Hexabromobenzene
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Homemade diaphragms for electrolysis. New developments
Many electrochemical syntheses require a diaphragm. However, there is very little information on amateur simple, cheap and reliable diaphragms on the
Internet. I decided to fix this. Amateurs use clay pots as a diaphragm, but they are expensive, heavy and conduct electricity poorly
I read the instructions mysteriusbhoice and decided to develop my own diaphragms. The basic material for them is meltblown polypropylene fabric as
well as any CYLINDRICAL container made of polyethylene or polypropylene (bottles, glasses, cans, etc.) on which you will wind this fabric.
The basic manufacturing technique is as follows: Using an electric soldering iron, many holes are made in a circle in a plastic container, then the
container is sanded with sandpaper to remove irregularities. Next, you wind the polypropylene fabric in several layers. After that, you make ropes
from the same fabric and wrap this fabric on top with considerable force and fix it with a knot. This is very important. Without a strong fit, your
diaphragm will leak.
And so you got a raw diaphragm. In this state, it is not a diaphragm but rather a filter. There are several ways to make this a diaphragm.
The most universal way is to wrap with a separator from of lithium-ion batteries the container BEFORE wrapping with polypropylene fabric. I do not
recommend separators from automotive lead batteries. These separators have poor geometry and are difficult to seal hermetically.
You can use such a diaphragm for organic and inorganic electrosynthesis. Polypropylene is resistant to acids, alkalis and organic solvents.
The second way is to soak the polypropylene fabric with a polymer solution and remove the solvent with water. This is what did mysteriusbhoice. The
downside of this method is that even such a durable plastic as PVC can be destroyed by organic solvents. Other varnishes and polymers are much less
durable. I did it this way: The workpiece for the diaphragm with polypropylene fabric was impregnated with varnish from old paint with settled filler.
Afterwards, the workpiece was immersed in a bucket of warm water with washing powder while actively stirring. Then the wet workpiece was wrapped on
top with new ropes made of polypropylene fabric and dried
With these actions, you reduce the porosity of the diaphragm, but the polymer filler usually has lower chemical resistance than polypropylene.
The last way is inorganic fillers. You can soak the workpiece with sodium silicate and add any acid. This way you will get a diaphragm for working
with organic substances and an acidic medium. For an alkaline medium you can use sodium hydroxide with magnesium sulfate or calcium salts instead acid
for silicate percipation.
Inorganic fillers are resistant to any organic solvents and can be used for organic electrosynthesis. But they are sensitive to the pH of the
environment.
Diaphragm test. The diaphragm should conduct current in salt solutions and not leak. Pour water into the diaphragm and leave it for about 10 minutes.
It should not leak a significant amount of water. A small amount of liquid is acceptable. If too much water leaks, add ropes for fixation or soak it
with fillers again.
P.S. If you preparing sulfuric acid by electrolysis of gypsum, you can not modify the polypropylene fabric. The gypsum layer is a diaphragm in itself
[Edited on 13-9-2024 by Hexabromobenzene]
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Hexabromobenzene
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Ion exchange resins are not discussed in this article. I have not found a way to make them from readily available materials. Non-crosslinked resins
will not be chemically stable and will not be suitable for organic solvents. Sulfonated polystyrene would work well in theory for inorganic syntheses
such as chlor-alkali cells. The manufacturing process is the same as with polymer filler.
Sample of workpiece on pic
[Edited on 13-9-2024 by Hexabromobenzene]
 
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Hexabromobenzene
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A more improved method for making porous diaphragm.
You no longer need solvents or adhesives anymore. Everything is very simple and cheap
You only need a polypropylene container and a piece of fabric meltblown. You can also make a container from a polypropylene pipe from the sewer
weldind bottom with an electric soldering iron
Polypropylene blank with holes is wrapped with a piece of polypropylene fabric. Thin iron sheet is wrapped on top. Blank with fabric is fixed with a
metal wire and heats up in the oven at 170-180 degrees for several minutes
Due to the temperature and pressure of the iron sheet, the layer of polypropylene becomes much less porous and is more like ceramics as we need.
Diaphragm is very light, chemically persistent and cheap
The porous layer of plastic gets wet, but the water does not leak significantly
  
[Edited on 28-9-2024 by Hexabromobenzene]
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Pumukli
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Looks promising. Hats off, Hexabromobenzene!
I like it when I see people use simple everyday things and assemble them a way no one tried before! This polypropylene wrap thingy looks exactly like
that.  The heat-treatment is also an interesting approach. Simple, cheap and with
the critical timing and temperature it might provide a useful "toy" for us hobbysts.
Now I would like to see the characterization attempts of this gadget!
E.g: fill the cell with a known concentration of acid then determine the acidity (leakage) in the outer container at 1 hour increments. Draw a graph
leaked acid versus time.  Or give us a number: leaked acid in an hour (in
millimol/hour)
Or fill the cells (both compartments) with a known (one molar maybe?) salt solution (NaCl) and measure the electric resistance of this assembly with a
DVM. This ohmic resistance value would be an interesting clue regarding the possible performance of the cell.
Or use this cell in a practical electrosynthesis and show us what can be achieved with such a "toy"!
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Hexabromobenzene
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I made the second according to the same technology. The temperature was increased to 180 degrees
The leak of water through the new backed diaphragm was 1 ml in 10 minutes. First noticeably more. Probably due to incorrect compression of an iron
sheet during baking.
For conducting an electrochemical test, stainless spoons were used as electrodes, a strong solution of sodium chloride and 2 batteries(3 volts) AA as
a source of current. Without diaphragm, the current of 400 mA. With backed diaphragm number 2 current about 30 mA.
The current of the first diaphragm was 3 mA. Current of another diaphragm without baking, but with a separator from lithium batteries was 2 mA
The volume of the diaphragms is 90ml.
A diaphragm without baking and without a separator from a post http://www.sciencemadness.org/talk/viewthread.php?tid=160566... with a volume of 400 ml shows a current of 20 mA
Definitely a working method, but more experiments are required.
During baking, the fabric is welded to the polypropylene container and you no longer need to fix it
Polypropylene is a wonderful material. Having an electric soldering iron, oven and electric stove can be made of various reactors, rectification
columns, distillators. Operating temperature of polypropylene up to 120 degrees
[Edited on 28-9-2024 by Hexabromobenzene]
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BlueSwordM
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If you're interested, I found a website blog discussing of many electrochemical subjects, but the most interesting part to me was related to cation
exchange membranes:
https://chemisting.com/2022/11/27/a-diy-cation-exchange-memb...
There's a whole series on this subject.
I've managed to replicate the first membrane and it works decently.
I'm slowly moving up the chain to replicate this results, but they're very promising.
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Hexabromobenzene
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Yes, it is a PVA ion exchange membrane. It is not chemically stable
I was able to find some ion exchange resin for water purification in the form of small balls. I will bake layer it between polypropylene fabric. It
will be an analogue of ionic cement cement from mysteriusbhoice.
This ion exchange resin is very stable. It does not dissolve in dichloromethane and DMSO is resistant to alkalis and acids
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semiconductive
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I'm curious; I found porous cups on ebay and bought one to try and fix a tin-plating problem. Background of issue, mentioned here:
https://www.sciencemadness.org/whisper/viewthread.php?tid=15...
How badly do membranes tend to clog in your experience?
This is the one I bought, for example:
Attachment: membrane.webp (13kB)
This file has been downloaded 52 times
It Sstarted out as white and had 2Amps of current flowing at 36Volts applied to the tin anode inside the cup with titanium dioxide, boric acid and
water in the anode compartment; Citric acid, and a steel target to plate were outside the cup, making the cathode portion (the bucket).
This does work, quite well. I can electroplate copper coins with tin, and get a very shiny smooth coating that's practically a mirror.
But, over the last week of use the current carrying capacity has dropped from 2Amps down to a measly 150 milliamps.
Increasing the conductivity of the solution by adding acid has no effect.
At first there were large white blocks of ceramic visible with small grey/black lines on it; I tried grinding them off and thinning the ceramic cup
wall thickness; but slowly the ceramic has turned to what's shown in the picture over a week.
I have been happy with the fact that the membrane does not leak water except very slowly. Maybe a teaspoon in a week's use. So there's no
degradation of the citric acid by electrolysis. Basically, I can wipe of a sponge of it from the ceramic filter and it keeps right on plating --
organics stay OUTSIDE the cup, ions pass through the cup, and I can use high anode voltages to get ions into solution.
But, how common is it to loose 92% of your current flow in a situation like I'm describing?
Since you're experimenting:
I bought some fish-tank bio-ceramic filters that have much larger pores, and was considering dissolving a little bit of cellulose acetate paper that I
got on ebay to turn them into a membrane so I could compare how they performed to my ceramic cup. Another thought that occurred to me was to dissolve
a bit of clear silicone caulk in a large quantity of ethyl acetate, in order to increase the chemical resistance/life of the cellulose acetate.
The plastics you are using -- do they completely block organic molecules from passing through; or are you just trying to mostly contain chemicals in
separate chambers with it?
Can the plastics you've experimented with be dissolved, or are the pores mechanical in nature and unable to be coated? I don't think it would be too
hard to wrap a bio-filter in plastic and cook at 180 in an oven. But, I'm curious as to how stable you think your membrane would be during tin
plating?
(I know very little chemistry. I'm a BSEE -- so this is all learn by bumps, crashes, and braile. ) But I enjoy experimenting.
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BlueSwordM
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Quote: Originally posted by Hexabromobenzene  | Yes, it is a PVA ion exchange membrane. It is not chemically stable
I was able to find some ion exchange resin for water purification in the form of small balls. I will bake layer it between polypropylene fabric. It
will be an analogue of ionic cement cement from mysteriusbhoice.
This ion exchange resin is very stable. It does not dissolve in dichloromethane and DMSO is resistant to alkalis and acids |
That is somewhat true, but further protocols designed membranes that are much tougher, as it seems the main bottleneck is in membrane chemical
resistance rather than PVA.
This doesn't fix the issue of low pH performance, so it limits PVA CEMs to mainly neutral/high pH environments.
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Hexabromobenzene
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Polypropylene is resistant to solvents and you can't dissolve it in anything. Ion exchange resin is also resistant to solvents, even such as
dichloromethane, because it is a cross-linked polymer
Water flows through the diaphragm at a rate of 10-20 ml per hour. You can reduce this by simply adding another layer of polypropylene, but the
resistance will increase. Adding ion exchange resin will probably reduce the porosity and reduce the resistance. I hope.
The task of the diaphragm is organic and inorganic electrosynthesis. In my case, I just need to limit diffusion as much as possible without
significantly reducing the current. I do not like diaphragm electrolysis. It requires more voltage, but the process occurs with less current. But
sometimes there is no other choice.
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Hexabromobenzene
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Diffusion test. A solution of melanoidin was poured into the container with the diaphragm. In the second container, pure water. In the photo, the
result of diffusion after 14 hours as well as a solution after direct mixing of the contents of 2 containers
The fluid level in 1 and in the 2nd vessel was the same.
The diaphragm is made by baking method
  
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Pumukli
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Looks promising.
Now, that you probably have something that would worth playing with, do you plan to use this membrane-setup for some sort of electro-synthesis?
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Hexabromobenzene
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Preliminary test showed a current up to 0.7a with 12 volts in a solution of salt. Other diaphragms do not conduct electricity. Probably a plastic
layer is too thick
Apparently, the diaphragm leaks at the place of contact of porous plastic with the workpiece.
The addition of ion exchange resin did not improve conductivity but increased leaks.
The size of the pores in the meltblown fabric several micrometers but probably was reduced significantly when the plastic is flattened during backing
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semiconductive
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I've tried some experiments;
1st attempt was to use biofilter ceramic filters with one level tablespoon of talc clay + 1 sheet of Cellulose DI (not tri) acetate paper. 8" x 12"
roughly.
I attempted to dissolve acetate paper in ethyl-acetate (MEK substitute), but it's extremely slow dissolving; so I added a small amount of acetone. I
added to this the talc, clay.
Then I simply poured it through the biofilter with the bottom plugged using silicone.
The next day I added about 1 cc of silicone to a cup of ethyl-acetate and made a re-enforcing rinse to block up large open pores.
I Poured this through the bio-filter several times allowing dry time in-between each pour. Each time I applied more sealant, the flow rate slowed
until the filter was able to hold liquid for 15 minutes.
I Allowed it to cure for two days.
As a test electrode I used a graphite bar that fit snugly inside the biofilter, 1 part boric acid, 2 parts titanium dioxide.
Even though this is a thick walled biofilter, it still conducted 0.8A at 36V and 0.25A at 12V.
I allowed it to run for about a week, but somewhere in the middle of the week the ceramic cracked in half spoiling the solution an wrecking the
filter.
Second attempt; I want to hardware store to see if I could get PP fabric, like you have. They didn't sell it, but they did sell paint strainer cloth.
Upon checking acetone resistance, it was good. After looking MSDS online, apparently this kind of netting is typically polyester.
I then put it in a sewing clamp to make it flat and tight. I mixed acetone + 2 sheets acetate, 1 teaspoon of TiO2. Made it fairly thin.
I then used a fan paintbrush 3cm wide, to paint liquid onto stretched netting. I coated it multiple times until I could see no more open netting
holes, and then once more coat to be safe.
I then wrapped a tin electrode bar with a ziplock bag, and that in the acetate cloth I had made. Putting a little silicone along the edges, I did my
best to seal the seams and wrapped the bar three times. There was excess netting sticking out after removing from the clamp, and it was convenient
for making a bottom seal with silicone and a top cylinder wall.
I then put zip-tie clamps around it to hold it fixed while it cured for several days. I think this is too much work; but it's very nice looking.
After removing the clamps, and working the tin bar loose, I took the manufactured cup and dipped it in water.
Unfortunately it has a pin hole somewhere as about 1CC of water fills it per minute when submerged to the next in a sink.
There are three layers of paper spiral wound, sealed at the top and bottom with silicone and along the final edge. Depending on where the leak is,
this might still be use-able. In theory, water will flow along the spiral -- but electricity will not follow the spiral, and instead will attempt to
take the shortest path which should be through the netting and cellulose acetate.
I'm debating whether to paint an extra coating of acetate on the outside to fully seal it, before trying it.
Third attempt:
I got polypropylene felt. This is from e-bay™, and meant to be used in Cars for covering speakers.
I used two sheets acetate, 1 teaspoon TiO2.
I cut a piece of cloth roughtly 6 inches high and 8 inches long. I saturated it with the acetate solution and TiO2. Then I rolled it into a tube
about 3/4 inch diameter with three to four full turns. Initially the felt wall looked to be about 3/16 inch thick. I then wrapped thread around it
to hold the tube closed and made a felt plug for the bottom.
It was not wrapped on a form. This was a very messy process, and I got quite a bit of acetate dried on my hands like paint.
I added one more acetate sheet to the remaining titanium in my mixing jar, and just enough acetone to dissolve it. Afterward I mixed in methanol, to
thin it. Then I used this as a rinse, pouring it into the tube and then dumping the solution back into the container I mixed it in. Giving a few
seconds to dry, I then repeated the process until the tube could hold the solution without dripping.
I then let it dry overnight. The longer it dried, the stiffer it became.
In the morning, I put it in a convection microwave oven and warmed it to 150 farenheight for a half hour. Then I set the temperature to 275 for 15
minutes.
I'm hoping this is hot enough to melt the polypropylene barely and cuase it to fill in any drying cracks in the acetate.
This produced an excellent stiff tube; roughly 1/8 inch thick. It's stiff enough that it doesn't need to have a form inside it once it's cooked.
Attempting to blow into it shows that it is nearly air-tight as well.
I think I may buy a glass rod or use hot water PVC pipe to make a form the next time I try this. It will make a straighter tube and allow me to
compress/thin the walls more.
After manufacture:
I filled it with 1 part H2BO3 to 2 parts TiO2 (roughly by volume.) And then inserted a graphite rod that is coated lightly with cellulose acetate --
but the bottom of it is scraped off. This is to make the rod preferably break down fastest at the bottom while reducing TiO2 to titanium ions, and
cause the electrode to be used up from the tip first for longest life.
The finished tube holds water, and drips about 2 drops per minute of water.
Unfortunately, the resistance is high. I only get 5mA of current at 12V.
But, with time, I hope some of the TiO2 in the acetate will be broken down by electricity passing, and the conductivity will rise.
But it is working, and I will run it at 36Volts for a week and see if it survives. Right now I'm plating tin with it. 30 mA from a tin electrode, and 10 mA from the titanium electrode, into a citric acid bath.
[Edited on 3-12-2024 by semiconductive]
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