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Oparic
Workflow referencePlus

CV/Cdl

Calculate double-layer capacitance from CV curves for use in electrochemically active surface area analysis.

CV/Cdl

This workflow uses CV data recorded at different scan rates to obtain the double-layer capacitance CdlC_{\text{dl}} through linear fitting of the difference between anodic and cathodic currents at the midpoint potential, which can be further used to calculate the electrochemically active surface area (ECSA).

Input Data

Select a folder containing instrument-exported raw CV data, or multi-select a group of raw CV data files.

The dataset should contain CV curves at multiple different scan rates for a reliable linear fit.

Procedure

  1. Select input data: choose a folder containing CV data at different scan rates, or multi-select a group of data files.
  2. The system automatically calculates ΔI/2\Delta I / 2 values at each scan rate, performs linear fitting, and generates a fitting plot.
  3. Use the interactive sampling-point verification plot in the app to inspect the final CV cycle at every scan rate and the actual anodic and cathodic data points used in the calculation.

Scientific Principles

Determination of Double-Layer Capacitance CdlC_{\text{dl}}

In the non-Faradaic potential region, only double-layer charging and discharging occurs at the electrode surface. Under these conditions, the charging current ici_c is proportional to the scan rate ν\nu:

ic=Cdl⋅νi_c = C_{\text{dl}} \cdot \nu

In practice, the average of the absolute values of the anodic current iai_a and cathodic current ici_c at the midpoint potential EmidE_{\text{mid}} is taken as the approximate double-layer charging current at that scan rate:

ΔI2=∣ia−ic∣2\frac{\Delta I}{2} = \frac{|i_a - i_c|}{2}

where EmidE_{\text{mid}} is defined as:

Emid=Ehigh+Elow2E_{\text{mid}} = \frac{E_{\text{high}} + E_{\text{low}}}{2}

Linear Fitting

A linear fit is performed with ν\nu on the x-axis and ΔI/2\Delta I / 2 on the y-axis:

ΔI2=Cdl⋅ν+b\frac{\Delta I}{2} = C_{\text{dl}} \cdot \nu + b

The slope of the fit yields the double-layer capacitance CdlC_{\text{dl}} (unit: F). Ideally, the intercept bb should approach zero.

Electrochemically Active Surface Area

Given the specific capacitance CsC_s (unit: μF/cm2\mu\text{F/cm}^2) of a particular electrode material in a specific electrolyte, the ECSA can be calculated as:

ECSA=CdlCs\text{ECSA} = \frac{C_{\text{dl}}}{C_s}

A common reference value: the CsC_s of a smooth metal electrode surface is typically taken as 2020–60  μF/cm260\;\mu\text{F/cm}^2.

Output

  • Linear fitting plot: The x-axis is scan rate ν\nu (V/s), and the y-axis is ΔI/2\Delta I / 2 (A). The plot includes experimental data points (scatter) and the least-squares fitting line, annotated with the CdlC_{\text{dl}} value and R2R^2.
  • Actual sampling-point verification plot: Overlays the final CV cycle at every scan rate and marks the actual anodic and cathodic raw data points used for each curve. Hovering over a marker shows the file name, potential, and current.
  • Result files are saved to the output folder.