Gamry Resonator Overview

Gamry Resonator Overview

The Resonator software is designed to acquire data from both an eQCM 10M and a Gamry Potentiostat. It is not necessary to have a Gamry Potentiostat to use the eQCM 10M. The acronym QCM is used to specify anything dealing with the quartz crystal microbalance. The acronym EQCM is used to specify electrochemical quartz crystal microbalance any time a potentiostat is interfaced to a QCM and data are acquired simultaneously. This Help file is divided into two parts. The first part relates to setting up the QCM. The second part relates to setting up a Gamry Potentiostat.

Potentiostat data will nearly always be acquired at a faster rate than QCM data. Echem Analyst combines the two sets of data into a single table for plotting purposes. It is best to set the experiment up so that the differences in acquisition rates is less than 10. For example, if the QCM is set up at a resolution and frequency window (both parameters are explained below) such that the rate of acquisition is 2 spectra per second, it is best to not take potentiostat data any faster than 20 points per second. In cyclic voltammetry at a scan rate of 100 mV/s, this is a 5 mV step. In chronoamperometry, chronopotentiometry or chronocoulometry, this is a sample period of 50 ms.

The practical limit for cyclic voltammetry when studying films on a quartz crystal is several hundred millivolts per second. The film must have adequate time to respond to the perturbation caused by the potentiostat. Please contact us should you have any questions regarding setting up your experiments.

Setting up the eQCM 10M

Setting up the QCM is achieved through the QCM Panel in Resonator. The QCM should be set up and data acquisition should start prior to starting the potentiostat, if a potentiostat is being used.

Charts

Figure 1. QCM Panel of Resonator

This is the last acquired relative impedance spectrum of the quartz crystal. The typical response is an S-shaped curve with a minimum at fs and a maximum at fp.

fs (red) and fp (blue) are plotted versus time in the bottom chart. The red curve is fs and the blue curve is fp.

Parameters Description This box allows you to provide a brief description of your experiment. This is different than the Notes section in the potentiostat section. If you are operating in stand-alone mode, then enter a description here, otherwise, enter a description in the Notes section on the potentiostat setup screens.

Center Freq. (Hz) Enter the nominal frequency of your crystal in here.

Freq. Width (Hz) Enter a starting frequency window to scan. Resonator automatically optimizes this window once continuous acquisition has started. Typical starting values are between 15 kHz and 50 kHz. This width can then be adjusted using the cursors that appear in the spectrum plot after pressing single scan.

Drag these two cursors in order to optimize the window prior to starting a continuous scan.

Figure 2. QCM Panel of Resonator after Single Scan was pressed.

Freq. Step (Hz) Enter the desired frequency resolution here. A lower resolution results in faster acquisition. There is a practical maximum which limits acquisition. When the step is too large spectra are acquired too quickly to obtain a good fit. An example of a large step (2 Hz) limiting the ability of the software to get a good fit is shown below.

The software cannot obtain a good fit (blue curve) of the spectrum (red curve) because the step size is too large.

Figure 3. QCM Panel of Resonator when Step Size is too large.

Amplitude (%) This is essentially the driving force used to make the crystal oscillate. Start at smaller amplitudes until the desired S-shaped spectrum is achieved as shown in Figure 1. Moving this slider will trigger the acquisition of another relative impedance spectrum. Increasing the amplitude further will drive the crystal harder. Eventually, the amplitude will be too large resulting in loss of signal. These two situations are shown below.

Figure 4. QCM Panel of Resonator showing response when magnitude is too large.

Figure 5. QCM Panel of Resonator showing response when magnitude is too large.

The amplitude is too large in Figure 4 showing a flat line around a magnitude of 4.9.

Increasing the magnitude further will result in all loss of signal as shown in the Figure 5.

Manual Damping Clicking on the Manual Damping will reveal a slider bar that controls the input voltage into the Analog-to-Digital converter (ADC). It is only necessary to change this when you have a very heavy sample and need a very large amplitude in order to maintain oscillation. Increasing the Manual Damping essentially divides the voltage entering the ADC.

Figure 6. QCM Panel of Resonator with increased Manual Damping.

The amplitude has not changed from Figure 5 yet the increased damping has brought the magnitude back down below 4.9 allowing a full spectrum to be shown.

Calibration Factor (Hz cm2 / ug) This is the factor that will be used to convert frequency changes to mass changes in Echem Analyst. Theoretical values for a 5 MHz crystal and a 10 MHz crystals are 56.6 and 226, respectively. The actual calibration factor might be slightly different once the crystal is immersed in solution.

Splines Quality Adjustment of this parameter is only necessary when fitting the relative impedance spectrum using Multidimensional Splines (see Advanced QCM Options).

fs [MHz]

This is the series resonant frequency for the last reported data point.

fp [MHz]

This is the parallel resonant frequency for the last reported data point.

Acq Time (s)

This is the total time needed to acquire the last relative impedance spectrum with the Freq. Width centered around the Center Freq.

Fit Time (s)

This is the time required for Resonator to fit the last acquired relative impedance spectrum using the linearized Pad approximant.

Fit Chi2

This is a parameter that reports how well Resonator fit the last acquired spectrum. Green represents a good fit, red represents a bad fit.

Rate (1/s)

This is the rate at which spectra are being acquired. It will depend upon the Freq. Step and the Freq. Width.

Single Scan

This button takes a single scan around the Center Freq with a window of Freq. Width. It is useful to use Single Scan to locate the resonant frequency prior to starting continuous acquisition.

Start

This button begins continuous QCM acquisition.

Stop

This button stops continuous QCM acquisition.

Save Data

This button saves the QCM data only. A dialog box will appear asking you for a file name and location. Data acquired during EQCM studies are saved automatically in the file name specified during potentiostat set up. Only the QCM points acquired during an electrochemical experiment are saved automatically. If you wish to save all of the QCM data, before, during and after an electrochemical experiment, please click the Save Data button.

QCM Options Fit Method

This is the method used to model the relative impedance spectrum in order to obtain fs and fp. Default is broken rational.

Database Options (PostgreSQL)

This section is for advanced use only and is only experimentally implemented at this time. The user must have installed PostgreSQL and the necessary ODBC drivers.

A DWORD registry key must be added to HKLM as shown below:

HKEY_LOCAL_MACHINE\SOFTWARE\Gamry Instruments\Resonator\DatabaseEnable

Any non-zero value will make the options visible.

Three tables must be set up in a public schema. How you create the tables is up to you but each table has specific requirements and constraints. Here is the text used to create each table.

-- Table: qcm_meas

-- DROP TABLE qcm_meas;

CREATE TABLE qcm_meas ( id serial NOT NULL, starttime double precision, description text, CONSTRAINT qcm_meas_pkey PRIMARY KEY (id) ) WITH ( OIDS=FALSE ); ALTER TABLE qcm_meas OWNER TO postgres;

-- Table: qcm_data

-- DROP TABLE qcm_data;

CREATE TABLE qcm_data ( id serial NOT NULL, idf integer, qcmpt bigint, reltime double precision, fs double precision, fp double precision, chiquad real, ms double precision, mp double precision, CONSTRAINT qcm_data_pkey PRIMARY KEY (id), CONSTRAINT qcm_data_idf_fkey FOREIGN KEY (idf) REFERENCES qcm_meas (id) MATCH SIMPLE ON UPDATE NO ACTION ON DELETE CASCADE

) WITH ( OIDS=FALSE ); ALTER TABLE qcm_data OWNER TO postgres;

-- Table: qcm_spectrum

-- DROP TABLE qcm_spectrum;

CREATE TABLE qcm_spectrum ( id bigserial NOT NULL, idf integer, freq double precision, ampl double precision, CONSTRAINT qcm_spectrum_pkey PRIMARY KEY (id), CONSTRAINT qcm_spectrum_idf_fkey FOREIGN KEY (idf) REFERENCES qcm_data (id) MATCH SIMPLE ON UPDATE NO ACTION ON DELETE CASCADE ) WITH ( OIDS=FALSE ); ALTER TABLE qcm_spectrum OWNER TO postgres;

-- Index: fki_

-- DROP INDEX fki_;

CREATE INDEX fki_ ON qcm_spectrum USING btree (idf);

The data analysis script in Echem Analyst can retrieve spectra collected during acquisition. This may be useful for long term studies. If for instance, an air bubble formed on the crystal face, the relative impedance spectrum would show a spike.

Active

Select Yes to turn save QCM data to the postgres database.

Server

This is address of the server running the postgres database. Typically this will be 127.0.0.1 which is the computer you are using.

Database

This is the name of the database where you are writing data. The database needs to have three preconfigured tables in order to accept the data from Resonator.

Username

Enter your user name for interfacing with the postgres server.

Password

Enter the password necessary for interfacing to the postgres server.

Spectra

This parameter determines how often spectra will be written to the database. A value of 0 means that no spectra will be written. fs and fp, along with their amplitudes at each point will still be written though. When you wish to write spectra to the database, the minimum value is 15, meaning every 15th spectrum will be written to the database. Due to the multithreaded nature of Reasonator, the actual value may vary slightly during acquisition. Echem Analyst will list the available spectra for a given run.

Test Database

Use this button to test interaction with the database. After pressing the button a message appears stating, starting with 15 s conn. timeout If the tables have been set up correctly and the correct ODBC drivers have been installed a second message appears stating Success: Database Ready. If the database has not been set up correctly an error message appears stating Error: Connection could not be established: followed by another error message establishing why.

Fit Options

Only advanced users should consider modifying these values. These options relate to how Resonator fits the relative impedance spectrum see image at left. Double-click on the value you wish to change. An image is shown in order to help you understand each parameter. Extremely heavy samples that significantly flatten the relative impedance spectrum may require modification of these parameters.

Setting up a Gamry Potentiostat This section describes setting up the physical electrochemistry techniques included in Resonator. These techniques are nearly identical to those found in PHE200 Physical Electrochemistry Package that runs in Framework. Included are techniques for performing linear sweep and cyclic voltammetry experiments, as well as chronopotentiometry, chronoamperometry, chronocoulometry, controlled potential coulometry, repeating chronoamperometry, and repeating chronopotentiometry techniques. This section will only consider discussions relating to processes involving films adsorption, desorption, or transport. A more detailed discussion can be found in Framework.

Current and Voltage Definitions

In the techniques for Resonator we follow the analytical convention for current. Positive currents are anodic, arising from an oxidation at the electrode under test. This is the convention used in other Gamry application software packages such as the DC105, and EIS300.

Potentials can also be a source of confusion. In Resonator, all potentials are specified or reported as the potential of the working electrode with respect to the reference electrode vs Eref with positive potentials plotted to the right.

Chronoamperometry

Chronoamperometry is used to study the kinetics of chemical reactions, diffusion processes (solution or films), and adsorption processes. In this technique, a potential step is applied to the electrode and the resulting current vs. time is observed. The Chronoamperometry experiment supports both single and double potential step experiments.

In general, before beginning the experiment the electrode is held at a potential at which no faradaic process occurs, then the potential is stepped to a value at which a redox reaction occurs to induce adsorption, desorption or changes in a film. Zero time is defined as the time at which the potential step is initiated. For reactions that are under diffusion control, the current will decay with a t1/2 decay obeying the Cottrell equation:

where n is the number of electrons in the redox process, F is the Faraday constant, A is electrode area, Do is the diffusion coefficient of the redox species, Co is the bulk concentration of the redox species, and t is time.

In some cases double potential step chronoamperometry experiments are used to determine the reversibility of a reaction by comparing the results from the two potential steps.

Chronoamperometry Setup Parameters

See below for a description of each of the setup parameters.

Test Identifier

See Test Identifier in the Common Potentiostat Setup Parameters section.

Output File

See Output File in the Common Potentiostat Setup Parameters section.

Electroactive Area

See Electroactive Area in the Common Potentiostat Setup Parameters section.

Area of Overlap

See Area of Overlap in the Common Potentiostat Setup Parameters section.

Notes

See Notes in the Common Potentiostat Setup Parameters section.

Pre-step Delay Time (s) The Pre-step Delay time is the time for which a Pre-step Voltage is applied. It is shown as negative time on the real time display.

Pre-step Voltage (V)

The voltage is typically 0 and the time is usually quite short.

Step 1 Time (s)

The Step 1 Time is the time for which the Step 1 Voltage is applied to the cell. This time is entered in seconds and should be greater than zero. The maximum time is based on the Sample Period setting, as the total number of points should not exceed 32000.

Step 1 Voltage (V)

The Step 1 Voltage is the first voltage to be applied to the cell. This voltage is entered in Volts and can be versus Reference or versus open circuit potential. The Step 1 Voltage is applied for the Step 1 Time.

Step 2 Time (s)


Step 2 Voltage (V)

The Step 2 Voltage is the second voltage to be applied to the cell. This voltage is entered in Volts and can be versus Reference or versus open circuit potential. The Step 2 Voltage is applied for the Step 2 Time.

Sample Period (s) The Sample Period parameter determines the spacing between data points. The units used for the Sample Period are seconds. The shortest Sample Period we recommend is

1.0 ms. The longest Sample Period allowed is 600 seconds. For speeds faster than 1.0 ms, the display of the real time data will be delayed. This will help insure that your system is able to keep up with the fast data acquisition rate.

I/E Range Mode

See I/E Range Mode in the Common Potentiostat Setup Parameters section.

Max Current (mA) See Max Current in the Common Potentiostat Setup Parameters section.

Limit I (mA/cm2) The Limit I parameter is used to prevent excessive cell current. If the absolute value of the current should exceed the Limit I, the data acquisition in the current step will be ended prematurely.

Exceeding the Limit I during the first step causes the experiment to skip to the second step. Exceeding the limit during the second step causes the experiment to terminate.

Sampling Mode defines whether or not the potentiostat will oversample and average during acquisition. These options are only relevant on the Reference family instruments. Selecting Surface will result in oversampling followed by averaging according to the Sample Period defined above. Selecting Noise Reject will result in oversampling and averaging during the remaining 20% of a Sample period. Selecting Fast will result in sampling according to the Sample Period.

Repeating Chronoamperometry

Setup for Repeating Chronoamperometry is nearly identical to Chronoamperometry. The difference is the addition of the Cycles Parameter. Enter the number of times that you wish to perform both potential steps.

Chronocoulometry

Chronocoulometry is used to study the kinetics of chemical reactions, diffusion processes, and adsorptions. In this technique, a potential step is applied to the electrode and the resulting cumulative charge vs. time is observed. This technique is very similar to Chronoamperometry, except that the integrated charge is recorded in Chronocoulometry instead of raw current. This integration is performed digitally, allowing the user to control the time per integration by changing the point timing. Chronocoulometry offers the following advantages over Chronoamperometry:

1. The signal increases over time instead of decreasing.

2. The act of integration minimizes noise, resulting in a smooth response curve.

3. Contributions from double layer charging and absorbed species are easily observed.

In the Resonator software, a double potential step Chronocoulometry experiment is supported.

Test Identifier


Output File


Electroactive Area


Area of Overlap


Notes





Step 1 Time (s)


Step 1 Voltage (V)


Step 2 Time (s)


Step 2 Voltage (V)


Charge Limit (C) The Charge Limit parameter is used to stop an experiment based on cumulative charge. If the absolute value of the charge should exceed the Charge Limit, the data acquisition in the current step will be ended prematurely.

Exceeding the Charge Limit during the first step causes the experiment to skip to the second step. Exceeding the limit during the second step causes the experiment to terminate.

Sample Period (s) The Sample Period parameter determines the spacing between data points. The units used for the Sample Period are seconds. The shortest Sample Period we recommend is 1.0 ms. The longest Sample Period allowed is 600 seconds. For speeds faster than 1.0 ms, the display of the real time data will be delayed. This will help insure that your system is able to keep up with the fast data acquisition rate.

I/E Range Mode



Chronopotentiometry

Chronopotentiometry is used to study mechanism and kinetics of chemical reactions. In this technique, the instrument operates in galvanostatic mode to control current and measure voltage. The applied current can consist of either a single or double step.

This technique can be used to investigate the mechanism of a redox process. For systems where only one redox species is present an S-shape response is expected. The potential of the electrode will change from open circuit potential to an approximately constant value until the concentration of the redox species at the electrode is depleted. Once this species is depleted at the electrode surface the potential will rapidly shift to a potential capable of sustaining the applied current. This sudden shift is called the "transition time" (tau in the equations, below). If only one redox species is present, the potential will shift

to a value that will cause either the supporting electrolyte or solvent to be reduced/oxidized.

The chronopotentiometry technique can also be used as a general purpose galvanostatic technique for applications such as plating, or measuring battery charge/discharge curves.

Test Identifier


Output File


Electroactive Area


Notes


Area of Overlap


Pre-step Delay Time (s) The Pre-step Delay time is the time for which a Pre-step Current is applied. It is shown as negative time on the real time display.

Pre-step Current (A)

The current is typically 0 and the time is usually quite short.

Step 1 Time (s)

The Step 1 Time is the time for which the Step 1 Current is applied to the cell. This time is entered in seconds and should be greater than zero. The maximum time is based on the Sample Period setting, as the total number of points should not exceed 32000.

Step 1 Current (A)

The Step 1 Current is the first current to be applied to the cell. This current is entered in Amperes. The Step 1 Current is applied for the Step 1 Time.

Step 2 Time (s)

The Step 2 Time is the time for which the Step 2 Current is applied to the cell. This time is entered in seconds and should be greater than zero. The maximum time is based on the Sample Period setting, as the total number of points should not exceed 32000.

Step 2 Current (A)

The Step 2 Current is the second current to be applied to the cell. This current is entered in Amperes. The Step 2 Current is applied for the Step 2 Time.

Sample Period (s)

The Sample Period parameter determines the spacing between data points. The units used for the Sample Period are seconds. The shortest Sample Period we recommend is 1.0 ms. The longest Sample Period allowed is 600 seconds. For speeds faster than 1.0 ms, the display of the real time data will be delayed. This will help insure that your system is able to keep up with the fast data acquisition rate.

Lower Limit V (V) The Lower Limit V parameter is used to prevent excessive cell voltage. If the value of the voltage should exceed the Lower Limit V, the data acquisition in the current step will be ended prematurely.

Exceeding the Lower Limit V during the first step causes the experiment to skip to the second step. Exceeding the limit during the second step causes the experiment to terminate.

Upper Limit V (V) The Upper Limit V parameter is used to prevent excessive cell voltage. If the absolute value of the voltage should exceed the Upper Limit V, the data acquisition in the current step will be ended prematurely.

Exceeding the Upper Limit V during the first step causes the experiment to skip to the second step. Exceeding the limit during the second step causes the experiment to terminate.


Repeating Chronopotentiometry Setup Parameters

Setup for Repeating Chronopotentiometry is nearly identical to Chronopotentiometry. The difference is the addition of the Cycles Parameter. Enter the number of times that you wish to perform both current steps.

Controlled Potential Coulometry Setup Parameters

Controlled Potential Coulometry (Bulk Electrolysis) can be used as an absolute (standards-less) analytical technique to determine many metals or compounds. By

completely electrolyzing the analyte of interest and noting the total charge consumed, the quantity of the analyte is easily determined.

Controlled Potential Coulometry can also be used to determine the overall number of electrons in a faradaic reaction. Unlike voltammetric techniques where the electrode area and diffusion coefficient of the redox species must be known, Controlled Potential Coulometry can determine the overall number of electrons in the redox process without prior knowledge of the electrode area or diffusion coefficient.

In this technique the potential of the electrode is held constant for a long time, minutes to hours, and the resulting integrated charge is recorded. All of the electrochemically active species which is being electrolyzed will react, resulting in a 100% efficiency. The total charge passed in this technique will obey Faraday's law, Q= nFNo, where Q is the total charge passed, n is the overall number of electrons consumed in the experiment, F is Faraday's constant (9.64853x104 C/equiv), and No is the total moles of redox species present.

Test Identifier


Output File


Electroactive Area


Area of Overlap


Notes





Step 1 Time (s)


Step 1 Voltage (V)


Step 2 Time (s)


Step 2 Voltage (V)


Sample Period (s) The Sample Period parameter determines the spacing between data points. The units used for the Sample Period are seconds. The shortest Sample Period we recommend is 1.0 ms. The longest Sample Period allowed is 600 seconds. For speeds faster than 1.0 ms, the display of the real time data will be delayed. This will help insure that your system is able to keep up with the fast data acquisition rate.

I/E Range Mode



Cyclic Voltammetry

Cyclic Voltammetry is used to study the mechanism, kinetics, and thermodynamics of chemical reactions. Both heterogeneous reactions occurring at the electrode surface, and homogeneous reactions in solution can be studied.

In the classical Cyclic Voltammetry triangle waveform, the potential is swept from an Initial E, to vertex E, and back to Final E, where Final E equals Initial E. An example of this applied waveform is shown below. Repeating this waveform for N times will perform N cycles of Cyclic Voltammetry.

In the PHE200 we use the more generic double vertex triangular waveform shown below. This applied waveform allows the user to set a second vertex potential (Scan Limit 2 in the software) which could be more positive than the initial potential. Setting Scan Limit2 and Final E to equal the Initial E can perform the classically defined triangle waveform for cyclic voltammetry.

Electron transfer kinetics can also be studied by varying the scan rate of the applied potential and observing the increase in Ep (Nicholson). An overall review of potential sweep voltammetry methods is covered in Chapter 6 Bard and Faulkner.

In cases where the chemistry of the system is more complicated, cyclic voltammetry can be used to determine the mechanisms and kinetics involved. In their work in the 1960's, Nicholson and Shain published a series of articles that discussed the use of cyclic voltammetry to study chemical systems which included chemical reactions either proceeding or following the electron transfer seen in the cyclic voltammogram (Nicholson and Shain). The user is encouraged to review these works for a better understanding of the versatility of the cyclic voltammetry experiment.

i

Test Identifier


Output File


Electroactive Area


Area of Overlap


Notes


Initial E (V) The Initial E parameter is the starting potential of the scan segment. This potential can be selected in a versus Eoc or versus Eref. This potential is entered in Volts.

Scan Limit 1 (V) The Scan Limit 1 parameter is the first apex potential in a Cyclic voltammetry scan. This potential can be selected in a versus Eoc or versus Eref. This potential is entered in Volts.

Scan Limit 2 (V) The Scan Limit 2 parameter is the second apex potential in a Cyclic voltammetry scan. This potential can be selected in a versus Eoc or versus Eref. This potential is entered in Volts.

Final E (V) The Final E parameter is the ending potential of the scan segment. This potential can be selected in a versus Eoc or versus Eref. This potential is entered in Volts.

Scan Rate (mV/s) The Scan Rate parameter defines the speed of the potential sweep during data acquisition.

The Scan Rate is entered in units of mV/sec. A practical bound on the Scan Rate is 1000 mV/sec. Higher Scan Rates may run, but can yield inaccurate data due to the inability of the software to acquire data points fast enough.

The Scan Rate parameter when combined with the Step Size parameter determines time between data points and thus the data acquisition rate used in the experiment.

Time (seconds/point) = [ Step Size (mV/point) ] / [ Scan Rate (mV/second) ]

The maximum data acquisition rate is dependent on the speed of the computer, the configuration of Windows and the other software currently executing. As a guideline, you should avoid sample times below 100 s. Note that for scans faster than 1 ms that the acquired data will only be displayed once the experiment has completed. This reduces the chance that the computer will limit the acquisition speed.

Step Size

The Step Size parameter determines the spacing between the data points in mV. A typical Step Size setting is between 1 and 5 mV.

The Step Size parameter combines with the scan range on any given cycle to determine the number of data points.

# Points = [ Scan Range (mV) ] / [ Step Size (mV) ]

The total number of data points must be less than 64000 for all cycles.

The Step Size parameter also combines with the Scan Rate parameter to determine the time interval between the data points.

Cycles

The Cycles parameter controls the number of times the potential scan will be repeated during the experiment. Conceptually it is the number of times the potential will cycle from the Initial E setting to Scan Limit 1 to Scan Limit 2 to the Final E setting.

I/E Range Mode



Sampling Mode


Linear Sweep Voltammetry

Linear Sweep Voltammetry is a simpler subset of Cyclic Voltammetry, consisting of a single unidirectional voltage sweep. In general, researchers will use Linear Sweep Voltammetry instead of Cyclic Voltammetry when there is no useful information on the return scan of the Cyclic Voltammogram, such as in the case where the electron transfer is followed by a very fast irreversible reaction.

Test Identifier


Output File


Electroactive Area


Area of Overlap


Notes


Initial E (V) The Initial E parameter is the starting potential of the scan segment. This potential can be selected in a versus Eoc or versus Eref. This potential is entered in Volts.

Final E (V) The Final E parameter is the ending potential of the scan segment. This potential can be selected in a versus Eoc or versus Eref. This potential is entered in Volts.

Scan Rate (mV/s) The Scan Rate parameter defines the speed of the potential sweep during data acquisition.

The Scan Rate is entered in units of mV/sec. A practical bound on the Scan Rate is 1000 mV/sec. Higher Scan Rates may run, but can yield inaccurate data due to the inability of the software to acquire data points fast enough.

The Scan Rate parameter when combined with the Step Size parameter determines time between data points and thus the data acquisition rate used in the experiment.

Time (seconds/point) = [ Step Size (mV/point) ] / [ Scan Rate (mV/second) ]

The maximum data acquisition rate is dependent on the speed of the computer, the configuration of Windows and the other software currently executing. As a guideline, you should avoid sample times below 100 s. Note that for scans faster than 1 ms that the acquired data will only be displayed once the experiment has completed. This reduces the chance that the computer will limit the acquisition speed.

Step Size

The Step Size parameter determines the spacing between the data points in mV. A typical Step Size setting is between 1 and 5 mV.

The Step Size parameter combines with the scan range on any given cycle to determine the number of data points.

# Points = [ Scan Range (mV) ] / [ Step Size (mV) ]

The total number of data points must be less than 64000 for all cycles.

The Step Size parameter also combines with the Scan Rate parameter to determine the time interval between the data points.

I/E Range Mode




Common Potentiostat Setup Parameters Test Identifier

The Identifier parameter is a string that is used as a name. It is written to the data file, so it can be used to identify the data in database or data manipulation programs.

The Identifier string defaults a name derived from the technique's name. While this makes an acceptable curve label, it does not generate a unique descriptive label for a data set.

The Identifier string is limited to 80 characters. It can include almost any normally printable character. Numbers, upper and lower case letters, and most normal punctuation characters including spaces are valid.

Output File

The Output File parameter is the pathname of the file in which the output data will be written. It can be a simple filename with no path information. In this case the output file is located in the default data directory. The default data directory is specified in the

Gamry.INI file under the [Framework] section with a Key named DataDir. This default pathname can be changed using the Paths command under the Options Menu.

It can also include path information, such as "C:\DATA\YOURDATA.DTA." In this example, the data will be written to the "YOURDATA.DTA" file in the "DATA" directory on drive C.

The default value of the Output File parameter is an abbreviation of the technique name with a ".DTA" filename extension. We recommend that you use a ".DTA" filename extension for your data filenames. The data analysis package assumes that all data files have ".DTA" extensions.

NOTE: The software does not automatically append the ".DTA" filename extension. You must add it yourself.

If the script is unable to open the file, an error message box, "Unable to Open File," is generated. Common causes for this type of problem include:

An invalid filename.

The file is already open under a different Windows application.

The disk is full.

After you select OK in the error box, the script returns to the Setup box where a new filename can be entered.

Electroactive Area

The Electroactive Area parameter is the surface area of the electrode (in cm) exposed to the sample solution.

Area of Overlap

The Area of Overlap parameter is the area overlap between the electrodes on the crystal faces. The area of overlap is typically smaller than the electroactive area in order to remove edge effects and maintain high sensitivity.

Notes

The Notes field allows you to enter several lines of text that describe the experiment. A typical use of Notes is to record the experimental conditions for a data set.

Notes defaults to an empty string.

The Notes string is limited to 400 characters. It can include all printable characters including numbers, upper and lower case letters, and the most normal punctuation including spaces. TAB characters are not allowed in the Notes string.

You can divide your Notes into lines using ENTER.

I/E Range Mode

The I/E Range Mode parameter controls the autorange state of the I/E converter. If Auto is selected, the I/E Range will be able to freely adjust based on measured currents. If Fixed is selected, the I/E Range will be fixed on a range which is able to measure the current entered in the Max Current parameter.

For fast experiments, it is recommended that Fixed be used for the I/E Range Mode. This setting will prevent glitches in the current measurement as the I/E Range resistor is switched.

Max Current (mA) The Max Current parameter controls the current measurement range when the I/E Range Mode is Fixed. When the I/E Range Mode is Auto, the Max Current parameter specifies the maximum expected starting current.

You enter a Max Current value that is the largest current that you expect to see during the experiment. From this information the software sets the current range used in the experiment. In order to use the most sensitive range that will not overload, the software will chose the current range based on a value that is 89% of the full scale current range. For example, when using a PC4/750, if a Max Current of 66 mA is input, the current range will be 75 mA. On the other hand, if a Max Current of 67 mA is entered, the 750 mA current range will be selected.

NOTE: The Max Current parameter is a current not a current density. The electrode area is not used calculation of the current range to use.

If your current data look very choppy and steppy, the problem could be a poorly selected current range. If you enter a Max Current value of 10 mA and the maximum current in your sweeps is only 100 A, you are only using 1/100th of the potentiostat's A/D converter range. The result is significant quantization error. Rerun the test entering a smaller Max Current in Setup.

If your current data shows perfectly flat, horizontal regions, the current has most likely overloaded the potentiostat's current measurement circuits. Check that the value that you entered for the Max Current parameter is larger that the actual measured cell current. Try rerunning the test with a larger value for the Max Current.

References The following are references are useful for learning more about the techniques that are available in the Resonator.

Cyclic Voltammetry/Linear Sweep Voltammetry

Electrochemical Methods: Fundamental and Applications, Allen J. Bard and Larry R. Faulkner, John Wiley & Sons, New York (2000) pp. 226ff. ISBN 0-471-04372-9.

R. S. Nicholson and I Shain, Anal. Chem., 36, 706 (1964), and Anal. Chem., 37, 178 (1965).

R. S. Nicholson, Anal. Chem., 37, 1351 (1965).

Chronoamperometry


Chronocoulometry


Chronopotentiometry


Documents

Gamry Resonator Overview