Actually, the electrochemical reaction mechanism may involve proton transfer. In this case, the voltammogram does depend on pH value. Another factor is electrode modifier stability and properties.

Hello Jieun Kim

You need to look at the Nernst equation.

For:

A + mH+ + ne- B

For a the case of electrochemical reversibility the midpoint potential varies by 2.303 m.R.T.n-1.F-1 per pH unit. If m = n, this is approximately 59 mV per pH unit at 25 oC.

See section 2.6 from the attached chapter, "interpreting electrochemistry" for a more detailed response.

Of course, you may have a reversible, quasi-reversible or irreversible process. Asymmetry may come from a multitude of factors (e.g. adsorption/desoprtion to/from the electrode interface). If the kinetics become important you should look at the Butler-Volmer equation.

The kinetics of systems can complicate matters as you alter the scan rate. By increasing the scan rate you can often outrun the kinetics (i.e. a chemically irreversible system starts to become chemically reversible whereas an electrochemically reversible system starts to become electrochemically irreversible).

Jules

Actually, the electrochemical reaction mechanism may involve proton transfer. In this case, the voltammogram does depend on pH value. Another factor is electrode modifier stability and properties.

You have a lot going on in your example. Differing concentration of phenol combined with a entirely different electrolyte. You need to go back to the basics and run a series of solutions containing the same constituents with varying pH to come to any sort of conclusion on the effect of pH on your oxidation peak.