A method for preparing an ordered platinum-based intermetallic compound octahedral catalyst

Abstract

This invention discloses a method for preparing an ordered platinum-based intermetallic compound octahedral catalyst. The method first prepares a disordered platinum-based octahedral catalyst by introducing a morphology control agent, hexadecyltrimethylammonium bromide. This catalyst is then used as a raw material for high-temperature thermal annealing, during which high-pressure gas is introduced to control the gas pressure, annealing time, and annealing temperature. The high-pressure gas helps to slow down atomic migration and movement on the catalyst particle surface, ultimately successfully preparing a platinum-based intermetallic compound catalyst with an ordered structure and octahedral morphology. The catalyst prepared by this method exhibits a clearly ordered structure, retains most of the octahedral morphology, shows no significant particle agglomeration, and has a uniform size distribution. The ordered structure greatly enhances the alloying effect, thereby further improving the catalyst's activity and stability.

Description

Technical Field

[0001] This invention relates to the field of preparation technology of platinum-based catalysts for proton exchange membrane fuel cells, and specifically to a method for preparing an ordered platinum-based intermetallic compound octahedral catalyst. Background Technology

[0002] Developing green and clean hydrogen energy is a crucial tool for achieving dual-carbon goals and sustainable development. Proton exchange membrane fuel cells (PEMFCs) can directly convert the chemical energy stored in hydrogen and oxygen into electrical energy, exhibiting higher energy conversion efficiency. However, the oxygen reduction reaction (ORR) at the fuel cell cathode is a four-electron process with inherently slow kinetics, thus requiring suitable catalysts to accelerate the reaction and improve the cell's power density. Platinum (Pt)-based alloys are considered promising ORR catalysts, exhibiting higher catalytic activity compared to pure Pt, especially certain catalysts with special morphologies, such as octahedral catalysts. However, octahedral catalysts synthesized using solvothermal methods are all disordered alloys with low intrinsic activity; furthermore, under operating conditions, the transition metals in the alloy dissolve rapidly, which exacerbates the decline in catalytic activity.

[0003] Therefore, to address the poor stability of disordered octahedral catalysts, introducing ordered structures into the octahedrons can enhance both activity and stability. High-temperature heat treatment is the most common method for inducing ordering, but due to the high surface energy of nanocatalysts, surface atoms easily migrate at high temperatures, causing changes in the original octahedral morphology and the disappearance of the highly active structure, which does not achieve the desired effect. For example, Xia et al. (Xia, et al., J. Am. Chem. Soc. 2021, 143, 8509-8518) reported the morphological evolution of PtCo octahedrons at the ordering temperature, where almost all octahedral particles were reshaped into spherical nanoparticles. Subsequently, the octahedral morphology of the catalyst was restored through Pt deposition, but the additional steps increased the process cost and made mass production difficult. Therefore, how to maintain the octahedral morphology at the ordering temperature still needs further exploration. Summary of the Invention

[0004] This invention addresses the poor catalytic performance of traditional spherical nanoparticles and the morphology reshaping of octahedral catalysts during high-temperature annealing by providing a method for preparing ordered platinum-based intermetallic compound octahedral catalysts. The method first prepares disordered platinum-based octahedral catalysts by introducing a morphology control agent, hexadecyltrimethylammonium bromide (CTAB). These catalysts are then used as raw materials for high-temperature thermal annealing, during which high-pressure gas is introduced to control the gas pressure, annealing time, and annealing temperature. Unlike traditional annealing processes, the high-pressure gas helps to slow down atomic migration and movement on the catalyst particle surface, ultimately successfully preparing a platinum-based intermetallic compound catalyst with an ordered structure and octahedral morphology. The catalyst prepared by this method exhibits a clearly ordered structure, retains most of the octahedral morphology, shows no significant particle agglomeration, and has a uniform size distribution. The ordered structure greatly enhances the alloying effect, thereby further improving the catalyst's activity and stability.

[0005] The technical solution of this invention is as follows:

[0006] A method for preparing an ordered platinum-based intermetallic compound octahedral catalyst, the method comprising the following steps:

[0007] (1) Add carbon powder, solid organic matter and metal precursor to an organic solvent to obtain a mixed solution.

[0008] The metal precursor is a platinum salt and a transition metal salt; the solid organic matter is benzoic acid and hexadecyltrimethylammonium bromide.

[0009] The mass ratio of platinum salt to transition metal salt is 1:0.2 to 1:0.8; the mass ratio of platinum salt to carbon powder is 1:1.5 to 1:2; the mass ratio of carbon powder to solid organic matter is 1:3 to 1:7; the mass ratio of hexadecyltrimethylammonium bromide to benzoic acid is 1:3 to 1:4; 0.7 mg to 1 mg of platinum salt is added per 1 mL of organic solvent;

[0010] The transition metal is Fe, Co, Ni, or Cu; the metal transition salt is an acetylacetone salt, a chloride salt, or a nitrate salt.

[0011] (2) The mixed solution was ultrasonically dispersed for 30 min to 60 min, and then heated in an oil bath at 140℃ to 200℃ for 5 h to 12 h to obtain a platinum-based catalyst reaction solution;

[0012] (3) The platinum-based catalyst reaction solution was centrifuged, washed and dried to obtain carbon-supported disordered platinum-based alloy catalyst powder with octahedral morphology.

[0013] The centrifuge operates at a speed of 6000 r / min to 10000 r / min, for a time of 3 min to 10 min, and for 3 to 5 centrifugations.

[0014] (4) The catalyst powder obtained in the previous step is placed in the heating tube of a high-pressure furnace and annealed at 550℃~850℃ and 0.5MPa~5.0MPa for 2h~3h to obtain an ordered platinum-based octahedral catalyst.

[0015] The annealing atmosphere is either argon or nitrogen.

[0016] The ordered platinum-based octahedral catalyst has a particle size of 5 nm to 20 nm.

[0017] In the obtained catalyst, platinum and transition metals form octahedral alloy nanoparticles, which are anchored on the support (carbon powder) to form the catalyst. The mass of platinum accounts for 10% to 20% of the total mass of the catalyst.

[0018] The ordered platinum-based octahedral catalyst prepared by the method is used as an oxygen reduction catalyst for the cathode of a proton exchange membrane fuel cell.

[0019] The essential features of this invention are:

[0020] This invention employs a solvothermal method to prepare disordered octahedral catalysts by introducing hexadecyltrimethylammonium bromide as a morphology control agent. Combined with a high-pressure-assisted high-temperature annealing process, ordered platinum-based intermetallic compound octahedral catalysts were successfully prepared. Unlike traditional annealing methods, which can cause particle agglomeration and morphology reshaping during heat treatment, the high-pressure annealing process used in this preparation method slows down atomic migration and movement on the particle surface. Ordered platinum-based intermetallic compound octahedral catalysts were successfully prepared; the annealed samples retained most of their octahedral morphology, exhibiting a high degree of ordering, and thus improving the catalyst's activity and stability.

[0021] The beneficial effects of this invention are as follows:

[0022] (1) This invention discloses a method for preparing an ordered platinum-based intermetallic compound octahedral catalyst. This method has the advantages of simple operation and low production cost, and can be used as a catalyst for the oxygen reduction reaction at the cathode of a proton exchange membrane fuel cell.

[0023] (2) In the process of solvothermal synthesis, the present invention introduces the morphology control agent hexadecyltrimethylammonium bromide to prepare a catalyst with an octahedral morphology, which has higher catalytic performance than traditional spherical nanoparticles.

[0024] (3) The catalyst prepared by this invention can suppress the agglomeration and deformation of octahedral particles during heat treatment under high-pressure gas assistance, and successfully achieves ordered phase transformation while maintaining morphology, which greatly improves the activity of the catalyst. Furthermore, the ordered structure enhances the d-orbital coupling between Pt and transition metals, which can suppress the dissolution of transition metals during electrochemical testing, thus better maintaining the catalytic performance of the catalyst and extending its service life.

[0025] (4) The catalyst of the present invention has high mass activity and stability, with a mass activity of 0.382A / mg and less activity decay after 30,000 cycles. Attached Figure Description

[0026] Figure 1 This is a high-angle annular dark-field scanning transmission electron microscope (HAADF-STEM) image of the ordered platinum-based intermetallic octahedral catalyst prepared in Example 1.

[0027] Figure 2 The image shows the XRD pattern of the ordered platinum-based intermetallic compound octahedral catalyst prepared in Example 1.

[0028] Figure 3 This is a high-resolution transmission electron microscope (HRTEM) image of the ordered platinum-based intermetallic octahedral catalyst prepared in Example 1.

[0029] Figure 4 Linear sweep voltammetry (LSV) curves of the catalyst in Example 1 and a commercial Pt / C catalyst are shown.

[0030] Figure 5 The cyclic voltammetry (CV) and linear sweep voltammetry (LSV) curves of the catalyst in Example 1 before and after the 30,000-cycle accelerated durability test (ADT) are shown; Figure 5 a represents the CV curve before and after ADT; Figure 5 b represents the LSV curves before and after ADT; Detailed Implementation

[0031] The following embodiments further illustrate the content of the present invention, but should not be construed as limiting the present invention. Any modifications and substitutions made to the methods, steps, or conditions of the present invention without departing from the spirit and essence of the present invention are within the scope of the present invention.

[0032] Unless otherwise specified, the technical means used in the embodiments are conventional means well known to those skilled in the art.

[0033] Example 1

[0034] (1) Using a four-position electronic balance with the level adjusted, first weigh 20.0 mg of XC-72R, 10.0 mg of platinum acetylacetonate, 6.6 mg of copper acetylacetonate, 15.0 mg of cetyltrimethylammonium bromide, and 60.0 mg of benzoic acid and put them into the lining of the high-pressure reactor, and then add 10.0 mL of NN dimethylformamide.

[0035] (2) Add a magnetic stir bar to the liner of the reactor and stir for 60 minutes. Then remove the magnetic stir bar, install the liner of the reactor into the high-pressure reactor, and tighten the device. Place the high-pressure reactor into a forced-air drying oven and react at 160°C for 12 hours.

[0036] (3) After the reaction is complete, remove the high-pressure reactor when the oven has cooled to room temperature. Unscrew the high-pressure reactor and evenly transfer the reaction solution from the liner into two 10.0 mL centrifuge tubes. Add anhydrous ethanol until the mixture reaches 8.0 mL. First, sonicate the mixture using an ultrasonic machine, then wash it three times repeatedly using a centrifuge (8000 r / min, 3 min). After drying, seal and store to obtain disordered PtCu octahedral catalyst powder.

[0037] (4) The catalyst powder was loaded into a crucible, then wrapped with copper foil, and placed in the heating tube of a high-pressure furnace. The heating rate was set to 10℃ / min, and the mixture was heat-treated at 600℃ for 2 hours in a N2 atmosphere at 1.0MPa pressure to obtain an ordered PtCu octahedral catalyst (the loading of the noble metal platinum in the catalyst in the prepared sample was 15% (measured by thermogravimetric method)).

[0038] A layer of filter paper was placed in a petri dish, and a copper mesh was placed on the filter paper. Then, a trace amount of catalyst powder was added to anhydrous ethanol and sonicated for 3 to 5 minutes to completely disperse the powder (0.1 mg to 0.5 mg of catalyst was added to 1.0 mL to 5.0 mL of anhydrous ethanol). A slightly translucent catalyst solution was obtained. 10 μL to 20 μL of the solution was pipetted onto the copper mesh. The solution was then dried under an infrared lamp. The morphology of the prepared sample was characterized under a transmission electron microscope to obtain electron microscope images.

[0039] from Figure 1 The STEM images show that the prepared ordered octahedrons retain good original morphology and do not exhibit obvious agglomeration and growth (the average size of the particles is about 10 nm).

[0040] Example 2

[0041] (1) Using a four-position electronic balance with the level adjusted, weigh 15.0 mg of Kejen Black EC300J, 10.0 mg of platinum acetylacetonate, 3.0 mg of iron acetylacetonate, 20.0 mg of cetyltrimethylammonium bromide, and 80.0 mg of benzoic acid and put them into the lining of the high-pressure reactor. Then add 10.0 mL of benzyl alcohol.

[0042] (2) Add a magnetic stir bar to the liner of the reactor and stir for 60 minutes. Then remove the magnetic stir bar, install the liner of the reactor into the high-pressure reactor, and tighten the device. Place the high-pressure reactor into a forced-air drying oven and react at 190°C for 10 hours.

[0043] (3) After the reaction is complete, remove the high-pressure reactor when the oven has cooled to room temperature. Unscrew the high-pressure reactor and evenly distribute the reaction solution from the liner into two 10.0 mL centrifuge tubes. Add anhydrous ethanol until the mixture reaches 8.0 mL. First, sonicate the mixture using an ultrasonic machine, then wash it three times repeatedly using a centrifuge (10000 r / min, 3 min). After drying, seal and store to obtain disordered PtFe octahedral catalyst powder.

[0044] (4) The catalyst powder was loaded into a crucible, then wrapped with copper foil, and placed in the heating tube of a high-pressure furnace. The heating rate was set to 10℃ / min, and the mixture was heat-treated at 550℃ for 2 hours in a N2 atmosphere at 0.5MPa pressure to obtain an ordered PtFe octahedral catalyst (the loading of the noble metal platinum in the catalyst in the prepared sample was 13%).

[0045] Example 3

[0046] (1) Using a four-position electronic balance with the level adjusted, weigh 15.0 mg of Ketjen Black EC-300J, 7.8 mg of chloroplatinic acid, 3.5 mg of cobalt acetylacetonate, 20.0 mg of cetyltrimethylammonium bromide, and 60.0 mg of benzoic acid and put them into the lining of the high-pressure reactor. Then add 10.0 mL of benzyl alcohol.

[0047] (2) Add a magnetic stir bar to the liner of the reactor and stir for 60 minutes. Then remove the magnetic stir bar, install the liner of the reactor into the high-pressure reactor, and tighten the device. Place the high-pressure reactor into a forced-air drying oven and react at 200°C for 5 hours.

[0048] (3) After the reaction is complete, remove the high-pressure reactor when the oven has cooled to room temperature. Unscrew the high-pressure reactor and evenly distribute the reaction solution from the liner into two 10.0 mL centrifuge tubes. Add anhydrous ethanol until the mixture reaches 8.0 mL. First, sonicate the mixture using an ultrasonic machine, then wash it three times repeatedly using a centrifuge (6000 r / min, 10 min). After drying, seal and store to obtain disordered PtCo octahedral catalyst powder.

[0049] (4) The catalyst powder was loaded into a crucible, then wrapped with copper foil, and placed in the heating tube of a high-pressure furnace. The heating rate was set to 10℃ / min, and the mixture was heat-treated at 650℃ for 3 hours in a N2 atmosphere at 2.0MPa pressure to obtain an ordered PtCo octahedral catalyst (the loading of the noble metal platinum in the catalyst in the prepared sample was 12%).

[0050] Example 4

[0051] (1) Using a four-position electronic balance with the level adjusted, weigh out 15.0 mg of Kejen Black BP2000, 10.0 mg of chloroplatinic acid, 7.7 mg of nickel acetylacetone, 20.0 mg of cetyltrimethylammonium bromide, and 60.0 mg of benzoic acid and place them in the lining of the high-pressure reactor, and then add 10.0 mL of ethylene glycol.

[0052] (2) Add a magnetic stir bar to the liner of the reactor and stir for 60 minutes. Then remove the magnetic stir bar, install the liner of the reactor into the high-pressure reactor, and tighten the device. Place the high-pressure reactor into a forced-air oven and react at 140°C for 12 hours.

[0053] (3) After the reaction is complete, remove the high-pressure reactor when the oven has cooled to room temperature. Unscrew the high-pressure reactor and evenly distribute the reaction solution from the liner into two 10.0 mL centrifuge tubes. Add anhydrous ethanol until the mixture reaches 8.0 mL. First, sonicate the mixture using an ultrasonic machine, then wash it three times repeatedly using a centrifuge (8000 r / min, 5 min). After drying, seal and store to obtain disordered PtNi octahedral catalyst powder.

[0054] (4) The catalyst powder was loaded into a crucible, then wrapped with copper foil, and placed in the heating tube of a high-pressure furnace. The heating rate was set to 10℃ / min, and the mixture was heat-treated at 580℃ for 2 hours in a N2 atmosphere at 0.5MPa pressure to obtain an ordered PtNi octahedral catalyst (the loading of the noble metal platinum in the catalyst in the prepared sample was 10%).

[0055] Performance testing methods:

[0056] 1. (1) Weigh 2.0 mg of the platinum-based octahedral catalyst finally prepared in Example 1 and add it to a 1.0 mL mixed solution composed of isopropanol (850.0 μL), Nafion (20.0 μL), and deionized water (130.0 μL). After ultrasonic dispersion for 60 min, a uniformly mixed ink is obtained. (2) Use a pipette with a volume of 20.0 μL to draw 12.5 μL of ink and drop it evenly onto a glassy carbon rotating disk electrode, and wait for it to air dry naturally. (3) Use this as the working electrode, a platinum wire as the counter electrode, and a reversible hydrogen electrode as the reference electrode. First, scan the catalyst 100 times in a nitrogen-saturated 0.1 mol / L perchloric acid solution at a scan rate of 100 mV / s within a potential range of 0 V to 1.25 V to achieve the purpose of activating the catalyst. Then, a cyclic voltammetric curve for calculating the electrochemical active area (ECSA) was obtained by scanning 5 times at a scan rate of 50 mV / s within a potential range of 0 V to 1.25 V. (4) Subsequently, in another oxygen-saturated 0.1 mol / L perchloric acid solution, a linear scanning voltammetric curve of the catalyst was obtained by scanning at a scan rate of 50 mV / s and a rotating disk electrode speed of 1600 r / min within a potential range of 0 V to 1.05 V.

[0057] The electrochemical performance testing of commercial Pt / C followed the same procedure as described above, ultimately yielding the oxygen reduction polarization (ORR) curves for commercial Pt / C. The results are compared as follows: Figure 4 As shown.

[0058] from Figure 4 As can be seen from the results, the ordered platinum-based octahedral catalyst prepared in Example 1 has a higher half-wave potential compared to commercial Pt / C. The octahedral catalyst has a half-wave potential of 0.912 V, while the commercial Pt / C has a half-wave potential of 0.871 V, indicating that the prepared ordered octahedral catalyst has better oxygen reduction activity than commercial Pt / C.

[0059] Table 1 compares the performance values ​​of Example 1 and commercial Pt / C.

[0060] <![CDATA[ECSA(m 2 / g)]]> MA (A / mg) <![CDATA[SA(mA / cm 2 )]]> Half-wave potential (V) Example 1 30.6 0.382 1.248 0.912 Commercial Pt / C 68.7 0.179 0.261 0.871

[0061] The data in Table 1 correspond to the numerical comparison of electrochemical active area, mass activity, area activity, and half-wave potential of ordered octahedral catalysts and commercial Pt / C, respectively.

[0062] II. Accelerated Durability Test (ADT) The electrochemical performance test of the octahedral catalyst is the same as that in (1)(2)(3)(4) above. ADT test: (5) The working electrode is subjected to 30,000 cyclic voltammetry scans in an oxygen-saturated 0.1 mol / L perchloric acid solution, with a scan range of 0.6 V to 1.0 V and a scan rate of 100 mV / s. (6) The cyclic voltammetry (CV) curves and linear sweep voltammetry (LSV) curves before and after 30,000 cycles are recorded in the same way, and the results are compared as follows. Figure 5 ( Figure 5 a represents the cyclic volt-ampere (CV) curves before and after the cycle. Figure 5 b represents the linear sweep voltammetry (LSV) curves before and after the cycle.

[0063] from Figure 5 As can be seen, after 30,000 cycles, the hydrogen desorption peak area of ​​the prepared ordered platinum-based intermetallic octahedral catalyst did not change significantly, and the electrochemical active area did not decrease significantly, indicating that the catalyst did not exhibit significant agglomeration after cycling, and the catalytic activity did not decrease significantly. The polarization curves show that the half-wave potential decreased by only 0.007 V before and after cycling.

[0064] Table 2 shows the numerical comparison before and after the cycle in Example 1.

[0065] <![CDATA[ECSA(m 2 / g)]]> MA (A / mg) <![CDATA[SA(mA / cm 2 )]]> Half-wave potential (V) Example 1 30.6 0.382 1.248 0.912 30,000 CV cycles 27.3 0.341 1.246 0.905

[0066] The data in Table 2 correspond to the numerical comparison of electrochemical active area, mass activity, area activity and half-wave potential of the ordered octahedral catalyst before and after cycling.

[0067] Matters not covered in this invention are common knowledge.

Claims

1. A method of preparing an ordered platinum-based intermetallic compound octahedral catalyst, characterized by, The method includes the following steps: (1) Add carbon powder, solid organic matter and metal precursor to an organic solvent to obtain a mixed solution; The metal precursor is a platinum salt and a transition metal salt; the solid organic matter is benzoic acid and hexadecyltrimethylammonium bromide. The mass ratio of platinum salt to transition metal salt is 1:0.2 to 1:0.8; the mass ratio of platinum salt to carbon powder is 1:1.5 to 1:2; the mass ratio of carbon powder to solid organic matter is 1:3 to 1:7; 0.7 mg to 1 mg of platinum salt is added per 1 mL of organic solvent; The transition metal salt is copper acetylacetonate; The mass ratio of hexadecyltrimethylammonium bromide to benzoic acid is 1:3 to 1:4; The organic solvent is benzyl alcohol, N,N dimethylformamide, or ethylene glycol; The platinum salt mentioned is specifically platinum acetylacetonate or chloroplatinic acid hydrate; The toner is Ketjen Black EC-300J, BP2000, or XC-72R. (2) The mixed solution was ultrasonically dispersed for 30 min to 60 min, and then heated in an oil bath at 140℃ to 200℃ for 5 h to 12 h to obtain the platinum-based catalyst reaction solution; (3) The platinum-based catalyst reaction solution was centrifuged, washed and dried to obtain carbon-supported disordered platinum-based alloy catalyst powder with octahedral morphology. The centrifugation is carried out by centrifuging at a speed of 6000 r / min to 10000 r / min for 3 min to 10 min, and 3 to 5 times. (4) The catalyst powder obtained in the previous step is placed in the heating tube of a high-pressure furnace and annealed at 550℃~850℃ and 0.5 MPa~5.0 MPa for 2 h~3 h to obtain an ordered platinum-based octahedral catalyst. The annealing atmosphere is either argon or nitrogen. The ordered platinum-based octahedral catalyst has a particle size of 5 nm to 20 nm. In the obtained catalyst, platinum accounts for 10% to 20% of the total mass of the catalyst; The ordered platinum-based octahedral catalyst prepared by the method is used as the oxygen reduction catalyst for the cathode of a proton exchange membrane fuel cell.

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