Electrodes to the Source of Current

The current is carried to the electrolyzer by copper or alluminium busbars from which it is distributed by cables or by a system of elastic copper lamellae to the terminals of the electrodes. The current passes through many points of contact which determine the magnitude of so called contact resistance. The more imperfect are the contacts at these points the greater the losses in electrical 

Anode lug A and carrier bar ot cathode B rest upon a copper strip conductor. 

The design of connection of the electrodes to the current conductors depends on the nature of the process. There is a considerable difference between the connections used in electrolyzers where periodical removal of electrodes from the bath is required and the connections used in electrolyzers where the electrodes are not removed and form a fixed part of the equipment. The first case is encountered mainly in electrometallurgical refining processes where anode scraps and cathodes with the deposited metal are removed. In such oases 

The way of connecting the current conductors to electrodes which remain permanently dipped into the solution of electrolytes depends on the material of the electrode (whether noninetallic, such as graphite, or metallic.) One possible method of connecting a graphite rod to the current conductor is schematically represented in Fig. 41. the upper end of the electrode has a small recess it is encompassed by a two-piece copper terminal which is connected to the current conductor. A terminal for connection of a plate shaped electrode to the current conductor is illustrated in Fig. 42. At first the upper edge of plate A is fitted 

A — graphite electrode, b, d — two-pleoe copper terminal, c — clamping bolts, f — current conductor. 

---

The 3-in.-square platinum plates are welded to a heavy platinum wire that protrudes through one of the holes cut in the glass lid. Heavy copper wire (No. 10) is used to connect the electrodes to the source of current. 

The connection of metal electrodes to the source of current can be made in a much simpler way using bolts, revets, welding, brazing, soldering etc. In case of wire gauze electrodes usually spot contacts are not satisfactory but the wire-gauze should be welded to a metal frame all around the current is then led into this frame. 

At the moment, when, due to this reaction, two electrons are consumed at the cathode an equal number of electrons is set free at the other electrode (the anode) by two chloride ions yielding one electron each whereby they are transformed into two chlorine atoms. The electrons so set free then return through the outer conductor from the electrode to the source of the current, while nascent chlorine atoms combine in pairs to form molecules of gaseous chlorine which escape into the atmosphere. The anodic reaction can thus be written as ... 

The direct current is conducted to and from the electrolyzed solution by means of electrodes. Chemical reactions proceed at the electrodes and electric energy is consumed. The electrode connected to the negative pole of the current source is called the cathode it is the electrode through which the electrons enter the electrolyte or through which the positive electricity leaves the solution. The electrode connected to the positive polo of the current source is called the anode it is the electrode through which the electrons leave the solution to return to the source of current or through which the positive electricity enters the solution. 

Apparatus. The source of current is a potentiostat which is used in conjunction with a reference electrode (commonly a saturated calomel electrode) to control the potential of the working electrode. The circuit will be essentially that shown in Fig. 12.2(a) but with the addition of the integrator or of a coulometer. 

The electrochemical polymerization process is achieved by polymerization of monomers in an electrolytic cell (Subramanian and Jakubowski, 1978). The electrode is the source of active species that initiates the polymerization. It is necessary to select a solvent electrolyte system which is capable of forming a solution with the monomer and having sufficient current-conducting properties. In the process employed by Bell and coworkers (Bell et al., 1987 Wimolkiatisak and... 

As a rule an electrolytic cell (electrolyzer) contains several electrodes. Depending on the kind in which the electrodes are connected to the source of the current we speak of either monopolar or bipolar electrodes. 

An electrolytic cell is similar to a voltaic cell except the electrochemical reactions involved do not occur spontaneously but require the input of current from an external source. Wires connected to each end of a battery and submerged in a suitable electrolyte can represent an electrochemical cell. As with voltaic cells, the creation and/or removal of ions at the electrodes facilitates the transfer of current into and out of solution. If the electrolytes in solution are redox-inert within the stability field of water (e.g., Na and Cf) and the voltage is over 1.2 volts, the hydrolysis of water may transfer current at the electrodes ... 

Apparatus. The source of current may be a generator, storage battery, or rectified alternating current with provisions to avoid fluctuations. An ammeter and a voltmeter are required. Electrodes may be solid or porous, bars of most any shape, sheets, gauze, or liquid (as mercury). Carbon,... 

It was assumed simultaneously that the application of electric field accelerate only the transport of ions through the paste without effect on the microstmcture of hardened cement paste. However, the experimental results do not support this assumption. On the contrary, at long term action of electric field the microstmcture of paste is altered [197], Application of electric field will also cause the effect of electroosmosis, consisting in the flow of ions towards an electrode being the source of electric current, with the double layer formation on the gel surfaces [197]. According to some authors this phenomenon can accelerate the transport of chloride ions through cement paste with microcracks [197],... 

Electrochemical methods for NO determination offer several features that are not available with spectroscopic approaches. Perhaps the most important is the capability of microelectrodes to directly measure NO in single cells in situ, in close proximity to the source of NO generation. Figure 2 shows sensors that have been developed for the electrochemical measurement of NO. One is based on the electrochemical oxidation of NO on a platinum electrode (the classical Clark probe for detection of oxygen) and operates in the amperometric mode [17]. The other is based on the electrochemical oxidation of NO on conductive polymeric porphyrin (porphyrinic sensor) [24]. The Clark probe uses a platinum wire as a working electrode (anode) and a silver wire serves as the counterelectrode (cathode). The electrodes are mounted in a capillary tube filled with a sodium chlo-ride/hydrochloric acid solution separated from the analyte by a gas-permeable membrane. A constant potential of 0.9 V is applied, and direct current (analytical signal) is measured from the electrochemical oxidation of NO on the platinum anode. In the porphyrinic sensor, NO is catalytically oxidized on a polymeric metalloporphyrin... 

Schematic diagram of a thermospray ion. source. This source, of current design, also incorporates (a) a discharge electrode so that the source can be operated in plasmaspray mode and (h) a repeller electrode to induce fragmentation. The vaporizer itself can be used as a discharge electrode.

Fig. 10.9 Diagram illustrating the source of the IR error in potential measurements on a cathodically protected structure. BA is the absolute electrode potential of the structure CD is the absolute electrode potential of the anode and CB is the field gradient in the environment due to cathodic protection current flux. A reference electrode placed at E will produce an IR error of EFin the potential measurement of the structure potential. If placed at G the error will be reduced to GH. At B there would be no error, but the point is too close to the structure to permit insertion of a reference electrode. If the current is interrupted the field immediately becomes as shown by the dotted line, and no IR is included...

If the circuit is broken after the e.m.f. has been applied, it will be observed that the reading on the voltmeter is at first fairly steady, and then decreases, more or less rapidly, to zero. The cell is now clearly behaving as a source of current, and is said to exert a back or counter or polarisation e.m.f., since the latter acts in a direction opposite to that of the applied e.m.f. This back e.m.f. arises from the accumulation of oxygen and hydrogen at the anode and cathode respectively two gas electrodes are consequently formed, and the potential difference between them opposes the applied e.m.f. When the primary current from the battery is shut off, the cell produces a moderately steady current until the gases at the electrodes are either used up or have diffused away the voltage then falls to zero. This back e.m.f. is present even when the current from the battery passes through the cell and accounts for the shape of the curve in Fig. 12.1. 

---