Abstract:
A fuel cell power generation system including: a hydrogen generating apparatus, controlling an amount of hydrogen generation by controlling an on/off status of a switch connected between electrodes; and a fuel cell, being supplied with hydrogen generated by the hydrogen generating apparatus and producing a direct current by converting chemical energy of the hydrogen to electrical energy. The hydrogen generating apparatus used in the system preferably includes an electrolyzer, filled with an aqueous electrolyte solution containing hydrogen ions; a first electrode, accommodated in the electrolyzer, submerged in the aqueous electrolyte solution, and generating electrons; a second electrode, accommodated in the electrolyzer, submerged in the aqueous electrolyte solution, receiving the electrons to generate hydrogen; a switch, located between the first electrode and the second electrode; a meter, measuring an amount of hydrogen generation or an output of a fuel cell; and a switch controller, receiving a set value, comparing the amount of hydrogen generation or the output of the fuel cell measured by the meter with the set value, and controlling an on/off status of the switch.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a U.S. divisional application filed under 37 USC 1.53(b) claiming priority benefit of U.S. Ser. No. 11/812,656 filed in the United States on Jun. 20, 2007, which claims earlier priority benefit to Korean Patent Application No. 10-2007-0017343 filed with the Korean Intellectual Property Office on Feb. 21, 2007, the disclosures of which are incorporated herein by reference. 
     
    
     BACKGROUND 
       [0002]    1. Field 
         [0003]    The present invention relates to a hydrogen generating apparatus, more particularly to a hydrogen generating apparatus that can control the amount of generation of hydrogen supplied to a fuel cell. 
         [0004]    2. Description of the Related Art 
         [0005]    A fuel cell refers to an energy conversion apparatus that directly converts chemical energy of a fuel (hydrogen, LNG, LPG, methanol, etc.) and air to electricity and/or heat by means of an electrochemical reaction. Unlike a conventional power generation technology that requires fuel combustion, steam generation, or a turbine or power generator, the fuel cell technology needs no combustion process or driving device, thereby boosting energy efficiency and curbing environmental problems. 
         [0006]      FIG. 1  illustrates an operational architecture of a fuel cell. 
         [0007]    Referring to  FIG. 1 , a fuel cell  100  is composed of an anode as a fuel pole  110  and a cathode as an air pole  130 . The fuel pole  110  is provided with hydrogen molecules (H 2 ), and decomposes them into hydrogen ions (H + ) and electrons (e). The hydrogen ion (H + ) moves toward the air pole  130  via a membrane  120 , which is an electrolyte layer. The electron moves through an external circuit  140  to generate an electric current. In the air pole  130 , the hydrogen ions and the electrons are combined with oxygen molecules in the atmosphere, generating water molecules. The following chemical formulas represent the above chemical reactions occurring in the fuel cell  100 . 
         [0000]      Fuel pole 110: H 2 →2H + +2e − 
 
         [0000]      Air pole 130: ½O 2 +2H + +2e − →H 2 0
 
         [0000]      Overall reaction: H 2 +½O 2 →H 2 0   CHEMICAL FORMULA 1
 
         [0008]    In short, the fuel cell  100  functions as a battery by supplying the electric current, generated due to the flowing of the decomposed electrons, to the external circuit  140 . Such a fuel cell  100  hardly emits an atmospheric pollutant such as Sox and NOx and makes little noise and vibration. 
         [0009]    Meanwhile, in order to produce electrons in the fuel pole  110 , the fuel cell  100  necessitates a hydrogen generating apparatus that can change a common fuel to hydrogen gas. 
         [0010]    A hydrogen storage tank, generally known as a hydrogen generating apparatus, however, occupies a large space and should be kept with care. 
         [0011]    Moreover, as a portable electronic device, such as a mobile phone and a notebook computer, requires a large capacity of power, it is necessary that the fuel cell have a large capacity and perform high performance while it is small. 
         [0012]    In order to meet the above needs, methanol or formic acid, permitted to be brought into an airplane by International Civil Aviation Organization (ICAO), is used for fuel reforming, or methanol, ethanol, or formic acid is directly used as a fuel for the fuel cell. 
         [0013]    However, the former case requires a high reforming temperature, has a complicated system, consumes driving power, and contains impurities (e.g., CO 2  and CO) in addition to pure hydrogen. The latter case deteriorates power density due to a low rate of a chemical reaction in the anode and a cross-over of hydrocarbon through the membrane. 
       SUMMARY 
       [0014]    The present invention provides a hydrogen generating apparatus, a fuel cell power generation system, a method of controlling the quantity of hydrogen generation, and a recorded medium recorded with a program performing the method that can generate pure hydrogen at room temperature through an electrochemical reaction. 
         [0015]    The present invention also provides a hydrogen generating apparatus, a fuel cell power generation system, a method of controlling the quantity of hydrogen generation, and a recorded medium recorded with a program performing the method that can control the quantity of hydrogen generation without a separate BOP (Balance of Plant) unit while maintaining a simple structure. 
         [0016]    The present invention also provides a hydrogen generating apparatus, a fuel cell power generation system, a method of controlling the quantity of hydrogen generation, and a recorded medium recorded with a program performing the method that are economical and eco-friendly. 
         [0017]    The present invention also provides a hydrogen generating apparatus, a fuel cell power generation system, a method of controlling the quantity of hydrogen generation, and a recorded medium recorded with a program performing the method that can control the quantity of hydrogen generation by use of On/Off time and/or On/Off frequency of a switch. 
         [0018]    Moreover, the present invention provides a hydrogen generating apparatus, a fuel cell power generation system, a method of controlling the quantity of hydrogen generation, and a recorded medium recorded with a program performing the method that can prevent waste or risk of leaking surplus hydrogen in the air simply by turning on the switch and reduce the noise and power consumption by not using a gas pump or a liquid pump. 
         [0019]    An aspect of the present invention features a hydrogen generating apparatus that is capable of controlling the amount of hydrogen generation. 
         [0020]    The hydrogen generating apparatus in accordance with an embodiment of the present invention includes an electrolyzer, which is filled with an aqueous electrolyte solution containing hydrogen ions, a first electrode, which is accommodated in the electrolyzer, is submerged in the aqueous electrolyte solution, and generates electrons, a second electrode, which is accommodated in the electrolyzer, is submerged in the aqueous electrolyte solution, and receives the electrons to generate hydrogen, a switch, which is located between the first electrode and the second electrode, a flow rate meter, which measures an amount of hydrogen generation in the second electrode, and a switch controller, which receives a set value, compares the amount of hydrogen generation measured by the flow rate meter with the set value, and controls an on/off status of the switch. 
         [0021]    The switch controller can be inputted with the set value directly from a user through an input unit. The hydrogen generating apparatus can be coupled to a fuel cell and supplies hydrogen, and the switch controller can be inputted with the set value in accordance with an amount of hydrogen generation that is required by the fuel cell. 
         [0022]    The metal forming the first electrode can have a higher ionization tendency than a metal forming the second electrode. 
         [0023]    The flow rate meter can measure the amount of hydrogen generation in units of flowrate. The switch controller can generate and output a switch control signal turning the switch on and off, and the switch controller can determine an on/off ratio of the switch within one cycle by varying a duty ratio of the switch control signal. 
         [0024]    The switch controller can control a fluctuation in the amount of hydrogen generation by varying an on/off frequency of the switch control signal. The switch controller can compare the set value with the measured amount of hydrogen generation, and can increase the duty ratio if the amount of hydrogen generation is smaller than the set value, reduce the duty ratio if the amount of hydrogen generation is greater than the set value, and maintain the duty ratio if the amount of hydrogen generation is equal to the set value. The set value includes an upper limit and a lower limit, and the switch controller can compare the set value with the measured amount of hydrogen generation, and can increase the duty ratio if the amount of hydrogen generation is smaller than the lower limit, reduce the duty ratio if the amount of hydrogen generation is greater than the upper limit, and maintain the duty ratio if the amount of hydrogen generation is between the lower limit and the upper limit. 
         [0025]    Another aspect of the present invention features a fuel cell power generation system including a hydrogen generating apparatus that is capable of controlling the amount of hydrogen generation. 
         [0026]    The fuel cell power generation system in accordance with an embodiment of the present invention has a hydrogen generating apparatus, which controls an amount of hydrogen generation by controlling an on/off status of a switch connected between electrodes, and a fuel cell, which is supplied with hydrogen generated by the hydrogen generating apparatus and produces a direct current by converting chemical energy of the hydrogen to electrical energy. 
         [0027]    The hydrogen generating apparatus can include an electrolyzer, which is filled with an aqueous electrolyte solution containing hydrogen ions, a first electrode, which is accommodated in the electrolyzer, is submerged in the aqueous electrolyte solution, and generates electrons, a second electrode, which is accommodated in the electrolyzer, is submerged in the aqueous electrolyte solution, and receives the electrons to generate hydrogen, a switch, which is located between the first electrode and the second electrode, a meter, which measures an amount of hydrogen generation or an output of a fuel cell, and a switch controller, which receives a set value, compares the amount of hydrogen generation or the output of the fuel cell measured by the meter with the set value, and controls an on/off status of the switch. 
         [0028]    The switch controller can be inputted with the set value directly from a user through an input unit. The hydrogen generating apparatus can be coupled to the fuel cell and supply hydrogen, and the switch controller can be inputted with the set value in accordance with an amount of electric power, voltage, current, impedance or a combination thereof or an amount of hydrogen generation that is required by the fuel cell. 
         [0029]    The metal forming the first electrode can have a higher ionization tendency than a metal forming the second electrode. 
         [0030]    The switch controller can generate and output a switch control signal turning the switch on and off, and the switch controller can determine an on/off ratio of the switch within one cycle by varying a duty ratio of the switch control signal. The meter can be a flow rate meter that measures the amount of hydrogen generated in the second electrode in units of flowrate. The switch controller can control a fluctuation in the amount of hydrogen generation by varying an on/off frequency of the switch control signal. The switch controller can compare the set value with the measured amount of hydrogen generation, and can increase the duty ratio if the amount of hydrogen generation is smaller than the set value, reduce the duty ratio if the amount of hydrogen generation is greater than the set value, and maintain the duty ratio if the amount of hydrogen generation is equal to the set value. The set value can include an upper limit and a lower limit, and the switch controller can compare the set value with the measured amount of hydrogen generation, and can increase the duty ratio if the amount of hydrogen generation is smaller than the lower limit, reduce the duty ratio if the amount of hydrogen generation is greater than the upper limit, and maintain the duty ratio if the amount of hydrogen generation is between the lower limit and the upper limit. 
         [0031]    The meter can be an output meter that measures an output of the fuel cell in units of watt (W), volt (V), ampere (A), ohm (Ω) or a combination thereof. The switch controller can control a fluctuation in the output of the fuel cell by varying an on/off frequency of the switch control signal. The switch controller can compare the set value with the measured output of the fuel cell, and can increase the duty ratio if the output of the fuel cell is smaller than the set value, reduce the duty ratio if the output of the fuel cell is greater than the set value, and maintain the duty ratio if the output of the fuel cell is equal to the set value. The set value can include an upper limit and a lower limit, and the switch controller can compare the set value with the measured output of the fuel cell, and can increase the duty ratio if the output of the fuel cell is smaller than the lower limit, reduce the duty ratio if the output of the fuel cell is greater than the upper limit, and maintain the duty ratio if the output of the fuel cell is between the lower limit and the upper limit. 
         [0032]    Another aspect of the present invention features a method of controlling an amount of hydrogen generation in a hydrogen generating apparatus controlling an amount of hydrogen generation by controlling an on/off status of a switch located between electrodes. 
         [0033]    The method of controlling an amount of hydrogen generation in accordance with an embodiment of the present invention includes the steps of being inputted with a set value; comparing a measured amount of hydrogen generation and the set value; and increasing a duty ratio of a switch control signal if the amount of hydrogen generation is smaller than the set value, reducing the duty ratio of the switch control signal if the amount of hydrogen generation is greater than the set value, and maintaining the duty ratio of the switch control signal if the amount of hydrogen generation is equal to the set value, in which the switch control signal controls the on/off status of the switch within one cycle in accordance with the duty ratio. 
         [0034]    The method of controlling an amount of hydrogen generation in accordance with another embodiment of the present invention includes the steps of being inputted with an upper value and a lower value; comparing a measured amount of hydrogen generation with the upper value and the lower value; and increasing a duty ratio of a switch control signal if the amount of hydrogen generation is smaller than the lower value, reducing the duty ratio of the switch control signal if the amount of hydrogen generation is greater than the upper value, and maintaining the duty ratio of the switch control signal if the amount of hydrogen generation is between the lower value and the upper value, in which the switch control signal controls the on/off status of the switch within one cycle in accordance with the duty ratio. 
         [0035]    The method of controlling an amount of hydrogen generation in accordance with yet another embodiment of the present invention includes the steps of being inputted with a set value; comparing an output of the fuel cell and the set value; and increasing a duty ratio of a switch control signal if the output of the fuel cell is smaller than the set value, reducing the duty ratio of the switch control signal if the output of the fuel cell is greater than the set value, and maintaining the duty ratio of the switch control signal if the output of the fuel cell is equal to the set value, in which the switch control signal controls the on/off status of the switch within one cycle in accordance with the duty ratio. 
         [0036]    The method of controlling an amount of hydrogen generation in accordance with yet another embodiment of the present invention includes the steps of being inputted with an upper value and a lower value; comparing a measured output of the fuel cell with the upper value and the lower value; and increasing a duty ratio of a switch control signal if the output of the fuel cell is smaller than the lower value, reducing the duty ratio of the switch control signal if the output of the fuel cell is greater than the upper value, and maintaining the duty ratio of the switch control signal if the output of the fuel cell is between the lower value and the upper value, in which the switch control signal controls the on/off status of the switch within one cycle in accordance with the duty ratio. 
         [0037]    Another aspect of the present invention features a recording medium having recorded a computer readable program to control an amount of hydrogen generation in a hydrogen generating apparatus controlling an amount of hydrogen generation by controlling an on/off status of a switch located between electrodes. A program performing a method of controlling an amount of hydrogen generation described above is recorded in the recording medium, which is readable by a computer. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0038]    These and other features, aspects and advantages of the present invention will become better understood with regard to the following description, appended claims and accompanying drawings where: 
           [0039]      FIG. 1  illustrates an operational architecture of a fuel cell; 
           [0040]      FIG. 2  shows a sectional view of a hydrogen generating apparatus in accordance with an embodiment of the present invention; 
           [0041]      FIG. 3  is a graph showing how the amount of electric current between a first electrode and a second electrode and the amount of generated hydrogen are related in a hydrogen generating apparatus in accordance with an embodiment of the present invention; 
           [0042]      FIG. 4  shows a block diagram of a control unit of a hydrogen generating apparatus in accordance with an embodiment of the present invention; 
           [0043]      FIG. 5  shows a block diagram of a control unit of a hydrogen generating apparatus in accordance with another embodiment of the present invention; 
           [0044]      FIG. 6  is a graph indicating quantities of generated hydrogen, expressed in flow rate, when the switch is turned on; 
           [0045]      FIG. 7A  shows a first example of On/Off frequencies of the switch of a hydrogen generating apparatus in accordance with an embodiment of the present invention; 
           [0046]      FIG. 7B  shows a second example of On/Off frequencies of the switch of a hydrogen generating apparatus in accordance with an embodiment of the present invention; 
           [0047]      FIG. 8  shows the relation between time and quantity of hydrogen generation when the On/Off frequency of the switch is controlled; 
           [0048]      FIG. 9A  shows a first example of duty ratios of the switch of a hydrogen generating apparatus in accordance with an embodiment of the present invention; 
           [0049]      FIG. 9B  shows a second example of duty ratios of the switch of a hydrogen generating apparatus in accordance with an embodiment of the present invention; 
           [0050]      FIG. 10  shows the relation between time and quantity of hydrogen generation when the duty ratio of the switch is controlled; 
           [0051]      FIG. 11  shows a flowchart of a method of controlling the quantity of hydrogen generation in a hydrogen generating apparatus in accordance with an embodiment of the present invention; and 
           [0052]      FIG. 12  shows a flowchart of a method of controlling the quantity of hydrogen generation in a hydrogen generating apparatus in accordance with another embodiment of the present invention. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0053]    Since there can be a variety of permutations and embodiments of the present invention, certain embodiments will be illustrated and described with reference to the accompanying drawings. This, however, is by no means to restrict the present invention to certain embodiments, and shall be construed as including all permutations, equivalents and substitutes covered by the spirit and scope of the present invention. Throughout the drawings, similar elements are given similar reference numerals. Throughout the description of the present invention, when describing a certain technology is determined to evade the point of the present invention, the pertinent detailed description will be omitted. 
         [0054]    Terms such as “first” and “second” can be used in describing various elements, but the above elements shall not be restricted to the above terms. The above terms are used only to distinguish one element from the other. For instance, the first element can be named the second element, and vice versa, without departing the scope of claims of the present invention. The term “and/or” shall include the combination of a plurality of listed items or any of the plurality of listed items. 
         [0055]    When one element is described as being “connected” or “accessed” to another element, it shall be construed as being connected or accessed to the other element directly but also as possibly having another element in between. On the other hand, if one element is described as being “directly connected” or “directly accessed” to another element, it shall be construed that there is no other element in between. 
         [0056]    The terms used in the description are intended to describe certain embodiments only, and shall by no means restrict the present invention. Unless clearly used otherwise, expressions in the singular number include a plural meaning. In the present description, an expression such as “comprising” or “consisting of” is intended to designate a characteristic, a number, a step, an operation, an element, a part or combinations thereof, and shall not be construed to preclude any presence or possibility of one or more other characteristics, numbers, steps, operations, elements, parts or combinations thereof. 
         [0057]    Unless otherwise defined, all terms, including technical terms and scientific terms, used herein have the same meaning as how they are generally understood by those of ordinary skill in the art to which the invention pertains. Any term that is defined in a general dictionary shall be construed to have the same meaning in the context of the relevant art, and, unless otherwise defined explicitly, shall not be interpreted to have an idealistic or excessively formalistic meaning. 
         [0058]    Hereinafter, certain embodiments will be described in detail with reference to the accompanying drawings. Identical or corresponding elements will be given the same reference numerals, regardless of the figure number, and any redundant description of the identical or corresponding elements will not be repeated. 
         [0059]      FIG. 2  is a sectional view of a hydrogen generating apparatus in accordance with an embodiment of the present invention. 
         [0060]    A hydrogen generating apparatus  200  includes an electrolyzer  210 , a first electrode  220 , a second electrode  230  and a control unit  240 . For the convenience of description and understanding, it will be presumed below that the first electrode  220  is composed of magnesium (Mg) and the second electrode  230  is composed of stainless steel. 
         [0061]    The electrolyzer  210  is filled with an aqueous electrolyte solution  215 . The aqueous electrolyte solution  215  contains hydrogen ions, which are used by the hydrogen generating apparatus  200  to generate hydrogen gas. 
         [0062]    Examples of the electrolyte for the aqueous electrolyte solution  215  are LiCl, KCl, NaCl, KNO 3 , NaNO 3 , CaCl 2 , MgCl 2 , K 2 SO 4 , Na 2 SO 4 , MgSO 4 , AgCl, or the like. 
         [0063]    The electrolyzer  210  accommodates the first electrode  220  and the second electrode  230 , the entirety or portions of which are submerged in the electrolyte solution  215 . 
         [0064]    The first electrode  220  is an active electrode, where the magnesium (Mg) is oxidized to magnesium ions (Mg 2+ ), releasing electrons due to the difference in ionization energies of magnesium and water. The released electrons move to the second electrode  230  through a first electric wire  225 , the control unit  240  and a second electric wire  235 . 
         [0065]    The second electrode  230  is an inactive electrode, where the water molecules receive the electrons moved from the first electrode  220  and then are decomposed into the hydrogen molecules. 
         [0066]    The above chemical reactions can be represented as the following chemical formula 2: 
         [0000]      First electrode 220: Mg→Mg 2+ +2 e− 
 
         [0000]      Second electrode 230: 2H 2 0+2 e− →H 2 +2(OH) − 
 
         [0000]      Overall reaction: Mg+2H 2 O→Mg(OH) 2 +H 2    CHEMICAL FORMULA 2
 
         [0067]    The reaction rate and the efficiency of the chemical reaction depend on various factors, including the area of the first electrode  220  and/or the second electrode  230 , the concentration of the aqueous electrolyte solution  215 , the type of the aqueous electrolyte solution  215 , the number of the first electrode  220  and/or the second electrode  230 , the method of connecting the first electrode  220  and the second electrode  230 , the electric resistance between the first electrode  220  and the second electrode  230 . 
         [0068]    Changing any of the above factors affects the amount of electric current (that is, the amount of electrons) flowing between the first electrode  220  and the second electrode  230 , thereby altering the reaction rate of the electrochemical reaction shown in CHEMICAL FORMULA 2, which in turn changes the amount of hydrogen generated in the second electrode  230 . 
         [0069]    Therefore, the amount of the hydrogen generated in the second electrode  230  can be controlled by controlling the amount of the electric current that flows between the first electrode  220  and the second electrode  230 . Faraday&#39;s law explains this as shown in MATHEMATICAL FORMULA 1 below. 
         [0000]    
       
         
           
             
                 
             
              
             
               MATHEMATICAL 
                
               
                   
               
                
               FORMULA 
                
               
                   
               
                
               1 
             
           
         
       
       
         
           
             
               N 
               hydrogen 
             
             = 
             
               i 
               nE 
             
           
         
       
       
         
           
             
               N 
               hydrogen 
             
             = 
             
               
                 i 
                 
                   2 
                   × 
                   96485 
                 
               
                
               
                   
               
                
               
                 ( 
                 mol 
                 ) 
               
             
           
         
       
       
         
           
             
               
                 
                   
                     V 
                     hydrogen 
                   
                   = 
                   
                     
                       i 
                       
                         2 
                         × 
                         96485 
                       
                     
                     × 
                     60 
                     × 
                     22400 
                      
                     
                         
                     
                      
                     
                       ( 
                       
                         ml 
                          
                         
                           / 
                         
                          
                         min 
                       
                       ) 
                     
                   
                 
               
             
             
               
                 
                   = 
                   
                     7 
                     × 
                     i 
                      
                     
                         
                     
                      
                     
                       ( 
                       
                         ml 
                          
                         
                           / 
                         
                          
                         min 
                       
                       ) 
                     
                   
                 
               
             
           
         
       
     
         [0070]    where N hydrogen  is the amount of hydrogen generated per second (mol/s), V hydrogen  is the volume of hydrogen generated per minute (ml/min), i is the electric current (C/s),  n  is the number of the reacting electrons, and E is the electron charge per mole (C/mol). 
         [0071]    In the case of the above CHEMICAL FORMULA 2,  n  has a value of 2 since two electrons react at the second electrode  230 , and  E  has a value of −96,485 C/mol. 
         [0072]    The volume of hydrogen generated per minute can be calculated by multiplying the time (60 seconds) and the molar volume of hydrogen (22400 ml) to the amount of hydrogen generated per second. 
         [0073]    For example, in the case that the fuel cell is used in a 2 W system, and it is assumed that the fuel cell is running a voltage of 0.6V at room temperature and that a hydrogen usage ratio is 60%, it takes 42 ml/mol of hydrogen and 6 A of electric current. In the case that the fuel cell is used in a 5 W system, it takes 105 ml/mol of hydrogen and 15 A of electric current. 
         [0074]    The hydrogen generating apparatus  200  can meet the variable hydrogen demand of the fuel cell connected thereto by controlling the amount of electric current flowing through the first electric wire  225 , connected to the first electrode  220 , and the second electric wire  235 , connected to the second electrode  230 . 
         [0075]    However, most of the factors that determine the rate of the hydrogen generation reaction occurring in the second electrode of the hydrogen generating apparatus  200 , except the electric resistance between the first electrode  220  and the second electrode  230 , are hardly changeable once the hydrogen generating apparatus  200  is manufactured. 
         [0076]    Therefore, the hydrogen generating apparatus  200  according to this embodiment of the present invention has the control unit  240  disposed between the first electric wire  225  and the second electric wire  235 , which connect the first electrode  220  and the second electrode  230 , in order to regulate the electric resistance between the first electrode  220  and the second electrode  230 . 
         [0077]    Thus, the hydrogen generating apparatus  200  controls the electric resistance between the first electrode  220  and the second electrode  230 , that is, the amount of the electric current flowing therebetween, thereby generating as much hydrogen as needed by the fuel cell. 
         [0078]    The first electrode  220  can be also composed of a metal having a relatively high ionization tendency, such as iron (Fe), aluminum (Al), zinc (Zn), or the like. The second electrode  230  can be also composed of a metal having a relatively low ionization tendency compared to the metal of the first electrode  220 , such as platinum (Pt), aluminum (Al), copper (Cu), gold (Au), silver (Ag), iron (Fe), or the like. 
         [0079]    The control unit  240  controls a transfer rate, that is, the amount of electric current, at which electrons generated in the first electrode  220  are transferred to the second electrode  230 . 
         [0080]    The control unit  240  receives information on the amount of power or hydrogen demanded for the fuel cell and, according to the information, controls the amount of electrons flowing from the first electrode  220  to the second electrode  230 . If the demanded amount of power or hydrogen is large, the control unit  240  increases the amount of electrons, and the control unit  240  reduces the amount of the electrons if the demanded amount of power or hydrogen is small. 
         [0081]    The hydrogen generating apparatus  200  can receive the information on the amount of the power or the hydrogen demanded for the fuel cell from the fuel cell combined with the hydrogen generating apparatus  200  or from a user, who inputs the information through a separate input unit. 
         [0082]    The hydrogen generating apparatus of the present invention can have a plurality of the first electrodes  220  and/or the second electrodes  230 . In the case that a plural number of the first electrode  220  and/or the second electrode  230  are disposed, it can take a shorter time to generate the demanded amount of hydrogen since the hydrogen generating apparatus  200  can generate more hydrogen per unit time. 
         [0083]      FIG. 3  is a graph showing how the amount of electric current flowing between the first electrode  220  and the second electrode  230  is related to the volume of hydrogen generated on the second electrode  230 . Here, it should be noted that the volume of hydrogen is shown in flow-rate measured per minute, because not the total volume of generated hydrogen but the flow-rate of hydrogen is significant to a fuel cell. 
       An Experiment for FIG. 3 was Conducted Under the Following Conditions: 
       [0000]    
       
         First electrode  220 : Magnesium (Mg) 
         Second electrode  230 : Stainless steel 
         Distance between the electrodes: 3 mm 
         Ingredients and concentration of electrolyte: 30 wt % KCl 
         Number of the electrodes: Magnesium 3 each, Stainless steel 3 each 
         Electrode connecting method: Serial 
         Volume of aqueous electrolyte solution: 60 cc (excessive condition) 
         Size of the electrode: 24 mm×85 mm×1 mm 
       
     
         [0092]    The above conditions were used for every graph referred to in describing the present invention. 
         [0093]      FIG. 3  shows a greater flow rate of the hydrogen than a theoretical value based on MATHEMATICAL FORMULA 1, due to an interaction of the three pairs of electrodes. 
         [0094]    Nevertheless, it is verified from  FIG. 3  that the flow-rate of hydrogen is correlated with the amount of electric current between the first electrode  220  and the second electrode  230 . Also, the graph shows an almost linear relation between the flow-rate and the amount of the electric current, which agrees with the MATHEMATICAL FORMULA 1. 
         [0095]      FIG. 4  is a block diagram of the control unit  240  of the hydrogen generating apparatus in accordance with an embodiment of the present invention. 
         [0096]    The control unit  240  comprises a flow rate meter  410 , a switch controller  420  and a switch  430 . 
         [0097]    The flow rate meter  410  measures the amount of hydrogen, in units of flow rate, generated from the second electrode  230  of the hydrogen generating apparatus. As described above, in order to use the hydrogen generating apparatus  200  in accordance with the present invention by coupling to a fuel cell, a certain amount of hydrogen generation, not a total quantity of hydrogen generation, should be maintained, and thus it is required that the amount of hydrogen generation be measured in units of ml/min. Of course, it is possible to use other measurement units as long as the unit is capable of measuring the flow rate. 
         [0098]    The switch controller  420  is inputted with a set value, which is related to the amount of hydrogen generation. The hydrogen generating apparatus  200  is disposed with a separate input unit (not shown), through which the set value can be inputted by the user. The required amount of output (i.e. electric power, voltage, current, impedance, or a combination thereof) or hydrogen generation may be inputted by a fuel cell that is coupled to the hydrogen generating apparatus  200 . In the latter case, the fuel cell may be separately equipped with a hydrogen requiring unit for inputting the amount of output or hydrogen generation that is needed by the hydrogen generating apparatus  200 . 
         [0099]    The switch controller  420  compares the inputted set value with the amount of hydrogen generation measured by the flow rate meter  410 . If the amount of generated hydrogen is smaller than the set value, the switch  430  is controlled to increase the amount of hydrogen generation, and if the amount of generated hydrogen is greater than the set value, the switch  430  is controlled to reduce the amount of hydrogen generation. It is assumed that the switch  430  is controlled by a switch control signal such that the switch controller  420  can turn the switch  430  on or off. 
         [0100]    The switch is disposed between the first electrode  220  and the second electrode  230 . Electrons generated in the first electrode  220  is transferred to the second electrode  230  if the switch  430  is turned on, and the electrons generated in the first electrode  220  is not transferred to the second electrode  230  if the switch  430  is turned off. 
         [0101]    That is, the control unit  240  controls the amount of hydrogen generation, using the switch  430  to control whether the electrons are to be transferred from the first electrode  220  to the second electrode  230 . 
         [0102]      FIG. 5  is a block diagram of the control unit  240  of the hydrogen generating apparatus in accordance with another embodiment of the present invention. 
         [0103]    The control unit  240  includes an output meter  510 , a switch controller  420  and a switch  430 . Here, the switch controller  420  and the switch  430  function the same way as described earlier with reference to  FIG. 4 , and thus their description will be omitted. 
         [0104]    The output meter  510  is connected to the fuel cell  100  to measure an output of the fuel cell  100 . Here, the output refers to, for example, the amount of electric power, voltage, current, impedance or a combination thereof of the fuel cell  100  that receives hydrogen, which is generated from the hydrogen generating apparatus  200 . The below description will focus on electric power as the output of the fuel cell. 
         [0105]    As described above, a certain amount of hydrogen generation during certain duration, not a total amount of hydrogen generation, has to be maintained in order to use the hydrogen generating apparatus  200  in accordance with an embodiment of the present invention by coupling with the fuel cell. Therefore, the amount of electric power of the fuel cell  100  based on the amount of hydrogen generation is measured in units of watt (W). Of course, it is possible to use other units as long as the amount of electric power can be measured. 
         [0106]    Although the below description focuses on the control with the switch  430  of a hydrogen generating apparatus that is equipped with the flow rate meter  410  shown in  FIG. 4 , it shall be evident that the same description applies to a hydrogen generating apparatus  200  equipped with the output meter  510  shown in  FIG. 5 . 
         [0107]      FIG. 6  is a graph of the amount of hydrogen generation, expressed in units of flow rate, when the switch  430  is turned on. 
         [0108]    If the switch  430  stays on for a while, the reaction becomes very fast at the beginning, raising the temperature and rapidly increasing the amount of hydrogen generation as much as 100 ml/min. Then, the amount of hydrogen generation quickly drops due to the reduction of water in the aqueous electrolyte solution and the metal composing the first electrode  220 . 
         [0109]    In such a case, it becomes difficult to control the amount of hydrogen generation, and thus the amount of hydrogen generation is controlled to a desired flow rate by having the switch controller  420  control the turning on/off of the switch  430  such that the switch  430  has a certain duty ratio and/or on/off frequency. This will be further described with reference to  FIG. 7A . 
         [0110]      FIG. 7A  is a first example of the on/off frequency of the switch of a hydrogen generating apparatus in accordance with an embodiment of the present invention, and  FIG. 7B  is a second example of the on/off frequency of the switch of a hydrogen generating apparatus in accordance with an embodiment of the present invention. Furthermore,  FIG. 8  shows how the amount of hydrogen generation is related to time when the on/off frequency of the switch is controlled. It will be assumed hereinafter that the switch  430  is turned on when the size of an inputted switch control signal is M (i.e., high) and turned off when the size of an inputted switch control signal is 0 (i.e., low). 
         [0111]    Referring to  FIG. 7A , the switch control signal inputted to the switch  430  has a frequency of T and a duty ratio of 50%. In other words, the switch control signal inputted to the switch  430  is high for ½ T and low for ½ T. 
         [0112]    Referring to  FIG. 7B , on the other hand, the switch control signal inputted to the switch  430  has a frequency of ¼ T and a duty ratio of 50%. In other words, the switch control signal inputted to the switch  430  is high for ⅛ T and low for ⅛ T. 
         [0113]    The switch control signal inputted to the switch  430  has a duty ratio (e.g., 50% in the case of  FIGS. 7A and 7B ), and thus the switch  430  is turned on and off for the same duration within one cycle. 
         [0114]    Referring to  FIG. 8 , when the duty ratio of the switch  430  is controlled such that 42 ml/min of hydrogen is generated for a fuel cell that requires 2 W of electric power, there is fluctuation in the amount of hydrogen generation according to the on/off frequency. The temperature  810  of the hydrogen generating apparatus  200  increases steadily but stays below 80° C. 
         [0115]    The amount of hydrogen generation  820  is close to 42 ml/min. When the on/off frequency is relatively small (i.e., a large cycle) as in  FIG. 7A , the fluctuation is strong, as shown in boxes represented by  840 . When the on/off frequency is relatively large (i.e., a small cycle) as in  FIG. 7B , the fluctuation is weak, as shown in boxes represented by  850 . 
         [0116]    Therefore, for the same duty ratio, a relatively larger on/off frequency of the switch control signal causes less fluctuation and is easier to maintain the desired amount of hydrogen generation. 
         [0117]      FIG. 9A  is a first example of duty ratios of the switch of a hydrogen generating apparatus in accordance with an embodiment of the present invention, and  FIG. 9B  is a second example of duty ratios of the switch of a hydrogen generating apparatus in accordance with an embodiment of the present invention.  FIG. 10  shows how the quantity of hydrogen generation is related to time when the duty ratio of the switch is controlled. 
         [0118]    Referring to  FIG. 9A , the switch control signal has a cycle of T and a duty ratio of 75%, that is, the switch control signal is high for ¾ T and low for ¼ T. 
         [0119]    Referring to  FIG. 9B , the switch control signal has a cycle of T, which is the same as that of  FIG. 9A , and a duty ratio of 25%, that is, the switch control signal is high for ¼ T and low for ¾ T. 
         [0120]    By controlling the duty ratio of the switch control signal that is inputted to the switch  430 , it becomes possible to control the amount of hydrogen generation per time that is generated in the hydrogen generating apparatus  200 . 
         [0121]    Referring to  FIG. 10 , the amount of hydrogen generation is left to increase naturally at the beginning (refer to the portion of graph represented by  1020 ), and then the switch controller  420  controls the on and off of the switch  430  to generate 42 ml/min ( 1021 ), 10 ml/min ( 1022 ), 42 ml/min ( 1023 ), 20 ml/min ( 1024 ) and 30 ml/min ( 1025 ) of hydrogen. 
         [0122]    When the amount of hydrogen generation is adjusted from 42 ml/min ( 1021 ) to 10 ml/min ( 1022 ), the ratio of off-time of the switch control signal within one cycle is increased, that is, the duty ratio is gradually decreased. Then, by steadily maintaining the duty ratio when the flow rate meter  410  reads 10 ml/min of hydrogen generation, the amount of hydrogen generation is kept at 10 ml/min. 
         [0123]    When the amount of hydrogen generation is adjusted from 10 ml/min ( 1022 ) to 42 ml/min ( 1023 ), the ratio of on-time of the switch control signal within one cycle is increased, that is, the duty ratio is gradually increased. Then, by steadily maintaining the duty ratio when the flow rate meter  410  reads 42 ml/min of hydrogen generation, the amount of hydrogen generation is kept at 42 ml/min. 
         [0124]    By repeatedly performing the above adjustment of duty ratio, the switch controller  420  can adjust the amount of hydrogen generation according to changing set values. 
         [0125]    As described with reference to  FIGS. 7A to 8 , it is possible to control the fluctuation in the amount of hydrogen generation by changing the on/off frequency of the switch  430  in case a certain amount of hydrogen generation is maintained. 
         [0126]    Moreover, the amount of hydrogen generation measured in units of flow rate in  FIGS. 6 to 10  may be the amount of electric power outputted from the fuel cell  100  in a hydrogen generating apparatus  200  shown in  FIG. 5 . For example, the flow rate of 42 ml/min shown in  FIGS. 6 to 10  can correspond to 2 W, depending on the operation condition of the fuel cell  100 . 
         [0127]    In other words, the earlier-measured amounts of hydrogen generation correspond to the output of the fuel cell (i.e., amount of electric power) that is measured by the output meter  510  of the hydrogen generating apparatus  200 . The amount of hydrogen generation to be controlled through the on/off control of the switch corresponds to the output of the fuel cell, that is, the amount of electric power. 
         [0128]    The switch of the hydrogen generating apparatus in accordance with an embodiment of the present invention can be made of an MOS (metal-oxide semiconductor) transistor. 
         [0129]    The switch controller of the hydrogen generating apparatus in accordance with an embodiment of the present invention can use a power circuit of the fuel cell and be included in a control unit of a fuel cell generating system. In other words, by including the switch controller in the control unit of a fuel cell generating system, the switch controller and the control unit of the fuel cell generating system can be made into one chip. 
         [0130]    Moreover, the hydrogen generating apparatus of the present invention can compose a fuel cell generating system by being connected to a fuel cell. The fuel cell generating system includes a hydrogen generating apparatus that is possible to control the amount of hydrogen generation and a fuel cell that generates electricity by being supplied with hydrogen from the hydrogen generating apparatus. 
         [0131]      FIG. 11  is a flowchart showing a method of controlling the amount of hydrogen generation in a hydrogen generating apparatus in accordance with an embodiment of the present invention. The hydrogen generating apparatus of  FIG. 11  is illustrated in  FIG. 4 . 
         [0132]    The switch controller  420  of the hydrogen generating apparatus  200  turns on the switch  430  and generates hydrogen over a certain threshold of flow rate, in the step represented by S 1100 . 
         [0133]    In step S 1110 , the flow rate meter  410  measures the amount of hydrogen generation, and in step S 1120  the switch controller  420  compares the amount of hydrogen generation, measured by the flow rate meter  410 , with an inputted set value. Here, the inputted set value can be one value, as shown in step S 1120   a,  or have an upper limit and a lower limit with a range, as shown in step  1120   b.    
         [0134]    The switch controller  420  generates a switch control signal for controlling the on/off of the switch according to the set value and applies the switch control signal to the switch  430 . 
         [0135]    If one set value is inputted, as shown in step S 1120   a,  the amount of hydrogen generation (A) and the set value (B) are compared in step S 1130   a.  In case the amount of hydrogen generation is smaller than the set value (A&lt;B), the duty ratio of the switch control signal is increased in step S 1132   a,  and if the amount of hydrogen generation is greater than the set value (A&gt;B), the duty ratio of the switch control signal is reduced in step S 1134   a.  If the amount of hydrogen generation is equal to the set value (A=B), the current duty ratio of the switch control signal is maintained, in step S 1136   a.    
         [0136]    In case the upper limit and the lower limit are inputted in step S 1120   b,  the amount of hydrogen generation (A), the upper limit (B 1 ) and the lower limit (B 2 ) are compared in step  1130   b.  If the amount of hydrogen generation is smaller than the lower limit (A&lt;B 2 ), the duty ratio of the switch control signal is increased in step  1132   b,  and if the amount of hydrogen generation is greater than the upper limit (A&gt;B 1 ), the duty ratio of the switch control signal is reduced in step S 1134   b.  If the amount of hydrogen generation is between the upper limit and the lower limit (B 2 =A=B 1 ), the current duty ratio of the switch control signal is maintained in S 1136   b.    
         [0137]    By repeating steps S 1120  to S 1136   a  or S 1136   b,  the hydrogen generating apparatus  200  can generate the amount of hydrogen according to the inputted set value. 
         [0138]      FIG. 12  is a flowchart showing a method of controlling the amount of hydrogen generation in a hydrogen generating apparatus in accordance with another embodiment of the present invention. The hydrogen generating apparatus of  FIG. 12  is illustrated in  FIG. 5 . 
         [0139]    The switch controller  420  of the hydrogen generating apparatus  200  turns on the switch  430  and generates hydrogen over a certain threshold of flow rate, in the step represented by S 1200 . 
         [0140]    The output meter  510  measures the output (e.g., amount of electric power) of the fuel cell, in the step represented by S 1210 , and the switch controller  420  compares the output of the fuel cell, measured by the output meter  510 , and the inputted set value in S 1220 . Here, the inputted set value can be one value, as shown in S 1220   a,  or have an upper limit and a lower limit with a range, as shown in S 1220   b.    
         [0141]    The switch controller  420  generates a switch control signal for controlling the on/off of the switch  430  according to the set value and applies the switch control signal to the switch  430 . 
         [0142]    If one set value is inputted, as shown in S 1220   a,  the output of the fuel cell (A) and the set value (B) are compared in S 1230   a.  In case the output of the fuel cell is smaller than the set value (A&lt;B), the duty ratio of the switch control signal is increased in S 1232   a,  and if the output of the fuel cell is greater than the set value (A&gt;B), the duty ratio of the switch control signal is reduced in S 1234   a.  If the output of the fuel cell is equal to the set value (A=B), the current duty ratio of the switch control signal is maintained in S 1236   a.    
         [0143]    In case the upper limit and the lower limit are inputted in step S 1220   b,  the amount of hydrogen generation (A), the upper limit (B 1 ) and the lower limit (B 2 ) are compared in step  1230   b.  If the amount of hydrogen generation is smaller than the lower limit (A&lt;B 2 ), the duty ratio of the switch control signal is increased in step  1232   b,  and if the amount of hydrogen generation is greater than the upper limit (A&gt;B 1 ), the duty ratio of the switch control signal is reduced in step S 1234   b.  If the amount of hydrogen generation is between the upper limit and the lower limit (B 2 =A=B 1 ), the current duty ratio of the switch control signal is maintained in S 1236   b.    
         [0144]    By repeating steps S 2120  to S 1236   a  or S 1236   b,  the hydrogen generating apparatus  200  can generate the amount of hydrogen according to the inputted set value. 
         [0145]    In the above method of controlling the amount of hydrogen generation, steps S 1120  to S 1136   a  or  1136   b,  or steps S 1220  to S 1236   a  or  1236   b,  can be written in a computer program. Codes and code segments, composing the program, can be easily realized by a computer programmer skilled in the art. Moreover, the program is stored in a computer readable medium, and realizes the method of controlling the amount of hydrogen generation by being read and run by a computer. The computer readable medium described above includes a magnetic recording medium, an optical recording medium and a carrier wave medium. 
         [0146]    The drawings and detailed description are only examples of the present invention, serve only for describing the present invention and by no means limit or restrict the spirit and scope of the present invention. Thus, any person of ordinary skill in the art shall understand that a large number of permutations and other equivalent embodiments are possible. The true scope of the present invention must be defined only by the ideas of the appended claims.