For my experiment, I'm currently using a Dropsen 110 Screen-printed carbon electrode (SPCE).
I need to take my material's CV, DPV, and EIS. But I can't seem to find the right DPV. The current response of the DPV was only 15 micro A, but the current response of the CV was 90 micro A.
EIS also exhibits enormous resistance semi-circles. Is anyone else having this issue?
Without knowing anything else about your experiment, I would start by checking the electrolyte. The response is as much dependent on electrolyte as the electrode.
Next, I'd recommend contacting your Metrohm salesperson, since they supply both your potentiostat and your SPEs. In my experience they have very good product support.
Anne Sawhney Hello ma'am,
I am using PBS/[Fe(CN)6]3−/KCl as an electrolyte solution. and yes all the products of Metrohm are really good. I didn't face any problems with their other product. My material shows accurate performance on Screnn-printed gold and platinum electrodes with the same electrolyte solution. But it doesn't show that much accurate results on Screen-printed carbon electrodes. For example, if the material shows CV current response at 150 microamperes in gold and platinum elecrode then in Carbon electrode it was showing around 60 to 75 microamperes. I tested all possible potential window and activation treatments of electrodes but DPV and EIS were not correctly received.
When you say CV response is "150 microamperes", is that the height of one of the oxidation peaks? Without seeing the graphed data, I cannot offer much advice: there are too many possible variables that could be causing higher impedance/lower current for each input signal. This is where the Metrohm staff can be very helpful: they can instantly compare your results to their own standards, and the secrecy that prevents most researchers from sharing information is unfounded in discussions with commercial sales support.
Just based on what you've told me, here are a few examples of considerations to start with: (1) carbon electrodes are naturally higher in impedance than gold and platinum and it's not clear what interfacial resistance/peak oxidation current you were expecting as a standard, (2) subtle changes in concentration of redox probes in electrolyte will have proportionally large effects on current response so batch-to-batch difference could be a factor, (3) [Fe(CN)6]3- will reduce in aqueous solution until an equilibrium is achieved with [Fe(CN)6]4-, so that requires rest time before stability for EIS, (4) you haven't mentioned OCP repeatability or stability before EIS measurements that are sensitive to lingering charges from voltammetry performed before EIS, (5) the reference electrodes react with [Fe(CN)6], especially if they are silver (but still somewhat if they are AgCl) and that will change the output over time, (6) the counter electrode in Dropsens SPEs is smaller than the working electrode so it can be a bottleneck to current and sensitive to surface changes (not sure what you mean by activation treatments but that sounds like more variables).
Anne Sawhney Hello ma'am
I have provided you graphical data in ppt. Please find attached
Of course, I ran OCP before running EIS.
Activation treatment means we cleaned electrodes with various solutions to remove unwanted reagents on the electrode surface. For that, you can wash the electrode with ethanol or water or sometimes you can run CV multiple-cycle in any diluted acidic solution.
Anne Sawhney Ma'am
As you mentioned, the "counter electrode in Dropsens SPEs is smaller than the working electrode so it can be a bottleneck to current and sensitive to surface changes". But it only gives problems to the Screen-printed carbon electrode, not any other like screen-printed gold and platinum electrode. All of them have the same system but the only difference is the Working and counter electrodes, For gold and platinum electrodes they used gold and platinum material as working and counter electrodes. and For carbon electrodes, they used carbon material as working and counter electrodes. All three have the same reference electrode like silver. The working electrode and Counter electrode size are also the same for all of them.
I found this old impedance spectra from when I used the dropsens carbon SPEs with similar electrolyte (it's also in a publication). Although your spectra shows higher impedance throughout, your redox probe is much lower in concentration (I used 10mM ferrocyanide AND 10mM ferricyanide, while your 5mM will equilibrate to 2.5mM of each). Therefore, I think the performance of your carbon SPEs is actually normal, since they should have higher impedance (therefore lower current response) than the gold and platinum.
The one thing in your spectra that might be concerning is the starting point of the Z' (often modelled as Rs), which is dependent on frequency but in your case it is unusually low in the case of gold SPEs (negative Z') and unusually high for carbon SPEs (almost 1000ohm). That must be diagnosed in person, it's not likely a material property. I don't see any problem with the rest of the spectra.
Anne Sawhney Thank you so much for your help, ma'am.
You said that my data is "unusually low for gold SPEs (negative Z') and unusually high for carbon SPEs (almost 1000ohm)." Then what is the standard value for that?
And what about DPV? Doesn't it need to be seen as a close CV Oxidation peak?
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