1. take one LSV curve at a particular rotation rate.

2. convert the current to current density and the take absolute value of the current density data.

3. take log value of abs current density data

4. plot the log value as x axis and potential as y axis. Zoom the graph in the kinetically controlled region. You will get the tafel plot. then you can straight fit the top portion of the tafel plot to get the tafel slope.

Thanks Dhrubajyoti!

I agree totally with Dhrubajyoti, but you have first to correct your net current obtained from LSV at defined rpm (normally at 900 or 1600 rpm) with the diffusion current (id) to get the kinetic current (ik)  according to the equation   ik  =  ( id * i )/ (id-i)  which finally plotted against the Potential to get the Tafel plot from which you can get the Tafel slope  and the kinetic current at specific potential to compare different catalysts.

The following book can help you to calculate Tafel slope and other kinetic parameters. Look at Chapter 7: Kinetics for corrosion:

Introduction to Corrosion Science. E. McCafferty. Springer

http://www.springer.com/us/book/9781441904546

I guess it will help you!

Thanks everyone, I think I figured it out!

So one has to plot potential or over-potential which in case of ORR must be 1.23-(V).

I always has this doubt

Dear Elli,

as mentioned above, there are several options. However , you are referring to an article which was published in nature recently of which authors have applied a tafel slope analysis by only taking into account the KINETIC CURRENT vs appl E (or overV, n)  I consider that this is your question:

1 - define your potential window (keep it wide enough to have a nice saturation current)

2- use a slow scan rate 5mVs-1 is usually fine but if your catalyst is stable and sat current is reached earlier than 1mVs-1 is surely better

3- increase the scan rates, as in the article and try to reach around 2500rpm

4- analyze your data by Koutechy-Levich method and find 1/jk which is the intercept of the slope for every potential value that you have used in your slope analysis

5- collect that data in step4 as; potential vs jk in V (or mV) vs mAcm-2 (or mA or A). Take abs(jk) and log(abs(jk))

6- If potential goes to Y-axis and log(abs(jk)) goes to X-axis, only then you may see one or two region and do the linear regression. the slope would be = mV/dec

7- Please do not forget to perform an EIS , impedance, to substract the ohmic drop from every single experiment file. (E-iR)

If you question was not this. then just perform method 1-4 of Mr. Dhrubajyoti Bhattacharjya, which is faster and not wrong but this J VALUE would (theoretically) include also the diffusion, polarization current...

As you see, the rotation would define you a better working j-V window...

Best of luck.

E.

i too have doubt in calculating tafel slope..

 how to find values in mV/dec

Narendran: I think if you plot potential on Y axis and log (current density) on X the slope of the linear zone will be mV/decade (do not forget the potential is V so fix the unit after you found the slope) 

I think Erdem means the potential that taken for calculation the slope of K-L plot and even if this right that means this potenial lies in the region of diffusion controlled current  but mainly the Tafel slope lies in the region of mixed diffuison and kinetics current. So, I consider that the follwing way is the best way to get the tafel plot and therefore all the other related parameters. First , the correction of the total current ( the net current ) to the diffusion controlled current ( by taking the diffusion current at one point potential , that lies in the midle of the diffusion current region ) to calculate the kinetic current (ik) . Then this ik current is plotted gainst the potenial ( which should be selected to be in the mixed diffuion -kinetic controlled current poteial, that is  0.7 

@Erdem Irtem,  could you please clearfiy the point 4 in your above comment .

4- analyze your data by Koutechy-Levich method and find 1/jk which is the intercept of the slope for every potential value that you have used in your slope analysis.

Thanks

Dear @Abu Bakr Nassr,

Thanks for the input. I do not disagree.

I compute the formula to all the potential range in every 50mV since its just one more click in say, excel or origin. (i.e. 0.9, 0.85, 0.8 and so on) As you described, when you plot the jk vs n (or E) you see clearly which region you need to have your linear regression... But still, yes, this region should be close to on-set potential. 

IUPAC Tech Report -  Pure Appl. Chem. 2014; 86(2): 245–258

pg. 247 // "it is apparent that the linear dependence of the anodic or the cathodic current density upon the applied potential E is only attained when E is sufficiently apart from the equilibrium potential Eeq, i.e., when the absolute value of η is  > > RT/(nF). When this condition is fulfilled, the extrapolation of the resulting Tafel plot to the η  =  0 axis yields the natural logarithm of the exchange current density" and which in this case, 6.419mV , (8.314*298 / 4 x 96485).

You see, when you compute the calculation for the full potential range of the test, it is relatively easier to observe the linear region. -and thats just my way of computing.

dear abu bakr nassr

4- please check out: Electroanalysis 2002, 14, No. 3

quote "Hence, for cathodic reactions governed by mixed transport-kinetic control, plots of 1/Icvs. 1/w1/2for constant values of kh,i.e., fixed h, are predicted to generate straight lines havingslopes proportional to 1/n and intercepts proportional to 1/kh. It is important to observe that the slopes of these plots areindependent of applied overpotential."

is that possible to use the LSV data to get tafel slope because tafel plot is overpotential vs Logj suppose if I have scanned at different applied voltage and rate which data I will use for plotting

Disha Soni I think your are mixing ORR with OER, the potential 1.23 V is standard theoretically calculated for OER. While we use -0.2 V or near to that as an onset potential to check the activity for ORR. please reply if i'm wrong. Thank you.

1. take one LSV curve at a particular rotation rate.

2. convert the current to current density and the take absolute value of the current density data.

3. take log value of abs current density data

4. plot the log value as x axis and potential as y axis. Zoom the graph in the kinetically controlled region. You will get the tafel plot. then you can straight fit the top portion of the tafel plot to get the tafel slope.

Thanks@ Bhattacharjya

Take any LSV plot in single rotation rate, make the current into current density along with log value and plot it and fit it. YOu will get exact data....

I thing above answer is well understood particularly Dr Dhrubajyoti Bhattacharjya and other member answers. best wish

How to convert potential vs RHE into overpotential vs RHE?

directly by using EC-Lab demo program