CN104014333A - Preparation method of carbon film coated platinum/graphene catalyst - Google Patents

Abstract

The invention discloses a method for preparing a platinum/graphene catalyst coated with a carbon film. The catalyst uses graphene as a carrier to hydrothermally reduce graphene oxide, sugars, polyvinylpyrrolidone and chloroplatinic acid, and then A cathode oxygen reduction reaction catalyst for a fuel cell is obtained by carbonization, and its platinum loading is 10wt%-50wt%. The catalyst has excellent methanol resistance and catalytic cycle stability, and its performance has been greatly improved in 10,000 cyclic voltammetry tests, far superior to commercial platinum/carbon catalysts.

Description

A kind of preparation method of platinum/graphene catalyst coated with carbon film

technical field

The invention relates to a method for preparing a cathode oxygen reduction reaction catalyst for a fuel cell, in particular to a method for preparing a carbon film-coated platinum/graphene catalyst.

Background technique

At present, the commonly used fuel cell cathode oxygen reduction reaction catalyst is a carbon-supported platinum-based catalyst. Although the platinum/carbon catalyst has good catalytic performance for the oxygen reduction reaction, it suffers from catalyst particle shedding, aggregation, and poor methanol tolerance. A series of serious problems such as poor cycle stability make it difficult to meet the needs of actual use. Alloying, morphology control, and carrier loading are three possible avenues to address these issues. Among them, as a two-dimensional layered material with ultra-high specific surface area, excellent electrochemical stability and electrical conductivity, graphene is expected to be widely used in the preparation of high-performance metal particle catalysts. On the other hand, some scholars have started to add a protective layer to the oxygen reduction catalyst, and found that the anchoring effect of the carbon coating on the platinum nanoparticles is the key to improving the stability of the catalyst. The representative research progress is as follows:

Advanced Materials magazine, 2008, volume 20, page 743, reported a preparation method of a mesoporous carbon-supported platinum catalyst with a core-shell structure. The catalyst has excellent methanol poisoning resistance, catalytic activity and cycle stability.

Chemical Communications magazine, 2010, volume 46, page 6998, reported an in-situ preparation method of a carbon film-coated platinum/carbon catalyst. The electrochemically active area of the catalyst decreased by only 31% after 1000 cycles under nitrogen.

Journal of American Chemical Society magazine 2012, volume 134, page 13252, reported a method for preparing a polyaniline-coated platinum/carbon catalyst. The thickness of the coating layer of the catalyst is 2.5-14nm, and it has good catalytic activity for oxygen reduction reaction , and can still work well when exposed to corrosive environments.

Until now, how to protect platinum nanoparticles from long-term erosion in corrosive environments and improve their resistance to methanol poisoning is still a challenge. Carbon film coating can greatly limit the migration of platinum nanoparticles on graphene, reducing the possibility of aggregation and shedding. On the other hand, it can also effectively avoid direct contact between platinum nanoparticles and harmful components, and achieve resistance to methanol poisoning by diluting the active sites on the particle surface.

Contents of the invention

The purpose of the present invention is to prepare a kind of fuel cell, the platinum/graphene catalyst of carbon film coating, and wherein platinum loading is 10wt%-50wt%. This catalyst uses graphene as a carrier, utilizes graphene's ultra-high specific surface area and excellent electrochemical stability to improve the reactivity and stability of the catalyst; uses sugar as a precursor, polyvinylpyrrolidone as a dispersant, and utilizes High-temperature carbonization forms a carbon coating layer (thickness 0-20nm) in situ to endow the catalyst with excellent resistance to methanol poisoning and cycle performance.

The technical solution of the present invention is: a certain proportion of graphene oxide, sugar precursor, polyvinylpyrrolidone and chloroplatinic acid are blended and hydrothermally reduced, followed by high-temperature carbonization to prepare a carbon film-coated platinum/graphene catalyst , its specific preparation method is as follows (all represent in parts by mass):

(1) Ultrasonic disperse graphene oxide in deionized water to form a 0.05wt%-1wt% graphene oxide dispersion, add 40-800 mass parts sugar precursor, 1-20 parts by mass of dispersant polyvinylpyrrolidone and 0.5-10 parts by mass of chloroplatinic acid are evenly mixed, the dispersion is transferred to a hydrothermal kettle, heated at 180°C for 3-18 hours, and the obtained liquid is deionized water, Repeated washing with ethanol, and freeze-drying to obtain platinum/graphene powder;

(2) Add platinum/graphene powder into a ceramic crucible, put it into a tube furnace, and heat it at 600-1000°C for 1-3 hours in a nitrogen atmosphere, with a heating rate of 5-20°C min ^-1 . Cool naturally under nitrogen atmosphere to obtain a platinum/graphene catalyst coated with carbon film.

In the present invention, the graphene oxide is prepared by Hummers method, Brodie method, or Staudenmaier method.

In the present invention, described polyvinylpyrrolidone molecular weight is 8000 (K-15) to 1,300,000 (K-90).

In the present invention, the carbohydrate precursor is any one of glucose, fructose or sucrose.

In the present invention, the particle diameter of the platinum nanoparticles of the catalyst is 2-5nm.

The platinum content of the catalyst obtained in the present invention is 10wt% ~ 50wt%.

The thickness of the carbon film covering layer of the catalyst obtained by the present invention is 0-20nm.

The technical effects of the present invention are: there is a strong interaction between the graphene sheet, the carbon coating layer and the platinum nanoparticles, so that the catalyst has excellent reactivity; the carbon coating layer can also serve as a sacrificial material. Oxidative detachment occurs preferentially in the environment, exposing the active sites of platinum, which not only protects platinum nanoparticles and graphene sheets to a certain extent, but also greatly improves the cycle performance of the catalyst.

Description of drawings

FIG. 1 is an atomic force microscope image of Example 1. FIG.

Fig. 2 is (a) transmission electron microscope and (b) high-resolution transmission electron microscope photograph of embodiment 1.

Fig. 3 is (a) embodiment 1, and (b) comparative example 1 obtains the oxygen reduction reaction catalyst, under saturated oxygen, add or not add the cyclic voltammogram of methanol in the sulfuric acid solution.

Fig. 4 is the platinum/graphene catalyst that embodiment 1 and embodiment 2 obtains under saturated oxygen, the rotating disc curve in sulfuric acid, methanol mixed solution.

Fig. 5 is the platinum/graphene catalyst that embodiment 1 obtains under saturated oxygen, the cycle stability test curve in sulfuric acid solution.

Detailed ways

The following examples help to further illustrate the present invention in detail, but should not be construed as limiting the scope of the present invention.

The cyclic voltammetric detection method of the carbon film-coated platinum/graphene catalyst of the present invention is carried out on a CHI 660E electrochemical workstation. The glassy carbon electrode with a diameter of 3 mm was polished successively with 0.3 μm and 0.5 μm alumina slurry, and then the electrode surface was rinsed with deionized water. Add 2.0 mg of dry catalyst to 200 μL of isopropanol, then add 200 μL of 5 wt% Nafion® ethanol solution purchased from Alfa Aesar, mix well and sonicate for 10 minutes to obtain 5 mg mL ^-1 catalyst ink. Take 2 μL of the ink drop and apply it to the surface of the glassy carbon electrode, and dry it in the air at room temperature. The obtained glassy carbon electrode was installed on a three-electrode device and connected to an electrochemical tester. The counter electrode was a platinum wire, the reference electrode was a silver/silver chloride electrode (Ag/AgCl), and the electrolyte was a 0.5 M sulfuric acid solution. Oxygen was passed into the solution for 30 minutes, the scanning range was -0.2-1.0 V, and the scanning speed was 50 mV s ^-1 , and the anti-methanol poisoning performance was verified by adding an additional 0.5 M methanol solution.

The rotating disk test of the present invention is carried out on a CHI 605 electrochemical workstation, and the catalyst ink and electrode polishing process adopted are the same as those of the cyclic voltammetry experiment. A 5 μL drop of ink was applied to the surface of a glassy carbon electrode with a diameter of 5 mm, and dried in air under an infrared lamp. Install the glassy carbon electrode with the sample attached on the three-electrode device and connect it to the electrochemical tester. The counter electrode is a platinum wire, the reference electrode is a standard hydrogen electrode (RHE) electrode, and the electrolyte contains 0.5 M sulfuric acid and 0.5 M methanol Oxygen was introduced into the solution for 30 minutes before the test, the scanning range was 0.1-1.1 V, and the scanning speed was 5 mV s ^-1 .

The cycle performance of the present invention is verified by performing 10,000 consecutive cyclic voltammetry tests in an oxygen-saturated 0.5 M sulfuric acid solution, with a scan range of -0.2 to 1.0 V and a scan speed of 50 mV s ^-1 .

Example 1.

(1) Add 40 parts by mass of glucose, 1 part by mass of polyvinylpyrrolidone, and 0.5 parts by mass of chloroplatinic acid to 1000 parts by mass of 0.05wt% graphene oxide dispersion, stir magnetically for 15 minutes and ultrasonically for 20 minutes to obtain a uniform of the dispersion. The dispersion was put into a hydrothermal kettle and heated at 180°C for 8 hours. The black liquid obtained after hydrothermal treatment was successively washed with deionized water (8-10 times) and ethanol (at least 10 times) and centrifuged until the supernatant was colorless. The resulting platinum/graphene catalyst was freeze-dried to constant weight with a platinum loading of 7.4 wt%.

(2) Add platinum/graphene powder into a ceramic crucible, put it into a tube furnace (SGL-1200, Shanghai Daheng Optics and Precision Instrument Co., Ltd.), and put it in a nitrogen atmosphere with a flow rate of 50 L h ^-1 at 700 °C. Heating under low temperature for 3 hours with a heating rate of 10 ℃ min ^-1 , and cooling naturally under nitrogen atmosphere to obtain a platinum/graphene catalyst with a carbon coating thickness of 2nm and a platinum loading of 13.7wt%. The cyclic voltammetry curve obtained by using the above test method is shown in Figure 3, the rotating disc curve is shown in Figure 4, and the cyclic stability test is shown in Figure 5.

Example 2.

(1) Add 1 mass part of polyvinylpyrrolidone and 0.5 mass part of chloroplatinic acid to 1000 mass parts of 0.05wt% graphene oxide dispersion, magnetically stir for 15 minutes and ultrasonic for 20 minutes to obtain a uniform dispersion. The dispersion was put into a hydrothermal kettle and heated at 180°C for 8 hours. The black liquid obtained after hydrothermal treatment was successively washed with deionized water (2-3 times) and ethanol (at least 2 times) and centrifuged until the supernatant was colorless. The resulting platinum/graphene catalyst was freeze-dried to constant weight with a platinum loading of 23.4 wt%.

(2) Add platinum/graphene powder into a ceramic crucible, put it into a tube furnace, heat at 700°C for 3 hours in a nitrogen atmosphere with a flow rate of 50 L h ^-1 , and heat up at a rate of 10°C min ^-1 , then cool to Naturally cooled under a nitrogen atmosphere to obtain a platinum/graphene catalyst with a carbon coating thickness of 0 nm and a platinum loading of 47.6 wt%. The rotating disk curve obtained by using the above test method is shown in Figure 4.

Example 3.

(1) Add 40 parts by mass of glucose, 20 parts by mass of polyvinylpyrrolidone, and 10 parts by mass of chloroplatinic acid to 20,000 parts by mass of 0.05wt% graphene oxide dispersion, stir magnetically for 15 minutes and ultrasonically for 20 minutes to obtain a uniform of the dispersion. Put this dispersion into a hydrothermal kettle and heat at 180°C for 3 hours. The black liquid obtained after hydrothermal treatment was successively washed with deionized water (3-5 times) and ethanol (at least 5 times) and centrifuged until the supernatant was colorless. The resulting platinum/graphene catalyst was freeze-dried to constant weight.

(2) Add platinum/graphene powder into a ceramic crucible, put it into a tube furnace, heat at 600°C for 1 hour in a nitrogen atmosphere with a flow rate of 50 L h ^-1 , and heat up at a rate of 10°C min ^-1 , then cool to Naturally cooled in a nitrogen atmosphere, a platinum/graphene catalyst with a low degree of reduction and a small thickness of the carbon coating was obtained.

Example 4.

(1) Add 40 parts by mass of glucose, 1 part by mass of polyvinylpyrrolidone, and 0.5 parts by mass of chloroplatinic acid to 1000 parts by mass of 0.05wt% graphene oxide dispersion, stir magnetically for 15 minutes and ultrasonically for 20 minutes to obtain a uniform of the dispersion. Put this dispersion into a hydrothermal kettle and heat at 180°C for 18 hours. The black liquid obtained after hydrothermal treatment was successively washed with deionized water (15-20 times) and ethanol (at least 15 times) and centrifuged until the supernatant was colorless. The resulting platinum/graphene catalyst was freeze-dried to constant weight.

(2) Add platinum/graphene powder into a ceramic crucible, put it into a tube furnace, heat at 1000°C for 3 hours in a nitrogen atmosphere with a flow rate of 50 L h ^-1 , and heat up at a rate of 10°C min ^-1 , then cool to Naturally cooled in a nitrogen atmosphere, a platinum/graphene catalyst with a high degree of reduction and a carbon coating thickness of about 2 nm was obtained, which has excellent electrical conductivity and catalytic activity.

Example 5.

(1) Add 40 parts by mass of fructose, 1 part by mass of polyvinylpyrrolidone, and 0.5 parts by mass of chloroplatinic acid into 1000 parts by mass of 0.05wt% graphene oxide dispersion, stir magnetically for 15 minutes and ultrasonically for 20 minutes to obtain a uniform Dispersions. The dispersion was put into a hydrothermal kettle and heated at 180°C for 8 hours. The black liquid obtained after hydrothermal treatment was successively washed with deionized water (8-10 times) and ethanol (at least 10 times) and centrifuged until the supernatant was colorless. The obtained platinum/graphene catalyst was freeze-dried to constant weight, and its carbon coating thickness was about 20 nm.

(2) Add platinum/graphene powder into a ceramic crucible, put it into a tube furnace, heat at 700°C for 3 hours in a nitrogen atmosphere with a flow rate of 50 L h ^-1 , and heat up at a rate of 10°C min ^-1 , then cool to Naturally cooled under a nitrogen atmosphere, a platinum/graphene catalyst with a carbon coating thickness of 5 nm was obtained.

Comparative example 1.

The platinum/carbon catalyst used in the comparative example is a commercial platinum/carbon catalyst from Alfa Aesar, the carrier is activated carbon, and the platinum loading is 20wt%. The cyclic voltammetry curve obtained using the above test method is shown in Figure 3.

Figure 1 illustrates the carbon film coating structure of the catalyst. The average thickness of platinum/graphene is about 6 nm, indicating that the obtained graphene is single-layer or oligolayer graphene, and the thickness of the carbon coating layer can be calculated as 2 nm by measuring the raised bulk part. Since the thickness of the carbon coating layer is smaller than the average particle size of the platinum nanoparticles, the active sites of the platinum nanoparticles are only partially covered, and the main catalytic activity of the catalyst can still be preserved.

Figure 2 illustrates the microscopic morphology of the carbon film-coated Pt/graphene catalyst, and the dispersion uniformity of the Pt nanoparticles. Graphene is relatively transparent in transmission electron microscope photos, indicating that it is single-layer or few-layer graphene. The high-resolution image shows that platinum nanoparticles can be uniformly dispersed on graphene, with an average particle size of 3.5 nm, and the subsequent carbon film coating will not cause the aggregation or shedding of platinum nanoparticles.

Figure 3 illustrates the difference in catalytic activity and anti-methanol poisoning activity between the carbon film-coated platinum/graphene catalyst and the commercial platinum/carbon catalyst. In the cyclic voltammetry test, the carbon film-coated platinum/graphene catalyst has comparable oxygen reduction catalytic activity to the platinum/carbon catalyst, and the difference is mainly due to the difference in platinum loading. However, the addition of methanol will lead to methanol oxidation peaks and carbon monoxide oxidation peaks on the platinum/carbon catalyst; while the catalytic performance of the catalyst sample with a carbon coating thickness of 2 nm is only reduced by about 18%, without the appearance of methanol oxidation peaks.

Figure 4 illustrates the difference in methanol poisoning resistance of platinum/graphene catalysts with and without carbon coating. In the rotating disk test, the addition of methanol will cause a significant methanol oxidation peak on the catalyst without carbon coating; while the catalyst sample with a carbon coating thickness of 2nm is basically unaffected.

Figure 5 illustrates that the carbon film-coated platinum/graphene catalyst has excellent cycle performance. As the carbon film falls off during use, the active sites of the platinum nanoparticles are gradually exposed, and the oxygen reduction reaction activity of the catalyst increases with the number of cycles. The increase was improved and reached the highest value (74 m ² g ^-1 ) at the 8000th cycle, which is the highest value so far compared with other literatures. Even after 10,000 cycles, the catalyst retained 69 percent of its peak catalytic activity.

Claims (7)

1. a preparation method for the platinum/graphen catalyst of carbon film coated, is characterized in that concrete steps are as follows:

(1) by the ultrasonic graphene oxide graphene oxide dispersion liquid that forms 0.05wt%-1wt% in deionized water that is dispersed in, in 1000-20000 mass parts graphene oxide dispersion liquids, add 40-800 mass parts carbohydrate presoma, 1-20 mass parts polyethylene of dispersing agent base pyrrolidones and 0.5-10 mass parts chloroplatinic acid to mix, dispersion liquid is transferred in water heating kettle, at 180 DEG C, heat 3-18 hour, gained is deionized water, ethanol cyclic washing for liquid, and freeze drying obtains platinum/graphen powder;

(2) platinum/graphen powder is joined in ceramic crucible, put into tube furnace, at nitrogen atmosphere, 600-1000 DEG C, heat 1-3 hour, heating rate is 5-20 DEG C of min ^-1, naturally cooling under nitrogen atmosphere when cooling, obtain a kind of platinum/graphen catalyst of carbon film coated.

2. the preparation method of the platinum/graphen catalyst of a kind of carbon film coated according to claim 1, is characterized in that, graphene oxide used is by Hummers method, Brodie method or Staudenmaier method, any is prepared from.

3. the preparation method of the platinum/graphen catalyst of a kind of carbon film coated according to claim 1, it is characterized in that, the molecular weight of polyethylene of dispersing agent base pyrrolidones used all can from 8000 (K-15) to 1,300,000 (K-90).

4. the preparation method of the platinum/graphen catalyst of a kind of carbon film coated according to claim 1, is characterized in that, carbohydrate presoma used be in glucose, fructose or sucrose any.

5. the preparation method of the platinum/graphen catalyst of a kind of carbon film coated according to claim 1, is characterized in that, the particle diameter of the nano platinum particle of described catalyst is 2 ~ 5nm.

6. the preparation method of the platinum/graphen catalyst of a kind of carbon film coated according to claim 1, is characterized in that, in gained catalyst, the content of platinum is 10wt% ~ 50wt%.

7. the preparation method of the platinum/graphen catalyst of a kind of carbon film coated according to claim 1, is characterized in that, the carbon film coated layer thickness of gained catalyst is 0 ~ 20nm.