The Tafel slope simply tells you how much you have to increase the overpotential to increase the reaction rate by a factor ten. This will be determined by the magnitude of the change in the activation energy for a given increase in overpotential (when you change your potential 1 V, the Gibbs energy of the process will change by 1 eV per electron transferred, but the activation energy will only change by a fraction of this, and this fraction determines the Tafel slope). In a reaction involving only one step with one electron transfer, the Tafel slope will be determined by the symmetry factor, which is usually 0.5 (corresponding to a Tafel slope of 120 mV). In a more complex reaction involving several steps and several electron transfers, the Tafel slope will be determined by the rate-determining step and by the number and nature (i.e., involving an electron transfer or not) of the preceding steps. So, essentially, from the Tafel slope you can deduce whether your rate-determining step involves an electron transfer or not, as well as the number of electrochemical (involving an electron transfer) and chemical (not involving an electron transfer) steps that precede it. If you propose a reaction mechanism, you can calculate what the corresponding Tafel slope should be and, if it does not coincide with the experimental one, the mechanism cannot be correct.

Have a look here :

http://www.doitpoms.ac.uk/tlplib/aqueous_corrosion/tafel.php

Why not to look at the textbooks?

This is an Open question. From Tafel slope you can get much information e.g. elucidation of reaction mechanism, RDS,...etc. I recommend to look at the basic articles and text books for this point.

use of Tafel slopes to mention a few

1. to know the mechanism of electrode reactions

2. to know the role of inhibitors

3. to find out electro catalyts

4. role of coatings

5. deeper in sight like activation energy and other energy aspects -

Agree with answer from Prof. Muralidharan but also with the other answers: the question is found in any textbook of  electrochemistry.

let me explain

 The Tafel slope will give you  Alpha which corresponds to how much of the applied voltage influenced the forward reaction Alpha is used for multistep electron process and the word symmetry factor for a single electron transfer reaction

see my ppt

The Tafel slope simply tells you how much you have to increase the overpotential to increase the reaction rate by a factor ten. This will be determined by the magnitude of the change in the activation energy for a given increase in overpotential (when you change your potential 1 V, the Gibbs energy of the process will change by 1 eV per electron transferred, but the activation energy will only change by a fraction of this, and this fraction determines the Tafel slope). In a reaction involving only one step with one electron transfer, the Tafel slope will be determined by the symmetry factor, which is usually 0.5 (corresponding to a Tafel slope of 120 mV). In a more complex reaction involving several steps and several electron transfers, the Tafel slope will be determined by the rate-determining step and by the number and nature (i.e., involving an electron transfer or not) of the preceding steps. So, essentially, from the Tafel slope you can deduce whether your rate-determining step involves an electron transfer or not, as well as the number of electrochemical (involving an electron transfer) and chemical (not involving an electron transfer) steps that precede it. If you propose a reaction mechanism, you can calculate what the corresponding Tafel slope should be and, if it does not coincide with the experimental one, the mechanism cannot be correct.

ok

OK. Right and concise explanation

Thank u Dr.Angel Cuesta

of course I agree with prof Muralidharan. I would like to add that applied to gas diffusion electrodes it also gives insight on when gas difuusion limitations set in. (deviation from linearity)

See bockris and s Srinivasan book Electrocatalysis

of course, but I think it was worth mentioning

See book by Gileadi Srinivasan jom bockris. A book on oxygen electrode is also there.

respected researcher can some one send some introduction about the Tafel plots?

I have a similar problem. I study ethanol electrooxidation on Pd thin film electrode. As the reaction involves many steps and pathways, the researchers do not agree on the rate limiting step, which might be the dissociative adsorption of ethanol or the removal of the strongly adsorbed carbonaceous species.

I started research in Electrochem at the age 0f 20. Still I do. when I started there are no books only in 1971 Vetter book in German came. My models of diffusion impedance and passivation and pitting are most popular I am 70 as USA man

Well. The Tafel slope is correspondent to the stable steady-state, which is easy to get and to maintain.

The synthesis or analysis in this case is the most efficient

Tafel slope is sweep rate dependent.E-log current densities can be plotted at all sweep rates.We also the system to reach equilibrium/ steady value of OCP and we do polarization

See papers on accelerated Tafel slope measurements

Tafel slop give the information about kinetics. Kinetics for water oxidation with change in tafel slop value shown in figure.

Basically its mechanism works by varying the potential from low to high over which the effect of current density is seen. Its range is generally very low than that of potentiodynamic curves because here the passivation region and transpassive regions are avoid. A lot of information can be obtain from Tafel slope,

1. Corrosion rate

2. Corrosion potential

3. Corrosion current density

4. Polarization resistance (at 10mV near to Ecorr from slope)

5. Cathodic and anodic behavior of the system

is it possible to define I-V curve by using Tafel techniques ?

@ prof V.S Muralidharan : How do Tafel slopes help to obtain information about coating performance, the role of inhibitors and activation energy ? I would like published material(s) on these information. Thanks

please see

My papers on Inhibitors and metallic coatings. inhibitors can change reaction path way and Tafel slopes will reveal this. Coatings it is only surface coverage and adsorption isotherm will change.

Please carry out experiments in sweep rates 5 to 10 mV/ sec for comparison. Do not use faster sweep rates. best of luck

From Philedelphia

Respected Prof V.S.Muralidharan, we find logrithmic scale of current density vs overpotential. Before that potential vs current density will be plotted. To my knowledge, the starting potential for hydrogen evolution is overpotential. There will be only one starting point. Then how come overpotential vs log j is plotted. Please clarify...

overpotential = E- E corr; E corr is the steady value before the start of the experiment. Now you can plot

regarding HER, the potential current start increasing is the decomposition potential. Over potential now is E- E decomposition potential. plot applied current vs overpotential. I think I understood you.

How to draw tafel plot and find the overpotential range from LSV curve of HER or OER with reference to saturated calomel electrode.@ prof V.S Muralidharan

Tafel slope tells how responsive the current is to the applied voltage. A high Tafel slope shows that the bandgap energy is high which leads to a high overpotential due to the large amount of energy required to achieve activity and vice versa. Tafel slope also gives information about the rate-determining step of the electrochemical reaction. In summary, the Tafel slope explains the amount of overpotential required to achieve an activity.

Victor Charles Your answer is interesting, please could you tell me more?... For example, Do you have any article, where I can read your explanations for high Tafel slope?? Because I'm looking an articles about thi but I don't found it. Thanks!

The Butler-Volmer equation can be written as :

log I= log I_o - (alpha . n.F/2.3 RT) x Overpotential.

On rearranging we have:

Overpotential = Constant x log(I/I_o) , where this constant (alpha . n .F/2.3 R T)is the Tafel slope.

The slope depends on alpha which is the transfer coefficient. This is a measure of the symmetry of the energy barrier in a standard free energy and reaction coordinate diagram indicating the reaction mechanism. Hence, the change in slope basically indicates a change in reaction mechanism.

The tafel slope shows how efficiently an electrode can produce current in response to change in applied potential. So if the slope (mV/decade) is lower means less overpotential is required to get high current.

So for ORR and HOR you would want a catalyst that gives higher current densities for these reactions at low overpotential i.e lower Tafel slope (when plotted as the 2nd equation).