Modified electrodes potential step experiments

The potential step provides the theoretical background for any potentiostatic regulation experiment and a basic understanding is necessary for the mathematical solution of any controlled potential, nonsteady-state voltammetric response, such as LSV, pulse or a.c. experiments. At a stationary electrode, the current response to a potential step is described by the Cottrell equation [eqn. (83)] but at hydro-dynamic electrodes, it needs to be modified to take account of forced convection. 

This chemically modified electrode exhibits quasi-reversible rates of heterogeneous electron transfer for the reduction of cytochrome c as determined by single potential step chronoabsorptometry. However, reductive and oxidative experiments did not yield kinetic results in agreement with Butler-Volmer theory. 

An interpretation of the potential dependent capacitance (Mott-Schottky analysis [14]) yields information about semiconducting properties of the electrode. The corresponding experiment requires a modified technique in non-stationary systems, because the complete function must be measured in extremely short times to avoid fundamental system changes. This was done by superimposing small pulse to each step of a potential staircase (Fig. 6). With this technique, the complete analysis requires less than 500 ps [15]. 

Edmund E. Bowden conducted potential step chronoabsorptometry experiments on the reaction of myoglobin at modified gold minigrid electrodes [40]. Although these experiments were very reproducible, the heterogeneous electron transfer kinetic parameters raised concerns, namely, the rate constant was very low (k° = 3.9 X 10-11 cm/s) and alpha was high (a = 0.88). These issues became muted as the work progressed, as will be discussed below. 

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