JPH04218267A - Solid electrolyte type fuel cell - Google Patents

Abstract

PURPOSE:To realize an operating temperature of 200 deg.C or more and enable the application for example, to an on-site fuel cell by maintaining sufficiently excellent characteristics such as high output density and compact structure possessed by a solid electrolyte type fuel cell. CONSTITUTION:An ion conductive solid electrolyte layer 1 is sandwiched between a pair of gas diffusing electrodes 2 and 3 having a porous catalytic layer. The ion conductive solid electrolyte layer 1 is constituted of an inorganic matrix which is filled with ion exchange resin and consists substantially of electronically non-conductive SiC, and further of an inorganic matrix which is substantially electronically non-conductive and consists of proton conductive NH4NbWO6.

Description

[Detailed description of the invention]

[Object of the invention]

0002

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel cell having an ionically conductive solid electrolyte layer.

0003

2. Description of the Related Art In recent years, fuel cells have attracted attention as highly efficient energy conversion devices. In general, a fuel cell forms a unit cell by sandwiching an electrolyte layer containing ionic species that contribute to electrode reactions between two types of electrodes, positive and negative, that can exchange electrons without being altered by electrode reactions and that allow the transfer of reactants. However, it is constructed by stacking a plurality of these unit cells with a current collector plate in between. Since the above-mentioned electrode provides a place where an electromotive reaction occurs, it is usually made of a porous material and is used as a catalytic electrode containing a catalyst that contributes to the electromotive reaction.

The flow of the reaction system in such a fuel cell differs depending on whether the ion species is acidic or alkaline. For example, in the case of acidity, the reaction proceeds according to the flow shown below, and the product ( water) is produced.

[0005]

[Chemical formula 1]

By the way, in the above-mentioned fuel cell, the electrolyte layer is made of a proton-conducting solid polymer electrolyte (So
Fuel cells (hereinafter referred to as PE fuel cells) with a lid polymer electrolyte (PE fuel cell) have a compact structure, high output density, and can be operated with a simple system, so they are used as mobile power sources for space applications and vehicles. It is attracting attention as

[0007]

[Problems to be Solved by the Invention] However, in the above-mentioned PE fuel cell, the ion-conducting solid electrolyte layer is an organic polymer membrane (ion exchange resin membrane), so the operating temperature of the battery is high. The drawback was that it could only be heated to about 100°C.

On the other hand, the development of on-site fuel cells that can be applied as a cogeneration system that recovers and utilizes the exhaust heat generated during power generation by fuel cells is progressing, but the operation of an absorption chiller is Considering this, it is desirable that the exhaust heat temperature be 170°C or higher. For this reason, the operating temperature of fuel cells must be approximately 200°C or higher, and currently, phosphoric acid fuel cells are being developed primarily.

[0009] When attempting to apply a PE fuel cell to such an on-site fuel cell, as mentioned above, the operating temperature of the PE fuel cell should be approximately 100°C, taking into account deterioration (decomposition) of the electrolyte layer, etc. Currently, it cannot be applied to on-site fuel cells that require an operating temperature of 200°C or higher. Therefore, it is strongly desired to enable the application of PE fuel cells with excellent characteristics (compact structure, high output density, and can be operated with a simple system) in on-site fuel cells as well. There is.

[0010] The present invention was made to address these problems, and it is possible to increase the operating temperature to 200°C or higher while sufficiently maintaining the excellent characteristics of the PE fuel cell described above. The purpose of this research is to provide a solid oxide fuel cell.

[Configuration of the invention]

0012

[Means for Solving the Problems] That is, the solid oxide fuel cell of the present invention comprises a pair of gas diffusion electrodes having a porous catalyst layer, and an ion conductive solid electrolyte layer sandwiched between the pair of gas diffusion electrodes. In the solid electrolyte fuel cell comprising:
It is characterized by consisting of an inorganic matrix filled with ion exchange resin.

The ion-conducting solid electrolyte layer of the present invention has an ion-exchange resin filled in a substantially non-electron-conducting inorganic matrix. As the above-mentioned ion exchange resin, various kinds of resins that are normally used as ion exchange resin membranes in various electrochemical devices (fuel cells, water electrolyzers, salt electrolyzers, etc.) can be used, and they have alkali resistance, Those with high acid resistance and heat resistance are preferred. Among them, ion exchange resins with fluorine-containing polymer skeletons,
For example, perfluorocarbon sulfonic acid resin is suitable.

Further, as the inorganic matrix filled with the above-mentioned ion exchange resin, a porous body having a porosity of 50% or more and having heat resistance and chemical resistance is used. Specifically, a substantially non-electron conductive ceramic material is used. Green compact using fine powder,
Examples include a sintered body and a bonded sheet made of resin. As the ceramic fine powder, Al2O3,
Examples include ZrO2, SiC, LiAlO2, and the like. Also, when considering the output of the fuel cell, NH4 N
Pyrochlore compounds such as bWO6, NH4TaWO6, α-Zr(HPO4)2・2H2O
, α-Zr(HPO4) 2 ・H2O, α
- α-ZrP compounds such as [Zr(PO4)2]H2/H2O, NH4-β-Al2O
3, NH4-β''-Al2O3, N
2H6SO4, N(CH3)4HSO4
It is preferable to use a ceramic material which has proton conductivity and is substantially non-electron conductive.

[0015] As a method of filling the above-mentioned inorganic matrix with an ion exchange resin, it is common and simple to turn the ion exchange resin into a solution and vacuum impregnate it. Further, when a green compact of fine ceramic powder is used as the inorganic matrix, it can be obtained by compression molding a mixture of fine ceramic powder and ion exchange resin. In this case, the ion exchange resin acts as a binder, and a material with sufficient strength for practical use can be obtained. Furthermore, a flexible sheet can be obtained by spreading a slurry containing fine ceramic powder, an ion exchange resin, and an organic solvent using a doctor blade and then drying the slurry. Further, in order to impart flexibility to the sheet, heat-resistant resins such as polyimide resin, polysulfone resin, polyphenylene sulfide resin, and fluororesin may be mixed and used. At this time, the amount of the heat-resistant resin added is preferably about 10% by volume or less based on the ion exchange resin so as not to inhibit the proton conduction path. Furthermore, when this ion-conductive solid electrolyte layer is integrated with a gas diffusion electrode, a material having proton conductivity and heat resistance may be interposed to improve compatibility between the two.

[0016]

[Operation] In the solid electrolyte fuel cell of the present invention, the ion exchange resin, which is an ion conductor, is stabilized by being filled in an inorganic matrix that has heat resistance and chemical resistance. The inorganic matrix is responsible for the main functions such as preventing short circuits between positive and negative electrodes, maintaining a constant distance, and preventing cross-mixing of oxidant gas and fuel gas, while ion exchange resins mainly have only ionic conductivity. Since it only needs to be carried, it can be operated at relatively high temperatures. Therefore, it is possible to operate at a temperature of 200° C. or higher, for example. Furthermore, by using a material with proton conductivity as the inorganic matrix, the electrolyte layer itself, which is a mixture of the inorganic matrix and ion exchange resin, is responsible for ionic conductivity, so it is expected that the battery output will be improved.

[0017]

[Embodiments] Hereinafter, embodiments of the solid oxide fuel cell of the present invention will be described with reference to the drawings.

FIG. 1 is a sectional view showing essential parts of a solid oxide fuel cell according to an embodiment of the present invention. In the same figure, 1
is an ionically conductive solid electrolyte layer. This ion-conductive solid electrolyte layer 1 is made of, for example, an inorganic matrix such as a porous SiC sintered body or a SiC powder compact, or an N
It has an inorganic matrix with proton conductivity such as H4 NbWO6 sintered body or NH4 NbWO6 green compact, and within these inorganic matrices, protons such as perfluorocarbon sulfonic acid resin Nafion (trade name, manufactured by DuPont) etc. It is filled with conductive ion exchange resin.

On both surfaces of the solid electrolyte layer 1, (-
) side catalyst electrode 2 and (+) side catalyst electrode 3 are integrally formed, and constitute a unit cell 4. These catalyst electrodes 2 and 3 are gas diffusion electrodes in a porous state, and have the functions of both a porous catalyst layer and a gas diffusion layer. These catalyst electrodes 2 and 3 are composed of a porous body in which conductive fine particles, such as carbon fine particles, carrying a catalyst such as platinum, palladium, or an alloy thereof are held by a hydrophobic resin binder such as polytetrafluoroethylene. ing.

Further, on the other surface of the (-) side catalyst electrode 2, a conductive material, such as carbon, is formed with grooves 6a, which serve as passages for fuel gas, such as hydrogen gas, through a porous carbon support 5. A current collecting plate 6 consisting of the following is arranged. Further, on the other surface of the (+) side catalyst electrode 3, a conductive material, such as carbon, is formed with grooves 8a, which serve as passages for an oxidizing gas, such as oxygen gas, through a porous conductive water-repellent layer 7. A current collecting plate 8 consisting of the following is arranged. Furthermore, when an oxidant gas is supplied to the (+) side catalyst electrode 3, reaction products such as water are generated on the (+) side catalyst electrode 3, so if necessary, a passage for moving the electrolyte and liquid reaction products may be formed. Wick 9 becomes
It is formed in a groove 8a provided in the current collector plate 8 on the (+) side catalyst electrode 3 side.

A fuel cell unit 10 is constituted by the solid electrolyte layer 1, (+) side and (-) side catalyst electrodes 2, 3, current collector plates 6, 8, etc. In the figure, reference numeral 11 denotes a cooling medium passage for controlling the operating temperature of the cells when the fuel cell units 10 are stacked in series to form a stack.

Next, a specific example of the solid oxide fuel cell having the above structure will be explained.

Example 1 First, S with a porosity of 50% was used as an inorganic matrix.
An iC sintered body was prepared. Next, in this SiC sintered body, a Nafion solution (Nafion 117, which is a solution of Nafion 117 (trade name, manufactured by DuPont), which is one of the perfluorocarbon sulfonic acid resins, was dissolved in a mixed solvent of lower alcohol and water. Approximately 5% by weight
was impregnated by a vacuum impregnation method to obtain the ion conductive solid electrolyte layer 1 according to the present invention. The conductivity of the obtained ion-conductive solid electrolyte layer is shown in FIG. 2 together with Nafion. As is clear from Fig. 2, the above Nafion is SiC
The solid electrolyte layer impregnated into the sintered body showed stable ionic conductivity even at temperatures above 200°C.

Next, 60 parts by weight of carbon black to which 10% by weight of platinum as a catalyst was added and polytetrafluoroethylene resin as a hydrophobic resin binder were mixed in a dispersion of 4 parts by weight.
About 10 times as much water as this dispersion was added to 0 parts by weight, and the mixture was thoroughly mixed, filtered, and dried to uniformly mix the hydrophobic resin binder and the catalyst-supported carbon particles. A mixture was obtained. Next, the above mixture was further sufficiently kneaded to fiberize the polytetrafluoroethylene resin to produce a rice cake-like product having a rice cake shape as a whole. Next, this cake-like material was formed into a sheet using a roller to produce a porous catalyst layer sheet. Thereafter, this catalyst layer sheet was heat treated in nitrogen gas at 320°C to obtain a gas diffusion electrode.

[0025] The above-described Nafion solution was further coated on the gas diffusion electrode thus obtained to contain it, and then used as the (+) side and (-) side catalyst electrodes 2 and 3. An ion conductive solid electrolyte layer 1 in which the above-mentioned Nafion is impregnated into a SiC sintered body is sandwiched between these two catalyst electrodes 2 and 3, and the temperature is 120°C to 130°C.
An electrode/electrolyte layer composite was obtained by hot pressing and integrating under a pressure of 60 kg/cm2. The electrode/electrolyte layer composite thus obtained was used as a unit cell 4 to assemble a fuel cell having the above configuration.

In addition, as a comparison with the present invention, an electrode/electrolyte layer composite (Comparative Example 1) was prepared in the same manner as in Example 1 except that an ordinary Nafion membrane was used for the ion-conductive solid electrolyte layer 1. A fuel cell was assembled in the same manner as in Example 1 using the following.

[0027] In order to evaluate the fuel cell characteristics of these Example 1 and Comparative Example 1, operational tests were conducted for each. The test conditions were: temperature 200°C, pressure 5 atm, fuel gas/hydrogen, oxidant gas/air, current density 400 mA.
/cm2. The results are shown in FIG. 3 as a change in cell voltage over time.

As is clear from FIG. 3, the fuel cell according to Example 1 has superior life characteristics compared to the fuel cell according to Comparative Example 1, and can be stably operated at an operating temperature of 200°C. I understand. This is because the solid electrolyte layer 1 uses an ion-conducting solid electrolyte layer stabilized by filling an ion-exchange resin, which is an ion conductor, into an inorganic matrix that has heat resistance and chemical resistance. The heat resistance of the layer has been improved, and operation is now possible even at temperatures of 200°C.

Example 2 First, SiC powder with an average particle size of 5 μm and Example 1 were prepared.
The Nafion solution used in the above was mixed at a weight ratio of 3:2 (Nafion as a solid weight), and this mixture was formed into a sheet shape, and then heated at a temperature of 120°C to 130°C.
C. and a pressure of 300 kg/cm2 to obtain an ion conductive solid electrolyte layer 1 according to the present invention.

Next, the ion conductive solid electrolyte layer 1 was prepared in the same manner as in Example 1, and two catalyst electrodes 2 and 3 were prepared.
An electrode/electrolyte layer composite was obtained by sandwiching the electrode and electrolyte layer composite by hot pressing and integrating under the same conditions as in Example 1. Then, using this electrode/electrolyte layer composite as the unit cell 4, a fuel cell was assembled in the same manner as in Example 1. When the characteristics of the fuel cell according to Example 2 were evaluated under the same conditions as in Example 1, excellent characteristics almost equivalent to those of the fuel cell of Example 1 were obtained.

Note that when an unsintered green compact is used as the inorganic matrix as in Example 2,
The ion exchange resin present in the matrix gives a little fluidity to the electrolyte layer, so it absorbs the unevenness of the surfaces of the two porous carbon supports 5 that sandwich the unit cell 4, and creates a gap between the unit cell and the porous carbon. In addition to improving the contact, it also shows the effect of alleviating the difference in thermal expansion coefficient between the porous carbon plate and the unit cell, as well as the thermal stress caused by the temperature distribution in the planar direction.

Example 3 To 100 parts by weight of the homogeneous mixture of the hydrophobic resin binder and catalyst-supported carbon fine particles produced in Example 1, 60 parts by weight of ammonium hydrogen carbonate as a pore-forming agent was further added and the mixture was uniformly mixed. mixed with. Next, a catalyst layer sheet was prepared using this mixture in the same manner as in Example 1, and this catalyst layer sheet was once heat-treated at 100°C to vaporize the pore-forming agent, and then heated in nitrogen gas at 320°C. A gas diffusion electrode was obtained by heat treatment.

[0033] Using the gas diffusion electrode thus obtained, an electrode/electrolyte layer composite was prepared under the same conditions as in Example 1, and a fuel cell was assembled in the same manner. When the characteristics of the fuel cell thus produced were evaluated under the same conditions as in Example 1, almost the same excellent characteristics as the fuel cell of Example 1 were obtained.

Example 4 An NH4NbWO6 sintered body with a porosity of 50% was prepared as an inorganic matrix having proton conductivity. Next, about 5% by weight of the same Nafion solution as in Example 1 was impregnated into this NH4NbWO6 sintered body by a vacuum impregnation method to obtain the ion conductive solid electrolyte layer 1 according to the present invention. The conductivity of the obtained ion-conductive solid electrolyte layer is shown in FIG. 4 together with Nafion. As is clear from FIG. 4, the solid electrolyte layer in which Nafion was impregnated into the NH4NbWO6 sintered body exhibited good and stable ionic conductivity even at temperatures above 200°C. Furthermore, it can be seen that, compared to Example 1 (FIG. 2), Example 4 (FIG. 4) has better ionic conductivity at temperatures of 200° C. or higher.

Next, the above Nafion was converted into NH4NbWO
6 Ion conductive solid electrolyte layer 1 impregnated into sintered body
Two catalyst electrodes 2 were prepared in the same manner as in Example 1.
, 3 and hot-pressed and integrated under the same conditions as in Example 1 to prepare an electrode/electrolyte layer composite, and then use this electrode/electrolyte layer composite as a unit cell to assemble a fuel cell. Ta. The operational test results of this fuel cell are shown in FIG. The test method was the same as in Example 1.

As is clear from FIG. 5, the fuel cell according to Example 4 has superior life characteristics compared to the fuel cell according to Comparative Example 1, and operates stably and with good output at an operating temperature of 200°C. It turns out that it is possible to do so. This is because the solid electrolyte layer 1 is an ion-conductive solid electrolyte layer stabilized by filling an ion-exchange resin into an inorganic matrix that has heat resistance, chemical resistance, and proton conductivity. The heat resistance of the electrolyte layer is improved, and good proton conductivity can be imparted, making it possible to operate with good output even at 200°C. Example 5 First, NH4NbWO6 powder with an average particle size of 5 μm and the Nafion solution used in Example 1 were mixed at a weight ratio of 3:2 (Nafion is the solid weight), and this mixture was formed into a sheet. After forming into a shape, the temperature is 12
Hot press molding was carried out under conditions of 0°C to 130°C and a pressure of 300 kg/cm 2 to obtain an ion conductive solid electrolyte layer 1 according to the present invention.

Next, the ion conductive solid electrolyte layer 1 was prepared in the same manner as in Example 1, and two catalyst electrodes 2 and 3 were prepared.
An electrode/electrolyte layer composite was obtained by sandwiching the electrode and electrolyte layer composite by hot pressing and integrating under the same conditions as in Example 1. Then, a fuel cell was assembled in the same manner as in Example 4 using this electrode/electrolyte layer composite as the unit cell 4. When the characteristics of the fuel cell according to Example 5 were evaluated under the same conditions as in Example 4, excellent characteristics almost equivalent to those of the fuel cell of Example 4 were obtained.

Example 6 Using a gas diffusion electrode prepared in the same manner as in Example 3,
An electrode/electrolyte layer composite was produced under the same conditions as in Example 4,
A fuel cell was assembled in the same way. When the characteristics of the fuel cell thus produced were evaluated under the same conditions as in Example 4, almost the same excellent characteristics as the fuel cell of Example 4 were obtained.

[0039] Although platinum was used as the catalyst in each of the above examples, Pd, Pt-Pd alloy, Pt-Cr alloy, Pt-Cr-Co alloy, Pt-V alloy, Pt-M
Similar effects were obtained with systems using n alloys, Pt-Mo alloys, and the like. In addition, the cooling medium passage 1 in FIG.
1 may be set to one for multiple cells instead of for each cell. Examples of the cooling medium include water, steam, and organic solvents that do not have ion conductivity, and methanol vapor may also be passed. In the case of methanol, its reforming reaction (
This makes it possible to remove heat using an endothermic reaction. Furthermore, the material of the current collector plates 6 and 8 may be either carbon or metal.

[0040]

As explained above, according to the solid electrolyte fuel cell of the present invention, the ion exchange resin, which is an ion conductor, is used as an ion conductive solid electrolyte layer in an inorganic matrix having heat resistance and chemical resistance. Since a stabilized electrolyte layer is used, the heat resistance of the electrolyte layer is improved by the inorganic matrix forming the skeleton of the electrolyte layer, and operation is possible even at temperatures of 200°C.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing essential parts of a fuel cell according to an embodiment of the present invention.

FIG. 2 is a diagram showing ion conductive characteristics of an ion conductive solid electrolyte layer used in a fuel cell according to an example of the present invention.

FIG. 3 is a diagram illustrating cell characteristics of a fuel cell according to an embodiment of the present invention in comparison with a conventional example.

FIG. 4 is a diagram showing ion conductive characteristics of an ion conductive solid electrolyte layer used in a fuel cell according to another example of the present invention.

FIG. 5 is a diagram showing cell characteristics of a fuel cell according to another embodiment of the present invention in comparison with a conventional example.

[Explanation of symbols]

1...Ion conductive solid electrolyte layer 2... (-) side catalyst electrode 3... (+) side catalyst electrode 4...Battery 5...Porous carbon support 6, 8... Current collector plate 7...Porous conductive water repellent layer

Claims (2)

[Claims] 1. A solid oxide fuel cell comprising a pair of gas diffusion electrodes having a porous catalyst layer and an ion conductive solid electrolyte layer sandwiched between the pair of gas diffusion electrodes, wherein the ion conductive solid A solid electrolyte fuel cell characterized in that the electrolyte layer is composed of an inorganic matrix filled with an ion exchange resin. 2. The solid oxide fuel cell according to claim 1, wherein the inorganic matrix has proton conductivity.