Multi-layer gradient microporous layer gas diffusion layer and preparation method thereof

Abstract

The invention relates to a preparation method of a multi-layer gradient microporous gas diffusion layer. The preparation method comprises the following steps: preparing slurry: respectively mixing four different proportions of water repellent agents and pore-forming agents with conductive carbon powder and isopropanol to prepare slurry I, slurry II, slurry III and slurry IV; screen printing of the sizing agents: screen-printing the first sizing agent, the second sizing agent, the third sizing agent and the fourth sizing agent on the supporting layer in sequence, namely a first microporous layer, a second microporous layer, a third microporous layer and a fourth microporous layer, during screen printing, placing the supporting layer in a drying tunnel after each layer of sizing agent is printed, and adjusting the speed of the drying tunnel to ensure that the sizing agents are completely dried; preparing a gas diffusion layer: roasting and sintering the completely dried gas diffusion layer; the gradient hydrophobicity is beneficial to discharge of water generated by reaction of the catalyst layer, meanwhile, the change of the pore structure improves the drainage capacity between the microporous layer and the supporting layer, mass transfer under high current density is effectively enhanced, the battery performance is improved, and the high current density performance is obviously improved.

Description

Technical Field

[0001] The invention belongs to the field of fully automated products and relates to a multi-layer gradient microporous gas diffusion layer and a preparation method thereof. Background Art

[0002] The membrane electrode is the core component of the fuel cell, and the gas diffusion layer is an important component. Its main function is to transmit the reaction gas and discharge the water and heat generated by the reaction. Its performance also directly affects the performance of the fuel cell. As a porous medium with a rich internal structure, the gas diffusion layer needs to have a suitable pore size distribution and porosity. During the actual operation of the battery, the structure of each component has different requirements for water vapor transmission. As the fuel cell operation time increases or works at a higher current density, a large amount of product water condenses into a liquid form. Due to the large span of the pore size gradient formed between the microporous layer and the macroporous matrix, and the strong hydrophobicity of the microporous layer surface, the discharge of liquid water is limited. If a large amount of accumulation cannot be discharged in time, it will hinder the mass transfer capacity of oxygen or air to the catalyst layer, that is, the cathode "flooding" phenomenon occurs, blocking the water vapor transmission channel and affecting the performance and stability of the fuel cell.

[0003] Therefore, it is of great significance to design a gradient microporous layer for the cathode diffusion layer to promote the rapid transmission of water vapor, avoid flooding between components, and improve the water management ability of fuel cells. Summary of the invention

[0004] In order to solve the above problems, the technical solution adopted by the present invention is: a multi-layer gradient microporous gas diffusion layer, comprising:

[0005] Support layer;

[0006] a first microporous layer disposed below the support layer;

[0007] A second microporous layer is disposed below the first microporous layer;

[0008] A third microporous layer is disposed below the second microporous layer;

[0009] A fourth microporous layer is disposed below the third microporous layer;

[0010] The support layer is made of carbon paper;

[0011] The first microporous layer, the second microporous layer, the third microporous layer and the fourth microporous layer are made of carbon powder and a hydrophobic agent.

[0012] Further: the contact angle range of the first microporous layer is: 165°±2, the contact angle range of the second microporous layer is: 160°±2, the contact angle range of the third microporous layer is: 155°±2, and the contact angle range of the fourth microporous layer is: 150°±2;

[0013] The density of the first microporous layer is: 0.53 g·cm -3 ±0.02, the density of the second microporous layer is: 0.49g·cm -3 ±0.02, the density of the third microporous layer is: 0.45g·cm -3 ±0.02, the density of the fourth microporous layer is: 0.41g·cm -3 ±0.02.

[0014] Furthermore, the thickness of the support layer, the first microporous layer, the second microporous layer, the third microporous layer and the third microporous layer is 10 μm.

[0015] A method for preparing a multi-layer gradient microporous gas diffusion layer comprises the following steps:

[0016] S1: preparing slurry: mixing four different proportions of hydrophobic agent and pore-forming agent with conductive carbon powder and isopropyl alcohol to prepare slurry No. 1, slurry No. 2, slurry No. 3 and slurry No. 4 respectively;

[0017] S2: Screen printing slurry: screen printing No. 1 slurry, No. 2 slurry, No. 3 slurry and No. 4 slurry on the support layer in order to form the first microporous layer, the second microporous layer, the third microporous layer and the fourth microporous layer. During screen printing, after each layer of slurry is printed, it is placed in a drying tunnel, and the drying tunnel speed is adjusted so that the gas diffusion layer stays in the drying tunnel for 80-100 seconds to ensure that the slurry is completely dry;

[0018] S3: preparing a gas diffusion layer: calcining and sintering the completely dried gas diffusion layer.

[0019] Furthermore, the conductive carbon powder is at least one of Vulcan XC-72 carbon powder, acetylene black or pearl carbon.

[0020] Furthermore: the pore-forming agent is at least one of ammonium carbonate, ammonium bicarbonate or ammonium oxalate.

[0021] Further: the amount of pore-forming agent added to the No. 1 slurry>the amount of pore-forming agent added to the No. 2 slurry>the amount of pore-forming agent added to the No. 2 slurry=the amount of pore-forming agent added to the No. 4 slurry;

[0022] The amount of hydrophobic agent added to the No. 1 slurry pore-forming agent = the amount of hydrophobic agent added to the No. 2 slurry pore-forming agent > the amount of hydrophobic agent added to the No. 3 slurry pore-forming agent > the amount of hydrophobic agent added to the No. 4 slurry pore-forming agent.

[0023] Further: when the pore-forming agent is ammonium oxalate, the amount of the hydrophobic agent added to the No. 1 slurry and the No. 2 slurry is the same;

[0024] The solid content ratio of carbon powder to hydrophobic agent in No. 1 slurry and No. 2 slurry is 1.5:1; the content ratio of carbon powder to pore-forming agent is 1:1.3 and 1:1 respectively;

[0025] The amount of pore former added in No. 3 slurry and No. 4 slurry is the same;

[0026] The solid content ratio of carbon powder to pore former in No. 3 slurry and No. 4 slurry is 1.3:1, and the solid content ratio of carbon powder to hydrophobic agent is 2:1 and 3:1 respectively.

[0027] Furthermore, the temperature for calcining the completely dried gas diffusion layer is 350°C, the time is 120 minutes, and the baking tunnel temperature is 120°C.

[0028] A multi-layer gradient microporous gas diffusion layer and a preparation method thereof provided by the present invention have the following advantages: in the gradient microporous gas diffusion layer prepared by the present invention, the content of pore-forming agent and hydrophobic agent in the screen printing slurry close to the support layer is large, and the microporous layer finally obtained has many pores and strong hydrophobicity. As the content of pore-forming agent and hydrophobic agent decreases, the microporous layer close to the catalyst layer has fewer pores but slightly weaker hydrophobicity. Therefore, the gradient of hydrophobicity is beneficial to the discharge of water generated by the reaction of the catalyst layer. At the same time, the change of pore structure improves the drainage capacity between the microporous layer and the support layer, effectively enhances mass transfer under high current density, and improves battery performance. Compared with the existing gas diffusion layer, the preparation process is not much different, but the high electrical density performance is significantly improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0030] Figure 1 is a schematic diagram of a multi-layer gradient microporous gas diffusion layer;

[0031] Figure 2 is the contact angle of the microporous layer;

[0032] Figure 3 is the microporous layer density;

[0033] Figure 4 The membrane electrode polarization curve

[0034] Figure numerals: 1, support layer, 2, first microporous layer, 3, second microporous layer, 4, third microporous layer, 5, fourth microporous layer. DETAILED DESCRIPTION

[0035] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments may be combined with each other. The present invention will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0036] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. The following description of at least one exemplary embodiment is actually only illustrative and is by no means intended to limit the present invention and its application or use. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0037] Figure 1 is a schematic diagram of a multi-layer gradient microporous gas diffusion layer;

[0038] A multi-layer gradient microporous gas diffusion layer, comprising:

[0039] Support layer 1;

[0040] A first microporous layer 2 disposed below the support layer 1;

[0041] A second microporous layer 3 is disposed below the first microporous layer 2;

[0042] A third microporous layer 4 is disposed below the second microporous layer 3;

[0043] A fourth microporous layer 5 is disposed below the third microporous layer 4;

[0044] The support layer 1 is made of carbon paper; commercial carbon paper that has been hydrophobically treated;

[0045] The first microporous layer 2 , the second microporous layer 3 , the third microporous layer 4 , and the fourth microporous layer 5 are made of carbon powder and a hydrophobic agent.

[0046] Further: the contact angle range of the first microporous layer 2 is: 165°±2, the contact angle range of the second microporous layer 3 is: 160°±2, the contact angle range of the third microporous layer 4 is: 155°±2, and the contact angle range of the fourth microporous layer 5 is: 150°±2;

[0047] The density of the first microporous layer 2 is: 0.53 g·cm -3 ±0.02, the density of the second microporous layer 3 is: 0.49 g·cm -3 ±0.02, the density of the third microporous layer 4 is: 0.45 g·cm -3±0.02, the density of the fourth microporous layer 5 is: 0.41 g·cm -3 ±0.02.

[0048] The thickness of the support layer 1 , the first microporous layer 2 , the second microporous layer 3 , the third microporous layer 4 , and the third microporous layer 4 is 10 μm.

[0049] The slurry formula is adjusted, and different slurries are sequentially coated on the carbon paper support layer 1 by screen printing technology. The pore-forming agent content of the microporous layer gradually increases in the direction close to the support layer 1, forming a pore gradient to avoid water accumulation between the microporous layer and the substrate layer due to the large span of the pore structure. The microporous layer close to the catalyst layer is hydrophobic by changing the amount of hydrophobic agent added in the slurry to create a hydrophobic gradient, making the microporous layer close to the catalyst layer less hydrophobic, which helps to discharge the product water in the catalyst layer, and finally obtains a multi-layer gradient structure microporous layer to improve the water management ability of the fuel cell.

[0050] A method for preparing a multi-layer gradient microporous gas diffusion layer comprises the following steps:

[0051] S1: preparing slurry: mixing four different proportions of hydrophobic agent and pore-forming agent with conductive carbon powder and isopropyl alcohol to prepare slurry No. 1, slurry No. 2, slurry No. 3 and slurry No. 4 respectively;

[0052] S2: Screen printing slurry: screen printing No. 1 slurry, No. 2 slurry, No. 3 slurry and No. 4 slurry on the support layer 1 in order to form the first microporous layer 2, the second microporous layer 3, the third microporous layer 4 and the fourth microporous layer 5. During screen printing, after each layer of slurry is printed, it is placed in a drying tunnel, and the drying tunnel speed is adjusted so that the gas diffusion layer stays in the drying tunnel for 80-100 seconds to ensure that the slurry is completely dry;

[0053] S3: preparing a gas diffusion layer: calcining the completely dried gas diffusion layer at a sintering temperature of 350° C. for 120 min.

[0054] The temperature for calcining the completely dried gas diffusion layer is 350° C., the time is 120 min, and the baking tunnel temperature is 120° C.

[0055] The conductive carbon powder is at least one of Vulcan XC-72 carbon powder, acetylene black or pearl carbon.

[0056] The pore-forming agent is at least one of ammonium carbonate, ammonium bicarbonate or ammonium oxalate.

[0057] The amount of pore-forming agent added to the No. 1 slurry>the amount of pore-forming agent added to the No. 2 slurry>the amount of pore-forming agent added to the No. 2 slurry=the amount of pore-forming agent added to the No. 4 slurry;

[0058] The amount of hydrophobic agent added to the No. 1 slurry pore-forming agent = the amount of hydrophobic agent added to the No. 2 slurry pore-forming agent > the amount of hydrophobic agent added to the No. 3 slurry pore-forming agent > the amount of hydrophobic agent added to the No. 4 slurry pore-forming agent.

[0059] When the pore-forming agent is ammonium oxalate, the amount of hydrophobic agent added to the No. 1 slurry and the No. 2 slurry is the same;

[0060] The ratio of the solid content of carbon powder to hydrophobic agent in No. 1 slurry and No. 2 slurry is 1.5:1; the ratio of the content of carbon powder to pore-forming agent is 1:1.3 and 1:1 respectively;

[0061] The amount of pore former added in No. 3 slurry and No. 4 slurry is the same;

[0062] The solid content ratio of carbon powder to pore-forming agent in No. 3 slurry and No. 4 slurry is 1.3:1, and the solid content ratio of carbon powder to hydrophobic agent is 2:1 and 3:1 respectively.

[0063] Embodiment 1:

[0064] Comparative example: The process of the existing gas diffusion layer preparation method is as follows:

[0065] S1: hydrophobic treatment: the porous carbon paper is immersed in a PTFE emulsion with a mass percentage content of 1% to 5% until the amount of PTFE added to the carbon paper accounts for 7% to 8% of the total mass, and then calcined at 340° C. to obtain a gas diffusion layer substrate;

[0066] S2: Prepare slurry: ammonium oxalate is selected as the pore-forming agent, and conductive carbon powder: PTFE and conductive carbon powder: pore-forming agent are added at a solid mass ratio of 1.5:1 and 1:1, and an appropriate amount of isopropanol is added and stirred at high speed to prepare a microporous layer slurry;

[0067] S3: Screen printing slurry: The microporous layer slurry is coated on the hydrophobic treated gas diffusion layer substrate by screen printing technology, and the thickness is controlled to be 30 μm to 40 μm;

[0068] S4: preparing a gas diffusion layer: calcining the completely dried gas diffusion layer at a sintering temperature of 350° C. for 120 min;

[0069] The process of the preparation method of the gas diffusion layer of the present application is as follows:

[0070] S1: Hydrophobic treatment: same as step 1 of the comparative case;

[0071] S2: Prepare slurry: mix four different proportions of hydrophobic agent and pore-forming agent with carbon powder, isopropyl alcohol and ethylene glycol to prepare slurry No. 1, slurry No. 2, slurry No. 3 and slurry No. 4; among which, ammonium oxalate is used as the pore-forming agent, the addition amount of PTFE (hydrophobic agent) in slurry No. 1 and slurry No. 2 is the same, the ratio of carbon powder: PTFE solid content is 1.5:1, and the ratio of carbon powder: pore-forming agent content is 1:1.3 and 1:1 respectively;

[0072] The amount of pore former added in No. 3 and No. 4 slurries was the same, the ratio of carbon powder to pore former solid content was 1.3:1, and the ratio of carbon powder to PTFE content was 2:1 and 3:1 respectively;

[0073] S3: Screen printing slurry: No. 1 slurry, No. 2 slurry, No. 3 slurry and No. 4 slurry are sequentially coated on the support layer 1 to form the first microporous layer 2, the second microporous layer 3, the third microporous layer 4 and the fourth microporous layer 5, each layer having a thickness of about 10 μm. During the coating process, after each layer of slurry is printed, it is placed in a drying oven at 120° C., and the drying oven speed is adjusted to ensure that the slurry is completely dry before proceeding to the next step;

[0074] S4: preparing a gas diffusion layer: calcining the completely dried gas diffusion layer at a sintering temperature of 350° C. for 120 min.

[0075] The hydrophilicity and density test of the gas diffusion layer of the present application: the four slurries of the embodiment were screen-printed on the hydrophobic treated substrate layer in turn, and after high-temperature calcination, the contact angle of the microporous layer surface was measured. The hydrophobic treated carbon paper and the gas diffusion layer were weighed and the microporous layer density was calculated. The results are shown in Figure 2 and Figure 3 ;

[0076] Preparation of membrane electrode: The same CCM (catalyst coated membrane) is used for the comparative example and the example. The cathode of the example is placed with a multi-layer gradient microporous gas diffusion layer designed and prepared by the present application, and the anode is a single-layer microporous gas diffusion layer of the comparative example. The microporous layers of the cathode and cathode of the comparative example membrane electrode sample are both single layers, and the membrane electrode is obtained by hot pressing;

[0077] Membrane electrode polarization curve test conditions: battery temperature 65 ~ 85 ℃, cathode air stoichiometric ratio 1.5 ~ 2.5, anode hydrogen stoichiometric ratio 1.5 ~ 2.0, positive and negative electrodes humidification 60 ~ 100% RH, both sides of the pressure 120 ~ 150Kpa for polarization curve test, data such as Figure 4 As shown. It can be seen that there is no difference in performance at medium and low current densities, and the embodiment has a significant advantage at high current density;

[0078] In summary, the multi-layer gradient microporous gas diffusion layer design adopted in this application is of obvious significance for avoiding battery flooding under high current density and improving battery performance.

[0079] At high current density, the fuel cell performance is improved by about 20mV.

[0080] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A multi-layer gradient microporous gas diffusion layer, characterized in that: include: Support layer; a first microporous layer disposed below the support layer; A second microporous layer is disposed below the first microporous layer; A third microporous layer is disposed below the second microporous layer; A fourth microporous layer is disposed below the third microporous layer; The support layer is made of carbon paper; The first microporous layer, the second microporous layer, the third microporous layer and the fourth microporous layer are made of carbon powder and a hydrophobic agent.

2. A multi-layer gradient microporous gas diffusion layer according to claim 1, characterized in that: The contact angle range of the first microporous layer is: 165°±2, the contact angle range of the second microporous layer is: 160°±2, the contact angle range of the third microporous layer is: 155°±2, and the contact angle range of the fourth microporous layer is: 150°±2; The density of the first microporous layer is: 0.53 g·cm -3 ±0.02, the density of the second microporous layer is: 0.49g·cm -3 ±0.02, the density of the third microporous layer is: 0.45g·cm -3 ±0.02, the density of the fourth microporous layer is: 0.41g·cm -3 ±0.

02.

3. A multi-layer gradient microporous gas diffusion layer according to claim 1, characterized in that: The thickness of the support layer, the first microporous layer, the second microporous layer, the third microporous layer and the third microporous layer is 10 μm.

4. A method for preparing a multi-layer gradient microporous gas diffusion layer according to any one of claims 1 to 3, characterized in that: S1: preparing slurry: mixing four different proportions of hydrophobic agent and pore-forming agent with conductive carbon powder and isopropyl alcohol to prepare slurry No. 1, slurry No. 2, slurry No. 3 and slurry No. 4 respectively; S2: Screen printing slurry: screen printing No. 1 slurry, No. 2 slurry, No. 3 slurry and No. 4 slurry on the support layer in order to form the first microporous layer, the second microporous layer, the third microporous layer and the fourth microporous layer. During screen printing, after each layer of slurry is printed, it is placed in a drying tunnel, and the drying tunnel speed is adjusted so that the gas diffusion layer stays in the drying tunnel for 80-100 seconds to ensure that the slurry is completely dry; S3: preparing a gas diffusion layer: calcining and sintering the completely dried gas diffusion layer.

5. The method for preparing a multi-layer gradient microporous gas diffusion layer according to claim 4, characterized in that: The conductive carbon powder is at least one of Vulcan XC-72 carbon powder, acetylene black or pearl carbon.

6. The method for preparing a multi-layer gradient microporous gas diffusion layer according to claim 4, characterized in that: The pore-forming agent is at least one of ammonium carbonate, ammonium bicarbonate or ammonium oxalate.

7. The method for preparing a multi-layer gradient microporous gas diffusion layer according to claim 4, characterized in that: The amount of pore-forming agent added to the No. 1 slurry>the amount of pore-forming agent added to the No. 2 slurry>the amount of pore-forming agent added to the No. 2 slurry=the amount of pore-forming agent added to the No. 4 slurry; The amount of hydrophobic agent added to the No. 1 slurry pore-forming agent = the amount of hydrophobic agent added to the No. 2 slurry pore-forming agent > the amount of hydrophobic agent added to the No. 3 slurry pore-forming agent > the amount of hydrophobic agent added to the No. 4 slurry pore-forming agent.

8. The method for preparing a multi-layer gradient microporous gas diffusion layer according to claim 4, characterized in that: When the pore-forming agent is ammonium oxalate, the amount of hydrophobic agent added to the No. 1 slurry and the No. 2 slurry is the same; The solid content ratio of carbon powder to hydrophobic agent in No. 1 and No. 2 slurries is 1.5:1; The ratios of carbon powder: pore-forming agent content are 1:1.3 and 1:1 respectively; The amount of pore former added in No. 3 slurry and No. 4 slurry is the same; The solid content ratio of carbon powder to pore former in No. 3 slurry and No. 4 slurry is 1.3:1, and the solid content ratio of carbon powder to hydrophobic agent is 2:1 and 3:1 respectively.

9. The method for preparing a multi-layer gradient microporous gas diffusion layer according to claim 4, characterized in that: The temperature for calcining the completely dried gas diffusion layer is 350° C., the time is 120 min, and the baking tunnel temperature is 120° C.

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