox couple for reference electrode in conventional nonaqueous electrolytes. The reference electrode based on Ag/Ag(l) has been also used in various ILs. However, the potentials of Ag/Ag(l) reference electrodes are different in different ILs since the Gibbs energy for formation of Ag(I) depends on the ions composing the ILs. Therefore, it is necessary to calibrate the potentials of reference electrodes against a conunon standard redox potential. A redox couple of ferrocenium (Fc" ) and ferrocene (Fc) is often used for this purpose although its redox potential is considered slightly dependent on BLs. Platinum or silver electrodes immersed in ILs are sometimes used as quasi-reference electrodes. The potentials of these quasi-reference electrodes may seem to be stable in the ILs without any redox species. However, their potentials are unstable and unreliable since they are not determined by any redox equilibrium. Thus, use of quasireference electrodes should be avoided even when the potentials are calibrated by Fc /Fc couple. 

A quasi-reference electrode (QRE) is a general phrase for any poorly defined or unpoised RE. A QRE typically consists of an inert metal wire such as platinum or gold. A silver wire can also be used, so long as silver ions do not interfere with the measurements. The potential should ideally be steady, but the actual potential is not predictable if it is unpoised. Some methods to circumvent the ill-defined potential are to compare the potential to a conventional RE, or to include an electrochemical couple as an internal standard (see Section 4.6.2). A QRE is a low-impedance RE, but is also a polarizable electrode. 

The auxiliary and reference electrodes in electronic and other spectroelectrochemical experiments are similar to those used in conventional electrochemical cells. They must be small enough to fit into the cell without complicating its construction. Common auxiliary electrodes are small platinum wires, paddles, or coils. Reference electrodes (see Chapter 4) are frequently Ag/Ag+ or AgCl because these can be miniaturized. In non-quantitative appUcations, silver wire coated with AgCl or a simple silver wire as a pseudo reference (quasi-reference electrode, QRE) can be used. However, commercially available aqueous and non-aqueous Ag/Ag+ in which the electrode is separated from the analyte solution via a frit are preferable because they are more stable. The majority of electronic spectroelectrochemical experiments are conducted using OTEs in either thin layer (finite) or semi-infinite diffusion regimes. 

The cyclic voltammetric curves were measured at a potential sweep rate varied from 5-10 to 2.0 V-s in the temperature range 973-1123 K. Cyclic voltammograms were recorded on molybdenum and glassy carbon working electrodes 0.5-2.0mm in diameter with respect to a platinum wire, which was used as a quasi-reference electrode, and a reference electrode Ag/NaCl-KCl-AgCl (2 wt%). The glassy carbon crucible served as an auxiliary electrode. 

Figure4.11.1 Cyclic voltammograms on a molybdenum electrode in the NaCI-KCI-Li2COj melt at various reverse potentials. The electrode area is 0.238 cm, the polarization rate is 0.1 V-s T T = 1023 K. Concentration ofLi2COj 2.37 0 mol-cm. The quasi-reference electrode platinum...

Besides these usual reference electrodes, mercury pool electrodes and pseudo- or quasi-reference electrodes of platinum or silver have often been used in nonaqueous solutions. Though these electrodes can have potentials approximately constant under appropriate conditions, the potentials are usually not defined. Thus, in this chapter, the use of these electrodes in nonaqueous solutions is not dealt with in a separate section. But see Chap. 14 for the problem of pseudo-reference electrodes. 

A large variety of quasi-reference electrodes have been used based on metal wires such as silver [40], platinum [41], aluminium [42], tungsten [43], magnesium [44], etc. Typically electrodes are placed directly into the IL solution or separated from the main solution inside a fritted glass tube/compart-ment. In order to minimise liquid junction potentials in the latter case, the same ionic liquids as per the measurements is used as electrolyte. It is the authors experience that separation of the quasi-reference electrode allows for a reduction in potential drift when compared to direct insertion into the electrochemical cell. 

Experiments maybe performed in either separated or unseparated cells, which typically have an electrolyte volume in the range of 0.1 to 1 mL, although larger cells have been used. A typical (imseparated) cell, for example. Fig. 4, is composed of a platinum wire counterelectrode, and a simple reference electrode, such as metal/metal ion, metal/metal hydride, metal/metal oxide, and/or Ag/AgCl/Cl . To date, unseparated cells have proven to be remarkably effective although care must be given to possible interference and/or contamination effects between the various electrodes. When a quasi-reference (metal wire) electrode is used, it is usual practice to compare the voltammetric results obtained in the unseparated STM cell with that ohtained in a conventional cell in order to verify the accuracy and precision of the potential scale. 

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