A method for synthesizing an electrochemically reconstructed boron-doped nickel phosphide nanomaterial

Abstract

The application discloses a synthesis method of an electrochemically reconstructed boron-doped nickel phosphide nanomaterial and applies the boron-doped nickel phosphide nanomaterial to water electrolysis hydrogen evolution under alkaline conditions, and excellent catalytic performance is obtained. The application mainly dopes boron elements in a precursor Ni(OH)2, generates Ni5P4-B through phosphorization treatment, and then forms Ni3(BO3)2 / Ni5P4 through electrochemical reconstruction. After preliminary hydrothermal synthesis of Ni(OH)2 nanosheets, the precursor with the nanosheets is suspended in ice water, and ice water solutions of different concentrations of NaBH4 are dropped to prepare boron-doped Ni(OH)2. The boron-doped Ni(OH)2 precursor is heated and phosphorized in a tube furnace, the sample after phosphorization is fully activated through electrochemical cyclic voltammetry, and a heterostructure Ni3(BO3)2 / Ni5P4 is obtained. The heterostructure Ni3(BO3)2 / Ni5P4 exhibits outstanding electrocatalytic hydrogen evolution activity under alkaline conditions.

Description

Technical Field

[0001] This invention belongs to the field of clean and sustainable new energy preparation and application, and specifically relates to electrochemically reconstructed boron-doped nickel phosphide nanomaterials and their synthesis methods, and applies them to electrocatalytic hydrogen evolution. Background Technology

[0002] With rapid economic and social development, energy issues have become one of the most critical problems for countries worldwide. In today's society, fossil fuels remain the primary energy source. The large-scale and rapid consumption of fossil fuels inevitably leads to energy shortages, the release of large amounts of harmful gases, and environmental pollution such as the greenhouse effect. Clean and sustainable hydrogen energy is one of the effective ways to solve environmental pollution and the energy crisis, and has received high attention from governments worldwide. It is considered the most promising clean energy source of the 21st century and a strategic energy development direction for humanity. Among various hydrogen evolution methods, electrochemical water splitting is highly efficient, produces stable output, has high product purity, and can be mass-produced, making it very popular. Electrochemical catalytic water splitting, consisting of the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER), is considered an ideal, efficient, pollution-free, and recyclable pathway. Currently, platinum (Pt)-based materials are ideal and efficient catalysts for HER, but their high price and scarce reserves are the biggest obstacles to further commercial development.

[0003] Nanoarrays based on Earth's abundant elements are highly attractive, and optimizing electrochemical performance can significantly reduce costs and accelerate commercialization through the tuning of nanoarray composition, morphology, and structure. Nickel-based catalysts offer advantages such as high conductivity and low cost. However, nickel phosphide generally exhibits strong adsorption of active hydrogen, slow bubble desorption, and low catalytic activity. If the hydrogen adsorption on the nickel phosphide surface can be modulated to weaken its adsorption, it is expected to significantly improve hydrogen evolution activity. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention proposes an electrochemically reconstructed boron-doped nickel phosphide nanomaterial and its synthesis method.

[0005] The boron-doped nickel phosphide nanomaterials of this invention include a Ni3(BO3)2 / Ni5P4 heterostructure formed by electrochemical reconstruction. The boron-doped nickel phosphide nanosheets are between 40-80 nm in size. After electrochemical reconstruction, a significant change in the morphology of the nanosheet surface can be observed, and the hydrogen evolution performance is significantly improved.

[0006] The synthesis method of Ni3(BO3)2 / Ni5P4 / NF according to the present invention includes:

[0007] (1) A substrate is placed in the liner of an autoclave containing a precursor solution, wherein the precursor solution is a mixed aqueous solution of Ni(NO3)2·6H2O with a concentration of 0.05-0.1M, urea with a concentration of 0.2-0.4M, and NH4F with a concentration of 0.1-0.2M; after hydrothermal reaction at 100-120℃ for 10 hours, the substrate is washed with deionized water and ethanol to remove adsorbed impurities on the surface, and Ni(OH)2 nanosheet precursor is obtained on the substrate.

[0008] (2) The Ni(OH)₂ precursor was suspended in 45 ml of ice water. A 20 ml solution of 0.5-1.5 M NaBH₄ ice water was prepared. After stirring thoroughly, this solution was added dropwise to the ice water containing the suspended Ni(OH)₂. The mixture was stirred for 3 minutes after the addition was complete. The sample was removed, washed with deionized water, and dried under vacuum at 60 °C overnight. The Ni(OH)₂-B precursor was obtained on the substrate.

[0009] (3) Synthesis of Ni5P4-B: The Ni(OH)2-B precursor was placed downstream of a tube furnace, with NaH2PO2·H2O upstream. Argon was used as the protective gas. The heating rate was 5℃ / min. The sample was heat-treated at 350℃ for 2 hours. After the tube furnace cooled naturally to room temperature, the sample was taken out and Ni5P4-B / NF was applied to the substrate.

[0010] (4) Ni5P4-B was directly mounted on an electrode clamp as the working electrode, Hg / HgO as the reference electrode, and a carbon rod as the counter electrode. CV activation was performed in the range of 0V to -0.5V (relative to the standard hydrogen electrode). Ni5P4-B-After was obtained, i.e., the heterostructure Ni3(BO3)2 / Ni5P4.

[0011] Specifically, in step 3, the mass of NaH2PO2·H2O is 0.6g, which can better form Ni5P4-B.

[0012] Specifically, in step 4, the scan rate is 50 mV / s and the number of activation cycles is 30, which can better form Ni3(BO3)2 / Ni5P4.

[0013] In particular, porous nickel can be used as a substrate to provide a three-dimensional network framework.

[0014] The beneficial effects of this invention are: the surface boron is constructed by using an ice-water bath environment, and after heat treatment phosphating, Ni3(BO3)2 is constructed in situ in an alkaline medium by electrochemical cyclic voltammetry to form a Ni3(BO3)2 / Ni5P4 heterostructure, which significantly reconstructs the elemental composition and morphology of the surface, thereby achieving deep optimization of hydrogen adsorption during the hydrogen evolution process.

[0015] I. Electrochemical reconstruction allows the outer Ni3(BO3)2 to bond more tightly with the underlying nickel phosphide nanosheets, and significantly increases the number of interfaces and active sites on the nanosheets, resulting in a substantial increase in the active area during the catalytic process.

[0016] II. The extent of electrochemical performance optimization, differences in morphological changes, and the content of the reconstructed outer Ni3(BO3)2 are all related to the content of B in the precursor. The weakening of hydrogen adsorption by the reconstructed outer Ni3(BO3)2 is beneficial to balancing hydrogen adsorption and desorption during water electrolysis. Attached Figure Description

[0017] Figure 1 This invention prepares Ni5P4-B 0.6 (Comparative Example 2) Ni5P4-B 0.9 (Comparative Example 3), Ni5P4-B 1.2 (Comparative Example 1), Ni5P4-B 1.5 X-ray diffraction patterns of (Comparative Example 4) and Ni5P4 (Comparative Example 5).

[0018] Figure 2 This invention prepares Ni5P4-B 0.6 -After (Example 2), Ni5P4-B 0.9 -After (Example 3), Ni5P4-B 1.2 -After (Example 1), Ni5P4-B 1.5 X-ray diffraction patterns of Ni5P4-After (Example 4) and Ni5P4-After (Comparative Example 6).

[0019] Figure 3 This invention prepares Ni5P4-B 0.6 -After (Example 2), Ni5P4-B 0.9 -After (Example 3), Ni5P4-B 1.2 -After (Example 1), Ni5P4-B 1.5 -Comparison of electrochemical cyclic voltammetry curves after (Example 4) under 1M KOH conditions.

[0020] Figure 4 This invention prepares Ni5P4-B 1.2 - Comparison of electrochemical polarization curves of After (Example 1), Ni5P4 (Comparative Example 5), pure NF, and Pt / C NF under 1M KOH conditions.

[0021] Figure 5 This invention prepares Ni5P4-B 0.6 (Comparative Example 2) Ni5P4-B 0.9(Comparative Example 3), Ni5P4-B 1.2 (Comparative Example 1), Ni5P4-B 1.5 Scanning electron microscope images of Ni5P4 (Comparative Example 4) and Ni5P4 (Comparative Example 5).

[0022] Figure 6 This invention prepares Ni5P4-B 0.6 -After (Example 2), Ni5P4-B 0.9 -After (Example 3), Ni5P4-B 1.2 -After (Example 1), Ni5P4-B 1.5 -After (Example 4) and Ni5P4-After (Comparative Example 6) scanning electron microscope images.

[0023] Figure 7 This invention prepares Ni5P4-B 0.6 -After (Example 2), Ni5P4-B 0.9 -After (Example 3), Ni5P4-B 1.2 -After (Example 1) and Ni5P4-B 1.5 - Comparison of electrochemical polarization curves after (Example 4) under 1M KOH conditions. Detailed Implementation

[0024] This invention addresses both morphology and activity, reconstructing complex catalytic interfaces in situ while optimizing the reaction barrier of nickel phosphide in the HER process using heterostructures, thereby significantly improving electrocatalytic hydrogen evolution performance and promoting the application of nickel phosphide materials in industrial catalysis.

[0025] The technical solutions of the present invention will be further described below with reference to the embodiments. These embodiments should not be construed as limiting the technical solutions.

[0026] Example 1:

[0027] (1) First, the nickel foam (abbreviated as NF) was pretreated to remove the surface oxide layer. It was ultrasonically cleaned with 4M hydrochloric acid, acetone, distilled water and ethanol for 10, 5, 5 and 5 min respectively, and then dried with a high-speed Ar gas flow.

[0028] (2) Synthesis of Ni(OH)2 precursor: 0.58 g Ni(NO3)2·6H2O, 0.6 g urea, and 0.15 g NH4F were dissolved in 30 mL of deionized water and stirred vigorously for 20 min. The mixture was then transferred to a PTFE-lined autoclave. 2 × 3 cm nickel foam treated using method (1) was immersed in the lining of an autoclave used for hydrothermal synthesis. The autoclave was heat-treated at 120 °C for 10 hours. After cooling to room temperature, a distinct light green substance appeared on the surface of the nickel foam. The impurities adsorbed on the surface of the nickel foam were removed using deionized water and ethanol. Finally, the mixture was dried under vacuum at 60 °C for 12 hours.

[0029] (3) Ni(OH)2-B 1.2 Synthesis: The Ni(OH)₂ precursor was suspended in 45 ml of ice water. 20 ml of a 1.2 mol / L NaBH₄ ice-water solution was prepared. After stirring thoroughly, this solution was added dropwise to the ice-water solution containing the Ni(OH)₂ suspension. The mixture was stirred for 3 minutes after the addition was complete. An ice-water bath environment was maintained throughout the reaction. The sample was collected and labeled as Ni(OH)₂-B. 1.2 Wash with deionized water and vacuum dry overnight at 60°C.

[0030] (4)Ni5P4-B 1.2 Synthesis: Ni(OH)2-B 1.2 The precursor was placed downstream of a tube furnace, and 0.6 g of NaH2PO2·H2O was placed upstream of the tube furnace. Argon was used as the protective gas, and the heating rate was 5℃ / min. The sample was heat-treated at 350℃ for 2 hours. After the tube furnace cooled naturally to room temperature, the sample was removed to obtain the product, which was labeled as Ni5P4-B. 1.2 .

[0031] (5)Ni5P4-B 1.2 -After synthesis: Ni5P4-B 1.2 The electrode was directly mounted on an electrode clamp as the working electrode, Hg / HgO as the reference electrode, and a carbon rod as the counter electrode. CV activation was performed in the range of 0V to -0.5V (relative to the standard hydrogen electrode) at a scan rate of 50mV / s. After 30 cycles of activation, a heterostructure Ni3(BO3)2 / Ni5P4 was obtained, labeled Ni5P4-B. 1.2 -After.

[0032] Example 2

[0033] This embodiment is the same as Embodiment 1, except that the concentration of the NaBH4 ice-water solution is 0.6 mol / L. The product before CV activation and the product after CV activation are labeled as Ni5P4-B, respectively. 0.6 and Ni5P4-B 0.6-After.

[0034] Example 3:

[0035] This embodiment is the same as Embodiment 1, except that the concentration of the NaBH4 ice-water solution is 0.9 mol / L. The product before CV activation and the product after CV activation are labeled as Ni5P4-B, respectively. 0.9 and Ni5P4-B 0.9 -After.

[0036] Example 4:

[0037] This embodiment is the same as Embodiment 1, except that the concentration of the NaBH4 ice-water solution is 1.5 mol / L. The product before CV activation and the product after CV activation are labeled as Ni5P4-B, respectively. 1.5 and Ni5P4-B 1.5 -After.

[0038] Comparative Example 1:

[0039] (1) First, the nickel foam (abbreviated as NF) was pretreated to remove the surface oxide layer. It was ultrasonically cleaned with 4M hydrochloric acid, acetone, distilled water and ethanol for 10, 5, 5 and 5 min respectively, and then dried with a high-speed Ar gas flow.

[0040] (2) Synthesis of Ni(OH)2 precursor: 0.58 g Ni(NO3)2·6H2O, 0.6 g urea, and 0.15 g NH4F were dissolved in 30 mL of deionized water and stirred vigorously for 20 min. The mixture was then transferred to a high-pressure sterilizer liner made of polytetrafluoroethylene. A 2×3 cm nickel foam treated using method (1) was immersed in the liner of a high-pressure reactor used for hydrothermal synthesis. The high-pressure reactor was heat-treated at 120 °C for 10 hours. After cooling to room temperature, a distinct light green substance appeared on the surface of the nickel foam. The impurities adsorbed on the surface of the nickel foam were removed using deionized water and ethanol. Finally, it was dried under vacuum at 60 °C for 12 hours.

[0041] (3) Synthesis of Ni5P4: Ni(OH)2 precursor was placed downstream of a tube furnace, and 0.6g of NaH2PO2.H2O was placed upstream of the tube furnace. Argon was used as the protective gas. The heating rate was 5℃ / min. The sample was heat-treated at 350℃ for 2 hours. After the tube furnace cooled naturally to room temperature, the sample was taken out to obtain the product Ni5P4.

[0042] Comparative Example 2:

[0043] The Ni5P4 obtained in Comparative Example 1 was directly mounted on an electrode clamp as the working electrode, Hg / HgO as the reference electrode, and a carbon rod as the counter electrode. CV activation was performed in the range of 0V to -0.5V (relative to the standard hydrogen electrode) at a scan rate of 50mV / s. After 30 cycles of activation, the product was obtained and labeled as Ni5P4-After.

[0044] Figure 1 It is Ni5P4-B 0.6 Ni5P4-B 0.9 Ni5P4-B 1.2 Ni5P4-B 1.5 X-ray diffraction pattern of Ni5P4. Characteristic peaks at 44.34°, 51.67°, and 76.09° are characteristic peaks of porous nickel substrate, corresponding to the (1 1 1), (2 0 0), and (2 2 0) crystal planes (PDF#89-7128). Characteristic peaks of Ni5P4 appeared at multiple angles (PDF#89-2588). With increasing boron doping, the peak intensity of the characteristic peaks corresponding to Ni5P4 gradually decreased.

[0045] Figure 2 This invention prepares Ni5P4-B 0.6 -After (Example 2), Ni5P4-B 0.9 -After (Example 3), Ni5P4-B 1.2 -After (Example 1), Ni5P4-B 1.5 X-ray diffraction patterns of Ni5P4-After (Example 4) and Ni5P4-After (Comparative Example 2). Ni5P4-After retains the original characteristic peaks of Ni5P4 (PDF#89-2588) and Ni (PDF#89-7128). However, the original characteristic peaks of Ni5P4 in the final products of Examples 1-4 are weakened, and the characteristic peak of Ni3(BO3)2 appears at 25.9°, corresponding to the (1 1 0) crystal plane (PDF#73-1276). This indicates that after boron is incorporated into the Ni5P4 lattice, a new phase Ni3(BO3)2 will be formed during the electrochemical activation process.

[0046] Figure 3 This invention prepares Ni5P4-B 0.6 -After (Example 2), Ni5P4-B 0.9 -After (Example 3), Ni5P4-B 1.2 -After (Example 1), Ni5P4-B 1.5- Comparison of electrochemical cyclic voltammetry curves after (Example 4) under 1M KOH conditions. The cyclic voltammetry curves clearly show that as the electrochemical activation process proceeds, the curve gradually shifts downwards, indicating an improvement in hydrogen evolution performance. The extent of electrocatalytic optimization is linearly correlated with the B doping content, suggesting that performance optimization is related to surface Ni3(BO3)2 reconstruction.

[0047] Figure 4 This invention prepares Ni5P4-B 1.2 - Comparison of electrochemical polarization curves of Ni5P4-After (Example 1), Ni5P4-After (Comparative Example 2), pure NF, and Pt / CNF under 1M KOH conditions. (For example...) Figure 4 As shown, the catalytic activity of Ni5P4 nanosheets is poor when they exist alone. However, after electrochemical reconstruction of the nanosheets, the construction of Ni3(BO3)2 on the surface compensates for the original excessive H adsorption, resulting in significantly improved electrochemical activity at 10 mA / cm². -2 The turn-on voltage at current density is 33mV, which is significantly better than NF and Pt / C NF.

[0048] Figure 5 It is Ni5P4-B 0.6 Ni5P4-B 0.9 Ni5P4-B 1.2 Ni5P4-B 1.5 Scanning electron microscope (SEM) images of Ni5P4. With increasing boron content, the morphology undergoes subtle changes, maintaining the overall nanosheet morphology while increasing the number of pores.

[0049] Figure 6 This invention prepares Ni5P4-B 0.6 -After (Example 2), Ni5P4-B 0.9 -After (Example 3), Ni5P4-B 1.2 -After (Example 1), Ni5P4-B 1.5 -Scanning electron microscope (SEM) images of Ni5P4 after (Example 4) and Ni5P4 after (Comparative Example 2). New structural morphologies are generated on the surface of the nanosheets after electrochemical reconstruction; the higher the B content, the greater the morphological difference after electroactivation.

[0050] Figure 7 This invention prepares Ni5P4-B 0.6 -After (Example 2), Ni5P4-B 0.9 -After (Example 3), Ni5P4-B 1.2 -After (Example 1) and Ni5P4-B 1.5- Comparison of electrochemical polarization curves after (Example 4) under 1M KOH conditions. With increasing boron doping, the electrochemical activity of the material first increases and then decreases, consistent with a volcanic eruption relationship. This indicates that there is an optimal value for the surface Ni3(BO3)2 construction, and appropriate electrochemical reconstruction can optimize the electrocatalytic hydrogen evolution of Ni3(BO3)2 / Ni5P4.

[0051] This method achieves in-situ electrochemical reconstruction of boron-doped nickel phosphide nanomaterials and applies it to hydrogen evolution via water electrolysis under alkaline conditions, yielding excellent catalytic performance. The invention primarily involves doping boron into the precursor Ni(OH)₂, generating Ni₅P₄-B through phosphating, and then electrochemically reconstructing it to form Ni₃(BO₃)₂ / Ni₅P₄. After initial hydrothermal synthesis of Ni(OH)₂ nanosheets, the precursor with attached nanosheets is suspended in ice water, and different concentrations of NaBH₄ ice-water solutions are added dropwise to prepare boron-doped Ni(OH)₂. The boron-doped Ni(OH)₂ precursor is then phosphated in a tube furnace. The phosphated sample is fully activated by electrochemical cyclic voltammetry to obtain the heterostructure Ni₃(BO₃)₂ / Ni₅P₄. Reconstruction significantly affects the surface elemental composition and morphology, achieving deep optimization of hydrogen adsorption during the hydrogen evolution process. Electrochemical reconstruction allows for a tighter bond between the outer Ni3(BO3)2 layer and the underlying nickel phosphide nanosheets, significantly increasing the number of interfaces and active sites on the nanosheets, thus greatly enhancing the active area during catalysis. The extent of electrochemical performance optimization, morphological changes, and the content of the reconstructed Ni3(BO3)2 layer are all related to the boron content in the precursor. The reduced hydrogen adsorption by the reconstructed Ni3(BO3)2 layer is beneficial for balancing hydrogen adsorption and desorption during water electrolysis. The optimal performance of the material prepared by this method is at 10 mA / cm². -2 The turn-on point requires only 33mV at current density, which has great potential for industrial applications.

Claims

1. A method for synthesizing electrochemically reconstructed boron-doped nickel phosphide nanomaterials, characterized in that, Includes the following steps: (1) A substrate is placed in the liner of a high-pressure reactor containing a precursor solution, wherein the precursor solution is a mixed aqueous solution of Ni(NO3)2·6H2O with a concentration of 0.05-0.1 M, urea with a concentration of 0.2-0.4 M, and NH4F with a concentration of 0.1-0.2 M; after hydrothermal reaction at 100-120 °C for 10 hours, the substrate is washed with deionized water and ethanol to remove adsorbed impurities on the surface, and Ni(OH)2 nanosheet precursor is obtained on the substrate; (2) The Ni(OH)2 precursor was suspended in 45 ml of ice water; 20 ml of 0.5-1.5 M NaBH4 ice water solution was prepared; after stirring evenly, it was added dropwise to the ice water containing Ni(OH)2; after the addition was completed, the solution was stirred for 3 minutes; the sample was removed, washed with deionized water, and dried under vacuum at 60 °C overnight to obtain the Ni(OH)2-B precursor on the substrate; (3) Synthesis of Ni5P4-B: The Ni(OH)2-B precursor was placed downstream of a tube furnace, with NaH2PO2·H2O upstream. Argon was used as the protective gas. The heating rate was 5 °C / min. The sample was heat-treated at 350 °C for 2 hours. The sample was removed after the tube furnace cooled naturally to room temperature. (4) Ni5P4-B was directly mounted on the electrode clamp as the working electrode, Hg / HgO was used as the reference electrode, and carbon rod was used as the counter electrode; CV activation was performed in the range of 0 V to -0.5 V to obtain the heterostructure Ni3(BO3)2 / Ni5P4.

2. The synthesis method according to claim 1, characterized in that, In step 3, the mass of NaH2PO2·H2O is 0.6 g.

3. The synthesis method according to claim 1, characterized in that, In step 4, the scanning rate is 50 mV / s and the number of activation cycles is 30.

4. The synthesis method according to claim 1, characterized in that, The substrate is porous nickel.

Images