Fuel cell low-platinum catalyst and preparation method and application thereof

Abstract

The invention discloses a fuel cell low-platinum catalyst and a preparation method and application thereof.The preparation method comprises the steps that firstly, a carbon carrier is subjected to fluoridation treatment, a carbon material and a fluorine-containing organic precursor are subjected to ball milling and mixing, then fluoridation is conducted at the high temperature under the vacuum packaging condition, washing and drying are conducted, and a fluorine-doped carbon carrier is obtained; and then mixing the fluorine-doped carbon carrier with a platinum precursor, a cobalt precursor and a lanthanide series metal precursor in a solvent, drying, and sequentially carrying out heat treatment and acid pickling under the conditions of inert atmosphere, vacuum and reducing atmosphere to obtain the PtCoM-CF catalyst, in which M is a lanthanide series metal element. The catalyst prepared by the method has relatively high platinum utilization efficiency and excellent hydrogen oxidation reaction and oxygen reduction reaction electro-catalytic performance, and is suitable for a cathode and anode catalyst of a proton exchange membrane fuel cell.

Description

Technical Field

[0001] This invention belongs to the field of fuel cell catalyst technology, specifically relating to a low-platinum catalyst for fuel cells, its preparation method, and its application. Background Technology

[0002] Proton exchange membrane fuel cells (PEMFCs) are a zero-emission power generation technology that directly converts the chemical energy of hydrogen into electrical energy. Their commercialization heavily relies on the use of the precious metal platinum to catalyze efficient and stable anode and cathode reactions. For example, in Toyota's Mirai fuel cell passenger vehicle, up to 36 grams of platinum are used per vehicle. However, to promote the sustainable development of fuel cell technology in the passenger vehicle market, the amount of platinum used needs to be controlled to be comparable to that of catalytic converters for internal combustion engine exhaust gases (2-8 grams of platinum per vehicle). Typically, the mass activity of a fuel cell catalyst is determined by the product of its specific activity and electrochemical surface area. In this regard, attempts have been made to increase the specific activity by reducing the platinum loading on the carbon support to decrease the size of platinum nanoparticles. However, this results in insufficient exposed active sites, necessitating an increase in catalyst layer thickness to compensate for these sites. This leads to increased mass transfer resistance and is also detrimental to reactant delivery and product removal. Furthermore, reducing the size of platinum particles introduces stability issues, making them prone to significant size increases through physical sintering and Oswald curing processes. This results in a loss of electrochemical surface area and mass activity, as well as poor durability. This, in turn, shortens the lifespan of the fuel cell power generation system, resulting in excessively high costs that put it at a disadvantage in market competition with internal combustion engines and lithium batteries.

[0003] Therefore, in order to obtain low-platinum catalysts for fuel cells with high durability, it is urgent to provide a supported, high-density, small-size platinum-based catalyst that can efficiently catalyze the anode hydrogenation reaction and the cathode oxygen reduction reaction of fuel cells, so that it meets the requirements of thin catalyst layer and high accessibility of active sites in fuel cell applications, and is doped with transition metals and lanthanides. Summary of the Invention

[0004] The purpose of this section is to outline some aspects of embodiments of the present invention and to briefly describe some preferred embodiments. Simplifications or omissions may be made in this section, as well as in the abstract and title of this application, to avoid obscuring the purpose of these documents; however, such simplifications or omissions should not be construed as limiting the scope of the invention.

[0005] In view of the problems existing in the above and / or prior art, the present invention is proposed.

[0006] Therefore, the purpose of this invention is to overcome the shortcomings of the prior art and provide a low-platinum catalyst for fuel cells, its preparation method, and its application.

[0007] To solve the above-mentioned technical problems, the present invention provides the following technical solution: a method for preparing a low-platinum catalyst for fuel cells, comprising, Fluorination of a carbon support yields a fluorinated carbon support. A low-platinum catalyst for fuel cells is obtained by mixing, drying, heat treatment, acid washing, and reduction of fluorine-doped carbon support with platinum-containing precursors, cobalt-containing precursors, and lanthanide-containing precursors. The carbon support is Ketjen black, the fluorinated precursor is tetrafluoroterephthalic acid, the platinum-containing precursor is platinum acetylacetonate, the cobalt-containing precursor is cobalt acetylacetonate, and the lanthanide elements include one of lutetium acetylacetonate and lanthanum acetylacetonate.

[0008] As a preferred embodiment of the preparation method of the present invention, the preparation method of the fluorine-doped carbon support includes: ball milling Ketjen black carbon support and tetrafluoroterephthalic acid; vacuum encapsulating the milled material for fluorination; and solvent washing and vacuum drying of the fluorinated material.

[0009] As a preferred embodiment of the preparation method described in this invention, the ball milling speed is 350~600 rpm, the ball milling is performed for 20~40 revolutions, each revolution is run for 3 minutes and then stopped for 7 minutes to cool down; the grinding balls are stainless steel balls with a diameter of 2~5 mm, and the mass ratio of grinding balls, carbon carrier and tetrafluoroterephthalic acid is 30~60 g:1.5~3 g:0.3~1 g.

[0010] In a preferred embodiment of the preparation method described in this invention, the fluorination is followed by washing with ethanol and then vacuum drying.

[0011] In a preferred embodiment of the preparation method described in this invention, the mass ratio of the fluorine-doped carbon support to the platinum-containing precursor, the cobalt-containing precursor, and the lanthanide-containing precursor is 1:0.8~1.6:0.~1.38:0.2~0.3.

[0012] In a preferred embodiment of the preparation method described in this invention, the ultrasonic time is 20-40 minutes, and the rotary evaporation is carried out at room temperature.

[0013] As a preferred embodiment of the preparation method of the present invention, the atmosphere treatment conditions are a heating rate of 2~10 ℃ / min.

[0014] Another objective of this invention is to overcome the shortcomings of the prior art and provide a low-platinum catalyst for fuel cells prepared by a specific method.

[0015] As a preferred embodiment of the low-platinum catalyst for fuel cells described in this invention, the platinum loading is 20.24~65.68 wt%.

[0016] Another objective of this invention is to overcome the shortcomings of the prior art and provide an application of a low-platinum catalyst for fuel cells: an anode and cathode catalyst for proton exchange membrane fuel cells.

[0017] Beneficial effects of this invention: The method for synthesizing low-platinum catalysts for fuel cells developed in this invention can achieve doping with all lanthanide elements, has universality, and is easy to scale up, showing potential for large-scale production. It can be used in anode and cathode reactions, and outperforms commercially available platinum-carbon catalysts in electrochemical and fuel cell testing, demonstrating potential for market application. While ensuring high metal content loading, it also ensures extremely small particle size, which helps to fully utilize the precious metal platinum, enabling it to achieve extremely high performance output as an ultrathin catalyst layer in the fuel cell membrane electrode assembly, while also exhibiting excellent durability, meeting the development goals for low-platinum catalysts for fuel cells set by the U.S. Department of Energy. Attached Figure Description

[0018] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. Wherein: Figure 1 The fuel cell catalyst PtCoM@C prepared in the embodiments of the present invention F TEM image.

[0019] Figure 2 PtCoM@C is an embodiment of the present invention. F (M is selected from at least one of La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb or Lu) Linear sweep voltammetric curves of the hydrogenation reaction of the catalyst (solid and dashed lines were obtained from tests in pure hydrogen and hydrogen containing 100 ppm carbon monoxide impurities, respectively).

[0020] Figure 3 PtCoM@C is an embodiment of the present invention. F (M is selected from at least one of La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb or Lu) Linear sweep voltammetric curves of oxygen reduction reaction of catalyst.

[0021] Figure 4 PtCoLu@C is used in embodiments of the present invention. F IV curves of fuel cells assembled as anode and cathode catalysts respectively (red line represents initial performance, black line represents performance after accelerated durability test). Detailed Implementation

[0022] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the examples in the specification.

[0023] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0024] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in different places in this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that is mutually exclusive with other embodiments.

[0025] Unless otherwise specified, all raw materials used in the embodiments of this invention are commercially available. See Table 1 for details.

[0026] Table 1

[0027] Example 1 (1) Fluorination treatment of carbon support: First, the precursor was mixed using a ball mill (Pulverisette 7, Fritsch). 2g of Ketjen Black EC-600JD, 0.5g of tetrafluoroterephthalic acid, and 45g of stainless steel grinding balls (2mm diameter) were placed in an 80ml stainless steel grinding bowl. The ball mill was run for 30 revolutions at 450rpm (3min per revolution, followed by 7min of cooling). The ground material was then loaded into a quartz tube and vacuum-sealed using a vacuum sealing machine. The sealed material was then placed in a tube furnace for high-temperature fluorination (500℃, 2h). Finally, the material was removed from the vacuum quartz tube, washed multiple times with ethanol, and then vacuum-dried (60℃) to obtain the fluorine-doped carbon support, denoted as C. F .

[0028] (2) PtCoLu@C F Catalyst preparation: 50 mg of fluorine-doped carbon support (C) was used. F66 mg of platinum acetylacetone, 53 mg of cobalt acetylacetone, 25 mg of lutetium acetylacetone, and 10 ml of acetone were ultrasonically mixed in a 50 ml reagent bottle for 20 min. The acetone solvent was then removed using a rotary evaporator at room temperature, and the resulting material was vacuum dried at 60°C for 6 h. Subsequently, it was placed in a tube furnace and heated to 230°C at a rate of 5°C / min in an argon (Ar) atmosphere, held for 8 h, and then cooled to room temperature. The furnace was then switched to a vacuum environment and rapidly heated to 350°C, held for 30 min, and then cooled to room temperature before the sample was removed. The sample was then acid-washed with 60 mM dilute sulfuric acid in a nitrogen atmosphere (80°C, 10 h), followed by water washing and vacuum drying. Finally, the resulting sample was placed in a tube furnace and heated to 200°C at a rate of 5°C / min in a 10% H₂ / Ar mixed atmosphere, held for 1 h, and then cooled to room temperature before the sample was removed and denoted as PtCoLu@C. F The platinum loading on the fluorine-doped carbon support was 30.24 wt%.

[0029] Example 2 The difference from Example 1 is that in step (2), lutetium acetylacetone is replaced with lanthanum acetylacetone; otherwise, the results are the same as in Example 1, yielding PtCoLa@C. F .

[0030] Comparative Example 1 The difference from Example 1 is that in step (2), lutetium acetylacetone is replaced with cerium acetylacetone; otherwise, the results are the same as in Example 1, yielding PtCoCe@C. F .

[0031] Comparative Example 2 The difference from Example 1 is that in step (2), lutetium acetylacetone is replaced with praseodymium acetylacetone; otherwise, it is the same as Example 1, yielding PtCoPr@C. F .

[0032] Comparative Example 3 The difference from Example 1 is that in step (2), lutetium acetylacetone is replaced with neodymium acetylacetone; otherwise, it is the same as Example 1, yielding PtCoNd@C. F .

[0033] Comparative Example 4 The difference from Example 1 is that in step (2), lutetium acetylacetone is replaced with samarium acetylacetone; otherwise, it is the same as Example 1, yielding PtCoSm@C. F .

[0034] Comparative Example 5 The difference from Example 1 is that in step (2), lutetium acetylacetone is replaced with europium acetylacetone; otherwise, it is the same as Example 1, yielding PtCoEu@C.F .

[0035] Comparative Example 6 The difference from Example 1 is that in step (2), lutetium acetylacetone is replaced with gadolinium acetylacetone; otherwise, it is the same as Example 1, yielding PtCoGd@C. F .

[0036] Comparative Example 7 The difference from Example 1 is that in step (2), lutetium acetylacetone is replaced with terbium acetylacetone; otherwise, it is the same as Example 1, yielding PtCoTb@C. F .

[0037] Comparative Example 8 The difference from Example 1 is that in step (2), lutetium acetylacetone is replaced with dysprosium acetylacetone; otherwise, it is the same as Example 1, yielding PtCoDy@C. F .

[0038] Comparative Example 9 The difference from Example 1 is that in step (2), lutetium acetylacetone is replaced with holmium acetylacetone; otherwise, it is the same as in Example 1, yielding PtCoHo@C. F .

[0039] Comparative Example 10 The difference from Example 1 is that in step (2), lutetium acetylacetone is replaced with erbium acetylacetone; otherwise, it is the same as Example 1, yielding PtCoEr@C. F .

[0040] Comparative Example 11 The difference from Example 1 is that in step (2), lutetium acetylacetone is replaced with thulium acetylacetone; otherwise, it is the same as Example 1, yielding PtCoTm@C. F .

[0041] Comparative Example 12 The difference from Example 1 is that in step (2), lutetium acetylacetone is replaced with ytterbium acetylacetone; otherwise, it is the same as Example 1, yielding PtCoYb@C. F .

[0042] Electrochemical performance testing: The test was conducted in a five-cell electrolytic cell using a rotating disk electrode apparatus. 2 mg of catalyst was weighed and mixed with 470 μL of isopropanol, 500 μL of water, and 30 μL of 5% Nafion. The mixture was sonicated for 10 min to obtain catalyst ink. This ink was then drop-coated onto the disk electrode as the working electrode, with Hg / HgO as the reference electrode and a graphite rod as the counter electrode. Activation was performed in 0.1 M perchloric acid electrolyte using cyclic voltammetry. Linear sweep voltammetry was then used for testing.

[0043] Fuel cell battery testing: The obtained catalyst was ultrasonically mixed with Nafion, isopropanol, and water in an ice bath for 1 h to obtain catalyst ink. The ink was then sprayed onto a Gore proton exchange membrane (12 μm; active area, 5 cm²). 2 The catalyst loadings at the anode and cathode were 0.02 and 0.08 mg, respectively. Pt cm -2 (Catalyst-coated membrane). The actual loading was determined by weighing the membrane before and after coating.

[0044] Fuel cell testing was conducted on a Scribner 850g. A membrane assembly (MEA) was prepared by assembling two gas diffusion layers (205 μm thick with microporous carbon layers), two gaskets (150 μm thick PTFE layers), and a catalyst-coated membrane. The MEA was sandwiched between two graphite plates. A 5 cm... 2 The single-channel plate was used for testing. Pure hydrogen and air were supplied to the anode and cathode at gas flow rates of 132 and 420 sccm, respectively. The membrane electrode was activated by cycling between 0.75 V and 0.35 V under hydrogen-air conditions until a stable current was obtained (80°C, 100% relative humidity). Polarization profiles were tested at 94°C, 100% relative humidity. Accelerated durability testing was performed by cycling potentials between 0.60 V and 0.95 V (each point held for 3 seconds, hydrogen and nitrogen flow rates both 100 sccm).

[0045] like Figure 1 As shown: the prepared PtCoM@C F The catalyst particles are small, uniformly distributed, and dense, with no agglomeration. For example... Figure 2 As shown, the hydrogen oxidation activity of the catalyst was tested in pure hydrogen (solid line) and hydrogen containing 100 ppm carbon monoxide (dashed line), respectively. The results showed that PtCoLu had the best resistance to carbon monoxide poisoning, with a current decay of only 3.97% at 50 mV overpotential. Figure 3 As shown, the oxygen reduction reaction activity of the catalyst was tested in an oxygen atmosphere, and the results showed that PtCoLu@C F The half-wave potential is the most positive, indicating that its reactivity is the highest; while PtCoLa@C F Its oxygen reduction reactivity is also excellent, second only to PtCoLu@C. F .like Figure 4 As shown, using PtCoLu@C F The catalysts were used as the anodic hydrogenation catalyst and the cathode oxygen reduction catalyst in a proton exchange membrane fuel cell, respectively. The assembled fuel cell output 1.09 W / cm² at a voltage of 0.67 V.2 It has a high power density and good durability.

[0046] This invention is the first to propose the construction of a fluorine-doped carbon support by solid-phase fluorination of tetrafluoroterephthalic acid in a closed space, and the formation of a ternary synergistic catalytic interface with PtCo alloy and lanthanide elements. This achieves high activity and long-term stability of hydrogen hydroxide reaction and oxygen reduction reaction under low platinum content conditions, which is significantly better than the existing Pt-based or PtCo system, and has outstanding innovation and practical value.

[0047] This invention involved systematic raw material screening and condition optimization, and a systematic comparative study on the effects of lanthanide doping on catalyst performance, including 14 elements: La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu. Through comparison using the same preparation route and testing conditions, the alkaline hydroxide reaction (HOR) and oxygen reduction reaction (ORR) activity data of each doped system were obtained, confirming that different lanthanide dopings have significant differences in catalytic performance. Among them, the Lu-doped system (PtCoLu@C...)... F The system exhibited the highest HOR activity and excellent ORR performance, while some doped systems (such as Tb, Eu, Ho, etc.) showed relatively lower performance, forming a clear performance hierarchy. Ultimately, Lu doping was chosen.

[0048] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the present invention.

Claims

1. A method for preparing a low-platinum catalyst for fuel cells, characterized in that: include, Fluorination of a carbon support yields a fluorinated carbon support. A low-platinum catalyst for fuel cells is obtained by mixing, drying, heat treatment, acid washing, and reduction of fluorine-doped carbon support with platinum-containing precursors, cobalt-containing precursors, and lanthanide-containing precursors. The carbon support is Ketjen black, the fluorinated precursor is tetrafluoroterephthalic acid, the platinum-containing precursor is platinum acetylacetonate, the cobalt-containing precursor is cobalt acetylacetonate, and the lanthanide elements include one of lutetium acetylacetonate and lanthanum acetylacetonate.

2. The preparation method according to claim 1, characterized in that: The method for preparing the fluorine-doped carbon support includes ball milling a Ketjen black carbon support and tetrafluoroterephthalic acid; vacuum encapsulating the milled material for fluorination; and solvent washing and vacuum drying of the fluorinated material.

3. The preparation method according to claim 2, characterized in that: The ball milling speed is 350~600 rpm, and the milling process is 20~40 revolutions, with each revolution running for 3 minutes and then stopping for 7 minutes to cool down. The grinding balls are stainless steel balls with a diameter of 2~5 mm, and the mass ratio of grinding balls, carbon carrier, and tetrafluoroterephthalic acid is 30~60 g:1.5~3 g:0.3~1 g.

4. The preparation method according to claim 3, characterized in that: The fluorinated material is washed with ethanol and then vacuum dried.

5. The preparation method according to claim 1, characterized in that: The mass ratio of the fluorine-doped carbon support to the platinum-containing precursor, the cobalt-containing precursor, and the lanthanide-containing precursor is 1:0.8~1.6:0.~1.38:0.2~0.

3.

6. The preparation method according to claim 5, characterized in that: The ultrasonic treatment lasts for 20 to 40 minutes, and the rotary evaporation is carried out at room temperature.

7. The preparation method according to claim 5 or 6, characterized in that: The atmosphere treatment conditions are a heating rate of 2~10℃ / min.

8. The low-platinum catalyst for fuel cells prepared by the preparation method according to any one of claims 1 to 7.

9. The low-platinum catalyst for fuel cells as described in claim 8, characterized in that: The platinum loading ranges from 20.24 to 65.68 wt%.

10. The application of the low-platinum catalyst for fuel cells as described in claim 9 in fuel cells, characterized in that: Anode and cathode catalysts for proton exchange membrane fuel cells.

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