RU2751535C2 - Membrane-electrode fuel cell block with polymer membrane - Google Patents

Abstract

FIELD: electrical engineering.SUBSTANCE: invention relates to the field of electrical engineering, namely to the membrane-electrode block (hereinafter – MEB), mainly for low-temperature fuel cells with an organic solid polymer membrane. The membrane is tightly clamped over its entire surface between the electrodes made of a strong carbon-graphite material. Sealing gaskets located on the peripheral part of each electrode are made from the gas supply side. The membrane is applied in any known way to the surface of one or two electrodes, followed by their connection (by pressing) with each other. To create an improved gas density of the membrane and its electrochemical parameters, it is proposed to use multilayer membranes using a suspension of various ionomers. It is also proposed to made the peripheral part of the membrane, located outside the core, by applying a suspension of non-conductive material that does not deform when the membrane is moistened.EFFECT: technical result of the invention is an increase in the resource indicators and reliability of the MEB operation.5 cl, 3 dwg

Description

The invention relates to the field of power plants on fuel cells, namely to a fuel cell stack and its main component - a membrane-electrode unit (MEA) of predominantly low-temperature fuel cells with an organic gas-tight proton-conducting polymer membrane (hereinafter referred to as the membrane).

It is known (see Lidorenko NS, Muchnik GF Electrochemical generators. - M: Energoizdat, 1982) that the MEA consists of two electrodes (anode and cathode) separated by a membrane. Electrodes containing a platinum-based catalyst undergo electrochemical reactions of fuel oxidation (at the anode) and reduction of the oxidant (at the cathode). The fuel used is hydrogen or its mixtures with gases that are not poisonous for the catalyst. Liquid fuels such as methanol, formic acid, etc. can also be used. Oxygen is used as an oxidizing agent, either pure or in the air. The transfer of positive charges (protons) formed at the anode to the cathode is realized through the membrane. Equal transfer of negative charges (electrons) from the anode to the cathode goes through an external circuit. As a result of the reaction, we obtain electrical energy, which is realized on the payload.

The role of the membrane is to effectively separate the electrodes, excluding both direct reaction of reagents (fuel and oxidizer) and direct contact of the electrodes. The membrane must have:

- high proton conductivity;

- lack of electronic conductivity;

- gas tightness (gas tightness);

- chemical stability;

- mechanical (fatigue) strength.

Without these qualities, it is difficult to expect good current-voltage and resource characteristics of the fuel cell. Meanwhile, from domestic and foreign sources are known (see N.V. Korovin, Electrochemical Energy. - M .: Energoatomizdat, 1991; Fuel Cell Handbook (Seventh Edition) US Department of Energy, November 2004) fuel cell designs in which the membrane is not only performs the above function, but also serves as a separator of gaseous media and is under the influence of the pressure difference between the fuel and the oxidizer, i.e. is the supporting structure of the OIE. At the same time, it must withstand the pressure drops of the reagents, which are especially dangerous along the periphery of its active part in the area of the seal. To maintain a low level of stress in the membrane under the influence of the differential pressure of the reactants, the membrane must be thick. Obviously, the thicker the membrane, the more reliably and successfully it will perform the functions of the supporting structure of the MEA.

It is also known that:

- the thinner the membrane, the lower the internal resistance of the MEA and, accordingly, the better the current-voltage characteristic and the efficiency of the fuel cell;

- the thinner the membrane, the cheaper it is, and is almost proportional to the decrease in thickness;

- the thinner the membrane, the easier it is to solve the issue of controlling its moisture content, i.e. the most important and difficult issue of operation;

- the thinner the membrane, the better it retains its integrity during periodic deformations associated with the degree of moisture, which can vary greatly during the periods of fuel cell I / O; in this case, a smaller membrane thickness leads to a lower absolute deformation of the membrane and, accordingly, lower forces acting on it, if it is unencumbered by the MEA sealing parts.

Thus, the use of an expensive membrane as the supporting structure of the MEA predetermines the choice of its thickness, as a rule, not less than 50 microns (limited to 25 microns with a reinforcing mesh), instead of, for example, 2-10 microns and, accordingly:

- the cost of the MEA is unreasonably overstated due to the excessive thickness of an expensive membrane;

- significantly (several times) reduced specific power characteristics of the MEA and proportionally overestimated costs due to high internal losses;

- operational difficulties caused by difficult moisture management of the thick membrane;

- mediocre resource and reliability indicators due to the difficulty of maintaining the integrity of the membrane during periodic deformations associated with the degree of its wetting, which can change especially strongly during the periods of the beginning and completion of the operation of fuel cells.

For this purpose, it is proposed to abandon the use of the membrane as the supporting structure of the MEA and assign these functions to one or both electrodes made of durable carbon-graphite material and having a thickness of about 200 microns. At the same time, it is proposed to abandon the use of thin polymer films as independent structural elements, but to apply them in any known way on the surface of one or two electrodes, followed by their connection (pressing) with each other.

Known analogue, taken as a prototype, the design of fuel cells with a polymer membrane. Its experimental sample with a working area of 50 cm ^{2 is} described below (see Lidorenko NS, Muchnik GF Electrochemical generators. - M: Energoizdat, 1982, Fig. 6.19, p. 310).

From the construction of FIG. 1 clearly shows that the sealing of the MEA is carried out with the help of sealing gaskets 3, which are pressed with force against the membrane 1, which is the supporting element of the MEA formed by this membrane pressed onto the electrodes 2.

The same construction is shown in FIG. 2 on a larger scale.

FIG. 1 and FIG. 2 indicates:

1 - gas-tight proton-conducting polymer membrane;

2 - electrodes;

3 - a sealing gasket.

The above diagram of a typical design of the MEA has the following disadvantages:

- the peripheral part of the membrane 1 between the sealing gaskets 3 and the electrodes 2 is under the influence of the pressure difference between the reagents of the fuel and the oxidizer, which can change cyclically during the operation of the MEA;

- to ensure the strength of the membrane 1, it must be thick, which increases its cost and, accordingly, the MEA.

The objective of the invention is to eliminate the above disadvantages, which makes it possible to reduce the cost of the MEA and the fuel cell battery (FFC) and increase their resource and reliability indicators.

The problem is solved due to the fact that the membrane-electrode block of fuel cells with a polymer membrane, consisting of two electrodes made of a porous carbon-graphite material, a gas-tight proton-conducting membrane and the cathode and anode active layers applied to the electrodes or the membrane, have the following differences: , which perceives pressure drops in gas cavities, electrodes are used, with active layers deposited on one or both electrodes, with a membrane enclosed between the electrodes, sealed around the periphery of the membrane-electrode unit.

In addition, the porous electrodes outside the core are gastight on all surfaces.

In addition, a suspension of non-proton-conducting organic matter that does not deform when the membrane is moistened is applied to the membrane outside the core.

In addition, the membrane can be formed by applying a monomer suspension in any known manner to the surface of one or both electrodes and then connecting them to each other.

In addition, the membrane can be made multilayer using a suspension of various ionomers.

The technical essence of the invention is illustrated by a drawing, where FIG. 3 shows the membrane electrode assembly of the fuel cell with the membrane of FIG. 3 where:

1 - gas-tight proton-conducting polymer membrane;

2 - electrodes;

3 - a sealing gasket;

4 - active layer (anodic and cathodic);

5 - specially processed gas-tight end part of the gas diffusion layer.

The membrane-electrode block of a fuel cell with a polymer membrane consists of a gas-tight polymer proton-conducting membrane 1 enclosed (pressed) between the cathode and anode electrodes 2 with active layers 4 applied to them and specially treated end (peripheral) parts 5.

As seen in FIG. 3, according to the proposed technical solution, the MEA seal is provided not along a thin 5-20 micron thick proton-conducting solid polymer membrane 1, but along the end parts of the electrodes 2, which in any known way, for example, a sealing gasket 3 (or glue, rubber, any non-poisonous catalyst and membrane filler) gas tightness is achieved, including the end parts of the active layer 4 and membrane 1.

In this case, as an option, the membrane 1 with a thickness of 5-20 microns is applied to one or both electrodes 2 in the form of a monomer suspension, which forms a dense film after evaporation of the solvent. To create an improved gas tightness of the membrane 1, as well as to improve its electrochemical parameters, it is proposed to use multilayer membranes using a suspension of various monomers. It is also proposed in the manufacture of membrane 1 by applying a suspension of an ioomer, the peripheral part of the membrane 1, located outside the active zone 4, is made by applying a suspension of a non-proton-conducting membrane that does not deform when moistened.

To create gas tightness, porous electrodes 2 are proposed outside the core 4 and, in particular, in the sealing zone of the MEA, compacted (processed) by any known method so as to ensure their gas tightness (gas tightness) on all surfaces, except for the zone of the active layer 4.

The work of the OIE is carried out as follows. Fuel (hydrogen) and oxidizer (oxygen) from the outside are directed to the electrodes 2 (respectively, the fuel - the anode, and the oxidizer - to the cathode), which penetrate through the porous material of the electrodes 2 from both sides to the membrane 1. In the active zone 4 of the membrane 1 occurs spatial transfer of positive charges - protons formed at the anode and absorbed at the cathode during the electrochemical reaction - carried out through membrane 1. Equal current transfer of negative charges - electrons - goes through an external circuit, which includes a payload. To exclude a direct chemical reaction between hydrogen and oxygen, sealing gaskets 3 were used, and a special treatment was applied - sealing the end part of the gas diffusion layer 5 of electrodes 2 outside the active zone 4 of membrane 1.

Thus, the proposed invention, due to tight compression of the membrane between two electrodes over its entire surface and sealing from the side of gaseous media using gaskets along the peripheral part of each electrode, allows increasing the resource and reliability indicators of the MEA, as well as reducing its cost.

Claims (5)

1 Membrane-electrode block of fuel cells with a polymer membrane, consisting of two electrodes made of porous carbon-graphite material, a gas-tight proton-conducting membrane and cathode and anode active layers applied to the electrodes or membrane, characterized in that, as a supporting structure, which perceives pressure drops in gas cavities , electrodes are used, which are sealed around the periphery of the membrane-electrode unit. 2 Membrane-electrode block of fuel cells with a polymer membrane according to claim 1, characterized in that the porous electrodes outside the core are gas-tight on all surfaces. 3 Membrane-electrode block of fuel cells with a polymer membrane according to claim 1, characterized in that a suspension of non-proton-conducting organic matter that does not deform when the membrane is moistened is applied to the membrane outside the core. 4 Membrane-electrode block of fuel cells with a polymer membrane according to claim 1, characterized in that the polymer membrane is formed by applying a suspension of the ionomer by any known method on the surface of the electrodes and then connecting them to each other. 5 Membrane-electrode block of fuel cells with a polymer membrane according to claim 1, characterized in that the proton-conducting membrane is made multilayer using a suspension of various ionomers.

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