We have used standard 3 electrode setup and also a 2 electrode setup, with 1M Na2So4 as the electrolyte. We perform CV to determine the capacitance. Then I calculated the area under the curve and got the capacitance to be in the range of 3000 f/g which is impossible. Also there is slight discoloration in the electrode for 3 Elec;cell setup and complete discoloration when 2 elec. setup. (graphene on copper as WE and Cu as CE) What mistake are we making? Should we not use copper as current collector?
Also most papers show CV chart as Sp. Cap vs Voltage. But when we measure we get the results I vs V. So how can I calculate Sp. Capacitance at each point of Voltage?
regards
Don't know whether Cu can be used for CE or not?
The specific capacitance C can be calculate from the CV curves as follows
C = [Integration (IdV)]/vmΔV ,
where v is the scan rate (V s − 1 ), m is the mass of graphene, and Δ V is the operating potential window. If your effective area of graphene 1x1 cm2. Otherwise you have to divide by surface area.
Have you use this formula?
Hi Subrata!
I use the same formula. I take the area under the curve and then divide by scanrate
Its not due to the fomula.i guess you should not use copper as current collector.the disolution is not occured from your active materials it comes from negative Cu electrode.
Hi Annamalai !
When we people have used Ni, Steel, Mo as current collectors, why can we use Cu? And also we have Graphene on it? If I need to use a diff. substrate as Current collector, can I use Pt or ni (with as grown Graphene?
Then I'm agree with Annamalai.
http://books.google.co.in/books?id=lmsAnfWp2w4C&pg=PA138&lpg=PA138&dq=why+noble+metal+and+graphite+are+used+for+counter+electrode&source=bl&ots=g4rkixA8D5&sig=Lw40waUHoIcZBdbr6AZcOU6xWio&hl=en&sa=X&ei=gpbEU4XDDImQuATxw4HIDA&ved=0CEUQ6AEwBg#v=onepage&q=why%20noble%20metal%20and%20graphite%20are%20used%20for%20counter%20electrode&f=false
Depending on the ionic concentration, noble metal can be oxidized.
https://www.researchgate.net/post/How_to_clean_Pt_counter_electrode?_tpcectx=home_feed
In my opinion, capacitance overestimation may be just because of graphene mass measuring errors. Also copper is not the best electrode material for aqueous electrolyte (Cu2+ + 2 e− -> Cu(s) E=+0.340). Could you attach the cv curve?
Hi Dr. Trzciński !
I have attached the CV curve. I am calculating the weight of G from SSA, about 2675 m2/g.....so 1cm2 has 3.73*10^-8.
regards
There might be holes in the graphene due to continuous growth and that will cause leakage which will be read as an excess capacitance. Also you could check this publication out " Measurement of the quantum capacitance
of graphene" they are using different graphene source and different electrolyte but it is still useful to read.
Deepak, I guess Ni will show a better results, According to your statement, have you achieved the theoretical surface area of G?
such high surface area was impossible if the graphene was not porous.
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