Anode in electrolytic cell

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. 

Since this is an oxidation, it must be the anode. In electrolytic cells, the anode is positively charged and will therefore attract anions. 

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 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. 

When conducting a differential scanning calorimetry (DSC) study on the stability of carbonaceous anodes in electrolytes, Tarascon and co-workers found that, before the major reaction between lithiated carbon and fluorinated polymers in the cell, there was a transition of smaller thermal effect at 120 °C, marked peak (a) in Figure 28. They ascribed this process to the decomposition of SEI into Li2C03, based on the previous understanding about the SEI chemical composition and the thermal stability of lithium alkyl carbonates.Interestingly, those authors noticed that the above transition would disappear if the carbonaceous anode was rinsed in DMC before DSC was performed, while the other major processes remained (Figure 28). Thus,... 

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. 

This is a process in which the surface coating of oxide on aluminium (A1203) is made thicker. In this process the aluminium object is made the anode in a cell in which the electrolyte is dilute sulfuric acid. During the electrolysis process, oxygen is produced at the anode and combines with the aluminium. 

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. 

The reverse process takes place at the anode in a cell of this type. Thus 1 — v equivalents of the anion migrate to the anode, where they react with the metal of the electrode to form the insoluble salt, leaving the concentration of the electrolyte unaltered. 

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,... 

A 55.5-kg slab of crude copper from a smelter has a copper content of 98.3%. Estimate the time required to purify it electrochemically if it is used as the anode in a cell that has acidic copper(II) sulfate as its electrolyte and a current of... 

Use Hardener for platinum and palladinum in jewelry, electrical contact alloys, catalyst, medical instruments, corrosion-resistant alloys, electrodeposited coatings, nitrogen-fixing agent (experimental), solar cells (experimental) the oxide is used to coat titanium anodes in electrolytic production of chloride the dioxide serves as an oxidizer in photolysis of hydrogen sulfide. 

Nickel and its alloys are extensively used in electrochemical applications due to its good corrosion resistance. In battery applications, nickel is used as the positive electrode in nickel-cadmium, nickel-iron, nickel-zinc, and nickel-hydrogen batteries, and as anodes in fuel cells, electrolyte cells and electro-organic syntheses . Because of the importance of nickel in battery applications, electrochemical properties of nickel have been studied for more than IOC years since 1887 when Dun and... 

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. 

Cominco in the late 1960 s developed a method to precondition the anodes in separate cells outside the circuit (2). The process involves the creation of a hard dense Pb02 layer on the surface of the anode by oxidation of the anode at high current density in an acidic fluoride-containing electrolyte. This preconditioning process takes 8-12 hours. In this process the... 

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. 

In the continuous electrolytic regeneration of cupric chloride etchant the cuprous chloride is oxidised anodically in a cell while the cathode of the cell recovers the copper as a solid flake deposit. The cell, developed by the Electricity Research Council in the UK is divided by a membrane which limits the transport of copper ions, which are in fact complexed, probably mainly as CuCl3 . An economic analysis of the process realised a two year payback on the capital investment. In the case of alternative etchants, such as ferric chloride, continuous regeneration is also feasible. 

In electrolytic cells, as in voltaic cells, oxidation occurs at the anode and reduction occurs at the cathode. 

Purification of copper is achieved by electrolysis, as illustrated in Figure 23.11 . Large slabs of crude copper serve as ihe anodes in tire cell, and thin sheets of pure copper serve as the catiiodes. The electrolyte consists of an acidic solution of CUSO4. Application of a suitable voltage to flie electrodes causes oxidation of copper metal at the anode and reduction of Cu to form copper metal at the cathode. This strategy can be used because copper is both oxidized and... 

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