Preparation method of plant tannin modified biomass carbon electrode material

Abstract

The application discloses a cheap biomass carbon electrode material for fuel cells, which is modified by plant tannin and solidly carries rare earth active components, and a preparation method of the biomass carbon electrode material. CS‑BT The fuel cell catalysts currently generally face the problems of single precursor and high synthesis cost, and the commercial platinum carbon catalysts are not only expensive but also poor in stability. In order to overcome the problems, the application develops a biomass carbon electrode material for fuel cells, which is modified by plant tannin and solidly carries double rare earth organic framework composites, based on the unique structure of double rare earth MOFs. The material has high potential and good limiting current, and has excellent stability. The adopted synthesis method is simple in operation, low in cost and short in preparation time, and is favorable for realizing large-scale commercial production.

Description

Technical Field

[0001] This invention relates to a low-cost biomass carbon electrode material for proton exchange membrane fuel cells, which is a biomass-modified biomass immobilized with rare earth active components using plant tannin. The invention also relates to a thermal decomposition process for preparing Ce-La@CCS-BT. Background Technology

[0002] Fuel cells produce non-toxic and harmless byproducts during the conversion process and do not release toxic gases. They have few mechanical parts, resulting in low friction and vibration noise during operation. Therefore, they offer advantages such as high efficiency, zero emissions, quiet operation, and renewable reactant sources. Currently, fuel cells are widely considered to provide an ultimate energy solution, a green and efficient energy device with promising development prospects. They can be widely used in stationary electrical equipment, transportation (powering cars, trains, and ships), and small portable electronic products. Metal-organic frameworks (MOFs) are a class of porous crystalline materials assembled from metal ion centers, clusters, and organic ligands. MOFs possess extremely high specific surface areas and easily tunable structures, enabling their widespread application in many fields, such as gas storage / separation, chemical sensors, and wastewater treatment. Rare earth elements form a large family in the periodic table. Most rare earth elements (except lanthanum) lack 5d orbital electrons; their 5d orbitals are empty. Generally, empty orbitals can provide good electron transfer pathways for catalytic reactions. Therefore, rare earth elements and their compounds have excellent catalytic properties and extremely wide applications, and are considered a treasure trove of new materials such as "new energy".

[0003] This invention relates to the preparation of a biomass carbon composite material using plant tannin-modified chitosan as a carbon source and cerium-lanthanum dual rare earth organic framework (CLE). The material is prepared using a biotemplate method, with plant tannin-modified chitosan serving as a template and carbon source to immobilize the Ce-MOFs / La-MOFs dual rare earth organic framework. Plant tannin acts as a bridging molecule for interface modification, effectively immobilizing the supramolecular structure of the dual rare earth MOFs on a biomass carrier in situ. This allows the preparation of a CS-BT@Ce-MOFs / La-MOFs nanocomposite precursor with a special morphology by utilizing the pore structure and physicochemical properties of chitosan. The precursor is then calcined at high temperature to finally form (Ce-La@CCS-BT). Electrochemical tests show that the Ce-La@CCS-BT catalyst has a limiting current density close to that of commercial Pt / C catalysts in 0.1 MkOH at a potential of 0.1 V. In addition, the ORR reaction mechanism is dominated by 4 electrons in alkaline media. Furthermore, this catalyst has better methanol resistance and stability than commercial Pt / C catalysts. Summary of the Invention

[0004] The purpose of this invention is to solve the problems existing in current fuel cell catalysts and overcome the defects of the prior art. At present, fuel cell catalysts generally face the obstacles of single precursors and synthesis costs, as well as the defects of high cost and toxicity of platinum-based catalysts. The invention provides a low-cost biomass carbon electrode material for fuel cells, which is a biomass modified with plant tannin and supported with rare earth active components. It has high potential, good limiting current and excellent stability.

[0005] To achieve the above objectives, the technical solution of the present invention is as follows:

[0006] A method for preparing inexpensive biomass carbon electrode materials for fuel cells, modified from plant tannin and immobilized with rare earth active components, includes the following steps:

[0007] (1) Modified chitosan: Weigh a certain amount of chitosan, disperse it in acetic acid solution, and sonicate until fully dissolved;

[0008] (2) Preparation of Ce-MOFs polymer substrate: A certain amount of pyromellitic acid white powder was weighed and dissolved in a certain amount of anhydrous ethanol. The dissolved liquid was a colorless and transparent solution. A certain amount of cerium nitrate hexahydrate colorless and transparent crystals was weighed and dissolved in a certain amount of deionized water. The dissolved liquid was also a colorless and transparent liquid. Then, the pyromellitic acid solution was slowly added dropwise to cerium nitrate hexahydrate and stirred on a magnetic stirrer to obtain a white mixture. The mixture was transferred to a water bath and shaken at a certain temperature. The sample obtained after the reaction was washed several times with deionized water and ethanol and dried at a certain temperature to obtain white powder Ce-MOFs. Ce-MOFs and plant tannin were dispersed in deionized water and sonicated at room temperature.

[0009] (3) Preparation of La-MOFs polymer substrate: Weigh a certain amount of white lanthanum nitrate hexahydrate powder and dissolve it in a certain amount of water. Dissolve a certain amount of trimesic acid in a water / ethanol mixture to prepare a ligand solution. Mix the two solutions together at a certain temperature, run them at a certain speed for a certain time, and then allow them to settle. Finally, wash the prepared product several times with a mixture of water and ethanol, and then dry it in an oven at a certain temperature to obtain white powder La-MOFs. Disperse La-MOFs and plant tannin in deionized water and sonicate at room temperature.

[0010] (4) Pour the solution from step (3) into the solution from step (2) and perform an ultrasonic reaction at room temperature;

[0011] (5) Pour the sonicated solution from step (4) back into step (1) and perform the sonication reaction at room temperature;

[0012] (6) Wash the product obtained in step (5) with deionized water and ethanol and centrifuge. Dry the product in an oven to obtain CS-BT@Ce-MOFs / La-MOFs.

[0013] (7) Disperse an appropriate amount of dried precursor evenly on the bottom of a ceramic boat, place it in a tube furnace and pyrolyze it at high temperature in a nitrogen atmosphere, and cool it naturally to room temperature to obtain a low-cost biomass carbon electrode material with plant tannin-modified biomass immobilized with rare earth active components for fuel cells.

[0014] As mentioned in step (1), the ultrasound time is 30 minutes.

[0015] As described in step (2), the ultrasonic time is 5-10 min, the stirring time on the magnetic stirrer is 30 min, the shaking time is 1 h at 60℃, and the drying time is 13-20 h at 60-80℃. The mass ratio of plant polyphenols to Ce-MOFs is (1-2):(1-2), and the ultrasonic time is 30-40 min.

[0016] In step (3), the process is carried out at a temperature of 25℃ and a rotation speed of 135r / min for 1-3 hours, with a settling time of 0.5-2 hours. The drying temperature is 60℃ and the drying time is 15-20 hours. The mass ratio of plant tannin to La-MOFs is (1-2):(1-2), and the ultrasonic time is 30-40 minutes.

[0017] The ultrasound time mentioned in step (4) is 30 minutes.

[0018] The ultrasound time mentioned in step (5) is 30 minutes.

[0019] The drying temperature in step (6) is 60-80℃ and the drying time is 15h.

[0020] The high-temperature pyrolysis described in step (7) is as follows: under a pure nitrogen atmosphere, the temperature is first heated to 400°C at a heating rate of 1-5°C / min, then held for 30-50 minutes, and then directly heated to 800°C at the same heating rate. After holding at this temperature for 2-4 hours, the temperature is naturally cooled to room temperature.

[0021] The proton exchange membrane fuel cell cathode material provided by this invention has Ce-La@CCS-BT as its active component. The dual rare-earth organic framework in the material is tightly bonded to the polyphenol network structure of plant tannin, effectively increasing the oxygen reduction catalytic active sites. The material possesses a rich porous structure, increasing its specific surface area and exposing abundant active sites, thereby promoting electrolyte penetration. Therefore, this material exhibits excellent oxygen reduction electrocatalytic performance, with high potential, good limiting current, and excellent stability.

[0022] Technical advantages and beneficial effects of the present invention:

[0023] (1) The present invention adopts a simple and convenient synthesis method, which has the characteristics of being economical, efficient and environmentally friendly; the synthesis steps are simple to operate, the reaction conditions are mild and easy to control, and the preparation cost is low; the oxygen reduction catalyst prepared not only exhibits high potential and good limiting current, but also has excellent stability.

[0024] (2) The inexpensive biomass carbon electrode material modified by plant tannin and supported on rare earth active components prepared for fuel cells has an initial potential of 1.0V, a half-wave potential of 0.50V, and a limiting current density of 6.23mAcm-2, which is slightly higher than that of commercial platinum carbon catalysts. Moreover, its electrocatalytic stability is better than that of commercial Pt / C catalysts. Overall, the catalyst is better than commercial platinum carbon catalysts.

[0025] (3) Unique metal polyphenol network structure; First, plant tannin has abundant phenolic hydroxyl structure, which can form a stable structure with metal ions and combine with rare earth-based organic framework, which can not only increase the active sites of the material but also avoid the accumulation of active components; Second, the free H released by plant tannin can penetrate into the polymer matrix and destroy its internal skeleton. At the same time, the plant tannin macromolecules will coat the exposed surface of the material, thereby protecting its exterior from further etching and shell collapse; Furthermore, by controlling the concentration of plant tannin and the reaction time, the porous structure is carefully sculpted, and the material is finally made into a layered porous structure, which is conducive to the penetration of electrolyte and improves the oxygen reduction catalytic performance of the material. Attached Figure Description

[0026] Figure 1 This is a scanning electron microscope image of the Ce-La@CCS-BT nanocomposite material;

[0027] Figure 2 This is the N2 adsorption-desorption isotherm curve of Ce-La@CCS-BT nanocomposite material;

[0028] Figure 3 This is a pore size distribution diagram of the Ce-La@CCS-BT nanocomposite material;

[0029] Figure 4 This is the Raman spectrum of the Ce-La@CCS-BT nanocomposite material;

[0030] Figure 5 This is a cyclic voltammetric curve of the Ce-La@CCS-BT catalyst (test voltage scan range: -0.9-0.1V, scan rate: 50mV / s);

[0031] Figure 6Linear cyclic voltammetry of Ce-La@CCS-BT with different Ce-MOFs to La-MOFs mass ratios of 1:2, 1:1, 2:1, and 3:1 in O2-saturated 0.1 MkOH (scan range: -0.9–0.1 V, scan rate: 10 mV / s);

[0032] Figure 7 The linear cyclic voltammetry (scan range -0.9-0.1 V, scan rate 10 mV / s) at different temperatures in 0.1 MkOH saturated with O2, with a Ce-MOFs to La-MOFs mass ratio of 1:1.

[0033] Figure 8 Linear cyclic voltammograms of Ce-La@CCS-BT catalyst under different rotation speeds (400, 625, 900, 1225, 1600, 2025 rpm) (scan rate: 10 mV / s);

[0034] Figure 9 It is the KL curve of Ce-La@CCS-BT;

[0035] Figure 10 The graphs show the methanol tolerance of Ce-La@CCS-BT catalyst and commercial Pt / C (20wt% Pt) catalyst, measured by constant voltage chronoamperometry.

[0036] Figure 11 This is a stability test chart of Ce-La@CCS-BT catalyst and commercial Pt / C (20wt% Pt) catalyst, measured by constant voltage chronoamperometry. Detailed Implementation

[0037] This invention provides a method for preparing Ce-La@CCS-BT catalyst, the steps of which are as follows:

[0038] (1) Weigh 0.5g of chitosan and disperse it in 50mL of 3% acetic acid solution. Sonicate for 15min until fully dissolved.

[0039] (2) To prepare the Ce-MOFs polymer substrate, 3.3620 g of trimellitic acid was weighed and dissolved in 60 mL of anhydrous ethanol. 6.9480 g of cerium nitrate hexahydrate was weighed and dissolved in 60 mL of deionized water. The trimellitic acid solution was then slowly added dropwise to the cerium nitrate hexahydrate solution. The mixture was stirred with a magnetic stirrer for 30 min to obtain a white mixture. The mixture was then dried at 70 °C to obtain white Ce-MOFs powder. 300 mg of the prepared Ce-MOFs and 300 mg of the plant polyphenol myricetin were dissolved in 30 mL of ultrapure water, and then mixed after sonication for 10 min at room temperature.

[0040] (3) Preparation of La-MOFs polymer substrate: 5.412 g of white lanthanum nitrate hexahydrate powder was weighed and mixed with ultrapure water to obtain 250 mL of solution. 2.63 g of trimesic acid was dissolved in a water / ethanol mixture (1:1) to prepare 250 mL of ligand solution. The two solutions were mixed together at 25 °C and run at 135 r / min for 1.5 h, followed by sedimentation for 0.5 h. Finally, the prepared product was washed 5 times with a water / ethanol mixture (1:1) and then dried in an oven at 60 °C to obtain white powder La-MOFs. 300 mg of La-MOFs and 300 mg of plant tannin were dissolved in 30 mL of ultrapure water and mixed after sonication for 10 min at room temperature.

[0041] (4) Pour the La-MOFs@BT solution from step (3) into the Ce-MOFs@BT solution from step (2) and perform an ultrasonic reaction at room temperature for 30 minutes;

[0042] (5) Pour the sonicated solution from step (4) back into the chitosan solution from step (1) and perform a sonication reaction at room temperature for 30 minutes.

[0043] (6) Wash the product obtained in step (5) with deionized water and ethanol and centrifuge. Dry the product in an oven to obtain CS-BT@Ce-MOFs / La-MOFs.

[0044] (7) Disperse an appropriate amount of dried precursor evenly on the bottom of a ceramic boat. Under a pure nitrogen atmosphere, heat it to 400°C at a heating rate of 5°C / min, hold it for 30 minutes, and then heat it directly to 800°C at the same heating rate. Hold it at this temperature for 2 hours and then cool it naturally to room temperature to obtain a low-cost biomass carbon electrode material with plant tannin-modified biomass immobilized with rare earth active components for fuel cells.

[0045] This invention provides a method for preparing a low-cost biomass carbon electrode material with plant tannin-modified biomass immobilized with rare earth active components for use in fuel cells, and the application of this material as an oxygen reduction catalyst.

[0046] The active substance described in this invention is abbreviated as Ce-La@CCS-BT.

[0047] This invention uses a carbon rod as the counter electrode, a saturated silver chloride electrode (Ag / AgCl) as the reference electrode, and a glassy carbon electrode as the working electrode.

[0048] The concentration of Nafion added during the preparation of the catalyst described in this invention is 5%, and the dosage is 15 μL.

[0049] The catalyst described in this invention was prepared by weighing 4 mg of the catalyst and dispersing it in 1 mL of a mixed solution (235 μL of deionized water, 735 μL of isopropanol, and 15 μL of 5 wt% Nafion solution) to obtain catalyst ink. Then, 28 μL of the ink was gradually added dropwise to the surface of a glassy carbon electrode (catalyst loading 0.25 mg cm⁻²), and after natural drying, electrocatalytic performance was tested.

[0050] All electrocatalytic performance tests described in this invention were conducted in a 0.1M KOH (pH = 13.62) electrolyte. The measured potentials can be converted to a potential relative to a reversible hydrogen electrode (RHE) using the following formula:

[0051] All potential values ​​involved in this invention are relative to the potential of a reversible hydrogen electrode.

[0052] The catalyst described in this invention requires CV activation for 3 cycles before electrochemical testing.

[0053] The catalysts described in this invention are all tested at room temperature to prevent large temperature variations from affecting the catalyst performance.

[0054] The present invention will be further illustrated below with reference to specific embodiments. To further understand the present invention, preferred embodiments are described in conjunction with the embodiments. However, it should be understood that these descriptions are merely for further illustrating the features and advantages of the present invention, and not for limiting the scope of the claims. Furthermore, it should be understood that after reading the disclosure of this invention, those skilled in the art can make various alterations or modifications to the present invention, and these equivalent forms also fall within the scope of protection defined by this invention.

[0055] Unless otherwise specified, the experimental methods used in the following examples are conventional methods; unless otherwise specified, the reagents and materials used in the following examples are commercially available.

[0056] Example 1:

[0057] This embodiment demonstrates a method for preparing a low-cost biomass carbon electrode material Ce-La@CCS-BT, which is a biomass modified with plant tannin and immobilized with rare earth active components for use in fuel cells.

[0058] (1) Weigh 0.5g of chitosan and disperse it in 50mL of 3% acetic acid solution. Sonicate for 15min until fully dissolved.

[0059] (2) To prepare Ce-MOFs polymer substrate, 3.3620 g of trimellitic acid was weighed and dissolved in 60 mL of anhydrous ethanol. 6.9480 g of cerium nitrate hexahydrate was weighed and dissolved in 60 mL of deionized water. The trimellitic acid solution was then slowly added dropwise to the cerium nitrate hexahydrate solution. The mixture was stirred with a magnetic stirrer for 30 min to obtain a white mixture. The mixture was then dried at 70 °C to obtain white Ce-MOFs powder. 300 mg of Ce-MOFs and 300 mg of the plant polyphenol myricetin were dissolved in 30 mL of ultrapure water and then sonicated at room temperature for 10 min before being mixed.

[0060] (3) Preparation of La-MOFs polymer substrate: 5.412 g of white lanthanum nitrate hexahydrate powder was weighed and mixed with ultrapure water to obtain 250 mL of solution. 2.63 g of trimesic acid was dissolved in a water / ethanol mixture (1:1) to prepare a 250 mL ligand solution. The two solutions were mixed together at 25 °C and run at 135 r / min for 1.5 h, followed by sedimentation for 0.5 h. Finally, the prepared product was washed 5 times with a water / ethanol mixture (1:1) and then dried in an oven at 60 °C to obtain white powder La-MOFs. 300 mg of La-MOFs and 300 mg of plant polyphenol mertannin were dissolved in 30 mL of ultrapure water, sonicated at room temperature for 10 min, and then mixed.

[0061] (4) Pour the La-MOFs@BT solution from step (3) into the Ce-MOFs@BT solution from step (2) and perform an ultrasonic reaction at room temperature for 30 minutes;

[0062] (5) Pour the sonicated solution from step (4) back into the chitosan solution from step (1) and perform a sonication reaction at room temperature for 30 minutes.

[0063] (6) Wash the product obtained in step (5) with deionized water and ethanol and centrifuge. Dry the product in an oven to obtain CS-BT@Ce-MOFs / La-MOFs.

[0064] (7) Disperse an appropriate amount of dried precursor evenly on the bottom of a ceramic boat. Under a pure nitrogen atmosphere, heat it to 400°C at a heating rate of 5°C / min, hold it for 30 minutes, and then heat it directly to 800°C at the same heating rate. Hold it at this temperature for 2 hours and then cool it naturally to room temperature to obtain a low-cost biomass carbon electrode material with plant tannin-modified biomass immobilized with rare earth active components for fuel cells.

[0065] The Ce-La@CCS-BT material obtained in this embodiment was subjected to phase identification and microstructure and structural characterization: the phase of the prepared material was identified using Raman spectroscopy, Fourier transform infrared spectroscopy, powder X-ray diffraction, and X-ray photoelectron spectroscopy, and the microstructure and structure of the obtained material were characterized using scanning electron microscopy.

[0066] Figure 1 This is a scanning electron microscope (SEM) image of the Ce-La@CCS-BT nanocomposite material. The image shows that the material exhibits a coral-like structure with abundant porous surfaces. This indicates that free hydrogen released from plant polyphenols permeates into the Ce-MOF / La-MOF and etches it, thereby forming a porous structure within and exposing more active sites.

[0067] Figure 2 This is the N2 adsorption-desorption isotherm curve of the Ce-La@CCS-BT nanocomposite material. The curve is a typical type IV, indicating that many mesoporous structures were generated during this process.

[0068] Figure 3 This is a pore size distribution diagram of the Ce-La@CCS-BT nanocomposite material, which shows that its pore size is 3.52 nm.

[0069] Figure 4 This is the Raman spectrum of the Ce-La@CCS-BT nanocomposite. The image shows two distinct carbon characteristic peaks, belonging to the D band (1314–1350 cm⁻¹) and the G band (1589–1609 cm⁻¹), respectively. The D band is the dislocation-induced band, representing various degrees of amorphization of carbon atoms, such as bond angle disorder, bond length disorder, and hybridization. The G band is the graphitization band, corresponding to the planar stretching vibrations of sp² hybridized carbon atoms. The ratio of the D band to the G band (ID / IG) is used to evaluate the degree of structural disorder; the calculated intensity value for Ce-La@CCS-BT is approximately 0.92.

[0070] Example 2:

[0071] This embodiment demonstrates the electrochemical performance study of Ce-La@CCS-BT, a low-cost biomass carbon electrode material modified from plant tannin and immobilized with rare earth active components, for use in fuel cells.

[0072] This invention uses a carbon rod as the counter electrode, a saturated silver chloride electrode (Ag / AgCl) as the reference electrode, and a glassy carbon electrode as the working electrode.

[0073] The concentration of Nafion added during the preparation of the catalyst described in this invention is 5 wt%, and the dosage is 15 μL.

[0074] The electrode pretreatment in the testing process of this invention involves adding α-Al2O3 electrode polishing powder and a small amount of deionized water to a nylon polishing cloth base, grinding the rotating disc electrode back and forth in a figure-eight pattern for 10 minutes, then cleaning the residual powder on the electrode with deionized water, and finally air-drying it to complete the treatment.

[0075] The catalyst prepared according to this invention involves weighing 4 mg of the catalyst and dispersing it in a 1 mL centrifuge tube, adding 235 μL of deionized water, 735 μL of isopropanol, and 15 μL of 5 wt% Nafion solution, and then sonicating at room temperature for 50 minutes to obtain catalyst ink. Then, 28 μL of the ink is gradually added dropwise to the surface of a glassy carbon electrode (catalyst loading 0.25 mg cm⁻²), and after natural drying, electrocatalytic performance is tested.

[0076] All electrocatalytic performance tests described in this invention were conducted in a 0.1M KOH (pH = 13.62) electrolyte. The measured potentials can be converted to a potential relative to a reversible hydrogen electrode (RHE) using the following formula:

[0077] All potential values ​​involved in this invention are relative to the potential of a reversible hydrogen electrode.

[0078] The catalyst described in this invention requires CV activation for 3 cycles before electrochemical testing.

[0079] The catalysts described in this invention are all tested at room temperature to prevent large temperature variations from affecting the catalyst performance.

[0080] The Nafion added during the preparation of the catalyst described in this invention is produced by Aldrichsigma and has a concentration of 5%.

[0081] Use a pipette to drop 7 μL of catalyst onto the working electrode. Allow it to air dry naturally, then repeat this step 3 times. Next, slowly immerse the working electrode into an oxygen-saturated 0.1 MkOH electrolyte. During this step, prevent air bubbles from forming on the working electrode. Throughout the test, oxygen should be continuously introduced into the electrolyte to ensure oxygen saturation.

[0082] Cyclic voltammetry and linear cyclic voltammetry tests were performed on the catalyst obtained in this embodiment. Cyclic voltammetry experiments were conducted using an electrochemical workstation manufactured by Pine Corporation (USA). The test voltage scan range was -0.9 to 0.1 V, and the scan rate was 50 mV / s. During the test, the catalyst was activated for 3 cycles at a current density of 50 mV / s before the cyclic voltammetry test. Similarly, linear cyclic voltammetry tests were performed using a Pine electrochemical workstation, with a test voltage scan range of -0.9 to 0.1 V and a scan rate of 50 mV / s. Rotation speed measurements were used to obtain the current density of the catalyst material at different rotation speeds, and the number of transferred electrons could be determined using the KL equation. The test current density was 10 mV / s, and the rotation speeds were 400, 625, 900, 1225, 1600, and 2025 rpm. Stability and methanol tolerance are also important indicators of catalyst performance. This test was also performed on an electrochemical workstation. The stability test voltage was -0.189V and the test duration was 20,000s. The methanol tolerance test voltage was -0.189V and the test duration was 1,000s. 3M methanol solution was added dropwise at 300s.

[0083] Figure 5 The figure shows the cyclic voltammetric characteristics of the Ce-La@CCS-BT catalyst (test voltage scan range: -0.9-0.1V, scan rate: 50mV / s). In an O2-saturated electrolyte, a significant cathode oxygen reduction peak is observed at 0.54V, indicating that a catalytic oxygen reduction reaction has occurred. The response to oxygen shows that Ce-La@CCS-BT has significant oxygen reduction catalytic activity in alkaline solution.

[0084] Figure 6 The figures show linear cyclic voltammetry of Ce-La@CCS-BT catalyst at different temperatures (test voltage range: -0.9-0.1V, scan rate: 10mV / s). The Ce-La@CCS-BT catalyst exhibits the best performance at a calcination temperature of 800℃.

[0085] Figure 7 The figure shows linear cyclic voltammetry (scan range -0.9-0.1 V, scan rate 10 mV / s) in O2-saturated 0.1 MkOH with different Ce-MOFs to La-MOFs mass ratios of 1:3, 1:2, 1:1, 2:1, and 3:1. As can be seen from the figure, the oxygen reduction (ORR) performance of the nanocomposite material is optimal when the Ce-MOFs to La-MOFs mass ratio is 1:1 at a heat treatment temperature of 800 °C, with the limiting current density increasing from 2.44 mA cm2 to 6.26 mA cm2.

[0086] Figure 8The linear cyclic voltammograms (scan rate: 10 mV / s) of Ce-La@CCS-BT catalyst under different rotation speeds (400, 625, 900, 1225, 1600, 2025 rpm) show that the limiting diffusion current density of the catalyst gradually increases with the increase of rotation speed. This is because the faster the rotation speed, the faster the oxygen diffusion rate, indicating that the oxygen reduction catalytic process is controlled by mass transfer and conforms to first-order kinetics.

[0087] Figure 9 The KL curves for the Ce-La@CCS-BT catalyst are shown. Linear fitting of the current density and rotational speed at different voltages reveals that the slope of the curve remains essentially constant across the entire scanning potential range. This indicates that oxygen reduction under this catalyst involves the same number of transferred electrons at different potentials. Based on RRDE test results, the oxygen reduction catalysis of the Ce-La@CCS-BT catalyst in an alkaline electrolyte within the potential range of 0.2V to 0.4V is a four-electron transfer process.

[0088] Figure 10 The methanol tolerance of the optimal Ce-La / CCS-BT catalyst and the commercial 20% Pt / C catalyst was determined using IT technology by adding 2 mL of methanol to 0.1 MkOH electrolyte at 300 s and running at 1600 rpm. The graph shows that the limiting current density of Ce-La@CCS-BT only changed slightly, while the Pt / C catalyst exhibited a significant change in current density due to methanol oxidation. After running for another 700 s, the current density of Ce-La@CCS-BT remained stable, while the retention rate of Pt / C decreased to below 50%. This indicates that Ce-La@CCS-BT is superior to Pt / C in terms of methanol tolerance.

[0089] Figure 11 The Ce-La@CCS-BT catalyst and Pt / C catalyst were tested using the chronoamperometry method at 800℃. After 20,000 s of testing, the initial current density of the Pt / C catalyst decreased significantly by 23%, while that of the Ce-La@CCS-BT catalyst decreased by 22%. This indicates that the stability of the Ce-La@CCS-BT catalyst is comparable to that of the commercial Pt / C catalyst.

[0090] The embodiments of the present invention have been described above. However, the present invention is not limited to the above embodiments. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a plant tannin-modified biomass carbon electrode material, characterized in that: The preparation method includes the following steps: (1) Modified chitosan: Weigh a certain amount of chitosan, disperse it in acetic acid solution, and sonicate until fully dissolved; (2) Preparation of Ce-MOFs polymer substrate: Weigh a certain amount of pyromellitic acid white powder and dissolve it in a certain amount of anhydrous ethanol. The dissolved liquid is a colorless and transparent solution. Weigh a certain amount of cerium nitrate hexahydrate colorless and transparent crystals and dissolve them in a certain amount of deionized water. The dissolved liquid is also a colorless and transparent liquid. Then, slowly add the pyromellitic acid solution to cerium nitrate hexahydrate and stir on a magnetic stirrer to obtain a white mixture. Transfer it to a water bath and shake it at a certain temperature. Wash the sample obtained after the reaction with deionized water and ethanol several times, and dry it at a certain temperature to obtain white powder Ce-MOFs. Then, disperse the prepared Ce-MOFs and plant tannin in deionized water and sonicate at room temperature. (3) Preparation of La-MOFs polymer substrate: Weigh a certain amount of white lanthanum nitrate hexahydrate powder and dissolve it in a certain amount of water. Dissolve a certain amount of trimesic acid in a water / ethanol mixture to prepare a ligand solution. Mix the two solutions together at a certain temperature, run them at a certain speed for a certain time, and then allow them to settle. Finally, wash the prepared product several times with a mixture of water and ethanol, and then dry it in an oven at a certain temperature to obtain white powder La-MOFs. Then disperse the prepared La-MOFs with plant tannin in deionized water and sonicate it at room temperature. (4) Pour the solution from step (3) into the solution from step (2) and perform an ultrasonic reaction at room temperature; (5) Pour the sonicated solution from step (4) back into step (1) and perform the sonication reaction at room temperature; (6) The product obtained in step (5) was washed with deionized water and ethanol and centrifuged. The product was dried in an oven to obtain CS-BT@Ce-MOFs / La-MOFs. (7) A suitable amount of dried precursor is evenly dispersed on the bottom of a ceramic boat, placed in a tube furnace and pyrolyzed at high temperature under a nitrogen atmosphere, and naturally cooled to room temperature to obtain a biomass carbon electrode material modified with a dual rare earth organic framework for fuel cells.

2. The method for preparing the plant tannin-modified biomass carbon electrode material according to claim 1, characterized in that: The ultrasound time described in step (1) is 15-30 min.

3. The method for preparing the plant tannin-modified biomass carbon electrode material according to claim 1, characterized in that: In step (2), the ultrasonic time is 5-10 min, the stirring time on the magnetic stirrer is 30-50 min, the shaking time is 1 h at 60℃, the drying time is 13-20 h at 60-80℃, the mass ratio of plant tannin to Ce-MOFs is 1:1, and the ultrasonic time is 30-40 min.

4. The method for preparing the plant tannin-modified biomass carbon electrode material according to claim 1, characterized in that: In step (3), the operation is carried out at a temperature of 25℃ and a rotation speed of 135r / min for 1.5h, a settling time of 0.5h, a drying temperature of 60℃, and a drying time of 15-20h; the mass ratio of plant polyphenols to La-MOFs is 1:1, and the ultrasonic time is 30-40min.

5. The method for preparing the plant tannin-modified biomass carbon electrode material according to claim 1, characterized in that: The ultrasonic reaction time in step (4) is 30 min.

6. The method for preparing the plant tannin-modified biomass carbon electrode material according to claim 1, characterized in that: The ultrasonic reaction time described in step (5) is 30-40 min.

7. The method for preparing the plant tannin-modified biomass carbon electrode material according to claim 1, characterized in that: The drying temperature in step (6) is 60-80℃ and the drying time is 15h.

8. The method for preparing the plant tannin-modified biomass carbon electrode material according to claim 1, characterized in that: The high-temperature pyrolysis described in step (7) is as follows: under a pure nitrogen atmosphere, the temperature is first heated to 400°C at a heating rate of 5°C / min, then held for 30 minutes, and then directly heated to 800°C at the same heating rate. After holding at this temperature for 2 hours, the temperature is naturally cooled to room temperature.

9. A plant tannin-modified biomass carbon electrode material prepared by the preparation method according to any one of claims 1-8.

10. The application of the plant tannin-modified biomass carbon electrode material according to claim 9 in a fuel cell, characterized in that: The plant tannin-modified biomass carbon electrode material is used as the cathode material of the fuel cell. The cathode material is prepared by uniformly mixing the plant tannin-modified biomass carbon electrode material with isopropanol, deionized water and Nafion solution.

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