Potential step quasireversible system

Nernstian boundary conditions, or those for quasireversible or irreversible systems. All of these cases have been analytically solved. As well, there are two systems involving homogeneous chemical reactions, from flash photolysis experiments, for which there exist solutions to the potential step experiment, and these are also given they are valuable tests of any simulation method, especially the second-order kinetics case. 

When the potential step is small and the system is chemically reversible three cases of interest are analyzed. First, when the reaction is kinetically sluggish (electrochemi-cally -> irreversible or quasireversible) and the -> mass transport effects are negligible. 

In this section, we will treat the one-step, one-electron reaction O + R using the general (quasireversible) i-E characteristic. In contrast with the reversible cases just examined, the interfacial electron-transfer kinetics in the systems considered here are not so fast as to be transparent. Thus kinetic parameters such as kf, and a influence the responses to potential steps and, as a consequence, can often be evaluated from those responses. The focus in this section is on ways to determine such kinetic information from step experiments, including sampled-current voltammetry. As in the treatment of reversible cases, the discussion will be developed first for early transients, then it will be redeveloped for the steady-state. 

As an example, consider the case of potential steps applied to a one-step, one-electron system containing only electroactive species O, which is reduced quasireversibly. In Section 5.5.1, we treated this case conventionally and found that the current-time function was... 

There are many instances in electrochemistry when we find it very difficult to obtain an explicit relationship between current, potential, and time. Either the system itself is intrinsically complex (e.g., a quasireversible charge transfer involving adsorbed and diffusing reactant species) or the experimental conditions are less than ideal (e.g., step experiments carried out on a time domain so short that the rise time of the potentiostat is not negligible). It is usually true in these and other cases that much simpler relationships exist in the Laplace domain between the perturbations and the observables. Thus it can be useful to transform the data and carry out the analysis in transform space (39-42). 

In contrast to classical cyclic voltammograms, AC-cyclic voltammograms have a clear baseline, which is advantageous for quantitative measurements. By extending AC linear sweep voltaimnetry by a reverse scan, AC cyclic voltammetry is obtained. If the surface concentrations of the electroactive species are the same at the same potential for forward and reverse scans, the peaks for forward and reverse scans are expected to be identical. If the DC process is not fully reversible, the surface concentrations of the electroactive species are different at a given DC potential for forward and reverse scans— that is, for quasi-reversible systems a displacement of the jjeaks for forward and reverse scan can be observed. This displacement can be used to derive kinetic parameters of the electrode reaction. For instance, the derivation (1, p. 393] (or Eq. 5-33) for sluggish one-step heterogeneous quasireversible and/or... 

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