Hello. I found that specific capacitance of three and two electrode in supercapcitor are different even with the same electrode.
The specific capacitance of three electrode (Cs,3) is four times lager than that of two electrdoe (Cs,2), that is Cs,3 = 4 * Cs,2.
So, to compare specific capacitance (Cs,2) in two electrode with specific capacitane performed in three electrode system (Cs,3, other reference data), Do I have to multiply Cs,2 by 4?
Thanks.
Two electrode measurements is more accurate. But you can check using each cyclic and charge discharge.
To me, it is completely okay if you multiply the capacitance obtained by 2-electrode systems by 4 for comparison.
But please keep in mind that since the two testing systems are not equivalent and may give you different current response, strictly speaking, it is not reasonable to compare performance collected by a 2-elec system with that by a 3-elec system.
If possible, I would suggest you evaluating capacitance based on a 3-electrode system to compare with others (with 3-electrode systems).
Dear Jihoon Kang,
if possible try a thick(er) electrode (material). A part of the difference in specific capacitance (among 2 vs 3 electrodes' measurements) originates from the (possible) pinholes[1] in
1) thin film electrode (materials), or even in some not very thin electrodes, but
2) upon prolonged[2] cycling.
Also, try EIS, if possible, it is illustrating better these differences in specific capacitance.
1. There exist many types of pinholes for the WE (films) in a supercapacitor . A general (simple) case is here : https://en.wikipedia.org/wiki/Pinhole
2. Self-assembled three-dimensional and compressible interdigitated thin-film supercapacitors and batteries http://web.stanford.edu/group/cui_group/papers/Gustav_Cui_Hamedi_NCOMMS_2015.pdf
Dear Kang,
I am completely agree with the respected viewers. In 2-electrode system (supercapacitor device) you will get the materials actual capacitance value, and in 3-electrode system you are estimating the capacitance value of the electrode only. Both systems are different and it will give you different value even though the electroactive material is same and some parameters responsible are the geometrical area of the substrate on which you are depositing the material, mass deposition, accessible electrolyte etc. I am herewith attaching some journals for your reference.
Subramanya, B. and Bhat, D.K., 2015. Novel eco-friendly synthesis of graphene directly from graphite using 2, 2, 6, 6-tetramethylpiperidine 1-oxyl and study of its electrochemical properties. Journal of Power Sources, 275, pp.90-98.
Zhang, L. and Shi, G., 2011. Preparation of highly conductive graphene hydrogels for fabricating supercapacitors with high rate capability. The Journal of Physical Chemistry C, 115(34), pp.17206-17212.
Ghosh, K. and Yue, C.Y., 2018. Development of 3D MoO3/graphene aerogel and sandwich-type polyaniline decorated porous MnO2− graphene hybrid film based high performance all-solid-state asymmetric supercapacitors. Electrochimica Acta, 276, pp.47-63.
All the best.
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