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INVENTION
Russian Federation Patent RU2230402

FUEL CELL solid polymer electrolyte MEMBRANE AND METHOD FOR MANUFACTURING THEREOF

FUEL CELL solid polymer electrolyte AND METHOD
MANUFACTURING MEMBRANE FOR HIM

Name of the inventor: Bobrova LP (RU); Timofeev SV (RU); Fateev VN (RU); Porembsky VI (RU); Lyutikova EK (RU)
The name of the patentee: Russian Research Center "Kurchatov Institute"
Address for correspondence: 123182, Moscow, pl. Kurchatov 1, RRC "Kurchatov Institute"
Starting date of the patent: 2002.09.27

The invention relates to the field of chemical current sources, in particular in fuel cells with solid polymer electrolyte.

Said invention is to increase the stability effect of reducing ohmic losses and decrease in the membrane voltage corresponding to the fuel cell growth. For this purpose, a fuel cell, wherein the system for maintaining water balance in the solid polymer electrolyte is carried out by using a membrane of a solid polymer electrolyte with hollow channels, which are constructed as hollow tubes from a material having ion conductivity similar to the ionic conductivity of the membrane material, the outer diameter less than the thickness of hollow tubes the membrane, and mechanical strength of the material of the hollow tube is higher than the mechanical strength of the membrane material. The hollow tubes are arranged closer to the membrane in the fuel cell and the anode in contact with the water reservoir located at the top and / or bottom of the fuel cell.

DESCRIPTION OF THE INVENTION

The invention relates to the field of chemical current sources, in particular in fuel cells with solid polymer electrolyte.

Membrane resistance of the solid polymer electrolyte (such as perfluorinated sulfonic acid functional membrane type Nafion - trademark of Du Pont Company) used in the fuel cell with a solid polymer electrolyte depends essentially on the water content in the membrane. With decreasing moisture resistance of the membrane increases, the ohmic losses in the membrane and decreases the voltage on the fuel cell, i.e. decreases its efficiency.

Reducing the moisture content, particularly in that part of the membrane that is adjacent to the anode, is a natural process that accompanies the operation of the fuel cell. It is due to the fact that hydrogen ions from the anode to transferring the cathode during operation of the fuel cell is transferred together with a few water molecules. Consequently, the greater the current density, the more intense is the draining of the anode region of the membrane. This reduces the current density at a given voltage, which can be regarded as instability and the fuel cell (voltage decrease with time), particularly at high current densities.

To solve this problem (increasing current density) is used in a fuel cell supplying humidified hydrogen to the anode, as described, for example, in M. Wakizoe, O. Velev, S. Srinivasan "Analysis of proton exchange membrane fuel cell performance with alternate membranes "Electrochimica Acta No 30, v.3, pp.335-344, 1995, is well justified in a single cell with a small linear dimensions. In the case of multi-cell battery with cells larger feeding humidified hydrogen does not ensure uniform distribution of water vapor in the battery cells and, moreover, the control and regulation of the necessary changes in pressure of water vapor in hydrogen as a function of current density (particularly with frequent changes of the current density) is technically a very difficult task.

Known fuel cell systems in maintaining water balance of the solid polymer electrolyte, described in U.S. Patent №5503944, 2 April 1996, in which the passive control is provided by moisture supply from the water cooling system of the cathode in the fuel cell and the water from the water cooling system to the anode through a finely porous plate due to the pressure difference between the gases and the reagent cooling water system. However, a system for maintaining water balance, as described in the patent is very complex, in particular due to the need to provide the required differential pressure between the reactants and the water coolant. In addition, contact with both water coolant gases reagents increases fire and explosion risk of a fuel cell by increasing the probability of mixing of gases.

Known fuel cell with a solid polymer electrolyte, described in U.S. Patent №5472799, MKI H 01 M 8/10, 5 December 1985, at a cathode current collector, a cathode in contact with a current collector, an ion exchange membrane having a catalyst layer and an anode contacting it with the anode current collector. The catalytic layer is electrically isolated from the current collector and is located closer to the cathode than the anode. As a material for the ion-exchange membrane of Nafion was used - a trademark of Du Pont. The catalytic layer consists of platinized carbon particles or platinum.

The advantage of this fuel cell is that the catalytic layer prevents a decrease in the cell voltage due to mutual diffusion of gases to the opposite electrodes as diffusing gases react with each other to produce water on the catalyst of the catalytic bed. The resulting water can provide the necessary humidification of the membrane and the electrode (particularly the anode) and the required low ohmic resistance of the electrodes and membranes.

Said fuel cell operates stably over 100 hours (current density of 1 A / cm 2, voltage of 80 mV at 610-655 0 C) when used as reactants humidified hydrogen and oxygen de-moisturized at atmospheric pressure.

The disadvantage of this fuel cell is a solid polymer electrolyte is to increase the flow of platinum metals, as they are used for the manufacture of the catalyst bed. Fuel cell applications require humidified hydrogen and, as gas diffusion rate and hence rate of water formation and does not depend on the current density, depending on the operating mode (specifically, current density) will require a different degree of hydration of hydrogen. This fuel cell does not provide stability in the presence of hydrogen impurities (such as CO) characteristic of most available hydrogen produced by conversion of organic fuel (natural gas, gasoline, methanol).

The closest to the claimed fuel element fuel cell is described in U.S. Patent №5529855, MKI H 01 M 8/10, H 01 M 8/02, 25 June 1996 which describes the structure of the fuel cell for humidifying the membrane of a solid polymer electrolyte and a method for its manufacture. Membrane fuel cell comprises a solid polymer electrolyte comprising one or more hollow transport channels in the bulk or on the surface of the solid polymer electrolyte and serve to provide a solid polymer electrolyte for wetting with water. Hollow Channels prepared by dissolving one or more water-soluble fibers placed in or on the membrane surface. The feed rate of water in the hollow channels controlled pump. The polyvinyl alcohol used as well as a solid polymer electrolyte material as the fibers (diameter 0.05 mm) - Nafion 117. For formation of hollow channels inside the two pieces of Nafion membrane 117 placed between them with the fibers compressed at a pressure of 50 kg / cm 2 and a temperature of 150 0> C. Polyvinyl alcohol is dissolved by treatment in water at 90 0> C, after which the membrane was treated with a solution of sulfuric acid to convert the membrane in the proton form.

The advantage of this fuel cell is lower membrane resistance, constitutes about 2/3 of the resistance of the membrane of the same material, but with a "standard" humidification by supplying humidified gases. This leads to a corresponding reduction in ohmic losses and higher stresses in the fuel element. Efficiency of the membrane and its moisture resistance is not dependent on the presence of carbon monoxide in hydrogen and / or the presence of other catalyst poisons.

The disadvantage of this fuel cell is that a fuel cell, said membrane can not use large forces pressing collector current to the membrane, resulting in a fuel cell has a large internal ohmic resistance due to the large contact resistance of the membrane coated with a catalytic layer and the collector current. Furthermore, during prolonged operation of the membrane with hollow channels obtained in this way, there is a reduction in their diameter and total disappearance by plastic deformation and flow of the polymer material, i.e. duration of effect of lowering the resistance of the membrane obtained according to the patent, is small. This is because in the multi-cell battery actually used in practice during the operation, the pressure on the collector current reaches the surface of the membrane high (several tens of kg / cm 2) and temperatures sufficient for this process (the temperature in the bulk of the membrane reaches 90-100 0 > C). As a result, the effect of moisture and reduce membrane resistance achieved by forming the channel disappears within a relatively short period of time - 200 hours. If the channels are formed on the surface of the membrane, they would not only disappear due to plastic deformation, but also degrade the contact of the membrane with a catalyst layer and a collector current, as shown by studies conducted by the present inventors, leading to a reduction in voltage on a cell.

The technical result that ensures achievement of the inventive fuel cell is a solid polymer electrolyte, is to enhance the effect of reducing the stability of the ohmic losses and decrease in the membrane voltage corresponding increase in the fuel element.

Said technical result is achieved in that a fuel cell with a solid polymer electrolyte membrane comprising a solid polymer electrolyte with hollow channels, wherein the channels are formed as hollow tubes from a material having ion conductivity similar to the conductivity of the membrane material.

Wherein the outer diameter of the tubes should be less than the thickness of the membrane, and a hollow tube located within the membrane closest to the anode. and the mechanical strength of the hollow tubing material should be higher than the mechanical strength of the membrane material. Furthermore, the hollow tube in contact with the water reservoir located at the top and bottom (or only the top or only the bottom) of the fuel cell, depending on the operating conditions of the fuel cell.

A method of manufacturing a fuel cell of a solid polymer electrolyte comprising forming hollow channels in the membrane of the solid polymer electrolyte by incorporating a hollow tube membrane volume. When this membrane with hollow tubes produced by applying the solution on the ion exchange copolymer substrate with hollow tubes positioned therein. When this solution is applied in several steps with intermediate drying at a temperature of 20-80 0> C. In this case the mechanical strength of the hollow tube material is higher than the mechanical strength of the base material of the membrane, which is achieved by using tubes for the same copolymer as that of the membrane, but with a higher equivalent weight. Thus tubes of heat treatment temperature exceeds the processing temperature of the membrane. Let us consider, thereby reach a higher technical result. The membrane introducing hollow tube of a material having ion conductivity similar to the conductivity of the membrane material. This ensures a good adhesion of the membrane material to the hollow tubes. Open ends of hollow tubes in contact with the water in the tank at the top of the fuel cell. Water from the reservoir is fed by gravity into the hollow tube, and further diffuses through the wall material of the membrane while maintaining the necessary humidity of the membrane. The outer diameter of these hollow tubes less than the thickness of the membrane. In that case, if the diameter of the hollow tube is larger than the thickness of the membrane, they will act on the membrane surface and degrade the membrane contact with a current collector. The tubes are arranged in the membrane near the anode, which provides a more efficient supply of water of anode side of the membrane which is dried more, compared with the cathode part. In this hollow tubes have a higher mechanical strength than the material of the membrane, whereby if the battery compression efforts fuel cell operating pressures and the current collector on the surface of the membrane with catalyst tubes diameter reduction does not take place, because primarily the deformation of the membrane material, and consequently, deterioration in membrane water occurs.

The hollow tube may be produced, for example, by wet-spinning a copolymer solution by feeding it through a die into a precipitation bath. The resulting hollow tube (a hollow fiber) before manufacturing the membrane is subjected to heat treatment at a temperature of 110-150 0> C, that it provides a higher mechanical strength (in particular, a higher resistance to squeezing) compared to the membrane.

As the copolymer for hollow tubes and membranes can be used perfluorinated ion exchange hydrolysed copolymer of tetrafluoroethylene with a vinyl ether perftorsulfosoderzhaschim (VSGE TFE) copolymer of the type to be used in the membranes of Nafion, having equivalent weight 900-2600, by the following structural formula

where m = 64,9-95,5 mol.%;

n = 4,5-35,1 mol.%;

M = H, Na, K or Li.

Moreover, it is preferred that the copolymer used for preparing the membrane had an equivalent weight greater equivalent weight of the membrane that provides higher mechanical strength of the hollow tubes and prevents their deformation.

The copolymer may contain a third modifying comonomer, for example perfluoro-2-methylene-4-methyl-1,3-dioxolane perfluoroolefins (from C 1 -C 3 alkyl).

Preparation of a fuel cell with a membrane with hollow tubes involves placing the hollow tube (and the optimum number of tubes is defined as a mode of operation of the fuel cell, and the dimensions of the membrane) on the smooth surface - a substrate, such as glass, and the subsequent application of the above copolymer solution in isopropyl alcohol, ethyl alcohol dimethylformamide or copolymer with a concentration of 1-15 wt.%, depending on the desired thickness of the membrane, the hollow glass tubes. The step of applying the solution is performed in several steps with intermediate drying at temperatures of 20-80 0> C to obtain the desired thickness of the membrane. Then the resulting membrane with hollow tubes are dried by heat treatment at 80-100 0> C for 4-6 hours to remove the organic solvent. Then the membrane treated with 1 M solution of sulfuric acid at room temperature for 20-30 minutes to convert sulfonate groups in the proton form and was washed 3-4 times with deionized water to remove the sulfuric acid. Then on the membrane surface coated electrocatalyst - platinum on carbon with platinum content of 10-30 wt.%.

example 1
Hollow tubes of TFE copolymer VSGE in proton form with an equivalent weight of 1150, an outer diameter of 60 mm, heat-treated at 140 0> C for 20 minutes, put on a smooth glass substrate at a distance of 0.9-1.1 mm. Thereafter, the substrate stacked tubes layers 5 layers with intermediate drying in air at 45 0> C, is sprayed 8% TFE VSGE copolymer solution in proton form with an equivalent weight of 1100 with isopropyl alcohol to obtain a membrane thickness of 180 micron meters. The resulting hollow tube membrane was heat treated at 100 0> C for 20 min. The resulting membrane tubes located closer to the surface lying on the glass (in the cell, this surface is located closer to the hydrogen electrode - the anode). After that the membrane coated on both sides with electrocatalyst particles (20% platinum on carbon black) of a 1% solution of TFE copolymer VSGE in the proton form of a spray. The catalytic layer is dried at 80 0> C in air Visible (geometric) surface of the catalyst layer was 5 cm 2. The resulting electrocatalyst membrane was washed with 10% sulfuric acid at room temperature, and distilled water at 90 0> C. The membrane was then placed between two porous carbon-graphite material from the collector (cloth TMP-5 with particulate sublayer) and placed in a cell of a fuel cell, having the top of the water tank, which are contacted with the open ends of the tubes. Side of the membrane, which are located closer to the tube is contacted with an oxygen chamber of the fuel cell. Pressure on the current collector membrane is 40 kg / cm 2.

The hydrogen is used as fuel, the resulting water electrolysis in an electrolytic cell with a solid polymer electrolyte (without special drying) and as oxidizer - obtained in the same electrolytic cell and dried over silica gel oxygen. The temperature of the fuel cell 85 0> C, the current density - 1 A / cm 2.

Resistance 1 cm 2 of the membrane with catalytic layer (between the current collectors) is 0.12 ohms, and remains unchanged for 700 hours.

example 2
The same as 1, but hollow tubes made from copolymer of TFE VSGE in proton form with the third modifying comonomer - perfluoroolefins C 2 alkyl with an equivalent weight of 1100, and a similar copolymer used to prepare the membrane, but with an equivalent weight of 1000. The heat treatment is conducted at a hollow tubes 110 0> C and the resultant membrane - at 85 0> C. The hollow tubes are arranged at a distance of 0.8-1.0 mm. The solution is applied in 6 copolymer layers with intermediate drying at 75 0> C. The two membranes thus obtained were pressed under a pressure of 50 kg / cm 2 at a temperature of 100 0> C, and is installed between the fuel cell current collectors.

Resistance 1 cm 2 of the membrane with catalytic layer (between the current collectors) is 0.26 ohms, and remains unchanged for 700 hours.

Example 3 (prototype)
According to example 1 a prototype two membrane 180 microns thick, prepared from a copolymer of TFE VSGE in proton form with the third modifying comonomer - perfluoroalkyl vinyl ether to C 2 alkyl with an equivalent weight of 1000 (as described in Example 1 of the present specification) with spaced between polyvinyl alcohol fibers, pressed at 150 0> C at a pressure of 50 kg / cm 2. Polyvinyl alcohol fibers Diameter - 60 mm, the distance between the fibers - 0.8-1.0 mm. The thus obtained "dual membrane" fuel cell is clamped into the cell and treated with water (90 0> C) until the complete removal of the polyvinyl alcohol. The membrane was then treated with 1 -normal sulfuric acid to be transferred in the proton form. The electrocatalyst is applied as described in Example 1 of the present invention. The resulting electrocatalyst membrane was washed with 10% sulfuric acid at room temperature, and distilled water at 90 0> C. The membrane was then placed between two porous carbon-graphite material from the collector (cloth TMP-5 with particulate sublayer) and placed in a cell of a fuel cell, having the top of the water tank, which are contacted with the membrane in the cavity formed by removing the polyvinyl alcohol. Pressure on the current collector membrane is 40 kg / cm 2.

The hydrogen is used as fuel, the resulting water electrolysis in an electrolytic cell with a solid polymer electrolyte (without special drying) and as oxidizer - obtained in the same electrolytic cell and dried over silica gel oxygen. The temperature of the fuel cell 85 0> C, the current density - 1 A / cm 2.

Resistance 1 cm 2 of the membrane with catalytic layer (between collector current) increases slowly and is 0.32 ohms after 700 hours.

Thus, the claimed fuel element allow for comparison with the prototype make the effect of reducing ohmic losses in the membrane stable, which, in turn, will provide a higher fuel cell efficiency (higher increase in voltage on a cell) in a wide range of operating current densities, and provide an opportunity to reduce requirements for water content in the oxidizer and fuel.

CLAIM

  1. A fuel cell with a solid polymer electrolyte, comprising an anode, a cathode and a membrane of solid polymer electrolyte with hollow channels, wherein the channels are in the form of hollow tubes made of a material with the same ion conductivity as the conductivity of the membrane material, and mechanical strength greater than the mechanical strength of the membrane material.

  2. A fuel cell with a solid polymer electrolyte according to claim 1, characterized in that the outer diameter of the hollow tube is less than the thickness of the membrane.

  3. A fuel cell with a solid polymer electrolyte according to claim 1, characterized in that the hollow tube in the membrane are arranged closer to the anode than to the cathode of the fuel cell.

  4. A fuel cell with a solid polymer electrolyte according to claim 1, wherein said hollow tube connected to the water reservoir located at the top and / or bottom of the fuel cell.

  5. A fuel cell with a solid polymer electrolyte according to claim 1, characterized in that hollow tubes made, for example, ion exchange copolymer.

  6. membrane manufacturing method for a fuel cell with a solid polymer electrolyte comprising forming a hollow channel in the membrane of the solid polymer electrolyte, wherein said membrane is formed by applying a protonic form of a solution of ion exchange copolymer onto the substrate disposed thereon hollow tubes subjected to a preliminary heat treatment and complied copolymer of ion exchange, and from which the membrane is made, but with a higher equivalent weight.

  7. A method of manufacturing a membrane for a fuel cell with a solid polymer electrolyte according to claim 6, characterized in that the ion exchange polymer solution is applied in several layers with intermediate drying at 20 0> C.

  8. A method for manufacturing a membrane for a fuel cell with a solid polymer electrolyte according to claim 6, characterized in that the membrane is heat treated at a lower temperature than the temperature of the heat treatment of the hollow tubes.

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Publication date 05.11.2006gg