Nano-networked iridium oxide, preparation method and proton exchange membrane membrane electrode

Abstract

The application discloses a nano-network iridium oxide, a preparation method and a proton exchange membrane membrane electrode. The preparation method comprises the following steps: mixing an iridium source and two-dimensional carbon nanosheets uniformly in a solvent, adjusting the pH of the solution to 9-10 to obtain an iridium precursor; grinding and mixing the iridium precursor with a nitrate to obtain a mixed powder; and performing heat treatment on the mixed powder in an oxidizing atmosphere, and cleaning to obtain the iridium oxide catalyst. The prepared iridium oxide catalyst is a pure iridium oxide network without a carbon carrier. The iridium oxide provides a through electron conduction path and a porous mass transfer channel on a macroscopic scale, avoids the problem of interruption of the conduction path caused by the increase of the particle spacing and the decrease of the contact points of the traditional granular catalyst at a low load, maximizes the active site density of the unit mass catalyst, and realizes low iridium load under the premise of ensuring high activity and high stability when the catalyst is used for a proton exchange membrane membrane electrode.

Description

Technical Field

[0001] This application relates to the field of electrochemical technology, and in particular to a nano-network iridium oxide, its preparation method, and a proton exchange membrane electrode. Background Technology

[0002] Proton exchange membrane (PEM) electrolysis is a novel electrochemical technology. The membrane electrode assembly (MEA) is one of the core components of a PEM electrolyzer, and it can be applied to various scenarios when paired with different electrocatalysts. For example, when the anode and cathode are the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), respectively, it can be used for water electrolysis to produce hydrogen and electrochemical humidity control; when the anode and cathode are the oxygen reduction reaction (ORR) and oxygen evolution reaction, respectively, it can be used for electrochemical oxygen removal. Both the OER and ORR reactions involve four complex electron transfer and proton coupling processes, exhibiting slow kinetics, high overpotentials, and dependence on noble metal catalysis. In particular, current research indicates that iridium and its oxides are the only effective OER catalysts for the OER reaction.

[0003] To ensure the activity and stability of PEM electrolysis, MEAs are typically coated with a high iridium loading, especially in PEM water electrolysis hydrogen production MEAs, where the iridium content can reach 1~1.5 mg / cm³. 2 However, iridium is extremely rare and expensive on Earth, which keeps the cost of PEM electrolyzers high. Currently, most commercially available iridium oxide catalysts are particulate, which are prone to agglomeration and difficult to disperse. Blindly reducing the amount used in MEAs will cause a sharp reduction in the number of active sites in the catalyst layer and break the electron and proton conduction pathways, ultimately leading to a significant decrease in the activity and stability of the MEA. Summary of the Invention

[0004] To address the aforementioned technical problems, this application provides a nano-network iridium oxide, its preparation method, and a proton exchange membrane electrode, which can improve the problem of high cost caused by the need for coating high iridium loads in existing membrane electrodes.

[0005] To address the aforementioned technical problems, in a first aspect, embodiments of this application provide a method for preparing a nano-network iridium oxide, comprising the following steps: The iridium source and two-dimensional carbon nanosheets were mixed evenly in a solvent, and the pH of the solution was adjusted to 9-10 to obtain the iridium precursor. The iridium precursor was ground and mixed with nitrate to obtain a mixed powder; The mixed powder was heat-treated in an oxidizing atmosphere and then cleaned to obtain the nano-network iridium oxide.

[0006] Optionally, the mass ratio of the iridium source to the two-dimensional carbon nanosheet is 1:(0.1~10).

[0007] Optionally, the mass ratio of the iridium precursor to the nitrate is 1:(0.1~1.5).

[0008] Optionally, the target temperature for the heat treatment is 400~600℃, the heating rate is 1~10℃ / min, and the holding time is 2~12 hours.

[0009] Optionally, the method for preparing the two-dimensional carbon nanosheets includes: Graphene nanosheets are obtained by high-energy ball milling of flake graphite powder in a dispersion. The solid-liquid ratio of the flake graphite powder to the dispersion is 1:(10~50) g:mL. The high-energy ball milling speed is 120~220 rpm. The single ball milling time is 3~6 hours and the total ball milling time is 20~30 hours.

[0010] Optionally, the dispersion comprises deionized water, ethanol, and a surfactant, wherein the surfactant is one or more of sodium dodecylbenzenesulfonate, sodium dodecyl sulfate, polyvinylpyrrolidone, Tween 80, and ethyl cellulose.

[0011] Optionally, the method for preparing the two-dimensional carbon nanosheets includes: Flake graphite powder was dispersed in a strong oxidant and stirred sequentially at 0~5℃ for 30~60 minutes, 5~10℃ for 1~3 hours, 20~45℃ for 2~4 hours, and 90~98℃ for 15~45 minutes. After cooling, hydrogen peroxide was added for post-treatment to obtain graphene oxide nanosheets.

[0012] Optionally, the iridium source is one or more selected from iridium chloroic acid, potassium iridium chloroic acid, iridium acetate, iridium nitrate, iridium trichloride, iridium tetrachloride, and iridium acetylacetonate; and / or, The nitrate is one or more of zinc nitrate, sodium nitrate, potassium nitrate, calcium nitrate, and ammonium nitrate; and / or, The oxidizing atmosphere is one or more of air, oxygen, an oxygen-argon mixture, and carbon dioxide.

[0013] Secondly, this application also provides a nano-network iridium oxide, prepared by the preparation methods described in the above embodiments.

[0014] Thirdly, embodiments of this application also provide a proton exchange membrane electrode, including an anode catalyst layer, a cathode catalyst layer, and a proton exchange membrane disposed between the anode catalyst layer and the cathode catalyst layer, wherein the anode catalyst layer includes the nano-network iridium oxide as described in the above embodiments.

[0015] As described above, the method for preparing the nano-networked iridium oxide of this application uses two-dimensional carbon nanosheets as a removable confining template, providing a two-dimensional planar confined space for the loading of the iridium precursor. During precipitation, the iridium source hydrolyzes in situ on the surface of the two-dimensional carbon nanosheets to generate iridium hydroxide nanoparticles. The two-dimensional carbon nanosheets isolate the iridium hydroxide particles from each other through steric hindrance, effectively preventing the pre-agglomeration of the iridium precursor before subsequent heat treatment. This confining effect is the basis for constructing the nano-network structure—only when the iridium precursor remains in a uniform and isolated dispersed state before heat treatment can the heat-treated iridium oxide particles form a continuous network of interconnected particles through appropriate sintering, rather than disordered aggregates of particles. Then, nitrate is introduced during heat treatment. The two-dimensional carbon nanosheets are oxidized into CO2 gas and escape during heat treatment, leaving a network framework composed of iridium oxide nanoparticles in situ. At the same time, the gas generated by the decomposition of nitrate creates pores in situ on the solid product, giving the resulting network a rich porous structure. The complete removal of the two-dimensional carbon nanosheets means that the final product is a pure iridium oxide network without a carbon support. This iridium oxide catalyst provides a continuous electronic conduction pathway and porous mass transfer channel on a macroscopic scale, avoiding the problem of conduction path interruption caused by increased particle spacing and reduced contact points in traditional particulate catalysts at low loadings. Since the product is a pure iridium oxide network without carbon support, the active site density per unit mass of catalyst is maximized. When used in proton exchange membrane electrodes, even if the iridium loading is significantly reduced from the traditional 1~1.5 mg / cm² to 0.1~0.5 mg / cm², continuous electronic conduction and mass transport channels can still be maintained. Thus, low iridium loading can be achieved under the premise of high activity and high stability, effectively solving the technical problem of high cost caused by the requirement of high iridium loading in existing membrane electrodes. Attached Figure Description

[0016] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application. To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, those skilled in the art can obtain other drawings based on these drawings without any creative effort.

[0017] Figure 1 This is a schematic flowchart of a method for preparing IrO2-NET provided in an embodiment of this application; Figures 2-5 TEM images of the two-dimensional graphite nanosheets prepared in Examples 1-4; Figure 6 The XRD patterns of IrO2-NET prepared in Examples 1-4 and IrO2 prepared in the comparative example are shown. Figures 7-8TEM image of IrO2-NET prepared in Example 1; Figures 9-13 TEM images of IrO2-NET prepared in Examples 1-4 and IrO2 prepared in the comparative example; Figure 14 The elemental distribution diagram of IrO2-NET prepared in Example 1; Figure 15 OER polarization curves of IrO2-NET prepared in Examples 1-4 and IrO2 prepared in the comparative example; Figure 16 and Figure 17 The application test of IrO2-NET prepared in Example 1 in PEM water electrolysis for hydrogen production MEA was conducted. Figure 16 This is a curve showing the relationship between current density and voltage. Figure 17 For the stability test of MEA under constant current condition of 2 A / cm²; Figure 18 and Figure 19 The application test of IrO2-NET prepared in Example 2 in PEM water electrolysis for hydrogen production MEA was conducted. Figure 18 This is a curve showing the relationship between current density and voltage. Figure 19 For the stability test of MEA under constant current condition of 2 A / cm²; Figure 20 and Figure 21 To test the application of IrO2 prepared in a comparative manner in a PEM water electrolysis hydrogen production MEA, among which... Figure 20 This is a curve showing the relationship between current density and voltage. Figure 21 For the stability test of MEA under constant current condition of 2 A / cm²; Figure 22 The application test of IrO2-NET prepared in Example 3 on PEM electrochemical deoxygenation MEA was conducted, specifically the test of deoxygenation efficiency. Figure 23 The application test of IrO2-NET prepared in Example 4 on PEM electrochemical humidity control MEA was conducted, specifically the test of dehumidification efficiency.

[0018] The realization of the objectives, functional features, and advantages of this application will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. The accompanying drawings have illustrated specific embodiments of this application, which will be described in more detail below. These drawings and textual descriptions are not intended to limit the scope of the concept in any way, but rather to illustrate the concepts of this application to those skilled in the art through reference to specific embodiments. Detailed Implementation

[0019] The technical solutions in the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application. In addition, it should be understood that the specific embodiments described herein are only for illustration and explanation of this application and are not intended to limit this application. In this application, unless otherwise stated, directional terms such as "upper" and "lower" specifically refer to the drawing directions in the accompanying drawings. In addition, in the description of this application, the term "including" means "including but not limited to". Various embodiments of the present invention may exist in the form of a range; it should be understood that the description in the form of a range is only for convenience and conciseness and should not be construed as a hard limitation on the scope of the present invention; therefore, it should be considered that the range description has specifically disclosed all possible sub-ranges and single values ​​within that range. For example, it should be assumed that the description of a range from 1 to 6 specifically discloses subranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., as well as single numbers within the range, such as 1, 2, 3, 4, 5, and 6, regardless of the range. Furthermore, whenever a numerical range is referred to herein, it means including any referenced number (fraction or integer) within the range referred to.

[0020] Please see Figure 1 , Figure 1 This is a schematic flowchart illustrating a method for preparing nano-networked iridium oxide (IrO2-NET) according to an embodiment of this application. The preparation method may include: S110. The iridium source and two-dimensional carbon nanosheets are mixed evenly in a solvent, and the pH of the solution is adjusted to 9-10 to obtain the iridium precursor.

[0021] In this step, an iridium source and two-dimensional carbon nanosheets are dispersed in a solvent. The two-dimensional carbon nanosheets serve as a confined template, providing a two-dimensional surface for loading the iridium precursor. The pH of the solution is then adjusted to 9-10 by adding an alkaline substance. Under alkaline conditions, iridium ions undergo hydrolysis to form iridium hydroxide precipitate (Ir(OH)₂). x The precipitate is deposited in situ on the surface of two-dimensional carbon nanosheets in an amorphous or low-crystallinity state. The two-dimensional geometry of the carbon nanosheets gives them extremely high specific surface area and surface energy, enabling them to anchor iridium hydroxide nanoparticles through surface adsorption, preventing homogeneous nucleation and aggregation in the liquid phase. For example, the two-dimensional carbon nanosheets can be graphene nanosheets or graphene oxide nanosheets.

[0022] Maintaining a pH range of 9-10 ensures complete hydrolysis and precipitation of the iridium source. Below pH 9, iridium ion hydrolysis is incomplete, with some iridium remaining in ionic form in the solution, leading to uneven iridium distribution. Above pH 10, excessive alkali may introduce metallic impurities or cause iridium hydroxide gelation, affecting subsequent filtration and cleaning efficiency. Through this step, the iridium precursor is uniformly loaded onto the surface of two-dimensional carbon nanosheets in the form of iridium hydroxide, forming a "two-dimensional carbon nanosheet@iridium hydroxide" composite structure. This structure is a key intermediate for subsequent nanonetwork construction.

[0023] S120. Grind and mix the iridium precursor with nitrate to obtain a mixed powder; In this step, the composite structure of "two-dimensional carbon nanosheets@iridium hydroxide" is physically ground and mixed with nitrate. The effects of grinding include: first, mechanically dispersing and uniformly mixing the iridium precursor and nitrate, ensuring that nitrate particles are evenly distributed around the composite structure; second, grinding can moderately break down and refine the size of the composite structure, making the conversion of the iridium precursor to iridium oxide more uniform and complete during subsequent heat treatment; third, the localized thermal and mechanochemical effects generated during grinding can enhance the solid-phase contact interface between the iridium precursor and nitrate, which is beneficial for the nitrate to play a pore-forming role in subsequent heat treatment. The introduction of nitrate as a pore-forming agent provides a key prerequisite for the formation of porous networks during subsequent heat treatment.

[0024] S130. The mixed powder is heat-treated in an oxidizing atmosphere and then cleaned to obtain the nano-network iridium oxide.

[0025] In this step, the mixed powder is subjected to high-temperature treatment in an oxidizing atmosphere. Several physicochemical transformations occur simultaneously during the heat treatment process: First, the iridium precursor (iridium hydroxide) undergoes thermal decomposition under heating conditions, transforming into iridium oxide; second, the two-dimensional carbon nanosheets are oxidized into CO2 gas in the oxidizing atmosphere, escaping from the system and leaving behind a network structure composed of iridium oxide nanoparticles in situ; third, nitrates decompose at high temperature to produce gas, which, during its escape, creates pores in the solid product, giving the resulting network a porous structure; fourth, the heat treatment promotes neck connections and sintering between iridium oxide nanoparticles, allowing independent particles to fuse through grain boundaries to form a continuous network structure. The cleaning step removes any residual nitrate decomposition products or other soluble impurities from the heat-treated product. Because the two-dimensional carbon nanosheet template is completely oxidized and removed during heat treatment, the final product is a pure iridium oxide nanonetwork, free of carbon support or other inert components.

[0026] In this embodiment, two-dimensional carbon nanosheets are used as removable confined templates, providing a two-dimensional planar confined space for the loading of the iridium precursor. During precipitation, the iridium source hydrolyzes in situ on the surface of the two-dimensional carbon nanosheets to generate iridium hydroxide nanoparticles. The two-dimensional carbon nanosheets isolate the iridium hydroxide particles from each other through steric hindrance, effectively preventing the pre-agglomeration of the iridium precursor before subsequent heat treatment. This confinement effect is the basis for constructing the nanonetwork structure—only when the iridium precursor remains in a uniform and isolated dispersion state before heat treatment can the heat-treated iridium oxide particles form a continuous network of interconnected particles through appropriate sintering, rather than disordered aggregates. Then, nitrate is introduced during heat treatment. The two-dimensional carbon nanosheets are oxidized into CO2 gas and escape during heat treatment, leaving behind a network framework composed of iridium oxide nanoparticles in situ. At the same time, the gas generated by the decomposition of nitrate creates pores in situ in the solid product, giving the resulting network a rich porous structure. The complete removal of the two-dimensional carbon nanosheets means that the final product is a pure iridium oxide network without a carbon support.

[0027] The nano-network structured iridium oxide catalyst prepared in this embodiment provides a continuous electronic conduction pathway and porous mass transfer channel on a macroscopic scale, avoiding the problem of conduction path interruption caused by increased particle spacing and reduced contact points in traditional particulate catalysts at low loading. Since the product is a pure IrO2 network without carbon support, the active site density per unit mass of catalyst is maximized. When used in proton exchange membrane electrodes, even if the iridium loading is significantly reduced from the traditional 1~1.5 mg / cm² to 0.1~0.5 mg / cm², continuous electronic conduction and mass transport channels can still be maintained. Thus, low iridium loading is achieved under the premise of high activity and high stability, effectively solving the technical problem of high cost caused by the requirement of high iridium loading in existing membrane electrodes.

[0028] In one embodiment, the mass ratio of iridium source to two-dimensional carbon nanosheets is 1:(0.1~10). This mass ratio determines the loading density and distribution of the iridium precursor on the template surface. When the mass ratio is less than 1:0.1, the iridium source is relatively excessive, resulting in a high density of iridium precursor on the surface of the two-dimensional carbon nanosheets. This is beneficial for forming a larger iridium oxide network framework. However, if the iridium source ratio is too high, it may exceed the confinement capacity of the two-dimensional carbon nanosheets, leading to over-sintering of some iridium precursors during heat treatment. When the mass ratio is greater than 1:10, the iridium source is relatively scarce, resulting in a sparse loading on the surface of the two-dimensional carbon nanosheets. This is beneficial for forming a structure with smaller particle sizes and a finer network. However, if the iridium source ratio is too low, there are insufficient connection points between the iridium oxide particles, making it difficult to form a continuous network structure. By controlling the mass ratio within the range of 1:(0.1~10), it can be ensured that the iridium precursor forms a suitable loading density on the surface of two-dimensional carbon nanosheets. This ensures that the iridium oxide particles are connected to each other to form a continuous network after heat treatment, while avoiding particle agglomeration or insufficient template confinement caused by iridium source overload.

[0029] In one embodiment, the mass ratio of iridium precursor to nitrate is 1:(0.1~1.5). This mass ratio determines the amount of pore-forming agent used and the pore-forming effect. When the nitrate ratio is low (1:0.1), the amount of gas produced by nitrate decomposition is small, resulting in a low porosity network structure, which may affect the mass transport efficiency during the catalytic process. When the nitrate ratio is high (1:1.5), the amount of gas produced by nitrate decomposition is sufficient, which is beneficial for forming a high-porosity network structure. However, excessive nitrate may introduce impurities that are difficult to completely remove or adversely affect the mechanical strength of the network structure. Controlling this mass ratio within the range of 1:(0.1~1.5) ensures sufficient pore formation to create a porous network while avoiding the introduction of impurities or damage to the integrity of the network structure by excessive nitrate.

[0030] In one embodiment, the target temperature for heat treatment is 400–600 °C, the heating rate is 1–10 °C / min, and the holding time is 2–12 hours. The heat treatment temperature is a key parameter determining the crystal structure, particle size, and network integrity of iridium oxide. When the temperature is below 400 °C, incomplete decomposition of the iridium precursor may occur, resulting in a slow oxidation and removal rate of the two-dimensional carbon nanosheets, low crystallinity of iridium oxide, and reduced catalytic activity. When the temperature is above 600 °C, significant sintering of the iridium oxide particles may occur, leading to increased particle size, decreased specific surface area and electrochemically active area, and impaired network structure fineness. Controlling the target temperature within the range of 400–600 °C allows the iridium precursor to be essentially converted into rutile IrO2, resulting in a highly catalytically active crystal structure. Furthermore, the two-dimensional carbon nanosheets are fully oxidized and removed, leaving almost no carbon residue. The iridium oxide particles sinter to form neck connections, constructing a continuous network while maintaining the particle size at the nanoscale. Furthermore, the heating rate affects the heat transfer and reaction uniformity during the heat treatment process. A heating rate that is too low (<1℃ / min) leads to an excessively long treatment cycle, while a heating rate that is too high (>10℃ / min) may result in localized overheating and uneven temperature distribution. The holding time affects the degree of grain growth and the perfection of the network structure. A holding time that is too short (<2 hours) may result in incomplete transformation, while a holding time that is too long (>12 hours) may result in excessive grain growth and coarsening of the network structure.

[0031] In one embodiment, this application provides a physical method for preparing two-dimensional carbon nanosheets, specifically including: high-energy ball milling of flake graphite powder in a dispersion to obtain graphene nanosheets, wherein the solid-liquid ratio of flake graphite powder to dispersion is 1:(10~50) g:mL, the high-energy ball milling speed is 120~220 rpm, the single ball milling time is 3~6 hours, and the total ball milling time is 20~30 hours.

[0032] High-energy ball milling is an effective method for physically exfoliating flake graphite powder to obtain graphene nanosheets. Flake graphite powder has a layered crystalline structure, with layers bonded together by relatively weak van der Waals forces. During high-energy ball milling, the grinding balls apply high-energy collision and shear forces to the graphite particles, causing the graphite layers to slip and ultimately exfoliate into single-layer or few-layer graphene nanosheets. The dispersion plays a wetting and dispersing role during ball milling, preventing the exfoliated graphene nanosheets from re-aggregating. The solid-liquid ratio determines the rheological properties of the slurry in the ball milling system. If the solid-liquid ratio is too high (e.g., greater than 1:10), the slurry viscosity is too high, reducing ball milling efficiency; if the solid-liquid ratio is too low (e.g., less than 1:50), the slurry is too thin, reducing the effective collisions between the grinding balls and the graphite powder. The setting of ball mill speed and time also affects the peeling efficiency. Too low a speed or insufficient time will result in insufficient peeling, leaving a large number of unpeeled graphite flakes in the product; too high a speed or too long a time may damage the two-dimensional structure of graphene and produce a large number of defects.

[0033] For example, the dispersion may include deionized water, ethanol, and a surfactant, wherein the surfactant may be one or more of sodium dodecylbenzenesulfonate, sodium dodecyl sulfate, polyvinylpyrrolidone, Tween 80, and ethyl cellulose. In the dispersion, deionized water serves as the primary dispersion medium, ethanol is used to reduce the surface tension of water and improve the wettability of graphite powder, and the surfactant is adsorbed onto the surface of the exfoliated graphene nanosheets through a hydrophilic-hydrophobic balance, preventing their re-aggregation by steric hindrance or electrostatic repulsion. Appropriate surfactant types and amounts can form a stable adsorption layer on the surface of the graphene nanosheets, ensuring their long-term stable dispersion in the dispersion, thereby providing a high-quality template material for the uniform loading of the subsequent iridium precursor.

[0034] In one embodiment, this application provides a chemical method for preparing two-dimensional carbon nanosheets, specifically comprising: dispersing flake graphite powder in a strong oxidant, stirring sequentially at 0~5℃ for 30~60 minutes, at 5~10℃ for 1~3 hours, at 20~45℃ for 2~4 hours, and at 90~98℃ for 15~45 minutes, and then adding hydrogen peroxide after cooling for post-treatment to obtain graphene oxide nanosheets.

[0035] This method is a modified Hummers chemical oxidation exfoliation method. Under the synergistic effect of strong oxidants (such as concentrated sulfuric acid, concentrated nitric acid, concentrated phosphoric acid, etc.) and potassium permanganate, the carbon atoms between the graphite layers are oxidized and oxygen-containing functional groups (such as hydroxyl, epoxy, carboxyl, etc.) are introduced. The introduction of oxygen-containing functional groups increases the distance between graphite layers and reduces the interlayer van der Waals forces, making the graphite layers easier to exfoliate into single-layer or few-layer graphene oxide nanosheets in subsequent processing.

[0036] Taking concentrated sulfuric acid as a strong oxidant as an example, the chemical principle of phased temperature control is as follows: The first stage (0~5℃) is the low-temperature intercalation period. Under this temperature condition, potassium permanganate reacts with concentrated sulfuric acid to generate manganese heptaoxide (Mn2O7), a strong oxidant. This active species slowly inserts into the graphite interlayer. At the same time, the low temperature condition inhibits the oxidation reaction rate and prevents the reaction from being too violent, leading to local overheating and safety hazards. The second stage (5~10℃) is the medium-temperature oxidation period. The reaction temperature rises gently, the degree of oxidation of the graphite interlayer deepens, and oxygen-containing functional groups are gradually formed. The third stage (20~45℃) is the high-temperature expansion period. As the temperature rises, the oxidation reaction intensifies, and the graphite interlayer expands further due to the introduction of oxygen-containing functional groups, significantly increasing the interlayer distance. The fourth stage (90~98℃) is the deep oxidation period. At high temperature, water is added to cause violent hydrolysis of the system. The graphite interlayer is fully oxidized and peeled off, while excess potassium permanganate is decomposed and reduced. The addition of hydrogen peroxide reduces unreacted potassium permanganate and manganese dioxide in the system, and the product color changes from dark brown to bright yellow, indicating the completion of the oxidation reaction.

[0037] Compared with physical exfoliation, the surface of graphene oxide nanosheets obtained by chemical oxidative exfoliation contains abundant oxygen-containing functional groups. These functional groups not only endow graphene oxide with good hydrophilicity and dispersibility, but also provide more chemical anchoring sites for the loading of iridium precursors, which is conducive to the uniform and firm loading of iridium species.

[0038] As examples, the iridium source can be one or more of chloroiridium acid, potassium chloroiridium, iridium acetate, iridium nitrate, iridium trichloride, iridium tetrachloride, and iridium acetylacetonate. The iridium source is selected from the above-mentioned soluble iridium compounds, all of which have good water or alcohol solubility, can be uniformly dispersed in a solvent to form an iridium ion solution, and hydrolyze under alkaline conditions to form iridium hydroxide precipitate. Different iridium sources have different types of anions (chloride, nitrate, acetate, acetylacetonate, etc.), which can all be effectively removed in subsequent cleaning steps, leaving no impurities that affect catalyst performance.

[0039] As examples, nitrates can be one or more of zinc nitrate, sodium nitrate, potassium nitrate, calcium nitrate, and ammonium nitrate. The nitrates selected from these types can decompose into the corresponding metal oxides (or metals) and nitrogen oxides at the heat treatment temperature. The gas escape process creates pores in the solid network, and most nitrate decomposition products (such as Na₂O, K₂O, ZnO, etc.) can be removed by subsequent water washing and do not remain in the final product.

[0040] As examples, the oxidizing atmosphere can be one or more of air, oxygen, an oxygen-argon mixture, and carbon dioxide. Air and oxygen are strong oxidizing atmospheres, effectively oxidizing and removing the two-dimensional carbon nanosheet template and converting the iridium precursor into IrO2. The rate and extent of the oxidation reaction can be controlled by adjusting the oxygen partial pressure. Carbon dioxide also has a certain oxidizing property at high temperatures and can react with carbon to produce CO, thus achieving the removal of the carbon template. The choice of different atmospheres can be adjusted according to the specific requirements of the heat treatment process.

[0041] This application also provides a nano-networked iridium oxide, prepared by the preparation method described in any of the above embodiments. The iridium oxide catalyst prepared by the above method has a nano-network structure, which is a continuous two-dimensional porous network formed by interconnected iridium oxide nanoparticles. The particles are connected by grain boundaries or necks to form a continuous structure, without interface interruptions between discrete particles, which is beneficial for the rapid conduction of electrons throughout the network; and the network structure has abundant pores, which is beneficial for the diffusion and transport of gases and liquids in the catalytic reaction; in addition, the network structure is a self-supporting structure, without any carbon support or other inert components, and has a high density of active sites per unit mass of catalyst. Thanks to its continuous network structure, when used as a proton exchange membrane electrode, this catalyst can maintain continuous electron and proton conduction pathways even at low iridium loadings of 0.1~0.5 mg / cm², thereby maintaining high OER activity and high stability.

[0042] This application also provides a proton exchange membrane electrode, comprising an anode catalyst layer, a cathode catalyst layer, and a proton exchange membrane disposed between the anode catalyst layer and the cathode catalyst layer, wherein the anode catalyst layer comprises nano-networked iridium oxide as described in the above embodiments. As an example, this membrane electrode can be prepared by the following method: dispersing nano-networked iridium oxide with an ionomer in a solvent to prepare an anode catalyst slurry; dispersing a cathode catalyst (such as a carbon-supported platinum catalyst) with an ionomer in a solvent to prepare a cathode catalyst slurry; coating the anode catalyst slurry and cathode catalyst slurry onto both sides of the proton exchange membrane, and then hot-pressing to obtain the membrane electrode. Because the iridium oxide catalyst in the anode catalyst layer has a continuous network structure, a continuous electron and proton conduction pathway can be constructed even with a low iridium loading. Simultaneously, the porous nature of the network structure facilitates the timely removal of oxygen during the oxygen evolution reaction at the anode. Therefore, this membrane electrode can achieve efficient and stable water electrolysis performance with a low iridium loading.

[0043] The present application will be further described in detail below through specific embodiments and comparative examples. The following embodiments are only some embodiments of the present application and are not intended to limit the present application.

[0044] Example 1 The preparation method of nano-networked iridium oxide includes the following steps: (1) Preparation of graphene nanosheets: 14 g of sodium dodecylbenzenesulfonate was completely dissolved in a mixed solution of 5 L ethanol and 2 L deionized water to obtain a dispersion. 87.5 g of flake graphite powder, 1.75 L of dispersion, 115 8 mm grinding balls and 225 6 mm grinding balls were weighed into four clean and dry 4 L zirconia ball milling jars to ensure that the graphite powder was completely wetted and the grinding balls were fully submerged in the slurry. The jars were symmetrically installed in a planetary ball mill. The ball milling speed was 180 rpm, and the milling was carried out for 6 hours at a time, followed by a 30-minute stop. Four cycles were performed for a total ball milling time of 24 hours. After the ball milling was completed, the milling liquid was transferred to centrifuge tubes after the jars cooled to room temperature. The mixture was centrifuged at 4000 rpm for 10 minutes, washed three times with deionized water, and then dried in a vacuum oven at 60℃ for 6 hours to obtain graphene nanosheets.

[0045] (2) Preparation of iridium precursor: Chloroiridic acid and 80 g of graphene nanosheets were dispersed in a mixed solution of 250 mL of deionized water and 50 mL of ethanol. The concentration of chloroiridic acid was 0.2 mol / L. 0.1 mol / L potassium hydroxide solution was added to adjust the pH to 9. The mixture was heated and stirred at 70 °C for 4 hours to allow iridium ions to be completely hydrolyzed and precipitated on the surface of the graphene nanosheets in the form of iridium hydroxide. The mixture was centrifuged and dried to obtain the iridium precursor solid.

[0046] (3) Grinding and mixing: The above-mentioned iridium precursor solid and 3 g of sodium nitrate are placed in a mortar and ground and mixed evenly to obtain a mixed powder.

[0047] (4) Heat treatment: The mixed powder was placed in a tube furnace and heated to 400°C in air at a heating rate of 2°C / min, and held for 6 hours. After cooling to room temperature naturally, it was washed three times with deionized water to obtain nano-network iridium oxide.

[0048] Example 2 The preparation method of nano-networked iridium oxide includes the following steps: (1) Preparation of graphene oxide nanosheets (modified Hummers method): Add 1.8 L of concentrated sulfuric acid and 0.5 L of concentrated phosphoric acid to the reactor. Use a circulating cooling pump to control the temperature at 0-5℃. Add 20 g of flake graphite powder in batches of 4 g each, with a 5 min interval between batches. After all the powder is added, keep stirring for 60 min. Add 175 g of potassium permanganate to the reactor in batches of 5 g each, with a 20 min interval between batches. Use a circulating cooling pump to control the temperature at 5-10℃. After the addition is complete, keep stirring at 5-10℃ for 1.5 h. Remove the circulating cooling pump, raise the temperature to 38℃, keep stirring for 3 h, and slowly add 6000 mL of deionized water. Then raise the temperature to 95℃ and stir for 40 min. Stop heating and allow the temperature to cool naturally to 45℃. Slowly add 30% hydrogen peroxide solution until the system stops bubbling. The amount of hydrogen peroxide used is 230 mL. Filter, wash, and dry while hot to obtain graphene oxide nanosheets.

[0049] (2) Preparation of iridium precursor: Iridium trichloride and 50 g of graphene oxide nanosheets were dispersed in a mixed solution of 500 mL deionized water, 50 mL ethanol, and 50 mL isopropanol, with an iridium trichloride concentration of 0.2 mol / L. 0.5 mol / L sodium hydroxide solution was added to adjust the pH to 9, and the mixture was heated and stirred at 80°C for 6 hours to allow the iridium ions to be completely hydrolyzed and precipitated on the surface of the graphene oxide nanosheets in the form of iridium hydroxide. The mixture was then centrifuged, dried, and the iridium precursor solid was obtained.

[0050] (3) Grinding and mixing: The above-mentioned iridium precursor solid and 7 g of zinc nitrate are placed in a mortar and ground and mixed evenly to obtain a mixed powder.

[0051] (4) Heat treatment: The mixed powder was placed in a tube furnace and heated to 400°C at a heating rate of 2°C / min in an oxygen atmosphere, and held at that temperature for 3 hours. After naturally cooling to room temperature, it was washed three times with deionized water to obtain nano-network iridium oxide.

[0052] Example 3 The preparation method of nano-networked iridium oxide includes the following steps: (1) Preparation of graphene nanosheets: 14 g of polyvinylpyrrolidone was completely dissolved in a mixed solution of 10 L ethanol and 4 L deionized water to obtain a dispersion. 87.5 g of flake graphite powder, 3.5 L of dispersion, 161 8 mm grinding balls and 311 6 mm grinding balls were weighed into four clean and dry 4 L zirconia ball milling jars. The jars were symmetrically installed in a planetary ball mill. The ball milling speed was 180 rpm, and the milling was carried out for 6 h in a single run, followed by a 30 min stop. Five cycles were performed for a total ball milling time of 30 h. After the ball milling was completed, the milling liquid was transferred to centrifuge tubes after the jars cooled to room temperature. The mixture was centrifuged at 4000 rpm for 10 minutes, washed three times with deionized water, and dried in a vacuum oven at 60 °C for 6 hours to obtain graphene nanosheets.

[0053] (2) Preparation of iridium precursor: Iridium trichloride and 80 g of graphene nanosheets were dispersed in a mixed solution of 200 mL deionized water, 50 mL ethanol and 50 mL isopropanol, with an iridium trichloride concentration of 0.2 mol / L. The pH was adjusted to 9 by adding 0.5 mol / L sodium hydroxide solution, and the mixture was heated and stirred at 70 °C for 8 hours. After centrifugation and drying, the iridium precursor solid was obtained.

[0054] (3) Grinding and mixing: The above-mentioned iridium precursor solid and 4 g of ammonium nitrate are placed in a mortar and ground and mixed evenly to obtain a mixed powder.

[0055] (4) Heat treatment: The mixed powder was placed in a tube furnace and heated to 400°C at a heating rate of 5°C / min in an oxygen atmosphere, and held at that temperature for 5 hours. After naturally cooling to room temperature, it was washed three times with deionized water to obtain nano-network iridium oxide.

[0056] Example 4 The preparation method of nano-networked iridium oxide includes the following steps: (1) Preparation of graphene oxide nanosheets (modified Hummers method): Add 2.3 L of concentrated sulfuric acid to the reactor. Use a circulating cooling pump to control the temperature at 0-5℃. Add 20 g of flake graphite powder in batches of 5 g each, with a 5 min interval between batches. After all the powder is added, keep stirring for 50 min. Add 175 g of potassium permanganate to the reactor in batches of 5 g each, with a 10 min interval between batches. Use a circulating cooling pump to control the temperature at 5-10℃. After the addition is complete, keep stirring at 5-10℃ for 2 h. Remove the circulating cooling pump, raise the temperature to 35℃, keep stirring for 2.5 h, and slowly add 6000 mL of deionized water. Then raise the temperature to 95℃ and stir for 20 min. Stop heating and allow the temperature to cool naturally to 50℃. Slowly add 30% hydrogen peroxide solution until the system stops bubbling. The amount of hydrogen peroxide used is 200 mL. Filter, wash, and dry while hot to obtain graphene oxide nanosheets.

[0057] (2) Preparation of iridium precursor: Chloroiridic acid and 40 g of graphene oxide nanosheets were dispersed in a mixed solution of 250 mL of deionized water and 50 mL of ethanol. The concentration of chloroiridic acid was 0.2 mol / L. 0.1 mol / L potassium hydroxide solution was added to adjust the pH to 9, and the mixture was heated and stirred at 80 °C for 4 hours. After centrifugation and drying, the iridium precursor solid was obtained.

[0058] (3) Grinding and mixing: The above-mentioned iridium precursor solid and 13 g of sodium nitrate are placed in a mortar and ground and mixed evenly to obtain a mixed powder.

[0059] (4) Heat treatment: The mixed powder was placed in a tube furnace and heated to 450°C at a heating rate of 2°C / min in a carbon dioxide atmosphere, and held for 10 hours. After cooling to room temperature naturally, it was washed three times with deionized water to obtain nano-network iridium oxide.

[0060] Example 5 The preparation method of nano-networked iridium oxide includes the following steps: (1) Preparation of graphene nanosheets: 14 g of polyvinylpyrrolidone was completely dissolved in a mixed solution of 4 L ethanol and 1.2 L deionized water to obtain a dispersion. 87.5 g of flake graphite powder, 1.3 L of dispersion, 46 8 mm grinding balls and 89 6 mm grinding balls were weighed into four clean and dry 4 L zirconia ball milling jars. The jars were symmetrically installed in a planetary ball mill. The ball milling speed was 180 rpm. The milling was carried out for 6 h in a single run, followed by a 30 min stop. Five cycles were performed for a total ball milling time of 30 h. After the ball milling was completed, the milling liquid was transferred to a centrifuge tube after the jars cooled to room temperature. The mixture was centrifuged at 4000 rpm for 10 minutes, washed three times with deionized water, and dried in a vacuum oven at 60 °C for 6 hours to obtain graphene nanosheets.

[0061] (2) Preparation of iridium precursor: Iridium acetate and 80 g of graphene nanosheets were dispersed in a mixed solution of 290 mL of deionized water and 10 mL of ethylene glycol. The concentration of iridium acetate was 0.2 mol / L. 1 mol / L potassium carbonate solution was added to adjust the pH to 9, and the mixture was heated and stirred at 70 °C for 4 hours. After centrifugation and drying, the solid iridium precursor was obtained.

[0062] (3) Grinding and mixing: The above-mentioned iridium precursor solid and 33 g of potassium nitrate are placed in a mortar and ground and mixed evenly to obtain a mixed powder.

[0063] (4) Heat treatment: The mixed powder was placed in a tube furnace and heated to 400°C in air at a heating rate of 2°C / min, and held for 2 hours. After cooling to room temperature naturally, it was washed three times with deionized water to obtain nano-network iridium oxide.

[0064] Example 6 The preparation method of nano-networked iridium oxide includes the following steps: (1) Preparation of graphene nanosheets: 14 g of sodium dodecylbenzenesulfonate was completely dissolved in a mixed solution of 10 L ethanol and 2 L deionized water to obtain a dispersion. 87.5 g of flake graphite powder, 3 L of dispersion, 69 8 mm grinding balls and 134 6 mm grinding balls were weighed into four clean and dry 4 L zirconia ball milling jars. The jars were symmetrically installed in a planetary ball mill. The ball milling speed was 150 rpm, and the milling was carried out for 3 h in a single run, followed by a 10 min stop. Seven cycles were performed for a total ball milling time of 21 h. After the ball milling was completed, the milling liquid was transferred to centrifuge tubes after the jars cooled to room temperature. The mixture was centrifuged at 4000 rpm for 10 minutes, washed three times with deionized water, and dried in a vacuum oven at 60 °C for 6 hours to obtain graphene nanosheets.

[0065] (2) Preparation of iridium precursor: Iridium nitrate and 120 g of graphene nanosheets were dispersed in a mixed solution of 300 mL of deionized water and 50 mL of ethanol. The concentration of iridium nitrate was 0.5 mol / L. The pH was adjusted to 10 by adding 5 mol / L ammonium bicarbonate solution, and the reaction was heated and stirred at 70 °C for 6 hours. After centrifugation and drying, the solid iridium precursor was obtained.

[0066] (3) Grinding and mixing: The above-mentioned iridium precursor solid and 9 g of calcium nitrate are placed in a mortar and ground and mixed evenly to obtain a mixed powder.

[0067] (4) Heat treatment: The mixed powder was placed in a tube furnace and heated to 500°C at a heating rate of 5°C / min in a carbon dioxide atmosphere, and held at that temperature for 5 hours. After naturally cooling to room temperature, it was washed three times with deionized water to obtain nano-network iridium oxide.

[0068] Comparative Example Preparation of conventional iridium oxide catalyst: Iridium nitrate was dispersed in a mixed solution of 300 mL deionized water and 50 mL ethanol, with an iridium nitrate concentration of 0.5 mol / L. The pH was adjusted to 10 by adding 5 mol / L ammonium bicarbonate solution, and the mixture was heated and stirred at 70°C for 6 hours to completely hydrolyze iridium ions to form iridium hydroxide precipitate. The precipitate was separated by centrifugation and dried to obtain solid iridium hydroxide. The solid iridium hydroxide was placed in a tube furnace and heated to 500°C at a heating rate of 5°C / min in air, and held at that temperature for 6 hours. After naturally cooling to room temperature, the catalyst was washed three times with deionized water to obtain the iridium oxide catalyst.

[0069] The difference between this comparative example and the embodiment is that: two-dimensional carbon nanosheets were not used as confining templates, nor were nitrates used as pore-forming agents; iridium hydroxide was directly converted into iridium oxide particles by high-temperature treatment in an air atmosphere.

[0070] Testing and Characterization 1. Characterization Test The two-dimensional carbon nanosheets prepared in Examples 1-4 were characterized by transmission electron microscopy (TEM), and the results are as follows: Figures 2-5 As shown. Figures 2-5 The two-dimensional carbon nanosheets corresponding to Examples 1-4 all exhibit a thin sheet-like morphology, indicating that both physical exfoliation and chemical oxidative exfoliation methods can effectively obtain carbon nanosheets with a two-dimensional sheet-like morphology.

[0071] The iridium oxide catalysts prepared in Examples 1-4 and the comparative examples were characterized by X-ray diffraction (XRD), and the results are as follows: Figure 6 As shown, the XRD patterns of all samples exhibit characteristic diffraction peaks belonging to the rutile phase IrO2, indicating that the products prepared in the examples and comparative examples are all IrO2 with a rutile structure.

[0072] The IrO2-NET prepared in Example 1 was characterized by high-resolution transmission electron microscopy (HRTEM), and the results are as follows: Figures 7-8 As shown, the lattice fringes of the IrO2 nanoparticles can be clearly observed, with a fringe spacing of 0.255 nm, which belongs to the (101) crystal plane of rutile IrO2, indicating that the catalyst has high crystallinity.

[0073] The iridium oxide catalysts prepared in Examples 1-4 and the comparative examples were characterized by TEM, and the results are as follows: Figures 9-13 As shown. Figures 9-12 Corresponding to IrO2-NET in Examples 1-4 respectively, Figure 13 Comparing the IrO2 in the comparative examples, it can be seen that the nanoparticles in Examples 1-4 are interconnected to form a continuous porous network morphology; while the IrO2 in the comparative examples shows a disordered stacked nanoparticle morphology without a network structure.

[0074] The elemental distribution (EDS-mapping) of the IrO2-NET prepared in Example 1 was characterized, and the results are as follows: Figure 14 As shown, Ir and O elements are uniformly distributed in the catalyst, indicating that the iridium oxide nanoparticles are uniformly distributed on the network and there is no elemental segregation.

[0075] 2. Electrochemical OER Activity Test The iridium oxide catalysts prepared in Examples 1-6 and the comparative examples were subjected to electrochemical oxygen evolution reaction (OER) activity tests.

[0076] Test Method: A three-electrode system was used with 0.5 M H₂SO₄ as the electrolyte. The catalyst-coated glassy carbon electrode served as the working electrode (S = 0.07 cm²), Hg / Hg₂SO₄ as the reference electrode, and a carbon rod as the counter electrode. The catalyst slurry was prepared as follows: 10 mg of catalyst was dissolved in 2.8 mL of deionized water, and 0.2 mL of 5 wt% Nafion solution was added to prepare a 3 mL catalyst slurry. After sonication for 30 min, the slurry was coated onto the glassy carbon working electrode, with a catalyst loading of 140 μg / cm². The test was conducted at room temperature with a scan rate of 5 mV / s.

[0077] The overpotential of the IrO2-NET catalyst in Example 1 was 292 mV at 10 mA / cm²; the overpotential in Example 2 was 288 mV; the overpotential in Example 3 was 298 mV; the overpotential in Example 4 was 296 mV; the overpotential in Example 5 was 290 mV; the overpotential in Example 6 was 295 mV; and the overpotential of the conventional IrO2 catalyst in the comparative example was 346 mV at 10 mA / cm². The test results for Examples 1-4 and the comparative example are as follows: Figure 15 As shown.

[0078] The results show that the OER overpotentials of the nano-networked iridium oxide catalysts in Examples 1-6 are significantly lower than those of the conventional particulate iridium oxide catalysts in the comparative examples, indicating that the nano-network structure prepared in this application has higher OER catalytic activity. This activity enhancement is attributed to the fact that the continuous network structure provides a larger electrochemical active area and faster electron transport pathways, while the porous nature of the network structure facilitates the diffusion and transport of reactants and products.

[0079] 3. Electrolysis membrane electrode performance testing The nano-network iridium oxide prepared in Examples 1, 2, 5, and 6, and the conventional iridium oxide catalyst prepared in the comparative example, were assembled into a proton exchange membrane electrolysis water electrolysis membrane electrode, and the performance of water electrolysis for hydrogen production was tested.

[0080] Membrane electrode preparation method: 0.5 g of iridium oxide catalyst (anodic catalyst) and 2 g of Nafion D520 perfluorosulfonic acid resin were dispersed in a cell disruptor for 1 h at a power of 1500 W to obtain an anode catalyst slurry. 0.5 g of Pt / C catalyst (cathode catalyst) and 2 g of Nafion D520 perfluorosulfonic acid resin were weighed and dispersed in a cell disruptor for 1 h at a power of 1500 W to obtain a cathode catalyst slurry. The anode and cathode catalyst slurries were respectively sprayed onto a PTFE substrate and then hot-pressed together with a proton exchange membrane. Examples 1, 5, and the comparative examples used N115 membranes, with a hot-pressing temperature of 120℃, a pressure of 3 MPa, and a time of 8 min; Examples 2 and 6 used Gore 80 μm proton exchange membranes, with a hot-pressing temperature of 120℃, a pressure of 2 MPa, and a time of 5 min.

[0081] The iridium loading at the anode and the platinum loading at the cathode of the membrane electrodes in each embodiment and comparative example are as follows: Example 1 (iridium loading 0.5 mg / cm², platinum loading 0.3 mg / cm²); Example 2 (iridium loading 0.4 mg / cm², platinum loading 0.3 mg / cm²); Example 5 (iridium loading 0.5 mg / cm², platinum loading 0.3 mg / cm²); Example 6 (iridium loading 0.4 mg / cm², platinum loading 0.3 mg / cm²); Comparative Example (iridium loading 0.5 mg / cm², platinum loading 0.3 mg / cm²).

[0082] Each membrane electrode was installed on the water electrolysis hydrogen production test platform for performance testing at a temperature of 60°C.

[0083] The membrane electrode test results of Example 1 are as follows: Figure 16 and Figure 17 As shown, the required battery voltage is 1.76 V at a current density of 2 A / cm². Stability was evaluated under a constant current of 2 A / cm², and the battery voltage showed no significant decay after 2000 hours of testing.

[0084] The membrane electrode test results of Example 2 are as follows: Figure 18 and Figure 19 As shown, the required battery voltage is 1.673 V at a current density of 2 A / cm². Stability was evaluated under a constant current of 2 A / cm², and the battery voltage showed no significant decay after 2000 hours of testing.

[0085] The cell voltage of the membrane electrode in Example 5 was 1.77 V at 2 A / cm², and the cell voltage showed no significant decay after 1000 hours of testing under a constant current of 2 A / cm².

[0086] The membrane electrode of Example 6 has a battery voltage of 1.68 V at 2 A / cm², and the battery voltage shows no significant decay after 1200 hours of testing under a constant current of 2 A / cm².

[0087] Comparative membrane electrode test results are as follows Figure 20 and Figure 21 As shown, the required battery voltage is 1.88 V at a current density of 2 A / cm². Under constant current conditions of 2 A / cm², the battery voltage rapidly increased to over 2.1 V in less than 25 hours.

[0088] The results show that the nano-network iridium oxide catalysts in Examples 1, 2, 5, and 6, with low iridium loadings of 0.4–0.5 mg / cm², exhibited electrolysis voltages of less than 1.77 V at 2 A / cm² when mounted on an N115 membrane and less than 1.68 V when mounted on an 80 μm Gore proton exchange membrane, with no significant voltage decay over 2000 hours. In contrast, the conventional particulate iridium oxide catalysts in the comparative examples, with the same iridium loading, exhibited a 2 A / cm² voltage as high as 1.88 V when mounted on an N115 membrane, and failed after only 25 hours. This demonstrates that the nano-network structure of this application can maintain continuous electron and proton conduction pathways even with low iridium loadings, thereby achieving both high activity and high stability.

[0089] 4. Electrochemical deoxygenation performance test The nano-network iridium oxide prepared in Example 3 was assembled into an electrochemical deoxygenation membrane electrode, and its deoxygenation performance was tested.

[0090] Membrane electrode preparation method: 0.5 g IrO2-NET catalyst and 2 g Nafion D520 perfluorosulfonic acid resin were dispersed in a cell disruptor for 1 h at 1500 W to obtain an anode catalyst slurry. 0.5 g Pt / C cathode catalyst and 2 g Nafion D520 perfluorosulfonic acid resin were also dispersed in a cell disruptor for 1 h at 1500 W to obtain a cathode catalyst slurry. The anode and cathode catalyst slurries were separately sprayed onto a PTFE substrate and then hot-pressed together with a Gore 10 μm proton exchange membrane at 120℃, 1.5 MPa, and 5 min. The iridium loading at the anode was 0.2 mg / cm², and the platinum loading at the cathode was 0.3 mg / cm².

[0091] The above-mentioned membrane electrode was installed in a dedicated test drawer for deoxygenation membrane electrodes and tested at a temperature of 10°C under a constant voltage of 1.7 V. The test results are as follows. Figure 22 As shown, it only takes 5 hours to reduce the oxygen concentration in the drawer from the initial value to below 10%.

[0092] 5. Electrochemical humidity control performance test The nano-network iridium oxide prepared in Example 4 was assembled into an electrochemical humidity control membrane electrode, and its humidity control performance was tested.

[0093] Membrane electrode preparation method: 0.5 g IrO2-NET catalyst and 2 g Nafion D520 perfluorosulfonic acid resin were dispersed in a cell disruptor for 1 h at 1500 W to obtain an anode catalyst slurry. 0.5 g Pt / C cathode catalyst and 2 g Nafion D520 perfluorosulfonic acid resin were also dispersed in a cell disruptor for 1 h at 1500 W to obtain a cathode catalyst slurry. The anode and cathode catalyst slurries were separately sprayed onto a PTFE substrate and then hot-pressed together with a Gore 10 μm proton exchange membrane at 120℃, 1.5 MPa, and 5 min. The iridium loading at the anode was 0.1 mg / cm², and the platinum loading at the cathode was 0.4 mg / cm².

[0094] The aforementioned membrane electrode was assembled in a test drawer for humidity control testing, and electrolysis at a constant voltage of 1.9 V was applied at room temperature. The test results are as follows. Figure 23 As shown, both dehumidification and humidification efficiencies are good.

[0095] 6. Comparative Analysis of Results The structural features and performance comparisons of the catalysts in each embodiment and the comparative example are shown in Table 1 below.

[0096] Table 1. Comparison of catalyst structural features and performance between the examples and comparative examples.

[0097] The test results in Table 1 and the attached figures show that: (1) The OER overpotentials (288-298 mV) of the nano-network iridium oxide in Examples 1-6 were significantly lower than those of the conventional particulate iridium oxide catalyst in the comparative example (346 mV), indicating that the nano-network structure of this application provides a higher electrochemical active area and a faster electron / proton transport rate, thereby greatly improving the OER catalytic activity.

[0098] (2) When equipped with an N115 membrane, the membrane electrodes of Examples 1 and 5, with a low iridium loading of 0.5 mg / cm², exhibited electrolysis voltages as low as 1.76 V and 1.77 V, respectively, at 2 A / cm², while the comparative example showed a voltage as high as 1.88 V at the same iridium loading. This indicates that the nano-network structure can still maintain continuous electron and proton conduction pathways even with low iridium loading, while conventional particulate catalysts experience a significant performance degradation due to agglomeration and interruption of conduction pathways at low loading.

[0099] (3) When equipped with an N115 membrane, the membrane electrodes of Examples 1 and 5 showed no significant voltage decay after running for 2000 and 1000 hours respectively under a constant current of 2 A / cm², while the comparative example failed after only 25 hours. This indicates that the nano-network structure has excellent stability, and its continuous network structure avoids the performance degradation caused by the dissolution, agglomeration or shedding of particulate catalysts during long-term operation.

[0100] (4) The nano-network iridium oxides in Examples 3 and 4 still achieved efficient electrochemical deoxygenation and electrochemical humidity control even at ultra-low iridium loadings of 0.1~0.2 mg / cm², further verifying the performance advantages of the nano-network structure at ultra-low loadings. The catalyst of this application is not only suitable for hydrogen production by water electrolysis, but can also be widely used in fields such as electrochemical deoxygenation in confined spaces and precision environmental humidity control.

[0101] In summary, this application successfully constructed a pure iridium oxide catalyst with a continuous network structure through a technical path of "two-dimensional carbon nanosheet confinement template—nitrate pore-forming—in-situ template removal via oxidizing atmosphere heat treatment." This network structure solves the performance degradation problem of traditional particulate catalysts caused by agglomeration and disruption of conduction pathways under low iridium loading, enabling the iridium loading of the membrane electrode to be reduced to 1 / 3 to 1 / 10 of the traditional amount while maintaining excellent long-term stability. This provides a low-cost, high-performance catalyst solution for applications such as PEM water electrolysis for hydrogen production, electrochemical deoxygenation, and electrochemical humidity control.

[0102] The foregoing has provided a detailed description of a nano-network iridium oxide, its preparation method, and a proton exchange membrane electrode provided in this application. Specific examples have been used to illustrate the principles and implementation methods of this application. It should be noted that the descriptions of each embodiment in this application have different emphases; parts not described in detail in a particular embodiment can be referred to in the relevant descriptions of other embodiments.

[0103] The above are merely preferred embodiments of this application and do not limit the patent scope of this application. The technical features of the technical solution of this application can be combined arbitrarily. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. Any equivalent structural or procedural transformations made using the content of this application's specification and drawings, or direct or indirect applications in other related technical fields, are also included within the patent protection scope of this application, as long as the combination of these technical features does not contradict each other.

Claims

1. A method for preparing a nano-networked iridium oxide, characterized by, Includes the following steps: An iridium source and two-dimensional carbon nanosheets were mixed evenly in a solvent, and the pH of the solution was adjusted to 9-10 to obtain an iridium precursor. The iridium precursor was ground and mixed with nitrate to obtain a mixed powder; The mixed powder was heat-treated in an oxidizing atmosphere and then cleaned to obtain the nano-network iridium oxide. The mass ratio of the iridium source to the two-dimensional carbon nanosheets is 1:(0.1~10); The mass ratio of the iridium precursor to the nitrate is 1:(0.1~1.5); The target temperature for the heat treatment is 400~600℃, the heating rate is 1~10℃ / min, and the holding time is 2~12 hours.

2. The production method according to claim 1, characterized by, The method for preparing the two-dimensional carbon nanosheets includes: Graphene nanosheets are obtained by high-energy ball milling of flake graphite powder in a dispersion. The solid-liquid ratio of the flake graphite powder to the dispersion is 1:(10~50) g:mL. The high-energy ball milling speed is 120~220 rpm. The single ball milling time is 3~6 hours and the total ball milling time is 20~30 hours.

3. The production method according to claim 2, characterized by, The dispersion comprises deionized water, ethanol, and a surfactant, wherein the surfactant is one or more of sodium dodecylbenzenesulfonate, sodium dodecyl sulfate, polyvinylpyrrolidone, Tween 80, and ethyl cellulose.

4. The method of claim 1, wherein, The method for preparing the two-dimensional carbon nanosheets includes: Flake graphite powder was dispersed in a strong oxidant and stirred sequentially at 0~5℃ for 30~60 minutes, 5~10℃ for 1~3 hours, 20~45℃ for 2~4 hours, and 90~98℃ for 15~45 minutes. After cooling, hydrogen peroxide was added for post-treatment to obtain graphene oxide nanosheets.

5. The preparation method according to claim 1, characterized in that, The iridium source is one or more selected from iridium chloroic acid, potassium iridium chloroic acid, iridium acetate, iridium nitrate, iridium trichloride, iridium tetrachloride, and iridium acetylacetonate; and / or, The nitrate is one or more of zinc nitrate, sodium nitrate, potassium nitrate, calcium nitrate, and ammonium nitrate; and / or, The oxidizing atmosphere is one or more of air, oxygen, an oxygen-argon mixture, and carbon dioxide.

6. A nano-networked iridium oxide, characterized in that, It is prepared by the preparation method according to any one of claims 1 to 5.

7. A proton exchange membrane electrode, comprising an anode catalyst layer, a cathode catalyst layer, and a proton exchange membrane disposed between the anode catalyst layer and the cathode catalyst layer, characterized in that, The anode catalyst layer comprises the nano-network iridium oxide as described in claim 6.

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