Integrated gas diffusion layer and preparation method and application thereof

Abstract

The invention provides an integrated gas diffusion layer and a preparation method and application thereof, and relates to the technical field of energy and cleaning, the integrated gas diffusion layer comprises a microporous layer and a substrate layer; the microporous layer is a three-dimensional porous structure layer formed by randomly arranging nanofibers; the nanofiber is of a core-shell structure, a shell layer material comprises a conductive material and perfluorinated sulfonic acid resin, and a core material is a polymer obtained through a cross-linked esterification reaction of polyacrylic acid and polyvinyl alcohol; the substrate layer is of a porous structure, one side of the substrate layer is loaded with perfluorinated sulfonic acid resin, and the other side of the substrate layer is provided with spaced grooves; the microporous layer is positioned on one side, loaded with Nafion, of the substrate layer; the average surface roughness of the substrate layer is less than or equal to 15 [mu] m. The integrated gas diffusion layer provided by the invention has the effects of greatly shortening the mass transfer path, greatly improving the mass transfer efficiency, simplifying the battery structure and reducing the battery volume, and achieves the effects of greatly enhancing the battery performance, greatly enhancing the battery volume power density and reducing the battery cost.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of energy and clean technology, and in particular to an integrated gas diffusion layer and a preparation method and application thereof. BACKGROUND

[0002] Proton exchange membrane fuel cell (PEMFC) has broad prospects in the field of hydrogen energy application due to its zero carbon emission, high energy conversion efficiency and other advantages. As a key component of PEMFC, gas diffusion layer (GDL) is responsible for transporting reactant gas, removing product water, conducting electricity, and transferring heat.

[0003] The gas diffusion layer is generally composed of a thin microporous layer (MPL) and a substrate layer (GDB). The microporous layer is in contact with the catalyst layer, and the substrate layer is in contact with the flow field on the bipolar plate. In the traditional PEMFC structure, the solid ridge in the flow field is in contact with the substrate layer, which leads to slow gas flow rate in the area under the ridge of the substrate layer, limited gas transport capacity, and difficulty in timely removal of product water. Moreover, the channel formed by the flow field ridge also serves as a transmission channel for the fuel cell coolant, responsible for transferring the heat generated by the fuel cell. Therefore, the temperature of the substrate layer under the ridge is much lower than that of the catalyst layer, which leads to condensation and accumulation of gaseous water produced by the catalyst layer in the area under the ridge, further deteriorating the gas transport under the ridge, and thus limiting the performance of the fuel cell.

[0004] To solve the above problems, some technologies have been disclosed to process flow channels on the substrate layer to solve the problems in the contact area between the flow field ridge and the substrate layer in the traditional battery structure. For example, patent application No. CN116826073A discloses a fuel cell integrated gas diffusion layer and a preparation method and application thereof. By etching flow channels on Toray carbon fiber carbon paper to prepare an integrated gas diffusion layer, the water vapor transport performance and battery power are improved. However, the integrated gas diffusion layer lacks a microporous layer (only composed of a carbon paper substrate layer and a processed flow field), which not only leads to poor interface contact between the gas diffusion layer and the catalyst layer, and increased contact resistance, but also leads to embedding of catalyst particles into the macropores of the substrate layer, resulting in active loss. Patent application No. CN117423846A discloses a gas diffusion layer and a preparation method and fuel cell thereof. A composite is obtained by hot pressing different face density carbon fiber raw paper, and a slurry containing carbon powder is coated on one side, dried and sintered to obtain a carbon powder microporous layer. A plurality of grooves are etched on the other side to obtain a gas diffusion layer. However, the microporous layer of the gas diffusion layer is prepared by coating the slurry on the substrate layer, which inevitably causes the slurry to penetrate into the substrate layer, affecting the pore structure of the substrate layer and limiting the water vapor transport, and thus affecting the performance of the battery. In addition, etching grooves on the substrate layer may cause pollution, scratching and denaturation of the microporous layer.

[0005] In order to solve the problems caused by the traditional commercial gas diffusion layer in the PEMFC structure, it is essential to prepare an integrated gas diffusion layer. However, the integrated gas diffusion layer in the prior art is based on a simple improvement of the traditional commercial gas diffusion layer, and still has the problems of poor interface contact and poor water vapor transmission capacity of the traditional commercial gas diffusion layer, so that when applied in the PEMFC, the performance output and durability of the battery are limited. SUMMARY

[0006] In view of the deficiencies in the prior art, the purpose of the present application is to provide an integrated gas diffusion layer, its preparation method and application, aiming to solve the problems of poor interface contact and limited water vapor transmission of the integrated gas diffusion layer in the prior art.

[0007] The present application provides an integrated gas diffusion layer, which comprises a microporous layer and a substrate layer. The microporous layer is a three-dimensional porous structure layer formed by random arrangement of nanofibers; the nanofibers have a core-shell structure, the shell material comprises conductive material and perfluorosulfonic acid resin, and the core material is a polymer obtained by crosslinking esterification of polyacrylic acid and polyvinyl alcohol; The substrate layer has a porous structure, one side of which is loaded with perfluorosulfonic acid resin, and the other side has spaced grooves; the microporous layer is located on the side of the substrate layer loaded with Nafion; The average surface roughness of the substrate layer is ≤ 15 μm.

[0008] In the integrated gas diffusion layer provided by the present application, the microporous layer has a macroporous fiber structure, the substrate layer has a porous structure and is provided with grooves, the grooves serve as the main transmission channel, the porous structure serves as the auxiliary transmission channel, the three transmission channels are integrated, the mass transfer path is greatly shortened, the mass transfer efficiency is greatly improved, the battery structure is simplified, the battery volume is reduced, the battery performance is greatly enhanced, the battery volume power density is greatly enhanced, and the battery cost is reduced; in addition, by processing the substrate layer to form spaced grooves, the gas transmission mode to the catalyst layer is changed from the original diffusion to convection transmission, which changes the water vapor transmission mode and path in the battery; since the space (ridge acting as a flow channel) of the grooves is a porous structure, the problem of water accumulation under the ridge of the traditional battery flow channel is solved, the oxygen concentration and uniformity on the catalyst layer surface are improved, the battery water management is enhanced, and the battery performance is greatly improved. Further, the nanofiber microporous layer with a core-shell structure is integrated with the porous structure substrate layer provided with grooves, which forms a continuous and through three-dimensional transmission framework, realizes efficient transport of reaction gas and product water, realizes high porosity of high-efficiency fluid transmission, maintains the balance of the conductive network for effective charge transmission, and fundamentally avoids the problems of structural deterioration and performance decay caused by slurry penetration.

[0009] The integrated gas diffusion layer provided by the present application can avoid the existence of burrs on the surface of the substrate layer, prevent the burrs from piercing the proton exchange membrane, improve the safety and stability of the fuel cell, and significantly improve the performance and reliability of the integrated gas diffusion layer.

[0010] The average surface roughness of the substrate layer is the arithmetic average surface roughness (Ra) specified in JIS B0601 (1994), and the unit is μm.

[0011] Preferably, the average surface roughness of the substrate layer is 7 μm to 10 μm.

[0012] The average surface roughness of the substrate layer is controlled to be 7 μm to 10 μm. On the one hand, the relatively smooth surface of the substrate layer can increase the interface contact area when it contacts with the microporous layer, reduce the interface contact resistance, and improve the performance of the battery. On the other hand, the existence of burrs on the surface of the substrate layer can be avoided, the burrs can be prevented from piercing the proton exchange membrane, the safety and stability of the fuel cell can be improved, and the performance and reliability of the integrated gas diffusion layer can be significantly improved.

[0013] Preferably, the average pore size of the substrate layer is 1 μm to 50 μm, and preferably 20 μm to 40 μm. and / or, The porosity of the substrate layer is 60% to 85%, and preferably 65% to 80%.

[0014] The average pore size of the substrate layer is controlled to be 1 μm to 50 μm, and the porosity of the substrate layer is controlled to be 60% to 85%. The substrate layer is responsible for transmitting reaction gas, conducting electrons, supporting catalyst coated membrane (CCM), etc. Too small pore size and porosity will cause the gas transmission resistance to increase, the transmission efficiency to decrease, and the battery to be prone to mass transfer polarization. Too large pore size and porosity will cause the effective contact area of the substrate layer with the polar plate and the microporous layer to decrease, the electron transmission resistance at the interface of both sides of the substrate layer to increase, the ohmic polarization of the battery to increase, and the performance to decrease. In addition, too large pore size and porosity of the substrate layer are difficult to support the CCM, which causes the CCM to swell during the operation of the battery, and reduces the durability thereof.

[0015] Preferably, the shape of the groove of the substrate layer and the porous ridge formed between any two adjacent grooves is not limited, and can be a regular polygon or an irregular curved shape.

[0016] As preferred, the depth of the groove is 0.1-0.5mm, preferably 0.2-0.4mm, the width of a single groove is 0.4-2mm, preferably 0.5-1mm, and the distance between two adjacent grooves is 0.4-2mm, preferably 0.5-1mm.

[0017] The depth of the groove is 0.1-0.5mm, the width of a single groove is 0.4-2mm, and the distance between two adjacent grooves is 0.4-2mm. By controlling the width of a single groove, the distance between two grooves, and the depth of the groove, the distribution of the gas transmission channel on the substrate layer, the gas transmission cross-sectional area, and the contact area between the substrate layer and the polar plate can be adjusted. Not only can the uniformity of the distribution of the reaction gas in the catalytic layer be optimized, the current density difference between different regions can be reduced, and the performance and durability of the battery can be improved, but also the gas flow rate can be adjusted by changing the gas transmission cross-sectional area, thereby optimizing the gas transmission efficiency and the drainage efficiency, and avoiding the occurrence of mass transfer problems caused by water flooding in the catalytic layer. In addition, the distance between the grooves affects the contact area between the polar plate and the substrate layer, thereby affecting the contact resistance of the integrated gas diffusion layer when applied in the battery, and thus affecting the performance of the battery As preferred, the bottom of the groove is a planar structure, the depth of the groove is 0.1-0.5mm, preferably 0.2-0.4mm, the width of the groove is 0.4-2mm, preferably 0.5-1mm, and the distance between two adjacent grooves is 0.4-2mm, preferably 0.5-1mm.

[0018] As preferred, the distance between two adjacent grooves is the same.

[0019] As preferred, the thickness of the substrate layer is 200μm-500μm, preferably 300μm-400μm. and / or, The hydrophobic angle of the substrate layer is 120°-155°, preferably 130°-150°.

[0020] As preferred, the substrate layer is selected from at least one of carbon paper and carbon felt with grooves on one side.

[0021] As preferred, the processing method of the substrate layer with groove structure includes at least one of mechanical milling, laser etching, ion beam etching, chemical etching, and mold pressing.

[0022] As preferred, the processing method of the substrate layer with groove structure is as follows: the groove parameters required for processing are designed using software, and then imported into a mechanical milling device or an etching device for processing the substrate layer; or a mold with the required groove parameters is processed, and then the substrate layer is pressed.

[0023] Preferably, the average pore size of the microporous layer is 100-1000 nm, preferably 200-800 nm; and / or, The porosity of the microporous layer is 60-85%, preferably 65-80%.

[0024] The average pore size of the microporous layer is controlled to be 100-1000 nm, and the porosity of the microporous layer is controlled to be 60-80%, which can reduce the water vapor transmission resistance and improve the transmission efficiency, and also ensure sufficient mechanical strength and electrical conductivity of the substrate layer The average pore size of the microporous layer is controlled to be 100-1000 nm, and the porosity of the microporous layer is controlled to be 60-80%, which can reduce the water vapor transmission resistance and improve the transmission efficiency, and also ensure sufficient mechanical strength and electrical conductivity of the substrate layer

[0025] The thickness of the microporous layer is 3-30 μm, further preferably 5-20 μm, and the hydrophobic angle of the microporous layer is 120-160°, further preferably 135-150°.

[0026] Preferably, the preparation method of the microporous layer comprises the following steps: S1. Dissolve a spinning high polymer in a first solvent to obtain a spinning high polymer solution, wherein the spinning high polymer is polyacrylic acid and polyvinyl alcohol; S2. Disperse a conductive material and a perfluorosulfonic acid resin in a second solvent, then add the spinning high polymer solution, and homogenize to obtain a microporous layer spinning slurry; S3. Perform electrospinning on the microporous layer spinning slurry to obtain a microporous layer precursor; S4. Perform heat treatment on the microporous layer precursor to cause cross-linking esterification reaction of polyacrylic acid and polyvinyl alcohol, and then press to obtain the microporous layer.

[0027] The independent microporous layer in the integrated gas diffusion layer can be prepared by electrospinning. The random stacking of nanofibers produces a three-dimensional disordered arrangement of macroporous fiber structure, which increases the pore size of the gas diffusion layer, improves the water vapor transport capacity of the gas diffusion layer, and reduces the water breakthrough pressure. On the other hand, the nanofibers of the microporous layer are of core-shell structure, i.e., the shell layer formed by the conductive material and perfluorosulfonic acid resin covers the nanofiber skeleton (core) formed by the crosslinking esterification of polyacrylic acid and polyvinyl alcohol. The core polymer that undergoes crosslinking reaction in this structure provides the independent microporous layer with good mechanical strength and flexibility, which avoids the generation of cracks in the microporous layer, enhances the interface contact between the subsequent microporous layer and the catalyst layer, solves the problem of interface water caused by the high roughness surface of the traditional microporous layer, and achieves the effects of enhancing the durability of the gas diffusion layer, reducing the water vapor transport resistance, reducing the ohmic impedance and mass transfer impedance of the battery, and improving the performance of the battery.

[0028] Preferably, the molecular weight of the polyacrylic acid is 85000-230000, and the molecular weight of the polyvinyl alcohol is 130000-1250000.

[0029] Preferably, in the S1, the mass ratio of the polyacrylic acid and the polyvinyl alcohol is (1-2):(1-2).

[0030] Preferably, in the S1, the concentration of the spinning high molecular polymer in the spinning high molecular polymer solution is 2 wt%-20 wt%, preferably 4 wt%-12 wt%.

[0031] The concentration of the spinning high molecular polymer in the spinning high molecular polymer solution is controlled to be 2 wt%-20 wt%, which can ensure the required viscosity of the spinning high molecular polymer solution, ensure the success and continuity of spinning, and avoid the occurrence of beaded fibers, and also avoid the situation that the viscosity of the spinning high molecular polymer solution is too large, resulting in a very uneven distribution of the diameter of the obtained nanofibers.

[0032] Preferably, the mass of the conductive material is a, the mass of the hydrophobic agent is b, and the mass of the spinning high molecular polymer is c, a / (a+b+c)=50%-80%, and / or, b:c=1:(2-6), preferably b:c=1:(2.5-4).

[0033] In the preparation method of the microporous layer provided in the scheme, the mass of the conductive material accounts for 50% to 80% of the total mass of the conductive material, the hydrophobic agent, and the spinning high polymer, so as to control the composition, structure, and performance of the nanofiber in the microporous layer. When the mass of the conductive material accounts for less than 50%, a uniform carbon-coated spinning high polymer nanofiber skeleton structure cannot be formed; when the mass of the conductive material accounts for more than 80%, the diameter and strength of the polymer nanofiber skeleton are greatly reduced, and the microporous layer cannot be applied.

[0034] The mass of the conductive material in the scheme is greater than 50%, and the homogenization can enhance the dispersibility of the conductive material in the viscous high polymer solution, thereby enhancing the uniformity of the carbon-coated spinning high polymer nanofiber.

[0035] As preferred, in the S2, the conductive material is selected from at least one of XC-72 carbon black, acetylene carbon black, conductive carbon black SuperP, carbon nanofiber, graphene, carbon nanotube, and high-surface-area graphite.

[0036] As preferred, the first solvent and the second solvent are each independently selected from one or more of water, isopropyl alcohol, n-propanol, propanol, and ethanol.

[0037] As preferred, in the S2, the homogenization is selected from at least one of high-shear homogenization, high-pressure homogenization, microfluidic homogenization, and ball-milling homogenization.

[0038] Further preferably, the rotation speed of the high-shear homogenization is 5000-50000 rpm, preferably 8000-30000 rpm.

[0039] Further preferably, the pressure of the high-pressure homogenization is 400-600 bar.

[0040] As preferred, in the S3, the environmental conditions of the electrospinning are a temperature of 20℃-40℃ and a relative humidity of greater than 50% RH.

[0041] In the scheme, a low-boiling-point (boiling point ≤100℃) solvent is used in the spinning slurry of the microporous layer, and the relative humidity in the environmental conditions of the electrospinning is greater than 50% RH, which can inhibit the volatilization speed of the solvent in the spinning process and reduce the solidification speed of the jet, thereby achieving the effect of smooth and continuous spinning without clogging the spinning needle.

[0042] Preferably, in the S3, the electrospinning spinning condition is that the microporous layer spinning dope pushing rate is 0.2 mL / h-1.0 mL / h, and / or the voltage is 6.0 kV-22.0 kV, and / or the rotation speed of the drum receiver is 100 rpm / min-1000 rpm / min, and / or the needle diameter is 10G-26G, and / or the distance between the needle and the receiver is 8 cm-18 cm.

[0043] Preferably, in the S4, the heat treatment temperature is 120℃-150℃, preferably 130-140℃.

[0044] The preparation method of the microporous layer provided in the present application uses two spinning high molecular polymers, polyacrylic acid (PAA) and polyvinyl alcohol (PVA), as raw materials, and the cross-linking esterification reaction occurs in the heat treatment process at a heat treatment temperature of 120℃-150℃. Through the cross-linking esterification reaction between the two polymers, the stability of the polymer nanofiber skeleton is enhanced, and the service life and durability of the microporous layer are greatly prolonged.

[0045] Preferably, in the S4, the pressing pressure is 0.2 MPa-2 MPa, and further preferably 0.8-1.5 MPa.

[0046] The preparation method of the integrated gas diffusion layer provided in the present application comprises the following steps: transferring the microporous layer to one side of the substrate layer loaded with perfluorosulfonic acid resin; The transfer temperature is 120℃-150℃, and the transfer pressure is 0.1 MPa-1 MPa.

[0047] The preparation method of the integrated gas diffusion layer provided in the present application transfers the microporous layer to the substrate layer after independently preparing the microporous layer, solves the problem of pore structure change caused by the penetration of the traditional microporous layer slurry into the substrate layer, and avoids the influence of the substrate layer processing on the microporous layer (such as contamination, scratching, denaturation, etc. of the microporous layer during the substrate layer processing). When the microporous layer is transferred to the substrate layer, the microporous layer nanofiber shell layer contains Nafion, and one side of the substrate layer is coated with Nafion. During heating, the Nafion in both melts, and under the action of pressure, the melted Nafion in both fuses. After the temperature drops to room temperature, solidification occurs, which plays the role of a bonding agent, enhances the bonding force between the microporous layer and the substrate layer, and reduces the contact resistance between the microporous layer and the substrate layer.

[0048] Further preferably, the transfer time is 30 s-300 s.

[0049] The present application provides an electrochemical device comprising the integrated gas diffusion layer. Further preferably, the electrochemical device comprises a fuel cell, a water electrolyzer, a carbon dioxide electrolyzer. BRIEF DESCRIPTION OF DRAWINGS

[0050] In order to more clearly illustrate the technical solutions of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or prior art description. Obviously, the drawings described below are some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without creative labor.

[0051] Figure 1 SEM image of the nanofiber independent microporous layer in Example 1 of the present application.

[0052] Figure 2 Actual image of the side of the carbon paper in Example 1 of the present application, which is engraved with grooves.

[0053] Figure 3 SEM image of the cross section of the traditional commercial gas diffusion layer in Comparative Example 1 of the present application.

[0054] Figure 4 Comparison chart of water breakthrough pressure test results of the integrated gas diffusion layer prepared in Example 1 of the present application and the traditional commercial gas diffusion layer in Comparative Example 1.

[0055] Figure 5 Polarization curve chart of the cell assembled by the integrated gas diffusion layer prepared in Example 1 of the present application and the traditional commercial gas diffusion layer in Comparative Example 1.

[0056] Figure 6 Power density curve chart of the cell assembled by the integrated gas diffusion layer prepared in Example 1 of the present application and the traditional commercial gas diffusion layer in Comparative Example 1.

[0057] Figure 7 And Figure 8 Surface profile test chart of the carbon paper in Example 1.

[0058] Figure 9 Morphology chart of the carbon paper combined with the microporous layer in Example 1.

[0059] Figure 10 And Figure 11 Surface profile test chart of the titanium felt in Comparative Example 2.

[0060] Figure 12 Morphology chart of the titanium felt combined with the microporous layer in Comparative Example 2.

[0061] Figure 13The image shows the battery performance of the battery assembled with an integrated gas diffusion layer when titanium felt is used as the substrate layer in Comparative Example 2.

[0062] Figure 14 and Figure 15 The surface profile test diagram of the foamed titanium in Comparative Example 3 is shown.

[0063] Figure 16 This is a morphology diagram of the foamed titanium combined with the microporous layer in Comparative Example 3.

[0064] Figure 17 The image shows the battery performance of the battery assembled with an integrated gas diffusion layer when titanium foam is used as the substrate layer in Comparative Example 3.

[0065] Figure 18 and Figure 19 The surface profile test diagram of foamed carbon is shown in Comparative Example 4.

[0066] Figure 20 This is a morphology diagram of the foamed carbon combined with the microporous layer in Comparative Example 4.

[0067] Figure 21 The image shows the battery performance of the battery assembled with an integrated gas diffusion layer when using foamed carbon as the substrate layer, as shown in Comparative Example 4.

[0068] Figure 22 This is a schematic diagram of the integrated gas diffusion layer in Example 1. Detailed Implementation

[0069] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0070] Example 1 This embodiment provides an integrated gas diffusion layer (structural schematic diagram shown below). Figure 22 As shown, the gas diffusion layer includes a microporous layer and a substrate layer; The microporous layer is a three-dimensional porous structure formed by the random arrangement of nanofibers; the nanofibers are a core-shell structure, the shell material in the core-shell structure includes conductive materials and perfluorosulfonic acid resin, and the core material in the core-shell structure is a polymer obtained by cross-linking and esterification reaction of polyacrylic acid and polyvinyl alcohol; The average pore size of the microporous layer is 600 nm, the porosity of the microporous layer is 78%, the thickness of the microporous layer is 7 μm, and the hydrophobic angle of the microporous layer is 143°. The substrate layer is a porous structure, one side of which is loaded with a perfluorosulfonic acid resin (Nafion), and the other side has spaced grooves; the microporous layer is located on the side of the substrate layer loaded with Nafion; The average surface roughness of the substrate layer is 8 μm; The average pore size of the substrate layer is 24 μm, the porosity of the substrate layer is 75%, the thickness of the substrate layer is 370 μm, and the hydrophobic angle of the substrate layer is 140°; The shape of the grooves is a cuboid (depth 0.2 mm, width 1 mm, length 22.5 mm), the shape of all the grooves of the substrate layer is the same, the spacing between the two adjacent grooves of the substrate layer is the same, and the spacing is 1 mm.

[0071] The preparation method of the microporous layer of the present embodiment specifically includes the following steps: S1. Polyvinyl alcohol (PVA, molecular weight 450000 g mol -1 ) and polyacrylic acid (PAA, molecular weight 195000 g mol -1 ) spinning high molecular polymer were added to deionized water and stirred, respectively, to prepare a 5wt% polyvinyl alcohol solution and a 5wt% polyacrylic acid solution, and the polyvinyl alcohol solution and the polyacrylic acid solution were mixed in a mass ratio of 1:1 to prepare a spinning high molecular polymer solution.

[0072] S2. XC-72 carbon black conductive material, Nafion solution (concentration 5wt%) and hydrophobic agent were ultrasonically dispersed in isopropyl alcohol, and then the spinning high molecular polymer solution was added to prepare a microporous layer spinning slurry by high shear homogenizer high shear homogenization stirring (speed 12000 rpm).

[0073] S3. The microporous layer spinning slurry was spun by electrospinning technology, and the environmental parameters of electrospinning were: temperature 27℃, relative humidity 65%RH; the spinning parameters were: microporous layer slurry advancing rate 0.3mL / h, voltage 8.0kV, rotating drum receiver speed 150 rpm / min, needle diameter 20G, distance between needle and receiver 15cm, to obtain a microporous layer precursor.

[0074] S4. The microporous layer precursor was heat treated at 140℃ for 1 hour, and then pressed at 1.2 MPa at ambient temperature to obtain a 7 μm thick nanofiber independent microporous layer. The mass ratio of the conductive material (XC-72 carbon black), the hydrophobic agent (Nafion) and the spinning high molecular polymer (polyvinyl alcohol and polyacrylic acid) used in the nanofiber independent microporous layer prepared in the present embodiment is 7:1:3.

[0075] The preparation method of the integrated gas diffusion layer provided in the embodiment includes the following steps: S1. Use Toray TGP-H-120 carbon paper (length 22.5 mm, width 22.5 mm) as a substrate layer, with a thickness of 370 μm, a porosity of 75%, an average pore size of 24 μm, and an average surface roughness of 8 μm. Use laser etching to form grooves with a depth of 0.2 mm, a width of 1 mm, a length of 22.5 mm, and a spacing of 1 mm as the main mass transfer channels, and the spacing parts as the auxiliary mass transfer channels. Perform hydrophobic treatment on the laser-etched carbon paper using a PTFE (polytetrafluoroethylene) dispersion liquid, and the hydrophobic angle is 140°. S2. Add 5%wt of Nafion solution to deionized water to dilute to 1%wt, and cover the surface of the carbon paper with a small amount of Nafion by ultrasonic spraying, and then dry, and the spraying load is 0.02 mg cm -2 .

[0076] The nanofiber independent microporous layer prepared in the embodiment is hot transferred to the substrate layer, the hot pressing temperature is 140°C, the hot pressing pressure is 0.1 MPa, and the hot pressing time is 90 s, to obtain an integrated gas diffusion layer.

[0077] The embodiment provides a fuel cell, and the specific preparation method is as follows: The integrated gas diffusion layer prepared in the embodiment is assembled with a catalyst coated membrane (CCM) to obtain a fuel cell membrane electrode, and then assembled with a graphite bipolar plate with a groove of 0.2 mm in depth to obtain an integrated fuel cell. Perform electrochemical performance evaluation on a single cell evaluation device.

[0078] Figure 1 The microporous layer morphology obtained by electrospinning in the embodiment is that the nanofibers are randomly stacked to form a three-dimensional disordered arrangement of macroporous fiber structure, which can increase the pore size of the gas diffusion layer, improve the water and gas transport capacity of the gas diffusion layer, and improve the performance of the battery. On the other hand, the nanofibers of the microporous layer are in a core-shell structure, that is, the shell layer formed by the conductive material and the perfluorosulfonic acid resin covers the nanofiber skeleton (core) formed by the crosslinking esterification of polyacrylic acid and polyvinyl alcohol, and the inner core polymer which undergoes crosslinking reaction in the structure provides good mechanical strength and flexibility to the microporous layer, avoiding the generation of cracks in the microporous layer.

[0079] Figure 7 And Figure 8 The surface profile test diagram of the carbon paper in the embodiment is shown in the figure, and it can be seen from the figure that the surface fluctuation is 19.49 μm, and the surface of the carbon paper is smooth. After the carbon paper in the membrane electrode is peeled off, the surface morphology of the microporous layer is characterized, and it is found that the microporous layer is not damaged, and the catalyst layer and the proton exchange membrane are also not deformed.

[0080] AsFigure 2 As shown, flow field processing is performed on carbon paper to achieve integration of the substrate layer and the flow field. In the integrated gas diffusion layer, the microporous layer is a macroporous fiber structure, and the substrate layer is a porous structure. At the same time, grooves are set in the substrate layer, which serve as the main transport channels, while the porous structure serves as the secondary transport channels. This integration of the three transport channels significantly shortens the mass transfer path, greatly improves the mass transfer efficiency, simplifies the battery structure, and reduces the battery volume.

[0081] Figure 9 This is a morphological image of the carbon paper bonded to the microporous layer in Example 1. Figure 9 It can be seen that after the microporous layer is bonded to the carbon paper, the microporous layer is not damaged due to the small average surface roughness of the carbon paper, and the porous structure is maintained.

[0082] like Figure 5 As shown, compared with traditional commercial gas diffusion layers, the performance of the integrated gas diffusion layer in this embodiment is greatly improved. Thanks to the significant improvement in mass transfer capability, the performance of the mass transfer polarization region in the polarization curve is significantly improved, and the limiting current density is doubled.

[0083] Figure 6 The power density curve of the battery assembled with the integrated gas diffusion layer prepared in this embodiment is shown. The test results show that the battery using the integrated gas diffusion layer has a maximum power density of 2.30 W / cm². -2 This achieves the effect of significantly enhancing battery performance, significantly increasing battery volumetric power density, and reducing battery manufacturing costs under the same power density output conditions.

[0084] Comparative Example 1 The gas diffusion layer provided in this comparative example is a traditional commercial gas diffusion layer.

[0085] The specific preparation method of the fuel cell provided in this comparative example differs from that in Example 1 in that the membrane electrode is prepared by directly using the conventional commercial gas diffusion layer and conventional graphite parallel flow field provided in this comparative example.

[0086] Figure 3 This is a cross-sectional SEM image of a traditional commercial gas diffusion layer. Because its fabrication process involves coating a microporous layer slurry onto a carbon paper substrate, from... Figure 3 It can be clearly seen that the microporous layer slurry penetrates into the carbon paper substrate, affecting the pore structure of the substrate and resulting in limited mass transfer. In addition, the traditional microporous layer structure is a carbon powder particle stacking type, and the small pore structure is not conducive to the rapid removal of water from the catalyst layer products. Figure 4 The results of water breakthrough pressure tests for two gas diffusion layers, Example 1 and Comparative Example 1, are shown. As can be seen from the figure, the water breakthrough pressure of the conventional commercial gas diffusion layer is 21 kPa, which is 2.16 times the water breakthrough pressure of the integrated gas diffusion layer in Example 1.

[0087] Figure 5 The battery performance of the battery assembled by the traditional commercial gas diffusion layer of Comparative Example 1 is much lower than that of the battery of Example 1, which is limited by the poor mass transfer capacity of the traditional commercial gas diffusion layer, and the performance of the mass transfer polarization zone is more significantly reduced.

[0088] Figure 6 The highest power density of the battery assembled by the traditional commercial gas diffusion layer of Comparative Example 1 is 1.30 W cm -2 , which is 1.0 W cm -2 lower than the highest power density of the battery assembled by the integrated gas diffusion layer of Example 1.

[0089] Comparative Example 2 The integrated gas diffusion layer provided in this comparative example is different from Example 1 in that the substrate layer is a titanium felt, the average surface roughness of the substrate layer is 16 μm, the average pore size of the substrate layer is 22 μm, the porosity of the substrate layer is 72%, and the thickness of the substrate layer is 400 μm.

[0090] The preparation method of the microporous layer provided in this comparative example is the same as that of Example 1.

[0091] The preparation method of the integrated gas diffusion layer provided in this example includes the following steps: S1. Adopting titanium felt as the substrate layer for groove processing, and combining with the microporous layer after hydrophobic treatment to prepare an integrated gas diffusion layer, the specific preparation method is: taking titanium felt (length 22.5 mm, width 22.5 mm) as the substrate layer, the thickness is 400 μm, the porosity is 72%, the average pore size is 22 μm, and the average surface roughness is 16 μm. A groove with a milling depth of 0.2 mm, a width of 1 mm, a length of 22.5 mm, and an interval of 1 mm is used as the main mass transfer channel, and the interval part is the auxiliary mass transfer channel. The titanium felt milled by the machine tool is treated with PTFE dispersion liquid for hydrophobic treatment, and the hydrophobic angle is 140°; S2. Add 5%wt of Nafion solution to deionized water to dilute to 1%wt, cover the surface of the titanium felt with a small amount of Nafion by ultrasonic spraying, and then dry, the spraying load is 0.02 mg cm -2 .

[0092] The nanofiber independent microporous layer prepared in this comparative example is hot transferred to the substrate layer, the hot pressing temperature is 140°C, the hot pressing pressure is 0.1 MPa, and the hot pressing time is 90 s, to obtain an integrated gas diffusion layer.

[0093] The specific preparation method of the fuel cell provided by the present comparative example is different from that of Example 1 in that an integrated gas diffusion layer is prepared using the present comparative example.

[0094] Figure 10 and Figure 11 The surface profile of the titanium felt of the present comparative example is shown. As can be seen from the figure, the fluctuation range of the surface of the titanium felt is 68.68 μm, and the maximum fluctuation range is 240.71 μm, which indicates that the surface of the titanium felt is more uneven than that of the carbon paper, resulting in a worse contact with the microporous layer when combined. In addition, as can be seen from the figure, Figure 12 It can be seen that deep indentations appear on the surface of the microporous layer, and during subsequent cell assembly, the uneven surface of the microporous layer will affect the morphology of the catalyst-coated membrane and the proton exchange membrane, causing deformation thereof.

[0095] Figure 13 It is shown that the performance of the cell using the titanium felt with a relatively rough surface as the substrate layer is lower than that of the cell using the carbon paper with a relatively smooth surface as the substrate layer, Figure 13 It is shown that the highest power density of the cell assembled using the integrated gas diffusion layer of Comparative Example 2 is 2.07 W cm -2 , which is 0.23 W cm -2 lower than the highest power density of the cell using the carbon paper as the substrate layer.

[0096] Comparative Example 3 The integrated gas diffusion layer provided by the present comparative example is different from that of Example 1 in that the substrate layer is a titanium foam, the average surface roughness of the substrate layer is 40 μm, the average pore size of the substrate layer is 45 μm, the porosity of the substrate layer is 68%, and the thickness of the substrate layer is 300 μm.

[0097] The preparation method of the microporous layer provided by the present comparative example is the same as that of Example 1.

[0098] The preparation method of the integrated gas diffusion layer provided by the present example includes the following steps: S1. The present comparative example is different from Example 1 in that a titanium foam is used as the substrate layer for groove processing, and after hydrophobic treatment, the titanium foam is combined with the microporous layer to prepare an integrated gas diffusion layer. The specific preparation method is as follows: a titanium foam (length 22.5 mm, width 22.5 mm) is used as the substrate layer, with a thickness of 300 μm, a porosity of 68%, an average pore size of 45 μm, and an average surface roughness of 40 μm. A groove with a milling depth of 0.2 mm, a width of 1 mm, and a length of 22.5 mm is machined using a machine tool, with an interval of 1 mm as the main mass transfer channel, and the interval part as the auxiliary mass transfer channel. The titanium felt machined by the machine tool is subjected to hydrophobic treatment using a PTFE dispersion liquid, and the hydrophobic angle is 140°; S2. Add 5%wt Nafion solution into deionized water to dilute to 1%wt, cover a trace of Nafion on the surface of the titanium foam by ultrasonic spraying, then dry, and weigh the spraying load to be 0.02mg cm -2 .

[0099] The nanofiber independent microporous layer prepared in the present comparative example is hot transferred to the substrate layer, the hot pressing temperature is 140°C, the hot pressing pressure is 0.1MPa, and the hot pressing time is 90s, to obtain an integrated gas diffusion layer.

[0100] The specific preparation method of the fuel cell provided by the present comparative example is different from that of Example 1 in that the integrated gas diffusion layer prepared by the present comparative example is used.

[0101] Figure 14 and Figure 15 The surface profile of the titanium foam of the present comparative example is shown, and it can be seen from the figure that the surface fluctuation of the titanium foam is huge, with a maximum fluctuation range of 903.98μm. The extremely rough surface of the titanium foam, and even the existence of the sharp skeleton, directly leads to the fact that the microporous layer is pierced when combined with the microporous layer. In addition, it can be seen from Figure 16 that the deep pits on the surface of the microporous layer will cause the morphology of the proton exchange membrane of the catalyst layer and the catalyst coated membrane to be deformed in the subsequent battery assembly.

[0102] Figure 17 It is shown that the performance of the battery using the titanium foam with an absolutely rough surface as the substrate layer is much lower than that of the battery using the relatively smooth carbon paper as the substrate layer, Figure 17 It is shown that the highest power density of the battery assembled by the integrated gas diffusion layer of Comparative Example 3 is 0.36W cm -2 , and even the film is pierced in the subsequent battery performance test, and the short circuit phenomenon occurs.

[0103] Comparative Example 4 The integrated gas diffusion layer provided by the present comparative example is different from that of Example 1 in that the substrate layer is a foam carbon, the average surface roughness of the substrate layer is 20μm, the average pore size of the substrate layer is 33μm, the porosity of the substrate layer is 70%, and the thickness of the substrate layer is 300μm.

[0104] The preparation method of the microporous layer provided by the present comparative example is the same as that of Example 1.

[0105] S1. The difference between this comparative example and Example 1 is that foam carbon is used as the base layer for groove processing, and after hydrophobic treatment, it is combined with the microporous layer to prepare an integrated gas diffusion layer. The specific preparation method is as follows: foam carbon (length 22.5 mm, width 22.5 mm) is used as the base layer, the thickness is 300 pm, the porosity is 70%, the average pore size is 33 pm, and the average surface roughness is 20 pm. The grooves with a milling depth of 0.2 mm, a width of 1 mm, a length of 22.5 mm, and an interval of 1 mm are used as the main mass transfer channels, and the interval part is the auxiliary mass transfer channel. The titanium felt after milling by the machine tool is treated with PTFE dispersion liquid, and the hydrophobic angle is 140°; S2. 5%wt of Nafion solution is added to deionized water to dilute to 1%wt, and a small amount of Nafion is sprayed on the surface of the foam carbon by ultrasonic spraying, and then dried. The spraying load is 0.02 mg cm -2 .

[0106] The nanofiber independent microporous layer prepared in this comparative example is hot transferred to the base layer, the hot pressing temperature is 140°C, the hot pressing pressure is 0.1 MPa, and the hot pressing time is 90 s, to obtain an integrated gas diffusion layer.

[0107] The specific preparation method of the fuel cell provided by this comparative example is different from that of Example 1 in that an integrated gas diffusion layer prepared by this comparative example is used.

[0108] Figure 18 and Figure 19 The surface profile of the foam carbon is shown. As can be seen from the figure, the surface of the foam carbon fluctuates greatly and appears frequently, and the maximum fluctuation range is 255.80 pm, which shows the common problem of uneven surface of the foam material. The rough surface of the foam carbon also causes the microporous layer to be pierced when combined with the microporous layer, and the Figure 20 It can be seen that the depressions on the surface of the microporous layer will cause the morphology of the catalyst layer and the catalyst-coated membrane to deform during the subsequent assembly of the battery.

[0109] Figure 21 It is shown that the performance of the battery using the foam carbon with a rough surface as the base layer is much lower than that of the battery using the relatively smooth carbon paper as the base layer, Figure 17 It is shown that the highest power density is 1.46 W cm -2 , which is a significant improvement over the performance of the foam titanium as a porous transport medium, but the highest power density is 0.84 W cm -2 lower than that of the carbon paper as the base layer.

[0110] It should be pointed out finally that the above embodiments are only used to illustrate the technical solutions of the present application, but not to limit the same; and although the present application has been described in detail with reference to the foregoing embodiments, it should be appreciated by those skilled in the art that the technical solutions recorded in the foregoing embodiments can be modified, or some technical features thereof can be replaced equivalently; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. An integrated gas diffusion layer, characterized in that, The integrated gas diffusion layer includes a microporous layer and a substrate layer; The microporous layer is a three-dimensional porous structure layer formed by the random arrangement of nanofibers; the nanofibers have a core-shell structure, the shell material includes conductive materials and perfluorosulfonic acid resin, and the core material is a polymer obtained by cross-linking and esterification reaction of polyacrylic acid and polyvinyl alcohol. The substrate layer has a porous structure, with perfluorosulfonic acid resin loaded on one side and spaced grooves on the other side; the microporous layer is located on the side of the substrate layer loaded with Nafion. The average surface roughness of the substrate layer is ≤15μm.

2. The integrated gas diffusion layer according to claim 1, characterized in that, The average surface roughness of the substrate layer is 7 μm to 10 μm.

3. The integrated gas diffusion layer according to claim 1 or 2, characterized in that, The average pore size of the substrate layer is 1μm~50μm, preferably 20μm~40μm; And / or, The porosity of the substrate layer is 60% to 85%, preferably 65% ​​to 80%.

4. The integrated gas diffusion layer according to claim 1 or 3, characterized in that, The depth of the groove is 0.1~0.5mm, preferably 0.2~0.4mm, the width of a single groove is 0.4~2mm, preferably 0.5~1mm, and the distance between two adjacent grooves is 0.4~2mm, preferably 0.5~1mm.

5. The integrated gas diffusion layer according to claim 1 or 4, characterized in that, The thickness of the substrate layer is 200μm~500μm, preferably 300μm~400μm; And / or, The hydrophobic angle of the substrate layer is 120°~155°, preferably 130°~150°.

6. The integrated gas diffusion layer according to any one of claims 1 to 5, characterized in that, The base layer is selected from at least one of carbon paper and carbon felt with grooves spaced apart on one side.

7. The integrated gas diffusion layer according to claim 1, 4, or 6, characterized in that, The average pore size of the microporous layer is 100nm~1000nm, preferably 200nm~800nm, and the porosity of the microporous layer is 60%~85%, preferably 65%~80%. And / or, The thickness of the microporous layer is 3 μm to 30 μm, preferably 5 μm to 20 μm, and the hydrophobic angle of the microporous layer is 120° to 160°, preferably 135° to 150°.

8. The integrated gas diffusion layer according to claim 1 or 7, characterized in that, The method for preparing the microporous layer includes the following steps: S1. Dissolve the spinning polymer in a first solvent to obtain a spinning polymer solution, wherein the spinning polymer is polyacrylic acid and polyvinyl alcohol; S2. Disperse the conductive material and perfluorosulfonic acid resin in a second solvent, then add the spinning polymer solution, homogenize, and obtain a microporous layer spinning slurry; S3. Electrospin the microporous layer spinning slurry to obtain a microporous layer precursor; S4. The microporous layer precursor is heat-treated to cause cross-linking and esterification of polyacrylic acid and polyvinyl alcohol, and then pressed to obtain the microporous layer.

9. A method for preparing an integrated gas diffusion layer as described in any one of claims 1 to 8, characterized in that, The process includes the following steps: transferring the microporous layer to the side of the substrate layer loaded with perfluorosulfonic acid resin; The transfer temperature is 120℃~150℃, and the transfer pressure is 0.1 MPa~1 MPa.

10. An electrochemical device, characterized in that, The electrochemical device includes the integrated gas diffusion layer as described in any one of claims 1 to 8; Preferably, the electrochemical device includes a fuel cell, a water electrolyzer, and a carbon dioxide electrolyzer.

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