Abstract:
In a unit cell that forms a water electrolysis device, which is an electrochemical device, an electrolyte membrane/electrode structure is sandwiched between an anode-side separator and a cathode-side separator. A load-applying mechanism is disposed between a cathode-side feeder and the cathode-side separator, while an anode-side feeder is set with a smaller contact area range than the aforementioned cathode-side feeder. The anode-side feeder and the cathode-side feeder are set with a larger contact area range than an anode electrode catalyst layer and a cathode electrode catalyst layer, and a contact surface that touches a solid polymer electrolyte membrane on the aforementioned anode-side feeder is disposed projecting farther to the side of the aforementioned solid polymer electrolyte membrane than a contact surface on the anode-side separator and a contact surface on a frame member.

Description:
RELATED APPLICATIONS 
     This application is a 35 U.S.C. 371 national stage filing of International Application No. PCT/JP2011/056326, filed Mar. 17, 2011, which claims priority to Japanese Patent Application No. 2010-066809 filed on Mar. 23, 2010 in Japan. The contents of the aforementioned applications are hereby incorporated by reference. 
     TECHNICAL FIELD 
     The present invention relates to an electrochemical device containing a first catalyst and a first current collector disposed on one surface of an electrolyte membrane, a second catalyst and a second current collector disposed on the other surface of the electrolyte membrane, a first flow path for supplying a first fluid formed between the first current collector and a first separator, and a second flow path, for collecting a second fluid generated by an electrolysis of the first fluid, formed between the second current collector and a second separator. 
     BACKGROUND ART 
     For example, a water electrolysis device is used to produce a hydrogen gas as a fuel gas for a power generation reaction in a fuel cell. The water electrolysis device contains a solid polymer electrolyte membrane for decomposing water to generate the hydrogen (and oxygen). Electrode catalyst layers are disposed on either side of the solid polymer electrolyte membrane to form a membrane-electrode assembly, and current collectors are disposed on either side of the membrane-electrode assembly to form a unit. 
     A plurality of the units are stacked, a voltage is applied to the stacking-direction ends, and the water is supplied to the anode-side current collector. Then, the water is decomposed to generate hydrogen ions (protons) at the anode side of the membrane-electrode assembly. The hydrogen ions are transferred through the solid polymer electrolyte membrane to the cathode side, and bonded with electrons to produce the hydrogen. Meanwhile, at the anode side, the oxygen generated simultaneously with the hydrogen is discharged together with the residual water from the unit. 
     Known water electrolysis devices include high-pressure hydrogen production devices capable of generating a high-pressure hydrogen (at a pressure of several tens MPa) at the cathode side. For example, as shown in  FIG. 7 , a high-pressure hydrogen production device disclosed in Japanese Laid-Open Patent Publication No. 2006-070322 contains a cathode current collector  2  and an anode current collector  3  disposed on either side of a solid polymer membrane  1 , separators  4   a  and  4   b , and flow paths  5   a  and  5   b . When water is supplied to the flow path  5   b  in the anode-side separator  4   b  and the current collectors  2  and  3  are energized, the water is electrolyzed to generate the high-pressure hydrogen gas in the flow path  5   a  in the cathode-side separator  4   a    
     The high-pressure hydrogen production device further contains a disc spring  6  as a pressing means for pressing the cathode current collector  2  into tight contact with the solid polymer membrane  1 . The disc spring  6  is disposed in the flow path  5   a  to press the cathode current collector  2  toward the solid polymer membrane  1 . Therefore, the contact resistance between the solid polymer membrane  1  and the cathode current collector  2  is not increased even under the high pressure at the cathode side. 
     SUMMARY OF INVENTION 
     On the above solid polymer membrane  1 , predetermined catalyst layers are formed on the anode and cathode sides. Thus, it is required that a satisfactory surface pressure is reliably applied to the catalyst layers by the cathode current collector  2  and the anode current collector  3  to ensure a desired electrolysis performance. 
     In view of such requirement, an object of the present invention is to provide an electrochemical device capable of utilizing current collectors for reliably applying a desired surface pressure to catalysts disposed on either side of an electrolyte membrane, thereby improving the electrolysis performance. 
     The present invention relates to an electrochemical device comprising an electrolyte membrane, a first catalyst and a first current collector disposed on one surface of the electrolyte membrane, a second catalyst and a second current collector disposed on an opposite surface of the electrolyte membrane, a first separator stacked on the first current collector, a first flow path, for supplying a first fluid, formed between the first current collector and the first separator, a second separator stacked on the second current collector, and a second flow path, for collecting a second fluid generated by an electrolysis of the first fluid, formed between the second current collector and the second separator, the pressure of the second fluid being higher than that of the first fluid. 
     In the electrochemical device, a load applying mechanism for pressing the second current collector onto the electrolyte membrane is interposed between the second current collector and the second separator, the first and second current collectors have different contact areas with the electrolyte membrane, and the contact surface between the electrolyte membrane and the first or second current collector whichever has the smaller contact area protrudes toward the electrolyte membrane from the contact surface between the first or second separator and the electrolyte membrane. 
     In the present invention, the contact surface between the current collector having the smaller contact area and the electrolyte membrane protrudes toward the electrolyte membrane from the contact surface between the separator and the electrolyte membrane. Therefore, when the first and second current collectors are pressed with the electrolyte membrane interposed therebetween, the current collector having the larger contact area does not come into contact with the separator on the current collector having the smaller contact area. 
     Thus, the desired surface pressure can be reliably applied by the first and second current collectors to the first and second catalysts disposed on either side of the electrolyte membrane, whereby the electrolysis performance can be improved even in the simple structure. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is an explanatory perspective view of a water electrolysis device according to a first embodiment of the present invention; 
         FIG. 2  is a partially sectioned side view of the water electrolysis device; 
         FIG. 3  is an explanatory exploded perspective view of a unit cell in the water electrolysis device; 
         FIG. 4  is a cross-sectional view of the unit cell taken along the line IV-IV of  FIG. 3 ; 
         FIG. 5  is an explanatory cross-sectional view of a unit cell in a water electrolysis device according to a second embodiment of the present invention; 
         FIG. 6  is an explanatory cross-sectional view of a unit cell in a water electrolysis device according to a third embodiment of the present invention; and 
         FIG. 7  is an explanatory view of a high-pressure hydrogen production device disclosed in Japanese Laid-Open Patent Publication No. 2006-070322. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     As shown in  FIGS. 1 and 2 , a water electrolysis device (electrochemical device)  10  according to a first embodiment of the present invention is a high-pressure hydrogen production device, which contains a stack  14  formed by stacking a plurality of unit cells  12  in the vertical direction (the arrow A direction) or the horizontal direction (the arrow B direction). 
     In one stacking-direction end (upper end) of the stack  14 , a terminal plate  16   a , an insulation plate  18   a , and an end plate  20   a  are disposed in this order in the upward direction. Similarly, in the other stacking-direction end (lower end) of the stack  14 , a terminal plate  16   b , an insulation plate  18   b , and an end plate  20   b  are disposed in this order in the downward direction. 
     In the water electrolysis device  10 , for example, the disc-shaped end plates  20   a  and  20   b  are integrally fastened and fixed by four tie rods  22  extending in the arrow A direction. Alternatively, the water electrolysis device  10  may be integrally fastened by a box casing (not shown) containing the end plates  20   a  and  20   b  at the ends. In addition, though the overall shape of the water electrolysis device  10  is an approximately cylindrical shape in this embodiment, it may be selected from various shapes such as cubic shapes. 
     As shown in  FIG. 1 , terminals  24   a  and  24   b  protrude outward from side surfaces of the terminal plates  16   a  and  16   b  respectively. The terminals  24   a  and  24   b  are electrically connected to a power source  28  by wirings  26   a  and  26   b . The positive electrode-side (anode-side) terminal  24   a  is connected to a positive post of the power source  28 , while the negative electrode-side (cathode-side) terminal  24   b  is connected to a negative post of the power source  28 . 
     As shown in  FIGS. 2 to 4 , the unit cell  12  contains an approximately disc-shaped membrane-electrode assembly  32 , and further contains an anode-side separator (first separator)  34  and a cathode-side separator (second separator)  36  sandwiching the membrane-electrode assembly  32 . The anode-side separator  34  and the cathode-side separator  36  have approximately disc shapes. For example, they may be composed of a carbon member or the like. Alternatively, they may be prepared by press-forming a steel plate, a stainless steel plate, a titanium plate, an aluminum plate, or a plated steel plate, and the metal plate may be subjected to an anticorrosion surface treatment before the press forming. Furthermore, they may be prepared by cutting the metal plate and then subjecting the resultant to an anticorrosion surface treatment. 
     For example, the membrane-electrode assembly  32  contains a solid polymer electrolyte membrane  38  prepared by impregnating a thin perfluorosulfonic acid membrane with water, and further contains a circular anode-side current collector (first current collector)  40  and a circular cathode-side current collector (second current collector)  42  disposed on either side of the solid polymer electrolyte membrane  38 . The outer edge of the solid polymer electrolyte membrane  38  protrudes outward from the outer peripheries of the anode-side current collector  40  and the cathode-side current collector  42  (see  FIG. 4 ). 
     An anode catalyst layer (first catalyst)  40   a  and a cathode catalyst layer (second catalyst)  42   a  are disposed on either side of the solid polymer electrolyte membrane  38 . For example, the anode catalyst layer  40   a  contains a Ru (ruthenium) catalyst, and the cathode catalyst layer  42   a  contains a platinum catalyst. 
     For example, the anode-side current collector  40  and the cathode-side current collector  42  contain a sintered body of a spherical atomized titanium powder (a porous conductor). The anode-side current collector  40  and the cathode-side current collector  42  each have a smooth surface portion formed by a grinding process and an etching treatment. The porosity thereof is 10% to 50%, more preferably 20% to 40%. 
     As shown in  FIG. 4 , the contact area between the anode-side current collector  40  and the solid polymer electrolyte membrane  38  is smaller than that between the cathode-side current collector  42  and the solid polymer electrolyte membrane  38 , and the contact areas of the anode-side current collector  40  and the cathode-side current collector  42  are larger than the areas of the anode catalyst layer  40   a  and the cathode catalyst layer  42   a  respectively. The anode catalyst layer  40   a  and the cathode catalyst layer  42   a  have the same areas. 
     The anode-side current collector  40  is fitted in an inner periphery of a ring-shaped frame member  43 . For example, the frame member  43  is composed of pure titanium, and the contact surface  43   a  between the frame member  43  and the solid polymer electrolyte membrane  38  and the contact surface  34   a  between the anode-side separator  34  and the membrane-electrode assembly  32  are in the same plane. The contact surface  40   b  between the anode-side current collector  40  and the solid polymer electrolyte membrane  38  protrudes toward the solid polymer electrolyte membrane  38  from the contact surface  34   a  of the anode-side separator  34  (and the contact surface  43   a  of the frame member  43 ). 
     A flow path plate  44  is interposed between the anode-side separator  34  and the anode-side current collector  40  (and the frame member  43 ). The flow path plate  44  has a plurality of pores or openings, or is composed of a porous conductor. A relatively small gap S 1  is formed between the outer periphery of the flow path plate  44  (and the outer periphery of the frame member  43 ) and the inner periphery of the anode-side separator  34 . 
     A load applying mechanism  45  for pressing the cathode-side current collector  42  onto the solid polymer electrolyte membrane  38  is disposed between the cathode-side current collector  42  and the cathode-side separator  36 . The load applying mechanism  45  contains a disc spring  46 , and a load is applied to the cathode-side current collector  42  by a disc spring holder  47  on the disc spring  46 . A relatively large gap S 2  (&gt;the gap S 1 ) is formed between the outer periphery of the cathode-side current collector  42  (and the outer periphery of the disc spring holder  47 ) and the inner periphery of the cathode-side separator  36 . R-shaped portions are formed on corners facing the solid polymer electrolyte membrane  38  on the outer peripheries of the anode-side current collector  40  and the cathode-side current collector  42 . 
     As shown in  FIG. 3 , a first projection  48   a , a second projection  48   b , and a third projection  48   c , protruding outward in the separator surface direction, are formed on the outer periphery of the unit cell  12 . A water supply through hole  50   a  for supplying a water (pure water) as a first fluid is formed in the first projection  48   a  continuously in the arrow A direction (the stacking direction). 
     A discharge through hole  50   b  for discharging oxygen generated by a reaction and the used water is formed in the second projection  48   b  continuously in the arrow A direction. A hydrogen through hole  50   c  for transferring hydrogen (a second fluid) generated by the reaction is formed in the third projection  48   c  continuously in the arrow A direction (the stacking direction). 
     As shown in  FIGS. 3 and 4 , a supply passage  52   a  connected to the water supply through hole  50   a  and a discharge passage  52   b  connected to the discharge through hole  50   b  are formed in the anode-side separator  34 . A first flow path  54  is connected to the supply passage  52   a  and the discharge passage  52   b  on the surface  34   a  of the anode-side separator  34  facing the membrane-electrode assembly  32 . The first flow path  54  is formed within a region corresponding to the contact area of the anode-side current collector  40 . 
     A discharge passage  56  connected to the hydrogen through hole  50   c  is formed in the cathode-side separator  36 . A second flow path  58  is connected to the discharge passage  56  on a surface  36   a  of the cathode-side separator  36  (substantially the disc spring holder  47 ) facing the membrane-electrode assembly  32 . The second flow path  58  is formed within a region corresponding to the contact area of the cathode-side current collector  42 . 
     The peripheral edges of the anode-side separator  34  and the cathode-side separator  36  are integrated by sealants  60   a  and  60   b . The sealants  60   a  and  60   b  may contain a seal material, a cushion material, or a packing material of an EPDM, an NBR, a fluorine-containing rubber, a silicone rubber, a fluorosilicone rubber, a butyl rubber, a natural rubber, a styrene rubber, a chloroprene rubber, or an acrylic rubber, etc. 
     As shown in  FIGS. 3 and 4 , a second seal groove  64   a  is circularly formed outside the first flow path  54  and the anode-side current collector  40  on the surface  34   a  of the anode-side separator  34  facing the membrane-electrode assembly  32 , and a second sealant  62   a  is disposed therein. 
     A third seal groove  64   b , a fourth seal groove  64   c , and a fifth seal groove  64   d  are circularly formed outside the water supply through hole  50   a , the discharge through hole  50   b , and the hydrogen through hole  50   c  on the surface  34   a , and a third sealant  62   b , a fourth sealant  62   c , and a fifth sealant  62   d  are disposed therein. For example, the second sealant  62   a , the third sealant  62   b , the fourth sealant  62   c  and the fifth sealant  62   d  are O rings. 
     A first seal groove  68   a  is circularly formed outside the second flow path  58  and the cathode-side current collector  42  on the surface  36   a  of the cathode-side separator  36  facing the membrane-electrode assembly  32 , and a first sealant  66   a  is disposed therein. 
     A third seal groove  68   b , a fourth seal groove (fourth seal portion)  68   c , and a fifth seal groove  68   d  are circularly formed outside the water supply through hole  50   a , the discharge through hole  50   b , and the hydrogen through hole  50   c  on the surface  36   a , and a third sealant  66   b , a fourth sealant  66   c , and a fifth sealant  66   d  are disposed therein. For example, the first sealant  66   a  and the third sealant  66   b  to the fifth sealant  66   d  are O rings. 
     The circular second seal groove  64   a  around the anode-side current collector  40  and the circular first seal groove  68   a  around the cathode-side current collector  42  are formed in different positions in the stacking direction (the arrow A direction) with the solid polymer electrolyte membrane  38  interposed therebetween. 
     The circular fifth seal groove  64   d  and the circular fifth seal groove  68   d  around the hydrogen through hole  50   c  are formed in different positions in the arrow A direction with the solid polymer electrolyte membrane  38  interposed therebetween. 
     As shown in  FIGS. 1 and 2 , pipes  76   a ,  76   b , and  76   c  are connected to the water supply through hole  50   a , the discharge through hole  50   b , and the hydrogen through hole  50   c , respectively on the end plate  20   a . A back pressure valve or a solenoid valve (not shown) is formed in the pipe  76   c  to maintain the pressure of the hydrogen in the hydrogen through hole  50   c  at a high level. A clamping force is applied to the end plates  20   a  and  20   b  by a clamping force applying unit (not shown), and the end plates  20   a  and  20   b  are fastened by the tie rods  22  in this state. 
     The operation of the water electrolysis device  10  will be described below. 
     As shown in  FIG. 1 , the water is supplied from the pipe  76   a  to the water supply through hole  50   a  in the water electrolysis device  10 . A voltage is applied to the terminals  24   a  and  24   b  on the terminal plates  16   a  and  16   b  by the power source  28  electrically connected thereto. Then, as shown in  FIG. 3 , in each of the unit cells  12 , the water is supplied from the water supply through hole  50   a  to the first flow path  54  on the anode-side separator  34 , and is transferred along the anode-side current collector  40 . 
     The water is electrically decomposed on the anode catalyst layer  40   a  to generate hydrogen ions, electrons, and oxygen. The hydrogen ions generated by the positive electrode reaction are transferred through the solid polymer electrolyte membrane  38  to the cathode catalyst layer  42   a , and bonded with electrons to produce hydrogen. 
     Thus, the hydrogen flows through the second flow path  58  between the cathode-side separator  36  and the cathode-side current collector  42 . The pressure of the hydrogen is maintained higher than the pressure in the water supply through hole  50   a , whereby the hydrogen can be transferred in the hydrogen through hole  50   c  and discharged to the outside of the water electrolysis device  10 . Meanwhile, the oxygen generated by the reaction and the used water flow in the first flow path  54 , and are discharged from the discharge through hole  50   b  to the outside of the water electrolysis device  10 . 
     In the first embodiment, as shown in  FIG. 4 , at the cathode side, in which the high-pressure hydrogen is generated, the load applying mechanism  45  is disposed between the cathode-side current collector  42  and the cathode-side separator  36 . The contact area between the cathode-side current collector  42  and the solid polymer electrolyte membrane  38  is larger than that between the anode-side current collector  40  and the solid polymer electrolyte membrane  38 , and the contact areas of the cathode-side current collector  42  and the anode-side current collector  40  are larger than the areas of the cathode catalyst layer  42   a  and the anode catalyst layer  40   a  respectively. 
     Furthermore, the contact surface  40   b  between the anode-side current collector  40  having the smaller contact area and the solid polymer electrolyte membrane  38  protrudes toward the solid polymer electrolyte membrane  38  from the contact surface  34   a  of the anode-side separator  34  (and the contact surface  43   a  of the frame member  43 ). Therefore, when the cathode-side current collector  42  is pressed toward the anode-side current collector  40  by the load applying mechanism  45  and the high-pressure hydrogen, the pressing force of the cathode-side current collector  42  is not distributed to the contact surface  34   a  of the anode-side separator  34  and the contact surface  43   a  of the frame member  43 , and can be applied only to the contact surface  40   b  of the anode-side current collector  40 . 
     Thus, a desired surface pressure can be reliably applied by the anode-side current collector  40  and the cathode-side current collector  42  to the anode catalyst layer  40   a  and the cathode catalyst layer  42   a  formed on either side of the solid polymer electrolyte membrane  38 , whereby the electrolysis performance can be improved even in the simple structure. 
     In addition, the relatively large gap S 2  is formed between the outer periphery of the cathode-side current collector  42  and the inner periphery of the cathode-side separator  36 . Therefore, the load of the load applying mechanism (the disc spring  46 ) on the cathode-side current collector  42  can be applied only to the anode-side current collector  40 , and a displacement of the cathode-side current collector  42  can be absorbed. 
       FIG. 5  is an explanatory cross-sectional view of a unit cell  82  in a water electrolysis device  80  according to a second embodiment of the present invention. 
     The same components are marked with the same numerals in the unit cell  82  of the second embodiment and the unit cell  12  of the first embodiment, and detailed explanations thereof are omitted in the second embodiment. Also in a third embodiment to be hereinafter described, the detailed explanations are omitted. 
     The unit cell  82  contains an anode-side separator  86  and the cathode-side separator  36  sandwiching a membrane-electrode assembly  84 . In the membrane-electrode assembly  84 , the anode catalyst layer  40   a  and the cathode catalyst layer  42   a  are formed on either side of the solid polymer electrolyte membrane  38 , and the anode-side current collector  40  and the cathode-side current collector  42  are disposed thereon. 
     The anode-side current collector  40  is supported on the flow path plate  44  without forming the frame member on its outer periphery. The inner wall surface of the anode-side separator  86  is close to the outer peripheries of the anode-side current collector  40  and the flow path plate  44 . Thus, the anode-side separator  86  extends to a position corresponding to the first seal groove  68   a  on the cathode-side separator  36 . 
     In the second embodiment, the contact surface  40   b  of the anode-side current collector  40  having the smaller contact area protrudes toward the solid polymer electrolyte membrane  38  from the contact surface  34   a  of the anode-side separator  86 . Consequently, the advantageous effects in the first embodiment can be achieved also in the second embodiment. 
       FIG. 6  is an explanatory cross-sectional view of a unit cell  92  in a water electrolysis device  90  according to a third embodiment of the present invention. 
     The unit cell  92  contains the anode-side separator  34  and the cathode-side separator  36  sandwiching a membrane-electrode assembly  94 . In the membrane-electrode assembly  94 , the anode catalyst layer  40   a  and the cathode catalyst layer  42   a  are formed on either side of the solid polymer electrolyte membrane  38 , and an anode-side current collector  96  and a cathode-side current collector  98  are stacked thereon. 
     The contact surface  96   a  between the anode-side current collector  96  and the solid polymer electrolyte membrane  38  and the contact surface  34   a  of the anode-side separator  34  are in the same plane. The contact surface  98   a  between the cathode-side current collector  98  and the solid polymer electrolyte membrane  38  protrudes toward the solid polymer electrolyte membrane  38  from the contact surface  36   a  of the cathode-side separator  36 . 
     In third embodiment, the contact surface  98   a  of the cathode-side current collector  98  having the smaller contact area protrudes toward the solid polymer electrolyte membrane  38  from the contact surface  36   a  of the cathode-side separator  36 . Therefore, when the cathode-side current collector  98  is pressed toward the anode-side current collector  96  by the load applying mechanism  45 , the pressing force of the cathode-side current collector  98  can be applied only to the anode-side current collector  96 . 
     Thus, a desired surface pressure can be reliably applied to the anode catalyst layer  40   a  and the cathode catalyst layer  42   a  formed on either side of the solid polymer electrolyte membrane  38 . Consequently, the advantageous effects in the first and second embodiments can be achieved also in the third embodiment.