Fuel cell stack

A fuel cell of a fuel cell stack includes a power generation reaction area, a marginal area around the power generation reaction area, and a first reactant gas flow area and a second reactant gas flow area. The first reactant gas flow area and the second reactant gas flow area are provided outside the power generation reaction area and inside the marginal area. The fuel cell stack includes a first load applying unit configured to apply a first load to the marginal area in the stacking direction and a second load applying area configured to apply a second load to the power generation reaction area in the stacking direction.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2014-088783 filed on Apr. 23, 2014, the contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

Field of the Invention

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

Description of the Related Art

In general, a solid oxide fuel cell (SOFC) employs a solid electrolyte of ion-conductive oxide such as stabilized zirconia. The electrolyte is interposed between an anode and a cathode to form an electrolyte electrode assembly, for example, a membrane electrode assembly (MEA). The electrolyte electrode assembly is interposed between separators (bipolar plates). In use, generally, predetermined numbers of the electrolyte electrode assemblies and the separators are stacked together to form a fuel cell stack.

In the fuel cell stack, in order to obtain the output voltage efficiently, the fuel cells need to be stacked together in a desired pressurized state. Further, in order to prevent leakage of a reactant gases such as a fuel gas and air as much as possible, it is required to apply pressure to the fuel cell stack in the stacking direction to seal reactant gas manifolds reliably.

To this end, an electrochemical cell stack disclosed in Japanese Laid-Open Patent Publication No. 2009-500525 (PCT) (hereinafter referred to as conventional technique 1) is known. As shown inFIG. 8, this electrochemical cell stack includes an electrochemical cell (proton exchange membrane (PEM) cell) stack1ainterposed between a first electrically conductive end plate2aand a second electrically conductive end plate3a.

An end plate4ais provided outside the second electrically conductive end plate3a, and the end plate4aand the first electrically conductive end plates2aare connected by a plurality of walls5a. An electrically insulating elastic pad6amade of silicone or elastic polymer material is interposed between the second electrically conductive end plate3aand the end plate4a. According to the disclosure, in operation, the electrically insulating elastic pad6acan compensate heat expansion or heat contraction of the electrochemical cell stack1a.

Further, in a flat plate type solid electrolyte fuel cell disclosed in Japanese Laid-Open Patent Publication No. 10-172594 (hereinafter referred to as the conventional technique 2), a separator1bas shown inFIG. 9is provided, and a plurality of unit cells (not shown) and separators1bare stacked alternately. Each of the unit cells includes a solid electrolyte layer and an air electrode and a fuel electrode provided on both surfaces of the solid electrolyte layer. A gas supply hole2band a gas discharge hole3bare formed at a pair of diagonal positions of the separator1b, and a plurality of gas flow grooves4bare formed at the central part of the separator1b.

A gas throttle section5band blocks6bare provided between the gas supply hole2band the inlet of the gas flow grooves4b. According to the disclosure, in the structure, the pressure loss of the gas discharged from the gas supply hole2bis increased, and it becomes possible to distribute the gas uniformly.

SUMMARY OF THE INVENTION

In the above conventional technique 1, the electrically insulating elastic pad6amade of silicone or elastic polymer material is used. However, in the SOFC operated at high temperature in comparison with the PEM cell, the above electrically insulating elastic pad6acannot be used.

Further, in the above conventional technique 2, it is required to achieve both of good sealing performance at the gas supply hole2band the gas discharge hole3band good current collection performance of the sandwiching section sandwiching the electrode section (area covered by the gas flow grooves4b). In this regard, if a load applied to the fuel cell is configured to reliably achieve the sufficient gas sealing performance, the electrode section may be damaged undesirably. If a load applied to the fuel cell is configured to reliably achieve the sufficient current collection performance, the gas sealing performance is degraded.

Further, in the conventional technique 1 and the conventional technique 2 described above, in a high temperature area having 500° C. or more as the operating temperature of the SOFC, it is difficult to apply pressures to the gas sealing area and the current collection area using optimum loads respectively for a long period of time. Therefore, it is impossible to suppress damages of the fuel cells while reliably achieving the good sealing performance and good current collection performance.

The present invention has been made to solve the problems of this type, and an object of the present invention is to provide a fuel cell stack which makes it possible to suppress damages of fuel cells as much as possible, and achieve improvement in the gas sealing performance and current collecting performance.

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

The fuel cell includes a power generation reaction area having a fuel gas channel configured to supply a fuel gas along an electrode surface of the anode and an oxygen-containing gas channel configured to supply an oxygen-containing gas along an electrode surface of the cathode formed separately on front and back sides of the power generation reaction area. Further, the fuel cell includes a frame shaped marginal area around the power generation reaction area and a first reactant gas flow area and a second reactant gas flow area.

A fuel gas passage and an oxygen-containing gas passage are formed in each of the first reactant gas flow area and the second reactant gas flow area. The fuel gas passage is configured to allow the fuel gas to flow in the stacking direction of the fuel cells, and is connected to the fuel gas channel. The oxygen-containing gas passage is configured to allow the oxygen-containing gas to flow in the stacking direction, and is connected to the oxygen-containing gas channel.

The first reactant gas flow area is provided outside one end of the power generation reaction area and inside the marginal area and the second reactant gas flow area is provided outside another end of the power generation reaction area and inside the marginal area.

The first reactant gas flow area has one of a fuel gas supply passage and a fuel gas discharge passage as the fuel gas passage and one of an oxygen-containing gas supply passage and an oxygen-containing gas discharge passage as the oxygen-containing gas passage. The second reactant gas flow area has another of the fuel gas supply passage and the fuel gas discharge passage and another of the oxygen-containing gas supply passage and the oxygen-containing gas discharge passage.

The fuel cell stack has a first load applying unit configured to apply a first load to the marginal area in the stacking direction and a second load applying unit configured to apply a second load to the power generation reaction area in the stacking direction.

In the present invention, the first load applying unit for applying the first load to the marginal area in the stacking direction of the fuel cells and the second load applying unit for applying the second load to the power generation reaction area in the stacking direction are provided. In the structure, it becomes possible to apply the first load to the marginal area to suppress leakage of the reactant gases as much as possible, and improve the gas sealing performance. Moreover, it becomes possible to apply the second load to the power generation reaction area to connect the current collection areas together further tightly, and improve the current collection performance. Therefore, it is possible to suppress damages of the fuel cells as much as possible while suitably maintaining the desired gas sealing performance and current collection performance.

Further, it becomes possible to effectively suppress leakage of the reactant gases flowing through the first reactant gas flow area and the second reactant gas flow area to the outside of the marginal area. Moreover, supply of the reactant gases to the power generation reaction area and discharge of the reactant gases from the power generation reaction area are facilitated. Accordingly, both of good gas sealing performance and good current collection performance are achieved further suitably.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

As shown inFIGS. 1 and 2, a fuel cell stack10according to a first embodiment of the present invention is formed by stacking a plurality of solid oxide fuel cells12in a vertical direction indicated by an arrow C. The fuel cell stack10may be used in a stationary application. Additionally, the fuel cell stack10may be used in various applications. For example, the fuel cell stack10may be mounted in a vehicle.

The fuel cells12generate electricity by electrochemical reactions of a fuel gas (hydrogen-containing gas such as a mixed gas of a hydrogen gas and methane or a carbon monoxide) and an oxygen-containing gas (air). A base frame14is provided at one end of the fuel cells12in the stacking direction, and a roof frame16is provided at the other end of the fuel cells12in the stacking direction. The base frame14and the roof frame16are fixed using a plurality of tightening bolts18. A plurality of guide pins20are provided at the base frame14for positioning the respective fuel cells12. Cutouts (or holes)21are formed in the roof frame16for inserting the guide pins20into the cutouts21, respectively. The guide pins20are removed after components of the fuel cell stack10are stacked together.

As shown inFIGS. 3 and 4, the fuel cell12includes an electrolyte22. The electrolyte22is an ion oxide conductor made of, e.g., stabilized zirconia, ceria based material, lanthanum gallate based material. An anode24is provided on one surface of the electrolyte22, and a cathode26is provided on the other surface of the electrolyte22to form an electrolyte electrode assembly (MEA)28. The surface size (outer size) of the cathode26is smaller than the surface size (outer size) of the anode24, and the surface size (outer size) of the anode24is smaller than the surface size (outer size) of the electrolyte22.

The electrolyte electrode assembly28is joined to a metal support body30. For example, the metal support body30is a thin plate of stainless steel material (SUS), and a large number of anode flow holes32are formed in the power generation area (central part) of the metal support body30(seeFIGS. 3 and 4). The anode flow holes32are formed, e.g., by etching or laser processing. Alternatively, a porous metal may be used for providing the anode flow holes32.

As shown inFIG. 3, the metal support body30has a rectangular shape, and a fuel gas supply passage34ais provided at one end of the metal support body30in a longitudinal direction indicated by an arrow A. Moreover, an oxygen-containing gas discharge passage36bis provided at the one end of the metal support body30in the longitudinal direction, around the fuel gas supply passage34a. The oxygen-containing gas discharge passage36bis mainly opened on both sides of the fuel gas supply passage34ain the direction indicated by the arrow B.

A fuel gas discharge passage34bis provided at the other end of the metal support body30in the longitudinal direction. Moreover, an oxygen-containing gas supply passage36ais provided at the other end of the metal support body30in the longitudinal direction, around the fuel gas discharge passage34b. The oxygen-containing gas supply passage36ais mainly opened on both sides of the fuel gas discharge passage34bin the direction indicated by the arrow B.

A channel member38of a thin metal plate is fixed to a surface of the metal support body30, opposite to the electrolyte electrode assembly28, e.g., by welding. The channel member38and the metal support body30have substantially the same shape. At one end of the channel member38in the longitudinal direction, the fuel gas supply passage34aand the oxygen-containing gas discharge passage36bare formed. At the other end of the channel member38in the longitudinal direction, the fuel gas discharge passage34band the oxygen-containing gas supply passage36aare formed.

A fuel gas channel40is formed on a surface38aof the channel member38joined to the metal support body30for allowing the fuel gas to flow along the fuel gas channel40in the direction indicated by the arrow A. The fuel gas channel40includes a plurality of ridges and a plurality of channel grooves formed between these ridges. An inlet side of the fuel gas channel40and the fuel gas supply passage34aare connected through an inlet connection channel42aformed by a plurality of ridges around the fuel gas supply passage34a. An outlet side of the fuel gas channel40and the fuel gas discharge passage34bare connected through an outlet connection channel42bformed by a plurality of ridges around the fuel gas discharge passage34b.

The metal support body30has an oxygen-containing gas channel44on a side facing the electrolyte electrode assembly28. The oxygen-containing gas channel44is connected between the oxygen-containing gas supply passage36aand the oxygen-containing gas discharge passage36b. The oxygen-containing gas channel44is formed between the cathode26and a cathode current collector54described later, specifically, inside the current collector54(internal space of porous material). The fuel gas in the fuel gas channel40and the oxygen-containing gas in the oxygen-containing gas channel44flow in opposite directions in a counterflow manner.

It should be noted that the fuel gas in the fuel gas channel40and the oxygen-containing gas in the oxygen-containing gas channel44may flow in the same direction in a parallel manner. In this case, the fuel gas supply passage34aand the oxygen-containing gas supply passage36aare positioned at the same end, and fuel gas discharge passage34band the oxygen-containing gas discharge passage36bare positioned at the same end.

The fuel cell12includes a power generation reaction area46where the fuel gas channel40and the oxygen-containing gas channel44are formed separately on front and back sides, a frame shaped marginal area48formed around the power generation reaction area46, and a first reactant gas flow area50and a second reactant gas flow area52. The first reactant gas flow area50has the fuel gas supply passage34aand the oxygen-containing gas discharge passage36b, and the second reactant gas flow area52has the fuel gas discharge passage34band the oxygen-containing gas supply passage36a.

The first reactant gas flow area50is formed outside of one end of the power generation reaction area46in the direction indicated by the arrow A and inside the marginal area48. The second reaction gas flow area52is formed outside the other end of the power generation reaction area46in the direction indicated by the arrow A and inside the marginal area48.

The cathode current collector54is stacked on the cathode26. The cathode current collector54and the cathode26have substantially the same size, and the cathode current collector54is relatively thick. For example, the cathode current collector54is made of foamed meal of, e.g., nickel or made of metal mesh, etc.

A ring shaped seal member56ais formed around the fuel gas supply passage34a, and a ring shaped seal member56bis formed around the fuel gas discharge passage34b. The ring shaped seal members56a,56bhave insulating capability and sealing capability. For example, each of the ring shaped seal members56a,56bis an incompressible seal member formed by applying glass paste to a ceramic plate.

A seal member58is formed on the marginal area48. The seal member58has substantially the same size as this marginal area48. The seal member58has insulating capability and sealing capability. For example, the seal member58is made of mica or Thermiculite (registered trademark). The seal member58seals the oxygen-containing gas supply passage36a, the oxygen-containing gas discharge passage36b, and the oxygen-containing gas channel44while allowing the oxygen-containing gas supply passage36aand the oxygen-containing gas discharge passage36bto be connected to the oxygen-containing gas channel44.

As shown inFIGS. 1 and 2, a fuel gas supply pipe60aconnected to the fuel gas supply passage34a, and a fuel gas discharge pipe60bconnected to the fuel gas discharge passage34bextend from the base frame14to the outside. Further, a pair of oxygen-containing gas supply pipes62aconnected to the oxygen-containing gas supply passage36aand a pair of oxygen-containing gas discharge pipes62bconnected to the oxygen-containing gas discharge passage36bextend from the base frame14to the outside.

As shown inFIG. 2, the roof frame16includes a first load applying unit64for applying a first load W1to the marginal area48in the stacking direction of the fuel cells12, and a second load applying unit66for applying a second load W2to the power generation reaction area46in the stacking direction. The first load W1is larger than the second load W2(W1>W2) (seeFIG. 1).

The first load applying unit64comprises an outer marginal portion of a surface of the roof frame16facing the fuel cells12. The second load applying unit66includes a recess68recessed from the first load applying unit64in a direction away from the fuel cells12(upward in the vertical direction inFIG. 2).

The recess68includes a rectangular portion68acorresponding to the shape of the power generation reaction area46of the fuel cells12. One end of the rectangular portion68ais connected to a circular arc end68bcorresponding to the shape of the ring shaped seal member56aprovided at the fuel gas supply passage34a. The other end of the rectangular portion68ais connected to a circular arc end68ccorresponding to the shape of the ring shaped seal member56bprovided at the fuel gas discharge passage34b.

A fiber mat (inorganic fiber mat)70at least containing alumina is provided in the recess68. The fiber mat70is made of ceramic material such as alumina, zirconia, silica, silicon carbide, mullite, or vermiculite, or material derived from mineral. Insulating material having heat-resistant stability of 900° C. or more can be used for the fiber mat70. In the first embodiment, among these materials, the fiber mat70chiefly containing alumina and silica is used. The alumina content of the fiber mat70is larger than the silica content of the fiber mat70. Alternatively, the fiber mat70may only contain a single material of alumina.

The shape of the fiber mat70corresponds to the shape of the recess68, and the fiber mat70includes a rectangular mat portion70ainserted into the rectangular portion68aand circular arc mat portions70b,70cinserted into the circular arc ends68b,68c. The thickness of the fiber mat70is larger than the depth of the recess68when a tightening load is applied to the fuel cell stack10(seeFIG. 5).

Though not shown, terminal plates and insulating plates are stacked between both ends of the fuel cells12in the stacking direction and the base frame14and the roof frame16.

Operation of the fuel cell stack10will be described below.

As shown inFIGS. 1 and 2, the fuel gas supply pipe60aand the pair of oxygen-containing gas supply pipes62aare connected to the base frame14of the fuel cell stack10. In the structure, a fuel gas (e.g., hydrogen gas) is supplied to the fuel gas supply pipe60a, and an oxygen-containing gas such as air is supplied to the pair of oxygen-containing gas supply pipes62a.

As shown inFIGS. 3 and 5, the fuel gas from the fuel gas supply pipe60aflows along the fuel gas supply passage34aupward in the vertical direction. In each of the fuel cells12, an inlet connection channel42ais formed between the metal support body30and the channel member38, and the fuel gas is supplied from the inlet connection channel42ato each fuel gas channel40.

Therefore, the fuel gas flows along the fuel gas channel40in the direction indicated by the arrow A, and flows through the anode flow hole32of the metal support body30, and the fuel gas is supplied to the anode24of the electrolyte electrode assembly28. The fuel gas moved along the fuel gas channel40to the outlet connection channel42bis discharged into the fuel gas discharge passage34b, and the fuel gas moves downward in the vertical direction to the fuel gas discharge pipe60b.

The air from the pair of oxygen-containing gas supply pipes62amoves along the oxygen-containing gas supply passage36aupward in the vertical direction. In each fuel cell12, the oxygen-containing gas channel44is formed, and the air is supplied from the oxygen-containing gas supply passage36ato each oxygen-containing gas channel44.

Therefore, the air moves along the oxygen-containing gas channel44in the direction indicated by the arrow A (the air and the fuel gas flow in the counterflow manner), and the air is supplied to the cathode26of the electrolyte electrode assembly28. The air moved along the oxygen-containing gas channel44is discharged into the pair of oxygen-containing gas discharge passages36b. Then, the air moves downward in the vertical direction, and the air is discharged into the pair of oxygen-containing gas discharge pipes62b.

Thus, in the electrolyte electrode assembly28, the fuel gas is supplied to the anode24and air is supplied to the cathode26. Therefore, oxide ions flow through the electrolyte22toward the anode24to perform power generation by chemical reactions.

In the first embodiment, as shown inFIG. 2, the roof frame16includes the first load applying unit64for applying the first load W1to the marginal area48of the fuel cells12in the stacking direction. Further, the roof frame16includes the second load applying unit66for applying the second load W2to the power generation reaction area46in the stacking direction.

In the structure, it becomes possible to apply the first load W1to the marginal area48to suppress leakage of the reactant gases (fuel gas and oxygen-containing gas) as much as possible, and improve the gas sealing performance. Moreover, it becomes possible to apply the second load W2to the power generation reaction area46to connect the current collection areas together further tightly, improve the current collection performance. Accordingly, it is possible to maintain the desired gas sealing performance and current collection performance while suppressing damages of the fuel cells12as much as possible.

Further, it becomes possible to effectively suppress leakage of the reactant gas flowing through the first reactant gas flow area50and the second reactant gas flow area52to the outside of the marginal area48. Moreover, supply of the reactant gases to the power generation reaction area46and discharge of the reactant gases from the power generation reaction area46are facilitated. Accordingly, both of good gas sealing performance and good current collection performance are achieved further suitably.

Further, as shown inFIG. 3, in the first reactant gas flow area50, the oxygen-containing gas discharge passage36bis provided around the fuel gas supply passage34a. In the second reactant gas flow area52, the oxygen-containing gas supply passage36ais provided around the fuel gas discharge passage34b.

In the structure, in the first reactant gas flow area50, by the oxygen-containing gas discharged from the power generation reaction area46, it is possible to raise the temperature of the fuel gas supplied to the power generation reaction area46. Accordingly, improvement in the heat efficiency is achieved, and thermally self-sustaining operation is facilitated easily. Thermally self-sustaining operation herein means operation where the entire amount of heat quantity required for operating the fuel cell stack10is supplied within the fuel cell stack10, and where the operating temperature of the fuel cell stack10is maintained using only heat energy generated in the fuel cell stack10, without supplying additional heat from the outside.

In the second reactant gas flow area52, by the fuel gas discharged from the power generation reaction area46, it is possible to raise the temperature of the oxygen-containing gas supplied to the power generation reaction area46. Accordingly, improvement in the heat efficiency is achieved, and thermally self-sustaining operation is facilitated easily.

Further, the fuel cell stack10includes the base frame14provided at one end in the stacking direction, and the roof frame16provided at the other end in the stacking direction for applying the load in the stacking direction. In this regard, as shown inFIGS. 2 and 5, the roof frame16includes the first load applying unit64and the second load applying unit66. The fiber mat70at least containing alumina is provided in the recess68of the second load applying unit66.

Therefore, the roof frame16applies the second load W2indirectly to the stacked fuel cells12through the fiber mat70. Thus, even if heat stress is generated within the fuel cell stack10, it becomes possible to absorb the heat stress by the elasticity of the fiber mat70.

Further, the first load W1is larger than the second load W2(seeFIG. 1). Therefore, it becomes possible to apply the first load W1to the marginal area48to suppress leakage of the reactant gases as much as possible, and improve the gas sealing performance. Further, it becomes possible to apply the second load W2to the power generation reaction area46to connect the current collection areas together further tightly and improve the current collection performance. Accordingly, it is possible to maintain the desired gas sealing performance and current collection performance while suppressing damages of the fuel cells12as much as possible.

Further, as shown inFIGS. 3 and 4, the fuel cell12is a metal support type fuel cell where the electrolyte electrode assembly28is joined to the metal support body30. Thus, reduction in the thickness of the fuel cell12itself is achieved as much as possible, and reduction in the overall size of the fuel cell stack10is achieved easily. Further, since the fuel cell12has the metal support body30, heat conductivity is relatively good, and it becomes possible to absorb the heat stress by the fuel cell12itself.

Further, the fuel cell12is a solid oxide fuel cell. Therefore, the fuel cell12is optimally applicable to high temperature type fuel cells such as SOFC.

FIG. 6is an exploded perspective view showing main components of a fuel cell stack80according to a second embodiment of the present invention. The constituent elements that are identical to those of the fuel cell stack10according to the first embodiment are labeled with the same reference numerals and description thereof will be omitted.

The fuel cell stack80includes a roof frame82instead of the roof frame16. The rood frame82includes a first load applying unit84for applying a first load W1to the marginal area48in the stacking direction of the fuel cells12and a second load applying unit86for applying a second load W2to the power generation reaction area46in the stacking direction.

The first load applying unit84comprises an outer marginal area of a surface of the roof frame82facing the fuel cells12. The second load applying unit86includes a recess88recessed from the first load applying unit84in a direction away from the fuel cells12. The recess88has a rectangular shape corresponding to the shape of the power generation reaction area46of the fuel cells12.

A fiber mat (inorganic fiber mat)90at least containing alumina is provided in the recess88. The fiber mat90is made of the same material as that of the fiber mat70. The fiber mat90has a rectangular shape corresponding to the shape of the recess88.

The fuel cell stack80includes ring shaped seal members92a,92binstead of the ring shaped seal members56a,56b. The ring shaped seal members92a,92bhave insulating capability and sealing capability. For example, each of the ring shaped seal members92a,92bis a compressible seal member using mica or Thermiculite (registered trademark).

As described above, in the second embodiment, the ring shaped seal members92a,92bare compressive seal members. Therefore, the fiber mat90is not required to have a shape to cover the fuel gas supply passage34aand the fuel gas discharge passage34b. It is because the ring shaped seal members92a,92bthemselves are deformable.

Accordingly, in the second embodiment, the same advantages as in the case of the first embodiment are obtained.

While 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 scope of the invention as defined by the appended claims.