Fuel cell and fuel cell stack having a filter mechanism

A fuel gas supply channel connecting a fuel gas supply passage and a fuel gas inlet are provided in a separator, a channel lid member, and a circular disk member. A filter mechanism for filtering a fuel gas supplied from the fuel gas supply passage to a channel unit is provided in the fuel gas supply channel. The filter mechanism has a plurality of holes, and the cross sectional area of the opening of the hole is smaller than the cross sectional area of the opening of the fuel gas inlet.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a fuel cell formed by stacking an electrolyte electrode assembly and a pair of separators. The electrolyte electrode assembly includes an anode, a cathode, and an electrolyte interposed between the anode and the cathode. Further, the present invention relates to a fuel cell stack formed by stacking a plurality of the fuel cells.

2. Description of the Related Art

Typically, a solid oxide fuel cell (SOFC) employs an electrolyte of ion-conductive solid oxide such as stabilized zirconia. The electrolyte is interposed between an anode and a cathode to form an electrolyte electrode assembly (unit cell). The electrolyte electrode assembly is interposed between separators (bipolar plates). In use, a predetermined number of the unit cells and the separators are stacked together to form a fuel cell stack.

In the fuel cell of this type, it is necessary to remove impurities such as dust from a fuel gas and an oxygen-containing gas as reactant gases. In this regard, for example, a fuel cell system as disclosed in Japanese Laid-Open Patent Publication No. 2003-317757 is known. As shown inFIG. 23, the fuel cell system includes a fuel cell1. The fuel cell1includes an anode1b, a cathode1c, and an electrolyte membrane1ainterposed between the anode1band the cathode1c.

A reformer2, a carbon monoxide remover3, and an electric dust collector4aare provided on the anode side of the fuel cell1. The reformer2produces a hydrogen rich gas from a raw material gas. The carbon monoxide remover3removes carbon monoxide from the hydrogen rich gas. The electric dust collector4aremoves impurity particles from the hydrogen rich gas. Further, a fan5and an electric dust collector4bare provided on the cathode side of the fuel cell1. The fan5supplies the air as the oxygen-containing gas to the cathode1c, and the electric dust collector4bremoves impurity particles from the air.

However, in the conventional technique, the electric dust collectors4a,4bare provided separately from the fuel cell1, and spaces for providing the electric dust collectors4a,4bare required. Therefore, the overall size of the fuel cell system is considerably large. Further, since the electric dust collectors4a,4bare provided outside the fuel cell1, it is not possible to remove dust or the like produced in the fuel cell1.

SUMMARY OF THE INVENTION

A main object of the present invention is to provide a fuel cell and a fuel cell stack having compact structure in which after impurities are removed from a fuel gas reliably, the fuel gas is supplied to an electrolyte electrode assembly, and the desired power generation performance is achieved.

The present invention relates to a fuel cell including an electrolyte electrode assembly and a pair of separators sandwiching the electrolyte electrode assembly. The electrolyte electrode assembly includes an anode, a cathode, and an electrolyte interposed between the anode and the cathode. Each of the separators comprises a single plate.

The fuel cell comprises a fuel gas channel provided on one surface of the separator for supplying a fuel gas along an electrode surface of the anode, an oxygen-containing gas channel provided on the other surface of the separator for supplying an oxygen-containing gas along an electrode surface of the cathode, and a fuel gas supply channel provided on the one surface or on the other surface of the separator, and connected to a fuel gas supply unit and a fuel gas inlet for supplying the fuel gas into the fuel gas channel. The fuel gas supply channel includes a filter mechanism for filtering the fuel gas supplied from the fuel gas supply unit.

Preferably, the filter mechanism includes a hole for allowing the fuel gas to flow through the hole, and the cross sectional area of the opening of the hole is smaller than the cross sectional area of the opening of the fuel gas inlet.

In the structure, large impurities that would close the fuel gas inlet are collected by the filter mechanism. Therefore, the fuel gas inlet is not closed, and the fuel gas is supplied reliably and smoothly to the electrode surface of the anode from the fuel gas inlet.

Preferably, the fuel gas supply channel includes a groove formed on the one surface or on the other surface of the separator, and the fuel cell further comprises a channel lid member on the one surface or on the other surface of the separator to cover the groove, and the hole is formed in the channel lid member. Further, the fuel cell comprises a plate member provided at the channel lid member to cover the hole, and having a channel unit connecting the fuel gas supply unit and the hole. Accordingly, the structure is simplified advantageously.

Further, preferably, protrusions forming the fuel gas channel are provided on one surface of the separator, and a deformable elastic channel unit forming the oxygen-containing gas channel and tightly contacting the cathode is provided on the other surface of the separator. Since the elastic channel unit is deformed elastically, the elastic channel unit tightly contacts the cathode. In the structure, the dimensional errors or distortions that occur at the time of production in the electrolyte electrode assembly or the separator can suitably be absorbed. The damage at the time of stacking the components of the fuel cell is also prevented. Since the elastic channel member and the cathode contact at many points, improvement in the performance of collecting electricity is achieved.

Further, preferably, the fuel cell further comprises an exhaust gas channel for discharging the fuel gas and the oxygen-containing gas consumed in the reaction in the electrolyte electrode assembly as an exhaust gas in the stacking direction of the electrolyte electrode assembly and the separators, the fuel gas supply unit for supplying the fuel gas before consumption in the stacking direction is provided hermetically inside the exhaust gas channel, and the fuel gas supply channel connects the fuel gas channel and the fuel gas supply unit, and is provided along the separator surface to intersect the exhaust gas channel extending in the stacking direction. In the structure, the fuel gas before consumption is heated beforehand by the heat of the exhaust gas. Thus, improvement in the heat efficiency is achieved.

Further, preferably, the exhaust gas channel is provided at the central region of the separators. In the structure, the separators can be heated radially from the center, and improvement in the heat efficiency is achieved.

Further, preferably, the fuel gas supply unit is provided hermetically at the center of the exhaust gas channel. The fuel gas is not consumed unnecessarily, while preventing the fuel gas and the exhaust gas from being mixed together. Thus, improvement in the heat efficiency is achieved.

Further, preferably, the fuel gas inlet is provided at the center of the electrolyte electrode assembly or at an upstream position deviated from the center of the electrolyte electrode assembly in the flow direction of the oxygen-containing gas. In the structure, the fuel gas supplied into the fuel gas inlet can be distributed radially from the center of the anode. Thus, the reaction occurs uniformly, and improvement in the fuel utilization ratio is achieved.

Further, preferably, the fuel cell further comprises an oxygen-containing gas supply unit for supplying the oxygen-containing gas before consumption to the oxygen-containing gas supply channel from the outer circumference of the electrolyte electrode assembly. In the structure, the exhaust gas is discharged smoothly toward the center of the separators.

Further, preferably, the fuel cell further comprises an exhaust gas channel for discharging the fuel gas and the oxygen-containing gas consumed in the reaction in the electrolyte electrode assembly as an exhaust gas in the stacking direction of the electrolyte electrode assembly and the separators, and an oxygen-containing gas supply unit for allowing the oxygen-containing gas before consumption to flow in the stacking direction to supply the oxygen-containing gas to the oxygen-containing gas channel. The fuel gas supply unit for supplying the fuel gas before consumption in the stacking direction is provided hermetically inside the oxygen-containing gas supply unit, and the fuel gas supply channel connects the fuel gas channel and the fuel gas supply unit, and is provided along the separator surface to intersect the oxygen-containing gas supply unit extending in the stacking direction. In the structure, the fuel gas before consumption can be heated by the oxygen-containing gas, and improvement in the heat efficiency is achieved.

Further, preferably, the exhaust gas channel is provided around the separators. In the structure, the exhaust gas is used as a heat insulating layer. Therefore, heat radiation from the separator members can be prevented, and improvement in the heat efficiency is achieved.

Further, preferably, the fuel gas supply unit is provided hermetically at the central region of the separators. In the structure, the fuel gas is not consumed unnecessarily, and improvement in the heat efficiency is achieved.

Further, preferably, the electrolyte electrode assembly comprises a plurality of electrolyte electrode assemblies, and the fuel cell further comprises an oxygen-containing gas supply unit for supplying the oxygen-containing gas before consumption to the oxygen-containing gas supply channel from the inner circumference of the electrolyte electrode assemblies arranged along a virtual circle. In the structure, the fuel gas before consumption is heated by the oxygen-containing gas, and improvement in the heat efficiency is achieved.

Further, preferably, an area where the elastic channel unit is provided is smaller than a power generation area of the anode. In the structure, even if the exhaust gas flows around to the anode of the electrolyte electrode assembly, the power generation area is not present in the outer circumferential edge of the cathode opposite to the outer circumferential edge of the anode. Thus, the loss in the collected electrical current is avoided, and the performance of collecting electricity is improved advantageously.

Further, preferably, the elastic channel unit is made of an electrically conductive metal mesh member. Thus, the structure is simplified economically.

Further, preferably, the protrusions are solid portions formed on one surface of the separator by etching. In the structure, the protrusions having the desired shape can be formed at the desired positions easily. Further, the protrusions are not deformed. Thus, the load is transmitted effectively, and improvement in the performance of collecting electricity is achieved.

Further, preferably, a plurality of electrolyte electrode assemblies are arranged along a virtual circle concentric with the center of the separators. Thus, the fuel cell has compact structure, and the influence of heat distortion can be avoided.

In the present invention, the fuel gas supply channel is formed in the separator, and the fuel gas supply channel has the filter mechanism for filtering the fuel gas supplied from the fuel gas supply unit. In the structure, since the filter mechanism is provided in the fuel cell, the overall size of the fuel cells is small. The fuel gas is supplied to the electrolyte electrode assembly after the impurities produced in the reformer and the fuel cell are removed reliably. Thus, with the economical and compact structure, the desired power generation performance is achieved.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A fuel cell system10is used in various applications, including stationary and mobile applications. For example, the fuel cell system10is mounted on a vehicle. As shown inFIG. 1, the fuel cell system10includes a fuel cell stack12, a heat exchanger14, a reformer16, and a casing18. The fuel cell stack12is formed by stacking a plurality of fuel cells11in a direction indicated by an arrow A. The heat exchanger14heats an oxygen-containing gas before it is supplied to the fuel cell stack12. The reformer16reforms a fuel to produce a fuel gas. The fuel cell stack12, the heat exchanger14, and the reformer16are disposed in the casing18.

In the casing18, a fluid unit19including at least the heat exchanger14and the reformer16is disposed on one side of the fuel cell stack12, and a load applying mechanism21for applying a tightening load to the fuel cells11in the stacking direction indicated by the arrow A is disposed on the other side of the fuel cell stack12. The fluid unit19and the load applying mechanism21are provided symmetrically with respect to the central axis of the fuel cell stack12.

The fuel cell11is a solid oxide fuel cell (SOFC). As shown inFIGS. 3 and 4, the fuel cell11includes electrolyte electrode assemblies26. Each of the electrolyte electrode assemblies26includes a cathode22, an anode24, and an electrolyte (electrolyte plate)20interposed between the cathode22and the anode24. For example, the electrolyte20is made of ion-conductive solid oxide such as stabilized zirconia. The electrolyte electrode assembly26has a circular disk shape. A barrier layer (not shown) is provided at least at the inner circumferential edge of the electrolyte electrode assembly26(central side of the separator28) for preventing the entry of the oxygen-containing gas.

A plurality of, e.g., eight electrolyte electrode assemblies26are sandwiched between a pair of separators28to form the fuel cell11. The eight electrolyte electrode assemblies26are concentric with a fuel gas supply passage (fuel gas supply unit)30extending through the center of the separators28.

InFIG. 3, for example, each of the separators28comprises a single metal plate. The separator28has a first small diameter end portion32. The fuel gas supply passage30extends through the center of the first small diameter end portion32. The first small diameter end portion32is integral with circular disks36each having a relatively large diameter through a plurality of first bridges34. The first bridges34extend radially outwardly from the first small diameter end portion32at equal angles (intervals).

The circular disk36and the electrolyte electrode assembly26have substantially the same size. A fuel gas inlet38for supplying the fuel gas is formed at the center of the electrolyte electrode assembly26, or at an upstream position deviated from the center of the electrolyte electrode assembly26in the flow direction of the oxygen-containing gas. The adjacent circular disks36are separated from each other by a cutout39.

Each of the circular disks36has a plurality of protrusions48on its surface36awhich contacts the anode24. The protrusions48form a fuel gas channel46for supplying the fuel gas along an electrode surface of the anode24. For example, the protrusions48are solid portions formed by etching on the surface36a. Various shapes such as a square shape, a circular shape, a triangular shape, or a rectangular shape can be adopted as the cross sectional shape of the protrusions48. The positions or the density of the protrusions48can be changed arbitrarily depending on the flow state of the fuel gas or the like.

As shown inFIGS. 5 and 6, each of the circular disks36has a substantially planar surface36bwhich contacts the cathode22. The first small diameter end portion32has a ring-shaped protrusion50around the fuel gas supply passage30. A recess52is formed around the protrusion50. A groove53is formed in each of the first bridges34. The groove53connects the fuel gas supply passage30to the fuel gas inlet38through the recess52. For example, the recess52and the groove53are fabricated by etching. The recess52and the groove53form a fuel gas supply channel54.

As shown inFIG. 3, a channel lid member56is fixed to a surface of the separator28facing the cathodes22, e.g., by brazing, laser welding or the like. As shown inFIGS. 3 and 6, the channel lid member56is a flat plate. A second small diameter end portion58is formed at the center of the channel lid member56. The fuel gas supply passage30extends through the second small diameter end portion58. The second small diameter end portion58has a plurality of holes59aforming a filter mechanism59for filtering the fuel gas supplied from the fuel gas supply passage30. The diameter (the cross sectional area of the opening) D1of the hole59ais smaller than the diameter (the cross sectional area of the opening) of the fuel gas inlet38(D1≦D2).

Eight second bridges60extend radially from the second small diameter end portion58. Each of the second bridges60is fixed to the separator28, from the first bridge34to the surface36bof the circular disk36, covering the fuel gas inlet38(seeFIG. 7).

A circular disk member (plate member)62is fixed to the channel lid member56, covering the holes59a. A plurality of slits64connected to the fuel gas supply passage30are radially formed in the circular disk member62. The slits64are connected to a recess66. The slits64and the recess66form a channel unit68connecting the fuel gas supply passage30to the holes59a.

As shown inFIGS. 3 and 7, a deformable elastic channel member such as an electrically conductive mesh member74is provided on the surface36bof the circular disk36. The mesh member74forms an oxygen-containing gas channel72for supplying the oxygen-containing gas along an electrode surface of the cathode22. The mesh member74tightly contacts the cathode22. For example, the mesh member74is made of wire rod material of stainless steel (SUS material), and has a substantially circular disk shape.

The thickness of the mesh member74is determined such that the mesh member74is deformed elastically desirably when a load in the stacking direction indicated by the arrow A is applied to the mesh member74. The mesh member74has a cutout76as a space for providing the second bridge60of the channel lid member56.

As shown inFIG. 7, the area where the mesh member74is provided is smaller than the area where the protrusions48are provided on the surface36a, i.e., smaller than the power generation area of the anode24. The oxygen-containing gas channel72formed on the mesh member74is connected to the oxygen-containing gas supply unit77. The oxygen-containing gas is supplied in the direction indicated by the arrow B through the space between the inner circumferential edge of the electrolyte electrode assembly26and the inner circumferential edge of the circular disk36. The oxygen-containing gas supply unit77extends inside the respective circular disks36between the first bridges34in the stacking direction.

Insulating seals79for sealing the fuel gas supply passage30are provided between the separators28. For example, the insulating seals79are made of mica material, or ceramic material. An exhaust gas channel78of the fuel cells11is formed outside the circular disks36.

As shown inFIGS. 1 and 2, the fuel cell stack12includes end plates80a,80bprovided at opposite ends of the fuel cells11in the stacking direction. The end plate80ahas a substantially circular disk shape. A ring shaped portion82protrudes from the outer circumferential end of the end plate80a, and a groove84is formed around the ring shaped portion82. A columnar projection86is formed at the center of the ring shaped portion82. The columnar projection86protrudes in the same direction as the ring shaped portion82. A stepped hole88is formed at the center in the projection86.

Holes90and screw holes92are formed in the same virtual circle around the projection86. The holes90and the screw holes92are arranged alternately, and spaced at predetermined angles (intervals), at positions corresponding to the respective spaces of the oxygen-containing gas supply unit77formed between the first and second bridges34,60. The diameter of the end plate80bis larger than the diameter of the end plate80a. The end plate80ais an electrically conductive thin plate.

The casing18includes a first case unit96acontaining the load applying mechanism21and a second case unit96bcontaining the fuel cell stack12. The end plate80band an insulating member are sandwiched between the first case unit96aand the second case unit96b. The insulating member is provided on the side of the second case unit96b. The joint portion between the first case unit96aand the second case unit96bis tightened by screws98and nuts100. The end plate80bfunctions as a gas barrier for preventing entry of the hot exhaust gas or the hot air from the fluid unit19into the load applying mechanism21.

An end of a ring shaped wall plate102is joined to the second case unit96b, and a head plate104is fixed to the other end of the wall plate102. The fluid unit19is provided symmetrically with respect to the central axis of the fuel cell stack12. Specifically, the substantially cylindrical reformer16is provided coaxially inside the substantially ring shaped heat exchanger14.

A wall plate106is fixed to the groove84around the end plate80ato form a chamber member108. The heat exchanger14and the reformer16are directly connected to the chamber member108. A chamber108ais formed in the channel member108, and the air heated at the heat exchanger14temporally fills the chamber108a. The holes90are openings for supplying the air temporally filling in the chamber108ato the fuel cell stack12.

A fuel gas supply pipe110and a reformed gas supply pipe112are connected to the reformer16. The fuel gas supply pipe110extends to the outside from the head plate104. The reformed gas supply pipe112is inserted into the stepped hole88of the end plate80a, and connected to the fuel gas supply passage30.

An air supply pipe114and an exhaust gas pipe116are connected to the head plate104. A channel118extending from the air supply pipe114, and directly opened to the channel member108through the heat exchanger14, and a channel120extending from the exhaust gas channel78of the fuel cell stack12to the exhaust gas pipe116through the heat exchanger14are provided in the casing18.

The load applying mechanism21includes a first tightening unit122afor applying a first tightening load T1to a region around (near) the fuel gas supply passage30and a second tightening unit122bfor applying a second tightening load T2to the electrolyte electrode assemblies26. The second tightening load T2is smaller than the first tightening load T1(T1>T2).

The first tightening unit122aincludes short first tightening bolts124ascrewed into the screw holes92formed along one diagonal line of the end plate80a. The first tightening bolts124aextend in the stacking direction of the fuel cells11, and engage a first presser plate126a. The first tightening bolts124aare provided in the oxygen-containing gas supply unit77extending through the separators28. The first presser plate126ais a narrow plate, and engages the central position of the separator28to cover the fuel gas supply passage30.

The second tightening unit122bincludes long second tightening bolts124bscrewed into screw holes92formed along the other diagonal line of the end plate80a. Ends of the second tightening bolts124bextend through a second presser plate126bhaving a curved outer section. Nuts127are fitted to the ends of the second tightening bolts124b. The second tightening bolts124bare provided in the oxygen-containing gas supply unit77extending through the separators28. Springs128and spring seats129are provided in respective circular portions of the second presser plate126b, at positions corresponding to the electrolyte electrode assemblies26on the circular disks36of the fuel cell11. For example, the springs128are ceramics springs.

Next, operation of the fuel cell system10will be described below.

As shown inFIG. 3, in assembling the fuel cell system10, firstly, the channel lid member56is joined to the surface of the separator28facing the cathodes22, and the circular disk member62is joined to the channel lid member56. Thus, a fuel gas supply channel54connected to the fuel gas supply passage30is formed between the separator28, and the channel lid member56and the circular disk member62. The fuel gas supply channel54is connected to the fuel gas channel46through the fuel gas inlet38(seeFIG. 7). The ring shaped insulating seal79is provided on each of the separators28around the fuel gas supply passage30, and the mesh member74is provided between the separator28and the cathode22.

In this manner, the separator28is fabricated. The eight electrolyte electrode assemblies26are interposed between a pair of the separators28to form the fuel cell11. As shown inFIGS. 3 and 4, the electrolyte electrode assemblies26are interposed between the surface36aof one separator28and the surface36bof the other separator28. The fuel gas inlet38is positioned at substantially the center in each of the anodes24.

A plurality of the fuel cells11are stacked in the direction indicated by the arrow A, and the end plates80a,80bare provided at opposite ends in the stacking direction. As shown inFIGS. 1 and 2, on the end plate80bside, the first presser plate126aof the first tightening unit122ais provided at a position corresponding to the center of the fuel cell11.

In this state, the short first tightening bolts124aare inserted through the first presser plate126aand the end plate80btoward the end plate80a. Tip ends of the first tightening bolts124aare screwed into, and fitted to the screw holes92formed along one of the diagonal lines of the end plate80a. The heads of the first tightening bolts124aengage the first presser plate126a. The first tightening bolts124aare rotated in the screw holes92to adjust the surface pressure of the first presser plate126a. In this manner, in the fuel cell stack12, the first tightening load T1is applied to the region near the fuel gas supply passage30.

Then, the springs128and the spring seats129are aligned axially with the electrolyte electrode assemblies26at respective positions of the circular disks36. The second presser plate126bof the second tightening unit122bengages the spring seats129provided at one end of the springs128.

Then, the long second tightening bolts124bare inserted through the second presser plate126band the end plate80btoward the end plate80a. The tip end of the second tightening bolts124bare screwed into, and fitted to the screw holes92formed along the other diagonal line of the end plate80a. The nuts127are fitted to the heads of the second tightening bolts124b. Therefore, by adjusting the state of the screw engagement between the nuts127and the second tightening bolts124b, the second tightening load T2is applied to the electrolyte electrode assemblies26by the elastic force of the respective springs128.

The end plate80bof the fuel cell stack12is sandwiched between the first case unit96aand the second case unit96bof the casing18. The first case unit96aand the second case unit96bare fixed together by the screws98and the nuts100. The fluid unit19is mounted in the second case unit96b. The wall plate106of the fluid unit19is attached to the groove84around the end plate80a. Thus, the channel member108is formed between the end plate80aand the wall plate106.

Next, in the fuel cell system10, as shown inFIG. 1, a fuel (methane, ethane, propane, or the like) and, as necessary, water are supplied from the fuel gas supply pipe110, and an oxygen-containing gas (hereinafter referred to as the “air”) is supplied from the air supply pipe114.

The fuel is reformed when it passes through the reformer16to produce a fuel gas (hydrogen-containing gas). The fuel gas is supplied to the fuel gas supply passage30of the fuel cell stack12. The fuel gas moves in the stacking direction indicated by the arrow A, and flows into the fuel gas supply channel54in the separator28through the holes59afrom the channel unit68of the circular disk member62of each fuel cell11(seeFIG. 7).

The fuel gas flows along the fuel gas supply channel54between the first and second bridges34,60, and flows into the fuel gas channel46formed by the protrusions48from the fuel gas inlets38of the circular disks36. The fuel gas inlets38are formed at positions corresponding to central regions of the anodes24of the electrolyte electrode assemblies26. Thus, the fuel gas is supplied to from the fuel gas inlets38to the substantially central positions of the anodes24, and flows outwardly from the central regions of the anodes24along the fuel gas channel46.

As shown inFIG. 1, the air from the air supply pipe114flows through the channel118of the heat exchanger14, and temporarily flows into the chamber108a. The air flows through the holes90connected to the chamber108a, and is supplied to the oxygen-containing gas supply unit77provided at substantially the center of the fuel cells11. At this time, in the heat exchanger14, as described later, since the exhaust gas discharged to the exhaust gas channel78flows through the channel120, heat exchange between the air before supplied to the fuel cells11and the exhaust gas is performed. Therefore, the air is heated to a desired fuel cell operating temperature beforehand.

The oxygen-containing gas supplied to the oxygen-containing gas supply unit77flows into the space between the inner circumferential edge of the electrolyte electrode assembly26and the inner circumferential edge of the circular disk36in the direction indicated by the arrow B, and flows toward the oxygen-containing gas channel72formed by the mesh member74. As shown inFIG. 7, in the oxygen-containing gas channel72, the oxygen-containing gas flows from the inner circumferential edge (central region of the separator28) to the outer circumferential edge (outer region of the separator28) of, i.e., from one end to the other end of the outer circumferential region of the cathode22of the electrolyte electrode assembly26.

Thus, in the electrolyte electrode assembly26, the fuel gas flows from the central region to the outer circumferential region of the anode24, and the oxygen-containing gas flows in one direction indicted by the arrow B on the electrode surface of the cathode22. At this time, oxygen ions flow through the electrolyte20toward the anode24for generating electricity by electrochemical reactions.

The exhaust gas discharged to the outside of the respective electrolyte electrode assemblies26flows through the exhaust gas channel78in the stacking direction. When the exhaust gas flows through the channel120of the heat exchanger14, heat exchange between the exhaust gas and the air is carried out. Then, the exhaust gas is discharged into the exhaust gas pipe116.

In the first embodiment, as shown inFIGS. 6 and 7, the fuel gas supply channel54connected to the fuel gas supply passage30and the fuel gas inlet38are formed in the separator28, the channel lid member56, and the circular disk member62. The filter mechanism59for filtering the fuel gas supplied from the fuel gas supply passage30to the channel unit68is formed in the fuel gas supply channel54.

In the structure, impurities such as dust that may be contained in the fuel gas are blocked by the holes59aof the filter mechanism59, and do not enter the groove53. After removal of the impurities, the fuel gas is supplied to the fuel gas channel46, and thus, the desired power generation performance is achieved.

Further, the filter mechanism59is provided in the fuel cell11. Therefore, in comparison with the conventional structure in which a dust collector or the like is provided outside the fuel cell11, the overall size of the fuel cells11, i.e., the fuel cell stack12is reduced significantly. Further, it is possible to remove dust or the like that may be raised in pipes or insulating material in the reformer16or the fuel cells11, and that cannot be collected by the external dust collector.

Further, in the first embodiment, the diameter D1of the hole59ais smaller than the diameter D2of the fuel gas inlet38. Thus, large impurities that would close the fuel gas inlet38are blocked by any of the holes59a, and collected by the filter mechanism59. Therefore, it is possible to supply the desired fuel gas from the fuel gas inlet38to the electrode surface of the anode24smoothly and reliably.

The anode24of the electrolyte electrode assembly26contacts the protrusions48on the circular disk36. The cathode22of the electrolyte electrode assembly26contacts the mesh member74. In this state, the load in the stacking direction indicated by the arrow A is applied to the components of the fuel cell11. Since the mesh member74is deformable, the mesh member74tightly contacts the cathode22.

In the structure, the dimensional errors or distortions that occur at the time of production in the electrolyte electrode assembly26or the separator28can suitably be absorbed by elastic deformation of the mesh member74. Thus, in the first embodiment, damage at the time of stacking the components of the fuel cell11is prevented. Since the components of the fuel cell11contact each other at many points, improvement in the performance of collecting electricity from the fuel cell11is achieved.

The load in the stacking direction is efficiently transmitted through the protrusions48on the circular disk36. Therefore, the fuel cells11can be stacked together with a small load, and distortion in the electrolyte electrode assemblies26and the separators28is reduced. In particular, even in the case of using the electrolyte electrode assembly26with small strength, having the thin electrolyte20and the thin cathode22(so called anode supported cell type MEA), the stress applied to the electrolyte20and the cathode22is released by the mesh member74, and reduction in the damage is achieved advantageously.

The protrusions48on the surface36aof the circular disk36are formed by etching or the like as solid portions. Thus, the shape, the positions, and the density of the protrusions48can be changed arbitrarily and easily, e.g., depending on the flow state of the fuel gas economically, and the desired flow of the fuel gas is achieved. Further, since the protrusions48are formed as solid portions, the protrusions48are not deformed, and thus, the load is transmitted through the protrusions48, and electricity is collected through the protrusions48efficiently.

Further, in the first embodiment, the fuel gas supply passage30is provided hermetically inside the oxygen-containing gas supply unit77, and the fuel gas supply channel54is provided along the separator surface. Therefore, the fuel gas before consumption is heated by the hot oxygen-containing gas which has been heated by the heat exchange at the heat exchanger14. Thus, improvement in the heat efficiency is achieved.

Further, the exhaust gas channel78is provided around the separators28. The exhaust gas channel78makes it possible to prevent heat radiation from inside of the separators28. Further, the fuel gas inlet38is provided at the center of the circular disk36, or provided at an upstream position deviated from the center of the circular disk36in the flow direction of the oxygen-containing gas. Therefore, the fuel gas supplied from the fuel gas inlet38is diffused radially from the center of the anode24easily. Thus, the uniform reaction occurs smoothly, and improvement in the fuel utilization ratio is achieved.

Further, the area where the mesh member74is provided is smaller than the power generation area of the anode24(seeFIG. 7). Therefore, even if the exhaust gas flows around to the anode24from the outside of the electrolyte electrode assembly26, the power generation area is not present in the outer circumferential edge of the cathode22opposite to the outer circumferential edge of the anode24. Thus, fuel consumption by the circulating current does not increase significantly, and a large electromotive force can be collected easily. Accordingly, the performance of collecting electricity is improved, and the fuel utilization ratio is achieved advantageously. Further, the present invention can be carried out simply by using the mesh member74as the elastic channel member. Thus, the structure of the present invention is simplified economically.

Further, the eight electrolyte electrode assemblies26are arranged along a virtual circle concentric with the separator28. Thus, the overall size of the fuel cell11is small, and the influence of the heat distortion can be avoided.

FIG. 8is an exploded perspective view showing a fuel cell130according to a second embodiment of the present invention. The constituent elements that are identical to those of the fuel cell11according to the first embodiment are labeled with the same reference numeral, and description thereof will be omitted. In the third to seventh embodiments as described later, the constituent elements that are identical to those of the fuel cell11according to the first embodiment are labeled with the same reference numeral, and description thereof will be omitted.

In the fuel cell130, a channel lid member134is fixed to a surface of the separator132facing the anodes24, and the circular disk member62is fixed to the channel lid member134. As shown inFIG. 9, a protrusion50, a recess52, and grooves53are formed on a surface36aof the separator132facing the anodes24by, e.g., etching.

As shown inFIGS. 8 and 10, the channel lid member134has a planar shape, and a plurality of fuel gas inlets136are formed at the front ends of the second bridges60. The diameter (the cross sectional area of the opening) D1of the hole59ais smaller than the diameter (the cross sectional area of the opening) D2of the fuel gas inlet136(D1≦D2).

An elastic channel member such as an electrically conductive mesh member138is provided on the surface36bof the circular disk36. The mesh member138has a circular disk shape. The cutout76of the mesh member74is not required for the mesh member138, and no fuel gas inlets38are required in the circular disks36.

In the second embodiment, the fuel gas supplied to the fuel gas supply passage30flows into the fuel gas supply channel54in the separator28through the holes59afrom the channel unit68of the circular disk member62of each fuel cell11. Further, the fuel gas is supplied toward the anode24from the fuel gas inlets136formed at the front end of each of the second bridges60of the channel lid member134.

The air flows from the oxygen-containing gas supply unit77to the oxygen-containing gas channel72formed in the mesh member138interposed between the cathode22and each of the circular disks36. The air flows in the direction indicate by the arrow B, and is supplied to the cathode22.

FIG. 11is a cross sectional view showing a fuel cell system150according to a third embodiment of the present invention.

The fuel cell system150includes a fuel cell stack152provided in the casing18. The fuel cell stack152is formed by stacking a plurality of fuel cells154in the direction indicated by the arrow A. The fuel cell stack152is sandwiched between the end plates80a,80b.

As shown inFIGS. 12 and 13, in the fuel cell154, the oxygen-containing gas flows along the cathode22of the electrolyte electrode assembly26in the direction indicated by an arrow C from the outer circumferential edge to the inner circumferential edge of the cathode22, i.e., in the direction opposite to the flow direction in the cases of the first and second embodiments.

In the separators155of the fuel cell154, an oxygen-containing gas supply unit77is provided outside the circular disks36. An exhaust gas channel78is formed by spaces between the first bridges34inside the circular disks36and the circle disks36. The exhaust gas channel78extends in the stacking direction. Each of the circular disks36includes extensions156a,156bprotruding toward the adjacent circular disks36on both sides, respectively. Spaces158are formed between the adjacent extensions156a,156b, and baffle plates160extend along the respective spaces158in the stacking direction.

As show inFIG. 13, the oxygen-containing gas channel72is connected to the oxygen-containing gas supply unit77for supplying the oxygen-containing gas from the space between the outer circumferential edge of the circular disk36and the outer circumferential edge of the electrolyte electrode assembly26in the direction indicated by the arrow C. The oxygen-containing gas supply unit77is formed around the separators155including the area outside the extensions156a,156bof the circular disks36(seeFIG. 12).

As shown inFIG. 11, a channel member162having a chamber162aconnected to the exhaust gas channel78through the holes90is formed at the end plate80a. The exhaust gas discharged from the fuel cells154temporarily fills in the chamber162a. The exhaust gas flows through the channel120in the heat exchanger14through an opening163opened directly to the chamber162a.

An air supply pipe164and an exhaust gas pipe166are connected to the head plate104. The air supply pipe164extends up to a position near the reformer16. An end of the exhaust gas pipe166is connected to the head plate104.

In the third embodiment, the fuel gas flows from the fuel gas supply pipe110to the fuel gas supply passage30through the reformer16. The air as the oxygen-containing gas flows from the air supply pipe164into the channel118of the heat exchanger14, and is supplied to the oxygen-containing gas supply unit77outside the fuel cells154. As shown inFIG. 13, the air flows from the spaces between the outer circumferential edge of the electrolyte electrode assembly26and the outer circumferential edge of the circular disk36in the direction indicated by the arrow C, and supplied to the oxygen-containing gas channel72formed by the mesh member74.

Thus, power generation is performed in each of the electrolyte electrode assemblies26. The exhaust gas as the mixture of the fuel gas and the air after consumption in the reactions of the power generation flows in the stacking direction through the exhaust gas channel78in the separators155. The exhaust gas flows through the holes90, and temporarily fills the chamber162ain the channel member162formed at the end plate80a(seeFIG. 11). Further, when the exhaust gas flows through the channel120of the heat exchanger14, heat exchange is performed between the exhaust gas and the air. Then, the exhaust gas is discharged into the exhaust gas pipe166.

In the third embodiment, the fuel gas supply passage30is provided hermetically inside the exhaust gas channel78, and the fuel gas supply channel54is provided along the separator surface. Therefore, the fuel gas flowing through the fuel gas supply passage30before consumption is heated by the heat of the exhaust gas discharged into the exhaust gas channel78.

Further, since the exhaust gas channel78extends through the central part of the separators155, it is possible to heat the separators155radially from the central part by the heat of the exhaust gas, and improvement in the heat efficiency is achieved.

FIG. 14is an exploded perspective view showing a fuel cell170according to a fourth embodiment of the present invention.

In the fuel cell170, a channel lid member174is fixed to a surface of a separator172facing the anode24. Further, the channel lid member174is fixed to the circular disk member62. The channel lid member174has a flat shape. A plurality of fuel gas inlets176are formed at the front ends of the second bridges60. The fuel gas inlets176are opened to the anode24.

In the fourth embodiment having the above structure, the oxygen-containing gas, the fuel gas, and the exhaust gas flow as shown inFIG. 15.

FIG. 16is an exploded perspective view showing a fuel cell200according to a fifth embodiment of the present invention.

The fuel cell200includes electrolyte electrode assemblies26ahaving a substantially trapezoidal shape. Eight electrolyte electrode assemblies26aare sandwiched between a pair of separators202. The separator202includes trapezoidal sections204corresponding to the shape of the electrolyte electrode assemblies26a. A plurality of protrusions48and a seal206are formed on a surface36aof the trapezoidal section204facing the anode24by e.g., etching. The seal206is formed around the outer edge of the trapezoidal section204, except the outer circumferential portion.

As shown inFIG. 17, a protrusion50, a recess52, and grooves53are formed on the surface36bof the separator202by, e.g., etching. Each of the grooves53is connected to a fuel gas inlet38formed at the inner edge portion of the trapezoidal section204. A channel lid member208is fixed to the separator202to cover the recess52, the grooves53and the fuel gas inlets38. The channel lid member208has a planar shape. Further, the circular disk member62is fixed to the channel lid member208.

As shown inFIG. 16, a deformable elastic channel member such as an electrically conductive mesh member210is provided on the surface36bof each of the trapezoidal sections204. The mesh member210has a substantially trapezoidal shape, and has a cutout212as a space for providing the second bridge60of the channel lid member208. The mesh member210has a substantially trapezoidal shape. The size of the mesh member210is smaller than the size of the trapezoidal section204.

In the fifth embodiment, the fuel gas from the fuel gas supply passage30flows through the holes59afrom the channel unit68of the circular disk member62of the fuel cell200into the fuel gas supply channel54. As shown inFIG. 18, the fuel gas flows through the fuel gas supply channel54. Then, the fuel gas flows through the fuel gas inlet38formed in the trapezoidal section204, and is supplied to the fuel gas channel46. Thus, the fuel gas flows outwardly in the direction indicated by the arrow B from the inner edge of the anode24toward the outer circumferential portion along the fuel gas channel46.

The oxygen-containing gas supplied to the oxygen-containing gas supply unit77provided around the fuel cell200flows into the oxygen-containing gas channel72on the mesh member210from the space between the outer circumferential edge of the electrolyte electrode assembly26aand the outer circumferential edge of the trapezoidal section204in the direction indicated by the arrow C. Thus, in the electrolyte electrode assembly26a, electrochemical reactions are induced for power generation.

The fifth embodiment substantially adopts the structure of the third embodiment. However, the present invention is not limited in this respect. The fifth embodiment may adopt the structure of the fourth embodiment, or the structure of the first and second embodiments in which the oxygen-containing gas flows from the inside to the outside of the separators.

FIG. 19is an exploded perspective view showing a fuel cell220according to a sixth embodiment of the present invention. A plurality of the fuel cells220are stacked together to form a fuel cell stack.

As shown inFIG. 20, each of circular disks36of the separator224of a fuel cell220has protrusions226on its surface which contacts the cathode22. The protrusions226form an oxygen-containing gas channel72for supplying the oxygen-containing gas along an electrode surface of the cathode22. The protrusions226are similar to the protrusions48formed on the surface36a. The protrusions226are solid portions formed on the surface36bby, e.g., etching.

The fuel cell220according to the sixth embodiment has the same structure as the fuel cell11according to the first embodiment, except that the protrusions226are used instead of the mesh member74. In the fuel cell220, the oxygen-containing gas, the fuel gas, and the exhaust gas flow as shown inFIG. 22. The sixth embodiment may be modified in the same manner as in the case of the second to fifth embodiments, except that the protrusions226are used.

FIG. 22is a front view showing a channel lid member240of a fuel cell according to a seventh embodiment of the present invention.

The channel lid member240includes a second small diameter end portion242, and a plurality of meshes246forming a filter mechanism244are provided at the second small diameter end portion242. The cross sectional area of one opening of the mesh246is smaller than the cross sectional area of the opening of the fuel gas inlet (not shown), and the total cross sectional area of the openings of the meshes246is sufficiently larger than the cross sectional area of the openings of the fuel gas inlets.

In the seventh embodiment, the filter mechanism244includes the meshes246instead of the holes, and substantially the same advantages as in the case of the first to sixth embodiments can be obtained.

The invention has been particularly shown and described with reference to preferred embodiments, it will be understood that variations and modifications can be effected thereto by those skilled in the art without departing from the spirit and scope of the invention as defined by the appended claims.