Hi Sujeevan, in any case, you cannot simply apply 0the desired voltage (e.g. +0.4 V) directly to the cell - this is wrong because the reference electrode has a certain potential that is added to the actual potential of your potential generator. If you consider the standard hydrogen electrode scale (SHE), then the potentials of the rerence electrodes are listed e.g. in wikipedia (https://en.wikipedia.org/wiki/Reference_electrode)

If you want to apply e.g. +0.4 V to your working electrode, and you are using a Ag/AgCl rereference with about +200 mV versus SHW, so you only need to feed in +0.2 V in your circuit.

See e.g.

http://chemwiki.ucdavis.edu/Core/Analytical_Chemistry/Analytical_Chemistry_2.0/11_Electrochemical_Methods/11.2%3A_Potentiometric_Methods

for practical details! Hope this helps, Dirk

Looking at your scheme, WE is connected to an i/V converter, that is, connected to virtual ground (0V). Then, if you want to see a reaction taking place at +0.2V difference potential between WE and REF, you must polarize REF at -0.2V). Not more (e.g. to correct the intrinsic reference potential), just because you will say you work at +0.2V vs. your ref electrode, then don't add or substract anything with respect your reference.

And this will be obtained by polarizing at -0.2V through I/P terminal (or any proportional value determined by ratio of resistances in between). Given no current can flow through REF terminal (infinite impedance input), REF and CE have to be mirrored (be at the same potential).

(10 years teaching the potentiostat operation at chemical instrumentation optional subject).

I am sure you don't want to apply 0.4V to ...the cell. If it is the case, you don't need a potentiostat or a 3 electrode cell.

I think  you want to polarize a WORK electrode at a constant potential E = + 0.4 V versus a REF electrode. In this case you need a variable dc source able to provide at least U=2V to be applied between WORK and AUX (and enough power, think to the maximum current to be supported) and a measuring option to monitor and control E (measured between WORK and REF). Now you may  manually increase  U until E=0.4 or solve the entire system using an electronic circuit .

What you need to solve :

- a source for U

- a control for E (to be maintained at 0.4V vs. REF during the process)

- a measuring option for I in the cell (between WORK and AUX)

About the redox process: The reference is only a reference. The electron flow is only between WORK and AUX. The oxidation and reduction are only at WORK and AUX. Usually the operator don't know the process occurring at AUX (the reaction and its potential). Thus for E=0.4 you may have very well U= 0.7 or 1.5 V.

Hi Dirk,

Many thanks for pointing me to the tutorial.  It helped me improve my understanding on the concepts of electrochemistry in great detail.  My interest is in Anodic Stripping Voltammetry. 

Regarding application of input, I was testing my circuit performing cyclic voltammetry on the standard ferrocyanide solution.  I had to apply a voltage sweep from -0.2V to +0.6V and I tried adding +0.2V to every sample applied to the electrode.   Not sure, if this is the right way to do it.  I did get positive results though.  Need to test it for anodic stripping voltammetry.

Hi Manel,

Do you mean, in case if I am using all equal resistances, say 10K, then I need not add/subtract any offset to the input? I mean if I have to give +0.2V, I have to just apply +0.2V at the input?

Hi Cornel,

Thank you for the detailed explanation.  I agree 100% with you.  Right now I am using a source that can provide up to 5V and struggling to find a way for the second step:

"a control for E (to be maintained at 0.4V vs. REF during the process)"

Right now I am having a "manual control" - eventually have to automate it.  I am trying to understand how it is done in commercially available potentiostats.

Thanks,

Sujeevan.