Quasi reference electrode

In the reductive regime, a strong, apparently irreversible, reduction peak is observed, located at -1510 mV vs. the quasi reference electrode used in this system. With in situ STM, a certain influence of the tip on the electrodeposition process was observed. The tip was therefore retracted, the electrode potential was set to -2000 mV, and after two hours the tip was reapproached. The surface topography that we obtained is presented in Figure 6.2-14. 

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

Fig. 28 Reductive electrochemistry data for (72). Cyclic voltammetric curves for a 0.1-mM CH2CI2 solution of (72) at 100 mV s , glassy carbon as a working electrode, Pt-mesh as a counter electrode, and a Ag wire as a quasi-reference electrode, T = 25 °C, TBAPFs (0.1 M) was used as supporting electrolyte.

Figure 6.2-13 UPD phenomena of Ge on Au(l 11) in dry [BMIM] PFe" two-dimensional islands with an average height of 250 + 20 pm start growing upon a potential step from the open circuit potential to -500 mV vs. the Pt quasi reference electrode (picture from [59] - with permission of the Peep owner soeietes).

Figure 8.9 Electrochemistry of functionalized nanotubes, 0.01 M tetrabutylammonium hexafhiorophosphate, THF solution 1.67 mg/mL. V—0.5 V/s. 7 — 25°C, and working electrode is Pt disk (r — 62.5 pm) potentials measured versus silver quasi-reference electrode (approximately —0.05 V versus SCE). Reproduced with permission from Ref. 120. Copyright 2004 American Chemical Society.

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]. 

Fig. 8.1 A metal-wire quasi-reference electrode combined with a dropping mercury electrode (a) and a circuit for a dualreference electrode system (b) [12].

Figure 10.2 Fe(CN) /4 voltammetry on glassy carbon (GC) fractured in solution, and on basal plane highly ordered pyrolytic graphite (HOPG). 1 mM K4Fe(CN)6 in 1 M KC1, scan rate = 0.2 V/s. AEp for fractured GC voltammogram = 64 mV, corresponding to k° > 0.1 cm/s, AEp for HOPG = 1005 mV, k° = 1 x 10 6 cm/s. Potential scale is relative to silver quasi-reference electrode.

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. 

Fig. 2.6 Current-potential curves for (A) p-InP, (B) p-GaAs, and (C) p-Si electrodes in 0.3 M TBAP in methanol (40 atm C02) (b) in the dark and (a, c) under illumination. Curves a and c correspond to the behavior corrected and uncorrected for ohmic losses, respectively. Curve d was obtained for a metallic Cu electrode. (QRE stands for quasi-reference electrode).

Quasi-reference electrodes. Precise potentiometric measurements require reference electrodes that are highly reproducible, but there are many applications where this is less essential. For example, in routine analytical polaro-graphic or voltammetric measurements, the accurate measurement of the current is more important than the precise measurement of potential. For these purposes a simple quasi-reference electrode is suitable. In a halide-containing supporting electrolyte, a silver wire or mercury pool will adopt a reasonably steady potential that is reproducible to within 10-20 mV. 

The solution iR drop at the DME will also be time-dependent because rt, the drop radius, is a function of time. For this reason a stationary hanging-mercury-drop electrode (HMDE) is to be preferred or the vertical orifice (Smo-ler) DME can be used (see Figure 5.14). The tip of a platinium-wire quasireference electrode can be placed as close as 0.1 drop diameter (about 0.003 cm) because the drop grows in the downward direction.7 This gives nearly complete compensation in an electrolyte with a specific resistance of 15,000 Q-cm for a cell with total resistance of about 105 12. The effect of the polargrams of placing the quasi-reference electrode at different distances from the electrode surface is shown in Figure 6.3. 

Figure 6.3 Polarograms as a function of reference-electrode placement in a solution system with a specific resistance of 15,000 12-cm (1) two-electrode polarogram (2-6) quasi-reference electrode placed increasingly close to DME (7) quasi-reference electrode less than 0.1 drop radius from DME.

The SG/TC mode of SECM was also applied by Martin et al. [86] to study the oxidation of DMPPD. The generator was a 2-mm2 substrate electrode, and the collector was a 25-pm diameter Pt disk electrode. The substrate potential was stepped from 0 V versus Ag quasi reference electrode, where no Faradic process took place, to +500 mV, where the oxidation of DMPPD was diffusion controlled. The tip potential was held at 0 V, at which the oxidized form of DMPPD could be reduced at a diffusion controlled rate. After the tip-substrate separation was found from the positive feedback current-distance curve, the rate constant was obtained from the current transient at the tip. The feedback and SG/TC modes were also used to study the reduction of... 

The formation of Cu-Sn alloy by galvanic contact deposition in the trimethyl-n-hexylammonium [bis(trifluoromethyl)sulfonyl]amide ([TMHAl TfiN ) ionic liquid at a temperature above 100 °C has been demonstrated by Katase et al. [41] Sn(II) was introduced into the liquid by dissolution of the SnflT N) salt which has a solubility of 0.2 mol dm f In the plating cell, a copper sheet was used as the cathodic substrate, a Sn sheet was used as the anode, and a Sn rod immersed in the same solution was used as a quasi-reference electrode. On short-circuiting, the Sn anode was oxidized to Sn(II) giving two electrons through external circuit to... 

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. 

Ag or Pt wire quasi-reference electrodes are used for experiments conducted in the absence of deliberately added electrolyte or in exotic solvents where no established reference electrode couple exists. 

---