Over the past couple of weeks I have been performing linear sweep voltammetry experiments to obtain Tafel plots. I have been using a scan rate of 0.0002 V/sec, and I am finding that I am getting very good looking Tafel plots (perfectly symmetric around the y-axis, linear regions at high positive and high negative overpotentials).
However, I am wary of this method, as another way I was taught was conditioning the electrode at OCV for a few minutes, applying an over potential starting at ~0.12 V until a steady state current is obtained, conditioning again, increasing over potential by 5 mV, conditioning, repeat. I feel like using the LSV method does not give the electrode time to condition, despite the fact that my results appear to make sense. Additionally when I do the later method, sometimes the applied over potential does not lead to a steady state potential even after holding the over potential for 10+ minutes, and so it appears like LSV is the better of the two methods.
Has anyone else made Tafel plots before and can confirm if the LSV method is appropriate for obtaining valid Tafel plots and therefore valid exchange current densities and transfer coefficients?
Thanks for any help.
Hello Alec,
I would be concerned with LVS. When you don't find a steady state current at a certain overpotential, how can you think that a transient sweep gives you the right potential-current relationship?
If it is a valid approach both methods should give the same value. You can just take the initial current value that you measure and compare it to the LSV.
But generally you should trust your supervisor more than a stranger from the internet who has obvisouly time to answer these questions ;-)
Generally, LSV is a good method to obtain Taffel plots.
However, I don't know how you consider the steady state is achieved. In my research group they obtain the OCV after hours of electrode conditioning.
I also suggest you to look for previous reports similar to your work.
Hello Alexander,
I'd prefer using chronoamperometry for a Tafel plot. There is a problem using LSV for that use: depending on your potentiostat hardware, the linear potential sweeping isn't linear at all. For example, some famous potentiostats brands uses a staircase for CV and LSV, and you can't control the relaxation time for a steady state current. And both Dominik and Jordi pointed out the consequence: how is possible to achieve the steady state current for a Tafel plot?
Chronoamperometry is better because you can see the steday state current, for example. But hypothetically a true linear sweeping potentiostat could overcome this limitation of staircase voltammetry.
Dear Alexander,
in a 3-steps proposal : you might
1) start with a LSV, using a "wide" V-window to find where is about the potential(s) of interest.
2) Then, apply some next LSV, with slower V-rates, using a smaller V-window (smaller overpotentials for your Tafel plot).
3) Finally, you might apply an optional chronoamperometry step, using only very small overpotentials in order to verify the potential from the step 2.
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