Co2P / Fe2P heterojunction nanosheet array material and preparation method and application thereof

Abstract

The invention discloses a Co2P / Fe2P heterojunction nanosheet array material as well as a preparation method and application thereof, and belongs to the technical field of electro-catalytic materials. The preparation method provided by the invention comprises the following steps: putting pretreated foamed nickel into a precursor solution containing cobalt salt, ferric salt, urea and ammonium fluoride, and growing a CoFe-LDH nanosheet array precursor on the surface of the foamed nickel through a hydrothermal reaction; and then low-temperature phosphating treatment is carried out in an inert atmosphere, the precursor is converted into a Co2P / Fe2P heterojunction, and finally the Co2P / Fe2P heterojunction nanosheet array material growing on the foamed nickel is obtained. The material shows excellent bifunctional electrocatalytic activity and stability in alkaline electrolyte, and when the material is used for full water decomposition, the current density of 20 mA cm <-2 > can be driven only by 1.50 V low cell voltage. The method is simple in process and low in cost, and a new scheme is provided for efficient and stable preparation of the non-noble metal water decomposition catalytic electrode.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of electrocatalytic materials, and particularly relates to a Co2P / Fe2P heterojunction nanosheet array material and a preparation method and application thereof. BACKGROUND

[0002] Water electrolysis hydrogen production technology can convert intermittent renewable energy (such as solar energy and wind energy) into storable and transportable hydrogen energy, and is a key approach to achieve the "double carbon" goal. However, the water electrolysis process involves two core half-reactions: hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), both of which have high kinetic energy barriers, resulting in high overpotential for the electrolysis process, thus causing huge energy consumption. Therefore, developing efficient and stable electrocatalysts to reduce the overpotential of the two reactions is the core of realizing large-scale and economic application of water electrolysis hydrogen production.

[0003] At present, the best HER and OER catalysts are platinum (Pt) and iridium (Ir) and ruthenium (Ru) based noble metal materials, respectively. However, these noble metals are scarce in reserves and expensive in price, which greatly limits their widespread application on an industrial scale. In order to reduce the cost of catalysts, researchers have focused on transition metal-based materials with abundant reserves and low prices, such as transition metal oxides, hydroxides, sulfides, phosphides and selenides. Among them, transition metal phosphides (TMPs) have great potential in the field of HER catalysis due to their unique metal-like characteristics, good electrical conductivity and moderate hydrogen adsorption free energy.

[0004] However, single TMP catalysts still have some inherent limitations. First, for the two reactions of HER and OER, a single component is usually difficult to provide optimal active sites at the same time. Second, the OER process involves complex four-electron transfer, and its kinetics is slower, and the activity and stability of most TMPs under OER conditions are insufficient. More critically, the electronic structure of a single catalyst is relatively fixed, making it difficult to simultaneously optimize the adsorption strength of H and various oxygen-containing intermediates (such as OH, *O, and *OOH).

[0005] In recent years, constructing heterostructures has been proved to be an effective strategy to improve the intrinsic activity of catalysts. The built-in electric field formed at the heterojunction due to the difference in Fermi level can induce the directional transfer and rearrangement of charges, thus effectively regulating the electronic structure of active sites and optimizing the adsorption energy of intermediates. In addition, the heterojunction itself can often become a high-activity site. Among the many heterostructures, bimetallic phosphide heterojunctions have attracted much attention due to their adjustable composition and significant interface effect. However, the existing bimetallic phosphide heterojunction catalysts still have room for improvement in terms of preparation method, active site exposure, structural stability, and high performance (i.e. bifunctionality) that simultaneously considers HER and OER. Therefore, developing a new type of bimetallic phosphide heterojunction self-supporting electrode material that is simple to prepare, structurally stable, and can fully utilize the synergistic effect of the heterojunction to simultaneously achieve high-efficiency HER and OER in alkaline environments is of great significance for promoting the practicalization process of water electrolysis hydrogen production technology. SUMMARY

[0006] In view of the above prior art, the present application provides a Co2P / Fe2P heterojunction nanosheet array material and a preparation method and application thereof, which solves the problems of low activity, insufficient stability, and poor bifunctional catalytic performance of the prior art.

[0007] To achieve the above-mentioned purpose, the technical scheme adopted by the present application is to provide a preparation method of a Co2P / Fe2P heterojunction nanosheet array material, comprising the following steps: S1: sequentially placing a foamed nickel into dilute hydrochloric acid, acetone and anhydrous ethanol for ultrasonic cleaning for 30 min, then washing with deionized water and vacuum drying at 60℃ for 6h to obtain a pretreated foamed nickel; S2: dissolving a cobalt salt, an iron salt, urea and ammonium fluoride in water to obtain a precursor solution; S3: placing the pretreated foamed nickel in the precursor solution for hydrothermal reaction, then cooling, washing and drying to obtain a CoFe-LDH / NF; S4: performing low-temperature phosphating treatment on the CoFe-LDH / NF and a phosphorus source to obtain the Co2P / Fe2P heterojunction nanosheet array material.

[0008] Further, the molar ratio of the cobalt salt, the iron salt, urea and ammonium fluoride is 1:1:15-25:6-10.

[0009] Further, the cobalt salt is cobalt nitrate hexahydrate, and the iron salt is ferric nitrate.

[0010] Further, the temperature of the hydrothermal reaction is 110-130℃, and the reaction time is 5-7h.

[0011] Further, the low-temperature phosphating treatment is to place the CoFe-LDH / NF and the phosphorus source in two different ceramic boats upstream and downstream of a tube furnace, and react at 300-400 DEG C for 1-3 hours under inert gas protection.

[0012] The application further provides a preparation method of the Co2P / Fe2P heterojunction nanosheet array material.

[0013] The application further provides application of the Co2P / Fe2P heterojunction nanosheet array material in full water splitting.

[0014] The application has the following beneficial effects: the Co2P / Fe2P heterojunction nanosheet array is successfully constructed on a nickel foam substrate through a two-step method (hydrothermal + phosphating), and a bimetallic phosphide electrocatalyst with rich heterojunction interfaces, high activity and high stability is obtained. 1. The material has a unique structure and rich active sites: the material has a three-dimensional porous structure, and the nanosheets grow vertically or obliquely and are connected to each other, thereby providing a large specific surface area and rich mass transfer channels, and the Co2P and Fe2P nanocrystals form a close heterojunction, and such a structure is beneficial to exposing more active sites.

[0015] 2. Excellent electrocatalytic performance: in a 1 M KOH electrolyte, the Co2P / Fe2P@NF catalyst prepared in the application exhibits excellent HER and OER performance. -2 For the HER, the overpotential required to reach 10 mA cm-2 is only 79 mV, and the Tafel slope is 54.8 mV dec-1. -1 For the OER, the overpotential required to reach the same current density is only 157 mV, and the Tafel slope is 31.5 mV dec-1. -1 .The performance is significantly better than that of single Co2P, Fe2P, precursor LDH and oxide control samples.

[0016] 3. High-efficiency and stable full water splitting capacity: the Co2P / Fe2P@NF is used as a cathode and an anode to assemble a full water splitting electrolytic cell, and only a low cell voltage of 1.50 V is required to drive a current density of 20 mA cm-2. -2 The efficiency is better than that of a noble metal reference system, and the electrolytic cell also exhibits excellent long-term stability, and the performance decay is very small after continuous operation for more than 6 hours, and has potential for practical application.

[0017] 4. Simple preparation method, low cost, and easy scale-up: The preparation method adopted in this invention is simple and mild, and the raw materials used are all inexpensive and readily available metal salts and phosphorus sources, requiring no precious metals. The process is easy to control and repeat, and has good prospects for large-scale production, providing a feasible technical route for developing efficient and low-cost water splitting catalysts for hydrogen production.

[0018] In summary, the Co2P / Fe2P heterojunction nanosheet array material provided by this invention achieves high activity, high stability, and excellent bifunctional catalytic performance through ingenious heterojunction structure design, and has important application value in the field of alkaline water splitting for hydrogen production. Attached Figure Description

[0019] Figure 1 a represents the SEM image of Co2P / Fe2P@NF. Figure 1 , Figure 1 b represents the SEM image of Co2P / Fe2P@NF. Figure 2 , Figure 1 c is the EDS surface scan of Co2P / Fe2P@NF. Figure 1 The left side of d shows the TEM image of Co2P / Fe2P@NF. Figure 1 The right side of d shows the HRTEM plot of Co2P / Fe2P@NF; Figure 2 XRD patterns of Co2P / Fe2P@NF, Fe2P@NF, and Co2P@NF; Figure 3 For Co2P / Fe2P@NF, Fe2P@NF, Co2P@NF, CoFe-LDH / NF, Fe 2.67 O4 / Co3O4 / NF and NF at 5mVs -1 Linear scan voltammetry curves (HER) at scan rate; Figure 4 For Co2P / Fe2P@NF, Fe2P@NF, Co2P@NF, CoFe-LDH / NF, Fe 2.67 O4 / Co3O4 / NF and NF at 10, 20 and 80 mA cm -2 The overpotential (HER); Figure 5 For Co2P / Fe2P@NF, Fe2P@NF, Co2P@NF, CoFe-LDH / NF, Fe 2.67 Tafel curves (HER) for O4 / Co3O4 / NF and NF; Figure 6 For Co2P / Fe2P@NF, Fe2P@NF, Co2P@NF, CoFe-LDH / NF, Fe 2.67Nyquist plot of Co2P / Fe2P@NF and NF (HER); Figure 7 For Co2P / Fe2P@NF, Fe2P@NF, Co2P@NF, CoFe-LDH / NF, Fe 2.67 Nyquist plot of Co2P / Fe2P@NF and NF (OER); Figure 8 For Co2P / Fe2P@NF at 20 mA cm -2 Chronoamperometry curve (OER) for 20 hours; Figure 9 For Co2P / Fe2P@NF, Fe2P@NF, Co2P@NF, CoFe-LDH / NF, Fe 2.67 Tafel plot of Co2P / Fe2P@NF and NF (OER) at 5 mVs -1 Linear sweep voltammetry curve (OER) at scan rate; Figure 10 For Co2P / Fe2P@NF, Fe2P@NF, Co2P@NF, CoFe-LDH / NF, Fe 2.67 Overpotential (OER) of Co2P / Fe2P@NF and NF at 10, 20 and 80 mA cm -2 ; Figure 11 For Co2P / Fe2P@NF, Fe2P@NF, Co2P@NF, CoFe-LDH / NF, Fe 2.67 Tafel plot of Co2P / Fe2P@NF and NF (OER); Figure 12 For Co2P / Fe2P@NF, Fe2P@NF, Co2P@NF, CoFe-LDH / NF, Fe 2.67 Scan rate vs. current density plot of Co2P / Fe2P@NF and NF (OER); Figure 13 For Co2P / Fe2P@NF, Fe2P@NF, Co2P@NF, CoFe-LDH / NF, Fe 2.67 Nyquist plot of Co2P / Fe2P@NF and NF (OER); Figure 14 For Co2P / Fe2P@NF at 20 mA cm -2 Chronoamperometry curve (OER) for 20 hours; Figure 15 For full water splitting performance plot. DETAILED DESCRIPTION

[0020] The specific embodiments of the present application will be described in detail below with reference to the examples.

[0021] Example A preparation method of a Co2P / Fe2P heterojunction nanosheet array material, comprising the following steps: S1: foam nickel (1cm*2cm*1cm) is sequentially placed in dilute hydrochloric acid, acetone and anhydrous ethanol for ultrasonic cleaning for 30min, then washed with deionized water and dried at 60°C for 6h in a vacuum oven to obtain pretreated foam nickel; S2: 0.5mmol of cobalt nitrate hexahydrate, 0.5mmol of iron nitrate, 10mmol of urea and 4mmol of ammonium fluoride (NHF) are dissolved in 30mL of deionized water to obtain a precursor solution; S3: the pretreated foam nickel is immersed in the precursor solution, then transferred into a 50ml autoclave, reacted at 120°C for 6h, washed with deionized water after cooling to room temperature, and finally dried at 60°C in a vacuum oven for 12h to obtain CoFe-LDH / NF; S4: CoFe-LDH / NF and sodium hypophosphite are respectively placed in two different porcelain boats upstream and downstream of a tube furnace, reacted at 350°C for 2h under an argon atmosphere, and Co2P / Fe2P heterojunction nanosheet array material Co2P / Fe2P@NF is obtained.

[0022] Comparative Example 1 A preparation method of a heterojunction nanosheet array material, comprising the following steps: S1: foam nickel (1cm*2cm*1cm) is sequentially placed in dilute hydrochloric acid, acetone and anhydrous ethanol for ultrasonic cleaning for 30min, then washed with deionized water and dried at 60°C for 6h in a vacuum oven to obtain pretreated foam nickel; S2: 1mmol of cobalt nitrate hexahydrate, 10mmol of urea and 4mmol of ammonium fluoride (NHF) are dissolved in 30mL of deionized water to obtain a precursor solution; S3: the pretreated foam nickel is immersed in the precursor solution, then transferred into a 50ml autoclave, reacted at 120°C for 6h, washed with deionized water after cooling to room temperature, and finally dried at 60°C in a vacuum oven for 12h to obtain Co(OH)2 / NF; S4: Co(OH)2 / NF and sodium hypophosphite are respectively placed in two different porcelain boats upstream and downstream of a tube furnace, reacted at 350°C for 2h under an argon atmosphere, and heterojunction nanosheet array material Co2P@NF is obtained.

[0023] Comparative Example 2 A preparation method of a heterojunction nanosheet array material, comprising the following steps: S1: The nickel foam (1cm×2cm×1cm) was placed in dilute hydrochloric acid, acetone and anhydrous ethanol in sequence and ultrasonically cleaned for 30min each. Then it was washed with deionized water and vacuum dried at 60℃ for 6h to obtain pretreated nickel foam. S2: Dissolve 1 mmol ferric nitrate, 10 mmol urea and 4 mmol ammonium fluoride (NHF) in 30 mL of deionized water and stir well to obtain the precursor solution; S3: Immerse the pretreated nickel foam in the precursor solution, then transfer it to a 50ml autoclave and react at 120℃ for 6h. After cooling to room temperature, wash the product with deionized water and finally dry it in a vacuum oven at 60℃ for 12h to obtain Fe(OH)2 / NF. S4: Fe(OH)2 / NF and sodium hypophosphite were placed in two different ceramic boats upstream and downstream of a tube furnace, respectively, and reacted at 350℃ for 2 hours under an argon atmosphere to obtain the heterojunction nanosheet array material Fe2P@NF.

[0024] Comparative Example 3 A method for preparing a heterojunction nanosheet array material includes the following steps: S1: The nickel foam (1cm×2cm×1cm) was placed in dilute hydrochloric acid, acetone and anhydrous ethanol in sequence and ultrasonically cleaned for 30min each. Then it was washed with deionized water and vacuum dried at 60℃ for 6h to obtain pretreated nickel foam. S2: Dissolve 0.5 mmol cobalt nitrate hexahydrate, 0.5 mmol ferric nitrate, 10 mmol urea and 4 mmol ammonium fluoride (NHF) in 30 mL of deionized water and stir well to obtain the precursor solution; S3: Immerse the pretreated nickel foam in the precursor solution, then transfer it to a 50ml autoclave and react at 120℃ for 6h. After cooling to room temperature, wash the product with deionized water and finally dry it in a vacuum oven at 60℃ for 12h to obtain CoFe-LDH / NF. S4: CoFe-LDH / NF was placed in a tube furnace and reacted at 350℃ for 2 hours under an argon atmosphere to form the heterojunction nanosheet array material Fe. 2.67 O4 / Co3O4 / NF.

[0025] Experimental Example 1 Material characterization: The Co2P / Fe2P@NF heterojunction nanosheet array material prepared in the examples was morphologically evaluated using scanning electron microscopy. The results are as follows: Figure 1 a and Figure 1As shown in b, the obtained Co2P / Fe2P@NF exhibits a large-scale layered nanosheet structure with a thickness of approximately 60 to 100 nanometers and a length of approximately 0.5 to 1.5 micrometers. These nanosheets are interconnected and arranged obliquely or perpendicularly to the NF substrate, forming a large number of obvious porous structures.

[0026] The composition of the Co2P / Fe2P@NF sample was determined by EDS surface scanning, and the results are as follows: Figure 1 As shown in c, Ni, Co, Fe, O and P elements are uniformly present in the Co2P / Fe2P@NF nanoplate.

[0027] To investigate the microstructure of the Co2P / Fe2P@NF samples, transmission electron microscopy was also used, and the results are as follows: Figure 1 As shown in Figure d, the Co2P and Fe2P crystalline nanoparticles tightly embedded in the nanosheets are in close contact with each other, forming a heterogeneous interface. The clear lattice fringes with a spacing of 0.2195 nm closely match the (1 1 2) crystal plane of Co2P. Similarly, high-resolution lattice fringes with spacings of 0.2255 nm, 0.1960 nm, and 0.1670 nm closely match the (1 1 1), (0 1 3), and (2 1 1) crystal planes of Fe2P, respectively, further confirming the heterogeneous interface structure between Co2P and Fe2P.

[0028] Experimental Example 2 XRD testing: The samples prepared in Examples 1 and 2 were analyzed using an X-ray diffractometer. The results are as follows: Figure 2As shown, Co2P / Fe2P@NF exhibits characteristic peaks at 2θ values ​​of 40.72°, 40.98°, 43.3°, 48.76°, and 52.07°, which can be attributed to the (1 1 2), (2 1 0), (2 1 1), (0 1 3), and (0 2 0) crystal planes of the orthorhombic Co2P (PDF#04-001-9150). Meanwhile, other characteristic peaks at 40.28°, 42.19°, 47.31°, 54.10°, and 54.62° match well with the (1 1 1), (2 0 1), (2 1 0), (3 0 0), and (2 1 1) crystal planes of the tetragonal Fe2P (PDF#00-027-1171). Furthermore, slight oxidation was observed in both Co2P@NF and Fe2P@NF. In the XRD pattern of Co2P@NF, the peak at 38.61° corresponds to the (1 0 2) crystal plane of Co2O3. Similarly, the peaks at 62.26° and 63.69° of Fe2P@NF are attributed to the (2 1 4) and (3 0 0) crystal planes of Fe2O3, respectively. Three strong peaks appear at 2θ values ​​of 44.5°, 51.8°, and 76.4°, which are attributed to the nickel foam substrate (PDF#00-04-0850).

[0029] Experimental Example 2 Electrochemical performance testing: Electrochemical performance was tested using a three-electrode system on a CHI 660E electrochemical workstation. The electrolyte was 1 M KOH, the reference electrode was Hg / HgO, and the counter electrode was a graphite rod. Test samples included Co2P / Fe2P@NF prepared in the examples, the precursor CoFe-LDH / NF in the examples, Co2P@NF from Comparative Example 1, Fe2P@NF from Comparative Example 2, and Fe from Comparative Example 3. 2.67 O4 / Co3O4 / NF, nickel foam NF.

[0030] Its HER performance is as follows Figures 3-8 As shown, Co2P / Fe2P@NF exhibits the best HER activity at 10 mA cm⁻¹. -2 The overpotential at current density is only 79 mV, which is much lower than that of Co2P@NF, Fe2P@NF, CoFe-LDH / NF, CoFe oxide / NF and pure nickel foam. Figures 3-4 Its Tafel slope is the lowest (54.8 mV dec⁻¹), indicating that it has faster reaction kinetics. Figure 5 Further exploration of the electrochemical active surface area (ECSA) was conducted to assess its intrinsic activity. The double-layer capacitance (CDL), extracted by plotting the capacitive current density of the non-Radial region as a function of scan rate, was used to obtain the ECSA. Figure 6As shown, the calculated double-layer capacitance (CDL) of Co2P / Fe2P is 17.4 MF cm², which is significantly higher than that of CoFe-LDH / NF (1.93 MF cm²). 2 This indicates a significant increase in the active surface area of ​​LDHs before and after the phosphating process, attributed to the formation of phosphides during phosphating. Notably, the ECSA of Co2P / Fe2P@NF increased 17-fold compared to CoFe-LDH / NF. However, there was no significant difference in ECSA from the original LDHs to Fe2.67O4 / Co3O4, but the overpotential showed a significant change. This comparison ultimately suggests that ECSA alone cannot explain the enhanced catalytic performance, consistent with the significantly reduced Tafel slope discussed earlier. It is worth mentioning that the phosphating process not only leads to an increase in the number of active sites but also significantly increases the total active surface area. Electrochemical impedance spectroscopy (EIS) measurements were used to investigate the charge transfer capacity at the electrode / electrolyte interface. Figure 7 As shown, Co2P / Fe2P exhibits the smallest charge transfer resistance (RCT), indicating that Co2P / Fe2P benefits the electrocatalytic kinetics of HER by increasing the charge transfer rate. Furthermore, it demonstrates good current density retention during long-term operation in alkaline solution. Figure 8 ).

[0031] Its OER, such as Figures 9-14 As shown, Co2P / Fe2P@NF also exhibits the best OER activity at 10 mA cm⁻¹. -2 The overpotential at current density is 157 mV ( Figures 9-10 The Tafel slope is 31.5 mV dec. -1 All of them are superior to other comparative samples ( Figure 11 Its double-layer capacitance is the largest, indicating the largest electrochemical active area. Stability tests also show excellent performance retention. Furthermore, the maximum CDL value of Co₂P / Fe₂P is 31.7 MF cm⁻¹. -2 The minimum RCT is 0.509 Ω, determined by measurements from EIS and ECSA, respectively. Figure 12 and Figure 13 As shown. This indicates enhanced charge transfer kinetics and a higher density of active sites on the surface. Long-term stability tests show that the heterostructure Co2P / Fe2P has excellent stability, with negligible decrease in current density over a long period of time. Figure 14An increase in the anodic peak area related to the oxidation of Co(II) / Fe(II) was observed near 1.4 V after phosphating, indicating that the phosphating process makes more active sites accessible. XRD analysis was performed after long-term stability tests at high current densities during OER and HER to compare the Co2P / Fe2P@NF and Fe2P / Fe2P@NF before and after the tests. 2.67 O4 / Co3O4 / NF. Studies have shown that after long-term operation, the characteristic peaks indicating phosphating did not significantly decrease or disappear, nor did any new peaks indicating oxidation appear. This further confirms the excellent long-term stability of the material.

[0032] Experiment Example 4 Full water splitting performance test: Two identical Co2P / Fe2P@NF electrodes were used as the cathode and anode, respectively, to assemble a dual-electrode electrolyzer for full water splitting testing. The results are as follows: Figure 15 As shown. This electrolytic cell requires only a cell voltage of 1.50V to achieve 20mA / cm. -2 The current density is superior to that of the noble metal reference system (Pt / C / / RuO). 2 N / NF). At 20mA cm -2 After more than 6 hours of chronopotential testing at current density, the voltage remained almost constant, demonstrating excellent long-term operational stability.

[0033] Although specific embodiments of the present invention have been described in detail with reference to examples, they should not be construed as limiting the scope of protection of this patent. Various modifications and variations that can be made by those skilled in the art without inventive effort within the scope described in the claims are still within the scope of protection of this patent.

Claims

1. A method for preparing a Co2P / Fe2P heterojunction nanosheet array material, characterized in that, Includes the following steps: S1: The nickel foam was ultrasonically cleaned in dilute hydrochloric acid, acetone and anhydrous ethanol for 30 min each, then washed with deionized water and vacuum dried at 60°C for 6 h to obtain pretreated nickel foam. S2: Dissolve cobalt salt, iron salt, urea and ammonium fluoride in water and stir until homogeneous to obtain the precursor solution; S3: Pretreated nickel foam is placed in a precursor solution for hydrothermal reaction, and then cooled, washed and dried to obtain CoFe-LDH / NF; S4: CoFe-LDH / NF and phosphorus source are subjected to low-temperature phosphating treatment to obtain Co2P / Fe2P heterojunction nanosheet array material.

2. The method for preparing the Co2P / Fe2P heterojunction nanosheet array material according to claim 1, characterized in that: The molar ratio of the cobalt salt, iron salt, urea, and ammonium fluoride is 1:1:15~25:6~10.

3. The method for preparing the Co2P / Fe2P heterojunction nanosheet array material according to claim 1 or 2, characterized in that: The cobalt salt is cobalt nitrate hexahydrate, and the iron salt is ferric nitrate.

4. The method for preparing the Co2P / Fe2P heterojunction nanosheet array material according to claim 1, characterized in that: The hydrothermal reaction temperature is 110~130℃, and the reaction time is 5~7h.

5. The method for preparing the Co2P / Fe2P heterojunction nanosheet array material according to claim 1, characterized in that: The phosphorus source is sodium hypophosphite.

6. The method for preparing the Co2P / Fe2P heterojunction nanosheet array material according to claim 1, characterized in that: The low-temperature phosphating treatment involves placing CoFe-LDH / NF and a phosphorus source in two different ceramic boats upstream and downstream of a tube furnace, and reacting at 300-400°C for 1-3 hours under inert gas protection.

7. The Co2P / Fe2P heterojunction nanosheet array material prepared by the method of any one of claims 1 to 6.

8. The application of the Co2P / Fe2P heterojunction nanosheet array material according to claim 7 in total water splitting.

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