Square root of Scan Rate vs Peak Current of Cyclic Voltammetry

Cyclic Voltammetry of Ferricyanide Using Carbon Screen-Printed Electrodes – Randles–Sevcik Analysis

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Time to read 2 min

Introduction

Cyclic voltammetry is a fundamental electrochemical technique used for characterizing redox systems. It involves sweeping the potential of a working electrode and monitoring the resulting current to explore redox behavior. In this study, we use the reversible Fe(III)/Fe(II) redox couple - ferricyanide/ferrocyanide to demonstrate the capabilities of CV using carbon screen-printed electrodes (SPEs).Unlike conventional three-electrode systems (e.g., glassy carbon, Ag/AgCl, Pt), SPEs are compact, disposable, and cost-effective. They integrate all three electrodes onto a single substrate, making them ideal for teaching and laboratory testing.

ZP Hypervalue Carbon SPE
Figure 1: Hypervalue Carbon Screen Printed Electrode
ZP Hypervalue 501 Carbon SPE
Figure 2: Hypervalue 501 Carbon Screen Printed Electrode

We will also evaluate the system using the Randles–Sevcik equation, which relates peakcurrent to scan rate and diffusion coefficients, confirming whether the reaction is diffusioncontrolled.

Table of contents

Introduction Randles–Sevcik equation Theory Experiment Running CV Data Analysis Result and Discussion Conclusion

Randles–Sevcik equation Theory

For a reversible redox couple at room temperature (25°C), the Randles–Sevcik equation is:

Randles-Sevcik Equation

Where:

  • i p = peak current (A)
  • n = number of electrons transferred
  • A = electrode area in cm 2
  • C = concentration in mol/cm 3
  • D = diffusion coefficient in cm 2 /s
  • V = scan rate in V/s

A linear relationship between the peak current ip and the square root of the scan rate (v1/2).

Experiment

Reagents


  • 5mM K 3 Fe(CN) 6 in 0.1M KCl
  • Distilled Water

Apparatus


Running CV

  1. Connect the SPE to the potentiostat.
  2. Apply 1 drop (around 50–80 µL) of the ferricyanide solution to the electrode so that all three zones are covered.
  3. In the software, select Cyclic Voltammetry and set parameters:
  4. Measure Open Circuit Potential (OCP) until a stable value is reached.
  5. Run the CV and observe the voltammogram.

Cyclic Voltammogram

Figure 3: CV Plot

Cyclic Voltammetry Parameters for Ferricyanide
Figure 4: CV Parameters

Data Analysis

After the CV is completed:

  • Locate oxidation and reduction peaks
  • Note down the peak potentials (Epa & Epc) and peak currents (Ipa & Ipc)
Overlay of Voltammogram with different scan rates
Figure 5: Overlay of voltammogram with different scan rates

To test the Randles- Sevick relationship:

  1. Repeat CV at multiple scan rates: 20, 40, 60,80 mV/s.
  2. Plot the scan rate1/2  v/s Ip graph.
  3. A linear trend indicates diffusion-controlled kinetics.
Square Root of Scan Rate vs Peak Current plot of cyclic voltammetry
Figure 6: (Scan rate)1/2 v/s Ipa (A)

Result and Discussion

Increasing scan rate result in:

  • Higher peak currents
  • Broader peaks
  • Greater ΔEp

At higher scan rates the rate of diffusion is more than the rate of reaction. Hence, more electrolytic ions reach the electrode electrolyte interface whereas very few ions participate in the charge transfer reaction. Therefore, the current at higher scan rate increase. Therefore, peak height increases with increase in scan rate. This is also evidenced by the increased voltage difference between anodic and cathodic peaks at higher scan rates

 

If the graph is linear the system behaviour agrees with Randles-Sevcik theory. From the slope, we can also estimate D (diffusion coefficient) if other parameters (A, n, C) are known.

Conclusion

This experiment successfully demonstrates cyclic voltammetry using carbon screen-printed electrodes with ferricyanide. This validates the use of SPEs in electroanalytical studies and highlights their potential for low cost analysis.

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