Preparation of lanthanum-doped nickel phosphide and nickel selenide heterojunction catalyst and application of lanthanum-doped nickel phosphide and nickel selenide heterojunction catalyst in urea electrocatalytic oxidation

Abstract

The invention discloses preparation of a lanthanum-doped nickel phosphide and nickel selenide heterojunction catalyst and application of the lanthanum-doped nickel phosphide and nickel selenide heterojunction catalyst in urea electrocatalytic oxidation. A hydrothermal-carbon coating-low-temperature selenium phosphorization method is adopted, foamed nickel is used as a nickel source and a conductive substrate, and the lanthanum-doped nickel phosphide and nickel selenide heterojunction electrocatalyst growing on the foamed nickel in situ is prepared. The catalyst shows a porous nanosheet shape, and the structure is beneficial to infiltration of electrolyte and exposure of active sites, and is beneficial to improvement of the overall performance and enhancement of the overall stability of the catalyst. Through doping of lanthanum and construction of a heterostructure, compared with commercial RuO2 / NF, the lanthanum-doped nickel phosphide and nickel selenide heterojunction catalyst prepared by the preparation method disclosed by the invention shows higher catalytic performance on a urea oxidation reaction.

Description

Technical Field

[0001] The present invention belongs to the field of electrocatalysis for urea-assisted water splitting, and specifically relates to the preparation of a lanthanum-doped nickel phosphide nickel selenide heterojunction and its application in urea electrocatalytic oxidation. Background Art

[0002] Facing the dual challenges of surging global energy demand and ecological protection, the development of a new renewable energy system has become an urgent need. As an energy carrier with zero carbon emissions, hydrogen energy is regarded as an ideal alternative to fossil fuels due to its high energy density and environmentally friendly characteristics. Among various hydrogen production technologies, electrochemical water splitting has attracted much attention due to its clean characteristics, and its core involves the coupling process of the hydrogen evolution reaction (HER) at the cathode and the oxygen evolution reaction (OER) at the anode. However, there are significant bottlenecks in the OER process - this four-electron transfer reaction (4OH⁻→2H2O+O2+4e⁻) requires a thermodynamic potential barrier as high as 1.23 V, severely restricting the overall hydrogen production efficiency. Constructing an organic matter-assisted water electrolysis system by introducing easily oxidizable small molecules is an effective strategy for efficient energy hydrogen production, and among them, the urea oxidation reaction (UOR) exhibits unique advantages. It is worth noting that the problem of urea pollution in industrial wastewater and domestic sewage is becoming increasingly severe, and the UOR technology can simultaneously achieve hydrogen production and wastewater purification, forming a closed-loop system for environmental-energy collaborative governance.

[0003] Compared with the theoretical decomposition voltage of 1.23 V for traditional water splitting, the urea-assisted hydrogen production system only requires 0.37 V to drive, with an energy-saving efficiency increase of nearly 70%. However, due to the inherent complexity of its six-electron transfer process and the lack of efficient and long-term stable catalysts, the practical application of UOR is limited. Although noble metal catalysts (such as IrO2, RuO2) exhibit good UOR performance, their high cost and sensitivity to CO poisoning severely limit their large-scale application. Therefore, the development of efficient, stable and low-cost UOR catalysts has become the key to breaking through the technical bottleneck. Transition metal-based heterostructures have adjustable electronic structures, which can effectively improve the activity of UOR. For example, the NiSe2 / FeSe2 heterojunction catalyst designed by the Yang team forms a built-in electric field at the interface due to the energy level difference, which is beneficial to improving the conductivity of the catalyst and has excellent electrocatalytic activity for both UOR and OER. In addition, element doping has also been proven to be effective in regulating the local coordination environment, inducing lattice strain and enhancing the ability of charge transfer. Summary of the Invention

[0004] The objective of the present invention is to provide a preparation of lanthanum-doped nickel phosphide nickel selenide heterojunction and its application in electrocatalytic oxidation of urea. The present invention adopts a hydrothermal-carbon coating-low-temperature selenium phosphidation method, using nickel foam as both the nickel source and the conductive substrate to prepare a lanthanum-doped nickel phosphide nickel selenide heterojunction electrocatalyst grown in situ on nickel foam. This catalyst exhibits a porous nanosheet structure, which helps the infiltration of the electrolyte and the exposure of active sites, facilitating the improvement of its overall performance and enhancing the overall stability of the catalyst. The doping of lanthanum and the construction of the heterostructure enable the lanthanum-doped nickel phosphide nickel selenide heterojunction catalyst prepared in the present invention to exhibit higher catalytic performance for the urea oxidation reaction compared with commercial RuO2 / NF. A preparation method of a lanthanum-doped nickel phosphide nickel selenide heterojunction of the present invention comprises the following steps: Step 1: Weigh a certain amount of urea, ammonium fluoride, and lanthanum salt into a beaker, add 30 mL of deionized water to dissolve, and denote it as solution A; Step 2: Transfer the solution A obtained in Step 1 to a Teflon-lined autoclave with pre-treated nickel foam, and maintain it at 100 °C to 120 °C for 4 to 8 hours; after the reaction ends, naturally cool it to room temperature, wash it with deionized water, and dry it in an oven to obtain a precursor, denoted as precursor A; Step 3: Immerse the precursor A obtained in Step 2 in a 50 mL glucose solution for 8 to 10 hours, and denote it as precursor B; Step 4: Transfer precursor B to the downstream of a tubular furnace, mix sodium hypophosphite and selenium powder, place them upstream, and perform annealing treatment in an N2 atmosphere to finally obtain a rare earth La-doped nickel phosphide nickel selenide heterojunction catalyst La-Ni2P / NiSe@C / NF.

[0005] In Step 1, the lanthanum salt is La(NO3)3·6H2O, and its molar amount is 0.9 to 3.6 mmol, and its optimal amount is 1.8 mmol.

[0006] In Step 1, the molar amount of the urea is 7.5 mmol, and the molar amount of the ammonium fluoride is 4 mmol.

[0007] In Step 2, the pre-treated nickel foam is obtained by the following method: Cut a piece of nickel foam electrode, and ultrasonically clean it with dilute acid solution, acetone, and deionized water, and dry it in an oven for standby. The glucose solution concentration in Step 3 is 0.12 mol / L.

[0008] In Step 4, the mass of the sodium hypophosphite is 0.8 g, and the mass of the selenium powder is 0.2 g.

[0009]

[0010] ​The application of a lanthanum-doped nickel phosphide-nickel selenide heterojunction of the present invention is to use the lanthanum-doped nickel phosphide-nickel selenide heterojunction as a catalyst to achieve the electrocatalytic oxidation reaction of urea under alkaline conditions.

[0011] Specifically, a standard three-electrode system is used. The in-situ grown La-Ni2P / NiSe@C / NF (1.0 cm×1.0 cm) is directly used as the working electrode, a platinum sheet electrode is used as the counter electrode, and a Hg / HgO electrode is used as the reference electrode. The urea oxidation performance of the La-Ni2P / NiSe@C / NF catalyst is tested in an alkaline electrolyte, and La-Ni2P / NiSe@C / NF is used as the anode electrocatalyst, and commercial Pt / C loaded on nickel foam is used as the cathode electrocatalyst in a urea-assisted overall water splitting device. Linear sweep voltammetry tests are carried out at a scanning rate of 5 mV / s in the potential range of 0.2 V - 1.0 V (relative to the Hg / HgO electrode) and compared with commercial RuO2 to explore the changes in its electrocatalytic performance; and stability tests are carried out for 30 h at a constant current density of 50 mA cm -2 -2.

[0012] The alkaline electrolyte is a 1 mol / L KOH solution, and the molar ratio of KOH to CO(NH2)2 is 1:0.33.

[0013] The beneficial effects of the present invention are reflected in: The lanthanum-doped nickel phosphide-nickel selenide urea oxidation catalyst in-situ grown on nickel foam of the present invention adopts a hydrothermal-carbon coating-low temperature phosphidation method. Nickel foam is used as both a nickel source and a conductive substrate, no additional nickel salt is added, and a lanthanum salt is added for heteroatom doping to optimize the electronic structure, thus showing excellent catalytic performance. There is a strong electronic interaction at the heterogeneous interface formed by nickel phosphide and nickel selenide, which is beneficial to adjusting the electron distribution of the catalyst and improving the catalytic activity. The catalyst of the present invention shows excellent catalytic performance in an actual electrochemical water splitting device. Brief Description of the Drawings

[0014] The technical solution of the present invention will be further described below in conjunction with the drawings and embodiments. It should be noted that these drawings are not limited to the scope of the present invention and are only an explanation of the technical solution of the present invention.

[0015] Figure 1 X-ray diffraction image (XRD) of the nickel phosphide catalyst prepared for Example 1.

[0016] Figure 2Linear sweep voltammograms of the nickel phosphide catalyst prepared for Example 1 and commercial RuO2 / NF supported on nickel foam in a 1 mol / L KOH + 0.33 mol / L CO(NH2)2 mixed solution.

[0017] Figure 3 Tafel slope plot of the nickel phosphide catalyst prepared for Example 1.

[0018] Figure 4 X-ray diffraction image (XRD) of the nickel phosphide nickel selenide heterojunction catalyst prepared for Example 2.

[0019] Figure 5 Linear sweep voltammograms of the nickel phosphide nickel selenide heterojunction catalyst prepared for Example 2 and commercial RuO2 / NF supported on nickel foam in a 1 mol / L KOH + 0.33 mol / L CO(NH2)2 mixed solution.

[0020] Figure 6 Tafel slope plot of the nickel phosphide nickel selenide heterojunction catalyst prepared for Example 2.

[0021] Figure 7 X-ray diffraction image (XRD) of the lanthanum-doped nickel phosphide nickel selenide heterojunction catalyst prepared for Example 3.

[0022] Figure 8 Scanning electron microscope image (SEM) of the lanthanum-doped nickel phosphide nickel selenide heterojunction catalyst prepared for Example 3.

[0023] Figure 9 X-ray photoelectron spectroscopy (XPS) of the lanthanum-doped nickel phosphide nickel selenide heterojunction catalyst prepared for Example 3.

[0024] Figure 10 Linear sweep voltammograms of the lanthanum-doped nickel phosphide nickel selenide heterojunction catalyst prepared for Example 3 and commercial RuO2 / NF supported on nickel foam in a 1 mol / L KOH + 0.33 mol / L CO(NH2)2 mixed solution.

[0025] Figure 11 Tafel slope plot of the lanthanum-doped nickel phosphide nickel selenide heterojunction catalyst prepared for Example 3.

[0026] Figure 12 Chronoamperometry curve of the doped nickel phosphide nickel selenide heterojunction catalyst prepared for Example 3 operating at a constant current density of 50 mA cm -2 in a 1 mol / L KOH + 0.33 mol / L CO(NH2)2 mixed solution.

[0027] Figure 13 The linear sweep voltammograms of the La-doped nickel phosphide-nickel selenide heterojunction catalyst prepared in Example 3 and commercial Pt / C / NF supported on nickel foam as the anode and cathode, respectively, in a 1 mol / L KOH + 0.33 mol / L CO(NH2)2 mixed solution to form a urea-assisted overall water splitting electrolyzer.

[0028] Figure 14 The chronopotentiometry curve of the urea-assisted overall water splitting electrolyzer composed of the La-doped nickel phosphide-nickel selenide heterojunction catalyst prepared in Example 3 and commercial Pt / C / NF supported on nickel foam as the anode and cathode, respectively, operating at a constant current density of 50 mA cm -2 in a 1 mol / L KOH + 0.33 mol / L CO(NH2)2 mixed solution.

[0029] Figure 15 The linear sweep voltammogram of the La-doped nickel phosphide-nickel selenide heterojunction catalyst prepared in Example 4 and commercial RuO2 / NF supported on nickel foam in a 1 mol / L KOH + 0.33 mol / L CO(NH2)2 mixed solution.

[0030] Figure 16 The Tafel slope diagram of the La-doped nickel phosphide-nickel selenide heterojunction catalyst prepared in Example 4.

[0031] Figure 17 The linear sweep voltammogram of the La-doped nickel phosphide-nickel selenide heterojunction catalyst prepared in Example 5 and commercial RuO2 / NF supported on nickel foam in a 1 mol / L KOH + 0.33 mol / L CO(NH2)2 mixed solution.

[0032] Figure 18 The Tafel slope diagram of the La-doped nickel phosphide-nickel selenide heterojunction catalyst prepared in Example 5. Detailed implementation manners

[0033] The technical solutions of the present invention will be further described below in conjunction with specific embodiments. It should be noted that the following specific descriptions of the embodiments are only used to illustrate the synthesis, characterization, and performance of the catalyst, and should not be construed as a limitation of the present invention. Those embodiments that are not directly mentioned herein may still be obtained by combining these technical solutions. Example 1

[0034] This example prepares the Ni2P@C / NF catalyst, including the following steps: 1. Ultrasonically clean a piece of NF (2.0 cm × 3.5 cm) in 3 mol / L dilute hydrochloric acid solution, acetone, and deionized water for 15 minutes each.

[0035] 2. Dissolve 7.5 mmol of urea and 4 mmol of ammonium fluoride in 30 mL of deionized water, denoted as solution A.

[0036] 3. Transfer solution A to a 100 mL Teflon-lined autoclave containing a piece of pretreated NF, and maintain it at 120 °C for 6 h to obtain precursor A.

[0037] 4. After vacuum drying precursor A at 60 °C for 12 h, transfer it to a 0.12 mol / L glucose solution and soak for 10 h to obtain precursor B.

[0038] 5. Place precursor B downstream of a tube furnace, and place a magnetic boat containing 0.8 g of sodium hypophosphite upstream of the tube furnace. Anneal at 320 °C under a N2 atmosphere to finally obtain the Ni2P@C / NF electrocatalyst.

[0039] Figure 1 XRD pattern of the Ni2P@C / NF catalyst prepared in Example 1. It can be seen from the figure that the XRD diffraction peaks of the sample correspond to Ni2P (PDF#03 - 6052), indicating the successful synthesis of Ni2P@C / NF.

[0040] Figure 2 Linear sweep voltammogram of Ni2P@C / NF electrocatalyst prepared in Example 1 and commercial RuO2 supported on nickel foam (commercial RuO2 / NF) in a mixed solution of 1 mol / L KOH + 0.33 mol / L CO(NH2)2. It can be seen that compared with commercial RuO2 / NF, the Ni2P@C / NF electrocatalyst prepared in Example 1 has a lower onset potential. Driving a large current density of 100 mA cm -2 only requires a voltage of 1.375 V, 66 mV lower than that of commercial RuO2 / NF, indicating that the Ni2P@C / NF electrocatalyst prepared in Example 1 has better urea oxidation performance.

[0041] Figure 3 Tafel curve of the Ni2P@C / NF electrocatalyst prepared in Example 1. It can be seen that the Ni2P@C / NF catalyst has a small Tafel slope (23.12 mV dec -1 ), indicating its fast reaction kinetics. Example 2

[0042] This example prepares a Ni2P / NiSe@C / NF catalyst, including the following steps: 1. Ultrasonically clean a piece of NF (2.0 cm × 3.5 cm) in 3 mol / L dilute hydrochloric acid solution, acetone, and deionized water for 15 minutes each.

[0043] 2. Dissolve 7.5 mmol of urea and 4 mmol of ammonium fluoride in 30 mL of deionized water, denoted as solution A.

[0044] 3. Transfer solution A to a 100 mL Teflon-lined autoclave containing a piece of pretreated NF, and maintain it at 120 °C for 6 h to obtain precursor A.

[0045] 4. After vacuum drying precursor A at 60 °C for 12 h, transfer it to a 0.12 mol / L glucose solution and soak for 10 h to obtain precursor B.

[0046] 5. Place precursor B downstream of a tubular furnace, and place a magnetic boat containing 0.8 g of sodium hypophosphite and 0.2 g of selenium powder upstream of the tubular furnace. Anneal at 320 °C under a N2 atmosphere to finally obtain the Ni2P / NiSe@C / NF electrocatalyst.

[0047] Figure 4 XRD pattern of the Ni2P / NiSe@C / NF catalyst prepared in Example 2. It can be seen from the figure that the XRD diffraction peaks of the sample correspond to Ni2P (PDF#03-6052) and NiSe (PDF#02-0892), indicating the successful synthesis of Ni2P / NiSe@C / NF.

[0048] Figure 5 Linear sweep voltammogram of Ni2P / NiSe@C / NF electrocatalyst prepared in Example 1 and commercial RuO2 supported on nickel foam (commercial RuO2 / NF) in a 1 mol / L KOH + 0.33 mol / L CO(NH2)2 mixed solution. It can be seen that compared with commercial RuO2 / NF, the Ni2P / NiSe@C / NF electrocatalyst prepared in Example 1 has a lower initial potential. Driving a large current density of 100 mA cm -2 only requires a voltage of 1.36 V, 81 mV lower than that of commercial RuO2 / NF, indicating that the Ni2P / NiSe@C / NF electrocatalyst prepared in Example 2 has better urea oxidation performance.

[0049] Figure 6 Tafel curve of the Ni2P / NiSe@C / NF electrocatalyst prepared in Example 2. It can be seen that the Ni2P / NiSe@C / NF catalyst has a small Tafel slope (22.63 mV dec -1 ), indicating its fast reaction kinetics. Example 3

[0050] In this example, the La-Ni2P / NiSe@C / NF catalyst was prepared through the following steps: 1. Ultrasonically clean a piece of NF (2.0 cm × 3.5 cm) in 3 mol / L dilute hydrochloric acid solution, acetone, and deionized water for 15 minutes each.

[0051] 2. Dissolve 7.5 mmol of urea, 4 mmol of ammonium fluoride, and 1.8 mmol of La(NO3)3·6H2O in 30 mL of deionized water, denoted as solution A.

[0052] 3. Transfer solution A to a 100 mL Teflon-lined autoclave containing a piece of pretreated NF, and keep it at 120 °C for 6 h to obtain precursor A.

[0053] 4. After vacuum drying the precursor A at 60 °C for 12 h, transfer it to a 0.12 mol / L glucose solution and soak for 10 h to obtain precursor B.

[0054] 5. Place precursor B downstream of a tube furnace, and place a magnetic boat containing 0.8 g of sodium hypophosphite and 0.2 g of selenium powder upstream of the tube furnace. Anneal at 320 °C under a N2 atmosphere to finally obtain the La-Ni2P / NiSe@C / NF electrocatalyst.

[0055] Figure 7 Figure 18 shows the XRD pattern of the La-Ni2P / NiSe@C / NF catalyst prepared in Example 3. It can be seen from the figure that the XRD diffraction peaks of the sample correspond to Ni2P (PDF#03-6052) and NiSe (PDF#02-0892), and no characteristic peaks related to La are shown, indicating the successful synthesis of La-Ni2P / NiSe@C / NF.

[0056] Figure 8 Figure 22 shows the SEM image of the La-Ni2P / NiSe@C / NF electrocatalyst prepared in Example 3. It can be seen that the prepared catalyst exhibits a porous nanosheet structure.

[0057] Figure 9 Figure 26 shows the XPS spectrum of the La-Ni2P / NiSe@C / NF electrocatalyst prepared in Example 3. It can be seen from the figure that La element exists in the catalyst. Combining with the XRD pattern, it indicates that we have successfully prepared a La-doped nickel phosphide-nickel selenide catalyst.

[0058] Figure 10Linear sweep voltammograms of the La-Ni2P / NiSe@C / NF electrocatalyst prepared in Example 3 and commercial RuO2 / NF in a mixed solution of 1 mol / L KOH + 0.33 mol / L CO(NH2)2. It can be seen that compared with commercial RuO2 / NF, the La-Ni2P / NiSe@C / NF electrocatalyst prepared in Example 3 has a higher current density at the same potential. To drive a large current density of 100 mA cm -2 , a voltage of only 1.346 V is required, which is 95 mV lower than that of commercial RuO2 / NF, indicating that the La-Ni2P / NiSe@C / NF electrocatalyst prepared in Example 3 has better electrocatalytic performance in urea oxidation. Figure 11 Tafel curve of the La-Ni2P / NiSe@C / NF electrocatalyst prepared in Example 3. It can be seen that the La-Ni2P / NiSe@C / NF catalyst has a small Tafel slope (18.3 mV dec - ), indicating its fast reaction kinetics.

[0059] Figure 12 Chronoamperometry curve of the La-Ni2P / NiSe@C / NF electrocatalyst prepared in Example 3 in a mixed solution of 1 mol / L KOH + 0.33 mol / L CO(NH2)2. It can be seen that the La-Ni2P / NiSe@C / NF electrocatalyst prepared in Example 3 can operate stably for more than 50 hours at a constant current density of 50 mA cm -2 . Its voltage does not increase significantly, indicating its high stability during the electrocatalytic oxidation process.

[0060] Figure 13 Linear sweep voltammograms of an electrolyzer for urea-assisted overall water splitting with the La-Ni2P / NiSe@C / NF electrocatalyst prepared in Example 3 as the anode and commercial Pt / C / NF as the cathode in a mixed solution of 1 mol / L KOH + 0.33 mol / L CO(NH2)2. The voltage of the electrolyzer composed of the La-Ni2P / NiSe@C / NF electrocatalyst prepared in Example 3 and commercial Pt / C / NF is only 1.39 V at 20 mA cm -2 , which is 156 mV lower than that of the electrolyzer composed of commercial RuO2 / NF and commercial Pt / C / NF, indicating that the La-Ni2P / NiSe@C / NF electrocatalyst prepared in Example 3 can be effectively used for energy-saving hydrogen production in a urea-assisted electrolyzed water system.

[0061] Figure 14The chronopotentiometry curves of the urea-assisted overall water splitting electrolyzer with the La-Ni2P / NiSe@C / NF electrocatalyst prepared in Example 3 and commercial Pt / C / NF used as the anode and cathode respectively can be seen. It can stably operate for more than 30 hours at a constant current density of 50 mA cm -2 . The voltage does not increase significantly, indicating its excellent stability in the urea-assisted overall water splitting electrolyzer. Example 4

[0062] The La-Ni2P / NiSe@C / NF electrocatalyst was prepared according to the method described in Example 3. Keeping other conditions unchanged, only the molar amount of La(NO3)3·6H2O was changed to 0.9 mmol.

[0063] Figure 15 The linear sweep voltammogram of the La-Ni2P / NiSe@C / NF electrocatalyst prepared in Example 4 and commercial RuO2 / NF in a 1 mol / L KOH + 0.33 mol / L CO(NH2)2 mixed solution. It can be seen from the figure that compared with commercial RuO2 / NF, the La-Ni2P / NiSe@C / NF electrocatalyst has a lower initial potential. Driving a large current density of 100 mA cm -2 only requires a voltage of 1.362 V, which is 79 mV lower than that of commercial RuO2 / NF, indicating that the La-Ni2P / NiSe@C / NF electrocatalyst prepared in Example 4 has better urea oxidation performance.

[0064] Figure 16 The Tafel curve of the La-Ni2P / NiSe@C / NF electrocatalyst prepared in Example 4 can be seen. The La-Ni2P / NiSe@C / NF catalyst has a smaller Tafel slope (28.3 mV dec -1 ), indicating its faster reaction kinetics. Example 5

[0065] The La-Ni2P / NiSe@C / NF electrocatalyst was prepared according to the method described in Example 3. Keeping other conditions unchanged, only the molar amount of La(NO3)3·6H2O was changed to 3.6 mmol.

[0066] Figure 17Linear sweep voltammograms of the La-Ni2P / NiSe@C / NF electrocatalyst prepared in Example 5 and commercial RuO2 / NF in a mixed solution of 1 mol / L KOH + 0.33 mol / L CO(NH2)2. It can be seen from the figure that compared with commercial RuO2 / NF, the La-Ni2P / NiSe@C / NF electrocatalyst has a lower initial potential. To drive a large current density of 100 mA cm -2 only requires a voltage of 1.368 V, which is 73 mV lower than that of commercial RuO2 / NF, indicating that the La-Ni2P / NiSe@C / NF electrocatalyst prepared in Example 5 has better urea oxidation performance.

[0067] Figure 18 Tafel curve of the La-Ni2P / NiSe@C / NF electrocatalyst prepared in Example 5. It can be seen that the La-Ni2P / NiSe@C / NF catalyst has a small Tafel slope (25.1 mV dec -1 ), indicating its fast reaction kinetics.

[0068] Analyzing the above examples, through the results of Examples 1 and 2, 3, 4, 5, we can clearly see that doping lanthanum salts and constructing heterostructures can effectively enhance the catalytic performance of the urea oxidation reaction and improve its kinetic rate. Through the results of Examples 3 and 4, 5, we found that the doping amount of lanthanum salts has an impact on the urea electrooxidation performance of the La-Ni2P / NiSe@C / NF electrocatalyst. Doping 1.8 mmol La(NO3)3·6H2O is the most preferred, and Example 3 has the best catalytic performance. The voltage required to drive a large current density of 100 mA cm -2 is the lowest, and its Tafel slope is also the smallest.

Claims

1. Preparation method of lanthanum-doped nickel phosphide / nickel selenide heterojunction catalyst, comprising the following steps: Step 1: Weigh urea, ammonium fluoride, and lanthanum salt into a beaker, add deionized water to dissolve, and denote it as solution A; Step 2: Transfer the solution A obtained in Step 1 into a Teflon-lined autoclave with pretreated nickel foam, and maintain it at 100 °C to 160 °C for 4 to 8 hours; after the reaction, naturally cool to room temperature, wash with deionized water, and dry in an oven to obtain a precursor, denoted as precursor A; Step 3: Immerse the precursor A obtained in Step 2 in a glucose solution for 8 to 10 hours, and denote it as precursor B; Step 4: Transfer precursor B to the downstream of a tubular furnace, mix sodium hypophosphite and selenium powder, place them upstream, and perform annealing treatment in an N2 atmosphere to finally obtain a lanthanum-doped nickel phosphide / nickel selenide heterojunction catalyst La-Ni2P / NiSe@C / NF.

2. The preparation method according to claim 1, wherein: In Step 1, the lanthanum salt is La(NO3)3·6H2O, and its molar amount is 0.9 to 3.6 mmol.

3. The preparation method according to claim 1, wherein: In Step 1, the molar amount of the urea is 7.5 mmol, and the molar amount of ammonium fluoride is 4 mmol.

4. The preparation method according to claim 1, wherein: In Step 2, the pretreated nickel foam is obtained by the following method: Cut a piece of nickel foam electrode, and ultrasonically clean it with dilute hydrochloric acid solution, acetone, and deionized water, and dry it in an oven for standby.

5. The preparation method according to claim 1, wherein: In Step 3, the concentration of the glucose solution is 0.12 mol / L.

6. The preparation method according to claim 1, wherein: In Step 4, the mass of sodium hypophosphite is 0.8 g, and the mass of selenium powder is 0.2 g.

7. Application of the lanthanum-doped nickel phosphide / nickel selenide heterojunction catalyst prepared by the preparation method according to any one of claims 1-6, wherein: Using the lanthanum-doped nickel phosphide / nickel selenide heterojunction as a catalyst, an electrocatalytic oxidation reaction of urea is realized under alkaline conditions.

8. The application according to claim 7, wherein: Using a three-electrode system, directly using the lanthanum-doped nickel phosphide / nickel selenide heterojunction catalyst as a working electrode, a platinum sheet electrode as a counter electrode, and a Hg / HgO electrode as a reference electrode, and performing catalytic oxidation of urea in an alkaline electrolyte.

9. The application according to claim 8, wherein: The alkaline electrolyte is 1 mol / L KOH solution, and the molar ratio of KOH to CO(NH2)2 is 1:0.

33. ​

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