JP2010010033A - Proton conductive membrane, and membrane electrode assembly and fuel cell using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a proton conductive membrane for producing a fuel cell which can suppress the cross-over of methanol. <P>SOLUTION: The proton conductive membrane comprises proton conductive polymer and proton conductive inorganic oxide. The proton conductive polymer has sulfonic acid groups and is incorporated with a weight W<SB>p</SB>. The proton conductive inorganic oxide has silicon oxide supported on the surface and is incorporated with a weight W<SB>SA+SiO2</SB>. A wight ratio (W<SB>SA+SiO2</SB>/W<SB>p</SB>) is within in a range of 0.03-0.43. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a proton conductive membrane, a membrane electrode assembly using the same, and a fuel cell.

  Proton conducting membranes have been used for electrochromic materials and sensors. Recently, extensive research has been conducted to apply to fuel cells that operate at low temperatures and have high energy density.

  In a fuel cell, a fuel electrode (anode) is provided on one side of an electrolyte membrane made of a proton conductive solid membrane, and an oxidant electrode (cathode) is provided on the other side. A fuel such as hydrogen or methanol supplied to the anode is electrochemically oxidized to generate electrons and protons. Electrons flow to the external circuit and protons reach the cathode through the proton conducting solid electrolyte. At the cathode, water is generated by the supplied oxidant and electrons from the external circuit to extract electric power.

  As the proton conductive membrane, a perfluorosulfonic acid-containing polymer, which is an organic polymer ion exchange membrane, is used. Specifically, it is based on a copolymer of tetrafluoroethylene and perfluorovinyl ether, Those having a sulfonic acid group as an exchange group (for example, trade name Nafion manufactured by DuPont) are known. In a fuel cell using a perfluorosulfonic acid polymer as an electrolyte membrane, a crossover occurs in which an organic liquid fuel such as methanol passes through the electrolyte membrane and reaches the cathode side. In this case, the supplied liquid fuel and oxidant react directly, and energy cannot be output as electric power. Therefore, there arises a problem that a stable output cannot be obtained.

As an inorganic solid acid-based ion exchange membrane, a sulfuric acid-supporting metal oxide having solid superacidity is known (see, for example, Patent Document 1). Specifically, sulfuric acid is supported on an oxide surface selected from zirconium, titanium, iron, tin, silicon, aluminum, molybdenum, and tungsten, and sulfuric acid is immobilized on the oxide surface by heat treatment. The sulfuric acid-supported metal oxide exhibits proton conductivity due to the immobilized sulfate radical, but the sulfate radical deviates due to hydrolysis, and the proton conductivity decreases. For this reason, it is unstable as a proton conductive solid electrolyte of a fuel cell that generates water in the process of power generation, particularly a fuel cell using liquid fuel, and there is a possibility that power cannot be stably supplied over a long period of time.
JP 2002-216537 A

  The present invention has been made in view of the above problems, and an object thereof is to provide a proton conductive membrane for obtaining a fuel cell capable of suppressing methanol crossover.

A proton conductive membrane according to one embodiment of the present invention is a proton conductive membrane comprising a proton conductive polymer and a proton conductive inorganic oxide,
The proton conducting polymer has a sulfonic acid group and is blended with a weight W _p .
The proton conductive inorganic oxide has silicon oxide supported on the surface, and is blended with a weight W _{SA + SiO 2} .
The weight ratio (W _{SA + SiO 2} / W _P ) is in the range of 0.03 to 0.43.

  A membrane electrode assembly according to an aspect of the present invention is a membrane electrode assembly comprising a fuel electrode, an oxidant electrode, and an electrolyte membrane disposed between the fuel electrode and the oxidant electrode, The electrolyte membrane includes the aforementioned proton conductive membrane.

  A fuel cell according to one embodiment of the present invention includes the above-described membrane electrode assembly.

  According to the present invention, a proton conductive membrane for obtaining a fuel cell capable of suppressing methanol crossover is provided.

  Embodiments of the present invention will be described below.

  In the proton conductive membrane according to the embodiment of the present invention, a proton conductive inorganic oxide is dispersed in a proton conductive polymer having a sulfonic acid group.

  The proton conductive polymer having a sulfonic acid group is not particularly limited. Specifically, a perfluorosulfonic acid polymer represented by nafion (manufactured by DuPont), sulfonated polystyrene, sulfonated polyetherketone, sulfone. Sulfonated polyethersulfone, sulfonated polysulfone, sulfonated polyethersulfone or other sulfonated engineering plastic materials.

  The proton conductive inorganic oxide has silicon oxide supported on the surface. Silicon oxide may be supported as fine particles or may be deposited in layers on the surface of the proton conductive inorganic oxide. In any state, as long as silicon oxide is supported on the surface of the proton conductive inorganic oxide, it is possible to prevent the proton conductive inorganic oxides from fusing together during synthesis and grain growth.

  It can be confirmed by instrumental analysis such as transmission electron microscope (TEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) that silicon oxide is supported on the proton conductive inorganic oxide. Is possible.

The silicon oxide is preferably supported at a weight of 0.1 to 0.5 times the weight of the proton conductive inorganic oxide. That is, when the weights of the components of silicon oxide and proton conductive inorganic oxide are W _SiO2 and W _SA , respectively, the weight ratio (W _SiO2 / W _SA ) is preferably 0.1 to 0.5. More preferably, the weight ratio is 0.05 to 0.5.

  The proton conductive inorganic oxide includes an oxide carrier and oxide particles supported on the surface of the oxide carrier. The oxide support can include, for example, at least one first element selected from the group consisting of Ti, Zr, and Sn, and the oxide particles are selected from the group consisting of W, Mo, and V At least one second element can be included. The average particle size of the oxide carrier is usually about 1 to 500 nm.

Specific examples of the oxide carrier containing the first element include TiO ₂ , ZrO ₂ , and SnO ₂ . Specific examples of the oxide particles containing the second element include WO ₂ , MoO ₂ , and V ₂ O ₅ . When the oxide particles are supported on the surface of such an oxide carrier, Lewis acid points are generated in the structure of the oxide particles. It is presumed that when this Lewis acid point is hydrated, it becomes a Bronsted acid point and a proton conduction field is formed. In addition, when the proton conductive inorganic oxide has an amorphous structure, the generation of Lewis acid points is promoted.

  Although the solubility of oxide particles containing the second element varies depending on the element and pH environment, the oxide particles may exhibit water solubility. On the other hand, the oxide carrier containing the first element has low water solubility. By supporting the oxide particles on an oxide carrier having low water solubility, it is possible to suppress dissolution of the oxide particles in water. As a result, the stability of the proton conductive inorganic oxide to water and liquid fuel is improved. Also, contamination of other fuel cell materials and devices by ions of the eluted oxide particles can be avoided.

  By using such a proton conductive inorganic oxide for the proton conductive membrane, crossover of methanol is suppressed, so that a fuel cell having high reliability over a long period of time can be obtained.

  The oxide carrier containing the first element can be synthesized by any method. For example, a vapor phase method in which a gas containing a first element is decomposed to produce an oxide, or a sol-gel method using a solution containing a first element or a metal alkoxide as a raw material can be given. The oxide carrier may be a complex oxide containing a plurality of types of metal elements.

  When Sn is used as the first element, the proton conductivity can be sufficiently increased. In addition, when Ti is used as the first element, high proton conductivity can be obtained while suppressing the manufacturing cost. The oxide carrier can have various shapes such as a particle shape, a fiber shape, a flat plate shape, a layer shape, and a porous shape, and the shape is not particularly limited. In the oxide carrier, the surface acts as a proton conduction site. For this reason, sufficient proton conduction sites can be obtained by using nano-sized fine particle oxide as an oxide carrier.

  The oxide particles containing the second element can be supported on the surface of the oxide carrier containing the first element, for example, by the following method. First, a solution in which a precursor containing the second element is dissolved, for example, an acidic or alkaline aqueous solution such as chloride, nitrate, hydrogen acid, or oxo acid salt, or an alcohol solution of a metal alkoxide is prepared. As a solvent which dissolves at this time, for example, water and alcohol can be used. Here, the oxide carrier containing the first element is dispersed, and the solvent is removed. As a result, the oxide particles containing the second element are supported on the oxide carrier and then subjected to heat treatment to obtain oxide particles.

  The oxide particles containing the second element may be supported on the oxide carrier in the state of a composite oxide containing a plurality of elements. The solvent is generally removed by heating, but is not limited thereto. The solvent can be removed under reduced pressure without heating. Furthermore, the solvent may be removed by simultaneously performing heating and decompression.

  The effect is exhibited if the oxide particles containing the second element are supported on at least a part of the surface of the oxide carrier containing the first element. For example, it may be a layered material that is scattered on the surface of the oxide support or covers the surface of the oxide support. It is sufficient that the oxide particles are supported on the surface of the oxide carrier. Further, the crystallinity of the oxide particles or the oxide carrier is not limited.

  Considering the promotion of Lewis acid point generation, the possibility of contributing to the improvement of acidity, the reduction of the manufacturing cost, and the ease of the manufacturing process, it is desirable that both the oxide particles and the oxide support are amorphous. . More preferably, the oxide particles are amorphous and the oxide support is crystalline. On the contrary, it is also possible to use both the oxide particles and the oxide carrier in the form of crystals, or the oxide particles can be used in the form of crystals and the oxide carrier can be used in an amorphous state.

  The state in which the raw material of the oxide particles is supported on the surface of the oxide carrier is the proton conductive inorganic oxide precursor particles. When the solvent is removed and the oxide particles are supported on the surface of the oxide carrier, the precursor particles are strongly aggregated into coarse aggregates. It is not easy to release this aggregation state, leading to an increase in manufacturing cost. On the other hand, when the heat treatment is continued in the agglomerated state, the oxide carriers are fused to cause grain growth.

  In particular, when the oxide carrier is a fine particle such as a nanoparticle, grain growth tends to occur at a temperature considerably lower than the melting point of the oxide carrier. When grain growth occurs, the specific surface area of the particles decreases and proton conduction sites decrease. As a result, the cell resistance increases, and the tendency that a high output cannot be obtained as a whole battery becomes strong.

  The present inventors have found a technique for easily canceling aggregation of precursor particles of a proton conductive inorganic oxide. Specifically, when the oxide carrier is dispersed in a solution in which the substance containing the second element is dissolved, the silicon oxide particles are added, and then the solvent is removed. As a result, silicon oxide particles adhere to the surface of the oxide support. Alternatively, silicon oxide dissolved in the solution can be deposited and deposited on the surface of the oxide support, and the silicon oxide can be supported on the surface of the oxide support. It was also confirmed that by performing the heat treatment with the silicon oxide particles added in this manner, it is possible to suppress the fusion and grain growth of the oxide carrier.

  The mechanism of this phenomenon is considered as follows. This is because silicon oxide is a hardly sinterable oxide, and the presence of silicon oxide between the aggregated oxide carrier particles suppresses fusion between the oxide carriers. In the proton conductive inorganic oxide synthesized by the above method, the oxide particles are supported not only on the surface of the oxide carrier but also on the surface of the silicon oxide particles. It is difficult to separate and remove only the oxide particles supported on the surface of the silicon oxide particles.

  As described above, silicon oxide is a hardly sinterable oxide, and oxide particles are difficult to bond. For this reason, oxide particles may elute during power generation, and the components of the fuel cell may be contaminated by the components. In order to avoid such an inconvenience, it is desired to remove the oxide particles supported on the surface of the silicon oxide particles by washing in advance with water or hot water.

  By washing, a proton conductive inorganic oxide composed of an oxide carrier and oxide particles and silicon oxide particles carried on the surface thereof is obtained. Silicon oxide is a hardly sinterable oxide, and the bond with the oxide carrier may be weak depending on the synthesis conditions. In this case, the silicon oxide particles can be removed by washing with water or hot water in advance.

As already explained, the weight (W _SiO2 ) of the _silicon oxide particles supported on the surface is 0.1 to 0.5 times the weight (W _SA ) of the proton conductive inorganic oxide (SA). preferable. That is, if the weight ratio (W _SiO2 / W _SA ) between the silicon oxide particles and the proton conductive inorganic oxide is within the range of 0.1 to 0.5, the proton conductivity and the electron conductivity of the electrode catalyst layer. The effect of suppressing grain growth can be obtained without lowering.

  It is preferable that the average particle diameter of silicon oxide does not exceed the average particle diameter of the oxide support. Considering the ease of handling and the effect of suppressing grain growth, the average particle diameter of silicon oxide is preferably in the range of 1 to 15 nm. The crystallinity and shape of the particles are not particularly limited, and an appropriate one may be selected in consideration of the cost.

The specific surface area of the proton conductive inorganic oxide is preferably in the range of 10 to 2000 m ² / g. When the specific surface area exceeds 2000 m ² / g, it is difficult to control handling and uniform synthesis, and when it is less than 10 m ² / g, sufficient proton conductivity cannot be obtained.

  In the proton conductive inorganic oxide, the atomic ratio (M2 / M1) between the second element (M2) contained in the oxide particles and the first element (M1) contained in the oxide carrier is: It is preferable to be within the range of 0.0001-5. When the atomic ratio (M2 / M1) is less than 0.0001, the supported amount is small and the proton conduction field is small. On the other hand, if it exceeds 5, the supported amount is too large and the proton conduction field is covered with oxide particles. In either case, sufficient proton conductivity may not be obtained. The atomic ratio (M2 / M1) is more preferably in the range of 0.01 to 1.

  The proton conductive inorganic oxide can be obtained, for example, by supporting a precursor of oxide particles on an oxide carrier and then heat-treating it in an oxidizing atmosphere such as the air. It is preferable that the temperature of heat processing shall be 200-1000 degreeC. When the temperature is lower than 200 ° C., the precursor of the oxide particles hardly becomes an oxide, and a sufficient chemical bond is not formed between the oxide carrier and the oxide particles. On the other hand, when the temperature exceeds 1000 ° C., grain growth occurs in addition to fusion between the particles, and the specific surface area becomes small. In either case, there is a possibility that sufficient proton conductivity cannot be obtained. The heat treatment temperature is more preferably 400 to 800 ° C.

It is desirable that the proton conductive inorganic oxide exhibits a solid superacidity. The degree of proton dissociation can be expressed as acid strength, and the acid strength of solid acid is expressed as Hammett acidity function H ₀ . For example, H _{0 of} 100% sulfuric acid is -11.93, and it is more preferable that the proton conductive inorganic oxide exhibits a solid superacidity that satisfies H ₀ <-11.93. Further, the proton conductive inorganic oxide, by optimizing the synthesis method, it is possible to increase the acidity to H ₀ = -20.00. Therefore, it is desirable to use a proton conductive inorganic oxide having an acid strength in the range of −20.00 <H ₀ <−11.93.

  The acidity of the proton-conductive inorganic oxide can be measured using an ammonia temperature rising desorption method (TPD) method. Specifically, ammonia gas is adsorbed on the solid acid sample, and the sample is heated. By detecting the desorption amount and desorption temperature of the desorbed ammonia, the acidity of the solid acid is analyzed.

The proton conductive membrane according to the embodiment of the present invention contains a proton conductive polymer having a sulfonic acid group as described above and a proton conductive inorganic oxide. In order to suppress the permeation of liquid fuel (methanol crossover) while maintaining high proton conductivity, solid super strong acid (SA + SiO ₂ ) carrying a silicon oxide (for example, SiO ₂ ) on the surface and a proton conducting polymer ( The weight ratio (W _{SA + SiO 2} / W _P ) to _P ) is preferably in the range of 0.03 to 0.43. Here, W _P is the weight of the proton conductive polymer (P).

  When a proton conductive membrane is used in a fuel cell, it is generally used in a membrane state, but is not limited thereto. For example, it can be used in a cylindrical shape. Specifically, a method of directly casting a dispersion mixture of a proton conductive inorganic oxide and a proton conductive polymer into a film shape, or impregnating the dispersion mixture into a porous core material, a woven fabric or a non-woven fabric. The method can be applied to a fuel cell.

  The thickness of the proton conductive membrane is not particularly limited, but it is preferably thicker than 10 μm in order to obtain a membrane that can withstand practical use, such as strength, liquid fuel permeability, and proton conductivity. In order to reduce the film resistance, it is preferable that the thickness is smaller than 300 μm. In particular, in order to reduce the internal resistance of the fuel cell, 10 to 150 μm is more preferable.

  The thickness of the film can be controlled by the following method. For example, when a dispersion solution containing a proton conductive inorganic oxide and a proton conductive polymer is directly cast into a film, a dispersion mixture of the proton conductive inorganic oxide to be cast and the above proton conductive polymer is used. It can be changed by quantity or cast area. Furthermore, after film formation, there is a method of reducing the film thickness by heating and pressurizing the film with a hot press machine or the like. It is not particularly limited to these.

  The membrane electrode assembly according to the embodiment of the present invention is configured using the proton conductive membrane as described above. That is, the membrane electrode assembly according to the embodiment includes a fuel electrode, an oxidant electrode, and an electrolyte membrane disposed between the fuel electrode and the oxidant electrode. The electrolyte membrane is formed by the proton conductive membrane described above. Composed.

  The fuel electrode can be produced by supporting a composition obtained by using a methanol oxidation catalyst as an active ingredient and adding a proton conductive material, a water repellent material, a binder and the like on an electrode support. As the methanol oxidation catalyst, catalysts such as PtRu, PtRuMo, PtRuW, PtIr, and PtRuSn can be used.

  As the proton conductive material, a material in which the above-described electrolyte membrane is formed can be used. The water repellent material is blended to prevent water from passing through the electrode film, and a fluorine resin or the like can be used. The binder is a component that binds the catalyst particles to each other and maintains a film shape, and a polymer resin can be used. In addition, since it has a function as a water repellent material, it is preferable to use a fluororesin as a water repellent material and a binder. Furthermore, in order to improve the electrical conductivity of the fuel electrode, a conductive agent can be added. As the conductive agent, it is preferable to use carbon particles such as carbon black. These additive components are those commonly used in direct methanol fuel cell technology.

  As the electrode support, it is preferable to use porous carbon paper in order to efficiently transport the raw material gas to the catalyst. Other than this, for example, a thin film such as gold, platinum, stainless steel, nickel or the like, a mesh or a sponge, or well-known conductive particles represented by titanium oxide, silica, or tin oxide can be used. A current collector can be further joined to the electrode support. The electrode support may also serve as a fuel electrode or oxidant electrode current collector.

  The catalyst can be supported on the electrode support by, for example, a coating method. Specifically, first, a desired electrode support such as porous carbon paper is prepared, and a suspension containing a methanol oxidation catalyst or an oxygen reduction catalyst is applied thereon. Next, by drying, an electrode support on which a catalyst is supported is obtained.

  In addition to the coating method, a catalyst may be supported on the electrode support by a chemical or electrochemical method such as a vacuum thin film preparation method represented by sputtering or chemical vapor deposition, plating, electroless plating, or impregnation method. it can. Furthermore, methods such as arc melting and mechanical milling may be used.

  The oxidant electrode can be produced by supporting a composition in which an oxygen reduction catalyst is an active ingredient and a proton conductive material, a water repellent material, a binder and the like are added to an electrode support. As the oxygen reduction catalyst, catalysts such as Pt, PtCo, PtNi, Fe, RuSe, and RuSeS can be used. These catalysts are preferably used in the form of particles because the catalyst function can be exhibited with high efficiency.

  The fuel electrode and the oxidant electrode are disposed in contact with the proton conductive membrane. As a method of bringing the fuel electrode and the oxidant electrode into contact with the electrolyte membrane, known methods such as hot pressing and cast film formation can be used.

In general, the fuel electrode and the oxidant electrode are brought into contact with the electrolyte membrane using a hot press machine. The press temperature in that case should just be more than the glass transition temperature of the polymeric material used as a binder for an electrode and an electrolyte membrane. Generally, it is 100-400 degreeC. The press pressure depends on the hardness of the electrode used, but is usually 5 to 200 kg / cm ² .

  Next, a fuel cell using the above-described membrane electrode assembly will be described in more detail with reference to the drawings.

  The fuel cell according to the present embodiment may be either an active type or a passive type. A single cell of an active fuel cell is schematically shown in FIG.

  As shown in the drawing, the electrolyte membrane 2 has an oxidant electrode (cathode) 1 and a fuel electrode (anode) 3 joined to both surfaces thereof, and is arranged as an electrode membrane composite (MEA). This MEA can be manufactured by the method described above. The end portions of the oxidant electrode 1 and the fuel electrode 3 are sealed by sealing materials 4 and 5 made of a material such as PTFE, so that fuel, exhaust gas and the like are prevented from leaking to the outside.

  An oxidant channel plate 7 having an oxidant channel 6 is disposed outside the oxidant electrode 1, and an oxidant such as air is supplied to the oxidant electrode 1. On the other hand, a fuel flow path plate 9 having a fuel flow path 8 is disposed outside the fuel electrode 3, and fuel such as methanol is supplied to the fuel electrode 3. The oxidant channel 6 and the fuel channel 8 can forcibly supply or discharge the oxidant and fuel by means such as a pump. Alternatively, the gas may be circulated by natural convection without using the forcing means.

  The oxidant flow path plate 7 and the fuel flow path plate 9 are preferably formed of a conductor in order to extract electric energy generated in the oxidant electrode 1 and the fuel electrode 3. Current collectors 10 and 11 made of a metal plate or the like are disposed outside the oxidant flow path plate 7 and the fuel flow path plate 9, and electric energy is taken out.

  In the illustrated example, heaters 12 and 13 are disposed outside the current collectors 10 and 11. By heating the fuel cell with the heater, the power generation efficiency of the fuel cell can be improved.

  Although the housing is not shown in the conceptual diagram of the direct methanol fuel cell shown in FIG. 1, the fuel cell can be configured by housing the above-described assembly in the housing. In FIG. 1, only a single cell that is a single assembly is shown as a power generation element. However, in this embodiment, this single cell may be used as it is, or a plurality of cells are connected in series. And / or it can also be connected in parallel to provide a mounted fuel cell.

  The connection method between cells is not specifically limited, For example, the conventional connection system which uses a bipolar plate is employable. It is also useful to adopt a plane connection method or other known connection methods.

  In FIG. 2, the schematic diagram which shows the single cell of a passive type fuel cell is shown.

  In the illustrated single cell, an electrolyte membrane 22 is sandwiched between a fuel electrode (anode) 23 and an oxidant electrode (cathode) 21, and an electromotive portion is formed by the electrolyte membrane 22, the fuel electrode 23, and the oxidant electrode 21. (MEA) 24 is configured. The fuel electrode 23 and the oxidant electrode 21 are made of a conductive porous body so that fuel and oxidant gas can be circulated and electrons can pass therethrough.

  Each unit cell is provided with a fuel permeation section 25 having a function of retaining liquid fuel, and a fuel vaporization section 26 for guiding the gaseous fuel vaporized by the liquid fuel retained in the fuel permeation section 25 to the fuel electrode 23. It is done. The fuel permeation unit 25 is surrounded by an anode separator 27. By stacking a plurality of unit cells including the fuel permeation unit 25, the fuel vaporization unit 26, and the electromotive unit 24 via the separator 28, a stack type fuel cell serving as a cell body is configured. An oxidant gas supply groove 29 for flowing an oxidant gas is provided as a continuous groove on the surface of the separator 28 facing the oxidant electrode 21. Reference numeral 30 is an oxidizing gas outlet. Moreover, you may provide the anode production | generation gas discharge port 31. FIG.

  In the case where a stack is formed by stacking single cells, the separator 28, the fuel permeation unit 25, and the fuel vaporization unit 26 contain carbon in order to function as a current collector plate that conducts generated electrons. It is formed of a conductive material such as a porous body.

  As described above, the separator 28 in the unit cell of FIG. 2 also has a function as a channel through which the oxidizing gas flows. In this way, the number of parts can be reduced by using parts having the functions of both separators and channels (hereinafter referred to as channel separators), and the fuel cell can be further reduced in size. It becomes. Alternatively, a normal channel can be used in place of the separator 28.

  Liquid fuel is supplied from a fuel tank through a pump, a fuel infiltration unit 25, and the like. Therefore, for example, when combined with the natural fall method, there is an advantage that the installation location of the fuel tank can be freely set.

  The fuel tank as described above can be detachable from the battery body. Thereby, it becomes possible to continue the operation of the battery for a long time by exchanging the fuel tank. In addition, the liquid fuel is supplied from the fuel tank to the fuel permeation unit 25 by a configuration in which the liquid fuel is pushed out by the natural fall or the internal pressure in the tank as described above, or by the capillary force of the fuel permeation unit 25. It can also be configured to be pulled out.

  The form of the fuel permeation unit 25 is not particularly limited as long as it has a function of holding the liquid fuel therein and supplying only the vaporized fuel to the fuel electrode 23 through the fuel vaporization unit 26. For example, a liquid fuel passage may be provided, and a gas-liquid separation membrane may be provided at the interface with the fuel vaporization unit 26.

  In the case where liquid fuel is supplied to the fuel permeation unit 25 by capillary force without using an auxiliary machine, the form of the fuel permeation unit 25 is not particularly limited as long as the liquid fuel can be permeated by capillary force. Absent. For example, a porous body composed of particles and fillers, a non-woven fabric produced by a papermaking method, a woven fabric woven with fibers, and the like can be used. Furthermore, a narrow gap formed between a plate made of glass or plastic may be used.

  Here, the case where a porous body is used as the fuel permeation portion 25 will be described. As the capillary force for drawing the liquid fuel to the fuel permeation unit 25 side, first, the capillary force of the porous body itself constituting the fuel permeation unit 25 is mentioned. When utilizing such a capillary force, it is a so-called continuous hole in which the holes of the fuel permeation part 25, which is a porous body, are connected, the hole diameter is controlled, and from the side of the fuel permeation part 25 at the liquid fuel inlet, By making the continuous hole continuous to at least one other surface, it becomes possible to supply the liquid fuel smoothly by capillary force in the lateral direction.

  The pore diameter and the like of the porous body used as the fuel permeation section 25 are not particularly limited as long as the liquid fuel can be drawn in. In consideration of the capillary force of the fuel penetration part 25, the pore diameter is preferably about 0.01 to 150 μm. When the pore diameter is smaller than 0.01 μm, it is difficult to manufacture the fuel permeation portion 25, while when it exceeds 150 μm, the capillary force may be reduced. Here, the pore diameter of the porous body refers to the maximum peak value of the pore distribution. The pore diameter of the porous body can be measured by a mercury intrusion method.

It is preferable that the pore volume serving as an index of pore continuity in the porous body is about 20 to 90 vol%. When the pore volume is less than 20 vol%, the amount of continuous pores decreases and the number of closed pores increases, making it difficult to obtain sufficient capillary force. On the other hand, when the volume of the pores exceeds 90 vol%, the amount of continuous pores increases, but the strength becomes weak and the manufacture becomes difficult.
Practically, the porous body constituting the fuel penetration part 25 preferably has a pore diameter in the range of 0.5 to 100 μm, and the pore volume is preferably in the range of 30 to 75%.

  In FIG. 2, only a single cell which is a single assembly is shown as a power generation element. However, in this embodiment, this single cell may be used as it is, or a plurality of cells may be connected in series and / or Or it can also be connected in parallel and it can also be set as a mounted fuel cell. As a method for connecting the cells, a known method such as a plane connection method can be employed.

  Such a fuel cell undergoes a cell reaction even from room temperature. However, when operated at a high temperature of 50 to 100 ° C., it is desirable because the catalytic activity of the electrode is enhanced and the electrode overvoltage is reduced. In addition, the proton conductive polymer electrolyte that forms the electrolyte membrane does not exhibit proton conductivity in the absence of moisture, and therefore needs to be operated at a temperature at which moisture management is possible. Considering these, the preferable range of the operating temperature of the fuel cell is room temperature to 100 ° C.

  Hereinafter, the present invention will be described in more detail with reference to specific but non-limiting examples.

Example 1
First, a proton conductive inorganic oxide was synthesized. As oxide particles, 1.5 g of vanadium oxide (V ₂ O ₅ ) was dissolved in 100 mL of ammonia water to prepare a solution. In 500 ml of distilled water, 13 g of titanium oxide (TiO ₂ ) was dispersed as an oxide carrier and mixed with the previously prepared solution containing vanadium oxide. 4.4 g of silicon oxide (SiO ₂ ) particles were dispersed in the obtained mixed solution, and the mixed solution was heated to 80 ° C. with constant stirring. The average particle diameter of the silicon oxide particles is about 6 nm. After removing water at an evaporation rate of 100 ml / hour, the mixture was kept in a dryer at 100 ° C. for 12 hours to obtain a powder.

  The powder was pulverized in an agate mortar, then housed in an alumina crucible, and heated to 500 ° C. at a temperature increase rate of 100 ° C./hour. Furthermore, by maintaining at 500 ° C. for 4 hours, a proton conductive inorganic oxide carrying silicon oxide particles was obtained. As described above, the first element M1 and the second element M2 are titanium and vanadium, respectively.

  X-ray diffraction measurement was performed on the proton conductive inorganic oxide carrying the silicon oxide particles. All of the observed diffraction peaks are attributed to titanium oxide, and it was confirmed that vanadium oxide and silicon oxide have an amorphous structure.

  The atomic ratio (M2 / M1) in the proton conductive inorganic oxide was determined by inductively coupled plasma emission spectroscopy (ICP-AES). The specific surface area was measured by the BET method, and the solid acidity was determined by an acid indicator or ammonia temperature programmed desorption (TPD) method. The results obtained are summarized in Table 1 below.

  An electrolyte membrane was produced using the obtained proton conductive inorganic oxide. To 0.50 g of the proton conductive inorganic oxide, 10.0 g of a commercially available 20% nafion solution (trademark, manufactured by Du Pont) was added. Furthermore, 2.0 g of ion-exchanged water and 2.0 g of 1-methoxy-2-propanol were added and dispersed for 2 hours with a paint shaker. Thereafter, the dispersion was defoamed for 2 minutes with a defoaming machine (Kuritaro (trademark): manufactured by Sinky Corporation) to prepare a solution.

  After pasting a polypropylene film on a glass plate, the prepared dispersion solution was applied. After drying at room temperature for 12 hours, it was dried at 140 ° C. for 30 minutes to obtain an electrolyte membrane having a thickness of 80 μm.

The obtained electrolyte membrane, the proton conductive inorganic oxide containing SiO ₂ (SA + SiO ₂₎ and the weight ratio of the proton-conductive organic polymer binder _{(P) (W SA + SiO2} / W P), and silicon oxide particles The weight ratio (W _SiO2 / W _SA ) between (SiO ₂ ) and proton conductive inorganic oxide ( _SA ) is determined and summarized in Table 2 below. Incidentally, W _P is determined from the proton conductive organic polymer binder solution used as the polymer content and (wt%).

  The electrolyte membrane was refluxed with a 1M aqueous sulfuric acid solution for 1 hour, and then thoroughly washed with ion exchange water. Further, the mixture was further refluxed in ion exchange water for 1 hour and washed with ion exchange water. Washing was repeated until the pH of the wash water became neutral. The electrolyte membrane after washing was stored in ion-exchanged water until use.

(Example 2)
Example 1 except that 1.5 g of vanadium oxide V ₂ O ₅ was changed to 2.4 g of molybdenum oxide MoO ₃ , the compounding amount of silicon oxide was changed to 4.6 g, and the firing temperature was changed to 600 ° C. A proton conductive inorganic oxide carrying silicon oxide was obtained by the same method. The first element and the second element are titanium and molybdenum, respectively.

  An electrolyte membrane was produced in the same manner as in Example 1 except that the obtained proton conductive inorganic oxide was used.

(Example 3)
Example 1 except that 1.5 g of vanadium oxide V ₂ O ₅ was changed to 4.0 g of tungsten oxide WO ₃ , the amount of silicon oxide was changed to 5.1 g, and the firing temperature was changed to 700 ° C. A proton conductive inorganic oxide carrying silicon oxide was obtained by the same method. The first element and the second element are titanium and tungsten, respectively.

  An electrolyte membrane was produced in the same manner as in Example 1 except that the obtained proton conductive inorganic oxide was used.

Example 4
Proton-conducting inorganic material supporting silicon oxide in the same manner as in Example 1 except that 13 g of titanium oxide TiO ₂ was changed to 20 g of zirconium oxide ZrO ₂ and the amount of silicon oxide was changed to 6.5 g. An oxide was obtained. The first element and the second element are zirconium and vanadium, respectively.

  An electrolyte membrane was produced in the same manner as in Example 1 except that the obtained proton conductive inorganic oxide was used.

(Example 5)
Proton-conducting inorganic material supporting silicon oxide in the same manner as in Example 2 except that 13 g of titanium oxide TiO ₂ was changed to 20 g of zirconium oxide ZrO ₂ and the amount of silicon oxide was changed to 6.7 g. An oxide was obtained. The first element and the second element are zirconium and molybdenum, respectively.

  An electrolyte membrane was produced in the same manner as in Example 1 except that the obtained proton conductive inorganic oxide was used.

(Example 6)
Proton-conducting inorganic material supporting silicon oxide in the same manner as in Example 3 except that 13 g of titanium oxide TiO ₂ was changed to 20 g of zirconium oxide ZrO ₂ and the amount of silicon oxide was changed to 7.2 g. An oxide was obtained. The first element and the second element are zirconium and tungsten, respectively.

  An electrolyte membrane was produced in the same manner as in Example 1 except that the obtained proton conductive inorganic oxide was used.

(Example 7)
Proton-conducting inorganic material supporting silicon oxide in the same manner as in Example 3 except that 13 g of titanium oxide TiO ₂ was changed to 25 g of tin oxide SnO ₂ and the compounding amount of silicon oxide was changed to 7.2 g. An oxide was obtained. The first element and the second element are tin and vanadium, respectively.

  An electrolyte membrane was produced in the same manner as in Example 1 except that the obtained proton conductive inorganic oxide was used.

(Example 8)
Proton-conducting inorganic material supporting silicon oxide in the same manner as in Example 2 except that 13 g of titanium oxide TiO ₂ was changed to 25 g of tin oxide SnO ₂ and the amount of silicon oxide was changed to 8.2 g. An oxide was obtained. The first element and the second element are tin and molybdenum, respectively.

  An electrolyte membrane was produced in the same manner as in Example 1 except that the obtained proton conductive inorganic oxide was used.

Example 9
Proton-conducting inorganic material supporting silicon oxide in the same manner as in Example 3 except that 13 g of titanium oxide TiO ₂ was changed to 25 g of tin oxide SnO ₂ and the amount of silicon oxide was changed to 8.7 g. An oxide was obtained. The first element and the second element are tin and tungsten, respectively.

  An electrolyte membrane was produced in the same manner as in Example 1 except that the obtained proton conductive inorganic oxide was used.

(Example 10)
Example 3 except that the compounding amount of the proton conductive inorganic oxide was changed to 0.2 g, and 10.0 g of the 20% nafion solution was changed to 10.0 g of the 10% sulfonated PEEK solution (ion exchange capacity 1.53). An electrolyte membrane was prepared by the same method as described above.

(Example 11)
An electrolyte membrane was produced in the same manner as in Example 3 except that the amount of the proton conductive inorganic oxide was changed to 0.2 g and the amount of the 20% nafion solution 10.0 was changed to 9.0 g. .

Example 12
An electrolyte membrane was produced in the same manner as in Example 3 except that the blending amount of the proton conductive inorganic oxide carrying silicon oxide was changed to 0.060 g.

(Example 13)
An electrolyte membrane was produced in the same manner as in Example 3 except that the blending amount of the proton conductive inorganic oxide carrying silicon oxide was changed to 0.860 g.

(Example 14)
An electrolyte membrane was produced in the same manner as in Example 3 except that the atomic ratio (M2 / M1) in the proton conductive inorganic oxide was changed to 0.05.

(Example 15)
An electrolyte membrane was produced in the same manner as in Example 3 except that the atomic ratio (M2 / M1) in the proton conductive inorganic oxide was changed to 0.10.

(Example 16)
An electrolyte membrane was produced in the same manner as in Example 3 except that the atomic ratio (M2 / M1) in the proton conductive inorganic oxide was changed to 0.50.

(Example 17)
An electrolyte membrane was produced in the same manner as in Example 3 except that the atomic ratio (M2 / M1) in the proton conductive inorganic oxide was changed to 0.70.

(Comparative Example 1)
An electrolyte membrane was prepared in the same manner as in Example 1 except that the proton conductive inorganic oxide carrying silicon oxide was changed to TiO ₂ having only an oxide carrier.

(Comparative Example 2)
An electrolyte membrane was produced in the same manner as in Example 1 except that the proton conductive inorganic oxide was composed of only WO ₃ / TiO ₂ without supporting silicon oxide.

(Comparative Example 3)
An electrolyte membrane was produced in the same manner as in Example 3 except that the blending amount of the proton conductive inorganic oxide carrying silicon oxide was changed to 0.040 g.

(Comparative Example 4)
An electrolyte membrane was produced in the same manner as in Example 3 except that the blending amount of the proton conductive inorganic oxide supporting silicon oxide was changed to 1.00 g.

(Comparative Example 5)
10.0 g of 20% nafion solution (trademark, manufactured by Du Pont), 2.0 g of ion-exchanged water, and 2.0 g of 1-methoxy-2-propanol were mixed with 20.0 g of 10% PVA (polyvinyl alcohol). An electrolyte membrane was produced in the same manner as in Example 3 except that the mixture was changed to a mixture of an aqueous solution and 2.0 g of ethanol.

  The proton conductive polymer contained in the electrolyte membrane of this comparative example does not contain sulfonic acid groups.

  For the electrolyte membranes of Examples 2 to 17 and Comparative Examples 1 to 5, the atomic ratio (M2 / M1), the specific surface area, and the solid acidity in the proton conductive inorganic oxide were determined by the same method as in Example 1. . The results obtained are summarized in Table 1 below.

Further, for the electrolyte membranes of Examples 2 to 17 and Comparative Examples 1 to 5, the weight ratio (W) of the proton conductive inorganic oxide containing silicon oxide (SA + SiO ₂ ) and the proton conductive organic polymer binder (P) _{SA + SiO 2} / W _P ), and the weight ratio (W _{SiO 2} / W _SA ) between the silicon oxide particles (SiO ₂ ) and the proton conductive inorganic oxide (SA) are summarized in Table 2 below.

  For the electrolyte membranes of Examples 1 to 17 and Comparative Examples 1 to 5, methanol permeability and conductivity were determined.

  Methanol permeability was measured by the following method. First, an H-type cell was used to partition between two glass containers kept at 25 ° C. with an electrolyte membrane, one side containing pure water and the other containing 3M aqueous methanol solution.

When time elapses, methanol permeates the pure water side and the methanol concentration increases. The concentration is measured every 4 minutes using gas chromatography, and the permeability is obtained from the gradient of concentration increase. Measure the permeability of Nafion 112 membrane (trademark, manufactured by Dupont) and use it as a reference. For the proton conductivity of each synthetic membrane, a value normalized by the characteristic value of nafion 112 was obtained. The methanol permeability of the Nafion 112 membrane is 3.0 μmol / min / cm ² as a measured value.

The results obtained are summarized in Table 3 below.
The conductivity is measured by the following method. A constant current (0.1 A) is passed through a sulfuric acid aqueous solution (1 mol / l) using a platinum electrode so that H ⁺ flows between the electrodes. When an electrolyte membrane is sandwiched between the electrodes, H ⁺ flows through the membrane, causing a voltage drop. By measuring this potential difference with a calomel electrode arranged on the membrane surface, a resistance value can be obtained.

Actually, the state where the film is not present and the state where the film is present are measured, and the resistance value is obtained from the difference. A Nafion 112 membrane was measured as a reference. A Nafion 112 membrane was measured as a reference. For the proton conductivity of each synthetic membrane, the values obtained by normalizing with the characteristic values of nafion 112 were obtained. The results obtained are summarized in Table 3 below.

  As shown in Table 3 above, both proton conductivity and methanol permeability change greatly, making it relatively difficult to evaluate membrane characteristics. Therefore, in order to clarify the relative methanol permeability of the synthesized electrolyte membrane, the methanol permeability (α) normalized by proton conductivity is shown in Table 3. α = (Methanol permeability normalized by nafion 112) ÷ (proton conductivity normalized by nafion 112).

  This α value indicates the methanol permeability per proton conductivity. In the case of nafion 112, α = 1, and the lower the α value, the more the permeation of methanol is suppressed. As shown in Table 3, since the α values of the electrolyte membranes of the examples were smaller than 1, it was confirmed that the methanol permeability per proton conductivity was suppressed from nafion 112.

Next, MEA was produced using each electrolyte membrane. First, an anode electrode and a cathode electrode were prepared by the following method.
Carbon paper (TGP-H-120, manufactured by Toray Industries, Inc., 3 × 4 cm ² ) in which 55 mg of about 42% of RuPt supported CNF catalyst and about RuPt42% of supported carbon (Printex25) are dispersed in water and water-repellent treated with 10% PTFE dispersion ) And suction filtered to form a catalyst layer.

After drying, it was impregnated with a 4% nafion solution for 2 minutes under reduced pressure, and then impregnated with a 6% nafion solution for 3 minutes. The excess nafion solution was absorbed on the filter paper and dried at room temperature to obtain an anode electrode (A-1). The amount of catalyst in the obtained anode electrode was about 3.6 mg / cm ² in terms of the amount of PtRu.
Meanwhile, in a 50 mL plastic container with a lid containing zirconia balls 10φ, 50 g, 5φ, and 25 g, 2.0 g of carbon (Ketjen) carrying about 70% Pt, 2.0 g of water, 8.0 g of methoxypropanol, and 20% Nafion solution. The mixture was mixed in the order of 0 g, and dispersed with a table-top ball mill for 6 hours to obtain a catalyst slurry.

Carbon paper (manufactured by Toray, 090, 20 × 10 cm ² ) treated with water repellent treatment with 20% PTFE dispersion was prepared. To 1.0 g of Denka black (FX-35) and 1.0 g of 54% FEP dispersion, 8 g of ion-exchanged water and 8 g of 2-propanol were added. This was dispersed with a paint shaker for 2 hours to prepare a slurry for a porous layer. The obtained slurry for porous layer was applied to the above-mentioned carbon paper with a flat coater (about 100 μm gap), and fired at 340 ° C. for 1 hour in a nitrogen atmosphere to form a porous layer (MPL) of about 30 μm.

On the porous membrane, the catalyst slurry was applied using a flat coater (about 400 μm gap) and dried at room temperature for a whole day and night. This was cut into 12 cm ² and used as a cathode electrode (C-1). The amount of cathode catalyst in the obtained cathode electrode was about 2.0 mg / cm ² in terms of Pt amount.

In preparing the MEA, first, the anode and the cathode were boiled with a hot sulfuric acid aqueous solution (water / concentrated sulfuric acid = 2/1 by weight) for 1 hour, and then the sulfuric acid was removed by washing the electrode with boiling water. Next, a Nafion 112 membrane subjected to protonation treatment was sandwiched between the two electrodes obtained by washing with running water, and thermocompression bonded under hot pressing conditions of 125 ^° C. for 5 minutes at 30 kg / cm ² to prepare an MEA.

  An MEA was produced by the same method as described above except that the nafion membrane was changed to the electrolyte membranes of Examples 1 to 17 and Comparative Examples 1 to 5.

The power generation characteristics of each MEA were evaluated using a single cell of an active DMFC fuel cell. As the fuel, a 1M methanol aqueous solution was used, the liquid feeding amount was 0.8 ml / min, the air feeding amount was 120 ml / min, and the cell temperature was 70 ° C. The results are shown in Table 4 below in terms of voltage (V) at a current density of 150 mA / cm ² .

Furthermore, the power generation characteristics of each MEA were evaluated using a passive DMFC standard cell. In the standard cell, vaporized pure methanol is supplied to the anode, and air is supplied to the cathode using convection that occurs spontaneously. The maximum power generation density is summarized in Table 4 below.

As shown in Table 4 above, when the MEA of the example is applied to an active DMFC fuel cell, a voltage of 0.385 V is obtained at the minimum and a voltage as high as 0.42 V is obtained. When applied to a passive DMFC, the maximum output reaches 26 mW / cm ² . It can be seen that in these examples, methanol crossover was suppressed.

  On the other hand, in the case of the MEA of the comparative example, when applied to both active type and passive type DMFCs, it is clear that methanol crossover cannot be suppressed and power generation characteristics are inferior. It is shown.

  Note that the present invention is not limited to the above-described embodiments as they are, and can be embodied by modifying the components without departing from the scope of the invention in the implementation stage. Various inventions can be formed by appropriately combining a plurality of constituent elements disclosed in the embodiments. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, constituent elements over different embodiments may be appropriately combined.

The schematic diagram of the single cell of the fuel cell concerning one Embodiment. The schematic diagram of the single cell of the fuel cell concerning other embodiments.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Oxidizer electrode; 2 ... Electrolyte membrane; 3 ... Fuel electrode; 4 ... Sealing material; 5 ... Sealing material 6 ... Oxidant channel; 7 ... Oxidant channel plate; 11 ... Current collector; 11 ... Current collector; 12 ... Heater; 13 ... Heater 21 ... Oxidant electrode; 22 ... Electrolyte membrane; 23 ... Fuel electrode; 24 ... Electromotive part 25 ... Fuel penetration part; 27 ... Anode separator 28 ... Separator; 29 ... Oxidant gas supply port; 30 ... Oxidant gas outlet 31 ... Anode product gas outlet

Claims (5)

A proton conducting membrane comprising a proton conducting polymer and a proton conducting inorganic oxide,
The proton conducting polymer has a sulfonic acid group and is blended with a weight W _p .
The proton conductive inorganic oxide has silicon oxide supported on the surface, and is blended with a weight W _{SA + SiO 2} .
A proton conductive membrane characterized in that the weight ratio (W _{SA + SiO 2} / W _P ) is in the range of 0.03 to 0.43.   The silicon oxide is supported on the surface of the proton conductive inorganic oxide at a weight of 0.1 to 0.5 times the weight of the proton conductive inorganic oxide. The proton conductive membrane as described.   The proton conductive inorganic oxide includes an oxide support containing at least one first element (M1) selected from the group consisting of Ti, Zr and Sn, and W supported on the surface of the oxide support, An oxide particle containing at least one second element (M2) selected from the group consisting of Mo and V, and an atomic ratio of the second element to the first element (atom of M2 3. The proton conductive membrane according to claim 1, wherein the number / number of atoms of M1 is 0.0001 or more and 1 or less. A membrane electrode assembly comprising a fuel electrode, an oxidant electrode, and an electrolyte membrane disposed between the fuel electrode and the oxidant electrode,
The membrane electrode assembly, wherein the electrolyte membrane includes the proton conductive membrane according to any one of claims 1 to 3.   A fuel cell comprising the membrane electrode assembly according to claim 4.

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