Fuel cell stack, fuel cell system, and method for controlling fuel cell stack

The present disclosure provides a fuel cell stack, a fuel cell system and a method for controlling a fuel cell stack, which can reduce obstruction of reactive gas fluid channels caused by freezing of retained water, while allowing size to be reduced. The fuel cell stack of the disclosure comprises water storage units that are formed between every two adjacent fuel cell unit cells, surrounded by the adjacent separators, the wall members and the gaskets, and that communicate with the reactive gas discharge manifold via the gaps of the wall members. The fuel cell system of the disclosure controls either or both the valve and compressor in a reactive gas supply channel and/or the valve in a reactive gas discharge channel, to cause liquid water retained in the water storage units to be discharged out of the fuel cell stack. The controlling method of the disclosure includes reducing the pressure in and scavenging the interior of the reactive gas discharge manifold, to cause the liquid water that has been discharged into the reactive gas discharge manifold to be discharged out of the fuel cell stack.

FIELD

The present disclosure relates to a fuel cell stack, to a fuel cell system and to a method for controlling a fuel cell stack.

BACKGROUND

Fuel cell unit cells are known that generate electricity by chemical reaction between an anode gas such as hydrogen and a cathode gas such as oxygen.

In a fuel cell system comprising a plurality of such fuel cell unit cells stacked together as a fuel cell stack, the water generated during electric power generation, or liquid water used for humidification of the reactive gases, i.e. the anode gas and/or cathode gas, sometimes pools in the reactive gas discharge manifold inside the fuel cell stack or in the fluid channels such as the pipes downstream from the fuel cell stack.

When the fuel cell system is exposed to a temperature below the freezing point while in this state, the retained water freezes in the fluid channels, obstructing the reactive gas fluid channels in the fuel cell system and potentially interfering with supply of reactive gas to the fuel cell unit cell.

The fuel cell system may therefore become difficult to operate at below the freezing point.

To counter this problem, PTL 1 discloses a fuel cell module having a construction in which a water storage unit is installed downstream from the fuel cell stack.

In addition, PTL 2 discloses a fuel cell module wherein, when the fuel cell is mounted in a vehicle, the reactive gas discharge manifold has a water storage unit in which liquid water pools, below the membrane electrode assembly. In the fuel cell module disclosed in that publication, the electrolyte membranes of a plurality of fuel cell unit cells are inserted in a manner extending to the water storage unit, with one of the pair of end plates having a draining fluid channel that can discharge liquid water retained in the water storage unit to the exterior of the fuel cell module.

CITATION LIST

Patent Literature

SUMMARY

Technical Problem

While one solution is to install a water storage unit in the fuel cell module from the viewpoint of inhibiting obstruction of reactive gas fluid channels in a fuel cell system, as in PTLs 1 and 2, installation of a water storage unit increases the size of the fuel cell system as a whole, including the fuel cell module.

However, when implementing a fuel cell system in a vehicle or the like which has limited mounting space, it is preferable to reduce the size of the fuel cell system as a whole.

It is an object of the present disclosure to provide a fuel cell stack, a fuel cell system and a method for controlling a fuel cell stack, which can reduce obstruction of reactive gas fluid channels caused by freezing of retained water, while allowing size to be reduced.

Solution to Problem

The present inventors have found that the aforementioned object can be achieved by the following means:

A fuel cell stack comprising two or more fuel cell unit cells stacked together, in which:

each fuel cell unit cell has a power generating element and a pair of separators stacked on either side of the power generating element,

the pair of separators have reactive gas discharge flow holes running through the pair of separators in the stacking direction of the fuel cell unit cells, and

every two adjacent fuel cell unit cells are stacked together with their separators mutually adjacent and with the reactive gas discharge flow holes of the separators connected to form a reactive gas discharge manifold,

the fuel cell stack has wall members and gaskets between the separators of the two mutually adjacent fuel cell unit cells,

the wall members are disposed so as to have gaps in at least portions of the regions between the separators of the two mutually adjacent fuel cell unit cells and so as to enclose the reactive gas discharge flow holes as viewed in the stacking direction, and

the gaskets join together the separators of the two mutually adjacent fuel cell unit cells and are disposed so as to at least partially have gaps with the wall members on the opposite sides of the wall members from the reactive gas discharge flow holes, as viewed in the stacking direction,

whereby water storage units are formed that are surrounded by the separators of the two mutually adjacent fuel cell unit cells, the wall members and the gaskets, and that communicate with the reactive gas discharge manifold via the gaps of the wall members.

The fuel cell stack according to aspect 1, wherein each wall member is formed by at least one of the separators of the two mutually adjacent fuel cell unit cells.

The fuel cell stack according to aspect 1 or 2, wherein the reactive gas discharge manifold is a cathode gas discharge manifold or an anode gas discharge manifold.

The fuel cell stack according to any one of aspects 1 to 3, wherein the power generating element has a cathode gas diffusion layer, a cathode catalyst electrode layer, an electrolyte layer, an anode catalyst electrode layer and an anode gas diffusion layer in that order.

A fuel cell system comprising a fuel cell stack according to any one of aspects 1 to 4, a reactive gas supply channel, a reactive gas discharge channel and a controller, wherein:

reactive gas is circulated through the reactive gas supply channel, the fuel cell stack and the reactive gas discharge channel in that order,

the reactive gas supply channel has a valve and/or a compressor,

the reactive gas discharge channel has a valve, and

the controller:

controls at least one from among the valve and compressor of the reactive gas supply channel and the valve of the reactive gas discharge channel,

to reduce the pressure in the reactive gas discharge manifold, thereby discharging liquid water formed by the cell reaction, which has been retained in the water storage unit, into the reactive gas discharge manifold, and

to scavenge the interior of the reactive gas discharge manifold, allowing the liquid water that has been discharged into the reactive gas discharge manifold to be discharged out of the fuel cell stack.

The fuel cell system according to aspect 5, wherein:

at least one from among the valve and compressor of the reactive gas supply channel and the valve of the reactive gas discharge channel is controlled to increase the pressure in the reactive gas discharge manifold, allowing liquid water that was not discharged out of the fuel cell stack to flow into and be retained in the water storage unit.

A method for controlling a fuel cell stack according to any one of aspects 1 to 4, wherein the method includes:

reducing the pressure in the reactive gas discharge manifold to discharge liquid water produced by electric power generation in the fuel cell stack, which has been retained in the water storage unit, into the reactive gas discharge manifold, and

scavenging the interior of the reactive gas discharge manifold, so that liquid water that was discharged into the reactive gas discharge manifold is discharged out of the fuel cell stack.

The method according to aspect 7, which further includes increasing the pressure in the reactive gas discharge manifold to cause liquid water that was not discharged out of the fuel cell stack by the scavenging, to flow into and be retained in the water storage unit.

Advantageous Effects of Invention

According to the present disclosure it is possible to provide a fuel cell stack, a fuel cell system and a method for controlling a fuel cell stack, which can reduce obstruction of reactive gas fluid channels caused by freezing of retained water, while allowing size to be reduced.

DESCRIPTION OF EMBODIMENTS

Embodiments of the disclosure will now be described in detail. The disclosure is not limited to the embodiments described below, however, and various modifications may be implemented which do not depart from the gist thereof

The fuel cell stack of the disclosure has two or more fuel cell unit cells stacked together, the fuel cell unit cells each comprising a power generating element and a pair of separators stacked on either side of the power generating element, the pair of separators having reactive gas discharge flow holes running through the pair of separators in the stacking direction of the fuel cell unit cell, and every two adjacent fuel cell unit cells being stacked together with their separators adjacent and having the reactive gas discharge flow holes of the separators connected together to form a reactive gas discharge manifold.

The fuel cell stack of the disclosure has wall members and gaskets between the separators of every two adjacent fuel cell unit cells. The wall members are disposed so as to have gaps in at least portions of the regions between the separators of every two adjacent fuel cell unit cells, and so as to enclose the reactive gas discharge flow holes, as viewed in the stacking direction. The gaskets join together the separators of every two adjacent fuel cell unit cells, and are disposed so as to at least partially have gaps with the wall members, on opposite sides of the wall members from the reactive gas discharge flow holes, as viewed in the stacking direction. In the fuel cell stack of the disclosure, therefore, water storage units are formed that are surrounded by the separators of every two adjacent fuel cell unit cells, the wall members and the gaskets, and that communicate with the reactive gas discharge manifold via the gaps of the wall members.

A more specific construction for the fuel cell stack of the disclosure will now be described usingFIGS.1to4.

FIGS.1to4are full or partial schematic views of the fuel cell stack100according to the first embodiment of the disclosure.

As shown inFIG.1, the fuel cell stack100of the first embodiment of the disclosure has a construction in which a plurality of fuel cell unit cells1are stacked together.

While not shown in the drawing, each fuel cell unit cell1has a power generating element, and a pair of separators10stacked on either side of the power generating element. As shown inFIG.2, the pair of separators10each have reactive gas supply flow holes20,40, reactive gas discharge flow holes30,50and coolant flow channels60,70, running through the pair of separators10in the stacking direction of the fuel cell unit cell1.

Every two adjacent fuel cell unit cells1also have their separators10adjacent to each other, the reactive gas supply flow holes20,40, reactive gas discharge flow holes30,50and coolant flow channels60,70of the adjacent separators10being mutually connected to form a reactive gas supply manifold2, a reactive gas discharge manifold3and a coolant flow manifold (not shown).

In the fuel cell stack100of the first embodiment of the disclosure, each fuel cell unit cell1has a wall member31and a gasket33between the separators10of the two adjacent fuel cell unit cells1.

As shown inFIG.3, the wall member31is disposed so as to enclose the reactive gas discharge flow hole30, as viewed in the stacking direction. In addition, as shown inFIG.4, the wall member31is also disposed so as to form a gap32at least partially between the separators10of the two adjacent fuel cell unit cells1. InFIG.4, each wall member31is joined to one of the separators10of the two adjacent fuel cell unit cells1, forming a gap32between the wall member31and the other separator10.

As shown inFIG.3, the gasket33is also disposed so as to have a gap with the wall member31on the opposite side of the wall member31from the reactive gas discharge flow hole30, as viewed from the stacking direction. As shown inFIG.4, it is also disposed so as to join the separators10of the two adjacent fuel cell unit cells1.

Since the wall members31and gaskets33have such a construction, water storage units34are formed that are surrounded by the separators10of every two adjacent fuel cell unit cells1, wall members31and gaskets33, and that communicate with the reactive gas discharge manifold3via the gaps32between the wall members31.

InFIG.4, the outlined arrows indicate the direction in which the reactive gas flows during electric power generation.FIGS.1to4are not intended to limit the fuel cell stack, fuel cell system or controlling method of the disclosure.

In the fuel cell stack of the first embodiment of the disclosure, as shown inFIG.5, liquid water produced during electric power generation in the fuel cell stack, as well as liquid water used for humidification of the reactive gases, i.e. the anode gas and/or cathode gas, flows into the reactive gas discharge manifold together with the reactive gas, with a portion thereof being discharged out of the fuel cell stack, while the remaining liquid water200flows through the gaps32through which the water storage units34and reactive gas discharge manifold3communicate, and into the water storage unit34. It is thus possible to reduce liquid water retained in the reactive gas discharge manifold3.

This can inhibit obstruction of the reactive gas discharge manifold by freezing of liquid water200that has been retained in the reactive gas discharge manifold during operation at below the freezing point, for example.

When the external air temperature falls and it is expected that the temperature in the fuel cell stack100and/or in the reactive gas discharge channel downstream from it will be below the freezing point during operation, it may be necessary to discharge the liquid water200from the water storage unit34beforehand to cause retention of liquid water200in the water storage unit34during operation. In such cases, the pressure inside the reactive gas discharge manifold3may be reduced to cause drainage from the water storage unit34into the reactive gas discharge manifold3, and further scavenging of the interior of the reactive gas discharge manifold3in a selective manner allows the difference in air pressure between the water storage unit34interior and the reactive gas discharge manifold3interior to be utilized for discharge out of the fuel cell stack, as shown inFIG.6. As shown inFIG.7, the pressure in the reactive gas discharge manifold3can be increased, utilizing the difference in air pressure between the water storage unit34interior and reactive gas discharge manifold3interior, allowing the liquid water that could not be discharged out of the fuel cell stack to be redrawn into the water storage unit34and retained.

InFIGS.5to7, the outlined arrows indicate the direction in which the reactive gas flows during electric power generation.FIGS.5to7are not intended to limit the fuel cell stack, fuel cell system or controlling method of the disclosure.

Since the fuel cell stack of the disclosure has gaskets disposed between adjacent fuel cell unit cells when the fuel cell unit cells are stacked together, a constant thickness is maintained between the fuel cell unit cells. Spaces are provided at the thick portions in the fuel cell stack of the disclosure, as water storage units. Therefore, the fuel cell stack of the disclosure does not need to provide a water storage unit downstream from the fuel cell stack or to expand the fuel cell unit cells in the in-plane direction to form water storage units, which increases the size of the fuel cell system as a whole including the fuel cell module, as in a conventional fuel cell system.

The fuel cell stack of the disclosure can therefore reduce obstruction of the reactive gas fluid channels and can be reduced in size.

Moreover, since the fuel cell stack of the disclosure can control drainage and retention of liquid water in the water storage units by reducing or increasing pressure inside the reactive gas discharge manifold, it facilitates control of the amount of water retained in the water storage units.

Each of the fuel cell unit cells in the fuel cell stack of the disclosure has a power generating element, and a pair of separators stacked on either side of the power generating element.

The direction of stacking of the power generating elements and the pair of separators stacked on either side of the power generating elements, i.e. the stacking direction of the fuel cell unit cell, may be the same as the direction in which each of the fuel cell unit cells are stacked in the fuel cell stack, i.e. the stacking direction of the fuel cell stack.

The power generating element is an element that can generate electricity by cell reaction in the fuel cell, and specifically electrochemical reaction between the anode gas (hydrogen) and the cathode gas (oxygen or air).

The power generating element may have a cathode gas diffusion layer, a cathode catalyst electrode layer, an electrolyte layer, an anode catalyst electrode layer and an anode gas diffusion layer in that order.

The materials and forms of the cathode gas diffusion layer, cathode catalyst electrode layer, electrolyte layer, anode catalyst electrode layer and anode gas diffusion layer may be those commonly employed for conventional fuel cells.

The pair of separators have reactive gas discharge flow holes running through them in the stacking direction of the fuel cell unit cell. The reactive gas discharge flow holes may be anode gas discharge flow holes or cathode gas discharge flow holes.

The pair of separators may also have reactive gas supply flow holes and coolant flow holes.

The material used for the pair of separators may be those commonly employed for fuel cells. The forms of the pair of separators may also be forms commonly employed for conventional fuel cells, so long as they can form water storage units together with the wall members and gaskets.

The reactive gas discharge manifold is formed by the reactive gas discharge flow holes of the separator of two adjacent fuel cell unit cells being connected together.

The reactive gas discharge manifold may extend in the stacking direction of the fuel cell stack.

The reactive gas discharge manifold may be a cathode gas discharge manifold or an anode gas discharge manifold, or both.

Between the separators of every two adjacent fuel cell unit cells, the wall members are disposed so as to have gaps in at least portions of the regions between the separators of the two adjacent fuel cell unit cells, and so as to enclose the reactive gas discharge flow holes, as viewed in the stacking direction.

The wall members may have any form that allows communication between the water storage units and the reactive gas discharge manifold through the gaps while also partitioning them.

For example, each wall member may be joined with one of the separators and not joined with the other separator, so as to have a gap with the other separator. Each of the wall members may also be joined with both separators, forming a gap that allows communication between the water storage unit and the reactive gas discharge manifold.

The gap may be of a size with an area of greater than 0% and no more than 50% of the surface area of the wall member, compared to the surface area when the wall member does not have a gap between the separators of two adjacent fuel cell unit cells. The gap may have a size such that the area is greater than 0%, 5% or greater, 10% or greater or 20% or greater, and no more than 50%, no more than 40% or no more than 30%, compared to the surface area of the wall member.

The material of the wall members may be a metal, carbon material or plastic material, or it may be the same material as the separators.

The wall members are preferably formed by at least one of the facing separators of every two adjacent fuel cell unit cells. If the wall members are formed by at least one of the separators, the number of parts in the fuel cell stack will be reduced, thus making it easier to assemble the fuel cell stack. Such a construction can also reduce dislocation between the wall members and the reactive gas discharge flow holes when the fuel cell unit cells are stacked together.

One mode in which the wall members are formed by at least one of the separators is the mode illustrated inFIG.8as an example.

InFIG.8, the wall members11are formed by separators10.

InFIG.8, the outlined arrows indicate the direction in which the reactive gas flows during electric power generation.FIG.8is not intended to limit the fuel cell stack, fuel cell system or controlling method of the disclosure.

The gaskets are disposed between the separators of every two adjacent fuel cell unit cells. The gaskets join together the separators of every two adjacent fuel cell unit cells, and are disposed so as to at least partially have gaps with the wall members, on opposite sides of the wall members from the reactive gas discharge flow holes, as viewed in the stacking direction.

The material of the gaskets may be a material commonly used in fuel cell gaskets, and it may be a resin material, for example. The resin material may be rubber, for example.

The water storage units are surrounded by the separators of every two adjacent fuel cell unit cells, the wall members and the gaskets, and communicate with the reactive gas discharge manifold via the gaps of the wall members.

For the liquid water retained in the reactive gas discharge manifold to be efficiently stored in the water storage units, it is preferred for the water storage units and gaps to be formed surrounding the reactive gas discharge manifold, as viewed from the stacking direction.

The volume of the water storage units is not particularly restricted, and it may be decided from the viewpoint of providing a sufficient volume to allow adequate uptake of water accumulated in the reactive gas discharge manifold, from among the liquid water formed during electric power generation in the fuel cell stack, or liquid water used for humidification of the reactive gases, i.e. the anode gas and/or cathode gas, which is present when water storage units are not provided.

The fuel cell system of the disclosure is a fuel cell system comprising a fuel cell stack of the disclosure, reactive gas supply channel, reactive gas discharge channel and controller. The fuel cell system of the disclosure is configured so that reactive gas circulates through the reactive gas supply channel, fuel cell stack and reactive gas discharge channel, in that order. The reactive gas supply channel has a valve and/or a compressor. The reactive gas discharge channel has a valve.

The controller controls at least the valve and compressor of the reactive gas supply channel or the valve of the reactive gas discharge channel, to reduce the pressure in the reactive gas discharge manifold, whereby liquid water formed by the cell reaction, which is retained in the water storage units, is discharged into the reactive gas discharge manifold and the interior of the reactive gas discharge manifold is scavenged, allowing liquid water discharged in the reactive gas discharge manifold to be discharged out of the fuel cell stack.

As mentioned above, this allows the fuel cell stack of the disclosure to decrease and increase pressure inside the reactive gas discharge manifold to control the amount of liquid water retained in the water storage units. In the fuel cell system of the disclosure, increase and decrease of pressure inside the reactive gas discharge manifold is carried out by the valves or compressor disposed in the reactive gas supply channel and reactive gas discharge channel, to allow easy control of the amount of liquid water retained in the water storage units.

In the fuel cell system of the disclosure, when liquid water generated by the cell reaction which is retained in the water storage unit is discharged into the reactive gas discharge manifold, and the liquid water discharged into the reactive gas discharge manifold is discharged out of the fuel cell stack, some liquid water often remains in the reactive gas discharge manifold and not being discharged out of the fuel cell stack.

In such cases, the controller may also control at least one from among the valve and compressor of the reactive gas supply channel and the valve of the reactive gas discharge channel, to increase the pressure in the reactive gas discharge manifold, allowing liquid water that was not discharged out of the fuel cell stack to flow into and be retained in the water storage unit.

The fuel cell system of the disclosure may have a configuration as shown inFIG.9andFIG.10, for example.

FIG.9is a schematic diagram of a fuel cell system700according to a first embodiment of the disclosure.

As shown inFIG.9, the fuel cell system700of the first embodiment of the disclosure comprises a fuel cell stack100, a reactive gas supply channel300, a reactive gas discharge channel400and a controller600. In the fuel cell system700of the first embodiment of the disclosure, the configuration is such that reactive gas circulates through the reactive gas supply channel300, fuel cell stack100and reactive gas discharge channel400, in that order. The reactive gas supply channel300has a valve310and a compressor320. The reactive gas discharge channel400also has a valve410.

In the fuel cell system700of the first embodiment of the disclosure, the controller600controls at least the valve310and compressor320of the reactive gas supply channel300or the valve410of the reactive gas discharge channel400, to reduce the pressure in the reactive gas discharge manifold3, whereby liquid water200formed by the cell reaction, which is retained in the water storage units34, is discharged into the reactive gas discharge manifold3, and the interior of the reactive gas discharge manifold3is scavenged, allowing liquid water200discharged into the reactive gas discharge manifold3to be discharged out of the fuel cell stack100.

In addition, the fuel cell system700of the first embodiment of the disclosure may control at least one from among the valve310and compressor320of the reactive gas supply channel300and the valve410of the reactive gas discharge channel400using the controller600, to increase the pressure in the reactive gas discharge manifold3, allowing liquid water200that was not discharged out of the fuel cell stack100to flow into and be retained in the water storage unit34.

More specifically, the controller600in the fuel cell system700of the first embodiment of the disclosure may control the valve310and/or the compressor320of the reactive gas supply channel300to reduce the flow rate of reactive gas supplied from the reactive gas supply channel300to the fuel cell stack100, and/or it may control the valve410of the reactive gas discharge channel400to increase the flow rate of the reactive gas discharged from the fuel cell stack100into the reactive gas discharge channel400, to decrease the air pressure inside the reactive gas discharge manifold3. For example, the controller600may control the valve310and/or compressor320of the reactive gas supply channel300to increase the flow rate of the reactive gas in the reactive gas discharge manifold3, to scavenge the interior of the reactive gas discharge manifold3.

Alternatively, the controller600in the fuel cell system700of the first embodiment of the disclosure may control the valve310and/or the compressor320of the reactive gas supply channel300to increase the flow rate of reactive gas supplied from the reactive gas supply channel300to the fuel cell stack100, and/or it may control the valve410of the reactive gas discharge channel400to decrease the flow rate of the reactive gas discharged from the fuel cell stack100into the reactive gas discharge channel400, to increase the air pressure inside the reactive gas discharge manifold3.

FIG.10is a schematic diagram of a fuel cell system700according to a second embodiment of the disclosure.

As shown inFIG.10, the fuel cell system700of the second embodiment of the disclosure comprises a fuel cell stack100, a reactive gas supply channel300, a reactive gas discharge channel400and a controller600. In the fuel cell system700of the second embodiment of the disclosure, the reactive gas supply channel300and the reactive gas discharge channel400are in communication via a fluid channel500. The fluid channel500has a compressor510.

The fluid channel500may be considered to be part of the reactive gas supply channel300, and in the fuel cell system700of the second embodiment of the disclosure, the controller600controls at least the valve310of the reactive gas supply channel300and the compressor510of the fluid channel500, and/or the valve410of the reactive gas discharge channel400, to reduce the pressure in the reactive gas discharge manifold3, whereby liquid water200formed by the cell reaction, which is retained in the water storage units34, is discharged into the reactive gas discharge manifold3, allowing the liquid water200discharged into the reactive gas discharge manifold3to be discharged out of the fuel cell stack100.

FIGS.9and10are not intended to limit the fuel cell stack, fuel cell system or controlling method of the disclosure.

The fuel cell stack of the fuel cell system of the disclosure is as described above for the fuel cell stack of the disclosure.

The reactive gas supply channel of the fuel cell system of the disclosure is a fluid channel for supply of reactive gas to the fuel cell stack. The reactive gas supply channel has a valve and/or a compressor.

When the reactive gas is an anode gas such as hydrogen gas, the reactive gas supply channel allows communication between the reactive gas source, such as an anode gas tank, and the reactive gas supply channel of the fuel cell stack. When the reactive gas is a cathode gas such as oxygen or air, the reactive gas supply channel allows communication between the exterior of the fuel cell system and the reactive gas supply channel of the fuel cell stack.

The reactive gas discharge channel of the fuel cell system of the disclosure is a fluid channel for discharge of reactive gas from the fuel cell stack. The reactive gas discharge channel has a valve. The reactive gas discharge channel allows communication between the reactive gas discharge manifold of the fuel cell stack and the exterior of the fuel cell system. Particularly when the reactive gas is an anode gas such as hydrogen gas, the reactive gas discharge channel may branch out into a fluid channel connected with the exterior of the fuel cell system and a fluid channel connected with the reactive gas supply channel. In this case, the valve is disposed in the fluid channel connected with the exterior of the fuel cell system, while the compressor is disposed in the fluid channel connected with the reactive gas supply channel. The fluid channel connected with the reactive gas supply channel can be considered to be part of the reactive gas supply channel.

The controller of the fuel cell system of the disclosure controls at least the valve and compressor of the reactive gas supply channel and/or the valve of the reactive gas discharge channel, to reduce the pressure in the reactive gas discharge manifold, whereby liquid water formed by the cell reaction, which is retained in the water storage units, is discharged into the reactive gas discharge manifold, allowing the liquid water discharged into the reactive gas discharge manifold to be discharged out of the fuel cell stack.

In such cases, the controller may control at least one from among the valve and compressor of the reactive gas supply channel and the valve of the reactive gas discharge channel, to increase the pressure in the reactive gas discharge manifold, allowing liquid water that was not discharged out of the fuel cell stack to flow into and be retained in the water storage unit.

Control of the valve and compressor of the reactive gas supply channel and the valve of the reactive gas discharge channel by the controller may be carried out when it is necessary to discharge liquid water from the water storage units.

The situation in which it is necessary to discharge liquid water from the water storage units is not particularly restricted, and it may be one in which it is expected that the fuel cell stack or the reactive gas discharge channel downstream from it will fall below the freezing point during operation of the fuel cell system, for example.

The method of control in such cases is not particularly restricted, and for example, it may be a method in which, when the outdoor air temperature has reached a prescribed temperature, a signal is sent to the controller by a temperature sensor and the controller begins control upon receipt of the signal.

The controlling method according to the disclosure is a method for controlling the fuel cell stack of the disclosure.

The controlling method of the disclosure includes reducing the pressure in the reactive gas discharge manifold, so that liquid water produced by electric power generation in the fuel cell stack, which has been retained in the water storage unit, is discharged into the reactive gas discharge manifold, and the interior of the reactive gas discharge manifold is scavenged, whereby the liquid water that was discharged into the reactive gas discharge manifold is discharged out of the fuel cell stack.

The controlling method of the disclosure may further include increasing the pressure in the reactive gas discharge manifold to cause liquid water that was not discharged out of the fuel cell stack by the scavenging, to flow into and be retained in the water storage units.

The controlling method of the disclosure may be carried out using the fuel cell system of the disclosure, for example.

The controlling method of the disclosure may also be carried out when it has been judged that drainage of the interior of the reactive gas discharge manifold is necessary. Judgment of whether or not drainage of the reactive gas discharge manifold is necessary may be judgment of whether or not the fuel cell stack or the reactive gas discharge channel downstream from it is expected to fall below the freezing point during operation of the fuel cell system, for example.

FIG.11is a flow chart illustrating a method of controlling the controlling method according to the first embodiment of the disclosure.

As shown inFIG.11, the controlling method of the first embodiment of the disclosure is carried out when drainage of the reactive gas discharge manifold is necessary (S1). When it is judged that drainage of the reactive gas discharge manifold is not necessary, the controlling method of the first embodiment of the disclosure is not carried out.

When it is judged that drainage of the reactive gas discharge manifold is necessary, the interior of the reactive gas discharge manifold is reduced in pressure to a predetermined pressure P1(S2), thus causing the liquid water generated by electric power generation in the fuel cell stack, which has been retained in the water storage units, to be discharged into the reactive gas discharge manifold.

The reactive gas discharge manifold interior is then scavenged (S3).

It is then judged whether or not a predetermined time has elapsed (S4), and when the predetermined time has elapsed, the reactive gas discharge manifold interior is increased in pressure to P2(S5), the scavenging causing the liquid water that was not discharged out of the fuel cell stack to flow into and be retained in the water storage unit.

FIG.11is not intended to limit the fuel cell stack, fuel cell system or controlling method of the disclosure.

Pressure reduction and increase in the reactive gas discharge manifold can be carried out by control as described for the fuel cell system of the present disclosure. It can be judged whether or not the reactive gas discharge manifold interior is at the predetermined air pressure by using an air pressure sensor situated in the reactive gas supply channel or in the reactive gas discharge channel, for example.

REFERENCE SIGNS LIST

1Fuel cell unit cell3Reactive gas discharge manifold10Separator30Reactive gas discharge flow hole31Wall member33Gasket34Water storage unit100Fuel cell stack300Reactive gas supply channel310Valve320Compressor400Reactive gas discharge channel410Valve600Controller700Fuel cell system