Homemade diaphragms for electrolysis. New developments

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]

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]

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"!

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 265 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.

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

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

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]

Cell for Testing diaphragm materials

Hello Hexabromobenzene,
thanks for your inspiring posts about finding the perfect DIY diaphragm.
In the past I have also searched for good materials for diaphragms and ion exchange membranes.
I made a small electrochemical cell for quick and easy testing of materials. [Photos 1 and 2]

Its made from two 50ml square wide-mouth PVC jars with 20mm diameter holes drilled in the 35mm lids.
I sealed electrodes and plugs with silicone tubing.
An aluminum U-rail serves as a holder and an M8 screw is used to press the bottles against each other.
A material to be tested as diaphragm is cut to a 30 mm diameter and clamped under the lid of a bottle. Sealing rings are used if necessary.

Three Tests are performed using this cell :

1. Porosity (aka Drip Test)
One bottle is filled with 35 ml of water and closed with the test material. The cell is placed upright, the lower bottle initially being empty. Measure how long it takes until the upper bottle is empty or how much water has dripped into the lower bottle after 24 hours.

2. Acid-Base exchange
One of the bottles is filled with 50 ml diluted sulphuric acid (H₂SO₄ 0.3 molar) and the other with water. 1 ml sodium hydroxide solution (NaOH 10%) is added to the water. Check ph every few minutes/hours whether the content of the water+alkali bottle has become acidic.

3. Current-Flow
Bottles are filled with 50 ml H₂SO₄ 0.3 molar each and fitted with a copper electrode. Current is measured in mA at voltages between 2 and 8 volts using an adjustable DC power source. Compared with the current flow without the diaphragm, the resistance of the diaphragm can be calculated in ohms.

I have now tested non-woven polypropylene. I hot-pressed the material at different temperatures and the results confirm yours. Below 160°C, the porosity is largely retained. At 180°, the fibers are fused into a dense film after 40 seconds. In between, you get more or less porous versions that might be suitable as a diaphragm.

Tested Materials
a) Brown wrapping paper
From an Amazon packing bag, tested in organic reduction, did not work

b) Baking paper
No-name, unbleached, silicone-coated on both sides, not to be glued, difficult to seal

c) Solid NaCl solution
Water with 10% table salt, heated, 2.5% gelatine dissolved, then left to solidify for 48 hours to a 2mm sheet.

d) Parchment paper
This material is mentioned in the literature, e.g. “Organic Electrochemistry” [Link]
It is a cellulose-based paper that's treated with sulphuric acid which makes it transparent, grease-proof and permanently wet-proof. When soaked, it tears easily, swells, wrinkles and is therefore difficult to seal.
Available as tracing paper for technical drawings, it is also used for the traditional packaging of butter or cheese.
Can be confused with other transparent materials that are also referred to as “parchment paper”. To test, genuine parchment paper:
- has a white crease
- is easy to tear (unlike synthetic paper-like wraps)
- can be wetted with water
- cannot be glued with paper glue (unlike glassine)
- can be written on with a felt-tip pen without it running off (unlike silicone-coated papers)
- is resistant to diluted acids and alkalis, even chlorine cleaner (2.47% hypochlorite) hardly attacks it

e) Non-Woven-165-20
PP non-woven cut out of a shopping bag, hot-pressed with low pressure at 165°C for 20 seconds between silicone baking foils.

f) Non-Woven-180-20
as e, but heated to 180°C

g) Non-Woven-180-40
as f, but for 40 seconds

Imho, the sintered non-woven PP performs well. It doesn't have the lowest electrical resistance, but other advantages:
The porosity can be variably controlled, it can be shaped as required, does not need any additional support structures and does not require any special storage conditions. Does not swell in electrolyte. It is also highly chemically stable. And, Oh yes, it's also cheap as spit ;-)
Many other materials were tested this way and found to be unsuitable, e.g. because they are impermeable to water and electricity [plaster (standard), concrete (standard), latex (condom)] because they decompose: [cellulose tissue, glassine, writing paper] or because they are hydrophobic [ tyvek, filter fleece].



Test-Cell

Test-Cell disassembled

Copper Electrode 20mm long, with silicone tube sealing

Hot pressed non-woven PP, F.l.t.r.: 20 sec @ 150, 20 sec @ 165°, 20 sec @ 180°, 40 sec @ 180°

Test results

Thank you for testing. As you can see, the problem with the non-woven diaphragm is leakage. I have not been able to solve this problem. Adding layers of fabric dramatically reduces conductivity to almost zero. This is probably due to the fact that polypropylene is hydrophobic. Using different types of fabric did not show any significant improvement in the result.
Wrapping the top layer of fabric helps a little. This probably fixes the fibers. Perhaps impregnation with an ion-exchange layer should help. But I have not yet found an affordable and stable material
Use the thickest fabric possible to wrap fewer layers. More porous fabric has better conductivity after baking. Maybe if you find a very thick fabric it will help you.

Here is a photo making diaphragm. Bottom of polypyropylene pipe is welded with a soldering iron, then wrapped in fabric, clamped with a steel sheet with wire and baked in the oven at 175 degrees.
Without a diaphragm about 5A, the current with a diaphragm is 1.9A



[Edited on 17-12-2024 by Hexabromobenzene]

The process of making diaphragm volume about 1300 ml from polypropylene containers
Welding was carried out using an electric soldering iron. Holes were melted as well. Further grinding and backing at 175C

I finally found a way to make microporous polypropylene. Polypropylene is fused with kerosene then kerosene evaporates for several days
To avoid a strong smell, you can use paraffin and extract it with a volatile solvent.
Polypropylene is poorly soak with water as polystyrene. But this can be fixed by processing by oxidizing agents. Permanganate, nitric acid, dichromate, chlorate
Porosity can be changed by the amount of polypropylen in composition 30-70%
Very good material. Wait for experiments
Already made samples of porous propylene/fiberglass with different porosity treated with nitric acid
Plans to fusion with ion exchange resin composite

Sample




[Edited on 27-7-2025 by Hexabromobenzene]

[Edited on 27-7-2025 by Hexabromobenzene]

Quote: Originally posted by Hexabromobenzene

The best samples from left to right.

1. Microporous composite polypropylene fiberglass (method with kerosene) treated with nitric acid
2. Pressed at 170 and treated with nitric acid vacuum cleaner filter (still wet)
3. Composite polypropylene (bag) polystyrene treated with sulfuric acid
4. Separator from car battery



[Edited on 30-7-2025 by Hexabromobenzene]

Quote: Originally posted by bearbot22

Hi Hexabromobenzene! I tested the use of a 3-layer vacuum cleaner bag as diaphragm using my test cell and conditions as described in my post from dec 14th 2024: Dripping: 12g in 24h Current: 40mA@2Volts ... 300mA@8Volts vs. 80mA ... 520mA without diaphragm Acid-Base: 80min Summary: Dripping is quite low, current is good, ion-exchange could be slower.

Testing a composite polypropylene/polypropylene diaphragm manufactured using the method described above. Voltage: 12 volts, sodium chloride: 40°C, 200 g/liter. Current 4.5 A
Liquid leakage is observed, but this is due to gaps between the blank and the fabric.



[Edited on 30-11-2025 by Hexabromobenzene]

Polypropylene polystyrene composite diaphragm treated with sulfuric acid. Current 1.5 amps(12V) with a solution of 200 grams of salt per liter. This is very low considering the large surface area. Other samples had current of 0.5 A.

Maybe complete sulfonation of polystyrene would help. Then it will become an ion exchange membrane. But then it become like gel. A cross-linked polymer is needed to manufacture such diaphragms. The project is on hold.



[Edited on 30-11-2025 by Hexabromobenzene]

Quick update. It was discovered that the first diaphragms made of PP/PS-SO4 show lower electrical resistance. It was manufactured using a different technology. Polystyrene solution was applied to a preform with pressed fabric and then treated with sulfuric acid. Apparently they had a thinner layer of polystyrene on them, which reduced the resistance.

It was also confirmed by combustion that after treatment with sulfuric acid, it was a different plastic. When heated, it smelled different from polystyrene and was charred, confirming its cross-linked structure.

A new test was also conducted on 30mm diameter samples. 35 grams of sodium chloride per liter at 12 volts.
Without diaphragm: 1.26 A
Vacuum cleaner bag: 1.2 A
Simple PP bag treated with a 20% polypropylene solution in kerosene: 1.17 A
Separator from a lithium-ion smartphone battery: 1.1 A

Industrial battery separators have higher resistance than fabric diaphragms. All samples were soaked in 50% ethanol before testing. A lithium-ion battery separator cannot be used without ethanol treatment. A similar problem was observed with a PP/PP composite diaphragm. A sample that had a current of 4.5 A in previous tests did not conduct current without prolonged soaking in water. Microporous diaphragms have poor wettability.


[Edited on 3-12-2025 by Hexabromobenzene]

I have made a another type of electrolyzer. 2 PET bottles were taken, holes were drilled. Then a pipe was taken and stuffed with polyster. The pipe was inserted in both the holes and the holes were sealed with epoxy putty to prevent leakage.

The system is resilient enough that enen blowing hard on one side of the container creates pressure. So it seems it will not leak.

I am currently making FeCl2 from this. I don't have a need for NaOH as I already have lots but I obviously don't waste reagents.

I will make a bigger scaled up version. I will post it as a new topic however.

Quote: Originally posted by Varungh

I have made a another type of electrolyzer. 2 PET bottles were taken, holes were drilled. Then a pipe was taken and stuffed with polyster. The pipe was inserted in both the holes and the holes were sealed with epoxy putty to prevent leakage. The system is resilient enough that enen blowing hard on one side of the container creates pressure. So it seems it will not leak. I am currently making FeCl2 from this. I don't have a need for NaOH as I already have lots but I obviously don't waste reagents. I will make a bigger scaled up version. I will post it as a new topic however.

Quote: Originally posted by Hexabromobenzene

I recently made a new diaphragm. It was made taking into account all my developments. Photo will be later in the topic A 2.5 liter black bucket was used as a blank for the diaphragm. Using a soldering iron, a lid was welded to it, a plumbing thread of an inch and a quarter was welded to it, and holes were also made using a soldering iron. Welding polypropylene with a soldering iron is similar to argon arc welding. Next, sanding and baking the fabric from the vacuum cleaner bag at 165-170. To prevent peeling, the fabric was also WELDED to the workpiece from the bottom and top using a soldering iron. Next, 10 grams of polypropylene were dissolved in 50 grams of mineral oil (cosmetic liquid paraffin) at 200-250 degrees. Next, the workpiece with the fabric was heated to 100 degrees and the plastic solution was cooled At 125 degrees, a solution of polyprolene in mineral oil was applied to the fabric using a brush. This must be done as quickly as possible since at 100 degrees the mixture crystallizes. Next, wash with 150 ml of kerosene and then the same amount of volatile white spirit After this, you need to dry the finished diaphragm for up to a week. This diaphragm has very little leakage but you will need to wet it with ethanol before use. Perhaps your surface layer of plastic will oxidize in the dichromate solution and in the future it will not require this treatment [Edited on 23-12-2025 by Hexabromobenzene]

Samples made using the same technology but earlier

Quote: Originally posted by Hexabromobenzene

Quote: Originally posted by Varungh   I have made a another type of electrolyzer. 2 PET bottles were taken, holes were drilled. Then a pipe was taken and stuffed with polyster. The pipe was inserted in both the holes and the holes were sealed with epoxy putty to prevent leakage. The system is resilient enough that enen blowing hard on one side of the container creates pressure. So it seems it will not leak. I am currently making FeCl2 from this. I don't have a need for NaOH as I already have lots but I obviously don't waste reagents. I will make a bigger scaled up version. I will post it as a new topic however. Your installation will likely have high resistance. What is your current and voltage? I use blanks with a large surface area and a flexible cathode surrounds the anode chamber Although in my case the main voltage drop occurs at the anode since its area is TENS of times smaller than that of the cathode in order to reduce the formation of hydroxides Material PP/PS-SO4 showed even lower alkali yield as in the case of simple polypropylene since chloride was only in the anode chamber 60 grams sodium hydroxide from about 300 grams salt Perhaps the ion exchange layer should have a larger capacity [Edited on 23-12-2025 by Hexabromobenzene]

Quote: Originally posted by Varungh

The resistance is rather high. At 12V I can see slight bubbling. At 30V heavy bubbling occurs and the cell gets warm. Unfortunately my multimeter seems to be cooked(apparently you should not measure 20kv with a cheap 5$ multimeter)