Bipolar plate of a fuel cell

Abstract

The present invention relates to a bipolar plate of an industrial-scale PEM fuel cell comprising a first active area face (14), which is an anode or cathode, intended to contact a membrane (12) and a second face (15) intended to contact an end plate (13) or another bipolar plate. The bipolar plate comprises: through holes (2, 3, 4, 5, 6); gas channels (7) in the first face (14) intended to guide the reactant gases; at least one cooling channel (1) in the second face (15) intended to guide the coolant; first obstacles (8) arranged in the gas channels (7) with a quarter cylinder, rectangular prism and another quarter cylinder geometry; and second obstacles (9) with a triangular prism geometry arranged in the gas channels (7) after each of the first obstacles (8).

Description

[0001] BIPOLAR FUEL CELL PLATE

[0002] DESCRIPTION

[0003] OBJECT OF THE INVENTION

[0004] The present invention falls within the field of electricity generation, and specifically the hydrogen sector applied to PEM fuel cells, these being devices that directly convert the chemical energy of fuels such as hydrogen into useful work with minimal environmental impact and high efficiency.

[0005] More specifically, the invention refers to a bipolar plate that includes modified gas channels with serpentine-shaped obstacles, with the aim of improving the performance of the fuel cell system.

[0006] BACKGROUND OF THE INVENTION

[0007] Fuel cells are known for their electrochemical nature, extracting electricity directly from a redox reaction. Within the fuel cell family are Proton Exchange Membrane (PEM) fuel cells, in which a membrane is placed between a bipolar plate on the cathode side and a bipolar plate on the anode side. One of the main components of these fuel cells is the bipolar plates (BPs), as they contribute approximately 80% of the total weight, 40% of the cost, and 60% of the volume of the cell.

[0008] These bipolar plates comprise gas channels through which the reactants circulate and are designed and machined to supply sufficient oxygen (air) and hydrogen to the gas diffusion layer (GDL) and the catalyst layer (CL). The bipolar plates perform several functions, including electron and water transport, as well as reactant delivery to the cathode and anode sides. Improved flow field design will lead to better water management and increased fuel cell performance. In PEMFC, Marappan et al., “Performance studies of proton exchange membrane fuel cells with different flow field designs—review,” The Chemical Record, (2021), 21(4), 663–714, described the main bipolar plate designs used, such as straight, parallel, serpentine, and interdigitated flow fields.The flow field design greatly affects PEMFC performance, leading to numerous modifications to further improve it. A serpentine flow field is one in which the flow path is continuous from inlet to outlet. This serpentine geometry increases pressure drop due to the bends in its path. Pressure drop benefits water extraction and gas distribution; however, an excessively high value can have an adverse effect, causing large concentration gradients of reactants and temperatures along the gas channels.

[0009] Among the known designs is the incorporation of obstacles or baffles along the gas channels at specific points. Baffles are structures designed to create an obstacle at a specific point, forcing the gas, through convection, from the gas channels toward the gas-oil-discharge (GOD) and then toward the catalyst layer. This also increases the reactant pressure in the gas channels by improving convection under the ribs, thus increasing the reactant mass flow rate in those areas. This baffle structure also causes eddies, which promote the mixing of the reactant gas from the gas channel with unreacted oxygen, contributing to an increase in the partial pressure of oxygen at the GOD surface. In this way, more gas can reach the active area, while water can be more easily extracted from the GOD, resulting in improved performance.

[0010] However, these obstacles have only been overcome in small-scale bipolar plates where accelerated gas diffusion is necessary. Attempts to manufacture industrial-scale bipolar plates with dimensions exceeding 150 cm² present challenges. 2 These obstacles cannot be arranged in the same way as on the smaller plates, since the path of the gases in the gas channels is longer and the conditions change.

[0011] DESCRIPTION OF THE INVENTION

[0012] The present invention describes the design of a bipolar plate for an industrial-scale PEM fuel cell, which has a plurality of parallel, serpentine gas channels. These channels consist of first, elongated obstacles that improve diffusion and increase gas velocity due to the pressure increase caused by the reduced cross-sectional area. Second, point-like obstacles, following the first obstacles, further increase gas velocity and result in less pressure drop than the first obstacles. Thus, the industrial-scale bipolar plate has a plurality of gas channels with obstacles that improve diffusion by controlling gas velocity.The bipolar plate includes through-holes on both sides for mounting, designed to accommodate fasteners for assembling the remaining components of the fuel cell system and tightening the assembly. This bipolar plate is positioned between a membrane that allows the reacting gases to react and a terminal plate or another bipolar plate, thus forming the fuel cell, which can be stacked.

[0013] The bipolar plate has a gas inlet and a gas outlet, both through-holes connected to the outside via the end plates. At one end of the cell, the reactant gas is introduced through the gas inlet, and at the other end, the resulting gas is extracted through the gas outlet. Each bipolar plate has surface gas channels on one side that connect the gas inlet to the gas outlet. The gas flowing through the inlet enters the gas channels in contact with the membrane, where it reacts. The gas exiting the gas channels and exiting the outlet is different from the gas entering the inlet, having reacted during its passage.

[0014] Since the bipolar plate can be either an anode or a cathode, the gas flowing through the gas channels differs depending on the plate's function, as the gases react with the membrane between the plates. In the cathode bipolar plate, the incoming reactant gas is oxygen or air, while the anode bipolar plate is designed to receive the other reactant, which is hydrogen. Furthermore, in the anode bipolar plate, the outgoing reactant gas is excess hydrogen, which can be reintroduced into the system if stored, while in the cathode bipolar plate, the outgoing reactant gas is air, which contains the water produced in the reaction between oxygen and hydrogen.

[0015] On the other hand, since these reactions generate heat, the bipolar plate has a coolant inlet, a coolant outlet, and at least one surface cooling channel on a second face facing the end plate or the cooling channel of another bipolar plate. Coolant enters the cooling channel through the inlet and exits through the outlet. The goal is to dissipate the excess heat generated by the fuel cell while maintaining an acceptable temperature gradient. The coolant can be deionized water.

[0016] The bipolar plate design can be used for both the anode and cathode bipolar plates, as they are interchangeable due to their symmetry. The membrane is placed on the gas channel side of the bipolar plate, and another bipolar plate, identical to the first but rotated 180° with its gas channels facing the membrane, is placed on top of the membrane. This way, the gas inlet and outlet ports of the two bipolar plates are in different positions, causing the gases to circulate differently in each plate. This allows one bipolar plate to function as the anode and the other as the cathode, depending on the fuel or oxidizer received and its polarity.

[0017] Thus, the bipolar plates have one through-hole gas inlet through which the gas passes only through the plate, and another gas inlet connected to the channel, into which some of the reactant gas is introduced. The same occurs with one through-hole gas outlet through which the gases pass through the plate, and another gas outlet connected to the gas channels, through which the gases exit to the outside of the fuel cell.

[0018] The bipolar plate can have an active area of ​​at least 150 cm² 2It can be manufactured by machining the gas channels, the cooling channel, the gas inlet and outlet ports, and the refrigerant inlet and outlet ports. The machined gas channels for gas circulation are serpentine in shape and parallel to each other along their length, ensuring a continuous path for the reacting gases from beginning to end between the gas inlet and outlet ports.

[0019] Optionally, the bipolar plate can have four or eight parallel gas channels running along its first face in a serpentine pattern. The longer the gas channel, the greater the amount of gas that reacts with the membrane, thus optimizing its performance. Along these gas channels, which carry uniformly distributed gases, a first and a second obstacle are arranged repeatedly.

[0020] The first and second obstacles in the gas channel are three-dimensional, reducing the channel's cross-section and thus modifying the pressure and velocity of the reactant gas to improve its diffusion. Therefore, the operation of the bipolar plates is optimized by controlling the parameters along the gas channels that favor reactant gas diffusion.

[0021] The first obstacle can consist of a quarter-cylinder, a rectangular prism, and another quarter-cylinder. These first obstacles can reduce the cross-sectional area by 50% of the cross-sectional area of ​​the unobstructed gas channel. This section of the gas channel with the first obstacle causes the gas pressure to increase due to the reduced cross-section, which promotes diffusion and generates an increase in velocity. This improves the diffusion of the reactant gas with the electrode in this section, but it also increases the pressure drop, so the first obstacle is of a limited length.

[0022] As the reactant gas passes through the first obstacle, its pressure drops as it moves from a smaller to a larger cross-section, thus decreasing its velocity. To counteract this deceleration, a second obstacle in the form of a triangular prism is placed downstream of the first obstacle. This prism reduces the cross-sectional area of ​​the gas channel, where the reactant gas is propelled, increasing its velocity and resulting in less pressure loss than with the first obstacle.

[0023] Furthermore, to prevent potential leaks, both the inlet and outlet ports for reactive gases and refrigerant have a recess in the thickness of the second side of the bipolar plate to house a seal. This seal ensures the introduction of the reactive gas into the gas channels and prevents leaks between bipolar plates or other components. The seal is made of a flexible, insulating material that conforms to the dimensions of the recess, establishing complete contact between the components.

[0024] In industrial-scale bipolar plates, unlike smaller bipolar plates, the gas channels forming the coil have considerable vertical sections between the horizontal sections. This allows the bipolar plates to place the first obstacles in the vertical sections, thus overcoming the lack of reactant transport in the gas channels to the electrode in the vertical sections.

[0025] In this respect, since the gas channels are parallel to each other, the outer gas channels are longer than the inner gas channels on each side. Thus, the uneven arrangement of obstacles in the gas channels allows for a balanced pressure drop across all parallel gas channels and in all horizontal and vertical sections, preventing an imbalance in reactant flow rates between the different gas channels.

[0026] Therefore, the described bipolar plates allow for control of the parameters that favor the diffusion of the reactant gas along the gas channels, resulting in an optimized bipolar plate. These first and second obstacles are distributed within the gas channels to control the reactant gas parameters and to promote diffusion. DESCRIPTION OF THE DRAWINGS

[0027] To complement the description being made and in order to help a better understanding of the characteristics of the invention, according to a preferred embodiment thereof, a set of drawings is included as an integral part of said description, in which, for illustrative and non-limiting purposes, the following has been represented:

[0028] Figure 1.- Shows an exploded view of a PEM type fuel cell.

[0029] Figure 2.- Shows a front view of the first face of the bipolar plate where the gas channels through which the reactant gas circulates are located.

[0030] Figure 3.- Shows a perspective view of the second face with the cooling channels for cooling the bipolar plate.

[0031] Figure 4.- Shows a detailed perspective view of the gas channels of the bipolar plate.

[0032] PREFERRED EMBODIMENT OF THE INVENTION

[0033] The following describes a preferred embodiment of a bipolar plate intended to form part of an industrial-scale PEM fuel cell, which is the subject of this invention.

[0034] The bipolar plate intended to form part of the industrial-scale PEM fuel cell has a first face (14) with an active area, anode or cathode, and a second opposite face (15), wherein the bipolar plate comprises: side holes (2) for stacking the plates in a stack, two gas inlet holes (3) and two gas outlet holes (4), a coolant inlet hole (5) and a coolant outlet hole (6), at least one cooling channel (1) on the second face (15) and gas channels (7) on the first face (14) intended to conduct the reactant gases between one of the gas inlet holes (3) and one of the gas outlet holes (4).

[0035] The basic structure of the industrial-scale PEM fuel cell with at least 150 cm 2The active area stack, shown in Fig. 1, comprises at least one bipolar plate functioning as the anode, a membrane (12), and another bipolar plate functioning as the cathode, with a terminal plate (13) at each end of the stack. In this way, in the anode bipolar plate and the cathode bipolar plate, the reacting gases flow through the gas channels (7) in contact with the membrane (12), through which the reacting gas reacts. On the bipolar plate, on the second face (15) opposite the first face (14), the cooling channel (1) is connected to the coolant inlet (5) and the coolant outlet (6), intended to conduct the coolant from the coolant inlet (5) to the coolant outlet (6).

[0036] The bipolar plate further comprises first obstacles (8) in the gas channels (7) formed by a quarter-cylinder, a rectangular prism, and another quarter-cylinder, designed to reduce the cross-section of the gas channel (7), and second obstacles (9) following each of the first obstacles (8), in the form of a triangular prism, designed to reduce the cross-section of the gas channel (7) at specific points and propel the fluid. In this way, the gas channels (7) have the first obstacle (8) followed by the second obstacle (9) repeatedly along the length of the gas channel (7).

[0037] The serpentine geometric configuration of these gas channels (7) is designed to optimize the distribution of the reactive gas throughout the active area of ​​the PEMFC. Because the gas flows continuously from the gas inlet (3) to the outlet (4), it is forced to travel the entire length of the gas channel (7). Therefore, industrial-scale designs require multiple parallel gas channels (7), for example, eight gas channels (8).

[0038] Figure 2 shows the first face (14), in which the gas channels (7) are serpentine and have the first obstacles (8) followed by the second obstacles (9) designed to force gas convection and diffusion. This plate has eight parallel gas channels (7) with some horizontal and some vertical sections, the distribution of the obstacles (8,9) depending on the length of each gas channel (7).

[0039] The reactant gas is introduced into the gas channels (7) through an inlet duct (10) that connects to one of the gas inlet ports (3), and the gas is removed from the gas channels (7) through an outlet duct (11) that connects to one of the gas outlet ports (4). The inlet duct (10) is connected to the gas inlet port (3) on the second face (15) and passes through the bipolar plate to the gas channels (7) on the first face (14). Similarly, the outlet duct (11) is connected to the gas outlet port (4) on the second face (15) and passes through the bipolar plate to the gas channels (7) on the first face (14).

[0040] The bipolar plate of this embodiment has two gas inlet holes (3) and two gas outlet holes (4), with only one of the gas inlet holes (3) connected diagonally via the gas channels (7) to one of the gas outlet holes (4). The other gas inlet hole (3) and the other gas outlet hole (4) pass through both faces (14,15), so that the gas passes through the plate during gas introduction and extraction from the stack.

[0041] On the first face (14), the refrigerant inlet (5) is located on one side of the coil formed by the gas channels (7), and the refrigerant outlet (6) is located on the opposite side. The refrigerant inlet (5) and the refrigerant outlet (6) are through-holes, passing through the bipolar plate from the first face (14) to the second face (15).

[0042] In addition, the plate has six through-holes (2) on two sides for attaching the fuel cell assembly. A fastening element passes through these holes (2) to secure the bipolar plate assembly, membranes (12), and other components, forming the fuel cell.

[0043] Figure 3 shows the second face (15) where the coiled cooling channels (1) are arranged to conduct the coolant and cool the bipolar plate. These cooling channels (1) connect the coolant inlet (5) and the coolant outlet (6). The coolant is introduced from outside the stack to the inlet (5) located on the stacked plates. At each bipolar plate, some of the coolant enters the cooling channel (1), while the rest flows to other plates. The coolant cools the bipolar plate as it passes through the cooling channels (1) to the outlet (6), where it is discharged to the outside of the stack.

[0044] The cooling channels (1) on the second face (15) are coiled and designed to cover an area equal to that of the active area on the first face (14), where the gas channels (7) are located. This ensures uniform cooling of the bipolar plate, preventing heat buildup and regulating the temperature according to the conditions or needs.

[0045] Furthermore, the inlet duct (10) has two sections joined perpendicularly in an “L” shape, one of the sections being on the second face (15) connected at one end to the gas inlet orifice (3) and the other section being between the second face (15) and the first face (14) connected at one end to the gas channels (7). Similarly, the duct (11) is the same with respect to the gas outlet orifice (4).

[0046] The holes (2), the gas inlet holes (3), the gas outlet holes (4), the refrigerant inlet holes (5) and the refrigerant outlet holes (6) are through between the first face (14) and the second face (15).

[0047] Therefore, when two bipolar plates are placed with the gas channels (7) facing each other and the membrane (12) between them, the gas inlet (3) and gas outlet (4) connected to the gas channels (7) are in different positions on each plate. Consequently, the gases circulating through the gas channels (7) differ depending on whether the plate functions as an anode or cathode, which corresponds to its position in the stack.

[0048] Given the symmetry of the bipolar plate, all the inlet holes (3) and the gas outlet holes (4) and the inlet hole (5) and the refrigerant outlet hole (6) are bidirectional, thus allowing the conduction of fluids in one direction or the other.

[0049] Figure 4 shows in detail a plurality of parallel gas channels (7) in which a plurality of obstacles (8,9) are arranged. Each gas channel (7) has the first obstacles (8) arranged longitudinally and then the second obstacles (9) arranged at specific points, repeatedly along the gas channels (7). The membrane (12) is arranged on the first face (14) of these gas channels (7) such that the gas reacts as it is conducted through the gas channels (7).

[0050] The first obstacles (8) consist of a quarter-cylinder, a rectangular prism, and another quarter-cylinder designed to reduce the cross-section of the gas channel (7), increase the pressure, and force convection. This first obstacle (8) is longitudinal, designed to reduce the cross-section of the gas channel (7) in a prolonged manner.

[0051] The second obstacles (9) following each of the first obstacles (8) are triangular in shape, designed to selectively reduce the cross-section of the gas channel (7) and propel the gas with less pressure loss than with the first obstacle (8). This second obstacle (9) is positioned in the gas channel (7) separately from the first obstacle (8), specifically in the middle of the gap between the two first obstacles (8). In the embodiments, the gas channels (7) are machined into the thickness of the bipolar plate, with the obstacles (8, 9) being formed during machining. Similarly, the cooling channels (1), side ports (2), gas inlet ports (3), gas outlet ports (4), coolant inlet port (5), coolant outlet port (6), inlet duct (10), and outlet duct (11) are also machined.

[0052] Regarding the bipolar plate material, a material is preferably used that strikes a balance between mechanical strength to withstand tightening by screws, the weight of the assembly, and resistance to corrosion due to direct contact with the chemical reactions that occur inside the fuel cell.

Claims

CLAIMS 1.- An industrial-scale PEM fuel cell bipolar plate having a first face (14) with an active area, anode or cathode, intended to contact a membrane (12) and a second face (15) opposite the first face (14) intended to contact a terminal plate (13) or another bipolar plate, wherein the bipolar plate comprises: - through holes (2, 3, 4, 5, 6) between the faces (14, 15) consisting of: side holes (2) intended to receive fastening elements, two gas inlet holes (3), two gas outlet holes (4), a coolant inlet hole (5) and a coolant outlet hole (6), - gas channels (7) defined on the first face (14) intended to conduct the reactant gases between one of the gas inlet holes (3) and one of the gas outlet holes (4), - at least one cooling channel (1) defined on the second face (15) intended to conduct the coolant between the coolant inlet orifice (5) and the coolant outlet orifice (6), and is characterized in that it additionally comprises: - some initial obstacles (8) arranged at intervals in the gas channels (7) which have the following consecutive geometries: quarter cylinder, rectangular prism and another quarter cylinder, which reduce the passage section of the gas channel (7), and - some second obstacles (9) that have a triangular prism geometry arranged in the gas channels (7) after each of the first obstacles (8).

2. The bipolar plate of claim 1, wherein the first obstacles (8) and second obstacles (9) have a height corresponding to 50% of the height of the gas channel (7) to reduce the passage area of ​​the gas channel to 50%.

3. The bipolar plate of claim 1, wherein the gas channels (7) comprise eight gas channels (7) parallel to each other and forming a serpentine by means of horizontal and vertical sections.

4. The bipolar plate of claim 3, wherein the obstacles (8,9) are located in the horizontal sections of the gas channels (7) and the first obstacles (8) are also located in the vertical sections of the gas channels (7), the obstacles (8,9) being distributed according to the length of each gas channel (7).

5. The bipolar plate of claim 1, further comprising an inlet conduit (10) connecting the gas inlet orifice (3) to the gas channel (7) and an outlet conduit (11) connecting the gas outlet orifice (4) to the gas channel (7).

6. The bipolar plate of claim 5, wherein the conduits (10, 11) comprise two perpendicular L-shaped sections; a first section is on the second face (15) connected at a free end to the gas inlet orifice (3) or the gas outlet orifice (4), and a second section is between the second face (15) and the first face (14) connected at a free end to the gas channels (7).

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