A porous cerium fluoride catalyst, its preparation method and use

Abstract

The application belongs to the technical field of fuel cells, and discloses a porous cerium fluoride catalyst, a preparation method and application thereof. The application adopts an impregnation method to synthesize a composite oxide precursor with silica as a template, obtains the composite oxide after calcination, and then adopts hydrofluoric acid etching and fluorination to prepare cerium fluoride. Finally, the porous cerium fluoride, a carrier, a platinum source aqueous solution and an alcohol solution are mixed to perform a hydrothermal reaction, and the porous cerium fluoride catalyst is obtained. The application etches away the template skeleton by using hydrofluoric acid to form a porous structure. The pore diameter of the cerium fluoride carrier is controlled by adjusting the concentration of the hydrofluoric acid, the specific surface area of the catalyst carrier is increased, more active sites are provided for the adsorption of platinum nanoparticles, the proton transmission speed is accelerated, the amount of noble metal is reduced, and the catalyst activity is improved.

Description

Technical Field

[0001] This invention relates to the field of fuel cell technology, and in particular to a porous cerium fluoride catalyst, its preparation method, and its application. Background Technology

[0002] Population growth and the increasing importance of science and technology have both led to a surge in energy demand.

[0003] Currently, electricity is primarily generated from fossil fuels, which has a negative impact on the environment, and the number of technology users reliant on electricity continues to increase. It was reported that nearly 6.2 billion tons of carbon dioxide were released into the atmosphere in 2000, with approximately 40% of that being emissions from electricity production. Therefore, researchers are encouraged to seek renewable and eco-friendly alternative energy sources. Recently, advancements in the field of direct methanol fuel cells (DAFCs) have become a trend among researchers and manufacturers seeking alternative fuels for generating electricity. The benefits of utilizing alcohol fuel cell technology include: biofriendliness, low cost, portability, and the high energy density of alcohols (such as methanol and ethanol). For example, direct methanol fuel cells (DMFCs) do not require charging, are cryogenically operable, have a long service life, and can be used in systems that can be quickly refueled. However, DMFCs still face challenges that need to be addressed. Problems encountered in DMFCs include high cost, methanol permeation through proton exchange membranes, and issues related to maintaining long-term stability and durability during operation. Therefore, solving these problems and developing highly active and stable anode catalysts are of great significance for the widespread application of DMFCs.

[0004] Cerium oxide has attracted considerable attention as a catalyst support, primarily due to its oxygen vacancies and variable valence (Ce). 4 + / Ce 3+ Therefore, cerium oxide can provide abundant OH- by storing and releasing oxygen. ads This effectively eliminates poisoning intermediates similar to CO. However, pure cerium dioxide has poor thermal stability at high temperatures and can sinter, leading to a loss of its crucial oxygen storage capacity and redox properties. Fluorination of cerium oxide can give it a porous structure, increasing its catalytic activity. Meanwhile, cerium fluoride (CeF3), as a composite component, exhibits reversible Ce... 3+ and Ce 4+Valence phase transitions have been used to optimize surface electronic states. CeF3, with its three strongly electronegative fluorine atoms (approximately 4.0), can serve as perfect electron acceptors, thereby further adjusting the electron distribution of the loaded noble metals. Currently, common fluorination methods include thermal decomposition of fluorides and acid fluorination. However, due to uneven heating during the fluoride heating process, the concentration of hydrogen fluoride gas produced is insufficient to meet the purity requirements for fluorination, resulting in incomplete reaction with cerium oxide. Only a portion of the reaction occurs on the surface, leading to insufficient crystallinity and a small specific surface area in the prepared cerium fluoride. Therefore, optimizing the preparation process of cerium fluoride is an urgent problem to be solved. Summary of the Invention

[0005] The purpose of this invention is to provide a porous cerium fluoride catalyst, its preparation method, and its application, thereby solving the aforementioned problems of existing anode catalysts in fuel cells.

[0006] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0007] This invention provides a method for preparing a porous cerium fluoride catalyst, comprising the following steps:

[0008] Cerium salt, dicyandiamide, silicon dioxide, and water are mixed, and then heated to evaporate the water to obtain a composite precursor; the composite precursor is calcined to obtain a composite oxide.

[0009] The composite oxide was etched in hydrofluoric acid to obtain porous cerium fluoride;

[0010] Porous cerium fluoride, a support, an aqueous solution of a platinum source, and an alcohol solution are mixed and then subjected to a hydrothermal reaction to obtain a porous cerium fluoride catalyst.

[0011] Preferably, in the above-mentioned method for preparing a porous cerium fluoride catalyst, the mass ratio of the cerium salt, dicyandiamide, and silicon dioxide is 1-10:1-5:1-10.

[0012] Preferably, in the above-mentioned method for preparing a porous cerium fluoride catalyst, the mixing process of the cerium salt, dicyandiamide, silica, and water further includes stirring; the stirring time is 12 to 72 hours; and the stirring speed is 300 to 1600 rpm.

[0013] Preferably, in the above-mentioned method for preparing a porous cerium fluoride catalyst, the calcination temperature is 360–750°C, and the calcination time is 4–12 h.

[0014] Preferably, in the above-mentioned method for preparing a porous cerium fluoride catalyst, the concentration of hydrofluoric acid is 1-10 mol / L; the etching temperature is 10-40℃; and the etching time is 1-3 h.

[0015] Preferably, in the above-mentioned method for preparing a porous cerium fluoride catalyst, the ratio of the amount of porous cerium fluoride, support, platinum source aqueous solution, and alcohol solution is 1-100g: 10-100g: 1-30L: 1-100L.

[0016] Preferably, in the above-mentioned method for preparing a porous cerium fluoride catalyst, the concentration of the platinum source aqueous solution is 0.01-0.2 mol / L; the platinum source in the platinum source aqueous solution is one of chloroplatinic acid, potassium chloroplatinate, sodium chloroplatinate, and platinum acetylacetonate.

[0017] Preferably, in the above-mentioned method for preparing a porous cerium fluoride catalyst, the temperature of the hydrothermal reaction is 120–150°C, and the time of the hydrothermal reaction is 1–4 h.

[0018] The present invention also provides a method for preparing a porous cerium fluoride catalyst, which yields a porous cerium fluoride catalyst.

[0019] The present invention also provides an application of porous cerium fluoride catalyst in fuel cells.

[0020] As can be seen from the above technical solution, compared with the prior art, the present invention has the following beneficial effects:

[0021] (1) This invention uses an impregnation method to synthesize a composite oxide precursor, and then uses hydrofluoric acid etching to prepare cerium fluoride. The advantage is that the concentration of hydrofluoric acid is easy to control, and the pore size of the cerium fluoride support can be controlled by adjusting the concentration of hydrofluoric acid, thus allowing it to be applied to different catalytic environments. Furthermore, this invention uses silica as a template, coats cerium dioxide on its surface, and finally uses hydrofluoric acid to etch away the template framework, forming a porous structure. This increases the specific surface area of ​​the catalyst support, providing more active sites for the adsorption of platinum and other noble metal nanoparticles, accelerating proton transport, and improving catalyst activity while reducing the amount of noble metal used.

[0022] (2) The catalyst preparation method of the present invention is simple, has low process requirements, and is suitable for large-scale application. Attached Figure Description

[0023] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below.

[0024] Figure 1 X-ray diffraction patterns of the catalysts prepared in Example 1 and Comparative Example 1;

[0025] Figure 2The images shown are transmission electron microscope (TEM) images and EDS spectra of porous cerium fluoride prepared in Example 1; where a) is a bright-field TEM image, b) is a dark-field TEM image, c) is a high-resolution TEM image, d) is a magnified TEM image with a scale bar of 200 nm, e) is a high-angle annular dark-field image, f) is the EDS spectrum of Ce, g) is the EDS spectrum of F, h) is the EDS spectrum of O, and i) is the EDS spectrum of Si.

[0026] Figure 3 ECSA diagrams of the catalysts prepared in Example 1 and Comparative Example 1;

[0027] Figure 4 Impedance diagrams of the catalysts prepared in Example 1 and Comparative Example 1;

[0028] Figure 5 The graphs show the stability test results of the catalysts prepared in Example 1 and Comparative Example 1. Detailed Implementation

[0029] This invention provides a method for preparing a porous cerium fluoride catalyst, comprising the following steps:

[0030] Cerium salt, dicyandiamide, silicon dioxide, and water are mixed, and then heated to evaporate the water to obtain a composite precursor; the composite precursor is calcined to obtain a composite oxide.

[0031] The composite oxide was etched in hydrofluoric acid to obtain porous cerium fluoride;

[0032] Porous cerium fluoride, a support, an aqueous solution of a platinum source, and an alcohol solution are mixed and then subjected to a hydrothermal reaction to obtain a porous cerium fluoride catalyst.

[0033] In this invention, the cerium salt is preferably cerium nitrate.

[0034] In this invention, the mass ratio of cerium salt, dicyandiamide, and silicon dioxide is preferably 1-10:1-5:1-10, more preferably 1-5:1-2:1-4, and even more preferably 1:1.1:2.

[0035] In this invention, the preferred ratio of silicon dioxide to water is 1-10g:1-100mL, more preferably 1-3g:10-50mL, and even more preferably 1g:12.5mL.

[0036] In this invention, the mixing process of cerium salt, dicyandiamide, silicon dioxide, and water also includes stirring; the stirring time is preferably 12-72 hours, more preferably 14-24 hours, and even more preferably 15 hours; the stirring speed is preferably 300-1600 rpm, more preferably 800-1600 rpm, and even more preferably 1600 rpm.

[0037] In this invention, the heating temperature is preferably 90-150°C, more preferably 100-140°C, and even more preferably 120°C; the heating time is preferably 2-5 hours, more preferably 4-5 hours, and even more preferably 5 hours.

[0038] In this invention, the roasting temperature is preferably 360-750°C, more preferably 650-750°C, and even more preferably 750°C; the roasting time is preferably 4-12 hours, more preferably 5-10 hours, and even more preferably 6 hours.

[0039] In this invention, the concentration of hydrofluoric acid is preferably 1-10 mol / L, more preferably 2-5 mol / L, and even more preferably 2 mol / L; the etching temperature is preferably 10-40°C, more preferably 20-30°C, and even more preferably 25°C; the etching time is preferably 1-3 h, more preferably 2-3 h, and even more preferably 3 h.

[0040] In this invention, the preferred ratio of the composite oxide to hydrofluoric acid is 1-100g:1-100L, more preferably 10-60g:10-30L, and even more preferably 50g:20L.

[0041] In this invention, the etching process also includes stirring; the stirring speed is preferably 400 rpm.

[0042] In this invention, the carrier is preferably one of a carbon source, a metal carbide, a nitride, a chloride, or a hydroxide, more preferably a carbon source or a metal carbide, and even more preferably graphene.

[0043] In this invention, the alcohol solution is preferably ethylene glycol, methanol or ethanol, more preferably ethylene glycol or methanol, and even more preferably ethylene glycol.

[0044] In this invention, the preferred ratio of the porous cerium fluoride, the support, the platinum source aqueous solution, and the alcohol solution is 1-100g:10-100g:1-30L:1-100L, more preferably 50-100g:60-100g:5-20L:40-70L, and even more preferably 100g:100g:10L:50L.

[0045] In this invention, the concentration of the platinum source aqueous solution is preferably 0.01-0.2 mol / L, more preferably 0.03-0.1 mol / L, and even more preferably 0.05 mol / L; the platinum source in the platinum source aqueous solution is preferably one of chloroplatinic acid, potassium chloroplatinate, sodium chloroplatinate, and platinum acetylacetonate, more preferably one of chloroplatinic acid, potassium chloroplatinate, and sodium chloroplatinate, and even more preferably chloroplatinic acid.

[0046] In this invention, the method of mixing the porous cerium fluoride, the support, the platinum source aqueous solution, and the alcohol solution is preferably to first sonicate and then stir; the frequency of the sonication is preferably 15-50 kHz, more preferably 20-40 kHz, and even more preferably 30 kHz; the duration of the sonication is preferably 10-100 min, more preferably 60-90 min, and even more preferably 80 min; the stirring speed is preferably 800 rpm; and the stirring time is preferably 1-5 h, more preferably 2-4 h, and even more preferably 3 h.

[0047] In this invention, the temperature of the hydrothermal reaction is preferably 120-150°C, more preferably 125-140°C, and even more preferably 130°C; the time of the hydrothermal reaction is preferably 1-4 hours, more preferably 2-4 hours, and even more preferably 2 hours.

[0048] In this invention, after the hydrothermal reaction is completed, the process further includes filtration and vacuum drying; the filtration pressure is preferably 0.05-0.09 MPa, more preferably 0.06-0.09 MPa, and even more preferably 0.09 MPa; the filtration time is preferably 1-8 h, more preferably 2-5 h, and even more preferably 3 h; the vacuum drying temperature is preferably 40-80 °C, more preferably 50-70 °C, and even more preferably 60 °C; the vacuum drying time is preferably 2-8 h, more preferably 3-6 h, and even more preferably 4 h.

[0049] The present invention also provides a method for preparing a porous cerium fluoride catalyst, which yields a porous cerium fluoride catalyst.

[0050] The present invention also provides an application of porous cerium fluoride catalyst in fuel cells.

[0051] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0052] Example 1

[0053] This embodiment provides a porous cerium fluoride catalyst, the preparation method of which includes the following steps:

[0054] Weigh 53.97g of cerium nitrate, 60g of dicyandiamide, and 120g of silicon dioxide, dissolve them in 1.5L of water, and stir at 800rpm for 18h to form a yellow solution. Evaporate at 120℃ for 4h, then calcine in a muffle furnace at 750℃ for 6h to obtain a composite oxide. Etch 50g of the composite oxide in 10L of 2mol / L hydrofluoric acid solution at 26℃ with stirring at 400rpm for 3h, then filter, wash, and dry to obtain porous cerium fluoride. Add 5g... Porous cerium fluoride, 10 L of 0.05 mol / L chloroplatinic acid solution, 100 g of graphene, and 50 L of ethylene glycol solution were mixed and sonicated at 30 kHz for 80 min, then stirred at 800 rpm for 3 h. The mixture was then placed in a reactor and hydrothermally reacted at 130 °C for 2 h to obtain a black turbid liquid. The liquid was then vacuum filtered at a pump pressure of 0.09 MPa for 3 h and then vacuum dried at 60 °C for 4 h to obtain a porous cerium fluoride catalyst, denoted as Pt-CeO2-KS / RGO.

[0055] The catalyst prepared in this example was subjected to electrochemical performance testing. After the addition of this catalyst, the peak current density for electrocatalytic methanol reached 1500 A / g. Pt .

[0056] Comparative Example 1

[0057] This comparative example provides a cerium oxide catalyst, as detailed in Example 1. The difference is that the composite oxide is not etched with hydrofluoric acid solution, and the final cerium oxide catalyst is denoted as Pt-CeO2 / RGO.

[0058] The catalysts prepared in Example 1 and Comparative Example 1 were subjected to X-ray diffraction analysis, and the results are as follows: Figure 1 As shown. From Figure 1 As can be seen from the data, the Pt in the catalyst of Example 1 has a face-centered cubic structure, and in addition to the Pt peak, there is also a significant cerium fluoride peak. Figure 1 It can also be seen that the crystallinity of the etched cerium fluoride supported catalyst is higher than that of pure cerium oxide.

[0059] The porous cerium fluoride prepared in Example 1 was observed under a transmission electron microscope, and the results are as follows: Figure 2 As shown. By Figure 2As can be seen, the obtained materials mainly consist of nanorods and nanospheres, with the nanospheres uniformly encapsulating the nanorods. Energy dispersive spectroscopy (EDS) analysis shows that the obtained materials are all cerium fluoride with smooth surfaces. The nanorods exhibit a hollow and transparent structure, which is due to the formation of a hollow nanorod structure with a large number of particles formed by HF etching and rapid reconstruction of metal fluorides, thereby increasing the electrochemical surface area and exposing more active sites. EDS surface scanning results show that F and Ce elements are uniformly distributed on the nanorods and nanospheres, proving that hydrofluoric acid successfully etched away the silicon oxide template and cerium oxide, and cerium fluoride was successfully prepared.

[0060] The catalysts prepared in Example 1 and Comparative Example 1 were subjected to ECSA testing, impedance testing, and stability testing. The results are as follows: Figures 3-5 As shown. By Figure 3 The electrochemical active area diagram of the catalysts shows that the porous cerium fluoride-supported platinum catalyst has the highest electrochemical active area. A larger area indicates more active sites on the catalyst, thus resulting in higher methanol catalytic performance. Figure 4 Impedance spectra showed that the porous cerium fluoride-supported platinum catalyst had the smallest impedance arc. This is because the introduction of fluoride ions reduced the impedance arc, indicating improved charge transfer efficiency and enhanced catalyst conductivity. Figure 5 The stability test spectra show that the current gradually decreases with increasing time, and the rate of current decrease is relatively rapid in the initial stage. This is attributed to the poisoning of Pt active sites by intermediate toxic species generated during the electrochemical process, which are difficult to release, leading to a rapid drop in current. However, after 600 s, the rate of current decrease in the catalyst samples tends to slow down, and the porous cerium fluoride-supported platinum catalyst exhibits the smallest rate of current decrease, indicating that the porous cerium fluoride-supported platinum catalyst has the best stability.

[0061] Example 2

[0062] This embodiment provides a porous cerium fluoride catalyst, the preparation method of which includes the following steps:

[0063] Weigh out 80g of cerium nitrate, 40g of dicyandiamide, and 160g of silicon dioxide, dissolve them in 4L of water, and stir at 600rpm for 12h to form a yellow solution. Evaporate at 120℃ for 5h, then calcine in a muffle furnace at 650℃ for 4h to obtain a composite oxide. Place 70g of the composite oxide in a 10L... Cerium fluoride was etched in a 5 mol / L hydrofluoric acid solution at 30 °C for 2 h with stirring at 400 rpm, then filtered, washed, and dried to obtain porous cerium fluoride. 20 g of porous cerium fluoride, 5 L of 0.02 mol / L chloroplatinic acid solution, 70 g of graphene, and 10 L of ethylene glycol solution were mixed, sonicated at 20 kHz for 30 min, and stirred at 800 rpm for 3 h. The mixture was then placed in a reactor and hydrothermally reacted at 120 °C for 2 h to obtain a black turbid liquid. The liquid was then vacuum filtered at a pump pressure of 0.09 MPa for 2 h and then vacuum dried at 60 °C for 8 h to obtain a porous cerium fluoride catalyst.

[0064] The catalyst prepared in this example was subjected to electrochemical performance testing. After the addition of this catalyst, the peak current density for electrocatalytic methanol reached 1600 A / g. Pt .

[0065] Example 3

[0066] This embodiment provides a porous cerium fluoride catalyst, the preparation method of which includes the following steps:

[0067] Weigh 100g of cerium nitrate, 100g of dicyandiamide, and 100g of silicon dioxide, dissolve them in 3L of water, and stir at 1100rpm for 24h to form a yellow solution. Evaporate at 120℃ for 5h, then calcine in a muffle furnace at 700℃ for 6h to obtain a composite oxide. Etch 100g of the composite oxide in 15L of 7mol / L hydrofluoric acid solution at 30℃ with stirring at 400rpm for 3h, then filter, wash, and dry to obtain... Porous cerium fluoride: 50g of porous cerium fluoride, 10L of 0.1mol / L chloroplatinic acid solution, 50g of graphene, and 20L of ethylene glycol solution were mixed and sonicated at 30KHz for 60min, then stirred at 800rpm for 3h. The mixture was then placed in a reactor and hydrothermally reacted at 140℃ for 2h to obtain a black turbid liquid. The liquid was then vacuum filtered at a pump pressure of 0.09MPa for 5h and then vacuum dried at 60℃ for 6h to obtain the porous cerium fluoride catalyst.

[0068] The catalyst prepared in this example was subjected to electrochemical performance testing. After the addition of this catalyst, the peak current density for electrocatalytic methanol reached 1700 A / g. Pt .

[0069] Example 4

[0070] This embodiment provides a porous cerium fluoride catalyst, the preparation method of which includes the following steps:

[0071] Weigh out 60g of cerium nitrate, 120g of dicyandiamide, and 180g of silicon dioxide, dissolve them in 1.2L of water, and stir at 1600rpm for 15h to form a yellow solution. Evaporate the solution at 120℃ for 5h, then calcine it in a muffle furnace at 750℃ for 8h to obtain a composite oxide. Etch 100g of the composite oxide in 20L of 6mol / L hydrofluoric acid solution at 30℃ with stirring at 400rpm for 3h, then filter, wash, and dry to obtain a multi-component composite oxide. Porous cerium fluoride: 80g of porous cerium fluoride, 30L of 0.08mol / L chloroplatinic acid solution, 60g of graphene, and 30L of ethylene glycol solution were mixed and sonicated at 50KHz for 100min, then stirred at 800rpm for 3h. The mixture was then placed in a reactor and hydrothermally reacted at 150℃ for 4h to obtain a black turbid liquid. The liquid was then vacuum filtered at a pump pressure of 0.09MPa for 4h and then vacuum dried at 60℃ for 8h to obtain the porous cerium fluoride catalyst.

[0072] The catalyst prepared in this example was subjected to electrochemical performance testing. After the addition of this catalyst, the peak current density for electrocatalytic methanol reached 1870 A / g. Pt .

[0073] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a porous cerium fluoride catalyst, characterized in that, Includes the following steps: Cerium salt, dicyandiamide, silicon dioxide and water are mixed and then heated to evaporate the water to obtain a composite precursor; the composite precursor is calcined to obtain a composite oxide. The composite oxide was etched in hydrofluoric acid to obtain porous cerium fluoride; the cerium fluoride was CeF3. Porous cerium fluoride, a support, an aqueous solution of a platinum source, and an alcohol solution are mixed and then subjected to a hydrothermal reaction to obtain a porous cerium fluoride catalyst. The roasting temperature is 360~750℃; the roasting time is 4~12h; The hydrothermal reaction temperature is 120~150℃; the hydrothermal reaction time is 1~4h.

2. The method for preparing a porous cerium fluoride catalyst according to claim 1, characterized in that, The mass ratio of the cerium salt, dicyandiamide, and silicon dioxide is 1~10:1~5:1~10.

3. The method for preparing a porous cerium fluoride catalyst according to claim 2, characterized in that, The mixing process of cerium salt, dicyandiamide, silica and water also includes stirring; the stirring time is 12~72h; the stirring speed is 300~1600rpm.

4. The method for preparing a porous cerium fluoride catalyst according to claim 1, characterized in that, The concentration of the hydrofluoric acid is 1~10 mol / L; the etching temperature is 10~40℃; and the etching time is 1~3h.

5. The method for preparing a porous cerium fluoride catalyst according to claim 3, characterized in that, The ratio of the porous cerium fluoride, the support, the platinum source aqueous solution, and the alcohol solution is 1~100g: 10~100g: 1~30L: 1~100L.

6. The method for preparing a porous cerium fluoride catalyst according to claim 5, characterized in that, The concentration of the platinum source aqueous solution is 0.01~0.2 mol / L; the platinum source in the platinum source aqueous solution is one of chloroplatinic acid, potassium chloroplatinate, sodium chloroplatinate, and platinum acetylacetonate.

7. A porous cerium fluoride catalyst prepared by the method of any one of claims 1 to 6.

8. The application of the porous cerium fluoride catalyst according to claim 7 in a fuel cell.

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