I made a three electrode cell of graphene + manganese oxide composite.
I use Ag/AgCl and Pt wire as a reference electrode, counter electrode.
When I measure CV or galvanostatic data, initial specific capacitance increases with cycle.
After several cycles, specific capacitance starts to decrease.
If I would like to report specific capacitance of my samples,
Which value should I use between initial capacitance and the increased value?
Usually, people use increased value after so-called activation process?
Thank you
I suggest that you run at least 20-40 cycles first to determine that your system has no instabilities. You may then report any value after that. I also suggest that you report the variation of capacitance with cycling. This will give the reader an overall idea of what is going on and how the capacitance changes with cycling. Please see this paper: http://www.researchgate.net/file.PostFileLoader.html?id=559b8f226225ff3e218b456a&assetKey=AS%3A272527534419982%401441987035909
I suggest that you run at least 20-40 cycles first to determine that your system has no instabilities. You may then report any value after that. I also suggest that you report the variation of capacitance with cycling. This will give the reader an overall idea of what is going on and how the capacitance changes with cycling. Please see this paper: http://www.researchgate.net/file.PostFileLoader.html?id=559b8f226225ff3e218b456a&assetKey=AS%3A272527534419982%401441987035909
I believe your composite making is not proper. If it is O.K., then during initial cycling there may be increase in opening of more space or increase of ion intercalation in between MnO2 layers. As it progresses there may be mechanical instability or chemical degradation and increase in contact resistance. You have to study it in detail.
Initial specific capacitance increases with the first cycles is quite normal for composite materials based electrodes. Then, it is quite unusual the specific capacitance decreased so rapidly after only a few more cycles. How did you prepare rGO-MnO2 electrodes? Did you just drop-cast rGO/MnO2 on a glassy carbon electrode? rGO/MnO2 is a system that has been extensively studied for supercapacitors. Try to compare the preparation procedure to those reported.
Initial specific capacitance increases with the first cycles is quite normal for composite materials based electrodes. Then, it is quite unusual the specific capacitance decreased so rapidly after only a few more cycles. How did you prepare rGO-MnO2 electrodes? Did you just drop-cast rGO/MnO2 on a glassy carbon electrode? rGO/MnO2 is a system that has been extensively studied for supercapacitors. Try to compare the preparation procedure to those reported.
Initial specific capacitance increases with the first cycles is quite normal for composite materials based electrodes. Then, it is quite unusual the specific capacitance decreased so rapidly after only a few more cycles. How did you prepare rGO-MnO2 electrodes? Did you just drop-cast rGO/MnO2 on a glassy carbon electrode? rGO/MnO2 is a system that has been extensively studied for supercapacitors. Try to compare the preparation procedure to those reported.
Thanks to all who replied very much!
@Qijin Chi
I didn't mean rapid decrease after a few cycles.
What I mean is that It didn't increase anymore, but specific capacitance maintained or started to decrease very slowly.
I prepared electrode by making slurry with PVDF binder, but I still have an adhesion problem with my sample.
Thanks
The specific capacity is defined by capacity of the condenser divided into weight or volume condenser. Capacity defined by its discharges on reference resistance. initial and final voltage, and also time of discharge of the condenser is measured. Further , where U0 - initial voltage of the condensers charge, V, U-voltage on the condensers charge through time t (s), R - size of reference resistance, (Ohm).
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