Voltammetric techniques potential wave-form

Janetski et al. (1977) also studied the behavior of a pyrite electrode in a solution of cyanide concentration in the absence and presence of xanthate using voltammetric technique. They reported that on increasing the concentration of cyanide at constant pH and xanthate concentration, the oxidation wave of xanthate is shifted to more anodic potential indicating that the presence of cyanide, which may react with the mineral surface to form an insoluble iron cyanide complex will result in the inhibition of the electrochemical oxidation of xanthate and the depression of pyrite. 

The measurement of the current for a redox process as a function of an applied potential yields a voltammogram characteristic of the analyte of interest. The particular features, such as peak potentials, halfwave potentials, relative peak/wave height of a voltammogram give qualitative information about the analyte electrochemistry within the sample being studied, whilst quantitative data can also be determined. There is a wealth of voltammetric techniques, which are linked to the form of potential program and mode of current measurement adopted. Potential-step and potential-sweep... 

Comparison of the half-wave potentials of the oxidizable and reducible forms of the redox reactants with the potentiometrically determined value of the standard redox potential is the simplest method for proof of reversibility and agreement between these two sets of data provides strong support for reversibility of the process being studied. However, in many polarographic reactions, it is found that one form of the conjugate redox pair is not sufficiently stable to be prepared or to permit determination of E% potentiometrically. In some of these cases, auxiliary methods can be used, particularly where the reactive species is relatively stable when formed at the surface of the mercury electrode. Such methods include the commutator method, an anodic stripping technique which has recently been reviewed by Barendrecht, and oscil-lopolarographic and cyclic voltammetric techniques. 

As the name implies, this voltammetric technique involves the square-wave potential component of a small amplitude (see Fig. 30). This form of superimposed potential enables the elimination of the capacitive current in an analogous way as is done in other pulse methods. 

The most important parameters for pulse voltammetric techniques are defined as follows. Pulse amplitude is the height of the potential pulse, which may or may not be constant depending on the technique. Pulse width is the duration of the potential pulse. Sample period is the time of the pulse at whieh the current is measured. A number of different pulse techniques are available in commercial potentiostats, which essentially differ in their potential step wave-forms and the number of sampling points [1]. 

The polarographic behavior of the 1-oxides and 1,4-dioxides of pyrazine, 2,5-dimethylpyrazine, and tetramethylpyrazine at various pH values has been investigated. It was assumed that at lower pH values, the A -oxide group was reduced in its protonated form. In acid media the 1-oxides exhibited double waves, the first of which is attributable to the reduction of jV-oxide groups and the second to that of the pyrazine nucleus (production of 1,4-dihydro compounds). Reduction of both A -oxide groups of pyrazine-1,4-dioxide proceeded simultaneously (588). Half-wave potentials of the voltammetric oxidation and reduction of pyrazine mono- and di-A -oxides have been measured in dimethylformamide, and in acetonitrile by the technique of a rotating platinum electrode (750). 

The catalytic modification of the bimetallic composition is in fact further reflected by the remarkable difference of the voltammetric characteristic observed in the reverse scan, especially in the alkaline electrolyte. For Pt/C and PtRu/C, the reverse wave for alkaline electrolyte occurs at a potential less positive than the forward wave by 2(X)mV. In contrast, the reverse wave for Aug2Pti8/C occurs at a potential which differs from the potential for the wave in the forward sweep by only 20mV. The relative peak current of the reverse/forward wave is also found to be dependent on Au% in the bimetallic nanopartide. The oxides formed on the catalyst surface at the potential beyond the anodic peak potential in the positive sweep are reduced in the reverse sweep [171]. Poisonous CO spedes formed on Pt surface can also be removed in the reverse sweep. The observation of the more positive potential for the reverse wave likely reflects the bimetallic effect on the re-activation of the catalyst surface after the anodic sweep, a scenario that is under further investigation using FTIR spectroscopic techniques. The re-activation of the surface catalytic sites after the anodic sweep is likely modified by the presence of Au in the catalyst, which leads to the shift of the peak potential of the reverse wave to a more positive potential (by 200mV) for Aug2Pti8/C than for Pt/C. 

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