CN109935846A - A kind of fuel cell electrocatalyst carrier and preparation method thereof - Google Patents

Abstract

The invention discloses a kind of fuel cell electro-catalyst carriers and preparation method thereof.The electro-catalyst carrier is functionalization carbon black/graphene composite material, preparation method includes the following steps: carrying out functional modification to carbon black with cationic polymer first keeps its positively charged, then functionalization carbon black/graphene oxide multilevel structure is formed by electrostatic self-assembled with negatively charged graphene oxide, graphene oxide therein is most reduced to graphene through the methods of chemistry, electrochemistry afterwards, to further increase the electric conductivity of composite material.This preparation method is simple and easy to do, low in cost, use easy to spread.The study found that composite material prepared by the present invention has three-dimensional porous structure, biggish specific surface area, good electric conductivity, and it is easier to capture and evenly dispersed nano metal particles.Electro-chemical test shows the active high and stable performance advantage of elctro-catalyst prepared using the functionalization carbon black/graphene composite material as carrier.

Description

A kind of fuel cell electrocatalyst carrier and preparation method thereof

technical field

The invention belongs to the field of fuel cells, and in particular relates to the preparation of a three-dimensional functionalized carbon black/graphene composite material and its application as a fuel cell electrocatalyst carrier.

Background technique

A fuel cell is a power generation device that directly converts chemical energy stored in fuel and oxidant into electrical energy. It has the advantages of high energy conversion efficiency, fast startup, and environmental friendliness. It is expected to be widely used in vehicles, portable electronic products and decentralized power plants. Its research has attracted great attention from governments of various countries.

Electrocatalysts are the key materials of fuel cells, and their activity and stability directly affect the performance and life of fuel cells. The carrier plays a crucial role in the performance of the catalyst. The support provides the possibility of high dispersibility and stability of metal particles, thereby improving the utilization, activity and stability of the catalyst. As a catalyst carrier, the following conditions should be met: (1) Good electrical conductivity to facilitate charge transport; (2) Large specific surface area to disperse active substances and improve active substance utilization; (3) Strong carrier-catalyst interaction to improve catalytic efficiency and reduce catalyst loss; (4) rich pore structure, so that reactants in the electrolyte can contact the catalyst and improve the three-phase reaction interface; (5) strong anti-corrosion ability to Improve the chemical stability of the catalyst in the reaction medium. Graphene is a two-dimensional structure composed of sp ² carbon atom bonds, with a large specific surface area (theoretical specific surface area up to 2620m ² g ^-1 ), good electrical conductivity, excellent chemical stability and easy surface modification, etc. It is an ideal catalyst carrier, which opens up a new direction for improving the performance of fuel cells. However, there are still many problems in the study of graphene as a catalyst support. For example, during the reduction or drying process of graphene sheets, due to van der Waals forces, irreversible agglomeration may occur, or even re-stack into a graphite structure, which will not only destroy the high specific surface area of graphene, but also be unfavorable for graphene-supported platinum pastes. The dispersion of materials; graphene introduces a large number of structural defects in the early preparation process, which reduces the conductivity of graphene and affects the electron transfer rate in the electrocatalytic process.

In order to solve the above problems, the researchers introduced conductive nanomaterials as spacers between the graphene sheets. On the one hand, by embedding the conductive materials between the graphene sheets, the stacking of the graphene sheets was prevented, and the graphene sheets were interconnected to form a hole structure. On the other hand, the structural defects of graphene are repaired by nanocomposite, and the conductivity of the composite carrier is improved. To date, many carbon materials have been used as spacers, effectively preventing graphene from restacking. Among them, carbon nanotubes/graphene composites can be effectively synthesized by embedding carbon nanotubes into graphene sheets by chemical vapor deposition method, but the preparation process is complicated and the cost is high, which limits the large-scale application of such graphene composites (Z. Lei, L. Lu and X.S. Zhao, Energy Environ. Sci., 2012, 5, 6391–6399.). Carbon black, as an inexpensive carbon material with excellent electrical conductivity, is an ideal graphene interlayer spacer. Li et al. reported a carbon black/graphene composite synthesized under the action of ultrasound, which supported Pt nanoparticles to effectively improve the stability of the catalyst (Y.J.Li, Y.J.Li, E.Zhu, T.Mclouth, C.Y. Chiu, X.Q.Huang and Y.Huang, J.Am.Chem.Soc., 2012, 134, 12326–12329.). However, due to the weak interaction between carbon black and graphene under this preparation condition, the carbon black is not uniformly distributed on the graphene sheets, resulting in partial stacking of the graphene sheets, which reduces the electrochemical active area and the catalyst activity is not high. Therefore, there is an urgent need to explore a facile and low-cost method to prepare carbon-based/graphene composite supports for improving the activity and stability of fuel cell catalysts.

SUMMARY OF THE INVENTION

In order to solve the above problems, the present invention designs a simple and cheap preparation method of functionalized carbon black/graphene. The carbon black was functionalized with a cationic polymer to make it positively charged, and then self-assembled with the negatively charged graphene oxide under the action of electrostatic force to form a stable functionalized carbon black/graphene oxide three-dimensional composite structure. It prevents the irreversible agglomeration of graphene sheets, increases the specific surface area of the catalyst, exposes more reaction sites, and creates a porous structure to provide a transport channel for reactants and promote mass transfer, thereby achieving the purpose of improving catalytic activity. .

The technical scheme adopted by the present invention comprises the following steps:

A preparation method of a fuel cell electrocatalyst carrier, the method steps are as follows:

1) ultrasonically dispersing carbon black in deionized water, adding a cationic polymer, and ultrasonically stirring to obtain mixture A;

2) Wash mixture A with deionized water and suction filtration, and obtain positively charged functionalized carbon black (FCB) after vacuum drying;

3) Redispersing the above functionalized carbon black into deionized water, adding an aqueous dispersion of graphene oxide (GO), ultrasonically oscillating to make it evenly mixed, and continuing to stir at room temperature for 5-20 h to obtain functionalized carbon black/ Graphene oxide mixture (FCB-GO);

4) The mixture in step 3) is reduced, centrifuged and washed, and then freeze-dried to obtain a functionalized carbon black/graphene composite (FCB-rGO).

In step 1), the mass ratio of carbon black to cationic polymer is 1:5-1:20; the ultrasonic stirring time is 3-12h.

In step 1), the cationic polymer includes ammonium salt N+, sulfur salt S+, phosphorus salt P+ cationic polymer, specifically polydiallyl dimethyl ammonium chloride (PDDA), polyvinylamine (PVAM) , polyacrylamide (PAM) and so on.

In step 2), the vacuum drying temperature is 60-120°C, and the time is 6-24h.

In step 3), the mass ratio of functionalized carbon black and graphene oxide is 1:5-5:1; the concentration of graphene oxide aqueous dispersion is 0.1-2 mg ml ^-1 , preferably 0.5 mg ml ^-1 .

In step 4), reduction methods mainly include chemical reduction method, solvothermal reduction method, electrochemical reduction method, thermal reduction method, microwave stripping method or combined multi-step reduction method.

In step 4), when the reduction method is chemical reduction method to reduce the mixture, the reaction conditions are: reaction temperature 25-95° C., reaction time 3-24 hours, and stirring at the same time.

In step 4), the reducing agent in the chemical reduction method includes hydrazine hydrate and its derivatives, sodium borohydride, ascorbic acid, strong base, HI, citric acid or urea, etc.; the mass ratio of the reducing agent to graphene oxide is 0.7-20.

In step 4), when the reduction method is a solvothermal reduction method to reduce the mixture, the reaction conditions are: a reaction temperature of 140-200° C. and a reaction time of 8-24 hours.

In step 4), when the reduction method is thermal reduction to reduce the mixture, the reaction conditions are: protection of an inert or reducing atmosphere, a heating rate of 5°C/min, a reaction temperature of 550-1100°C, and a reaction time of 0.5-2h.

The present invention successfully prepares the functionalized carbon black/graphene composite material based on a simple and cheap solution self-assembly method, and using it as a fuel cell catalyst carrier can effectively improve the electrocatalytic performance. In this composite structure, carbon black is distributed evenly on the surface of graphene, and is interconnected with graphene to form a three-dimensional pore structure. It has high specific surface area, good electrical conductivity, excellent ion transport ability, and is easier to capture and uniformly disperse nano-metal particles. Etc. The electrocatalyst prepared with the functionalized carbon black/graphene composite material as a carrier has significantly improved catalytic performance and stability. The preparation method is simple and feasible, and has broad application prospects in the fields of fuel cells and electrocatalysis.

Description of drawings

Fig. 1 is the scanning electron microscope photograph of functionalized carbon black/graphene composite material;

Fig. 2 is the Raman spectrum of graphene and functionalized carbon black/graphene composite material;

Fig. 3 is the nitrogen adsorption-desorption isotherm curve of graphene and functionalized carbon black/graphene composite;

Figure 4 is a transmission electron microscope photograph of PtCo/FCB-rGO;

Figure 5a shows the cyclic voltammetry (CV) curves of PtCo/rGO and PtCo/FCB-rGO. The electrolyte used in the test is N ₂ saturated 0.1 mol/L HClO ₄ aqueous solution, and the scan rate is 50 mV/s;

Figure 5b shows the oxygen reduction (ORR) polarization curves of PtCo/rGO and PtCo/FCB-rGO. The electrolyte used in the test is 0.1 mol/L HClO ₄ aqueous solution saturated with O ₂ , the scan rate is 10 mV/s, and the RDE speed is 1600 rpm;

Figure 6 shows the oxygen reduction polarization curves of PtCo/FCB-rGO before and after the accelerated decay. The accelerated decay test used N ₂ -saturated 0.1 mol/L HClO ₄ solution as the electrolyte, the scanning voltage range was 0.6-1.2 V, and the scanning speed was 50 mV s ^-1 , scan 1500 circles;

Fig. 7 is the transmission electron microscope photograph of PtRu/FCB-rGO;

Figure 8 is a transmission electron microscope photograph of PdNiAu/FCB-rGO.

Detailed ways

The technical solution of the present invention will be further described below in conjunction with the accompanying drawings and embodiments, but it is not limited to this. Any modification or equivalent replacement of the technical solution of the present invention without departing from the spirit and scope of the technical solution of the present invention should be included in the within the protection scope of the present invention.

Example 1

The carbon black was ultrasonically dispersed in deionized water, and the cationic polymer PDDA was added to make the mass ratio of carbon black and PDDA 1:10. After ultrasonic stirring for 3 hours, washing with deionized water, suction filtration, and vacuum drying to obtain positively charged functionalized carbon black (FCB). The FCB was redispersed in deionized water, and an aqueous dispersion of graphene oxide with a concentration of 1 mg/ml was added to make the mass ratio of functionalized carbon black and graphene oxide 2:1. Stirring was continued for 7 h to obtain functionalized carbon black/graphene oxide mixture (FCB-GO). Ascorbic acid was added to this mixture dispersion to make the mass ratio of ascorbic acid to graphene oxide 20, the reaction was stirred at 95°C for 12 hours, and then centrifuged and washed to obtain a functionalized carbon black/graphene composite (FCB-rGO) . Using the composite material prepared by the above method as a carrier, using a polyol reflux method, and after pickling, a PtCo catalyst was obtained. As a comparison, a PtCo catalyst with pure graphene as a carrier was prepared according to the above method. The performance test results are shown in Figure 1-6. It can be seen from Figure 1 that the functionalized carbon black particles are uniformly distributed on the graphene sheet, forming a three-dimensional pore structure with it. This structure is beneficial to increase the specific surface area of the catalyst, expose more active sites, and enable better ion transport, thereby increasing the electrocatalytic reaction rate. It can be seen from Figure 2 that from graphene to functionalized carbon black/graphene composite, the _IG / _ID value increases from 0.72 to 0.97, indicating that the structural defects of graphene have been repaired, which is also to improve the electrocatalytic activity of oxygen reduction. important factor. It can be seen from Figure 3 that compared with graphene, the BET specific surface area of the functionalized carbon black/graphene composite has been greatly improved. It can be seen from Figure 4 that the PtCo nanoparticles have a strong interaction with the composite carrier, can be evenly distributed on the surface of the composite carrier, and have a small particle size without agglomeration. It can be seen from Figure 5a, Figure 5b and Figure 6 that the functionalized carbon black/graphene composite carrier shows superior performance, and the activity of the supported PtCo catalyst is much higher than that of the ordinary PtCo/graphene catalyst. It can be seen from Figure 7 that the PtCo/FCB-rGO catalyst also shows excellent stability.

Example 2

The carbon black was ultrasonically dispersed in deionized water, and the cationic polymer PVAM was added so that the mass ratio of carbon black to PVAM was 1:15. After ultrasonic stirring for 6 hours, washing with deionized water, suction filtration, and vacuum drying to obtain positively charged functionalized carbon black (FCB). The FCB was re-dispersed in deionized water, and an aqueous dispersion of graphene oxide with a concentration of 2 mg/ml was added to make the mass ratio of functionalized carbon black and graphene oxide 1:1. Stirring was continued for 12 h to obtain functionalized carbon black/graphene oxide mixture (FCB-GO). To this mixture dispersion liquid, add hydrazine hydrate so that the mass ratio of hydrazine hydrate and graphene oxide is 1:1, and after stirring and reacting at 95 ° C for 6 hours, centrifugal washing is performed to obtain functionalized carbon black/graphene composite material ( FCB-rGO). Using the composite material prepared by the above method as a carrier, a PtRu catalyst was prepared by a microwave-assisted polyol method, and its transmission electron microscope photo is shown in Figure 7.

Example 3

The carbon black was ultrasonically dispersed in deionized water, and the cationic polymer PAM was added to make the mass ratio of carbon black to PAM 1:20. After ultrasonic stirring for 3 hours, washing with deionized water, suction filtration, and vacuum drying to obtain positively charged functionalized carbon black (FCB). The FCB was redispersed in deionized water, and an aqueous dispersion of graphene oxide with a concentration of 0.5 mg/ml was added, so that the mass ratio of functionalized carbon black and graphene oxide was 3:1, and the mixture was uniformly mixed by ultrasonic vibration. Stirring was continued for 10 h at room temperature to obtain functionalized carbon black/graphene oxide mixture (FCB-GO). To this mixture dispersion liquid, add sodium borohydride so that the mass ratio of sodium borohydride and graphene oxide is 10, and after stirring and reacting at 60 ° C for 12 hours, centrifugal washing is performed to obtain functionalized carbon black/graphene composite material ( FCB-rGO). Using the composite material prepared by the above method as a carrier, a PdNiAu catalyst was prepared by a solvothermal method, and its transmission electron microscope photo is shown in Figure 8.

Example 4

The carbon black was ultrasonically dispersed in deionized water, and the cationic polymer PDDA was added to make the mass ratio of carbon black and PDDA 1:10. After ultrasonic stirring for 3 hours, washing with deionized water, suction filtration, and vacuum drying to obtain positively charged functionalized carbon black (FCB). The FCB was redispersed in deionized water, and an aqueous dispersion of graphene oxide with a concentration of 2 mg/ml was added to make the mass ratio of functionalized carbon black and graphene oxide 2:1. Stirring was continued for 10 h to obtain functionalized carbon black/graphene oxide mixture (FCB-GO). This mixture was transferred to an autoclave, reacted at 180 °C for 12 hours, and washed by centrifugation to obtain a functionalized carbon black/graphene composite (FCB-rGO).

Example 5

The carbon black was ultrasonically dispersed in deionized water, and the cationic polymer PDDA was added to make the mass ratio of carbon black and PDDA 1:10. After ultrasonic stirring for 5 hours, washing with deionized water, suction filtration, and vacuum drying to obtain positively charged functionalized carbon black (FCB). The FCB was redispersed in deionized water, and an aqueous dispersion of graphene oxide with a concentration of 0.5 mg/ml was added to make the mass ratio of functionalized carbon black and graphene oxide 4:1. Stirring was continued for 6 h at room temperature to obtain a functionalized carbon black/graphene oxide mixture (FCB-GO). After the mixture was suction filtered, washed and dried, it was transferred to a quartz tube, heated to 800°C at a rate of 5°C/min under a 5% H ₂ /Ar atmosphere and kept for 1 hour, purged with nitrogen to cool down, and functionalized Carbon black/graphene composite (FCB-rGO).

Claims (10)

1. a preparation method of a fuel cell electrocatalyst carrier, is characterized in that: described method steps are as follows: 1) ultrasonically dispersing carbon black in deionized water, adding a cationic polymer, and ultrasonically stirring to obtain mixture A; 2) Wash mixture A with deionized water and suction filtration, and obtain positively charged functionalized carbon black (FCB) after vacuum drying; 3) redispersing the above-mentioned functionalized carbon black into deionized water, adding an aqueous dispersion of graphene oxide (GO), ultrasonically oscillating to make it evenly mixed, and continuing to stir at room temperature for 5-20 h to obtain functionalized carbon black/ Graphene oxide mixture (FCB-GO); 4) The mixture in step 3) is reduced, centrifuged and washed, and then freeze-dried to obtain a functionalized carbon black/graphene composite (FCB-rGO). 2. preparation method according to claim 1, is characterized in that: in step 1), the mass ratio of carbon black and cationic polymer is 1:5-1:20; Ultrasonic stirring time is 3-12h. 3. preparation method according to claim 1 and 2 is characterized in that, in step 1), cationic polymer comprises ammonium salts N+, sulfur salts S+, phosphorus salts P+ cationic polymer, is specifically polydiene Propyldimethylammonium chloride (PDDA), polyvinylamine (PVAM), polyacrylamide (PAM), etc. 4. preparation method according to claim 1, is characterized in that: in step 2), vacuum drying temperature is 60-120 ℃, and time is 6-24h. 5. preparation method according to claim 1, is characterized in that: in step 3), the mass ratio of functionalized carbon black and graphene oxide is 1:5-5:1; The concentration of graphene oxide aqueous dispersion is 0.1-2 mg ml ^-1 , preferably 0.5 mg ml ^-1 . 6. preparation method according to claim 1 is characterized in that: in step 4), reduction method mainly contains chemical reduction method, solvothermal reduction method, electrochemical reduction method, thermal reduction method, microwave stripping method or combined multi-step restore etc. 7. preparation method according to claim 1 or 6, is characterized in that: in step 4), adopting reduction method is when chemical reduction method is used to reduce mixture, reaction conditions are: temperature of reaction 25-95 ℃, reaction times 3 -24 hours while stirring. 8. preparation method according to claim 7, is characterized in that: in step 4), in chemical reduction method, reducing agent comprises hydrazine hydrate and derivative thereof, sodium borohydride, ascorbic acid, strong base, HI, citric acid or urea etc.; the mass ratio of reducing agent to graphene oxide is 0.7-20. 9. preparation method according to claim 6, is characterized in that: in step 4), when reduction method is solvothermal reduction method when mixture is reduced, reaction conditions are: reaction temperature 140-200 ℃, reaction time 8-24h . 10. preparation method according to claim 6, is characterized in that: in step 4), when reduction method is that thermal reduction method reduces mixture, reaction condition is: inert or reducing atmosphere protection, heating rate 5 ℃/min , the reaction temperature is 550-1100 ℃, and the reaction time is 0.5-2h.