Chronoamperometry

Discussion: In the first part of the experiment, chronoamperometry was used to determine the diffusion coefficient of ferricyanide. The chronoamperogram can be seen in Graph 1. The chronoamperogram shows three distinct regions. [1A] Region “a” is where the electrode potential is higher than the ferricyanide’s potential, so no reduction reaction takes place. Region “b” is where the potential is decreased to a potential much lower than that of ferricyanide. This results in the ferricyanide consuming electrons to be reduced rapidly. This results in a very sharp decrease in current. Region “c” is where the ferricyanide is nearing is almost fully reacted and the current begins to balance out. The diffusion coefficient can be determined by using
By making a plot of i vs t(-1/2) (Graph 2 in the Appendix) of Region C for the ferricyanide chronoamperogram (Graph 1), the equation of the best-fit line was determined to be i = 3x10-5t(-1/2) - 1 x10-5. The slope of the graph would be equal to nFAcπ(-1/2)D01/2. Since nFAcπ(-1/2) were known, the diffusion coefficient was determined to be 2.25 x 10-6 cm2∙s-1 from Equation 2, where m was the slope of the i vs t(-1/2)
Region “a” is the region where the potential is higher than the reduction potential of ferricyanide, so no reduction occurs. Region “b” is the region where the potential is slowly decreased to the reduction potential of ferricyanide and ferricyanide is reduced. Region “c” represents the cathodic peak potential (Epc), where the concentration of ferricyanide reaches zero and the cathodic current is at its max. In region “d’ the current drops due to no ferricyanide being present at the electrode, meaning no electrons are consumed. Region “d” balances out and the reverse potential scan from low to high potential is observed. Region “e” is where the potential is increased until it is high enough to oxidize the reduced ferricyanide and then ferricyanide is oxidize. This is opposite of what was seen in region “b.” The potential is increased until region “f” which is the anodic peak potential (Epa), where the anodic current is at its max due to full oxidation of the reduced ferricyanide. In region “g,” no more reduced ferricyanide is present near the electrode surface so the current balances out back to the starting