Preparation method of platinum-carbon catalyst

Abstract

The invention discloses a preparation method of a platinum-carbon catalyst, which comprises the following steps: adding a metal oxide and a hydrophilic surfactant into deionized water to form a mixed pre-reaction solution; adding carbon powder subjected to hydrophilic treatment, uniformly dispersing to obtain a carbon dispersion liquid, adding an alcoholic solution into the carbon dispersion liquid, stirring, and carrying out hydrothermal or solvothermal reaction; a platinum precursor, a reducing agent and salt or organic matter providing an alkaline environment are added into deionized water to form a platinum precursor solution, a reducing agent solution and an alkaline precursor solution; adding into the treated carbon dispersion liquid; and carrying out acid treatment and water washing to obtain the platinum-carbon catalyst. According to the invention, a surfactant and an oxide are used for adjusting the distance between carbon-loaded platinum nano-metal particles, and a Pt / C precursor with high-loading platinum nano-particles dispersed on carbon carriers with different specific surface areas can be obtained, so that the growth of platinum particles is prevented in a hydrothermal or solvothermal process, and the particle size is controlled.

Description

Technical Field

[0001] The invention belongs to the technical field of manufacturing key materials for fuel cells, and specifically relates to a method for preparing a platinum-carbon catalyst. Background Art

[0002] In recent years, fuel cells have attracted much attention due to their high energy conversion efficiency and green environmental protection, and have become a powerful alternative to traditional energy storage devices. Among them, proton exchange membrane fuel cells have low operating temperatures and fast startup speeds, and are widely used in transportation, power backup, and mobile fields. Pt-based materials play a vital role in improving the cathode kinetics of proton exchange membrane fuel cells due to their high oxygen reduction activity. However, Pt-based materials are in short supply and expensive. At the same time, Pt has a high surface migration energy. At high temperatures, Pt-based catalysts are prone to agglomeration, and the grain size increases, resulting in a decrease in specific surface area, thereby reducing oxygen reduction activity and durability. Therefore, it is urgent to explore solutions to the problem of Pt-based catalyst agglomeration.

[0003] In order to reduce the agglomeration of Pt nanoparticles, a large number of studies have been conducted at home and abroad, such as introducing transition metals to form platinum alloys with platinum, but their physical and chemical stability is low. During the test, transition metals are easily dissolved, and the disordered arrangement in the alloy leads to reduced electrochemical activity and stability, which limits the improvement of oxygen reduction performance. It is worth noting that by introducing surfactants or metal oxides, the spatial restriction strategy may help control the growth of platinum at high temperatures. Among them, the introduction of surfactants can assist in dispersing the precursors when the carbon carrier loads the platinum nanoparticle precursors to prevent them from being subsequently converted into platinum nanoparticles. However, the hydrophilicity of the surfactant can also change the surface binding force of the carbon powder after dispersion to varying degrees, thereby effectively reducing the agglomeration of Pt nanoparticles on the surface of the carbon powder. Therefore, the selection of surfactants will affect the performance of platinum-based catalysts to a certain extent. The introduction of high-content metal oxides such as MgO, SnO, etc. is easy to form an oxide layer on the surface of the material. The steric hindrance can effectively stabilize the platinum particles from agglomeration at high temperatures, limit the size of the platinum particles, and the oxides are easily dissolved by acid or alkali, which is convenient for removal in the catalyst and does not affect the activity of the platinum-based catalyst in the subsequent process. Therefore, the present invention provides a new method for preparing a platinum-carbon catalyst with highly dispersed platinum particles by simultaneously introducing metal oxides and surfactants. Summary of the invention

[0004] In order to solve the defects of the prior art, an appropriate ratio of surfactant to metal oxide has a promoting effect on inhibiting the agglomeration of platinum particles. The present invention provides a method for preparing an efficient platinum-carbon catalyst.

[0005] In order to solve the above technical problems, the present invention provides the following technical solutions:

[0006] The present invention provides a method for preparing a platinum-carbon catalyst, comprising the following steps:

[0007] Step 1: adding the oxide and the hydrophilic surfactant into deionized water and dispersing them evenly to form a mixed pre-reaction solution;

[0008] Step 2: Add the hydrophilically treated carbon powder to the mixed pre-reaction solution in step 1, disperse it evenly to obtain a carbon dispersion, add an alcohol solution to the carbon dispersion, stir it, and perform a hydrothermal or solvothermal reaction;

[0009] Step 3: Adding a platinum precursor, a reducing agent, and a salt or organic matter providing an alkaline environment into deionized water to form a platinum precursor solution, a reducing agent solution, and an alkaline precursor solution;

[0010] Step 4: Adjust the pH of the carbon dispersion treated in step 2 to 10-12, add the platinum precursor solution, the reducing agent solution, and the alkaline precursor solution in batches while stirring, and control the temperature at 60-150° C. during the addition process, react for 2-8 hours, and stir at a rate of 300-1000 rpm;

[0011] Step 5: The solution obtained by the reaction in step 4 is treated with acid and washed with water to obtain a platinum-carbon catalyst.

[0012] Preferably, in step 1, at least one of magnesium oxide, aluminum oxide, zinc oxide, iron oxide, nickel oxide, cobalt oxide and chromium oxide is used;

[0013] The hydrophilic surfactant is at least one of cellulose, vinyl acetate polymer, copolymer with vinyl acetate, hemicellulose, starch, pectin, alginic acid, polyacrylamide, H+ type polyacrylic acid, H+ type polymethacrylic acid, H+ type polymaleic acid, condensation product of sulfonated bisphenols, and lignin; these hydrophilic polymers are hydrophilized by hydrophilic groups such as hydroxyl group, ether group, carboxyl group, ketone group, amide group, H+ type sulfonic acid group, sulfonyl group, ester group, etc.

[0014] The added masses of the oxide and the hydrophilic surfactant are both 1:10 to 1:100 of the preset carbon mass; the ratio of the added volume of the deionized water to the preset carbon mass is 0.1 L / g to 1 L / g.

[0015] Preferably, the dispersion method in step 1 and step 2 is one of dispersion using a homogenizer, a shearing machine, an ultrasonic machine, and an ultrasonic rod.

[0016] Preferably, the carbon powder in step 2 is at least one of activated carbon, mesoporous carbon, carbon nanotubes, and carbon fibers, and the hydrophilicity treatment method of the carbon powder is one of plasma etching and strong acid oxidation.

[0017] Preferably, in step 2, the volume ratio of alcohol to carbon dispersion is 1:10 to 3:1, the stirring rate is 300 to 1000 rpm, the hydrothermal or solvent thermal reaction time is 12 to 18 hours, and the reaction temperature is 120°C.

[0018] Preferably, in step 3, the volume ratio of the platinum precursor mass to deionized water is 1g / L to 20g / L, the volume ratio of the reducing agent to deionized water is 10g / L to 20g / L, the volume ratio of the salt or organic matter providing an alkaline environment to deionized water is 10g / L to 50g / L, the molecular ratio of the platinum precursor to the reducing agent is 1:10 to 1:40, and the molecular ratio of the platinum precursor to the salt or organic matter providing an alkaline environment is 1:20 to 1:40.

[0019] Preferably, the platinum precursor in step 3 is at least one of chloroplatinic acid, potassium chloroplatinate, potassium chloroplatinite, platinum chloride, platinum nitrate, tetraaminoplatinum nitrate, and platinum acetylacetonate;

[0020] The reducing agent is at least one of sodium borohydride, potassium borohydride, hydrazine hydrate, hydrazine hydrochloride hydrate, ethanol, formic acid, ethylene glycol, and glycerol;

[0021] The salt or organic matter providing the alkaline environment is at least one of ammonium bicarbonate, urea and melamine.

[0022] Preferably, in step 4, the pH is adjusted by adding one of aqueous ammonia, sodium hydroxide and potassium hydroxide.

[0023] Preferably, the acid solution used for the acid treatment in step 5 includes at least one of sulfuric acid, nitric acid, perchloric acid and hydrochloric acid, the concentration of the acid solution used is controlled at 0.5M to 2M, the pickling temperature is 50°C to 90°C, and the pickling time is 0.2 to 4 hours.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] (1) The present invention uses surfactants and oxides to adjust the spacing between carbon-loaded platinum nanoparticles, and can obtain a Pt / C precursor with high-loaded platinum nanoparticles dispersed on carbon carriers with different specific surface areas, thereby ensuring that platinum particle growth is prevented during the hydrothermal or solvothermal process and controlling the particle size. The carbon powder is hydrophilized by using a surfactant, and a double electric layer is formed on the surface of the carbon powder after the surfactant is attached, and the double electric layer repel each other, so that the carbon powder is evenly dispersed in the solvent, which is conducive to exposing a larger effective load area of ​​the carbon powder. At the same time, the spatial barrier effect of the surfactant further makes the metal ions evenly distributed on the carbon surface.

[0026] (2) The present invention introduces a surfactant onto the carbon carrier in advance, which serves to assist in dispersing the precursor when loading the platinum nanoparticle precursor and prevent it from migrating when it is subsequently converted into platinum nanoparticles. At the same time, the hydrophilicity of the surfactant can also change the surface binding force of the carbon powder after dispersion, and introduce an oxide to form a steric hindrance on the surface of the carbon powder, further enhancing the dispersion of the platinum particle precursor, thereby obtaining a well-dispersed platinum-carbon catalyst.

[0027] (3) The oxide is easily dissolved by acid or alkali in the subsequent process, which is convenient for removal from the catalyst and does not affect the activity of the catalyst in the subsequent process. The oxide space barrier is deposited on the surface of the carbon powder by self-precipitation, hydrolysis, etc. to form nano-sized particles. It is not a single particle or other morphology. Surfactants and oxide space barrier agents are first complexed with oxides and hydrophilic surfactants, and then an oxide layer with a surface coating layer is formed on the surface of the carbon powder; the oxide nanoparticles in the coating layer have a certain nano-size effect as space barrier. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 is the XRD pattern of the platinum-carbon catalyst obtained in Examples 1-4 of the present invention;

[0029] Figure 2 CV diagram of the platinum-carbon catalyst obtained in Examples 1-4 of the present invention;

[0030] Figure 3 is the LSV diagram of the platinum-carbon catalyst obtained in Examples 1-4 of the present invention;

[0031] Figure 4 It is a TEM image of the platinum-carbon catalyst obtained in Examples 1-4 of the present invention. DETAILED DESCRIPTION

[0032] The preferred embodiments of the present invention are described below in conjunction with the accompanying drawings. It should be understood that the preferred embodiments described herein are only used to illustrate and explain the present invention, and are not used to limit the present invention.

[0033] Define the ratio a of the metal loading to the actual specific surface area of ​​the carbon powder used. For example, for a 20 wt.% platinum metal loading, the specific surface area of ​​the carbon powder is 80 m 2 / g, then the parameter is a=80*0.8 / 0.2 / 100=3.2; the proposed reasonable range of a ratio is 2.8 to 60; wherein the preferred range of a is 2.8 to 7.2. When the a value is in the preferred range, the uniformity of platinum nanoparticles and the dispersion distance between each particle are improved, so that the dispersion of each particle is uniform.

[0034] Embodiment 1:

[0035] 1) Weigh 0.3 g of cellulose and 1 g of magnesium oxide and disperse them in 15 L of water. Use a homogenizer to disperse them evenly to obtain a mixed pre-reaction solution.

[0036] 2) Add 30 g of carbon powder that has been hydrophilized by etching with hydrofluoric acid and ammonia gas step by step to the mixed pre-reaction solution, disperse it evenly with an ultrasonic rod and a homogenizer, add 3 L of ethylene glycol and continue stirring, maintain a stirring rate of 800 rpm, heat the solution to 120° C. and maintain it for 12 hours.

[0037] 3) Weigh 43.47 g of potassium chloroplatinite and dissolve it in 2.5 L of deionized water, weigh 8.43 g of sodium borohydride and dissolve it in 0.5 L of deionized water, and weigh 123 g of urea and dissolve it in 3 L of deionized water, and disperse them evenly.

[0038] 4) The pH value of the carbon powder dispersion was adjusted to 11 with potassium hydroxide and the temperature was raised to 90° C. Potassium chloroplatinite solution, sodium borohydride solution and urea solution were added in batches while the stirring rate was maintained at 800 rpm.

[0039] 5) washing with 0.5 M sulfuric acid at 60° C. for 2 h, and then filtering and washing with deionized water to obtain a platinum-carbon catalyst.

[0040] The XRD, CV and LSV data obtained in this example are marked as Figure 1-3 The middle curve is TEM. Figure 4-1 .

[0041] Embodiment 2:

[0042] The steps of Example 1 are the same as those of Example 1, except that in step 1), the surfactant is 1 g of alginic acid, the oxide is 2 g of aluminum oxide, and in step 3), the potassium chloroplatinite is 123 g of a platinum nitrate solution containing 16% platinum. The remaining steps are the same as those of Example 1.

[0043] The XRD, CV and LSV data obtained in this example are marked as Figure 1-3 The middle 2 curves, TEM is Figure 4-2 .

[0044] Embodiment 3:

[0045] The steps of Example 1 are as follows, except that in step 1), the surfactant is 1g H+ type polymaleic acid, the oxide is 1.5g chromium oxide, in step 2), the content of ethylene glycol is adjusted to 2L, the stirring rate is maintained at 800rpm to heat the solution to 15h, and the reaction temperature remains unchanged; in step 4), the pH is adjusted to 11 with concentrated ammonia water, and the platinum precursor solution, the reducing agent solution, and the alkaline precursor solution are added in batches, the temperature is controlled at 90°C, and the reaction is carried out for 4 hours. The remaining steps are the same as those of Example 1.

[0046] The XRD, CV and LSV data obtained in this example are marked as Figure 1-3 The 3 curves in the middle are TEM Figure 4-3 .

[0047] Embodiment 4:

[0048] The steps of Example 1 are followed, except that in step 1), the surfactant is 1 g of lignin, the oxide is 2 g of nickel oxide, and in step 4), the pH is adjusted to 10 using concentrated ammonia water and the temperature is raised to 90° C. The remaining steps are the same as those of Example 1.

[0049] The XRD, CV and LSV data obtained in this example are marked as Figure 1-3 The 4 curves in the middle are TEM Figure 4-4 .

[0050] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art can still modify the technical solutions described in the aforementioned embodiments or replace some of the technical features therein by equivalents. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for preparing a platinum-carbon catalyst, characterized in that: The following steps are involved: Step 1: adding metal oxide and hydrophilic surfactant into deionized water and dispersing them evenly to form a mixed pre-reaction solution; Step 2: Add the hydrophilically treated carbon powder to the mixed pre-reaction solution in step 1, disperse it evenly to obtain a carbon dispersion, add an alcohol solution to the carbon dispersion, stir it, and perform a hydrothermal or solvothermal reaction; Step 3: Adding a platinum precursor, a reducing agent, and a salt or organic matter providing an alkaline environment into deionized water to form a platinum precursor solution, a reducing agent solution, and an alkaline precursor solution; Step 4: Adjust the pH of the carbon dispersion treated in step 2 to 10-12, add the platinum precursor solution, the reducing agent solution, and the alkaline precursor solution in batches while stirring, and control the temperature at 60-150° C. during the addition process, react for 2-8 hours, and stir at a rate of 300-1000 rpm; Step 5: The solution obtained by the reaction in step 4 is treated with acid and washed with water to obtain a platinum-carbon catalyst.

2. The method for preparing a platinum-carbon catalyst according to claim 1, characterized in that: In step 1, at least one of magnesium oxide, aluminum oxide, zinc oxide, iron oxide, nickel oxide, cobalt oxide, and chromium oxide is used; The hydrophilic surfactant is at least one of cellulose, vinyl acetate polymer, copolymer with vinyl acetate, hemicellulose, starch, pectin, alginic acid, polyacrylamide, H+ type polyacrylic acid, H+ type polymethacrylic acid, H+ type polymaleic acid, condensation product of sulfonated bisphenols, and lignin; The added masses of the oxide and the hydrophilic surfactant are both 1:10 to 1:100 of the preset carbon mass; the ratio of the added volume of the deionized water to the preset carbon mass is 0.1 L / g to 1 L / g.

3. The method for preparing a platinum-carbon catalyst according to claim 1, characterized in that: The dispersion method in step 1 and step 2 is one of a homogenizer, a shearing machine, ultrasound, and a ball mill.

4. The method for preparing a platinum-carbon catalyst according to claim 1, characterized in that: The carbon powder in step 2 is at least one of activated carbon, mesoporous carbon, carbon nanotubes, and carbon fibers, and the hydrophilicity treatment method of the carbon powder is one of plasma etching and strong acid oxidation.

5. The method for preparing a platinum-carbon catalyst according to claim 1, characterized in that: In step 2, the volume ratio of alcohol to carbon dispersion is 1:10 to 3:1, the stirring rate is 300 to 1000 rpm, the hydrothermal or solvent thermal reaction time is 12 to 18 hours, and the reaction temperature is 120°C.

6. The method for preparing a platinum-carbon catalyst according to claim 1, characterized in that: In step 3, the volume ratio of the platinum precursor mass to deionized water is 1g / L to 20g / L, the volume ratio of the reducing agent to deionized water is 10g / L to 20g / L, the volume ratio of the salt or organic matter providing an alkaline environment to deionized water is 10g / L to 50g / L, the molecular ratio of the platinum precursor to the reducing agent is 1:10 to 1:40, and the molecular ratio of the platinum precursor to the salt or organic matter providing an alkaline environment is 1:20 to 1:

40.

7. The method for preparing a platinum-carbon catalyst according to claim 1, characterized in that: The platinum precursor in step 3 is at least one of chloroplatinic acid, potassium chloroplatinate, potassium chloroplatinite, platinum chloride, platinum nitrate, tetraaminoplatinum nitrate, and platinum acetylacetonate; The reducing agent is at least one of sodium borohydride, potassium borohydride, hydrazine hydrate, hydrazine hydrochloride hydrate, ethanol, formic acid, ethylene glycol, and glycerol; The salt or organic matter providing the alkaline environment is at least one of ammonium bicarbonate, urea and melamine.

8. The method for preparing a platinum-carbon catalyst according to claim 1, characterized in that: In step 4, the pH is adjusted by adding one of ammonia water, sodium hydroxide and potassium hydroxide.

9. The method for preparing a platinum-carbon catalyst according to claim 1, characterized in that: The acid solution used for the acid treatment in step 5 includes at least one of sulfuric acid, nitric acid, perchloric acid and hydrochloric acid. The concentration of the acid solution used is controlled at 0.5M to 2M, the pickling temperature is 50°C to 90°C, and the pickling time is 0.2 to 4 hours.

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