A low iridium loading multilayer gradient anode catalyst layer structure and a method of making the same

Abstract

This invention discloses a low-iridium-loading multilayer gradient anode catalyst layer structure and its preparation method. From the membrane side outwards, the structure consists of an Ir-anchored stabilizing first sublayer, a highly active doped core-shell second sublayer, and a weakly defective nanowire mass transfer third sublayer. The first sublayer uses a highly defective, acid-resistant oxide to support ultrathin IrO2, with high-density oxygen vacancies capturing migrating iridium ions. The middle layer is a doped and modified core-shell heterojunction catalyst, carrying the majority of the oxygen evolution reaction. The iridium loading of the three layers is inverted, with a high loading in the middle and low loading on both sides. The outer modified IrO2 nanowires construct macroporous mass transfer channels and assist in intercepting iridium species. The three layers synergistically form a dynamic self-healing closed loop of iridium dissolution-anchoring-redeposition, with the total Ir loading controlled at 0.20-0.45 mg·cm³. ‑2 This invention balances excellent electrolytic activity under low load with ultra-long-term operational stability, exhibits lower polarization loss across the entire current density range, and shows a voltage decay of only 18mV during 1000-hour constant current testing. Its manufacturing process is compatible with existing spraying production lines, making it suitable for large-scale application in wind-solar coupled hydrogen production electrolyzers.

Description

Technical Field

[0001] This invention relates to the field of proton exchange membrane water electrolysis catalytic electrode technology, specifically to a low-iridium loading multilayer gradient anode catalytic layer structure and its preparation method. Background Technology

[0002] Proton exchange membrane water electrolysis is a green hydrogen production technology adapted to the consumption of new energy sources. The oxygen evolution reaction at the anode is subject to harsh conditions and requires a large amount of iridium-based catalyst. Iridium resources are scarce and expensive. The industry generally adopts a forward-layered catalyst structure with near-membrane highly active iridium particles, a middle core-shell stable catalyst, and an outer nanowire mass transfer network. This structure reduces the amount of iridium used and improves static electrolysis performance by relying on functional layering. However, this structure suffers from a degradation defect that is difficult to eradicate in long-term operation.

[0003] The interface between the proton exchange membrane and the catalyst layer is the region with the highest anodic potential. Current methods place ultrafine nano-iridium oxide in this area. However, the lattice stability of ultrafine particles is poor, and Ir-O bonds are prone to breakage at high potentials, generating soluble iridium oxygen anions. These ions continuously migrate into the membrane under the influence of the electric field and proton permeation, which not only blocks the membrane proton conduction channels and increases ohmic impedance, but also causes irreversible loss of active components from the catalyst layer. At the same time, the ultrafine iridium particles continuously dissolve and recrystallize, undergoing Ostwald ripening, and the active surface area continues to shrink. The middle core-shell support can only delay the degradation, but cannot fundamentally prevent iridium loss.

[0004] Existing forward-layered structures lack gradient defect trapping sites. Dissolved iridium ions either permeate into the membrane or are washed away from the catalyst layer by bubbles and electrolytes, lacking a self-repair mechanism for in-situ recovery and redeposition. This results in unidirectional loss of active components, with particularly significant degradation in low-iridium loading systems. Industry consensus dictates placing highly active catalysts near the membrane to utilize high proton concentrations, but this creates an inherent contradiction: highly active materials come into direct contact with a highly corrosive environment. Reducing the iridium loading on the membrane side increases activation polarization, while maintaining a high iridium loading makes cost control impossible; a balance between these two approaches is difficult to achieve.

[0005] Traditional layering relies solely on static porosity and ionomer gradient optimization for mass transfer and conductivity. Each layer is physically stacked without dynamic self-healing synergistic effects. Multiple degradation factors accumulate over time, making it difficult to simultaneously meet the industrial requirements of low cell voltage and long lifespan under ultra-low iridium loading.

[0006] For the reasons mentioned above, it is necessary to propose a low-iridium-loading multilayer gradient anode catalyst layer structure and its preparation method to solve the above problems. Summary of the Invention

[0007] The purpose of this invention is to address the shortcomings of existing technologies by providing a low-iridium-loading multilayer gradient anode catalyst layer structure and its preparation method.

[0008] To achieve the above objectives, the technical solution of the present invention is as follows: A low-iridium loading multilayer gradient anode catalyst layer structure includes a multilayer gradient structure, wherein the multilayer gradient structure includes at least a first catalytic sublayer, a second catalytic sublayer and a third catalytic sublayer stacked sequentially from one side of the proton exchange membrane outwards; The first catalytic sublayer comprises a nano-iridium oxide catalyst and an ionomer. The second catalytic sublayer comprises a core-shell structured catalyst and an ionomer, wherein the core-shell structured catalyst has an acid-resistant conductive oxide core and an iridium oxide shell. The third catalytic sublayer comprises an iridium oxide nanowire network and an ionomer, and the porosity of the third catalytic sublayer is greater than that of the second catalytic sublayer, which is greater than that of the first catalytic sublayer.

[0009] Clear division of labor in three-layer functional decoupling: First layer: Ultra-small nano IrO2 (3-7nm) → High activity; Second layer: Core-shell supported catalyst → Stability framework; Third layer: Nanowire macroporous network → mass transfer enhancement; The three functional layers are designed with different micro-morphologies / materials.

[0010] Furthermore, the first catalytic sublayer nano-iridium oxide has a grain size of 3-7 nm and a thickness of 0.5-2.0 μm; The thickness of the IrO2 shell in the second catalytic sublayer is 1-3 nm, and the particle size of the core-shell structure catalyst is 20-50 nm. The iridium oxide nanowires in the third catalytic sublayer have a diameter of 10-30 nm and a length of 0.5-3 μm. Open channels with a pore size of 50-200 nm are formed between the nanowires. The thickness of this layer is 1.0-5.0 μm, and the average pore size of the third catalytic sublayer is ≥50 nm.

[0011] Furthermore, the mass fraction of the ionomer in the second catalytic sublayer is 10%-20%, and the mass fraction of the ionomer in the first catalytic sublayer is 18%-25%. The mass fraction of the ionomer in the third catalytic sublayer is 12%-22%. Furthermore, the mass fraction of ionomers in the second catalytic sublayer is lower than that in the first and third catalytic sublayers, in order to reduce charge transfer resistance.

[0012] Furthermore, the acid-resistant conductive oxide core in the second catalytic sublayer is selected from at least one of antimony-doped tin oxide (ATO), titanium oxide (TiO2), titanium suboxide (Ti4O7), and tungsten-doped titanium oxide.

[0013] Furthermore, the first catalytic sublayer contains an Ir loading of 0.10-0.20 mg·cm³.-2 , The second catalytic sublayer contains an Ir loading of 0.05-0.15 mg·cm³. -2 , The third catalytic sublayer contains an Ir loading of 0.03–0.10 mg·cm³. -2 , The total Ir loading of the multilayer gradient anode catalyst layer was controlled between 0.20 and 0.45 mg·cm³. -2 More preferably 0.25-0.35 mg·cm³ -2 .

[0014] All three layers contain Ir but have different morphologies. All three layers use Ir-based materials, but employ three different morphologies: particles, core-shell, and nanowires, forming a continuous Ir conductive network with clearly defined performance characteristics. This differs from the cost-reduction strategy of "using Ir only in the bottom layer and non-precious metals in the top layer."

[0015] Total Ir load: 0.20-0.45 mg / cm³ -2 Performance exceeding 2.0 mg·cm under certain conditions -2 Conventional electrode.

[0016] A method for preparing a low-iridium-loading multilayer gradient anode catalyst layer structure, characterized by comprising the following steps: S1: Prepare a first slurry containing nano-iridium oxide and ionomer, spray it onto one side of the proton exchange membrane, and dry it to form the first catalytic sublayer; S2: Prepare a second slurry containing a core-shell structured catalyst and ionomer, spray it onto the first catalytic sublayer, and dry it; S3: Prepare a third slurry containing iridium oxide nanowires, ionomers and pore-forming agents (such as ammonium carbonate, ammonium bicarbonate, etc.), spray it onto the second catalytic sublayer, dry it and then soak it in water to remove the pore-forming agent, forming a porous third catalytic sublayer.

[0017] Furthermore, the first catalytic sublayer is an Ir-directed anchoring stabilizing sublayer, which comprises a support (a high-defect, acid-resistant, conductive oxide) and nano-iridium oxide catalyst and ionomer, with an Ir loading of 0.03-0.08 mg·cm³. -2 The nano-iridium oxide catalyst is supported on a support, and the surface of the support is provided with inner adsorption sites for capturing Ir ions; it comprises an ultrathin iridium oxide catalyst supported on a high-defect acid-resistant conductive oxide and an ionomer; the support (high-defect acid-resistant conductive oxide) supports the ultrathin iridium oxide catalyst to form a support for an acid-resistant conductive oxide rich in oxygen vacancies and low-valence metal sites, and the surface is covered with a continuous ultrathin iridium oxide shell layer of 1-2 nm thickness; The second catalytic sublayer is a highly active main catalytic sublayer, which includes a doped core-shell heterojunction catalyst and an ionomer. The doped core-shell heterojunction catalyst uses a doped and modified acid-resistant conductive oxide as the core and iridium oxide as the active shell. The Ir loading of the second catalytic sublayer is higher than that of the first and third catalytic sublayers. The third catalytic sublayer has iridium oxide nanowires with outer adsorption sites for capturing Ir ions, and the concentration of the outer adsorption sites is set lower than that of the inner adsorption sites.

[0018] Furthermore, the support for the first catalytic sublayer is selected from at least one of titanium suboxide (Ti4O7), antimony-doped tin oxide (ATO), and tungsten-doped titanium oxide; the concentration of inner adsorption sites (oxygen vacancies) on the support is ≥12 at%, and the concentration of low-valence metal sites (Ti) is ≥12 at%. 3+ / Sb 3+ The atomic percentage is ≥8at%, which has the ability to chemically adsorb and anchor dissolved Ir oxygen-containing anions; the nano-iridium oxide catalyst is a continuous amorphous or microcrystalline IrO2; the shell thickness uniformity deviation is ≤±0.3nm; the dissolution rate of this shell at high anodic potential is reduced by more than 60% compared with 3-7nm nano IrO2 particles.

[0019] The thickness of the first catalytic sublayer is 0.5-1.5 μm, and the mass fraction of the ionomer is 18%-25%, forming a continuous proton conduction interface with the proton exchange membrane.

[0020] The second catalytic sublayer is a doped and modified acid-resistant conductive oxide core selected from at least one of Ru-doped Ti4O7, Co-doped antimony-doped tin oxide, and Nb-doped TiO2, with the doping element atomic ratio being 3%-10%. This allows the core layer and the IrO2 shell to form a lattice-matched epitaxial growth interface with strong electronic interactions, which can optimize the adsorption energy barrier of OER intermediates at the Ir active sites. The thickness of the IrO2 active shell is 1-3 nm, and the overall particle size of the catalyst is 20-50 nm. The intrinsic mass activity of the catalyst is more than 80% higher than that of the core-shell catalyst supported by pure inert oxide.

[0021] The thickness of the second catalytic sublayer is 1.0-3.0 μm, and the mass fraction of the ionomer is 10%-20%, which is lower than that of the first and third catalytic sublayers, in order to reduce charge transfer resistance.

[0022] The concentration of oxygen vacancies at the outer adsorption sites on the surface of the iridium oxide nanowires in the third catalytic sublayer is 3-8 at.

[0023] The surface-weakly defective iridium oxide nanowires have a diameter of 10-30 nm and a length of 0.5-3 μm; the oxygen vacancy concentration on the nanowire surface is 3-8 at%, which is lower than the defect concentration of the first catalytic sublayer support, and it has both gas-liquid mass transfer channel and Ir ion-assisted capture function.

[0024] Nanowires interlock to form a three-dimensional continuous network, creating open, through-hole channels with a pore size of 50-200 nm; the third catalytic sublayer has a porosity of 50%-65% and a thickness of 1.0-5.0 μm.

[0025] The third catalytic sublayer has an ionomer mass fraction of 12%-22%. The ionomer only coats the surface of the nanowires, does not block the pores, and ensures smooth gas-liquid mass transfer.

[0026] Furthermore, the mass ratio of Ir loading in the first catalytic sublayer, the second catalytic sublayer, and the third catalytic sublayer is 1:(1.5-3.0):(0.5-1.2), so that the distribution of Ir loading in each layer forms a distribution configuration with high loading in the middle layer and low loading in the two side layers.

[0027] The advantages and beneficial effects of this invention are as follows: 1. Balancing ultra-low iridium loading with excellent static electrolysis performance. This scheme employs an inverted layered design with a doped core-shell heterojunction main catalytic layer. It leverages strong metal-oxide electron interactions to enhance intrinsic OER activity, compensating for the three-phase interface loss caused by reduced iridium loading in the near-film layer. The total iridium loading is only 0.20-0.45 mg·cm³. -2 The cell voltage across the entire current density range is lower than that of traditional high-iridium monolayer electrodes and monolayer catalytic electrodes with the same loading. There is no obvious mass transfer polarization inflection point under high current, which greatly reduces electrolysis energy consumption and precious metal raw material costs.

[0028] 2. A bidirectional gradient anchoring system is constructed to achieve dynamic self-repair and long-term stability of the catalyst layer. The high-defect support with high-density oxygen vacancies in the near-membrane layer can deeply capture iridium ions migrating to the membrane, while the weak defect sites of the outer nanowires assist in intercepting iridium species escaping outward. Dissolved iridium is redeposited in situ to replenish active sites, breaking the industry rule that the catalyst layer will inevitably decay during operation. The voltage decay in the 1000-hour durability test is only 18 mV, and the amount of iridium lost across the membrane is greatly reduced, significantly extending the service life of the membrane electrode.

[0029] 3. Compatible with existing preparation processes, achieving simultaneous and synergistic improvement of multiple properties. The overall process adopts a step-by-step spray coating process, eliminating the need for additional complex preparation steps. The three layers retain the gradient advantages of a high proton conduction interface, a low-impedance conductive framework, and highly interconnected mass transfer channels, simultaneously resolving the inherent trade-offs between activity, stability, and mass transfer. There is no defect where a single performance improvement is accompanied by the degradation of other performances, making it suitable for large-scale industrial production. Attached Figure Description

[0030] Figure 1 This is a performance comparison of the electrolytic polarization curves of the proton exchange membrane electrolyzer membrane electrode in Scheme 1. Figure 2This is a performance comparison of the electrolytic polarization curves of the proton exchange membrane electrolyzer membrane electrode in Scheme 2. Detailed Implementation

[0031] The specific embodiments of the present invention will be further described below with reference to examples. These examples are only used to more clearly illustrate the technical solutions of the present invention and should not be construed as limiting the scope of protection of the present invention.

[0032] Option 1: A low-iridium loading multilayer gradient anode catalytic layer structure is a three-layer continuous functionalized structure stacked from the proton exchange membrane side to the outside, consisting of a first catalytic sublayer, a second catalytic sublayer, and a third catalytic sublayer. The structure follows a design with increasing porosity gradient, i.e., the porosity of the third catalytic sublayer is greater than that of the second catalytic sublayer, and the porosity of the second catalytic sublayer is greater than that of the first catalytic sublayer. Through differentiated design of the three-layer microstructure, material system, and component parameters, complete functional decoupling and precise division of labor are achieved in catalytic activity, structural stability, and gas-liquid mass transfer performance.

[0033] The first catalytic sublayer employs ultrafine iridium oxide nanoparticles with a grain size of 3-7 nm, combined with an ionomer system containing 18%-25% by mass, with a layer thickness controlled at 0.5-2.0 μm. Leveraging the high specific surface area of ​​the ultrafine nanoparticles, a sufficient three-phase reaction interface is constructed in the region closest to the proton exchange membrane, where the proton concentration is highest, ensuring high initial oxygen evolution activity of the entire catalytic layer. The iridium loading in this layer is controlled at 0.10-0.20 mg·cm³. -2 This provides the core active basis for the overall catalytic reaction.

[0034] The middle second catalytic sublayer employs a core-shell structure catalyst with an acid-resistant conductive oxide core and an iridium oxide shell. Acid-resistant conductive materials such as antimony-doped tin oxide (ATO), titanium oxide (TiO2), titanium suboxide (Ti4O7), and tungsten-doped titanium oxide can be selected as the core, paired with an ultrathin iridium oxide shell layer with a thickness of 1-3 nm. The overall particle size of the catalyst is controlled at 20-50 nm. Simultaneously, the ionomer mass fraction of this layer is adjusted to 10%-20%, lower than the ionomer content of the upper and lower layers, effectively reducing the overall charge transfer impedance of the catalytic layer. The iridium loading of this layer is set to 0.05-0.15 mg·cm³. -2 It relies on a stable core-shell framework structure to provide mechanical support for the overall catalyst layer and long-term corrosion resistance and stability, thus avoiding the defects of easy agglomeration and easy dissolution of ultrafine nano-iridium particles.

[0035] The outermost third catalytic sublayer employs an iridium oxide nanowire network structure with a diameter of 10-30 nm and a length of 0.5-3 μm. Open, interconnected channels with a pore size of 50-200 nm are constructed by adding pore-forming agents such as ammonium carbonate, resulting in an average pore size of no less than 50 nm. The layer thickness is controlled at 1.0-5.0 μm, achieving the highest porosity among the three-layer structure. Combined with 12%-22% by mass of ionomer, which coats the nanowire surface without clogging the channels, this significantly optimizes oxygen bubble desorption and electrolyte transport during the anodic reaction, overcoming the mass transfer bottleneck at high current densities. The iridium loading in this layer is controlled at 0.03-0.10 mg·cm³. -2 .

[0036] This scheme constructs a three-layer structure, with each layer forming a continuous iridium conductive network based on three different micromorphologies: nanoparticles, core-shell particles, and nanowires. Unlike the industry's conventional cost-reduction modification approach of "iridium-based bottom layer and non-precious metal top layer," this scheme reduces the overall iridium loading to 0.20-0.45 mg·cm³ while ensuring the intrinsic corrosion resistance and activity of the catalytic system without the use of low-cost non-precious metal substitutes throughout the entire process. -2 And it can be further controlled within 0.25-0.35 mg·cm⁻¹. -2 Leveraging the synergistic effect of multi-layer gradient functions, it achieves significantly higher iridium loading than the traditional 1.0 mg·cm³. -2 The above describes the oxygen evolution performance of a high-iridium-loading monolayer catalytic electrode.

[0037] The scheme adopts a step-by-step spray coating process, which sequentially prepares a nano-iridium oxide slurry for spray coating to form the first catalytic sublayer, prepares a core-shell catalyst slurry for spray coating to form the second catalytic sublayer, and prepares an iridium oxide nanowire slurry containing a pore-forming agent for spray coating and then soaks in water to remove the pore-forming agent to form a porous third catalytic sublayer. The process is controllable and suitable for large-scale preparation.

[0038] Example 1: The preparation of a multilayer anode catalyst layer involves the following steps: First catalytic sublayer slurry: IrO2 nanoparticles (approximately 5 nm in diameter) prepared by the Adams melt method were mixed with a Nafion (perfluorosulfonated tetrafluoroethylene copolymer (PFSA)) ionomer solution at a mass ratio of IrO2 to ionomer of 80:20. The solvent was isopropanol / water, and the mixture was ultrasonically dispersed until uniform. This mixture was then sprayed onto an N115 membrane and dried to obtain an Ir loading of 0.15 mg·cm³. -2 The first catalytic sublayer is approximately 1.2 μm thick.

[0039] The second catalytic sublayer slurry: An IrO2 / ATO core-shell catalyst (ATO particle size approximately 30 nm, IrO2 shell thickness approximately 2 nm, Ir mass fraction approximately 35%) was prepared using a deposition-precipitation method. This catalyst was mixed with Nafion ionomer at a mass ratio of 85:15 to prepare a slurry, which was then sprayed onto the first layer and dried to obtain an Ir loading of 0.12 mg·cm³. -2 A second catalytic sublayer with a thickness of approximately 2.0 μm.

[0040] The third catalytic sublayer slurry was prepared by hydrothermal synthesis of IrO2 nanowires (approximately 15 nm in diameter and 1-2 μm in length). It was mixed with Nafion ionomer (82:18 by mass) and ammonium carbonate pore-forming agent (15% by solid mass) to form a slurry, which was then sprayed onto the second layer. After drying, the pore-forming agent was removed by immersion in an 80°C water bath for 2 hours, resulting in a third catalytic sublayer with approximately 55% porosity, an average pore size of 80 nm, and a thickness of approximately 3 μm, with an Ir loading of 0.08 mg·cm³. -2 .

[0041] The total Ir loading of the resulting anode catalyst layer was 0.35 mg·cm³. -2 The cathode uses commercially available Pt / C (0.3 mg Pt·cm⁻¹). -2 Assemble a single electrolytic cell and test it under 80°C and normal pressure conditions.

[0042] Comparative Example 1 (Conventional High Loading): Direct spraying of IrO2 nanoparticle monolayer anode, Ir loading 1.0 mg·cm³ -2 The ionomer content was 22%, and other conditions were the same as in Example 1.

[0043] Comparative Example 2 (same as low-loading monolayer catalyst): Monolayer anodes were prepared using only IrO2 / ATO core-shell catalysts, with an Ir loading of 0.35 mg·cm⁻¹. -2 The ionomer content is 15%.

[0044] As shown in Table 1, Example 1 achieves a current density of 1.4 A·cm⁻¹ at 1.6 V. -2 It exceeds 0.8 A·cm in Comparative Example 1. -2 And 0.6 A·cm of Comparative Example 2 -2 At 2.0 A·cm -2 At the specified current density, the tank voltage in Example 1 is only 1.67 V, while that in Comparative Example 1 is 1.85 V and that in Comparative Example 2 is 2.03 V. This demonstrates that the present invention achieves superior performance at extremely low Ir loads.

[0045] 0 0 0 0 0.1 1.43 1.44 1.45 0.2 1.46 1.48 1.49 0.4 1.5 1.53 1.55 0.6 1.53 1.57 1.61 0.8 1.55 1.61 1.66 1 1.57 1.64 1.71 1.2 1.59 1.68 1.76 1.4 1.61 1.72 1.82 1.6 1.63 1.76 1.88 1.8 1.65 1.8 1.95 2 1.67 1.85 2.03 2.2 1.7 1.9 2.12 2.4 1.73 1.95 2.23 2.6 1.76 2.01 2.35 2.8 1.8 2.08 2.49 3 1.84 2.15 2.6 Table 1. Polarization curve data for Scheme 1 (80℃, ambient pressure, cathode Pt / C 0.3 mgPt·cm⁻¹)-2 ) Option 2: This solution further improves and upgrades the aforementioned solution by constructing an inverted three-layer catalytic structure with iridium ion directional anchoring and dynamic self-healing functions. It still has the three-layer stacked architecture of the aforementioned solution, and performs functional reconstruction, defect site modification, and inverted iridium loading distribution on each layer to solve the industry problems of iridium ion dissolution and migration, transmembrane loss, and activity decay during long-term operation of the aforementioned solution. In the upgraded structure, the original highly active near-film first catalytic sublayer has been reconstructed into an iridium-directed anchoring stabilizing sublayer, replacing the traditional "high" loading ultrafine iridium particle design. Instead, a composite structure with a high-defect, acid-resistant, conductive oxide (i.e., support) supporting an ultrathin iridium oxide layer has been adopted. The support consists of titanium suboxide, antimony-doped tin oxide, and tungsten-doped titanium oxide. Through lattice defect modification, the support surface is made to form oxygen vacancies with a concentration of not less than 12 at% and low-valence metal sites (i.e., adsorption sites) of not less than 8 at%, constituting high-density inner iridium ion adsorption anchoring points. The support surface is coated with a continuous ultrathin iridium oxide shell with a thickness of 1-2 nm and a thickness uniformity deviation of no more than ±0.3 nm, significantly reducing the iridium material dissolution rate and lowering its iridium loading to 0.03-0.08 mg·cm³. -2 The layer thickness is controlled at 0.5-1.5μm, while maintaining a high ionomer content of 18%-25% to ensure proton conduction at the membrane interface. Because the layer has internal adsorption sites, it can capture dissolved iridium oxygen anions that migrate to the membrane side under anodic conditions, preventing permanent loss of iridium ions across the membrane.

[0046] This scheme reconstructs the original stabilizing second catalytic sublayer into a highly active main catalytic sublayer, becoming the core reaction region with the highest iridium loading in the three-layer structure. The iridium loading is increased and satisfies the inverted distribution characteristic of a mass ratio of iridium loading of 1:(1.5-3.0):(0.5-1.2) between the first, second, and third catalytic sublayers, with a high loading in the middle and low loading on both sides. This layer abandons the traditional inert core-shell support and adopts a doped modified acid-resistant oxide core consisting of Ru-doped Ti4O7, Co-doped antimony-doped tin oxide, and Nb-doped TiO2. The atomic percentage of the doped elements is controlled within a certain range. With a content of 3%-10%, the core and the 1-3nm thick iridium oxide active shell form a lattice-matched epitaxial growth structure with strong electronic interactions, effectively optimizing the adsorption energy barrier of oxygen evolution reaction intermediates at the iridium active sites. This increases the intrinsic catalytic activity by more than 80% compared to conventional inert core-shell catalysts, while retaining a low ionomer content of 10%-20% to maintain low charge transfer resistance. The layer thickness is controlled at 1.0-3.0μm. By placing the main active region later, the strong electric field corrosion environment near the film side is avoided, and the dissolution and ripening rate of highly active iridium sites is significantly reduced.

[0047] The third catalytic sublayer in the upgraded structure undergoes weak defect modification based on the original high-porosity mass transfer nanowire network. Low-density oxygen vacancies with a concentration of 3-8 at% are constructed on the surface of the iridium oxide nanowires as auxiliary adsorption sites for iridium ions on the outside (outer adsorption sites). The concentration of the outer sites is significantly lower than that of the inner anchoring sites in the first catalytic sublayer. Under the premise of excellent mass transfer characteristics with a wire diameter of 10-30 nm, a wire length of 0.5-3 μm, a macroporous structure of 50-200 nm, a high porosity of 50%-65%, and an ionomer ratio of 12%-22%, the iridium oxide nanowire network achieves the auxiliary capture of a small number of iridium ions diffusing to the outside, forming a two-way iridium ion protection system with strong inner anchoring and auxiliary outer interception. The overall upgraded structure relies on a three-layer differentiated defect site design and inverted loading distribution to form a complete dynamic self-repairing closed loop of "iridium dissolution and migration - fixed-point anchoring - in-situ redeposition". It reverses the negative phenomenon of iridium dissolution under normal operating conditions and transforms it into a positive mechanism for the self-replenishment of active sites. Under the premise of low loading, high activity and excellent mass transfer, it solves the problem of continuous activity decay of traditional layered catalyst layers during long-term operation.

[0048] Traditional layered structures typically place the catalyst layer with the highest activity and highest iridium loading on the side immediately adjacent to the proton exchange membrane. Although this region has the best proton conduction conditions, it is also the region with the highest anodic electric field strength, the strongest potential polarization, and the most severe electrolyte corrosion. This makes the highly active ultrafine iridium particles extremely prone to lattice oxidation, dissolution, migration, and Ostwald ripening. The inevitable cost of high activity is rapid decay and iridium transmembrane loss, forming a technical bottleneck of "mutual constraint between activity and stability" that has been difficult to overcome in this field for a long time. Therefore, this second scheme reverses the three-layer functional logic and iridium distribution logic. Instead of pursuing the optimal superposition of static layer performance, it constructs a "stable anchoring, active gradient mass transfer" coupling system adapted to the dynamic operating conditions of electrolysis. By placing the highly active main catalytic region in the middle layer region (second catalytic sublayer) where the electric field stress is mild and the proton and electron conduction is balanced, it avoids near-membrane strong electric field corrosion damage. At the same time, a high-density defect anchoring interface is constructed in the first layer on the membrane side, and a low-density auxiliary defect trapping interface is constructed in the outermost third layer. Through the gradient design of differentiated defect sites (adsorption sites) in the inner and outer double layers, a two-way binding system is formed for dissolved and escaped iridium ions, with strong inner anchoring and auxiliary outer interception. By utilizing the controllable interlayer defect gradient, iridium loading inversion gradient, and pore mass transfer gradient in synergy, the "iridium dissolution and migration" which is a failure mechanism in traditional processes is transformed into a usable "dynamic active site self-repair mechanism". This solves the technical problems of insufficient activity, poor stability, and severe long-term decay under low iridium loading from the structural root.

[0049] This scheme possesses a complete and closed-loop dynamic working process under long-term operation of PEM water electrolysis, unlike the traditional working mode where the catalyst layer relies solely on a static structure to perform its function. During the normal oxygen evolution reaction in the electrolyzer, the highly active doped core-shell heterojunction catalyst in the middle layer undertakes the majority of the oxygen evolution reaction. Because this layer is separated from the membrane-side strong electric field region by a first catalytic sublayer, the overall structural stability is greatly improved. However, under continuous anodic polarization, trace amounts of iridium species will still dissolve, generating soluble iridium oxygen anions, which migrate vertically under the combined drive of the electric field and proton percolation. Iridium ions migrating towards the proton exchange membrane directly contact the high-density oxygen vacancies and low-valence metal defect sites on the first layer surface. These defect sites possess strong chemisorption binding properties, rapidly capturing free iridium ions and fixing them to the membrane-side interface region. Under continuous anodic potential, they are re-oxidized and deposited in situ, forming new ultrafine iridium oxide active sites, continuously replenishing and repairing the catalytic activity near the membrane interface. Meanwhile, a small number of iridium ions escaping towards the outer gas diffusion layer are captured by the low-density defect sites on the surface of the third catalytic sublayer nanowires, preventing physical loss of iridium due to bubble shedding or electrolyte scouring. As electrolysis continues, the trace amounts of iridium dissolved in the intermediate layer continuously migrate to the upper and lower layers and are anchored and redeposited, forming a continuous, spontaneous, and closed-loop process of active site regeneration and structural repair. This ensures that the number of active sites, interfacial contact state, and pore mass transfer structure of the entire catalytic layer can maintain an optimal state for a long time, changing the inherent working law of traditional iridium-based catalytic layers that "decline as soon as it starts operating."

[0050] Based on the aforementioned inverted functional reconstruction and dynamic self-repair mechanism, this solution breaks through the technical bias in the field. While actively reducing the relatively high-activity iridium loading on the near-membrane side, seemingly sacrificing initial activity, it achieves the reverse technical effect of maintaining the initial activity of the catalytic layer and significantly improving long-term stability. This solution completely offsets the negative impact of the reduced loading through the intermediate high-activity layer's central gain and self-repair compensation for interlayer defects, achieving performance parity or even improvement. Secondly, this invention achieves decoupled and simultaneous improvement of activity and stability in a low-iridium loading system, breaking through the industry-recognized performance trade-off, while maintaining a total iridium loading of 0.20-0.45 mg·cm³. -2 The ultra-low iridium loading significantly reduces the transmembrane ion loss rate, and the voltage decay rate during long-term operation is much lower than that of conventional layered structures, thus completely solving the technical problem of poor stability caused by low iridium loading.

[0051] This solution achieves positive feedback of dynamic self-repair of the catalyst layer. Traditional catalyst layers have a continuous decrease in active sites and a continuous deterioration of structure as the operating time increases. However, with the increase of the operating time, the active sites anchored and redeposited in this solution are continuously replenished, and the three-phase reaction structure of the interface becomes more and more stable, showing a reverse trend of "long-term operating performance without decay or even slightly improved".

[0052] Example 2: First, a high-defect Ti4O7 support was prepared. Commercially available Ti4O7 powder was placed in a tube furnace and subjected to reduction etching at 520°C for 1.5 hours in a 10% hydrogen-argon mixed atmosphere, yielding a surface oxygen vacancy concentration of 14 at% and Ti 3+ A high-defect support with a low-valence metal site ratio of 9 at% was used. A uniform, continuous IrO2 ultrathin shell layer of 1.5 nm thickness was then coated onto the support surface using atomic layer deposition to obtain the anchored composite catalyst required for the first catalytic sublayer. This catalyst was then mixed with Nafion ionomer at a solid-to-mass ratio of 82:18 to prepare a first slurry. After ultrasonic dispersion, the slurry was sprayed onto the surface of an N115 proton exchange membrane and dried at 80°C to form a 1.0 μm thick Ir catalyst with an Ir loading of 0.06 mg·cm³. -2 The first anchoring and stabilizing sublayer was then prepared. Subsequently, a Ru-doped Ti4O7 core-based doped core-shell heterojunction catalyst was prepared. Ti4O7 particles with a Ru doping atom content of 6% and a particle size of 30 nm were hydrothermally synthesized. A 2 nm IrO2 active shell was grown in situ using thermal oxidation, resulting in an overall Ir mass fraction of 36%. This core-shell catalyst was mixed with Nafion ionomer at a mass ratio of 86:14 to prepare a second slurry, which was sprayed onto the surface of the first sublayer and dried to obtain a thickness of 2.2 μm and an Ir loading of 0.16 mg·cm³. -2 The intermediate highly active main catalytic sublayer naturally exhibits an iridium loading ratio of 1:2.67:1.17, with a high central ratio and low iridium loading on both sides. Finally, the hydrothermally synthesized original IrO2 nanowires were subjected to mild reduction modification at 260℃ under a low-concentration hydrogen atmosphere for 30 minutes, resulting in weak defect adsorption sites with an oxygen vacancy concentration of 6 at% on the nanowire surface. The nanowires had a diameter of 15 nm and a length of 1.5 μm. A third slurry was prepared by mixing the modified nanowires, Nafion ionomer, and ammonium carbonate pore-forming agent at a solid mass ratio of 83:17:15. After spraying and molding, the slurry was immersed in an 80℃ water bath for 2 hours to completely remove the pore-forming agent, yielding a thickness of 3 μm, a porosity of 56%, an average pore size of 80 nm, and an Ir loading of 0.07 mg·cm³. -2 The third auxiliary anchoring mass transfer sublayer has a total iridium loading of 0.29 mg·cm³. -2 The cathode uniformly adopts commercially available 0.3mgPt·cm -2 After assembling a single electrolytic cell with a Pt / C catalyst layer, steady-state polarization performance and 1000-hour constant-current accelerated durability tests were conducted under controlled conditions of 80℃ and atmospheric pressure. Three sets of control samples were set up for comparative performance. Comparative Example 3: A conventional single-layer high-iridium catalyst layer with an Ir loading of 1.0 mg·cm³. -2 Only a single 5nm IrO2 nanoparticle combined with 22% ionomer is sprayed and formed. Comparative Example 4: Based on Scheme 1, it consists of a three-layer gradient catalytic layer, namely, a positively positioned highly active near-membrane structure, defect-free anchoring modification, and a doped heterogeneous core-shell catalyst, with a total Ir loading of 0.35 mg·cm³. -2 , Comparative Example 5: A single-layer doped core-shell catalyst with the same total iridium loading, using only a Ru-doped Ti4O7@IrO2 catalyst for single-layer spraying, with a total Ir loading of 0.29 mg·cm³. -2 All other test assembly, temperature, electrolyte, gas pressure and other external conditions were kept completely consistent with those in Example 2 to eliminate the interference of external variables on the performance comparison.

[0053]

[0054] Table 2. Polarization curve data for the scheme (80℃, ambient pressure, cathode Pt / C 0.3 mgPt·cm⁻¹) -2 ) As shown in Table 2, Figure 2 As shown, the steady-state polarization test recorded values ​​from 0 to 3.0 A·cm throughout the entire process. -2 Slot voltage data corresponding to current density across the entire range; within the low current density activation control range, 0.1 A·cm. -2 Under operating conditions, the tank voltage in Example 2 is 1.43V, which is almost the same as the initial potential of Scheme 4 (Comparative Example 4) and the conventional high-load single-layer comparative example 3 (0.8A·cm). -2 In Example 2, the cell voltage was 1.54V, a decrease of 70mV compared to 1.61V in Comparative Example 3, and 130mV lower than 1.67V in Comparative Example 5 with the same iridium loading. Within this range, it achieved an activation polarization level nearly identical to the basic three-layer scheme 1, overturning the conventional wisdom that "reducing iridium loading near the membrane and removing ultrafine highly active particles would degrade low-current activation performance." The core reason is that the intermediate-layer doped core-shell heterojunction catalyst exhibits strong metal-oxide electron interactions, significantly enhancing intrinsic oxygen evolution activity and completely compensating for the three-phase interface loss caused by the reduced iridium loading in the near-membrane layer. Simultaneously, the gradient distribution of ionomers in each layer constructs a continuous proton transport pathway, preventing proton conduction blockage. (The last sentence appears to be incomplete and possibly refers to a specific temperature range: 1.0 to 2.0 A·cm⁻¹). -2 The ohmic activation mixing control range shows that the performance advantages of Scheme 2 and Example 2 continue to expand, 2.0 A·cm -2The bottom voltage is only 1.65V, which is 200mV lower than that of the traditional high-load single-layer electrode in Comparative Example 3. Compared with the 1.67V of the basic three-layer structure in Comparative Example 4, it still has a slight improvement of 20mV. Compared with the 2.05V of the single-layer core-shell electrode with the same load in Comparative Example 5, it has an advantage of 400mV. The lower ionomer content in the middle layer effectively reduces the overall charge transfer impedance. The integrated iridium-based particles, core-shell, and nanowire three-dimensional conductive network continuously ensures rapid electron conduction. At the same time, the three-layer gradient porous structure gradually disperses the electrolyte and oxygen, preventing the phenomenon of interlayer bubble accumulation that increases ohmic loss. (2.0 to 3.0 A·cm) -2 High current mass transfer control range, Example 2: 3.0 A·cm -2 The tank voltage is only 1.81V, and the voltage rises with increasing current at a gentle slope, with no obvious mass transfer polarization inflection point. Comparative Example 3 shows a high-load monolayer electrode at 3.0 A·cm. -2 The voltage reaches 2.15V. In Scheme 1, the basic three-layer structure has a voltage of 1.84V under the same current. The single-layer low-iridium comparative example 5 achieves 2.2A·cm. -2 The voltage spiked dramatically, making it impossible to maintain a stable high current output. In Scheme Two, the third layer of modified nanowires retains the original 50-200nm large through-holes, and the low-density defect sites on the surface do not block the mass transfer channels. The bubble desorption efficiency remains at the same high level as the basic mass transfer layer in Scheme One. Simultaneously, the inner and outer double-layer defect anchoring structure reduces pore blockage and interface structure degradation caused by iridium ion loss. After long-term operation, the mass transfer performance degradation is significantly lower than other control samples. Under a constant voltage of 1.80V, Scheme Two can output 2.92A·cm⁻¹. -2 The limiting current density is higher than that of Scheme 1 (2.80 A·cm). -2 Comparative Example 3: 1.80A·cm -2 Compared with Comparative Example 5, 1.42A·cm -2 Further breakthroughs have been achieved in limiting electrolysis performance under ultra-low total iridium loading conditions.

[0055]

[0056] Table 3. Summary of voltage changes at the 1000h durability endpoint Aside from the static performance advantages of steady-state polarization, the most crucial and unexpected technical effect of Scheme 2, which distinguishes it from all existing conventional layered structures, is concentrated in its ability to maintain a constant current of 1A·cm for 1000 hours. -2The accelerated durability test results are shown in Table 3. Traditional single-layer high-iridium comparative example 3 exhibited continuous monotonic decay throughout the entire test, with an overall voltage increase of 230mV after 1000 hours of operation. While the stability of the three-layer upright catalyst layer in Scheme 1 was better than the single-layer structure, it still showed continuous decay, with a total voltage increase of 120mV. Single-layer core-shell comparative example 5 with the same loading showed the most severe decay, with a voltage increase of 310mV. In contrast, in Example 2, the cell voltage remained stable with no significant increase during the first 400 hours of operation. From 400 to 800 hours, the voltage decreased slightly by about 12mV, and from 800 to 1000 hours, only a slight rebound occurred. Finally, at the 1000-hour mark, the voltage increased by only 18mV compared to the initial state, showing an overall trend of initial stability followed by a slight decrease. The unconventional trend of slow, slight decline after the initial increase in activity stems from the unique dynamic self-repairing closed-loop mechanism of Scheme 2. Iridium oxygen-containing anions, which are slightly dissolved in the middle main catalytic layer, migrate to both sides under the drive of the electric field. The high-concentration oxygen vacancies and low-valence metal sites in the first layer near the membrane quickly capture the iridium ions diffusing towards the membrane side, and generate new IrO2 active sites through in-situ oxidation and deposition, replenishing the catalytic sites lost at the near-membrane interface. The low-density defect sites on the surface of the outer nanowires help intercept a small number of iridium species escaping outward, preventing iridium from being permanently lost with the erosion of bubbles. During continuous operation, new three-phase reaction interfaces are constantly generated, offsetting the activity decline caused by normal catalyst dissolution, and even improving the overall catalytic activity in stages.

[0057] Based on all the test data, it is clear that Scheme 2, with a lower total iridium loading than the basic three-layer structure of Scheme 1, has slightly better steady-state polarization performance across the entire current range than the basic three-layer scheme. At the same time, it achieves ultra-long cycle stability that none of the existing control samples can achieve. It also utilizes the conventional failure mechanism of iridium dissolution to construct a dynamic self-healing system, thereby simultaneously improving four performance dimensions: catalytic activity, charge transport, gas-liquid mass transfer, and long-term stability.

[0058] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A low-iridium loading multilayer gradient anode catalyst layer structure, characterized in that, It includes a multilayer gradient structure, wherein the multilayer gradient structure includes at least a first catalytic sublayer, a second catalytic sublayer and a third catalytic sublayer stacked sequentially from one side of the proton exchange membrane outward; The first catalytic sublayer comprises a nano-iridium oxide catalyst and an ionomer. The second catalytic sublayer comprises a core-shell structured catalyst and an ionomer, wherein the core-shell structured catalyst has an acid-resistant conductive oxide core and an iridium oxide shell. The third catalytic sublayer comprises an iridium oxide nanowire network and an ionomer, and the porosity of the third catalytic sublayer is greater than that of the second catalytic sublayer, which is greater than that of the first catalytic sublayer.

2. The low-iridium loading multilayer gradient anode catalyst layer structure according to claim 1, characterized in that, The first catalytic sublayer, iridium oxide nanoparticles, has a grain size of 3-7 nm and a thickness of 0.5-2.0 μm. The thickness of the IrO2 shell in the second catalytic sublayer is 1-3 nm, and the particle size of the core-shell structure catalyst is 20-50 nm. In the third catalytic sublayer, the iridium oxide nanowires have a diameter of 10-30 nm and a length of 0.5-3 μm. Open channels with a diameter of 50-200 nm are formed between the nanowires, and the thickness of this layer is 1.0-5.0 μm.

3. The low-iridium loading multilayer gradient anode catalyst layer structure according to claim 1, characterized in that, The mass fraction of ionomers in the second catalytic sublayer is 10%-20%, and the mass fraction of ionomers in the first catalytic sublayer is 18%-25%. The mass fraction of the ionomer in the third catalytic sublayer is 12%-22%. Furthermore, the mass fraction of ionomers in the second catalytic sublayer is lower than that in the first and third catalytic sublayers.

4. The low-iridium loading multilayer gradient anode catalyst layer structure according to claim 1, characterized in that, The acid-resistant conductive oxide core in the second catalytic sublayer is selected from at least one of antimony-doped tin oxide, titanium oxide, titanium suboxide, and tungsten-doped titanium oxide.

5. The low-iridium loading multilayer gradient anode catalyst layer structure according to claim 1, characterized in that, The first catalytic sublayer has an Ir loading of 0.10-0.20 mg·cm³. -2 , The second catalytic sublayer contains an Ir loading of 0.05-0.15 mg·cm³. -2 , The third catalytic sublayer contains an Ir loading of 0.03–0.10 mg·cm³. -2 , The total Ir loading of the multilayer gradient anode catalyst layer was controlled between 0.20 and 0.45 mg·cm³. -2 .

6. The low-iridium loading multilayer gradient anode catalyst layer structure according to claim 1, characterized in that, The first catalytic sublayer includes a support and a nano-iridium oxide catalyst and an ionomer, wherein the nano-iridium oxide catalyst is supported on the support and the surface of the support is provided with inner adsorption sites for capturing Ir ions. The second catalytic sublayer comprises a doped core-shell heterojunction catalyst and an ionomer. The doped core-shell heterojunction catalyst has a doped modified acid-resistant conductive oxide as the core and iridium oxide as the active shell. The Ir loading of the second catalytic sublayer is higher than that of the first and third catalytic sublayers. The third catalytic sublayer has iridium oxide nanowires with outer adsorption sites for capturing Ir ions, and the concentration of the outer adsorption sites is set lower than that of the inner adsorption sites.

7. The low-iridium loading multilayer gradient anode catalyst layer structure according to claim 6, characterized in that, The support for the first catalytic sublayer is selected from at least one of titanium suboxide, antimony-doped tin oxide, and tungsten-doped titanium oxide; the concentration of inner adsorption sites on the support is ≥12at%, and the proportion of low-valence metal sites is ≥8at%; the nano-iridium oxide catalyst is a continuous microcrystalline IrO2. The second catalytic sublayer has an acid-resistant conductive oxide core that is doped and modified by selecting at least one of Ru-doped Ti4O7, Co-doped antimony-doped tin oxide, and Nb-doped TiO2, with the doping element atomic ratio being 3%-10%; thus forming a lattice-matched epitaxial growth interface between the core layer and the IrO2 shell layer. The concentration of adsorption sites on the outer side of the iridium oxide nanowire surface in the third catalytic sublayer is 3-8 at.

8. The low-iridium loading multilayer gradient anode catalyst layer structure according to claim 7, characterized in that, The mass ratio of Ir loading in the first catalytic sublayer, the second catalytic sublayer, and the third catalytic sublayer is 1:(1.5-3.0):(0.5-1.2), so that the distribution of Ir loading in each layer forms a distribution configuration with high loading in the middle layer and low loading in the two side layers.

9. A method for preparing the low-iridium loading multilayer gradient anode catalyst layer structure according to any one of claims 1-6, characterized in that, Includes the following steps: S1: Prepare a first slurry containing nano-iridium oxide and ionomer, spray it onto one side of the proton exchange membrane, and dry it to form the first catalytic sublayer; S2: Prepare a second slurry containing a core-shell structured catalyst and ionomer, spray it onto the first catalytic sublayer, and dry it; S3: Prepare a third slurry containing iridium oxide nanowires, ionomers and pore-forming agents, spray it onto the second catalytic sublayer, dry it and then soak it in water to remove the pore-forming agent, forming a porous third catalytic sublayer.

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