Gas diffusion layer and preparation method and application thereof

Abstract

The invention provides a gas diffusion layer and a preparation method and application thereof, and relates to the technical field of energy and cleaning. The preparation method of the gas diffusion layer comprises the following steps: carrying out heat transfer printing on the microporous layer to one side of the perfluorosulfonic acid resin of the substrate layer with the surface loaded with the perfluorosulfonic acid resin to prepare the gas diffusion layer; the microporous layer is a porous structure layer formed by anisotropic arrangement of nanofibers, the nanofibers are of a core-shell structure, a core material is a polymer obtained through a cross-linking esterification reaction of polyacrylic acid and polyvinyl alcohol, and a shell material comprises a conductive material and perfluorinated sulfonic acid resin; the loading capacity of the perfluorinated sulfonic acid resin in the substrate layer with the surface loaded with the perfluorinated sulfonic acid resin is 0.01-0.1 mg cm <-2 >. According to the preparation method of the gas diffusion layer provided by the invention, the water vapor transmission efficiency of the gas diffusion layer is improved, and the effect of improving the battery performance is achieved.

Description

Technical Field

[0001] This invention relates to the fields of energy and clean technology, and in particular to a gas diffusion layer, its preparation method, and its application. Background Technology

[0002] Hydrogen energy, with its advantages of zero carbon emissions and high energy density, is hailed as the ultimate energy source of the 21st century. Proton exchange membrane fuel cells (PEMFCs), as hydrogen energy conversion devices, can directly convert chemical energy into electrical energy, and have therefore attracted widespread attention. The gas diffusion layer (GDL), as one of the key components of a PEMFC, is located between the bipolar plates and the catalyst layer, playing a crucial role.

[0003] Traditional gas diffusion layers typically consist of two layers: a microporous layer and a substrate layer. The microporous layer is generally prepared by coating a carbon paper substrate with a slurry containing carbon powder, hydrophobic binder, and other components. This leads to some common problems with traditional gas diffusion layers, such as the microporous layer slurry penetrating into the substrate layer and affecting the pore structure of the substrate layer, cracks appearing in the microporous layer during the drying stage, and high surface roughness of the microporous layer.

[0004] To address the aforementioned issues, some technologies have disclosed methods for modifying the preparation of microporous layers to resolve common problems inherent in traditional gas diffusion layers. For example, patent CN115020736A discloses a gas diffusion layer based on a fiber-arranged microporous layer, which solves the problems associated with traditional microporous layer slurry coating of the support layer by electrospinning a microporous layer slurry onto a support layer (substrate). However, spinning directly onto the support layer results in solvents evaporating during the spinning process contaminating the substrate layer, which can poison the catalyst and lead to battery performance degradation. Furthermore, spinning directly onto the support layer results in no bonding force between the microporous layer and the support layer, increasing interfacial contact resistance and making the thin microporous layer prone to interfacial separation, hindering its application in subsequent battery assembly. Summary of the Invention

[0005] This invention provides a gas diffusion layer, its preparation method, and its application, to solve the defect of poor interfacial contact between the microporous layer and the substrate layer in the prior art gas diffusion layer, thereby improving the interfacial contact between the microporous layer and the substrate layer in the gas diffusion layer.

[0006] This invention provides a method for preparing a gas diffusion layer, wherein a microporous layer is thermally transferred to the perfluorosulfonic acid resin side of a substrate layer loaded with perfluorosulfonic acid resin to obtain the gas diffusion layer; The microporous layer is a porous structure layer formed by anisotropic arrangement of nanofibers. The nanofibers have a core-shell structure. The core material is a polymer obtained by cross-linking and esterification reaction of polyacrylic acid and polyvinyl alcohol. The shell material includes conductive materials and perfluorosulfonic acid resin. The loading of perfluorosulfonic acid resin in the substrate layer with its surface loaded with perfluorosulfonic acid resin is 0.01~0.1 mg / cm³. -2 .

[0007] The present invention provides a method for preparing a gas diffusion layer. A microporous layer with an anisotropic arrangement of nanofibers, forming a porous structure, is hot-pressed onto a substrate layer loaded with perfluorosulfonic acid resin. This solves the problem of slurry penetration and impact on the pore structure of the substrate layer caused by the coating of the microporous layer slurry onto the substrate layer during traditional gas diffusion layer preparation. This method improves the water vapor transport efficiency of the gas diffusion layer, thereby enhancing battery performance. Furthermore, the present invention features a microporous nanofiber outer shell containing Nafion and a Nafion coating on one side of the substrate layer during the hot-pressing process. During heating, the molten Nafion in both components contacts and fuses under pressure, then solidifies during cooling, acting as a binder to enhance the bonding force between the microporous layer and the substrate layer. Moreover, since the gas diffusion layer provided by this invention does not require additional binders to suppress shrinkage of the microporous layer during heat treatment, and because the nanofiber outer shell contains Nafion, only a trace amount of Nafion (0.01~0.1 mg cm⁻¹) is needed on the substrate side. -2 This can satisfy the required interfacial bonding force while reducing the contact resistance between the microporous layer and the substrate layer, and reducing the resistance of the gas diffusion layer.

[0008] The present invention provides a method for preparing a gas diffusion layer. The nanofibers of the microporous layer have a core-shell structure, that is, a shell formed by conductive materials and perfluorosulfonic acid resin encapsulates a nanofiber skeleton (core) formed by a polymer obtained by cross-linking and esterification of polyacrylic acid and polyvinyl alcohol. In this structure, the cross-linked core polymer provides good mechanical strength and flexibility to the independent microporous layer, thereby enhancing the interfacial contact between the subsequent gas diffusion layer and the catalyst layer. This avoids the poor interfacial contact between the traditional gas diffusion layer and the catalyst layer due to cracks and high roughness surfaces, thus reducing the ohmic impedance of the battery and increasing the electrochemical active area of ​​the catalyst layer.

[0009] Preferably, the perfluorosulfonic acid resin loading in the substrate layer with the surface loaded with perfluorosulfonic acid resin is 0.01~0.02 mg / cm³. -2 .

[0010] In this invention, the loading of perfluorosulfonic acid resin in the substrate layer with a surface loaded with perfluorosulfonic acid resin is controlled to be 0.01~0.02 mg / cm³. -2While meeting the required interfacial bonding force, it also reduces the contact resistance between the microporous layer and the substrate layer, and lowers the resistance of the gas diffusion layer.

[0011] Preferably, the method for preparing the substrate layer with the surface loaded with perfluorosulfonic acid resin includes the following steps: coating a perfluorosulfonic acid resin solution onto one side of the heated substrate layer; The concentration of the perfluorosulfonic acid resin solution is 1wt%~10wt%; The temperature of the heated substrate layer is 100℃ ~ 110℃.

[0012] The method provided in this solution for preparing a substrate layer loaded with perfluorosulfonic acid resin achieves this by controlling the concentration of the perfluorosulfonic acid resin solution to 1wt%~10wt% and the heating temperature of the substrate layer to 100℃~110℃. This coordination ensures that when the low-concentration perfluorosulfonic acid resin solution is coated onto the substrate layer, the solvent evaporates rapidly, preventing the perfluorosulfonic acid resin solution from penetrating into the surface, thus avoiding solution waste and increased substrate layer resistance. Furthermore, when combined with the microporous layer of this invention, the required amount of perfluorosulfonic acid resin is met while simultaneously reducing the resistance of the composite gas diffusion layer and improving its performance.

[0013] Preferably, the temperature of the heat transfer is 125°C to 150°C, and / or the pressure of the heat transfer is 0.02 MPa to 0.2 MPa; More preferably, the temperature of the heat transfer is 135~150℃, and / or the pressure of the heat transfer is 0.05MPa~0.1MPa.

[0014] This scheme controls the heat transfer pressure to be 0.02 MPa~0.2 MPa. Within this pressure range, it can ensure that there is enough pressure to achieve good fusion and bonding of the molten perfluorosulfonic acid resin in the base layer and the microporous shell layer loaded with perfluorosulfonic acid resin on the surface, while avoiding excessive pressure that could damage the microporous layer and affect the transmission efficiency and conductivity of the gas diffusion layer.

[0015] In the microporous layer, the perfluorosulfonic acid resin accounts for 6% to 15% of the mass of the microporous layer; preferably 8% to 15%.

[0016] This method controls the loading of perfluorosulfonic acid resin in the substrate layer with a surface loaded with perfluorosulfonic acid resin to be 0.01~0.1 mg / cm³. -2 In the microporous layer, the perfluorosulfonic acid resin accounts for 6% to 15% of the mass of the microporous layer. The two work together to further enhance the bonding force between the microporous layer and the substrate layer, and further reduce the contact resistance between the microporous layer and the substrate layer, thereby reducing the resistance of the gas diffusion layer.

[0017] Preferably, the porosity and pore size of the substrate layer exhibit an increasing trend or remain consistent in the direction from the substrate layer to the thickness of the flow field.

[0018] This scheme controls the distribution of porosity and pore size of the substrate layer in the direction from the substrate layer to the thickness of the flow field to increase the capillary pressure difference and improve the discharge efficiency of product water.

[0019] Preferably, the heat transfer time is 30 s to 120 s, and more preferably 45 s to 90 s.

[0020] This method controls the heat transfer time to 30 s to 120 s, which can ensure the transformation of perfluorosulfonic acid resin to the molten state and avoid the effect of excessive time on the uniformity of perfluorosulfonic acid resin distribution in the microporous layer.

[0021] Preferably, the diameter of the nanofibers is 100 nm to 1000 nm, and / or the porosity of the microporous layer is 60% to 80%, and / or the average pore size of the microporous layer is 100 nm to 1000 nm.

[0022] Preferably, the thickness of the microporous layer is 3 μm to 30 μm.

[0023] Preferably, the hydrophobic angle of the microporous layer is 120°~160°.

[0024] This scheme controls the average pore size of the microporous layer to be 100nm~1000nm. By optimizing the pore size gradient between the microporous layer and the substrate layer within this range, the efficiency of water vapor transport in the gas diffusion layer is enhanced, thereby improving battery performance.

[0025] Preferably, the porosity and pore size of the microporous layer exhibit an increasing trend or remain consistent in the thickness direction from the microporous layer to the substrate layer.

[0026] This scheme controls the porosity and pore size of the microporous layer to increase in the thickness direction from the microporous layer to the substrate layer, which can generate capillary pressure difference and improve drainage efficiency.

[0027] Preferably, 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.

[0028] The microporous layer preparation method provided in this scheme produces nanofiber microporous layers with uniform thickness and controllable pore size and porosity. By adjusting the composition of the spinning slurry (such as the mass ratio of spinning polymer in the spinning slurry) and spinning parameters (such as spinning voltage), microporous layers with variable gradient pore size and porosity in the thickness direction can be prepared, thereby further enhancing the water vapor transport capacity of the gas diffusion layer. This solves the problem of uneven microporous layer thickness distribution caused by microporous layer slurry infiltration in traditional gas diffusion layers, which leads to uneven in-plane water vapor transport capacity. On the other hand, the microporous layer is prepared by spinning the prepared slurry in a single step. Compared with traditional microporous layer preparation methods, it does not require high-temperature (>300℃) heat treatment, reducing production energy consumption and thus reducing production costs. Compared with traditional spun microporous layers, it does not require high-temperature carbonization (>1000℃) and subsequent hydrophobic treatment, further reducing production costs and simplifying the production process.

[0029] Preferably, the molecular weight of the polyacrylic acid is 85,000 to 230,000, and the molecular weight of the polyvinyl alcohol is 130,000 to 1250,000.

[0030] Preferably, in S1, the mass ratio of polyacrylic acid to polyvinyl alcohol is (1~2):(1~2).

[0031] Preferably, in step S1, the concentration of the spinning polymer in the spinning polymer solution is 2 wt% to 20 wt%, more preferably 4 wt% to 12 wt%.

[0032] This method controls the concentration of the spinning polymer in the spinning polymer solution to be 2 wt%~20 wt%. This ensures the required viscosity of the spinning polymer solution, guaranteeing successful and continuous spinning without fiber beading, while also preventing excessively high viscosity of the spinning polymer solution from causing highly uneven distribution of nanofiber diameter.

[0033] Preferably, the mass of the conductive material is a, the mass of the hydrophobic agent is b, and the mass of the spinning polymer is c. a / (a+b+c) = 50%~80%, And / or, b:c=1:(2~6), preferably b:c=1:(2.5~4).

[0034] In the microporous layer preparation method provided in this scheme, the mass of conductive material is controlled to account for 50% to 80% of the total mass of conductive material, hydrophobic agent, and spinning polymer, thereby controlling the composition, structure, and properties of nanofibers in the microporous layer. When the mass proportion of conductive material is less than 50%, a uniform carbon-coated spinning polymer nanofiber skeleton structure cannot be formed; when the mass proportion of conductive material is greater than 80%, the diameter and strength of the polymer nanofiber skeleton are significantly reduced, making it unsuitable for application.

[0035] In this scheme, the conductive material accounts for more than 50% of the mass. Combined with homogeneity, it can enhance the dispersibility of the conductive material in the viscous polymer solution, thereby enhancing the uniformity of carbon-coated spun polymer nanofibers.

[0036] Preferably, in step S2, the conductive material is selected from at least one of XC-72 carbon black, acetylene black, conductive carbon black SuperP, carbon nanofibers, graphene, carbon nanotubes, and high surface area graphite.

[0037] Preferably, the first solvent and the second solvent are each independently selected from one or more of water, isopropanol, n-propanol, propanol, and ethanol.

[0038] Preferably, in S2, the homogenization method is selected from at least one of high-shear homogenization, high-pressure homogenization, microfluidic homogenization, and ball milling homogenization.

[0039] Further preferably, the rotational speed for high shear homogenization is 5000-50000 rpm, more preferably 8000-30000 rpm.

[0040] Furthermore, preferably, the pressure of the high-pressure homogenizer is 400~600 bar.

[0041] Preferably, in step S3, the environmental conditions for electrospinning are: temperature 20℃-40℃, relative humidity greater than 50%RH.

[0042] This solution uses a low-boiling-point (boiling point ≤ 100℃) solvent in the microporous layer spinning slurry. The relative humidity in the electrospinning environment is greater than 50%RH, which can suppress the evaporation rate of the solvent during the spinning process and reduce the jet solidification rate, thus achieving smooth and continuous spinning without clogging the spinning needle.

[0043] Preferably, in S3, the electrospinning conditions are as follows: the microporous layer spinning slurry feed rate is 0.2 mL / h to 1.0 mL / h, and / or the voltage is 6.0 kV to 22.0 kV, and / or the rotational speed of the drum receiver is 100 rpm / min to 1000 rpm / min, and / or the needle diameter is 10G to 26G, and / or the distance between the needle and the receiver is 8 cm to 18 cm.

[0044] Preferably, in step S4, the temperature of the heat treatment is 120°C to 150°C, more preferably 130°C to 140°C.

[0045] The microporous layer preparation method provided in this scheme uses two spinning polymers, polyacrylic acid (PAA) and polyvinyl alcohol (PVA), as raw materials, and allows them to undergo a cross-linking esterification reaction during heat treatment at a temperature of 120℃~150℃. Through the cross-linking esterification reaction between the two polymers, the stability of the polymer nanofiber skeleton is enhanced, resulting in a significant extension of the service life and durability of the microporous layer.

[0046] Preferably, in step S4, the pressing pressure is 0.2 MPa to 2 MPa, and more preferably 0.8 to 1.5 MPa.

[0047] The present invention provides a gas diffusion layer prepared by a method for preparing the aforementioned gas diffusion layer.

[0048] This invention provides an electrochemical device, the electrochemical device including the gas diffusion layer; Preferably, the electrochemical device includes a fuel cell, a water electrolyzer, and a carbon dioxide electrolyzer. Attached Figure Description

[0049] To more clearly illustrate the technical solutions in this invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0050] Figure 1 This is a scanning electron microscope (SEM) image of the nanofiber independent microporous layer in Example 1 of the present invention.

[0051] Figure 2 This is a cross-sectional SEM image of the carbon paper substrate layer in Embodiment 1 of the present invention.

[0052] Figure 3 This is a SEM image of one side of the microporous layer in the conventional gas diffusion layer in Comparative Example 1 of the present invention.

[0053] Figure 4 This is a cross-sectional SEM image of the conventional gas diffusion layer in Comparative Example 1 of the present invention.

[0054] Figure 5 A comparison of the polarization curves and power density curves of the battery assembled with the gas diffusion layer prepared in Example 1 of the present invention and the conventional gas diffusion layer in Comparative Example 1.

[0055] Figure 6 The image shows a comparison of the electrochemical impedance spectroscopy results of the battery assembled with the gas diffusion layer prepared in Example 1 of the present invention and the conventional gas diffusion layer in Comparative Example 1.

[0056] Figure 7 Comparison of cyclic voltammetry curves of batteries assembled with the gas diffusion layer prepared in Example 1 of the present invention and the conventional gas diffusion layer in Comparative Example 1.

[0057] Figure 8 Comparison of oxygen mass transfer resistance test results for the battery assembled with the gas diffusion layer prepared in Example 1 of the present invention and the conventional gas diffusion layer in Comparative Example 1.

[0058] Figure 9 This is a schematic diagram of the structure of the gas diffusion layer prepared by the gas diffusion layer preparation method of the present invention.

[0059] Figure 10 The polarization curves are for the batteries assembled from the gas diffusion layers prepared in Examples 2, 3, 5 and 6 of this invention. Detailed Implementation

[0060] 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.

[0061] Example 1 The preparation method of the microporous layer in this embodiment specifically includes the following steps: S1. Polyvinyl alcohol (PVA, molecular weight 450,000 g / mol) -1 ) and polyacrylic acid (PAA, molecular weight 195000 g mol) -1 The spinning polymer was added to deionized water and stirred to prepare 5 wt% polyvinyl alcohol solution and 5 wt% polyacrylic acid solution respectively. The polyvinyl alcohol solution and polyacrylic acid solution were then mixed at a mass ratio of 1:1 to obtain the spinning polymer solution.

[0062] S2. XC-72 carbon black conductive material and Nafion solution (concentration of 5wt%) hydrophobic agent are ultrasonically dispersed in isopropanol, and then a spinning polymer solution is added. The microporous layer spinning slurry is prepared by high-shear homogenization stirring (speed of 12000rpm) using a high-shear homogenizer.

[0063] S3. Electrospinning technology is used to spin the microporous layer spinning slurry. The environmental parameters for electrospinning are: temperature 27℃, relative humidity 65%RH; the spinning parameters are: microporous layer slurry feed rate 0.3mL / h, voltage 8.0kV, drum receiver rotation speed 150 rpm / min, needle diameter 20G, and distance between needle and receiver 15cm, to obtain the microporous layer precursor.

[0064] S4. The microporous layer precursor was heat-treated at 140°C for 1 hour, and then pressed at 1.2 MPa at ambient temperature to obtain a 7 μm thick nanofiber independent microporous layer. In this embodiment, the mass ratio of the conductive material (XC-72 carbon black), hydrophobic agent (Nafion), and spinning polymer (polyvinyl alcohol and polyacrylic acid) used in the nanofiber independent microporous layer was 7:1:3. In the prepared nanofiber independent microporous layer, the mass of perfluorosulfonic acid resin (Nafion) accounted for 9.1% of the mass of the nanofiber independent microporous layer.

[0065] The preparation method of the gas diffusion layer in this embodiment specifically includes the following steps: S1. Preparation of carbon paper with perfluorosulfonic acid resin loaded on its surface: The carbon paper was placed on a heating plate at 105°C. A 5% wt Nafion solution was added to deionized water and diluted to 1% wt. A small amount of Nafion was then coated onto the surface of the carbon paper by ultrasonic spraying. After drying, the coating load was measured to be 0.02 mg / cm³. -2 .

[0066] S2. The nanofiber-based microporous layer prepared in this embodiment is thermally transferred onto the surface of carbon paper loaded with perfluorosulfonic acid resin on the perfluorosulfonic acid resin side. The hot-pressing temperature is 140°C, the hot-pressing pressure is 0.1 MPa, and the hot-pressing time is 90 s. The resulting gas diffusion layer (structural schematic diagram shown) is then applied. Figure 9 (As shown).

[0067] The specific steps in the preparation method of the fuel cell in this embodiment are as follows: The gas diffusion layer prepared in this embodiment is assembled together with the catalyst coating membrane (CCM) to obtain the fuel cell membrane electrode, which is then assembled to obtain the fuel cell, and the electrochemical performance is evaluated on a single cell evaluation device.

[0068] Figure 1This is a morphology image of the microporous layer in the gas diffusion layer prepared in Example 1. Figure 1 As can be seen, the nanofibers of the microporous layer have a core-shell structure, meaning that the shell formed by the conductive material and perfluorosulfonic acid resin encapsulates the nanofiber framework (core) formed by the cross-linking and esterification reaction of polyacrylic acid and polyvinyl alcohol. In this structure, the cross-linked core polymer provides the independent microporous layer with good mechanical strength and flexibility, thereby enhancing the interfacial contact between the subsequent gas diffusion layer and the catalyst layer. This avoids the poor interfacial contact between the cracked and high-roughness surfaces of traditional microporous layers and the gas diffusion layer, increasing the electrochemically active area of ​​the catalyst layer. This effect can be seen from… Figure 7 The increased electrochemical active area of ​​the battery with the gas diffusion layer prepared in this embodiment was confirmed.

[0069] Figure 2 The image shown is a cross-sectional SEM image of the carbon paper substrate used in Example 1. The nanofiber microporous layer prepared by electrospinning was transferred to the substrate by hot pressing, solving the problem of... Figure 4 The conventional gas diffusion layer fabrication process, as shown, suffers from slurry penetration and impacts the pore structure of the substrate due to the coating of the microporous layer slurry onto the substrate. In this case, both the microporous layer and the substrate in the gas diffusion layer are fibrous structures. By increasing the pore size of the microporous layer and optimizing the pore size gradient between them, the water vapor transport efficiency of the gas diffusion layer is enhanced, thereby improving battery performance. Figure 5 Indeed, the battery performance of the gas diffusion layer in Example 1 is significantly better than that of the conventional gas diffusion layer. This is due to the excellent water vapor transport capability of the gas diffusion layer in Example 1, which significantly improves the performance of its mass transfer region.

[0070] To investigate the reasons for the significant performance improvement of batteries equipped with the gas diffusion layer of this invention, physicochemical characterization methods were used to characterize the battery performance. For example... Figure 7 As shown, the battery using the gas diffusion layer in Example 1 exhibits significantly lower electrochemical impedance and mass transfer impedance compared to batteries with conventional gas diffusion layers. This is primarily due to the unique structure of the gas diffusion layer in this invention, which enhances the interfacial contact between the microporous layer and the catalyst layer, as well as the water vapor transport capability. Figure 8 The test results show that the oxygen mass transfer resistance of the gas diffusion layer of the present invention is reduced by 36.4% compared with the traditional gas diffusion layer. This result also confirms the excellent mass transfer capability of the gas diffusion layer of the present invention.

[0071] Example 2 The difference between the preparation method of the microporous layer in this embodiment and that in Example 1 is that the mass ratio of the conductive material (XC-72 carbon black), hydrophobic agent (Nafion), and spinning polymer (polyvinyl alcohol and polyacrylic acid) used in the preparation of the nanofiber independent microporous layer in this embodiment is 7:1.12:3. In the prepared nanofiber independent microporous layer, the mass of perfluorosulfonic acid resin (Nafion) accounts for 10.1% of the mass of the nanofiber independent microporous layer.

[0072] The preparation method of the gas diffusion layer in this embodiment specifically includes the following steps: S1. Preparation of carbon paper with perfluorosulfonic acid resin loaded on its surface: The carbon paper was placed on a heating plate at 105°C. A 5% wt Nafion solution was added to deionized water and diluted to 1% wt. A trace layer of Nafion was then coated onto the surface of the carbon paper by ultrasonic spraying. After drying, the coating load was measured to be 0.1 mg / cm³. -2 .

[0073] S2. The nanofiber independent microporous layer prepared in this embodiment is thermally transferred onto the surface of the perfluorosulfonic acid resin side of carbon paper loaded with perfluorosulfonic acid resin. The hot-pressing temperature is 130°C, the hot-pressing pressure is 0.1 MPa, and the hot-pressing time is 90 s. The resulting gas diffusion layer is then applied.

[0074] The difference between the fuel cell preparation method in this embodiment and that in Embodiment 1 is that the gas diffusion layer prepared in this embodiment is used.

[0075] Example 3 The difference between the preparation method of the microporous layer in this embodiment and that in Example 1 is that the mass ratio of the conductive material (XC-72 carbon black), hydrophobic agent (Nafion), and spinning polymer (polyvinyl alcohol and polyacrylic acid) used in the preparation of the nanofiber independent microporous layer in this embodiment is 7:1.75:3. In the prepared nanofiber independent microporous layer, the mass of perfluorosulfonic acid resin (Nafion) accounts for 14.9% of the mass of the nanofiber independent microporous layer.

[0076] The preparation method of the gas diffusion layer in this embodiment specifically includes the following steps: S1. Preparation of carbon paper with perfluorosulfonic acid resin loaded on its surface: The carbon paper was placed on a heating plate at 105°C. A 5% wt Nafion solution was added to deionized water and diluted to 1% wt. A trace amount of Nafion was then coated onto the surface of the carbon paper by ultrasonic spraying. After drying, the coating load was measured to be 0.01 mg / cm³. -2 .

[0077] S2. The nanofiber independent microporous layer prepared in this embodiment is thermally transferred onto the surface of the perfluorosulfonic acid resin side of carbon paper loaded with perfluorosulfonic acid resin. The hot-pressing temperature is 150°C, the hot-pressing pressure is 0.1 MPa, and the hot-pressing time is 45 s. The resulting gas diffusion layer is then applied.

[0078] The difference between the fuel cell preparation method in this embodiment and that in Embodiment 1 is that the gas diffusion layer prepared in this embodiment is used.

[0079] Example 4 The preparation method of the microporous layer in this embodiment is the same as that in Example 1.

[0080] The difference between the gas diffusion layer preparation method in this embodiment and the gas diffusion layer preparation method in Example 1 is that the Nafion loading sprayed on the carbon paper surface is doubled to 0.04 mg / cm³. -2 .

[0081] The difference between the fuel cell preparation method in this embodiment and that in Embodiment 1 is that the gas diffusion layer prepared in this embodiment is used.

[0082] Because the loading of the non-conductive binder Nafion sprayed onto the carbon paper surface was doubled, the planar resistivity of the prepared gas diffusion layer also increased accordingly. Compared to Example 1, the planar resistivity decreased from 5.8 mOhm cm⁻¹. 2 Increased to 6.2 mOhm cm 2 This increases the ohmic impedance of the battery, thereby reducing battery efficiency.

[0083] Example 5 The difference between the preparation method of the microporous layer in this comparative example and that in Example 1, the mass ratio of the conductive material (XC-72 carbon black), hydrophobic agent (Nafion), and spinning polymer (polyvinyl alcohol and polyacrylic acid) used in the preparation of the nanofiber independent microporous layer in this comparative example is 7:0.72:3, and the mass of perfluorosulfonic acid resin (Nafion) accounts for 6.7% of the mass of the nanofiber independent microporous layer.

[0084] The difference between the preparation method of the gas diffusion layer in this comparative example and that in Example 1 is that the microporous layer prepared in this comparative example is used.

[0085] The difference between the preparation method of this comparative fuel cell and that of Example 1 is that the gas diffusion layer prepared in this comparative example is used.

[0086] Example 6 The difference between the preparation method of the microporous layer in this comparative example and that in Example 1, the mass ratio of the conductive material (XC-72 carbon black), hydrophobic agent (Nafion), and spinning polymer (polyvinyl alcohol and polyacrylic acid) used in the preparation of the nanofiber independent microporous layer in this comparative example is 7:3:3, and the mass of perfluorosulfonic acid resin (Nafion) accounts for 23% of the mass of the nanofiber independent microporous layer.

[0087] The difference between the preparation method of the gas diffusion layer in this comparative example and that in Example 1 is that the microporous layer prepared in this comparative example is used.

[0088] The difference between the preparation method of this comparative fuel cell and that of Example 1 is that the gas diffusion layer prepared in this comparative example is used.

[0089] Comparative Example 1 The difference between the preparation method of this comparative fuel cell and the preparation method of the fuel cell in Example 1 is that the membrane electrode cathode side directly uses a conventional commercial gas diffusion layer for membrane electrode preparation, battery assembly and electrochemical performance evaluation.

[0090] Test Results Traditional commercial gas diffusion layer fabrication processes involve coating a microporous slurry onto a carbon paper substrate. Figure 3 The SEM image of the microporous layer shows that its surface roughness is large, which leads to deterioration of the interfacial contact with the catalyst layer and a decrease in the electrochemical active area of ​​the fuel cell. Figure 7 The cyclic voltammetry curve test results confirm this. Figure 4 The image shows a cross-sectional SEM image of a traditional gas diffusion layer. It can be seen from the image that the microporous layer slurry penetrates into the carbon paper substrate, affecting the pore structure of the substrate and resulting in limited mass transfer. Figure 5 The battery performance of conventional gas diffusion layers is lower than that of the gas diffusion layer of this invention, especially the performance degradation in its mass transfer polarization region is more significant. Figure 6 Electrochemical impedance and Figure 8 The oxygen mass transfer resistance test results can all be confirmed.

[0091] The battery performance of Examples 2, 3, 5, and 6 is as follows: Figure 10As shown. The battery performance of Examples 2 and 3 is similar to that of Example 1, indicating that changing the proportion of Nafion in the microporous layer and / or the amount of perfluorosulfonic acid resin sprayed on the carbon paper within the technical solution of this invention has no significant impact on battery performance, and both exhibit excellent performance. Compared with Example 1, the mass proportion of perfluorosulfonic acid resin in the microporous layer of Example 5 is smaller, and the mass transfer polarization phenomenon of the battery appears earlier. This is because the reduced proportion of perfluorosulfonic acid resin leads to a decrease in the hydrophobicity of the microporous layer, which in turn makes flooding more likely to occur. Compared with Example 1, the mass proportion of perfluorosulfonic acid resin in the microporous layer of Example 6 is larger, and the ohmic impedance of the battery increases. As the current density increases, the voltage drops at a faster rate. This is because the increased proportion of perfluorosulfonic acid resin leads to a decrease in the conductivity of the microporous layer, which in turn leads to an increase in ohmic impedance and a deterioration in the performance of the ohmic polarization region.

[0092] Comparative Example 2 The method for preparing the microporous layer in this embodiment is the same as in Embodiment 1.

[0093] The difference between the gas diffusion layer preparation method in this embodiment and that in Embodiment 1 is that the Nafion spray loading is 0.005 mg / cm³. -2 .

[0094] The difference between the preparation method of this comparative fuel cell and that of Example 1 is that the gas diffusion layer prepared in this comparative example is used.

[0095] Because the amount of non-conductive Nafion adhesive sprayed on the carbon paper surface is too small, the microporous layer separates from the carbon paper and cannot be bonded together after the subsequent thermal transfer bonding preparation step of the gas diffusion layer, indicating that a gas diffusion layer cannot be prepared with this amount of Nafion.

[0096] Comparative Example 3 The method for preparing the microporous layer in this embodiment is the same as in Embodiment 1.

[0097] The difference between the gas diffusion layer preparation method in this embodiment and that in Embodiment 1 is that the Nafion spray loading is 0.15 mg / cm³. -2 .

[0098] The difference between the preparation method of this comparative fuel cell and that of Example 1 is that the gas diffusion layer prepared in this comparative example is used.

[0099] Because the loading of the non-conductive binder Nafion sprayed onto the carbon paper surface was 6.5 times greater than in Example 1, the planar resistivity of the prepared gas diffusion layer also increased significantly. Compared to Example 1, the planar resistivity decreased from 5.8 mOhm cm⁻¹. 2 Increased to 8.3 mOhm cm 2This increases the ohmic impedance of the battery, thereby reducing the battery's energy conversion efficiency.

[0100] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a gas diffusion layer, characterized in that, The gas diffusion layer is prepared by thermally transferring the microporous layer to the perfluorosulfonic acid resin side of the substrate layer loaded with perfluorosulfonic acid resin. The microporous layer is a porous structure layer formed by anisotropic arrangement of nanofibers. The nanofibers have a core-shell structure. The core material is a polymer obtained by cross-linking and esterification reaction of polyacrylic acid and polyvinyl alcohol. The shell material includes conductive materials and perfluorosulfonic acid resin. The loading of perfluorosulfonic acid resin in the substrate layer with its surface loaded with perfluorosulfonic acid resin is 0.01~0.1 mg / cm³. -2 .

2. The method for preparing the gas diffusion layer according to claim 1, characterized in that, The perfluorosulfonic acid resin loading in the substrate layer with the surface loaded with perfluorosulfonic acid resin is 0.01~0.02 mg / cm³. -2 .

3. The method for preparing the gas diffusion layer according to claim 1 or 2, characterized in that, The method for preparing the substrate layer loaded with perfluorosulfonic acid resin includes the following steps: coating a perfluorosulfonic acid resin solution onto one side of the heated substrate layer; The concentration of the perfluorosulfonic acid resin solution is 1wt%~10wt%; The temperature of the heated substrate layer is 100℃ ~ 110℃.

4. The method for preparing the gas diffusion layer according to claim 1 or 3, characterized in that, The heat transfer temperature is 125℃~150℃, and / or the heat transfer pressure is 0.02 MPa~0.2 MPa; Preferably, the temperature of the heat transfer is 135~150℃, and / or the pressure of the heat transfer is 0.05 MPa~0.1 MPa.

5. The method for preparing the gas diffusion layer according to claim 1 or 4, characterized in that, In the microporous layer, the perfluorosulfonic acid resin accounts for 6% to 15% of the mass of the microporous layer; preferably 8% to 15%.

6. The method for preparing the gas diffusion layer according to claim 1 or 5, characterized in that, The nanofibers have a diameter of 100 nm to 1000 nm, and / or the microporous layer has a porosity of 60% to 80%, and / or the microporous layer has an average pore size of 100 nm to 1000 nm.

7. The method for preparing the gas diffusion layer according to claim 1 or 6, characterized in that, The porosity and pore size of the substrate layer exhibit an increasing trend or remain consistent in the distribution direction from the substrate layer to the thickness of the flow field, and / or the porosity and pore size of the microporous layer exhibit an increasing trend or remain consistent in the distribution direction from the microporous layer to the thickness of the substrate layer.

8. The method for preparing the 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 gas diffusion layer prepared by the method of any one of claims 1 to 8.

10. An electrochemical device, characterized in that, The electrochemical device includes the gas diffusion layer as described in claim 9; Preferably, the electrochemical device includes a fuel cell, a water electrolyzer, and a carbon dioxide electrolyzer.

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