Reference electrode pseudoreference

Quasireference electrode (QRE) — (-> reference electrode, pseudoreference electrode). An electrode that maintains a given, but generally not well-defined, potential during the course of a series of electrochemical experiments. It has the advantage of not contaminating the test solution by solvent or ions that a conventional reference electrode might contain and transfer. Thus in studies in aprotic solvents, like acetonitrile, a silver wire can behave as a QRE. It must be calibrated with respect to a true reference electrode or reference redox couple that is added at the end of the experiments to obtain meaningful potential values. 

In amperometric detection, a reference electrode was usually employed. However, in one report, a platinized Au electrode was used as a pseudoreference electrode in a three-electrode system for amperometric detection. The operation principle follows that of the hydrogen reference electrode [242]. 

The most popular pseudo-reference electrodes are Pt or Ag wires. Other pseudoreference electrodes have employed coating, for example Pt with polypyrrole [39] or Ag with AgCl [40] (but in the absence of deliberately added solution phase, ... 

It is also possible to scan a pair of reference or pseudoreference electrodes separated by a small, fixed distance of a few micrometers to measure the local potential field gradient, dvldl, and estimate the local current density from Eq. (48) (128). This is a slightly more sophisticated measurement because the anodic or cathodic character of local sites can be determined from the polarity of the current, and the intensity of the attack can be estimated from the current density flowing in solution. The difficulty with this arrangement is that the potential difference between two closely spaced reference electrodes in a conductive solution is usually less than 1 microvolt. The stability of reference electrodes is on the order of microvolts, and thus it often exceeds the magnitude of the potential difference signal. This imposes a fundamental limitation on the usefulness of this technique. 

Here, Z(co) local is the magnitude of the local impedance, V((o)apPiied is the magnitude of the voltage between the working electrode and a distant reference electrode, and VXcoVbe is the AC voltage drop measured by the pseudoreference electrode pair. Again, it is implicitly assumed that the current density measured in solution is equal to the current density at the electrode surface. 

Pseudoreference electrode reference electrodes, and -> quasireference electrode... 

In many cases platinum or silver wires serve as quasireference electrodes, however, they have to be calibrated by a reference redox systems. [The term pseudoreference (literally false reference) electrode is also used in the literature, however, the term quasireference electrode is preferred]. 

Fuel cell researchers have also investigated other reference electrodes, such as a pseudo-reference electrode constructed by inserting a micro-sized carbon filament between two polymer electrolyte membranes [73], The main advantage of pseudoreference electrodes is their easy implementation, although one disadvantage is that their DC potential is unknown. However, this DC potential may not be that critical because EIS measurements mainly rely on the AC perturbation signal from which the impedance is calculated. 

A scheme of electrochemical cell and electrode design is reported in (Fig. 1). The sensors can be obtained from Ecobioservices and Researches S.r.l. (Florence, Italy). A typical electrode modification formulation is reported in Note 1. Further explanations regarding electrode composition are reported in Note 2. Before use, the pseudo Ag reference electrode is oxidized using NaCIO 14% solution, in order to avoid the oxidation of the Ag pseudoreference by thiols during measurements. For storage conditions rrrNote 3. 

Quasi implies that it is almost or essentially a reference electrode. Sometimes such electrodes are also called pseudoreference electrodes pseudo, meaning false) this terminology seems less appropriate. 

Figure 2.3. DPV scans of the thrombin substrate (/ -Ala-Gly-Arg-p-nitroaniline] solutions incubated with aptamer-thrombin modified beads. Different concentrations of thrombin in the concentration range 100 to 600 nM were incubated with the aptamer-modified beads, while a fixed concentration of thrombin substrate was used (200 pM). The thrombin substrate and the p-nitroaniline released during hydrolysis showed different redox potentials (the DPV peak potential of 8-Ala-Gly-Arg-p-nitroaniline was —730 mV vs. Ag/AgCI pseudo-reference electrode, whereas the released p-nitroaniline peak potential was —870mV vs. Ag/AgCl pseudoreference electrode).

An HRP substrate was prepared containing a mixture of 3,3, 5,5 -tetramethylbenzidine and H2O2 in a 1 10 ratio, and this substrate mixture was applied to the SPC reservoir area to cover the working, counter and reference electrodes. The enzymatic reaction occurring on the working electrode was detected using a portable pulse amperometric reader. The reader used intermittent pulse amperometry in which a 15 s incubation period was followed by an applied potential of -0.1 V (vs. a silver pseudoreference electrode) with a measurement time of 10 s and a pulse time of 10 s at a frequency of 5 Hz and a current range of 10 fiA [8]. 

In certain experimental configurations, reference electrodes of this type, i.e., with an internal compartment, may be difficult to implement. In such cases a pseudo-reference might need to be used. For instance, it may be a metal wire (silver, platinum, etc.) or indeed the Ag,AgCI in direct contact with the electrolytic medium. In these examples the interface between the pseudo-reference and the electrolyte studied is generally not in thermodynamic equilibrium , in contrast to the case of the interface in usual reference systems which have a suitable internal solution. However, thanks to the use of a potentiostat , no current flows in the electrode, and therefore it is correct to assume that its open-circuit potential remains constant in the course of the experiment. This hypothesis has to be checked in each experimental situation. Moreover, the value of this open-circuit potential is most of the time not known in precise terms. Using a pseudoreference therefore requires that the potential shift of this electrode be determined, e.g., by implementing a reference compound at the end of the experiment... 

A three-electrode cell with one or two compartments. If the potentiostatic or potentiodynamic method is used, a reference electrode is necessary. The reference electrode may be simply a silver wire, pseudoreference. Its potential is not particularly stable and it should be standardized before or after every use by measuring a cyclic voltammogram of ferrocene. The redox potential of the ferrocene-ferricinium couple is well known in all common solvents and hence this couple is generally used as a potential standard. 

Figure 62.2 illustrates an experimental setup for biosensor measurements. Electrochemical measurements using biosensors require three electrodes, which are called the working electrode (enzyme-modified electrode), reference electrode, and counter electrode. In some cases, the three electrodes can be assembled into a single-body electrode. It is also possible to eliminate the reference electrode and use the counter electrode as a pseudoreference electrode for specific reasons, such as miniaturization. The experimental setup shown in Figure 62.2 is a batch system, in which the electrodes are immersed in the sample solution to obtain an output signal. For constructing flow systems, the electrodes are set at a... 

Fig. 2 Illustration of various reported array element complexities. WE working electrode, CE counter electrode, RE reference electrode, CE+RE pseudoreference electrode, OE other electrodes. Striped band WE, RE, and CE+RE are shared by several WE...

For AFM, commercial tips and cantilevers are used whereas for STM tips are prepared in various ways. W tips are easily obtained by electrochemical etching in NaOH. They have to be isolated with wax or varnish for electrochemical in situ studies to reduce electrochemical currents at the tip to less than 0.05 nA. Small electrochemical cells made of PCTFE (polycholorotri fluoroethylene) are pressed with a Viton O-ring onto the crystal surface [142]. They contain a Pt coimterelectrode and a small reference electrode. Often a Pt pseudoreference electrode is used, which yields a reproducible potential that can be calibrated using the characteristic features of the polarization curve for a given system. A simple Pt wire may be cleaned much better and does not introduce impurities to the small electrolyte volume. With oxygen present in the electrolyte, the Pt-wire potential is in the domain of the 02/OH reaction. 

Unfortunately, for samples with bulk resistance in excess of 1 Mohm accurate impedance characterization becomes difficult and requires a careful analysis of several contributions. Traditional "aqueous type" reversible reference electrodes such as Ag/AgCl cannot be used in nonaqueous environments, and metal "pseudoreference" electrodes have to be employed [25,27], That leads to experimental complications, represented in Figure 8-11. The frequency analysis of the input, reference, and sample impedances demonstrated that the difference between Z p and Z p is minimal at high frequencies, leading to a relatively high /,... 

The impedance spectra measured in a one-dimensional PEM fuel cell studied by locally resolved EIS [36] for A. half cell between the pseudoreference electrode and the anode B. half cell between the pseudo- reference electrode and the cathode C.the whole cell D. the impedance model at current densities j = 100-500 mA/cm" [37] (with permission from The Electrochemical Society and the authors)... 

Figure 14.8 Cyclic voltammetry curves recorded using a Pt working electrode at a 100 mV/s sweep rate (CH3CN/CH2CI2 (4 1), supporting electrolyte NBu4BF4, 0.1 M, Ag wire pseudoreference). (a) Compound 4(4) + (b) chemically prepared 4(5)2 +. Curve (ii) refers to a second potential sweep following immediatly the first one (i).

Figure 53 Schematic illustration of the pseudoreference electrode pair used to make LEIS measurements. In this diagram, d refers to the electrode separation and h refers to the height of the probe from the working electrode surface. (From F. Zou, D. Thierry, H. S. Isaacs. J. Electrochem. Soc. 144, 1957 (1997).)...

Figure 5.1 Disassembled view of the spectroelectrochemical cell. (1) Tightening brass cap (threaded inside). (2) Brass ring required to tighten the cell. (3) Working electrode (brass rod with platinum soldered to the base). (4) Auxiliary electrode platinum wire with the tip made flush to the teflon base of the cell. (5) Pseudoreference electrode silver wire, also made flush to the teflon. (6,7) Luer-lock-type injection ports. (8) Cell body, top part aluminium, lower part teflon. (All three electrodes and both filling ports are press fitted into the cell body, so that they can be replaced if needed.) (9) Teflon spacer, determines the pathlength of the cell and masks the reference and counter electrodes from the incident beam. (10) Calcium fluoride window (Wilmad, standard 38.5 x 19.5 x 4mm). (11) Rubber gasket. (12) Hollow brass cell body with threaded inlet and outlet ports (Swagelock) for connection to circulating bath. (13) Two-mirror reflectance accessory (Thermo-SpectraTech FT-30). (14,15) Mirrors.

Fig. 57a, b. Cyclic voltammetric responses recorded on CH2CI2 solutions of a) PhSiCo3(CO)n b) PhSnCo3(CO)]2. Scan rate 0.2 Vs-1. Potential values refer to a pseudoreference Ag electrode [from Ref. 122]... 

---