I am trying to estimate and also calculate the E1/2 of a redox reaction under different pH conditions. Is it correct that I can quickly estimate the E1/2 of a given reaction just by connecting the anodic and cathodic peak potentials and reading the value at the intersection on the x-axis (voltage sweep)? Or do I have to use the Nernst equation every time?
E1/2 =(Ec,p+Ea,p)/2 : Ec,p-peak potential of the cathodic peak: Ea,p -peak potential of the anodic peak
E1/2 =(Ec,p+Ea,p)/2 : Ec,p-peak potential of the cathodic peak: Ea,p -peak potential of the anodic peak
You don't need something difficult.
Just calculate a simple mean between the two potential peaks, at the cathode and at the anode.
E1/2 potential can be estimated from the related cyclic voltammogram. For this subject, I would recommend that you have to read page 219 in A. J. Bard, L.R. Faulkner’s book named Electrochemical Methods, Fundamentals and Applications, John Wiley & Sons, 1988. Good Luck.
The characteristic half‐wave potential E1/2 of a redox couple is typically within a few mV of the formal potential E° for the couple according to the Nernst equation where the ratio of the diffusion coefficients DOx and DRed is usually very close to unity. The easy determination of halfwave potentials and estimation of formal potentials is an extremely attractive feature of CV.
E1/2=E0/ - RT/(nF) Ln (Dred/Dox)
The average of the two peak potentials affords the half‐wave potential for the corresponding couple,
E1/2=(Epc + Epa)/2
If your volammogram shows a reversible or at least quasi-reversible pattern, you may calculate E1/2 by the average of the two peak potentials. If irreversible, a numerical (and complicated) calculation using a computer is required for the accurate determination of E1/2.
I would recommend this book Electrochemical Methods which is written by Alan J. Bard,
I also recommend Bard's textbook. It has been already "classical", but is evergreen.
Thanks guys. I actually got the book now. Thanks again for your help!
E1/2=(Ec,a+Ec,p)/2. you can use this expresion if you have a reversible redox wave. the mean between anodic peak and cathodic peak. in a reversible couple:
- in the reverse scan of the anodic sweep, the complementary reduction peak shows an ip backward/ip forward relationship of approximately one (ipc/ipa = 1) in the entire range of scan rate studied.
-Ep is independant of the scan rate
-Epa-Epc = 59 mV/n
- ip is proportional to scan rate
The best way is to base the decision concerning which approach has to be used (see reply by Yusuke Okawa) is the classical paper by Richard Nicolson:
http://pubs.acs.org/doi/citedby/10.1021/ac60230a016
R. S. Nicholson
Anal. Chem. 1965, 37 (11), 1351–1355.
Theory and Application of Cyclic Voltammetry for Measurement of Electrode Reaction Kinetics
It might be best to deceide which approach one should use (see reply by Yusuke Okawa) base on the classical paper by Richard Nicolson:
http://pubs.acs.org/doi/citedby/10.1021/ac60230a016
R. S. Nicholson
Anal. Chem. 1965, 37 (11), 1351–1355.
Theory and Application of Cyclic Voltammetry for Measurement of Electrode Reaction Kinetics
Average of the cathodic and anodic peak potentials of a reversible or quasi reversible system or potential at half of the maximum peak current is the best way to calculate the half wave potential.
The average of the peak potentials of the redox couple is a the simplest way
Only calculate a simple mean between the two potential peaks, at the cathode and at the anode.
If your analyte gives complete reversible peak then you should use R.S Nicholson method of (85.17% of Ipa) record the potential it will be E1/2
if your syestem nearly reversible then you used e1/2= (E(cathodic peak)+E anodic peak)/2.
Basically, half wave potential (E1/2) only works for a reversible redox system. E1/2 being the mid potential value of the redox couple peaks, it is related to the so-called formal potential (E0) in a fashion similar to the relationship between reaction quotient (Q) and equilibrium constant (K) for a system. Under standard conditions of concentration and temperature, E1/2 = E0.
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