Electrode stability

Accuracy is a measure of how close the result is to the true value while reproducibility or precision is a measure of how close a series of measurements on the same sample are to each other. The accuracy and reproducibility of pH measurements can be highly variable and are dependent on several factors electrode stability (drift and hysteresis), response slope/calibration curve, and accuracy of the pH meters. While some of these factors are determined by the properties of electrodes, some measures can be taken to improve measurement accuracy and reproducibility. 

Electrode Stability and Photoelectrolysis Using Appropriate Bandgap Semiconductors... 

The effect of a-Si H TFT threshold voltage variation on pixel electrode stability can be somewhat reduced by introducing an additional n-channel a-Si H TFT into the 2-a-Si H TFT pixel electrode circuit. Several such possible 3-TFTs pixel circuits are discussed below. 

Electrode stability has been demonstrated (on a laboratory scale) for a period of... 

Liquid chromatography with electrochemical detection (LCEC) is in widespread use for the trace determination of easily oxidizable and reducible organic compounds. Detection limits at the 0.1-pmol level have been achieved for a number of oxidizable compounds. Due to problems with dissolved oxygen and electrode stability, the practical limit of detection for easily reducible substances is currently about 10-fold less favorable. As with all detectors, such statements of the minimum detectable quantity must be considered only with the proverbial grain of salt. Detector performance varies widely with the analyte and the chromatographic conditions. For example, the use of 100- m-diameter flow systems can bring attomole detection limits within reach, but today this is not a practical reality. 

Vjb are expected and none are observed as shown in the top half or Table I. While enhanced red response is clearly useful in these photoelectrodes, the consequences in terms of overall electrode stability may outweigh any advantage gained. Clearly substitutional doping would avert these problems and may be a preferable technique. 

We should point out that the temperature effects on emission intensity and photocurrent are completely reversible. Although this result suggests that electrode stability obtains over the duration of the experiments, the properties measured may not be very sensitive to variations in surface or near-surface composition. There is now considerable evidence, in fact, that surface reorganization processes do occur in CdS- and CdSe- based PECs in polychalcogenide electrolytes (17, 21-26). In particular, the occurrence of such an exchange reaction for CdS Te in polyselenide electrolyte would yield CdSe to whose lower band gap... 

In general, restricted hypertonic junctions can introduce EMF errors due to protein contamination (amorphous or precipitate overcoats) and isotonization of the junction with a subsequent influence of ionic strength. Open junctions, on the other hand, are apparently affected by the ionic form of proteins. The problem of reference electrode stability is especially important in direct measurements, as discussed above and elsewhere [9,33]. 

Table 1. References for specific materials, temperature effects and electrode stability.

In all of the discussion of this chapter we have used an aqueous solution as the electrolyte, and electrodes suitable to those aqueous solutions. However, cells are not limited to aqueous solutions. Indeed, other solvents have been used for which liquid ammonia would be an example. Molten salts, such as mixtures of lithium chloride and potassium chloride, have been used for the study of cells at high temperatures. Some studies have been made at higher temperatures, in which solid electrolytes were used. Electrodes compatible with such solvents have also been devised. For example, a zirconium-zirconium oxide electrode stabilized with calcium oxide was used to measure the oxygen potential in nonstoichiometric metal oxides. However, no matter what the electrolytes or the electrodes are, the principles discussed in this chapter such as reversibility and proper measurement must be followed. 

Most of the reference electrodes embedded in concrete are used for control of cathodic protection (CP) systems. Potential stability is then less important, compared to corrosion state monitoring. Control of CP systems requires only short-term stability, maximum 24 hours. Corrosion rate measurement, like linear polarisation resistance (LPR) measurements, also requires short-term reference electrode stability. However, regardless of application, a reference electrode which is to be permanently embedded in the test solution, e.g. concrete, must have a long life when exposed to this environment. 

Figured Effect of Stabilizers on Alcohol Oxidase Electrode Stability.

Besides the electrochemical performance, the selection of graphite additives depends on electrode processing aspects. Flaky graphite particles have a higher dibutyl phthalate absorption (DBPA) and, thus, require more polymer binder than isometric graphite particles to achieve a sufficiently high mechanical electrode stability, as shown in Table 7.1. 

It is well- known that the presence of catalytic poisons (CO for example) in hydrogen gas exerts strong influence on the effectiveness and long-term stability of the electrodes containing Pt, Pd and other noble metals as a catalyst. The modification of this catalyst by such metals as Nb, Mo, Ta and Ru increased electrode life in presence of CO [8, 9]. Utilization of tungsten oxide (WO3) jointly with Pt and Ru increase also electrode stability towards CO [28]. 

Cardon, F., Gomes, W.P., Vanden Kerchove, F., Vanmaekelbergh, D, and Van Overmeire, F. 1980. On the kinetics of semiconductor electrode stabilization. Faraday Disc., 70, 153-164. 

Coteiro s group studied the influence of the solvent to the ternary oxide, Ru-Ti-Sn, electrode stability (Coteiro et al. 2006). The precursor mixtures were prepared by dissolving RuCh H20, TiCl4, and SnCl2 2H20 salts into the solvent. Two different solvents, HC1/H20 (1 1 v/v) or isopropanol, were applied. The results with isopropanol as solvent showed that tin loss can be eliminated and higher elec-trochemically active area and stability can be achieved, when compared with HC1 solution. 

Suppression of Surface Dissolution of CdS Photoanode by Reducing Agents. As above but a variety of electron donors used. The use of sulfite for electrode stabilization demonstrated. 488... 

---