Biomass-derived carbon-supported iron phosphide nano-catalyst as well as preparation method and application thereof

Abstract

The invention relates to the field of new energy materials, and particularly provides a biomass-derived carbon-supported iron phosphide nano-catalyst and a preparation method and application thereof.The biomass-derived carbon-supported iron phosphide nano-catalyst is prepared by taking waste biomass as a raw material and sodium hypophosphite as a phosphorus source through high-temperature carbonization and activation treatment to obtain a biochar carrier with a high specific surface area and a porous structure; the method is used for loading iron phosphide so as to improve the stability and the conductivity, a traditional high-energy-consumption and high-pollution ammonia synthesis process is replaced with an electro-catalysis technology, and a new way is provided for achieving green and efficient synthesis of ammonia. The invention not only helps to solve the problems of energy and environment, but also opens up a new direction for resource utilization of agricultural wastes.

Description

Technical Field

[0001] This invention belongs to the field of electrocatalytic materials and sustainable energy technology, specifically relating to a biomass-derived carbon-supported iron phosphide nanocatalyst, its preparation method, and its application. Background Technology

[0002] Ammonia, an indispensable cornerstone of modern agriculture and a major driving force behind human progress since the 20th century, holds a pivotal position. It is not only a core raw material for fertilizer production but also an essential element in the pharmaceutical and fine chemical industries, contributing to human health and technological advancement. More notably, ammonia, as an ideal zero-carbon fuel, demonstrates enormous potential in the clean energy sector. Furthermore, ammonia is widely used in the manufacturing processes of various industrial products, becoming an indispensable part of industrial production. However, currently, the global annual ammonia production of approximately 150 million tons relies primarily on the traditional Haber-Bosch process, which requires high temperature (400-500℃) and high pressure (15-25MPa) conditions, consuming about 1% of global energy supply and generating significant amounts of greenhouse gases (accounting for 1.3% of global CO2 emissions). With the increasing prominence of the global energy crisis and environmental problems, developing green, low-carbon new ammonia synthesis technologies has become an urgent priority.

[0003] Electrocatalytic ammonia synthesis is considered a promising nitrogen fixation method due to its potential for cleanliness and high efficiency. It enables the efficient, sustainable, and environmentally friendly synthesis of ammonia under environmentally friendly conditions. However, the direct ammonia synthesis process faces significant challenges, namely overcoming the nitrogen-nitrogen triple bond problem. Because the dissociation energy of the nitrogen-nitrogen triple bond is quite high, the system tends to undergo hydrogen evolution reaction during synthesis, which not only affects the selectivity of ammonia synthesis but also leads to low ammonia yield. In contrast, the indirect ammonia synthesis method, due to its unique advantages, shows a broader range of application possibilities than the direct method. On the other hand, the damage of nitrogen-containing pollutants to the aquatic environment has become a global environmental problem, with nitrite (NO2) being a significant contributor. - Nitrogen oxides, a common pollutant in water bodies, not only cause eutrophication but also transform into nitrosamines, potent carcinogens, seriously threatening ecosystem security and human health. Therefore, the development of efficient, economical, and environmentally friendly technologies for controlling nitrogen-containing pollutants is urgently needed. Converting nitrogen oxides in industrial and agricultural wastewater into high-value-added ammonia via green electrocatalysis overcomes the challenges of high nitrogen-nitrogen triple bond energy (difficult to break) and low nitrogen solubility in water, providing a promising solution for the treatment of industrial and agricultural wastewater.

[0004] The key to achieving electrocatalytic synthesis of ammonia from nitrite lies in developing a highly stable and selective catalyst. Transition metal phosphides have shown great potential in this field, not only replacing expensive precious metal catalysts but also possessing the characteristics of selective adsorption of active hydrogen and charge-separated selective adsorption of species. This avoids competition for active sites, improving catalytic efficiency and reducing byproduct formation. However, in chemical reactions involving oxygen reduction, the surface characteristics of metal phosphides make them highly susceptible to alternating oxidation and reduction processes. This series of complex reaction changes inevitably causes corrosive damage to the catalyst, affecting its overall performance and stability. In-depth analysis of relevant scientific research indicates that when the reaction system is under high potential conditions, metal phosphides are at risk of being oxidized to phosphates. The formation of phosphates significantly alters the surface structure and chemical properties of the catalyst, ultimately leading to a significant decline in catalyst performance and reducing its catalytic efficiency and lifespan in oxygen reduction reactions.

[0005] Biomass resources are widely distributed in nature, not only abundant in reserves but also renewable, and relatively inexpensive. Biomass-based carbon materials possess advantages such as high specific surface area, rich pore structure, good conductivity, and high electrochemical stability, providing ample loading sites for metal phosphides and increasing the exposure of active sites. Loading metal phosphides onto biomass can improve the overall electrode conductivity and stability of the catalyst. Large quantities of waste biomass, if not treated promptly and effectively, will form stubborn solid waste, threatening the ecological environment and affecting the quality of human life. Therefore, utilizing chemical methods to convert waste biomass can both realize its potential value and alleviate environmental pressure, achieving resource recycling and environmental protection.

[0006] Currently, the main method for preparing metal phosphides is gas-solid reaction. At a relatively high temperature, gaseous phosphorus-containing substances (such as red phosphorus or white phosphorus) are used as phosphorus sources to react with solid metal or metal oxide precursors to synthesize metal phosphides. However, both red phosphorus and white phosphorus are highly toxic and are extremely prone to spontaneous combustion or explosion.

[0007] 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, utilizes organic phytic acid solution as the phosphorus source and iron salt as the iron source, and obtains FeP / PGP nanocatalysts directly in situ by calcination in a tube furnace under an argon atmosphere. However, this method uses grapefruit peel as the carbon material, which has a relatively loose structure. The mesoporous and microporous structures formed after carbonization may not be ideal, limiting the exposure of active sites and the transport of reactants, thus affecting the catalytic performance.

[0008] Therefore, there is an urgent need to develop a new technology that can simultaneously achieve multiple objectives, such as the resource utilization of solid waste biomass, the safe and efficient preparation of metal phosphides, and the efficient electrocatalytic synthesis of ammonia. Summary of the Invention

[0009] To address the serious waste and environmental pollution caused by biomass resources, and considering the challenges of insufficient stability of metal phosphide catalysts, high energy consumption in traditional ammonia synthesis processes, and low efficiency in electrocatalytic ammonia synthesis, this invention proposes a biomass-derived carbon-supported iron phosphide nanocatalyst, its preparation method, and its applications. The core objective of this invention is to efficiently utilize waste biomass resources such as peanut shells, sugarcane bagasse, and corn stalks. Through meticulous design and synthesis processes, the conductivity and long-term stability of the iron phosphide catalyst are significantly improved, thereby substantially enhancing the efficiency of the electrocatalytic conversion of nitrite to ammonia, providing strong support for achieving a green and efficient ammonia synthesis process.

[0010] This invention makes full use of biomass resources, using sodium hypophosphite as a phosphorus source, to synthesize biomass-derived carbon-supported iron phosphide nanocatalysts in situ in one step. The iron phosphide nanoparticles exist in the form of FeP2, and the catalyst as a whole is represented by FeP2 / PS.

[0011] The first aspect of the present invention provides a biomass-derived carbon-supported iron phosphide nanocatalyst, comprising biomass carbon material and iron phosphide nanoparticles supported on biomass carbon, abbreviated as FeP2 / PS, wherein the loading of iron phosphide accounts for 5.22%-39.46 wt% of the total mass of the catalyst, preferably 16.78 wt%.

[0012] In terms of elemental composition, Fe accounts for 2.3-17.4 wt% of the total weight of the nanocatalyst, P accounts for 15.76-28.89 wt% of the total weight of the nanocatalyst, and O accounts for 2.46-24.34 wt% of the total weight of the nanocatalyst. In addition, it also contains C derived from biocarbon materials and other impurity elements.

[0013] Preferably, in the biomass-derived carbon-supported iron phosphide nanocatalyst, the Fe content accounts for 7.4 wt% of the total weight of the nanocatalyst, the P content accounts for 16.79 wt% of the total weight of the nanocatalyst, and the O content accounts for 11.15 wt% of the total weight of the nanocatalyst.

[0014] A second aspect of this invention provides a method for preparing the biomass-derived carbon-supported iron phosphide nanocatalyst, comprising the following steps: 1) Mix the pretreated waste biomass powder with phosphorus source precursor and iron source precursor, add deionized water, stir evenly and then sonicate to obtain a mixed solution. 2) Dry the mixed solution from step 1), grind it, put it into a tube furnace, calcine it with inert gas, let the calcined material cool naturally to room temperature, wash it with deionized water until neutral, and dry it.

[0015] The biomass mentioned in step 1) is selected from peanut shells, sugarcane bagasse, or corn stalks, with peanut shells being the preferred biomass. Peanut shells are rich in cellulose and lignin, and after carbonization, they are easy to form carbon carriers with a multi-level porous structure, providing a larger specific surface area and better conductivity. This structure is conducive to the high dispersion and fixation of iron phosphate, which can significantly increase the active sites and improve the mass transfer efficiency in the electrocatalytic synthesis of ammonia.

[0016] Furthermore, in step 1), the mass ratio of biomass powder, iron source precursor, phosphorus source precursor, and deionized water is 0.5:(0.15-0.45):(1-4):(2-10), preferably 0.5:0.35:2:2.

[0017] The phosphorus source precursor mentioned in step 1) is sodium hypophosphite; the iron source precursor is at least one of ferric chloride hexahydrate, ferric nitrate and ferric sulfate, preferably ferric chloride hexahydrate.

[0018] The ultrasound conditions described in step 1) are 500W ultrasound for 1-2 hours.

[0019] In step 2), the sample is ground into a fine powder to ensure that the different raw materials are mixed evenly before calcination. Otherwise, the phosphorus source and iron source of the catalyst obtained after calcination will not be evenly distributed.

[0020] The drying conditions described in step 2) are both drying at 60-80℃ in an oven for 12-24 hours.

[0021] Step 2) The inert gas is argon or nitrogen.

[0022] The tubular furnace setting program in step 2) is to raise the temperature to 600-1000℃ at a heating rate of 5-10℃ / min and hold it for 1-2 hours; preferably, it is to raise the temperature to 900℃ at a heating rate of 5℃ / min and hold it for 2 hours.

[0023] The pretreatment method for the waste biomass powder includes the following steps: Waste biomass is crushed into powder and placed in a beaker. Potassium hydroxide and deionized water are added, with a mass ratio of biomass powder, potassium hydroxide, and deionized water of 1:(1-1.5):2. The mixture is stirred for 2-3 hours until homogeneous, then placed in an oven and heated at 90-100℃ for 10-12 hours to activate and create pores. After cooling to room temperature, 1M hydrochloric acid solution is added to adjust the pH to 6.8-7.2. The mixture is then washed with deionized water to obtain clean biomass. The clean biomass is then pulverized and passed through an 80-mesh sieve to obtain biomass powder.

[0024] The formation mechanism of the above FeP2 / PS is as follows: Biomass, as a carbon source, provides the necessary surface area and active sites for the reaction due to its abundant porous structure and carbon-containing functional groups. During calcination, sodium hypophosphite decomposes to generate PH3. Since phosphorus (P) in PH3 has strong reducing properties, it can reduce the iron ions released from the iron source precursor. These reduced iron ions combine with P, gradually forming Fe-P bonds through a series of complex chemical transformations. Due to the presence of biochar, biomass-derived carbon-supported FeP2 is ultimately generated. FeP2 particles are mainly loaded in the internal channels and cavities of the carbon support, with a small number of particles possibly present on the outer surface, but primarily encapsulated internally. This structure effectively prevents FeP2 particles from agglomerating or leaking during the catalytic reaction. Because the generated biochar has small pore size and good dispersion, the loaded FeP2 particles are finer and more uniform. Furthermore, the material inherits the macroscopic pores of biomass, generating micropores and mesopores during activation / carbonization, forming hierarchical channels. This facilitates reactant transport and provides ample loading space for FeP2.

[0025] The third aspect of this invention provides the application of the above-mentioned biomass-derived carbon-supported iron phosphide nanocatalyst in the electrocatalytic synthesis of ammonia from sodium nitrite.

[0026] Preferably, the electrocatalytic synthesis of ammonia from sodium nitrite is carried out in an H-type electrolytic cell, with a glassy carbon electrode coated with a biomass-derived carbon-supported iron phosphide nanocatalyst slurry as the working electrode, an Ag / AgCl electrode as the reference electrode, and a carbon rod as the counter electrode.

[0027] Preferably, the specific steps for the electrocatalytic synthesis of ammonia from sodium nitrite are as follows: 1) The biomass-derived carbon-supported iron phosphide nanocatalyst is prepared into a slurry, coated onto a glassy carbon electrode, dried, and used as the working electrode; 2) Dissolve sodium nitrite in 1M sodium hydroxide solution to prepare 0.1M sodium nitrite solution as electrolyte. The mass ratio of the biomass-derived iron carbon phosphide nanocatalyst to NaNO2 is (0.72-1.45):(1000-2000). Pour the solution into the electrolytic cell to carry out electrocatalytic ammonia production.

[0028] Preferably, the preparation method of the slurry in step 1) is as follows: Take 1-10 mg of the biomass-derived carbon-supported iron phosphide nanocatalyst, dissolve it in a mixed solution of 0.75-1.0 mL of anhydrous ethanol and 0.20-0.50 mL of deionized water, then add 50-80 μL of a perfluorosulfonated naphthol solution with a resin solid content of 5-10 wt%, and sonicate at 500 W for 0.5-1 h to obtain a slurry; more preferably, take 5 mg of the biomass-derived carbon-supported iron phosphide nanocatalyst, with 0.75 mL of anhydrous ethanol, 0.20 mL of deionized water, and 50 μL of perfluorosulfonated naphthol solution.

[0029] Preferably, during the electrolytic testing of the above-mentioned electrocatalytic sodium nitrite to ammonia synthesis, ammonia detection was performed using Nessler's reagent spectrophotometry. 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 Faradaic efficiency of ammonia production was calculated using a formula. The electrolysis test was conducted at voltages ranging from 0.5V to -0.6V vs. RHE. The results showed that at -0.3V, the ammonia yield reached 308.46 ± 10.71 μmol·h⁻¹. -1 ·cm -2 The Faraday efficiency reached 98.94±0.56%. This demonstrates that the biomass-derived carbon-supported iron phosphide nanocatalyst provided by this invention exhibits excellent electrocatalytic activity and high selectivity. Furthermore, a 16-hour cycle stability test showed that its ammonia production Faraday efficiency remained consistently above 91%, indicating that the catalyst possesses high stability.

[0030] Compared to existing technologies, the beneficial effects achieved by this invention are as follows: 1) This invention features a lower optimal voltage and higher ammonia production Faraday efficiency. The biomass-derived carbon from peanut shells, sugarcane bagasse, or corn stalks, compared to other waste biomass such as grapefruit peels, is richer in cellulose and lignin. After carbonization, it easily forms a carbon carrier with a multi-level porous structure, providing a larger specific surface area and better conductivity. Compared to phytic acid, sodium hypophosphite decomposes under heating conditions to produce PH3 (phosphine), which more readily undergoes a highly efficient and thorough phosphating reaction with an iron source, thereby generating high-purity iron phosphide nanoparticles. Furthermore, sodium hypophosphite's lower cost and wider availability make it more suitable for industrial production.

[0031] 2) This invention uses waste biomass as raw material and sodium hypophosphite as the phosphorus source. Through high-temperature carbonization and activation, a bio-carbon carrier with a high specific surface area and porous structure is obtained. This carrier is then used to load iron phosphide to improve its stability and conductivity. Electrocatalysis technology replaces the traditional high-energy-consuming and high-polluting ammonia synthesis process, providing a new pathway for the green and efficient synthesis of ammonia. This invention not only helps solve energy and environmental problems but also opens up new directions for the resource utilization of agricultural waste. Attached Figure Description

[0032] Figure 1 These are scanning electron microscope images of FeP2 / PS at 900 °C prepared in Example 1 of this invention at different magnifications. Figure 2 The elemental mapping distribution of FeP2 / PS at 900 °C prepared in Example 1 of this invention; Figure 3 The X-ray diffraction pattern of FeP2 / PS at 900 °C prepared in Example 1 of this invention; Figure 4 The X-ray photoelectron spectrum of FeP2 / PS at 900 °C prepared in Example 1 of this invention is shown, where a is the full spectrum, b is the C 1s fine spectrum, c is the Fe 2p fine spectrum, and d is the P 2p fine spectrum. Figure 5 The Raman spectrum of FeP2 / PS prepared at 900 °C in Example 1 of this invention; Figure 6 This is a scanning electron microscope image of FeP2 / PS-700 ℃ prepared in Example 2 of the present invention; Figure 7 This is the elemental mapping distribution diagram of FeP2 / PS at 700 °C prepared in Example 2 of the present invention; Figure 8 The X-ray diffraction pattern of FeP2 / PS at 700 °C prepared in Example 2 of this invention; Figure 9 This is a scanning electron microscope image of FeP2 / PS-800 ℃ prepared in Example 3 of the present invention; Figure 10 The elemental mapping distribution of FeP2 / PS at 800 °C prepared in Example 3 of this invention; Figure 11 The X-ray diffraction pattern of FeP2 / PS at 800 °C prepared in Example 3 of this invention; Figure 12 This is a scanning electron microscope image of FeP2 / PS-1000 ℃ prepared in Example 4 of the present invention; Figure 13 The elemental mapping distribution of FeP2 / PS at 1000 °C prepared in Example 4 of this invention; Figure 14 The X-ray diffraction pattern of FeP2 / PS at 1000 °C prepared in Example 4 of this invention; Figure 15 This is a scanning electron microscope image of FeP2 / PS-900 ℃ prepared in Example 5 of the present invention; Figure 16This is a scanning electron microscope image of FeP2 / PS-900 ℃ prepared in Example 6 of the present invention; Figure 17 This is a scanning electron microscope image of FeP2 / PS prepared at -900 °C in Example 7 of the present invention; Figure 18 This is a scanning electron microscope image of FeP2 / PS prepared at -900 °C in Example 8 of the present invention; Figure 19 FeP2 / PS-900 °C was used to reduce NO2 at different voltages in Example 1 of this invention. - Faraday efficiency and ammonia yield curves; Figure 20 This is a cyclic electrolysis experiment diagram of FeP2 / PS prepared in Example 1 of the present invention at 900 °C under the optimal voltage; Figure 21 This is a diagram of the cyclic electrolysis experiment of Fe / PS prepared in Comparative Example 1 of this invention at 900 °C under the optimal voltage; Figure 22 FeP2 / PS-700 °C was used to reduce NO2 at different voltages in Example 2 of this invention. - Faraday efficiency and ammonia yield curves; Figure 23 FeP2 / PS-800 °C was used to reduce NO2 at different voltages in Example 3 of this invention. - Faraday efficiency and ammonia yield curves; Figure 24 FeP2 / PS-1000 °C was used to reduce NO2 at different voltages in Example 4 of this invention. - Faraday efficiency and ammonia yield curves; Figure 25 This is a scanning electron microscope image of Fe / PS prepared at 900 °C in Comparative Example 1 of this invention; Figure 26 The elemental mapping distribution of Fe / PS prepared at 900 °C in Comparative Example 1 of this invention is shown. Figure 27 Fe / PS prepared for Comparative Example 1 of this invention reduced NO2 at 900 °C under different voltages. - Faraday efficiency and ammonia yield curves; Figure 28 The Fe / PS-900 °C prepared in Comparative Example 1 and the FeP2 / PS-900 °C prepared in Example 1 were used to reduce NO2 at different voltages. - A comparison chart of Faraday efficiency; Figure 29The Fe / PS-900 °C prepared in Comparative Example 1 and the FeP2 / PS-900 °C prepared in Example 1 reduced NO2 at different voltages. - Ammonia yield comparison chart. Detailed Implementation

[0033] To ensure that those skilled in the art can fully and clearly grasp the technical solutions proposed in this application, the following sections will provide a detailed description of the technical solutions in close conjunction with specific implementation examples and related drawings. These carefully selected implementation examples are intended to provide a more detailed explanation of the technical solutions of this invention, rather than constituting any form of limitation on its scope of protection.

[0034] In the description of the implementation cases, if the specific conditions of certain experiments are not explicitly stated, the standard operating conditions in that field should be followed, or the standard conditions recommended by the reagent supplier should be consulted. Furthermore, unless otherwise specified, all reagents, consumables, and other items mentioned in the following implementation cases can be procured through legitimate commercial channels to ensure the smooth conduct of the experiments and the reliability of the results.

[0035] Example 1 A biomass-derived carbon-supported iron phosphide nanocatalyst was prepared according to the following steps: 1) Peanut shell biomass pretreatment: 20 g of waste peanut shells were crushed into powder and placed in a beaker. Potassium hydroxide activator and deionized water were added. The mass ratio of peanut shell powder, potassium hydroxide and deionized water was 1:1:2. After stirring for 2 h until uniform, the mixture was placed in an oven and heated at 100 ℃ for 12 h to activate and create pores. After cooling to room temperature, 1 M hydrochloric acid solution was added to adjust the pH to 7.0. The mixture was washed with deionized water to obtain clean peanut shell biomass. The peanut shell biomass was then pulverized and passed through an 80-mesh sieve to obtain peanut shell powder. 2) Calcination of FeP2 / PS-900 ℃ nanocatalyst: 0.5 g of peanut shell powder was weighed and dispersed in 2 mL of deionized water. Then, 0.35 g of ferric chloride hexahydrate and 2 g of sodium hypophosphite were added. After stirring evenly, the mixture was sonicated at 500 W for 1 h to obtain a homogeneous mixed solution. The mixed solution was dried in an oven at 60 ℃ for 12 h. After drying, the sample was placed in a porcelain boat and placed in a tube furnace with a heating rate of 5 ℃·min. -1 The sample was heat-treated at 900 °C for 2 h under an argon atmosphere, and then naturally cooled to room temperature. The sample was washed with deionized water until neutral. After washing, it was dried at 80 °C for 12 h to obtain FeP2 / PS nanocatalyst.

[0036] like Figure 1As shown, scanning electron microscopy (SEM) characterization tests revealed that the catalyst material exhibits a blocky, tightly packed structure with a highly irregular, loose, and porous three-dimensional structure, resembling a sponge or honeycomb.

[0037] like Figure 2 As shown, elemental mapping distribution tests reveal that C, Fe, P, and O elements are uniformly distributed within the selected material region. The Fe content is 7.4 wt%, the P content is 16.79 wt%, and the O content is 11.15 wt%. P is in excess in FeP, and the Fe mass percentage is calculated using the formula (wt%). Fe ×M FeP2 ) / M Fe The calculated FeP2 loading was 16.78 wt%, of which wt% was... Fe M represents the mass content of iron. FeP2 M is the relative molecular mass of FeP2. Fe is the relative atomic mass of Fe.

[0038] like Figure 3 As shown, X-ray diffraction (XRD) tests on the catalyst prepared in Example 1 showed the formation of iron phosphide. The characteristic peaks of the catalyst were located at 2θ = 31.54° and 48.60°, which were attributed to the (002) and (022) crystal planes of FeP2, respectively, consistent with the standard card (PDF#06-0561), confirming the formation of iron phosphide.

[0039] like Figure 4 As shown, the surface of the FeP2 / PS catalyst material was analyzed using X-ray photoelectron spectroscopy (XPS), in which... Figure 4 Several significant peaks can be observed, namely P 2p (137 eV), P 2s (195 eV), C 1s (288 eV), O 1s (535 eV) and Fe 2p (718 eV), indicating that C, O, P and Fe elements are present in the catalyst material.

[0040] Figure 4 b is the C 1s spectrum, showing four peaks: 284.8 eV, 286.11 eV, 287.64 eV, and 289.27 eV, corresponding to C-C, CP, OC=O, and C=O bonds, respectively. This indicates that phosphorus has been doped into the carbon material, demonstrating the successful incorporation of phosphorus.

[0041] Figure 4 c is the Fe 2p spectrum, which shows 2p. 3 / 2 and 2p 1 / 2 The Fe-P bonds on the orbitals correspond to 710.8 eV and 722.55 eV, Fe2+ (713.06 eV and 726.36 eV), Fe 3+ (715.94 eV and 729.46 eV), with satellite peaks corresponding to 718.28 eV and 733.25 eV, respectively. Fe exists in multiple positively charged forms in the catalyst, which can more effectively react with NO. 2- Combine.

[0042] Figure 4 d is the P 2p spectrum, showing four peaks: 128.42 eV, 129.17 eV, 134.15 eV, and 135.00 eV, corresponding to the P 2p peaks associated with the P-Fe bond, respectively. 1 / 2 and P 2p 3 / 2 The presence of PO and P=O bonds, and Fe-P bonds, indicates that Fe and P are chemically linked together, confirming the formation of iron phosphide.

[0043] like Figure 5 As shown in the Raman spectroscopy, the FeP2 / PS catalyst, compared to the Fe / PS catalyst prepared by the same method but without the addition of sodium hypophosphite (Comparative Example 1), the P / PS catalyst without the addition of ferric chloride hexahydrate, and the peanut shell biochar PS catalyst without the addition of iron and phosphorus sources, exhibits significantly higher Ig content. D / I G The larger ratio indicates that the addition of sodium hypophosphite as a phosphorus source reduces the graphitization degree of carbon materials, increases carbon defects, and facilitates the exposure of FeP2 / PS active sites.

[0044] Example 2 A biomass-derived carbon-supported iron phosphide nanocatalyst was prepared according to the following steps: 1) Peanut shell biomass pretreatment: 30 g of waste peanut shells were crushed into powder and placed in a beaker. Potassium hydroxide activator and deionized water were added. The mass ratio of peanut shell powder, potassium hydroxide and deionized water was 1:1.5:2. After stirring for 2 hours until uniform, the mixture was placed in an oven and heated at 90 °C for 10 hours to activate and create pores. After cooling to room temperature, 1 M hydrochloric acid solution was added to adjust the pH to 7.0. The mixture was washed with deionized water to obtain clean peanut shell biomass. The peanut shell biomass was then pulverized and passed through an 80-mesh sieve to obtain peanut shell powder. 2) Calcination of FeP2 / PS-700 ℃ nanocatalyst: 0.5 g of raw peanut shell powder was weighed and dispersed in 2 mL of deionized water. Then, 0.35 g of ferric chloride hexahydrate and 2 g of sodium hypophosphite were added, stirred evenly, and ultrasonicated at 500 W for 1 h to obtain a homogeneous mixed solution. The mixed solution was dried in an oven at 60 ℃ for 12 h. After drying, the sample was placed in a porcelain boat and placed in a tube furnace with a heating rate of 5 ℃·min.-1 The sample was heat-treated at 700 °C for 2 h under an argon atmosphere and then naturally cooled to room temperature. The sample was washed with deionized water until neutral and then dried at 80 °C for 12 h to obtain FeP2 / PS-700 °C nanocatalyst.

[0045] like Figure 6 As shown, scanning electron microscopy (SEM) tests revealed that the catalyst material exhibits a solid, tightly packed block structure with few pores.

[0046] like Figure 7 As shown, the elemental mapping distribution test reveals that C, Fe, P, and O elements are uniformly distributed within the selected material region, with Fe content at 8.6 wt%, P content at 17.88 wt%, and O content at 10.6 wt%. The FeP2 loading, calculated as the Fe element mass percentage according to the formula described in Example 1, is 19.5 wt%.

[0047] like Figure 8 As shown, X-ray diffraction (XRD) tests confirmed the formation of iron phosphide. The characteristic peaks of the catalyst were located at 2θ = 31.54° and 48.60°, which were attributed to the (002) and (022) crystal planes of FeP2, respectively, consistent with the standard card (PDF#06-0561), thus confirming the formation of iron phosphide.

[0048] Example 3 A biomass-derived carbon-supported iron phosphide nanocatalyst was prepared according to the following steps: 1) Peanut shell biomass pretreatment: 20g of waste peanut shells were crushed into powder and placed in a beaker. Potassium hydroxide activator and deionized water were added. The mass ratio of peanut shell powder, potassium hydroxide and deionized water was 1:1:2. After stirring for 2 hours until uniform, the mixture was placed in an oven and heated at 100℃ for 12 hours to activate and create pores. After cooling to room temperature, 1M hydrochloric acid solution was added to adjust the pH to 7.0. The mixture was washed with deionized water to obtain clean peanut shell biomass. The peanut shell biomass was then pulverized and passed through an 80-mesh sieve to obtain peanut shell powder. 2) Calcination of FeP2 / PS-800 ℃ nanocatalyst: 0.5 g of peanut shell powder was weighed and dispersed in 2 mL of deionized water. Then, 0.35 g of ferric chloride hexahydrate and 2 g of sodium hypophosphite were added, stirred evenly, and sonicated at 500 W for 1 h to obtain a homogeneous mixed solution. The mixed solution was dried in an oven at 60 ℃ for 12 h. After drying, the sample was placed in a porcelain boat and placed in a tube furnace with a heating rate of 5 ℃·min. -1The sample was heat-treated at 800 °C for 2 h under an argon atmosphere and then naturally cooled to room temperature. The sample was washed with deionized water until neutral and then dried at 80 °C for 12 h to obtain FeP2 / PS-800 °C nanocatalyst.

[0049] like Figure 9 As shown, scanning electron microscopy (SEM) tests reveal that the catalyst material is a solid, tightly packed mass with numerous pores.

[0050] like Figure 10 As shown, the elemental mapping distribution test reveals that C, Fe, P, and O elements are uniformly distributed within the selected material region, with Fe content at 6.83 wt%, P content at 16.75 wt%, and O content at 11.98 wt%. The FeP2 loading, calculated as the Fe element mass percentage according to the formula described in Example 1, is 15.49 wt%.

[0051] like Figure 11 As shown, the characteristic peaks of the catalyst, obtained by X-ray diffraction (XRD), are located at 2θ = 31.54° and 48.60°, which are attributed to the (002) and (022) crystal planes of FeP2, respectively, consistent with the standard card (PDF#06-0561), confirming the formation of iron phosphide and its loading onto biochar.

[0052] Example 4 A biomass-derived carbon-supported iron phosphide nanocatalyst was prepared according to the following steps: 1) Peanut shell biomass pretreatment: Example 4 uses the same method as Example 1 to prepare peanut shell biomass; 2) Calcination of FeP2 / PS-1000 ℃ nanocatalyst: 0.5 g of peanut shell powder was weighed and dispersed in 2 mL of deionized water. Then, 0.35 g of ferric chloride hexahydrate and 2 g of sodium hypophosphite were added, stirred evenly, and ultrasonicated at 500 W for 1 h to obtain a homogeneous mixed solution. The mixed solution was dried in an oven at 60 ℃ for 12 h. After drying, the sample was placed in a porcelain boat and placed in a tube furnace with a heating rate of 5 ℃·min. -1 The sample was heat-treated at 1000 °C for 2 h under an argon atmosphere and then naturally cooled to room temperature. The sample was washed with deionized water until neutral and then dried at 80 °C for 12 h to obtain FeP2 / PS-1000 °C nanocatalyst.

[0053] like Figure 12 As shown, scanning electron microscopy (SEM) tests revealed that the catalyst material exhibits a blocky accumulation, a rough granular texture, and pores on the surface, resulting in a large specific surface area.

[0054] like Figure 13 As shown, SEM elemental mapping distribution tests indicate that C, Fe, P, and O elements are uniformly distributed within the selected material region, with Fe content of 7.85 wt%, P content of 18.63 wt%, and O content of 17.79 wt%. The FeP2 loading was calculated to be 16.54 wt% based on the Fe mass percentage calculated using the formula described in Example 1.

[0055] like Figure 14 As shown, the characteristic peaks of the catalyst, obtained by X-ray diffraction (XRD), are located at 2θ = 31.54° and 48.60°, which are attributed to the (002) and (022) crystal planes of FeP2, respectively, consistent with the standard card (PDF#06-0561), confirming the formation of iron phosphide and its loading onto biochar.

[0056] Example 5 A biomass-derived carbon-supported iron phosphide nanocatalyst, prepared according to the following steps: 1) Peanut shell biomass pretreatment: 20 g of waste peanut shells were crushed into powder and placed in a beaker. Potassium hydroxide activator and deionized water were added. The mass ratio of peanut shell powder, potassium hydroxide and deionized water was 1:1:2. After stirring for 2 hours until uniform, the mixture was placed in an oven and heated at 100 °C for 12 hours to activate and create pores. After cooling to room temperature, 1 M hydrochloric acid solution was added to adjust the pH to 7.0. The mixture was washed with deionized water to obtain clean peanut shell biomass. The peanut shell biomass was then pulverized and passed through an 80-mesh sieve to obtain peanut shell powder. 2) Calcination of FeP2 / PS-900℃ nanocatalyst: 0.5 g of peanut shell powder was weighed and dispersed in 2 mL of deionized water. Then, 0.35 g of ferric nitrate and 2 g of sodium hypophosphite were added, stirred evenly, and sonicated at 500 W for 1 h to obtain a homogeneous mixed solution. The mixed solution was dried in an oven at 60 ℃ for 12 h. After drying, the sample was placed in a porcelain boat and placed in a tube furnace with a heating rate of 5 ℃·min. -1 The sample was heat-treated at 900 °C for 2 h under an argon atmosphere and then naturally cooled to room temperature. The sample was washed with deionized water until neutral and then dried at 80 °C for 12 h to obtain FeP2 / PS-900 °C nanocatalyst.

[0057] like Figure 15 As shown, scanning electron microscopy (SEM) tests revealed that the catalyst material has many pores and is stacked in a blocky manner.

[0058] Example 6 A biomass-derived carbon-supported iron phosphide nanocatalyst, prepared according to the following steps: 1) Peanut shell biomass pretreatment: 20 g of waste peanut shells were crushed into powder and placed in a beaker. Potassium hydroxide activator and deionized water were added. The mass ratio of peanut shell powder, potassium hydroxide and deionized water was 1:1:2. After stirring for 2 hours until uniform, the mixture was placed in an oven and heated at 100 ℃ for 12 hours to activate and create pores. After cooling to room temperature, 1M hydrochloric acid solution was added to adjust the pH to 7.0. The mixture was washed with deionized water to obtain clean peanut shell biomass. The peanut shell biomass was then pulverized and passed through an 80-mesh sieve to obtain peanut shell powder. 2) Calcination of FeP2 / PS-900℃ nanocatalyst: 0.5 g of peanut shell powder was weighed and dispersed in 2 mL of deionized water. Then, 0.35 g of ferric sulfate and 2 g of sodium hypophosphite were added, stirred evenly, and sonicated at 500 W for 1 h to obtain a homogeneous mixed solution. The mixed solution was dried in an oven at 60 ℃ for 12 h. After drying, the sample was placed in a porcelain boat and placed in a tube furnace with a heating rate of 5 ℃·min. -1 The sample was heat-treated at 900 °C for 2 h under an argon atmosphere and then naturally cooled to room temperature. The sample was washed with deionized water until neutral and then dried at 80 °C for 12 h to obtain FeP2 / PS-900 °C nanocatalyst.

[0059] like Figure 16 As shown, scanning electron microscopy (SEM) tests reveal a clear three-dimensional structure on the surface of the catalyst material, including wrinkles and particles.

[0060] Example 7 A biomass-derived carbon-supported iron phosphide nanocatalyst, prepared according to the following steps: 1) Sugarcane bagasse biomass pretreatment: 20 g of sugarcane bagasse was crushed into powder and placed in a beaker. Potassium hydroxide activator and deionized water were added. The mass ratio of sugarcane bagasse powder, potassium hydroxide and deionized water was 1:1:2. After stirring for 2 hours until uniform, the mixture was placed in an oven and heated at 100 ℃ for 12 hours to activate and create pores. After cooling to room temperature, 1M hydrochloric acid solution was added to adjust the pH to 7.0. The mixture was washed with deionized water to obtain clean sugarcane bagasse biomass. The sugarcane bagasse biomass was then pulverized and passed through an 80-mesh sieve to obtain sugarcane bagasse powder. 2) Calcination of FeP2 / PS-900℃ nanocatalyst: Weigh 0.5 g of sugarcane bagasse powder, disperse it in 2 mL of deionized water, then add 0.3 g of ferric chloride hexahydrate and 2 g of sodium hypophosphite, stir evenly, and sonicate at 500 W for 1 h to obtain a homogeneous mixed solution; place the mixed solution in an oven at 60 ℃ and dry for 12 h; after drying, place the sample in a porcelain boat in a tube furnace, and heat at a rate of 5 ℃·min. -1The sample was heat-treated at 900 °C for 2 h under an argon atmosphere and then naturally cooled to room temperature. The sample was washed with deionized water until neutral and then dried at 80 °C for 12 h to obtain FeP2 / PS-900 °C nanocatalyst.

[0061] like Figure 17 As shown, scanning electron microscopy (SEM) tests reveal that the catalyst material exhibits a tubular structure with abundant specific surface area.

[0062] Example 8 A biomass-derived carbon-supported iron phosphide nanocatalyst, prepared according to the following steps: 1) Pretreatment of corn stalk biomass: 20 g of corn stalks were crushed into powder and placed in a beaker. Potassium hydroxide activator and deionized water were added. The mass ratio of corn stalk powder, potassium hydroxide and deionized water was 1:1:2. 2 mL of deionized water was added and stirred for 2 h until uniform. The mixture was then placed in an oven and heated at 100 ℃ for 12 h to activate and create pores. After cooling to room temperature, 1 M hydrochloric acid solution was added to adjust the pH to 7.0. The mixture was washed with deionized water to obtain clean corn stalk biomass. The corn stalk biomass was then pulverized and passed through an 80-mesh sieve to obtain corn stalk powder. 2) Calcination of FeP2 / PS-900℃ nanocatalyst: 0.5 g of corn stalk powder was weighed and dispersed in 2 mL of deionized water. Then, 0.35 g of ferric chloride hexahydrate and 2 g of sodium hypophosphite were added, stirred evenly, and sonicated at 500 W for 1 h to obtain a homogeneous mixed solution. The mixed solution was dried in an oven at 60 ℃ for 12 h. After drying, the sample was placed in a porcelain boat and placed in a tube furnace with a heating rate of 5 ℃·min. -1 The sample was heat-treated at 900 °C for 2 h under an argon atmosphere and then naturally cooled to room temperature. The sample was washed with deionized water until neutral and then dried at 80 °C for 12 h to obtain FeP2 / PS-900 °C nanocatalyst.

[0063] like Figure 18 As shown, scanning electron microscopy (SEM) tests reveal that the catalyst material exhibits a blocky accumulation with numerous surface pores and a rich specific surface area.

[0064] Application Example 1 Electrocatalytic synthesis of ammonia from nitrite using FeP2 / PS-900 ℃ nanocatalyst and performance testing: 1) Preparation of slurry: Take 0.005 g of the FeP2 / PS-900 ℃ nanocatalyst prepared in Example 1, dissolve it in a mixed solution of 0.75 mL of anhydrous ethanol and 0.20 mL of deionized water, then add 0.05 mL of a perfluorosulfonate naphthol solution with a resin solid content of 5-10 wt%, and sonicate at 500 W for 1 h to obtain a slurry; take 50 μL of the solution and drop it onto a glassy carbon electrode, dry it under an infrared lamp, and then perform electrochemical tests; 2) Electrocatalytic nitrite-to-ammonia synthesis performance test: 100 mL of 0.1 M NaNO₂ solution (dissolved in 1 M NaOH solution) was placed in an H-type electrolytic cell. Using Ag / AgCl as the reference electrode and Pt as the counter electrode, electrolysis was performed for 1 h under the following conditions: -0.1 V vs. RHE, -0.2 V vs. RHE, -0.3 V vs. RHE, -0.4 V vs. RHE, -0.5 V vs. RHE, and -0.6 V vs. RHE. After the reaction was complete, 0.5 mL of electrolyte was transferred to a 25 mL colorimetric tube, and the volume was adjusted to 25 mL with 1 M NaOH. 1 mL of potassium sodium tartrate solution (0.58 g / mL) was added dropwise and shaken well. Then, 1 mL of potassium mercuric iodide solution (0.172 g / mL) was added dropwise. After standing for 15 min, the absorbance at 420 nm was measured using a UV-Vis absorption spectrometer. According to the national standard "Water quality - Determination of ammonia nitrogen - Nessler's reagent spectrophotometric method (HJ 535-2009)", a standard ammonia solution was used to prepare a standard curve, and the ammonia yield and Faraday efficiency of the electrocatalytic system were obtained based on the sample test results.

[0065] like Figure 19 As shown, the FeP2 / PS-900℃ nanocatalyst electrocatalytic system prepared in Example 1 achieved a maximum Faradaic efficiency of 98.94% at -0.3 V. The ammonia yield reached 447.22 μmol·h⁻¹ at -0.6 V. -1 ·cm -2 This indicates that the prepared FeP2 / PS-900℃ nanomaterials possess excellent catalytic performance for the electrocatalytic synthesis of ammonia from nitrite.

[0066] like Figure 20-21 As shown, the FeP2 / PS nanocatalysts prepared in Example 1 and the Fe / PS nanocatalysts prepared in Comparative Example 1 were subjected to 15 electrolysis cycles at an optimal voltage of -0.3V. Figure 20 It can be seen that the FeP2 / PS catalyst maintained good stability and had excellent electrocatalytic ammonia synthesis performance in 15 electrolysis cycles; however, as shown in Figure 21, the Fe / PS nanocatalyst had poor stability after 15 cycles.

[0067] Application Example 2 Electrocatalytic synthesis of ammonia from nitrite using FeP2 / PS-700 ℃ nanocatalyst and performance testing: 1) Preparation of slurry: Take 0.005 g of the FeP2 / PS-700℃ nanocatalyst prepared in Example 2, dissolve it in a mixed solution of 0.75 mL of anhydrous ethanol and 0.20 mL of deionized water, then add 0.05 mL of a perfluorosulfonate naphthol solution with a resin solid content of 5-10 wt%, and sonicate at 500 W for 1 h to obtain a slurry; take 50 μL of the solution and drop it onto a glassy carbon electrode, dry it under an infrared lamp, and then perform electrochemical tests. 2) Electrocatalytic nitrite-to-ammonia synthesis performance test: Application Example 2 uses the same method as Application Example 1 to electrocatalyze the synthesis of ammonia from nitrite and performs electrochemical detection.

[0068] like Figure 22 As shown, the FeP2 / PS-700 ℃ nanocatalyst electrocatalyst system exhibits the highest Faradaic efficiency, reaching 87.84% for ammonia synthesis at -0.5 V, with an ammonia yield of 421.69 μmol·h⁻¹ at -0.6 V. -1 ·cm -2 This indicates that the FeP2 / PS-700 °C nanomaterials prepared above possess excellent catalytic performance for the electrocatalytic synthesis of ammonia from nitrite.

[0069] Application Example 3 Electrocatalytic synthesis of ammonia from nitrite using FeP2 / PS-800 ℃ nanocatalyst and performance testing: 1) Preparation of slurry: Take 0.005 g of the FeP2 / PS-800 ℃ nanocatalyst prepared in Example 3, dissolve it in a mixed solution of 0.75 mL of anhydrous ethanol and 0.20 mL of deionized water, then add 0.05 mL of a perfluorosulfonate naphthol solution with a resin solid content of 5-10 wt%, and sonicate at 500 W for 1 h to obtain a slurry; take 50 μL of the solution and drop it onto a glassy carbon electrode, dry it under an infrared lamp, and then perform electrochemical tests. 2) Electrocatalytic nitrite-to-ammonia synthesis performance test: Application Example 3 uses the same method as Application Example 1 to electrocatalyze the synthesis of ammonia from nitrite and performs electrochemical detection.

[0070] like Figure 23 As shown, the FeP2 / PS-800 ℃ nanocatalyst electrocatalytic system exhibits the highest Faradaic efficiency, reaching 82.55% for ammonia synthesis at -0.5 V, with an ammonia yield of 385.23 μmol·h⁻¹ at -0.6 V. -1·cm -2 This indicates that the FeP2 / PS-800 ℃ nanomaterials prepared above possess excellent catalytic performance for the electrocatalytic synthesis of ammonia from nitrite.

[0071] Application Example 4 Electrocatalytic synthesis of ammonia from nitrite using FeP2 / PS-1000 ℃ nanocatalyst and performance testing: 1) Preparation of slurry: Take 0.005 g of the FeP2 / PS-1000 ℃ nanocatalyst prepared in Example 4, dissolve it in a mixed solution of 0.75 mL of anhydrous ethanol and 0.20 mL of deionized water, then add 0.05 mL of a perfluorosulfonate naphthol solution with a resin solid content of 5-10 wt%, and sonicate at 500 W for 1 h to obtain a slurry; take 50 μL of the solution and drop it onto a glassy carbon electrode, dry it under an infrared lamp, and then perform electrochemical tests. 2) Electrocatalytic nitrite-to-ammonia synthesis performance test: Application Example 4 uses the same method as Application Example 1 to electrocatalyze the synthesis of ammonia from nitrite and performs electrochemical detection.

[0072] like Figure 24 As shown, the FeP2 / PS-1000 ℃ nanocatalyst electrocatalytic system exhibits the highest Faradaic efficiency, reaching 82.79% for ammonia synthesis at -0.4 V, with an ammonia yield of 435.06 μmol·h⁻¹ at -0.6 V. -1 ·cm -2 This indicates that the FeP2 / PS-1000 °C nanomaterials prepared above possess excellent catalytic performance for the electrocatalytic synthesis of ammonia from nitrite.

[0073] Comparative Example 1 Preparation of Fe / PS-900 ℃ catalyst and performance testing of electrocatalytic nitrite-to-ammonia synthesis: 1) Preparation of Fe / PS-900 ℃ catalyst: Weigh 0.5 g of peanut shell powder prepared in Example 1, disperse it in 2 mL of deionized water, then add 0.35 g of ferric chloride hexahydrate, stir evenly, sonicate for 1 h, and dry in an oven at 60 ℃ for 12 h. After drying, place the sample in a porcelain boat and put it in a tube furnace, with a heating rate of 5 ℃·min. -1 The sample was heat-treated at 900 °C for 2 h under an argon atmosphere. After cooling to room temperature, the sample was washed with deionized water until the wash water was neutral. After washing, the sample was dried at 80 °C for 12 h to obtain Fe / PS-900 °C nanocatalyst. 2) Electrocatalytic nitrite-to-ammonia synthesis performance test: Comparative Example 1 used the same method as Application Example 1 to prepare the slurry and electrocatalytically synthesize ammonia from nitrite, and performed electrochemical detection.

[0074] like Figure 25 As shown, the Fe / PS-900 ℃ catalyst synthesized without sodium hypophosphite exhibits a blocky structure, with relatively fewer pores and a relatively thicker carbon layer compared to the FeP2 / PS-900 ℃ catalyst prepared with sodium hypophosphite.

[0075] like Figure 26 As shown, the elemental mapping distribution test shows that C, Fe, and O elements are uniformly distributed in the selected material region, with Fe content of 8.73 wt% and O content of 11.83 wt%.

[0076] like Figure 27 As shown, the maximum Faradaic efficiency of the Fe / PS-900℃ nanocatalyst electrocatalyst system reached 81.83% at -0.4V; the ammonia yield reached 324.47 μmol·h⁻¹ at -0.6V. -1 ·cm -2 Compared to the FeP2 / PS-900℃ catalyst prepared by adding sodium hypophosphite in Example 1, the ammonia yield decreased by 122.75 μmol·h⁻¹ at -0.6 V. -1 ·cm -2 This indicates that the addition of a phosphorus source improved the catalytic activity of the catalyst.

[0077] like Figure 28 As shown in the figure, the electrocatalytic faradaic efficiency of the Fe / PS-900 ℃ catalyst prepared in Comparative Example 1 and the FeP2 / PS-900 ℃ catalyst prepared in Example 1 at different voltages is compared. As can be seen from the figure, the electrocatalytic faradaic efficiency of the FeP2 / PS-900 ℃ catalyst material is higher than that of the Fe / PS-900 ℃ catalyst material over a wide voltage range.

[0078] like Figure 29 The figure shows a comparison of the ammonia yields of NO2- reduction at different voltages between the Fe / PS-900℃ catalyst prepared in Comparative Example 1 and the FeP2 / PS-900℃ catalyst prepared in Example 1. As can be seen from the figure, the ammonia yield of the FeP2 / PS-900℃ catalyst is higher than that of the Fe / PS-900℃ catalyst over a wide voltage range.

[0079] In summary, the FeP2 / PS composite material prepared by the method provided in this invention can be efficiently used as a catalyst in the electrocatalytic reduction of nitrate to ammonia synthesis under mild conditions of room temperature and pressure. Furthermore, this material exhibits significant Faradaic efficiency and ammonia yield, and maintains excellent catalytic stability after multiple cycles, demonstrating good cycling stability. In contrast, the catalytic stability of Fe / PS catalysts is inferior to that of FeP2 / PS catalysts.

[0080] The above embodiments are merely illustrative of preferred embodiments of the present invention and are not intended to limit it. Any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention without departing from the essential content of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A biomass-derived carbon-supported iron phosphide nanocatalyst, characterized in that, The catalyst includes biomass carbon materials and FeP2 nanoparticles supported on the biomass carbon materials, wherein the loading of iron phosphide accounts for 5.22%-39.46 wt% of the total mass of the catalyst, and the phosphorus source of the FeP2 nanoparticles is sodium hypophosphite.

2. The biomass-derived carbon-supported iron phosphide nanocatalyst according to claim 1, characterized in that, Based on elemental composition, Fe accounts for 2.3-17.4 wt% of the total weight of the nanocatalyst, P accounts for 15.76-28.89 wt% of the total weight of the nanocatalyst, and O accounts for 2.46-24.34 wt% of the total weight of the nanocatalyst.

3. The biomass-derived carbon-supported iron phosphide nanocatalyst according to claim 1, characterized in that, The loading of iron phosphide accounts for 16.78 wt% of the total mass of the catalyst; the content of Fe accounts for 7.4 wt% of the total weight of the nanocatalyst, the content of P accounts for 16.79 wt% of the total weight of the nanocatalyst, and the content of O accounts for 11.15 wt% of the total weight of the nanocatalyst.

4. The method for preparing biomass-derived carbon-supported iron phosphide nanocatalysts according to claims 1-3, characterized in that, Includes the following steps: 1) Mix the pretreated waste biomass powder with phosphorus source precursor and iron source precursor, add deionized water, stir evenly and then sonicate to obtain a mixed solution. 2) Dry the mixed solution from step 1), grind it, and place it in a tube furnace. Inert gas is introduced for calcination. The calcined material is then washed with deionized water and dried.

5. The method for preparing biomass-derived carbon-supported iron phosphide nanocatalyst according to claim 4, characterized in that, The biomass is selected from peanut shells, sugarcane bagasse, or corn stalks; the iron salt precursor is at least one of ferric chloride hexahydrate, ferric nitrate, and ferric sulfate; the phosphate salt precursor is sodium hypophosphite; the mass ratio of the biomass powder, iron source precursor, phosphate source precursor, and deionized water is 0.5:0.15-0.45:1-4:2-10; the inert gas is argon or nitrogen.

6. The method for preparing biomass-derived carbon-supported iron phosphide nanocatalyst according to claim 4, characterized in that, The ultrasound conditions described in step 1) are 500W ultrasound for 1-2 hours; The drying conditions described in step 2) are both drying at 60-80℃ in an oven for 12-24 hours; Step 2) The inert gas is argon or nitrogen; The tubular furnace setting program in step 2) is to raise the temperature to 600-900℃ at a heating rate of 5-10℃ / min and hold it for 1-2 hours.

7. The method for preparing biomass-derived carbon-supported iron phosphide nanocatalyst according to claim 4, characterized in that, The biomass is peanut shells, the iron source precursor is ferric chloride hexahydrate, and the mass ratio of biomass powder, iron source precursor, phosphorus source precursor and deionized water is 0.5:0.35:2:2; the tubular furnace setting program in step 2) is to heat to 900℃ at a heating rate of 5℃ / min and hold for 2 hours.

8. The method for preparing biomass-derived carbon-supported iron phosphide nanocatalyst according to claim 4, characterized in that, The pretreatment of the biomass powder includes the following steps: The biomass was crushed into powder and placed in a beaker. Potassium hydroxide and deionized water were added, with a mass ratio of biomass powder, potassium hydroxide and deionized water of 1:1-1.5:

2. The mixture was stirred for 2-3 hours until homogeneous, then placed in an oven and heated at 90-100℃ for 10-12 hours to activate and create pores. After cooling to room temperature, 1M hydrochloric acid solution was added to adjust the pH to 6.8-7.

2. The mixture was washed with deionized water to obtain clean biomass. The clean biomass was then pulverized and passed through an 80-mesh sieve to obtain biomass powder.

9. The application of the biomass-derived carbon-supported iron phosphide nanocatalyst according to any one of claims 1-4 in the electrocatalytic synthesis of ammonia from sodium nitrite, characterized in that, The electrocatalytic synthesis of ammonia from sodium nitrite is carried out in an H-type electrolytic cell, with a glassy carbon electrode coated with biomass-derived carbon-supported iron phosphide nanocatalyst slurry as the working electrode, an Ag / AgCl electrode as the reference electrode, and a carbon rod as the counter electrode. The specific steps for the electrocatalytic synthesis of ammonia from sodium nitrite are as follows: 1) The biomass-derived carbon-supported iron phosphide nanocatalyst is prepared into a slurry, coated onto a glassy carbon electrode, dried, and used as the working electrode; 2) Dissolve sodium nitrite in 1M sodium hydroxide solution to prepare 0.1M sodium nitrite solution as electrolyte. The mass ratio of the biomass-derived iron carbon phosphide nanocatalyst to NaNO2 is 0.72-1.45:1000-2000. Pour the solution into the electrolytic cell to carry out electrocatalytic ammonia production. The preparation method of the slurry in step 1) is as follows: Take 1-10 mg of the biomass-derived carbon-supported iron phosphide nanocatalyst, dissolve it in a mixed solution of 0.75-1.0 mL of anhydrous ethanol and 0.20-0.50 mL of deionized water, then add 50-80 μL of a perfluorosulfonate naphthol solution with a resin solid content of 5-10 wt%, and sonicate at 500 W for 0.5-1 h to obtain a slurry.

10. The application of the biomass-derived carbon-supported iron phosphide nanocatalyst according to claim 9 in the electrocatalytic synthesis of ammonia from sodium nitrite, characterized in that, Step 1) The preparation method of the slurry is as follows: Take 5 mg of the biomass-derived carbon-supported iron phosphide nanocatalyst, dissolve it in a mixed solution of 0.75 mL of anhydrous ethanol and 0.20 mL of deionized water, then add 50 μL of a perfluorosulfonate naphthol solution with a resin solid content of 5-10 wt%, and sonicate at 500 W for 0.5-1 h to obtain the slurry.

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