For fabricated symmetric/asymmetric device, sometimes CV includes +ve and –ve voltage.
For an example, a specific electrode gives CV in the potential window from -0.4 to +0.4 V (vs. Ag/AgCl) in three-electrode system. We fabricate a symmetric device (two-electrode system) and logically the device should give a CV from the voltage window 0 to 1.6 V. There is a huge asymmetry in the maximum +ve and –ve currents which is not acceptable for supercapacitor. We can’t even get appropriate charge-discharge (CD) behavior as well. But if we take the window -0.4 to +0.4 V, then it gives symmetric current behavior and optimum electrochemical results.
The same issue can arise in asymmetric supercapacitor device also. What is the physical interpretation of such nature?
Some papers include CV enclosing both +ve and –ve voltage for device (attached below). So, what is correct and why?
In my point of view, the potential window depends on your material behavior, although there is some know range of windows for suitable materials for supercapacitors. If your materials behave totally in a new range then there wl be some reasons of that behavior. Which material you have to used?
Electrodes can exhibit any of the potential window (three electrode system) whether it may be +ve (ex. to 1 V), -ve (ex. 0 to -1) or both included (ex. -0.4 to +0.4) in different electrolytes. that is okay. here potential difference is measured with reference electrode (ex. Ag/AgCl, SCE). so, whatever the potential window exhibited by electrode can be accepted.
But sometimes problem arises because of fabricating symmetric or asymmetric device (two electrode system). the device may be aqueous or solid-state device. for device it should be in +ve voltage frame because here voltage difference is measured with respect to one another electrode.
you can consider material FeS, MoS2 for solid-state device using PVA-LiClO4 gel. I tried for them.
But some papers are reported where devices include -ve voltage window as well. I have attached the papers. please go through them.
So, my question is that what is correct? and physical interpretation.
Dear Bidhan,
CV type curves are approximate measurements of the dc voltage bias dependence of a capacitor (normal, super or anything else like sapphire disc with metal electrodes). The essential information about he behaviour of a capacitor is though "hidden" in the frequency dependence of the measured complex capacitance, the bias dependence being just another (admittedly also useful) piece of information (just as temperature for example).
Not knowing the frequency dependence of the complex impedance/capacitance of your supercapacitor limits very seriously possible interpretation of your measurements (physical interpretation). In fact , at least in my opinion, there is almost no point to try to interpret CV curves at a single frequency (your measurements - my guess) of an "unknown" system(sample).
There is NO such a thing as a particular positive/negative voltage window. It might be that the changes in the measured complex capacitance are small for some voltages, but that is all to be said. The window for a given material is given by a positive and negative voltage, where you destroy your capacitor (dielectric breakdown voltage). Once you know that , you know also your "voltage window".
With best regards
Petr
Dear Petr Viscor,
The interpretation is really will help me a lot.
How can I get CV curves for different frequencies??
thanks,
Dear Bidhan,
the machine you need is called Impedance Analyzer and I will recommend you to look it up at web pages of :
1.Hewlett&Packard->Agilent->Keysight
2. Novocontrol
3. Gamry
4. Solartron
There are others, but these might be sufficient. At the Keysight web site, there are also some Application notes that are quite useful.
With best regrads
Petr
Dear Petr Viscor,
thank you so much for your suggestions. Is there any reference paper for the same where researcher has done such kind of analysis? then please provide me.
regards,
Dear Bidham,
I really do not know, but please consult the following :
Electrochemical Impedance Spectroscopy by Mark E. Orazem and Bernard Tribollet (Wiley 2008).
i will write something on this matter during spring/summer, but I do not haver anything yet.
Best regards
Petr
Dear Petr Viscor,
ok then. whenever you'll complete, plz send me.
regards,
Dear Bidham,
yes, I will. Can you remind me around June/July ? My address is :
With best regards
Petr
dear Petr Viscor,
sure sir. thanks for giving your mail-id.
I will definately remind you.
regards,
Dear Christian Punckt sir,
thanks for such conceptual interpretation. this really helps me a lot.
the concept of asymmetric device is now cleared as you interpreted.
now, the question is for the symmetric device.
what voltage should be given manually to symmetric device during cyclic voltametry measuraments related to electrochemical analysis? can we include both +ve and -ve? I mean, for example,
0 to 1.6 V or -0.8 to +0.8 V, for both the cases voltage difference is 1.6 V. but which one can be considered as logically correct for supercapacitors?
regards,
Dear Christian Punckt sir,
Thanks for your answer. I'll do that as per your suggestion.
regards,
- Badges
- Science topic
- Similar topics
- Physical Sciences
- Materials Science