Preparation method and application of high-performance formic acid electrooxidation platinum-based catalyst

Abstract

The invention provides a preparation method of a high-performance formic acid electrooxidation platinum-based catalyst, and belongs to the technical field of electrocatalysis. The micromolecule reducing agent assisted wet chemical method provided by the invention can quickly promote dissolution of a metal precursor and inhibit homogeneous nucleation of noble metal, so that a two-dimensional structure is formed, epitaxial growth of the edge of platinum metal is promoted, and the mixed-phase PtTe2 (at) Pt core-shell nanosheet catalyst is obtained. The two-dimensional structure is beneficial for the catalyst to expose more catalytic active sites, and the oxidation reaction of formic acid is accelerated. The design of the core-shell structure enhances the structural stability of the catalyst under an acidic condition. The catalytic coordination effect of different crystal phases enables the reaction path of formic acid oxidation reaction to be adjusted, so that the catalytic performance is improved. The use of the small molecule reducing agent effectively controls the diffusion and aggregation of platinum metal ions, further adjusts the number of active sites of Pt in the platinum tellurium catalyst, and significantly improves the catalytic performance of formic acid electro-oxidation reaction (FAOR).

Description

Technical Field

[0001] The present invention belongs to the technical field of electrocatalytic formic acid oxidation, and particularly relates to a preparation method and application of a high-performance platinum-based catalyst for electrocatalytic formic acid oxidation. Background Art

[0002] With the current environmental pollution and shortage of fossil fuels, finding environmentally friendly and renewable clean energy has become an urgent task to promote the innovation strategy of energy utilization. Fuel cells are the fourth-generation power generation devices that directly convert chemical energy into electrical energy, and they have the advantages of no pollution, low noise, and renewable raw materials. Due to the advantages of good reaction kinetics at low temperatures, high theoretical open-circuit voltage, non-toxic formic acid, and low fuel crossover, it has become the most advantageous candidate for commercially viable fuel cells. Considering the activity and stability of formic acid oxidation catalysts, platinum-based material catalysts exhibit better catalytic performance among many catalysts. However, due to the anisotropy of metal materials, platinum atoms tend to form a three-dimensional close-packed structure, which is not conducive to the full utilization of platinum atoms in the catalytic formic acid oxidation reaction and limits the catalytic activity of platinum-based materials. In addition, the formic acid oxidation reaction involves two reaction pathways (dehydrogenation path and dehydration path). Among them, carbon monoxide generated by the dehydration path is likely to poison the catalyst. Therefore, synthesizing low-dimensional Pt-based catalysts with high electrocatalytic activity, fast chemical reaction kinetics, and good tolerance to CO is the key problem to be solved urgently at present.

[0003] Tellurium (Te) has a high electrooxidation potential. Selecting tellurium as the second element can improve the catalytic stability of the catalyst. In addition, tellurium has good tolerance to carbon monoxide and can reduce the possibility of poisoning of platinum-based catalysts by carbon monoxide. The Chinese invention patent document with the publication number CN117497779B discloses a catalyst for formic acid oxidation reaction and its preparation method, which is an integrated carbon-supported platinum tellurium nanosheet. The method includes dispersing a platinum precursor, a tellurium metal precursor, a small molecule reducing agent, and a catalyst support in a solvent, ultrasonically mixing them, and then reacting at a certain temperature to finally obtain a carbon-supported platinum tellurium nanosheet catalyst. However, the introduction of catalytically inert Te significantly reduces the atomic ratio of Pt, which is the catalytic active site in the catalyst, in the whole catalyst and limits the activity of the catalyst. Summary of the Invention

[0004] The purpose of the present invention is to provide a preparation method of a high-performance platinum-based catalyst for electrocatalytic formic acid oxidation. By adding a small molecule reducing agent, Pt metal grows epitaxially on the surface of PtTe 2 two-dimensional nanosheets to generate a high-performance catalyst with a mixed-phase PtTe 2 @Pt core-shell nanosheet structure. Applying the above catalyst to the electrocatalytic formic acid oxidation reaction shows excellent catalytic activity and stability.

[0005] To achieve the above object, the present invention adopts the following technical solutions: On the one hand, the present invention provides a preparation method of a high-performance platinum-based catalyst for formic acid electrooxidation, comprising the following steps: Dissolve platinum acetylacetonate, tellurium metal precursor, and small molecule reducing agent in ethylene glycol by ultrasonic treatment to obtain a mixed solution; in a closed environment, heat the mixed solution in an oil bath to obtain a suspension; after centrifugation, washing, and drying of the suspension, a mixed-phase PtTe 2 @Pt core-shell nanosheet catalyst powder, namely a high-performance platinum-based catalyst for formic acid electrooxidation.

[0006] Further, the tellurium metal precursor is any one of sodium tellurite, potassium tellurite, and telluric acid; the small molecule reducing agent is any one of citric acid, sodium acetate, phloroglucinol, and urea; the molar ratio of platinum acetylacetonate, tellurium metal precursor, and small molecule reducing agent is 1:1~3:1~6; Further, the temperature of the oil bath heating is 150~200°C; the time of the oil bath heating is 1~12h; On the other hand, the present invention provides an application of the high-performance platinum-based catalyst for formic acid electrooxidation prepared by the above method, and applies it to the electrocatalytic formic acid oxidation reaction (FAOR).

[0007] Compared with the prior art, the technical solution of the present invention has the following beneficial effects: The preparation method disclosed by the present invention has simple process, mild conditions, easily available raw materials, strong controllability, good repeatability, and can be mass-produced. Compared with the traditional preparation method, by adding a small molecule reducing agent to the reaction system, the present invention promotes the rapid dissolution of the two-dimensional nanosheet-like platinum tellurium phase metal precursor, and at the same time inhibits the homogeneous nucleation of platinum metal, thereby promoting the epitaxial growth of platinum metal on the surface of the two-dimensional nanosheet of platinum tellurium metal, forming a mixed-phase two-dimensional core-shell nanosheet structure catalyst with a two-dimensional nanosheet of platinum tellurium metal as the core and platinum metal as the shell, having the following structural advantages: a. Compared with the catalyst of the traditional three-dimensional closely packed structure platinum-based material, the catalyst of the mixed-phase two-dimensional core-shell nanosheet structure of the present invention provides a huge specific surface area, fully exposes the active sites, and significantly improves the catalytic activity of the catalyst.

[0008] b. Tellurium (Te) has a high electrooxidation potential and good tolerance to carbon monoxide. The present invention selects tellurium as the second element to be introduced into the catalyst core-shell structure, which can significantly improve the tolerance of the catalyst to carbon monoxide, reduce the possibility of the catalyst being poisoned by carbon monoxide, and further improve the oxidation kinetics and catalytic activity of the catalyst; at the same time, the synergistic effect of the platinum tellurium phase inner core and the platinum phase outer shell makes the catalyst mainly dehydrogenate in the formic acid oxidation reaction, showing higher catalytic activity and stability, and significantly improving the performance of the formic acid dye battery. Description of the Drawings

[0009] Figure 1 PtTe prepared for Example 1 2 Transmission electron microscopy (TEM) image of @Pt, where Figure a is PtTe prepared for Example 1 2 Low-magnification transmission electron microscopy (TEM) image of @Pt core-shell nanosheets, Figures b and c are PtTe prepared for Example 1 2 High-resolution transmission electron microscopy images of different regions of @Pt core-shell nanosheets.

[0010] Figure 2 PtTe prepared for Example 1 2 Element distribution map of @Pt.

[0011] Figure 3 PtTe prepared for Example 1 2 X-ray powder diffraction (XRD) pattern of @Pt.

[0012] Figure 4 PtTe prepared for Example 1 2 @Pt and commercial Pt / C in 0.5 M H 2 SO 4 and cyclic voltammograms in 0.5 M HCOOH, the test rate is 0.05 V / s, and the test range is 0 - 1.3 V vs. RHE.

[0013] Figure 5 PtTe prepared for Example 1 2 @Pt core-shell nanosheets and commercial Pt / C in 0.5 M H 2 SO 4 and stability curves in 0.5 M HCOOH.

[0014] Figure 6 PtTe prepared for Example 1 2 Polarization curve and power density curve of @Pt core-shell nanosheets in formic acid fuel cells. Detailed Description of the Invention

[0015] The present invention will be further described below in conjunction with the drawings and specific embodiments, so that those of ordinary skill in the art can better understand the implementation of the present invention, but the protection scope of the present invention is not limited thereto.

[0016] Unless otherwise specified, the raw materials used in the embodiments of the present invention are all commercially available materials; unless otherwise specified, all technical and scientific terms used in the present invention have the same meaning as commonly understood by those skilled in the art. Example 1

[0017] Dissolve 0.025 mol of platinum acetylacetonate, 0.025 mol of sodium tellurite and 0.05 mol of citric acid in 10 mL of ethylene glycol by ultrasonic treatment. Then transfer the obtained mixed solution to a 50 mL three-necked flask, seal it with a rubber stopper and place it in an oil bath at 180 °C for continuous heating for 2 h to obtain a suspension; wash the obtained suspension by centrifugation 1-3 times, and the washing solvent is a mixed solvent of ethanol and acetone with a volume ratio of 3:7. The centrifugation speed for washing is 11,000 rpm / min, the centrifugation time is 2 min, and after centrifugation and drying, a mixed-phase PtTe is obtained 2 @Pt core-shell nanosheet catalyst powder, that is, a high-performance platinum-based catalyst for formic acid electrooxidation, denoted as PtTe 2 @Pt.

[0018] For the prepared mixed-phase PtTe 2 @Pt core-shell nanosheet catalyst, perform transmission electron microscopy test, element distribution test, and X-ray diffraction test. The test results are shown in Figures 1-3 ; Figure 1 (a) is a low-magnification transmission electron microscopy (TEM) image of the PtTe 2 @Pt core-shell nanosheet. It can be seen from this that the PtTe 2 @Pt presents a core-shell nanosheet structure and shows good dispersion without agglomeration. Compared with the traditional three-dimensional closely packed platinum-based material catalyst, the two-dimensional core-shell nanosheet structure catalyst has a huge specific surface area, which can fully expose the active sites, thereby significantly improving the catalytic activity of the catalyst. Figure 1 (b, c) are high-resolution images of the PtTe 2 @Pt core-shell nanosheet. The internal lattice spacing is 0.228 nm, corresponding to the (209) crystal plane of trigonal phase PtTe 2 and the edge lattice spacing is 0.210 nm, corresponding to the 111 crystal plane of cubic phase Pt; Figure 2 is the element mapping image of the PtTe 2 @Pt core-shell nanosheet. It can be seen from the figure that the Pt element is enriched at the edge, and the edge contains almost no Te element, indicating that the PtTe 2 @Pt is an obvious core-shell structure; Figure 3 is the XRD pattern of the mixed-crystalline-phase PtTe 2 @Pt core-shell nanosheet, indicating that the PtTe 2 @Pt core-shell nanosheet is a mixed-crystalline phase composed of trigonal phase PtTe 2 and cubic phase Pt.

[0019] The test results Figures 1-3 jointly corroborate the PtTe prepared in Example 12 @Pt is composed of PtTe 2 phase and Pt phase to form a two-dimensional core-shell nanosheet structure. This two-dimensional core-shell structure endows the catalyst with more Pt-based edge active sites. Meanwhile, the inner core PtTe 2 has good tolerance to carbon monoxide, which can reduce the possibility of PtTe 2 @Pt catalyst being poisoned by carbon monoxide, and improve the oxidation kinetics and catalytic activity of the catalyst. In addition, the synergistic effect between PtTe 2 phase and Pt phase enables PtTe 2 @Pt to mainly follow the dehydrogenation path in the formic acid oxidation reaction, showing higher electrocatalytic activity and stability for formic acid oxidation and excellent performance in formic acid fuel cells. Example 2

[0020] The difference between Example 2 and Example 1 is that 0.05 mol of citric acid is replaced by 0.05 mol of sodium acetate, and the remaining methods are the same as those in Example 1, denoted as PtTe 2 @Pt-2. Example 3

[0021] The difference between Example 3 and Example 1 is that 0.05 mol of citric acid is replaced by 0.05 mol of phloroglucinol, and the remaining methods are the same as those in Example 1, denoted as PtTe 2 @Pt-3. Example 4

[0022] The difference between Example 4 and Example 1 is that 0.05 mol of citric acid is replaced by 0.05 mol of urea, and the remaining methods are the same as those in Example 1, denoted as PtTe 2 @Pt-4. Example 5

[0023] The difference between Example 5 and Example 1 is that 0.025 mol of sodium tellurite is replaced by 0.025 mol of potassium tellurite, and the remaining methods are the same as those in Example 1, denoted as PtTe 2 @Pt-5. Example 6

[0024] The difference between Example 6 and Example 1 is that 0.025 mol of sodium tellurite is replaced by 0.025 mol of telluric acid, and the remaining methods are the same as those in Example 1, denoted as PtTe 2 @Pt-6. Example 7

[0025] The difference between Example 7 and Example 1 is that the oil bath heating temperature is changed to 150 °C and the oil bath heating time is changed to 12 h, and the remaining methods are the same as those in Example 1, denoted as PtTe 2 @Pt-7. Example 8

[0026] The difference between Example 8 and Example 1 is that the oil bath heating temperature is changed to 200 °C and the oil bath heating time is changed to 1 h, and the remaining methods are the same as those in Example 1, denoted as PtTe 2 @Pt-8 Example 9

[0027] The difference between Example 9 and Example 1 is that 0.05 mol of citric acid is replaced with 0.025 mol of citric acid, and the remaining methods are the same as those in Example 1, denoted as PtTe 2 @Pt-9 Example 10

[0028] The difference between Example 10 and Example 1 is that 0.025 mol of sodium tellurite is replaced with 0.075 mol of sodium tellurite, and 0.05 mol of citric acid is replaced with 0.15 mol of citric acid, and the remaining methods are the same as those in Example 1, denoted as PtTe 2 @Pt-10

[0029] The catalysts prepared in the examples and commercial Pt / C catalysts were respectively used for formic acid oxidation reaction (FAOR) applications, including the following application steps: (1) Dissolve 3 mg of the catalyst powder prepared in Example 1 in 2 mL of ethanol, add 10 mg of carbon black for ultrasonic reaction, and obtain a highly active platinum-based catalyst for formic acid electrooxidation supported on carbon black after centrifugation, washing, and drying. (2) Disperse 5 mg of the highly active platinum-based catalyst for formic acid electrooxidation supported on carbon black and commercial Pt / C catalyst into an isopropanol-Nafion mixed solution (1 mL of isopropanol and 0.02 mL of 0.5% Nafion solution mixed), and obtain a uniformly dispersed catalyst solution after ultrasonic treatment for 0.5 h; Take 5 μl of the catalyst solution and drop it on a glassy carbon electrode, and obtain a glassy carbon electrode modified with the catalyst after natural drying. Using the glassy carbon electrode modified with the catalyst as the working electrode, a graphite rod as the counter electrode, and a saturated calomel electrode as the reference electrode, 0.5 M H 2 SO 4 and 0.5 M HCOOH solutions as the reaction solutions, and perform cyclic voltammetry (CV) tests for formic acid oxidation reaction. The test results are shown in Figure 4 , Figure 5 and Table 1

[0030] Figure 4 is PtTe 2 @Pt core-shell nanosheets in 0.5 M H 2 SO 4 and 0.5 M HCOOH for FAOR cyclic voltammograms. It shows that PtTe 2@Pt has a relatively high current density at a low potential of 0.6 V (V vs RHE), and its reaction mainly follows the dehydrogenation reaction path. Commercial Pt / C has a current density at a high potential of 0.93 V (V vs RHE), and its reaction mainly follows the dehydration reaction path.

[0031] Figure 5 is PtTe 2 @Pt core-shell nanosheets and commercial Pt / C in 0.5 M H 2 SO 4 and stability curves in 0.5 M HCOOH. It shows that PtTe 2 @Pt catalysts are difficult to be dissolved by acidic solutions and mainly follow the dehydrogenation reaction path, thus improving the stability and CO tolerance of the catalysts.

[0032] Table 1 shows the mass activities of FAOR of Examples 1-10 and commercial Pt / C in 0.5 M H 2 SO 4 and 0.5 M HCOOH. The mass activities of Examples 1-10 are much higher than those of commercial Pt / C for FAOR, which is attributed to the morphological design of the core-shell two-dimensional nanosheet structure and the catalytic synergy between different crystal phases, optimizing the reaction path of FAOR and improving the reaction kinetics.

[0033]

[0034] The catalysts prepared in the examples and commercial Pt / C were tested for the performance of formic acid fuel cells. The instrument used was an 850e fuel cell test system. The proton exchange membrane used was a Nafion NR115 membrane, and the area of the membrane electrode test was 5 cm 2 , the catalyst was sprayed on the gas diffusion layer (carbon paper), and the loadings of the catalysts on the cathode and anode were 2 and 1 mg cm -2 (Pt) respectively. The cathode used a commercial platinum-carbon catalyst with a mass fraction of 40%, and the anode used a self-prepared high-activity platinum-based catalyst for formic acid electrooxidation supported on carbon black. For the commercial Pt / C test of formic acid fuel cells, except that the anode used commercial Pt / C, the other test methods were the same as those for the self-prepared catalysts. The test results are shown in Figure 6 and Table 2.

[0035] Figure 6 is PtTe 2 @Pt core-shell nanosheets in the polarization curve and power density curve of formic acid fuel cells. It can be seen from the figure that its open-circuit voltage is 0.66 V, and its maximum power density is 58.5 mW cm -2 .

[0036] Table 2 shows the power density of Examples 1-10 and commercial Pt / C in formic acid fuel cells (formic acid concentration is 9 M HCOOH). The power density of Examples 1-10 is much higher than that of commercial Pt / C, which is attributed to the catalytic synergy between different crystal phases promoting formic acid oxidation mainly through the dehydrogenation reaction path, significantly enhancing the performance of the catalyst in formic acid fuel cells.

[0037]

[0038] From the electrochemical performance test results of Examples 1-10 and commercial Pt / C, it can be concluded that the mixed-phase PtTe 2 @Pt core-shell nanosheets exhibit high mass activity and fuel cell power density in the formic acid electrooxidation reaction. This is mainly because the wet chemical method assisted by small molecule reducing agents can rapidly promote the dissolution of metal precursors while inhibiting the homogeneous nucleation of noble metals, thus forming a two-dimensional structure and promoting the edge epitaxial growth of platinum metal. This two-dimensional structure can expose more catalytic active sites, helping to accelerate the oxidation reaction of formic acid. The design of the platinum core-shell structure also ensures the structural stability of the catalyst under acidic conditions. The catalytic coordination of different crystal phases enables the regulation of the reaction path of formic acid oxidation, thereby enhancing the catalytic activity. The use of small molecule reducing agents effectively controls the diffusion and aggregation of platinum metal ions, and then regulates the number of active sites of Pt in the platinum telluride catalyst, which significantly improves the catalytic performance of the formic acid electrooxidation reaction (FAOR).

[0039] The role of the above examples is to illustrate the substantial content of the present invention, but does not limit the protection scope of the present invention. Those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the essence and protection scope of the technical solutions of the present invention.

Claims

1. A method for preparing a high-performance formic acid electro-oxidation platinum-based catalyst, characterized in that: The following steps are involved: Platinum acetylacetonate, a tellurium metal precursor, and a small molecule reducing agent are ultrasonically dissolved in ethylene glycol to obtain a mixed solution; in a closed environment, the mixed solution is placed in an oil bath and heated to obtain a suspension; the suspension is centrifugally washed and dried to obtain a mixed-phase PtTe2@Pt core-shell nanosheet catalyst powder, i.e., a high-performance formic acid electro-oxidation platinum-based catalyst.

2. The method for preparing a high-performance formic acid electro-oxidation platinum-based catalyst according to claim 1, characterized in that: The tellurium metal precursor is any one of sodium tellurite, potassium tellurite and telluric acid.

3. The method for preparing a high-performance formic acid electro-oxidation platinum-based catalyst according to claim 1, characterized in that: The small molecule reducing agent is any one of citric acid, sodium acetate, phloroglucinol and urea.

4. The method for preparing a high-performance formic acid electro-oxidation platinum-based catalyst according to claim 1, characterized in that: The molar ratio of the platinum acetylacetonate, the tellurium metal precursor and the small molecule reducing agent is 1:1-3:1-6.

5. The method for preparing a high-performance formic acid electro-oxidation platinum-based catalyst according to claim 1, characterized in that: The temperature of the oil bath heating is 150-200°C; the time of the oil bath heating is 1-12h.

6. An application of a high-performance formic acid electro-oxidation platinum-based catalyst prepared by the preparation method according to any one of claims 1 to 5, characterized in that: The high-performance formic acid electro-oxidation platinum-based catalyst is applied to the electro-catalytic formic acid oxidation reaction.

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