Fuel cell

A fuel cell comprises: a cell plate (11; 110; 110A, 110B); an electroconductive gas separator (13; 130; 130A; 130B) which cooperates with the cell plate, to form a gas passage; and a holder member (15; 150; 150A; 150B) which holds a part of the cell plate. The cell plate includes a supporting body (37; 370; 370A; 370B), and a cell (39; 390; 390A; 390B) formed on the supporting body. The cell includes a solid electrolyte (43), a cathode substance layer (45) formed on one surface of the solid electrolyte, and an anode substance layer (41) formed on the other surface of the solid electrolyte.

TECHNICAL FIELD

The present invention relates to a fuel cell, and more particularly to a fuel cell including a solid electrolyte having one surface provided with a cathode substance and the other surface provided with an anode substance.

BACKGROUND ART

To ensure gas seal and electric connection in a solid electrolyte-type fuel cell (SOFC) having solid electrolyte layers, it has been proposed to prepare two kinds of catalyst layers in thick rectangular plate shapes and formed with gas passages except for peripheral portions thereof, to arrange the catalyst layers at both surfaces of each solid electrolyte layer, respectively, to arrange current collector layers at outer surfaces of the catalyst layers, respectively, to plurally stack such arranged structures so as to constitute a fuel cell stack, and to apply a large load to the fuel cell stack in the stacking direction thereof.

Particularly, because materials such as yttria-stabilized zirconia (YSZ) to be used as solid electrolyte layers are extremely brittle in SOFC which operates at high temperature, it has been proposed to adopt thick members as the solid electrolyte layers on the order of millimeter inclusive of associated neighboring members and in order to attain a strength against thermal stress.

U.S. Pat. No. 6,344,290 discloses a constitution to form the whole of fuel cell into a donut shape and to supply the gases through the central portions of the donut, so as to deal with thermal stresses. Concretely, at that region of the donut outside the central portions for supplying the gases, there are successively formed an anode substance layer, a solid electrolyte layer, and a cathode substance layer on a porous electric-conductor layer. Further, such structures are stacked via corrugated gas separators, respectively, to thereby constitute a fuel cell stack. It is further intended to ensure the electric connection of the whole of the fuel cell stack including electric-power generating regions having the anode substance layers, solid electrolyte layers and cathode substance layers, respectively, by applying a stacking directional pressure to the fuel cell stack.

DISCLOSURE OF INVENTION

However, the present inventors have studied the above-mentioned fuel cell stack and found that the pressure is applied to the whole of the fuel cell stack including the electric-power generating regions, and that these electric-power generating regions are further applied with uneven stresses by convex portions of the corrugations of the gas separators, thereby causing a possibility of affection on the brittle solid electrolyte layers. Particularly, in SOFC, such an affection is likely to become serious due to repeated high and low temperatures during operation.

The present invention has been carried out through such a study conducted by the present inventors, and it is therefore an object of the present invention to provide a fuel cell which particularly has a high-quality solid electrolyte layer and is capable of exhibiting and keeping a higher electric-power generating ability.

To achieve the above object, in one aspect, the fuel cell of the present invention comprises a cell plate provided with: a supporting body, and a cell formed on the supporting body, the cell including a solid electrolyte, a cathode substance layer formed on one surface of the solid electrolyte, and an anode substance layer formed on the other surface of the solid electrolyte; an electroconductive gas separator which cooperates with the cell plate, to form a gas passage; and a holder member which holds a part of the cell plate.

Other and further features, advantages, and benefits of the present invention will become more apparent from the following description taken in conjunction with the following drawings.

BEST MODE FOR CARRYING OUT THE INVENTION

There will be explained hereinafter fuel cells of the embodiments according to the present invention in detail with reference to the drawings.

First Embodiment

There will be firstly explained a fuel cell of a first embodiment according to the present invention in detail with reference toFIG. 1throughFIG. 11C.

FIG. 1is a perspective view of fuel cells (i.e., fuel cell stack) of this embodiment in a state accommodated within a casing.FIG. 2is a schematic II-II cross-sectional view of the fuel cell stack inFIG. 1, showing an inner structure of the stack viewed from a direction perpendicular to a stacking direction of the stack, so as to show a gas supplying conduit5and its associated constitution mainly at the right side and a gas exhausting conduit7and its associated constitution mainly at the left side.FIG. 3is a partially enlarged cross-sectional view of the fuel cell stack ofFIG. 2, enlargingly showing a cell plate and a gas separator in the stack, mainly, at an inner peripheral side and an outer peripheral side of the disk-like constitution thereof, while omitting intermediate portions of the cell plate and gas separator. Note, the up-and-down direction inFIG. 2is the stacking direction of the fuel cell stack.

FIG. 1shows representatively numbered one cell unit1functioning as a single fuel cell by itself and, as shown inFIG. 2, including a central opening, and multiple cell units1are stacked in the up-and-down direction (stacking direction) in a mutually electrically connected state to thereby constitute a fuel cell stack3. The fuel cell stack3exhibits a cylindrical shape as a whole, and is accommodated within a casing2. The casing2includes a main body portion2afor accommodating therein the fuel cell stack3, a fuel supplying portion2bfor supplying a fuel gas for electric-power generation, and a fuel exhausting portion2cfor exhausting the remainder of the fuel consumed for an electric-power generating reaction, and these portions2a,2b,2care integral with each other.

Concretely, the fuel cell stack3is fastened and clamped between a flange portion5aof the lower gas supplying conduit5and a flange portion7aof the upper gas exhausting conduit7by a fastening force applied between the flange portion5aand the flange portion7a. That is, after the flange portion5aof the gas supplying conduit5is attached to a bottom of the main body portion2aof the casing2while the flange portion7aof the gas exhausting conduit7is attached to a top portion of the main body portion2avia spring9, the fastening force is applied between the top and the bottom of the main body portion2aof the casing2, resulting in that cell units1of the fuel cell stack3are applied with a compressive force in the stacking direction by the spring9and are elastically held within the main body portion2aof the casing2.

As also enlargedly shown inFIG. 3, each cell unit1is constituted of: a cell plate11; an electroconductive gas separator13provided on the cell plate11; a holder member15for clamping and holding a part of the cell plate11from the above and bottom thereof. The holder member15is arranged through a central through-hole of the disk-like cell plate11. By fastening the holder members15of the cell units1between the flange portion5aof the gas supplying conduit5and the flange portion7aof the gas exhausting conduit7to clamp the holder members15therebetween while making the gas separators13intervened, respectively, the cell units1are held between the flange portion5aand flange portion7a. In other words, resultantly, the holder member15, which is a main portion where the fastening portion is applied, holds a part of the cell plate11and a part of the gas separator13, that is, inner periphery potions of cell plate11and the gas separator13while applying the compressive force due to the fastening force.

Formed between the cell plate11and gas separator13of each cell unit1is a gap which acts as a gas passage17and which is filled with a porous medium19(e.g. a medium of silver-made thin wires such as silver-made wool-like material) which is an electric conductor having a lower electrical resistance. The gas passage17is supplied with air as an oxidative gas (oxidizer gas) for electric-power generation, from the gas supplying conduit5and via air supplying channel21established throughout the center of stacked multiple holder members15. The remainder of the air consumed for the electric-power generating reaction is exhausted to the exterior, via air exhausting channel23established around the air supplying channel21and then via gas exhausting conduit7.

Meantime, defined between two cell units1neighboring in the up-and-down direction is a fuel gas passage25shown inFIG. 2. The fuel gas passage25is supplied with the fuel gas, which is hydrogen gas in this embodiment, as ambient gas from a conduit unit27, via fuel supplying portion2bconnected with the conduit unit27. The remainder of the fuel consumed for the electric-power generating reaction is exhausted to the conduit unit27, via fuel exhausting portion2cof the casing2connected with the conduit unit27.

The conduit unit27connected to the casing2comprises a fuel supplying conduit portion27aconnected to the fuel supplying portion2bof the casing2, a fuel exhausting conduit portion27bconnected to the fuel exhausting portion2cof the casing2, and a fuel circulating conduit portion27cfor connecting the fuel supplying conduit portion27aand fuel exhausting conduit portion27bwith each other.

Connected to the fuel supplying conduit portion27ais a fuel filing conduit29, at a position upstream of a joint of the fuel circulating conduit portion27cto the fuel supplying conduit portion27a. The exhausted fuel gas exhausted from an outlet33of the fuel exhausting conduit portion27bis treated in an exhaust gas treating system (not shown), and the treated fuel gas is returned to the fuel supplying conduit portion27avia its inlet35. The fuel circulating conduit portion27cis provided with a blower31for circulating the fuel gas from the fuel exhausting conduit portion27bto the fuel cell stack3via fuel supplying conduit portion27a.

Thus, the fuel cell stack3is supplied with the fuel gas from the fuel filing conduit29, with the exhausted fuel gas forcibly circulated by the blower31, and with the fuel gas treated by the exhaust gas treating system.

Incidentally, insofar as concerned with cooling of the center of the cell unit1where heat tends to be accumulated, the flow rate of the fuel gas to be forcibly circulated by the blower31is preferably as high as possible, so as to improve efficiencies of gas exchange, heat exchange and the like at the surface of cell unit1as well as the stability thereof. Practically, such a flow rate is preferably determined taking account of the stacking dimension between two neighboring cell units1and of a balance between an electric-power generating efficiency and an energy consumed therefor, because some energy is naturally consumed to attain such a flow rate.

Next, there will be explained hereinafter the cell plate11in each cell unit1.

As shown inFIGS. 2 and 3, the cell plate11comprises a porous metal plate37as a supporting body, and a cell39provided on one surface, i.e., on an upper surface of the porous metal plate37. The cell39is constituted by stacking an anode substance layer41, a solid oxide electrolyte layer (hereinafter simply called “solid electrolyte layer”)43and a cathode substance layer45, successively from the porous metal plate37side. The porous metal plate37has substantially the same thermal expansion coefficient as the solid electrolyte layer43.

As shown inFIG. 3, such three layers are provided with the anode substance layer41, solid electrolyte layer43and cathode substance layer45on the porous metal plate37are formed in a manner that the upper one is not protruded beyond an outer periphery of the lower one. Namely, the anode substance layer41is formed over substantially the whole of porous metal plate37, the solid electrolyte layer43is formed on the anode substance layer41in an area smaller than that of the anode substance layer41, and so is the cathode substance layer45relative to the solid electrolyte layer43.

FIG. 4Ais an IV-IV cross-sectional view of the porous metal plate37inFIG. 3viewed from the stacking direction, andFIG. 4Bis an IVB-IVB cross-sectional view of the plate inFIG. 4A.

As shown inFIG. 3throughFIG. 4B, the porous metal plate37is fixed, at its inner and outer peripheral sides, with annular bulk members47and49as gas-impermeable metal members, each being made of the same material and having substantially the same thermal expansion coefficient as the porous metal plate37.

Adhered onto the bulk members47and49are insulating ceramic plates51,53as insulating members by ceramic adhesives55,57, respectively. The insulating ceramic plates51,53and ceramic adhesives55,57have substantially the same thermal expansion coefficients as the bulk members47,49, and may be preferably based on zirconium oxide when the solid electrolyte layer43is made of YSZ.

The adhering interfaces of the ceramic adhesives55,57are closely contacted with the inside and outside peripheries of the cell39including the solid electrolyte layer43so as to cover the gas permeating areas along the inside and outside peripheries of the porous metal plate37, respectively, thereby ensuring a gas sealability. Note, the insulating ceramic plates51,53have mirror-polished upper surfaces, respectively.

Joined to the upper surface of the insulating ceramic plate53is an outer periphery of the gas separator13.

Although the ceramic adhesives55,57are necessary so as to airtightly seal the interior of the cell unit1such as the gas passage17by providing the gas separator13onto the cell plate11after mounting the holder member15to the cell plate11, extremely less usage amounts of adhesives are preferable. Instead of the ceramic adhesives55,57, it is possible to alternatively ultrasonic join the insulating ceramic plates51,53to the bulk members47,49, respectively, through brazing materials.

Next, there will be explained hereinafter the holder member15in each cell unit1.

FIG. 5is a top view of an upper electrode part59viewed from the above in the stacking direction.FIG. 6Ais a bottom view of the upper electrode part59viewed from the bottom in the stacking direction, andFIG. 6B,FIG. 6CandFIG. 6Dare a VIB-VIB cross-sectional view, a VIC-VIC cross-sectional view and a VID-VID cross-sectional view of the upper electrode part inFIG. 6A, respectively.FIG. 7is a top view of a lower electrode part61viewed from the above in the stacking direction.FIG. 8Ais a bottom view of the lower electrode part61viewed from the bottom in the stacking direction, andFIG. 8BandFIG. 8Care a VIIIB-VIIIB cross-sectional view and a VIIIC-VIIIC cross-sectional view of the lower electrode part inFIG. 8A, respectively.FIG. 9Ais a top view of an insulating part63viewed from the above in the stacking direction, andFIG. 9B,FIG. 9CandFIG. 9Dare an IXB-IXB cross-sectional view, an IXC-IXC cross-sectional view and an IXD-IXD cross-sectional view of the insulating part63inFIG. 9A, respectively. Note,FIGS. 6B through 6Dalso show the insulating part63, for better understanding of the positional alignment thereof. Similarly,FIGS. 9A through 9Dshow the lower electrode part61, for better understanding of the positional alignment thereof.

The holder member15is constituted of three members, i.e., the upper electrode part59as a first member shown inFIG. 5throughFIG. 6D, the lower electrode part61as a second member shown inFIG. 7throughFIG. 8C, and the insulating part63acting as an electrically insulative member shown inFIGS. 9A through 9Dfor interconnecting the upper and lower electrode parts59,61with each other in an electrically insulative manner. The upper and lower electrode parts59,61are to ensure the electric connections at the obverse and reverse sides of the cell plate11, respectively, while the insulating part63is to ensure the insulation between the upper and lower electrode parts59,61.

As shown inFIGS. 5 through 6D, the upper electrode part59is centrally formed with a central circular through-hole59a. This central through-hole59aconstitutes a part of the air supplying channel21shown inFIG. 2, and is communicated with gas flow-paths65.

The upper electrode part59has a bottom surface formed with a plurality of gas partitioning walls59bat equal circumferential intervals so as to be protruded toward the lower electrode part61.

Provided among gas partitioning walls59bare flat-plate portions59c, respectively. Alternately provided between and at the inner peripheral sides of the flat-plate portions59care side through-holes59dalong the circumferential direction. The side through-holes59dconstitute a part of the air exhausting channel23shown inFIG. 2. The side through-holes59dare communicated with gas flow-paths67, respectively. The gas partitioning walls59bseparate the gas flow-paths65communicating with the central through-hole59a, from the gas flow-paths67communicating with the side through-holes59d, respectively.

Formed on an upper surface of the upper electrode part59is an annular convex portion59eoutside the side through-holes59d. As shown inFIG. 2, the annular convex portion59eis fitted into a concave portion69aof the lower electrode part61of the neighboring upper cell unit1, while interposing an upward bent portion13aof the gas separator13therebetween. Concerning an annular convex portion59eof the upper electrode part59of the topmost cell unit1, it is fitted into a concave portion7bformed on a lower surface of the flange portion7aof the gas exhausting conduit7, while interposing a bent portion13aof the associated gas separator13therebetween.

Namely, the upper electrode part59is electrically connected to the associated gas separator13, and the gas separator13spreads between the annular convex portion59eand the concave portion7bor concave portion69a, thereby also ensuring the gas sealability.

Incidentally, preferably, the upper electrode part59is a metal having the same thermal expansion coefficient as the porous metal plate37.

As shown inFIGS. 7 through 8C, the lower electrode part61includes an electrode body69, and a ring71mounted on that outer peripheral side of the electrode body69away from the upper electrode part59. The electrode body69is formed with a circular central through-hole69baligned with the central through-hole59aof the upper electrode part59, and formed with multiple side through-holes69caround the central through-hole69band aligned with the side through-holes59d, respectively. The central through-hole69bconstitutes a part of the air supplying channel21shown inFIG. 2, while the side through-holes69cconstitute a part of the air exhausting channel23shown inFIG. 2.

The gas flow-paths65,67shown inFIG. 6are defined between the upper electrode part59and lower electrode part61while interposing therebetween an insulating part63to be described later in detail, by pressingly arranging the gas partitioning walls59bat the lower surface of the upper electrode part59toward positions between the side through-holes69cat the upper surface of the lower electrode part61, respectively, via insulating part63.

The ring71is incorporated into the cell unit1and pressed from a direction opposite to the upper electrode part59, so as to be held in a state where the inner peripheral portion of the cell unit1corresponding to the bulk member47shown inFIG. 3is positioned between the upper electrode part59and lower electrode part61. In this way, incorporation of the ring71separated from the electrode body69facilitates the assembling of the cell unit1.

Mutual contacting areas S of the ring71and electrode body69and of the ring71and bulk member47are mirror polished. Bringing the respective contacting areas S into the mirrored states in this way enables to realize a practically sufficient seal by virtue of surface joints, by pressing the contacting areas S by a pressure on the order of 100 MPa to 200 MPa. Further, since the sealing portions are not fixed at all, the contacting areas are allowed to correspondingly release stresses upon occurrence thereof, thereby avoiding affection of stresses and thereby improving the reliability.

Incidentally, the lower electrode part61is preferably a metal having a thermal expansion coefficient equivalent to that of the porous metal plate37.

As shown inFIGS. 9A through 9D, the insulating part63is formed with a circular central through-hole63ato be aligned with the central through-hole69bof the lower electrode part61. The central through-hole63aconstitutes a part of the air supplying channel21shown inFIG. 2. The insulating part63comprises a ring portion63bat an outer peripheral side positioned on the outer peripheral side of the electrode body69of the lower electrode part61as also shown inFIGS. 9B and 9D, and comprises radial portions63ccontacted with the gas partitioning walls59bof the upper electrode part59, respectively, as also shown inFIG. 6C.

Incidentally, the insulating part63preferably has a thermal expansion coefficient equivalent to those of the upper and lower electrode parts59,61.

As described above, the central through-holes59a,69b,63aof the upper and lower electrode parts59,61and insulating part63as well as the gas flow-paths65defined between the upper and lower electrode parts59,61via insulating part63, cooperatively constitute a gas supplying passage for supplying the gas (i.e., air for electric-power generation) to each gas passage17positioned between the associated cell plate11and gas separator13. Further, the side through-holes59d,69cof the upper and lower electrode parts59,61and the gas flow-paths67defined between the upper and lower electrode parts59,61via insulating part63(specifically, those portions of the insulating part63corresponding to the side through-holes59d,69c), cooperatively constitute a gas exhausting passage for exhausting the gas (i.e., the remainder of air after electric-power generation) from the gas passage17.

In the holder member15comprising the upper and lower electrode parts59,61and insulating part63, the three members are provided with the upper electrode part59, lower electrode part61and insulating part63except for the ring71of the lower electrode part61are previously joined to one another such as by brazing, thereafter the thus airtightly joined three members are incorporated with the cell plate11and gas separator13, and then the bulk member47at the inner peripheral edge is pressed by the ring71to thereby ensure the gas sealability.

Such a constitution of the holder member15brings about a freedom of mutual dimensions of the cell plate11and holder member15, and appropriate pressurization upon stacking allows the assembling capable of compensating for dimensional deviations such as in the thickness direction (i.e., stacking direction) of the cell plate11and holder member15.

Incidentally, it is of course unnecessary to separately provide the ring71such as when dimensional variances in the thickness direction are not required to be compensated for or the assembling of the holder member15can be performed simultaneously with the cell plate11and gas separator13, so that the holder member15may be then simply constituted of the only three members.

FIG. 10is a top view of the cell unit1viewed from the above in the stacking direction, in a state where a part of the gas separator13is cut away by approximately ¼. FIG.11A is an XIA-XIA cross-sectional view of the cell unit1inFIG. 10and shows a constitution for communicating the air exhausting channel23to each gas passage17via associated gas flow-paths67,FIG. 11Bis an XIB-XIB cross-sectional view of the cell unit inFIG. 10and shows a constitution of positions corresponding to the gas partitioning walls59bof the upper electrode part59, andFIG. 11Cis an XIC-XIC cross-sectional view of the cell unit1inFIG. 10and shows a constitution for communicating the air supplying channel21to each gas passage17via associated gas flow-paths65. Note, the wool material (porous medium)19is omitted inFIG. 10. Seen below the gas separator13are the upper electrode part59of the holder member15, and the anode substance layer41, cathode substance layer45, solid electrolyte layer43and anode substance layer41of the cell plate11, sequentially from the center side.

Next, there will be explained hereinafter an operation of the fuel cell stack3having the above constitution.

As shown inFIGS. 1 and 2, air as an oxidative gas is supplied from the lower gas supplying conduit5to the air supplying channel21within the fuel cell stack3, so that the supplied air is further fed to the gas passages17each accommodating therein the wool material (porous medium)19, respectively, via associated gas flow-paths65between these mutually opposed upper electrode parts59and lower electrode parts61, respectively.

Meanwhile, the fuel gas, that is, hydrogen gas as ambient gas is supplied from the fuel supplying conduit portion27aof the conduit unit27into the casing2accommodating the fuel cell stack3therein, so that the supplied hydrogen gas is fed from the periphery of the fuel cell stack3to the fuel gas passages25between cell plates11and gas separators13of the neighboring cell units1, respectively (inFIG. 2, the hydrogen gas is fed in a direction substantially perpendicular to the drawing plane).

In this way, electric-power generation is performed in the fuel cell stack3, by feeding air and fuel to one side and the other of each cell unit1, respectively.

Further, the air fed to each gas passage17is flowed out after an electric-power generating reaction, via associated gas flow-paths67into the air exhausting channel23, and to the exterior of the fuel cell stack3via gas exhausting conduit7.

Meanwhile, the exhaust gas of the fuel fed to the periphery of the fuel cell stack3is exhausted from the fuel exhausting portion2cto the fuel exhausting conduit portion27b, and then partially to the fuel circulating conduit portion27c, and partially through the outlet33to the exhaust gas treating system (not shown) for treating the exhaust gas. The treated gas is returned to the fuel supplying conduit portion27afrom the inlet35, and again supplied to the fuel cell stack3.

The following effects are exhibited by the fuel cell stack of this embodiment having the above constitution.

(1) Concerning each cell plate11in which the associated cell39is constituted to include the cathode substance layer45and anode substance layer41at one surface and the other of the solid electrolyte layer43, respectively, and in which the cell39is supported by one surface of the porous metal plate37acting as a supporting body, the associated holder member15holds a part of the cell plate11(corresponding to the bulk member47). Thus, the holding force by the holder member15never affects largely on the cell39including the solid electrolyte layer43, thereby allowing to restrict the affection on the solid electrolyte layer43and to prevent deterioration of the electric-power generating ability.

(2) It is unnecessary for the solid electrolyte layer43to have an excessive strength, thereby enabling to thin the cell39, so that both the heat capacity and weight thereof can be remarkably reduced.

(3) Concerning sealability, the fixing portion for the cell plate11is separated from the solid electrolyte layer43included in the electric-power generating region and is not placed at the solid electrolyte layer43and porous metal plate37which are relatively brittle, so that the affection of thermal expansion on the sealed portion of the cell plate11is remarkably reduced, thereby allowing to keep the gas sealability over a long period of time.

(4) By supplying a necessary and sufficient amount of air to the air supplying channel21through the respective holder members15, the air after consumption can be freely flowed out via air exhausting channel23, thereby remarkably simplifying the control. In the fuel cell constituted as a solid oxide electrolyte type, substantially no reaction products except for water are conveyed into the air side, so that the system can be simplified without affecting the environment and human body and without requiring a catalyst treatment of the exhaust gas.

(5) The gas flow at the fuel side is never contaminated with nitrogen which is existent within the exhaust gas at the air side, thereby allowing a limited flow rate of the fuel gas, so that the scale of exhaust gas treatment at the fuel side is extremely reduced, and the number of kinds of gases is reduced to allow a simplified system constitution.

(6) In the fuel cell stack3in the constitution of this embodiment, the output voltage of the most effective electric power obtainable from a single cell unit1is on the order of 1 V, thereby causing a possibility that the output voltage is largely affected by a contact resistance at electric connecting portions of the cell unit.

Thus, at those sites of each cell unit1where electric connecting surfaces are exposed to oxygen such as the surface of upper electrode part59of the holder member15and that surface of the gas separator13which is contacted with the surface of upper electrode part59in this embodiment, there are formed thin films made of silver such as by vapor deposition, which thin films are relatively soft and rarely form oxide films at surfaces of the thin films themselves even at high temperatures. In this way, the electric contact can be satisfactorily maintained.

Such thin films by vapor deposition of materials like silver which are soft and rarely form oxides even at high temperatures are not limited to the above-mentioned sites of course, and may be applied as a thin film F to at least one of surfaces of the above-mentioned joining areas S for achieving gas seal by surface joint utilizing mirror surfaces, to thereby fill up fine irregularities on the matrix surfaces of the mirror surface joints, thereby extremely enhancing the effects for improving the sealability and electrical joint of joining areas S.

Further, concerning the joint between the holder member15and gas separator13, it is selectable to join them by using a so-called diffusion bonding technique, other than the silver vapor deposition onto the surfaces of joining areas S. In the case of such a technique, substantially no stresses nor gas leak are caused particularly when both materials are the same, thereby improving the reliability.

Incidentally, in this embodiment, the outer shapes of the holder member15, cell plate11and gas separator13may be elliptical or polygonal (regular penta- or more polygons) in addition to circular (perfect circle). In this case, that opening of the cell plate11, through which the holder member15is arranged, is to have a shape corresponding to the outer shape of the holder member15. Further, it is preferable for the holder member15to fix the cell plate11and gas separator13at insides thereof excluding outer peripheries of the cell plate11and gas separator13, particularly at the gravity centers of the faces thereof. Moreover, there can be obtained the best balance for stresses when the above-mentioned outer shapes are perfect circles or regular penta- or more polygons, which are particularly suited for installation into vibratory vehicles.

Second Embodiment

Next, there will be described hereinafter a fuel cell of a second embodiment according to the present invention in detail, mainly with reference toFIG. 12. While the first embodiment has been constituted to exhaust the air as an oxidative gas from the gas supplying conduit5at the lower side to the gas exhausting conduit7at the upper side inFIG. 1, this second embodiment is mainly differentiated therefrom in that the air supplied to gas supplying holes73formed at the centers of holder members150is discharged from outer peripheral sides of cell units10. Thus, the second embodiment will be described by emphasizing such a difference, while using like reference numerals for the identical constitutions and appropriately omitting or simplifying the explanation thereof.

FIG. 12is a cross-sectional view of the fuel cell stack of this embodiment, showing a constitution exemplarily including two stages of cell units10.

As shown inFIG. 12, each cell unit10includes a cell plate110, a gas separator130and the holder member150, similarly to the first embodiment. Filled within a gas passage170defined between each cell plate110and the associated gas separator130is a wool material (porous medium)190, and so is a wool material (porous medium)77between cell units10, similar to the wool material190. Note, each cell plate110is shown in a simplified manner, as a combination of a porous metal plate370and a cell390.

Similarly to the first embodiment, each holder member150comprises an upper electrode part590, a lower electrode part610, and an insulating part630between both electrode parts590,610. Defined between the electrode parts590,610is a gas flow-path75for communicating the gas supplying hole73with the gas passage170, while the outer periphery of the cell plate110, i.e., the outer peripheral side of the gas passage170is not closed but opened to the exterior. The gas supplying hole73and gas flow-path75cooperatively constitute a gas supplying passage for supplying the gas to the associated gas passage170.

In the above constitution, the air as an oxidative gas is supplied to the gas supplying holes73formed at the centers of the holder members150, flowed through the gas flow-paths75and gas passages170, and then discharged from the outer peripheral side of the cell units10.

Meanwhile, hydrogen gas acting as a fuel gas is supplied as an ambient gas into the casing accommodating the fuel cell stack therein, similarly to the first embodiment.

Provided at an inner peripheral side of the porous metal plate370of each cell plate110is a bulk member470, and the portion of the cell plate110corresponding to the bulk member470is held by the associated holder member150.

Also in the constitution of this embodiment, part of each cell plate110is held by the associated holder member150, so that the holding force by the holder member150never largely affects on the associated cell390including its solid electrolyte layer, thereby allowing to exclude disadvantageous affection onto the solid electrolyte layer.

Further, each cell plate110has a fixed central portion and an outer peripheral side unfixed to the associated gas separator130, so that the cell plate110is noway applied with a disadvantageous radial stress, thereby providing higher resistances such as against stress and thermal shock, than the first embodiment.

Moreover, each wool material77to be inserted between cell units10is capable of absorbing that vibration of the gas separator130having its unfixed outer periphery which may be caused by the ambient gas flow. Additionally, electric connection resistances between respective cell units10can be also reduced by the associated wool materials77, respectively.

Incidentally, the wool materials77to be inserted between respective cell units10can be applied to the first embodiment, thereby reducing the electric connection resistances between respective cell units10.

Third Embodiment

Next, there will be described hereinafter a fuel cell of a third embodiment according to the present invention in detail, mainly with reference toFIG. 13. This third embodiment is mainly differentiated from the second embodiment in that the third embodiment is constituted such that hydrogen gas as a fuel gas is supplied to a fuel supplying channel79provided at a center of a holder member150A, then through a fuel gas passage250A under each cell plate110A, and then discharged from an outer peripheral side of a cell unit10A, similarly to air as an oxidative gas. Thus, the third embodiment will be described by emphasizing such a difference, while using like reference numerals for the identical constitutions and appropriately omitting or simplifying the explanation thereof.

FIG. 13is a cross-sectional view of the fuel cell stack of this embodiment, showing a constitution exemplarily including two stages of cell units10A.

As shown inFIG. 13, each cell unit10A includes a cell plate110A, a gas separator130A and a holder member150A, similarly to the first embodiment. Filled within a gas passage170A defined between each cell plate110A and the associated gas separator130A is a wool material (porous medium)190A, and so is a wool material (porous medium)77A between cell units10A, similar to the wool material190A. Note, each cell plate110A is shown in a simplified manner, as a combination of a porous metal plate370A and a cell390A.

Similarly to the first embodiment, each holder member150A comprises an upper electrode part590A, a lower electrode part610A, and an insulating part630A between both electrode parts590A,610A.

Defined between the electrode parts590A,610A is a gas flow-path83for communicating an air supplying path81with a gas passage170A, while the outer periphery of the cell plate110A, i.e., the outer peripheral side of the gas passage170A is not closed but opened to the exterior. Separately defined between the electrode parts590A,610A is a fuel gas flow-path85for communicating the fuel supplying channel79with the fuel gas passage250A, while the outer periphery of the gas separator130A, i.e., the outer peripheral side of the fuel gas passage250A is not closed but opened to the exterior.

The air supplying path81and gas flow-path83cooperatively constitute a first gas supplying passage for supplying air to the associated gas passage170A. Further, the fuel supplying channel79and fuel gas flow-path85cooperatively constitute a second gas supplying passage for supplying the hydrogen gas to the associated fuel gas passage250A.

In the above constitution, the hydrogen gas as a fuel gas is supplied through the fuel supplying channel79provided at the centers of holder members150A, flowed through fuel gas flow-paths85to each fuel gas passage250A defined between an upper side of the gas separator130A of one cell unit10A and a lower side of the upper cell plate110A, and then discharged from an outer periphery of the fuel gas passage250A.

Meanwhile, air as an oxidative gas is supplied through air supplying paths81provided outside the fuel supplying channel79, to the respective gas passages170A at upper sides of the cell plates110A, and then discharged from outer peripheries of the respective gas passages170A.

Provided at an inner peripheral side of each porous metal plate370A is a bulk member470A, and the portion of the cell plate110A corresponding to the bulk member470A is held by the associated holder member150A.

Also in the constitution of this embodiment, part of each cell plate110A is held by the associated holder member150A, so that the holding force by the holder member150A never largely affects on the associated cell390A including its solid electrolyte layer, thereby allowing to exclude disadvantageous affection onto the solid electrolyte layer.

Similarly to the second embodiment, it is enough to provide one gas separator130A for each cell unit10A, to thereby establish such a simplified structure that both of air and fuel gas required for electric-power generation by the fuel cell stack are allowed to be forcibly supplied from the central holder members150A, thereby facilitating the operational control concerning gas flow control.

Moreover, each wool material77A inserted between one cell plate110A and a gas separator130A of the neighboring cell unit10A allows to reduce the electric connection resistance between the cell units10A.

Fourth Embodiment

Next, there will be described hereinafter a fuel cell of a fourth embodiment according to the present invention in detail, mainly with reference toFIG. 14. This fourth embodiment is similar to the third embodiment in that the fourth embodiment is constituted such that hydrogen gas as a fuel gas is supplied to a fuel supplying channel79B provided at the centers of holder members150B, then through a fuel gas passage250B under each cell plate110B, and then discharged from an outer peripheral side of a cell unit10B similarly to air as an oxidative gas. However, the fourth embodiment is mainly differentiated from the third embodiment, in the provided number of gas separators130B. Thus, the fourth embodiment will be described by emphasizing such a difference, while using like reference numerals for the identical constitutions and appropriately omitting or simplifying the explanation thereof.

FIG. 14is a cross-sectional view of the fuel cell stack of the fourth embodiment, showing a constitution exemplarily including two stages of cell units10B.

As shown inFIG. 14, each cell unit10B includes a cell plate110B, gas separators130B and a holder member150B, similarly to the first embodiment. The gas separators130B is comprised of totally two gas separators provided at the topmost and lowermost of each cell unit10B, respectively. Filled within a gas passage170B defined between each cell plate110B and the associated one gas separator130B is a wool material (porous medium)190B, and so is a wool material (porous medium)77B between cell units10B, similar to the wool material190B. Note, each cell plate110B is shown in a simplified manner, as a combination of a porous metal plate370B and a cell390B.

Similarly to the first embodiment, each holder member150B comprises an upper electrode part590B, a lower electrode part610B, and an insulating part630B between both electrode parts590B,610B.

Defined between the electrode parts590B,610B is a gas flow-path83B for communicating an air supplying path81B with a gas passage170B, while the outer periphery of the cell plate110B, i.e., the outer peripheral side of the gas passage170B is not closed but opened to the exterior. Separately defined between the electrode parts590B,610B is a fuel gas flow-path85B for communicating the fuel supplying channel79B with the fuel gas passage250B, while the outer periphery of the gas separator130B, i.e., the outer peripheral side of the fuel gas passage250B is not closed but opened to the exterior.

The air supplying path81B and gas flow-path83B cooperatively constitute a first gas supplying passage for supplying air to the associated gas passage170B. Further, the fuel supplying channel79B and fuel gas flow-path85B cooperatively constitute a second gas supplying passage for supplying the hydrogen gas to the associated fuel gas passage250B provided under the cell plate110B.

In the above constitution, the hydrogen gas as a fuel gas is supplied through the fuel supplying channel79B provided at the centers of holder members150B, flowed through fuel gas flow-paths85B to fuel gas passages250B at lower sides of the cell plates110B, and then discharged from outer peripheries of the fuel gas passage250B.

Incidentally, air as an oxidative gas is supplied through air supplying paths81B provided outside the fuel supplying channel79B, to the gas passages170B at upper sides of the cell plates110B, and then discharged from outer peripheries of the respective gas passages170B.

Provided at an inner peripheral side of each porous metal plate370B is a bulk member470B, and the portion of the cell plate110B corresponding to the bulk member470B is held by the associated holder member150B.

Also in the constitution of this embodiment, part of each cell plate110B is held by the associated holder member150B, so that the holding force by the holder member150B never largely affects on the associated cell390B including its solid electrolyte layer, thereby allowing to exclude disadvantageous affection onto the solid electrolyte layer.

Further, the gas separators130B are provided at both surfaces of each cell plate110B, respectively, and the outer peripheral sides of the gas separators130B are not fixed, so that the cell plate110B is not applied with any stress except from the cell plate110B itself with the best balance as compared with the first through third embodiments, while achieving a well-balanced thermal conduction between the obverse and reverse sides of each cell plate110B.

Incidentally, in a case where the electrical joint between electric-power generating regions of neighboring cell units in the first embodiment can be alternatively ensured by providing the wool material (porous medium) of lower resistance described in the second through fourth embodiments, the ring71is unrequited and then it is possible to adopt such a constitution that the holder member itself is previously fabricated by integral formation from an electrically insulative material such as ceramics and that the gas separator is superposed onto such a holder member. Such a constitution enables to reduce the number of parts of each holder member, thereby achieving a reduced cost.

Further, in the fourth embodiment, the electrical joint between neighboring cell units10B shown inFIG. 14may also be achieved between gas separators130B themselves, and the holder member can also be fabricated by integral formation of ceramics in such a case.

The entire content of a Patent Application No. TOKUGAN 2002-374452 with a filing date of Dec. 25, 2002 in Japan is hereby incorporated by reference.

INDUSTRIAL APPLICABILITY

As described above, the fuel cell according to the present invention comprises: a cell plate provided with a supporting body, and a cell formed on the supporting body; an electroconductive gas separator which cooperates with the cell plate to define a gas passage; and a holder member holding a part of the cell plate. The cell includes a solid electrolyte, a cathode substance layer formed on one surface of the solid electrolyte, and an anode substance layer formed on the other surface of the solid electrolyte. According to such a constitution, the holding force by the holder member never acts largely on the cell including the solid electrolyte, thereby allowing to exclude disadvantageous affection onto the solid electrolyte, and enabling to realize a fuel cell of a higher reliability, so that the applicability can be expected widely including a fuel cell powered vehicle.