Cathode reductions, electrochemical cells

Use the following terms to create a concept map cathode, electrodes, electrochemical cell, anode, oxidation, and reduction. 

A battery is a collection of one or more electrochemical cells that convert chemical energy into electrical energy via electrochemical reactions (oxidation-reduction reactions). These reactions take place at the battery s anode and cathode. The electrochemical cells are connected in series or in parallel depending on the desired voltage and capacity. Series connections provide a higher voltage, whereas parallel connections provide a higher capacity, compared with one cell. 

In electrogravimetry the analyte is deposited as a solid film on one electrode in an electrochemical cell. The oxidation of Pb +, and its deposition as Pb02 on a Pt anode is one example of electrogravimetry. Reduction also may be used in electrogravimetry. The electrodeposition of Cu on a Pt cathode, for example, provides a direct analysis for Cu +. 

Reduction of Fe + to Fe + occurs at the working electrode, making it the cathode in the electrochemical cell. 

Identify the anode and cathode for the following electrochemical cells, and write the oxidation or reduction reaction occurring at each electrode. 

In an electrochemical cell, these two half-reactions occur at two different electrodes, which most often consist of metal plates or wires. Reduction occurs at the cathode a typical half-reaction might be... 

In an electrochemical cell, electrical work is obtained from an oxidation-reduction reaction. For example, consider the process that occurs during the discharge of the lead storage battery (cell). Figure 9.3 shows a schematic drawing of this cell. One of the electrodes (anode)q is Pb metal and the other (cathode) is Pb02 coated on a conducting metal (Pb is usually used). The two electrodes are immersed in an aqueous sulfuric acid solution. 

FIGURE 12.2 In an electrochemical cell, J a reaction takes place in two separate 2" regions. Oxidation takes place at one 3 electrode (the antxle), and the electrons released travel through the external circuit to the other electrode, the cathode, where they cause reduction. The circuit is completed by ions, which carry the electric charge through the solution. 

In case (c), a voltage opposite to and higher than the emf of the galvanic cell is imposed as a consequence, the current flow and hence also the electrochemical reactions are reversed, which means that half-reaction 1 becomes an anodic oxidation and half-reaction 2 is a cathodic reduction, so that Zn is deposited instead of Cu. 

Further, it can be seen from Fig. 1.1 that under all conditions prevailing Cu is the positive and Zn the negative pole however, in case (b) Cu is the cathode (reduction) and Zn the anode (oxidation). Considering the flow direction within the electrolyte, one usually finds that the anode is upstream and the cathode downstream. It is also clear that by the electrochemical conversions the original galvanic cell is depleted in case (b), but can be restored by the external electrical energy source in case (c). 

For forced-convection studies, the cathodic reaction of copper deposition has been largely supplanted by the cathodic reduction of ferricyanide at a nickel or platinum surface. An alkaline-supported equimolar mixture of ferri- and ferrocyanide is normally used. If the anolyte and the catholyte in the electrochemical cell are not separated by a diaphragm, oxidation of ferrocyanide at the anode compensates for cathodic depletion of ferricyanide.3... 

The cathode is defined as the electrode at which reduction occurs, i.e., where electrons are consumed, regardless of whether the electrochemical cell is an electrolytic or voltaic cell. In both electrolytic and voltaic cells, the electrons flow through the wire from the anode, where electrons are produced, to the cathode, where electrons are consumed. In an electrolytic cell, the dc source forces the electrons to travel nonspontaneously through the wire. Thus, the electrons flow from the positive electrode (the anode) to the negative electrode (the cathode). However, in a voltaic cell, the electrons flow spontaneously, away from the negative electrode (the anode) and toward the positive electrode (the cathode). 

The correct statement is (d). Electrons are produced at the anode and move toward the cathode, regardless of the electrode material. The electrons do not move through the salt bridge ions do. Electrons do not leave the cell they provide current within the circuitry. Reduction occurs at the cathode in both galvanic and electrolytic cells—in all types of electrochemical cells, in fact. 

In the cathodic reduction of activated olefins, chlorosilanes also act as trapping agents of anionic intermediates. Nishiguchi and coworkers described the electrochemical reduction of a,/ -unsaturated esters, nitriles, and ketones in the presence of Me3SiCl using a reactive metal anode (Mg, Zn, Al) in an undivided cell to afford the silylated compounds [78]. This reaction provides a valuable method for the introduction of a silyl group into activated olefins. 

FIGURE 14.2 A representation of an electrochemical cell as described in the text. One electrode is the anode, the other the cathode, and electrons generated by the oxidation process at the anode flow through the external circuit to the cathode, where reduction takes place. This flow of electrons constitutes electrical current in the external circuit. 

The reduction is usually made in a multi-compartment electrochemical cell, where the reference electrode is isolated from the reaction solution. The solvent can be water, alcohol or their mixture. As organic solvent A,A-dimethyl form amide or acetonitrile is used. Mercury is often used as a cathode, but graphite or low hydrogen overpotential electrically conducting catalysts (e.g. Raney nickel, platinum and palladium black on carbon rod, and Devarda copper) are also applicable. 

In an electrochemical cell, oxidation occurs on the anode and reduction on the cathode. The measured current density j (current per unit area of the electrode) is proportional to the difference in the rate of the two reactions... 

Fuel cells, like batteries, convert the chemical energy residing in a fuel into electrical energy on demand. As in batteries and other electrochemical cells, fuel cells consist of an anode, where oxidation occurs, a cathode, where reduction occurs, and an electrolyte, where ions carry the current between the electrodes. Fuel cells differ from batteries in that the fuel and oxidant are not contained within the fuel... 

The a-substitution product from oxidation of methylbenzenes in acetic acid can be eliminated by electrochemical hydrogenolysis at the cathode. An undivided cell is used and a palladium on carbon catalyst is suspended in the medium. The necessary hydrogen is generated by reduction of protons at the cathode. In this way, the... 

Most effort over the electrochemical reduction of benzene hydrocarbons has centred on finding a reaction medium, which is also a better solvent for the substrate than liquid ammonia. Aliphatic amines have proved useful solvents and they may be used in an undivided electrochemical cell. Base is generated at the cathode while an equivalent of acid is generated in the anode reaction so that mixing of the cel contents maintains a neutral solution. An alcohol is usually added as a proton donor to prevent the build-up of a localised highly basic environment. The simultaneous anode reaction is oxidation of the amine. Electrodes of platinum, aluminium or graphite have been used. Under these conditions, benzene [38] is converted... 

The electrochemical reduction of nitric oxide in solid-state electrochemical cell is an interesting field surveyed in [95]. The working principle of the cells is the cathodic reduction of NO to nitrogen and oxygen anions. In [95], the properties of various types of solid-state electrochemical cells used for NO reduction are presented and discussed. It is shown that the cathode materials with a high redox capacity and oxygen vacancies are most active for the electrochemical reduction of nitric oxide, whereas noble metal-based electrodes show a much lower selectivity. As an alternative route, the promotion of the reduction with a reductive agent is also considered. 

The Daniell cell illustrates the basic features of an electrochemical cell. Electrochemical cells always involve a redox reaction. Oxidation occurs at the cathode of the cell and reduction takes place at the anode. Electrons always flow from the anode to the cathode. Electrochemical cells come in many arrangements. To gain an appreciation for the variety of electrochemical cells, consider all the types of batteries available. 

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