Composite diffusion layer, composite anode and composite membrane electrode suitable for iridium-based catalytic layer with ultra-low loading

Abstract

The application relates to a composite diffusion layer suitable for an ultralow-amount iridium-based catalytic layer, which comprises a nano-porous metal interface layer and an anode porous transport layer; the nano-porous metal interface layer is a metal film with a nano-scale bi-continuous structure of pores and ligaments; the anode porous transport layer has a micron-scale pore diameter; the surface amount of the iridium-based catalytic layer is <=0.2 mg cm ‑2 . The application studies the difference factors and key bottlenecks affecting the catalytic effect of the iridium-based catalyst under the conventional amount and the ultralow amount, explores the role of the functional interface layer in regulating the key bottlenecks of the ultralow iridium amount under different paths, successfully realizes that the ultralow-amount iridium-based catalytic layer reaches or even surpasses the performance of the conventional amount and the high-amount system through the innovative interface structure design, and opens up a new path for the cost reduction and efficiency increase of the proton exchange membrane water electrolysis.

Description

Technical Field

[0001] This invention relates to the field of water electrolysis technology, specifically to a composite diffusion layer suitable for ultra-low loading iridium-based catalyst layers, as well as its composite anode and composite membrane electrode. Background Technology

[0002] With the global energy structure transitioning towards low-carbon energy, proton exchange membrane (PEM) water electrolysis for hydrogen production has become a core technology for large-scale green hydrogen production due to its advantages such as fast response, high current density, high hydrogen purity, and perfect coupling with fluctuating renewable energy sources (wind and solar power). In this technology system, the membrane electrode assembly (MEA) is the most crucial component determining the performance, lifespan, and cost of the electrolyzer. A typical MEA mainly consists of a central proton exchange membrane (PEM), two flank anode and cathode catalyst layers, and an outer porous transport layer (anode titanium felt / cathode carbon paper). The PEM conducts protons, isolates anode and cathode gases, and insulates electrons; the porous transport layer distributes the reacting water / gas, conducts current, and supports the catalyst layer; while the catalyst layer is the site of the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), significantly impacting the electrolyzer's energy conversion efficiency.

[0003] Under the operating conditions of a PEM electrolyzer, the anode side is subjected to an extreme environment of strong acidity (pH≈2), high potential (>1.5 V vs. RHE), and high oxidizing properties. Therefore, the anode side is not only the main site of electrochemical reactions but also the bottleneck determining the device's lifespan. Currently, the only commercially available anode catalyst recognized by the industry is iridium-based catalysts. Due to its unique electronic structure, iridium (Ir) can maintain the thermodynamic stability of its oxide in strong acid environments, avoiding rapid dissolution like other inexpensive transition metals (such as nickel and cobalt) and the failure of ruthenium (Ru)-based catalysts due to the formation of volatile RuO4 at high potentials. However, iridium is one of the rarest metals on Earth, with a global annual production of only about 7 tons. Its high cost and limited reserves severely restrict the megawatt-scale expansion of PEM electrolyzers. Therefore, how to minimize iridium loading while ensuring the stability and activity of the anode catalyst layer structure is the most pressing challenge currently facing PEM electrolysis technology.

[0004] Currently, iridium-based catalysts are widely used in industry, with loadings typically as high as 2-4 mg / cm³. -2To reduce iridium loading, researchers have developed numerous novel iridium-based catalysts with ultra-high intrinsic activity. While these catalysts perform excellently in rotating disk electrode (RDE) tests, a significant performance precipitate occurs when assembled into ultra-low loading membrane electrodes. The study found that as the iridium-based catalyst layer's loading decreases sharply towards ultra-low levels, the overall thickness of the iridium-based catalyst layer decreases drastically, significantly reducing the contact probability between catalyst particles. The iridium-based catalyst layer transforms from a continuous interface to a discontinuous interface, limiting its in-plane electron transport paths. Although the porous anode transport layer, which is in direct contact with the iridium-based catalyst layer, plays a fundamental role in conducting current, its pore size is typically fabricated to the micrometer scale to distribute the reaction water / gas. This leads to severe microstructural dislocations between the iridium-based catalyst layer and the porous anode transport layer, especially at ultra-low catalyst loadings where the dislocation scale grows exponentially. This disrupts the electronic conductivity network, creating an electrochemically inert island effect. At this point, the intrinsic activity of the catalyst and the particle aggregation state are no longer the fundamental factors contributing to performance failure; the electron transport bottleneck becomes the primary reason requiring targeted solutions.

[0005] Researchers have attempted to directly load iridium-based catalysts onto the surface of nanoporous gold (NPG) as a composite catalytic layer, utilizing the continuous nanoscale pores of nanoporous gold to eliminate the islanding effect of the catalyst. However, this study found that this approach has the following limitations: (1) The catalyst is directly loaded onto the NPG framework, which is limited by the surface characteristics of the complex three-dimensional structure of NPG. The deposited catalyst has poor dispersion and crystallinity, and its intrinsic activity is far inferior to that of pre-synthesized nanopowder catalysts; (2) The NPG nanopores (~60 nm) do not match the size of Nafion aggregates (tens to hundreds of nanometers). Nafion is difficult to effectively introduce into the NPG pores. Without the effective coverage of Nafion resin, the proton transport channels are discontinuous, and the deep catalytic sites are difficult to participate in the reaction; (3) The catalyst is directly loaded onto the NPG framework. The degradation behavior of the catalyst, such as dissolution and aggregation, will directly lead to the loss of active sites on the NPG surface and may block the NPG nanopores. The potential decay rate is further amplified, resulting in poor electrochemical stability. Summary of the Invention

[0006] To address the aforementioned issues, this invention systematically studies the different factors and key bottlenecks affecting the catalytic performance of iridium-based catalysts under conventional and ultra-low loading conditions. It also explores the role of functional interface layers in regulating key bottlenecks under different pathways. Through innovative interface structure design, it successfully achieves performance of ultra-low loading iridium-based catalyst layers that reach or even surpass those of conventional and high loading systems, opening up a new path for cost reduction and efficiency improvement in proton exchange membrane water electrolysis.

[0007] This invention discovers that, under ultra-low loading conditions, using nanoporous metal materials as an independent interface layer rather than a composite catalytic layer supporting iridium-based catalysts, and bonding them with the iridium-based catalytic layer, can not only eliminate the islanding effect of the catalyst and repair the electronic conductivity network, but also effectively improve the potential decay rate of the iridium-based catalyst and obtain good electrochemical stability.

[0008] Based on the above findings, this invention innovatively proposes a crucial solution for improving the performance of ultra-low loading iridium-based catalyst layers: setting an independent nanoporous metal interface layer on the anode side. The technical solution of this invention is implemented as follows:

[0009] In a first aspect, the present invention provides a composite diffusion layer suitable for ultra-low loading iridium-based catalyst layers, comprising a nanoporous metal interface layer and an anode porous transport layer;

[0010] The nanoporous metal interface layer is a metal thin film with a nanoscale bicontinuous structure of pores and ligaments.

[0011] The porous transport layer of the anode has micron-sized pores;

[0012] The areal loading of the iridium-based catalyst layer is ≤0.2 mg cm⁻¹. -2 .

[0013] Secondly, the present invention also provides a composite anode with ultra-low loading, comprising an iridium-based catalyst layer, a nanoporous metal interface layer and an anode porous transport layer sequentially disposed on the anode side of a proton exchange membrane;

[0014] The nanoporous metal interface layer is a metal thin film with a nanoscale bicontinuous structure of pores and ligaments.

[0015] The porous transport layer of the anode has micron-sized pores;

[0016] The areal loading of the iridium-based catalyst layer is ≤0.2 mg cm⁻¹. -2 .

[0017] Thirdly, the present invention also provides a composite membrane electrode, comprising an iridium-based catalyst layer, a nanoporous metal interface layer and an anode porous transport layer sequentially disposed on the anode side of a proton exchange membrane, and a cathode catalyst layer and a cathode porous transport layer disposed on the cathode side of a proton exchange membrane.

[0018] The nanoporous metal interface layer is a metal thin film with a nanoscale bicontinuous structure of pores and ligaments.

[0019] The porous transport layer of the anode has micron-sized pores;

[0020] The areal loading of the iridium-based catalyst layer is ≤0.2 mg cm⁻¹. -2 .

[0021] The above-mentioned solution of the present invention, on the one hand, breaks through the cognitive bias of improving membrane electrode technology under ultra-low loading in terms of technical understanding, and takes the electron transport bottleneck caused by the island effect as one of the key factors for targeted solutions, thus adjusting the key technical research and development direction; on the other hand, in terms of technical means to further solve this problem, it eliminates the mindset that catalysts can be better optimized for electron transport and improved for electrochemical performance only when the catalyst is loaded on the surface of nanoporous metal materials; and in terms of technical effect, it also improves the problem of unexpected potential decay rate exacerbation that occurs in traditional catalyst-supported composite catalyst layers under ultra-low loading.

[0022] In some schemes, the areal loading of the iridium-based catalyst layer is ≤0.1 mg cm⁻¹. -2 Ideally, the dosage should be 0.05~0.1 mg cm. -2 The optimal approach is to use an appropriately low areal loading, which saves on catalyst usage while ensuring sufficient active sites.

[0023] In some designs, the pore size and ligament size of the nanoporous metal interface layer are 10–200 nm; further, a pore size of 30–100 nm and a ligament size of 30–100 nm are preferred. Appropriate pore and ligament sizes not only facilitate efficient electron transport pathways but also ensure good mass transfer efficiency with both the iridium-based catalyst layer and the proton exchange membrane. Simultaneously, they ensure sufficient flexibility and strength of the interface layer to withstand transfer processing and pressure stress, thereby promoting close contact and interface formation among the functional layers on the anode side.

[0024] In some schemes, the thickness of the nanoporous metal interface layer is 50–500 nm, with 50–200 nm being preferred and 60–120 nm being even better. Thickness control is also beneficial for improving the mass transfer efficiency between the anolyte porous transport layer and the proton exchange membrane, forming a better micro-nano interface with the anolyte porous transport layer, synergistically promoting the optimization of electron transport paths, and ensuring sufficient interface layer strength.

[0025] In some schemes, the nanoporous metal interface layer material is selected from one or more of gold, platinum, and iridium, preferably nanoporous gold (Au). Nanoporous gold exhibits higher stability under the extreme reaction environment on the anode side, which is beneficial to ensuring the stable performance of the nanoporous metal interface layer in eliminating electron transport bottlenecks. At the same time, Au has good ductility, which is conducive to forming a good and tight interfacial contact during the membrane electrode assembly process. This allows for the rapid construction of a three-phase integrated interface and a three-dimensional network while the ultra-low loading iridium-based catalyst resin binder is uniformly coated on one side of the proton exchange membrane.

[0026] In some designs, the porous anode transport layer is a porous body made of refractory and acid-resistant metal material through fiber sintering or weaving. The base material is selected from one or more of pure titanium (Ti), titanium alloy, tantalum (Ta), niobium (Nb), zirconium (Zr), or tungsten (W), with titanium (Ti) or titanium alloy being preferred. The titanium alloy can be further improved by introducing elements such as tantalum to enhance the material's passivation resistance in a high-potential anode environment.

[0027] In some designs, the anode porous transport layer can have one or more of the following macroscopic physical forms, including but not limited to fiber felt, fiber woven mesh, metal foam, or powder metallurgy porous plate. The thickness can be 0.1 to 2.0 mm, preferably 0.2 to 0.5 mm, to balance conductivity and fluid transport resistance.

[0028] In some designs, the porous anode transport layer has a porosity of 30%–95% and an average pore size of 10–200 μm, preferably 20–100 μm. The higher porosity facilitates the rapid transport of reacting water and oxygen, while the suitable pore size effectively forms a micro-nano gradient with the nanoporous metal interface layer, balancing micron-level gas-liquid transport with nanoscale rapid electron collection.

[0029] In some schemes, the iridium-based catalyst of the iridium-based catalyst layer can be a substance containing iridium and having oxygen evolution reaction (OER) activity, including but not limited to metallic iridium, iridium oxide (IrO2), hydrated iridium oxide, and composite oxides or solid solutions of iridium with other acid-resistant metal elements. Other acid-resistant metal elements are selected from one or more of tantalum (Ta), niobium (Nb), titanium (Ti), ruthenium (Ru), tin (Sn), and tungsten (W).

[0030] In some schemes, iridium-based catalysts include crystalline, amorphous, and crystalline-amorphous heterojunction structures. In the ultra-low loading system of this invention, the amorphous structure is more advantageous.

[0031] In some schemes, the particle size of iridium-based catalysts ranges from 2 to 20 nm. A good particle size is beneficial for better exposing more surface active sites under ultra-low loading, thereby improving utilization.

[0032] In some schemes, the specific surface area of ​​the iridium-based catalyst is between 10 and 75 m². 2 g -1 between.

[0033] In some schemes, iridium-based catalysts can also have composite constructions, including but not limited to core-shell structures and supported structures. In core-shell structures, at least one of the core and shell is a material containing iridium and having oxygen evolution reaction activity, such as iridium oxide (IrO2) as the shell and an iridium-containing or non-iridium metal or its alloy as the core. This structure can utilize the core layer to provide high conductivity support and the shell layer to provide catalytic activity, achieving atomic-level efficient utilization of precious metals. In supported structures, the iridium-based catalyst is supported on an acid-resistant conductive support, which is preferably a titanium-based oxide, niobium-based oxide, tantalum-based oxide, or conductive ceramic. Specifically, the acid-resistant conductive support includes, but is not limited to, titanium oxide, antimony-doped tin oxide, tantalum-doped tin oxide, or niobium-doped titanium oxide. This structure utilizes the support to assist in electron conduction and structural framework functions, and iridium, as an active component, is highly dispersed on the surface of the support.

[0034] In this invention, the material of the proton exchange membrane is not limited, and can be any commonly used ion-conducting polymer, including but not limited to perfluorosulfonic acid resins (such as perfluorosulfonyl fluoride vinyl ether or its copolymer with tetrafluoroethylene), partially fluorinated polymers (such as polyvinylidene fluoride grafted styrene sulfonic acid copolymer), non-fluorinated hydrocarbon polymers (such as polyaryletherketone, polyarylethersulfone, polybenzimidazole, polyimide or polystyrene derivatives), or composite modified polymers in which inorganic fillers (such as silica, titanium dioxide, zirconium oxide, etc.) are introduced into at least one of the above polymers.

[0035] In some schemes, iridium-based catalyst particles in the iridium-based catalyst layer are bonded to the surfaces of the proton exchange membrane and the nanoporous metal interface layer, respectively, in a form where they are partially coated with a binder. The binder is also selected from at least one of ion-conducting polymers, including but not limited to perfluorosulfonic acid resins, partially fluorinated polymers, and non-fluorinated hydrocarbon polymers, and preferably can be made of the same material as the proton exchange membrane to improve interfacial compatibility.

[0036] In this invention, the use of the cathode catalytic layer and the cathode porous transport layer is not limited.

[0037] For example, the cathode catalyst in the cathode catalyst layer can be selected from at least one of platinum group metals, non-platinum group metals, or composite catalysts. Platinum group metals include platinum (Pt), palladium (Pd), rhodium (Rh), ruthenium (Ru), and their alloys. Non-platinum group metals include carbides, nitrides, sulfides, or phosphides (such as MoS2, WC) of molybdenum (Mo), tungsten (W), cobalt (Co), and nickel (Ni). Composite catalysts include amorphous alloys formed from the above metals and non-metallic elements (such as B, P, S). Platinum and its alloys are preferred active components due to their highest exchange current density and best corrosion resistance in acidic media.

[0038] For example, the cathode porous transport layer material can be selected from at least one of carbon-based materials, metallic materials, and composite materials. Carbon-based materials include carbon fiber paper, carbon fiber woven fabric, and graphitized carbon felt; metallic materials include stainless steel mesh, nickel mesh, copper mesh, or gold / silver-plated titanium mesh; and composite materials include carbon-polymer composite sheets or metal-carbon composite felt, etc. Carbon-based materials are preferred due to their excellent electrical conductivity, chemical stability, and low cost.

[0039] The composite diffusion layer, composite anode, or composite film electrode provided by this invention can achieve at least one of the following performance indicators:

[0040] (1) The bubbles on the surface of the iridium-based catalyst layer are evenly distributed and can spontaneously desorb below 5 μm;

[0041] (2) The mass-to-activity ratio at 1.8 V is increased by more than 3 times, preferably more than 15 times, and more preferably more than 23 times compared to the absence of a composite diffusion layer (no independent NPG layer);

[0042] (3) The membrane electrode at 0.5 A cm -2 The decay rate at constant current density decreased to 2.5 mV / h. -1 The following values ​​are preferably 1~2mV h -1 .

[0043] Fourthly, the present invention also provides a method for preparing the above-mentioned composite diffusion layer, composite anode, or composite film electrode. This method includes the following steps:

[0044] S1: Preparation of nanoporous metal interface layer (NPG):

[0045] By employing a dealloying method, an alloy film containing a nanoporous metal interface layer material and a sacrificial metal is placed in a corrosive solution for selective corrosion to remove at least part of the sacrificial metal component, thereby obtaining a nanoporous metal interface layer film with a nanoscale bicontinuous structure of pores and ligaments.

[0046] S2: Preparation of the iridium-based catalyst layer:

[0047] An iridium-based catalyst was dispersed in a solvent and an ionomer was added to prepare a catalyst layer precursor spraying solution. The catalyst layer precursor spraying solution was sprayed onto one side of the proton exchange membrane using an ultrasonic spraying method. The amount of spraying was controlled to adjust the iridium-based catalyst loading.

[0048] S3: Assembly:

[0049] The layers are assembled on the anode side of the proton exchange membrane in the order of porous anode transport layer - nanoporous metal interface layer - iridium-based catalyst layer. Pressure is applied to make the layers come into close contact to obtain a composite diffusion layer, or a composite anode or membrane electrode can be obtained simultaneously.

[0050] Among the methods described above, the dealloying method for preparing nanoporous metal interface layers is a commonly used method in the field of nanoporous metal material preparation. By changing the alloy composition, specifications, type of iridium-based corrosive solution, and corrosion conditions, a bicontinuous structure with target pores and ligaments can be obtained. Alternatively, commercially available nanoporous metal interface layers conforming to the specifications of this invention can be directly purchased and used in this invention.

[0051] In some schemes, step S1 specifically includes: selecting an Au-Ag alloy film with an Au-Ag mass ratio of (1~9):(9~1), etching it in a 0.5~3 mol / L nitric acid solution at 5~60℃ for 0.5~24 h to obtain a nanoporous gold film with a nanoscale bicontinuous structure.

[0052] In the above method, step S2 can obtain an iridium-based catalyst layer with good uniform dispersion effect under ultra-low loading by ultrasonic spraying. The addition of ionomer is beneficial to the high dispersion uniformity of nanoscale primary catalyst particles under ultra-low loading, and at the same time helps to properly expose the catalyst to promote the construction of three-dimensional network.

[0053] In some embodiments, the solvent in step S2 may be selected from polar solvents, including at least one of water, lower monohydric alcohols (such as methanol, ethanol, isopropanol, n-propanol, n-butanol, tert-butanol), polyols (such as ethylene glycol, propylene glycol, glycerol), ketones (such as acetone, butanone), amides (such as N,N-dimethylformamide, N,N-dimethylacetamide), sulfoxides (such as dimethyl sulfoxide), carboxylic acids (such as formic acid, acetic acid), and nitriles (such as acetonitrile), with water and at least one of lower monohydric alcohols or a mixture thereof being preferred.

[0054] In some embodiments, in step S2, the mass ratio of the ionomer to the iridium-based catalyst in the catalyst precursor spraying solution is 0.1–0.2, and the concentration of the iridium-based catalyst in the catalyst precursor spraying solution is 1.0–2.0 mg / mL. -1 Appropriate concentration control is beneficial for further optimizing the dispersion of catalyst particles and interfacial effects.

[0055] In the above method, the assembly order and method of step S3 are not limited. For example, it further includes two steps:

[0056] S31: Transfer of nanoporous metal interface layer

[0057] The nanoporous metal interface layer prepared in step S1 is floated on the surface of deionized water. The nanoporous metal interface layer is retrieved using the proton exchange membrane with iridium-based catalyst layer obtained in step S2 or using the anodic porous transport layer, so that the nanoporous metal interface layer is transferred and adhered to the surface of the iridium-based catalyst layer or the anodic porous transport layer, and then dried.

[0058] S32: Electrode Assembly

[0059] The structure obtained in step S31 is further assembled on the anode side of the proton exchange membrane in the order of anode porous transport layer - nanoporous metal interface layer - iridium-based catalyst layer, while a cathode catalyst layer and a cathode porous transport layer are assembled on the cathode side of the proton exchange membrane.

[0060] Specifically, when the nanoporous metal interface layer is transferred and bonded to the iridium-based catalyst layer in step S31, the anode porous transport layer can be further placed on the other side of the nanoporous metal interface layer to complete the anode-side assembly; when the nanoporous metal interface layer is transferred and bonded to the surface of the anode porous transport layer in step S31, the proton exchange membrane with the iridium-based catalyst layer obtained in step S2 can be further placed on the other side of the nanoporous metal interface layer in sequence to complete the anode-side assembly.

[0061] The composite diffusion layer consists of a porous anode transport layer and a nanoporous metal interface layer (NPG), while the composite anode consists of a porous anode transport layer, a nanoporous metal interface layer (NPG), an iridium-based catalytic layer, and a proton exchange membrane.

[0062] In some schemes, during the pressurization operation in step S3, a gasket is used to control the cathode compression ratio at 70-80%, the anode compression ratio at 80-95%, the pressurization pressure at 0.5-10 MPa, the pressurization temperature at 100-180℃, and the pressurization time at 0.5-30 min. A preferred gasket controls the cathode compression ratio at 75-80%, the anode compression ratio at 85-92%, the pressurization pressure at 4-8 MPa, the pressurization temperature at 120-150℃, and the pressurization time at 1-10 min. Optimizing the pressurization operation helps to ensure sufficient adhesion of each functional layer and the construction of a stable interface while reducing the impact on the mechanical damage to the functional layers.

[0063] Compared with the prior art, the present invention has the following advantages:

[0064] (1) This invention breaks through the cognitive bias and mindset of the core technology of the catalyst layer under ultra-low loading in water electrolysis technology. It proposes an innovative structure based on micro-nano diffusion of composite diffusion layer. While eliminating the key bottleneck of electron transport caused by island effect under ultra-low loading, it also takes into account interface and proton transport, forming multiple synergistic gain effects. It successfully improves the activity and long-term stability of iridium-based catalyst layer under ultra-low loading, reaching or even surpassing the level of existing conventional loading iridium-based catalyst layer.

[0065] (2) In this invention, the nanoporous metal interface layer is a functional layer independent of the iridium-based catalyst layer, rather than a catalyst support. This “functional decoupling” design allows the electron collection function (nanoporous metal film), the catalytic reaction function (powder catalyst layer), and the ion conduction function (proton-conducting resin) to be independently optimized to the best state, fundamentally avoiding the structural contradictions such as poor catalyst dispersion and poor stability that exist in the “catalyst supported on NPG framework” scheme.

[0066] (3) The composite diffusion layer of the present invention has strong universality and can be applied to a variety of iridium-based catalysts with different structural types. It also has a relatively better improvement effect and compatibility for amorphous IrO2 and other systems with poor intrinsic electronic conductivity in traditional categories.

[0067] (4) By introducing a nanoporous metal interface layer, the present invention effectively shortens the electron lateral transport distance (from ~50 μm to ~30 nm), and increases the theoretical utilization rate of the catalyst from ~14% to more than 63%, fundamentally solving the bottleneck problem of electron transport under ultra-low loading. Attached Figure Description

[0068] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0069] For ease of labeling, in the figures, Normal MEA represents samples of conventional membrane electrodes without a composite diffusion layer (i.e., without an NPG layer), including membrane electrodes with different catalyst loadings such as Comparative Examples 1, 4, and 5; +NPG represents membrane electrode samples with a composite diffusion layer, including membrane electrodes with different catalyst types and loadings in each embodiment and Comparative Examples 2 and 3.

[0070] Figure 1 This is a structural diagram of a specific embodiment of the present invention. Wherein a is a schematic diagram of the composite anode structure, b is a planar SEM image of NPG, c is a cross-sectional SEM image of NPG and the iridium-based catalyst layer, and d is a planar SEM image of the titanium felt.

[0071] Figure 2 The difference in oxygen bubble nucleation behavior on the catalyst layer surface between Example 1 and Comparative Example 1 of the present invention is shown. Wherein, a represents Comparative Example 1 without NPG, and b represents Example 1 with NPG.

[0072] Figure 3 The diagram shows the structural distribution of catalysts with different loadings. Where a represents the structure of Comparative Example 3 at ~1.0 mg / cm³. -2SEM images of the catalyst layer under varying loading levels; b represents comparative example 2 at ~0.5 mg / cm². -2 SEM images of the catalyst layer at various loading levels, c represents Example 1 at ~0.1 mg / cm². -2 SEM images of the catalyst layer at various loading levels: d is a microscopic detail image of Example 1, and e is a microscopic detail image of Comparative Example 1 at ~0.1 mg / cm². -2 Elemental distribution of the anode side section under loading, f is the elemental distribution of Example 1 at ~0.1 mg / cm³. -2 Cross-sectional view of the catalyst contact interface under loading conditions.

[0073] Figure 4 This represents the modulating effect of the composite diffusion layer on the performance of the film electrode with different catalyst loadings. Where 'a' represents the catalyst loadings in Example 1 and Comparative Example 1 at ~0.1 mg / cm³. -2 Polarization curves at loading levels, b represents comparative examples 2 and 4 at ~0.5 mg cm⁻¹. -2 Polarization curves at loading levels, where c represents the polarization curves of Comparative Examples 3 and 5 at ~1.0 mg / cm². -2 Polarization curves at loading levels, d represents the values ​​of Example 1 and Comparative Example 1 at ~0.1 mg / cm². -2 Tafel curves at different loading rates, e represents the values ​​of Comparative Examples 2 and 4 at ~0.5 mg / cm². -2 Tafel curves at different loading rates, f represents the values ​​of Comparative Examples 3 and 5 at ~1.0 mg / cm². -2 Tafel curve under load.

[0074] Figure 5 The EIS test results for the composite diffusion layer on catalysts with different loadings are shown. Where a represents the values ​​of Example 1 and Comparative Example 1 (~0.1 mg cm⁻¹). -2 EIS spectra of loading at open circuit potential, b represents comparative examples 2 and 4 (~0.5 mg cm⁻¹). -2 EIS spectra of loading at open circuit potential, c represents comparative examples 3 and 5 (~1.0 mg cm⁻¹). -2 EIS spectra of the loading at open circuit potential, d represents the loading of Example 1 and Comparative Example 1 at ~0.1 mg cm⁻¹. -2 Load capacity, 10 mA cm -2 EIS spectra at current densities, e represents comparative examples 2 and 4 at ~0.5 mg cm⁻¹ -2 Load capacity, 10 mA cm -2 EIS spectra at current densities, f represents comparative examples 3 and 5 at ~1.0 mg cm⁻¹. -2 Load capacity, 10 mA cm -2 EIS spectrum at current density.

[0075] Figure 6This illustrates the modulating effect of the composite diffusion layer on the catalytic activity of membrane electrodes with different catalyst loadings. Where 'a' represents the Ir mass activity (left) and 20 mA cm⁻¹ of the membrane electrodes with different loadings at 1.8 V. -2 Comparison of overpotential under current (right), where b represents the ohmic internal resistance (R) of the film electrode with different loadings. Ω Comparison of charge transfer resistance (R) ct ).

[0076] Figure 7 The results show the overpotential decomposition of catalysts with different loadings in the composite diffusion layer. Where 'a' represents the values ​​of Example 1 and Comparative Example 1 at ~0.1 mg / cm². -2 Overpotential decomposition results under different current conditions at different loads, b represents the values ​​of Comparative Example 2 and Comparative Example 4 at ~0.5 mg cm⁻¹ -2 Overpotential decomposition results under different current conditions at different loads, where c represents the values ​​of Comparative Example 3 and Comparative Example 5 at ~1.0 mg cm⁻¹. -2 Overpotential decomposition results under different current conditions at different loads.

[0077] Figure 8 The images show the XRD patterns of different iridium-based catalysts in Examples 1-4.

[0078] Figure 9 Electron micrographs of different types of commercial iridium-based catalysts are shown. a represents Ir-rich catalysts, b represents amorphous IrO2, c represents core-shell catalyst Ir@IrO2, and d represents supported catalyst IrO2. x / TiO2.

[0079] Figure 10 The composite diffusion layer enhances the electrochemical performance of different catalysts under ultra-low loading conditions as described in this invention. Here, a represents the polarization curve, b represents the Tafel slope curve, c represents the mass-to-analyte activity (MA), and d represents the internal resistance.

[0080] Figure 11 This section compares the EIS of different types of catalysts at different current densities. Where 'a' represents a current density of 10 mA / cm². -2 Impedance comparison below, b is the current density of 100 mA cm⁻¹ -2 Impedance comparison at current density of 1 A cm⁻¹ -2 Impedance comparison is shown below, where d represents the DRT spectrum under different current densities.

[0081] Figure 12 The effect of the composite diffusion layer on the catalytic stability of different catalysts at ultra-low loadings is shown. Here, a represents the stability curve, and b represents a statistical comparison with the performance of other commercially available catalysts reported in the literature.

[0082] Figure 13This demonstrates the difference in potential stability between the embodiments of the present invention and Comparative Example 9. Detailed Implementation

[0083] The embodiments of this invention provide detailed preparation methods and technical steps, aiming to fully illustrate the specific implementation process of this invention. However, these detailed technical details represent only one specific way of implementing this invention and are not intended to limit the core content of this invention or its scope of protection. Those skilled in the art should understand that these embodiments are for illustrative purposes only and should not be considered as limiting the only or exclusive implementation of this invention.

[0084] Example 1

[0085] (1) Preparation of nanoporous metal interface layer (NPG):

[0086] An Au-Ag alloy film with a thickness of approximately 100 nm and an Au-Ag mass ratio of 4:6 was etched in a 1 mol / L nitric acid solution at 30 °C for 1 h to selectively remove at least the Ag component, resulting in an NPG film with a nanoscale bicontinuous structure of pores and ligaments.

[0087] (2) Preparation of iridium-based catalyst layer:

[0088] A mixed solvent of isopropanol and deionized water was prepared at a volume ratio of 9:1. 2 mg of Ir-rich catalyst (IrO2-Ir or Ir-rich) was dispersed in the mixed solvent, and then a 5% (w / w) Nafion solution was added, controlling the volume of Nafion solution added to be ~5 μL so that the mass of resin in the solution was 0.25 mg. The mixture was ultrasonically dispersed to form a catalyst precursor spraying solution. The concentration of iridium-based catalyst in the catalyst precursor spraying solution was 1 mg / mL. -1 The catalyst precursor coating solution was sprayed onto one side of the proton exchange membrane using ultrasonic spraying, and the Ir loading was adjusted to approximately 0.1 mg / cm³ by controlling the spraying amount. -2 After drying, an iridium-based catalyst layer is formed and adheres to one side of the proton exchange membrane.

[0089] (3) NPG transfer:

[0090] The NPG prepared in step (1) was floated on the surface of deionized water. The NPG was retrieved using the proton exchange membrane with the iridium-based catalyst layer obtained in step (2), so that the NPG was transferred and attached to the iridium-based catalyst layer, and then dried.

[0091] (4) Assembly of membrane electrodes

[0092] A titanium felt with a pore size of approximately 100 μm was placed on the NPG to form a complete anode side, while a Pt / C diffusion electrode was used on the cathode side. The cathode compression ratio was controlled to be 70–80%, and the anode compression ratio to be 80–95% using gaskets. Hot pressing was performed at a pressure of approximately 6 MPa and a temperature of 130 °C for 3 minutes to fabricate the membrane electrode.

[0093] Example 2

[0094] The Ir-rich catalyst in Example 1 was replaced with an iridium-based catalyst, IrO. x / TiO2.

[0095] Example 3

[0096] The Ir-rich catalyst in Example 1 was replaced with the iridium-based catalyst amorphous IrO2.

[0097] Example 4

[0098] The Ir-rich catalyst in Example 1 was replaced with the iridium-based catalyst Ir@IrO2.

[0099] Comparative Example 1

[0100] Using a conventional anode without an NPG composite diffusion layer, the Ir loading is still approximately 0.1 mg / cm³. -2 That is, compared to Example 1, no NPG layer is provided.

[0101] Comparative Example 2

[0102] An anode with a composite diffusion layer containing NPG was used, but with an iridium-based catalyst layer having a different loading; that is, relative to Example 1, the Ir loading was adjusted to approximately 0.5 mg / cm³ by controlling the spraying amount. -2 .

[0103] Comparative Example 3

[0104] An anode with a composite diffusion layer containing NPG was used, but with an iridium-based catalyst layer having a different loading; that is, relative to Example 1, the Ir loading was adjusted to approximately 1.0 mg / cm³ by controlling the spraying amount. -2 .

[0105] Comparative Example 4

[0106] A conventional anode without an NPG composite diffusion layer was used, along with iridium-based catalyst layers with different loadings. Specifically, compared to Comparative Example 1, the Ir loading was adjusted to approximately 0.5 mg / cm² by controlling the spraying amount. -2 .

[0107] Comparative Example 5

[0108] A conventional anode without an NPG composite diffusion layer was used, along with iridium-based catalyst layers with different loadings; specifically, relative to Comparative Example 1, the Ir loading was adjusted to approximately 1.0 mg / cm³ by controlling the spraying amount. -2 .

[0109] Comparative Example 6

[0110] Using a conventional anode without an NPG composite diffusion layer, the Ir loading is still approximately 0.1 mg / cm³. -2 The Ir-rich catalyst in Example 1 was replaced with an iridium-based catalyst, IrO. x / TiO2, meaning that, compared to Example 2, no NPG layer was provided.

[0111] Comparative Example 7

[0112] Using a conventional anode without an NPG composite diffusion layer, the Ir loading is still approximately 0.1 mg / cm³. -2 Furthermore, the Ir-rich catalyst in Example 1 was replaced with amorphous IrO2, meaning that, compared to Example 3, no NPG layer was provided.

[0113] Comparative Example 8

[0114] Using a conventional anode without an NPG composite diffusion layer, the Ir loading is still approximately 0.1 mg / cm³. -2 Furthermore, the Ir-rich catalyst in Example 1 was replaced with the iridium-based catalyst Ir@IrO2, meaning that, compared to Example 4, no NPG layer was provided.

[0115] Comparative Example 9 (Comparative scheme: composite catalyst layer supported on NPG surface)

[0116] Using the NPG film prepared in Example 1, an iridium-based catalyst was prepared on the NPG film by electrodeposition. The iridium-based catalyst was then supported on the surface of a nanoporous metal material as a composite catalyst layer, with an Ir loading of approximately 0.14 mg / cm³. -2 The specific preparation method is as follows: using an NPG thin film as the working electrode, electrodeposition is performed in an electrolyte containing an iridium precursor (such as chloroiridic acid) (concentration ~0.1-0.5 mM) under constant current mode, and the deposition time is controlled to achieve an Ir loading of approximately 0.14 mg cm⁻¹. -2 After electrodeposition, the composite catalyst layer was annealed at 350°C in air for 3 hours. After annealing, the NPG composite catalyst layer loaded with iridium-based catalyst was hot-pressed onto the surface of the proton exchange membrane. No separate powder catalyst layer was set on the anode side. The remaining assembly conditions were the same as in Example 1.

[0117] The membrane electrodes of the above embodiments and comparative examples were tested for water electrolysis performance in an electrolyzer at 80°C with deionized water supply.

[0118] Figure 1 Example 1 illustrates a structural schematic diagram of the composite anode of the present invention. Figure 1 As shown in Figure a, oxygen evolution reaction (OER) occurs on the anode side of the proton exchange membrane to generate oxygen bubbles. The iridium-based catalyst is in close contact with the proton exchange membrane as a catalyst layer with a very low loading. On the other side of the iridium-based catalyst layer are NPG and titanium felt in sequence. Figure 1 Figures b and c show that NPG exhibits a uniform bicontinuous structure with pore and ligament sizes of approximately 60 nm and a thickness of approximately 80 nm. Figure 1 The figure in d shows that the titanium felt has an average pore size of about 100 μm.

[0119] Figure 2 This paper presents the oxygen bubble nucleation behavior on the catalyst layer surface of Example 1 and Comparative Example 1, observed by in-situ optical microscopy. It can be seen that the conventional catalyst layer surface without NPG forms bubbles with a large diameter (~40 μm), and these bubbles remain attached to the electrode surface, making desorption difficult. These large bubbles cover the electrode active sites, hindering the contact between the electrolyte and the catalyst layer, leading to increased local current density and intensified concentration polarization, especially with the exacerbated shielding effect of these large bubbles under ultra-low catalyst loading conditions. On the catalyst layer surface with independently placed NPG, oxygen bubbles exhibit high-density nucleation and rapid growth, spontaneously and uniformly desorbing even at a relatively small size (~3 μm). This shows that the independent NPG provides a large number of uniformly distributed bubble nucleation sites for the ultra-low catalyst loading layer, resulting in high-density synchronous nucleation of oxygen bubbles across the entire electrode surface. Figure 2 (b) This avoids excessive growth of localized bubbles. This result provides direct visual evidence for the improvement of high current density performance of ultra-low loading iridium-based catalyst layers by composite diffusion layers with NPG.

[0120] To investigate the performance differences of iridium-based catalysts at ultra-low loadings, we characterized the catalyst layer structure under different loadings. For example... Figure 3 As shown, this is for high loading (~1.0 mg cm⁻¹) -2 Comparative Example 3 Figure 3 Under condition a), the catalyst particles form a continuous and dense catalytic layer structure, with close packing between particles and almost no exposed substrate. At this point, the continuity of the catalytic layer depends entirely on the overlap of the high-load catalyst particles. When the loading decreases to a medium loading (~0.5 mg cm⁻¹), -2 Comparative Example 2 Figure 3In step b), the continuity of the catalyst layer begins to decline, and the catalyst particles exhibit a state of localized agglomeration and dispersion, with a significant increase in the gaps between particles and the appearance of a small number of discontinuous exposed areas on the substrate surface. Furthermore, when the loading is further reduced to an ultra-low loading (~0.1 mg cm⁻¹), the catalyst layer becomes increasingly discontinuous. -2 Example 1 Figure 3 In case c), the continuous structure of the catalyst layer is completely destroyed, and the catalyst particles are uniformly dispersed on the substrate surface in the form of isolated clusters. The connectivity between the particles is extremely poor, forming an island-like distribution feature. At this time, the continuity of the electron transport network and active sites of the catalyst layer faces severe challenges. Figure 3 Image d shows a high-magnification SEM image of the catalyst and Nafion resin in the catalyst layer, clearly revealing the interfacial bonding state between the active component and the Nafion resin. Morphological features indicate that the catalyst particles are not isolated but are uniformly coated and interconnected by the resin binder. The Nafion resin forms a continuous three-dimensional network between the particles, serving to fix the catalyst particles and providing channels for proton transport. Simultaneously, the relatively low Nafion resin content results in partial coating on the catalyst particle surface, retaining uniformly distributed exposed areas that provide direct active sites for electrochemical reactions. However, this may also hinder electron channels between catalyst particles, highlighting the necessity of bonding catalyst particles to the proton exchange membrane, independently setting up the NPG, and controlling the NPG thickness. Figure 3 As can be seen from e and f, under ultra-low loading, the continuity of the catalyst layer is extremely poor, and when the pore size of the titanium felt is large, the catalyst in the middle of the pore is easily unusable. For catalyst layers with composite diffusion layers with independent NPGs, the NPGs effectively connect isolated catalyst particles to form a continuous electronic pathway, thereby improving catalyst utilization.

[0121] Figure 4 This demonstrates the differences in electrochemical gain effect of the composite diffusion layer of the present invention with different catalyst loadings. At low Ir loading (~0.1 mg cm⁻¹), -2 () Figure 4 In example a), the cell voltage of Comparative Example 1 can only reach 0.14 A cm at 1.8 V. -2 In Example 1, the improvement was significantly increased to 0.54 Å cm⁻¹. -2 The current density increased by nearly four times. This indicates that the composite diffusion layer has a particularly significant effect on improving the utilization of catalyst active sites under low loading conditions. However, under medium to high Ir loading (~0.5, ~1.0 mg cm⁻¹), the current density increased by nearly four times. -2 () Figure 4In examples b and c), the performance improvement is limited; Comparative Example 2 shows only a ~2.0-fold and 2.1-fold improvement compared to Comparative Example 4, and Comparative Example 3 shows only a ~2.0-fold and 2.1-fold improvement compared to Comparative Example 5, respectively. This indicates that the performance gain of the composite diffusion layer is significantly enhanced on ultra-low loading catalysts. After eliminating the interference of ohmic voltage drop through iR-free overpotential correction, the Tafel slope reflects the difference in the influence of the composite diffusion layer on the intrinsic OER kinetics under different Ir loadings. Figure 4 As shown in d~f, the ultra-low loading (~0.1 mg cm⁻¹) -2 The optimization effect is particularly outstanding under the given conditions, with the Tafel slope decreasing from 142.2 mV / dec. -1 Decreased to 113.1 mV dec -1 It reduced by 29.1 mV dec -1 At medium to high Ir loading (~0.5, ~1.0 mg cm⁻¹), -2 The Tafel slope decrease was not significant, indicating that under ultra-low loading, the OER kinetics of the membrane electrode were severely limited, and the rate-controlling step transformed into a multi-electron transfer process. The composite diffusion layer effectively accelerated the reaction kinetics by lowering the OER reaction energy barrier, and this kinetic optimization was particularly crucial under low loading. The core mechanism lies in optimizing charge transfer kinetics through a dual pathway: on the one hand, the three-dimensional continuous high conductivity of NPG can effectively construct a continuous electron transport pathway, improving electron transport efficiency; on the other hand, the catalyst layer-titanium felt contact interface is optimized, increasing physical contact. Especially under ultra-low loading, this compensates for the discontinuous electron transport defect under low loading, reactivating active sites that were previously unable to participate in the reaction due to islanding, greatly improving catalyst utilization.

[0122] Figure 5 The EIS test results further revealed the performance enhancement mechanism of the composite diffusion layer. The value at the intersection of the EIS spectrum and the real axis at open-circuit potential represents the internal resistance of the membrane electrode, 10 mA / cm. 2 The semicircular radius of the EIS spectrum at current density represents the charge transfer impedance of the anodic reaction, reflecting the anodic catalytic activity. The continuity of the catalyst layer gradually deteriorates with decreasing catalyst loading. Catalyst loadings higher than ~0.5 mg / cm² are suitable for this purpose. -2 At that time, its catalyst layer structure exhibited relatively good continuity, while when the loading decreased to ~0.1 mg cm⁻¹, the catalytic layer structure showed relatively good continuity. -2 The presence of numerous isolated islands in the catalyst layer leads to the breakage of its conductive network, thereby significantly reducing the internal resistance of the MEA. The catalyst loading is ~0.5 mg cm⁻¹. -2 It exhibits threshold characteristics; when the loading is below this threshold, the electronic conductivity decreases exponentially. When the loading is ~0.1 mg / cm³, the electronic conductivity decreases evenly. -2 At that time, the electronic conductivity of the catalyst layer had decreased by about four orders of magnitude. Figure 5The values ​​of a and d relative to b, e, c, and f demonstrate the significant islanding effect of electrode internal resistance under ultra-low loading, as well as the good elimination ability of the composite diffusion layer for this phenomenon.

[0123] like Figure 6 As shown, for comparative examples 1, 4, and 5, which do not have a composite diffusion layer, the catalyst loading ranges from ~1.0 mg / cm³. -2 Decreased to ~0.1 mg cm -2 At 1.8 V, the mass-to-mass activity (MA) showed a continuous decreasing trend, while the overpotential increased sharply from 305.5 mV to 461.5 mV, demonstrating the performance collapse characteristics of the catalyst layer at low loading. In stark contrast, the composite diffusion layer significantly suppressed the performance degradation trend at low loading, and the gain effect increased exponentially with decreasing loading, reaching ~0.1 mg cm⁻¹. -2 At ultra-low loads, the MA in Example 1 reached 5.36 A mg. -1 This is compared to Example 1 (1.39 mg). -1 The efficiency of the catalyst layer is 3.9 times that of the standard catalyst layer, while its overpotential is reduced by 75.9 mV, demonstrating the dual optimization of the composite diffusion layer for both dynamic range (MA) and overpotential. The core reason for this phenomenon is that under low loading, the catalyst layer exhibits an island-like particle distribution, and the breakage of the electron transport network results in a large number of active sites being unable to participate in the reaction. The composite diffusion layer compensates for this defect by introducing NPG, thereby maximizing the activation of active sites under low loading. Figure 6 The internal resistance (R) of b Ω ) and charge transfer resistance (R ct The data reveals the root cause of performance differences at the interface transmission level. For conventional film electrodes without a composite diffusion layer (Comparative Examples 1, 4, and 5), R Ω and R ct All showed a significant increasing trend with decreasing catalyst loading, reflecting the problem of disrupted electron transport continuity at low loading. The optimization effect of the composite diffusion layer on impedance also varied significantly with the continuity of loading, reaching ~0.1 mg cm⁻¹. -2 Under ultra-low loading conditions, two types of membrane electrodes R Ω and R ct The reductions in NPG and MA reached 48.2% and 24.1%, respectively, significantly higher than the optimized levels under high loading (31.8% and 10.4%, respectively). The NPG in the composite diffusion layer provides a highly conductive porous framework, connecting the dispersed catalyst particles, significantly reducing interfacial contact resistance, improving catalyst utilization, and lowering the charge transfer barrier for the OER reaction in the catalyst layer. This is entirely consistent with the changing trends of polarization performance and MA.

[0124] Figure 7The ohmic overpotential (η) of the membrane electrode under different catalyst loadings was demonstrated by the composite diffusion layer. Ω ), activation overpotential (η) act ) and mass transfer overpotential (η) mt The modulation effect of the composite diffusion layer, combined with the dual variables of current density and load, further reveals the optimization mechanism of polarization loss by the composite diffusion layer. In ultra-low load ( Figure 7 In the middle a) below, 0.3 A cm -2 At that time, the composite diffusion layer achieved a significant synergistic reduction in overpotential across all types, η Ω η act η mt These represent reductions of approximately 42.7%, 17.3%, and 82.0%, respectively. Medium load ( Figure 7 In section b), the overpotential level of the conventional membrane electrode is significantly lower than that of the ultra-low loading system, and the modulation effect of the composite diffusion layer exhibits differentiated characteristics at 0.3 and 1.0 A cm⁻¹. -2 Below, η Ω η act The reduction rates were not significantly different, remaining around 20% and 14% respectively, but the current density η increased. mt The improvement effects showed significant differences, with 34.0% @ 0.3 A cm. -2 And 11.3% @ 1.0A cm -2 This indicates that a locally continuous electron transport network has been formed in the catalyst layer at this point, and activation polarization is no longer the core bottleneck. The focus of the composite diffusion layer shifts to optimizing the mass transfer process and finely controlling the interfacial contact. For high loading ( Figure 7 (c) Although its conductive network is well-developed, the increased thickness of the catalyst layer leads to a greater longitudinal internal resistance, resulting in a faster longitudinal voltage decay. According to Ohm's law, the nanoscale pore size of NPG can significantly reduce the internal resistance of the catalyst layer within the pores, therefore η Ω Each decreased by 33.0% @ 0.3 A cm. -2 And 34.4% @ 1.0 A cm -2 η act and η mt There was no significant difference compared to the medium-load catalyst layer, with reductions remaining at 35% and 13.3% respectively. These results further confirm that the composite diffusion layer effectively addresses the electron transport bottleneck caused by the island effect under ultra-low loading, a key bottleneck that medium- and high-loading catalyst layers do not exhibit.

[0125] This invention further investigates the improvement effect of composite diffusion layers on different iridium-based catalysts under ultra-low loading. Examples 1-4 used four different commercial catalysts: amorphous IrO2 (Example 3), supported catalyst (IrO2), and... x / TiO2, Example 2), Ir-rich catalyst (IrO2-Ir or Ir rich, Example 1) and core-shell structure catalyst (Ir@IrO2, Example 4).

[0126] Figure 8 XRD patterns showed that both the Ir-rich catalyst (IrO2-Ir) and the core-shell catalyst (Ir@IrO2) exhibited clear and sharp diffraction peaks. The diffraction peaks of the Ir-rich catalyst were completely consistent with the characteristic diffraction peaks of the IrO2 standard PDF card (PDF#43-1019), indicating that the main phase of the catalyst was rutile IrO2. Furthermore, the sharpness and high intensity of the diffraction peaks indicated high crystallinity and good crystal integrity. No obvious impurity peaks were observed in the spectra, suggesting high phase purity of the catalyst. The core-shell catalyst Ir@IrO2 also showed multiple distinct diffraction peaks, which corresponded to the characteristic peak positions of the metallic Ir standard PDF card (PDF#06-0598) and the IrO2 standard PDF card (PDF#43-1019), respectively. Among them, metallic Ir belongs to the face-centered cubic (fcc Ir) structure, while IrO2 has a rutile structure. This indicates that both metallic Ir and IrO2 crystal phases coexist in the sample. The relatively sharp diffraction peaks further indicate that the catalyst has high crystallinity. Unlike the two crystalline catalysts mentioned above, the XRD pattern of the amorphous IrO2 catalyst does not show obvious characteristic diffraction peaks, but only a broad and diffuse diffraction background. This phenomenon is mainly attributed to the lack of long-range ordered crystal structure in amorphous IrO2. For supported catalysts IrO2... x The XRD pattern of / TiO2 mainly showed several broad and obvious diffraction peaks, which were completely consistent with the diffraction peak positions of the standard PDF card (PDF#21-1276) for rutile structure TiO2, indicating that the TiO2 support of this catalyst is rutile. Meanwhile, weak IrO2-related diffraction signals were observed at some positions. However, due to the IrO2... x The active component exhibits high dispersion on the TiO2 support surface, with small particle size and low content. Its diffraction signal is weak and shows some peak broadening, making it difficult to form obvious and clear IrO in the XRD pattern. x Diffraction peaks.

[0127] Different iridium-based catalysts were further characterized using transmission electron microscopy (TEM) and selected area electron diffraction (SAED). For example... Figure 9 As shown, the IrO2-Ir catalyst (Ir-rich) ( Figure 9 a) and amorphous IrO2 ( Figure 9(b) and supported catalysts (IrO) x / TiO2)( Figure 9 (d) represents the agglomeration morphology of nanoparticles, among which the IrO2-Ir catalyst has the highest degree of agglomeration, and the core-shell structure catalyst (Ir@IrO2) ( Figure 9 c) exhibits a regular cubic structure with a particle size of 5–10 nm. Its diffraction pattern shows concentric diffraction rings composed of discrete bright spots, indicating that the catalyst has a polycrystalline structure and can be classified as a coexisting crystal phase of metallic Ir and rutile IrO2, possessing a core-shell structure of Ir core and IrO2 shell. x / TiO2 catalyst, TEM images show that IrOx nanoparticles are uniformly dispersed on the surface of the TiO2 support, with particle sizes mainly ranging from 3 to 8 nm, forming a loose nanocluster structure; the spectrum shows multiple distinct diffraction rings, indicating that the sample has a polycrystalline structure, which can be attributed to the TiO2 support and the IrO2 active phase, respectively, indicating that IrO x Good loading was achieved on the TiO2 surface. The amorphous IrO2 catalysts exhibited a cluster structure composed of 4–10 nm nanoparticles in TEM, but no obvious lattice fringes were observed; the main phase was amorphous IrO2. Specific surface area measurements showed that these catalysts had a specific surface area of ​​10–75 m². 2 g -1 between.

[0128] Figure 10 The performance comparison of several different iridium-based catalysts in Examples 2-4 before and after the improvement of the composite diffusion layer is shown. Figure 4 a, d and Figure 6 The comparative results of Examples 1 in sections a and b show that, for different iridium-based catalysts, the composite diffusion layer can effectively reduce the total polarization loss of the electrolyzer and significantly improve the electrolysis performance. Among them, the performance gain of the amorphous IrO2 system is the most outstanding. Figure 10 (a) Figure 10 Figure b shows that the composite diffusion layer can effectively promote the OER reaction kinetics of different types of anode catalysts. Among them, the Tafel slope of amorphous IrO2 decreased the most, reaching 101.8 mV dec. -1 (from 160.2 mV dec) -1 Dropped to 58.4 mV dec -1 ), IrO x The reduction rate of the TiO2 system was similar to that of the amorphous IrO2 system, from 131.6 mVdec. -1 Significantly reduced to 53.9 mV dec -1 This indicates that NPG has the most significant effect on enhancing the intrinsic catalytic activity of these two catalytic layer systems with low electronic conductivity. The change in Ir@IrO2 was the smallest, only increasing by 88.4 mV dec.-1 Reduced to 66.1 mV dec -1 The decrease in the Tafel slope indicates a lower energy barrier for the charge transfer step during the reaction, thus significantly accelerating the OER reaction rate of the catalyst layer. This demonstrates that the composite diffusion layer can effectively improve the catalyst layer environment on the anode side, especially in terms of the anode catalytic interface structure, promoting electron transport, and improving catalyst utilization. Furthermore, the improvement effect varies depending on the catalyst system, showing greater advantages in catalyst systems with lower intrinsic electronic conductivity.

[0129] Figure 10 The results show that at a typical operating potential of 1.8 V, the composite diffusion layer significantly improved the mass-to-activity (MA) of different catalysts by several times. Specifically, the MA of amorphous IrO2 increased by 1.0 A mg / L. -1 Increased to 24.5 mg -1 The largest increase was observed (approximately 24 times); Ir@IrO2 increased from 6.0 A mg. -1 Increased to 21.5 mg -1 (Approximately 3.5 times higher); IrO x / TiO2 is 1.4 A mg -1 Increased to 22.0 A mg -1 (Approximately 15.5 times improvement). The significant improvement in MA indicates that the introduction of the composite diffusion layer not only improves the overall output performance of the electrolyzer, but more importantly, it significantly enhances the atomic utilization efficiency of the noble metal Ir, enabling more active sites to participate in the reaction, thus achieving excellent electrocatalytic performance even at ultra-low loading.

[0130] also, Figure 10 The effect of the composite diffusion layer on the total internal resistance of the membrane electrode was compared. The results showed that the internal resistance of all three catalyst systems decreased significantly. Among them, the amorphous IrO2 showed the largest decrease, from 113.2 mΩ cm⁻¹. -2 Reduced to 69.3 mΩ cm -2 Ir@IrO2 has a strength of 84.1 mΩ cm⁻¹ -2 Reduced to 58.7 mΩ cm -2 IrO x / TiO2 is 111.3 mΩ cm -2 Reduced to 79.7 mΩ cm -2The reduction in internal resistance is mainly attributed to the composite diffusion layer constructing a more continuous electron transport network within the catalyst layer, while simultaneously optimizing the contact state at the electrode / proton exchange membrane interface. This reduces interfacial contact resistance and charge transfer resistance, effectively lowering ohmic losses. This result corroborates the findings from polarization curves and Tafel kinetic analysis, indicating that the composite diffusion layer, through a synergistic effect of multiple mechanisms including improved electron transport, enhanced catalyst utilization, and optimized interfacial structure, overcomes key bottlenecks under ultra-low iridium-based catalyst loading while optimizing transport pathways, significantly improving the overall electrochemical performance of the membrane electrode.

[0131] Figure 11 As can be seen from AC, at low current densities (10 mA cm⁻¹) -2 Under the conditions described, all catalyst systems without composite diffusion layer improvement exhibited large impedance arcs, with the amorphous IrO2 system exhibiting the largest impedance arc and high charge transfer resistance. After improvement with composite diffusion layer, the impedance arc radii of all systems decreased significantly, indicating a significant reduction in charge transfer resistance. The decrease was most pronounced in amorphous IrO2, demonstrating the most significant optimization effect of NPG on its electron transport network. As the current density increased to 100 mA cm⁻¹... -2 The overall impedance arc further decreased, and the differences between the systems gradually narrowed, indicating that the charge transfer process at the electrode interface was further enhanced under moderate current density. When the current density increased to 1.0 A cm⁻¹... -2 At this point, the impedance arc significantly decreased, indicating that both the interfacial reaction impedance and the transport impedance of the system were significantly reduced, and the electrolytic cell gradually entered a working state dominated by the mass transfer process. Overall, the catalyst systems improved by the composite diffusion layer all exhibited smaller impedance arcs at the three current densities, indicating that they can effectively reduce the electrode interfacial resistance and improve the charge transport efficiency.

[0132] like Figure 11 As shown in Figure d, DRT analysis results indicate that the relaxation peak of the catalyst system improved by the composite diffusion layer is significantly weakened and shifts to a shorter relaxation time, indicating that the charge transfer process is significantly accelerated, reflecting a significant improvement in the electron transport environment of the catalyst layer and the interfacial reaction kinetics. With increasing current density, the relaxation peak generally shifts to a shorter time scale (10⁻⁶). -4 ~10 -3 The movement of s indicates that as the current density increases, the interfacial reaction kinetics further accelerate, 10 -2 ~10 -1 A weak peak appears in the s-interval, corresponding to mass transfer-related processes. When the current density reaches 1.0 A cm⁻¹... -2 At that time, the main peak further moved towards 10 -4The concentration near the s-value indicates that under high current density conditions, the reaction process is dominated by rapid charge transfer and mass transfer coupling. The peak values ​​for each system significantly decreased throughout the relaxation time range, indicating that both interfacial reaction resistance and mass transfer resistance were effectively reduced. This result demonstrates that the composite diffusion layer not only optimizes the electron transport path but also improves reactant diffusion and gas evolution processes within the catalyst layer. This is closely related to the design of NPG as an independent interfacial layer, thereby improving the interfacial performance of the NPG-iridium-based catalyst layer-proton exchange membrane.

[0133] Figure 12 Figure a shows the membrane electrode before and after improvement by the composite diffusion layer at 0.5 A cm⁻¹. -2 The stability test results at 80℃ under constant current for 50 h at current density show that the voltage decay of the film electrode after improvement by the composite diffusion layer is within 1~2 mVh. -1 Within the range, the reduction in attenuation of amorphous IrO2 was the most significant (approximately 91%). Performance comparisons with many other commercial catalysts reported in the literature ( Figure 12 (b) shows that, through interface modulation of the composite diffusion layer, even with an iridium-based catalyst loading of only 1 / 3 to 1 / 5 of the conventional level (≤0.1 mg cm⁻¹), -2 This invention achieves a mass activity (MA) that is comparable to or even several times greater than that of traditional systems, fundamentally overturning the traditional understanding that high loading equals high performance, and overcoming the contradiction between low loading and high performance, highlighting the core breakthrough of this invention in the utilization efficiency of ultra-low loading iridium-based catalyst layers.

[0134] To further demonstrate the advantages of the composite diffusion layer of this invention, we show the difference in electrochemical stability using Comparative Example 9 with a composite catalytic layer employing an iridium-based catalyst (i.e., an integrated scheme where the catalyst is directly supported on the NPG surface). Figure 13 As shown, 0.5 A cm -2 The voltage decay of Comparative Example 9, operating at a constant current at 80°C under current density, is also improved compared to the membrane electrode without NPG (approximately 5 mV / h). -1 However, the decay rate is still the same as that of the composite diffusion layer of this invention (1~2 mV h). -1More than twice that of NPG. The present invention believes that the reason is that although loading the iridium-based catalyst onto the surface of the nanoporous metal material repairs the electron transport path, (1) the catalyst is directly deposited on the surface of the NPG framework. Due to the complex three-dimensional structure of NPG, the deposited catalyst has poor dispersion and poor crystallinity, and its intrinsic activity is far inferior to that of the pre-synthesized nanopowder catalyst; (2) under ultra-low loading, the catalyst is distributed on the surface of the NPG framework in the form of islands, lacking effective coverage by Nafion resin, the proton transport channel is discontinuous, and the deep catalytic sites are difficult to participate in the reaction; (3) the catalyst is directly supported on the NPG framework, and the degradation behavior of the catalyst such as dissolution and aggregation will directly lead to the loss of active sites on the NPG surface and may block the NPG nanopores. Therefore, the catalyst-supported scheme cannot construct a stable interface of NPG-iridium-based catalyst layer-proton exchange membrane. The rapid charge transfer cannot be coupled with the same efficient mass transfer. At the same time, the weak connection between the catalyst particles and the surface of the nanoporous metal material under ultra-low loading amplifies the loss of active sites, making it difficult to achieve the expected potential decay rate.

[0135] The technical features of the embodiments described above can be combined arbitrarily. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as the combination of these technical features does not contradict each other, it should be considered within the scope of this specification. Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make modifications, alterations, substitutions, and variations to the above embodiments within the scope of the present invention. Furthermore, without contradiction, those skilled in the art can combine and integrate different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

Claims

1. A composite diffusion layer suitable for ultra-low loading iridium-based catalyst layers, comprising a nanoporous metal interface layer and an anode porous transport layer; The nanoporous metal interface layer is a metal thin film with a nanoscale bicontinuous structure of pores and ligaments. The porous transport layer of the anode has micron-sized pores; The areal loading of the iridium-based catalyst layer is ≤0.2 mg cm⁻¹. -2 .

2. The composite diffusion layer suitable for ultra-low loading iridium-based catalyst layers according to claim 1, characterized in that, The areal loading of the iridium-based catalyst layer is ≤0.1 mg cm⁻¹ -2 Ideally, the dosage should be 0.05~0.1 mg cm. -2 It is excellent.

3. The composite diffusion layer suitable for ultra-low loading iridium-based catalyst layers according to claim 1, characterized in that, The pore size of the nanoporous metal interface layer is 10~200nm, and the ligament size is 10~200nm; Preferably, the pore size is 30~100nm and the ligament size is 30~100nm; Preferably, the thickness of the nanoporous metal interface layer is 50~500nm, preferably 50~200nm, and even more preferably 60~120nm.

4. The composite diffusion layer suitable for ultra-low loading iridium-based catalyst layers according to claim 1, characterized in that, The nanoporous metal interface layer material is selected from one or more of gold, platinum, and iridium; Preferably, it is nanoporous gold; Preferably, the anode porous transport layer is a porous body made of refractory and strong acid-resistant metal material through fiber sintering or weaving, and the base material is selected from one or more of pure titanium, titanium alloy, tantalum, niobium, zirconium or tungsten; Preferably titanium or titanium alloy; Preferably, the physical form of the anode porous transport layer is one or more of the following: fiber felt, fiber woven mesh, metal foam, or powder metallurgy porous plate; Preferably, the thickness of the porous anode transport layer is 0.1~2.0 mm, more preferably 0.2~0.5 mm; Preferably, the porous transport layer of the anode has a porosity of 30% to 95% and an average pore size of 10 to 200 μm, preferably 20 to 100 μm.

5. The composite diffusion layer suitable for ultra-low loading iridium-based catalyst layers according to claim 1, characterized in that, The iridium-based catalyst of the iridium-based catalyst layer is selected from at least one of metallic iridium, iridium oxide, hydrated iridium oxide, and composite oxides or solid solutions of iridium with other acid-resistant metal elements; Other acid-resistant metal elements are selected from one or more of tantalum, niobium, titanium, ruthenium, tin, and tungsten; Preferably, the iridium-based catalyst has a structure including crystalline, amorphous, and crystalline-amorphous heterojunction structures; Preferably, the primary particle size of the iridium-based catalyst is 2-20 nm; Preferably, the specific surface area of ​​the iridium-based catalyst is in the range of 10 to 75 m². 2 g -1 between; Preferably, the iridium-based catalyst has a composite structure, including a core-shell structure and a supported structure; Preferably, at least one of the core and shell in the core-shell structure is a substance containing iridium and having oxygen evolution reaction activity; Preferably, it has an iridium oxide shell and an iridium-containing or non-iridium metal or its alloy as a core; Preferably, the supported structure supports the iridium-based catalyst on an acid-resistant conductive support, which is selected from titanium-based oxides, niobium-based oxides, tantalum-based oxides, or conductive ceramics; specifically, the acid-resistant conductive support is selected from titanium oxide, antimony-doped tin oxide, tantalum-doped tin oxide, or niobium-doped titanium oxide.

6. The composite diffusion layer suitable for ultra-low loading iridium-based catalyst layers according to claim 1, characterized in that, The proton exchange membrane is selected from at least one of perfluorosulfonic acid resin, partially fluorinated polymer, and non-fluorinated hydrocarbon polymer, or at least one of composite modified polymers in which inorganic fillers are introduced into at least one of the above polymers.

7. The composite diffusion layer suitable for ultra-low loading iridium-based catalyst layers according to claim 1, characterized in that, The iridium-based catalyst particles of the iridium-based catalyst layer are bonded to the surfaces of the proton exchange membrane and the nanoporous metal interface layer in the form of being partially coated with a binder. Preferably, the binder is selected from at least one of ion-conducting polymers, including at least one of perfluorosulfonic acid resin, partially fluorinated polymer, and non-fluorinated hydrocarbon polymer, and preferably the same material as the proton exchange membrane.

8. The composite diffusion layer suitable for ultra-low loading iridium-based catalyst layers according to claim 1, characterized in that, The composite diffusion layer in the membrane electrode can achieve at least one of the following performance indicators: (1) The bubbles on the surface of the iridium-based catalyst layer are evenly distributed and can spontaneously desorb below 5 μm; (2) The mass-to-activity ratio at 1.8 V is increased by more than 3 times compared to the ratio without a composite diffusion layer, preferably more than 15 times, and more preferably more than 23 times; (3) The membrane electrode at 0.5 A cm -2 The decay rate at constant current density decreased to 2.5 mV / h. -1 The following values ​​are preferred: 1~2 mV h -1 .

9. A method for preparing the composite diffusion layer according to any one of claims 1-8, comprising the following steps: An iridium-based catalyst was dispersed in a solvent and an ionomer was added to prepare a catalyst layer precursor spraying solution. The catalyst layer precursor spraying solution was sprayed onto one side of the proton exchange membrane using an ultrasonic spraying method. The amount of spraying was controlled to adjust the iridium-based catalyst loading. The layers are assembled on the anode side of the proton exchange membrane in the order of porous anode transport layer - nanoporous metal interface layer - iridium-based catalyst layer, and pressure is applied to make each layer come into close contact to obtain a composite diffusion layer. Preferably, the solvent may be selected from a polar solvent, including at least one of water, lower monohydric alcohols, polyhydric alcohols, ketones, amides, sulfoxides, carboxylic acids, and nitriles; Preferably, the mass ratio of the ionomer to the iridium-based catalyst in the catalyst precursor spraying solution is 0.1~0.2, and the concentration of the iridium-based catalyst in the catalyst precursor spraying solution is 1.0~2.0 mg / mL. -1 ; Preferably, in the pressurization operation, a gasket is used to control the cathode compression ratio to be 70-80%, the anode compression ratio to be 80-95%, the pressurization pressure to be 0.5-10 MPa, the pressurization temperature to be 100-180℃, and the pressurization time to be 0.5-30 min. The preferred gasket controls the cathode compression ratio to be 75-80%, the anode compression ratio to be 85-92%, the pressurization pressure to be 4-8 MPa, the pressurization temperature to be 120-150℃, and the pressurization time to be 1-10 min.

10. A composite anode with ultra-low loading, comprising an iridium-based catalyst layer disposed on the anode side of a proton exchange membrane, and a composite diffusion layer as described in any one of claims 1-8.

11. A composite membrane electrode, comprising the composite anode of claim 10, and a cathode catalytic layer and a cathode porous transport layer disposed on the cathode side of a proton exchange membrane.

12. The method for preparing the composite film electrode according to claim 11, comprising the following steps: S1: Preparation of nanoporous metal interface layer: By employing a dealloying method, an alloy film containing a nanoporous metal interface layer material and a sacrificial metal is placed in a corrosive solution for selective corrosion to remove at least part of the sacrificial metal component, thereby obtaining a nanoporous metal interface layer film with a nanoscale bicontinuous structure of pores and ligaments. S2: Preparation of the iridium-based catalyst layer: An iridium-based catalyst was dispersed in a solvent and an ionomer was added to prepare a catalyst layer precursor spraying solution. The catalyst layer precursor spraying solution was sprayed onto one side of the proton exchange membrane using an ultrasonic spraying method. The amount of spraying was controlled to adjust the iridium-based catalyst loading. S3: Assembly: The layers are assembled on the anode side of the proton exchange membrane in the order of porous anode transport layer - nanoporous metal interface layer - iridium-based catalyst layer. Pressure is applied to make each layer come into close contact to obtain a composite diffusion layer, or a composite anode or membrane electrode can be obtained simultaneously. Preferably, step S1 specifically includes: Au-Ag alloy films with an Au-Ag mass ratio of (1~9):(9~1) were selected and etched in 0.5~3 mol / L nitric acid solution at 5~60℃ for 0.5~24 h to obtain nanoporous gold films with a nanoscale bicontinuous structure. Preferably, step S3 includes two steps: S31: Transfer of nanoporous metal interface layer: The nanoporous metal interface layer prepared in step S1 is floated on the surface of deionized water. The nanoporous metal interface layer is retrieved using the proton exchange membrane with iridium-based catalyst layer obtained in step S2 or using the anodic porous transport layer, so that the nanoporous metal interface layer is transferred and adhered to the surface of the iridium-based catalyst layer or the anodic porous transport layer, and then dried. S32: Electrode assembly: The structure obtained in step S31 is further assembled on the anode side of the proton exchange membrane in the order of anode porous transport layer - nanoporous metal interface layer - iridium-based catalyst layer, while a cathode catalyst layer and a cathode porous transport layer are assembled on the cathode side of the proton exchange membrane. Preferably, in step S3, the pressurization operation uses a gasket to control the cathode compression ratio at 70-80%, the anode compression ratio at 80-95%, the pressurization pressure at 0.5-10 MPa, the pressurization temperature at 100-180°C, and the pressurization time at 0.5-30 min; more preferably, a gasket is used to control the cathode compression ratio at 75-80%, the anode compression ratio at 85-92%, the pressurization pressure at 4-8 MPa, the pressurization temperature at 120-150°C, and the pressurization time at 1-10 min.

13. The application of the composite diffusion layer according to any one of claims 1-8 in a composite anode or composite membrane electrode for hydrogen production by water electrolysis.

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