Membrane electrode with nanowire conductive network as well as preparation method and application of membrane electrode

Abstract

The invention discloses a membrane electrode with a nanowire conductive network, and a preparation method and application thereof, and belongs to the technical field of membrane electrodes and preparation thereof. The membrane electrode comprises a cathode catalyst layer, a proton exchange membrane layer, an iridium-based catalyst layer and a nanowire conductive grid layer which are arranged in sequence, the nanowire conductive grid layer is formed by metal nanowires, perfluorinated sulfonic acid resin and an organic polymer thickening agent; the metal nanowire is one or more of a platinum nanowire, a gold nanowire and a palladium nanowire. Due to the addition of the nanowire conductive grid layer, the thickness of the catalyst layer of the anode can be increased; the catalytic material for forming the grid is mainly slender metal platinum nanowires (gold and palladium nanowires), the electric contact between the anode catalytic layer and the PTL can be improved, the utilization rate of the catalyst is increased, the nanowires in the grid can be cross-linked to form a conductive network, the total amount of precious metal can be reduced, the cost is remarkably reduced, and the service life of the anode catalytic layer is prolonged. Meanwhile, excellent electrochemical performance is ensured.

Description

Technical Field

[0001] The present invention belongs to the technical field of membrane electrodes and their preparation, and particularly relates to a membrane electrode with a nanowire conductive network, a preparation method thereof, and an application thereof, including a membrane electrode with a platinum nanowire conductive grid, a preparation method thereof, and an application in PEM hydrogen production. Background Art

[0002] Currently, the world is in the process of seeking ways to mitigate climate change and transition to a sustainable energy future, and hydrogen has received wide attention as a versatile and promising energy carrier. In the technology of electrolytic water hydrogen production driven by renewable energy, proton exchange membrane electrolytic water (PEMWE) has become a key promoter for producing high-purity hydrogen due to its compact equipment structure, flexible operation, indirect operation, low maintenance cost, high performance, and good compatibility with renewable energy.

[0003] In proton exchange membrane electrolyzers (PEMECs), the membrane electrode assembly (MEA) is a key component and plays an important role in improving performance and reducing costs. The MEA (abbreviated as membrane electrode) is mainly composed of a proton exchange membrane, a catalyst material layer (abbreviated as the catalytic layer), etc.; among them, the anode catalytic layer (CL) is the key position where the electrochemical reaction occurs. The anodic oxygen evolution reaction (OER) of electrolytic water is a four-electron transfer process, and currently, iridium-based materials are often used as PEM anode catalysts. The kinetics of OER is slow and the overpotential is high; at the same time, the anode of the PEM membrane electrolyzer is in a strong acidic environment and the electrolysis voltage is high, and the good activity and stability of the iridium-based material catalyst are more suitable for this anodic catalytic reaction. However, due to the extreme scarcity and high price of iridium, the large-scale application of PEM membrane electrolytic water hydrogen production still faces huge challenges.

[0004] In recent years, reducing the iridium usage in the oxygen evolution reaction has still been one of the key challenges in PEM water electrolysis. If only the anode catalyst loading in the membrane electrode assembly is reduced, the thickness of the catalytic layer will decrease. The lower iridium loading and thinner electrode will also lead to poor electrical contact between the catalytic layer and the external porous transport layer (PTL), and there are some isolated parts in the anode catalytic layer that do not contribute to OER, which is the main reason for the high overpotential and poor efficiency. Therefore, it is very necessary to propose a new membrane electrode to solve the above problems. Summary of the Invention

[0005] In view of this, the present invention provides a membrane electrode with a nanowire conductive network, a preparation method thereof, and an application thereof. The membrane electrode provided by the present invention can ensure excellent electrochemical performance while having a low noble metal loading, has a cost advantage, and is conducive to its application in PEM hydrogen production.

[0006] The present invention provides a membrane electrode with a nanowire conductive network, comprising: a cathode catalyst layer, a proton exchange membrane layer, an iridium-based catalyst layer, and a nanowire conductive grid layer arranged in sequence;

[0007] The nanowire conductive grid layer is formed by metal nanowires, perfluorosulfonic acid resin, and an organic polymer thickener; the metal nanowires are one or more of platinum nanowires, gold nanowires, and palladium nanowires.

[0008] Preferably, the gap between adjacent squares of the nanowire conductive grid layer is 500 - 1000 μm.

[0009] Preferably, the perfluorosulfonic acid resin is Nafion D520 resin and / or Nafion D2020 resin, and the organic polymer thickener is one or several of polyacrylamide, polyacrylate, and polyvinyl alcohol.

[0010] Preferably, the cathode catalyst layer comprises a platinum-carbon catalyst; the proton exchange membrane layer is a Nafion membrane layer; the iridium loading in the iridium-based catalyst layer is 0.1 - 0.5 mg / cm 2 .

[0011] The present invention provides a method for preparing a membrane electrode with a nanowire conductive network, comprising the following steps:

[0012] On two surfaces of a proton exchange membrane, a cathode catalyst layer and an anode composite catalyst layer are respectively formed to obtain a membrane electrode;

[0013] The anode composite catalyst layer comprises an iridium-based catalyst layer and a nanowire conductive grid layer formed in sequence, and the iridium-based catalyst layer is composite on one surface of the proton exchange membrane; the nanowire conductive grid layer is formed by metal nanowires, perfluorosulfonic acid resin, and an organic polymer thickener; the metal nanowires are one or more of platinum nanowires, gold nanowires, and palladium nanowires.

[0014] Preferably, the preparation of the metal nanowires comprises: mixing a metal source, an alkali, ethylene glycol, and N,N-dimethylformamide, and then performing a hydrothermal reaction to obtain the metal nanowires.

[0015] Preferably, the formation of the anode composite catalyst layer on one surface of the proton exchange membrane comprises:

[0016] Dissolving metal nanowires, a perfluorosulfonic acid resin solution, and an organic polymer thickener in a solvent to prepare a printing ink; forming a nanowire conductive grid layer on the surface of a substrate by microelectronic printing of the printing ink in a grid pattern;

[0017] Spraying an iridium-based catalyst on the surface of the nanowire conductive grid layer on the substrate to form an iridium-based catalyst layer;

[0018] Transfer the nanowire conductive grid layer and the iridium-based catalytic layer on the substrate to one surface of the proton exchange membrane by hot embossing transfer to form an anode composite catalytic layer.

[0019] Preferably, the perfluorosulfonic acid resin solution is Nafion D520 resin solution and / or Nafion D2020 resin solution, the organic polymer thickener is one or more of polyacrylamide, polyacrylate and polyvinyl alcohol; the solvent is water and isopropanol; the gap between adjacent squares in the grid pattern is 500 - 1000 μm.

[0020] Preferably, during the hot embossing transfer process, the hot embossing temperature is 100 - 130 °C and the hot embossing time is 150 - 200 s.

[0021] The present invention provides a PEM electrolysis device, comprising: the membrane electrode as described above or the membrane electrode obtained by the preparation method as described above.

[0022] Compared with the prior art, in the solution for improving the membrane electrode of the present invention, a conductive network of metal nanowires is added to the iridium-based catalytic layer of the anode, that is, a nanowire conductive grid layer is additionally provided. The addition of the nanowire conductive grid layer of the present invention can increase the thickness of the anode catalytic layer; the catalytic material used to form this grid is mainly slender metal platinum nanowires (or gold, palladium nanowires), which can improve the electrical contact between the anode catalytic layer and the PTL, increase the catalyst utilization rate, and the nanowires in the grid can also crosslink with each other to form a conductive network. The design and addition of such a grid can reduce the total amount of precious metals including platinum and iridium, significantly reduce the cost, and at the same time ensure excellent electrochemical performance. Therefore, the new membrane electrode structure design of the present invention provides a new solution to the development problem of proton exchange membrane electrolysis water technology. Description of the Drawings

[0023] Figure 1 XRD pattern of the Pt nanowires prepared in Example 1 of the present invention;

[0024] Figure 2 TEM image of the Pt nanowires prepared in Example 1 of the present invention;

[0025] Figure 3 SEM image of the Pt nanowire grid printed in Example 1 of the present invention;

[0026] Figure 4 Performance comparison chart of the membrane electrodes with two-dimensional printed platinum nanowire conductive grids prepared in Examples 1 and 2 of the present invention and the membrane electrodes prepared in Comparative Examples 1 - 2 for use in PEM electrolysis devices. Detailed Embodiments

[0027] In order to more clearly understand the technical features, objectives, and effects of the present invention, the technical solutions of the present invention will be described in detail below with reference to specific embodiments. The described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments.

[0028] The present invention provides a membrane electrode with a nanowire conductive network, comprising: a cathode catalyst layer, a proton exchange membrane layer, an iridium-based catalyst layer, and a nanowire conductive grid layer arranged in sequence;

[0029] The nanowire conductive grid layer is formed by metal nanowires, perfluorosulfonic acid resin, and an organic polymer thickener; the metal nanowires are one or more of platinum nanowires, gold nanowires, and palladium nanowires.

[0030] The membrane electrode with a nanowire conductive network provided by the present invention can ensure excellent electrochemical performance while having a low noble metal loading, with a low cost, which is conducive to its application in PEM hydrogen production, etc., and has a broad market prospect.

[0031] The structure of the membrane electrode described in the embodiments of the present invention includes a proton exchange membrane layer. A cathode catalyst layer can be sprayed on one surface thereof, and an iridium-based catalyst layer and a nanowire conductive grid layer are sequentially provided on the other surface. The proton exchange membrane layer is the proton exchange membrane, which is an insulating proton-permeable membrane, and can specifically be a Nafion membrane (the trademark name of the proton exchange membrane PEM produced by DuPont is "Nafion", and its Nafion proton exchange membranes include Nafion115, 117, 212, etc., and can also be written as nafion). For example, the thickness of Nafion 117 (perfluorosulfonic acid ion membrane) is 183 μm; the thickness of Nafion 115 is 127 μm.

[0032] Among them, the cathode catalyst layer preferably includes a platinum-carbon catalyst and a certain content of perfluorosulfonic acid resin; as the cathode catalyst layer, the platinum loading can be 0.1 - 0.5 mg / cm 2 , further 0.2 - 0.4 mg / cm 2 .

[0033] Moreover, the embodiments of the present invention can use commercially available iridium oxide catalysts as the main components of the iridium-based catalyst layer of the anode, which have good catalytic activity and stability; it also contains a certain content of perfluorosulfonic acid resin as a binder. In the embodiments of the present invention, in the iridium-based catalyst layer, the iridium loading can be 0.1 - 0.5 mg / cm 2 , preferably 0.2 - 0.3 mg / cm 2 .

[0034] In an embodiment of the present invention, a two-dimensional printed nanowire conductive grid is constructed on the surface of a low-loading anode catalyst layer, which is the nanowire conductive grid layer. It can improve the electrical contact between the anode catalyst layer and the PTL, increase the catalyst utilization rate, and has better water electrolysis performance.

[0035] The nanowire conductive grid layer is a square cross-array with uniform spacing, formed by metal nanowires, perfluorosulfonic acid resin, and an organic polymer thickener. Among them, the metal nanowire is one or more of platinum nanowires, gold nanowires, and palladium nanowires, preferably platinum nanowires. Nanowires are slender forms at the nanoscale with a large aspect ratio; platinum nanowires, etc. have excellent electrical conductivity and activity. In the nanowire conductive grid layer, the metal nanowires crosslink with each other to form a two-dimensional conductive uniform network; the gap between adjacent squares is preferably 500 - 1000 μm, and further 600 - 800 μm. The width of the metal nanowires synthesized in some embodiments is between 15 - 50 nm, and the nanowire length is relatively long, about a dozen micrometers (there is a certain cross phenomenon); the width of the printed grid includes but is not limited to between 500 - 1000 μm.

[0036] In the nanowire conductive grid layer described in the embodiment of the present invention, the perfluorosulfonic acid resin can be Nafion D520 resin and / or Nafion D2020 resin, which mainly plays a binding role; the organic polymer thickener is preferably one or several of polyacrylamide (PAM), polyacrylate (PAA), and polyvinyl alcohol (PVA), and more preferably polyvinyl alcohol as the thickener. Specifically, Nafion D520 is a 5wt% nafion solution, and Nafion D2020 is a 20wt% nafion solution, which are commercially available products. For the molecular weight range of the organic polymer thickener, the molecular weight of polyacrylamide is usually between 3 million and 25 million; the molecular weight of polyacrylate is 700,000 - 1.1 million; the molecular weight of polyvinyl alcohol is about 20,000 - 300,000, such as the Mw of the polyvinyl alcohol thickener is 85,000 - 124,000.

[0037] In some embodiments of the present invention, the mass ratio of the metal nanowire, Nafion resin, and organic polymer thickener is between 1:2 - 3:1 - 4, preferably 1:2.5:2.5 - 4. Correspondingly, the present invention provides a method for preparing a membrane electrode with a nanowire conductive network, including the following steps:

[0038] On the two surfaces of the proton exchange membrane, a cathode catalyst layer and an anode composite catalyst layer are respectively formed to obtain a membrane electrode;

[0039] The anode composite catalytic layer includes an iridium-based catalytic layer and a nanowire conductive network layer formed in sequence. The iridium-based catalytic layer is composite on one surface of the proton exchange membrane; the nanowire conductive network layer is formed by metal nanowires, perfluorosulfonic acid resin and an organic polymer thickener; the metal nanowires are one or more of platinum nanowires, gold nanowires and palladium nanowires.

[0040] In the specific embodiment of the present invention, first, a cathode catalytic slurry is sprayed on one surface of the proton exchange membrane to form a cathode catalytic layer, and then an anode composite catalytic layer is formed on the other surface of the proton exchange membrane. The cathode catalytic layer includes a platinum-carbon catalyst (Pt / C catalyst, the active ingredient content is 10-20wt%), and its formation process includes: placing a commercial Pt / C catalyst in a ball mill tank, adding zirconia ball milling beads and ultrapure water thereto, placing this ball mill tank in a ball mill for ball milling, after completion, adding a Nafion solution as a binder thereto, and then transferring it to a mixed solvent of ultrapure water and isopropanol; finally, performing low-temperature ultrasonic dispersion in a fuel cell slurry disperser to make a cathode catalyst slurry of 1-5mg cat. / mL; a catalyst coated membrane (CCM) is prepared by ultrasonic spraying. Specifically, a Nafion 115 proton exchange membrane can be fixed on a heatable spraying table by vacuum adsorption, and the temperature of the spraying table is preferably set to 70-80°C; further, by precisely controlling the frequency of the ultrasonic atomizing nozzle (preferably 20-120kHz) and the slurry flow rate (preferably 0.1-1.0mL / min), the pre-dispersed and uniform cathode catalyst slurry is sprayed on one side of the proton exchange membrane to form a cathode catalytic layer.

[0041] For the anode composite catalytic layer, in the embodiment of the present invention, metal nanowires are first prepared. The preparation of the metal nanowires includes: mixing a metal source, an alkali, ethylene glycol and N,N-dimethylformamide (DMF) in proportion, and a homogeneous solution can be obtained by oil bath heating, and then a hydrothermal reaction is carried out to obtain the metal nanowires which are the basic materials for preparing the membrane electrode.

[0042] Among them, the metal source can be a platinum source, a gold source and a palladium source, preferably a platinum source. Further, the platinum source includes one or several of chloroplatinic acid, potassium chloroplatinate, platinum acetylacetonate, preferably chloroplatinic acid. The alkali can be selected from one or several of sodium hydroxide, potassium hydroxide, lithium hydroxide and ammonia water, and usually sodium hydroxide (NaOH) is used. And the mass ratio of the platinum source to the alkali is preferably 1:(8-12); the volume ratio of ethylene glycol to DMF is preferably 1-2:1, more preferably 1.5:1.

[0043] The temperature of the oil bath heating is preferably 50-90 °C, and the heating time can be 1-4 h; after the system becomes a homogeneous solution, it is transferred to a polytetrafluoroethylene inner container for hydrothermal reaction. The temperature of the hydrothermal reaction is preferably 110-170 °C, further 150-160 °C, and the reaction time can be 6-11 h, further 8-10 h. After cooling, in the examples of the present invention, the obtained product is washed and centrifuged with water and absolute ethanol, and dried in a vacuum oven to obtain dry metal nanowires such as Pt nanowires; they are slender and uniform, which is beneficial for the subsequent preparation of membrane electrodes.

[0044] After that, in the examples of the present invention, the prepared metal nanowires are uniformly mixed with water, isopropanol, perfluorosulfonic acid resin solution and organic polymer thickener to prepare a printing ink with suitable rheological properties. In the examples of the present invention, a microelectronic printing device is used to print the printing ink on the surface of the substrate in a grid pattern, that is, a nanowire conductive grid layer is formed.

[0045] Specifically, the perfluorosulfonic acid resin solution is preferably Nafion D520 resin solution and / or Nafion D2020 resin solution; the organic polymer thickener is one or more of polyacrylamide, polyacrylate and polyvinyl alcohol. The metal nanowires, Nafion and isopropanol can be put into a ball milling tank according to a mass ratio of 1:2-3:4, and large zirconia ball milling beads and small zirconia ball milling beads are added, and this ball milling tank is placed in a ball mill for ball milling for 20-30 minutes; after ball milling and dispersion, take it out and add an organic polymer thickener to make a printing ink. The mass ratio of the metal nanowires, Nafion resin and organic polymer thickener is between 1:2-3:1-8, preferably 1:2.5:2.5-7.5; the mass ratio of the metal nanowires, Nafion resin, thickener and isopropanol can be 1:2.5:2.5:4, or 1:2.5:7.5:4, and the ratio between the two. In addition, the ratio of the ball milling beads is determined according to the mass of the added materials. Here, preferably, nanowire powder: large ball milling beads: small ball milling beads = 1:10:30.

[0046] The substrate in the examples of the present invention can be a polyimide film, but is not limited to this material substrate; after injecting the printing ink into the syringe of the microelectronic printer and designing the printing grid pattern, the corresponding grid pattern can be printed on the substrate. The gap of the printed grid and the pattern type are one of the influencing factors of the performance, and they can be adjusted by setting the printing pattern and gap parameters in the system of the two-dimensional printer. When appropriate parameters are selected, better effects will be obtained. However, it should be noted that different gaps and grid widths need to use different syringe needles and adjust the printing ink formula. As a preference, the gap between adjacent squares in the grid pattern is 500-1000 μm, further 600-800 μm.

[0047] In the embodiments of the present invention, the metal nanowires are regarded as the solid content (both nafion and the thickener are added in the form of solutions), and the solid content is approximately 5%-10%. The preparation of the printing ink is mainly adapted to the printer needle to prevent the problem of needle clogging; the viscosity of the printing ink is not measured. In the embodiments of the present invention, the concentration of the printing ink is mainly adjusted by adjusting the amount of the organic polymer thickener to meet the requirements of the printing needle. For example, if a large pitch and a smaller grid are desired, a small-sized needle needs to be selected. To prevent the ink from clogging the needle, an ink with a small content of the organic polymer thickener needs to be prepared. When a large-sized needle is selected, to prevent the ink droplets from dripping before printing starts, a printing ink with a high content of the organic polymer thickener needs to be prepared.

[0048] The printing process is set through the program on the printer. In the "physical layer" area, a suitable pattern form is selected, such as a straight line, a dot, a circle, etc.; after drawing a straight line in the "drawing area", it is set in an array form, and it is specified that multiple lines are arranged within a certain length range, thereby setting the line spacing.

[0049] In addition, the substrate involved in the printing needs to be smooth and flat without any unevenness, otherwise it will affect the smoothness of the printing process. In some embodiments, the size of the substrate is preferably the size of a b6 paper, that is, 125*176 mm, so as to cover the adsorption holes on the printing table flatly and completely, so that the substrate can achieve excellent flatness through adsorption.

[0050] On the surface of the nanowire conductive grid layer of the substrate, in the embodiments of the present invention, a certain loading of an iridium-based catalyst can be sprayed to form an iridium-based catalytic layer. Specifically: after dispersing iridium oxide catalyst, a certain content of Nafion and isopropanol by ball milling, it is preferably spray-coated on the substrate printed with the nanowire conductive grid layer by ultrasonic spraying, thereby forming an anodic composite catalytic layer with a nanowire conductive grid layer; the loading of iridium is preferably 0.2-0.3 mg / cm 2 。

[0051] In the embodiments of the present invention, the nanowire conductive grid layer and the iridium-based catalytic layer on the substrate are transferred to a proton exchange membrane (usually a Nafion membrane) sprayed with a cathode catalytic layer by using a hot embossing transfer technology to make the membrane electrode with a nanowire conductive network.

[0052] The hot embossing transfer process transfers the pattern on the transfer substrate to the surface of the product by heating and pressing. After forming, the ink pattern layer is integrated with the surface of the product. In the hot embossing transfer process described in the embodiments of the present invention, the hot embossing temperature is preferably 100-130 °C, further 120 °C, and the hot embossing time is preferably 150-200 s, further 180 s.

[0053] The present application also provides an application of the membrane electrode with a nanowire conductive network obtained by the described preparation method in proton exchange membrane electrolysis of water and its industrial PEM devices. That is, the embodiment of the present invention provides a PEM electrolysis device, which includes: a membrane electrode obtained by the preparation method as described above.

[0054] The embodiment of the present invention has no special restrictions on other components of the PEM electrolysis device, and conventional PEM device structural components and electrolysis operations are adopted. For example, a PEM electrolytic cell mainly includes bipolar plates, an anode flow field plate, an anode porous transport layer (PTL), an anode gasket, a membrane assembly (MEA, the described membrane electrode), a cathode gasket, a cathode porous transport layer, and a cathode flow field plate. In the selection of the electrolytic cell components, the bipolar plates of both the cathode and anode use titanium plates with serpentine flow channels pre-coated with a corrosion-resistant conductive coating. As a preference, a carbon paper is used for the cathode PTL; a platinum-coated titanium felt is used for the anode PTL. The MEA is placed between the bipolar plates of the electrolytic cell, and a gasket made of polytetrafluoroethylene is placed between the bipolar plate and the membrane electrode for sealing, so that the membrane electrode is tightly combined with the single cell. When assembling the electrolytic cell, a torque wrench can be used to tighten the bolts to a pressure of 3 N·m, and the electrolytic cell assembly is completed. During the electrolysis test process, the system water temperature can be maintained at 80 °C, and the flow rate of the circulating water is 50 - 80 mL / min.

[0055] In the embodiment of the present application, a metal nanowire material is made into printing ink, and through a two-dimensional printing technology combined with thermal transfer printing, a layer of nanowire conductive grid is added on the surface of the traditional anode catalytic layer. The preparation method is simple, stable and reliable, and has good repeatability. The anode composite catalytic layer prepared by this method effectively improves the problem of poor electrical contact between the catalytic layer and the external PTL caused by a lower loading amount and a thinner electrode, and the membrane electrode prepared thereby shows good performance in PEM tests.

[0056] To better illustrate the present invention, the following examples are used to further illustrate the membrane electrode with a nanowire conductive network provided by the present invention, its preparation method, and its application in a PEM electrolysis device. In the examples, all the original reagents and materials are commercially available, and the experimental methods without specific experimental conditions are conventional methods and conditions well-known in the art.

[0057] Example 1

[0058] (1) Synthesis of Pt nanowires, the steps are as follows:

[0059] First, ethylene glycol and DMF were mixed in a volume ratio of 1.5:1. Then, NaOH and chloroplatinic acid were added to the mixed solution with a mass ratio of 10:1. The system was mixed at 70 °C for 1 h. After the system became a homogeneous solution, it was transferred to a polytetrafluoroethylene inner liner and subjected to hydrothermal reaction at 150 °C for 9 h. After cooling, the obtained product was washed and centrifuged with deionized water and absolute ethanol, and then dried in a vacuum oven to obtain platinum nanowire materials.

[0060] The above-prepared Pt nanowires were determined to be in the metallic phase by X-ray diffraction (XRD) patterns. The XRD patterns are shown in Figure 1 .

[0061] From the transmission electron microscope (TEM) images, it can be seen that the above-prepared Pt nanowires are slender and uniform. The TEM images are shown in Figure 2 . The width of the nanowires is between 20 - 40 nm, and the length is more than ten micrometers.

[0062] (2) Two-dimensional printing of Pt nanowire grids, the steps are as follows:

[0063] 50 mg of the prepared Pt nanowires, Nafion, and isopropanol were put into a ball milling jar according to a mass ratio of 1:2.5:4, and 500 mg of large zirconia milling beads and 1.5 g of small zirconia milling beads were added; this ball milling jar was placed in a ball mill and ball milled for 30 minutes. After ball milling and dispersion, it was taken out and 125 mg of polyvinyl alcohol thickener (molecular weight Mw is 85000 - 124000) was added to make printing ink. The printing ink was injected into the syringe of a microelectronic printer. After designing the printing grid pattern through the program settings on the printer, the gap was adjusted to 600 μm, and the pattern was printed on a polyimide film (substrate).

[0064] (3) Spraying a certain loading of iridium-based catalyst on the substrate printed with Pt nanowire grids, the steps are as follows:

[0065] 20 mg of commercial iridium oxide catalyst was taken in a ball milling jar, 200 mg of large zirconia milling beads, 600 mg of small zirconia milling beads, and 100 mg of ultrapure water were added to it. This ball milling jar was placed in a ball mill and ball milled for 20 minutes. After completion, 30 μL of 5 wt% Nafion solution was added as a binder, and then ball milled for 10 minutes. Finally, it was transferred to a solvent with a volume ratio of 3:1 of 4 mL of isopropanol and ultrapure water and ultrasonically dispersed at low temperature in a fuel cell slurry disperser for 40 minutes to make an anode catalyst slurry with a loading of 5 mg cat. / mL. Using an ultrasonic spraying device, the prepared slurry was ultrasonically sprayed on the polyimide film printed with Pt nanowire grids. The frequency of the ultrasonic atomization nozzle is 100 kHz, and the slurry flow rate is 0.187 mL / min; the loading of iridium is 0.3 mg / cm 2 .

[0066] (4) Preparation of Membrane Electrode:

[0067] Take 300 mg of commercial 20 wt% Pt / C catalyst in a ball milling jar, add 5 g of large zirconia ball milling beads, 5 g of small zirconia ball milling beads and 3 g of ultrapure water to it, and place this ball milling jar in a ball mill for ball milling for 20 minutes. After ball milling is completed, add 2.16 g of 5 wt% Nafion solution as a binder, and then transfer it to a mixed solvent of 4.885 g of ultrapure water and 23.655 g of isopropanol. Finally, ultrasonically disperse it at low temperature for 40 minutes in a fuel cell slurry disperser to make a 5 mg cat . / mL cathode catalyst slurry. Fix the Nafion 115 proton exchange membrane (PEM) on a heatable spraying table by vacuum adsorption, and set the temperature of the spraying table to 80 °C. Spray the prepared slurry on the other side of the proton exchange membrane as the cathode catalyst layer, and the platinum loading is 0.3 mg / cm 2 . By precisely controlling the frequency (100 kHz) of the ultrasonic atomization nozzle and the slurry flow rate (0.187 mL / min), spray the pre-dispersed and uniform cathode catalyst slurry on one side of the membrane; the spraying area is 5 cm × 5 cm, and the effective catalyst working area (Active area) is 2 cm × 2 cm. Finally, obtain a cathode catalyst layer with a platinum loading of 0.3 mg / cm 2 .

[0068] Transfer the patterns and catalysts on the aforementioned polyimide film to the Nafion membrane sprayed with the cathode catalyst by hot pressing to make a membrane electrode with a nanowire conductive network. Among them, the hot pressing temperature is 120 °C and the hot pressing time is 180 s. The SEM image of the surface grid after hot pressing transfer is shown in Figure 3 .

[0069] Assemble the prepared membrane electrode into a PEM electrolytic cell for PEM device testing. Under the test conditions of 80 °C, obtain the polarization curve of the electrolytic cell; at a current density of 3 A / cm 2 , the test voltage is 1.942 V, as shown in Figure 4 .

[0070] The PEM electrolyzer mainly consists of bipolar plates, anode flow field plates, anode porous transport layer (PTL), anode gaskets, MEA, cathode gaskets, cathode porous transport layer, and cathode flow field plates; the bipolar plates of both the cathode and anode use titanium plates with serpentine flow channels pre-coated with corrosion-resistant conductive coatings. The cathode PTL uses carbon paper; the anode PTL uses platinum-coated titanium felt. Place the prepared MEA between the bipolar plates of the electrolyzer, and place gaskets made of polytetrafluoroethylene material between the bipolar plates and the membrane electrode for sealing. Use a torque wrench to tighten the bolts to a pressure of 3 N·m, and the assembly of the electrolyzer is completed. During the test, the system water temperature is maintained at 80 °C (Working temperature: 80 °C), the flow rate of the circulating water is 50 - 80 mL / min, and record the voltages corresponding to different current densities (the same for the following tests).

[0071] Comparative Example 1

[0072] Preparation of commercially available iridium oxide membrane electrode:

[0073] Take 20 mg of commercial iridium oxide catalyst in a ball milling jar, add 200 mg of large zirconia ball milling beads, 600 mg of small zirconia ball milling beads, and 100 mg of ultrapure water to it. Place this ball milling jar in a ball mill and ball mill for 20 minutes; after completion, add 30 μL of 5 wt% Nafion solution as a binder, and then ball mill for 10 minutes. Finally, transfer it to a solvent with a volume ratio of 3:1 of 4 mL of isopropanol and ultrapure water, and ultrasonically disperse it at low temperature in a fuel cell slurry disperser for 40 minutes to make a 5 mg cat. / mL anode catalyst slurry.

[0074] Take 300 mg of commercial 20 wt% Pt / C catalyst in a ball milling jar, add 5 g of large zirconia ball milling beads, 5 g of small zirconia ball milling beads, and 3 g of ultrapure water to it. Place this ball milling jar in a ball mill and ball mill for 20 minutes. After ball milling is completed, add 2.16 g of 5 wt% Nafion solution as a binder, and then transfer it to a mixed solvent of 4.885 g of ultrapure water and 23.655 g of isopropanol. Finally, ultrasonically disperse it at low temperature in a fuel cell slurry disperser for 40 minutes to make a 5 mg cat. / mL cathode catalyst slurry.

[0075] Using an ultrasonic spraying device, spray the cathode and anode catalyst slurries on both sides of the proton exchange membrane respectively. The platinum loading of the cathode catalyst layer is 0.3 mg / cm 2 and the iridium loading of the anode catalyst layer is 0.5 mg / cm 2 .

[0076] Assemble the prepared membrane electrode into a PEM device for testing. Under the test conditions of 80 °C, obtain the polarization curve of the electrolytic cell. At 3 A / cm 2At a current density of, the test voltage is 2.03 V, as shown in Figure 4 . According to Figure 4 , the membrane electrode with a nanowire conductive grid added in the present invention is compared with the membrane electrode without the grid. The membrane electrode with the grid and a low iridium loading has obtained more excellent performance than the membrane electrode with a high iridium loading.

[0077] Comparative Example 2

[0078] Preparation of anode paste and coating:

[0079] Take 20 mg of commercial iridium oxide catalyst and 10 mg of Pt nanowires in a ball milling jar, and add 300 mg of large zirconia milling beads, 900 mg of small zirconia milling beads and 150 mg of ultrapure water thereto. Place this ball milling jar in a ball mill and ball mill for 20 minutes; after completion, add 45 μL of 5 wt% Nafion solution as a binder thereto, and then ball mill for 10 minutes. Finally, transfer it to a solvent with a volume ratio of 3:1 of 4 mL of isopropanol and ultrapure water, and ultrasonically disperse it at low temperature in a fuel cell paste disperser for 40 minutes to prepare an anode catalyst paste. The prepared paste is sprayed on one side of the Nafion 115 membrane, and the iridium loading in the anode catalyst layer is 0.3 mg / cm 2 , and the Pt loading is 0.15 mg / cm 2 .

[0080] Preparation of cathode paste and coating:

[0081] Take 300 mg of commercial 20 wt% Pt / C catalyst in a ball milling jar, and add 5 g of large zirconia milling beads, 5 g of small zirconia milling beads and 3 g of ultrapure water thereto. Place this ball milling jar in a ball mill and ball mill for 20 minutes. After ball milling is completed, add 2.16 g of 5 wt% Nafion solution as a binder thereto, and then transfer it to a mixed solvent of 4.885 g of ultrapure water and 23.655 g of isopropanol. Finally, ultrasonically disperse it at low temperature in a fuel cell paste disperser for 40 minutes to prepare a 5 mg cat . / mL cathode catalyst paste. The prepared paste is sprayed on the other side of the proton exchange membrane as the cathode catalytic layer, and the platinum loading is 0.3 mg / cm 2 .

[0082] Assemble the prepared membrane electrode into a PEM device for testing. Under the test conditions of 80 °C, the polarization curve of the electrolytic cell is obtained. At a current density of 3 A / cm 2 , the test voltage is 1.968 V, as shown in Figure 4 .

[0083] In this comparative sample, Pt nanowires are directly added to the anode paste; from Figure 4From the performance comparison, it can be seen that directly adding nano platinum wires to the anode paste may affect the structure of the catalytic layer. However, the two-dimensional printed nanowire grid of the present invention is more uniform and orderly, has excellent performance, and strong experimental repeatability and uniformity.

[0084] Example 2

[0085] (1) Synthesis of Pt nanowires, the steps are as follows:

[0086] First, mix ethylene glycol and DMF in a volume ratio of 1.5:1, and then add NaOH and chloroplatinic acid to the mixed solution with a mass ratio of 10:1. Mix the system at 70 °C for 1 h. After the system becomes a homogeneous solution, transfer it to a polytetrafluoroethylene inner liner and carry out a hydrothermal reaction at 150 °C for 9 h. After cooling, wash and centrifuge the obtained product with deionized water and absolute ethanol, and dry it in a vacuum oven to obtain platinum nanowire material.

[0087] (2) Two-dimensional printing of Pt nanowire grid, the steps are as follows:

[0088] Put 50 mg of the Pt nanowires, Nafion, and isopropanol into a ball mill jar according to a mass ratio of 1:2.5:4, and add 500 mg of large zirconia ball milling beads and 1.5 g of small zirconia ball milling beads. Place this ball mill jar in a ball mill and mill for 30 minutes. After ball milling and dispersing, take it out and add 200 mg of polyvinyl alcohol thickener (the same as in Example 1) to make printing ink. Inject the printing ink into the syringe of a microelectronic printer. After designing the printing grid pattern through the program settings on the printer, adjust the gap to 800 μm and print the pattern on a polyimide film (substrate).

[0089] (3) Spraying a certain loading of iridium-based catalyst on the substrate printed with the platinum nanowire grid, the steps are as follows:

[0090] Take 20 mg of commercial iridium oxide catalyst in a ball mill jar, add 200 mg of large zirconia ball milling beads, 600 mg of small zirconia ball milling beads and 100 mg of ultrapure water to it. Place this ball mill jar in a ball mill and mill for 20 minutes. After completion, add 30 μL of 5 wt% Nafion solution as a binder to it and mill for another 10 minutes. Finally, transfer it to a solvent with a volume ratio of 3:1 of 4 mL of isopropanol and ultrapure water, and perform low-temperature ultrasonic dispersion in a fuel cell slurry disperser for 40 minutes to make an anode catalyst slurry of 5 mg cat. / mL. Using an ultrasonic spraying device, spray the prepared slurry ultrasonically on the polyimide film printed with the platinum nanowire grid, and the loading of iridium is 0.3 mg / cm 2 .

[0091] (4) Membrane electrode preparation:

[0092] Take 300 mg of commercial 20 wt% Pt / C catalyst in a ball milling jar, add 5 g of large zirconia ball milling beads, 5 g of small zirconia ball milling beads and 3 g of ultrapure water to it, and place this ball milling jar in a ball mill for ball milling for 20 minutes. After the ball milling is completed, add 2.16 g of 5 wt% Nafion solution as a binder, and then transfer it to a mixed solvent of 4.885 g of ultrapure water and 23.655 g of isopropanol. Finally, disperse it by low-temperature ultrasonic for 40 minutes in a fuel cell slurry disperser to prepare a cathode catalyst slurry of 5 mg cat . / mL. The prepared slurry is sprayed on the other side of the proton exchange membrane as the cathode catalyst layer, and the platinum loading is 0.3 mg / cm 2 . Transfer the pattern and catalyst on the polyimide film to the Nafion film sprayed with the cathode catalyst by hot pressing to prepare a membrane electrode with a nanowire conductive network. Among them, the hot pressing temperature is 120 °C and the hot pressing time is 180 s.

[0093] Assemble the prepared membrane electrode into a PEM device for testing. Under the test conditions of 80 °C, obtain the polarization curve of the electrolytic cell. At a current density of 3 A / cm 2 , the test voltage is 1.942 V, as shown in Figure 4 .

[0094] The PEM electrolyzed water test results show that the anode composite catalyst layer / membrane electrode prepared by this method in the embodiment of the present invention has better electrolyzed water performance compared with the traditional membrane electrode, provides a new choice for the preparation of the commercial anode catalyst layer for electrolyzed water to produce hydrogen, and has a broad market prospect. The method for preparing the membrane electrode described in the present invention is simple, stable and reliable, has good repeatability, has significant cost advantages, and is conducive to application.

[0095] The description of the above embodiments is only used to help understand the method and its core idea of the present invention. It should be pointed out that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and modifications can still be made to the present invention, and these improvements and modifications still belong to the protection scope of the technical solution and claims of the present invention.

Claims

1. A membrane electrode with a nanowire conductive network, characterized in that Comprising: A cathode catalyst layer, a proton exchange membrane layer, an iridium-based catalyst layer, and a nanowire conductive grid layer are sequentially arranged; The nanowire conductive grid layer is formed by metal nanowires, perfluorosulfonic acid resin, and an organic polymer thickener; the metal nanowires are one or more of platinum nanowires, gold nanowires, and palladium nanowires.

2. The membrane electrode according to claim 1, wherein The gap between adjacent squares of the nanowire conductive grid layer is 500 - 1000 μm.

3. The membrane electrode according to claim 1, wherein The perfluorosulfonic acid resin is Nafion D520 resin and / or Nafion D2020 resin, and the organic polymer thickener is one or several of polyacrylamide, polyacrylate, and polyvinyl alcohol.

4. The membrane electrode according to any one of claims 1 to 3, characterized in that, The cathode catalyst layer includes a platinum-carbon catalyst; the proton exchange membrane layer is a Nafion membrane layer; the iridium loading in the iridium-based catalyst layer is 0.1 to 0.5 mg / cm 2 .

5. A preparation method of a membrane electrode with a nanowire conductive network, characterized in that, Including the following steps: On the two surfaces of the proton exchange membrane, a cathode catalyst layer and an anode composite catalyst layer are respectively formed to obtain a membrane electrode; The anode composite catalyst layer includes an iridium-based catalyst layer and a nanowire conductive grid layer formed in sequence, and the iridium-based catalyst layer is composite on one surface of the proton exchange membrane; the nanowire conductive grid layer is formed by metal nanowires, perfluorosulfonic acid resin, and an organic polymer thickener; the metal nanowires are one or more of platinum nanowires, gold nanowires, and palladium nanowires.

6. The preparation method according to claim 5, characterized in that, The preparation of the metal nanowires includes: mixing a metal source, an alkali, ethylene glycol, and N,N-dimethylformamide, and then performing a hydrothermal reaction to obtain the metal nanowires.

7. The preparation method according to claim 5, characterized in that, Forming an anode composite catalyst layer on one surface of the proton exchange membrane includes: Dissolving metal nanowires, a perfluorosulfonic acid resin solution, and an organic polymer thickener in a solvent to prepare printing ink; forming a nanowire conductive grid layer on the surface of the substrate with the printing ink in a grid pattern by microelectronic printing; Spraying an iridium-based catalyst on the surface of the nanowire conductive grid layer on the substrate to form an iridium-based catalyst layer; Transferring the nanowire conductive grid layer and the iridium-based catalyst layer on the substrate to one surface of the proton exchange membrane by thermal compression transfer to form an anode composite catalyst layer.

8. The preparation method according to claim 7, wherein, The perfluorosulfonic acid resin solution is Nafion D520 resin solution and / or Nafion D2020 resin solution, the organic polymer thickener is one or several of polyacrylamide, polyacrylate, and polyvinyl alcohol; the solvent is water and isopropyl alcohol; the gap between adjacent squares in the grid pattern is 500 - 1000 μm.

9. The preparation method according to claim 8, characterized in that, During the thermal compression transfer process, the thermal compression temperature is 100 - 130 °C, and the thermal compression time is 150 - 200 s.

10. A PEM electrolysis device, characterized in that, Comprising: The membrane electrode according to any one of claims 1 - 4 or the membrane electrode obtained by the preparation method according to any one of claims 5 - 9.

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