Electrodes temperature effects

The e.m.f. of a thermogalvanic cell is the result of four main effects (a) electrode temperature, (b) thermal liquid junction potential, (c) metallic thermocouple and (d) thermal diffusion gradient or Soret. 

Kardash D, Korzeniewski C. 2000. Temperature effects on methanol dissociative chemisorption and water activation at polycrystalhne platinum electrodes. Langmuir 16 ... 

Wang H, Baltruschat H. 2007. DEMS study on methanol oxidation at poly- and monocrystalline platinum electrodes The effect of anion, temperature, surface structure, Ru adatom, and potential. J Phys Chem C 111 7038-7048. 

Gasteiger HA, Markovic NM, Ross PN. 1995. H2 and CO electrooxidation on well-characterized PL Ru, and Pt-Ru. 1. Rotating disk electrode studies of the pure gases including temperature effects. J Phys Chem 99 8290-8301. 

Background currents of all NO electrodes are sensitive to changes of temperature and pH. Depending on type of electrodes, the effect may be more or less. Clark type NO electrodes are very sensitive to temperature change. The temperature induced response... 

FIGURE 10.2 A schematic diagram of a combination glass pH electrode. A thin glass bulb with an inner Ag/AgCI electrode responds to pH changes in the test solution. A second Ag/AgCI in an outer jacket with a liquid junction serves the reference electrode for potentiometric measurement. An attached temperature probe is used to compensate for temperature effects. 

Voltage, Electrode Surface Area, and Temperature Effects... 

Solutions in a conductance cell are often stirred to hasten salt dissolution, to promote solution mixing, or to prevent temperature gradients. Some workers observe an upward drift in measured resistances of unstirred solutions 12-17) while others report a downward drift unless the unstirred solution is mixed by shaking of the cell immediately before the measurement9-18-26>. The magnitude of this change is often 0.1 % or more. The effect has not been observed in other cases 8>10). The source of this problem has been variously attributed to temperature variations, electrode adsorption effects and solvent impurities, although the problem has not been analyzed in detail. In all but one of the above cases 12> the resistance of the stirred solution was taken as the true value. 

The gas phase detection of iodine vapor with an electrochemical probe has been investigated [195]. The Ag AgI Au electrochemical cell was observed to be sensitive to interference from both oxygen and humidity. A sensor based on a Ag Ag(Cs)I graphite electrode system has been reported by Sola etal. [196]. Temperature effects were studied and the effect of Csl doping of the Agl explored to widen the working temperature range. 

Temperature effect on the electrodeposition of zinc on the static mercury drop electrode (SMDE) and glassy carbon (GG) electrode was studied in acetate solutions [44]. From the obtained kinetic parameters, the activation energies of Zn(II)/Zn(Hg) process were determined. 

Since the early 1990s, however, the use of a powerful laser to fire pulses of increasing intensity at the back of an electrode in the form of a thin plate (Velev, 1991) has allowed reaction rates at a series of increasing temperatures to be measured in a few minutes. Such measurement times may be short enough (in systems where good control is practiced to reduce impurities) to make values of i0 independent of changes in the electrode surface that occur with time. The more meaningful data on temperature effects measured with this technique will stimulate attention to clear up the effects of the inclusion of A/7 ev in Eq. (7.89), which seeks to get only at AHox. 

Temperature Effects The pH of a buffer solution is influenced by temperature. This effect is due to a temperature-dependent change of the dissociation constant (pK ) of ions in solution. The pH of the commonly used buffer Tris is greatly affected by temperature changes, with a ApKa/C° of —0.031. This means that a pH 7.0 Tris buffer made up at 4°C would have a pH of 5.95 at 37°C. The best way to avoid this problem is to prepare the buffer solution at the temperature at which it will be used and to standardize the electrode with buffers at the same temperature as the solution you wish to measure. 

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... 

The solubility product of the Hg2Cl2 (calomel) is very low (Ksp = 1.3 x 10 l7). The potential of this electrode is again determined by the concentration of the chloride ion in the inner compartment. When a saturated solution of KC1 is used its potential against the SHE is n = +241 mV. Use of a saturated KC1 solution hides a certain danger the higher temperature sensitivity, which is due to the temperature effect on solubility. 

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

The impedance is dependent on temperature, as can be seen in Figure 4, which shows the area specific resistance (ASR) of a cell as a function of cell temperature for different gas flow rates. For the same cell temperatures, lower ASR was observed for increasing gas flow rates due to the increased gas diffusion near the electrodes that effectively reduced the overpotential resistances [4], Because the anode and cathode are often conductive, the impedance of the cell is dependent largely on the thickness of the electrolyte. Using an anode supported cell structure, a YSZ electrolyte can be used as thin as 10-20 pm or even 1-2 pm [32, 33] as compared to 0.5 mm for a typical electrolyte supported cell [26],... 

If anodic bonding between glass and Si fails (due to a thick oxide layer [1 im] on Si or platinum electrode on Si), a low-melting spin-on-glass (SOG) can be applied as an adhesive. SOG, which is a methylsilsesquioxane polymer, flows very well at the temperature between 150°C and 210°C, and therefore it fills the grooves (i.e., around the Pt electrodes) for effective bonding [93]. 

Temperature effects. The ordinary glass electrode-reference electrode pair that is used for pH measurements is not well suited to measurements far removed from room temperature. This is because the electrodes are immersed only partially, with the tips of the electrodes in the solution and the tops of the electrodes at ambient temperature. This creates a thermal gradient in the body... 

In comparison with the perturbations to rate constants induced by the electrode potential, relatively little attention has been directed to experimental examinations of temperature effects in electrochemical kinetics. This is probably due, in part, to uncertainties in how to control the electrical variable while the temperature is altered. However, as noted in Sect. 3.4, in actuality there are no more ambiguities in interpreting electrochemical activation parameters than for the commonly encountered Arrhenius par-... 

Fig. 21.11. Oil-sensitive MIPs sensitivity increases with the layer thickness of the QCM coatings. Sensor effects have been gathered by differential measurements between uncoated and MIP-coated electrodes (difference eliminates viscosity and temperature effects).

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