Great video! really illustrative and complete. Thanks for the clarity in the exposure and for the useful tips to calculate/estimate and apply the iR compensation. (Potentiostats user's manuals are usually confusing on this respect)
Just to clarify, are you talking about the bandgap for a semi-conductor or for a redox active molecule? I don't think CV is best technique for determining the HOMO/LUMO energy gap. I'd probably use a technique like UV/Vis spectroscopy, because the energy from a photon of light will excite an electron from the LUMO to the HOMO, and that energy will be your HOMO/LUMO band gap. Same with a semi-conductor.
Amazing video! I think this is the clearest and most complete explanation on the internet about this topic! :D Please keep making these great videos! I have one question though. If I use C.I. for potential correction during an LSV, since I am increasing the potential, the current also increases. So how does the potentiostat estimate the iR drop? Also, if the solution resistance is changing during the reaction, then C.I. would be a more suited method than P.F. right? I assume this because with C.I. the potential is constantly being corrected with the " resistance in real time" and not by a fixed Ru value % given at the beginning of the experiment. Please correct me if I am wrong! :)
We're glad you liked it! Thank you. So you'll actually find the answer to how a potentiostat corrects for the iR drop in this video ua-cam.com/video/3Odj97ql2aY/v-deo.html. The idea is that the solution resistance remains constant during an experiment. Both C.I, P.F, and all the other techniques assume the solution resistance remains constant. But you are correct, the current changes and hence the iR drop changes during an LSV experiment. If you watch the other video it will explain how a potentiostat corrects for the iR drop :)
@@Pineresearch Thanks for your reply! I watched already both videos. But I don't understand why the C.I. method assumes that the resistance remains constant. With the C.I. method what is know is 1) the current input at time 0 ms and b) the potential drop at time 1 ms, after the current was interrupted . Then, from this 2 variables, the resistance is being estimated. Therefore, resistance in this measurement method is a function of delta V. --> R(V)=(V2-V1)/ i From this estimated resistance, than the potential value is being adjusted to the "real" values. To my understanding, this whole process is continuously being repeated DURING the whole electrochemical reaction. Therefore, if the resistance changes, this is not a problem because it is being estimated anyway from the input current and recorded voltage drop. So the resistance doesn't need to be a constant. However, with the P.F. mode the resistance is being estimated BEFORE the electrochemical reaction, and applied as a constant during the measurement, where either V(i)=R*I or I(V)=V/R is being calculated. Am I making any mistakes? Is there something I am missing? Sorry if I am insisting on this issue. I really want to understand why this is not the case if I am mistaken. Thanks in advance for your time and help! :)
@@kiraraashura Ahhhh, okay I think there is a small misunderstanding. The C.I method is performed once, and it's performed before doing any electrochemical reactions or experiments. In fact, you don't want the applied current to be too high because you don't want faradaic processes to occur which would make Rct low. All of the solution resistance techniques assumes that the solution resistance is constant. Rct can change as a function of potential, but Ru does not. It's an assumption, but I think it's pretty accurate. Once the Ru is determined for a single C.I experiment, that Ru value is plugged into the potentiostat when using iR compensation (the other video). In a CV experiment for example, the multiplier adjusts the output potential by the measured current (dynamically changing), times the resistance (constant). Both C.I and P.F are used to determine a single solution resistance value. I hope this was helpful. As a side note. We are planning on starting a UA-cam Live Stream Q&A session in the coming months. Do you mind if we use this for one of the questions to kick off the Live Stream?
@@Pineresearch Thank you so much for the clarification! However, my potentiostat (from another company :( sorry! ) does have a constant C.I. correction. So I am wondering, why is it an issue if the C.I. method is applied at high currents, causing Rct to be low? From the video I assume that if Rct is low the Voltage drop is not only going to be caused by Ru but by the combination of Ru and Rct, right? But what if Ru is waaay larger than Rct and the error caused by this is not too big? Would you say that it would be "ok" to use this method at high currents under this assumption? Btw I don't mind it if you use my question :) I would be glad if I can help you back in any way for the support you are providing me!
@@kiraraashura Well your first problem is you are using a potentiostat from another company :D just kidding. I think you are correct, if Ru is much much larger than Rct, then the error associated with Rct will be small. But in general you don't want faradaic current to flow when performing C.I because you are really just interested in getting Ru value and Rct becomes another path for current to flow. The real problem you'll run into, is if you start overcompensating when using the iR compensation circuit in your potentiostat. I hope that's helpful. Of course every electrochemical system is different so you might need to do some troubleshooting to figure out what is optimal for you.
The short answer is that the system oscillates badly if you compensate at, or too close to, the actual amount of uncompensated resistance. The longer answer is actually well-described near the end of this video, which discusses and even illustrates the oscillations that occur during a Positive Feedback experiment and the kinds of errors that you can observe if compensating too much.
A very nice explanation! I have a couple of questions: Firstly how does the distance between working and reference electrodes effect solution resistance? And would changing the distance between working and counter electrodes have an effect on the RC time constant for EDL charging/discharging, or is this primarily determined by electrode/solution composition? Thanks in advance :)
Great questions! As the distance between the working and reference electrodes increase the uncompensated solution resistance also increases. As such, most electrochemists try to place the working and reference electrode close together to minimize the uncompensated solution resistance in their cell. Changing the distance between the working and counter electrode should have no effect on the electrical double layer of the working electrode. Only the electrode/electrolyte and potential should affect the EDL. I hope this was helpful!
Hello. In doing iR correction using Rs (solution resistance) from EIS, i expected only having very little changes on my corrected potentials..however i get really big iR drops in high currents like 100 mA. For example, my Rs = 5 ohms and i = 118 mA, i already have 0.59 V iR to be compensated. Even with 80% iR correction, i still have 0.472 V to be subtracted on my potential. Am i doing something wrong here? You're help is much appreciated.
Follow-up question, for testing OER water splitting and doing EIS, is it okay to use 0.65 V applied current? Most papers i read have different voltage used. And im confuse whether to use non-faradaic or faradaic potential during EIS. Thank you
Regarding your first question, it sounds like you are doing it correctly. I don't know enough about your electrochemical system but if you're generating 100 mA of current, yes your iR drop is going to be big even with 5 ohms of resistance. The question I would pose to you, is what exactly are you trying to figure out? If you are doing a fundamental study and doing cyclic voltammetry, then half a volt is quite a big difference in the reported potential. But if it's compensated, then it should be okay. Regarding your 2nd question, I need a little more clarification, you said "0.65 V applied current" are you doing a galvanostatic or potentiostatic experiment? Are you applying a current or a voltage? Also, faradaic vs non-faradaic potential isn't a thing. You can only have faradaic current or non-faradaic current. So I'll need a little more clarification to help with your second point.
@@Pineresearch hello! I'm so sorry I don't understand much jargons as I'm only just starting with electrochem. What does "fundamental study" mean? I am also a little confused about the line "if it's compensated it should be okay". Isn't the iR drop (0.47 V in this case) the compensation giving 1.43 V the reported potential instead of 1.9 V for example? I am doing LSV study for Oxygen evolution reaction (OER) by the way. and i need to report the onset potential as well as overpotential at 10mA/cm2 and 50 mA/cm2, so having that very large difference at high current densities bothers me a bit. For my second question, i written it wrong. It should be "0.65V applied potential". Apologies for that. I will use my EIS nyquist plot to get Rs and Rct. So i don't know what applied potential to use since papers varies a lot in range. Thank you very much!
@@clarik.9418 Gotcha, not a problem. Echem is tough and full of jaragon. When I said "fundamental study" I meant that your experiments are trying to extract a fundamental property of the system. For example, calculating things like diffusion coefficients, heterogeneous rate constant, standard redox potential, etc. These are things that shouldn't change if you adjust say the volume of your cell. This is opposed to something like performing bulk electrolysis where you are trying to convert one molecule into another, like in the case of OER you are trying to evolve oxygen, but I don't know if the goal of your experiment is to try to evolve the most oxygen, or if you are trying to determine the standard redox potential for the catalyst you are using to evolve oxygen. If you are trying to evolve the most oxygen, the extra voltage you apply shouldn't matter as long as you are generating oxygen, and getting high current densities. However, if you are trying to determine the standard redox potential of your catalyst, then the iR compensation will play a very important role and you might aim to use smaller electrodes that give you a lower iR drop and hence a more accurate potential for catalytic behavior. Does that make sense? So based on what you wrote, you might run into an issue, because by virtue of measuring an overpotential at 10 mA/cm2 and 50 mA/cm2 you inherently will have a large iR drop because 10 - 50 mA even with 1 Ohm of resistance will change the potential by 10 to 50 mV (which might be okay for your experiment). But alternatively, you might be able to use a low area electrode, minimize the iR drop, but report an accurate potential because you can extrapolate the current to a current density by dividing by the area. Remember, the measured current, instead of the current density is what will contribute to the iR drop. So I'd try looking at that. Regarding your second question, thank you for the clarification. I couple things to consider, the 0.65 V needs to be with respect to a reference electrode. You will need to know what reference electrode those papers are using so you can use the same potential, if that's what you want. I think what is best, is that you do a CV experiment to determine the potential of your system and compare it to what was done in the literature as well as take into account the thermodynamics associated with OER. Fundamentally, what is the delta G and corresponding E for the OER reaction you are doing. Then you can decide what potential you should use. Also, (one last thing). For these questions you should join us for the "Ask us Anything about Electrochemistry" Livestream. We usually do them on Fridays at 1 pm EST. You can then ask all your questions and we'll be able to answer them in a way that isn't typing.
@@Pineresearch thank you so much! That makes so much sense that for three electrode system, most papers only use 0.5 cm x 0.5 cm area. I use 1cm² just to lessen calculation 😂. That helps alot! I'm still a bit confused with the EIS though. My reference electrode is Ag/AgCl in 3M KCl (im not sure about the concentration of KCl, need to check first). But I'll just try to check at least two applied potentials (0.65V and 10mV) just to be sure. Do you think it could affect my potentiostat? I mean will it damage potentiostat if I apply wrong voltage during EIS? thank you very much, for your invite on the livestream. I wish i could watch it sometime. But my schedule is full on fridays :((
You would need to contact Autolab to determine if their potentiostat can perform iR compensation. But I'm pretty sure most of their potentiostats have this capability.
@@shahidahmad7803 We don't have access to Autolab potentiostats. I think it would be best to contact Metrohm who produces the autolab potentiostat to have them make a video on performing iR compensation.
Great video! really illustrative and complete. Thanks for the clarity in the exposure and for the useful tips to calculate/estimate and apply the iR compensation. (Potentiostats user's manuals are usually confusing on this respect)
Thank you! We are glad you enjoyed it! Always trying to make things as easy as possible to understand.
I have a question. How to calculate HOMO and LUMO, and so bandgap from cyclic voltammetry? Could you please make the video on this?
Just to clarify, are you talking about the bandgap for a semi-conductor or for a redox active molecule? I don't think CV is best technique for determining the HOMO/LUMO energy gap. I'd probably use a technique like UV/Vis spectroscopy, because the energy from a photon of light will excite an electron from the LUMO to the HOMO, and that energy will be your HOMO/LUMO band gap. Same with a semi-conductor.
Amazing video! I think this is the clearest and most complete explanation on the internet about this topic! :D Please keep making these great videos! I have one question though. If I use C.I. for potential correction during an LSV, since I am increasing the potential, the current also increases. So how does the potentiostat estimate the iR drop? Also, if the solution resistance is changing during the reaction, then C.I. would be a more suited method than P.F. right? I assume this because with C.I. the potential is constantly being corrected with the " resistance in real time" and not by a fixed Ru value % given at the beginning of the experiment. Please correct me if I am wrong! :)
We're glad you liked it! Thank you. So you'll actually find the answer to how a potentiostat corrects for the iR drop in this video ua-cam.com/video/3Odj97ql2aY/v-deo.html. The idea is that the solution resistance remains constant during an experiment. Both C.I, P.F, and all the other techniques assume the solution resistance remains constant. But you are correct, the current changes and hence the iR drop changes during an LSV experiment. If you watch the other video it will explain how a potentiostat corrects for the iR drop :)
@@Pineresearch Thanks for your reply! I watched already both videos. But I don't understand why the C.I. method assumes that the resistance remains constant. With the C.I. method what is know is 1) the current input at time 0 ms and b) the potential drop at time 1 ms, after the current was interrupted . Then, from this 2 variables, the resistance is being estimated. Therefore, resistance in this measurement method is a function of delta V. --> R(V)=(V2-V1)/ i
From this estimated resistance, than the potential value is being adjusted to the "real" values.
To my understanding, this whole process is continuously being repeated DURING the whole electrochemical reaction. Therefore, if the resistance changes, this is not a problem because it is being estimated anyway from the input current and recorded voltage drop. So the resistance doesn't need to be a constant.
However, with the P.F. mode the resistance is being estimated BEFORE the electrochemical reaction, and applied as a constant during the measurement, where either V(i)=R*I or I(V)=V/R is being calculated.
Am I making any mistakes? Is there something I am missing? Sorry if I am insisting on this issue. I really want to understand why this is not the case if I am mistaken.
Thanks in advance for your time and help! :)
@@kiraraashura Ahhhh, okay I think there is a small misunderstanding. The C.I method is performed once, and it's performed before doing any electrochemical reactions or experiments. In fact, you don't want the applied current to be too high because you don't want faradaic processes to occur which would make Rct low. All of the solution resistance techniques assumes that the solution resistance is constant. Rct can change as a function of potential, but Ru does not. It's an assumption, but I think it's pretty accurate. Once the Ru is determined for a single C.I experiment, that Ru value is plugged into the potentiostat when using iR compensation (the other video). In a CV experiment for example, the multiplier adjusts the output potential by the measured current (dynamically changing), times the resistance (constant). Both C.I and P.F are used to determine a single solution resistance value. I hope this was helpful.
As a side note. We are planning on starting a UA-cam Live Stream Q&A session in the coming months. Do you mind if we use this for one of the questions to kick off the Live Stream?
@@Pineresearch Thank you so much for the clarification! However, my potentiostat (from another company :( sorry! ) does have a constant C.I. correction. So I am wondering, why is it an issue if the C.I. method is applied at high currents, causing Rct to be low? From the video I assume that if Rct is low the Voltage drop is not only going to be caused by Ru but by the combination of Ru and Rct, right? But what if Ru is waaay larger than Rct and the error caused by this is not too big? Would you say that it would be "ok" to use this method at high currents under this assumption?
Btw I don't mind it if you use my question :) I would be glad if I can help you back in any way for the support you are providing me!
@@kiraraashura Well your first problem is you are using a potentiostat from another company :D just kidding. I think you are correct, if Ru is much much larger than Rct, then the error associated with Rct will be small. But in general you don't want faradaic current to flow when performing C.I because you are really just interested in getting Ru value and Rct becomes another path for current to flow. The real problem you'll run into, is if you start overcompensating when using the iR compensation circuit in your potentiostat. I hope that's helpful. Of course every electrochemical system is different so you might need to do some troubleshooting to figure out what is optimal for you.
Excellent video, very informative! I have one question, why do we only compensate for 90% of the measured solution resistance? Thank you
The short answer is that the system oscillates badly if you compensate at, or too close to, the actual amount of uncompensated resistance. The longer answer is actually well-described near the end of this video, which discusses and even illustrates the oscillations that occur during a Positive Feedback experiment and the kinds of errors that you can observe if compensating too much.
A very nice explanation! I have a couple of questions:
Firstly how does the distance between working and reference electrodes effect solution resistance?
And would changing the distance between working and counter electrodes have an effect on the RC time constant for EDL charging/discharging, or is this primarily determined by electrode/solution composition?
Thanks in advance :)
Great questions! As the distance between the working and reference electrodes increase the uncompensated solution resistance also increases. As such, most electrochemists try to place the working and reference electrode close together to minimize the uncompensated solution resistance in their cell. Changing the distance between the working and counter electrode should have no effect on the electrical double layer of the working electrode. Only the electrode/electrolyte and potential should affect the EDL. I hope this was helpful!
Please make a vedio on debye layer calculation in electrochemical cell.
That's a great idea, I'll have to take a look into that. I haven't received too many requests for debye layer length calculations.
@@Pineresearch Bcz most of the people are unaware of it, I would really appreciate it
@@muhsinali8386 It might be some time before we can make a video like that. But we'll put it on the list.
Hello. In doing iR correction using Rs (solution resistance) from EIS, i expected only having very little changes on my corrected potentials..however i get really big iR drops in high currents like 100 mA. For example, my Rs = 5 ohms and i = 118 mA, i already have 0.59 V iR to be compensated. Even with 80% iR correction, i still have 0.472 V to be subtracted on my potential. Am i doing something wrong here? You're help is much appreciated.
Follow-up question, for testing OER water splitting and doing EIS, is it okay to use 0.65 V applied current? Most papers i read have different voltage used. And im confuse whether to use non-faradaic or faradaic potential during EIS. Thank you
Regarding your first question, it sounds like you are doing it correctly. I don't know enough about your electrochemical system but if you're generating 100 mA of current, yes your iR drop is going to be big even with 5 ohms of resistance. The question I would pose to you, is what exactly are you trying to figure out? If you are doing a fundamental study and doing cyclic voltammetry, then half a volt is quite a big difference in the reported potential. But if it's compensated, then it should be okay. Regarding your 2nd question, I need a little more clarification, you said "0.65 V applied current" are you doing a galvanostatic or potentiostatic experiment? Are you applying a current or a voltage? Also, faradaic vs non-faradaic potential isn't a thing. You can only have faradaic current or non-faradaic current. So I'll need a little more clarification to help with your second point.
@@Pineresearch hello! I'm so sorry I don't understand much jargons as I'm only just starting with electrochem. What does "fundamental study" mean? I am also a little confused about the line "if it's compensated it should be okay". Isn't the iR drop (0.47 V in this case) the compensation giving 1.43 V the reported potential instead of 1.9 V for example? I am doing LSV study for Oxygen evolution reaction (OER) by the way. and i need to report the onset potential as well as overpotential at 10mA/cm2 and 50 mA/cm2, so having that very large difference at high current densities bothers me a bit.
For my second question, i written it wrong. It should be "0.65V applied potential". Apologies for that. I will use my EIS nyquist plot to get Rs and Rct. So i don't know what applied potential to use since papers varies a lot in range. Thank you very much!
@@clarik.9418 Gotcha, not a problem. Echem is tough and full of jaragon. When I said "fundamental study" I meant that your experiments are trying to extract a fundamental property of the system. For example, calculating things like diffusion coefficients, heterogeneous rate constant, standard redox potential, etc. These are things that shouldn't change if you adjust say the volume of your cell. This is opposed to something like performing bulk electrolysis where you are trying to convert one molecule into another, like in the case of OER you are trying to evolve oxygen, but I don't know if the goal of your experiment is to try to evolve the most oxygen, or if you are trying to determine the standard redox potential for the catalyst you are using to evolve oxygen. If you are trying to evolve the most oxygen, the extra voltage you apply shouldn't matter as long as you are generating oxygen, and getting high current densities. However, if you are trying to determine the standard redox potential of your catalyst, then the iR compensation will play a very important role and you might aim to use smaller electrodes that give you a lower iR drop and hence a more accurate potential for catalytic behavior. Does that make sense?
So based on what you wrote, you might run into an issue, because by virtue of measuring an overpotential at 10 mA/cm2 and 50 mA/cm2 you inherently will have a large iR drop because 10 - 50 mA even with 1 Ohm of resistance will change the potential by 10 to 50 mV (which might be okay for your experiment). But alternatively, you might be able to use a low area electrode, minimize the iR drop, but report an accurate potential because you can extrapolate the current to a current density by dividing by the area. Remember, the measured current, instead of the current density is what will contribute to the iR drop. So I'd try looking at that.
Regarding your second question, thank you for the clarification. I couple things to consider, the 0.65 V needs to be with respect to a reference electrode. You will need to know what reference electrode those papers are using so you can use the same potential, if that's what you want. I think what is best, is that you do a CV experiment to determine the potential of your system and compare it to what was done in the literature as well as take into account the thermodynamics associated with OER. Fundamentally, what is the delta G and corresponding E for the OER reaction you are doing. Then you can decide what potential you should use.
Also, (one last thing). For these questions you should join us for the "Ask us Anything about Electrochemistry" Livestream. We usually do them on Fridays at 1 pm EST. You can then ask all your questions and we'll be able to answer them in a way that isn't typing.
@@Pineresearch thank you so much! That makes so much sense that for three electrode system, most papers only use 0.5 cm x 0.5 cm area. I use 1cm² just to lessen calculation 😂. That helps alot!
I'm still a bit confused with the EIS though. My reference electrode is Ag/AgCl in 3M KCl (im not sure about the concentration of KCl, need to check first). But I'll just try to check at least two applied potentials (0.65V and 10mV) just to be sure. Do you think it could affect my potentiostat? I mean will it damage potentiostat if I apply wrong voltage during EIS?
thank you very much, for your invite on the livestream. I wish i could watch it sometime. But my schedule is full on fridays :((
The videos are amazing
Thank you!
Can we remove the solution resistance through Autolab Instrument?
You would need to contact Autolab to determine if their potentiostat can perform iR compensation. But I'm pretty sure most of their potentiostats have this capability.
@@Pineresearch Sir, can you make a video on this?
@@shahidahmad7803 We don't have access to Autolab potentiostats. I think it would be best to contact Metrohm who produces the autolab potentiostat to have them make a video on performing iR compensation.
@@Pineresearch Thank you very much. Your videos are very informative.
great!
Thank you!