JP2018172230A - Silver acetylide and method of producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide silver acetylide which is capable of producing a porous carbon material comprised of a dendritic carbon nano structure of a large specific surface area and a large mesopore volume (especially mesopore volume of mesopores having a pore diameter of 2 to 5 nm) and is useful in producing a carrier carbon material for preparing a catalyst for use in a solid polymer type fuel cell excellent in durability and power generation characteristics (especially output voltage characteristics at a low current density), and a method of producing the same.SOLUTION: The silver acetylide is of a MCtype derived from acetylene by substituting hydrogen atoms thereof with monovalent silver atoms, is of a three dimensional dendritic structure, and has a silver-carbon molar ratio, i.e., (M/M) in a range of 1.0≤M/M≤1.06, provided that (M) represents the molar amount of silver calculated from the residual amount at about 400°C in a thermogravimetric analysis under an air atmosphere up to 400°C using a decomposition product resulting from an autolytic explosion reaction as a measurement sample, and (M) represents the molar amount of carbon which is the molar amount thereof other than the molar amount of silver. The method of producing silver acetylide as described above is provided.SELECTED DRAWING: None

Description

  The present invention relates to silver acetylide and a method for producing the same, and is not particularly limited. However, the present invention relates to a carbon nanostructure suitable as a carrier carbon material used for producing a catalyst for a polymer electrolyte fuel cell, and particularly to the preparation thereof. The present invention relates to a silver acetylide useful for producing a dendritic carbon nanostructure sometimes having a three-dimensional dendritic structure and a method for producing the same.

  In recent years, polymer electrolyte fuel cells that can operate at a low temperature of 100 ° C. or less have attracted attention, and are being developed and put into practical use as driving power sources for vehicles and stationary power generators. A general polymer electrolyte fuel cell has a membrane electrode assembly (MEA) in which a catalyst layer serving as an anode and a cathode is disposed on both sides of a proton conductive electrolyte membrane, respectively. In addition, the basic structure (unit cell) is a structure in which gas diffusion layers are arranged on both sides of the membrane electrode assembly and separators are arranged on both sides of the membrane electrode assembly. It is configured by stacking as many unit cells as necessary to achieve.

In the unit cell of such a polymer electrolyte fuel cell, from the gas flow path of the separator disposed on the anode side and the cathode side, an oxidizing gas such as oxygen or air is provided on the cathode side, A reducing gas such as hydrogen is supplied to the anode side, and the supplied oxidizing gas and reducing gas (which may be referred to as “reactive gas”) are respectively supplied to the catalyst layer via the gas diffusion layer. Work can be taken out by utilizing the energy difference (potential difference) between the chemical reaction occurring in the anode catalyst layer and the chemical reaction occurring in the cathode catalyst layer. For example, when hydrogen gas is used as the fuel gas and oxygen gas is used as the oxidizing gas, a chemical reaction occurring in the catalyst layer of the anode [oxidation reaction: H ₂ → 2H ⁺ + 2e ⁻ (E ₀ = 0V) And the chemical reaction [reduction reaction: O ₂ + 4H ⁺ + 4e ⁻ → 2H ₂ O (E ₀ = 1.23 V)] that takes place in the catalyst layer of the cathode to take out work to the outside. be able to.

  Here, for the catalyst that forms the catalyst layer and causes a chemical reaction, a porous carbon material is usually used as the catalyst carrier from the viewpoint of electronic conductivity, chemical stability, and electrochemical stability. Further, Pt or a Pt alloy that can be used in a strongly acidic environment and exhibits high reaction activity for both oxidation and reduction reactions is mainly used as the catalyst metal. For catalytic metals, the above oxidation and reduction reactions generally occur on the catalytic metal. In order to increase the utilization of the catalytic metal, it is necessary to increase the specific surface area per mass. Specifically, particles having a size of about several nm are used.

  And about the catalyst support | carrier which carry | supports such a catalyst metal, in order to raise the carrying | supporting capability as a support | carrier, ie, in order to increase the site for adsorb | sucking and carrying | supporting said catalyst metal of about several nanometers, It is necessary that the porous carbon material has a large specific surface area, and the mesopore volume having a pore diameter of 2 to 50 nm, that is, the mesopore volume is large so that the catalyst metal can be easily supported in a highly dispersed state. It is required to be a porous carbon material, and at the same time, when a catalyst layer to be an anode and a cathode is formed, formation of pores is required for the reaction gas to diffuse through the catalyst layer without resistance.

  Therefore, conventionally, as a porous carbon material having a relatively large specific surface area and mesopore volume, and at the same time having a tree-like structure with three-dimensionally developed branches, for example, CABOT Vulcan XC-72, Lion EC600JD made by the company and EC300 made by Lion Corporation are used. In addition, attempts have been made to develop a porous carbon material having a more suitable specific surface area and mesopore volume as a support carbon material and a more suitable dendritic carbon nanostructure, and has recently received particular attention. As a starting material, there is a dendritic carbon nanostructure produced using a metal acetylide such as silver acetylide having a dendritic structure as an intermediate, and several proposals have been made so far.

For example, Patent Document 1 discloses a step of preparing a solution containing a metal or a metal salt, a step of blowing acetylene gas into the solution to generate a dendritic carbon nanostructure made of metal acetylide, and the carbon nanostructure. A step of heating the body at 60 to 80 ° C. to produce a metal-encapsulated dendritic carbon nanostructure in which metal is encapsulated in the dendritic carbon nanostructure, and 160 of the metal-encapsulated dendritic carbon nanostructure. Heating to 200 ° C. to eject metal to produce a dendritic carbon mesoporous structure, heating the carbon mesoporous structure to 1600-2200 ° C. under a reduced pressure atmosphere or an inert gas atmosphere, A porous carbon material prepared by a production method comprising: a pore diameter of 1 to 20 nm and an integrated pore volume of 0.2 to 1.5 cc / g determined by analyzing a nitrogen adsorption isotherm by a Dollimore-Heal method Have Rutotomoni, a BET specific surface area 200~1300m ² / g, low reduction rate of the current amount for a long time, the catalyst can be prepared carrier carbon material for a solid polymer fuel cell having excellent durability Has been proposed.

Moreover, in patent document 2, the acetylene production | generation process which blows in acetylene gas in the ammoniacal aqueous solution containing a metal or a metal salt, and produces | generates a metal acetylide, the said metal acetylide is heated at the temperature of 60-80 degreeC, and a metal particle A first heat treatment step for creating an inclusion intermediate, and heating the metal particle inclusion intermediate at a temperature of 120 to 200 ° C. to eject metal particles from the metal particle inclusion intermediate to obtain a carbon material intermediate A second heat treatment step, a washing treatment step of bringing the carbon material intermediate into contact with hot concentrated sulfuric acid to purify the carbon material intermediate, and further cleaning the carbon material intermediate at 1000 to 2100 ° C. A porous carbon material prepared by a manufacturing method comprising a third heat treatment step for obtaining a support carbon material by heat treatment, having a predetermined hydrogen content, and a BET ratio table Product 600~1500m ² / g, and the range of the peak intensity of Raman range of peak intensity of the spectrum obtained from D- band 1200~1400cm ^-1 (l _D) and G- band 1500~1700cm ^-1 (l _G) Carbon material having a relative strength ratio (l _D / l _G ) of 1.0 to 2.0 and capable of preparing a catalyst for a polymer electrolyte fuel cell capable of exhibiting high battery performance under high humidification conditions Has been proposed.

Furthermore, in Patent Document 3, an acetylide generating step of generating acetylene gas by blowing acetylene gas into an ammoniacal aqueous solution containing a metal or a metal salt, and heating the metal acetylide at a temperature of 40 to 80 ° C. to form metal particles A first heat treatment step for producing an inclusion intermediate, the metal particle inclusion intermediate is compacted, and the resulting molded article is heated to 400 ° C. or higher at a temperature rising rate of 100 ° C. or more per minute. A second heat treatment step of ejecting metal particles from the particle inclusion intermediate to obtain a carbon material intermediate; and contacting the carbon material intermediate with hot concentrated nitric acid or hot concentrated sulfuric acid to clean the carbon material intermediate And a third heat treatment step for obtaining a carrier carbon material by heat-treating the cleaned carbon material intermediate in a vacuum or in an inert gas atmosphere at 1400 to 2100 ° C. A porous carbon material prepared by the manufacturing process comprising, the specific surface area S _A of the mesopores of pore diameters 2~50nm obtained by analyzing the nitrogen adsorption isotherm of adsorption process in Dollimore-Heal method 600 1600 m ² / g, and the peak intensity (l _{G ′} ) in the range of G′-band 2650-2700 cm ⁻¹ and the peak intensity (l _G ) in the range of 1550-1650 cm ⁻¹ in the Raman spectrum. The relative intensity ratio (l _{G ′} / l _G ) is 0.8 to 2.2, and the specific pore area S _{2-10 of the} mesopores having a pore diameter of 2 nm or more and less than 10 nm in the mesopores is 400 to 1100 m. ² / g, the specific pore volume V _2-10 is 0.4 to 1.6 cc / g, and the specific pore area S _{10− of the} mesopores having a pore diameter of 10 nm or more and 50 nm or less in the mesopores. ₅₀ is 20-150 m ² / g, specific pore volume V _2-10 is 0.4-1.6 cc / g, and the nitrogen adsorption isotherm of the adsorption process is Horva The specific pore area S ₂ of pores having a pore diameter of less than 2 nm determined by analysis by th-Kawazoe method is 250 to 550 m ² / g, which is excellent against potential fluctuations while maintaining high power generation performance. A support carbon material capable of preparing a catalyst for a polymer electrolyte fuel cell capable of exhibiting durability has been proposed.

Furthermore, in Patent Document 4, a porous carbon material having a dendritic carbon nanostructure prepared through a self-decomposing explosion reaction using metal acetylide as an intermediate [trade name: ESCARBON, manufactured by Nippon Steel & Sumikin Chemical Co., Ltd.] (Registered trademark) -MCND] as a raw material, and after carrying out graphitization treatment, the carrier carbon material obtained by further performing oxidation treatment using hydrogen peroxide, nitric acid, a submerged plasma device, etc. Content O _ICP 0.1-3.0% by mass, oxygen remaining amount remaining after heat treatment at 1200 ° C. in an inert gas (or vacuum) atmosphere O _{1200 ° C.} 0.1-1.5% by mass, BET specific surface area 300 ˜1500 m ² / g, G-band half-value width ΔG30-70 cm ⁻¹ detected in the range of 1550-1650 cm ⁻¹ of the Raman spectrum, and remaining after heat treatment at 1200 ° C. in an inert gas (or vacuum) atmosphere Hydrogen remaining amount _{1200 ° C.} is 0.005 to 0.080 wt%, excellent durability against repeated load fluctuations such starting and stopping, also a solid polymer fuel that has excellent power generation performance under operating conditions at the time of low humidification Support carbon materials capable of preparing battery catalysts have been proposed.

WO 2014/129597 A1 Publication WO 2015/088025 A1 Publication WO 2015/141810 A1 Publication WO 2016/133132 A1 Publication

The carrier carbon materials described in the above-mentioned Patent Documents 1 to 4 each exhibit desired power generation characteristics in preparing a polymer electrolyte fuel cell catalyst. A detailed examination of the power generation characteristics revealed that there was room for further improvement in the output voltage at a low current density (0.1 A / cm ² ).
In order to improve the output voltage at the low current density, it is important to increase the specific surface area of the support carbon material and increase the mesopore volume of the pore diameter of 2 to 50 nm. In particular, in order to support Pt or a Pt alloy in a highly dispersed state and improve the utilization rate, the mesopore volume V _2-5 having a pore diameter of ₂ to ₅ nm, particularly a mesopore, is increased while increasing the pore area. I found it important to make it bigger.

  That is, the utilization factor of the catalyst is evaluated by comparing the catalyst area obtained from the amount of electricity of hydrogen adsorption / desorption by potential sweep in the sulfuric acid electrolyte and the similar catalyst area in the state of being incorporated in the cell. The ratio (utilization rate) of the catalyst area in the state incorporated in the latter cell with respect to the catalyst area in the former sulfuric acid electrolyte is only about 20 to 30%. One of the causes is that the proton conductive resin blocks the pores of the carrier carbon and the reaction gas is difficult to diffuse into the pores. This is because proton conductive resin enters the pores when the pores are large, but when the pores are about several nanometers, the degree of freedom of arrangement of the polymer decreases and the entropy when entering the pores is reduced. This is because it is considered that the loss is so large that it hardly penetrates. The mesopores having a pore diameter of 2 to 5 nm do not infiltrate the proton conductive resin, but support a catalyst particle having a size of several nanometers, and a void with little hindrance to gas diffusion is secured even after the catalyst particle is supported. From the idea that it is the optimum size, it was found that the Pt utilization rate can be increased by increasing the pore volume with a pore diameter of 2 to 5 nm.

  By the way, when the method for producing the carrier carbon material proposed in Patent Documents 1 to 4 above is examined in detail, in the silver acetylide synthesis step, acetylene gas is introduced into an ammoniacal aqueous solution of silver nitrate to produce silver acetylide. However, when this acetylene gas was introduced, the molar ratio of silver nitrate in the reaction system to acetylene that reacts with silver nitrate in this reaction system was taken into account, and the acetylene introduced into the reaction system was slightly excessive. The amount of acetylene gas blown was controlled so that the acetylene gas was blown out until the acetylene gas began to be released from the reaction system over a period of about 30 minutes, and when the acetylene gas began to be released, the reaction of silver nitrate was completed Judging from the point, the injection of acetylene gas into the reaction system was stopped. For the silver acetylide obtained in this synthesis step, since silver acetylide is an explosive substance, usually, for example, the reaction mixture formed as a precipitate in the reaction system is collected by filtration through a membrane filter. The reaction mixture is washed by performing a redispersion-filtration washing operation in which the reaction mixture is redispersed in a solvent such as methanol and then filtered again, and the “reaction product after washing” obtained after this washing is washed. Used as it is in the next step.

For this reason, the amount of silver and the amount of carbon in the decomposition product (carbon material intermediate before cleaning treatment) obtained by heating the obtained silver acetylide to a predetermined temperature and inducing an autolytic explosion reaction are obtained. When measured, the theoretical molar ratio of silver to carbon obtained from the molecular formula of silver acetylide (Ag-C≡C-Ag) is 1.0, whereas the actual silver acetylide synthesized is silver. -The carbon molar ratio is around 1.1, and it has been found that the abundance of carbon is excessive with respect to silver, and the present inventors have found that excess carbon present in such silver acetylide. (C) was estimated to be an acetylene molecule.
In the present invention, “silver acetylide” refers to the reaction product after washing obtained in the silver acetylide synthesis step as described above, not the compound itself represented by the molecular structural formula Ag—C≡C—Ag. .

  Therefore, the present inventors have determined between the silver-carbon molar ratio of silver acetylide during the self-decomposition explosion reaction of silver acetylide, the decomposition energy of silver acetylide, and the size of the pore diameter of mesopores in the decomposition product. Considering that there is some relationship, the self-decomposition of silver acetylide is controlled by controlling the silver-carbon molar ratio in the three-dimensional dendritic structure of silver acetylide synthesized in the synthesis of silver acetylide as a production intermediate. Mesopores of dendritic carbon nanostructures obtained by washing and removing silver particles, etc., from the decomposition products generated by this self-decomposition explosion reaction by controlling the decomposition energy during the explosion reaction We have reached the idea that it is possible to control the volume.

  And under this idea, when synthesizing silver acetylide, while controlling the amount of carbon present in the synthesized three-dimensional tree structure of silver acetylide within a range smaller than the existing amount of carbon, Also, a dendritic tree produced by self-decomposing explosion reaction of silver acetylide by introducing a slight excess of carbon (C) and controlling the decomposition energy during the self-decomposing explosion reaction of silver acetylide. As a result of trying to control the mesopore volume in the carbon nanostructure, the inventors succeeded in controlling the mesopore volume, in particular, increasing the mesopore volume having a pore diameter of 2 to 5 nm. This is because the amount of excess carbon (C) introduced in the production process of silver acetylide is controlled to control the decomposition energy, the formation of branches during the silver acetylide self-decomposition explosion reaction, the intensity of silver particle emission Etc., and the size of the silver particles formed is released to the outside without excessive growth, and the pore diameter is relatively small, and the distribution of the pore diameters of the mesopores having a pore diameter of 2 to 50 nm. It is considered that the mesopore volume with a pore diameter of 2 to 5 nm was increased.

Furthermore, the present inventors conducted a thermogravimetric analysis in an air atmosphere for a decomposition product after the autolysis explosion reaction (carbon material intermediate before washing treatment) with respect to the silver-carbon molar ratio of the synthesized silver acetylide. The silver-carbon molar ratio calculated from the molar amount of carbon (M _C ) determined as the carbon other than this silver relative to the molar amount of silver (M _Ag ) determined from the final remaining amount to be measured. We found that (M _C / M _Ag ) is in good agreement with the theoretical molar ratio, and that the amount of silver and the amount of carbon in silver acetylide can be quantified by the above silver-carbon molar ratio (M _C / M _Ag ). I found it. The “other than silver” may slightly contain elements other than carbon such as oxygen and hydrogen.

  As a result of further study on how to control the amount of carbon present in the synthesized silver acetylide during the synthesis of silver acetylide, the present inventors have determined that the ammoniacal nature of silver nitrate is not limited. By controlling the blowing rate of the acetylene gas introduced into the aqueous solution, the reaction time is made longer than before, and if necessary, the reaction temperature is made lower than before to waste the acetylene molecules introduced into the reaction system. The present invention has been completed by finding that it can be reliably reacted with silver nitrate.

The present invention has been invented based on each of the above-mentioned findings, and the object of the present invention is a three-dimensional dendritic tree suitable as a support carbon material used for producing a catalyst for a polymer electrolyte fuel cell. An object of the present invention is to provide a silver acetylide useful for producing a dendritic carbon nanostructure having a structure.
Another object of the present invention is to produce a dendritic carbon nanostructure having a three-dimensional dendritic structure suitable as a support carbon material used in producing such a polymer electrolyte fuel cell catalyst. It is to provide a method for producing silver acetylide useful above.

That is, the present invention is as follows.
(1) M ₂ C ₂ type silver acetylide in which hydrogen atoms of acetylene are substituted with monovalent silver atoms,
Silver having a three-dimensional dendritic structure and calculated from the remaining amount in the vicinity of 400 ° C. in a thermogravimetric analysis up to 400 ° C. in an air atmosphere using the decomposition product after the self-decomposing explosion reaction as a measurement sample the molar amount (M _Ag) obtained something other than silver as the molar amount of carbon (M _C) of silver - carbon molar ratio (M _C / M _Ag) is _{1.0 ≦ M C / M Ag ≦} 1 Silver acetylide, characterized by 0.06.
(2) In the thermogravimetric analysis in an air atmosphere using the decomposition product after the self-decomposition explosion reaction as a measurement sample, the temperature T _0.5 when the mass reduction rate becomes 0.5% (0.5% mass reduction temperature) ) Is 130 ° C. or higher. The silver acetylide as described in (1) above.

(3) In producing silver acetylide having a three-dimensional dendritic structure by injecting acetylene gas into an aqueous ammonia solution of silver nitrate to react silver nitrate with acetylene gas.
A method for producing silver acetylide, wherein the molar ratio of acetylene gas to silver nitrate is controlled in the range of 0.50 to 0.53, and the blowing time of the acetylene gas is adjusted to 10 to 30 hours.
(4) The method for producing silver acetylide according to (3) above, wherein the reaction temperature in the reaction between the silver nitrate and acetylene gas is adjusted to 0 to 20 ° C.

According to the silver acetylide of the present invention, it is composed of a dendritic carbon nanostructure having a large specific surface area and a large mesopore volume, particularly a mesopore volume having a pore diameter of 2 to 5 nm, and is durable by subjecting it to an autolytic explosion reaction. It is possible to produce a porous carbon material that is useful as a support carbon material for a catalyst for a polymer electrolyte fuel cell that has excellent power generation characteristics, in particular, excellent output voltage characteristics at a low current density.
In addition, according to the method for producing silver acetylide of the present invention, the solid polymer fuel cell comprising the dendritic carbon nanostructure having the above specific surface area and mesopore volume, particularly the mesopore volume having a pore diameter of 2 to 5 nm is large. Silver acetylide useful as a raw material for producing a support carbon material for a catalyst can be easily produced.

FIG. 1 is a graph for explaining a method for performing thermogravimetric analysis in the present invention. FIG. 2 is a graph showing the results of thermogravimetric analysis measured in Examples 17 to 20 of the present invention.

Hereinafter, the silver acetylide of the present invention and the production method thereof will be described in detail.
The silver acetylide of the present invention is an M ₂ C ₂ type silver acetylide in which a hydrogen atom of acetylene is substituted with a monovalent silver atom, has a three-dimensional tree-like structure, and is a decomposition product after an autolytic explosion reaction In thermogravimetric analysis under air atmosphere for (composite of metallic silver and carbon), the molar amount of silver (M _Ag ) calculated from the final remaining amount and the molar amount of carbon other than silver (M _Ag ) silver is determined as M _C) - carbon molar ratio (M _C / M _Ag) is in the range of _{1.0 ≦ M C / M Ag ≦} 1.06. The “other than silver” may slightly contain elements other than carbon such as oxygen and hydrogen.

Silver acetylide is an M ₂ C ₂ type in which the hydrogen atom of acetylene is replaced with a monovalent silver atom, and has a molecular formula (Ag-C≡C-Ag). While the ratio (silver-carbon molar ratio) is theoretically 1.0, the silver acetylide of the present invention is a silver mole calculated from the final remaining amount in thermogravimetric analysis under an air atmosphere. the amount (M _Ag) and the molar amount of carbon than it when the (M _C), silver molar amount of silver and (M _Ag) molar amount of carbon and (M _C) - carbon molar ratio (M _C / M _Ag ) is in the range of 1.0 ≦ M _C / M _Ag ≦ 1.06, preferably 1.01 ≦ M _C / M _Ag ≦ 1.06, more preferably 1.02 ≦ M _C / It is in the range of M _Ag ≦ 1.06. When the silver-carbon molar ratio (M _C / M _Ag ) is less than 1.0, silver nitrate is taken into silver acetylide, the explosive force becomes weak, the pore volume becomes small, and it becomes unsuitable as a catalyst support. On the contrary, when the silver-carbon molar ratio (M _C / M _Ag ) exceeds 1.06, the pore diameter of the dendritic carbon nanostructure obtained by subjecting the silver acetylide to a self-decomposing explosion reaction is 2 to 5 nm. The mesopore volume V _2-5 is reduced, and a porous carbon material as a carrier carbon material useful for preparing a catalyst for a polymer electrolyte fuel cell excellent in output voltage characteristics at a low current density cannot be obtained.

≪Method of thermogravimetric analysis≫
In the present invention, thermogravimetric analysis up to 400 ° C. in an air atmosphere using the decomposition product of the self-decomposing explosion reaction performed for examining the characteristics of silver acetylide as a measurement sample (hereinafter, this thermogravimetric analysis is simply referred to as “ In order to accurately measure the silver-carbon molar ratio (M _C / M _Ag ) of silver acetylide, thermogravimetric analysis must be performed according to the following method. is there.
First, in the thermogravimetric analyzer, the measurement sample is used up to the upper limit of the charged amount of the apparatus so that the weight loss up to about 0.01% by mass can be detected as accurately as possible, and the air used Uses the compressed dry air to keep the flow rate constant and suppress the movement of the measurement sample during measurement as much as possible. In addition, in order to sufficiently remove moisture contained in the measurement sample in advance, after setting the measurement sample in the apparatus, for example, holding at 50 ° C. overnight under a nitrogen gas flow and sufficiently drying, Lower the temperature and switch to dry air for measurement. Furthermore, in actual measurement and analysis, the measurement was performed from room temperature to 400 ° C. under the measurement conditions of an air flow rate of 200 cc / min and a heating rate of 10 ° C./min. Therefore, the origin of mass is analyzed as a value at 70 ° C. For example, in the example shown in FIG. 1, since the remaining amount in the vicinity of 400 ° C. is 89.62% by mass, the silver atomic weight ratio (M) is considered in consideration of the atomic weight of carbon 12.01 and the atomic weight 107.87 of silver. _C / M _Ag ) is calculated to be 1.04.

Further, the silver acetylide of the present invention is preferably a temperature (0.5%) when the mass reduction rate is 0.5% when the mass at 70 ° C. is 100% in the thermogravimetric analysis of the silver acetylide. Mass decreasing temperature) is 130 ° C. or higher, more preferably 140 ° C. or higher. The silver-carbon molar ratio (M _C / M _Ag ) indicates the amount of acetylene contained in the decomposition product obtained in the silver acetylide synthesis step, and is an index of control regarding the magnitude of the explosion energy. The% mass reduction temperature indicates the property of excess carbon contained in the decomposition product after the autolytic explosion reaction. Excess carbon derived from acetylene is not easily converted into aromatic carbon during the explosion reaction due to weak contact with silver, and easily becomes an amorphous rod-like substance through the subsequent manufacturing process of porous carbon material. There is a risk of impairing the properties of the porous carbon material produced from silver acetylide, such as crushing the pores of the material or reducing the pore volume, and as a result, the support for the catalyst for the polymer electrolyte fuel cell When used as a carbon material, the power generation characteristics, particularly the Pt utilization rate, may be reduced.

In order to produce such a silver acetylide having a large mesopore volume V _2-5 , the silver acetylide production step for producing silver acetylide is controlled as much as possible with respect to the silver ions present in the reaction system. It is necessary to replace the acetylene hydrogen with silver by reliably reacting the introduced acetylene with silver ions as much as possible, and for this purpose, in the ammoniacal aqueous solution of silver nitrate, that is, The amount of carbon introduced as the acetylene gas is controlled with respect to the amount of silver present in the reaction system in consideration of the target silver / carbon theoretical molar ratio, and at the same time, the reaction time is increased, that is, It is necessary to slow down the blowing rate of the acetylene gas introduced into the reaction system to ensure contact between silver ions and acetylene in the reaction system. In order to obtain the silver acetylide according to the present invention more stably, it is preferable that the silver nitrate-acetylene molar ratio of acetylene introduced into the reaction system (C ₂ H ₂ / AgNO _{3) with} respect to silver nitrate in the reaction system. ) Is 0.50 or more and 0.53 or less, more preferably 0.505 or more and 0.53 or less, and the acetylene gas blowing time is 1 hour or more and 30 hours or less, more preferably It is good to set it as 10 hours or more and 30 hours or less, More preferably, it is 20 hours or more and 30 hours or less.

In order to more accurately control the reaction between silver ions and acetylene in the reaction system, it is also effective to lower the reaction temperature and increase the amount of acetylene dissolved in the reaction system. The reaction temperature in the reaction between the silver nitrate and the acetylene gas should be adjusted to 0 ° C. or higher and 30 ° C. or lower, more preferably 0 ° C. or higher and 20 ° C. or lower, more preferably 10 hours or longer. It is better to react slowly. By making the reaction temperature lower than the room temperature (25 ° C.) conventionally performed, the silver-carbon molar ratio (M _C / M _Ag ) is within the range of 1.0 ≦ M _C / M _Ag ≦ 1.06. It can be controlled more accurately. Furthermore, by slowly reacting over a long period of time of 10 hours or more at low temperature, the acetylene molecules are uniformly dispersed in the silver acetylide molecular aggregate and converted to aromatic skeleton carbon during the self-decomposing explosion reaction. A ratio becomes high and the production | generation of a soot-like substance is suppressed.

  According to the silver acetylide of the present invention, this silver acetylide is heat-treated at a temperature of 40 to 80 ° C., preferably 60 to 80 ° C., in the same manner as in the conventional method to produce a silver particle encapsulating intermediate (first 1 heat treatment step), the obtained silver particle-containing intermediate is heat-treated at a temperature of 120 to 400 ° C., preferably 160 to 200 ° C., and silver particles are ejected by a self-decomposing explosion reaction to produce a decomposition product (washing). Carbon material intermediate before treatment) (second heat treatment step), and then the obtained decomposition product (carbon material intermediate before washing treatment) is contacted with an acid such as nitric acid or sulfuric acid to produce this carbon. Silver particles and the like in the material intermediate are removed and cleaned (cleaning process step), and the cleaned carbon material intermediate is vacuumed or in an inert gas atmosphere at 1400 to 2400 ° C, preferably 1500 to 2300 ° C. Heat treatment ( 3), a porous carbon material comprising a dendritic carbon nanostructure having a three-dimensional dendritic structure suitable as a carrier carbon material for a catalyst for a polymer electrolyte fuel cell can be easily produced. .

  And the porous carbon material obtained by using the silver acetylide of the present invention as a production intermediate is only equivalent or superior in BET specific surface area and durability as compared with the conventional dendritic carbon nanostructure of this type. In addition, the mesopore volume, particularly the mesopore volume with a pore diameter of 2 to 5 nm, which is important in improving the utilization by supporting Pt or a Pt alloy of a catalytic metal in a highly dispersed state, is increased. When used as a carrier carbon material for a catalyst for a polymer electrolyte fuel cell, the output voltage characteristics at a low current density can be remarkably improved.

Hereinafter, based on an Example and a comparative example, the silver acetylide of this invention and its manufacturing method are demonstrated concretely.
In the following examples and comparative examples, the silver-carbon molar ratio (M _C / M _Ag ) and 0.5% mass reduction temperature of the prepared silver acetylide and the silver acetylide of each example and comparative example were used. The BET specific surface area and mesopore volume V _{2-5 of} the obtained support carbon material were measured as follows.

[Measurement of silver-carbon molar ratio (M _C / M _Ag ) of silver acetylide]
Using the silver acetylide obtained in each of the examples and comparative examples, a decomposition product (carbon material intermediate before washing treatment) was subjected to a self-decomposing explosion reaction in a first heat treatment step and a second heat treatment step described later. Was measured, and about 10 mg of a measurement sample was measured from the obtained decomposition product, and measurement and analysis were performed by the above-described method using a thermogravimetric analyzer [STA7200 manufactured by Hitachi High-Tech Science Co., Ltd.]. The molar amount of silver measured by measuring the molar amount of silver (M _Ag ) calculated from the final remaining amount and the molar amount of carbon (M _C ) measured by regarding this other than silver as carbon calculated molar ratio of the molar amount of carbon (M _C) for (M _Ag) to (M _C / M _Ag). The thermogravimetric analysis was performed three times on the same measurement sample under the same measurement conditions, and the average value was taken as the measurement value, but the three measurement results were consistent within a few percent.

(Measurement of 0.5% mass loss temperature of silver acetylide)
Using the result of the silver-carbon molar ratio (M _C / M _Ag ) measurement in the thermogravimetric analysis of silver acetylide, read the temperature when the remaining weight was reduced from 100% to 99.5%, The temperature was reduced by 0.5%.

[Measurement of BET specific surface area and mesopore volume V _2-5 of support carbon material]
Dendritic carbon nanostructures prepared by a first heat treatment step, a second heat treatment step, a washing step, and a third heat treatment step, which will be described later, using the silver acetylide obtained in each Example and Comparative Example About 30 mg of the carrier carbon material consisting of the body is weighed and vacuum-dried at 120 ° C. for 2 hours. Then, using an automatic specific surface area measurement device (BELSORP MAX manufactured by Microtrack Bell), nitrogen is used as the adsorbate and nitrogen. The gas adsorption isotherm was measured. In the range of p / p ₀ of the isotherm at the time of adsorption, 0.05 to 0.15, BET analysis was performed using analysis software attached to the apparatus, and the BET specific surface area was calculated.

<< Examples 1 to 6 and Comparative Example 1 >>
(1) Silver acetylide production step A silver nitrate-containing ammonia aqueous solution is prepared by dissolving silver nitrate in a 2.0 mass% ammonia solution in an ammonia aqueous solution having an ammonia concentration of 2.0 mass%. An inert gas such as nitrogen was blown for 40 to 60 minutes to replace the dissolved oxygen with an inert gas, and the risk that the silver acetylide produced in this silver acetylide production step would decompose and explode was eliminated.
The molar ratio of acetylene introduced into the reaction system (C ₂ H ₂ / AgNO _{3) with} respect to silver nitrate in the reaction system in the silver nitrate-containing aqueous ammonia solution having a silver nitrate concentration of 2.0% by mass prepared as described above. ) Is set to the value shown in Table 1, the acetylene gas blowing rate and blowing speed are set, and the acetylene gas is slowly and constantly blown at room temperature (25 ° C) over 30 hours under stirring. And a white precipitate of silver acetylide was produced in the reaction system.
The produced silver acetylide precipitate is filtered through a membrane filter to collect the precipitate. The collected precipitate is redispersed in methanol, filtered again, and the resulting precipitate is taken out into a petri dish and added to a small amount. The silver acetylide of Examples 1 to 6 and Comparative Example 1 (experimental symbols E1-1 to E1-6 and C1-1) was prepared.

(2) First heat treatment step About 0.5 g of a stainless steel pellet formed with about 0.5 g of the silver acetylide of each example and comparative example obtained in the above silver acetylide production step while being impregnated with methanol. The product was placed in a mold, and the pressure was slowly increased to 0.5 kg / cm ² to form pellets.
The pellets thus formed are transferred into a stainless steel cylindrical container having a diameter of about 5 cm, placed in a vacuum heating electric furnace, and vacuum dried at 60 ° C. for about 15 to 30 minutes. A silver particle encapsulating intermediate derived from silver acetylide was prepared.

(3) Second heat treatment step Next, the 60 ° C silver particle inclusion intermediate immediately after vacuum drying obtained in the first heat treatment step is heated without taking it out of the vacuum heating electric furnace as it is. The temperature is raised to 200 ° C. at a rate of about 10 ° C./minute, and in this process, a self-decomposition explosion reaction of silver acetylide is induced, and a decomposition product composed of a composite of silver and carbon (carbon before washing treatment) Material intermediate) was prepared.

(4) Cleaning treatment step For the carbon material intermediate of the decomposition product composed of the composite of silver and carbon obtained in the second heat treatment step, a washing treatment with concentrated nitric acid having a concentration of 60% by mass is performed. Silver particles remaining on the surface of the carbon material intermediate and other unstable carbon compounds were removed and cleaned.

(5) Third heat treatment step The carbon material intermediate cleaned in the above washing treatment step is subjected to a heat treatment for 2 hours under the heating temperature conditions shown in Table 1 in an inert gas atmosphere. The carrier carbon material derived from the silver acetylide of the comparative example was obtained. The heat treatment temperature in the third heat treatment step is a temperature generally employed so far for controlling the crystallinity, and the carbon material derived from silver acetylide in each of Examples and Comparative Examples by this heat treatment. The effect on the physical property change and battery characteristics was investigated.

The silver-carbon molar ratio (M _C / M _Ag ) and 0.5% mass reduction temperature of each of Examples 1 to 6 and Comparative Example 1 prepared as described above, and each of Examples 1 to 6 and The BET specific surface area and pore diameter mesopore volume V _2-5 of the carrier carbon material derived from silver acetylide of Comparative Example 1 were measured.
The results are shown in Table 1.

<< Examples 7 to 12 >>
In the above silver acetylide production step, the silver nitrate-acetylene molar ratio (C ₂ H ₂ / AgNO ₃ ) is fixed at 0.53, and the reaction temperature at the time of blowing acetylene gas is fixed at room temperature (25 ° C.). Silver acetylide was the same as in Examples 1 to 6 and Comparative Example 1 except that the acetylene gas blowing time during acetylene gas blowing was changed to the time shown in Table 1 to synthesize silver acetylide. The production step, the first heat treatment step, the second heat treatment step, the washing treatment step, and the third heat treatment step were carried out, and each of Examples 7 to 12 (experiment symbols E2-1 to E2-6) In addition to the silver acetylide, a carrier carbon material derived from these silver acetylides was prepared.

The silver-carbon molar ratio (M _C / M _Ag ) and 0.5% mass reduction temperature of the silver acetylide of each of Examples 7 to 12 prepared in this way, and the carrier derived from the silver acetylide of each of these Examples 7 to 12 The BET specific surface area and pore diameter mesopore volume V _{2-5 of the} carbon material were measured.
The results are shown in Table 1.

<< Examples 13 to 16 >>
In the above silver acetylide production step, the silver nitrate-acetylene molar ratio (C ₂ H ₂ / AgNO ₃ ) is fixed at 0.53, and the acetylene gas blowing time at the time of blowing acetylene gas is fixed at 20 hours. In the same manner as in Examples 1 to 6 and Comparative Example 1, except that the reaction temperature at the time of blowing acetylene gas was changed to the time shown in Table 1 to synthesize silver acetylide, a silver acetylide production step, The first heat treatment step, the second heat treatment step, the washing treatment step, and the third heat treatment step were performed, and the silver acetylides of Examples 13 to 16 (experimental symbols E3-1 to E3-4), respectively. And a carrier carbon material derived from these silver acetylides.

The silver-carbon molar ratio (M _C / M _Ag ) and the 0.5% mass reduction temperature of the silver acetylide of Examples 13 to 16 prepared in this way, and the carrier derived from the silver acetylide of these Examples 13 to 16 The BET specific surface area and pore diameter mesopore volume V _{2-5 of the} carbon material were measured.
The results are shown in Table 1.

«Comparative Examples 2-8»
In the above silver acetylide production step, the silver nitrate-acetylene molar ratio (C ₂ H ₂ / AgNO ₃ ) is set to 0.60, and the acetylene gas blowing time and reaction temperature during acetylene gas blowing are shown in Table 1. In the same manner as in Examples 1 to 6 and Comparative Example 1, except that the synthesis of silver acetylide was carried out by changing to the silver acetylide production step, the first heat treatment step, the second heat treatment step, The cleaning treatment step and the third heat treatment step are carried out to prepare silver acetylides of Comparative Examples 2 to 8 (experimental symbols C4-1 to C4-7), respectively, and the carrier carbon material derived from these silver acetylides is prepared. Prepared.

The silver-carbon molar ratio (M _C / M _Ag ) and 0.5% mass reduction temperature of the silver acetylides of Comparative Examples 2 to 8 prepared in this way, and the carrier derived from the silver acetylide of each of Comparative Examples 2 to 8 The BET specific surface area and pore diameter mesopore volume V _{2-5 of the} carbon material were measured.
The results are shown in Table 1.

<< Examples 17 to 20 >>
In the above silver acetylide production step, the silver nitrate-acetylene molar ratio (C ₂ H ₂ / AgNO ₃ ) is set to 0.53, the acetylene gas blowing time at the time of blowing acetylene gas is set to 30 hours, and the acetylene gas blowing is performed. In the same manner as in Examples 1 to 6 and Comparative Example 1, except that the reaction temperature was 5 ° C. and the heat treatment temperature in the third heat treatment step was changed to the temperature shown in Table 1, silver was used. An acetylide production step, a first heat treatment step, a second heat treatment step, a washing treatment step, and a third heat treatment step were carried out, and each of Examples 17 to 20 (Experimental symbols E5-2 to E5-5) ) And a support carbon material derived from these silver acetylides.

The silver-carbon molar ratio (M _C / M _Ag ) and 0.5% mass reduction temperature of the silver acetylide of each of Examples 17 to 20 prepared in this manner, and the carrier derived from the silver acetylide of each of these Examples 17 to 20 The BET specific surface area and pore diameter mesopore volume V _{2-5 of the} carbon material were measured.
The results are shown in Table 1. Moreover, the result of the thermogravimetric analysis of the silver acetylide obtained in these Examples is shown in FIG.

<< Comparative Examples 9-12 >>
Moreover, the commercially available porous carbon material was also examined as Comparative Examples 9-12.
The porous carbon material used was a porous carbon material A (Ketjen Black EC600JD manufactured by Lion Corporation) having a dendritic structure, developed fine pores, and a large specific surface area (Comparative Example 9). Porous carbon material B (Comparative Example 10) heat-treated under argon flow for 2 hours at ° C., porous carbon material C (CNOVEL-MH manufactured by Toyo Tanso Co., Ltd.) as a typical porous carbon material having no dendritic structure ( Comparative Example 11) and porous carbon material D (Comparative Example 12) obtained by heat-treating this porous carbon material C in an inert atmosphere at 2000 ° C. for 2 hours.
The BET specific surface area and the pore diameter mesopore volume V _2-5 of each of the porous carbon materials A to D of Comparative Examples 9 to 12 were measured.
The results are shown in Table 1.

≪Catalyst preparation, catalyst layer preparation, MEA preparation, fuel cell assembly, and battery performance evaluation≫
Next, using the carrier carbon material prepared as described above and prepared, a catalyst for a polymer electrolyte fuel cell carrying a catalyst metal as described below was prepared and obtained. A catalyst layer ink solution is prepared using a catalyst, then a catalyst layer is formed using the catalyst layer ink solution, and a membrane electrode assembly (MEA: Membrane Electrode Assembly) is produced using the formed catalyst layer. The produced MEA was incorporated into a fuel cell, and a power generation test was performed using a fuel cell measuring device. Hereinafter, preparation of each member and cell evaluation by a power generation test will be described in detail.

(1) Production of solid polymer fuel cell catalyst (platinum-supported carbon material) The carrier carbon material produced above or a commercially available carbon material is dispersed in distilled water, and formaldehyde is added to this dispersion. The mixture was set in a water bath set at 0 ° C., and after the temperature of the dispersion reached 40 ° C. which was the same as that in the bath, a dinitrodiamine Pt complex nitric acid aqueous solution was slowly poured into the dispersion with stirring. Thereafter, stirring was continued for about 2 hours, followed by filtration, and washing of the obtained solid was performed. The solid material thus obtained is vacuum-dried at 90 ° C., pulverized in a mortar, and then heat-treated at 200 ° C. for 1 hour in an argon atmosphere containing 5% by volume of hydrogen to produce a carbon material carrying platinum catalyst particles. did.
The platinum carrying amount of this platinum carrying carbon material is adjusted to 30% by mass with respect to the total mass of the carrier carbon material and the platinum particles, and inductively coupled plasma emission spectroscopy (ICP-AES: Inductively Coupled Plasma). -Confirmed by measuring with Atomic Emission Spectrometry.

(2) Preparation of catalyst layer The platinum-supported carbon material (Pt catalyst) prepared as described above was used, and Nafion (registered trademark: Nafion; persulfonic acid ion exchange resin) manufactured by Dupont was used as the electrolyte resin. Using these Pt catalyst and Nafion in an Ar atmosphere, the mass of Nafion solids is 1.0 times that of the platinum catalyst particle-supporting carbon material, and 0.5 times that of non-porous carbon. After blending and agitating lightly, the Pt catalyst is crushed with ultrasonic waves, and ethanol is further added to adjust the total solid concentration of the Pt catalyst and the electrolyte resin to 1.0% by mass. A catalyst layer ink liquid in which a Pt catalyst and an electrolyte resin were mixed was prepared.

Ethanol was further added to each catalyst layer ink liquid having a solid content concentration of 1.0% by mass thus prepared to produce a catalyst layer ink solution for spray coating having a platinum concentration of 0.5% by mass. The spray conditions were adjusted so that the mass per unit area of the layer (hereinafter referred to as “platinum weight”) was 0.1 mg / cm ^2, and the above-mentioned catalyst layer ink for spray coating was placed on the Teflon (registered trademark) sheet. After spraying, a drying process was performed in argon at 120 ° C. for 60 minutes to prepare a catalyst layer.

(3) Production of MEA Using the catalyst layer produced as described above, a MEA (membrane electrode assembly) was produced by the following method.
A square electrolyte membrane having a side of 6 cm was cut out from a Nafion membrane (NR211 manufactured by Dupont). In addition, each of the anode and cathode catalyst layers coated on the Teflon (registered trademark) sheet was cut into a square shape having a side of 2.5 cm with a cutter knife.
The electrolyte membranes are sandwiched between the anode and cathode catalyst layers thus cut out so that the catalyst layers are in contact with each other with the center of the electrolyte membrane interposed therebetween and are not displaced from each other. After pressing at 10 cm / cm 2 for 10 minutes and then cooling to room temperature, only the Teflon (registered trademark) sheet was carefully peeled off for both the anode and cathode, and the catalyst layer-electrolyte membrane junction in which the anode and cathode catalyst layers were fixed to the electrolyte membrane The body was prepared.

Next, as a gas diffusion layer, a pair of square carbon paper having a side of 2.5 cm is cut out from carbon paper (35BC manufactured by SGL Carbon Co.), and the catalyst layers of the anode and the cathode are sandwiched between these carbon papers. So that there is no deviation and the catalyst layer-electrolyte membrane assembly was sandwiched, and pressed at 120 ° C. and 50 kg / cm 2 for 10 minutes to prepare an MEA.
In addition, about the estimated amount of each component of the catalyst metal component, carbon material, and electrolyte material in each produced MEA, the mass of the Teflon (registered trademark) sheet with the catalyst layer before pressing and the Teflon (registered trademark) peeled off after pressing The mass of the catalyst layer fixed on the Nafion membrane (electrolyte membrane) was determined from the difference from the mass of the sheet, and calculated from the mass ratio of the composition of the catalyst layer.

(4) Performance evaluation of fuel cell MEAs prepared using the carrier carbon materials prepared and prepared in each of the examples and comparative examples were each incorporated into a cell, set in a fuel cell measurement device, and The fuel cell performance was evaluated according to the procedure.
Regarding the reaction gas, the pressure was adjusted by a back pressure valve provided downstream of the cell so that the utilization rate would be 40% and 70%, respectively, with air at the cathode and pure hydrogen at the anode, and a back pressure of 0.05 MPa. Supplied with. The cell temperature is set to 80 ° C., and the gas to be supplied is bubbled with distilled water kept at 65 ° C. in a humidifier for both the cathode and the anode to contain steam equivalent to reformed hydrogen. Supplied to the cell.

Under the conditions where gas was supplied to the cell under such settings, the load was gradually increased, and the voltage between the cell terminals at 100 mA / cm ² and 1000 mA / cm ² was recorded as the output voltage. The performance was evaluated according to the criteria of the following pass ranks ◎ and ○ and the fail ranks × by the voltage of each current density. The results are shown in Table 1.
[Acceptance rank]
A: The output voltage at 100 mA / cm ² is 0.83 V or more, and the output voltage at 1000 mA / cm ² is 0.65 V or more.
○: The output voltage at 100 mA / cm ² is 0.81 V or more and less than 0.83, and the output voltage at 1000 mA / cm ² is 0.60 V or more and less than 0.65 V.
[Failed rank]
X: Less than pass grade (circle).

[Evaluation of durability]
In the above cell, while maintaining the anode as it is and flowing argon gas under the same humidification condition as above to the cathode, the cell voltage is set to 1.0 V and held for 4 seconds and the cell voltage is set to 1.3 V and held for 4 seconds. The operation that repeats the operation (repetitive operation of rectangular wave voltage fluctuation) is one cycle, and after repeating this rectangular wave voltage fluctuation operation for 400 cycles, based on the output voltage at 1000 mA / cm ² , The “maintenance ratio” of the output voltage at 1000 mA / cm ² after the cycle was calculated. This maintenance rate was evaluated on the basis of the following pass ranks ◎ and ○ and a reject rank ×. The results are shown in Table 1, and the evaluation results of the maintenance rate are shown.
[Acceptance rank]
A: The decrease rate of the output voltage at 1000 mA / cm ² is 10% or less.
○: The rate of decrease in output voltage at 1000 mA / cm ² is 10 to 15% [failed rank]
X: Less than the pass rank ○, that is, the output voltage drop rate is 15% or more.

Claims (4)

M ₂ C ₂ type silver acetylide in which hydrogen atoms of acetylene are substituted with monovalent silver atoms,
Silver having a three-dimensional dendritic structure and calculated from the remaining amount in the vicinity of 400 ° C. in a thermogravimetric analysis up to 400 ° C. in an air atmosphere using the decomposition product after the self-decomposing explosion reaction as a measurement sample the molar amount (M _Ag) obtained something other than silver as the molar amount of carbon (M _C) of silver - carbon molar ratio (M _C / M _Ag) is _{1.0 ≦ M C / M Ag ≦} 1 Silver acetylide, characterized by 0.06. In thermogravimetric analysis in an air atmosphere using the decomposition product after the self-decomposing explosion reaction as a measurement sample, the temperature T _0.5 (0.5% mass reduction temperature) when the mass reduction rate is 0.5% is 130. Silver acetylide according to claim 1, characterized in that it is at or above ° C. In producing silver acetylide having a three-dimensional dendritic structure by blowing acetylene gas into an aqueous ammonia solution of silver nitrate to react silver nitrate with acetylene gas,
A method for producing silver acetylide, wherein the molar ratio of acetylene gas to silver nitrate is controlled in the range of 0.50 to 0.53, and the blowing time of the acetylene gas is adjusted to 10 to 30 hours. The method for producing a silver acetylide according to claim 3, wherein a reaction temperature in the reaction of the silver nitrate and the acetylene gas is adjusted to 0 to 20 ° C.

Images