A foam-like iridium oxide catalyst, a preparation method and application thereof in proton exchange membrane water electrolysis hydrogen production technology

Abstract

The application relates to a foamy iridium oxide catalyst, a preparation method and application thereof in hydrogen production technology of proton exchange membrane water electrolysis, and belongs to the technical field of acidic water oxidation. A surfactant is used as a morphology directing agent, sodium citrate and ethylene glycol are used as complexing agents, potassium hexachloroiridate and the like are used as iridium sources, and the above are dissolved in water to obtain a uniform solution; the precursor obtained after the uniform solution is dried is subjected to programmed temperature calcination, and after cooling to room temperature, washing and drying, a foamy iridium oxide (f-H-IrO x ) catalyst is obtained. The f-H-IrO x ) catalyst prepared by the application not only has high catalytic activity (overpotential 273 mV@10 mA / cm 2 ), but also has excellent structural stability and good mass transfer performance, so that a low iridium membrane electrode prepared by using the catalyst has excellent catalytic activity (2.0 V@3.2 A / cm 2 ) and stability (500 h@2.0 A / cm 2 ) in a proton exchange membrane water electrolysis cell.

Description

Technical Field

[0001] This invention belongs to the field of acidic water oxidation technology, specifically relating to a foam-like iridium oxide catalyst, its preparation method, and its application in proton exchange membrane (PEM) water electrolysis for hydrogen production. Background Technology

[0002] The transition from a fossil fuel-dominated energy structure to a low-carbon, clean energy structure has become a global consensus and mission. Hydrogen energy, due to its high energy density and carbon-free combustion process, is considered a core component of the future energy structure. Coupled with renewable electricity (such as wind, hydro, and solar power) to produce hydrogen through water electrolysis, utilizing green electricity to produce green hydrogen not only meets major national development needs but also addresses the challenge of integrating renewable energy sources. PEM (Polymerized Electricity Extraction) water electrolysis technology is currently the only hydrogen production technology that can be effectively coupled with fluctuating renewable energy sources, making it an ideal pathway to convert electricity into hydrogen. However, the activity of currently commercially available anode catalysts (rutile IrO2) is not ideal, resulting in excessive energy consumption at the anode of the electrolyzer (approximately 30-50% of the total energy consumption of the electrolyzer). Therefore, developing efficient and long-term stable anode catalysts is crucial for promoting the large-scale deployment of PEM water electrolysis hydrogen production technology.

[0003] In the past decade, significant progress has been made in the development of novel iridium-based oxygen evolution catalysts. These include perovskite catalysts (Science, 2016, 353, 1011-1014; Adv. Mater. 2020, 32, 2001430; Angew. Chem. Int. Ed. 2020, 59, 19654), solid solution oxide catalysts (Nat. Commun. 2019, 10, 4875; Nat. Commun. 2023, 14, 5365), and supported catalysts (Angew. Chem. Int. Ed. 2022, 61, e202212341; Chem 2023, 9, 2931-2942), all of which exhibit higher intrinsic activity than rutile IrO2. However, they generally suffer from severe ion desolvation and poor structural stability, making them difficult to apply in practical PEM water electrolyzers. Even though a few low-iridium catalysts exhibit excellent hydrogen production performance in electrolyzers, a high iridium loading is still required on the membrane electrode assembly (MEA) to ensure stability. Given the scarcity of iridium, this severely restricts its large-scale development. Therefore, developing water oxidation catalysts that balance high performance, long durability, and low iridium loading at the MEA level is extremely challenging. Summary of the Invention

[0004] This invention aims to prepare a low-iridium membrane electrode for PEM water electrolysis hydrogen production technology with high performance, long durability, and low iridium loading. It provides a foam-like iridium oxide catalyst, a preparation method, and its application in proton exchange membrane (PEM) water electrolysis hydrogen production technology.

[0005] This invention utilizes the sol-gel method to controllably synthesize foam-like iridium oxide (fH-IrO). x This invention utilizes the advantages of sol-gel synthesis to construct a PEM anode low-iridium film electrode with high catalytic activity and long durability, while effectively improving the catalytic activity and stability of the iridium oxide catalyst.

[0006] The first objective of this invention is to provide a foam-like iridium oxide fH-IrO x The preparation method of the catalyst includes the following steps:

[0007] (1) Dissolve sodium citrate, ethylene glycol, surfactant and iridium source in deionized water to obtain a homogeneous solution;

[0008] The molar amount of sodium citrate is 2 to 8 times that of the iridium source, the molar amount of ethylene glycol is 2 to 8 times that of the iridium source, the mass of the surfactant is 1 to 3 times that of the iridium source, and the mass of deionized water is 20 to 100 times that of sodium citrate.

[0009] This invention uses a surfactant as a morphology directing agent and sodium citrate and ethylene glycol as complexing agents; the surfactant can be one of polyvinylpyrrolidone (PVP), polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer (P123), and hexadecyltrimethylammonium bromide (CTAB); the iridium source can be one of potassium hexachloroiridate (K2IrCl6), iridium trichloride (IrCl3), and iridium acetylacetonate;

[0010] (2) The homogeneous solution obtained in step (1) is stirred in an oil bath at 100-140°C for 1-2 hours, and then dried at 160-200°C for 24-48 hours to obtain the precursor.

[0011] (3) The precursor obtained in step (2) is calcined at 200-250℃ for 1-6 hours (heating rate of 1-3℃ / min) and at 500-700℃ for 1-6 hours (heating rate of 2-6℃ / min) and then cooled to room temperature.

[0012] (4) The product obtained in step (3) is washed sequentially with 0.5M HCl and deionized water, and dried to obtain the foamy iridium oxide catalyst of the present invention, denoted as fH-IrO. x .

[0013] A second objective of this invention is to provide a foam-like iridium oxide catalyst prepared by the above method.

[0014] The third objective of this invention is to provide the application of the foamed iridium oxide catalyst in proton exchange membrane (PEM) water electrolysis for hydrogen production. Specifically, the foamed iridium oxide catalyst is used to prepare a low-iridium membrane electrode, and the electrode is applied to the PEM water electrolysis for hydrogen production.

[0015] The foam-like iridium oxide catalyst provided by this invention is a micron-sized sheet material. Whether in a three-electrode test system or a PEM electrolyzer test system, its special foam-like morphology is conducive to exhibiting high activity under low iridium loading. At the same time, its special microscopic atomic structure (closely packed IrO6 octahedra forming a stable honeycomb structure) endows it with excellent structural stability.

[0016] Beneficial effects

[0017] 1. This invention can realize fH-IrO x The catalyst was synthesized and exhibited a foamy morphology. The sample was a light blue powder. The preparation method was simple, with high yield, good reproducibility, and easy mass production.

[0018] 2. The fH-IrO prepared by this invention x The catalyst not only exposes a large number of active sites, improving the oxidation performance of acidic water, but also enhances the charge and mass transfer performance of the catalyst layer under high current density. Furthermore, the unique honeycomb structure helps improve the structural stability of the material.

[0019] 3. The fH-IrO provided by this invention x Catalyst, at an acidic oxygen evolution current density of 10 mA / cm² 2 At that time, only 273mV overpotential is required, and it remains stable for more than 100 hours.

[0020] 4. The fH-IrO provided by this invention x Low-iridium film electrode (0.35 mg / cm²) prepared as an anode catalyst 2 The activity reached 2.0V@3.2A / cm in a PEM water electrolyzer. 2 It can operate stably for 500 hours at 2.0A / cm². 2 This indicates that it has application prospects in PEM water electrolyzers. Attached Figure Description

[0021] Figure 1 fH-IrO prepared in Example 1 x X-ray diffraction (XRD) pattern of the catalyst;

[0022] Figure 2 a: fH-IrO prepared in Example 1 x Scanning electron microscope (SEM) image of the catalyst;

[0023] Figure 2 b: fH-IrO prepared in Example 1 x Transmission electron microscopy (TEM) image of the catalyst;

[0024] Figure 3 a: fH-IrO prepared in Example 1 x Polarization curves of the acidic water oxidation reaction of the catalyst, measured in a three-electrode test system;

[0025] Figure 3 b: fH-IrO prepared in Example 1 x Stability curves of the catalyst in the acidic water oxidation reaction measured in a three-electrode test system;

[0026] Figure 4 a: fH-IrO prepared in Example 1 x Activity curves of the catalyst in a PEM electrolyzer;

[0027] Figure 4 b: fH-IrO prepared in Example 1 x Stability curves of the catalyst in a PEM electrolyzer. Detailed Implementation

[0028] The present invention will be further described in conjunction with the embodiments and accompanying drawings. However, the scope of protection of the present invention includes, but is not limited to, the following embodiments. Any changes and adjustments made without departing from the spirit and scope of the present invention will also be included within the scope of protection of the present invention.

[0029] The present invention will now be described with reference to specific embodiments. The process condition values ​​used in the following embodiments are exemplary, and their possible value ranges are as shown in the foregoing description of the invention. For process parameters not specifically noted, conventional techniques can be referred to.

[0030] Example 1

[0031] fH-IrO xCatalyst preparation: 1.58 g sodium citrate, 0.34 g ethylene glycol, 0.8 g CTAB, and 0.4 g iridium trichloride were dissolved in 50 mL of deionized water. After complete dissolution, a homogeneous solution was obtained and stirred in an oil bath at 120 °C for 2 h. The solution was then transferred to 180 °C and dried for 36 h to obtain the precursor. The precursor was then calcined at 250 °C for 4 h (heating rate 2 °C / min) and 600 °C for 4 h (heating rate 4 °C / min), followed by natural cooling to room temperature. The product was washed once with 0.5 M HCl, then repeatedly washed four times with deionized water. After drying, approximately 180 mg of fH-IrO was obtained. x catalyst.

[0032] fH-IrO x Structural characterization of catalysts: Figure 1 The XRD pattern of the prepared sample showed characteristic diffraction peaks of iridium oxide with a honeycomb structure, indicating that the synthesized sample belongs to iridium oxide with a honeycomb structure. Figure 2 To prepare SEM and TEM images of the sample, it can be observed that the sample has a foam-like micron sheet morphology.

[0033] fH-IrO x Characterization of oxygen evolution catalytic performance of the catalyst: The prepared fH-IrO was tested in a three-electrode system with 0.1 M HClO4 electrolyte. x The electrocatalytic OER performance of the catalyst was evaluated. 8 mg of fH-IrO was weighed. x The catalyst was ultrasonically dispersed in 400 μL of isopropanol and 400 μL of naphthol solution (0.5 wt%) to prepare a homogeneous slurry. 2.0 μL of this slurry was dropped onto a glassy carbon electrode (3 mm in diameter). Using the glassy carbon electrode with the catalyst as the working electrode, a platinum wire as the counter electrode, and a saturated calomel electrode as the reference electrode, its oxygen evolution catalytic performance was evaluated using a Chenhua electrochemical workstation. Figure 3 a is fH-IrO x The polarization curve of the catalyst at an oxygen evolution current density of 10 mA cm⁻¹ -2 At a constant 10 mA cm⁻¹, its overpotential is 273 mV, indicating that the catalyst has good oxygen evolution catalytic activity. Furthermore, at a constant 10 mA cm⁻¹... -2 Its catalytic stability was evaluated at current densities, such as... Figure 3 As shown in b, after 100 hours of testing, the voltage did not increase significantly, indicating that it has excellent catalytic stability.

[0034] PEM electrolytic cell performance characterization: fH-IrO xA low-iridium membrane electrode was prepared using the catalyst as an anode catalyst in a PEM water electrolyzer, and its performance was evaluated. First, 24.8 mg Pt / C (40%) was dispersed in 10 mL of deionized water and ultrasonically dispersed for 30 min. Then, 300 μL of naphthol (5 wt%) and 15 mL of isopropanol were added and ultrasonically dispersed for 30 min. Subsequently, the mixture was uniformly sprayed onto one side of an N115 membrane using an ultrasonic sprayer. Then, 26.3 mg fH-IrO was... x The catalyst was dispersed in 10 mL of deionized water and ultrasonically dispersed for 30 min. Then, 200 μL of naphthol (5 wt%) and 15 mL of isopropanol were added, and the mixture was ultrasonically dispersed for 2 h. Subsequently, it was uniformly sprayed onto the other side of an N115 membrane using an ultrasonic sprayer to prepare a low-iridium membrane electrode. The prepared low-iridium membrane electrode was assembled into a PEM water electrolyzer for performance evaluation. Note: The active area of ​​the electrolyzer is 5 cm². 2 The cathode gas diffusion layer was made of carbon paper, and the anode gas diffusion layer was made of titanium felt. During the electrolytic cell performance test, the anode pure water flow rate was 30 mL / min, and the test temperature was 80℃. X-ray fluorescence spectroscopy (XRF) and inductively coupled plasma optical emission spectrometry (ICP-OES) confirmed that the Ir loading on the low-iridium film electrode was 0.35 mg / cm³. 2 The Pt loading was 0.2 mg / cm³. 2 . Figure 4 a is fH-IrO x The activity curve when the catalyst is an anode catalyst, with a current density of 3.2 A cm⁻¹. -2 At this voltage, only 2.0V is required, indicating that the catalyst exhibits excellent catalytic performance. Furthermore, its catalytic stability was evaluated under constant current density, such as… Figure 4 As shown in b, the electrolytic cell operates at 2.0 A / cm². 2 It operates stably for 500 hours at a given current density, indicating that it has excellent catalytic stability.

[0035] Example 2

[0036] This embodiment is the same as Example 1, except that CTAP is replaced with PVP (same mass). All other synthesis conditions remain unchanged, and fH-IrO can still be obtained. x The catalyst has an oxygen evolution overpotential of 275 mV at 10 mA cm⁻¹. -2 .

[0037] Example 3

[0038] This embodiment is the same as Example 1, except that CTAB is replaced with P123 (same mass). All other synthesis conditions remain unchanged, and fH-IrO can still be obtained. x The catalyst has an oxygen evolution overpotential of 272 mV at 10 mA cm⁻¹. -2 .

[0039] Example 4

[0040] This embodiment is the same as Example 1, except that the iridium source is changed to K2IrCl6 (same molar amount). All other synthesis conditions remain unchanged, and fH-IrO can still be obtained. x Catalyst. Its oxygen evolution overpotential is 272 mV @ 10 mA cm⁻¹. -2 .

[0041] Example 5

[0042] This embodiment is the same as Example 1, except that the iridium source is changed to iridium acetylacetone (same molar amount). All other synthesis conditions remain unchanged, and fH-IrO can still be obtained. x Catalyst. Its oxygen evolution overpotential is 273 mV @ 10 mA cm⁻¹ -2 .

[0043] The results of Examples 4 and 5 demonstrate that modulated iridium sources can still synthesize highly active fH-IrO. x It acts as a catalyst without affecting the foam morphology.

[0044] Example 6

[0045] This embodiment is the same as Example 1, except that the calcination temperature was changed from 600℃ to 500℃ and then to 700℃. All other synthesis conditions remained unchanged, and fH-IrO could still be obtained. x Catalyst. This indicates that fH-IrO can be successfully prepared when the calcination temperature is controlled within the range of 500℃ to 700℃. x The catalysts have oxygen evolution overpotentials of 275 mV and 279 mV at 10 mA cm⁻¹, respectively. -2 This indicates that highly active fH-IrO can still be synthesized even when the temperature is adjusted to 500–700℃. x catalyst.

Claims

1. A method for preparing a foam-like iridium oxide catalyst, comprising the following steps: (1) Dissolve sodium citrate, ethylene glycol, surfactant and iridium source in deionized water to obtain a homogeneous solution; The molar amount of sodium citrate is 2 to 8 times that of the iridium source, the molar amount of ethylene glycol is 2 to 8 times that of the iridium source, the mass of the surfactant is 1 to 3 times that of the iridium source, and the mass of deionized water is 20 to 100 times that of sodium citrate; the iridium source is one of potassium hexachloroiridate, iridium trichloride, or iridium acetylacetonate. (2) Stir the homogeneous solution obtained in step (1) in an oil bath at 100-140°C for 1-2 h, and then transfer it to 160-200°C to dry for 24-48 h to obtain the precursor; (3) The precursor obtained in step (2) is calcined at 200~250 ℃ for 1~6 h and at 500~700 ℃ for 1~6 h, and then cooled to room temperature; (4) The product obtained in step (3) is washed with 0.5 M HCl and deionized water in sequence, and dried to obtain the foam-like iridium oxide catalyst with honeycomb structure.

2. The method for preparing a foam-like iridium oxide catalyst as described in claim 1, characterized in that: In step (1), the surfactant is one of polyvinylpyrrolidone, polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer, and hexadecyltrimethylammonium bromide.

3. The method for preparing a foam-like iridium oxide catalyst as described in claim 1, characterized in that: In step (2), the heating rate during calcination at 200~250 ℃ is 1~3 ℃ / min, and the heating rate during calcination at 500~700 ℃ is 2~6 ℃ / min.

4. A foam-like iridium oxide catalyst, characterized in that: It is prepared by the method described in any one of claims 1 to 3.

5. The foam-like iridium oxide catalyst as described in claim 4, characterized in that: The microscopic atomic structure is a honeycomb layer structure formed by tightly connected IrO6 octahedra sharing the same edge.

6. The application of the foamed iridium oxide catalyst as described in claim 4 or 5 in proton exchange membrane water electrolysis for hydrogen production.

Images