Preparation method and application of Ni2P-loaded rare earth doped nickel-based micro-mesoporous material

Abstract

The invention discloses a preparation method and application of a Ni2P-loaded rare earth doped nickel-based micro-mesoporous material, and the method comprises the following steps: jointly dissolving hypophosphite, nickel salt and rare earth metal salt in a solvent for hydrothermal reaction, cleaning, drying and grinding the product to obtain rare earth metal doped nickel phosphite with a micro-mesoporous structure, and drying to obtain the Ni2P-loaded rare earth doped nickel-based micro-mesoporous material. And under the protection of inert atmosphere, co-calcining the Re-NiPO and phosphite in a non-mixing manner, and carrying out phosphating reaction to form nickel phosphide particles on the surface and in pores of the Re-NiPO, thereby obtaining the Ni2P-loaded rare earth doped nickel-based micro-mesoporous material. A series of Ni2P-coated Re-NiPO (Re = La, Ce, Sm) heterojunction materials are prepared through a hydrothermal-phosphating method, and the hard magnetic property and the catalytic activity can be improved at the same time.

Description

Technical Field

[0001] This invention relates to a method for preparing nickel-based microporous materials and their applications, and more particularly to a method for preparing rare-earth-doped nickel-based micro-mesoporous materials loaded with Ni2P and their applications. Background Technology

[0002] Electrocatalytic water splitting is a crucial reaction in renewable energy conversion and is essential for rechargeable metal-air batteries and hydrogen electrolysis technology. In recent years, microporous catalytic materials have become a research hotspot in catalysis and separation technologies due to their combined advantages of molecular sieving capabilities and efficient exposure of active sites. However, in the electrocatalytic hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), simultaneously improving catalytic efficiency and material stability remains a key challenge. Developing microporous materials with high specific surface area and stable structure, and optimizing the distribution of surface active sites and molecular mass transfer pathways, can significantly improve catalytic reaction kinetics and product selectivity. While metal-organic frameworks (MOFs) possess designable pore structures and functional sites, their insufficient chemical and thermal stability limits their practical application. In contrast, nickel-based microporous materials such as Ni11(HPO4)2 have shown promise. 38 (OH)6 (NiPO) also possesses a high specific surface area (reaching 200-300 m²). 2 With its excellent thermal stability (decomposition temperature > 800℃), NiPO4 has demonstrated significant catalytic activity in OER reactions. Its unique pore system formed by its hexagonal crystal structure (P63mc space group) provides a structural basis for molecular sieving and active site regulation. Despite these advantages, NiPO4's catalytic performance still needs further improvement.

[0003] Imbuing microporous materials with permanent magnet properties can significantly enhance catalytic activity. Ferromagnetic materials can effectively improve OER efficiency by promoting triplet reactions of oxygen molecules, accelerating charge transfer, and lowering the reaction energy barrier.

[0004] NiPO can be converted into nickel phosphide (Ni2P) through phosphating, and its ferromagnetism gives it excellent performance in electrocatalytic water splitting. However, conventional Ni2P has a coercivity of only about 10 Oe and lacks practical hard magnetic properties. Summary of the Invention

[0005] Purpose of the invention: The purpose of this invention is to provide a method for preparing rare earth-doped nickel-based micro-mesoporous materials supported on Ni2P that can simultaneously improve hard magnetic properties and catalytic activity;

[0006] Another object of the present invention is to provide the application of the method for preparing Ni2P-loaded rare earth-doped nickel-based micro-mesoporous materials obtained by the above method in the electrocatalytic water desorption hydrogen reaction.

[0007] Technical solution: The preparation method of rare earth-doped nickel-based micro-mesoporous material loaded with Ni2P according to the present invention includes the following steps:

[0008] (1) Dissolve hypophosphite, nickel salt and rare earth metal salt together in a solvent and carry out a hydrothermal reaction; wash, dry and grind the product to obtain rare earth metal doped micro-mesoporous nickel phosphite, denoted as Re-NiPO;

[0009] (2) Under the protection of an inert atmosphere, Re-NiPO and phosphite are calcined together in a non-mixed manner, so that the phosphite generates phosphine gas after being heated in an inert gas, which enters the pores of Re-NiPO and undergoes a phosphating reaction with Re-NiPO, thereby forming nickel phosphide particles on the surface and in the pores of Re-NiPO, and obtaining rare earth doped nickel-based micro-mesoporous material loaded with Ni2P, denoted as Ni2P@Re-NiPO.

[0010] In step (1), the rare earth metal salt is at least one of lanthanum salt, cerium salt or samarium salt.

[0011] In step (1), the molar ratio of hypophosphite, nickel salt, and rare earth metal salt is 1.5:1:0.2 to 1.5:1:0.5.

[0012] In step (1), the hydrothermal reaction temperature is 180-200 ℃ and the time is 24-36 h.

[0013] In step (2), the molar ratio of Re-NiPO to phosphite is 1:2 to 1:5; the heating rate of the first stage and the second stage is 3-5 ℃ / min.

[0014] In step (2), the calcination process involves two stages of heating. In the first stage, the temperature is raised from room temperature to 120-150°C and held for 60-120 minutes. In the second stage, the temperature is further raised to 350-280°C and held for 120-240 minutes.

[0015] In step (1), before hydrothermal treatment, a carbon matrix material is added so that rare earth metal-doped nickel phosphite is loaded in situ onto the carbon matrix material during the hydrothermal process; preferably, the carbon matrix material is carbon fiber cloth.

[0016] The above method is used to obtain rare earth-doped nickel-based micro-mesoporous materials loaded with Ni2P for electrocatalytic hydrogen evolution reaction.

[0017] Invention principle: First, a rare earth-doped hexagonal micro-mesoporous nickel-based precursor (Re-NiPO) is prepared by hydrothermal method. Then, it is calcined together with phosphite under an inert atmosphere and subjected to phosphating treatment. Ni2P nanoparticles are generated in situ in the pores and surface of the rare earth-doped hexagonal micro-mesoporous nickel-based precursor, thereby forming a heterojunction structure Ni2P@Re-NiPO.

[0018] In the process of calcination in a closed tube furnace, phosphite is placed upstream of the hexagonal micro-mesoporous nickel-based precursor (Re-NiPO). In an inert gas environment, when the heating temperature exceeds 250°C, phosphine gas, which is highly toxic, is generated. It can enter the pores of the downstream hexagonal micro-mesoporous nickel-based precursor (Re-NiPO) and form nickel phosphide particles on the surface and in the pores of Re-NiPO through a phosphating reaction, thereby obtaining rare earth-doped nickel-based micro-mesoporous material loaded with Ni2P.

[0019] Phosphating treatment simultaneously modulates the band structure, compressing the band gap from 2.7 eV (Re-NiPO) to 1.7 eV (Ni2P@Re-NiPO), resulting in a 2-3 fold increase in photocurrent response and providing a new pathway for photoelectrocatalysis. Rare earth doping induces lattice distortion through 4f-3d orbital hybridization, and combined with RKKY magnetic exchange, significantly enhances long-range spin order, causing the coercivity of Ni2P to jump from 10 Oe in traditional materials to 2000 Oe.

[0020] When synthesizing rare-earth-doped hexagonal micro-mesoporous nickel-based precursors (Re-NiPO), carbon matrix materials are added to allow Re-NiPO to be in situ supported on the surface of the carbon matrix. Following phosphating, optimized Ni2P@Sm-NiPO-CF is obtained, exhibiting superior bifunctional catalytic performance in 1 M KOH. This performance advantage stems from the multi-level mass transfer channels of the micro-mesoporous structure and the synergistic enhancement effect of hard magnetic properties and catalytic activity induced by rare-earth doping. Theoretical calculations further reveal that the Sm-4f orbitals significantly increase the d-band electronic state density near the Fermi level through indirect exchange interactions. Simultaneously, a linear positive correlation between the p-band center of phosphorus and OER activity is established for the first time, providing a universal descriptor for the rational design of rare-earth phosphides.

[0021] Beneficial effects: Compared with the prior art, the present invention achieves the following significant effects:

[0022] (1) This invention prepares a series of rare earth-doped nickel-based micro-mesoporous materials Ni2P@Re-NiPO (Re=La,Ce,Sm) heterojunction materials supported on Ni2P by hydrothermal-phosphating method, which can simultaneously improve hard magnetic properties and catalytic activity. (2) Rare earth doping induces lattice distortion through 4f-3d orbital hybridization, which, combined with RKKY magnetic exchange, significantly enhances the long-range spin order, causing the coercivity of Ni2P to jump from 10 Oe in traditional materials to 2000 Oe. (3) Ni2P@Sm-NiPO-CF supported on carbon fiber cloth exhibits excellent bifunctional catalytic performance in 1 M KOH: the hydrogen evolution (HER) and oxygen evolution (OER) overpotentials are within 10 mA cm⁻¹. -2 At current densities as low as 180 mV and 320 mV respectively, the Tafel slope is only 26 mV dec. -1 and 33 mV dec -1 Its performance advantage stems from the multi-level mass transfer channels of the micro-mesoporous structure and the synergistic enhancement effect of hard magnetic properties and catalytic activity induced by rare earth doping. (4) This invention constructs Ni2P@Re-NiPO heterojunction material through the in-situ reaction of micro-mesoporous nickel-based precursor (Re-NiPO) and phosphite. It combines rare earth doping and spin regulation to synergistically optimize catalytic activity and stability, providing new ideas and theoretical support for the design of high-efficiency water electrolysis catalytic materials. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the preparation process of Ni2P@Re-NiPO according to the present invention;

[0024] Figure 2 The XRD patterns of NiPO(a), Re-NiPO(b), Ni2P@NiPO, Ni2P@Re-NiPO(c) and Ni3P@NiPO(d) of the present invention are shown below.

[0025] Figure 3 These are TEM, SEM, and EDS images of NiPO and Re-NiPO from this invention.

[0026] Figure 4 These are TEM images of Ni2P@NiPO and Ni2P@Re-NiPO of the present invention;

[0027] Figure 5 The images show the XRD patterns (a), scanning electron microscope (SEM) images (b) and (c) of the carbon fiber cloth and Ni2P@Re-NiPO-CF, and the EDS image (dg) of Ni2P@Sm-NiPO-CF of the present invention.

[0028] Figure 6The XPS full spectrum test results are for the NiPO and Re-NiPO (Re=La, Ce, Sm) samples of this invention;

[0029] Figure 7 The high-resolution spectra of rare earth elements La, Ce, and Sm in Re-NiPO are shown in this invention.

[0030] Figure 8 The XPS full spectrum test results are for the Ni2P@NiPO-CF and Ni2P@Re-NiPO-CF (Re=La, Ce, Sm) samples of this invention;

[0031] Figure 9 High-resolution spectra of rare earth elements La, Ce, and Sm in Ni2P@Re-NiPO-CF, respectively;

[0032] Figure 10 VSM diagrams (a) of NiPO and Re-NiPO at 1.5T and (b) of Ni2P@NiPO and Ni2P@Re-NiPO at 1.5T are shown below.

[0033] Figure 11 The present invention provides the UV-Vis diffuse reflectance absorption spectra, Mott-Schottky diagrams, and schematic diagrams of conduction and valence band energy levels for NiPO and Re-NiPO.

[0034] Figure 12 The UV-Vis diffuse reflectance absorption spectra, Mott-Schottky diagrams, and schematic diagrams of conduction and valence band energy levels of Ni2P@NiPO and Ni2P@Re-NiPO of this invention are shown below.

[0035] Figure 13 The transient photocurrents of NiPO, Re-NiPO, Ni2P@NiPO, and Ni2P@Re-NiPO were measured under continuous simulation of cyclic conditions with and without sunlight in an alkaline environment (1 M KOH) according to the present invention.

[0036] Figure 14 This is a nitrogen adsorption isotherm curve of NiPO and Re-NiPO according to the present invention;

[0037] Figure 15 (ac) Polarization LSV curves, (d) Tafel plots, (e) scan rates of Ni2P@NiPO-CF and Ni2P@Re-NiPO-CF at 1.0 M KOH at 2 mV s. -1 At 10, 100 mA cm -2 The required overpotential and Tafel slope; (d) HER at 10 mA cm⁻¹ under 1.0 M KOH conditions, using Ni₂P@Sm-NiPO-CF as a catalyst. -2The curve of current density versus time;

[0038] Figure 16 (ac) Polarization LSV curves, (d) Tafel plots, (e) scan rates of Ni2P@NiPO-CF and Ni2P@Re-NiPO-CF at 1.0 M KOH at 2 mV s. -1 At 10, 100 mA cm -2 The required overpotential and Tafel slope; (d) Under 1.0 M KOH conditions, with Ni2P@Sm-NiPO-CF as the catalyst, the OER at 10 mA cm⁻¹ -2 The curve of current density versus time;

[0039] Figure 17 (a) Cross-sectional charge density maps of Ni₂P and Re(La, Ce, Sm)-Ni₂P (001) models; (b) Density of states (DOS) of specific Ni atoms in Ni₂P and RE(La, Ce, Sm)-Ni₂P; (c) 0.5 mA cm⁻¹ -2 The evolution of the iR correction potential under current density shows the Ni d-band and P p-band centers of Ni2P and Re(La, Ce, Sm)-Ni2P(001) relative to Ni2P E. f The location. Detailed Implementation

[0040] The present invention will now be described in further detail.

[0041] Example 1

[0042] (1) Add 8.8g of sodium hypophosphite, 29g of nickel nitrate hexahydrate, and 0.44g of lanthanum nitrate to a beaker, add 80ml of deionized water to the beaker, and stir thoroughly on a magnetic stirrer for 30min. Then transfer to a hydrothermal reactor, tighten the hydrothermal reactor, heat at 180℃ for 10h, and then clean, dry, and grind to obtain rare earth element La-doped micro-mesoporous nickel hypophosphite, denoted as La-NiPO;

[0043] (2) La-NiPO and NaH2PO2 are placed separately in a tube furnace, with NaH2PO2 placed upstream of La-NiPO. Inert argon gas is introduced into the tube furnace, and the temperature is programmed to perform phosphating treatment. The heating process is as follows: use 30 min to heat from room temperature to 120℃, hold for 1 h, then heat to 350℃ for 120 min and hold for 120 min, and then cool naturally to room temperature to obtain rare earth element La-doped nickel phosphite loaded with nickel phosphide, denoted as Ni2P@La-NiPO.

[0044] Example 2

[0045] Based on Example 1, but differing from Example 1, in step (1), 0.44g of lanthanum nitrate was replaced with 0.43g of cerium nitrate. Ni2P@Ce-NiPO-CF was thus prepared.

[0046] Example 3

[0047] Based on Example 1, the difference is that in step (1), 0.44g of lanthanum nitrate was replaced with 0.34g of samarium nitrate. Ni2P@Sm-NiPO-CF was then prepared.

[0048] Figure 1 The synthesis process of Ni2P@Re-NiPO (Re=La,Ce,Sm) in Examples 1-3 is shown.

[0049] Example 4

[0050] Based on Example 1, the difference is that in step (1), carbon fiber cloth was added to the beaker. The resulting sample was denoted as Ni2P@La-NiPO-CF.

[0051] Comparative Example 1

[0052] Based on Example 1, the difference from Example 1 is that step (2) is omitted, and lanthanum nitrate is not added in step (1), only nickel phosphite is prepared.

[0053] The preparation process is as follows: At room temperature, 8.8 g of sodium hypophosphite was weighed into a 100 ml beaker, and 20 ml of deionized water was added and stirred until homogeneous. Then, nickel nitrate hexahydrate crystals (molar ratio 1:1) were dissolved in 60 ml of deionized water and stirred until homogeneous. This solution was then added to the beaker and stirred thoroughly on a magnetic stirrer for 30 min. Finally, the liquid was transferred to a 100 ml high-pressure reactor lined with polytetrafluoroethylene (PTFE). The reactor was heated at 180 °C for 10 h. After cooling to room temperature, the reactor was opened, the liquid was poured out, and the inner wall of the reactor was thoroughly rinsed with deionized water. The reactor was then centrifuged, with the supernatant poured out after each centrifugation. A total of five centrifugations were performed. The sample with centrifuge tubes was placed in a 70 °C constant-temperature electric drying oven and dried for 12 hours. The sample was then scraped from the inner wall of the centrifuge tubes and thoroughly ground in a mortar and pestle to ensure uniform particle size and absence of lumps, yielding nickel phosphate, denoted as NiPO.

[0054] Comparative Example 2

[0055] Based on Examples 1, 2, and 3 respectively, the difference from Examples 1, 2, and 3 is that step (2) is omitted, and only rare earth element-doped nickel phosphite is prepared.

[0056] The preparation process is as follows: 0.44g of lanthanum nitrate, 8.8g of sodium hypophosphite, and 29g of nickel nitrate hexahydrate were added to a beaker. 80ml of deionized water was added to the beaker, and the mixture was stirred thoroughly on a magnetic stirrer for 30 minutes. The mixture was then transferred to a hydrothermal reactor, which was tightened. The reactor was heated at 180℃ for 10 hours. After cooling to room temperature, the reactor was opened, the liquid was poured out, and the inner wall of the reactor was thoroughly rinsed with deionized water. The mixture was then centrifuged, with the supernatant poured out after each centrifugation. After five centrifugations, the sample with centrifuge tubes was placed in a constant-temperature electric drying oven at 70℃ and dried for 12 hours. The sample was then scraped from the inner wall of the centrifuge tubes and thoroughly ground in a mortar and pestle to ensure uniform particle size and absence of lumps, thus obtaining the precursor Re-NiPO. Where Re = La, Ce, Sm.

[0057] Comparative Example 3

[0058] NiPO was placed in a tube furnace, and inert hydrogen gas was introduced into the furnace. Phosphating was performed using a programmed temperature rise process: the temperature rose from room temperature to 120°C over 30 minutes and held for 1 hour, then rose to 350°C over 120 minutes and held for 120 minutes, followed by natural cooling to room temperature to obtain the sample Ni3P@NiPO. Figure 2 As shown in d.

[0059] 1. Test conditions and test methods:

[0060] Characterization of catalysts:

[0061] X-ray diffraction (XRD): Analyzed using an AXS D8-Advance X-ray diffractometer with Cu Kα radiation (λ = 0.15406 nm). Transmission electron microscopy (TEM): Observed using a JEOL 2100F microscope at an operating voltage of 200 kV. The catalyst was first ultrasonically dispersed in anhydrous ethanol and then placed on a copper grid with a carbon support film for observation. Ultraviolet-visible diffuse reflectance spectroscopy (UV-Vis DRS): Measured using a Cary 300 Scan UV-Vis spectrophotometer. The scanning wavelength range was 200 to 800 nm, and the scan rate was 100 nm / min. BaSO4 was used as a reference sample. X-ray photoelectron spectroscopy (XPS): Analyzed using an Axis Ultra DLD (Kratos). Physico-adsorption (BET): Experiments were performed on a Micromeritics Tristar 3000 automated physisorption analyzer. The catalyst was degassed at 100 Pa and 110 °C. Nitrogen adsorption-desorption isotherms were measured at -196 °C, and the specific surface area of ​​the catalyst was calculated using the BET equation. Pore size distribution was obtained through the desorption branch of the nitrogen isotherm using the BJH method.

[0062] Catalyst performance testing:

[0063] Electrochemical performance testing: The electrocatalytic hydrogen evolution and oxygen evolution performance of the catalyst was tested using a CHI760E electrochemical workstation manufactured by Shanghai Chenhua Co., Ltd., employing a standard three-electrode system. In the three-electrode system used in this experiment, an Ag / AgCl electrode was used as the reference electrode, a platinum wire electrode as the counter electrode, and a glassy carbon electrode loaded with the prepared water electrolysis catalyst was used as the working electrode. The working electrode was first prepared by immersing it in an appropriate amount of ethanol and then cleaning it using an ultrasonic cleaner. Ultrasonic cleaning effectively removed organic matter and contaminants from the electrode surface. The cleaned glassy carbon electrode was then polished using polishing powders with particle sizes of 1 μm and 0.05 μm, respectively. The polished glassy carbon electrode was then thoroughly cleaned again with deionized water and anhydrous ethanol, and finally gently dried with lens paper and set aside for later use. The catalyst dispersion was prepared using the following procedure: First, 1.6 mg of carbon black and 8 mg of electrocatalyst were accurately weighed using an electronic balance and added to a small centrifuge tube. Then, 4 ml of anhydrous ethanol was pipetted into the same centrifuge tube. Next, 50 μl of a 5% Nafion solution was added to the centrifuge tube using a microsyringe. The mixture was then ultrasonically dispersed for 60 min. The working electrode was then baked for 2 min using a baking lamp. Then, 15 μl of the prepared catalyst dispersion was measured using a 50 μl microsyringe and uniformly coated onto the working electrode surface using a drop-casting method, one drop at a time, using liquid surface tension. The electrode was dried immediately after each drop-casting to ensure strong catalyst adhesion. The calculated catalyst loading on the working electrode was 0.25 mg cm⁻².

[0064] Density functional theory calculations:

[0065] Density functional theory (DFT) calculations were performed using the VASP atomic-scale materials simulation software package. The cutoff energy for plane waves was set to 500 eV. During geometry optimization, a 3×3×2 k-point grid was used for sampling the Brillouin zone. A higher density k-point grid of 6×6×6 was used for calculating the density of states (DOS).

[0066] 2. Results and Analysis:

[0067] (1) Analysis of structural characterization results of rare earth-doped nickel phosphides:

[0068] XRD analysis was performed on the catalysts NiPO, Re-NiPO, Ni2P@NiPO, and Ni2P@Re-NiPO. The results are as follows. Figure 2 As shown. Figure 2 (a) in the figure shows the XRD results for NiPO4. Figure 2(b) shows the XRD results for La-NiPO, Ce-NiPO, and Sm-NiPO.

[0069] Figure 2 As shown in (a), the diffraction angles 2θ of the NiPO sample are 13.836°, 19.532°, 27.777°, and 37.009°. Referring to the PDF card, the diffraction angles correspond to crystal planes (110), (101), (211), and (401), respectively, and are consistent with Ni… 11 The standard PDF card (JCPDS No. 44-1326) for (HPO3)8(OH)6 corresponds to this, and no impurity phase was found upon comparison. The strong peak at ~14° indicates a periodic microporous structure, suggesting that the NiPO catalyst prepared in this application is a microporous catalyst. Compared to the precursor NiPO, the XRD peaks of the La, Ce, and Sm-doped samples are significantly higher than those of NiPO. 11 The significant decrease in (HPO3)8(OH)6 may be due to factors such as smaller grain size or the presence of numerous defects or dislocations.

[0070] Figure 2 Image (c) shows the XRD patterns of Ni2P@NiPO and Ni2P@Re-NiPO samples obtained after phosphating the precursor and doped sample. The XRD patterns show that the diffraction angles 2θ of the samples are 27.871° and 39.824°, corresponding to crystal planes (200) and (220), respectively. A new diffraction peak consistent with the PDF card of Ni2P (JCPDS No. 89-2742) appears in the XRD pattern, indicating that Ni is selectively phosphated in the NiPO precursor to form Ni2P nanoparticles. In addition, it was observed in the XRD pattern that the phosphated sample still has the characteristic diffraction peaks of NiPO sample at 13.836°, 19.532°, and 27.777°, proving that while there is a phosphated sample, some unphosphated sample is still retained, which is consistent with the expectation and proves that Ni2P nanoparticles can be loaded on the prepared NiPO.

[0071] (2) Morphological analysis of rare earth-doped nickel phosphides:

[0072] This invention used TEM to observe and study NiPO and Re-NiPO, and the results are as follows: Figure 3 As shown.

[0073] Figure 3In the figures, i, ii, iii, and iiii are transmission electron microscope (TEM), scanning electron microscope (SEM), and EDS (Electron Spectroscopy) images of NiPO and Re-NiPO, respectively. Figure (a) in each group is a TEM image, and Figure (b) is a high-resolution TEM image of each sample. The comparison shows that for samples without carbon fiber support, doping has little effect on the sample structure. Both undoped and doped samples exhibit a very regular layered structure and good crystallinity. However, doping significantly affects the cell parameters. TEM images show that the interplanar spacing of the doped samples is smaller than that of the undoped samples. The interplanar spacing of the undoped samples is 1.048 nm, while the interplanar spacing of the doped Re-NiPO samples is reduced to 0.3419 nm, 0.4214 nm, and 0.5814 nm, respectively. This is consistent with the conclusions drawn from the XRD images.

[0074] To verify the successful doping of rare earth elements in the Re-NiPO prepared in this invention, the elemental composition of Re-NiPO was studied and analyzed using an EDS kit on a TEM. The results are shown in Figures (f), (g), and (h) of each group. The figures show that La, Ce, and Sm elements were successfully incorporated into NiPO and are uniformly distributed. The proportions of La, Ce, and Sm elements in the figures are 16.66%, 21.57%, and 27.46%, respectively, which also demonstrates the successful doping and uniform dispersion of rare earth elements. The SEM images of NiPO and Re-NiPO are shown in Figures (c) and (d) of each group. The microstructure of NiPO and Re-NiPO is a flower-like structure formed by the accumulation of a series of layered crystals. This structure greatly expands the surface area of ​​the material and provides abundant active sites, offering favorable conditions for improved catalytic reactions.

[0075] This invention conducted TEM tests on Ni2P@NiPO and Ni2P@Re-NiPO, and the results are as follows: Figure 4 As shown. Figure 4 (a), (b); (c), (d); (e), (f) and (g), (h) are TEM images of Ni2P@NiPO, Ni2P@La-NiPO, Ni2P@Ce-NiPO and Ni2P@Sm-NiPO, respectively. The test results show that the interplanar spacing of Ni2P@NiPO, Ni2P@La-NiPO, Ni2P@Ce-NiPO and Ni2P@Sm-NiPO are 0.46 nm, 0.33 nm, 0.45 nm and 0.216 nm, respectively. Among them, the interplanar spacing of undoped Ni2P@NiPO is significantly reduced, and the interplanar spacing of Ni2P@Sm-NiPO is the smallest. The interplanar spacing of the other samples does not change much before and after phosphating.

[0076] This invention conducted XRD tests on carbon fiber cloth and Ni2P@Re-NiPO-CF, such as... Figure 5 As shown in (a), the results obtained include not only a large peak at around 25° for the carbon fiber cloth, but also a significant Ni2P peak and a less obvious NiPO peak. This may be due to the peaks of the high-strength carbon fiber cloth and Ni2P, as well as the smaller particle size. Figure 5 Images (b) and (c) are scanning electron microscope (SEM) images of the sample Ni2P@Sm-NiPO-CF. The microstructure of Ni2P@Sm-NiPO-CF is a fibrous structure loaded with catalyst. This structure greatly expands the surface area of ​​the material and can provide a very rich number of active sites. In addition, since the carbon matrix structure of the carbon fiber cloth is an excellent conductor, it can accelerate the transfer of electrons, which provides favorable conditions for improving the catalytic reaction. Figure 5 (dg) is the EDS image of Ni2P@Sm-NiPO-CF. The EDS image shows that Ni, P, O and Sm in the catalyst are uniformly distributed on the carbon fiber cloth.

[0077] (3) XPS electronic valence state analysis of NiPO, Re-NiPO, Ni2P@NiPO and Ni2P@Re-NiPO

[0078] In order to obtain information such as the surface elemental composition and chemical state of the prepared catalyst, this invention uses XPS to detect and analyze the sample. Figure 6 XPS test results for NiPO and Re-NiPO samples are presented. Figure 6 In (a), the characteristic peaks of Ni, La, Ce, Sm, P, and O were identified by XPS testing. The presence of characteristic peaks of La, Ce, and Sm in the XPS spectrum of the catalyst indicates that these elements were successfully doped into the catalyst. Figure 6 As shown in (b), the O 1s peak of NiPO in the undoped state has two peaks: one at 531.3 eV for the metal-oxygen bond and the other at 532.7 eV for the hydroxyl group of the metal hydroxide. Doping significantly increases the area of ​​the peak with the metal-oxygen bond, indicating that the introduction of rare earth elements promotes Ni-O bonding. Furthermore, the O 1s peak of samarium-doped NiPO shifts approximately 0.5 Ev towards the lower binding energy direction, indicating that the binding energy of the O atoms in the samarium-doped sample is reduced. Figure 6As shown in (c), NiPO exhibits peaks at 133.4 eV and 134.7 eV at the P 2p level, corresponding to metal phosphates with different valence states. This indicates that undoped NiPO contains phosphates with two valence states. In cerium-doped Ce-NiPO, the P 2p peak positions shift towards higher binding energies, and the peak area containing lower valence phosphates decreases significantly, indicating that cerium doping alters the binding energy of phosphorus and significantly changes its valence state. Furthermore, nickel in nickel phosphate doped with lanthanum and samarium both exhibits a low valence state. Figure 6 As shown in Figure (d) and the literature, the XPS spectrum of the Ni 2p orbital of NiPO can be divided into two main peaks. These two main peaks, Ni 2p³ / 2 and Ni 2p¹ / 2, each have their own satellite peaks. Figure (d) shows that Ni 2p orbitals at 856.0 eV, 857.3 eV, 856.7 eV, and 874.2 eV are present. 2+ In addition, a peak of 852.0 eV for elemental nickel was found after doping with lanthanum, and peaks of 870 eV and 852 eV for elemental nickel were found after doping with cerium. This indicates that doping changes the valence state of nickel, and the presence of metallic nickel can provide better conductivity for electron transport.

[0079] Figure 7 XPS high-resolution spectra of rare earth elements La, Ce, and Sm in Re-NiPO were obtained. It can be seen that the La 3d orbital region has a clearly separated spin-orbit splitting peak, with its main peak located at 835 eV, and the difference between the main peak and the splitting peak is ΔE = 3.5 eV. Therefore, according to the handbook, the corresponding phase is trivalent lanthanum. Ce 3d shows a peak at ~900 eV. Due to the high intensity of the Ni 2p orbital peak, which partially overlaps with the Ce 3d peak, the Ce 3d splitting peak is still visible at 900 eV, indicating only divalent cerium oxide. The Sm 3d orbital has a particularly obvious characteristic peak at 1080 eV. However, because the valence of samarium is easily changed, XPS testing cannot directly determine the initial valence state of samarium in the sample.

[0080] Figure 8 These are the XPS spectra of Ni2P@NiPO and Ni2P@Re-NiPO. Figure 8 The test in (a) identified the characteristic peaks of Ni, La, Ce, Sm, P, and O. The presence of characteristic peaks of La, Ce, and Sm in the XPS spectrum of the catalyst indicates that these elements were successfully doped into the catalyst. Figure 8As shown in (b), the O 1s peak of Ni2P@NiPO has two peaks in the undoped state: one for the metal-oxygen bond at 531.3 eV and the other for the hydroxyl group of the metal hydroxide at 532.9 eV. After doping, the ratio of the peak area of ​​the metal-oxygen bond to the peak area of ​​the hydroxyl group of the metal hydroxide does not change significantly. Furthermore, the O 1s peak of cerium-doped samples shifts to a lower binding energy direction by approximately 0.5 eV, indicating a decrease in the binding energy of the O atoms in the cerium-doped samples; the O 1s peak of samarium-doped samples shifts to a higher binding energy direction by approximately 0.3 eV, indicating an increase in the binding energy of the O atoms in the samarium-doped samples. Figure 8 As shown in (c), Ni₂P@NiPO exhibits peaks at 133.3 eV and 134.1 eV at P₂p, corresponding to metal phosphates with different valence states. This indicates that undoped NiPO contains phosphates with two valence states. In cerium-doped Ni₂P@Ce-NiPO, the P₂p peak positions shift towards lower binding energies, and the peak area of ​​phosphates with lower valence states decreases, indicating that cerium doping alters the binding energy of phosphorus and changes its valence state. In samarium-doped Ni₂P@Sm-NiPO, the P₂p peak positions shift towards higher binding energies, and the peak area of ​​phosphates with lower valence states decreases significantly, suggesting that most of the phosphorus in Ni₂P@Sm-NiPO is converted to higher valence phosphorus. Figure 8 As shown in (d) and the literature, the XPS spectrum of the Ni 2p orbital of Ni2P@NiPO can be divided into two main peaks. These two main peaks, Ni 2p3 / 2 and Ni 2p1 / 2, each have their own satellite peaks. Figure 8 As shown in (d), Ni exists at values ​​of 856.7 eV, 856.9.3 eV, 855.4 eV, and 874.2 eV. 2+ The peak indicates that doping, phosphating, and loading of carbon fiber cloth did not change the valence state of nickel.

[0081] Figure 9 The XPS high-resolution spectra of rare earth elements La, Ce, and Sm in Ni2P@Re-NiPO are shown. It can be seen that the La 3d orbital region has a clearly separated spin-orbit splitting peak, with its main peak located at 835 eV, and the difference between the main peak and the splitting peak is ΔE = 3.5 eV. Therefore, according to the handbook, the corresponding phase is trivalent lanthanum. Ce 3d shows a peak at ~900 eV. Due to the high intensity of the Ni 2p orbital peak, which partially overlaps with the Ce 3d peak, the splitting peak of Ce 3d is still visible at 900 eV, indicating only divalent cerium oxide. The Sm 3d orbital has a particularly obvious characteristic peak at 1080 eV. However, because the valence of samarium is easily changed, XPS testing cannot directly determine the initial valence state of samarium in the sample.

[0082] (4) Magnetic analysis of the catalyst

[0083] To investigate the influence of the magnetic properties of catalysts on catalytic performance, this invention conducted VSM tests on catalysts NiPO, Re-NiPO, Ni2P@NiPO, and Ni2P@Re-NiPO under a 1.5T condition. The test results are as follows: Figure 10 As shown. By Figure 10 As can be seen in (a) above, both the undoped precursor NiPO and the rare-earth lanthanum-doped La-NiPO exhibit paramagnetic properties. Figure 10 In (b), phosphated Ni2P@NiPO and Ni2P@Re-NiPO were subjected to VSM testing at 1.5T. The tests revealed that the phosphated samples exhibited a certain degree of ferromagnetism. Regarding the relationship between magnetism and catalytic performance, in magnetic materials, the spin state of electrons becomes polarized, generating a spin-polarized current that promotes electron transfer. Spin polarization on magnetic catalysts can also increase the number of available electrons on the catalyst surface, thereby enhancing the catalytic efficiency. Magnetic materials can influence their magnetic and electronic structure through electron-mediated long-range magnetic coupling. This effect is known as the RKKY effect. This effect can further modulate the electronic states of the catalyst surface, increasing the activity of the catalytic reaction. Magnetism can also affect the adsorption behavior of the catalyst surface. The surface state of a magnetic catalyst can alter the interaction forces between reactants and the catalyst surface, optimizing adsorption behavior and thus increasing the reaction rate.

[0084] (5) Catalyst band gap and photoelectric properties

[0085] UV absorption properties and band gap calculation:

[0086] Ultraviolet-visible-near-infrared spectrophotometry (UV-Vis) and Mott-Schottky analysis are important methods for obtaining the band structure of catalytic materials. UV-Vis measurements, by analyzing the light absorption characteristics of materials in the ultraviolet, visible, and near-infrared bands, can estimate the band gap (band width) of the material, providing fundamental data support for evaluating the material's photocatalytic performance. Figure 11 The UV-Vis diffuse reflectance absorption spectra of NiPO and Re-NiPO are presented. The band gaps of each sample were calculated using the Tauc Plot method. Based on the corresponding Tauc Plot curves, the direct band gaps of NiPO and Re-NiPO were determined to be 2.64 eV, 2.65 eV, 2.65 eV, and 2.65 eV, respectively. Mott-Schottky diode tests were performed on the NiPO and Re-NiPO samples at frequencies of 500 Hz, 700 Hz, and 900 Hz, and the results are shown below. Figure 11As shown. Calculations and analysis of the Mot Schottky curve data of the catalyst, measured using an electrochemical workstation at 500 Hz, 700 Hz, and 900 Hz, revealed that the slopes of the samples were all positive. A positive slope indicates that the samples possess n-type semiconductor properties. The intercepts of the Mot Schottky curves were 0.35 eV, 0.30 eV, 0.32 eV, and 0.31 eV, respectively. Converting these to NHE yielded flat-band potentials of 0.548 eV, 0.498 eV, 0.518 eV, and 0.508 eV. Since the flat-band potential is 0.1-0.3 V positive than the conduction band potential for n-type semiconductors... Here, using a voltage of 0.2 V, the conduction band energy levels of the NiPO, Re-NiPO, Ni2P@NiPO, and Ni2P@Re-NiPO samples are obtained as 0.348 eV, 0.298 eV, 0.318 eV, and 0.308 eV, respectively, by analyzing the intercepts of the Mott-Schottky diagram of the hydrogen electrode. Since their band gaps are 2.64 eV, 2.65 eV, 2.65 eV, and 2.65 eV, respectively, their valence band energy levels are 2.988 eV, 2.948 eV, 2.968 eV, and 2.958 eV, respectively. A schematic diagram of their conduction and valence band energy levels is shown below. Figure 11 As shown.

[0087] Figure 12 The UV-Vis diffuse reflectance absorption spectra of Ni2P@NiPO and Ni2P@Re-NiPO are presented. Based on the corresponding Tauc Plot curves, the direct band gaps of Ni2P@NiPO and Ni2P@Re-NiPO are determined to be 1.74 eV, 1.59 eV, 1.81 eV, and 1.70 eV, respectively. Calculations and analysis of the Motter-Schottky data of the catalysts measured using an electrochemical workstation at 500 Hz, 700 Hz, and 900 Hz revealed that the slopes of the samples were all positive. A positive slope indicates that the samples possess n-type semiconductor properties, since for n-type semiconductors, the flat band potential is 0.1-0.3 V more positive than the conduction band potential. Here, a voltage of 0.2 V is used. The intercepts obtained from the Mott-Schottky diagram are 0.548 eV, 0.578 eV, 0.508 eV, and 0.498 eV. Converting these to NHE, the flat band potentials of the Ni₂P@NiPO and Ni₂P@Re-NiPO samples are 0.348 eV, 0.378 eV, 0.298 eV, and 0.298 eV, respectively. Since their band gaps are 1.74 eV, 1.59 eV, 1.81 eV, and 1.70 eV, respectively, their valence band levels are 2.088 eV, 1.968 eV, 2.118 eV, and 1.998 eV, respectively. A schematic diagram of their conduction band and valence band levels is shown below. Figure 12As shown in the figure. Analysis and comparison of the experimental results revealed that the band gaps of Ni2P@NiPO and Ni2P@Re-NiPO after Ni2P loading were significantly lower than those of NiPO and Re-NiPO without Ni2P loading, proving that this invention successfully regulated the band gaps of NiPO and Re-NiPO compounds through Ni2P loading. This result indicates that the band gap of rare earth compounds decreases with the phosphating loading of Ni2P, and this invention successfully regulated the band gaps of NiPO and Re-NiPO compounds through sample phosphating. For visible light photocatalysis, the band gap should be controlled between 1.5 eV and 3.0 eV. This range ensures that the material can absorb most of the visible light and has sufficient energy to excite electrons. Based on this result, NiPO-P and Re-NiPO-P can be used in photocatalysis fields requiring enhanced visible light. Comparison of the valence band positions of NiPO and Re-NiPO samples, and Ni2P@NiPO and Ni2P@Re-NiPO samples, shows that the Ni2P loading method effectively reduces the valence band of the samples, which is beneficial to the catalytic reaction.

[0088] Photocurrent testing

[0089] This invention investigated the experimental photocurrent under a 1 M KOH alkaline environment and tested the transient photocurrent response of the catalysts under simulated sunlight irradiation. The test conditions were 0.4 V vs. Ag / AgCl potential, with a total test duration of 1000 seconds. The experiment compared the difference between irradiated and unirradiated conditions by simulating the on / off state of the light every 100 seconds. The results showed that all catalyst samples exhibited rapid and repeatable responses to changes in light intensity, indicating good charge separation capabilities under varying light conditions. Under illumination, the oxygen evolution reaction (OER) performance of all catalysts was improved, demonstrating that light irradiation enhances the catalytic effect. The principle of photocurrent testing is as follows: light excites electrons in the material, causing them to transition from the valence band to the conduction band, thereby generating a current in an external circuit.

[0090] The present invention tested the sample before phosphating, and the results are as follows: Figure 13 As shown in (a), the tests indicate that Ce-NiPO has the largest photoresponse, and the photoresponse magnitudes of the four samples are: Ce-NiPO > NiPO > Sm-NiPO > La-NiPO. The phosphating samples were tested in this invention, and the results are as follows: Figure 13As shown in (b), the tests indicate that Ni2P@La-NiPO exhibits the strongest light response, with the light response magnitudes of the four samples being: Ni2P@La-NiPO > Ni2P@Ce-NiPO > Ni2P@Sm-NiPO > Ni2P@NiPO. The significant change in light response after phosphating is attributed to the interaction and influence of Ni2P nanoparticles loaded onto the microporous structure of the phosphating material, leading to improved catalytic performance.

[0091] (6) Catalyst specific surface area and pore size distribution

[0092] By analyzing the nitrogen adsorption isotherms of NiPO and Re-NiPO, the changes in adsorption and desorption amounts under different relative pressures (P / Po) are shown. Table 1 summarizes the test data. Figure 14 The figures show the nitrogen adsorption isotherms for NiPO and Re-NiPO, with the inset showing the pore size distribution determined by nonlocal density functional theory (NLDFT). Adsorption curves (represented by gray dots) show that the adsorption amount gradually increases with increasing relative pressure, reaching a significant increase when the relative pressure approaches 1. Desorption curves (represented by red dots) typically appear near or slightly above the adsorption curves. At lower relative pressures, the adsorption and desorption curves are relatively close, but with increasing relative pressure, especially near 1, the desorption curve is significantly higher than the adsorption curve, exhibiting typical capillary condensation. The inset shows the adsorption amount variation under different pore sizes, with the horizontal axis representing pore size (nm) and the vertical axis representing adsorption amount. The inset shows that the adsorption amount is higher in the 3nm-4nm pore size range, indicating that adsorption is most significant at this pore size. BET testing shows that the catalyst's adsorption performance is closely related to pore size. BET testing revealed that the pore size of most catalysts is between 2-3 nm, making them a standard mesoporous material. However, except for the Sm-NiPO catalyst, there is no significant distribution of pore sizes larger than 4 nm. Furthermore, the fact that Sm-NiPO has the largest average pore volume also indirectly illustrates this point. Larger pore volumes can accommodate more active sites, thus having a more positive effect on catalytic reactions.

[0093] Table 1 Summary of Physical Adsorption Test Data

[0094] sample Specific surface area (m² / g) <![CDATA[ Pore volume (cm 3 / g)]]> Average pore size (nm) NiPO 13.1102 0.033639 9.1501 La-NiPO 21.251 0.047482 7.82665 Ce-NiPO 20.3792 0.041701 7.2894 Sm-NiPO 17.1990 0.050242 10.41385

[0095] (7) Characterization of the catalytic performance of rare earth-doped nickel phosphide

[0096] This invention uses an electrochemical workstation to test the LSV polarization curves and IT stability curves of the samples, which allows for the evaluation of the catalyst's performance.

[0097] The electrochemical performance of catalysts NiPO and Re-NiPO, Ni2P@NiPO and Ni2P@Re-NiPO, and Ni2P@NiPO-CF and Ni2P@Re-NiPO-CF in the oxygen evolution reaction (HER) was tested using linear sweep voltammetry (LSV). The results are as follows: Figure 15 As shown in (a), (b), and (c), doping, phosphating, and carbon fiber cloth loading all promote the HER reaction of the samples in a 1 M KOH alkaline environment. Among them, the phosphating samples Ni2P@NiPO-CF and Ni2P@Re-NiPO-CF after loading with carbon fiber cloth showed the best effect, with their activity in the HER reaction ranking as follows: Ni2P@Sm-NiPO-CF > Ni2P@Ce-NiPO-CF > Ni2P@La-NiPO-CF > Ni2P@NiPO-CF. This is particularly relevant when a 10 mA cm⁻¹ reaction is required. -2 At a current density of 100 mA cm⁻¹, the required overpotential for Ni₂P@Sm-NiPO-CF is only 180 mV; when a current density of 100 mA cm⁻¹ is required... -2 At the given current density, the overpotential of Ni2P@Sm-NiPO-CF is significantly lower than that of other samples.

[0098] This invention obtained the Tafel slopes of Ni2P@NiPO-CF and Ni2P@Re-NiPO-CF samples in the alkaline HER reaction by calculating the LSV polarization curves, such as... Figure 15 As shown in (d), Ni2P@Sm-NiPO-CF has the lowest Tafel slope (26 mV dec) among these samples. -1 The Tafel slope can reflect catalytic activity to some extent; a lower Tafel slope indicates a faster electrochemical response rate of the synthesized catalyst. The samples were tested at a current density of 10 mA cm⁻¹. -2 100 mAcm - The results of statistical analysis of the Tafel slope are as follows: Figure 15 As shown in (e). This was achieved by applying 10 mA cm⁻¹ of KOH in 1.0 M KOH. -2 The time-varying current density of the HER reaction was measured at the specified current density. The test results are as follows: Figure 15 As shown in (f), the current decay of Ni2P@Sm-NiPO-CF was negligible during the 8-hour potentiostatic test, demonstrating the stability of the catalyst in the alkaline HER reaction.

[0099] This invention used linear sweep voltammetry (LSV) to test the electrochemical performance of catalysts NiPO and Re-NiPO, Ni2P@NiPO and Ni2P@Re-NiPO, and Ni2P@NiPO-CF and Ni2P@Re-NiPO-CF in the hydrogen evolution reaction (OER). The results are as follows: Figure 16 As shown in (a), (b), and (c), it can be seen that doping and phosphating do not significantly promote the OER reaction of the samples in a 1 M KOH alkaline environment. However, phosphating after loading with carbon fiber cloth significantly promotes the OER reaction of the samples in a 1 M KOH alkaline environment. Among them, the Ni2P@Sm-NiPO-CF sample after loading with carbon fiber cloth and then phosphating showed the best effect. In the OER reaction, the activity order was Ni2P@Sm-NiPO-CF > Ni2P@Ce-NiPO-CF > Ni2P@La-NiPO-CF > Ni2P@NiPO-CF. The desired OER reaction rate was 10 mA cm⁻¹. -2 At a current density of 100 mA cm⁻¹, the required overpotential for Ni₂P@Sm-NiPO-CF is only 320 mV; when a current density of 100 mA cm⁻¹ is required... -2 At a current density of [value missing], the overpotential of Ni2P@Sm-NiPO-CF is significantly lower than that of other samples. Calculations of the LSV polarization curves yielded the Tafel slopes of the Ni2P@NiPO-CF and Ni2P@Re-NiPO-CF samples in the alkaline OER reaction as follows: Figure 16 In (d), it was found that Ni2P@Sm-NiPO-CF has the lowest Tafel slope (33 mV dec) among these samples. -1 The Tafel slope can reflect catalytic activity to some extent; a lower Tafel slope indicates a faster electrochemical response rate of the synthesized catalyst. The samples were tested at a current density of 10 mA cm⁻¹. -2 100 mA cm -2 The results of statistical analysis of the Tafel slope are as follows: Figure 16 As shown in (e). This was achieved by applying 10 mA cm⁻¹ solution to 1.0 M KOH. -2 The time-varying current density of the OER response under different current densities was measured, and the test results were as follows: Figure 16 As shown in (f), the current decay of Ni2P@Sm-NiPO-CF is negligible during the 8-hour potentiostatic test, demonstrating the stability of the catalyst in the alkaline OER reaction.

[0100] (8) Density functional theory calculations

[0101] This invention uses DFT to study the electronic structure of Ni₂P and La, Sm, and Ce-doped NiPO, and investigates the influence of rare earth element f electrons and orbitals on the electronic structure of RE-NiPO. The results show that the La-f and Ce-f orbitals above the Fermi level contribute little to the cruise electron density and Ni-d electronic states near the Fermi level. However, in Sm-NiPO, Sm-f electrons, located near the Fermi level, hybridize with cruise electrons near the Fermi level. The overlap of Sm-4f electrons with Ni-3d electrons at the Fermi level also indicates hybridization between Ni-3d electrons and Sm-4f electrons. Further differential charge density analysis shows that the negative charge density on the surface of Sm atoms in Sm-NiPO is lower than that of La and Ce, thus confirming a stronger electronic interaction between Sm and Ni atoms.

[0102] Experimental and theoretical calculations show that the order of d-band centers is NiPO > La-NiPO > Ce-NiPO > Sm-NiPO, indicating that d-band centers are related to catalytic activity. Compared with La and Ce, Sm has a smaller d-band center value, closer to the Fermi level, making it easier for reactants to desorb from the catalyst surface and improving catalytic activity. Although d-band centers are positively correlated with catalytic activity, the relationship is not linear. This invention reveals a strong linear relationship between PP band centers and catalytic activity, with the order also being NiPO > La-NiPO > Ce-NiPO > Sm-NiPO. Therefore, PP band centers can serve as a linear catalytic descriptor for the RE-NiPO system. The above analysis shows that rare-earth-doped nickel phosphide's f electrons and cruise electrons near the Fermi level, including df hybridization, enhance its electron density near the Fermi level, thereby improving the catalytic activity of HER and OER. This invention also finds that Pp band centers can serve as a linear descriptor reflecting the OER and HER catalytic activity of RE-NiPO.

[0103] Furthermore, magnetic studies show that the coercivity (Hc) of Ni2P@La-NiPO, Ni2P@Ce-NiPO, and Ni2P@Sm-NiPO is approximately 2000 Oe, while the order of saturation magnetization is Ni2P@La-NiPO < Ni2P@Ce-NiPO < Ni2P@Sm-NiPO. This phenomenon can be attributed to the magnetic characteristics of rare earth elements and their influence on band structure and density of states (DOS). Specifically, Ni2P@La-NiPO has a lower saturation magnetization, mainly due to the failure of lanthanum (La) to provide a significant magnetic contribution. Its 5d orbitals are relatively saturated, resulting in a lower density of states near the Fermi level, thus leading to weaker overall magnetism. In contrast, cerium (Ce) in Ni2P@Ce-NiPO enhances the density of states through magnetic coupling of 4f electrons, resulting in a higher saturation magnetization than Ni2P@La-NiPO. Although the magnetism of Ni2P@Ce-NiPO is not as strong as that of Ni2P@Sm-NiPO, its saturation magnetization is improved. Ni₂P@Sm-NiPO exhibits the highest saturation magnetization, attributed to the strong magnetism of samarium (Sm), the abundance of unpaired electrons in its 4f orbitals, and the significantly increased density of states near the Fermi level. This promotes spin ordering and enhanced magnetic anisotropy, thereby increasing the magnetization. Furthermore, these experimental results are consistent with theoretically calculated density of states distributions.

[0104] Meanwhile, DFT calculations were used to investigate the influence mechanism of rare earth element (La, Ce, Sm) doping on the structure and catalytic activity of Ni2P catalysts. The results showed that the adsorption energy of active species on the catalyst surface directly affects its catalytic activity. Ni2P(001) is an easily exposed hexagonal active surface and can be used as a model to study the adsorption energy of species. Therefore, this invention constructed Re-Ni2P(001) and Ni2P(001) calculation models and evaluated the changes in surface adsorption energy through DFT calculations to reveal the intrinsic mechanism of HER and OER catalytic activity. The HER process involves H adsorption (step 1), H intermediate adsorption state (step 2), and H2 dissociation (step 3), among which the adsorption of H intermediate (step 2) is the rate-determining step (RDS). Generally, the adsorption free energy (ΔG) of H species on the surface of a highly active HER catalyst is... H* The adsorption energies should be close to 0 eV to promote H2 generation. Figure 17 (de) shows the adsorption energies of H intermediates on the Ni2P and Re-Ni2P (001) active surfaces. Compared to Ni2P, the adsorption energies of H species on La-Ni2P, Ce-Ni2P, and Sm-Ni2P surfaces are reduced to 1.45 eV, 1.2 eV, and 1.83 eV, respectively. The results indicate that rare earth doping effectively reduces the ΔG of the (001) crystal plane. H*The value, thus enhancing HER activity, is consistent with experimental results. Figure 17 Yellow and blue represent the positive and negative values ​​of the electron quantity, respectively.

[0105] In summary, this invention successfully prepared nickel-based microporous material NiPO, rare-earth-doped nickel-based microporous material Re-NiPO, and carbon fiber cloth-supported composite catalyst Ni2P@NiPO-CF using a hydrothermal method. Further, through phosphating treatment, composite catalysts Ni2P@NiPO, Ni2P@Re-NiPO, and Ni2P@Re-NiPO-CF supported on nickel phosphide were prepared. The structure, morphology, valence state, specific surface area, and electrocatalytic water splitting performance of the catalysts were systematically explored, and the effects of rare-earth doping and carbon fiber cloth support on the catalytic performance were revealed in detail.

[0106] Experimental results show that NiPO possesses a hexagonal microporous structure, and Ni2P nanoparticles are generated in situ during phosphating, endowing the material with excellent catalytic activity. Magnetic tests show that the saturation magnetization (Ms) of phosphated Ni2P@NiPO is 0.3 emu / g, with low coercivity. However, after doping with rare earth elements (La, Ce, and Sm), the coercivity is significantly increased to around 2000 Oe. This change is attributed to the enhanced spin long-range ordering due to fd orbital hybridization and RKKY effects. Furthermore, optical tests show that NiPO absorbs in both the ultraviolet and red light regions, matching the solar spectrum. Phosphating treatment can reduce the band gap from 2.7 eV to 1.7 eV, extending the light absorption range to the red-visible region (~729 nm) and significantly enhancing the photocurrent, providing possibilities for photo-assisted electrocatalysis. In terms of electrocatalytic water splitting performance, Ni2P@NiPO-CF and Ni2P@Re-NiPO-CF supported on carbon fiber cloth exhibit excellent hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) catalytic activities due to the three-dimensional conductive network effect. Specifically, in 1 M KOH alkaline medium, Ni2P@Sm-NiPO-CF at 10 mA cm⁻¹... -2 At current density, the HER overpotential is only 180 mV, and the Tafel slope is 26 mV dec. -1 The OER overpotential is only 320 mV, and the Tafel slope is 33 mVdec. -1This high activity stems from the synergistic effect of the hierarchical pore structure of the nickel-based microporous material and the carbon fiber cloth, which optimizes the electron transfer path. Microporous structural defects promote electron transport, while the flower-like nanostructure expands the specific surface area, thereby improving catalytic efficiency. Theoretical calculations further reveal the sources of the magnetism and catalytic activity of the rare-earth-doped catalyst. Rare-earth-doped Ni2P@NiPO optimizes the d-band center through 4f-3d orbital coupling, particularly since the Sm-4f electron band is near the Fermi level, overlapping with the Ni-3d density of states, thus enhancing the Fermi level density of states. This not only enhances catalytic performance but also explains the mechanism of increased coercivity. Furthermore, calculations show a linear positive correlation between the p-band center of phosphorus and OER activity. Therefore, the p-band center of phosphorus in the compound can serve as an activity descriptor for predicting the catalytic performance of rare-earth and other metal-doped metal phosphides, providing a theoretical basis for the rational design of highly efficient catalysts. In summary, this study achieved a synergistic enhancement of electronic spin order and interfacial mass transfer by constructing Ni2P hard magnetic heterostructures in situ within nickel-based microporous materials and combining this with a carbon fiber cloth loading strategy. This reveals the universality of phosphorus p-band centers as descriptors of OER activity. This invention provides cross-scale theoretical guidance for the design of hard magnetic-catalytic coupling materials and the development of high-efficiency energy conversion devices.

Claims

1. A method for preparing a rare-earth-doped nickel-based micro-mesoporous material loaded with Ni₂P, characterized in that, Includes the following steps: (1) Dissolve hypophosphite, nickel salt and rare earth metal salt together in a solvent and carry out a hydrothermal reaction; wash, dry and grind the product to obtain rare earth metal doped micro-mesoporous nickel phosphite, denoted as Re-NiPO; (2) Under the protection of an inert atmosphere, Re-NiPO and phosphite are calcined together in a non-mixed manner, so that the phosphite generates phosphine gas after being heated in an inert gas, which enters the pores of Re-NiPO and undergoes a phosphating reaction with Re-NiPO, thereby forming nickel phosphide particles on the surface and in the pores of Re-NiPO, and obtaining rare earth doped nickel-based micro-mesoporous material loaded with Ni2P, denoted as Ni2P@Re-NiPO.

2. The method for preparing rare-earth-doped nickel-based micro-mesoporous materials supported on Ni₂P according to claim 1, characterized in that, In step (1), the rare earth metal salt is at least one of lanthanum salt, cerium salt or samarium salt.

3. The method for preparing rare-earth-doped nickel-based micro-mesoporous materials supported on Ni₂P according to claim 1, characterized in that, In step (1), the molar ratio of hypophosphite, nickel salt and rare earth metal salt is 1.5:1:0.2~1.5:1:0.

5.

4. The method for preparing rare-earth-doped nickel-based micro-mesoporous materials supported on Ni₂P according to claim 1, characterized in that, In step (2), the molar ratio of Re-NiPO to phosphite is 1:2 to 1:

5.

5. The method for preparing rare-earth-doped nickel-based micro-mesoporous materials supported on Ni₂P according to claim 1, characterized in that, In step (2), the phosphite is located upstream of Re-NiPO according to the direction of inert gas introduction.

6. The method for preparing rare-earth-doped nickel-based micro-mesoporous materials supported on Ni₂P according to claim 1, characterized in that, In step (2), the calcination process involves two stages of heating. In the first stage, the temperature is raised from room temperature to 120-150 ℃ and held for 60-120 min. In the second stage, the temperature is further raised to 350-380 ℃ and held for 120-240 min.

7. The method for preparing rare-earth-doped nickel-based micro-mesoporous materials supported on Ni₂P according to claim 6, characterized in that, The heating rate in the first stage is 3~5 ℃ / min; the heating rate in the second stage is 3~5 ℃ / min.

8. The method for preparing rare-earth-doped nickel-based micro-mesoporous materials supported on Ni₂P according to claim 1, characterized in that, In step (1), the hydrothermal reaction temperature is 180-200 ℃ and the time is 24-36 h.

9. The method for preparing rare-earth-doped nickel-based micro-mesoporous materials supported on Ni₂P according to claim 1, characterized in that, In step (1), before hydrothermal treatment, a carbon matrix material is added so that rare earth metal-doped nickel phosphite is loaded in situ onto the carbon matrix material during the hydrothermal process.

10. The application of a rare-earth-doped nickel-based micro-mesoporous material loaded with Ni2P obtained by the method of claim 1 in the electrocatalytic hydrogen evolution reaction of water.

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