EIS300 Electrochemical Impedance Spectroscopy Software

EIS300 Electrochemical Impedance Spectroscopy Software
Redefining Electrochemical Measurement
EIS300 TM 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, paint testing, and
physical electrochemistry.
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
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 100 kHz.
With three 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!
The EIS300 Electrochemical Impedance Spectroscopy System
packs a powerful punch in a pristine package! The clean, spacesaving design liberates bench space in your lab.
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.
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”.
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
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.
A Gamry EIS System can be configured in a desktop or in
a portable 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:
●
∑
●
●
∑
●
∑
●
∑
●
Potentiostatic EIS
Multiplexed Potentiostatic EIS
Galvanostatic EIS
Hybrid EIS
Single Frequency EIS
Mott Schottky
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.
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 700 mV rms
may be applied to the sample. Measure up to 1000
points/decade and collect up to 65,535 data points!
Potentiostatic EIS is the most popular EIS technique and is
favored by corrosion scientists and sensor developers.
A Lissajous Figure Displayed During Data Acquisition provides a
snapshot of the data quality and potentiostat performance.
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 often 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
Hybrid EIS1 overcomes this problem by continually
adjusting the applied current during the experiment.
The EIS measurement at the Initial Frequency is made
in Potentiostatic mode using the user-specified “Initial
Potential”. The impedance at all other frequencies is
performed in galvanostatic mode by first using the
current measured at the Initial Frequency, and then
adjusting the current value throughout the frequency
range 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 (100 kHz – 1 Hz).
Gamry’s unique circuit design insures that the excitation
waveform from the DDS is precisely synchronized with the
Potentiostat’s data acquisition.
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 Speed is selected, the precision criteria
are relaxed and a minimum amount of information is
displayed during the experiment. 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 48 seconds in High Speed mode. The EIS
scan is completed in 156 seconds in High Accuracy mode.
Sub-Harmonic Sampling transforms high frequency AC
waveforms to lower frequency waveforms. Above a
frequency of 8 Hz, 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.
The accuracy of the EIS measurement is dependent upon
the potentiostat, the impedance of the sample, and frequency.
Every potentiostat is less accurate at high frequencies than
at low frequencies, particularly at the extremes of impedance.
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).
EIS may be measured under conditions where the DC values
are zero, e.g., open-circuit, or under conditions of high
background levels of voltage and/or current for batteries,
fuel cells, and physical electrochemistry. In these cases, 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
Sub-Harmonic Sampling transforms the high-frequency voltage and
current signals to a lower frequency while maintaining the
amplitude and the phase relationship.
Presentation and analysis of your EIS300 data is done in
the Echem Analyst. Bode and Nyquist Plots are standard
and 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 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.
Other Technical Stuff
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.
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.
Applications Assistance
If you’re new to EIS, we can provide some suggestions. Pay
a visit to www.gamry.com, go to the App Note section, and
take a look at “The EIS Primer”. 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
distributor.
Modeling the EIS Results
The EIS300 includes a complete modeling package for
interpretation of the results. Use the six pre-configured
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
Capacitor
Inductor
Bounded Warburg
Gerischer
The equivalent circuit is fit to the data using the
Marquardt-Levenberg 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.
The EIS300 Model Editor employs an easy-to-use click-and-drag
mechanism to build an equivalent circuit. Build it once and save it.
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® 98, Me, 2000,
or XP is required for operation of the EIS300. Gamry
recommends a computer with a 450 MHz processor or
higher with 64 Mb of RAM or higher.
Gamry Instruments can supply complete systems installed
in a desktop or portable 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.
If you prefer, you can use other EIS modeling programs.
The data format of the EIS300 is tab-delimited ASCII text,
so it can be easily imported into other EIS data analysis
software such as Equivalent Circuit, Zview 2, or ZsimpWin.
EIS300 Rev 1.0 9/15/02
© Copyright 1990-2002 Gamry Instruments
All specifications subject to change without notice.
734 Louis Drive
Fax: +215-682-9331
Warminster, PA 18974 USA
+215-682-9330
[email protected]
www.gamry.com
Was this manual useful for you? yes no
Thank you for your participation!

* Your assessment is very important for improving the work of artificial intelligence, which forms the content of this project

Download PDF

advertisement