Abstract:
A process and apparatus to modify the conventional proton exchange membrane fuel cell by applying a proton exchange semiconductor membrane that allows electrons to migrate from the catholde to the anode and cylindrical-conical fuel cell elements that allow internally stacking the fuel cell elements by a simple method. These modifications in the operating principle and construction configuration of the proton exchange membrane fuel cell are designed to result in a major increase in the power density output necessary for transport vehicle and stationary power generation applications.

Description:
FIELD OF INVENTION  
         [0001]    This invention relates to a modified operating principle, construction and configuration of fuel cells and a method of internal stacking of the fuel cell elements to produce higher power density to make fuel cells suitable for use in transport vehicles and for small to large stationary electric power generation units.  
           [0002]    The invention will be particularly discussed with reference to the proton membrane fuel cell using hydrogen fuel but is also applicable to other fuels and to other types of fuel cells such as solid oxide fuel cells.  
         PRIOR ART  
         [0003]    Fuel cells under development during the last four decades include the phosphoric acid fuel cell, the proton electrolytic membrane fuel cell, the molten carbonate fuel cell, and the solid oxide fuel cell. While phosphoric add fuel cells up to 250 kilowatts capacity are commercially available, the most advanced fuel cell is the proton electrolytic membrane fuel cell, however, its further commercial application is limited by the low power density of current designs and reported highest power capacity for transport vehicles and stationary power generation units is about 300 kilowatts.  
           [0004]    This invention consists of modifying the operating principle, the construction of the proton electrolytic membrane fuel cell, and a method of internal stacking of the fuel cell elements to increase the power density of the fuel cell group so that it is suitable for application to transport vehicles and small and large stationary power generation. The objective is about 85 to 120 kilowatts for small transport vehicles and 300 to 400 kilowatts for large transport vehicles. In stationary power generation, the objective is to provide 3 to 5 kilowatts for home use, 250 kilowatts and 1,000 kilowatts for dispersed community power requirements, and 10,000 to 500,000 kilowatts for centralized power generation.  
         Construction of Proton Electrolytic Membrane Fuel Cells and Other Fuel Cells  
         [0005]    Most proton electrolytic membrane fuel cells are planar in construction such as the Ballard Power fuel cell where the fuel cell elements have been “stacked” in a neat cubical configuration. Passageways are provided for the supply of hydrogen and oxygen and the removal of the reaction products. The disadvantage of this construction is that pressure on the hydrogen side is limited as high pressure may cause rupture and seal failure allowing the hydrogen to mix directly with the oxygen with catastrophic results.  
           [0006]    A cylindrical cell construction would offer the possibility of higher pressure differential between the hydrogen side and the oxygen side. Several U.S. patents have been granted for proton electrolytic membrane fuel cells that are cylindrical in shape such as:  
           [0007]    U.S. Pat. No. 5,458,989 (Oct. 17, 1995)—Tubular fuel cells with structural current collectors—Dodge, C. et al,  
           [0008]    U.S. Pat. No. 5,509,942 (Apr. 23, 1996)—Manufacture of tubular fuel cells with structural current collectors—Dodge C. et al,  
           [0009]    U.S. Pat. No. 6,001,500 (Dec. 14, 1999)—Cylindrical proton exchange membrane fuel cells and methods of making same—Bass E. et al,  
           [0010]    U.S. Pat. No. 6,007,932 (Dec. 28, 1999)—Tubular fuel cell assembly and method of manufacture—Steyn W. et al,  
           [0011]    U.S. Pat. No. 6,060,188 (May 9, 2000)—High pressure coaxial fuel cell—Muthuswamy S. et al, and  
           [0012]    U.S. Pat. No. 6,063,517 (May 16, 2000)—Spiral wrapped cylindrical proton exchange membrane fuel cells and method of making same—Montemayor A. et al.  
           [0013]    The proton electrolytic membrane fuel cells above describe several cylindrical configurations of the proton electrolytic membrane fuel cell. A major shortcoming of the above construction is how to maintain good contact between the proton exchange membrane and the anode and cathode electrodes under all operating conditions of the proton electrolytic membrane fuel cell, particularly under varying temperatures. Loosening of the contact between the membrane and the electrodes would increase the impedance of the proton electrolytic membrane fuel cell and even cause the proton electrolytic membrane fuel cell to cease functioning.  
           [0014]    U.S. Pat. No. 5,244,752 (Sep. 14, 1993)—Apparatus tube configuration and mounting for solid oxide fuel cell—Zymboly, G. concerns a tubular configuration for a solid oxide fuel cell.  
           [0015]    It is an objective of this invention to overcome one or more of the above problems.  
         BRIEF DESCRIPTION OF THE INVENTION  
         [0016]    In one form therefore the invention is said to reside in a proton exchange membrane fuel cell including an anode and a cathode separated by a proton exchange membrane characterised by the proton exchange member comprising a semiconductor adapted to allow transfer of electrons from the cathode to the anode.  
           [0017]    Preferably the anode has a catalytic surface adapted to catalyse hydrogen to hydrogen ions. The anode catalytic surface may be fine platinum or compounds of metals. For other types of fuel cells alternative catalysts may be used.  
           [0018]    Similarly the cathode may have a catalytic surface selected from the group comprising platinum and nickel or compounds of metals.  
           [0019]    In an alternative form the invention may be said to reside in a fuel cell having an anode cell and an anode at one wall thereof, a cathode cell and a cathode at one wall thereof and a proton exchange membrane between the anode cell and the cathode cell and engaged against the anode and the cathode characterised by the proton exchange membrane being a semiconductor and adapted to allow transfer of electrons from the cathode to the anode.  
           [0020]    In one embodiment the proton exchange membrane is homogeneous and hence is formed from a material which will conduct electrons in one direction and will allow the passage of protons in the opposite direction.  
           [0021]    Alternatively the proton exchange membrane is segmented and comprises a first portion which is non-electrically conductive and which allows protons to move from the anode electrode to the cathode electrode and a second which portion which is semiconductive and allows transfer of electrons from the cathode electrode to the anode electrode.  
           [0022]    Preferably the anode surface within the anode cell has a catalytic surface adapted to catalyse hydrogen to hydrogen ions. The anode catalytic surface may be fine platinum or compounds of metals.  
           [0023]    Preferably the cathode surface with the cathode cell has a catalytic surface selected from the group comprising platinum and nickel or compounds of metals.  
           [0024]    Both the cathode and anode may be formed from material which allows easy passage of hydrogen ions which may be selected from the group carbon or metal hydrides.  
           [0025]    Alternatively the cathode and the anode are formed from a material which allows easy passage of hydrogen and the anode has a catalytic surface engaged against the proton exchange membrane.  
           [0026]    In an alternative form the invention may be said to reside in a fuel cell including an anode having an angled face, a cathode having a complimentary angled face and a proton exchange membrane between the angled face of the anode and the complimentary angled face of the cathode and a force means to draw the angled faces together with the proton membrane engaged therebetween.  
           [0027]    Preferably the anode electrode is cylindrical and the angled face is an internal frusto-conical surface and the cathode electrode is cylindrical and the complimentary angled surface is an external frusto-conical surface and the force means causes engagement of the internal frustoconical surface and the external frustoconical surface with the proton exchange membrane sandwiched therebetween.  
           [0028]    Preferably the proton exchange membrane is a semiconductor adapted to allow transfer of electrons from the cathode electrode to the anode electrode.  
           [0029]    The proton exchange membrane may be selected from a group comprising a polymer, a rubber or a ceramic each of which is doped to make it semiconductive. The dopant may be silicon or other material that preferably allow electrons to move in one direction only.  
           [0030]    Instead of a homogenous material, the proton exchange membrane may also be constructed in discrete segments where one segment may be a proton exchange membrane that allows the hydrogen proton to pass readily from the anode electrode to the cathode electrode but not electrons, and the next segment connected to the first segment may be a material that is a semiconductor that allows the flow of electrons from the cathode electrode to the anode electrode. There may be several segments in this type of proton exchange membrane. The net effect of this segmental construction is that protons are allowed to travel from the anode electrode to the cathode electrode while electrons are allowed to travel only from the cathode electrode to the anode electrode.  
           [0031]    The operating principle of a fuel cell based on a complete electronic circuit of this invention may also be used to improve the power output of other types of fuel cells such as the planar or tubular solid oxide fuel cell or ceramic cell. The solid electrolyte that allows the movement of the oxygen ion is further doped to allow the travel of electrons in one direction only providing a complete electronic circuit. As in proton membrane fuel cells, the solid electrolyte may be homogenous or constructed in segments connected to each other, one segment allowing the movement of the oxygen ion and the adjacent segment allowing the movement of electrons in one direction only.  
           [0032]    The surface of each of the anode and cathode not being the angled faces may have an increased surface area by means including grooving, pyramiding or roughening of the surface.  
           [0033]    The anode and the cathode may be formed from material permeable to protons being selected from a group comprising carbon or metal hydrides and the active surfaces of each of the anode and cathode include a catalyst which may be fine platinum or nickel.  
           [0034]    Alternatively the cathode and the anode are formed from a material which allows easy passage of hydrogen and the anode has a catalytic surface engaged against the proton exchange membrane.  
           [0035]    Alternatively the cathode and anode catalyst may be formed from compounds that catalyze the oxidant and the fuel.  
           [0036]    In an alternative form the invention may be said to reside in a process to produce electricity from the reaction of hydrogen and oxygen to produce water, the process including the steps of:  
           [0037]    a) pressurising hydrogen at the outer catalyst surface of an outer cylindrical anode electrode;  
           [0038]    b) catalysing the hydrogen to hydrogen ions and electrons wherein the electrons travel in an external electrical circuit through an electrical load to an inner cylindrical cathode and the hydrogen ions travel through the anode, a proton exchange semi-conductor membrane between the anode and the cathode and the cathode to an inner catalytic surface of the cathode; and  
           [0039]    c) reacting the hydrogen ions with oxygen at the catalytic surface of the cathode to produce water,  
           [0040]    wherein the proton exchange membrane is a semiconductor adapted to allow transfer of electrons from the cathode to the anode.  
           [0041]    In this process the anode electrode may have a cylindrical shape outside and a slightly conical shape inside and the cathode electrode may have a cylindrical shape inside and a slightly conical shape outside complementary to the conical shape of the anode.  
           [0042]    An alternative construction is the anode may be a cubical shape outside and a slighting trapezoidal shape inside and the cathode electrode may be cubical inside with slightly trapezoidal shape outside matching the inside anode trapezoidal shape with the proton membrane sandwiched between the anode and cathode electrodes.  
           [0043]    There may be further included means to apply a force to draw the anode and cathode together to engage the proton exchange membrane therebetween.  
           [0044]    The hydrogen may be at a pressure of up to 333 bars and the oxygen may be provided at a pressure up to 10 bars at the cathode and the process may be operated at a temperature of up to 250° C.  
           [0045]    In an alternative form the invention may be said to reside in a fuel cell assembly formed from a stack of a plurality of fuel cells as described above.  
           [0046]    The fuel cells may be electrically connected in series or in parallel.  
           [0047]    The fuel cell assembly may include annular non-conducting seals between the fuel cells with the seals incorporating electrical connections between the adjacent fuel cells.  
           [0048]    The stack of fuel cells may be within a cylindrical container to allow hydrogen to be pressurised on the outer side of the anode cells and oxygen or air is passed through the inside of the fuel cells.  
           [0049]    There may be included means to provide good contact between the oxygen or air and the cathode surface such as a helical baffle.  
           [0050]    The fuel cell stack may include force application means on the stack of fuel cells to promote sealing at each of the annular seals and to promoting engagement of the respective anodes and cathodes to the proton exchange membrane therebetween.  
           [0051]    In an alternative form the invention may be said to reside in a process of producing electricity from the reaction of hydrogen and oxygen to produce water, the process including the steps of providing a stack of fuel cells and operating them as described above.  
           [0052]    In an alternative form the invention is said to reside in a proton exchange membrane fuel cell including an anode electrode and a cathode electrode characterized by;  
           [0053]    a proton exchange semiconductor membrane that allows movement of the hydrogen ion from the anode electrode to the cathode electrode and electrons from the cathode electrode to the anode electrode; and  
           [0054]    the anode electrode having a frusto-conical surface on the inner surface and the cathode electrode with a frusto-conical outer surface matching the frusto-conical inner surface of the anode electrode and the proton exchange semiconductor membrane held between the anode electrode and cathode electrode.  
           [0055]    Alternatively, the invention is said to reside in a proton exchange fuel cell arrangement comprising a plurality of fuel cell elements, each fuel cell element having an anode electrode and a cathode electrode and characterised by;  
           [0056]    a proton exchange semiconductor membrane that allows movement of the hydrogen ion from the anode electrode to the cathode electrode and electrons from the cathode electrode to the anode electrode;  
           [0057]    the anode electrode having a frusto-conical surface on the inner surface and the cathode electrode with a frusto-conical outer surface matching the frusto-conical inner surface of the anode electrode and the proton exchange semiconductor membrane held between the anode electrode and cathode electrode; and  
           [0058]    the fuel cells having a simple internal stacking of the fuel cell elements in a cylindrical cell container to allow high pressure hydrogen operation of the fuel cell arrangement.  
           [0059]    The operating principle of this proton exchange fuel cell with the homogenous or segmented membrane providing a complete electronic circuit for the fuel cell may be applied to other types of fuel cells with solid electrolyte such as the solid oxide fuel cell to improve the power output.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0060]    This then generally describes the invention but to assist with understanding of the invention reference will now be made to the accompanying drawings which show preferred embodiments of the invention.  
         [0061]    In the drawings:  
         [0062]    [0062]FIG. 1A shows a schematic view of a proton exchange membrane fuel cell with a homogenous membrane according to the invention;  
         [0063]    [0063]FIG. 1B shows a schematic view of a proton exchange membrane fuel cell with a segmented membrane according to the invention;  
         [0064]    [0064]FIG. 2 shows a cross section of an embodiment of a fuel cell according to this invention;  
         [0065]    [0065]FIG. 3 shows a cross section of a stack of fuel cells of the type shown in FIG. 2;  
         [0066]    [0066]FIG. 4 shows a cross section of an alternative embodiment of a stacked fuel cell;  
         [0067]    [0067]FIGS. 5A and 5B show a still further embodiment of a fuel cell stack; and  
         [0068]    [0068]FIGS. 6A, 6B and  6 C show an alternative construction of a fuel cell with increased surface area. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0069]    The operating principle of the proton electrolytic membrane fuel cell modified according to the present invention is shown on FIG. 1A with a homogenous membrane and  1 B with a segmented membrane. Referring to FIG. 1A, the fuel cell has and anode  1  and a cathode  3  separated by a homogenous proton exchange membrane  5  wherein the proton exchange membrane is also a semiconductor adopted to allow transfer of electrons from the cathode to the anode instead of being a non-conductor as in the prior art. Each of the anode  1  and the cathode  3  have a catalytic surface  2  and  4  respectively. The catalytic reaction at the anode converts the hydrogen to hydrogen ions or protons and these are allowed to travel from the anode through the proton exchange semiconductor membrane  5  to the cathode while electrons produced are allowed to travel to the external load  7  then to the cathode and then through the proton exchange semiconductor membrane to the anode. This provides a complete electronic circuit.  
         [0070]    [0070]FIG. 1B shows a fuel cell of the invention where the membrane is made of segments. Proton exchange non-conductor membrane segment  6  allows the hydrogen proton to travel from the anode to the cathode while semiconductor membrane segment  8  allows the electrons to travel from the cathode to the anode. Segments  6  and  8  may or may not be connected to each other and may be shaped planar, conical, or trapezoidal similar to the shape of the homogenous proton exchange semiconductor membrane.  
         [0071]    Hydrogen is provided at the anode and is catalysed in the following reaction:  
         H 2 →2H + +2 e   −   
         [0072]    At the cathode oxygen is supplied and the reaction is catalysed as follows:  
         ½O 2 +2H + +2 e   − →H 2 O  
         [0073]    The proton exchange semiconductor membrane that allows the hydrogen proton to pass from the anode to the cathode and electrons to travel from the cathode to the anode may be constructed of a homogenous doped polymer or doped rubber or ceramic material or the proton exchange membrane may be constructed of connected segments, one segment allowing the hydrogen proton to pass from the anode to the cathode and the adjacent segments allowing the electrons to travel from the cathode to the anode. It must be sufficiently pliable so that it will conform to the conical or trapezoidal surfaces of the anode electrode and the cathode electrode it is in contact with. Further, the membrane must be stable at the operating temperature and pressure of the fuel cell.  
         [0074]    A further aspect of the invention relates to a cubical-trapezoidal configuration of the fuel cell but preferably a cylindrical-conical configuration of the fuel cell. Axial opposing forces may be applied to a fuel cell with such a configuration forcing the cathode electrode against the anode electrode with the proton electrolytic membrane sandwiched between. This will allow good contact to be maintained between the membrane and the anode and cathode electrodes for a proper operation of the fuel cell under all operating conditions.  
         [0075]    [0075]FIG. 2 shows the preferred construction of one embodiment of a cell element of the cylindrical-conical fuel cell.  
         [0076]    In this embodiment the anode catalyst  10  is located outside of the anode electrode  12  in a cylindrical anode cell  11 . Where the hydrogen fuel has impurities such as carbon oxides, the anode catalyst may be located in the inside of the anode electrode. As shown in FIG. 2, the cylindrical anode electrode  12  with the anode catalyst  10  located on the outer surface is slightly conical on the inside. The proton electrolytic membrane  14  which is semi-conductive is also slightly conical and fits into the inside of the anode electrode  12 . The outer surface of the cylindrical cathode electrode  16  is slightly conical and fits into the cone of the proton electrolytic membrane  14  and the inside cone of the anode electrode  12 . The cathode electrode  16  is pushed axially upward  18  while the anode electrode is restrained so that there is a force causing the inside of the anode electrode  12  to maintain contact with the outside of the cathode electrode  16  with the proton electrolytic membrane  14  sandwiched in-between. The material of the anode and cathode electrode is electrically conducting and needs to allow easy passage of the hydrogen ion and must have structural strength to withstand the high pressure differential between the hydrogen in the anode cell  11  and the air or oxygen in the cathode cell  17  at the operating temperature of the fuel cell.  
         [0077]    The inner surface of the cathode electrode  16  has a catalyst  20  on it.  
         [0078]    The anode and cathode electrodes are made of electrically conducting material such as metals, alloys, hydrides and carbon that allows easy passage of the hydrogen ion through the crystal lattice or grain boundaries of the material. There are many such materials known due to the extensive research into the use of these materials for the storage of hydrogen.  
         [0079]    In operation, the hydrogen atom is catalyzed to hydrogen ion by the anode catalyst at the anode electrode. The electrons travel to the external circuit via the electrical load  22  and return to the cathode electrode. The hydrogen ion travels to the cathode catalyst  20  located at the inner surface of the cathode electrode  16  where the hydrogen ion reacts with the oxygen and the electrons from the external electrical circuit to form water. The electronic circuit is completed by the passage of electrons from the cathode electrode through the semi-conductor membrane  14  to the anode electrode.  
         [0080]    A simple model to explain the operating principle of the fuel cell is that there is a continuous flow of electrons in the electronic circuit. At the anode, electrons from the oxidation of the hydrogen join this electronic circuit. The hydrogen ion travels to the cathode. At the cathode, some electrons are used by the cathode reaction to carry out the reaction forming water from the hydrogen ions and the oxygen available at the catalyst surface of the cathode electrode.  
         [0081]    The cylindrical-conical construction allows a large pressure differential between the anode (hydrogen) and the cathode (oxygen). This creates a stronger driving force for the diffusion of the hydrogen ion due to the substantially higher concentration of hydrogen ions at the anode electrode. This will result in a higher current density for the fuel cell even without considering the higher power density of the fuel cell as a result of the complete electronic circuit provided by the proton exchange semiconductor membrane.  
         [0082]    It is projected that the fuel cell according to the invention can operate at hydrogen pressures of up to 333 bars and up to 10 bars of air or oxygen pressure. The higher the operating temperature, the higher the diffusion rate of the hydrogen ion through the anode and cathode electrodes. The normal operating temperature of the fuel cell may range from 25° C. up to 250° C. or more. The operating temperature will be limited mainly by the materials of construction of the fuel cell.  
         [0083]    Fuel cells can produce high currents but the voltage of each cell is theoretically 1.229 volts for the hydrogen-oxygen fuel cell and is usually lower under load in an operating system. It is desirable to connect the cells in series or “stack” these to produce a high working voltage.  
         [0084]    In the third aspect of this invention, the fuel cell elements may be stacked internally as shown in one alternate in FIG. 3. Each cell is the same as that shown in FIG. 2 and the same reference numerals are used for the same components.  
         [0085]    The cell elements are held in a tube  30  pressurized with hydrogen. Each cell element is electrically isolated by a non-conducting annular ring  32  that is made of a plastic or ceramic material. An outer annular conducting ring  34  in contact with the anode electrode and an inner annular conducting ring  35  in contact with the cathode electrode are imbedded in the non-conducting ring. These two rings are connected by a conductor wire  36  imbedded in the non-conducting annular ring  32 . Sealing O-rings  38  or similar are installed between the anode electrode  12  and the non-conducting annular ring  32  to separate the hydrogen from the oxygen. The dimension and compressibility of the inner and outer conducting rings and the O-ring seals selected so that when a compressive force is applied to the fuel cell elements, the anode electrodes are forced against the annular ring  32  to seal against it and at the same time achieve sealing of the hydrogen from the air or oxygen and the conical surfaces of the anode and cathode electrodes forced against each other to hold the proton membrane in good contact.  
         [0086]    Larger diameter non-conducting rings  40  with holes are installed at appropriate intervals to center the fuel cell elements within the cylindrical container  30 . An inner cylinder  42  with continuous helical vane or baffle  44  is installed in the cathode cell cavity to ensure good contact of the air or oxygen with the cathode catalyst and to effect the efficient removal of the fuel cell reaction product.  
         [0087]    The electronic circuit is described as follows. Starting from cell element  46 , electrons travel from the cathode electrode to the anode electrode to the outer conducting ring through the imbedded wire conductor to the inner conducting ring of cell element  48  to the cathode electrode of cell element  48  to the anode electrode of cell element  48  to the outer conducting ring through the imbedded wire conductor to the inner conducting ring of cell element  50  to the cathode electrode of cell element  50  to the anode electrode to the outer conducting ring through the imbedded wire conductor to the inner conducting ring of cell element  52  to the cathode electrode of cell element  52  to the anode electrode of cell element  52  to the external conductor to the electrical load  54  and to the cathode electrode of cell element  46 .  
         [0088]    Another method of internal stacking is shown on FIG. 4. Each cell is the same as that shown in FIG. 2 and the same reference numerals are used for the same components. In this method, instead of opposing forces achieving contact between the membrane and the electrodes, each fuel cell element is bolted to the next fuel cell element to achieve the force to keep the membrane in contact with the electrodes.  
         [0089]    The device consists of a plurality of fuel cells  60  each composed of an anode  12  and a cathode  16  separated by a semiconductive proton exchange membrane  14 . Each cell is connected to adjacent cells by insulated bolts  62  and compressible seals  64  are filled between the cells and electrical connection  66  is provided between the cathode of one cell and the anode of the next.  
         [0090]    The entire stack is received in a cylindrical tank  68  so that hydrogen can be pressurised around the anodes of the cells. The cylindrical inner surfaces of the cathodes are exposed to air or oxygen and a central cylinder  70  with helical baffles  72  ensures good contact of the air with the catalytic surface  20  of the cathode  16 .  
         [0091]    In the device shown in FIG. 4, the dimension and compression characteristics of the seals  64  are important to achieve the seal between the hydrogen and the oxygen and the force required to maintain contact between the anode electrode  12  the membrane  14  and the cathode electrode  16 .  
         [0092]    Another method of internal stacking the fuel cells is shown in FIG. 5.  
         [0093]    The anode stack, FIG. 5A, is a set of anode electrodes  74  held together by at least three long bolts  75  through non-conductor annular rings  76 . The anode non-conducting annular rings  76  incorporate the necessary electrical connections and the seals to maintain the pressure differential between the hydrogen side and the oxygen side and are grooved to center the cylindrical-conical anode electrodes.  
         [0094]    The cathode stack, FIG. 5B, is a set of cathode electrodes  78  which are separated by non-conducting annular rings  79  incorporating electrical connections and grooves to centre the cylindrical-conical cathode electrodes.  
         [0095]    The assembly, FIG. 5C, shows the anode electrode stack installed inside a cylindrical container  81  with seals  85  to contain the hydrogen at the anode side. The cathode electrode stack with matching conical dimensions are installed inside the anode electrode stack with the semiconductive proton exchange membrane  80  sandwiched between the anode electrodes and the cathode electrodes. A force  82  is applied at bottom end of the cathode electrode stack so that the cathode electrodes  78  are firmly in contact with the membrane  80  and the anode electrodes  74 . An inner cylinder  84  with helix  86  is installed through the cathode electrode  78  stack to ensure good contact of the air or oxygen with the catalyst  83  of the cathode electrodes  78 .  
         [0096]    Heat is produced during the fuel cell reaction. Part of this heat is used for pre-heating the hydrogen and the oxygen or oxygen-nitrogen feed to the fuel cell. Excess heat from the fuel cell may be used for external application such as domestic or industrial heating or water desalination.  
         [0097]    It is desirable to have the largest specific surface of the electrodes to achieve the highest possible power density for a given volume of the fuel cell. The active surfaces of the anode and cathode electrodes may be grooved or of pyramidal structure to give a high specific surface area of the catalysts.  
         [0098]    Another method is to increase the total surface area of the electrodes for a given volume of the fuel cell as shown in an example in FIG. 6.  
         [0099]    [0099]FIG. 6A shows an individual fuel cell element, FIG. 6B shows a cross section of the assembly and FIG. 6C shows a plan view of the assembly.  
         [0100]    V-shaped fuel cell elements  90  are installed in a non-conducting frame  91  located inside a cylinder  92 .  
         [0101]    The frame  91  is cylindrical with rectangular apertures  93  to receive each of the fuel cells  90 . Each fuel cell  90  is made up of a cathode  94 , a proton exchange semiconductor membrane  95  and a cathode electrode  96 . Suitable sealing is provided around each cell.  
         [0102]    The fuel cell elements are held in place by two conducting straps, one for connecting the anode electrodes and the other strap connecting the cathode electrodes. A cylinder  97  with circular baffles  98  is installed inside the non-conducting frame.  
         [0103]    Hydrogen is pressurized between the cylinder container  92  and the non-conducting frame  91  while air or oxygen is passed between the inner cylinder  97  and the non-conducting frame  91 . The circular baffles  98  of the inner cylinder ensure good contact between the air and the cathode catalyst and the efficient removal of the reaction product. A construction of the fuel cell as shown in FIG. 6C would provide a substantially higher power density per unit volume of the fuel cell.  
         [0104]    In the cell stacking alternatives described above, there may be as many cell elements in a fuel cell stack as required to produce the desired working voltage. For instance, there may be about 12 cell elements in the stack to produce 12 volts or 120 cell elements in the stack to produce 120 volts. There may be two 12 cell stacks and these may be connected in series to produce 24 volts or a higher current output at 12 volts if the 12 cell stacks are connected in parallel. There may be several fuel cell stacks inside a cell container.  
         [0105]    Aside from the current density and electrical efficiency achieved in the fuel cell, the dimensions of the fuel cell element and the number of fuel cell elements in a stack determine the power output. Table 1 shows a projection of the dimensions of the fuel cell from 3 kilowatts up to 50,000 kilowatts. The highest reported power density in conventional proton exchange membrane fuel cell is Ballard Power with a power density of 1.3 kilowatts per liter that is equivalent to about 1.3 amperes per square centimeter. In Table 1, the assumption is 3.0 amperes per square centimeter and the electrical efficiency is 73.2 percent. Table 1 shows that the fuel cell dimensions and the number of stacks are practical and achievable for commercial application.  
                                                                                                                                       TABLE 1                       Fuel Cell Size for Commercial Plants                   Assumptions:                Fuel Cells are cylindro-conical in shape with diameter approximately equal to the height.               Current Density, amperes per square centimeter   3           Theoretical Cell Voltage, volts   1.229           Ratio of Cell Voltage at Load   0.732                                    Projections:                Voltage                                                   Required       Fuel Cell   in   Cells       Total   Area of   Nominal   Nominal   Selected   Selected   Height of   Final Fuel       Output   Stack,   in the   Number   Current   Each Cell   Cell Dia.   Cell Height   Diameter   Height   Stack plus   Cell Output       Kilowatts   Volts   Stack   of Stacks   Amperes   cm2   cm   Cm   cm   cm   20%, cm   Kilowatts                    3   20   22   2   75   25   2.8   2.82   2.7   3   80   3.05       3   12   13   2   125   42   3.6   3.64   4   3.4   54   3.08       5   20   22   1   250   83   5.2   5.15   5   5.4   144   5.09       5   12   13   2   208   69   4.7   4.70   5   5   80   5.65       50   20   22   6   417   139   6.6   6.65   7   7   187   55.42       75   12   13   8   781   260   9.1   9.10   10   8.3   133   75.10       100   80   89   2   625   208   8.1   8.14   8.2   8.2   875   101.40       250   80   89   5   625   208   8.1   8.14   8.2   8.2   875   253.49       1000   80   89   14   893   298   9.7   9.73   10   10   1067   1055.58       10000   80   89   20   6250   2083   25.8   25.75   26   26   2773   10193.86       50000   80   89   40   15625   5208   40.7   40.72   50   33.5   3573   50516.93                  
 
         [0106]    Throughout this specification various indications have been given as to the scope of this invention but the invention is not limited to any one of these but may reside in two or more of these combined together. The examples are given for illustration only and not for limitation.  
         [0107]    Throughout this specification and the claims that follow unless the context requires otherwise, the words ‘comprise’ and ‘include’ and variations such as ‘comprising’ and ‘including’ will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers.