Preparation and application of two-dimensional layered ammonia oxidation catalyst based on MXene

Abstract

This invention discloses a two-dimensional layered ammonia oxidation catalyst based on MXene, its preparation method, and its application in low-temperature ammonia fuel cells. The catalyst comprises an active component and a support. The active component is one or two of the transition metals Pt, Ir, and Pd, and the support is accordion-shaped MXenes. The catalyst support prepared by this invention has a large specific surface area, in which the transition metal nanoparticles are uniformly dispersed and have strong interactions with the MXenes, which can significantly improve its ammonia electrocatalytic oxidation activity, showing good application prospects in ammonia fuel cells.

Description

Technical Field

[0001] This invention belongs to the field of ammonia oxidation catalyst and ammonia fuel cell technology, specifically relating to a two-dimensional layered ammonia oxidation catalyst based on MXene, its preparation and its application in low-temperature ammonia fuel cells. Background Technology

[0002] Hydrogen energy, due to its high energy density, high efficiency, cleanliness, and zero carbon emissions, is an ideal energy carrier for generating electricity from fuel cells or combustion turbines and is considered the most promising clean energy source. However, hydrogen energy faces numerous challenges in transportation, storage, and supply networks. Therefore, achieving the safe storage and utilization of hydrogen energy is a breakthrough for its development. This problem can be effectively solved by using easily liquefied hydrogen-containing fuels. Among them, ammonia, as a carbon-free hydrogen-rich energy carrier, has a high hydrogen content (17.7 wt.%) and is easily liquefied at room temperature, making it an ideal hydrogen storage carrier. Furthermore, ammonia can be directly used as fuel in alkaline membrane fuel cells, where electrocatalytic oxidation of ammonia occurs on the anode side, and a reduction reaction occurs on the cathode side, producing OH-. - The ammonia is transferred to the anode side through an alkaline membrane and participates in the ammonia catalytic reaction to produce water and nitrogen. At the same time, the lost electrons flow through the external circuit via wires, thereby converting the chemical energy of ammonia into electrical energy.

[0003] Cathode half-reaction: O₂ + 2 H₂O + 4e⁻ — → 4 OH — E 0 = +0.401 V / SHE

[0004] Anodic half-reaction: 2 NH3 + 6 OH- — → N2 + 6 H2O + 6 e — , E 0 = –0.77 V / SHE

[0005] Overall battery reaction: 4 NH3 + 3 O2 → 2 N2 + 6 H2O, E 0 = 1.171 V

[0006] This is one of the effective ways to convert and utilize ammonia energy. However, the electrocatalytic oxidation reaction of ammonia on the anode side suffers from slow kinetics and easy catalyst deactivation, thus requiring the design and preparation of highly efficient electrocatalysts.

[0007] Currently, among numerous ammonia oxidation electrocatalysts, metallic Pt is considered the best active metal for AOR (ammonia oxidation). Carbon materials, due to their excellent conductivity and stability, are one of the most important catalyst supports for Pt. However, commonly used carbon supports have a relatively inert surface chemical environment. Because of insufficient bonding sites on their surface, they are not easily anchored to the active metal, resulting in poor dispersion of metal nanoparticles. They serve only as mechanical supports for the active metal and are prone to agglomeration during the reaction, leading to irreversible reduction in catalyst activity. Summary of the Invention

[0008] This invention provides a two-dimensional layered ammonia oxidation catalyst based on MXene and its preparation method. The catalyst uses modified accordion-shaped MXenes as a support and is prepared by loading one or two of the active metals Pt, Ir, and Pd. The abundant functional groups on the surface of the MXenes in this catalyst optimize the electronic structure of the metal atoms, leading to strong interactions between the carbon support and the active metal, thus exhibiting high activity in the electrocatalytic oxidation of ammonia. Simultaneously, the metal atoms are more stably loaded on the support, reducing metal particle aggregation and increasing the catalyst's stability.

[0009] To achieve the above objectives, the present invention adopts the following technical solution:

[0010] A two-dimensional layered ammonia oxidation catalyst based on MXene includes an active component and a support, wherein the active component is one or two of the transition metals Pt, Ir, and Pd, and the support is accordion-shaped MXenes.

[0011] Furthermore, the MXenes specifically refer to Mo2CT. x Nb2CT x Mo3C2T x Ti3C2T x Ti2CT x 、(W 2 / 3 Y 1 / 3 )2CT x Mo2Ti2CT x (Mo) 2 / 3 Sc 1 / 3 )2CT x Any one of them, where T x Its surface functional groups are -OH, -F, and -OH.

[0012] Furthermore, the content of the active component in the two-dimensional layered ammonia oxidation catalyst is 1.0-60.0 wt.% by mass percentage.

[0013] The preparation method of the MXene-based two-dimensional layered ammonia oxidation catalyst includes the following steps:

[0014] (1) Using MAX as a precursor, in-situ HF etching was performed by adding fluoride and acid;

[0015] (2) The etching product obtained in step (1) is centrifuged at low and medium speed with deionized water until the solution is turbid after centrifugation and the pH value of the centrifuged liquid reaches above 6. The precipitate is then ultrasonically dispersed in the solvent, filtered, rinsed with deionized water, and vacuum dried to obtain accordion-shaped MXenes.

[0016] (3) At room temperature, the accordion-shaped MXenes obtained in step (2) were ultrasonically dispersed in a mixture of isopropanol and deionized water. Then, a transition metal precursor was added and stirred until homogeneous. The mixture was then reduced with NaBH4 alkaline solution. After filtration and vacuum drying, the transition metal catalyst supported on MXene was obtained.

[0017] Further, in step 1), MAX is Mo2Ga2C, Mo3AlC2, Mo2TiAlC2, Mo2TiAlC3, (W 2 / 3 Y 1 / 3 )2AlC、(Mo 2 / 3 Sc 1 / 3 Any one of )2AlC, Ti2AlC, and Ti3AlC2.

[0018] Further, the fluoride mentioned in step 1) is one or more of NH4F, LiF, and NaF.

[0019] Further, the acid mentioned in step 1) is one or more of concentrated nitric acid, concentrated hydrochloric acid, and concentrated sulfuric acid.

[0020] Furthermore, the mass ratio of MAX to fluoride and acid used in step 1) is 1:1.6:30.

[0021] Furthermore, the etching temperature in step 1) is 120-200 °C, and the time is 12-48 h.

[0022] Furthermore, in step 2), the low-to-medium speed centrifugation speed is 3000~5500 r / s, the time is 1 min each time, and the centrifugation is repeated 10-20 times.

[0023] Further, the solvent mentioned in step 2) is one of deionized water, DMSO, TBAOH and TMAOH.

[0024] Furthermore, in step 2), the power of ultrasonic dispersion is 100~200 W, and the time is 0.5~2 h.

[0025] Further, in step 3), the volume ratio of isopropanol to deionized water in the mixture is 1:1.

[0026] Further, the transition metal precursor mentioned in step 3) is one or more of chloroplatinic acid, chloroiridic acid, and palladium chloride.

[0027] Furthermore, in step 3), the molar ratio of NaBH4 in the NaBH4 alkaline solution to the transition metal in the transition metal precursor is 20:1.

[0028] Further, in step 3), the concentration of NaBH4 in the NaBH4 alkaline solution is 0.05 mol / L, the concentration of the alkali is 0.025 mol / L, and the alkali used is NaOH.

[0029] Further, in step 3), the reduction involves first adding the NaBH4 alkaline solution dropwise at a rate of 50 μL / min for 1 h, and then continuing to add it dropwise at a rate of 500 μL / min.

[0030] Furthermore, the vacuum drying temperature described in steps 2) and 3) is 60~90 ℃, and the time is 12 h.

[0031] The above-mentioned MXene-based two-dimensional layered ammonia oxidation catalyst can be used to prepare anodes for low-temperature ammonia fuel cells.

[0032] The significant advantages of this invention are:

[0033] 1. This invention utilizes a mechanical peeling method, employing multiple low-speed centrifugations and ultrasonic disruption to obtain multilayer MXene.

[0034] 2. In this invention, MXene is first synthesized by etching MAX in situ with HF, and then the active component is reduced by NaBH4 reduction method. This preparation method is simple, less harmful, and easy to operate. Moreover, the particle growth rate can be controlled by controlling the drop rate of the reducing agent, which is conducive to the formation of small-sized active component particles.

[0035] 3. The accordion-shaped MXene prepared by this invention has a large specific surface area, and the surface functional groups and metal support can anchor the active metal particles, making the active component particles small in size and uniformly dispersed, and with a high metal loading. This increases the contact area between the catalyst active center and the reactants, and also enhances the interaction between the carbon support and the active metal.

[0036] 4. The two-dimensional layered catalyst prepared by this invention can be used for the anode reaction of low-temperature ammonia oxidation and low-temperature direct ammonia fuel cells, and its activity is significantly better than that of commercial catalysts. Attached Figure Description

[0037] Figure 1 Mo2CT obtained by centrifuging once and 15 times during the etching process. x SEM image.

[0038] Figure 2 To illustrate the different dropping rates used in the preparation of Mo2CT using NaBH4 alkaline solution during the preparation process. x SEM images (left: always added at a rate of 500 μl / min, right: first added at a rate of 50 μl / min for 1 hour, then continued to be added at a rate of 500 μl / min).

[0039] Figure 3 Pt / Mo2CT prepared for Example 1 x SEM image of the catalyst.

[0040] Figure 4 Mo2CT x Carrier and Pt / Mo2CT prepared in Example 1 x XRD pattern of the catalyst.

[0041] Figure 5 Mo2CT x Carrier, Mo2C carrier and Pt / Mo2CT prepared in Example 1 x N2 adsorption-desorption curves of the catalyst.

[0042] Figure 6 XRD patterns of the Pt / XC-72 catalyst prepared for XC-72 support and Comparative Example 1.

[0043] Figure 7 XRD patterns of the Pt / Mo2C catalyst prepared with Mo2C support and Comparative Example 2.

[0044] Figure 8 Pt / Mo2CT prepared for Example 1 x Cyclic voltammetry curves of the catalyst in argon-saturated ammonia and KOH solutions.

[0045] Figure 9 Pt / Mo2CT prepared in Example 1 x Comparison of the performance of the catalyst and commercial Pt / C in ammonia fuel cells.

[0046] Figure 10 PtPd / Mo2CT prepared for Example 2 x XRD patterns of PtPd / XC-72 and PtPd / Mo2C prepared in Comparative Examples 3 and 4.

[0047] Figure 11 PtPd / Mo2CT prepared for Example 2 x Cyclic voltammetry curves of the catalyst in argon-saturated ammonia and KOH solutions.

[0048] Figure 12 PtIr / Mo2CT prepared for Example 3 x XRD patterns of PtIr / XC-72 and PtIr / Mo2C prepared in Comparative Examples 5 and 6.

[0049] Figure 13 PtIr / Mo2CT prepared for Example 3 x Cyclic voltammetry curves of the catalyst in argon-saturated ammonia and KOH solutions.

[0050] Figure 14 PtIr / Mo2CT prepared for Example 3 x The current density of the cyclic voltammetry curve of the catalyst at 0.5 V vs RHE.

[0051] Figure 15 Pt / Mo2CT prepared in Example 1 x IT stability tests of the catalyst and comparative Pt / Mo2C and Pt / C catalysts. Detailed Implementation

[0052] A method for preparing a two-dimensional layered ammonia oxidation catalyst based on MXene includes the following steps:

[0053] (1) Add fluoride and acid to MAX at a mass ratio of 1:1.6:30 and etch in situ at 120-200 °C for 12-48 h;

[0054] (2) Add the etching product obtained in step (1) to deionized water, centrifuge at 3000~5500 r / s for 1 min, repeat centrifugation 10-20 times until the solution is turbid after centrifugation and the pH value of the centrifuged liquid reaches above 6, then disperse the precipitate in the solvent, sonicate at 100~200 W for 0.5~2 h, filter, rinse with deionized water, and vacuum dry at 60~90 ℃ for 12 h to obtain accordion-shaped MXenes;

[0055] (3) At room temperature, the accordion-shaped MXenes obtained in step (2) were ultrasonically dispersed in a mixture of isopropanol and deionized water in a volume ratio of 1:1. Then, the transition metal precursor was added and stirred until homogeneous. The NaBH4 alkaline solution was first added dropwise at a rate of 50 μL / min for 1 h at a molar ratio of NaBH4 to transition metal of 20:1, and then added dropwise at a rate of 500 μL / min for reduction. After filtration, the catalyst was vacuum dried at 60~90 ℃ for 12 h to obtain the transition metal catalyst supported on MXene, wherein the content of transition metal was 1.0-60.0 wt.%.

[0056] Wherein, MAX in step 1) is Mo2Ga2C, Mo3AlC2, Mo2TiAlC2, Mo2TiAlC3, (W 2 / 3 Y 1 / 3 )2AlC、(Mo 2 / 3 Sc 1 / 3 The fluoride is any one of 2AlC, Ti2AlC, and Ti3AlC2. The fluoride is one or more of NH4F, LiF, and NaF. The acid is one or more of concentrated nitric acid, concentrated hydrochloric acid, and concentrated sulfuric acid.

[0057] The solvent mentioned in step 2) is one of deionized water, DMSO, TBAOH and TMAOH.

[0058] The transition metal precursor mentioned in step 3) is one or more of chloroplatinic acid, chloroiridiumic acid, and palladium chloride. The concentration of NaBH4 in the NaBH4 alkaline solution is 0.05 mol / L, the concentration of the alkali is 0.025 mol / L, and the alkali used is NaOH.

[0059] To make the content of this invention easier to understand, the technical solution of this invention will be further described below with reference to specific embodiments, but this invention is not limited thereto.

[0060] Preparation of chloroplatinic acid solution: Weigh 1 g of H2PtCl6∙6H2O into a 100 mL brown volumetric flask, add deionized water to make up to volume, and prepare a chloroplatinic acid solution with a concentration of 19.3 mmol / L.

[0061] Preparation of palladium chloride solution: Weigh 1 g of 60% PdCl2 into a 100 mL brown volumetric flask, add deionized water to make up to volume, and prepare a chloroiridium acid solution with a concentration of 33.8 mmol / L.

[0062] Preparation of chloroiridium acid solution: Weigh 1 g H2IrCl6∙6H2O into a 100 mL brown volumetric flask, add deionized water to make up to volume, and prepare a chloroiridium acid solution with a concentration of 19 mmol / L.

[0063] To prepare a NaBH4 alkaline solution: Weigh 40 mg of NaBH4 and 20 mg of NaOH and dissolve them in 20 ml of deionized water.

[0064] Preparation of XC-72 support: 150 mL of concentrated nitric acid was poured into a 500 mL round-bottom flask, 3 g of XC-72 was added, and the flask was heated to 80 °C in an oil bath and stirred vigorously for 12 h. The sample was washed multiple times by centrifugation with ethanol and deionized water, and then dried in a vacuum oven at 60 °C for 12 h to obtain a black solid. The solid was then placed in a tube furnace and reduced at 400 °C for 2-4 h in a hydrogen atmosphere. After that, the solid was cooled to room temperature and dried in a vacuum oven at 60 °C for 12 h to obtain the XC-72 support.

[0065] Preparation of MXene (Mo2CT) x Carrier: Weigh 2 g Mo2Ga2C and add it to the liner of a 200 ml reactor. Add 50 ml concentrated HCl and 3.2 g LiF. Place the reactor liner in a 180 ℃ environment for hydrothermal treatment for 48 h. Then, add the etching product to deionized water and centrifuge at 3500 r / min for 1 min. Repeat the centrifugation and washing 10 times until the sample solution is still turbid after centrifugation, the sample shows swelling, and the pH value of the centrifuged liquid reaches above 6. Then disperse the precipitate in 100 ml of deionized water and sonicate in an ice-water bath for 2 h (ultrasonic power of 100-300W). Filter, wash with 500 ml of 0.01 M NaOH solution, wash with 1-2 L of deionized water, and then dry in a 60 ℃ vacuum oven for 12 h to obtain accordion-shaped Mo2CT. x Carrier.

[0066] Example 110 wt.% Pt / Mo2CT x Catalyst Synthesis:

[0067] Weigh out 90 mg Mo2CT x The support was placed in a 200 mL beaker, and 30 mL of isopropanol and 30 mL of deionized water were added. The mixture was sonicated for 30 min and then vigorously stirred magnetically for 30 min to form a homogeneous dispersion. 2.655 mL of prepared chloroplatinic acid solution was added, and the mixture was stirred for 30 min. Then, under vigorous stirring, 20 mL of prepared NaBH4 alkaline solution was added dropwise over 1 hour at a rate of 50 μl / min using a peristaltic pump, followed by a further addition at a rate of 500 μl / min. After the addition was complete, stirring continued for 2 hours. The mixture was then filtered, washed, and dried in a vacuum oven at 60 °C for 12 h to obtain a 10 wt% Pt-supported MXene active metal Pt catalyst, namely Pt / Mo2CT. x catalyst.

[0068] Synthesis of comparative example 110 wt.% Pt / XC-72 catalyst:

[0069] Weigh 90 mg of XC-72 carrier into a 200 mL beaker, add 30 mL of deionized water and 30 mL of isopropanol, sonicate for 30 min, and then stir vigorously magnetically for 30 min to form a homogeneous dispersion. Add 2.655 mL of prepared chloroplatinic acid solution and stir for 30 min to ensure the metal salt precursor is uniformly impregnated on the carrier surface. Then, under vigorous stirring, use a peristaltic pump to add 20 mL of prepared NaBH4 alkaline solution dropwise at a rate of 50 μl / min for 1 hour, and then dropwise at a rate of 500 μl / min into the beaker. After the addition is complete, continue stirring for 1-3 h. After filtration and washing, dry in a vacuum oven at 60 ℃ for 12 h to obtain Pt / XC-72 with a Pt loading of 10 wt%.

[0070] Synthesis of comparative example 210 wt.% Pt / Mo2C catalyst:

[0071] 90 mg of Mo₂C support was weighed into a 200 mL beaker, and 30 mL of deionized water and 30 mL of isopropanol were added. The mixture was sonicated for 60 min and then vigorously stirred magnetically for 30 min to form a homogeneous dispersion. 2.655 mL of prepared chloroplatinic acid solution was added, and the mixture was stirred for 30 min to ensure the metal salt precursor was uniformly impregnated on the support surface. Then, under vigorous stirring, 20 mL of prepared NaBH₄ alkaline solution was added dropwise over a peristaltic pump at a rate of 50 μl / min for 1 hour, followed by a dropwise addition of 500 μl / min to the beaker. After the addition was complete, stirring was continued for 1–3 h. The mixture was then filtered, washed, and dried in a vacuum oven at 60 °C for 12 h to obtain a Pt / Mo₂C catalyst with a Pt loading of 10 wt%.

[0072] Example 220 wt.% PtPd / Mo2CT x Catalyst Synthesis:

[0073] Weigh out 80 mg Mo2CT xThe support was placed in a 200 mL beaker, and 30 mL of isopropanol and 30 mL of deionized water were added. The mixture was sonicated for 30 min and then vigorously magnetically stirred for 30 min to form a homogeneous dispersion. 3.452 mL of prepared chloroplatinic acid solution and 1.97 mL of prepared palladium chloride solution were added, and the mixture was stirred for 30 min. Then, under vigorous stirring, 40 mL of prepared NaBH4 alkaline solution was added dropwise over 1 hour at a rate of 50 μl / min using a peristaltic pump, followed by a dropwise addition of 500 μl / min to the beaker. After the addition was complete, stirring continued for 2 hours. The mixture was then filtered, washed, and dried in a vacuum oven at 60 °C for 12 h to obtain an MXene-supported active metal Pt and Pd catalyst with a Pt and Pd loading of 10 wt%, namely Pt1Pd1 / Mo2CT. x catalyst.

[0074] Synthesis of comparative example 320 wt.% PtPd / XC-72 catalyst:

[0075] Weigh 80 mg of XC-72 support into a 200 mL beaker, add 30 mL of isopropanol and 30 mL of deionized water, sonicate for 30 min, and then stir vigorously magnetically for 30 min to form a homogeneous dispersion. Add 3.452 mL of prepared chloroplatinic acid solution and 1.97 mL of prepared palladium chloride solution, and stir for 30 min. Then, under vigorous stirring, add 40 mL of prepared NaBH4 alkaline solution dropwise at a rate of 50 μl / min for 1 hour using a peristaltic pump, and then add it dropwise at a rate of 500 μl / min to the beaker. After the addition is complete, continue stirring for 2 hours. After filtration and washing, dry in a vacuum oven at 60 °C for 12 h to obtain an XC-72-supported active metal Pt and Pd catalyst with a Pt and Pd loading of 10 wt%, namely the Pt1Pd1 / XC-72 catalyst.

[0076] Synthesis of comparative example 420 wt.% PtPd / Mo2C catalyst:

[0077] Weigh 80 mg of Mo₂C support into a 200 mL beaker, add 30 mL of isopropanol and 30 mL of deionized water, sonicate for 30 min, and then stir vigorously magnetically for 30 min to form a homogeneous dispersion. Add 3.452 mL of prepared chloroplatinic acid solution and 1.97 mL of prepared palladium chloride solution, and stir for 30 min. Then, under vigorous stirring, add 40 mL of prepared NaBH₄ alkaline solution dropwise at a rate of 50 μl / min for 1 hour using a peristaltic pump, and then add it dropwise at a rate of 500 μl / min to the beaker. After the addition is complete, continue stirring for 2 hours. After filtration and washing, dry in a vacuum oven at 60 °C for 12 h to obtain a Mo₂C-supported active metal Pt and Pd catalyst with a Pt and Pd loading of 10 wt%, namely the Pt₁Pd₁ / Mo₂C catalyst.

[0078] Example 320 wt.% PtIr / Mo2CT x Catalyst Synthesis:

[0079] Weigh out 80 mg Mo2CT x The support was placed in a 200 mL beaker, and 30 mL of isopropanol and 30 mL of deionized water were added. The mixture was sonicated for 30 min and then vigorously magnetically stirred for 30 min to form a homogeneous dispersion. 2.655 mL of prepared chloroplatinic acid solution and 2.665 mL of prepared chloroiridium acid solution were added, and the mixture was stirred for 30 min. Then, under vigorous stirring, 40 mL of prepared NaBH4 alkaline solution was added dropwise over 1 hour at a rate of 50 μl / min using a peristaltic pump, followed by a dropwise addition of 500 μl / min to the beaker. After the addition was complete, stirring was continued for 2 hours. The mixture was then filtered, washed, and dried in a vacuum oven at 60 °C for 12 h to obtain an MXene-supported active metal Pt and Ir catalyst with a Pt and Ir loading of 10 wt%, namely Pt1Ir1 / Mo2CT. x catalyst.

[0080] Synthesis of comparative example 520 wt.% PtIr / XC-72 catalyst:

[0081] Weigh 80 mg of XC-72 support into a 200 mL beaker, add 30 mL of isopropanol and 30 mL of deionized water, sonicate for 30 min, and then stir vigorously magnetically for 30 min to form a homogeneous dispersion. Add 2.655 mL of prepared chloroplatinic acid solution and 2.665 mL of prepared chloroiridium acid solution, and stir for 30 min. Then, under vigorous stirring, add 40 mL of prepared NaBH4 alkaline solution dropwise at a rate of 50 μl / min for 1 hour using a peristaltic pump, and then add it dropwise at a rate of 500 μl / min to the beaker. After the addition is complete, continue stirring for 2 hours. After filtration and washing, dry in a vacuum oven at 60 °C for 12 h to obtain an XC-72-supported active metal Pt and Ir catalyst with a Pt and Ir loading of 10 wt%, i.e., PtIr / XC-72 catalyst.

[0082] Synthesis of comparative 620 wt.% PtIr / Mo2C catalyst:

[0083] Weigh 80 mg of Mo₂C support into a 200 mL beaker, add 30 mL of isopropanol and 30 mL of deionized water, sonicate for 30 min, and then stir vigorously magnetically for 30 min to form a homogeneous dispersion. Add 2.655 mL of prepared chloroplatinic acid solution and 2.665 mL of prepared chloroiridium acid solution, and stir for 30 min. Then, under vigorous stirring, use a peristaltic pump to add 40 mL of prepared NaBH₄ alkaline solution dropwise at a rate of 50 μl / min for 1 hour, and then dropwise at a rate of 500 μl / min to the beaker. After the addition is complete, continue stirring for 2 hours. After filtration and washing, dry in a vacuum oven at 60 °C for 12 h to obtain a Mo₂C-supported active metal Pt and Ir catalyst with a Pt and Ir loading of 10 wt%, i.e., PtIr / Mo₂C catalyst.

[0084] Physical structure characterization test:

[0085] XRD tests were performed on an X'pert Pro powder diffractometer (Panalytical, Netherlands) equipped with an X'Celerator detector. Cu Kα radiation (λ = 0.154 06 nm) was used, with an operating voltage of 45 kV and an operating current of 40 mA. The test range was 2θ = 5–100 °.

[0086] Scanning transmission electron microscopy (STEM-EDX) images were acquired on a Philips TECNAI G2 F20 field emission electron microscope equipped with energy dispersive X-ray (EDX) and high-angle annular dark field (HAADF).

[0087] The electrocatalytic activity of the catalyst prepared in the examples in alkaline ammonia solution was tested using the following method:

[0088] Weigh 2.0-8.0 mg of catalyst, 900-980 µL of isopropanol, 20.0-60.0 µL of ultrapure water, and 20.0-60.0 µL of Nafion membrane solution into a 3 mL weighing bottle. Disperse the solution ultrasonically in an ice-water bath for at least 30 min to obtain a uniformly dispersed solution. Transfer 9.8 µL of the solution and slowly add it dropwise onto a glassy carbon electrode. After drying under an infrared lamp, perform electrochemical testing. A traditional three-electrode system is used for testing: the catalyst-coated glassy carbon electrode is the working electrode, the graphite rod is the counter electrode, and the mercury / mercury oxide electrode is the reference electrode. The electrodes are first activated in blank KOH solution. The scanning voltage range is -0.85 V to 0.10 V, and the scan rate is 100 mV s. -1 Then, the test was conducted using a 0.1 M ammonia alkaline solution, with a scan voltage range of -0.85 V to 0.10 V and a scan rate of 5 mV / s. -1 Stability was tested at a constant voltage of -0.25 V.

[0089] A battery testing system was constructed to perform performance tests on the assembled single cells. This system mainly consists of four parts: an air intake system, a temperature control system, a humidification system, and a back pressure system. Polarization curves of the single cells were acquired using an electrochemical workstation (Gamryreference 5000). The assembled single cells were placed inside the power generation device, and the gas pipelines were insulated. The experimental test conditions were as follows: anode fuel: 4.0 mL / min -1 In 3 M NH3+ and 3 M KOH; cathode fuel: 1000 mL / min -1 O2, bubbling humidification temperature 75 ℃, battery operating temperature 80 ℃.

[0090] Figure 1 Mo2CT obtained by centrifuging once and 15 times during the etching process. x The SEM image shows that although the Ga layer atoms are etched after one centrifugation, the interlayer space is not fully opened, while after multiple centrifugations the interlayer space is significantly opened.

[0091] Figure 2 To prepare Mo2CT using different NaBH4 alkaline solution dropping rates x SEM images (left: always added at a rate of 500 μl / min; right: first added at a rate of 50 μl / min for 1 hour, then continued to be added at a rate of 500 μl / min). The results show that when added at a single rate, obvious transition metal agglomeration occurred; while by adjusting the dropping rate, the transition metal loading was more uniform.

[0092] Figure 3 Pt / Mo2CT prepared for Example 1 x SEM image of the catalyst. The image shows that the Pt metal particles are uniformly dispersed on the support, and no aggregation is observed.

[0093] Figure 4 Mo2CT x Carrier and Pt / Mo2CT prepared in Example 1 x XRD pattern of the catalyst. The figure shows that the diffraction peaks at 39.9°, 47.4°, 67.7°, 81.6° and 86° correspond to (111), (200), (220), (331) and (222) of Pt, respectively, which proves that the synthesized catalyst has a face-centered cubic (fcc) structure.

[0094] Figure 5 And Table 1 shows Mo2CT x Carrier and Pt / Mo2CT prepared in Example 1 x N2 adsorption-desorption curves of the catalyst. As can be seen from the graph, after etching, Mo2CT... x Its specific surface area is 5 times that of Mo2Ga2C and 11 times that of Mo2C, indicating that Mo2CT... x It has a high specific surface area.

[0095] Table 1

[0096]

[0097] Figure 6 The XRD patterns of the Pt / XC-72 catalyst prepared for the XC-72 support and Comparative Example 1 are shown in the figure. The diffraction peaks at 39.9°, 47.4°, 67.7°, 81.6° and 86° correspond to the (111), (200), (220), (331) and (222) of Pt, respectively, which proves that the synthesized catalyst has a face-centered cubic (fcc) structure.

[0098] Figure 7 The XRD patterns of the Pt / Mo2C catalyst prepared on the Mo2C support and in Comparative Example 2 are shown. The figures show that the diffraction peaks at 39.9°, 47.4°, 67.7°, 81.6°, and 86° correspond to the (111), (200), (220), (331), and (222) peaks of Pt, respectively. This demonstrates that Pt nanoparticles were successfully supported by the NaBH4 reduction method, and that the synthesized catalyst possesses a face-centered cubic (fcc) structure.

[0099] Figure 8 The Pt / Mo2CT prepared in Example 1 xElectrochemical test results of the catalyst. As shown in the figure, Pt / Mo2CT x The peak current density of the catalyst is 104.3 A g. -1 Pt Compared to commercial Pt / C catalysts (19 Ag), Pt -1 The electrocatalytic activity of the catalyst was significantly improved by 5.4 times compared to that of the Pt / XC-72 catalyst (46 A g). Pt -1 (Increased by 2.26 times)

[0100] Figure 9 Pt / Mo2CT prepared in Example 1 x A comparison of the performance of the prepared Pt / Mo2CT catalyst with that of commercial Pt / C in ammonia fuel cells. As can be seen from the figure, the Pt / Mo2CT catalyst... x The catalyst's single-cell performance is 168 mW cm⁻¹. -2 Compared to the 61 mW / cm² of commercial Pt / C -2 The 170% improvement demonstrates its excellent performance in ammonia fuel cells.

[0101] Figure 10 PtPd / Mo2CT prepared for Example 2 x XRD patterns of the catalyst and PtPd / XC-72 and PtPd / Mo2C prepared in Comparative Examples 3 and 4. As shown in the figure, the diffraction peaks at 40.1°, 46.6°, 68.0°, 81.9° and 86.5° correspond to the characteristic diffraction peaks (111), (200), (220), (331) and (222) of PdPt, respectively, which proves that the synthesized catalyst has a face-centered cubic (fcc) structure.

[0102] Figure 11 The PtPd / Mo2CT prepared in Example 2 x Electrochemical test results of the catalyst. As shown in the figure, PtPd / Mo2CT x The peak current density of the catalyst is 73.6 A g. -1 PGM Furthermore, its starting point is significantly lower than that of the commercial catalyst Pt / C, while the current density of PtPd / XC-72 is 37.3 A g. -1 PGM The prepared PtPd / Mo2C had a current density of 45.2 A g. -1 PGM Compared to the commercial catalyst Pt / C, its catalytic activity increased by 3.8 times. However, the starting point is also very important in fuel cells. The addition of Pd lowers the starting point, while Pd / Mo2CT... xThere is no ammonia oxidation potential peak in argon-saturated ammonia and KOH solutions. Relative to the current activity per gram of noble metal catalyst, its activity is higher than that of Pt / Mo2CT. x It is lower, but under the same conditions its activity is better than PtPd / Mo2C and PtPd / C.

[0103] Figure 12 PtIr / Mo2CT prepared for Example 3 x XRD patterns of the catalyst and PtIr / XC-72 and PtIr / Mo2C prepared in Comparative Examples 5 and 6. As shown in the figure, the diffraction peaks at 40.2°, 46.7°, 68.2°, 82.3° and 86.8° correspond to the characteristic diffraction peaks of PtIr (111), (020), (022), (131) and (222), respectively, which proves that the synthesized catalyst has a face-centered cubic (fcc) structure.

[0104] Figure 13 , 14 The PtIr / Mo2CT prepared in Example 3 x The electrochemical test results of the catalyst are shown in the figure. As shown, its electrocatalytic activity is significantly higher than that of the commercial Pt / C catalyst. The current density of the commercial PtIr / C catalyst is 23.3 A g. -1 PGM The prepared PtIr / Mo2C had a current density of 48.8 A g. -1 PGM PtIr / Mo2CT x The current density is 59.1 A g. -1 PGM Compared to the commercial catalyst PtIr / C, its catalytic activity is increased by 2.5 times. However, the starting point is also very important in fuel cells. A common method for evaluating fuel cell catalysts is to compare their current densities at a 0.5 V potential under standard electrode potential. This comparison includes commercial Pt / C, PtIr / C, PtIr / Mo2C, and PtIr / Mo2CT. x The current density at a potential of 0.5 V is 5.1 A g. -1 PGM 13.9 A g -1 PGM 18.0 A g -1 PGM 35.2 A g -1 PGM .

[0105] Figure 15 Pt / Mo2CT prepared in Example 1 xIT stability tests were conducted on the catalysts Pt / Mo2C and Pt / C. The results showed that the stability, from highest to lowest, was Pt / Mo2C / C. x The Pt / Mo2C catalyst >Pt / C catalyst indicates that the introduction of Mo will improve the stability of the catalyst, which is attributed to the strong interaction between the metal and the support.

[0106] The above description is only a preferred embodiment of the present invention. All equivalent changes and modifications made within the scope of the claims of the present invention should be included in the scope of the present invention.

Claims

1. Use of a two-dimensional layered ammonia oxidation catalyst based on MXene in the preparation of an anode for a low-temperature ammonia fuel cell, characterized in that, The catalyst comprises an active component and a carrier, the active component is one or two of transition metals Pt, Ir and Pd, and the carrier is organ-like MXenes; and the preparation specifically comprises the following steps: 1) in-situ HF etching by adding fluoride and acid with MAX as a precursor; 2) low-speed centrifugation of the etching product obtained in step (1) with deionized water until the solution is turbid after centrifugation and the pH value of the centrifugal liquid is above 6, then ultrasonic dispersion of the precipitate in a solvent, filtration, washing with deionized water and vacuum drying to obtain organ-like MXenes; 3) ultrasonic dispersion of the organ-like MXenes obtained in step (2) in a mixture of isopropanol and deionized water at room temperature, then adding a transition metal precursor, stirring and mixing, then reducing with NaBH4 alkali solution, then filtering and vacuum drying to obtain a transition metal catalyst loaded on MXenes; The power of the ultrasonic dispersion in step 2) is 100-200 W, and the time is 0.5-2 h; The reduction in step 3) is that the NaBH4 alkali solution is first added at a rate of 50 μL / min for 1 h, and then added at a rate of 500 μL / min.

2. Use according to claim 1, characterized in that, MAX in step 1) is any one of Mo2Ga2C, Mo3AlC2, Mo2TiAlC2, Mo2TiAlC3, (W 2 / 3 Y 1 / 3 )2AlC, (Mo 2 / 3 Sc 1 / 3 )2AlC, Ti2AlC, Ti3AlC2; The fluoride is one or more of NH4F, LiF and NaF; The acid is one or more of concentrated nitric acid, concentrated hydrochloric acid and concentrated sulfuric acid; The mass ratio of the used MAX, fluoride and acid is 1:1.6:30; The etching temperature is 120-200 ℃, and the time is 12-48 h.

3. Use according to claim 1, characterized in that, The speed of the low-speed centrifugation in step 2) is 3000-5500 r / s, and the time is 1 min each time, and the centrifugation is repeated for 10-20 times; The solvent is one of deionized water, DMSO, TBAOH and TMAOH.

4. Use according to claim 1, characterized in that, The volume ratio of isopropanol to deionized water in the mixture in step 3) is 1:1; The transition metal precursor is one or more of chloroplatinic acid, chloroiridic acid and palladium chloride; The molar ratio of NaBH4 in the NaBH4 alkali solution to the transition metal in the transition metal precursor is 20:1; The concentration of NaBH4 in the NaBH4 alkali solution is 0.05 mol / L, the concentration of the base is 0.025 mol / L, and the base used is NaOH.

5. The use according to claim 1, characterized in that, MXenes are specifically any one of Mo2CT x , Mo3C2T x , Ti3C2T x , Ti2CT x , (W 2 / 3 Y 1 / 3 )2CT x , Mo2Ti2CT x , (Mo 2 / 3 Sc 1 / 3 )2CT x , wherein T x is a surface functional group -OH, -F, -OH.

6. Use according to claim 1, characterized in that, The content of the active component in the two-dimensional layered ammonia oxidation catalyst is 1.0-60.0 wt.% in mass percentage.

Images