Lanthanum oxide-doped molybdenum-based supported catalysts, methods for their preparation and use

Abstract

The application provides a lanthanum oxide doped molybdenum-based supported catalyst and a preparation method and application thereof, and belongs to the technical field of electrocatalytic decomposition of hydrogen catalysts. The preparation method of the lanthanum oxide doped molybdenum-based supported catalyst comprises the following steps: mixing ammonium molybdate or a hydrate thereof, lanthanum oxide and a modifier in water to form a mixed solution; adding a pretreated porous carrier to the mixed solution to perform a hydrothermal reaction, so as to obtain a catalyst precursor; and performing calcination treatment on the catalyst precursor in an inert atmosphere, and obtaining the lanthanum oxide doped molybdenum-based supported catalyst after cooling. The modifier comprises at least one of ethanol, glucose and acetic acid. The doping of lanthanum oxide can adjust the electronic structure of MoO2, optimize the hydrogen adsorption free energy, improve the catalytic activity of the molybdenum-based supported catalyst, the introduced modifier inhibits the excessive oxidation of MnO2 into MoO3, maintains the stability of the molybdenum-based supported catalyst, and further strengthens the catalytic activity of the molybdenum-based supported catalyst.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of electrocatalytic decomposition of hydrogen catalyst, and particularly relates to a lanthanum oxide doped molybdenum-based supported catalyst and a preparation method and application thereof. BACKGROUND

[0002] Hydrogen has become one of the substitutes for fossil energy in the future due to its high energy density (120 MJ / kg), environmental protection and renewability. At present, in the hydrogen production technology, water electrolysis catalytic hydrogen evolution is a widely used scheme. However, the reaction has a high overpotential on the cathode, resulting in a high cost of hydrogen production. At present, a catalyst is usually added to reduce the overpotential on the cathode, and the commonly used catalyst is metal platinum and its compounds, but the cost of metal platinum is high and the reserves are limited, which limits its further development and application.

[0003] Therefore, it is necessary to find a catalyst with abundant reserves, low price and high replaceability, and with high hydrogen production catalytic efficiency. SUMMARY

[0004] Therefore, in order to at least partially solve the above-mentioned technical problems, the present application provides a lanthanum oxide doped molybdenum-based supported catalyst and a preparation method and application thereof.

[0005] According to an embodiment of the present application, a preparation method of a lanthanum oxide doped molybdenum-based supported catalyst is provided, which comprises: mixing ammonium molybdate or its hydrate, lanthanum oxide and a modifier in water to form a mixed solution; adding a pretreated porous carrier to the mixed solution to perform a hydrothermal reaction, to obtain a catalyst precursor; and performing a calcination treatment on the catalyst precursor under an inert atmosphere, and obtaining the lanthanum oxide doped molybdenum-based supported catalyst after cooling; wherein the modifier comprises at least one of ethanol, glucose and acetic acid; the pretreated porous carrier is prepared by sequentially performing ultrasonic washing on the porous carrier with an acidic solution, an ethanol solution and water, and then drying; and the porous carrier comprises any one of foamed nickel and graphite.

[0006] In some embodiments, in the case that the modifier is ethanol, the volume ratio of water to ethanol is 1: (0.5-1); in the case that the modifier is glucose, the mass ratio of glucose to ammonium molybdate or its hydrate is (0.4-1):1; and in the case that the modifier is acetic acid, the volume ratio of water to acetic acid is 1: (0.5-1).

[0007] In some embodiments, in the case that the modifier is ethanol, the volume ratio of water to ethanol is 1:0.9.

[0008] In some embodiments, the mass of lanthanum oxide is a, the mass of ammonium molybdate or its hydrate is b, and a / b is 5-12%.

[0009] In some embodiments, the temperature of the hydrothermal reaction is 100-210℃, and the reaction time is 12-24h.

[0010] In some embodiments, the temperature of the calcination treatment is 650-700℃, the calcination time is 150-180min, and the inert atmosphere includes a nitrogen atmosphere.

[0011] According to an embodiment of another aspect of the present application, there is provided a lanthanum oxide doped molybdenum-based supported catalyst prepared by the preparation method as described above, comprising a porous carrier and La2O3 doped MoO2 nanoparticles grown in situ on the surface of the porous carrier.

[0012] In some embodiments, the average particle size of the La2O3 doped MoO2 nanoparticles is 0.6-1.5μm.

[0013] According to an embodiment of another aspect of the present application, there is provided a use of the lanthanum oxide doped molybdenum-based supported catalyst as described above in alkaline water electrolysis for hydrogen production.

[0014] According to the preparation method of the lanthanum oxide doped molybdenum-based supported catalyst of the embodiments of the present application, the introduction of lanthanum oxide (La2O3) can adjust the electronic structure of MoO2 in the formed molybdenum-based supported catalyst, shift the d-band center, optimize the hydrogen adsorption free energy, and improve the catalytic activity of the lanthanum oxide doped molybdenum-based supported catalyst. Moreover, the addition of lanthanum oxide promotes the formation of more La2O3 doped MoO2 composite particles, increases the effective electrochemical surface area, and further improves the catalytic activity. In the preparation process of the lanthanum oxide doped molybdenum-based supported catalyst, the addition of the above-mentioned modifier can inhibit the excessive oxidation of MoO2 to MoO3 during the reaction, further enhance the catalytic performance of the lanthanum oxide doped molybdenum-based supported catalyst. At the same time, the addition of the modifier can promote the uniform dispersion of ammonium molybdate or its hydrate, reduce the agglomeration of La2O3 doped MoO2 composite particles, form relatively uniform active sites, and strengthen the catalytic activity. In addition, the addition of the porous carrier provides a large specific surface area, and its three-dimensional porous structure is beneficial to the rapid diffusion of gas in subsequent application in alkaline water electrolysis for hydrogen production, avoiding the mass transfer limitation caused by the accumulation of gas bubbles on the electrode. BRIEF DESCRIPTION OF DRAWINGS

[0015] The above and other objects, features and advantages of the present application will become more apparent from the following description of embodiments of the present application taken in conjunction with the accompanying drawings.

[0016] Figure 1 Flow chart of the preparation method of the lanthanum oxide doped molybdenum-based supported catalyst of the embodiments of the present application;

[0017] Figure 2Scanning electron microscope (SEM) images of the catalysts prepared for Comparative Example 1 and Example 1, respectively;

[0018] Figure 3 Linear sweep voltammetry (LSV) plots of the catalysts of Examples 1-5 and Comparative Example 1;

[0019] Figure 4 Tafel plots of the catalysts of Examples 1-5 and Comparative Example 1;

[0020] Figure 5 LSV plots of the catalysts of Examples 1, 6-7 and Comparative Examples 2-3;

[0021] Figure 6 Tafel plots of the catalysts of Examples 1, 6-7 and Comparative Examples 2-3;

[0022] Figure 7 48-hour chronoamperometry (CA) plot of the catalyst of Example 1;

[0023] Figure 8 48-hour chronopotentiometry (CP) plot of the catalyst of Example 1. DETAILED DESCRIPTION

[0024] Hereinafter, embodiments of the present application will be described with reference to the accompanying drawings. It is to be understood, however, that the description is merely exemplary of the present application, and is not intended to limit the scope of the present application. In the following detailed description of the embodiments of the present application, numerous specific details are set forth in order to provide a thorough understanding of the embodiments of the present application. However, it will be apparent to one skilled in the art that the embodiments of the present application can be practiced without these specific details. In other instances, well-known structures and functions have not been described in detail in order to avoid obscuring aspects of the present application.

[0025] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the present application. As used herein, the term "includes" indicates the presence of the features, steps, operations, but does not preclude the presence or addition of one or more other features.

[0026] Currently, water electrolysis hydrogen production process conditions are relatively simple, the equipment requirements are relatively low, and the product purity is relatively high, which is considered as an important development path for future industrial hydrogen production. However, due to the slow kinetics of the hydrogen evolution reaction in water electrolysis hydrogen production, the energy consumption is relatively high, and the current catalytic material is difficult to balance the performance, stability and use cost. Therefore, it is urgent to develop a hydrogen evolution reaction (HER) catalyst with high activity, low cost and stable durability.

[0027] Among transition metal oxides, MoO2 has relatively excellent electronic conductivity, high chemical stability and abundant edge active sites (including molybdenum vacancies and oxygen vacancies in intrinsic defect structures), and exhibits potential application value in electrocatalysis. However, the material is prone to nanoparticle agglomeration during catalysis, which leads to insufficient exposure of active sites and seriously restricts the improvement of the electrochemical active surface area, thereby limiting its catalytic efficiency in HER. Moreover, the preparation process of MoO2 requires relatively strict synthesis conditions, has high requirements for equipment, and is complex to operate.

[0028] In the process of implementing the present application, it is found that MoO2 is synthesized on a porous carrier substrate through a hydrothermal reaction, and the electronic structure of MoO2 is adjusted by doping La2O3 to optimize the hydrogen adsorption free energy and improve the catalytic activity. By introducing a modifier, the excessive oxidation of MoO2 is inhibited to control the valence state and morphology of MoO2. In combination with the synergistic effect of lanthanum oxide and the modifier, the durability and stability of the molybdenum-based supported catalyst can be improved without damaging the basic skeleton of the porous carrier, and good catalytic performance is also considered.

[0029] Specifically, according to an embodiment of one aspect of the present application, a preparation method of a lanthanum oxide-doped molybdenum-based supported catalyst is provided. Figure 1 The flowchart of the preparation method of the lanthanum oxide-doped molybdenum-based supported catalyst of the embodiment of the present application is shown as follows. Figure 1 As shown in the figure, the preparation method includes steps S101-S103.

[0030] In step S101, ammonium molybdate or its hydrate, lanthanum oxide and a modifier are mixed in water to form a mixed solution.

[0031] In step S102, the mixed solution is added to the pretreated porous carrier for hydrothermal reaction to obtain a catalyst precursor.

[0032] In step S103, the catalyst precursor is subjected to calcination treatment under an inert atmosphere, and the lanthanum oxide-doped molybdenum-based supported catalyst is obtained after cooling.

[0033] According to an embodiment of the present application, the introduction of lanthanum oxide is based on the similarity of atomic radius, which helps to adjust the electronic structure of MoO2, optimize the hydrogen adsorption free energy, and promote the formation of a large number of La2O3-doped MoO2 composite particles (hereinafter referred to as MoO2 composite particles), thereby increasing the effective surface area for subsequent application as an electrode for water electrolysis to produce hydrogen and improving the overall catalytic efficiency. Based on the hydrothermal reaction, in-situ growth of lanthanum oxide-doped molybdenum-based catalysts on the inner and outer surfaces of the porous carrier is achieved, and no impurities (anion impurities such as chloride ions, nitrate ions, sulfate ions, etc.) are introduced during the hydrothermal reaction, thereby reducing the adverse effects on the electrochemical performance of the lanthanum oxide-doped molybdenum-based supported catalyst.

[0034] According to an embodiment of the present application, the modifier includes at least one of ethanol, glucose, and acetic acid. It can be understood that the addition of ethanol helps to improve the solubility of ammonium molybdate or its hydrate, promotes uniform dispersion, and reduces agglomeration. Moreover, the decomposition of ethanol during the hydrothermal reaction can generate hydroxyl groups on the surface, thereby modifying the surface of the MoO2 composite particles, providing proton transfer sites, and promoting the subsequent adsorption of hydrogen in the electrocatalytic process. At the same time, the weak reducing property of ethanol can inhibit the excessive oxidation of MoO2 to MoO3 during the reaction process, thereby helping to maintain the stability of the lanthanum oxide-doped molybdenum-based supported catalyst. During the preparation process and / or application in the electrocatalytic process, the addition of ethanol can reduce the Mo 4+ further reduced to Mo 3+ , forming oxygen vacancies, and enhancing the electron transport capacity and adsorption capacity of the lanthanum oxide-doped molybdenum-based supported catalyst.

[0035] The aldehyde group (as well as other groups such as hydroxyl groups) on the glucose molecule releases reducing gases such as hydrogen or carbon monoxide during the hydrothermal reaction and / or calcination process, thereby reducing Mo 6+ to Mo 4+ (which exists in the form of MoO2 after calcination) and introducing oxygen vacancies. In addition, glucose can guide MoO2 to form a porous or nanosheet structure during the hydrothermal reaction and / or calcination process, thereby further increasing the number of exposed active sites.

[0036] The addition of acetic acid can improve the agglomeration of MoO2 and modify the surface of the lanthanum oxide-doped molybdenum-based supported catalyst, providing proton adsorption and transport sites, and helping to maintain the stable state of Mo 4+ . Through the interaction between lanthanum oxide and the above-mentioned several modifiers, the lanthanum oxide-doped molybdenum-based supported catalyst has high electrocatalytic activity, excellent durability, and long-term stability when used as a hydrogen evolution catalyst.

[0037] The porous carrier, such as the porous metal carrier, has a rich porous structure and excellent electrical conductivity, provides support of a large specific surface area, and facilitates in-situ growth of a lanthanum oxide-doped molybdenum-based catalyst thereon. The three-dimensional porous structure of the porous carrier is conducive to rapid diffusion of gas away from the electrode surface in an electrocatalytic process, avoiding mass transfer limitations caused by bubble accumulation. The formed lanthanum oxide-doped molybdenum-based supported catalyst can be directly used as a working electrode at a large current density. According to an embodiment of the present application, the preparation method is relatively simple, low in cost, and mild in reaction conditions, and the lanthanum oxide-doped molybdenum-based supported catalyst prepared has excellent durability and good stability. Moreover, the commonly used precursor salt in a hydrothermal reaction is avoided, the introduction of anion impurities such as chloride and nitrate is avoided, the process is saved, and the risk of residual of the aforementioned anion impurities in the related art is avoided. The anion impurities in the related art are not only difficult to completely remove in the subsequent process, but also can be left on the surface of the catalyst, further affecting the electrochemical performance of the catalyst.

[0038] According to an embodiment of the present application, the pretreated porous carrier is prepared by sequentially ultrasonically washing the porous carrier with an acidic solution, an ethanol solution, and water, and then drying. In this way, the surface impurities of the porous carrier are removed, the inner and outer surfaces thereof are activated, and the uniformity and stability of the loading are improved.

[0039] In some embodiments, the porous carrier includes any one of foamed nickel and graphite. Foamed nickel and graphite have a porous structure and excellent electrical conductivity, and after being used as a carrier to in-situ grow a lanthanum oxide-doped molybdenum-based catalyst, they can be directly used as a working electrode at a large current density without the need for a binder. They not only provide support of a large specific surface area for the lanthanum oxide-doped molybdenum-based catalyst, but also have a three-dimensional porous structure that is conducive to rapid diffusion of gas away from the electrode surface, avoiding mass transfer limitations caused by bubble accumulation. Foamed nickel is preferred.

[0040] In some embodiments, the drying can include air drying or vacuum drying at room temperature.

[0041] In some specific embodiments, the pretreatment includes sequentially ultrasonically immersing and cleaning the foamed nickel carrier with a 2 mol / L hydrochloric acid solution, anhydrous ethanol, and deionized water for 15 minutes, and a vacuum drying step.

[0042] In some embodiments, the ammonium molybdate hydrate can include ammonium molybdate tetrahydrate.

[0043] In some embodiments, when the modifier is ethanol, the volume ratio of water and ethanol is 1 : (0.5-1). In this way, the addition of ethanol helps to adjust the solvent polarity, optimize the dissolution and depolymerization state of ammonium molybdate or its hydrate, and tend to dissociate into smaller molybdenum oxygen units, more easily diffuse into the small pores of the porous carrier, achieve high dispersion, effectively prevent the agglomeration of molybdenum oxygen units, and make the active sites formed after calcination treatment smaller in size and more uniform in distribution. The addition of ethanol helps to adjust the surface tension after mixing water and ethanol, promotes the penetration of the mixed solution into the pores of the porous carrier, and further promotes the uniform loading of molybdenum oxygen units inside the porous carrier. After subsequent calcination, the molybdenum oxygen units form MoO2. By adjusting the ratio of water to ethanol to the above range, the MoO2 can be uniformly dispersed while providing proton transfer sites; at the same time, the weak reducing property of ethanol further enhances the electronic transmission ability and adsorption performance of the above-mentioned catalyst. If the proportion of ethanol is too low, for example, lower than the above lower limit, the surface tension and depolymerization effect are not obvious, which is not conducive to the dispersion of molybdenum oxygen units; if the proportion of ethanol is too high, for example, higher than the above upper limit, it may cause the solubility of ammonium molybdate or its hydrate to decrease, making the mixture uneven, and the proportion of water is too low, which makes the dispersion of lanthanum oxide poor.

[0044] Alternatively, the volume ratio of water and ethanol may be, for example, 1 : 0.5, 1 : 0.6, 1 : 0.7, 1 : 0.8, 1 : 0.9, or 1 : 1, or a range consisting between any two of the above values.

[0045] In some preferred embodiments, the volume ratio of water and ethanol is 1 : 0.9. In this way, the agglomeration of ammonium molybdate or its hydrate is effectively prevented, and the efficiency and uniformity of hydrogen adsorption in the electrocatalytic process are further optimized.

[0046] In some embodiments, when the modifier is glucose, the mass ratio of glucose to ammonium molybdate or its hydrate is (0.4-1) : 1. In this way, by introducing an appropriate amount of glucose, it helps to fully guide the MoO2 to form a porous or nanosheet structure, and increase the number of exposed active sites. If the content of glucose is too low, for example, lower than the above lower limit, it is difficult to provide sufficient structure guiding effect; if the proportion of glucose is too high, for example, higher than the above upper limit, it may block the pores of the porous carrier, resulting in coverage of the active sites, and reducing the catalytic activity of the lanthanum-doped molybdenum-based supported catalyst.

[0047] Alternatively, the mass ratio of glucose to ammonium molybdate or its hydrate may be, for example, 0.4: 1, 0.5: 1, 0.6: 1, 0.7: 1, 0.8: 1, 0.9: 1, or 1: 1, or a range consisting between any two of the above values.

[0048] In some embodiments, when the modifier is acetic acid, the volume ratio of water and acetic acid is 1: (0.5-1). Acetic acid has weak acidity, so that at this time the molybdate ion tends to be protonated, prompting the stable formation of Mo 4+ . And in a weak acid environment, it helps the negatively charged molybdate ion to be adsorbed on the surface of the porous carrier by electrostatic action, improving the agglomeration phenomenon. In addition, the electronic effect of acetic acid helps to stabilize the formation of Mo 4+ , reducing the excessive oxidation of Mo 6+ . If the content of acetic acid is too low, for example, lower than the above lower limit value, the acidity is too weak to effectively inhibit the polymerization of molybdate ions, and the valence state regulation effect on molybdenum is limited; if the proportion of acetic acid is too high, for example, higher than the above upper limit value, it may corrode the porous carrier, damage its pore structure, and cause the mechanical strength to decrease.

[0049] Alternatively, the volume ratio of water and acetic acid may be, for example, 1:0.5, 1:0.6, 1:0.7, 1:0.8, 1:0.9 or 1:1, or a range consisting between any two of the above values.

[0050] In some embodiments, the mass of lanthanum oxide is a, and the mass of ammonium molybdate or its hydrate is b, a / b is 5-12%. By doping lanthanum oxide, the electronic distribution of MoO2 is effectively adjusted, causing the d-band center to shift, so that the hydrogen adsorption free energy is in a good state. When subsequently applied to the electrolysis of water to produce hydrogen, it improves the adsorption and activation ability of water molecules, reduces the reaction energy barrier of steps such as water molecule dissociation and hydrogen atom recombination, and improves the intrinsic catalytic activity of lanthanum oxide-doped molybdenum-based supported catalyst. In terms of apparent morphology, the doping of lanthanum oxide increases the surface roughness of the formed lanthanum oxide-doped molybdenum-based supported catalyst, which, together with the modifier, induces the refinement and dispersion of MoO2 composite particles, constructs a rough surface with abundant nanoparticles, provides more active sites, and optimizes the interface wettability of the electrode, providing favorable conditions for efficient mass transfer. If the amount of lanthanum oxide doping is too low, the above effect is not significantly improved; if the amount of lanthanum oxide doping is too high, the excess lanthanum oxide exists in the form of agglomeration, so that it will physically cover the active sites activated by the electronic effect, and may also block the three-dimensional porous structure of the lanthanum oxide-doped molybdenum-based supported catalyst, hindering the mass transfer process and weakening the catalytic performance.

[0051] Alternatively, a / b may be, for example, 5%, 7.5%, 10% or 12%, or a range consisting between any two of the above values.

[0052] In some embodiments, the temperature of the hydrothermal reaction is 100-210°C, and the reaction time is 12-24h. The temperature is set in this way to effectively promote the reaction, so that the mixed solution penetrates into the pores of the porous carrier, lays the foundation for uniform loading, and significantly accelerates the hydrolysis, polycondensation reaction of the metal precursor (such as ammonium molybdate or its hydrate, lanthanum oxide), and the chemical bonding between the metal precursor and the surface functional groups of the porous carrier. The reaction time is set in this way to help achieve uniform and sufficient loading of the active components of the metal precursor (such as ammonium molybdate or its hydrate, lanthanum oxide) on the porous carrier.

[0053] Optionally, the temperature of the hydrothermal reaction may, for example, be 100°C, 120°C, 140°C, 160°C, 180°C, 200°C, or 210°C, or a range consisting between any two of the aforementioned values.

[0054] Optionally, the reaction time of the hydrothermal reaction may, for example, be 12h, 14h, 16h, 18h, 20h, 22h, or 24h, or a range consisting between any two of the aforementioned values.

[0055] In some embodiments, the temperature of the calcination treatment is 650-700°C, and the calcination time is 150-180min. This setting helps to ensure the sufficient decomposition of ammonium molybdate or its hydrate, the modifier, and the catalyst precursor formed by the hydrothermal reaction, promotes the formation and growth of MoO2, and makes the lanthanum oxide-doped molybdenum-based catalyst firmly anchored on the outer and inner surfaces of the porous carrier, thereby improving the thermal stability and service life of the lanthanum oxide-doped molybdenum-based supported catalyst. In addition, the calcination treatment can remove impurities in the reaction process, avoiding the occupation of active sites by impurities.

[0056] Optionally, the temperature of the calcination treatment may, for example, be 650°C, 660°C, 670°C, 680°C, 690°C, or 700°C, or a range consisting between any two of the aforementioned values.

[0057] Optionally, the calcination time may, for example, be 150min, 160min, 170min, or 180min, or a range consisting between any two of the aforementioned values.

[0058] In some embodiments, the inert atmosphere includes a nitrogen atmosphere. The nitrogen atmosphere avoids the excessive oxidation of MoO2 into MoO3, which has lower catalytic activity, thereby improving the catalytic activity and stability of the lanthanum oxide-doped molybdenum-based supported catalyst.

[0059] According to an embodiment of another aspect of the present application, there is provided a lanthanum oxide-doped molybdenum-based supported catalyst prepared by the preparation method as described above, comprising a porous carrier, and La2O3-doped MoO2 nanoparticles grown in situ on the surface of the porous carrier.

[0060] According to the embodiments of the present application, in the prepared lanthanum oxide doped molybdenum-based supported catalyst, the lanthanum oxide doping regulates the electronic structure of the molybdenum-based supported catalyst, and the modifier regulates the valence and morphology of MoO2. In combination of the synergistic effect of the lanthanum oxide and the modifier, the catalytic activity, durability and stability of the lanthanum oxide doped molybdenum-based supported catalyst can be improved without destroying the basic framework. The La2O3 doped MoO2 nanoparticles have a large specific surface area, thereby increasing the adsorption sites and further improving the catalytic reaction efficiency. The lanthanum oxide doped molybdenum-based supported catalyst has high catalytic activity, low cost and long service life.

[0061] In some embodiments, the average particle size of the La2O3 doped MoO2 nanoparticles is 0.6-1.5 μm. In this way, the roughness of the surface of the lanthanum oxide doped molybdenum-based supported catalyst can be further improved, the specific surface area is increased, and the number of active sites is expanded.

[0062] Alternatively, the average particle size of the La2O3 doped MoO2 nanoparticles may, for example, be 0.6 μm, 0.9 μm, 1.1 μm, 1.3 μm or 1.5 μm, or a range between any two of the above-mentioned values.

[0063] According to the embodiments of the present application, the lanthanum oxide doped molybdenum-based supported catalyst has high activity, durability and stability, can improve the reaction rate of the hydrogen evolution reaction, and has good hydrogen production catalytic efficiency and low cost when applied in the hydrogen production by alkaline water decomposition.

[0064] According to the embodiments of the present application, similarly to the foregoing, the lanthanum oxide doped molybdenum-based supported catalyst has high activity, durability and stability, can improve the reaction rate of the hydrogen evolution reaction, and has good hydrogen production catalytic efficiency and low cost when applied in the hydrogen production by alkaline water decomposition.

[0065] The technical solutions of the present application are further described and illustrated by specific examples. It should be noted that the specific examples described below are only illustrative, and the protection scope of the present application is not limited thereto.

[0066] Example 1

[0067] The preparation process of the lanthanum oxide doped molybdenum-based supported catalyst is as follows.

[0068] The foamed nickel is cut into small pieces with a size of 1 cm x 2 cm, and then the foamed nickel is pretreated. The pretreated porous nickel carrier is obtained by sequentially cleaning the foamed nickel in 2 mol / L hydrochloric acid solution, anhydrous ethanol and deionized water under ultrasonic conditions for 15 min, and then drying the cleaned foamed nickel at room temperature.

[0069] La2O3-MoO2 / Ni, 2.5% La2O3-MoO2 / Ni, 5% La2O3-MoO2 / Ni, 10% La2O3-MoO2 / Ni, 12% La2O3-MoO2 / Ni, MoO2 / Ni

[0070] Then, the pretreated porous nickel carrier was added into the premixed solution for hydrothermal reaction, the reaction temperature was 210℃, the reaction time was 20h, and the reaction system was cooled to room temperature, washed with deionized water and ethanol, and vacuum dried to obtain a precursor.

[0071] The precursor was placed into a furnace for calcination under N2 atmosphere, calcined at 650℃ for 180min, and then cooled to room temperature to obtain a lanthanum oxide doped molybdenum-based supported catalyst, which was 7.5% La2O3-MoO2 / Ni.

[0072] Example 2

[0073] The difference from Example 1 was that the amount of lanthanum oxide was 2.5% of the mass of ammonium molybdate tetrahydrate, and other experimental conditions were the same as those of Example 1, and a lanthanum oxide doped molybdenum-based supported catalyst was obtained, which was 2.5% La2O3-MoO2 / Ni.

[0074] Example 3

[0075] The difference from Example 1 was that the amount of lanthanum oxide was 5% of the mass of ammonium molybdate tetrahydrate, and other experimental conditions were the same as those of Example 1, and a lanthanum oxide doped molybdenum-based supported catalyst was obtained, which was 5% La2O3-MoO2 / Ni.

[0076] Example 4

[0077] The difference from Example 1 was that the amount of lanthanum oxide was 10% of the mass of ammonium molybdate tetrahydrate, and other experimental conditions were the same as those of Example 1, and a lanthanum oxide doped molybdenum-based supported catalyst was obtained, which was 10% La2O3-MoO2 / Ni.

[0078] Example 5

[0079] The difference from Example 1 was that the amount of lanthanum oxide was 12% of the mass of ammonium molybdate tetrahydrate, and other experimental conditions were the same as those of Example 1, and a lanthanum oxide doped molybdenum-based supported catalyst was obtained, which was 12% La2O3-MoO2 / Ni.

[0080] Comparative Example 1

[0081] The difference from Example 1 was that no lanthanum oxide was added, and other experimental conditions were the same as those of Example 1, and a molybdenum-based supported catalyst was obtained, which was MoO2 / Ni.

[0082] Figure 2SEM images of the catalysts prepared in Comparative Example 1 and Example 1, respectively; wherein (a) is the SEM image of Comparative Example 1; (b) is the SEM image of Example 1; (c) is a partial enlarged view of (b). From (a) to (c) in Figure 2 It can be observed from (a) to (c) in FIG. 1 that there is a relatively obvious difference in the morphology of the microstructure of the catalysts of MoO2 / Ni of Comparative Example 1 and 7.5% La2O3-MoO2 / Ni of Example 1. The surface of MoO2 / Ni of Comparative Example 1 is relatively smooth, and the pore structure is relatively regular, but there is no obvious nano-particle or roughness on the pore wall, which indicates that the specific surface area is limited, and the exposed active sites are less. Although some larger holes can be seen, these holes help the electrolyte to penetrate and the gas to escape, but the smoothness of the pore wall limits the number of active sites. In contrast, the surface of 7.5% La2O3-MoO2 / Ni of Example 1 is obviously rougher, and there are a large number of nano-particles uniformly dispersed on the pore wall. These nano-particles on the pore wall increase the roughness and irregularity of the surface, thereby greatly increasing the specific surface area of the catalyst. The presence of these nano-particles not only increases the physical contact area, but also introduces new chemical active sites, such as La-O bonds, Mo-O-La interfaces, etc., which play an important role in the adsorption and activation of water molecules.

[0083] Test Example

[0084] The electrochemical performance of Examples 1-5 and Comparative Example 1 was tested in 1.0 M KOH electrolyte, with a saturated calomel electrode as the reference electrode, and a scan rate of 5 mV·s -1 . The current curve as a function of voltage was recorded, and the results are shown in Table 1.

[0085] Table 1 Performance data of Examples 1-5 and Comparative Example 1

[0086]

[0087] Figure 3 LSV curve of the catalysts of Examples 1-5 and Comparative Example 1 at a current density of 10 mA / cm 2 . Figure 4 Tafel curve of the catalysts of Examples 1-5 and Comparative Example 1. It can be understood that the abscissa in FIG. 2 represents the logarithm of the absolute value. In combination with Table 1 and FIG. 2, Figure 4 Figure 3~Figure 4 ​It can be seen that, compared with Comparative Example 1, after doping La2O3 in Example 2, the overpotential does not change significantly, and the Tafel slope is relatively poor. After gradually increasing the doping amount of La2O3, the overpotential is significantly reduced, which indicates that the further increase of La2O3 significantly improves the catalytic activity. Among them, the 7.5% La2O3-MoO2 / Ni sample (Example 1) has a relatively lower overpotential (-0.115 V) and Tafel slope, which means that under this condition, the catalyst requires a relatively smaller overpotential and is more efficient; and as shown in Figure 2 As shown, although the unmodified MoO2 / Ni has macroscopic pores, the smooth surface severely limits its adsorption and activation ability to the reactants (such as H2O molecules), which is directly reflected in its relatively higher overpotential (-0.214 V), indicating that its catalytic intrinsic activity is low. After the increase of the doping amount of La2O3 from 2.5%, the overpotential of the catalyst for hydrogen evolution first decreases sharply and then slowly rises, and reaches a relatively optimal value of -0.115 V at a doping amount of 7.5%, with a decrease of about 100 mV. This significant performance improvement is not caused by a single factor, but by the deep synergistic effect between La2O3 and MoO2 in the electronic microstructure and macroscopic physical morphology.

[0088] From the perspective of electronic structure, the introduction of La2O3 plays a key role. As an efficient electronic regulator, it can effectively modulate the electronic distribution of MoO2, causing the shift of the d-band center. This fine-tuning of the electronic structure directly optimizes the adsorption behavior of the hydrogen intermediate on the catalyst surface, making the hydrogen adsorption free energy approach the ideal state of thermal neutrality, thereby significantly reducing the reaction energy barrier of steps such as water molecule dissociation and hydrogen atom recombination, and fundamentally improving the intrinsic activity of the catalytic site. At the level of morphology construction, La2O3 also shows excellent structure promotion function. It effectively induces the refinement and dispersion of MoO2 composite particles during synthesis with the modified agent ethanol, successfully constructing a rough surface with abundant nanostructures. This morphology evolution directly leads to a significant increase in the electrochemically active surface area, not only providing more available active sites for the reaction, but also optimizing the interface wettability of the electrode, creating favorable conditions for efficient mass transfer. When the doping amount of La2O3 exceeds 7.5%, the excess La2O3 (such as more than 12% doping amount) begins to exist in the form of agglomerates. These agglomerates not only physically cover the high-activity sites activated by the electronic effect, but also may block the three-dimensional porous structure of the catalyst, hindering the mass transfer process, ultimately leading to the breakdown of the synergistic balance and the decline of the catalytic performance.

[0089] Based on the analysis of the Tafel slope data and the overpotential, it can be seen that the introduction of La2O3 not only regulates the electronic structure of MoO2, but also provides more available active sites for the hydrogen evolution reaction, thereby significantly enhancing the HER activity of the catalyst.

[0090] Example 6:

[0091] The preparation process of this example 6 is substantially the same as that of example 1, except that the modifier added is different, which is glucose, and the mass of the added glucose is 0.125 g, to obtain a lanthanum oxide doped molybdenum-based supported catalyst, which is 7.5% La2O3-MoO2 / Ni (glucose).

[0092] Example 7:

[0093] The preparation process of this example 7 is substantially the same as that of example 1, except that the modifier added is different, which is acetic acid, and the volume of the added acetic acid is 10 mL, to obtain a lanthanum oxide doped molybdenum-based supported catalyst, which is 7.5% La2O3-MoO2 / Ni (acetic acid).

[0094] Comparative Example 2:

[0095] The preparation process of this comparative example 2 is substantially the same as that of example 1, except that no modifier is added, to obtain a lanthanum oxide doped molybdenum-based supported catalyst, which is 7.5% La2O3-MoO2 / Ni (no modifier).

[0096] Comparative Example 3:

[0097] The preparation process is substantially the same as that of example 1, except that cerium oxide is added instead of lanthanum oxide, which is 7.5% CeO2-MoO2 / Ni.

[0098] Test Example

[0099] The electrochemical performance of examples 6-7 and comparative examples 2-3 is tested in a 1.0 M KOH electrolyte, with a saturated calomel electrode as the reference electrode, and a scan rate of 5 mV·s -1 , and the current-voltage curve is recorded, the results of which are shown in Table 2 below.

[0100] Table 2 Hydrogen evolution overpotential and Tafel slope of the catalysts of examples 1, 6-7 and comparative examples 2-3 at a current density of 10 mA / cm 2

[0101]

[0102] Figure 5 LSV curve of the catalysts of examples 1, 6-7 and comparative examples 2-3 at a current density of 10 mA / cm 2 Figure 6 Tafel curve of the catalysts of examples 1, 6-7 and comparative examples 2-3, it can be understood that, similarly, Figure 4 Figure 6 ​​​The abscissa in the figure represents the logarithm of the absolute value. In combination with Table 2 and Figure 5~Figure 6 It can be seen that when glucose or acetic acid is used as a modifier, the catalyst performance is superior to that of Comparative Example 2 without adding a modifier, which fully proves the key role of the modifier in improving the catalytic performance. Specifically, the superiority of glucose lies in that the aldehyde group in its molecule can release a strong reducing gas during heat treatment, which not only ensures the reduction of Mo 6+ The precursor is efficiently reduced to active Mo 4+ , at the same time, creates abundant oxygen vacancies in the MoO2 lattice, significantly enhances the intrinsic conductivity of the catalyst and the adsorption capacity of the reaction intermediates. At the same time, glucose can also act as a soft template during decomposition, guiding the generation of nanostructures with larger specific surface area and more exposed active sites. As for acetic acid, its advantages lie in two aspects: on the one hand, its acidity can improve the dispersibility of the precursor solution, effectively inhibiting the agglomeration of MoO2 nanoparticles during growth, making them smaller in size and more uniform in distribution; on the other hand, the oxygen-containing functional groups produced by the decomposition of acetic acid at high temperatures can modify the catalyst surface, providing additional proton adsorption and transport sites, and its weak reducing property also helps to maintain the stable state of Mo 4+ , preventing its deactivation.

[0103] However, compared with ethanol, the above-mentioned modifiers have the following problems, for example, when glucose is used as a modifier, its carbonized product itself acts as a physical barrier to quickly consume and cover the active sites, in the acidic hydrothermal medium of the aforementioned pH, the stability of Mo 4+ is destroyed, and MoO2 precursor tends to form soluble [MoO2] 2+ cations, rather than the target product MoO2, which may cause the entire synthesis system to deviate from the preset path, generating a low-activity mixture wrapped in amorphous carbon, with uncertain components and fuzzy interfaces; similarly, the carboxyl group (-COOH) on acetic acid will have strong coordination with the metal precursor, and this competitive coordination seriously interferes with the in-situ and orderly growth and compounding process of MoO2 and La2O3 on the foamed nickel, i.e. prevents the formation of "La2O3-MoO2 composite particles" with high active interfaces, and instead generates a low-activity agglomerate with unknown morphology, at the same time, the acidic acetic acid environment is also not conducive to the exposure of specific crystal planes.

[0104] Without adding modifier, even if the amount of La2O3doping is the same (7.5%), the catalyst obtained has a higher overpotential (-0.339 V) and Tafel slope (353.2 mV / dec), which proves that without the induction of oxygen vacancies and structural regulation by the modifier, La2O3is difficult to disperse effectively and form an active interface with MoO2. The catalyst surface not only has a small number of active sites, but also has low intrinsic activity, so that water molecule dissociation becomes more difficult and the kinetic process is more sluggish. Finally, La2O3is easy to form isolated clusters or surface coating layers, which cannot effectively regulate the electronic structure of Ni / Mo.

[0105] Ethanol is the preferred modifier of the present application. As a monohydroxy modifier, ethanol has a mild and controllable chemical behavior, and it does not undergo a severe self-carbonization reaction, which does not significantly disturb the solution pH, thereby providing a stable reaction field for the in-situ and synchronous crystallization and compounding of MoO2and La2O3. In addition, the reducing property of ethanol and its weak coordination with metal centers can selectively induce oxygen vacancies in the MoO2lattice, and these defect sites become active sites for preferential anchoring and growth of MoO2compound nanoparticles, ultimately cooperatively constructing an ideal compound structure rich in oxygen vacancies and Mo-O-La high-activity interfaces.

[0106] In addition, under the same experimental conditions, not all rare earth element doping can significantly improve the overpotential, for example, doping CeO2. The reason is that the ionic radius of Ce 4+ (~0.87 Å) is quite different from that of Mo 4+ (~0.65 Å), which leads to stress or phase separation in the MoO2lattice, which in turn promotes particle aggregation. La 3+ ions can partially dope into the rutile structure lattice of MoO2, or exist in the form of La-O-Mo at the grain boundaries, which helps to stabilize the MoO crystal phase and prevent it from phase transition or dissolution during the hydrogen evolution reaction (especially under alkaline conditions for a long time); and La 3+ as a Lewis acid site can adsorb water molecules and promote their dissociation (H-OH bond breaking). Although CeO2also has a certain ability to adsorb and activate water molecules, its redox properties may lead to poor stability of surface species (such as Ce 3+ and -OH), so under the strong reducing environment of hydrogen evolution, CeO2surface may be over-reduced, losing its catalytic function, and even becoming an inert layer.

[0107] Figure 7 Figure 1 is a 48-hour chronoamperometry (CA) curve of the catalyst of Example 1; Figure 8 Figure 2 is a 48-hour chronopotentiometry (CP) curve of the catalyst of Example 1. Catalyst stability test: CA and CP tests were performed on the sample of Example 1, as described in Figure 7The stability of the catalyst of Example 1 was studied in 1.0M KOH electrolyte, and the CA test graph thereof with an applied potential of-1.25V (vs. RHE) showed that the current density rapidly decreased in the initial period of time, indicating that a rapid reaction or material consumption occurred on the electrode surface after the applied potential, resulting in a rapid decrease in the current density. With the passage of time, the current density gradually tended to be stable, and entered a relatively flat plateau, in which the current density value fluctuated slightly, indicating that a dynamic equilibrium state was reached, the reaction rate became relatively stable, and the catalyst still maintained a high current density within 48 hours, which proved that the 7.5% doped catalyst had good electrochemical stability and durability in an alkaline environment, and was suitable for subsequent application as a high-efficiency HER catalyst. See Figure 8 The CP test graph thereof with an applied current density of 0.1A / cm 2 The stability of the sample of Example 1 was studied in 1.0M KOH electrolyte, and the catalyst showed a large increase in potential in the initial period of time, followed by a gradual decrease in subsequent fluctuations, and finally tended to be stable, with a voltage of 2.0539V at the end, which was 0.31% lower than the highest voltage of 2.0604V at 1200 seconds. During the entire experiment, the potential was continuously maintained in a relatively stable range, indicating that the catalyst could maintain a relatively stable state in the reaction for a long time, which further proved that the doped sample exhibited good electrochemical performance and durability in long-time operation.

[0108] Mechanism analysis: Since La2O3 has good stability in an alkaline environment, and La2O3-doped MoO2 can form a stable solid solution structure, effectively inhibiting the dissolution of MoO2, the catalyst can still maintain good structure and catalytic performance in long-time operation. The synergistic effect of La2O3 and MoO2 significantly improves the electrocatalytic activity and durability of the lanthanum oxide-doped molybdenum-based supported catalyst, making it a high-efficiency HER catalyst with application prospects.

[0109] The above specific embodiments further illustrate the purpose, technical solutions and beneficial effects of the present application, and it should be understood that the above description is only for specific embodiments of the present application and is not intended to limit the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A method for preparing a lanthanum oxide-doped molybdenum-based supported catalyst, characterized in that, The preparation method includes: Ammonium molybdate or its hydrate, lanthanum oxide, and a modifier are mixed in water to form a mixture. A pretreated porous support is added to the mixture to carry out a hydrothermal reaction to obtain a catalyst precursor; The catalyst precursor was calcined under an inert atmosphere and then cooled to obtain the lanthanum oxide-doped molybdenum-based supported catalyst. The modifier includes at least one of ethanol, glucose, and acetic acid; The pretreated porous carrier was prepared by the following method: The porous carrier was ultrasonically washed sequentially with acidic solution, ethanol solution and water, and then dried. The porous carrier includes either nickel foam or graphite. Wherein, when the modifier is ethanol, the volume ratio of water to ethanol is 1:(0.5~1). When the modifier is glucose, the mass ratio of glucose to ammonium molybdate or its hydrate is (0.4~1):1; When the modifier is acetic acid, the volume ratio of water to acetic acid is 1:(0.5~1).

2. The preparation method according to claim 1, characterized in that, When the modifier is ethanol, the volume ratio of water to ethanol is 1:0.

9.

3. The preparation method according to claim 1, characterized in that, Let the mass of lanthanum oxide be a, and the mass of ammonium molybdate or its hydrate be b, with a / b being 5~12%.

4. The preparation method according to claim 1, characterized in that, The hydrothermal reaction is carried out at a temperature of 100~210℃ for 12~24h.

5. The preparation method according to claim 1, characterized in that, The calcination treatment is carried out at a temperature of 650~700℃ for 150~180 min, and the inert atmosphere includes a nitrogen atmosphere.

6. A lanthanum oxide-doped molybdenum-based supported catalyst prepared by the preparation method according to any one of claims 1 to 5, comprising a porous support and La2O3-doped MoO2 nanoparticles grown in situ on the surface of the porous support.

7. The lanthanum oxide-doped molybdenum-based supported catalyst according to claim 6, characterized in that, The average particle size of the La2O3-doped MoO2 nanoparticles is 0.6~1.5μm.

8. The application of a lanthanum oxide-doped molybdenum-based supported catalyst as described in claim 6 or 7 in alkaline water splitting for hydrogen production.

Images