Hi guys,
I'm performing a chronoamperometry on a steel sample with a silver / silver chloride reference and a large titanium wire spiral as counter electrode. I perform the measurement with a PalmSens4. The solution contains around 0.1 M NaCl. This setup seems to lead to issues.
I skip the symptoms here, because we have identified the cause: The potential between the counter electrode and working electrode runs into the compliance voltage, i.e. it is too high.
No surprise: As soon the 10 V compliance voltage are reached the potentiostat behaves strange.
I don't understand why the compliance voltage is so high. I don't see any gas evolution or yellow color on the counter electrode, which I would expect due to hydrogen or chlorine evolution. The counter electrode should be big enough. I tried a graphite electrode, which lead to the same results.
So I was wondering, if there are other reasons for a high cell potential then a too small counter electrode and low conducting solution?
Any ideas for troubleshooting are appreciated.
Is it, really, chronoamperometry (?), and if so, it is under which (presetting) Potential value ?
Yes, a potential is applied and a current is measured over time.
The OCP is around -700 mV and the set potential is -850 mV.
I suggest you have a broken circuit/wire/electrode. The potentiostat is trying to polarise WE; it doesn't find -850 mV between WE and RE, thus it continuously increases the voltage applied between WE and CE (until the compliance voltage limit is reached).
Verify if PalmSens is OK, with a dummy cell ( use a 1...10 kohm resistor). Then verify the continuity of your metal electrodes (use a common voltmeter). Verify if RE is clogged or not.
RE's troubleshooting issue is the most frequent headache in such debugging studies.
Also, is it, possible, to reduce the surface of the WE (use a smaller) part, exposed to the electrolyte, in order to fit better into the smaller power (and current limitation) compliance specs of your setup ?
Hi guys,
Sorry for not responding for a long time.
Cornel Radu Yes, that were my initial thoughts as well and the cables were fine. However, I tried a new cable and that didn't change the situation. The PalmSens4 was working fine. This was tested by the quality management.
Ioannis Samaras That was also an idea we had and it didn't seem to change anything as well, this is why I started to think, something is going on, which I don't comprehend.
Unfortunately, I won't be able to perform any experiments myself for some time, but I appreciated the input you provided.
Hi Lutz,
I would have also bet on a bad contact or on a bad counter electrode.
How much current are you expecting? Does it work if you polarize to a different potential? Can you perform a cyclic voltammetry or nothing work at all? Did you try to perform the experiment in 2-electrode configuration?
Maybe the most important question since you use Ti counter electrode. Is the experiment working and then reaching the overpotential after maybe few seconds? Did it maybe work for a while the first time and then it did not work anymore? If so then the problem is the anodization of the Ti.
Also, the initially good (ohmic, electrical) contact of the CE (Ti) with the cell's external (usually a Cu?) wire, upon soldering (and/or mechanical) scales in sub-ohm (contact resistance) values, measured with a common 2-electrode mode, say a "fresh" resistance: RTi;Cu,#1 ~1 ohm, or less.
However, complex character aging effects of pure Ti-surfaces, under humidity,
might increase by several orders (in ohms, RTi;Cu,#1 --> Mohm, or less), this, single, "dummy" (metallic) electrical contact on Ti.
We propose to form an additional (2nd, same) electrical contact (with the 2nd Cu wire) on the Ti (-wire, CE), away, about 1mm (or so, in length) from the 1st electrical contact.
So, now, you will be able, not only,
1)to check, any time, whether this RTi;Cu,#1 (
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