Hello everyone,
I have got into a technical issue. I have been doing capacitance measuremments for my materials in a three-electrode system. After having a suitable capcitance, in order to calculate exact energy and power density, I planned to use two electrode symmetrical system analogous to a coin cell setup. But, after the change of setup, I have not been able to optimize the software to solve the problem. The capacitance of 150 F/g on a three electrode system now shows upto only 0.5F/g which seems a bit illogical. I am using carbon based material on a Biologic SP300 system using EC Lab software. I am not sure if I should use Eoc or Eref for measurements as OI have short-circuited the reference and the counter electrode for these tests. I have attached some pictures from the settings below for reference.
I suggest you to observe some practical rules:
- in a common PEIS, Ew is Eoc value measured vs Eref or 0.0 vs Eoc; you must have a reason to choose a different value; in any case 0.0 V vs Eref is a common mistake (it is an arbitrary value, think what is happening if you instal a different reference electrode).
- for a CV, Ei=0.0 V vs Eoc is a correct option, but vertex potentials +0.5 and -0.5 V vs Eref are also arbitrary ; try Eoc-0.5 V and Eoc+0.5 V both vs Eref
- from a charging experiment (an electrochemical process) at constant current you may calculate a cell capacity (not a capacitance), even if you use the same measurement unit (F)
- from an EIS experiment you may calculate a capacitance value (for the double layer near the working electrode); charging a capacitor is a physical process.
- for GCPL, try to understand how to use Hold and Limit (or di/dt) options.
You have to give more details about your tests to allow more people to help you.
Chère Madame,
je crois que vous faites erreur, je suis spécialiste de Littérature italienne contemporaine. Désolée...
Cordialement,
Anna Frabetti
There should not be any problem for using the two electrode config. You dont have to use E vs Eoc always for the start of any measurement as before followed by E vs none. The formula used by the eclab software for measuring the capacitance will be the cell capacitance. If you want to measure electrode capacitance, multiply it by factor of 2 or 4 depending on whether you are considering the mass of single electrode or both. The EC lab software can be directly used for measuring the energy and power density also. If you need further help, let me know at [email protected].
Cornel Radu Thanks for the information sir. Sorry for the delay in response.I am having these confusion because of switching the same system from a three-electrode setup to a two-electrode setup. It consists of symmetric equal weighed carbon material based electrodes. Because of this, there is no more reference electrode, so the counter and the reference electrode are the same.
With this setup in mind, I have few more follow-up queries:
-My biggest confusion is how the nature of input changes when I switch Eoc with Eref for the given measurements. I think I have a mistake in understanding the basic concept behind this and would like to know it in deeper.
-For PEIS, I will try to use both the techniques suggested.
-For CV, the vertex potentials are chosen based on the EDLC nature of the electrodes. Initially, I tried to do with a range of -0.4 to +0.7 only to find that the CV curve showing regions of pseudocapacitance . Thus, I planned to modify the vertex potentials to restrict it to the EDLC region of the electrodes. The choice of Eref over Eoc was suggested by the electrochem personnel of the lab which he explains is becaus of the usage of two electrode setup instead of three-electrode.
-For GCPL, the Hold and Limit options are already defined by the machine setup. I just generally change the Ewe and Is values. Kindly let me know if that is wrong?
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