ES2310484B1 - ORGANIC-INORGANIC HYBRID MEMBER OF ION EXCHANGE, ITS PREPARATION AND USE IN ELECTROCHEMICAL DEVICES. - Google Patents

Abstract

Hybrid membrane organic-inorganic ion exchange, its Preparation and use in electrochemical devices.

Organic-inorganic hybrid membrane composed of
a polymer matrix prepared from natural rubber pre-vulcanized latex and an inorganic filler with protonic conductor properties that can act as a separator and solid electrolyte in electrochemical devices such as sensors and gas separators, batteries or fuel cells. This gives them excellent mechanical properties, especially in elongation at break, a flexibility far superior to that of their competitors, and an excellent elasticity.

The production process is fast and simple, it doesn't need high temperatures or pressures, so it doesn't It is a great energy expenditure. Moreover, it does not require the use of any solvent, so it is not polluting and is also cheaper.

Description

Hybrid membrane organic-inorganic ion exchange, its Preparation and use in electrochemical devices.

Hybrid membrane organic-inorganic composed of a matrix polymer prepared from rubber pre-machined latex natural and an inorganic load with conductor properties proton that can act as a separator and solid electrolyte in electrochemical devices such as sensors and separators gases, batteries or fuel cells. This gives them some excellent mechanical properties, especially in elongation at breakage, flexibility far superior to that of its competitors, and An excellent elasticity.

The production process is fast and simple, it doesn't need high temperatures or pressures, so it doesn't It is a great energy expenditure. Moreover, it does not require the use of any solvent, so it is not polluting and is also cheaper.

Technical sector

The present invention is part of the area of chemistry and in particular falls within the membrane sector ion exchange that can act as a separator and electrolyte solid in electrochemical devices such as sensors and gas separators, batteries or fuel cells.

State of the art

Fuel cells with electrolyte Proton exchange (PEMFC) have generated great interest due to the advantages they offer in automotive applications and in electronic equipment, as a result of its operation to low temperatures (60-80ºC). With them it is possible obtain good current densities (~ 500 mA / cm2) and If the amount of platinum could be reduced, it should be used as a catalyst, its costs would also be reduced quickly. In addition, the energy density acquired with them is the highest within the different types of fuel cells.

In general, so that an exchange membrane ionic could be used in all those applications should have a high ionic selectivity, good ionic conductivity, low permeability to electrolyte-free diffusion, as well as Good chemical stability, high mechanical strength, high flexibility and good dimensional stability. In addition, in the case of used in fuel cells, it should be impermeable to gases such as hydrogen and oxygen. Two other features fundamental would be that it had a low cost and that it was easy to Recycle to avoid damage to the environment.

There are currently several ion exchange membranes on the market based on perfluorosulfonated polymers, Aciplex (from Asahi Chemical), Dow (from Dow Chemical) or the most used of all, Nafion, manufactured by DuPont, which has produced good results in batteries of fuel due to its high ionic conductivity at temperatures below 80ºC, and good chemical resistance. However, perfluorosulfonated polymers have a high price and a negative effect on the environment, since they are difficult to recycle. In addition, they are not effective at temperatures above 80 ° C because they suffer from remarkable dehydration (Kundu PP Reviews in Chemical Engineering 2006 Vol. 22, No. 3 pp. 125).

In recent years, a new generation of non-fluorinated ion exchange membranes based on polymers with high thermal and mechanical stability has emerged. They are generally polyaromatic or polyheterocyclic in nature: polysulfones (PSU), poly (ether-sulfone) (PSE), poly (ether-ketone) (PEK), poly (ether-ether-ketone) (PEEK), polybenzoimidazoles (PBI) or polyimides (PI). However, these polymers, by themselves, are insulators, so they must be modified in some way. Usually this modification is usually of the chemical type and there are several possibilities: doped with acids and bases, direct sulfonation of the polymer chain, graft of sulphonated or phosphorus functional groups, graft of side polymer chains and subsequent sulfonation of the same, etc. Once modified, these non-fluorinated polymeric membranes can have phonic conductivities similar to those of perfluorosulfonated polymers, even at temperatures between 80º and 135ºC, where the latter failed (Roziere J. Jones, DJ Annual Review of Materials Research , 2003 Vol. 33 pp 503) . However, its price is similar or higher, since its synthesis, which is expensive, joins the second step of modification, which necessarily increases its price. On the other hand, although these polymers have good mechanical properties, they lack flexibility. In addition, the modification, which usually consists of a sulfonation reaction, usually significantly reduces the mechanical properties of said membranes. From the ecological point of view it must be said that both the synthesis and the modification reactions of all these polymers require the use of large amounts of solvents, mostly organochlorine, which implies a certain risk for both nature and health. .

During the last decade, organic-inorganic hybrid membranes have been developed, composed of a polymeric ionomeric matrix and an inorganic charge with moderate or high proton conductivity of the type: silica, heteropolyacids, lamellar metal phosphates or phosphates (Albertini, G., Casciola, M., Annual Review of Materials Research , 2003 Vol. 33 pp 129 ). This type of inorganic fillers have been incorporated into both traditional perfluorosulfonated polymers, Nafion type, as well as the more recently developed sulfonated polyaromatic or polyheterocyclic membranes.

Various elastomeric membranes prepared from solid-state mixtures of EPDM and HSBS (hydrogenated styrene-butadiene block copolymer) sulfonated (Escribano, PG; Del Rio, C. J. of Applied Polymer Science 2006 , 102 have been patented and applied , and Bashir, H .; Acosta, JL J. of Membrana Science 2005 , 253 , 33), as well as the latter with various thermoplastics (Escribano, PG; Acosta, JL J. of Applied Polymer Science 2004 , 93 , 2394) . However, only one appointment was found in which natural rubber was incorporated into these sulfonated elastomeric membranes (Nacher, A. Doctoral Thesis , Complutense University of Madrid, 2006 ). Various articles have also appeared on the use of synthetic latex copolymers of butyl acrylate (BA) and methyl methacrylate (MMA) with sulfonated styrene (NaSS) (Gao, J .; Lee, D .; Frisken, BJ Macromolecules 2005 , 38 , 5854 and Gao, J .; Lee, D .; Frisken, BJ Macromolecules 2006 , 39 , 8060), but we have not found any work in which membranes for PEMFC and DMFC stacks are prepared from natural rubber latex. As for the charges used in this invention, it must be said that there are many works in which silica synthesized by the sol-gel method is incorporated into proton exchange membranes prepared from both Nafion (Sahu AK; Selvarini G. J. of Electrochemical Society 2007 , 154 , B123 and Miyake, N .; Savinell, RF J. of Electrochemical Society 2001 , 148 , A898) and other polymers (Shahi, VK Solid State Ionics 2007 , 177 , 3395 and Lee, CH; Hwang , SY J. of Power Sources 2006 , 163 , 339). However, in the case of fluoro acids there is no application in the field of fuel cells.

Description of the invention Brief Description of the Invention

The main obstacles to greater commercialization of electrolyte fuel cells polymeric are the high cost of the membranes known to the moment, its recycling, its low humidity conductivity relatively low, high permeability to methanol and the poor mechanical properties at temperatures above 130 ° C.

The object of this invention is the preparation and industrial development of a new type of exchange membrane phonic that can act as a separator and solid electrolyte in electrochemical devices such as sensors and separators gases, batteries or fuel cells. It is a membrane organic-inorganic hybrid composed of a polymer matrix prepared from pre-machined latex of natural rubber and an inorganic filler with conductor properties protonic.

Our membranes have a conductivity proton similar to that of Nafion (the best known until moment), with good thermal and chemical stability. Is about organic-inorganic hybrid membranes in which the polymer matrix is a natural rubber latex crisscrossed This gives them excellent properties. mechanical, especially in elongation at break, flexibility far superior to that of all its competitors, and an unbeatable elasticity, so they could act both as a membrane and as a seal, necessary in the assembly of the battery, reducing the weight, volume, and finally the cost of it. Besides, his price would be much lower than the rest of the membranes commercial, since, being natural rubber latex a product of absolutely recyclable plant origin, and mass consumption, its price is several times lower than that of synthetic polymers petroleum derivatives used in other membranes. The process Production is fast and simple, it does not need temperatures or high pressures, so it does not involve a large energy expenditure. On the other hand, it does not require the use of any solvent, since all dispersions are in the aqueous phase, so it is not pollutant and is also much cheaper.

Detailed description of the invention

The manufacturing process of our membranes It consists of several steps. First, the latex is pre-vulcanized, then the pre-machined latex is mixed with a dispersion aqueous of the inorganic filler and finally the mixture is deposited in thin film form. In this way they have been achieved excellent mechanical properties, especially elongation at the breakage, a flexibility far superior to that of all its competitors, and an excellent elasticity. Its price would be very lower than the rest of the commercial membranes, since the Raw materials are very cheap and the production process is Fast and simple and does not involve a large energy expenditure. For other part, its recycling is not problematic, and in manufacturing it is not They use solvents, so it is cheaper and ecological.

As an inorganic filler, it can be incorporated any protonic conductor, both known today, silica, heteropolyacids, laminar metallic phosphates or phofacenes, as developed in the future. In this sense, the other achievement of this invention has consisted in developing, for the first time, a method to prepare protonic conductors from hexafluorosilicate dispersions, hexafluorotitanatos, hexafluorozirconates and tetrafluoroborates that are incorporated into a latex matrix

Elastomeric membranes have been prepared to from pre-machined natural rubber latex with thicknesses between 30 and 300 µm and with inorganic filler contents between the 0.1 and 50% by weight. Both inorganic fillers have been incorporated with low proton conductivities, such as metal oxides prepared by the sol-gel method: SiO2, TiO2, ZrO2, as with high conductivities, such as fluorosilicates of: lithium (Li2 SiF6), sodium, potassium, rubidium, cesium, ammonium, magnesium, calcium, barium, copper (II) and manganese (II); Fluoroborates such as sodium (NaBF4), fluorotitates, such as Na 2 TiF 6 or fluorozirconates such as Na 2 ZrF 6.

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The process of preparing the membranes is You can divide into four stages:

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 Prevulcanization of latex

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 Dispersion Preparation of the inorganic load

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 Inorganic Charge Mix with latex

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 Conformed of membranes

Prevulcanization of latex

First of all you have to make a dispersion of All reagents necessary for crosslinking of latex: sulfur or sulfur donors, accelerators, antioxidants and corresponding surfactants and dispersants that will help the formation and stability of said dispersion. To do this introduce all the ingredients mixed with water in a proportion less than 50% by weight in a ball mill and stirred for the time necessary to obtain a particle size optimum. Then the pre-vulcanization of the latex is carried out, for which the dispersion of the agents of the system is added vulcanization and heated between 30 and 70 ° C for 2-15 hours needed to reach the degree of desired crosslinking of the latex. Once this is done, the latex Pre-machining is conveniently stabilized with surfactants more suitable to guarantee its stability during expected storage time.

Preparation of dispersion of inorganic filler

The way to prepare the dispersion depends on the type of inorganic filler In the case of salts of fluoroacids the dispersion is prepared with a concentration between 20 and 50 g by weight by grinding said load in a ball mill with the amount of water and surfactants needed. Dispersions of the oxides obtained by the sol-gel method, prepared by hydrolyzing a solution of an alkoxide of the metal of Split in an ethanol-water mixture.

Mixing inorganic filler with latex

The pre-machined latex is placed in a container with mechanical agitation and little is added to little dispersion of the inorganic charge. Meanwhile, it control mixing parameters such as viscosity, tension surface or pH to prevent coagulation, for which it they must be adding different additives to the mixture as ionic and non-ionic surfactants or acids and bases.

Conformed membranes

Once the mixture is prepared inorganic latex-loading the next step is Prepare the membrane. At this point it is essential that the viscosity and surface tension of the mixture are the adequate, and that they are controlled at all times. Extends a film the mixture on a glass mold and let it dry a temperature between 50 and 80 ° C for a time less than 60 minutes, suitable for each mixture. To unmold the membranes the mold is immersed in a water bath and the membrane is demoulded keeping it always submerged and as extended as possible. One time unmoulded is extracted from water and spread over a surface not adherent to let it dry.

Properties

As for the mechanical properties, regardless of the type of load used the modules 100% deformation are less than 1.6 MPa, while 900% they exceed 20 MPa in most cases, which means that the films are quite elastic despite having Built-in inorganic charge. All the films present a breakage behavior with good performance, since the load at the break varies between 15 and 30 MPa with maximum deformations over 700%, very suitable for assembly under high MEA's pressures.

To calculate water absorption capacity of the membranes, these have been submerged in distilled water during 24 hours and have been weighed before and after drying under vacuum. The amount of water absorbed increased depending on the content of load between 5 and 25% by weight.

As regards thermal resistance, in none of the membranes tested by analysis thermogravimetric weight loss has been observed below the thermal decomposition temperature of the latex itself, which produces around 380ºC, and in all cases exceeds 330 ° C

Conductivity measurements have been made at 81% of relative humidity between 30 and 80ºC finding that the conductivity is a function of the content and type of inorganic filler, reaching conductivities of 4x10 -2 S / cm at 80 ° C. Measuring under identical conditions a 100 \ mum Nafion film a conductivity of 6.2x10 -2 S / cm was observed. In addition, it has proven that the conductivity of the films does not change after of three months of storage.

Example 1 Preparation of a membrane with 25% by weight of K 2 TiF 6

First a dispersion is prepared with the necessary ingredients to preulcanize the latex. For it 100 gr of sulfur, 50 gr of zinc diethyldithiocarbamate, 20 gr of zinc oxide, 20 gr of antioxidant, 2 gr of potassium caprylate, 2 gr of casein and 200 gr of water, and stir for two hours. To preulcanize latex they are added to a tank equipped with a mechanical agitation system 500 gr of concentrated latex (55% by weight of rubber) and the amount of the dispersion, prepared as previously mentioned, necessary so that for every 100 parts of rubber there are 2 parts of sulfur. For stabilize the mixture add 10 g of aqueous solution of potassium caprilat and 10 grams of Emulvin (a non-surfactant  ionic). The mixture is stirred at 200 rpm and heated for 6 hours at 60 ° C.

To prepare the dispersion of the load inorganic are added to a ball mill 100 gr of K 2 TiF 6 400 gr of water and a few drops of the surfactant Dolapix and stir for 40 minutes.

The last step is the preparation of the mixture, for which they are added in a glass equipped with mechanical agitation (200 rpm) 200 gr of pre-machined latex, 185 gr of the dispersion of K 2 TiF 6, 1 ml of 10% KOH solution and 1 ml of 10% potassium Caprylate solution. Stir for 3 hours at room temperature. After that time they are taken with a Pipette 3 ml of the mixture, spread on a level glass until the proper thickness is achieved and dried in an oven at 70 ° C for 60 minutes Then the mold is immersed in a bath of water and the membrane is demoulded keeping it always submerged and as widespread as possible. Once unmolded it is extracted from the water and extends over a non-adherent surface to leave it dry off.

In this way 150 membranes have been prepared um thick with a conductivity of 2x10 -3 S / cm at 60 ° C and 81% relative humidity. As for the mechanical properties, these membranes were very elastic, with a 100% module of Very low deformation, 1.03 MPa, and a 500% module of 6.15 MPa. However, they are also very resistant since they extend 770% before breaking with a breaking load of 21.1 MPa. Further, they have a great thermal resistance, since their temperature of decomposition, calculated by thermogravimetry is 365ºC. In as for water absorption, after 24 hours of immersion in Distilled water had absorbed 10% by weight.

Claims (9)

1. Organic-inorganic hybrid ion exchange membranes characterized by containing a matrix prepared from natural rubber latex and an inorganic filler with low or high proton conductivities and therefore adjustable proton conductor properties. 2. Method of preparing organic-inorganic ion exchange hybrid membranes according to claim 1 characterized in that it comprises the steps:

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latex pre-machining

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load dispersion preparation inorganic

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mixture of inorganic filler with latex

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Conformed membranes.

3. Method of preparing organic-inorganic ion exchange hybrid membranes according to claim 2 characterized in that the pre-vulcanization of the latex is produced by a cross-linking system based on sulfur, accelerators and antioxidants, between 30 and 70 ° C for 2-15 hours . 4. Method of preparing organic-inorganic phonic exchange hybrid membranes according to claim 2 and 3 characterized in that the inorganic fillers used are SiO2, TiO2 and ZrO2 obtained by sol-gel. 5. Method of preparing organic-inorganic phonic exchange hybrid membranes according to claim 2 to 4, characterized in that the inorganic fillers used are lithium fluorosilicates (Li 2 SiF 6), sodium, potassium, rubidium, cesium , ammonium, magnesium, calcium, barium, copper (II) and manganese (II); Fluoroborates such as sodium (NaBF4), fluorotitates, such as Na2 TiF6 or fluorozirconates such as Na2ZrF6. 6. Method of preparing organic-inorganic hybrid phonic exchange membranes according to claim 2 to 5, characterized in that the content of inorganic fillers used is between 0.1 and 50% by weight. 7. Method of preparing organic-inorganic ion exchange hybrid membranes according to claim 2 to 6, characterized in that the forming is carried out at a temperature between 50 and 80 ° C for a time of less than 60 minutes, by demolding them by immersion in a bath of Water. 8. Use of the membranes defined in the previous claims as separator and solid electrolyte in electrochemical devices such as sensors and separators gases, etc. 9. Use of the membranes defined in the previous claims as proton exchange membranes in fuel cells.