DE10148132A1 - Ion conducting membranes based on aromatic polyimide- or copolyimide polymers useful for electrochemical applications, especially fuel cells - Google Patents

Abstract

Ion conducting membranes for electrochemical applications, especially fuel cells, and based on aromatic polyimide- or copolyimide polymers containing units which can be the same or different are new. Ion conducting membranes for electrochemical applications, especially fuel cells, and based on aromatic polyimide- or copolyimide polymers containing units which can be the same or different and of formula (I). Independent claims are included for the following: (1) preparation of the membrane by direct reaction of a diamine, diaminopyridine, and/or diaminopyrimidine with naphthalene-1,4,5,8-tetracarboxylic acid dianhydride, a bis-(nahthalenic acid anhydride) and/or a diacid-dialkyl ester or diacyl chloride-dialkylester derivative of this dianhydride; and (2) preparation of the membrane by cast-blocking (sic) of polyimide- or copolyimide polymer. B = at least one optionally substituted heterocyclic compound of formula (II); R = H, phenyl, a phosphonic acid group or at least one chain containing a phosphonic acid group; and A = one of naphthalene containing groups of formula (III), and forms 6-atom rings with the adjacent imide groups.

Description

The invention relates to an ion-conducting membrane for electrochemical Applications based on an aromatic polyimide and copolymid Polymers and their use.

Currently, intensive work is being done on fuel cells, which is a very represent a promising alternative for energy conversion Develop market maturity. For mobile applications, the so-called polyelectrolyte membrane fuel cell (polyelectrolyte membrane fuel cell; PEFC) was found to be particularly suitable, one see 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 key criterion, this Bringing technology to market is the availability more appropriate Membrane with a high proton conductivity, a low one Fuel or energy carrier permeability (hydrogen or methanol) and high chemical stability, which, however, is inexpensive are to be produced.

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

One of the major disadvantages of these Nation® membranes is their Costs. Therefore, various non-fluorinated membranes were used in the tested in fuel cells in recent years. Most of them are based on sulfonated polymers and copolymers. Membranes sulfonated polysulfone, sulfonated polyether ether ketone, sulfonated Polyphosphazene and sulfonated polyamides are different Passages described, compare Q. Guo, P.N. 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 water deprivation. However, operation in a temperature range of 100-150 ° C would be advantageous to reduce the poisoning of the catalyst by CO. A polymer that is believed to be in this Temperature range can be used, represents polybenzimidazole, which is usually doped with phosphoric acid [R. F. Savinell, M.H. 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 imidazole 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 in Fuel cells examined [C. Genies, R. Mercier, B. Sillion, N. Cornet, G. Gebel, 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. Gebel. M. Pineri. Stability study of sulfonated phtalic and naphtalenic polyimide structures in aqueous medium. Polymer 42 (2001) 5097-5105]. The Synthesis options are very flexible, and there can be many be maintained by structures. Nevertheless, the ones examined so far Membranes are inadequate in many ways.

The object of the present invention is therefore an improved To provide membrane for electrochemical applications and can be used in particular in fuel cells.

This task is solved by an ion conducting membrane according to the Teaching claims.

The membrane of the invention is made of polyimide or Copolyimide polymers, the structure of which is heterocyclic groups, in particular contain imidazole, pyridine and / or pyrimidine groups. 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, one Phosphonic acid group or at least one phosphonic acid group Chain containing group.

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 imide groups (compare the general formula I) rings with 6 atoms.

Preferred are the polymers from which the invention Membranes are constructed from recurring units of the general formula I built.

The used to manufacture the membrane of the invention Polymers are preferably made by direct reaction of diamines (especially 4,5-di (3-aminophenyl) imidazole and 5- (2-benzimidazole) - 1,3-phenylenediamine, diaminopyridines and / or diaminopyrimidines with Naphtalene-1,4,5,8-tetracarboxylic 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 be modified. These include acids in general and in particular Phosphonic acid groups, which include proton conductivity can increase. The membranes are preferably cast by pouring the Solution of the polymer made. It is also possible to use the membrane Modify acids or inorganic substances, for example with phosphates to improve conductivity.

The invention is explained in more detail below with the aid of examples, which relate to preferred embodiments.

example 1

A 250 ml three-necked flask equipped with a mechanical stirrer, a Inlet for an inert gas (argon) and a Dean-Stark system with one Cooler and a drying tube at the top, was mixed with 0.4365 g (4 mmol), 2,6-diaminopyridine, 1.601 g (8 mmol) (4-aminophenyl) ether, 3.2182 g (12 mmol) naphthalene-1,4,5,8- tetracarboxylic acid dianhydride, 7.82 g (64 mmol) of benzoic acid and 45 g Load 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 in Poured ethyl acetate. The light brown precipitate was filtered off with Ethyl acetate and then washed with ethanol and in vacuo at 80 ° C dried.

Example 2

In a 100 ml three-necked flask, which is equipped 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 added and at Room temperature stirred for a few minutes. Thereafter, 0.1091 g (1 mmol) 2,6-diaminopyridine, 0.2002 g (1 mmol) bis- (4-aminophenyl) - ether, 0.80454 g (3 mmol) Naphthalene-1,4,5,8-tetracarboxylic dianhydride and 18 g benzoic acid added; this mixture was heated to 140 ° C in a thermostated silicone oil bath. To The stirrer was started to melt the benzoic acid. The Temperature was raised to 160 ° C and the mixture was left overnight stirred at this temperature. After cooling to room temperature Add acetone to the mixture to dissolve benzoic acid and remove them 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, which is equipped with a mechanical stirrer, an inlet for an inert gas (argon) and a Dean-Stark system with a cooler and a drying tube at 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 dianhydride, 2.56 g (21 mmol) benzoic acid and 45 g of m-cresol. This mix was stirred in a thermostated silicone oil bath at 80 ° C for 4 h and heated to 190 ° C for 20 h. Then 10 g of m-cresol added and the mixture was cooled to room temperature and in Poured ethyl acetate. The precipitate was filtered off with ethyl acetate and then washed with ethanol and dried in vacuo at 80 ° C.

A solution is used to produce the membranes according to the invention of the polymers described in Examples 1 to 3. from that the membranes are cast in a manner known per se Polymer solution shaped.

Claims (8)

1. 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. 2. membrane according to claim 1, characterized in that the polymer of repeating units of the general Formula I is built. 3. Membrane according to claim 1 or 2, obtainable in that at least one diamine, diaminopyridine and / or diaminopyrimidine with naphthalene-1,4,5,8-tetracarboxylic acid dianhydride, a bis- (Naphtalic anhydride) and / or a diacid dialkyl ester or diacyl chloride dialkyl ester derivative of these dianhydrides directly is implemented. 4. Membrane according to claim 3, obtainable in that a 4,5-di (3-aminophenyl) imidazole and / or 5- (2- Benzimidazole) -1,3-phenylenediamine is used. 5. Membrane according to one of claims 1 to 4, characterized in that the polymer by introducing another group, in particular a phosphonic acid group, is modified and / or the membrane is doped with an acid or an inorganic modifier. 6. membrane according to one of the preceding claims, characterized in that them with the help of a casting solution of the polyimide or copolyimide Polymers is produced. 7. Use of a membrane according to one of the preceding Requirements for electrochemical applications. 8. Use according to claim 7, wherein the membrane in one Fuel cell is used.