Making Proton Exchange Membranes

Added: 2026-05-12

[00:00:00]Welcome back. In this video, I'm going to make some proton exchange membranes.

[00:00:05]Now, proton exchange membranes are really useful in electrochemistry.

[00:00:09]Basically, everywhere you want your reaction products to be separated, but you still need a path for protons to flow from one side of the reaction to the other.

[00:00:21]And if you research about proton exchange membranes, you learn really quickly that the top-tier material for this is called Nafion.

[00:00:30]This stuff is patented by DuPont, and they want to squeeze out every bit of value from this product, so it's ridiculously expensive. But, the manufacturing costs probably add to this as well.

[00:00:43]So, could we maybe make this stuff at home? Well, one ingredient for this is, and I have to read it from a paper, perfluoro-3,6-dioxa-4-methyl-7-octene-1-sulfonic acid. Not sure if I said that right, but yeah, that's basically PFAS, actually.

[00:01:03]And I think I can't even get this anywhere, so that's already a bad start.

[00:01:09]And what's the other ingredient? Well, it's tetrafluoroethylene.

[00:01:13]Tetrafluoroethylene is really nasty stuff. First of all, it can explosively polymerize or form explosive oxides. And on top of that, it actually is a gas, and it's a carcinogen. So, there's no way I can safely store it or handle it.

[00:01:32]So, Nafion is out of the game, but there are alternatives. If we look at Nafion, what makes it proton conducting are these sulfonic acid groups. And while all of the other fluorine-to-carbon bonds make it very durable, if we give up this property, we can find other more friendly polymers to stick the sulfonic acid group onto.

[00:01:53]A sulfonation reaction is easily done on an aromatic ring, and a very common polymer with an aromatic ring is polystyrene.

[00:02:02]However, dissolving a bunch of polystyrene and then sulfonated, and then I have to cast it into a membrane, that seems a bit hard. However, there is a polymer that this can be done with, and I will get to this later in the video.

[00:02:17]A much simpler and easier way to do it is to just take an existing sheet of polystyrene and just sulfonate this.

[00:02:23]However, the problem with this one is that the sulfonation might not happen all the way through the material, and obviously if your material is very thick, this problem gets worse.

[00:02:35]The polystyrene sheets that I got are 0.2 mm thick. Maybe you can find something thinner, but that's the best I got.

[00:02:44]And I cut out a little piece from one of them, and sulfonating this is actually very easy, and you just have to put it into some sulfuric acid, and that's it.

[00:03:05]I'm holding the polystyrene sheet down with a glass rod to prevent it from floating.

[00:03:11]Also, because sulfuric acid is hygroscopic and will pull water out of the air and will dilute itself, I have everything in this Ziploc bag, and this way the concentration should stay the same.

[00:03:28]I'm going to leave the polystyrene sheet in there for around 3 days. I'm going to set a timer. I still have to figure out how long the best duration would be. You could also probably speed this up by raising the temperature, but I'm just going to leave it at room temperature for 3 days, and then we will see how well this works, and then maybe it in for a bit longer and see if there's any improvement.

[00:03:57]All right, it has been 3 days. This is actually the exact time, 3 days and a couple hours, because it's only science if you write it down.

[00:04:07]But, the polystyrene sheet got really dark, and I'm going to wash it a little bit with distilled water.

[00:04:15]And for storage, I'm going to put it in 15% sulfuric acid, because I think you should not let them dry out, but I think this should be fine for storage.

[00:04:40]Okay, next I want to try to make a membrane out of a different material, and I talked about the problem before that the sulfonation might not happen all the way through, but there is a polymer that does dissolve fully in concentrated sulfuric acid, and therefore I can sulfonate it.

[00:04:56]And this is PEEK, polyether ether ketone, and the membranes out of the sulfonated material are pretty expensive, but the non-sulfonated material is pretty cheap.

[00:05:09]I picked this rod up for a couple bucks online, and I'm going to try to make a sulfonated membrane out of this.

[00:05:17]And I'm surprised nobody on YouTube has tried this already, because it seems possible. So, I'm going to try it.

[00:05:24]While this polymer does dissolve in sulfuric acid, I'm going to take a knife, scrape off some stuff to have some finer bits that actually dissolve reasonably fast.

[00:05:44]Now that the polymer is grinded up, I'm ready for the and for that I have here 12 ml of concentrated sulfuric acid. And this is for around 0.6 g of the polymer. So, the ratio is 1 g of polymer to 20 ml of sulfuric acid.

[00:06:04]And I'm following a research paper and it says to dissolve the polymer first in the sulfuric acid at 25° for 16 hours. And this seems a little bit long to me. I'm not sure if I should do that.

[00:06:20]I tried this before without the step and it it worked, but yeah.

[00:06:27]After that, you have to heat this up to 50° and let it run for the actual sulfonation for 5 hours.

[00:06:37]So, I think I'm just going to try to add the polymer at room temperature, see how well it dissolves, and yeah, see how how I'm going to do that.

[00:06:49]And then I will run the sulfonation.

[00:07:13]All right, this actually dissolved really well in a couple minutes. And I think in the research paper they used pellets, so much bigger.

[00:07:21]And I'm going to put a water bath underneath now and start heating this to 50° C.

[00:07:42]It has now been 5 hours and to get the polymer back out of this reaction mix, I'm going to pour it into some ice cold distilled water.

[00:08:34]I washed the polymer multiple times with distilled water and the pH should be above six, so neutral.

[00:08:46]I think that's close enough. Maybe I'll do another washing.

[00:08:49]And after that, I'm going to dry the polymer and then it's ready to make some membranes out of this.

[00:09:06]All right, and here is my dried sulfonated PEEK. And to make a membrane out of this, I need to dissolve this into a solvent. And usually the solvents are very specialized for laboratory use, but there is one that actually is very accessible and that's DMSO. And the reason why this is very accessible is because it's used in alternative medicine. So, that's a bit unfortunate, but you can get this stuff very easily online.

[00:09:38]And I'm going to make a 10% by weight solution. So, for example, 1 g of the sulfonated PEEK and 9 ml of DMSO.

[00:09:50]And I'm going to just put it into a vial, dissolve it, and then I'm going to pour this out into a thin sheet, let the solvent evaporate, and then I should have a membrane.

[00:10:20]To make the membrane, I put this piece of borosilicate glass on this hot plate, and I leveled it out so it's as level as possible, and I'm going to pour the solution on there. I'm going to heat this up to 80°, and let the solvent evaporate.

[00:10:36]And later, I'm also going to heat it up to 120°, and apparently that does some cross-linking and makes the membrane stronger.

[00:11:04]And here's the finished membrane. Now, I had to spread it out a little bit, and I just grabbed the nearest thing that I had, which was some paper. And yeah, that was a little bit of a stupid idea because you can see this this paper kind of dissolved in there.

[00:11:22]The middle seems still fine.

[00:11:25]And yeah, that was kind of stupid. But, to get this off the plate, what I'm going to do is I'm going to put some distilled water on there and then this should come off the plate really easily.

[00:11:42]I thought I have to scrape it off, but it seems to just float there. It's like already loose just from the water.

[00:11:50]Uh so, yeah, that's really great. Just peels off really easily.

[00:11:56]Very good.

[00:11:58]I want to keep following the research paper and there they put the membrane in a 1 mol per liter hydrochloric acid solution for 1 and 1/2 hours. So, I'm going to do that next.

[00:12:19]To test the membranes, I put together this electrolysis cell and I'm just going to fill this with 15% sulfuric acid and I will basically have a chamber with the plates and in between the plates is going to be the membrane and I'm going to start with just the polystyrene unsulfonated and make sure that no current is flowing through there.

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[00:13:48]All right, this looks a little bit messy, but basically I'll put together the test cell, and that's just two chambers, two electrodes, and that's separated by the membrane.

[00:13:59]And I have a voltage regulator thing wired up, and one multimeter is going to show some current, and this is going to show voltage. So, I can apply a voltage and see how much current I can get to flow through there at any given voltage.

[00:14:20]I'm going to start with 2.1 volts, something like that.

[00:14:25]But, there should be no current flowing.

[00:14:27]Yeah, indeed.

[00:14:29]I'll turn it up further.

[00:14:32]10 volts.

[00:14:34]Yeah, still no current flowing because that's to be expected. The polystyrene is an insulator both for protons or electrons, so nothing is going to happen. So, let's see what the sulfonated polystyrene does, and if that's [snorts] actually conducting.

[00:15:07]All right, that's the polystyrene sulfonate sheet, and I'm going to start again at 2 volts.

[00:15:17]Okay, 16 That's settling 16 Now it's jumping down a little bit, but like 16 milliamps.

[00:15:30]16.3 Yeah, something like that. 16.3 milliamps at 2 volts. I think that's a good comparison. I don't have to turn the voltage up higher.

[00:15:45]So, let's test the sulfonated PEEK next and see how that performs.

[00:15:54]To make this fit the test cell, I have to pull it out of the HCL solution and I'm going to cut it up, use the this one as a template.

[00:16:12]All right.

[00:16:14]That is very thin.

[00:16:17]All right, let's put together the cell and test it.

[00:16:29]All right, and this is the sulfonated PEEK membrane.

[00:16:33]Again, at the same voltage and we are getting Whoa!

[00:16:38]80 80 milliamps.

[00:16:43]That's way more. That's way better.

[00:16:48]Oh, yeah, it's also bubbling a lot and overflowing because the cell is not meant to produce hydrogen.

[00:16:58]But, this works really well.

[00:17:02]To store these membranes, you do have to keep them in deionized water distilled water. You should not let them dry out as far as I know.

[00:17:11]And these only really work in acidic conditions. So, you could not build an alkaline hydrogen generator or something as far as I know as well.

[00:17:22]But, yeah, if you have any suggestions what to do in terms of electrochemistry, then leave that in the comments. But, my goal is to build an actual fuel cell that can generate power from hydrogen and oxygen. And if I get that to work, I'm obviously going to make a video. So, if you don't want to miss that, then subscribe and until next time.