On Arrhenius plots in cyclic voltammetry

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Discussion Overview

The discussion revolves around the use of Arrhenius plots in cyclic voltammetry for calculating the apparent activation energy in catalytic studies involving platinum nanoparticles. Participants explore the methodology for obtaining voltammograms at various temperatures and the implications of current density measurements in this context.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant describes their experimental setup and expresses confusion about how to handle current density values for plotting log i vs. 1000/T.
  • Another participant clarifies that when calculating the slope, the units will cancel out, but does not specify how to handle the current density readings.
  • A participant references a specific paper related to their study and questions how to determine the values of I1 and I2 for the calculations.
  • It is suggested that I1 should come from the same experiment at a different temperature.
  • Participants discuss the implications of starting with different temperatures for I1, noting that this affects the sign of the log values.
  • Concerns are raised about the range of negative values observed in the log i axis in the referenced paper, with one participant questioning the expected range of values.
  • Another participant expresses uncertainty about the negative values and their interpretation, particularly in relation to the logarithmic scale.
  • A later reply indicates that impedance spectroscopy was used for activation energy calculation, which resolved the initial participant's issue.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the interpretation of current density values or the implications of negative log values. Multiple competing views remain regarding the methodology and calculations involved.

Contextual Notes

Participants express uncertainty about the definitions and relationships between current density readings and their logarithmic transformations. There are also unresolved questions about the expected range of values in the log i axis based on different temperature references.

Who May Find This Useful

Researchers and students involved in electrochemistry, particularly those studying catalytic processes and activation energy calculations in cyclic voltammetry.

hitech1
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I am doing a catalytic study on my Pt nanoparticles. My experiment set-up is a three-electrode cell with sulfuric acid as electrolyte for methanol electrooxidation reaction. Now, i want to calculate the apparent activation energy and for that I need to get the voltammograms at various temperatures (eg. between 30oC - 60oC). After that I have to plot log i(current density, mA/cm2) vs 1000/T(in K) at a certain potential (eg. 0.6V) and then from the slope i can calculate the activation energy (this is based from a paper i read). I am having some doubts as to how to settle with the values of i because I`m kind of confused with the conversions and units like if I "log" the unit what will happen to "mA/cm2" and the like. Also, should I use the actual current density reading from the CV plot as is or do i need to consider other things? anyone with experience on this area, please kindly share some insights. Thanks.
 
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If you're just looking at the slope, then you'll be calculating [itex]\log I_2-\log I_1=\log(I_2/I_1)[/itex] and the units will cancel out.

What paper are you referring to (just curious)?
 
Thank you for the reply.
This is the paper I am referring to : Electrooxidation of methanol on platinum doped polyaniline electrodes: deposition potential and temperature effect

here is the linkk :
http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6TGB-3SDCCFC-28&_user=130270&_rdoc=1&_fmt=&_orig=search&_sort=d&_docanchor=&view=c&_searchStrId=1047223999&_rerunOrigin=google&_acct=C000010799&_version=1&_urlVersion=0&_userid=130270&md5=5914e803ab0f43e6ca00f8fbe6780dda

Based from your equation, I should be getting two I`s. If I2 is the current density from the CV plot at a certain potential, where can I get the corresponding I1? Is I1 related to the double layer current or something else?
 
[itex]I_1[/itex] comes from the same experiment at a different temperature.
 
if that is the case, for example if my temperatures are 30oC, 35oC,40oC,...,60oC;
I will have I(35oC)/I(30oC), I(40oC)/I(30oC),...,I(60oC)/I(30oC)?
that being the case, there would have been no negative values on the log i - axis since an increasing temperature normally increases current density. but from the graph on the paper that i was reading, log i - axis has negative values.
 
It depends on the reference chosen - if you start with I(30°C) there are no negative values, but if you start with I(40°C) you will get them.

Not that it matters.

--
 
i see. thanks for the enlightenment.
 
by the way, if ill get negative values that way, is it supposed to be between -1 and 0 only? but from the paper, the range in the y-axis (log i) is -2.5 to -4. it doesn't seem to add up...
 
Why -1..0? That will mean current ratio between 1 and 0.1 (assuming log10).

I don't have access to the paper.

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methods
 
  • #10
I was not really sure about that. For now I will continue with the measurements and try to see whether I will arrive at a similar result.
 
  • #11
good day.
I have settled the issue, thanks for all the inputs from you guys. i used impedance spectroscopy for the activation energy calculation and it did suit for me well.
 
  • #12
Mapes said:
[itex]I_1[/itex] comes from the same experiment at a different temperature.

This is exactly my point and I1 always taken for different temperatures everytime.

Thanks!
 

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