Abstract:
A fuel cell system has: a fuel cell having a first reactant inlet, a first reactant outlet, a second reactant inlet, a second reactant outlet, and optionally a coolant inlet and coolant outlet. A first reactant supply subsystem supplies a first reactant incoming stream to the first reactant inlet of the fuel cell. A second reactant supply subsystem supplies a second reactant incoming stream to the second reactant inlet of the fuel cell. A first reactant recirculation subsystem recirculates at least a portion of the first reactant exhaust stream from the first reactant outlet to an enthalpy shifting subsystem in which one portion of the heat and moisture in first reactant exhaust stream is transferred to one of the first reactant incoming stream in the first reactant supply subsystem and the second reactant incoming stream in the second reactant supply subsystem. Another portion of the heat and moisture is transferred to the other stream. A method of controlling reactant and water in a fuel cell system is also disclosed.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates generally to an apparatus and method for management of process gases for a fuel cell system. More particularly, the present invention relates to an apparatus and method for controlling the humidity, temperature and flow of fuel cell process gases.  
         BACKGROUND OF THE INVENTION  
         [0002]    Fuel cell systems are seen as a promising alternative to traditional power generation technologies due to their low emissions, high efficiency and ease of operation. Fuel cells operate to convert chemical energy into electrical energy. Proton exchange membrane fuel cells comprise an anode, a cathode, and a selective electrolytic membrane disposed between the two electrodes. In a catalyzed reaction, a fuel such as hydrogen, is oxidized at the anode to form cations (protons) and electrons. The ion exchange membrane facilitates the migration of protons from the anode to the cathode. The electrons cannot pass through the membrane and are forced to flow through an external circuit thus providing an electrical current. At the cathode, oxygen reacts at the catalyst layer, with electrons returned from the electrical circuit, to form anions. The anions formed at the cathode react with the protons that have crossed the membrane to form liquid water as the reaction product.  
           [0003]    Proton exchange membranes require a wet surface to facilitate the conduction of protons from the anode to the cathode, and otherwise to maintain the membranes electrically conductive. It has been suggested that each proton that moves through the membrane drags at least two or three water molecules with it (U.S. Pat. No. 5,996,976). U.S. Pat. No. 5,786,104 describes in more qualitative terms a mechanism termed “water pumping”, which results in the transport of cations (protons) with water molecules through the membrane. As the current density increases, the number of water molecules moved through the membrane also increases. Eventually the flux of water being pulled through the membrane by the proton flux exceeds the rate at which water is replenished by diffusion. At this point the membrane begins to dry out, at least on the anode side, and its internal resistance increases. It will be appreciated that this mechanism drives water to the cathode side, and additionally the water created by reaction is formed at the cathode side. Nonetheless, it is possible for the flow of gas across the cathode side to be sufficient to remove this water, resulting in drying out on the cathode side as well. Accordingly, the surface of the membrane must remain moist at all times. Therefore, to ensure adequate efficiency, the process gases must have, on entering the fuel cell, appropriate humidity and temperature which are based on the system requirements.  
           [0004]    A further consideration is that there is an increasing interest in using fuel cells in transport and like applications, e.g. as the basic power source for cars, buses and even larger vehicles. Automotive application, are quite different from many stationary applications. For example in stationary applications, fuel cell stacks are commonly used as an electrical power source and are simply expected to run at a relatively constant power level for an extended period of time. In contrast, in an automotive environment, the actual power required from the fuel cell stack can vary widely. Additionally, the fuel cell stack supply unit is expected to respond rapidly to changes in power demand, whether these be demands for increased or reduced power, while maintaining high efficiencies. Further, for automotive applications, a fuel cell power unit is expected to operate under an extreme range of ambient temperature and humidity conditions.  
           [0005]    All of these requirement are exceedingly demanding and make it difficult to ensure a fuel cell stack will operate efficiently under all the possible range of operating conditions. While the key issues are ensuring that a fuel cell power unit can always supply a high power level and at a high efficiency and simultaneously ensuring that it has a long life, accurately controlling humidity levels within the fuel cell power unit is necessary to meet these requirements. More particularly, it is necessary to control humidity levels in both the oxidant and fuel gas streams. Most known techniques of humidification are ill designed to respond to rapidly changing conditions, temperatures and the like. Many known systems can provide inadequate humidification levels, and may have high thermal inertia and/or large dead volumes, so as to render them incapable of rapid response to changing conditions.  
           [0006]    An apparatus and method of controlling temperature and humidity in fuel cell systems is disclosed in the applicant&#39;s co-pending U.S. patent application Ser. No. 09/801,916. The method comprises humidifying a fuel cell process gas stream at a first temperature so as to provide the process gas stream with excess humidity, cooling the process gas stream at a second temperature, lower than the first temperature, to cause condensation of excess moisture, removing excess condensed moisture from the process gas stream and delivering the process gas stream at a known temperature, whereby the relative humidity level in the process gas stream is determined from the ratio of the saturation pressures of the second and the said known temperatures. Particularly, the method includes recovering humidity from the exhausted process gas generated by the fuel cell and using the recovered moisture to humidify the incoming at least one of the fuel and oxidant streams. However, this method requires a large number of components and hence reduces the overall efficiency of the fuel cell system.  
           [0007]    Another method is disclosed in U.S. Pat. No. 6,013,385. In this patent, a fuel cell gas management system is disclosed. The system comprises: a first reactant humidification subsystem for supplying a first reactant inlet stream to the first reactant inlet of the fuel cell and receiving a first reactant exhaust stream from the first reactant outlet of the fuel cell, said first reactant humidification subsystem comprising an enthalpy wheel for collecting moisture from the first reactant (oxidant) exhaust stream and transferring a portion of the collected moisture to the first reactant inlet stream; a second reactant (fuel) humidity retention subsystem comprising a recirculation loop for collecting excess second reactant from the second reactant outlet of the fuel cell, a source of second reactant mixing means for mixing second reactant from a reactant source with second reactant collected from the second reactant outlet of the fuel cell and motive means for circulating second reactant in said recirculation loop and for introducing second reactant into the second reactant inlet of the fuel cell. However, this patent still fails to fully utilize the waste heat and humidity from fuel cell exhaust.  
           [0008]    There remains a need for a fuel cell gas management system that can offer rapid dynamic control of temperatures and relative humidities for incoming fuel cell process gases. More particularly, such a system should be highly efficient and be able to provide sufficient humidity over a wide variety of flow rates, for both the oxidant and fuel systems.  
         SUMMARY OF THE INVENTION  
         [0009]    In accordance with one aspect of the present invention, there is provided a fuel cell system comprising;  
           [0010]    a fuel cell having a first reactant inlet, a first reactant outlet, a second reactant inlet, a second reactant outlet, a coolant inlet and coolant outlet;  
           [0011]    a first reactant supply subsystem for supplying a first reactant incoming stream to the first reactant inlet of the fuel cell,  
           [0012]    a second reactant supply subsystem for supplying a second reactant incoming stream to the second reactant inlet of the fuel cell;  
           [0013]    a first reactant recirculation subsystem for recirculating at least a portion of the first reactant exhaust stream from the first reactant outlet to an enthalpy shifting subsystem in which at least a portion of the heat and moisture in the at least a portion of first reactant exhaust stream is transferred to at least one of the first reactant incoming stream in the first reactant supply subsystem and the second reactant incoming stream in the second reactant supply subsystem.  
           [0014]    Preferably, the enthalpy shifting subsystem comprises a first enthalpy shifting device for transferring at least a portion of the heat and moisture from the first reactant exhaust stream in the first reactant recirculation subsystem to the first reactant incoming stream in the first reactant supply subsystem, and a second enthalpy shifting device for transferring at least a portion of the heat and moisture from the first reactant exhaust stream in the first reactant recirculation subsystem to the second reactant incoming stream in the second reactant supply subsystem  
           [0015]    More preferably, the fuel cell system further comprises a second reactant recirculation system for recirculating at least a portion of the second reactant exhaust stream from the second reactant outlet to the second reactant supply subsystem so that the at least a portion of the second reactant exhaust stream mixes with the second reactant incoming stream.  
           [0016]    In accordance with another aspect of the present invention, there is provided a method of controlling the reactants and water in a fuel cell system, the fuel cell has a first reactant inlet, a first reactant outlet, a second reactant inlet, a second reactant outlet, a coolant inlet and coolant outlet, said method comprises:  
           [0017]    (a) providing a first reactant incoming stream to be supplied to the first reactant inlet;  
           [0018]    (b) providing a second reactant incoming stream to be supplied to the second reactant inlet;  
           [0019]    (c) collecting at least a portion of a first reactant exhaust stream from the first reactant outlet;  
           [0020]    (d) transferring at least a portion of the heat and moisture in the at least a portion of the first reactant exhaust stream to at least one of the first reactant incoming stream and the second reactant incoming stream.  
           [0021]    Preferably, in step (d): transferring at least a portion of the heat and moisture in the at least a portion of the first reactant exhaust stream to both the first reactant incoming stream and the second reactant incoming stream  
           [0022]    More preferably, the method further comprises: collecting at least a portion of a second reactant exhaust stream from the second reactant outlet; and mixing the at least a portion of the second reactant exhaust stream with the second reactant incoming stream.  
           [0023]    The present invention has many advantages over the prior art. The only onboard fluid in the present invention is the coolant. All the water used to humidify the fuel and oxidant is generated by the fuel cell  12  itself. This reduces the weight and number of components in the system, making the overall system compact and highly efficient. The system is capable of rapid response of power demand. All these features are particularly desirable for vehicular applications. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWING FIGS  
       [0024]    For a better understanding of the present invention, and to show more clearly how it may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, which show a preferred embodiment of the present invention and in which:  
         [0025]    [0025]FIG. 1 illustrates a schematic flow diagram of a first embodiment of a fuel cell gas and water management system according to the present invention;  
         [0026]    [0026]FIG. 2 illustrates a variant of the first embodiment of the fuel cell gas and water management system according to the present invention, in which only one cooling loop is shown; and  
         [0027]    [0027]FIG. 3 illustrates a partial schematic flow diagram of a second embodiment of the fuel cell gas and water management system according to the present invention operating under high pressure. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0028]    Referring first to FIG. 1, this shows a schematic flow diagram of a first embodiment of a fuel cell gas management system  10  according to the present invention. The fuel cell gas management system  10  comprises a fuel supply line  20 , an oxidant supply line  30 , a cathode exhaust recirculation line  40  and an anode exhaust recirculation line  60 , all connected to a fuel cell  12 . It is to be understood that the fuel cell  12  may comprise a plurality of fuel cells or just a single fuel cell. For simplicity, the fuel cell  12  described herein operates on hydrogen as fuel and air as oxidant and can be a Proton Exchange Membrane (PEM) fuel cell. However, the present invention is not limited to this type of fuel cells and applicable to other types of fuel cells.  
         [0029]    The fuel supply line  20  is connected to a fuel source  21  for supplying hydrogen to the anode of the fuel cell  12 . A hydrogen humidifier  90  is disposed in the fuel supply line  20  upstream from the fuel cell  12  and an anode water separator  95  is disposed between the hydrogen humidifier  90  and the fuel cell  12 . The oxidant supply line  30  is connected to an oxidant source  31 , e.g. ambient air, for supplying air to the cathode of the fuel cell  12 . An enthalpy wheel  80  is disposed in the oxidant supply line  30  upstream of the fuel cell  12  and also in the cathode recirculation line  40 . A cathode water separator  85  is disposed between the enthalpy wheel  80  and the fuel cell  12 . The enthalpy wheel  80  comprises porous materials with a desiccant. In known manner, a motor  81  drives either the porous materials or a gas diverting element to rotate around the axis of the enthalpy wheel so that gases from the oxidant supply line  30  and the oxidant recirculation line  40  alternately pass through the porous materials of the enthalpy wheel. Dry ambient air enters the oxidant supply line  30  and first passes through an air filter  32  that filters out the impurity particles. A blower  35  is disposed upstream of the enthalpy wheel  80 , to draw air from the air filter  32  and to pass the air through a first region of the enthalpy wheel  80 . The enthalpy is wheel  80  may be any commercially available enthalpy wheel suitable for fuel cell system, such as the one described in the applicant&#39;s co-pending U.S. patent application Ser. No. 09/941,934.  
         [0030]    A fuel cell cathode exhaust stream contains excess air, product water and water transported from the anode side, the air being nitrogen rich due to consumption of at least part of the oxygen in the fuel cell  12 .  
         [0031]    The cathode exhaust stream is recirculated through the cathode exhaust recirculation line  40  connected to the cathode outlet of the fuel cell  12 . The humid cathode exhaust stream first passes through a hydrogen humidifier  90  in which the heat and humidity is transferred to incoming dry hydrogen in the fuel supply line  20 . The humidifier  90  can be any suitable humidifier, such as that commercially available from Perma Pure Inc, Toms River, N.J. It may also be a membrane humidifier and other types of humidifier with either high or low saturation efficiency. In view of the gases in the anode and cathode streams, an enthalpy wheel or other device permitting significant heat and humidity interchange between the two streams cannot be used.  
         [0032]    From the hydrogen humidifier  90 , the fuel cell cathode exhaust stream continues to flow along the recirculation line  40  and passes through a second region of the enthalpy wheel  80 , as mentioned above. As the humid cathode exhaust passes through the second region of the enthalpy wheel  80 , the heal and moisture is retained in the porous paper or fiber material of the enthalpy wheel  80  and transferred to the incoming dry air stream passing through the first region of the enthalpy wheel  80  in the oxidant supply line  30 , as the porous materials or the gas diverting element of the enthalpy wheel  80  rotate around its axis. Then the cathode exhaust stream continues to flow along the recirculation line  40  to an exhaust water separator  100  in which the excess water, again in liquid form, that has not been transferred to the incoming hydrogen and air streams is separated from the exhaust stream. Then the exhaust stream is discharged to the environment along a discharge line  50 .  
         [0033]    A drain line  42  may optionally be provided in the recirculation line  40  adjacent the cathode outlet of the fuel cell to drain out any liquid water remaining or condensed out. The drain line  42  may be suitably sized so that gas bubbles in the drain line actually retain the water in the drain line and automatically drain water on a substantially regular basis, thereby avoiding the need of a drain valve that is commonly used in the field to drain water out of gas stream. Such a drain line can be used anywhere in the system where liquid water needs to be drained out from gas streams. Pressure typically increases with gas flow rate and water regularly produced or condensed, and a small flow rate of gas is not detrimental such as cathode exhaust water knockout separator and drain line  42 .  
         [0034]    The humidified hydrogen from the hydrogen humidifier  90  flows along the fuel supply line  20  to an anode water separator  95  in which excess water is separated before the hydrogen enters the fuel cell  12 . Likewise, the humidified air from the enthalpy wheel  80  flows along the oxidant supply line  30  to a cathode water separator  85  in which excess liquid water is separated before the air enters the fuel cell  12 .  
         [0035]    Fuel cell anode exhaust comprising excess hydrogen and water is recirculated by a pump  64  along an anode recirculation line  60  connected to the anode outlet of the fuel cell  12 . The anode recirculation line  60  connects to the fuel supply line  20  at a joint  62  upstream from the anode water separator  95 . The recirculation of the excess hydrogen together with water vapor not only permits utilization of hydrogen to the greatest possible extent and prevents liquid water from blocking hydrogen reactant delivery to the reactant sites, but also achieves self-humidification of the fuel stream since the water vapor from the recirculated hydrogen humidifies the incoming hydrogen from the hydrogen humidifier  90 . This is highly desirable since this arrangement offers more flexibility in the choice of hydrogen humidifier  90  as the humidifier  90  does not then need to be a highly efficient one in the present system. By appropriately selecting the hydrogen recirculation flow rate, the required efficiency of the hydrogen humidifier  90  can be minimized. For example, supposing the fuel cell  12  needs 1 unit of hydrogen, hydrogen can be supplied from the hydrogen source in the amount of 3 units with 2 units of excess hydrogen recirculated together with water vapor. The speed of pump  64  may be varied to adjust the portion of recirculated hydrogen in the mixture of hydrogen downstream from joint  62 . The selection of stoichiometry and pump  64  speed may eventually lead to the omission of the hydrogen humidifier  90   
         [0036]    In practice, since air is used as oxidant, it has been found that nitrogen crossover from the cathode side of the fuel cell to the anode side can occur, e.g. through the membrane of a PEM fuel cell. Therefore, the anode exhaust actually contains some nitrogen and possibly other impurities. Recirculation of anode exhaust may result in the build-up of nitrogen and poison the full cell. Preferably, a hydrogen purge line  70  branches out from the fuel recirculation line  60  from a position  74  adjacent the fuel cell cathode outlet. A purge control device  72  is disposed in the hydrogen purge line  70  to purge a portion of the anode exhaust out of the recirculation line  60 . The frequency and flow rate of the purge operation is dependent on the power on which the fuel cell  12  is running. When the fuel cell  12  is running on high power, it is desirable to purge a higher portion of anode exhaust. The purge control device  72  may be a solenoid valve or other suitable device.  
         [0037]    The hydrogen purge line  70  runs from the position  74  to a joint point  92  at which it joins the cathode exhaust recirculation line  40 . Then the mixture of purged hydrogen and the cathode exhaust from the enthalpy wheel  80  passes through the exhaust water separator  100 . Water is condensed in the water separator  100  and the remaining gas mixture is discharged to the environment along the discharge line  50 . Alternatively, either the cathode exhaust recirculation line  40  or the purge line  70  can be connected directly into the water separator  100 .  
         [0038]    Preferably, water separated by the anode water separator  95 , cathode water separator  85 , and the exhaust water separator  100  are not discharged, but rather the water is recovered respectively along line  96 , line  84  and line  94  to a product water tank  97 , for use in various processes. For this purpose, the tank  97  includes a line  98  for connection to other processes and a drain  99 .  
         [0039]    As is known to those skilled in the art, a coolant loop  14  runs through the fuel cell  12 . A pump  13  is disposed in the cooling loop  14  for circulating the coolant. The coolant may be any coolant commonly used in the field, such as any nonconductive water, glycol, etc. An expansion tank  11  can be provided in known manner. A heat exchanger  15  is provided in the cooling loop  14  for cooling the coolant flowing through the fuel cell  12  to maintain the coolant in appropriate temperature range.  
         [0040]    [0040]FIG. 1 shows one variant, in which a secondary loop  16  includes a pump  17 , to circulate a secondary coolant. A heat exchanger  18 , e.g. a radiator, is provided to maintain the temperature of the coolant in the secondary loop and again, where required, an expansion tank  19  is provided. The coolant in the cooling loop  16  may be any type of coolant as the cooling loop  14  and  16  do not mix.  
         [0041]    However, it is to be understood that the separate second cooling loop is not essential. Instead, as shown in FIG. 2, a heat exchanger  15 ′, e.g. a radiator, is provided in the cooling loop  14  to maintain the temperature of the coolant in the cooling loop  14 . In this case, the secondary cooling loop  16  is omitted. It is to be understood that the heat exchanger  15  in FIG. 1 could also be an isolation, brazed plate heat exchanger disposed in an “open” cooling loop, as may be desired in some applications. That is to say, the second cooling loop  16  can be an open cooling loop in which coolant is drawn from and returned to a coolant reservoir, such as atmosphere, sea, etc.  
         [0042]    When water is used as coolant in either of the above variants, since the water from the separators  95 ,  85 ,  100  is product water from the fuel cell, and hence pure and non-conductive, it can be collected and directed to the expansion tank  11  or  19 , or coolant reservoir as coolant during the fuel cell operation.  
         [0043]    Preferably, a flow regulating device  22  is disposed in the fuel supply line  20  upstream from the hydrogen humidifier  90 . The flow regulating device or valve  22  permits the flow of hydrogen from the hydrogen source  21  to the fuel cell  12  in response to the pressure drop in the fuel supply line  20 . The flow regulating device  22  may be a forward pressure regulator having a set point and it permits hydrogen to be supplied to the fuel cell  12  when the pressure in the fuel supply line  20  is below the set point due to the hydrogen consumption in the fuel cell  12 . This forward pressure regulator avoids the need for an expensive mass flow controller and provides more rapid response and accurate flow control. To provide more control flexibility, the flow regulating means  22  may comprise a plurality of pre-set forward pressure regulators arranged in parallel with each forward pressure regulator having a different set point. This makes it possible to operate the fuel cell  12  with fuel supplied at different pressures and different rates at each pressure.  
         [0044]    It is to be understood that although in this embodiment, the cathode exhaust is used to first humidify the incoming hydrogen and then the incoming air, this order is not essential. Instead, the cathode exhaust may be used to first humidify the incoming air and then the incoming hydrogen. Alternatively, the hydrogen humidifier  90  and the enthalpy wheel  80  may be placed in parallel instead of series in the cathode exhaust recirculation line  60 , so that the humidification of both hydrogen and air occurs simultaneously. Optionally, depending on the operation condition of the fuel cell  12 , when the simultaneous humidification is employed, a line (not shown) may be further provided to connect the hydrogen humidifier  90  and the enthalpy wheel  80  in series so that the cathode exhaust first humidifies, for example, hydrogen in the hydrogen humidifier  90  and then the air in the enthalpy wheel  80  with a portion of the cathode exhaust bypassing the hydrogen humidifier  90 .  
         [0045]    However, in practice it may be preferable to humidify hydrogen stream first since anode dew point temperature is desired to be higher than the cathode dew point temperature because water is naturally transferred from the anode to the cathode in the fuel cell  12 . The desired relative humidity of hydrogen is also often higher than that of air in the fuel cell  12  so that the fuel cell  12  will not be flooded. Therefore, it is preferable to use the cathode exhaust stream to exchange heat and humidity with incoming hydrogen stream first.  
         [0046]    In known manner, various sensors can be provided for measuring parameters of the steam of fuel, oxidant and coolant, supplied to the fuel cell  12 . Another aspect of the present invention relies on measuring just the temperature of the reactants and determining humidity from known temperature—humidity characteristics, i.e. without directly measuring humidity.  
         [0047]    It can be appreciated that in the present invention it is not essential to over saturate process gases, condense water out to obtain 100% relative humidity and then deliver the process gases at certain temperature to get desired relative humidity before they enter the fuel cell  12 , as in the applicant&#39;s co-pending U.S. patent application Ser. No. 09/801,916. The present system is applicable to fuel cell systems where fuel and oxidant stream either have or do not have 100% relative humidity. An anode dew point heat exchanger and a cathode dew point heat exchanger may be provided to control the humidity of fuel and oxidant when the fuel cell  12  is not operable with fuel or oxidant having 100% relative humidity. However, this totally depends on the characteristic of the fuel cell  12 , such as the operating condition of the proton exchange membrane.  
         [0048]    It is also to be understood that this first embodiment of the fuel cell system according to the present invention operates under ambient pressure or near ambient pressure. Now, referring to FIG. 3, this shows cooling loops for use in a second embodiment of the fuel cell system of the present invention, that operates under high pressure, i.e. greater than atmospheric pressure.  
         [0049]    In the second embodiment, similar components are indicated with same reference numbers, and for simplicity and brevity, the description of those components is not repeated.  
         [0050]    In this second embodiment, a high pressure compressor  105  is provided in the oxidant supply line  30  upstream from the enthalpy wheel  80  to pressurize the incoming air from the air filter  32 . An after cooler heat exchanger  110  is provided between the compressor  105  and the enthalpy wheel  80  to cool the compressed air having an elevated temperature. Hence, in addition to the cooling loop  14  for the fuel cell  12 , an additional cooling loop  114  is provided including a water-water heat exchanger  110  and a coolant tank  111 . The cooling loop  114  may also run through the compressor motor  106 , compressor motor controller  107  and other power switching board  108  for the compressor  105 . The coolant in both cooling loops  14  and  114  is driven by the pump  13 . A heat exchanger  108  can be provided in the loop  114  for cooling additional components. A radiator  116  with a powered fan is provided in the additional cooling loop  114 , as for the radiator  18  in the second cooling loop; again the same alternatives to the heat exchanger  15  apply to the radiator  116 .  
         [0051]    The present invention has many advantages over the prior art. All the water used to humidify the fuel and oxidant is generated by the fuel cell  12  itself. This reduces the weight and number of components in the system, making the overall system compact and highly efficient. The system is capable of rapid response to power demands. All these features are particularly desirable for vehicular applications.  
         [0052]    While the above description constitutes the preferred embodiments, it will be appreciated that the present invention is susceptible to modification and change without departing from the fair meaning of the proper scope of the accompanying claims. For example, the present invention might have applicability in various types of fuel cells, which include but are not limited to, solid oxide, alkaline, molton-carbonate, and phosphoric acid. In particular, the present invention may be applied to fuel cells which operate at much higher temperatures. As will be appreciated by those skilled in the art, the requirement for humidification is very dependent on the electrolyte used and also the temperature and pressure of operation of the fuel cell. Accordingly, it will be understood that the present invention may not be applicable to many types of fuel cells.