JP2016131098A - Electrode, and electrochemical device using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrode which can achieve a good conversion efficiency of a reactive gas to ions even with a small amount of a catalyst metal; and an electrochemical device using such an electrode.SOLUTION: An electrode 3 comprises: a conductive porous body 12 including an electron conductor 10 and an ion-conducting solid electrolyte 11; and metal nanoparticles 13 held by the conductive porous body 12. The quantity of the metal nanoparticles 13 in contact with the electron conductor 10 and the ion-conducting solid electrolyte 11 on the surface of the conductive porous body 12 is larger than the quantity of the metal nanoparticles included in the conductive porous body 12.SELECTED DRAWING: Figure 3

Description

  The present invention relates to an electrode and an electrochemical device using the electrode.

According to UN Intergovernmental Panel on Climate Change (IPCC), global warming due CO ₂ concentration increases in the atmosphere is an important environmental issue. A hydrogen society has been proposed as a countermeasure. Combustion of fossil fuels produces CO ₂ , but if hydrogen is burned, water is produced, so that the concentration of CO _{2 in} the atmosphere is not increased. A fuel cell is a device that generates electricity by reacting a reaction gas such as hydrogen with oxygen, and since it generates water and does not generate CO ₂ , it has been put to practical use as an environmentally friendly main application. In addition, since hydrogen is explosive, it is expected that many hydrogen sensors that detect hydrogen leakage will be required for safety measures.

  Electrochemical devices include fuel cells and hydrogen sensors, which include an anode that is an electrode that emits electrons, a cathode that accepts electrons, and an electrolyte that conducts ions therebetween. The fuel cell is composed of two gas diffusion electrodes, an anode and a cathode, and a solid electrolyte. A reactive gas such as hydrogen, methane, or alcohol is supplied to the anode, and oxygen gas is supplied to the cathode. Since the catalyst is supported on the surface of the gas diffusion electrode, the oxidation of hydrogen and the reduction of oxygen are promoted. Protons generated by the oxidation of hydrogen and oxygen ions generated by the reduction of oxygen react through the solid electrolyte to become water. On the other hand, also in the hydrogen sensor, hydrogen gas is oxidized into protons by the catalyst on the anode, and the hydrogen gas concentration is measured by the resulting current.

  These electrochemical devices require efficient conversion of reaction gas to protons by a catalyst.

  In the gas diffusion electrode, hydrogen gas is oxidized to protons on the catalyst surface and moves to the on-conducting solid electrolyte contained in the gas diffusion electrode. On the other hand, in the counter electrode gas diffusion electrode, the oxygen gas is reduced to oxygen ions and moves to the solid electrolyte. Protons move through the ion conductive solid electrolyte and react with oxygen ions to become water. In this way, a circuit is formed by electrons and ions in the electrochemical device. However, if the distance between the catalyst surface and the ion conductive solid electrolyte is so long that protons generated on the catalyst surface cannot move to the ion conductive solid electrolyte, the circuit is cut off between the catalyst surface and the solid electrolyte. Cannot function as. Thus, the design of the three-phase interface of the catalyst, ion conductive solid electrolyte, and gas at the electrode is important for the performance of the electrochemical device.

  In Patent Document 1, in order to provide a method for producing an electrolyte membrane-electrode assembly that is excellent in power generation performance in a fuel cell, the reaggregation of the electrolyte is suppressed and a sufficient and uniform contact state between the catalyst and the polymer electrolyte is maintained. It is described to do. In this example, an electrode catalyst in which platinum is supported on carbon black is added to a polymer electrolyte dispersion, mixed and dispersed, and a catalyst ink prepared by applying a vacuum degassing operation is spray-coated on a solid polymer electrolyte membrane. A method for producing an electrolyte membrane-electrode assembly is described.

Japanese Patent No. 5458503

  In the technique described in Patent Document 1, a catalyst ink made of a catalyst, carbon, and polymer electrolyte is simply mixed. Here, the polymer electrolyte is an ion conductive solid electrolyte. In this manufacturing method, a three-phase interface consisting of a catalyst, carbon, and a polymer electrolyte, which is a gas reaction field, is created by chance. That is, since the solid electrolyte does not necessarily exist in the vicinity of the proton generated on the catalyst surface, the distance between the catalyst surface and the polymer electrolyte is the distance that the proton generated on the catalyst surface can move to the polymer electrolyte. The frequency with which such a three-phase interface is created is not necessarily high. Therefore, the technique described in Patent Document 1 has a problem in that the conversion efficiency of the reaction gas to ions is low, and it is necessary to increase the amount of the expensive catalyst that is a scarce resource in order to increase the conversion efficiency.

  The present invention has been made in view of the above problems, and provides an electrode with high conversion efficiency of reaction gas to ions and an electrochemical device using the electrode even when the amount of the catalytic metal is small. The purpose is to do.

  The electrode of the present invention includes a conductive porous body having an electron conductor and an ion conductive solid electrolyte, and metal nanoparticles held by the conductive porous body, and the electrons are formed on the surface of the conductive porous body. The amount of the metal nanoparticles in contact with the conductor and the ion conductive solid electrolyte is larger than the amount of the metal nanoparticles contained in the conductive porous body.

  A metal nanoparticle functions as a catalyst by contacting with an electronic conductor. Further, when the metal nanoparticles are in contact with the ion conductive solid electrolyte, ions generated on the surface of the metal nanoparticles (catalyst) can smoothly move to the ion conductive solid electrolyte. Therefore, in such an electrode, a large number of metal nanoparticles in contact with the electron conductor and the ion conductive solid electrolyte are unevenly distributed on the surface of the conductive porous body in contact with the reaction gas at a large flow rate. A three-phase interface composed of particles, an ion conductive solid electrolyte, and a reaction gas exists at a high frequency, and the conversion amount of the reaction gas into ions with respect to the amount of metal nanoparticles (amount of catalyst metal) is improved.

  The surface of the conductive porous body in the present invention is a surface where the conductive porous body is in contact with the gas, and includes the surface of the through hole of the conductive porous body. Moreover, the inside of the conductive porous body in the present invention is a portion that does not come into contact with the gas in the conductive porous body.

  The ion conductive solid electrolyte in the present invention is a solid that exhibits electrical conductivity due to movement of ions. Here, the solid includes a gel. A gel is a substance containing a liquid in the gap between polymers having a cross-linked structure, and has a high viscosity, so it loses fluidity and is solid as a whole system.

  In the electrode of the present invention, it is preferable that the metal nanoparticles are held on the exposed surface of the electron conductor on the surface of the conductive porous body. Since the metal nanoparticles need to be in contact with the electron conductor in order to function as a catalyst, this configuration allows the metal nanoparticles to function efficiently as a catalyst, and the amount of metal nanoparticles Can be reduced. Such a configuration can be easily made by electrodepositing metal nanoparticles on the surface of the electron conductor.

  In the electrode of the present invention, the ion conductive solid electrolyte is preferably obtained by solidifying or polymerizing an ionic liquid. Since the ionic liquid does not evaporate, maintenance such as replenishment of water is unnecessary, the reliability is high, and the operating temperature can be 100 ° C. or higher.

  The electrochemical device of the present invention uses an ion conductive solid electrolyte and the above electrode. Thereby, even if there is little quantity of metal nanoparticles (amount of catalyst metal), an electrochemical device with good conversion efficiency of reaction gas to ions can be provided.

  ADVANTAGE OF THE INVENTION According to this invention, even if there is little catalyst amount, the electrode with the high conversion efficiency of the reaction gas to the proton, and the electrochemical device using the electrode can be provided.

FIG. 1 is a schematic diagram of a fuel cell according to an embodiment of the present invention. FIG. 2 is a schematic diagram of a hydrogen sensor according to an embodiment of the present invention. FIG. 3 is a conceptual diagram of an electrode according to an embodiment of the present invention. FIG. 4 is a conceptual diagram of a conventional electrode. FIG. 5 is an enlarged view of a part of the electrode according to the embodiment of the present invention. FIG. 6 is a partially enlarged view of a conventional electrode.

  Preferred embodiments for carrying out the present invention will be described in detail with reference to the drawings. The present invention is not limited by the contents described in the following embodiments. The constituent elements described below include those that can be easily assumed by those skilled in the art, those that are substantially the same, and those that are equivalent. Furthermore, the constituent elements described below can be appropriately combined. In addition, various omissions, substitutions, or changes of components can be made without departing from the scope of the present invention.

  In FIG. 1, the schematic diagram of the fuel cell 1 as an example of the electrochemical device of this invention is shown. As shown in FIG. 1, the fuel cell 1 is provided in the electrode 3 with metal nanoparticles, the gas diffusion electrode 4, the separator 6 and the separator 6 on both sides (the anode side and the cathode side) of the ion conductive solid electrolyte membrane 2. The gas flow path 5 is provided.

  Here, hydrogen gas and oxygen gas will be described as examples of the reaction gas. On the anode side, hydrogen gas is introduced into the gas flow path 5, and the hydrogen gas diffuses and moves through the gaps of the gas diffusion electrode 4, diffuses into the electrode 3 with metal nanoparticles, and is oxidized into protons. The proton moves through the ion conductive solid electrolyte membrane 2 and reaches the cathode side. On the cathode side, oxygen gas is introduced into the gas flow path 5, and the oxygen gas diffuses and moves through the gap between the gas diffusion electrodes 4, diffuses into the electrode 3 with metal nanoparticles, and is reduced to oxygen ions. Oxygen ions move through the ion conductive solid electrolyte membrane 2 and react with protons that reach the cathode side to become water and are discharged. A series of these reactions creates a potential difference between the anode and the cathode. When an external load such as a light bulb is connected between the anode and the cathode, a current flows through the light bulb to emit light. Here, it is preferable to use a stable porous conductive material that is not easily oxidized, such as carbon fiber, for the gas diffusion electrode 4.

  Next, an example of a hydrogen sensor will be described as another example of the electrochemical device of the present invention.

  FIG. 2 shows a schematic diagram of the hydrogen sensor 7. The hydrogen sensor includes a current detection type and a voltage detection type. Here, the current detection type will be described as an example. The hydrogen sensor 7 includes an electrode 3 with metal nanoparticles and a gas diffusion electrode 4 on both sides (anode side and cathode side) of the ion conductive solid electrolyte membrane 2, and further includes a reference electrode 8 and an external circuit 9.

  Here, a potentiostat is used for the external circuit 9. The potentiostat can measure the current flowing between the working electrode and the counter electrode by controlling the working electrode to an arbitrary potential with respect to the reference electrode 8. This current is proportional to the reaction rate of the electrochemical reaction, and the hydrogen gas concentration can be obtained by measuring the current value at which hydrogen gas is oxidized into protons. The anode-side gas diffusion electrode 4 is connected to the working electrode terminal W of the potentiostat, the reference electrode 8 of the hydrogen sensor is connected to the reference electrode terminal R, and the cathode-side gas diffusion electrode 4 is connected to the counter electrode terminal C. Since the reference electrode 8 shows a constant potential, the gas diffusion electrode 4 on the anode side and the electrode 3 with metal nanoparticles, which are working electrodes, are held at a potential at which hydrogen is oxidized into protons. Hydrogen gas diffuses and moves through the gap between the gas diffusion electrode 4 on the anode side, diffuses into the electrode 3 with metal nanoparticles, and is oxidized into protons. The proton moves through the ion conductive solid electrolyte membrane 2 and reaches the cathode side. On the cathode side, air containing oxygen gas is introduced, oxygen gas diffuses and moves through the gap of the gas diffusion electrode 4, diffuses into the electrode 3 with metal nanoparticles and is reduced to oxygen ions, and the ion conductive solid electrolyte membrane. It reacts with the protons that move 2 and reach the cathode side to become water and are discharged. From this series of electrochemical reactions, the hydrogen gas concentration is obtained from a current value detected by a potentiostat as the external circuit 9 using a calibration curve prepared in advance. The calculation from the current value to hydrogen gas may be performed by a computer using software.

  Next, the metal nanoparticle-attached electrode 3 of this embodiment, which is an example of the electrode of the present invention, will be described. The conceptual diagram of the electrode 3 with a metal nanoparticle of this embodiment is shown in FIG. On the other hand, in FIG. 4, the catalyst metal 13x, the carbon 10x constituting the conductive porous body 12x, and the catalyst ink made of the polymer electrolyte that is the ion conductive solid electrolyte 11x are manufactured by simply mixing them. The conceptual diagram of the electrode 3x is shown.

  As shown in FIG. 3, the electrode 3 with metal nanoparticles of the present embodiment includes a conductive porous body 12 having an electron conductor 10 and an ion conductive solid electrolyte 11, and a metal held by the conductive porous body 12. And nanoparticles 13. A part of the metal nanoparticles 13 is held in contact with the electron conductor 10 and the ion conductive solid electrolyte 11 on the surface of the conductive porous body 12, and the electron conductor 10 and the ion conductive solid are held on the surface of the conductive porous body 12. The amount of the metal nanoparticles 13 in contact with the electrolyte 11 is larger than the amount of the metal nanoparticles 13 contained in the conductive porous body 12. In the electrode 3 with metal nanoparticles of the present embodiment, the metal nanoparticles 13 are held on the surface of the conductive porous body 12, and the metal nanoparticles 13 are not contained inside the conductive porous body 12. Further, on the surface of the conductive porous body 12, the metal nanoparticles 13 are held on the exposed surface of the electron conductor 10. The metal nanoparticles 13 have catalytic activity.

  On the other hand, as shown in FIG. 4, the conventional electrode 3x is produced by mixing carbon 10x, which is an electron conductor, ion conductive solid electrolyte 11x, and catalyst metal 13x. It exists uniformly not only on the surface of the conductive porous body 12x but also inside.

  The electron conductor 10 has a function of supplying electrons to the metal nanoparticles 13 that are catalysts. The metal nanoparticles 13 have catalytic activity and convert the reaction gas into ions. The ion conductive solid electrolyte 11 conducts ions converted from the reaction gas.

  The conductive porous body 12 is a porous body having through holes as holes, and the reaction gas flows smoothly through the through holes. The surface of the conductive porous body 12 in the present embodiment is a surface where the conductive porous body 12 is in contact with the reaction gas, and includes the surface of the through-hole that the conductive porous body 12 has. Further, the inside of the conductive porous body 12 in the present embodiment is a portion of the conductive porous body 12 that does not come into contact with the reaction gas.

  The electron conductor 10 may be a solid such as a metal, an inorganic compound, or carbon. In addition, the electron conductor 10 can be preferably made by binding carbon particles in order to withstand chemical changes such as deterioration, corrosion, oxidation, hydrogen embrittlement, and physical destruction. The carbon particles are preferably acetylene black, ketjen black, mesophase pitch, graphite, soft graphitized carbon and the like. Carbon fibers, carbon nanotubes, carbon nanohorns, and the like can also be used.

  The metal nanoparticles 13 may be any metal having catalytic activity. For example, transition metals such as platinum, gold, iridium, rhodium, osmium, palladium, silver, rhodium, ruthenium, nickel, copper, cobalt, iron, or a metal mixture selected from these groups, or an alloy selected from these groups Is mentioned. The size of the metal nanoparticles 13 is 1 to 1000 nm, preferably 3 to 100 nm, and more preferably 5 to 20 nm. If the particle size is small, the analysis is difficult, and if the particle size is large, the total amount of metal increases even though the catalyst activity is the same.

  The ion conductive solid electrolyte membrane 2 and the ion conductive solid electrolyte 11 are solids that exhibit electrical conductivity due to movement of ions such as protons. Here, the solid includes a gel. A gel is a substance containing a liquid in the gap between polymers having a cross-linked structure, and has a high viscosity, so it loses fluidity and is solid as a whole system. For example, sulfonic acid type perfluorocarbon polymer, perfluorocarbon polymer having phosphonic acid group or carboxylic acid group, sulfonated polyetheretherketone, sulfonated polysulfone, sulfonated polyethersulfone, sulfonated polysulfone, SEBS (styrene- ( Sulfonated products of ethylene-butylene) -styrene), sulfonated polyphenylene sulfide, sulfonated polyphenylene oxide, sulfonated polyetherimide, sulfonated polyimide, aromatic polyetheretherketone, ionic liquid solids, and the like.

  The ion conductive solid electrolyte membrane 2 and the ion conductive solid electrolyte 11 are preferably those obtained by gelling or polymerizing a solid material obtained by gelling an ionic liquid. Since the ionic liquid does not evaporate, maintenance such as replenishment of water is unnecessary, the reliability is high, and the operating temperature can be 100 ° C. or higher. Gelation of the ionic liquid is performed by adding a gelling agent to the ionic liquid. Examples of the gelling agent include a monomer having two or more polymerizable groups capable of thermal polymerization per molecule, an oligomer, and a copolymer oligomer. As this gelling component, ethylene glycol diacrylate, diethylene glycol diacrylate, triethylene glycol diacrylate, tetraethylene glycol diacrylate, propylene glycol diacrylate, dipropylene glycol diacrylate, tripropylene glycol forming an acrylic polymer Bifunctional acrylates such as diacrylate, 1,3-butanediol diacrylate, 1,4-butanediol diacrylate, 1,6-hexanediol diacrylate, and 3 such as trimethylolpropane triacrylate and pentaerythritol triacrylate Functional acrylates and tetrafunctional acrylics such as ditrimethylolpropane tetraacrylate and pentaerythritol tetraacrylate Rate, and, like the methacrylate monomers. In addition to these, monomers such as urethane acrylate and urethane methacrylate, copolymer oligomers thereof, and copolymer oligomers with acrylonitrile are exemplified. In addition, polymers that can be dissolved in a plasticizer and gelled, such as polyvinylidene fluoride, polyethylene oxide, polyacrylonitrile, and sulfonated polyimide, can also be used.

  The ionic liquid used for the ion conductive solid electrolyte membrane 2 and the ion conductive solid electrolyte 11 is preferably a proton conductive ionic liquid when hydrogen gas is used as a reaction gas. The proton conductive ionic liquid is synthesized by neutralizing a Bronsted acid and a Bronsted base. The proton conductive ionic liquid is preferably one having a highly active N—H proton. Examples of the proton conductive ionic liquid include salts of the following cations and anions. The cations are 4,4′-trimethylenediamine, piperidine, benzimidazole, 1,2,4-triazole, morpholine, butylamine, dipropylamine, pyridine, imidazole, pyrazole, diethylmethylamine triethylammonium, diethylmethylammonium, Examples thereof include dimethylethylammonium, ethylammonium, a-picolinium, pyridinium, 1,8-bis (dimethylamino) naphthalene, 2,6-di-tert-butylpyridine, guanidine, and derivative cations thereof. Anions include phosphoric acid, borohydrofluoric acid, sulfuric acid, nitric acid, acetic acid, trifluoromethanesulfonate, trifluoromethylsulfonylamide, trifluoromethanesulfonate, and fluorohydrogenated tetrachloroaluminate, bis (trifluoromethanesulfonyl) imide, methyl Examples thereof include sulfonates and derivative anions thereof.

  The conductive porous body 12 is composed of, for example, carbon particles that are the electronic conductor 10 and a gelled ionic liquid that is the ion conductive solid electrolyte 11.

  In order to make the electrode of this embodiment, for example, the particles of the electron conductor 10 and the particles of the ion conductive solid electrolyte 11 are mixed and formed into the conductive porous body 12, and then the conductive porous body 12 is used as the electrode. The metal nanoparticles 13 may be electrodeposited on the surface of the conductive porous body 12 in an ionic liquid. The metal nanoparticles 13 are electrodeposited on the surface of the electron conductor 10 in contact with the ionic liquid among the surface of the conductive porous body 12. The surface of the electron conductor 10 that is in contact with the ionic conductive solid electrolyte 11 cannot be in contact with the ionic liquid, but the surface that is in contact with the ionic liquid, that is, the exposed surface that is subsequently in contact with the gas (ion On the surface exposed from the conductive solid electrolyte 11, the metal nanoparticles 13 can be electrodeposited. Thereby, the metal nanoparticles 13 are held on the exposed surface of the electron conductor 10.

  A part of the metal nanoparticles 13 electrodeposited on the surface of the electron conductor 10, that is, the metal nanoparticles 13 in the vicinity of the boundary between the electron conductor 10 and the ion conductive solid electrolyte 11, are the electron conductor 10 and the ion conductive solid. It contacts both of the electrolyte 11. As a result, the three-phase interface of the metal nanoparticles 13, the ion conductive solid electrolyte 11 and the reactive gas can be efficiently produced on the surface of the conductive porous body 12. Moreover, it is possible to electrodeposit the metal nanoparticle 13 which is a catalyst from an ionic liquid. Some ionic liquids strongly adsorb to metals or coordinate to metal ions and have strong inhibition with metals. Because of its action, the metal stays in nucleation and cannot continue crystal growth, so the nanoparticles are electrodeposited. When a metal such as platinum having a high catalytic activity is made into nanoparticles, it can have a large catalytic activity even with a small amount of catalyst due to its large specific surface area.

  Next, the effect | action of the electrode 3 of this embodiment is demonstrated. In the electrode 3 with metal nanoparticles of the present embodiment, the amount of the metal nanoparticles 13 in contact with the electron conductor 10 and the ion conductive solid electrolyte 11 on the surface of the conductive porous body 12 is equal to the inside of the conductive porous body 12. It is larger than the amount of the metal nanoparticles 13 contained in. The metal nanoparticles 13 function as a catalyst by being in contact with the electron conductor 10. Further, the metal nanoparticles 13 are in contact with the ion conductive solid electrolyte 11 so that ions generated on the surface of the metal nanoparticles 13 as a catalyst can smoothly move to the ion conductive solid electrolyte 11.

  Therefore, in such an electrode 3, many metal nanoparticles 13 in contact with the electron conductor 10 and the ion conductive solid electrolyte 11 are unevenly distributed on the surface of the conductive porous body 12 in contact with the reaction gas having a large flow rate. A three-phase interface composed of the metal nanoparticles 13 functioning as a catalyst, the ion conductive solid electrolyte 11 and the reaction gas exists at a high frequency, and the reaction gas ions to the amount of metal nanoparticles 13 (amount of catalyst metal) The amount of conversion is improved.

On the other hand, the conventional electrode 3x is manufactured by simply mixing the catalyst metal 13x, the carbon 10x which is an electron conductor, and the ion conductive solid electrolyte 11x. In this manufacturing method, a three-phase interface consisting of the catalytic metal 13x, the catalytic metal 13x, and the ion conductive solid electrolyte 11x, which serves as a gas reaction field, is created by chance. That is, since the ion conductive solid electrolyte 11x does not necessarily exist in the vicinity of the protons generated on the surface of the catalyst metal 13x, the distance between the surface of the catalyst metal 13x and the ion conductive solid electrolyte 11x is the catalyst metal 13x. The frequency at which a three-phase interface is formed so that the protons generated on the surface of the surface can move to the ion conductive solid electrolyte 11x is not necessarily high.

  FIG. 5 is an enlarged view of a part of the electrode 3 of the present embodiment. FIG. 6 is a partially enlarged view of a conventional electrode 3x. In FIG. 5, the three-phase interface 16 comprised by the metal nanoparticle 13, the ion conductive solid electrolyte 11, and the reactive gas is shown. FIG. 6 shows a three-phase interface 16 composed of a catalytic metal 13x, an ion conductive solid electrolyte 11x, and a reactive gas. A three-phase interface 16x composed of both catalysts, an ion conductive solid electrolyte, and a gas is shown. As shown in FIG. 5, in the electrode 3 of this embodiment, the three-phase interface 16 extends around the ion conductive solid electrolyte 11. However, as shown in FIG. 6, in the conventional electrode 3x, the three-phase interface 16x is formed by chance, and the area is not so many.

  Further, in the electrode 3 with metal nanoparticles of the present embodiment, the metal nanoparticles 13 are held on the surface of the conductive porous body 12 where the electron conductor 10 is exposed. Since the metal nanoparticle 13 needs to be in contact with the electron conductor 10 in order to function as a catalyst, the metal nanoparticle 13 can efficiently function as a catalyst with such a configuration. The amount of particles 13 can be reduced. Such a configuration can be easily made by electrodepositing the metal nanoparticles 13 on the surface of the electron conductor 10.

  In the present embodiment, an example in which the metal nanoparticles 13 are not included in the conductive porous body 12 has been described. However, the metal nanoparticles 13 may be included in the conductive porous body 12. Even if the metal nanoparticles 13 are contained inside the conductive porous body 12, the amount of the metal nanoparticles 13 in contact with the electron conductor 10 and the ion conductive solid electrolyte 11 on the surface of the conductive porous body 12 is as follows. If the amount is larger than the amount of the metal nanoparticles 13 contained in the conductive porous body 12, an electrode with high conversion efficiency of the reaction gas to ions can be provided even if the amount of the catalyst is small.

  In the present embodiment, hydrogen and oxygen have been described as examples of the reaction gas. However, the reaction gas includes hydrocarbons such as methane, propane and ethylene, alcohols such as methanol, carbon dioxide, air and water quality in addition to hydrogen and oxygen. Examples include contaminated organic matter. Electrochemical devices to which they can be applied include fuel cells and electrochemical sensors equipped with hydrocarbon and methanol oxidation electrodes, artificial photosynthesis devices and carbon dioxide sensors equipped with carbon dioxide reduction electrodes, and oxidation and reduction of organic substances that pollute the atmosphere and water quality. Applications other than fuel cells and hydrogen sensors are also conceivable, such as decontaminated organic substance removal devices.

  Examples are shown below, but the present invention is not limited thereto.

Example 1
A sulfonated polyimide was dissolved in diethylmethylammonium trifluoromethanesulfonate to prepare an ionic liquid electrolyte membrane adjusted to a thickness of 25 μm.

  Polytetrafluoroethylene dispersion (manufactured by Daikin Industries, Ltd.) and acetylene black (manufactured by Denki Kagaku Co., Ltd., particle size 40-50 nm) were mixed so that acetylene black: PTFE = 7: 3 (weight ratio), 10 g of the mixture was mixed with water (100 mL) and Triton (registered trademark) X-100 (manufactured by Aldrich Chemical) (1 g), and further 5 g of an electrolyte in which sulfonated polyimide was dissolved in diethylmethylammonium trifluoromethanesulfonate was mixed. . Subsequently, this mixture was stirred and mixed, dried and pulverized. To this pulverized product, a sodium chloride powder containing 80% by weight or more of sodium chloride having a particle size of 1 μm or more was mixed in a PTFE-supported carbon black: NaCl powder = 1: 4 (weight ratio), and naphtha was added in an amount of 6 mL to 1 g of PTFE-supported carbon. Added and mixed. Next, this mixture was formed into a sheet having a thickness of 0.3 mm, dried at 250 ° C. for 1 hour, and then sintered at 350 ° C. for 5 minutes. The sintered sheet was immersed in a sufficient amount of 80% by volume of ethyl alcohol / 20% by volume of distilled water, and sodium chloride in the sheet was eluted and dried to obtain a conductive porous electrode.

  Tetraammineplatinum (II) chloride hydrate (2.3 mmol) and silver trifluoromethanesulfonate (4.6 mmol) were dissolved in 50 mL of water and stirred. The white precipitate of silver chloride was filtered, and the filtrate was dried by heating at 130 ° C. under reduced pressure for 24 hours to obtain platinum trifluoromethanesulfonate. After 0.01 M of this platinum trifluoromethanesulfonate was dissolved in diethylmethylammonium trifluoromethanesulfonate, this solution was uniformly applied to the conductive porous electrode. An electrolytic cell was constructed using a conductive porous electrode, a carbon sheet as the counter electrode, and diethylmethylammonium trifluoromethanesulfonate as the electrolyte. Platinum nanoparticles were deposited on the surface of the conductive porous electrode by applying a voltage so that the conductive porous electrode had a negative potential with respect to the counter electrode. Thereafter, the electrolytic solution was removed to prepare a conductive porous electrode with metal nanoparticles. The amount of platinum nanoparticles deposited determined from the amount of electricity deposited was 1.4 g.

(Example 2)
A sulfonated polyimide was dissolved in 1-ethyl-3-methylimidazolium bis (trifluoromethylsulfonyl) imide to prepare an ionic liquid electrolyte membrane adjusted to a thickness of 25 μm.

  A conductive porous electrode with metal nanoparticles was prepared in the same manner as in Example 1 except that 1-ethyl-3-methylimidazolium bis (trifluoromethylsulfonyl) imide was used instead of diethylmethylammonium trifluoromethanesulfonate. Produced. The amount of platinum nanoparticles deposited determined from the amount of electricity deposited was 1.3 g.

(Comparative Example 1)
A 25 μm thick Nafion (registered trademark) was used for the electrolyte membrane.

  Polytetrafluoroethylene dispersion (manufactured by Daikin Industries, Ltd.) and acetylene black (manufactured by Denki Kagaku Co., Ltd., particle size 40-50 nm) were mixed so that acetylene black: PTFE = 7: 3 (weight ratio), Water (100 mL) and Triton (registered trademark) X-100 (manufactured by Aldrich Chemical) (1 g) were mixed with 10 g of the mixture, and further, Nafion (electrolyte content 10% by mass and water content 90% by mass) 5 g of Dupont DE-1020) (registered trademark) dispersion and 5 g of platinum-supported electrode catalyst (platinum content: 46 mass%) were added and mixed. Subsequently, this mixture was stirred and mixed, dried and pulverized. To this pulverized product, a sodium chloride powder containing 80% by weight or more of sodium chloride having a particle size of 1 μm or more was mixed in a PTFE-supported carbon black: NaCl powder = 1: 4 (weight ratio), and naphtha was added in an amount of 6 mL to 1 g of PTFE-supported carbon. Added and mixed. Next, this mixture was formed into a sheet having a thickness of 0.3 mm, dried at 250 ° C. for 1 hour, and then sintered at 350 ° C. for 5 minutes. The sintered sheet was immersed in a sufficient amount of 80% by volume of ethyl alcohol / 20% by volume of distilled water, and sodium chloride in the sheet was eluted and dried to obtain a conductive porous electrode. The platinum content of this conductive porous electrode is 5 g × 0.46 = 2.3 g.

(Comparative Example 2)
A sulfonated polyimide was dissolved in diethylmethylammonium trifluoromethanesulfonate to prepare an ionic liquid electrolyte membrane adjusted to a thickness of 25 μm.

  Polytetrafluoroethylene dispersion (manufactured by Daikin Industries, Ltd.) and acetylene black (manufactured by Denki Kagaku Co., Ltd., particle size 40-50 nm) were mixed so that acetylene black: PTFE = 7: 3 (weight ratio), 10 g of the mixture was mixed with water (100 mL) and Triton (registered trademark) X-100 (manufactured by Aldrich Chemical) (1 g), and further 5 g of an electrolyte in which sulfonated polyimide was dissolved in diethylmethylammonium trifluoromethanesulfonate, platinum Was mixed with 5 g of an electrode catalyst (platinum content: 46% by mass). Subsequently, this mixture was stirred and mixed, dried and pulverized. To this pulverized product, a sodium chloride powder containing 80% by weight or more of sodium chloride having a particle size of 1 μm or more was mixed in a PTFE-supported carbon black: NaCl powder = 1: 4 (weight ratio), and naphtha was added in an amount of 6 mL to 1 g of PTFE-supported carbon. Added and mixed. Next, this mixture was formed into a sheet having a thickness of 0.3 mm, dried at 250 ° C. for 1 hour, and then sintered at 350 ° C. for 5 minutes. The sintered sheet was immersed in a sufficient amount of a mixed solvent of 80% by volume of ethyl alcohol / 20% by volume of distilled water to elute sodium chloride in the sheet and dried to prepare a conductive porous electrode. The platinum content of this conductive porous electrode is 5 g × 0.46 = 2.3 g.

  The electrodes and electrolyte membranes described in Examples 1 and 2 and Comparative Examples 1 and 2 were used for fuel cells. The fuel cells of Examples 1 and 2 and Comparative Example 2 could generate power even at 120 ° C., but the fuel cell of Comparative Example 1 could not generate power.

In addition, the characteristics at 120 ° C. of the fuel cells using the electrodes and electrolyte membranes described in Examples 1 and 2 and Comparative Example 2 are as follows: current density is 131, 128, 83 mA / cm at cell voltage 0.5 V in this order. ² .

  Thus, the fuel cell using the metal nanoparticle-attached porous electrode of the present invention has a high conversion efficiency of the reaction gas to ions even if the catalyst amount is smaller than that of the conventional catalyst-attached porous electrode. The conversion efficiency of gas to proton is good. Furthermore, the fuel cell using the porous electrode with metal nanoparticles of the present invention and the ionic liquid electrolyte membrane which is an ion conductive solid electrolyte has excellent characteristics even at an operating temperature of 100 ° C. or higher.

  Moreover, the electrochemical hydrogen sensor was produced using the electrodes and electrolyte membranes described in Examples 1 and 2 and Comparative Examples 1 and 2, respectively.

The current density detected by the electrochemical hydrogen sensor using the electrode and electrolyte membrane described in Examples 1 and 2 and Comparative Example 1 and 2 for 100 mL / min of air containing 500 ppm of hydrogen at 25 ° C. and 70% RH is In this order, they were 0.06, 0.05, 0.01, and 0.02 μA / cm ² , respectively.

Detection was continued with an electrochemical hydrogen sensor using the electrode and electrolyte membrane described in Examples 1 and 2 and Comparative Example 1 and 2 for 100 mL / min ^{1 of} air containing 500 ppm of hydrogen at 25 ° C. and 0% RH. However, in the sensor of Comparative Example 1, the detected current density decreased to 0.00 μA / cm ² after 28 hours from the start of detection, but the detected current density after 28 hours from the start of detection of the sensors of Examples 1 and 2 and Comparative Example 2 is , In order, 0.06, 0.05, 0.02 μA / cm ² .

  As described above, the hydrogen sensor using the metal nanoparticle-attached porous electrode of the present invention has a higher conversion efficiency to the reaction gas ions even if the catalyst amount is smaller than that of the conventional catalyst-attached porous electrode. Good detection sensitivity. Furthermore, the hydrogen sensor using the porous electrode with metal nanoparticles of the present invention and the ionic liquid electrolyte membrane that is an ion conductive solid electrolyte has excellent characteristics even when operated continuously for a long time.

  Table 1 summarizes fuel cells and hydrogen sensors using the electrodes and electrolyte membranes described in Examples and Comparative Examples, and Examples and Comparative Examples.

1: Fuel cell 2: Ion conductive solid electrolyte membrane 3: Electrode with metal nanoparticles 4: Gas diffusion electrode 5: Gas flow path 6: Separator 7: Hydrogen sensor 8: Reference electrode 9: External circuit 10: Electronic conductor 11 : Ion conductive solid electrolyte
12: Conductive porous material 13: Metal nanoparticles 16: Three-phase interface

Claims (4)

A conductive porous body having an electron conductor and an ion conductive solid electrolyte, and metal nanoparticles held in the conductive porous body,
The amount of the metal nanoparticles in contact with the electron conductor and the ion conductive solid electrolyte on the surface of the conductive porous body is larger than the amount of the metal nanoparticles contained in the conductive porous body. An electrode characterized by that.   The electrode according to claim 1, wherein the metal nanoparticles are held on the exposed surface of the electron conductor on the surface of the conductive porous body.   The electrode according to claim 1 or 2, wherein the ion conductive solid electrolyte is obtained by solidifying or polymerizing an ionic liquid.   An electrochemical device using an ion conductive solid electrolyte and the electrode according to claim 1.

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