I've run an electrochemical impendance spectra for my chitosan-Fe3O4 composite and compared it with Fe3O4. As expected the charge transfer resistance (Rct) increased (from 200 ohms to 600 ohms) due to the nonconductive chitosan film in the composite.
What I'm unsure is why the equivalent series resistance (ESR) is not increased in the sample but the it is the same and sometimes even slightly decreased for other samples.
I know that the ESR is attributed to the resistance of the electrolyte; the contact resistance between the electrolyte, current collector, and active material; and the intrinsic resistance of the active material itself.
So the increased Rct in the composite means the electron transfer is obstructed due to decreased conductivity in the composite but the unchanged/slight lowered ESR could mean that the intrinsic resistance (or other factors) of the composite remains unchanged. Is that even possible?
Your interpretation of ESR is wrong, ESR does not mean "resistance of the electrolyte; the contact resistance between the electrolyte, current collector, and active material; and the intrinsic resistance of the active material itself" ESR means equivalent series resistance. ESR is measured by extending straight line at low freq to x-axis. the value determines the total internal resistance of the system. On the other hand the starting point of semicircle represents only electrolyte resistance not others. the impedance parameters starts from the electrolyte at high freq and end at electrode at low freq.
Jhon Kevin, your interpretation of ESR is right only. Dear Dhrubajyoti , i think "ESR is measured by extending straight line at low freq to x-axis" this statement is not correct. EDR is measured by extending straight line at low freq to x-axis.
please check the link
http://www.sciencedirect.com/science/article/pii/S0013468600003546
Dear all,
I found a similar trend from a reported work, Rct is increased due to the nonconductive film of chitosan but ESR is reduced. The author didn't explain about the reduction of ESR though.
http://www.sciencedirect.com/science/article/pii/S0013468611010954
The system you describe: electronically conducting particles embedded in dielectric matrix, the whole system supported on a conducting material can be described using a transmission line model. The high frequency resistance shifts because of the relative values of the ionic and electronic conductivities through the system. Please check:
http://dx.doi.org/10.1016/j.jelechem.2014.06.035
Dear John,
If I'm not wrong, you are modified Fe3O4 with chitosan and compare the electrochemical properties with Fe3O4. Can I ask the purpose of using chitosan since has very very low conductivity and it can hinder the electrochemical properties of your composite.
Best Regards,
Casey
Dear Casey,
I used the PPy chitosan composite as a electrochemical sensor.
Indeed the chitosan will increase the resistivity of my samples but it will increase the hydrophilic properties of the sample as well as increasing the stability of the composite.
After optimization, with the right amount of chitosan, the electrochemical determinaition properties of Fe3O4 can be enhanced. On the other hand, too much of chitosan will increase the resistivity by a large factor and retard the detection process.
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