What is iR drop in Electrochemistry
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- Опубликовано: 12 июл 2024
- Hey Folks in this video we will be talking about what is iR drop, sometimes called Ohmic drop or voltage drop. iR drop tends to cause problems in electrochemistry experiments, most noticeably cyclic voltammetry, and is the result of solution resistance between the working and reference electrode.
How a Potentiostat Works
• What is a potentiostat...
How to Measure the Solution Resistance
• How to measure solutio...
Time Stamps
Intro - 00:00
What is iR drop - 01:10
How to Fix iR drop - 05:09
How a Potentiostat compensates for iR drop - 06:32
Why large peak splitting in CV with iR drop - 10:13
You need the solution resistance to use iR compensation - 11:50 
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People have requested this topic in webinars. Pine Research promised. And here it is! Thank you very much for another great video.
So happy to hear that!
Easy to understand Description about iR drop... Thanks from South Korea😊
You're welcome 😊
You nailed the explanation. Great. Keep making such videos.
Thanks a ton
This is awesome! Thanks a lot!
Glad you like it!
Helpful video, thank you! This reminds me of some issues I encountered before:
1. I was taught that the Luggin capillary is helpful to getting RE closer to point B.
2. Due to the iR drop, the ΔV between anodic and cathodic peaks will become larger than it should be, but this won't affect the E1/2, right? Because iR drop affect anodic and cathodic process with the same extent.
3. Theoretically, in three-electrode setup the solution is in a great excess so it would be ok for the iR compensation to just tune with the changing current. I think it would be complicated if the resistance of the solution can also change in some special cases (like dual ion batteries, where the conductivity of the electrolyte can change).
Yes, you are correct. The luggin capillary does help get the reference electrode closer to the working electrode (point B). Now, even though the peak splitting between the anodic and cathodic waves should be equal and opposite from E1/2, I think it practice it could be off a bit. I think you'll still be pretty close to the E1/2, but generally speaking, its best to try to remove the iR drop. Additionally, your redox reaction might have slow kinetics that would be convoluted in the iR drop. Your last point is also correct, we assume one R value for a 3 electrode system to use when applying iR compensation to your echem experiments. Thanks for watching!
I aspire to be able to explain chemistry as well as you do :D
Thank you, that is very kind to say!
Thank you very much for the explanation, it helped me a lot.
I have a question, if I want to recover Lithium from a leachate, what potentials should I use to obtain the appropriate curve with the use of the potentiostat?
Very grateful for your response.
Thanks for your question. Unfortunately, I don't have very much experience with lithium leaching experiments, and it also seems like your question is somewhat broad. For instance, it is not clear what "appropriate curve" means. As well, have you looked into the scientific literature to see what lithium leaching curves and experiments other researchers have done? Typically this is a good place to start when finding the parameters to apply with your research.
@@Pineresearch thank you so much. greetings.
Hello.
Thank you very much for your video. It is very useful for me.
I'm starting to do corrosion measurements, and also LPR and Tafel plots.
How do you think, If I use the solution of 3 g/l NaCl, do I need to measure solution resistance, or use the IR compensation LPR sweep on my GillAc potentiostat? Or it will be enough to use only LPR sweep?
And one more question - do I need to use Luggin capilary for Ag/AgCl reference electrode, or I can place ref electrode directly into the solution, close to the working electrode?
For most LPR experiments, it is not necessary to perform iR compensation. You may wish to perform a high frequency EIS test to determine the iR drop of your solution mainly as a way to convince yourself everything is set up properly. I would expect with a sufficiently high enough concentration brine solution you should expect the uncompensated resistance to be less than 100 Ω or so, provided there are no other detrimental effects present.
Furthermore, the reason iR compensation is not usually necessary for LPR is because LPR is a very gentle, non-destructive technique where the potential is only shifted by a few mV from OCP, which does not typically induce much of a current response, meaning the effect of iR drop is likely quite minimal.
Regarding a Luggin capillary, this is a fairly common practice in corrosion electrochemistry, and indeed in electrochemistry in general as well. Similarly to my comment above about having a high enough brine concentration largely negating the impact of uncompensated resistance, in many cases I think if you can get the reference electrode relatively close to the working electrode, a Luggin capillary may not be necessary. In some cases, however, it may help reduce the iR drop between working and reference electrode, particularly if using non-aqueous electrolyte or low salt concentrations. With corrosion, though, sometimes during long term LPR experiments bubbles can occasionally form (especially if using temperatures above room temperature), and if using a Luggin capillary you will run the risk of the bubble blocking the capillary. If that happens, the electrochemistry results will likely be disastrous. For that reason, sometimes corrosion researchers prefer to not use the Luggin capillary. Your specific testing protocol may vary though, and I recommend trying both arrangements to see which works better for you.
@@Pineresearch Thank you very much for such extended answer.
How to do iR compensation in pinewave driver 200 in linear sweep voltametry
Under the advanced tab for LSV you should see an option for iR compensation. You can then manually adjust the amount of iR compensation. I hope this is helpful.
I am new to all these things, can you help me understand one thing. when you showed the CV curve of 59 mV potential difference, that is meant for one electron transfer right? Does it mean that we should always get the potential difference within 59 mV for every CV be it for any working electrode? I apologize in advanced if my questions are trivial. Thank you guys.
Hello Matbiang, not a problem, and it isn't a trivial question. In short, yes. If you have a fast homogeneous one electron transfer process at any working electrode the difference between the anodic and cathodic peaks in your CV should be 59 mV. FYI, I'm hoping to have another ask us anything livestream tomorrow to answer questions live.
@@Pineresearch can't wait for tomorrow.. Thank you.. Just one follow up questions. I saw in many research article the potential difference is always more than 59mV some even 120mV.. That is why it is confusing.. Can you please take some time tommorow, to address this in detail if possible.. Thank you..
@@MatbiangShadap Yeah we can definitely talk about it later today during the livestream. I can give you a few reasons why the peak difference is greater than 59 mV
Thanks for the video. I have a question regarding the equivalent circuit of the system. You have assumed a series association of the counter electrode, the reference electrode and the working electrode (Counter-Rcomp-Reference-Ru-[(RctCdl)Working)]. In this way the working electrode has no direct connection with the counter electrode, however, in the real system the working and the counter also have a connection. This connection would be given by a resistance in parallel to Rcomp and Ru and would join the Working electrode to the point that you have called B (point prior to [(RctCdl)Working]). In this way, could the potential at point B be modified by the potential of the counter, preventing the potential experienced by the working from not being the one that we impose in the reference?
By the way, you do a great job teaching electrochemistry and you are a great communicator!
Thank you!
That is correct. There is a resistance directly between the counter and the working electrode that isn't through the reference electrode. However, all measurements at the working electrode are measured and applied with respect to the reference electrode. So the counter electrode potential should not affect the potential at point B. The counter electrode will always drive current to the working electrode, but the measured and applied potential is only based on the reference electrode. Good question.
@@Pineresearch Thanks for your response from a year ago! I've been revisiting the video and comments, and I have a new question about your explanation.
We agreed that there is a resistance directly between the counter and working electrodes, and that the counter electrode will drive current to the working electrode and the measured and applied potential is only based on the reference electrode.
Then, how do we determine the exact current flowing between the reference and working electrodes to calculate the ohmic drop (iR)? The current flowing through RE-WE resistance is only a part of the total current detected at the WE, since some of the current flows from CE-WE resistance. For example, in a system where the CE electrode is closer to the WE than the RE, the CE-WE resistance would be lower than the RE-WE resistance. Therefore, most of the current would flow through the CE-WE, and the ohmic drop in the RE-WE would be negligible due to low current is flowing through this resistance?
On the other hand, I've seen people mention that the Luggin capillary brings the RE closer to the WE. However, the Luggin capillary is long, and the distance between the WE and the RE is usually larger than the distance between the WE and the CE. I understood the Luggin capillary as a way to avoid contaminating the RE or the working solution.
Greetings and thanks in advance, I promise not to bother you anymore.😉
@@samuelcalabuigmompo That's a good question. So my colleague Neil and I will host an Ask us anything about electrochemistry livestream (episode #46) and we'll talk about this question. I think it will require some detail. Also, I believe I made a mistake earlier when I said that there is a separate resistance between the counter and working electrode, I actually don't necessarily think that is true and I'll talk more about that later.
would you please tell us about what is overflow when we measure the the CV?
Overflow or sometimes called overload, is when the current measured by the potentiostat is above the current range selected. Your potentiostat has different current ranges to help you measure the most accurate data for the current you are measuring. However, you could select a current range that is too small for the current you are measuring and you get an overflow/overload error. I hope this was helpful.
@@Pineresearch wow thanks a lot for your reply...The way you explain is so easy and understandable..😃
Thanks for the beneficial video, I have a question, if we are working on screen printed electrodes, considering the smaller surface area and close distance of electrodes, is this still important? I prepared a glucose sensor of first generation and i noticed when the glu concentration is higher, the response is not as consistent and accurate as lower concentrations and I am sure it is not enzyme saturation, could it be due to ohmic drop? how can I fix it?
Great question. I'm guessing that this isn't an iR compensation issue, but rather a chemistry issue. It's nice to have a linear calibration curve for your sensor, but it sounds like the fit breaks down at high concentrations. I think I would need to know a little more about your system and what kind of experiments you are running. For example, if you are using cyclic voltammetry to measure the current for your glucose sensor there are a bunch of experimental parameters you might choose to change how the concentration of glucose is measured. There are also other techniques like chronoamperometry which are better for quantitative measurements that might give you more consistent results across a wider concentration range. These are some ideas, I hope this is helpful.
@@Pineresearch thanks alot
@@Pineresearch Thanks again, I noticed I didn't read your reply completely. Here is some information: after preparing functionalized electrodes, I do a CV with and without Glucose, I get the peak potential for responding to the glucose, I do the amperometry and measure the current around that peak potential. I tried to do chronoamperomety, I read that the potential step should be set from a potential of no current to the highest current. I assumed the second is the peak potential of my CV, but finding a potential for no current didn't work. I couldn't find it. for example in case of second generation sensors, using Fe3+(we measure Fe2+ oxidation current), Peak potential is around 400 mV, for no current potential, if I lower beyond the commence of oxidation to make sure I don't interfere the produced fe2+ concentration by glucose, there will be reduction Of Fe3+ to Fe2+ which interferes with Fe2+ produced by Glucose, I got totally confused and gave up using chronoamperometry. again I appreciate your attention, Thanks
@@amenehmohammadnezhad7889 Thank you for the additional information. I think I know what your are talking about, but would probably need some additional clarification. It sounds like you are using a surface bound Fe3+ catalyst for glucose detection. Specifically, glucose oxidizes converting Fe3+ to Fe2+. Chronoamperometry isn't working because you can't find a potential step where there is little to no current. I presume that the CV you get with glucose has a reasonably large background current because it contains oxidation current of Fe2+ going to Fe3+. I think my question to you, would be to try double potential step chronoamperometry. You apply a forward step followed by the reverse step and look at the difference in current. You might be able to get away with potentials where you have some baseline current, because it would get subtracted from the difference in the chronoamperograms. This might be a bit complicated to describe via the comment section, but we do hold livestream Q&A's on Fridays at 1 pm EST. If you are able to make it you can ask use questions live and we can use other tools to describe the process.
@@Pineresearch I really appreciate your patience and consideration, thanks for comprehensive response. I could somehow get what you meant and will definitely take part if I can since I am scheduled that time every week and I will need arrangements.
Is this live is hold every Friday or you will post it on social media?
Again thanks alot.
I didnt see you mentioning a Luggin Capillary tube to minimize IR drop
Correct. Technically the Luggin Capillary is adjusting the position of the reference and working electrode, so it's somewhat implied as a method.
What is the hydrodynamic voltammetry
Hydrodynamic voltammetry is a form of voltammetry where the movement of solution is controlled. For example, performing voltammetry at a rotating disk electrode will produce a different response than if the electrode was stationary and the solution wasn't moving. Hydrodynamic voltammetry is a whole field in and of itself. I hope this was helpful.
Hello, guys. A question.
If the internal resistance of the battery is caused by reversible processes, where no heat is generated or only part of the donated energy is converted into heat, then internal resistance should be complex?
What you are compensating for is active resistance, but active resistance normally depends on the temperature and not on the state of charge of the battery. I guess this Ru is a projection from the complex resistance to the real axis.
What do you think about it?
Thanks for your question. First, I just want to note that I think some of the language you used is a little confusing to me, but I believe I understand the idea of what you are saying. For instance, when you say Ru is a projection from the "complex resistance" to the real axis, I assume you mean the imaginary impedance axis (the y-axis on a Nyquist plot) and the intersection at Zi = 0 on the Zr axis is equivalent to Ru. If that is what you mean, then yes, I agree.
The other thing about what you said I am not sure I understand is that "the internal resistance of the battery is caused by reversible processes." I'm not honestly sure what this means. What processes do you mean, exactly? The internal resistance, the Ru so to speak, is generally considered to be a consequence of electrolyte resistance, and other physical things like connections/leads from potentiostat to the cell. I don't know what reversible processes would be considered incorporated into the measurement of Ru.
The last thing I will say is the one part you said I do agree with is that, ideally, "the [Ru] normally depends on the temperature and not on the state of charge of the battery." This is in theory true, though in practice I suppose it is possible your experimental measurement of Ru might change slightly due to normal measurement error and/or subtle changes to the electrolyte during charge/discharge tests.
@@Pineresearch
I mean processes in which energy is used so that the Poyting vector is not 0, but entropy does not increase as in the case of heat generation. (e.g. ionization, work function etc.).
You make an approximation that Ru is a dessipative resistance, but this can also have non-linear dependence on current, voltage or frequenq.
Where I am not sure... Internal resistance of Battarie what they all measure and your Ru is the same or not... I may well be wrong at this point.
@@xelth You know, I actually think you are making a very interesting point I've never quite considered before. Thank you for bringing this up. To be perfectly honest, I really don't know the answer. However, I do think you are 100% correct about one thing: that is, we actually do make an implicit assumption virtually every time we do EIS on an electrochemical system - whether a battery, fuel cell, 3 electrode setup, etc - which is that we assume Ru is dissipative resistance, and therefore governed by Ohm's Law. I wonder if there may be situations where this is not the case and there may be some non-linear dependence going on. In a sense, because almost every set of EIS tests never give exactly the same Ru value, it is at least conceivable this could be resulting from simple repeated measurement error, some non-linear dependence, or a little of both.
With respect to the internal resistance of a battery specifically, my personal research observations and also from those I have seen in literature typically show that Ru is not perfectly constant throughout a set of EIS tests. Often, this is something like performing EIS at various states of charge, or over a period of time to measure degradation of the battery for example. Your comment is making me wonder if perhaps there could be some factor of non-linear dependence, even if somewhat minor, that is accounting for the change in Ru. I do not know of many instances where people have discussed this either. I would say that your hypothesis is certainly plausible.