End part gas passing gradient structure of fuel cell stack and preparation method and application of end part gas passing gradient structure

Abstract

The invention discloses an end part gas passing gradient structure of a fuel cell stack in the field of cell stack manufacturing. The device comprises blind end inflation sheets, porous medium filling sheets and overflowing sheets which are arranged in sequence, when the number of the porous medium filling sheets is larger than or equal to 2, the porosity is in gradient distribution, and the porosity at the edge is smaller than that at the center; cathode and anode runners of the blind end inflatable sheet are separated and communicated through carbon paper, and according to different anodes and cathodes, single-channel conduction is adopted, and the air pressure balance design that the other electrode is closed in a full-channel mode is adopted. A gas passing gradient structure is constructed, so that uniform temperature regulation and control and ordered fluid transition are realized, water accumulation at the end part is avoided, and the voltage consistency is guaranteed; the water pressure difference is avoided, the end flow field is optimized, the flow resistance step and the air inlet single low are avoided, and the working medium waste is reduced; multiple targets of heat preservation, flow changing and water diversion are achieved, and the problem of single-low end of the full-working-condition stack is solved.

Description

Technical Field

[0001] The present invention belongs to the field of fuel cell stack manufacturing, and particularly relates to an end gas passing gradient structure of a fuel cell stack, a preparation method thereof, and an application thereof. Background Art

[0002] The single-cell voltage consistency of a fuel cell stack is one of the important indicators for evaluating the performance of the stack. A higher single-cell voltage consistency indicates better performance and stability of the stack. Due to the influence of operating parameters, structure, materials, etc., the current single-cell voltage consistency of fuel cell stacks is not very satisfactory.

[0003] The prominent reasons for the unsatisfactory single-cell voltage consistency of fuel cell stacks are mainly related to the design of the stack end in the following aspects: First, the heat preservation condition at the stack end is poor, and under the influence of the temperature gradient at the end, the problems of internal liquid water precipitation and water accumulation are relatively serious; Second, obvious vortex problems exist at the end, resulting in poor air intake at the end; Third, under the anode circulation condition or the cathode pure oxygen circulation condition, the intake air of the fuel cell stack may contain liquid water, which has the most significant impact on the end. In the current technology, the end design of the fuel cell stack uses a combination of multiple current-carrying plates. The structure of the current-carrying plate is as Figure 1 shown, including a cathode plate and an anode plate. The cathode and anode flow channels are separated and gas-connected through carbon paper, and both the cathode and anode are single-channel conduction on the same side.

[0004] To solve the above problems, the current technical solutions mainly introduce dummy plates with airtight gas paths and unobstructed water paths at the end to achieve end heat preservation. However, this method may cause a large pressure difference between the water vapor on both sides inside the dummy plate, resulting in mechanical damage or seal failure under large water flow conditions; Or directly introduce dummy plates with gas circulation at the end to achieve water drainage, but this method is extremely likely to cause flow waste, and simply adding current-carrying plates is also not conducive to improving the system efficiency.

[0005] Therefore, the current structural form of the fuel cell stack end is too single, which not only fails to completely solve the problem of low single-cell voltage consistency of the stack, but also makes the problems existing at the stack end occur frequently. At the same time, there is a lack of effective multi-dimensional structure and optimization design methods for the fuel cell stack end, making it difficult to achieve multiple goals such as heat preservation, flow modification, and water diversion, and it is also impossible to achieve synchronous optimization of the two-phase flow and temperature field at the end. Summary of the Invention

[0006] The present invention aims to provide an end gas passing gradient structure of a fuel cell stack and a preparation method thereof to better solve the problem of low single-cell voltage consistency of the stack.

[0007] An end gradient structure of a fuel cell stack in this solution. The end gradient structure includes a blind-end inflation sheet, a porous medium filling sheet, and a flow-through sheet arranged in sequence. The flow-through sheet is adjacent to the fuel cell stack. When the number of porous medium filling sheets is greater than or equal to 2, the porosity parameter k of the filling medium n shows a gradient distribution, and k n near the edge of the fuel cell stack is less than k n near the center of the fuel cell stack;

[0008] The anode and cathode flow channels of the blind-end inflation sheet are separated by carbon paper to achieve regional separation and gas connection. When it is used as the cathode blind-end inflation sheet, a pressure balance design of single-channel conduction for the cathode and full-channel closure for the anode is implemented; when it is used as the anode blind-end inflation sheet, single-channel conduction for the anode and full-channel closure for the cathode are adopted.

[0009] The present invention also provides a preparation method for the end gradient structure of a fuel cell stack, including the following steps:

[0010] a) Establish an initial reference structure system for the edge of the fuel cell stack

[0011] i) Determine m blind-end inflation sheets, where the number m≥0 and the positions of the blind-end inflation sheets are arranged on the edge side of the fuel cell stack;

[0012] ii) Determine n porous medium filling sheets, where the number n≥0 and the positions are between the blind-end inflation sheets and the flow-through sheets; when n≥1, an initial porosity parameter k of the filling medium needs to be set n ; when n≥2, implement a porosity gradient distribution, that is, k n near the edge of the fuel cell stack is less than k n near the center of the fuel cell stack;

[0013] iii) Determine p flow-through sheets, where the number p≥0 and the positions of the flow-through sheets are close to the center side of the fuel cell stack;

[0014] b) Determine the pass / fail judgment threshold of 1 to 10 for the edge gradient structure of the fuel cell stack;

[0015] c) Carry out end gas distribution optimization for the edge gradient structure of the fuel cell stack

[0016] i) Conduct a sensitivity analysis of the excess coefficient λ under low gas supply humidity conditions where the humidity is below 20%. When λ drops to the critical value λ low , collect voltage parameters: measure the difference Δ1 between the lowest voltage within the end range and the average voltage of the fuel cell stack; measure the mean square deviation F1 of the maximum single-cell voltage fluctuation;

[0017] ii) Implement a judgment logic: The passing condition needs to satisfy Δ1≤threshold 1 and F1≤threshold 2, otherwise increase the value of m or n, or adjust k n , until the parameters meet the standards;

[0018] d) Optimize the heat preservation performance of the edge gradient structure of the battery stack

[0019] i) Conduct a sensitivity analysis of the excess coefficient λ under the condition of near-saturated or saturated humidification of the supplied gas. When λ drops to the critical value λ low , simultaneously collect the parameter group: measure the difference Δ2 between the lowest voltage within the end range and the average voltage of the battery stack, and the difference term Δ2 - Δ1; obtain the mean square deviation F of the maximum single-cell voltage fluctuation 2， and the difference term F2 - F1;

[0020] ii) Determine that the compliance condition needs to satisfy all the constraint conditions of Δ2 ≤ threshold 3, F2 ≤ threshold 4, (Δ2 - Δ1) ≤ threshold 5, and (F2 - F1) ≤ threshold 6. Otherwise, implement an upgrade by increasing the value of m or injecting a heat preservation medium into the flow channels of the blind-end inflatable sheet, and conduct the determination again until the parameters meet the standards and the determination is qualified;

[0021] e) Special optimization of drainage characteristics

[0022] If the anode edge design or the cathode structure of the pure oxygen fuel cell is involved, the following additional steps are performed:

[0023] i) Conduct a sensitivity analysis of the excess coefficient λ under the condition of supersaturated humidification of the supplied gas. When λ = λ low , obtain the difference Δ3 between the lowest voltage within the end range and the average voltage of the battery stack, and the difference term Δ3 - Δ1, obtain the mean square deviation F3 of the maximum single-cell voltage fluctuation, F3 - F1;

[0024] ii) Determine that the compliance condition needs to satisfy all the constraint conditions of Δ3 ≤ threshold 7, F3 ≤ threshold 8, (Δ3 - Δ1) ≤ threshold 9, and (F3 - F1) ≤ threshold 10. Otherwise, conduct an optimization upgrade by increasing the value of p and conduct the determination again until the parameters meet the standards and the determination is qualified.

[0025] Furthermore, when the end gradient structure is the end of the cathode side of the battery stack, the anode side must use low-humidity hydrogen with a humidity below 20% and ensure saturated gas supply to avoid anode water accumulation and water ingress at the front end of the anode;

[0026] When designing the edge gradient structure of the anode side of the battery stack, the cathode side must maintain low-humidity gas supply with a humidity below 20% and ensure saturated gas supply to avoid cathode water accumulation and water ingress at the front end of the cathode.

[0027] Furthermore, the internal flow channels of the porous medium filling sheet are filled with a hydrophobic material. It realizes the dual functions of blocking the penetration of liquid water at the front end and optimizing the drainage path at the rear end, avoiding the inflow of liquid water at the front end and ensuring the timely and effective discharge of liquid water.

[0028] Further, after increasing the number n of the porous medium filling sheets, the porosity k of the filling medium needs to be adjusted correspondingly n , still ensuring that k n has a gradient distribution characteristic.

[0029] Further, when the gas inside the blind-end inflatable sheet does not flow, air pressure is introduced to balance the water pressure.

[0030] Further, the above-mentioned gas supply supersaturated humidification condition can be simulated by injecting liquid water at the front end of the intake air.

[0031] During the operation of the fuel cell stack, due to problems such as water accumulation caused by poor end heat preservation conditions and poor air intake caused by eddy currents, the fuel cell monomers near the end are prone to problems of poor voltage consistency. In the present invention, the blind-end inflatable sheet does not allow air to pass through, the porous medium filling sheet allows a small amount of air to pass through, and the flow-through sheet allows a large amount of air to pass through, forming an air intake gradient at the end of the fuel cell stack, realizing uniform regulation of temperature, orderly transition of fluids, avoiding water accumulation at the end, and ensuring the consistency of the single-cell voltage of the fuel cell stack. Through the blind-end inflatable sheet at the end, the problem of pressure difference on both sides of water vapor is avoided. Through the porous medium filling sheet, the end flow field is optimized, avoiding the step transition of the flow resistance between end sheets, realizing gradient orderly transition, avoiding the problem of single low air intake, and controlling the waste of working medium at the lowest level. By reasonably setting the flow-through water diversion sheet, the problem of water accumulation at the end is avoided. Thus, the optimization of two-phase flow and temperature field at the end of the battery stack is realized synchronously, the multi-objectives of heat preservation, flow modification, and water diversion are realized synchronously, the large pressure difference between water and gas is avoided, and the waste of working medium is minimized as much as possible. The present invention is an efficient solution to completely solve the problem of single low at the end of the stack under all working conditions. Description of the Drawings

[0032] Figure 1 is the structure of the flow-through sheet in the prior art;

[0033] Figure 2 is a structure of a fuel cell stack combined with its end provided according to Embodiment 1 of the present application;

[0034] Figure 3 is a structure of a blind-end inflatable sheet provided according to Embodiment 1 of the present application;

[0035] Figure 4 is a structure of a porous medium filling sheet provided according to Embodiment 1 of the present application;

[0036] Figure 5 is a flowchart of a method for designing the end air intake gradient structure of a fuel cell stack provided according to Embodiment 2 of the present application;

[0037] Figure 6 is a test chart of the rated point stack voltage consistency of a fuel cell stack prepared according to Embodiment 2 of the present invention;

[0038] Figure 7 It is a test chart of the rated point stack voltage consistency of a fuel cell stack with only an overcurrent sheet at the end in the comparative example. Specific Embodiments

[0039] The following is a further detailed description through specific embodiments:

[0040] The reference numerals in the accompanying drawings of the specification include: fuel cell stack 1, blind-end inflation sheet 2, porous medium filling sheet 3 (with a relatively small medium porosity), porous medium filling sheet 4 (with a relatively large medium porosity), overcurrent sheet 5, plugging body 6, cathode plate 7, carbon paper 8, anode plate 9, and porous medium 10.

[0041] Example 1, A fuel cell stack, its structure is as Figure 2 shown. The end gradient structure of the fuel cell stack 1 includes a blind-end inflation sheet 2, a porous medium filling sheet 3, a porous medium filling sheet 4, and an overcurrent sheet 5 arranged in sequence. The overcurrent sheet 5 is adjacent to the fuel cell stack 1.

[0042] There are two overcurrent sheets 5, and their structures are the same as those in the prior art. As Figure 1 shown, it includes a cathode plate 7 and an anode plate 9. The cathode and anode flow channels are separated in area and connected in gas through carbon paper 8. Both the cathode and anode are single-channel conductive on the same side, and the closed part is closed by a plugging body 6.

[0043] As Figure 3 shown, there is one blind-end inflation sheet 2. The difference between it and the overcurrent sheet 5 is that the cathode and anode flow channels of the blind-end inflation sheet 2 are separated in area and connected in gas through carbon paper 8. When it is used as the cathode blind-end inflation sheet 2, it performs a pressure balance design of single-channel conduction at the cathode and full-channel closure at the anode, and is closed by a plugging body 6; when it is used as the anode blind-end inflation sheet 2, it uses single-channel conduction at the anode and full-channel closure at the cathode. When the internal gas of the blind-end inflation sheet 2 does not flow, air pressure is introduced to balance the water pressure.

[0044] As Figure 4 shown, there are two porous medium filling sheets. The difference between them and the overcurrent sheet 5 is that their internal flow channels are filled with a hydrophobic porous medium 10. For example, common foams and porous carbons can be used. The number of porous medium filling sheets is greater than or equal to two, and the porosity parameter k of the filled porous medium 10 n shows a gradient distribution. Taking two sheets as an example, the porosity of the porous medium filling sheet 3 near the edge of the battery stack is less than the porosity of the porous medium filling sheet 4 near the center of the battery stack.

[0045] Example 2, A method for preparing the end gradient structure of the fuel cell stack described in Example 1, in combination with Figure 5 shown, includes the following steps:

[0046] a) Establish the initial reference structure system for the battery stack edge

[0047] i) Determine that the number of blind-end inflatable sheets 2 is 1, and the position of the blind-end inflatable sheet 2 is arranged on the edge side of the battery stack;

[0048] ii) Determine that the number of porous medium filling sheets is 2, and the porosity gradient distribution of the two porous medium filling sheets, that is, the porosity parameter k of the porous medium filling sheet 3 near the battery stack edge n is less than the porosity parameter k of the porous medium filling sheet 4 near the battery stack center n ;

[0049] iii) Determine that the number of current-carrying sheets 5 is 2, and the position of the current-carrying sheets is close to the center side of the battery stack;

[0050] b) Determine the qualified judgment threshold of 1 - 10 for the battery stack edge gradient structure;

[0051] c) Carry out end gas distribution optimization for the battery stack edge gradient structure

[0052] i) Conduct an analysis of the sensitivity of the excess coefficient λ under low supply air humidity conditions. When λ drops to the critical value λ low , collect voltage parameters: measure the difference Δ1 between the lowest voltage within the end range and the average voltage of the battery stack; measure the mean square deviation F1 of the maximum single-cell voltage fluctuation;

[0053] ii) Implement the judgment logic: The judgment of reaching the standard requires that Δ1 ≤ threshold 1 and F1 ≤ threshold 2. Otherwise, increase the value of m or n, or adjust k n , until the parameters reach the standard; where after increasing the number n of porous medium filling sheets, the porosity k of the filling medium needs to be adjusted correspondingly n , still ensuring the gradient distribution characteristics of k n ;

[0054] d) Carry out heat preservation performance optimization for the battery stack edge gradient structure

[0055] i) Conduct an analysis of the sensitivity of the excess coefficient λ under near-saturated or saturated humidification conditions of the supply air. When λ drops to the critical value λ low , synchronously collect parameter groups: measure the difference Δ2 between the lowest voltage within the end range and the average voltage of the battery stack, and the difference term Δ2 - Δ1; obtain the mean square deviation F 2， of the maximum single-cell voltage fluctuation and the difference term F2 - F1; The supply air supersaturated humidification condition can be simulated by injecting liquid water at the front end of the intake air;

[0056] ii) The determination of meeting the standard conditions requires that all constraint conditions of Δ2 ≤ threshold 3, F2 ≤ threshold 4, (Δ2 - Δ1) ≤ threshold 5, and (F2 - F1) ≤ threshold 6 be satisfied. Otherwise, upgrade is implemented by increasing the value of m or injecting a heat preservation medium into the flow channel of the blind end inflatable sheet 2, and the determination is carried out again until the parameters meet the standard and the determination is qualified;

[0057] e) Special optimization of drainage characteristics

[0058] If the anode edge design or the cathode structure of a pure oxygen fuel cell is involved, the following additional steps are executed:

[0059] i) Conduct a sensitivity analysis of the excess coefficient λ under the condition of supersaturated humidification of the supplied gas. When λ = λ low , obtain the difference Δ3 between the lowest voltage within the end range and the average voltage of the fuel cell stack, and the difference term Δ3 - Δ1, obtain the mean square deviation F3 of the maximum single-cell voltage fluctuation, and F3 - F1;

[0060] ii) The determination of meeting the standard conditions requires that all constraint conditions of Δ3 ≤ threshold 7, F3 ≤ threshold 8, (Δ3 - Δ1) ≤ threshold 9, and (F3 - F1) ≤ threshold 10 be satisfied. Otherwise, optimize and upgrade by increasing the value of p, and carry out the determination again until the parameters meet the standard and the determination is qualified.

[0061] When the end gradient structure is used as the end of the cathode side of the fuel cell stack, low-humidity hydrogen gas must be used on the anode side and the supplied gas must be ensured to be saturated to avoid anode water accumulation and water ingress at the front end of the anode; when designing the end gradient structure on the anode side of the fuel cell stack, low-humidity supplied gas must be maintained on the cathode side and the supplied gas must be ensured to be saturated to avoid cathode water accumulation and water ingress at the front end of the cathode.

[0062] Test example: 20 fuel cell stacks were prepared, with the end being the gradient structure prepared in Example 2. The voltage consistency of the rated-point fuel cell stack is as follows Figure 6 As shown, the results show that there is no obvious single low voltage situation in the end single cells, and the voltage range of the single cells is only 11 mV.

[0063] Comparative example: 20 fuel cell stacks were assembled using the same membrane electrode and bipolar plate materials as in the test example, with the difference that only the currently commonly used structure with only an overcurrent sheet was used at the end. Under the same operating conditions, as Figure 7 shown, there is an obvious single low voltage situation at the end of the fuel cell stack at the rated point, and the voltage range of the single cells reaches 65 mV.

Claims

1. A fuel cell stack end gas gradient structure, characterized in that: The end gradient structure comprises a blind end inflation sheet, a porous medium filling sheet and a flow sheet arranged in sequence, wherein the flow sheet is adjacent to the battery stack, and when the number of the porous medium filling sheets is greater than or equal to 2, the filling medium porosity parameter k n The k distribution is gradient, and the k near the edge of the battery stack n Smaller than k near the center of the battery stack n ; The anode and cathode flow channels of the blind-end inflatable sheet are separated by carbon paper and connected to the gas phase. When the blind-end inflatable sheet is used as a cathode blind-end inflatable sheet, a pressure balance design with a cathode single channel turned on and anode full channel closed is implemented; when the blind-end inflatable sheet is used as an anode blind-end inflatable sheet, anode single channel turned on and cathode full channel closed is adopted.

2. The method for preparing the end gas gradient structure of a fuel cell stack according to claim 1, characterized in that The following steps are involved: a) Establish the initial reference structure system of the battery stack edge i) determining m blind-end inflatable sheets, wherein the number m is ≥ 0 and the blind-end inflatable sheets are arranged at the edge of the battery stack; ii) Determine the number of porous medium filling pieces n, whose number n ≥ 0 and whose position is between the blind end inflation piece and the flow piece; when n ≥ 1, the initial filling medium porosity parameter k needs to be set n ; When n ≥ 2, a porosity gradient distribution is implemented, that is, k near the edge of the battery stack n Smaller than k near the center of the battery stack n ; iii) determining the number of over-current sheets p, the number of which p ≥ 0 and the location of the over-sulfur sheets is close to the center of the battery stack; b) Determine the qualified judgment threshold value of the battery stack edge gradient structure from 1 to 10; c) Optimize the end gas distribution of the battery stack edge gradient structure i) Carry out sensitivity analysis of excess coefficient λ under low air humidity conditions below 20%. When λ drops to the critical value λ low When the voltage parameters are collected: the difference Δ1 between the lowest voltage in the end range and the average voltage of the battery stack is measured; the maximum single-chip voltage fluctuation mean square error F1 is measured; ii) Implement judgment logic: The judgment condition must meet Δ1≤threshold 1 and F1≤threshold 2, otherwise increase the value of m or n, or adjust k n , until the parameters meet the standards; d) Optimize the thermal insulation performance of the gradient structure at the edge of the battery stack i) Carry out sensitivity analysis of excess coefficient λ under near-saturated or saturated humidification conditions. When λ drops to the critical value λ low When the parameter group is collected synchronously: the difference Δ2 between the lowest voltage in the end range and the average voltage of the battery stack and the difference term Δ2-Δ1 are measured; the maximum single-chip voltage fluctuation mean square error F is obtained. 2， and the difference term F2-F1; ii) The conditions for judging compliance must meet the full constraint conditions of Δ2≤threshold 3, F2≤threshold 4, (Δ2-Δ1)≤threshold 5, (F2-F1)≤threshold 6. Otherwise, the upgrade is implemented by increasing the m value or injecting insulation medium into the flow channel of the blind-end inflatable sheet, and re-judgment is carried out until the parameters meet the standards and are judged as qualified; e) Special optimization of drainage characteristics If it involves anode edge design or pure oxygen fuel cell cathode construction, perform the following additional steps: i) Under the condition of supersaturated air humidification, the excess coefficient λ sensitivity analysis is carried out. low The difference Δ3 between the lowest voltage in the end range and the average voltage of the battery stack and the difference term Δ3-Δ1 are obtained, and the maximum single-chip voltage fluctuation mean square error F3 and F3-F1 are obtained; ii) The conditions for judging whether the system meets the standard must meet the full constraints of Δ3≤threshold 7, F3≤threshold 8, (Δ3-Δ1)≤threshold 9, and (F3-F1)≤threshold 10. Otherwise, the optimization and upgrading are carried out by increasing the p value, and the judgment is carried out again until the parameters meet the standard and the system is judged to be qualified.

3. The method according to claim 2, characterized in that: When the end gradient structure is the end of the cathode side of the battery stack, the anode side must use low-humidity hydrogen with a humidity below 20% and ensure that the gas supply is saturated to avoid water accumulation at the anode and water ingress at the front end of the anode; When designing the edge gradient structure of the anode side of the battery stack, the cathode side must maintain a low-humidity air supply with a humidity below 20% and ensure that the air supply is saturated to avoid water accumulation at the cathode and water ingress at the front end of the cathode.

4. The method according to claim 2, characterized in that: The inner flow channel filling medium of the porous medium filling sheet is made of hydrophobic material.

5. The method according to claim 3, characterized in that: When the number of porous medium filling pieces n is increased, the porosity k of the filling medium needs to be adjusted accordingly. n , still guaranteeing k n Gradient distribution characteristics.

6. The method according to claim 4, characterized in that: When the internal gas of the blind-end inflatable sheet does not circulate, air pressure is introduced to balance the water pressure.

7. The method according to claim 5, characterized in that: The above-mentioned supersaturated humidification condition of the air supply can be simulated by injecting liquid water at the front end of the air intake.

8. The end gas gradient structure of a fuel cell stack as described in claim 1 is used to prepare the end of a fuel cell stack.

9. A fuel cell stack, characterized in that The fuel cell comprises an end gradient structure prepared by the method according to any one of claims 2 to 7.

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