a part of fundamentals.of.electrochemistry book :
When alternating current is used for the measurements, a transient state arises at the
electrode during each half-period, and the state attained in any half-period changes
to the opposite state during the next half-period. These changes are repeated according
to the ac frequency, and the system will be quasisteady on the whole (i.e., its
average state is time invariant).
For measurements, an ac component IIm sin ωt with the amplitude Im and angular
frequency ω (ω2πf, where f is the ac frequency) is passed through the electrode
(alone or in addition to a direct current). Alternating potential (polarization) changesΔE having the same frequency and an amplitude ΔEm are the response. Sometimes
alternating potential components are applied, and the resulting alternating current component
is measured. In all cases the potential changes are small in amplitude (10 mV).
For an electrode behaving like a pure (ohmic) resistance R, the relation between
the instantaneous values of current and the changes in potential at all times would be
ΔE/IΔEm /ImR. This is actually not found in real electrodes, but instead, a
phase shift α analoguous to that observed in electric circuits containing reactive elements
appears between alternating current and alternating polarization. In electrochemical
systems the potential changes always lag the current changes: ΔEΔEm
sin(ωtα), which corresponds to an electric circuit with capacitive elements. Thus,
the ac behavior of an electrode cannot be described in terms of a simple polarization
resistance R (even if variable) but only in terms of an impedance Z characterized by
two parameters: the modulus of impedance ZΔEm/Im and the phase shift α. The
reciprocal of impedance, Y1/Z, is known as admittance or ac conductance.
A model for the ac response of real electrodes is the simple electric equivalent circuit
consisting of a resistance Rs and capacitance Cs connected in series (Fig. 12.12a).
It follows from the rules for ac circuits that for this combination
Battery is a two electrode system
Two interfaces plus one resistor
one interface has Cdl+Rct
you can model - if you want see my papers on Li batteries
Dear Prof V. S Muraidharan
Thanks a lot .
but i want to know how to do EIS for my flow battery?
In Attachment there is 4 steps that must be set parameters
Can someone help set this parameters?
it is Warburg impedance play a part
let me think
2 RC with Warburg + Rsolution
Dear Prof V. S Muraidharan
Thanks a lot .
Do you think the initial parameters have an effect on response.
To run the program, i must set the parameters in 4 steps.I do not know how I set these parameters. Do you know? Have you worked with PowerSuit software ?
Dear Hassan Yousofian,
from your data it is not really possible do determine if you can model this by a series of two C/R parralel circuits or if there are other elements like Warburg Impedance as Prof. V.S Muralidharan mentioned. I am quite sure, you could use both ways and fit then equally good to your data.
From the measurement point of view lower frequencys would be intressting, if your equipment and set-up are able to do so.
But as always i would suggest to develop a model based on your knowledge of the different processes occuring in your cell. Then you can translate this into a equivalent circuit for EIS. For example a C/R parallel circuit can be understood as an interface at which a charge is accumulated (the capacitor) but also is able to penetrate the interface with a certain kinetic inhibition (resistor).
To really learn something from your data, you need to know the physical meaning of your equivalent circuit before the measurement . Otherwise there is a high potential for misinterpretations.
Kind regards,
S.Wolter
permit me to visualize your system
1. It is a flow battery and a redox couple having very good exchange current density
2. The flow is steady ( Laminar flow)
3. Your electrodes are inert
There is mass transfer effects are nearly nil as the electro active species are avilabale in plenty
There is enough conductivity in the solution and your Rs is small
Now it a RC circuits with small Rs
you will get a distorted semicircle and low diffusion tail at low frequencies
try 10 KHz to 10 mill Hz
Dear Wolter please follow
best of luck
You can measure the battery impedance spectra and perform fitting them to the sutable equalent cirquit. You can obtaine the values of the circuit elements. They alow to evaluate the battery state of charge (SOC) and other battery paremeters.
Dear Prof. V.S Muralidharan and Wolter
thanks alot,
Is there a way to understand, a redox couple having very good exchange current density or not?(please explain step by step).
my electrolytic cell volume is very low and does not flow.what the matter?
one electrode is graphite and it is inert but another one is copper that cadmium is deposited on and xidation and reduction of cadmium, which makes up one side of the cell.
How do I measure the mass transfer rate? And how to understand the mass transfer rate is adequate or not?
How do I know the solution resistance is low or not?
what is your battery system?
what are the electrodes? is the battery electrolyte is stagnant?
redox exchange CD is available in books
what are the Cell reactions?why you use copper/ Cd?
many un certainity--
what is your battery system? it is a hybrid sistem
what are the electrodes? 1- graphite 2- cadmiume deposited on the copper
is the battery electrolyte is stagnant? yes the electrolyte is stagnant only It is stirred with a magnet and stirrer.
redox exchange CD is available in books
what are the Cell reactions? 1-(Cd2+ +2e Cd) and 2- (H2Q Q + 2H+ 2e)
why you use copper/ Cd? Cadmium only depose on the copper in sulphoric acid medium
please tell me how you recharge? will you replace The electrodes?
EIS can tell you impedance of the electrodes or the electrolyte depending on how you use it.
thanks alot Claudiu Bucur.
i want to determine of impedance of the electrodes and the electrolyte.
But I do not know how to do the basic settings.
can you help me?
hi,,can any one tell me what is the input function (like voltage) in electrochemical impedance spectroscopy method on a battery in experimental ??for my study I need a voltage that it is function of time and frequency..and also its frequency is function of time..please help me..thanks.
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