JP2012223693A - Method for producing electrode catalyst - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing an electrode catalyst made of material which is stable even in a high electrical potential in an acidic electrolyte, comparatively inexpensive, comparatively large in resource quantities, and capable of obtaining a higher current value.SOLUTION: In the method for producing the electrode catalyst, mixed material including the following first material and second material is hydrothermally reacted under presence of water in a super critical state or in a subcritical state to obtain a mixed precursor slurry. The mixed precursor slurry is dried by a freeze-drying method to obtain a mixed precursor. The obtained mixed precursor is burned under a condition that the second material can be changed into carbon material. The first material: a metal compound constituted of one or more kinds of elements selected from a group consisting of 4A and 5A groups, and one or more kinds of elements selected from a group consisting of hydrogen, nitrogen, chlorine, carbon, boron, sulfur, and oxygen. The second material: carbon material precursor or conductive material mixture with the carbon material precursor.

Description

  The present invention relates to a method for producing an electrode catalyst.

  The electrode catalyst is a solid catalyst supported on an electrode, particularly on a surface portion of the electrode, and is used in, for example, an electrochemical system such as a fuel cell in addition to water electrolysis and organic electrolysis. As an electrode catalyst used in an acidic electrolyte, a noble metal, particularly platinum, is widely used because it is stable even at a high potential in the acidic electrolyte.

  However, since platinum is expensive and has a limited amount of resources, there is a need for an electrocatalyst made of a material that is stable at a high potential in an acidic electrolyte, is relatively inexpensive, and has a relatively large amount of resources. Yes.

  As such an electrode catalyst, an electrode catalyst made of zirconium oxide is known (see Non-Patent Document 1).

  However, the zirconium oxide described in Non-Patent Document 1 has a small current value that can be taken out during use. Therefore, in order to solve this problem, a production method has been proposed in which a slurry obtained by supercritical hydrothermal synthesis is solid-liquid separated by a heat drying method and then calcined to obtain an electrode catalyst composed of zirconium oxide ( Patent Document 1).

Yan Liu et al., “Electrochemical and Solid-State Letters” 8 (8), 2005, A400-402.

JP 2011-25232 A

  However, the electrode catalyst obtained by the method described in Patent Document 1 has an insufficient current value. An object of the present invention is to provide a method for producing an electrode catalyst that is stable even at a high potential in an acidic electrolyte, is relatively inexpensive, is made of a material with a relatively large amount of resources, and can obtain a higher current value. There is.

In order to achieve the above object, the present invention provides the following inventions.
<1> A mixed precursor slurry obtained by hydrothermal reaction of a mixed material containing the following first material and the following second material in the presence of water in a supercritical state or a subcritical state is dried by freeze drying. Then, a mixed precursor is obtained, and the obtained mixed precursor is calcined under conditions that allow the second material to transition to a carbon material.
First material: composed of one or more elements selected from the group consisting of groups 4A and 5A and one or more elements selected from the group consisting of hydrogen, nitrogen, chlorine, carbon, boron, sulfur and oxygen Metal compound second material: carbon material precursor or mixture of conductive material with carbon material precursor <2> The following first material is hydrothermally reacted in the presence of supercritical or subcritical water. The mixed precursor slurry obtained by mixing the precursor obtained in the following and the following second material is dried by freeze drying to obtain a mixed precursor, and the resulting mixed precursor is a carbon material. A method for producing an electrode catalyst, characterized by firing under conditions capable of transitioning to
First material: composed of one or more elements selected from the group consisting of groups 4A and 5A and one or more elements selected from the group consisting of hydrogen, nitrogen, chlorine, carbon, boron, sulfur and oxygen Metal compound second material: carbon material precursor or mixture of conductive materials with carbon material precursor <3> one or more elements selected from the group consisting of groups 4A and 5A in the first material are Zr Or the manufacturing method as described in said <1> or <2> which is Ti.
<4> The production method according to any one of <1> to <3>, wherein the firing is performed in an oxygen-free atmosphere.
<5> An electrode catalyst obtained by the production method according to any one of <1> to <4>.
<6> An electrode catalyst composition having the electrode catalyst according to <5>.
<7> A fuel cell having the electrode catalyst according to <5>.

  According to the present invention, there is provided a method for producing an electrode catalyst that is stable even at a high potential in an acidic electrolyte, is relatively inexpensive, is made of a material with a relatively large amount of resources, and can obtain a higher current value. be able to.

It is a schematic diagram which shows the outline | summary of the flow-type reaction apparatus for performing a hydrothermal reaction continuously. It is a schematic diagram which shows the outline | summary of the reactor in a flow-type reaction apparatus. It is a schematic diagram which shows the outline | summary of the flow-type reaction apparatus for performing a hydrothermal reaction continuously. It is a schematic diagram which shows the outline | summary of the reactor in a flow-type reaction apparatus.

(First invention)
The method for producing an electrode catalyst of the present invention comprises a mixed precursor obtained by hydrothermal reaction of a mixed material containing the following first material and the following second material in the presence of supercritical or subcritical water. The slurry is dried by a freeze drying method to obtain a mixed precursor, and the obtained mixed precursor is fired under conditions that allow the second material to transition to a carbon material.
First material: composed of one or more elements selected from the group consisting of groups 4A and 5A and one or more elements selected from the group consisting of hydrogen, nitrogen, chlorine, carbon, boron, sulfur and oxygen Metal compound second material: carbon material precursor or mixture of carbon material precursor and conductive material

(Second invention)
In the method for producing an electrode catalyst of the present invention, a precursor obtained by hydrothermal reaction of the following first material in the presence of supercritical or subcritical water and the following second material are mixed. The obtained mixed precursor slurry is dried by a freeze drying method to obtain a mixed precursor, and the obtained mixed precursor is fired under conditions that allow the second material to transition to a carbon material.
First material: composed of one or more elements selected from the group consisting of groups 4A and 5A and one or more elements selected from the group consisting of hydrogen, nitrogen, chlorine, carbon, boron, sulfur and oxygen Metal compound second material: carbon material precursor or mixture of carbon material precursor and conductive material

  According to the present invention, an electrode catalyst exhibiting a relatively high activity can be obtained in an acidic electrolyte at a relatively high potential of, for example, 0.4 V or higher.

  The first material used in the production method of the present invention is one or more elements selected from the group consisting of groups 4A and 5A, and 1 selected from hydrogen, nitrogen, chlorine, carbon, boron, sulfur and oxygen It is a metal compound composed of more than seed elements. The element in the metal compound of the first material is a 4A or 5A group element, preferably Zr, Ti, Ta or Nb, and more preferably Zr or Ti. Moreover, the preferable element in the said metal compound is 1 or more types of elements selected from hydrogen, chlorine, and oxygen. In particular, examples of the metal compound when the element is Zr include zirconium hydroxide and zirconium oxychloride. Examples of the metal compound when the element is Ti include titanium hydroxide, titanium tetrachloride, metatitanic acid, orthotitanic acid, titanium sulfate, and titanium alkoxide.

  The second material used in the production method of the present invention is a carbon material precursor or a mixture of a carbon material precursor and a conductive material. In the present invention, the carbon material precursor is led to the carbon material by firing. Examples of the carbon material precursor include sugars such as glucose, fructose, sucrose, cellulose and hydropropyl cellulose; alcohols such as polyvinyl alcohol; glycols such as polyethylene glycol and polypropylene glycol; polyesters such as polyethylene terephthalate; acrylonitrile, poly Nitriles such as acrylonitrile; various proteins such as collagen, keratin, ferritin, hormones, hemoglobin, and albimine; biological materials such as amino acids such as glycine, alanine, and methionine; organic acids such as ascorbic acid, citric acid, and stearic acid It is done. In the present invention, the conductive material may be any material having conductivity excluding the carbon material precursor, such as carbon black, graphite, graphite, activated carbon, carbon fiber, carbon nanotube, carbon nanofiber, carbon nanohorn, fullerene, etc. The conductive material is preferable. Conductive oxides, conductive oxide fibers, and conductive resins can also be used.

  In said 1st invention, it is preferable to obtain a mixed material by mixing said 1st material and said 2nd material in coexistence of water. At the time of mixing, a surface modifier, a dispersant, and a pH adjuster such as ammonia can be used. As a mixing method, an ultrasonic disperser, a bead mill, a sand grinder, a homogenizer, a wet jet mill, a ball mill, a V-type mixer, a stirrer, or the like can be used. The mixed material is hydrothermally reacted in the presence of supercritical or subcritical water to obtain a mixed precursor slurry.

  In the second invention, the precursor obtained by hydrothermal reaction of the first material in the presence of supercritical or subcritical water and the second material are mixed and mixed. A precursor slurry is obtained. For the mixing, industrially used apparatuses such as an ultrasonic disperser, a bead mill, a sand grinder, a homogenizer, a wet jet mill, a ball mill, a V-type mixer, and a stirrer can be used. The mixing at this time may be either dry mixing or wet mixing.

  The mixed precursor slurry obtained in the first invention is obtained by repeating the steps of performing solid-liquid separation such as centrifugal separation and suction filtration and re-dispersing in a solvent such as water. It is preferable to perform cleaning to remove the above. The mixed precursor slurry obtained after washing is atomized using equipment generally used in industry, such as ultrasonic dispersers, bead mills, sand grinders, homogenizers, wet jet mills, ball mills, V-type mixers, and stirrers. It is preferable to do. Moreover, the density | concentration of the mixing precursor slurry obtained after washing | cleaning can be arbitrarily changed by adjusting the solvent addition amount at the time of performing the said solid-liquid separation and redispersion process. As the solvent, alcohol such as methanol and ethanol and water are used, and water is preferably used.

  The concentration of the precursor slurry is preferably higher from the viewpoint of the drying speed in the freeze drying method, and preferably lower from the viewpoint of dispersibility in the solvent. Specifically, it is 1 to 80% by mass, preferably 3 to 60% by mass, and more preferably 5 to 50% by mass.

  The supercritical point of water is 374 ° C. and 22 MPa. In the present invention, water in a supercritical state means water having a temperature of 374 ° C. or higher and a pressure of 22 MPa or higher. In the present invention, the subcritical water is preferably at a temperature of 200 ° C. or higher and a pressure of 20 MPa or higher, excluding the supercritical state. In the present invention, as a reaction apparatus for performing the hydrothermal reaction, a batch-type reaction apparatus or a continuous (circulation type) reaction apparatus can be used. In the case of a batch type reactor, an aqueous solution or slurry is sealed in a reaction vessel, which is kept at a predetermined temperature for a predetermined time, then cooled, and a product is recovered from the vessel. As a reaction vessel, it has sufficient heat resistance to the holding temperature, sufficient pressure resistance to the pressure during the reaction, and has a structure with sufficient corrosion resistance to the aqueous solution or slurry, intermediates and products used Select a material. The material of the reaction vessel may be selected appropriately based on conditions such as the type of aqueous solution or slurry, reaction temperature, and pressure. For example, stainless steel such as SUS316; nickel alloys such as Hastelloy and Inconel, and titanium alloys may be used. I can give you. Further, the inner surface of the container may be lined with a material having high corrosion resistance such as gold. In order to maintain at a predetermined temperature, for example, an electric furnace can be used. In this case, the electric furnace may be structured such that the reaction container can be inserted into the heating portion of the electric furnace so that operations such as installation and removal of the reaction container can be easily performed. In addition, the reaction vessel may be shaken in order to maintain the uniformity of the contents when the temperature is raised and when the predetermined temperature is maintained. The pressure in the reaction vessel at the time of the hydrothermal reaction can be adjusted by adjusting the amount of the aqueous solution or slurry put in the reaction vessel according to the predetermined temperature to be held. As a method of cooling the reaction vessel after being held for a predetermined time, there is a method of quenching the reaction vessel by immersing it in water. As a method for recovering the product, it is recovered in a slurry state and dried by freeze drying. By drying by freeze-drying, a mixed precursor that suppresses product aggregation during drying can be obtained.

  A conductive material may be further mixed with the obtained mixed precursor.

  The freeze-drying method is a technique in which an object to be dried is frozen and the frozen object is placed under vacuum to sublimate the solvent and dry it. The evaporated solvent is recovered by the cold trap so that the evaporated solvent is not taken into the vacuum pump and is not adsorbed again on the object. Unlike the drying by normal heating, it has a feature that it can be dried while maintaining the dispersion state in the solvent for drying without concentration or aggregation.

  Due to the above characteristics, it is important to freeze while maintaining a dispersed state in the freezing step. For this purpose, in general, the object to be dried is frozen as soon as possible, or it is frozen while stirring or rotating while maintaining a dispersed state, or it is made finer and frozen using a spray or the like. . The freezing temperature needs to be lower than or equal to the freezing point of the solvent used, and is preferably a lower temperature from the viewpoint of the freezing rate.

  The degree of vacuum at which freeze drying is performed is preferably as low as possible from the viewpoint of evaporation rate, and it is also as low as possible from the viewpoint of heat transfer in freeze-drying equipment without functions such as shelf cooling. Is preferred. For example, the ultimate vacuum when using a general-purpose rotary pump is 1 to 10 Pa.

  The temperature at which the freeze-drying method is carried out is preferably as high as possible within the range where the solvent is not thawed by heat transfer from the viewpoint of the evaporation rate. For example, when water is used as the solvent, it is usually −20 ° C. to 20 ° C., preferably −10 to 20 ° C., more preferably 0 to 20 ° C.

  Below, the reaction apparatus for performing a hydrothermal reaction continuously in this invention is demonstrated, referring drawings. FIG. 1 is a diagram showing an outline of a flow reactor for continuously performing a hydrothermal reaction. The water tanks 11 and 21 are tanks for supplying water. The raw material tank 22 is a tank for supplying the raw material slurry. By opening the valves 110, 210, and 220, liquid is supplied from these tanks. The raw material slurry is a slurry or an aqueous solution of a mixed material containing the first material and the second material in the case of the first invention, and is a slurry or an aqueous solution of the first material in the case of the second invention. It is. Liquid is sent from the water tank 11 to the heater 14 by the liquid feed pump 13, and liquid is sent from the water tank 21 or the raw material tank 22 to the heater 24 by the liquid feed pump 23. The sent liquids are mixed in the mixing unit 30 and mainly hydrothermally react in the reactor 40. FIG. 2 is a diagram showing an outline of the reactor. In the reactor 40, there is an internal pipe 41 and a heater 44 for heating the pipe, and the internal pipe 41 is connected to an external pipe. The produced slurry after the hydrothermal reaction is cooled by the cooler 51, passes through the back pressure valve 53, and is collected by the collection container 60.

  In FIG. 1, the valve 110 and the valve 210 or the valve 220 are opened, the liquid feeding pumps 13 and 23 are moved, and the back pressure valve 53 is opened and closed, so that the inside of the piping from the liquid feeding pumps 13 and 23 to the back pressure valve 53 The supercritical or subcritical water can be obtained by adjusting the pressure and adjusting the temperature of the heaters 14, 24 and the heater 44 in the reactor 40.

  More specifically, the liquid feed pumps 13 and 23 are activated, the pressure in the piping is adjusted as appropriate using the back pressure valve 53, and the temperatures of the heaters 14 and 24 and the heater 44 in the reactor 40 are appropriately adjusted. The temperature is adjusted so that the water in the reactor is in a supercritical state or a subcritical state. When the raw material slurry is sent from the raw material tank 22, a hydrothermal reaction is performed in the pipes after the mixing unit 30 to generate a precursor or a mixed precursor, and these generated slurry can be recovered in the recovery container 60. Further, before and after the raw material slurry is sent from the raw material tank 22, it is possible to send water from the water tank 21 and perform preheating of the piping, cleaning of the piping, and the like. In addition, the particle size of the produced slurry after the hydrothermal reaction may be adjusted by removing coarse particles using the filter 52.

  Further, the reaction time can be adjusted by adjusting the length of the internal piping 41 in the reactor 40. In adjusting the length of the internal pipe 41, various shapes such as a zigzag shape and a spiral shape may be selected and used as the shape of the internal pipe 41.

  The material of the piping and internal piping may be selected appropriately based on conditions such as the type of raw slurry and the temperature and pressure of the hydrothermal reaction. For example, stainless steel such as SUS316, Hastelloy, Inconel, etc. A nickel alloy and a titanium alloy can be mentioned. Further, depending on the characteristics of the liquid passing therethrough, a part or all of the inner surface of the pipe may be lined with a material having high corrosion resistance such as gold.

  In the second invention, the precursor slurry recovered in the recovery container 60 may be used in a powder state after solid-liquid separation, washing and drying when mixing with the second material, or in a slurry state. Good.

  The electrode catalyst of the present invention is obtained by firing the mixed precursor under conditions that allow the second material to transition to a carbon material. The firing atmosphere is preferably fired in an oxygen-free atmosphere in order to efficiently synthesize the electrode catalyst. From the viewpoint of cost, the oxygen-free atmosphere is preferably a nitrogen atmosphere. Nitrogen may contain a reducing gas such as hydrogen or ammonia. The oxygen concentration in the atmosphere is preferably 3% or less, more preferably 1% or less, and even more preferably 0.1% or less. The furnace used for this firing may be any furnace that can control the atmosphere, such as a tubular electric furnace, tunnel furnace, far-infrared furnace, microwave heating furnace, roller hearth furnace, rotary furnace, etc. It is done. It may be performed batchwise or continuously. Alternatively, the mixed precursor may be fired in a stationary manner in which the mixed precursor is left standing, or may be fired in a fluid manner in which the mixed precursor is fired in a fluid state.

  Firing may be appropriately set depending on the type of the carbon material precursor and the firing atmosphere, but may be performed at a temperature at which the carbon material precursor can transition to the carbon material, that is, a temperature at which the carbon material precursor is decomposed and carbonized. More specifically, the firing temperature is, for example, 400 to 1500 ° C, preferably 500 to 1400 ° C. The BET specific surface area of the electrode catalyst can be controlled by controlling the calcination temperature. In the present invention, the condition that the second material can transition to the carbon material means a condition that the second material can be decomposed and carbonized to become a carbon material.

  The temperature raising rate during firing is not particularly limited as long as it is in a practical range, and is usually 10 to 600 ° C./hour, preferably 50 to 500 ° C./hour. The temperature is raised to the firing temperature, and the firing is performed for 0.1 to 24 hours, preferably about 1 to 12 hours.

It is preferable that carbon remains in the electrode catalyst after calcination, and the amount of carbon in the electrode catalyst in the present invention is 0.1% by mass or more and 50% by mass or less, more preferably 0.5% by mass or more. It is 45 mass% or less, More preferably, it is 3 mass% or more and 40 mass% or less, Most preferably, it is 15 mass% or more and 35 mass% or less. In the present invention, an ignition loss value (hereinafter referred to as “igros value”) is used as the amount of carbon. Specifically, when an electrode catalyst is placed in an alumina crucible and calcined at 1000 ° C. for 3 hours in an air atmosphere. The value of carbon amount calculated by the following formula is used.
Carbon amount (mass%) = (W _I −W _A ) / W _I × 100
(Wherein, W _I is the mass of the mixed precursor, the W _A is the mass of the electrode catalyst.)

  The electrode catalyst obtained by the above-described production method of the present invention is an electrode catalyst that can exhibit relatively high activity in an acidic electrolyte solution without being dissolved even at a high potential.

In the present invention, the electrode catalyst preferably has a BET specific surface area of 15 m ² / g or more and 1000 m ² / g or less, more preferably 50 m ² / g or more and 1000 m ² / g or less. By setting the BET specific surface area in this way, the activity can be further increased.

In the present invention, the electrode catalyst preferably has a carbon coverage determined by the following formula (1) of 0.05 or more and 0.5 or less, more preferably 0.1 or more and 0.3 or less.
Carbon coverage = carbon content (mass%) / BET specific surface area (m ² / g) (1)

  In the present invention, the electrode catalyst preferably has a low work function value in order to promote the electrode reaction, preferably 2 eV or more and 6 eV or less, more preferably 3 eV or more and 5 eV or less. As a work function value, use a photoelectron spectrometer “AC-2” manufactured by Riken Keiki Co., Ltd., measure the light intensity at 500 nW, measure energy 4.2 to 6.2 eV, and use the energy value at the time of current detection. Can do.

As a preferred embodiment of the present invention, an electrode composed of a metal compound containing zirconium and an oxygen atom and a carbon material covering at least a part of the compound, and having a BET specific surface area of 15 m ² / g or more and 1000 m ² / g or less Catalyst. The electrode catalyst makes it possible to extract a larger oxygen reduction current in the electrochemical system. Zirconium also has abundant resources, which is advantageous for the spread or enlargement of electrochemical systems such as fuel cells.

  The obtained electrode catalyst may be crushed. The powder crushing method may be carried out dry or wet. Examples of dry crushing methods include a ball mill, a planetary mill, a pin mill, and a jet mill. Examples of wet crushing methods include an ultrasonic disperser, a bead mill, a sand grinder, a homogenizer, and a wet jet mill. The solvent used for wet disintegration is not particularly limited, but alcohols such as methanol, ethanol, isopropanol, and normal propanol, water such as ion-exchanged water, and the like can be used. It is also possible to control the BET specific surface area of the electrode catalyst by crushing treatment.

  The electrode catalyst composition of the present invention has the electrode catalyst of the present invention. The electrode catalyst composition usually has a dispersion medium. The electrode catalyst composition can be obtained by dispersing the electrode catalyst in a dispersion medium. Examples of the dispersion medium include alcohols such as methanol, ethanol, isopropanol, and normal propal, and water such as ion exchange water.

  In dispersing, a dispersing agent may be used. Examples of the dispersant include inorganic acids such as nitric acid, hydrochloric acid, and sulfuric acid, organic acids such as oxalic acid, citric acid, acetic acid, malic acid, and lactic acid, water-soluble zirconium salts such as zirconium oxychloride, ammonium polycarboxylate, and polycarboxylic acid. Examples include surfactants such as sodium acid, and catechins such as epicatechin, epigallocatechin, and epigallocatechin galade.

  The electrode catalyst composition of the present invention may contain an ion exchange resin. When it contains an ion exchange resin, it is particularly suitable for a fuel cell. Examples of the ion exchange resin include fluorine ion exchange resins such as Nafion (registered trademark of DuPont) and hydrocarbon ion exchange resins such as sulfonated phenol formaldehyde resins.

  The electrode catalyst composition of the present invention may contain a conductive material. Examples of the conductive material include carbon fiber, carbon nanotube, carbon nanofiber, conductive oxide, conductive oxide fiber, and conductive resin. The electrode catalyst composition of the present invention can also contain a noble metal such as Pt and Ru and a transition metal such as Ni, Fe and Co. When these noble metals and transition metals are contained, the content ratio is preferably a trace amount (for example, about 0.1 to 10 parts by mass with respect to 100 parts by mass of the electrode catalyst).

  The electrode catalyst of the present invention can be used in an electrochemical system, preferably as an electrode catalyst for a fuel cell, more preferably as an electrode catalyst for a polymer electrolyte fuel cell, still more preferably a polymer electrolyte fuel. It can be used as an electrode catalyst for the cathode part of a battery.

  The electrode catalyst in the present invention can be suitably used at a potential of 0.4 V or more with respect to the reversible hydrogen electrode potential in an acidic electrolyte and is relatively high in activity. And is useful as an oxygen reduction catalyst used to reduce oxygen. A suitable upper limit of the potential when used as an oxygen reduction catalyst can be used up to about 1.6 V, which is a potential for generating oxygen, depending on the stability of the electrode catalyst. When the voltage exceeds 1.6 V, the electrode catalyst is gradually oxidized from the surface simultaneously with the generation of oxygen, and the electrode catalyst may be completely converted into an oxide and deactivated. If the potential is less than 0.4 V, it can be said that it is preferable from the viewpoint of stability of the electrode catalyst, but it may be less useful from the viewpoint of an oxygen reduction catalyst.

  The electrode catalyst of the present invention can be supported on an electrode such as carbon cloth or carbon paper in the form of an electrode catalyst composition and used for electrolysis of water in an acidic electrolyte, electrolysis of organic matter, or the like. It can also be used by being supported on an electrode constituting a fuel cell such as a polymer electrolyte fuel cell or a phosphoric acid fuel cell.

  EXAMPLES Hereinafter, although an Example demonstrates this invention in detail, this invention is not limited by these Examples.

In addition, the evaluation method in each Example is as follows.
(1) The BET specific surface area (m ² / g) was determined by a nitrogen adsorption method.
(2) The crystal structure was performed using a powder X-ray diffractometer.
(3) The amount of carbon is obtained by placing the obtained electrode catalyst in an alumina crucible, firing it in a box furnace at 1000 ° C. for 3 hours in the atmosphere, and calculating the carbon amount value (igross value) calculated by the following equation: Using.
Carbon amount (mass%) = (W _I −W _A ) / W _I × 100
(Wherein, W _I is the mass of the mixed precursor, the W _A is the mass of the electrode catalyst.)
(4) The carbon coverage was calculated by the following formula.
Carbon coverage = carbon content (mass%) / BET specific surface area (m ² / g)

Production Example 1: Preparation of first material (Zr-containing compound) Zirconium oxychloride (manufactured by Wako Pure Chemical Industries) dissolved in pure water (8 mass% zirconium oxychloride) and NH ₃ water (Kanto Chemical ( The product was neutralized with 4% by mass diluted, and the resulting precipitate was filtered and washed to obtain a first material (Zr-containing compound). As a result of powder X-ray diffraction measurement, this first material was found to be zirconium hydroxide. This first material was dispersed in NH ₃ water having a pH adjusted to 10.5 at a concentration such that the first material was 1% by mass to obtain a Zr-containing compound slurry.

Example 1
(Preparation of electrode catalyst)
As the first material, the Zr-containing compound slurry obtained in Production Example 1 was used. Glucose (manufactured by Wako Pure Chemical Industries) was used as the second material. A mixed material obtained by adding 37.5 g of glucose to 1500 g of the Zr-containing compound slurry was charged into the raw material tank 22 of the flow reactor. The water tanks 11 and 21 were charged with water, the liquid feed pumps 13 and 23 were started, the valves 110 and 210 were opened, and the liquid feed of these waters was started. Here, the flow rate in the liquid feed pump 13 was adjusted to 16.7 mL / min, and the flow rate in the liquid feed pump 23 was adjusted to 6.67 mL / min. Using the back pressure valve 53, the pressure in the pipe was adjusted to 30 MPa. The heater 14 was adjusted to 320 ° C, the heater 24 was adjusted to 250 ° C, and the temperature of the heater 44 in the reactor 40 was adjusted to 350 ° C. It was 320 degreeC when the liquid temperature of the mixing part 30 in a steady state was measured, and it confirmed that it was water of a subcritical state. Thereafter, the valve 210 is closed and the valve 220 is opened, so that the water tank 21 is switched to the raw material tank 22, the mixed material is supplied from the raw material tank 22, a hydrothermal reaction is performed, and the mixing precursor is mixed in the recovery container 60. Body slurry was collected. 500 ml of the collected mixed precursor slurry is separated into solid and liquid by centrifugation, and then 100 ml of water is added and dispersed using an ultrasonic disperser. The sample is dispensed into a screw tube and then frozen by placing the screw tube in liquid nitrogen. It was. The frozen sample was dried for one week using a vacuum freeze dryer (FZ-4.5CL, manufactured by Asahi Life Science) to obtain a mixed precursor. The ultimate vacuum in the freeze dryer was 2.0 Pa. The mixed precursor is put in an alumina boat and the rate of temperature rise is made while flowing nitrogen gas at a flow rate of 1.5 L / min in a tubular electric furnace (manufactured by Motoyama Co., Ltd.) having an internal volume of 13.4 L. The temperature was raised from room temperature (about 25 ° C.) to 800 ° C. at 300 ° C./hour and calcined by holding at 800 ° C. for 1 hour to obtain an electrode catalyst 1. The obtained electrode catalyst 1 was a zirconium oxide coated with carbon. The electrode catalyst has a BET specific surface area of 186 m ² / g, a carbon content of 18.5% by mass, a carbon coverage of 0.10, and the crystal form of the zirconia constituting the electrode catalyst is a mixed phase of tetragonal system and orthorhombic system. there were.

[Evaluation by electrochemical system]
0.02 g of electrode catalyst 1 was weighed, added to a mixed solvent of 5 mL of pure water and 5 mL of isopropyl alcohol, and irradiated with ultrasonic waves to form a suspension. 20 μL of this suspension was applied to a glassy carbon electrode (6 mm diameter, electrode area: 28.3 mm ² ), dried, and then “Nafion (registered trademark)” (manufactured by DuPont, solid content concentration of 5% by mass). After coating and drying 13 μL of the [double diluted sample], a modified electrode carrying the electrode catalyst 1 on the glassy carbon electrode was obtained by treating with a vacuum dryer for 1 hour. This modified electrode is immersed in an aqueous sulfuric acid solution having a concentration of 0.1 mol / L, and is −0.25 to 0.75 V (reversible) with respect to the silver-silver chloride electrode potential at room temperature, atmospheric pressure, oxygen atmosphere and nitrogen atmosphere. The potential was cycled at a scanning speed of 50 mV / s in a scanning range of hydrogen electrode potential conversion 0.025 to 1.025 V). When the current stability at each potential for each cycle was compared and the electrode stability was confirmed, the current value did not fluctuate within the scanning potential range and was stable. Further, when the current values of the oxygen atmosphere and the nitrogen atmosphere at a potential of 0.4 V with respect to the reversible hydrogen electrode potential were compared and the oxygen reduction current was determined, it showed 2539 μA / cm ² per unit area of the electrode. The oxygen reduction current was determined by comparing the current values of the oxygen atmosphere and the nitrogen atmosphere at a potential of .6 V. The result showed 1649 μA / cm ² per unit area of the electrode.

Example 2
(Preparation of electrode catalyst)
A mixed precursor slurry was obtained under the same conditions as in Example 1 except that the heater 14 in the hydrothermal reaction was adjusted to 250 ° C. and the temperature of the heater 44 in the reactor 40 was adjusted to 250 ° C. When the liquid temperature of the mixing part 30 in a steady state was measured, it was 250 ° C., and it was confirmed to be subcritical water. The obtained electrode catalyst 2 was a zirconium oxide coated with carbon. The electrode catalyst had a BET specific surface area of 233 m ² / g, a carbon content of 24.5% by mass, a carbon coverage of 0.11, and the crystal form of zirconia constituting the electrode catalyst was a tetragonal single phase.

[Evaluation by electrochemical system]
When the electrochemical system was evaluated under the same conditions as in Example 1 except that the electrode catalyst 2 was used instead of the electrode catalyst 1, the current value did not fluctuate within the scanning potential range and was stable. It was. Further, when the current values of the oxygen atmosphere and the nitrogen atmosphere at a potential of 0.4 V with respect to the reversible hydrogen electrode potential were compared and the oxygen reduction current was determined, it showed 4629 μA / cm ² per unit area of the electrode, and 0 The oxygen reduction current was determined by comparing the current values of the oxygen atmosphere and the nitrogen atmosphere at a potential of .6 V, and found to be 3134 μA / cm ² per unit area of the electrode.

Comparative Example 1
The collected mixed precursor slurry of Example 1 was subjected to solid-liquid separation by centrifugation, then water was added and dispersed, and the sample was frozen using liquid nitrogen, and the frozen sample was subjected to a vacuum freeze dryer (FZ-4, manufactured by Asahi Life Sciences). In this case, the recovered mixed precursor slurry is subjected to solid-liquid separation by centrifugation, dispersed by adding water, centrifuged again, and solid-liquid separation, followed by 60 ° C. for 3 hours. The electrode catalyst 3 was obtained under the same conditions as in Example 1 except that the mixed precursor was obtained by drying using the heat drying method. The obtained electrode catalyst 3 was a zirconium oxide coated with carbon. The electrocatalyst has a BET specific surface area of 162 m ² / g, a carbon content of 19.3% by mass, a carbon coverage of 0.12, and the zirconia constituting the electrocatalyst has a tetragonal and orthorhombic mixed phase. there were.

[Evaluation by electrochemical system]
When the electrochemical system was evaluated in the same manner as in Example 1 except that the electrode catalyst 3 was used instead of the electrode catalyst 1, the current value did not vary within the scanning potential range and was stable. . Further, when the current values of the oxygen atmosphere and the nitrogen atmosphere at a potential of 0.4 V with respect to the reversible hydrogen electrode potential were compared and the oxygen reduction current was determined, it showed 2144 μA / cm ² per unit area of the electrode, and 0 The oxygen reduction current was determined by comparing the current values of the oxygen atmosphere and the nitrogen atmosphere at a potential of .6 V, and found to be 1195 μA / cm ² per unit area of the electrode.

Comparative Example 2
The collected mixed precursor slurry of Example 2 was subjected to solid-liquid separation by centrifugation, water was added and dispersed, and the sample was frozen using liquid nitrogen, and the frozen sample was vacuum freeze-dried (FZ-4, manufactured by Asahi Life Sciences). In this case, the recovered mixed precursor slurry is subjected to solid-liquid separation by centrifugation, dispersed by adding water, centrifuged again, and solid-liquid separation, followed by 60 ° C. for 3 hours. The electrode catalyst 4 was obtained under the same conditions as in Example 2 except that the electrode catalyst precursor was obtained by drying using a heat drying method. The obtained electrode catalyst 4 was zirconium oxide coated with carbon. The electrode catalyst had a BET specific surface area of 183 m ² / g, a carbon content of 26.4% by mass, a carbon coverage of 0.14, and the zirconia constituting the electrode catalyst had a tetragonal single phase.

[Evaluation by electrochemical system]
When the electrochemical system was evaluated in the same manner as in Example 1 except that the electrode catalyst 4 was used instead of the electrode catalyst 1, the current value did not vary within the scanning potential range and was stable. . Further, the current value of the oxygen atmosphere and the nitrogen atmosphere at a potential of 0.4 V with respect to the reversible hydrogen electrode potential was compared, and the oxygen reduction current was determined to be 2116 μA / cm ² per unit area of the electrode. The current values of the oxygen atmosphere and the nitrogen atmosphere at a potential of .6 V were compared and the oxygen reduction current was determined to be 1126 μA / cm ² per unit area of the electrode.

  The conditions and results of Examples 1 and 2 and Comparative Examples 1 and 2 are shown in Table 1 below.

11, 21 ... Water tank, 22 ... Raw material tank, 13, 23 ... Liquid feed pump, 14, 24 ... Heater, 30 ... Mixing unit, 40 ... Reactor, 41 ... Internal piping, 44 ... Heater, 51 ... Cooler, 52 ... Filter, 53 ... Back pressure valve, 60 ... Collection container, 110, 210, 220 ... Valve, 1011 ... Water tank, 1022 ... Raw material tank, 1013, 1023 ... Liquid feed pump, 1014, 1024 ... Heater, 1040 ... Reactor, 1070 ... Recovery unit, 1060 ...・ Recovery container

Claims (7)

A mixed precursor slurry obtained by hydrothermal reaction of a mixed material containing the following first material and the following second material in the presence of water in a supercritical state or a subcritical state is dried by a freeze drying method and mixed. A method for producing an electrode catalyst, comprising: obtaining a precursor; and calcining the obtained mixed precursor under conditions that allow the second material to transition to a carbon material.
First material: composed of one or more elements selected from the group consisting of groups 4A and 5A and one or more elements selected from the group consisting of hydrogen, nitrogen, chlorine, carbon, boron, sulfur and oxygen Metal compound second material: carbon material precursor or mixture of carbon material precursor and conductive material Freeze-drying a mixed precursor slurry obtained by mixing the following first material with a precursor obtained by hydrothermal reaction of the following first material in the presence of supercritical or subcritical water: A method for producing an electrocatalyst, comprising drying the mixture to obtain a mixed precursor, and calcining the obtained mixed precursor under conditions that allow the second material to transition to a carbon material.
First material: composed of one or more elements selected from the group consisting of groups 4A and 5A and one or more elements selected from the group consisting of hydrogen, nitrogen, chlorine, carbon, boron, sulfur and oxygen Metal compound second material: carbon material precursor or mixture of carbon material precursor and conductive material   The manufacturing method according to claim 1 or 2, wherein the one or more elements selected from the group consisting of groups 4A and 5A in the first material are Zr or Ti.   The manufacturing method according to claim 1, wherein the firing is performed in an oxygen-free atmosphere.   The electrode catalyst obtained by the manufacturing method in any one of Claims 1-4.   An electrode catalyst composition comprising the electrode catalyst according to claim 5.   A fuel cell comprising the electrode catalyst according to claim 5.

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