goldberg
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Low resistance electrolytic cell divider
I hope that this is right place in forum and i'm not repeating topic.
I'm thinking about material for electrolytic cell divider that will have low resistance to be able to conduct preparative electrolysis in resonable
time.
U-shaped tube filled with KCl solution gelled by agar turned out to to have too high resitance. Not jelled solution tends to leak from tube if i have
different levels of solution in both cells and still have too high resistance.
Unfortunately i do not have unglazed porcelain at hand.
How about wrapping one of electrodes in a few layers of filter paper soaked in electrolyte?
Or using polymer foam that is commonly used in kitchen to clean tableware?
Say i'm going to carry out electroreduction and my substrate will be destroyed at anode.
If anode will be wrapped in foam or paper soaked in electrolyte it should be harder for my substrate to diffuse to anode where ions of supporting
electrolyte still be able to move between both electrodes.
Unfortunately i do not have access to nafion membranes.
Any ideas will be welcome.
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draculic acid69
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Can a pair of beakers with a salt bridge or a copper wire between them not work?
What exactly are you electrolyzing?
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goldberg
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Typical salt bridge has too high resistance and i have problem with solution leaking out of it,
Right now i would like to electrolytically reduce ketones to alcohols but i'm interested in general case to use this setup for another reactions.
I can not use arbitrally high voltage becouse it can cause other reactions in general case.
I would be able to pass current of a few amperes (say 1A to 5A) to complete reaction in reasonable time.
So the only way is to lower resistance of whole system and from my observation elecrolytic key has biggest resistance of whole system.
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Twospoons
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So you need to increase cross-section area and reduce thickness. Try making a KCl gel plate, on a suitable support mesh (fiber glass? polymer?).
Helicopter: "helico" -> spiral, "pter" -> with wings
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goldberg
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What concentration of KCl should i use? And will gelled KCl withstand high current?
How about immersing tube ended with thin plate of gelled KCl filled with anolyte into beaker with cathode and it's solution since interesting reaction
will occur only at cathode?
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Mateo_swe
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You say you dont have access to unglazed porcelain, are you sure?
Maybe there is some hobby pottery enthusiasts in your area that you can ask to make a unglazed cup?
Its a quite popular hobby.
But you would want the top 2-3cm to be glazed if possible.
One can try find unglazed clay/porcelain flowerpots but unfortunatley most have a hole in the bottom.
Or maybe its possible to remove the glazing on the lower parts somehow.
The glass frits in filter funnels and similar in other lab glassware can also be used as cell membranes, maybe you have any damaged filterfunnels that
can be used.
Or you can ask for such a frit to be made to your specification from any local labglass manufaturer or even from the chinese based companys on ebay.
Im sure they could help you and i doubt it would be very expensive, but it would take some time for it to be made and delivered.
Or just order some anion or cation membrane online from Fumatech, all of them are not very expensive.
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dawt
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I vaguely remember some old German papers describe the use of cups made from newspaper impregnated with gelatin and electrolyte as cell dividers.
Dunno how they hold up to heat, though.
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RustyShackleford
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PVA+citrate membranes are quite low resistance and handle a suprising range of conditions.
https://www.youtube.com/watch?v=UdQ9OThC7ZI
PVC memranes are also quite easy to make and handle more extreme conditions.
https://www.youtube.com/watch?v=foQHygE2Mkw
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yobbo II
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You can obtain a glazed tile and rub off the glaze using an 'angel grinder' or some sort of abrasive wheel.
In my limited experiency the tile, even when grinded to a very thin width, gives a large voltage drop.
Yob
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goldberg
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Mateo_swe: Unfortunately typical flower pots are too big for scale of my electrolysis.
Thanks for idea with glass frit. I have spare funnel with sintered glass frit i will give it a try.
dawt: interesting idea, maybe agar and filter paper would be better.
RustyShackleford: PVC sounds good and this process looks very simple.
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monolithic
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https://www.aliexpress.com/item/1005002201964132.html
Still very expensive, even from China. You'll need a membrane of some sort, which is another challenge, as you said.
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goldberg
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I have tried putting small piece of paper towel rolled in a ball into end of disposable tip for 1000ul automatic pipette (last few milimeters of this
tips were cutted to get bigger diameter). Then i have filled this tip placed vertically in beaker with electrolyte and inserted strip of steel as
anode. Unfrotunately resistance was very. At 15V i had 100mA of current(electrolyte was 10% NaOH, beaker had volume of 50ml).
Bigger diameter of pipe containing anolyte should help to lower resistance.
Wrapping anode in a few layers of filter paper do not seem to be very effective in preventing substrate to reach anode.
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WGTR
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I have been following this thread for a bit. Is there a reference for what you are trying to do, that you can post?
Generally, the voltage at the electrode interface is what drives one reaction or another. You need a reference electrode placed very near the
electrode to be able to measure this directly. The voltage drop across a salt bridge isn’t important to the reaction.
If there’s too much power being dissipated in the salt bridge, however, it can heat up and even boil.
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goldberg
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I plan to improve my setup for electrolysis to add reference electrode.
I made electrolytic key from plastic tube(3ml Syringe with cutted end) with foam(one used to wash dishes) at end secured with filter paper soaked in
electrolyte. Resistance was still quite high and electrolyte was leaking from it but at least my substrate did not seem to reach anode.
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