Biomass-based carbon-supported ferronickel bimetallic phosphide catalyst as well as preparation method and application thereof

Abstract

The invention relates to the field of electrocatalyst new materials, and particularly provides a biomass-based carbon-supported ferronickel bimetallic phosphide catalyst and a preparation method and application thereof.The catalyst is prepared from waste corn straw biomass, phytic acid as a phosphorus source and bimetallic nickel and iron, and the catalyst is applied to electrocatalytic synthesis of ammonia. According to the present invention, the efficiency is improved and the problems of high energy consumption, high pollution and the like are effectively solved through the electro-catalysis technology at the normal temperature and the normal pressure, the prepared catalyst has excellent ammonia production performance, the ammonia production efficiency and the Faraday efficiency are improved and the optimal voltage is reduced compared with the single metal catalyst, and the technical and use requirements in the actual production process can be met.

Description

Technical Field

[0001] This invention relates to the field of novel electrocatalyst materials, and in particular to a biomass-based carbon-supported nickel-iron bimetallic phosphide catalyst, its preparation method, and its application. Background Technology

[0002] Ammonia is a crucial raw material for synthetic chemicals. In agriculture, it's used to produce nitrogen fertilizers such as urea and ammonium bicarbonate. Industrially, it's used for refrigeration, and in the synthesis of resins, plastics, and desulfurization. It also has applications in semiconductor manufacturing and as a precursor to explosives. Currently, global annual synthetic ammonia production exceeds 100 million tons, supporting global food security and industrial development. Traditional industrial ammonia production has received widespread attention due to its high energy consumption and pollution levels. Research is being conducted combining renewable energy and electrochemical technologies to produce N2 or NO3... - The reduction to NH3 at room temperature and normal pressure has dual advantages: on the one hand, it significantly reduces energy consumption and carbon emissions; on the other hand, it can utilize nitrates in wastewater for pollution control and resource utilization. Therefore, the development of efficient and low-cost electrocatalysts, especially carbon-supported metal materials prepared from renewable biomass, has significant scientific importance and application prospects.

[0003] Biomass-derived carbon has four main advantages: First, the pyrolysis of biomass precursors (such as straw, fruit shells, and algae) forms a rich microporous network, providing numerous metal loading sites, promoting reactant diffusion and product desorption. Second, its high specific surface area and porous structure facilitate catalyst preparation. Third, controllable surface functional groups are beneficial for metal particle anchoring and electronic regulation. Fourth, the use of waste biomass makes resources renewable and cost-effective. Finally, the surface functional groups and pore structure can be further modified to meet different reaction requirements, achieving precise control of catalytic sites and facilitating subsequent functionalization. However, current technologies for preparing biomass-derived carbon still suffer from several drawbacks, including the influence of impurity elements and limited conductivity.

[0004] Metal phosphides possess excellent electrical conductivity. Phosphorus forms strong covalent bonds with the metal, facilitating rapid electron transport at the catalytic interface and reducing charge transfer impedance. Simultaneously, the electronegativity of phosphorus atoms and the coordination between metals allow for fine-tuning of the metal's d-level distribution, thereby optimizing intermediate adsorption and activation barriers, resulting in a tunable electronic structure. Metal phosphides also contribute to increasing the number of exposed active sites on the catalyst, enriching the active sites. However, the active sites of single-metal phosphide catalysts are often not well-defined, limiting catalytic selectivity and efficiency. This means the catalyst may simultaneously promote multiple reactions, reducing the selectivity of the target product. Furthermore, metal phosphide catalysts exhibit poor stability and durability over long-term use; the phosphorus composition may change, or the catalyst surface may undergo reconstruction, leading to decreased catalytic activity. Due to the complexity and high toxicity of organophosphorus synthesis processes, their limited large-scale application is restricted. Additionally, the production of large amounts of toxic PH3 gas during the preparation of metal phosphides from hypophosphite also limits their large-scale use.

[0005] Patent CN119465241A discloses a biomass-based carbon-supported iron phosphide nanocatalyst, its preparation method, and its application. This invention uses waste biomass grapefruit peel as the raw material for carbon materials, organic phytic acid solution as the phosphorus source, and iron salt as the iron source. The FeP / PGP nanocatalyst is obtained directly in situ by calcination in a tube furnace under an argon atmosphere. However, the optimal voltage of this patent is -0.5V, which is relatively high and consumes a lot of energy, making it unsuitable for electrocatalytic ammonia synthesis at low voltages.

[0006] Patent CN119465231A discloses a nitrogen-phosphorus co-doped nickel-iron based porous biochar catalyst, its preparation method and application. However, this invention uses a two-step method to prepare the catalyst, which is divided into two independent stages: support preparation and active component loading. The reaction system needs to change the reaction environment or separate intermediate products. This discontinuous operation results in a low LSV current density and poor catalytic effect.

[0007] Therefore, there is an urgent need to develop a catalyst that is inexpensive, safe, environmentally friendly, and can efficiently catalyze the synthesis of ammonia. Summary of the Invention

[0008] In response to the environmental problems and resource waste caused by large amounts of biomass waste, as well as the energy consumption and environmental pollution caused by traditional industrial ammonia production, this invention provides a biomass-based carbon-supported nickel-iron bimetallic phosphide catalyst, its preparation method, and its application. This invention aims to make full use of waste corn stalk biomass, using phytic acid as a phosphorus source, and utilizing nickel and iron bimetals to improve electrocatalytic performance and stability, thereby meeting the needs of actual production.

[0009] This invention provides a bimetallic phosphorus source catalyst. Compared to monometallic catalysts, the bimetallic structure enhances the catalyst's structural stability, reduces the loss and aggregation of active components, and allows for more flexible electronic structure control, optimizing the adsorption energy of reaction intermediates and lowering the reaction energy barrier, thereby improving catalytic efficiency. Iron and nickel exhibit complementary activities in catalytic reactions; iron has a strong adsorption capacity, while nickel has a good dissociation capacity for hydrogen, and their combined structure is relatively stable. The alloy structure formed by iron and nickel can improve the catalyst's structural stability. Nickel-iron bimetallic phosphides can fully utilize the advantages of these two metals to achieve efficient nitrogen activation and hydrogen addition, thereby increasing the reaction rate of ammonia synthesis compared to monometallic catalysts.

[0010] This invention makes full use of waste biomass materials, converting them in situ into bimetallic phosphide catalysts, and applying them to electrocatalytic ammonia synthesis, thereby providing a new ammonia synthesis catalyst.

[0011] The first aspect of the present invention provides a biomass-based carbon-supported nickel-iron bimetallic phosphide catalyst, comprising corn stalk biomass and FeP4 and NiP particles supported on carbon materials.

[0012] The biomass-based carbon-supported nickel-iron bimetallic phosphide catalyst is prepared by loading FeP4 and NiP particles onto corn stalk powder, abbreviated as NiFeP / PBC, wherein the loading of FeP4 accounts for 19.08-26.45% of the total mass of the catalyst, and the loading of NiP accounts for 19.82-22.71% of the total mass of the catalyst; wherein the phosphorus source is phytic acid.

[0013] Preferably, the biomass-based carbon-supported nickel-iron bimetallic phosphide catalyst contains, by elemental proportion, 5.93-8.22% Fe, 12.97-14.86% Ni, and 19.93-26.05% P. In addition, it also contains C and other impurity elements derived from biochar materials.

[0014] A second aspect of this invention provides a preparation method for a biomass-based carbon-supported nickel-iron bimetallic phosphide catalyst, comprising the following steps: 1) Add phosphorus source precursor, iron source precursor and nickel source precursor to pretreated corn stalk powder, pour in an appropriate amount of deionized water, stir for 6-12 hours until the mixture is uniform, adjust the pH value with alkaline solution, and place in an oven to dry. 2) The dried material from step 1) and the alkali metal hydroxide are mixed and ground in a mass ratio of 1:2 until the sample and alkali metal hydroxide are evenly mixed and in powder form. The mixture is placed in a tube furnace, inert gas is introduced, and the mixture is calcined at high temperature and then cooled to room temperature. The mixture is washed with water and anhydrous ethanol until neutral and then dried to obtain the catalyst.

[0015] Preferably, the iron source precursor is one of ferric chloride hexahydrate, ferric nitrate, ferric sulfate, and ferric acetate; the nickel source precursor is one of nickel chloride hexahydrate, nickel nitrate, and nickel acetate; and the phosphorus source precursor is phytic acid. The mass ratio of the phosphorus source precursor, iron source precursor, nickel source precursor, and corn stalk powder is (20-30):(6-9):(3.5-5.5):(5-15), and the mass ratio of corn stalk powder to deionized water is 1:15. The inert gas is nitrogen or argon, and the alkali metal hydroxide is sodium hydroxide or potassium hydroxide.

[0016] Preferably, the alkaline solution in step 1) is a 1M sodium hydroxide solution or a 1M potassium hydroxide solution. The original system in step 1) is a strongly acidic solution due to the presence of phytic acid. Adding an alkaline solution to adjust the pH of the system to 4-5 can promote the chelation of phytic acid with iron and nickel ions.

[0017] Preferably, the temperature of the oven in step 1) is set to 70-100℃ and the time is 8-12h.

[0018] Preferably, the alkali metal hydroxide mentioned in step 2) is sodium hydroxide or potassium hydroxide, and more preferably solid potassium hydroxide, in order to increase the porosity of corn stalk biochar, increase the surface area, and form porous carbon.

[0019] Preferably, the procedure for the tubular furnace in step 2) is to heat to 500-800°C at a rate of 5°C / min and hold for 2 hours.

[0020] Preferably, the drying conditions in step 2) are drying in an oven at 70-80°C for 8-12 hours.

[0021] Preferably, the pretreatment of the corn stalk powder specifically includes the following steps: The corn stalks are crushed, passed through a 40-mesh sieve, washed with deionized water, and then a 1M hydrochloric acid solution is added, with the solid-liquid ratio of corn stalk powder to 1M hydrochloric acid solution being 1:10. The mixture is completely soaked for 4-6 hours and then placed in an oven to dry at 70-100℃ for 8-12 hours to obtain the treated corn stalk powder.

[0022] The formation mechanism of the above NiFeP / PBC is as follows: Phytic acid contains abundant phosphate groups and has a strong chelating ability. Further adjusting the pH of the system to 4-5 can promote the reaction of phosphate groups with Fe. 3+ Ni 2+Chelation occurs, forming stable metal-phosphate complexes. After high-temperature pyrolysis, the strong coordination between phytic acid and metal ions drives the in-situ formation of metal phosphides, which are loaded in the form of particles on the surface and pore edges of the biomass carbon support. The resulting catalyst exhibits a blocky aggregate morphology, with metal phosphide particles uniformly anchored on the surface and pore edges of the biomass carbon.

[0023] Furthermore, in the ammonia synthesis reaction, iron has a strong nitrogen adsorption capacity, while nickel has a good hydrogen dissociation capacity. The iron-nickel bimetallic catalyst can make full use of the advantages of these two metals to achieve efficient nitrogen activation and hydrogen addition, thereby increasing the reaction rate of ammonia synthesis. Moreover, the alloy structure formed by iron and nickel can improve the structural stability of the catalyst. This alloy structure can prevent the metal particles from agglomerating and sintering under high-temperature reaction conditions, thereby maintaining the active surface area of ​​the catalyst.

[0024] The nickel-iron bimetallic catalyst prepared by the above method exhibits a blocky, strongly magnetic appearance and a light brown color.

[0025] The third aspect of this invention provides the application of a biomass-based carbon-supported nickel-iron bimetallic phosphide catalyst in the electrocatalytic synthesis of ammonia from nitrite.

[0026] Preferably, the electrocatalysis is carried out in an H-type electrolytic cell, using a biomass-based carbon-supported nickel-iron bimetallic phosphide catalyst as the working electrode, Ag / AgCl as the reference electrode, and C as the counter electrode.

[0027] Preferably, the specific steps of the electrocatalysis are as follows: 1) The biomass-based carbon-supported nickel-iron bimetallic phosphide catalyst is prepared into a slurry and drop-coated onto a glassy carbon electrode as a working electrode; 2) Dissolve NaNO2 in 1M NaOH solution to make the concentration of NaNO2 0.1M, and then perform electrochemical electrolysis.

[0028] Preferably, the mass ratio of the biomass-based carbon-supported nickel-iron bimetallic phosphide catalyst to NaNO2 is (0.8-1.0):(5000-10000).

[0029] Preferably, the preparation steps of the slurry in step 1) are as follows: Take 8-10 mg of the biomass-based carbon-supported nickel-iron bimetallic phosphide catalyst and dissolve it in 0.9-1 mL of anhydrous ethanol, add 50-60 μL of a perfluorosulfonate naphthol membrane solution with a resin solid content of 5-10 wt%, and sonicate at 480 W for 40-60 min to obtain the slurry.

[0030] Preferably, the above electrolysis system was subjected to an electrochemical electrolysis test for 1 hour. The ammonia yield was tested according to the national standard "Determination of Ammonia Nitrogen in Water - Nessler's Reagent Spectrophotometric Method (HJ 535-2009)," and the Faraday efficiency was calculated. The electrolysis test was conducted at voltages ranging from 0.0V to -0.6V vs. RHE. The results showed that at -0.2V vs. RHE, the ammonia yield reached 120-176.51 μmol·h⁻¹. -1 ·cm -2 Faraday efficiency reached 60%-92%.

[0031] The beneficial effects of this invention are as follows: (1) This invention uses waste biomass corn stalk powder as raw material and phytic acid as phosphorus source. It uses nickel and iron bimetallic catalysts to prepare the catalyst. The preparation method of this material is a new method in the field of electrocatalytic ammonia synthesis. The electronic interaction between different metal elements in the bimetallic phosphide can regulate the electronic structure, enhance the selective adsorption and catalytic ability of the active center, and make it easier to optimize the reaction path by adjusting the composition, reduce the generation of by-products, and improve the selectivity of the target product. When this material is applied to the field of electrocatalytic ammonia synthesis, it greatly saves energy consumption and reduces the application of harmful reagents and solutions. Compared with single metal catalysts, it improves the ammonia production efficiency and Faraday efficiency and reduces the optimal voltage.

[0032] (2) The present invention uses waste biomass to greatly solve the environmental pollution problems such as straw burning, realizes waste utilization, and provides solutions and application value for the construction of cheap, green and efficient synthetic ammonia catalysts.

[0033] (3) The present invention adopts a one-step preparation method. The carbonization of the carrier (PBC) and the phosphating of the active component (NiFeP) are completed simultaneously in the same reaction system and the same temperature reaction process. There is no need to separate intermediate products. The reaction environment is continuous and the component ratio is easier to control. This makes the NiFeP particles more uniform in size and better dispersed. It is also highly compatible with the pore structure of PBC, ensuring the exposure of active sites.

[0034] In summary, this invention has developed a biomass-based carbon-supported nickel-iron bimetallic phosphide catalyst. By combining biomass with metal phosphides, it not only improves production efficiency but also reduces production costs. Attached Figure Description

[0035] Figure 1 These are scanning electron microscope images of NiFeP / PBC prepared in Example 1 of this invention at different magnifications. Figure 2 The elemental mapping distribution of NiFeP / PBC prepared in Example 1 of this invention; Figure 3The X-ray diffraction pattern of NiFeP / PBC prepared in Example 1 of this invention; Figure 4 The image shows the X-ray photoelectron spectrum of NiFeP / PBC prepared in Example 1 of this invention, where a is the C 1s fine spectrum, b is the Fe 2p fine spectrum, c is the Ni 2p fine spectrum, and d is the P 2p fine spectrum. Figure 5 These are scanning electron microscope images of NiFeP / PBC prepared in Example 2 of this invention at different magnifications. Figure 6 These are scanning electron microscope images of NiFeP / PBC prepared in Example 3 of this invention at different magnifications. Figure 7 These are scanning electron microscope images of NiFeP / PBC prepared in Example 4 of this invention at different magnifications. Figure 8 The reduction of NO2 under different voltages of NiFeP / PBC prepared in Example 1 of this invention. - Ferrari efficiency and ammonia yield graph; Figure 9 The cyclic electrolysis diagram of NiFeP / PBC prepared in Example 1 of this invention under the optimal voltage; Figure 10 The reduction of NO2 under different voltages of NiFeP / PBC prepared in Example 2 of this invention. - Ferrari efficiency and ammonia yield graph; Figure 11 The cyclic electrolysis diagram of NiFeP / PBC prepared in Example 2 of this invention under the optimal voltage; Figure 12 The reduction of NO2 under different voltages of NiFeP / PBC prepared in Example 3 of this invention. - Ferrari efficiency and ammonia yield graph; Figure 13 The cyclic electrolysis diagram of NiFeP / PBC prepared in Example 3 of this invention under the optimal voltage; Figure 14 These are scanning electron microscope images of NiFe / BC prepared in Comparative Example 1 of this invention at different magnifications. Figure 15 The reduction of NO2 by NiFe / BC under different voltages prepared in Comparative Example 1 of this invention - Ferrari efficiency and ammonia yield graph; Figure 16 This is a comparison diagram of the electrochemical active areas of NiFe / BC prepared in Comparative Example 1 of this invention; Figure 17 This is a comparison diagram of the electrical impedance of NiFe / BC prepared in Comparative Example 1 of this invention; Figure 18These are scanning electron microscope images of NiP / PBC prepared in Comparative Example 2 of this invention at different magnifications. Figure 19 The linear sweep voltammetry (LSV) plots obtained by measuring the catalysts prepared in Comparative Example 2 and Example 1 at a voltage of -0.5 to 0.1 V are shown below. Figure 20 These are scanning electron microscope images of NiFeP / BC prepared using Comparative Example 3 at different magnifications in this invention. Figure 21 The image shows the linear sweep voltammetry (LSV) plots obtained by measuring the catalysts prepared in Comparative Example 3 and Example 1 at a voltage of -0.5 to 0.1 V. Detailed Implementation

[0036] Other materials used in this invention, unless otherwise stated, are commercially available. Other terms used in this invention, unless otherwise specified, generally have the meanings commonly understood by those skilled in the art. The invention is further described in detail below with reference to specific embodiments and data. The following embodiments are merely illustrative and not intended to limit the scope of the invention in any way.

[0037] Example 1 A biomass-based carbon-supported nickel-iron bimetallic phosphide catalyst was prepared according to the following steps: 1) Sample preparation: 10g of corn stalks were crushed, passed through a 40-mesh sieve, washed with deionized water, and then soaked in 1M hydrochloric acid solution at a solid-liquid ratio of 1:10 for 6 hours to remove impurities. The soaked corn stalks were then placed in an 80℃ oven and dried for 12 hours until completely dry. 1g of the dried corn stalks were mixed with ferric chloride hexahydrate, nickel chloride hexahydrate, and phytic acid in a mass ratio of 1:0.81:0.48:2.5. 15mL of deionized water was added, and the mixture was stirred continuously for 6 hours to ensure homogeneity. The stirred sample was then adjusted to pH 4 by adding 1M NaOH dropwise and placed in an 80℃ oven for 12 hours until completely dry to obtain sample NFP-1. 2) Weigh and grind 1g of sample NPB-1 and potassium hydroxide solid at a mass ratio of 1:2, place them in a porcelain boat, and put them in a tube furnace. Introduce argon gas and heat the furnace to 600℃ at a heating rate of 5℃ / min. Hold the temperature for 2 hours. After cooling to room temperature, wash the sample with deionized water and anhydrous ethanol until neutral, and place it in an 80℃ oven to dry for 12 hours to obtain NiFeP / PBC catalyst.

[0038] Figure 1 The medium scanning electron microscope image clearly shows that the NiFeP / PBC sample exhibits a blocky accumulation.

[0039] Figure 2The elemental mapping diagram shows that Ni, Fe, P, and C are uniformly distributed. Fe accounts for 7.08 wt% of the total catalyst mass, Ni accounts for 13.92 wt%, and P accounts for 22.99 wt%. The FeP4 loading is 22.75 wt%, and the NiP loading is 21.26 wt%. The FeP4 loading is calculated according to the formula (wt...). Fe ×M FeP4 ) / M Fe Calculations show that the NiP loading amount is calculated according to the formula (wt) Ni ×M NiP ) / M Ni Calculations show that wt Fe M represents the mass content of iron. FeP4 M is the relative molecular mass of FeP4. Fe wt represents the relative atomic mass of Fe. Ni M represents the mass content of nickel. NiP M is the relative molecular mass of NiP. Ni Here is the relative atomic mass of Ni.

[0040] Figure 3 The X-ray diffraction pattern shows that the prepared NiFeP / PBC sample corresponds to the (-251) crystal plane of FeP4 and the (212) crystal plane of NiP, which is consistent with the standard card.

[0041] Figure 4 X-ray photoelectron spectroscopy (XPS) was used to analyze it. Figure 4 The fitted C 1s fine spectrum contains three different peaks at 284.80 eV, 286.66 eV and 288.48 eV, corresponding to OC=O, COP and CC bonds, respectively.

[0042] Figure 4 The fitted fine 2p spectrum of Fe contains five identifiable peaks, with Fe as the dominant element. 2+ Fe 3+ Two chemical states coexist: Fe 2+ 2p 3 / 2 (710.5 eV) and 2p 1 / 2 (724 eV) Peak intensity is significant; Fe 3+ 2p 3 / 2 (712 eV) and 2p 1 / 2 The (726 eV) peak also makes a significant contribution; the satellite peak (719 eV) is clearly identifiable.

[0043] Figure 4 The fine 2p spectrum of Ni fitted with c-fit contains eight identifiable peaks.0 2p 3 / 2 (852.5 eV) and 2p 1 / 2 The (870.0 eV) peak is identifiable; Ni 2+ 2p 3 / 2 (855.0 eV) and 2p 1 / 2 The peak intensity (873.0 eV) is significant; Ni 3+ 2p 3 / 2 (856.5 eV) and 2p 1 / 2 The (874.5 eV) peak also makes a clear contribution; the satellite peak in the figure is 2p. 3 / 2 Satellite peak (865 eV) and 2p 1 / 2 (880 eV).

[0044] Figure 4 d is the fine 2p spectrum of P. P is chemically bonded to carbon, forming structural defects. Three peaks appear at 133.66 eV, 130.69 eV, and 130.12 eV, corresponding to the 2p phases of the PO bond and the Ni / Fe-P bond, respectively. 1 / 2 2p 3 / 2 peak.

[0045] Example 2 A biomass-based carbon-supported nickel-iron bimetallic phosphide catalyst was prepared according to the following steps: 1) Sample preparation: 10g of corn stalks were crushed, passed through a 40-mesh sieve, washed with deionized water, and then soaked in 1M hydrochloric acid solution at a solid-liquid ratio of 1:10 for 6 hours to remove impurities. The soaked corn stalk powder was then placed in an oven at 85℃ and dried for 8 hours until completely dry. 0.8g of the dried corn stalk powder was mixed with ferric sulfate, nickel chloride hexahydrate, and phytic acid in a mass ratio of 0.8:0.75:0.38:2. 12mL of deionized water was added, and the mixture was stirred continuously for 8 hours until homogeneous. The stirred sample was then adjusted to pH 4 by adding 1M KOH dropwise and placed in an oven at 85℃ for 12 hours until completely dry to obtain sample NFP-2. 2) Weigh and grind 1g of sample NFP-2 and potassium hydroxide solid at a mass ratio of 1:2, place them in a porcelain boat, and put them in a tube furnace. Introduce argon gas and heat to 500℃ at a rate of 5℃ / min, then hold at that temperature for 2 hours. After cooling to room temperature, wash the sample with deionized water and anhydrous ethanol until neutral, and then dry it in an 85℃ oven for 10 hours to obtain the NiFeP / PBC catalyst.

[0046] Figure 5 The medium-scan electron microscope image clearly shows that the sample is stacked in blocks.

[0047] Example 3 A biomass-based carbon-supported nickel-iron bimetallic phosphide catalyst was prepared according to the following steps: 1) Sample preparation: 10g of corn stalks were crushed, passed through a 40-mesh sieve, washed with deionized water, and then soaked in 1M hydrochloric acid solution at a solid-liquid ratio of 1:10 for 6 hours to remove impurities. The soaked corn stalk powder was then placed in an oven at 80℃ and dried for 12 hours until completely dry. 1.2g of the dried corn stalk powder was mixed with ferric sulfate, nickel acetate, and phytic acid in a mass ratio of 1.2:0.9:0.55:3, and 18mL of deionized water was added. The mixture was stirred continuously for 6 hours until homogeneous. The stirred sample was then adjusted to pH 4 by adding 1M KOH dropwise and placed in an oven at 85℃ for 12 hours until completely dry to obtain sample NFP-3. 2) Weigh and grind 1g of sample NFP-3 and potassium hydroxide solid at a mass ratio of 1:2, place them in a porcelain boat, and put them in a tube furnace. Introduce argon gas and heat to 700℃ at a rate of 5℃ / min, then hold at that temperature for 2 hours. After cooling to room temperature, wash the sample with deionized water and anhydrous ethanol until neutral, and then place it in an 80℃ oven to dry for 8 hours to obtain the NiFeP / PBC catalyst.

[0048] Figure 6 The medium scanning electron microscope image clearly shows that the sample is in the form of blocky accumulation.

[0049] Example 4 A biomass-based carbon-supported nickel-iron bimetallic phosphide catalyst was prepared according to the following steps: Sample preparation: 10g of corn stalks were crushed, passed through a 40-mesh sieve, washed with deionized water, and then soaked in 1M hydrochloric acid solution at a solid-liquid ratio of 1:10 for 6 hours to remove impurities. The soaked corn stalk powder was then placed in an oven at 100℃ and dried for 9 hours until completely dry. 1.5g of the dried corn stalk powder was mixed with ferric acetate, nickel acetate, and phytic acid in a mass ratio of 1.5:0.7:0.4:2.8, and 22.5mL of deionized water was added. The mixture was stirred continuously for 6 hours until homogeneous. The stirred sample was then adjusted to pH 4 by adding 1M NaOH dropwise and placed in an oven at 85℃ for 12 hours until completely dry to obtain sample NFP-4. 1g of sample NFP-4 and potassium hydroxide solid were weighed and ground at a mass ratio of 1:2, placed in a porcelain boat, and placed in a tube furnace. The temperature was increased to 800℃ at a rate of 5℃ / min and held for 2 hours. After cooling to room temperature, the sample was washed with deionized water and anhydrous ethanol until neutral, and then placed in an 80℃ oven to dry for 8 hours to obtain the NiFeP / PBC catalyst.

[0050] Figure 7 The medium scanning electron microscope image clearly shows that the sample is in the form of blocky accumulation.

[0051] Application Example 1 Electrocatalytic performance test of NiFeP / PBC catalyst for ammonia synthesis from nitrite: 1) Preparation of slurry: Take 0.008g of the sample prepared in Example 1, put it into a 10mL centrifuge tube, add 995μL of anhydrous ethanol and 50μL of perfluorosulfonyl naphthol membrane solution with a resin solid content of 5wt%, and place it in an ultrasonic machine to sonicate at a power of 480w for 1h to make it uniformly mixed. 2) Take 50 μL of the ultrasonically treated sample and drop it onto a glassy carbon electrode with a diameter of 1 cm. After it air dries naturally, place it in an H-type three-electrode electrolytic cell for electrochemical testing. 3) Weigh 25g of solid sodium potassium tartrate into a beaker, add 40mL of deionized water, heat and stir until boiling, so that the solid is completely dissolved and bubbles are generated in the solution. Stop heating and cool to room temperature, then make up to 50mL for later use. 4) Weigh 8.6g of solid potassium mercuric iodide and dissolve it in 20mL of deionized water. Weigh 8.0g of solid NaOH and dissolve it in 20mL of deionized water. After cooling to room temperature, mix the two solutions and stir well. Make up to 50mL for later use. 5) Electrocatalytic nitrite-to-ammonia synthesis test: Add 50 mL of 0.1 M NaNO2 to each of the left and right chambers of the H-type electrolytic cell, and connect the Ag / AgCl reference electrode and the C counter electrode, respectively. Conduct an electrolysis experiment for 1 hour at a voltage of 0.0 V vs. RHE to 0.6 V vs. RHE. After the reaction is complete, take an appropriate amount of electrolyte from the side of the electrolytic cell where the working electrode is located for later use.

[0052] Take 1 mL of the electrolyzed electrolyte using a pipette and place it in a 25 mL colorimetric tube. Dilute to volume with 1 M NaOH, then add 1 mL of prepared potassium sodium tartrate solution and 1 mL of potassium mercuric iodide solution. Let stand for 15 min. Measure the absorbance of the electrolyte using a UV-Vis absorption spectrometer at a wavelength of 420 nm to obtain the Faraday efficiency and ammonia yield.

[0053] Figure 8 To reduce NO2 at different voltages using the NiFeP / PBC catalyst prepared in Example 1 - The Ferrari efficiency and ammonia yield plots show that, at -0.2V vs. RHE voltage, the ammonia yield reaches 166.48 μmol·h⁻¹. -1 ·cm -2 The Faraday efficiency reached 91.16%, indicating that the prepared NiFeP / PBC catalyst has high efficiency.

[0054] Figure 9The NiFeP / PBC catalyst was subjected to a 15-hour cyclic electrolysis test at a voltage of -0.2V vs. RHE, which showed that the prepared NiFeP / PBC catalyst has very good stability.

[0055] Application Example 2 Electrocatalytic performance test of NiFeP / PBC catalyst for ammonia synthesis from nitrite: 1) Preparation of slurry: Take 0.008g of the sample prepared in Example 2, put it into a 10mL centrifuge tube, add 995μL of anhydrous ethanol and 50μL of perfluorosulfonyl naphthol membrane solution with a resin solid content of 5wt%, and place it in an ultrasonic machine to sonicate at a power of 480w for 1h to make it uniformly mixed. 2) The remaining steps are the same as in Application Example 1; 3) Electrocatalytic nitrite-to-ammonia synthesis test: The electrochemical testing procedure in Application Example 2 is the same as that in Application Example 1.

[0056] Figure 10 To reduce NO2 at different voltages using the NiFeP / PBC catalyst prepared in Example 2 - The Ferrari efficiency and ammonia yield plots show that, at -0.2V vs. RHE voltage, the ammonia yield reached 176.51 μmol·h⁻¹. -1 ·cm -2 The Faraday efficiency reached 61.72%, indicating that the prepared NiFeP / PBC catalyst has high efficiency.

[0057] Figure 11 The NiFeP / PBC catalyst was subjected to a 9-hour cyclic electrolysis test at a voltage of -0.2V vs. RHE, which indicates that the prepared NiFeP / PBC catalyst has very good stability.

[0058] Application Example 3 Electrocatalytic performance test of NiFeP / PBC catalyst for ammonia synthesis from nitrite: 1) Preparation of slurry: Take 0.008g of the sample prepared in Example 3, put it into a 10mL centrifuge tube, add 995μL of anhydrous ethanol and 50μL of perfluorosulfonate naphthol membrane solution with a resin solid content of 5wt%, and place it in an ultrasonic machine to sonicate at a power of 480w for 1h to make it uniformly mixed. 2) The remaining steps are the same as in Application Example 1; 3) Electrocatalytic nitrite-to-ammonia synthesis test: The electrochemical testing procedure in Application Example 3 is the same as that in Application Example 1.

[0059] Figure 12 To reduce NO2 at different voltages using the NiFeP / PBC catalyst prepared in Example 3- The Ferrari efficiency and ammonia yield plots show that, at -0.2V vs. RHE voltage, the ammonia yield reaches 121.44 μmol·h⁻¹. -1 ·cm -2 The Faraday efficiency reached 66.50%, indicating that the prepared NiFeP / PBC catalyst has high efficiency.

[0060] Figure 13 The NiFeP / PBC catalyst was subjected to a 12-hour cyclic electrolysis test at a voltage of -0.2V vs. RHE, which showed that the prepared NiFeP / PBC catalyst has very good stability.

[0061] Comparative Example 1 The NiFe / BC catalyst was prepared according to the following steps: 1) Sample Preparation: Weigh 10g of corn stalks, crush them, pass them through a 40-mesh sieve, wash them with deionized water, and then add 1M hydrochloric acid solution. The solid-liquid ratio of corn stalk powder to 1M hydrochloric acid solution is 1:10. Soak for 6 hours to remove impurities. Place the soaked corn stalk powder in an 80℃ oven and dry for 8 hours until completely dry. Take 1g of the dried corn stalk powder and mix it with ferric chloride hexahydrate and nickel chloride hexahydrate in a mass ratio of 1:0.81:0.48. Add 15mL of deionized water and stir continuously for 8 hours to make it uniform. Place it in an 85℃ oven for 12 hours until completely dry to obtain sample NF. 2) Weigh and grind 1g of sample NF and KOH in a mass ratio of 1:2, place them in a porcelain boat, and put them in a tube furnace. Purge with nitrogen and heat to 600℃ at a rate of 5℃ / min. Hold at this temperature for 2 hours. After cooling to room temperature, wash the sample with deionized water and anhydrous ethanol until neutral. Place it in an 80℃ oven and dry for 10 hours to obtain the NiFe / BC sample.

[0062] Figure 14 The image, taken using a scanning electron microscope, clearly shows that the sample is arranged in a blocky mass.

[0063] The electrocatalytic performance of nitrite to ammonia synthesis was tested using the NiFe / BC catalyst prepared in Comparative Example 1, following the method of Application Example 1.

[0064] Figure 15 To utilize the NiFe / BC prepared in Comparative Example 1 to reduce NO2 under different voltages - The Ferrari efficiency and ammonia yield plots show that, at -0.2V vs. RHE voltage, the ammonia yield reached 153.24 μmol·h⁻¹. -1 ·cm -2The Faraday efficiency reached 62.66%, indicating that the NiFe / BC catalyst has a lower efficiency compared to Example 1. The Faraday efficiency and ammonia yield decreased significantly, and the effect was poor.

[0065] Figure 16 The graph shows a comparison of the electrochemical active areas of Comparative Example 1 and Experimental Example 1. The double-layer capacitance is represented by the slope k, and the electrochemical active area is calculated using the formula k × 1000 / 60. The double-layer capacitance of Experimental Example 1 is 3.098 mF / cm². 2 The electrochemical active area is 51.64 cm². 2 / mg; the double-layer capacitance of Comparative Example 1 was 0.579 mF / cm. 2 The electrochemical active area is 9.65 cm². 2 / mg.

[0066] Figure 17 The graph shows a comparison of the electrochemical impedance spectroscopy between Comparative Example 1 and Experimental Example 1. The electrochemical impedance radius of Experimental Example 1 is smaller than that of Comparative Example 1, which proves that the phosphorus-doped catalyst has better conductivity and electrocatalytic performance than the undoped catalyst.

[0067] Comparative Example 2 The single-metal NiP / PBC catalyst was prepared according to the following steps: 1) Sample preparation: Weigh 10g of corn stalks, crush them, pass them through a 40-mesh sieve, wash them with deionized water, and then add 1M hydrochloric acid solution. The solid-liquid ratio of corn stalk powder to 1M hydrochloric acid solution is 1:10. Soak for 6 hours to remove impurities. Place the soaked corn stalk powder in an 80℃ oven and dry for 8 hours until dry. Take 1g of the dried corn stalk powder and mix it with polyphosphoric acid and nickel chloride hexahydrate in a mass ratio of 1:2.5:0.48. Add 15mL of deionized water, stir continuously for 8 hours to make it uniform, and place it in an 85℃ oven for 12 hours to dry, to obtain the sample NiP / PBC. 2) Weigh and grind 1g of sample NiP / PBC and KOH in a mass ratio of 1:2, place them in a porcelain boat, and put them in a tube furnace. Introduce argon gas and heat the sample to 600℃ at a heating rate of 5℃ / min. Hold the temperature for 2 hours. After cooling to room temperature, wash the sample with deionized water and anhydrous ethanol until neutral, and place it in an 85℃ oven to dry for 10 hours to obtain the NiP / PBC sample.

[0068] Figure 18 The image, taken using a scanning electron microscope, clearly shows that the sample exhibits a blocky accumulation. The NiP / PBC catalyst has a similar structure to the NiFeP / PBC catalyst prepared in Example 1, and both have a large specific surface area.

[0069] The electrocatalytic performance of nitrite to ammonia synthesis was tested using the NiP / PBC catalyst prepared in Comparative Example 2, following the method of Application Example 1.

[0070] Figure 19 Linear sweep voltammetry (LSV) plots of the catalysts prepared in Comparative Example 2 and Example 1 were obtained at voltages of -0.5 to 0.1 V. The results show that at voltages of -0.5 to 0.1 V vs. RHE, Example 1 has a lower onset voltage and a higher current density than Comparative Example 2, which proves that the bimetallic phosphide catalyst is more effective than the monometallic phosphide catalyst.

[0071] Comparative Example 3 The NiFeP / BC catalyst was prepared according to the following steps: 1) Sample preparation: Weigh 10g of corn stalks, crush them, pass them through a 40-mesh sieve, wash them with deionized water, and then add 1M hydrochloric acid solution. The solid-liquid ratio of the corn stalk powder to the 1M hydrochloric acid solution is 1:10. Soak for 6 hours to remove impurities. Place the soaked corn stalk powder in a 90℃ oven and dry for 8 hours until completely dry. 2) Place the dried corn stalk powder in a tube furnace, introduce nitrogen gas, raise the temperature to 800℃ at a rate of 10℃ / min and hold for 2 hours. After cooling to room temperature, wash the obtained biochar with deionized water and anhydrous ethanol until neutral, and place it in an 80℃ oven to dry for 10 hours to obtain biochar BC. 3) The dried biochar BC was mixed with ferric chloride hexahydrate, nickel chloride hexahydrate and phytic acid in a mass ratio of 1:0.81:0.48:2.5. 15 mL of deionized water was added and the mixture was stirred continuously for 8 h to make it uniform. The mixture was then placed in an 85℃ oven for 12 h to dry, and the sample NFP-5 was obtained. 4) Place the NFP-5 sample in a ceramic boat and put it in a tube furnace. Introduce argon gas and heat the sample to 600℃ at a rate of 5℃ / min. Hold the temperature for 2 hours. After cooling to room temperature, wash the sample with deionized water and anhydrous ethanol until neutral. Place the sample in an 80℃ oven and dry for 10 hours to obtain the NiFeP / BC sample.

[0072] Figure 20 The image, taken using a scanning electron microscope, clearly shows that the sample is arranged in a blocky mass.

[0073] Performance testing of NiFeP / BC catalyst in electrocatalytic synthesis of ammonia from nitrite: 1) Preparation of slurry: Weigh 0.008g of NiFeP / BC catalyst, put it into a 2mL centrifuge tube, add 995μL of anhydrous ethanol and 50μL of perfluorosulfonyl naphthol membrane solution with a resin solid content of 5wt%, and place it in an ultrasonic machine and sonicate at 240W power for 1h to make it uniformly mixed. 2) The remaining steps are the same as in Application Example 1; 3) Electrocatalytic nitrite-to-ammonia synthesis test: The electrochemical testing procedure is the same as in Application Example 1.

[0074] Figure 21 Linear sweep voltammetry (LSV) plots of the catalysts prepared in Comparative Example 3 and Example 1 were obtained at voltages of -0.5 to 0.1 V. The results show that, at voltages of -0.5 to 0.1 V vs. RHE, the NiFeP / BC catalyst prepared by the two-step method has a lower onset voltage and a higher current density at the same voltage compared to the NiFeP / PBC catalyst prepared by the one-step method in Example 1. This indicates that the one-step in-situ synthesized catalyst NiFeP / PBC exhibits better catalytic performance.

[0075] The data above show that the NiFeP / PBC catalyst prepared by the method provided in this invention can be carried out at room temperature and pressure and achieves high Faraday efficiency and ammonia yield.

[0076] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention in any other way. Any person skilled in the art can utilize the above technical content to make changes or modifications to create equivalent embodiments. Any simple modifications, equivalent changes, and modifications made to the above embodiments without departing from the technical essence of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A biomass-based carbon-supported nickel-iron bimetallic phosphide catalyst, characterized in that, The catalyst comprises corn stalk carbon material and FeP4 and NiP particles supported on the carbon material. The loading of FeP4 accounts for 19.08-26.45% of the total mass of the catalyst, and the loading of NiP accounts for 19.82-22.71% of the total mass of the catalyst. The phosphorus source is phytic acid.

2. The biomass-based carbon-supported nickel-iron bimetallic phosphide catalyst according to claim 1, characterized in that, The catalyst contains, by elemental proportions, 5.93-8.22% Fe, 12.97-14.86% Ni, and 19.93-26.05% P.

3. The preparation method of the biomass-based carbon-supported nickel-iron bimetallic phosphide catalyst according to claim 1, characterized in that, Includes the following steps: 1) Add phosphorus source precursor, iron source precursor and nickel source precursor to pretreated corn stalk powder, pour in an appropriate amount of deionized water, stir for 6-12 hours until the mixture is uniform, adjust the pH value with alkaline solution, and place in an oven to dry. 2) The dried material from step 1) and the alkali metal hydroxide are mixed and ground in a mass ratio of 1:2 until the sample and alkali metal hydroxide are evenly mixed and in powder form. The mixture is placed in a tube furnace, inert gas is introduced, and the mixture is calcined at high temperature and then cooled to room temperature. The catalyst is obtained by using water and anhydrous ethanol to neutralize the mixture and drying it.

4. The preparation method of the biomass-based carbon-supported nickel-iron bimetallic phosphide catalyst according to claim 3, characterized in that, The iron source precursor is one of ferric chloride hexahydrate, ferric nitrate, ferric sulfate, and ferric acetate; the nickel source precursor is one of nickel chloride hexahydrate, nickel nitrate, and nickel acetate; and the phosphorus source precursor is phytic acid.

5. The method for preparing the biomass-based carbon-supported nickel-iron bimetallic phosphide catalyst according to claim 3 or 4, characterized in that, The mass ratio of the phosphorus source precursor, iron source precursor, nickel source precursor and corn stalk powder is 20-30:6-9:3.5-5.5:5-15; the mass ratio of the corn stalk powder to deionized water is 1:15; the inert gas is nitrogen or argon; the alkali metal hydroxide is sodium hydroxide or potassium hydroxide.

6. The method for preparing the biomass-based carbon-supported nickel-iron bimetallic phosphide catalyst according to claim 3, characterized in that, The alkaline solution mentioned in step 1) is a 1M sodium hydroxide solution or a 1M potassium hydroxide solution, and the pH of the system is adjusted to 4-5 by adding the alkaline solution; the temperature of the oven mentioned in step 1) is 70-80℃, and the time is 8-12h; the alkali metal hydroxide mentioned in step 2) is solid potassium hydroxide; the program of the tube furnace mentioned in step 2) is to heat up to 500-800℃ at a rate of 5℃ / min and hold for 2h; the drying conditions mentioned in step 2) are drying in an oven at 70-80℃ for 8-12h.

7. The method for preparing the biomass-based carbon-supported nickel-iron bimetallic phosphide catalyst according to claim 3, characterized in that, The pretreatment method for corn stalk powder includes the following steps: crushing corn stalks, passing them through a 40-mesh sieve, washing them with deionized water, adding 1M hydrochloric acid solution, wherein the solid-liquid ratio of corn stalk powder to 1M hydrochloric acid solution is 1:10, soaking completely for 4-6 hours, and then drying them in an oven at 70-100℃ for 8-12 hours to obtain the treated corn stalk powder.

8. The application of the biomass-based carbon-supported nickel-iron bimetallic phosphide catalyst of claim 1 in the electrocatalytic synthesis of ammonia from sodium nitrite.

9. The application of the biomass-based carbon-supported nickel-iron bimetallic phosphide catalyst according to claim 8 in the electrocatalytic synthesis of ammonia from sodium nitrite, characterized in that, The electrocatalysis is carried out in an H-type electrolytic cell, using a biomass-based carbon-supported nickel-iron bimetallic phosphide catalyst as the working electrode, Ag / AgCl as the reference electrode, and C as the counter electrode.

10. The application of the biomass-based carbon-supported nickel-iron bimetallic phosphide catalyst according to claim 9 in the electrocatalytic synthesis of ammonia from sodium nitrite, characterized in that, The specific steps are as follows: 1) The biomass-based carbon-supported nickel-iron bimetallic phosphide catalyst is prepared into a slurry and drop-coated onto a glassy carbon electrode as a working electrode; 2) Dissolve NaNO2 in 1M NaOH solution to make the NaNO2 concentration 0.1M, and then perform electrochemical electrolysis; The mass ratio of the biomass-based carbon-supported nickel-iron bimetallic phosphide catalyst to NaNO2 is 0.8-1.0:5000-10000; The preparation steps of the slurry in step 1) are as follows: Take 8-10 mg of the biomass-based carbon-supported nickel-iron bimetallic phosphide catalyst and dissolve it in 0.9-1 mL of anhydrous ethanol. Add 50-60 μL of a perfluorosulfonate naphthol membrane solution with a resin solid content of 5-10 wt%. Sonicate at 480 W for 40-60 min to obtain the slurry.

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