Cyclic voltammetry, laboratory experiments

A technique which is becoming increasingly important in our laboratory is a.c. cyclic voltammetry. This experiment is run on a stationary electrode [Hanging Hg drop (HMDE), Pt, Au, graphite, etc.]. The d.c. potential staircase is swept first in one direction and then the other. The slopes for the forward and reverse scans usually are equal in magnitude, but opposite in sign. The ramp amplitude encompasses one or more admittance peaks. The FT-FAM measurement is performed in this context. 

Electrochemically generated nickei(lll) oxide, deposited onto a nickel plate, is generally useful for the oxidation of alcohols in aqueous alkali [49]. The immersion of nickel in aqueous alkali results in the formation of a surface layer of nickel(ll) oxide which undergoes reversible electrochemical oxidation to form nickel(lll) oxide with a current maximum in cyclic voltammetry at 1.13 V vj. see, observed before the evolution of oxygen occurs [50]. This electrochemical step is fast and oxidation at a prepared oxide film, of an alcohol in solution, is governed by the rate of the chemical reaction between nickel oxide and the substrate [51]. When the film thickness is increased to about 0.1 pm, the oxidation rate of organic species increases to a rate that is fairly indifferent to further increases in the film thickness. This is probably due to an initial increase in the surface area of the electrode [52], In laboratory scale experiments, the nickel oxide electrode layer is prepared by prior electrolysis of nickel sulphate at a nickel anode [53]. It is used in an undivided cell with a stainless steel cathode and an alkaline electrolyte. 

The Schwenz and Moore book called for inclusion of modem laboratory instrumentation and techniques, as well as modem research topics in the laboratory curriculum. Under the umbrella of modem instrumentation, the authors included experiments with lasers, mass spectrometers and cyclic voltammetry. In modem topics, computational chemistry, experiments with biological relevance, atmospheric chemistry and polymer chemistry were... 

Recently a series of dialkylpyrrolidinium (Pyr+) cations have been studied in our laboratory 7-9). These cations are reduced at relatively positive potentials and could be investigated electrochemically as low concentration reactants in the presence of (C4H9)4N+ electrolytes. Using cyclic voltammetry, polarography and coulometry, it was shown that Pyr+ react by a reversible le transfer. The products are insoluble solids which deposit on the cathode and incorporate Pyr+ and mercury from the cathode. Both the cation and the metal can be regenerated by oxidation. Quantitative analysis of current-time transients, from potential step experiments, showed that the kinetics of the process involve nucleation and growth and resemble metal deposition. 

As a consequence, in our laboratories in Qausthal, any newly delivered ionic liquid is first tested by cyclic voltammetry and in situ STM on Au(lll) thoroughly before it is used for fundamental studies. This approach is somewhat time-consuming and in part frustrating for the students, on the other hand it is currently the only chance to avoid misinterpretation of electrochemical experiments, especially with the in situ STM. This is one of the challenges in ionic liquids electrochemistry. 

Most electrochemical experiments in the laboratory make use of the principle of non-steady state diffusion. Certainly this is the case for cyclic voltammetry, potential step, a.c. methods, and spectroelectrochemical techniques, and hence we must develop the techniques to solve the partial differential equations which describe non-steady state diffusion. 

The use of electrochemical methods to smdy protein and enzyme electron transfer reaction kinetics, thermodynamics, and mechanisms directly with electrodes is becoming a mature field. Twenty years ago such studies were rarely conducted outside of laboratories with substantial experience in electrochemistry. Now scientists in diverse fields have taken up cyclic voltammetry, square wave voltammetry, and other electrochemical methods to study biological systems. Clearly much has been learned about how to conduct reliable electrochemical experiments on complex biological samples using direct electron transfer at electrodes. Progress in this field was slow, and some background is provided to put the current state of this field in context. 

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