Patent Publication Number: US-2023143558-A1

Title: Membrane-electrode-gasket assembly for alkaline water electrolysis

Description:
This application is a Divisional of copending application Ser. No. 16/767,532 filed on May 27, 2020, which is the U.S. National Phase of PCT/JP2018/044311, filed on Nov. 30, 2018, and which claims priority under 35 U.S.C. § 119(a) to Application No. JP 2017-233704, filed in Japan on Dec. 5, 2017, the entire contents of all of which are expressly incorporated by reference into the present application. 
    
    
     TECHNICAL FIELD 
     The present invention relates to a gasket used for electrolysis vessels for alkaline water electrolysis, and more specifically to a membrane-electrode-gasket assembly for alkaline water electrolysis, and an electrolysis vessel for alkaline water electrolysis which includes the same. 
     BACKGROUND ART 
     The alkaline water electrolysis method is known as a method of producing hydrogen gas and oxygen gas. In the alkaline water electrolysis method, water is electrolyzed using a basic solution (alkaline water) in which an alkali metal hydroxide (such as NaOH and KOH) dissolves as an electrolytic solution, to generate hydrogen gas at a cathode and oxygen gas at an anode. As an electrolysis vessel for alkaline water electrolysis, an electrolysis vessel including an anode chamber where an anode is arranged and a cathode chamber where a cathode is arranged is known: the electrolysis vessel is partitioned into the anode chamber and the cathode chamber by an ionic-permeable separating membrane. Further proposed for reducing energy loss is an electrolysis vessel having a zero-gap configuration (zero-gap electrolysis vessel) which holds an anode and a cathode so that each of them is directly in contact with a separating membrane. 
     CITATION LIST 
     Patent Literature 
     Patent Literature 1: WO 2013/191140 
     Patent Literature 2: JP 2002-332586 A 
     Patent Literature 3: JP 4453973 B 
     Patent Literature 4 WO 2014/178317 
     Patent Literature 5 JP 6093351 B 
     Patent Literature 6: JP 2015-117417 A 
     SUMMARY OF INVENTION 
     Technical Problem 
       FIG.  1    is a schematically explanatory partial cross-sectional view of a conventional zero-gap electrolysis vessel  900  according to one embodiment. The zero-gap electrolysis vessel  900  includes electrode chamber units  910 ,  910 , . . . each including an electroconductive separating wall  911  that separates an anode chamber A and a cathode chamber C, and a flange part  912 ; an ionic-permeable separating membrane  920  arranged between adjacent electrode chamber units  910 ,  910 ; gaskets  930 ,  930  each arranged between the separating membrane  920  and the flange parts  912  of the electrode chamber units  910 , between which the periphery of the separating membrane  920  is sandwiched; an anode  940  held by electroconductive ribs  913 ,  913 , . . . that are provided to stand at the separating wall  911  of one electrode chamber unit; and a flexible cathode  970  held by a current collector  950  that is held by electroconductive ribs  914 ,  914 , . . . that are provided to stand at the separating wall  911  of the other electrode chamber unit, and an electroconductive elastic body  960  that is arranged in contact with the current collector  950 . The periphery of the cathode  970  and the periphery of the electroconductive elastic body  960  are fixed to the periphery of the current collector  950 . In the zero-gap electrolysis vessel  900 , the electroconductive elastic body  960  pushes the flexible cathode  970  toward the separating membrane  920  and the anode  940 , which makes the separating membrane  920  sandwiched between adjacent cathode  970  and anode  940 . As a result, the separating membrane  920  is in direct contact with the anode  940  and the cathode  970  (that is, zero-gap), which reduces the solution resistance between the anode  940  and the cathode  970 , and thus reduces energy loss. 
     As shown in  FIG.  1   , however, the separating membrane  920  is not in direct contact with the anode  940  and the cathode  970  (that is, non zero-gap) along the periphery thereof, that is, in the vicinity of the flange part  912  (or the gasket  930 ), which leads to a large solution resistance between the electrodes along this portion, and as a result leads to an increased operating voltage. 
     An object of the present invention is to provide a membrane-electrode-gasket assembly for alkaline water electrolysis which makes it possible for a separating membrane to be in direct contact with electrodes even along its periphery. The present invention also provides an electrolysis vessel for alkaline water electrolysis which includes the membrane-electrode-gasket assembly. 
     Solution to Problem 
     The present invention encompasses the following embodiments [1] to [14]: 
     [1] A membrane-electrode-gasket assembly for alkaline water electrolysis, the assembly comprising: 
     a separating membrane having a first membrane face and a second membrane face; 
     a first electrode arranged in contact with the first membrane face; and 
     an insulating gasket holding the separating membrane and the first electrode as one body; 
     the gasket comprising:
         a first face for contacting with an anode-side frame;   a second face for contacting with a cathode-side frame;   a slit part opening toward an inner peripheral side of the gasket and receiving an entire periphery of the separating membrane and an entire periphery of the first electrode;   a first part and a second part, the first part and the second part facing each other across the slit part in a direction crossing the first face and the second face, the first part having the first face and the second part having the second face; and   a continuous part arranged on an outer peripheral side of the slit part, the continuous part uniting the first part and the second part into one body and sealing an outer peripheral end of the slit part,       

     wherein the first part and the second part sandwich therebetween the entire periphery of the separating membrane and the entire periphery of the first electrode, to hold the entire periphery of the separating membrane and the entire periphery of the first electrode as one body. 
     [2] The membrane-electrode-gasket assembly according to [1], 
     wherein the first electrode is a flexible first porous plate. 
     [3] The membrane-electrode-gasket assembly according to [1] or [2], further comprising: 
     a second electrode arranged in contact with the second membrane face of the separating membrane, 
     wherein the gasket holds the separating membrane, the first electrode, and the second electrode as one body; 
     the slit part receives the entire periphery of the separating membrane, the entire periphery of the first electrode, and the entire periphery of the second electrode; and 
     the first part and the second part sandwich therebetween the entire periphery of the separating membrane, the entire periphery of the first electrode, and the entire periphery of the second electrode, to hold the entire periphery of the separating membrane, the entire periphery of the first electrode, and the entire periphery of the second electrode as one body. 
     [4] The membrane-electrode-gasket assembly according to [3], 
     wherein the second electrode is a rigid porous plate. 
     [5] The membrane-electrode-gasket assembly according to [3], 
     wherein the second electrode is a flexible second porous plate. 
     [6] An electrolysis vessel for alkaline water electrolysis, the electrolysis vessel comprising: 
     an anode-side frame defining an anode chamber; 
     a cathode-side frame defining a cathode chamber; 
     the membrane-electrode-gasket assembly as in [1] or [2], wherein the anode-side frame and the cathode-side frame sandwich therebetween the assembly, to hold the assembly; 
     a second electrode arranged in contact with the second membrane face of the separating membrane, wherein the second electrode is not held by the gasket, 
     wherein the assembly is arranged such that the first membrane face of the separating membrane faces the anode chamber and the second membrane face of the separating membrane faces the cathode chamber; 
     the first electrode is an anode; and 
     the second electrode is a cathode. 
     [7] An electrolysis vessel for alkaline water electrolysis, the electrolysis vessel comprising: 
     an anode-side frame defining an anode chamber; 
     a cathode-side frame defining a cathode chamber; 
     the membrane-electrode-gasket assembly as in [1] or [2], wherein the anode-side frame and the cathode-side frame sandwich therebetween the assembly, to hold the assembly; 
     a second electrode arranged in contact with the second membrane face of the separating membrane, wherein the second electrode is not held by the gasket, 
     wherein the assembly is arranged such that the first membrane face of the separating membrane faces the cathode chamber and the second membrane face of the separating membrane faces the anode chamber; 
     the first electrode is a cathode; and 
     the second electrode is an anode. 
     [8] An electrolysis vessel for alkaline water electrolysis, the electrolysis vessel comprising: 
     an anode-side frame defining an anode chamber; 
     a cathode-side frame defining a cathode chamber; 
     the membrane-electrode-gasket assembly as in any one of [3] to [5], wherein the anode-side frame and the cathode-side frame sandwich therebetween the assembly, to hold the assembly, 
     wherein the assembly is arranged such that the first membrane face of the separating membrane faces the anode chamber and the second membrane face of the separating membrane faces the cathode chamber; 
     the first electrode is an anode; and 
     the second electrode is a cathode. 
     [9] An electrolysis vessel for alkaline water electrolysis, the electrolysis vessel comprising: 
     an anode-side frame defining an anode chamber; 
     a cathode-side frame defining a cathode chamber; 
     the membrane-electrode-gasket assembly as in any one of [3] to [5], wherein the anode-side frame and the cathode-side frame sandwich therebetween the assembly, to hold the assembly, 
     wherein the assembly is arranged such that the first membrane face of the separating membrane faces the cathode chamber and the second membrane face of the separating membrane faces the anode chamber; 
     the first electrode is a cathode; and 
     the second electrode is an anode. 
     [10] The electrolysis vessel according to any one of [6] to [9], further comprising: 
     an electroconductive first elastic body pushing the first electrode toward the second electrode, 
     wherein the first electrode is a flexible first porous plate. 
     [11] The electrolysis vessel according to [10], 
     wherein the second electrode is a rigid porous plate. 
     [12] The electrolysis vessel according to [11], further comprising: 
     an electroconductive second elastic body pushing the second electrode toward the first electrode. 
     [13] The electrolysis vessel according to [10], further comprising: 
     an electroconductive second elastic body pushing the second electrode toward the first electrode, wherein the second electrode is a flexible second porous plate. 
     [14] The electrolysis vessel according to [10], further comprising: 
     an electroconductive rigid current collector arranged in contact with the second electrode, 
     wherein the rigid current collector is arranged such that the rigid current collector and the separating membrane sandwich therebetween the second electrode; 
     the second electrode is a flexible second porous plate; and 
     the second electrode is supported by the rigid current collector. 
     Advantageous Effects of Invention 
     The membrane-electrode-gasket assembly for alkaline water electrolysis of the present invention makes it possible for a separating membrane to be in direct contact with (an) electrode(s) even along its periphery. Thus, an electrolysis vessel for alkaline water electrolysis which includes the membrane-electrode-gasket assembly for alkaline water electrolysis of the present invention can further reduce an operating voltage, which makes it possible to further reduce energy loss. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG.  1    is a schematically explanatory cross-sectional view of the conventional zero-gap electrolysis vessel  900  according to one embodiment. 
         FIGS.  2 (A),  2 (B),  2 (C),  2 (D) and  2 (E)  are schematically explanatory views of a membrane-electrode-gasket assembly for alkaline water electrolysis  100  according to one embodiment of the present invention:  FIG.  2 (A)  is a front view;  FIG.  2 (B)  is a right side view;  FIG.  2 (C)  is a rear view;  FIG.  2 (D)  is a cross-sectional view taken along the line X-X of  FIG.  2 (A) ; and  FIG.  2 (E)  is an exploded view of  FIG.  2 (D) . 
         FIGS.  3 (A),  3 (B),  3 (C),  3 (D) and  3 (E)  are schematically explanatory views of a membrane-electrode-gasket assembly for alkaline water electrolysis  200  according to another embodiment of the present invention:  FIG.  3 (A)  is a front view;  FIG.  3 (B)  is a right side view;  FIG.  3 (C)  is a rear view;  FIG.  3 (D)  is a cross-sectional view taken along the line X-X of  FIG.  3 (A) ; and  FIG.  3 (E)  is an exploded view of  FIG.  3 (D) . 
         FIGS.  4 (A),  4 (B),  4 (C),  4 (D) and  4 (E)  are schematically explanatory views of a membrane-electrode-gasket assembly for alkaline water electrolysis  300  according to another embodiment of the present invention:  FIG.  4 (A)  is a front view;  FIG.  4 (B)  is a right side view;  FIG.  4 (C)  is a rear view;  FIG.  4 (D)  is a cross-sectional view taken along the line X-X of  FIG.  4 (A) ; and  FIG.  4 (E)  is an exploded view of  FIG.  4 (D) . 
         FIG.  5    is a schematically explanatory cross-sectional view of an electrolysis vessel for alkaline water electrolysis  1000  according to one embodiment of the present invention. 
         FIG.  6    is a schematically explanatory cross-sectional view of an electrolysis vessel for alkaline water electrolysis  2000  according to another embodiment of the present invention. 
         FIG.  7    is a schematically explanatory cross-sectional view of an electrolysis vessel for alkaline water electrolysis  3000  according to another embodiment of the present invention. 
         FIG.  8    is a schematically explanatory cross-sectional view of an electrolysis vessel for alkaline water electrolysis  4000  according to another embodiment of the present invention. 
         FIG.  9    is a schematically explanatory cross-sectional view of an electrolysis vessel for alkaline water electrolysis  5000  according to another embodiment of the present invention. 
         FIG.  10    is a schematically explanatory cross-sectional view of an electrolysis vessel for alkaline water electrolysis  6000  according to another embodiment of the present invention. 
         FIG.  11    is a schematically explanatory cross-sectional view of an electrolysis vessel for alkaline water electrolysis  7000  according to another embodiment of the present invention. 
         FIG.  12    is a schematically explanatory cross-sectional view of an electrolysis vessel for alkaline water electrolysis  8000  according to another embodiment of the present invention. 
         FIG.  13    is a schematically explanatory cross-sectional view of an electrolysis vessel for alkaline water electrolysis  9000  according to another embodiment of the present invention. 
         FIG.  14    is a schematically explanatory cross-sectional view of an electrolysis vessel for alkaline water electrolysis  10000  according to another embodiment of the present invention. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     The above described operations and advantages of the present invention will be made clear from the following description of the embodiments. Hereinafter the embodiments of the present invention will be described with reference to the drawings. The present invention is not limited to these embodiments. The measures in the drawings do not always represent exact measures. Some reference signs may be omitted in the drawings. In the present description, expression “A to B” concerning numeral values A and B means “no less than A and no more than B” unless otherwise specified. In such expression, if a unit is added only to the numeral value B, this unit is applied to the numeral value A as well. A word “or” means a logical sum unless otherwise specified. Expression “E 1  and/or E 2 ” concerning elements E 1  and E 2  means “E 1 , or E 2 , or the combination thereof”, and expression “E 1 , . . . , E N-1 , and/or E N ” concerning elements E 1 , . . . , E N  (N is an integer of 3 or more) means “E 1 , . . . , E N-1 , or E N , or any combination thereof”. 
     &lt;1. Membrane-Electrode-Gasket Assembly for Alkaline Water Electrolysis&gt; 
       FIGS.  2 (A),  2 (B),  2 (C),  2 (D) and  2 (E)  are schematically explanatory views of the membrane-electrode-gasket assembly for alkaline water electrolysis  100  according to one embodiment of the present invention (hereinafter may be referred to as “assembly  100 ”).  FIGS.  2 (A) to  2 (C)  are respectively a front view, a right side view, and a rear view of the assembly  100 ,  FIG.  2 (D)  is a cross-sectional view taken along the line X-X of  FIG.  2 (A) , and  FIG.  2 (E)  is an exploded view of  FIG.  2 (D) . The assembly  100  includes a separating membrane  10  having a first membrane face  11  and a second membrane face  12 ; a cathode (first electrode)  20  arranged in contact with the first membrane face  11 ; and an insulating gasket  30  holding the separating membrane  10  and the cathode (first electrode)  20  as one body. The gasket  30  includes a first face  31  for contacting with an anode-side frame; a second face  32  for contacting with a cathode-side frame; a slit part  33  opening toward an inner peripheral side of the gasket  30  and receiving the entire periphery of the separating membrane  10  and the entire periphery of the cathode (first electrode)  20 ; a first part  34  and a second part  35 , the first part  34  and the second part  35  facing each other across the slit part  33  in a direction crossing the first face  31  and the second face  32  (vertical direction of  FIGS.  2 (D) and  2 (E)  on the sheet), the first part  34  having the first face  31  and the second part  35  having the second face  32 ; and a continuous part  36  arranged on an outer peripheral side of the slit part  33 , the continuous part  36  uniting the first part  34  and the second part  35  into one body and sealing an outer peripheral end of the slit part  33 . In the assembly  100 , the first part  34  and the second part  35  sandwich therebetween the entire periphery of the separating membrane  10  and the entire periphery of the cathode (first electrode)  20 , to hold the entire periphery of the separating membrane  10  and the entire periphery of the cathode (first electrode)  20  as one body. As shown in  FIGS.  2 (A),  2 (C) and  2 (D) , the cathode (first electrode)  20  is arranged on the same side as the second face  32  of the gasket  30  with respect to the separating membrane  10 . A cross-sectional view taken along the line Y-Y of  FIG.  2 (A)  is the same as the cross-sectional view taken along the line X-X of  FIG.  2 (A) , that is,  FIG.  2 (D) . 
     As the separating membrane  10 , any known ionic-permeable separating membrane used for zero-gap electrolysis vessels for alkaline water electrolysis may be used without particular limitations. The separating membrane  10  desirably has low gas permeability, low electric conductivity, and high strength. Examples of the separating membrane  10  include porous separating membranes such as porous membranes formed of asbestos and/or modified asbestos, porous separating membranes using a polysulfone-based polymer, cloths using a polyphenylene sulfide fiber, fluorinated porous membranes, and porous membranes using a hybrid material that includes both inorganic and organic materials. Other than these porous separating membranes, an ion-exchange membrane such as a fluorinated ion-exchange membrane may be used as the separating membrane  10 . 
     As the cathode (first electrode)  20 , any known cathode for generating hydrogen which is used for zero-gap electrolysis vessels for alkaline water electrolysis may be used without particular limitations. The cathode  20  usually includes an electroconductive base material, and a catalyst layer covering the surface of the base material. As the electroconductive base material of the cathode  20 , for example, nickel, a nickel alloy, stainless steel, mild steel, a nickeled nickel alloy, nickeled stainless steel, or nickeled mild steel may be preferably employed. As the catalyst layer of the cathode  20 , a noble metal oxide, nickel, cobalt, molybdenum, or manganese, or a coating formed of an oxide or a noble metal oxide thereof may be preferably employed. The cathode  20  may be, for example, a flexible porous plate, and may be, for example, a rigid porous plate. As the cathode  20  of a rigid porous plate, a porous plate including a rigid electroconductive base material (such as an expanded metal) and the above described catalyst layer may be used. As the cathode  20  of a flexible porous plate, a porous plate including a flexible electroconductive base material (such as gauze woven (or knitted) out of metal wire, and a thin punching metal) and the above described catalyst layer may be used. The area of one hole of the cathode  20  of a flexible porous plate is preferably 0.05 to 2.0 mm 2 , and more preferably 0.1 to 0.5 mm 2 . The ratio of the area of holes of the cathode  20  of a flexible porous plate to the area of a current-carrying cross section is preferably no less than 20%, and more preferably 20 to 50%. The bending flexibility of the cathode  20  of a flexible porous plate is preferably no less than 0.05 mm/g, and more preferably 0.1 to 0.8 mm/g. Bending flexibility in the present description is represented by a value obtained in such a way that: one side of a square sample of 10 mm in length x 10 mm in width is fixed so that the sample is horizontal, and a deflection (mm) of another side (end of the sample) when a given load is downwardly applied to the other side, which is opposite to the fixed side, is divided by the load (g). That is, the bending flexibility is a parameter showing an inverse characteristics to bending rigidity. The bending flexibility may be adjusted by a material and thickness of a porous plate, and in the case of gauze, by a way of weaving (or knitting) metal wire constituting the gauze etc. 
     The gasket  30  has, as shown in  FIGS.  2 (A) and  2 (C) , a shape corresponding to the shapes of the anode-side frame and the cathode-side frame. As shown in  FIGS.  2 (B),  2 (D) , and  2 (E), the first face  31  and the second face  32  of the gasket  30  are flat faces. The gasket  30  is preferably formed of an alkali-resistant elastomer. Examples of the material of the gasket  30  include elastomers such as natural rubber (NR), styrene-butadiene rubber (SBR), polychloroprene (CR), butadiene rubber (BR), acrylonitrile-butadiene rubber (NBR), silicone rubber (SR), ethylene propylene rubber (EPT), ethylene propylene diene monomer rubber (EPDM), fluoro rubber (FR), isobtylene isoprene rubber (IIR), urethane rubber (UR), and chlorosulfonated polyethylene rubber (CSM). When a gasket material that does not have alkali resistance is used, a layer of an alkali-resistant material may be provided for the surface of the gasket material by coating or the like. 
     The method of producing the assembly  100  is not particularly limited. For example, the peripheries of the separating membrane  10  and the cathode  20  are sandwiched between a gasket member on the anode side which includes the first face  31 , and a gasket member on the cathode side which includes the second face  32 , and thereafter the periphery of the gasket member on the anode side and the periphery of the gasket member on the cathode side are united into one body by welding, adhering, or the like, which makes it possible to obtain the assembly  100  where the slit part  33  of the gasket  30  that includes the slit part  33  and the continuous part  36  holds the peripheries of the separating membrane  10  and the cathode  20  (see  FIGS.  2 (D) and  2 (E) ). For example, one may separately prepare the separating membrane  10 , the cathode  20 , and the gasket  30 , and thereafter may insert the peripheries of the separating membrane  10  and the cathode  20  into the slit part  33  of the gasket  30  as temporarily changing the shape of the gasket  30 . 
     In the membrane-electrode-gasket assembly for alkaline water electrolysis  100 , the entire periphery of the separating membrane  10  and the entire periphery of the cathode  20 , which are received in the slit part  33  of the gasket  30 , are sandwiched between and held by the first part  34  and the second part  35  of the gasket  30  as one body, which makes it possible for at least the separating membrane  10  and the cathode  20  to be in direct contact with each other all over the faces thereof (that is, even the periphery). Thus, employing the assembly  100  for a zero-gap electrolysis vessel for alkaline water electrolysis offers further reduced operating voltage and energy loss. In conventional zero-gap electrolysis vessels, each electrode is fixed to an electrolysis element (anode-side frame or cathode-side frame), and measures such as welding and pinning are necessary for fixing electrodes. In contrast, according to the assembly  100 , since the cathode  20  is united with the separating membrane  10  and the gasket  30  into one body, there is no need to fix the cathode  20  to the cathode-side frame. Therefore, employing the assembly  100  for a zero-gap electrolysis vessel for alkaline water electrolysis offers easy assembly of the electrolysis vessel. Further, while the slit part  33  of the gasket  30  receives the periphery of the separating membrane  10 , the gasket  30  includes the continuous part  36  sealing the outer peripheral end of the slit part  33  on the outer peripheral side of the slit part  33 , which makes it possible for capillary action to prevent an electrolytic solution and gas from leaking from an end part of the separating membrane  10  to the outside of the electrolysis vessel. 
     In the foregoing description concerning the present invention, the assembly  100  of the embodiment of including the separating membrane  10 , the cathode  20 , and the gasket  30  has been described as an example. The present invention is not limited to this embodiment. For example, an embodiment of a membrane-electrode-gasket assembly for alkaline water electrolysis may comprise an anode instead of the cathode  20 . 
       FIGS.  3 (A),  3 (B),  3 (C),  3 (D) and  3 (E)  are schematically explanatory views of a membrane-electrode-gasket assembly for alkaline water electrolysis  200  according to such another embodiment (hereinafter may be referred to as “assembly  200 ”).  FIGS.  3 (A) to  3 (C)  are respectively a front view, a right side view, and a rear view of the assembly  200 ,  FIG.  3 (D)  is a cross-sectional view taken along the line X-X of  FIG.  3 (A) ; and  FIG.  3 (E)  is an exploded view of  FIG.  3 (D) . In  FIGS.  3 (A) to  3 (E) , elements already shown in  FIGS.  2 (A) to  2 (E)  are given the same reference signs as in  FIGS.  2 (A) to  2 (E) , and the descriptions thereof may be omitted. The assembly  200  includes the separating membrane  10  having the first membrane face  11  and the second membrane face  12 ; an anode (first electrode)  40  arranged in contact with the first membrane face  11 ; and the insulating gasket  30  holding the separating membrane  10  and the anode (first electrode)  40  as one body. The gasket  30  includes the first face  31  for contacting with the anode-side frame; the second face  32  for contacting with the cathode-side frame; the slit part  33  opening toward the inner peripheral side of the gasket  30  and receiving the entire periphery of the separating membrane  10  and the entire periphery of the anode (first electrode)  40 ; the first part  34  and the second part  35 , the first part  34  and the second part  35  facing each other across the slit part  33  in the direction crossing the first face  31  and the second face  32 , the first part  34  having the first face  31  and the second part  35  having the second face  32 ; and the continuous part  36  arranged on the outer peripheral side of the slit part  33 , the continuous part  36  uniting the first part  34  and the second part  35  into one body and sealing the outer peripheral end of the slit part  33 . In the assembly  200 , the first part  34  and the second part  35  sandwich therebetween the entire periphery of the separating membrane  10  and the entire periphery of the anode (first electrode)  40 , to hold the entire periphery of the separating membrane  10  and the entire periphery of the anode (first electrode)  40  as one body. As shown in  FIGS.  3 (A),  3 (C) and  3 (D) , the anode (first electrode)  40  is arranged on the same side as the first face  31  of the gasket  30  with respect to the separating membrane  10 . A cross-sectional view taken along the line Y-Y of  FIG.  3 (A)  is the same as the cross-sectional view taken along the line X-X of  FIG.  3 (A) , that is,  FIG.  3 (D) . 
     The separating membrane  10  and the gasket  30  in the assembly  200  are the same as the separating membrane  10  and the gasket  30  in the assembly  100 . As the anode (first electrode)  40 , any known anode for generating oxygen which is used for zero-gap electrolysis vessels for alkaline water electrolysis may be used without particular limitations. The anode  40  usually includes an electroconductive base material, and a catalyst layer covering the surface of the base material. The catalyst layer is preferably porous. As the electroconductive base material of the anode  40 , for example, ferronickel, vanadium, molybdenum, copper, silver, manganese, platinum group metals, graphite, or chromium, or any combination thereof may be used. In the anode  40 , an electroconductive base material formed of nickel may be preferably used. The catalyst layer includes nickel as an element. The catalyst layer preferably includes nickel oxide, metallic nickel or nickel hydroxide, or any combination thereof, and may include an alloy of nickel and at least one other metal. The catalyst layer is especially preferably formed of metallic nickel. The catalyst layer may further include chromium, molybdenum, cobalt, tantalum, zirconium, aluminum, zinc, platinum group metals, or rare earth elements, or any combination thereof. Rhodium, palladium, iridium, or ruthenium, or any combination thereof may be further supported on the surface of the catalyst layer as an additional catalyst. The anode  40  may be, for example, a flexible porous plate, and may be, for example, a rigid porous plate. As the anode  40  of a rigid porous plate, a porous plate including a rigid electroconductive base material (such as an expanded metal) and the above described catalyst layer may be used. As the anode  40  of a flexible porous plate, a porous plate including a flexible electroconductive base material (such as gauze woven (or knitted) out of metal wire, and a thin punching metal) and the above described catalyst layer may be used. The ratio of the area of holes of the anode  40  of a flexible porous plate is preferably 0.05 to 2.0 mm 2 , and more preferably 0.1 to 0.5 mm 2 . The ratio of the area of holes of the anode  40  of a flexible porous plate to the area of a current-carrying cross section is preferably no less than 20%, and more preferably 20 to 50%. The bending flexibility of the anode  40  of a flexible porous plate is preferably no less than 0.05 mm/g, and more preferably 0.1 to 0.8 mm/g. 
     The method of producing the assembly  200  is not particularly limited. For example, the peripheries of the separating membrane  10  and the anode  40  are sandwiched between a gasket member on the anode side which includes the first face  31 , and a gasket member on the cathode side which includes the second face  32 , and thereafter the periphery of the gasket member on the anode side and the periphery of the gasket member on the cathode side are united into one body by welding, adhering, or the like, which makes it possible to obtain the assembly  200  where the slit part  33  of the gasket  30  that includes the slit part  33  and the continuous part  36  holds the peripheries of the separating membrane  10  and the anode  40  (see  FIGS.  3 (D) and  3 (E) ). For example, one may separately prepare the separating membrane  10 , the anode  40 , and the gasket  30 , and thereafter may insert the peripheries of the separating membrane  10  and the anode  40  into the slit part  33  of the gasket  30  as temporarily changing the shape of the gasket  30 . 
     In the membrane-electrode-gasket assembly for alkaline water electrolysis  200 , the entire periphery of the separating membrane  10  and the entire periphery of the anode  40 , which are received in the slit part  33  of the gasket  30 , are sandwiched between and held by the first part  34  and the second part  35  of the gasket  30  as one body, which makes it possible for at least the separating membrane  10  and the anode  40  to be in direct contact with each other all over the faces thereof (that is, even the periphery). Thus, employing the assembly  200  for a zero-gap electrolysis vessel for alkaline water electrolysis offers further reduced operating voltage and energy loss. In conventional zero-gap electrolysis vessels, each electrode is fixed to an electrolysis element (anode-side frame or cathode-side frame), and measures such as welding and pinning are necessary for fixing electrodes. In contrast, according to the assembly  200 , since the anode  40  is united with the separating membrane  10  and the gasket  30  into one body, there is no need to fix the anode  40  to the anode-side frame. Therefore, employing the assembly  200  for a zero-gap electrolysis vessel for alkaline water electrolysis offers easy assembly of the electrolysis vessel. Further, while the slit part  33  of the gasket  30  receives the periphery of the separating membrane  10 , the gasket  30  includes the continuous part  36  sealing the outer peripheral end of the slit part  33  on the outer peripheral side of the slit part  33 , which makes it possible for capillary action to prevent an electrolytic solution and gas from leaking from an end part of the separating membrane  10  to the outside of the electrolysis vessel. 
     In the foregoing description concerning the present invention, the assembly  100  of the embodiment of including the separating membrane  10 , the cathode  20  and the gasket  30 , and the assembly  200  of the embodiment of including the separating membrane  10 , the anode  40  and the gasket  30  have been described as an example. The present invention is not limited to these embodiments. For example, an embodiment of a membrane-electrode-gasket assembly for alkaline water electrolysis may comprise both of a cathode and an anode. 
       FIGS.  4 (A),  4 (B),  4 (C),  4 (D) and  4 (E)  are schematically explanatory views of a membrane-electrode-gasket assembly for alkaline water electrolysis  300  according to such another embodiment (hereinafter may be referred to as “assembly  300 ”).  FIGS.  4 (A) to  4 (C)  are respectively a front view, a right side view, and a rear view of the assembly  300 ,  FIG.  4 (D)  is a cross-sectional view taken along the line X-X of  FIG.  4 (A) ; and  FIG.  4 (E)  is an exploded view of  FIG.  4 (D) . In  FIGS.  4 (A) to  4 (E) , elements already shown in  FIGS.  2 (A) to  2 (E) and  3 (A) to  3 (E)  are given the same reference signs as in  FIGS.  2 (A) to  2 (E) and  3 (A) to  3 (E) , and the description thereof may be omitted. The assembly  300  includes the separating membrane  10  having the first membrane face  11  and the second membrane face  12 ; the anode (first electrode)  40  arranged in contact with the first membrane face  11 ; the cathode (second electrode)  20  arranged in contact with the second membrane face  12 ; and the insulating gasket  30  holding the separating membrane  10 , the anode (first electrode)  40 , and the cathode (second electrode)  20  as one body. The gasket  30  includes the first face  31  for contacting with the anode-side frame; the second face  32  for contacting with the cathode-side frame; the slit part  33  opening toward the inner peripheral side of the gasket  30  and receiving the entire periphery of the separating membrane  10  and the entire periphery of the anode (first electrode)  40  and the entire periphery of the cathode (second electrode)  20 ; the first part  34  and the second part  35 , the first part  34  and the second part  35  facing each other across the slit part  33  in the direction crossing the first face  31  and the second face  32  (vertical direction of  FIGS.  4 (D) and  4 (E)  on the sheet), the first part  34  having the first face  31  and the second part  35  having the second face  32 ; and the continuous part  36  arranged on the outer peripheral side of the slit part  33 , the continuous part  36  uniting the first part  34  and the second part  35  into one body and sealing the outer peripheral end of the slit part  33 . In the assembly  300 , the first part  34  and the second part  35  sandwich therebetween the entire periphery of the separating membrane  10 , the entire periphery of the anode (first electrode)  40 , and the entire periphery of the cathode (second electrode)  20 , to hold the entire periphery of the separating membrane  10 , the entire periphery of the anode (first electrode)  40 , and the entire periphery of the cathode (second electrode)  20  as one body. As shown in  FIGS.  4 (A),  4 (C) and  4 (D) , the anode (first electrode)  40  is arranged on the same side as the first face  31  of the gasket  30  with respect to the separating membrane  10 , and the cathode (second electrode)  20  is arranged on the same side as the second face  32  of the gasket  30  with respect to the separating membrane  10 . A cross-sectional view taken along the line Y-Y of  FIG.  4 (A)  is the same as the cross-sectional view taken along the line X-X of  FIG.  4 (A) , that is,  FIG.  4 (D) . 
     The separating membrane  10 , the anode  40 , the cathode  20 , and the gasket  30  in the assembly  300  are respectively the same as the separating membrane  10 , the anode  40 , the cathode  20 , and the gasket  30  in the assemblies  100  and  200 . 
     The method of producing the assembly  300  is not particularly limited. For example, the peripheries of the anode  40 , the separating membrane  10 , and the cathode  20  are sandwiched between a gasket member on the anode side which includes the first face  31 , and a gasket member on the cathode side which includes the second face  32 , and thereafter the periphery of the gasket member on the anode side and the periphery of the gasket member on the cathode side are united into one body by welding, adhering, or the like, which makes it possible to obtain the assembly  300  where the slit part  33  of the gasket  30  that includes the slit part  33  and the continuous part  36  holds the peripheries of the anode  40 , the separating membrane  10 , and the cathode  20  (see  FIGS.  4 (D) and  4 (E) ). For example, one may separately prepare the separating membrane  10 , the anode  40 , the cathode  20 , and the gasket  30 , and thereafter may insert the peripheries of the separating membrane  10 , the anode  40 , and the cathode  20  into the slit part  33  of the gasket  30  as temporarily changing the shape of the gasket  30 . 
     In the membrane-electrode-gasket assembly for alkaline water electrolysis  300 , the entire periphery of the separating membrane  10 , the entire periphery of the anode  40 , and the entire periphery of the cathode  20 , which are received in the slit part  33  of the gasket  30 , are sandwiched between and held by the first part  34  and the second part  35  of the gasket  30  as one body, which makes it possible for the anode  40  and the separating membrane  10  to be in direct contact with each other all over the faces thereof (that is, even the periphery), and for the separating membrane  10  and the cathode  20  to be in direct contact with each other all over the faces thereof (that is, even the periphery). Thus, employing the assembly  300  for a zero-gap electrolysis vessel for alkaline water electrolysis offers further reduced operating voltage and energy loss. In conventional zero-gap electrolysis vessels, each electrode is fixed to an electrolysis element (anode-side frame or cathode-side frame), and measures such as welding and pinning are necessary for fixing electrodes. In contrast, according to the assembly  300 , since the anode  40  and the cathode  20  are united with the separating membrane  10  and the gasket  30  into one body, there is no need to fix the anode  40  to the anode-side frame, and there is no need to fix the cathode  20  to the cathode-side frame either. Therefore, employing the assembly  300  for a zero-gap electrolysis vessel for alkaline water electrolysis offers easy assembly of the electrolysis vessel. Further, while the slit part  33  of the gasket  30  receives the periphery of the separating membrane  10 , the gasket  30  includes the continuous part  36  sealing the outer peripheral end of the slit part  33  on the outer peripheral side of the slit part  33 , which makes it possible for capillary action to prevent an electrolytic solution and gas from leaking from an end part of the separating membrane  10  to the outside of the electrolysis vessel. 
     In the foregoing description concerning the present invention, the assemblies  100 ,  200 , and  300  of the embodiment of including the quadrangular gasket  30  have been described as an example. The present invention is not limited to this embodiment. For example, an embodiment of a membrane-electrode-gasket assembly for alkaline water electrolysis may include a gasket having an annular shape, or a polygonal shape other than a quadrangular shape (such as a hexagonal or octagonal shape). The shapes of the separating membrane, the cathode, and the anode are determined according to the shape of the gasket. 
     &lt;2. Electrolysis Vessel for Alkaline Water Electrolysis&gt; 
       FIG.  5    is a schematically explanatory cross-sectional view of an electrolysis vessel for alkaline water electrolysis  1000  according to one embodiment of the present invention (hereinafter may be referred to as “electrolysis vessel  1000 ”). The electrolysis vessel  1000  is an electrolysis vessel for alkaline water electrolysis which includes the above described membrane-electrode-gasket assembly  100  (see  FIGS.  2 (A) to  2 (E) ). As shown in  FIG.  5   , the electrolysis vessel  1000  includes an electroconductive anode-side frame  51  defining an anode chamber A; an electroconductive cathode-side frame  52  defining a cathode chamber C; the assembly  100  sandwiched between and held by the anode-side frame  51  and the cathode-side frame  52  so that the anode-side frame  51  is in contact with the first face  31  and the cathode-side frame  52  is in contact with the second face  32 ; and an anode (second electrode)  41  arranged in contact with the second membrane face  12  of the separating membrane  10 , wherein the anode  41  is not held by the gasket  30 . In the electrolysis vessel  1000 , the assembly  100  is arranged so that the first membrane face  11  of the separating membrane  10  faces the cathode chamber C, and the second membrane face  12  of the separating membrane  10  faces the anode chamber A. In the electrolysis vessel  1000 , the cathode (first electrode)  20  is a flexible porous plate (first porous plate), and the anode (second electrode)  41  is a rigid porous plate (second porous plate). The electrolysis vessel  1000  further includes electroconductive ribs  61 ,  61 , . . . (hereinafter may be referred to as “electroconductive rib  61 ”) that are provided so as to stick out from the inner wall of the anode-side frame  51 . The anode  41  is held by the electroconductive rib  61 . The electrolysis vessel  1000  also includes electroconductive ribs  62 ,  62  . . . (hereinafter may be referred to as “electroconductive rib  62 ”) that are provided so as to stick out from the inner wall of the cathode-side frame  52 , a current collector  72  that is held by the electroconductive rib  62 , and an electroconductive elastic body (first elastic body)  82  that is held by the current collector  72 . The cathode  20  is pushed by the elastic body  82  toward the anode  41 . 
     As the anode-side frame  51  and the cathode-side frame  52 , any known frame used for electrolysis vessels for alkaline water electrolysis may be used without particular limitations as long as the anode chamber A and the cathode chamber C can be separately defined. The anode-side frame  51  has an electroconductive backside separating wall  51   a , and a flange part  51   b  uniting with the entire periphery of the backside separating wall  51   a  so as to have watertightness. Likewise, the cathode-side frame  52  has an electroconductive backside separating wall  52   a , and a flange part  52   b  uniting with the entire periphery of the backside separating wall  52   a  so as to have watertightness. The backside separating walls  51   a  and  52   a  each define adjacent electrolytic cells, and electrically connect the adjacent electrolytic cells in series. The flange part  51   b , together with the backside separating wall  51   a , the separating membrane  10  and the gasket  30 , defines the anode chamber, and the flange part  52   b , together with the backside separating wall  52   a , the separating membrane  10  and the gasket  30 , defines the cathode chamber. The flange parts  51   b  and  52   b  have shapes corresponding to the gasket  30  of the assembly  100 . That is, when the gasket  30  of the assembly  100  is sandwiched between and held by the anode-side frame  51  and the cathode-side frame  52 , the flange part  51   b  of the anode-side frame  51  is in contact with the first face  31  of the gasket  30  without any gap, and the flange part  52   b  of the cathode-side frame  52  is in contact with the second face  32  of the gasket  30  without any gap. While not shown in  FIG.  5   , the flange part  51   b  includes an anolyte supply flow path to supply an anolyte to the anode chamber A, and an anolyte collection flow path to collect the anolyte and gas generated at the anode from the anode chamber A. The flange part  52   b  includes a catholyte supply flow path to supply a catholyte to the cathode chamber C, and a catholyte collection flow path to collect the catholyte and gas generated at the cathode from the cathode chamber C. As the material of the backside separating walls  51   a  and  52   a , any alkali-resistant rigid electroconductive material may be used without particular limitations. Examples of such a material include simple metals such as nickel and iron; stainless steel such as SUS304, SUS310, SUS310S, SUS316, and SUS316L; and metal materials obtained by nickeling any of them. As the material of the flange parts  51   b , and  52   b , any alkali-resistant rigid electroconductive material may be used without particular limitations. Examples of such a material include simple metals such as nickel and iron; stainless steel such as SUS304, SUS310, SUS310S, SUS316, and SUS316L; metal materials obtained by nickeling any of them; and non-metal materials such as reinforced plastics. The backside separating wall  51   a  and the flange part  51   b  of the anode-side frame  51  may be united by welding, adhesion, or the like, and may be formed of the same material into one body. Likewise, the backside separating wall  52   a  and the flange part  52   b  of the cathode-side frame  52  may be united by welding, adhesion, or the like, and may be formed of the same material into one body. While only a single electrolytic cell (electrolysis vessel  1000 ) is shown in  FIG.  5   , the flange part  51   b  of the anode-side frame  51  may extend to the opposite side of the backside separating wall  51   a  (right side of the sheet of  FIG.  5   ) as well, to define, together with the backside separating wall  51   a , a cathode chamber of a neighboring electrolytic cell, and the flange part  52   b  of the cathode-side frame  52  may extend to the opposite side of the backside separating wall  52   a  (left side of the sheet of  FIG.  5   ), to define, together with the backside separating wall  52   a , an anode chamber of a neighboring electrolytic cell. 
     As the electroconductive rib  61  and the electroconductive rib  62 , any known electroconductive rib used for electrolysis vessels for alkaline water electrolysis may be used without particular limitations. In the electrolysis vessel  1000 , the electroconductive rib  61  is provided to stand at the backside separating wall  51   a  of the anode-side frame  51 , and the electroconductive rib  62  is provided to stand at the backside separating wall  52   a  of the cathode-side frame. The shape, number, and arrangement of the electroconductive rib  61  are not particularly limited as long as the electroconductive rib  61  can fix the anode  41  to the anode-side frame  51  to hold the anode  41 . The shape, number, and arrangement of the electroconductive rib  62  are not particularly limited either as long as the electroconductive rib  62  can fix the current collector  72  to the cathode-side frame  52  to hold the current collector  72 . As the material of the electroconductive rib  61  and the electroconductive rib  62 , any alkali-resistant rigid electroconductive material may be used without particular limitations. Examples of such a material include materials such as simple metals such as nickel and iron; stainless steel such as SUS304, SUS310, SUS310S, SUS316, and SUS316L; and metals obtained by nickeling any of them. 
     As the current collector  72 , any known current collector used for electrolysis vessels for alkaline water electrolysis may be used without particular limitations. For example, an expanded metal or punching metal made from an alkali-resistant rigid electroconductive material may be preferably employed. Examples of the material of the current collector  72  include simple metals such as nickel and iron; stainless steel such as SUS304, SUS310, SUS310S, SUS316, and SUS316L; and metals obtained by nickeling any of them. When the electroconductive rib  62  holds the current collector  72 , any known means such as welding and pinning may be employed without particular limitations. 
     As the elastic body  82 , any known electroconductive elastic body used for electrolysis vessels for alkaline water electrolysis may be used without particular limitations. For example, an elastic mat, a coil spring, a leaf spring, or the like that is made of an aggregate of metal wires of an alkali-resistant electroconductive material may be preferably employed. Examples of the material of the elastic body  82  include simple metals such as nickel and iron; stainless steel such as SUS304, SUS310, SUS310S, SUS316, and SUS316L; and metals obtained by nickeling any of them. When the current collector  72  holds the elastic body  82 , any known means such as welding, pinning, and bolting may be employed without particular limitations. 
     As the anode  41 , any anode of a rigid porous plate for alkaline water electrolysis which is the same as the anode  40  described above concerning the assembly  200  ( FIGS.  3 (A) to  3 (E) ) may be used without particular limitations. When the rib  61  holds the anode  41 , any known means such as welding, pinning, and bolting may be employed without particular limitations. 
     The electrolysis vessel  1000  includes the membrane-electrode-gasket assembly for alkaline water electrolysis  100 , which makes it possible for at least the separating membrane  10  and the cathode  20  to be in direct contact with each other all over the faces thereof (that is, even the periphery). Thus, the electrolysis vessel  1000  offers reduced operating voltage and energy loss more than conventional zero-gap electrolysis vessels. Since the cathode  20  is united with the separating membrane  10  and the gasket  30  into one body, there is no need to fix the cathode  20  to the cathode-side frame  52 . Therefore, the electrolysis vessel  1000  offers easy assembly of the electrolysis vessel. Further, while the slit part  33  of the gasket  30  receives the periphery of the separating membrane  10 , the gasket  30  includes the continuous part  36  sealing the outer peripheral end of the slit part  33  on the outer peripheral side of the slit part  33 , which makes it possible for capillary action to prevent an electrolytic solution and gas from leaking from an end part of the separating membrane  10  to the outside of the electrolysis vessel. 
     In the foregoing description concerning the present invention, the electrolysis vessel for alkaline water electrolysis  1000  of the embodiment of including the assembly  100  has been described as an example. The present invention is not limited to this embodiment. For example, an embodiment of an electrolysis vessel for alkaline water electrolysis may comprise the above descried assembly  200  ( FIGS.  3 (A) to  3 (E) ).  FIG.  6    is a schematically explanatory cross-sectional view of an electrolysis vessel for alkaline water electrolysis  2000  according to such another embodiment (hereinafter may be referred to as “electrolysis vessel  2000 ”). In  FIG.  6   , elements already shown in  FIGS.  2 (A) to  2 (E),  3 (A) to  3 (E),  4 (A) to  4 (E)  and  5  are given the same reference signs as in  FIGS.  2 (A) to  2 (E),  3 (A) to  3 (E),  4 (A) to  4 (E)  and  5 , and the description thereof may be omitted. As shown in  FIG.  6   , the electrolysis vessel  2000  includes the electroconductive anode-side frame  51  defining the anode chamber A; the electroconductive cathode-side frame  52  defining the cathode chamber C; the assembly  200  sandwiched between and held by the anode-side frame  51  and the cathode-side frame  52  so that the anode-side frame  51  is in contact with the first face  31  and the cathode-side frame  52  is in contact with the second face  32 ; and a cathode (second electrode)  21  arranged in contact with the second membrane face  12  of the separating membrane  10 , wherein the cathode  21  is not held by the gasket  30 . In the electrolysis vessel  2000 , the assembly  200  is arranged so that the first membrane face  11  of the separating membrane  10  faces the anode chamber A, and the second membrane face  12  of the separating membrane  10  faces the cathode chamber C. In the electrolysis vessel  2000 , the anode (first electrode)  40  is a flexible porous plate (first porous plate), and the cathode (second electrode)  21  is a rigid porous plate (second porous plate). The electrolysis vessel  2000  further includes the electroconductive rib  62  that is provided so as to stick out from the inner wall of the cathode-side frame  52 . The cathode  21  is held by the electroconductive rib  62 . The electrolysis vessel  2000  also includes the electroconductive rib  61  that is provided so as to stick out from the inner wall of the anode-side frame  51 , a current collector  71  that is held by the electroconductive rib  61 , and an electroconductive elastic body (first elastic body)  81  that is held by the current collector  71 . The anode  40  is pushed by the elastic body  81  toward the cathode  21 . 
     As the current collector  71 , any known current collector used for electrolysis vessels for alkaline water electrolysis may be used without particular limitations. For example, an expanded metal, a punching metal, or a net made from an alkali-resistant rigid electroconductive material may be preferably employed. Examples of the material of the current collector  71  include simple metals such as nickel and iron; stainless steel such as SUS304, SUS310, SUS310S, SUS316, and SUS316L; and metals obtained by nickeling any of them. When the electroconductive rib  61  holds the current collector  71 , any known means such as welding and pinning may be employed without particular limitations. 
     As the elastic body  81 , any known electroconductive elastic body used for electrolysis vessels for alkaline water electrolysis may be used without particular limitations. For example, an elastic mat, a coil spring, a leaf spring, or the like that is made of an aggregate of metal wires of an alkali-resistant electroconductive material may be preferably employed. Examples of the material of the elastic body  81  include simple metals such as nickel and iron; stainless steel such as SUS304, SUS310, SUS310S, SUS316, and SUS316L; and metals obtained by nickeling any of them. When the current collector  71  holds the elastic body  81 , any known means such as welding and pinning may be employed without particular limitations. 
     As the cathode  21 , any cathode of a rigid porous plate for alkaline water electrolysis which is the same as the cathode  20  described above concerning the assembly  100  ( FIGS.  2 (A)- 2 (E) ) may be used without particular limitations. When the rib  62  holds the cathode  21 , any known means such as welding, pinning, and bolting may be employed without particular limitations. 
     The electrolysis vessel  2000  includes the membrane-electrode-gasket assembly for alkaline water electrolysis  200 , which makes it possible for at least the separating membrane  10  and the anode  40  to be in direct contact with each other all over the faces thereof (that is, even the periphery). Thus, the electrolysis vessel  2000  offers reduced operating voltage and energy loss more than conventional zero-gap electrolysis vessels. Since the anode  40  is united with the separating membrane  10  and the gasket  30  into one body, there is no need to fix the anode  40  to the anode-side frame  51 . Therefore, the electrolysis vessel  2000  offers easy assembly of the electrolysis vessel. Further, while the slit part  33  of the gasket  30  receives the periphery of the separating membrane  10 , the gasket  30  includes the continuous part  36  sealing the outer peripheral end of the slit part  33  on the outer peripheral side of the slit part  33 , which makes it possible for capillary action to prevent an electrolytic solution and gas from leaking from an end part of the separating membrane  10  to the outside of the electrolysis vessel. 
     In the foregoing description concerning the present invention, the electrolysis vessel for alkaline water electrolysis  1000  of the embodiment of holding the second electrode  41  of a rigid porous plate by the electroconductive rib  61 , and the electrolysis vessel for alkaline water electrolysis  2000  of the embodiment of holding the second electrode  21  of a rigid porous plate by the electroconductive rib  62  have been described as an example. The present invention is not limited to these embodiments. For example, an electrolysis vessel for alkaline water electrolysis of the embodiment of pushing the second electrode of a rigid porous plate by an electroconductive second elastic body toward the first electrode may be employed.  FIG.  7    is a schematically explanatory cross-sectional view of an electrolysis vessel for alkaline water electrolysis  3000  according to such another embodiment (hereinafter may be referred to as “electrolysis vessel  3000 ”). In  FIG.  7   , elements the same as those already shown in  FIGS.  2 (A) to  2 (E),  3 (A) to  3 (E),  4 (A) to  4 (E) ,  5  and  6  are given the same reference signs as in  FIGS.  2 (A) to  2 (E),  3 (A) to  3 (E),  4 (A) to  4 (E) ,  5  and  6 , and the description thereof may be omitted. As shown in  FIG.  7   , the electrolysis vessel  3000  includes the electroconductive anode-side frame  51  defining the anode chamber A; the electroconductive cathode-side frame  52  defining the cathode chamber C; the assembly  100  sandwiched between and held by the anode-side frame  51  and the cathode-side frame  52  so that the anode-side frame  51  is in contact with the first face  31  and the cathode-side frame  52  is in contact with the second face  32 ; and the anode (second electrode)  41  arranged in contact with the second membrane face  12  of the separating membrane  10 , wherein the anode  41  is not held by the gasket  30 . In the electrolysis vessel  3000 , the assembly  100  is arranged so that the first membrane face  11  of the separating membrane  10  faces the cathode chamber C, and the second membrane face  12  of the separating membrane  10  faces the anode chamber A. In the electrolysis vessel  3000 , the cathode (first electrode)  20  is a flexible porous plate (first porous plate), and the anode (second electrode)  41  may be a rigid porous plate, and may be a flexible porous plate (second porous plate). The anode (second electrode)  41  is preferably a rigid porous plate. The electrolysis vessel  3000  includes the electroconductive rib  62  that is provided so as to stick out from the inner wall of the cathode-side frame  52 , the current collector  72  that is held by the electroconductive rib  62 , and the electroconductive elastic body (first elastic body)  82  that is held by the current collector  72 . The cathode  20  is pushed by the elastic body  82  toward the anode  41 . The electrolysis vessel  3000  also includes the electroconductive rib  61  that is provided so as to stick out from the inner wall of the anode-side frame  51 , the current collector  71  that is held by the electroconductive rib  61 , and the electroconductive elastic body (second elastic body)  81  that is held by the current collector  71 . The anode  41  is pushed by the elastic body  81  toward the cathode  20 . 
     According to the electrolysis vessel  3000 , not only the first elastic body  82  pushes the first electrode  20 , which is united with the assembly  100  into one body, toward the anode  41  (toward the separating membrane  10 ), but also the second elastic body  81  pushes the second electrode  41 , which is not united with the assembly  100  into one body, toward the cathode  20  (that is, toward the separating membrane  10 ). Thus, there is no need to fix not only the first electrode  20 , which is united with the assembly  100  into one body, to the frame  52 , but also the second electrode  41 , which is not united with the assembly  100  into one body, to the frame  51 . Therefore, the electrolysis vessel  3000  offers further easy assembly of the electrolysis vessel. The separating membrane  10  receives the pressure from the elastic bodies on both the anode side and the cathode side, which makes it easy to suppress deformation of the separating membrane  10  in the vicinity of the periphery of the second electrode  41 . The above described effects concerning the electrolysis vessel  1000  may be also obtained. 
     In the foregoing description concerning the present invention, the electrolysis vessels for alkaline water electrolysis  1000 ,  2000  and  3000  of the embodiment of the second electrode of a rigid porous plate, which is not united with the assembly  100  into one body, have been described as an example. The present invention is not limited to this embodiment. For example, an electrolysis vessel for alkaline water electrolysis of the embodiment of a second electrode of a flexible porous plate which is not united with a membrane-electrode-gasket assembly for alkaline water electrolysis as one body may be employed.  FIG.  8    is a schematically explanatory cross-sectional view of an electrolysis vessel for alkaline water electrolysis  4000  according to such another embodiment (hereinafter may be referred to as “electrolysis vessel  4000 ”). In  FIG.  8   , elements already shown in  FIGS.  2 (A) to  2 (E),  3 (A) to  3 (E),  4 (A) to  4 (E) ,  5 ,  6  and  7  are given the same reference signs as in  FIGS.  2 (A) to  2 (E),  3 (A) to  3 (E),  4 (A) to  4 (E) ,  5 ,  6  and  7 , and the description thereof may be omitted. As shown in  FIG.  8   , the electrolysis vessel  4000  includes the electroconductive anode-side frame  51  defining the anode chamber A; the electroconductive cathode-side frame  52  defining the cathode chamber C; the assembly  100  sandwiched between and held by the anode-side frame  51  and the cathode-side frame  52  so that the anode-side frame  51  is in contact with the first face  31  and the cathode-side frame  52  is in contact with the second face  32 ; and an anode (second electrode)  42  arranged in contact with the second membrane face  12  of the separating membrane  10 , wherein the anode  42  is not held by the gasket  30 . In the electrolysis vessel  4000 , the assembly  100  is arranged so that the first membrane face  11  of the separating membrane  10  faces the cathode chamber C, and the second membrane face  12  of the separating membrane  10  faces the anode chamber A. In the electrolysis vessel  4000 , the cathode (first electrode)  20  is a flexible porous plate (first porous plate), and the anode (second electrode)  42  is a flexible porous plate (second porous plate). The electrolysis vessel  4000  includes the electroconductive rib  62  that is provided so as to stick out from the inner wall of the cathode-side frame  52 , the current collector  72  that is held by the electroconductive rib  62 , and the electroconductive elastic body (first elastic body)  82  that is held by the current collector  72 . The cathode  20  is pushed by the elastic body  82  toward the anode  42 . The electrolysis vessel  4000  also includes the electroconductive rib  61  that is provided so as to stick out from the inner wall of the anode-side frame  51 , the current collector  71  that is held by the electroconductive rib  61 , the electroconductive elastic body (second elastic body)  81  that is held by the current collector  71 , and an electroconductive rigid current collector  91  that is arranged between the elastic body  81  and the anode  42 . The anode  42  is pushed by the elastic body  81  toward the cathode  20  via the rigid current collector  91 . That is, in the electrolysis vessel  4000 , the rigid current collector  91  is arranged so that the second electrode (anode)  42  is sandwiched between the rigid current collector  91  and the separating membrane  10 . The second electrode (anode)  42  is supported by the rigid current collector  91 . 
     As the rigid current collector  91 , any known electroconductive rigid current collector may be used. For example, an expanded metal or punching metal made from an alkali-resistant rigid electroconductive material may be preferably employed. Examples of the material of the rigid current collector  91  include simple metals such as nickel and iron; stainless steel such as SUS304, SUS310, SUS310S, SUS316, and SUS316L; and metals obtained by nickeling any of them. The rigid current collector  91  may be, but is not necessarily held by the elastic body  81 . When the elastic body  81  holds the rigid current collector  91 , any known means such as welding, pinning, and bolting may be employed without particular limitations. 
     According to the electrolysis vessel  4000 , not only the first elastic body  82  pushes the first electrode  20 , which is united with the assembly  100  into one body, toward the anode  42  (that is, toward the separating membrane  10 ), but also the second elastic body  81  pushes the second electrode  42 , which is not united with the assembly  100  into one body, toward the cathode  20  (that is, toward the separating membrane  10 ) via the rigid current collector  91 . Thus, there is no need to fix not only the first electrode  20 , which is united with the assembly  100  into one body, to the frame  52 , but also the second electrode  42 , which is not united with the assembly  100  into one body, to the frame  51 . Therefore, the electrolysis vessel  4000  offers further easy assembly of the electrolysis vessel. The elastic body  81  pushes the second electrode  42  via the rigid current collector  91  (that is, the second electrode  42  is supported by the rigid current collector  91  from the back), which offers further uniform pressure all over the faces of both electrodes by which both electrodes are pushed toward the separating membrane  10  even when the second electrode, which is not united with the assembly into one body, is flexible, and thus offers further uniform current density. The separating membrane  10  receives the pressure from the elastic bodies on both the anode side and the cathode side, which makes it easy to suppress deformation of the separating membrane  10  in the vicinity of the gasket  30 . The above described effects concerning the electrolysis vessel  1000  may be also obtained. 
     In the foregoing description concerning the present invention, the electrolysis vessels for alkaline water electrolysis  1000 ,  2000 ,  3000  and  4000  ( FIGS.  5  to  8   ) including the assembly  100  ( FIGS.  2 (A)- 2 (E) ) of uniting the separating membrane  10  and cathode  20  with the gasket  30  into one body, or the assembly  200  ( FIGS.  3 (A)- 3 (E) ) of uniting the separating membrane  10  and the anode  40  with the gasket  30  into one body have been described as an example. The present invention is not limited to this embodiment. For example, an electrolysis vessel for alkaline water electrolysis of the embodiment of including the assembly  300  ( FIGS.  4 (A)- 4 (E) ) of uniting the separating membrane  10 , the cathode  20 , and the anode  40  with the gasket  30  into one body may be employed.  FIG.  9    is a schematically explanatory cross-sectional view of an electrolysis vessel for alkaline water electrolysis  5000  according to such another embodiment (hereinafter may be referred to as “electrolysis vessel  5000 ”). In  FIG.  9   , elements already shown in  FIGS.  2 (A) to  2 (E),  3 (A) to  3 (E),  4 (A) to  4 (E) ,  5 ,  6 ,  7  and  8  are given the same reference signs as in  FIGS.  2 (A) to  2 (E),  3 (A) to  3 (E),  4 (A) to  4 (E) ,  5 ,  6 ,  7  and  8 , and the description thereof may be omitted. As shown in  FIG.  9   , the electrolysis vessel  5000  includes the electroconductive anode-side frame  51  defining the anode chamber A; the electroconductive cathode-side frame  52  defining the cathode chamber C; and the assembly  300  sandwiched between and held by the anode-side frame  51  and the cathode-side frame  52  so that the anode-side frame  51  is in contact with the first face  31  and the cathode-side frame  52  is in contact with the second face  32 . In the electrolysis vessel  5000 , the assembly  300  is arranged so that the anode  40  faces the anode chamber A, and the cathode  20  faces the cathode chamber C. In the electrolysis vessel  5000 , the cathode (first electrode)  20  is a flexible porous plate (first porous plate). The anode (second electrode)  40  may be a flexible porous plate (second porous plate), and may be a rigid porous plate. The electrolysis vessel  5000  includes the electroconductive rib  62  that is provided so as to stick out from the inner wall of the cathode-side frame  52 , the current collector  72  that is held by the electroconductive rib  62 , and the electroconductive elastic body (first elastic body)  82  that is held by the current collector  72 . The cathode  20  is pushed by the elastic body  82  toward the anode  40 . The electrolysis vessel  5000  also includes the electroconductive rib  61  that is provided so as to stick out from the inner wall of the anode-side frame  51 , and the current collector  71  that is held by the electroconductive rib  61 . The anode  40  is supported by the current collector  71  from the back. 
     The electrolysis vessel  5000  includes the membrane-electrode-gasket assembly for alkaline water electrolysis  300 , which makes it possible for the separating membrane  10  and the cathode  20  to be in direct contact with each other all over the faces thereof (that is, even the periphery), and also makes it possible for the separating membrane  10  and the anode  40  to be in direct contact with each other all over the faces thereof (that is, even the periphery). Thus, the electrolysis vessel  5000  offers reduced operating voltage and energy loss more than conventional zero-gap electrolysis vessels. Since the anode  40  and the cathode  20  are united with the separating membrane  10  and the gasket  30  into one body, there is no need to fix the anode  40  to the anode-side frame  51 , and there is no need to fix the cathode  20  to the cathode-side frame  52  either. Therefore, the electrolysis vessel  5000  offers easy assembly of the electrolysis vessel. Further, while the slit part  33  of the gasket  30  receives the periphery of the separating membrane  10 , the gasket  30  includes the continuous part  36  sealing the outer peripheral end of the slit part  33  on the outer peripheral side of the slit part  33 , which makes it possible for capillary action to prevent an electrolytic solution and gas from leaking from an end part of the separating membrane  10  to the outside of the electrolysis vessel. 
     In the foregoing description concerning the present invention, the electrolysis vessel for alkaline water electrolysis  5000  of the embodiment of including the current collector  71  supported by the electroconductive rib  61 , and supporting the anode  40  by the current collector  71  from the back has been described as an example. The present invention is not limited to this embodiment. For example, an electrolysis vessel for alkaline water electrolysis of the embodiment of not including the current collector  71  when the anode  40  is a rigid porous electrode, and directly supporting the anode  40  by the electroconductive rib  61  from the back may be employed. 
     In the foregoing description concerning the present invention, the electrolysis vessel for alkaline water electrolysis  5000  of the embodiment of pushing the cathode  20  of a flexible porous plate toward the anode  40  by the elastic body  82 , and supporting the anode  40  by the electroconductive rib  61  and the current collector  71  from the back has been described as an example. The present invention is not limited to this embodiment. For example, an electrolysis vessel for alkaline water electrolysis of the embodiment of pushing an anode of a flexible porous plate toward a cathode by an elastic body, and supporting the cathode by an electroconductive rib and a current collector from the back may be employed.  FIG.  10    is a schematically explanatory cross-sectional view of an electrolysis vessel for alkaline water electrolysis  6000  according to such another embodiment (hereinafter may be referred to as “electrolysis vessel  6000 ”). In  FIG.  10   , elements already shown in  FIGS.  2 (A) to  2 (E),  3 (A) to  3 (E),  4 (A) to  4 (E) ,  5 ,  6 ,  7 ,  8  and  9  are given the same reference signs as in  FIGS.  2 (A) to  2 (E),  3 (A) to  3 (E),  4 (A) to  4 (E) ,  5 ,  6 ,  7 ,  8  and  9 , and the description thereof may be omitted. As shown in  FIG.  10   , the electrolysis vessel  6000  includes the electroconductive anode-side frame  51  defining the anode chamber A; the electroconductive cathode-side frame  52  defining the cathode chamber C; and the assembly  300  sandwiched between and held by the anode-side frame  51  and the cathode-side frame  52  so that the anode-side frame  51  is in contact with the first face  31  and the cathode-side frame  52  is in contact with the second face  32 . In the electrolysis vessel  6000 , the assembly  300  is arranged so that the anode  40  faces the anode chamber A, and the cathode  20  faces the cathode chamber C. In the electrolysis vessel  6000 , the anode (first electrode)  40  is a flexible porous plate (first porous plate). The cathode (second electrode)  20  may be a flexible porous plate (second porous plate), and may be a rigid porous plate. The electrolysis vessel  6000  includes the electroconductive rib  61  that is provided so as to stick out from the inner wall of the anode-side frame  51 , the current collector  71  that is held by the electroconductive rib  61 , and the electroconductive elastic body (first elastic body)  81  that is held by the current collector  71 . The anode  40  is pushed by the elastic body  81  toward the cathode  20 . The electrolysis vessel  6000  also includes the electroconductive rib  62  that is provided so as to stick out from the inner wall of the cathode-side frame  52 , and the current collector  72  that is held by the electroconductive rib  62 . The cathode  20  is supported by the current collector  72  from the back. The same effects as the above described electrolysis vessel  5000  may be obtained from the electrolysis vessel for alkaline water electrolysis  6000  of such an embodiment. 
     In the foregoing description concerning the present invention, the electrolysis vessel for alkaline water electrolysis  6000  of the embodiment of including the current collector  72  supported by the electroconductive rib  62 , and supporting the cathode  20  by the current collector  72  from the back has been described as an example. The present invention is not limited to this embodiment. For example, an embodiment of an electrolysis vessel for alkaline water electrolysis is not necessarily comprise the current collector  72  when the cathode  20  is a rigid porous electrode, and directly supporting the cathode  20  by the electroconductive rib  62  from the back. 
     In the foregoing description concerning the present invention, the electrolysis vessels for alkaline water electrolysis  5000  and  6000  of the embodiment of pushing the first electrode of a flexible porous plate toward the second electrode by the electroconductive first elastic body, and supporting the second electrode by the electroconductive rib from the back have been described as an example. The present invention is not limited to this embodiment. For example, an electrolysis vessel for alkaline water electrolysis of the embodiment of pushing the first electrode of a flexible porous plate toward the second electrode by the electroconductive first elastic body, and pushing the second electrode toward the first electrode by the electroconductive second elastic body may be employed.  FIG.  11    is a schematically explanatory cross-sectional view of an electrolysis vessel for alkaline water electrolysis  7000  according to such another embodiment (hereinafter may be referred to as “electrolysis vessel  7000 ”). In  FIG.  11   , elements already shown in  FIGS.  2 (A) to  2 (E),  3 (A) to  3 (E),  4 (A) to  4 (E) ,  5 ,  6 ,  7 ,  8 ,  9  and  10  are given the same reference signs as in  FIGS.  2 (A) to  2 (E),  3 (A) to  3 (E),  4 (A) to  4 (E) ,  5 ,  6 ,  7 ,  8 ,  9  and  10 , and the description thereof may be omitted. As shown in  FIG.  11   , the electrolysis vessel  7000  includes the electroconductive anode-side frame  51  defining the anode chamber A; the electroconductive cathode-side frame  52  defining the cathode chamber C; and the assembly  300  sandwiched between and held by the anode-side frame  51  and the cathode-side frame  52  so that the anode-side frame  51  is in contact with the first face  31  and the cathode-side frame  52  is in contact with the second face  32 . In the electrolysis vessel  7000 , the assembly  300  is arranged so that the anode  40  faces the anode chamber A, and the cathode  20  faces the cathode chamber C. In the electrolysis vessel  7000 , at least one of the cathode (first electrode)  20  and the anode (second electrode)  40  is a flexible porous plate. Both the cathode (first electrode)  20  and the anode (second electrode)  40  may be flexible porous plates. Preferably, one of the cathode (first electrode)  20  and the anode (second electrode)  40  is a flexible porous plate, and the other thereof is a rigid porous plate. The electrolysis vessel  7000  includes the electroconductive rib  62  that is provided so as to stick out from the inner wall of the cathode-side frame  52 , the current collector  72  that is held by the electroconductive rib  62 , and the electroconductive elastic body (first elastic body)  82  that is held by the current collector  72 . The cathode  20  is pushed by the elastic body  82  toward the anode  40 . The electrolysis vessel  7000  also includes the electroconductive rib  61  that is provided so as to stick out from the inner wall of the anode-side frame  51 , the current collector  71  that is held by the electroconductive rib  61 , and the electroconductive elastic body (second elastic body)  81  that is held by the current collector  71 . The anode  40  is pushed by the elastic body  81  toward the cathode  20 . 
     The same effects as the above described electrolysis vessel  5000  may be obtained from the electrolysis vessel for alkaline water electrolysis  7000  of such an embodiment. The separating membrane  10  receives the pressure from the elastic bodies on both the anode side and the cathode side, which makes it easy to suppress deformation of the separating membrane  10  in the vicinity of the gasket  30 . 
       FIG.  12    is a schematically explanatory cross-sectional view of an electrolysis vessel for alkaline water electrolysis  8000  (hereinafter may be referred to as “electrolysis vessel  8000 ”) according to still another embodiment. In  FIG.  12   , elements already shown in  FIGS.  2 (A) to  2 (E),  3 (A) to  3 (E),  4 (A) to  4 (E) ,  5 ,  6 ,  7 ,  8 ,  9 ,  10  and  11  are given the same reference signs as in  FIGS.  2 (A) to  2 (E),  3 (A) to  3 (E),  4 (A) to  4 (E) ,  5 ,  6 ,  7 ,  8 ,  9 ,  10  and  11 , and the description thereof may be omitted. As shown in  FIG.  12   , the electrolysis vessel  8000  includes the electroconductive anode-side frame  51  defining the anode chamber A; the electroconductive cathode-side frame  52  defining the cathode chamber C; and the assembly  300  sandwiched between and held by the anode-side frame  51  and the cathode-side frame  52  so that the anode-side frame  51  is in contact with the first face  31  and the cathode-side frame  52  is in contact with the second face  32 . In the electrolysis vessel  8000 , the assembly  300  is arranged so that the anode  40  faces the anode chamber A, and the cathode  20  faces the cathode chamber C. In the electrolysis vessel  8000 , the cathode (first electrode)  20  is a flexible porous plate (first porous plate). The anode (second electrode)  40  may be a rigid porous plate, and may be a flexible porous plate (second porous plate). The anode (second electrode)  40  is preferably a flexible porous plate. The electrolysis vessel  8000  includes the electroconductive rib  62  that is provided so as to stick out from the inner wall of the cathode-side frame  52 , the current collector  72  that is held by the electroconductive rib  62 , and the electroconductive elastic body (first elastic body)  82  that is held by the current collector  72 . The cathode  20  is pushed by the elastic body  82  toward the anode  40 . The electrolysis vessel  8000  also includes the electroconductive rib  61  that is provided so as to stick out from the inner wall of the anode-side frame  51 , the current collector  71  that is held by the electroconductive rib  61 , the electroconductive elastic body (second elastic body)  81  that is held by the current collector  71 , and the electroconductive rigid current collector  91  that is arranged between the elastic body  81  and the anode  40 . The anode  40  is pushed by the elastic body  81  toward the cathode  20  via the rigid current collector  91 . That is, in the electrolysis vessel  8000 , the rigid current collector  91  is arranged so that the second electrode (anode)  40  is sandwiched between the rigid current collector  91  and the separating membrane  10 . The second electrode (anode)  40  is supported by the rigid current collector  91 . 
     According to the electrolysis vessel  8000 , the elastic body  81  pushes the anode  40  via the rigid current collector  91  (that is, the anode  40  is supported by the rigid current collector  91  from the back), which offers further uniform pressure all over the faces of both electrodes by which both electrodes are pushed toward the separating membrane  10  even when both the anode  40  and the cathode  20  are flexible, and thus offers further uniform current density. The above described effects concerning the electrolysis vessel  7000  may be also obtained. 
     In the foregoing description concerning the present invention, the electrolysis vessel for alkaline water electrolysis  8000  of the embodiment of pushing the anode  40  toward the cathode  20  by the electroconductive elastic body  81  via the rigid current collector  91  has been described as an example. The present invention is not limited to this embodiment. For example, an electrolysis vessel for alkaline water electrolysis of the embodiment of pushing a cathode toward an anode by an electroconductive elastic body via a rigid current collector may be employed.  FIG.  13    is a schematically explanatory cross-sectional view of an electrolysis vessel for alkaline water electrolysis  9000  (hereinafter may be referred to as “electrolysis vessel  9000 ”) according to such another embodiment. In  FIG.  13   , elements already shown in  FIGS.  2 (A) to  2 (E),  3 (A) to  3 (E),  4 (A) to  4 (E) ,  5 ,  6 ,  7 ,  8 ,  9 ,  10 ,  11  and  12  are given the same reference signs as in  FIGS.  2 (A) to  2 (E),  3 (A) to  3 (E),  4 (A) to  4 (E) ,  5 ,  6 ,  7 ,  8 ,  9 ,  10 ,  11  and  12 , and the description thereof may be omitted. As shown in  FIG.  13   , the electrolysis vessel  9000  includes the electroconductive anode-side frame  51  defining the anode chamber A; the electroconductive cathode-side frame  52  defining the cathode chamber C; and the assembly  300  sandwiched between and held by the anode-side frame  51  and the cathode-side frame  52  so that the anode-side frame  51  is in contact with the first face  31  and the cathode-side frame  52  is in contact with the second face  32 . In the electrolysis vessel  9000 , the assembly  300  is arranged so that the anode  40  faces the anode chamber A, and the cathode  20  faces the cathode chamber C. In the electrolysis vessel  9000 , the anode (first electrode)  40  is a flexible porous plate (first porous plate). The cathode (second electrode)  20  may be a rigid porous plate, and may be a flexible porous plate (second porous plate). The cathode (second electrode)  20  is preferably a flexible porous plate. The electrolysis vessel  9000  includes the electroconductive rib  61  that is provided so as to stick out from the inner wall of the anode-side frame  51 , the current collector  71  that is held by the electroconductive rib  61 , and the electroconductive elastic body (first elastic body)  81  that is held by the current collector  71 . The anode  40  is pushed by the elastic body  81  toward the cathode  20 . The electrolysis vessel  9000  also includes the electroconductive rib  62  that is provided so as to stick out from the inner wall of the cathode-side frame  52 , the current collector  72  that is held by the electroconductive rib  62 , the electroconductive elastic body (second elastic body)  82  that is held by the current collector  72 , and the electroconductive rigid current collector  91  that is arranged between the elastic body  82  and the cathode  20 . The cathode  20  is pushed by the elastic body  82  toward the anode  40  via the rigid current collector  91 . That is, in the electrolysis vessel  9000 , the rigid current collector  91  is arranged so that the second electrode (cathode)  20  is sandwiched between the rigid current collector  91  and the separating membrane  10 . The second electrode (cathode)  20  is supported by the rigid current collector  91 . 
     The same effects as the above described electrolysis vessel  8000  may be also obtained from the electrolysis vessel for alkaline water electrolysis  9000  of such an embodiment. That is, according to the electrolysis vessel  9000 , the elastic body  82  pushes the cathode  20  via the rigid current collector  91  (that is, the cathode  20  is supported by the rigid current collector  91  from the back), which offers further uniform pressure all over the faces of both electrodes by which both electrodes are pushed toward the separating membrane  10  even when both the anode  40  and the cathode  20  are flexible, and thus offers further uniform current density. The above described effects concerning the electrolysis vessel  7000  may be also obtained. 
     In the foregoing description concerning the present invention, the electrolysis vessels for alkaline water electrolysis  1000  to  9000  of the embodiment of including the electroconductive rib  61  in the anode chamber, and including the electroconductive rib  62  in the cathode chamber have been described as an example. The present invention is not limited to this embodiment. For example, an embodiment of an electrolysis vessel for alkaline water electrolysis of the embodiment is not necessarily comprise an electroconductive rib in one or both of an anode chamber and a cathode chamber.  FIG.  14    is a schematically explanatory cross-sectional view of an electrolysis vessel for alkaline water electrolysis  10000  (hereinafter may be referred to as “electrolysis vessel  10000 ”) according to such another embodiment. In  FIG.  14   , elements already shown in  FIGS.  2 (A) to  2 (E),  3 (A) to  3 (E),  4 (A) to  4 (E) ,  5 ,  6 ,  7 ,  8 ,  9 ,  10 ,  11 ,  12  and  13  are given the same reference signs as in  FIGS.  2 (A) to  2 (E),  3 (A) to  3 (E),  4 (A) to  4 (E) ,  5 ,  6 ,  7 ,  8 ,  9 ,  10 ,  11 ,  12  and  13 , and the description thereof may be omitted. As shown in  FIG.  14   , the electrolysis vessel  10000  includes the electroconductive anode-side frame  51  defining the anode chamber A; the electroconductive cathode-side frame  52  defining the cathode chamber C; and the assembly  300  sandwiched between and held by the anode-side frame  51  and the cathode-side frame  52  so that the anode-side frame  51  is in contact with the first face  31  and the cathode-side frame  52  is in contact with the second face  32 . In the electrolysis vessel  10000 , the assembly  300  is arranged so that the anode  40  faces the anode chamber A, and the cathode  20  faces the cathode chamber C. In the electrolysis vessel  10000 , at least one of the cathode (first electrode)  20  and the anode (second electrode)  40  is a flexible porous plate. Both the cathode (first electrode)  20  and the anode (second electrode)  40  may be flexible porous plates. Preferably, one of the cathode (first electrode)  20  and the anode (second electrode)  40  is a flexible porous plate, and the other thereof is a rigid porous plate. The electrolysis vessel  10000  includes the electroconductive elastic body (first elastic body)  82  that is arranged between the electroconductive backside separating wall  52   a  of the cathode-side frame  52  and the cathode  20  so as to be in direct contact with the backside separating wall  52   a  and the cathode  20 . The cathode  20  is pushed by the elastic body  82  toward the anode  40 . The electrolysis vessel  10000  also includes the electroconductive elastic body (second elastic body)  81  that is arranged between the electroconductive backside separating wall  51   a  of the anode-side frame  51  and the anode  40  so as to be in direct contact with the backside separating wall  51   a  and the anode  40 . The anode  40  is pushed by the elastic body  81  toward the cathode  20 . 
     The effects same as the above described electrolysis vessel  7000  may be also obtained from the electrolysis vessel for alkaline water electrolysis  10000  of such an embodiment. Further, in the electrolysis vessel  10000 , the anode chamber A and the cathode chamber C do not include any electroconductive rib, which makes it possible to thinner each electrolytic cell, which offers a downsized electrolysis vessel, which offers increased gas production per occupied site area. One or both of the anode chamber and the cathode chamber include(s) no electroconductive rib, which makes it possible to reduce materials to constitute the electrolysis vessel, and steps necessary for making the electrolysis vessel. 
     EXAMPLES 
     Hereinafter the present invention will be described in more detail based on example and comparative example. The present invention is not limited to these examples. 
     Examples 
     Alkaline water was electrolyzed under the conditions of: current-carrying cross section 0.5 dm 2 , electrode solution temperature 80° C., KOH concentration 25 mass %, and current density 60 A/dm 2 , using the electrolysis vessel for alkaline water electrolysis  5000  ( FIG.  9   ) including the membrane-electrode-gasket assembly for alkaline water electrolysis  300  ( FIGS.  3 (A)- 3 (E) ), which is encompassed in the present invention, to measure a necessary voltage. 
     Comparative Example 
     Alkaline water was electrolyzed under the same conditions as in the example except that a zero-gap electrolysis vessel having a conventional structure of not uniting a gasket and electrodes into one body (see  FIG.  1   ) was used instead of the electrolysis vessel for alkaline water electrolysis used in example, to measure a necessary voltage. 
     &lt;Evaluation Result&gt; 
     The electrolysis vessel for alkaline water electrolysis used in example made it possible to reduce a voltage necessary for electrolysis by 1.5% compared to the conventional zero-gap electrolysis vessel used in comparative example although their electric conduction area and current value were the same. This shows that an increased area where zero-gap was achieved (the electrodes and the separating membrane were in direct contact with each other) led to a further uniform current flow all over the conducting surface. While crystal deposition due to leakage of the electrode solution was confirmed around the gasket of the electrolysis vessel of comparative example one day after the start of the electrolysis, no crystal deposition due to leakage of the electrode solution was confirmed in the electrolysis vessel for alkaline water electrolysis used in example even after the electrolysis had continued for 2 weeks. 
     REFERENCE SIGNE LIST 
     
         
           10  (ionic-permeable) separating membrane 
           11  first membrane face 
           12  second membrane face 
           20 ,  21  cathode 
           30  gasket 
           31  first face 
           32  second face 
           33  slit part 
           34  first part 
           35  second part 
           36  continuous part 
           40 ,  41 ,  42  anode 
           100 ,  200 ,  300  membrane-electrode-gasket assembly for alkaline water electrolysis 
           51  anode-side frame 
           52  cathode-side frame 
           51   a ,  52   a  (conductive) backside separating wall 
           51   b ,  52   b  flange part 
           61 ,  62  electroconductive rib 
           71 ,  72  current collector 
           81 ,  82  electroconductive elastic body 
           91  rigid current collector 
           900  conventional zero-gap electrolysis vessel 
           910  electrode chamber unit 
           911  electroconductive separating wall 
           912  flange part 
           913 ,  914  electroconductive rib 
           920  ionic-permeable separating membrane 
           930  gasket 
           940  anode 
           950  current collector 
           960  electroconductive elastic body 
           970  cathode 
           1000 ,  2000 ,  3000 ,  4000 ,  5000 ,  6000 ,  7000 ,  8000 ,  9000 ,  10000  electrolysis vessel for 
         alkaline water electrolysis 
         A anode chamber 
         C cathode chamber