Hello, so this is something that has been bothering me, and I can't seem to find the answer. I am running characterization CV experiments using the redox couple ferri-/ferrocyanide. My working and counter electrodes are both gold. My question is how does my choice in reference electrode material affect my results. If I were to run identical experiments, one using a platinum reference and one using a SHE, would I get different results?
I assume would see a shift in the voltammogram, but doesn't this mean I'm observing a different equilibrium potential?
Thanks,
Hunter
This is an interesting question. In electrochemistry, the key point is that the measured electrode potentials are always relative to each other. All efforts to practically determine absolute electrode potentials have been unsuccessful. As you said, the potentials will shift as we would switch from one reference electrode to the other. However, historically, electrochemists have agreed upon using the standard hydrogen electrode as the reference and arbitrarily assigned it a value of 0.000 V. Since we know the potential of the reference electrode say gold, or Ag/AgCl wrt to the standard hydrogen electrode, it is easy to go back and forth the and determine the equilibrium potential wrt to the hydrogen electrode, against which all potentials are quoted. The punch line is that for experimental purposes (a) we should always mention the reference electrode with any potential measurement and (b) the potential of the reference electrode should be known with respect to the standard hydrogen electrode so that we can always go back to the SHE.
The above mentioned arguments will fail, if electrodes interfere in the redox processes either catalytically or take part in chemical reactions or the electron transfer is slow. More details of the electrode characterization are given here:
www.asdlib.org/onlineArticles/elabware/kuwanaEC_lab/PDF-19-Experiment1.pdf
Right, so essentially, I should be seeing a shift based on the potential wrt SHE? If I'm using a Au reference (+1.5 V vs. SHE), then I should see the equilibrium potential of my ferricyanide shifted +1.5 V right? Again assuming the electrodes do not take part in the redox process.
"If I'm using a Au reference (+1.5 V vs. SHE), then I should see the equilibrium potential of my ferricyanide shifted +1.5 V right? Again assuming the electrodes do not take part in the redox process."
You can also think of it this way: If you are measuring the potential of an electrode with respect to Au, then whatever value you get, temporarily assume the potential of Au electrode as 0.00 V. This is only possible when we would subtract 1.5 V from the measured ferricyanide value. The resulting potential would be the ferricyanide/ferrocyanide potential wrt to SHE.
Assume, we were using a reference electrode to measure the ferricyanide/ferrocyanide potential whose potential was -1.5 V vs SHE, in that case we would have assumed that ref. electrode to be 0.00 V; this would be possible when one would add 1.5 V to the ferricyanide/ferrocyanide couple. The resulting potential would be the ferricyanide/ferrocyanide potential wrt to SHE.
This is a very useful link for interconversion along with the explanation. http://www.consultrsr.net/resources/ref/refpotls2.htm
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