TWI418083B - The preparation method of well-dispersed electrocatalyst with superior performance - Google Patents

Description

High-performance and high-dispersion electrode catalyst preparation method

The present invention relates to the field of electrode catalysts for proton exchange membrane fuel cells (PEMFC). More specifically, the present invention relates to a method for producing a platinum/carbon black (Pt/C) catalyst, which is characterized by a surfactant. As a dispersing agent for platinum (Pt) and carbon black (C), a heat treatment method is used to uniformly distribute the platinum nanoparticles to the carbon black to achieve optimum synthesis characteristics.

Proton exchange membrane fuel cells (PEMFC) have attracted attention from all walks of life due to their high energy density, high conversion efficiency, easy operation and zero pollution. Since the proton exchange membrane fuel cell (PEMFC) operates at a lower temperature than other fuel cells, the electrode reaction of the Membrane Electrode Assembly (MEA) must be assisted by a catalyst. Platinum in precious metals has superior chemical catalysis and chemical stability than general metals, and is therefore often used as an electrode catalyst for membrane electrode sets. However, the cost of platinum is extremely high. How to improve the effective utilization of platinum, reduce the amount of platinum and increase the activity of the catalyst will be the key factors affecting the power generation efficiency of proton exchange membrane fuel cells. It is known that it can be improved in the following ways:

1. Platinum catalyst nanocrystallization to increase the active area.

Second, the surface of the catalyst carrier is modified to increase the functional groups of the platinum particles, so that the platinum particles can be better dispersed and used.

Third, adding a second element or a plurality of elements to enhance the activity catalyzed by the platinum catalyst.

4. Apply a layer of microporous layer (MPL) on carbon cloth or carbon paper to prevent the catalyst from falling into the fiber and reduce the efficiency of use.

The second improvement described above relates to a catalyst carrier. The reason for using the catalyst carrier is that when only the platinum nanoparticles are used as the catalyst, since the particle size is too small, the agglomeration phenomenon of the nano platinum particles is easily caused by the action of the van der Waals force and the surface coulomb electrostatic force. The catalytic effect is that the platinum particles are coated on the carrier, and the agglomeration of the platinum particles can be reduced by the support of the carrier.

Most of the catalysts widely used in fuel cells today use carbon as a carrier, but the effect of reducing the concentration of platinum particles is still limited. One of the reasons is that carbon black is not effectively dispersed, the surface area for platinum catalyst bonding is reduced, and platinum particles are attracted by functional devices (>C=O, -OH, -COOH, etc.) on the surface of carbon black, resulting in Platinum particles tend to aggregate together, form larger particles, and cause uneven distribution of platinum particles.

The object of the present invention is to provide a high-performance and high-dispersion electrode catalyst preparation method. The electrode catalyst is mainly composed of a nano-catalyst particle and a carrier. The invention disperses the carrier and has a high surface area characteristic, thereby increasing the touch. The dispersibility and drape of the media particles on the carrier achieve an optimized synthesis effect.

The object of the present invention is to provide a high-performance and high-dispersion electrode catalyst preparation method, which can make the size of the nano-precious metal catalyst particles smaller, highly dispersed on the carrier, and improve the utilization rate of the precious metal catalyst particles. And reduce the use of precious metal catalyst particles, reduce the cost of using precious metals in the electrode catalyst, increase the electrochemical catalytic activity area, improve the efficiency of the electrode catalyst and the overall reaction efficiency of the fuel cell.

In the preparation method of the present invention, the carrier particles are dispersed by a dispersing agent to form a three-dimensional barrier layer on the surface of the carrier particles, and then the nano-precious metal catalyst precursor is bonded to the stereoscopic barrier layer to be a reducing agent. The material is reduced to nanometer precious metal catalyst particles, and the stereo barrier layer is removed by heat treatment, and the nano precious metal catalyst particles are uniformly distributed on the carrier particles by Face-Centered Cubic Crystal Structure (FCC). The above-mentioned purpose is achieved by achieving the optimal synthesis conditions for the degree of dispersion and coverage of the nano precious metal catalyst particles on the carrier.

For the convenience of the description, the central idea expressed in the column of the above summary of the present invention is expressed by a specific embodiment. Various items in the embodiments are depicted in terms of ratios, dimensions, amounts of deformation, or displacements that are suitable for illustration, and are not drawn to the proportions of actual elements, as set forth above. In the following description, like elements are denoted by the same reference numerals.

The electrode catalyst of the present invention is composed of a nanocatalyst particle and a carrier. The nanocatalyst particles are platinum particles (Pt) and the carrier is carbon black (C). The main technique of the present invention is to use a low concentration of a cationic surfactant (cetyltrimethylammonium bromide, CTABr) as a dispersing agent for the carbon black carrier, supplemented by heat reflux and heat treatment to make the nanoscale Platinum particles were bound to the carbon black particles and CTABr was removed to form a platinum/carbon black (Pt/C) catalyst. In the examples described below, the cationic surfactant was mixed with a certain concentration of carbon black (C) at different concentrations to prepare a platinum/carbon black (Pt/C) catalyst, respectively. Then, the electrode catalyst prepared by different concentrations of cationic surfactant (CTABr) was analyzed by various analytical instruments and the analysis results were revealed in detail to confirm the feasibility of the present case. Finally, the battery performance analysis proves that the case can improve the overall reaction efficiency of the fuel cell.

<Preparation of platinum/carbon black (Pt/C) catalyst>

The preparation method of the present invention will be described below by taking a 20% wt platinum/carbon black (Pt/C) catalyst as an example. As shown in the first figure, the preparation method includes:

Step one, 1 gram of carbon black, and a cationic surfactant (cetyltrimethylammonium bromide, CTABr) at a concentration of 4.12 mM/L, 2.75 mM/L, 1.37 mM/L, respectively. Add 3 ml of acetone and 30 ml of deionized water to a 100 ml beaker and place in an ultrasonic oscillator for 1 hour.

In the second step, 0.66 g of chloroplatinic acid ( H ₂ PtCl ₆ *6 H ₂ O ) and 10 ml of NaOH (1 M) were added to the mixture of the first step, and the shaking was continued for 1 hour.

In the third step, the mixture of the second step was placed in a hot reflux bottle, and 10 ml of methanol was added thereto, and the mixture was refluxed at 80 ° C for 4 hours.

Step 4, the product of step 3 is filtered with filter paper, washed with deionized water, placed in a vacuum oven and heated at 80 ° C for 5 hours to dry, and then heated to 300 ° C at a step temperature of 1 ° C per minute. During the heating to 100 ° C, 150 ° C, 200 ° C, 300 ° C, respectively, the temperature was held for 30 minutes, and finally naturally cooled to room temperature, and dried and sintered at a high vacuum of 9 × 10 ^-3 Pa.

<Carbon black dispersion mechanism>

The carbon black dispersion mechanism of the first step and the reduction and dispersion mechanism of the Pt precursor hexachlorochloroplatinic acid ( H ₂ PtCl ₆ *6 H ₂ O ) in the third step are illustrated by the second to fourth figures.

As shown in the second figure, a typical surfactant has a hydrophilicity at one end and a lipophilic property at the other end. The surface of the carbon black particles 10 has an -OH group, a -COOH group and a >C=O group, and can be adsorbed with a long lipophilic group of the cationic surfactant 20 CTABr, so the surface of each carbon black particle 10 A steric barrier layer 11 is formed to break the aggregation of the carbon black particles to produce a dispersion effect.

As shown in the third figure, as shown in the fourth figure, chloroplatinic acid 21 ( H ₂ PtCl ₆ *6 H ₂ O ) in step ₂ is a precursor of platinum (Pt), and the dissociated CTABr is linked to the ionic PtCl ₆ ^{2 -} The ionic PtCl ₆ ^{2 - is} reduced to the platinum (Pt) 12 in a metallic state using a weak reducing agent methanol 30.

As shown in the fourth figure, the third step and the fourth step can make the weak reducing agent methanol completely utilized in the auxiliary ionic state of PtCl ₆ ^{2 -} reduction to the metallic platinum (Pt) 12, and remove the above-mentioned three-dimensional barrier layer 11 so that Metallic platinum (Pt) particles 12 are capable of being dispersed and bonded to the surface of the carbon black particles 10.

<Carbon black dispersion test>

In order to prove that the cationic surfactant (CTABr) has the effect of dispersing the carbon black carrier, the dispersion effect of the carbon black carrier was tested by a laser particle size analyzer (DLS). First, the carbon black solution in the first step is placed in a spectroscope bottle and subjected to a carbon black dispersion test by an electro-radiation particle size analyzer (DLS). From the fifth figure, it is known that the carbon black is not added with a dispersant before the dispersion. After dispersion, the particle size distribution of the carbon black as a whole differs by 140 nm to 205 nm, and it can be initially understood that it is feasible to use a cationic (CTABr) surfactant as a dispersing agent to disperse carbon black.

Hereinafter, through X-ray diffractometer (XRD), field emission scanning electron microscope (FE-SEM), transmission electron microscope (TEM), electrochemical analyzer (CV), gas absorption and desorption analyzer ( BET), thermogravimetry/thermal differential analyzer (TG/DTA), inductively coupled plasma mass spectrometer (ICP-MS), laser particle size analyzer (DLS), etc., analysis of catalyst crystal structure, composition, specific gravity, Thermal stability, the size of the Pt particles and the degree of dispersion on the support as well as the active area of the catalyst.

<<X-ray diffraction analysis>>

It is known that the nature of the carrier used in the synthesis of the catalyst, the reaction conditions and the type of the precursor have a direct influence on the particle size of the catalyst, so the X-ray diffractometer (XRD) is used in the platinum/carbon black catalyst. The crystal phase and grain size of the platinum metal were analyzed.

The fifth picture is reported in the literature (ZQ Tian, FD Xie, and PK Shen, J. Mater. Sic ., 39 (2004) 1507.) Unreduced platinum oxide (PtO _x ) and different levels of platinum/carbon black catalyst XRD pattern after reduction treatment. Since the strongest diffraction peaks of PtO ₂ and Pt ₃ O ₄ are located at 34.74° and 35.92°, respectively, the diffraction peak of the sixth graph at 35.09° should be caused by the overlap of two diffraction peaks of PtO ₂ and Pt ₃ O ₄ . From this, it can be judged that the platinum catalyst which is not completely reduced has both the Pt ²⁺ and Pt ⁴⁺ valence states. The most intense diffraction peaks of the Pt/C catalyst after reduction treatment are located at (111), (200), (220) and (311), respectively, which are characteristic diffraction peaks of atomic platinum.

In the seventh figure, in order to use a thermal reflux reduction method, CTABr at a concentration of 4.12 mM/L, 2.75 mM/L, and 1.37 mM/L was separately added as a dispersant to prepare a catalyst and a 20% Pt/C commercial catalyst ( Johnson Matthey) X-ray diffraction pattern. The strongest diffraction planes of these four catalysts are (111), while the characteristic peaks (200), (220) and (311) of other atomic states also have obvious signal peaks, which are confirmed by the three concentrations of CTABr. Helps to reduce and obtain atomic platinum metal and is known by JCPDS card number 04-0802 as (111), (200), (220), and (311) planes, and is obtained by a transmission electron microscope (TEM). The structure of the ring ring is consistent with that shown in the twentieth to twenty-second figures. It can be confirmed that the crystal structure of the platinum metal crystallized is a Face-Centered Cubic [fcc] Crystal Structure (FCC) structure. .

The signal peaks of 10°~50° in the eighth figure are all background values, which is confirmed by the seventh figure.

The ninth picture shows the CTABr X-ray diffraction analysis. No residual of CTABr is found. It is speculated that CTABr should have been removed. In addition, no diffraction peaks belonging to PtO ₂ and Pt ₃ O ₄ were found, and the catalyst after reduction was also proved. There is no obvious platinum oxide residue. This result also shows the seventh picture.

According to the diffraction peak intensity of platinum characteristic and the full width at half maximum formula of Scherrer Equation, the Pt(111) diffraction plane (2θ~40°) is selected by Scherrer equation as the tenth to tenth tenth The crystal grain diameter of the platinum crystal is calculated as shown in Fig. D. The platinum crystal grain of the commercial catalyst is about 4.35 nm, the platinum crystal grain with the dispersant 4.12 mM/L is about 4.16 nm, and the platinum crystal grain with the dispersing agent of 2.75 mM/L is added. It is about 3.92 nm, and the platinum crystal having a dispersing agent of 1.37 mM/L is about 5.66 nm.

Another Pt (200) diffraction plane (2θ~40°) is selected. The crystal grain diameter of the platinum crystal is calculated as shown in the eleventh to eleventh D. The platinum crystal of the commercial catalyst is about 3.18 nm, and the dispersion is added. The platinum crystallites of 4.12 mM/L were about 3.71 nm, the platinum crystal grains with a dispersing agent of 2.75 mM/L were about 3.38 nm, and the platinum crystal grains with a dispersing agent of 1.37 mM/L were about 4.15 nm.

The above results show that the crystallinity of platinum grains prepared by different concentrations of dispersant (CTABr) is better than that of commercial catalyst (20% wt) (Johnson Matthey) (JM), and the average particle size of Pt is known. The platinum catalyst prepared by the dispersant (CTABr) having a concentration of 1.37 mM/L was larger than the commercial catalyst, and the other concentrations were 4.12 mM/L and 2.75 mM/L, which were smaller than those of the commercial catalyst.

The particle size calculated by Scherrer Equation is the average particle size, and the particle size measured does not determine whether the particle size of the nano platinum changes with the concentration of the dispersant. It is speculated that the platinum metal prepared in this experiment is presumed. Both have reached nano-scale particles, and the extremely high surface of the metal surface may still cause local aggregation, which is further confirmed by further SEM and TEM analysis.

The chemical activity area of Pt was determined by substituting d (particle size) obtained by XRD, and the preparation was as shown in Table 1.

Where d : average particle diameter, K : constant 0.9, β: half-height width of the diffraction peak, λ: incident wavelength of X-ray, θ: diffraction angle.

Wherein S _CSA is the chemically active area, ρ is the Pt density of 21.4 g / cm ³ , and d is the particle size (nm) obtained by XRD.

<<Scanning Electron Microscopy (FE-SEM) and Transmissive Electron Microscopy (TEM) Analysis >>

The source of the scanning electron microscope (FE-SEM) is secondary electrons, and the atomic order of platinum (78) is larger than that of carbon black (6). The larger the atomic order, the more signals are obtained, so the image is seen. The brighter it is, the more it can be judged which is carbon black, which is platinum, and the degree of dispersion of platinum on carbon black. Transmissive electron microscopy (TEM) is a study of the fine structure of matter by using electrons and matter, the electromagnetic field deflects electrons, and focuses electrons to produce diffraction and scattering. It can be clearly seen from the bright field image. The crystalline carbon black appears relatively grayish, and is darker than that exhibited by platinum.

From the diffraction principle analysis of the selected area diffraction pattern (SAD) (12th to 14th), the crystal structure of F.C.C in platinum can be clearly understood.

The average particle size of carbon black (XC-72) is about 30 nm, and the average particle diameter of platinum particles calculated by XRD is about 1.50-3.5 nm. Therefore, it can be inferred that the smaller particles and the brighter brightness are more platinum. The darker particles are carbon black. Figure 15: Scanning electron microscopy analysis of platinum/carbon black of commercial catalyst (Johnson Matthey) at 300,000 magnification, and 16th to 18th drawings of platinum prepared by different concentrations of CTABr. A scanning electron microscope analysis of carbon black at a magnification of 300,000. From these photographs, there are platinum and carbon black particles, and almost every platinum black has a distribution of platinum, but a small amount of platinum particles are in a state of aggregation. Under the observation of high magnification, particle agglomeration can be observed more or less faintly as indicated by the arrow. This agglomeration can also be observed from the TEM bright field image, 19th to 22nd, resulting in particle agglomeration. The reason for this is that one of the reasons is that the nanometer particle size is small and the surface energy is high, and the other factor is caused by the concentration of the cationic surfactant (CTABr). When the concentration is high, the carbon black has good dispersibility. The formed three-dimensional space barrier protection reduces the possibility of aggregation of nano particles. When the concentration of (CTABr) is low, the dispersibility of carbon black is poor, and the formed stereoscopic barrier protection is deteriorated, thereby increasing the possibility of aggregation of nanoparticles.

This experiment uses the hydrophilic-hydrophobic relationship between cationic surfactant (CTABr), carbon black (XC-72) and deionized water to construct the dispersion effect of the stereoscopic space barrier and the energy of the nanoparticles to accumulate with each other. Reduce or offset each other. After the carbon black is thoroughly mixed with the cationic surfactant (CTABr), chloroplatinic acid is added, so that the carbon black has been dispersed rather than aggregated before the platinum precursor is added, so the carbon black has a large surface area. The reduced metallic platinum is adsorbed or bonded on the carbon black. However, although the cationic surfactant (CTABr) can effectively disperse the carbon black particles, the carbon black particles cannot be uniformly dispersed (mono-disperse) due to the concentration relationship, and the fine nanometer size with high surface energy is matched. Platinum particles, so there is still some platinum particles in the catalyst.

From the microscopic point of view, the particle size of the platinum catalyst prepared increases with the addition concentration of the dispersant (CTABr), which can be obtained from the SEM surface topography (fifteenth to eighteenth). According to the TEM bright-field image map (19th to 22nd), the platinum particle diameters prepared by the order concentration of 1.37mM/L, 2.75mM/L, and 4.12mM/L were 1.8nm. , 2.0nm, 2.5nm, and Johnson Matthey commercial (20% wt) Pt / C catalyst 2.5nm relatively small, which can be proved that the cationic surfactant (CTABr) as a dispersant can effectively carry the dispersion of platinum Nano particle role.

<<EDS energy dispersive spectroscopy, TG/DTA thermogravimetry/thermal differential analysis and ICP-AES inductively coupled plasma atomic emission spectrometry>>

The main purpose of using these three instruments in this experiment is to verify that the Pt/C catalyst is prepared by using CTABr as a dispersant and hot reflux method, and the Pt loading is the same as the preset value. EDS can be used to understand the composition of the elements contained in the Pt/C catalyst and its proportion. Although it is semi-quantitative and qualitative, it is also of reference value. The Pt composition analyzed by EDS is quite different from the preset value of 20% Pt/C. Except for the Pt/C catalyst prepared by 4.12 mM/L (CTABr), 18.76% is close to the other two concentrations. Both are different from the default values, so seek further confirmation of TGA and ICP. Table 2 shows the Pt/C catalyst composition analysis table prepared by commercial catalyst and different concentrations (CTABr).

<<Platinum/carbon black catalyst active area analysis>>

The performance of the catalyst is closely related to the size of its surface area and the distribution of the pore size. Since the surface of the catalyst is in direct contact with the reactive gas, the size of the surface area controls the activity of the catalyst. Pt/C electrode catalyst prepared by different concentration of dispersant CTABr, the nitrogen absorption and desorption analysis of the twenty-third to twenty-sixth, and the calculation of the particle size value formula by BET (K geometry factor, sample density, specific surface area) reversed, with the SEM image to confirm the correctness of the analytical values. Table 3 shows the surface area measured values of the commercial catalyst and the concentration of the Pt/C electrode catalyst and the particle size of the catalyst powder. It can be seen from Table 4-2 that 18% Pt/C electrode catalyst and 2.75 mM/L CTABr 15% Pt/C electrode catalyst prepared by CTABr with dispersant concentration of 4.12 mM/L are larger than Johnson Matthey 20% Pt/C electrode. Catalyst, so it can be inferred that the Pt/C electrode catalyst activity of both of them is greater than that of Johnson Matthey commercial catalyst.

<<Electrochemical analysis of platinum / carbon black catalyst analysis>>

Cyclic voltammetry (CV) is the most common measurement method for electrochemical analysis. The main principle is to apply a triangular wave to the working electrode to scan the potential from one potential to another and scan back to the original potential. And record the measured current at the same time. Cyclic voltammetry is mainly to explore the dynamic behavior of electrode surface reaction. By changing the control parameters (such as potential, scanning speed, scanning lap) to achieve the results of analysis, it is applied to the qualitative, quantitative analysis and electrode reaction mechanism of species. The investigation and measurement of the area of electrocatalytic activity of the electrode and the like. In this experiment, the catalyst synthesized by different concentrations of cationic surfactant (CTABr) was coated on the working electrode in the three-electrode system to analyze the catalytic electrochemical behavior of Pt/C catalyst, and the obtained cyclic voltammetry was obtained. The experimental results are shown in Figure 27. In the twenty-seventh figure, the potential-0.3V to 0.0V~0.2V (vs. Ag/AgCl) belongs to the adsorption and desorption reaction of a single layer of hydrogen. The amount of electricity scanned between this potential can be directly converted into the surface area of the catalyst (also known as the active area), and the conversion formula is as shown in Equation 4-4 to Formula 4-6.

Wherein Q _H is the transfer charge of hydrogen per square centimeter of the catalyst to be tested, Q _T is the total transfer charge of hydrogen desorption, Q _DL is the charge of the electric double layer, and I _a and I _d are hydrogen adsorption desorption The current, Q _H ^{0 ,} is the charge transferred per square centimeter of Pt monolayer hydrogen adsorption (Q _H ⁰ = 210 μC/cm ² ). The active area is the surface area of the catalyst that is electrically conductive and has water molecules or electrolyte contact, which is often smaller than the area of the catalyst that is actually coated on the electrode. From the calculation of Formula 4-4 to Formula 4-6, the active area of the catalyst prepared by different concentrations of surfactant (CTABr) can be determined. This is because the platinum particles prepared at a concentration of 4.12 mM / L (18% Pt / C) and 2.75 mM / L (15% Pt / C) have smaller average particle diameters and better dispersibility, so platinum particles With a large active area, the utilization rate of the catalyst can be greatly improved. The part between the potential of 0.1V and 0.8V is the Electric Double Layer. The width of the electric double layer is related to the voltage scanning speed. The faster the speed, the larger the width of the electric double layer. The scanning speed of this experiment is 0.01V/s, so the catalyst double layer prepared by the concentration of 4.12mM/L (18% Pt/C) and 2.75mM/L (15% Pt/C) is more sensitive than commercial catalyst. The media width is not affected by the voltage scanning rate. It is presumed that the reason is that the catalyst platinum particles are more uniform in the experiment, so the charged solid surface area increases, thus covering the solid surface charge and its adjacent movable ions. The cloud will also increase.

<<Platinum / carbon black catalyst analysis summary>>

According to the foregoing experimental results, it was shown that the use of a surfactant (CTABr) as a dispersant in combination with a hot reflux method to reduce platinum on carbon black does not affect the structure of the Pt/C catalyst. The diffraction plane of platinum metal is still (111), (200), (220) and (311). It is obvious that the crystal structure is F.C.C., and the catalyst after reduction has no obvious residual platinum oxide. According to the Debye-Scherrer equation, the average particle size of platinum particles on carbon black (XC-72) is 3.71~5.66nm, and the particle size is slightly smaller than the 4.35nm of platinum particles of commercial catalyst on carbon black, only 1.37mM/L CTABr. The 5.66 nm prepared by 10% Pt/C is slightly larger than the commercial catalyst, which is also caused by the too small particle size.

It can be clearly seen by SEM and TEM that Pt is highly dispersed on carbon black, and as the concentration of the dispersant decreases, the particle size of the reduced Pt nanoparticle decreases, and the relative particle size decreases. Low, the higher the degree of aggregation. Although the particle size decreases, the crystal structure of the Pt reduced by the three dispersion concentrations is confirmed by the diffraction pattern of the SAD selection region. The F.C.C. structure and the XRD analysis echo each other.

The Pt/C wt% weight percentage analyzed by EDS and TGA was analyzed by the Pt precursor self-made platinum/carbon black catalyst component, which was different from the preset content of 20%, and the concentration of the dispersant decreased Pt. The /C wt% weight percentage also decreased with the decrease (18.24%, 15.21%, 10.02%), and only 18.24% of the difference was the smallest, which is still acceptable. In addition, from the analysis of the composition of EDS, from another angle analysis, when the selected analysis position is the same as the difference of the metal composition, the meaning represented can be interpreted as uneven dispersion, and the relative metal composition difference is small, which means uniform dispersion. It can be inferred that the Pt particles in this study are uniformly dispersed on the carrier carbon black as the concentration of the dispersant increases, which also echoes the SEM and TEM aggregation analysis. Compared with the previously analyzed carbon black dispersion Pt particle size becomes smaller, the surface area increases, the overall BET value of the Pt/C catalyst increases, and the electrochemical catalytic activity area also increases.

<<The effect of different concentrations of dispersed platinum/carbon black catalyst (Pt/C) on fuel cell performance >>

The above platinum/carbon black catalyst (Pt/C) needs to be applied to a proton exchange membrane for use in a fuel cell, and an ion exchange membrane is required for the membrane electrode. The pre-processing steps of the proton exchange membrane (Nafion) in this case are disclosed below:

Step 1: First cut the Nafion film to a size of 4 cm x 4 cm, and immerse it in deionized water for 30 minutes.

Step 2: The Nafion film was taken out and placed in 5 wt.% hydrogen peroxide and heated at 80 ° C for 1 hour.

Step 3: Remove the Nafion film and immerse it in deionized water for 30 minutes.

Step 4: The Nafion film was taken out again into 1 M sulfuric acid and heated at 80 ° C for 1 hour.

Step 5: Remove the Nafion film and immerse it in deionized water for 30 minutes.

Step 6: Remove the Nafion film and store it in deionized water for later use.

The following is a method for preparing a platinum/carbon black catalyst (Pt/C) in a standard membrane electrode (such as the twenty-ninth figure):

Step 1: Take 0.1 gram of platinum/carbon black catalyst, 0.3 gram of 5 wt.% Nafion solution and 1 ml of alcohol into the sample bottle, and ultrasonically oscillate for 1 hour to prepare a catalyst slurry, as shown in the twenty-eighth figure. The platinum particles 12 are dispersed and bonded to the carbon black particles 10 and mixed in the proton exchange membrane fibers 15.

Step 2: The catalyst slurry uniformly mixed in step 1 is coated on a carbon cloth and dried by heating at 60 ° C for 3 hours.

Step 3: The proton exchange membrane and the two dried carbon cloths are subjected to hot pressing.

<<Single battery test>>

In this case, the three states of Dry air, Middle temperature and High wet are discussed in the single cell test. The three states set the temperature of the anode humidifier, the single cell and the cathode humidifier to (25). ⁰ C -25 ⁰ C -25 ⁰ C ), (45 ⁰ C -45 ⁰ C -45 ⁰ C ) and (75 ⁰ C -70 ⁰ C -75 ⁰ C ), and use (Johnson Matthey) commercial catalyst Pt /C 20 wt% compares the performance of a single cell.

<<Pt/C electrode catalyst with different weight percentages and overall temperature change of the battery>>

The Pt/C electrode catalysts of different weight percentages were fixed, and the Pt loading of the anode and the cathode was fixed at 0.4 mg/cm ² . The catalyst slurry was coated on a hydrophobic carbon cloth and a Nafion proton exchange membrane, and hot pressed at a pressure of 100 kgf and a temperature of 80 ° C for 120 seconds to prepare a membrane electrode (MEA). The membrane electrode was assembled into a single cell with a gas tight gasket, a bipolar plate, etc., and placed in a single cell test system (Beam 300) for measurement. The effect of different weight percentages of Pt/C electrode catalyst on the performance of the fuel cell as a function of the overall temperature of the battery was observed. Figures 30 to 33 show the voltage-current density curves and power-current density curves of Pt/C electrode catalysts with different weight percentages.

In this case, the self-made electrode catalysts Pt/C 18wt%, Pt/C 15wt% and Pt/C 10wt%, and the battery performance changes at low temperature and medium temperature were significantly improved. According to the inference of the electrode catalyst in the slightly humid state, the resistance Decreased relative battery performance. The high-humidity effect has many factors. The internal resistance effect caused by high temperature, the flooding of the anode and the cathode, the poor drainage and the high temperature change of the Nafion proton exchange membrane will affect the battery efficiency. Therefore, the battery performance is also varied. This experiment focuses on the feasibility and performance of this process, so it is not optimized for individual cells with different weight percentages of catalyst electrodes, so it is not discussed here.

The open circuit voltage, maximum current density and maximum power of the 30th to 33rd are shown in Table 4 and Table 5.

<<Dry Air battery efficiency>>

In the low-temperature dry air state of the single cell, the most primitive state of the electrode catalyst is mainly discussed. The catalyst and the integral membrane electrode set (MEA) have the highest resistivity, as shown in the thirty-fourth figure, the current density and The higher the power density, the better the performance, and the better the performance, which is better than the commercial catalyst (Johnson Matthey) Pt/C 20%. Firstly, the battery performance of the self-made catalyst is deduced. Since the dispersion effect is better as the concentration of the dispersant is increased, the average electrode catalyst particle size is also smaller, so the battery efficiency is improved. Compared with the commercial catalyst, the main factors are estimated to be three points. (1) The self-made Pt/C electrode catalyst particle size is equal to less than the commercial catalyst, which is proved by SEM and TEM. (2) BET specific surface area analysis is higher than that of commercial catalysts. (3) It can be seen from the electrochemical active area of CV that the electrochemical active area of the self-made Pt/C electrode catalyst is also larger than that of the commercial catalyst.

<<Medium temperature micro-wet (Middle Temperature) battery performance>>

As shown in the thirty-fifth figure, the single cell is in the medium temperature and slightly wet state, and the anode and cathode provide the micro-wet water vapor to reduce the resistance, so the battery performance is improved, and the same single cell performance using the self-made battery catalyst is better than the commercial use. The cell performance of the electrode catalyst is good.

<<High Temperature Wet Battery Performance>>

As shown in the thirty-sixth figure, the high-temperature wet state of the single cell has an extremely vicious environment, such as the overflow of the anode water, the lack of cathode drainage, the high humidity, the dissociation of the electrode catalyst and the Nafion membrane, and the thermal stability of the Nafion membrane, etc. The stability of the catalyst and the effect on the performance of the battery, the electrode catalyst made in this study is still excellent, and the current density and power density of the single cell are superior to those of the single cell using the commercial catalyst.

<<Single battery test summary>>

According to Table 4, as the electrode catalyst of the self-made electrode catalyst decreases, the open circuit voltage increases, but the difference value is about 1 to 3%. It is relatively impossible to investigate the active area of the catalyst, but the particle size of the Pt can be reduced. Out of the way, the current density becomes smaller, which is caused by Pt aggregation and internal resistance, and the relative power density also becomes smaller. According to Table 5, the self-made electrode catalyst is superior to the commercial catalyst Pt/C 20wt.% in the overall performance of the battery regardless of the low temperature drying, the moderate temperature and the low humidity and the high temperature.

Single cell test of 18.52% Pt/C electrode catalyst prepared using a dispersant (CTABr) concentration of 4.12 mM/L, whether in low temperature dry air or medium temperature low humidity and high temperature wet state, current density and power Density is best compared to the other two groups and compared to commercial catalysts. The cell performance of the self-made catalyst used in this study was superior to that of the single cell using commercial catalyst. It can be seen that the high-dispersion electrode catalyst prepared by the experimental process is quite excellent.

Although the present case is illustrated by a preferred embodiment, those skilled in the art can make various forms of changes without departing from the spirit and scope of the present invention. The above embodiments are only used to illustrate the present case and are not intended to limit the scope of the present invention. All kinds of modifications or changes that are not in violation of the spirit of the case are the scope of patent application in this case.

10. . . Carbon black particles

11. . . Stereo barrier layer

12. . . Platinum particles

15. . . Proton exchange membrane fiber

20. . . Cationic surfactant

twenty one. . . Chloroplatinic acid

30. . . reducing agent

The first figure shows a flow chart of the preparation method of platinum/carbon black (Pt/C) catalyst.

The second figure dispersant provides a schematic view of the surface of each carbon black particle forming a steric barrier layer.

The third figure is a schematic diagram of reduction of chloroplatinic acid to metallic platinum particles.

The fourth figure is a schematic diagram of the thermal reflow method in which metal platinum particles are dispersed and bonded to the surface of the carbon black particles.

The fifth graph adds a laser particle size analysis map of different concentrations of CTABr dispersed in a carbon black solution.

Figure 6 is a graph of platinum/carbon black catalyst X-ray diffraction literature.

Figure 7 is an X-ray diffraction analysis of platinum/carbon black (Pt/C) catalyst prepared at different concentrations (CTABr).

Figure 8 shows the background value X-ray diffraction analysis of ⁰ ~ 50 ⁰ .

Ninth of ¹⁰⁰ ~ ⁷⁰⁰ (CTABr) X-ray diffraction analysis of FIG.

The X-ray diffraction analysis of the (111) crystal plane of Pt prepared by different concentrations of dispersant (CTABr) from the tenth to the tenth D.

Fig. 11A to Fig. 11D are graphs of (220) crystal plane X-ray diffraction of Pt prepared by different concentrations of dispersant (CTABr).

Figure 12 is a Pt/C catalyst (SAD) diffraction pattern prepared at a concentration of 4.12 mM / L (CTABr).

Figure 13 is a Pt/C catalyst (SAD) diffraction pattern prepared at a concentration of 2.75 mM/L (CTABr).

Figure 14 is a Pt/C catalyst (SAD) diffraction pattern prepared at a concentration of 1.37 mM/L (CTABr).

The fifteenth figure commercial (Johnson Matthey) (20% wt) platinum / carbon black catalyst at 300,000 magnification scanning electron micrograph.

Figure 16 Scanning electron micrograph of a platinum/carbon black catalyst synthesized at a concentration of 4.12 mM/L at a magnification of 300,000.

Figure 17 Scanning electron micrograph of a platinum/carbon black catalyst synthesized at a concentration of 2.75 mM/L at a magnification of 300,000.

Figure 18. Scanning electron micrograph of a platinum/carbon black catalyst synthesized at a concentration of 1.37 mM/L at a magnification of 300,000.

Figure 19 is a transmission electron micrograph of a commercial (Johnson Matthey) catalyst at 100,000 magnification.

Figure 20 is a transmission electron micrograph of a commercial (Johnson Matthey) catalyst at 100,000 magnification.

Figure 21 is a transmission electron microscope photograph of a synthetic catalyst at a concentration of 2.75 mM/L at a magnification of 100,000.

Figure 22 is a transmission electron micrograph at a concentration of 1.37 mM/L of the synthesized catalyst at 100,000 magnification.

Twenty-third figure Johnson Matthey 20% Pt / C electrode catalyst nitrogen isothermal adsorption desorption curve.

Twenty-fourth figure 4.12 mM / L CTABr 18% Pt / C electrode catalyst nitrogen isothermal adsorption desorption curve.

Figure 25. 2.75 mM / L CTABr 15% Pt / C electrode catalyst nitrogen isothermal adsorption desorption curve.

Figure 26. Figure 1.37 mM/L CTABr 15% Pt/C catalyst nitrogen isothermal adsorption desorption curve.

Figure 27 is a cyclic voltammetry plot of platinum/carbon black catalyst.

Figure 28 is a schematic diagram of the catalyst slurry.

The twenty-ninth figure platinum/carbon black catalyst (Pt/C) is realized in the preparation method of the standard membrane electrode.

Figure 30 Johnson Matthey 20% Pt / C electrode catalyst Pt loading 0.4 mg / cm ² voltage - current density - power density curve.

Figure 31 4.12 mM / L CTABr 18% Pt / C electrode catalyst Pt loading 0.4 mg / cm ² voltage - current density - power density curve.

Thirty-second graph 2.75 mM / L CTABr 15% Pt / C electrode catalyst Pt loading 0.4 mg / cm ² voltage - current density - power density curve.

Thirty-third graph 1.37 mM / L CTABr 10% Pt / C electrode catalyst Pt loading 0.4 mg / cm ² voltage - current density - power density curve.

Figure 34. Dry Air Pt loading 0.4 mg / cm ² voltage-current density-power density curve.

Figure 35: Middle Temperature Pt loading 0.4 mg / cm ² voltage-current density-power density curve.

Figure 36 High Wet Pt loading 0.4 mg / cm ² Voltage-current density-power density curve

Claims (9)

A high-performance and high-dispersion electrode catalyst preparation method comprises the following steps: mixing a dispersant with a catalyst carrier to form a steric barrier layer on the surface of each catalyst carrier to produce a dispersion effect; Adding a nano-precious metal catalyst particle precursor to the mixture of the above dispersant and the catalyst carrier, the precursor is linked to the stereo barrier layer; and step 3, the dispersant, the catalyst carrier and the former Adding a reducing agent to the mixture of the reactants, and performing hot reflux at 80 ° C for several hours; in step 4, the product of the third step is sequentially filtered and washed, and the stereoscopic barrier layer is removed by heat treatment to reduce the precursor to The nano-precious metal catalyst particles are evenly distributed and bonded to the surface of each particle of the catalyst carrier; the heat treatment method comprises vacuum heating and drying, sequential heating and temperature holding, natural cooling and high vacuum drying and sintering. Wait for steps. The high-performance and high-dispersion electrode catalyst preparation method according to claim 1, wherein the dispersant is a surfactant. The high-performance and high-dispersion electrode catalyst preparation method according to the first aspect of the invention, wherein the dispersant is a cationic surfactant. The high-performance and high-dispersion electrode catalyst preparation method according to claim 3, wherein the cationic surfactant is cetyltrimethylammonium bromide (CTABr). The high-performance and high-dispersion electrode catalyst preparation method according to claim 1, wherein the catalyst carrier is carbon black. The high-performance and high-dispersion electrode catalyst preparation method according to claim 1, wherein the nano-precious metal catalyst particles are platinum. The method for preparing a high-performance and high-dispersion electrode catalyst according to the first aspect of the patent application, wherein the vacuum heating drying temperature in step 4 is 80 ° C; the step temperature heating and temperature-holding system are stepwise heating at 1 ° C per minute. At 300 ° C, the temperature was raised to 100 ° C, 150 ° C, 200 ° C, and 300 ° C for 30 minutes. The high-performance and high-dispersion electrode catalyst preparation method according to the first aspect of the invention, wherein the nano precious metal catalyst particles are uniformly distributed in the carrier particles in a face-centered cubic crystal structure. A high-performance and high-dispersion electrode catalyst preparation method, comprising: step one, mixing quantitative black carbon, acetone, deionized water, and low-concentration cationic surfactant for ultrasonic vibration; step two, chlorine Platinum acid ( H ₂ PtCl ₆ *6 H ₂ O ), sodium hydroxide (NaOH) is added to the mixture of step one, and ultrasonic vibration is continued; in step three, the mixture of step two is added to the weak reducing agent at 80 ° C The heat is refluxed for several hours; in step four, the product of step three is filtered with filter paper, washed with deionized water, and dried in a vacuum environment at 80 ° C; then heated in an environment of 1 ° C per minute to a temperature of 300 ° C. When the temperature is raised to 100 ° C, 150 ° C, 200 ° C, and 300 ° C, the temperature is maintained for 30 minutes, and finally, the temperature is naturally lowered to room temperature, and then dried and sintered in a high vacuum environment.