Cathode in electrolytic cell

In electrochemistry the same phenomenon (essentially related to charge conservation) occurs, yet the reduction of the acceptor A occurs at one electrode (the cathode in electrolytic cells) and the oxidation of the donor D at the other (anode). Thus the kinetics of the overall cell reaction depends on both half-reactions, in a similar way as the kinetics of a homogeneous electron transfer depends on the acceptor and the donor. However,... 

OTHER COMMENTS used for lead pencils, crucibles, stove polish, molds, lubricants, paints, and coatings other uses include electroplating, cathodes in electrolytic cells, matches, and explosives. 

An electrochemical cell in which electrolysis takes place is called an electrolytic cell. The arrangement of components in electrolytic cells is different from that in galvanic cells. Typically, the two electrodes share the same compartment, there is only one electrolyte, and concentrations and pressures are far front standard. As in all electrochemical cells, the current is carried through the electrolyte by the ions present. For example, when copper metal is refined electrolytically, the anode is impure copper, the cathode is pure copper, and the electrolyte is an aqueous solution of CuS04. As the Cu2f ions in solution are reduced and deposited as Cu atoms at the cathode, more Cu2+ ions migrate toward the cathode to take their place, and in turn their concentration is restored by Cu2+ produced by oxidation of copper metal at the anode. 

The various possible electrode reactions at the cathode and at the anode in electrolytic cells have been shown in Table 6.2. It has been pointed before that the outcome of an electrolytic process can be made on the basis of knowledge of electrode potentials and of overvoltages. The selection of the ion discharged depends on the following factors (i) the position of the metal or group in the electrochemical series (ii) the concentration and (iii) the nature of the electrode. Examples provided hereunder deliberate on these aspects. 

The electrolysis of alumina is carried out in electrolyte cells made of mild steel which are lined inside with an insulating refractory and carbon (either carbon bricks or carbon and coal tar pitch). The cell bottom is connected to the cathode terminal and serves as the cathode. Carbon electrodes introduced from the top serve as anodes. A more detailed description is given below. 

In chlorate production the EMOS system has also been used to determine the formation of deposits on the electrodes, either the anode or cathode and combined with the information on process and electrolyte composition the system determines the need for cell cleaning or acid rinsing. The close monitoring of individual cell voltages has allowed plant engineers to establish the most appropriate current density for production lines dependent upon the state of the anode coatings. This allows for the same overall production capacity while permitting the operation of two different cell lines in the cell room at different current densities based upon the state of the anodes and cathodes in the cell. 

FIGURE 18.19 Electrorefining of copper metal, (a) Alternating slabs of impure copper and pure copper serve as the electrodes in electrolytic cells for the refining of copper, (b) Copper is transferred through the CuS04 solution from the impure Cu anode to the pure Cu cathode. More easily oxidized impurities (Zn, Fe) remain in solution as cations, but noble metal impurities (Ag, Au, Pt) are not oxidized and collect as anode mud. 

For silver plating the electrolyte is a solution of a silver salt. The article to be plated is made the cathode in the cell so that the metal ions move to it when the current is switched on. The cathode reaction in this process is ... 

When aqueous solutions are placed in electrolytic cells, the collection of the solute at the cathode and anode may be affected by the presence of hydrogen and hydroxide ions in the solution. 

During electrochemical deposition of metal oxides, metal hydroxides and metals, current are passed between an anode and cathode in a cell containing weakly alkaline electrolyte. The anion of the electrolyte is such that it does not form an insoluble salt with the metal anode. Metal ions issuing from the metal anode make contact with hydroxyl ions in solution and form finely divided oxides or hydroxides. The oxides or hydroxides are removed and chemically reduced to finely divided metal particles. The voltage necessary for carrying out the oxidation of the metal to metal ions is reduced through the use of an electrode as cathode, thereby reducing the cost of the process. 

Recently, much interest has centered on the electrocatalytic behavior of Ni-Mo alloyst (prepared electrolytically or by thermal reduction of oxide or molybdate mixtures) for cathodic H2 evolution in alkaline-water electrolyzers or as cathodes in electrolytic CI2 cells. The h.e.r. at these electrode materials exhibits remarkably low Tafel slopes, in the range 22-26 mV, at elevated temperatures, 363 K. This is one of the reasons for their excellent behavior as electrocatalysts for the h.e.r. However, the Tafel slopes exhibited by these materials depend on temperature in a most unusual way, decreasing with increasing temperature, as do some of the results at NP (Fig. 4). 

Let us consider only the cathode (negative electrode in electrolytic cells) at this time. What happens if we make the cathode slightly negative Electrons are forced into the cathode by the external battery. The negative charge attracts the positive ions (Mn, Sn ) in the solution. If the metal ions pick up these electrons, they will be reduced to the... 

There are two kinds of electrochemical cells, voltaic (galvanic) and electrolytic. In voltaic cells, a chemical reaction spontaneously occurs to produce electrical energy. The lead storage battery and the ordinary flashlight battery are common examples of voltaic cells. In electrolytic cells, on the other hand, electrical energy is used to force a nonspontaneous chemical reaction to occur, that is, to go in the reverse direction it would in a voltaic cell. An example is the electrolysis of water. In both types of these cells, the electrode at which oxidation occurs is the anode, and that at which reduction occurs is the cathode. Voltaic cells wOl be of importance in our discussions in the next two chapters, dealing with potentiometry. Electrolytic cells are important in electrochemical methods such as voltammetry, in which electroactive substances like metal ions are reduced at an electrode to produce a measurable current by applying an appropriate potential to get the nonspontaneous reaction to occur (Cha]pter 15). The current that results from the forced electrolysis is proportional to the concentration of the electroactive substance. 

This experimental run used a membrane manufactured by wicking an equilibrium composition electrolyte into a partially sintered MgO matrix. The cathode in this cell was carbon and the anode was CoSg. The process gas supplied to the cathode had an HjS concentration of 1.33% and a CO, concentration of 19.3%. H,S concentrations were driven as low as 2000 ppm as shown in Figure 5 (corresponding to 84.9% removal), but CO, removal was also observed as shown in Figure 6. Condensed sulfur was recovered from the anode sweep lines, but poor cell seals on the anode side made complete sulfur recovery impossible. 

The main current-producing reaction is described by Equation (11.11). The product of this reaction is lithium dithionite that is insoluble in the electrolyte. Therefore, a reasonable porous cathode structure is of great importance for provision of high capacity and power characteristics of sulfur dioxide-lithium cells. The cathodes in such cells are similar to cathodes of thionyl chloride-lithium cells. The cells of the "lithium-sulfur dioxide" system are also produced using the rammed and wound coil designs. Porous polypropylene is applied as a separator. 

Educational research has shown that students are often confused about the nature of electric current both in metallic conductors and in electrolytes (assuming, for example, that current always involves drifting electrons, even in solution). Misconceptions have also been detected in identifying the anode and the cathode, its sign and its function in electrolytic cells. Students need to remember that an oxidation half reaction occurs always at the anode and a reduction half reaction occurs always at the cathode. 

Popov KI, Maksimovic MD, Totovski DC, Nakic VN (1983) Some aspects of current dcmsily distribution in electrolytic cells I dendritic growth of cadmium at the cathode edge in galvanostatic electrodeposition. Surf Technol 19 173-180... 

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