Dear Dr. Donghoon Lee,

it is better to place the reference electrode and the working electrode as close as possible; this gives the lowest resistance to the system, thus a more accurate result from your electrochemistry (lower iR drops from Galvanostatic measurements and no odd tails during voltammetric). Where you place the counter-electrode within the system does not matter. The best configuration should give more accurate results but I would not image will affect the corrosion rate.

For more details, I suggest you to have a look at the following notes/paper:

-Reference electrodes by Gamry Instruments

Available at: https://www.gamry.com/application-notes/instrumentation/reference-electrodes/

-Electrodes of a potentiostat by PalmSens

Available at: https://www.palmsenscorrosion.com/knowledgebase/electrodes-of-a-potentiostat/

-The Effect of an SEI Layer on Anode and Cathode Particles

Available at: https://www.forgenano.com/education/effect-sei-layer-anode-cathode-particles/

-Factors Affecting the Accuracy of Reference Electrodes

Frank J. Ansuini, James R. Dimond

MATERIALS PERFORMANCE, Vol. 33, No. 11, pp 14-17 (1994)

Available at: http://www.edi-cp.com/pdf/factors.pdf

Best regards, Pierluigi Traverso

Dear Dr. Donghoon Lee,

it is better to place the reference electrode and the working electrode as close as possible; this gives the lowest resistance to the system, thus a more accurate result from your electrochemistry (lower iR drops from Galvanostatic measurements and no odd tails during voltammetric). Where you place the counter-electrode within the system does not matter. The best configuration should give more accurate results but I would not image will affect the corrosion rate.

For more details, I suggest you to have a look at the following notes/paper:

-Reference electrodes by Gamry Instruments

Available at: https://www.gamry.com/application-notes/instrumentation/reference-electrodes/

-Electrodes of a potentiostat by PalmSens

Available at: https://www.palmsenscorrosion.com/knowledgebase/electrodes-of-a-potentiostat/

-The Effect of an SEI Layer on Anode and Cathode Particles

Available at: https://www.forgenano.com/education/effect-sei-layer-anode-cathode-particles/

-Factors Affecting the Accuracy of Reference Electrodes

Frank J. Ansuini, James R. Dimond

MATERIALS PERFORMANCE, Vol. 33, No. 11, pp 14-17 (1994)

Available at: http://www.edi-cp.com/pdf/factors.pdf

Best regards, Pierluigi Traverso

Dear all, Thank you so much for your answering. I'll study for that!

Yes ofcourse

First of all, the position of the reference electrode is only important when current is flowing (in a three electrode cell, between the working and the counter electrode).

The question is not how much current flows on the reference electrode. Current is flowing between the working electrode and the counterelectrode and the flow of charges induces a potential gradient accross the current pathway.

Thus, the question is on how the reference electrode will sense that potential. If it is placed close to the working electrode, the measure will be not too much affected by the above mentioned potential gradient (again, between working and counter electrodes).

To simplify, imagine that the working, reference and counter electrodes are placed along a straight line, with the reference electrode somewhere between the other two. As you move the reference electrode in the direction of the counterelectrode, the portion of the total IR that is sensed by the reference electrode increases, so the measured "working electrode potential" is more affected by the IR.

As an example, I am sending an electrochemial impedance plot obtained with a Pt working electrode in a NaCl solution. As you may know, the distance from the origin to the beggining of the plot (high frequency points) corresponds to the IR drop, and in this example it steadily increases with the distance between the working and the reference electrode.

Good luck

Hope you are well,

Yes the current is flowing in the working and counter electrode and reference electrode is just to sense the potential where it is inserted.

The potential difference between the working electrode and the reference electrode can be expressed as:

Vwe + I Rs where:

Vwe is the potential of the working electrode , I is the current flowing in the circuit and Rs is the series resistance between the reference electrode and the working electrode. The value of Rs is proportional to the distance between the two electrodes in the path of the current.

So in order to reduce Rs one has to reduce the distance between the electrodes.

As the colleagues this is also valid for the distance between the working electrode and the counter electrode.

Best wishes

Hi. The reference electrode shoud be at a distance ten times greater the greatest dimension of the working electrodo.

In a 3 electrode system current flows between the working electrode WE, and counter electrode, CE. That entails a potential drop between those two electrodes.

Ideally no current flows through the WE reference electrode, RE loop.

In practice, we can assume, very small current flows in this loop. This current can change the potential of RE. But in view of the fact that it is a reversible electrode, the property of reversibility allows the electrode to maintain its potential constant even when a small current flows through it.

The potential measured includes the working electrode potential and IR drop arising out of current flowing through the cell between WE and CE. The placement of reference electrode gives a potential that includes various values of IR drop depending on the relative disposition of WE and RE in addition to the potential of the WE - which alone is the quantity of interest. Therefore, the placement of reference electrode assumes importance in getting accurate values of WE potential. If we take it very near the WE, screening effects creep in, making the measured potentials unrealistic but taking it farther away introduces IR drop. Therefore, experience teaches the best placement of RE in the vicinity of WE.

An ideal (fixed position) for a single RE is on a equipotential surface[1] crossing, also, the WE, under the ideal condition of a zero cell current (iWE-CE=0). In practice, a triangular pattern might approach this condition, for common cases.

Upon nonzero iWE-CE: the (uncompensated) resistance declines dramatically as RE approaches WE, if we minimize the 'WE-RE' triangular side; also, a high(er) triangular angle of the 'WE-RE' side in respect to iWE-CE current 'line(s)', helps on approaching a quasi-equipotential surface, for (common noncomplicated, and) low iWE-CE values.

1. plus the offset of the standard electrode potential https://en.wikipedia.org/wiki/Equipotential

Thank you for additional answering.

So the position of the RE is important when the current or voltage bias is applied to the system and this is even more important when the current flowing through the system is greater. However, it may not be affected while measuring OCV when the current is not flowing.

In my experiment, just measuring OCV is fine so in this case, exceptionally, the position of RE is not important !

Dear Ioannis Samaras , what do you mean by triangular pattern(side)? I couldn't get it.

Just a common triangle with 3-vertices A,B,C (WE, RE, CE) and 3-edges (sides).

Ioannis Samaras Abdelhalim abdelnaby Zekry How to find time constant from EIS curves ? How I can optain the operating frequency from the Nyquist plot?

Dear Emad,

The electrical impedance spectroscopy is a plot the complex impedance of the electrodes or cells. At low frequency the impedance will be pure real giving the dynamic resistance of the interface in the electrode. As the frequency increases the capacitive reactive component begins to increase. At a specific frequency where the imaginary component X equals the real component R, the inverse of this angular frequency will be the time consatnt of the rate of reaction at the electrode.

So, Tau= 1/w at X=R

I made this plot for silicon solar cells. You can follow it by yourself.

Article A distributed SPICE-model of a solar cell

I would like to add here one hint that the equivalent circuit of the electrochemical electrode is exactly similar to that of the pn junction diode.

Best wishes

Dear Emad Sobhy, as Prof. Abdelhalim abdelnaby Zekry.

In more complex cases, with multiple time constants, you can, also,

1) fit your exp. EIS data using a good ECM (Equivalent Circuit Model),

or, alternatively, you can, easily, form

2) a 3D-plot, using, simply, your exp. EIS data: X->Log(Freq.), Y->Zreal, Z->Zimag.

Thank you so much professors I appreciate your help. However is the value calculation is different with respect to the supercapacitor electrode @Ioannis Samaras Abdelhalim abdelnaby Zekry

Dear Emad Sobhy ,

no, it is not different.

Could you, please, show a related[1] (3D-)plot for your (supercapacitor) electrode ?

1. Physical Interpretations of Nyquist Plots for EDLC Electrodes and Devices https://pubs.acs.org/doi/abs/10.1021/acs.jpcc.7b10582

Thank you so much professor Ioannis Samaras , I know the theory, but how to get the value mathematically, I am so sorry it is hard for me to calculate, so can you help me by apply the excel file format of my sample please (equation for imaginary capacitance and relaxation time)

Dear Emad Sobhy,

it is 'hard' for you to calculate[1], because the related electrode (material) behaves, rather, as a coating electrode, instead of a nominal capacitor electrode, since it shows a LOW capacitance value (Celectrode < 0.004 F).

So, look for an ECM (Equivalent Circuit Model) class[1] of a thin film coating electrode, instead of an ECM of a (non-)supercapacitor electrode, then it will be not so 'hard' for you to fit (-calculate).

1. By fitting your exp. EIS data using an(other) ECM (Equivalent Circuit Model) class, e.g. another list of ECM(s).

Ioannis Samaras thank you so much professor@ Ioannis Samaras for helping I will try

Positioning of the reference electrode is often not important, if you have a well conducting solution. If you have a solution with low conductivity, you might experience Ohmic drop. The Ohmic drop is the amount of potential that is lost on the way from the reference electrode to the working electrodes.

Nice Dear S Kalaiselvan

Donghoon Lee The position of the reference electrode matteres and affacts strongly results. You need to perform a symetric cell and put your reference exaxtly between working electrodes. I do not know which cell configuration you ara using. But there is specially designed cells for this kind of measurements.

Noha Sabi I'm experimenting pouch-type Li-ion cell. I have to decide which position should the reference electrode (Lithium metal) be put into the cell. I'm thinking several option.

1. position between cathode and anode.

2. position outside the cathode and anode, but close to them.

Option 1 has advantage in terms of minimum iR drop, but since during charge and discharge, salt concentration should vary so potential of reference electrode itself also vary.

Option 2 has advantage in terms of maintaining consistent environment around the reference electrode, but iR drop should be larger than Option 1.

Which option do you preferred ?

Donghoon Lee I would recommend first option 1 between anode and cathode.

In batteries, the term close is not appropriate. you need to choose a fixed position.

To have consistent results: put your reference between anode and cathode, try to fix the same position that you can repeat your experiemnts in the same conditions.