End gas passage gradient structure of fuel cell stack and preparation method and application thereof

Abstract

The application discloses an end gas gradient structure of a fuel cell stack in the field of battery stack manufacturing. The end gas gradient structure comprises blind end gas filling sheets, porous medium filling sheets and flow sheets arranged in sequence. When the number of the porous medium filling sheets is greater than or equal to 2, the porosity of the porous medium filling sheets is distributed in a gradient mode, and the porosity at the edge is smaller than that at the center. The cathode and anode flow channels of the blind end gas filling sheets are connected by carbon paper in a separated mode, and the single-channel conduction and the other-pole full-channel sealing are adopted according to the cathode and the anode. The end gas gradient structure is constructed, temperature uniformity is regulated, fluid orderly transition is realized, water accumulation at the end is avoided, and voltage consistency is ensured. The water pressure difference is avoided, the end flow field is optimized, the flow resistance step and the single low inlet are avoided, and the working medium waste is reduced. The multi-targets of heat preservation, flow improvement and water guiding are realized, and the single low problem of the end of the stack under all working conditions is solved.

Description

TECHNICAL FIELD

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

[0002] The single piece voltage consistency of a fuel cell stack is one of important indicators of the working performance of the stack, and the higher the single piece voltage consistency, the better the performance and stability of the stack. Due to the influence of factors such as operating parameters, structure and materials, the single piece voltage consistency of the fuel cell stack is not very ideal at present.

[0003] The main reasons for the poor single piece voltage consistency of the fuel cell stack are mainly related to the end design of the stack, as follows: firstly, the heat preservation condition at the end of the stack is not good, and under the influence of the temperature gradient at the end, the problems of internal liquid water precipitation and water accumulation are more serious; secondly, there are obvious vortexes and other problems at the end, which cause the end to be prone to poor air intake; thirdly, under the conditions of anode circulation or cathode pure oxygen circulation, the intake air of the stack may contain liquid water, which has the most significant influence on the end. In the current technology, the end of the fuel cell stack is designed by using a combination of multiple flow plates, and the structure of the flow plate is as shown in Figure 1

[0004] To solve the above problems, the current technical solution mainly introduces a false plate with closed gas path and unobstructed water path at the end to achieve end heat preservation, but this method may cause a large pressure difference between the water and gas on both sides of the false plate, thereby causing mechanical damage or sealing failure under a large water flow; or a false plate is directly introduced at the end to realize water drainage, but this method is prone to cause flow waste, and the simple addition of flow plates is also not conducive to the improvement of system efficiency.

[0005] Therefore, the current structure of the end of the fuel cell stack is too single, which not only cannot completely solve the problem of low single piece voltage consistency of the stack, but also causes frequent problems at the end of the stack. At the same time, there is a lack of effective multi-dimensional structure and optimization design method for the end of the stack, which makes it difficult to achieve the multiple goals of heat preservation, flow improvement and water drainage, and also cannot achieve the synchronous optimization of the end two-phase flow and temperature field. SUMMARY

[0006] The present application aims to provide an end gas passage gradient structure of a fuel cell stack and a preparation method, which better solves the problem of low single piece voltage consistency of the stack.

[0007] ​The end part gradient structure of the fuel cell stack comprises blind end gas filling sheets, porous medium filling sheets and flow sheets arranged in sequence, the flow sheets are adjacent to the fuel cell stack, the number of the porous medium filling sheets is greater than or equal to 2, and the filling medium porosity parameter k n is in gradient distribution and k n near the edge of the fuel cell stack is less than k n ;

[0008] The anode and cathode flow channels of the blind end gas filling sheets are separated by carbon paper and connected with gas phase, when the blind end gas filling sheet is a cathode blind end gas filling sheet, the cathode single channel is conducted and the anode full channel is closed for gas pressure balance design; when the blind end gas filling sheet is an anode blind end gas filling sheet, the anode single channel is conducted and the cathode full channel is closed.

[0009] The application further provides a preparation method of the end part gradient structure of the fuel cell stack, comprising the following steps:

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

[0011] i) determining m blind end gas filling sheets, the number m is greater than or equal to 0, and the blind end gas filling sheets are arranged at the edge side of the fuel cell stack;

[0012] ii) determining n porous medium filling sheets, the number n is greater than or equal to 0, and the porous medium filling sheets are arranged between the blind end gas filling sheets and the flow sheets; when n is greater than or equal to 1, the initial filling medium porosity parameter k n is set; when n is greater than or equal to 2, the porosity gradient distribution is implemented, that is, k n near the edge of the fuel cell stack is less than k n ;

[0013] iii) determining p flow sheets, the number p is greater than or equal to 0, and the flow sheets are arranged near the center side of the fuel cell stack;

[0014] b) determining the qualified judgment threshold 1-10 of the edge gradient structure of the fuel cell stack;

[0015] c) optimizing the end part gas distribution of the edge gradient structure of the fuel cell stack

[0016] i) carrying out the excess coefficient λ sensitivity analysis under the low gas supply humidity condition with the humidity below 20%, when the λ drops to the critical value λ low , collecting the voltage parameters: measuring the difference Δ1 of the lowest voltage in the end part range and the average voltage of the fuel cell stack; measuring the maximum single sheet voltage fluctuation mean square error F1;

[0017] ii) implementing the judgment logic: the judgment reaching standard condition needs to meet Δ1≤threshold 1 and F1≤threshold 2, otherwise, the m or n value is increased or the k n is adjusted until the parameters reach the standard.

[0018] d) Optimization of thermal insulation performance for the edge gradient structure of the cell stack

[0019] i) Sensitivity analysis of excess coefficient λ under near-saturation or saturation humidification conditions of the gas supply, when λ drops to the critical value λ low , simultaneously collect parameter groups: the difference Δ2 between the minimum voltage in the end range and the average voltage of the cell stack, and the difference item Δ2-Δ1; obtain the maximum single-piece voltage fluctuation mean square error F 2， and the difference item F2-F1;

[0020] ii) Determine if the full constraint conditions of Δ2≤threshold value 3, F2≤threshold value 4, (Δ2-Δ1)≤threshold value 5, (F2-F1)≤threshold value 6 are met, otherwise upgrade by increasing the value of m or injecting thermal insulation medium into the flow channel of the blind end gas injection piece, and re-determine until the parameters meet the standard and pass the determination;

[0021] e) Special optimization of drainage characteristics

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

[0023] i) Sensitivity analysis of excess coefficient λ under super-saturation humidification conditions of the gas supply, when λ = λ low , obtain the difference Δ3 between the minimum voltage in the end range and the average voltage of the cell stack, and the difference item Δ3-Δ1, obtain the maximum single-piece voltage fluctuation mean square error F3, F3-F1;

[0024] ii) Determine if the full constraint conditions of Δ3≤threshold value 7, F3≤threshold value 8, (Δ3-Δ1)≤threshold value 9, (F3-F1)≤threshold value 10 are met, otherwise optimize and upgrade by increasing the value of p, and re-determine until the parameters meet the standard and pass the determination.

[0025] Further, when the end gradient structure is on the cathode side of the cell 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 in the anode and water entering the front end of the anode;

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

[0027] Further, the internal flow channel filling medium of the porous medium filling piece uses a hydrophobic material. This realizes the dual functions of front-end liquid water penetration barrier and rear-end drainage path optimization, avoiding the flow of liquid water into the front end and ensuring the timely and effective drainage of liquid water.

[0028] Further, increase the number of porous medium filling piece n, need to adjust the filling medium porosity k n , still guarantee the gradient distribution characteristics of k n .

[0029] Further, the internal gas of the blind end gas filling piece does not circulate, and the gas pressure is introduced for balancing the water pressure.

[0030] Further, the gas supply supersaturation humidification condition can be simulated by injecting liquid water at the front end of the inlet gas.

[0031] When the fuel cell stack is working, the fuel cell monomer close to the end is prone to have poor voltage consistency due to problems such as water accumulation caused by poor heat preservation condition at the end and poor gas inlet caused by vortex. The present application forms a gas passing gradient at the end of the fuel cell stack by the blind end gas filling piece, the porous medium filling piece and the large amount of gas passing piece, realizes uniform temperature regulation, orderly transition of fluid, avoids water accumulation at the end, and guarantees the consistency of the single cell voltage of the fuel cell stack. Through the blind end gas filling piece at the end, the problem of water pressure difference between the two sides is avoided, the end flow field is optimized through the porous medium filling piece, the step transition of flow resistance between the end pieces is avoided, the gradient orderly transition is realized, the single low problem of gas inlet is avoided, and the working medium waste is controlled at the lowest level. By reasonably setting the water guide piece, the problem of water accumulation at the end is avoided. Thus, the optimization of the two-phase flow and temperature field at the end of the battery stack is realized, the multi-objective of heat preservation, flow improvement and water guide is realized, the large pressure difference between water and gas is avoided, and the working medium waste is minimized. The present application is a high-efficiency solution to completely solve the single low problem at the end of the battery stack in the whole working condition range. BRIEF DESCRIPTION OF DRAWINGS

[0032] Figure 1 for the structure of the flow piece in the prior art;

[0033] Figure 2 for the structure of a fuel cell stack provided according to embodiment 1 of the present application and the end thereof;

[0034] Figure 3 for the structure of a blind end gas filling piece provided according to embodiment 1 of the present application;

[0035] Figure 4 for the structure of a porous medium filling piece provided according to embodiment 1 of the present application;

[0036] Figure 5 for the end gas passing gradient structure design method flow chart of a fuel cell stack provided according to embodiment 2 of the present application;

[0037] Figure 6 for the rated point stack voltage consistency test chart of a fuel cell stack prepared according to embodiment 2 of the present application;

[0038] Figure 7 The rated point stack voltage consistency test chart of the fuel cell stack with end part only flow by-pass in the comparative example. DETAILED DESCRIPTION

[0039] Further details are described below through specific embodiments:

[0040] The reference signs in the attached drawings of the specification include: fuel cell stack 1, blind end gas charging piece 2, porous media filling piece 3 (smaller media porosity), porous media filling piece 4 (larger media porosity), flow by-pass piece 5, blocking body 6, cathode plate 7, carbon paper 8, anode plate 9, porous media 10.

[0041] Example 1, a fuel cell stack, as shown in Figure 2 The end part gradient structure of the fuel cell stack 1 includes blind end gas charging piece 2, porous media filling piece 3, porous media filling piece 4 and flow by-pass piece 5 arranged in sequence, and the flow by-pass piece 5 is adjacent to the fuel cell stack 1.

[0042] The flow by-pass piece 5 has two pieces, and its structure is the same as the prior art, as shown in Figure 1 It includes cathode plate 7 and anode plate 9, and the cathode and anode flow channels are separated by carbon paper 8 to realize regional separation and gas phase communication, and the cathode and anode are both single-channel conduction on the same side, and the blocking body 6 is used for sealing.

[0043] As shown in Figure 3 The blind end gas charging piece 2 has one piece, and the difference from the flow by-pass piece 5 is that the blind end gas charging piece 2 realizes regional separation and gas phase communication of the cathode and anode flow channels through carbon paper 8, and as the cathode blind end gas charging piece 2, it performs cathode single-channel conduction and anode full-channel sealing pressure balance design, and uses the blocking body 6 for sealing; as the anode blind end gas charging piece 2, it adopts anode single-channel conduction and cathode full-channel sealing. When the internal gas of the blind end gas charging piece 2 does not flow, the gas pressure is introduced to balance the water pressure.

[0044] As shown in Figure 4 The porous media filling piece has two pieces, and the difference from the flow by-pass piece 5 is that the internal flow channel is filled with hydrophobic porous media 10, such as commonly used foam and porous carbon, and the number of porous media filling pieces is greater than or equal to two, and the porosity parameter k n of the porous media 10 filled in the porous media filling piece is gradient distributed, and taking two pieces as an example, the porosity of the porous media filling piece 3 close to the edge of the cell stack is smaller than the porosity of the porous media filling piece 4 close to the center of the cell stack.

[0045] Example 2, a method for preparing the end part gradient structure of the fuel cell stack described in Example 1, as shown in Figure 5 It includes the following steps:

[0046] a) Establish the initial benchmark structure system at the edge of the battery stack

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

[0048] ii) Determine that the number of porous dielectric filler sheets is 2, and the porosity gradient distribution of the two porous dielectric filler sheets, i.e., the porosity parameter k of the porous dielectric filler sheet 3 near the edge of the battery stack. n The porosity parameter k is smaller than that of the porous dielectric packing sheet 4 near the center of the battery stack. n ;

[0049] iii) Determine the number of flow plates 5 to be 2, and position the flow plates close to the center side of the battery stack;

[0050] b) Determine the acceptable threshold for the edge gradient structure of the battery stack from 1 to 10;

[0051] c) Optimize the end gas distribution of the battery stack edge gradient structure.

[0052] i) Conduct sensitivity analysis of the excess coefficient λ under low gas supply humidity conditions, and when λ decreases to the critical value λ... low During the process, voltage parameters were collected: the difference Δ1 between the lowest voltage in the end range and the average voltage of the battery stack was measured; the root mean square deviation of the maximum voltage fluctuation of a single cell was measured;

[0053] ii) Implement the judgment logic: the judgment condition must meet the following conditions: Δ1≤threshold1 and F1≤threshold2. Otherwise, increase the value of m or n, or adjust k. n Until the parameters meet the standards; among them, after increasing the number of porous media packing sheets n, the porosity k of the packing medium needs to be adjusted accordingly. n still guarantee k n Gradient distribution characteristics;

[0054] d) Optimize the thermal insulation performance of the gradient structure at the edge of the battery stack.

[0055] i) Conduct sensitivity analysis of the excess coefficient λ under near-saturated or saturated humidification conditions. When λ decreases to the critical value λ low Simultaneously, the following parameter sets are collected: the difference Δ2 between the lowest voltage and the average voltage of the battery stack within the end range is measured, and the difference term Δ2-Δ1 is obtained; the root mean square error F of the maximum single-cell voltage fluctuation is acquired. 2， And the difference term F2-F1; the supersaturated humidification condition of the air supply can be simulated by injecting liquid water at the front end of the air intake;

[0056] ii) Determine if the conditions are met: Δ2≤ threshold 3, F2≤ threshold 4, (Δ2- Δ1)≤ threshold 5, (F2- F1)≤ threshold 6, otherwise, upgrade by increasing m or injecting thermal medium into the flow channel of the blind end gas injection piece 2, and re-determine until the parameters meet the requirements, and determine the eligibility;

[0057] e) Special optimization of drainage characteristics

[0058] If the anode edge design or the pure oxygen fuel cell cathode structure is involved, the following steps are additionally performed:

[0059] i) Perform excess coefficient λ sensitivity analysis under gas over-saturation humidification conditions, and obtain the difference Δ3 between the lowest voltage in the end range and the average voltage of the cell stack when λ = λ low , and the difference item Δ3- Δ1, and obtain the maximum single cell voltage fluctuation mean square error F3, F3- F1;

[0060] ii) Determine if the conditions are met: Δ3≤ threshold 7, F3≤ threshold 8, (Δ3- Δ1)≤ threshold 9, (F3- F1)≤ threshold 10, otherwise, optimize and upgrade by increasing p, and re-determine until the parameters meet the requirements, and determine the eligibility.

[0061] When the end gradient structure is used as the end of the cathode side of the cell stack, low-humidity hydrogen gas must be used on the anode side and the gas saturation must be ensured to avoid water accumulation in the anode and water entering the front end of the anode; When designing the edge gradient structure of the anode side of the cell stack, low-humidity gas must be used on the cathode side and the gas saturation must be ensured to avoid water accumulation in the cathode and water entering the front end of the cathode.

[0062] Test example: 20 fuel cell stacks were prepared, the ends of which were gradient structures prepared in Example 2, and the voltage consistency of the rated point stacks was as follows Figure 6 as shown in the figure, the results show that there is no obvious voltage single low situation in the end single cell, and the single cell voltage difference is only 11 mV.

[0063] Comparative example: 20 stacks were assembled using the same membrane electrode and bipolar plate materials as in the test example, the difference being that only the currently commonly used structure of placing only the flow piece was used at the end, and the same operating conditions were used, such as Figure 7 as shown in the figure, at the rated point, the fuel cell stack ends have a clear voltage single low situation, and the single cell voltage difference reaches 65 mV.

Claims

1. An end gas crossover gradient structure for a fuel cell stack, characterized by: The end gradient structure comprises blind end air-filled sheet, porous medium filling sheet and flow sheet arranged in sequence, the blind end air-filled sheet does not pass air, the porous medium filling sheet passes a small amount of air, and the flow sheet passes a large amount of air, thereby forming an air passing gradient of the end of the fuel cell stack; the flow sheet is adjacent to the fuel cell stack, when the number of the porous medium filling sheet is 1, the porous medium filling sheet has an initial filling medium porosity parameter k n , when the number of the porous medium filling sheet is greater than or equal to 2, the filling medium porosity parameter k n is in 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. The anode and cathode flow channels of the blind end gas filling piece are separated by carbon paper to realize regional separation and gas phase communication. When the blind end gas filling piece is used as a cathode blind end gas filling piece, a cathode single-channel conduction and anode full-channel closed gas pressure balance design are performed. When the blind end gas filling piece is used as an anode blind end gas filling piece, an anode single-channel conduction and cathode full-channel closed gas pressure balance design are performed.

2. A method of making an end gas crossover gradient structure for a fuel cell stack as claimed in claim 1, wherein The method comprises the following steps: a) Establishing an initial reference structure system at the edge of the cell stack; i) determining m pieces of blind end gas filling pieces, the number m is greater than or equal to 1, and the blind end gas filling pieces are arranged at the edge side of the cell stack; ii) determine the number of porous media packing pieces n, set initial packing porosity parameter k when n = 1 n ; implement porosity gradient distribution when n > 2, i.e. k n near the edge of the cell stack is less than k n near the center of the cell stack iii) determining p pieces of overcurrent pieces, the number p is greater than or equal to 1, and the overcurrent pieces are arranged near the center side of the cell stack; b) determining a cell stack edge gradient structure qualification threshold value 1~10; c) optimizing the end gas distribution of the cell stack edge gradient structure; i) Sensitivity analysis of excess factor λ under low supply humidity conditions with humidity below 20%, when λ drops to the critical value λ low When λ drops to the critical value λ c, the following parameters are measured: the difference Δ1 between the lowest voltage in the end range and the average voltage of the stack; the maximum single cell voltage fluctuation mean square deviation F1; ii) Implement decision logic: decide if the conditions are met Δ1≤ threshold 1 and F1≤ threshold 2, otherwise increase m or n values, or adjust k to parameter compliance n . d) optimizing the heat preservation performance of the cell stack edge gradient structure; i) Sensitivity analysis of excess factor λ under near-saturation or saturation humidification conditions of supplied gas, when λ drops to critical value λ low , synchronously collect parameter groups: difference Δ2 between the lowest voltage in the end range and the average voltage of the cell stack, and difference item Δ2-Δ1; obtain maximum single-piece voltage fluctuation mean square error F 2， and difference item F2-F1; ii) determining that the full constraint condition needs to meet Δ2≤threshold value 3, F2≤threshold value 4, (Δ2-Δ1)≤threshold value 5, (F2-F1)≤threshold value 6, otherwise, upgrading is implemented by increasing the value of m or injecting a heat preservation medium into the flow channel of the blind end gas filling piece, and the determination is redeveloped until the parameters meet the standard and are qualified; e) special optimization of drainage characteristics; If the anode edge design or the cathode structure of the pure oxygen fuel cell is involved, the following steps are additionally performed: i) Excess factor λ sensitivity analysis under supersaturated gas humidification conditions, when λ = λ low When λ = λ the difference Δ3 between the lowest voltage in the end range and the average voltage of the stack, and the difference Δ3 - Δ1, the maximum single cell voltage fluctuation mean square deviation F3, F3 - F1 are obtained. ii) determining that the full constraint condition needs to meet Δ3≤threshold value 7, F3≤threshold value 8, (Δ3-Δ1)≤threshold value 9, (F3-F1)≤threshold value 10, otherwise, optimization upgrading is developed by increasing the value of p, and the determination is redeveloped until the parameters meet the standard and are qualified.

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

4. The method of claim 2, wherein: The internal flow channel of the porous medium filling piece is filled with a hydrophobic material.

5. The method of claim 3, wherein: Increasing the number of porous media filled sheets n Subsequently, the porosity of the filled medium needs to be adjusted accordingly k n , still ensuring k n gradient distribution characteristics.

6. The method of claim 4, wherein: When the internal gas of the blind end gas filling piece does not flow, gas pressure is introduced to balance the water pressure.

7. The method of claim 5, wherein: The gas supply supersaturation humidification condition can be simulated by injecting liquid water at the front end of the gas inlet.

8. Use of the end gas gradient structure of the fuel cell stack according to claim 1 in the preparation of the end of the fuel cell stack.

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

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