Dear All,

My Procedures:

I am performing 2 EIS experiments as follows: I used a 3 electrode cell (CE, RE, WE, S electrodes) with a 0.05M Vanadium (4) in 3M H2SO4 electrolyte. The frequency ranged from 100,000 to 0.01 Hz, and an amplitude of 10mV. I use Autolab NOVA software and instrumentation.

Experiment 1: WE is Carbon Paper

Experiment 2: WE is CNTs

After obtaining the EIS results, I performed fitting to quantify Rct and Cdl. My eq circuit was a randles circuit which included a resistor, and a (resistor, warburg term, and a constant phase element in parallel) as in FIGURE 5.

My Analysis of Results:

Experiment 1:

Fitting worked well for experiment 1 (carbon paper), which included a more apparent and defined semi-circle arch. The software automatically snapped to the experimental results as soon as I entered the equivalent circuit fit components. (SEE FIGURE 1)

Experiment 2:

However, fitting didn’t work well for experiment 2 (CNTs), which included a less defined semi circle arch. The software didn’t snap automatically to my experimental results, and showed me very wrong results. (SEE FIGURE 2)

So, I tried to enter some values manually (for Rs and Rct which I determined graphically from the EIS results), and the fit improved, however, I am not sure if this would be accurate, as the Warburg term is still well off. (SEE FIGURE 3) I couldn’t get a better fit of my EIS results than this. Please note I tried fitting with 3 different softwares (EISAnalyser, Nova Autolab, Zfit)

Please (SEE FIGURE 4) for an example of literature results on similar WE material with similar experimental setup. Taken from: http://publicationslist.org/data/jochen.friedl/ref-8/FRIEDL%20Electron%20Transfer%20Kinetics%20of%20the%20VO2+-VO2+%20reaction%20on%20MWCNTs.pdf

I used Randles equivilant circuit for all experiment (SEE FIG. 5).

My question is:

How can I get a more accurate fitting of my EIS results? What am I doing wrong please?

Your help and input is very much appreciated.

Thank you very much for your comments,

Ibrahim

http://publicationslist.org/data/jochen.friedl/ref-8/FRIEDL%20Electron%20Transfer%20Kinetics%20of%20the%20VO2+-VO2+%20reaction%20on%20MWCNTs.pdf

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