I can clearly see plateau region in your charge-discharge profiles. You are not suppose to use slop of the curve as it have different regions with different slops. So, you have to integrate the discharge curves for calculating capacitance value. I would like to see CV curves as well. 

see this paper

http://www.sciencedirect.com/science/article/pii/S1002007113000610

Thanks for kind reply. please fine the attached CV file. I calculated Integrate The curve( area of curve) but still it also was too small.

The potential ranges are different in your CV and GCD experiments. You should use the same potential range. In this specific case, the potential range of the GCD should be the same as that of the CV.

Dear George Zheng Chen, I used the same potential but I got this curves.I am sure i used the same potential (-0.2 to 0.5) . you can see the right side of the GS curves for potential range. 

Have you forgotten to attach the new GCD plots? Your original GCD plot has a potential range from -1.6 V to +1.6 V, but your CV was recorded between -0.2 V to +0.5 V.

yes I know the potential range are different,the potential range for both were same .i used -0.2 to 0.5 v for CV and GCD, but the curves show other thing.

Hi Nazanin,

From the GCD file, my suggestion for getting different potential range even after commanding -0.2 to 0.5 is that the current is too much for the mass loading, so is either the mass of the electrode is very smaller than the calculated. Anyway, Is this results from a 2 electrode system or 3 electrode system? Is good to know that, since the calculation equation differs..

Dear Katlego Makgopa thank you for kind reply. I used the 3 electrode system. for preparation of electrode , 5 mg of sample was used. on your opinion I should use too small current or increasing mass loading?

thanks

You decrease the current

سلام

توی تنظیمات دستگاه (برا شارژ و دشارژ) تعداد نقاط رو بیشتر کن که از پنجره پتانسیلی که براش تعریف کردی بیرون نزنه

برا محاسبه ظرفیت هم، زمان دشارژ رو در دانسیته جریان ضرب کن و بر پنجره پتانسیل تقسیم کن

مقدار ظرفیت رو از دشارژ درست حساب کردین همون 7 میشه منتها از سی وی درست محاسبه نکردین حدود 10 میشه دیگه فارسی هم نوشتم که تو گرامر گیر نکنیم

Capacitance of a elctrochemical capacitor depens on many experimental parameter. If  you change scan rate or current density then it will change. May be you have use very high current density for charge discharge but ypu compared with the CV result with very low scan rate. Your charge discharge potential window is very high and there are many losses occur.

please  can you help me to write equation to calculate capacitance from chornopotentiometry  to 3 electrode

Based on your CDC curve, your discharge time is very small (around 1.1 sec) so your slope will be (3.2 V/1.1 s=2.9). So the specific cap= I/m*slope= 0.00132/(0.00044*2.9)=0.32 F/g. Your current density is 0.00132/0.00044= 3 A/g which is not so high. So i think this very low spec cap is due to ur materials or due to mistake in the parameter, try to make sure of sample mass, charging current, .......

Dear Deepak, thanks for your question.

If we are dealing with an ideal capacitor, changing the potential window will not affect the capacitance value.

However, if we are studying an electrochemical capacitor, the potential window is an important factor affecting the capacitance value in practice.

For example, in the EDLC, the application of a correct potential window is to at least avoid the decomposition of the electrolyte (or the electrode materials), which may contribute to non-capacitive charge consumption. Further, for an individual electrode, changing the potential window will determine if it is the anion (in the positive potential range vs. the potential of zero charge, PZC) or cation (in the negative potential range vs. PZC) that is responsible for charge storage in the electrode.  The measured capacitance resulting from cation storage is highly likely different from that from anion storage.

Hope you are better informed now. (I notice you posted your query three times, but hope it was just due to unintended errors.)

please doctor  i can not calculate  specific capacitance from this equation  I *delta T /delta v*m

can you help me  calculate specific capacitance?

where  delta v= 1   

m=0.00005

delta t =100

current

10 A /g 

Dalia, what are the units of the numbers in your message?

Deepak,

Thank you for your question. Except for fundamental research, it is practically wrong to charge or discharge a supercapacitor into the negative voltage range, even for the so called symmetrical supercapacitors. The only case I can see the research need for charging into the negative voltage range is to check how symmetrical of the device is in terms of electrochemical behaviour.

Hi, Deepak sir, Dalia sir, George sir, Gomaa sir,

I am working Supercapacitors, Graphene Carbon Nanotube. 

The Specific capacitance difficult calculate from  the  from CV Cure, May be to choose better Charge-Discharge using specific capacitance calculations.

The charge discharge cure equation - Scp = I *delta T /delta v*m

I - is current (A/g), how to calculate the A/g ( (A/g ) - mean (current (A) / Mass (mg)), please tell me how to set (A/g) correct one ?.

Another one important, what is exact mass of Active materials in working electrode (milligram (mg)), somebody's using 0.00002, and 0.000001, these wights (micro gram or very low mass of active materials) some researchers was taken active mass (2 milligram to 4 milligram) , Active materials weight is very important because to calculate or set current value (A/g) is important !.  

The working electrode preparation -

Active Mass -80%, Binder-10%, Activated carbon 10%

Which is best/good  working electrode - Glassy carbon electrode (GCE), GC is very low mass (active materials) coating due to low area. May be to good choice of stainless steel Mesh, Metal foils (Ni, Al, Cu, S.S) depend upon the electrolyte solutions. ( i am using S.S Mesh working electrode in 0.5 M H2SO4 Electrolyte).     Ni foam (expensive), 

my doubt is Active mass decreased (inversely proportional to) Specific capacitance increased ?!

Please give me suggestion,Thank You.

Deepak sir, Dalia sir, George sir, Gomaa sir,

Deepak, please be reminded that what we are discussing here is on testing a two electrode supercapacitor.

For measuring the single electrode in a three-electrode cell, you can change the potential range (NOT voltage range) according to the nature of the electrode material, and negative potentials are often studied as well.

Dalia, I still do not know clearly what you have described. What do you mean by "i weight 0.005g in 500 M distl water"? What does 500 M mean in your email? Also, in your sentence "charge current is   0.0001    &       dis charge current is -0.0001", what is the unit after the number 0.0001 and -0.0001?   

Thank you Prof. Chen and Deepak, your answers have helped me overcome certain questions in similar line.

further while going through your answer George Zheng Chen, I have one question why do we use the term potential range for a three electrode system and voltage range for two electrode system?

good question, When using three electrode system in Half cell, the Electrical potential is the energy per unit charge gained or lost when a charge is moved from some reference point at which the potentials are Reference, Counter electrode, and working electrode (potential range difference in three electrodes). Voltage is the difference in potential between two arbitrary points (two electrode system-full cell device) at which the potential is not zero, working electrodes voltage range depend upon the active materials (negative and positive electrodes).

Which one correct formula for specific capacitance for single electrode:

1. Gravimetric capacitance from galvanostatic charge/discharge was calculated by using the formula C= 4I/mdv/dt

where I is the constant current and m the total mass for both carbon electrodes, and dV/dt was calculated from the slope obtained by fitting a straight line to the discharge curveover the range of Vmax (the voltage at the beginning of discharge) to ½ Vmax.

https://science.sciencemag.org/content/sci/suppl/2011/05/11/science.1200770.DC1/Zhu-SOM.pdf

or

2. C = = I *delta T /delta v*m

please, if have you answer, send me the response, i have also this problem,

[email protected]

thanks for advance@