RU2504868C2 - Fuel cell and fuel cell battery - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: fuel cell comprises: a polymer membrane, a hydrogen gas-diffusion collector, a air gas-diffusion collector, a polymer frame, a bipolar plate, a hydrogen current collector, a corrugated air current collector and an adhesive-carrying film. The fuel cell battery comprises multiple fuel cells, sealing rings and end plates tied by fastening elements.

EFFECT: weight of the fuel cell battery is reduced 2,5-fold compared to a prototype of the same power and emf owing to lighter weight of the fuel cells; the fuel cell battery is repairable.

7 cl, 13 dwg

Description

The invention relates to the field of chemical current sources with direct conversion of the chemical energy of hydrogen oxidation by atmospheric oxygen into electrical energy, in particular to a fuel cell (TE) and a TE battery (BFC) with a polymer electrolyte membrane.

Known designs of TE and BFC with a metal distribution grid used in TE (US No. 6207310 B1). In accordance with this patent, the BFC consists of at least two FC separated by an electrically conductive thin bipolar cooling plate (BOP). BOP is made of thin metal foil and a metal wicker mesh located in the rectangular region of the frame, having an entrance in one corner and an exit in another, located diagonally to each other. The frame is sealed around the perimeter, forming a flow part for the cooling medium. In the hydrogen and oxygen chambers of the fuel cell, metal grids are also installed each in its own frame, which, like the BOP frame, has input and output channels located diagonally. Grids provide a uniform distribution of reagents on the surface of the electrodes.

MES is a complete assembly unit. The membrane is placed between two stainless steel frames (sheet thickness 0.254 mm) and sealed around the perimeter with adhesive. Gas diffusion electrodes from the hydrogen and oxygen sides are pressed onto the membrane. Mesh current collectors embedded in intermediate gaskets-frames are located on each side of the MES. The channels for supplying reagents to the gas chambers of the fuel cell are made directly in the intermediate gaskets-frames. The TE is sealed in the battery by compressing the intermediate gaskets-frames made of silicone tape reinforced with fabric. The compression ratio of the TE package in the battery is controlled and limited by the limiters provided for in the intermediate framework.

In the variant with a rigid combined polysulfone plastic frame excluding the intermediate gasket-frame, the TE is sealed in the battery with a special adhesive applied to both surfaces of the rigid plastic frame.

Current grid collectors are made of a set of grids with small and large cells. The mesh with small cells is in contact with gas diffusion collectors. The surface of these nets is hydrophobized with a composition of carbon and teflon to prevent water droplets from accumulating in the cells.

The disadvantages of the technical solutions implemented in the analogue are:

- lack of protection of the membrane around the perimeter in the places of sealing and contact of gas diffusion collectors and metal frames from mechanical damage and possible damage,

- concentrated (local) supply / removal of working fluids in the fuel cell, not guaranteeing a uniform distribution of fluids over the surface of the electrodes in a wide range of flow rates,

- "sticking" of water in the cells of the grid current collectors and the formation as a result of this in the grid sections with water-filled cells, eliminating the supply of reagents to the electrodes and leading to a decrease in the efficiency of the electrodes,

- the presence of intermediate gaskets-frames for the placement of grid current collectors, complicating the design of the fuel cell and doubling the number of mating surfaces that require sealing (for the variant with intermediate frames),

- certain restrictions on minimizing the gap in the gas chambers of the fuel cell, associated with the need to form channels that communicate the collector system of the battery with the gas chambers of the fuel cell directly within the fuel cell, subject to the requirements for the strength of the frame and the permissible size of the channels.

Known designs of TE and BFC with a polymer electrolyte membrane, adopted as a prototype of the invention, using hydrogen as fuel and oxygen in pure form, or contained in air as an oxidizing agent (RU, patent No. 2328060, IPC Н01М 8/00, priority November 23, 2006 d). TE and BTE with a polymer electrolyte membrane, using hydrogen and oxygen in its pure form or contained in air.

The fuel cell includes a hydrogen electrode, an oxygen electrode located between the electrodes, a polymer electrolyte, hydrogen and oxygen gas diffusion collectors, current collectors made of metal grids.

Adjacent TEs in the battery are separated by a bipolar cooling plate (BOP) made in the form of a plate heat exchanger made of thin, metal foil and a metal mesh inside to distribute the cooling medium over the surface of the heat exchanger and remove heat generated in the TE. BOP has contact with current collectors and also performs the function of transmitting electricity. TEs with the help of covers and pins are collected in the battery.

Membrane-electrode assembly (MES), in which gas diffusion collectors together with the membrane are embedded in the groove of the polymer frame, composed of two or three plates, protect the membrane from mechanical damage over the entire surface.

The membrane and collectors in the frame are sealed with a sealant placed in the free space of the groove along the perimeter of the membrane beyond the electrodes, and with an adhesive film located in the seal assembly.

The design of the MES framework simultaneously provides for the placement of grid current collectors in it above the gas diffusion collectors. BOP consists of two sheets of thin foil (from the hydrogen and oxygen sides) and metal grids located between them and a frame with channels on the peripheral surface for supply through the BOP and uniform distribution of reagents on the surface of the electrodes. In the rectangular field of the frame, partitions are provided for organizing the flow of the cooling medium through the grids according to the “serpentine” principle.

The disadvantage of the prototype TE are:

1. The complex design of the frame, containing two to three plates, fastened together by an adhesive transfer film.

2. The unreliability of sealing a 50-micron membrane with a sealant, due to the fact that during sealing the membrane is crushed due to its low stiffness, which leads to the formation of leaky MES, ie to marriage.

3. The sealing process is long, the curing of the sealant occurs no earlier than a day after application.

The disadvantage of the prototype BTE are:

1. The complex design of the frame, containing two to three plates, fastened together by an adhesive transfer film.

2. The unreliability of sealing a 50-micron membrane with a sealant, due to the fact that during sealing the membrane is crushed due to its low stiffness, which leads to the formation of leaky MES, ie to marriage.

3. The sealing process is long, the curing of the sealant occurs no earlier than a day after application.

4. Air ducts have a high resistance to air flow due to their small cross-section and long extent, which does not allow BTE to operate at pressures close to atmospheric, and require powerful compressors for pumping air, which leads to an increase in energy consumption for own needs and, as consequence, a drop in battery efficiency.

5. Thermostatic control of the BFC is carried out using plate heat exchangers with coolant circulation, which also worsens the weight and size characteristics and the efficiency of the BFC due to the presence of a circulating liquid pump in the system and the weight of the coolant itself.

6. Unavailability of BFCs and, as a consequence, the impossibility of replacing individual FCs when they fail due to the fact that after the assembly of BFCs, all battery cells are glued together with an adhesive transfer film.

The features of the prototype FCs that match those of the FCs according to the invention: a hydrogen electrode, an air electrode located between the electrodes, a polymer electrolyte (membrane), hydrogen and air gas diffusion collectors, a hydrogen current collector.

The signs of the BTE prototype, coinciding with the signs of the BTE according to the invention:

at least two fuel cells, each of which includes a hydrogen electrode, an air electrode located between the electrodes, a polymer electrolyte (membrane), hydrogen and air gas diffusion collectors, a hydrogen current collector made of metal meshes, an air current collector made of thin corrugated metal tape and a bipolar a plate for separating adjacent fuel cells, made in the form of a thin metal foil.

The technical result of the use of fuel cells are:

1. Simplified frame design.

2. Increased reliability of sealing a 50 micron membrane with sealant.

3. Acceleration of the process of sealing the membrane.

The technical result of using BFCs is to simplify the design and improve the manufacturing technology of FCs and FC batteries, the ability to repair and replace failed FCs, and reduce the weight and size characteristics of the battery by at least two times due to the use of FCs according to the invention.

The overall dimensions of the invention are reduced from 2 to 6 times by reducing the thickness of the BOP from 1.5 mm to 0.1-0.2 mm and cooling it with air, rather than water, as in the prototype.

The list of drawings:

Figure 1 presents a diagram of the fuel cell.

Figure 2 presents the scheme of BFC.

Figure 1 and 2 introduced the notation:

1 - polymer membrane;

2 - hydrogen gas diffusion collector;

3 - air gas diffusion manifold;

4 - polymer frame;

5 - bipolar plate;

6 - hydrogen current collector;

7 - corrugated air current collector;

8 - adhesive film;

9 - holes made in frame 4, designed to supply hydrogen;

10 - channels in the frame 4, connecting the holes 9 with the window of the frame and designed to supply hydrogen;

11 - sealing rings;

12 - end plates;

Figure 3 presents a sketch of the corrugated air current collector.

Figure 4 presents a sketch of the polymer frame.

Figure 5 presents a sketch of a bipolar plate.

Figure 6 presents a sketch of a hydrogen gas diffusion collector.

Figure 7 presents a sketch of an air gas diffusion manifold.

On Fig presents a sketch of the membrane.

Figure 9 presents a sketch of a hydrogen current collector.

Figure 10 presents a sketch of the sealing ring.

Figure 11 presents a sketch of the end plate of the BFC.

On Fig presents a schematic diagram of a fuel cell.

On Fig presents TE with an ion-exchange membrane.

The technical result of using the TE according to the invention is achieved due to the fact that it contains: a polymeric membrane 1, a hydrogen gas diffusion manifold 2, an air gas diffusion manifold 3, a polymer frame 4, a bipolar plate 5, a hydrogen current collector 6, a corrugated air current collector 7, an adhesive transfer film 8 , holes 9, channels 10 for communicating holes in the frame with the frame window (Fig. 1).

Polymer membrane 1, its material: ion exchange membrane Nafion or MF4-SK. Dimensions - according to the external dimensions of the frame 4 of figure 1. Appointment: for gas separation and current transmission. Mounted on the frame 4 of figure 1. on the opposite side of the channels 10 of figure 1 on the adhesive film 8.

Hydrogen gas diffusion collector 2, its material: carbon-graphite paper. Dimensions of the hydrogen collector - the size of the window frame 4 of figure 1. Appointment: the carrier of electrocatalytic layers, permeable to hydrogen, and current transfer. Installed in the window frame 4 of figure 1 with an electrocatalytic layer to the membrane.

Air gas diffusion collector 3, its material: carbon-graphite paper. The dimensions of the air manifold - the width of the frame 4 of figure 1. The collector 3 is a carrier of electrocatalytic layers, permeable to oxygen and current transfer. It is mounted on the membrane on the opposite side from the hydrogen gas diffusion collector with an electrocatalytic layer to the membrane.

The polymer frame 4, its material is polycarbonate or other plastic, for example, silicone rubber. Purpose: for fixing a hydrogen gas diffusion collector, a hydrogen current collector, a membrane and a bipolar plate 5.

Bipolar plate 5, its material, for example, titanium foil. Dimensions of the external dimensions of the frame 4 of figure 1. Appointment: for separation of adjacent TE and current transmission. It is mounted on an adhesive-transfer film to the frame 4 of Fig. 1 of one TE and is electrically in contact with the corrugated air current collector of the adjacent TE.

The hydrogen current collector 6, its material, for example, a titanium expanded metal mesh in two or more layers. Dimensions - the size of the window frame 4 of figure 1. Purpose: for supplying hydrogen to a gas diffusion hydrogen collector and for transmitting current. Mounted in frame 4 of figure 1 between the hydrogen gas diffusion manifold and the bipolar plate.

The corrugated air current collector 7 is made of a corrugated thin metal tape, for example, of titanium foil, 0.05-0.25 mm thick. The dimensions of the collector correspond to the external dimensions of the frame 4 of figure 1. Appointment: current transmission and ensuring the passage of cooling air to the air gas diffusion manifold. By changing the intensity of the air purge, the fuel cell is cooled. It is installed between the bipolar plate and the air gas diffusion manifold.

Adhesive film 8, for example, type Scotch® ATG.

Holes 9 in frame 4 for supplying hydrogen with a diameter of 3 to 20 mm (the diameter of the holes depends on the overall dimensions of the frames and the number of MES in the battery).

The channels 10 in the frame 4, are designed to communicate the holes 9 of the frame 4 with the frame window. Their width can vary from 1 to 4 mm, and a depth of 0.5 mm or more, depends on the thickness of the frame material.

The technical result of using the BFC according to the invention is achieved due to the fact that it contains two or more TE according to the invention, O-rings 11 and end plates 12, tightened by fasteners, for example, studs.

O-rings 11, the material is rubber, for example fluororubber.

Purpose: for sealing channels between adjacent frames 4.

End plates 12, their material is metal or hard plastic. Appointment: for fastening of TE in BTE with the help of fasteners, for example, threaded rods.

All other elements of the BFC are part of the fuel cell.

Description of the design of BTE (figure 2)

BTE includes a monolithic polymer frame, a hydrogen electrode with a gas diffusion layer, an air electrode with a gas diffusion layer located between the electrodes, a polymer electrolyte (membrane), a hydrogen current collector from a metal mesh, and an air current collector made by corrugating from a thin metal foil. Adjacent FCs in the battery are separated by a bipolar plate (BP) made in the form of a thin metal foil. BP has electrical contact with current collectors and also performs the function of transmitting electricity. TEs with the help of end plates and pins are assembled into a TE battery. Features of the invention are: MES, in which a hydrogen electrode with a gas diffusion layer, together with a hydrogen current collector made of a metal mesh, is embedded in a window of a monolithic polymer frame.

The membrane is sealed to the outer surface of the frame using adhesive film without the use of sealant. On the opposite side of the frame, a bipolar plate is glued with an adhesive film. On the outside, an air electrode with a gas diffusion layer and a corrugated air current collector are adjacent to the membrane. Their sizes coincide with the outer dimensions of the frame. Seals of the channels for supplying hydrogen are carried out by elastic sealing rings. Thanks to this design, it is possible to partially disassemble the battery along the abutment lines of air current collectors to bipolar plates and replace a failed fuel cell or fuel cell group. The channels of the air current collector are open from two sides, communicate with the atmosphere, and have practically zero resistance to the flow of air flow, which allows maintaining the thermal regime of the fuel cell and battery, changing the amount of air blown through the fuel cell and battery.

The principle of operation of fuel cells

The fuel cell (Fig. 12) consists of two electrodes separated by an electrolyte and fuel supply systems on one electrode and an oxidizing agent on the other, as well as a system for removing reaction products. In most cases, catalysts are used to accelerate the chemical reaction. An external electrical circuit of the fuel cell is connected to a load that consumes electricity.

In the acidic electrolyte fuel cell shown in FIG. 12, hydrogen is supplied through the hollow anode and enters the electrolyte through very small pores in the electrode material. In this case, hydrogen molecules decompose into atoms, which, as a result of chemisorption, each giving one electron each, turn into positively charged ions. This process can be described by the following equations:

H ₂ ⇔ 2H

2H⇔2H ⁺ + 2e ^- .

Hydrogen ions diffuse through the electrolyte to the positive side of the cell. Oxygen supplied to the cathode passes into the electrolyte and also reacts on the electrode surface with the participation of a catalyst. When it is combined with hydrogen ions and electrons that come from an external circuit, water is formed:

_^1/2 O ₂ ⁺ 2H + + 2e ^- → H ₂ O.

Similar fuel reactions occur in alkaline electrolyte fuel cells (usually concentrated sodium or potassium hydroxides). Hydrogen passes through the anode and reacts in the presence of a catalyst with hydroxyl ions (OH-) in the electrolyte to form water and an electron:

H ₂ + 2OH ^- → 2H ₂ O + 2e ^- .

At the cathode, oxygen reacts with water contained in the electrolyte and electrons from the external circuit. In subsequent stages of the reaction, hydroxyl ions (as well as perhydroxide O2H-) are formed. The resulting reaction at the cathode can be written as:

_^1/2 O ₂ + H ₂ O + 2e ^- → 2OH ^-.

The flow of electrons and ions maintains a balance of charge and matter in the electrolyte. The water resulting from the reaction partially dilutes the electrolyte. In any fuel cell, part of the energy of a chemical reaction is converted into heat. The flow of electrons in the external circuit is a direct current that is used to perform work. Most reactions in fuel cells provide an emf of about 1 V. Opening the circuit or stopping the movement of ions stops the fuel cell.

The process taking place in a hydrogen-oxygen fuel cell is inherently the opposite of the well-known electrolysis process in which the dissociation of water occurs when an electric current passes through the electrolyte. Indeed, in some types of fuel cells that can be assembled on electrodes, the process can be reversed - by applying voltage to the electrodes, water can be decomposed into hydrogen and oxygen. If you stop charging the cell and connect the load to it, such a regenerative fuel cell will immediately start working in its normal mode.

Theoretically, the dimensions of a fuel cell can be arbitrarily large. However, in practice, several cells are combined into small modules or batteries that are connected either in series or in parallel.

Hydrogen through the holes in the end plates 12 is fed into the holes 9 and through the channels 10 and the hydrogen current collector 6 enters the hydrogen gas diffusion collector 2.

Air through the open ends of the corrugated air current collector 7 enters the air gas diffusion manifold 3. On the membrane 1, hydrogen is oxidized with the release of heat and electric current.

The current from the extreme bipolar plates of the BFC is discharged to the consumer, and heat with the flow of air passing through the open ends of the corrugated air current collector 7 is removed to the outside.

One of the types of elements capable of operating on hydrogen and oxygen at normal temperature and pressure are elements with ion-exchange membranes (Fig.13). In these elements, instead of a liquid electrolyte, a polymer membrane is located between the electrodes, through which ions freely pass. In such elements, air can be used along with oxygen. The water formed during the operation of the cell does not dissolve the solid electrolyte and can be easily removed.

Holes 9 in frame 4 for supplying hydrogen with a diameter of 3 to 20 mm (the diameter of the holes depends on the overall dimensions of the frames and the number of MES in the battery).

The channels 10 in the frame 4 are designed to communicate the holes 9 of the frame 4 with the frame window. Their width can vary from 1 to 4 mm, and a depth of 0.5 mm or more depends on the thickness of the frame material.

The technical result of using the BFC according to the invention is achieved due to the fact that it contains two or more TE according to the invention, O-rings 11 and end plates 12, tightened by fasteners, for example, studs.

O-rings 11, the material is rubber, for example fluororubber.

Purpose: to seal the channels between adjacent frames 4. End plates 12, their material is metal or hard plastic. Appointment: for fastening of TE in BTE with the help of fasteners, for example threaded rods.

All other elements of the BFC are identical to the elements of the FC.

Implementation of TE and BTE

The fuel cell battery was implemented in accordance with the design, which is described and shown in Fig. 11, and the fuel cell in Fig. 13.

The BFC consists of 56 TE connected in series, the circuit diagram of which is shown in FIGS. 12, 13 and had an electromotive force (EMF) of 36 V, power of 250 W.

The polymer membrane 1 is made in the form of an ion exchange membrane Nation, its dimensions are 112 × 50 mm.

The hydrogen gas diffusion collector 2 is made of carbon graphite paper, its dimensions are 40 × 88 mm.

The polymer frame 4 is made of polycarbonate.

The bipolar plate 5 is made of titanium foil with a thickness of 0.1 mm, its dimensions are 112 × 50 mm.

The hydrogen current collector 6 is made of a titanium expanded metal mesh, with mesh sizes of 1.5 × 3 mm, in three layers, its dimensions are 40 × 88 mm.

Corrugated air current collector 7 is made of corrugated titanium foil with a thickness of 0.1 mm, its dimensions are 92.5 × 50 mm.

Scotch® ATG type 8 adhesive film.

The technical result of the use of TE and BFC according to the invention was achieved, with the same power and EMF as the prototype, by reducing the weight of the TE, the weight of the BFC decreased by 2.5 times, and it became maintainable.

Distinctive features of TE according to the invention

The air current collector is made of thin corrugated metal tape.

A hydrogen electrode with a gas diffusion collector and a current collector (metal mesh) is embedded in a polymer frame with a membrane glued to it on one side, and an air electrode with a gas diffusion collector and a current collector are made in accordance with the dimensions of the outer dimension of the frame.

An air electrode with a gas diffusion collector and a current collector are shorter than the frame, overlays are applied to the frame to limit the degree of compression of the fuel cell.

The membrane is glued to the frame using an adhesive film that acts as an adhesive sealing layer.

Distinctive features of the BFC according to the invention

The fuel cells are made according to any one of claims 1 to 4, the polymer frames are provided with channels and holes for supplying hydrogen through the hydrogen chamber and removing reaction products, holes are made in the membrane and bipolar plates, aligned with the holes for communicating the battery collector systems with hydrogen, and air is blown through the open ends of the air current collector.

The bipolar plate is glued to the polymer frame on the opposite side of the membrane with a glue transfer film.

Holes for supplying hydrogen between adjacent fuel cells are sealed with rings of elastic material.

Claims (7)

1. A fuel cell including a corrugated air current collector (7), an air gas diffusion collector (3), a polymer electrolyte membrane (1), a polymer frame (4), a hydrogen gas diffusion collector (2) and a hydrogen current collector (6), characterized in that the air gas diffusion current collector (7) is made of corrugated metal tape with a thickness of 0.05-0.25 mm. 2. A fuel cell according to claim 1, characterized in that the hydrogen gas diffusion collector (2) and the hydrogen current collector (6) are made of a metal mesh and are embedded in a polymer frame (4) with a polymer membrane glued to it on one side (1) moreover, the air gas diffusion collector (3), gas diffusion current collector (7) and hydrogen current collector (6) are made according to the dimensions of the outer dimension of the polymer frame (4). 3. The fuel cell according to claim 1, characterized in that the air gas diffusion manifold (3), the hydrogen gas diffusion manifold (2) and the hydrogen current collector (6) are made shorter than the frame, and overlays are applied to the frame to limit the compression ratio of the fuel element. 4. The fuel cell according to claim 1, characterized in that the polymer membrane (1) is glued to the polymer frame (4) using an adhesive transfer film that acts as an adhesive sealing layer. 5. A fuel cell battery consisting of at least 2 fuel cells, each of which includes a corrugated air current collector (7), an air gas diffusion collector (3), a polymer electrolyte membrane (1), a polymer frame (4), which has a hydrogen gas diffusion collector (2), a hydrogen current collector (6) and a bipolar plate (5), characterized in that the air gas diffusion current collector (7) is made of corrugated metal tape with a thickness of 0.05-0.25 mm, and the fuel items vyp filled according to any one of claims 1 to 4, the polymer frames are provided with channels and holes for supplying hydrogen through the hydrogen chamber and removing reaction products, and holes are made in the membrane and bipolar plates aligned with the holes for communicating the collector systems of the battery with hydrogen, and air blown through the open ends of the air current collector. 6. The fuel cell battery according to claim 5, characterized in that the bipolar plate is glued to the polymer frame on the opposite side of the membrane with a sticking film. 7. The fuel cell battery according to claim 5, characterized in that the holes for supplying hydrogen between adjacent fuel cells are sealed with rings of elastic material.

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