Abstract:
Disclosed is a fuel cell system ( 101 ) having: a reaction container ( 103 ) that has a first heater ( 114 ); and a fuel cell ( 120 ) provided with a fuel electrode ( 121 ), an oxygen electrode ( 122 ), and an electrolyte membrane ( 123 ); wherein the reaction container ( 103 ) is attachable to/removable from the fuel cell ( 120 ).

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a fuel cell system, more particularly, to a fuel cell system that includes a hydrogen occlusion material. 
       BACKGROUND ART 
       [0002]    In recent years, because of high performance of electronic apparatuses, demand for a large capacity and a long life of a cell is increasing. As for a capacity of a conventional lithium ion battery, energy density per volume is reaching a theoretical limitation, and a dramatic performance increase is not expected any more. Under this circumstance, a fuel cell, which is dramatically excellent in energy density per volume compared with a conventional battery and able to have a large capacity, is attracting attention. 
         [0003]    For example, a patent document 1 describes a chargeable fuel cell system; in this fuel system, a fuel cell and a hydrogen occlusion material are integrally formed with each other; and as the fuel cell, a solid polymer electrolyte fuel cell (hereinafter, called a PEFC) is used.  FIG. 6  is a schematic view showing a reaction mechanism of a PEFC during a power generation time, and  FIG. 7  is a schematic view showing a reaction mechanism of a PEFC during a charge time. A PEFC  200  is composed of a fuel electrode  221 , an oxygen electrode  222 , and an electrolyte membrane  223 ; and during a power generation time, at the fuel electrode  221 , protons and electrons are generated from hydrogen; at the oxygen electrode  222 , protons moving from the fuel electrode  221  and oxygen ions generated from oxygen react to each other to generate water. 
         [0000]      The fuel electrode: H 2 →2H + +2 e   − 
 
         [0000]      The oxygen electrode: 4H + +O 2 +4 e   − →2H 2 O
 
         [0004]    During a charge time, when reverse voltages are applied to the fuel electrode  221  and the oxygen electrode  222 , reactions reverse to those during the power generation time occur at the fuel electrode  221  and the oxygen electrode  222 . 
         [0000]      The fuel electrode: 2H + +2 e   − →H 2  
 
         [0000]      The oxygen electrode: 2H 2 O→4H + +O 2 +4 e   − 
 
         [0005]    In the fuel cell system described in the patent document 1, the hydrogen occlusion material for generating hydrogen is disposed; accordingly, during the power generation time, it is possible to supply hydrogen from the hydrogen occlusion material to the fuel electrode; and during the charge time, it is possible to make the hydrogen occlusion material occlude and store the hydrogen generated by the fuel electrode. 
       CITATION LIST 
     Patent Literature 
       [0000]    
       
         PLT1: JP-A-2002-151094 
       
     
       SUMMARY OF INVENTION 
     Technical Problem 
       [0007]    However, generally, to generate hydrogen from a hydrogen occlusion material or store hydrogen in the hydrogen occlusion material, it is necessary to prompt the reaction by heating the hydrogen occlusion material. However, in the fuel cell system described in the patent document 1, a reaction adjustment mechanism is not studied, and it is conceivable that it is impossible to repeat the charging and discharging in a sustainable manner. 
         [0008]    Because of this, to solve this problem, it is an object of the present invention to provide a fuel cell system that is renewable in a sustainable manner. 
       Solution to Problem 
       [0009]    To achieve the above object, a fuel cell system according to the present invention includes: a fuel cell that includes: a fuel electrode, an oxygen electrode, and an electrolyte membrane disposed between the fuel electrode and the oxygen electrode; a hydrogen occlusion material that supplies hydrogen to the fuel electrode; and an reaction container that incorporates the hydrogen occlusion material and has a temperature adjustment mechanism which adjusts an internal condition; wherein the fuel electrode generates water by means of the fuel electrode during a power generation time, and supplies the water to an inside of the reaction container. 
         [0010]    According to this structure, it is possible to adjust the internal condition of the reaction container by means of the temperature adjustment mechanism, and control a reaction start condition of the hydrogen occlusion material and a reaction stop condition of the hydrogen occlusion material. In this way, during a power generation time, it is possible to make the hydrogen occlusion material emit hydrogen stably; and during a charge time, it is possible to stably store the hydrogen in the hydrogen occlusion material. 
       Advantageous Effects of Invention 
       [0011]    According to the present invention, it is possible to provide a fuel cell system that is renewable in a sustainable manner. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0012]      FIG. 1  is a schematic view of a fuel cell system according to a first embodiment during a power generation time. 
           [0013]      FIG. 2  is a schematic view of a fuel cell system according to the first embodiment during a charge time. 
           [0014]      FIG. 3  is a view showing a reaction mechanism of an SOFC during a power generation time. 
           [0015]      FIG. 4  is a view showing a reaction mechanism of an SOFC during a charge time. 
           [0016]      FIG. 5  is a schematic view of the fuel cell system according to the first embodiment. 
           [0017]      FIG. 6  is a view showing a reaction mechanism of a PEFC during a power generation time. 
           [0018]      FIG. 7  is a view showing a reaction mechanism of a PEFC during a charge time. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0019]    Hereinafter, a fuel cell system according to the present invention is described with reference to the drawings. 
       First Embodiment 
       [0020]      FIG. 1  and  FIG. 2  are schematic views of a fuel cell system according to a first embodiment, of which  FIG. 1  shows a state during a power generation time, and  FIG. 2  shows a state during a charge time. As shown in  FIG. 1  and  FIG. 2 , a fuel cell system  101  is composed of a solid oxide fuel cell  120  (hereinafter, called an SOFC) and a reaction container  103 . The SOFC  120  is composed of a fuel electrode  121 , an electrolyte membrane  123 , and an oxygen electrode  122 . Besides, an air chamber  124  is formed on an oxygen electrode  122  side of the SOFC  120 , and a fuel chamber  128  is formed on a fuel electrode  121  side. The fuel chamber  128  is formed of an air space between the fuel electrode  121  and an inside of the reaction container  103  that is disposed adjacently to the fuel electrode  121 . The reaction container  103  is mounted so as not to be electrically connected to the SOFC  120  via a first connection portion  112  and a second connection portion  113 . 
         [0021]    In the inside of the reaction container  103 , iron microparticles are disposed as a hydrogen occlusion material  106  at a predetermined position. The reaction container  103  includes a heat-insulated structure having a cavity  170  between an outer wall and an inner wall, and has a first heater  114  for heating the inside of the reaction container  103 . Here, although not shown, a fuel diffusion layer is formed on a surface of the fuel electrode  121 , whereby it is possible to evenly supply hydrogen to the fuel electrode  121 , and an air diffusion layer is formed on a surface of the oxygen electrode  122 , whereby it is possible to evenly supply air to the oxygen electrode  121 . 
         [0022]    On the other hand, the air chamber  124  communicates with an oxygen supply line  125  and an oxygen discharge line  127 , whereby air containing oxygen is supplied into an inside of the air chamber  124  via the oxygen supply line  125 . Besides, the oxygen supply line  125  is provided with a valve  125   a  and the oxygen discharge line  127  is provided with a valve  127   a , whereby it is possible to control the air supply into the air chamber  124 . 
         [0023]    The hydrogen occlusion material  106  is formed of the iron microparticles, which allow the following oxidation and reduction reactions to occur in the reaction container  103 . 
         [0000]      The oxidation reaction: 3Fe+4H 2 O→Fe 3 O 4 +4H 2  
 
         [0000]      The reduction reaction: Fe 3 O 4 +4H 2 →3Fe+4H 2 O
 
         [0024]    According to these reactions, the hydrogen occlusion material  106  emits hydrogen by means of an iron oxidation reaction during a power generation time, and stores hydrogen by means of an iron oxide reduction reaction during a charge time. The reduction reaction at the hydrogen occlusion material  106  is an endothermic reaction and the reaction temperature is high; however, by adjusting the internal temperature of the reaction container  103  by means of the first heater  114 , it is possible to control the reaction at the hydrogen occlusion material  106 . 
         [0025]      FIG. 3  is a schematic view showing a reaction mechanism of the SOFC during a power generation time, and  FIG. 4  is a schematic view showing a reaction mechanism of the SOFC during a charge time. As shown in  FIG. 3  and  FIG. 4 , in the SOFC  120 , during a power generation time, the following reactions occur at the fuel electrode  121  and the oxygen electrode  122 , whereby at the fuel electrode  121 , protons and electrons are generated from hydrogen and at the oxygen electrode  122 , oxygen ions are generated from oxygen. During this time, oxygen ions moving from the oxygen electrode  122  and protons react to each other, whereby water is generated at the fuel electrode  121 . 
         [0000]      The fuel electrode: H 2 +O 2 →H 2 O+2 e   − 
 
         [0000]      The oxygen electrode: O 2 +4 e   − →2O 2− 
 
         [0026]    Besides, when reverse voltages are applied to the fuel electrode  121  and the oxygen electrode  122  during a charge time, the following reactions reverse to those during the power generation time occur at the fuel electrode  121  and the oxygen electrode  122 , whereby hydrogen is generated from the fuel electrode  121 . By storing this hydrogen generated from the fuel electrode  121  in a hydrogen storing portion, it is possible to use the SOFC  120  as a chargeable secondary cell. 
         [0000]      The fuel electrode: H 2 O+2 e   − →H 2 −O 2− 
 
         [0000]      The oxygen electrode: 2O 2− →O 2 +4 e   − 
 
         [0027]    Next, an operation method of the fuel cell system  101  is described. During a power generation time, the first connection portion  112  and the second connection portion  113  are closed to tightly seal the reaction container  103 , and the inside of the fuel chamber  128  is heated by means of the first heater  114 , whereby the iron as the hydrogen occlusion material  106  is oxidized in the reaction container  103  to generate hydrogen, which is supplied to the fuel electrode  121 . Here, the first connection portion  112  and the second connection portion  113  may be normally closed in a state where the reaction container  103  is mounted on the SOFC  120 . 
         [0028]    On the other hand, in the air chamber  124 , the valve  125   a  of the oxygen supply line  125  and the valve  127   a  of the oxygen discharge line  127  are opened, whereby oxygen is supplied to the oxygen electrode  122  and the inside of the air chamber  124  is heated by means of a second heater  126 . In this way, the SOFC  120  generates electric power by means of the electrochemical reaction. During this time, the water generated at the fuel electrode  121  is supplied to the hydrogen occlusion material  106  in the inside of the reaction container  103 , thereby prompting the hydrogen generation reaction at the hydrogen occlusion material  106 . 
         [0029]    Accordingly, the water used for the hydrogen generation reaction at the hydrogen occlusion material  106  is directly suppliable from the fuel electrode  121 , so that it is possible to efficiently use the water generated in the fuel cell system  101 ; and it is possible to achieve size reduction of the entire fuel cell system  101  and increase energy density per volume. 
         [0030]    To stop the fuel cell system  101 , the heating by means of the first heater  114  is stopped to stop the reaction at the hydrogen occlusion material  106 ; the valve  125   a  of the oxygen supply line  125  is closed to stop the oxygen supply and the heating by means of the second heater  126  is stopped, whereby it is possible to stop the electrochemical reaction at the SOFC  120 . 
         [0031]    Besides, to charge the fuel cell system  101 , the first connection portion  112  and the second connection portion  113  are closed to tightly seal the reaction container  103 ; the inside of the reaction container  103  is heated by means of the first heater  114 ; the valve  125   a  of the oxygen supply line  125  is closed and the valve  127   a  of the oxygen discharge line  127  is opened; and the inside of the air chamber  124  is heated by means of the second heater  126 . Besides, a negative voltage is applied to the fuel electrode  121 , while a positive voltage is applied to the oxygen electrode  122 . In this way, a reaction reverse to the reaction during the power generation time occurs at the SOFC  120 , whereby hydrogen is generated from thee fuel electrode  121  and oxygen is generated from the oxygen electrode  122 . During this time, the hydrogen generated from the fuel electrode  121  reduces the iron oxide in the reaction container  103  and is stored in the hydrogen occlusion material  106 . Besides, the oxygen generated from the oxygen electrode  122  is discharged from the oxygen discharge line  127 . 
         [0032]    As described above, the operations of power generation, stop and charge in the fuel cell system  101  are controllable by means of the temperature adjustment in the reaction container  103  and the air chamber  124 . Besides, the fuel electrode  121  of the SOFC  120  functions as a water supply source and a hydrogen supply source, so that it is possible to dispose the reaction container  103  adjacently to the fuel electrode  121 , achieve the size reduction of the entire fuel cell system  101 , and increase the energy density per volume. 
         [0033]    Besides, as the fuel cell  120 , instead of the SOFC, it is possible to use a fuel cell that generates water by means of the fuel electrode  121 . 
         [0034]    The iron used for the hydrogen occlusion material  106  is iron microparticles; to enlarge an actual surface area, a powdering process is performed; thereafter, micro-cracks are formed by means of hydrogen embrittlement; and an addition process is performed to add a sintering material into the micro-cracks by means of liquid phase deposition. The oxidation and reduction reactions between the iron and the water are promoted by this process, and the emission and absorption of the hydrogen in the reaction container  103  are stabilized. 
         [0035]    Besides, in the present embodiment, the iron is used as the hydrogen occlusion material  106  that is renewable; however, it is possible to emit and occlude hydrogen by means of metal microparticles instead of the iron; and it is possible to use aluminum or magnesium to obtain the same reaction. 
         [0036]    Besides, as shown in  FIG. 5 , in the fuel cell system  101  according to the present embodiment, the reaction container  103  is detachable from the SOFC  120 . Because of this, when the hydrogen generation amount by the hydrogen occlusion material  106  in the reaction container  103  decreases and the output of the fuel cell  121  declines, by replacing the hydrogen occlusion material  106  together with the reaction container  103 , it is possible to recover the output of the fuel cell  121 . According to this, even if the negative voltage is not applied to the fuel electrode  121  of the SOFC  120  and the positive voltage is not applied to the oxygen electrode  122  for the charge, if the reaction container  103 , which has the hydrogen occlusion material  106  that sufficiently stores hydrogen, is replaced as a charge cartridge, it is possible to renew and use the fuel cell system  101 . Besides, it is possible to charge the reaction container  103 , which has the hydrogen occlusion material  106 , by means of another apparatus. 
       INDUSTRIAL APPLICABILITY 
       [0037]    The present invention is not limited in usage and is preferably applicable as a power supply of an electronic apparatus. 
       REFERENCE SIGNS LIST 
       [0000]    
       
         
           
               101  fuel cell system 
               103  reaction container 
               106  hydrogen occlusion material 
               112  first connection portion 
               113  second connection portion 
               114  first heater 
               120  fuel cell 
               121  fuel electrode 
               122  oxygen electrode