Iron phosphosulphide catalyst for the electrolytic separation of hydrogen isotopes and process for its preparation

Abstract

The application discloses a kind of iron sulfide-phosphide catalyst for electrolysis water separation hydrogen isotope and preparation method thereof.The catalyst is with conductive carbon paper as substrate, by in-situ growth of iron oxyhydroxide precursor by hydrothermal method, then simultaneously introduce sulfur source and phosphorus source by chemical vapor deposition technology, to obtain the nano-structured catalyst with Fe-S-P active component.The catalyst not only shows excellent hydrogen evolution reaction activity in alkaline electrolyte, but also can realize efficient separation of hydrogen and deuterium by using kinetic isotope effect, with high hydrogen / deuterium separation factor.The application also provides the application of the catalyst in electrolysis water hydrogen production and hydrogen isotope separation, as well as the electrolysis separation method based on the catalyst.The application has simple process and low cost, provides efficient integrated material and process scheme for solving the green and low-cost extraction of deuterium resources.

Description

Technical Field

[0001] This invention relates to an iron phosphide catalyst for separating hydrogen isotopes by water electrolysis and its preparation method, belonging to the field of catalyst preparation technology. Background Technology

[0002] Hydrogen has three isotopes: protium, deuterium (heavy hydrogen), and tritium (superheavy hydrogen). Heavy water, also known as deuterated water, has the chemical formula D₂O. In nature, the vast majority of hydrogen exists as protium; deuterium has a relatively low abundance, approximately 0.0156%, and tritium has an abundance of less than 0.001%. Heavy water is colorless, transparent, odorless, non-flammable, and non-explosive. Pure heavy water has a boiling point of 101.4℃ and a density of 1.1 g / cm³. 3 Deuterium (at room temperature) is 10% heavier than ordinary water, hence the name heavy water. Heavy water (deuterium) has a wide range of uses and is considered a "natural fuel of the future," a crucial raw material for controlled nuclear fusion, and is used extensively in semiconductors, medicine, and other fields. Early production of heavy water involved cascaded electrolysis and volume reduction concentration of raw water, achieving commercial production. However, due to the low concentration of raw water and high power consumption, later technologies such as hydrogen sulfide dual-temperature exchange and electrolytic catalytic exchange (CECE) were developed, becoming the main production processes both domestically and internationally. However, these methods also suffer from high energy consumption and significant hazards.

[0003] In the process of hydrogen production through water electrolysis, due to the kinetic isotope effect (KIE), light water (H2O) is more easily electrolyzed than heavy water (D2O), leading to the continuous enrichment of deuterium in the electrolyte. This phenomenon provides a new approach for green, electrochemically driven deuterium extraction. However, while traditional water electrolysis catalysts (such as Pt / C) possess excellent hydrogen evolution reaction (HER) activity, their hydrogen / deuterium separation factor (S-Factor) is typically low, resulting in limited deuterium extraction efficiency and making it difficult to simultaneously achieve high HER rates and high deuterium selectivity. This invention is therefore proposed. Summary of the Invention

[0004] The purpose of this invention is to provide an iron phosphide sulfide catalyst for separating hydrogen isotopes in water electrolysis. This catalyst is a bifunctional catalyst based on modified iron phosphide sulfide grown on carbon paper. First, iron hydroxyl oxide is grown on carbon paper using a hydrothermal method, and then phosphorus and sulfur are deposited on the iron hydroxyl oxide precursor using chemical vapor deposition (CVD) to obtain the iron phosphide sulfide catalyst. While achieving hydrogen production, it significantly enhances the hydrogen / deuterium isotope separation effect, realizing "deuterium extraction within hydrogen production." This has significant scientific value and application prospects for reducing the production cost of deuterium resources and promoting the development of fusion energy.

[0005] The catalyst for separating hydrogen isotopes by electrolysis of water provided by this invention is iron phosphide sulfide nanoparticles containing iron, sulfur and phosphorus elements; The iron phosphide nanoparticles are grown in situ on a carbon paper substrate to form an electrode material for water electrolysis.

[0006] The molar ratio of sulfur to phosphorus in the iron sulfide phosphorus nanoparticles is 1:1 to 5:1.

[0007] The method for preparing the catalyst provided by the present invention includes the following steps: S1. Dissolve iron-containing compounds, ammonium fluoride and urea in water, mix them evenly to obtain a hydrothermal precursor solution, and immerse the pretreated carbon paper in the hydrothermal precursor solution. The pretreatment steps for the carbon paper are as follows: Cut the carbon paper into sheets of a certain size, and rinse the cut carbon paper with deionized water or ultrapure water to remove surface dust and impurities. Further clean with ethanol or isopropanol to ensure the carbon paper surface is clean and free of contaminants. Dry at room temperature.

[0008] S2. The hydrothermal precursor solution impregnated with carbon paper is subjected to a hydrothermal reaction to grow an iron-containing precursor on the surface of the carbon paper, followed by drying. S3. The dried carbon paper loaded with iron-containing precursors, sulfur-containing compounds, and phosphorus-containing compounds are placed in a tube furnace and chemical vapor deposition reaction is carried out under a protective atmosphere to dope sulfur and phosphorus into the iron-containing precursors, thereby generating iron phosphide nanoparticles in situ on the carbon paper to obtain the iron phosphide catalyst. Specifically, the sulfur-containing compound and the phosphorus-containing compound are mixed and loaded into a ceramic boat, which is placed upstream of a tube furnace. The dried carbon paper is loaded into the ceramic boat and placed downstream of the tube furnace. A protective gas is introduced, and the reaction is carried out at a certain temperature to obtain an iron sulfide phosphorus catalyst grown in situ on the carbon paper. The finished product is carbon paper.

[0009] The iron-containing compound is ferric nitrate nonahydrate, and the molar ratio of the iron-containing compound, the ammonium fluoride, and the urea is 1:1-3:4-6; The hydrothermal reaction is carried out at a temperature of 100℃-150℃ for 4-8 hours.

[0010] The sulfur-containing compound is sublimed sulfur, and the phosphorus-containing compound is sodium hypophosphite; The molar ratio of sublimed sulfur to sodium hypophosphite is 1:1 to 5:1.

[0011] The chemical vapor deposition reaction is carried out at a temperature of 250℃-350℃ for a reaction time of 0.5-2 hours. The protective atmosphere is argon or nitrogen.

[0012] The present invention also provides the application of the catalyst in hydrogen production by water electrolysis and hydrogen isotope separation; The catalyst, as a cathode (or working electrode) material, can preferentially electrolyze light water (H2O) based on the kinetic isotope effect while producing hydrogen through water electrolysis, thereby achieving efficient enrichment of deuterium (D) in the electrolyte and realizing an integrated process of "deuterium extraction in hydrogen production".

[0013] Based on the above catalyst, the present invention further provides a method for separating hydrogen isotopes by electrolysis of water, comprising: using carbon paper loaded with the ferric phosphide catalyst of the present invention as a working electrode, forming an electrolysis system together with a counter electrode and a reference electrode (no reference electrode is required in a two-electrode system), and carrying out an electrolysis reaction in an electrolyte containing deuterium water (such as naturally abundant water or heavy water dilution).

[0014] During the electrolysis process, due to the differentiated adsorption-desorption energy barriers and reaction kinetics of the catalyst for hydrogen / deuterium atoms, protium (H) preferentially precipitates as hydrogen gas, while deuterium (D) is enriched in the electrolyte. Efficient and continuous separation of hydrogen isotopes can be achieved by monitoring and controlling the electrolysis conditions.

[0015] Preferably, the electrolysis reaction is carried out in an alkaline electrolyte, such as a 1 M potassium hydroxide (KOH) solution. Under this environment, the catalyst can simultaneously maintain high hydrogen evolution reaction (HER) activity and a high hydrogen / deuterium separation factor (S-Factor), while also exhibiting good chemical stability.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention directly grows sulfur- and phosphorus-modified iron on carbon paper, achieving efficient separation of protium and deuterium. This is beneficial for enhancing the differentiation of the zero-point vibrational energy of protium and deuterium under microscopic conditions. At the same time, the addition of sulfur and phosphorus helps to improve the hydrogen evolution reaction performance and corrosion resistance, and exhibits a stronger catalytic effect in alkaline environments such as 1M KOH.

[0017] The present invention has simple preparation conditions, convenient operation process, low production cost, and is easy to mass-produce; it also has strong universality and can be applied to hydrogen evolution reaction catalysts, while separating hydrogen and deuterium. It can be applied to the deuterium extraction process coupled with wind power and photovoltaic hydrogen production, and has broad prospects for industrial application. Attached Figure Description

[0018] Figure 1 This is a flowchart of the catalyst preparation process of the present invention.

[0019] Figure 2 This is a transmission electron microscope image of the catalyst prepared in Example 1 of the present invention.

[0020] Figure 3 This is an EDX image of the catalyst prepared in Example 1 of this invention.

[0021] Figure 4This is the XRD pattern of the catalyst prepared in Example 1 of this invention.

[0022] Figure 5 This is a graph showing the catalytic performance of the catalysts prepared in Examples 1-2 and Comparative Examples 1-2 of this invention for the hydrogen evolution reaction.

[0023] Figure 6 This is a durability diagram of the catalyst prepared in Example 1 of the present invention for deuterium extraction during the hydrogen evolution reaction.

[0024] Figure 7 This is a graph showing the deuterium enrichment performance of the catalysts prepared in Examples 1-2 and Comparative Examples 1-2 of this invention. Detailed Implementation

[0025] Unless otherwise specified, the experimental methods used in the following examples are conventional methods.

[0026] Unless otherwise specified, all materials and reagents used in the following examples are commercially available.

[0027] This invention relates to an iron sulfide phosphorus catalyst for hydrogen isotope separation in water electrolysis, its preparation and application, aiming to solve the technical problems of low separation factor (S-Factor), limited deuterium extraction efficiency, and difficulty in achieving both high hydrogen evolution rate and high selectivity in existing water electrolysis catalysts during hydrogen / deuterium isotope separation. It provides an electrode material that can simultaneously achieve efficient hydrogen production and efficient deuterium enrichment under alkaline conditions, its simple preparation method and supporting electrolysis separation process.

[0028] To achieve the above objectives, the present invention adopts the following technical solution: Catalyst product: Provides an iron sulfide phosphorus catalyst, which uses carbon paper as a substrate and grows nanoparticles containing iron (Fe), sulfur (S) and phosphorus (P) elements in situ.

[0029] Preparation method: The preparation method of the catalyst includes: (1) The precursor of iron hydroxide was grown on pretreated carbon paper by hydrothermal method; (2) By using chemical vapor deposition, the precursor is simultaneously sulfided and phosphated using sulfur and phosphorus sources to finally obtain a sulfidated iron phosphate catalyst supported on carbon paper.

[0030] Application: This invention provides a method for separating hydrogen isotopes by electrolysis of water. The above-mentioned iron phosphide sulfide catalyst is used as the working electrode, and electrolysis is carried out in the electrolyte. By utilizing the difference in hydrogen / deuterium reaction kinetics, hydrogen is generated and deuterium is enriched in the electrolyte.

[0031] Compared with the prior art, the present invention has the following significant advantages: High performance: The catalyst’s unique Fe-SP composition and structure ensure excellent hydrogen evolution reaction activity while significantly improving the hydrogen / deuterium separation factor, achieving the integration of hydrogen production and deuterium extraction.

[0032] High stability: The catalyst is grown directly on carbon paper, with a strong bond and good conductivity. It exhibits good structural stability and corrosion resistance in alkaline electrolyte.

[0033] Low cost and easy operation: The raw materials used are inexpensive and readily available, the preparation process is simple and the conditions are mild, making it suitable for large-scale production; the supporting electrolytic separation method has a simple process and low energy consumption.

[0034] This technology offers promising applications: it provides an effective material and process solution for the green and economical extraction of high-value-added deuterium resources, and has significant application potential in fields such as nuclear energy, semiconductors, and fine chemicals. Example 1 Preparation process as follows Figure 1 As shown.

[0035] S1. Cut the carbon paper into 1 cm × 2 cm pieces. Rinse the carbon paper with deionized water or ultrapure water to remove surface dust and impurities. Further clean with ethanol or isopropanol to ensure the carbon paper surface is clean and free of contaminants. Dry at room temperature.

[0036] S2. Weigh out ferric nitrate nonahydrate, ammonium fluoride, and urea in the amounts of 2.0 mmol, 4.0 mmol, and 10 mmol respectively, place them in a beaker and mix them. Add 35 ml of deionized water, stir for 30 min, transfer to a polytetrafluoroethylene liner, and place clean carbon paper inside.

[0037] S3. Place the hydrothermal reactor in a vacuum drying oven and react at 120°C for 5 hours.

[0038] S4. After the reaction is complete, remove the hydrothermally heated carbon paper and place it in an oven to dry.

[0039] S5. Weigh sublimed sulfur, water and sodium hypophosphite in a molar ratio of 3:1 and mix them, with the amount of sulfur being 0.015 mol. The mixture is then placed in a ceramic boat and placed upstream of a tube furnace. The dried carbon paper is placed in the ceramic boat and placed downstream of the tube furnace. Ar gas is introduced and the mixture is reacted at 300℃ for 1 h with a heating rate of 2℃ / min. This yields an in-situ grown sulfur-iron phosphide catalyst on carbon paper. The finished product is carbon paper with a loading of approximately 0.2 mg.

[0040] The transmission electron microscope (TEM) image of the catalyst prepared in this embodiment is as follows: Figure 2As shown, the main body of the material is a dense cluster of particles with high electronic contrast, which is the main component of the material; the edges of the material are accompanied by thin-film epitaxial morphology, and these regions have shallower electronic contrast (corresponding to thinner or lower density structures).

[0041] The EDX image of the catalyst prepared in this embodiment is as follows. Figure 3 As shown, the elemental distribution of the sample (nanoscale aggregate morphology observed by TEM) was characterized by energy-dispersive X-ray spectroscopy (EDX) elemental mapping equipped with TEM (scale bar: 1 pm), and the results are described below: Elemental Composition The sample is composed of three elements: P, S, and Fe, confirmed by the EDX mapping signals. Spatial Distribution of Individual Elements Sulfur (S, red mapping): S exhibits a global distribution throughout the nanoscale aggregates, covering the core dense region of the sample and the peripheral dendritic / lamellar extensions. Iron (Fe, green mapping): Fe signals are detected throughout the spatial extent of the aggregates; consistent with the distribution of S, Fe is uniformly distributed in the core dense region and the peripheral low-density extensions. Phosphorus (P, blue mapping): P shows a regionally concentrated distribution—its signal is mainly localized in the core dense region of the aggregates, while the signal intensity in the peripheral lamellar structures is significantly weaker. Elemental Co-distribution Overlay Mapping (Merged Image) shows that Fe and S exhibit extensive co-distribution throughout the aggregate structure. In contrast, the co-distribution region of P with Fe / S is mainly confined to the core dense region of the nanoscale aggregates.

[0042] The XRD pattern of the catalyst prepared in this embodiment is as follows: Figure 4 As shown, the XRD diffraction peaks (green curve) of Example 1 mainly correspond to the standard diffraction peaks of FePS3 (PDF#33-0672), indicating that the main phase of the sample is FePS3. Some regions of the spectrum show overlap with characteristic peaks of the FeP (PDF#01-1286) and FeS (PDF#97-029-1017) standard cards, but these peaks are weak, suggesting they represent a small amount of coexisting phases (or intermediate products).

[0043] Example 2 S1. Cut the carbon paper into 1 cm × 2 cm pieces. Rinse the carbon paper with deionized water or ultrapure water to remove surface dust and impurities. Further clean with ethanol or isopropanol to ensure the carbon paper surface is clean and free of contaminants. Dry at room temperature.

[0044] S2. Weigh ferric nitrate nonahydrate, ammonium fluoride, and urea in amounts of 2.0 mmol, 4.0 mmol, and 10 mmol respectively, place them in a beaker, mix them, add 35 ml of deionized water, stir for 30 min, transfer to a polytetrafluoroethylene liner, and place clean carbon paper inside.

[0045] S3. Place the hydrothermal reactor in a vacuum drying oven and react at 120°C for 5 hours.

[0046] S4. After the reaction is complete, remove the hydrothermally heated carbon paper and place it in an oven to dry.

[0047] S5. Weigh sublimed sulfur, water and sodium hypophosphite in a molar ratio of 5:2 and mix them, with the amount of sulfur being 0.0125 mol. The mixture is then placed in a ceramic boat and placed upstream of a tube furnace. The dried carbon paper is then placed in the ceramic boat and placed downstream of the tube furnace. Ar gas is introduced and the mixture is reacted at 300℃ for 1 h with a heating rate of 2℃ / min. This yields an in-situ grown sulfur-iron phosphide catalyst on carbon paper. The finished product is carbon paper with a loading of approximately 0.2 mg.

[0048] Comparative Example 1 S1. Cut the carbon paper into 1cm x 2cm pieces. Rinse the carbon paper with deionized water or ultrapure water to remove surface dust and impurities. Further clean with ethanol or isopropanol to ensure the carbon paper surface is clean and free of contaminants. Dry at room temperature.

[0049] S2. Weigh ferric nitrate nonahydrate, ammonium fluoride, and urea in amounts of 2.0 mmol, 4.0 mmol, and 10 mmol respectively, place them in a beaker, mix them, add 35 ml of deionized water, stir for 30 min, transfer to a polytetrafluoroethylene liner, and place clean carbon paper inside.

[0050] S3. Place the hydrothermal reactor in a vacuum drying oven and react at 120°C for 5 hours.

[0051] S4. After the reaction is complete, remove the hydrothermally heated carbon paper and place it in an oven to dry.

[0052] S5. Weigh 0.015 mmol of sublimed sulfur and place it in a ceramic boat. Place the boat in the upper part of a tube furnace. Place the dried carbon paper in the ceramic boat and place it in the lower part of the tube furnace. Introduce Ar gas and react at 300℃ for 1 h with a heating rate of 2℃ / min to obtain an iron sulfide catalyst grown in situ on carbon paper. The finished product is carbon paper with a loading of approximately 0.2 mg.

[0053] Comparative Example 2 S1. Cut the carbon paper into 1cm x 2cm pieces. Rinse the carbon paper with deionized water or ultrapure water to remove surface dust and impurities. Further clean with ethanol or isopropanol to ensure the carbon paper surface is clean and free of contaminants. Dry at room temperature.

[0054] S2. Weigh ferric nitrate nonahydrate, ammonium fluoride, and urea in amounts of 2.0 mmol, 4.0 mmol, and 10 mmol respectively, place them in a beaker, mix them, add 35 ml of deionized water, stir for 30 min, transfer to a polytetrafluoroethylene liner, and place clean carbon paper inside.

[0055] S3. Place the hydrothermal reactor in a vacuum drying oven and react at 120°C for 5 hours.

[0056] S4. After the reaction is complete, remove the hydrothermally heated carbon paper and place it in an oven to dry.

[0057] S5. Weigh 0.005 mmol of water and sodium hypophosphite into a ceramic boat and place it in the upper part of a tube furnace. Place the dried carbon paper into the ceramic boat and place it in the lower part of the tube furnace. Introduce Ar gas and react at 300℃ for 1 h with a heating rate of 2℃ / min to obtain an iron phosphide catalyst grown in situ on the carbon paper. The finished product is carbon paper with a loading of approximately 0.2 mg.

[0058] Application Example 1: Test of the hydrogen evolution and deuterium enrichment performance of the catalyst in alkaline electrolyte. The hydrogen evolution performance of the catalyst prepared in this invention is shown in the figure below. Figure 5 As shown, it can be seen that under the same current density (e.g., 10 mA cm⁻¹), -2 The hydrogen evolution overpotentials of Example 2 and Comparative Example 2 were significantly lower than those of Example 1 and Comparative Example 1, indicating that the H2 generation rate of the former two was faster at this potential. The HER electrocatalytic activity of the samples was ranked from high to low as follows: Example 2 > Comparative Example 2 > Example 1 > Comparative Example 1, among which Comparative Example 1 had the worst hydrogen evolution reaction kinetics and activity in the system.

[0059] The deuterium enrichment performance of the catalyst prepared in this invention is shown in the figure below. Figure 7 As shown, Figure 7 As shown in Figure a, the voltage curves of Example 1, Example 2, Comparative Example 1, and Comparative Example 2 all remained at around 4V within 100h, indicating that the battery voltage stability of all groups was good during the electrolysis process. Among them, the voltage of Example 1 was always lower than that of the other samples, and its performance was better than the other three samples.

[0060] Figure 7 As shown in Figure b, the liquid phase deuterium concentration in all groups continued to increase with prolonged electrolysis time; the rate of increase was fastest in Example 1, with a concentration approaching 240 ppm at 100 h, significantly higher than the other groups; Example 2 was next, while the rates of increase in Comparative Examples 1 and 2 were relatively slower. This indicates that Example 1 is more effective in enriching liquid phase deuterium.

[0061] Figure 7As shown in Figure c, unlike the continuous rise in the liquid phase, the deuterium concentration in the gas phase exhibits a fluctuating change. The concentration fluctuations of different groups at different time points vary greatly. The peak concentration of Example 1 is higher than that of other groups, while the gas phase deuterium concentration of Comparative Example 2 shows a gradual upward trend in the later stage.

[0062] Figure 7 As shown in Figure d, the overall separation factor α gradually increases with the increase of electrolysis time; the highest value is 3.02 (Example 1), indicating that as the electrolysis process progresses, the electrolysis separation performance gradually becomes more prominent, and the overall separation effect continues to improve.

[0063] Application Example 2: Catalyst Durability and Long-Term Deuterium Enhancement Performance Testing The durability diagram of the catalyst prepared in Example 1 of this invention is shown in the figure. Figure 6 As shown, during the 100-hour continuous deuterium extraction process, the electrolytic cell voltage remained at approximately 4 V with minimal fluctuations and no significant decreases or abrupt changes. Under long-term water replenishment conditions, the catalyst of this invention exhibited no significant deterioration in structural integrity or active site stability (no obvious agglomeration, corrosion, or loss of active sites), demonstrating excellent long-term working durability.

Claims

1. A catalyst for separating hydrogen isotopes by electrolysis of water, comprising iron phosphide sulfide nanoparticles containing iron, sulfur and phosphorus elements; The iron phosphide nanoparticles are grown in situ on a carbon paper substrate to form an electrode material for water electrolysis.

2. The catalyst according to claim 1, characterized in that: The molar ratio of sulfur to phosphorus in the iron sulfide phosphorus nanoparticles is 1:1 to 5:

1.

3. A method for preparing the catalyst according to claim 1 or 2, comprising the following steps: S1. Dissolve iron-containing compounds, ammonium fluoride and urea in water, mix them evenly to obtain a hydrothermal precursor solution, and immerse the pretreated carbon paper in the hydrothermal precursor solution. S2. The hydrothermal precursor solution impregnated with carbon paper is subjected to a hydrothermal reaction to grow an iron-containing precursor on the surface of the carbon paper, followed by drying. S3. The dried carbon paper loaded with iron-containing precursors, sulfur-containing compounds, and phosphorus-containing compounds are placed in a tube furnace and subjected to chemical vapor deposition reaction under a protective atmosphere to dope sulfur and phosphorus into the iron-containing precursors, thereby generating iron phosphide nanoparticles in situ on the carbon paper to obtain the iron phosphide catalyst.

4. The preparation method according to claim 3, characterized in that: The iron-containing compound is ferric nitrate nonahydrate, and the molar ratio of the iron-containing compound, the ammonium fluoride, and the urea is 1:1-3:4-6; The hydrothermal reaction is carried out at a temperature of 100℃-150℃ for 4-8 hours.

5. The preparation method according to claim 3 or 4, characterized in that: The sulfur-containing compound is sublimed sulfur, and the phosphorus-containing compound is sodium hypophosphite; The molar ratio of sublimed sulfur to sodium hypophosphite is 1:1 to 5:

1.

6. The preparation method according to any one of claims 3-5, characterized in that: The chemical vapor deposition reaction is carried out at a temperature of 250℃-350℃ for a reaction time of 0.5-2 hours. The protective atmosphere is argon or nitrogen.

7. The application of the catalyst according to claim 1 or 2 in hydrogen production by water electrolysis and hydrogen isotope separation.

8. A method for separating hydrogen isotopes by electrolysis of water, wherein the catalyst described in claim 1 or 2 is used as the electrode material to carry out the water electrolysis reaction to achieve the separation of hydrogen and deuterium.

9. The method according to claim 8, characterized in that: The electrolysis is carried out in an alkaline electrolyte.

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