I am working on electrochemical Oxidation of primary alcohols. For different catalyst the onset potential is same but the oxidation peak sharpness varies. I want to know what that means ?
There are few parameters characterizing CVAM: hal-wave potential E1/2 = (Ea + Ek)/2 and the Tomesh criterion - deltaE = Ea - Ek, and Ia/Ik - current peak intensities ratio
Ea & Ek - potentials of anode & cathode respectively, Ia & Ik - current of anode and cathode respectively. At the beginning of oxidation process when potential of electrode approaches E1/2. The value of current depends on two phenomena: (1) value of potential and (2) diffusion rate of substance to electrode. At E > E1/2 the amount of non-oxidized molecules near the main electrode gets significantly depressed, whereas the diffusion of non-oxidized molecules is limiting process. It results in the current suppression with the growth of potential. These are conditions of the CVAM peak formation. So if the right side of a peak is too broad, the diffusion plays the principal role.
Actually, the Tomesh criterion allows to suggest the character of a process. As you can conclude, it depends on the width of a peak. The broader a peak is, the greater is the value of the Tomesh criterion.
In the case of electrochemical one-electron reversible process, deltaE = 56-90 mV and Ia/Ik = 1. Provided delta E = 90-150 mV, a quasiinvertible action occurs. Finally, at delta E > 150 mV, the redox process is irreversible. Ia/Ik is not equal to 1 in two latter cases.
You're welcome!
Cyrille Costentin , Samuel Drouet , Marc Robert , and Jean-Michel Savéant *
Turnover Numbers, Turnover Frequencies, and Overpotential in Molecular Catalysis of Electrochemical Reactions. Cyclic Voltammetry and Preparative-Scale Electrolysis
J. Am. Chem. Soc., 2012, 134 (27), pp 11235–11242
Aside from theoretical aspect, for a reversible single electron redox system it usually gives a sharp peak. If there is a 2 electron-process, a much broader peak will be viewed. There is also important issue, it could also related to electrocatalytic or catalytic reaction that can go along with the main electrochemical process.
For a reversible electrode process, broad peak means that more than one specie is reducing or oxidising at the same or very close potential whereas sharp peak indicates a single electron single specie redox process is taking place in solution.
Dears Roto and Emmanuel. Your answers are not correct. Read the refs given by Elza and me. I know personally Cyrille Costentin , Jean-Michel Savéant, and Alan Bond. They are the most knowledgeble experts in this area.
It depends on what your doing, ie in evaluation of capacitance of a supercapacitor through CV it is good to have a broad peak, in other fields of course not
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