Analysis of electrochemical impedance spectra (EIS)
Reporter: LingChen Mar. 3rd 2006
Introduction of EIS
? Electrochemical impedance spectroscopy (EIS) is a very powerfu
l tool to analyze the electrochemical electrode reactions and has been commonly used to analyze the electrochemical interface. ? Impedance spectrums are often modeled using an electrical circuit which produces a similar spectrum. The electrical components (resistors, capacitors, inductors, etc) and some 'components' that have no electrical analog (constant phase elements, Warburg impedances, etc) are then matched to physical characteristics of the measured cell.
? 1.Fit by Zview Software ? 2.Data preparation ? 3.Examples
1. Fit by Zview 1.1 Circle Fit
The semi-circle fit is a geometric fit not an RC
or Equivalent Circuit fit.
1. Fit by Zview 1.2 Instant Fit
? One method of producing initial values
CPE = Constant Phase Element Parameters: CPE-T, CPE-P Z = 1 / [T(i×ω)P] CPE-P = 0.5 CPE-P = 1 a 45 degree line a capacitor
Often a CPE is used in a model in place of a capacitor to compensate for non-homogeneity in the system.
1. Fit by Zview
1.3 Equivalent Circuits Fit
? Example 1 ? Example 2
2.Data preparation 2.1 Experiment results
Z’ ~ Z’’
2.Data preparation 2.2 Data Transformation
Frequency (Hz) Z’ (Real) Z’’ (imaginary) IZI phase
0.01 0.01314 … 76095
1167.99 1149.63 … 4.00774
-78.6652 -66.5861 … -0.64123
1170.64 1151.56 … 4.05871
-0.85309 -3.31484 … -9.09017
The data is transformed to ASCII form by Origin software
? We must rely on our own knowledge of the physical system we are measuring. It can also be helpful to see if the model gives “reasonable” values. ? Real experimental data is usually harder to model so we need take our time and work our way to finally fitting the data.