Synthesis method of iron-doped cobalt phosphide catalyst for hydrogen production by electrolysis of untreated seawater

Abstract

The invention discloses a synthesis method of an iron-doped cobalt phosphide catalyst for hydrogen production through electrolysis of untreated seawater, and the method comprises the following steps: doping Fe into a cobalt-based catalyst precursor through a solution gel-vapor deposition method, and further phosphorizing in the vapor deposition process to form a Fe / Co2P structure; the high-performance seawater direct electrolysis oxygen desorption catalyst with a specific structure is obtained, and Fe doping is utilized to improve the catalytic activity of Co2P and inhibit dissolution of Co < 2 + >. The preparation method is simple and efficient, the electrode material has excellent OER activity and extremely high chlorine resistance in untreated natural seawater, only 1.866 V potential is needed when the current density in untreated neutral seawater reaches 100 mA. Cm <-2 >, and stable electrolysis can be carried out for more than 100 h. The catalyst has the advantages of low synthesis cost, high stability, good catalytic activity and the like, and provides a brand new material research and development thought for hydrogen production by electrolysis of alkalization-free seawater.

Description

Technical Field

[0001] The present invention belongs to the technical field of hydrogen production by electrolyzing water, and relates to a preparation method of a cobalt-based catalyst, in particular to a preparation method of an efficient iron-doped cobalt phosphide catalyst for hydrogen production by electrolyzing seawater. Background Art

[0002] The increasingly severe global environmental problems and energy crises have promoted the rapid development of renewable clean energy, especially in the fields of hydrogen energy, solar energy, and wind energy. Among them, hydrogen energy is regarded as an ideal substitute for traditional fossil fuels due to its advantages such as pollution-free, high energy density, and wide sources. At present, hydrogen energy is mainly produced by coal and biomass pyrolysis, natural gas reforming, and electrolyzing water. The hydrogen production method based on electrolyzing water is considered to be the most potential technical path in the future due to its high efficiency and cleanliness. However, electrolyzing water for hydrogen production requires a large amount of pure water. With the continuous growth of energy demand, this process will further exacerbate the global water shortage problem. Seawater accounts for 97% of the earth's water resources. If direct electrolysis of seawater for hydrogen production can be achieved, it will effectively alleviate the water resource competition contradiction between domestic water and industrial hydrogen production.

[0003] The hydrogen production process by electrolyzing water consists of two half-reactions: the oxygen evolution reaction (OER) occurs at the anode, and the hydrogen evolution reaction (HER) occurs at the cathode. Among them, the energy consumption of the anode reaction accounts for more than 90% of the total energy consumption of electrolyzing water, which is the key link restricting the hydrogen production efficiency. However, during the seawater electrolysis process, not only the OER occurs at the anode, but also the chlorine evolution reaction (CER) occurs due to the presence of a large amount of Cl - in seawater. This not only increases the anode energy consumption but also causes electrode corrosion, seriously affecting the stability of the electrolytic cell. Although there is a theoretical potential difference of 0.48 V between OER and CER, due to the insufficient OER activity of existing catalysts, the potential difference between the two is further reduced during actual operation, restricting the long-term stable operation of seawater electrolysis for hydrogen production under high current conditions. Therefore, developing efficient and stable OER catalysts to inhibit the CER side reaction has become the key challenge for realizing the large-scale application of seawater electrolysis for hydrogen production.

[0004] CN115505961A discloses a synthesis method of a nanosheet structure catalyst (NiFeS / NF). The dual-metal synergistic effect of nickel and iron improves the catalytic activity, and sulfate ions can inhibit the binding of chloride ions to catalytic sites during the catalytic process. However, the synthesis process of this catalyst is complex, so it is difficult to achieve industrial application. CN118996494A discloses a seawater electrolysis catalyst (Ru@TiC) with stable interfacial Ru particles. This catalyst has a larger specific surface area and richer chemical reaction active sites, making it have higher catalytic activity. In addition, due to the good chemical stability and corrosion resistance of Ru@TiC, high-efficiency electrolysis of seawater to produce hydrogen can be carried out under acidic or alkaline conditions. However, this catalyst uses precious metal Ru, making the catalyst cost higher and it is difficult to achieve large-scale industrial application in a strong seawater corrosion environment.

[0005] At present, the non-precious metal catalysts that have been disclosed generally have problems such as high cost, insufficient corrosion resistance, and difficulty in industrial application, and it is difficult to directly meet the actual needs of seawater electrolysis. Therefore, developing a new catalyst with high oxygen evolution reaction (OER) catalytic activity, high selectivity, and excellent corrosion resistance is of great significance for realizing the large-scale application of direct seawater electrolysis to produce hydrogen. Summary of the Invention

[0006] The present invention provides a synthesis method of an iron-doped cobalt phosphide catalyst for electrolyzing untreated seawater to produce hydrogen. This method dopes Fe into the cobalt-based catalyst precursor through a solution gel-vapor deposition method and is further phosphated during the vapor deposition process to form an Fe / Co2P structure, so as to obtain a high-performance seawater direct electrolysis oxygen evolution catalyst with a specific structure, and uses the doping of Fe to enhance the catalytic activity of Co2P and inhibit the 2+ dissolution of Co. The preparation method of the present invention is simple and efficient, and can be applied to the synthesis of a large amount of catalyst powder. This electrode material has excellent OER activity and strong anti-chlorine characteristics in untreated natural seawater, and the current density reaches 100 mA·cm -2 in untreated neutral seawater only requires a potential of 1.866 V and can stably electrolyze for more than 100 h. At the same time, this catalyst has the advantages of low synthesis cost, high stability, and good catalytic activity, providing a new material research and development idea for hydrogen production by electrolyzing non-alkalized seawater.

[0007] The object of the present invention is achieved through the following technical solutions:

[0008] A synthesis method of an iron-doped cobalt phosphide catalyst for electrolyzing untreated seawater to produce hydrogen, comprising the following steps:

[0009] Step 1: Place metal salts in a container, and slowly inject a potassium oxalate solution into the container under ice bath and stirring to obtain an emulsion, and stir, wherein:

[0010] The metal salt is a cobalt salt and an iron salt;

[0011] The cobalt salt is one of cobalt chloride, cobalt sulfate, and cobalt nitrate, with a concentration of 0.15 - 0.25 mol / L. For example, it can be 0.15 mol / L, 0.18 mol / L, 0.20 mol / L, 0.23 mol / L, and 0.25 mol / L, but is not limited to the listed concentrations. Other unlisted concentrations within this range are also applicable;

[0012] The iron salt is one of ferrous chloride and ferrous sulfate, with a concentration of 0.03 - 0.08 mol / L. For example, it can be 0.03 mol / L, 0.04 mol / L, 0.05 mol / L, 0.06 mol / L, 0.07 mol / L, and 0.08 mol / L, but is not limited to the listed concentrations. Other unlisted concentrations within this range are also applicable;

[0013] The solvent used for the potassium oxalate solution is deionized water, with a concentration of 1.0 mol / L;

[0014] The stirring time of the emulsion is 10 - 12 h. For example, it can be 10 h, 11 h, and 12 h, but is not limited to the listed durations. Other unlisted times within this range are also applicable;

[0015] Step 2: Centrifuge, wash, and then dry the stirred emulsion overnight to obtain precursor A, where:

[0016] The drying temperature is 60 - 80 °C. It can be 60 °C, 70 °C, and 80 °C, but is not limited to the listed temperatures. Other unlisted temperatures within this range are also applicable;

[0017] The reagent used for washing is deionized water or a mixture of anhydrous ethanol and deionized water;

[0018] Step 3: Place the dried precursor A in a crucible and heat it for decomposition to obtain precursor B, where:

[0019] The atmosphere environment for the pyrolysis is one of argon and nitrogen, with a flow rate of 200 - 400 mL / min. For example, it can be 200 mL / min, 300 mL / min, and 400 mL / min, but is not limited to the listed flow rates. Other unlisted flow rates within this range are also applicable;

[0020] The pyrolysis temperature is 350 - 400 °C. For example, it can be 350 °C, 360 °C, 370 °C, 380 °C, 390 °C, and 400 °C, but is not limited to the listed temperatures. Other unlisted temperatures within this concentration range are also applicable;

[0021] The pyrolysis time is 1 to 2 h. For example, it can be 1 h, 1.5 h, and 2 h, but is not limited to the listed times, and other unlisted times within this time range are equally applicable;

[0022] Step 4: Place NaH2PO2 upstream of the tubular furnace and precursor B downstream of the tubular furnace, and heat to phosphide precursor B to obtain an iron-doped cobalt phosphide catalyst, where:

[0023] The atmosphere environment for phosphidation is one of argon and nitrogen, and the flow rate is 200 to 400 mL / min. For example, it can be 200 mL / min, 300 mL / min, and 400 mL / min, but is not limited to the listed flow rates, and other unlisted flow rates within this flow rate range are equally applicable;

[0024] The mass ratio of NaH2PO2 to precursor B is 3:0.1 to 0.2. For example, it can be 3:0.1, 3:0.15, and 3:0.2, but is not limited to the listed mass ratios, and other unlisted mass ratios within this mass ratio range are equally applicable;

[0025] The temperature for phosphidation is 300 to 350 °C. For example, it can be 300 °C, 310 °C, 320 °C, 330 °C, 340 °C, and 350 °C, but is not limited to the listed temperatures, and other unlisted temperatures within this temperature range are equally applicable;

[0026] The heating rate of the heating is 5 to 10 °C / min. For example, it can be 5 °C / min, 7 °C / min, 10 °C / min, and other unlisted heating rates within this heating rate range are equally applicable;

[0027] The phosphidation time is 1 to 2 h. For example, it can be 1 h, 1.5 h, and 2 h, but is not limited to the listed times, and other unlisted times within this time range are equally applicable.

[0028] OER is a typical four-electron transfer process, involving multiple intermediate steps (OH -→OH*→O*→OOH*→O2), and its theoretical potential is 1.23 V. However, due to the unsatisfactory adsorption strength (too strong or too weak) of reaction intermediates (such as OH*, O*, and OOH*) on the catalyst surface, a higher overpotential is often required during the actual OER process, resulting in reduced energy efficiency. Cobalt-based catalysts (such as Co2P) can exhibit a moderate adsorption strength towards OER intermediates due to their unique d-orbital electron structure, thus demonstrating good catalytic activity. In recent years, studies have shown that by introducing transition metal elements such as Fe for doping, the electronic structure of the catalyst surface can be further optimized, the adsorption energy of reaction intermediates can be regulated, and thus the OER performance can be improved. The introduction of Fe can not only regulate the electronic state of Co sites but also form a synergistic effect, enhancing the conductivity and stability of the catalyst. Therefore, Fe-modified Co2P catalysts have important research value and application potential in the field of OER. The present invention utilizes Fe doping to regulate the activity of Co2P catalysts and further constructs catalysts for electrolyzing untreated seawater to produce hydrogen.

[0029] Compared with the anode catalysts used in existing electrolytic seawater hydrogen production technologies, the present invention has the following advantages:

[0030] 1. The catalyst prepared by the present invention can not only be used for alkaline seawater electrolysis but also be directly applied to electrolyze untreated seawater to produce hydrogen, having a broad pH adaptability.

[0031] 2. The catalyst prepared by the present invention has low requirements for equipment and a simple synthesis process, and can achieve large-scale industrial preparation.

[0032] 3. The catalyst prepared by the present invention has strong seawater adaptability, and its corrosion voltage in seawater is as high as 0.57 V. After Fe is incorporated into the Co2P lattice, the interaction between Co and the catalytic substrate is enhanced. Experimental results show that the potential required for the catalyst prepared by the present invention to reach 100 mA·cm -2 in electrolyzing untreated seawater to produce hydrogen is only 1.866 V, and it can stably operate in natural seawater for more than 100 h at a current density of 100 mA·cm -2 .

[0033] 4. The materials required for the synthesis of the catalyst in the present invention are cheap transition metal salts, and the catalyst has excellent catalytic performance, with advantages such as low electrolysis energy consumption and high stability, and has broad application prospects in fields such as marine wind power consumption for producing green hydrogen and high-salt wastewater treatment. Description of the Drawings

[0034] Figure 1 SEM image of the catalyst in Example 1;

[0035] Figure 2 TEM image of the catalyst in Example 1;

[0036] Figure 3 It is the LSV curve of the catalyst in Example 1;

[0037] Figure 4 It is the potential curve under a constant current for directly electrolyzing untreated seawater in Example 1;

[0038] Figure 5 It is the Faraday efficiency test chart in Example 1;

[0039] Figure 6 It is the LSV curve of the catalyst in Example 2;

[0040] Figure 7 It is the LSV curve of the catalyst in Example 3; Specific implementation mode

[0041] The technical solutions of the present invention will be further described below in conjunction with the embodiments, but are not limited thereto. Any modification or equivalent replacement of the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention shall be covered within the protection scope of the present invention.

[0042] Example 1

[0043] The iron-doped cobalt phosphide catalyst is prepared according to the following steps in this example:

[0044] Step 1: Dissolve potassium oxalate in a solvent to obtain a 1.0 mol / L potassium oxalate solution. Subsequently, 0.15 mol / L cobalt chloride and 0.03 mol / L ferrous chloride are placed in a container, and the 1.0 mol / L potassium oxalate solution is slowly injected into the container under ice bath and stirring to obtain an emulsion, and stir for 10 h.

[0045] Step 2: Centrifuge the stirred emulsion, wash it with absolute ethanol and deionized water, and dry it overnight at 60 °C to obtain precursor A.

[0046] Step 3: Place the dried precursor A in a crucible and heat it to 350 °C under an argon gas flow of 200 mL / min to decompose A, and the pyrolysis time is 1 h. After cooling, obtain precursor B.

[0047] Step 4: Place 3.0 g of NaH2PO2 upstream of the tubular furnace and 0.1 g of precursor B downstream of the tubular furnace. Under an argon gas flow of 200 mL / min, heat it to 300 °C at a heating rate of 5 °C / min, and the phosphidation time is 1 h to phosphidate precursor B to obtain an iron-doped cobalt phosphide catalyst.

[0048] The iron-doped cobalt phosphide catalyst prepared in this example was characterized by SEM and TEM tests, and the results are as Figure 1 andFigure 2 As shown. From Figure 1 it can be seen that hollow nanosphere structures grow on the catalyst surface; from Figure 2 it can be seen that not only Co2P exists on the surface, but also the unphosphated Co3O4 structure is present.

[0049] The OER performance of the catalyst was tested. The test method is as follows: Pour untreated natural real seawater into a single-chamber electrolytic cell and conduct tests under a three-electrode system. The working electrode is the iron-doped cobalt phosphide catalyst prepared in this example, the counter electrode is a platinum sheet, and the reference electrode is Hg / Hg2SO4. The performance of the iron-doped cobalt phosphide catalyst was evaluated by linear sweep voltammetry. The test results are as Figure 3 shown. From Figure 3 it can be seen that when the current density reaches 100 mA·cm -2 , the potential is 1.866 V.

[0050] The stability of the catalyst was tested. The test method is as follows: Pour untreated natural seawater into a single-chamber electrolytic cell. Use the iron-doped cobalt phosphide catalyst prepared in this example as the working electrode, Pt / C / NF as the counter electrode, and Hg / Hg2SO4 as the reference electrode. Electrolysis was carried out at a constant current of 100 mA·cm -2 . The electrolytic cell voltage data obtained are as Figure 4 shown, and the Faraday efficiency of the electrode is as Figure 5 shown. It can be seen that Fe / Co2P can achieve stable seawater electrolysis for hydrogen production for 100 h, and the OER selectivity can reach 64.68% during the electrolysis process.

[0051] Example 2

[0052] The iron-doped cobalt phosphide catalyst was prepared according to the following steps in this example:

[0053] Step 1: Dissolve potassium oxalate in a solvent to obtain a 1.0 mol / L potassium oxalate solution. Subsequently, place 0.20 mol / L cobalt sulfate and 0.05 mol / L ferrous sulfate in a container, and slowly inject the 1.0 mol / L potassium oxalate solution into the container under ice bath and stirring to obtain an emulsion, and stir for 11 h.

[0054] Step 2: Centrifuge the stirred emulsion, wash it with deionized water, and dry it overnight at 70 °C to obtain precursor A.

[0055] Step 3: Place the dried precursor A in a crucible and heat it to 380 °C under an argon gas flow of 300 mL / min to decompose A. The pyrolysis time is 1.5 h. After cooling, obtain precursor B.

[0056] Step 4: Place 3.0 g of NaH2PO2 upstream of the tubular furnace and 0.15 g of precursor B downstream of the tubular furnace. Under a nitrogen gas flow rate of 300 mL / min, heat it to 330 °C at a heating rate of 7 °C / min, and the phosphating time is 2 h to phosphorate precursor B to obtain an iron-doped cobalt phosphide catalyst.

[0057] Perform OER performance testing on the catalyst prepared in this example. The test results are as Figure 6 shown. When the current density reaches 100 mA·cm -2 , the potential is 1.941 V.

[0058] Example 3

[0059] Prepare an iron-doped cobalt phosphide catalyst according to the following steps in this example:

[0060] Step 1: Dissolve potassium oxalate in a solvent to obtain a 1.0 mol / L potassium oxalate solution. Subsequently, place 0.25 mol / L cobalt nitrate and 0.08 mol / L ferrous sulfate in a container, and slowly inject the 1.0 mol / L potassium oxalate solution into the container under ice bath and stirring to obtain an emulsion, and stir for 12 h.

[0061] Step 2: Centrifuge the stirred emulsion, wash it with absolute ethanol and deionized water, and dry it overnight at 80 °C to obtain precursor A.

[0062] Step 3: Place the dried precursor A in a crucible and heat it to 400 °C under a nitrogen gas flow rate of 400 mL / min to decompose A, and the pyrolysis time is 2 h. After cooling, obtain precursor B.

[0063] Step 4: Place 3.0 g of NaH2PO2 upstream of the tubular furnace and 0.2 g of precursor B downstream of the tubular furnace. Under a nitrogen gas flow rate of 400 mL / min, heat it to 350 °C at a heating rate of 10 °C / min, and the phosphating time is 2 h to phosphorate precursor B to obtain an iron-doped cobalt phosphide catalyst.

[0064] Perform OER performance testing on the iron-doped cobalt phosphide catalyst prepared in this example. It can be seen from Figure 7 that when the current density reaches 100 mA·cm -2 , the potential is 2.027 V.

Claims

1. A synthesis method of an iron-doped cobalt phosphide catalyst for electrolyzing untreated seawater to produce hydrogen, characterized in that The method comprises the following steps: Step 1: Place the metal salt in a container, and slowly inject the potassium oxalate solution into the container under ice bath and stirring to obtain an emulsion, and stir, wherein: the metal salt is cobalt salt and iron salt, the concentration of cobalt salt is 0.15 - 0.25 mol / L, the concentration of iron salt is 0.03 - 0.08 mol / L, and the concentration of the potassium oxalate solution is 1.0 mol / L; Step 2: Centrifuge, wash and dry the stirred emulsion overnight to obtain precursor A; Step 3: Place the dried precursor A in a crucible and heat it for decomposition to obtain precursor B; Step 4: Place NaH2PO2 at the upstream of a tubular furnace and precursor B at the downstream of the tubular furnace, and heat to phosphorate precursor B to obtain an iron-doped cobalt phosphide catalyst, wherein: the mass ratio of NaH2PO2 to precursor B is 3: 0.1 - 0.

2.

2. The synthesis method of the iron-doped cobalt phosphide catalyst for electrolyzing untreated seawater to produce hydrogen according to claim 1, characterized in that The cobalt salt is one of cobalt chloride, cobalt sulfate, and cobalt nitrate, the iron salt is one of ferrous chloride and ferrous sulfate, and the solvent used for the potassium oxalate solution is deionized water.

3. The synthesis method of the iron-doped cobalt phosphide catalyst for electrolyzing untreated seawater to produce hydrogen according to claim 1, wherein The stirring time of the emulsion is 10 - 12 h.

4. The synthesis method of the iron-doped cobalt phosphide catalyst for electrolyzing untreated seawater to produce hydrogen according to claim 1, characterized in that The drying temperature is 60 - 80 °C, and the reagent used for washing is deionized water or a mixture of absolute ethanol and deionized water.

5. The synthesis method of the iron-doped cobalt phosphide catalyst for electrolyzing untreated seawater to produce hydrogen according to claim 1, characterized in that The pyrolysis atmosphere environment is one of argon and nitrogen, and the flow rate is 200 - 400 mL / min.

6. The synthesis method of the iron-doped cobalt phosphide catalyst for electrolyzing untreated seawater to produce hydrogen according to claim 1, characterized in that The pyrolysis temperature is 350 - 400 °C, and the time is 1 - 2 h.

7. The synthesis method of the iron-doped cobalt phosphide catalyst for electrolyzing untreated seawater to produce hydrogen according to claim 1, characterized in that The phosphating atmosphere environment is one of argon and nitrogen, and the flow rate is 200 - 400 mL / min.

8. The synthesis method of the iron-doped cobalt phosphide catalyst for electrolyzing untreated seawater to produce hydrogen according to claim 1, characterized in that The phosphating temperature is 300 - 350 °C, the time is 1 - 2 h, and the heating rate is 5 - 10 °C / min.

9. An iron-doped cobalt phosphide catalyst synthesized by the method according to any one of claims 1 - 8.

10. Application of an iron-doped cobalt phosphide catalyst synthesized by the method according to any one of claims 1 - 8 in electrolyzing untreated seawater to produce hydrogen.

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