A rare earth Ce-doped Ni5P4 porous nanosheet array and its preparation method and application

Abstract

The present invention belongs to the field of nanostructure preparation and discloses a rare earth Ce-doped Ni5P4 porous nanosheet array, its preparation method, and application. The present invention provides a method for improving the catalytic activity of nickel-based phosphides by heteroatom doping. By introducing heteroatom Ce, the intermediate adsorption / desorption behavior and electronic structure of the catalyst can be effectively adjusted, thereby achieving the effect of improving catalytic performance. The preparation process of the present invention is simple and easy, and the purpose of improving catalytic performance can be achieved by combining a coprecipitation reaction with a low-temperature phosphating treatment. The doping amount of the Ce element in the Ni5P4 porous nanosheet can be controlled by the addition amount of the Ce source, and the nanosheet can be used as an excellent bifunctional electrocatalyst in the electrocatalytic complete water splitting reaction.

Description

Technical Field

[0001] The present invention belongs to the field of nanostructure preparation, and in particular relates to a rare earth Ce-doped Ni5P4 porous nanosheet array and a preparation method and application thereof. Background Art

[0002] Over the past few decades, the search for new clean energy sources to replace traditional fossil fuels has been intensive, and significant progress has been made. Increasing amounts of green electricity generated by clean energy sources such as solar cells, wind turbines, and nuclear power plants contribute to sustainable development. However, the efficient storage of intermittent and excess electricity remains a significant challenge. Using intermittent and excess electricity to drive the electrocatalytic water splitting reaction into hydrogen is considered a promising energy storage method. However, the sluggish reaction kinetics of the two half-reactions in water electrolysis (including the hydrogen evolution reaction and the oxygen evolution reaction) result in significant energy consumption, hindering the widespread industrial application of water electrolysis technology. Although commercial electrocatalysts (primarily the precious metals Pt and Ir / Ru) can significantly accelerate the reaction kinetics of water electrolysis, their scarcity and high cost have hindered their large-scale industrial application. The search for alternative non-precious metal-based electrocatalysts, particularly bifunctional electrocatalysts that can operate efficiently in a simple two-electrode system, has become a research priority.

[0003] In recent years, various nickel-based materials, such as nickel phosphides, sulfides, nitrides, hydroxides, and oxides, have been developed as catalysts for water electrolysis. Among them, nickel phosphides (including Ni2P and Ni5P4) have attracted considerable attention due to their excellent conductivity and chemical stability. However, their catalytic activity lags far behind the requirements of practical applications due to a lack of active sites and unsatisfactory adsorption / desorption of reaction intermediates.

[0004] As the most abundant and typical rare earth element, Ce is particularly attractive due to its rich redox ability, good electronic / ionic conductivity, and high affinity for oxygen donors. In addition, the excellent multivalence of Ce provides flexible opportunities for strong electronic interactions with other metal cations or intermediates during water splitting. Therefore, Ce doping is expected to greatly enhance the electrolytic water splitting performance of nickel-based phosphides. However, related research is still very lacking. There is an urgent need to develop a method for simple and controllable Ce doping in nickel-based phosphides to further promote their practical application in the field of water electrolysis. Summary of the Invention

[0005] The purpose of the present invention is to address the deficiencies of the prior art and provide a rare earth Ce-doped Ni5P4 porous nanosheet array and its preparation method and application, specifically adopting the following technical solutions:

[0006] According to a first aspect of the present invention, a method for preparing a rare earth Ce-doped Ni5P4 porous nanosheet array is provided, comprising the following steps:

[0007] (a) Nickel nitrate, ammonium fluoride, urea, cerium nitrate, and water were mixed uniformly and sonicated for 0.5 h to 1 h to obtain a reaction precursor solution;

[0008] (b) placing the nickel foam substrate into the reaction precursor solution obtained in step (a), reacting for 5 h to 12 h, washing, and drying to obtain nickel-cerium double hydroxide nanosheet arrays;

[0009] (c) The nickel-cerium double hydroxide nanosheet array obtained in step (b) is subjected to a phosphating reaction to obtain a rare earth Ce-doped Ni5P4 porous nanosheet array.

[0010] The present invention provides a method for improving the catalytic activity of nickel-based phosphides by heteroatom doping. The introduction of heteroatom Ce effectively modulates the intermediate adsorption / desorption behavior and electronic structure of the catalyst, thereby improving catalytic performance. The preparation process of the present invention is simple and easy, requiring only a coprecipitation reaction combined with a low-temperature phosphating treatment to achieve the goal of improving catalytic performance. The addition of cerium nitrate achieves the nucleation growth of nickel-cerium double hydroxide in a single step, and further, the in-situ doping of cerium into nickel phosphide is achieved through a single-step phosphating process. The doping level can be conveniently controlled by adjusting the amount of cerium nitrate added.

[0011] Moreover, the doping amount of Ce element in Ni5P4 porous nanosheets can be controlled by the addition amount of Ce source, which is more suitable for industrial large-scale production.

[0012] Preferably, the molar ratio of nickel nitrate, ammonium fluoride, urea, and cerium nitrate in step (a) is 1:4:5:(0.03-0.1). Nickel nitrate, ammonium fluoride, urea, and cerium nitrate are added to a polytetrafluoroethylene autoclave, followed by addition of deionized water until the autoclave is 60%-80% filled, and ultrasonic stirring is performed to obtain a reaction precursor solution. A clean nickel foam substrate is then added to the reaction precursor solution, followed by a coprecipitation reaction. Ammonium fluoride and urea are used as coprecipitation regulators, which play a key role in product formation. The reaction is then carried out at 100°C for 5-12 hours to obtain nickel-cerium double hydroxide nanosheet arrays.

[0013] Preferably, in step (b), the nickel foam substrate is pretreated by sequentially immersing the nickel foam substrate in acetone and dilute hydrochloric acid solutions for ultrasonic cleaning, then washing with water and anhydrous ethanol, and drying. More preferably, the ultrasonic cleaning time is 10 minutes.

[0014] Preferably, in step (b), the washing and drying steps are: washing the nickel foam substrate after the reaction is completed with water and anhydrous ethanol repeatedly and alternately, and then drying at 60° C. for 4 h to 8 h.

[0015] Preferably, in step (c), the phosphating reaction process is as follows: the nickel foam substrate and sodium hypophosphite after washing and drying in step (c) are placed in two quartz boats respectively, and reacted in an argon protective atmosphere for 1 h to 3 h. More preferably, the amount of sodium hypophosphite used is 0.5 g to 1.5 g, the temperature is 350 ° C, and the heating rate is 2 ° C min -1 .

[0016] According to the second aspect of the present invention, there is also provided a rare earth Ce-doped Ni5P4 porous nanosheet array, which is prepared by the above-mentioned preparation method.

[0017] The rare earth Ce-doped Ni5P4 porous nanosheet array obtained in the present invention comprises a substrate and rare earth Ce-doped Ni5P4 porous nanosheets grown in situ on the substrate surface. The rare earth Ce-doped Ni5P4 porous nanosheets are uniformly and staggeredly grown in an array on a nickel foam substrate. The nanosheets have lateral dimensions of 2 to 10 μm and a thickness of 10 to 50 nm. The surface is rich in pores, each approximately 30 nm in size.

[0018] According to the third aspect of the present invention, there is also provided an application of the rare earth Ce-doped Ni5P4 porous nanosheet array in electrocatalytic water splitting, which can be used as an excellent bifunctional electrocatalyst in the electrocatalytic water splitting reaction.

[0019] The present invention provides a method for enhancing the catalytic activity of nickel-based phosphides by heteroatom doping. The introduction of heteroatom Ce effectively modulates the intermediate adsorption / desorption behavior and electronic structure of the catalyst, thereby enhancing catalytic performance. The preparation process is simple and easy, requiring only a coprecipitation reaction combined with a low-temperature phosphating treatment to achieve the desired catalytic performance. Furthermore, the Ce doping level in the Ni5P4 porous nanosheets can be controlled by adjusting the Ce source. The resulting nanosheets can be used as an excellent bifunctional electrocatalyst in electrocatalytic water splitting reactions. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 Shown are scanning electron microscope (SEM) images of nickel-cerium double hydroxide nanosheets not doped with Ce and nickel-cerium double hydroxide nanosheet arrays prepared in Example 1;

[0021] Figure 2Shown are scanning electron microscope (SEM) images, transmission electron microscope (TEM) images, and element distribution maps of the Ni5P4 porous nanosheet arrays not doped with Ce and the rare earth Ce-doped Ni5P4 porous nanosheet arrays prepared in Example 1;

[0022] Figure 3 Shown are X-ray diffraction (XRD) patterns of the Ni5P4 porous nanosheet arrays not doped with Ce and the rare earth Ce-doped Ni5P4 porous nanosheet arrays prepared in Example 1;

[0023] Figure 4 Shown are the nitrogen adsorption / desorption isotherms and the corresponding pore size distribution curves of the rare earth Ce-doped Ni5P4 porous nanosheet array prepared in Example 1;

[0024] Figure 5 Shown are scanning electron microscopy (SEM) images of Ni5P4 porous nanosheet arrays with different Ce doping amounts;

[0025] Figure 6 Shown is the electrocatalytic water splitting performance curve of the rare earth Ce-doped Ni5P4 porous nanosheet array prepared in Example 1. DETAILED DESCRIPTION

[0026] The following will be combined with the embodiments and drawings to clearly and completely describe the concept of the present invention and the technical effects produced, so as to fully understand the purpose, scheme and effect of the present invention. It should be noted that the embodiments and features in the embodiments of this application can be combined with each other unless there is a conflict.

[0027] Example 1

[0028] A rare earth Ce-doped Ni5P4 porous nanosheet array, the preparation method of which comprises the following steps:

[0029] The nickel foam substrate required for growth was prepared by the following steps: soaking the nickel foam substrate in acetone and dilute hydrochloric acid solutions, ultrasonically washing it for 10 minutes, then repeatedly washing it in deionized water and anhydrous ethanol before drying. Nickel nitrate, ammonium fluoride, urea, and cerium nitrate were then added to a polytetrafluoroethylene autoclave in a molar ratio of 1:4:5:0.05. Deionized water was then added to the autoclave to a fill level of 72%, and ultrasonic stirring was performed for 0.5 hours to obtain a reaction precursor solution. The prepared nickel foam substrate was then added to the reaction precursor solution and a coprecipitation reaction was carried out at 100°C for 8 hours. After the reaction, the substrate was alternately washed with deionized water and anhydrous ethanol, then placed in an oven and dried at 60°C for 6 hours to obtain nickel-cerium double hydroxide nanosheet arrays. The nickel-cerium double hydroxide nanosheet arrays grown on the nickel foam substrate and 1.0 g of sodium hypophosphite were placed in two quartz boats respectively. The quartz boats were then placed in a tube furnace and phosphated at 350 °C for 2 h in an argon protective atmosphere with a heating rate of 2 °C min -1 , that is, rare earth Ce-doped Ni5P4 porous nanosheet arrays are obtained.

[0030] Example 2

[0031] A rare earth Ce-doped Ni5P4 porous nanosheet array, the preparation method of which comprises the following steps (compared with Example 1, the amount of cerium nitrate, ultrasonic stirring time, and drying time are changed):

[0032] The nickel foam substrate required for growth was prepared by the following steps: soaking the nickel foam substrate in acetone and dilute hydrochloric acid solutions, ultrasonically washing for 10 minutes, then repeatedly washing in deionized water and anhydrous ethanol before drying. Nickel nitrate, ammonium fluoride, urea, and cerium nitrate were then added to a polytetrafluoroethylene autoclave in a molar ratio of 1:4:5:0.1. Deionized water was then added to the autoclave to a fill level of 72%, and ultrasonic stirring was performed for 1 hour to obtain a reaction precursor solution. The prepared nickel foam substrate was then added to the reaction precursor solution and a coprecipitation reaction was carried out at 100°C for 8 hours. After the reaction, the substrate was alternately washed in deionized water and anhydrous ethanol, then placed in an oven and dried at 60°C for 8 hours to obtain nickel-cerium double hydroxide nanosheet arrays. The nickel-cerium double hydroxide nanosheet arrays grown on the nickel foam substrate and 1.0 g of sodium hypophosphite were placed in two quartz boats respectively. The quartz boats were then placed in a tube furnace and phosphated at 350 °C for 2 h in an argon protective atmosphere with a heating rate of 2 °C min -1 , that is, rare earth Ce-doped Ni5P4 porous nanosheet arrays are obtained.

[0033] Example 3

[0034] A rare earth Ce-doped Ni5P4 porous nanosheet array, the preparation method of which comprises the following steps (compared with Example 1, the amount of cerium nitrate and the ultrasonic stirring time are changed):

[0035] The nickel foam substrate required for growth was prepared by the following steps: soaking the nickel foam substrate in acetone and dilute hydrochloric acid solutions, ultrasonically washing it for 10 minutes, then repeatedly washing it in deionized water and anhydrous ethanol before drying it for later use. Nickel nitrate, ammonium fluoride, urea, and cerium nitrate were added to a polytetrafluoroethylene autoclave in a molar ratio of 1:4:5:0.03. Deionized water was then added to the autoclave to a fill level of 72%, and ultrasonic stirring was performed for 1 hour to obtain a reaction precursor solution. The prepared nickel foam substrate was added to the reaction precursor solution and a coprecipitation reaction was carried out at 100°C for 10 hours. After the reaction, the substrate was alternately washed with deionized water and anhydrous ethanol, then placed in an oven and dried at 60°C for 6 hours to obtain nickel-cerium double hydroxide nanosheet arrays. The nickel-cerium double hydroxide nanosheet arrays grown on the nickel foam substrate and 1.0 g of sodium hypophosphite were placed in two quartz boats respectively. The quartz boats were then placed in a tube furnace and phosphated at 350 °C for 2 h in an argon protective atmosphere with a heating rate of 2 °C min -1 , that is, rare earth Ce-doped Ni5P4 porous nanosheet arrays are obtained.

[0036] Example 4

[0037] This example tests the electrocatalytic water splitting performance of the rare earth Ce-doped Ni5P4 porous nanosheet array prepared in Example 1, specifically comprising the following steps:

[0038] Electrocatalytic performance was tested using a symmetrical two-electrode system on an electrochemical workstation. Nanosheet arrays grown on nickel foam substrates were cut into 3 mm × 3 mm sections and used as both cathode and anode for water electrolysis. A 1 mol / L aqueous KOH solution was used as the electrolyte. Polarization curves were measured using linear sweep voltammetry at a scan rate of 0.002 V / s. All measured potentials were converted to reversible hydrogen electrode potentials.

[0039] Figure 1 a and 1b are photos of the prepared nickel metal hydroxide nanosheets (not doped with Ce) taken after SEM observation; Figure 1 Figures c and 1d are SEM images of the prepared nickel-cerium double hydroxide nanosheets (obtained in Example 1). As can be seen, the nickel-cerium double hydroxide nanosheets exhibit uniform nanosheet morphology on the nickel foam substrate. The nanosheets are arranged vertically and crosswise, with a smooth surface.

[0040] Figure 2 a and 2b are the prepared Ni5P4 porous nanosheet arrays (not doped with Ce). Figure 2 c and Figure 2 d is a photograph of the prepared rare earth Ce doped Ni5P4 porous nanosheet array (obtained in Example 1) taken after SEM and TEM observation. It can be seen that the rare earth Ce doped Ni5P4 porous nanosheet array obtained after low-temperature phosphating treatment maintains the nanosheet morphology. However, after phosphating, the nanosheet becomes rough and has a large number of holes. TEM image ( Figure 2 e. Figure 2 f. Figure 2 g) The porous structure was further verified. High-resolution TEM images of rare earth Ce-doped Ni5P4 porous nanosheets showed uniform lattice fringes with a spacing of 0.248 nm, corresponding to the (104) crystal plane of Ni5P4. Selected area electron diffraction patterns showed diffraction spots corresponding to Ni5P4 single crystals. The results showed that Ce doping did not produce a new phase, but only partially replaced Ni in the Ni5P4 lattice. In addition, the element distribution map ( Figure 2 h. Figure 2 i. Figure 2 j) Verification of the uniform distribution of Ni, Ce, and P elements in the rare earth Ce-doped Ni5P4 porous nanosheets. It is worth noting that due to the limited content of Ce, its signal is not particularly obvious.

[0041] Figure 3 is the undoped Ce ( Figure 3 a) and the rare earth Ce-doped Ni5P4 porous nanosheet array prepared in Example 1 ( Figure 3 b) XRD spectrum obtained by detection using an X-ray diffractometer. From the spectrum of the undoped Ni5P4 porous nanosheet array, it can be seen that three obvious characteristic peaks appear at 44.5°, 51.8° and 76.4°, which are typical characteristic peaks of the nickel foam substrate. In addition, the remaining diffraction peaks are very consistent with the diffraction peaks in the Ni5P4 standard card (JCPDS No.18-0883), which indicates the successful synthesis of the Ni5P4 phase. The XRD spectrum of the rare earth Ce-doped Ni5P4 porous nanosheet array does not show any new diffraction peaks compared to the undoped Ni5P4 porous nanosheet array, which indicates that the introduction of Ce will not change the original phase of Ni5P4. However, in Figure 3 As can be seen from the XRD pattern of the rare earth Ce-doped Ni5P4 porous nanosheet array, compared with the undoped Ni5P4 porous nanosheet array, the diffraction peak intensity of the Ni5P4 (210) crystal plane is significantly reduced, and the peak position also shifts significantly to the low-angle direction. This phenomenon can be attributed to the fact that the ionic radius of Ce is larger than that of Ni, and Ce doping will cause lattice distortion of Ni5P4.

[0042] Figure 4The nitrogen adsorption / desorption isotherm and the corresponding pore size distribution curve of the rare earth Ce-doped Ni5P4 porous nanosheet array prepared in Example 1 are shown in FIG. As can be seen, the nitrogen adsorption / desorption curve is a typical type IV isotherm ( Figure 4 a), there is an obvious adsorption hysteresis loop in the middle part, indicating that the rare earth Ce doped Ni5P4 porous nanosheet array has an obvious porous structure. Figure 4 As shown in b, the corresponding pore size distribution curve further shows that its pore size is mainly distributed in 30 nm.

[0043] Figure 5 The scanning electron microscope (SEM) images of Ni5P4 porous nanosheet arrays with different Ce doping amounts in Examples 1-3 are shown. Figure 5 a and Figure 5 b is a sample with a doping ratio of 1% (molar ratio) (obtained in Example 3), Figure 5 c and Figure 5 d is the sample with a doping ratio of 5% (obtained in Example 1), Figure 5 e and Figure 5 f is a sample with a doping ratio of 10% (obtained in Example 2). It can be seen that samples with different doping levels all have similar porous nanosheet morphologies, which shows that our preparation method can simply and conveniently adjust the Ce doping level without changing the sample morphology.

[0044] Figure 6 This is a graph showing the electrocatalytic water splitting performance of the rare earth Ce-doped Ni5P4 porous nanosheet array (at a doping ratio of 5%) prepared in Example 1. It can be seen that the rare earth Ce-doped Ni5P4 porous nanosheet array only requires a potential of 1.56 V to drive 10 mA / cm 2 The total water splitting current density ( Figure 6 a), and has obvious advantages over undoped Ni5P4 porous nanosheet arrays and recently reported related Ni-based phosphide bifunctional electrocatalysts (including Fe-doped Ni5P4 nanosheet arrays, Ni5P4 nanofilms, NiSe2 / Ni5P4 heterojunction nanosheets, etc.). In addition to having excellent catalytic activity, rare earth Ce-doped Ni5P4 porous nanosheet arrays also have excellent durability in the overall water splitting process, showing a very weak current density change within 10 hours at a constant voltage ( Figure 6 b).

[0045] Although the present invention has been described in considerable detail and with particularity with respect to several described embodiments, it is not intended to be limited to any of these details or embodiments or any particular embodiment, but rather should be construed as providing a broad possible interpretation of these claims in view of the prior art by reference to the appended claims, thereby effectively encompassing the intended scope of the invention. In addition, the invention has been described above in terms of embodiments foreseen by the inventors for the purpose of providing a useful description, and those insubstantial modifications of the invention that are not currently foreseen may still represent equivalent modifications of the invention.

Claims

1. A method for preparing rare earth Ce-doped Ni5P4 porous nanosheet array, characterized in that: The following steps are involved: (a) Nickel nitrate, ammonium fluoride, urea, cerium nitrate, and water were mixed uniformly and sonicated for 0.5 h to 1 h to obtain a reaction precursor solution; (b) placing the nickel foam substrate into the reaction precursor solution obtained in step (a), reacting for 5 h to 12 h, washing, and drying to obtain nickel-cerium double hydroxide nanosheet arrays; (c) subjecting the nickel-cerium double hydroxide nanosheet array obtained in step (b) to a phosphating reaction to obtain a rare earth Ce-doped Ni5P4 porous nanosheet array; In step (a), the molar ratio of nickel nitrate, ammonium fluoride, urea, and cerium nitrate is 1:4:5:(0.03-0.1); In step (c), the obtained rare earth Ce-doped Ni5P4 porous nanosheet array includes a substrate and rare earth Ce-doped Ni5P4 porous nanosheets in situ grown on the surface of the substrate; the nanosheets have a lateral size of 2 μm-10 μm, a thickness of 10 nm-50 nm, and abundant pores on the surface.

2. The preparation method according to claim 1, characterized in that In step (b), the nickel foam substrate needs to be pretreated. The specific process is: the nickel foam substrate is immersed in acetone and dilute hydrochloric acid solution in sequence for ultrasonic cleaning, then washed with water and anhydrous ethanol, and dried.

3. The preparation method according to claim 2, characterized in that The ultrasonic cleaning time is 10 min.

4. The preparation method according to claim 1, characterized in that In step (b), the washing and drying steps are: washing repeatedly and alternately with water and anhydrous ethanol, and then drying at 60° C. for 4 h to 8 h.

5. The preparation method according to claim 1, characterized in that In step (c), the phosphating reaction process is as follows: the nickel foam substrate and sodium hypophosphite washed and dried in step (c) are placed in two quartz boats respectively, and reacted in an argon protective atmosphere for 1 h to 3 h.

6. The preparation method according to claim 5, characterized in that The amount of sodium hypophosphite used is 0.5 g-1.5 g.

7. The preparation method according to claim 5, characterized in that The phosphating reaction conditions are: temperature of 350 °C, heating rate of 2 °C min -1 .

8. Rare earth Ce doped Ni5P4 porous nanosheet array, characterized in that, Prepared by the preparation method according to any one of claims 1 to 7.

9. Use of the rare earth Ce-doped Ni5P4 porous nanosheet array according to claim 8 in electrocatalytic water splitting.

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