CN113113624B - A kind of nano-platinum catalyst with carbon nanotubes as carrier and preparation method thereof - Google Patents

Abstract

The invention relates to a nano-platinum catalyst with carbon nanotubes as a carrier used in an oxygen reduction electrochemical reaction of a fuel cell and a preparation method thereof. The characteristic surface of the carbon nanotube carrier is covered with a layer of in-situ-grown manganese oxide hydrophilic The functional layer, platinum nanoparticles are uniformly dispersed on the manganese oxide hydrophilic layer, and form a composite crystal phase with it. The preparation method is characterized in that the functional layer of manganese oxide covered on the surface of carbon nanotubes makes platinum ions in the liquid phase undergo replacement reaction with manganese in a lower valence state, so that the nano-platinum atomic layer is uniformly deposited on the manganese oxide to form. The preparation method has the advantages of simple procedure, high oxygen reduction performance of the synthesized catalyst, and good industrial application prospect.

Description

A kind of nano-platinum catalyst with carbon nanotubes as carrier and preparation method thereof

technical field

The invention relates to an oxygen reduction catalyst for hydrogen fuel cells and a manufacturing method thereof, belonging to the technical field of fuel cell catalysts.

Background technique

Hydrogen fuel cell is an important energy conversion device for the future hydrogen energy society, which can efficiently convert hydrogen energy into electricity, and can achieve zero carbon emissions in the process. In the research and development process of hydrogen fuel cells, an important aspect is to develop fuel cell electrode catalysts with high oxygen reduction activity, low noble metal usage, and long service life.

The existing XC-72R activated carbon that is mainly used for supporting Pt catalysts has good electrical conductivity, but there are problems such as reduced specific surface area after surface treatment and low loading capacity. In the non-patent literature (Xue Shi. Research on platinum nanoparticle catalyst supports based on nitrogen-doped porous carbon [D]. Xiamen University, 2018.), it was disclosed that a nitrogen-doped porous carbon material was first prepared, and the nitrogen-doped porous carbon material was prepared by platinum nanoparticles. After the source loading and reduction treatment, a fuel cell catalyst with Pt supported on a carbon support was obtained.

Studies have shown that the high specific surface area activated carbon supports currently widely used in hydrogen fuel cells have problems such as poor chemical stability, low electrical conductivity and too strong surface hydrophobicity, which are not conducive to the formation of a good three-phase reaction interface on the catalyst surface. In order to better solve the above problems, it is necessary to find new and more advanced carbon carriers to have the corresponding functions and properties required.

In addition, carbon nanotubes (CNTs) have also been extensively studied, such as in the non-patent literature (Chen Weixiang, Han Gui, LEE Jim Yang, et al. Microwave rapid synthesis of Pt/CNT nanocatalysts and their effects on the electrochemical oxidation of methanol). Electrocatalytic performance [J]. Journal of Chemistry of Universities, 2003, 24(12): 2285-2287.) also disclosed the preparation process of a CNT-supported Pt catalyst. However, due to the hydrophobicity of the CNT surface, the loading of Pt catalyst on the surface is low, which makes the catalytic activity of the material poor.

SUMMARY OF THE INVENTION

The present invention is devoted to solving the above-mentioned technical problems. By using one-dimensional carbon nanotubes with high chemical stability and high electrical conductivity as a new carrier, and carrying out surface oxide coating layer modification and functionalization on them, Effectively enhance its surface hydrophilicity. Through the substitution reaction between the functionalized layer on the surface of carbon nanotubes and platinum ions, the carrier can efficiently disperse nano-platinum particles on the surface to form a composite phase structure. When the catalyst obtained by the preparation method is used as a fuel cell cathode, it exhibits better electrochemical properties.

A nano-platinum catalyst using carbon nanotubes as a carrier, which is supported by metal oxides and Pt on the carbon nanotube carriers.

Preferably, the carbon nanotube carrier refers to single-walled carbon nanotubes, multi-walled carbon nanotubes or solids containing them.

Preferably, the general formula of the metal oxide is: M _x O _y , x and y are atomic numbers, M is a metal element, and the valence state of M is below +4.

Preferably, the M is an element of Group VIB, Group VIIB, Group IB or Group IIB.

Preferably, the M is one of manganese, iron, copper or zinc.

Preferably, the Pt is in the state of nano-platinum particles, and its particle size is 1-50 nm; more preferably 1-10 nm; more preferably 1-3 nm.

A preparation method of a nano-platinum catalyst with carbon nanotubes as a carrier, comprising the following steps:

Step 1, adding a metal soluble inorganic salt and a carbon nanotube carrier into water to perform hydrothermal synthesis, and forming a metal oxide on the surface of the carbon nanotube carrier;

Step 2, calcining the carbon nanotube carrier obtained in step 1;

In step 3, the carbon nanotube carrier obtained in step 2 is immersed in an aqueous solution containing a platinum source, so that the platinum source and the metal oxide undergo a substitution reaction to obtain a nano-platinum catalyst.

Preferably, in step 1, the soluble inorganic salt is selected from inorganic salts of metal M, where M is an element of group VIB, group VIIB, group IB or group IIB.

Preferably, the soluble inorganic salt is an inorganic salt containing manganese, iron, copper or zinc.

Preferably, the soluble inorganic salt is potassium permanganate.

Preferably, in step 1, the hydrothermal synthesis conditions are 60-90° C. for 1-10 h.

Preferably, in step 2, the calcination temperature is 300-600°C.

Preferably, in step 2, the calcination process is performed in an inert or reducing atmosphere.

Preferably, in step 3, the platinum source is selected from chloroplatinic acid, sodium chloroplatinate, potassium chloroplatinate or platinum nitrate.

Preferably, in step 3, the replacement reaction conditions are 50-90° C. for 1-5 hours.

beneficial effect

The catalyst of the invention is a preparation process for the application of hydrogen fuel cells, where a manganese oxide coating layer is grown in-situ on a carbon nanotube carrier to form a functional composite, and then a nano-platinum catalyst is supported by a liquid phase reduction and replacement method. The main component of the manganese oxide coating layer before heat treatment is hydrated manganese oxide (manganese is +4 valence), and the main component after heat treatment is manganese tetroxide (manganese is +2 valence and +3 valence complex).

The carbon nanotube carrier used in the present invention can be single-walled carbon nanotube powder, multi-walled carbon nanotube powder, and ordered array films composed of single-walled/multi-walled carbon nanotubes, disordered films, carbon nanotubes Paper, carbon cloth, silk thread and other products of different macroscopic forms.

The advantages of the present invention lie in that the use of carbon nanotubes as the new carbon carrier of the catalyst can effectively improve the electrical conductivity and chemical stability of the catalyst itself. In addition, in the present invention, the material functional design of in-situ growth of an oxide coating layer on the surface of carbon nanotubes is proposed, which can effectively make up for the deficiency caused by the strong hydrophobicity of carbon nanotubes. The surface of the coated carbon nanotube carrier becomes hydrophilic, which is more favorable for the platinum replacement reaction in the next aqueous solution, thereby improving the dispersibility of the nano-platinum catalyst, and finally enhancing the overall performance of the composite catalyst.

Description of drawings

Figure 1 is a schematic diagram of the preparation process used in the present invention.

FIG. 2 is an electron microscope (SEM) image of the Pt20/Mn ₃ O ₄ /VACNT sample prepared in Example 1. FIG.

FIG. 3 is the XRD images of the MWCNT sample with the manganese oxide functionalized coating layer prepared in Example 2 before and after heat treatment reduction calcination.

FIG. 4 is a TEM image of the Pt10/Mn ₃ O ₄ /MWCNT product prepared in Example 2. FIG.

FIG. 5 is an XRD image of the Pt10/Mn ₃ O ₄ /MWCNT product prepared in Example 2. FIG. Figure 6 shows the performance comparison of Pt20/Mn ₃ O ₄ /MWCNT and Pt20//WCNT; Figure 7 shows the performance of Pt20/Mn ₃ O ₄ /MWCNT (N ₂ ) and Pt20/Mn ₃ O ₄ /MWCNT (H ₂ ). Performance comparison chart.

Detailed ways

The preparation steps of the present invention are described in detail as follows:

The first step is to use carbon nanotubes as a carrier and potassium permanganate as a manganese source, and stir and react at a constant temperature of 60-90 °C in an aqueous solution for 1-10 hours, so that a layer of hydrophilic hydrated manganese oxide coating is uniformly grown on the surface of carbon nanotubes. cladding.

In the second step, the manganese oxide-coated carbon nanotubes in the first step are heat-treated, and calcined at 300-600 °C in an inert/reducing atmosphere to obtain a lower valence manganese tetroxide coating layer as Functionalized layer on the surface of carbon nanotubes.

In the third step, the surface-functionalized carbon nanotube carrier in the second step is immersed in a platinum-containing aqueous solution, and stirred at a constant temperature of 50-90 °C for 1-5 hours, so that the high-valent platinum ions are reduced by low-valent manganese into nanometers. The platinum particles are firmly deposited in the manganese tetroxide coating layer on the surface of the carbon nanotubes to form a composite phase, and finally through the processes of suction filtration, washing and drying, the carbon nanotubes as the carrier described in this patent are obtained. Nano platinum catalyst products.

Carbon nanotube supports, including but not limited to, single-wall carbon nanotube powder, multi-wall carbon nanotube powder, and ordered array films composed of single-wall/multi-wall carbon nanotubes, disordered films, carbon paper, Carbon cloth, silk thread and other products with different macroscopic forms.

Inert/reducing atmospheres, including but not limited to nitrogen, argon, and hydrogen-argon mixtures and hydrogen-nitrogen mixtures in various proportions. The platinum-containing aqueous solution described in the third step includes but is not limited to various water-soluble platinum salts, such as chloroplatinic acid, sodium chloroplatinate, potassium chloroplatinate, platinum nitrate, and the like.

Example 1:

The preparation method described in the present invention is shown in Scheme 1. 0.1 g of ordered carbon nanotube array membrane was soaked in 50 mL of water, 0.1 g of potassium permanganate was added, fully dissolved, heated in a water bath at 60 °C for 2.5 h, and then the membrane was taken out, washed and dried. The dried precursor membrane was calcined at 400 °C for 2 h under an argon atmosphere, and then immersed in 25 mL of chloroplatinic acid aqueous solution. The Pt20/Mn ₃ O ₄ /VACNT composite catalyst material can be obtained by replacing the platinum nanoparticles with manganese tetroxide and depositing them on the surface of the carbon nanotube coating layer, and finally taking out the membrane for washing and drying. An electron microscope image of the material is shown in Figure 2, from which it can be seen that the distribution of Pt nanoparticles supported on the Mn ₃ O ₄ /VACNT support is very uniform, and the order of the carbon nanotube arrays is largely well preserved.

Embodiment 2:

Soak 1.0 g of commercial multi-walled carbon nanotube powder in 100 mL of water, add 1.0 g of potassium permanganate, fully dissolve, heat and react in a 90°C water bath for 1 hour, then filter, wash and dry. The dried powder was calcined at 300°C under nitrogen atmosphere for 6h. The comparison of the XRD crystal phase structure characteristic curves of the MWCNT samples with manganese oxide functionalized coating layer before and after reduction roasting is shown in Figure 3. It can be seen that the product after reduction roasting has obvious Mn3O4 crystal phase. Then, the Mn ₃ O ₄ /MWCNT composite obtained by thermal reduction was soaked in an aqueous solution of 250 mL of chloroplatinic acid, the theoretical feeding ratio of platinum raw materials was set to 10 wt %, and the reaction was performed at a constant temperature of 50 °C for 5 h, so that manganese tetroxide would convert the nano-platinum The particles are replaced and deposited on the surface of the carbon nanotube coating layer, and finally the product is taken out, washed, and dried to obtain the Pt10/Mn ₃ O ₄ /MWCNT composite catalyst material. The TEM image of this material is shown in Figure 4, from which it can be seen that the Pt nanoparticles are uniformly distributed on the Mn ₃ O ₄ /VACNT support and have a small particle size. Figure 5 shows the XRD crystal structure of Mn ₃ O ₄ /VACNT loaded with Pt.

Embodiment 3:

1.0 g of commercial single-walled carbon nanotube powder was soaked in 100 mL of water, 0.5 g of potassium permanganate was added, fully dissolved, heated in a 60°C water bath for 10 hours, and then filtered, washed and dried. The dried powder was calcined at 600 °C for 0.5 h under a hydrogen-nitrogen mixture (hydrogen ratio of 5%) for 0.5 h, and then immersed in a 250 mL aqueous solution of chloroplatinic acid. The theoretical feeding ratio of platinum raw materials was set to 5 wt. %, 90 ℃ constant temperature reaction for 1h, so that manganese tetroxide replaces the nano-platinum particles and deposits on the surface of the carbon nanotube coating layer, and finally the product is taken out, washed, and dried to obtain Pt5/Mn ₃ O ₄ / SWCNT composite catalyst material. Through electrochemical tests, the results show that the prepared Pt5/Mn ₃ O ₄ /SWCNT composite catalyst is 0.117 A/mgPt, which is higher than the oxygen reduction electrochemical activity of the commercial Pt/C catalyst with 20 wt% platinum loading (0.131 A/mgPt ) was slightly lower, while the actual platinum loading in this product was 5 wt%. The above results show that the carbon nanotube-supported nano-platinum catalyst produced by this technical method can effectively reduce the required platinum content in the catalyst.

Comparative Example 1

The difference from Example 3 is that the carbon nanotubes are directly compounded with the chloroplatinic acid solution, and platinum is supported on the carbon nanotubes.

Soak 1.0 g of commercial multi-walled carbon nanotube powder in 100 mL of water, add 1.0 g of potassium permanganate, fully dissolve, heat and react in a 90°C water bath for 1 hour, then filter, wash and dry. The dried powder was calcined at 300°C under nitrogen atmosphere for 6h. After reduction calcination, MWCNT samples with manganese oxide functionalized coating were obtained. Then, the Mn ₃ O ₄ /MWCNT composite obtained by thermal reduction was soaked in an aqueous solution of 250 mL of chloroplatinic acid, the theoretical feeding ratio of platinum raw materials was set to 20 wt %, and the reaction was performed at a constant temperature of 50 °C for 5 h, so that manganese tetroxide would convert the nano-platinum The particles are replaced and deposited on the surface of the carbon nanotube coating layer, and finally the product is taken out, washed, and dried to obtain a Pt20/Mn ₃ O ₄ /MWCNT composite catalyst material. 1.0 g of commercial multi-walled carbon nanotube powder was calcined at 300 °C for 6 h under nitrogen atmosphere. Then, the calcined sample was immersed in 250 mL of chloroplatinic acid aqueous solution, the theoretical feeding ratio of platinum raw material was set to 20 wt%, and the reaction was performed at a constant temperature of 50 °C for 5 h. Finally, the product was taken out for washing and drying to obtain a Pt20//WCNT composite catalyst. Material. Figure 6 is a performance comparison diagram of Pt20/Mn ₃ O ₄ /MWCNT and Pt20//WCNT, which shows that the samples obtained by directly supporting Pt on commercial multi-walled carbon nanotube powders without Mn treatment have basically no catalytic activity. The pristine WCNTs without Mn treatment proved to be unfavorable for the loading of Pt.

Comparative Example 2

The difference from Example 3 is that the carbon nanotubes loaded with manganese oxide are not calcined in an atmosphere containing hydrogen.

Soak 1.0 g of commercial multi-walled carbon nanotube powder in 100 mL of water, add 1.0 g of potassium permanganate, fully dissolve, heat and react in a 90°C water bath for 1 hour, then filter, wash and dry. The dried powder was calcined at 300°C under nitrogen atmosphere for 6h. After calcination, MWCNT samples with manganese oxide functionalized coating were obtained. Then, the Mn ₃ O ₄ /MWCNT composite obtained by thermal reduction was soaked in an aqueous solution of 250 mL of chloroplatinic acid, the theoretical feeding ratio of platinum raw materials was set to 20 wt %, and the reaction was performed at a constant temperature of 50 °C for 5 h, so that manganese tetroxide would convert the nano-platinum The particles are replaced and deposited on the surface of the carbon nanotube coating layer. Finally, the product is taken out, washed and dried to obtain a Pt20/Mn ₃ O ₄ /MWCNT(N ₂ ) composite catalyst material. Soak 1.0 g of commercial multi-walled carbon nanotube powder in 100 mL of water, add 1.0 g of potassium permanganate, fully dissolve, heat and react in a 90°C water bath for 1 hour, then filter, wash and dry. The dried powder was calcined at 300°C under a hydrogen atmosphere for 6h. After reduction calcination, MWCNT samples with manganese oxide functionalized coating layer were obtained. Then, the Mn ₃ O ₄ /MWCNT composite obtained by thermal reduction was soaked in an aqueous solution of 250 mL of chloroplatinic acid, the theoretical feeding ratio of platinum raw materials was set to 20 wt %, and the reaction was performed at a constant temperature of 50 °C for 5 h, so that manganese tetroxide would convert the nano-platinum The particles are replaced and deposited on the surface of the carbon nanotube coating layer. Finally, the product is taken out, washed and dried to obtain a Pt20/Mn ₃ O ₄ /MWCNT(H ₂ ) composite catalyst material. Figure 7 is a performance comparison diagram of Pt20/Mn ₃ O ₄ /MWCNT (N ₂ ) and Pt20/Mn ₃ O ₄ /MWCNT (H ₂ ), which shows that the valence state of manganese oxide can be reduced after hydrogen reduction, which can promote the conversion reaction. Making Pt in WCNT shows better loading.

Claims (2)

1. a preparation method of a nano-platinum catalyst with carbon nanotube as carrier, described nano-platinum catalyst is to be loaded with metal oxide and Pt on carbon nanotube carrier, and described metal oxide manganese tetroxide, It is characterized in that, comprises the following steps: Step 1, adding a metal soluble inorganic salt and a carbon nanotube carrier into water to perform hydrothermal synthesis, and forming a metal oxide on the surface of the carbon nanotube carrier; Step 2, calcining the carbon nanotube carrier obtained in step 1; In step 3, the carbon nanotube carrier obtained in step 2 is immersed in an aqueous solution containing a platinum source, so that the platinum source and the metal oxide undergo a displacement reaction to obtain a nano-platinum catalyst; The soluble inorganic salt of the metal is potassium permanganate; In step 1, the hydrothermal synthesis condition is 60-90 ℃ reaction 1-10h; In step 2, the roasting temperature is 300-600°C; the roasting process is treatment in a reducing atmosphere, and the reducing atmosphere is a mixture of hydrogen and nitrogen, and hydrogen accounts for 5%; The platinum source is selected from chloroplatinic acid, sodium chloroplatinate, potassium chloroplatinate or platinum nitrate; The displacement reaction conditions are 1-5h at 50-90°C. 2. the preparation method of the nano-platinum catalyst with carbon nanotubes as carrier according to claim 1, is characterized in that, described carbon nanotube carrier refers to single-walled carbon nanotubes, multi-walled carbon nanotubes or contains their solids.

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