I am testing out my Pt microelectrode (diameter=10um, bought from C-H instruments) to determine the diffusion coefficient of a 1mM solution of ferrocene in 0.2M TBAPF6/ACN. I want to use this set up to determine the diffusion coefficient of newly synthesized conjugated oligomers, but I am having problems with this control experiment. I want to use an accurate method to first define my experimental setup and prove its works before moving on to unknown organic compounds.
Hi Saadia,
You don't need to fit the whole Shoup-Szabo equation. If you apply a potential step for a long enough time scale (at a diffusion-limited potential) the current should eventually reach a steady state (Iss) described by
Iss = 4nFDCr
where r is the electrode radius, C is concentration and the other symbols have their usual meaning.
Mithran Somasundrum Thank you for your reply. I am aware that I can use that equation. However, I have seen people use this to determine the radius of their electrode and then use that radius value to put into the Shoup-Szabo equation to determine the diffusion coefficient. The shoup szabo equation should be more accurate if I am working with new molecules, right?. Or should the Iss=4nFDCr equation be enough?
Hi Saadia
Radial diffusion is measurable even for millimeter radius electrodes
give recommendations on the size of the macro electrodes for the quantitative study and must exceed 4 mm radius in
aqueous solution.
Hi Saadia
The 4nFCDr expression will be good enough if you do actually observe a steady state current.
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