RU2563029C2 - Method of preparing membrane-electrode units - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to fuel cells, particularly a membrane-electrode unit for a solid-polymer fuel cell, as well as a method for preparation thereof and a composition. Described method of preparing a membrane-electrode unit is characterised by that the method comprises spraying catalytic inks on a cathode of a membrane-electrode unit using an air brush at high temperature, followed by pressing the membrane-electrode unit between teflon discs. The catalytic inks have the following composition: concentration of organic substance - not higher than 70 vol %; mass of Pt/C catalyst - 0.3-60 mg; content of Pt in the Pt/C catalyst - 10-60 wt %; content of ionomeric binder - 0.03-40 mg; content of porous material - not more than 20 mg.

EFFECT: preparation of efficient cathode electrodes with Pt/C catalysts and ultra-low platinum load for a solid-polymer fuel cell.

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Description

The invention relates to the field of fuel cells (TE), in particular to a membrane-electrode block (OIE) for a solid polymer fuel cell (TPTE), as well as to a method for its manufacture and composition.

On porous electrodes (anode and cathode) containing catalysts (mainly platinum), mounted on a proton-conducting polymer membrane, electrochemical reactions of oxidant reduction and fuel oxidation occur. As a result, the energy stored in chemical bonds goes into electrical energy, which is then used as an energy source. Oxygen or air can be used as an oxidizing agent, and a whole set of organic compounds can be used as fuel, including hydrogen, methanol, ethanol, etc.

Fuel cells of fuel cells are the most effective converters of the energy of chemical bonds directly into electrical energy. The proliferation of fuel cells is constrained by a number of factors, among which the key is the high platinum content in the catalyst, the cost of which is up to 30% of the cost of fuel cells.

The effectiveness of a fuel cell depends on many factors. First of all, from the degree of use of platinum in the cathode catalyst, the efficiency of removal of reaction products (water) from the reaction zone and the supply of reagents (fuel and oxidizer) to the active component throughout the cathode electrode layer, the degree of bond strength of the electrode with the membrane, and also from the efficiency of the proton and electron transfer along the electrode layer.

As cathodic catalysts, the most effective are supported platinum supported catalysts. As a result, with a decrease in the loading of platinum (from ordinary 200 μg _Pt / cm ² to 2-10 μg _Pt / cm ² ), the weight of the deposited catalyst is significantly reduced, which leads to a decrease in the thickness of the electrode layer (from 10 to 2 μm). The low thickness of the electrode layer leads to a deterioration in the removal of reaction products (water) from the electrode layer, as a result of which the active component either does not work or is unstable.

Another problem is the limited ability to use platinum catalysts supported on other types of carbon carriers, for example carbon-carbon carriers of the Sibunit type. Due to the morphological characteristics of such carriers, the adhesion of the resulting electrode layer to the proton-conducting polymer membrane is insufficient and the strength of such a compound is low and does not allow the use of these catalysts in the reaction.

To increase the efficiency of the OIE for TE, various materials are added to the electrode layer in order to improve mass transfer along the electrode layer.

Known (RU 2421849, H01M 4/88, 06/10/2011) is a method of manufacturing a catalytic material for a fuel cell, which includes the simultaneous deposition of graphite and platinum on a substrate, removing the resulting composite layer from the substrate in the form of a powder, mixing it with carbon nanotubes in a mass ratio 1: (1-2), adding to the resulting solid mixture of isopropanol in an amount of 0.1-0.3 ml per 1 mg of the solid mixture and Nafion in the amount of 1 mg per 2.3-4.0 mg of the solid mixture and homogenizing the resulting catalytic material in an ultrasonic bath. The disadvantage of this method is the difficulty of preparation and the high consumption and loss of expensive platinum catalyst when spraying on a substrate and the subsequent removal of the composite layer in the form of a powder.

Known (RU 2456717, H01M 4/88, 20.07.2012) is a method of forming a catalytic layer of a solid polymer fuel cell, comprising treating multi-walled carbon nanotubes with a gas plasma in an inorganic gas or a mixture of inorganic gases, followed by their treatment with concentrated nitric acid, washing and drying. The obtained multi-walled carbon nanotubes with platinum carbon black containing 20-40 wt.% Platinum, mixed with isopropanol and an aqueous Nafion solution, taken in a certain ratio, are treated with ultrasound for 30-60 minutes and sprayed onto it heated to a temperature of 70-90 ° C proton-conducting membrane based on perfluorinated sulfopolymer. The disadvantage of this method is the inability to use low loading of platinum due to the reduction of the thickness of the electrode layer.

Known (JP 2008311154, H01M 4/86, 12/25/2008)) a method of increasing the conductivity of the electrode layer by using a mixture of Pt / C catalyst, carbon fibers and a conductive polymer having high conductivity. To increase the mechanical strength of the OIE, a mixture of Pt / C catalyst and carbon fibers with a thermosetting resin was used. Since voids in the catalyst layer communicate with each other by entangling the carbon fibers, the catalyst layer has a high ability to diffuse gas. Thus, the conductivity, gas diffusion and mechanical strength of the catalyst layer are increased, such a layer can also be considered as gas diffusion, and there is no need to use a separate gas diffusion layer. The disadvantage of this method is the reduction of proton conductivity in the layer.

There is a known (RU 2208271, H01M 8/10, 07/10/2003) method for additionally introducing fluoroplastic particles into the electrode layer of agglomerates with an agglomerate concentration per unit volume of the active layer from 0.2 to 0.65 vol.%, As well as the fulfillment of the condition when the diameter agglomerates and catalyst particles on a carbon support do not exceed 3 microns. However, this reduces the electronic conductivity in the layer.

Known (RU 2360330 H01M 4/86, 06/37/2009) a method of preparing a hydrophobic catalyst layer formed from a catalyst obtained by reduction of platinum oxide; hydrophobic agent and proton conductive electrolyte, and the hydrophobic agent consists mainly of alkylsiloxane. The disadvantage is the decrease in proton conductivity in the layer.

Known (RU 2414772, H01M 4/86, 10.11.2010) a method for improving the structure of gas diffusion electrodes. According to the invention, the gas diffusion electrode comprises: a) at least one gas diffusion medium, b) at least one catalyst layer on top of said gas diffusion medium, containing at least one supported catalyst and c) at least one catalyst layer without a carrier on top of the catalyst layer on the carrier indicated above in b), said catalyst layer without a carrier having a higher overall catalyst loading. The disadvantage of this method is the inability to reduce the loading of platinum in the layer.

Known (CN 102110819, B01J 23/62, 06/29/2011) a method for adding a catalyst promoter to a catalytic layer consisting of TiO ₂ modified with nitrogen and other metal oxides. The disadvantage is the decrease in proton conductivity in the layer.

The closest analogue of the claimed method is the ink composition described in the work (EN Gribov, A.Yu. Zinovieva, IN Voropaev, PA Simonov, AV Romanenko, AG Okunev, Int. J. Hydrogen Energy, 2012, vol. 37, pp. 1194 -11903). Ink includes a Pt / Sibunit 1562 catalyst with the addition of a Vulcan XC-72 carbon carrier. Ink is prepared by adding a carbon-supported catalyst to a solution of isopropanol-water (30% vol.), Dispersing the suspension in an ultrasonic bath, adding the required amount of a nafionic binder, dispersing it in an ultrasonic bath and applying it to a proton-conducting polymer membrane. Application is carried out by spraying on a membrane at a temperature of 60 ° C, followed by pressing at a temperature of 120 ° C, pressure 3-5 atm for 2-3 minutes.

The disadvantages of this method include the insufficiently high degree of use of platinum, which leads to the need to increase the load of platinum.

The invention solves the following problems: 1) the possibility of preparing efficient cathode electrodes with Pt / C catalysts and ultra-low platinum loading of up to 6 μg _Pt / cm ² for TPTE; 2) the possibility of preparing OIEs based on Pt / C catalysts having a carbon carrier with various morphological properties, while the electrode has low adhesion to the proton-conducting polymer membrane; 3) the ability to adjust the thickness of the electrode layer to ensure the most efficient mass transfer; 4) the ability to increase proton and electronic conductivity in the OIE electrode layer; 5) the possibility of increasing the specific power of the fuel cell per mass of platinum.

The problem is solved by optimizing the composition of the catalytic ink for the TPTE cathode, consisting of a solvent consisting of an aqueous solution of an organic substance, a Pt / C catalyst, an ionomer binder, a porous material with the following components:

The volume of the solution is 100-1000 μl;

organic matter concentration - not higher than 70 vol.%;

the mass of Pt / C catalyst is 0.3-60 mg;

the content of Pt in the Pt / C catalyst is 10-60 wt.%;

the content of ionomer binder is 0.03-40 mg;

the content of porous material is not higher than 20 mg.

As the organic substance, for example, isopropyl alcohol and acetone are used.

As the ionomer binder, a nafion binder or a sulfonated block copolymer of polystyrene and a polyethylene-butylene copolymer is used.

As the carbon support in the Pt / C catalyst, a mesoporous carbon-carbon composite is used.

Carbon nanotubes are used as the carbon support in the Pt / C catalyst.

Carbon nanofibers are used as the carbon support in the Pt / C catalyst.

Carbon black with a high specific surface is used as the carbon support in the Pt / C catalyst.

Soot with a high specific surface is used as a porous material.

A mixture of carbon black with a high specific surface and carbon nanotubes is used as a porous material.

A mixture of soot with a high specific surface and carbon nanofibers is used as a porous material.

The problem is also solved by the method of preparation of the OIE, which consists in hot pressing of the electrode layers with a membrane without the use of gas diffusion layers.

Ink is sprayed by airbrushing on a membrane heated to 60-80 ° C, subsequent pressing of the MEA between Teflon disks is carried out at a temperature of 100-130 ° C, a pressure of 3-5 atm for 3-5 minutes.

The essence of the invention consists in sequential processing of proton-conducting polymer membranes at 80 ° C for 1 h in 1 M H ₂ SO ₄ (s.h.), 1 M H ₂ O ₂ (s.h.) and distilled water . As the anode catalyst, a Pt / C catalyst is used. Cathode inks were prepared as follows. A portion of the Pt / C cathode catalyst was mixed with a porous material, placed in an aqueous solution of organic matter, mixed, sonicated for 25 minutes, mixed again and sonicated for 25 minutes. Then, a dispersion of an ionomeric binder was added to the suspension, mixed and subjected to sonication for 25 minutes. Anode inks were prepared in the same way, but without the addition of porous material. Ink was applied to the proton-conducting polymer membrane by spraying with an airbrush at a temperature of 60-80 ° C. To improve the adhesion characteristics, the obtained MEA with the cathodic and anodic electrode layers was pressed between Teflon sheets at a temperature of 120 ° C, a pressure of 4-5 atm for 1.5 minutes. The obtained OIE was clamped between the anode and cathode GDS and installed in a fuel cell (Electrochem. Inc.). The working surface of the electrodes was 5 cm ² .

The invention is illustrated by the following examples and illustrations.

Example 1

0.312 mg of catalyst 20 wt. % Pt / Vulcan-XC72 (superficial carbon black) is mixed with 7 mg of the porous carbon carrier Vulcan XC-72 and added to 300 μl of a 50 vol.% Solution of isopropyl alcohol in water. The solution is shaken vigorously and dispersed for 25 minutes in an ultrasonic bath. This procedure is repeated twice. Then the required amount of 10 wt. A% Nafion® dispersion (Aldrich) is added to the ink, followed by an ultrasonic bath for another 25 minutes. Ink is sprayed onto a membrane heated at 60-80 ° C. In order to ensure better contact of the membrane with the cathode and anode electrode layers, it is pressed between two Teflon plates at a temperature of 120 ° C, a pressure of 4.5 bar for 1.5 minutes. Before measurements, the catalytic membrane is clamped between the anode and cathode GDL and placed in a fuel cell (Electrochem. Inc.). The working surface of the electrodes is 5 cm ² . The resulting OIE has a high specific power compared to standard catalyst 33 versus 2.8 W / mg _Pt . (Fig. 1)

Example 2

As Pt / C catalyst using 20 wt. % Pt / Sibunit-1562. The weight of the catalyst is 0.625 mg. As the porous material, the commercial carrier Vulcan XC-72 (high surface soot) is used. Its mass was 7.5 mg. As organic matter, acetone is used.

Example 3

As a Pt / C catalyst, 60 wt. % Pt / Sibunit-1562. The weight of the catalyst is 1.67 mg. As the porous material used commercial media Vulcan XC-72. Its mass is 7.3 mg.

Example 4

As a Pt / C catalyst, Pt supported on carbon nanotubes with a platinum content of 20 wt. % The weight of the catalyst is 2.5 mg. As the porous material used commercial media Vulcan XC-72. Its mass is 6.5 mg.

Example 5

As Pt / C catalyst using 40 wt. % Pt / KetjenBlack DJ-600 (high surface soot). The weight of the catalyst is 2.5 mg. As the porous material used commercial media Vulcan XC-72. Its mass is 6.5 mg.

Specific power increased from 3.7 to 4.8 W / mg _Pt (Fig. 2)

Example 6

As Pt / C catalyst using 40 wt. % Pt / Vulcan XC-72. The weight of the catalyst is 2.5 mg. As the porous material, a commercial carbon nanofiber carrier is used. Their mass is 6.5 mg.

Example 7

As Pt / C catalyst using 20 wt. % Pt / Sibunit-1562. The weight of the catalyst is 0.625 mg. As the porous material, the commercial carrier Vulcan XC-72 (high surface soot) is used. Its mass was 7.5 mg. As the ionomer binder, a sulfonated block copolymer of polystyrene and a polyethylene-butylene copolymer is used).

Example 8

It is similar to example 7, but differs in that when pressing is carried out at a temperature of 110 ° C, a pressure of 3-5 atm for 2-3 minutes.

Claims (10)

1. A method of manufacturing a membrane-electrode blocks of the OIE, including the spraying of catalytic ink on the surface of the OIE membrane, heated to a temperature of 60-80 ° C using an airbrush, followed by pressing the OIE between Teflon disks at a temperature of 100-130 ° C, pressure 3-5 atm for 3-5 minutes, characterized in that the catalytic ink has the following composition:
organic matter concentration - not higher than 70 vol. %;
the mass of Pt / C catalyst is 0.3-60 mg;
the content of Pt in the Pt / C catalyst is 10-60 wt. %;
the content of ionomer binder is 0.03-40 mg;
the content of porous material is not higher than 20 mg,
in this case, the catalytic ink is prepared as follows, a weighed portion of the Pt / C cathode catalyst is mixed with a porous material, placed in an aqueous solution of an organic substance, mixed, sonicated, mixed again and sonicated, then an ionomer binder dispersion is added to the suspension, mixed and subjected to sonication. 2. The method according to p. 1, characterized in that as an organic substance is used, for example, isopropyl alcohol, acetone. 3. The method according to p. 1, characterized in that as the ionomer binder use a nafionic binder or sulfonated block copolymer of polystyrene and a copolymer of polyethylene butylene. 4. The method according to p. 1, characterized in that the mesoporous carbon-carbon composite is used as the carbon support in the Pt / C catalyst. 5. The method according to p. 1, characterized in that carbon nanotubes are used as the carbon support in the Pt / C catalyst. 6. The method according to p. 1, characterized in that carbon nanofibers are used as the carbon support in the Pt / C catalyst. 7. The method according to p. 1, characterized in that as a carbon carrier in the Pt / C catalyst, carbon black with a high specific surface area is used. 8. The method according to p. 1, characterized in that as a porous material using carbon black with a high specific surface area. 9. The method according to p. 1, characterized in that as a porous material using a mixture of soot with a high specific surface area and carbon nanotubes. 10. The method according to p. 1, characterized in that as a porous material using a mixture of soot with a high specific surface area and carbon nanofibers.

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