Sciencemadness Discussion Board

More on PbO2 electrodes

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Swede - 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!

Rosco Bodine - 28-1-2013 at 12:59

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

Attachment: US20110226634 Bismuth Metal Oxide Pyrochlore Electrode Materials.pdf (455kB)
This file has been downloaded 683 times


Nitro-esteban - 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.

jpsmith123 - 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)
This file has been downloaded 279 times

Attachment: Bi2O3 on Glassy Carbon Electrodes.pdf (405kB)
This file has been downloaded 343 times

Xenoid - 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.

jpsmith123 - 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]

papaya - 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. ?

jpsmith123 - 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. ?

papaya - 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 ?

jpsmith123 - 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 ?

papaya - 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!

testimento - 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?

testimento - 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).

bfesser - 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 <a href="http://scholar.google.com/" target="_blank">Google Scholar</a> <img src="../scipics/_ext.png" />. Also, what is "lead valve"? Please check that "valve" is the word you intend.

papaya - 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.

testimento - 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.

testimento - 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]

testimento - 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?

papaya - 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

testimento - 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.

plante1999 - 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.

phlogiston - 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]

plante1999 - 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.


Metacelsus - 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?

plante1999 - 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.

testimento - 26-2-2014 at 16:29

Does anyone have knowledge or experience on lead acetate electroplating PbO2 on graphite?

use tin as a substrate?

UncleJoe1985 - 23-4-2015 at 02:32

Quote:
Does anyone have knowledge or experience on lead acetate electroplating PbO2 on graphite?


I've made 2 attempts using the easier to obtain acetate.
The results are extremely crude due to not controlling the parameters to be within spec.

1st attempt (simple proof of concept):
coating was extremely flaky and crystal like, with minimal adhesion (could easily wipe it off)

Not surprising since I used no agitation to remove bubbles, room temperature, current density was too high (15mA/cm2), used too much CuSO4 that it seemed to displace the lead from solution, cathode current density too low (why does it recommend it to be 2x the anode current density - to prevent lead from plating out?)

2nd attempt - this time I used a heat gun to heat the solution and provide slight agitation

Result:
No longer flaky and better adhesion after drying, but very spongy instead of solid. I measured the resistance between 2 points 1cm apart and it was ~200 ohms. The graphite rod I used was 10cm x 1cm.

Next: use lower current density, do better job of removing bubbles, use less CuSO4



UncleJoe1985 - 10-5-2015 at 05:52

OMG, I'm an idiot for using CuSO4 :(

That would ruin the plating solution by precipitating the lead out as sulfate! And I used so much CuSO4.

I was wondering what all that white crud at the bottom was. Guess I'll try again with copper acetate.

I think I intuitively understand why copper plates out before lead at the cathode. To explain it in simple physics principles, copper is less reactive than lead, meaning it's harder to ionize. That would mean the Cu ions have a higher electrostatic potential energy. Since the lowest potential energy state is favored, the electrons go to Cu2+.

But what about at the anode? Does oxidation of copper to copper oxides compete with Pb2+ + 2 H2O -> PbO2 + 4 H+ + 4e- (correct me if I'm wrong)

Can anyone point me to the relevant electrode potentials involved?


[Edited on 10-5-2015 by UncleJoe1985]

Jstuyfzand - 2-4-2016 at 14:29

What do you all think of this video? Seems pretty good!
https://www.youtube.com/watch?v=bZMWEYiTtso

Laboratory of Liptakov - 15-7-2016 at 12:44

Is possible pure PbO2 pressed ? Pressure 12 000 Kg on cm2. And making 10 cm long rod from pure PbO2 ? Diameter 15 mm. How is electric conduction - resistance for PbO2 ? And If is impossible pressed pure PbO2, is possible adding some material for increase solid ? For example, 7% nitrocellulose is confirmed as very good solid - agent. For any fine-powder materials. What using 5% epoxide ? Or some different additivum for increase solidity? Anode will be for prepare NaClO4, of course. Will be nitrocellulose do it problems ? Thanks, ...LL...:cool:

PHILOU Zrealone - 17-7-2016 at 04:38

Quote: Originally posted by Laboratory of Liptakov  
Is possible pure PbO2 pressed ? Pressure 12 000 Kg on cm2. And making 10 cm long rod from pure PbO2 ? Diameter 15 mm. How is electric conduction - resistance for PbO2 ? And If is impossible pressed pure PbO2, is possible adding some material for increase solid ? For example, 7% nitrocellulose is confirmed as very good solid - agent. For any fine-powder materials. What using 5% epoxide ? Or some different additivum for increase solidity? Anode will be for prepare NaClO4, of course. Will be nitrocellulose do it problems ? Thanks, ...LL...:cool:

I don't know for the pressed PbO2 stick/rod and properties...

What I know:
Nitrocellulose will be unstable cement because in basic media (what the cell will increase (bleach is already stongly basic for stability and to avoid toxic Cl2, Cl2O, ClO2 gas generation)) it will be hydrolysed into cellulose...thus setting NO3(-) free (good or bad?)...
Now, I don't know how cellulose behaves into a bleach-chlorate-perchlorate cell...but that's easy to find out (by experiment))...will it remain integer or will it be chewed/schreded into pieces?
The following document:
Cellulose solvents and dissolution medias seems to mention that NaOH (7-10%) is able to dissolve cellulose...
You can also make Sweitzers type of solvent or Cellulose xanthan and the precipitate the cellulose into the PbO2 rod...maybe you could work with cellophane another form of polymerized cellulose.

Epoxyde should remain stable into basic media...only into strongly acidic media it would be hydrolysed (but acidic is uncompatible with bleach...so should be OK).


PbO2 anode

Laboratory of Liptakov - 17-7-2016 at 07:19

Thanks, epoxide as binder can be maybe a good material. During next study is clearly , that surface must be perfectly, without micro holes in the surface. Thus, electro deposition on some substrate is necessary process. Unfortunately. Still more thanks, I making it on this. ..LL...:cool:

yobbo II - 11-1-2017 at 10:39

Lead dioxide anode for sale 30 dollars + shipping

read all about it here

http://www.amateurpyro.com/forums/topic/1629-making-potassiu...



leadioxide.jpg - 19kB

ecos - 12-2-2017 at 05:23

Quote: Originally posted by yobbo II  
Lead dioxide anode for sale 30 dollars + shipping

read all about it here

http://www.amateurpyro.com/forums/topic/1629-making-potassiu...



what is the thickness of the coating and the anode size?

Ziggy4 - 19-7-2017 at 11:24

I have a thought that should apply to this thread. Upon my own interest in perchlorate synthesis, and reading this thread, and ideas about using inert plastics and solvents like MEK etc. to create a slurry of lead dioxide then coating some metallic substrait with it to use as an anode has me thinking that possibly softening plexiglass with solvent and esssentially rolling it in PbO2, then electroplating more of it onto it electrolytically would work too. I also read Sweede's blog about the subject, and his offset weighted agitator to facilitate degassing of the electrode. He was using surficants to help with that too. How about using an ultrasonic cleaning tank as the plating bath to agetate and mix the entire soln? I found a couple studies on this method and one that uses a probe to deliver the ultrasonic energy past the electrode perpendicularly. The results were very favorable.
http://www.sciencedirect.com/science/article/pii/S0009250914...
And http://www.sonochemistry.info/electro.htm
Hopefully I didn't step out of line here since I am brand new to this forum, and very interested in many topics here. I just couldn't hold back on this possibility though and so I joined in order to make this post and see what you all think.

markx - 18-3-2018 at 06:44

Ladies and gentlemen!

Allow me to present the first practical results regarding the realization of an idea I have had sprouting around in my head for the better part of the current decade: "electrodeposition of lead dioxide coatings with soluble Pb+2 generated in situ"

As we are well aware, the lead dioxide electrodeposition process tends to be rather inconvenient due to the coupious amounts of soluble lead componds involved (lead nitrate, acetate or plumbate). Not having the personal inclination towards engaging in close contact with these substances during the electrolyte preparation stage, I had the idea of starting from more benign materials and forming the required soluble lead in the electrodeposition process as a byproduct.

The starting materials being : metallic lead, ammonium nitrate, nitric acid

The process itself would be conducted in a cell having ammonium nitrate solution acidified with nitric acid as the electrolyte and three metallic electrodes submersed into the liquor. Two of the electrodes would be metallis lead and one the substrate on which the electrodeposition of lead dioxide shall take place.

The electrodes would have a current divider constructed between them to separate the required electrochemical processes to the respective electrodes and the cell would be driven in a "semi alternating current" mode. The latter is accomplished by a mosfet H bridge, wich allows to reverse the currents and redirect the processes onto different electrodes.


DSCF1603.JPG - 1MB

DSCF1604.JPG - 960kB
Fig.1 the simplified illustration of the process and setup

The idea is to dissolve lead from Pb electrode nr 1 during period t1 by routing current from the h-bridge output through the current divider diodes to electrodes 1 and 3 and thus creating a resident net concentration of soluble lead in the cell liquor. This takes place at an uncontrolled current density as the anodic solution of lead does not need to be currnt controlled in this application.
After that the current from the h-bridge output is reversed and routed again through the cell during a period of t2, but the current divider giving it a different path this time: the central substrate electrode nr 2 being anodically porarised against electrode nr 1.
Thus partial electrodeposition of lead dioxide should start on the central inert substrate electrode, accompanied by the cathodic deposition of metallic lead on electrode nr 1 from which the lead was originally dissolved in previous period.
The current density is being reduced during this process by the 270 ohm resistor in the current divider, as this step needs to be conducted at low currents (in vincinity of 3mA/cm2) to minimize internal stresses in the formed PbO2 layer.


So it was proceeded with preparing eletrolyte with the following composition :
200g/l ammonium nitrate
40ml/l 68% nitric acid
*surfactant (dish soap) in trace amount was added to supress possible lead bearing spray during elecrodeposition stage and form a stable foam instead.

Electrodes:
1: metallic lead
2: 316 type stainless alloy (abrasively cleaned and pretreated electrolytically to enhance adhesion*)
3: metallic lead


H bridge parameters:

frequency: 2Hz
duty: 3/97 (t1/t2)



DSCF1605.JPG - 1.3MB
Fig.2 The cell with 50ml of electrolyte and the three electrodes suspended in it.



DSCF1607.JPG - 1.1MB
Fig. 3 One can see lead whiskers at the bottom of cell originating from cathodic overdeposition of lead during t1 period.




DSCF1608.JPG - 1.1MB
Fig.4 A more generic view of the setup (I apologize for the crude setting)

The deposition process was continued for 30 minutes under room temperature (21C) and at the aforementioned parameters. The electrodeposition of lead dioxide at the central stainless substrate electrode started as different colored batches and stripes on the surface and the proceeded to take on a dark, almost black glossy appearance over the entire submersed surface area of the central electrode surface. Gas evolution on central electrode was minimal, but more pronounced during the first minutes and died down after that to only some bubbles sticking to electrode surface. These were removed periodically, by lifting the electrode out of the cell momentarily and submersing it back in.



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Fig. 5 The resulting lead dioxide layer on the central stainless substrate after 30min of deposition time


The resultant layer is of a bluish black coloration, has a glossy appearance and seems to be well adhered. At least visually what one could classify as a most impressive result.

Closer observation under a USB microscope reveals that the sample is quite uniformly coated and seems intact.



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Fig. 6 The coating as seen under magnification of USB microscope



[Edited on 18-3-2018 by markx]

markx - 20-3-2018 at 04:10


Here one can observe the results of a "thicker" coating of presumably beta PbO2 that failed to adhere to substrate due to internal stresses that develop during the layer formation process.

The layer was formed via the method described in previous post, but the plating conditions were altered as following:

t1/t2: 2/98
frequency: 10Hz
plating duration: 120min
current density: around 3mA/cm2

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The higher freqency seems to allow for a thicker coating of PbO2 to form without stress cracking.
The coats formed at 2Hz frequency were subject to stress cracking only after 40min of electrodeposition vs. the same occuring at about 120min plating duration at 10Hz.

j_sum1 - 20-3-2018 at 04:25

Surprised no one has commented yet markx. This is impressive work. If they test out ok under use then this is worthy of prepub. That finish looks really tidy.

woelen - 20-3-2018 at 04:46

At first when I read about this, I was thinking in the lines of "a difficult way to get some PbO2 on an electrode", but this setup actually really is smart :)

I myself have thought about similar things, but I always ended up with a 2-stage process. First taking a lead anode and a cathode of any material, and pushing a lot of current through this, making the anode dissolve. You always lose some lead though on the cathode again. The second step then is replacing the cathode by a fresh piece of material and using that as anode. That's a lot of plugging and hard to control.

In this setup you will finally get a certain fairly stable Pb(2+) concentration and deposition of lead on the cathode (rightmost electrode) and deposition of PbO2 on the center electrode.

I am looking forward to see how the electrodes, made in this process, perform when used for electrolysis. If you can make some perchlorate from chlorate with this setup, then that would be really interesting. Perchlorates are quite hard to make electrolytically and using the chlorate melting method is quite risky, with risk of explosion or uncontrolled runaway and foaming of molten KClO3/KClO4. So, any progress in this direction is welcome.

markx - 20-3-2018 at 04:57

Quote: Originally posted by j_sum1  
Surprised no one has commented yet markx. This is impressive work. If they test out ok under use then this is worthy of prepub. That finish looks really tidy.


Thanks for the kind words! :)
It is a really facinating subject and has been haunting me for the longest time....there seems to be great potential in this approach and I try to follow it to the extent that my abilities and resources allow me to.
To be honest, the current substrate material is not really the best option to choose for a functional and durable anode in agressive electrosynthesis conditions (halide bearing solutions e.g.), but it allows me to study the effect of the parameters related to the "novel" electrodeposition process and that in itself is quite satisfactory at the time.
I did test the small anodes in an improvised perchlorate cell containing relatively pure (carefully recristallised) KClO3 solution as the electrolyte and to my amazement they held up for several hours of torture before I could see the iron starting to slowly dissolve from beneath the areas of most current density and dicoluring the solution slightly yellow. The coating itself remained intact (did not discolor, deform or peel off in the cell). But after removing the anode from perchlorate cell, flushing with water and wiping with a paper towel, the coating broke partly off in the most afftected areas: corners, edges. A rather predictable outcome as the stainless steel corroded beneath the oxide and broke the adhesive bond.
In defence of this awaited failure I must say that these coatings used in the perchlorate cell were really thin: deposited during 15 and 30 min of plating time in the lead cell and despite their fragile nature they still managed to hold up for far longer than I could have predicted.
A proper thicker coating will no doubt resist for far longer and perhaps even yield a working anode on a stainless substrate (now that would be outstanding)....although I would preferably switch to titanium once the optimum plating conditions are worked out. This of course creates another obstacle regarding the passivation blocking layer that need to be applied on a Ti substrate before PbO2 coating can be deposited, but prior art exists and we all love a good challenge :)

markx - 24-3-2018 at 13:11


Here one can observe the formation of PbO2 forming through different colored deposit layers on the verge of the electrolyte contact point with the stainless substrate:

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The upper part is the uncoated stainless substrate and lower part is unifrom layer of PbO2 formed on it at following conditions:

t1/t2: 2/98
frequency: 10Hz
deposition time: 60min
@ 21C electrolyte temperature



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[Edited on 24-3-2018 by markx]

markx - 26-3-2018 at 05:44


The sample from last post happily bubbling away in a small perchlorate cell (KClO3 solution):

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Unfortunately the coating is not perfect enough to shield the substrate metal and it starts to corrode after about two hours of operation.

Titanum still seems to be the only viable option for a durable anode of this type.

This brings me to the aforementioned obstacle regarding choices of passivation prevention coating for titanium....I guess the tin oxide option is one of the most doable routes? Does anyone have any other reasonably simple options to suggest for this purpose?

I guess manganese oxide could also be one of the things to try....

markx - 26-3-2018 at 08:42

The result of trying to deposit PbO2 on a mechanically cleaned Ti substrate without an intermediate layer to counteract passivation:

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As can be seen the deposition is uneven and takes place on only the centers that passivated slow enough to allow for a conductive PbO2 layer to form before the current flow ceased.

t1/t2: 2/98
frequency: 10Hz
deposition time: 35min
current density: unknown due to the passivated surface
electrolyte temperature: 21C

The blotchy layer is strongly adhered and can not be wiped off the surface.



You know what the weirdest part is.....this abomination actually conducts:


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Going to see for how long though....

[Edited on 26-3-2018 by markx]

markx - 26-3-2018 at 11:43

As could be expected the Ti substrate anode is passivating at a rather progressive rate....

The initial current through the perchlorate cell was around 10mA

at 60min the current was 7mA
at 100min the current was 4,5mA
at 170min the current was 2mA

I project that around 200min the anode shall be passivated permanently....

[Edited on 26-3-2018 by markx]

markx - 26-3-2018 at 12:04


Yup.....I see a dead anode :D

USB 2.0 Camera-3.26-22;57;44;879.jpg - 292kB

By 190min the current has fallen below 1mA and gas evolution has practically stopped on the surface.

The PbO2 layer looks quite identical to what it was in the beginning, but clearly the titanium substrate has passivated to a point where current can no longer pass to the lead dioxide deposit.



markx - 26-3-2018 at 16:20

Here one can observe another interesting sample of lead dioxide deposition on "bare" Ti substrate:

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In this case I thoroughly sanded the lower edge of a Ti strip to clean metal and left the upper part as it was....under a deposit of years worth of oxide. It was immediately placed into the PbO2 deposition bath under the same conditions as before:

t1/t2: 2/98
frequency: 10Hz
deposition time: 30min
electrolyte temperature: 21C

What is interesting is that most of the deposition centers occur in the pitting of the uncleaned and presumably thoroughly passivated upper part of the strip and the abrasively cleaned lower part of Ti is virtually void of any deposit.
I find that highly intriguing.....does the titanium oxide layer under some favorable conditions create a preferred site for the deposition of lead dioxide?

I also cleaned another strip of the same Ti stock thoroghly by sanding it completely to bare metal and placed it into the lead dioxide bath for 30min....virtually no deposition occurred on the surface.




Now look at the sample below:

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In an attempt to create a slightly oxidised surface favoring deposition, I thoroughly sanded this sample to bare metal and then electrochemically etched it in ammonium heptamolybdate solution (30g/l) in alternating current mode of 50% anodic duty and 5Hz frequency for 20 min.
During that treatment the titanium first showed signs of passivation coloring, which appeared as different colored stripes of red, green and brown on the surface. After about 5 minutes the surface of Ti turned a matte black and remained as such for the whole duration of the treatment. The black layer was not adherent and could be wiped/washed off with some effort, revealing an ever so slightly beige colored surface.
In such state it was placed into the lead dioxide bath under the same conditions as previous Ti sample and at first it seemed to be passivated. After 10min it was apparent that deposition of PbO2 is taking place quite evenly over the entire submersed surface of the sample. There was an obvious abundance of initial deposition centers compared to previous samples. The initially even deposition then progressed into an uneven one, favoring some regions of the substrate, but still it was more uniform than in previous attempts. After 2 hours of deposition I ended up with the sample that can be seen in the last pictures.

markx - 29-3-2018 at 12:04

Status update:

For practical purposes it seems I have solved at least the problem of creating a passivation blocking intermediate layer on Ti.


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Fig. 1 Take a piece of raw Ti with desired dimensions and sand clean to expose bare metal surface


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Fig. 2 Acquire chloroplatinic acid solution from convenient sources.


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Fig. 3 Cover Ti substrate with chloroplatinic acid solution and heat carefully to 300-400C, obtain Pt clad titanium substrate.


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Fig. 5 Plate over with PbO2 at preferred conditions.


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Fig. 6 Subject the anodes to torture in perchlorate cell conditions.


j_sum1 - 29-3-2018 at 13:06

Markx, I think you have made stunning progress here.
It would be great if you could write up the full procedure including electronics and put it in prepub.

markx - 30-3-2018 at 12:25

Quote: Originally posted by j_sum1  
Markx, I think you have made stunning progress here.
It would be great if you could write up the full procedure including electronics and put it in prepub.


I'm honored by the proposal :)

But I would like to first work out a more or less working solution for this topic and then proceed to summarizing it in a compact form....


As far as current experimentation shows the PbO2 coatings deposited by the bath composition that I have used so far are not stable in the perchlorate cell conditions. The coatings tend to deform and flake off from the surface of the anode.



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Fig. 1 Initial coating on Pt clad Ti substrate (60min deposition at 10Hz)



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Fig. 2 Same coating after 30h in perchlorate cell conditions (facing away from cathode vs. facing to cathode respectively from left to right)

As one can clearly see the PbO2 coating is completely flaked off and rendered ineffective. The Pt clad substrate is still conductive and shows no signs of passivation, which is a great succes in its own so far.
What is even better....the substrate can be chemically etched clean and reused to deposit a new coating.

To achieve that one has to immerse it into solution of citric acid+ammonium citrate+ acorbic acid for a few minutes. The proportions are not critical and all of the PbO2 remnants shall be dissolved completely leaving the substrate unharmed and ready dor a new coating.


To combat the internal stresses and flaking of the coatings I decided to modify the deposition bath composition by adding 1g/l of Silipon RN 31 (sodium lauryl sulfate). This seems to have reduced the deposition rate of the PbO2, at least by visual assessment, but allows to deposit a uniform and much thicker coating without developing stress cracking.




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Fig. 3 Deposits on Pt clad Ti substrate from the Silipon modified bath at 60/120/180 min deposition time at 10Hz from left to right respecitvely

As can be seen the deposit is of a matte apperance as opposed to shiny and looks totally uniform without any stress cracking or other defects across the entire surface. Pervious bath composition allowed for a maximum of 120 minutes of deposition before stress cracks appeared on the surfave of coatings.

I also measured the deposition rate by weighing the sample after every hour ant the rate was pretty much constant at 20mg/h. Quite low, but if it allows to build a stress free thick coating, then it might be the way to a durable anode.


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Fig. 4 Deposit at 240 minutes....still totally uniform and no cracking or defects (deposition rate holds constant at 20mg/h)

The white fibres that can be seen on surface originate from paper towel I use to dry the deposit after removing from deposition bath. They get snagged on suface and can not be removed completly....also they seem to codeposit as can be seen on last image :)



[Edited on 30-3-2018 by markx]

markx - 30-3-2018 at 13:53

The coating at 300 minutes. The corner broke off because I dropped it onto the floor :D Makes a great illustration of the thickness though...

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markx - 30-3-2018 at 14:55

360 minutes....all healed up :)

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markx - 1-4-2018 at 09:24

While I am waiting for my PbO2 layer to grow thicker I decided to experiment with just the bare Pt clad Ti substrate as the anode in a small perchlorate cell:



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Anode is on the right side of the pictures. As one can observe there is magnificent potassium perchlorate formation taking place. It grows on the anode as white layer of cristals and flakes off forming a nice pile under it. The thicker bottom layer is undissolved KClO3.

What was also interesting is that there was virtually no perchlorate formation visible on anode if the applied voltage was below 5V. There was current passing the cell and vigorous gas evolution on both electrodes, but no visible perchlorate cristals on anode. Immedaiately after raising the cell voltage to 5V or slightly above, there began a visible formation of KClO4 on the anode.
Quite interesting....I guess the anode was not polarized enough to permit the electrosynthesis of ClO4- at the lower voltages (4,5V) and concequently also at lower current density?



DSCF1687.JPG - 996kB

That pile of KClO4 really is growing by the minute, constant visual percepitation is taking place around and on the anode.
There is 5,5V currently applied across the cell and 5,1W of power being consumed by the setup, which should bring us around 0,9A being passed (takeing into account slight switching losses). The surface area of the anode is 5,6cm2 and that brings us to a current density of around 160mA/cm2, which should be quite safe for a homemade Pt clad abomination :D

[Edited on 1-4-2018 by markx]

Diachrynic - 2-4-2018 at 04:32

This is very exciting! I'm curious about your further experiments, markx. This is very very cool.

markx - 3-4-2018 at 09:03


Short update:

I spent upwards of 14h growing the anode to a beefier state in terms of coating thickness and managed to deposit about 340mg of PbO2 from the SLS modified bath:

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Fig. After 14h of deposition (slight dendritic formations visible)

The current density was doubled for the last 4 hours, but this resulted in dendritic growth as can be seen on the picture.
The coating was totally fine in terms of uniformity and lack of stress cracking after 14h of deposition time...looked really promising.



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Fig. 2 After 20h in perchlorate cell. The coating is totally destroyed and flakes off in bulk.

Sigh....that was a disappointment, but at least I know now that it does not work this way. Time to introduce some changes and try again.

There seems to be a cristalline transformation taking place in the PbO2 coating under perchlorate cell conditions: a coating that is well adherent and without defects seems to expand and develop huge compressive stress that deforms the layers and forces the coating to flake off in bulk. It does not erode of dust off the anode, but instead peels off in deformed huge flakes.
The Pt clad substrate is totally fine, conductive and unharmed. I shall etch it clean and redeposit under different conditions.

After quite a bit of searching there seems to be mentioned in several sources that fluoride doped PbO2 offers better adhesion to substrates and also deposits as a finer grained coat....

markx - 4-4-2018 at 03:48

I think that my deposition bath has become contaminated by all that experimentation and the possible additives in the technical grade lead that I use as anodes (also the surfactants are for sure decomposing and altering the properties).
I do not seem to get the kind of dense start coatings I used to observe as the bath was fresh. Also there is a precipitate forming and last coatings were pretty loose and of low density.
I trust there is a time for resetting the bath and starting with a new fresh filling.
Also I managed to dig up an old stock of strontium fluoride that I can possibly use as a plating additive for the fluoride doped deposit. It has quite low solubility though, but the acidity of the bath composition should partly compensate for that shortcoming.

Also I really must find the time to incorporate the electronics of the H bridge into a manageable casing. The loose bundle of wires is really interfering with my ability to concentrate on performing the experimentation :D

markx - 4-4-2018 at 13:16

A few shots of the KClO4 "stockpile" that I have managed to produce with the miniature cell during the tryouts ot the anodes and substrates so far (perhaps in the range of 15-20g total):



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It looks very pretty and is inherently insoluble in water.....a rather strong indication that it is what it is claimed to be (omitting the chlorate impurities)

I also tore down the barbaric H-bridge bundle and it shall be correctly incorporated into a proper casing:


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Now that looks already more like it :)

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[Edited on 5-4-2018 by markx]

markx - 12-4-2018 at 00:01

Update:

I rigged the h-bridge system to a permanent DC voltage source (adjustable sepic converter) to be able to deposit for longer durations without messing about with the Li cells after every hour....that part works well and can be left to function for days.

I also dumped the old bath and made a new one with the same composition:

200g/l Nh4NO3
40g/l HNO3
Silipon RN 31 SLS (0,5-1,0g/l)

Well....it deposits....nicely....but the internal stresses in the coating tend to deform and crack it if SLS content is below 1g/l and deposition time goes over 240min.

I also tried to raise the bath acid content to much higher level (150g/l HNO3): that reduces deposition rate considerably and produces a highly hydrophobic coating of PbO2, but still the internal stress remains.

Also none of the coatings tend to hold up in anodic perchlorate cell conditions for prolonged time (the Pt clad substrate is all that remains operational after 24h of electrosynthesis).

I guess there is a combination that produces a durable coating, but so many variables to choose from....sigh...I do not even know which direction to head to?

Leaning on the claims of several sources the internal stress situation has been conquered by depositing an initial alpha PbO2 layer from alkaline plumbate bath and then proceeding to deposit an outer shell of beta PbO2 from acidic bath. A rather annoying extra procedure that defies my initial goal of producing a coating with minimal effort and avoiding excessively unpleasant bath compositions. I will probably try it out though....

Another route would be to use different bath compositions in the single stage H-bridge driven setup. Theoretically any salt of an acid that has a soluble lead counterpart can be used in the h-bridge setup (acetate, methanesulfonate, chlorate, iodide, tetrafluoborate etc.)

Yet another way would be to try out different plating additives that are known or can be suspected to have an influence on the coating stress development (surfactants, dodecyl trimethyl ammonium type of compounds etc.)

Amazing how complex "simple" things can get in a heartbeat :D !

[Edited on 12-4-2018 by markx]

Sulaiman - 12-4-2018 at 01:51

I'm just guessing here, but it seems to me that the root of your problem is the platinum.

If you an master plating with PbO2 then why not try less inert substrates ?
Lead sheet ?

markx - 12-4-2018 at 03:44

Quote: Originally posted by Sulaiman  
I'm just guessing here, but it seems to me that the root of your problem is the platinum.

If you an master plating with PbO2 then why not try less inert substrates ?
Lead sheet ?


Different substrate is an option. But eventually I would still like to grow the anode onto a Ti substrate...for perchlorate electrosynthesis this is probably one of the best routes because of the inherent corrosion resistance of titanium (unfortunately that property also requires a passivation proof coating undeneath the lead dioxide).

I did try stainless substrates in the beginning and although they produced very excellent thin coatings, the internal stress problem still remained.
Also I must mention that the stainless substrates also required electrolytic pretreatment to initiate a uniform and well adherent electrodeposition of PbO2....namely they had to be coated with a blue interference layer in the ammonium molybdate bath under pulsed AC conditions.
Omitting that step would produce the formation of brightly colored PbO2 deposits (ranging from red to violet) which turned into loose brown flakes as the coating thickened or even a black sooty deposit that could be wiped off the substrate.

The colored PbO2 deposit on untreated stainless substrate:

http://www.sciencemadness.org/talk/files.php?pid=510797&...



On wee bit brighter note we have this fugly monstrosity currently growing in the cell:


DSCF1700.JPG - 1.1MB

This weird coating formed on Pt clad Ti substrate as I let the high acid (150g/l HNO3) cell work despite the initial deformation and partial flaking of coating. The picture shows resultant coating after 24h in the deposition cell under following conditions:

Frequency: 5Hz
t1/t2 : 1/99
temp: 21C
current density: 3-4mA/cm2

Apparently the initially deformed and flaked areas have grown over and a rather massive coat is forming. I currently did not see any cracking or obvious deformations hinting to it as I pulled it out of the cell to incpect more closely. The coat has gathered some obvious volume over night and looks very dense and smooth...almost shiny on microscopic level. But it is quite uneven....like a natural rock formation. There are no obvious dendritic formations and the unevenness across the anode surface is totally random, not concentrated in just areas of obviously higher current density. A weird mostrosity, I shall let it grow and see what comes out of this particular "mishap" :)

[Edited on 12-4-2018 by markx]

Sulaiman - 12-4-2018 at 07:27

A new PbO2 anode video from AllChemystery
PbO2 onto a spinning carbon rod.


https://www.youtube.com/watch?v=tXSpqy2TNWo

[Edited on 12-4-2018 by Sulaiman]

markx - 16-4-2018 at 10:15

Update:



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Fig. 1 General view of the "monstrosity" coating after 72h of deposition.

It is fugly, but rather massive and relatively compact. The mass of deposited coating is within error 2,2g.



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Fig. 2 The coating under magnification: quite extraordinary structure, it very much resembles a solidified mass of lava.




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Fig. 3 Assembled to test cell and bubbling away under 5W of input power and 4,6V across the cell.

I see a uniform gas formation and no loose particles emanating from the anode after 15min of operation....somewhat of a good sign that it will not break apart instantly, but lets see what happens overnight...

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