A small molecule-modified bimetallic phosphide catalyst and its preparation and application

Abstract

This invention provides a small-molecule-modified bimetallic phosphide catalyst, its preparation, and its application. The invention employs a low-temperature phosphating strategy to preserve the organic small-molecule ligands in their intact molecular form during the bimetallic phosphide formation process, and to chemically bond them to the surface of nanoparticles through functional groups. The method includes: constructing a metal-organic hybrid precursor by solvothermal reaction of a first and second metal salt with the organic small-molecule ligand, followed by low-temperature phosphating treatment at 200–400 °C. Crucially, the heat treatment temperature is lower than the complete carbonization temperature of the small molecules, thereby obtaining a bimetallic phosphide catalyst with a completely modified surface of organic small molecules. In this catalyst, the small molecules are stably linked through M-N coordination bonds, achieving molecular-level dispersion and electronic structure regulation, while their nitrogen-containing heterocycles provide additional hydrophilic sites. Unlike existing high-temperature carbonization coating technologies, this invention avoids the obstruction of active sites by a thick carbon layer, exhibiting excellent catalytic activity in the alkaline oxygen evolution reaction and achieving efficient complete water splitting. It can replace noble metal catalysts for industrial water electrolysis to produce hydrogen.

Description

Technical Field

[0001] This invention belongs to the field of catalytic materials technology, specifically relating to a method for preparing a small molecule modified bimetallic phosphide catalyst and its application in alkaline water electrolysis. Background Technology

[0002] Transition metal phosphides (TMPs, such as CoP, Ni2P, FeP, MoP, etc.) are considered ideal alternatives to noble metal catalysts due to their unique "metal-like" properties, high conductivity, and good chemical stability. However, single metal phosphides still face many challenges in practical applications: First, nanoparticles are prone to aggregation during high-temperature phosphating, leading to a reduction in active sites; second, the electronic structure of active sites on the material surface is simple, resulting in insufficient optimization of adsorption energy for reaction intermediates; and third, single metal phosphides have limited catalytic ability for the water dissociation step in alkaline media, leading to slow hydrogen evolution kinetics.

[0003] Studies have shown that bimetallic phosphides (such as CoFeP, NiCoP, and FeNiP) often exhibit superior catalytic performance compared to monometallic phosphides due to the synergistic effect between the two metals. However, bimetallic phosphides also face challenges such as aggregation and insufficient regulation of surface electronic structure.

[0004] In existing technologies, carbon coating strategies are widely used to improve the dispersibility and stability of phosphides, i.e., carbonizing organic carbon sources at high temperatures to form a core-shell structure in which a carbon layer encapsulates phosphide nanoparticles. Although this method can effectively inhibit nanoparticle aggregation, it still has the following inherent limitations: (1) High-temperature carbonization (usually >500 °C) can easily lead to excessive growth of metal phosphides and an increase in particle size; (2) The continuous and dense carbon layer can physically block reactant molecules (such as OH-) - (2) Direct contact with active sites increases mass transfer resistance and is not conducive to efficient mass transfer at the gas-liquid-solid three-phase interface; (3) The thick carbon layer covers the intrinsic active sites on the phosphide surface, reducing the accessibility of active sites.

[0005] Unlike the carbon coating strategies mentioned above, the small molecule modification strategy proposed in this invention has unique advantages in regulating the gas-liquid-solid interface of catalytic reactions: First, the molecular-scale modification layer is extremely thin, completely without hindering the diffusion of reactant molecules to active sites, achieving "modification without obstruction"; second, the abundant nitrogen-containing heterocycles and polar functional groups on the surface of organic small molecules can serve as "hydrophilic anchors," significantly improving the wettability of the electrode surface in alkaline electrolytes and promoting the reaction of reactants (H2O, OH-) at the gas-liquid-solid three-phase interface. -The invention facilitates the rapid transport of phosphide particles and their products (O2). Furthermore, small molecules are anchored to the phosphide surface via MN coordination bonds, and their steric hindrance effectively prevents nanoparticle aggregation. Simultaneously, the intact molecular structure allows for precise tuning of the electronic states of the active sites through push / pull electron effects. Therefore, this invention achieves a synergistic optimization of "molecular-level protection, interface wettability, and full exposure of active sites," an effect difficult to achieve with traditional continuous carbon layer coatings.

[0006] Therefore, developing a preparation method that can achieve molecular-level modification of bimetallic phosphide surfaces under mild conditions is of great theoretical and practical significance. Summary of the Invention

[0007] A small molecule-modified bimetallic phosphide catalyst, the catalyst comprising an organic small molecule and a bimetallic phosphide, wherein the organic small molecule is chemically bonded to the surface of the bimetallic phosphide through its functional groups to form a small molecule-modified bimetallic phosphide nanocomposite material. The bimetallic phosphide has a nanoparticle morphology, and the bimetals M1 and M2 are selected from two of iron, cobalt, nickel, molybdenum, tungsten, and vanadium, and M1 and M2 are different elements; the metal molar ratio of M1:M2 in the bimetal is 1:0.2 to 1:5. The organic small molecule is a nitrogen-containing heterocyclic small molecule compound selected from adenine, guanine, cytosine, thymine, uracil, histidine, tryptophan, imidazole, triazole or pyridinecarboxylic acid; The organic small molecules exist in their complete molecular form on the surface of the bimetallic phosphide without being carbonized.

[0008] Furthermore, the particle size of the bimetallic phosphide nanoparticles is 2–8 nm; The organic small molecule achieves chemical bonding by forming MN coordination bonds with the metal sites on the surface of the bimetallic phosphide through nitrogen atoms on its nitrogen-containing heterocycle; The organic small molecules form a molecular-scale modification layer on the surface of the bimetallic phosphide, with a modification layer thickness of less than 1 nm.

[0009] Furthermore, in the catalyst, the molar ratio of the small organic molecule to the bimetallic phosphide is 1:(0.05-2) (based on the total molar amount of the bimetal).

[0010] In a preferred embodiment, the bimetallic compound is cobalt and iron, and the organic small molecule is adenine, forming an adenine-modified CoFe phosphide catalyst, denoted as CoFeP@Ade.

[0011] In a preferred embodiment, the bimetallic compound is nickel and cobalt, and the organic small molecule is adenine, forming an adenine-modified NiCo phosphide catalyst, denoted as NiCoP@Ade.

[0012] In this invention, small organic molecules achieve chemical bonding by forming coordination bonds between nitrogen atoms on their nitrogen-containing heterocycles and metal sites on the surface of bimetallic phosphides. This structure has the following characteristics: (1) Organic small molecules exist in their complete molecular form, without being carbonized, and retain the chemical activity of their functional groups; (2) Molecular-scale modification layers (<1 nm) fully expose active sites and do not affect the mass transfer process; (3) The MN coordination bond provides a stable interfacial bond, ensuring that small molecules are not easily detached in the electrolyte; (4) Organic small molecules finely regulate the electronic structure of the active center of bimetallic phosphides through push / pull electron effects.

[0013] This invention also provides a method for preparing the above-mentioned small molecule modified bimetallic phosphide catalyst, comprising the following steps: (1) Precursor construction The first metal salt, the second metal salt, and the small organic molecule ligand are dissolved in a solvent, mixed evenly, and then subjected to a hydrothermal or solvothermal reaction to obtain a metal-organic hybrid precursor.

[0014] Wherein, the first metal salt and the second metal salt are independently selected from nitrates, chlorides, acetates or acetylacetone salts of iron, cobalt, nickel, molybdenum or tungsten; and the first metal and the second metal are different elements.

[0015] The molar ratio of the first metal salt to the second metal salt is 1:0.2 to 1:5, preferably 1:0.5 to 1:2.

[0016] The organic small molecule ligand is a nitrogen-containing heterocyclic small molecule compound selected from adenine, guanine, cytosine, thymine, uracil, histidine, tryptophan, imidazole, triazole or pyridinecarboxylic acid.

[0017] The ratio of the total molar amount of the first metal salt and the second metal salt to the molar amount of the organic small molecule ligand is 1:0.05 to 1:2, preferably 1:0.2 to 1:1.

[0018] The solvent is selected from water, N,N-dimethylformamide, methanol, or mixtures thereof.

[0019] The conditions for the hydrothermal or solvothermal reaction are: heating at 80–200 °C for 6–24 hours.

[0020] During the precursor construction process, the coordinating groups on the small organic molecule ligands (such as nitrogen atoms on nitrogen-containing heterocycles) undergo coordination reactions with metal ions, self-assembling to form a metal-organic hybrid precursor. This process achieves uniform dispersion of metal ions at the molecular level, laying the foundation for the subsequent formation of small-sized, uniformly distributed bimetallic phosphides.

[0021] (2) Low-temperature phosphating treatment The precursor obtained in step (1) is heat-treated in an inert or reducing atmosphere at a temperature range of 200–400 °C to allow the first and second metal ions in the precursor to react with the phosphorus source to generate bimetallic phosphide nanoparticles. At the same time, the organic small molecule ligand is retained in its molecular form and chemically bonded to the surface of the bimetallic phosphide through its functional groups to obtain a small molecule modified bimetallic phosphide catalyst.

[0022] The heat treatment temperature is lower than the complete carbonization temperature of the organic small molecule ligand, so that the molecular structure of the organic small molecule ligand is preserved.

[0023] The heating rate of the heat treatment is 1 to 10 °C / min, preferably 2 to 5 °C / min.

[0024] The heat treatment temperature is 200–400 °C, preferably 250–380 °C.

[0025] The heat preservation time is 1 to 6 hours, preferably 2 to 4 hours.

[0026] The phosphorus source is selected from at least one of sodium hypophosphite, ammonium hypophosphite, diammonium hydrogen phosphate, phytic acid, or red phosphorus.

[0027] The ratio of the total molar amount of the first metal salt and the second metal salt to the molar amount of the phosphorus source is 1:0.5 to 1:5, preferably 1:1 to 1:3.

[0028] The inert atmosphere is nitrogen or argon; the reducing atmosphere is a mixture of nitrogen and hydrogen, wherein the hydrogen volume percentage is 5% to 10%.

[0029] This invention employs low-temperature phosphating (200–400 °C), and its key technical feature is that this temperature range is sufficient to allow metal ions to react with the phosphorus source to form bimetallic phosphides, while remaining below the complete carbonization temperature of the organic small molecule ligands, thus ensuring that the organic small molecules are preserved in their intact molecular form. This is fundamentally different from the existing strategy of high-temperature (typically >500 °C) carbonization to form a carbon coating layer.

[0030] The superior performance of the catalyst of this invention in alkaline media is attributed to the following synergistic mechanism: (1) Bimetallic synergistic effect: The difference in electronic structure between two different metals leads to charge redistribution, which optimizes the reaction intermediate (such as OH) of the phosphide. 、 This reduces the adsorption free energy of OOH and provides a richer number of active sites.

[0031] (2) Molecular-level dispersion: The small organic molecules chemically bonded to the surface of the phosphide effectively prevent the aggregation of bimetallic phosphide nanoparticles through steric hindrance, thereby achieving uniform dispersion at the nanoscale and obtaining small-sized (2-8 nm) active nanoparticles.

[0032] (3) Hydrophilic interface promotion: Nitrogen-containing heterocycles (such as purine rings and imidazole rings) and polar functional groups on the surface of organic small molecules serve as hydrophilic sites, which are beneficial to the wetting of the catalyst surface by the electrolyte and promote the mass transfer process.

[0033] (4) Electronic structure regulation: Organic small molecules provide electrons to the active center of phosphide or generate electron-withdrawing effect through the MN coordination of nitrogen atoms and metal sites, thereby optimizing the adsorption free energy of phosphide for oxygen-containing intermediates.

[0034] (5) Active site protection: The molecular-scale modification layer acts as a "molecular fence" to protect the phosphide active center from OH⁻ poisoning and oxidative corrosion in the electrolyte, significantly improving long-term stability.

[0035] Modification layer morphology Amorphous carbon or graphite carbon layers Complete organic small molecules Modification layer thickness From several nanometers to tens of nanometers Molecular scale (<1 nm) Interface integration method Physical contact Chemical bonding (MN coordination) Active site exposure Partially obscured by a thick carbon layer Fully exposed Electronic structure adjustment weak Strong (through coordination) Preparation temperature Typically >500 °C 200～400 °C Therefore, the present invention has the following beneficial effects: (1) Bimetallic synergistic effect: By introducing two different metals, the intrinsic catalytic activity is significantly enhanced by utilizing the differences in electronic structure and synergistic effects. Compared with monometallic phosphides, the catalytic activity of bimetallic phosphides is increased by more than 50%.

[0036] (2) Low temperature preparation: The phosphating temperature is as low as 200-400 °C, avoiding particle agglomeration and small molecule carbonization caused by high temperature. It has low energy consumption, safe process and is suitable for large-scale production.

[0037] (3) Molecular-level dispersion: Chemically bonded small molecules achieve uniform dispersion of bimetallic phosphide nanoparticles through steric hindrance, resulting in small particle size (2-8 nm) and full exposure of active sites.

[0038] (4) Hydrophilic interface promotion: Nitrogen-containing heterocycles and polar functional groups on the surface of small molecules improve the wettability of the electrode surface, which is beneficial to the contact between the electrolyte and the active site.

[0039] (5) Electronic effect regulation: Organic small molecules finely regulate the electronic structure of the phosphide active center through MN coordination, thereby optimizing the adsorption free energy of the reaction intermediate.

[0040] (6) Interface stability: Chemical bonding ensures that small molecules are not easily detached in the electrolyte, providing a long-term stable modification effect with stability exceeding 100 hours.

[0041] (7) Strong universality: The method of the present invention can be extended to a variety of bimetallic combinations (CoFe, NiCo, NiFe, etc.) and a variety of nitrogen-containing heterocyclic small molecules (adenine, histidine, imidazole, etc.), and has a wide range of applicability. Attached Figure Description

[0042] Figure 1 This is a scanning electron microscope (SEM) image of the adenine-modified CoFe phosphide catalyst prepared in Example 1 of this invention.

[0043] Figure 2 This is a transmission electron microscope (TEM) image of the adenine-modified CoFe phosphide catalyst prepared in Example 1 of the present invention.

[0044] Figure 3 This is a comparison of the Raman spectra of the catalysts in Example 1 and the comparative example of the present invention, used to demonstrate the presence of the adenine functional group.

[0045] Figure 4 This is a comparison of the oxygen evolution reaction polarization curves of the catalysts in Example 1 and the comparative example of the present invention in 1.0 M KOH. Detailed Implementation

[0046] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be described in detail below with reference to specific embodiments. In the following embodiments, adenine is used as the organic small molecule ligand and CoFe phosphide is used as the bimetallic phosphide system for illustration, but the scope of protection of this invention is not limited thereto.

[0047] Example 1: Adenine-modified CoFe phosphide catalyst (CoFeP@Ade) (1) Precursor preparation: Weigh 0.582 g (2 mmol) cobalt nitrate hexahydrate, 0.808 g (2 mmol) ferric nitrate nonahydrate, and 0.270 g (2 mmol) adenine, and dissolve them in a mixed solvent of 40 mL deionized water and 10 mL anhydrous ethanol. Stir for 30 minutes until completely dissolved, transfer to a 100 mL polytetrafluoroethylene-lined high-pressure reactor, and react at 150 °C for 12 hours. After natural cooling, centrifuge to collect the precipitate, wash it three times with deionized water and ethanol, and dry it under vacuum at 60 °C for 12 hours to obtain the metal-organic hybrid precursor.

[0048] (2) Low-temperature phosphating treatment: The precursor was placed in a ceramic boat and placed below a tube furnace. 0.848 g (8 mmol) of sodium hypophosphite was placed in the ceramic boat above. The temperature was increased to 300 ℃ at 5 ℃ / min under Ar atmosphere (flow rate 50 sccm), held for 2 hours, and then naturally cooled to room temperature to obtain adenine-modified CoFe phosphide catalyst (CoFeP@Ade).

[0049] Example 2: Adenine-modified CoFe phosphide catalysts with different Co / Fe ratios The method is basically the same as in Example 1, except that the amount of cobalt salt and iron salt is adjusted in step (1) so that the molar ratio of Co:Fe is 3:1 and 1:3 respectively.

[0050] Example 3: Adenine-modified NiCo phosphide catalyst (NiCoP@Ade) The process was essentially the same as in Example 1, except that the iron salt was replaced with nickel acetate tetrahydrate (0.498 g, 2 mmol) to obtain an adenine-modified NiCo phosphide catalyst (NiCoP@Ade).

[0051] Example 4: Histidine-modified CoFe phosphide catalyst (CoFeP@His) The process was essentially the same as in Example 1, except that adenine was replaced with histidine (0.310 g, 2 mmol) to obtain a histidine-modified CoFe phosphide catalyst (CoFeP@His).

[0052] Example 5: Different phosphorus sources It is basically the same as Example 1, except that sodium hypophosphite is replaced with phytic acid (1.32 g, 2 mmol).

[0053] Comparative Example 1: High-temperature carbonization (complete carbonization of small molecules) The process is essentially the same as in Example 1, except that the heat treatment temperature in step (2) is 600 °C. At this temperature, adenine is completely carbonized, forming a carbon-coated CoFe phosphide (CoFeP@C).

[0054] Comparative Example 2: CoFe phosphide without small molecule modification The process is basically the same as in Example 1, except that the addition of adenine is omitted in step (1), and cobalt nitrate and ferric nitrate are mixed and directly phosphated (300 °C) to obtain unmodified CoFe phosphide (CoFeP).

[0055] Comparative Example 3: Single Metal Contrast (Adenine-Modified CoP) The process was essentially the same as in Example 1, except that no iron salt was added and only cobalt nitrate (4 mmol) was used to obtain an adenine-modified CoP catalyst (CoP@Ade).

[0056] Comparative Example 4: Single Metal Comparison (Adenine-Modified FeP) The process was essentially the same as in Example 1, except that no cobalt salt was added and only ferric nitrate (4 mmol) was used to obtain an adenine-modified FeP catalyst (FeP@Ade).

[0057] Comparative Example 5: Physically Mixed Small-Molecular CoFe Phosphates The unmodified CoFeP obtained in Example 1 (Comparative Example 2) was physically ground and mixed with an equal mass of adenine without heat treatment to obtain a physically mixed sample (CoFeP + Ade).

[0058] Comparative Example 6: Commercial Precious Metal Catalysts Commercial IrO2 was used as a comparative catalyst for total water splitting. Structural characterization

[0059] (1) Example 1 was characterized by scanning electron microscopy and transmission electron microscopy. The results showed that the morphology of Example 1 (CoFeP@Ade) was a three-dimensional continuous network structure constructed by interconnecting and interweaving ultrathin nanosheets.

[0060] (2) Raman tests were performed on Example 1 and Comparative Example 2. The results showed that Example 1 (CoFeP@Ade) showed a high performance at ~1330 and 1460 cm⁻¹. -1 (CC / CN stretching vibration), ~565 cm -1 (-NH2 rocking vibration) and ~731-737 cm -1 A distinct adenine characteristic peak was observed at the (purine ring respiratory vibration) location. Comparative Example 2 did not exhibit the aforementioned characteristic peak.

[0061] The above results demonstrate that the low-temperature phosphating treatment of the present invention allows adenine to be retained in its complete molecular form and firmly bonded to the surface of CoFe phosphide.

[0062] (3) XPS tests were performed on Example 1 and Comparative Example 2. The results showed that the Co 2p binding energy of Example 1 was negatively shifted by 0.34 eV compared to Comparative Example 2 (unmodified CoFeP), and the Fe 2p binding energy was negatively shifted by 0.79 eV. The N 1s spectrum of Example 1 showed a characteristic peak of MN bond (~399.5 eV), proving that adenine formed a chemical coordination bond with the metal site through the nitrogen atom.

[0063] The above results demonstrate that adenine is chemically bonded to the surface of CoFe phosphide through MN coordination, and effectively modulates the electronic structure of the bimetal.

[0064] The XPS and Raman characterization results confirmed the core technical feature of this invention: under low-temperature phosphating conditions, adenine remains stably linked to the surface of the bimetallic phosphide in its intact molecular form via MN coordination bonds, without being carbonized. This unique molecular-level modified structure is key to achieving excellent alkaline electrocatalytic performance. Electrochemical testing

[0065] The electrochemical performance of the materials was evaluated using a three-electrode system on a CHI 760E electrochemical workstation (CH Instruments, Inc., Shanghai). The obtained materials were used directly as the working electrode without further processing, a graphite rod as the counter electrode, and a saturated calomel electrode or an Ag / AgCl electrode as the reference electrode.

[0066] OER catalytic test: The electrolyte is 1 M KOH.

[0067] In polarization curves, overpotential is one of the most important electrode parameters for evaluating electrochemical performance. Under the same current, the smaller the overpotential, the higher the energy efficiency.

[0068] Polarization curves were obtained using linear sweep voltammetry (LSV) at a scan rate of 5 mV / s. Electrochemical impedance spectroscopy (EIS) was investigated in the frequency range of 0.1–1,000,000 Hz.

[0069] For comparison, the working electrode of the commercial catalyst was prepared by dispersing 10 μL of RuO2 catalyst ink. The ink was prepared by mixing 1 mg of RuO2 powder with a small amount of Nafion (10 μL, 5%) in 190 μL of ethanol.

[0070] To characterize the electrochemical performance of the catalysts in the examples and comparative examples, as well as commercial catalysts, the results of their application in an alkaline OER catalytic process are shown in Table 1.

[0071] Table 1. Alkaline catalytic effect of OER Example 1 (CoFeP@Ade) 235 mV 1.51 V Attenuation <8% Example 2-1 (Co:Fe=3:1) 260 mV 1.58 V 10% attenuation Example 2-2 (Co:Fe=1:3) 270 mV 1.62 V 11% attenuation Example 3 (NiCoP@Ade) 242 mV 1.53 V 7% attenuation Example 4 (CoFeP@His) 259 mV 1.58 V 10% attenuation Example 5 (phytic acid as phosphorus source) 255 mV 1.56 V 9% attenuation Comparative Example 1 (CoFeP@C, high temperature) 296 mV 1.69 V 22% attenuation Comparative Example 2 (CoFeP, unmodified) 265 mV 1.60 V 50% attenuation (ineffective after 20 hours) Comparative Example 3 (CoP@Ade) 303 mV 1.70V 15% attenuation Comparative Example 4 (FeP@Ade) 267 mV 1.61 V 18% attenuation Comparative Example 5 (CoFeP+Ade, physical) 284 mV 1.67 V Attenuation rate: 48% (ineffective after 10 hours, small molecules detach). <![CDATA[Comparative Example 6 (RuO2)]]> 260 mV 1.56 V Results Analysis

[0072] (1) Small molecule modification significantly improves OER activity: Compared with Comparative Example 1 and Comparative Example 2, after adenine modification, the OER overpotential was significantly reduced from 265 mV to 235 mV, a decrease of 30 mV, which proves that small molecule modification effectively improves the catalytic performance of oxygen evolution reaction.

[0073] (2) Small molecule retention is better than carbonization: Compared with Comparative Example 1 (235 mV) and Comparative Example 1 (high temperature carbonization, 296 mV), the OER overpotential of the sample that retains the complete adenine molecular structure is reduced by 61 mV, which proves that the complete molecular modification layer has a better catalytic promotion effect than the carbon coating layer.

[0074] (3) Significant bimetallic synergistic effect: Compared with Comparative Example 1 (CoFeP@Ade, 235 mV) and Comparative Example 3 (CoP@Ade, 303 mV) and Comparative Example 4 (FeP@Ade, 267 mV), the OER overpotential of the bimetallic samples decreased by 68 mV and 32 mV, respectively, which confirms that the electronic synergistic effect between Co and Fe bimetals effectively optimizes the adsorption energy of oxygen-containing intermediates.

[0075] (4) Chemical bonding is superior to physical mixing: The OER performance of Example 1 (235 mV) is far superior to that of Comparative Example 5 (physical mixing, 284 mV), and the adenine in the physically mixed sample was rapidly detached during long-term testing, proving that chemical bonding is the key to achieving stable molecular modification.

[0076] (5) The water splitting performance is close to that of commercial precious metal catalysts: The water splitting voltage (1.51 V) of Example 1 and that of Example 3 (NiCoP@Ade, 1.53 V) are both excellent and have outstanding stability (attenuation of <8% after 100 hours), indicating that the non-precious metal catalyst of the present invention has the potential to replace precious metal catalysts.

[0077] (6) Verification of the universality of the method: The OER performance (242 mV) and the total water splitting voltage (1.53 V) obtained in Example 3 (NiCoP@Ade) and the good performance (259 mV) in Example 4 (CoFeP@His) prove that the method of the present invention can be extended to a variety of bimetallic combinations and a variety of nitrogen-containing heterocyclic small molecules.

[0078] The preparation method provided by this invention is simple, low-temperature, and low-energy-consumption. The small-molecule modified bimetallic phosphide catalyst obtained exhibits excellent activity and stability in alkaline water electrolysis for oxygen production and in total water electrolysis. It can be used in industrial alkaline water electrolysis devices, regenerative fuel cells, metal-air batteries, and other fields, and has broad industrial application prospects.

Claims

1. A method for preparing a small molecule-modified bimetallic phosphide catalyst, characterized in that, Includes the following steps: (a) Precursor construction: The first metal salt, the second metal salt and the small organic molecule ligand are dissolved in a solvent, mixed evenly, and then subjected to a hydrothermal reaction or a solvothermal reaction to obtain a metal-organic hybrid precursor. (b) Low-temperature phosphating treatment: The precursor obtained in step (a) is heat-treated in an inert or reducing atmosphere at a temperature range of 200–400°C, so that the first and second metal ions in the precursor react with the phosphorus source to generate bimetallic phosphide nanoparticles. At the same time, the organic small molecule ligand is retained in its molecular form and is chemically bonded to the surface of the bimetallic phosphide through its functional groups to obtain a small molecule modified bimetallic phosphide catalyst. The heat treatment temperature is lower than the complete carbonization temperature of the organic small molecule ligand, so that the molecular structure of the organic small molecule ligand is preserved.

2. The preparation method according to claim 1, characterized in that, The first metal salt and the second metal salt are independently selected from nitrates, chlorides, acetates or acetylacetones of iron, cobalt, nickel, molybdenum, tungsten, and vanadium; and the first metal and the second metal are different elements.

3. The preparation method according to claim 1, characterized in that, The organic small molecule ligand is a nitrogen-containing heterocyclic small molecule compound.

4. The preparation method according to claim 3, characterized in that, The nitrogen-containing heterocyclic small molecule compound is selected from at least one of adenine, guanine, cytosine, thymine, uracil, histidine, tryptophan, imidazole, triazole, or pyridinecarboxylic acid.

5. The preparation method according to claim 1, characterized in that, The phosphorus source is selected from at least one of sodium hypophosphite, ammonium hypophosphite, diammonium hydrogen phosphate, phytic acid, or red phosphorus.

6. The preparation method according to claim 1, characterized in that, In step (a), the molar ratio of the first metal salt to the second metal salt is 1:(0.2 to 5).

7. The preparation method according to claim 1, characterized in that, In step (a), the ratio of the total molar amount of the first metal salt and the second metal salt to the molar amount of the organic small molecule ligand is 1:(0.05~2).

8. The preparation method according to claim 1, characterized in that, In step (a), the ratio of the total molar amount of the first metal salt and the second metal salt to the molar amount of the phosphorus source is 1:(1-5).

9. The preparation method according to claim 1, characterized in that, The heating rate of the heat treatment in step (b) is 1 to 10 °C / min, the heat treatment temperature is 250 to 380 °C, and the holding time is 1 to 6 hours.

10. The preparation method according to claim 1, characterized in that, The inert atmosphere in step (b) is nitrogen or argon, and the reducing atmosphere is a mixture of nitrogen and hydrogen, wherein the hydrogen volume percentage is 5% to 10%.

11. The small molecule-modified bimetallic phosphide catalyst prepared by the preparation method according to any one of claims 1 to 10, characterized in that, The surface of the bimetallic phosphide nanoparticles is chemically bonded with small organic molecules, which exist in their complete molecular form and are not carbonized.

12. The application of the small molecule modified bimetallic phosphide catalyst according to claim 11 as an electrocatalytic oxygen evolution reaction or a total water splitting catalyst in an alkaline electrolyte; wherein the alkaline electrolyte is preferably a 0.1-6 M KOH solution or NaOH solution.

13. An alkaline water electrolysis device, characterized in that, The anode of the device comprises the small molecule-modified bimetallic phosphide catalyst as described in claim 11.

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