Method for preparing methanol fuel cell anode catalyst by doping modified multi-walled carbon nanotube carrier

Abstract

The invention discloses a method for preparing a methanol fuel cell anode catalyst by doping a modified multi-walled carbon nanotube carrier. The method comprises the following steps: 1) acidizing an unmodified multi-walled carbon nanotube; (2) preparing the cerium oxide doped modified multi-walled carbon nanotube; and 3) preparing the cerium oxide doped modified multi-walled carbon nanotube carrier loaded PtFe bimetallic alloy catalyst. According to the method disclosed by the invention, the MWCNTs are induced by doping CeO2 to generate more oxygen vacancy defects, so that anchoring of more active sites of the PtFe alloy is facilitated, and MOR is promoted to improve the activity of the catalyst; the stable Ce < 4 + > can deform the surface structure of Pt, so that the binding bond energy of COads and-OH is stronger, and an anti-poisoning effect is achieved; the introduced Fe element and Pt have metal electronegativity difference, so that the adsorption bond energy of formic acid, formaldehyde and carbon monoxide intermediates generated by gradual dehydrogenation of Pt and methanol can be weakened, and the anti-toxicity effect is achieved; and the PtFe alloy and the CeO2 / MWCNTs are in synergistic interaction, so that the stability of the catalyst can be enhanced.

Description

Technical Field

[0001] The present invention relates to a method for preparing a methanol fuel cell anode catalyst, in particular to a method for preparing a methanol fuel cell anode catalyst by doping and modifying a multi-walled carbon nanotube carrier. Background Art

[0002] Direct methanol fuel cells (DMFCs) are devices that convert chemical energy directly into electrical energy. Their core principle is to convert the chemical energy of methanol into electricity through an electrochemical reaction. However, the large-scale commercialization of DMFCs is limited by issues such as slow anode reaction kinetics, the cost of the precious metal platinum (Pt), and poor stability over long periods of operation.

[0003] To date, platinum (Pt) has been recognized as the most active metal-based electrocatalyst for the methanol oxidation reaction (MOR) due to its moderate surface adsorption energy and excellent catalytic dissociation performance for methanol molecules, and has therefore been widely used in DMFCs. However, Pt-based catalysts still have several inherent drawbacks: first, Pt resources are scarce and expensive, which seriously restricts their large-scale commercial application; second, the MOR reaction kinetics are slow, and even the most optimized Pt catalyst still requires a high activation overpotential; third, the formic acid-like intermediates (HCOOH) produced during the reaction are ads ), carbon monoxide intermediate (CO ads ) will strongly adsorb to the Pt active sites, causing catalyst poisoning and deactivation. In order to improve the dispersion, utilization efficiency and chemical stability of metal particles in the catalyst, carbon materials are usually used as catalyst supports.

[0004] Currently, commonly used carbon materials as catalyst supports for direct methanol fuel cells include carbon black, mesoporous carbon, graphene and carbon nanotubes.

[0005] Carbon black is a common carrier for methanol fuel cell anode catalysts. Its high surface area and electrical conductivity facilitate the dispersion of precious metals and maintain stability in acidic environments. However, it has significant drawbacks: surface impurities can poison active sites; its microporous structure hinders mass transfer, reducing catalytic efficiency; and its structural instability at high temperatures can easily lead to catalyst deactivation.

[0006] Mesoporous carbon, as a new catalyst carrier, offers significant advantages over traditional carbon black: its ordered mesoporous structure provides a larger specific surface area and uniform pore size, enhancing mass transfer efficiency and optimizing catalyst dispersion. It also exhibits excellent thermal stability and corrosion resistance, ensuring long-term operational stability. However, its complex preparation process and high cost have limited its large-scale application.

[0007] Graphene, a novel catalyst support with a high surface area and excellent electrical conductivity, can enhance the dispersibility and activity of precious metal catalysts. Its outstanding thermal stability and corrosion resistance ensure the long-term stability of the catalytic system, and its tunable performance parameters hold great potential for application. However, graphene nanosheets are prone to agglomeration due to π-π interactions, which affects catalyst durability. Furthermore, the high cost of mass production limits their commercial application.

[0008] Carbon nanotubes are made of graphene-like curls. The interlayer defects in their multi-walled structure are conducive to anchoring active sites, improving the dispersion and activity of precious metal catalysts, thereby enhancing the performance of methanol fuel cells. In addition, the high specific surface area and excellent conductivity of carbon nanotubes can promote the reaction of methanol molecules and improve catalytic efficiency. Their good thermochemical stability and corrosion resistance also ensure the long-term stability of the catalyst. However, due to their strong hydrophobicity, pristine carbon nanotubes lack effective metal anchoring sites on the surface, which easily triggers the aggregation of metal nanoparticles, thereby affecting catalytic activity. Therefore, in practical applications, it is usually necessary to pre-treat the surface of carbon nanotubes to enhance their loading performance.

[0009] CN100462421 C discloses an invention patent entitled "Method for Preparing a Direct Methanol Fuel Cell Anode Catalyst." The patent relates to a method for preparing a catalyst using a polyaniline / multi-walled carbon nanotube composite material as a carrier and platinum deposited on its surface. The method involves adding a sulfuric acid solution containing a dispersant to a container, followed by multi-walled carbon nanotubes. After ultrasonic oscillation, aniline and ammonium persulfate solution are added. After reaction, the reaction is washed and dried. Polyaniline / multi-walled carbon nanotube composite carrier powder is added to a container, an acetic acid buffer solution containing an additive is added, and ultrasonic oscillation is performed to obtain a dispersion. A chloroplatinic acid solution is added to the dispersion and continued to oscillate. An excess of sodium borohydride solution is added dropwise at elevated temperature, followed by reaction, filtering, washing until free of chloride ions, and drying the product.

[0010] CN102751513A discloses an invention patent application entitled “A Methanol Fuel Cell Anode Material Catalyst and Preparation Method”. The methanol fuel cell anode material catalyst of the present invention is a phosphomolybdic acid platinum iridium carbon nanotube composite material. The raw materials for preparing the catalyst of the present invention are iridium chloride, platinum chloride, multi-walled carbon nanotubes, phosphomolybdic acid, ethylene glycol and water. The preparation method of the catalyst of the present invention comprises the following steps: (1) preparing purified multi-walled carbon nanotubes; (2) loading phosphomolybdic acid on the multi-walled carbon nanotubes by ultrasonic method; (3) adding iridium and platinum chlorides and ethylene glycol to (2) and then performing ultrasonic dispersion treatment; (4) passing nitrogen through the solution in (3), stirring and refluxing at high temperature under nitrogen protection to obtain a precipitate, and the precipitate is centrifuged, washed and vacuum dried to obtain the catalyst of the present invention.

[0011] The above documents all claim that the preparation of methanol fuel cell anode catalysts can be achieved. However, they all suffer from the problem of low-temperature reduction to form PtIr metal clusters, which results in a lag in the methanol oxidation reaction. Summary of the Invention

[0012] The purpose of the present invention is to provide a method for preparing anode catalysts for methanol fuel cells using doped modified multi-walled carbon nanotube carriers, which is beneficial to improving catalyst activity, resisting poisoning, and enhancing catalyst stability.

[0013] The objective of the present invention is achieved through such a technical solution, a method for preparing a methanol fuel cell anode catalyst by doping and modifying multi-walled carbon nanotube carriers, the method comprising the following steps: 1) acidifying unmodified multi-walled carbon nanotubes; 2) preparing cerium oxide doped modified multi-walled carbon nanotubes; 3) preparing a PtFe bimetallic alloy catalyst loaded on the cerium oxide doped modified multi-walled carbon nanotube carrier.

[0014] Wherein, in step 1), the acidification treatment includes purification treatment and functionalization treatment;

[0015] Purification treatment:

[0016] Weigh 1g~3g of carbon nanotubes, grind them, and place them in a rotary evaporator collection bottle. Add 160mL~500mL of concentrated sulfuric acid and react under heating reflux conditions for 4h~5h. After the system cools to room temperature, dilute with ultrapure water, filter and wash several times, dry, grind and set aside.

[0017] Functional processing:

[0018] Weigh 0.1g~0.3g of purified carbon nanotubes and place them in a polytetrafluoroethylene reaction cup, add a mixed solution of V(H2O2):V(H2SO4)=1:4, and continue magnetic stirring for 3h~4h after ultrasonic treatment for 0.5h~1h; after the reaction is completed, dilute with ultrapure water, filter and wash multiple times, dry, and grind to obtain functionalized carbon nanotubes.

[0019] Further description, in the step 2), 0.1g to 0.3g of acidified multi-walled carbon nanotubes are added to 40mL to 50mL of cyclohexane solution, cerium oxide is added and stirred for 24h to 26h, moved to an oven for drying, and then scraped in a porcelain boat under N2 component conditions at 800℃ to 900℃ for calcination, and after cooling, a sample is taken and ground.

[0020] Further description: In step 3), 0.1g to 0.3g of the doped and modified cerium oxide multi-walled carbon nanotube powder is dissolved in an ethanol solution and ultrasonically stirred for 30min to 40min; chloroplatinic acid and ferric chloride are then added and stirred for 24h to 28h, and 2mL to 4mL of hydrogen chloride solution and 3mL to 6mL of tetraethyl orthosilicate are added in sequence to form a Pt 2+ Fe 3+ @CeO2 / MWCNTs suspension was magnetically stirred for 0.5h~1h to fully mix it;

[0021] The mixed solution was then transferred to a Petri dish and dried in an oven at a constant temperature of 60°C to 70°C for 8h to 10h;

[0022] In a mixed atmosphere of 5% H2 and 95% N2, the precursor was heated to 600°C to 700°C at a heating rate of 5°C / min and maintained at that temperature for 2h to 4h to obtain a cerium oxide-doped modified multi-walled carbon nanotube-supported PtFe bimetallic alloy catalyst intermediate;

[0023] The silicon dioxide coating layer was removed by etching with 30 wt % hydrofluoric acid; the product was washed with deionized water and ethanol in sequence; and vacuum dried at 80° C. to 90° C. for 12 h to 14 h to obtain the final product.

[0024] Due to the adoption of the above technical solution, the present invention has the advantages of being green and clean, having high energy efficiency, low noise, rapid fuel replenishment, easy access to raw materials, long-term reliability and low cost. The method of the present invention utilizes CeO2 doping to induce MWCNTs to produce more oxygen vacancy defects, which is beneficial to the anchoring of more active sites of PtFe alloy, and is beneficial to promoting MOR and improving the activity of the catalyst; stable Ce 4+ It can deform the Pt surface structure and make CO ads The bonding energy with -OH is stronger, which has an anti-poisoning effect; secondly, the introduction of Fe element and the difference in metal electronegativity between Pt and Pt can weaken the adsorption bond energy of formic acid, formaldehyde, and carbon monoxide intermediates produced by the gradual dehydrogenation of Pt and methanol, which has an anti-poisoning effect; secondly, it can reduce the amount of Pt used and reduce costs; the synergistic interaction between PtFe alloy and CeO2 / MWCNTs can enhance the stability of the catalyst. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The accompanying drawings of the present invention are as follows:

[0026] Figure 1 It is a schematic diagram of the process of the present invention. DETAILED DESCRIPTION

[0027] The specific embodiments of the present invention are further described in detail below with reference to the accompanying drawings, but the present invention is not limited to these embodiments. Any improvement or substitution based on the basic spirit of the present embodiment still falls within the scope of protection required by the claims of the present invention.

[0028] Example 1, as Figure 1 As shown, a method for preparing a methanol fuel cell anode catalyst by doping and modifying multi-walled carbon nanotube carriers, the method comprising the following steps: 1) acidifying unmodified multi-walled carbon nanotubes; 2) preparing cerium oxide doped and modified multi-walled carbon nanotubes; 3) preparing a PtFe bimetallic alloy catalyst loaded on the cerium oxide doped and modified multi-walled carbon nanotube carrier.

[0029] Wherein, in the step 1), the acidification treatment includes purification treatment and functionalization treatment;

[0030] Purification treatment:

[0031] Weigh 1g~3g of carbon nanotubes, grind them, and place them in a rotary evaporator collection bottle. Add 160mL~500mL of concentrated sulfuric acid and react under heating reflux conditions for 4h~5h. After the system cools to room temperature, dilute with ultrapure water, filter and wash several times, dry, grind and set aside.

[0032] Functional processing:

[0033] Weigh 0.1g~0.3g of purified carbon nanotubes and place them in a polytetrafluoroethylene reaction cup, add a mixed solution of V(H2O2):V(H2SO4)=1:4, and continue magnetic stirring for 3h~4h after ultrasonic treatment for 0.5h~1h; after the reaction is completed, dilute with ultrapure water, filter and wash multiple times, dry, and grind to obtain functionalized carbon nanotubes.

[0034] In the step 2), 0.1 g to 0.3 g of acidified multi-walled carbon nanotubes are added to 40 mL to 50 mL of cyclohexane solution, and cerium oxide is added and stirred for 24 h to 26 h. The mixture is then moved to an oven for drying, and then scraped into a porcelain boat and calcined at 800° C. to 900° C. under N2 component conditions. After cooling, the sample is ground into powder.

[0035] After the multi-walled carbon nanotubes are pretreated, cerium oxide is directly added to cyclohexane and stirred at low temperature, and then calcined at high temperature to form cerium oxide multi-walled carbon nanotubes, thereby realizing cerium oxide-doped multi-walled carbon nanotubes.

[0036] Wherein, in the step 3), 0.1g to 0.3g of the doped and modified cerium oxide multi-walled carbon nanotube powder is dissolved in an ethanol solution and ultrasonically stirred for 30min to 40min; chloroplatinic acid and ferric chloride are then added and stirred for 24h to 28h, and 2mL to 4mL of hydrogen chloride solution and 3mL to 6mL of tetraethyl orthosilicate are added in sequence to form Pt2+ Fe 3+ @CeO2 / MWCNTs suspension was magnetically stirred for 0.5h~1h to fully mix it;

[0037] The mixed solution was then transferred to a Petri dish and dried in an oven at a constant temperature of 60°C to 70°C for 8h to 10h;

[0038] In a mixed atmosphere of 5% H2 and 95% N2, the precursor was heated to 600°C to 700°C at a heating rate of 5°C / min and maintained at that temperature for 2h to 4h to obtain a cerium oxide-doped modified multi-walled carbon nanotube-supported PtFe bimetallic alloy catalyst intermediate;

[0039] The silicon dioxide coating layer was removed by etching with 30 wt % hydrofluoric acid; the product was washed with deionized water and ethanol in sequence; and vacuum dried at 80° C. to 90° C. for 12 h to 14 h to obtain the final product.

[0040] This method combines the oxygen vacancy effect and uses Ce doping to induce MWCNTs to produce more oxygen vacancy defects, providing abundant anchoring sites for Pt active sites and significantly improving Pt dispersion. 4+ The electron interaction causes the Pt surface lattice distortion, which enhances the CO ads The adsorption energy of the surface -OH groups is increased, thereby significantly improving the catalyst's resistance to CO poisoning. At the same time, the synergistic effect between the PtFe alloy and the CeO2 / MWCNTs support enhances the stability of the catalyst.

Claims

1. A method for preparing a methanol fuel cell anode catalyst by doping and modifying multi-walled carbon nanotube carriers, characterized in that: The method comprises the following steps: 1) acid-treating unmodified multi-walled carbon nanotubes; 2) preparing cerium oxide-doped modified multi-walled carbon nanotubes; and 3) preparing a PtFe bimetallic alloy catalyst supported on a cerium oxide-doped modified multi-walled carbon nanotube carrier.

2. The method for preparing anode catalyst of methanol fuel cell by using doped modified multi-walled carbon nanotube carrier as claimed in claim 1, characterized in that: In the step 1), the acidification treatment includes purification treatment and functionalization treatment; Purification treatment: Weigh 1g~3g of carbon nanotubes, grind them, and place them in a rotary evaporator collection bottle. Add 160mL~500mL of concentrated sulfuric acid and react under heating reflux conditions for 4h~5h. After the system cools to room temperature, dilute with ultrapure water, filter and wash several times, dry, grind and set aside. Functional processing: Weigh 0.1g~0.3g of purified carbon nanotubes and place them in a polytetrafluoroethylene reaction cup, add a mixed solution of V(H2O2):V(H2SO4)=1:4, and continue magnetic stirring for 3h~4h after ultrasonic treatment for 0.5h~1h; after the reaction is completed, dilute with ultrapure water, filter and wash multiple times, dry, and grind to obtain functionalized carbon nanotubes.

3. The method for preparing anode catalyst of methanol fuel cell by using doped modified multi-walled carbon nanotube carrier as claimed in claim 2, characterized in that: In the step 2), 0.1 g to 0.3 g of acidified multi-walled carbon nanotubes are added to 40 mL to 50 mL of cyclohexane solution, and cerium oxide is added and stirred for 24 h to 26 h. The mixture is then moved to an oven for drying, and then scraped and calcined at 800° C. to 900° C. under N2 component conditions in a porcelain boat. After cooling, a sample is taken and ground.

4. The method for preparing anode catalyst of methanol fuel cell by using doped modified multi-walled carbon nanotube carrier as claimed in claim 3, characterized in that: In the step 3), Take 0.1g~0.3g of doped and modified cerium oxide multi-walled carbon nanotube powder and dissolve it in ethanol solution, ultrasonically stir for 30min~40min; then add chloroplatinic acid and ferric chloride and stir for 24h~28h, then add 2mL~4mL hydrogen chloride solution and 3ml~6ml tetraethyl orthosilicate in sequence to form Pt 2+ Fe 3+ @CeO2 / MWCNTs suspension was magnetically stirred for 0.5h~1h to fully mix it; The mixed solution was then transferred to a Petri dish and dried in an oven at a constant temperature of 60°C to 70°C for 8h to 10h; In a mixed atmosphere of 5% H2 and 95% N2, the precursor was heated to 600°C to 700°C at a heating rate of 5°C / min and maintained at that temperature for 2h to 4h to obtain a cerium oxide-doped modified multi-walled carbon nanotube-supported PtFe bimetallic alloy catalyst intermediate; The silicon dioxide coating layer was removed by etching with 30 wt % hydrofluoric acid; the product was washed with deionized water and ethanol in sequence; and vacuum dried at 80° C. to 90° C. for 12 h to 14 h to obtain the final product.

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