Actually the conductivity of the solution should be independent from the capacitance. The capacitance is probably related wuth the charging process of the doble layer. How about the capacitance from de impedance? It is ok with the one that you obtained from the CV? how about the conditons of the experiments? Did you used the same electrolyte?

Dear Andre

Thank you for ur answer.all condition is same. I didnt calculate capacitance from impedance. Generally, the material with high conductivity can give high capacitance , It means the impedance results can confirmed the CV results.  

So, you were talking about the conductivity of the material itself, something like the resistor that should be parallel with the doble layer capacitor? Sorry, I think that I got your question wrong so. But, as far as I know, this resistence should be related with a electrochemical process, so should be related with a charge transfer resistence. I think that I have nor read anything about the relationship between this two values. How are you relating them?

What you can also do to relate this data is to thake from de CV the polarization curve and by this get information of the charge resistence. This value must be related with the one you get from the impedance, for a simple one-step, one-electron process

The capacitance you are calculating from CV depends on anodic and cathodic current and weight and scan rate. There are so many resistances which are incorporated in ESR. The total effect is not only capacitance in CV. All the effects will come in to play when capacitance is calculated from charging and discharging.

Dear Nazanin,

1. If your electrical impedance data have been taken over sufficiently large frequency region, I would always trust Impedance data more than C-V data.

2. As Asit points out correctly, C-V instrument deduces the capacitance from charge-discharge currents and these are almost NEVER single exponentials. In other words, the deduced capacitance is an average of all the relaxation processes taking place. Some instruments though measure ac capacitance direrctly, but the problem is that this is done at a single frequency (I recall somethibg like ~1 kHz). If that is so, the real part of the complex capacitance  at this frequency, as measured by impedance, should coincide with the value  deduced/measured by C-V instrument. The reason is that C-V measurement at this characteristic frequency is just a single point on the real part capacitance frequency dependence  curve.

3. Your system can be modelled to a reasonable degree of accuracy, by three parallel R,C terms in series. The capacitances here are the geometrical capacitance of the bulk of the electrolyte Cbulk, the geometrical capacitance of the diffuse layer Cdiff and the geometrical capacitance of the double layer (electrode-liquid interface) Cinterf.  In order to see them directly in the impedance experiment, the corresponding resistances must be sufficiently different which is usually the case. It is important to stress here that the resistances are dc ohmic resistances of the respective layers, not some model resistances of possible polarisation processes, (inclusive variouis electrochemical reactions) within the bulk and/or within the interface. These can be added/modelled at a later stage of the analysis. Our experience has been that in typical aqueous solutions , the bulk properties are measured beyond some 10 kHz, while the properties/characteristics of the diffuse and interface layers are clear first bellow some 10 Hz.

I hope this helps

With best regards

Petr