Echem Analyst Software

Echem Analyst Software................................................................................................ 1Introduction to This Guide .............................................................................................. 2General Information and Overview ................................................................................. 3Installation ................................................................................................................... 3File Formats ................................................................................................................. 3To Open a Gamry Data File......................................................................................... 3Working with Plots in Echem Analyst ........................................................................... 5Changing the Axes on a Plot (the Curve Selector): ........................................................ 8Selecting Portions of a Curve for Analysis ..................................................................... 8Selecting Portions of a Curve for Analysis ..................................................................... 9Cutting and Pasting Images and Data ......................................................................... 10To Get On-Line Help:................................................................................................ 11Common Tools and Tabs ............................................................................................... 13Accessing Common Tools ........................................................................................... 13List of Common Tools ................................................................................................ 13Experimental Setup.................................................................................................... 15Experimental Notes.................................................................................................... 16Hardware Settings...................................................................................................... 17Open Circuit Voltage (Corrosion Potential) Data........................................................ 19Analysis of Cyclic Voltammetry Data.............................................................................. 20Cyclic Voltammetry Special Tools .............................................................................. 20Integrating the Voltammogram................................................................................... 22Modeling Polarization Resistance Data .......................................................................... 24Polarization Resistance Special Tools ......................................................................... 24Finding the Polarization Resistance ............................................................................ 24Modeling Potentiodynamic (Tafel) Data......................................................................... 26Tafel Fit...................................................................................................................... 26E Log I Fit ................................................................................................................... 27Modeling EIS Data ......................................................................................................... 28Bode and Nyquist Plot View ...................................................................................... 28EIS Special Tools ........................................................................................................ 29Fitting the Data to the Equivalent-Circuit Model ........................................................ 33Appendix....................................................................................................................... 36Headings in Data-File Columns.................................................................................. 36Current Conventions According to Framework and Echem Analyst......................... 37To Edit Visual Basic Scripts:........................................................................................ 37Simulating an EIS Curve ............................................................................................. 38Index ............................................................................................................................. 40

Windows, Excel, and Powerpoint are registered trademarks of Microsoft Corporation. Originis a registered trademark of OriginLab Corporation. DigiSim is a registered trademark ofBioanalytical Systems, Inc. Contents of this manual copyright 2011 by Gamry Instruments.

1

Introduction to This Guide

The Echem Analyst is Gamrys dedicated data-analysis program, the companion toGamrys data-acquisition program called Framework. Data files generated byexperiments in Gamry Framework then can be analyzed in the Echem Analyst. TheEchem Analyst is a single program that runs data-analysis for all types of experiments,such as those used in DC Corrosion, EIS and Physical Electrochemistry.

The Echem Analyst is designed with the specific functions to make data analysis asstraightforward as possible. This manual will explain the most common analysis routines.The tools discussed here in the examples are common to many data files created byother experiments. This document is a guide, and is not intended to have the same scopeas the on-line help or a complete operating manual. In order to create a concisedocument, we assume the user has a working knowledge of Windows-basedapplications. Details on common functions, such as opening, saving, and closing files, areintentionally ignored, so as not to obscure the goal of this guide.

This textbox indicates a helpful hint to know about Echem Analyst.

2

General Information and Overview

InstallationEchem Analyst installs separately from other Gamry software. If Echem Analyst isnot installed yet, you can find it on the CD-ROM, orif you already own one ofour potentiostatson our website at www.gamry.com.

You may install copies of the Echem Analyst on multiple computers. Often usersprefer the convenience of performing data-analysis at an office workstation, ratherthan the laboratory setting.

File FormatsGamry data files acquired using Framework software have the extension *.DTA.DTA files are ASCII text, and therefore may be opened directly into variousprograms, such as Excel or Origin. When DTA files are opened in EchemAnalyst, then saved, their extension becomes *.GData. Gdata files includeinformation on curve-fits and graphing options, thus Gdata files are only viewablein Echem Analyst.

Do not delete your DTA files! They are the raw data and may needto be reloaded for certain analyses, such as area normalization.

To Open a Gamry Data FileThere are several different methods to open data files in the Echem Analyst:1. Launch the Echem Analyst icon on your desktop. Then use theFile\Open function.2. Use the link on your desktop to open the My Gamry Data folder.Double-click on the data file. You may have to instruct yourcomputer to associate the *.DTA extension with the EchemAnalyst program.3. There are two quick ways to open a recent Gamry Data File.

a.

A recently generated file can be opened using the hotlink in the Analysis menu in the

Gamry Framework. (The last eight generated data files are listed there for quick access.)The Echem Analyst automatically launches and opens your selected data file.b. A recently opened file in the Echem Analyst is shown at the bottom of the File menu. Thisis similar to how other Windows-based programs display links to Most Recently Useddocuments.

3

By default, files acquired in the Framework are saved into the My Gamry Datafolder. A shortcut for My Gamry Data installs on the Windows desktop. You canchange this default under Tools\Options, which opens the Gamry AnalysisFramework Options window. Choose the General tab, and change the Path foreach type of data file as desired.

Don't change the directory for Analysis Script Files. These are theVBA programs that do the actual analysis.

The data set appears in the main window. The menu items, tabs, and toolbar areadjusted for the particular type of data set you chose. In the example below, aPotentiostatic EIS data set is shown:

Note the tab-based display. The Experimental Setup tab displays all theinformation from the parameters used to run the experiment, such as Voltage,Time, etc. The Experimental Notes tab stores any notes written into the setupscreen in Framework. The Open Circuit Voltage tab shows the voltage measuredduring the Initial Delay of the experiment. The Hardware Settings tab recordsinformation on the filters, ranges, gains. Additional information on date of lastcalibration, software version, etc. is also stored here.

4

Working with Plots in Echem AnalystIntroductionEchem Analyst boasts a number of graphical tools to help you get the mostinformation out of your data. Once you open a data set, these tools appear in thetoolbars immediately above the plot:

In the data file, Framework writes a line that indicates the type of experimentused to generate that file. Echem Analyst displays both general and specific menuscontaining the analysis routines pertinent to your experiment.

Toolbars:

The main toolbars are:

GeneralToolbar

Selection

General functions for replotting and printing in various formats

Tools to select and view data points

Toolbar

5

The following charts are references for buttons on the default toolbars.Descriptions of the most commonly used functions are highlighted in blue.

General Toolbar Functions

Button

NameCopy toclipboardGallery

Color

Vertical Grid

Horizontal Grid

Legend Bar

Data Viewer

Properties

3D/2D

Rotate

Z-clustered

Zoom

Print preview

Print

Tools

ActionCopy the selection to the Windows clipboard. Can paste directly inMicrosoft programs for reports or presentations.Choose, via the dropdown menu, from scatter (no line), line, curve, andsteps between data pointsChoose the color of the selection from the dropdown menu. To change thecolor menu, use the Palette button on the PaletteBar.Toggle between showing and hiding vertical grid lines on the plot

Toggle between showing and hiding horizontal grid lines on the plot

Toggle between showing and hiding a legend bar underneath the plot

Toggle between showing and hiding numerical data to the left of the plot

Open the GamryChart Properties window, so that you can adjust effects,colors, markers, 3-D effects, lines, etc.Toggle between two-dimensional and three-dimensional graphing

Rotate the three-dimensional graph. Only active if the graph is 3D.

Offset two data sets so that they can be distinguished within one plot.Only operates in 3D mode.Zoom in on a selected region. Also open a zoom slider at the bottom of thegraph for continuous adjustment of zoom.Open the Page setup window to adjust orientation of plot and printermarginsPrint the plot

Open a dropdown menu, for choices of various toolbars and viewers to

appear on the screen

6

Selection Toolbar Functions

Button

NameShow curve selector

Select x region

Select y region

Select Portion of Curveusing the MouseSelect Portion of Curveusing the KeyboardDraw Freehand Line

Mark Found Peaks

Apply Template

Save Template

Show Disabled Points

ActionOpen the Curve Selector area to the right of the plot, so that you canchoose which data are used as the x-, y-, or y2-coordinate, andwhich curve is the active trace.Select a desired region of the plot across the x-axis. Commonly usedto specify a region for Quick-Integrate.Select a desired region of the plot across the y-axis Commonly usedto specify a region for Quick-Integrate.Left-click on the active trace using the mouse to select a section ofthe curveOpen an area to the right of the plot, in which you can choose asegment of the trace numerically. See below for more details.Draw a line on the plot

Place a tag on peaks that the software finds. A portion of the curvemust be selected first.Open the Apply User-Defined Chart Template window, andchoose a previously created template to apply to the plotOpen the Save User-Defined Chart Template window, and savethe templateShow data points not being used in the plot

7

Changing the Axes on a Plot (the Curve Selector):To choose a different variable plotted on an axis, use the Curve Selector button

as follows:(The example shown below is a Differential Pulse Voltammetry plot.)

1. With the plot open and displayed on the screen, click the Curve Selector

button

.

The Curve Selector area appears on the right side of the window.2. Choose which trace is active by clicking on the drop-down menu in the ActiveTrace area.The Active Trace is the data series on which the analysis will be performed.Use this, for example, if multiple files or cycles are displayed on the graph.3. Choose which trace is visible on the plot by activating the checkbox next to thedesired trace(s) in the Visible Traces area.Visible Traces also contain any data fits that are performed.4. Choose which variable is plotted on the x-axis by highlighting the variable inthe X-Axis column.5. Choose which variable is plotted on the y-axis by highlighting the variable inthe Y-Axis column.6. Choose which variable is plotted on the second y-axis by highlighting thevariable in the Y2-Axis column.

If there is a data column graphed on the Y2-Axis, those data appear ina different color and a different scale.

8

Selecting Portions of a Curve for AnalysisFor certain types of analysis, you must select a region of the curve, for example,within the Peak Find function in Cyclic Voltammetry or Tafel Fit function inPotentiodynamic. You can select regions by mouse or keyboard.

1. Left-click the mouse on the Mouse button

in the Selection toolbar.

2. Use the left mouse-button to select each endpoint of the curve.Each endpoint is marked with a blue cross. The selected portion of the curveis shown as a thick blue line. (In the figure below, the color of the data hasbeen changed to red for contrast to the selected region).

3. Another click on the Mouse button clears the selected region, and readies thegraph for a different region to be selected.

9

Cutting and Pasting Images and DataMany users want to present, publish, or otherwise share their data and chartsfrom the Echem Analyst. To create a bitmap image of the graph,

As a Bitmap:

1. Choose the Copy to Clipboard button

from the General Toolbar.

2. In the drop-down menu select As a Bitmap.

3. A bitmap image of the graph enters the clipboard. This bitmap may be pastedinto a presentation program such as Word or Powerpoint.

This is a quick and easy way toimport a picture of the graph for

a presentation or report.

Bitmap is not an editable format.

As Text:Because Gamry Data Files are ASCII text, they can be opened easily in othergraphing programs, such as Excel or Origin. Right-click on the DTA file andselect Open With and select for favored program. These programs, however, donot contain fitting routines specific to the analysis of electrochemical data. This AsText feature lets you fit the data in Echem Analyst and then copy and paste thedata and fit into another graphing program.

This is a quick and easy way to import both the data and the fit into anothergraphing program.

If you are using the As Text feature, be sure to note the currentlygraphed parameters. The coordinates of this currently displayed graph arecopied and can be pasted to graphing programs.

10

Plotting ConventionsBy right-clicking the mouse on a non-zero value on an axis, you can choose toshow that axis in logarithmic or linear scale, or to reverse the direction of thenumbers.

Alternatively, you can use the Transform Axes selection (if available) under theCommon Tools menu.

Default plotting of graphs is auto-scale. Therefore, please note they-axiss scale when a plot first appears. If bad data points obscure your databecause of auto-scaling, you can choose to disable and hide those offendingpoints.

To Get On-Line Help:In the toolbar, choose Help.

a.

Click Gamry Help to obtain

information about variouscommands and functions withinEchem Analyst.

A separate Gamry Echem Analyst Helpwindow appears. You can find much information about the details of Echem Analyst here, such asplotting and analysis.

On-line help is a great resource for more involved questions. Helpis divided up according to software package.

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b. Click About the Gamry Echem Analyst to view the software version number.

12

Common Tools and Tabs

While each type of experimental data has its own method and parameters, thereare certain commands that are common to many analyses. This section shows youthese Common Tools.

Accessing Common Tools1. Open a dataset.In the toolbar, the function Common Tools appears.2. ChooseCommonTools.A drop-downmenuappears.3. Select the desired command.In this example, chronoamperometrys Common Tools includes threecommands, Add I Constant, Linear Fit, and Smooth Data.

The list of Common Tools varies depending upon the type ofexperiment.

List of Common Tools

CommandAdd EConstant

Add IConstant

C from CPE,omega(max)

Type of experimentCyclic Voltammetry, DC Voltammetry,Differential Pulse Voltammetry, GalvanicCorrosion, Normal Pulse Voltammetry, PittingScan, Polarization Resistance,Potentiodynamic Scan, Square-WaveVoltammetry

Chronoamperometry, Chronopotentiometry,Cyclic Voltammetry, Galvanic Corrosion,Pitting Scan, Polarization Resistance,Potentiodynamic Scan

Potentiostatic EIS, AC Voltammetry, Mott-Schottky

ResultAdds a constantpotential to allvoltages in the plot.Used to easilyconvert betweendifferent ReferenceElectrodes scales.

Adds a constantvalue to all currentsin the plot.

Calculatescapacitance frompreviously fit CPEvalues and data13

from the Nyquistplot.

C from CPE,R(parallel)

Linear Fit

Post-Run iRCorrection

Potentiostatic EIS, AC Voltammetry, Mott-Schottky

Chronoamperometry, Potentiostatic EIS, ACVoltammetry, Chronocoulometry,Chronopotentiometry, Cyclic Voltammetry,DC Voltammetry, Differential PulseVoltammetry, EMF Trend, GalvanicCorrosion, Mott-Schottky, Normal PulseVoltammetry, Polarization Resistance,Potentiodynamic Scan, Square-WaveVoltammetryCyclic Voltammetry, Polarization Resistance,Potentiodynamic Scan

Calculatescapacitance frompreviously fit CPEand fit R data.When a region ofthe plot is selected,fits the data toy = mx + b.

Corrects a previouslyrun scan for voltage-drop caused by iR.

Smooth Data Chronoamperometry, Chronopotentiometry,Cyclic Voltammetry, DC Voltammetry,Differential Pulse Voltammetry, EMF Trend,Galvanic Corrosion, Normal PulseVoltammetry, Pitting Scan, PolarizationResistance, Potentiodynamic Scan, Square-Wave Voltammetry

Smoothes the data.Useful for locatingpeaks in regions ofhigh data-density.

TransformAxes

Galvanic Corrosion, Pitting Scan, PolarizationResistance, Potentiodynamic Scan

Changes x- and y-axes from linear to

logarithmic, etc.

14

Experimental Setup

This particular Experimental Setup tab is from a Cyclic Voltammetry experiment. Thisexample has many of the same parameters as other experiments. It shows:

Initial E, Scan Limit 1,Scan Limit 2, Final ETest Identifier

TimeScan RateStep SizeElectrode AreaEquil. Time

I/E Range ModeMax Current

Conditioning

Init. DelayCyclesIR CompOpen Circuit

Sampling Mode

The potentials defining the waveform, and whether measuredvs. a reference electrode (Eref) or the open circuit potential (Eoc).Read from the Framework Setup. This field also becomes thedefault title of the plot.Time the experiment was startedHow fast (in mV/s) the scan was takenThe interval between potentialsThe size of the electrodeHow much time was spent letting the electronics settle beforethe scan was startedAutomatically adjusted or fixed I/E (Current) Range mode.The current value that sets the I/E Range in Fixed Mode anddetermines the range in which to start in Auto ModeWhether off or on, for how long, and under what potential.This Potential is vs. Reference.Whether off or on. This is when the Eoc is measured.Number of how many voltammetry cycles were runIf IR Compensation was used and the mode.The value of the Open circuit voltage (Corrosion Potential). It isthe value of the last point in the Initial Delay.Data-acquisition mode (for Reference Family Potentiostats)

15

Experimental NotesClick the Experimental Notes tab:Any notes entered in the Framework are automatically displayed here. Youmay enter any additional comments about the experiment in the Notesfield.

This is a version of a modern laboratory notebook. Enter as many details aboutyour experiment as you can. Information here can help you avoid having longstrings of descriptive file names.

16

Hardware Settings

This section documents the hardware settings that were used whenthe experiment was run, e.g., everything from the offsets, filters, and gains tothe last time the potentiostat was calibrated.

This information is used primarily by Gamry Technical Support staff to helptroubleshoot. Gamry determines defaults for these settings based onexperience. Advanced users can adjust these settings manually before theexperiment is run.

For DC Corrosion experiments, the Hardware Settings are set in theexperiment code. For Physical Electrochemistry experiments, users haveaccess to these features through the Advanced Panel, but Gamry recommendsthat only advanced users make changes to these settings. Consult Help orGamry Technical Support for advice.

Click the Hardware Settings tab:

The hardware settingsdisplayed here are:

PotentiostatControl ModeControl Amp SpeedI/E AutoRangeIch AutoRangeIch RangeIch FilterIch Offset EnableIch OffsetPositive Feedback IRCompI/E Range Lower Limit

Ach select

Shows the potentiostats labelHow the experiment was controlledShows the speed of the control amplifierShows if the I/E autorange function was enabledShows if the Ich autorange function was enabledShows the Ich range (gain). 3 Volts = x1 Gain.Shows the Ich cut-off filter frequencyShows if Ich Offset was enabledShows the Ich offset voltageShows if the IR positive feedback was enabled

Shows the lowest available I/E Range available to use in thisexperimentShows the input connector for Ach

17

DC Calibration DateFramework VersionPstat ModelCurrent ConventionI/E StabilityI/E RangeVch AutoRangeVch RangeVch FilterVch Offset EnableVch OffsetPositive FeedbackResistanceAch RangeCable ID

AC Calibration DateInstrument Version

Shows the date of last DC calibration

Gives the model number of the potentiostatShows which currents are positiveShows the I/E stability speedShows the I/E (or current) range usedShows if Vch autoranging is enabledShows the maximum value for VchShows the Vch cut-off filter frequencyShows if Vch Offset was enabledShows the Ich offset voltageShows the positive feedback resistance applied to the system

Shows the voltage range of the auxiliary channel(for Reference Family Potentiostats only.) Gives the type ofcable connected to the systemShows the date of last AC calibrationShows the Firmware Version of a Reference Family Pstat

Detailed explanations of these parameters are beyond the scope of this guide.

18

Open Circuit Voltage (Corrosion Potential) DataClick the Open Circuit Voltage tab:

Because default plotting of graphs is auto-scale, please note they-axiss scale when the Open Circuit Voltage first appears.

19

Analysis of Cyclic Voltammetry Data

This is a sample cyclic voltammetry file that installs in \My Gamry Data\ whenFramework installs.

Cyclic Voltammetry Special ToolsThis menu analyzes the cyclic voltammetry data.1. In the main menu, choose Cyclic Voltammetry.A drop-down menuappears.2. Choose the desiredtool:

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ToolMin/Max

Quick Integrate

Integrate

Region Baselines

Clear Regions

Normalize by ScanRateNormalize bySquare Root of theScan RatePeak Find

Clear Peaks

Automatic Baseline

Peak Baselines

Clear Lines

Delta Ep

SubtractBackground fromFileExport to DigiSim

Options

FunctionFinds the minimum and maximumcurrents and voltages within the dataset.Results appear in a window below theplot.Integrates to find the total charge. Resultsappear in a window below the plot.Integrates over a specified portion of theplot to find the total charge.

Defines a line as the baseline for aspecified region.Clears all baselines from the dataset.

Normalizes the dataset based on the scanrate.Normalizes the dataset based on thesquare-root of the scan rate.

Finds peaks within a specified region ofthe dataset.

Clears all peaks found within the dataset.

Finds the baseline automatically.

Defines a line as a baseline for aspecified peak.Clears all lines from the dataset.

Finds the potential difference betweentwo peaks.Subtracts a background amount from thedataset.

Exports the file to a DigiSim-compatibleformat.Changes units and grids for plotting the

Notes

For multi-cycle CVexperimentsPortion of thecurve must beselectedRegion must beselectedRegion must beselected

Portion of thecurve must beselectedPeaks must beidentifiedPeaks must beidentifiedPeaks must beidentifiedLines must beassociated withgraphPeaks must beidentified

data.

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Integrating the VoltammogramAll integration methods integrate current versus time to get the total charge. Thereare two different ways to integrate under a curve with Echem Analyst.

Quick IntegrateQuick Integrate breaks the data into curves. Each curve is integrated to a zerocurrent. Quick Integrate integrates the entire area of each curve, unless an area isspecified using the x-region icon.

IntegrateIntegrate requires you first to select a portion of the curve. (See how to select aportion of the curve in the Starting Echem Analyst chapter.) After an integrationis performed, you can change the baseline from the default 0 A to another line,either a line that you draw, or an Automatic Baseline.1. Open the data file.2. Select the Draw a Freehand Linebutton:

3. Left-click and hold on the graphto place an anchor point.Holding down the mouse button,extend the line with the mouse.Move or extend the line as youwish.

Directions to accept theline are printed at thebottom of the window.4. Right-click the mouse onthe line and either Ac-cept or Delete.After you accept theline, it turns fromdashed to solid.5. Select the portion of thecurve to integrate.This function is de-scribed in detail earlier.

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6. Select Integrate from theCyclic Voltammetrymenu.This integrates the sec-tion between the curveand the zero amp line.7. To change the baselineto the desired user-drawn line, select RegionBaselines from the CyclicVoltammetry menu.

The Region BaselineSettings window appears.8. Select the Region Baselinefrom the available lines. Youmay draw multiple lines fromwhich to choose.Note that theintegratedregion movesfrom thedefault 0Amps baselineto the user-drawn line.

23

Modeling Polarization Resistance Data

Polarization Resistance Special ToolsThis menu analyzes the polarization resistance data.1. In the main menu, choose Polarization Resistance.A drop-downmenuappears.

2. Choose the desired tool:Tool functionQuick Integrate Integrates to find the total charge. Results appear in a windowbelow the plot.Min/Max Finds the minimum and maximum currents and voltages withinthe dataset. Results appear in a window below the plot.

PolarizationResistanceOptions

Within a selected portion of the curve, finds the polarizationresistance.Changes units and grids for plotting the data.

Finding the Polarization ResistanceMethod 1: Manual Eentry of the Tafel Constants1. Select the desired portion of the curve. (See section.)2. In the main menu, choose Polarization Resistance.A drop-downmenuappears.

3. Choose Polarization Resistance.The Polarization Resistance windowopens.4. In the Seed Values area, enter anodic(Beta A) and cathodic (Beta C) Tafelconstants.5. Click the Calculate button.The calculated Corrosion Rate appears ina window below the plot.

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Method 2: Automatic Selection of Voltage RegionGamry offers another way to select automatically the voltage region over whichthis analysis is done.1. In the Polarization Resistance menu, choose Options.

The Polarization Resistance Options window opens.2. Select this Automatic radiobutton, specify the regionaround Ecorr to use, and Saveas Defaults. You are prompteddirectly for Tafel constantswhen a polarization resistancefile is opened.

This is how Gamrys RpEc Trendexperiments calculate corrosionrate.

25

Modeling Potentiodynamic (Tafel) Data

A Tafel experiment is also a very popular electrochemical corrosion technique.The following analysis is performed on the sample Potentiodynamic data file.Tafel Fit1. Select the region over which to perform the Tafel fit.This region must encompass the Ecorr (Open Circuit Potential).2. Select Tafel Fit from the Potentiodyanmic menu:

3. A Tafel Fit window appears where you mayinput seed values optionally for the fit.The better the information we provide thefitting routine, the more likely it will be ableto generate an acceptable fit.

If you have reasonable starting parametersfor the fit, input them in the Seed Valuesarea, and check the Use Seed Valuescheckbox. If you do not have anyconfidence at all in your range ofparameters, do not check the Use SeedValues checkbox.

We recommend using the seed valuessupplied by the Echem Analyst.

4. Click the Calculate button.When the Calculate button is pressed, the changes can be subtle. Thefollowing events occur:

26

The parameters in the Tafel Fit window become the fit parameters.

A fit line is displayed on the graph.A new Tafel tab is created (to the right of the Hardware Settings tab) that

holds the information about the fit.

E Log I FitThe E Log I fit is a useful fit if you want to fit the data one branch (anodic orcathodic) at a time. This can be important if one branch doesnt show linearbehavior, but the other does.

The fit is called E Log I because of the semi-logarithmic nature of a Tafel plot. Thex-axis is the logarithm of current, while the y-axis is potential on a linear scale.Method1. Select a portion of the curve.Here you need only the linear section of one of thebranches. This selection does not include Ecorr (Eoc(open circuit potential)).2. In the E Log I Fit window, enter an approximatevalue for Ecorr.3. Click the Calculate button.A single branch of the Tafeldata is fit. The fit is shownon the graph, and the resultsof the fit are contained in anew E Log I tab.

You can run a PolarizationResistance fit on thisPotentiodynamic data, if theaxes of current are changedto the linear scale. Generallywe suggest running a separate experiment on a new sample of the samematerial because of the more-polarizing, more-destructive nature of thePotentiodynamic experiment.

27

Modeling EIS Data

The data-analysis features shown here are common to many of the AC-basedtechniques. By far the most popular type of AC experiment is Potentiostatic EIS.

Bode and Nyquist Plot ViewClick the Bode tab or the Nyquist tab of the plot you prefer to work with. All fitsare displayed on both the Bode and Nyquist plots. Because they are differentrepresentations of the same data, the fit results are identical.

Bode plot

Nyquist plot

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EIS Special ToolsEIS data-analysis uses an equivalent-circuit approach. This menu creates and runsfits for EIS data. Commands in this menu allow you to build an equivalent-circuitmodel in the Model Editor, then fit that model to your data. This menu also letsyou run advanced procedures, such as Subtract Impedance, and run Kramers-Kronig transforms.1. In the main menu, choose Impedance.A drop-down menu appears.2. To create oredit anequivalentcircuit,chooseModelEditor.TheImpedanceModelEditorwindow appears. See the next page for how to use it.3. To fit the data using the Levenberg-Marquardt method, choose Fit A Model(Levenberg-Marquardt Method).The Select Model File window opens.Choose the appropriate model file, and click the OK button.4. To fit the data using the Simplex method, choose Fit A Model (SimplexMethod).Simplex method weighs the users seed values less. We recommend using theSimplex method.5. To subtract an impedance from the data, choose Subtract Impedance.The Impedance Subtraction window appears.Choose:Element Choose a circuit element from the drop-down menu.Model Browse for a previously defined model.Spectrum Browse for a data-set.Click the Close button.6. To use the Kramers-Kronig method,Choose Kramers-Kronig.Kramers-Kronig is a model-independent transform that checks the EIS data forconsistency.The Kramers-Kronig window appears.7. To clear all fits from the plot,Choose Clear All Fits.8. To change time or impedance units,Choose Options.This option let you normalize the data and fits to the normalized area.

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The Model EditorThe Impedance Model Editor allows you to create an equivalent circuit, via adrag-and-drop method.

Thereare several pre-loaded models.Often users find itconvenient to startwith one of thesemodels and edit it asneeded.

Circuit Elements

Symbol

30

ElementResistor

Capacitor

Inductor

ConstantPhaseElementWire

Gerischerelement

InfiniteWarburgBoundedWarburg

PorousBoundedWarburg

CommentsAbbreviated as R. Z = R

Abbreviated as C. Z = i/C

Abbreviated as L. Z = iL

Models an inhomogeneous property of the system, or aproperty with a distribution of values. Often abbreviated asCPE.Connects one element to the next.

Models a reaction in the surrounding solution that happenedalready; also used for modeling a porous electrode. Oftenabbreviated as G.Models a linear diffusion to an infinite planar electrode.Often abbreviated as W.Models diffusion within a thin layer of electrolyte, such aselectrolyte trapped between a flat electrode and a glassmicroscope slide. Often abbreviated as T.Models diffusion through a thin layer of electrolyte, such aselectrolyte trapped between an electrode and a permeablemembrane covering it. Often abbreviated as O.

Building an Equivalent Circuit1. Adding an element

a.

Click on an element symbol.

The element appears in the central window.b. Place the mouse cursor over the element. Left-click and drag to move the element to itsdesired position.2. Connecting elements

a. Click on the Wire symbol .b. Left-click one end of the wire and drag theend to the element.The elements border turns green when the wires

Be sure to connectthe circuit to the reference-

end reaches the element.3. Deleting an element

electrode symbol

and the

a.

Right-click on the element.

working-electrode symbol

.

The Delete command

appears.

b. Left-click on the Delete command.The element vanishes.Here is an example of a simple equivalent circuit (a Randles model) constructedin the ImpedanceModel Editor:

4. Relabeling andfixing parametersfor an elementThis lets you rename theelement, and specify aLower and Upper Limitfor its value. Renamingthe element helps youdistinguish betweenelements of the same typeduring fitting. Giving theprogram limits on the parameters mayhelp the mathematical algorithm. Forexample, we know values are generallypositive, so a Lower Limit = 0 isreasonable to set.

a.

Left-click on the name of the

element (here, R4).The Parameter window appears.b. Enter a new Parameter Name.

c.

Enter an Initial Value, i.e., the

first trial value for fitting.d. In the Lower Limit Test andUpper Limit Test fields, enterlower and upper limits, andcheck the Enable checkbox, asdesired.

e.

Click the OK button.

The Parameter window closes, and the element is set to these parameters.

31

Compiling the Equivalent CircuitWhen the equivalent circuit is complete, the circuit can be compiled before useto check for connectivity of the wires. Compiling is only used to checkconnections1. In the toolbar, choose Tools.A drop-down menu appears.

2. Choose Compile or click the Test Compile buttonin the toolbar.The software compiles the equivalentcircuit.If there is a problem, such as a missingconnection, an error message appears,and a red box outlines the problemelement:3. Click the OK button to continue.4. Inspect the schematic and make necessary corrections.If the equivalent circuitcompiles properly, theModel Editor windowappears:5. Click the OK button tocontinue.6. You may save the equivalent circuit with a *.mdlextension by clicking File in the toolbar, andchoosing Save or Save As.

7. The File Save As windowappears.The default folder for savingmodel equivalent circuits isthe Models folder.8. Name and save the file here,or choose a different folder.The model shown abovewas saved as trialmodel.mdl.The File Save As windowcloses.

32

Fitting the Data to the Equivalent-Circuit Model1. With the data openand plotted, clickImpedance, and chooseFit A Model (SimplexMethod).The Select Model Filewindow appears.2. Choose the desiredmodel.The default folder for models is the Models folder. This Models folder is in theC:\Documents andSettings\AllUsers\ApplicationData\GamryInstruments\EchemAnalyst\Modelsby default. As ourexample, we choosethe model trialmodel.mdl createdpreviously.

3. Click the Openbutton.The Select Model File window closes, and the Impedance Fit by the SimplexMethod window appears.4. Set parameters.Choose the maximumnumber of Iterations to loopbefore stopping the fit. Enterestimates for all the circuitelements in the ModelParameters area. Fixparticular elements byenabling their Lockcheckboxes.In our example, we try 100for Ru, 2500 for Rp,and 100 nF for Cf and leaveall of them free (unlocked).5. Click the Calculate button to start the fit.The software attempts to fit the model to the data. When finished, the fittedparameters appear next to each circuit element.

33

Our model results giveRp = 3 kRsolution = 199.7Cf = 980 nF

Like other Echem Analyst fits, the fit also appears superimposed upon the dataand a new tab is created that contains those results.

If you try another fit using the same model, this fit will be overwritten. If you fit toanother model, the fit results of both models will be displayed.

34

This new tab shows the residual errors and goodness of fit, along with the variousplotting tools. Residuals are a point-by-point Goodness of Fit, which quantifieshow closely the data match the fit. A smaller number indicates a better fit.

The blue data (Zreal) correspond to the y1-axis (on the left); the green data(Zimag) correspond to the y2-axis (on the right).

35

Appendix

Headings in Data-File ColumnsDC Data Files

AbbreviationPtTVm, VfImVuSigAchIE Range

Over0

EIS Data Files

MeaningPoint numberTimeMeasured voltageMeasured currentUncompensated voltageSignal from the signal generatorAuxiliary channelI/E (Current Measurement) range on which measurement wasmadeAny overloads. Numeric record of different overload typesNo overloads

36

AbbreviationFreqZreal, Zimag, Zmod, ZphzIdc, VdcYreal, Yimag

MeaningFrequencyCalculated values of impedanceDC component of current and voltage,Admittance (calculated from Z)

Current Conventions According to Framework andEchem AnalystThe current convention in the Framework for all experimental packages is that ananodic/oxidation current is positive.

To change the current convention (whether anodic/oxidation currents orcathodic/reduction currents are positive), in the menu Tools\Options\Units tab,specify the current you want represented as positive. The current convention canbe changed by editing the experimental script (contact Gamry or your Gamryrepresentative if you need to do this). Regardless of the current convention usedin the Framework, it can be changed in the Echem Analyst to the one you desireby the user (see below for exceptions).

The current convention affects all experiments run under thePHE200 Physical Electrochemistry and PV220 Pulse Voltammetryheading. No other data files are affected.

To change the current convention in the Echem Analyst, in the menuTools/Options/Units tab specify the current you want represented as positive.

To change the current convention in other experimental packages (DC105,EIS300 etc) please contact Gamry or your Gamry representative.

To Edit Visual Basic Scripts:1. In the toolbar, choose Tools.A dropdown menu appears.

Echem Analyst runs on Open Sourcescripts written in VBA. Most customizedanalysis routines are done by Gamry in thefactory for you, the user, and that makesEchem Analyst extremely flexible. The typicaluser will never need to edit the scripts forelectrochemical analysis.

37

Simulating an EIS CurveIt is often useful to simulate the response of an equivalent circuit.1. Launch the Echem Analyst.2. Select Tools/Run Named Script/select EIS Model Simulation Script.Gscript.This opens a blank chart.

3. Select EIS Simulation/Simulate (use the Model Editor to build or edit the model).The EIS Model Simulation window appears.

4. Select the saved model, and input parameters for the experiment (frequenciesand data-point density) and values of all circuit elements.5. Click the Simulate button.The simulation appears under new tabs.

38

This is a simulated Bode plot.

This is a simulated Nyquist plot.

39

Index

Corrosion Rate

24

*

Current ConventionCurrent conventions

1837

*.DTA*.GData*.mdl

3D/2D

3

A

3332

6

Curve SelectorCurve Selector areaCurve Selector buttonCurve Selector buttonCutting and pastingCyclesCyclic Voltammetry

D

87, 888101520, 23

AC Calibration Date 18

Data Viewer

6

AcceptAchAch RangeAch select

22361817

DC Calibration DateDeleteDelta EpDigiSim

1822, 312121

Active Trace area 8Add E Constant 13Add I Constant13Analysis menu 3Apply Template 7Apply User-Defined Chart Template window 7

Draw a Freehand Line buttonDraw Freehand Line

EE Log I Fit window

227

27

As a BitmapAs TextASCII

10103, 10

E Log I tabEcorrEIS Model Simulation window

272738

Automatic Baseline 21, 22Automatic radio button 25

B

Electrode AreaelementElementEnable checkboxEquil. Time

1531293115

Beta ABeta Cbitmap imageBode tabBounded Warburg

C

2424102830

equivalent circuitExcelExperimental Notes tabExperimental Setup tabExport to DigiSim

F

29, 30, 31, 32, 383, 104, 164, 1521

C from CPE, omega(max)C from CPE, R(parallel)Cable IDCalculate buttonCapacitorCD-ROMChanging the axesClear All FitsClear LinesClear PeaksClear RegionsColorCommon ToolsCommon Tools menu

13141824, 26, 27, 33303829212121611, 1311

FileFile Save As windowFinal EFirmware VersionFit A Model (Levenberg-Marquardt Method)Fit A Model (Simplex Method)FrameworkFramework VersionFrameworkFreq

GGallery

323215182929, 3320182, 3736

6

CompileConditioning

3215

Gamry Analysis Framework Options window 4Gamry Echem Analyst Help window 11

Constant Phase Element

30

Gamry Help

11

Control Amp Speed

17

GamryChart Properties window 6

Control ModeCopy to clipboard

176

General tabGeneral Toolbar

45, 6, 10

Copy to Clipboard button40

10

Gerischer element 30

Goodness of Fit

Hardware Settings tabhelpHelpHorizontal Grid

H

35

4, 17, 2711116

Model Editor windowModel Parameters areaModels folderMouse buttonMy Gamry Data folder

Normalize by Scan Rate

N

323332, 3393, 4

21

II/E AutoRange 17I/E Range18I/E Range Lower Limit 17I/E Range Mode 15

Normalize by Square Root of the Scan RateNotes fieldNyquist tab

O

211628

I/E Stability

18

OK button

29, 31, 32

Ich AutoRange 17

open

3

Ich FilterIch Offset

1717

Open buttonOpen Circuit

3315

Ich Offset Enable 17

Open Circuit Voltage tab

4, 19

Ich RangeIdc36IE RangeIm 36Impedance

17

36

29

Open functionOpen WithOptionsOriginOver

3104, 21, 24, 25, 293, 1036

Impedance Fit by the Simplex Method window 33

Impedance Model Editor 29, 30, 31Impedance Model Editor window 29

P

Impedance Subtraction window 29

Page setup window

6

Inductor

30

Palette button

6

Infinite Warburg 30

PaletteBar

6

Init. Delay

15

Parameter Name

31

Initial Delay 4, 15

Parameter window

31

Initial EInitial ValueInstallation

15313

PathPeak BaselinesPeak Find

42121

Instrument Version 18Integrate 21, 22, 23Integrating the voltammogram 22

Peak Find functionplotsPolarization Resistance

9513, 14, 24, 25, 27

IR CompIterations

Kramers-Kronig methodKramers-Kronig transformsKramers-Kronig window

Legend Bar

K

L

1533

292929

6

Polarization Resistance windowPorous Bounded WarburgPositive Feedback IR CompPositive Feedback ResistancePost-Run iR CorrectionPotentiodyanmicPotentiostatPowerpointPrintPrint previewPropertiesPstat Model

243017181426171066618

Levenberg-Marquardt methodLinear FitLock checkboxLower Limit Test

2913, 143331

Pt 36

Quick Integrate

Q

21, 22, 24

Mark Found PeaksMax Current

M

715

Quick-Integrate

R

7

Min/MaxModelModel Editor

21, 242929, 30, 38

Randles modelRegion BaselineRegion Baseline Settings window

312323

41

Region BaselinesResistor

21, 2330

Transform Axes selection

11

Rotate

S

6

Units tabUpper Limit Test

U

3731

Sampling ModeSaveSave AsSave as DefaultsSave TemplateSave User-Defined Chart Template windowScan RateSeed Values areaSelect Model File windowSelect Portion of Curve using the KeyboardSelect Portion of Curve using the MouseSelect x regionSelect y regionSelecting portions of a curveSelection toolbarSelection ToolbarShow curve selector

15323225771524, 2629, 337777995, 77

Use Seed Values checkbox

Vch AutoRangeVch FilterVch OffsetVch Offset EnableVch RangeVdcVertical GridVf 36Visible Traces areaVisual BasicVmVu 36

V

26

1818181818366

83736

Show Disabled PointsSig 36

7

W

Simplex methodSimulate buttonSimulating an EIS curveSmooth DataSpectrumStep SizeSubtract Background from FileSubtract Impedance

29383813, 1429152129

websiteWireWord

X-Axis column

X

330, 3110

8

Subtract Impedance

T 36

T

29

Y2-Axis columnY-Axis columnYimag

Y

8836

Tafel constantsTafel FitTafel Fit functionTafel Fit windowTafel tabTest Compile buttonTest IdentifierTimetoolbarsToolsTools.Transform Axes

24, 259, 269262732151556, 323714

Yreal

Z-clusteredZimagZmodZoomZphzZreal

Z

36

635, 363663635, 36

42