More on PbO2 electrodes

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...)

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. ?

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 ?

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?

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).

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]

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 ?

use tin as a substrate?

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]

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...

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...

PbO2 anode

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...

Lead dioxide anode for sale 30 dollars + shipping

read all about it here

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

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...

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.





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)




Fig.2 The cell with 50ml of electrolyte and the three electrodes suspended in it.




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





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.







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.








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



[Edited on 18-3-2018 by markx]

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



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.

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.

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

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:





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





[Edited on 24-3-2018 by markx]

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







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....

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



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:




Going to see for how long though....

[Edited on 26-3-2018 by markx]

Yup.....I see a dead anode



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.

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



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:






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.

Status update:

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



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



Fig. 2 Acquire chloroplatinic acid solution from convenient sources.



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



Fig. 5 Plate over with PbO2 at preferred conditions.



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

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.




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




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.





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.



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]

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

360 minutes....all healed up

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:





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?





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

[Edited on 1-4-2018 by markx]

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:


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.




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....

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

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):







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:








Now that looks already more like it



[Edited on 5-4-2018 by markx]

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 !

[Edited on 12-4-2018 by markx]

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:




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]

Update:




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.




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





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...

Update:

The "monstrocity" coating was a failure. Alhough it seemed very promising during the first hours of operation, it still started to flake off and did so in very bulky pieces during a rather short period. Again the only working component was the Pt clad sbstrate that remained.

I decided to give a try to depositing alpha lead dioxide from alkaline plumbate bath and acetate bath. See if that would work as an intermediate layer between the Pt and beta oxide coat.






Fig.1 From left to right (alpha?)PbO2 coatings obtained from acetate bath, alkaline plumbate bath in operation, lead whiskers formed on acetate bath cathode.


The acetate bath was simply 20% acetic acid solution into which Pb electrodes were submersed (Pt clad Ti as the center substrate electrode) and also Pb strips at the bottom of beaker to enhance the soluble lead levels.
Bath was operated at 5Hz frequency and 97% anodic duty. Deposition onto Pt clad Ti substrate was very slow and partly the oxide coating formed as a loose brownish dusty layer which could be wiped off. But underneath that loose layer there was a strongly adherent brownish coat. It was very thin, almost translucent, as can be seen on the leftmost picture.
The samples on the picture conform to 24h and 72h of deposition time in the acetate bath.

The attempt at the plumbate bath was made by immersing lead strips in 5M NaOH solution in the hopes of driving at least some metal into the soluble complex form (unfortunately no litharge was available). The reaction does occur, but it takes days to dissolve any appreciable amount of metal. In the hope to speed up the reaction a small amount (about 2ml) of 30% hydrogen peroxide was added to the bath (80ml) dropwise and under stirring. That brought about an immediate reaction which formed precipitate of lead oxides in the solution, confirming that some soluble lead complex had formed in the bath. The lead oxide precipitate quickly redissolved in the alkaline conditions, but bubbling from the surface of lead metal at the bottom of the beaker persisted for several days. After that a slow formation of Pb3O4 began in the beaker and it percipitated as a thin layer on the walls and bottom of the cell. The liberally chosen amount of peroxide was probably too much. I trust the orange sediment on the second picture is quite obvious.
The formation of red lead oxide was slow and seemed to stop after a few days. Lead electrodes were immersed in the solution (Pt clad Ti as center electrode) and the bath was set up to operate at 5Hz frequency and 97% anodic duty.
Contrary to the acetate bath a rather fast formation of a well adherent PbO2 layer began immediately on the center electrode. No visible gas formation is observed, but the layer is clearly depositing....


[Edited on 25-4-2018 by markx]

ingenious setup for in situ generation!

your main problem though seems to be centered around
a) adhesion to substrate
b) internal stress/ductility of the coating

I have not tried to deposit PbO2 but maybe I have some insights into the stress/ductility issues that can be transferred to this problem .cant help with the adhesion problem though,maybe proper undercoat and/or prep plays a big role here esp on titanium which is hard to get good adhesion on.

I have had very good success using a pulse/pulse reverse waveform regimen on thicker copper deposits to impart ductility. I used a arduino controlled cheap h-bridge chip and set it to 10millisecond fwd(deposition) followed by 500microseconds(0,5milliseconds) reverse (deposit removal) . The resulting copper deposit (about 0,5mm(500micron) on a brass strip was ductile enough that I could bend it 180° without cracking or separation from the brass substrate. If I deposit the same thickness from the same bath under straight DC or single pulse the resulting deposit is much harder, it takes considerably more force to bend the strip and the coating will crack at a bend of about 30° and separates from the brass substrate. so a simple change from a straight or pulsed plating regimen to a pulse/pulse reverse waveform regimen was able to change the deposit quality profundly in terms of ductility/internal stress. I cannot say if this can be transferred 1:1 to the deposition of Pb - this was copper after all - and lead may behave differently. But as your 3 electrode setup is practically a pulse deposition vs a pulse/pulse reverse setup rearding deposition on the target anode I think it would be worth a try. You probably will have to use a regular 2 electrode setup with lead salts already present in the solution though to test this out.

brass strip with 0,5mm copper deposit ,pulse/pulse reverse waveform regimen
image1


the same, bent 180° without cracking or separation
image2


this is 0,5mm copper deposit from same bath but under single pulse . it started cracking at 30° bend and was then bent further to better show crack and separation .same happens under straight dc conditions.
image3



the arduino and h-bridge chip used for that.
image4



It might well be that lead behaves differently than copper under those conditions and may require an adjustment to the specific timing of the used waveform regimen - if you want to try this take my settings as a starting point and possibly experiment from there. Its just another idea to try since you did use only pulse deposition so far and the effects on copper are clearly visible. I also attached a file I found on pulse reverse electrodeposition of PbO2 electrodes which briefly covers this subject. good luck!



[Edited on 31-5-2018 by rolynd]

[Edited on 31-5-2018 by rolynd]

Attachment: JEAC_3835.pdf (1.7MB)
This file has been downloaded 625 times

Quote: Originally posted by mysteriusbhoice

I have created relatively good graphite substrate PbO2 electrodes with brush electrolysis of lead acetate solution at 12v I have experimented with 3v and 5v but the precipitant PbO2 would flake off and produce black gunk on the brush while it seems 12v produces a coating which doesnt peel off in the abrasive brush electrolysis process. Running the anode in an solution of sodium chlorate and sulfuric acid worked well. The only con of this method is the extremely laborous process of RUB RUB RUB RUB RUB!!!! edit: im thinking of using sand/abrasive soaked with a bit of lead acetate with a rotating motor to consolidate a good coating that will be refined and ensure that only PbO2 that adheres to the surface will stay on and all else will fall off the electrode while plating. [Edited on 22-10-2019 by mysteriusbhoice]

Quote: Originally posted by Σldritch

Really nice work markx, i was just wondering, did you try putting titanium at a negative potential to get rid of Titanium Dioxide? Seems so obvious but i can't see that you mentioned it anywhere.

Quote: Originally posted by markx

As far as i’ve observed cathodic potential does not really reduce titanium dioxide back to nonexistance but merely changes the cristalline structure into a state that is able to conduct charge under said potential. At least in aqueous solutions. Mechanical removal is quicker and more effective, especially if the metal is coated under decades worth of reinforced scale.

Quote: Originally posted by yobbo II

Magnetite can be used for making chlorate. It only makes perchlorate at 11% efficiency according to a patent. 11% is not that bad if the anode were to last a long time. ...."For all intentive purposes the ultrathin Pt layers endured much better and outperformed any lead dioxide deposit that I’ve tried so far."... Do you mean you used the platinum coated Ti on it's own (no lead dioxide) and it lasted longer than any other lead dioxide anode? I think the way to go for perchlorate is pt bullion as per pinko or yob.

Just for fun I tried to produce graphite and graphite substrate lead dioxide anodes completely OTC... with some success. They are a lot of work though, only suitable for miniature cells and compared to commercially available MMO anodes, Ti-substrate LD or platinum they probably suck, but that was not main goal here. Anyway...here it goes:

A preweighed amount of a cyclohexanone/MEK based PVC cement was dried fully and then weighed again to determine the amount of low MW PVC polymer present, and was found to be 25% by w/w..

Magnetite/hematite was made from steelwool that was burned thoroughly with a blowtorch until it fell apart easily. The result was a silver-grey powder that after light crushing with a teaspoon in a bowl, consisted of small magnetite fibers.

To make the miniature anodes (70 mm long, 12 mm wide, 4-5 mm thick):

5 g finely powdered graphite powder (dry lubricant) was mixed with 0.56 g of the burned steelwool and 2.9 g of the PVC based glue (12% binder), forming a soft clay-like consistency. While mixing occasionally, most of the volatile MEK was allowed to evaporate off until the consistency of slightly wetted sand (seemingly loose powder, though sticks on compacting) was reached. The powder was then pushed into a mold made from a piece of 12mm thick plywood with a 70mm x 12 mm slot sawed out using a fretsaw. Baking paper was put into the mold to prevent anything from sticking and the powder compacted using a hammer and another piece of 12 mm plywood as a dowel. The anodes were dried over the radiator for a week, until no more smell of cyclohexanone was noticable. Depending on how far you let the cyclohexanone evaporate before hammering, binder percentage, and how hard you hammer, the resulting resistance over the entire anode is 3-5 ohm. The burned steelwool is essential, without it the anode will form large cracks and weak spots on drying, but too much and the resistance will increase. Despite the fact that these anodes are slightly porous by themselves they hardly erode during sodium chloride electrolysis and they are not porous enough that he electrolyte will reach the connection to the anode itself, Mechanically they are very strong and almost impossible to break by hand. When used in a 50 ml sat. sodium chloride cell at 3.5-4 volts will give about 0.3-0.4 Amps of current (<40 mA/cm2) and when chloride levels are kept high and cathode placing is right for even current distribution, they will go on for a very, very, very long time as they erode only at an estimated 1 mg/ 10 amp hours or so.

One of these graphite/magnetite/PVC anodes was plated with roughly 1 mm of b-lead dioxide (25% lead nitrate, copper nitrate, pH of 1, 10mA/cm2 for 12h at 60 C. which seems to hold very well, probably due to the porosity of the anodes made this way (and perhaps the magnetite). The conductivity is much higher after the lead dioxide coating, probably due to the lower resistance of the LD coating compared to the substrate anode itself. I'm thinking the relatively high resistance of the graphite /magnetite/PVC anodes may be advantageous since (unlike highly dense graphite as a substrate) almost all of the current will pass through the LD, leaving the substrate anode intact for longer. Sort of the middle ground between an inert ceramic substrate anode (which is hard to coat evenly) and dense graphite substarte anode.

There is only one funny thing . The resulting LD anode was used in a 50 ml cell with a 39% solution of sodium chlorate as electrolyte. Cell was run at 6V-0.9 A at a temperature of 40-45C with a stainless steel cathode. Strangely, after 2 days of running the cell not a single mg of perchlorate had formed, while it is able to produce chlorate just fine.The anode has not shown any kind of wear and seems to produce only oxygen.

What is going on here?! From what I have read fluoride additions are not requisite for complete conversion of chlorate to perchlorate, only increasing current effiency. Things that I though of are:
- Is there maybe increased cathodic reduction going on due to the fact that I used salt with 100 mg/KG iodide added?
- Is the magnetite/presence or soluble iron in the electrolyte aiding to cathodic reduction?
- The lead nitrate was made by dissolving lead metal of unknown purity, could bismuth contamination or something screw up the LD anode for perchlorate synthesis?

If the presence of iron and/or iodide in the electrolyte or a magnetite anode would be such a good catalyst for perchlorate reduction, might be of some use in perchlorate removal from wastewater at least...

Anyway, any help would be appreciated. Any ideas why no perchlorate was formed?

[Edited on 17-4-2020 by nitro-genes]

interesting comment on the reconditioning of the anode...

Not really any plans for the perchlorate myself, the physics and chemistry of these anodes is just fascinating, being able to oxidize chloride all the way to perchlorate in solution! Yesterday I decided to crank the power all the way up in the perchlorate cell, and behold, today almost all chlorate has been converted to perchlorate.

By rearranging the cathode position, the cell was run at 6V and 1.6 A, a current density close to the optimum of 0.22 A/cm2. More things changed though. When freshly plated, the GSLD anode did not look a deep black as expected, but a plastic like, matt dark grey colour. After running the anode very hard for 24 hours, the anode had turned to a deep black. Some stuff also seemed to have erroded away from the anode and covered the cathode with a dark powdery coating that seems as conductive as the SS itself. I'm guessing lead metal itself, or maybe bismuth or antimony.

I couldn't find a "minimum voltage" for the Lead dioxide plating procedure, so I used about 1.6 V, maybe this was on the low side for LD plating? Maybe some mixed lead(II)/Lead(IV) oxides plated along? Alternatively, maybe some bismuth oxides plated along with the lead dioxide itself. If this is the case, the lead nitrate bath will probably produce better anodes the next time, since bismuth(III) would probably be plated first as compared to lead(IV). Maybe worth looking at...would bismuth nitrate also plate into a conductive layer? Maybe not suitable for perchlorates, though maybe for chlorates yes...

So...success! Though if it was the higher current density, the SS cathode being covered with lead/bismuth or the reconditioning of the anode still needs to be worked out.

[Edited on 20-4-2020 by nitro-genes]

Quote: Originally posted by nitro-genes

interesting comment on the reconditioning of the anode... Not really any plans for the perchlorate myself, the physics and chemistry of these anodes is just fascinating, being able to oxidize chloride all the way to perchlorate in solution! Yesterday I decided to crank the power all the way up in the perchlorate cell, and behold, today almost all chlorate has been converted to perchlorate. By rearranging the cathode position, the cell was run at 6V and 1.6 A, a current density close to the optimum of 0.22 A/cm2. More things changed though. When freshly plated, the GSLD anode did not look a deep black as expected, but a plastic like, matt dark grey colour. After running the anode very hard for 24 hours, the anode had turned to a deep black. Some stuff also seemed to have erroded away from the anode and covered the cathode with a dark powdery coating that seems as conductive as the SS itself. I'm guessing lead metal itself, or maybe bismuth or antimony. I couldn't find a "minimum voltage" for the Lead dioxide plating procedure, so I used about 1.6 V, maybe this was on the low side for LD plating? Maybe some mixed lead(II)/Lead(IV) oxides plated along? Alternatively, maybe some bismuth oxides plated along with the lead dioxide itself. If this is the case, the lead nitrate bath will probably produce better anodes the next time, since bismuth(III) would probably be plated first as compared to lead(IV). Maybe worth looking at...would bismuth nitrate also plate into a conductive layer? Maybe not suitable for perchlorates, though maybe for chlorates yes... So...success! Though if it was the higher current density, the SS cathode being covered with lead/bismuth or the reconditioning of the anode still needs to be worked out. [Edited on 20-4-2020 by nitro-genes]

Glad to hear your experiment was a success! I'm tempted to resurrect my pulse reverse LD plating method and give it another try with different substrates. It did not work on platinised titanium, but perhaps a composite substrate like yours or a variety of graphite might work better.
I totally agree about the process and material manipulations being much more captivating than the end product

The higher current density probably electropolished away the dendritic growths on the oxide layer, exposing a smooth black finish beneath. Other experimenters have reported similar effects with LD anodes. After a while of running the electrode appearance changes to a smooth black luster and some deposits gather in the electrolyte and on cathode surfaces.

I had a similar case with Ti substrate Pt anode regarding a power rise that triggered an abrupt formation of perchlorate. It happened with KClO3 solution that had been bubbling away for a while without any perchlorate being formed. Instantly after upping the power setting a massive visible formation on the anode surface began. At first I thought I had run the cell below a critical anode polarisation level and that hindered the synthesis, but later on I could not replicate the results, the 48h delay remained and the synthesis could be carried through very nicely at low voltage and current densities (with e.g. 4,5V across the cell). So I became more confident that it was not the low anode polarisation, but a ceratin preconditioning phase is most likely at play here.
It seems that electrosynthesis mechanism for perchlorate formation is not a straightforward phenomenon...especially if Pt is involved.

Thanks for the information, still have much to read about the surface chemistry of perchlorate formation at anode surfaces it seems (and electrochemistry in general). I think you are right about dendrite formation being the cause of the greyish colour, it is interesting to see that the anode surface changes to a deep black only where current density is the highest indeed (see attached picture). So, a critical anode polarization level seems about right, though since above this critical amount of voltage/current, there is also anode surface changes and cathode deposition it is hard to exclude these other factors. A high chromium stainless steel cathode was used for the sodium chlorate and perchlorate synthesis and I noticed that the sodium chlorate solution has a slight yellow colour at the start. Maybe the yellow colour could be from slight iron/chromium contamination, inhibiting perchlorate synthesis, since LD and chromates are a known incompatibility. Perhaps at a certain voltage/current, this simply "burns off" the anode? From what I have read, a high voltage should not be a requisite for perchlorate synthesis with a good quality LD coating. IIRC, highest current efficiencies are realised at just a slight oxygen-overpotential of 2 Volts.

Another factor might be the resistance of the composite graphite substrate anode itself, since the anode connection was not made directly on the LD coating, but just the graphite substrate anode (first 2 cm). It seems that the 2 Ohm resistance of the composite graphite anode might result in a large loss of current by heating up (it heats up to 50 C or so). This loss of current might also make the anode surface see a different current than the PSU displays. Pfff, really wish I had payed more attention to electricity classes in high school. Anyway, yesterday I took one of the GSLD anodes apart after roughly 200 amp/h, and surprisingly the graphite/magnetite/PVC was nearly completely intact beneath the LD coating. The anode broke just above the boundary of the LD layer were there was a lot of errosion visible, so a better design would be to plate the LD along the entire anode, up until the electrical connection.

When measured with a multimeter, how much resistance should a good LD coating have? I have a feeling a larger plating bath, I used 150 ml, (acid and nitrite build up) and using pure lead nitrate might lead to much better results and might be really worthwhile, since the LD itselfs seems to adhere very strongly to the composite anode and is really hard to peel off.



[Edited on 22-4-2020 by nitro-genes]

Would something like this work? Seems like this way the lead dioxide layer would grow like a plant from the soil, right through the porous ceramic, like roots that hold it firmly attached. Capillary forces would supply the lead nitrate solution, even when it is not fully submerged. When the first LD "sprouts" would emerge and form a layer, the graphite layer could be removed and the anode plated again to also coat the other side.

Would the lack of in and out flow of the lead nitrate solution in the ceramic cause problems? Would the graphite simply be "pushed off" by the growing LD layer. I think the "right kind" of porous (probably very porous) is key here resistance wise.



[Edited on 24-4-2020 by nitro-genes]

"Glad to hear your experiment was a success! I'm tempted to resurrect my pulse reverse LD plating method and give it another try with different substrates. It did not work on platinised titanium, but perhaps a composite substrate like yours or a variety of graphite might work better."

The composite anodes show some promise IMO. By using a steel mold for pressing, a binder percentage of only 5% PVC, evaporating off ~50% of the glue solvents and beating the living daylight out of the composite mix in the mold, I was able to get under 1 ohm resistance for the composite anodes!

The real benefit for OTC lead dioxide anodes might be the magnetite addition IMO. I remember to have read somewhere that alpha LD does not adhere very well (or at all) on graphite substrates. It would be really convenient if the magnetite addition would allow an adherent plating of a-LD, which would allow plating with lead acetate instead of nitrates. Perhaps just burning some steelwool, binding it with PVC glue and than plating with lead acetate would make an easy LD anode for perchlorate synthesis. Supposedly, whereas graphite is oxidized to some extend in the perchlorate cell, magnetite should be almost totally inert from what I've read. Not sure how the PVC glue would hold up, but due to the expected high resistance of such a magnetite/PVC substrate anode compared to the LD layer, I don't see any problems.

The difference between an LD-coated graphite anode and just graphite is amazing to see during NaCl electrolysis. When the cell is started up, a graphite anode produces a lot of bubbles of chlorine at its surface due to the neutral pH. The LD coated anode, even when run at 3 or 4 times the current density ,forms no bubbles at all at the surface. Just looks like it is doing nothing. Very interesting, it seems like the chloride just skips the chlorine stage on an LD surface and is instantly oxidized further.

Anyway, I made several of of the new composite substrate anodes and found some OTC algea remover which contains a Quaternary ammonium salt, so I'm gone have me some fun. .

https://www.youtube.com/watch?v=eFFgbc5Vcbw

[Edited on 4-5-2020 by nitro-genes]

well using sonication and strong stirring via an old PSU fan with its blades cut off running at 3v 5amps i got these 3 electrodes, they are not done due to my copper brush touching the solution causing it to corrode.
But 1 had a very bad spotty coating instead of nice smooth so I ran it in a cell to see how long it will last which was about 3 hours.






[Edited on 16-5-2020 by mysteriusbhoice]

Quote: Originally posted by RogueRose

I have a question about an alternative method for an anode. What about taking a PbO2 plate from a battery and using that? I know they tend to become brittle after many charge/discharge cycles, but I suspect plates from a new battery would be much more sturdy. Also, what about backing them with some kind of liquid plastic (PVC or ABS dissolved in acetone or MEK) or even silicone. You could even use epoxy for this. I suggest even trying to use vacuum infusion which would impregnate the spaces between the PbO2. Then I would take something like an angle grinder with a grinding disc and grind the surface off to fully expose all the PbO2. I have all the stuff to do this, but no new batteries though I do have some that are relatively new, so I can try with those. Does anyone see a reason why this would not work, using these plates alone or give me some suggestions before I ruin some plates and waste time? Is there any benefit to having a cylindrical anode vs one that is a flat plate?

Quote: Originally posted by mysteriusbhoice

Quote: Originally posted by RogueRose   I have a question about an alternative method for an anode. What about taking a PbO2 plate from a battery and using that? I know they tend to become brittle after many charge/discharge cycles, but I suspect plates from a new battery would be much more sturdy. Also, what about backing them with some kind of liquid plastic (PVC or ABS dissolved in acetone or MEK) or even silicone. You could even use epoxy for this. I suggest even trying to use vacuum infusion which would impregnate the spaces between the PbO2. Then I would take something like an angle grinder with a grinding disc and grind the surface off to fully expose all the PbO2. I have all the stuff to do this, but no new batteries though I do have some that are relatively new, so I can try with those. Does anyone see a reason why this would not work, using these plates alone or give me some suggestions before I ruin some plates and waste time? Is there any benefit to having a cylindrical anode vs one that is a flat plate? I tried using battery electrodes and even pure lead plates impregnating them with all kinds of plastics. One issue with epoxy is that the caustic environment will destroy it! The only coating I have tested and confirmed to resist chlorate and perchlorate cells when used as a composite with anodes is. 1.) Polyolefins 2.) Hot glue sticks 3.) Wax or similar compounds PVC cement fails hard due to additives in the cement and after usage in anode composite embrittlement occurs. Hot glue is good for PbO2 composites since you need to keep the temp of the anode and cell low anyway and it seems to hold up however its viscosity is a huge issue and high temps can cause the PbO2 to act as an oxidizer and combust spontaneously when mixed with organics. Polyolefins have the issue with high melting temps but some at 98-124 Celsius seems safe enough to try. Epoxy is BAD and will embrittle just like PVC. Linseed oils also embrittle since they dont completely stop graphite corrosion either. CPVC cement might work but I havent tested that. The only plastics that can survive anode products from looking at chemical resistance charts. 1. PVC (pure no additives) 2. PTFE 3. Polyolefins 4. PVDF 5. CPVC these 5 can widthstand perchloric acid, chloric acid and ozone at low concentrations which are all anode intermediate products. of this list only 3 could be viable. PVC cement I got probably is crap but others may work! CPVC might be a safer bet Polyolefins and waxes also work well i suggest going with those since thermoplastics are more reliable than thermosetting due to them not liberating any products when setting.

PVC seems to be tried and true since ive seen some posts here using PVC but just like any plastic composite you need lots of compression to get good conductivity.
I got an idea to plate any surface which is using spent lantern batteries the formed Mn2O3 can be dissolved in acetic acid to form manganese acetate which like magnanese nitrate can be converted into MnO2 when thermally baked together with a suitable oxidizer maybe some dillute chlorate!!.
OFC nurdrage said that this impure sludge wont last shit in chlorate cell but we are going to plate thicc PbO2 onto it so it wont matter and will survive an acetate bath or two atleast in theory.

heres a comparison of pure Alpha plated PbO2 electrode (bad conductivity) silvery gray vs Beta PbO2 (black shiny)
the plating bath pH and temperature affect the kind of PbO2 you plate.
highly acidic plates mostly beta at room temp purely beta PbO2 will form if you use lead nitrate.
pure beta PbO2 is not desirable due to porosity and brittleness hence lead nitrate baths are heated.
Lead acetate can make Beta PbO2 when mixed with a small amount of HCl to drop the pH but not so much as to cause PbCl2 to precipitate out.
PbCl2 can also form PbO2 beta form but its highly insoluble and this will be a slow process but its also viable.
I use sonication + strong stirring for my plating


[Edited on 17-5-2020 by mysteriusbhoice]





[Edited on 17-5-2020 by mysteriusbhoice]

my nitrate free bath electrodes work!
https://youtu.be/Q0GsZ72x7eg
The one in the video is just very thin layers of α-β and i use 2 plating baths for my process
heres my other short video on how i made these using sonication + old pc fan for stirring
https://youtu.be/7yTDT8oJwpE
aswell as heres a pic of my proper α-β-α-β layered GSLD

From what I've read, the colour of lead dioxide coatings says nothing about whether it is alpha or beta. The colour likely relates more to the surface morphology of the lead dioxide film. Seeing some SEM images of LD films formed at different conditions, a black or shiny appearance of the LD coating does not necessarily imply low surface area. What are actually the most determining factors for efficient perchlorate synthesis from an LD anode? Low resistivity? High surface area? High purity LD (high oxygen content)? Crystal morphology? Something else?...

The higher acidity and/or nitrate bath seems to produce a somewhat "grainy" texture above 4 mA/cm2 that have a shiny silvery-grey appearance, but have very high resistance when measured with a multimeter, where as the shiny black stuff from slow plating/detergents seems to have very little resistance, probably from less interference of oxygen evolution at the anode. In my experience, plating the LD at high current densities from a nitrate bath and then lowering the current density to as low as possible to "plug all the pores" afterwards does not seem to improve the conductivity much. Interestingly though, a somewhat porous LD layer from plating at very high current densities did seem to plug itself somewhat during electrolysis of sodium chloride solutions, maybe an effect of the high stresses created in the LD. There was little difference in measuring resistance between the substrate anode and LD coating and the LD coating itself, so it does not seem to be related to the graphite/LD interface, just the LD.

How does the LD bind to graphite anyway? It is interesting why etching in NaOH seems inportant prior to plating, maybe just to remove skin grease from handeling the substrate anode, though would sites of graphite oxidation also be important? From what I've read, fully oxidized graphene oxide itself is not conductive though...

The pH is the most determining factor for distinguishing between alpha and beta...IIRC alkaline baths always produce alpha. It gets somewhat shady between neutral and a pH>1, where lower current density and higher temperatures seem to favour beta. Some old paper I found tested the predominant crystal modification of lead dioxide using plating baths containing 1, 0.1 and 0.01 M lead acetate in 1 M acetic, where 1 M lead acetate produced alpha only, 0.1 M a mix of alpha and beta and 0.01 M almost exclusively beta lead dioxide. Adherence to graphite does seem a problem though with acetates, irrespective of the concentration of Pb2+. Even adding lead acetate to a lead nitrate bath in concentrations above 70 g/L creates this adherence problem on a graphite substrate, so this seems inherent to using acetate somehow (https://doi.org/10.1016/0013-4686(71)85118-6), since it would seem that the adherence is mainly something determined very early during plating (stresses created later not taken into account) . Alternatively, beta LD is the only thing that wants to stick to graphite....so maybe plating LD on graphite from an enormous volume of 0.01M lead acetate in 1M acetic would work, but the volume of plating solution needed would likely be impractical. Tartaric might be an OTC option, it has a pka1 of 3.1 compared to 4.75 for acetic. Similar for lead citrate though...not sure how soluble lead tartrate is in the presence of excess tartaric.

Speaking of citrates: Has anyone ever experimented with ditin(II)citrate and the very soluble diammonium tin(II)citrates? (https://doi.org/10.1039/A704511E) Not sure how easily these are oxidized while in solution, otherwise seems like an interesting precursor for producing ATO and AITO thin films from OTC stuff.

[Edited on 18-5-2020 by nitro-genes]

Heres another test creation.
crappy graphite rod roughed up in NaOH then mixed PVC + PbO2 powder from sulfate + lead anode electrolysis.
Put into a PbO2 alkaline plumbite bath + PbCl2 + PbAc bath plated under ultrasound for strong adherent coating.
The porous polymer composite should prevent expansion and stress cracking from occuring i hope...
Heres the Lead dioxide composite substrate lead dioxide electrode.

GSLD anode version 3.0.

The pressed graphite/magnetite/pvc composite anodes I posted earlier about had too high of a resistance to really function properly in a perchlorate cell. So I moved on to isostatically pressed graphite used for ESD applications, which would be kind of hard to make as an amateur. What a wonderful material this is...almost as hard as ceramic, finely polisable and consistent electric conductivity due to the isostatic pressing. I think especially the smooth surface morphology of this this type of graphite after polishing is really making a difference during the LD plating, probably due to decreased adherence of oxygen bubbles during the start of plating.

This time, a more pure source of lead metal was also used to prepare the lead nitrate bath, as the first batch of lead nitrate was made from fishing weights, which seemed to contain antimony for hardening purposes and/or bismuth as well.


Substrate anode preparation:

To a 10 cm long rod of 7.5 mm diameter isostatically pressed graphite was glued 4 cm of transparent PVC-U tube (7.6 mm ID- 10 mm OD) using PVC cement. Additionally, a 1 cm long piece of 12 mm PVC-U was glued on as well to act as a retainer ring in the cell later on. The PVC cement was allowed to thoroughly dry for 2 weeks before moving on. The anode was loaded into a drill and the surface was finely polished using a wet scouring pad while turning in the drill. The surface of the substrate anode was then pre-polarized/cleaned by electrolysis in 5% NaOH for 30 minutes at 1 Amp, thorougly washed in 0.5% acetic and finally destilled water. It was then thoroughy wiped dry/polished using clean paper towels. I think this step may be important, since judging by the amount of graphite adhering to the paper towels afterwards, the NaOH etching step seems to produce a small layer of loosely bound graphite, which may create adherence problems for the lead dioxide film later on. The substrate anode was then covered in paper towels to prevent any skin grease surface contamination from further handeling.

Plating procedure:

100 g Lead carbonate and 15 g basic copper carbonate were added to 1 liter erlenmeyer flask, together with 100 ml of destilled water. Several layers of tissue paper held on by a rubber band were used to cover the flask opening, this to minimize aerosolization of the lead salts. Then 30% nitric (degassed by blowing air through it) was slowly added through a small hole in the tissue papers until a pH of 1 was reached. The flask was then gently heated for several hours to remove all remaining CO2. Unfortunately, a small amount of precipite remained after adding the nitric, that was allowed to settle for a day. The precipitate is most likely lead sulfate due to the (almost unavoidable) presence of basic copper sulfate in the basic copper carbonate when prepared from copper sulfate and sodium bicarbonate. After cooling and settling for a day, the now clear blue solution was pipetted off into a 500 ml beaker and 50 mg of didecyldimethylammonium chloride detergent (OTC anti-algea) was added. The substrate anode was then placed into a transparent plastic plate containing two opposing pieces of 2.5 mm2 solid copper wire to act as a cathode during plating, the cathodes were placed as far away as possible from the centrally placed substrate anode. The 500 ml beaker containing the lead/copper nitrate solution was then placed into a stainless steel container filled with water, put on the hotplate and the waterbath heated to 65 deg C. A 3.5 cm long stirrer bar was added to the 500 ml beaker and stirring set to 500 rpm. The plastic cover containing the substrate anode and copper cathodes was then placed over the 500 ml beaker and the volume of the lead/copper nitrate solution adjusted to reach slightly higher than the PVC-tube attached to the substrate anode. Plating conditions: First 8 hours of plating at 30-40 mA (3-4 mA/cm2), then 1.5 hours of plating at 600 mA (50 mA/cm2), and finally, 6 hours of plating at 60 mA (4 mA/cm2). In total 10 g of lead dioxide was plated onto the substrate anode.

Overall, the lead dioxide seems to have a smooth shiny and deep-black appearance (photo). The coating seems completely without any visible pinholes, although some "pustule-like" irregularities seem present. Curious why this did not seem possible with the earlier batch of lead nitrate I was using, that only produced rough and grey looking LD coatings. Maybe iron contamination in the lead nitrate bath contributes in producing these rough looking coatings? Maybe it is just a function of the graphite surface and consistency in conductivity along the surface?

Also seemed interesting to try and plate the substrate anode after attaching the insulating PVC-U tubing, since the LD seems to create a very good seal around the PVC-U and thus hopefully prevents any corrosion at the graphite/LD transition. It could also reduce the amount of lead dioxide that needs to be plated. Curious how the PVC-U will hold up in the cell though... it won't be in direct contact with the electrolyte (1.5 cm headspace was designed) in the 125 ml cell (photo) but still... teflon would probably do better, though since you can't glue it, everything would have to be machined to tight tolerances. Dry machining graphite on a lathe is not going to make anyone happy anyway.

If this doesn't work I'm going ground-glass/titanium/teflon...




[Edited on 16-6-2020 by nitro-genes]

@Markx

After reading through the pulse reverse method of LD plating...It seems that adherence and stresses are a problem using this method. Instead of using pure lead metal as the source of Pb2+, what would happen if an alloy of lead and tin would be used instead? Seeing how well tin(IV)oxide adheres to almost anything, maybe the incorporation of only a few percent tin(IV)oxide could be an improvement? Not sure it would negatively influence the oxygen overpotential of the resulting coating. Curious what would happen, maybe the tin(IV)oxide would already form on the lead electrode or in solution (although nitric concentration is probably not high enough) and just precipitate as a powder or maybe the conductivity of the LD coat would suffer to much or morphology would be bad... anyway worth a try maybe?

Also, I noticed you used ammonium nitrate as component of the electrolyte, would this also be useful in preventing nitrite buildup in a regular lead nitrate plating bath?

[Edited on 16-6-2020 by nitro-genes]

Was curious if using isostatic graphite as substrate would allow a good coat of LD to form from a more impure lead nitrate bath. An identical isostatic graphite rod was plated excactly as posted 2 posts above, using same setup and conditions. First 8 hours of plating at 30-40 mA (3-4 mA/cm2), then 1.5 hours of plating at 600 mA (50 mA/cm2), and finally, 6 hours of plating at 60 mA (4 mA/cm2). Only differences were (1) that both Cu(II) and Pb(II) concentrations were lower, (2) that the lead nitrate used in this bath was made from fishing weights and (3) the bath had been used several times for previous plating runs. Very little nitrite was present at the start of the run though.

The result was a visibly good, 1mm thick, coating of lead dioxide. No pinholes or large imperfections. This is probably mainly a function of the isoelectric and smooth surface properties of the isostatic graphite. Overall the coating seemed very porous though and consisted of small spherical nodules and/or dendrites loosely held together. When a drop of water was placed on the anode, the water would slowly migrate as through filter paper. The anode failed after 5 days of use at 2 A (200 mA/cm2) in the cell. The part of the anode above the surface of the electrolyte was completely intact. The part immersed in the electrolyte completely powdered and eroded away. The LD on the intact part of the anode was extremely well adhered and could not be separated from the graphite substrate without breaking parts out of the graphite substrate. The LD was recovered as large shards at the bottom of the cell, without any graphite still attached to it. A cross section of the LD recovered seems to indicate that the porous nature of the LD is not limited to the surface only, so overall this seems the most likely cause of failure.

Interesting what causes this effect...The lead nitrate produced from the fishing weights always produced these grainy textures, so it seems the purity of the lead nitrate is very important for plating. From what I've read a nodular appearance could also be due to break down products of the detergent used or maybe iron contamination. Just shows that even a visibly good coating of LD is no guarantee, it really needs to be dense and shiny.



[Edited on 27-6-2020 by nitro-genes]

The GSLD anode of a few posts above (shiny and dense LD coat) held nicely in the perchlorate cell. Unlike the anode coated with the porous lead dioxide, the cell voltage was almost rock solid during the entire run this time, (5.8 V - 2.0 Ampere), and seemed to only change somewhat depending on electrolyte fluid level (surface area). The LD submersed in the electrolyte turned a brownish colour, presumably some powdery LD from chloride mediated erosion. Even though lots of ozone was produced, it seems current efficiency becomes really low during the last part of the run (high perc/low chlorate). The run was ended at an estimated 95-99% conversion, which was tested by adding a few drops of concentrated HCl to a few drops of the electrolyte withdrawn from the cell, until almost no yellow colour/odour of chlorine was noticable.

Anode material: 1mm thick b-lead dioxide
Anode surface area: 10 cm2
Cathode material: 316 stainless steel
Cathode surface area: 2.5 cm2
Anode-cathode spacing: 1 cm
Electrolyte: 20% W/V NaCl
Electrolyte volume: 135 ml
Run voltage: 5.8 V
Run Amperage: 2A
Current density on anode: 200 mA (average)
Total cell resistance (V/I): 2.9 Ohm
Temperature run: 35-40 deg C
Ph: 7-8 (was adjusted every day during perc formation)

Wonder how the cell could be made more efficient, (apart from additives to reduce cathodic reduction). All connections of the cell were measured with a multimeter to have almost negligible resistance, so no losses there. The cell was designed for operation at 2A, which I guessed would just be able to do without any heavy external cooling for the 135 ml cell. I guess a large anode surface area compared to total electrolyte volume combined with a small cathode surface area would be most efficient in shifting the steady state conditions towards perc, though would probably need good external cooling. Would a centrally-placed-small-surface-area-cathode, surrounded by a cylindrically shaped LD coated mesh be most efficient? How does the minimal current density for perchlorate formation relate to total anode surface area and electrolyte volume. If you would use a very large anode surface area on the smallest total electrolyte volume possible, would the minimal current density for perc formation needed also become lower?
For my cell, I had hoped that only 4-5 V would be needed to achieve the 200 mA current density, instead of the 5.8 V needed. From what I've read it seems you are tied to the cathode/anode surface area ratio in determining electrolyte resistance and a fixed optimal current density on the LD for making perchlorate? How small can you make the anode-cathode spacing, before becoming detrimental for the LD or cell efficiency? Is a larger cathode surface area (lowering electrolyte resistance) really detrimental in that cathodic reduction increases? Is there a cathode material that significantly reduces reduction processes, like titanium for example? Are larger current densities than 250 mA/cm2 and/or a voltage of >7 Volts really breaking down the lead dioxide coating? Anyway, there is probably a better thread for discussing that here...just curious



[Edited on 1-7-2020 by nitro-genes]

Quote: Originally posted by nitro-genes

@Markx After reading through the pulse reverse method of LD plating...It seems that adherence and stresses are a problem using this method. Instead of using pure lead metal as the source of Pb2+, what would happen if an alloy of lead and tin would be used instead? Seeing how well tin(IV)oxide adheres to almost anything, maybe the incorporation of only a few percent tin(IV)oxide could be an improvement? Not sure it would negatively influence the oxygen overpotential of the resulting coating. Curious what would happen, maybe the tin(IV)oxide would already form on the lead electrode or in solution (although nitric concentration is probably not high enough) and just precipitate as a powder or maybe the conductivity of the LD coat would suffer to much or morphology would be bad... anyway worth a try maybe? Also, I noticed you used ammonium nitrate as component of the electrolyte, would this also be useful in preventing nitrite buildup in a regular lead nitrate plating bath? [Edited on 16-6-2020 by nitro-genes]

I really do not have answers for your questions....only speculations At this point in research we dwell into the dark unknown of factors, the nature and effect of which are unpredictable to say the least. Only physical experimentation can offer some insight to the problems at hand.

But I must compliment you on the stunning progress that you have made here meanwhile. My own efforts were rather negligible as far as creating a functional lead dioxide anode is concerned.

The coating from the "impure" bath looks very much like the ones I achieved in my setup. Especially when I used sodium lauryl sulfate as a surfactant in hopes to release the tensions in the formed coatings. They seemed to have a nodular and somewhat porous structure.
It is very encouraging to see that the dense coating has held up in perchlorate cell conditions ( the slight surface erosion is to be expected). In my attempts even the shiniest coatings did fail in perchlorate cell within a few hours.
Your results seem to conclude that contaminants have a rather profound effect upon the functionality of the formed coating and I trust they also contributed to my failures, as I did not use pure materials, but rather technical grade ingredients in my work. E.g. the lead originated from heavy duty electrical cable coating, so I highly doubt it can be deemed chemically pure.
But please keep up the great work and keep us posted on the results...I'm following with great interest Would be extremely interesting to see how long the successful anode lasts in perchlorate synthesis before final failure and if creating such a successful specimen is repeatable...

Quote: Originally posted by nitro-genes

The GSLD anode of a few posts above (shiny and dense LD coat) held nicely in the perchlorate cell. Unlike the anode coated with the porous lead dioxide, the cell voltage was almost rock solid during the entire run this time, (5.8 V - 2.0 Ampere), and seemed to only change somewhat depending on electrolyte fluid level (surface area). The LD submersed in the electrolyte turned a brownish colour, presumably some powdery LD from chloride mediated erosion. Even though lots of ozone was produced, it seems current efficiency becomes really low during the last part of the run (high perc/low chlorate). The run was ended at an estimated 95-99% conversion, which was tested by adding a few drops of concentrated HCl to a few drops of the electrolyte withdrawn from the cell, until almost no yellow colour/odour of chlorine was noticable. Anode material: 1mm thick b-lead dioxide Anode surface area: 10 cm2 Cathode material: 316 stainless steel Cathode surface area: 2.5 cm2 Anode-cathode spacing: 1 cm Electrolyte: 20% W/V NaCl Electrolyte volume: 135 ml Run voltage: 5.8 V Run Amperage: 2A Current density on anode: 200 mA (average) Total cell resistance (V/I): 2.9 Ohm Temperature run: 35-40 deg C Ph: 7-8 (was adjusted every day during perc formation) Wonder how the cell could be made more efficient, (apart from additives to reduce cathodic reduction). All connections of the cell were measured with a multimeter to have almost negligible resistance, so no losses there. The cell was designed for operation at 2A, which I guessed would just be able to do without any heavy external cooling for the 135 ml cell. I guess a large anode surface area compared to total electrolyte volume combined with a small cathode surface area would be most efficient in shifting the steady state conditions towards perc, though would probably need good external cooling. Would a centrally-placed-small-surface-area-cathode, surrounded by a cylindrically shaped LD coated mesh be most efficient? How does the minimal current density for perchlorate formation relate to total anode surface area and electrolyte volume. If you would use a very large anode surface area on the smallest total electrolyte volume possible, would the minimal current density for perc formation needed also become lower? For my cell, I had hoped that only 4-5 V would be needed to achieve the 200 mA current density, instead of the 5.8 V needed. From what I've read it seems you are tied to the cathode/anode surface area ratio in determining electrolyte resistance and a fixed optimal current density on the LD for making perchlorate? How small can you make the anode-cathode spacing, before becoming detrimental for the LD or cell efficiency? Is a larger cathode surface area (lowering electrolyte resistance) really detrimental in that cathodic reduction increases? Is there a cathode material that significantly reduces reduction processes, like titanium for example? Are larger current densities than 250 mA/cm2 and/or a voltage of >7 Volts really breaking down the lead dioxide coating? Anyway, there is probably a better thread for discussing that here...just curious [Edited on 1-7-2020 by nitro-genes]

Cathodic reduction has in my practice not really been a limiting factor, neither in chlorate nor perchlorate electrosynthesis and I would not prioritize it as a major threat....although opinions differ on the matter, so I do not claim that it is of insignificant importance on some setups.
Titanium seems to offer a cure for cathodic reduction and I can reccommend the material. All of my cells are composed of Ti components and the resistance to corrosion is really excellent. But when using Ti, make sure that it is CP Ti not an alloyed grade like Gr 5 (Al, V, Ti alloy). The alloyed grades are of lesser resilience towards corrosion and tend to erode in cell conditions, releasing soluble contaminants into the electrolyte. Not to mention they are a serious pain to machine and work into shape. Tapping is an especially "sweet" operation on alloyed Ti . The CP grade is a breeze to work with in comparison....quite comparable to stainless as far as machining operations are concerned.

There is a general concensus about the need to minimize the active surface are of the cathodic setup in relation to the anodic side, but I've rather boldly ignored this principle when using Ti cathodes and I really must admit that doing the reverse has worked out much better in my instance. Especially in perchlorate synthesis. My cathodes were of about twice the surface area of the anode and it really helped to boost the cell operation in terms of being able to move more charge through it at a lower applied potential. I tried the reverse (with just having cathode stems submerged in the cell) and it created a major bottleneck that limited currents to nonreasonable level. Reversing the setup made a world of a difference.
Electrode spacing....well, common sense suggests even distribution of charge (symmetrical placement of electrodes) and enough space between electrodes to facilitate efficient replenishment of reagents through convection or forced stirring. 10-20mm distance and a reasonably symmetrical placement to ditribute current densities evenly should satisfy the conditions.

As far as applied voltages across the cell, my generic experience has been that usually less tends to be more. Again, not absolutely true all the time and in all the setups, but the higher the applied voltage, the higher the electrode polarisation and at a certain point the polarised electrodes become "energetic" enough to allow detrimental sidereactions to occur. The high polarisation levels can make the inert electrode materials appear quite reactive under the given circumstances. As a result we have erosion, pitting, passivation of surfaces, dissolution of some components and just a generic mess that shall likely do more harm than good. As a personal rule of thumb I take below 5V of applied potential as the "general safe area of operations". Above 5V volts the probability of "what new fresh hell is this??" type of situations seems to rise drastically.

Long story short, I would suggest you use Ti cathodes, evenly placed around or at opposing sides of anode, increase the cathode area to boost current carrying capability at lesser applied voltage, lower the applied potential to around 5V or below and see how it works. If a lot of improvement seems to be in order then by all means you can reverse the electrode area ratio and tune the voltages at will. But at 7V across the cell I would be completely struck if no detrimental developments arise...
My experiences are based on experiments with Pt coated electrodes, so in case of lead dioxide perhaps not all of my suggestions are valid, but in general I think that most of them shall be of help, rather than misleading.

Happy experimenting and keep us posted !

Well....not sure if stunning progress is the right word. Still not fully understanding all the factors involved in the manufacture of LD coatings, for example why heating of the lead nitrate bath is commonly used. I get the feeling however, that despite large amounts of literature pertaining to this subject, every plating bath/setup/condition seems to produce its own unique surface morphology. Probably depends on so many interacting small factors that it is almost impossible to accurately predict beforehand. In general, using a large lead nitrate bath, with highest concentration of pure lead nitrate possible and the substrate rod spinning to remove any air bubbles is probably giving best results. For home experimenting, using a 5 litre volume, 800 g/l lead nitrate bath with a 1000 rpm spinning substrate anode (Probably spraying lead salts everywhere when setup is not correct) was too much for me. Your pulse method of plating would obviously be a real advantage there! Have you ever tried your method with a graphite substrate?

The only thing that seems reasonable to assume from my experiments is that the smooth surface and/or electrical properties of the isostatic graphite as substrate significantly reduces gross defects and pinholes from occurring in the LD coating. Another potentially interesting thing for home experimenters is that very high concentrations of copper nitrate also may improve plating from small baths. Maybe just by interfering with dendrite formation during plating or perhaps by decreasing cathodic formation of nitrite.

Quote: "There is a general concensus about the need to minimize the active surface are of the cathodic setup in relation to the anodic side..."

Exactly! Also during my first experiments using the LD plated composite anodes and a stainless steel cathode, I noticed that in some cases perchlorate was forming above a certain current density, however at a certain concentration of perchlorate the cell became "stuck" and no further increase in perchlorate synthesis was noticed even on prolonged electrolysis. Even more surprising, in one instance when the voltage was reduced again, the concentration of perchlorate even seemed to drop! It could be that the oxygen overpotential of the LD was somehow screwed up by impurities within the LD, or even a lack of stirring contributing like you mention as well. Also not sure if anodic processes could also somehow react/reduce perchlorates to explain this, though I therefore assumed cathodic reduction was indeed occurring and the formation of perchlorate the result of a steady state condition between anodic oxidation and cathodic reduction. This would also explain the generally very sharp boundary in current density needed to start producing perchlorate. The reduction potential of the cathode would be one of these factors indeed and wondered if titanium would do better in this regard than stainless steel. Maybe some conductive metal-oxide thin film coated material would completely eliminate reduction from occurring, though can't think of any that would be stable for use as cathode. The titanium in itself may form some stable conductive oxide/hydride coating that reduces reduction, or maybe ebonex would work better as cathode? Would magnetite be stable under cathodic conditions, seen that the Schikorr reaction actually produces hydrogen?

High cell voltage indeed seems to be detrimental, including overal efficiency. Left some room for inserting a second opposing cathode for a reason. So will try this first...If the cell becomes stuck, it would always be possible to cover one of the cathodes again using a PVC cover. Also have some titanium lying around (large blocks, probably grade 5), but after some reading on the pains of machining titanium (especially the poor heat conductivity and resulting hardening), haven't found the courage yet to start. Like you say however, some grades appear to be more machinable than others and from what I understand most grades are not much more difficult in some aspects as stainless.

[Edited on 3-7-2020 by nitro-genes]

Quote: Originally posted by nitro-genes

Well....not sure if stunning progress is the right word. Still not fully understanding all the factors involved in the manufacture of LD coatings, for example why heating of the lead nitrate bath is commonly used. I get the feeling however, that despite large amounts of literature pertaining to this subject, every plating bath/setup/condition seems to produce its own unique surface morphology. Probably depends on so many interacting small factors that it is almost impossible to accurately predict beforehand. In general, using a large lead nitrate bath, with highest concentration of pure lead nitrate possible and the substrate rod spinning to remove any air bubbles is probably giving best results. For home experimenting, using a 5 litre volume, 800 g/l lead nitrate bath with a 1000 rpm spinning substrate anode (Probably spraying lead salts everywhere when setup is not correct) was too much for me. Your pulse method of plating would obviously be a real advantage there! Have you ever tried your method with a graphite substrate? The only thing that seems reasonable to assume from my experiments is that the smooth surface and/or electrical properties of the isostatic graphite as substrate significantly reduces gross defects and pinholes from occurring in the LD coating. Another potentially interesting thing for home experimenters is that very high concentrations of copper nitrate also may improve plating from small baths. Maybe just by interfering with dendrite formation during plating or perhaps by decreasing cathodic formation of nitrite. Quote: "There is a general concensus about the need to minimize the active surface are of the cathodic setup in relation to the anodic side..." Exactly! Also during my first experiments using the LD plated composite anodes and a stainless steel cathode, I noticed that in some cases perchlorate was forming above a certain current density, however at a certain concentration of perchlorate the cell became "stuck" and no further increase in perchlorate synthesis was noticed even on prolonged electrolysis. Even more surprising, in one instance when the voltage was reduced again, the concentration of perchlorate even seemed to drop! It could be that the oxygen overpotential of the LD was somehow screwed up by impurities within the LD, or even a lack of stirring contributing like you mention as well. Also not sure if anodic processes could also somehow react/reduce perchlorates to explain this, though I therefore assumed cathodic reduction was indeed occurring and the formation of perchlorate the result of a steady state condition between anodic oxidation and cathodic reduction. This would also explain the generally very sharp boundary in current density needed to start producing perchlorate. The reduction potential of the cathode would be one of these factors indeed and wondered if titanium would do better in this regard than stainless steel. Maybe some conductive metal-oxide thin film coated material would completely eliminate reduction from occurring, though can't think of any that would be stable for use as cathode. The titanium in itself may form some stable conductive oxide/hydride coating that reduces reduction, or maybe ebonex would work better as cathode? Would magnetite be stable under cathodic conditions, seen that the Schikorr reaction actually produces hydrogen? High cell voltage indeed seems to be detrimental, including overal efficiency. Left some room for inserting a second opposing cathode for a reason. So will try this first...If the cell becomes stuck, it would always be possible to cover one of the cathodes again using a PVC cover. Also have some titanium lying around (large blocks, probably grade 5), but after some reading on the pains of machining titanium (especially the poor heat conductivity and resulting hardening), haven't found the courage yet to start. Like you say however, some grades appear to be more machinable than others and from what I understand most grades are not much more difficult in some aspects as stainless. [Edited on 3-7-2020 by nitro-genes]

Well, having produced an actually functional lead dioxide anode in a homeshop environment....how much closer to stunning can we really get There are not too many documented cases of this happening around as far as I've looked. Mostly just gruntled attemps shrouded in disappointment.

You are quite correct about the vast collection of parameters and factors interacting upon the process. They make navigating this subject most difficult and repeatability seems notoriously low. It is a classic case of a seemingly prosperous and rather simple matter turning into a large scale mystery of poisonous and foggy nature. The inherent toxicity of soluble lead salts is what drowned my enthusiasm for the classic approach on the subject. The pulse plating method was devised in hopes of not having to deal with coupious amounts of soluble lead and as a preliminary test of the hypothesis it worked, but the constant failures related to the functionality of the formed coatings led me to investigate the Pt route. I found that manipulating soluble Pt salts offers a much higher reward including just a fraction of the effort, time and quantities of reagents involved in the lead dioxide route to perchlorate. Not that soluble Pt compounds would be less dangerous compared to lead, on the contrary actually. But the amounts are minuscule and can be handled reasonably safely. Also the repeatabilty of the results was outstanding.
I did not try any other substrates in my process except platinized Ti and electrochemically pretreated 316 stainless, both of which offered nonfunctional coatings for the perchlorate process. But for practical purposes I really should try it out on diffrent carriers (lead metal, gaphite, MMO) ....would be easy enough really, as I still have the setup and even the original electrolyte stored away.

As for the cathode material, I really suggest to try out Ti....I think for cathode application the alloyed grades also might work, but it would be safer to order some unalloyed grade 2 sheet to exclude at least some factors. Oxide based electrodes usually do not bode well for cathode application...for obvious reasons.
The machining of Ti is really not something to be afraid of. Just try not to let a pile of Ti swarf build up in the chip tray and catch a spark in there...it is impressive, destructive and blindingly bright There are more common materials that tend to be way more difficult to get into shape compared to alloyed Ti...work hardening alloy steels e.g. high tensile fastener steels, manganese alloy steels, chrome vanadium steels, low alloy boron steels, etc. I've worked on plenty of them and it can be a true pain to yield them sometimes. Try drilling through a manganese alloy steel rod....titanium is a breeze compared to this nightmare

[Edited on 3-7-2020 by markx]

Decided to introduce a second and opposing stainless steel cathode (photo) in order to lower the voltage needed to produce the 200 mA/cm2 current density for perc synthesis. With the second cathode installed, the difference in resistance was immediately apparent. Whereas with the single cathode 5.8 V was needed for 2.0 Amp, the second cathode lowered this to 4.5 V, so almost perfect IMO.

A second perc run was started, starting from 20% w/v sodium chloride. In order to limit the chloride/hypochlorite mediated erosion of the lead dioxide, I tried running the cell at 1.0 A (100 mA/cm2) for the first 7 days. After 7 days, almost all chloride had converted to chlorate, although a slight smell of bleach was still noticeable. Although almost no erosion of the lead dioxide had occurred during this period, the voltage needed to maintain the 1.0 A controlled current slowly crept up by about 50 mV a day. After the 7 day chlorate run, the cell was run at 2.0 A, as before to start perc synthesis. The voltage needed at this point had increased to 4.9 V, compared to the 4.5 V needed earlier. Cell temperature during the run did not go above 35 C at any time. The voltage needed kept increasing steadily and at the third day, quite suddenly the electrolyte started to become a murky brown colour and the cathodes became covered with large amounts of lead metal (photo, yellow colour probably oxidation to lead(II)oxide). Most of the chlorate had been converted into perchlorate at this point. When taken out of the cell, the anode was seemingly fine at first sight, though when looked under the binoc (10X) it became apparent that the anode had developed many tiny cracks along it's surface. The cracks were only visible on the part of the anode that had been submerged in the electrolyte.

Quite sure the anode will fail in a short amount of time now. Curious what caused the cracking and the massive amount of lead metal buildup at the cathode. What was first in this case? the development of cracks or electrolyte/gasses reaching the graphite substrate? Since the voltage kept creeping up slowly and steadily the whole time (even when run at 1.0 A), it seems that somehow, over time, the electrolyte or gasses produced found some way to the graphite substrate, slowly eroding the interface. Maybe in the presence of the electrolyte, the graphite substrate can also react directly with the lead dioxide, explaining the cathodic buildup of powered lead. Overall, I think this is the most likely scenario, although it could be that running the cell previously with only 1 SS cathode installed did start cracking the anode first. Out of curiosity, I ran one of the composite LD coated anodes before at extremely high current densities and temperatures (>2000 mA/cm2 - 60 deg. C.) for several hours, which surprisingly did no damage at all to the lead dioxide itself. Is a dense and shiny LD coating inherent to more interenal stress buildup? Maybe it could be an effect of residual chloride present somehow? Somehow it seems that the most "dangerous" part of the run is when the cell is just at the boundary of switching from chlorate to perchlorate synthesis, is this true and why exactly? Anyway, the benefit of titanium as substrate is pretty obvious by now...graphite is just such an interesting stuff by itself. Maybe adding a thicker layer of LD (>3mm) would help.

I must say that, like Markx also pointed out, that working with these large amounts of poisonous lead salts and dealing with the lead dioxide erosion in the cell drains the fun of experimenting with this further. Despite the fascinating properties of lead dioxide itself and the factors involved in producing a working GSLD anode, I'm inclined to throw in the towel. Since I have some fresh lead nitrate electrolyte (for plating) still standing, I think I'll coat one final graphite substrate with a thicker layer of LD to see if it lasts longer, then call it a day.



[Edited on 15-7-2020 by nitro-genes]