Cathode in electrochemical cell

History began for the lithium/SVO cell in 1982, when the first of two U.S. patents for the use of metal vanadium oxides as cathodes in electrochemical cells was granted to Liang et al. [40], Thermal decomposition methods were utilized to... 

Knowledge Required (1) The electrolysis of aqueous solutions. (2) Definitions of anode and cathode in electrochemical cells. 

When hydrogen is formed electrochemically on a metal that easily forms hydrides, a superficial layer of metal hydride may form and grow with time. Metal hydrides are generally brittle and exhibit poor mechanical resistance. The formation of a hydride layer therefore corresponds to a deterioration of the material. The described behavior, of limited practical importance, has been observed for example with titanium used as cathode in electrochemical cells. 

Stainless steels are electrochemically noble materials in the passive state, i.e. they can form cathodes in electrochemical cells. Information with regards to this is given in Section Unalloyed steels . 

Shorthand Notation for Electrochemical Cells Although Figure 11.5 provides a useful picture of an electrochemical cell, it does not provide a convenient representation. A more useful representation is a shorthand, or schematic, notation that uses symbols to indicate the different phases present in the electrochemical cell, as well as the composition of each phase. A vertical slash ( ) indicates a phase boundary where a potential develops, and a comma (,) separates species in the same phase, or two phases where no potential develops. Shorthand cell notations begin with the anode and continue to the cathode. The electrochemical cell in Figure 11.5, for example, is described in shorthand notation as... 

Mechanically robust materials are metals, for example, different chromium-nickel steels, or titanium. Their use in electrochemical cells is limited because they are conductive and may corrode. The corrosion is significantly influenced when the metal is insulated or connected to the anode or to the cathode (see Fig. 9). 

Two earlier reviews were published on high temperature cells and batteries based on molten salt and solid electrolytes. The first one (69) describes the Li/Cl2 cells, particularly the LiA.l/LiCl-KCl/Cl2 cell with gaseous CI2. Li cells with chalcogenides as cathode materials are mentioned, as well as some details of construction. This review, and the 26 references attached to it, reflects the state of the Li molten salt batteries to the end of 1970 (69). The second review (70), prepared two years later is more comprehensive. It discusses in detail some theoretical problems, the thermodynamics and rate processes in electrochemical cells, and presents tables and... 

Electron Transfer in Electrochemistry. In electrochemical cells electron transfer occurs within the electrode-solution interface, with electron removal (oxidation) at the anode, and with electron introduction (reduction) at the cathode. The current through the solution is carried by the ions of the electrolyte, and the voltage limits are those for electron removal from and electron insertion into the solvent-electrolyte [e.g., H20/(H30+)(C10j ) (Na )(-OH) ... 

Electrolytes are used in electrochemistry to ensure the current passage in -> electrochemical cells. In many cases the electrolyte itself is -> electroactive, e.g., in copper refining, the copper(II) sulfate solution provides the ionic conductivity and the copper(II) ions are reduced at the - cathode simultaneous to a copper dissolution at the - anode. In other cases of -> electrosynthesis or - electroanalysis, or in case of - sensors, electrolytes have to be added or interfaces between the electrodes, as, e.g., in case of the -> Lambda probe, a high-temperature solid electrolyte. 

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. 

The main processes occurring in electrochemical cells are simultaneous oxidation and reduction reactions, or redox reactions. At one electrode, the anode, a reduced species is oxidized here meaning to release electrons, while at the other electrode, the cathode, an oxidized species absorbs electrons and is reduced. It is common to think of an electrochemical cell as consisting of two half-cells. (one containing the anode and the second containing the cathode) and to describe the processes in terms of halfcell reactions. For example, one common cell consists of a copper cathode in a copper sulfate solution, and a zinc anode in a zinc sulfate solution. The overall reaction is... 

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. 

Electrochemical cell with quartz window and saturated calomel electrode as a reference electrode was used (Fig. 3). Photoelectrochemical measurements were conducted with Pl-50-1 potentiostat under illumination power density of 75 mW/cm. At first the efficiency of energy accumulation (in the form of absorbed hydrogen) was estimated from the cathode discharge curves and from the hydrogen volume released under cathode heating. The volume of hydrogen released was measured in the tailor-made setup. The discharge capacity measurements were performed in electrochemical cell with nickel counter electrode. 

Albagli, D., Ballinger, R., Cammarata, V. et al. (1990) Measurements and analysis of neutron and gamma-ray emission rates, other fusion products, and power in electrochemical cells having Pd cathodes. Journal of Fusion Energy, 9, 133-147. 

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