A protonated layered iridium oxide (H-IrO2) nanosheet, its preparation method and application
By preparing protonated layered iridium oxide (H-IrO2) nanosheets, combining the layered structure and local defects, the problem of the imbalance between the activity and stability of the anode catalyst in an acidic environment was solved, achieving electrocatalytic performance with low overpotential and high stability, which is suitable for industrial water electrolysis systems.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- TIANJIN UNIV
- Filing Date
- 2024-10-22
- Publication Date
- 2026-05-26
AI Technical Summary
In the prior art, it is difficult for anode catalyst materials to achieve a balance between activity and stability in the oxygen evolution reaction in acidic environments. Traditional layered iridium oxide materials have insufficient catalytic activity and unstable structure under acidic conditions.
Protonated layered iridium oxide (H-IrO2) nanosheets were prepared by a rapid and gentle Joule heating and proton exchange process. By combining the layered structure with local defects, iridium oxide nanosheets with long-range ordered connections and local disordered defects were formed, avoiding the instability caused by long-term high-temperature calcination and exfoliation.
Protonated layered iridium oxide nanosheets exhibit low overpotential and high stability in the electrochemical oxygen evolution reaction, and can maintain catalytic activity for a long time under high current density, making them suitable for industrial water electrolysis systems.
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Figure CN119372697B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of electrocatalysis technology, and in particular to a novel protonated layered iridium oxide (H-IrO2) nanosheet, its preparation method, and its applications. Background Technology
[0002] Proton exchange membrane electrolysis of water is one of the mature commercial hydrogen production technologies currently available, offering advantages such as high current density, high hydrogen purity, and fast response. However, the strongly acidic environment and high oxidation potential limit the selection of anode catalyst materials. Iridium oxide is widely used as an anode catalyst for water splitting reactions due to its excellent stability in acidic environments. Amorphous iridium oxide exhibits excellent catalytic activity but poor stability; conversely, rutile iridium dioxide (IrO2) has a stable rigid structure but insufficient catalytic activity. Currently, achieving a balance between activity and stability in acidic oxygen evolution reaction (OER) catalysts remains a challenge, and a high-performance anode electrocatalyst is still lacking to meet the needs of industrial-scale water electrolysis.
[0003] Layered iridium oxide exhibits excellent catalytic potential due to its unique structure and properties, which differ from rutile phase and amorphous structures. Willinger et al. discovered that a high proportion of edge- and corner-shared IrO6 octahedra is a key structural feature that significantly enhances the activity of acidic OERs. Traditionally, layered iridium oxide is synthesized through prolonged high-temperature calcination, resulting in materials with high crystallinity and large particle size. Due to limited surface area and lack of active sites, their direct use as acidic OER catalysts is unsatisfactory. The introduction of intercalation exfoliation and proton exchange has been used to prepare ultrathin or monolayer iridium oxide nanosheets. Due to their increased surface area and abundant defects, iridium oxide nanosheets exhibit higher activity than rutile phase IrO2. Reduced structural stability may stem from the large number of structural defects generated by exfoliation, which weakens intralayer connections and reduces the stability of active sites. Therefore, integrating long-range order and local defects into the crystal structure of the same catalytic system is crucial for optimizing catalyst activity and stability, and is also a highly challenging research topic. Summary of the Invention
[0004] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide a protonated layered iridium oxide H-IrO2 nanosheet with both high activity and high stability, as well as its preparation method and application.
[0005] As one aspect of this invention, a protonated layered iridium oxide (H-IrO2) nanosheet is provided. The iridium oxide nanosheet has a layered structure, with protons accommodating between the layers and metallic iridium vacancy defects within the planes of the layered structure. In this invention, the octahedral units within the layers of the iridium oxide layered structure have stable connections, and the local defects provide a large number of active sites. The open interlayer spaces and abundant edges further increase the exposed surface area, which is beneficial for efficient mass transfer and reaction.
[0006] As a second aspect of the invention, the invention also provides a method for preparing the above-mentioned protonated layered iridium oxide H-IrO2 nanosheets. This method utilizes a rapid and gentle Joule heating process combined with a proton exchange process to prepare iridium oxide with long-range ordered connections and localized disordered defects. This synthesis method avoids prolonged high-temperature calcination or time-consuming intercalation and exfoliation, promotes protonation and defect construction, and avoids instability problems caused by excessive defects.
[0007] Specifically, the preparation method of the present invention includes the following steps:
[0008] 1) Iridium metal salts are hydrolyzed in alkaline solution to obtain amorphous iridium oxide precursors;
[0009] 2) Amorphous iridium oxide precursor iridium was subjected to Joule heating treatment to obtain layered iridium oxide nanosheets;
[0010] 3) Proton exchange reaction was carried out on layered iridium oxide nanosheets in acidic solution to obtain protonated layered iridium oxide nanosheets.
[0011] Furthermore, in the iridium metal salt, IrCl4 2- The concentration was 0.0001-0.0005 mol / L, and the solution pH was 10-14.
[0012] Furthermore, the Joule heating reaction is subjected to a medium heat treatment at a constant temperature of 300-900 °C for 0.5-60 seconds.
[0013] Furthermore, the acidic solution has a pH of 0 ≤ pH ≤ 5, and the treatment time is 6-24 hours.
[0014] As a third aspect of the invention, this invention also provides an application of the above-mentioned protonated layered iridium oxide nanosheets as an electrocatalyst for the oxygen evolution reaction (OER). The synergistic effect of the layered structure, interlayer protons, and surface defects of the protonated layered iridium oxide nanosheets results in excellent activity and stability of the iridium oxide H-IrO2 nanosheets as a catalyst in electrochemical tests. The excellent catalytic stability stems from the robust Ir-Ir connections in the layered structure and the highly reversible stretching properties of the Ir-O bonds within the IrO6 octahedral units during the OER process. The structural flexibility and robustness of the protonated layered iridium oxide achieve a synergistic improvement in catalyst activity and stability. Therefore, this catalyst structure, combining flexibility and stability, provides more options for industrial OER catalysts.
[0015] Compared with the prior art, the advantages of the present invention are as follows:
[0016] 1. The protonated layered iridium oxide nanosheet catalyst of the present invention can achieve a 10 mA cm⁻¹ reaction with only a low overpotential of 231 mV. -2 .
[0017] 2. The protonated layered iridium oxide nanosheet catalyst of the present invention maintains a wavelength of 10 mA cm⁻¹. -2 The oxygen evolution reaction was stable for 225 hours under high current density without significant activity degradation.
[0018] 3. In the assembled membrane electrode electrolytic cell, the prepared electrode is at 1 A cm⁻¹ -2 The electrode can maintain good activity for up to 120 hours under high current density, which demonstrates the high stability of the prepared electrode.
[0019] 4. The excellent activity and stability of the oxygen evolution catalyst of the present invention make it possible for practical industrial applications of high-current acidic water electrolysis. Attached Figure Description
[0020] Figure 1 These are electron microscope images of protonated layered iridium oxide nanosheets, where image a is a scanning electron microscope image, and images b and d are local structural images of the material obtained by high-magnification transmission electron microscopy.
[0021] Figure 2 The compositional analysis of protonated layered iridium oxide nanosheets is shown in Figure a, where Figure a is the thermogravimetric analysis diagram, and Figures b and c are the X-ray photoelectron spectra of metallic iridium and oxygen, respectively.
[0022] Figure 3 The protonated layered iridium oxide nanosheets were used as a catalyst in an acidic water electrolysis system (0.5 mol / L H2SO4) with a scan rate of 5 mV s. -1Comparison of cyclic voltammetry curves at 10 mA cm⁻¹ (Figure a), and the corresponding cyclic voltammetry curves at 10 mA cm⁻¹. -2 The constant current test at current density (Figure c) and Figure b show the curve of current density versus time at high current density in the membrane electrode electrolyzer.
[0023] Figure 4 Electrochemical iso-in-situ X-ray absorption spectra of protonated layered iridium oxide nanosheets and rutile phase iridium dioxide. Detailed Implementation
[0024] The present invention will be further described below with reference to specific preferred embodiments, but this does not limit the scope of protection of the present invention.
[0025] Example 1:
[0026] (1) Preparation of iridium oxide precursor: Dissolve chloroiridic acid in ethanol solution, then add 1 mol / L KOH solution. In the final solution system, IrCl4 2- The concentration of the solvent was 0.0005 mol / L, and the pH of the solution was 14. The solution was stirred and heated for 5 hours. After the solvent had completely evaporated, the sample powder was collected for later use.
[0027] (2) Preparation of layered iridium oxide nanosheets by Joule heating: Take an appropriate amount of precursor powder and place it on the Joule heating device, spread it evenly, and heat it at 900 °C for 0.5 seconds. After the reaction is completed, let it cool naturally, take out the powder sample, wash it with deionized water and ethanol respectively, centrifuge it, and dry it in an oven at 60 °C for later use.
[0028] (3) Protonated layered iridium oxide nanosheets were obtained by proton exchange: The dried layered iridium oxide nanosheet powder was placed in sulfuric acid solution (pH 0), left to stand for 6 hours, and then washed and centrifuged with deionized water and ethanol respectively. It was then dried in an oven at 60 degrees Celsius for later use. It is referred to as H-IrO2 catalyst below.
[0029] (4) As a comparison, we heated the H-IrO2 catalyst at 600 degrees for 2 hours in a tube furnace to obtain a sample of rutile phase iridium dioxide, which is referred to as R-IrO2 catalyst below.
[0030] Morphology and structural characterization: Scanning electron microscopy images show that the lateral dimensions of the H-IrO2 catalyst nanosheets reach the micrometer scale, and they overlap to form a three-dimensional structure. Figure 1a) Due to the electron sensitivity of the ultrathin layered nanosheets, low-dose transmission electron microscopy was used for morphological and structural characterization. High-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) images show a clear layered structure with an interlayer spacing of approximately 0.46 nm (Fig. 1b). In Fig. 1c, differential phase-contrast scanning transmission electron microscopy (iDPC-STEM) images reveal crystallographic features with long-range order. Furthermore, disordered regions within the layers and defects such as metal vacancies can be observed, as shown by dashed circles (Fig. 1d). These defects may be due to alkali metal ions occupying these sites during Joule heating and subsequently being removed during ion exchange. Meanwhile, the interatomic distance between adjacent Ir atoms was measured to be 0.315 nm.
[0031] We used thermogravimetric analysis (TGA) to study the mass variation of protonated layered iridium oxide with temperature. Figure 2 a). Weight loss below 200 °C primarily reflects the release of adsorbed water. Upon reaching 1000 °C, the continued weight loss is due to the removal of structural water and hydroxide ions, corresponding to proton loss in the layered structure and the H-IrO2 phase transformation into the thermally stable rutile structure (R-IrO2). Weight reduction above 1000 °C is due to the release of oxygen, forming metallic iridium. Surface analysis of the elemental oxidation states of layered iridium oxide and rutile IrO2 was performed. High-resolution XPS spectra of Ir 4f (…) Figure 2 b) shows that H-IrO2 contains Ir 3+ (62.2 eV), Ir in R-IrO2 4+ (62.0 eV). Oxygen species analysis showed that the proportion of hydroxyl groups on the surface of H-IrO2 was significantly higher than that of R-IrO2 (Figure 2c). These results indicate that protons in H-IrO2 effectively share the positive charge of Ir by forming hydroxyl groups with oxygen, thereby enriching the surface with hydroxyl and Ir sites and reducing its oxidation state.
[0032] Electrochemical performance testing: Room temperature electrochemical tests were conducted using a three-electrode system on a Shanghai Chenhua CHI760E electrochemical workstation. The working electrode was carbon paper supported on the prepared H-IrO2 catalyst powder, the reference electrode was an Hg / Hg2SO4 electrode (with saturated potassium sulfate as the electrolyte), and the counter electrode was a platinum sheet electrode. The electrolyte was 0.5 M H2SO4. The scan rate was 5 mV / s. -1 Linear voltammetry scanning was performed. All polarization curves were 95% ohmic compensated. The current density was 10 mA cm⁻¹. -2 The stability of the electrocatalyst was investigated by continuous electrolysis for 225 hours under certain conditions. A constant current of 1 A cm⁻¹ was maintained in the membrane electrode electrolysis cell. -2Under these conditions, an oxygen evolution test was conducted for 120 hours.
[0033] The OER electrocatalytic performance of two iridium oxides was evaluated in an acidic electrolyte of 0.5 M H₂SO₄. H-IrO₂ required only 231 mV overpotential to reach 10 mA cm⁻¹. -2 The current density required for H-IrO2 is 10 mA cm⁻¹, while that required for R-IrO2 is 319 mV (Figure 3a). -2 The H-IrO2 exhibited long-term stability of up to 225 hours at a high current density, while the rutile phase showed a gradual decrease in activity in less than 70 hours (Figure 3c). To further evaluate the industrial potential of H-IrO2, it was subjected to high current density (1 A cm⁻¹) in a membrane electrode electrolyzer. -2 Performance testing under operating conditions. As shown in Figure 3b, H-IrO2 can maintain excellent stability for up to 120 hours.
[0034] In-situ X-ray absorption spectroscopy (XAS) was used to monitor and characterize the changes in the oxidation state and coordination environment of the iridium sites during the OER process to further elucidate the potential structure-property relationship. The applied potentials were sequentially increased from the open-circuit potential (OCP), 1.2 V, 1.35 V to 1.5 V vs. RHE, and then symmetrically decreased back to OCP, resulting in a series of XAS spectra. For H-IrO2, the white line peak position shifted to higher energies with increasing applied potential (…). Figure 4 a) indicates that Ir is oxidized to a higher oxidation state, with the highest oxidation state exceeding that of Ir. +4 Conversely, the position of the white line in R-IrO2 showed no significant change. Figure 4 (b) indicates that the Ir sites in the rutile phase are not easily affected by protonation and oxidation, thus exhibiting good structural stability, but their activity is not ideal. Figure 4 c shows that the change in Ir-O bond length in H-IrO2 is negatively correlated with the applied potential. When the applied potential is reversed, the bond length returns to its initial state. Conversely, the Ir-O bond length in R-IrO2 remains essentially unchanged. Figure 4d). Furthermore, the variation in Ir-Ir distance is related to a certain degree of distortion in the IrO6 octahedral arrangement. In-situ observation of the Ir-Ir coordination environment shows that the Ir-Ir bonds in the second coordination shell of H-IrO2 remain almost unchanged during the application and removal of potentials (Fig. 4c), confirming the overall stability of the connections between the common-edge IrO6 octahedra in the layered structure. This means that structural perturbations at high applied potentials are limited to the IrO6 octahedral units, while the overall structural integrity is maintained. In the rutile phase, the Ir-Ir bond elongation at 1.5 V vs. RHE indicates an increase in disorder at elevated oxidation potentials (Fig. 4d). Although the bond length recovers to its original value after the potential decreases, prolonged operation at high potentials may gradually disrupt the structural integrity of R-IrO2. Therefore, the dynamic structural changes of the Ir-O bonds, combined with the rigid connections of the IrO6 units in the two-dimensional framework H-IrO2, synergistically promote its enhanced activity and stability.
[0035] Example 2:
[0036] (1) Preparation of iridium oxide precursor: Dissolve chloroiridic acid in ethanol solution, then add 1 mol / L KOH solution. In the final solution system, IrCl4 2- The concentration of the solvent was 0.0001 mol / L, and the pH of the solution was 10. The solution was stirred and heated for 5 hours. After the solvent had completely evaporated, the sample powder was collected for later use.
[0037] (2) Preparation of layered iridium oxide nanosheets by Joule heating: Take an appropriate amount of precursor powder and place it on the Joule heating device, spread it evenly, and heat it at 300 °C for 60 seconds. After the reaction is completed, let it cool naturally, take out the powder sample, wash it with deionized water and ethanol respectively, centrifuge it, and dry it in an oven at 60 °C for later use.
[0038] (3) Protonated layered iridium oxide nanosheets were obtained by proton exchange: The dried layered iridium oxide nanosheet powder was placed in sulfuric acid solution (pH 5), left to stand for 24 hours, then washed and centrifuged with deionized water and ethanol respectively, and dried in an oven at 60 degrees for later use. It is referred to as H-IrO2 catalyst below.
[0039] (4) As a comparison, we heated the H-IrO2 catalyst at 600 degrees for 2 hours in a tube furnace to obtain a sample of rutile phase iridium dioxide, which is referred to as R-IrO2 catalyst below.
[0040] The test was conducted according to the method described in Example 1. The results showed that the product obtained in this example has a typical layered structure, with long-range ordered regions and local defects within the layers. Further catalytic performance testing was performed according to the method described in Example 1. The results showed that the obtained layered protonated iridium oxide exhibits excellent catalytic activity at 10 mA cm⁻¹.-2 The overpotential is approximately 235mV.
[0041] The above description is merely a preferred embodiment of this application and does not constitute any limitation on this application. Although this application discloses preferred embodiments as described above, it is not intended to limit this application. Any modifications or alterations made by those skilled in the art without departing from the scope of the technical solution of this application using the disclosed technical content are equivalent to equivalent implementation cases and fall within the scope of the technical solution.
Claims
1. A method for preparing protonated layered iridium oxide (H-IrO2) nanosheets, wherein the iridium oxide nanosheets have a layered structure, protons are accommodated between the layers, and metallic iridium vacancy defects are present in the planes of the layered structure; characterized in that, Includes the following steps: 1) Alkaline hydrolysis of iridium metal salts yields amorphous iridium oxide precursors; 2) Joule heating treatment was performed to obtain layered iridium oxide nanosheets; the Joule heating reaction was carried out under constant temperature of 300-900 ℃ for 0.5-60 seconds. 3) Proton exchange reaction was carried out on layered iridium oxide nanosheets in acidic solution to obtain protonated layered iridium oxide nanosheets.
2. The method for preparing protonated layered iridium oxide (H-IrO2) nanosheets according to claim 1, characterized in that, In alkaline hydrolysis systems, among iridium metal salts, IrCl4 2- The concentration is 0.0001-0.0005 mol / L, and the solution pH is ≥10.
3. The method for preparing protonated layered iridium oxide (H-IrO2) nanosheets according to claim 1, characterized in that, The acidic solution has a pH of 0 ≤ pH ≤ 5, and the treatment time is 6-24 hours.
4. The application of the protonated layered iridium oxide (H-IrO2) nanosheets prepared by the method described in claim 1 as an electrocatalyst for the oxygen evolution reaction in acidic water electrolysis.