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Author: Subject: More on PbO2 electrodes
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[*] posted on 4-1-2013 at 09:03


While not a PbO2 effort, pyrochlores, especially of the Bi Ru varieties, apparently will make perchlorate. Someone else here at science madness found the preliminary patent on this... I forgot who, but he gets the credit for what may be an interesting, new pathway to perchlorate.

I cannot save the patent, but it is available on Google Patent search. Enter 2011/0226634 for the search string, it'll pop up.

From that document, I searched for more dealing with Bismuth Ruthenium Pyrochlores. There are a handful of them. Usually, pyrochlores are formed in a solid-state reaction at high temperature, but there are a couple of patents that discuss their aqueous formation in an alkaline solution.

While adhering solid pyrochlores to a Ti substrate is going to be problematic, it may be possible to attach pyrochlores formed in solution using the standard Henri Beer "paint & bake" methodology, or using electrophoresis, or some other sol method.

There is a slight possibility of adding Bismuth to a section of standard, commercial MMO, which is predominantly Ru as the electrocatalyst, firing at high temperature, and forming the pyrochlore in situ.

I am currently in a research mode on these compounds, and am gathering reagents to give it a shot. The notion of a perchlorate MMO is very appealing, even one that is relatively inefficient, so long as it actually holds together for any length of time!
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Rosco Bodine
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[*] posted on 28-1-2013 at 12:59


This appears to be the patent
US20110226634 Bismuth Metal Oxide Pyrochlore Electrode Materials.pdf

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[*] posted on 10-4-2013 at 19:16


Quote: Originally posted by axehandle  
Hmm, that's a point I've given some thought actually --- I don't know if a welding transformer can cope with "continous" running for long; I would suspect that those that can cope with it are not the cheapest kind.

Anyone know or have a pointer?

MadHatter, do you have data as regards to your cell volume and your anode area?

Also, a question for those more versed in electronics than me: Are there any caveats to connecting 2 or more power supplies in parallell to the cell? (if this works ATX PSUs can be used...)



Power supplies often fail catastrophically when used in parallel. They can be used in series provided that they have the same ratings and that proper isolation is maintained.
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[*] posted on 5-5-2013 at 08:47


I found another interesting, earlier patent (1974): "Pyrochlore Electrodes" (attached).

Although the patent doesn't specifically mention perchlorates (it seems intended for chlor-alkali cells), I think the "meat" of this patent is what the latest patent - which does mention perchlorates - is based on.

The patent also mentions using a titanium substrate - with a hydride layer - underneath the pyrochlore surface.

Also attached is a paper where the performance of a glassy carbon anode was improved by simply pressing/rubbing some kind of microcrystalline Bi2O3 onto the surface:

Abstract
Bismuth oxide (Bi2O3) modified glassy carbon electrode (GCE) was fabricated by mechanical attachment. Electrochemical performance of microparticles of Bi2O3/GCE shows excellent electrooxidation of ascorbic acid (AA) in 0.1M KH2PO4 using cyclic voltammetry. The effect of Bi2O3/GCE is evident by the observation of high peak oxidation current of AA, showing an increase of 2 folds as compared to bare GCE. The detection limit of this modified electrode was found to be 8.1 x 10-6M. Hydrodynamic method (RDE) was used to determine the diffusion coefficient and rate constant of AA with values of 5.4x10-6 cm2s-1 and 2.7x10-3 cms-1 for unmodified electrode, while the values of 6.2x10-6 cm2s-1 and 2.3x10-3 cms-1 for GCE modified with Bi2O3, respectively.

I can't help but see these several patents regarding Bi based pyrochlores (and one or two with Bi2O3/TiO2 and/or SnO2 coatings) as merely an extension of Beer's work with MMO anodes. (Apparently for some reason he just didn't go there...otherwise we'd probably be able to buy perchlorate-capable MMO anodes on ebay right now). Anyway I could be wrong but it seems to me from the various patents and the literature that if you can get a surface with a conductive, stable, crystalline form of bismuth oxide, you'll have a perchlorate-capable anode.


Attachment: US3801490.pdf (433kB)
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Attachment: Bi2O3 on Glassy Carbon Electrodes.pdf (405kB)
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[*] posted on 5-5-2013 at 19:20


Hi JP

Re. the pyrochlore electrodes patent. Whilst they may make perchlorate as well as chlorate, I guess there is not all that much commercial demand for such an electrode. There is already the LDO electrode, and this pyrochlore electrode looks tricky to make and in its various forms, uses a swag of Pt group metals.

Nothing makes perchlorate better than Pt, and a Pt plating on Ti seems to have been perfected industrially, so why bother with anything else. The perchlorate industry is relatively small, I would imagine, compared to the chlor-alkali industry, only demand being from rocket propellant and pyrotechnics. I guess the economics just didn't stand up.
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[*] posted on 6-5-2013 at 11:23


Hello Xenoid,

I agree about the platinum. As of right now, it's probably the best choice. (Not too long ago I got some platinum-clad niobium mesh material from Anomet, and it's nice stuff).

I was hoping that by now, somebody would be offering boron-doped diamond material at a competitive price...alas it never happened, AFAIK.

And I agree that the pyrochlore material seems like it would be a real PITA to do anything with. As I see it, the pyrochlore info is interesting because of the implication (to me at least) that to the extent it works to make perchlorate, it works mainly because it presents a stable form of bismuth to the electrolyte.

This leads me to the one thing that still bothers me: it seems the use of Bi2O3 for perchlorate has not been fully explored. I think there's one last experiment that's worth doing for anyone so inclined: electrodepositing a layer of delta-Bi2O3 over MMO or platinum.

According to the literature, delta-Bi2O3 has been electrodeposited from a solution of Bi(NO3)3, KOH and some tartaric acid (or something like that). That makes me wonder: What if you put a layer of it on a cheap MMO anode? Maybe you'd end up with a perchlorate-capable MMO anode. Or what about over platinum? Maybe it would spare the platinum and make the anode last a lot longer. I don't know...it's all speculation of course...but if the literature shows that you can simply mechanically rub a glassy carbon anode with Bi2O3 powder and make the anode work better in some application, then it seems possible to me that a thin electrodeposited layer over the right substrate could be useful. IOW think about it as a possible "improvement" to an already established technology.

If it works, it seems that it would be relatively cheap and easy to do and doesn't involve any nasty chemicals.



[Edited on 6-5-2013 by jpsmith123]
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[*] posted on 6-5-2013 at 12:48


I've seen somewhere written, that a mixture of PbO(PbO2?) with glycerol will solidify and this is used as a glue, is that true? So, if we make such a mixture and rub it on Ti sheet, and then turn it on as an anode in some sulfate solution (to convert all kind of Pb oxide(s) to PbO2) won't it give us a type of working PbO2 anode without electrolytic deposition, etc. ?
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[*] posted on 6-5-2013 at 20:04


Check out this thread:

I don't think anyone's tried it (or if anyone has they've never reported it, AFAIK).

Quote: Originally posted by papaya  
I've seen somewhere written, that a mixture of PbO(PbO2?) with glycerol will solidify and this is used as a glue, is that true? So, if we make such a mixture and rub it on Ti sheet, and then turn it on as an anode in some sulfate solution (to convert all kind of Pb oxide(s) to PbO2) won't it give us a type of working PbO2 anode without electrolytic deposition, etc. ?
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[*] posted on 6-5-2013 at 23:35


Unfortunately I don't have any PbO or a handy Pb compound to try this, but it's interesting why this mixture will solidify at all, what's the chemistry ?
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[*] posted on 7-5-2013 at 09:37


http://ir.library.oregonstate.edu/xmlui/bitstream/handle/195...

Quote: Originally posted by papaya  
Unfortunately I don't have any PbO or a handy Pb compound to try this, but it's interesting why this mixture will solidify at all, what's the chemistry ?
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[*] posted on 7-5-2013 at 14:49


Thank you jpsmith123, I wish there was some information about electrical conductivity of such mortars, but it's not an as it seems to be sort of organic polymer, I doubt it'll conduct. Only value I think if one takes a large excess of PbO, that most of it will stay unreacted in forming binder. Seems too simple, but may work, especially if the mortar is water proof, it'll prevent the passivation of Ti. I don't have any source of Pb compounds, except metal form, if someone finds this easy to try and responds results backt - 'll be very appreciated!
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[*] posted on 18-7-2013 at 12:10


Sources like wikipedia cites that lead dioxide can be plated directly on lead, but it has tendency to peel off.

How easily this coating comes off from lead plate?
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[*] posted on 19-7-2013 at 12:40


Maybe this can be found on this thread, but I have a few questions.

1) Why is nobody using "cheap and easy" valve metals, like steel, aluminium, copper, etc. to impregnant a coating consisting of MnO2, PbO2 or MMO either electrolytically, chemically or mechanically? Does titanium carry such chemical or mechanical properties that it is ideal for valve metal? It's electrical conductivity happens to be one of the worst of all metals, only 4.1% of that of a copper, and it's still quite a pricely commodity, or those who sell it, know that those who want to buy it, will pay everything to get it...

2) How well will MnO2 withstand pure chlorine gas? How long will a rather thin layer of MnO2 withstand chlorate, chlorine, hypochlorite and similar conditions(no Percs)?

3) How much force would it need from a hydraulic press to compress finely powdered MnO2 or PbO2 into a solid, monolithic electrode? I could get my hands on a 100-ton press with hardened carbide inserts that could generate forces in excess of 10 tons per square centimeter.

4) Why there are no other sources except wikipedia (https://en.wikipedia.org/wiki/Lead_dioxide#Production) and this blog (http://the-rocketblog.blogspot.com/2012/07/how-to-make-ammon...) that describe the direct impingement of PbO2 on lead valve with sulfuric acid electrolysis bath? This is by far the easiest and most straightforward method of producing CCP-resistant(chlorine, chlorate, perchlorate) electrodes, compared to those which need water soluble lead salts and precoatings with third metals.

I have studied that one major problem with PbO2 is the hardness difference, which could cause the breaking and possible flaking of PbO2 from lead element. This can be caused from mechanical stress(bending), or the well known creeping of lead, especially on hot environment. Although creep is mostly limited on material under load or very long periods of time(like several decades), it would be enough to cause the PbO2 crack, depending on the conditions, within days or months.

Few methods to prevent this may exist, although. I figured out that I could make thicker electrodes, consisting of at least 5mm thick lead plate, and insert a steel sheet, maybe hardened one, thickness of 1-2mm, inside the lead electrode to rigidify the structure and virtually prevent any vertical creep. I calculated that I'd need about 1-1.5kg of lead per every electrode (300x100mm, 5-6mm thick).
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[*] posted on 19-7-2013 at 13:13


Quote: Originally posted by testimento  
4) Why there are no other sources except wikipedia (https://en.wikipedia.org/wiki/Lead_dioxide#Production) and this blog (http://the-rocketblog.blogspot.com/2012/07/how-to-make-ammon...) that describe the direct impingement of PbO2 on lead valve with sulfuric acid electrolysis bath?
There probably are other sources, perhaps you're just not searching effectively. Try Google Scholar . Also, what is "lead valve"? Please check that "valve" is the word you intend.



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[*] posted on 19-7-2013 at 14:30


Quote: Originally posted by testimento  
Maybe this can be found on this thread, but I have a few questions.

1) Why is nobody using "cheap and easy" valve metals, like steel, aluminium, copper, etc. to impregnant a coating consisting of MnO2, PbO2 or MMO either electrolytically, chemically or mechanically? Does titanium carry such chemical or mechanical properties that it is ideal for valve metal? It's electrical conductivity happens to be one of the worst of all metals, only 4.1% of that of a copper, and it's still quite a pricely commodity, or those who sell it, know that those who want to buy it, will pay everything to get it...

2) How well will MnO2 withstand pure chlorine gas? How long will a rather thin layer of MnO2 withstand chlorate, chlorine, hypochlorite and similar conditions(no Percs)?

3) How much force would it need from a hydraulic press to compress finely powdered MnO2 or PbO2 into a solid, monolithic electrode? I could get my hands on a 100-ton press with hardened carbide inserts that could generate forces in excess of 10 tons per square centimeter.

4) Why there are no other sources except wikipedia (https://en.wikipedia.org/wiki/Lead_dioxide#Production) and this blog (http://the-rocketblog.blogspot.com/2012/07/how-to-make-ammon...) that describe the direct impingement of PbO2 on lead valve with sulfuric acid electrolysis bath? This is by far the easiest and most straightforward method of producing CCP-resistant(chlorine, chlorate, perchlorate) electrodes, compared to those which need water soluble lead salts and precoatings with third metals.

I have studied that one major problem with PbO2 is the hardness difference, which could cause the breaking and possible flaking of PbO2 from lead element. This can be caused from mechanical stress(bending), or the well known creeping of lead, especially on hot environment. Although creep is mostly limited on material under load or very long periods of time(like several decades), it would be enough to cause the PbO2 crack, depending on the conditions, within days or months.

Few methods to prevent this may exist, although. I figured out that I could make thicker electrodes, consisting of at least 5mm thick lead plate, and insert a steel sheet, maybe hardened one, thickness of 1-2mm, inside the lead electrode to rigidify the structure and virtually prevent any vertical creep. I calculated that I'd need about 1-1.5kg of lead per every electrode (300x100mm, 5-6mm thick).


Base metals are readily attacked under anodic conditions and Ti is passivated by formation of TiO2 insulating film where it contacts with solution(so needs to be covered with something conductive like PbO2) thus further attack is prevented, that's the most valuable property of this metal. From my experience - PbO2 was tried once then given up (too hard form me) and the same with SnO2, MnO2 on Ti worked some hours well, then it passivated (I suspect Ti is oxidized by MnO2 itself during operation), and the only thing that worked for a week continuously and produced some 50gr of chlorate under about 1.3A current was - Co3O4 on Ti(5 coats, very thin and shiny), but finally it wore down.
I don't like to see that this anode threads are not interesting to anyone anymore, since there are many untested ideas even after so many years, particularly metal oxides, like (from memory) - cobalt/nickel oxides (from some chinese paper I found in similar threads that states nickel oxides are increasing Co3O4 service time) also ''nickel oxide'' is used in alkaline batteries so must be conductive itself and who knows maybe it withstands in chlorine cell. What about silver oxide (also used in batteries), I never met anything about it, had I some Ag I would try that for sure. Then, somewhere in a similar thread I've mentioned that once the mixture of PbO2 (or other oxide, don't remember) with glycerol was used as a waterproof cement for glass because it solidifies, also never tried as anode and there's a small hope that it can be conductive (while many are playing with PbO2/epoxy mixtures with little success as I know).
From other curious things I've done I can remember CuO on Ti (after I found out that CuO is conductive with the help of piezo from lighter - good and easy way) - actually it worked for a minute and then the whole coating was lost (not mechanically), so this doesn't worth to continue. Also many mention magnetite, however I never heard - is it possible to coat Ti with it (like MnO2 or Co3O4) instead of trying to melt a lump of it which is very difficult. I tried once by dissolving iron in HNO3 obtained Fe(NO3)3 i guess, but thermal decomposition of it gave some non-conductive oxide unfortunately.
In short - I wish to see this thread revived.
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[*] posted on 20-7-2013 at 10:17


Yes. I made some tests today, I made about 5-6 liters solution which I poured one liter bottle of batteric acid, so the conc was about 10% of H2SO4. I attached the anode to the lead electrode pack and cathode into copper plate and inserted them into this solution and let it run for about an hour for now. Dark brown coating of PbO2 formed on the lead.

Next im gonna test how these will work in real combat situation by attempting a perchlorate electrolysis. Im afraid it may flake off, but then we'll see. The manufacture of these pbo2 is so easy compared to the others I rather make this every week than mess up with all the nitrates and stuff.

Gonna post some pics soon.
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[*] posted on 21-7-2013 at 09:09


Well, I did test the anode in real action.

Within first five seconds, the PbO2 was gone, and the whole solution turned into brown mess. Maybe the coating was too thin.

Well, Im gonna go with lead, then. I filtered the really-gooish brown solution through a sand filter and obtained a clear, but yellowish solution, which likely contains chlorine in several forms which can probably be clarified by boiling. Lead costs me a quit for kg and its piss-easy to cast lead sheets suitable for action. Gonna use this for chlorine too. So sad my titanium plates are now useless. :(

[Edited on 21-7-2013 by testimento]
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[*] posted on 22-7-2013 at 13:04


Few notes on PbO2:

-At least, when using lead as anode and cathode simultaneously, when dipped even in dilute NaOH solution, an uniform layer of PbO2 seems to form on the anode almost instantly when using heavy currents. I was using 400A at 4.5V. This layer was supposedly holding itself rather well at pure sodium chloride solution.

-Stainless steel, probably 304, causes the anodes to passivate rater quickly. I tried this because I was intending of using SS pot for chlorates because I could have put a heating plate underneath it. Within few minutes, the anodic activity almost ceases.

Havent tested for chlorate nor perchlorate yet, but I probably need to get some ceramic container for the chlorate production because all my ware are from 304, 316 or something. Could normal steel be used?
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[*] posted on 22-7-2013 at 13:15


Quote: Originally posted by testimento  
This layer was supposedly holding itself rather well at pure sodium chloride solution.
...
-Stainless steel, probably 304, causes the anodes to passivate rater quickly. I tried this because I was intending of using SS pot for chlorates because I could have put a heating plate underneath it. Within few minutes, the anodic activity almost ceases.
...


I don't understand what you write. was supposedly? SS as an anode passivates in chlorate cell which you never tested ? :o
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[*] posted on 22-7-2013 at 14:48


I used a SS pot as a cell, where I put the electrode pack consisting of pure lead cathode and PbO2 coated lead anode. The electrolysis started off nicely, but ceased within few minutes. I suspect that enough chromium or other stuff leached from the container to cause partial passivation of the anodes. This phenomenom is cited on few sites concerning PbO2 anodes.
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[*] posted on 18-1-2014 at 08:06


An idea of substrate for lead dioxide anode that as been explored is graphite, however there is problems with it. I thought to a possible solution to make a graphite substrate anode.

The trick could be to first platinum plate the graphite, then to plate a fairly thick layer of silver, and a final layer of platinum, this way, the graphite would not be directly exposed, and would still be the substrate. A layer of lead dioxide could then be platted over that.




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[*] posted on 18-1-2014 at 14:28


What is the purpose of the silver layer?
To help against imperfections in the final Pt layer?

What is the purpose of the initial Pt layer, since it is possible to plate Ag onto the graphite directly?

[Edited on 18-1-2014 by phlogiston]




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[*] posted on 18-1-2014 at 14:38


The idea was to make a double-protection from the electrolyte, but I guess it can be omitted. Silver is used mostly because it is cheap, and a good layer of it would not ruin most people. As silver will not louse conductivity while in contact with the PbO2, this is a very interesting mean to save money on the platinum, and also it is very conductive, possibly lowering resistance from the coating to the graphite, however, a final platinum layer is needed as silver will not hold the electrolyte really well. The imperfection in the platinum coating would be the place where the PbO2 coat would start, and make a very good contact as the mixed lead/silver oxides are still very conductive.





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[*] posted on 18-1-2014 at 15:52


What's the point of putting PbO2 on platinum if platinum can form perchlorate by itself? Is it that the anode surface erodes, and you'd rather lose Pb than Pt?



As below, so above.
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[*] posted on 18-1-2014 at 15:54


Because making a suitable platinum anode require a fair amount of work, and it will corrode, wasting Pt, making coat of PbO2 is quite easy, and then you only loose Pb, which is not particularly valuable.



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