RU2421850C1 - Method of producing nano-sized platinum-nickel catalyst - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: method of producing nano-sized Pt-Ni catalyst involves preparation of a mixture of starting compounds - carbonaceous material, hexachloroplatinic acid, a nickel salt in a solution containing ethylene glycol, adding to the mixture of starting compounds an alkali solution, reducing Pt and Ni metals, cooling the mixture to room temperature, washing and drying the catalyst. The ethylene glycol solution also contains ethyl alcohol in accordance with 2-3 parts of ethylene glycol and 1-2 parts of ethyl alcohol. Pt and Ni metals are reduced by adding to the solution 1M sodium boron hydride in 1M sodium hydroxide solution for 1-1.5 hours, and the mixture is treated with ultrasound while bubbling inert gas through the mixture. The carbonaceous material used is Vulcan XC-72 soot or nanotubes, or nanofibre. The inert gas used is argon, helium or neon.

EFFECT: shorter time and low power consumption of the process of producing the catalyst.

10 cl, 10 ex

Description

The invention relates to catalytic chemistry, and in particular to methods for producing Pt-based cathodic catalysts intended for use in electrolytic cells and solid polymer electrolyte (TPE) fuel cells.

In electrolyzers with TPE, the replacement of the traditionally used Pt cathode catalyst with Pt-Ni along with a significant reduction in the cost of electrochemical devices also leads to a decrease in the overvoltage at the electrode at high current densities due to the fact that Ni has a lower adsorption bond with hydrogen atoms on the electrode surface and does not allow adsorbed hydrogen atoms to block the electrode surface, which is especially relevant in water electrolyzers at ultrahigh pressures.

The work "Supported platinum quaternary alloy elektrocatalyst" (EP 0469514, published December 8, 1992) showed that the alloy of Pt with Ni increases the stability of the fuel cell electrode compared to pure Pt by 1.7 times, while the catalytic activity increases 2.2 times.

In the work “Chemical and effects of Ni in Pt / Ni and Pt / Ru / Ni alloy nanoparticles in methanol electrooxidation” (J. Phys. Chem. B, 106 (2002) 1869) it was shown that the addition of Ni to the Pt catalyst increases its chemical resistance to carbon monoxide.

Various methods for producing Pt-Ni catalysts are known, involving the deposition and chemical reduction of Pt and Ni particles onto carbon, both with and without high temperature treatment.

The work "Electrocatalyst material comprising a platinum alloy on a conductive support" (patent EP 0698299, publ. 5.21.1997) describes a method for the synthesis of Pt-Ni catalyst on carbon. Chlorides of Pt and Ni were deposited on carbon and reduced with formaldehyde at 90 ° С, after which they were annealed at 930 ° С for 1 hour in an inert atmosphere.

In the work "Platinum alloy skeleton supported electrocatalyst, electrode using the electrocatalyst, and process for producing the electrocatalyst" (patent EP 0827225, published April 3, 1998), Pt is reduced on carbon from hexachloroplatinic acid with a 5% formic acid solution with subsequent precipitation of Ni from Ni (II) nitrate in an aqueous solution of 0.5 N. HNO ₃ , after which the catalyst was annealed at 900 ° C for 1.2 hours in an inert atmosphere.

Platinum alloy carbon-supported catalysts (application WO / 2006/056470, publ. 6.01.2006) proposed the first sequential precipitation of hexachloroplatinic acid on carbon when heated from an aqueous solution of 4M HNO ₃ by increasing the pH by adding NaOH first to 3 , 5, and then, continuing to increase the pH to 8.5, precipitated nickel (II) nitrate. At the end of the deposition, the catalyst was first annealed at 500 ° C for 30 minutes, and then at 850 ° C for 1 hour in an argon stream.

In all the cited works, the final stage is the high-temperature treatment of the catalyst at a temperature of 800 ° C and higher in an inert gas stream. This is the main disadvantage of the obtained electrocatalysts - sintering of metal particles occurs at high temperatures, their size increases and, as a result, the surface of the catalyst decreases.

The work "Core / shell-type catalyst particles and methods for their preparation" (application WO / 2008/025750, published on June 3, 2008) describes a method for producing Pt-Ni catalyst on carbon by reducing Pt and Ni from hexachloroplatinic acid solutions and nickel (II) acetate by diethylene glycol in the presence of a stabilizer, followed by precipitation on carbon by changing the pH of the solution.

The disadvantage of this method is: a large size of the obtained catalyst particles from 20 to 26 nm; the need for the presence of a stabilizer, which complicates the washing process and increases the loss of catalyst.

A known method of producing a Pt-Ni catalyst is a prototype ("PtNi based supported electrocatalyst for proton exchange membrane fuel cell having CO tolerance", application US 2006280997, publ. 12/14/2006), including:

- manufacture of a mixture of the starting compounds - carbon black Vulcan XC-72, hexachloroplatinic acid, nickel salts (nickel nitrate II) in ethylene glycol solution;

- adding to the mixture of the starting compounds a solution of alkali NaOH to pH = 10-14;

- heating the mixture of starting compounds in a microwave oven with a frequency of 1-50 kHz and a power of 400-1000 W for 1-30 minutes;

- cooling the mixture to room temperature followed by the addition of 3M HCl to pH = 1;

- washing the solid phase of the cooled mixture to pH = 7;

- drying the solid phase;

- heat treatment of the solid phase at a temperature of 300 ° C-800 ° C for 1-8 hours in an atmosphere of a mixture of inert and reducing gases until the catalyst metals are completely reduced. Hydrogen and methane are used as reducing gases. The resulting catalyst consists of Pt-Ni from 30 to 80% of the mass. in a ratio of 1: 1 on carbon. The particle size was 2-6 nm.

The disadvantage of the prototype is the long heat treatment time and, as a consequence, the high energy consumption of the process of obtaining the catalyst. This is due to the fact that ethylene glycol used in the work is not a sufficiently strong reducing agent; therefore, additional thermal treatment of the catalyst at sufficiently high temperatures is required to restore the catalyst.

The technical result, which the invention is directed to, is to reduce the time and energy consumption of the process for producing a catalyst.

For this, a method for producing a nanosized Pt-Ni catalyst is proposed, which consists in manufacturing a mixture of the starting compounds — carbon material, hexachloroplatinic acid, a nickel salt in an aqueous solution containing ethylene glycol, adding an alkali solution to the mixture of starting compounds, reducing Pt and Ni metals, cooling the mixture to room temperature, washing and drying the catalyst, while the ethylene glycol solution additionally contains ethanol in a ratio of 2-3 parts of ethylene glycol 1-2 parts of ethanol, restores Adding metals are Pt and Ni, when added to a solution of 1 M solution of sodium borohydride in 1 M sodium hydroxide solution for 1-1.5 hours the mixture was sonicated and treated by bubbling it with an inert gas.

In this case, Vulcan XC-72 soot, or nanotubes, or nanofibers are used as carbon material.

Argon or helium or neon are used as an inert gas.

The ultrasound parameters are: frequency 37-40 kHz, power 150-200 watts.

As alkali use 1-2 ml of an aqueous solution of ammonia.

Nickel (II) chloride or nickel (II) nitrate is used as a nickel salt in the preparation of a mixture of the starting compounds.

In addition, the carbon material is pre-mixed with ethyl alcohol.

Stirring is carried out with a dispersion homogenizer at a speed of 20,000-22,000 rpm for 30 minutes.

The content of Pt-Ni metals in the catalyst is 20-80% of the mass. in the ratio of Pt from 0.9 to 3.1% at., Ni from 3.1 to 0.9% at.

The ratio of the mixture of ethylene glycol: ethyl alcohol to the total amount of water is (3-3.5): 1-1.2.

In the inventive method for producing a platinum-nickel catalyst in a ratio of Pt from 0.9 to 3.1% at., Ni from 3.1 to 0.9% at. on a carbon carrier, for example, Vulcan XC-72 soot with a metal content of 20-80%, the reduction process of sodium starting compounds (solutions of hexachloroplatinic acid and nickel chloride) takes place in ethylene glycol - ethyl alcohol medium at the stated proportions when the reaction mixture is treated with ultrasound at a frequency of 37 -40 kHz and a power of 150-200 W per liter with simultaneous adsorption-reduction of the starting compounds on a carbon carrier, which was pre-treated with ethanol.

Along with nickel (II) chloride, nickel (II) nitrate can also be used as a nickel salt; the synthesis parameters and characteristics of the resulting catalyst do not change.

The synthesis time is not more than 1.5 hours, because a mixture of sodium borohydride with ethylene glycol is a very powerful reducing agent. In this case, a complete reduction of the metals in the catalyst occurs, which eliminates the need for additional heat treatment. When using ultrasound, a greater uniformity of adsorption is achieved, the efficiency of the recovery process increases, the formation of nanosized catalyst particles, and agglomeration of the formed particles is excluded.

During sonication, the mixture is bubbled with an inert gas. Argon, helium, and neon are used as an inert gas. The choice of gas does not affect the quality of the catalyst. The result is a binary nanosized catalyst Pt-Ni on a carbon carrier with a given mass fraction of metals (20-80% wt.). Vulcan XC-72 soot, or nanotubes, or nanofibers, is used as the carbon material; the characteristics of the resulting catalyst remain virtually unchanged.

According to x-ray phase analysis, the obtained particles are a solid solution, have a basic size of 2-6 nm, a spherical shape and a uniform distribution on the carrier. This catalyst with an atomic ratio of Pt: Ni = 1: 1 allows 1.5 times to reduce the consumption of platinum.

Example 1 (prototype).

In a 500 ml glass, 100 ml of ethylene glycol and 1 g of Vulcan XC-72 carbon black are placed, with constant stirring, 12.8 ml of hexachloroplatinic acid (containing 4.9 mg Pt / ml) in a solution of ethylene glycol and 99.2 mg of nickel nitrate ( II). A 2.5 M NaOH solution was added to the mixture to pH = 13. The mixture is placed in a microwave oven with a frequency of 2.45 kHz with a power of 700 watts for 1.5 minutes. The mixture was then cooled to room temperature and 3M HCl was added to pH = 1. The precipitate is washed by decantation with a 3-fold change of water, dried at 60 ° C. The dried precipitate is annealed at 300 ° C. under nitrogen for 8 hours.

The result is a PtNi / C catalyst in an atomic ratio of Pt: Ni = 1: 1 with a metal content of 30%. Direct synthesis time is at least 8 hours.

Examples 2-8 of the implementation of the claimed invention.

Example 2

Synthesis of PtNi (1: 1 at.) On carbon with a PtNi content of 30% by mass.

220 mg of Vulcan XC-72 carbon black is placed in a 500 ml reaction vessel, and 2.5 ml of ethylene glycol-ethanol (A) mixture is added in a ratio of 2.5: 1, which is what is claimed. The amount of mixture (A) is taken at the rate of 40-50 ml for every 100 mg of carbon black. The resulting mixture was stirred with a dispersion homogenizer at a speed of 20,000-22,000 rpm for 20 minutes. Then the vessel with the mixture is placed in an ultrasonic bath, at room temperature, 31.3 ml of an aqueous solution of nickel chloride (with a Ni content of 21.29 mg) and 2.0 ml of an aqueous solution of hexachloroplatinic acid (with a Pt content of 72.36 mg) are added. The ratio of the mixture (A) to the total amount of water is 3: 1, which corresponds to the claimed, add 1 ml of an aqueous solution of ammonia and include sonication when sparging with an inert gas, such as argon. After 15 minutes, 50 ml of a 1M sodium borohydride solution in a 1M NaOH solution are added dropwise. The synthesis is carried out for one hour. Spontaneous heating of the reaction mixture to 40 ° C is allowed. After 1 hour, the reaction mass is stratified. The upper transparent part is drained, and the lower is washed with double-distilled water using a centrifuge until the drain solution is neutral. The resulting catalyst was dried. Direct synthesis time is 1 hour.

The resulting catalyst was used in the manufacture of the catalytic composition of the cathode of the membrane-electrode unit (OIE) of the water electrolyzer. The cathodic catalyst composition is a dispersion of catalyst particles ((PtNi) ³⁰ / V) (1: 1) and a solution of an ionomer (MF-4SK) in propanol-2 (20-25 wt.%). After processing in an ultrasonic disperser, the emulsion obtained is applied to porous titanium by air spraying. A catalytic mixture consisting of iridium black and a solution of an ionomer (MF-4SK) in propanol-2 (5-7 wt.%) Is used at the anode. Next, the cathode, anode and gas separation membrane are combined into an integrated OIE electrolyzer by thermal compression. Then the assembly is installed in the cell for electrolysis of deionized water and serves an electric current density of 0.5 A / cm ² at 90 ° C for 1 hour. After an hour, the current density is increased. The voltage on the cell is 1.61 V at a current density of 1 A / cm ² and a temperature of 90 ° C. The cell stably works for 3500 hours without changing the indicators.

Example 3

Synthesis of PtNi (1: 1 at.) On carbon with a PtNi content of 60% by mass. As an example 2, but after being placed in an ultrasonic bath, 26.3 ml of a solution of nickel chloride (with a Ni content of 76.7 mg) and 7.0 ml of a solution of hexachloroplatinic acid (with a Pt content of 253.3 mg) are added.

The resulting catalyst was deposited on porous titanium and tested in the OIE of the electrolyzer, as in example 2. The voltage on the cell is 1.61 V at a current density of 1 A / cm ² and a temperature of 90 ° C. The cell stably works for 3500 hours without changing the indicators.

Example 4

Synthesis of PtNi (1: 1 at.) On carbon with a PtNi content of 40% by weight.

As example 2, but after being placed in an ultrasonic bath, 30.2 ml of a solution of nickel chloride (with a Ni content of 34.1 mg) and 3.1 ml of a solution of hexachloroplatinic acid (with a Pt content of 112.6 mg) are added.

The resulting catalyst was deposited on porous titanium and tested in the OIE of the electrolyzer, as in example 2. The voltage on the cell is 1.61 V at a current density of 1 A / cm ² and a temperature of 90 ° C. The cell stably works for 3500 hours without changing the indicators.

Example 5

Synthesis of PtNi (1: 3 at.) On carbon with a PtNi content of 40% by weight.

As an example 2, but after being placed in an ultrasonic bath, 31.2 ml of a solution of nickel chloride (with a Ni content of 69.86 mg) and 2.12 ml of a solution of hexachloroplatinic acid (with a Pt content of 76.84 mg) are added.

The resulting catalyst was deposited on porous titanium and tested in the OIE of the electrolyzer, as in example 2. The voltage on the cell is 1.75 V at a current density of 1 A / cm ² and a temperature of 90 ° C. The cell stably works for 3500 hours without changing the indicators.

Example 6

Synthesis of PtNi (3: 1 at.) On carbon with a PtNi content of 40% by weight.

As example 2, but after being placed in an ultrasonic bath, 29.65 ml of a solution of nickel chloride (with a Ni content of 13.46 mg) and 3.68 ml of a solution of hexachloroplatinic acid (with a Pt content of 133.24 mg) are added.

The resulting catalyst was deposited on porous titanium and tested in the OIE of the electrolyzer, as in example 2. The voltage on the cell is 1.61 V at a current density of 1 A / cm ² and a temperature of 90 ° C. The cell stably works for 3500 hours without changing the indicators.

Example 7

Synthesis of PtNi (1: 1 at.) On carbon with a PtNi content of 40% by weight.

As an example 2, but in a 500 ml reaction vessel with 220 mg of Vulcan XC-72 carbon black, 110 ml of ethylene glycol-ethanol (A) mixture are added in a ratio of 3: 2, which corresponds to the claimed one.

The resulting catalyst was deposited on porous titanium and tested in the OIE of the electrolyzer, as in example 2. The voltage on the cell is 1.61 V at a current density of 1 A / cm ² and a temperature of 90 ° C. The cell stably works for 3500 hours without changing the indicators.

Example 8

Synthesis of PtNi (1: 1 at.) On carbon with a PtNi content of 40% by weight.

As example 2, but 110 ml of ethylene glycol-ethanol mixture (A) is added to a 500 ml reaction vessel with 220 mg of Vulcan XC-72 carbon black, and 20 ml of nickel chloride solution (containing Ni 34.1 is added to the ultrasonic bath) mg) and 17.5 ml of a solution of hexachloroplatinic acid (with a Pt content of 112.6 mg). The ratio of the mixture (A) to the total amount of water is 3.2: 1.2, which corresponds to the declared

The resulting catalyst was deposited on porous titanium and tested in the OIE of the electrolyzer, as in example 2. The voltage on the cell is 1.61 V at a current density of 1 A / cm ² and a temperature of 90 ° C. The cell stably works for 3500 hours without changing the indicators.

Example 9

The catalyst obtained in example 4 with a PtNi content of 40 mass% (1: 1 at) on a carbon support was used in the preparation of the catalytic composition of the cathode of the membrane-electrode block (OIE) of a fuel cell (TE). The cathode catalyst composition is a dispersion of catalyst particles ((PtNi) ⁴⁰ / V) (1: 1) and a solution of an ionomer (MF-4SK) in propanol-2 (35 wt.%). After processing in an ultrasonic disperser, the emulsion obtained is applied to a Pantex-type material with a carbon black hydrophobic sublayer by air spraying. A catalytic mixture consisting of a Pt monocatalyst on a carbon support and a solution of an ionomer (MF-4SK) in propanol-2 (35 wt.%) Is used at the anode. Next, the cathode, anode and gas separation membrane are combined in the OIE of the fuel cell. The OIE was placed in a stainless thermostatic cell. The cell temperature is 85 ° C. The test blocks were carried out using hydrogen and oxygen from the electrolyzer and air from the compressor. Hydrogen and air were additionally humidified (humidification temperature - 85 ° С). The gas pressure was maintained constant with the help of reducers installed at the outlet of the gas paths, controlled by manometers (for oxygen - 3 ati, for hydrogen and air - 2 ati). The current-voltage characteristics were measured after the current and voltage reached steady-state values. The following characteristics were obtained: voltage on the cell - 0.7 V; current density - 700 mA / cm ² for hydrogen-air fuel cell; current density - 1 A / cm ² for hydrogen-oxygen fuel cell. The fuel cell worked stably for 3500 hours at a cell voltage of 0.87 V.

Example 10

The catalyst obtained in example 5 with a PtNi content of 40 wt.% (1: 3 at) on a carbon carrier was tested in the OIE of the fuel cell, as in example 7. The following characteristics were obtained: voltage on the cell - 0.7 V; current density - 600 mA / cm ² for hydrogen-air fuel cell; current density - 800 mA / cm ² for hydrogen-oxygen fuel cells. The cell stably works for 3500 hours without changing the indicators.

Thus, the proposed method will allow to obtain a cathode catalyst with high characteristics based on Pt, intended for use in electrolyzers and fuel cells with solid polymer electrolyte (TPE), while reducing time and energy consumption in the process of its production.

Claims (10)

1. A method of producing a nanosized platinum-nickel catalyst consisting in the manufacture of a mixture of the starting compounds — carbon material, hexachloroplatinic acid, a nickel salt in an aqueous solution containing ethylene glycol, adding an alkali solution to the mixture of the starting compounds, reducing Pt and Ni metals, cooling the mixture to room temperature , washing and drying the catalyst, characterized in that the ethylene glycol solution further comprises ethyl alcohol in a ratio of 2-3 parts of ethylene glycol 1-2 parts of ethyl alcohol That, Pt and Ni metals are reduced by adding 1 M sodium borohydride solution in 1 M sodium hydroxide solution to the solution for 1-1.5 hours and treating the mixture with ultrasound while sparging it with an inert gas. 2. The method according to claim 1, characterized in that as the carbon material using soot Vulcan XC-72, or nanotubes, or nanofibres. 3. The method according to claim 1, characterized in that argon or helium or neon is used as an inert gas. 4. The method according to claim 1, characterized in that the ultrasound parameters are: frequency 37-40 kHz, power 150-200 watts. 5. The method according to claim 1, characterized in that as alkali use 1-2 ml of an aqueous solution of ammonia. 6. The method according to claim 1, characterized in that as the Nickel salt in the manufacture of a mixture of the starting compounds using Nickel chloride (P) or Nickel nitrate (P). 7. The method according to claim 1, characterized in that the carbon material is pre-mixed with ethyl alcohol. 8. The method according to claim 7, characterized in that the mixing is carried out by a dispersion homogenizer at a speed of 20,000-22,000 rpm for 30 minutes 9. The method according to claim 1, characterized in that the content of Pt-Ni metals in the catalyst is 20-80 wt.% In the ratio of Pt from 0.9 to 3.1 at.%, Ni from 3.1 to 0.9 at.%. 10. The method according to claim 1, characterized in that the ratio of the mixture of ethylene glycol-ethyl alcohol to the total amount of water is (3-3.5): 1-1.2.