How to Perform EIS Circuit Fitting of a Proton-Exchange Membrane (PEM) Water Electrolyzer

[@riya6688]

Extremely helpful video, with minute details of the electrochemical processes going on in a cell. Thanks.

[@Pineresearch]

We are glad you liked it! Stay tuned for more!

[@fazilaashraf7860]

Thank you so much for this helpful video.

[@Pineresearch]

We are very glad that you liked it! Stay tuned for more, especially on EIS!

[@GeorgeChristiansen-k3l]

Interesting video and very helpful in terms of rearranging the order of the semicircles so that the lower frequency semicircle corresponds to the anode reaction! I have a question and perhaps a comment on the fit of the high frequency region. In the final fit you provided, the high frequency intercept (ohmic resistance, R1) shrinks down to 0.001 ohm, which seems far too low for such a system. I know that in this example you were more interested in fitting the anode behavior, but R1 is an important value to assessing losses in electrolyzer systems. Is it possible that the proper fit for the cathode semicircle is actually to the right of where you placed it? By excluding a few more of the high frequency points, it looks like there might be another small semicircle in the real 13-16 mOhm range. This would give a realistic R1, a small cathode R2, a large anode R3, and would maintain the expected frequency order of R2 vs R3. Thanks!

[@Pineresearch]

Hi George, thanks for your comment. I can address your comment in a couple ways. In short, I think you may absolutely be correct in your analysis and assessment. To be fair, as I think I mentioned in this webinar, the EIS data is not mine, so certainly my analysis cannot be considered the final say, so to speak. I was trying to illustrate some possibilities based on data I received from a researcher and not my own data from which I had prior and intimate knowledge. That being said, if you even see one of the initial fits I did with two Randles elements around the 14:00 mark, while I continued to go with some Warburg models after that, you might also consider this initial fit to be something like what you've described and could be accurate too. The R1 is in the 13 mΩ range, and there are 2 semicircles. Perhaps another model could even be tried with 3 semicircles in this vein, taking into account that slight first semicircle as the cathode, as you suggest. There are a number of ways this could be interpreted, and I think it's tricky to exactly determine how to analyze (or whether to not analyze) that high frequency portion. But you do make an excellent point that this R1 being around 13 mΩ or so probably makes a little more sense than being effectively negligible at something like

[@joseRodriguez-zi9cy]

Hello, Good morning, I appreciate the knowledge shared on this channel. Studying about the EIS technique I have a doubt that I have not yet been able to solve clearly, the question is What does it mean that a material has its phase angle at lower or higher frequencies than another material? In which of these cases would there be a higher resistance to corrosion?

[@Pineresearch]

Hello Jose, thanks for your question. First of all, I want to clarify that when you write "...material has its phase angle..." I assume you are referring to a kind of graphical dip in the phase angle on the Bode plot that is observed for features that are often fitted with a Randles circuit. If this is the case, then the simplest answer I can give you (neglecting all other processes that might be occurring on your materials of interest) is that the phase angle peak is related to the capacitance and the time constant. To elaborate just a little bit: if the capacitive effects being observed are very small, it means it can be charged/discharged very rapidly, meaning the peak will manifest at higher frequencies. Conversely, if the capacitive effects are very large, it will take longer, or be slower, for the charge/discharge phenomena to occur, meaning the phase peak will appear at lower frequencies. All of the above is also neglecting the resistance, which can also have an effect on where the phase angle peak appears; and on the time constant, which is a pseudo-measurement of how long this charge/discharge process takes. Finally, to address your question about corrosion resistance: the position of the peak *may* give insight into the corrosion resistance, but not necessarily. For example, following the previous discussion on capacitance: if the phase angle peak is at high frequency, it likely implies lower capacitance and a somewhat smaller time constant, which could also imply a smaller resistance. But it is not guaranteed that is the case. You can have a large resistance even with a small time constant if the capacitance is just extremely small. Conversely, a phase angle peak at low frequency might imply higher capacitance and a larger time constant, which could imply a larger resistance; but again, this is not guaranteed because you could still have a small resistance even with a large time constant. This is because the time constant is equal to R times C, so a proper circuit fitting analysis would likely be required to reveal whether your material is exhibiting high or low corrosion resistance.

[@LuizEnger]

In a three-electrodes electrochemical cell in which I do not have a diffusion layer neither a redox reaction, I would only consider the charge transfer resistance, double layer capacitance and solution resistance? Maybe swap the capacitor for a CPE? Thanks!

[@Pineresearch]

Hi Luiz, thanks for watching and for the comment! You make a good point: in general, I do recommend using a CPE instead of a capacitor for fitting because it can account for non-idealities, surface inhomogeneities, and (for lack of a more elegant description) the fact that nothing - not even an actual capacitor - behaves like a perfect capacitor. The other thing I will mention, without seeing your specific data, of course, is that without a redox reaction, I wonder whether you have any charge transfer resistance at all? Usually, charge transfer resistance refers to just that: charge transfer. Without any Faradaic processes or redox reactions, there may be no transfer of charge at all. In any case, apologies for the lengthy response, but I hope it may be helpful. If you wish to continue this discussion, please feel free to email me directly at [e-mail].

[@syedawais4303]

Need your email address

[@mozhy5013]

I am a total beginer in this area, so my question might be a very naive one. I would like to measure the throuh-plane electric conductivity of an anode coated membrane (half-cell). we made a very simplistic cell using plates of aluminum and plastic. simplistically we measure EIS with applying pressure on the cell about 300-1400 psi. However, the Nyquist plot is very strange and not even close to a semi-circle. Is EIS a good choice in for this question? what I am missing here?

[@Pineresearch]

To be honest, I am not sure how best to answer your question without knowing (or seeing) the physical cell setup you have constructed and are using. Almost certainly EIS can be used for measuring conductivity, but your results might have something to do with your cell setup and the data are convoluted as a result. Also, I think it is not guaranteed you should see a semicircle, depending on what your EIS parameters are. In general here, there are a lot of additional details that would be needed to be able to effectively pass judgment on your situation.

[@sreemathim9771]

Can you explain how to get correct semicircle for membrane eis study

[@Pineresearch]

I am not sure how to succinctly answer your question. Are you trying to figure out how to make proper experimental measurements? How to construct a fuel cell or electrolyzer? How to perform circuit fitting? There are a lot of possible things you might be asking and I do not know what you are asking about specifically. If you want to elaborate on your question, I encourage you to join our weekly livestream on Fridays at 1pm EST and you can ask questions, then we will try to answer them live for you.

[@tomtom-fv7op]

There is water in contact with the cathode? It is only H2 gas in the cathodic side or some water is use for membrane or H2 transportation? Thanks

[@Pineresearch]

Great question. Yes, there is almost certainly water vapor on both sides of a PEM fuel cell or electrolyzer, and the main reason is that the membrane (most commonly Nafion) only functions and shuttles protons effectively when humidified. Typically, you send humidified streams (often 90% humidity or higher) across both sides to ensure the membrane stays wet. So there is usually an implicit inclusion of H2O that isn't always depicted in these kinds of diagrams or animations of fuel cells and electrolyzers.

[@tomtom-fv7op]

@@Pineresearch Ok ! Thanks !

[@marsszeera4064]

May i know from which website i can refer to download the AfterMatch software that you used in this video

[@Pineresearch]

Absolutely! pineresearch.com/shop/kb/knowledge-category/downloads/

[@SixTough]

Why is the cathode the easy part in this case?

[@Pineresearch]

The cathode reaction in a PEM Electrolyzer (much like the analogous anode reaction in a PEM Fuel Cell) is considered easy or facile in comparison to the anode reaction (cathode reaction in the PEM Fuel Cell - again, a Fuel Cell is essentially exactly opposite to an Electrolyzer in this regard). This is mainly due to the sluggish kinetics and relatively large overpotentials required to make the oxygen reduction reaction (ORR) take place. In a Fuel Cell, this ORR happens at the cathode and is a reduction reaction (backwards from what I showed in this video). In the Electrolyzer, it is the same reaction but it happens in reverse, as an oxidation, at the anode (as you see in the video starting at around 3:40). In both cases, it suffers from poor kinetics and is often represented by a multi-step mechanism. It is also typically the most heavily-studied half reaction and researched side of a Fuel Cell or Electrolyzer because it is the one, for lack of a more elegant phrase, holding everything back. In comparison, the cathode in the Electrolyzer performs a simple combination reaction to form hydrogen gas, and this reaction is fast (i.e., has quick kinetics, or at the very least quick compared to the ORR). In a way, due to the kinetics mismatch I just described, an Electrolyzer cathode is essentially in a constant waiting state for the anode to finish its half-reaction. As soon as it does, the protons that eventually migrate through the membrane reach the catalyst and the hydrogen reaction occurs almost instantaneously with no delay. (That explanation is not perfectly mechanistically accurate to be honest, but just a mental representation to try to help you understand the different kinetics of each half-reaction) Finally, here are a couple literature references that discuss some of these concepts in a bit more detail if you're interested: doi.org/10.1016/j.electacta.2018.05.150 and doi.org/10.1021/cs3000864" Redirecting doi.org

[@SixTough]

@@Pineresearch thank you so much, this now makes sense. The diffusion of protons/hydronium is extremely rapid, compared to everything else. I suppose the voltage on the anode is also typically unknown in a three electrode system