I know this is an old discussion, but I just wanted to point out (with all due respect) that the idea that applying a +1 V (vs ref) potential on the working electrode leads to a counter electrode potential of -1 V (vs ref) is fully incorrect. This seems to be the misunderstanding of several in this thread.

Indeed the counter electrode current is equal and opposite to that of the working electrode, but regarding potential, it is a completely different story. In brief, during chronoamperometry, the counter electrode potential is whatever it needs to be to match the current flowing through the working electrode. This depends on numerous factors, including the relative size of the counter electrode, its material, and which reaction(s) occur at the counter. (Some potentiostats provide the ability to measure the counter electrode potential during experiments, but this does not seem to be very common.)

If you are using any kind of potentiostat, the applied voltage is measured between the reference (RE) and working electrode (WE), but is applied (and current flows) between the counter (CE) and working electrode. Assuming that you have an ideally conducting electrolyte, if you apply +1V at WE (vs. RE), the potential at the CE (vs. RE) will be -1V. In a real electrolyte, this potential will be slightly farther from 0V (e.g. -1.2V), due to the resistance of the electrolyte (and cell geometry and several other factors).

Since you typically don't record (and don't even have the option of doing so) the potential of the CE, it may be very difficult to apply the same potential wave to the WE and then to the CE.

That said, allow me to pose you a question: does the application of reductive potentials in excess of -1V to the WE, which was already coated with your layer, not harm the layer? This may be the source of your lower than expected specific capacitance.

Frankly, I would recommend using a larger WE (or multiple connected WEs) to achieve the result rather than attempting to replicate on your CE the coating process taking place on the WE.

Tomasz Jarosz

Thank you for your answer and suggestion.

However just for further understanding, since the applied voltage on CE might differ slightly from the actual, I would expect similar if not slightly different amounts of composite coating although uneven as the voltage steps. Instead what I am getting is barely any coating on CE when using applied voltage levels of -1.0/1.0V.

Also, may I clarify on what you meant by your question so I may provide an answer?

I agreen with that the applied voltage is measured between the reference (RE) and working electrode (WE), at the same time, the reaction is happened between the WE and CE (just like the cathode and anode in two electrodes system) so it's very important to choose suitable CE and WE.

Soon Heng Keng

What I meant by my question is that since you synthesise your coating by applying -1V at the WE, the subsequent application of +1V to the WE might affect the already deposited coating. This may be both beneficial or, as I expected, harmful (I would expect the coating to be partially oxidised and dissolved, making it lose capacitance).

As for you not getting much coating on the CE: Since the potential at CE will be more negative than expected, either your coating may undergo further reactions and be degrading during the experiment or the surface of the CE might be getting poisoned with the product of another reaction and hindering the deposition of your coating.

That said, without knowing more details on your system, I can only point you to the most likely "culprits" in a general case - you need to evaluate whether these phenomena are possible and likely in your particular system.

A three electrode system consist of the working electrode , the counter electrode and the reference electrode. If an anodic reaction is undergoing at the working electrode ( generation of electrons) there must be a cathodic reaction undergoing at the counter electrode. The electrons generated at the anode must consumed at the cathode. Some times you find that hydrogen evolves at the counter electrode

2 Hydrogen ions + e electrons ---- Hydrogen gas is a cathodic reaction or reduction ( hydrogen lost positive charge). In this case there must an anodic reaction at the working electrode such as

Fe ---- Fe(II) + 2 electrons. This is oxidation or gain of positive charge.

Both platinum ( e.g platinum sheet) or carbon ( e.g carbon rod) are nonreactive during petrochemical reactions.

Tomasz Jarosz make good sense. Indeed you measure current density i in unite of A/square cm and not Ampere. So current density depend on the area of the electrode. This is very clear if you understand mixed potential theory. See book of Fontana and Green. Corrosion Engineering