CN111569868A - Method for preparing catalyst loaded on carbon - Google Patents

Abstract

The invention relates to the field of electrochemical catalysts, and in particular to a method for making a carbon-supported catalyst, comprising the steps of (i) adjusting chemical parameters in an acidic aqueous solution to form an insoluble platinum oxide, said aqueous solution comprising a slurry of suspended carbon support particles such that the platinum oxide is attached to the carbon particles; (ii) the pH value of the aqueous solution is controlled to be 1.5-5.5, and the temperature is controlledThe temperature is controlled at 35-95 ℃; (iii) the attached platinum oxide is reduced in solution with a reducing agent under different conditions, the reducing agent being N₂H₂,NaBH₄,NaH₂PO₂,HCHO,H₂C₂O₄(ii) a (iv) (iv) filtering and drying the product obtained in step (iii). Various loading levels, such as 5% or 95% Pt/C (weight percent), can be made using a carbon-supported catalyst manufacturing process in which the platinum particles are small and are distributed uniformly on the carbon support, having a high total surface area and thus high activity.

Description

Method for preparing catalyst loaded on carbon

Technical Field

The invention relates to the field of electrochemical catalysts, in particular to a method for preparing a catalyst loaded on carbon.

Background

There are several methods for making the catalyst. An early approach was as described in U.S. Pat. Nos. 3,992,512 and 4,059,5Platinum sulfite complexes are used as precursors 41. This method first synthesizes H₃Pt(SO₃)₂OH, then reacts with hydrogen peroxide to produce a colloid, which can be adsorbed on carbon or left in solution and finally reduced (e.g. with N)₂H₂Or hydrogen) into platinum particles. The pH value of the prepared platinum particles is generally large, the platinum particles are unevenly distributed on a carbon carrier, and sulfur is not easily removed completely, so that the performance of the catalyst is negatively influenced.

The other path is S₂O₃ ^2-Reduction of chloroplatinic acid, H₂PtCl₆In the case of a carbon support, the formed colloidal platinum particles are adsorbed on the carbon support, but this adsorption is complicated and difficult to reproduce, and particularly difficult to achieve when the platinum loading is high. Therefore, the reaction is very slow, large particles are easily formed, the total area of the particles is small, the particles are not uniformly distributed on the carbon carrier, and the performance is poor.

In another method, the platinum catalyst particles are first precipitated as a metal hydroxide and then reduced. For example, in US4,392,927, a platinum precursor is added to a sodium carbonate solution to precipitate it, which is finally reduced. However, the intermediate metal hydroxide has no fixed composition and is generally not very reproducible and is not formed uniformly in solution, with the result that the final catalyst particles are very non-uniform and have poor properties.

In the preparation of platinum catalysts, the complexes are synthesized in combination with reducing agents. Chloroplatinic acid (H) as in patent US8012905B2₂PtCl₆) At 140 ° f, platinum particles form and are protected by ethylene glycol from polymerizing into large particles. This patent also uses ethanol/water as a solvent with a reducing agent, polyvinyl pyrrolidone (PVP) as the ligand, and reacts at 90 degrees Celsius to give a slightly inferior catalyst. As described in the patent, this method requires a long washing time to wash the chloride ions to<300ppm, and can not meet the industrial requirement. Also, the ethylene glycol and PVP remaining in the catalyst can affect performance. In the Catalysis Letters volume 129, pages 1-6 (2009), the authors Jeong Y.park et al complex with several nitrogen and sulfurTo prevent platinum particles from polymerizing into large particles. The precursor is K₂PtCl₄The reducing agent is NaBH₄The reaction was carried out in a 50-degree aqueous solution. The platinum particles thus produced are large (12nm) and the ligands are difficult to remove, using UV light, which is difficult to achieve in mass production.

Disclosure of Invention

In order to solve the above problems in the background art, the present invention provides a method for preparing a catalyst supported on carbon, comprising the steps of:

(i) adjusting the chemical parameters in an acidic aqueous solution comprising a slurry of suspended carbon support particles such that the platinum oxide is attached to the carbon particles to form an insoluble platinum oxide;

(ii) the pH value of the aqueous solution is controlled to be 1.5-5.5, and the temperature is controlled to be 35-95 ℃;

(iii) the attached platinum oxide is reduced in solution with a reducing agent under different conditions, the reducing agent being N₂H₂,NaBH₄,NaH₂PO₂,HCHO,H₂C₂O₄；

(iv) (iv) filtering and drying the product obtained in step (iii).

On the basis of the scheme, the insoluble platinum oxide is formed by taking a halogen complex of platinum as a precursor, reacting the halogen complex of platinum with a water-soluble silver compound in a high-temperature aqueous solution to form an insoluble halogen compound, and filtering; the precursor is H₂PtCl₆,Na₂PtCl₆,Na₂PtCl₄,K₂PtCl₄,Na₂PtBr₆,Na₂PtI₆The water-soluble silver compound is silver nitrate or silver acetate, and the insoluble halogen compound is AgCl, AgBr or AgI; insoluble platinum oxides are formed in the filtrate after adjusting the temperature and the pH.

On the basis of the scheme, further, the chemical parameter adjustment comprises the adjustment of pH through NaOH, KOH and Na₂CO₃,NH₄And (4) adjusting OH.

On the basis of the scheme, further, the adjusting of the chemical parameters comprises adjusting the temperature to increase from room temperature to 35-95 ℃.

Based on the above scheme, further, the surface area of the carbon carrier particles is more than 40m²/g。

In addition to the above, further, before forming the insoluble platinum oxide, the slurry of suspended carbon support particles is first dispersed in a strong acid which is one of the following or a mixture of the following: HClO₄,HBrO₄,HNO₃,CF₃COOH,CH₃C₆H₅SO₃H,CF₃SO₃H,HCl,HBr。

A method of making a carbon-on-carbon catalyst comprising the steps of:

(i) adjusting the chemical parameters in an acidic aqueous solution comprising a slurry of suspended carbon support particles such that the platinum oxide is attached to the carbon particles to form an insoluble platinum oxide;

(ii) the pH value of the aqueous solution is controlled to be 1.5-5.5, and the temperature is controlled to be 35-95 ℃;

(iii) the attached platinum oxide is reduced at 100 to 600 ℃ in hydrogen or a mixed gas containing hydrogen after being filtered and dried.

The object of the present invention is to provide a platinum catalyst on carbon carrier and a method for preparing the same, which is advantageous in that various loading amounts, such as 5% or 95% Pt/C (weight percentage), etc., can be prepared, wherein platinum particles are small and distributed uniformly on the carbon carrier, and have a high total surface area, and thus, high activity.

It is a further object of the present invention to provide a gas diffusion electrode for electrochemical applications, in which the catalyst employs a platinum catalyst on a carbon support; in this catalyst, the platinum particles are small and are distributed uniformly on the carbon support, and have a high total surface area, and therefore, the activity is high.

It is yet another object of the present invention to provide a CCM (catalyst-coated membrane) for electrochemical applications, wherein the catalyst in the CCM employs a platinum catalyst on a carbon support; in this catalyst, the platinum particles are small and are distributed uniformly on the carbon support, and have a high total surface area, and therefore, the activity is high.

It is a further object of the present invention to provide a membrane-electrode assembly (membrane-electrode-assembly) for electrochemical applications, wherein the catalyst in the membrane-electrode assembly employs a platinum catalyst on a carbon support; in this catalyst, the platinum particles are small and are distributed uniformly on the carbon support, and have a high total surface area, and therefore, the activity is high.

The catalyst on carbon obtained by the preparation process of the present invention may be very small particles, e.g. in the order of nanometers (10-9 meters), and therefore have a very high surface area. The catalyst may be supported on a highly conductive support, such as a carbon support, or unsupported 100% precious metal catalyst particles. The main applications are in the electrochemical industry, such as batteries and electrolysis, where CCM (catalyst-coated membrane) or gas diffusion electrodes made according to the present invention have superior performance in hydrogen/oxygen or hydrogen/air or other fuel cell operations.

Detailed Description

In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the following description will clearly and completely describe the embodiments of the present invention, and obviously, the described embodiments are a part of the embodiments of the present invention, but not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

The invention makes use of the special chemistry of platinum metals: the lower solubility of platinum ions in neutral or slightly acidic aqueous solutions forms platinum hydroxides of low solubility. The platinum hydroxide can be adsorbed on a carbon support and post-treated to obtain a carbon-supported catalyst. We can derive from precursors of platinum, e.g. K₂PtCl₄Initially, chloride ions are removed and platinum is removed to form hydrated ions. However, prior to removal, the pH of the solution is adjusted to a slightly acidic pH, e.g., 1-5, and the pH is raised after the chloride ions are removed to form a precipitate of platinum hydroxide, which is adsorbed onto the carbon particles if present. The carbon support may be selected from the following, as desired: vulcan XC-72and Black Pearl 2000(Cabot Corp.), and Ketjen Black (Akzo Nobel); other higher graphitizable conductive carbon blacks such as acrylonitrile blacks may also be used as desired.

The present invention provides the following examples:

the first embodiment is as follows: 100 g of 20% Pt on Vulcan XC-72 carbon

47.17 g Na₂PtCl₄·xH₂O (Pt 42.4%) was dissolved in 334mL of deionized water, and 66mL of 70% hcl lo was added₄(11.6mol/L) and stirring uniformly. Preparing 1mol/L silver nitrate solution: 71.4 grams of silver nitrate was dissolved in 420mL of deionized water. The solution was added dropwise over 40 minutes with continued stirring to which Na had been added₂PtCl₄·xH₂O in solution. After stirring for a further 30 minutes, the silver chloride precipitate was filtered and washed three times with 200mL of deionized water and the filtrate was added.

Additionally, 80 grams of Vulcan XC-72 from Cabot corp. was suspended in 2.8 liters of deionized water and treated with a homogenizer for 15 minutes to give a carbon slurry. The above filtrate was added to the carbon slurry over 10 minutes with constant stirring. After addition, the mixture was stirred for another 10 minutes, heated to 90 ℃ after half an hour, and reacted at 90 ℃ for one hour. The heating and stirring were then stopped, and after allowing the slurry precipitate to cool, it was filtered and washed with deionized water. The collected catalyst cake was dried at 115 degrees celsius, broken up, and then heat treated at 250 degrees celsius under hydrogen.

Example two: 100 g of 20% Pt on Vulcan XC-72 carbon

47.17 g Na₂PtCl₄·xH₂O (Pt 42.4%) was dissolved in 334mL of deionized water, and 66mL of 70% hcl lo was added₄(11.6mol/L) and stirring uniformly. Preparing 1mol/L silver nitrate solution: 71.4 grams of silver nitrate was dissolved in 420mL of deionized water. The solution was added dropwise over 40 minutes with continued stirring to which Na had been added₂PtCl₄·xH₂O in solution. After stirring for a further 30 minutes, the silver chloride precipitate was filtered and washed three times with 200mL of deionized water and the filtrate was added.

Additionally, 80 grams of Vulcan XC-72 from Cabot corp. was suspended in 2.8 liters of deionized water and treated with a homogenizer for 15 minutes to give a carbon slurry. The above filtrate was added to the carbon slurry over 10 minutes with constant stirring. After addition, the mixture was stirred for another 10 minutes, heated to 90 ℃ after half an hour, and reacted at 90 ℃ for one hour. The pH was adjusted to 4-5 with NaOH, and then 234mL of formaldehyde was slowly added to the reaction solution over a short period of time. After the addition was complete, stirring was continued for an additional hour, then heating and stirring were stopped, and after allowing the slurry to settle and cool, it was filtered and washed with deionized water. The collected catalyst cake was dried at 115 deg.C and broken up.

Example three: 100 g of 30% Pt supported on Ketjen Black (Akzo Nobel) carbon

70.76 g of Na₂PtCl₄·xH₂O (Pt 42.4%) was dissolved in 501mL of deionized water, and 66mL of 70% hcl lo was added₄(11.6mol/L) and stirring uniformly. Preparing 1mol/L silver nitrate solution: 107.1 grams of silver nitrate was dissolved in 630mL of deionized water. The solution was added dropwise over 40 minutes with continued stirring to which Na had been added₂PtCl₄·xH₂O (Pt ═ 42.4%) in solution. After stirring for a further 30 minutes, the silver chloride precipitate was filtered and washed three times with 200mL of deionized water and the filtrate was added.

Further, 70 g of Ketjen Black carbon powder from Akzo Nobel was suspended in 2.45L of deionized water and treated with a homogenizer for 15 minutes to obtain a carbon slurry. The above filtrate was added to the carbon slurry over 10 minutes with constant stirring. After addition, the mixture was stirred for another 10 minutes, heated to 90 ℃ after half an hour, and reacted at 90 ℃ for one hour. The heating and stirring were then stopped, and after allowing the slurry precipitate to cool, it was filtered and washed with deionized water. The collected catalyst cake was dried at 115 degrees celsius, broken up, and then heat treated at 250 degrees celsius under hydrogen.

Example four: 100 g of 50% Pt on Black Pearl 2000 carbon

117.93 g of Na₂PtCl₄·xH₂O (Pt 42.4%) was dissolved in 835mL of deionized water, 66mL of 70% hcl lo was added₄(11.6mol/L) and stirring uniformly. Preparing 1mol/L silver nitrate solution: 178.5 grams of silver nitrate was dissolved in 1050mL of deionized water. The solution was stirred continuously for 40 minutesAdding Na dropwise₂PtCl₄·xH₂O (Pt ═ 42.4%) in solution. After stirring for a further 30 minutes, the silver chloride precipitate was filtered and washed three times with 200mL of deionized water and the filtrate was added.

In addition, 50 g of Black Pearl 2000 carbon powder from Cabot Corp. was suspended in 1.75L of deionized water and treated with a homogenizer for 15 minutes to obtain a carbon slurry. The above filtrate was added to the carbon slurry over 10 minutes with constant stirring. After addition, the mixture was stirred for another 10 minutes, heated to 90 ℃ after half an hour, and reacted at 90 ℃ for one hour. The heating and stirring were then stopped, and after allowing the slurry precipitate to cool, it was filtered and washed with deionized water. The collected catalyst cake was dried at 115 degrees celsius, broken up, and then heat treated at 250 degrees celsius under hydrogen.

The invention also provides a method for testing the performance of the catalyst, which comprises the following steps:

the test method is a rotating disk electrode method. This procedure can be found in t.schmidt, h.a. gasteiger, g.d.stab, p.m.urban, d.m.kolb, r.j.behm, j.electrochem.soc, 146(1999) 1296; h.a. gasteiger, s.s.kocha, b.sampalli, f.t.wagner.applied Catalysis, B2005, 56, 9-35. The latter document concludes from the results of the analysis that the rotating electrode is in HClO₄In the electrolyte, the measured current at 0.9V can correspond well to the current observed in the MEA test.

The method for preparing the slurry and the electrode comprises the following steps: after the catalyst is fully homogenized in a mixed solution of water and alcohol, a fixed amount of catalyst dispersion is taken by a pipette and smeared on a carbon indefinite rotary electrode (Pine Research, usa), after the catalyst dispersion is dried, a layer of film is deposited on the electrode, and the electrode is generally controlled to be coated with 16 micrograms of platinum or platinum/metal composite per square centimeter.

And (3) electrode testing: placing the electrode prepared by the above steps in 0.1mol/L HClO₄The voltage was swept (100mv/s) between 0.05Volts and 0.95Volts (relative to RHE) in the solution to remove the negatively acting chemicals introduced during the preparation of the catalyst coating. The electrochemical active area (ECSA) is determined by cyclic voltammetry (cy)The hydrogen adsorption current in the clic voltametry, hereinafter referred to as CV) graph was calculated (50 mv/s). The oxygen reduction activity is measured by 0.1mol/L HClO saturated with oxygen₄In (1), the electrode was swept from 0.3V to 0.95V at 1600RPM (1600 RPM) to measure the activity of the reduced oxygen, expressed as specific mass activity (a/mgPt, MA), 0.9V (relative to RHE), and during the test the factors due to the oxygen diffusion rate were corrected using standard methods, i.e. the limiting current plateau through low voltage corresponds to the oxygen diffusion rate correction. The specific area activity is calculated from the specific mass activity and ECSA.

The results of the rotating disk electrode tests are listed in table 1. A commercial 20% Pt/C, 50% Pt/C catalyst was used as a comparative standard.

Table 1 comparison of performance data for electrodes made with different catalyst types

Catalyst type	Specific mass activity A/mg Pt	Specific area Activity, uA/cm2 Pt
			Example 20% Pt/C	0.217	244
Example two 20% Pt/C	0.225	213
			Commercial 20% Pt/C	0.201	181
Example two 30% Pt/C	0.220	266
			Example III 50% Pt/C	0.214	289
Commercial 50% Pt/C	0.175	202

As shown in table 1, the 20% Pt/C or 50% Pt/C catalysts prepared by using the present invention have higher specific mass activity and specific area activity than the equivalent commercial catalysts, and these advantages can be explained by the superiority of the preparation method of the present invention, and the resulting catalysts have more complete platinum crystals and are uniformly distributed on the carbon support, so that the activity of reducing oxygen is high.

Finally, it should be noted that: the above embodiments are only used to illustrate the technical solution of the present invention, and not to limit the same; while the invention has been described in detail and with reference to the foregoing embodiments, it will be understood by those skilled in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some or all of the technical features may be equivalently replaced; and the modifications or the substitutions do not make the essence of the corresponding technical solutions depart from the scope of the technical solutions of the embodiments of the present invention.

Claims (7)

1. A method of making a carbon-on-carbon catalyst comprising the steps of:

(i) adjusting the chemical parameters in an acidic aqueous solution comprising a slurry of suspended carbon support particles such that the platinum oxide is attached to the carbon particles to form an insoluble platinum oxide;

(ii) the pH value of the aqueous solution is controlled to be 1.5-5.5, and the temperature is controlled to be 35-95 ℃;

(iii) the attached platinum oxide is reduced in solution with a reducing agent under different conditions, the reducing agent being N₂H₂,NaBH₄,NaH₂PO₂,HCHO,H₂C₂O₄；

(iv) (iv) filtering and drying the product obtained in step (iii).

2. A method of making a carbon-on-carbon catalyst as recited in claim 1, wherein: the insoluble platinum oxide is formed by taking a halogen complex of platinum as a precursor, reacting the precursor with a water-soluble silver compound in a high-temperature aqueous solution to form an insoluble halogen compound, and filtering;

the precursor is H₂PtCl₆,Na₂PtCl₆,Na₂PtCl₄,K₂PtCl₄,Na₂PtBr₆,Na₂PtI₆The water-soluble silver compound is silver nitrate or silver acetate, and the insoluble halogen compound is AgCl, AgBr or AgI; insoluble platinum oxides are formed in the filtrate after adjusting the temperature and the pH.

3. A method of making a carbon-on-carbon catalyst as recited in claim 1, wherein: the adjusting of the chemical parameters comprises adjusting the pH by NaOH, KOH, Na₂CO₃,NH₄And (4) adjusting OH.

4. A method of making a carbon-on-carbon catalyst as recited in claim 1, wherein: adjusting the chemical parameter includes adjusting the temperature from room temperature to 35-95 ℃.

5. A method of making a carbon-on-carbon catalyst as recited in claim 1, wherein: the surface area of the carbon support particles is greater than 40m²/g。

6. A catalyst as claimed in claim 1 on carbonThe preparation method of the agent is characterized by comprising the following steps: prior to forming the insoluble platinum oxide, the slurry of suspended carbon support particles is first dispersed in a strong acid, which is one or a mixture of: HClO₄,HBrO₄,HNO₃,CF₃COOH,CH₃C₆H₅SO₃H,CF₃SO₃H,HCl,HBr。

7. A method of making a carbon-on-carbon catalyst comprising the steps of:

(i) adjusting the chemical parameters in an acidic aqueous solution comprising a slurry of suspended carbon support particles such that the platinum oxide is attached to the carbon particles to form an insoluble platinum oxide;

(ii) the pH value of the aqueous solution is controlled to be 1.5-5.5, and the temperature is controlled to be 35-95 ℃;

(iii) the attached platinum oxide is reduced at 100 to 600 ℃ in hydrogen or a mixed gas containing hydrogen after being filtered and dried.