it may help this link

A Review of Techniques for Electrochemical Analysis (http://www.princetonappliedresearch.com/download.asbx?AttributeFileId=da907eee-6988-4cd6-a8f5-c38aa06d5ab0)

Dear Ioannis Sir, 

This document mentions only overview of the chronopotentiometry (CP). I want to know the procedure to follow in order to find the capacitance from the galvanostatic charge discharge method using CP.

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Somewhere in questions in researchgate, I found out, somebody have mentioned this procedure:-

[1]. Check Imax with CV.  

[2]. At this Imax value, run the CP for 500 Cycles (Basically to get Saturation Voltage).

[3]. Now, for slope (dv/dt) calculated from single cycle of charging on Voltage Vs. time plot (for 2-electrode cell) and Imax current, capacitance will be obtained as C= I/(dV/dt). 

[4]. Is the Currrent chosen (Imax) gives best approximate value or some other current ?

[5] is there any reference for such method of electrochemical analysis ?

Kindly solve the confusion !

Dear Pankaj Rohilla,

step [1]  is a good starting point as initial indication for Imax in CP. However, one must note the critical parameter of the rate(s)  a=dV/dt  in that initial CV test(s), since Imax ~ a1/2) .

A Note:  for a Nernstian system, Eequil should be independent of scan rate a, but Imax will depend on the square root of scan rate [for more : http://www2.chemistry.msu.edu/courses/cem419/cem372cyclicvoltammetry.pdf].

I got plots different (not what i expected)... i can not interpret these curves of potential vs. time... 

Can anybody help in this regard ?

Your CV and other results suggest that your cell was possibly incorrectly constructed and/or connected. Could you describe how you prepared your working electrode, counter electrode and reference electrode, and the electrochemical cell?

Sir,

I have used carbon electrodes in 2 electrodes system with aqueous electrolyte (KCl) .

then i performed CV at 10 mV/s scan rate and from there i checked Imax (=8mA, from the CV Plot).

Using this Imax I have performed chronopotentiometry, and the obtained E/V vs t plots are attached in previous comment. 

What are the possible causes of errors ? and is this chronopotentiometry procedure as galvanostatic charge discharge wrong or right ?

Thanks for the experimental information. How did you make/assemble your two electrode cell? Did you use a separator? I am asking because your CV shows an electronically leaking cell. In other words, there may be some "resistive" short-circuiting in your cell.

Sir,

I have used Whatman filter paper as separator here. I have used it earlier too. Should i check with any other separator !

Whatman filter paper is fine for use with an aqueous electrolyte. How did you prepare your electrode? What was the loading in mg/cm2? How did you assemble your cell?

As I said, your cell looks to have some "resistive" short-circuiting. I need you to confirm if this was the case.

0.081 gm of electrode material coating (activated carbon) on the 4 cm2 torey carbon paper, then these electrodes i have put into a plexi glass cell assembly, steel bolts on either side for charging and discharging. that is all about the assembly.

I do not fully understand your description.

Did you use any binder with the activated carbon? If yes, what was the carbon/binder ratio?  How did you add the liquid electrolyte to your cell? What do you mean by "steel bolts on either side for charging and discharging"?Can you upload a photo of your cell?

Nevertheless, I guess the problem is at least partly your use of the very resistive  "torey carbon paper" as the electrode substrate, and to a less degree, your fairly high loading of activated carbon (>20 mg/cm2) which also makes the electrode more resistive.

My suggestion for improving your results.

(1) Replace the "torey carbon paper" by a solid graphite substrate (platinum is better for testing only). 

(2) Reduce the loading to about 1~2 mg/cm2.

(3) Assemble the new cell and run the CV at a scan rate sufficiently slow so that a rectangular CV is recorded. If you see a fish-like CV as the one you showed, it means that your cell is too resistive (and possibly electronically leaking).

Dear Sir, 

• Carbon : binder :: 90:10 [ Binder : PMMA ].

• I injected liquid from the top into the cell as I keep my cell assembly vertical. [Cell attached as figure ]

• Steel bolts are used like strips to take out current from the current collectors. [check figure]

Sir, I am mainly concerned with the Galvanostatic charge discharge method using chronopotentiometry. for other experiments i have done i got the rectangular type CV plots. but the chronopotentiometry results are not those triangles' shape as we get for charging and dicharging [e.g. is attached in figure ] and the curve i am getting is already i have attached as results in previous comments.

What to do with chronopotentiometry (CP) to get triangles shapes for charging discharging ? i am taking Imax from CV and for that constant current i am performing CP. but, curves are not in triangle shape, is my method wrong ?

Thanks, Pankaj Rohilla. How you manage to include a Ag|Ag+ reference electrode in the cell? Nevertheless, it seems to me that your GCD seems to have been measured from the positrode potential, instead of the cell voltage.  If so, your upper limit of the potential was set a little too high because the plots have all curved at potentials above 0.6 V, indicating non-capacitive Faradayic reactions. Therefore, you should lower upper limit of the potential to be or lower than 0.6 V vs. Ag|Ag+.

Dear Chen Sir,

I have shown GCD figure u saw in last comment to show type of general E vs. t plot, we generally get for GCD, actually what i am getting is in pdf i attached earlier. The figure i am getting, i am attaching again.

Also, I have not used any reference electrode for my cell. just a two electrode cell i am using.

My question is why i am not getting triangles as we generally get ?

You need to switch the current polarity when the potential has reached at the upper limit, i.e. 1.2 V. In other words, if you applied 1 mA current for recording your plot on the left (charging), when the potential has increased to 1.2 V, you need to change the current to - 1 mA (discharging). The change should be automatically done by properly setting up your potentiostat. Read the instruction of your potentiostat for details.

Dear Pankaj Rohilla,

at about (so high V for water)) 1.230V you force an electrical breakdown of the solute (water). So, clip the V, i.e. use as Vmax=1.20V (or lower)  in your E vs. t  tests,

Dear I. Samaras and G. Z. Chen,

I have tried to run it for Vmax=1.2 V and current 2 mA, but my potential doesn't reach to zero limit ? check the image ? what could be the possible reason ?

Dear Pankaj Rohilla,

1. set, also, and a 2ndV2Limit  :  V2Limit >-1.2V

2. take more V points per cycle, in case you miss important points V(t).

3. try to change the current i :  i1=0.1mA, i2=1mA, i3=5mA, i4=10mA, i5=20mA.

Dear Sir, 

I tried all the three points you mentioned, but the potential is not reaching 0 volts. No change is observed. 

Dear Pankaj Rohilla,

try a new cell. May be there is a pollution of the interfaces from the older tests using higher Vmax resulting in hazardous substances e.g. older tests with Vmax>1.2V.

Hey Pankaj,

Can you send a picture with the parameters you are using for the discharge cycle too?

Charge cycle: Try reversing the - when cycling to from 0V to 1.2V. It seems counter-intuitive, but I believe having the less than or equal to pointed towards the number 1.2V instead of the word Potential is the correct convention  -- Also make sure to use a positive current.

Discharge cycle: use the symbol

Hi Pankaj. I am looking for the same as you were looking 2 years before. Can you help me in finding a way to measure charge-discharge? thanks

@Shatrudhan Palsaniya, I tried but am getting same as Pankaj gets. i mean ideal result.

Oneeb,

Check the files attached.

I have attached the program i used.

Change your window as per your requirement.