Characteristics, electrode

Current efficiency depends on operating characteristics, eg, pH, temperature, and cell design, and is generally in the 90—98% range. The cell voltage is a function of electrode characteristics and electrolyte conductivity and can be expressed as... 

The influence of factor series to electrode characteristics has been established. Dependency of the potential of ISE from concentration of defined substance is linear in interval of concentration l lO - l lO mol/1 at the pH 2,0-6,5. Slopping of the graduated graph form 55-56 mV/pC for single-chai ge cation. Potentiometric factors of the selectivity K,, ISE for alkaloids of Papaver Somnifemm has been determined. 

The half-wave potential is also independent of the electrode characteristics, and can, therefore, serve for the qualitative identification of an unknown substance. Owing to the proximity of many different half-wave potentials, its use for qualitative analysis is of limited application unless the number of... 

In view of the limitations referred to above, and particularly the influence of electrode characteristics upon the peaks in the voltammogram, some care must be exercised in setting up an apparatus for stripping voltammetry. The optimum conditions require ... 

Interdigitated band electrode characteristics length = 29 mm, width = I m m and inter-elecirode gap width =500 pm... 

Figure 26b shows the impedance predicted by eqs 8 and 9. As previously discussed, this function is known as the Gerischer impedance, derived earlier in section 3.4 for a situation involving co-limited adsorption and surface diffusion (in the context of Pt). As with the surface-mediated case, the present result corresponds to a co-limited reaction regime where both kinetics and transport determine the electrode characteristics (as reflected in the dependency of 7 chem and Qs on both fq and T eff)- The essential difference between this and the Pt case is that here the kinetics and diffusion parameters refer to a bulk-mediated rather than surface-mediated process. 

The other important factor to affect the operational conditions of the cell is the voltage increase between the carbon and copper lead. This problem has been solved individually in industry. For example, a 250 pm thick layer of nickel can be coated onto the upper part of the carbon anode using the atmospheric plasma spraying method.7 This electrode has been operated at 15 to 17 A dm-2 in a 1000 A scale industrial cell for 19 months. The cell voltage was 9.5 V and polarization did not occur with this electrode. Characteristic points of this new carbon electrode are low polarizability and no anode effect, and the concentration of carbon tetrafluoride contaminating the fluorine is below 2 ppm. 

In Figure 4 the effect of prothrombin on the differential capacity of a PS monolayer is presented. The overall capacitance, which is proportional to the out-of-phase (quadrature) ac current, increases upon interaction with the prothrombin. Moreover, a pseudocapacitance peak (at —0.7 V relative to the N-AgCl electrode) characteristic of cystine-cysteine redox potential appears. The peak potential moves as expected toward more... 

In the case of disc electrodes, a similar behavior to that observed for spherical ones is obtained (although in this case the diffusion layer thickness is an average magnitude), whereas for band or cylinder electrodes, the diffusion layer thickness is always potential dependent, and no constant limit is achieved, even for very small values of the electrode characteristic dimension, confirming the impossibility of these electrodes achieving a true stationary response [5, 8, 16, 29, 30]. 

When the electrochemical properties of some materials are analyzed, the timescale of the phenomena involved requires the use of ultrafast voltammetry. Microelectrodes play an essential role for recording voltammograms at scan rates of megavolts-per-seconds, reaching nanoseconds timescales for which the perturbation is short enough, so it propagates only over a very small zone close to the electrode and the diffusion field can be considered almost planar. In these conditions, the current and the interfacial capacitance are proportional to the electrode area, whereas the ohmic drop and the cell time constant decrease linearly with the electrode characteristic dimension. For Cyclic Voltammetry, these can be written in terms of the dimensionless parameters yu and 6 given by... 

Of primary importance in evaluating new electrode materials to be used in electrolysis, electroanalysis, electrochemical sensors, etc., are their corrosion stability, reproducibility of characteristics, value of background current, and the potential window in which the background current remains low and thus does not interfere with the electrode characteristics. Diamond meets all these criteria perfectly. 

To conclude with the primary electrode characteristics, we describe briefly the DLC electrodes. The data are scarce and partly contradictory, probably due to the differences in film preparation methods. According to Howe [60], even films as thin as 50 nm are quite stable against corrosion. However, in later works [61, 62] such thin films turned permeable for electrolytes. The penetration of the electrolyte to a substrate metal resulted in its corrosion and, ultimately, in film peeling. Thicker films (0.1 to 1 pm) were less subjected to damage. The current-potential curves in supporting electrolytes resemble those for crystalline diamond electrodes (see Figs. 7, 8) the potential window is narrower, however [63], Fluorination of a-C H enhances corrosion resistance of the films significantly [64],... 

A PPy/PQQ modified GC electrode was used for amperometric detection of V-type nerve agent decomposition products. The electropolymerization of pyrrole was efficiently used for immobilization of the biocatalyst, PQQ. The introduction of CaCl2 as a supporting electrolyte during electrodeposition significantly improves the response of the sensor to DMAET and DEAET. Amperometric studies targeted to detection of DMAET and DEAET by PPy/PQQ electrode were performed at a constant potential set at 0.25 V, and the electrode characteristics such as sensitivity and the analyte detection limit were determined. 

Recall that the Wagner number depends on the solution conductivity, characteristic length, as well as the interfacial electrode characteristics. A solution has been given for the primary current distribution where the entire interior pipe surface (radius r0) is uniformly cathodically protected to / and the pipe interface is considered to be nonpolarizable (16). The IR drop down the pipe to a distance, L, can be calculated so that the maximum tolerable potential drop from the entrance to the far end is known ... 

Ionic path impedance through the ceramic phase and electronic path impedance through the metallic phase have been found to be dominant factors in determining the electrode characteristics.In order to provide a low sheet resistance anode, it is imperative that the metallic and ceramic phases have maximized continuous paths that allow ionic and electronic migration from the electrolyte/anode interface throughout the entire anode. 

For monovalent ions the slope of the electrode characteristic (2.303 RTri F ) is theoretically equal to 59.1 mV for 10 concentration units each at 25° C. 

Ni-Ti films prepared by the flash evaporation technique showed similar electrodic characteristics (86). High roughness factors for the Ni and Cu amorphous alloys were determined from the double-layer capacitances [2-300 (61, 84, 85) and 102—103 (62), respectively]. And lower activities were found for the crystalline samples (Fig. 1), but the Pd-Zr specimen did not exhibit these differences (60). The electrocatalytic activity per true unit area was practically the same as that of pure Ni and Cu electrodes (62, 85). 

THE YSZ ELECTROLYTE SURFACE LAYER EXISTENCE, PROPERTIES, AND EFFECT ON ELECTRODE CHARACTERISTICS... 

Table 4.5. Electrode characteristics of metal pairs M1-P-M2 in systems AE -potential difference of standard metal electrodes [19], AUox potential difference of oxide pair [50], Acp - difference of metal work functions...

Fig. 1.28 Effect of perfluorocarbon additives on the kinetics of oxygen reduction on Pt-based electrodes. Characteristics of flooded cell.

SEIRAS is emerging as a powerful technique for interfacial studies in electrochemistry and electrochemical catalysis. Chapter 9 of this volume is devoted to SEIRAS and describes experimental aspects and many applications. Highlights are presented below, and the reader is referred to Chapter 9 for details regarding cell design, working electrode characteristics, and preparation techniques and applications. 

This compression leads to a smaller pore volume in the anode, reflected in the degree of the electrode s gas Ailing and, thus, in the electrode characteristics. In addition, anode creep may disturb the contact between anode and matrix. Both factors are limiting factors for the lifetime of molten carbonate fuel cells. Nickel is alloyed with chromium and/or aluminum in order to reduce the plasticity of the nickel anode and make it more rigid. 

We carried out comparative studies of the effect of the porous structure of carbon materials on electrochemical electrode characteristics using various carbide carbons (CCs). Main structural characteristics for CCs based on silicon carbide are presented in Table 27.3 and those for titanium carbide are in Table 27.4. Specific surface areas were calculated on the basis of the nitrogen adsorption data with calculation using the DFT technique. This method is used to measure micropores and mesopores, but not macropores. 

High-rate electrode characteristics of V2O5 sol/carbon composites were studied. The V2O5 sol was prepared by a reaction between metallic vanadium and a hydrogen peroxide solution. The acetylene carbon black powder was added to the sol together with acetone in the form of a homogeneous suspension. A composite of amorphous V2O5 and carbon black was introduced into a macroporous nickel... 

In 1988, a pioneering work dealing with electrode characteristics of an immobilized enzyme chemically modified electrode based on bilayer-film coating for amperometric determination of glucose was reported. In this work, a substrate was coated with two kinds of polymeric films in a bilayer state, that is, first with the cobalt tetrakis(o-aminophenyl)porphyrin polymer film and then with the enzyme film consisting of bovine serum albumin and glucose oxidase that were... 

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