Electrode short-circuited

This implies that Electrochemical Promotion or NEMCA is an electrochemically controlled metal-support interaction. It also implies that metal-support interactions on these supports can be viewed as a self-driven wireless NEMCA system, such as the one explored by Cavalca, Haller and Vayenas for the CH3OH oxidation system under catalyst-counter electrode short-circuit conditions where gaseous 02 replenishes O2 in the YSZ support at the vicinity of the counter electrode.24... 

Simple electroless techniques have been used for the formation of CdTe layers following an anodic or a cathodic route of deposition. For instance, spontaneous cathodic formation of CdTe was observed on Ti or glass electrodes short circuited with a corroding A1 contact (electron source) in a solution of Cd " " and HTe02 ions [96]. After thermal treatment and subsequent growth of an a-Pb02 layer on them, the as-obtained CdTe thin films were found to exhibit n-type behavior in alkaline polysulfide PEC cells. 

Figure 2.33 Theoretical conversion efficiencies for photoelectrochemical H2O cleavage (a) -type electrode combined with a metal connter electrode (b) -type electrode short-circuited with a p-type electrode of equal bandgap. Calculated for different overvoltages of (a) O.V (b) 0.3 V (c) 0.5 V (d) 0.7 V. Source Memming (1990).

Fig. 11.17 Theoretical conversion efficiencies for photoelectrochemical H20-splitting a) n-type electrode combined with a metal counter electrode b) n-typc electrode short-circuited with a p-electrode of equal bandgap calculated for different overvoltages of a = 0 V b = 0.3 V c = 0..5 V d = 0.7 V. (After ref. [27])...

The standard procedure for stability testing utilizes the 2-electrode short-circuit measurement detailed in Chapter 2-Electrode Short Circuit and j-v . See Section Cell Setup and Connections for 3- and 2- Electrode Configurations for a discussion on basic cell setup and electrolyte selection. 

It is typical feature for the electret transducers that in most cases the electret is one-side metahzed and is placed between two plate electrodes short-circuited by a resistor. The charged electret surface gives rise to an electric field in the air gap which is formed between the non-metahzed electret surface and its adjacent electrode. This field can be found by an equation analogous to the one in (Palaia et al.) ... 

R.H.-independent signal output has been achieved in thefour-probe type sensor shown in Fig. 36.4, where two additional Ag probes are inserted in the proton conductor bulk (AA) beneath the Pt electrodes. One of the Pt electrodes is covered by a layer of AA sheet, which acts as a sort of gas diffusion layer. The short-circuit current flowing between the two Pt electrodes is proportional to H2 concentration but dependent on R.H., just as in the previous amperometric sensor. On the other hand, the difference in potential between the two Ag probes (inner potential difference, AE g) with the outer Pt electrodes short-circuited is shown to be not only proportional to H2 concentration but also independent of R.H. as shown in Fig. 36.3b and Table 36.2. This mode of sensing has no precedence, and is noted as a new method to overcome the greatest difficulty in using proton conductor-based devices, i.e. their R.H. dependence. 

Handheld Gauss or individual electrode current measuring tools require operators to be continuously roaming the tankhouse to take measurements. They often walk on top of the electrode header bars, which imposes both safety issues and in some cases can increase the likelihood of moving the electrodes out of alignment and actually causing electrode short circuits. 

As botli processes, reduction and oxidation, take place on tlie same electrode surface (a short-circuited system), it is not possible to directly measure tlie corrosion current. Experimentally, only tlie sum of tlie anodic and catliodic... 

The roof, in the form of a dome, is either comprised of refractory brick held in place by a water-cooled steel roof ring, or it may be composed of water-cooled panels. Sometimes water-cooled rings or glands are placed on the roof around the electrodes to maintain the refractory. On high power furnaces refractory is used around the electrodes to minimize the possibiUty of electrical short circuits. 

This inherent feature of ECM, whereby an equiHbriumgap width is obtained, is used widely in ECM for reproducing the shape of the cathode tool on the workpiece. (J) Under short-circuit conditions the gap width goes to zero. If process conditions such as too high a feed rate arise the equiHbrium gap may be so small that contact between the two electrodes ensues. This condition causes a short circuit between the electrodes and hence premature termination of machining. 

There are four basic variations of the linear MHD channel (Fig. 5) which differ primarily in their method of electrical loading. The simplest is the two-terrninal Faraday or continuous electrode generator, Figure 5a, where a single pair of current-collecting electrodes spans the channel in the axial direction, short-circuiting the channel from end to end. Hence, for this configuration, = 0, andj can be obtained from equations 21 and 22 ... 

When the electrodes are connected by a short circuit, the voltage is zero but only the average field need vanish local values are often quite large. 

An electrochemical reaction is said to be polarized or retarded when it is limited by various physical and chemical factors. In other words, the reduction in potential difference in volts due to net current flow between the two electrodes of the corrosion cell is termed polarization. Thus, the corrosion cell is in a state of nonequilibrium due to this polarization. Figure 4-415 is a schematic illustration of a Daniel cell. The potential difference (emf) between zinc and copper electrodes is about one volt. Upon allowing current to flow through the external resistance, the potential difference falls below one volt. As the current is increased, the voltage continues to drop and upon completely short circuiting (R = 0, therefore maximum flow of current) the potential difference falls toward about zero. This phenomenon can be plotted as a polarization diagram shown in Figure 4-416. 

Salt Concentration Cells. In this type of cell the two electrodes are of the same metal (i.e., copper). These electrodes are immersed completely in electrolytes of the same salt solution (i.e., copper sulfate) but of different concentrations. When the cell is short circuited, the electrodes (anode) exposed to the dilute solution will dissolve into the solution and plate the electrode (cathode) exposed to the more concen-trated solution. These reactions will continue until the solutions are of the same concentration. Figure 4-432 shows a schematic of a salt concentration cell. 

It is apparent from this that since the rates of the cathodic and anodic processes at each electrode are equal, there will be no net transfer of charge in fact, with this particular cell, consisting of two identical electrodes in the same electrolyte solution, a similar situation would prevail even if the electrodes were short-circuited, since there is no tendency for a spontaneous reaction to occur, i.e. the system is at equilibrium and AG = 0. 

If the two electrodes are short-circuited R 0, and IR 0, and fp ctu will attain its minimum value. If the conductivity is very high and fp ceii is small enough to be disregarded it follows from equation 1.62 that... 

Another complication had to be matched when the zinc electrode was made reversible in a battery with unstirred electrolyte or an electrolyte gel, dendritic growth of the electrolytically deposited metal takes place. The formation of dendrites cannot be fully suppressed by the use of current collectors with large surface areas (grids, wire fabrics). However, by using improved separators combined in multi layer arrangements, the danger of short-circuiting is reduced. 

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