DE102024201244A1 - Electrochemical energy converter - Google Patents

Abstract

The invention relates to an electrochemical energy converter (10), in particular a fuel cell or an electrolyzer. The electrochemical energy converter (10) has
- a first bipolar plate (20),
- a second bipolar plate (30),
- a frame structure (40),
- a membrane electrode assembly (50),
- an elastically deformable layer (60) and
- a fluid-permeable transport layer (70).
The frame structure (40) has a central opening (45) and is arranged between the first bipolar plate (20) and the second bipolar plate (30). The elastically deformable layer (60) and the fluid-permeable transport layer (70) are arranged within the central opening (45) of the frame structure (40). The membrane electrode assembly (50) is arranged directly above the second bipolar plate (30) and directly below the fluid-permeable transport layer (70). The elastically deformable layer (60) is arranged directly above the fluid-permeable transport layer (70).
The invention further relates to an electrochemical energy converter stack (100) comprising a plurality of such electrochemical energy converters (10).

Description

The invention relates to an electrochemical energy converter, in particular a fuel cell or an electrolyzer, according to claim 1. The invention further relates to an electrochemical energy converter stack having a plurality of such electrochemical energy converters.

State of the art

Electrochemical energy converters in the form of fuel cells or electrolyzers are generally known from the state of the art.

A fuel cell converts the chemical reaction energy of a continuously supplied fuel and an oxidizer into electrical energy. In conventional fuel cells, hydrogen and oxygen are converted into water, electrical energy, and heat.

In electrolyzers, the electrochemical process runs in the other direction. Unlike a fuel cell, an electrolyzer is an energy converter that splits water into hydrogen and oxygen by applying an electrical voltage.

Typically, such electrochemical energy converters comprise a plurality of components for carrying out the electrochemical process, such as a membrane electrode assembly, a gas diffusion layer, a carbon fleece, a stretch material, a sintered titanium layer, etc., wherein said components are arranged between two opposing bipolar plates.

The electrochemical energy converters are stacked on top of each other for use in a system to form an electrochemical energy converter stack. The individual electrochemical energy converters, particularly the aforementioned components, are pressed together by the end plates of the electrochemical energy converter stack. This pressing process causes the components, particularly the gas diffusion layer, to undergo plastic deformation. This makes cleaning individual components, particularly the porous components, very difficult or even impossible.

Furthermore, the construction of such electrochemical energy converters is very expensive, complex, and requires a large amount of space. For example, the sintered titanium layer must be manufactured using a very complex process and positioned within the electrochemical energy converter.

Disclosure of the invention

• - eine erste Bipolarplatte,
• - eine zweite Bipolarplatte,
• - eine Rahmenstruktur,
• - eine Membran-Elektroden-Einheit,
• - eine elastisch verformbare Schicht und
• - eine Fluid durchströmbare Transportschicht auf.

According to a first aspect of the invention, an electrochemical energy converter, in particular a fuel cell or an electrolyzer, is presented. The electrochemical energy converter has

• - a first bipolar plate,
• - a second bipolar plate,
• - a framework structure,
• - a membrane electrode assembly,
• - an elastically deformable layer and
• - a fluid-permeable transport layer.

The frame structure has a central opening and is arranged between the first bipolar plate and the second bipolar plate. The elastically deformable layer and the fluid-permeable transport layer are arranged within the central opening of the frame structure. The membrane electrode assembly is arranged directly above the second bipolar plate and directly below the fluid-permeable transport layer. The elastically deformable layer is arranged directly above the fluid-permeable transport layer.

The core idea of the invention is to design the components of the electrochemical energy converter and arrange them relative to one another in such a way that the use of a large number of components can be dispensed with. In particular, an electrochemical energy converter without a gas diffusion layer is to be provided, which allows for elastic assembly.

In other words, the electrochemical energy converter according to the invention is distinguished from the prior art by its simpler and more cost-effective design.

By reducing the number of components within the electrochemical energy converter, costs, especially series production costs, can be drastically reduced. On the other hand, thinner stack arrangements can be created to increase the overall efficiency of the subsequent electrochemical energy converter stack.

Further features and advantages of the invention are set forth below.

It has been shown that the number of components and thus the overall height of the electrochemical energy converter can be reduced through a targeted arrangement of the membrane electrode assembly. It is particularly advantageous if the membrane electrode assembly is designed to be smaller and preferably arranged within the frame structure.

Further investigations have shown that material costs can be reduced if the membrane electrode assembly is preferably arranged below the frame structure.

In order to ensure a homogeneous pressure distribution during pressing, the elastically deformable layer is preferably designed as a spring plate.

The spring plate allows the contact pressure to be distributed evenly over the entire surface of the transport layer through which the fluid can flow.

Since the elastically deformable layer, in particular the spring plate, cannot be in direct contact with the membrane electrode assembly, an intermediate contact surface for the elastically deformable layer, in particular the spring plate, is advantageous. This contact surface must be dimensionally stable and non-compliant and, in particular, must have high permeability. Therefore, the fluid-permeable transport layer is preferably designed as a perforated plate or a sintered plate.

In order to be able to distribute the fluid through which it can flow evenly, the first bipolar plate and/or the second bipolar plate each have, at least in some areas, a fluid distribution area designed as a column structure.

It has been shown that the density of the column structure has a particularly beneficial effect on the efficiency of fluid flow. Accordingly, the column structures each comprise a plurality of columns arranged at a distance from one another.

Preferably, the columns have a rectangular, circular or oval cross-section.

According to a second aspect of the invention, an electrochemical energy converter stack comprising a plurality of such electrochemical energy converters is presented. Advantages described in detail for the electrochemical energy converter according to the first aspect of the invention equally apply to the electrochemical energy converter stack according to the second aspect of the invention.

Further advantages, features, and details of the invention will become apparent from the following description, which describes exemplary embodiments of the invention in detail with reference to the drawings. The features mentioned in the claims and in the description may be essential to the invention individually or in any combination.

The invention is explained in more detail below with reference to the accompanying drawings.

• 1 einen Schnitt durch einen aus dem Stand der Technik bekannten elektrochemischen Energiewandler;
• 2 einen Schnitt durch einen elektrochemischen Energiewandler gemäß einem ersten Ausführungsbeispiel der vorliegenden Erfindung; und
• 3 einen Schnitt durch einen elektrochemischen Energiewandler gemäß einem zweiten Ausführungsbeispiel der vorliegenden Erfindung.

The diagrams show:

• 1 a section through an electrochemical energy converter known from the prior art;
• 2 a section through an electrochemical energy converter according to a first embodiment of the present invention; and
• 3 a section through an electrochemical energy converter according to a second embodiment of the present invention.

At this point it is noted that the 1 to 3 The electrochemical energy converters 10 and 10S shown are to be understood as fuel cells by way of example. It is expressly stated that the electrochemical energy converter 10 according to the invention can also be described and understood as an electrolyzer in further embodiments.

1 shows a section through an electrochemical energy converter 10S, as known from the state of the art.

The known electrochemical energy converter 10S comprises a first bipolar plate 20S, a second bipolar plate 30S, a first frame structure 41S, a second frame structure 42S, a membrane electrode assembly 50S, a stretch material 60S, a sintered titanium layer 70S and a gas diffusion layer 80S.

As in 1 As can be clearly seen, the well-known 10S electrochemical energy converter has a large number of components and therefore a higher overall height. This is primarily due to the "dual-core frame" design of the well-known 10S electrochemical energy converter.

In addition, the well-known electrochemical energy converter 10S has a plastically deformable gas diffusion layer 80S, so that the cleaning of the individual components is very difficult and sometimes impossible.

2 shows a section through an electrochemical energy converter 10 according to a first embodiment of the present invention.

As in 2 As can be clearly seen, the electrochemical energy converter 10 according to the invention has a simpler structure than the electrochemical energy converter 10S known from the prior art. This is due in particular to the "single-core frame structure" of the electrochemical energy converter 10 according to the invention.

The core idea of the invention is to move away from an uncontrolled plastic deformation of a “dual-core frame structure” to a controlled elastic reversible deformation of a “single-core frame structure”.

This is achieved in particular by carrying out a targeted design and relative arrangement of the components to one another, so that the number of components and the overall height of the electrochemical energy converter 10 according to the invention are significantly reduced.

Therefore, the electrochemical energy converter 10 according to the invention comprises only a first bipolar plate 20, a second bipolar plate 30, a frame structure 40, a membrane electrode assembly 50, an elastically deformable layer 60, and a fluid-permeable transport layer 70. Like the transport layer 70, the elastically deformable layer 60 is fluid-permeable.

The frame structure 40 has a central opening 45 and is arranged between the first bipolar plate 20 and the second bipolar plate 30.

The frame structure 40 serves in particular to ensure the rigidity and tightness of the membrane electrode assembly 50 and is a non-active region of the electrochemical energy converter 10 according to the invention.

The elastically deformable layer 60 and the fluid-permeable transport layer 70 are arranged within the central opening 45 of the frame structure 40.

The membrane electrode unit 50 is arranged directly above the second bipolar plate 30 and directly below the fluid-permeable transport layer 70.

The membrane electrode assembly 50 is arranged within the frame structure 40. For this purpose, the frame structure 40 has a stepped or groove-shaped recess 43 into which the membrane electrode assembly 50 is circumferentially embedded or enclosed.

This design approach has the particular advantage that the membrane electrode unit 50 does not have to be formed over the entire width of the frame structure 40, but can only be formed approximately over the width of the central opening 45 of the frame structure 40.

The membrane electrode assembly 50 comprises a membrane, for example a polymer electrolyte membrane (PEM), and two porous electrode layers, each with a catalyst layer, wherein the electrode layers are each arranged on one side or surface of the membrane.

The elastically deformable, in particular fluid-permeable, layer 60 is arranged directly above the fluid-permeable transport layer 70.

3 shows a section through an electrochemical energy converter 10 according to a second embodiment of the present invention. In this embodiment, it is possible to make the "single-core frame structure" even more compact by arranging the membrane electrode assembly 50 below the frame structure 40.

This design approach has the advantage that, in particular, the thickness or height of the frame structure 40 can be further reduced, so that even thinner stack arrangements can be created in order to increase the efficiency, in particular the power density per electrochemical energy converter 10 according to the invention, of the electrochemical energy converter stack 100 as a whole.

The electrochemical energy converter 10 according to the invention is characterized in particular by its structure without a gas diffusion layer 80S and its elastic properties.

In contrast to the known electrochemical energy converter 10S, which has plastically deformable properties due to the stretch material 60S and the gas diffusion layer 80S, the electrochemical energy converter 10 according to the invention has elastically reversible properties due to the elastically deformable layer 60.

The state of the art particularly uses "low-cost gas diffusion layers," also called "LCGDLs." These are typically based on nonwoven, woven, or paper.

Due to their specific material properties, such 80S gas diffusion layers exhibit different behavior during cell construction and cell operation than previously common thermally bonded papers. Due to their comparatively low stiffness, they exhibit significantly reduced compression in the channel regions of the flow field, which, as a result of the material structure, leads to increased electrical resistances within the material and at the interfaces between neighboring layers. As a result of these effects, the ohmic resistance loss within the known 10S electrochemical energy converter increases, and the performance of the stack arrangement decreases.

The elastically deformable layer 60 allows compression to be increased, in particular the contact pressure to be distributed evenly over the entire surface of the fluid-permeable transport layer 70. The elastically deformable layer 60 allows, in particular, the tolerances in an electrochemical energy converter stack 100 to be compensated, wherein the individual stacked electrochemical energy converters 10 are clamped to one another in a largely homogeneous manner.

In particular, in the design of the elastically deformable layer 60 as a spring plate, the previously fixed distance between the first bipolar plate 20 and the second bipolar plate 30 can be changed in such a way that tolerances can be compensated so that the most homogeneous surface pressure possible is achieved in one plane.

In other words, plastically deformed rigid structures (stretch material 60S, gas diffusion layer 80S), which cause a fixed, non-changeable height of the bipolar plates 20, 30 relative to each other, are supplemented or replaced by flexible structures (spring plate).

Further investigations have shown that the uniform contact pressure of the spring plate over the fluid-permeable transport layer 70 can also achieve a homogeneous current distribution and thus minimize cell aging.

It is conceivable for the elastically deformable layer 60 to be designed as a plate comprising individual spring elements spaced apart from one another. The individual spring elements can each have the same or different spring stiffnesses. It is also conceivable for the spring elements to be designed as rubber elements or to comprise rubber elements in some regions. It is further conceivable for the spring elements to be made of structured polymer. It is also further conceivable for the spring elements to be designed as compression-elastic elements, in particular elastic compression elements, in particular compression spring structures or elastic bodies of a non-spring structure. It is further conceivable for the compression spring structures to be designed as cylindrical compression springs, conical compression springs, wave springs, disc springs or plastic compression springs.

Since the elastically deformable layer 60, in particular the spring plate, is arranged directly above the fluid-permeable transport layer 70, the elastically deformable layer 60 influences the flow field fluidically.

The fluid-permeable transport layer 70 is designed as a perforated plate. It is also conceivable that the fluid-permeable transport layer 70 is also designed as a sintered plate.

In the form of a perforated plate, the fluid-permeable transport layer 70 has a plurality of cavities 71 through which a medium, for example oxygen or water, can flow.

The fluid-permeable transport layer 70, in particular the perforated plate, should be very dimensionally stable and non-compliant in order to serve as a contact surface for the spring plate. Furthermore, it should exhibit high permeability. Furthermore, it is advantageous for the fluid-permeable transport layer 70 to have hydrophilic properties to promote fluid removal, particularly water removal. Therefore, it is conceivable for the fluid-permeable transport layer 70 to have a hydrophilic coating to improve water removal.

It is important that the elastically deformable layer 60, in particular the spring plate, and the fluid-permeable transport layer 70, together, exhibit good mechanical, thermal, and electrical properties. The mechanical properties are crucial for the contacting and bracing in the electrochemical energy converter 10. The high permeability and compressibility inevitably have a direct impact on the structural, electrical, and thermal mass transport properties.

At this point, it should be noted again that water transport on the anode side can occur through the elastically deformable layer 60, particularly through the spring plate. With perforated plates and sintered titanium, water cannot be transported in-plane through the transport layer 70.

During operation, a varying pressure is built up across the membrane electrode assembly 50, which places additional stress on the fluid-permeable transport layer 70, particularly the perforated plate. The settlement behavior of the fluid-permeable transport layer 70 should be as constant as possible or very low over the operating time. Typical compression values are in the range of 1.0 MPa to 5.0 MPa.

The electrical properties are highly dependent on the material selection. For example, in the form of the fluid-permeable transport layer 70 as a carbon fiber-reinforced perforated plate, the carbon fibers and their orientation are crucial for the electrical conductivity of the perforated plate. The electrical resistance is determined by the fiber properties or the machine direction. The electrical resistance depends on the degree of carbonization, thickness, and density of the carbon fibers, which is linearly related to the fiber quantity and weight. The electrical resistance is also highly dependent on compression, since the electrical contact points for electrical conductivity must be ensured by the fiber/fiber contacts or the binder points.

The thermal properties are similar to the electrical properties. Due to the exothermic reaction in the electrochemical energy converter 10 or in the fuel cell, heat conduction through the elastically deformable layer 60 and the fluid-permeable transport layer 70 is crucial. Good heat transfer improves cell performance and extends the cell's service life. The water balance is also significantly influenced by thermal conductivity.

The first bipolar plate 20 has a fluid distribution region formed as a column structure 25. The second bipolar plate 30 has a fluid distribution region formed as a column structure 35. It is conceivable that only one of the bipolar plates 20, 30 has a fluid distribution region formed as a column structure 25.

A cathode flow field is formed by the columnar structure 25 of the first bipolar plate 20, and an anode flow field is formed by the columnar structure 35 of the second bipolar plate 30. In other words, the columnar structures 25, 35 of the bipolar plates 20, 30 serve to evenly distribute the fuel to the anode and to evenly distribute the oxidant to the cathode.

The column structures 25, 35 each comprise a plurality of columns 26, 36 arranged at a distance from one another. The column structures 25, 35 can be understood as filigree web-channel structures with a significantly reduced spacing. The columns 26, 36 have a rectangular cross-section. It is conceivable that the columns 26, 36 also have a circular or oval cross-section. The cross-section of the columns 26, 36 can vary over the height, and the columns can have a tapered shape or a larger cross-section at the contact point with the CCM than at the base of the column.

The distribution of the fluids is more efficient the denser the column structures 25, 35 are, i.e., the density of the column structures 25, 35 has a particularly beneficial effect on the efficiency of the flow of the fluids.

Claims (9)

An electrochemical energy converter (10), in particular a fuel cell or an electrolyzer, comprising: - a first bipolar plate (20), - a second bipolar plate (30), - a frame structure (40), - a membrane-electrode assembly (50), - an elastically deformable layer (60), and - a fluid-permeable transport layer (70), wherein the frame structure (40) has a central opening (45) and is arranged between the first bipolar plate (20) and the second bipolar plate (30), wherein the elastically deformable layer (60) and the fluid-permeable transport layer (70) are arranged within the central opening (45) of the frame structure (40), wherein the membrane-electrode assembly (50) is arranged directly above the second bipolar plate (30) and directly below the fluid-permeable transport layer (70), and wherein the elastically deformable layer (60) is arranged directly above the fluid-flowable transport layer (70). Electrochemical energy converter (10) according to Claim 1 , characterized in that the membrane electrode unit (50) is arranged within the frame structure (40). Electrochemical energy converter (10) according to Claim 1 or 2 , characterized in that the membrane electrode unit (50) is arranged below the frame structure (40). Electrochemical energy converter (10) according to one of the preceding claims, characterized in that the elastically deformable layer (60) is designed as a spring plate. Electrochemical energy converter (10) according to one of the preceding claims, characterized in that the fluid-flowable transport layer (70) is designed as a perforated plate or as a sintered plate. Electrochemical energy converter (10) according to one of the preceding claims, characterized in that the first bipolar plate (20) and/or the second bipolar plate (30) each have, at least in some regions, a fluid distribution region designed as a column structure (25, 35). Electrochemical energy converter (10) according to Claim 6 , characterized in that the column structures (25, 35) each have a plurality of columns (26, 36) arranged at a distance from one another. Electrochemical energy converter (10) according to Claim 7 , characterized in that the columns (90) have a rectangular, circular or oval cross-section. Electrochemical energy converter stack (100) comprising a plurality of electrochemical energy converters (10) according to one of the Claims 1 until 8 .