Iridium black nanoparticles containing multiple twin and grain boundary structures and methods of making the same

Abstract

The application discloses an iridium black nanoparticle containing multiple twin crystals and grain boundary structures and a preparation method thereof. 4+ The application adjusts the pH of a precursor solution to reduce Ir, adopts Joule heat to rapidly heat the iridium precursor, performs rapid cooling after short-time heat preservation, restrains particle coarsening while retaining high-density twin crystal boundaries, and obtains the iridium black nanoparticle which is uniformly dispersed and contains defects.

Description

Technical Field

[0001] This invention belongs to the field of electrocatalytic nanomaterial catalysts, specifically relating to an iridium black nanoparticle containing multiple twins and grain boundary structures and its preparation method. Background Technology

[0002] Proton exchange membrane (PEM) water electrolysis for hydrogen production has become a core route for green hydrogen production due to its advantages such as fast response speed and high energy efficiency. The oxygen evolution reaction (OER) at the anolyte involves a four-electron transfer process (2H₂O → O₂ + 4H₂O). + +4e - The reaction kinetics are extremely slow, with the overpotential (η) accounting for 50%-70% of the total voltage loss in the electrolyzer (J. Electrochem. Soc., 2021, 168, 054522). Therefore, the OER catalyst is crucial for the performance and cost of the electrolyzer. PEM electrolyzers require operation under strongly acidic (pH≈2) and high-potential (>1.5 V) conditions, which limits the choice of catalyst. Non-precious metal (such as Ni and Co-based) catalysts dissolve completely in acidic conditions within hours, necessitating the selection of precious metals with strong acid resistance. Considering both activity and stability, iridium-based materials are the preferred choice for OER anode catalysts. However, iridium is expensive and scarce, with a global annual production of only 7-8 tons. Therefore, effectively improving iridium utilization and developing efficient and stable iridium-based catalysts are key issues that must be addressed in this field.

[0003] The two most commonly used iridium-based catalysts in industry are iridium dioxide and iridium black. However, the catalytic activity and stability of existing catalysts are not ideal, and the iridium concentration in PEM electrolyzers exceeds 3 mg / cm². Currently, the main method for preparing iridium dioxide is the Adams process. Because the Adams process is carried out in a molten nitrate system, the reaction kinetics are difficult to control precisely, and the products may have mixed morphologies, making it difficult to obtain uniform nanostructures. Furthermore, the decomposition of nitrates at high temperatures may produce harmful gases such as NOx (CN118272834A, J. Xu et al. / Electrochimica Acta 56 (2011) 10223–10230). Common methods for preparing iridium black require the addition of NaBH₄ reducing agent, surfactants, polyols, and other organic solvents (CN118773645A, J.Am. Chem. Soc. 2018, 140, 12434-12441), generating large amounts of organic wastewater and polluting the environment.

[0004] Iridium black nanoparticles prepared by existing technologies are generally highly crystalline nanoparticles. This uniform crystal structure can lead to significant defects in practical industrial applications. On the one hand, highly crystalline crystals have few defects, and only a limited number of active sites are exposed on the surface. On the other hand, under strong acid and high potential conditions, the catalyst material may dissolve or agglomerate, resulting in a sharp decline in catalytic activity. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides iridium black nanoparticles containing multiple twins and grain boundary structures, and a method for preparing the same. This invention reduces Ir by adjusting the pH of the precursor solution. 4+ By rapidly heating the iridium precursor using Joule heating, holding it at that temperature for a short time, and then rapidly cooling it, high-density twin boundaries were preserved while particle coarsening was suppressed, resulting in uniformly dispersed iridium black nanoparticles containing defects. This approach maintained high activity while extending the stability of the nanoparticles.

[0006] One of the technical solutions of this invention is to provide a method for preparing iridium black nanoparticles containing multiple twins and grain boundary structures, comprising the following steps: (1) Add Na2SO4 to an ethanol solution of 5 mg / mL chloroiridic acid, and then adjust the pH of the solution to 10~11 with 0.1 M NaOH; then stir at 80°C, add water to completely dissolve Na2SO4, and continue stirring until dry to obtain powder; (2) Spread the obtained powder on a heated substrate and apply electricity to the heated substrate in an air atmosphere to achieve thermal shock treatment of the iridium precursor powder; the thermal shock treatment is as follows: heat up to 750°C at a rate of 2000 K / s and hold for 10 s, then cool down to room temperature at a rate of 700 K / s; wash and dry to obtain iridium black nanoparticles containing multiple twins and grain boundary structures.

[0007] Furthermore, the mass ratio of chloroiridic acid to Na2SO4 is 1:20.

[0008] Furthermore, the heating substrate is carbon cloth, carbon paper, or metal foil.

[0009] Furthermore, the washing method involves centrifugation washing with ultrapure water and ethanol.

[0010] The second technical solution of the present invention is to provide an iridium black nanoparticle prepared by the above method.

[0011] Furthermore, these iridium black nanoparticles contain multiple twin and grain boundary structures. The coordination unsaturated sites formed at the intersection of twin and heterojunction grain boundaries lower the formation energy barrier of the *OOH intermediate, accelerating the OER kinetics. The twin structure can suppress the extraction of lattice oxygen and reduce the high-valence state Ir. n+ To IrOx The irreversible transformation of iridium atoms, coupled with the heterogeneous grain boundaries acting as atomic diffusion barriers, effectively prevents the dissolution and loss of iridium atoms in strongly acidic environments and significantly reduces the agglomeration tendency of nanoparticles. These synergistic mechanisms can fundamentally resolve the contradiction between activity and stability in traditional iridium black catalysts during acidic oxygen evolution reactions.

[0012] Furthermore, the average particle size of the iridium black nanoparticles is no greater than 10 nm.

[0013] The third technical solution of the present invention is to provide the catalytic application of the above-mentioned iridium black nanoparticles in the electrocatalytic oxygen evolution reaction.

[0014] The advantages of this invention are: 1. Iridium black nanoparticles with an average particle size of 6 nm were rapidly prepared by calcining samples with high-temperature thermal shock. This unsteady-state synthesis mechanism overcomes the diffusion limitations of traditional calcination processes, enabling stable control of grain size within the sub-10 nm range. A pulsed rapid heating and cooling strategy was employed during the calcination process, utilizing non-equilibrium phase transition kinetics to successfully construct iridium black nanoparticles with multiple twin boundaries and heterogeneous grain boundaries. The preparation process is simple and rapid, facilitating large-scale production.

[0015] 2. The iridium black nanoparticles prepared by this invention exhibit excellent acidic OER activity and stability, while also possessing outstanding proton exchange membrane water electrolysis activity and stability. In acidic OER, at 10 mA cm⁻¹ -2 The overpotential at current density is only 185 mV, and at 10 mA cm⁻¹ -2 It can operate stably for 1000 hours at a given current density. In PEM, the current can reach 1A at 1.7 V, while maintaining stability for over 400 hours.

[0016] 3. This invention does not require chemical reducing agents such as ethylene glycol, NaBH4, and formaldehyde, thus avoiding the covering of active sites by unreacted reducing agents and effectively preventing impurity contamination.

[0017] 4. The method for preparing iridium black nanoparticles provided by this invention is simple, time-consuming, energy-efficient, environmentally friendly, and conducive to industrial production. Attached Figure Description

[0018] Figure 1 The image shows the X-ray diffraction (XRD) pattern of the iridium black nanocatalyst prepared in Example 1. Figure 2 This is a transmission electron microscope (TEM) image of the iridium black nanocatalyst prepared in Example 1; Figure 3 This is an aberration-corrected transmission electron microscope image of the iridium black nanocatalyst prepared in Example 1; Figure 4 The graphs show a comparison of polarization curves (LSV) and Tafel slopes of the iridium black nanocatalyst prepared in Example 1, the commercial iridium black catalyst, and the commercial iridium oxide catalyst. Figure 5 This is a comparison of the LSV curves of the iridium black nanocatalyst prepared in Example 1 before and after the accelerated degradation stability test with those of commercial iridium black catalyst and commercial iridium oxide catalyst. Figure 6 This is a comparison of the half-cell stability of the iridium black nanocatalyst prepared in Example 1, commercial iridium oxide, and commercial iridium black. Figure 7 The image shows a comparison of the PEMWE activities of the iridium black nanocatalyst prepared in Example 1, commercial iridium oxide, and commercial iridium black. Figure 8 This is a comparison chart of the PEMWE stability of the iridium black nanocatalyst prepared in Example 1 and commercial iridium oxide. Detailed Implementation

[0019] The following examples are provided to further illustrate the present invention and are intended to explain the invention, not to limit its scope. Unless otherwise specified, all figures are expressed in parts by weight and weight percentages.

[0020] Unless otherwise specified, the raw materials used in this invention are all conventional commercially available products; unless otherwise specified, the methods used in this invention are all conventional methods in the field.

[0021] The embodiments of the present invention will be further described below with reference to several examples.

[0022] It should be understood that the described embodiments are merely some, not all, of the embodiments in this application. All other embodiments obtained by those skilled in the art based on the embodiments in this application without inventive effort are within the scope of protection of this application.

[0023] The terminology used in the embodiments of this application is for the purpose of describing particular embodiments only and is not intended to be limiting of this application. The singular forms “a,” “the,” and “the” used in the embodiments of this application and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise.

[0024] Example 1 (1) Dissolve chloroiridic acid in ethanol to prepare a solution of 5 mg / mL, stir evenly at room temperature to obtain solution A, add Na2SO4 to solution A; then add 0.1 M NaOH dropwise to solution A to adjust the pH to 10~11 to obtain solution B.

[0025] (2) Heat solution B to 80°C and stir. Then add an appropriate amount of ultrapure water to completely dissolve Na2SO4. Continue stirring until dry. Scrape the sample off and collect it. Grind it into powder.

[0026] (3) Spread the powder obtained in step (2) on the heating substrate and apply an electric current to the heating substrate in an air atmosphere to achieve thermal shock treatment of the iridium precursor powder. During the thermal shock process, the temperature is raised to 750°C at a rate of 2000 K / s and held for 10 s, and then cooled to room temperature at a rate of 700 K / s.

[0027] (4) The powder obtained in step (3) was washed by centrifugation with ultrapure water and ethanol, and then dried at 80°C overnight. The dried solid was then ground to obtain iridium black nanoparticles.

[0028] Figure 1 The X-ray diffraction (XRD) pattern of the catalyst prepared according to Example 1 is shown. The results show that the diffraction peaks in the XRD pattern of the catalyst prepared in Example 1 correspond to metallic iridium (PDF #87-0715), with peaks at 40.7° and 43.3° corresponding to the (111) and (002) crystal planes of Ir, respectively. The average particle size of the iridium black nanoparticles was calculated to be 6.15 nm according to the Scherrer equation.

[0029] Figure 2 The image shows a transmission electron microscope (TEM) image of the catalyst prepared according to Example 1. The TEM image shows that the prepared iridium black catalyst consists of well-dispersed nanoparticles with uniform particle size, and the particle size is consistent with the particle size calculated by the Scherrer equation.

[0030] Figure 3 The image shows an aberration-corrected transmission electron microscope (TEM) image of the catalyst prepared according to Example 1. The HAADF-STEM image reveals abundant atomic-level defects within the iridium black nanoparticles. This high-density defect composite system is formed by twin-grain boundary synergy, creating a microstructure substrate with both geometric heterogeneity and electronic control capabilities.

[0031] At 10 mA cm 2 At a current density of 100 mA cm⁻¹, the overpotential of the iridium black catalyst in Example 1 was only 185 mV, while the overpotential of commercial iridium oxide was 330 mV; 2 At the specified current density, the overpotential of the iridium black catalyst in Example 1 was only 243 mV. Simultaneously, the Tafel slope of Example 1 was only 50.4 mV dec. -1 .

[0032] After 5000 CV cycles, the iridium black nanocatalyst reached 100 mA cm⁻¹. 2The potential difference at the current density is only 7 mV. In a 0.5 M H₂SO₄ solution at 100 mA cm⁻¹ 2 At the specified current density, the catalyst of Example 1 remained stable for 120 h with almost no degradation.

[0033] Figure 8 The iridium black nanocatalyst prepared in Example 1 was tested at 1 A cm⁻¹. -2 Under high current density, the electrolytic cell exhibits a stable operating voltage curve, which does not decay even after more than 400 hours of continuous operation.

[0034] Comparative Example 1 (1) Dissolve chloroiridic acid in a certain volume of ethanol solution to prepare a 5 mg / mL solution. Stir well at room temperature to obtain solution A. Add Na2SO4 to solution A. Then add 0.1 M NaOH dropwise to solution A to adjust pH = 14 to obtain solution B.

[0035] (2) Heat solution B to 80°C and stir. Then add an appropriate amount of ultrapure water to completely dissolve Na2SO4. Continue stirring until dry. Scrape the sample off and collect it. Grind it into powder.

[0036] (3) Spread the powder obtained in step (2) on the heating substrate and apply an electric current to the heating substrate in an air atmosphere to achieve thermal shock treatment of the iridium precursor powder. During the thermal shock process, the temperature is raised to 750°C at a rate of 2000 K / s and held for 10 s, and then cooled to room temperature at a rate of 700 K / s.

[0037] (4) The powder obtained in step (3) was washed by centrifugation with ultrapure water and ethanol, and then dried at 80°C overnight. The dried solid was then ground to obtain iridium black nanoparticles.

[0038] Comparative Example 2 (1) Dissolve chloroiridic acid in a certain volume of ethanol solution to prepare a 5 mg / mL solution. Stir well at room temperature to obtain solution A. Add Na2SO4 to solution A. Then add 0.1 M NaOH dropwise to solution A to adjust pH = 9 to obtain solution B.

[0039] (2) Heat solution B to 80°C and stir. Then add an appropriate amount of ultrapure water to completely dissolve Na2SO4. Continue stirring until dry. Scrape the sample off and collect it. Grind it into powder.

[0040] (3) Spread the powder obtained in step (2) on the heating substrate and apply an electric current to the heating substrate in an air atmosphere to achieve thermal shock treatment of the iridium precursor powder. During the thermal shock process, the temperature is raised to 750°C at a rate of 2000 K / s and held for 10 s, and then cooled to room temperature at a rate of 700 K / s.

[0041] (4) The powder obtained in step (3) was washed by centrifugation with ultrapure water and ethanol, and then dried at 80°C overnight. The dried solid was then ground to obtain iridium black nanoparticles.

[0042] Comparative Example 3 (1) Dissolve chloroiridic acid in a certain volume of ethanol solution to prepare a 5 mg / mL solution. Stir well at room temperature to obtain solution A. Add Na2SO4 to solution A. Then add 0.1 M NaOH dropwise to solution A to adjust the pH to 10~11 to obtain solution B.

[0043] (2) Heat solution B to 80°C and stir. Then add an appropriate amount of ultrapure water to completely dissolve Na2SO4. Continue stirring until dry. Scrape the sample off and collect it. Grind it into powder.

[0044] (3) Spread the powder obtained in step (2) on a ceramic boat, heat it to 750°C in a muffle furnace at a heating rate of 10°C / min, keep it at that temperature for 1 h, and then cool it to room temperature with the furnace.

[0045] (4) The powder obtained in step (3) was washed by centrifugation with ultrapure water and ethanol, and then dried overnight at 80°C. The dried solid was then ground to obtain iridium dioxide nanoparticles.

[0046] Results: Iridium dioxide forming the rutile phase lacks multiple twin boundaries and heterogeneous grain boundaries, resulting in a reduced active surface area and decreased oxygen evolution reaction performance in the OER.

[0047] Comparative Example 4 A commercial iridium dioxide catalyst was used, purchased from Shanghai Jiuling.

[0048] Comparative Example 5 Commercial iridium black catalyst was used, purchased from Premetek, USA.

[0049] Figure 4 This is a comparison of the OER polarization curves of the iridium black nanocatalyst prepared in Example 1 and the commercial iridium oxide in Comparative Example 4 in 0.5 M H2SO4 solution. (At 10 mA cm⁻¹) 2 At a current density of 100 mAcm, the overpotential of the iridium black catalyst in Example 1 was only 185 mV, while the overpotential of commercial iridium oxide was 330 mV and the overpotential of commercial iridium black catalyst was 261 mV; 2 At the specified current density, the overpotential of the iridium black catalyst in Example 1 was only 243 mV, while the overpotential of commercial iridium oxide was 567 mV and the overpotential of commercial iridium black was 339 mV. Simultaneously, the Tafel slope of Example 1 was only 50.4 mV dec. -1 This is far lower than that of commercial iridium oxide (142.7 mV dec).-1 ) and commercial iridium black (76.7 mV dec) -1 This indicates that the iridium black nanocatalyst prepared in this invention has superior acidic OER activity compared to commercial iridium oxide and commercial iridium black.

[0050] Figure 5 The iridium black nanocatalyst prepared in Example 1, the commercial iridium black catalyst, and the commercial iridium oxide catalyst were subjected to a reaction in 0.5 M H2SO4 solution at 100 mV s. -1 The LSV curves (without iR compensation) of the iridium black nanocatalyst before and after 5000 CV cycles were tested at a high potential range of 1.2–2 V vs. RHE. The solid line is the initial LSV curve of the working electrode, and the dashed line is the LSV curve after 5000 cycles. After 5000 CV cycles, the iridium black nanocatalyst at 100 mA cm⁻¹ 2 The potential difference at the current density is only 7 mV, while the potential difference between commercial iridium black catalyst and commercial iridium oxide catalyst is 160 mV and 186 mV, respectively.

[0051] Figure 6 The iridium black nanocatalyst prepared in Example 1 and the commercial iridium oxide from Comparative Example 4 were reacted in 0.5 M H₂SO₄ solution at 100 mA cm⁻¹ 2 The stability at current densities was assessed. The catalyst in Example 1 maintained long-term stability with almost no degradation for 120 hours, while commercial iridium black stability was maintained for only 40 hours, and commercial iridium oxide experienced severe degradation after only a few hours.

[0052] Figure 7 The iridium black nanocatalyst prepared in Example 1, commercial iridium oxide, and commercial iridium black P were subjected to PEMWE performance testing at 60 °C. MEAs were constructed on both sides of a Nafion 115 proton exchange membrane using the iridium black nanocatalyst sample and a commercial platinum-carbon catalyst as the anode and cathode catalysts, respectively. For comparison, MEAs using commercial iridium oxide and commercial iridium black as anode catalysts were prepared under the same conditions. Specifically, the Ir-Black‖Pt / C electrolyzer could generate 1 A cm⁻¹ at a cell voltage of 1.69 V. -2 The current density is lower than the 1.86 V required for the COM-IrO2‖Pt / C electrolytic cell and the 1.80 V required for the COM-IrB‖Pt / C electrolytic cell.

[0053] Table 1: Performance Comparison of Examples 1, 2, and 3 with Comparative Examples 4 and 5 Example 1 <![CDATA[10 mA cm 2 @185 mV]]> <![CDATA[1.69 V@1 A cm -2 ]]> <![CDATA[400 h@1 A cm -2 ]]> Comparative Example 1 <![CDATA[10 mA cm 2 @238 mV]]> <![CDATA[1.74 V@1 A cm -2 ]]> <![CDATA[100 h@1 A cm -2 ]]> Comparative Example 2 <![CDATA[10 mA cm 2 @241 mV]]> <![CDATA[1.76 V@1 A cm -2 ]]> <![CDATA[70 h@1 A cm -2 ]]> Comparative Example 3 <![CDATA[10 mA cm 2 @492 mV]]> <![CDATA[2 HYPERLINK "mailto:V@0.516" V@0.516 A cm -2 ]]> — Comparative Example 4 <![CDATA[10 mA cm 2 @330 mV]]> <![CDATA[1.86 V@1 A cm -2 ]]> <![CDATA[60 h@1 A cm -2 ]]> Comparative Example 5 <![CDATA[10 mA cm 2 @261 mV]]> <![CDATA[1.80 V@1 A cm -2 ]]> <![CDATA[70 h@1 A cm -2 ]]> As shown in Table 1, the oxygen evolution activity and stability of the iridium black nanocatalysts prepared in Examples 1, 2 and 3 are higher than those of Comparative Examples 4 and 5.

[0054] The synthesis method of iridium black nanocatalyst provided by this invention is simple, time-saving, low-cost, green and pollution-free, and easy to scale up. The prepared iridium black catalyst particles are small in size, uniformly dispersed, and rich in defects.

[0055] In particular, the iridium black nanocatalyst prepared in Example 1 only requires 1.69 V to achieve 1 A cm⁻¹ in the PEMWE full cell test. -2 The iridium black nanocatalyst prepared in the examples achieved a current density that allowed it to operate stably for 400 hours, demonstrating optimal oxygen evolution reaction catalytic performance. The iridium black nanocatalyst prepared in these examples also showed significant effects in the electrochemical oxygen evolution reaction, achieving a current density of 10 mA cm⁻¹. 2 The overpotential is only 185 mV, which is far superior to commercial iridium-based catalysts, and it has excellent half-cell stability and PEMWE full-cell stability.

[0056] The above embodiments describe in detail the structure, features, and effects of the present invention. The above description is only a preferred embodiment of the present invention. Any changes made in accordance with the concept of the present invention, or equivalent embodiments modified to have equivalent changes, shall still fall within the scope of protection of the present invention if they do not exceed the scope covered by the specification.

Claims

1. A method for preparing iridium black nanoparticles containing multiple twins and grain boundary structures, characterized in that, It includes the following steps: (1) Add Na2SO4 to the ethanol solution of chloroiridic acid, and then adjust the pH of the solution to 10~11; then stir at 80°C, add water to completely dissolve Na2SO4, and dry to obtain powder; (2) Spread the obtained powder on a heated substrate and apply electricity to the heated substrate in an air atmosphere to achieve thermal shock treatment of the iridium precursor powder; the thermal shock treatment is as follows: heat up to 750°C at a rate of 2000 K / s and hold for 10 s, then cool down to room temperature at a rate of 700 K / s; wash and dry to obtain iridium black nanoparticles containing multiple twins and grain boundary structures.

2. The method according to claim 1, characterized in that, The concentration of the chloroiridic acid ethanol solution is 5 mg / mL.

3. The method according to claim 1, characterized in that, The mass ratio of chloroiridic acid to Na2SO4 is 1:

20.

4. The method according to claim 1, characterized in that, The method for adjusting the pH of the solution to 10-11 is to add 0.1 M NaOH to the solution.

5. The method according to claim 1, characterized in that, The heating substrate is carbon cloth, carbon paper, or metal foil.

6. The method according to claim 1, characterized in that, The washing method involves centrifuging with ultrapure water and ethanol.

7. An iridium black nanoparticle prepared by the method described in claim 1.

8. The iridium black nanoparticles according to claim 7, characterized in that, The average particle size is no greater than 10 nm.

9. The catalytic application of iridium black nanoparticles as described in claim 7 in the electrocatalytic oxygen evolution reaction.

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