CN111686727A - Preparation method of supported oxygen evolution catalyst and water electrolyzer membrane electrode - Google Patents

Abstract

The invention discloses a preparation method of a supported oxygen evolution catalyst and a membrane electrode of a water electrolyzer. A supported oxygen evolution catalyst comprises transition metal oxide carrier nanoparticles subjected to conductive treatment at room temperature and alkali metal-doped noble metal oxide nanoparticles loaded on the surface of the transition metal oxide carrier nanoparticles, wherein the mass of alkali metal is 1-20% of that of the transition metal oxide, and the mass of noble metal is 5-30% of that of the transition metal oxide. According to the invention, the active nano-particles of the high-activity noble metal are loaded on the surface of the oxide carrier with high conductivity and high specific surface area, so that the purposes of increasing the utilization rate of the noble metal and improving the activity of the catalyst are achieved.

Description

A kind of supported oxygen evolution catalyst and preparation method of membrane electrode of water electrolyzer

technical field

The invention relates to the technical field of electrochemical oxygen evolution materials and hydrogen energy, in particular to a preparation method of a supported oxygen evolution catalyst and a membrane electrode of a water electrolyzer.

Background technique

The polymer water electrolyzer is a technology that converts electrical energy into hydrogen and oxygen, and has broad application prospects in renewable energy storage, hydrogen production, and oxygen production. The biggest constraint on the technology at present is its high manufacturing cost. At present, platinum, iridium, ruthenium and other precious metal materials are still widely used in membrane electrodes of water electrolyzers, and the amount of these precious metals is relatively large, generally around 0.5-3 mg/cm ² . Therefore, it is urgent to reduce the amount and reduce its cost. In the proton exchange membrane water electrolyzer, the membrane electrode is in an acidic system, and the current anode catalysts with the best comprehensive performance are iridium and ruthenium oxides. However, the use of a large amount of precious metals also brings about an increase in the cost of membrane electrodes, so it is urgent to develop new catalytic materials to improve the mass specific activity of precious metals. At present, in the development of new catalysts, transition oxides are generally used as supports to support noble metal active substances. However, most of the transition metal oxides are wide bandgap semiconductors, so the electronic conductivity is poor, and the activity of the supported catalyst cannot be improved. The conductivity of transition metal oxides can be improved by doping, but the oxide materials obtained by the sintering process have a low specific surface area, resulting in a low utilization rate of noble metal materials supported and on the surface, which cannot meet the requirements of high activity catalysts. At the same time, the activity of crystalline iridium oxide obtained by sintering by traditional methods is still insufficient, and the quality activity needs to be improved. In the actual preparation process, the current preparation methods of supported oxygen evolution catalysts are equally divided into the treatment steps of the carrier and the synthesis steps of noble metal oxides. The preparation process requires multiple steps such as adsorption, drying, sintering, washing, and separation. , the preparation process is complicated and the cost is high.

In addition, in the application process, some of the current highly active catalysts do not actually reflect their performance in the membrane electrode, resulting in a high amount of precious metals. Therefore, it is still necessary to develop a corresponding membrane electrode preparation process according to the characteristics of the catalyst.

SUMMARY OF THE INVENTION

The invention provides a method for preparing a supported oxygen evolution catalyst and a membrane electrode of a water electrolyzer. The supported oxygen evolution catalyst proposed by the invention can significantly reduce the amount of precious metals in the current polymer water electrolyzer, so as to reduce the amount of the membrane electrode. cost and improve the efficiency of water electrolyzers.

The purpose of the present invention is to provide a supported oxygen evolution catalyst, the supported oxygen evolution catalyst is composed of transition metal oxide carrier nanoparticles after conductive treatment at room temperature and alkali metal doped noble metal oxides supported on the surface thereof Nanoparticle composition, the mass of the alkali metal is 1%-20% of the mass of the transition metal oxide, and the mass of the noble metal is 5%-30% of the mass of the transition metal oxide. In the present invention, the high-activity precious metal active nanoparticles are loaded on the surface of the transition metal oxide carrier with high conductivity and high specific surface area, so as to achieve the purpose of improving the utilization rate of the precious metal and improving the catalyst activity.

Preferably, the diameter of the noble metal oxide nanoparticles is 0.8-2.5 nanometers.

The present invention also protects the preparation method of the above-mentioned supported oxygen evolution catalyst, comprising the following steps:

(1) Mix the transition metal oxide and the alkali metal powder, and perform a ball milling reaction at room temperature for 1-5 hours, wherein the mass of the alkali metal is 1%-20% of the mass of the transition metal oxide to obtain the transition metal oxide and the alkali metal a mixture of oxides;

(2) adding water to the mixture of transition metal oxide and alkali metal oxide obtained in step (1) and stirring, under argon atmosphere, then adding precious metal precursor, stirring at 25°C-80°C for 1-2 hours, to obtain a suspension;

(3) drying the suspension obtained in step (2), and sintering the powder obtained after drying at 250-500° C. under an inert atmosphere for 1-4 hours to obtain a supported oxygen evolution catalyst.

In the present invention, the oxide carrier is first treated with an alkali metal at room temperature, and the obtained product is then added with a precious metal precursor to synthesize a high-efficiency oxygen evolution catalyst by a one-pot method. On the one hand, the addition of alkali metals can react with transition metal oxide particles to generate conductive transition metal oxides, which can enhance the conductivity of transition metal oxides at room temperature and avoid the reduction of specific surface area of oxides caused by reduction under traditional high temperature conditions. Small disadvantage; on the other hand, the alkali metal oxide obtained after the reaction of the alkali metal and the transition metal oxide in the preceding steps can continue to react with the precious metal precursor, and the alkali metal ion is doped into the precious metal oxide (iridium oxide) to further Improve the catalytic activity of noble metal oxides (iridium oxides) to achieve the purpose of strengthening the intrinsic activity of noble metals. In this process, alkali metal substances do not need to be separated, and the synthesis process is simple and pollution-free.

Preferably, the specific steps described in step (1) are: mixing transition metal oxide and alkali metal powder, then adding dimethyl carbonate and acetone solution in sequence, and ball milling at room temperature for 1-5 hours to obtain transition metal oxide Mixture with alkali metal oxide, wherein the mass of alkali metal is 1%-20% of the mass of transition metal oxide, and the solid-liquid ratio of transition metal oxide and dimethyl carbonate is 1:25-1:100g/ mL, the volume ratio of dimethyl carbonate to acetone solution is 10:1-1:1.

Preferably, the transition metal is one or more selected from titanium, niobium, tantalum, tungsten and cerium.

Preferably, the alkali metal is selected from one or more of lithium, sodium and potassium.

Preferably, the precious metal precursor is an iridium compound and/or a ruthenium compound, and the mass of the precious metal is 5%-30% of the mass of the transition metal oxide. The iridium compound and/or the ruthenium compound are both soluble salts or acids, such as ruthenium oxide or chloroiridic acid. When the noble metal is a mixture of the iridium compound and the ruthenium compound, the mass ratio of the iridium compound and the ruthenium compound is 1:2.

The present invention also protects a method for preparing a membrane electrode of a water electrolyzer, using the above-mentioned supported oxygen evolution catalyst as an anode catalyst, comprising the following steps: adding water, isopropanol and a membrane solution to the anode catalyst, and ultrasonically preparing the catalyst ink After spraying on the surface of the polymer membrane; adding water, isopropanol and membrane solution to the cathode catalyst, ultrasonically preparing the catalyst ink, spraying on the other side of the polymer membrane, and drying to obtain the water electrolyzer membrane electrode.

Preferably, the above-mentioned preparation method of a membrane electrode for a water electrolyzer specifically includes the following steps: adding water, isopropanol and a membrane solution to the supported oxygen evolution catalyst, ultrasonically preparing the catalyst ink and spraying it on the surface of the polymer membrane; The mass ratio of , isopropanol and supported oxygen evolution catalyst is 5:20:1; after adding water, isopropanol and membrane solution to platinum carbon catalyst, ultrasonically prepared catalyst ink and sprayed on the other side of polymer membrane, The mass ratio of water, isopropanol and platinum-carbon catalyst is 5:20:1, and vacuum drying is carried out at 80° C. for 12 hours to obtain the water electrolyzer membrane electrode.

Compared with the prior art, the beneficial effects of the present invention are:

1. The precious metal content in the membrane electrode of the existing polymer water electrolyzer is generally 0.8-3 mg/cm ² , and the method provided by the present invention can reduce the total amount of precious metal in the membrane electrode to within 0.2 mg/cm ² and There is no performance degradation, so the cost of membrane electrodes can be significantly reduced;

2. The present invention has developed a simple and easy one-pot method for preparing supported oxygen evolution catalysts. The treatment of oxide materials and the hydrolysis and loading of precious metal precursors are completed in the same container, and the precursor materials do not produce waste and are not wasteful. The preparation process requires no separation step and is easy to operate, suitable for large-scale preparation;

3. The modification treatment of transition metal oxide materials is carried out at room temperature, which avoids the reduction process under traditional high temperature conditions, and the specific surface area of the carrier material will not decrease, which is conducive to the formation of highly dispersed active sites, and reduces the amount of time spent in the preparation process. energy consumption;

4. The alkali metal oxide formed by the reaction of the alkali metal particles with the transition metal oxide carrier material does not need to be separated, and can be directly used as the raw material for the preparation of the subsequent noble metal active oxide material, and reacts with it to obtain the noble metal oxide active material; The addition of alkali metal ions can achieve higher activity than traditional noble metal oxides and further improve the catalyst performance.

Description of drawings

Fig. 1 is the flow chart that the present invention prepares supported oxygen evolution catalyst;

Fig. 2 is the transmission electron microscope picture of the supported oxygen evolution catalyst prepared in Example 1 of the present invention;

Fig. 3 is the mass activity diagram of the supported oxygen evolution catalyst prepared in Example 1 and Example 2 of the present invention;

4 is a polarization curve diagram of the polymer water electrolyzer of Example 1 and Comparative Example 1 of the present invention.

Detailed ways

The following examples are further illustrations of the present invention, rather than limitations of the present invention. Unless otherwise specified, the equipment and reagents used in the present invention are conventional commercially available products in the technical field.

Example 1

As shown in Figure 1, a supported oxygen evolution catalyst is prepared, and a method for preparing a membrane electrode of a water electrolyzer includes the following steps:

(1) take 1 g of titanium dioxide powder, add 0.05 g of lithium metal powder, 50 mL of dimethyl carbonate and 15 mL of acetone solution, add the above mixture into a ball milling jar, ball mill at room temperature for 1 h, take out and dry to obtain gray-blue oxide particles;

(2) Add 100 mL of pure water to the product obtained in step (1), stir at room temperature for 15 min, then continue to pass argon into it, and add a chloroiridic acid solution to make the iridium content 0.1 g, then place the above solution in Stir at 60°C for 2h to obtain a suspension;

(3) drying the suspension obtained in step (2) at 80° C., drying the obtained powder at 250° C. under an argon atmosphere for 1 h, and filtering and washing the final heat-treated powder to obtain the final 10% iridium Loaded oxygen evolution catalyst;

(4) get the oxygen evolution catalyst 20mg that step (3) obtains, add water and isopropanol, wherein the mass ratio of water, isopropanol and catalyst is 5:20:1, add Nafion film solution subsequently, and wherein Nafion resin quality is 30% of the catalyst mass, after sonicating for 15 minutes, the catalyst ink was obtained, and the catalyst ink was sprayed on the surface of the proton exchange membrane (DuPont Nafion212), and the spraying area was 8cm ² ;

(5) get platinum carbon catalyst 10mg, add water and isopropanol, wherein the mass ratio of water, isopropanol and platinum carbon catalyst is 5:20:1, add Nafion film solution subsequently, and wherein Nafion resin quality is 30% of catalyst quality %, sonicated for 15 min to obtain catalyst ink, sprayed the catalyst ink on the other side of the proton exchange membrane with a spraying area of 8 cm ² , and vacuum-dried at 80°C for 12 h to finally obtain a membrane electrode with ultra-low precious metal loading.

Fig. 2 is a transmission electron microscope picture of the supported oxygen evolution catalyst prepared in this example. It can be seen from Fig. 2 that the particle size of the prepared titanium oxide carrier is in the range of 20-50 nm, and the particle size of the iridium oxide is in the range of 1-50 nm. about 1.5 nm, indicating that the catalyst has a high electrochemical active area.

Fig. 3 is the electrochemical activity of the commercial iridium oxide and the composite catalyst obtained in this example tested by the electrochemical workstation, wherein the precious metal mass activity of the supported oxygen evolution catalyst prepared in this example reaches 7.3 times that of the commercial iridium oxide catalyst .

The catalyst loading in the membrane electrode prepared above was measured by weight, and the total amount of noble metal in the membrane electrode was determined to be 0.2 mg/cm ² . The water electrolyzer was operated in the mode of bidirectional water supply and constant current electrolysis, at 80°C, 1A/cm ² , and the polarization curve was measured after running for 12 hours under normal pressure, as shown in Figure 4 .

The polarization curve of the water electrolyzer in Figure 4 shows that at 1 A/cm ² , the single cell voltage is 1.718 V at 80° C., and the electrolysis efficiency reaches more than 72% (LHV).

Comparative Example 1

The anode catalyst in the membrane electrode adopts commercial iridium oxide nano-catalyst, and the electrochemical performance test of other catalysts, the amount of cathode catalyst, the preparation process of membrane electrode, the assembly process of water electrolyzer, and the performance test method are all the same as those in Example 1.

The total noble metal loading of the membrane electrode was determined to be 0.5 mg/cm ² . It can be seen from the polarization curve in FIG. 4 that the single cell voltage is 1.806V at 1A/cm ² and 80 degrees, which is higher than 1.7V in Example 1, indicating that the electrolysis energy consumption is higher. In addition, mass transfer polarization occurs at high current densities, indicating the poor performance of membrane electrodes at high currents. The above results show that the energy consumption of the water electrolyzer using the commercial catalyst is still higher than that of Example 1 even if more precious metals are used.

Example 2

Same as Example 1, the difference is:

In step (1), the consumption of metallic lithium powder is 0.2g, 25mL of dimethyl carbonate, 25mL of acetone, and ball-milled for 5h at room temperature; the quality of the iridium added in step (2) is 0.3g (the iridium loading is 30%) , and stirred at 25° C. for 1 h; in step (3), the heat treatment temperature was 500° C. and the time was 4 h.

It can be concluded from FIG. 3 that the catalyst activity of this example still reaches 4 times that of the commercial catalyst.

Example 3

Same as Example 1, the difference is:

In step (1), the consumption of metallic lithium powder is 0.01g, 100mL of dimethyl carbonate, 10mL of acetone, and ball-milled for 4h at room temperature; the quality of the iridium added in step (2) is 0.05g (the iridium loading is 5% ), and stirred at 80° C. for 2 h. In step (3), the heat treatment time was 2 h, and the electrochemical performance test methods of the remaining catalysts were identical to those in Example 1.

It is measured that the mass activity of the noble metal iridium of this embodiment is 2.8 times that of commercial iridium oxide.

Example 4

Same as Example 1, the difference is:

In step (1), metal sodium powder is used, and it is ball-milled for 5h at room temperature; in step (2), the precious metal added is a mixture of ruthenium trichloride and chloroiridic acid, wherein the mass of ruthenium is 0.2 g, and the mass of iridium is 0.1 g (total). The precious metal loading is 30%), and stirred at 80° C. for 2 h; in step (3), the heat treatment time is 1 h, and the electrochemical performance testing methods of the remaining catalysts are the same as those in Example 1.

It is measured that the mass activity of the precious metal in this example is 5.6 times that of commercial iridium oxide.

Example 5

Same as Example 1, the difference is:

In step (1), metal potassium powder is used, and the ball is milled at room temperature for 5 hours; in step (2), chloroiridic acid is added, wherein the mass of iridium is 0.2 g (the iridium loading is 20%), and the mixture is stirred at 80° C. for 2 hours; step In (3), the heat treatment time was 1 h, and the electrochemical performance test methods of the remaining catalysts were all identical to those in Example 1.

It is measured that the mass activity of the precious metal in this example is 3.7 times that of commercial iridium oxide.

Example 6

Same as Example 1, the difference is:

Niobium pentoxide powder is used in step (1). The electrochemical performance test methods of other catalysts are all the same as in Example 1.

It is measured that the mass activity of the precious metal in this example is 3.2 times that of commercial iridium oxide.

Example 7

Same as Example 1, the difference is:

Tantalum pentoxide powder is used in step (1). The electrochemical performance test methods of other catalysts are all the same as in Example 1.

It is measured that the mass activity of the precious metal in this embodiment is 4.5 times that of commercial iridium oxide.

Example 8

Same as Example 1, the difference is:

Tungsten trioxide powder is used in step (1). The electrochemical performance test methods of other catalysts are all the same as in Example 1.

It is measured that the mass activity of the precious metal in this example is 5.9 times that of commercial iridium oxide.

Example 9

Same as Example 1, the difference is:

In step (1), cerium oxide powder is used. The electrochemical performance test methods of other catalysts are all the same as in Example 1.

It is measured that the mass activity of the precious metal in this example is 1.8 times that of commercial iridium oxide.

The above are only the preferred embodiments of the present invention. It should be noted that the above preferred embodiments should not be regarded as limitations of the present invention, and the protection scope of the present invention should be based on the scope defined by the claims. For those skilled in the art, without departing from the spirit and scope of the present invention, several improvements and modifications can also be made, and these improvements and modifications should also be regarded as the protection scope of the present invention.

Claims (9)

1. The supported oxygen evolution catalyst is characterized by consisting of transition metal oxide carrier nanoparticles subjected to conductive treatment at room temperature and alkali metal doped precious metal oxide nanoparticles loaded on the surface of the transition metal oxide carrier nanoparticles, wherein the mass of the alkali metal is 1-20% of that of the transition metal oxide, and the mass of the precious metal is 5-30% of that of the transition metal oxide.

2. The supported oxygen evolution catalyst of claim 1, wherein the noble metal oxide nanoparticles have a particle size of 0.8 to 2.5 nm.

3. A method of preparing the supported oxygen evolution catalyst of claim 1, comprising the steps of:

(1) mixing transition metal oxide and alkali metal powder, and performing ball milling reaction for 1-5 hours at room temperature, wherein the mass of alkali metal is 1% -20% of that of the transition metal oxide, so as to obtain a mixture of the transition metal oxide and the alkali metal oxide;

(2) adding water into the mixture of the transition metal oxide and the alkali metal oxide obtained in the step (1), stirring, adding a noble metal precursor in an argon atmosphere, and stirring at 25-80 ℃ for 1-2 hours to obtain a suspension;

(3) and (3) drying the suspension obtained in the step (2), and sintering the powder obtained after drying at the temperature of 250-500 ℃ for 1-4 hours in an inert atmosphere to obtain the supported oxygen evolution catalyst.

4. The method for preparing the supported oxygen evolution catalyst according to claim 3, wherein the specific steps of step (1) are: mixing transition metal oxide and alkali metal powder, sequentially adding dimethyl carbonate and acetone solution, and performing ball milling reaction for 1-5 hours at room temperature to obtain a mixture of the transition metal oxide and the alkali metal oxide, wherein the mass of the alkali metal is 1-20% of that of the transition metal oxide, the solid-to-liquid ratio of the transition metal oxide to the dimethyl carbonate is 1:25-1:100g/mL, and the volume ratio of the dimethyl carbonate to the acetone solution is 10:1-1: 1.

5. The method for preparing a supported oxygen evolution catalyst according to claim 3 or 4, characterized in that the transition metal is selected from one or more of titanium, niobium, tantalum, tungsten and cerium.

6. The method for preparing a supported oxygen evolution catalyst according to claim 3 or 4, characterized in that the alkali metal is selected from one or more of lithium, sodium and potassium.

7. The method for preparing a supported oxygen evolution catalyst according to claim 3, wherein the noble metal precursor is an iridium compound and/or a ruthenium compound, and the mass of the noble metal is 5 to 30% of the mass of the transition metal oxide.

8. A preparation method of a membrane electrode of a water electrolyzer, which is characterized in that the supported oxygen evolution catalyst of claim 1 is used as an anode catalyst, and comprises the following steps: adding water, isopropanol and membrane solution into an anode catalyst, preparing catalyst ink by ultrasonic treatment, and spraying the catalyst ink on the surface of a polymer membrane; adding water, isopropanol and membrane solution into the cathode catalyst, ultrasonically preparing catalyst ink, spraying the catalyst ink on the other surface of the polymer membrane, and drying to obtain the membrane electrode of the water electrolyzer.

9. The method for preparing a membrane electrode assembly for a water electrolyzer according to claim 8, characterized in that it comprises the following steps: adding water, isopropanol and a membrane solution into a supported oxygen evolution catalyst, ultrasonically preparing catalyst ink, and spraying the catalyst ink on the surface of a polymer membrane, wherein the mass ratio of the water to the isopropanol to the supported oxygen evolution catalyst is 5:20: 1; adding water, isopropanol and a membrane solution into a platinum-carbon catalyst, ultrasonically preparing catalyst ink, spraying the catalyst ink on the other surface of the polymer membrane, wherein the mass ratio of the water to the isopropanol to the platinum-carbon catalyst is 5:20:1, and drying the catalyst ink in vacuum at 80 ℃ for 12 hours to obtain the membrane electrode of the water electrolyzer.

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