The difference between using ferricyanide and ferrocyanide is essentially in which (oxidation or reduction) signal you will first see on your CV. If you are using K4[Fe(CN)6] and scanning towards increasingly positive potentials, you will see the oxidation signal of K4[Fe(CN)6] and, after reversing the scanning direction, the reduction signal of the electro-generated K3[Fe(CN)6]. If using K3[Fe(CN)6] and scanning towards increasingly positive potentials, you will see no signals in the anodic half-cycle, the reduction signal of K3[Fe(CN)6] in the cathodic half-cycle and the oxidation of the electro-generated K4[Fe(CN)6] in the NEXT anodic half-cycle.

Using both salts essentially means that you should see both the oxidation and reduction signals (in the anodic and cathodic half-cycles respectively) regardless of the direction of scanning the potential.

Tomasz Jarosz Thank you for the speedy answer. Just to clarify your second to last sentence:

If using K3[Fe(CN)6] and scanning towards increasingly positive potentials, you will see no signals in the anodic half-cycle, the reduction signal of K3[Fe(CN)6] in the cathodic half-cycle and the oxidation of the electro-generated K4[Fe(CN)6] in the NEXT anodic half-cycle.

I will not see any signals in the first anodic trace, but I will see the reduction signal in the reversed cathodic trace and the oxidation in the next anodic trace?

Yes, since K3[Fe(CN)6] is the oxidised form. You need to electrochemically reduce it to K4[Fe(CN)6] (or, more accurately reduce the [Fe(CN)6]3- anion to the [Fe(CN)6]4- anion) to be able to see an oxidation signal.

To add more to my previous answer, if you will be using a sufficiently low potential scanning rate, you may find that the electro-generated K4[Fe(CN)6] can partially diffuse away from the electrode before you are able to re-oxidise it, yielding a smaller than expected peak.

Tomasz Jarosz , that information was very helpful to me. Thanks a lot!

The hair follicle emitted electromagnetic radiation could be displayed by either solutions of Ferrocyanide or Ferricyanide.

Tomasz Jarosz your explaination is very helpful! I further wanted to ask, if you know if it could be, that a CV is shifted to more negative currents (so the 'negative area' under the curve is way bigger than the positive one) when one only uses Potassium Ferricyanide?

Lara Marie Novak thank you very much, it is good to know that you found my comments helpful.

As to the negative current shift, it is possible, but can be caused by numerous reasons. To elaborate, the current observed in a CV experiment is typically either faradaic (electron transfer between the electrode and redox active species) or capacitive (e.g. formation of an electric double layer at the electrode/electrolyte interface).

A faradaic current would be derived from species that are continuously undergoing reduction at your working electrode (or oxidation at the counter electrode), but if the shift appears for a very broad potential range, it is unlikely to be associated with a faradaic current, as you should be observing a current peak / slope instead.

If the current shift appears in a broad range of applied potential and is fairly uniform, it is most likely caused by some capacitive phenomenon. Is your electrode perhaps non-standard, e.g. porous? I would recommend assembling your electrochemical setup exactly as for the measurement, but instead of a standard measurement, please try to measure the OCP (open circuit potential) of your system (performing such an experiment is now a feature in most potentiostat software, but if you're using an analog potentiostat or one without such a function, such a measurement can be performed manually if needed). If the OCP is far beyond the range of applied potentials that you want to be working with, it may explain this shift.

Apart from the two above, a number of other phenomena might be at play, but more details about your system would be needed to provide any kind of educated guess.

Tomasz Jarosz thank you so much for that comprehensive answer!

The potential range for which the shift to negative currents occurs is only around the reduction peak, on the 'reduction side' so to say (on the oxidation side the current peaks and then approaches zero towards the 'edge' of the measurement, which looks like in literature).

So if I get you right this could be caused by continously reducing the ferricyanide at my working electrode - which is present in a much bigger amount compared to the reduced form as I only add the potassium ferricyanide and no ferrocyanide?

Lara Marie Novak you're most welcome!

As to the reason, this shift can be caused by the reduction of ferricyanide, especially if you apply potentials significantly lower than the potential of the ferricyanide reduction peak.

This may also be caused by an excessively high (I say excessively high, but this typically corresponds to concentrations on the order of 10mM and with some references, such as ferrocene, I've seen issues even for 1mM concentrations) concentration of ferricyanide (the shape of the peaks and eventually their potential separation begin to be distorted with increasing concentrations) and may possibly be resolved by using a smaller amount / lower concentration of ferricyanide (as long as the peak is still observable, you can safely use less ferricyanide).

Benjamin Befeler

Just send some answers explaining the role of Ferricyanide or ferrocynide in detecting hair follicles electromagnetism.

Thanks for the info.

I am using potassium ferricyanide solution as a catholyte in my microbial fuel cell experiment. How do we come to know whether the potassium ferricyanide present as catholyte is accepting the electrons from the anolyte and is getting converted to potassium ferrocyanide? Which test needs to be performed for studying the conversion of potassium ferricyanide to potassium ferrocyanide?

Sumit,

Under oxic conditions it is quite difficult to estimate how much of potassium ferricyanide is reduced.

It is easier if you create anoxic conditions in cathodic chamber - then, you can easily quantify the amount of potassium ferricyanide reduced by using standard molar coefficient of absorbance either potassium ferricyanide either ferrocyanide

Regarding the oxidation and reduction behavior of the individual probes (Ferri or ferro potassium), if you use the couple in equimolar concetration, you can avoid the use of reference electrode and replace with use a pseudo reference of gold or platinum electrode, so your voltagramm will be centered in "cero" in the X axis. Very useful for electrode, cell and electrochemical system validation. Good luck!

Can someone explain about why 1mM ferri-ferro in KCL solution?