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     CV (Cyclic Voltammetry)
 
  CV (Cyclic Voltammetry) Analysis Method

 

CV (Cyclic Voltammetry)


CV is a representative method of the Potentiostat (CV, CA, SV, LSV) measurement method among the Potentiostat(constant voltage) measurement method and the Galvanostat(constant current) measurement method.

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.


* WizECM-1200Premium


Block diagram (constant potential circuit)


 


Waveform



 


Parameter








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.
Start at the initial potential E and inject at a constant speed.
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

Increase Cathodic flow
 




* CV Graph Analysis

Decrease Cathodic flow
 



* CV Graph Analysis

Increase Anodic flow
 




* CV Graph Analysis

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.










*  Significance of CV, CA, etc. measurement

For example, when proceeding with a chemical experiment, the CV measurement is usually done first.
It uses the CV measurement method to check whether the experiment is proceeding properly or whether the results have been obtained properly. In order to observe the progress of the experiment without CV measurement, we visually confirmed how the experiment progressed during the experiment, but with the CV measurement method, it can be confirmed by the measuring instrument immediately.

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 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 experiment process and results. Especially useful for comparing peak points.


 
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