DE10338404A1 - Composite membrane for fuel cells contains a water-soluble polymer with sulfonic, phosphonic and/or carboxylic groups and zirconium phosphate - Google Patents

Abstract

Composite membrane contains a water-soluble polymer with sulfonic, phosphonic and/or carboxylic groups and zirconium phosphate. The membrane has a source of less than 120 % in a temperature region of 0-120[deg] C in moist gas stream. An independent claim is also included for a process for producing acid-base blends comprising dissolving a polymer containing a sulfonic group and a basic group in water, and forming into a thin film with subsequent evaporation of water followed by post-treatment in a diluted mineral acid.

Description

Acid-base blend membranes are state of the art. They are used, inter alia, in membrane fuel cells. They consist of a polymeric acid and at least one polymeric base. Both components are prepared by known methods in aprotic solvents dissolved. The solvent is evaporated and the membranes are optionally one more After treatment.

disadvantage This method is the use of mostly high boiling aprotic Solvents. With these solvents the corresponding costs are connected. The solvents are mostly harmful to health and have to be processed accordingly. On the other hand, there is no way The necessities Polymers in solution bring to.

It was now the task to find a method that allows the aprotic solvents in as possible to use a small scale or if it is completely to renounce them.

Description:

polymers sulfonic acids are water soluble an ion exchange capacity (IEC) of about 1.8 meq / g (milli equivalent per gram). The ion exchange capacity can be easily achieved by titration methods determine. Sulfonated PEEK (polyetheretherketone) is from a IEC of about 1.8 in hot Water soluble. The same applies to Polysulfones (PSU, PES) and many more sulfonated or phosphonic acid groups provided polymers, in particular for thermoplastics.

The invention will now be described by way of example also for PEEK, PSU and PES. However, the method is generally applicable and not limited to any particular polymer. PEEK can be easily sulfonated with concentrated sulfuric acid up to an IEC of 2.7. From Kenes et.al. Methods have been described for preparing polymers having basic groups and sulfonic acid groups on the same polymer backbone. So a PEEK carrying sulfonic acid groups and amino groups on the same backbone. This polymer was dissolved in aprotic solvents and further processed into a membrane. It has now surprisingly been found, if there are sulfonic acid groups with an IEC of more than 2.0 on the polymer and at the same time amino groups corresponding to an IEC of 0.2 to 0.6 are present on the same polymer backbone, then the polymer is water-soluble, under the requirement that the sulfonic acid groups are cation-exchanged. The preferred cations are monovalent and divalent cations, especially Na ⁺ , K ⁺ , Li ⁺ , Ca ²⁺ , Mg ²⁺ , and ZrO ²⁺ ( 1 ).

This allows a much simplified representation of the membranes. Sulfonated PEEK or PSU with an IEC of 2.2 at sulfonic acid groups and an IEC of 0.5 at amino groups (S-PEEK-NH ₂ ) is converted to the salt form by means of ion exchange. According to the presentation method of Kerres et.al. the sulfonic acid is already present as the sodium salt. This polymer, having the two functional groups, is dissolved in water, optionally with heating. Thereafter, the aqueous solution is processed into a film by removing the water. For example, this is done by pouring the solution in a Petri dish and evaporating the solvent water in a drying oven. By aftertreatment of the film in dilute mineral acid, the sulfonic acid groups are released, which in turn partially undergo an acid-base interaction with the basic component. Due to the forming hydrogen bonds, the film is now water insoluble. This gives a membrane with very good proton conductivities.

This process can be further improved by the use of ZrO ²⁺ exchanged sulfonic acids. Zirconia chloride-exchanged polymeric sulfonic acids (IEC> 2.0) containing another basic component on the same polymer backbone are dissolved in water. Thereafter, formed on a surface into a film and the water is removed by evaporation. The film, potentially still water-soluble, is post-treated with phosphoric acid (5-80% by weight). After-treatment, the acid groups are formed and subsequently the hydrogen bonds with the basic component. In addition zirconium phosphate and the corresponding hydrogen phosphates are precipitated in the membrane. This gives a composite membrane consisting of a polymeric acid and base (same backbone) and an inorganic phase of zirconium phosphate and zirconium hydrogen phosphates. By a mutual aftertreatment of the membrane with zirconium oxychloride dissolved in water and / or an aprotic solvent and phosphoric acid more zirconium phosphate is incorporated into the membrane. The swelling of the membrane decreases very much even though it has a high IEC at sulfonic acid groups. Membranes have been obtained by the mutual aftertreatment with a specific resistance of less than 20 ohms × cm. This is on the same scale as Nafion ^™ by DuPont.

It has now surprisingly found a second improvement of the invention. Sulfonated PEEK or PSU with an IEC of 1.85 is dissolved in water in addition to this solution is added with an aqueous solution of 5-30 wt.% Zirkonoxychlorid (ZrOCl ₂ ) based on the dry mass of the sulfonated polymer. The solution is doctored to a thin film and the solvent is evaporated. Not only water but also HCl is removed. The resulting film is post-treated in aqueous phosphoric acid. The membrane is then post-treated one or more times in alternating manner in zirconium oxychloride solution and aqueous phosphoric acid. After 2-5 post-treatment steps, the membrane is placed in dist. Water is freed from excess phosphoric acid. The membrane has a greatly reduced swelling compared to the comparison membrane, which consists only of the sulfonated polymer. The membrane has very good properties in a membrane fuel cell, which is operated with hydrogen. It is also suitable for temperatures over 80 ° C.

following another way of displaying the composite membrane. sulfonated preferably thermoplastic, water-soluble polymer is dissolved in water disbanded and to a thin one Film is ripped off, the water is evaporated off and you get a film preferred is a thickness of 10-100 microns. After that This film is in aqueous Zirkonoxychloridlösung for 1 to 24 hours. In the next step The film is diluted in dilute Post-treated phosphoric acid for about. 1 to 24 hours. This process is repeated 2 to 5 times. The Swelling of the membrane decreases with each post-treatment step.

alternative to the previous illustration is sulfonated water-soluble Polymer with zirconyl cations, used as cation of sulfonic acid. The polymer is dissolved in water and processed again into a membrane. This will be an aftertreatment step saved.

Claims (2)

Composite membrane containing a water-soluble Polymer with sulfone, phosphonic and / or carboxylic acid groups and zirconium phosphate or zirconium hydrogen phosphate, characterized in that they are in a temperature range of 0 to 120 ° C in a humidified gas stream has a swelling of less than 120%. Process for the preparation of acid-base blends, characterized a polymer containing a sulfonic acid group and a basic Group dissolved in water becomes, to a thin film The ironing is followed by subsequent evaporation of the water from a post-treatment in a dilute mineral acid.