High surface area, high porosity iridium-based catalysts and methods of making same

Abstract

Iridium-based catalysts and methods of making the catalysts are described. The catalyst comprises a catalyst material comprising particles comprising iridium or a mixture of iridium and iridium oxide. The particles include an interconnected network of nanoparticles. The particles are in the range of 50 nm to 1 [mu] m, and the nanoparticles are in the range of 2 nm to 15 nm. It may have a BET surface area of 30 m2 / g or greater and a pore volume of at least 0.10 cc / g. The catalyst is prepared using an organic structure directing agent.

Description

[0001] Priority Claim

[0002] This application claims priority to U.S. Provisional Patent Application Serial No. 63 / 477,422, filed on December 28, 2022, the entire content of which is incorporated herein by reference. Background Art

[0003] Hydrogen plays an important role in the path towards an environmentally friendly low-carbon energy structure as an energy carrier for grid balancing or power-to-gas and power-to-liquid processes. Water electrolysis produces high-quality hydrogen by electrochemically decomposing water into hydrogen and oxygen; the reaction is given by Equation 1 below. The water electrolysis process is an endothermic process and electricity is the energy source. When the method is operated by renewable energy sources such as wind, solar, or geothermal energy, water electrolysis has a zero carbon footprint. The main water electrolysis technologies include alkaline electrolysis, proton exchange membrane (PEM) water electrolysis (such as Figure 1 PEMWE as shown), anion exchange membrane (AEM) water electrolysis (such as Figure 2 AEMWE as shown), and solid oxide water electrolysis.

[0004] As Figure 1 shown in PEMWE system 100, the anode 105 and the cathode 110 are separated by a solid PEM electrolyte 115, such as a sulfonated tetrafluoroethylene-based cofluoropolymer sold under the trademark by Chemours company. The anode and cathode catalysts typically comprise IrO2 and Pt, respectively. At the positively charged anode 105, pure water 120 is oxidized to produce oxygen 125, electrons (e - ) and protons; the reaction is given by Equation 2. Protons are transported from the anode 105 to the cathode 110 through the proton-conducting PEM 115. At the negatively charged cathode 110, a reduction reaction occurs where electrons from the cathode 110 are given to protons to form hydrogen 130; the reaction is given by Equation 3. The PEM 115 not only conducts protons from the anode 105 to the cathode 110 but also separates the H2 gas 130 and O2 gas 125 produced in the water electrolysis reaction. PEM water electrolysis is one of the favorable methods for converting renewable energy into high-purity hydrogen, with advantages such as a compact system design under high pressure differential, high current density, high efficiency, fast response, small footprint, low-temperature (20 °C - 90 °C) operation, and high-purity oxygen by-products. However, one of the main challenges of PEM water electrolysis is the high capital cost of the cell stack, including expensive acid-resistant stack hardware (such as Pt-coated Ti bipolar plates), expensive noble metal catalysts required for the electrodes, and expensive PEMs.

[0005] Water electrolysis reaction: 2 H2O → 2 H2 + O2 (1)

[0006] Anodic oxidation reaction of PEMWE: 2 H2O → O2 + 4 H + + 4 e - (2)

[0007] Cathodic reduction reaction of PEMWE: 2 H + + 2 e - → H2 (3)

[0008] AEMWE is a developing technology. As Figure 2 shown, in AEMWE system 200, anode 205 and cathode 210 are separated by a solid AEM electrolyte 215. Generally, a water feed 220 with an added electrolyte (such as diluted KOH or K2CO3 or deionized water) is fed to the cathode side. Anode and cathode catalysts generally include Ni-based or Ni-alloy catalysts without platinum group metals. At the negatively charged cathode 210, water is reduced by adding four electrons to form hydrogen gas 225 and hydroxide ions; this reaction is given by Equation 4. The hydroxide ions diffuse from the cathode 210 to the anode 205 through the AEM 215 that conducts hydroxide ions. At the positively charged anode 205, the hydroxide ions recombine to form water and oxygen gas 230; this reaction is given by Equation 5. The AEM 215 not only conducts hydroxide ions from the cathode 210 to the anode 205, but also separates the H2 225 and O2 230 produced in the water electrolysis reaction. The AEM 215 allows the production of hydrogen gas 225 with a very high purity of at least 99.9% at a high pressure of up to 35 bar.

[0009] Cathodic reduction reaction of AEMWE: 4 H2O + 4 e - → 2 H2 + 4 OH - (4)

[0010] Anodic oxidation reaction of AEMWE: 4 OH - → 2 H2O + O2 + 4 e - (5)

[0011] IrO2 is widely accepted as the most effective oxygen evolution reaction (OER) catalyst in PEM-WE due to its high activity and stability. However, the limited supply and high price of IrO2 limit its use.

[0012] Therefore, there is a need for a highly active IrO2 that can be used at a lower loading while providing comparable or improved performance compared to commercial IrO x catalysts. Description of the Drawings

[0013] Figure 1It is a diagram of the PEMWE system.

[0014] Figure 2 It is a diagram of the AEMWE system.

[0015] Figure 3A 、 Figure 3B 、 Figure 3C They are scanning transmission electron microscopy (STEM) images of the Ir-oleylamine catalyst at different length scales.

[0016] Figure 4 It is a graph showing the comparison of the OER activities of (a) synthesized Ir-oleylamine according to the present invention, (b) oxidized Ir-oleylamine according to the present invention, and (c) commercial IrO2 catalyst.

[0017] Figure 5 It is a graph showing the polarization curves of a water electrolysis cell containing (a) Ir-oleylamine prepared according to the present invention and (b) commercial IrO2 catalyst. Detailed Description

[0018] 2 mg / cm in the anode layer of the catalyst-coated membrane (CCM) for PEMWE 2 IrO x A high loading of the OER catalyst is required for state-of-the-art PEM water electrolyzers to maintain high performance and high stability. Reducing the IrO x OER catalyst loading to 0.5 mg / cm 2 or lower results in low durability and low electrolyzer efficiency due to the poor mechanical stability of the very thin IrO x -based anode catalyst layer and defects in the CCM. The current state-of-the-art commercial IrO x catalyst using spherical IrO x nanoparticles has less contact between adjacent particles and thus is prone to forming defects in the very thin anode coating on the PEM. A low loading of the IrO x OER catalyst in the anode layer of the CCM results in a defective coating and poor electrical contact between the catalyst coating and the porous transport layer (PTL). Therefore, a low-loading catalyst coating with defects leads to a high cell / stack voltage, thus resulting in low electrolyzer efficiency. The BET surface areas of several commercial IrO x catalysts were measured, and all catalysts had a BET surface area of less than 25 m 2 / g. The pore volumes of these commercial IrO x catalysts were also measured, and the pore volume was 0.05 cc / g or less.

[0019] The present invention provides a significant reduction in IrO xSolutions for loading without sacrificing performance and durability. A new family of Ir / IrO2 catalysts for the oxygen evolution reaction (OER) in PEMWE or AEMWE has been developed. The highly active iridium-based materials have high porosity and high surface area. The catalyst comprises particles that contain iridium or a mixture of iridium and iridium oxide in the range of 50 nm to 1 μm ( Figure 3A ). The particles include an interconnected network of nanoparticles, where one nanoparticle is connected to one or more adjacent nanoparticles to form a network of Ir particles ( Figure 3B ). The size of each nanoparticle is in the range of 2 nm to 15 nm ( Figure 3C ). The CCM prepared using the high surface area, high porosity, highly active Ir / IrO2 as the OER catalyst has performance comparable to that of commercial IrO2 catalysts at lower IrO2 loadings.

[0020] The morphology of IrO2 is important, specifically when the IrO x loading in the anode catalyst layer is low (e.g., 0.5 mg / cm 2 or lower). Commercial IrO2 has a spherical morphology, which introduces too many defects in the catalyst layer to maintain activity when the IrO2 loading is reduced. Due to less overlap between adjacent particles, the defects in the thin IrO2 catalyst coating are typically areas without a catalyst coating. In contrast, the morphology of the particles including an interconnected network of nanoparticles maintains a continuous and well-connected catalyst layer structure in the thin catalyst coating, resulting in low resistance and good performance. The Ir / IrO x with the desired morphology of particles including an interconnected network of nanoparticles has a higher tendency to form a continuous anode catalyst layer without pinholes in the CCM. The structure of the interconnected network of nanoparticles provides better contact between Ir / IrO x particles in the anode catalyst layer, resulting in lower resistance. The uniform anode catalyst layer also helps maintain its low contact resistance with the porous transport layer.

[0021] PEM electrolyzer test results (discussed below) show that, under the same test conditions, the CCM of the catalyst of the present invention with an IrO2 loading of 0.2 mg / cm 2 exhibits performance comparable to that of commercial IrO2 with a loading of 1.0 mg / cm 2 .

[0022] The catalyst particles are in the range of 50 nm to 1 μm, or 50 nm to 500 nm, or 100 nm to 500 nm, or 200 nm to 500 nm. The nanoparticles are in the range of 2 nm to 15 nm, or 2 nm to 10 nm, or 2 nm to 5 nm.

[0023] The catalyst has a pore volume of 0.10 cc / g or greater, or 0.20 cc / g or greater, or 0.30 cc / g or greater, or in the range of 0.10 cc / g to 0.70 cc / g, in the range of 0.10 cc / g to 0.60 cc / g, or in the range of 0.10 cc / g to 0.50 cc / g, or in the range of 0.10 cc / g to 0.40 cc / g.

[0024] The catalyst has 30 m 2 / g or greater, or 50 m 2 / g or greater, or in the range of 30 m 2 / g to 800 m 2 / g, or in the range of 50 m 2 / g to 700 m 2 / g, or in the range of 50 m 2 / g to 600 m 2 / g, or in the range of 50 m 2 / g to 500 m 2 / g, or in the range of 50 m 2 / g to 400 m 2 / g, or in the range of 50 m 2 / g to 300 m 2 / g of BET surface area.

[0025] In one embodiment, the catalyst has a BET surface area in the range of 30 m 2 / g to 300 m 2 / g and a pore volume in the range of 0.10 cc / g to 0.70 cc / g.

[0026] In one embodiment, the particles have a size in the range of 50 nm to 500 nm, the nanoparticles have a size in the range of 2 nm to 5 nm, and the pore volume is in the range of 0.10 cc / g to 0.40 cc / g.

[0027] In one embodiment, the particles have a size in the range of 200 nm to 500 nm, the nanoparticles have a size in the range of 2 nm to 5 nm, and the pore volume is in the range of 0.10 cc / g to 0.40 cc / g.

[0028] The catalyst is prepared using an organic structure-directing agent. The organic structure-directing agent coordinates with the Ir precursor to form a coordination complex. Due to the steric hindrance of the organic structure-directing agent, the presence of the coordinating ligands affects the packing of the Ir species of the material in solution. After adding a reducing agent, due to the organic structure-directing agent, the Ir species are reduced to the metallic form in a controlled manner, thus preventing the formation of much larger Ir / IrO2 nanoparticles, such as those in commercial IrO2 catalysts. The organic structure-directing agent plays an important role in determining the morphology of the final Ir / IrO x material. During synthesis, a solution is prepared from an iridium-based precursor in a first solvent. An organic structure-directing template is added to the first solution. A second solution containing a reducing agent is provided. The first solution and the second solution are mixed to form a wet iridium-based catalyst.

[0029] The wet iridium-based catalyst is then dried. Suitable drying temperatures include, but are not limited to, 30 °C to 100 °C, or 30 °C to 50 °C. Suitable drying times include, but are not limited to, 20 minutes to 600 minutes, or 20 minutes to 600 minutes, 20 minutes to 300 minutes, or 20 minutes to 240 minutes, or 20 minutes to 120 minutes, or 30 minutes to 600 minutes, 30 minutes to 300 minutes, or 30 minutes to 240 minutes, or 30 minutes to 120 minutes.

[0030] In some embodiments, before drying, the wet iridium-based catalyst is washed with water, or an organic solvent, or a combination thereof.

[0031] The organic structure-directing template includes multiple heteroatoms, such as oxygen, nitrogen, sulfur, and / or phosphorus, which can coordinate with the Ir metal center during the heating process. Suitable organic structure-directing templates include, but are not limited to, oleylamine, cysteamine, tetradecyltrimethylammonium bromide, 2,2'-bipyridine, terpyridine, trioctylamine, tris(2-aminoethyl)amine, ethylenediamine, 3-aminopropane-1-thiol, glycine, ethanolamine, polyethyleneimine, or a combination thereof.

[0032] The reducing agent is used to reduce Ir 3+ to its metallic form, which subsequently forms Ir nanoparticles. Suitable reducing agents include, but are not limited to, sodium borohydride, hydrazine, sodium bis(2-methoxyethoxy)aluminum hydride, diisobutylaluminum hydride, lithium aluminum hydride, ascorbic acid, or a combination thereof.

[0033] Example

[0034] Example 1: Synthesis of Ir-octylamine catalyst

[0035] A sample of 400 mg of IrCl3 hydrate was mixed with 90 mL of ethanol in a flask, and the mixture was subjected to ultrasonic treatment for 30 minutes to assist in the dissolution of the solid. An aliquot of 1 mL of oleylamine was added to the solution, after which a brown precipitate formed. The flask was heated to 70 °C in a water bath, and then a 50 mL ethanol solution containing 600 mg of NaBH4 was slowly added to the mixture. The flask was maintained at this temperature for 20 minutes. The resulting black precipitate was recovered by centrifugation, washed 3 times with ethanol and 1 time with water. The typical yield of the synthesis based on Ir was approximately 85%.

[0036] Example 2: Evaluation of the intrinsic oxygen evolution reaction (OER) activity of two iridium-based catalysts

[0037] The commercial IrO2 catalyst and the new Ir-oleylamine catalyst prepared in Example 1 were evaluated in a bench-top electrochemical test cell. The catalyst ink was prepared by mixing the catalyst and ionomer (5 wt% solution in alcohol) in a mixture of deionized water and ethanol. The mixture was finely dispersed using an ultrasonic bath. An aliquot of 10 μL of the prepared ink was drop-cast onto a glassy carbon working electrode. After drying in air for 20 minutes, the electrode with the drop-cast catalyst was placed in an electrochemical test cell together with a counter electrode prepared from a Pt sheet and an Ag / AgCl (4M KCl) reference electrode.

[0038] Linear sweep voltammetry (LSV) measurements were carried out in the range from 0.5 V to 1.35 V (versus Ag / AgCl) at a rate of 10 mV / s, and the results for the two samples were pooled in Figure 4 . In the LSV measurement, when the voltage applied to the working electrode was scanned (which serves as a measure of the energy applied to the reaction), the current was measured as a measure of the oxygen evolution reaction rate. An ideal OER catalyst has a high current at a low applied voltage, e.g., this catalyst can reach 10 mA / cm at an overpotential of 250 mA 2 . As Figure 4 shown in a, the synthesized Ir-oleylamine catalyst has better OER activity because it has a higher OER current at any applied cell voltage (versus Ag / AgCl) within the measurement range. Commercial IrO2 is a less active catalyst because it exhibits the lowest OER current at any applied cell voltage ( Figure 4c). Another remarkable feature of the new Ir-based catalyst is the redox event that occurs at an applied voltage of 0.7 V to 1.3 V (versus Ag / AgCl). It is believed that this is due to the oxidation of Ir-related substances, indicating that the synthesized Ir-oleylamine catalyst is mainly Ir. Once the Ir-oleylamine catalyst is electrochemically oxidized, this feature disappears. Upon oxidation, the Ir-oleylamine catalyst also becomes more active than its as-synthesized form due to the higher current density at 1.35 V (versus Ag / AgCl). Figure 4 b).

[0039] Example 3: Evaluation of the water electrolysis performance of two iridium-based catalysts

[0040] The water electrolysis performance of a commercial IrO2 catalyst and the new Ir-oleylamine prepared in Example 1 was evaluated using a single water electrolyzer at 80 °C and atmospheric pressure.

[0041] The membrane coated with the commercial IrO2 catalyst and the membrane coated with the Ir-oleylamine catalyst were prepared using a perfluorosulfonic acid polymer-based membrane with a thickness of 55 μm, a commercial Pt / C catalyst as the cathode coating on one side of the membrane for the hydrogen evolution reaction (HER), and a commercial IrO2 catalyst (or Ir-oleylamine nanonet catalyst) as the anode coating on the other side of the membrane for the OER. The Ir loading and Pt loading on the membrane coated with the commercial IrO2 catalyst were 0.9 mg / cm 2 and 0.15 mg / cm 2 . The Ir loading and Pt loading on the membrane coated with the Ir-oleylamine catalyst were 0.21 mg / cm 2 and 0.18 mg / cm 2 . The catalyst-coated membrane was placed between two Pt-coated Ti felts as the anode and cathode porous transport layers to form a catalyst-coated membrane electrode assembly. Then, a test cell was installed using this catalyst-coated membrane electrode assembly.

[0042] A proton exchange membrane (PEM) water electrolysis test station (Scribner 600 electrolyzer test system) was used to evaluate the membrane electrode assembly coated with the commercial IrO2 catalyst and the membrane electrode assembly coated with the Ir-oleylamine catalyst in a cell with a 5 cm 2The water electrolysis performance in a single electrolytic cell with the active membrane area. The porous transport layer (PTL) and the compression factor (defined as the ratio between the gasket thickness and the PTL thickness) are the same among these components. The test station includes an integrated power supply, a voltage regulator, an impedance analyzer for electrochemical impedance spectroscopy (EIS) and high-frequency resistance (HFR), and real-time sensors for product flow rate and permeation monitoring. The test is conducted at 80 °C and 15 psig pressure. Ultra-pure water is supplied to the anode of the cell at a flow rate of 100 mL / min. Polarization curves are plotted (holding each data point for 1 minute at the end), as Figure 5 shown.

[0043] From Figure 5 it can be seen that the membrane electrode assembly coated with an Ir-oleylamine catalyst with a very low Ir loading of 0.21 mg / cm 2 ( Figure 5 a) shows comparable water electrolysis performance to the membrane electrode assembly coated with a commercial IrO2 catalyst with a higher Ir loading of 0.9 mg / cm 2 ( Figure 5 b), as demonstrated by comparable current densities at equal voltages.

[0044] Specific implementation scheme

[0045] Although the following is described in connection with specific embodiments, it should be understood that the description is intended to illustrate and not limit the scope of the foregoing description and the appended claims.

[0046] A first embodiment of the present invention is an iridium-based catalyst, the iridium-based catalyst comprising a catalyst material, the catalyst material comprising particles, the particles comprising iridium or a mixture of iridium and iridium oxide, and the iridium-based catalyst having 30 m 2a BET surface area of 0.10 m² / g or greater and a pore volume of 0.10 cc / g or greater, the particles having a size in the range of 50 nm to 1 µm, and wherein the particles comprise an interconnected network of nanoparticles having a size in the range of 2 nm to 15 nm. One embodiment of the present invention is one, any, or all of the previous embodiments in this paragraph up to the first embodiment in this paragraph, wherein the particles have a size in the range of 50 nm to 500 nm. One embodiment of the present invention is one, any, or all of the previous embodiments in this paragraph up to the first embodiment in this paragraph, wherein the particles have a size in the range of 100 nm to 500 nm. One embodiment of the present invention is one, any, or all of the previous embodiments in this paragraph up to the first embodiment in this paragraph, wherein the particles have a size in the range of 200 nm to 500 nm. One embodiment of the present invention is one, any, or all of the previous embodiments in this paragraph up to the first embodiment in this paragraph, wherein the nanoparticles have a size in the range of 2 nm to 10 nm. One embodiment of the present invention is one, any, or all of the previous embodiments in this paragraph up to the first embodiment in this paragraph, wherein the nanoparticles have a size in the range of 2 nm to 5 nm. One embodiment of the present invention is one, any, or all of the previous embodiments in this paragraph up to the first embodiment in this paragraph, wherein the pore volume is 0.20 cc / g or greater. One embodiment of the present invention is one, any, or all of the previous embodiments in this paragraph up to the first embodiment in this paragraph, wherein the pore volume is in the range of 0.10 cc / g to 0.70 cc / g. One embodiment of the present invention is one, any, or all of the previous embodiments in this paragraph up to the first embodiment in this paragraph, wherein the pore volume is in the range of 0.10 cc / g to 0.40 cc / g. One embodiment of the present invention is one, any, or all of the previous embodiments in this paragraph up to the first embodiment in this paragraph, wherein the catalyst particles have a size in the range of 200 nm to 500 nm, the nanoparticles have a size in the range of 2 nm to 5 nm, and the pore volume is in the range of 0.10 cc / g to 0.40 cc / g.

[0047] A second embodiment of the present invention is a method for preparing an iridium-based catalyst, the method comprising providing a first solution that comprises an iridium-based precursor in a first solvent; adding an organic structure-directing template to the first solution; providing a second solution that comprises a reducing agent in a second solvent; mixing the first solution with the second solution to form a wet iridium-based catalyst; and drying the wet iridium-based catalyst to form an iridium-based catalyst comprising a mixture of iridium or iridium and iridium oxide particles, the iridium-based catalyst having a BET surface area of 30 m2 / g or greater and a pore volume of 0.10 cc / g or greater, the particles having a size in the range of 50 nm to 1 μm, and wherein the particles comprise an interconnected network of nanoparticles having a size in the range of 2 nm to 15 nm. One embodiment of the present invention is one, any, or all of the previous embodiments in this paragraph up to the second embodiment in this paragraph, wherein the organic structure-directing template comprises oleylamine, cysteamine, tetradecyltrimethylammonium bromide, 2,2'-bipyridine, terpyridine, trioctylamine, tris(2-aminoethyl)amine, ethylenediamine, 3-aminopropane-1-thiol, glycine, ethanolamine, polyethyleneimine, or a combination thereof. One embodiment of the present invention is one, any, or all of the previous embodiments in this paragraph up to the second embodiment in this paragraph, wherein the reducing agent comprises sodium borohydride, hydrazine, sodium bis(2-methoxyethoxy)aluminum hydride, diisobutylaluminum hydride, lithium aluminum hydride, ascorbic acid, or a combination thereof. One embodiment of the present invention is one, any, or all of the previous embodiments in this paragraph up to the second embodiment in this paragraph, wherein the wet iridium-based catalyst is dried at a temperature in the range of 30 °C to 100 °C. One embodiment of the present invention is one, any, or all of the previous embodiments in this paragraph up to the second embodiment in this paragraph, wherein the wet iridium-based catalyst is dried at a temperature in the range of 30 °C to 50 °C. One embodiment of the present invention is one, any, or all of the previous embodiments in this paragraph up to the second embodiment in this paragraph, further comprising washing the wet iridium-based catalyst with water, an organic solvent, or a combination thereof before drying. One embodiment of the present invention is one, any, or all of the previous embodiments in this paragraph up to the second embodiment in this paragraph, wherein the particles have a size in the range of 50 nm to 500 nm. One embodiment of the present invention is one, any, or all of the previous embodiments in this paragraph up to the second embodiment in this paragraph, wherein the nanoparticles have a size in the range of 2 nm to 10 nm.One embodiment of the present invention is one, any, or all of the previous embodiments in this paragraph up to the second embodiment in this paragraph, wherein the particles have a size in the range of 50 nm to 500 nm, the nanoparticles have a size in the range of 2 nm to 5 nm, and the pore volume is in the range of 0.10 cc / g to 0.40 cc / g. One embodiment of the present invention is one, any, or all of the previous embodiments in this paragraph up to the second embodiment in this paragraph, wherein the particles have a size in the range of 200 nm to 500 nm, the nanoparticles have a size in the range of 2 nm to 5 nm, and the pore volume is in the range of 0.10 cc / g to 0.40 cc / g.

[0048] Although no further detailed description is provided, it is believed that those skilled in the art can make the most of the present invention by using the foregoing description and can easily determine the basic features of the present invention without departing from the essence and scope of the present invention to make various changes and modifications thereto and adapt it to various uses and conditions. Therefore, the foregoing preferred specific embodiments should be construed as merely illustrative and not in any way limiting the remainder of the disclosure, and are intended to cover various modifications and equivalent arrangements included within the scope of the appended claims.

[0049] In the foregoing, all temperatures are shown in degrees Celsius and all parts and percentages are by weight unless otherwise indicated.

Claims

1. An iridium-based catalyst, the iridium-based catalyst comprising: A catalyst material, the catalyst material comprising particles, the particles comprising iridium or a mixture of iridium and iridium oxide, and the catalyst having a BET surface area of 30 m 2 / g or greater and a pore volume of 0.10 cc / g or greater, the particles having a size in the range of 50 nm to 1 μm, and wherein the particles comprise an interconnected network of nanoparticles having a size in the range of 2 nm to 15 nm.

2. The catalyst according to claim 1, wherein the particles have a size in the range of 50 nm to 500 nm.

3. The catalyst according to any one of claims 1-2, wherein the nanoparticles have a size in the range of 2 nm to 10 nm.

4. The catalyst according to any one of claims 1-2, wherein the pore volume is in the range of 0.10 cc / g to 0.70 cc / g.

5. The catalyst according to any one of claims 1-2, wherein the catalyst particles have a size in the range of 200 nm to 500 nm, the nanoparticles have a size in the range of 2 nm to 5 nm, and the pore volume is in the range of 0.10 cc / g to 0.40 cc / g.

6. A method for preparing an iridium-based catalyst, the method for preparing an iridium-based catalyst comprising: Providing a first solution, the first solution comprising an iridium-based precursor in a first solvent; Adding an organic structure-directing template to the first solution; Providing a second solution, the second solution comprising a reducing agent in a second solvent; Mixing the first solution with the second solution to form a wet iridium-based catalyst; And The wet iridium-based catalyst is dried to form the iridium-based catalyst comprising a mixture of iridium or iridium and iridium oxide particles, the iridium-based catalyst having a BET surface area of 30 m 2 / g or greater and a pore volume of 0.10 cc / g or greater, the particles having a size in the range of 50 nm to 1 μm, and wherein the particles comprise an interconnected network of nanoparticles having a size in the range of 2 nm to 15 nm.

7. The method according to claim 6, wherein the organic structure-directing template comprises oleylamine, cysteamine, tetradecyltrimethylammonium bromide, 2,2'-bipyridine, terpyridine, trioctylamine, tris(2-aminoethyl)amine, ethylenediamine, 3-aminopropane-1-thiol, glycine, ethanolamine, polyethyleneimine, or a combination thereof.

8. The method according to any one of claims 6-7, wherein the reducing agent comprises sodium borohydride, hydrazine, sodium bis(2-methoxyethoxy)aluminum hydride, diisobutylaluminum hydride, lithium aluminum hydride, ascorbic acid, or a combination thereof.

9. The method according to any one of claims 6-7, wherein the wet iridium-based catalyst is dried at a temperature in the range of 30 °C to 100 °C.

10. The method according to any one of claims 6-7, the method further comprising: Before drying, washing the wet iridium-based catalyst with water, or an organic solvent, or a combination thereof.

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