Sodium chlorate cell questions.

[WSM]

Ok today for some reason my PSU stop... and it did not want to start again... I tried another PSU and the same was happened....

Maybe the cell draw too much Amps and they burned out... I am not 100% sure tho, 1st time is happening to me.

 

To calculate your cell's current draw, measure the area of the anode in cm^2. Multiply that by 0.3 (the maximum amount of Amps suggested per square centimeter for MMO). If using one cathode, the answer is what you just came up with. If using two cathodes, double that number.

 

Double check this calculation by comparing it with what's in my blog, homegrown oxdizers.

 

When used properly, the calculations are fairly accurate.

 

WSM

Edited November 21, 2019 by WSM

[TomasBrod]

Knowing and being able to regulate the current going into your cell is important for successful operation. Both the power supply and the electrodes have a maximum current that should not be exceeded. If exceeded, the component in question will break down. Your 20A raring of power supply is the maximum current it can supply without damage. It will happily supply more. The electric current in the system obeys Ohm's law. The electric resistance of the cell varies during the run time, depending on temperature and chemistry.

 

On the other hand, I would like to hear about your manganese dioxide electrodes. How you made them?

[Arthur]

It's essential to know, and know how to regulate, the current in your cell. It's also important to keep significantly below the current rating of your power supply (say never exceed 80% of the psu's rated current.

 

A power supply will die if you draw too much current. the electrodes will have a short life if you feed them too much current.

 

You can usually regulate the current by selecting the supply voltage and adjusting the length or gauge of the low voltage supply lead.

[WSM]

It's my understanding that the electrode size (in area) determines the current draw of the circuit.

 

A large electrode assembly CAN demand more current than a low capacity power supply is possible of delivering (causing premature failure), but a large capacity power supply can't "force feed" more amperage into a smaller electrode set. The cell will take only what it CAN take, if the voltage remains constant.

 

With a fixed voltage (of, say 4.0 Volts DC), the current draw of the cell is self-limiting. So a 100 Amp power supply may be offering 100 Amps, but a 10 Amp capacity electrode assembly will only take what it can use and ignore the rest of the power supply's capacity.

 

This is borne out in my research using volt meters and ammeters in line with the power supplies I've used in running my cell experiments.

 

There may be more to it in the overall view of what we're discussing, but my opinion on this is based on my own observations and experiences over the past two decades.

 

WSM

Edited November 24, 2019 by WSM

[Arthur]

If you use a constant voltage supply then it will force current into the electrodes If you pick an unsuitable (too high a voltage) psu then it may force more current into the electrodes than they will want for a good service life. Remember that the cell needs about 3v at the electrodes but losses in cables and connectors can easily add up to 2v.

 

You should reduce the voltage applied to the electrodes by varying the power supply adjustment or by varying the resistance of the psu cables so that the resultant current will not exceed the useful current of the electrodes and be safely in the top third of the PSU rating.

 

Given a 60A PSU at 5v I was easily able to pick a voltage that would let 40A pass through the cell and be adjustable for less current. Part of the adjustment is the PSU trimmer pot, part of the adjustment is starting with 2 metres of 4AWG flex and cutting it shorter to get a little less resistance.

It's better to use the distributed resistance of a length of wire than the localised resistance of a very low value resistance so that nothing gets burned.

[markx]

There are many factors which determine the amperage that is able to pass a cell at a given moment: PSU output voltage, voltage drops across passive resistances, temperature of the cell electrolyte, concentration of the cell electrolyte, the kind of electrolyte (chloride, sulfate, chlorate, nitrate etc), surface area of the electrodes, geometry and placement (distance and shape e.g) of electrodes, type of electrode material and probably there are a dozen more which I can not even fathom at the moment.

 

The most obvious and important ones to use for control of amperage being the PSU output voltage, distance across electrodes in the cell and surface area (dimensions) of electrodes. Since we are on the topic of chlorate electrosynthesis, then we usually face a situation that requires current limiting. Especially once the cell has warmed up to normal operation temperature. Whenever possible the adjustment of power supply output voltage should be used as a means for regulation of the current. It is by far the most straightforward, efficient and safe method to reach a wanted amperage value. If power supply does not allow for satisfactory manipulations with the output voltage value then the next best option would be to vary the distance of the electrodes in the cell.

Limiting current with electrode surface area is viable if it is done by limiting the size of the cathode. If one limits the size of anode or both electrodes, then very likely the current densities at anode shall go over the safe limit for longevity. For as much as the cathode is concerned in chlorate electrosynthesis, the high current densities usually are not a problem. On the contrary they are beneficial in preventing cathodic reduction of products on certain cathode materials and thus yield a higher current efficacy for the cell.

It is generically true that a cell's amperage is selflimiting depending on the surface area of the electrodes, but it may not always be safe to run into that limitation if the electrode configuration favors excessive current densities on the anode. E.g. anode and cathode are of comparable surface area or even worse the cathode is of a larger surface area compared to the anode.

[THEONE]

Knowing and being able to regulate the current going into your cell is important for successful operation. Both the power supply and the electrodes have a maximum current that should not be exceeded. If exceeded, the component in question will break down. Your 20A raring of power supply is the maximum current it can supply without damage. It will happily supply more. The electric current in the system obeys Ohm's law. The electric resistance of the cell varies during the run time, depending on temperature and chemistry.

 

On the other hand, I would like to hear about your manganese dioxide electrodes. How you made them?

 

 

 

 

So marx you suggest to keep a high surface area for the anode (MMO) and reduce the surface area of the cathode in order to reduce the amps right? My electrodes are quite big so i guess it draws too much current for the power supplies. The temp of about 8L cell was about 90C (I thermally insulate it). That is a very good idea, reducing the cathode you reduce the amps but the anode is still big for low surface area amps. Actually the cell was working but i add some more salt because it could dissolve more, to keep the anode safe, but i guess by adding more salt, more current could flow.

Edited November 26, 2019 by THEONE

[markx]

 

 

 

 

 

So marx you suggest to keep a high surface area for the anode (MMO) and reduce the surface area of the cathode in order to reduce the amps right? My electrodes are quite big so i guess it draws too much current for the power supplies. The temp of about 8L cell was about 90C (I thermally insulate it). That is a very good idea, reducing the cathode you reduce the amps but the anode is still big for low surface area amps. Actually the cell was working but i add some more salt because it could dissolve more, to keep the anode safe, but i guess by adding more salt, more current could flow.

 

You guess it draws too much current? Do you not have any measurement devices on the system? If not then start by adding a decent ampmeter and voltmeter, so you can actually assess what is going on. One can not tune the cell "by feeling". Panel meter type of devices are readily available from online sources and they do not cost much at all. Just for a few dollars you can have voltage and current monitoring....then proceed to changing the electrode configuration if needed.

In fact I would suggest to configure a dedicated and decently built power supply with voltage regulation capability and current/volt meters. Messing around with old computer power supplies or battery chargers and doing it blind is not going to yield a reasonable result. Most likely you shall kill either the power supply, the anode or boil the cell....or even worse, set something on fire if the connections or leads overheat due to overly high currents.

 

Compact modular switch mode power supplies are available for very reasonable prices e.g:

 

https://www.ebay.com/itm/10W-350W-AC110-220V-TO-DC-5V-Switch-Power-Supply-Driver-adapter-For-LED-Strip/252408375715?hash=item3ac4b629a3:m:mBAIZNa5OQdMwcKkuBgOP0A

 

Monitoring device e.g. :

 

https://www.ebay.com/itm/DC-100V-50A-100A-Voltmeter-Ammeter-LED-Dual-Digital-Volt-Amp-Meter-Gauge-New-US/272788962354?hash=item3f837d3c32:m:msf4T6_2S6RtO5uTmgw4uhQ

 

Combine them in a suitable package and you shall have a very nice dedicated power supply for electrochemical purposes. The cited power supply has output voltage regulation from about 4,2-5.5V as a standard option (most of them do). This is spot on for chlorate type electrosynthesis process. There is a small trimmer pot beside the output terminals and the green "ON" led. By turning the pot with a small screw driver one can vary the output voltage of the unit. I would suggest to replace that trim pot by a reasonable knob pot that can be placed on the panel of the power supply case and comfortably regulated by hand. Messing around with screw driver is not really a convenient option. Just make sure you get a knob pot of same resistance value and solder the leads correctly.

[THEONE]

Thanks for reply markx. Are those linked PSU good or some trash Chinese,? Also how many watts do you suggest to buy?

[TomasBrod]

The chineese can manufacture some high quality electronics. Power rating of the supply is releated to max current and voltage. I am sure, while looking up Ohm's law, you also came across a formula P = U *I. Eg 200W 5V supply is rated at max 40A.

[THEONE]

Ok thanks, i just order the 350w to be sure it won't get burned. I will also decrease the area of the cathode to 1/2. The MMO anode area inside the water would be 20x7 cm

Edited November 28, 2019 by THEONE

[pyrojig]

I have a question for you Arthur, and your earlier post you mentioned the crystalline size that drops out of solution via temperature and addition time. Could you elaborate a little more on that and your experience and getting super fine particulate. I have done this with other materials, but never put this into action for dropping (per) chlorate salt out of solution.(as with my bucket cell) . Usually I did the drop out at room temperature and a pretty fast edition. But I also wonder if the particle size being colder and slow editions would give fine particulate as well as with some agitation/ movement in the solution via stirring.

[Arthur]

Sorry, it's one of my recollections from reading lots of pages of info from the web, mostly patents. IIRC counter intuitively faster and warmer additions of KCl caused finer powder if it crystallises slowly the crystals can grow.

[THEONE]

Ok i found out that one pc power supplies are ok so i cut vertically the cathode in half to reduce the surface area and it works quite good so far.

[THEONE]

A quick question. was thinking to add some potassium dichromate to cell in order to improve efficiency. Any ide how much i have to add per Litre ?

[abc159201]

A quick question. was thinking to add some potassium dichromate to cell in order to improve efficiency. Any ide how much i have to add per Litre ?

 

Probably about 2-4 g per liter . But I highly recommend you NOT to messing around with hexavalent chromium. You would need to treat your cell much more carefully since hexavalent chromium is well-known carcinogen.

[markx]

I do concur with the last statement. It is better not to mess around with the chromate additive. At least not in the beginning, just try to get the process going and get a feel for it. If you absolutely feel the need to improve the yields after initial tries and all other efforts have failed to deliver, then start thinking about chromate additive use. Be sure to seal the cell properly if you use chromates, the spray that develops due to hydrogen bubbles is really persistant and creeps out to fill the room with carcinogenic mist if the cell is not well sealed and vented to the outside.

But there are other methods that work very well to improve the yield by preventing cathodic reduction of chlorates: magnesium and calcium salts can be added to electrolyte, caustics can be added (KOH NaOH e.g), high cathodic current densities also have the same effect of preventing product reduction (cathode surface area is reduced in relation to anode surface area). But most notably the yields tend to be improved by using pure titianium as the cathode material. It's what I've done even by using cathodes that amount to double the surface area of the anode and I've never felt the neccessity to use chromates for yield boosting. Although others sometimes tend to disagree, so just experiment with it and see from there.

[THEONE]

Ok then, you change my mind. I will stay like this for now and i will may decrease more the cathode area, even at 1/2 area it still performs really good so i possibly decrease it even further to 1/3 or something. My cathode is pure titanium stirp

 

Edit: A person on eBay selling MMO, claim not to use fluorine salts and that persulfate salts do the same. So maybe i could add persulfates instead of dichromates. Have you ever hear anything bout persulfates ? They can easily bought as PCP board etching.

Edited December 9, 2019 by THEONE

[markx]

Ok then, you change my mind. I will stay like this for now and i will may decrease more the cathode area, even at 1/2 area it still performs really good so i possibly decrease it even further to 1/3 or something. My cathode is pure titanium stirp

 

If you use Ti as cathode then it really does not make much of a difference to use high current density (reduced cathode surface area). At least my experience has shown that the cathodic area/ratio manipulations are of very limited effect on Ti. It is beneficial if steel or stainless steel are used as the cathode material.

[THEONE]

Ok markx, thanks for your reply

[abc159201]

If you really want to improve your yield, try pH control instead. I've been successfully improve my current efficiency from 50-ish to 70/80-ish. But first of all,you need to have some kind of measurement equip in order to monitor how much current you applied.

Edited December 10, 2019 by abc159201

[THEONE]

Current can be easily measured with an Ampmeter. I read somewhere that there is a connection between Amp/H and HCL for ph control

[WSM]

Current can be easily measured with an Ampmeter. I read somewhere that there is a connection between Amp/H and HCL for ph control

That's true. Swede determined the amount of HCl per Amp-hour. Read through his blogs and I think you'll find it.

If not, it may be found, quoted in my blogs.

 

Try Homegrown Oxidizers, part four.

 

WSM

Edited December 10, 2019 by WSM

[THEONE]

Ok my cell works really well. I am really amazed so far. It actually converts 1kg of KCL to KCLO3 in about 36Hrs. MMO anodes really woth their weight in gold. I produced about 4KG of kclo3 in less than a week. Really satisfied. I just now moved to Nacl in order to go for perchlorates. I have a 2x3 Inches plat electrode and i want to try it out. Big thanks to everyone

[Arthur]

Two points about platinum electrodes.

 

1/ Low ripple power supply

2/ Do not over drive the electrode it will shed the platinum and stop working (the platinum coating is only microns thin)