* Electrochemical Analysis and Understanding Principles Using PotentioStat.
The
purpose of this course is to analyse Electrochemical Basic Analysis Method [
CV(Cyclic Voltammetry), CA(ChronoAmperometry), CP(ChronoPotentiometry),
SV(Stripping Voltammetry), LSV(Linear Sweep Voltammetry) ] to understand the
fundamentals of electrochemistry.
It can measure typical properties of electrochemical specimens using CV, CP, CA, SV, LSV. Electrochemical samples are composed of electrodes and electrolyte, which are equivalent properties as a resistance and capacitor. Through the above basic analysis method, it measures a chemical reaction experiment in which an electro- chemical circuit or electrolyte exists, such as a resistance or capacitor.
By doing
so, we can figure out how electrical chemicals are organized and what
characteristics they have. Electrical you can see what voltage oxidation and
reduction occurs at, and you can also see a number of characteristics, such as
whether it is impurities or whether the reaction has occurred correctly.
By CV(Cyclic Voltametry) scanning a constant voltage area, it is possible to know what kind(&characteristics) of substances present in the electrolyte contribute to oxidation, reduction and so on.
It is also possible to check impurities, and to check whether the test environment is organized as intended.
In addition, various characteristics can be derived depending on the purpose of the experiment.
In addition, we prepared the following data to understand the characteristics of CA, CP, SV, LSV, and others and to make various use of them.
* Understand electrochemical analysis methods
* Understands the principles of electrochemical analysis.
* Understand linear injection voltage current, circular current voltage
method
* View Cyclic Voltammetry Graph
* Cyclic Voltammetry Measurement Method
* Understands electrode and electrochemical
* Understand the comparisons between electrochemistry and electrical
circuits.
When measuring, we focus on the three electrode or the resistor and capacitor. Electro-chemical is focusing on resistance and capacitors.
When measuring chemical reactions, the counter electrode, working electrode, and reference electrode (the three electrode) are connected.
There are many ways to classify measurements electro-chemical.
This material presents two main aspects : Potentiostat and Galvanostat.
The Potentiostat mode is measured in constant voltage.
Methods of measurement include CV, CA, LSV, SV.
And CA can be measured separated by dynamics and static.
The
Galvanostat mode is measured as a constant current.
The method
of measurement includes a ChronoPotentiometry (CP)
It also
can be measured separated by dynamic and static.
Electrochemical measurement method CV, CA, and CP can be analyzed when resistance is in a circuit and capacitors are present.
To help
understand the analysis method, assuming an electrocardiography sample. And
Counter Electrode (CE) and Reference Electrode (RE) are connected on a 3
electrode system and make a two electrode system. Then, connect to Work
Electrode (WE) follow..
1. Resistance Material
2. Capacitor Material
It was
explained in two separate ways to understand the characteristics of each
analysis method.
*[ Electrochemical case1 ] When connect the Resistance (R) to
WE, on a two electrode system.
*[ Electrochemical case2 ] When capacitors (C) are present in a two electrode system
The graph
of capacitors differs from the graph of resistance.
When
analyzing circuits with capacitors, it is possible to identify [the
reproducibility of the capacitance and capacitor] or [the mechanism that makes
the charge and the discharge]. 
As per the above table,
The fundamental analysis method represented
by constant voltage is ( PotentioStat Mode )
1. Cyclic
Voltammetry (CV)
2. Linear Sweep Voltammetry(LSV)
3.
Differential Pulse Voltammetry(DPV)
4.
Constant ChronoAmperometry (CA)
5. I - V
Curve ( Current - Voltage Curve )
The fundamental analysis method represented
by constant current is ( GalvanoStat Mode )
1.
Constant ChronoPotentiometry (CP)
2.
Constant Current Charge and DisCharge
3. V - I
Curve ( Voltage - Current Curve )
Electrochemical
samples are represented by resistance and components of capacitors.
Therefore, the role of PotentioStat / GalvanoStat can be seen as :
Constant voltage( PotentioStat Mode )
=> To maintain a constant voltage, the current varies according to sample resistance (Time
dependent) and capacitance(Not time dependent).
=> Apply a constant voltage and measure current
Constant current( GalvanoStat Mode )
=> To maintain a constant current, the voltage varies according to sample resistance (Time
dependent) and capacitance(Not time dependent).
=> Apply a constant current and measure voltage
The reason
why each method of analysis is divided is because the measurement method varies
depending on the purpose and the analysis target. Different measures exist because each analysis method
has different parts to view and analyze waveforms.
The most
basic measurement is a cyclic voltmetry (CV).
The monitoring
below first is a great help in determining the direction of the experiment.
1.Check if
oxidation and reduction are occurring using CV measurement
2. How
many chemical species contribute to oxidation and reduction?
3. Is it
reversible or irreversible? and so on
The measurement method varies depending on what you want to analyze.
* Definition of Cyclic Voltammetry (CV)
In the presence of chemical species capable of oxidation and reduction in the electrical system,
Apply voltage to the work electrode as a circular potential, and a current response occurs on or near the electrode surface.
The
material at that time is a method of analysis to obtain thermodynamic (of
electrochemical reaction)and speed-like parameters .
Potential
injection method is a method of recording the current flow as a
current-potential curve when the potential changes in proportion to time. If
this is repeated several times, the injection of potential is referred to as
the Cyclic Voltammetry.
* Definition of CV
¡æ Apply an increasing voltage in one direction at a given rate.
And then apply [the voltage changing at the same rate] in the opposite direction when the voltage reaches a certain size.
It is possible to graph [Time vs Potential difference] over time by giving and changing constant voltage and measuring the resulting current
?? ) A favorite question
Why is the voltage changing, even though it's a constant voltage?
=> Scanning
voltages of a given range while maintaining constant voltage.
Step by
step, it automatically scan the process of maintaining constant voltage,
manually setting each voltage, recording the amount of current, and repeating
it. At each voltage, the resistance would change if there were [oxidation &
reduction] of that voltage, and to maintain that voltage, PotentioStat would
change the current.
By observing the current, the amount of current contributing to oxidation and reduction is measured and the characteristics of electrochemical specimens are analyzed.
In addition, if the scan rate is different, the [Cyclic Voltammogram characteristics of the concentration of ions related to oxidation and reduction] present at the interface is changed
This relates to the rate of depletion of ions that contribute to oxidation and reduction depending on how much constant voltage is maintained at every moment.
¡Ø About CV (Cyclic Voltammetry)
When measuring CV, when chemically reacting on an electrochemical circuit or aqueous solution, two measurements can be made.
If you look at the Cyclic Voltammogram, you will notice the characteristics of CV analysis.
1 Cyclic Voltamograms with Resistance (R) connected to the CV system
2 Cyclic Voltamograms when capacitors (C) are connected to the CV system
3 Cyclic Voltamograms without oxidation and reduction in the electrolyte
4 Cyclic Voltamograms with oxidation and reduction of the electrolyte
It is possible to analyze the characteristics of the shape.
Therefore, CV measurement is most often used to analyze test results.
* When the resistance (R ) is connected to the CV measuring equipment as follows:
[Y-axis left : current (blue ), Y-axis right: voltage (red ), same value as X-axis ]
[ When the X-axis appears as a voltage
]
We can observe the graph by setting the X-axis to either time or to an applied voltage.
In CV, the X-axis is often viewed after the mode is set to the applied voltage.
In the figure above, the right-hand side of the X-axis and Y-axis are duplicated with the same value, but for many purposes this expression is used.
When measuring resistance, plot the graph with CV (current vs voltage).
As shown above, the form of the Linear equation (y=ax) is presented. You can see that the current rises as a result of giving constant voltage. This is measured with an electrochemical circuit, not a chemical reaction experiment with aqueous solution.
Connect a resistor to a Potentiostat/Galvanostat measuring instrument and schematize CV is a different form than previously known chemical reaction experimental graph.
* When the capacitors (C) is connected to the CV measuring equipment as follows:
[Y-axis left : current (blue ), Y-axis right: applied voltage ]
[ When the X-axis appears as a voltage
]
* When electrochemical samples are connected to the CV measuring equipment as follows:
Cyclic Voltamogram(Distilled water) on samples that do not contain oxidation or reduction
The graph below shows the Cyclic Voltammogram when measuring the CV graph directly with distilled water. The graph shows a long circular graph with no oxidation and reduction peak.
* Cyclic
Voltammogram(Distilled water) on samples with oxidation and reduction when
electrochemical specimens are connected to the CV measuring equipment as
follows:
[ Y-axis left : current (blue ), Y-axis right: applied voltage ]
[ When the X-axis appears as a voltage
]
The above
graph is actually a three-electrodes system measurement.
You can
observe the peak oxidized and reduced as shown. This is a graph that comes from
measuring chemical reactions in which oxidation and reducing species exist.
The
difference between electrolyte can be checked as whether or not oxidation and
reduction peak exists.
If you
want to observe a 3-pole or plating or any chemical reaction, you can analyze
the experimental process and results by checking the voltage at the time of
peaking by looking at the oxidation and reduction peak points.
* When a
resistor (R) exists in a two-electrode system
CV graph [
Current VS Time( X axis ) ]
[ Y-axis left : current (blue ), Y-axis right: applied voltage ]
[When the
X axis appears in time ]
In the graph above, the left side of the Y axis is the current and the right side is the applied voltage.
In the
method of displaying the X axis in time, it is possible to change the setting
by viewing the X axis as a voltage.
This graph is plotted with the resistance (100K) connected and the x-axis of the CV graph in time. Current and voltage are plotted equally and observe current flow while giving a constant potential.
* When resistance (R) exists in two-electrodes system
CV graph [
Current VS Voltage ]
[ Y-axis left : current (blue), Y-axis right: applied voltage (Red)]
[ When the X-axis appears as a voltage ]
In the
graph above, the left side of the Y-axis is the current and the right side is
the applied voltage.
If the
setting is changed from [How the X-axis is viewed as time] to [How the X-axis
is viewed as a voltage], the Y-axis right-hand applied voltage and the X-axis
can be viewed as the same value. For convenience, we made redundant
expressions. When observe the Cyclic Voltammogram with oxidation and reduction
provide convenience.
This graph
is plotted with the resistance (100K) connected and the CV graph in voltage on
the X-axis. Following Ohm's law (V = IR equation), the current vs. voltage
graph is in the form of a proportional graph as shown above.
* When capacitor (C) exists in two-electrodes system
CV graph [
Current VS Time ]
[ Y-axis left : current (blue), Y-axis right: applied voltage (Red)]
[ When the X-axis appears as time ]
When a capacitor
is connected, it increases and decreases the voltage rapidly, resulting in a
sudden charge and discharge of the current. This graph shows the degree of
charge and discharge.
* When capacitor (C) exists in two-electrodes system
CV graph [ Current VS Voltage ]
[Y-axis left : current (blue) ]
[ When the X-axis appears as a voltage ]
The
previous graph is converted to the current vs voltage format. Going up to the
right with based on voltage, indicates charging, going down to the left
represents discharge.
* K2[Fe(CN)6]
CV experiment
CV graph [ Current VS Voltage ]
[ Y-axis left : current (blue ), Y-axis right: applied voltage
(Red) ]
[ When the X-axis appears as a voltage ]
This is the most commonly used CV graph and shows that oxidation and reduction responses are observed. This is a diagram of the current VS voltage..
* CV Definition
In the experiment, the initial potential E is set as the potential for the Faraday current not to flow.
¡æ Start at the initial potential E and inject at a constant speed.
¡æ Reverse the direction of the injection from the reverse to inject the potential at the same forward speed and return to E.
The method of performing such a cycle once is a single CV,
Repeatedly repeating the same type of potential injection is the multiple CV.
* General
Experiments with Electrolytes with Chemical Reactions – Three-Electrode System
Reference
electrode - Ag/AgCl ,
Electrolyte - KNO3 ,
Counter
electrode - pt electrode
Working
electrode - carbon electrode
What was used in the experiment was A.
Connect electrodes to each device to plot the graph using CV measurement.
* CV Graph Analysis
¨ç Increase
Cathodic flow
* CV Graph Analysis
¨è Decrease Cathodic flow
* CV Graph Analysis
¨é Increase
Anodic flow 
* CV Graph Analysis
¨ê Decrease Anodic flow
* CV Graph Analysis 
As shown
in the table, when the CV curve is drawn, the potential and current at which
oxidation and reduction occur. It is possible to analyze the results of an
experiment and publish a thesis.
* When
analyzing the CV graph, the graph of the above picture does not always come
out. Due to various factors of the experiment, other forms of graph can be
shown. Two examples are as follows. 
[Y-axis left : current (blue ), Y-axis right: applied voltage (Red)]
* Figure 3
shows the CV graph for the three-electrode system using a WizECM-1200Premium
measuring instrument.
When
plotting the CV graph, set the Voltage Range, Scan Rate, and Scan Number
(number of repetitions of scan) according to the experiment sample and purpose.
WizECM-1200Premium
derives the most suitable Current Range by Auto Current range function
according to the sample.
It may not
be shown, so it should be set carefully. Point Per Cycle calculates and
determines how many sample data you want in one cycle according to Scan Rage.
Higher Point Per Cycle can display precise data, but it has a long storage time
when there are many Scan Numbers.
The energy
range of 0.7 ~ -0.3V and the current range of 1mA ~ 10mA are the same, but only
ScanRate was measured differently.
Graph
types are slightly different depending on ScanRate. This is because the higher
the ScanRate, the faster the scanning speed.
Here, the
reason why the shape of the graph changes when ScanRate is fast is that it
takes a minimum of time for the reaction to take place in a chemical reaction
experiment with oxidation and reduction species. However, when ScanRate is very
fast, the graph is plotted in relation to the reaction rate and concentration of
the ions involved in the reaction. The principle of this graph is to apply a
constant voltage to one by one point and observe the current. In other words,
if the ScanRate is very fast, then even the one point-to-point time is very
fast, and the distribution and concentration of the ions at the interface
progress differently for a short period of time, So we can observe that the
ScanRate differs from the late graph. When you measure the CV later, you should
analyze the graph by setting the appropriate ScanRate value.
To
illustrate more accurate graphs, you can increase the point per cycle or set
the scan number higher. Point per cycle refers to the number of points plotted
per cycle, and scan number refers to how many cycles are plotted.
* CV Advantages
The
meanings of CV is various than the other measurement methods.
- It is
possible to judge whether the reaction is reversible / irreversible.
-
Potential window where oxidation or reduction reaction occurs can be observed.
- By
plotting the concentration / current curve, it is possible to deduce the
concentration of unknown substance.
It is
possible to various experiment with different scanning speed, temperature,
reactant concentration and ionization intensity of supporting electrolyte.
Therefore,
CV measurement is generally used to analyze various experiments.
*
ChronoAmperometry (CA) Definition
When a
stepwise application of a sufficiently large potential to induce an
electrochemical reaction is observed on the electrode in equilibrium, a current
flow is observed. That is, the potential is applied in the form of a step and
current is measured with time.
Chronoamperometry
is the observation of the current signal over time for the potential step
applied in this way.
This
method is used when measuring the diffusion coefficient of an active material
in a solution or when analyzing kinetics and mechanisms.
Like CV,
PotentioStat Mode or voltage waveform applied during analysis is significantly
different is differ markedly.
That is,
it is widely used to observe the capacitance effect at the interface by
maximizing the transient state.
* When resistance (R) exists in two-electrode system
CA graph [
Current VS Time ] 
[ When the X-axis appears as a voltage
]
The
resistance does not show the amount of change of the current with respect to
time, the current flows in proportion to the applied voltage.
CA gives
constant voltage and sees current flow. The reason for this is that in order to
keep the potential constant, the current changes accordingly, and the current
peak also depends on the voltage setting value. The meaning of the 'constant
voltage' is not to apply only the voltage of a specific value for a long time.
It is to maintain the potential during a momentary reaction.
The
graphical scheme is to repeat [Print current values for constant voltage at one
point] for a very short period of time at every moment.
In
general, CA measurement is used in electrochemical circuit analysis (mainly
when measuring capacitors).
In the
capacitor, the charge and discharge are observed by the current flow to the
voltage. Check the current value according to the voltage, and you can see
whether it is charging properly or a reproducible capacitor. Reproducibility
refers to how much the same value is maintained in repeated charge and
discharge cycles. If the reproducibility is not good, the performance is
getting worse as the time is getting less and less charged. That is, the better
the reproducibility, the better the performance.
* When capacitor (C) exists in two-electrode system
CA graph [
Current VS Time ] 
[ When the X-axis appears as a voltage
]
When the
voltage is suddenly increased, it can be observed that the current flows high
in the characteristics of the capacitor, and the current flow decreases with
time.
By
analyzing the graph, you can see what the characteristics are and can suggest
that there is a capacitor.
* In a
typical experiment in which [electrolyte with chemical reaction] exists
* CA Definition 
*The significance of measurement of CV , CA etc.
For example, when performing a chemical experiment, CV measurement is usually performed first.
This uses the CV measurement method to ensure that the experiment is progressing properly or that the results are obtained correctly. Originally, we used eyes in order to observe the experiments carried out without CV measurement. But the measuring device can be checked immediately without the need for direct observation at eyes.
First,
perform the CV measurement method, not the measurement method such as CA and CP.
This is because we need to verify that this experiment is done properly, that
the oxidation and reduction are done properly, and what impurities are added.
After confirming that the experiment is perfectly complete, it is common to
measure it with CA, CP, etc. and to grasp the characteristics of this
experiment.
We mainly
compare the CV and CA graphs, and analyze the experimental process and results.
Especially useful for comparing peak points.
* If the
degree of agitation is the same and the constant voltage is the same, but the
peak points in CA and CA are different, why?
We have to
ask why. You have to think about whether this experiment is wrong, or if there
was an error in the measurement. However, there are two reasons why have these
different peak points.
The first
is the sample concentration or the extent of the interface.
The second
is the degree of stirring.
In CA, the
peak point is derived in a short time by the abrupt current supply. This is
because the peak point is almost unaffected by the ion concentration around the
interface and is the value which should be originally appeared. In contrast, CV
depends on the concentration of the electrode and the concentration of the
surrounding ions depending on the size of the interface. In other words, the
concentration around the electrode decreases and which means that there is a
limit to the experiment that needs to proceed and it may have a peak point
lower than CA.
*
Potential Analysis (PA), OCV( Open Cirucuit Voltametry ) Definition
When no load
is applied to the battery, that is, when no current is emitted to the outside
A method
of analyzing the potential difference between two terminals of a battery.
*
Stripping Voltammetry (SV) Definition
The
substance to be tested is electrolytically precipitated on the electrode and
concentrated,
Followed
by measuring the current potential curve when redissolving the concentrated
material.
That is,
the analyte component present in the sample solution is precipitated on the
indicating electrode through the electrolysis step for the sample solution.
The
component precipitated on the surface of the electrode is peeled back into the
solution using a voltage-current method.
Through
this process, the concentration of the component in the solution can be
determined from the measured current.
If a solid
electrode such as platinum (Pt) is used as the indicator electrode, it is
called Stripping Voltammetry.
* Definition
of SV 
* Reduction
process (= precipitation process): When a certain potential is applied to the
working electrode, the heavy metal ions present in the sample attach to the
working electrode and are concentrated.
* Oxidation
process (= peeling process): The electric potential applied to the working
electrode rises above from the negative potential to positive potential, and
the heavy metal ions plated on the working electrode dissolve while peeling off
from the neutral oxidation potential of the heavy metal. The heavy metal ions
eluted during the oxidation process are measured at the counter electrode to
calculate the heavy metal concentration.
* Definition
of SV
* Stripping
Voltammetry Type: Anode Stripping & Cathode Stripping
¡æ In
cathodic stripping, is similar to the anode stripping except that in the
plating step the potential is maintained at the oxidation potential and the
oxidized species are actively swept out of the electrode to remove it from the
electrode.
*
Advantages: Because stripping voltammetry has the effect of preconcentration
It can be applied to dilute sample solution and may show sensitivity of 10-10 ~
10-11M.
That is,
it is a high sensitivity measurement method capable of measuring up to a very
low concentration.
* Definition
of ChronoPotentiometry (CP)
The most
typical method for the analysis using a constant current (GalvanoStat Mode) is
to measure the voltage while applying a constant current and to use the
principle of changing the voltage when the resistance of the sample changes in
order to maintain the constant current.
That is,
it is a principle that GalvanoStat can observe the resistance change of the
sample by observing the electric field value which is changed to maintain the
set constant current.
It is a
form of electrical analysis that measures the rate of change of potential at
the electrode with a constant current.
This is an
analytical method in which the electrolytic solution is kept stationary and a
constant current is flowed between the indicating electrode and the auxiliary
electrode to track the visual change of the indicating electrode potential.
This is
the most basic constant current experiment, and the current step is applied to
the electrochemical cell.
* When capacitor
(C) exists in two-electrode system
CP graph [
Voltage VS Time ] 
[ When the X axis is expressed in time, charge /
discharge by constant current => voltage change ]
The constant current is applied and the flow of the
voltage is observed. The higher the voltage is, the better the capacitance of
the capacitor is. Also, if the graph of the voltage shows the same size
repeatedly, it can be said that the capacitor has good reproducibility.
[ When the X axis is expressed in time, charge /
discharge by constant current => voltage change ]
* The
graph below shows the CV graph for the three-electrode system using WizMAC
WizECM-1200Premium measuring equipment. 
[ When the X-axis is expressed in time, Ion c
oncentration
change by constant current => Voltage change ]
It is a CP
graph type in which the potential difference is measured by giving a constant
current, and repeats the form of increasing and decreasing.
This is
the result of a three-electrode system test. Ag / AgCl was used as a reference
electrode and KNO3 was used as an electrolyte.
A pt
electrode was used as a counter electrode, and a carbon electrode was used as a
working electrode.
K2 [Fe
(CN) 6] was used in the experiment.
¡æ CP, CV
Another CA PA SV LSV Also, the values that must be specified when measuring
each are different in this way.
*
Potentialstat / Galvanostat Single channel model (
WizECM-1200Premium)
This model can measure Cyclic Voltammetry, Chrono Amperometry, Chrono Potentiometry,
Potential Analysis, Stripping Voltametry and Linear Sweep Voltammetry., The
whole operation is convenient and it is possible to compare several data
analysis.
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