please see my ppts

i am working in the field of electrochemistry for the past 48 years

[email protected]

It is better to use linear cyclic voltammetry.

Start at the equilibrium potential (i=0 ) and go further up or down for about 200 mV range.

You can use galvanodynamic tests butattention at the selected impressed currents.

If you contact me via my Email ([email protected] ) I can send you a paper.

If the instrument has its iR compensation you do not need to do anything more.

Thank you so much Prof.César Sequeira. i will contact you through mail.

Dear sirs. IMHO the Tafel plot should be used only in the potentiostatic mode (point by point) or in the linear sweep voltammetry with slow scan rate (few then 1 mV/s) otherwise you should obtain distorted data, especially in case of irreversible or quasi-reversible reaction.

I do agree. It is a stationary plot, therefore should be obtained either by small and slow potentials or by using very small currents to not deviate the electrode kinetics (charge transfer) from its stationary state.

Hi Munaiah Yeddala

I just started doing some nitrogen reduction electrochemical experiment in 3-electrode setup cell and I have the same issue as you had at the moment of posing this question. Would you please send me a few documents elaborating on the practical way of doing these experiments?

Best regards,

Younes

A1)Tafel plots can be obtained via CV or LSV, but this is not very correct.

A1a)Tafel plots should be obtained in a domain in which the electrode process is controlled by charge transfer, and there is a lineariyi E-log i.

A1b)I prefer to use LSV.

A2)It is not appropriate to use the galvanodynamic technique.

A3)There are lots of papers in which Tafel plots are described and obtained experimentally.

B1)It is correct to use EIS to measure the iR drop.

B2)Modern instruments compensate automatically.

B3)If you compensate for iR drop, for what to subtract?

Hi Younes Abghoui

I did record tafel plots by using LSV and Galvanodynamic technique. more or less both the techniques gave the same values.

But in galvanodynamic technique need extremely low current ( i used 1 micro Amp / Sec) sweep rates.In this X axis is Current and Y axis is potential, convert current to current density and take log for those values, and Y axis you can leave as such or you can convert to over potential by subtracting the OCP value from each value of Y axis. In order to calculate the Tafel slop, exchange current density and rate constant i have followed the methods described in the text ( I referred the book electrochemical methods fundamentals and applications by bard & faulkner. you can get E copy ( free of cost) from web. Or i can send you a copy of this, if you want. you can contact me through mail > [email protected])

Same procedure you have to follow to convert the LSV graph to tafel plot( log i vs over potential) if you do LSV, .

*******

IR correction you can do in two ways.

1.The way suggested by Prof.César Sequeira, if you have modern potentiostat it can compensate the IR value automatically.

2. If you dont have the this option in your instrument, measure the Rct value from impedance and multiple the Current ( Y axis) in CV with Rct value (V = iR). subtract those value from Potential ( X axis).

I have done both the ways, i could see no difference.got the same values.

Hi Munaiah Yeddala,

Thank you so much for your detailed respond. I do have the book at my disposal. I will be in touch with you through email

The answer of Munaiah Yeddala is very good and complements my previous comments.

@ Professor Cesar: on your answer for Munaiah's question number 2, you said that the domain must be where there is a linear relationship between E and log i. Is it possible to tell that from CV diagram? Or, do we need to plot the tafel plot for all points on the CV diagram then remove all the points where it is not linear?

rising portion of the current we can use

you plot E vs log i in the rising portion or

plot log( ip-i) vs E  for a given slow sweep rate

to calculate  the IR drop run a current step experiment on the system

Hi all,

It's not correct to measure the Rct (as mentioned by Yeddala), if EIS method is used to do IR correction. We should measure the Rs value instead of Rct. Alternatively, the uncompensated resistance can be obtained using DC techniques, for instance the current interrupt method.

There are many useful instructions provided by electrochemistry workstation manufacturers:

Gamry:

http://www.gamry.com/application-notes/instrumentation/understanding-ir-compensation/

Hi I am doing analysis on the oxygen evolution reactions. I am RDE to perform the reactions .I was little confused about how to measure the tafel plot and ir-corrected data. can any one explain me in detail about the tafel plot and the steps the way to measure the tafel plot.

Thanks in advance,

Padmini Kukkapalli.

please see my ppts

i am working in the field of electrochemistry for the past 48 years

[email protected]

Thanks for the ppts sir.....very informative and concise

Thanks,[email protected]

HI, all

i work on corrosion rebar embedded in concrete and measuring macrocell(galvanic) current between them. current in my experimental sample is about 10 up to 200 micro amp.in some paper researcher use ZRA(zero resistance ammeter)for measuring galvanic current .

my question is, can i use ordinary ammeter with 0.1 or 0.01 precision micro amper instead of ZRA?

Happy Christmas

thank you very much prof V.S Muralidharan