JP3780971B2 - SOLID ELECTROLYTE FUEL CELL, CATALYST ELECTRODE FOR SOLID ELECTROLYTE FUEL CELL, SOLID ELECTROLYTE MEMBRANE FOR SOLID ELECTROLYTE FUEL CELL, AND METHOD FOR PRODUCING THEM - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a fuel cell, a fuel cell electrode, a solid electrolyte membrane for a fuel cell, and a method for producing the same, and more particularly to a fuel cell in which liquid fuel is supplied to a fuel electrode.
[0002]
[Prior art]
A polymer electrolyte fuel cell has a solid electrolyte membrane such as a perfluorosulfonic acid membrane as an electrolyte, and a fuel electrode and an oxidant electrode joined to both sides of the membrane. Hydrogen is added to the fuel electrode and oxygen is added to the oxidant electrode. It is a device that supplies and generates electricity by electrochemical reaction.
The following electrochemical reactions occur at each electrode.
Fuel electrode: H₂→ 2H⁺+ 2e⁻
Oxidant electrode: 1 / 2O₂+ 2H⁺+ 2e⁻→ H₂O
[0003]
By this reaction, the polymer electrolyte fuel cell is 1 A / cm at normal temperature and normal pressure.²The above high output can be obtained.
[0004]
The fuel electrode and the oxidant electrode are provided with a mixture of carbon particles carrying a catalyst material and a solid polymer electrolyte. In general, the mixture is applied on an electrode substrate such as carbon paper that serves as a fuel gas diffusion layer. A fuel cell is constructed by sandwiching a solid electrolyte membrane between these two electrodes and thermocompression bonding.
[0005]
In the fuel cell having this configuration, the hydrogen gas supplied to the fuel electrode passes through the pores in the electrode, reaches the catalyst, emits electrons, and becomes hydrogen ions. The emitted electrons are guided to the external circuit through the carbon particles in the fuel electrode and the electrode substrate, and flow into the oxidant electrode from the external circuit.
[0006]
On the other hand, hydrogen ions generated in the fuel electrode reach the oxidant electrode through the solid polymer electrolyte in the fuel electrode and the solid electrolyte membrane disposed between the two electrodes, and oxygen supplied to the oxidant electrode and an external circuit It reacts with more flowing electrons to produce water as shown in the above reaction formula. As a result, in the external circuit, electrons flow from the fuel electrode toward the oxidant electrode, and electric power is taken out.
[0007]
In order to improve the characteristics of the fuel cell configured as described above, it is important that the adhesion between the electrode and the solid electrolyte membrane is good. That is, the conductivity of hydrogen ions generated by the electrode reaction is required to be high at the interface between the two. If the adhesion at the interface is poor, the conductivity of hydrogen ions is reduced, the electrical resistance is increased, and this causes a decrease in battery efficiency.
[0008]
Although the fuel cell using hydrogen as the fuel has been described above, research and development of a fuel cell using an organic liquid fuel such as methanol has been actively conducted in recent years.
[0009]
Fuel cells that use organic liquid fuels can be used without reforming organic liquid fuels, such as those that reform organic liquid fuels into hydrogen gas and use them as fuel, and direct methanol fuel cells. Those that supply directly to the fuel electrode are known.
[0010]
In particular, the fuel cell that directly supplies the organic liquid fuel to the fuel electrode without reforming has a structure for supplying the organic liquid fuel directly to the fuel electrode, and thus does not require a device such as a reformer. Therefore, the configuration of the battery can be simplified, and the entire apparatus can be reduced in size. Moreover, compared with gaseous fuels, such as hydrogen gas and hydrocarbon gas, the organic liquid fuel also has the characteristic that it can be conveyed easily and safely.
[0011]
In general, in a fuel cell using an organic liquid fuel, a solid electrolyte membrane made of a solid polymer ion exchange resin is used as an electrolyte. Here, in order for the fuel cell to function, it is necessary for hydrogen ions to move through the membrane from the fuel electrode to the oxidant electrode, and it is known that this movement of hydrogen ions involves the movement of water. Therefore, it is necessary that the film contains a certain amount of moisture.
[0012]
However, when an organic liquid fuel such as methanol having a high affinity for water is used, the organic liquid fuel diffuses into the solid electrolyte membrane containing moisture, and further reaches the oxidant electrode (crossover). There was a problem to be overcome. This crossover causes an organic liquid fuel that should originally provide electrons at the fuel electrode to be oxidized on the oxidant electrode side and is not used effectively as a fuel, thus causing a decrease in voltage and output, and a decrease in fuel efficiency.
[0013]
In order to improve the characteristics of such a solid oxide fuel cell, the diffusibility of the gas used for the reaction in the electrode is high, and the conductivity of hydrogen ions and electrons generated by the electrode reaction is high. In addition, it is necessary to prevent the fuel substance from moving in the solid electrolyte membrane toward the oxidant electrode.
[0014]
[Problems to be solved by the invention]
In view of the above circumstances, the technical problem of the present invention is to provide a structure that suppresses the movement of liquid fuel to a solid electrolyte membrane without impairing the conductivity of hydrogen ions generated in the catalyst electrode reaction of the fuel electrode. An object of the present invention is to provide a fuel cell having an electrolyte membrane and a method for manufacturing the fuel cell.
[0015]
The present invention suppresses the permeation of organic liquid fuel while maintaining good hydrogen ion conductivity in the catalyst electrode, and suppresses crossover of the organic liquid fuel, thereby improving battery characteristics and battery reliability. It aims to plan.
[0016]
[Means for Solving the Problems]
  According to the present invention, there is provided a fuel cell including a fuel electrode, an oxidant electrode, and a solid electrolyte membrane sandwiched between the fuel electrode and the oxidant electrode, wherein liquid fuel is supplied to the fuel electrode, Between the fuel electrode or the oxidant electrode and the solid electrolyte membrane,Limits permeation of the liquid fuel and includes carbon nanohornsThere is provided a fuel cell comprising a restricted permeation layer.
[0017]
  According to the present invention, between the fuel electrode or oxidant electrode and the solid electrolyte membrane,Limits the permeation of liquid fuel and includes carbon nanohornsSince the restricted permeation layer is provided, liquid fuel crossover can be effectively prevented. As the restricted permeation layer, those having various configurations can be adopted, and those having excellent ability to restrict the permeation of liquid fuel and good conductivity of hydrogen ions are preferably used.
[0018]
  In the above fuel cell, the limited permeation layerIs, Including carbon nanohornMuThe carbon nanohorn in the present invention is a tubular body in which one end of a carbon nanotube has a conical shape. The carbon nanohorns are aggregated in a configuration in which the conical portions protrude from the surface like horns (horns) around the tube side by van der Waals forces acting between the conical portions to form a carbon nanohorn aggregate. . The diameter of the carbon nanohorn aggregate is 120 nm or less, typically about 10 nm to 100 nm. In addition, each nanotube of the carbon nanohorn aggregate has a diameter of about 2 nm and a length of about 30 nm to about 50 nm, and the cone portion has an average inclination angle of an axial section of about 20 °.
[0019]
The carbon nanohorn aggregate having such a unique structure and having a distribution in particle diameter forms a dense and dense packing structure by packing the projections of the nanohorn. Since the densified carbon nanohorn aggregate has an action of inhibiting the penetration of liquid, a thin layer of the carbon nanohorn aggregate is provided between the catalyst electrode and the solid electrolyte membrane, so that the liquid can be obtained using this inhibitory action. Permeation of the solid electrolyte membrane of fuel can be suppressed. According to the present invention, the crossover is suppressed by the action of the carbon nanohorn, the leakage of the liquid fuel to the oxidant electrode can be prevented, and the decomposition of the liquid fuel at the oxidant electrode can be suppressed. Thereby, the fall of a battery voltage can be suppressed and an energy density can be improved.
[0020]
Here, in order to suppress the permeation of liquid fuel, it is also conceivable that the limited permeation layer is constituted by carbon particles and a solid electrolyte membrane, and the permeation of liquid fuel is suppressed by the carbon particles. In this case, it is necessary to increase the permeation limiting ability of the liquid fuel by increasing the filling rate of the carbon particles in the limited permeation layer in which the carbon particles are miniaturized. However, when the particles are made finer in this way, the conductivity of hydrogen ions is hindered and the efficiency of the battery is lowered. In this respect, since the fuel cell having the above-described structure includes a layer containing a substance having a unique structure called carbon nanohorn, the conductivity of hydrogen ions can be secured and the permeation of liquid fuel can be effectively limited. Although it is not always clear why the carbon nanohorn can be used to achieve both hydrogen ion conductivity and liquid fuel permeation limiting ability, the carbon nanohorn is present in a properly packed state in the layer, and the solid electrolyte is present in the void. This is presumably because the hydrogen ion conduction path is suitably formed.
[0021]
In the present invention, the restricted permeation layer may further include a solid electrolyte. By doing so, a hydrogen ion conduction path by the solid electrolyte is suitably formed in the gap of the carbon nanohorn existing in the restricted permeation layer, and excellent liquid fuel permeation restriction ability is obtained while maintaining good hydrogen ion conductivity. be able to.
[0022]
  According to the present invention, a substrate, a catalyst layer formed on the substrate and including at least catalyst-supporting carbon particles and a solid polymer electrolyte, and formed on the catalyst layer,Suppresses the permeation of liquid fuel and contains carbon nanohornsThere is provided a fuel cell catalyst electrode comprising a restricted permeation layer.
[0023]
  According to the present invention, on the catalyst layer,Suppresses the permeation of liquid fuel and contains carbon nanohornsSince the restricted permeation layer is provided, it is possible to effectively prevent liquid fuel crossover by contacting the solid electrolyte membrane in the fuel cell. As the limiting permeation layer, the same one as in the case of the fuel cell can be used.
[0024]
  The catalyst electrode for a fuel cell of the present invention contains carbon nanohorns in the restricted permeation layer.Mu
[0025]
According to the catalyst electrode for a fuel cell of the present invention, by providing a thin layer structure containing a substance having a unique structure called carbon nanohorn, conductivity of hydrogen ions is ensured and liquid fuel permeates to the oxidant side. It is possible to effectively limit what is done.
[0026]
Further, the fuel cell catalyst electrode of the present invention may be configured to further include a solid electrolyte in the restricted permeation layer. By doing so, a hydrogen ion conduction path by the solid electrolyte is suitably formed in the gap of the carbon nanohorn existing in the restricted permeation layer, and excellent liquid fuel permeation restriction ability is obtained while maintaining good hydrogen ion conductivity. be able to.
[0027]
  According to the present invention, comprising a membrane mainly composed of a solid electrolyte, and a restricted permeable layer provided on at least one surface of the membrane for restricting permeation of liquid fuel, the restricted permeable layer comprises:Including carbon nanohornA solid electrolyte membrane for a fuel cell is provided.
[0028]
  According to the present invention, at least one surface of the solid electrolyte membrane is provided with a restricted permeable layer that restricts the permeation of liquid fuel, and the restricted permeable layer comprises:Including carbon nanohornTherefore, liquid fuel crossover can be effectively prevented by contacting the catalyst electrode in the fuel cell. As the limiting permeation layer, the same one as in the case of the fuel cell or the fuel cell catalyst electrode can be used.
[0029]
  The solid electrolyte membrane for a fuel cell according to the present invention includes carbon nanohorns in the limited transmission layer.Mu
[0030]
According to the solid electrolyte membrane for a fuel cell of the present invention, by providing a thin layer structure containing a substance having a unique structure called carbon nanohorn, conductivity of hydrogen ions is ensured, and liquid fuel is on the oxidant side. It is possible to effectively limit the transmission.
[0031]
Moreover, the solid electrolyte membrane for a fuel cell of the present invention may be configured to further include a solid electrolyte in the restricted permeation layer.
[0034]
According to the present invention, there is provided a method for producing a fuel cell electrode in which a catalyst layer is provided on a substrate, the coating liquid containing conductive particles carrying a catalyst substance and particles containing a solid polymer electrolyte, A step of coating the substrate to form the catalyst layer, and a step of coating the surface of the catalyst layer with a dispersion containing carbon nanohorns to form a liquid fuel restricted permeation layer. A method of manufacturing a fuel cell electrode is provided.
[0035]
Further, in the present invention, after obtaining the fuel cell electrode by the method for producing a fuel cell electrode, the fuel cell electrode is brought into contact with the restricted permeation layer and the solid electrolyte membrane. There is provided a method for manufacturing a fuel cell, comprising a step of pressure-bonding the solid electrolyte membrane.
[0036]
According to the present invention, there is provided a fuel cell comprising a step of applying a dispersion containing carbon nanohorns to at least one surface of a membrane mainly composed of a solid electrolyte to form a restricted permeation layer for liquid fuel. A method for producing a solid electrolyte membrane is provided.
[0037]
Further, according to the present invention, a process for obtaining an electrolyte membrane for a fuel cell by the above-described method for producing a solid electrolyte membrane for a fuel cell, and a coating containing particles containing conductive particles carrying a catalyst substance and a solid polymer electrolyte The fuel is applied in a state in which a catalyst electrode is formed by applying a liquid on a substrate to form a catalyst layer, the restricted permeation layer of the electrolyte membrane for a fuel cell, and the catalyst layer are in contact with each other. There is provided a method for producing a fuel cell comprising the step of pressure-bonding a solid electrolyte membrane for a battery and the catalyst electrode.
[0038]
According to the manufacturing method of the present invention, a fuel cell excellent in hydrogen ion conductivity and liquid fuel permeation limiting ability can be stably manufactured.
[0039]
The fuel cell obtained by the above manufacturing method can have a structure containing carbon nanohorns. By carrying out like this, by providing the thin layer structure containing the substance which has a peculiar structure called carbon nanohorn between the catalyst layer of at least one catalyst electrode, and a solid electrolyte membrane, crossover is suppressed and an oxidizing agent The leakage of the liquid fuel to the electrode can be prevented, and the decomposition of the liquid fuel at the oxidant electrode can be suppressed. Thereby, the fall of a battery voltage can be suppressed and an energy density can be improved.
[0040]
In the fuel cell manufacturing method of the present invention, the limited permeation layer may further include a solid electrolyte. By doing so, a hydrogen ion conduction path by the solid electrolyte is suitably formed in the gap of the carbon nanohorn existing in the restricted permeation layer, and excellent liquid fuel permeation restriction ability is obtained while maintaining good hydrogen ion conductivity. be able to.
[0041]
DETAILED DESCRIPTION OF THE INVENTION
The fuel cell in the present invention includes a fuel electrode, an oxidant electrode, and an electrolyte layer. The fuel electrode and the oxidizer electrode are collectively referred to as a catalyst electrode. A limiting permeation layer is provided between the fuel electrode and the electrolyte layer. Here, the restricted permeation layer is a layer that restricts the movement of the liquid fuel supplied to the fuel electrode side.
[0042]
FIG. 1 is a cross-sectional view schematically showing the structure of the fuel cell of this embodiment. The catalyst electrode-solid electrolyte membrane assembly 101 includes a fuel electrode 102, an oxidant electrode 108, and a solid electrolyte membrane 114. The fuel electrode 102 includes a substrate 104, a catalyst layer 106, and a restricted permeation layer 181. The oxidant electrode 108 includes a base 110 and a catalyst layer 112. The plurality of catalyst electrode-solid electrolyte membrane assemblies 101 are electrically connected via the fuel electrode side separator 120 and the oxidant electrode side separator 122 to constitute the fuel cell 100.
[0043]
In the fuel cell 100 configured as described above, the fuel 124 is supplied to the fuel electrode 102 of each catalyst electrode-solid electrolyte membrane assembly 101 via the fuel electrode-side separator 120. Further, an oxidant 126 such as air or oxygen is supplied to the oxidant electrode 108 of each catalyst electrode-solid electrolyte membrane assembly 101 via the oxidant electrode side separator 122.
[0044]
  The limited transmission layer 181 is, Mosquito-Including Bonn NanohornMu
[0045]
The carbon nanohorn used in the present invention has a tubular body portion of carbon atoms like the carbon nanotube. However, unlike carbon nanotubes, carbon nanohorns have a structure that is conical in air, that is, on a horn (corner), because the tube diameter is not constant and varies continuously. However, the term “conical” is not limited to a strictly geometric definition. The carbon nanohorn is specified as a structure in which at least a part of the structure has a tip portion at the top and the diameter of the tube-shaped portion continuously changes, and the tip portion may or may not be bent.
[0046]
The carbon nanohorn used in the present invention may be a single-layer carbon nanohorn or a multi-layer carbon nanohorn.
[0047]
As the shape of the carbon nanohorn of the present invention, for example, one having an axial length of 10 nm to 80 nm, an outer diameter orthogonal to the axial direction of 1 nm to 10 nm, and an aspect ratio of 50 or less can be used. However, the aspect ratio here is the ratio of the length in the axial direction to the diameter perpendicular to the axis, that is, (length in the axial direction) / (outer diameter). Alternatively, one having one end of the carbon nanohorn closed in a conical shape, and an angle formed by the generatrix and the generatrix can be 15 ° or more and 40 ° or less.
[0048]
The carbon nanohorn used in the present invention may be closed at one end or may not be closed. Moreover, you may terminate in the shape where the vertex of the cone shape of the one end was round.
[0049]
In addition, the carbon nanohorn used in the present invention may have an incomplete structure and have fine pores. Here, the opening diameter of the fine holes may be about 0.3 nm to 5 nm, but is not particularly limited. The micropores here are different from the macropores between the carbon nanohorn aggregates formed when a thin layer containing the carbon nanohorn aggregates is produced, that is, the “pores” in the present invention.
[0050]
The carbon nanohorns are gathered radially by van der Waals forces, for example, as schematically shown in FIG. A collection of carbon nanohorns is called a carbon nanohorn aggregate 401.
[0051]
The term “aggregation” used herein refers to a state in which a plurality of carbon nanohorns are gathered by any force acting on the carbon nanohorns, for example, van der Waals force. Here, the aggregate means an aggregate in which carbon molecules mainly including carbon nanohorns are aggregated.
[0052]
The carbon nanohorn aggregate 401 may be a carbon nanohorn aggregated in a spherical shape. The term “spherical” as used herein does not necessarily mean a true sphere, but includes a collection of various shapes such as an elliptical shape and a donut shape.
[0053]
When the carbon nanohorn aggregate 401 is nearly spherical, the radial direction and the axial direction of the tubular body of the carbon nanohorn are aggregated in a substantially parallel and nearly parallel state. That is, the carbon nanohorn aggregate is formed in a radial structure so that one end of the carbon nanohorn protrudes outward. Because of such a unique structure, not only has a very large specific surface area, but also a structure in which the catalyst substance and the electrolyte are integrated in a suitable amount, type, and dispersion state can be formed. In FIG. 3, the solid polymer electrolyte 403 is illustrated as being provided only on a part of the carbon nanohorn aggregate 401, but actually, it is formed on the entire carbon nanohorn aggregate 401.
[0054]
In addition, the shape of the carbon nanohorn aggregate in which the carbon nanohorns are chemically bonded to each other or the carbon nanotubes are rounded like a kick is also conceivable, but is limited by the structure of these central portions. It is not a thing. Or what has a hollow center part is also considered.
[0055]
Moreover, when the carbon nanohorn which comprises a carbon nanohorn aggregate | assembly is terminated with the shape where the vertex of the conical shape of the one end was rounded, the part where the vertex rounded is gathered radially toward the outer side.
[0056]
As the carbon nanohorn aggregate used in the present invention, for example, a carbon nanohorn aggregate having a distance between adjacent carbon molecules of 0.3 nm to 1 nm and an outer diameter of 10 nm to 200 nm can be selected.
[0057]
Moreover, the carbon nanohorn aggregate used in the present invention can contain carbon nanotubes.
[0058]
Furthermore, in the carbon nanohorn aggregate, a plurality of aggregates may aggregate to form a secondary aggregate. A plurality of such secondary assemblies are present in the solid electrolyte to form a thin layer. However, the solid polymer electrolyte can also enter the secondary assemblies as in the case where the assemblies are integrated with the solid polymer electrolyte in a dispersed manner.
[0059]
The carbon nanohorn aggregate used in the present invention is not simply a mixture of carbon nanohorn aggregates, but a carbon nanohorn aggregate that is firmly fused or aggregated on the surface of the carbon nanohorn to form a secondary structure can be used.
[0060]
Next, the carbon nanohorn aggregate used in the present invention is obtained when excess energy is applied by oxidation treatment, ultrasonic treatment, mechanical force, pulverization, acid treatment, heat treatment in vacuum, or the like.
[0061]
For example, the carbon nanohorn aggregate used in the present invention can be usually produced by a laser evaporation method (laser ablation method) using a solid carbon simple substance such as graphite as a target in an inert gas atmosphere at room temperature. Here, the shape of each carbon molecule or carbon nanohorn, the size of the diameter, the length, the shape of the tip, the spacing between the carbon molecules and the carbon nanohorns, and the pores between the carbon molecules and the carbon nanohorn aggregates The size can be controlled variously according to the manufacturing conditions by the laser evaporation method and the oxidation treatment after the manufacturing.
[0062]
In the laser ablation method, a solid carbon material is irradiated with laser light in an inert gas atmosphere to evaporate the carbon laser, and a powder in which spherical materials are aggregated is obtained as a soot-like material. Furthermore, by suspending the obtained powder as the soot-like substance in, for example, a solvent, the carbon nanohorn aggregate particles in a state in which a single substance or a plurality are aggregated can be recovered.
[0063]
For example, in a reaction inert gas atmosphere including rare gases such as Ar and He, high output CO₂Laser light such as gas laser light can be incident on the surface of the solid carbon material at an appropriate angle. The output of the laser light can be 20 W or more, the pulse width can be 20 ms or more and 500 ms or less, and it is desirable that continuous oscillation is performed. The irradiation angle can be in the range of 100 ° to 170 °, preferably 120 ° to 140 °, as the angle between the solid carbon material surface and the irradiation laser beam. The spot diameter of the laser beam on the surface of the solid carbon material at the time of irradiation can be, for example, 0.5 nm or more and 5 nm or less. Furthermore, the container in which the carbon laser evaporation is performed is, for example, 10^-2Nm^-2The following is evacuated to 10% with a reaction inert gas such as Ar.³Nm^-210 or more⁵Nm^-2It can be as follows. Further, as the solid carbon material, for example, round bar-like sintered carbon, compression-molded carbon, or the like can be used.
[0064]
The obtained soot-like substance can be collected by being deposited on a suitable substrate or by a method of collecting fine particles using a dust bag. Alternatively, the soot-like substance can be recovered by flowing an inert gas in the reaction vessel and flowing the inert gas.
[0065]
The collected soot-like substance mainly contains carbon nanohorn aggregates, and is collected, for example, as a substance containing 90 wt% or more of carbon nanohorn aggregates.
[0066]
Furthermore, the oxidation process for providing a micropore to carbon nanohorn can be performed. Examples of the oxidation treatment method include heat treatment in which treatment conditions such as atmosphere, treatment temperature, and treatment time are controlled. Here, although the atmospheric pressure varies depending on the gas type used, for example, the oxygen partial pressure can be adjusted in the range of about 0 Torr or more and 760 Torr or less. Regarding the processing temperature, the processing temperature can be controlled in a relatively low temperature range of about 250 ° C. to 700 ° C. The treatment time under such oxidation treatment conditions can be adjusted in the range of about 0 minutes to 120 minutes.
[0067]
By controlling the conditions of the above oxidation treatment in various ways, micropores of an arbitrary size can be opened in the wall portion and the tip portion of the carbon molecule or carbon nanohorn. The oxidation treatment may be a one-step treatment that is held at a constant temperature within the above temperature range, a multi-step treatment that is held at a plurality of temperatures within the above temperature range, or a treatment temperature within the above temperature range. It is also possible to consider a processing method for changing the value as needed. Furthermore, besides the above method, the carbon nanohorn aggregate may be subjected to an oxidation treatment by heating in an acid solution having an oxidizing action such as nitric acid or hydrogen peroxide.
[0068]
In addition to the oxidation treatment, powders obtained as aggregates or soot-like substances are suspended in a liquid solvent and irradiated with ultrasonic waves to collect single or multiple aggregated state particles and collect them. Micropores can be formed in the carbon nanohorn forming the body. As the dispersion solvent, an inorganic solvent, a hydrocarbon, an organic solvent, or the like can be used.
[0069]
By heat-treating the carbon nanohorn aggregate in a vacuum, a structure in which the carbon nanohorn aggregates are firmly fused or aggregated can be obtained. Although the heat processing temperature in vacuum is not specifically limited, For example, it can be set as 400 degreeC or more and 2000 degrees C or less.
[0070]
The aggregates of the carbon nanohorns all have a large specific surface area and a unique surface form. Therefore, in the solid oxide fuel cell, the function of the fuel cell electrode as a carbon substance and the solid electrolyte membrane side of the liquid fuel The effect which suppresses movement of can be provided.
[0071]
As the fuel of the fuel cell according to the present invention, a liquid organic fuel can be used. By providing the restricted permeation layer 181, the cell efficiency can be improved while suppressing the crossover of the liquid fuel, and the effect of the present invention is exhibited.
[0072]
Further, the limited transmission layer 181 may further include a solid electrolyte.
[0073]
The solid electrolyte membrane in the fuel cell according to the present invention functions to separate the fuel electrode 102 and the oxidant electrode 108 and to move hydrogen ions and water molecules between the two. For this reason, the solid electrolyte membrane 114 is preferably a membrane having high hydrogen ion conductivity. Further, it is preferably chemically stable and has high mechanical strength. As a material constituting the solid electrolyte membrane 114, an organic polymer having a polar group such as a strong acid group such as a sulfone group, a phosphate group, a phosphone group, or a phosphine group, or a weak acid group such as a carboxyl group is preferably used. Examples of the organic polymer include aromatic-containing polymers such as sulfonated poly (4-phenoxybenzoyl-1,4-phenylene) and alkylsulfonated polybenzimidazole; polystyrene sulfonic acid copolymer, polyvinyl sulfonic acid copolymer, Copolymers such as cross-linked alkyl sulfonic acid derivatives, fluorine-containing polymer skeletons and fluorine-containing polymers composed of sulfonic acids; acrylamides such as acrylamide-2-methylpropane sulfonic acid and acrylates such as n-butyl methacrylate. A copolymer obtained by polymerization;
Examples include sulfone group-containing perfluorocarbons (Nafion (manufactured by DuPont: registered trademark), Aciplex (manufactured by Asahi Kasei)); carboxyl group-containing perfluorocarbon (Flemion S membrane (manufactured by Asahi Glass: registered trademark)). Among these, when an aromatic-containing polymer such as sulfonated poly (4-phenoxybenzoyl-1,4-phenylene) or alkylsulfonated polybenzimidazole is selected, the permeation of organic liquid fuel can be suppressed, and a battery by crossover A decrease in efficiency can be suppressed.
[0074]
FIG. 2 is a cross-sectional view schematically showing the structure of the fuel electrode 102, the oxidant electrode 108, the solid electrolyte membrane 114, and the restricted permeation layer 181. As shown in the figure, the fuel electrode 102 and the oxidant electrode 108 in the present embodiment can include, for example, carbon particles carrying a catalyst and fine particles of a solid polymer electrolyte. 104, formed on the substrate 110. The substrate surface may be subjected to a water repellent treatment.
[0075]
As the substrate 104 and the substrate 110, porous substrates such as carbon paper, a carbon molded body, a carbon sintered body, a sintered metal, and a foam metal can be used. A water repellent such as polytetrafluoroethylene can be used for the water repellent treatment of the substrate.
[0076]
Examples of the catalyst for the fuel electrode 102 include platinum, an alloy of platinum and ruthenium, gold, rhenium, rhodium, palladium, iridium, osmium, ruthenium, rhenium, gold, silver, nickel, cobalt, lithium, lanthanum, strontium, yttrium, and the like. Is exemplified. On the other hand, as the catalyst for the oxidant electrode 108, the same catalyst as that for the fuel electrode 102 can be used, and the above-mentioned exemplified substances can be used. The catalyst for the fuel electrode 102 and the oxidant electrode 108 may be the same or different.
[0077]
Examples of the carbon particles supporting the catalyst include acetylene black (DENKA BLACK (manufactured by Denki Kagaku: registered trademark), XC72 (manufactured by Vulcan), etc.), ketjen black, amorphous carbon, carbon nanotube, carbon nanohorn, and the like. . The particle size of the carbon particles is, for example, 0.01 μm or more and 0.1 μm or less, preferably 0.02 μm or more and 0.06 μm or less.
[0078]
In addition, the solid polymer electrolyte that is a constituent of the catalyst electrode of the present invention electrically connects the carbon particles supporting the catalyst and the solid electrolyte membrane 114 on the surface of the catalyst electrode and allows the organic liquid fuel to reach the catalyst surface. It has a role, hydrogen ion conductivity and water mobility are required, the fuel electrode 102 is required to be permeable to organic liquids such as methanol, and the oxidant electrode 108 is required to be oxygen permeable. . As the solid polymer electrolyte, a material excellent in hydrogen ion conductivity and organic liquid fuel permeability such as methanol is preferably used in order to satisfy these requirements. Specifically, an organic polymer having a polar group such as a strong acid group such as a sulfone group or a phosphoric acid group or a weak acid group such as a carboxyl group is preferably used. Examples of such organic polymers include sulfone group-containing perfluorocarbons (Nafion (manufactured by DuPont), Aciplex (manufactured by Asahi Kasei), etc.); carboxyl group-containing perfluorocarbons (Flemion S membrane (manufactured by Asahi Glass Co., Ltd.));
Polystyrene sulfonic acid copolymer, polyvinyl sulfonic acid copolymer, cross-linked alkyl sulfonic acid derivative, copolymer such as fluorine-containing polymer composed of fluororesin skeleton and sulfonic acid; acrylamide such as acrylamide-2-methylpropane sulfonic acid And a copolymer obtained by copolymerizing an acrylate such as n-butyl methacrylate; and the like.
[0079]
In addition, examples of the polymer to which the polar group is bonded include polybenzimidazole derivatives, polybenzoxazole derivatives, polyethyleneimine cross-linked products, polysilamine derivatives, amine-substituted polystyrenes such as polydiethylaminoethylpolystyrene, diethylaminoethylpolymethacrylate, and the like. Nitrogen-substituted polyacrylates or other resins having nitrogen or hydroxyl groups; silanol-containing polysiloxanes, hydroxyl-containing polyacrylic resins represented by hydroxyethyl polymethyl acrylate; hydroxyl-containing polystyrene resins represented by parahydroxypolystyrene; it can.
[0080]
In addition, a crosslinkable substituent such as a vinyl group, an epoxy group, an acrylic group, a methacryl group, a cinnamoyl group, a methylol group, an azide group, or a naphthoquinonediazide group may be appropriately introduced into the above-described polymer. .
[0081]
The solid polymer electrolytes in the fuel electrode 102 and the oxidant electrode 108 may be the same or different.
[0082]
Next, the manufacturing method of the solid oxide fuel cell of the present invention will be described in detail.
[0083]
The method for producing the fuel electrode and the oxidant electrode in the present invention is not particularly limited, but can be produced, for example, as follows.
[0084]
First, the catalyst of the fuel electrode and the oxidant electrode can be supported on the carbon particles by a generally used impregnation method. Next, the carbon particles carrying the catalyst and the solid polymer electrolyte particles are dispersed in a solvent to form a paste, and this is applied to a substrate and dried to obtain a fuel electrode and an oxidant electrode. Here, the particle size of the carbon particles is, for example, 0.01 μm or more and 0.1 μm or less. The particle size of the catalyst particles is, for example, 1 nm or more and 10 nm or less. The particle diameter of the first and second solid polymer electrolyte particles is, for example, 0.05 μm or more and 1 μm or less. For example, the carbon particles and the solid polymer electrolyte particles are used in a weight ratio of 2: 1 to 40: 1. Further, the weight ratio of water and solute in the paste is, for example, about 1: 2 to 10: 1. Although there is no restriction | limiting in particular about the coating method of the paste to a base | substrate, For example, methods, such as brush coating, spray coating, and screen printing, can be used. The paste is applied with a thickness of about 1 μm to 2 mm, for example. After applying the paste, heating is performed at a heating temperature and a heating time according to the fluororesin to be used, and a fuel electrode or an oxidizer electrode is produced. The heating temperature and the heating time are appropriately selected depending on the material to be used. For example, the heating temperature may be 100 ° C. or more and 250 ° C. or less, and the heating time may be 30 seconds or more and 30 minutes or less.
[0085]
The solid electrolyte membrane in the present invention can be produced by employing an appropriate method depending on the material used. For example, when the solid electrolyte membrane is composed of an organic polymer material, a liquid obtained by dissolving or dispersing the organic polymer material in a solvent is obtained by casting on a peelable sheet such as polytetrafluoroethylene and drying it. Can do.
[0086]
Furthermore, a restricted permeation layer is applied to the catalyst layer (paste application surface) of the catalyst electrode or the solid electrolyte membrane surface. For example, the restricted permeation layer containing the carbon nanohorn can be applied to the catalyst layer of the catalyst electrode, and in this case, it may be applied to at least one electrode. Further, for example, when the limited transmission layer containing the carbon nanohorn is applied to the surface of the solid electrolyte membrane, it may be applied to at least one surface.
[0087]
The application of the limited transmission layer can be performed, for example, as follows. The fuel electrode and the oxidant electrode can be obtained by dispersing the carbon nanohorn (here, the carbon nanohorn aggregate) and the solid electrolyte described above in a solvent to form a paste, and applying and drying the paste on a substrate. . Here, the solid polymer electrolyte may be in the form of particles, and the particle diameter may be the same as or different from the solid electrolyte used for the catalyst electrode, for example, 0.05 μm or more and 0.5 μm or more. The amount of carbon nanohorn in the limited transmission layer is, for example, 1% or more, preferably 30% or more by weight. By setting the content to 1% or more, the penetration of the liquid fuel can be effectively limited. Further, the amount of the carbon nanohorn in the limited transmission layer can be 95% or less, preferably 99.5% or less, in weight ratio. By setting the content to 99.5% or less, the conductivity of hydrogen ions in the restricted transmission layer can be kept good. The weight ratio of water and solute in the paste in the limited permeation layer can be, for example, about 1: 2 to 10: 1.
[0088]
The solid electrolyte described above can be selected, for example, from materials that can be used for the catalyst electrode or the solid electrolyte membrane.
[0089]
Here, from the viewpoint of suppressing the crossover, it is preferable to use a material having a low permeability of the organic liquid fuel as the solid electrolyte. For example, it is preferable to use an aromatic condensed polymer such as sulfonated poly (4-phenoxybenzoyl-1,4-phenylene) and alkylsulfonated polybenzimidazole.
[0090]
Although there is no restriction | limiting in particular about the coating method of the paste to the catalyst electrode surface or the solid electrolyte membrane surface, For example, methods, such as brush coating, spray coating, and screen printing, can be used. After applying the paste, by heating and drying, a catalyst electrode having a thin layer containing the carbon nanohorn as a restricted transmission layer or a solid electrolyte membrane having a thin layer containing the carbon nanohorn as a restricted transmission layer is produced.
[0091]
Here, the limited transmission layer (here, a thin layer containing carbon nanohorns) can have a thickness of, for example, 1 nm or more, preferably 10 nm or more. By setting the thickness to 1 nm or more, the penetration of the liquid fuel can be effectively limited. Further, the thickness of the limited transmission layer can be, for example, 1000 nm or less, preferably 500 nm or less. By setting the thickness to 1000 nm or less, the conductivity of hydrogen ions in the limited transmission layer can be kept good. The heating temperature and the heating time are appropriately selected depending on the material to be used. For example, the heating temperature may be 100 ° C. or higher and 250 ° C. or lower, and the heating time may be 30 seconds or longer and 30 minutes or shorter.
[0092]
The solid electrolyte membrane produced as described above is sandwiched between the fuel electrode and the oxidant electrode and hot pressed to obtain an electrode-electrolyte assembly. At this time, the surface on which the catalyst of both electrodes is provided is in contact with the solid electrolyte membrane. The hot press conditions are selected according to the material, but when the solid electrolyte membrane or the electrolyte membrane on the electrode surface is composed of an organic polymer having a softening point or glass transition, the softening temperature or glass transition of these polymers. It can be set to a temperature exceeding the unit temperature. Specifically, for example, the temperature is 100 ° C. or more and 250 ° C. or less, and the pressure is 1 kg / cm.²100 kg / cm or more²Hereinafter, the time is 10 to 300 seconds.
[0093]
As described above, a solid oxide fuel cell can be obtained in which a limited permeation layer including carbon nanohorns (here, carbon nanohorn aggregates) is formed between the catalyst electrode and the solid electrolyte membrane. In the solid oxide fuel cell, the fine structure specific to the carbon nanohorn aggregate suppresses the movement of the liquid fuel supplied to the fuel electrode to the solid electrolyte membrane and has excellent cell characteristics.
[0094]
The limited permeation layer may be formed between at least one catalyst electrode and the solid electrolyte membrane.
[0095]
Methanol permeability can be measured as follows. In a liquid container separated by an electrolyte membrane to be measured (film thickness 50 μm, area 1 cm square), 50 cc of 99.5% methanol on one side and 50 cc of pure water on the other side are sealed so that each liquid does not evaporate. . The methanol permeation amount can be determined by measuring the time change of the concentration of methanol permeating through the electrolyte membrane to be measured in pure water using a gas chromatograph.
[0096]
Further, the pore size distribution of the thin layer can be measured by a method such as a gas permeation method or a mercury intrusion method.
[0097]
【Example】
Hereinafter, a solid polymer fuel cell using the carbon nanohorn aggregate of the present invention at the interface between a solid polymer electrolyte and a catalyst electrode composed of catalyst-supported carbon fine particles and a solid polymer electrolyte membrane will be described in detail by way of examples. However, the present invention is not limited to these.
[0098]
[Example 1]
Aldrich's 5% Nafion solution was added to 100 mg of Ketjen Black carrying a ruthenium-platinum alloy, and stirred at 50 ° C. for 3 hours with an ultrasonic mixer to obtain a catalyst paste. The alloy composition used above was 50 atom% Ru, and the weight ratio of the alloy to the fine carbon powder was 1: 1. 2 mg / cm of this paste on 10 cm × 10 cm carbon paper (TGP-H-120; manufactured by Toray Industries, Inc.)²It apply | coated and dried at 120 degreeC and it was set as the catalyst electrode.
[0099]
The carbon nanohorn aggregate was produced by a laser ablation method. That is, sintered round bar carbon as a solid carbon material is placed in a vacuum container, and the container is filled with 10^-2After evacuating to Pa, Ar gas was introduced to an atmospheric pressure of 760 Torr. Next, high output CO₂The solid carbon material was irradiated with laser light for 30 minutes at room temperature. The output of the laser was 100 W, the pulse width was 20 ms, and irradiation was performed so that the angle formed with the solid carbon material surface was 120 °. When the soot-like substance thus obtained was observed with a transmission electron microscope (TEM), it was confirmed to have a carbon nanohorn aggregate structure.
[0100]
The obtained soot-like substance was subjected to ultrasonic treatment (400 kHz, 60 minutes) and decantation in ethanol four times, whereby a carbon nanohorn aggregate composed of single or several particles could be obtained.
[0101]
The particle diameter of the obtained carbon nanohorn aggregate was in the range of 10 nm to 100 nm from TEM observation of the particles.
[0102]
After adding 10 ml of 1% Nafion solution to 100 mg of the carbon nanohorn aggregate and stirring at 50 ° C. for 3 hours with an ultrasonic mixer, the weight after drying is 0.1 mg / cm on the surface of the catalyst layer of the catalyst electrode.²It was applied to the surface of the catalyst membrane so as to be dried at 120 ° C. This was made into the catalyst electrode-restricted permeation layer composite. When the cross section of the catalyst electrode-restricted transmission layer composite was observed with a scanning electron microscope (SEM), the carbon nanohorn aggregate layer had a thickness of 100 nm.
[0103]
The catalyst electrode-restricted permeation layer composite was thermocompression bonded at 120 ° C. to both surfaces of a Nafion 117 (manufactured by DuPont: registered trademark) membrane, and the resulting catalyst electrode-solid electrolyte membrane assembly was used as a fuel cell.
[0104]
The fuel cell was supplied with 10 v / v% methanol aqueous solution and oxygen gas as fuel at 2 cc / min and 30 cc / min, respectively, and the battery characteristics were measured. The current density was 100 mA / cm.²The battery voltage at that time was 0.43V. This characteristic did not change after 12 hours. Further, the output of the fuel cell according to the present invention was hardly observed even at a concentration of 30% or more.
[0105]
[Example 2]
A catalyst electrode was produced in the same manner as in Example 1. Next, 100 mg of the carbon nanohorn aggregate produced in the same manner as in Example 1 was added to 10 ml of 1% Nafion solution and stirred at 50 ° C. for 3 hours in an ultrasonic mixer. This was dried on one side of a Nafion 117 (manufactured by DuPont) membrane with a weight of 0.1 mg / cm after drying.²And dried at 50 ° C. to prepare a carbon nanohorn aggregate-solid electrolyte membrane composite. When observed with a scanning electron microscope (SEM), the thickness of the carbon nanohorn aggregate layer was 100 nm. The catalyst electrode obtained above was thermocompression bonded to this carbon nanohorn aggregate-solid electrolyte membrane composite at 120 ° C. to obtain a fuel cell.
[0106]
A 10 v / v% aqueous methanol solution and oxygen gas were supplied to the fuel cell as 2 cc / min and 30 cc / min, respectively, and the battery characteristics were measured. Here, a methanol aqueous solution was supplied to the side on which the carbon nanohorn aggregate was applied. At this time, the current density is 100 mA / cm.²The battery voltage at that time was 0.42 V, and this characteristic did not change after 12 hours.
[0107]
[Comparative Example 1]
A catalyst electrode was produced in the same manner as in Examples 1 and 2. The obtained catalyst electrode was thermocompression bonded to both surfaces of a Nafion 117 (DuPont) membrane at 120 ° C., and the resulting catalyst electrode-solid electrolyte membrane assembly was used as a fuel cell. The fuel cell was supplied with a 10 v / v% methanol aqueous solution and oxygen gas at 2 cc / min and 30 cc / min, respectively, and the battery characteristics were measured. The current density was 100 mA / cm.²The battery voltage at that time was 0.3V. Further, when the methanol concentration exceeded 30 v / v%, the output was significantly reduced.
[0108]
From the above examples and comparative examples, it was revealed that the battery characteristics are greatly improved by the present invention. That is, in the embodiment according to the present invention, excellent packing permeation ability of methanol is obtained by a unique packing structure of carbon nanohorns present in the restricted permeation layer provided in the fuel cell, and a solid electrolyte is provided in the voids of the carbon nanohorns. It was revealed that the hydrogen ion conduction path was suitably formed and the hydrogen ion conductivity could be maintained well.
[0109]
【The invention's effect】
  As described above, according to the present invention, between the catalyst electrode and the solid electrolyte membrane,Limits the permeation of liquid fuel and includes carbon nanohornsSince the restricted permeation layer is provided, the crossover of the organic liquid fuel can be suppressed while maintaining good hydrogen ion conductivity on the electrode surface. For this reason, it is possible to improve battery characteristics and battery reliability.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view schematically showing an example of the structure of a fuel cell according to the present invention.
FIG. 2 is a cross-sectional view schematically showing a fuel electrode, an oxidant electrode, a solid electrolyte membrane, and a restricted permeation layer in an example of the fuel cell of the present invention.
FIG. 3 is a view showing an example of a basic structure of a composite electrolyte including at least a carbon nanohorn aggregate and a solid electrolyte that can be used in the fuel cell of the present invention.
[Explanation of symbols]
100 Fuel cell
101 catalyst electrode-solid electrolyte membrane assembly
102 Fuel electrode
104 Substrate
106 Catalyst layer
108 Oxidant electrode
110 substrate
112 Catalyst layer
114 Solid electrolyte membrane
120 Fuel electrode side separator
122 Oxidant electrode side separator
124 Fuel
126 Oxidizing agent
181 Restricted transmission layer
401 Carbon nanohorn aggregate
403 Solid polymer electrolyte

Claims (11)

A fuel cell comprising a fuel electrode, an oxidant electrode, and a solid electrolyte membrane sandwiched between the fuel electrode and the oxidant electrode, wherein liquid fuel is supplied to the fuel electrode, wherein the fuel electrode or the oxidant A fuel cell comprising a limiting permeation layer including carbon nanohorns, which restricts permeation of the liquid fuel between an electrode and the solid electrolyte membrane.   2. The fuel cell according to claim 1, wherein the layer containing the carbon nanohorn further contains a solid electrolyte. A base, a catalyst layer formed on the base and including catalyst-supporting carbon particles and a solid polymer electrolyte, and a limited permeation layer formed on the catalyst layer and suppressing permeation of liquid fuel and including carbon nanohorns And a catalyst electrode for a fuel cell.   4. The fuel cell catalyst electrode according to claim 3, wherein the restricted permeation layer further contains a solid polymer electrolyte. A fuel comprising: a membrane mainly composed of a solid electrolyte; and a restricted permeable layer provided on at least one surface of the membrane for restricting permeation of liquid fuel, wherein the restricted permeable layer includes carbon nanohorns. Solid electrolyte membrane for batteries.   6. The solid electrolyte membrane for a fuel cell according to claim 5, wherein the limited permeation layer further contains a solid electrolyte. A method for producing an electrode for a fuel cell having a catalyst layer provided on a substrate,
Applying a coating liquid containing conductive particles carrying a catalyst substance and particles containing a solid polymer electrolyte on the substrate to form the catalyst layer;
Applying a dispersion containing carbon nanohorns on the surface of the catalyst layer to form a limited permeation layer that restricts permeation of liquid fuel; and
The manufacturing method of the electrode for fuel cells characterized by including these.   After obtaining the fuel cell electrode by the method for producing a fuel cell electrode according to claim 7, the restricted permeation layer and the solid electrolyte membrane constituting the fuel cell electrode are in contact with each other, A method for producing a fuel cell, comprising a step of pressure-bonding a fuel cell electrode and the solid electrolyte membrane.   A solid electrolyte membrane for a fuel cell comprising a step of applying a dispersion containing carbon nanohorns on at least one surface of a membrane mainly composed of a solid electrolyte to form a limited permeation layer that restricts the permeation of liquid fuel. Production method. Obtaining a fuel cell electrolyte membrane by the method for producing a fuel cell solid electrolyte membrane according to claim 9;
Producing a catalyst electrode by applying a coating liquid containing conductive particles carrying a catalyst substance and particles containing a solid polymer electrolyte on a substrate to form a catalyst layer;
A step of pressure-bonding the solid electrolyte membrane for a fuel cell and the catalyst electrode in a state where the restricted permeation layer and the catalyst layer of the solid electrolyte membrane for the fuel cell are in contact with each other;
A method for producing a fuel cell, comprising:   11. The method of manufacturing a fuel cell according to claim 8, wherein the restricted permeation layer further contains a solid electrolyte.

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