A fuel cell negative electrode catalyst, a method for preparing the same, and an application thereof

Abstract

The application discloses a fuel cell negative electrode catalyst and a preparation method and application thereof, and belongs to the technical field of fuel cells. The preparation method comprises the following steps: S1, mixing glacial acetic acid and anhydrous ethanol, adding butyl titanate dropwise to form solution A; mixing anhydrous ethanol and deionized water, adding CS / Cys-MWCNT, and ultrasonicating to form solution B; adding solution A into solution B dropwise, then standing, aging, drying, heat treating under a nitrogen atmosphere, and cooling to obtain TiO2 / CS / Cys-MWCNT; S2, adding 0.05mol / L H2PtCl6 into ethylene glycol, then adding TiO2 / CS / Cys-MWCNT obtained in the step S1, ultrasonicating for 1-2 hours, heat reacting, centrifuging, washing, and drying to obtain the negative electrode catalyst. The catalyst obtained in the application exhibits the synergistic advantages of low initial potential, high peak current and high stability in a methanol oxidation reaction.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of fuel cells, in particular to a fuel cell negative electrode catalyst and a preparation method and application thereof. BACKGROUND

[0002] A fuel cell is a power generation device that converts chemical energy into electrical energy through electrochemical reactions. Fuel cells can be classified into alkaline fuel cells, solid oxide fuel cells, molten carbonate fuel cells, phosphoric acid fuel cells, and proton exchange membrane fuel cells according to the electrolyte used. Proton exchange membrane fuel cells, also known as polymer membrane fuel cells, are the fifth generation of fuel cells developed after alkaline fuel cells, solid oxide fuel cells, molten carbonate fuel cells, and phosphoric acid fuel cells.

[0003] Proton exchange membrane fuel cells (PEMFC) can be divided into two categories according to the fuel used: one is a fuel cell that uses hydrogen or reforming gas as fuel; the other is a fuel cell that directly uses methanol as fuel, also known as a direct methanol fuel cell (DMFC). Originally, a fuel cell that uses hydrogen / oxygen as fuel is the most ideal chemical power source, but a fuel cell that uses hydrogen / oxygen as fuel has safety issues during fuel preparation, transportation, storage, and use. Therefore, in recent years, the concept of a direct methanol fuel cell (DMFC) that directly uses methanol as fuel has been proposed. A direct methanol fuel cell (DMFC) does not need to convert methanol into hydrogen, but directly uses methanol as fuel for the positive electrode, and pure oxygen or air is used as the electrode active material for the negative electrode, and electrochemical reactions occur directly on the electrodes to convert chemical energy into electrical energy for use by the load. Compared with a fuel cell that uses hydrogen as fuel for the positive electrode and pure oxygen or air as the electrode active material for the negative electrode, a direct methanol fuel cell has the advantages of small size, light weight, simple structure, high reliability, easy fuel carrying and replenishment, and the like. In addition, a direct methanol fuel cell also has the functions of rapid start-up and fast response to load speed. Therefore, a direct methanol fuel cell is an ideal power source that can be used as a small household power station, a portable electronic appliance mobile power source, and a power source for electric vehicles, and has a broad application prospect.

[0004] Currently, Pt-based catalysts have become the most widely used catalysts in methanol oxidation reactions due to their excellent catalytic activity, but Pt-based catalysts are easily deactivated due to the poisoning of intermediate species (CO-like), which reduces the durability of the catalysts. Patent CN118099455B describes a nitrogen-doped three-dimensional graphene-supported Pt-based catalyst and a preparation method and application thereof. The patent converts some GO nanosheets into nitrogen-doped graphene, improves the anchoring effect of the carrier on platinum particles, and thus improves the stability of the catalyst. However, the electrocatalytic performance of the catalyst still needs to be improved. SUMMARY

[0005] The application provides a fuel cell negative electrode catalyst, a preparation method and application thereof, and can solve the problem that the electrocatalytic performance of a catalyst in the prior art needs to be improved.

[0006] The object of the application can be achieved by the following technical solutions.

[0007] In a first aspect, the application provides a preparation method of a fuel cell negative electrode catalyst, comprising the following steps:

[0008] S1, mixing glacial acetic acid and anhydrous ethanol, adding butyl titanate dropwise to form solution A; mixing anhydrous ethanol and deionized water, adding CS / Cys-MWCNT, and ultrasonicating to form solution B; adding solution A dropwise into solution B, and then standing, aging, drying, and heat treating under a nitrogen atmosphere to obtain TiO2 / CS / Cys-MWCNT;

[0009] S2, adding 0.05 mol / L H2PtCl6 into ethylene glycol, and then adding TiO2 / CS / Cys-MWCNT obtained in step S1, ultrasonicating for 1-2 h, heating and reacting, centrifuging, washing, and drying to obtain a negative electrode catalyst.

[0010] Further, in step S1, the volume ratio of the glacial acetic acid, the anhydrous ethanol and the butyl titanate is 6:15:(5-6); the amount ratio of the anhydrous ethanol, the deionized water and the CS / Cys-MWCNT is 7 mL:10 mL:0.3 g; and the volume ratio of solution A to solution B is 1:1.

[0011] Further, in step S1, the heat treatment under the nitrogen atmosphere is performed at a temperature of 600-700 DEG C for 2-3 h.

[0012] Further, in step S2, the amount ratio of H2PtCl6, ethylene glycol and TiO2 / CS / Cys-MWCNT is 1.5 mL:100-120 mL:1-1.4 g.

[0013] Further, in step S2, the heating and reaction is performed at a temperature of 150-170 DEG C for 3-4 h.

[0014] Further, the preparation method of the CS / Cys-MWCNT is as follows:

[0015] S11, adding MWCNT into a mixed acid solution, ultrasonicating for 1-2 h, and then stirring and reacting at 55 DEG C for 6-7 h to obtain MWCNT-COOH;

[0016] S12, dispersing MWCNT-COOH and L-cysteine in deionized water, then adding EDC·HCl and NHS, stirring at room temperature for 22-24 hours, centrifuging, washing, and drying to obtain Cys-MWCNT;

[0017] S13, dissolving chitosan in a 2% acetic acid solution, stirring for 12 hours to obtain a CS solution; dispersing Cys-MWCNT in deionized water, slowly adding the Cys-MWCNT to the CS solution after ultrasonic treatment for 30 minutes, magnetically stirring the mixed solution at 98 DEG C under condensation reflux for 6 hours, adjusting the pH of the solution to 10 with dilute ammonia water, adding glutaraldehyde, magnetically stirring at 60 DEG C for 3 hours, washing, and freeze-drying to obtain CS / Cys-MWCNT.

[0018] Further, in step S11, the amount ratio of MWCNT to mixed acid solution is 2g:30-40mL; the mixed acid solution is composed of concentrated sulfuric acid and concentrated nitric acid in a volume ratio of 3:1.

[0019] Further, in step S12, the amount ratio of MWCNT-COOH, L-cysteine, deionized water, EDC·HCl, and NHS is 0.2g:0.2-0.25g:50-60mL:1.2g:0.6g.

[0020] Further, in step S13, the amount ratio of chitosan, dilute acetic acid solution, Cys-MWCNT, deionized water, and glutaraldehyde is 0.8-1g:200mL:0.2g:20mL:1-1.2mL.

[0021] In a second aspect, the application provides a fuel cell negative electrode catalyst prepared by the preparation method described in any one of the above.

[0022] In a third aspect, the application provides a fuel cell negative electrode catalyst for use in a direct methanol fuel cell.

[0023] The beneficial effects of the application are as follows:

[0024] 1. In step S1 of the application, the hydrolysis rate of butyl titanate is regulated by an ice acetic acid and anhydrous ethanol mixed system, and the TiO2 is in-situ controllably grown on the surface of the double-modified carbon nanotube by precise mixing with solution B containing CS / Cys-MWCNT, so that the TiO2 is combined with the amino and thiol functional groups of CS and Cys on the surface of the double-modified carbon nanotube through the Ti-OH bond, and the TiO2 is combined with the amino and thiol functional groups of CS and Cys on the surface of the double-modified carbon nanotube through the Ti-OH bond. 4+The coordination of the Cys ensures the uniform dispersion of the TiO2 nanoparticles and the formation of a firm interface between the MWCNT, and the TiO2 crystal form is optimized simultaneously through heat treatment in a nitrogen atmosphere, so that the composite carrier TiO2 / CS / Cys-MWCNT with high conductivity, rich anchoring sites and excellent stability is finally obtained; in step S2, H2PtCl6 is reduced in an ethylene glycol system, and the Pt precursor is uniformly adsorbed on the anchoring sites of the carrier through the reducing property and dispersing property of the ethylene glycol and 1-2h ultrasonic treatment, so that the controllable reduction and loading of Pt nanoparticles are realized under heating conditions, and finally the negative electrode catalyst with high Pt dispersity and strong metal-carrier interaction is obtained, which exhibits the synergistic advantages of low initial potential, high peak current and high stability in the methanol oxidation reaction.

[0025] 2. The CS / Cys-MWCNT prepared in the application is obtained by modifying the MWCNT with Cys, which improves the polarity of the MWCNT and the compatibility with chitosan (hydrophilicity), ensures the uniform coating of chitosan, provides a uniform substrate for subsequent glutaraldehyde crosslinking, and can form a uniform network structure, which is helpful to improve the electrocatalytic activity after subsequent sintering.

[0026] 3. The CS / Cys-MWCNT contains thiol and amino groups, which can serve as anchoring sites for Ti 4+ When the butyl titanate is condensed in situ to form TiO2, it grows around these anchoring sites, so that the uniform dispersion of TiO2 is realized and its own agglomeration is prevented, a stable conductive network is formed, the charge transfer resistance is greatly reduced, and the kinetic speed of the catalytic reaction is improved.

[0027] 4. After the in-situ polymerization of TiO2 on the CS / Cys-MWCNT, sintering can be performed to form a carrier doped with nitrogen and sulfur, the doping of nitrogen and sulfur elements can provide anchoring for the loading of Pt particles, strengthen the stability of the overall catalyst, and solve the problem of self-agglomeration of metal particles during the reduction process, reduce the CO stripping potential, and improve the poison resistance of the catalyst. The doping of nitrogen and sulfur elements can also improve the electrocatalytic performance of TiO2, the high conductivity of TiO2 plus the conductive network of CS / Cys-MWCNT can improve the electron transfer rate of the Pt active site, and accelerate the kinetics of the catalytic reaction. DETAILED DESCRIPTION

[0028] In order to make the above-mentioned purposes, features and advantages of the application more obvious and easy to understand, the specific embodiments of the application are described in detail below.

[0029] In a first aspect, the application provides a preparation method of a fuel cell negative electrode catalyst, comprising the following steps:

[0030] S1. Mix glacial acetic acid and anhydrous ethanol, add tetrabutyl titanate dropwise to form solution A; mix anhydrous ethanol and deionized water, add CS / Cys-MWCNT, sonicate to form solution B; add solution A dropwise to solution B, then let stand, age, dry, heat treat under nitrogen atmosphere, cool to obtain TiO2 / CS / Cys-MWCNT;

[0031] In the above steps, the hydrolysis rate of tetrabutyl titanate is slowed down by solubilizing and chelating it using a mixture of glacial acetic acid and anhydrous ethanol to form a stable solution A. Simultaneously, the compatibility of the mixed solvent of anhydrous ethanol and deionized water, combined with ultrasonic dispersion, ensures that CS / Cys-MWCNTs are uniformly dispersed and their surface thiol and amino groups are fully exposed, forming solution B. After adding solution A to solution B, tetrabutyl titanate undergoes controlled hydrolysis to form Ti under the synergistic effect of a weakly acidic environment and the active functional groups of the carrier. 4+ The TiO2 precursor is anchored to the CS / Cys-MWCNT surface through coordination. After static aging, it undergoes in-situ condensation to form a uniformly dispersed TiO2 precursor. Subsequent drying and nitrogen atmosphere heat treatment not only optimize the crystal form of TiO2, but also promote the in-situ doping of the nitrogen source provided by CS and the sulfur source provided by Cys into the TiO2 lattice and carbon-based support. At the same time, some active functional groups on the support surface are retained, and finally a TiO2 / CS / Cys-MWCNT composite support with high conductivity, abundant anchoring sites and excellent structural stability is obtained.

[0032] S2. Add 0.05 mol / L H2PtCl6 to ethylene glycol, then add TiO2 / CS / Cys-MWCNT obtained in step S1, sonicate for 1-2 h, heat to react, centrifuge, wash, and dry to obtain the negative electrode catalyst.

[0033] In the above steps, ethylene glycol is used as a solvent and reducing agent to dissolve 0.05 mol / L H2PtCl6. TiO2 / CS / Cys-MWCNT composite support is then added and subjected to ultrasonic treatment for 1–2 hours. Utilizing the cavitation and dispersion effects of ultrasound, the abundant N / S doping sites and other active groups on the support surface are fully exposed. Platinum ions in H2PtCl6 are then precisely captured through coordination, achieving uniform adsorption of the Pt precursor on the support surface. Subsequently, under heating conditions, ethylene glycol controllably reduces the adsorbed platinum ions to Pt nanoparticles. Simultaneously, the dispersibility of ethylene glycol inhibits Pt particle aggregation. Combined with the interaction between the support and Pt, the Pt nanoparticles are firmly anchored on the support surface. Finally, after centrifugation and washing to remove unreacted precursors and byproducts, and drying, a fuel cell negative electrode catalyst with high Pt dispersibility, excellent electron transport efficiency, and strong structural stability is obtained.

[0034] In some embodiments, in step S1, the volume ratio of glacial acetic acid, anhydrous ethanol, and tetrabutyl titanate is 6:15:(5-6); the volume ratio of anhydrous ethanol, deionized water, and CS / Cys-MWCNT is 7mL:10mL:0.3g; and the volume ratio of solution A to solution B is 1:1. This invention precisely controls the amount of titanium source, obtaining a catalyst with the best catalytic effect. If the titanium source is excessive, TiO2 will be over-coated on the surface of CS / Cys-MWCNT, blocking the conductive network; if the titanium source is insufficient, the TiO2 loading will be insufficient, failing to exert its corrosion resistance and anchoring auxiliary effects. The 1:1 volume ratio of solution A to solution B ensures that CS / Cys-MWCNT is uniformly dispersed in the mixed system and that the surface active functional groups are fully exposed, while also allowing the TiO2 generated by the hydrolysis of tetrabutyl titanate to be fully utilized. 4+ Efficient coordination with CS / Cys-MWCNT functional groups enables in-situ uniform growth of TiO2 on the CS / Cys-MWCNT surface.

[0035] In some embodiments, in step S1, the heat treatment under a nitrogen atmosphere is carried out at a temperature of 600–700°C for 2–3 hours. This not only promotes the full crystallization of the TiO2 precursor but also enables in-situ doping of CS (nitrogen source) and Cys (sulfur source), further enhancing the conductivity, structural stability, and anchoring ability of the composite carrier.

[0036] In some embodiments, in step S2, the ratio of H2PtCl6, ethylene glycol, and TiO2 / CS / Cys-MWCNT is 1.5 mL: 100–120 mL: 1–1.4 g. This allows for an optimal ratio between the Pt precursor and the active sites of the support, ensuring sufficient adsorption and reduction of the Pt precursor while avoiding particle agglomeration caused by excessive Pt. Simultaneously, the sufficient amount of ethylene glycol balances reduction efficiency and dispersion effect, guaranteeing high dispersibility and high loading of Pt nanoparticles.

[0037] In some embodiments, in step S2, the heating reaction temperature is 150–170°C, and the time is 3–4 hours. This allows for precise control of the ethylene glycol reduction rate, ensuring that platinum ions are stably reduced to uniformly sized Pt nanoparticles, avoiding particle agglomeration caused by rapid reduction at high temperatures. Simultaneously, sufficient reaction time strengthens the metal-support interaction between Pt and the support, firmly anchoring the Pt particles to the support surface and enhancing the catalyst's structural stability and catalytic activity.

[0038] In some embodiments, the preparation method of the CS / Cys-MWCNT is as follows:

[0039] S11. Add MWCNT to the mixed acid solution, sonicate for 1-2 hours, and then stir at 55°C for 6-7 hours to obtain MWCNT-COOH;

[0040] After adding MWCNTs to a mixed acid solution, sonication for 1–2 hours can break up the MWCNT aggregates and increase their contact area with the mixed acid. Then, the mixture is stirred at 55°C for 6–7 hours. The strong oxidizing components in the mixed acid will oxidize and etch the surface of MWCNTs, introducing a large number of carboxyl groups (-COOH) onto their graphitized framework. At the same time, surface impurities and defective carbons are removed, ultimately yielding MWCNT-COOH with a surface rich in active carboxyl groups and improved dispersibility, providing reaction sites for subsequent covalent grafting with L-cysteine.

[0041] S12. Disperse MWCNT-COOH and L-cysteine ​​in deionized water, then add EDC·HCl and NHS, stir at room temperature for 22-24 h, centrifuge, wash, and dry to obtain Cys-MWCNT.

[0042] After dispersing MWCNT-COOH and L-cysteine ​​in deionized water, EDC was added. HCl and NHS activate the carboxyl groups on the surface of MWCNT-COOH, causing them to undergo amidation with the amino group in the L-cysteine ​​molecule to form a stable amide bond (-CONH-). The reaction is ensured to proceed fully by stirring at room temperature for 22-24 hours. After centrifugation, washing, and drying, L-cysteine ​​is covalently grafted onto the surface of MWCNTs, resulting in Cys-MWCNTs rich in thiol groups (-SH).

[0043] S13. Dissolve chitosan in 2% dilute acetic acid solution and stir for 12 hours to obtain CS solution; disperse Cys-MWCNT in deionized water, sonicate for 30 minutes and slowly add it to CS solution. Under reflux conditions, magnetically stir the mixture at 98°C for 6 hours. After cooling the mixture to room temperature, adjust the pH of the solution to 10 with dilute ammonia, add glutaraldehyde, magnetically stir at 60°C for 3 hours, wash, freeze dry to obtain CS / Cys-MWCNT.

[0044] Chitosan was first dissolved in a 2% dilute acetic acid solution and stirred for 12 hours. The protonation effect of acetic acid allowed the chitosan molecular chains to fully expand and disperse, forming a stable CS solution. Cys-MWCNT was dispersed in deionized water and sonicated for 30 minutes before being slowly added to the CS solution. Under the conditions of reflux at 98°C and magnetic stirring for 6 hours, the temperature increase promoted the formation of hydrogen bonds and electrostatic interactions between Cys-MWCNT and chitosan molecular chains, achieving uniform coating of chitosan. After cooling the mixture, the pH was adjusted to 10 with dilute ammonia to provide an alkaline environment for glutaraldehyde crosslinking. The added glutaraldehyde, as a crosslinking agent, can undergo a condensation reaction with the amino groups (-NH2) on the chitosan molecular chains to form Schiff base bonds. After stirring at 60°C for 3 hours, crosslinking and curing were completed. Finally, a structurally stable CS / Cys-MWCNT composite carrier with both thiol and amino active sites was obtained by washing and freeze-drying.

[0045] In some embodiments, in step S11, the ratio of MWCNT to the mixed acid solution is 2g:30-40mL; the mixed acid solution is composed of concentrated sulfuric acid and concentrated nitric acid in a volume ratio of 3:1. This 3:1 ratio and amount of concentrated sulfuric acid and concentrated nitric acid can efficiently introduce abundant and uniform carboxyl groups onto the surface of carbon nanotubes, providing a high density of reaction sites for subsequent covalent grafting of cysteine, which is the basis for constructing a stable functionalized interface.

[0046] In some embodiments, in step S12, the ratio of MWCNT-COOH, L-cysteine, deionized water, EDC·HCl, and NHS is 0.2g:0.2-0.25g:50-60mL:1.2g:0.6g. This ratio, through the EDC / NHS catalytic system, ensures the efficient amidation reaction of cysteine ​​with carboxylated carbon nanotubes, successfully introducing key functional groups and creating conditions for subsequent chitosan crosslinking and metal anchoring.

[0047] In some embodiments, in step S13, the ratio of chitosan, dilute acetic acid solution, Cys-MWCNT, deionized water, and glutaraldehyde is 0.8–1 g: 200 mL: 0.2 g: 20 mL: 1–1.2 mL. This ratio allows chitosan to fully encapsulate the thiolized carbon nanotubes, and glutaraldehyde enables uniform and robust cross-linking between the two, forming a stable three-dimensional network structure.

[0048] Secondly, the present invention provides a fuel cell negative electrode catalyst, which is prepared by any one of the preparation methods described above.

[0049] Thirdly, the present invention provides an application of a fuel cell negative electrode catalyst in a direct methanol fuel cell.

[0050] The specific embodiments of the present invention will be described in detail below, but it should be understood that the scope of protection of the present invention is not limited to the specific embodiments.

[0051] Preparation Example 1

[0052] The preparation method of CS / Cys-MWCNT in this preparation example is as follows:

[0053] S11. Add 2g of MWCNT to 30mL of mixed acid solution, which is composed of concentrated sulfuric acid and concentrated nitric acid in a volume ratio of 3:1. Sonicate for 1h, then stir at 55℃ for 6h to obtain MWCNT-COOH.

[0054] S12. Disperse 0.2g MWCNT-COOH and 0.2g L-cysteine ​​in 50mL of deionized water, then add 1.2g EDC·HCl and 0.6g NHS, stir at room temperature for 22h, centrifuge, wash, and dry to obtain Cys-MWCNT;

[0055] S13. Dissolve 0.8g of chitosan in 200mL of 2% dilute acetic acid solution and stir for 12h to obtain CS solution; take 0.2g of Cys-MWCNT and disperse it in 20mL of deionized water, sonicate for 30min and slowly add it to CS solution. Under reflux conditions, stir the mixed solution magnetically at 98℃ for 6h. After cooling the mixed solution to room temperature, adjust the pH of the solution to 10 with dilute ammonia, add 1mL of glutaraldehyde, stir magnetically at 60℃ for 3h, wash, freeze dry to obtain CS / Cys-MWCNT.

[0056] Preparation Example 2

[0057] The preparation method of CS / Cys-MWCNT in this preparation example is as follows:

[0058] S11. Add 2g of MWCNT to 35mL of mixed acid solution, which is composed of concentrated sulfuric acid and concentrated nitric acid in a volume ratio of 3:1. Sonicate for 1.5h, then stir at 55℃ for 6.5h to obtain MWCNT-COOH.

[0059] S12. Disperse 0.2g MWCNT-COOH and 0.22g L-cysteine ​​in 55mL of deionized water, then add 1.2g EDC·HCl and 0.6g NHS, stir at room temperature for 23h, centrifuge, wash, and dry to obtain Cys-MWCNT;

[0060] S13. Dissolve 0.9g of chitosan in 200mL of 2% dilute acetic acid solution and stir for 12h to obtain CS solution; take 0.2g of Cys-MWCNT and disperse it in 20mL of deionized water, sonicate for 30min and then slowly add it to CS solution. Under reflux conditions, stir the mixture magnetically at 98℃ for 6h. After cooling the mixture to room temperature, adjust the pH of the solution to 10 with dilute ammonia, add 1.1mL of glutaraldehyde, stir magnetically at 60℃ for 3h, wash, freeze dry to obtain CS / Cys-MWCNT.

[0061] Preparation Example 3

[0062] The preparation method of CS / Cys-MWCNT in this preparation example is as follows:

[0063] S11. Add 2g of MWCNT to 40mL of mixed acid solution, which is composed of concentrated sulfuric acid and concentrated nitric acid in a volume ratio of 3:1. Sonicate for 2h, then stir at 55℃ for 7h to obtain MWCNT-COOH.

[0064] S12. Disperse 0.2g MWCNT-COOH and 0.25g L-cysteine ​​in 60mL of deionized water, then add 1.2g EDC·HCl and 0.6g NHS, stir at room temperature for 24h, centrifuge, wash, and dry to obtain Cys-MWCNT;

[0065] S13. Dissolve 1g of chitosan in 200mL of 2% dilute acetic acid solution and stir for 12h to obtain CS solution; take 0.2g of Cys-MWCNT and disperse it in 20mL of deionized water, sonicate for 30min and then slowly add it to CS solution. Under reflux conditions, stir the mixture magnetically at 98℃ for 6h. After cooling the mixture to room temperature, adjust the pH of the solution to 10 with dilute ammonia, add 1.2mL of glutaraldehyde, stir magnetically at 60℃ for 3h, wash, freeze dry to obtain CS / Cys-MWCNT.

[0066] Compare with Example 1

[0067] The only difference between this control example and preparation example 1 is that L-cysteine ​​is omitted. The specific steps are as follows:

[0068] S11. Add 2g of MWCNT to 30mL of mixed acid solution, which is composed of concentrated sulfuric acid and concentrated nitric acid in a volume ratio of 3:1. Sonicate for 1h, then stir at 55℃ for 6h to obtain MWCNT-COOH.

[0069] S12. Dissolve 0.8g of chitosan in 200mL of 2% dilute acetic acid solution and stir for 12h to obtain CS solution; take 0.2g of MWCNT-COOH and disperse it in 20mL of deionized water, sonicate for 30min and then slowly add it to CS solution. Under reflux conditions, stir the mixture magnetically at 98℃ for 6h. After cooling the mixture to room temperature, adjust the pH of the solution to 10 with dilute ammonia, add 1mL of glutaraldehyde, stir magnetically at 60℃ for 3h, wash, freeze dry to obtain CS-MWCNT.

[0070] Compare with Example 2

[0071] The only difference between this comparative example and preparation example 1 is that L-cysteine ​​and chitosan are omitted. The specific steps are as follows:

[0072] 2g of MWCNT was added to 30mL of mixed acid solution, which consisted of concentrated sulfuric acid and concentrated nitric acid in a volume ratio of 3:1. The mixture was sonicated for 1 hour and then stirred at 55℃ for 6 hours to obtain MWCNT-COOH.

[0073] Example 1

[0074] This embodiment provides a method for preparing a negative electrode catalyst for a fuel cell, including the following steps:

[0075] S1. Mix 12 mL of glacial acetic acid and 30 mL of anhydrous ethanol, add 10 mL of tetrabutyl titanate to form solution A; mix 7 mL of anhydrous ethanol and 10 mL of deionized water, add 0.3 g of CS / Cys-MWCNT obtained in Preparation Example 1, sonicate to form solution B; add 10 mL of solution A to 10 mL of solution B, then let stand, age, dry, and heat-treat at 600 °C for 2 h under a nitrogen atmosphere to obtain TiO2 / CS / Cys-MWCNT;

[0076] S2. Add 1.5 mL of 0.05 mol / L H2PtCl6 to 100 mL of ethylene glycol, then add 1 g of TiO2 / CS / Cys-MWCNT obtained in step S1, sonicate for 1 h, heat at 150 °C for 3 h, centrifuge, wash, and dry to obtain the negative electrode catalyst.

[0077] Example 2

[0078] This embodiment provides a method for preparing a negative electrode catalyst for a fuel cell, including the following steps:

[0079] S1. Mix 12 mL of glacial acetic acid and 30 mL of anhydrous ethanol, and add 10.5 mL of tetrabutyl titanate to form solution A; mix 7 mL of anhydrous ethanol and 10 mL of deionized water, add 0.3 g of CS / Cys-MWCNT obtained in Preparation Example 1, and sonicate to form solution B; add 10 mL of solution A to 10 mL of solution B, then let stand, age, and dry, and heat-treat at 650 °C for 2.5 h under a nitrogen atmosphere to obtain TiO2 / CS / Cys-MWCNT;

[0080] S2. Add 1.5 mL of 0.05 mol / L H2PtCl6 to 110 mL of ethylene glycol, then add 1.1 g of TiO2 / CS / Cys-MWCNT obtained in step S1, sonicate for 1.5 h, heat at 160 °C for 3.5 h, centrifuge, wash, and dry to obtain the negative electrode catalyst.

[0081] Example 3

[0082] This embodiment provides a method for preparing a negative electrode catalyst for a fuel cell, including the following steps:

[0083] S1. Mix 12 mL of glacial acetic acid and 30 mL of anhydrous ethanol, and add 11 mL of tetrabutyl titanate to form solution A; mix 7 mL of anhydrous ethanol and 10 mL of deionized water, add 0.3 g of CS / Cys-MWCNT obtained in Preparation Example 2, and sonicate to form solution B; add 10 mL of solution A to 10 mL of solution B, then let stand, age, and dry, and heat-treat at 650 °C for 2.5 h under a nitrogen atmosphere to obtain TiO2 / CS / Cys-MWCNT;

[0084] S2. Add 1.5 mL of 0.05 mol / L H2PtCl6 to 110 mL of ethylene glycol, then add 1.2 g of TiO2 / CS / Cys-MWCNT obtained in step S1, sonicate for 1.5 h, heat at 160 °C for 3.5 h, centrifuge, wash, and dry to obtain the negative electrode catalyst.

[0085] Example 4

[0086] This embodiment provides a method for preparing a negative electrode catalyst for a fuel cell, including the following steps:

[0087] S1. Mix 12 mL of glacial acetic acid and 30 mL of anhydrous ethanol, and add 11.5 mL of tetrabutyl titanate to form solution A; mix 7 mL of anhydrous ethanol and 10 mL of deionized water, add 0.3 g of CS / Cys-MWCNT obtained in Preparation Example 3, and sonicate to form solution B; add 10 mL of solution A to 10 mL of solution B, then let stand, age, and dry, and heat-treat at 650 °C for 2.5 h under a nitrogen atmosphere to obtain TiO2 / CS / Cys-MWCNT;

[0088] S2. Add 1.5 mL of 0.05 mol / L H2PtCl6 to 110 mL of ethylene glycol, then add 1.3 g of TiO2 / CS / Cys-MWCNT obtained in step S1, sonicate for 1.5 h, heat at 160 °C for 3.5 h, centrifuge, wash, and dry to obtain the negative electrode catalyst.

[0089] Example 5

[0090] This embodiment provides a method for preparing a negative electrode catalyst for a fuel cell, including the following steps:

[0091] S1. Mix 12 mL of glacial acetic acid and 30 mL of anhydrous ethanol, and add 12 mL of tetrabutyl titanate to form solution A; mix 7 mL of anhydrous ethanol and 10 mL of deionized water, add 0.3 g of CS / Cys-MWCNT obtained in Preparation Example 3, and sonicate to form solution B; add 10 mL of solution A to 10 mL of solution B, then let stand, age, and dry, and heat-treat at 700 °C for 3 h under a nitrogen atmosphere to obtain TiO2 / CS / Cys-MWCNT;

[0092] S2. Add 1.5 mL of 0.05 mol / L H2PtCl6 to 120 mL of ethylene glycol, then add 1.4 g of TiO2 / CS / Cys-MWCNT obtained in step S1, sonicate for 2 h, heat at 170 °C for 4 h, centrifuge, wash, and dry to obtain the negative electrode catalyst.

[0093] Comparative Example 1

[0094] The only difference between this comparative example and Example 1 is that the CS / Cys-MWCNT obtained in Preparation Example 1 was replaced with an equal amount of CS-MWCNT obtained in Control Example 1.

[0095] Comparative Example 2

[0096] The only difference between this comparative example and Example 1 is that the CS / Cys-MWCNT obtained in Preparation Example 1 was replaced with an equal amount of MWCNT-COOH obtained in Control Example 2.

[0097] Comparative Example 3

[0098] The only difference between this comparative example and Example 1 is that "10 mL of tetrabutyl titanate" in step S1 is changed to "9 mL of tetrabutyl titanate".

[0099] Comparative Example 4

[0100] The only difference between this comparative example and Example 5 is that "12 mL of tetrabutyl titanate" in step S1 is changed to "13 mL of tetrabutyl titanate".

[0101] The electrocatalytic performance of the catalysts obtained in Examples 1-5 and Comparative Examples 1-4 for the electrochemical oxidation of methanol was characterized at room temperature using cyclic voltammetry and potentiostatic polarization chronoamperometry. 5 mg of catalyst, 100 mg of Nafion solution, and 250 mg of deionized water were thoroughly mixed by ultrasonic treatment. 2.0 μL of the mixture was pipetted onto a glassy carbon electrode and dried in an oven at 80 °C for 5 minutes to obtain the working electrode. A saturated calomel electrode (SCE) was used as the reference electrode, and a platinum electrode as the counter electrode. The electrolyte solution was an aqueous solution of 2 mol / L CH3OH + 1 mol / L H2SO4. Cyclic voltammetry was performed for five activation cycles in the range of 0–1.0 V at a scan rate of 50 mV / s to test the onset potential and peak current of methanol oxidation. Potentiostatic polarization chronoamperometry was used to monitor the current change at a fixed potential of 0.4 V for 1 hour. The test results are shown in Table 1.

[0102] Table 1

[0103]

[0104] As shown in Table 1, the catalytic performance and stability of the catalysts prepared in Examples 1 to 5 are all higher than those of the comparative example. Comparative Example 1 omitted cysteine, and its catalytic performance and stability were lower than those of Example 1, indicating that the thiol group of cysteine ​​can act as a Ti... 4+ The anchoring points allow tetrabutyl titanate to grow around the TiO2 particles during in-situ condensation, resulting in uniform dispersion of TiO2 and preventing its aggregation. This forms a stable conductive network, significantly reducing charge transport resistance and thus improving the kinetic rate of the catalytic reaction. Furthermore, cysteine ​​enables sulfur doping, providing anchoring for Pt particle loading while also enhancing the electrocatalytic performance of TiO2.

[0105] Comparative Example 2 omitted cysteine ​​and chitosan, and its stability was lower than that of Example 1, indicating that the supports obtained in this invention have a synergistic effect in promoting electrocatalytic performance.

[0106] The addition of titanium source in Comparative Example 3 was too small, and the addition of titanium source in Comparative Example 4 was too large. Their performance was lower than that of Example 1 and Example 5, respectively. This shows that the present invention precisely controls the amount of titanium source and obtains the catalyst with the best catalytic effect. If the titanium source is too large, TiO2 will be over-coated on the CS / Cys-MWCNT surface, blocking the conductive network. If the titanium source is too small, the TiO2 loading will be insufficient and it will not be able to exert its corrosion resistance and anchoring assistance effect.

[0107] The above-disclosed embodiments are merely a few specific examples of the present invention. However, the embodiments of the present invention are not limited thereto, and any variations that can be conceived by those skilled in the art should fall within the protection scope of the present invention.

Claims

1. A method for preparing a negative electrode catalyst for a fuel cell, characterized in that, Includes the following steps: S1. Mix glacial acetic acid and anhydrous ethanol, add tetrabutyl titanate dropwise to form solution A; mix anhydrous ethanol and deionized water, add CS / Cys-MWCNT, sonicate to form solution B; add solution A dropwise to solution B, then let stand, age, dry, heat treat under nitrogen atmosphere, cool to obtain TiO2 / CS / Cys-MWCNT; S2. Add 0.05 mol / L H2PtCl6 to ethylene glycol, add TiO2 / CS / Cys-MWCNT obtained in step S1, sonicate for 1-2 h, heat to react, centrifuge, wash, and dry to obtain the negative electrode catalyst; In step S1, the volume ratio of glacial acetic acid, anhydrous ethanol, and tetrabutyl titanate is 6:15:(5-6). The ratio of anhydrous ethanol, deionized water, and CS / Cys-MWCNT used was 7 mL: 10 mL: 0.3 g. The volume ratio of solution A to solution B is 1:1; The preparation method of the CS / Cys-MWCNT is as follows: S11. Add MWCNT to the mixed acid solution, sonicate for 1-2 hours, and then stir at 55°C for 6-7 hours to obtain MWCNT-COOH; S12. Disperse MWCNT-COOH and L-cysteine ​​in deionized water, then add EDC·HCl and NHS, stir at room temperature for 22-24 h, centrifuge, wash, and dry to obtain Cys-MWCNT. S13. Dissolve chitosan in 2% dilute acetic acid solution and stir for 12 hours to obtain CS solution; disperse Cys-MWCNT in deionized water, sonicate for 30 minutes and slowly add it to CS solution. Under reflux conditions, magnetically stir the mixture at 98°C for 6 hours. After cooling the mixture to room temperature, adjust the pH of the solution to 10 with dilute ammonia, add glutaraldehyde, magnetically stir at 60°C for 3 hours, wash, freeze dry to obtain CS / Cys-MWCNT.

2. The method for preparing the fuel cell negative electrode catalyst according to claim 1, characterized in that, In step S1, the heat treatment under a nitrogen atmosphere is carried out at a temperature of 600–700°C for 2–3 hours.

3. The method for preparing the fuel cell negative electrode catalyst according to claim 1, characterized in that, In step S2, the ratio of H2PtCl6, ethylene glycol, and TiO2 / CS / Cys-MWCNT is 1.5mL:100-120mL:1-1.4g; The heating reaction is carried out at a temperature of 150–170°C for 3–4 hours.

4. The method for preparing the fuel cell negative electrode catalyst according to claim 1, characterized in that, In step S11, the ratio of MWCNT to mixed acid solution is 2g:30-40mL; the mixed acid solution is composed of concentrated sulfuric acid and concentrated nitric acid in a volume ratio of 3:

1.

5. The method for preparing the fuel cell negative electrode catalyst according to claim 1, characterized in that, In step S12, the ratio of MWCNT-COOH, L-cysteine, deionized water, EDC·HCl, and NHS is 0.2g:0.2-0.25g:50-60mL:1.2g:0.6g.

6. The method for preparing the fuel cell negative electrode catalyst according to claim 1, characterized in that, In step S13, the ratio of chitosan, dilute acetic acid solution, Cys-MWCNT, deionized water, and glutaraldehyde is 0.8-1g: 200mL: 0.2g: 20mL: 1-1.2mL.

7. A negative electrode catalyst for a fuel cell, characterized in that, It is prepared by the preparation method according to any one of claims 1-6.

8. The application of the fuel cell negative electrode catalyst according to claim 7 in a direct methanol fuel cell.

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