Porous flow plate for increasing power capacity in fuel cells

Abstract

The invention relates to a new flow plate (bipolar plate) for increasing the power output capacity of the cell for Proton Exchange Membrane (PEM type) fuel cells. Our invention carries out the task of delivering more H2 and O2 molecules to the catalyst surface compared to traditional flow plates by providing a balanced distribution throughout the active area of the cell. In this way, it increases the current / power density produced by the cell.

Description

[0001] POROUS FLOW PLATE FOR INCREASING POWER CAPACITY IN FUEL CELLS

[0002] TECHNICAL FIELD

[0003] The invention relates to a new flow plate (bipolar plate) for increasing the power output capacity of the cell for Proton Exchange Membrane (PEM type) fuel cells. Our invention carries out the task of delivering more H2 and O2 molecules to the catalyst surface compared to traditional flow plates by providing a balanced distribution throughout the active area of the cell. In this way, it increases the current / power density produced by the cell.

[0004] PRIOR ART

[0005] Proton Exchange Membrane Fuel Cells (PEMFC) are devices in which the chemical energy of hydrogen fuel is converted into electrical energy by chemical reactions. There are some advantages of PEM fuel cells among fuel cells that vary according to their operating conditions, membrane, and reactant types. The most important of these are high power density, fast "start-up", low operating temperature, and being suitable for portable applications. PEM fuel cells used in the automotive, space, and energy sectors are of interest because they are practical, more efficient than conventional energy generators, suitable for portable applications, environmentally friendly, and the hydrogen used as fuel can be produced from renewable energy sources. Fuel cells are seen as a clean technology type that is expected to be widely used in the automotive sector in the future.

[0006] In a typical fuel cell, fuel is continuously fed to the anode (negative electrode) and an oxidant (usually oxygen from the air) is continuously fed to the cathode (positive electrode). Electrochemical reactions occur at the electrodes to produce an electric current through the electrolyte, which drives a complementary electric current that does work on the load. A fuel cell is similar to a typical battery in many ways, but it differs in some ways. A battery is an energy storage device in which all available energy is stored in the battery itself (at least as a reductant). When the chemical reactants are used up (i.e., discharged), the battery will cease to produce electrical energy. A fuel cell is an energy conversion device in which fuel and oxidant are continuously fed.

[0007] In principle, the fuel cell produces power as long as fuel is supplied. A conventional fuel cell has a proton-conducting membrane at its core. There are electrodes (anode and cathode) on both sides of this membrane. PEMFCs consist of a membrane, catalyst layer, gas diffusion layer (GDL), bipolar plate (BP), current collection and compression plates. The reactants (usually hydrogen and air) fed from the anode and cathode sides are distributed to the catalyst surface via the GDL through the flow channels on the BPs. On the anode side, the hydrogen molecules coming to the catalyst surface are separated into positively charged hydrogen ions and negatively charged electrons. The membrane allows only positively charged hydrogen ions to pass to the cathode side, while electrons flow from the external circuit to the cathode side. This electron flow provides the production of electric current. Subsequently, the oxygen molecules fed from the cathode side react with the hydrogen ions coming from the membrane and the electrons coming from the external circuit on the cathode catalyst surface, causing the formation of liquid water and the release of heat. PEM fuel cells mainly consist of membrane, catalyst, gas diffusion layer, bipolar plate (BP), current collection and compression plate.

[0008] Among the vital components of fuel cells, flow plates (bipolar plates) cover 14- 27% of the cost of a fuel cell stack and 60-80% of its weight. When evaluated physically, flow plates are the most important components of fuel cells in terms of both weight and area. The basic functions of flow plates can be summarized as follows:

[0009] • isolate the cathode and anode reactants,

[0010] • distribute the reactive gases equally to the active area through channels,

[0011] • collect and conduct current,

[0012] • provide mechanical support,

[0013] • the membrane electrode to maintain a stable stack structure,

[0014] • evacuate the heat generated in the cell,

[0015] • evacuate the liquid water formed as a result of the reactions,

[0016] • connect each cell structure to each other.

[0017] Flow plates are basically responsible for distributing the reactants entering the cell homogeneously throughout the active area on the catalyst and membrane surface. For this reason, they directly affect the hydrogen and oxygen distributions on the catalyst surface. In addition, flow plates provide electrical and heat conduction through them. In other words, while flow plates affect the reactions in the cell, they also affect the distribution and direction of the heat and electrical energy generated as a result of the reactions. This important component, which affects all the process stages of the fuel cell, has a serious effect on the electrical performance of the cell, both in terms of design and material structure.

[0018] Another cell dynamics affected by BPs is water formation and management. In regions where BPs direct reactants and intensify reactions, liquid water formation also increases. This density being above normal causes the water ratio to increase regionally, restricting the reactants from reaching the catalyst layer on the GDL. In such cases, areas with local low current density are formed in the cell active area, reducing the power produced by the cell. In addition, the design features of BPs may be dominant in the discharge of the formed liquid water from the cell. The excess corner areas of the flow channel may increase water accumulation in these regions together with the pressure drop.

[0019] Many studies have been conducted from past to present in order to bring the flow plates to the ideal form. These studies have been conducted to increase the current produced by the fuel cell stack with the least amount of hydrogen gas consumed in fuel cells. In general, there are several basic parameters that affect the electrical performance of the cell in fuel cells. These factors are the operating conditions of the fuel cell, mass transport, water management, electrochemical kinetics of the fuel cell, compression pressure and hydrogen gas leaks. Studies conducted for the development of flow plates can be divided into two groups. The first group is based on the reconfiguration of the flow areas of the plates, and the second group is based on the development of the material structure of the flow plates. The development of the design structures of BPs generally consists of the flow channel pattern, geometric dimensions and shapes of the flow channel, flow areas in the channelless structure and the placement of various obstacle forms in the flow channels.

[0020] The serpentine flow field is the most commonly used flow field type today. In the single serpentine flow field, the reactants are spread over the entire catalyst surface with the help of a single channel from the inlet to the outlet. The serpentine design forces the reactant gases to flow throughout the entire active area region, which improves the coverage area of the reactant gases on the catalyst layer, optimizes gas distribution, and ensures that the water produced due to the high flow in the flow channel is quickly discharged. Therefore, the serpentine flow field has better water- gas transport properties. On the other hand, in the cell with a single serpentine structure, the consumption / decrease of reactants along the channel causes the formation of regions with low current density by decreasing the fresh fuel near the exit region of the channel and the insufficient use of the active area. In addition, the most notable disadvantage of serpentine designs is the relatively high difference between the cell inlet and outlet pressure values. This situation is due to the pressure drop in the channel return regions (corner turns) of the serpentine design. Pressure drop causes an increase in the pumping power (loss) which is considered as parasitic loss. Unlike single serpentine, multiple serpentine flow areas carry reactants from the inlet to the outlet in a serpentine curve form with multiple channels instead of a single channel. Multiple serpentine have fewer corner turns than single serpentine, which results in lower pressure drop and pumping loss values. Multiple serpentine models are generally preferred in commercial applications. Another type of flow area that is widely used is the parallel flow area. In a parallel flow area, reactants are transported from the inlet to the outlet by means of channels located parallel to each other. These parallel channels continue without interruption. The parallel flow area has low pressure drop, is easy to use and does not require an external blower. However, the flow rate is low, the convective mass transfer between adjacent flow channels is low, the utilization rate of the reactant gas is low, the distribution is uneven and the water discharge performance is poor. The main feature of the interdigitated flow field is that it facilitates the reactants to reach the catalyst surface by directing the flow to the under-rib path due to the closed channel ends, increases convective mass transfer and increases the fuel and oxidant density on the catalyst membrane surface. It has also been reported in the studies that the flow directed to the GDL region contributes to the removal of the formed liquid water. Despite these beneficial effects, this type of flow field is not widely used. High pressure drop is observed in interdigitated flow fields depending on the GDL porosity and thickness. The pin-type flow field is based on a parallel flow field with additional flow paths. The advantage of this structure is that it reduces the flow resistance, reduces the pressure drop and prevents overflow in a single flow path. However, in long-term operation, liquid water tends to accumulate and uneven distribution of reactant gas or blockage in the gas flow may occur. In addition, the contact resistance is also high.

[0021] Classical type flow fields used in literature and commercially have advantages and disadvantages compared to each other. For this reason, it has been stated by many researchers that an ideal flow field form has not been reached yet. Flow field designs are being developed to achieve higher current and power densities of PEMFCs, to achieve lower pressure drops, to provide more uniform gas distribution, and to provide more efficient water management. Therefore, optimization or renewal of the original basic flow field to obtain a new flow field with more commercialization potential has become the main subject of PEMFC water-gas management research.

[0022] The shapes of the flow fields of bipolar plates affect the distribution of reactants in the cell to the catalyst surface, affecting the reaction distribution in the cell, cell life, cell efficiency, net power value obtained, and the discharge of water formed in the cell. The disadvantages of BPs and the issues that need to be improved can be summarized as follows:

[0023] • Uneven reactant distribution across the active area,

[0024] • Insufficient drainage of liquid water,

[0025] • High pressure drop,

[0026] • Insufficient reactant amount on the catalyst surface,

[0027] • Low current / power density values.

[0028] BRIEF DESCRIPTION OF THE INVENTION

[0029] The invention relates to a new flow plate (bipolar plate) for increasing the power output capacity of the cell for Proton Exchange Membrane (PEM type) fuel cells. Our invention carries out the task of delivering more H2 and O2 molecules to the catalyst surface by providing a balanced distribution throughout the active area of the cell compared to the flow plates tested in the literature and used commercially. In this way, it increases the current / power density produced by the cell. In other words, the power produced by the cell per unit fuel (H2) increases.

[0030] The flow plates in our invention solve the following problems:

[0031] • Depletion of reactants along the channel and decrease in reactions due to concentration and pressure losses in regions close to the outlet,

[0032] • High pressure drop,

[0033] • Unbalanced reactant distribution,

[0034] • Insufficient water discharge,

[0035] • Formation of regional high reaction (hot spot) regions and related extremely hot membrane surfaces,

[0036] • Low current density,

[0037] • Formation of regional low reaction dead zones. LIST OF FIGURES

[0038] Figure 1. General View of Fuel Cell

[0039] Figure 2. Detail View - A of Fuel Cell

[0040] Figure 3. Disassembled View of Fuel Cell Elements

[0041] Figure 4. Front View of Bipolar Plate with Porous Area

[0042] Figure 5. Perspective View of Bipolar Plate with Porous Area

[0043] Figure 6. Detail View - A of Bipolar Plate with Porous Area

[0044] CORRESPONDING NUMBERS IN THE FIGURES

[0045] 1. Anode flow plate

[0046] 2. Cathode flow plate

[0047] 3. Anode gas diffusion layer

[0048] 4. Cathode gas diffusion layer

[0049] 5. Anode catalyst

[0050] 6. Cathode catalyst

[0051] 7. Proton exchange membrane

[0052] 8. Open pore foam blocks placed on anode plate

[0053] 9. Open pore foam blocks placed on cathode plate

[0054] 10. Cathode plate reactant inlet port

[0055] 11. Cathode plate reactant outlet port

[0056] 12. Reactant flow channel

[0057] DETAILED DESCRIPTION OF THE INVENTION

[0058] The invention is characterized by the following components: an anode flow plate (1 ), a cathode flow plate (2), an anode gas diffusion layer (3), a cathode gas diffusion layer (4), an anode catalyst (5), a cathode catalyst (6), a proton exchange membrane (7), open-pore foam blocks placed on the anode plate (8), open-pore foam blocks placed on the cathode plate (9), a cathode plate reactant inlet port (10), a cathode plate reactant outlet port (11 ), and a reactant flow channel (12).

[0059] In our invention, the flow plate (bipolar plate) directs more reactants to both the anode flow plate (1 ) and the cathode flow plate (2), increasing the reaction intensity on the catalyst surface. The increased reaction intensity on the cathode catalyst (6) surface leads to higher current / power density being obtained from the cell. The process of directing hydrogen (H2) and oxygen (O2) molecules from the reactant flow channel (12) of the flow plate in the cell to the catalyst surface within the anode flow plate (1 ) and cathode flow plate (2) is facilitated by the open-pore foam blocks (8) placed on the anode plate and the open-pore foam blocks (9) placed on the cathode plate. The open porous foam blocks (8) placed on the anode plate and the open porous foam blocks

[0060] (9) placed on the cathode plate have a hollow structure, their pores are in random directions and their pore sizes vary between 10 - 100 PPI. In other words, the pores within the open-pore foam blocks (8) on the anode plate and the open-pore foam blocks (9) on the cathode plate allow the H2 or O2 inside them to move or be directed in more than one direction simultaneously. This allows the flow to penetrate both along the reactant flow channel (12) and into the anode gas diffusion layer (3) and cathode gas diffusion layer (4). The use of open-pore foam blocks (8) on the anode plate and open-pore foam blocks (9) on the cathode plate leads to a higher reactant density on the surfaces of the anode catalyst (5) and cathode catalyst (6) compared to traditional channel structures.

[0061] The open-pore foam blocks (8) placed on the anode flow plate (1 ) and the openpore foam blocks (9) placed on the cathode flow plate (2) are positioned in a crosswise arrangement within the active area of the cell, from top to bottom, ensuring a more balanced distribution of reactants on the catalyst surfaces of the anode flow plate (1 ) and cathode flow plate (2). Therefore, starting from the cathode plate reactant inlet port

[0062] (10), the flow divides into two branches. There are two reasons for the flow splitting into two branches and circulating through the active area:

[0063] • Distributing the flow more homogeneously on the catalyst surface,

[0064] • Reducing the pressure drop by reducing the corner turning areas of the channels.

[0065] In the anode flow plate (1 ) and cathode flow plate (2), the cathode plate is divided into two branches starting from the reactant inlet port (10) in a serpentine form from top to bottom of the reactant flow channel (12) and the open-pore foam blocks (8) placed on the anode plate and the open-pore foam blocks (9) placed on the cathode plate are placed on these branches in a crosswise position from top to bottom. Under normal conditions, the regions beneath the open-pore foam blocks (8) on the anode plate and (9) on the cathode plate correspond to areas of the cathode catalyst (6) that exhibit high reaction intensity. Therefore, the open-pore foam blocks (8) on the anode plate and (9) on the cathode plate are positioned not to cover a single region or the entire flow area, but instead are arranged in multiple positions and crosswise along the reactant flow channels (12). In this way, the reaction intensity in the active area has been balanced, preventing the formation of excessive reaction areas or dead zones (areas where no reaction occurs). Additionally, some of the open-pore foam blocks (8) placed on the anode plate and (9) placed on the cathode plate have not been positioned in the upper corner areas of the flow plate, but rather in the lower corner areas. This is because, in the reactant flow channels (12), near the cathode plate reactant inlet port (10), the concentrations of fresh H2 and O2 are high. By placing the open-pore foam blocks (8) on the anode plate and (9) on the cathode plate in the lower comers, it prevents the formation of hot spots, particularly on the cathode catalyst (6) surface. These localized excessive temperatures could lead to the drying of the proton exchange membrane (7), reducing the electrical output in that area. On the other hand, by placing the open-pore foam blocks (8) on the anode plate and (9) on the cathode plate in the lower corner areas of the anode flow plates (1 ) and cathode flow plates (2), the disadvantages associated with the reduction of H2 and O2 concentrations near the cathode plate reactant outlet port (11 ) due to consumption are minimized. Furthermore, the corners at the junctions where the anode flow plates (1 ) and cathode flow plates (2) meet the reactant flow channels (12), and where the open-pore foam blocks (8) on the anode plate and (9) on the cathode plate are located, have been curved. These curves are present both at the points where the flow enters the open-pore foam blocks (8) on the anode plate and (9) on the cathode plate, and at the regions where the flow exits from the open-pore foam blocks (8) on the anode plate and (9) on the cathode plate to connect to the channel. These curves allow the H2 and O2 molecules to spread more widely within the open-pore foam blocks (8) placed on the anode plate and (9) placed on the cathode plate, ensuring that the molecules reach the corner regions of the porous area. The reactant flow, which is divided into two branches, merges again towards the lower section of the plate, allowing the excess H2 and O2 gases and liquid water (H2O) to be discharged from the reactant outlet port (11 ) as a result of the reaction. The open-pore foam blocks (8) placed on the anode plate and (9) placed on the cathode plate, due to their porous internal structure and the multiple directions of their pores, facilitate the discharge of the liquid water formed as a result of the reactions. The number of open-pore foam blocks (8) placed on the anode plate and (9) placed on the cathode plate in the active area of the cell can be increased or decreased. In flow plates with large active areas, the flow is directed to circulate through the active area in a serpentine form by dividing into at least two branches. The dimensions (width and length) of the open-pore foam blocks (8) placed on the anode plate and (9) placed on the cathode plate can be increased or reduced. The sizes (width and length) of the open-pore foam blocks (8) on the anode plate and (9) on the cathode plate can range from 1 mm to 100 mm. The open-pore foam blocks (8) placed on the anode plate and (9) placed on the cathode plate can have a square, rectangular, or circular shape, or at least one of these shapes. The pore size of the open-pore foam blocks (8) placed on the anode plate and (9) placed on the cathode plate can range from 10 to 100 ppi (pores per inch). The open-pore foam blocks (8) placed on the anode plate and (9) placed on the cathode plate are made of at least one material from metal and carbon-based materials.

Claims

CLAIMS1. It is a flow plate that increases the power output capacity of the cell for fuel cells, characterized by; open porous foam blocks (8) placed on the anode flow plate (1 ) and cathode flow plate (2), which direct the hydrogen (H2) and oxygen (O2) molecules in the reactant flow channel (12) of the flow plate in the cell to the catalyst surface through the anode flow plate (1 ) and cathode flow plate (2), whose pores are in random directions and whose pore sizes vary, and which are placed in a way that they are positioned crosswise from top to bottom with each other, and open porous foam blocks (9) placed on the cathode plate, the reactant flow channel (12) that is divided into two branches in the anode flow plate (1 ) and cathode flow plate (2), starting from the cathode plate reactant inlet port (10), and descending in a serpentine manner from top to bottom.

2. It is the flow plate mentioned in claim 1 , characterized in that the comers located in the junction areas where the anode flow plates (1 ) and cathode flow plates (2) meet the reactant flow channels (12) with the open porous foam blocks (8) placed on the anode plate and the open porous foam blocks (9) placed on the cathode plate being curved.

3. Open porous foam blocks (8) placed on the anode plate and open porous foam blocks (9) placed on the cathode plate mentioned in claim 1 , characterized in that their internal structure being porous and these pores being in more than one direction.

4. The open porous foam blocks (8) placed on the anode plate and the open porous foam blocks (9) placed on the cathode plate mentioned in claim 1 , characterized in that the fact that they are blocks positioned crosswise with each other from top to bottom in more than one position along the reactant flow channels (12) and within the active area of the cell.

5. There are open porous foam blocks (8) placed on the anode plate and open porous foam blocks (9) placed on the cathode plate mentioned in claim 1 , characterized in that their pore sizes being in the range of 10 - 100 PPI.

6. Open porous foam blocks (8) placed on the anode plate and open porous foam blocks (9) placed on the cathode plate mentioned in claim 1 , characterized by being made of at least one of metal and carbon-based materials.

7. The open porous foam blocks (8) placed on the anode plate and the open porous foam blocks (9) placed on the cathode plate mentioned in claim 1 , characterized by being in the shape of at least one of the square, rectangular and circular structures.

8. There are open porous foam blocks (8) placed on the anode plate and open porous foam blocks (9) placed on the cathode plate mentioned in claim 1 , characterized by their dimensions (width and length dimensions) being between 1 mm - 100 mm.

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