Hello Leonhardt,

Are you going to prepare the membranes or you want to modify the functional groups in the polymers which you have selected? If you are trying the latter, then I would suggest you to use poly(ether ether ketone) or poly(sulfide sulfone) membranes and you can tune the functional groups accordingly. I suggest you to read this review article.

Article Additives in proton exchange membranes for low- and high-tem...

Anu Karthi Swaghatha A I I wanted to prepare the membranes myself, first hand the membranes won need to be selective, a semipermeable membrane will do the job as well since I can add some functional groups myself, the only real problem is that this membrane needs to be stiff and have almost no swelling in water.

André Leonhardt If you need to prepare membranes with high mechanical strength i.e. stiffness, the polymeric backbone should be hydrophobic enough to prevent the swelling. You can adjust the number of molecular units in the polymer which you are synthesizing as required after which you can add the desired ionic end groups.

Dear André,

if the membrane is not the focus of your research I would suggest to keep it as simple as possible and use a commercially available material.

You write that you work on novel alkaline fuel cells, so Zirfon might be a good solution, if using a diaphragm is ok for your application. As you mention that the membrane should be mechanically stable, KOH-doped PBI might be an option. Maybe you can buy PBI-membranes and dope them with little effort. See e.g. Article Understanding ternary poly(potassium benzimidazolide)-based ...

Article Highly KOH Doped para-Polybenzimidazole Anion Exchange Membr...

Dear André,

If you are looking for commercial material, as Felix suggested, have a look at the following sources:

https://www.fuelcellstore.com/fuel-cell-components/membranes

or alternatively contact FumaTech (German company) directly:

https://www.fumatech.com/Startseite/index.html

Hi André,

Yes, you are right. As you have mentioned, alkali doped chemically crossinked PVA membranes are not stable and having low tensile strength.

I would suggest you to add some additives such as SiO2, TiO2 to PVA based membranes, so it's mechanical strength could be improved.

Alternative options may be PBI membranes. PBI membranes are mechanically stable and it can be used for high temperature operations.

Other options might be to look forward commercially available membranes as Armin Michel suggested.

The addition of ceramic filler into polymer matrix is allow to reduce the glass transition temperature (Tg) and the crystallinity of the polymer, and also allow the increase the amorphous phases of polymer matrix, then increase the ionic conductivity.

Ref: Journal of Membrane Science 288 (2007) 51–60.

1. Nanocrystalline TiO2 fillers (anatase, 10–30 nm, 330 m2 g−1, CBT, Taiwan)

Ref: Journal of Power Sources 184 (2008) 44–51.

2. 3-(trimethyl ammonium) propyl functionalized silica (Q-SiO2) (Aldrich),

The addition of hydrophilic SiO2 fillers into the polymer matrix in the form of nanoparticles reduces the crystallinity of the PVA polymer, therefore increasing the amorphous phases of the PVA polymer matrix, resulting in an increase of its ionic conductivity.

Ref:Journal of Power Sources 199 (2012) 37– 45.

To the best of my knowledge there are three companies with materials potentially suitable to alkaline AEMFCs.

1. FuMa-Tech was mentioned above - FAA-3 was an early standard in AEM fuel cells and I used it extensively. To the best of my knowledge it is QA-based but not styrenic backbone chemistry, and from first-hand experience the membranes are quite tough. I can't find the FC-grade in the store, but it's in the spec below; ionomer solution should be available in NMP even if I can't find it listed on the site either.

https://www.fumatech.com/EN/Membranes/Water+treatment/Products+fumasep/

2. Dioxide Materials has materials available but I have much less first-hand experience and don't know the suitablility in fuel cell applications. They appear to have styrenic backbone chemistry and need to be treated right but they may be suitable to your needs. There is ionomer but the disclaimer is that it is designed for CO2 electrolysis so again I'm not sure about the compatibility.

https://dioxidematerials.com/product-category/anion-exchange-membranes/

3. With full disclosure I'm a co-founder and part of the company, Ionomr has alkaline-stable AEMs with a set designed for AEMFCs and ionomer compatible with low-boiling solvents for consistent electrodes.

https://ionomr.com/solutions/aemion/

4. While not a company, Prof. John Varcoe is an amazing person and his materials are well-known enough to comprise a research standard.

There are a handful of other companies mainly in the US at early stages but to the best of my knowledge this is it with regards to commercial availability for materials suitable for AEM fuel cells.