Three-dimensional composite cathode catalyst and application thereof in direct lignin fuel cell

Abstract

The invention discloses a three-dimensional composite cathode catalyst and application thereof in a direct lignin fuel cell, and the preparation method comprises the following steps: S1, dispersing carboxylated multi-walled carbon nanotubes in deionized water, then adding urea, and carrying out ultrasonic and heating reaction to obtain nitrogen-doped carbon nanotubes; s2, dispersing iron phthalocyanine in isopropanol, then adding nitrogen-doped carbon nanotubes, and carrying out ultrasonic dispersion, stirring and rotary evaporation drying to obtain an NCNT-FePc composite material; and S3, dispersing the NCNT-FePc composite material and superconductive carbon black in isopropanol, stirring, carrying out ultrasonic treatment, and carrying out rotary evaporation drying to obtain the three-dimensional composite cathode catalyst. When the catalyst is used for a direct lignin fuel cell, the obtained open-circuit voltage is 0.68 V, the power density is 4039 mW.m <-2 >, which is far higher than that of Pt / C, and the methanol tolerance and stability are excellent. The preparation method has the characteristics of simple process, low cost, environmental protection and the like, is suitable for popularization, and provides an efficient and low-cost fuel cell solution for high-value utilization of lignin.

Description

Technical Field

[0001] This invention belongs to the field of fuel cell technology, and specifically relates to a three-dimensional composite cathode catalyst and its application in direct lignin fuel cells. Background Technology

[0002] Direct lignin fuel cells (DLFCs) represent a significant approach to the high-value utilization of lignin. They directly convert the chemical energy in lignin into electrical energy through electrochemical oxidation, simultaneously generating high-value aromatic compounds, thus providing a new pathway for the high-value utilization of lignin. However, the large-scale application of fuel cells is hampered by the slow kinetics of the oxygen reduction reaction (ORR), making the search for an efficient, stable, and inexpensive ORR catalyst a challenge. Slow ORR kinetics is a key bottleneck restricting fuel cell development. Currently, commercially available platinum-based (Pt / C) catalysts are expensive and prone to poisoning and deactivation. While transition metal phthalocyanines (such as iron phthalocyanine, FePc) possess ORR potential, they suffer from problems such as active site aggregation and poor electronic conductivity. Nitrogen-doped carbon materials (such as nitrogen-functionalized carbon nanotubes) can improve ORR performance, but carbon nanotubes tend to stack, leading to a decrease in specific surface area. Furthermore, as an abundant biomass resource, the high-value utilization of lignin urgently requires the support of efficient fuel cell technology. Therefore, developing low-cost, high-performance, and stable non-precious metal ORR catalysts is of great significance. Transition metal phthalocyanines (TMPcs) are highly efficient bifunctional oxygen catalysts, exhibiting significant catalytic potential in the oxygen reduction reaction (ORR) due to their tunable electronic structure and well-defined active sites, especially demonstrating excellent cycling stability in alkaline media. The molecular structure of phthalocyanines is highly similar to that of widely found metalloporphyrins (MPors) compounds, both possessing well-defined M-N4 active centers and conjugated macrocyclic structures. Among TMPcs, iron phthalocyanine (FePc), cobalt phthalocyanine (CoPc), nickel phthalocyanine (NiPc), copper phthalocyanine (CuPc), and manganese phthalocyanine (MnPc), FePc exhibits the best ORR performance. Its inherent Fe-N4 active site enables it to react via a direct four-electron pathway at relatively low overpotentials. However, due to the central aggregation and electronic defects of Fe atoms, the activity of FePc-based catalysts will rapidly decline under oxygen reduction environment, resulting in "poisoning" and eventual deactivation. Studies have shown that FePc molecules can be combined with carbon materials to improve conductivity and provide more active sites. Such composite catalysts usually exhibit a 4-electron transfer process and have greater research potential. In recent years, transition metal-based nitrogen-doped carbon (MNC) materials have attracted widespread attention due to their large specific surface area, pore size and good catalytic activity. Heteroatom doping of MNC materials can significantly improve their ORR performance in alkaline and acidic environments. Their excellent catalytic efficiency and tunable characteristics make them a substitute for platinum (Pt) in fuel cells. Summary of the Invention

[0003] To address the problems existing in the prior art, the present invention aims to provide a three-dimensional composite cathode catalyst and its application in direct lignin fuel cells by using carboxylated multi-walled carbon nanotubes to achieve nitrogen doping and combining them with iron phthalocyanine and superconducting carbon black.

[0004] To achieve the above objectives, the present invention adopts the following technical solution: A first aspect of the present invention provides a method for preparing a three-dimensional composite cathode catalyst, comprising the following steps: S1. Carboxylated multi-walled carbon nanotubes (MWCNTs) are dispersed in deionized water, then urea is added, and the mixture is sonicated and heated to obtain nitrogen-doped carbon nanotubes (NCNTs). S2. Iron phthalocyanine (FePc) was dispersed in isopropanol, and then nitrogen-doped carbon nanotubes (NCNT) were added. The mixture was ultrasonically dispersed, stirred, and dried by rotary evaporation to obtain the NCNT-FePc composite material. S3. The obtained NCNT-FePc composite material and superconducting carbon black (CB) are dispersed in isopropanol, stirred, ultrasonically treated, and dried by rotary evaporation to obtain the NCNT-FePc / CB composite material, i.e., the three-dimensional composite cathode catalyst. Preferably, in step S1, the mass ratio of carboxylated multi-walled carbon nanotubes (MWCNTs) to urea is 1:0.9–1.2. Preferably, in step S1, the ultrasonic treatment time is 1–4 hours; the temperature is raised to 60–120°C, and the reaction time is 1–4 hours. Preferably, in step S2, the mass ratio of iron phthalocyanine to nitrogen-doped carbon nanotubes is 1 to 4:5. Preferably, in step S2, the ultrasonic dispersion time is 1-4 hours and the stirring time is 18-24 hours. Preferably, in step S3, the mass ratio of the superconducting carbon black to the NCNT-FePc composite material is 0.6 to 1.2:1. Preferably, in step S3, the stirring time is 2-8 hours and the ultrasonic treatment time is 1-4 hours.

[0005] A second aspect of the present invention provides a three-dimensional composite cathode catalyst prepared by the above-described preparation method.

[0006] A third aspect of the present invention provides the application of the above-described three-dimensional composite cathode catalyst in a direct lignin fuel cell.

[0007] The present invention has the following beneficial effects: (1) In the three-dimensional composite cathode catalyst provided by this invention, superconducting carbon black (CB) acts as a spacer to increase the specific surface area of ​​the catalyst, thereby exposing more Fe-N4 active sites; FePc is uniformly anchored on the NCNT substrate through π-π coupling, enhancing electron conduction. Experimental results show that the three-dimensional composite cathode catalyst prepared by this invention has the highest half-wave potential (0.88V) and the lowest Tafel slope (37.4mV dec). -1 The double-layer capacitance is similar to that of Pt / C (9.58 mF / cm). -2 When this three-dimensional composite cathode catalyst was used in a direct lignin fuel cell, an open-circuit voltage of 0.68 V and a power density of 4039 mW·m were obtained. -2 The efficiency of this material far exceeds that of Pt / C, and it exhibits excellent methanol tolerance (current retention rate of 89.8%) and stability (30,000s retention rate of 85.9%). These findings provide a high-efficiency, low-cost fuel cell solution for the high-value utilization of lignin. (2) The preparation method of the present invention has a simple synthesis process, is environmentally friendly and easy to operate, and is suitable for large-scale production. Attached Figure Description

[0008] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. Figure 1 (a) SEM images of CNT(a), NCNT(b), CNT-FePC(c), NCNT-FePC(d), NCNT-FePC / CB(e), and enlarged NCN-TFePC / CB(f); (g) EDS image of NCN-TFePC / CB; Figure 2 (a) N2 adsorption-desorption isotherm; (b) pore size distribution; (c) infrared spectrum; (d) Raman spectrum; Figure 3 For: (a) XPS full spectrum; (b) NCNT-FePC / CB high-resolution N1s; (c) NCNT-FePC / CB high-resolution Fe2p; (d) NCNT high-resolution N1s; Figure 4 The CV curves (a), LSV curves (b), LSV curves (c), and KL equation curves (d) for four catalysts at different scan rates are shown. Figure 5Tafel slope curves (a), double layer capacitance (b), methanol tolerance curves (c) and chronoamperometry curves (d) for four catalysts are shown. Figure 6 (a) Open-circuit voltage-time curve; (b) Polarization and power density curve; (c) Discharge curve; (d) Polarization and power density curve of Pt / C. Detailed Implementation

[0009] In the following description, specific details such as particular system architectures and techniques are set forth for illustrative purposes and not for limitation, in order to provide a thorough understanding of the embodiments of the invention. However, those skilled in the art will understand that the invention can be implemented in other embodiments without these specific details. In other instances, detailed descriptions of well-known systems, apparatuses, circuits, and methods are omitted so as not to obscure the description of the invention with unnecessary detail.

[0010] Example 1 S1. Disperse 1g MWCNTs in 200ml deionized water, add 1.2g urea, sonicate for 3h to achieve complete dispersion, heat the dispersion at 90℃ for 3h, wash the reaction mixture with ethanol, purify it, and dry it in a vacuum oven at 80℃ to obtain nitrogen-doped carbon nanotubes (NCNTs). S2. 10 mg of iron phthalocyanine (FePc) and 50 mg of nitrogen-doped carbon nanotubes (NCNT) were dispersed in 50 mL of isopropanol, ultrasonically dispersed for 1 h, stirred for 24 h, and dried by rotary evaporation to obtain NCNT-FePc. S3. First, disperse 1g of NCNT-FePc composite material in isopropanol and stir for 1h. Then add 0.8g of superconducting carbon black CB, stir mechanically for 2h, sonicate for 1h, and dry by rotary evaporation to obtain nitrogen-doped carbon nanotube-phthalocyanine iron / carbon black composite material, abbreviated as NCNT-FePc / CB composite material, i.e., three-dimensional composite cathode catalyst.

[0011] Example 2 S1. Disperse 1g of MWCNTs in 200ml of deionized water, add 1g of urea, sonicate for 3h to achieve complete dispersion, heat the dispersion at 90℃ for 3h, wash the reaction mixture with ethanol, purify it, and dry it in a vacuum oven at 80℃ to obtain nitrogen-doped carbon nanotubes (NCNTs). S2. 10 mg of iron phthalocyanine (FePc) and 25 mg of nitrogen-doped carbon nanotubes (NCNT) were dispersed in 50 mL of isopropanol, ultrasonically dispersed for 1 h, stirred for 24 h, and dried by rotary evaporation to obtain NCNT-FePc. S3. First, disperse 1g of NCNT-FePc composite material in isopropanol and stir for 1h. Then add 0.8g of superconducting carbon black CB, stir mechanically for 2h, sonicate for 1h, and dry by rotary evaporation to obtain nitrogen-doped carbon nanotube-phthalocyanine iron / carbon black composite material, abbreviated as NCNT-FePc / CB composite material, i.e., three-dimensional composite cathode catalyst.

[0012] Example 3 S1. Disperse 1g of carboxylated multi-walled carbon nanotubes (MWCNTs) in deionized water, add 1.1g of urea, sonicate for 3h, heat at 100℃ for 3h, wash and dry to obtain nitrogen-doped carbon nanotubes (NCNTs). S2. 10 mg of iron phthalocyanine (FePc) and 16.6 mg of the obtained nitrogen-doped carbon nanotubes (NCNT) were dispersed in isopropanol, ultrasonically dispersed for 1 h, stirred for 22 h, and dried by rotary evaporation to obtain NCNT-FePc composite material. S3. Disperse 1g of NCNT-FePc composite material in isopropanol and stir for 2h. Then add 1g of superconducting carbon black CB, stir for 6h, sonicate for 3h, and dry by rotary evaporation to obtain NCNT-FePc / CB composite material, i.e., three-dimensional composite cathode catalyst.

[0013] Example 4 S1. Disperse 1g of carboxylated multi-walled carbon nanotubes (MWCNTs) in deionized water, add 0.9g of urea, sonicate for 4h, heat at 120℃ for 4h, wash and dry to obtain nitrogen-doped carbon nanotubes (NCNTs). S2. 10 mg of iron phthalocyanine (FePc) and 12.5 mg of nitrogen-doped carbon nanotubes were dispersed in isopropanol, ultrasonically dispersed for 1 h, stirred for 24 h, and dried by rotary evaporation to obtain NCNT-FePc composite material. S3. First, disperse 1g of NCNT-FePc composite material in isopropanol and stir for 1h. Then add 1.2g of superconducting carbon black CB, mechanically stir for 8h, sonicate for 4h, and dry by rotary evaporation to obtain NCNT-FePc / CB composite material, i.e., three-dimensional composite cathode catalyst.

[0014] Compare with Example 1 S1. Disperse 1g MWCNTs in 200ml deionized water, add 1.2g urea, sonicate for 3h to achieve complete dispersion, heat the dispersion at 90℃ for 3h, wash the reaction mixture with ethanol, purify it, and dry it in a vacuum oven at 80℃ to obtain nitrogen-doped carbon nanotubes (NCNTs). S2. 10 mg of iron phthalocyanine (FePc) and 50 mg of nitrogen-doped carbon nanotubes (NCNT) were dispersed in 50 mL of isopropanol, ultrasonically dispersed for 1 h, stirred for 24 h, and dried by rotary evaporation to obtain NCNT-FePc.

[0015] Compare with Example 2 10 mg of iron phthalocyanine (FePc) was dissolved and dispersed in 50 mL of isopropanol. Then, 50 mg of carboxylated multi-walled carbon nanotubes were added to the above suspension containing FePc. The mixture was dispersed by strong ultrasonication for 1 h, stirred for 24 h, and dried by rotary evaporation to obtain CNT-FePc.

[0016] 1. Characterization Test (1) Scanning electron microscope images of CNT, NCNT, CNT-FePC, NCNT-FePC, NCNT-FePC / CB and magnified images, such as Figure 1 As shown. Figure 1 (e) and (f) show that after the introduction of the intercalating agent carbon black (CB), the distribution of carbon nanotubes is more uniform, and the catalyst has a more three-dimensional structure. This structure increases the specific surface area and the spacing between adjacent carbon nanotubes, exposing more active sites. (2) EDS elemental distribution image as follows Figure 1 As shown in (g), a uniform distribution of the four elements C, O, N, and Fe can be observed, indicating the successful synthesis of NCNT-TFePc / CB. (3) Since specific surface area and porosity are key factors affecting the oxygen reduction reaction (ORR), the specific surface area and pore structure of three catalysts, CNT-FePc, NCNT-FePc, and NCNT-FePc / CB, were determined by N2 adsorption-desorption tests as follows: Figure 2 (a) and Figure 2 As shown in (b). Figure 2 (a) and Figure 2 In (b), it can be clearly observed that the porosity and specific surface area of ​​the NCNT-FePc / CB catalyst are much higher than those of CNT-FePc and NCNT-FePc. This is attributed to the fact that carbon black (CB) acts as an intercalating agent and fills around the carbon nanotubes, avoiding their stacking, thereby increasing the specific surface area and exposing more active sites. (4) Fourier transform infrared spectroscopy (FT-IR) such as Figure 2 As shown in (c) Figure 2 727cm in (c) -1 The vibrational peak at the point showed the presence of the Fe-N bond unique to iron phthalocyanine (FePc), which is not present in CNTs and NCNTs, indicating that FePc was successfully introduced into carbon nanotubes, further confirming the successful synthesis of the catalyst. (5) To study the effects of heteroatom doping and superconducting carbon black on defects in carbon materials, Raman spectroscopy was used to test the catalyst. The Raman spectrum is as follows: Figure 2 As shown in (d). Raman spectroscopy Figure 2(d) Shows all samples at 1350 cm. -1 and 1580cm -1 Both D and G bands are present at various locations. The ID / IG value can effectively reflect the degree of defect and graphitization of the material. The ID / IG value is significantly improved after nitrogen doping of carbon nanotubes, indicating that nitrogen doping increases the material defects. The ID / IG value of CNT-FePc is lower than that of pure CNT because the phthalocyanine iron molecule particles are smaller, and filling the carbon material reduces its defect degree. After adding superconducting carbon black (CB), the catalyst ID / IG value reaches 1.34, indicating that it has a higher defect density, which helps to improve the catalytic reaction efficiency and stability. (6) To investigate the conjugation information of NCNT and FePc in the NCNT-FePc / CB catalyst, X-ray photoelectron spectroscopy (XPS) was performed. The results are shown below. Figure 3 . Figure 3 In (a), signals of C1s (283.3 eV), N1s (401 eV), O1s (532.3 eV) and Fe2p (712.9 eV) can be observed. Due to the low content of iron phthalocyanine, the signals are not obvious in the image. The N1s high-resolution XPS spectra of NCNT-FePc / CB and NCNT materials are as follows: Figure 3 As shown in (b) and (d), the NCNT spectrum, after peak fitting, can be deconvolved into four characteristic peaks: pyridine nitrogen 398.1 eV, pyrrole 399.9 eV, graphitic nitrogen 401.2 eV, and nitrogen oxide 403.9 eV. Figure 3 In (d), a significant increase in pyridine nitrogen and graphite content and a decrease in nitrogen oxide content can be observed. Higher contents of pyrrole nitrogen and graphitic nitrogen facilitate the formation of positively charged hybrid carbon atoms on adjacent sp atoms, thereby effectively improving the electrochemical performance of the catalyst. The Fe2p spectrum of the NCNT-FePc / CB material is shown below. Figure 3 (c) is convolved into five peaks at 706.9 eV, 711.2 eV, 713.4 eV, 720.4 eV and 724.3 eV. The characteristic peak at 711 eV corresponds to the Fe 2p3 / 2 energy level, while the peak at 720.4 eV belongs to the Fe 2p1 / 2 energy level.

[0017] 2. ORR Performance Analysis (1) To evaluate the ORR activity of the catalyst, rotating disk electrode (RDE) tests were performed in a standard three-electrode system. All tests were conducted under 0.1 M KOH and saturated oxygen conditions. Comparison of CV plots for NCNT-FePc / CB, NCNT-FePc, CNT-FePc, and Pt / C is shown below. Figure 4As shown in (a), NCNT-FePc / CB exhibits the highest reduction peak current density, indicating its optimal oxygen reduction performance. The linear sweep voltammetry (LSV) results for the four catalysts are shown below. Figure 4 As shown in (b), the onset potential (Eonset) of NCNT-FePc / CB is 0.93V, and the half-wave potential (E1 / 2) is 0.88V, both exceeding those of commercial Pt / C (Eonset = 0.83V, E1 / 2 = 0.80V). The catalyst performance ranking is: NCNT-FePc / CB > NCNT-FePc > CNT-FePc. The LSV curve at speeds of 400–2025 rpm is as follows: Figure 4 As shown in (c), this indicates that the higher the rotational speed, the stronger the gas diffusion and the greater the current density. The KL equation curve is as follows: Figure 4 As shown in (d), excellent linearity is observed in the potential range of 0.2–0.5 V (vs. RHE). The average electron transfer number (n) calculated by the slope is 3.74, which is close to the ideal value (n=4) for the four-electron transfer path, indicating that the NCNT-FePc / CB catalyst dominates the efficient four-electron oxygen reduction process. (2) The Tafel slope in the oxygen reduction reaction process is as follows: Figure 5 (a) shows the kinetic characteristics of ORR. Figure 5 (a) The results showed that the Tafel slope of NCNT-FePc / CB was 37.4 mV dec. -1 Less than NCNT-FePc(40mVdec) -1 CNT-FePc (46.1mV dec) -1 ) and Pt / C (106mV dec -1 A lower Tafel slope indicates better catalyst performance, meaning the catalyst can achieve higher current densities at lower potentials. The electric double layer capacitance (Cdl) value is as follows: Figure 5 (b) reflects the density of active sites on the catalyst surface that can participate in electrochemical reactions. Figure 5 (b) The results showed that the Cdl value of NCNT-FePc / CB was 9.58 mF cm⁻¹. -2 , with Pt / C10.13 mF cm -2 Similar to, but much higher than NCNT-FePc (1.93mF cm⁻¹) -2 ) and CNT-FePc (1.62mF cm -2 This result indicates that the NCNT-FePc / CB catalyst exhibits superior catalytic performance in ORR due to the increased exposure of active sites. To investigate the catalyst's resistance to poisoning and stability, it was tested at 1600 rpm under oxygen saturation conditions. Figure 5 (c, d) At 300 s, 5 ml of 5M methanol was added, and the test was continued until 1200 s. The current retention rate of NCNT-FePc / CB was 89.8%, higher than that of Pt / C (74%), demonstrating excellent anti-poisoning properties. An iterative test (IT) of 30,000 s was conducted to determine the catalyst's stability. The results showed that the current retention rate of NCNT-FePc / CB was 85.9%, higher than that of Pt / C (45.6%), and also higher than the stability of commercially available Pt / C.

[0018] 3. Fuel Cell Performance Analysis To investigate the application effect of the catalyst in fuel cells, it was coated onto the cathode membrane, and a nickel mesh was used as the anode to construct a direct lignin fuel cell. The electrolyte was prepared as follows: 0.05 g of sulfate lignin was dissolved in 10 ml of deionized water, mixed with 10 ml of 5 M NaOH solution, and 5 mL of 0.08 M dibromodibromide solution was added as an electron transporter. After stirring thoroughly, the solution was injected into the fuel cell casing. Results are shown below. Figure 6 . Figure 6 (a) shows that the open-circuit voltages of NCNT-FePc / CB, NCNT-FePc, CNT-FePc and Pt / C are 0.68V, 0.62V, 0.60V and 0.57V respectively, with NCNT-FePc / CB having the highest open-circuit voltage. The power density and polarization curves of the four catalysts are shown in the figure. Figure 6 (b) and Figure 6 (d). Power density ranking: NCNT-FePc / CB (4039mW / m 2 )>NCNT-FePc(1412mW / m 2 CNT-FePc (1211mW / m 2 Pt / C (92.3mW / m 2 The current density ranking is: NCNT-FePc / CB (6658 mA / m²). 2 )>NCNT-FePc(4842mA / m 2 CNT-FePc (4267 mA / m 2 Pt / C(1701mA / m) 2 This indicates that NCNT-FePc / CB exhibits the best catalytic performance. A 24-hour discharge test was performed with a 1000Ω resistor connected to the battery. Figure 6(c) The results show that the fuel cell using the NCNT-FePc / CB catalyst has a higher output voltage than the Pt / C catalyst. This invention applies the NCNT-FePc / CB composite material as a cathode catalyst in a lignin fuel cell, and the resulting fuel cell exhibits better performance than commercial Pt / C in terms of open-circuit voltage, maximum power density, current density, and voltage stability, demonstrating its excellent performance as a cathode catalyst in practical applications.

[0019] This invention is not limited to the specific embodiments described above. Any modifications made by those skilled in the art based on the above concept without creative effort are within the scope of protection of this invention.

Claims

1. A method for preparing a three-dimensional composite cathode catalyst, characterized by, The method comprises the following steps: S1, dispersing carboxylated multi-walled carbon nanotubes in deionized water, then adding urea, ultrasonic treatment, and heating to obtain nitrogen-doped carbon nanotubes; S2, dispersing iron phthalocyanine in isopropyl alcohol, then adding nitrogen-doped carbon nanotubes, ultrasonic dispersion, stirring, and rotary evaporation drying to obtain NCNT-FePc composite material; S3, dispersing the obtained NCNT-FePc composite material and superconducting carbon black in isopropyl alcohol, stirring, ultrasonic treatment, and rotary evaporation drying to obtain a three-dimensional composite cathode catalyst.

2. The method for preparing the three-dimensional composite cathode catalyst according to claim 1, characterized in that, In step S1, the mass ratio of the carboxylated multi-walled carbon nanotubes to urea is 1:0.9-1.

2.

3. The method for preparing the three-dimensional composite cathode catalyst according to claim 2, characterized in that, In step S1, the ultrasonic treatment time is 1-4h; the temperature is raised to 60-120℃, and the reaction time is 1-4h.

4. The method for preparing the three-dimensional composite cathode catalyst according to claim 1, characterized in that, In step S2, the mass ratio of the iron phthalocyanine to nitrogen-doped carbon nanotubes is 1-4:

5.

5. The method for preparing the three-dimensional composite cathode catalyst according to claim 1, characterized in that, In step S2, the ultrasonic dispersion time is 1-4h, and the stirring time is 18-24h.

6. The method for preparing the three-dimensional composite cathode catalyst according to claim 1, characterized in that, In step S3, the mass ratio of the superconducting carbon black to the NCNT-FePc composite material is 0.6-1.2:

1.

7. The method for preparing the three-dimensional composite cathode catalyst according to claim 1, characterized in that, The stirring time is 2-8h, and the ultrasonic treatment time is 1-4h.

8. A three-dimensional composite cathode catalyst prepared by the preparation method of any one of claims 1-7.

9. Application of the three-dimensional composite cathode catalyst prepared by the preparation method of any one of claims 1-7 in a direct lignin fuel cell.

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