Shunt electrode

The life span of solid-state membrane electrodes is determined by the frequency of repolishing. If the membrane surface does not need to be cleaned off very often, then the electrode can last for years. Electrodes with inner solutions should be filled enough to insure undisturbed contact between membrane and shunt element. If unseen air bubbles have formed inside the electrode between the membrane surface and the shunt electrode, irreproducible measurements may result, or under some circumstances the measuring circuit current may be interrupted. This is evident from unstable... 

In the liquid ion-exchanger electrodes of Corning, a ceramic frit imbedded in the electrode body serves as an interface-stabilizer. As shown in Fig. 28, the inner shunt electrode, with its own electrolyte, dips directly into the exchanger phase. 

If it is desired to use the biamperometric method for detecting the end point, then the calomel electrode and also the silver rod (if used) must be removed and replaced by two platinum plates 1.25 cm x 1.25 cm. The potentiometer (or pH meter) used to measure the e.m.f. must also be removed, and one of the indicator electrodes is then joined to a sensitive galvanometer fitted with a variable shunt. The indicator circuit is completed through a potential divider... 

Cell construction, current feeders and power supply are less expensive for the hipolar connection (see also Fig. 12), but the different potentials of all electrodes can be problematical (e.g. shunt currents, additional by-products, and corrosion in the channels). 

In the previous papers(12,13), we reported on the vessel access type, i.e. tubular type, glucose sensor. It consisted of a glucose electrode system with a GOX enzyme immobilized Nylon membrane and a glucose semipermeable membrane, and a reference oxygen electrode system. The sensor could directly measure up to 700 mg/dl of BGL in an arterial blood stream when it was placed into an external A-V shunt. This sensor, however, has some problems such as thrombus during in vivo testing without heparin and clinical complexity associated with implanting the sensor in a blood stream. 

Fig. 48. Influence of electrodes and central buffer feed on electrical field and pH. (A) Apparatus with lateral wicks covering the electrodes starting in buffer vessels A and C separated from central buffer feed B. (B) The electrical field is curved as the result of the shunt over buffer feed B (G4). (C) Insufficient rinsing of the electrodes causes modification of pH on the curtain (LI).

Increasing separation toward the bottom Bottom electrodes Buffer shunt Evaporation Feeding by supplementary wicks Trickle feeding of background Good dissipation of heat (thin wall and cooling system) reduction of heat (lower n, thinner paper)... 

When an a.c. voltage is applied to a perfect capacitor, no energy is dissipated. However, a real capacitor dissipates energy because of lead and electrode resistances, d.c. leakage resistance and, most importantly, dielectric losses. These account for the capacitor s dissipation factor or loss tangent tan 3. It is sometimes convenient to regard the lossy capacitor as an ideal capacitor shunted by a resistance Rp or in series with a resistance rs, as shown in Fig. 5.5. 

In general, a large serial resistance and an over-small parallel resistance (shunt) tend to reduce the FF. Strategies for reducing the serial resistivity by improving the quality of the Ohmic contact will be discussed. The insertion of very thin polar layers like LiF have been shown to reduce the interface barrier at the cathode in bulk heterojunction solar cells, if they are evaporated between the photoactive material and an A1 electrode [93,94]. 

For practical solar cells, the ideal equivalent circuit will be modified to include the series resistance from Ohmic loss in the two electrodes and the shunt resistance from leakage currents (Fig. 5.36a). The diode current for a realistic setup is then given by... 

The Randles circuit is at the electrode/polymer interface (case a). The imaginary component of the impedance is dominated by the double-layer capacitance, and the real one is controlled by the double layer. The capacitance of the transmission line is shunted and the transmission fine is not involved. 

The equivalent circuit of Fig. 37 clearly demonstrates the main experimental difficulties encountered in determining Rac it is evident that only d.c. measurements are likely to prove practical else ZF will be too small and the semiconductor will be shunted by Rel (which is likely to be very small). The bulk resistor RB is only larger than Rac for intrinsic semiconductors and it has proved difficult to extend the technique to extrinsic materials as R becomes effectively shunted by RB. Evidently, only Rsc and Rel vary with potential applied across the semiconductor between the back contact and the reference electrode in solution however, the change in Rel is normally much smaller than Rsc as the mobility of the ions in solution is so much smaller than that of the carriers in the semiconductor. 

Many start-up/shutdown procedures have aimed to reduce the corrosion current through practices such as anode purging and shunting. Others have attempted to nse more stable carbon materials such as graphitized carbon and carbon nanotnbes (CNTs). - To delay the onset of the COR during fuel starvation, WOR catalysts have been incorporated into the anode electrodes. Increasing anode ionomer content has also been recommended for a fnel starvation-resistant anode because it increases the amount of water available for the WOR. - In general, the materials approaches are applicable to all kinds of carbon corrosion. 

Electrolyte pathways in the porous electrodes, which shunt the insulating material down to the electronically conducting zone of the electrode. 

A bipolar electrode consists of an anode in electrical contact with a cathode—it is polarized in the electric field of the cell. Bipolar cells have two feeder electrodes and a number of bipolar electrodes between them. Ideally, the current supplied to the system can be multiplied by the number of anodes or cathodes to calculate the charge that is passed to the electrolyte. In reality, some current losses occur due to bypass or shunt currents, so-... 

Fig. 2-39. The basic mode of the contact polarisation curve (CPC) field installation 1- ore body 2- borehole 3- compensation resistor 4- electric current source 5- resistance of shunt 6-potentiometer 7- recorder A- current eleetrode B- auxiliary current electrode M- measuring electrode N- non-polarisable measuring (reference) electrode (reproduced with permission from Ryss, 1983).

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