Industrial electrochemical potentials

We managed to obtain dense and solid thin films of 3d-metal oxides using the techniques of electrochemical deposition from aqueous fluorine-containing electrolytes. The films have been studied as a possible cathode material for secondary cells. The best samples show good cycle retention and acceptable specific capacity in the range of 180 mAh/g. They also feature a plateau of electrochemical potential at approximately 3,5 V, which is acceptable for present industrially produced electrochemical devices. 

Another question concerns the relevant time domain for the investigation. It is always simpler to carry out the reaction as quickly as possible, i.e., to carry out potential sweeps or even cyclic voltammetry (Section 8.6). Among the reasons for this is that the catalyst surface may undergo a degree of deactivation in minutes, let alone hours or months. Polymerized and largely unreactive side products ( gunk ) may build up on the electrode surface at the longer times (weeks, months) in which an industrial electrochemical reaction must work without attention. 

During the last two decades, pressure-driven membrane processes namely reverse osmosis (RO), nanofiltration (NF), and ultrafiltration (UF) have found increased applications in water utilities and chemical industries. Unlike RO, NF, and UF, the Donnan membrane process (DMP) or Donnan dialysis is driven by an electrochemical potential gradient across an ion-exchange membrane. Theoretically, the DMP is not susceptible to fouling because particulate matter or large organic molecules do not concentrate on the membrane surface, as commonly observed with pressure-driven membrane processes. DMP has been used in the past in hydrometallurgical operations [19,20], for concentration of ionic contaminants [21,22] and for separation of... 

Ion exchange membranes have been used in various industrial fields, and have great potential for use in new fields due to their adaptable polymer membrane. As mentioned in the Introduction, membranes are characterized mainly by ion conductivity, hydrophilicity and the existence of carriers, which originate from the ion exchange groups of the membrane. Table 6.1 shows reported examples of applications of ion exchange membranes and the membrane species used in various fields. Various driving forces are usable for separation electrochemical potential, chemical potential, hydraulic pressure such as piezodialysis and pervaporation, temperature difference (thermo-osmosis), etc. Of these, the main applications of the membrane are to electrodialysis, diffusion dialysis, as a separator for electrolysis and a solid polymer electrolyte such as in fuel cells. 

As mentioned in Chapter 5, ion exchange membranes have no permselectivity for specific ions. If an ion exchange membrane had permselectivity for specific ions, separation of ions with the same charge would be possible by electrochemical potential, which would be a remarkable contribution to industry. In the anion exchange membrane, permselectivity between anions is reported to be controlled by the difference of the hydrophilicity of the membrane. New methods other than controlling the hydrophilicity of the membrane should be found on the basis of another mechanism. 

Surface force measurements have also been carried under much higher ionic strength conditions, in which the solution conditions and substrates employed are more akin to those encountered in industrial electrochemical processes. In one set of experiments [46], the surface force was measured between a silica sphere and a copper electrode, as a function of electrode potential, in concentrated (0.01 and O.lmoldm" ) solutions of... 

Anodic protection s is a modern electrochemical technique for protecting metallic equipment used in the chemical-process industry against corrosion and handling highly corrosive chemicals (e.g., concentrated sulfuric and orthophosphoric acids). The technique consists in impressing a very low anodic current (i.e., usually 10 irA.m" ) on a piece of metallic equipment (e.g., tanks, thermowells, columns) to protect against corrosion. This anodic polarization puts the electrochemical potential of the metal in the passivity region of its Pourbaix... 

The silver-silver chloride electrode simplicity of fabrication and fundamental ruggedness makes it a good candidate for many industrial applications where the electrochemical potential has to be measured or controlled. An important industrial example where this half-cell has become indispensable is to provide a measure of applied potential during the impressed current cathodic protection (ICCP) of sea-going ships. 

Electrochemical noise (intrusive). Contrary to common perceptions, the underl5dng measurement principles of this electrochemical technique are extremely simple. The technique is not related to acoustic noise in any way rather, fluctuations in potential and current between freely corroding electrodes are measured. Because of the small scale of these fluctuations of interest (in many cases <1 piV and <1 nA), sensitive instrumentation is required. Many high-precision digital multimeters facilitate these measurements. A measurement frequency of 1 Hz usually suffices. For simultaneous measurement of electrochemical potential and current noise, a three-electrode sensor is required. The current noise is measured between two of these sensor elements. The potential noise is measured between the third element and the two coupled (for current measurements) elements. For industrial corrosion monitoring purposes, all three sensor elements are usually constructed from the same material. 

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