Abstract:
A fuel cell system ( 101 ) comprising a fuel cell ( 120 ) and a reaction container ( 103 ), wherein the fuel cell ( 120 ) comprises a fuel electrode ( 121 ), an air electrode ( 122 ) and an electrolyte film ( 123 ) and the reaction container ( 103 ) comprises a hydrogen storage material ( 106 ) and a heater ( 114 ) and can supply hydrogen to the fuel cell ( 120 ), and wherein a water flow path ( 109 ) for supplying water produced in the air electrode ( 122 ) to the reaction container ( 103 ) is provided.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a reaction container that allows reactions of a fuel cell to be controlled and a fuel cell system equipped with the same. 
       Background Art 
       [0002]    In recent years, along with an improvement in performance of electronic equipment, there has been a growing demand for a cell having a larger capacity and a longer life. Conventional lithium-ion cells are limited in capacity since they have almost reached their theoretical limits of an energy density per volume and, therefore, can hardly be expected to achieve any further significant improvement in performance. With this being the situation, attention has been focused on a fuel cell that is significantly improved in energy density per volume compared with conventional cells and thus can achieve an increased capacity. 
         [0003]    For example, Patent Document 1 proposes a regenerative fuel cell system.  FIG. 11  is a schematic view showing a reaction mechanism of a fuel cell during power generation, and  FIG. 12  is a schematic view showing a reaction mechanism of the fuel cell during charging. A fuel cell  520  described in Patent Document 1 is composed of a fuel electrode  521 , an oxygen electrode  522 , and an electrolyte membrane  523 . At the time of power generation, upon supply of hydrogen to the fuel electrode  521 , protons and electrons are generated from the hydrogen, and the protons move from the fuel electrode  521  through the electrolyte membrane  523  to the oxygen electrode  522 . At the oxygen electrode  522 , oxide ions generated from oxygen react with the protons that have moved thereto to generate water, and by these electrochemical reactions, motive power is generated. Furthermore, at the time of charging, upon application of voltages of opposite polarities to the fuel electrode  521  and to the oxygen electrode  522 , respectively, reactions reverse to the reactions that occur during power generation occur at the fuel electrode  521  and at the oxygen electrode  522 , respectively, so that hydrogen is generated at the fuel electrode  521 , and oxygen is generated at the oxygen electrode  522 . The fuel cell system described in Patent Document 1 performs charging by taking the hydrogen generated at the fuel electrode  521  into a hydrogen occlusion material and power generation by emitting the hydrogen thus taken thereinto. 
       LIST OF CITATIONS 
     Patent Literature 
       [0004]    Patent Document 1: JP-A-2002-151094 
       SUMMARY OF THE INVENTION 
     Technical Problem 
       [0005]    Generally speaking, however, the reaction of storing hydrogen in a hydrogen occlusion material and the reaction of emitting hydrogen therefrom are endothermic reactions that require a high temperature, and thus, in order for the reactions to progress, it is required to heat the hydrogen occlusion material so as to accelerate the reactions. To this end, some type of reaction adjustment mechanism should be provided in a reaction container in which the hydrogen occlusion material is housed. The fuel cell system described in Patent Document 1, however, has given no consideration to a reaction adjustment mechanism for this purpose and is, therefore, conceivably unable to perform charging and discharging in a continuously repeated manner. 
         [0006]    In order to solve the above-described problem, it is an object of the present invention to provide a reaction container that, in a fuel cell system, allows reactions of starting and stopping charging and discharging to be controlled and the fuel cell system equipped with the reaction container. 
       Solution to the Problem 
       [0007]    In order to achieve the above-described object, the present invention provides a reaction container that supplies hydrogen to a fuel cell including: a fuel electrode; an oxygen electrode; and an electrolyte membrane that is disposed between the fuel electrode and the oxygen electrode. The reaction container has a hydrogen occlusion material provided therein and is provided with at least one of a temperature adjustment mechanism and an internal pressure adjustment mechanism. 
         [0008]    According to this configuration, an internal condition in the reaction container is adjusted by the temperature adjustment mechanism or the internal pressure adjustment mechanism, and thus conditions for starting and stopping reactions of the hydrogen occlusion material can be controlled. Thus, during power generation, hydrogen can be emitted stably from the hydrogen occlusion material, and during charging, hydrogen can be stored stably in the hydrogen occlusion material. 
         [0009]    Furthermore, in the present invention, in the reaction container configured as above, the temperature adjustment mechanism includes at least one of a heater and a heat-insulated structure. 
         [0010]    According to this configuration, the reactions of the hydrogen occlusion material can be controlled by adjusting heating by the heater. Furthermore, when the heat-insulated structure is used as the temperature adjustment mechanism, thermal efficiency of the reaction container as a whole can be increased. 
         [0011]    Furthermore, in the present invention, in the reaction container configured as above, as the internal pressure adjustment mechanism, at least one of a valve mechanism and a pump is provided. 
         [0012]    According to this configuration, the amount of a gas to be supplied that is intended to react with the hydrogen occlusion material and the discharge of products generated by the reactions of the hydrogen occlusion material can be adjusted by use of a valve or the pump. 
         [0013]    Furthermore, in the present invention, in the reaction container configured as above, the hydrogen occlusion material is constituted by at least any one of iron, aluminum, and magnesium. 
         [0014]    According to this configuration, in a case where the hydrogen occlusion material is constituted by iron, hydrogen can be emitted by utilizing an oxidation reaction between the iron and water, and hydrogen can be stored by reducing iron oxide resulting from the oxidation with hydrogen. Similarly, oxidation and reduction reactions of aluminum or magnesium also allow hydrogen emission and occlusion. 
         [0015]    Furthermore, in the present invention, in the reaction container configured as above, the hydrogen occlusion material is prepared by being subjected to crushing so as to have an increased real surface area and then by forming minute cracks therein by hydrogen embrittlement, into which a sintering material is added by liquid phase deposition. 
         [0016]    According to this configuration, reaction activity of the hydrogen occlusion material is enhanced, and thus hydrogen emission and occlusion can be performed stably. The above-described addition of a sintering material into any metallic hydrogen occlusion material can provide a similar effect. 
         [0017]    Furthermore, in the present invention, in the reaction container configured as above, a water supply mechanism for supplying water to the reaction container is provided. 
         [0018]    According to this configuration, water is supplied from the water supply mechanism to the reaction container, and thus the reaction between the hydrogen occlusion material and water can be accelerated. 
         [0019]    Furthermore, in the present invention, in the reaction container configured as above, the water supply mechanism is provided with a valve mechanism. 
         [0020]    According to this configuration, the amount of water to be supplied to the reaction container is adjusted by the valve mechanism, and thus the reaction between the hydrogen occlusion material and water can be controlled. 
         [0021]    Furthermore, in the present invention, in the reaction container configured as above, water generated in the fuel cell is supplied to the reaction container via the water supply mechanism. 
         [0022]    According to this configuration, water generated during electrochemical reactions of the fuel cell is removed, and thus the electrochemical reactions of the fuel cell can be accelerated. Furthermore, water generated in the fuel cell is used in the reaction container, and thus there is no need to newly provide a device for supplying water, thereby allowing size reduction of an apparatus as a whole. 
         [0023]    Furthermore, in the present invention, in the reaction container configured as above, a water discharging mechanism for discharging water generated by a reaction of the hydrogen occlusion material is provided. 
         [0024]    According to this configuration, water generated in the reaction of the hydrogen occlusion material is discharged from the water discharging mechanism, and thus the reaction of the hydrogen occlusion material can be accelerated. 
         [0025]    Furthermore, in the present invention, in the reaction container configured as above, the water discharging mechanism utilizes a partial pressure difference of water vapor. 
         [0026]    According to this configuration, water vapor generated by the reaction of the hydrogen occlusion material can be discharged efficiently from the reaction container. 
         [0027]    Furthermore, in the present invention, in the reaction container configured as above, the water discharging mechanism discharges water generated by cooling of water vapor. 
         [0028]    According to this configuration, since water vapor generated by the reaction of the hydrogen occlusion material is liquefied easily compared with other types of gases that build up in the reaction container, by utilizing this fact, water vapor can be discharged efficiently from the reaction container. 
         [0029]    Furthermore, in the present invention, in the reaction container configured as above, the water discharging mechanism uses a water absorbent. 
         [0030]    According to this configuration, by use of a water absorbent, water vapor can be discharged efficiently from the reaction container. 
         [0031]    Furthermore, in the present invention, in the reaction container configured as above, the water discharging mechanism performs electrolysis of water and discharges oxygen by use of an oxygen permeable membrane. 
         [0032]    According to this configuration, hydrogen can be generated from water vapor generated by the reaction of the hydrogen occlusion material, and thus a reaction of the hydrogen occlusion material can be accelerated. 
         [0033]    Furthermore, in the present invention, in the reaction container configured as above, the hydrogen occlusion material is constituted by one of an organic hydride and a metal hydride. 
         [0034]    According to this configuration, by use of an organic hydride or a metal hydride, hydrogen occlusion and emission can be performed efficiently. 
         [0035]    Furthermore, in the present invention, in the reaction container configured as above, the hydrogen occlusion material is constituted by a complex hydride. 
         [0036]    According to this configuration, by use of a complex hydride, hydrogen occlusion and emission can be performed efficiently. 
         [0037]    Furthermore, in the present invention, in the reaction container configured as above, the hydrogen occlusion material is constituted by a carbon material. 
         [0038]    According to this configuration, by use of a carbon material, hydrogen occlusion and emission can be performed efficiently. Examples of a carbon material include a carbon nanotube. 
         [0039]    Furthermore, in the present invention, in the reaction container configured as above, a hydrogen supply mechanism for supplying hydrogen to the reaction container is provided. 
         [0040]    According to this configuration, during charging, hydrogen is supplied from the hydrogen supply mechanism to the reaction container and can be stored in the reaction container. 
         [0041]    Furthermore, in the present invention, in the reaction container configured as above, the hydrogen supply mechanism is provided with a valve mechanism. 
         [0042]    According to this configuration, the amount of hydrogen to be supplied from the hydrogen supply mechanism to the reaction container is adjusted by use of a valve, and thus the amount of hydrogen to be stored in the reaction container can be controlled. Furthermore, during power generation by the fuel cell, hydrogen supply to the reaction container is stopped, and during charging of the fuel cell, the hydrogen supply to the reaction container is started, whereby power generation by and charging of the fuel cell can be controlled. 
         [0043]    Furthermore, in the present invention, in the reaction container configured as above, the hydrogen supply mechanism is provided with a hydrogen separation membrane. 
         [0044]    According to this configuration, only hydrogen can be supplied form the hydrogen supply mechanism to the reaction container. 
         [0045]    Furthermore, in the present invention, in the reaction container configured as above, the hydrogen supply mechanism generates hydrogen by electrolysis of water. 
         [0046]    According to this configuration, hydrogen can be generated easily from water, and thus a fuel for generating hydrogen can be obtained easily. 
         [0047]    Furthermore, in the present invention, in the reaction container configured as above, the hydrogen supply mechanism generates hydrogen by a water decomposition reaction of a photocatalyst. 
         [0048]    According to this configuration, hydrogen can be generated merely by irradiation with light and used to perform charging. 
         [0049]    Furthermore, in the present invention, in the reaction container configured as above, surface plasmon resonance is used as an excitation source for the photocatalyst. 
         [0050]    According to this configuration, a water decomposition reaction of a photocatalyst is further activated, and thus the generation of hydrogen can be accelerated. 
         [0051]    Furthermore, in the present invention, as a material of the reaction container configured as above, any one of Si, glass, ceramic, metal, and plastic is used. 
         [0052]    According to this configuration, a reaction container having excellent resistance to heat and pressure can be provided. 
         [0053]    Furthermore, the present invention also provides a fuel cell system having the reaction container configured as above and the fuel cell. In the fuel cell system, the fuel cell is any one of a solid oxide fuel cell (SOFC), a polymer electrolyte fuel cell (PEFC), a phosphoric acid fuel cell (PAFC), and an alkaline fuel cell (AFC). 
         [0054]    According to this configuration, a fuel cell system can be provided in which hydrogen storage in the reaction container and hydrogen supply to the reaction container are performed stably and that thus is continuously regenerative. 
         [0055]    Furthermore, in the present invention, in the fuel cell system configured as above, in the fuel cell, when a negative voltage is applied to the fuel electrode and a positive voltage is applied to the oxygen electrode, reactions reverse to reactions that occur during power generation occur at the fuel electrode and at the oxygen electrode, respectively. 
         [0056]    According to this configuration, hydrogen can be generated at the fuel cell by such reverse reactions of the fuel cell. The hydrogen thus generated is supplied to and stored in the reaction container, thereby allowing charging of the fuel cell to be performed. 
         [0057]    Furthermore, in the present invention, the fuel cell system configured as above has a capacitor. 
         [0058]    According to this configuration, electricity generated in the fuel cell can be charged in the capacitor. Furthermore, the capacitor can be used as a power source for the temperature adjustment mechanism, the internal pressure adjustment mechanism, and the hydrogen supply mechanism. 
         [0059]    Furthermore, in the present invention, the fuel cell system configured as above has a lithium-ion cell. 
         [0060]    According to this configuration, electricity generated in the fuel cell can be charged in the lithium-ion cell. Furthermore, the lithium-ion cell can be used as a power source for the temperature adjustment mechanism, the internal pressure adjustment mechanism, and the hydrogen supply mechanism. 
       Advantageous Effects of the Invention 
       [0061]    According to the present invention, there can be provided a reaction container that is capable of controlling reactions of a reversible hydrogen occlusion material and a fuel cell system that supplies hydrogen to a fuel cell by use of the reaction container. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0062]    [ FIG. 1 ] is schematic view showing part of a fuel cell system according to a first embodiment. 
           [0063]    [ FIG. 2 ] is a schematic view showing a water discharging mechanism. 
           [0064]    [ FIG. 3 ] is a schematic view showing a water discharging mechanism. 
           [0065]    [ FIG. 4 ] is a schematic view showing a water discharging mechanism. 
           [0066]    [ FIG. 5 ] is a schematic structural view of a fuel cell system according to a second embodiment. 
           [0067]    [ FIG. 6 ] is a schematic view showing a reaction mechanism of the fuel cell system according to the second embodiment. 
           [0068]    [ FIG. 7 ] is a schematic structural view of a fuel cell system according to a third embodiment. 
           [0069]    [ FIG. 8 ] is a schematic view showing a reaction mechanism of the fuel cell system according to the third embodiment. 
           [0070]    [ FIG. 9 ] is a schematic structural view of a fuel cell system according to a fourth embodiment. 
           [0071]    [ FIG. 10 ] is a schematic view showing a reaction mechanism of the fuel cell system according to the fourth embodiment. 
           [0072]    [ FIG. 11 ] is a schematic view showing a reaction mechanism of a fuel cell during power generation. 
           [0073]    [ FIG. 12 ] is a schematic view showing a reaction mechanism of the fuel cell during charging. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0074]    The following describes in detail a fuel cell system according to the present invention with reference to the appended drawings. 
       First Embodiment 
       [0075]      FIG. 1  is a schematic view showing part of a fuel cell system according to a first embodiment. A fuel cell system  101  includes a polymer electrolyte fuel cell  120  (hereinafter, abbreviated as PEFC), a reaction container  103 , and an air chamber  124 . The PEFC  120  is composed of a fuel electrode  121 , an electrolyte membrane  123 , and an oxygen electrode  122 , with a fuel diffusion layer  121   a  formed on the fuel electrode  121  on the side of the reaction container  103  and an air diffusion layer  122   a  formed on the oxygen electrode  122  on the side of the air chamber  124 . A first hydrogen separation membrane  116  is provided between the reaction container  103  and the fuel electrode  121 , and inside the reaction container  103 , as a hydrogen occlusion material  106 , iron particles are provided at a predetermined position. Furthermore, the reaction container  103  adopts a two-tier structure in which a cavity  170  is provided between an outer wall and an inner wall and is provided with a heater  114  for heating the inside of the reaction container  103 . 
         [0076]    The reaction container  103  communicates with a hydrogen supply line  112 , and hydrogen is supplied into the reaction container  103  via the hydrogen supply line  112 . Furthermore, the reaction container  103  communicates with a water discharge line  113 , and water is discharged out of the reaction container  103  via the water discharge line  113 . The hydrogen supply line  112  and the water discharge line  113  are provided with a valve  112   a  and a valve  113   a,  respectively, and these valve mechanisms allow water supply into the reaction container  103  and water discharge out of the reaction container  103  to be controlled. 
         [0077]    The air chamber  124 , on the other hand, communicates with an oxygen supply line  125 , and oxygen is supplied into the air chamber  124  via the oxygen supply line  125 . Furthermore, the oxygen supply line  125  is provided with a valve  125   a,  and this allows air supply into the air chamber  124  to be controlled. Furthermore, the air chamber  124  and the reaction container  103  communicate with each other via a water flow path  109 , and a gas-liquid separation filter  110  and a pump  111  are provided on the water flow path  109 . Water generated at the oxygen electrode  122  is subjected to separation by the gas-liquid separation filter  110 , and resulting water is supplied to the reaction container  103  via the pump  111 . The water flow path  109 , the gas-liquid separation filter  110 , and the pump  111  represent one example of the “water supply mechanism” of the present invention. 
         [0078]    The hydrogen occlusion material  106  is constituted by iron particles, and the following oxidation and reduction reactions occur in the reaction container  103 .
   Oxidation reaction: 3Fe+4H 2 O→Fe 3 O 4 +4H 2      Reduction reaction: Fe 3 O 4 +4H 2 →3Fe+4H 2 O   
 
         [0081]    By these reactions, during power generation, the hydrogen occlusion material  106  emits hydrogen based on an oxidation reaction of iron, and during charging, it stores hydrogen based on a reduction reaction of iron oxide. Although the oxidation and reduction reactions of the hydrogen occlusion material  106  are endothermic reactions that require a high temperature, the heater  114  is used to adjust a temperature inside the reaction container  103 , and thus the reactions of the hydrogen occlusion material  106  can be controlled. By use of the first hydrogen separation membrane  116  formed between the reaction container  103  and the fuel electrode  121 , only hydrogen is separated from a gas containing water vapor and so on and then supplied to the fuel electrode  121 . 
         [0082]    In the PEFC  120 , during power generation, the following reactions occur at the fuel electrode  121  and at the oxygen electrode  122 , respectively, so that at the fuel electrode  121 , protons and electrons are generated from hydrogen, and at the oxygen electrode  122 , the protons that have moved thereto from the fuel electrode  121  and oxide ions generated from oxygen react with each other to generate water.
   Fuel electrode: H 2 →2H + +2e −     Oxygen electrode: 4H + +O 2 +4e − →2H 2 O   
 
         [0085]    Furthermore, upon application of voltages of opposite polarities to the fuel electrode  121  and the oxygen electrode  122 , respectively, reactions reverse to the reactions that occur during power generation occur at the fuel electrode  121  and at the oxygen electrode  122 , respectively.
   Fuel electrode: 2H + +2e − →H 2      Oxygen electrode: 2H 2 O→4H + +O 2 +4e −     
 
         [0088]    Next, the following describes a method of operation of the fuel cell system  101 . At the time of power generation, the reaction container  103  is sealed by closing the valve  112   a  of the hydrogen supply line  112  and the valve  113   a  on the water discharge line  113 , and the inside thereof is heated by the heater  114 , so that in the reaction container  103 , an oxidation reaction of iron constituting the hydrogen occlusion material  106  occurs to generate hydrogen. The hydrogen is then supplied through the first hydrogen separation membrane  116  to the fuel electrode  121 . 
         [0089]    Meanwhile, in the air chamber  124 , oxygen is supplied to the oxygen electrode  122  by opening the valve  125   a  of the oxygen supply line  125 , so that water is generated, and by these electrochemical reactions in the reaction container  103  and in the air chamber  124 , the PEFC  120  generates power. Furthermore, water generated in the air chamber  124  is supplied into the reaction container  103  via the water flow path  109 . 
         [0090]    In a case of bringing the fuel cell system  101  to a halt, the reaction of the hydrogen occlusion material  106  is stopped by stopping the heating by the heater  114 , and the oxygen supply is stopped by closing the valve  125   a  of the oxygen supply line  125 , so that the electrochemical reactions of the PEFC  120  are stopped. 
         [0091]    Furthermore, in a case of charging the fuel cell system  101 , the valve  112   a  on the hydrogen supply line  112  and the valve  113   a  on the water discharge line  113  are opened, and the inside of the reaction container  103  is heated by the heater  114 . This causes hydrogen supplied through the hydrogen supply line  112  into the reaction container  103  to reduce iron oxide and thus to be stored in the hydrogen occlusion material  106 . Furthermore, in the reaction container  103 , a water discharging mechanism is provided that is connected to the water discharge line  113 , and thus water vapor generated in the reduction reaction of iron oxide is discharged thereby out of the reaction container  103 , and thus the reduction reaction can be accelerated. 
         [0092]      FIG. 2  is a schematic view showing one example of the water discharging mechanism, and as shown in  FIG. 2 , a water discharging mechanism  117  is composed of a circulation path  130  and a cooling portion  131 . The circulation path  130  communicates at one end with the water discharge line  113  and at the other end with the hydrogen supply line  112 , and the cooling portion  131  is provided on the circulation path  130 . Part of hydrogen supplied through the hydrogen supply line  112  into the reaction container  103  reacts with iron oxide constituting the hydrogen occlusion material  106  to generate water vapor, and the residual part of the hydrogen left without contributing to the reaction and the water vapor flow through the water discharge line  113  into the circulation path  130 . The water vapor contained in a gas that has thus flowed thereinto is cooled to be liquefied and separated in the cooling portion  131 . The hydrogen contained in the gas passes through the cooling portion  131  and flows through the hydrogen supply line  112  into the reaction container  103 . As described above, the residual part of hydrogen left without reacting with the hydrogen occlusion material  106  circulates in the circulation path  130  and thus prevents a decrease in hydrogen concentration in the reaction container  103 , so that the reduction reaction between the hydrogen occlusion material  106  and hydrogen is accelerated. A Peltier device can be used as the cooling portion  131 , and providing the cooling portion  131  with a water-repellent structure allows liquefied water to be discharged efficiently. 
         [0093]      FIG. 3  is a schematic view showing one example of the water discharging mechanism, and as shown in  FIG. 3 , a configuration is possible in which in the water discharging mechanism  117 , a water vapor separation membrane  132  is provided at some point in the circulation path  130  so that water vapor is removed by use thereof.  FIG. 4  is a schematic view showing one example of the water discharging mechanism, and as shown in  FIG. 4 , a configuration is possible in which an electrolysis bath  134  and an oxygen permeable membrane  133  are provided on the circulation path  130  so that circulating water vapor is separated into oxygen and hydrogen by electrolysis and thus is removed. At this time, the oxygen is eliminated by use of the oxygen permeable membrane  133 , and the resulting hydrogen is made to flow again into the reaction container  103 , so that the reduction reaction between the hydrogen occlusion material  106  and hydrogen can be accelerated. Furthermore, in addition to the above, a method utilizing a partial pressure difference of water vapor or a method using a water absorbent may be used to remove water vapor. 
         [0094]    Although this embodiment uses the PEFC  120  as a fuel cell, any one of a solid oxide fuel cell (hereinafter, abbreviated as SOFC), a phosphoric acid fuel cell (hereinafter, abbreviated as PAFC), and an alkaline fuel cell (hereinafter, abbreviated as AFC) may be used as a fuel cell. In a case of using a fuel cell in which, during power generation, water is generated at the fuel electrode  121 , such as an SOFC, it is not required that the air chamber  124  and the reaction container  103  communicate with each other by way of the water flow path  109 . 
         [0095]    As the hydrogen occlusion material  106 , iron in the form of iron particles is used, which is prepared by being subjected to crushing so as to have an increased real surface area and then by forming minute cracks therein by hydrogen embrittlement, into which a sintering material is added by liquid phase deposition. By this treatment, reactivity of the oxidation and reduction reactions between iron and water is enhanced, and thus in the reaction container  103 , hydrogen emission and occlusion are performed stably. 
         [0096]    Furthermore, although this embodiment uses iron as the reversible hydrogen occlusion material  106 , hydrogen occlusion materials of other types than iron can also be used to perform hydrogen emission and occlusion, and the use of aluminum or magnesium can bring about a similar reaction. 
         [0097]    Furthermore, as a hydrogen occlusion material, an organic hydride or a metal hydride, a complex hydride, a carbon material, a hydrogen occlusion material based on a hydration reaction, and an alloy-based hydrogen occlusion material can also be used. Furthermore, as a material of the reaction container  103 , any one of Si, glass, ceramic, metal, and plastic is used, and a material having excellent resistance to heat, chemicals, and pressure can be used favorably. 
       Second Embodiment 
       [0098]    Next, the following describes a second embodiment of the fuel cell system according to the present invention with reference to the appended drawings. In the following, duplicate descriptions of components identical to those in the fuel cell system according to the first embodiment are omitted.  FIG. 5  is a schematic structural view of a fuel cell system according to the second embodiment of the present invention, and  FIG. 6  is a schematic view showing a reaction mechanism of the fuel cell system according to the second embodiment. A fuel cell system  201  includes a PEFC  220 , a reaction container  203  that supplies hydrogen to the PEFC  220 , a controller  204  that performs control of the entire fuel cell system  201 , a capacitor  205 , a charging power source  215 , and a hydrogen supply mechanism  207  that, during charging, supplies hydrogen to the reaction container  203 . 
         [0099]    The reaction container  203  and the PEFC  220  communicate with each other by way of a hydrogen flow path  208  and a water flow path  209 , and the hydrogen flow path  208  is connected to the side of a fuel electrode  221  of the PEFC  220 , while the water flow path  209  is connected to the side of an oxygen electrode  222  of the PEFC  220 . Furthermore, a first hydrogen separation membrane  216  is provided on the hydrogen flow path  208  and used to supply only hydrogen separated from a gas containing water vapor and so on to the fuel electrode  221 . A gas-liquid separation filter  210  and a pump  211  are provided on the water flow path  209 . Water vapor generated at the oxygen electrode  222  is liquefied, after which only water is separated from the water vapor thus liquefied by the gas-liquid separation filter  210 , and water vapor obtained by gasifying the water by use of a gasifier is supplied to the reaction container  303 . Furthermore, an oxygen supply line  225  is connected to the side of the oxygen electrode  222 . 
         [0100]    The reaction container  203  and the hydrogen supply mechanism  207  communicate with each other by way of a hydrogen supply line  212  and a water discharge line  213 , and a second hydrogen separation membrane  218  is provided on the hydrogen supply line  212 . By use of the second hydrogen separation membrane  218 , only hydrogen is supplied from the hydrogen supply mechanism  207  to the reaction container  203  via the hydrogen supply line  212 , and water inside the reaction container  203  is supplied to the hydrogen supply mechanism  207  via the water discharge line  213 . 
         [0101]    Furthermore, the hydrogen supply line  212 , the water discharge line  213 , and the oxygen supply line  225  are each provided with a valve (not shown), and these valve mechanisms allow hydrogen supply into the reaction container  203 , water discharge out of the reaction container  203 , and oxygen supply to the oxygen electrode  222  to be controlled. 
         [0102]    A heater  214  adjusts a temperature inside the reaction container  203  so as to control reactions of a hydrogen occlusion material  206 . The capacitor  305  is used to provide an external voltage for the heater  214 . Furthermore, the capacitor  205  is connected to the charging power source  215  and to the PEFC  220 , and part of electricity generated in the PEFC  220  is stored therein. As the charging power source  215 , a lithium-ion cell can be used. 
         [0103]    The controller  204  is connected to the heater  214 , to the charging power source  215 , to the pump  211 , and to, though not shown, each of the valves on the hydrogen supply line  212 , the water discharge line  213 , and the oxygen supply line  225  and controls an adjustment of heating by the heater  214 , driving of the hydrogen supply mechanism  207  by the charging power source  215 , and opening and closing of the valves. Specifically, at the time of power generation, the reaction container  203  is sealed by closing the valve on the hydrogen supply line  212  and the valve on the water discharge line  213 , and the inside thereof is heated by the heater  214 , so that an oxidation reaction of iron constituting the hydrogen occlusion material  206  is caused to generate hydrogen. At this time, only hydrogen that has permeated through the first hydrogen separation membrane  216  provided on the hydrogen flow path  208  is supplied to the fuel electrode  221 . Furthermore, at the oxygen electrode  222 , oxygen is supplied thereto by opening the valve of the oxygen supply line  225 , and by electrochemical reactions at the fuel electrode  221  and at the oxygen electrode  222 , the PEFC  220  generates power. Furthermore, by the pump  211 , water generated at the oxygen electrode  222  is conveyed through the water flow path  209  to the reaction container  203 . 
         [0104]    At the time of stopping the power generation, the heating by the heater  214  is stopped, and the oxygen supply to the oxygen electrode  222  is stopped by closing the valve on the oxygen supply line  225 , so that the electrochemical reactions of the PEFC  220  are stopped. 
         [0105]    Furthermore, at the time of charging, with the valve on the hydrogen supply line  212  and the valve on the water discharge line  213  opened, the inside of the reaction container  203  is heated by the heater  214 , and a voltage is applied from the charging power source  215  to the hydrogen supply mechanism  207 . This causes hydrogen generated in the hydrogen supply mechanism  207  to be supplied into the reaction container  203  via the hydrogen supply line  212 , and the hydrogen occlusion material  206  then occludes the hydrogen. These mechanisms of adjusting a temperature and an internal pressure in the reaction container  203  are controlled by the controller  204 , and thus hydrogen emission and storage by the reversible hydrogen occlusion material  206  are performed stably, thereby allowing charging and discharging of the PEFC  220  to be controlled. 
         [0106]    In the above-described fuel cell system  201 , the oxidation reaction between iron and water that occurs in the reaction container  203  during power generation uses water generated at the oxygen electrode  222  during power generation by the PEFC  220 . By discharging water generated at the oxygen electrode  222  during power generation in this manner, the electrochemical reaction that occurs at the oxygen electrode  222  during power generation is prevented from being impaired, and the oxidation reaction between iron and water in the reaction container  203  can be accelerated. 
         [0107]    Furthermore, during charging, water generated in the reaction container  203  is discharged actively through the water discharge line  213 , and thus the reduction reaction that occurs in the reaction container  203  is accelerated, so that the reaction can be made to progress even in a case where a temperature in the reaction container  203  is relatively low. At this time, the water discharging mechanism described with regard to the first embodiment can be used to eliminate water through the water discharge line  213 . Furthermore, the hydrogen supply mechanism  207  is a mechanism that generates hydrogen by electrolysis of water, and as water to be subjected to the electrolysis, water generated in the reaction container  203  during charging is used and supplied from the reaction container  203  to the hydrogen supply mechanism  207  via the water discharge line  213 . As a power source used for the electrolysis, the charging power source  215  is used. 
         [0108]    Furthermore, the hydrogen supply mechanism  207  according to the present invention is not limited to the mechanism utilizing electrolysis of water and may utilize a water decomposition reaction of a photocatalyst. Since in a water decomposition reaction of a photocatalyst, hydrogen can be generated by irradiating the photocatalyst with natural light, there is no need to connect the hydrogen supply mechanism  207  to the charging power source  215 . The use of surface plasmon resonance as an excitation source for the photocatalyst is preferable in that it activates a water decomposition reaction of a photocatalyst and thus can accelerate the generation of hydrogen. 
       Third Embodiment 
       [0109]    Next, the following describes a third embodiment of the fuel cell system according to the present invention with reference to the appended drawings. In the following, duplicate descriptions of components identical to those in the fuel cell systems according to the first and second embodiments are omitted.  FIG. 7  is a schematic structural view of a fuel cell system according to the third embodiment of the present invention, and  FIG. 8  is a schematic view showing a reaction mechanism of the fuel cell system according to the third embodiment. A fuel cell system  301  includes a PEFC  320 , a reaction container  303 , a controller  304 , a capacitor  305 , a charging power source  315 , and a hydrogen supply mechanism  307 . 
         [0110]    The reaction container  303  and the PEFC  320  communicate with each other by way of a hydrogen flow path  308  that is connected to the side of a fuel electrode  321 , and a first hydrogen separation membrane  316  is provided on the hydrogen flow path  308 . Furthermore, an oxygen supply line  325  is connected to the side of an oxygen electrode  322 . 
         [0111]    The reaction container  303  and the hydrogen supply mechanism  307  communicate with each other by way of a hydrogen supply line  312 , and a second hydrogen separation membrane  318  is provided on the hydrogen supply line  312 . By use thereof, only hydrogen is supplied from the hydrogen supply mechanism  307  into the reaction container  303 . On each of the hydrogen supply line  312  and the oxygen supply line  325 , a valve (not shown) is provided, and these valve mechanisms allow hydrogen supply into the reaction container  303  and oxygen supply to the oxygen electrode  322  to be controlled. 
         [0112]    Inside the reaction container  303 , as a reversible hydrogen occlusion material  306 , a complex hydride, Mg(BH 4 ) 2 , is provided, which emits hydrogen during power generation and stores hydrogen during charging based on the following reactions.
   During power generation: Mg(BH 4 ) 2 →MgH 2 +2B+3H 2 :MgH 2 →Mg+H 2      During charging: MgH 2 +2B+3H 2 →Mg(BH 4 ) 2 :Mg+H 2 →MgH 2      
 
         [0115]    Since these reactions of hydrogen emission and hydrogen occlusion are endothermic reactions that require a relatively high temperature, a temperature adjustment mechanism for heating the inside of the reaction container  303  to a high temperature is required, and to that end, the reaction container  303  is provided with a heater  314 . The capacitor  305  is used to provide an external voltage for the heater  314 . The capacitor  305  is connected to the charging power source  315  and to the PEFC  320 , and part of electricity generated in the PEFC  320  is stored in the capacitor  305 . 
         [0116]    The controller  304  is connected to the heater  314 , to the charging power source  315 , and to, though not shown, each of the valves on the hydrogen supply line  312  and the oxygen supply line  325  and controls an adjustment of heating by the heater  314 , driving of the hydrogen supply mechanism  307  by the charging power source  315 , and opening and closing of the valves. Specifically, at the time of power generation, the reaction container  303  is sealed by closing the valve on the hydrogen supply line  312 , and the inside thereof is heated by the heater  314 , so that a reaction of the hydrogen occlusion material  306  is caused to generate hydrogen. At this time, only hydrogen that has permeated through the first hydrogen separation membrane  316  provided on the hydrogen flow path  308  is supplied to the fuel electrode  321 . Furthermore, at the oxygen electrode  322 , oxygen is supplied thereto by opening the valve of the oxygen supply line  325 , and by electrochemical reactions at the fuel electrode  321  and at the oxygen electrode  322 , the PEFC  320  generates power. 
         [0117]    At the time of stopping the power generation, the heating by the heater  314  is stopped, and the oxygen supply to the oxygen electrode  322  is stopped by closing the valve on the oxygen supply line  325 , so that the electrochemical reactions of the PEFC  320  are stopped. 
         [0118]    Furthermore, at the time of charging, with the valve on the hydrogen supply line  312  opened, the inside of the reaction container  303  is heated by the heater  314 , and a voltage is applied from the charging power source  315  to the hydrogen supply mechanism  307 . This causes hydrogen generated in the hydrogen supply mechanism  307  to be supplied into the reaction container  303  via the hydrogen supply line  312 , and the hydrogen occlusion material  306  then occludes the hydrogen. These mechanisms of adjusting a temperature and an internal pressure in the reaction container  303  are controlled by the controller  304 , and thus hydrogen emission and storage by the reversible hydrogen occlusion material  306  are performed stably, thereby allowing charging and discharging of the PEFC  320  to be controlled. 
         [0119]    In the fuel cell system  301 , as shown in  FIG. 8 , the following is also possible. That is, water vapor generated at the oxygen electrode  322  during power generation is stored in a liquefied state so as to be used in the hydrogen supply mechanism  307  during charging. By discharging water generated at the oxygen electrode  322  during power generation in this manner, the electrochemical reaction that occurs at the oxygen electrode  322  during power generation can be prevented from being impaired, and water to be used for the hydrogen supply mechanism  307  can be secured in the fuel cell system  301 . 
       Fourth Embodiment 
       [0120]    Next, the following describes a fourth embodiment of the fuel cell system according to the present invention with reference to the appended drawings. In the following, duplicate descriptions of components identical to those in the fuel cell systems according to the first to third embodiments are omitted.  FIG. 9  is a schematic structural view of a fuel cell system according to the fourth embodiment of the present invention, and  FIG. 10  is a schematic view showing a reaction mechanism of the fuel cell system according to the fourth embodiment. A fuel cell system  401  includes a PEFC  420 , a reaction container  403 , a controller  404 , a capacitor  405 , a charging power source  415 , a hydrogen supply mechanism  407 , and a first liquefier tank  440  and a second liquefier tank  443  for storing a gasified hydrogen occlusion material  406 . 
         [0121]    The reaction container  403  and the PEFC  420  communicate with each other via a hydrogen flow path  408  that is connected to the side of a fuel electrode  421 , and a first hydrogen separation membrane  416  is provided on the hydrogen flow path  408 . Furthermore, the reaction container  403  and the first liquefier tank  440  communicate with each other via a first flow path  441  and a second flow path  442 , with the first flow path  441  branching off from the hydrogen flow path  408  at the first hydrogen separation membrane  416  and communicating with the first liquefier tank  440 . Furthermore, the reaction container  403  and the second liquefier tank  443  communicate with each other via a third flow path  444  and a fourth flow path  445 . Furthermore, an oxygen supply line  425  is connected to the side of an oxygen electrode  422 . 
         [0122]    The reaction container  403  and the hydrogen supply mechanism  407  communicate with each other by way of a hydrogen supply line  412 , and hydrogen is supplied from the hydrogen supply mechanism  407  into the reaction container  403  via the hydrogen supply line  412 . On each of the hydrogen supply line  412  and the oxygen supply line  425 , a valve (not shown) is provided, and these valve mechanisms allow hydrogen supply into the reaction container  403  and oxygen supply to the oxygen electrode  422  to be controlled. 
         [0123]    Inside the reaction container  403 , as the reversible hydrogen occlusion material  406 , an organic hydride, C 6 H 12 , is provided. Herein, the organic hydride, C 6 H 12 , emits hydrogen during power generation and stores hydrogen during charging based on the following reactions.
   During power generation: C 6 H 12 (g)→C 6 H 6 (g)+3H 2      During charging: C 6 H 6 (g)+3H 2 →C 6 H 12 (g)   
 
         [0126]    Since these reactions of dehydrogenation and hydrogenation are endothermic reactions that require a relatively high temperature, a temperature adjustment mechanism for heating the inside of the reaction container  403  to a high temperature is required, and to that end, the reaction container  403  is provided with a heater  414 . The capacitor  405  is used to provide an external voltage for the heater  414 . The capacitor  405  is connected to the charging power source  415  and to the PEFC  420 , and part of electricity generated in the PEFC  420  is stored in the capacitor  405 . 
         [0127]    Furthermore, C 6 H 6  generated by the dehydrogenation reaction of C 6 H 12  during power generation is in a gasified state and is therefore conveyed together with hydrogen to the hydrogen flow path  408  where C 6 H 6  is separated from the hydrogen by use of the first hydrogen separation membrane  416 , after which C 6 H 6  passes through the first flow path  441  to be stored in the first liquefier tank  440 . Then, during charging, C 6 H 6  in the first liquefier tank  440  is gasified and supplied in that state into the reaction container  403  via the second flow path  442 . 
         [0128]    Furthermore, C 6 H 12  generated by the hydrogenation reaction of C 6 H 6  during charging is also in the form of a gas, and C 6 H 12  generated in the reaction container  403  is supplied to the second liquefier tank  443  via the third flow path  444  and stored in a liquefied state in the second liquefier tank  443 . Then, during power generation, C 6 H 12  in the second liquefier tank  443  is gasified and supplied in that state into the reaction container  403  via the fourth flow path  445 . By eliminating C 6 H 6  or C 6 H 12  generated in the reaction container  403  in the above-described manner, the dehydrogenation reaction of C 6 H 12  or the hydrogenation reaction of C 6 H 6  can be accelerated. 
         [0129]    The controller  404  is connected to the heater  414 , to the charging power source  415 , and to, though not shown, each of the valves on the hydrogen supply line  412 , the oxygen supply line  425 , the second flow path  442 , the third flow path  444 , and the fourth flow path  445  and controls an adjustment of heating by the heater  414 , driving of the hydrogen supply mechanism  407  by the charging power source  415 , and opening and closing of the valves. Specifically, at the time of power generation, the valve on the hydrogen supply line  412  is closed, while the valve on the fourth flow path  445  is opened so that C 6 H 12  in the second liquefier tank  443  is supplied into the reaction container  403 , and the inside of the reaction container  403  is heated by the heater  414 , so that hydrogen is generated from the hydrogen occlusion material  406 . At this time, only hydrogen that has permeated through the first hydrogen separation membrane  416  provided on the hydrogen flow path  408  is supplied to the fuel electrode, while C 6 H 6  in a gasified state, after being separated from the hydrogen by use of the first hydrogen separation membrane  416 , passes through the first flow path  441  to be supplied to the first liquefier tank  440 . Meanwhile, at the oxygen electrode  422 , oxygen is supplied thereto by opening the valve of the oxygen supply line  425 , and by electrochemical reactions at the fuel electrode  421  and at the oxygen electrode  422 , the PEFC  420  generates power. 
         [0130]    At the time of stopping the power generation, the heating by the heater  414  is stopped, and the supply of the organic hydride into the reaction container  403  is stopped by closing the valve on the fourth flow path  445 , while the oxygen supply to the oxygen electrode  422  is stopped by closing the valve on the oxygen supply line  425 , so that the electrochemical reactions of the PEFC  420  are stopped. 
         [0131]    Furthermore, at the time of charging, with the valve on the hydrogen supply line  412 , the valve on the second flow path  442 , and the valve on the third flow path  444  opened, the inside of the reaction container  403  is heated by the heater  414 , and a voltage is applied from the charging power source  415  to the hydrogen supply mechanism  407 . This causes hydrogen to be supplied from the hydrogen supply mechanism  407  through the hydrogen supply line  412  into the reaction container  403  and C 6 H 6  to be supplied from the first liquefier tank  440  into the reaction container  403 , and by the hydrogenation reaction, C 6 H 12  is generated. Then, C 6 H 12  thus generated is supplied to the second liquefier tank  443  via the third flow path  444 . These mechanisms of adjusting a temperature and an internal pressure in the reaction container  403  are controlled, and thus hydrogen emission and occlusion by the reversible hydrogen occlusion material  406  are performed stably, thereby allowing charging and discharging of the PEFC  420  to be controlled. 
       INDUSTRIAL APPLICABILITY 
       [0132]    The present invention is favorably applicable as a power source for electronic equipment without any limitation on the form of use thereof. 
       List of Reference Symbols 
       [0133]      101 ,  201  fuel cell system 
         [0134]      103 ,  203  reaction container 
         [0135]      204  controller 
         [0136]      205  capacitor 
         [0137]      106 ,  206  hydrogen occlusion material 
         [0138]      207  hydrogen supply mechanism 
         [0139]      208  hydrogen flow path 
         [0140]      109 ,  209  water flow path 
         [0141]      210  gas-liquid separation filter 
         [0142]      111 ,  211  pump 
         [0143]      112 ,  212  hydrogen supply line 
         [0144]      113 ,  213  water discharge line 
         [0145]      114 ,  214  heater 
         [0146]      215  charging power source 
         [0147]      116 ,  216  first hydrogen separation membrane 
         [0148]      117  water discharging mechanism 
         [0149]      218  second hydrogen separation membrane 
         [0150]      120 ,  220  PEFC (fuel cell) 
         [0151]      121 ,  221  fuel electrode 
         [0152]      121   a  fuel diffusion layer 
         [0153]      122 ,  222  oxygen electrode 
         [0154]      122   a  air diffusion layer 
         [0155]      123 ,  223  electrolyte membrane 
         [0156]      125 ,  225  oxygen supply line 
         [0157]      124  air chamber 
         [0158]      130  circulation path 
         [0159]      131  cooling portion 
         [0160]      132  water vapor separation membrane 
         [0161]      133  oxygen permeable membrane 
         [0162]      160  gasifiier 
         [0163]      170  cavity 
         [0164]      440  first liquefier tank 
         [0165]      441  first flow path 
         [0166]      442  second flow path 
         [0167]      443  second liquefier tank 
         [0168]      444  third flow path 
         [0169]      445  fourth flow path