A nitrogen and phosphorus co-doped iron-nickel-based porous biomass charcoal catalyst, a preparation method and application thereof

Abstract

The application discloses a nitrogen and phosphorus co-doped iron-nickel-based porous biomass charcoal catalyst and a preparation method and application thereof, and belongs to the technical field of electrocatalytic materials. The biomass charcoal is subjected to a hydrothermal reaction to obtain hydrothermal charcoal, the obtained hydrothermal charcoal is subjected to cold-alkali activation to obtain cold-alkali activated hydrothermal charcoal as a carbon source, Fe and Ni are in-situ complexed on the carbon source to obtain a precursor, then the precursor is subjected to N and P co-doping, and after high-temperature calcination, the nitrogen and phosphorus co-doped iron-nickel-based porous biomass charcoal catalyst is obtained. The catalyst has high specific surface area and porosity, and has many active sites, wherein the specific surface area is 160-163 m 2 / g, the pore volume is 0.15-0.18 cm 3 / g, and the average pore diameter is 5.5-7.4 nm. The preparation method of the catalyst comprises the following steps: (1) preparing hydrothermal charcoal; (2) cold-alkali activating the hydrothermal charcoal; (3) synthesizing a precursor; and (4) nitrogen and phosphorus co-doping. The catalyst is applied to an oxygen evolution reaction and exhibits excellent catalytic performance at a current density of 10 mA·cm ‑2 , and the overpotential is as low as 291 mV.

Description

Technical Field

[0001] The present invention belongs to the technical field of electrocatalytic materials, and in particular relates to a nitrogen-phosphorus co-doped iron-nickel based porous biomass carbon catalyst, a preparation method thereof, and an application thereof. Background Art

[0002] With the intensification of the energy resource crisis and the pressure of environmental pollution, the development and utilization of new energy and the high-value utilization of green resources are particularly important. Hydrogen energy, as a clean and pollution-free new energy source, is produced, stored and utilized through electrochemical reactions such as fuel cells, metal-air batteries and water splitting. The oxygen evolution reaction (OER) plays an important role and is a key step in electrochemical water splitting. During this reaction, the OH bond breaks and the OO bond forms, resulting in the formation of a high energy barrier. However, it requires a large overpotential, resulting in slow kinetics, so a catalyst is needed to accelerate the reaction. Currently, the most effective electrocatalysts are made of precious metals such as platinum, iridium and ruthenium. However, their limited supply, controlled deposition amount, scarcity and high cost greatly limit their commercial application. Therefore, it is necessary to develop catalysts that are easy to synthesize, have minimal interference, are easy to cooperate and exhibit high efficiency in OER, which is crucial for achieving efficient utilization of hydrogen energy.

[0003] Numerous studies have shown that transition metal elements such as Fe, Co, and Ni exhibit high activity in the oxygen reduction reaction (OER). Their widespread distribution, low cost, and significantly superior catalytic stability compared to precious metals have led them to become increasingly popular alternatives to precious metals. For example, the paper "Preparation and Performance of Nitrogen-Phosphorus Co-doped Iron-Based Biocarbon Catalysts for the Oxygen Reduction Reaction (ORE)" describes the preparation of phosphorus-nitrogen co-doped iron-based biocarbon materials with hierarchical porous carbon microspheres via a simple hydrothermal followed by co-pyrolysis method using bagasse as a carbon source, phytic acid as a phosphorus source, melamine as a nitrogen source, and Fe(NO₃)₃·9H₂O as an iron source. These materials were then applied to the oxygen reduction reaction (ORE). Studies of transition metal electrocatalysts have revealed that Ni, Co, and Fe-based catalysts have moderate binding energies, second only to those of precious metals. Nickel-based compounds are widely used in energy generation and storage devices due to their excellent catalytic performance, good electrical properties, low cost, and availability. However, the main challenge currently facing nickel-based OER catalysts is their low electrical conductivity and stability.

[0004] To solve this problem, Ni can form alloys with other 3d transition metals, which can improve the electronic and structural properties of the catalyst, and the catalytic performance of binary alloys is better than that of single transition metals. Since the addition of adjacent Fe atoms changes the electronic structure of the surface Ni atoms, the OER activity is improved. Nickel-iron alloying is a better choice for developing highly active and stable water oxidation electrocatalysts, and its performance is better than that of a single catalyst. For example, patent publication number CN 116314857 A discloses a method for preparing an iron-nickel alloy / nitrogen-doped carbon nanocomposite electrocatalyst. During the preparation process, uniform FeNi alloyed active sites are formed in FeNi-CNC, which can improve the ORR / OER electrocatalytic activity of the composite material, which is better than commercial Pt / C catalysts. Therefore, the synergistic use of FeNi binary alloys and carbon supports is an effective method to improve the catalytic OER performance at a lower cost.

[0005] The performance of porous carbon materials as electrodes depends on the chemical properties that lead to the high density of OER-active pyridinic N and ORR-active quaternary N groups, as well as the porosity of the material. These factors determine the exposure of the active sites to the relevant chemical species and help prevent rapid clogging of the planar electrode surface. Transition metal phosphides (TMPs) are promising catalysts for the OER reaction due to their high conductivity and good electrochemical performance. Phosphorus-containing compounds have high electronegativity and weak metal-phosphorus bond dissociation, making them susceptible to surface remodeling. The phosphorus element in metal phosphides has two functions: first, it acts as a hydride acceptor to promote hydrogen adsorption; second, it modulates the adsorption characteristics of surrounding metal atoms by donating or withdrawing electrons, thereby changing their electron density. In metal phosphides, the metal typically has two additional functions: one is to act as a proton acceptor, and the other is to enhance the conductivity of the catalyst. Therefore, phosphorus-doped sites can modulate the charge distribution of the carbon framework and FeNi / N, thereby optimizing the adsorption and desorption capacity of intermediates and products, ultimately improving the activity of the catalyst. Summary of the Invention

[0006] In response to the above problems, the present invention provides a nitrogen-phosphorus co-doped iron-nickel-based porous biomass carbon catalyst, a preparation method and application thereof. The nitrogen-phosphorus co-doped iron-nickel-based porous biomass carbon catalyst is prepared by self-assembly precipitation and in situ pyrolysis. The catalyst has a three-dimensional network porous structure, high specific surface area and porosity, multiple active sites, and good catalytic performance in the oxygen evolution reaction.

[0007] The present invention is achieved through the following technical solutions:

[0008] A nitrogen-phosphorus co-doped iron-nickel-based porous biomass carbon catalyst is prepared by subjecting biomass carbon to a hydrothermal reaction to obtain hydrothermal carbon, which is then subjected to cold alkali activation to obtain cold alkali-activated hydrothermal carbon as a carbon source, and Fe and Ni are in situ complexed on the carbon source to obtain a precursor, which is then co-doped with N and P and calcined at high temperature to obtain a nitrogen-phosphorus co-doped iron-nickel-based porous biomass carbon catalyst.

[0009] Furthermore, the nitrogen and phosphorus co-doped iron-nickel based porous biomass carbon catalyst is a three-dimensional network porous structure with a specific surface area of ​​160 to 163 m 2 / g, pore volume of 0.15~0.18cm 3 / g, and the average pore diameter is 5.5~7.4nm.

[0010] A method for preparing the nitrogen and phosphorus co-doped iron and nickel-based porous biochar catalyst as described above comprises the following steps:

[0011] (1) Preparation of hydrothermal charcoal: sugarcane bagasse is added to a hydrochloric acid solution, stirred, and then transferred to a reactor for hydrothermal reaction. After the reaction is completed, the mixture is naturally cooled to room temperature. The resulting product is washed and dried to obtain hydrothermal charcoal.

[0012] (2) Cold alkali activation of hydrothermal carbon: The hydrothermal carbon prepared in step (1) is placed in a NaOH solution for cold alkali activation. After the activation is completed, the carbon is centrifuged, washed, and dried to obtain cold alkali activated hydrothermal carbon;

[0013] (3) Synthesis of the precursor: Fe(NO3)3·9H2O and Ni(CH3COO)2·4H2O were dissolved in water, stirred vigorously to mix evenly, and the resulting mixed solution was added dropwise to the aqueous solution of the cold alkali-activated hydrothermal carbon in step (2). After stirring, the pH of the solution was adjusted to alkaline. After filtration, the resulting product was washed and dried to obtain a precursor;

[0014] (4) Nitrogen and phosphorus co-doping: The precursor of step (3) is mixed with urea and uniformly ground, and sodium dihydrogen phosphate is added, followed by high-temperature calcination. After calcination, the mixture is cooled to room temperature to obtain a nitrogen and phosphorus co-doped iron-nickel-based porous biomass carbon catalyst.

[0015] Furthermore, in step (1), the mass ratio of the bagasse to the hydrochloric acid solution is 4 g:40-45 mL, and the concentration of the hydrochloric acid solution is 0.1-0.15 mol / L.

[0016] Furthermore, in step (1), the temperature of the hydrothermal reaction is 210-230° C., and the time is 10-12 h.

[0017] Furthermore, in step (2), the mass ratio of the hydrothermal charcoal to the NaOH solution is 2.5 g:45-50 mL, the concentration of the NaOH solution is 1.3-1.5 mol / L; and the cold alkali activation time is 1.5-2 h.

[0018] Furthermore, in step (3), the mass ratio of Fe(NO3)3·9H2O and Ni(CH3COO)2·4H2O is 2.3:1.3~1.6; and the mass ratio of cold alkali activated hydrothermal carbon to water in the aqueous solution of cold alkali activated hydrothermal carbon is 1g:100~120mL.

[0019] Furthermore, in step (4), the mass ratio of the precursor, urea and sodium dihydrogen phosphate is 5:3-4:100-120.

[0020] Furthermore, in step (4), the high-temperature calcination is calcined in a nitrogen atmosphere at 280-300° C. for 1.5-2 hours, and then the temperature is raised to 700-800° C. and maintained for 1.5-2 hours.

[0021] An application of the nitrogen and phosphorus co-doped iron and nickel-based porous biochar catalyst in catalytic oxygen evolution reaction.

[0022] Preparation principle of the nitrogen and phosphorus co-doped iron-nickel based porous biomass carbon catalyst of the present invention:

[0023] (1) Preparation of hydrothermal charcoal: Sugarcane bagasse is added to a hydrochloric acid solution and subjected to a hydrothermal reaction. The cellulose, hemicellulose, and lignin in the bagasse are first decomposed into sugars and other small molecular compounds. These small molecules are then transformed into more complex structures through a series of hydrolysis and polymerization reactions. During the hydrothermal treatment, the small molecular compounds formed are further dehydrated and polymerized, eventually forming a carbon-rich solid substance, namely hydrothermal charcoal.

[0024] (2) Cold alkali activation of hydrothermal carbon: Placing hydrothermal carbon in NaOH solution for cold alkali activation can increase the oxygen-containing functional groups (such as hydroxyl and carboxyl) of hydrothermal carbon, enhance the surface chemical activity of carbon-based materials, and provide additional catalytic sites.

[0025] (3) Synthesis of precursor: Fe(NO3)3·9H2O and Ni(CH3COO)2·4H2O were dissolved in water, and the resulting mixed solution was added dropwise to the aqueous solution of cold alkali activated hydrothermal carbon. 2+ and Ni 2+ The ions form stable coordination compounds in water and combine with cold alkali activated hydrothermal carbon through ion exchange or adsorption, adjusting the pH of the solution to alkaline, causing the metal ions to precipitate or form nanoparticles and form a composite structure on the surface of the hydrothermal carbon.

[0026] (4) Nitrogen-phosphorus co-doping: The precursor is mixed and ground with urea, and then sodium dihydrogen phosphate is added. The urea decomposes to produce ammonia, which reacts with the carbon material to form a nitrogen-doped structure. At the same time, sodium dihydrogen phosphate also begins to decompose. After that, high-temperature calcination is performed to further promote the formation of phosphoric acid and the fixation of phosphorus in the carbon structure. At the same time, high temperature helps to form more stable metal oxides and more developed pore structures. The introduction of nitrogen and phosphorus heteroatoms can change the charge density and spin density of carbon atoms and increase active sites. At the same time, nitrogen and phosphorus doping can produce a synergistic effect, thereby improving the reduction performance of carbon materials.

[0027] Compared with the prior art, the advantages and beneficial effects of the present invention are:

[0028] 1. The present invention prepares nitrogen and phosphorus co-doped iron-nickel-based porous biomass carbon catalyst by self-assembly precipitation and in-situ pyrolysis. Specifically, the biomass carbon is subjected to a hydrothermal reaction to obtain hydrothermal carbon, the obtained hydrothermal carbon is subjected to cold alkali activation to obtain cold alkali activated hydrothermal carbon as a carbon source, Fe and Ni are in situ complexed on the carbon source to obtain a precursor, and then the precursor is co-doped with N and P, and after high-temperature calcination, a nitrogen and phosphorus co-doped iron-nickel-based porous biomass carbon catalyst is obtained. The catalyst has a three-dimensional network porous structure and a specific surface area of ​​160 to 163 m 2 / g, pore volume of 0.15~0.18cm 3 / g, with an average pore size of 5.5-7.4 nm, high specific surface area and porosity, and many active sites, and has good catalytic performance in oxygen evolution reaction.

[0029] 2. The present invention utilizes a FeNi alloy derived from a carbon layer of nitrogen-doped bagasse to optimize the electronic structure and enhance electron transfer. The porous structure is formed by the PH3 gas generated during the pyrolysis of NaH2PO3, which mixes thoroughly with the carbon material at high temperatures and low gas velocities. This microstructured catalytic layer has a larger active surface area than pure carbon nanoporous structures, providing more catalytically active sites for the oxygen evolution reaction.

[0030] 3. The catalyst of the present invention is a carbon material doped with multiple heteroatoms including N, P, Fe, and Ni. It is assembled from nanoparticles and is a porous bimetallic nitrogen phosphide with a three-dimensional porous network structure and a high density of electrochemically active sites. The catalyst's mesoporous pore structure provides more reaction sites for the oxygen evolution reaction, improving molecular diffusion efficiency.

[0031] 4. The catalyst of the present invention is applied to oxygen evolution reaction, and its -2 It exhibits excellent catalytic performance at a current density of 1.5 wt %. In the oxygen evolution reaction, the overpotential is as low as 291 mV, with high catalytic activity and high reaction efficiency, and has great application value for achieving efficient utilization of hydrogen energy. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 These are the XRD patterns of FeNi / AHC-NP, FeNi / HC-N, FeNi / HC-P and FeNi / HC prepared in Example 1 and Comparative Examples 1-3, respectively.

[0033] Figure 2 This is the SEM image of FeNi / AHC-NP prepared in Example 1.

[0034] Figure 3 This is the EDS element distribution diagram of FeNi / AHC-NP prepared in Example 1.

[0035] Figure 4 Graph showing the N2 adsorption-desorption isotherm and pore size distribution curve of FeNi / AHC-NP prepared in Example 1.

[0036] Figure 5 The OER-LSV curves and Tafel slope diagrams of FeNi / AHC-NP, FeNi / HC-N, FeNi / HC-P and FeNi / HC in Application Example 1 and Comparative Examples 1-3 are shown. DETAILED DESCRIPTION

[0037] The present invention is further described in detail below through examples. These examples are only used to illustrate the present invention and do not limit the scope of protection of the present invention.

[0038] Example 1

[0039] Preparation of Nitrogen and Phosphorus Co-doped Iron-Ni Based Porous Biochar Catalyst:

[0040] (1) Preparation of hydrothermal charcoal: 4 g of bagasse was added to 40 mL of 0.1 mol / L hydrochloric acid solution and stirred for 4 h. The mixture was then placed in a 100 mL polytetrafluoroethylene liner of a hydrothermal autoclave. The autoclave was placed in an oven at 220 °C for 12 h. After the reaction was completed, the mixture was naturally cooled to room temperature, washed with water and ethanol in sequence, and dried to obtain hydrothermal charcoal (denoted as HC).

[0041] (2) Cold alkali activated hydrothermal carbon: 2.5 g of hydrothermal carbon was placed in 50 mL of 1.5 mol / L sodium hydroxide solution and activated for 2 h. After activation, the mixture was centrifuged, washed, and dried to obtain cold alkali activated hydrothermal carbon (denoted as AHC).

[0042] (3) Synthesis of precursor: 2.302 g of Fe(NO3)3·9H2O and 1.434 g of Ni(CH3COO)2·4H2O were vigorously stirred into 50 mL of pure water and added dropwise to a 1 g / 100 mL aqueous solution of cold alkali-activated hydrothermal carbon. After stirring for 10 min, the pH was adjusted to 8, filtered, washed, and washed with ultrapure water until neutral, and then dried at 80 °C for 24 h to obtain the precursor.

[0043] (4) Nitrogen-phosphorus co-doping: 50 mg of the precursor and 30 mg of urea were mixed and evenly ground, 1 g of sodium dihydrogen phosphate was added upstream, and the mixture was calcined at 300 °C in a nitrogen atmosphere for 2 h, then heated to 800 °C and maintained for 2 h, and cooled to room temperature to obtain a nitrogen-phosphorus co-doped iron-nickel-based porous biochar catalyst (denoted as FeNi / AHC-NP).

[0044] Example 2

[0045] Preparation of Nitrogen and Phosphorus Co-doped Iron-Ni Based Porous Biochar Catalyst:

[0046] (1) Preparation of hydrothermal charcoal: 4 g of bagasse was added to 45 mL of 0.1 mol / L hydrochloric acid solution and stirred for 4 h. The mixture was then placed in a 100 mL polytetrafluoroethylene liner of a hydrothermal autoclave. The autoclave was placed in an oven at 210 °C for 12 h. After the reaction was completed, the mixture was naturally cooled to room temperature, washed with water and ethanol, and dried to obtain hydrothermal charcoal.

[0047] (2) Cold alkali activated hydrothermal carbon: 2.5 g of hydrothermal carbon was placed in 45 mL of 1.5 mol / L sodium hydroxide solution and activated for 2 h. After activation, the carbon was centrifuged, washed, and dried to obtain cold alkali activated hydrothermal carbon.

[0048] (3) Synthesis of precursor: 2.301 g of Fe(NO3)3·9H2O and 1.375 g of Ni(CH3COO)2·4H2O were vigorously stirred into 50 mL of pure water and added dropwise to a 1 g / 110 mL aqueous solution of cold alkali-activated hydrothermal carbon. After stirring for 10 min, the pH was adjusted to 8, filtered, washed, and washed with ultrapure water until neutral, and then dried at 80 °C for 24 h to obtain the precursor.

[0049] (4) Nitrogen-phosphorus co-doping: 50 mg of the precursor and 35 mg of urea were mixed and evenly ground, 1.1 g of sodium dihydrogen phosphate was added upstream, and the mixture was calcined at 280 °C in a nitrogen atmosphere for 2 h, then heated to 700 °C and maintained for 2 h, and cooled to room temperature to obtain a nitrogen-phosphorus co-doped iron-nickel-based porous biomass carbon catalyst.

[0050] Example 3

[0051] Preparation of Nitrogen and Phosphorus Co-doped Iron-Ni Based Porous Biochar Catalyst:

[0052] (1) Preparation of hydrothermal charcoal: 4 g of bagasse was added to 40 mL of 0.15 mol / L hydrochloric acid solution and stirred for 4 h. The mixture was then placed in a 100 mL polytetrafluoroethylene liner of a hydrothermal autoclave. The autoclave was placed in an oven at 230 °C for 10 h. After the reaction was completed, the mixture was naturally cooled to room temperature, washed with water and ethanol in sequence, and dried to obtain hydrothermal charcoal.

[0053] (2) Cold alkali activated hydrothermal carbon: 2.5 g of hydrothermal carbon was placed in 45 mL of 1.3 mol / L sodium hydroxide solution and activated for 1.5 h. After activation, the carbon was centrifuged, washed, and dried to obtain cold alkali activated hydrothermal carbon.

[0054] (3) Synthesis of precursor: 2.302 g of Fe(NO3)3·9H2O and 1.571 g of Ni(CH3COO)2·4H2O were vigorously stirred into 50 mL of pure water and added dropwise to a 1 g / 120 mL aqueous solution of cold alkali-activated hydrothermal carbon. After stirring for 10 min, the pH was adjusted to 8, filtered, washed, and washed with ultrapure water until neutral, and then dried at 80 °C for 24 h to obtain the precursor.

[0055] (4) Nitrogen-phosphorus co-doping: 50 mg of the precursor and 40 mg of urea were mixed and evenly ground, 1.2 g of sodium dihydrogen phosphate was added upstream, and the mixture was calcined at 290 °C in a nitrogen atmosphere for 1.5 h, then heated to 750 °C and maintained for 1.5 h, and cooled to room temperature to obtain a nitrogen-phosphorus co-doped iron-nickel-based porous biomass carbon catalyst.

[0056] Comparative Example 1

[0057] The difference between Comparative Example 1 and Example 1 is that in Comparative Example 1, no sodium dihydrogen phosphate is added in step (4), and the rest of the preparation process and conditions are the same as those of Example 1, to obtain a nitrogen-doped iron-nickel-based biomass carbon catalyst (denoted as FeNi / AHC-N).

[0058] Comparative Example 2

[0059] The difference between Comparative Example 2 and Example 1 is that in Comparative Example 2, urea is not added in step (4), and the rest of the preparation process and conditions are the same as those of Example 1, to obtain a phosphorus-doped iron-nickel-based biomass carbon catalyst (denoted as FeNi / AHC-P).

[0060] Comparative Example 3

[0061] The difference between Comparative Example 3 and Example 1 is that in Comparative Example 3, urea and sodium dihydrogen phosphate are not added in step (4), and the rest of the preparation process and conditions are the same as those of Example 1 to obtain an iron-nickel-based biomass carbon catalyst (denoted as FeNi / AHC).

[0062] Material characterization analysis

[0063] (1) X-ray diffraction (XRD) analysis

[0064] The FeNi / AHC-NP, FeNi / HC-N, FeNi / HC-P and FeNi / HC prepared in Example 1 and Comparative Examples 1-3 were characterized and analyzed by X-ray diffractometer (XRD) to reveal the crystal structure of the prepared samples. The characterization results are shown in FIG. Figure 1 As shown. Figure 1 It can be seen that the doping of N, P or NP has a significant effect on the phase composition and crystal structure of the final sample. When the sample is not doped with N, P or NP, the samples NiFe@C and NiFe@C-NaOH simultaneously generate diffraction peaks of nickel ferrite (PDF#99-000-3769) and Ni (PDF#04-002-752). When the sample is doped with N, P or NP, the diffraction peaks at 2θ=43.6°, 50.8°, 74.7° and 90.7° of these samples are related to the (111), (200), (220) and (311) planes of the face-centered cubic (fcc) FeNi alloy (04-002-1863). The main reason may be that they improve the adsorption capacity of metal ions, provide a reducing environment and stabilize the metal nanoparticles.

[0065] (2) Scanning electron microscopy (SEM) analysis

[0066] The FeNi / AHC-NP prepared in Example 1 was characterized and analyzed using a scanning electron microscope (SEM). Figure 2 shown. Figure 2 (a), 2(b), and 2(c) are carbon microsphere structures magnified 2000 times, 5000 times, and 10000 times, respectively. Figure 2 (d), 2(e), and 2(f) are the flake morphologies magnified 2000 times, 5000 times, and 10000 times, respectively. Figure 2 As can be seen in Figures 2(a), 2(b), and 2(c), samples hydrothermally treated with hydrochloric acid exhibit distinct carbon microsphere structures. This is because the cellulose and hemicellulose in the bagasse undergo hydrolysis under acidic conditions to form water-soluble products, which then undergo dehydration, polymerization, polycondensation, and aromatization under hydrothermal pressure to form carbon microspheres. Figure 2Figures (d), (e), and (f) show the flaky structure of the bagasse biomass material. Compared to the flaky morphology, the flaky morphology has a higher specific surface area, exposing more active sites. The surface of the FeNi / AHC-NP composite material is uneven, and the carbon nanopores and particles have irregular geometries. On the one hand, the bagasse-derived carbon, as a carbon support for the catalyst material, has the advantages of being a naturally porous carbon material, providing a rich pore structure for the catalyst. On the other hand, the PH3 gas produced during the pyrolysis of NaH2PO2 is thoroughly mixed with the carbon material precursor at high temperature and low gas flow rate. This microstructured catalytic layer has an activated surface area greater than that of pure carbon nanoporous structures, providing more catalytic active sites for the oxygen evolution reaction. The particles have better adhesion to the catalyst cross-section and between the catalytic layer and the substrate. The fine nanoparticles (white phase) are more evenly embedded in the pores and between the catalytic layer and the substrate.

[0067] (3) Energy dispersive spectroscopy (EDS) analysis

[0068] The FeNi / AHC-NP prepared in Example 1 was characterized and analyzed by energy dispersive chromatograph (EDS). Figure 3 As shown. Figure 3 It can be seen that FeNi / AHC-NP2 is composed of C, O, Fe, Ni, N and P, and is uniformly distributed in the composite material.

[0069] (IV) Specific surface area and pore size analysis

[0070] The specific surface area and pore size of FeNi / AHC-NP prepared in Example 1 were analyzed. Figure 4 As shown. Figure 4 It can be seen that the Brunauer-Emmett-Teller (BET) of FeNi / AHC-NP is Figure 4 (a) Typical type IV adsorption isotherms and H1 hysteresis loops can be observed, which are the characteristics of mesoporous structures. The BET area reaches 161m 2 / g, pore volume of 0.15~0.16cm 3 / g, with an average pore size of 5.5-7.4 nm, which can provide an electrocatalytically active surface and expose active sites during the oxygen evolution reaction. Figure 4 (b) shows that the pore size of FeNi / AHC-NP is primarily distributed in the mesopores, although macropores are also present. This porous structure provides more reaction sites for oxygen evolution and improves molecular diffusion efficiency. The formation of a certain surface area and porous structure can enhance the catalytic activity of the oxygen evolution reaction and accelerate electron transfer.

[0071] (5) Elemental composition and atomic ratio analysis

[0072] Elemental analysis of HC and AHC in Example 1 is shown in Table 1 below.

[0073] Table 1 Elemental composition and atomic ratio of HC and AHC

[0074]

[0075] As shown in Table 1, after HC is activated by cold alkali, AHC is obtained. The oxygen content in AHC is significantly increased, and the O / C ratio of AHC increases, indicating that more oxygen-containing functional groups are generated on the surface of AHC, which is beneficial to improving the surface chemical activity of strong carbon-based materials and providing additional catalytic sites.

[0076] 4 mg of the FeNi / AHC-NP catalyst from Example 1 was dispersed in 375 mL of pure water, 125 mL of ethanol solution, and 50 mL of a 5% Nafion membrane solution. Ultrasonic treatment was performed for 60 min to obtain a uniformly dispersed suspension. The suspension was drop-coated on the surface of a glassy carbon electrode with a loading of 453 μg / cm 2 , and then tested after standing for 4 hours. Using an electrochemical workstation, -1 The catalyst was tested by cyclic voltammetry in a three-electrode system in a KOH electrolyte solution. The test showed that FeNi / AHC-NP required an overpotential of 290 mV to reach 10 mA cm -2 current density.

[0077] Comparative Application Example 1

[0078] The difference between Comparative Example 1 and Example 1 is that the catalyst used in Comparative Example 1 is the FeNi / AHC-N catalyst of Comparative Example 1, and the other reaction conditions and test conditions are the same as those of Example 1. From this test, it can be seen that FeNi / AHC-N requires an overpotential of 323mV to reach 10mA·cm -2 current density.

[0079] Application Comparative Example 2

[0080] The difference between Application Example 2 and Application Example 1 is that the catalyst used in Application Example 2 is the FeNi / AHC-P catalyst of Application Example 2, and the other reaction conditions and test conditions are the same as those of Application Example 1. From this test, it can be seen that FeNi / AHC-P requires an overpotential of 331mV to reach 10mA·cm -2 current density.

[0081] Application Comparative Example 3

[0082] The difference between Comparative Example 3 and Example 1 is that the catalyst used in Comparative Example 3 is the FeNi / AHC catalyst of Comparative Example 3, and the other reaction conditions and test conditions are the same as those of Example 1. From this test, it can be seen that FeNi / AHC requires an overpotential of 549 mV to reach 10 mA·cm -2 current density.

[0083] Analysis of material catalytic properties

[0084] The catalytic performance of FeNi / AHC-NP, FeNi / HC-N, FeNi / HC-P and FeNi / HC in Example 1 and Comparative Examples 1-3 was analyzed. Figure 5 shown. Figure 5 (a) is the OER-LSV curve, Figure 5 (b) Tafel slope plot. Figure 5 (a) It can be seen that the FeNi / AHC-NP catalyst only needs an overpotential of 290 mV to reach 10 mA cm -2 The current density is better than that of FeNi / AHC-N and FeNi / AHC-P (323 and 331 mV), and much lower than that of FeNi / AHC (549 mV). Figure 5 (b) It can be seen that the Tafel slope corresponding to FeNi / AHC-NP is 66.29 mV·dec -1 , slightly lower than FeNi / AHC-N and FeNi / AHC-P (73.80 and 117.09 mV·dec, respectively). -1 ), but significantly lower than FeNi / AHC (258.11mV·dec -1 ). This indicates that the introduction of nitrogen and phosphorus further improves the OER electrocatalytic activity and reaction kinetics of FeNi alloy.

[0085] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing a nitrogen and phosphorus co-doped iron and nickel-based porous biomass carbon catalyst, characterized in that: The following steps are involved: (1) Preparation of hydrothermal charcoal: sugarcane bagasse is added to a hydrochloric acid solution, stirred, and then transferred to a reactor for hydrothermal reaction. After the reaction is completed, the mixture is naturally cooled to room temperature. The resulting product is washed and dried to obtain hydrothermal charcoal. (2) Cold alkali activated hydrothermal carbon: The hydrothermal carbon prepared in step (1) is placed in a NaOH solution for cold alkali activation. After activation, the carbon is centrifuged, washed, and dried to obtain cold alkali activated hydrothermal carbon. (3) Synthesis of the precursor: Fe(NO3)3·9H2O and Ni(CH3COO)2·4H2O were dissolved in water, stirred vigorously to mix evenly, and the resulting mixed solution was added dropwise to the aqueous solution of the cold alkali-activated hydrothermal carbon in step (2). After stirring, the pH of the solution was adjusted to alkaline. After filtration, the resulting product was washed and dried to obtain the precursor; (4) Nitrogen-phosphorus co-doping: The precursor of step (3) is mixed with urea and uniformly ground. After adding sodium dihydrogen phosphate, it is calcined at high temperature in a nitrogen atmosphere. After calcination, it is cooled to room temperature to obtain a nitrogen-phosphorus co-doped iron-nickel-based porous biomass carbon catalyst.

2. The method for preparing the nitrogen and phosphorus co-doped iron-nickel based porous biomass carbon catalyst according to claim 1, characterized in that: In step (1), the mass ratio of the bagasse to the hydrochloric acid solution is 4 g:40-45 mL, and the concentration of the hydrochloric acid solution is 0.1-0.15 mol / L.

3. The method for preparing the nitrogen and phosphorus co-doped iron-nickel based porous biomass carbon catalyst according to claim 1, characterized in that: In step (1), the temperature of the hydrothermal reaction is 210-230° C., and the time is 10-12 h.

4. The method for preparing the nitrogen and phosphorus co-doped iron-nickel based porous biomass carbon catalyst according to claim 1, characterized in that: In step (2), the mass ratio of the hydrothermal charcoal to the NaOH solution is 2.5 g:45-50 mL, the concentration of the NaOH solution is 1.3-1.5 mol / L, and the time of the cold alkali activation is 1.5-2 h.

5. The method for preparing the nitrogen and phosphorus co-doped iron-nickel based porous biomass carbon catalyst according to claim 1, characterized in that: In step (3), the mass ratio of Fe(NO3)3·9H2O and Ni(CH3COO)2·4H2O is 2.3:1.3-1.6; and the mass ratio of cold alkali activated hydrothermal carbon to water in the aqueous solution of cold alkali activated hydrothermal carbon is 1 g:100-120 mL.

6. The method for preparing the nitrogen and phosphorus co-doped iron-nickel based porous biomass carbon catalyst according to claim 1, characterized in that: In step (4), the mass ratio of the precursor, urea and sodium dihydrogen phosphate is 5:3-4:100-120.

7. The method for preparing the nitrogen and phosphorus co-doped iron-nickel based porous biomass carbon catalyst according to claim 1, characterized in that: In step (4), the high-temperature calcination is carried out in a nitrogen atmosphere at 280-300°C for 1.5-2 hours, and then the temperature is raised to 700-800°C and maintained for 1.5-2 hours.

8. A nitrogen and phosphorus co-doped iron and nickel-based porous biomass carbon catalyst prepared by the preparation method according to any one of claims 1 to 7.

9. The nitrogen and phosphorus co-doped iron and nickel-based porous biomass carbon catalyst according to claim 8, characterized in that: The nitrogen and phosphorus co-doped iron-nickel based porous biomass carbon catalyst has a three-dimensional network porous structure and a specific surface area of ​​160 to 163 m 2 / g, pore volume of 0.15~0.18cm 3 / g, and the average pore diameter is 5.5~7.4nm.

10. Use of the nitrogen and phosphorus co-doped iron-nickel based porous biochar catalyst as claimed in claim 8 in catalytic oxygen evolution reaction.

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