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     CA (Chrono Amperometry)
 
  CA (ChronoAmperometry) Analysis Method


* CA (Chrono Amperometry)


When a potential having a sufficiently large value capable of inducing an electrochemical reaction is applied in steps to the electrode having a balance, a current flow is observed. In other words, the potential is given in the form of a step and the current is measured with time.

For the potential step applied in this way, CA (Chronoamperometry) is to observe the current signal with time.

This method is used when measuring the diffusion coefficient of an active material in a solution or when analyzing kinetics and mechanisms.
Like CV, the voltage waveform applied during the constant voltage (PotentioStat Mode) method or analysis is significantly different.
That is, it is widely used to observe the capacitance effect at the interface by maximizing the transient state.

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Dynamic Mode


Block diagram (constant potential circuit)
 


 Waveform


 

Parameter






Static Mode


Block diagram (constant potential circuit)





Waveform


 

Parameter





* 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.


 
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