Often when measuring oxidation (or reduction) of a species in a microfluidic system we see a linear, ohmic type slope instead of a limiting current. I am curious about the origin of this behavior. The slope, thus the conductance, is proportional to the oxidation current of the redox species. Is this just some form of leakage current from ion conductance or is it something else? It does not appear if there is no redox species present.
This phenomenon is not uncommon, but may be due to several causes. For example, consider oxidation, R = O + ne, a minute amount of reducing species (e.g. impurities) in the electrolyte can bring a small portion of O back to R in the diffusion layer. Such impurities can also contribute directly to the sloped oxidation current.
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