Shape of Voltammograms

In voltammetry we measure current as a function of the applied potential. The shape of a voltammogram is determined by several experimental factors, the most important of which are how we measure the current and whether convection is included as a means of mass transport. As suggested here, there are three common shapes for voltammograms.

For the voltammogram in (a), the current increases from a background residual current to a limiting current, il. Because the faradaic current is inversely proportional to the thickness of the diffusion layer, δ, a limiting current occurs only if the thickness of the diffusion layer remains constant because we are stirring the solution. In the absence of convection the diffusion layer increases with time, and the resulting voltammogram has a peak current instead of a limiting current (b).

For the voltammograms in (a) and (b), we measure current as a function of the applied potential. We also can monitor the change in current, Δi, following a change in potential. As shown in (c), the resulting voltammogram also exhibits a peak current.

Figure11.42

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