Electrochemistry Open LessonsSustainable Electrochemical Science & Technology, BRIN

Lessons / Tools

Cyclic voltammetry simulator

Change the scan rate, the concentration or the speed of electron transfer, and the voltammogram is recalculated as you move the slider. Use it next to Lesson 2.

Things to try

  1. Randles–Sevcik. Start from Fast (reversible). Double the concentration and the peak doubles. Make the scan rate four times faster and the peak only doubles, because ip grows with √v. Then press Run a scan-rate study and check that the diffusion coefficient recovered from the slope matches the one you set.
  2. Reversible versus slow. Keep a curve, then lower k⁰ step by step. The peaks move apart, get broader and lower, and the regime box changes colour. At very low k⁰ the return peak may fall outside the window or vanish.
  3. The same k⁰ looks different at different scan rates. Pick Medium and sweep from 10 mV/s to 2 V/s. Whether a couple looks reversible depends on Λ = k⁰/√(D f v), not on k⁰ alone.
  4. iR drop mimics slow kinetics. Pick Fast, with iR drop. ΔEp grows with scan rate even though the electron transfer is fast. Lower Ru to zero and it returns to about 59 mV.
  5. Charging current. Raise the double-layer capacitance and the scan rate together. The box-shaped background grows in proportion to v, faster than the peak, which grows with √v.
  6. The diffusion layer. Press Watch the diffusion layer to see the reduced form being used up near the electrode and the oxidised form building up, then the reverse on the way back.

What the model assumes

A one-step couple R ⇌ O + n e⁻ at a flat electrode, with semi-infinite linear diffusion, equal diffusion coefficients for both forms, Butler–Volmer kinetics and only R present at the start. Diffusion is solved with explicit finite differences in your browser. The double-layer charging current is added as Cdl·A·v, and the uncompensated resistance is handled by solving for the true interfacial potential E − iRu at every step.

Checked against theory, the reversible peak comes within about 0.2% of the Randles–Sevcik value with ΔEp = 58 mV at 25 °C, and the slow limit follows the irreversible form within about 0.2%. Real cells add effects the model leaves out, such as adsorption, coupled chemical steps, uneven current distribution and non-ideal capacitance.

Readouts. Peak currents are given above the capacitive baseline. The Randles–Sevcik prediction switches to the irreversible form once Λ falls below the Matsuda–Ayabe limit of 10−2(1+α). In the quasi-reversible zone neither limiting form holds exactly.

References

  1. N. Elgrishi, K. J. Rountree, B. D. McCarthy, E. S. Rountree, T. T. Eisenhart, J. L. Dempsey, A practical beginner's guide to cyclic voltammetry, J. Chem. Educ. 95 (2018) 197–206. doi:10.1021/acs.jchemed.7b00361
  2. A. J. Bard, L. R. Faulkner, Electrochemical Methods: Fundamentals and Applications, 2nd ed., Wiley, 2001, chapter 6.
  3. R. S. Nicholson, Theory and application of cyclic voltammetry for measurement of electrode reaction kinetics, Anal. Chem. 37 (1965) 1351–1355. doi:10.1021/ac60230a016
  4. H. Matsuda, Y. Ayabe, Zur Theorie der Randles-Sevčikschen Kathodenstrahl-Polarographie, Z. Elektrochem. 59 (1955) 494–503.