DE2132786A1 - Heterogeneous membranes - for fuel cells, contg polytetrafluorethylene powder and ion exchange resin and/or inert pow - Google Patents

Abstract

Heterogeneous membranes for use in electrochemical devices, esp. in fuel cells, for sepg. substances dissolved in anolytes and catholytes, are prepd. by homogenising, esp. in a ball-mill, powdered ion exchanger resin and/or powdered inert material with PTFE powder and a highly viscous liq. to form a suspension removing highly viscous liq. by suction from suspension while evenly distributed on a filter device; washing remaining filter cake with a solvent which decomposes the highly viscous liq. and then pressing. Pref. carrier support consists of a coarse-meshed fabric, opt. of PTFE, embedded in suspension on filter device in a way such that fabric is surrounded on al sides by filter cake after removal of highly viscous liq. Pref. PTFE is hydrophilised on surface by etching.

Description

Process for making heterogeneous ones. The invention relates to a Process for the production of heterogeneous membranes for electrochemical devices in particular fuel elements, consisting of ion exchange resins and / or inert materials and binders, for the separation of substances dissolved in the anolyte and catholyte and / or to exclude harmful repercussions from in the anolyte or catholyte dissolved substances on the reaction process at the counter electrode.

Essentially three types of membranes are known: 1. homogeneous Ion exchange membranes 2. heterogeneous ion exchange membranes 3. membranes made of inert materials.

Homogeneous ion exchange membranes are mostly made by polycondensation of phenol-formaldehyde or phenol ether-formaldehyde resins, into the ionogenic groups were built in, won.

For example, it was proposed in DP 971 729, still liquid Pour the ether-formaldehyde reaction mixture onto a glass plate, the whole thing cover with a second plate and place the solution between the two plates. ' even heating to condense into a gel. Different exchange resins, like e.g. sulfonated polystyrene, which have a relatively good resistance, are due to their mechanical properties for membranes because of their brittleness and lower elastic properties not suitable.

Despite the good ion conductivity and permselectivity of the homogeneous Ion exchange membranes is because of the low mechanical and application properties chemical stability current 3.

Swelling or shrinking, limited. The chemical stability; L-ity of a homogeneous ion exchange membrane can through a higher degree of crosslinking be improved, but this causes increasing embrittlement The Momb In contrast to the homogeneous ion exchange membrane is the manufacture heterogeneous ion exchange membranes and membranes made of inert materials from each Suitable ion exchange resin or inert material possible if ground ion exchangers - or inert material powder wrc.

plastic binders are held together. by a c-t.-tion the ion exchanger or the inert material and C e binder can be used in heterogeneous Membranes Depending on the intended use, the properties required can be largely achieved will.

For example, a method is known from US Pat. No. 2,660,558 that of ion exchangers with polyvinyl chloride (PVC) and other plastic materials is calendered.

From Z. phys. Chem. 8, (1956), 265 it is still known.

to dissolve the binder in a suitable solvent, the Suspend ion exchanger, then evaporate the solvent and to be pressed into a membrane.

Membranes made of inert materials should essentially be microporous Have structure that is filled with electrolyte. This microporous structure can be generated that chemically. inert powders or fibers, such as asbestos, Mg 0, etc., are pressed with a binder.

Selective ion permeability and barrier effect can be achieved with these Hardly reach membranes. The ion conductivity of such membranes is generally very good.

All previously known processes for the production of heterogeneous membranes however, have the disadvantages resulting from the uneven distribution of the to produce the membranes related materials. The after known The membranes manufactured using methods often have a different density distribution, different porosity and / or differences in the content of ion exchangers respectively.

Sheet metal supports. this results in a for the individual membranes different conductivity as well as different gas or electrolyte permeability. In addition, these inhomogeneities in the structure of the membranes often lead to localized various sources of swelling, malformations and faults.

The method according to the invention eliminates these disadvantages.

In the claims is the ancestor according to the invention, that is Invention principle and its configurations, defined with regard to the essential, in each case achievable technical effects (= technical "tasks" as well as with regard to the respective essential technical means (= the "solutions").

The technical progress that can be achieved with the process according to the invention is in particular that the previously occurring inhomogeneities in the structure the membrane can be largely avoided.

The method according to the invention also offers the possibility of Manufacture membranes by varying the ion exchange resins, inert materials and binders as well as their mixing ratios, grain size 2 and layer thicknesses, in their essential properties such as ionic conductivity, mechanical, chemical and thermal stability address the specific problems of electrochemical devices can be optimally adapted.

For example, in electrochemical devices, a particularly good Separation of substances dissolved in the anolyte and catholyte are required and / or the exclusion of a serious reaction of one dissolved in the anolyte or catholyte Substance may be required for the reaction process at the counter electrode. By the inventive method it is possible, for example, a membrane It high Ion exchanger antell and a small proportion of free pores to produce on this 1Jeise to prevent diffusion fer, -eli ;; ten. 'Substances. There the ionic conduction here quantitatively About the ion exchange rate lä @@ t, where such membranes generally have a relative high resistance.

In electrochemical devices with higher current densities, in which but a minor chemical reaction of anolyte and dissolved catholyte Substances or el ge.- ~ submissive influence of one dissolved in the anolyte or catholyte Substance can be bought on the reaction process at the counter electrode, while the voltage drop across the membrane should be as low as possible, it is with the method according to the invention possible to achieve a high electrolytic Conductivity to produce a heterogeneous membrane that acts as an electrolyte matrix inert carrier such as asbestos powder.

The following examples are intended to illustrate the invention.

Example 1 50 g of polytetrafluoroethylene powder with a grain size of <200 to be for the purpose of surface hydrophilization with 30 ml of an organometallic Sodium compound (as an etching agent) is placed in a beaker and stirred for about 1 minute. The reaction is stopped with 100 ml of acetone and stirred for a further 5 minutes. Then the Iolytetrafluoräthylen-Powder is sucked off and dried; 5 g this superficially hydrepolated posytetrafluorothylene powder of grain size < 200 μm and 5 g of asbestos powder with a grain size of <200 μm are mixed with 63 ml of paraffin oil Homogenized for 1 hour in the ball mill. Then the suspension degassed. 6 ml of this suspension are placed on a 28 cm² suction filter, covered with a coarse-meshed polyamide net and another o ml of suspension poured over it the suspension is evenly distributed with the help of a vibrator, the paraffin oil becomes sucked off with a water jet pump and the remaining filter cake washed with petroleum benzine. This filter cake is made with two feinmaschigon Polyethylene fabric covered and pressed at room temperature with approx. 3.5 to / cm². Then the polyethylene threads are deformed. An inert material ion membrane set up in this way has a low ohmic dependence ne is preferably used in alkaline Hydrazine hydrogen peroxide high performance fuel cells.

Example 2 Following the procedure described in Example 1, from 5 g of the surface-hydrophilized polytetrafluoroethylene powder of the grain size <200 µm, 5 g of Mg 0 powder with a grain size of <200 µm and using a superficial hydrophilized polytetrafluoroethylene network an inertial membrane manufactured, which can preferably be used in such fuel cells, which - like an NH3 air cell - in the medium temperature range (100-250 ° C) with highly concentrated alkali lye or alkali melt work.

Example 3 A heterogeneous ion exchange membrane is according to the in the method described in Example 1 prepared in such a way that instead of the 6 g asbestos powder 5 g anion exchange powder can be used.

Membranes of this type can preferably be used in such alkaline fuel elements or other electrochemical devices operating at relatively low Current densities work, but compared to a membrane with particularly high separability Require reactants dissolved in the anolyte and / or in the catholyte.

Example 4 Another heterogeneous ion exchange membrane is according to dom Process described in Example 1 in such a way that 2.5 g of anion exchanger powder the size of <200 µm and 2.5 g of asbestos powder with a grain size of <200 µm of 5 g of asbestos powder are used.

This Mombran can preferably be used in such low-temperature alkaline fuel elements or other electrochem.

rule devices are used, which at medium current densities (50 - 100 mA / cm²) work and need a membrane that is even more useful Separability from substances dissolved in the anolyte and / or in the catholyte at the same time also has a relatively good ion conductivity.

Claims (4)

P a t e n t a n s p r ü c h e 1. Process for the production of heterogeneous membranes for eloitrochemical Devices, in particular fuel elements, consisting of ion exchange resins and / or oils and quinizers, for the separation of catholytes dissolved in the anolyte Substances and / or to the exclusion of Schäalicher reactions from in the anolyte or Catholytes dissolved substances on the reaction sequence at the counterelectrede, according to the invention it is noted that powdered ion exchange resin and / or pulverized inert material with polytetrafluoroethylene powder and a highly viscous liquid is homogenized to a suspension that from this, Then the highly viscous suspension is evenly distributed on a filter device Liquid is sucked off and that the remaining filter cake with a highly viscous Liquid-decomposing solvent is washed and then pressed. 2. The method according to claim 1, d a d u r c h g e k e n n z e i c h n e t, as a coarse-meshed fabric is used as the support on the filter device distributed suspension is embedded in such a way that the tissue after suctioning off the highly viscous The liquid is surrounded on all sides by the filter cake 5. Method according to claim 1 and 2, characterized in that the polytetrafluorathaylene powder used as a binder and / or the coarse-meshed one which serves as a support beam and consists of dolytetrafluoroethylene Tissue is superficially hydrophillized by etching. 4. The method according to claim 1, characterized in that the suspension is homogenized in a ball mill.