How is the diffusion current maintained at the limiting plateau? If the diffusion current is formed because of the discharge of charges for reducible ions, then how is the diffusion current maintained when there is no availability of reducible ions at the bulk of the solution?
These are very old fashioned terms almost never used today. To learn about diffusion and hydrodynamic mass transport, see the excellent introductions in basic books on electroanalytical chemistry by Bard and Faulkner, Joseph Wang, Kissinger and Heineman and many others. To answer properly requires pictures which are in all of these books. If there are no ions to reduce, there can be no diffusion current.
Polarography in aqueous solutions involves two electrodes - th potential of one ( calomel, mercurosulfate, or silver-silverchlorideelctrodes consist of a metal, covere by its slightly soluble salt..Potential of such electrode depends on concentration of the salt (chlorides, sulfates, e.g) inthesolution. If used as an anode, some metal is dissolved and reacts immediately with the anion,so the potential,of this electrode during electrolysis remains constant.. The otherelectrode is an indicator or working electrode. When a potential is applied, electrons are transferred either from electrode to a species in the solution (reduction) or from the dissolved species to the electrode (oxidation.. The elctroactive species lose to theelectrode surface is changed by electrolysis.
It is replaced by another species from the bulk of the solution, often bydiffusion.
@ Peter Kissinger
Well, if there is no ions left for reducing, then how a current(limiting) is maintained at the end of the experiment?
If there is a limiting (steady state) current, there is a reaction. The current is derived from the differential form of Faraday's law. The reactant concentration at the surface of an electrode is zero because it is "instantly" consumed. New reactant continues to come to the electrode by diffusion down a concentration profile over a short distance called the diffusion layer.
This is best seen by studying pictures and the laws of diffusion presented in basic electrochemistry books.
@ Kissinger
Can I have soft copy (pdf format) of any of those Electroanalytical chemistry books, you mentioned here? Thanks.
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