CN116072889A

CN116072889A - Platinum-carbon catalyst, preparation method and application thereof, and hydrogen fuel cell

Info

Publication number: CN116072889A
Application number: CN202111275071.9A
Authority: CN
Inventors: 王厚朋; 顾贤睿; 张家康; 彭茜; 谢南宏; 张云阁; 夏庆山
Original assignee: Sinopec Research Institute of Petroleum Processing; China Petroleum and Chemical Corp
Current assignee: Sinopec Research Institute of Petroleum Processing; China Petroleum and Chemical Corp
Priority date: 2021-10-29
Filing date: 2021-10-29
Publication date: 2023-05-05

Abstract

The invention discloses a platinum-carbon catalyst, a preparation method and application thereof, and also discloses a hydrogen fuel cell adopting the platinum-carbon catalyst. The platinum-carbon catalyst contains a carbonaceous carrier and metal platinum particles supported on the carbonaceous carrier, and the contact angle between platinum nanoparticles and the carbon carrier in the platinum-carbon catalyst is 50 DEG or less. The preparation method comprises dispersing carbonaceous material, platinum precursor, complexing agent and dispersion medium with ultrasonic wave, adjusting pH value, and reducing with reducer containing polyvinylpyrrolidone and formic acid. The platinum carbon catalyst according to the present invention has improved structural dispersibility, and exhibits improved electrochemical catalytic activity and stability. According to the preparation method of the platinum-carbon catalyst, the preparation process is simple, the interaction between the metal platinum particles and the carrier can be effectively improved, the dispersity of the metal platinum particles on the carrier is improved, and the electrochemical catalytic activity and stability of the prepared platinum-carbon catalyst are improved.

Description

Platinum-carbon catalyst, preparation method and application thereof, and hydrogen fuel cell

Technical Field

The invention relates to a platinum-carbon catalyst, a preparation method and application thereof, and also relates to a hydrogen fuel cell adopting the platinum-carbon catalyst.

Background

Due to the increasing consumption of fossil energy and the aggravation of environmental pollution, the proton exchange membrane fuel cell technology with high efficiency, no pollution and zero carbon emission has been developed. However, at present, the development of the whole fuel cell technology is still in a starting stage, and further development is still subject to the following technical limitations: high cost, low lifetime and limited energy density. Wherein the cathodic oxygen reduction reaction (Oxygen Reduction Reaction, ORR) is slow in kinetics and has an exchange current density of 10 ^-6 A/cm ² The current density is far smaller than the hydrogen oxidation exchange current density of the anode, and the existence of polarization resistance phenomenon makes the actual potential of the battery far lower than the theoretical value. While the most effective catalyst for the oxygen reduction reaction is the noble metal platinum, which costs about 40% of the total fuel cell cost. Through many years of research, the attenuation of the catalytic activity of the catalyst is one of the main reasons for the performance attenuation of the fuel cell, so that the development of the oxygen reduction reaction electrode catalyst with high performance and durability has great significance for accelerating the commercialization of the fuel cell.

At present, the methods for preparing the carbon-supported platinum catalyst are relatively more, such as a liquid phase reduction method, a gas phase reduction method, a colloid method, a gas phase deposition method, a microwave method and the like, and each preparation method has the corresponding advantages and disadvantages, such as the colloid method, the gas phase deposition method, the microwave method and the like, so that the highly dispersed platinum-based catalyst can be prepared, but the three processes have higher cost, and a plurality of problems exist in the amplifying process, so that the amplifying is difficult to realize. For the gas phase reduction method, such as a hydrogen reduction process, the method has the advantages that the combination of platinum and carrier carbon is compact, the stability is good, the morphology of the catalyst is difficult to control, and the loading of platinum is often below 40 weight percent and is difficult to promote, so that the universality of the platinum-based catalyst process is limited. Whereas the common liquid phase reduction method: such as glycol high-temperature reduction process, organic acid reduction process, etc., has the advantages of simple process, easy pilot scale up, but has the disadvantages of poor structural dispersibility and weak binding force between platinum nano particles and a carrier.

Therefore, it is important to develop a synthesis process which is easy to realize mass production and synthesizes a catalyst with excellent activity and stability.

Disclosure of Invention

The invention aims to provide a platinum-carbon catalyst and a preparation method thereof, wherein the platinum-carbon catalyst has improved structural dispersity and catalytic activity, and the preparation method is easy to realize mass production.

According to a first aspect of the present invention, there is provided a platinum carbon catalyst comprising a carbonaceous carrier and platinum nanoparticles supported on the carbonaceous carrier, wherein the platinum carbon catalyst has a contact angle of 50 ° or less with the carbon carrier.

According to a second aspect of the present invention, there is provided a method of preparing a platinum carbon catalyst, the method comprising the steps of:

s1, dispersing a carbonaceous material, a platinum precursor, a complexing agent and a dispersion medium by ultrasonic waves to obtain a first dispersion, wherein the complexing agent is one or more than two of water-soluble salts of dicarboxylic acid and polycarboxylic acid, and the dispersion medium is glycerol and water;

s2, adjusting the pH value of the first dispersion to 11-14 to obtain a second dispersion;

S3, adding a reducing agent into the second dispersion, and enabling the reducing agent to be in contact with a platinum precursor in the second dispersion to perform a reduction reaction, wherein the reducing agent contains polyvinylpyrrolidone and formic acid, and the molar ratio of the reducing agent to the platinum precursor is 150-1000:1.

according to a third aspect of the present invention there is provided a platinum carbon catalyst prepared by the method of the second aspect of the present invention.

According to a fourth aspect of the present invention there is provided the use of a platinum carbon catalyst according to the first or third aspect of the present invention in a fuel cell.

According to a fifth aspect of the present invention there is provided a hydrogen fuel cell having an anode and/or cathode comprising a platinum carbon catalyst according to the first or third aspect of the present invention.

The platinum carbon catalyst according to the present invention has improved structural dispersibility, and exhibits improved electrochemical catalytic activity and stability. According to the preparation method of the platinum-carbon catalyst, the preparation process is simple, the interaction between the metal platinum particles and the carrier can be effectively improved, the dispersity of the metal platinum particles on the carrier is improved, and the electrochemical catalytic activity and stability of the prepared platinum-carbon catalyst are improved.

Drawings

FIG. 1 is a schematic diagram for illustrating the contact angle of metallic platinum with a carbonaceous carrier in a platinum-carbon catalyst;

FIG. 2 is a spherical aberration electron micrograph showing a contact angle of metallic platinum with a carbonaceous carrier in the platinum-carbon catalyst prepared in example 1;

FIG. 3 is a transmission electron micrograph of the platinum carbon catalyst prepared in example 1;

FIG. 4 is a transmission electron micrograph of the platinum carbon catalyst prepared in comparative example 1;

fig. 5 is an oxygen reduction (ORR) polarization curve of the platinum carbon catalysts prepared in example 1 and comparative example 1.

Detailed Description

The endpoints and any values of the ranges disclosed herein are not limited to the precise range or value, and are understood to encompass values approaching those ranges or values. For numerical ranges, one or more new numerical ranges may be found between the endpoints of each range, between the endpoint of each range and the individual point value, and between the individual point value, in combination with each other, and are to be considered as specifically disclosed herein.

According to a first aspect of the present invention there is provided a platinum carbon catalyst comprising a carbonaceous support and metallic platinum particles supported on the carbonaceous support.

The platinum carbon catalyst according to the present invention, in which the contact angle of the platinum nanoparticles with the carbon support is 50 ° or less, generally in the range of 30 ° -50 °, shows that there is a strong interaction between the metal platinum particles and the carbonaceous support.

In the present invention, the specific definition of the contact angle between the platinum metal particles and the carbonaceous carrier is shown in FIG. 1, and the straight line L where the edge region of carbon is located ₁ On the line tangent to the platinum nano-particles, a line L tangent to the nano-particles is led at the tangent point ₂ Straight line L ₁ And straight line L ₂ The included angle between the two is the contact angle theta. The invention adopts an appearance image method to measure the contact angle between metal platinum particles and a carbonaceous carrier, and the specific test method comprises the following steps: and randomly selecting 8 non-overlapping and widely dispersed transmission electron microscope images of catalyst particles on a tested sample by adopting a transmission electron microscope, selecting all nano particles positioned at the edge of a carbon carrier from each image, and counting the contact angle between the metal platinum particles and the carbon carrier.

According to the platinum carbon catalyst of the present invention, the carbonaceous carrier is preferably conductive carbon black. Preferred examples of the conductive carbon black may include, but are not limited to, one or more of Vulcan XC72, ketjen EC300J, ketjen EC600J, blackpearls 2000, and blackpears 3000. According to the platinum carbon catalyst of the present invention, The specific surface area of the carbonaceous carrier is preferably 200-2000m ² Preferably 250-1500m ² /g。

In the present invention, the specific surface area is measured by a specific surface area and pore size analyzer (BET) method.

The platinum carbon catalyst according to the present invention may contain 20 to 90 wt%, preferably 30 to 80 wt%, more preferably 40 to 75 wt%, still more preferably 40 to 70 wt%, of the platinum element, and the carbonaceous carrier may contain 10 to 80 wt%, preferably 20 to 70 wt%, more preferably 25 to 60 wt%, still more preferably 30 to 60 wt%, of the carbonaceous carrier based on the carbon element, based on the total amount of the platinum carbon catalyst.

In the invention, the content of platinum element and carbonaceous carrier in the platinum-carbon catalyst is measured by an Inductively Coupled Plasma (ICP) method.

The platinum carbon catalyst according to the present invention has highly uniform platinum cluster particles. According to the platinum carbon catalyst of the present invention, the average particle diameter of the platinum nanoparticles is in the range of 3 to 4 nm.

In the invention, the average particle diameter of the metal platinum particles in the platinum-carbon catalyst is measured by a transmission electron microscope method. The specific test method comprises the following steps: on the test samples, random selection of 8 non-overlapping, widely dispersed transmission electron microscope images of catalyst particles were carried out, 50 (400 in total) catalyst platinum particle sizes were selected for each image for statistics, and each image was taken as the average particle size.

The platinum carbon catalyst according to the present invention shows an increased electrochemically active area and electrochemical catalytic activity. According to the platinum carbon catalyst of the present invention, the half-wave potential is 0.86V or more, preferably 0.87V or more, and more preferably 0.88V or more. The platinum carbon catalyst according to the invention has an electrochemical active area (ECSA) of 50m ² ·g ^-1 Pt or more (e.g. 50-65m ² ·g ^-1 -Pt), preferably 55-60m ² ·g ^-1 -Pt。

s1, dispersing a carbonaceous material, a platinum precursor, a complexing agent and a dispersion medium by ultrasonic waves to obtain a first dispersion;

s3, adding a reducing agent into the second dispersion, and enabling the reducing agent to be in contact with a platinum precursor in the second dispersion to carry out reduction reaction.

In step S1, the platinum precursor may be a platinum compound that can be reduced to metallic platinum by a reducing agent under a reducing reaction condition. According to the method of the present invention, the platinum precursor may be one or two or more selected from chloroplatinic acid, potassium chloroplatinate, and sodium chloroplatinate. Preferably, the platinum precursor is chloroplatinic acid.

In step S1, the complexing agent is one or more of dicarboxylic acid salts and polycarboxylic acid salts, and may be, for example: one or more of alkali metal salts of dicarboxylic acids, ammonium salts of dicarboxylic acids, alkali metal salts of polycarboxylic acids, and ammonium salts of polycarboxylic acids. The polycarboxylic acid refers to an organic compound containing more than three carboxyl groups in a molecular structure. In a preferred embodiment, the complexing agent is one or more selected from sodium citrate, sodium oxalate, sodium ethylenediamine tetraacetate and sodium tartrate. More preferably, the complexing agent is sodium citrate. The amount of complexing agent may be selected based on the amount of platinum precursor. Preferably, the mass ratio of the platinum precursor to the complexing agent is 1:0.1-7. More preferably, the mass ratio of the platinum precursor to the complexing agent is 1:0.15-5. Further preferably, the mass ratio of the platinum precursor to the complexing agent is 1:0.2-3. Still further preferably, the mass ratio of the platinum precursor to the complexing agent is 1:0.25-1. Particularly preferably, the mass ratio of the platinum precursor to the complexing agent is 1:0.3-0.6.

In step S1, the dispersion medium is glycerol and water. According to the method of the present invention, the particle diameter and the surface property of the metal platinum particles in the prepared platinum-carbon catalyst can be effectively controlled, compared with the case where only water is used as the dispersion medium or only glycerol is used as the dispersion medium, so that the finally prepared platinum-carbon catalyst exhibits an improved electrochemical active area and electrochemical catalytic activity. According to the method of the present invention, from the viewpoint of further improving the electrochemical catalytic activity and stability of the prepared platinum carbon catalyst, the volume of glycerol and water in step S1 is preferably 0.2 to 5:1, more preferably 0.3 to 3:1, further preferably 0.5 to 2:1, and still more preferably 0.8 to 1.2:1. according to the method of the present invention, in step S1, the dispersion medium is used in such an amount that the concentration of the platinum precursor relative to the dispersion medium is preferably 1 to 20g/L, more preferably 2 to 10g/L, still more preferably 3 to 8g/L, still more preferably 3 to 5g/L.

In step S1, the carbonaceous material is conductive carbon black. Preferred examples of the conductive carbon black may include, but are not limited to, one or more of Vulcan XC72, ketjen EC300J, ketjen EC600J, blackpearls 2000, and blackpears 3000. According to the method of the invention, the specific surface area of the carbonaceous carrier is preferably 200-2000m ² Preferably 250-1500m ² /g。

According to the method of the present invention, in step S1, the carbonaceous material may be a carbonaceous material that has not been surface-treated, may be a carbonaceous material that has been surface-treated, or may be a combination of a carbonaceous material that has not been surface-treated and a carbonaceous material that has been surface-treated.

In an embodiment, in which the carbonaceous material is a surface-treated carbonaceous material, the method according to the invention further comprises a step S0 of pre-treating the carbonaceous material in step S1, in which step S0 the carbonaceous material is subjected to a solvent treatment, a first oxidation treatment, a second oxidation treatment and a high temperature treatment in that order, resulting in a pre-treated carbonaceous material, and the pre-treated carbonaceous material is used in step S1.

In the solvent treatment, the carbonaceous material is soaked with an organic solvent to obtain the carbonaceous material soaked with the organic solvent. The organic solvent is one or more selected from ketone solvents, preferably acetone. The soaking can be carried out at normal temperature or at elevated temperature. Preferably, the temperature of the organic solvent is 50-70 ℃. The duration of the soaking may be selected according to the soaking temperature, and in general, the duration of the soaking may be 5 to 24 hours. The organic solvent is used in an amount sufficient to submerge the carbonaceous material, and generally the volume ratio of the solvent to the carbonaceous material may be from 1 to 3:1.

In the solvent treatment, after the completion of the soaking, the solid phase and the liquid phase may be separated by a conventional method (e.g., filtration), and the resulting solid phase may be dried, thereby obtaining the solvent-treated carbonaceous material. The drying may be carried out at a temperature of 80-120 ℃ and the duration of the drying may be 5-15 hours, preferably 8-12 hours. The drying may be performed under normal pressure or under reduced pressure.

In the first oxidation treatment, the carbonaceous material soaked in the organic solvent is contacted with a first oxidant to obtain the carbonaceous material subjected to the first oxidation treatment, wherein the first oxidant is one or more than two selected from hydrogen peroxide and organic peroxides shown in a formula (I):

in the formula I, R ₁ And R is ₂ Each selected from H, C ₄ -C ₁₂ Alkyl, C of (2) ₆ -C ₁₂ Aryl, C of (2) ₇ -C ₁₂ Aralkyl of (a)

And R is ₁ And R is ₂ Not simultaneously H, R ₃ Is C ₄ -C ₁₂ Straight or branched alkyl or C ₆ -C ₁₂ Aryl groups of (a).

In the invention, C ₄ -C ₁₂ Specific examples of alkyl groups of (a) may include, but are not limited to, n-butyl, sec-butyl, isobutyl, tert-butyl, n-pentyl, neopentyl, isopentyl, tert-pentyl, hexyl (including the various isomers of hexyl), cyclohexyl, octyl (including octyl) Nonyl (including various isomers of nonyl), decyl (including various isomers of decyl), undecyl (including various isomers of undecyl), and dodecyl (including various isomers of dodecyl).

In the invention, C ₆ -C ₁₂ Specific examples of the aryl group of (a) may include, but are not limited to, phenyl, naphthyl, methylphenyl and ethylphenyl.

In the invention, C ₇ -C ₁₂ Specific examples of the aralkyl group of (a) may include, but are not limited to, phenylmethyl, phenylethyl, phenyl-n-propyl, phenyl-n-butyl, phenyl-t-butyl, phenyl-isopropyl, phenyl-n-pentyl and phenyl-n-butyl.

Specific examples of the organic peroxide may include, but are not limited to: tert-butyl hydroperoxide, cumene hydroperoxide, ethylbenzene hydroperoxide, cyclohexylhydroperoxide, dicumyl peroxide, dibenzoyl peroxide, di-tert-butyl peroxide and lauroyl peroxide.

Preferably, the first oxidizing agent is hydrogen peroxide.

In the first oxidation treatment, the carbonaceous material immersed in the organic solvent is contacted with the first oxidizing agent in a liquid phase in the presence of a liquid dispersion medium. The liquid dispersion medium may be water and/or C ₁ -C ₄ Preferably water. In a preferred embodiment, a first oxidizing agent is dissolved in a liquid dispersion medium to form a first oxidizing agent solution, and the first oxidizing agent solution is contacted with the carbonaceous material immersed in the organic solvent. In this preferred embodiment, hydrogen peroxide is preferably used as the first oxidant solution. The concentration of hydrogen peroxide in the hydrogen peroxide may be 8-20 wt%.

In the first oxidation treatment, the contacting is preferably carried out at a temperature of 50-70 ℃. The duration of the contact may be selected according to the temperature of the contact, preferably 5 to 12 hours. The amount of the first oxidizing agent may be selected according to the amount of carbonaceous material immersed in the organic solvent. Preferably, the mass ratio of the first oxidant to the carbonaceous material soaked in the organic solvent is 1-3:1.

in the first oxidation treatment, after the first oxidizing agent treatment is completed, the solid phase and the liquid phase may be separated by a conventional method (e.g., filtration), and the resulting solid phase may be dried, thereby obtaining the carbonaceous material treated with the first oxidizing agent. The drying may be carried out at a temperature of 80-120 ℃ and the duration of the drying may be 5-15 hours, preferably 8-12 hours. The drying may be performed under normal pressure or under reduced pressure.

In the second oxidation treatment, the carbonaceous material subjected to the first oxidation treatment is contacted with a second oxidant to obtain the carbonaceous material subjected to the second oxidation treatment, wherein the second oxidant is HNO ₃ And/or H ₂ SO ₄ . Preferably, the second oxidant is HNO ₃ 。

In the second oxidation treatment, the carbonaceous material subjected to the first oxidation treatment is contacted with a second oxidizing agent in the presence of a liquid dispersion medium. The liquid dispersion medium may be water and/or C ₁ -C ₄ Preferably water. In a preferred embodiment, the second oxidant is dissolved in a liquid dispersion medium to form a second oxidant solution, and the second oxidant solution is contacted with the first oxidized carbonaceous material. In this preferred embodiment, nitric acid is preferably used as the second oxidizer solution. The concentration of the nitric acid may be 10-30 wt%.

In the second oxidation treatment, the contacting is preferably performed at a temperature of 50-70 ℃. In the second oxidation treatment, the duration of the contact may be selected according to the temperature of the contact, and preferably, the duration of the contact may be 5 to 12 hours.

In the second oxidizing treatment, after the second oxidizing agent treatment is completed, the solid phase and the liquid phase may be separated by a conventional method (e.g., filtration), and the resulting solid phase may be dried, thereby obtaining a carbonaceous material treated with the second oxidizing agent. The drying may be carried out at a temperature of 80-120 ℃ and the duration of the drying may be 5-15 hours, preferably 8-12 hours. The drying may be performed under normal pressure or under reduced pressure.

In the high temperature treatment, the carbonaceous material subjected to the second oxidation treatment is calcined in an inert atmosphere at a temperature of 300-600 ℃ to obtain a pretreated carbonaceous material. The inert atmosphere may be an atmosphere formed of nitrogen and/or a group zero gas, for example: an atmosphere formed of one or two or more gases of nitrogen, argon and helium. The duration of the calcination may be selected according to the calcination temperature, and preferably, the duration of the calcination may be 5 to 24 hours, preferably, 6 to 12 hours.

In a more preferred embodiment, the carbonaceous material is a carbonaceous material that has not been subjected to a surface modification treatment, including but not limited to oxidation treatment, acid washing, high temperature treatment, and the like, such as the surface treatments described above. It will be appreciated by those skilled in the art that in this more preferred embodiment, the carbonaceous material may be washed prior to use in the platinum carbon catalyst using methods conventional in the art to remove impurities, etc. adhering to the surface of the carbonaceous material. According to the more preferred embodiment, the platinum carbon catalyst prepared by the method still shows improved electrochemical catalytic activity and stability, and the preparation method is simpler and more suitable for large-scale production.

According to the method of the present invention, in step S1, the carbonaceous material, the platinum precursor, the complexing agent and the dispersion medium are dispersed by ultrasonic waves, and the carbonaceous material and the platinum precursor can be sufficiently mixed. Preferably, the power of the ultrasonic wave is 100-1000W, preferably 100-500W. The duration of the ultrasonic dispersion may be from 0.2 to 5 hours, preferably from 0.5 to 3 hours, more preferably from 1 to 2 hours. The present invention is not particularly limited to the ultrasonic dispersing device, and may be carried out in a common ultrasonic dispersing device.

According to the method of the present invention, in step S2, the pH of the first dispersion obtained in step S1 is adjusted to 11 to 14, resulting in a second dispersion. In step S2, the pH of the first dispersion obtained in step S1 is preferably adjusted to 12 to 13 to obtain a second dispersion, from the viewpoint of further improving the electrochemical active area and electrochemical catalytic activity of the prepared platinum carbon catalyst. A pH adjuster may be added to the first dispersion to adjust the pH to 11-14 (preferably 12-13). The pH regulator is preferably one or more of sodium carbonate, potassium hydroxide and sodium hydroxide, more preferably sodium carbonate and/or potassium carbonate. The pH adjustor is preferably provided in the form of an aqueous solution, and the concentration of the aqueous solution may be conventionally selected without particular limitation.

According to the method of the invention, in step S3, the reducing agent contains polyvinylpyrrolidone and formic acid. In a preferred embodiment, in step S3, the reducing agents are polyvinylpyrrolidone and formic acid. According to the method of the invention, polyvinylpyrrolidone and formic acid are adopted as reducing agents, and compared with the method of adopting formic acid alone or adopting polyvinylpyrrolidone alone as reducing agents, the electrochemical activity area and electrochemical catalytic activity of the prepared platinum carbon catalyst can be effectively improved, and the reasons are probably that: the polyvinylpyrrolidone and the formic acid are combined for use, so that the nucleation and the loading of platinum can be synchronously carried out, the interaction between the metal platinum particles and the carrier can be effectively enhanced, the stability of the metal platinum particles on the carrier can be improved, and the electrochemical active area and the electrochemical catalytic activity of the platinum-carbon catalyst can be further improved.

According to the method of the present invention, from the viewpoint of further improving the electrochemical catalytic activity and stability of the finally prepared platinum carbon catalyst, the molar ratio of polyvinylpyrrolidone to formic acid in the reducing agent of step S3 is preferably 1:1-5, more preferably 1:1-3.

In step S3 of the method according to the invention, the reducing agent is preferably used in excess of the stoichiometric ratio. In the step S3, the mol ratio of the reducing agent to the platinum precursor is 150-1000:1. from the viewpoint of further improving the electrochemical catalytic activity and stability of the finally prepared platinum carbon catalyst and reducing the cost, the molar ratio of the reducing agent to the platinum precursor in step S3 is preferably 160 to 800:1, more preferably 170-600:1, further preferably 180-500:1, and still more preferably 190-400:1, particularly preferably 200 to 300:1, the platinum precursor is calculated by platinum element.

According to the method of the present invention, step S3 may be performed under conventional reduction reaction conditions. Preferably, in step S3, the reduction reaction is performed at a temperature of 50-140 ℃. More preferably, in step S3, the reduction reaction is performed at a temperature of 60 to 120 ℃. Further preferably, in step S3, the reduction reaction is performed at a temperature of 70 to 100 ℃. Still more preferably, in step S3, the reduction reaction is performed at a temperature of 80 to 90 ℃. In step S3, the duration of the reduction reaction may be selected according to the temperature at which the reduction reaction is performed. In general, in step S3, the duration of the reduction reaction may be 4 to 15 hours, preferably 5 to 13 hours, more preferably 8 to 12 hours. In step S3, the reduction reaction is performed in an inert atmosphere, for example, an atmosphere formed of nitrogen and/or a zero group gas (e.g., argon and/or helium).

According to the method of the present invention, a conventional separation method may be employed to separate a solid phase substance from the reduction mixture obtained in step S3, and the separated solid phase substance may be sequentially subjected to water washing and drying to obtain a platinum carbon catalyst. In general, the reduced mixture obtained in step S3 may be subjected to solid-liquid separation by a combination of one or more of filtration, centrifugation and sedimentation to obtain a solid phase substance. The drying is preferably carried out at a temperature of 60-120 ℃, more preferably at a temperature of 80-110 ℃, and the duration of the drying may be 12-24 hours. The drying may be carried out at normal pressure or at a pressure lower than atmospheric pressure.

The platinum carbon catalyst prepared by the method of the invention shows improved electrochemical activity and stability.

The platinum carbon catalyst according to the third aspect of the present invention, in which the contact angle of the platinum nanoparticles with the carbon support is 50 ° or less, typically in the range of 30 ° -50 °, shows that there is a strong interaction between the metal platinum particles and the carbonaceous support. The platinum carbon catalyst according to the third aspect of the present invention has highly uniform platinum cluster particles, and in the platinum carbon catalyst, the average particle diameter of the platinum nanoparticles is in the range of 3 to 4 nm.

According to the platinum carbon catalyst of the third aspect of the present invention, the half-wave potential is 0.86V or more, preferably 0.87V or more, more preferably 0.88V or more. According to the platinum carbon catalyst of the third aspect of the invention, the electrochemical active area (ECSA) is 50m ² ·g ^-1 Pt or more (e.g. 55-65m ² ·g ^-1 -Pt), preferably 55-60m ² ·g ^-1 -Pt。

The platinum carbon catalyst according to the invention is particularly suitable for use in fuel cells. According to a fourth aspect of the present invention there is provided the use of a platinum carbon catalyst according to the first or third aspect of the present invention in a fuel cell.

The present invention will be described in detail with reference to examples, but the scope of the present invention is not limited thereto.

In the following examples and comparative examples, the contents of the platinum element and the carbonaceous carrier in the platinum-carbon catalyst were measured by an Inductively Coupled Plasma (ICP) method.

In the following examples and comparative examples, transmission electron microscope analysis was performed on a transmission electron microscope available from FEI company under the model Tecnai G2F 20, and the sample preparation method was: about 1mg of a sample is taken and dispersed in 60-80 wt% of ethanol, ultrasonic dispersion is carried out for 10 minutes, a small amount of dispersion liquid is sucked by a suction pipe, the dispersion liquid is dripped on a copper mesh tested by an electron microscope, the adopted copper mesh is a micro grid or an ultrathin micro grid, and an ultrathin carbon film or a carbon support film is not used.

In the following examples and comparative examples, the average particle diameter of the metal platinum particles in the platinum-carbon catalyst was measured by transmission electron microscopy. The specific test method comprises the following steps: on the test samples, random selection of 8 non-overlapping, widely dispersed transmission electron microscope images of catalyst particles were carried out, 50 (400 in total) catalyst platinum particle sizes were selected for each image for statistics, and each image was taken as the average particle size.

In the following examples and comparative examples, the contact angle between the metallic platinum particles and the carbonaceous carrier in the platinum-carbon catalyst was measured by transmission electron microscopy: as shown in FIG. 1, a straight line L where the edge region of carbon is located ₁ On the line tangent to the platinum nano-particles, a line L tangent to the nano-particles is led at the tangent point ₂ Straight line L ₁ And straight line L ₂ The included angle between the two is the contact angle theta.

In the following examples and comparative examples, specific surface areas were measured on a specific surface area meter of model JW-BK200 available from Beijing micro-advanced.

In the following examples and comparative examples, the electrochemical activity test method of the platinum carbon catalyst was a rotary disk test method, the catalyst was prepared into slurry and was applied dropwise to a glassy carbon electrode having a diameter of 5mm, and the electrode was dried to be tested (ensuring that the Pt loading on the electrode was 18-22. Mu.g/cm) ² Within a range of (2); wherein the test conditions of the catalyst polarization curve are as follows: 0.1M HClO ₄ The solution is saturated by oxygen, the voltage scanning range is 0-1.0V vs RHE, the scanning speed is 10mV/s, and the rotating speed of the rotating disc electrode is 1600r/min; the test conditions for the electrochemically active area were: 0.1M HClO ₄ The solution is saturated by nitrogen, the voltage scanning range is 0-1.0V vs RHE, the scanning speed is 50mV/s, the area of the hydrogen desorption peak on the curve is integrated,

wherein, the calculation formula of the electrochemical active area (ECSA) of the platinum carbon catalyst is as follows:

wherein S is _H In order to be the area of the peak,

v is the scanning speed, which is 0.05V/s,

M _pt the mass of Pt which is dripped on the glass carbon electrode;

mass of platinum carbon catalystSpecific Activity (The mass specific activity, A/mg) _Pt ) The calculation formula of (2) is as follows:

wherein i is _k Is kinetic current, unit is mA/cm ² The calculation is calculated according to a K-L equation, and the equation is as follows:

i _L for limiting diffusion current, reading directly through ORR curve;

m _Pt the unit of Pt loaded on the glassy carbon electrode is mg _Pt /cm ² 。

The following conductive carbon blacks are referred to in the following examples and comparative examples:

(1) Conductive carbon black with Ketjen EC 300J, available from Japanese lion king company, having particle diameter in the range of 50nm to 100nm and specific surface area of 1400m ² /g；

(2) Conductive carbon black with the trade name of Vulcan XC72, which is purchased from the Kabot corporation of America, has a particle diameter in the range of 50nm to 100nm and a specific surface area of 260m ² /g。

Examples 1-7 illustrate the platinum carbon catalysts of the present invention and methods of making and using the same.

Example 1

(1) 0.3g Ketjen EC300J conductive carbon black was added to 400mL of a mixed solution of deionized water and glycerol (the volume ratio of deionized water to glycerol was 1:1), after mixing well, 0.7g of sodium citrate was added, then an aqueous solution of chloroplatinic acid (chloroplatinic acid: 3.6 mmol) was added, and the resulting mixture was subjected to ultrasonic dispersion to form a first dispersion. Wherein, the power of the ultrasonic wave is 100W, and the ultrasonic dispersion time is 2h.

(2) An aqueous sodium carbonate solution was added as a pH adjuster to the first dispersion to adjust the pH of the dispersion to 13, to obtain a second dispersion.

(3) Heating the third dispersion to 80 ℃ by a heater, adding formic acid and polyvinylpyrrolidone as reducing agents with stirring to perform reduction reaction, wherein the molar ratio of the reducing agents to chloroplatinic acid is 200:1, the molar ratio of formic acid to polyvinylpyrrolidone in the reducing agent is 1:1. after the addition of the reducing agent is completed, the heating condition of the heater is kept unchanged, and the reaction is continued for 10 hours.

After the reaction is completed, the reduction reaction mixture is filtered, solid phase substances are collected, and the solid phase substances are washed by deionized water until washing liquid is neutral. The washed solid phase material was dried in vacuo at 100℃for 12 hours to give 1g of the platinum carbon catalyst according to the present invention, in which the mass content of platinum was 69% as determined, and in which the contact angle of platinum nanoparticles with the carbon support was in the range of 30℃to 50℃and the average particle diameter of the platinum nanoparticles was 3 to 4nm. The electrochemical properties of the prepared platinum carbon catalyst were measured, and the experimental results are shown in table 1.

Example 2 (including example 2a, example 2b and example 2 c)

A platinum carbon catalyst was prepared in the same manner as in example 1 except that the pH adjuster used in step (2) was different, wherein in example 2a, potassium carbonate was used as the pH adjuster; in example 2b, sodium bicarbonate was used as pH regulator; in example 2c, sodium hydroxide was used as pH regulator. The electrochemical properties of the prepared platinum carbon catalyst were measured, and the experimental results are shown in table 1.

The platinum carbon catalyst prepared in example 2a, in which the platinum nanoparticles have a contact angle with the carbon support in the range of 30 ° to 50 ° and an average particle diameter in the range of 3-4nm, was measured with a mass content of platinum of 70%;

The platinum carbon catalyst prepared in example 2b, in which the platinum nanoparticles have a contact angle with the carbon support in the range of 30 ° to 45 ° and an average particle diameter in the range of 3-4nm, was measured with a platinum mass content of 70%;

the platinum carbon catalyst prepared in example 2c, in which the contact angle of the platinum nanoparticles with the carbon support was in the range of 30 ° to 45 ° and the average particle diameter of the platinum nanoparticles was in the range of 3 to 4nm, was measured with a mass content of 69%.

Example 3 (including example 3a and example 3 b)

A platinum carbon catalyst was prepared in the same manner as in example 1 except that the pH value in step (2) was different, wherein in example 3a, the pH value was adjusted to 11; in example 3b, the pH was adjusted to 12. The electrochemical properties of the prepared platinum carbon catalyst were measured, and the experimental results are shown in table 1.

The platinum carbon catalyst prepared in example 3a, in which the platinum nanoparticles have a contact angle with the carbon support in the range of 30 ° to 45 ° and an average platinum nanoparticle particle diameter in the range of 3 to 4nm, had a mass content of 69.5% by mass;

the platinum carbon catalyst prepared in example 3b, in which the contact angle of the platinum nanoparticles with the carbon support was in the range of 30 ° to 45 ° and the average particle diameter of the platinum nanoparticles was in the range of 3 to 4nm, was measured with a mass content of 69.5%.

Comparative example 1 (including comparative example 1a, comparative example 1b and comparative example 1 c)

A platinum carbon catalyst was prepared in the same manner as in example 1 except that the pH value in step (2) was different, wherein in comparative example 1a, the pH value was adjusted to 8; in comparative example 1b, the pH was adjusted to 9; in comparative example 1c, the pH was adjusted to 10. The mass content of platinum in the platinum carbon catalysts prepared in comparative example 1a, comparative example 1b and comparative example 1c was 70%, and it was determined that the platinum nano-particles in the platinum carbon catalysts had an average particle diameter in the range of 3 to 4.5 nm. The electrochemical properties of the prepared platinum carbon catalyst were measured, and the experimental results are shown in table 1.

Example 4

A platinum carbon catalyst was prepared in the same manner as in example 1, except that the reaction time in step (3) was 12 hours. The electrochemical properties of the prepared platinum carbon catalyst were measured, and the experimental results are shown in table 1. The mass content of platinum in the prepared platinum carbon catalyst is 69.3 percent, and the contact angle of platinum nano particles and a carbon carrier in the platinum carbon catalyst is in the range of 30 DEG to 50 DEG, and the average particle diameter of the platinum nano particles is in the range of 3-4 nm.

Comparative example 2

A platinum carbon catalyst was prepared in the same manner as in example 1, except that glycerol and sodium citrate were not used in step (1), wherein the dispersion medium was 400mL of deionized water. The mass content of platinum in the prepared platinum-carbon catalyst is 69%, and the contact angle of platinum nano particles and a carbon carrier in the platinum-carbon catalyst is in the range of 0-180 degrees, no obvious distribution rule exists, and the average particle size of the platinum nano particles is in the range of 4.5-6.5 nm. The electrochemical properties of the prepared platinum carbon catalyst were measured, and the experimental results are shown in table 1.

Comparative example 3

A platinum carbon catalyst was prepared in the same manner as in example 1, except that in step (1), glycerol was not used, wherein the dispersion medium was 400mL of deionized water. The mass content of platinum in the prepared platinum-carbon catalyst is 69%, and the contact angle of platinum nano particles and a carbon carrier in the platinum-carbon catalyst is in the range of 0-180 degrees, no obvious distribution rule exists, and the average particle size of the platinum nano particles is in the range of 4.5-7.0 nm. The electrochemical properties of the prepared platinum carbon catalyst were measured, and the experimental results are shown in table 1.

Comparative example 4

A platinum carbon catalyst was prepared in the same manner as in example 1, except that sodium citrate was not used in step (1). The mass content of platinum in the prepared platinum-carbon catalyst is 70%, and the contact angle of platinum nano particles and a carbon carrier in the platinum-carbon catalyst is in the range of 0-180 degrees, no obvious distribution rule exists, and the average particle size of the platinum nano particles is in the range of 4.5-7.0 nm. The electrochemical properties of the prepared platinum carbon catalyst were measured, and the experimental results are shown in table 1.

Comparative example 5

A platinum carbon catalyst was prepared in the same manner as in example 1 except that in step (3), the amount of the reducing agent was maintained unchanged, but formic acid was not used, and formic acid was replaced with an equimolar amount of polyvinylpyrrolidone. The mass content of platinum in the prepared platinum-carbon catalyst is 69.5%, and the contact angle of platinum nano particles and a carbon carrier in the platinum-carbon catalyst is in the range of 0-180 degrees, no obvious distribution rule exists, and the average particle size of the platinum nano particles is in the range of 4.5-7.0 nm. The electrochemical properties of the prepared platinum carbon catalyst were measured, and the experimental results are shown in table 1.

Comparative example 6

A platinum carbon catalyst was prepared in the same manner as in example 1 except that in step (3), the amount of the reducing agent was kept unchanged, but polyvinylpyrrolidone was not used, and polyvinylpyrrolidone was replaced with an equimolar amount of formic acid. The mass content of platinum in the prepared platinum-carbon catalyst is 70.1%, and the contact angle of platinum nano particles and a carbon carrier in the platinum-carbon catalyst is in the range of 0-180 degrees, no obvious distribution rule exists, and the average particle size of the platinum nano particles is in the range of 4.5-7.5 nm. The electrochemical properties of the prepared platinum carbon catalyst were measured, and the experimental results are shown in table 1.

Comparative example 7

A platinum carbon catalyst was prepared in the same manner as in example 1, except that in step (3), polyvinylpyrrolidone was replaced with citric acid in equimolar amounts. The mass content of platinum in the prepared platinum-carbon catalyst is 69%, and the contact angle of platinum nano particles and a carbon carrier in the platinum-carbon catalyst is in the range of 0-180 degrees, no obvious distribution rule exists, and the average particle size of the platinum nano particles is in the range of 4.5-7.5 nm. The electrochemical properties of the prepared platinum carbon catalyst were measured, and the experimental results are shown in table 1.

Example 5 (including example 5a and example 5 b)

A platinum carbon catalyst was prepared in the same manner as in example 1 except that in step (3), the ratio of polyvinylpyrrolidone to formic acid was changed, wherein in example 5a, the molar ratio of formic acid to polyvinylpyrrolidone was 2:1, a step of; in example 5b, the molar ratio of formic acid to polyvinylpyrrolidone was 3:1. the electrochemical properties of the prepared platinum carbon catalyst were measured, and the experimental results are shown in table 1.

The platinum carbon catalyst prepared in example 5a, in which the platinum nanoparticles have a contact angle with the carbon support in the range of 30 ° to 50 ° and an average particle diameter in the range of 3 to 4nm, had a mass content of 69% by mass of platinum;

the platinum carbon catalyst prepared in example 5b, in which the contact angle of the platinum nanoparticles with the carbon support was in the range of 30 ° to 50 ° and the average particle diameter of the platinum nanoparticles was in the range of 3-4nm, was measured with a mass content of platinum of 70%.

The electrochemical properties of the prepared platinum carbon catalyst were measured, and the experimental results are shown in table 1.

Comparative example 8 (comprising comparative example 8a and comparative example 8 b)

A platinum carbon catalyst was prepared in the same manner as in example 1 except that in step (3), the molar ratio of formic acid to polyvinylpyrrolidone in the reducing agent was not changed, and the amount of the reducing agent was changed, wherein in comparative example 8a, the molar ratio of the reducing agent to chloroplatinic acid was 100:1, a step of; in comparative example 8b, the molar ratio of reducing agent to chloroplatinic acid was 50:1. the platinum carbon catalyst prepared in comparative example 8a had a platinum mass content of 69% and the platinum carbon catalyst prepared in comparative example 8b had a platinum mass content of 70%. The electrochemical properties of the prepared platinum carbon catalyst were measured, and the experimental results are shown in table 1.

Example 6

A platinum carbon catalyst was prepared in the same manner as in example 1, except that a pretreatment step of conductive carbon black was performed before step (1), and conductive carbon black pretreated by the following method was used in step (1):

(1) 0.3g Ketjen EC 300J conductive carbon black was soaked with acetone (analytically pure) at 60 ℃ for 24 hours, wherein the mass ratio of acetone to carbon black was 2:1. after the soaking is finished, carrying out suction filtration to obtain a solid phase substance, and drying the solid phase substance at 100 ℃ for 6 hours to obtain the carbon black soaked by the acetone.

(2) Mixing the carbon black soaked by the acetone with hydrogen peroxide with the mass concentration of 8% (the mass ratio of the hydrogen peroxide to the carbon black is 2:1), and reacting for 12 hours at 60 ℃. After the reaction is completed, the reaction mixture is subjected to suction filtration, and the obtained solid phase substance is dried for 12 hours at 100 ℃ to obtain the carbon black subjected to the first oxidation treatment.

(3) Mixing the carbon black subjected to the first oxidation treatment with 30% by mass of aqueous nitric acid solution (HNO) ₃ The mass ratio of the carbon black to the carbon black is 2: 1) The reaction was carried out at 60℃for 12h. After the reaction is completed, the reaction mixture is subjected to suction filtration, and the obtained solid phase substance is dried at 100 ℃ for 8 hours, so that the carbon black subjected to the second oxidation treatment is obtained.

(4) The carbon black subjected to the second oxidation treatment was calcined at 400℃for 6 hours in a nitrogen atmosphere to obtain a pretreated carbon black.

The mass content of platinum in the prepared platinum-carbon catalyst is 69 percent, and the contact angle of platinum nano particles and a carbon carrier in the platinum-carbon catalyst is in the range of 30 DEG to 50 DEG, and the average particle diameter of the platinum nano particles is in the range of 3-4 nm. The electrochemical properties of the prepared platinum carbon catalyst were measured, and the experimental results are shown in table 1.

Example 7

(1) 0.3g Ketjen EC600J conductive carbon black was added to 600mL of a mixed solution of deionized water and glycerol (the volume ratio of deionized water to glycerol was 1:1), after mixing well, 0.9g of sodium citrate was added, then an aqueous solution of chloroplatinic acid (chloroplatinic acid: 3.6 mmol) was added, and the resulting mixture was subjected to ultrasonic dispersion to form a first dispersion. Wherein, the power of the ultrasonic wave is 200W, and the ultrasonic dispersion time is 2h.

(3) Heating the third dispersion to 90 ℃ by a heater, adding formic acid and polyvinylpyrrolidone as reducing agents with stirring to perform reduction reaction, wherein the molar ratio of the reducing agents to chloroplatinic acid is 200:1, the molar ratio of formic acid to polyvinylpyrrolidone in the reducing agent is 1:1. after the addition of the reducing agent is completed, the heating condition of the heater is kept unchanged, and the reaction is continued for 12 hours.

After the reaction is completed, the reduction reaction mixture is filtered, solid phase substances are collected, and the solid phase substances are washed by deionized water until washing liquid is neutral. The washed solid phase material was dried in vacuo at 100℃for 12 hours to give 1g of the platinum carbon catalyst according to the present invention, in which the platinum mass content was 69.5% as determined, the contact angle of the platinum nanoparticles with the carbon support was in the range of 30℃to 50℃and the average particle diameter of the platinum nanoparticles was in the range of 3 to 4 nm. The electrochemical properties of the prepared platinum carbon catalyst were measured, and the experimental results are shown in table 1.

As can be seen from fig. 2, in the platinum-carbon catalyst according to the present invention prepared by the method of the present invention, the contact angle between the metal platinum particles and the carbonaceous carrier is 50 ° or less, and is between 30 ° and 50 °, indicating that in the platinum-carbon catalyst according to the present invention, there is a relatively strong interaction between the metal platinum particles and the carbonaceous carrier.

Fig. 3 and 4 are transmission electron micrographs of the platinum carbon catalysts prepared in example 1 and comparative example 1, respectively, and it can be seen from a comparison of fig. 3 and 4 that the platinum carbon catalyst prepared by the method of the present invention has highly uniform metal platinum cluster particles, and the metal platinum particles have uniform size, and the average particle diameter of the platinum nanoparticles is in the range of 3 to 4 nm.

As can be seen from fig. 5 and table 1, example 1 prepared a platinum carbon catalyst using the method of the present invention, and the platinum carbon catalyst prepared in example 1 showed significantly improved electrochemical catalytic activity compared to comparative example 1.

TABLE 1

The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited thereto. Within the scope of the technical idea of the invention, a number of simple variants of the technical solution of the invention are possible, including combinations of the individual technical features in any other suitable way, which simple variants and combinations should likewise be regarded as being disclosed by the invention, all falling within the scope of protection of the invention.

Claims

1. A platinum-carbon catalyst comprising a carbonaceous carrier and platinum nanoparticles supported on the carbonaceous carrier, wherein the platinum-carbon catalyst has a contact angle of 50 DEG or less with the carbonaceous carrier.

2. The platinum carbon catalyst according to claim 1, wherein in the platinum carbon catalyst, a contact angle of the platinum nanoparticle with the carbonaceous carrier is 30 ° -50 °.

3. The platinum carbon catalyst according to claim 1, wherein in the platinum carbon catalyst, an average particle diameter of the platinum nanoparticles is in a range of 3 to 4 nm.

4. The platinum carbon catalyst according to claim 1, wherein the content of platinum in the platinum carbon catalyst is 20 to 90% by weight and the content of carbonaceous carrier is 10 to 80% by weight in terms of elements, based on the total amount of the platinum carbon catalyst, the carbonaceous carrier being in terms of carbon elements;

preferably, the platinum carbon catalyst has a platinum content of 40 to 70 wt% and a carbonaceous carrier content of 30 to 60 wt% in terms of elemental carbon, based on the total amount of the platinum carbon catalyst.

5. The platinum carbon catalyst according to claim 1 or 4, wherein the carbonaceous carrier is conductive carbon black.

6. The platinum carbon catalyst according to any one of claims 1 to 5, wherein the platinum carbon catalyst has a half-wave potential of 0.86V or more, preferably 0.88V or more;

preferably, the platinum carbon catalyst has an electrochemical active area of 50m ² ·g ^-1 Pt or more, preferably 55-60m ² ·g ^-1 -Pt。

7. A method for preparing a platinum carbon catalyst, the method comprising the steps of:

s1, dispersing a carbonaceous material, a platinum precursor, a complexing agent and a dispersion medium by using ultrasonic waves to obtain a first dispersion, wherein the complexing agent is one or more than two of dicarboxylic acid salts and polycarboxylic acid salts, and the dispersion medium is glycerol and water;

8. the method according to claim 7, wherein the volume of glycerol and water in the dispersion medium of step S1 is 0.2 to 5:1, preferably 0.3-3:1, more preferably 0.5-2:1, a step of;

preferably, in step S1, the concentration of the platinum precursor relative to the dispersion medium is 1 to 20g/L, preferably 2 to 10g/L, more preferably 3 to 8g/L.

9. The method according to claim 7, wherein in step S1, the complexing agent is one or more selected from sodium citrate, sodium oxalate, sodium ethylenediamine tetraacetate and sodium tartrate;

preferably, in step S1, the mass ratio of the platinum precursor to the complexing agent is 1:0.1 to 7, preferably 1:0.2-3, more preferably 1:0.25-1.

10. The method according to any one of claims 7 to 9, wherein in step S1, the platinum precursor is one or more selected from chloroplatinic acid, potassium chloroplatinate, and sodium chloroplatinate.

11. The method according to any one of claims 7-10, wherein in step S1, the carbonaceous material is conductive carbon black.

12. The method according to any one of claims 7-11, wherein in step S1, the power of the ultrasonic wave is 100-1000W;

preferably, in step S1, the duration of the ultrasonic dispersion is between 0.2 and 5 hours, preferably between 0.5 and 3 hours.

13. The method of claim 7, wherein the molar ratio of polyvinylpyrrolidone to formic acid in the reducing agent of step S3 is 1:1-5, preferably 1:1-3.

14. The method according to claim 7 or 13, wherein in step S3 the molar ratio of reducing agent to platinum precursor is 160-800:1, preferably 180-500:1, more preferably 200-300:1, the platinum precursor is calculated by platinum element.

15. The method according to any one of claims 7, 13 and 14, wherein in step S3 the reduction reaction is performed at a temperature of 50-140 ℃, preferably at a temperature of 70-100 ℃;

preferably, in step S3, the duration of the reduction reaction is 4-15 hours.

16. A platinum carbon catalyst prepared by the method of any one of claims 7-15.

17. Use of the platinum carbon catalyst of any one of claims 1 to 6 and 16 in a fuel cell.

18. A hydrogen fuel cell having an anode and/or a cathode comprising the platinum carbon catalyst of any one of claims 1 to 6 and claim 16.