CS258526B1 - A method for treating perfluorinated ion exchange copolymers, especially their surface - Google Patents

Abstract

The solution relates to a method for treating perfluorinated ion-exchange copolymers, sulfonated and/or carboxylated and their salts, especially their surface. The subject of the solution makes it possible to chemically or physically treat the surface of these copolymers and their salts to the required depth into a compact, brittle layer having electrical conductivity, a high specific surface area of about 3,000 m^/g, onto which catalytically active substances can be adsorbed, high chemical reactivity and ion-exchange capabilities. The repair is carried out by reacting these copolymers and their salts with alkali metal amalgams at temperatures up to 200 °C in an inert environment. Due to their properties, these treated copolymers and their salts are used primarily as electrodes for electrocatalysis purposes

Description

It is an object of the present invention to provide a process for treating perfluorinated ion exchange copolymers, sulfonated and / or carboxylated copolymers, and salts thereof, particularly their surface.

These sulfonated and / or carboxylated perfluorinated copolymers and their salts (trade name of Du Pont de Nemours and Co., USA = Nafion) are chemically very stable ionomers or polymers containing ionic groups which are used in electrochemistry in particular as separators in brine electrolysers, in hydrogen-hydrogen fuel cells as a solid electrolyte, in galvanic chrome bath treatments, and in preparation of chemically modified electrodes.

In many applications, catalytically active layers or electronically conductive coatings need to be applied to the membrane surface of these copolymers. Until now, this has been solved mainly by vacuum metal vapor deposition. This results in coatings that are well conductive, but with a relatively small specific surface area, which is disadvantageous for catalysis purposes. Also, the choice of materials suitable for coating with this technology is limited.

It has therefore proven beneficial and advantageous to solve a process which overcomes the above-mentioned disadvantages, in particular allowing the surface of these copolymers to be chemically and / or physically altered to the required depth so as to obtain electronically conductive, catalytically active or of a large specific surface.

These objects have been achieved by the present invention of a process for the treatment of perfluorinated ion exchange copolymers, sulfonated and / or carboxylated, and their salts, in particular their surface.

A similar type of reaction from other conditions was described for polytetrafluoroethylene in AO 173 786, dated October 3, 1973 by Jansta and Doušek.

It has been found that surface treatment is also possible for perfluorinated ion-exchange copolymers, sulfonated and / or carboxylated and their salts by reaction with alkali metal amalgams, even with dilutions, e.g. at 20 ° C, where the reaction having an electrochemical 1/2 character penetrates With time to the depth of the membrane according to the parabolic law d - kt, where d is the thickness of the reacted polymer layer at time t, k the constant depends only on the temperature and type of alkali metal.

Based on this law and the experimentally determined constant k for a given condition, it is possible to control the copolymer to a predetermined desired depth in a controlled manner. The polymer on the membrane surface thus turns the reaction into a compact, adhering layer of reaction products containing polymeric, electronically conductive carbon mixed with an alkali metal fluoride, the polymeric carbon constituting a separate skeleton in the reaction products is further characterized by a high specific surface area in addition to electrical conductivity. 3000 m / g, to which, for example, catalytically active substances can be adsorbed, as well as high chemical reactivity which allows its further chemical treatment in order to obtain the desired catalytic properties.

However, the catalytic effects of this layer are strongly supported by the high specific surface area of the carbon thus obtained. Since the reaction leaves the sulfo groups respectively. The carboxyl groups in the original polymer are intact, and since these are also part of the reaction products, polymeric carbon gains an additional important advantage, namely ion-exchange capability.

Its electronic conductivity then has a favorable effect when this layer is used as an electrode, especially for the purpose of electrocatalysis.

The advantages of this solution are evident from the following examples which illustrate the invention without limiting it in any way.

Example 1

The sulfonated perfluorinated ion exchange copolymer (Nafion 117) in the form of a 10x15x0.19 mm foil was purified for 5-10 min in conc. nitric acid at boiling, degreased for 30 min at 100 ° C in 2N potassium hydroxide solution and dried at 180 ° C and 1.3 MPa. The treated film was sealed into an evacuated glass vial with 100 g of 0.04 wt.% Lithium amalgam. Li, Li. The temperature of the vials was maintained at 25 ° C. Proceeded electrochemical reduction of sulfonated perfluorinated ion exchange copolymer of lithium by the total formula ^C 20 ° ^F 39 5 ^{43.1 SK + Li} - ^C 20 ^LI 4, l ^{(LIF) SK} 39 ° 5

1/2 penetrating evenly into the depth according to said parabolic law d = kt, where + -1 / 2 k = 0.9.2 - 0.06 ₍ jum ha covering the membrane surface firmly adhering, compact brittle layer of the above mentioned properties).

Example 2

The procedure was as in Example 1, except that the reaction of the sulfonated perfluorinated ion exchange copolymer with lithium almalganate was carried out at 100 ° C. The + 1/2 reaction followed the same laws and its rate constant was k = 6.9 - 0.4 pm h '.

Example 3

The procedure was as in Example 1, except that the reaction was carried out with the sodium salt of a sulfonated perfluorinated ion exchange copolymer (Nafion 125). Again, the reaction followed the same laws.

Example 1 a d 4

The procedure was analogous to Example 2, except that the reaction was carried out with the potassium salts of the sulfonated and carboxylated perfluorinated copolymer. The membrane was reinforced with a Teflon mesh. Again, the reaction followed the same laws.

Claims (3)

Process for the treatment of perfluorinated ion exchange copolymers sulfonated and / or carboxylated and their salts, in particular their surface, characterized in that the treatment is carried out by treatment with an alkali metal amalgam at a temperature of up to 200 ° C. 2. The process of claim 1 wherein the alkali metal amalgam is an alkali metal solution, preferably lithium in mercury, saturated at a given temperature. 3. Process according to claim 1, characterized in that it is operated in an inert environment.