Temperature dependence of electrode

In addition, the temperature dependence of the diffusion potentials and the temperature dependence of the reference electrode potential itself must be considered. Also, the temperature dependence of the solubility of metal salts is important in Eq. (2-29). For these reasons reference electrodes with constant salt concentration are sometimes preferred to those with saturated solutions. For practical reasons, reference electrodes are often situated outside the system under investigation at room temperature and connected with the medium via a salt bridge in which pressure and temperature differences can be neglected. This is the case for all data on potentials given in this handbook unless otherwise stated. 

The temperature dependence of the electrical double-layer parameters has been determined for real393,398 as well as quasi-perfect Ag planes.382,394 For quasi-perfect Ag electrodes, the value of 3 ffa0/9rhas been found to be higher for Ag(100) than for Ag(lll), and so it was concluded that Ag(lll) is more hydrophilic than Ag(100). For real surfaces,382,385,386 dEff=0/BT increases in the order (110) < (100) <(111). The same order of planes has been observed for Au 446-448 BEa /BT linearly increases as AX (interfacial parameter) decreases, i.e., as the hydrophilicity of Ag and Au electrodes decreases.15 32 393 397 398 446 48... 

As the temperature is varied, the Galvani potentials of all interfaces will change, and we cannot relate the measured value of d"S dT to the temperature coefficient of Galvani potential for an individual electrode. The temperature coefficient of electrode potential probably depends on the temperature coefficient of Galvani potential for the reference electrode and hence is not a property of the test electrode alone. 

Thus, the temperature coefficient of Galvanic potential of an individual electrode can be neither measured nor calculated. Measured values of the temperature coefficients of electrode potentials depend on the reference electrode employed. For this reason a special scale is used for the temperature coefficients of electrode potential It is assumed as a convention that the temperature coefficient of potential of the standard hydrogen electrode is zero in other words, it is assumed that the value of Hj) is zero at all temperatures. By measuring the EMF under isothermal conditions we actually compare the temperature coefficient of potential of other electrodes with that of the standard hydrogen electrode. 

According to Eq. (14.2), the activation energy can be determined from the temperature dependence of the reaction rate constant. Since the overall rate constant of an electrochemical reaction also depends on potential, it must bemeasured at constant values of the electrode s Galvani potential. However, as shown in Section 3.6, the temperature coefficients of Galvani potentials cannot be determined. Hence, the conditions under which such a potential can be kept constant while the temperature is varied are not known, and the true activation energies of electrochemical reactions, and also the true values of factor cannot be measured. 

Parthasarathy A, Srinivasan S, Appleby AJ, et al. 1992a. Temperature dependence of the electrode kinetics of oxygen reduction at the platinum/Nafion interface—A microelectrode investigation. J Electrochem Soc 139 2530-2537. 

Henero E, Feliu JM, Blais S, Jerkiewicz G. 2000. Temperature dependence of CO chemisorption and its oxidative desorption on the Pt(lll) electrode. Langmuir 16 4779-4783. 

The ORR has been studied with a rotating ring-disk electrode (RRDE), which can provide theand the H2O2 yield P(H202) at around room temperamre. However, for improving the ORR activity, PEFCs should be operated at high temperature (> 80 °C). In this section, we demonstrate the temperature dependencies of ORR activity and P(H202) at pure Pt (both bulk and supported catalyst) and bulk Pt alloys (Pt-Ni, Pt-Co, and Pt-Fe). 

Uchida H, Izumi K, Watanabe M. 2006. Temperature dependence of CO-tolerant hydrogen oxidation reaction activity at Pt, Pt-Co, and Pt-Ru electrodes. J Phys Chem B 110 21924-21930. 

Wakabayashi N, Takeichi M, Itagaki M, Uchida M, Watanabe M. 2(X)5a. Temperature-dependence of oxygen reduction activity at a platinum electrode in an acidic electrolyte solution investigated with a channel flow double electrode. J Electroanal Chem 574 339-346. 

Climent V, G6mez R, Orts JM, Feliu JM. 2006. Thermodynamic analysis of the temperature dependence of OH adsorption on Pt(lll) and Pt(lOO) electrodes in acidic media in the absence of specific anion adsorption. J Phys Chem B 110 11344. 

Zinola CF, AM Castro Luna, Arvia AJ. 1994. Temperature dependence of kinetic parameters related to oxygen electroreduction in acid solutions on platinum electrodes. Electrochim Acta 39 1951-1959. 

FIG. 3 Temperature dependence of the standard potential of the saturated calomel electrode (1) and Ag/AgCl electrode (2). 

Jia,., Fujitani, Mv Yae, S., and Nakato, Y., Hole diffusion length and temperature dependence of photovoltages for n-Si electrodes modified with LB layers of ultrafine platinum particles, Electrochim. Acta, 42, 431,1997. 

The transfer coefficient a has a dual role (1) It determines the dependence of the current on the electrode potential. (2) It gives the variation of the Gibbs energy of activation with potential, and hence affects the temperature dependence of the current. If an experimental value for a is obtained from current-potential curves, its value should be independent of temperature. A small temperature dependence may arise from quantum effects (not treated here), but a strong dependence is not compatible with an outer-sphere mechanism. 

This potential-energy surface will change when the electrode potential is varied consequently the energy of activation will change, too. These changes will depend on the structure of the double layer, so we cannot predict the value of the transfer coefficient a unless we have a detailed model for the distribution of the potential in the double layer. There is, however, no particular reason why a should be close to 1/2. Also, a temperature dependence of the transfer coefficient is not surprising since the structure of the double layer changes with temperature. 

Figure 6. Temperature dependence of the electrode capacity of copper and silver (taken from ref. 16, with permission of the Electrochemical Society, Pennington, NJ).

Agar had suggested in 1947 that there might be a temperature dependence of p, the electrode kinetic parameter, and Conway took this up in 1982 and showed experimentally that in certain reactions this was the case. 

S02 vapor pressure (pgn2) was measured by dynamic saturation and by a gas-sensing S02 electrode over solutions containing 0.5 to 2.0 M sodium citrate at pH 3.5 to 5 with up to 1 M NaHSOj, Na2S04, and NaCl. Pgo2 was measured at 25° to 168°C pH at 25° to 95°C. Both pH and the vapor pressure ratio Ps02/pH20 were independent of temperature. The composition and temperature dependence of the data are correlated by the semiempirical expressions ... 

Fig. 3-41 Temperature dependance of methanol oxidation current denai after 2 min. potential holding at 500 mV for Nafion SPE platinum electrode at various methanol concentration in the electrolyte or in the feed gas. 

In 10 there a great variety of materials is used, and their optical constants may be affected e.g. by film deposition technologies. What is thus required is the access to data for material dispersion with relation to technological parameter as well, either as Sellmeier or related formula, or as tabulated values. Additionally, refractive indices respond to temperature, which may be intended for device operation in case of a TO-switch, or unintended in field use. The temperature dependence of the refractive index can be attributed to the individual material, simply, but the influence of heater electrodes needs special consideration. If an 10 design-tool comes with inherent TO or EO capabilities, those effects are taken into account in the optical design directly. 

The latter authors used anode and cathode symmetrical cells in EIS analysis in order to simplify the complication that often arises from asymmetrical half-cells so that the contributions from anode/ electrolyte and cathode/electrolyte interfaces could be isolated, and consequently, the temperature-dependences of these components could be established. This is an extension of their earlier work, in which the overall impedances of full lithium ion cells were studied and Ret was identified as the controlling factor. As Figure 68 shows, for each of the two interfaces, Ra dominates the overall impedance in the symmetrical cells as in a full lithium ion cell, indicating that, even at room temperature, the electrodic reaction kinetics at both the cathode and anode surfaces dictate the overall lithium ion chemistry. At lower temperature, this determining role of Ra becomes more pronounced, as Figure 69c shows, in which relative resistance , defined as the ratio of a certain resistance at a specific temperature to that at 20 °C, is used to compare the temperature-dependences of bulk resistance (i b), surface layer resistance Rsi), and i ct- For the convenience of comparison, the temperature-dependence of the ion conductivity measured for the bulk electrolyte is also included in Figure 69 as a benchmark. Apparently, both and Rsi vary with temperature at a similar pace to what ion conductivity adopts, as expected, but a significant deviation was observed in the temperature dependence of R below —10 °C. Thus, one... 

The activation overpotentials for both electrodes are high therefore, the electrochemical kinetics of the both electrodes can be approximated by Tafel kinetics. The concentration dependence of exchange current density was given by Costamagna and Honegger.The open-circuit potential of a SOFC is calculated via the Nernst equation.The conductivity of the electrolyte, i.e., YSZ, is a strong function of temperature and increases with temperature. The temperature dependence of the electrolyte conductivity is expressed by the Arrhenius equation. 

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