A bit of a complex situation but I was hoping that possibly you might be able to assist me with understanding what is happening in my system and how I might quantify it.
Basically I am attempting to perform chrono amperometry on TiO2 films in KOH. Many studies have looked at LiClO4/PC and H2SO4 as an electrolyte with TiO2 and I cannot, or rather do not wish to use these as I wish to have basic conditions and have issues with LiClO4 as PC reacts with my cell and H2SO4 as it dissolves my ITO electrode from beneath the porous TiO2.
What is happening is that if I use the following setups (with 0.1M KOH) I see no activity:-
Setup 1:
WE - TiO2
CE - Pt
Ref - Ag/AgCl
Potentials - +0.6 / -0.7V Vs ref
Setup 2:
WE - Pt
CE - TiO2
Ref - Ag/AgCl
Potentials - +0.7 / -0.6V Vs ref
Setup 3:
WE - TiO2
CE - NiOx
Ref - Ag/AgCl
Potentials - +0.6 / -0.7V Vs ref
However when I use the following setup I see expected activity and get what seems like very good results:-
Setup 4:
WE - NiOx
CE - TiO2
Ref - Ag/AgCl
Potentials - +0.7 / -0.6V Vs ref
Why do I get activity only in setup 4?
I measured the potentials between the CE and ref using a multimeter and found that the potentials were most stable at -1.38/1.74v (initially over 3v in the positive direction), however if I use -1.38v/1.74v or even less (i.e. +/-1.2v) for setups 1 & 3 and I do get 'some activity' but the TiO2 delaminates / the ITO underneath is damaged.
How can I test my charge capacity for the TiO2 layer without damaging it and why would the charge capacity be greater when using a reactive NiO counter electrode. (The TiO2 layer receives more charge not just the NiO in this situation, as confirmed by other means)
Hi John,
Thank you for your quick reply, as always it is very helpful.
I checked another reference electrode with similar results. The setup appears to work fine when testing NiO on its own with a Pt CE. I have used a salt bridge in the past to avoid any issues with KOH attacking my reference but this appears not to assist either. Positioning within the cell also does not appear to solve my predicament.
Ideally should setups 3 and 4 produce identical results in a 3 electrode setup? I am assuming that since the reference is used only to determine the potential of the WE we can not know the CE potential (vs reference) as this will vary significantly?
I which I had a bistat at this point, not saying it solves anything but it would help identify the issue.
ADDITIONAL INFORMATION:
Ok so, I just tested once again just the stability of the electrolyte using two identical Pt electrodes as blocking electrodes and found that current increased linearly with potentials greater than 1V as would be expected from other studies. This resulted in gas evolution to begin over time.
At WE potental of around -1.5V (Setup 1) I manage to get the expected redox reaction occur, however it is accompanied by electrode damage and eventual destruction as mentioned before.
This suggests that in KOH we require a high potential when working with a Pt counter electrode and the side effect is that the electrolyte is not stable and 'eats' my TiO2electrode.
However when I have the NiO as WE I only need a potential of 0.7/-0.6V and this is acompanied with redox reactions occuring in BOTH electrodes.
I am struggling to understand how this might be occurring? Is it possible that protons are being transferred directly from the NiO electrode to the TiO2 electrode? And that in the absence of the NiO electrode, the protons can only be produced at higher potentials which results in the electrolyte becoming unstable?
This is beginning to drive me insane just attempting to understand why it can work when used with an NiO electrode but not with a Pt one... and only in Setup 4 configuration.
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