A variable cross-section series parallel flow channel flow field plate, bipolar plate and fuel cell stack

Abstract

The present invention provides a flow field plate with variable cross-section and parallel flow channels in series, a bipolar plate and a fuel cell stack, wherein the flow channel area of ​​the flow field plate is a parallel flow field composed of mutually parallel flow channel ridges and flow channel grooves, and a plurality of adjacent common channels are respectively provided at both ends of the parallel flow field opening, and the areas of the common channels decrease successively, and the common channels are separated by a sealing structure, and the common channels at both ends of the parallel flow field opening are symmetrically distributed, and a group of parallel flow channel groups are formed between the common channels with the same areas at both ends of the parallel flow field opening, and the two edges of the flow field plate parallel to the parallel flow field flow channel ridges and flow channel grooves are provided with inlet common channels and outlet common channels for other media. In the present invention, the medium flow cross-sectional area in the flow field plate gradually decreases, so that the gas flow rate or stoichiometric ratio in the entire flow field area does not decrease with the reaction consumption of the medium, which has the effect of enhancing the liquid water discharge efficiency and reducing the apparent stoichiometric ratio.

Description

Technical Field

[0001] The present invention belongs to the technical field of fuel cells, and in particular relates to a variable-section series parallel flow channel flow field plate, a bipolar plate and a fuel cell stack. Background Art

[0002] A fuel cell is a device that generates electricity by electrochemically redox reacting an oxidant (air, oxygen, etc.) with a fuel (hydrogen, hydrogen storage material, etc.), and generates a certain amount of heat during the power generation process. The fuel cell bipolar plate assembly serves to evenly distribute the fuel, oxidant, and coolant in the reactive area. The bipolar plate assembly consists of two to three stacked flow field plates, which form flow field structures for the fuel, oxidant, and coolant, respectively, under a specific flow channel ridge and groove structure to achieve medium distribution. Under the traditional flow field form with a constant flow cross-sectional area, as the reaction medium (fuel and oxidant) is consumed, the flow rate, pressure, and concentration of the gas medium along the flow direction of the flow channel all decrease. The uneven distribution of the physical properties of the reaction medium leads to an uneven distribution of the electrochemical reaction, thereby reducing the average electrical performance. At the same time, as the water generated by the reaction continues to accumulate, the reduction in the gas flow rate is likely to cause local flooding, further deteriorating the electrochemical reaction environment, causing the power generation voltage to continue to decrease in the constant current mode, and reducing the reliability of fuel cell power generation.

[0003] In response to the above problems, on the basis of the traditional multi-channel serpentine flow field, the number of channels of the serpentine flow field is gradually reduced along the flow direction of the medium in the reaction active area to form a flow field structure with a gradually reduced flow cross-sectional area, which can increase the gas flow rate near the flow field outlet. However, the reduction in the number of channels in the serpentine flow field is achieved by merging two or more flow channel grooves inside the flow field plate. On the one hand, this leads to an increase in the pressure drop of the flow field and increases the power consumption of external auxiliary components. On the other hand, the merging of the flow channel grooves intensifies the aggregation of water generated by the reaction. Water is easily flooded at the merging of the flow channel grooves, causing voltage and gas pressure fluctuations, and reducing the reliability of fuel cell power generation. Summary of the invention

[0004] In order to overcome the deficiencies in the prior art, the inventors have conducted intensive research and provided a variable-section series parallel flow channel flow field plate, which connects multiple groups of parallel flow channel groups in series with an external manifold through a common channel in order of the number of flow channels from large to small, thereby reducing the difficulty of flow field plate design and forming an effect of gradually shrinking medium flow cross-sectional area, so that the gas flow rate or stoichiometric ratio in the entire flow field area does not decrease with the reaction consumption of the medium, thereby enhancing the liquid water discharge efficiency and reducing the apparent stoichiometric ratio.

[0005] The technical solution provided by the present invention is as follows:

[0006] In the first aspect, a flow field plate with variable cross-section serial parallel flow channels, the flow channel area of ​​the flow field plate is a parallel flow field composed of mutually parallel flow channel ridges and flow channel grooves, a plurality of adjacent common channels are respectively provided at both ends of the parallel flow field opening, the areas of the common channels decrease successively, the common channels are separated by sealing structures, the common channels at both ends of the parallel flow field opening are symmetrically distributed, and a group of parallel flow channel groups are formed between the common channels with the same areas at both ends of the parallel flow field opening, the flow field plate contains two or more parallel flow channel groups, and the two edges of the flow field plate parallel to the parallel flow field flow channel ridges and flow channel grooves are provided with inlet common channels and outlet common channels for other media.

[0007] In a second aspect, a bipolar plate assembly uses the variable cross-section series parallel flow channel flow field plate described in the first aspect as an anode plate or a cathode plate.

[0008] In a third aspect, a single cell uses the variable cross-section series parallel flow channel flow field plate described in the first aspect as an anode plate or a cathode plate.

[0009] In a fourth aspect, a fuel cell stack uses the variable cross-section series parallel flow channel flow field plate described in the first aspect as the anode plate or cathode plate in a bipolar plate assembly.

[0010] A variable cross-section series parallel flow channel flow field plate, bipolar plate and fuel cell stack provided by the present invention have the following beneficial effects:

[0011] (1) High drainage efficiency: The public channels at both ends of the parallel flow field openings are connected in pairs through external manifolds, and gas-water separation can be performed at the external manifolds. Compared with the traditional flow field plate structure that can only discharge generated water at the flow field outlet, the serial parallel flow field structure of the present invention can achieve multiple gas-water separations from the flow field inlet to the flow field outlet through the external manifold, shortening the drainage distance, increasing the drainage frequency, and improving the drainage efficiency of the flow field plate;

[0012] (2) Low flow field resistance: Since the flow field plate adopts a parallel flow field structure, the gas flow resistance is low; the parallel flow channel groups are connected in series through an external manifold, and the manifold flow resistance is lower than the flow resistance at the turning point of the serpentine flow field, thus achieving the low flow resistance effect of multi-channel variable cross-section series parallel flow field;

[0013] (3) Uniform distribution of media: The number of flow channels in the series parallel flow channel group gradually decreases along the flow direction, avoiding the reduction of flow velocity and pressure caused by the consumption of reaction media; in addition, the parallel flow fields are grouped and connected in series, which reduces the inlet cross-sectional area of ​​the parallel flow fields, and there is no problem of uneven gas distribution in a wide inlet area, thereby improving the uniformity of the distribution of reaction media in the reaction active area of ​​the fuel cell;

[0014] (4) High system efficiency: The fuel cell system includes power-consuming components such as gas circulation pumps or compressors to provide excess supply of reaction medium to ensure sufficient electrochemical reaction. After the parallel flow channel groups are connected in series, the excess medium of the upstream flow channel group can be consumed by the reaction of the downstream flow channel group. Since the reactive area of ​​the last flow channel group is much smaller than the complete reactive area of ​​the flow field plate, the apparent metering ratio requirement can be reduced. At the same time, the flow field plate structure of the present invention has a low flow resistance. The overall result is that the demand for the flow rate and pressure rise of the circulation pump or compressor is reduced, which has a high system efficiency in terms of energy conversion rate and economic benefit.

[0015] (5) Low design and development cost of flow field plates: The present invention connects the common channel with the external manifold of the fuel cell stack to realize the series connection of grouped parallel flow channels and the gradual reduction of the flow field cross-sectional area. Compared with the gradient multi-channel serpentine flow field plate, the parallel flow field plate has a simpler structure and can flexibly change the common channel grouping method according to the design working point of the fuel cell without changing the flow field structure. Therefore, the design and development of the flow field plate is less difficult, and the processing cost of the parallel flow field plate with a simple structure is also lower. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 Schematic diagram of the flow field plate structure of Example 1.

[0017] Description of Figure Numbers:

[0018] 1-flow field plate; 21-first common channel of the first parallel flow channel group; 22-second common channel of the first parallel flow channel group; 23-first common channel of the second parallel flow channel group; 24-second common channel of the second parallel flow channel group; 25-first common channel of the third parallel flow channel group; 26-second common channel of the third parallel flow channel group; 31-medium B inlet common channel; 32-medium B outlet common channel; 41-medium C inlet common channel; 42-medium C outlet common channel; 5-flow channel groove; 6-flow channel ridge; 7-group sealing ridge; 8-flow field sealing ridge; 9-flow field sealing groove. DETAILED DESCRIPTION

[0019] The following detailed description of the present invention will make the features and advantages of the present invention more clear and explicit.

[0020] The word "exemplary" is used exclusively herein to mean "serving as an example, embodiment, or illustration." Any embodiment described herein as "exemplary" is not necessarily to be construed as preferred or advantageous over other embodiments. Although various aspects of the embodiments are shown in the drawings, the drawings are not necessarily drawn to scale unless otherwise noted.

[0021] According to a first aspect of the present invention, there is provided a flow field plate with variable cross-section serial parallel flow channels, wherein the flow channel region of the flow field plate is a parallel flow field composed of mutually parallel flow channel ridges and flow channel grooves, a plurality of adjacent common channels are respectively provided at both ends of the parallel flow field opening, the areas of the common channels decrease successively, the common channels are separated by sealing structures, the common channels at both ends of the parallel flow field opening are symmetrically distributed, a group of parallel flow channel groups is formed between the common channels with the same areas at both ends of the parallel flow field opening, the number of common channels at one end of the parallel flow field opening is the same as the number of parallel flow channel groups, the flow field plate may include two or more parallel flow channel groups, and the two edges of the flow field plate parallel to the parallel flow field flow channel ridges and flow channel grooves are provided with inlet common channels and outlet common channels for other media.

[0022] When forming a fuel cell stack, the common channels with decreasing areas at both ends of the parallel flow field are connected through the external manifold of the stack, and the common channels with large areas are connected alternately in a manner of gradually decreasing areas. After each upstream and downstream common channel is connected through the external manifold, it is necessary to connect with the common channel at the other end of the channel through the parallel channel group corresponding to the downstream common channel, thereby forming a series connection between different parallel channel groups. Furthermore, the external manifold connecting the upstream and downstream common channels is connected to the gas-water separation device to implement gas-water separation.

[0023] Furthermore, the public channel connection methods include the following two methods:

[0024] (i) The upstream common channel is connected to the downstream common channel on the opposite side, and the downstream common channel is connected to the downstream common channel on the opposite side, and the upstream and downstream common channels are connected in this connection mode; this mode is the preferred connection mode;

[0025] (ii) The upstream public channel is connected to the downstream public channel on the same side, and another downstream public channel is connected to the downstream public channel on the same side, and the upstream and downstream public channels are connected in this way.

[0026] In the present invention, a flow field sealing ridge is provided at the edge of the flow channel region of the flow field plate, so as to form a contact seal with the membrane electrode frame when a fuel cell stack is formed.

[0027] In the present invention, flow field sealing grooves are provided around the flow field sealing ridge, other medium inlet common channels and outlet common channels, and cooperate with the sealing ring to seal the flow field plate.

[0028] According to a second aspect of the present invention, a bipolar plate assembly is provided, wherein the variable cross-section series parallel flow channel flow field plate described in the first aspect is selected as an anode plate or a cathode plate.

[0029] According to a third aspect of the present invention, a single cell is provided, wherein the variable cross-section series parallel flow channel flow field plate described in the first aspect is selected as an anode plate or a cathode plate.

[0030] According to a fourth aspect of the present invention, a fuel cell stack is provided, wherein the variable cross-section series parallel flow field plate described in the first aspect is used as an anode plate or a cathode plate in a bipolar plate assembly.

[0031] Example 1

[0032] The fuel cell bipolar plate assembly described in the present invention includes inlet and outlet channels for three media: fuel cell fuel, oxidant, and coolant. It is defined that medium A, medium B, and medium C can be arranged and combined to correspond to the three media of fuel cell fuel, oxidant, and coolant, respectively. In this embodiment, medium A represents the oxidant, medium B represents the fuel, and medium C represents the coolant. In this embodiment, the parallel flow fields are divided into three groups, and can also be divided into any multiple groups of two or more.

[0033] The structure of the flow field plate can be found in Figure 1 . The flow channel area of ​​the flow field plate 1 is a parallel flow field composed of mutually parallel flow channel ridges 6 and flow channel grooves 5. A plurality of adjacent common channels are respectively provided at both ends of the parallel flow field opening. The areas of the common channels decrease successively. The common channels are separated by grouping sealing ridges 7. The common channels at both ends of the parallel flow field opening are symmetrically distributed. A group of parallel flow channel groups is formed between the common channels with the same area at both ends of the parallel flow field opening, that is, the number of common channels at one end of the parallel flow field opening is the same as the number of parallel flow channel groups. The flow field plate may contain two or more parallel flow channel groups. Common channels for other media are provided on the two edges of the flow field plate parallel to the parallel flow field flow channel ridges 6 and flow channel grooves 5, including a medium B inlet common channel 31, a medium B outlet common channel 32, a medium C inlet common channel 41 and a medium C outlet common channel 42. After forming a fuel cell stack, the common channels with decreasing areas at both ends of the parallel flow field are connected through the external manifold of the stack, and the common channels with large areas are connected alternately in a manner of gradually decreasing areas. After each upstream and downstream common channel is connected through the external manifold, it is necessary to connect the common channel at the other end of the flow channel through the parallel flow channel group corresponding to the downstream common channel, thereby forming a series connection between different parallel flow channel groups. The first common channel 21 of the first parallel flow channel group serves as the inlet of medium A, and the second common channel 26 of the third parallel flow channel group serves as the outlet of medium A. There are two ways to connect the common channels:

[0034] ① The second common channel 22 of the first parallel channel group is connected to the first common channel 23 of the second parallel channel group; the second common channel 24 of the second parallel channel group is connected to the first common channel 25 of the third parallel channel group;

[0035] ② The second common channel 22 of the first parallel flow channel group is connected to the second common channel 24 of the second parallel flow channel group; the first common channel 23 of the second parallel flow channel group is connected to the first common channel 25 of the third parallel flow channel group.

[0036] The difference between the above two common channel connection methods lies in the different external manifold structures of the fuel cell stack. When the parallel flow channel direction is perpendicular to the gravity direction, the first connection method can also use gravity drainage, which is a more recommended connection method.

[0037] In the present embodiment, there are three parallel flow channel groups. Medium A flows from the first common channel 21 of the first parallel flow channel group to the second common channel 26 of the third parallel flow channel group through the three parallel flow channel groups connected in series. The number of flow channels in each parallel flow channel group gradually decreases. The regulation of the number of flow channels can achieve regulation of the intrinsic stoichiometric ratio of each parallel flow channel group, so that the intrinsic stoichiometric ratios in each parallel flow channel group are basically the same. At the same time, the apparent stoichiometric ratio from the inlet of medium A to the outlet of medium A can be counted to achieve a lower apparent stoichiometric ratio and improve the efficiency of the battery stack system. Because the number of flow channels of parallel flow channels is proportional to the reactive area, and the reactive area is proportional to the medium consumption, it is assumed that 1 flow channel represents a consumption of medium A of 1 SLPM. Taking connection method ① as an example, Figure 1 As shown, the medium consumption of the first parallel flow channel group I connected to the first common channel 21 of the first parallel flow channel group is 12SLPM. If 24SLPM of medium A is supplied to the flow channel from the first common channel 21 of the first parallel flow channel group, the amount of medium A discharged to the second common channel 22 of the first parallel flow channel group after passing through the first parallel flow channel group I is 12SLPM. The first common channel 23 of the second parallel flow channel group is connected to the second common channel 22 of the first parallel flow channel group, and the amount of medium A entering the second parallel flow channel group II is 12SLPM. Since the reaction active area of ​​the second parallel flow channel group II is smaller, 6SLPM of medium A is consumed, and the amount of medium A discharged to the second common channel 24 of the second parallel flow channel group after passing through the second parallel flow channel group II is 6SLPM. By analogy, the medium A consumption and discharge of the three parallel flow channel groups are shown in Table 1. The sum of the reactive areas of the three parallel flow channel groups is the total reactive area of ​​the flow field plate, so the total consumption of medium A through the flow field plate is 12+6+3=21SLPM. In addition, the flow rate of medium A entering the flow field plate 1 is 24SLPM, and the flow rate of medium A flowing out of the flow field plate 1 is 3SLPM. The chemical dosage ratio of the electrochemical reaction of the fuel cell is defined as (consumption of medium A+discharge of medium A) / consumption of medium A, so the intrinsic stoichiometric ratio of each parallel flow channel group and the apparent stoichiometric ratio of the flow field plate 1 can be obtained, as shown in the last column of Table 1. It can be seen that the series connection of parallel flow channel groups with gradually decreasing flow channel numbers achieves the effect of balancing the stoichiometric ratio within the reactive area, so that the entire reactive area has a higher stoichiometric ratio, which is conducive to improving the electrochemical reaction performance and improving the water management efficiency; at the same time, a very low apparent stoichiometric ratio of the flow field plate is achieved, which reduces the flow demand for circulating pumps, compressors, etc., and improves the system efficiency of the fuel cell.

[0038] Table 1 Analysis of the implementation principle of low metering ratio

[0039]

[0040] The flow field plate of the present invention can be combined with the same type of flow field plate or serpentine flow field plate, traditional parallel flow field plate and other flow field forms to form a bipolar plate assembly, realize the flow distribution of medium A, medium B and medium C, and can be stacked with the membrane electrode to form a fuel cell stack structure. The flow field sealing ridge 8 forms a contact seal with the membrane electrode frame, and the flow field sealing groove 9 can be sealed by welding to achieve the sealing of the bipolar plate intermediate cooling flow field.

[0041] The present invention has been described in detail above in conjunction with specific implementations and exemplary examples, but these descriptions cannot be understood as limiting the present invention. Those skilled in the art understand that, without departing from the spirit and scope of the present invention, a variety of equivalent substitutions, modifications or improvements may be made to the technical solution of the present invention and its implementation methods, all of which fall within the scope of the present invention. The scope of protection of the present invention shall be subject to the attached claims.

[0042] The contents not described in detail in the specification of the present invention belong to the common knowledge of those skilled in the art.

Claims

1. A variable cross-section series parallel flow channel flow field plate, characterized in that: The flow channel area of ​​the flow field plate is a parallel flow field composed of mutually parallel flow channel ridges and flow channel grooves. A plurality of adjacent common channels are respectively provided at both ends of the parallel flow field opening. The areas of the common channels decrease successively. The common channels are separated by a sealing structure. The common channels at both ends of the parallel flow field opening are symmetrically distributed. A group of parallel flow channel groups is formed between the common channels with the same areas at both ends of the parallel flow field opening. The flow field plate contains two or more parallel flow channel groups. The two edges of the flow field plate parallel to the parallel flow field flow channel ridges and flow channel grooves are provided with inlet common channels and outlet common channels for other media. The common channels with decreasing areas at both ends of the parallel flow fields are connected through the external manifold of the fuel cell stack, and are alternately connected in a manner of gradually decreasing areas from large-area common channels. After each upstream and downstream common channels are connected through the external manifold, they are connected to the common channel at the other end of the channel through the parallel channel group corresponding to the downstream common channel, thereby forming a series connection between different parallel channel groups; the number of channels in the series parallel channel groups gradually decreases along the flow direction.

2. The variable cross-section serial parallel flow channel flow field plate according to claim 1, characterized in that: The external manifold connecting the two upstream and downstream common channels is connected to the gas-water separation device.

3. The variable cross-section serial parallel flow channel flow field plate according to claim 1, characterized in that: The edge of the flow channel area of ​​the flow field plate is provided with a flow field sealing ridge, which forms a contact seal with the membrane electrode frame when forming a fuel cell stack.

4. The variable cross-section serial parallel flow channel flow field plate according to claim 1, characterized in that: The flow field sealing ridge, other medium inlet common channel and outlet common channel are provided with flow field sealing grooves at the periphery thereof, which cooperate with the sealing ring to seal the flow field plate.

5. A bipolar plate assembly, characterized in that: The variable cross-section serial parallel flow channel flow field plate as claimed in any one of claims 1 to 4 is selected as an anode single plate or a cathode single plate.

6. A single battery, characterized in that: The variable cross-section serial parallel flow channel flow field plate as claimed in any one of claims 1 to 4 is selected as an anode single plate or a cathode single plate.

7. A fuel cell stack, characterized in that: The variable cross-section series parallel flow channel flow field plate as claimed in any one of claims 1 to 4 is selected as the anode plate or cathode plate in the bipolar plate assembly.

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