Hi everyone,
Currently, I am doing the cyclic voltammetry measurement using 1 M KOH as the electrolyte. Since this electrolyte has high pH (~14), which reference electrode that most suitable for this condition? Should I use Ag/AgCl or Hg/Hg2SO4 reference electrode?
Last time I use Hg/Hg2SO4 but after couples month of using that electrode, the mercury and sulfate layer disappear (I attached the photos). I am not sure is it possible that high pH concentration can destroy Hg/Hg2SO4 reference electrode.
Thank you for the answers.
Dear Dr. Anafi Nuraini,
everyone agrees that an ideal reference electrode has a stable, well-defined electrochemical potential. Common reference electrodes (SCE, Ag/AgCl, Cu/CuSO4) meet this criterion when they are functioning properly. Many workers do not realize how often reference electrodes fail, causing drastic changes in their potential. Many complaints of potentiostat failures turn out to be reference electrode failures.
An ideal reference electrode should also have zero impedance. As discussed below, a reference electrode’s impedance can strongly affect the performance of a potentiostat.
For more details, please see the source:
-Reference Electrodes by Gamry Instruments
Available at: https://www.gamry.com/application-notes/instrumentation/reference-electrodes/
I suggest you also to have a look at the following, interesting paper:
-Hydrogel-based flexible micro-reference electrodes for use in alkaline and neutral pH solutions
Schimo, G., Grill, C.D., Kollender, J.P. et al.
J Solid State Electrochem 20, 2749–2757 (2016)
Available at: https://link.springer.com/article/10.1007/s10008-016-3257-9
Best regards, Pierluigi Traverso
@ Anafi, I think you may try with the silver chloride electrode which is most commonly used as a reference electrode in pH meters.
Anafi Nuraini,
My personal experience is that any compositions that can react with KOH chemically will not survive long. Hg/Hg2SO4 and Ag/AgCl are proven to be dead after a while in strongly alkaline solutions. I used Hg/HgO reference electrodes and they are fine. Hope my suggestion will help you.
Dear Dr.Anafi Nuraini,
I faced the same problem, When i was using Hg/HgCl2 in KOH. Mostly it happen when you are using Long tests (CV 1000cyc or CP-24h). Now i am using Hg/HgO reference electrodes for KOH electrolyte and they are fine. Hope it will help you.
Best regards,
Sajed
When using a Hg/HgO reference electrode, you may easily adapt the concentration of OH in the reference electrode to the pH you have in your experiment.
Dear Anafi
you may use ther Hg/HgO reference as it is filled with KOH. A better choice would be the Hydrogen Electrode RHE. We produce that electrode now for 20 years - especially for the use in KOH. Trademark Hydroflex. Good luck
https://www.sciencedirect.com/topics/chemistry/reference-electrode
Dear Anafi Nuraini
I have used Hg/HgO/1 M NaOH for many years since 1993, where I made (home-made) my electrodes at the laboratory of Anderzej Lasia during my PhD Thesis (Canada-Sherbrooke) by myself.
You can make Hg/Hg/1 M NaOH by yourself , it may not look like so beautiful, but it works nice.
Use a glass body, with a piece of Pt connecting the bottom of glass tube (e.g. a testing tube) to outside, put a 2-3 mL metal Hg inside, connected to internal-side of Pt. Mix Hg+HgO 1:1, 2-3 mL in a porcelain Mortar to get an amalgam sludge! Use a use a spatula and put sludge (1-2 mL) on metal Hg inside the tube slowly (take care to avoid mixing the Hg now with sludge amalgam!). Use a pipette and put 1-2 or 3 mL of ready prepared 1 M NaOH of top of sludge amalgam. close the tube and keep it motionless for 24 hours in a clean atmosphere. use a male tube filled with 1 M NaOH AND a free line Pt (optional) inside and connect the your home made reference to your electrochemical cell. E=0.926 to 0.930 mV vs RHE. Good luck and enjoy your research.
The reference electrodes are commercially available too, but they thiny and expensive, I do not use them.
But i think Hg/HgO impedance is about 10k ohm, such value will be a problem during EIS measurement?? also in high pH solutions you can found many authors used Ag/AgCl and SCE electrodes which both are recommended for neutral solutions. it depends on the quality of the recorded data and the appearance of the electrode it self. if no precipitate on the inner glass of the electrode after the long time i think it is ok. also you can always check the electrode with another new of reliable one in the same solution.
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