Analysis of Diffusion to Electrode Arrays

For lower coverages at fast scan rates, the overlap between neighbouring diffusion zones is not total because these are more distantly spaced than for high coverage. Therefore, the diffusion layer is not ideally planar and a lower current is observed than expected from the Randles-Sevcik equation since some material between the electrodes will not react. At slower scan rates, however, the diffusion zone is larger since the experimental timescale is longer, and so fuller overlap is attained. Therefore we see a scan rate dependent transition from Case 3 to Case 4 behaviour. 

The correctness of the edge plane activity model for HOPG electrode kinetics is best justified by the close correlation of experiment and two-dimensional simulated voltammetry, using the diffusion domain approximation. 

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