What is Electrochemical Impedance Spectroscopy?
Electrochemical impedance spectroscopy (EIS) is a technique that applies a small sinusoidal voltage perturbation to an electrochemical system across a range of frequencies and measures the resulting current response. The ratio of voltage to current at each frequency gives the complex impedance of the system, which can be analyzed to extract information about interfacial processes, diffusion, charge transfer kinetics and bulk electrolyte properties.
How EIS Works
A potentiostat applies a small AC perturbation (typically 5–10 mV amplitude) superimposed on the DC potential of interest. By sweeping frequency from typically 100 kHz down to 1 mHz or lower, different physicochemical processes are probed at their characteristic timescales. Fast processes (charge transfer, double layer capacitance) appear at high frequency, while slow processes (diffusion, adsorption) appear at low frequency. The data is displayed as a Nyquist plot (imaginary vs. real impedance) or Bode plot (magnitude and phase vs. frequency).
Equivalent Circuit Analysis
EIS data is typically analyzed by fitting an equivalent circuit model, where each element represents a physical process. Common elements include: solution resistance (Rs), charge transfer resistance (Rct), double layer capacitance (Cdl), Warburg diffusion element (W) and constant phase elements (CPE). Fitting software such as EC-Lab provides automated circuit fitting with statistical confidence intervals.
EIS Applications
- Battery research — in-situ measurement of SEI layer formation, Li-ion intercalation kinetics and electrolyte resistance during cycling
- Corrosion science — measurement of coating barrier properties, pitting initiation and inhibitor effectiveness
- Fuel cells — membrane resistance, oxygen reduction kinetics and mass transport limitations
- Biosensors — detection of binding events at functionalized electrode surfaces
- Supercapacitors — characterization of capacitance and ESR across frequency
- Electrodeposition — monitoring layer growth kinetics and deposit quality
Choosing a Potentiostat for EIS
Key specifications for EIS-capable potentiostats include: frequency range (wider is better for resolving all processes), phase accuracy at high frequency, current resolution at low current, and ability to measure very high impedances (important for thin films and coatings). The Bio-Logic VSP-300 provides EIS from 10 µHz to 7 MHz with phase error below 0.1° and current resolution down to 10 fA, making it suitable for the most demanding EIS applications. For battery multichannel testing, the BCS-815 and MPG2 systems provide per-channel EIS on up to 16 channels simultaneously.
Common EIS Measurement Pitfalls
- Applying too large a perturbation amplitude — EIS assumes linearity, requiring perturbations small enough to stay within the linear regime
- Insufficient low-frequency data — diffusion processes require measurement down to mHz or sub-mHz frequencies
- Cable and connection artifacts at high frequency — 4-terminal connection and proper cable management are essential above 10 kHz
- Non-stationary systems — EIS requires the system to be at steady state; drifting potentials invalidate the measurement
NewRoad distributes Bio-Logic potentiostats and battery testing systems with full EIS capability. Contact us to discuss the right instrument for your electrochemistry application.
