DE10148132A9 - Ion-conducting membrane for electrochemical applications - Google Patents

Abstract

An ion-conducting membrane is provided for electrochemical applications based on a polyimide or copolyimide polymer which contains heterocyclic groups in its structure, in particular in the form of imidazole, pyridine and / or pyrimidine groups. The membrane according to the invention can advantageously be used in fuel cells.

Description

The invention relates to an ion-conducting Membrane for electrochemical applications based on an aromatic polyimide and copolymid polymers as well as their use.

Work is currently underway intensively on Fuel cells, which are a very promising alternative for energy conversion represent to develop to market maturity. Has for mobile application the so-called polyelectrolyte membrane fuel cell (polyelectrolyte membrane fuel cell; PEFC) was found to be particularly suitable, compare F. R. Kalhammer, P. R. Prokopius, V. P. Roan, G. E. Voecks, Status and Prospects of Fuel Cells as Automobile Engines, State of California Air Resources Board, 1998. A Essential The criterion for bringing this technology to market is the Availability suitable membrane with high proton conductivity, a low fuel or energy carrier permeability (hydrogen or Methanol) and high chemical stability, which, however, are inexpensive to manufacture are.

So-called Nafion ^® membranes, which are fluorinated membranes from Du Pont, or similar membranes that were marketed by Dow and Asahi, have been used intensively for fuel cells [O. Savadogo. J. New Materials for Electrochemical Systems 1 (1998) 47].

One of the main disadvantages of these Nafion ^® membranes is their cost. Therefore, various non-fluorinated membranes have been tested in fuel cells in recent years. Most of them are based on sulfonated polymers and copolymers. Membranes made of sulfonated polysulfone, sulfonated polyether ether ketone, sulfonated polyphosphazene and sulfonated polyamides are described in various places, see Q. Guo, PN Pintauro, H. Tang, S. O'Connor, Sulfonated and crosslinked polyphosphazene-based proton-exchange membranes. J. Membrane Sci. 154 (1999) 175; E. Vallejo, G. Pourcelly, C. Gavach, R. Mercier and M. Pineri. Sulfonated polyimides as proton conductor exchange membranes. Physicochemical properties and separation H + / Mz + by electrodialysis comparison with a perfluorosulfonic membrane. J. Membrane Sci. 160 (1999) 127; S. Faure, M. Pineri, P. Aldebert, R. Mercier, B. Sillion, US 6245881 B1 ,

Another disadvantage of Nafion ^® membranes is the decrease in proton conductivity above 100 ° C due to the deprivation of water. Operation in a temperature range of 100-150 ° C would, however, be advantageous in order to reduce the poisoning of the catalyst by CO. A polymer that is believed to work in this temperature range is polybenzimidazole, which is commonly doped with phosphoric acid [RF Savinell, MH Litt. Proton conducting polymers prepared by direct acid casting. US-A-5716727 ].

Polybenzimidazole (PBI) was also modified by sulfonation to increase the conductivity below 100 ° C [D. J. Jones and J. Rozière. Recent advances in the functionalization of polybenzimidazole and polyether ketones for fuel applications. J. Membrane Sci. 185 (2001) 41]. The basic character of the imidazal groups plays a role here essential role in the transport of protons in PBI membranes and with their good performance above 100 ° C.

Sulfonated polyimides have also been used already examined for their use in fuel cells [C. Genies, R. Mercier, B. Sillion, N. Cornet, G. Prayer, M. Pineri. Soluble sulfonated naphtalenic polyimides as materials for proton exchange membranes. Polymer 42 (2001) 359-373; C. Genies, R. Mercier, B. Sillion, R. Petiaud, N. Cornet, G. Prayer. M. Pineri. Stability study of sulfonated phtalic and naphtalenic polyimide structures in aqueous medium. Polymer 42 (2001) 5097-5105]. The synthesis options While they are very flexible, there can be a variety of structures be preserved. Nevertheless, the membranes examined so far insufficient in many ways.

Object of the present invention is therefore to provide an improved membrane that is suitable for electrochemical Applications and are used in particular in fuel cells can.

This task is solved by an ion-conducting membrane according to the teaching of claims.

The membrane according to the invention is produced made of polyimide or copolyimide polymers, which are heterocyclic in structure Groups, especially imidazole, pyridine and / or pyrimidine groups contain. These heterocyclic groups can be part of the main chain or can be attached to it as a side chain of different sizes.

The polyimide or copolyimide polymers contain units which can be the same or different and which correspond to the following general formula I:

In this general formula I, the radical B denotes at least one optionally substituted aromatic heterocycle of the following general formula II:

The radical R here represents a hydrogen atom, a phenyl radical, a phosphonic acid group or at least one containing a phosphonic acid group Chain.

Group A in general formula I stands for one of the following groups, containing at least one naphthalene unit, of general formula III:

Group A forms with the neighboring ones Imide groups (compare general formula I) with rings 6 atoms.

The polymers are preferably made of which the membranes of the invention are built up from recurring units of the general formula I built up.

The manufacture of the membrane of the invention Polymers used are preferably by direct implementation diamines (especially 4,5-di (3-aminophenyl) imidazole and 5- (2-benzimidazole) -1,3-phenylenediamine, Diaminopyridines and / or diaminopyrimidines with naphthalene-1,4,5,8-tetracarboxylic acid dianhydride (NTCDA) or bis (naphthalic anhydrides) and the diacid dialkyl ester or diacyl chloride dialkyl ester derivatives of these dianhydrides.

The polymer can also by introducing other groups. These include acids in general and in particular phosphonic, which among other things can increase the proton conductivity. The membranes are preferably by pouring the solution of the polymer. It is also possible to acid or membrane modify inorganic substances, for example with phosphates, about conductivity to improve.

The invention is illustrated below of examples closer explains what preferred embodiments affect.

Example 1:

A 250 ml three-necked flask with a mechanical stirrer, an inlet for an inert gas (Argon) and a Dean-Stark system with a cooler and a drying tube the tip of which was equipped with 0.4365 g (4 mmol), 2,6-diaminopyridine, 1.601 g (8 mmol) bis (4-aminophenyl) ether, 3.2182 g (12 mmol) naphthalene-1,4,5,8-tetracarboxylic acid dianhydride, 7.82 g (64 mmol) benzoic acid and load 45 g of m-cresol. This mixture (dark red colored solution) was in a thermostated silicone oil bath for 8 h at 80 ° C and 24 h at 190 ° C heated and stirred. Then 10 g of m-cresol was added and the reaction mixture was cooled to room temperature and poured into ethyl acetate. The light brown precipitate was filtered off, washed with ethyl acetate and then with ethanol and in vacuo 80 ° C dried.

Example 2:

In a 100 ml three-necked flask, the with a mechanical stirrer, an inlet for an inert gas (argon) and a drying tube 0.1882 g (1 mmol) of 2,4-diaminobenzenesulfonic acid and 0.17 ml (1.2 mmol) of dry triethylamine and at room temperature for some Minutes stirred. Thereafter, 0.1091 g (1 mmol) of 2,6-diaminopyridine, 0.2002 g (1 mmol) bis (4-aminophenyl) ether, 0.80454 g (3 mmol) naphthalene-1,4,5,8-tetracarboxylic acid dianhydride and 18 g benzoic acid added; this mixture was placed in a thermostated silicone oil bath Heated 140 ° C. After melting the benzoic acid became the stirrer hired. The temperature was raised to 160 ° C and the mixture was left overnight stirred at this temperature. After cooling to room temperature, acetone was added to the mixture to benzoic acid to solve and remove it afterwards. The light brown residue was filtered off, washed with acetone and dried in vacuo at 70 ° C.

Example 3:

In a 250 ml three-necked flask, the with a mechanical stirrer, an inlet for an inert gas (argon) and a Dean-Stark system with a cooler and a drying tube equipped with the top of it, 1.7941 g (8 mmol) of 5- (2-benzimidazole) -1,3-phenylenediamine, 0.8001 g (4 mmol) bis (4-aminophenyl) ether, 3.2182 g (12 mmol) naphthalene-1,4,5,8-tetracarboxylic acid dianhydride, 2.56 g (21 mmol) benzoic acid and 4.5 g of m-cresol. This mixture was stirred in a thermostated silicone oil bath 4 h at 80 ° C and 20 h at 190 ° C heated. Then 10 g of m-cresol was added and the mixture was cooled to room temperature and poured into ethyl acetate. The precipitate was filtered off with Ethyl acetate and then washed with ethanol and dried in vacuo at 80 ° C.

For the production of the membranes according to the invention will be a solution of the polymers described in Examples 1 to 3. From this, the membranes are cast in a manner known per se polymer solution shaped.

Claims (8)

Ion-conducting membrane for electrochemical applications based on an aromatic polyimide or copolyimide polymer which contains units, which may be the same or different, of the following general formula I:

in which the radical B denotes at least one optionally substituted aromatic heterocycle of the following general formula II:

R represents H, a phenyl radical, a phosphonic acid group or a chain containing at least one phosphonic acid group, and A represents one of the following groups of the general formula III which contain at least one naphthalene unit:

and forms rings with 6 atoms with the neighboring imide groups. Membrane according to claim 1, characterized in that the polymer consists of repeating units of the general formula I is built. Membrane according to claim 1 or 2, thereby obtainable that at least one diamine, diaminopyridine and / or diaminopyrimidine with naphthalene-1,4,5,8-tetracarboxylic acid dianhydride, one bis (naphthalic acid anhydride) and / or a diacid dialkyl ester or diacyl chloride dialkyl ester derivative this dianhydride is directly implemented. Membrane according to claim 3, obtainable thereby, that a 4,5-di (3-aminophenyl) imidazole and / or 5- (2-benzimidazole) -1,3-phenylenediamine as diamine is used. Membrane according to one of claims 1 to 4, characterized in that the polymer by insertion another group, especially a phosphonic acid group, is modified and / or the membrane with an acid or an inorganic Modifier is doped. Membrane according to one of the preceding claims, characterized characterized in that they are produced with the aid of a casting solution of the polyimide or copolyimide polymer becomes. Use of a membrane according to one of the preceding Expectations for electrochemical Applications. Use according to claim 7, wherein the membrane in a fuel cell is used.