Quick Start with EC-Lab CYCLIC VOLTAMMETRY - CePoL/MC ...

Quick Start
with
EC-Lab Ä
CYCLIC VOLTAMMETRY
EC-Lab Ä Version 9.9
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Starting a Cyclic Voltammetry with EC-Lab Ä
This short tutorial goes through the states
of selecting, setting up and running a typical Cyclic
voltammetry experiment. The setting file (.mps),
raw data file (.mpr) and processed file (.mpp)
corresponding to this experiment are in the data
directory.
Cyclic voltammetry (CV) is the most widely used
technique for acquiring qualitative information
about electrochemical reactions. CV provides
information on redox processes, heterogeneous
electron-transfer reactions and adsorption
processes. It offers a rapid location of redox
potential of the electroactive species. CV consists
of scanning linearly the potential of a stationary
working electrode using a triangular potential
waveform. During the potential sweep, the
potentiostat measures the current resulting from
electrochemical reactions (consecutive to the
applied potential).
The cyclic voltammogram is a current response as
a function of the applied potential.
The aim of this tutorial is to lead the user
for the first time in EC-Lab Ä
software. A Cyclic
voltammetry protocol will be built and run to
describe the instrument and the software. The
operating conditions will be described in the
experimental part (conditions just given as
example). These experiments should not be
considered as scientific results but just as example
to start EC-Lab Ä
software. This paper is not a
scientific article.
I- Starting a Cyclic voltammetry experiment
with EC-Lab Ä software
When starting with EC-Lab Ä for the first time, the
user has to report to the corresponding part in
EC-Lab Ä software Help Menu. The user has to set
his name and choose a channel on the global view
(double click on the channel). On the setting
window, click “Modify” and “New
experiment”. The technique selection window
appears.
Fig.1: EC-Lab Ä technique window with a description of the protocol.
1) In “Voltamperometric Techniques”, choose
“Cyclic voltammetry” and click on “Ok”.
One can see a picture and a description of this
protocol on the right window. This protocol
corresponds to one or several potential sweep
between two potential limits.
2) Then the setting window with Cyclic
voltammetry protocol appears. Three different
tabs are shown: “Advanced settings, Cell
characteristics and Parameter settings”. The
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default setting window is “Parameter settings”.
II- Cyclic voltammetry protocol description
Let's consider the Parameter settings window with
Cyclic voltammetry detailed flow diagram. It is
made with four different blocks (fig. 2). This
protocol begins with an open circuit period (block
1). No potential or current is applied to the
electrochemical cell. Then the potential where the
experiment will start (E i ) is defined (block 2) in
absolute or according to the previous open circuit
or measured or controlled potential. The sweep
potential is scanned with a scan rate dE/dt from Ei
to E 1 and E 2 (block 3). An average current is
measured and recorded. The cyclic voltammetry
experiment can be repeated n c times in order to
have more than one cycle. The final potential of
the experiment is defined (block 4).
Block 1
Block 2
Block 3
Block 4
Fig. 2: Cyclic Voltammetry detailed flow diagram.
II.1 Description of a CV experiment:
Block 1: Open circuit potential sequence.
Rest for t R = 1 s
This block becomes colored when it is taken into
account in the experiment. When its color was
grey, the block was ignored.
Note: This part of the experiment can be
considered as a preconditioning period.
If there are no parameters in the boxes of one
block, the block is grey.
Block 2: starting potential.
Set E we to E i = 0 vs. E oc
The experiment will begin at the open circuit
potential. It is possible to define the initial potential
as a function of the reference potential, the value
of previously controlled or measured potential.
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Block 3: Potential sweep.
Scan E we with dE/dt = 20 mV/s, (50 ÅV /
26 ms)
Notes:
1) Scan rate setting
If entering the potential scan rate in mV/s
the default choice of the system proposes a
scan rate, as close as possible to the
requested one and obtained with the
smallest possible step amplitude. To adjust
the potential control resolution report to the
technical note # 8.
2) The scan rate is defined by dE/dt in
absolute (it is not needed to set a negative
value for a scan through lower potential
values).
to vertex potential E 1 = 0.7 V vs. Ref
Definition of the potential limit of the reverse scan.
reverse scan to vertex E 2 = -0.3 V vs. Ref
windows are available in EC-Lab Ä
depending on the experiment.
software
A particular window has been designed for battery
electrode materials acting as intercalation
electrode. For cyclic voltammetry and all other
experiments the “Cell characteristics” window is
used to:
1) Describe the electrochemical cell (experimental
conditions).
2) Select the recording of the counter electrode
potential.
3) Select the recording of external signals ( pH, T,
P,...) using auxiliary inputs 1, 2 and 3.
4) Set the electrode surface area, characteristic
mass of the material and the reference
electrode used.
Note: It is very important to set comments in
maximum boxes in order to find the
experimental conditions easily.
Repeat n c = 2 times
Measure over the last 50 % of the step
duration
Note:
The user can select the part of the potential
step for the current average ()
calculation. It can be interesting to exclude
the first points where the current may be
perturbed by the step establishment.
Record averaged over N = 1 voltage
step(s)
Once selected, an estimation of the number of
points per cycle is displayed into the flow diagram.
with I range = 100 ÅA bandwidth = 5-
medium
Note: The experiment will be made with three
cycles (the first one is repeated two times).
Block 4: final potential.
End scan to Ef = 0 V vs. E oc
The user can find and load the setting file of the
experiment described on figure 2 in
C:\EC-Lab\data\samples\CV_Fe_basique_1.mps.
To do that click on “Load set” in the experiment
frame and choose the file in the correct directory.
II.3- Setting “Cell characteristics”
The second window called “Cell characteristics”
(fig. 3) is dedicated to the electrochemical cell
parameters. Two different “Cell characteristics”
Fig. 3: Cell characteristics window for the cyclic
voltammetry protocol.
III- Experimental part
The system used in the CV experiment
was a three electrodes system with an Au/Pd alloy
as working electrode, a platinum wire as counter
electrode and Saturated calomel electrode as
reference electrode. The electrochemical cell
contained a solution with NaCl (0.1 mol.L -1 ) as
electrolyte and K 3 Fe(CN) 6 /K 4 Fe(CN) 6 equimolar
(2.10 -3 mol.L -1 ). The pH of the solution was
adjusted to 10.5 with NaOH (5 mol.L -1 ).
The electrochemical conditions of the experiment
can be found in
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C:\EC-Lab\data\samples\CV_Fe_1.mps.
IV- Running a Cyclic voltammetry
experiment.
IV.1- Running the experiment on the
standard testing box
1) Click “Accept”. The following warning message
will be displayed:
“Warning: line 0 relaxation, there will be no
recorded point (dE R =dt R =o)! Continue”
This message says that no data point will be
recorded during the OCV period.
2) Click “Ok” and “Run” to start the experiment.
The “Save As” window appears. The user has
to define the file name and the directory to put
the raw data file before the beginning of the
experiment.
3) Click on “Ok” and the graphic window is
displayed. The data points are displayed
automatically.
4) On the graphic window one can see the
graphic of figure 4.
The operating conditions are described in the
figure 1. At the beginning of the experiment, the
cell was to the open circuit potential.
Fig. 4: Cyclic voltammetry on the linear system of
testing box 1 with the conditions defined before.
The results of this experiment can be used to
check that the instrument works fine and to be sure
that the experiment has been well performed by
the user. With the ohm law (U=R.I) it is very easy
to compare the resistance value on the test box 1
(5069 ohms) with the experimental value resulting
from potential and current measurement for a
given time (for example Ewe = -0.3 V and
I = -0.059 mA). The current response follows the
potential sweep.
IV.2- Running an experiment in an
electrochemical cell
After the test box 1, the user can repeat the
experiment in a real electrochemical cell with the
solution defined in the experimental part. Figure 5
shows the cyclic voltammetry curve resulting from
this experiment.
The user can find the data corresponding to this
experiment in C:\ EC-Lab\ Data\ Samples\
Cv_Fe_basique_1.mpr.
Fig. 5: Fe(III)/Fe(II) Cyclic voltammetry.
The user can press and hold the CTRL button on
the keyboard to show the data point’s coordinates
on the graphic window.
He can process the raw data file after the
experiment in order to extract specific values. A
process is a function of EC-Lab Ä software (in the
computer) that allows the user to calculate and
display values on the graphic that are not
measured by the instrument. All the processes are
available in the Analysis menu. Typically in a CV
protocol, the measured values are t, control, Ewe
and .
For example, variables that can be processed are
the cycle number or the total charge variation.
Processes depend on the protocol used.
For cyclic voltammetry experiments, it is often
necessary to do several cycles to have a real
picture of the system. In fact the first cycle
depends a lot on the experiment starting potential.
Generally a CV experiment is made of several
cycles. While processing the cycle number the
user can display the cycles he wants. The way to
do that is as follow:
1) Process cycle number. In Analysis\ process
(cycle, data…), load the CV file and click on
Process. The processed file will be located in
the same directory as the raw file. Its name is
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C:\ECLab \Data \samples\
CV_Fe_basique_1_n.mpp.
Fig. 7: CV cycle selection.
Fig. 6: CV off-line process window.
2) In the graphic window, right click on the mouse
and choose “Selector” and “Load”. Then select
the processed file in the directory
3) At the right bottom corner of the graphic
window one can see a frame allowing the user
to highlight all or several cycles. Choose the
cycle(s) you want to see (see the red circle on
figure 7).
After this quick start about cyclic voltammetry,
another document describing voltammetric peak
analysis will be soon available.
Conclusion
Cyclic voltammetry is the most used
electrochemical technique. It is the reason why we
designed this quick start with CV. Moreover
EC-Lab Ä
software offers lots of other abilities in
general electrochemistry experiments. In addition
pulsed techniques have been developed and
added in EC-Lab Ä
software for electroanalytical
applications. A very interesting tool called protocol
linker has been developed in EC-Lab Ä . It can be
used to build complex experiments with
preconditioning steps. The user should also note
that two protocols have been designed to be very
modular (Modular Potentio and Modular Galvano).
For more information about them, see the user
manual.
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