In which area is zirconium hydrogen phosphate used
The invention is also described below by way of example for PEEK, PSU and PES. However, the method is generally applicable and not limited to any particular polymer. PEEK can be sulfonated with concentrated sulfuric acid without problems up to an IEC of 2.7. From Kenes et al. processes have been described for making polymers having basic groups and sulfonic acid groups on the same polymer backbone. So a PEEK that carries sulfonic acid groups and amino groups on the same backbone. This polymer was dissolved in aprotic solvents and processed into a membrane accordingly. It has now surprisingly been found that if the polymer contains sulfonic acid groups with an IEC of over 2.0 and, at the same time, amino groups corresponding to an IEC of 0.2 to 0.6 are also present on the same polymer backbone, then the polymer is water-soluble, below the prerequisite that the sulfonic acid groups are cation-exchanged. The preferred cations are mono- and divalent cations, especially Na+, K+, Li+, Approx2+, Mg2+, and ZrO2+ ().
This enables a greatly simplified representation of the membranes. Sulphonated PEEK or PSU with an IEC of 2.2 for sulphonic acid groups and an IEC of 0.5 for amino groups (S-PEEK-NH2) is converted into the salt form by means of ion exchange. According to the representation method of Kerres et al. the sulfonic acid is already available as a sodium salt. This polymer, with the two functional groups, is dissolved in water, optionally with heating. Thereafter, the aqueous solution is made into a film by removing the water. This is done, for example, by pouring the solution into a Petri dish and evaporating the solvent, water, in a drying cabinet. Subsequent treatment of the film in dilute mineral acid releases the sulfonic acid groups, some of which in turn enter into an acid-base interaction with the basic component. As a result of the hydrogen bridges that are formed, the film is now insoluble in water. A membrane with very good proton conductivities is obtained.
This method can also be carried out using ZrO2+ improve exchanged sulfonic acids. Polymeric sulfonic acids (IEC> 2.0) exchanged with zirconium oxychloride and containing a further basic component on the same polymer backbone are dissolved in water. Then formed into a film on a surface and the water is removed by evaporation. The film, which is still potentially water-soluble, is treated with phosphoric acid (5-80% by weight). The aftertreatment results in the formation of the acid groups and, as a result, the hydrogen bonds with the basic component. In addition, zirconium phosphate and the corresponding hydrogen phosphates are precipitated in the membrane. A composite membrane is obtained consisting of a polymeric acid and base (same backbone) and an inorganic phase made of zirconium phosphate and zirconium hydrogen phosphates. By alternately treating the membrane with zirconium oxychloride dissolved in water and / or an aprotic solvent and phosphoric acid, even more zirconium phosphate is stored in the membrane. The swelling of the membrane is greatly reduced as a result, although it has a high IEC number of sulfonic acid groups. The mutual aftertreatment resulted in membranes with a specific resistance of less than 20 ohm × cm. This is of the same order of magnitude as NafionTM by DuPont.
A second improvement of the invention has now been found, surprisingly. Sulphonated PEEK or PSU with an IEC of 1.85 is dissolved in water. In addition, this solution is mixed with an aqueous solution of 5–30% by weight of zirconium oxychloride (ZrOCl2) based on the dry weight of the sulfonated polymer. The solution is knife-coated into a thin film and the solvent is evaporated off. This removes not only water but also HCl. The resulting film is treated in aqueous phosphoric acid. The membrane is then post-treated one or more times alternately in zirconium oxychloride solution and aqueous phosphoric acid. After 2–5 post-treatment steps, the membrane is dissolved in dist. Excess phosphoric acid is removed from water. 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 that is operated with hydrogen. It is also suitable for temperatures above 80 ° C.
The following is another representation of the composite membrane. Sulphonated, preferably thermoplastic, water-soluble polymer is dissolved in water and knife-coated to form a thin film, the water is evaporated and a film is obtained, preferably a thickness of 10-100 μm. This film is then placed in aqueous zirconium oxychloride solution for 1 to 24 hours. In the next step, the film is treated in diluted phosphoric acid for approx. 1 to 24 hours. This process is repeated 2 to 5 times. The swelling of the membrane decreases with each post-treatment step.
As an alternative to the previous illustration, sulfonated water-soluble polymer with zirconyl cations is used as the sulfonic acid cation. The polymer is dissolved in water and made into a membrane again. This saves one post-treatment step.