CV/Cdl: Double-Layer Capacitance and Electrochemically Active Surface Area Analysis

This Workflow uses the output data from Cyclic Voltammetry (CV) Data Extraction and Preprocessing or Cyclic Voltammetry (CV) Data Extraction and Preprocessing to determine the double-layer capacitance $C_{\text{dl}}$ by linear fitting of the difference between anodic and cathodic currents at the mid-point potential across different scan rates. This can be further used to calculate the Electrochemically Active Surface Area (ECSA).

Prerequisites

First execute Cyclic Voltammetry (CV) Data Extraction and Preprocessing or Cyclic Voltammetry (CV) Data Extraction and Preprocessing to complete CV data extraction. The input folder should contain CV extraction results at multiple different scan rates.

Steps

1. Select input folder: Use the file picker to select the folder containing the output from Cyclic Voltammetry (CV) Data Extraction and Preprocessing or Cyclic Voltammetry (CV) Data Extraction and Preprocessing with CV data at different scan rates.
2. The system automatically calculates the $\Delta I / 2$ values at each scan rate, performs linear fitting, and generates a fitting plot.

Scientific Principles

Determination of Double-Layer Capacitance $C_{\text{dl}}$

In the non-Faradaic potential region, only double-layer charging and discharging occurs at the electrode surface. The charging current $i_c$ is proportional to the scan rate $\nu$:

In practice, the average of the absolute values of the anodic current $i_a$ and cathodic current $i_c$ at the mid-point potential $E_{\text{mid}}$ is used as the approximate double-layer charging current at that scan rate:

where $E_{\text{mid}}$ is defined as:

Linear Fitting

Linear fitting is performed with $\nu$ on the x-axis and $\Delta I / 2$ on the y-axis:

The fitting slope is the double-layer capacitance $C_{\text{dl}}$ (unit: F). Ideally, the intercept $b$ should approach zero.

Electrochemically Active Surface Area

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

Common reference values: the $C_s$ of smooth metal electrode surfaces is typically $20$–$60\;\mu\text{F/cm}^2$.

Output

• Linear fitting plot: x-axis is scan rate $\nu$ (V/s), y-axis is $\Delta I / 2$ (A). The plot includes experimental data points (scatter) and the least-squares fitting line, annotated with $C_{\text{dl}}$ value and $R^2$.
• Result files are saved to the output folder.

Related Workflows

• CV/Pseudocapacitance Analysis: b-Value Kinetic Analysis: Uses the same mid-point current extraction strategy as this Workflow, but focuses on power-law $b$ value kinetic analysis
• CV: Coulombic Efficiency and Capacitance Calculation: Evaluates electrode reaction reversibility from the perspective of charge quantity