Industrial standard electrode potentials

Theoretically, by poising the potential of an electrochemical cell at a value which is sufficient to reduce chromium(III) but not aluminium(III), chromium could be removed preferentially from solution. As chromium is a common contaminant of bauxitic alloys (the main feedstock for aluminium industry) electrochemistry may provide a means of selectively removing chromium from aluminium products. However, this process may be impractically slow. Much depends on the relative concentrations of aluminium and chromium, temperature, pH and cell design. Nevertheless, standard electrode potentials can be used as a preliminary evaluation of the feasibility of electrochemical methods for clean-up. 

The application of inorganic electroactive compounds in aqueous RFBs have been the subject of the vast majority of the literature to date. Table 2 summarizes the standard electrode potentials of common redox couples while Table 3 highlights prominent cell chemistries based on combinations of these redox couples. Of these chemistries, iron-chromium (ICB) [33], polysulfide-bromide (PSB) [14], and aU-vanadium (VRB) [31] systems have yielded industry-level demonstrations (order of 100 kW-10 MW). Below, these RFB chemistries are introduced in some detail with key advantages, disadvantages, and challenges highlighted. 

When such shifts are found in the charging and discharging curves, they can often be correlated back to different trace elements. Certain trace elanents can function as a shuttle mechanism for ion transfer and actually increase the rate of selfdischarge. Other elanents can cause a shift in the electrode potential and initiate the hydrolysis of water and should be avoided [10,11]. Through experience, the battery industry has developed different standards for trace elements to be present in the battery. Obviously, the concentration of any detrimental elanents will need to be considered in aU materials in the battery, including the separator [12],... 

Two methods are used to measure pH electrometric and chemical indicator (1 7). The most common is electrometric and uses the commercial pH meter with a glass electrode. This procedure is based on the measurement of the difference between the pH of an unknown or test solution and that of a standard solution. The instmment measures the emf developed between the glass electrode and a reference electrode of constant potential. The difference in emf when the electrodes are removed from the standard solution and placed in the test solution is converted to a difference in pH. Electrodes based on metal—metal oxides, eg, antimony—antimony oxide (see Antimony AND ANTIMONY ALLOYS Antimony COMPOUNDS), have also found use as pH sensors (8), especially for industrial appHcations where superior mechanical stabiUty is needed (see Sensors). However, because of the presence of the metallic element, these electrodes suffer from interferences by oxidation—reduction systems in the test solution. 

The wide applicability of the electrochemical processes in the chemical processing industry (CPI) derives from the fact that the electron is a versatile reagent. Thus the electron can - unlike standard chemical reagents - be readily removed (oxidation) or added (reduction). Depending on its potential, the electrode can either oxidize or reduce various chemical species to convert them into profitably salable products without the undesirable byproducts. 

Although the nickel-containing systems have been extensively studied also by electrochemical methods [1] due to their practical importance, for example, in electrochemical power sources (Ni—Fe, Ni—Cd, Fi—NiF2 batteries), in corrosion-resistant alloys (tableware, coins, industrial instruments) as well as due to their interesting (magnetic, spectral, catalytic) properties most of the standard potentials of electrode... 

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