Perchlorate cell additives for Pt anode

I'm new here. Hello!

Inspired originally by NurdRage's video on chlorate production, I've been dabbling with the electrolysis of K/Na chlorides. I've managed to obtain a Pt plated Ti anode for use in a perchlorate cell but, naturally, I'm worried about its longevity.

Reduction of chlorate back to chloride at the cathode resulting in constant low levels of chloride seems to be greatly detrimental when using platinum, and chromate is commonly used to prevent this. However, if I've understood correctly, there is the option to use either persulfate or fluoride instead, though I haven't managed to find further information on the use of these alternatives. I can use any one of these three, but I would like to avoid using hexavalent chromium where possible.

Furthermore, I wish to find out what kind of drop in life expectancy one might expect when using platinum to go straight from NaCl to NaClO4. This is what I'm planning as I do not require several kilos of product.

If anyone can shed some light on the subject I would greatly appreciate it.

Here you can see the electrodes I'm going to be using. The coating thickness is 2.5-3 µm.

Quote: Originally posted by mackolol

Sodium fluoride is used when your cathode is PbO2 and it increases the current efficiency. When you use any other cathode K2Cr2O7 is used and as you have said it prevents reducing chlorates to chlorides.

The cell has now been running for a few hours at roughly 5A, 4.4V. I figured stirring might be beneficial so I dug my old DIY magnetic stirrer out of storage. The electrolyte volume is roughly one liter. Roughly 3 grams of sodium persulfate was added. The electrodes were adhered to the lid using RTV silicone.

if only one side is platinized then yea your current density is about 100ma/cm^2 which is above the 80ma/cm^2 so with that your ce would be around 30-50% for your perchlorate run.
as for your chlorate run if the cell will go to alkaline then it will be at 54% efficiency due to hypochlorite formation.
I just hope your anode survives the low chloride level right before it starts using up the chlorate since that would be the danger zone.

below is one of my yield from thermal decomposition of mixed NaClO3 + KClO3 to make KClO4.
tested with no horrible yellow puddle of "MMS" forming when mixed with HCl also very poorly soluble when compared with KClO3 and thats how you know.
tho i prolly used up around 150 grams of mixed Chlorate didnt measure it this time since yield averages around 80% when using mixed and 60% when using pure KClO3.




[Edited on 23-6-2020 by mysteriusbhoice]

So after almost exactly 7 days (=roughly 840 Ah) of operation, the cell kind of shit the bed. I monitored the cell closely for hours before anything odd occurred. Over the course of its operation the cell saw voltage creep up at a slow pace starting from 4.8V, averaging 100 millivolts of increase per day. During the last 12 or so hours the cell went from 5.4 all the way to 6.0 when finally the power supply switched over to controlled voltage and the input current dropped from 5A to 0.6A.

I was quick about turning off the power and removing the electrodes to dry. Surprisingly they looked just fine.


So, I proceeded to test the electrolyte with methylene blue which to my surprise gave me a positive for perchlorate. Or so I thought. I was thrilled but still skeptical seeing as I had only fed in under 1000 ampere hours. I also chilled down some fresh electrolyte with equal persulfate added and tested that. Positive. So obviously it has to be the sodium persulfate, right? Apparently that's exactly right. I repeated the test with fresh brine but left out the persulfate - no reaction.

Here's the presumed false positive:


I then tested the electrolyte for chloride using silver nitrate and found that there was plenty of it.


I also tried to run the cell with fresh electrolyte. Barely any current flowed until I manually turned the voltage up to as much as 9.3V. I had to do this twice because minutes after the first test something constricted the flow of current again. I don't believe that I damaged the electrodes much since the voltage increase lasted for a split second before voltage normalized to below 6V and the current rose to 5A.

The voltage kept creeping and after about 10 hours I realized what must be happening. The insulation near where the negative wire was crimped to the alligator clip had hardened and even begun melting. The cathode connection was hot enough to cause a burn. So, while I re-saturated the electrolyte with sodium chloride (figured I might as well) I made some adjustments. This is v2.1, where I added the flat pieces of metal to help with efficiency and heat distribution. I can now touch any part of the connections without any discomfort.


I powered up the cell and everything is fine again. The voltage is 4.7, the lowest it's been so far. The road to perchlorates continues.




[Edited on 11-7-2020 by Benignium]

[Edited on 11-7-2020 by Benignium]

Thanks! I'll definitely shop around for some of those for v3.

Quote: Originally posted by markx

Connections to Ti electrodes tend to passivate, especially if the contact surface is negligible like when one uses an alligator clip or just wraps the wires around the electrode stems. It is a constant problem with quickly improvised current leads. But even solid connections secured by bolts tend to passivate on Ti over time. So it makes sense to move and clean them regularily. On my large cell I have the Ti electrode stems drilled, tapped and the current leads connected to them by stainless bolts, but even these connections passivate from time to time.

22 days and 20 hours (548 h, 2640 Ah) have passed with the cell being operational, and it's time for some results. As my previous MMO chlorate cell had an abysmal CE of around 20%, I thought it only reasonable to grossly underestimate the new cell design despite clear improvements like the use of additives and a significantly higher current density.

Anyway, at this point if I had a cell efficiency of 50% I would have used something like 110% of the electricity required to fully convert 1000 mL of saturated NaCl solution. The electrolyte was no longer as opaque from dispersed bubbles and the color of hypochlorite ions had disappeared some time ago, so I took a 10 mL sample for testing. The voltage had been staying comfortably at around 5 volts for a long time.

First, a 1 mL sample was taken to qualitatively test for perchlorate. This sample was diluted and acidified with a drop of ~36% H2SO4. The sample was boiled and 5 milligrams in total of potassium metabisulfite was added which, based on sulfur dioxide production, was an excess. An equivalent volume of hot saturated KCl solution was added and an immediate precipitate was observed. The precipitate was washed with room temperature DH2O, which was decanted off and discarded. The washing was repeated four times and the a sample was taken from the fourth washing. Perchlorate was identified from the sample using methylene blue.



Something to note is that when I got a false positive due to persulfate earlier, that only happened with chilled electrolyte samples. At room temperature the normal methylene blue color prevailed. This time even at RT there was an instant reaction, and the color wouldn't fade away as it did with the persulfate. The clumps of precipitate were much more defined, with no fine enough precipitate to even partially give the solution a purple/violet appearance.

Next, a more quantitative test was carried out on the remaining 9 mL of electrolyte. The sample was treated with sulfuric acid and potassium metabisulfite followed by the addition of hot saturated KCl solution. The precipitate was vacuum filtered and washed thoroughly twice using 2x25 mL RT DH2O. The fluffy, crystalline precipitate was dried and weighed. 8050 milligrams of dry precipitate was obtained.



At this point I powered off the cell and inspected the electrodes. The anode looks pretty rough. The silicone had also visibly corroded.



The electrolyte was no longer perfectly clear and contained silvery solid in suspension as clouds and flakes. When compacted the solid stuff had the consistency of watery jelly. Filtering it out was a pain in the anus. The solution is now crystal clear, but I'm fairly certain there are still some colloidal particles in it. It has a shimmering quality similar to a solution of silver nitrate shortly after dropping in a piece of copper. I hope that the majority of however much platinum it contained can be recovered eventually by burning the filter papers and dumping the remains in some aqua regia.



As a final test to further examine the purity I took 100 mg of the assumed KClO4, mixed it thoroughly with 100 mg of sugar in a test tube and added a few drops of concentrated H2SO4. The mixture did not ignite, which should mean it's relatively free of chlorates. I will now process the rest of the electrolyte in the same manner.



In many ways (at least one) this project has been a success. Certainly not wallet friendly at roughly 8.5 €cents/gram, assuming that the anode is ruined and cannot withstand another run. But happiness is the number two priority and I sure am happy.


I will attempt another batch from chloride and I will share the results here. I will also confirm the yield as soon as I've processed the perchlorate.

Good job! And congratulations on a successfull conversion run!

The fluffy percipitate is well known to me. I trust it is a combination of titanium and platinum compounds that from a gel like slime in the electrolyte. It is near to impossible to filter out effectively and the best action that I've found to deal with it is "pure classic": just do nothing....
It shall settle at the bottom of the cell eventually (afer several days) and decanting or carefully siphoning the clear solution on top of it makes for a complete separation. The small amount of contaminated electrolyte left can be filtered or discarded or turned into a contaminated batch of perchlorate. Anyways the losses are not considerable with such an approach.
The anode may look rather spent, but it shall remain fuctional as long as it conducts evenly over the surface (gas evolution) and the cell voltage does not rise. I've managed to squeeze 2-3 full conversion runs out of DIY Pt anodes before they give up the ghost. More product than I can reasonably consume in years of activity, so it is quite an effective method. Especially if one does not resort to buying the anodes, but makes them in home workshop starting from chloroplatinic acid.

[Edited on 28-7-2020 by markx]

Thank you markx! I was too impatient to let the gunk settle, and thankfully regular qualitative filter paper worked adequately well. I really hope the anode is good for more perchlorate. Based on cell voltage and gas evolution it just might be. I'm starting over with fresh electrolyte tonight. Whatever happens, at this point I already have more than I will probably ever need. I might have to get into rocketry!




[Edited on 29-7-2020 by Benignium]

Quote: Originally posted by mysteriusbhoice

I wonder how much chloroplatinic acid costs and with how much its needed and the platinum price being half that of gold. how cheaply can you make DIY platinized electrodes.

Quote: Originally posted by Benignium

@markx, do you have pictures of your anode preparation that you can share?

Quote: Originally posted by B(a)P

I recently acquired some barium chloride with the view to convert it via electrolysis first to chlorate then to perchlorate. I have a cell with a platinised titanium anode and titanium cathode. Without doing a whole lot of research I jumper into the setup like I usually would for the sodium or potassium salts. To aid with efficiency I usually add 1 g of potassium dichromate along with the chloride when I am first setting up. I failed to look into what might happen when dichromate is added to a saturated solution of barium chloride. I didn't realise how insoluble barium dichromate was and I immediately got a fine yellow precipitate in my previously clear solution. Given barium dichromate is only soluble at 0.3 mg/L per 100 mL water will I have enough free dichromate to prevent the reduction of chlorate at the cathode? Has anyone else tried the electrolysis of barium chloride? If so what additives did you use? This paper explores pH, temp and current density, but does not mention any additives, they used an MMO anode. They also used a rotating cathode which is quite interesting. https://krc.cecri.res.in/ro_2006/044-2006.pdf Any assistance would be greatly appreciated!

Quote: Originally posted by markx

Dichromates (also other additives) are not a must for chlorate electrosynthesis. I've never been a fan of the practice and have done just fine without it. The mass production industry uses steel cathodes because of the cost factor and adds dichromate to hinder the reduction of chlorate on steel. This is done to squeeze the last bit of possible efficacy out of their setup. In an amateur setting such efforts are often rather in vain and just complicate the process by introducing more risk factors. Especially if one uses a titanium based electrode set...Ti already hinders the cathodic reduction of chlorate and using dichromate is utter overkill. Soluble barium compounds are nasty enough poisons on their own, so introducing dichromates to the setup seems a bit undue. Do not intend to run a barium chlorate cell with an open top.....the spray is persistant and shall contaminate your premises. Also, producing barium perchlorate is not of a practical purpose, as the salt is highly hygroscopic and shall be of little use in any compositions that do not include water. [Edited on 27-9-2020 by markx]

Quote: Originally posted by Antiswat

so, mysteroisbchoice, 1.4kg in 4 days? how many amps is the device pulling in total? i usually just let my cell run with a total excess of NaCl sitting at the bottom and the cell would trade out the NaCl with NaClO3 crystals, they grew really big and nice, big and rectangular. sadly NaClO3 is illegal in europe these days, ive thought of Ba(ClO3)2 but it might form insoluble Ba(OH)2 at the electrodes or did i remember something wrong? i recall there was one site with calculator on it called v2zkays or some shit, but its several computers ago, it featured calcium barium potassium sodium and probably even rubidium, the only difference was relative to the molar weight of the molecule, how much chlorate it could contain per gramme as for additives, chromate can be made as easily as just plonking in some NaHCO3 precipitated stainless steel chloride (316 SS is 18% chrome) the iron will ppt out over time (which isnt an issue unless youre trying to decompose it thermally to perchlorate) as for the thermal decomposition, what setup do you have for that? i remember dr lipton on YT did the whole thing with a heatgun and a small refractory build and got .. well some results. but 80%+ yield? thats pretty wild, could vacuum maybe be used to increase yields or have you found some catalyst? maybe if you have a solid setup you could try messing around with catalysts to really revolutionize the no-no's

So I decided to try out a bromate cell.




After producing one batch of potassium perchlorate and another of sodium perchlorate, I decided that's enough of that and made a new electrolyte comprising 507 grams of KBr and plain water, no additives. Initially everything was fine. Then, along with small crystals of bromate, some garbage started to appear. Eventually there was so much solid stuff in suspension that the electrodes were completely obscured. The solid stuff that settled on the bottom of the cell soon overwhelmed the stirring. With stirring gone, a lot more solids settled and suddenly current practically stopped flowing. Upon investigation it turned out that inside a bromate cell the conditions are somewhat different. What happened exactly beats the shit out of me.









I managed to produce and isolate a whopping 63 grams of very pure potassium bromate. Even that is going to last me a long time, so it wasn't all for nothing.