Electrode, area indicator

As A will be a function of current density, T will be a function of electrode area, and comparisons should therefore be made with cells of standard size. Equation 12.12 shows that high throwing indices will result when polarisation rises steeply with current (AE, AEj) and cathode efficiency falls steeply (cj >> f i)- The primary current ratio, P = affects the result because... 

Now, if we assume throughout the entire concentration step a current yield of 100% and no perceptible alteration of the bulk concentration, in view of its function as an indicator in the stripping step the electrode area cannot be taken as large, Faraday s law can be applied to calculate the final amalgam concentration according to... 

So far we have discussed only the reversible case. The equivalence of the net Faradaic current at the NEE and at a macroelectrode of the same geometric area (Fig. 7) means that the flux at the individual elements of the NEE are many orders of magnitude larger than the flux at the macroelectrode. Indeed, the experimentally determined fractional electrode areas (Table 1) indicate that, for the reversible case, the flux at the elements of a... 

Because the fractional electrode area at the lONEE is lower than at the 30NEE (Table 1), the transition to quasireversible behavior would be expected to occur at even lower scan rates at the lONEE. Voltammograms for RuCNHs) at a lONEE are shown in Eig. 8B. At the lONEE it is impossible to obtain the reversible case, even at a scan rate as low as 5 mV s . The effect of quasireversible electrochemistry is clearly seen in the larger AEp values and in the diminution of the voltammetric peak currents at the lONEE (relative to the 30NEE Fig. 8). This diminution in peak current is characteristic of the quasireversible case at an ensemble of nanoelectrodes [78,81]. These preliminary studies indicate that the response characteristics of the NEEs are in qualitative agreement with theoretical predictions [78,81]. 

The fuel gas composition also has a major effect on the cell voltage of SOFCs. The performance data (33) obtained from a 15 cell stack (1.7 cm active electrode area per cell) of the tubular configuration (see Figure 8-1) at 1000°C illustrate the effect of fuel gas composition. With air as the oxidant and fuels of composition 97% H2/3% H2O, 97% CO/3% H2O, and 1.5% H2/3% CO/75.5% CO2I2OV0 H2O, the current densities achieved at 80% voltage efficiency were -220, -170, and -100 mA/cm, respectively. The reasonably close agreement in the current densities obtained with fuels of composition 97% H2/3% H2O and 97% CO/3% H2O indicates that CO is a useful fuel for SOFCs. However, with fuel gases that have only a low concentration of H2 and... 

Figure 3.5 Energy diagram showing the energy overlap of the electronic states of electrode and solution under consideration. Dark shaded areas indicate occupied electronic states, and light shaded areas indicate unoccupied electronic states.

Fig. 20. Pyroelectric current of 15 specimens of poly(vinyl chloride) film cut out from a calender-rolled sheet as indicated in Fig. 21. Electrode area = 1 x 1 cm2 film thickness = 0.2 mm heating rate=6 K/min. Reproduced from Furukawa and others [J. Appl. Polymer Sci. 12,2675 (1968)] by permission of John Wiley Sons,...

The way in which the three main processes (electrode reaction, doublelayer charging, and conduction) at one electrochemical interface concomitantly influence the relation between current and voltage is illustrated in Fig. 1. In the experiments, the total electrochemical cell contains two such interfaces. For kinetic studies, however, this complication is usually eliminated by making the surface area of the electrode of interest (the working electrode or indicator electrode ) much smaller than that of the second electrode (the auxiliary electrode or counter electrode ). 

Figure 3.43 Titration of Cl- with Ag+. (CF + Ag+ =5= AgCl(s)). (A) Volt-ammograms at Ag electrode for 0, 50, 100, 150, and 200% of the equivalence point during the titration. (B) Amperometric titration curve for applied potential at Ej and E2. (C) Amperometric titration curve for two Ag electrodes. AE indicated by the shaded areas in A.

Figure 10.4 Depiction of electrode roughness compared to diffusion layer thickness, vDt. Dotted line indicates approximate boundary of diffusion layer, with (A) diffusion layer thickness greater than surface roughness, resulting in an observed area equal to the projected area, and (B) diffusion layer thickness on the order of surface roughness, resulting in a larger apparent electrode area.

The actual functional dependence of k on the variables is more complex than indicated by Eq. (6.5),40 but as a rule of thumb, the ratio of solution volume to electrode area should be as small as possible and b should be made as small as possible by efficient stirring. 

Figure 8.3 Voltammograms for dissolved H2 (1 atm) in Me2SO (0.5 M TEAP) at a Pt electrode (area 0.458 cm2). Cyclic voltammograms initiated at the rest potential (-0.5 V vs. SCE) after the electrode was preanodized for 2 min at the indicated activation potential. EA scanrateO.l V s l. The dashed (—) voltammogram represents the response of activated electrodes in the presence of an argon atmosphere. Oxidation current is in a downward direction.

Fig. 4.9. (a, top) The 8iph/iph vs. v 1 dependence for W03 electrode sensitized by Dye II in monomeric form ( ) partially aggregated by coprecipitation with PD IV (O). The excitation wavelength 560 nm. / = 20 s. The total surface concentration of Dye II 10 8 mol cm 2. Electrolyte 0.25 M Na2S04. (b, bottom) The potential-time programme and corresponding photocurrent-time curves used for x evaluation. Hatched areas indicate the exposure periods. 

In spite of the much smaller background currents for contact materials, these currents have been omitted (without subtraetion) in further diseussion of the results. The curves usually remained constant after the electrode had been immersed for several hours in the eleetrolyte solution and after the first few sweeps, indicating that the electrochemically active electrode area remained constant during the potential. scans. 

From all these observations it is concluded that the contact resistance is not a function of the surface roughness when an applied pressure of 13-8 MPa is used. This indicates the possibility that the air gaps between the fibers and the electrode are contributing to the electrode surface area as a result of an electrical breakdown phenomenon. This hypothesis would lead to a very low contact resistance since almost all the electrode area would be effective whether the current is carried directly from the electrode to the paper fibers or through a conductive air gap. 

Area indicates the number of fibers adjacent to the electrode however, unlike MUP amphtude, MUP area depends on MUP duration and is therefore influenced by fibers in a larger region compared with that of MUP amplitude. 

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