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I'm sorry to hear you're having trouble with your EIS data. Unfortunately, without more specific information there is probably very little I can do to help you. You can join us on one of our Friday livestreams and ask your questions more thoroughly, otherwise I might need to see your data or setup to understand what you are currently doing and what you might need to change to get better EIS data.

​@@Pineresearch Thank you for the prompt reply. I believe it is caused by setting the OCV to zero during EIS. When we set it to 0.6 V we got a nice semi circle. I hope you don't mind for my novice questions- How do you set the OCV as you do ELS. Do you have to measure OVC versus time pick the value where its change is very small ?

@@Llmakebede First, I think you have a slight terminology issue here. I assume when you say "setting the OCV to zero" you mean that you applied 0 V vs REF. You cannot "set" the OCV, it is whatever it is. It's a thermodynamic quantity, and very often EIS is done at 0 V vs OCV, which is still an applied potential. Where you pick for your setpoint for EIS depends on what you are looking for. What are you studying? Some particular redox reaction? Does that reaction occur at OCV? If not, then why would you do EIS at OCV? Treat EIS the same way you would treat any other electrochemistry experiment. Adjust the potential to induce whatever reaction you want to study, and use that as your setpoint for EIS. The EIS spectra will reflect characteristics of your system as well as the processes occurring at the setpoint, so if OCV is where nothing of interest is occurring then there is no reason to do EIS there.

To be honest, there is only really one tried-and-true method I know of that is used very frequently, and that is with respect to Pt. Very briefly, you use the knowledge that the Pt-H adsorption/desorption process has a theoretical specific capacity of 210 µC/cm2, and then you run a CV and take the area under the curve of i vs. time. You get units of C, then you divide by 210 µC/cm2 and you get a value of cm2. This is often considered the ECSA. There are likely other methods for other materials that are used, but the clearest and most common one is what I just described for Pt. I am not 100% certain what other methods researchers use, or perhaps they simply use geometric surface area and assume that is also equivalent to ECSA. I also understand this explanation is rather complex for a comment answer. What I will do is this upcoming Friday, August 9 2024 at 1pm EST, I will try to give a detailed demonstration of how this is done using real data and software calculations. This will be during our weekly "Ask Us Anything About Electrochemistry" livestream, it will be episode #62. Here is the link, whether you can watch live or you can see the recording on RUclips afterwards: ruclips.net/video/jNMp9a9J0lA/видео.html

Thank you for the great question. Unfortunately, I cannot provide you very many details on these EIS data because they were collected by another researcher and submitted to me for use in my Advanced EIS Circuit Fitting webinar series. All I know is what the researcher told me, which is that the two EIS data sets I showed in this video were from a HDG sample with different immersion times (24 hours, then 360 hours). Beyond this information, I am not completely certain about other experimental parameters or details.

@@Pineresearch I appreciate your honest answer. I am using Biologic premium potentiostat. Though this instrument is excellent but I am missing wonderful webinars and online videos like yours of Pine research. And I am learning a lot from you guys. Thanks for sharing wonderful information on EIS.

@@growthinvestor1430 Thank you for your kind words! We strive to be a company that does both things - that is, make quality instruments, potentiostats, electrodes, software, etc., and also make good content like videos and webinars. I am glad you've found our content and hope you continue to enjoy it.

The use of "imaginary impedance" arises entirely from mathematics. Analyzing the sine wave signals (E and i) from an EIS experiment results in the use of Euler's formula, which simplifies the mathematics into complex coordinates, or having the form "a + bi" as you might have learned it in a university math course. Final simplification results in a real and imaginary component of the impedance, and thus we get those terms (Zreal and Zimag) when we analyze and obtain final EIS data. I worked out the mathematics of EIS signals in our Knowledgebase here: pineresearch.com/shop/kb/theory/eis-theory/eis-mathematical-theory/

The sign of the current will depend on whether you are using the US or IUPAC convention for plotting a cyclic voltammogram. If you are using the IUPAC convention then positive current refers to an oxidation reaction and negative current refers to a reduction reaction. It is very strange that you would observe a different sign in the current if you applied a -0.6 vs -0.8 V potential for electrodeposition. If you are using the IUPAC convention you should observe a negative current associated with the reduction of your ion X. Unless there is another process occurring at those potentials that induces an oxidation reaction, although that seems very unlikely. If you hold the potential and measure the current for the electrodeposition, you should see (Again IUPAC convention) and sharp negative spike followed by a gradual increase in the current. The current should still be negative, but less negative over time, meaning that the current increases slowly over the course of the deposition. I hope this helps.

Thank you so much for your answer. Could you explain me more why, in the oxidation process, the sign of the current is positive, while in the reduction process, the sign of the current is negative? Is it always true that if we apply any potential more negative than the reduction potential of a metal ion, the ion will be reduced to form a metal?

@@Alex-t98 To reiterate the previous point, there is no real "reason" why oxidation current is positive. This is simply convention in the IUPAC system. In fact, in a very fundamental sense, there is no such thing as + or - current. Think about what current physically is: simply put, the flow of electrons (or more broadly, the flow or movement of charge over time). The unit of current is Ampere, which is equivalent to Coulombs per second, or the flow of charge over time. The sign simply indicates which direction it is flowing, nothing more. If you have 2 electrodes, the flow of current can either be from electrode A to electrode B, or vice versa. So we arbitrarily assign + to one of those directions, and - to the other. That is quite literally all it is. The other thing to recognize in relation to a real electrochemistry experiment using a potentiostat is that the current you observe is the *NET* current. As noted in the previous answer, depending on your applied potential and its relation to any number of redox processes that can occur in your experiment, you will get current indicating some oxidation (+) or reduction (-) taking place. But let's say you have some reduction occurring (like the deposition of X) as well as simultaneously some other oxidation happening too. The current the potentiostat reports to you will be the aggregate, or net, current from both those processes. Now, in many cases, you try to design your experiment such that there is only 1 main reaction that can take place, like say the deposition of X. So you can presume all or most of your current is arising from that process and that process alone. But this is not always the case, since if you had -100 mA from X deposition, but also +30 mA from some auxiliary oxidation reaction for instance, your potentiostat would report to you -70 mA.

@@Pineresearch I also observed the trend of current as you said but still dont really know the reason why the current spikes, then gradually increases and becomes less negative overtime. Please help me clarify it

@@raven-tn I am not completely certain what you are referring to - are you running a chronoamperometry experiment at a set potential and observing a negative current? And the current you say starts at some large negative number, then goes towards zero over time? It seems like you are describing where it looks like a current decay but it's "upside-down" so to speak. If this is accurate, it is just the phenomenon described by the Cottrell equation, which defines the current behavior over time due to diffusional effects. This is most commonly applied to a chronoamperometry experiment under normal conditions, and the fact that the current is negative simply goes back to my previous comment explaining that it is just convention describing a reduction process.

I think you would need to design a series of electrochemistry experiments with different chemical methods to test the binding mechanism. Cyclic voltammetry by itself won't help. It will give you the potential of the redox reaction, which might give you a sense of the binding mechanism. But you would need to adjust different parameters of the test solution to elucidate the binding mechanism.

As long as the area you want deposited is submerged in solution it will be deposited. However, I do believe that the uniformity of the deposition will be based on a bunch of other factors such as the rate on deposition (applied current in chronopotentiometry) as well as stirring of the solution. Also the size and position of the counter electrode will affect the flow of current.

Depending on the device, CV studies of electrochromic materials are the same as molecules like ferrocene or ferrocyanide, they just change color when the potential is switched.

Glad it was helpful!

Currently, there is no way to adjust the CV parameters in the middle of an experiment. Once the parameters are set the potentiostat will perform them, but can't be changed on the fly.

@@Pineresearch Thank you for the reply.

Cl- leaching will happen regardless of the AgCl precipitate, it's necessary for the reference electrode to maintain electrical contact with your test solution. But generally speaking, you should store the Ag/AgCl reference electrode in a solution of 4 M KCl, this will equilibrate the Ag/AgCl reference electrode and make sure it has a consistent potential between experiments. If it isn't stored in a 4 M KCl solution the potential will shift around as the inner fill solution will change (and thus changes the potential). But I do believe that a double junction reference electrode will help reduce the precipitation, as the secondary fill solution is 10% KNO3, so you should observe precipitation. I think there are a few things to consider regarding you Ag+ and Ag3+ deposition. I would figure out what the open circuit potential of your cell is and make sure you start your CV scan sufficiently positive of it. I'm not 100% sure but if you have a combination of Ag+ and Ag3+ (depending on the concentration of each) you might have homogeneous electron transfer between the Ag+ and Ag3+. Maybe. But either way, you will want to start sufficiently positive such that no reduction reactions occur. If you were to start your scan at a negative potential you would already be plating silver onto your electrode and the results regarding the deposition of both oxidation states of Ag won't be accurate. But I think you make a good point, you only need to scan in one direction, what we would call an LSV (linear sweep voltammetry) experiment. Some people scan to positive potentials to look for reversibility of the molecule, but because you are doing deposition, this is not necessary.

Definitely planning on it. Stay tuned :)

Is your Ag/AgCl reference electrode in its own contained compartment, or are you using a standalone Ag wire with AgCl coating dipped directly into solution? In either case, probably what you are seeing is precipitation of AgCl from Cl- ions that are in contact with your bulk solution. I suspect you are seeing some whispy silvery kind of precipitates forming? AgNO3 is the only salt of silver that is soluble, which means when almost any other anion is present the Ag+ cations will precipitate with it. It is actually why AgNO3 is a great solution to use for checking for Cl- contamination. I am not sure if the AgCl precipitates will impact your electrochemistry. They might, but i suppose I might say possibly it is not that concerning because the Ksp of AgCl is extremely small, meaning AgCl that precipitates will likely sink to the bottom and remain passively out of the way from your electrode surface. Of course, if it does somehow float around and contact your working electrode, it could interfere and you might get some unwanted redox associated with AgCl, which would be bad. On your second question, the direction you scan matters sometimes, but it probably depends on what you are doing. Since you are doing electrodeposition, I think I also wonder why you are performing CV at all. Normally, electrodeposition would involve setting potential or current and measuring the other variable, then determining the charge passed and relating it to how much material you deposited. But if you are studying it via CV, typically electrodeposition is a reduction so you would probably want to start at a positive potential, where you are not reducing Ag+, then scan negative to induce the reduction/deposition process. CV is usually best when you begin where "nothing" is happening and scan into the region of interest so you can observe the contrast.

@@Pineresearch Thank you for your prompt reply, I really appreciate it. Regarding my first question, I am using a single junction Ag/AgCl electrode from Pine Research. If AgCl precipitation forms due to Cl- leaking out from the KCl solution, should I refill the KCl filling solution after each use to maintain the proper KCl concentration? Do you think using a double junction electrode could help reduce precipitation? For my second question, I am performing CV to determine the reduction peaks of two different metals using a mixed solution of Ag3+ and Ag+ to deposit both metals simultaneously. As you mentioned, since we only need to reduce the metal ions, do I just need to scan in one direction (from positive to negative) to determine the reduction peak? From the references I have read, I do not understand why they scan in both directions.

Glad you enjoyed it!

Depends. How the energy is stored is generally independent of the method for energy generation.

I do have a video about EIS, what do you mean the lin and DFT. I don't know how DFT is related to EIS.

Glad you enjoyed it!

Yes, there are many resources for learning electrochemistry. This video is really to help people gain a general understanding of the technique if they aren't familiar with it. Thanks for watching.

Glad to hear that

You're welcome!

Glad it was helpful!!

I think in general it might be difficult to get good EIS data on blood glucose strips, compared to a more traditional 3 electrode setup. First I would do something like CV of the blood glucose system to get a sense of where the redox process you are looking at is coming from. One possibility regarding the high Rct at 1.2 and 1.5 V is that there is another electrochemical process occurring at those potentials that is interfering with you measurements. This is just a guess. I would perform EIS at a series of different on set potentials to see how Rct changes. Regarding point number 2, we'd need to see the data to know what the "random thing" is. Generally speaking at low frequencies it's hard to get stable EIS as the system can drift, and considering it's a blood glucose strip I'm guessing the potential is drifting at the lower frequency region.

You're very welcome!

I would be happy to explain chronopotentiometry in a little more detail. I have added this question to my list for tomorrow's Ask Us Anything About Electrochemistry livestream, and I will try to cover it for you. This will be live tomorrow (Friday, June 14, 1pm EST time), or if you wish to watch it after and cannot catch live, it will be episode #56.

Most probably, there is no easy way to definitively confirm whether the line would continue at 45° (infinite Warburg), curl down after the initial 45° (finite Warburg), or make an actual semicircle (Randles element). You would need to continue the EIS experiment to lower frequencies (and hope diffusion/drift doesn't cause instability to make the measurements invalid). I wouldn't say there's a "danger" in assuming an infinite Warburg, that might be too strong. Some of your assessment should be based on knowledge of the physical setup. If you have a small electrode with plenty of electrolyte, and not a rotating electrode or a microelectrode, it might be safe enough to assume the diffusion layer thickness is large in comparison and an infinite Warburg is valid.

We can probably talk more about this during the next livestream if you attend. First I must say that I'm not a corrosion expert, so take what I say with a large grain of salt. I'm not sure about the 50 mV difference in OCP between the anodic and cathodic branch. I feel like a 50 mV difference in OCP is a fairly large deal in corrosion seeing as LPR experiments are only done within a +/- 10 mV range. It only takes a little bit of voltage to induce corrosion is most systems so I feel as though a 50 mV difference could be significant. However, I think OCP should be one measurement and you are sweeping the potential around OCP. It's possible that your OCP is drifting during the experiment (something to consider.) Lastly, with regards to the difference in tafel slopes. 0.8 M NaCl (pH 6.2) and pH 3 H2SO4 are very different types of solutions, that I would imagine the tafel slope to very very different. Again, it's much easier to generate cathodic current under acidic conditions (lower cathodic tafel slope) than it is under more neutral pH values (0.8 M NaCl). The way I interpret this, is it takes twice/three times more voltage to drive the same amount of anodic current (corrosion of SS-304) in neutral pH than it does in acidic pH. But I don't know for sure.

​@@PineresearchThank you for your response I will take this drifting of the OCP into account. Might have to reconsider recording the cathodic and anodic branch in one test instead of seperately. Since I always have some drift in OCP. Based on literature I expect the anodic tafel slope of SS_304 in a chlorine rich environment to be low. I will definitely try to join this weeks livestream, again thanks for the help.

Yes, I think I should be able to go through it during the next livestream (Today at 1 pm EST)

Hey Ruchika. I got swamped with question on the last live stream and couldn't answer your question. I'm hoping that episode #56, next week we'll be able to answer your question and K-K testing.

Thanks a lot

Thank you!!

Glad it was helpful!

What kind of data are you working with? If you only have current vs potential data you would need additional information about how often a data point is collected to get the current vs time data.

@@Pineresearch okk thank you soo much sir

Much appreciated, glad you enjoyed it!

I think what is hard to know for me to pass judgment on your experiments are the distinct differences between your two types of tests - LSV (potentiostatic) and GCD (galvanostatic). Since they both involve different modes of potentiostat operation, I think it might be tough to make direct comparisons. For instance, in your LSV you are not observing what you believe is substantial water splitting until a certain potential, but you are controlling the potential. With GCD, you are controlling current, so it may not be a perfectly direct comparison since the pairs of i and E you observe in each experiment may not match up the same. As well, to my knowledge, titanium electrochemistry is kind of complex and involves passive film formation and maybe oxides or other kinds of phenomena, and it might be that these processes are occurring in different ways for LSV vs GCD, such that the water splitting you are looking for is convoluted by other electrochemical processes depending on whether you are operating galvanostatically or potentiostatically. Apart from this general thought, probably I would need to see the data to be able to draw any other conclusions for you.

I would need to know more about the system you are studying to be able to answer that question. If you have 3 semicircles that you are fitting with 3 (RC)s, presumably there are 3 distinct processes occurring in your system, and each (RC) should be applied to one of those processes. Every R in those (RC)s is representative of the charge transfer resistance associated with that particular process, but again which processes they are will depend on what your system under study is.

I am doing EIS analysis of the coating on ti alloy and perfectly fit was found with (R3C3) (R2C2)(R1C1)series with RS. Then my question is which is Rct , Cdl, what is Rp value, kindly elaborate me

I have seen all your vidio about the basic s of the eis, find more helpfull,

@@kamalyadav437 First, I must tell you that I will not be able to elaborate fully on your data because rather obviously, I do not have access to your data and your experimental system. There is only so much I can assume from just text. I am not extremely familiar with Ti or Ti alloy electrochemistry, though from what I recall it does tend to form a kind of passivation layer in solution and under polarization, so my best guess is there may be some kind of complex surface film/passivation layer forming on the metal surface during your experiment, and the various RCs you are observing might have to do with a few different interfaces that have formed as a consequence. However, it is also notable to mention that systems like this are notoriously tricky and at times the EIS data itself can be fundamentally inaccurate. For this reason, you should be in the routine of performing Kramers-Kronig analysis on the EIS data to make sure it is valid. It is possible some of the features you believe are additional RCs are just noise or invalid EIS completely.

Thank you very much, I am glad you enjoyed the video! We can certainly add a bipot operation to our ideas for possible content in the future, though to be honest the explanation of bipotentiostat operation is considerably more complicated than even the potentiostat is, and the schematic we use to describe a potentiostat here is already very simplified for educational purposes. To be blunt, I am not sure how easy or understandable it would be to simplify a bipotentiostat schematic and operation. But we appreciate the suggestion and we will keep it in mind for sure!

Thank you kindly!

Thank you! It takes a lot of work trying to make these videos. Some people, Some people, Some people call it insane, yeah they call it insane.

Thank you sir!!

Glad it was helpful! Thank you!

I would ask, is the flow cell active when you take chronoamperometry (CA) experiments? You want the solution to be very still when performing CA. How frequently are the "heart beat" fluctuations occurring? Also, how long are you taking chronoamperometry experiments for and what are you trying to measure?

@@Pineresearch I am measuring the CO2 Reduction reaction products which are release at specific potential ,each batch are tested for 1 hour then i increase the potential for next testing(0.7 -1.3 V vs RHE testing window)which is applied during CA,Yes flow cell is active during whole CA experiment,frequency is very high at higher potential

@@behrozkhan3179 ​ Just to clarify, the potentials you mentioned (0.7 - 1.3 V) vs RHE, I assume those are negative potentials, and when you say "higher potentials" you are referring to higher negative potentials. If you are running CA for 1 hour, one thing to note is how often are you sampling? If you are sampling quickly, every 100 millisecond, then you are going to capture a lot of noise and processes that are occurring during those time scales. You also will generate too many data points (36,000 data points). But if you are sampling at a lower rate (1 data point every 1 second --> 3,600 data points) you might observe a different amount of noise or recurring "heart beat" signals. All that being said, it's hard to diagnose the issue without seeing the CA data, but I hope this helps.

@@Pineresearch I can send you the data but don't know where to send it.Yes sampling rate is 0.1V/s . anyway thanks a lot for your kind help.

@@behrozkhan3179 You can email us at pinewire@pineresearch.com. Mention that you've been talking with Alex via RUclips, and we can continue our conversation via email.

Thank you!!

We can definitely talk about this on the next livestream! Episode #53

Glad you liked it!! :D

Actually there are a few decently Arduino build your own potentiostat papers out there. I don't know if they use the same circuit as this one, but they do exist.

Without seeing your data to know for certain, my best educated guess is to tell you that no, you should not use these LSV data to make a Tafel plot and calculate the Tafel slope. As I mentioned in this episode, the Tafel equation and slope are derived directly from the Butler-Volmer equation, which is an equation that describes exclusively kinetic information, including current. There is no purely kinetic current-time or current-potential curve that results in a peak. The fact that you are observing a peak essentially and fundamentally disqualifies the data, at least in its entirety over that potential range, from being used for Tafel analysis. Regarding your second question, there is basically no difference between CV and LSV. A CV is just two or more LSVs performed back to back.

In the video at 1:27:28 you can see in small font the error statistic for the K-K analysis. There are 3 tabs above the error statistic (small and a little hard to see in the video), those other tabs have fit and measured data, which is the extrapolated K-K data. I hope this was helpful.

Extrapolation from Kramers-Kronig analysis is both unnecessary and, to a certain degree, inappropriate. Kramers-Kronig provides an indication whether your EIS data are valid - that is, linear, causal, and stable. It is not strictly a circuit fit, nor is it a type of analysis designed to extrapolate EIS data. If you are instead performing a circuit fit (after running K-K to determine if the data is properly valid first), then it is perhaps reasonable to see semicircles extrapolated as a visualization of what the data would look like at lower frequencies, for instance. But from K-K analysis this is not needed and does not really provide any useful information.

Out 5-part EIS webinar series is general for EIS and can be useful for anybody trying to learn EIS regardless of the potentiostat they use. For parts of the webinar that go over circuit fitting, we will be using Pine Research's AfterMath software to perform the circuit fitting. But you can use other software to perform circuit fitting. I hope this was helpful.

@@Pineresearch thank you so much

I think that means you like it.