EIS300 Electrochemical Impedance Spectroscopy Software

EIS300   Electrochemical Impedance Spectroscopy Software
Redefining Electrochemical Measurement
EIS300
EIS300
 Electrochemical Impedance Spectroscopy Software
Electrochemical impedance spectroscopy (EIS) is a
powerful electrochemical technique that has enjoyed wide
acceptance in the modern electrochemical laboratory. EIS
is routinely employed in battery development, sensor
evaluation, fuel cell characterization, corrosion science,
and paint testing.
The EIS300 Electrochemical Impedance Spectroscopy
Software from Gamry is an exceptional value in EIS with
unsurpassed performance and versatility. Use the EIS300
to measure the impedance between 10 µHz and 1 MHz.
With four research Potentiostats and three modes of EIS
measurement, a Gamry EIS system can reliably measure
impedances as low as 1 mΩ or as high as 1013 Ω!
The EIS experiment places some critical demands upon
potentiostat performance. Gamry understands sometimessubtle potentiostat behavior and how it is affected by the
sample. More than anyone, Gamry designs potentiostats
for EIS – every Gamry Potentiostat leaves the factory
ready to perform EIS!
In 1995, Gamry pioneered a novel single-sine EIS technique
called Sub-Harmonic Sampling. Every Gamry Potentiostat
includes the electronics for Sub-Harmonic Sampling, so
there's no need to purchase any additional
instrumentation. When the EIS300 software is installed,
the Potentiostat is ready to record impedance spectra.
A Gamry EIS System with Sub-Harmonic Sampling has
several benefits:
• Accuracy and precision are equal to or better than other
EIS techniques.
• The instrumental footprint is small, saving bench space.
• The instrumental configuration is simplified -- no
tangled web of BNC cables connecting several instruments.
• Your ability to tailor the Gamry EIS System to your
specific sample is not compromised.
• Lower cost than alternative techniques.
If a special application arises, Gamry’s Open Source
Scripting allows you to make software changes to perform
your custom experiment -- either in the data acquisition or
the data analysis! If you like, Gamry can modify the
software under your direction.
The EIS300 Electrochemical Impedance Spectroscopy System packs a
powerful punch in a pristine package! The clean, space-saving design
liberates bench space in your lab.
You can also use the Sequence Wizard with the EIS300
Software to combine an EIS measurement with other
electrochemical techniques to form a single experiment.
A Gamry EIS System can be configured in a desktop or in a
notebook computer for experiments in the field or for
convenient transport to other locations. All Gamry
Potentiostats are electrically floating, so you can perform
experiments on grounded samples.
The EIS300 performs the following electrochemical
impedance spectroscopy techniques:
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Potentiostatic
Potentiostatic EIS
Multiplexed Potentiostatic EIS
Galvanostatic EIS
Hybrid EIS
Single Frequency EIS
Mott Schottky
Potentiostatic EIS
Potentiostatic EIS measures the impedance by applying a
sinusoidal voltage to the sample and measuring the
current. A DC voltage of ±8 volts and an AC voltage of
3600 mV rms may be applied to the sample. Measure up to
1000 points/decade and collect up to 262,143 data points!
Potentiostatic EIS is the most popular EIS technique and is
favored by corrosion scientists and sensor developers.
Hybrid EIS1 is a modified form of Galvanostatic EIS in
which the applied AC current is continually adjusted to
optimize the value of the measured potential. In the Setup
for Hybrid EIS, the user specifies the desired AC Voltage
and the estimated impedance of the sample. Based on
these values, the EIS300 Software calculates and applies an
AC current at the Initial Frequency. The actual AC voltage
is measured and the AC current is adjusted to bring the
measured voltage into agreement with the desired AC
Voltage.
Setup Window for Potentiostatic EIS. Every parameter required to
make the EIS measurement is available on the single Setup Window.
Multiplexed Potentiostatic EIS
Multiplexed Potentiostat EIS is used with the ECM8
Multiplexer to automate the measurement on as many as
eight samples. The ECM8 is an excellent tool to move more
samples through your laboratory and is commonly used in
paint testing and corrosion inhibitor testing programs.
Galvanostatic EIS
Galvanostatic EIS involves the application of an AC current
and measurement of the potential. Galvanostatic EIS is
commonly used in battery and fuel cell studies. It is also
often recommended for corrosion samples with an
unstable open-circuit potential.
Hybrid EIS
Galvanostatic EIS is a perfectly valid technique for EIS, but
it must be used carefully to obtain valid results. It is
possible for the sample to encounter voltage levels during
Galvanostatic EIS that threaten the integrity of the
experiment. For example, a sample impedance of 1 Ω at
100 kHz will result in a voltage of 10 mV with a 10 mA
excitation. If the impedance increases to 100 Ω at 100 Hz,
however, the 10 mA excitation will produce a voltage of
1000 mV, almost certainly outside the linear range and
possibly even damaging to the sample.
A Lissajous Figure Displayed During Data Acquisition provides a
snapshot of the data quality and potentiostat performance.
The impedance at all other frequencies is performed by
adjusting the applied AC current throughout the frequency
range to obtain the desired AC Voltage as the impedance of
the sample changes. In this manner, the amplitude of the
AC current is continually regulated so that the AC voltage
does not extend beyond the linear, non-destructive range.
1
Orazem et al, Electrochimica Acta, 41, 977 (1996).
A galvanostatic EIS measurement provides higher accuracy
and precision than potentiostatic EIS on low impedance
samples such as batteries and fuel cells. This is because
the potential can be measured (galvanostatic) with higher
accuracy than it can be controlled (potentiostatic).
Single Frequency EIS
Single Frequency EIS measures the impedance at a fixed
frequency versus time. The user controls the experiment
with a Repeat Time and a Total Time. Single Frequency EIS
can be used for sensor evaluation, process monitoring, or
to evaluate slow time-dependent changes in a sample.
Mott Schottky EIS
In Mott Schottky EIS, the impedance is measured at a fixed
frequency as a function of applied DC potential. It is used
most often in the studies of semiconductor interfaces or
space charge regions.
Sub-Harmonic Sampling
The AC waveform for EIS is generated using Direct Digital
Synthesis (DDS). The DDS electronic circuitry is built into
every Gamry Potentiostat. DDS employs digital signal
processing techniques to generate a low-distortion, true
sine wave excitation at the desired frequency (1 MHz – 1
Hz). Gamry’s unique circuit design insures that the
excitation waveform from the DDS is precisely
synchronized with the Potentiostat’s data acquisition.
Sub-Harmonic Sampling transforms high frequency AC
waveforms to lower frequency waveforms. The
Potentiostat’s Analog/Digital Converter samples the
excitation and response (voltage and current) waveforms
at many points on different cycles of the waveform. The
exact sampling position on the waveform is precisely
controlled because the data acquisition frequency is an
exact sub-harmonic (fractional harmonic) of the excitation
waveform.
impedance of the sample and frequency. The Accuracy
Contour Plot details the accuracy of a potentiostat as a
function of impedance and frequency and is available for
all Gamry Potentiostats (see www.gamry.com). Every
potentiostat is less accurate at high frequencies than at low
frequencies, particularly at the extremes of impedance.
Esignal
Isignal
Sampling Interval
SubSub-Harmonic Sampling transforms the high-frequency voltage and
current signals to a lower frequency while maintaining the amplitude
and the phase relationship.
The result is a sine wave of lower frequency but with the
same amplitude as the original current or voltage
waveform. The relative phase shift between voltage and
current is also preserved in these lower frequency curves
because current and voltage are synchronously sampled.
After the current and voltage curves have been sampled,
they are each transformed into the frequency domain using
a discrete Fourier Transform. The impedance is calculated
from the voltage and current signals.
For corrosion, EIS is usually measured at open-circuit
where the DC current is zero, For batteries and fuel cells,
the EIS response is typically made under conditions of high
background current. In this case, the EIS300 System
offsets these DC levels to zero so that the AC values can be
measured at a high gain for maximum accuracy.
Data Presentation and Analysis
Presentation and analysis of your EIS300 data is done in
the Echem Analyst. Bode and Nyquist Plots are standard
and a wide range of other plotting formats are available
through the Curve Selector. Multiple EIS curves can be
easily overlaid. Place the cursor over a data point and
detailed information (frequency, Zreal, Zimag, etc.) is
displayed, particularly useful for Nyquist Plots.
The AC waveform for frequencies less than 1 Hz are
generated using the D/A converter in the Gamry
Potentiostat. The voltage and current are measured
directly by the A/D Converters.
Other Technical Details
The precision of a dynamic electrochemical measurement
such as EIS is an important issue. Unlike other instruments
where the user can only control the number of cycles, the
Gamry EIS300 performs a statistical analysis of the data at
each frequency during acquisition. The data is accepted
only after the precision criteria are met. The precision
criteria can be adjusted by the user.
An electrochemical system is a dynamic sample and it can
be important to make the measurement quickly. The
EIS300 user has a choice of optimizing speed or accuracy
during acquisition. When Fast is selected, the precision
criteria are relaxed, a minimum number of cycles are
applied, and a minimum amount of information is
displayed during the experiment. For Low Noise, the
precision is enhanced and more cycles are allowed. If your
system is stationary, operating in Low Noise can
significantly improve the quality if your data. The
measurement time for a Potentiostatic EIS measurement
on the Gamry Universal Dummy Cell from 100 kHz to 0.1 Hz
with 6 points per decade is only 54 seconds in Fast mode.
The EIS scan is completed in 116 sec in Normal mode and
217 seconds in Low Noise mode.
The accuracy of the EIS measurement is very, very
dependent upon the Potentiostat, but also on the
A Nyquist Plot in the Echem Analyst. Notice the detailed information
on the selected data point.
Convenient tabs are available to quickly display the
Experimental Setup and Experimental Notes. Notes can be
entered during setup for a detailed description of your
sample. The data for Open Circuit Voltage vs. Time,
measured prior to the EIS curve, is always saved and is
available from a tab. The Hardware Settings tab contains
detailed information on the Potentiostat during the EIS
experiment.
The quality of EIS data can be evaluated with the KramersKronig Transform in the Echem Analyst. If the system’s EIS
response is not K-K compliant, then the system is not
linear, causal, or stable and the EIS data will not model
well.
Modeling the EIS Results
The EIS300 includes a complete modeling package for
interpretation of the results. Use the various preconfigured models or build and save your own model using
the graphical Model Editor. The following elements are
included in the EIS300:
• Resistor
• Constant Phase Element
• Infinite Warburg
• Porous Bounded Warburg
• Transmission Line (Open)
• Transmission Line (Short)
• Capacitor
• Inductor
• Bounded Warburg
• Gerischer
• Unified Transmission Line
The EIS300 also allows you to implement your own circuit
element. All you need are the equations defining the
frequency response of your circuit element. See the App
Note section of our website for details.
A Bode Plot of a Randles Cell with the fit overlaid on the data. Click the
“Randles” tab to view the values of the elements in the equivalent circuit
and the Goodness of Fit coefficient.
System Information
The EIS300 Electrochemical Impedance Spectroscopy
Software requires a Gamry Potentiostat to conduct
experiments. Gamry Potentiostats are described in a
separate brochure. Microsoft Windows 7, Vista, or XP is
required for operation of the EIS300.
Like most Gamry software, the EIS300 and a Gamry
Potentiostat use the Gamry Framework for data
acquisition and the Echem Analyst for data analysis. The
general features of the Gamry Framework and the Gamry
Echem Analyst are described in a separate brochure
entitled “An Overview of Gamry Software”.
The EIS300 Model Editor employs an easy-to-use click-and-drag
mechanism to build an equivalent circuit. Build it once and save it.
The equivalent circuit is fit to the data using a MarquardtLevenberg or Simplex algorithm. The EIS300 overlays the
fit onto the data and generates a goodness-of-fit
coefficient that approximates the relative error. If you
wish, you can model a portion of the EIS curve and
undesirable data points can be excluded from the fit. The
data with the fit can be saved in the Echem Analyst.
If you prefer, you can use other commercial EIS modeling
programs. The EIS300 data can be easily imported into
other EIS data analysis software such as Equivalent Circuit,
Zview 2, or ZsimpWin.
Gamry has an instrument for virtually every technique in
the electrochemical laboratory. Other Gamry software
includes DC Corrosion Techniques, Cyclic Voltammetry,
Pulse Voltammetry, Electrochemical Noise, and Critical
Pitting Temperature. Measure the impedance of a fuel cell
with the FC350 Fuel Cell Monitor. You can be confident
that your Gamry system can adapt as your electrochemical
needs expand.
Gamry Instruments can supply complete systems installed
in a desktop or notebook computer. Custom computer
configurations, software, training, and installation are
available by special order. Contact the factory or your
local Gamry Distributor for further details on these
systems
Specfications
Applications Assistance
If you’re new to EIS, we can help. Pay a visit to
www.gamry.com, go to the App Note section, and take a
look at the “Basics of EIS”. There’s an excellent list of
references at the end of the Application Note. For specific
questions, call us at our factory or your local Gamry sales
office.
734 Louis Drive
Warminster, PA 18974 USA
+215-682-9330
See Potentiostat specifications for additional information.
EIS300. Rev 4.1 9/8/10  Copyright 1990-2010 Gamry Instruments
specifications subject to change without notice.
Fax: +215-682-9331
[email protected]
All
www.gamry.com
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