Abstract:
A fuel cell system has a plurality of fuel cells each having a cathode and an anode disposed on opposite sides of an electrolyte membrane, having an air supply passage through which atmospheric air is supplied to the cathode. A fuel gas supply passage supplies hydrogen gas from a hydrogen storing alloy to the anode; and water spray nozzles spray liquid water directly onto the cathode. The hydrogen storing alloy is heated by heat exchange with the exhaust air at an elevated temperature discharged from the cathode, to facilitate its endothermic reaction in which it produces hydrogen gas to be supplied to the anode. The sprayed water is fed to the hydrogen storing alloy so as to cool the same to thereby enhance its exothermic reaction in which hydrogen gas is stored in the hydrogen storing alloy.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a fuel cell system with hydrogen storing alloy from which hydrogen gas is introduced to an anode of a fuel cell unit. 
     2. Description of the Prior Art 
     A fuel cell system comprises in general a fuel cell unit, an air supplying means and a fuel supplying means. The fuel cell unit has an electrolyte membrane such as a proton exchange membrane (PEM) between two electrodes, that is a cathode to which an atmospheric air (or oxygen) is supplied through the air supplying means and an anode to which hydrogen gas is supplied through the fuel supplying means. Oxygen at the cathode and hydrogen at the anode react with each other to generate electricity. In actual application, the system includes a plurality of fuel cells which are stacked in series with a separator being interposed between adjacent fuel cells. 
     An attempt has been proposed that a hydrogen storing alloy is used as a hydrogen gas supply source. As known, the hydrogen storing alloy is capable of storing therein and discharging therefrom hydrogen gas depending upon the ambient temperature and the partial pressure of hydrogen therearound. The hydrogen storing alloy stores hydrogen gas in an exothermic reaction whereas it discharges hydrogen gas in an endothermic reaction. For example, in a fuel cell system disclosed in Japanese un-examined patent publication No. 7-192743, water circulates between the fuel cell and the hydrogen storing alloy. More particularly, water is heated after it is used to cool down the fuel cell and then fed to around the hydrogen storing alloy which is activated by the heated water to discharge hydrogen gas which is supplied to the anode of the fuel cell. Water of a lowered temperature as a result of the endothermic reaction of the hydrogen storing alloy is returned to the fuel cell for use as a coolant. 
     Although this prior art system provides improved heat circulation throughout the fuel cell system, water circulation comprises various components including conduits, pumps, valves and radiators. It also requires energy which is a part of electricity generated by the fuel cell unit in the system. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the present invention to provide a fuel cell system capable of eliminating disadvantages of the above-described prior art technology. 
     Another object of the present invention is to provide a fuel cell system which is simple in construction, small in size, easy to install and, therefore, particularly suitable to be mounted on a vehicle. 
     According to an aspect of the present invention there is provided a fuel cell system comprising one or more fuel cell units each having an anode, a cathode and an electrolyte membrane interposed between the anode and the cathode; a hydrogen storing alloy from which hydrogen gas is discharged, when heated, to be supplied to the anode of the fuel cell unit; and heating means for heating the hydrogen storing alloy by contact with an exhaust gas from the fuel cell unit. 
     With this fuel cell system, the hydrogen storing alloy is heated by the exhaust gas which has been heated during operation of the fuel cell unit, thereby producing hydrogen gas. In other words, heat in the exhaust gas enhances the endothermic reaction of the hydrogen storing alloy in which hydrogen gas stored therein is discharged which is supplied to the anode of the fuel cell unit. 
     The fuel cell unit in the fuel cell system of the present invention may be of any suitable arrangement and construction. By way of example, it comprises a proton exchange membrane (PEM) between the cathode and the anode. PEM acts as an electrolyte and transports therethrough hydrogen ions obtained at the anode of the fuel cell toward the cathode, in the form of proton (H + ). The hydrogen storing alloy used in the fuel cell system of the present invention includes LaNi 5 , TiFe, ZrMn 2 , Mg 2 Ni and any other alloy which is capable of discharging hydrogen gas stored therein, when heated. For example, LaNi 5  is known to provide endothermic reaction LaNi 5 H 6 →LaNi 5 +3H 2 , when heated to about 50-80° C., causing hydrogen gas to be produced by about 300 liters per hour. 
     A casing of the hydrogen storing alloy should preferably have a greater a surface area which facilitates heat transmission from the discharge gas. In a preferred embodiment, the casing has a plurality of apertures which allows the discharge gas to enter the interior of the casing. In another preferred embodiment, there are a plurality of tubular casings each containing the hydrogen storing alloy. 
     The exhaust gas to be used in this invention for heating the hydrogen storing alloy may be either one of the remaining air discharged from the cathode and the remaining hydrogen gas discharged from the anode. 
     The air discharged from the cathode contains water (vapor) generated by the fuel cell reaction. Accordingly, where the hydrogen storing alloy is heated by the discharged air from the cathode of the fuel cell unit, it is preferable that a condenser is arranged downstream of the hydrogen storing alloy for cooling down the discharged air to collect water. The water collected by the condenser may be reused to moisten the air to be supplied to the cathode. Since, in this invention, the discharged air has been cooled to at least some extent by heat exchange with the hydrogen storing alloy for achieving the endothermic reaction, the condenser may be subjected to a decreased load. 
     In a preferred embodiment of the fuel cell system of this invention, liquid water is supplied to the cathode. More specifically, liquid water is sprayed directly onto the cathode, which is hereinbelow referred to by “water spray type fuel cell system”. In the water spray type fuel cell system, the exhaust gas from the cathode has a greater water content than that from the anode. A part of water in the exhaust gas is collected by heat exchange with the hydrogen storing alloy and the remainder is collected by the condenser. 
     In accordance with another aspect of the present invention there is provided a fuel cell system comprising one or more of fuel cell units each having an anode, a cathode and an electrolyte membrane interposed between the anode and the cathode; a hydrogen storing alloy which produces hydrogen gas, when heated, to be supplied to the anode of the fuel cell unit; and water spray means for spraying liquid water onto the cathode. The sprayed water is then supplied to the hydrogen storing alloy so as to cool the hydrogen storing alloy to thereby enhance exothermic reaction thereof in which hydrogen gas is stored in the hydrogen storing alloy. The sprayed water functions to suitably moisten the electrolyte membrane such as PEM during operation of the fuel cell unit. In this aspect of the present invention, the sprayed water also functions to cool the hydrogen storing alloy while the fuel cell unit is at a standstill, which facilitates the exothermic reaction by which the hydrogen storing alloy is filled with hydrogen gas. This system makes it unnecessary to provide separate cooling means for cooling the hydrogen storing alloy, or at least minimizes the energy for driving such a separate cooling means. 
     In accordance with still another aspect of the present invention there is provided a fuel cell system comprising one or more fuel cell units each having an anode, a cathode and an electrolyte membrane interposed between the anode and the cathode; an exhaust port arranged below the fuel cell unit for passing therethrough exhaust gas from the cathode of the fuel cell unit; a suction port arranged below the exhaust port for passing therethrough an air to be supplied to the cathode of the fuel cell unit; and a partition member between the exhaust port and the suction port for effecting heat exchange between the exhaust gas in the exhaust port and the air in the suction port. With this system, the exhaust gas from the cathode having an elevated temperature may be cooled by heat exchange with the air in the suction port having a lower temperature. The exhaust gas from the cathode of the fuel cell unit is relatively weighty because it contains water, which may smoothly fall down with gravity toward the exhaust port. This is particularly suitable when applied to the water spray type fuel cell system in which liquid water is sprayed directly onto the cathode, which will fall down together with the exhaust gas from the cathode. The term “exhaust port” includes an exhaust manifold and any chamber or passage through which the exhaust gas from the cathode is discharged to the open air, whereas the term “suction port” includes any chamber or passage through which the open air is introduced to the cathode of the fuel cell unit. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The foregoing and other objects and features of the present invention can be apparent from the following description when read in conjunction with the accompanying drawings in which: 
     FIG. 1 is a schematic view diagrammatically showing the structure of a fuel cell system embodying the present invention; 
     FIG. 2 is a cross-section of a single fuel cell unit in the system shown in FIG. 1; 
     FIG. 3 is a schematic view diagrammatically showing an example of a casing for receiving hydrogen storing alloy; 
     FIG. 4 is a schematic view diagrammatically showing another example of a casing for receiving hydrogen storing alloy; 
     FIG. 5 is a flowchart showing energy transfers in the fuel cell system in accordance with an embodiment of the present invention; 
     FIG. 6 is a flowchart showing energy transfers in an equivalent example of the prior art fuel cell system; 
     FIG. 7 is a schematic view diagrammatically showing the structure of a fuel cell system in accordance with another embodiment of the present invention; 
     FIG. 8 is a schematic view diagrammatically showing the structure of a fuel cell system in accordance with still another embodiment of the present invention; 
     FIG. 9 is a schematic view diagrammatically showing the structure of a fuel cell system in accordance with still another embodiment of the present invention; 
     FIG. 10 is a side view showing an actual example of application in which the fuel cell system of FIG. 9 is mounted on a vehicle; 
     FIG. 11 is a cross-section of a chamber including exhaust and suction ports with a partition wall that may be used in the fuel cell system of the present invention; FIG. 12 is a plan view, partially broken, showing an air manifold attached to the fuel cell unit of the present invention; and 
     FIG. 13 is a schematic view diagrammatically showing the structure of a fuel cell system in accordance with still another embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     FIG. 1 diagrammatically shows the structure of a fuel cell system  1  according to an embodiment of the present invention, which comprises in general a fuel cell unit  2 , a fuel gas supply system  10  including a hydrogen storing alloy  11 , an air supply system  40 , a water supply system  50  and an output system  70 . 
     Shown in FIG. 2 is the structure of a single fuel cell unit which, as known in the art, comprises cathode  3 /electrolyte membrane  5 /anode  4  formed in a thin film, which is held between a pair of carbon connector plates or separators  6 ,  7 . Between separator  6  and cathode  3  are provided a plurality of air passages  8 , whereas between separator  7  and anode  4  are provided a plurality of hydrogen gas passages  9 . In a preferred embodiment, air passages  8  and hydrogen gas passages  9  extend perpendicular to each other. For example, the former extends vertically and the latter extends horizontally. In actual application, a plurality of fuel cell units  2  are stacked one upon another to form a fuel cell stack. 
     In this embodiment, hydrogen storing alloy  11  is TiuZrvCrwFexMnyCuz where u to z represent any integers. A known system may be used to facilitate the endothermic reaction of hydrogen storing alloy  11  for release of hydrogen gas therefrom. For example, a heater (not shown) is provided to heat hydrogen storing alloy  11  and its casing to above a predetermined temperature. The heater operates when the exhaust gas from cathode  3  of fuel cell unit  2  has not reached a predetermined temperature that is sufficiently high to cause the endothermic reaction of hydrogen storing alloy  11 , for example, at the start-up phase of fuel cell unit  2 . Once the exhaust gas temperature has risen to the predetermined temperature, the heater operation is discontinued. Another heating means may be used solely or in combination with the heater. For example, a coolant passage surrounding fuel cell unit  2  is extended to the casing of hydrogen storing alloy  11  so that hydrogen storing alloy  11  is heated by the coolant which has been heated by fuel cell unit  2  during continuous operation thereof. 
     A supply pipe  26  is connected between a hydrogen source  27  and hydrogen storing alloy  11  for supplying hydrogen gas from the former to the latter. When fuel cell unit  2  is at a standstill, hydrogen storing alloy  11  is cooled down by the water sprayed onto the surface of cathode  3 . Accordingly, the exothermic reaction of hydrogen storing alloy  11  proceeds effectively so that hydrogen storing alloy  11  becomes saturated with hydrogen gas. In some cases, there is provided an additional cooling unit, such as a heat exchanger, for cooling hydrogen storing alloy  11 . 
     An example of the casing is shown in FIG. 3 which provides a good heat exchange capacity with the exhaust gas from fuel cell unit  2  and a decreased resistance to the exhaust gas flow. In this example, a casing  12  has a plurality of vertically extending holes  13  for passing the exhaust gas therethrough. When the exhaust gas of a raised temperature passes through holes  13 , it is subjected to heat exchange with the casing  12  and, therefore, heats the hydrogen storing alloy contained therein. Each hole  13  has a rectangular cross-section in the illustrated example, but of course may have polygonal, oval or circular cross-sectional shape. Holes  13  preferably extend vertically to facilitate water drops in the exhaust gas flow falling with gravity, but another design such as slanted or spiral holes may be adopted. 
     In another example shown in FIG. 4, a casing  15  comprises a plurality of elongated pipes  16 , each containing hydrogen storing alloy, supported between a pair of opposed retainers  17 ,  17 . Each pipe  16  has any suitable cross-sectional shape. In a preferred design, each pipe  16  extends not horizontally, but slantwise which allows water drops to fall down therealong into guide grooves (not shown) in retainers  17 . 
     Hydrogen gas discharged from alloy  11  is fed to hydrogen gas passages  9  of fuel cell unit  2  via a feed pipe  20  with a control valve  21  which is operated by electromagnetic valve  23  to regulate a hydrogen gas pressure in pipe  20 . The hydrogen gas pressure is monitored by a pressure gauge  25  located just before fuel cell unit  2 . A signal representing the monitored pressure is sent back to electromagnetic valve  23  for regulation of the degree of opening of control valve  21 . 
     Fuel gas supply system  10  also includes an exhaust pipe  30  through which the remainder of the hydrogen gas which has not been consumed in fuel cell unit  2  is exhausted to the open air. Exhaust pipe  30  is provided with a check valve  31  and an electromagnetic valve  32 . Check valve  31  prevents entry of the ambient air into anode  4  of fuel cell unit  2  through exhaust pipe  30 . Electromagnetic valve  32  is opened intermittently for full combustion of hydrogen gas. 
     Air supply system  40  has a feed pipe, with a fan  43 , through which the ambient air is introduced into an air intake manifold  45  and then into air passages  8  of fuel cell unit  2 . The exhaust air from cathode  3  is subjected to heat exchange with hydrogen storing alloy  11  so that steam in the exhaust air is condensed into water drops, which is collected by a condenser  51 , and then discharged to the open air. The temperature of the exhaust air is monitored by a thermometer  47 . 
     In the illustrated embodiment, air intake manifold  45  is provided with a plurality of water injection nozzles  55  from which liquid water is sprayed onto the surface of cathode  3 . Most of the sprayed water is fed to condenser  51  while remaining in liquid state, which is then fed into a water tank  53 . A part of the sprayed water evaporates while passing through air passages  8  at cathode  3  of fuel cell unit  2 , which is condensed into water drops by heat exchange with hydrogen storing alloy  11  or by condenser  51 , and is also fed into water tank  53 . The exhaust air from cathode  3  may include water (steam) that is generated by the fuel cell reaction between hydrogen and oxygen. Condenser  51  is also used where system  1  involves humidifying the ambient air before introducing it into air intake manifold  45 , as disclosed in Japanese un-examined patent publication No. 7-176313. 
     Water supply system  50  is a closed system in which water in tank  53  is pumped up by a pump  61  and sprayed from nozzles  55  onto the surface of cathode  3 , which is collected by condenser  51  to be fed again to tank  53 . The water level in tank  53  is monitored by a level sensor  56 . When the water level is found to be below a predetermined level, tank  53  is refilled with water from an outside water source. Tank  53  has a heater  57  and an electromagnetic valve  58  for preventing water from freezing in the Winter. Another electromagnetic valve  60  prevents evaporation of water in tank  53 . 
     During operation of fuel cell unit  2 , water sprayed from nozzles  55  continuously or intermittently onto the surface of cathode  4  will take latent heat away from the ambient air and the surface itself as it evaporates, which effectively prevents evaporation of water contained in electrolyte membrane  5 . Accordingly, electrolyte membrane  5  remains suitably moist. Another function of the sprayed water is to take away heat from cathode  4 , which contributes to temperature control of fuel cell unit  2 . This makes it unnecessary to employ a separate cooling unit in which fuel cell unit  2  is cooled with a coolant. The output of pump  61  is regulated in response to the temperature of the exhaust air detected by thermometer  47  to control the temperature of the fuel cell unit below a predetermined temperature. 
     In output system  70  includes a switch relay  71 , a rectifying diode  73  and a secondary battery  75 , and feeds the output of fuel cell unit  2  to a motor  77 . The output is monitored by a voltmeter  76 , the result of which is supplied to a control circuit (not shown) for regulating the degree of opening of electromagnetic valve  33 . 
     With system  1  as described above, the exhaust gas or air at an elevated temperature from cathode  3  of fuel cell unit  2  is supplied to hydrogen storing alloy  11  for heating the same. In addition, when water (steam) contained in the discharge air from cathode  3  of fuel cell unit  2  contacts the hydrogen storing alloy  11  it condenses into water drops, giving up its latent heat to hydrogen storing alloy  11 . This enhances the endothermic reaction to discharge hydrogen gas, which is supplied through feed pipe  20  to anode  4  of fuel cell unit  2 . Accordingly, there is no need to convey heat, which has been taken away from fuel cell unit  2  with a coolant or water, to hydrogen storing alloy  11 . In other words, no feed pipe connected between fuel cell unit  2  and hydrogen storing unit  11  for feeding the heated water to the latter is required. This of course reduces the number of components of the overall system, lowers the manufacturing costs and improves capacity and durability of the system. 
     FIG. 5 is a flowchart showing energy transfer in system  1  by way of example, in which change state of the air are shown at right and changes to the water are shown at left. The conditions of the water at each stage are represented by its flow rate and temperature, whereas for air, flow rate, temperature and humidity are given. As shown, the system of the present invention provides a favorable energy exchange throughout the air flow path to facilitate the endothermic reaction of hydrogen storing alloy  11  to thereby produce a sufficient amount of hydrogen gas. 
     For comparison, FIG. 6 shows energy transfer in an example of the prior art fuel cell system in which fuel cell unit  2 , hydrogen storing alloy  11  and condenser  51  are all equivalent to those in system  1  of FIG.  5 . This prior art system has a water circulation path  80 , with a pump  81 , between fuel cell unit  2  and hydrogen storing alloy  11 . A coolant or water heated by fuel cell unit  2  in operation is used for heating hydrogen storing alloy  11 . The coolant is somewhat cooled due to the endothermic reaction of hydrogen storing alloy  11  and then fed again to fuel cell unit  2  for cooling the same. As is apparent from comparison between the arrangements in FIG.  5  and FIG. 6, the system of the present invention is much more simple in construction than the prior art. 
     In normal operation of the system of the present invention, fuel cell unit  2  can be made inoperative by closing valve  23  in fuel gas supply system  10 . During this inoperative phase, fan  43  is not driven so that no air (oxygen) is supplied to cathode  3  of fuel cell unit  2  by air supply system  40 , whereas in water supply system  50  water in tank  53  is pumped up to nozzles  55  from which it is continuously or intermittently sprayed onto the surface of cathode  3  of fuel cell unit  2 . As described above, the sprayed water is discharged, together with the exhaust air, from cathode  3  and introduced to the hydrogen storing alloy  11  for cooling the same, which facilitates its exothermic reaction in which it absorbs hydrogen gas that is supplied from a refill station or other external source (not shown). The water quantity to be supplied from tank  53  to nozzles  55  is regulated in response to the exhaust air temperature detected by thermometer  47 . If a necessary cooling effect can not be obtained by the sprayed water alone, an additional cooling unit may be provided. For example, there may be provided a coolant passage surrounding the casing of hydrogen storing alloy  11  and an auxiliary heat exchanger. 
     FIG. 7 shows another embodiment of a fuel cell system  100  in which identical parts and members are shown by the same numerals. System  100  has an air supply system that is modified from the air supply system  40  in FIG.  1 . More specifically, in system  100 , an air intake manifold  45 , a fuel cell unit  2  and a hydrogen storing alloy  11  are arranged in series in a substantially vertical direction as in the foregoing system  1 , but beneath hydrogen storing alloy  11  are arranged an exhaust port  101  and a suction port  105  divided by a slanting partition wall  103  of heat conductive material, such as stainless steel, which provides effective heat exchange between air in exhaust port  101  and in suction port  105 . Exhaust port  101  has a drain at the lowermost end of partition wall  103 . Air in suction port  105  is supplied, via a fan  107  and a passage  108 , to air intake manifold  45 . 
     With this system  100 , water sprayed by nozzles  55  passes through air passage  8  at cathode  3  of fuel cell unit  2  so that cathode  3  remains in a suitably moist condition and fuel cell unit  2  is effectively cooled. The exhaust air from cathode  3  which has been heated to an elevated temperature is supplied to hydrogen storing alloy  11  for heating the same. By heat exchange with hydrogen storing alloy  11 , a part of the water (steam) contained in the exhaust air is condensed into water drops, so that hydrogen storing alloy  11  is further heated by the latent heat generated in condensation. The exhaust air is then introduced into exhaust port  101 . Since the exhaust air at the outlet of hydrogen storing alloy  11  is 47° C. (FIG.  5 ), for example, which is considerably higher than the temperature of the ambient air introduced into suction port  105 , the exhaust air in exhaust port  101  is effectively cooled by heat exchange with the air in suction port  105 . At this time, steam in the exhaust air in exhaust port  101  is condensed into waterdrops which adhere to the upper surface of partition wall  103  and then falls down therealong to be discharged through drain  110 . The discharged water is fed to tank  53  for water circulation throughout water supply system  50 . A part of the sprayed water remains in liquid state. Another part of the sprayed water evaporates when heated by fuel cell unit  2  but is soon condensed into waterdrops on the surface of the casing of hydrogen storing alloy  11 . This liquid water will drop with gravity onto partition wall  103  and is then fed to tank  53  in the manner as described above. 
     In a modified system  200  in FIG. 8, a water condenser  201  is mounted downstream of an air exhaust port  120  for collecting water still remaining in the exhaust air, which is also returned to water supply system  50 . In this system  200 , water in tank  53  is supplied to a humidifier  210  where it is evaporated into steam which is introduced into the air supply system. 
     System  300  in FIG. 9 is substantially identical with system  100  in FIG. 7 except that it includes no hydrogen storing alloy. In this system, a hydrogen storing alloy (not shown) is not a part of the system but is mounted independent of the system at a remote location. In this case, the exhaust air from the cathode of fuel cell unit  2  is not supplied to the hydrogen storing alloy. The exhaust air from an air exhaust port  120  may be introduced to a water condenser, as shown in FIG. 8, so that water contained therein is fed to a tank  53 . 
     With system  300  in FIG. 9, water sprayed by nozzles  55  passes through air passage  8  at the cathode of fuel cell unit  2  so that cathode  3  remains in a suitably moist condition and fuel cell unit  2  is effectively cooled. The exhaust air from the cathode which has been heated to an elevated temperature is introduced into an exhaust port  101  where it is cooled by heat exchange with the air of a lower temperature in a suction port  105 . At this time, steam in the exhaust air in exhaust port  101  is condensed into waterdrops which adhere on the upper surface of a partition wall  103  and then fall down therealong to be discharged through a drain  110 . The discharged water is fed to tank  53  for water circulation throughout water supply system  50 . A part of the sprayed water remains in liquid state, which will drop with gravity onto partition wall  103  and then be conveyed to tank  53  in the manner as described above. 
     In actual application, the fuel cell system of the present invention may be mounted on a vehicle, a typical example of which is shown in FIG.  10 . In FIG. 10, the air feed passage  108  for feeding the air in the suction port  105  to the air intake manifold  45  is mounted behind the fuel cell unit  2 . The system in FIG. 10 employs a chamber or receptacle comprising exhaust port  101 , partition wall  103  and suction port  105 , which is specifically shown in FIG. 10 as a cross-section thereof. 
     The air intake manifold  45  in the system of the present invention may have an arrangement as shown in FIG. 12 where manifold  45  is shown as having an air inlet opening  301  and a water inlet opening  303 . Water introduced through opening  303  flows along a surrounding trough  305  and then is sprayed by nozzles  55  that communicate with trough  305 . 
     System  400  in FIG. 13 is substantially identical with system  200  in FIG. 8 except that it includes no hydrogen storing alloy. In this system, a hydrogen storing alloy (not shown) is not a part of the system but is mounted independent of the system at a remote location. In this case, the exhaust air from the cathode of fuel cell unit  2  is not supplied to the hydrogen storing alloy. In this system, a part of steam in the exhaust air from an air exhaust port  120  is collected at the surface of a partition wall  103  by heat exchange with the air in a suction port  105  and another part is collected by a water condenser  201 , both parts of which are fed to a tank  53 . Water condenser  201  may be omitted in another modified system. 
     Although the present invention has been described in conjunction with specific embodiments thereof, it is to be understood that it is capable of considerable variation and modification without departure from the scope of the appended claims. For example, the water spray nozzle is preferably mounted on the air intake manifold at the cathode but may be provided at any location and at any distance from the cathode, as long as it can supply liquid water to the cathode. When the fuel cell system is installed at the factory or home, it may be coupled to waterworks so that city water is supplied to the cathode.