In some reported works for biosensors, they study the cathodic peak current vs various scan rates. The linear relationship indicating that the electrochemical kinetics of electrode biosensor was a typical surface-controlled process. What does “surface-controlled process” mean?
Surface controlled means that the species being oxidized or reduced is stuck to or part of the electrode. The alternative is an analyte species that is dissolved in the electrolyte solution (diffusion controlled). Surface confined redox peaks differ from solution based redox peaks because the analyte does not need to diffuse to the electrode surface. Surface confined peak current magnitude should be linear with scan rate and diffusion controlled redox peak magnitude linear with sqare root of scan rate.
diffusion -control...Fick's law...capacitive process...check Allan Bard's book...is more or less the bible for electrochemistry.
Surface controlled means that the species being oxidized or reduced is stuck to or part of the electrode. The alternative is an analyte species that is dissolved in the electrolyte solution (diffusion controlled). Surface confined redox peaks differ from solution based redox peaks because the analyte does not need to diffuse to the electrode surface. Surface confined peak current magnitude should be linear with scan rate and diffusion controlled redox peak magnitude linear with sqare root of scan rate.
Surface controlled process refers to a type of redox reaction where both the reactant and the product are strongly attached on the electrode surface. The oxidation and reduction will occur in the molecules present in the surface itself. for instance if quinone was immoblized in electrode surface, the oxidation and reduction of quinone takes place in the electrode surface.
In electrochemistry, redox processes may be surface controlled or diffusion controlled. if a specie is attached to the surface of electrode, then the oxi or red occur at the surface of electrode directly, it is surface controlled. and as it occurs directly so by increasing the scan rate the peak intensity increases and vice versa i.e peak intensity is directly proportional to scan rate. But if the specie is not directly attach to the electrode but is a part of reaction system i.e. is a part of solution, then its oxidation or reduction would be dependent on how faster it diffuses from solution toward the electrode, so this system is under diffusion controlled. here the peak intensity is proportional to square root of the scan rate.
http://www.chem.uoa.gr/applets/AppletDiffus/Appl_Diffus2.html
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