Calculator Inputs
Example Data Table
Illustrative reversible scan set for n = 1, A = 0.071 cm², D = 7.60 × 10-6 cm²/s, C = 1.0 mM, and 298.15 K.
| Scan rate (mV/s) | √Scan rate (V/s)1/2 | Predicted peak current (µA) | Comment |
|---|---|---|---|
| 25 | 0.1581 | 36.99 | Lower sweep rate reduces peak current. |
| 50 | 0.2236 | 52.31 | Current rises with the square-root trend. |
| 100 | 0.3162 | 73.98 | Common reference point for validation. |
| 250 | 0.5000 | 116.98 | Useful for quick linearity checks. |
Formula Used
General form: ip = 0.4463 n F A [n F v D / (R T)]1/2 C
Simplified 25°C form: ip = 2.69 × 105 n3/2 A D1/2 C v1/2
Where ip is peak current, n is electrons transferred, A is electrode area, D is diffusion coefficient, C is bulk concentration, v is scan rate, T is absolute temperature, F is Faraday’s constant, and R is the gas constant.
The calculator also rearranges the same equation to solve for diffusion coefficient, concentration, area, or scan rate when measured peak current is available.
How to Use This Calculator
- Select whether you want peak current, diffusion coefficient, concentration, area, or scan rate.
- Choose the general temperature equation or the 25°C simplified equation.
- Enter electron count, electrode area, diffusion coefficient, concentration, scan rate, temperature, and measured current as needed.
- Pick the correct units for area, concentration, scan rate, and current.
- Press Calculate to show the result above the form.
- Use the export buttons to save the displayed result as CSV or PDF.
Frequently Asked Questions
1. What does the Randles Sevcik equation estimate?
It estimates reversible voltammetric peak current from diffusion control. With rearrangement, it can also estimate concentration, diffusion coefficient, effective area, or scan rate from measured current data.
2. When should I use the simplified form?
Use the simplified form only at 25°C, or 298.15 K. At other temperatures, use the general expression so the temperature term is handled correctly.
3. Why does peak current increase with scan rate?
The equation predicts ip is proportional to the square root of scan rate. Faster sweeps create steeper concentration gradients near the electrode, which increases diffusion-limited current.
4. Which concentration unit is most practical?
Many electrochemistry experiments report concentration in mM, but the equation internally uses mol/cm³. This calculator converts common concentration units automatically before computing the result.
5. Can I use geometric or effective area?
You may enter either, depending on your goal. Geometric area fits nominal design calculations, while effective area is better when roughness, porosity, or activation changes the true electroactive surface.
6. What assumptions does this model make?
It assumes reversible electron transfer, diffusion control, and a planar electrode approximation. Strong adsorption, kinetic limitations, uncompensated resistance, or coupled chemistry can make observed currents deviate.
7. Why are my anodic and cathodic peaks different?
Unequal peaks may indicate kinetic limitations, follow-up chemical reactions, adsorption, ohmic drop, or baseline issues. In an ideal reversible system, forward and reverse peak magnitudes should be similar.
8. Is this suitable for reporting final literature values?
It is excellent for screening, teaching, and first-pass analysis. For publication-quality values, combine it with experimental calibration, baseline correction, uncertainty analysis, and full electrochemical interpretation.