Abstract:
A fuel cell system is provided which generates electricity by supplying fuel gas and oxidant gas to a fuel cell stack comprising a fuel cell stack, a DC power supply, and a controller. The DC power supply comprises at least one of a generator and battery. The controller is programmed to determine whether or not the fuel cell stack is generating electricity, and to supply current to the fuel cell stack by at least one of the generator and the battery when generation of electricity by the fuel cell stack is terminated. The current supplied to the fuel cell stack removes residual water in the fuel cell stack by electrolytically reducing the water into hydrogen and oxygen gasses which are subsequently purged from the fuel cell stack.

Description:
TECHNICAL FIELD OF THE INVENTION  
       [0001]     This invention relates to fuel cell systems and in particular fuel cell systems for use in motor vehicle applications.  
       BACKGROUND OF THE INVENTION  
       [0002]     Fuel cells have been developed as alternative power sources for motor vehicles, such as electrical vehicles. A fuel cell is a demand-type power system in which the fuel cell operates in response to the load imposed across the fuel cell. Typically, a liquid hydrogen containing fuel, for example, gasoline, methanol, diesel, naphtha, etc. serves as a fuel supply for the fuel cell after the fuel has been converted into a gaseous stream containing hydrogen. The conversion to the gaseous steam is usually accomplished by passing the fuel through a fuel reformer to convert the liquid fuel to a hydrogen gas stream that usually contains other gases such as carbon monoxide, carbon dioxide, methane, water vapor, oxygen, and unburned fuel. The hydrogen is then used by the fuel cell as a fuel in the generation of electricity for the vehicle.  
         [0003]     A polymer electrolyte membrane type of fuel cell is generally composed of a stack of unit cells comprising a polymer electrolyte membrane enclosed between electrodes and gas diffusion layers, and further enclosed between separators that contain channels for fuel gas and oxidant gas. The stack is fixed by end plates. A current collector may be provided between the end plate and stack, or the end plate itself may function as current collector. When hydrogen is used as the fuel gas and oxygen is used as the oxidant gas, electrons are released due to a chemical reaction, and water is formed as a by-product, via the reaction:
 
H 2 +½O 2  H 2 O.
 
 Consequently, the fuel cell is an energy source that has no adverse impact on the global environment, and has been the focus of much research for use in automobiles in recent years. 
 
         [0005]     Although the water that is the product of the reaction is environmentally benign, when a large quantity of water reaction product accumulates in the fuel cell, it blocks the gas channels and the gas diffusion layers, causing a drop in electrical generation efficiency. In addition, if the fuel cell is exposed to sub-freezing temperatures, which are common in the temperate and polar latitudes, the accumulated water freezes in the fuel cell and blocks the gas channels. It is not possible to generate electricity from frozen fuel cells when the gas channels are clogged with ice. Even if a heater is used to melt the ice, it takes time melt the ice and thus rapid start up of an electrical vehicle is not possible with a frozen fuel cell.  
         [0006]     Therefore, methods have been tried to reduce the quantity of water in the fuel cell stack before the stack freezes, to facilitate the generation of electricity in subfreezing ambients. One such method is to increase the flow rate of fuel gas and oxidant gas to blow the accumulated water out of the channels after electrical generation is shut down. Another method is to vacuum dry the channels, as in U.S. Pat. No. 6,358,637. However, these methods take a substantial amount of time to dry the fuel cell to an acceptable level. This is probably because it is difficult to eliminate water from the small cavities in the gas diffusion layer and the electrode when attempting to dry the fuel cell by gas purge or vacuum drying.  
         [0007]     Deterioration of electrical generation performance is especially problematic when water freezes in the portion of the electrode formed by a three-way interface, because the electrode reaction is obstructed.  
         [0008]     Time-consuming methods of drying or heating fuel cells in automotive applications are not feasible, because rapid startup is required and the fuel cell frequently cycles between operating and shut down states.  
       SUMMARY OF THE INVENTION  
       [0009]     There exists a need in the fuel cell art for a fuel cell system that reduces the amount of water that remains in the fuel cell after terminating electricity generation. There exists a need in the fuel cell art to prevent water produced by the fuel cell reaction from blocking gas channels and gas diffusion layers of fuel cells. There also exists a need in the fuel cell art to prevent water from freezing in fuel cell gas channels and gas diffusion layers. There exists a need in the fuel cell art for a rapid and efficient method of removing water from a fuel cell after terminating electricity generation.  
         [0010]     There exists a need in the electrical vehicle art for electrical vehicles powered by fuel cells that rapidly and efficiently generate electricity upon demand. There exists a need in the electrical vehicle art for electrical vehicles powered by fuel cells which do not suffer from electrical generation startup delay due to frozen water blocking gas channels and gas diffusion layers.  
         [0011]     These and other needs are met by certain embodiments of the present invention, which provide a fuel cell system which generates electricity by supplying fuel gas and oxidant gas to a fuel cell stack comprising a fuel cell stack, a DC power supply, and a controller. The DC power supply comprises at least one of a generator and battery. The controller is programmed to determine whether or not the fuel cell stack is generating electricity, and to supply current to the fuel cell stack by at least one of the generator and the battery when generation of electricity by the fuel cell stack is terminated.  
         [0012]     The earlier stated needs are also met by certain embodiments of the present invention, which provide a motor vehicle comprising a fuel cell system which generates electricity by supplying fuel gas and oxidant gas to a fuel cell stack comprising a fuel cell stack, a DC power supply, and a controller. The DC power supply comprises at least one of a generator and battery. The controller is programmed to determine whether or not the fuel cell stack is generating electricity, and to supply current to the fuel cell stack by at least one of the generator and the battery when generation of electricity by the fuel cell stack is terminated.  
         [0013]     The earlier stated needs are also met by certain embodiments of the present invention, which provide a fuel cell system which generates electricity by supplying fuel gas and oxidant gas to a fuel cell stack comprising a fuel cell stack, DC power supply, and a means of controlling a flow of current to the fuel cell stack. The DC power supply comprises at least one of a generator and battery. The means of controlling a flow of current to the fuel cell stack is equipped with a means of measuring the current flowing to the fuel cell stack while it is flowing. The means controls a voltage impressed on the fuel cell stack so that the current flowing to the fuel cell stack reaches a predetermined amperage.  
         [0014]     The earlier stated needs are further met by certain embodiments of the present invention, which provide a motor vehicle comprising a fuel cell system which generates electricity by supplying fuel gas and oxidant gas to a fuel cell stack comprising a fuel cell stack, DC power supply, and a means of controlling a flow of current to the fuel cell stack. The DC power supply comprises at least one of a generator and battery. The means of controlling a flow of current to the fuel cell stack is equipped with a means of measuring the current flowing to the fuel cell stack while it is flowing. The means controls a voltage impressed on the fuel cell stack so that the current flowing to the fuel cell stack reaches a predetermined amperage.  
         [0015]     In addition, the earlier stated needs are also met by certain embodiments of the present invention, which provide a method of removing water from a fuel cell system. The fuel cell system comprises a fuel cell stack having at least one unit cell, a DC power supply and a programmable controller. The DC power supply comprises at least one of a generator and battery. The method comprises the steps of generating electricity from the fuel cell stack by supplying fuel gas and oxidant gas to the fuel cell stack. When generation of electricity from the fuel cell stack is terminated, the termination of the generation of electricity is determined by the fuel cell stack using the programmable controller, which is also used to supply current to the fuel cell stack from the DC power supply.  
         [0016]     The present invention addresses the need for a fuel cell system that rapidly and efficiently removes water from a fuel cell after the termination of the generation of electricity. The present invention further addresses the need for a method that rapidly and efficiently removes water from a fuel cell after terminating the generation of electricity. The present invention also addresses the need for a motor vehicle with a fuel cell system that rapidly and efficiently starts up in subfreezing ambients.  
         [0017]     The foregoing and other features, aspects, and advantages of the present invention will become apparent in the following detailed description of the present invention when taken in conjunction with the accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0018]      FIG. 1A  schematically illustrates a cross-section of a fuel cell stack according to an embodiment of the present invention.  
         [0019]      FIG. 1B  schematically illustrates a cross-section of a fuel cell stack and a system of supplying current to individual cells according to an embodiment of the present invention.  
         [0020]      FIG. 2  illustrates a fuel cell system according to an embodiment of the present invention, as described in Example 1.  
         [0021]      FIG. 3  is a flow chart illustrating the operation of the means of controlling the flow of current to the fuel cell stack.  
         [0022]      FIG. 4  is a flow chart illustrating operation of the means of shutting off the flow of current to the fuel cell stack according to an embodiment of the present invention, as described in Example 1.  
         [0023]      FIG. 5  illustrates a fuel cell system according to an embodiment of the present invention, as described in Example 2.  
         [0024]      FIG. 6  is a flow chart illustrating operation of the means of shutting off the flow of current to the fuel cell stack according to an embodiment of the present invention, as described in Example 2.  
         [0025]      FIG. 7  illustrates a fuel cell system according to an embodiment of the present invention, as described in Example 3.  
         [0026]      FIG. 8  is a flow chart illustrating operation of the means of shutting off the flow of current to the fuel cell stack according to an embodiment of the present invention, as described in Example 3.  
         [0027]      FIG. 9  illustrates a fuel cell system according to an embodiment of the present invention, as described in Example 4.  
         [0028]      FIG. 10  is a flow chart illustrating operation of the means of shutting off the flow of current to the fuel cell stack according to an embodiment of the present invention, as described in Example 4. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0029]     The present invention provides a fuel cell system that rapidly and efficiently removes water from a fuel cell after terminating the generation of electricity. The present invention also provides a motor vehicle with a fuel cell system that rapidly and efficiently starts up in subfreezing ambients. These benefits are provided by providing current to a fuel cell stack after terminating the generation of electricity to electrolytically breakdown the water remaining in the fuel cell into hydrogen gas and oxygen gas.  
         [0030]     A fuel cell stack  10  used in certain embodiments of the present invention is illustrated in  FIG. 1A . Fuel cell stacks  10  comprise at least one unit cell  132  equipped with a membrane electrode assembly  130  constructed of a polymer electrolyte membrane  11  enclosed between two electrodes  12 , gas diffusion layers  13 , and separator  15 . Fuel gas and oxidant gas are supplied to the unit cells via gas channels  14  and the unit cells are  132  are stacked between end plates  16 . Electrical current is supplied to the fuel cell stack  10  according to the present invention via conductors  134  and the current flow is controlled by a means for controlling current flow  17 . When current flows to the fuel cell stack  10 , an electrolytic reaction takes place, opposite to that of electricity generation, as follows:
 
H 2 O H 2 +½O 2 .
 
         [0031]     This reaction consumes water in the polymeric solid electrolyte membranes  11 , electrode areas  12 , gas channels  14 , and gas diffusion layers  13  of the fuel cell stack  10 . Thus, the quantity of water retained in the fuel cell stack  10  is reduced, and the fuel cell stack  10  can be easily started when the ambient temperature is below the freezing point because gas flow is not blocked by ice. The electrolytic decomposition of water requires that the current flows to the fuel cell stack in such a way that hydrogen is produced at the fuel electrode, and oxygen is produced at the oxidant electrode. For this purpose, an anode of a DC power supply selected from at least one of a generator and a battery is connected with an anode of the fuel cell stack  10  and a cathode of the DC power supply of at least one of the generator and the battery is connected with a cathode of the fuel cell stack. In a fuel cell, the reaction that electrolyzes water occurs when the voltage impressed when the current flows to the fuel cell stack is 1.23 V or more. To avoid damage to the fuel cell stack, it is desirable that the maximum impressed voltage be about 5 V.  
         [0032]     In certain embodiments of the present invention, the means of controlling the flow of current to the fuel cell stack  17  is equipped with a means of measuring the current flowing to the fuel cell stack. The means of controlling the flow of current to the fuel cell stack  17  also controls the voltage impressed on the fuel cell stack  10 , so that the current flowing to the said fuel cell stack reaches a predetermined amperage and the reaction that electrolyzes water proceeds at a constant amperage. If the voltage, rather than the current were constant, the electrolysis reaction of the water would cease when there was only a small amount of water inside the fuel cell stack. Therefore, it is desirable to control the voltage so that current flows at a constant amperage.  
         [0033]     In certain embodiments of the present invention, the means of controlling the flow of current to the fuel cell stack  10  is connected to each unit cell  132  that composes the fuel cell stack  10 . Thus, current can flow simultaneously to all the unit cells  132 , shortening the time required to electrolyze the water, as shown in  FIG. 1B .  
         [0034]     In another embodiment of the fuel cell system according to the present invention, the flow of electrical current is controlled so that current can be supplied at discretion to at least one or more of the unit cells  132  that compose the fuel cell stack  10 . Each unit cell  132  is electrically insulated from neighboring unit cells by electrical insulation  18  positioned between each unit cell  132 . Therefore, according to this embodiment of the present invention, it is possible to selectively electrolyze the water in only the unit cells that have a high moisture content. In certain embodiments of the invention, more than two unit cells can be isolated from the other cells. If the resistance of a particular unit cell is low and the cell voltage is lower than the average cell voltage of the stack or a predetermined value, the fuel cell system of the present invention can determine that the cell is flooding, (i. e.—there is too much water in the unit cell, thus fuel and oxidant gas is blocked).  
         [0035]     In certain embodiments of the present invention, the flow of electrical current to selected unit cells is controlled by an array of switches A, B, and C.  FIG. 1B  illustrates individual, electrically insulated, unit fuel cells  132  wherein switches A, B, C are adapted to electrically connect and disconnect the unit cells  132  so that current can be selectively supplied where needed. In normal operation, the status of switches A, B, and C for each cell is as follows: 
    Switch A: Open     Switch B: Close     Switch C: Open.    
 
         [0039]     Closing switch B and opening switch A allows the center cell, which is isolated from the other cells by electrical insulation  18 , to connect to the other cells in series.  
         [0040]     If the center cell has too much water, the status of switches for only the center cell are changed as follows in order to supply current to the center cell: 
    Switch A: Close     Switch B: Open     Switch C: Close.    
 
         [0044]     Opening switch B and closing switch C electrically isolates the center cells from the other cells. The cells adjacent the center cell are connected to each other. Therefore, the power supply  19  can selectively supply current to the center cell without stopping fuel cell stack operation.  
         [0045]     In another embodiment of the present invention, the system is controlled so that current flows to the unit cell  132  that contacts the end plate  16  and to a continuous series of at least one and at most ten unit cells. According to an embodiment of the present invention it is possible to electrolyze water only in the unit cells adjacent both ends of the stack  10 , where water is most likely to condense. The heat capacity of the end plates  16  is larger than the unit cells  132  so that the unit cells that contact the end plate are more likely to have larger amounts of water condensed within than other unit cells.  
         [0046]     In another embodiment of the present invention, the fuel cell system comprises a means of shutting off the flow of current to the fuel cell stack that shuts off the flow of current to a fuel cell stack when the duration of current flow to the fuel cell stack reaches a predetermined time.  
         [0047]     In another embodiment of the present invention, the fuel cell system has a means of measuring the flow rate of fuel gas (H 2 ) in the gas discharged from a fuel gas discharge port of the fuel cell stack. The means of shutting off the current flow to the fuel cell stack shuts off the flow of current to the fuel cell stack if it determines that the flow rate of the fuel gas falls below the value that is measured before supplying current to the stack.  
         [0048]     In another embodiment of the present invention, the fuel cell system has a means of measuring the humidity of the gas discharged from a fuel gas discharge port or an oxidant gas discharge port of the fuel cell stack. The means of shutting off the current flow to the fuel cell stack shuts off the flow of current to the fuel cell stack if the means of measuring humidity determines that the humidity of the gas discharged from the fuel gas discharge port or the oxidant gas discharge port falls below a predetermined value.  
         [0049]     In another embodiment of the present invention, the fuel cell system has a means of measuring the moisture content of the polymer electrolyte membrane in the fuel cell stack. The means of shutting off the current flow is controlled so that the flow of current to the fuel cell stack is shut off if the means of measuring the moisture content of polymer electrolyte membrane determines that the moisture content falls below a predetermined value.  
         [0050]     Thus, the various embodiments of the invention make it possible to avoid damage to the fuel cell stack due to excessive current flow, and to reduce the energy consumption needed for electrolysis.  
         [0051]     In another embodiment of the present invention, the fuel cell system has a means of measuring the moisture content of the polymer electrolyte membrane in the fuel cell stack. The means of measuring the moisture content of the polymer electrolyte membrane measures the resistance of at least some of the cells in the fuel cell stack, and calculates the moisture content based on the resistance of the cells. Thus, it is possible to measure the moisture content of the polymer electrolyte membrane without providing a humidity sensor inside the unit cell.  
         [0052]     In another embodiment of the present invention, the fuel cell system is controlled, so that, when current flows to the fuel cell stack, the fuel gas and oxidant gas inside the fuel cell stack are simultaneously discharged from the fuel cell. The progress of the electrolytic reaction is not obstructed, as it would be if the hydrogen and oxygen produced by electrolysis remained in the unit cell. This can be implemented by purging the cell with an inert gas, such as nitrogen, or by providing a pump to suction the gas at the gas discharge port of the fuel cell stack.  
         [0053]     In another embodiment of the invention, the fuel cell system contains a means of burning the fuel gas discharged from the fuel cell stack. Burning the fuel gas discharged from the fuel cell stack prevents the undesirable release of flammable gases, such as hydrogen, into the atmosphere.  
         [0054]     This invention will be further described in conjunction with the following specific examples of fuel cell systems. However, these are exemplary only, as the claimed invention is not limited to the specific examples disclosed herein.  
       Example 1  
       [0055]      FIG. 2  shows the outline of a fuel cell system  140  according to an embodiment of the present invention. Hydrogen is supplied to the fuel cell stack  21  via the anode gas supply line  27 . Air is supplied to the fuel cell stack  21  via the cathode gas supply line  28 . Nitrogen gas supply valves  30  are also provided for the purpose of purging the fuel cell stack  21  during shutdown. A catalytic hydrogen burner  34  is provided in the anode discharge line  144 , to burn the hydrogen produced by electrolysis. A battery  22  is charged by electric power from a generator  23 . An ammeter  32  and a voltmeter  33  are provided in the electrical current line  142  to the fuel cell stack  21 . An output signal from the ammeter  32  is outputted to a means  24  of controlling the flow of current to the fuel cell stack. The output signal from the voltmeter  33  is outputted to a means  26  of shutting off the flow of current to the fuel cell stack. The means  26  of shutting off the flow of current to fuel cell stack outputs the control signal of means  24  of controlling the flow of current to the fuel cell stack. While the fuel cell system is generating electricity, the hydrogen supply valve  29  and air supply valve  31  are open, and the nitrogen supply valves  30  are closed.  
         [0056]     The generator  23  generates electricity to charge the battery  22 , and the switch  25  is shut off, while the fuel cell stack  21  is generating electricity. When the fuel cell stack electrical generation is shut down, the hydrogen supply valve  29  and air supply valve  31  are closed, the nitrogen supply valve  30  is opened, and a nitrogen purge of fuel cell system is started.  
         [0057]     The flow of current to the fuel cell is controlled by a means  24  of supplying current to the fuel cell.  FIG. 3  shows a flow chart of this process. Although the specified value at step  43  is 200 mA/cm 2  in this example, the specified value varies with the structure of the fuel cell system  140 . When current starts to flow to the fuel cell stack  21 , means  26  of shutting off the flow of current to the stack monitors the status of current flow to the fuel cell stack  21 .  FIG. 4  shows an operational flow chart of the means  26  of shutting off the flow of current to the fuel cell. The specified value at step  50  varies with the structure of the fuel cell system, but in this example the value is 5V. Although, the specified time at step  51  is 10 minutes in this example, the specified time varies with the structure of the fuel cell system. After electrical generation was terminated, the fuel cell stack  21  of this example was stored for 8 hours at −20° C. and then fuel gas and oxidant gas was again introduced into the fuel cell stack  21 . The fuel cell stack  21  was then able to generate electricity without any special means of thawing.  
       Example 2  
       [0058]      FIG. 5  illustrates the outline of a fuel cell system  150  according to another embodiment of the present invention. The fuel cell stack  61  is composed of 20 unit cells. Hydrogen is supplied via an anode gas supply line  67 , and air is supplied via a cathode gas supply line  68 . Nitrogen gas supply valves  70  are also provided for the purpose of purging the fuel cell stack  61  during shutdown. A catalytic hydrogen burner  74  is provided in the anode discharge line  152 , to burn the hydrogen produced by electrolysis. A humidity sensor  75  is provided in the cathode discharge line  154 . The fuel cell stack  61  and the battery  62  are connected via the battery switch  63 . The battery  62  is also connected to a means  64  of controlling the flow of current to the fuel cell stack. In addition, five unit cells (not shown) from each of the two end plates of the fuel cell stack  61  are each connected, via a switch  65  to a means  64  of controlling the flow of current to the fuel cell stack. Each of these unit cells is also provided with a unit cell ammeter  72  and a unit cell voltmeter  73 . The output signal of the unit cell ammeter  72  is outputted to the means  64  of controlling the flow of current to the fuel cell stack. The output signal of the unit cell voltmeter  73  is outputted to the means  66  of shutting off the flow of current to the fuel cell stack. The means  66  of shutting off the flow of current to the fuel cell stack outputs the control signal of the means  64  of controlling the flow of current to the fuel cell stack.  
         [0059]     While the fuel cell stack is generating electricity, the hydrogen supply valve  69  and air supply valve  71  are open, and the nitrogen supply valve  70  is closed. The battery switch  63  is connected, and the switch  65  is shut off. When the fuel cell stack electrical generation is shut down, the hydrogen supply valve  69  and air supply valve  71  are closed, and the nitrogen supply valve  70  is opened, and the nitrogen purge of the fuel cell system  150  is started. Current is flowed to the fuel cell stack  61  and the flow of current to the fuel cell stack  61  is controlled by a means  64  of supplying current to the fuel cell stack. The flow chart for this process is the same as in  FIG. 3 .  
         [0060]     When current starts to flow to the fuel cell stack  61 , a means  66  of shutting off the flow of current to the fuel cell stack monitors the status of current flow to the fuel cell stack  61 .  FIG. 6  shows a flow chart of the operation of the means  66  of shutting off the flow of current to the fuel cell stack. The specified value at step  80  varies with the structure of the fuel cell system, but in this example the value is 5V. The specified value for the relative humidity at step  81  is 50% in this example, but it varies with the structure of the fuel cell system. After electrical generation was terminated, the fuel cell stack  61  of this example was stored for 8 hours at −20° C. and then fuel gas and oxidant gas was again introduced into the fuel cell stack  61 . The fuel cell stack  61  was then able to generate electricity without any special means of thawing.  
       Example 3  
       [0061]     An outline of a fuel cell system  160  according to another embodiment of the present invention is illustrated in  FIG. 7 . A H 2  flow meter  90  is located on the anode outlet  162 . Other components are the same as example  2 . Flow of current to the fuel cell stack  61  is controlled by a means  64  of supplying current to the fuel cell stack. The flow chart for this process is the same as in  FIG. 3 .  FIG. 8  shows an operational flow chart of the means  66  of shutting off the flow of current to the fuel cell stack  61 . The specified value at step  102  varies with the structure of the fuel cell system, but in this fuel cell system  160  the value is 5V. The H 2  flow meter  90  measures H 2  flow rate before the current is supplied at step  100 . While current is supplied, the H 2  flow rate is checked at step  103 . If the H 2  flow rate is lower than the value that is measured at step  100 , it is determined that the excess water is eliminated from the fuel cell stack  61 , and current flow to the fuel cell stack  61  is terminated at step  104 .  
       Example 4  
       [0062]     An outline of a fuel cell system  170 , according to another embodiment of the present invention, is illustrated in  FIG. 9 . A resistance meter  110  is connected to each unit cell (not shown). The resistance meter  110  measures each cell&#39;s resistance by the AC impedance method. A cathode exhaust pump  111  and an anode exhaust pump  112  are used for discharging gas from the cathode and anode of the fuel cell stack  61 , respectively, after terminating electrical generation by the fuel cell stack  61 . Other components of the fuel cell system  170  are the same as in example  2 . The flow of current to the fuel cell stack is controlled by a means  64  of supplying current to the fuel cell stack. The flow chart for this process is the same as in  FIG. 3 .  FIG. 10  illustrates a flow chart of the operation of a means  66  of shutting off the flow of current to the fuel cell stack. The specified value at step  122  is 5V in this example, but it varies with the structure of the fuel cell system. The resistance meter  110  measures each unit cell&#39;s resistance and calculates the average unit cell resistance before supplying current at step  120 . While current is being supplied, the average unit cell resistance is measured at step  123 . If the average cell resistance is higher than the value that is measured at step  120 , it is determined that excess water is eliminated from the fuel cell stack  61 , and current flow to the fuel cell stack  61  is terminated at step  124 .  
         [0063]     The embodiments illustrated in the instant disclosure are for illustrative purposes. They should not be construed to limit the scope of the claims. Though the fuel cell systems described are particularly well suited to electrical vehicles, such as automobiles, the instant fuel cell systems are suitable for a wide variety of motor vehicles that are included within the scope of the instant claims including, motorcycles, buses, trucks, recreational vehicles, and agricultural and industrial equipment. As is clear to one of ordinary skill in this art, the instant disclosure encompasses a wide variety of embodiments not specifically illustrated herein.