plante1999
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bromide electrolysis
It is known that mmo anode will degrade in bromide solution because the substrate is titanium, which is attacked by bromine. We also know that carbon
and platinum will make bromine without extreme degradation.
I read patents about mixed precious metal film with about 25% teflon in them for the substrate for such anode, or as the anode themselves, however, I
wanted to know if anyone had tried lead dioxide, or any anode material for bromide electrolysis.
It could even be possible to make a plain lead dioxide anode by sintering teflon and lead dioxide together.
Thanks
[Edited on 14-1-2014 by plante1999]
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Metacelsus
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I have used MMO without any problems, but I was forming sodium bromate, not bromine. I later acidified the solution to form the bromine.
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plante1999
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In my experimentation, the mmo anode mesh degraded in bromide solution to make bromate (in situe making bromine).
Woelen also observed some degradation on mmo anode that he reported on his website.
It is strange, what was your anode source?
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WGTR
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I've made small amounts (< 1mL) of electrolytic bromine from sodium bromide solution, using a graphite anode. The cell was
not divided. The graphite held up just fine, up until a non-specific point where the pH of the solution began to rise. Then
I'd start seeing some erosion of the anode.
Another post that I made describes a few details of the setup:
https://www.sciencemadness.org/whisper/viewthread.php?tid=26...
The idea is to keep the solution saturated with bromide to protect the anode; ice-cold and with the tip of the anode near
the bottom, so that the bromine is less likely to mix into (and react with) the rest of the solution.
It is a very inefficient use of NaBr, but it works if you want small amounts of Br2.
As an aside, if you mix the solution up you'll end up with sodium hypobromite (if the solution is ice-cold). I've made a few small
oily drops of bromoform this way (by adding acetone, not to excess).
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plante1999
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I was very aware of bromine dissolution in the base formed to make hypobromite, that readily disproportionnate into bromate, however, my interest lyes
more into divided cell, although the point that the carbon does not seams to degrade when in neutral or acidic condition is very interesting.
The idea would be to make a cell using electrodes plates, gaskets, and membrane, and passing the lye solution in the cathodic compartement, and the
strong bromide solution in the anodic compartement. The flow of the bromide could be calculated so most if not all the bromide as been oxidized when
it exit the cell. As such, the bromine could be boiled/extracted/stripped, and the remaining solution sent back to thec cycle.
Much like the membrane cell technology for chlor-alkaly industry, but working on bromide. If carbon do not degrade much, it would be perfect as easy
to find sheet of it quite cheaply.
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WGTR
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Can you access this paper? I looked through it briefly, and it gives a solubility curve for bromine in aqueous solutions of
sodium bromide. It may be useful to you. Edit: all of the important information is available on the preview page.
I agree, a divided cell would work much better for something like this. Also, with bromine being quite heavy, the first thing it
does is run to the bottom of the container if the solution is kept very cold. It may be possible to withdraw the bromine-rich
anolyte from the bottom of the cell, minimizing the amount of electrolyte turn-over required.
The graphite rod that I was using for an anode was from POCO Graphite, type DFP-2. This is a high-purity form of graphite.
It sounds like you have another fun project planned out.
[Edited on 1-15-2014 by WGTR]
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plante1999
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I does not have acces to papers.
The problem I foresee with graphite is that in the cell I planned out, the electrodes also serve themself as seals, which could be problematic if the
anode degrades.
I do have something planned out, although, I'm currently very very low on cash, so I simply gather all the informations needed until I can manage to
work on it.
Here was a rough draft I made a few day ago for something similar, that migth help to get the idea. The membrane would be nafion. Two inlet, and two
outlet. One inlet for NaOH sol, and one for the NaBr sol.. And one outlet from bromine + water and one for the sligthly more concentrated NaOH. The
electrodes and gaskets are used as conduits for the solutions.
http://i1103.photobucket.com/albums/g469/plante1999/Draftchl...
http://i1103.photobucket.com/albums/g469/plante1999/Draftchl...
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jock88
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See paper
Attachment: bromates.pdf (130kB)
This file has been downloaded 549 times
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WGTR
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I looked at your drawings, plante1999, and I think I understand what you're planning to do. Most of the time the surface of
the graphite has to be converted to a glassy form before it will seal very well. Moisture (and especially molten salts) will seep
through it otherwise. The speed at which this happens depends on the quality of the graphite. It might not be a problem for you.
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plante1999
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Thanks jock88, very interesting method to make plain PbO2 electrode.
To try to explain better the drawings, there would be layer made as such:
Backplate, gasket, anode, gasket, membrane, gasket, cathode,
and so on to the desired amount of electrodes, based on the amperage and voltage that can be given to the cell. All theses would be bolted within two
backplate made of a fluorinated polymer. The gaskets would be of fluorinated rubber, such as viton. all gaskets of the cathode would for example have
the "grooves" on the right, and inverse for the anode, so only cathode(s) would be able to have access to those conduits, and similar for the anodes.
A mean to separate catholyte from anolyte, which would be stored in tanks outside of the cell.
I have heard of glassy carbon, however I doubt in my capacity of making it. An idea might be to impregnate the graphite with a liquid fluorinated
monomer of some sort and cure it to fill the pores of the graphite electrode with inert polymer?
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MrHomeScientist
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This all sounds overly complicated. Granted, I am definitely no expert at electrolysis, but I had amazing results with just plain-old graphite
electrodes in a mason jar. My graphite rods were bought on eBay as stirring rods for metallurgy. I coated the metal jar lid with electrical tape to
prevent corrosion, and that held up beautifully. The seal between the rods and lid wasn't perfect, but I never smelled anything and did the
electrolysis inside the whole time. After 26 hours of electrolysis, there was almost zero corrosion - only a light dusting of carbon particles at the
bottom of the jar.
Here's a link to part 1 of my synthesis: http://www.youtube.com/watch?v=NKjyM2AkZSY
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plante1999
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You probably did not understand the idea. In your set-up, you are making a mixture of bromide and bromate that you then acidify to make bromine. I'm
speaking of a device that continuisly make liquid bromine out of sodium bromide, and make sodium/potassium hydroxide at the same time.
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MrHomeScientist
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Ah I see. Sounds like a very interesting project. Sorry for the confusion!
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plante1999
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It explain the complexity of the devise too. By the way, your video was quite nice. I look forward when you will try theses mmo anodes!
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MrHomeScientist
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Thanks! I found the procedure on woelen's website and really liked it because I didn't have to distill and it only used OTC chemicals (well, except
the dichromate).
I definitely need to find a good experiment for the MMO and titanium electrodes. I might start with electrolytic potassium chlorate, since I've
already made that via boiling bleach. That's not particularly interesting, though - any other ideas? Perchlorate, perhaps? Then again I'm not really
interested in pyrotechnic applications.
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plante1999
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Chlorate are the easiest to start with. This type of anode will not make perchlorate, however, you can use it in presence of chloride to in-situe
oxidize a subrate, you can also electrolise sulphates.
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Metacelsus
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I guess I spoke too soon . . .
I tried using my MMO anode for another bromide electrolysis, and it began to corrode. Interestingly, I was using a lower current density than before.
Thus, I do not recommend using MMO anodes for bromide electrolysis.
Will platinum-coated titanium hold up?
[Edited on 13-2-2014 by Cheddite Cheese]
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