A niobium-doped ammonium lanthanum molybdate electrocatalyst and its application

Abstract

The present invention discloses a novel niobium-doped ammonium lanthanum molybdate electrocatalyst and its application. Fumaric acid and urea are respectively dissolved in water, and the two obtained aqueous solutions are mixed evenly to obtain a fumaric acid-urea mixed solution; ammonium molybdate is dissolved in water and mixed evenly to obtain an ammonium molybdate aqueous solution; a soluble niobium salt is dissolved in water and mixed evenly to obtain a niobium salt aqueous solution; a soluble lanthanum salt is dissolved in water and mixed evenly to obtain a lanthanum salt aqueous solution; the four obtained aqueous solutions are mixed evenly, and the obtained mixed solution is transferred to the inner liner of a high-pressure reaction kettle fixed with a current collector, and heated for a sealed hydrothermal reaction; after the reaction, it is cooled to room temperature, the current collector is taken out, washed, and vacuum dried to obtain a self-supporting niobium-doped ammonium lanthanum molybdate electrocatalyst. The present invention prepares a lanthanum-based self-supporting electrocatalyst with a novel structure by a simple one-step hydrothermal method. The metal doping strategy introduces lattice defects, increases the reaction sites, and improves the electrochemical performance of the ammonium lanthanum molybdate catalyst.

Description

I. Technical Field:

[0001] The present invention belongs to the field of electrocatalyst synthesis, and particularly relates to a niobium-doped ammonium molybdate lanthanum electrocatalyst and its application. II. Background Art:

[0002] As a sustainable and green way to produce hydrogen and oxygen, water electrolysis has received extensive attention. Noble metal-based catalysts are considered to be the most effective electrocatalysts for water electrolysis at present, but their scarcity and high cost seriously affect the industrial application of water electrolysis. In addition, it is difficult for existing non-noble metal electrocatalysts to simultaneously meet the requirements of effective and stable performance and low cost, which also limits the large-scale application of water electrolysis.

[0003] Bifunctional electrocatalysts have dual electrocatalytic capabilities for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), and the research on them has promoted the development and application of water electrolysis. The application of bifunctional electrocatalysts avoids the problem of electrolyte incompatibility, further simplifies the electrolytic cell device, and reduces the cost of water electrolysis. In recent years, researchers in this field have adopted various strategies to develop transition metal-based bifunctional electrocatalysts for water electrolysis. The strategies for effectively developing bifunctional electrocatalysts with high activity and high stability are as follows: (1) Metal doping is one of the methods to induce defects in nanocatalytic materials. By doping other metal elements, the electronic structure and coordination environment can be adjusted, the catalytic active sites can be increased, the energy barrier of the hydrolysis reaction can be reduced, and the intrinsic activity and stability of the catalyst can be improved, so that it exhibits excellent electrocatalytic activity and stability; (2) Introducing rare earth elements, the unique properties of the 4f electrons of rare earth elements and the easy formation of lattice defects are beneficial to form a controllable pore environment; (3) Directly combining the active substance with the conductive matrix to ensure the high structural stability of the electrocatalyst and reduce the bubble attachment on the electrode surface.

[0004] In addition, since molybdate has excellent corrosion resistance and electrochemical redox activity, it can be an excellent candidate material for commercial active electrocatalysts. It is usually dynamic in the electrocatalytic system and can stably exist in alkaline media. At present, there are few reports on preparing molybdate with high distribution and high activity by a simple method.

[0005] Therefore, in-situ growth of niobium-doped ammonium molybdate lanthanum electrocatalyst on a conductive substrate by a one-step hydrothermal method can increase the reaction active sites by the strategies of metal doping and introducing rare earth elements while retaining the stable structure of the conductive substrate itself, which provides a simple way for developing efficient bifunctional electrocatalysts. III. Summary of the Invention:

[0006] The technical problem to be solved by the present invention is: According to the current research and development of bifunctional electrocatalysts for hydrogen evolution and oxygen evolution reactions, the present invention provides a niobium-doped ammonium molybdate lanthanum electrocatalyst and its application. The niobium-doped ammonium molybdate lanthanum electrocatalyst prepared by the technical solution of the present invention is a self-supporting lanthanum-based electrocatalyst with good electrochemical performance; its preparation process is simple and easy to operate, and it is a fast and efficient synthesis method.

[0007] In order to solve the above problems, the technical solution adopted by the present invention is:

[0008] The present invention provides a niobium-doped ammonium molybdate lanthanum electrocatalyst, and the catalyst is prepared by the following method:

[0009] a. Dissolve fumaric acid and urea in water respectively to obtain an aqueous fumaric acid solution and an aqueous urea solution, and stir and mix the two obtained aqueous solutions. After mixing evenly, a fumaric acid-urea mixed solution is obtained;

[0010] b. Dissolve ammonium molybdate in water and stir and mix. After mixing evenly, an aqueous ammonium molybdate solution is obtained;

[0011] c. Dissolve soluble niobium salt in water and stir and mix. After mixing evenly, an aqueous niobium salt solution is obtained;

[0012] d. Dissolve soluble lanthanum salt in water and stir and mix. After mixing evenly, an aqueous lanthanum salt solution is obtained;

[0013] e. Add the obtained fumaric acid-urea mixed solution, aqueous ammonium molybdate solution, aqueous niobium salt solution and aqueous lanthanum salt solution into a container and stir and mix. After mixing evenly, transfer the obtained mixed solution to the inner liner of a high-pressure reaction kettle fixed with a current collector, and carry out a hydrothermal reaction under closed conditions; after the reaction, cool to room temperature, then take out the current collector for washing, and carry out vacuum drying after washing. After drying, a self-supporting niobium-doped ammonium molybdate lanthanum electrocatalyst is obtained.

[0014] According to the above niobium-doped ammonium molybdate lanthanum electrocatalyst, in step a, the concentration of the aqueous fumaric acid solution is 0.02-0.2 mol / L, and the concentration of the aqueous urea solution is 0.1-1 mol / L; the volume ratio of the aqueous fumaric acid solution and the aqueous urea solution when mixing is 1:1.

[0015] According to the above niobium-doped ammonium molybdate lanthanum electrocatalyst, in step b, the concentration of the aqueous ammonium molybdate solution is 0.1-1 mol / L.

[0016] According to the above niobium-doped ammonium molybdate lanthanum electrocatalyst, in step c, the soluble niobium salt is niobium oxalate or ammonium niobium oxalate; calculated in terms of niobium atoms, the concentration of the aqueous niobium salt solution is 0.02-0.2 mol / L.

[0017] According to the above niobium-doped ammonium molybdate lanthanum electrocatalyst, the lanthanum salt in step d is any one of lanthanum sulfate, lanthanum nitrate, lanthanum chloride, and lanthanum acetate; calculated in terms of lanthanum atoms, the concentration of the lanthanum salt aqueous solution is 0.02 - 0.4 mol / L.

[0018] According to the above niobium-doped ammonium molybdate lanthanum electrocatalyst, after the fumaric acid urea mixed solution, ammonium molybdate aqueous solution, niobium salt aqueous solution, and lanthanum salt aqueous solution are mixed in step e, the molar ratio of niobium element, lanthanum element, and molybdenum element in the resulting mixed solution is 0.1 - 1:2:4; when stirring and mixing, the temperature is controlled at 20 - 35 °C and the time is 0.5 - 2 h.

[0019] According to the above niobium-doped ammonium molybdate lanthanum electrocatalyst, the current collector in step e is any one of titanium mesh, nickel mesh, carbon paper, and carbon cloth, and the added area of the current collector is 2 - 15 cm -2 .

[0020] According to the above niobium-doped ammonium molybdate lanthanum electrocatalyst, the temperature during the hydrothermal reaction in step e is 60 - 150 °C and the reaction time is 3 - 12 h.

[0021] According to the above niobium-doped ammonium molybdate lanthanum electrocatalyst, during the vacuum drying in step e, the drying temperature is 60 - 120 °C and the drying time is 6 - 24 h.

[0022] In addition, an application of the niobium-doped ammonium molybdate lanthanum electrocatalyst in catalyzing hydrogen evolution and oxygen evolution reactions is provided.

[0023] The positive and beneficial effects of the present invention:

[0024] 1. The technical solution of the present invention synthesizes a niobium-doped ammonium molybdate lanthanum structure on the current collector through a simple one-step hydrothermal method. While maintaining the self-conductive structure and three-dimensional channels of the current collector, lanthanum-based active species are introduced, making full use of the advantages of the high specific surface area and conductivity of the conductive current collector, so that the niobium-doped ammonium molybdate lanthanum is uniformly coated on the current collector, effectively inhibiting the aggregation and stacking of niobium-doped ammonium molybdate lanthanum, increasing the reaction area, increasing the number of effective active sites, enhancing stability, and at the same time doping niobium can cause lattice defects in ammonium molybdate lanthanum, activating more reaction sites. The prepared catalyst has good overall water splitting performance and cyclic stability.

[0025] 2. The electrocatalyst prepared by the technical solution of the present invention has stable and reliable performance. The voltage required for the two-electrode system with it directly as the working electrode at a current density of 10 mA cm -2 is only 1.52 V, and the OER and HER overpotentials do not increase significantly after 10,000 CV cycles.

[0026] In summary, the present invention prepares a lanthanum-based self-supporting electrocatalyst with a novel structure by a simple one-step hydrothermal method. The metal doping strategy introduces lattice defects, increases the active sites, and improves the electrochemical performance of the lanthanum ammonium molybdate catalyst. At the same time, its preparation method is simple, which is conducive to further scale-up applications, thus becoming a promising new material in the field of electrocatalysis. IV. DESCRIPTION OF THE DRAWINGS:

[0027] Figure 1 is the XRD pattern of the niobium-doped lanthanum ammonium molybdate material prepared in Example 1 of the present invention;

[0028] Figure 2 is the scanning electron microscope photograph of the niobium-doped lanthanum ammonium molybdate material prepared in Example 2 of the present invention;

[0029] Figure 3 is the transmission electron microscope photograph of the niobium-doped lanthanum ammonium molybdate material prepared in Example 3 of the present invention;

[0030] Figure 4 is the performance test chart of the undoped lanthanum ammonium molybdate material prepared in Example 4 of the present invention for catalyzing hydrogen evolution and oxygen evolution reactions in 1 mol / L KOH;

[0031] It can be seen from Figure 4 that the overpotential required for the catalyst to catalyze the hydrogen evolution reaction to reach a current density of 100 mA cm -2 is -0.38 V, and the voltage required for the catalyst to catalyze the oxygen evolution reaction to reach a current density of 100 mA cm -2 is 1.61 V.

[0032] Figure 5 is the performance test chart of the niobium-doped lanthanum ammonium molybdate material prepared in Example 5 of the present invention for catalyzing hydrogen evolution and oxygen evolution reactions in 1 mol / L KOH;

[0033] It can be seen from Figure 5 that the overpotential required for the catalyst to catalyze the hydrogen evolution reaction to reach a current density of 100 mA cm -2 is -0.32 V, and the voltage required for the catalyst to catalyze the oxygen evolution reaction to reach a current density of 100 mA cm -2 is 1.56 V, and the overpotential is significantly reduced compared with the undoped lanthanum ammonium molybdate.

[0034] Figure 6 is the performance test chart of the niobium-doped lanthanum ammonium molybdate material in 1 mol L -1 KOH for catalyzing hydrogen evolution and oxygen evolution reactions in Example 6 of the present invention;

[0035] It can be seen from Figure 6 that the overpotential required for the catalyst to catalyze the hydrogen evolution reaction to reach a current density of 100 mA cm -2The overpotential required for a current density of -0.29 V is for the catalytic oxygen evolution reaction to reach 100 mA cm -2 The voltage required for a current density of is 1.51 V, and the overpotential is further reduced compared to the catalyst in the above embodiment.

[0036] Figure 7 Figure 6 is a stability performance test chart of the hydrogen evolution and oxygen evolution reactions of the niobium-doped ammonium molybdate lanthanum material prepared in Example 6 of the present invention in 1 mol / L KOH;

[0037] From Figure 7 it can be seen that the overpotential of the catalyst does not increase significantly after 10,000 cycles of CV.

[0038] Figure 8 Figure 15 is a schematic diagram and an electrolytic water performance test chart of the niobium-doped ammonium molybdate lanthanum material prepared in Example 6 of the present invention directly used as a working electrode in a two-electrode system;

[0039] From Figure 8 it can be seen that the voltage required to reach a current density of 10 mA cm -2 is only 1.52 V. V. Specific implementation manners:

[0040] The present invention will be further described below in conjunction with embodiments, but does not limit the scope of protection of the technical solution of the present invention.

[0041] Example 1:

[0042] The niobium-doped ammonium molybdate lanthanum electrocatalyst of the present invention is prepared by the following method:

[0043] a. Dissolve fumaric acid and urea in water respectively to obtain a fumaric acid aqueous solution with a concentration of 0.02 mol / L and a urea aqueous solution with a concentration of 0.1 mol / L. Stir and mix the two obtained aqueous solutions in a volume ratio of 1:1, and after mixing evenly, obtain a fumaric acid-urea mixed solution;

[0044] b. Dissolve ammonium molybdate in water and stir and mix it. After mixing evenly, obtain an ammonium molybdate aqueous solution with a concentration of 0.4 mol / L;

[0045] c. Dissolve niobium oxalate in water and stir and mix it. After mixing evenly, obtain a niobium oxalate aqueous solution with a concentration of 0.02 mol / L (calculated based on niobium atoms);

[0046] d. Dissolve lanthanum sulfate in water and stir and mix it. After mixing evenly, obtain a lanthanum sulfate aqueous solution with a concentration of 0.2 mol / L (calculated based on lanthanum atoms);

[0047] e. Add the obtained urea fumarate mixed solution, ammonium molybdate aqueous solution, niobium oxalate aqueous solution, and lanthanum sulfate aqueous solution into a beaker, stir and mix them at 25 °C for 30 min. The molar ratio of niobium, lanthanum, and molybdenum elements in the obtained mixed solution is 0.1:2:4. Transfer the mixed solution into the inner liner of a high-pressure reaction kettle fixed with a 2 cm × 3 cm carbon cloth, and carry out a hydrothermal reaction under closed conditions. The reaction temperature is 90 °C and the reaction time is 6 h. After the reaction, cool it to room temperature, then take out the carbon cloth, wash it 3 times with deionized water, and vacuum dry it at 60 °C for 12 h. After drying, a self-supporting niobium-doped ammonium molybdate lanthanum electrocatalyst is obtained (the XRD pattern of the obtained product powder is shown in the attached Figure 1 ).

[0048] Example 2:

[0049] The niobium-doped ammonium molybdate lanthanum electrocatalyst of the present invention is prepared by the following method:

[0050] a. Dissolve fumaric acid and urea in water respectively to obtain a fumaric acid aqueous solution with a concentration of 0.04 mol / L and a urea aqueous solution with a concentration of 0.2 mol / L. Stir and mix the obtained two aqueous solutions according to a volume ratio of 1:1. After mixing evenly, a urea fumarate mixed solution is obtained;

[0051] b. Dissolve ammonium molybdate in water and stir and mix it. After mixing evenly, an ammonium molybdate aqueous solution with a concentration of 0.4 mol / L is obtained;

[0052] c. Dissolve ammonium niobium oxalate in water and stir and mix it. After mixing evenly, an ammonium niobium oxalate aqueous solution with a concentration of 0.02 mol / L (calculated based on niobium atoms) is obtained;

[0053] d. Dissolve lanthanum acetate in water and stir and mix it. After mixing evenly, a lanthanum acetate aqueous solution with a concentration of 0.2 mol / L (calculated based on lanthanum atoms) is obtained;

[0054] e. Add the obtained urea fumarate mixed solution, ammonium molybdate aqueous solution, ammonium niobium oxalate aqueous solution, and lanthanum acetate aqueous solution into a beaker, stir and mix them at 25 °C for 60 min. The molar ratio of niobium, lanthanum, and molybdenum elements in the obtained mixed solution is 0.1:1:2. Transfer the mixed solution into the inner liner of a high-pressure reaction kettle fixed with a 3 cm × 3 cm carbon paper, and carry out a hydrothermal reaction under closed conditions. The reaction temperature is 80 °C and the reaction time is 6 h. After the reaction, cool it to room temperature, then take out the carbon paper, wash it 3 times with deionized water, and vacuum dry it at 90 °C for 9 h. After drying, a self-supporting niobium-doped ammonium molybdate lanthanum electrocatalyst is obtained (the scanning electron microscope photo of the obtained product powder is shown in the attached Figure 2 ).

[0055] Example 3:

[0056] The niobium-doped ammonium molybdate lanthanum electrocatalyst of the present invention is prepared by the following method:

[0057] a. Dissolve fumaric acid and urea in water respectively to obtain an aqueous fumaric acid solution with a concentration of 0.04 mol / L and an aqueous urea solution with a concentration of 0.2 mol / L. Stir and mix the two obtained aqueous solutions according to a volume ratio of 1:1, and after mixing evenly, obtain a fumaric acid-urea mixed solution;

[0058] b. Dissolve ammonium molybdate in water and stir to mix, and after mixing evenly, obtain an aqueous ammonium molybdate solution with a concentration of 0.4 mol / L;

[0059] c. Dissolve ammonium niobium oxalate in water and stir to mix, and after mixing evenly, obtain an aqueous ammonium niobium oxalate solution with a concentration of 0.05 mol / L (calculated based on niobium atoms);

[0060] d. Dissolve lanthanum chloride in water and stir to mix, and after mixing evenly, obtain an aqueous lanthanum chloride solution with a concentration of 0.2 mol / L (calculated based on lanthanum atoms);

[0061] e. Add the obtained fumaric acid-urea mixed solution, ammonium molybdate aqueous solution, ammonium niobium oxalate aqueous solution and lanthanum chloride aqueous solution into a beaker, stir and mix at 25 °C for 60 min. The molar ratio of niobium element, lanthanum element and molybdenum element in the obtained mixed solution is 1:4:8; transfer the mixed solution to the inner liner of a high-pressure reaction kettle fixed with a 3 cm × 4 cm titanium mesh, and carry out a hydrothermal reaction under a closed condition. The reaction temperature is 90 °C and the reaction time is 6 h; after the reaction, cool to room temperature, then take out the titanium mesh, wash it 3 times with deionized water, and dry it in vacuum at 60 °C for 12 h. After drying, obtain a self-supporting niobium-doped ammonium molybdate lanthanum electrocatalyst (for the transmission electron microscope photo of the obtained product powder, see the appendix Figure 3 ).

[0062] Example 4:

[0063] The undoped ammonium molybdate lanthanum electrocatalyst of the present invention is prepared by the following method:

[0064] a. Dissolve fumaric acid and urea in water respectively to obtain an aqueous fumaric acid solution with a concentration of 0.08 mol / L and an aqueous urea solution with a concentration of 0.4 mol / L. Stir and mix the two obtained aqueous solutions according to a volume ratio of 1:1, and after mixing evenly, obtain a fumaric acid-urea mixed solution;

[0065] b. Dissolve ammonium molybdate in water and stir to mix, and after mixing evenly, obtain an aqueous ammonium molybdate solution with a concentration of 0.8 mol / L;

[0066] c. Dissolve lanthanum nitrate in water and stir to mix. After mixing evenly, an aqueous solution of lanthanum nitrate with a concentration of 0.4 mol / L (calculated based on lanthanum atoms) is obtained.

[0067] d. Add the obtained maleic acid - urea mixed solution, ammonium molybdate aqueous solution, and lanthanum nitrate aqueous solution into a beaker, stir and mix at 25 °C for 1.5 h. The molar ratio between lanthanum element and molybdenum element in the obtained mixed solution is 1:2. Transfer the obtained mixed solution to the inner liner of a high - pressure reaction kettle fixed with a 3 cm × 4 cm nickel mesh, and carry out a hydrothermal reaction under closed conditions. The reaction temperature is 90 °C and the reaction time is 6 h. After the reaction, cool to room temperature, then take out the nickel mesh, wash it 3 times with deionized water, and vacuum dry it at 60 °C for 12 h. After drying, a self - supported undoped ammonium lanthanum molybdate electrocatalyst is obtained.

[0068] Example 5:

[0069] The niobium - doped ammonium lanthanum molybdate electrocatalyst of the present invention is prepared by the following method:

[0070] a. Dissolve maleic acid and urea in water respectively to obtain an aqueous solution of maleic acid with a concentration of 0.08 mol / L and an aqueous solution of urea with a concentration of 0.4 mol / L. Stir and mix the obtained two aqueous solutions according to a volume ratio of 1:1. After mixing evenly, a maleic acid - urea mixed solution is obtained.

[0071] b. Dissolve ammonium molybdate in water and stir to mix. After mixing evenly, an aqueous solution of ammonium molybdate with a concentration of 0.8 mol / L is obtained.

[0072] c. Dissolve ammonium niobium oxalate in water and stir to mix. After mixing evenly, an aqueous solution of ammonium niobium oxalate with a concentration of 0.1 mol / L (calculated based on niobium atoms) is obtained.

[0073] d. Dissolve lanthanum nitrate in water and stir to mix. After mixing evenly, an aqueous solution of lanthanum nitrate with a concentration of 0.4 mol / L (calculated based on lanthanum atoms) is obtained.

[0074] e. Add the obtained maleic acid - urea mixed solution, ammonium molybdate aqueous solution, ammonium niobium oxalate aqueous solution, and lanthanum nitrate aqueous solution into a beaker, stir and mix at 25 °C for 1.5 h. The molar ratio between niobium element, lanthanum element, and molybdenum element in the obtained mixed solution is 1:4:8. Transfer the obtained mixed solution to the inner liner of a high - pressure reaction kettle fixed with a 3 cm × 4 cm nickel mesh, and carry out a hydrothermal reaction under closed conditions. The reaction temperature is 90 °C and the reaction time is 6 h. After the reaction, cool to room temperature, then take out the nickel mesh, wash it 3 times with deionized water, and vacuum dry it at 80 °C for 12 h. After drying, a self - supported niobium - doped ammonium lanthanum molybdate electrocatalyst is obtained.

[0075] Example 6:

[0076] The niobium-doped ammonium molybdate lanthanum electrocatalyst of the present invention is prepared by the following method:

[0077] a. Dissolve fumaric acid and urea in water respectively to obtain an aqueous fumaric acid solution with a concentration of 0.16 mol / L and an aqueous urea solution with a concentration of 0.8 mol / L. Stir and mix the two obtained aqueous solutions in a volume ratio of 1:1, and after mixing evenly, obtain a fumaric acid-urea mixed solution;

[0078] b. Dissolve ammonium molybdate in water and stir and mix it. After mixing evenly, obtain an aqueous ammonium molybdate solution with a concentration of 0.8 mol / L;

[0079] c. Dissolve ammonium niobium oxalate in water and stir and mix it. After mixing evenly, obtain an aqueous ammonium niobium oxalate solution with a concentration of 0.2 mol / L (calculated based on niobium atoms);

[0080] d. Dissolve lanthanum nitrate in water and stir and mix it. After mixing evenly, obtain an aqueous lanthanum nitrate solution with a concentration of 0.4 mol / L (calculated based on lanthanum atoms);

[0081] e. Add the obtained fumaric acid-urea mixed solution, ammonium molybdate aqueous solution, ammonium niobium oxalate aqueous solution, and lanthanum nitrate aqueous solution into a beaker, stir and mix them at 25 °C for 2 h. The molar ratio of niobium element, lanthanum element, and molybdenum element in the obtained mixed solution is 1:2:4; transfer the obtained mixed solution to the inner liner of a high-pressure reaction kettle fixed with a 3 cm × 4 cm nickel mesh, and carry out a hydrothermal reaction under closed conditions. The reaction temperature is 90 °C and the reaction time is 6 h; after the reaction, cool it to room temperature, then take out the nickel mesh, wash it 3 times with deionized water, and vacuum dry it at 80 °C for 12 h. After drying, obtain a self-supporting niobium-doped ammonium molybdate lanthanum electrocatalyst.

[0082] Application of the niobium-doped ammonium molybdate lanthanum electrocatalyst prepared by the present invention in the catalytic hydrogen evolution and oxygen evolution reactions:

[0083] 1) Apply the undoped ammonium molybdate lanthanum material prepared in Example 4 of the present invention in the catalytic hydrogen evolution and oxygen evolution reactions in 1 mol / L KOH. The performance test diagram of the obtained application is shown in the attached Figure 4 as shown.

[0084] From Figure 4 it can be seen that the overpotential required for the catalyst to catalyze the hydrogen evolution reaction to reach a current density of 100 mA cm -2 is -0.38 V, and the voltage required for the catalyst to catalyze the oxygen evolution reaction to reach a current density of 100 mA cm -2 is 1.61 V.

[0085] 2) The niobium-doped ammonium lanthanum molybdate electrocatalyst prepared in Example 5 of the present invention was applied to catalyze the hydrogen evolution and oxygen evolution reactions in 1 mol / L KOH. The performance test diagrams of the obtained application are shown in the appendix Figure 5 as follows.

[0086] It can be seen from Figure 5 that the overpotential required for the catalyst to catalyze the hydrogen evolution reaction to reach a current density of 100 mA cm -2 is -0.32 V, and the voltage required for the catalyst to catalyze the oxygen evolution reaction to reach a current density of 100 mA cm -2 is 1.56 V. Compared with the undoped ammonium lanthanum molybdate prepared in Example 4, the overpotential is significantly reduced.

[0087] 3) The performance test diagrams of the niobium-doped ammonium lanthanum molybdate electrocatalyst prepared in Example 6 of the present invention for catalyzing the hydrogen evolution and oxygen evolution reactions in 1 mol / L KOH are shown in the appendix Figure 6 as follows, and the stability test diagrams are shown in the appendix Figure 7 , and the performance test diagrams of water electrolysis in a two-electrode system are shown in the appendix Figure 8 .

[0088] It can be seen from Figure 6 that the overpotential required for the catalyst to catalyze the hydrogen evolution reaction to reach a current density of 100 mA cm -2 is -0.29 V, and the voltage required for the catalyst to catalyze the oxygen evolution reaction to reach a current density of 100 mA cm -2 is 1.51 V. Compared with the catalysts in the above examples, the overpotential is further reduced.

[0089] It can be seen from Figure 7 that after 10,000 cycles of CV, the overpotential of the catalyst does not increase significantly.

[0090] It can be seen from Figure 8 that the voltage required to reach a current density of 10 mA cm -2 is only 1.52 V.

[0091] In summary, the present invention in-situ grows niobium-doped ammonium lanthanum molybdate by a one-step hydrothermal method to obtain a self-supporting electrocatalyst with excellent performance. The self-supporting electrocatalyst of niobium-doped ammonium lanthanum molybdate prepared by the present invention makes full use of the advantages of the high specific surface area and conductivity of the conductive current collector, so that niobium-doped ammonium lanthanum molybdate is uniformly coated on the current collector, effectively inhibiting the agglomeration and stacking of niobium-doped ammonium lanthanum molybdate, increasing the reaction area, increasing the number of effective active sites, enhancing the stability, and at the same time, doping niobium can cause lattice defects in ammonium lanthanum molybdate, thereby obtaining an electrocatalyst with more reaction sites.

[0092] The self-supported electrocatalyst of niobium-doped ammonium lanthanum molybdate prepared by the present invention, as a new and promising material in the field of electrocatalysis, can effectively reduce the electrolysis overpotential and improve the catalyst stability during the electrolysis of water. At the same time, due to the simple preparation method, it is conducive to further scale-up applications.

[0093] The above embodiments are only illustrative of the principles and effects of the present invention and some applied embodiments. For those of ordinary skill in the art, without departing from the inventive concept of the present invention, several modifications and improvements can be made, and these all belong to the protection scope of the present invention.

Claims

1. A niobium-doped ammonium lanthanum molybdate electrocatalyst, characterized in that, The catalyst is prepared by the following method: a. Dissolve fumaric acid and urea in water respectively to obtain an aqueous fumaric acid solution and an aqueous urea solution. Stir and mix the two obtained aqueous solutions, and after mixing evenly, obtain a fumaric acid-urea mixed solution; b. Dissolve ammonium molybdate in water and stir and mix. After mixing evenly, obtain an aqueous ammonium molybdate solution; the concentration of the aqueous ammonium molybdate solution is 0.1 - 1 mol / L; c. Dissolve soluble niobium salt in water and stir and mix. After mixing evenly, obtain an aqueous niobium salt solution; the soluble niobium salt is niobium oxalate or ammonium niobium oxalate; calculated by niobium atoms, the concentration of the aqueous niobium salt solution is 0.02 - 0.2 mol / L; d. Dissolve soluble lanthanum salt in water and stir and mix. After mixing evenly, obtain an aqueous lanthanum salt solution; the lanthanum salt is any one of lanthanum sulfate, lanthanum nitrate, lanthanum chloride and lanthanum acetate; calculated by lanthanum atoms, the concentration of the aqueous lanthanum salt solution is 0.02 - 0.4 mol / L; e. Add the obtained fumaric acid-urea mixed solution, aqueous ammonium molybdate solution, aqueous niobium salt solution and aqueous lanthanum salt solution into a container and stir and mix. After mixing evenly, transfer the obtained mixed solution to the inner liner of a high-pressure reaction kettle fixed with a current collector, and carry out hydrothermal reaction under closed conditions; after the reaction, cool to room temperature, then take out the current collector for washing, and carry out vacuum drying after washing to obtain a self-supporting niobium-doped ammonium molybdate lanthanum electrocatalyst.

2. The ammonium lanthanum niobium-doped molybdate electrocatalyst according to claim 1, characterized in that: In step a, the concentration of the aqueous fumaric acid solution is 0.02 - 0.2 mol / L, and the concentration of the aqueous urea solution is 0.1 - 1 mol / L; the volume ratio of the aqueous fumaric acid solution and the aqueous urea solution during mixing is 1:

1.

3. The ammonium lanthanum niobium-doped molybdate electrocatalyst according to claim 1, wherein: In step e, after mixing the fumaric acid-urea mixed solution, aqueous ammonium molybdate solution, aqueous niobium salt solution and aqueous lanthanum salt solution, make the molar ratio of niobium element, lanthanum element and molybdenum element in the obtained mixed solution be 0.1 - 1:2:4; during the stirring and mixing, control the temperature to be 20 - 35 °C and the time to be 0.5 - 2 h.

4. The ammonium lanthanum niobium-doped molybdate electrocatalyst according to claim 1, wherein: The current collector described in step e is any one of titanium mesh, nickel mesh, carbon paper and carbon cloth, and the added area of the current collector is 2-15 cm -2 .

5. The ammonium lanthanum niobium-doped molybdate electrocatalyst according to claim 1, characterized in that: In step e, the temperature during the hydrothermal reaction is 60 - 150 °C and the reaction time is 3 - 12 h.

6. The ammonium lanthanum niobium-doped molybdate electrocatalyst according to claim 1, characterized in that: In step e, during the vacuum drying, the drying temperature is 60 - 120 °C and the drying time is 6 - 24 h.

7. Application of the niobium-doped ammonium molybdate lanthanum electrocatalyst described in claim 1 in catalytic hydrogen evolution and oxygen evolution reactions.

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