Partition wall for electrolytic cell, partition wall assembly, and electrolytic cell

Abstract

Provided is a partition wall for an electrolytic cell, the partition wall partitioning the electrolytic cell into an anode chamber and a cathode chamber and being capable of suppressing generation of gas accumulation even when recesses are formed therein. A partition wall 8 of an electrolytic cell has a first main surface 20 and a second main surface 22 positioned opposite to the first main surface 20. The first main surface 20 includes a first flat part 24 and a plurality of first recesses 36 recessed with respect to the first flat part 24. Edges 40 of the first recesses 36 are rounded. The second main surface 22 includes a second flat part 30 and a plurality of second recesses 42 recessed with respect to the second flat part 30. Edges 46 of the second recesses 42 are rounded.

Description

Partition wall for electrolytic cell, partition wall assembly and electrolytic cell

[0001] The present invention relates to a partition for an electrolytic cell, a partition assembly and an electrolytic cell.

[0002] A bipolar alkaline water electrolytic cell is known as an apparatus for producing hydrogen gas and oxygen gas. In a bipolar alkaline water electrolytic cell, a plurality of electrolytic cell units and a plurality of diaphragms are arranged alternately. Each electrolytic cell unit includes an anode disposed in an anode chamber, a cathode disposed in a cathode chamber, and a conductive partition wall that separates the anode chamber from the cathode chamber. A first main surface of the partition wall is provided with a plurality of ribs, and an anode is fixed to the first main surface of the partition wall via the plurality of ribs. This defines an anode chamber between the first main surface of the partition wall and the anode. Similarly, a second main surface of the partition wall (the surface opposite to the first main surface) is also provided with a plurality of ribs, and a cathode is fixed to the second main surface of the partition wall via the plurality of ribs. This defines a cathode chamber between the second main surface of the partition wall and the cathode.

[0003] In a bipolar alkaline water electrolytic cell, instead of a plurality of ribs, a plurality of protrusions and recesses may be provided on each of the first and second main surfaces of the partition wall. In this case, an anode is fixed to the apex of the protrusion on the first main surface, thereby defining an anode chamber between the first main surface and the anode. Also, a cathode is fixed to the apex of the protrusion on the second main surface, thereby defining a cathode chamber between the second main surface and the cathode (see, for example, Patent Document 1).

[0004] International Publication No. 2021 / 256472

[0005] However, when multiple recesses are formed on the first and second main surfaces of the partition wall, gas generated at the electrodes may accumulate inside the recesses, causing gas accumulation. When gas accumulation occurs, the flow of the electrode solution in the electrode chamber becomes non-uniform, resulting in a difference in the concentration of the electrode solution in the electrode chamber. When the difference in the concentration of the electrode solution becomes large, the current distribution becomes non-uniform, causing a problem of reduced electrolysis efficiency. This problem can occur not only in alkaline water electrolytic cells for producing hydrogen gas and oxygen gas, but also in other electrolytic cells, such as salt electrolytic cells for producing hydrogen gas, chlorine gas, and caustic soda.

[0006] An object of the present invention is to provide a partition wall of an electrolytic cell, a partition wall assembly, and an electrolytic cell that can suppress the occurrence of gas accumulation even when a recess is formed in the partition wall of the electrolytic cell that separates the anode chamber and the cathode chamber.

[0007] According to the present invention, the following partition wall of an electrolytic cell is provided to solve the above-mentioned problems. That is, "An electrolytic cell partition wall separating an anode chamber and a cathode chamber, the partition wall having a first main surface and a second main surface located opposite to the first main surface, the first main surface including a first flat portion and a plurality of first depressions recessed from the first flat portion, the edges of the first depressions being rounded, and the second main surface including a second flat portion and a plurality of second depressions recessed from the second flat portion, the edges of the second depressions being rounded."

[0008] Preferably, the first main surface includes a plurality of first mountain-shaped projections that protrude beyond the first flat portion, and the second main surface includes a plurality of second mountain-shaped projections that protrude beyond the second flat portion.

[0009] A first inclined portion inclined with respect to the first flat portion may be provided between the first protrusion and the first recess on the first main surface, and a second inclined portion inclined with respect to the second flat portion may be provided between the second protrusion and the second recess on the second main surface. It is desirable that the positions of the plurality of first recesses correspond to the positions of the plurality of second protrusions, and that the positions of the plurality of second recesses correspond to the positions of the plurality of first protrusions.

[0010] The first protrusions, the second protrusions, the first depressions, and the second depressions may be hemispherical. When the radius of curvature of the edges of the first depressions and the second depressions is R3 and the radius of curvature of the bottoms of the first depressions and the second depressions is R4, the ratio of the radii of curvature R4 / R3 is preferably 0.1 or more and 19 or less. The bottoms of the first protrusions and the second protrusions may be rounded. When the radius of curvature of the bottoms of the first protrusions and the second protrusions is R1 and the radius of curvature of the tops of the first protrusions and the second protrusions is R2, the ratio of the radii of curvature R2 / R1 is preferably 0.6 or more and 40 or less. When the radius of curvature of the edges of the first depressions and the second depressions is R3 and the radius of curvature of the bottoms of the first depressions and the second depressions is R4, the ratio of the radii of curvature R4 / R3 is preferably 0.1 or more and 19 or less.

[0011] The first protrusion, the second protrusion, the first depression, and the second depression may be conical, and the tops of the first protrusions and the second protrusions and the bottoms of the first depressions and the second depressions may be rounded. When the radius of curvature of the edges of the first depressions and the second depressions is R7 and the radius of curvature of the bottoms of the first depressions and the second depressions is R8, the ratio of the radii of curvature R8 / R7 is preferably 0.05 or more and 190 or less. The bottoms of the first protrusions and the second protrusions may be rounded. When the radius of curvature of the bottom of the first protrusion and the second protrusion is R5 and the radius of curvature of the top of the first protrusion and the second protrusion is R6, it is desirable that the ratio of the radii of curvature R6 / R5 is 0.6 or more and 400 or less, and when the radius of curvature of the edges of the first depression and the second depression is R7 and the radius of curvature of the bottom of the first depression and the second depression is R8, it is desirable that the ratio of the radii of curvature R8 / R7 is 0.05 or more and 190 or less.

[0012] The first protrusion, the second protrusion, the first recess, and the second recess may be frustoconical, and the bottom peripheral edge of the first recess and the bottom peripheral edge of the second recess may be rounded. When the radius of curvature of the edges of the first recess and the second recess is R11 and the radius of curvature of the bottom peripheral edge of the first recess and the second recess is R12, the ratio of the radii of curvature R12 / R11 is preferably 0.05 or more and 50 or less. The bottom portions of the first protrusion and the second protrusion and the top peripheral edges of the first protrusion and the second protrusion may be rounded. When the radius of curvature of the base of the first protrusion and the second protrusion is R9 and the radius of curvature of the top peripheral edge of the first protrusion and the second protrusion is R10, the ratio of the radii of curvature R10 / R9 is preferably 0.1 or more and 100 or less, and when the radius of curvature of the edge of the first depression and the second depression is R11 and the radius of curvature of the bottom peripheral edge of the first depression and the second depression is R12, the ratio of the radii of curvature R12 / R11 is preferably 0.05 or more and 50 or less.

[0013] The present invention also provides the following partition wall assembly that solves the above-mentioned problems. That is, there is provided "a partition wall assembly including the above-mentioned partition wall and a partition wall support frame that supports a peripheral edge of the partition wall." The partition wall may be circular, and the partition wall support frame may be annular. The partition wall assembly of the present invention may include an electrode or current collector joined to a top of each of the plurality of first projections, and a current collector or electrode joined to a top of each of the plurality of second projections. Preferably, the partition wall assembly includes an electrode or current collector joined to a top of each of the plurality of first projections by welding, and a current collector or electrode joined to a top of each of the plurality of second projections. Furthermore, the partition wall assembly may include an electrode or current collector joined to a top of each of the plurality of first projections by welding, and a current collector or electrode joined to a top of each of the plurality of second projections by welding.

[0014] Furthermore, according to the present invention, there is provided the following electrolytic cell that solves the above-mentioned problems: "An electrolytic cell in which a plurality of partition wall assemblies and a plurality of membrane assemblies as described above are alternately arranged, wherein the membrane assemblies include a membrane and a membrane support frame that supports the peripheral edge of the membrane."

[0015] In the present invention, the edges of the first and second recesses are rounded, so that gas generated at the electrode does not stagnate inside the first and second recesses, preventing the occurrence of gas accumulation. Therefore, the flow of the electrode solution in the electrode chamber is made uniform, preventing excessively large differences in the concentration of the electrode solution in the electrode chamber. As a result, the current distribution is made uniform, preventing a decrease in electrolysis efficiency.

[0016] 4(a)-4(a) are schematic partial cross-sectional views of an electrolytic cell according to the present invention. Schematic partial cross-sectional views of the electrolytic cell shown in FIG. 1. Front view of the partition wall assembly shown in FIG. 1. (a) Partial cross-sectional view taken along line IV-IV in FIG. 3, (b) Partial cross-sectional view of a partition wall in which an inclined portion is provided between a protrusion and a depression (cross-section corresponding to the cross-section of (a)). Explanatory view for explaining the radius of curvature R1 of the bottom portion of the first protrusion (partially enlarged view of FIG. 4(a)). Explanatory view for explaining the radius of curvature R2 of the top portion of the first protrusion (partially enlarged view of FIG. 4(a)). Explanatory view for explaining the radius of curvature R3 of the edge of the first depression (partially enlarged view of FIG. 4(a)). Explanatory view for explaining the radius of curvature R4 of the bottom portion of the first depression (partially enlarged view of FIG. 4(a)). Front view of the membrane assembly shown in FIG. 1. (a) Partial cross-sectional view of a partition wall according to a first modified example (cross-section corresponding to the cross-section of FIG. 4(a)), (b) Partial cross-sectional view of a partition wall according to a first modified example in which an inclined portion is provided between the protrusion and the depression (cross-section corresponding to the cross-section of FIG. 4(a)). (a) A partial cross-sectional view of a partition wall according to a second modified example (a cross-section corresponding to the cross-section of FIG. 4(a)), (b) A partial cross-sectional view of a partition wall according to a second modified example in which an inclined portion is provided between the protrusion and the depression (a cross-section corresponding to the cross-section of FIG. 4(a)). An explanatory view for explaining the radius of curvature R10 of the periphery of the top of the first protrusion in the second modified example (a partial enlarged view of FIG. 11(a)). An explanatory view for explaining the radius of curvature R12 of the periphery of the bottom of the first depression in the second modified example (a partial enlarged view of FIG. 11(a)).

[0017] Hereinafter, preferred embodiments of a partition wall for an electrolytic cell, a partition wall assembly, and an electrolytic cell according to the present invention will be described with reference to the drawings.

[0018] (Electrolytic cell 2) Referring to Figures 1 and 2, the electrolytic cell generally designated by reference numeral 2 is a zero-gap bipolar electrolytic cell in which the membrane and the electrode are in contact with each other. The electrolytic cell 2 includes a plurality of partition assemblies 4 and a plurality of membrane assemblies 6. The partition assemblies 4 and the membrane assemblies 6 are arranged alternately in the depth direction (X direction) of the electrolytic cell 2, as indicated by the arrow X in Figure 1. The Y direction indicated by the arrow Y in Figure 1 is a direction perpendicular to the X direction and is the width direction of the electrolytic cell 2. The Z direction indicated by the arrow Z in Figure 1 is a vertical direction perpendicular to the X and Y directions.

[0019] (Partition Wall Assembly 4) The partition wall assembly 4 includes partition walls 8 and partition wall support frames 10 that support peripheral portions of the partition walls 8. The partition wall assembly 4 of the present embodiment further includes an electrode 12 arranged on one side of the partition wall 8 in the X direction, and a current collector 14 arranged on the other side of the partition wall 8 in the X direction. In the present embodiment, a cushion material 76 and an electrode 78, which will be described later, are provided on a surface of the current collector 14 opposite to the surface that is bonded to the partition wall 8. Note that a configuration may also be possible in which the current collector 14 and the electrode 12 are arranged on one side of the partition wall 8 in the X direction, and the current collector 14, the cushion material 76, and the electrode 78 are arranged on the other side of the partition wall 8 in the X direction.

[0020] (Partition Wall 8) The partition wall 8 separates the anode chamber 16 from the cathode chamber 18 (see FIG. 2 ). As shown in FIGS. 3 and 4( a), the partition wall 8 of this embodiment is in the form of a circular sheet having a first main surface 20 and a second main surface 22 located opposite the first main surface 20. However, the shape of the partition wall 8 is not limited to a circular sheet shape and may be, for example, a rectangular sheet shape. In such a case, the shape of the partition wall support frame 10 described below may be a shape corresponding to the partition wall 8. For example, if the partition wall 8 is in the form of a rectangular sheet, the partition wall support frame 10 will also be in the form of a rectangle. The size of the partition wall 8 can be appropriately determined taking into account the electrolysis capacity, operating conditions, installation area, cost, and the like of the electrolytic cell 2. For example, when the partition wall 8 is in the form of a circular sheet, the diameter of the partition wall 8 can be 0.1 m to 5 m, and when the partition wall 8 is in the form of a rectangular sheet, one side of the partition wall 8 can be 0.1 m to 5 m, but is not limited to these values. The partition wall 8 can be formed from a conductive material (for example, a metal material such as a steel plate). The surface of the partition wall 8 may be subjected to a surface treatment such as nickel plating. The thickness of the partition wall 8 can be determined appropriately taking into consideration the shape, size, and material of the partition wall 8, the number, shape, and arrangement of the protrusions and depressions, and the like; for example, the thickness is 0.5 mm or more and 10 mm or less, preferably 1 mm or more and 7 mm or less, and more preferably 2 mm or more and 5 mm or less.

[0021] (First main surface 20) The first main surface 20 includes a first flat portion 24 and a plurality of mountain-shaped first protrusions 26 that protrude beyond the first flat portion 24. In this embodiment, the first protrusions 26 are hemispherical, with the diameter gradually decreasing with increasing distance from the first flat portion 24. The radius of curvature of the first protrusions 26 may be, for example, 3 mm or more and 20 mm or less, more preferably 5 mm or more and 15 mm or less, and even more preferably 7 mm or more and 10 mm or less. The height H of the first protrusions 26, based on the first flat portion 24, may be, for example, 3 mm or more and 20 mm or less, more preferably 5 mm or more and 15 mm or less, and even more preferably 7 mm or more and 10 mm or less.

[0022] The arrangement of the multiple first projections 26 is arbitrary. For example, the multiple first projections 26 may be aligned along the width direction (Y direction) of the electrolytic cell 2 and also along the up-down direction (Z direction). Alternatively, the multiple first projections 26 may be arranged in a staggered pattern, or may be arranged concentrically. Furthermore, the number and spacing of the multiple first projections 26 may also be set arbitrarily.

[0023] The bottom 28 of the first protrusions 26 may or may not be rounded. The bottom 28 is the boundary between the first flat portion 24 and the first protrusions 26, or the boundary between the first inclined portion 38 (described later) and the first protrusions 26. If the bottom 28 of the first protrusions 26 on the first main surface 20 is not rounded, the electrode solution that strikes the first protrusions 26 spreads along the first flat portion 24, improving the uniformity of the electrode solution in the electrode chamber. Furthermore, when the electrode solution strikes the first protrusions 26, a shear force acts on the flow of the electrode solution, breaking down the air bubbles contained in the electrode solution. This further promotes uniformity of the electrode solution and is expected to contribute to improved electrolysis efficiency. Furthermore, when rounding the bottom 28 of the first protrusions 26, it is important that the bottom 28 of each of the multiple first protrusions 26 is rounded evenly. However, when the first protrusions 26 are formed by, for example, press working, the force is applied differently at the center and the ends (e.g., ends in the Y and Z directions) of the partition wall 8, making it generally difficult to uniformly round the bottom 28. This not only tends to disrupt the symmetry of the protrusion shape of the first protrusions 26 at the ends of the partition wall 8, but also tends to cause variations in the orientation of the tops 26 a (deviations from the direction perpendicular to the first main surface 20) among the multiple first protrusions 26 within the first main surface 20. In such cases, there is a risk of impairing the flatness of the electrode when fixing the electrode to the tops 26 a of the first protrusions 26, which is a major problem in zero-gap electrolytic cells. For these reasons, it is preferable that the bottom 28 of the first protrusions 26 is not rounded; however, the bottom 28 of the first protrusions 26 may be rounded for reasons of manufacturing and processing the partition wall 8.

[0024] As shown in Fig. 4(a) , in the partition wall 8, the bottom 28 of the first protrusion 26 may be rounded. If rounding is applied, it is preferable that the rounding be applied to the entire circumference of the bottom 28. By rounding the bottom 28, gas generated at the electrode flows smoothly near the first protrusion 26. As a result, the generation of gas accumulation near the first protrusion 26 can be suppressed.

[0025] When the radius of curvature of the bottom portion 28 of the first projection 26 is R1 and the radius of curvature of the top portion 26a of the first projection 26 is R2, the ratio of the radii of curvature R2 / R1 is preferably 0.6 or more and 40 or less. This enhances the effect of gas generated at the electrode flowing smoothly near the first projection 26. The radius of curvature R1 of the bottom portion 28 may be, for example, 0.5 mm or more and 5 mm or less. If the radius of curvature R1 of the bottom portion 28 is 0.5 mm or more and 5 mm or less, the effect of the electrode solution spreading into the electrode chamber along the first flat portion 24 described above and the effect of shear force acting on the flow of the electrode solution are simultaneously obtained.

[0026] The radius of curvature R1 of the skirt 28 of the first protrusion 26 will be described with reference to FIG. 5 . The intersection point P1 between a straight line L1 extending along the first flat portion 24 and a tangent line L2 to the first protrusion 26 passing through the skirt 28 is defined as P1. An auxiliary line L3 is defined that passes through the intersection point P1 and bisects the angle θ1 between the straight line L1 and the tangent line L2. A virtual circle C1 having a center O1 on the auxiliary line L3 is assumed. The radius of the virtual circle C1 when the circumference of the virtual circle C1 passes through the intersection point Q1 between the skirt 28 of the first protrusion 26 and the auxiliary line L3 and is tangent to both the straight line L1 and the tangent line L2 is defined as the radius of curvature R1 in the present invention.

[0027] The radius of curvature R2 of the apex 26a of the first protrusion 26 will be described with reference to Figure 6. A straight line L1 extending along the first flat portion 24 and a straight line L4 passing through the apex 26a of the first protrusion 26 and perpendicularly intersecting the line L1 are defined. An imaginary circle C2 having a center O2 on the line L4 is assumed. The radius of the imaginary circle C2, whose circumference passes through the apex 26a of the first protrusion 26 and whose overlap with the outline of the first protrusion 26 is maximized, is defined as the radius of curvature R2 in the present invention.

[0028] The radii of curvature R1 and R2 can be determined by, for example, cutting the partition wall 8 along a plane that passes through the tops 26a of the first projections 26 and is perpendicular to the first main surfaces 20 of the partition walls 8 to expose a cross section corresponding to Fig. 4 , and directly measuring the radii of curvature R1 and R2 on the cut surface (cross section corresponding to Fig. 4 ) of the partition wall 8. Alternatively, the cut surface (cross section corresponding to Fig. 4 ) of the partition wall 8 may be photographed to obtain a cross-sectional image of the partition wall 8, and the obtained cross-sectional image may be subjected to image analysis to determine the radii of curvature R1 and R2.

[0029] As described above, the radii of curvature R1 and R2 may be determined by cutting the partition wall 8. However, it is preferable to determine the radii of curvature R1 and R2 without cutting the partition wall 8. For example, resin, clay, plaster, impression material, or the like is pressed against the first main surface 20 of the partition wall 8 to form a mold that copies the shape of the first main surface 20 of the partition wall 8. Next, the mold is cut along a plane that passes through a point on the mold that corresponds to the apex 26a of the first protrusion 26 and is perpendicular to the plane that corresponds to the first main surface 20 of the partition wall 8. Then, the cut surface of the mold is photographed to obtain a cross-sectional image of the mold, and the obtained cross-sectional image is subjected to image analysis, thereby making it possible to determine the radii of curvature R1 and R2 without cutting the partition wall 8.

[0030] 3 and 4(a), the second main surface 22 includes a second flat portion 30 and a plurality of mountain-shaped second protrusions 32 that protrude beyond the second flat portion 30. Like the first protrusions 26, the second protrusions 32 of this embodiment are hemispherical in shape and have a diameter that gradually decreases with increasing distance from the second flat portion 30. The dimensions of the second protrusions 32 may be the same as or different from the dimensions of the first protrusions 26.

[0031] The arrangement of the multiple second projections 32 is arbitrary. For example, the multiple second projections 32 may be aligned along the width direction (Y direction) of the electrolytic cell 2 and also along the up-down direction (Z direction). Alternatively, the multiple second projections 32 may be arranged in a staggered pattern, or may be arranged concentrically. Furthermore, the number and spacing of the multiple second projections 32 may also be set arbitrarily.

[0032] The bottom 34 of the second protrusions 32 may or may not be rounded. The bottom 34 is the boundary between the second flat portion 30 and the second protrusions 32, or the boundary between the second inclined portion 44 (described later) and the second protrusions 32. If the bottom 34 of the second protrusions 32 on the second main surface 22 is not rounded, the electrode solution that strikes the second protrusions 32 spreads along the second flat portion 30, improving the uniformity of the electrode solution in the electrode chamber. Furthermore, when the electrode solution strikes the second protrusions 32, a shear force acts on the flow of the electrode solution, breaking down the air bubbles contained in the electrode solution. This further promotes uniformity of the electrode solution and is expected to contribute to improved electrolysis efficiency. Furthermore, when rounding the bottom 34 of the second protrusions 32, it is important that the bottom 34 of each of the multiple second protrusions 32 is rounded evenly. However, when the second protrusions 32 are formed by, for example, press working, the force is applied differently at the center and the ends (e.g., ends in the Y and Z directions) of the partition wall 8, making it generally difficult to uniformly round the bottom 34. This not only tends to disrupt the symmetry of the protrusion shape of the second protrusions 32 at the ends of the partition wall 8, but also tends to cause variations in the orientation of the tops 32 a (deviations from the direction perpendicular to the second main surface 22) among the multiple second protrusions 32 within the second main surface 22. In such cases, there is a risk of impairing the flatness of the electrode when fixing the electrode to the tops 32 a of the second protrusions 32, which is a major problem in zero-gap electrolytic cells. For these reasons, it is preferable that the bottom 34 of the second protrusions 32 is not rounded; however, the bottom 34 of the second protrusions 32 may be rounded for reasons of manufacturing and processing the partition wall 8.

[0033] As shown in Figure 4(a) , in the partition wall 8, the bottom 34 of the second projection 32 may also be rounded. If rounded, it is preferable that the rounded bottom be rounded around the entire circumference of the bottom 34. By rounding the bottom 34, gas generated at the electrode flows smoothly near the second projection 32, thereby preventing gas from accumulating near the second projection 32. The radius of curvature of the bottom 34 of the second projection 32 may be the same as or different from the radius of curvature of the bottom 28 of the first projection 26.

[0034] (First Depressions 36) In this embodiment, the first main surface 20 includes a plurality of first depressions 36 recessed from the first flat portion 24. As shown in FIG. 4A , the positions of the plurality of first depressions 36 correspond to the positions of the plurality of second protrusions 32. That is, the arrangement, quantity, and spacing of the first depressions 36 correspond to the arrangement, quantity, and spacing of the second protrusions 32. The first depressions 36 are hemispherical, with the diameter gradually decreasing with increasing distance from the first flat portion 24. The radius of curvature of the first depressions 36 may be, for example, 2 mm to 19 mm, more preferably 3 mm to 15 mm, and even more preferably 4 mm to 10 mm. The depth D of the first depressions 36 relative to the first flat portion 24 may be, for example, 3 mm to 20 mm, more preferably 5 mm to 15 mm, and even more preferably 7 mm to 10 mm. The greater the depth D of the first recess 36, i.e., the deeper the first recess 36, the greater the risk of gas accumulating and forming a gas pocket in the first recess 36. However, as will be described later, by performing R processing on the edge 40 of the first recess 36, gas that has entered the first recess 36 is quickly discharged from the first recess 36 and does not accumulate in the first recess 36.

[0035] The diameter d of the first depression 36 may be, for example, 5 mm or more and 50 mm or less. As shown in Figure 4(a) , the diameter d is the diameter at the edge 40 of the first depression 36, that is, the maximum diameter of the portion recessed in the X-axis direction from the first flat portion 24 of the first main surface 20. When the diameter d of the first depression 36 is 5 mm or more and 50 mm or less, as described below, by performing a rounding process on the edge 40 of the first depression 36, gas that has entered the first depression 36 is more likely to be quickly discharged from the first depression 36.

[0036] As shown in Fig. 4(a) , the first recess 36 and the first protrusion 26 may be connected via the first flat portion 24. Alternatively, as shown in Fig. 4(b) , a first inclined portion 38 that is inclined with respect to the first flat portion 24 may be provided between the first recess 36 and the first protrusion 26. When the first inclined portion 38 is provided, gas generated at the electrode can easily flow between the first recess 36 and the first protrusion 26.

[0037] The edge 40 of the first depression 36 on the first main surface 20 is rounded. The edge 40 is the boundary between the first flat portion 24 and the first depression 36, or the boundary between the first inclined portion 38 and the first depression 36. It is desirable that the rounding be performed around the entire periphery of the edge 40. By rounding the edge 40, gas generated in the electrode can flow smoothly through the first depression 36, thereby preventing gas from accumulating in the first depression 36.

[0038] If the radius of curvature of the edge 40 of the first recess 36 is R3 and the radius of curvature of the bottom 36a of the first recess 36 is R4, the ratio of the radii of curvature R4 / R3 is preferably 0.1 to 19, and more preferably 0.3 to 5. This enhances the effect of allowing gas generated at the electrode to flow smoothly through the first recess 36. The radius of curvature R3 of the edge 40 may be, for example, 1 mm to 20 mm, and more preferably 3 mm to 10 mm.

[0039] The radius of curvature R3 of the edge 40 of the first recess 36 will be described with reference to FIG. 7 . The intersection point P2 between a straight line L1 extending along the first flat portion 24 and a tangent line L5 to the first recess 36 passing through the edge 40 is defined as P2. An auxiliary line L6 is defined that passes through the intersection point P2 and bisects the angle θ2 between the straight line L1 and the tangent line L5. A virtual circle C3 having a center O3 on the auxiliary line L6 is assumed. The radius of the virtual circle C3 when its circumference passes through the intersection point Q2 between the edge 40 of the first recess 36 and the auxiliary line L6 and is tangent to both the straight line L1 and the tangent line L5 is defined as the radius of curvature R3 in this invention.

[0040] The radius of curvature R4 of the bottom 36a of the first recess 36 will be described with reference to Figure 8. A line L1 extending along the first flat portion 24 and a line L7 passing through the bottom 36a of the first recess 36 and perpendicularly intersecting the line L1 are defined. An imaginary circle C4 having a center O4 on the line L7 is assumed. The radius of the imaginary circle C4, whose circumference passes through the bottom 36a of the first recess 36 and whose overlap with the outline of the first recess 36 is maximized, is defined as the radius of curvature R4 in the present invention.

[0041] The radii of curvature R3 and R4 can be determined in the same manner as the radii of curvature R1 and R2 described above.

[0042] When a first inclined portion 38 that is inclined with respect to the first flat portion 24 is provided between the first recess 36 and the first protrusion 26 (see FIG. 4B ), the radius of curvature R1 of the skirt portion 28 of the first protrusion 26 is defined in the same manner as the radius of curvature R1 described above, with P1 being the intersection point between a straight line extending along the first inclined portion 38 and a tangent line L2 of the first protrusion 26 that passes through the skirt portion 28. Furthermore, when the first inclined portion 38 is provided, the radius of curvature R3 of the edge 40 of the first recess 36 is defined in the same manner as the radius of curvature R3 described above, with P2 being the intersection point between a straight line extending along the first inclined portion 38 and a tangent line L5 of the first recess 36 that passes through the edge 40.

[0043] (Second Depressions 42) In this embodiment, the second main surface 22 includes a plurality of second depressions 42 recessed from the second flat portion 30. The positions of the second depressions 42 correspond to the positions of the first protrusions 26, and the arrangement, quantity, and spacing of the second depressions 42 correspond to the arrangement, quantity, and spacing of the first protrusions 26. The second depressions 42 are hemispherical, with diameters gradually decreasing with increasing distance from the second flat portion 30. The dimensions of the second depressions 42 may be the same as or different from the dimensions of the first depressions 36. The greater the depth of the second depressions 42, i.e., the deeper the second depressions 42, the greater the risk of gas stagnation within the second depressions 42 and the formation of gas pockets. However, as described below, by performing a rounded processing on the edges 46 of the second depressions 42, gas that enters the second depressions 42 is quickly discharged from the second depressions 42, preventing it from stagnating within the second depressions 42.

[0044] The diameter of the second depression 42 may be, for example, 5 mm or more and 50 mm or less, similar to the diameter d of the first depression 36. The diameter of the second depression 42 is the diameter at the edge 46 of the second depression 42, that is, the maximum diameter of the portion recessed in the X-axis direction from the second flat portion 30 of the second main surface 22. When the diameter of the second depression 42 is 5 mm or more and 50 mm or less, as described below, by performing a rounding process on the edge 46 of the second depression 42, gas that has entered the second depression 42 is more likely to be quickly discharged from the second depression 42.

[0045] As shown in Fig. 4(a), the second recess 42 and the second protrusion 32 may be connected via the second flat portion 30. Alternatively, as shown in Fig. 4(b), a second inclined portion 44 that is inclined with respect to the second flat portion 30 may be provided between the second recess 42 and the second protrusion 32. When the second inclined portion 44 is provided, gas generated in the electrode can easily flow between the second recess 42 and the second protrusion 32.

[0046] The edge 46 of the second depression 42 on the second main surface 22 is also rounded. The edge 46 is the boundary between the second flat portion 30 and the second depression 42, or the boundary between the second inclined portion 44 and the second depression 42. The rounding is preferably performed around the entire periphery of the edge 46. By rounding the edge 46, gas generated at the electrode can flow smoothly through the second depression 42, thereby preventing gas from accumulating in the second depression 42. The radius of curvature of the edge 46 of the second depression 42 may be the same as or different from the radius of curvature of the edge 40 of the first depression 36.

[0047] The first and second protrusions 26, 32 and the first and second recesses 36, 42 described above may be formed by embossing. Similarly, the rounded edges of the skirts 28, 34 and edges 40, 46 and the first and second sloped portions 38, 44 may also be formed by embossing.

[0048] The radius of curvature R1 of the bottom 34 of the second protrusion 32 on the second main surface 22, the radius of curvature R2 of the top 32a of the second protrusion 32, the radius of curvature R3 of the edge 46 of the second depression 42, and the radius of curvature R4 of the bottom 42a of the second depression 42 are defined in the same way as the radii of curvature R1 to R4 on the first main surface 20, and can be determined in the same way as the method for determining the radii of curvature R1 to R4 on the first main surface 20.

[0049] (Partition Wall Support Frame 10) As shown in Figures 1 and 3, the annular partition wall support frame 10 has a first main surface 48 and a second main surface 50 opposite the first main surface 48. The partition wall support frame 10 is disposed radially outward of the circular partition wall 8, and the inner peripheral edge of the partition wall support frame 10 and the outer peripheral edge of the partition wall 8 are mechanically joined using fasteners such as screws, bolts, or rivets, or are joined by welding. Joining the inner peripheral edge of the partition wall support frame 10 and the outer peripheral edge of the partition wall 8 by welding is preferred because this eliminates the risk of the fasteners falling off and provides sufficient joint strength for long-term use. The material of the partition wall support frame 10 may be a conductive material (e.g., a metal material such as a steel plate) or an insulating material (e.g., a resin). When a metal material is used for the partition wall support frame 10, the surface of the partition wall support frame 10 may be subjected to a surface treatment such as nickel plating. The partition wall support frame 10 may be provided with a bracket (not shown) extending radially outward from the outer peripheral edge of the partition wall support frame 10 .

[0050] (Supply channel of partition wall support frame 10) The partition wall support frame 10 has a supply channel formed therein for supplying the electrode solution to the electrode chambers. Specifically, as shown in FIG. 3 , the partition wall support frame 10 has a first supply channel 52 formed therein for supplying the anode solution to the anode chamber 16 and a second supply channel 54 formed therein for supplying the cathode solution to the cathode chamber 18. The first supply channel 52 includes a first supply opening 56 penetrating a lower part of the partition wall support frame 10 and a first supply recess 58 extending from the first supply opening 56 radially inward of the partition wall support frame 10 in the first main surface 48 of the partition wall support frame 10. The second supply channel 54 includes a second supply opening 60 penetrating a lower part of the partition wall support frame 10 and a second supply recess 62 extending from the second supply opening 60 radially inward of the partition wall support frame 10 in the second main surface 50 of the partition wall support frame 10.

[0051] (Discharge Channel of Partition Wall Support Frame 10) The partition wall support frame 10 is also formed with a discharge channel for discharging the electrode solution and gas from the electrode chambers. Specifically, as shown in FIG. 3 , the partition wall support frame 10 is formed with a first discharge channel 64 for discharging the anode solution and gas from the anode chamber 16 and a second discharge channel 66 for discharging the cathode solution and gas from the cathode chamber 18. The first discharge channel 64 includes a first discharge opening 68 penetrating an upper part of the partition wall support frame 10 and a first discharge recess 70 extending from the first discharge opening 68 radially inward of the partition wall support frame 10 in the first main surface 48 of the partition wall support frame 10. The second discharge channel 66 includes a second discharge opening 72 penetrating an upper part of the partition wall support frame 10 and a second discharge recess 74 extending from the second discharge opening 72 radially inward of the partition wall support frame 10 in the second main surface 50 of the partition wall support frame 10.

[0052] (Electrode 12) The electrode 12 of this embodiment is configured as an anode. As shown in FIGS. 1 and 2 , the electrode 12 is joined by welding to the tops 26 a of the first projections 26 on the first main surfaces 20 of the partition walls 8. This defines an anode chamber 16 between the first main surfaces 20 of the partition walls 8 and the electrode 12 (anode). The electrode 12 is formed into a circular sheet shape as a whole from a perforated plate such as an expanded metal or a punched metal, or a plain woven wire mesh. The material of the electrode 12 may be an electrically conductive material (for example, a metal material such as nickel, or a metal material such as a steel plate plated with nickel). A known catalyst for water electrolysis, such as nickel oxide or a noble metal oxide, may be appropriately provided on the electrode 12.

[0053] (Current Collector 14) The current collector 14 is joined by welding to the apexes 32a of the second projections 32 on the second main surfaces 22 of the partition walls 8. The current collector 14 is formed into a circular sheet shape as a whole from a perforated plate such as an expanded metal or a punched metal. The current collector 14 may be made of an electrically conductive material (for example, a metal material such as a steel plate). The surface of the current collector 14 may be subjected to a surface treatment such as nickel plating.

[0054] In the present invention, the method for joining the electrode or current collector to the top of each of the primary projections or secondary projections is not limited to the welding described above, and any method can be used as long as it ensures electrical conduction between the partition wall and the electrode or current collector, and may be, for example, screwing, crimping with a press, etc. From the viewpoint of reducing electrical resistance and achieving excellent long-term stability, it is preferable that the electrode or current collector be joined to the top of at least one of the primary projections or the secondary projections by welding, and it is more preferable that the electrode or current collector be joined to the top of each of the primary projections and the secondary projections by welding.

[0055] 1 and 2 , a cushion material 76 is provided on the surface of the current collector 14 opposite to the surface bonded to the partition wall 8, for pressing the electrode 12 and the electrode 78 described below against the film 80 described below to bring them into close contact. The cushion material 76 is an elastic mat with woven wires, and is formed into a circular sheet shape as a whole. The material of the cushion material 76 may be a conductive material (for example, a metal material such as nickel).

[0056] (Electrode 78) An electrode 78 is provided on the surface of the cushion material 76 opposite to the surface that contacts the current collector 14. The electrode 78 in this embodiment is configured as a cathode. As described above, the current collector 14 is joined to the tops 32a of the second projections 32, and the electrode 78 (cathode) is in contact with the current collector 14 via the cushion material 76. This defines a cathode chamber 18 between the second main surface 22 of the partition wall 8 and the electrode 78. Like the electrode 12, the electrode 78 is formed into a circular sheet shape as a whole from a perforated plate such as an expanded metal or a punched metal, or a plain woven wire mesh. The material of the electrode 78 may be a conductive material (for example, a metal material such as nickel, or a metal material such as a steel plate plated with nickel). A known catalyst for water electrolysis, such as nickel oxide or a noble metal oxide, may be appropriately provided on the electrode 78.

[0057] In this embodiment, the electrode 12 is an anode and the electrode 78 is a cathode, but the opposite may be true, with the electrode 12 being the cathode and the electrode 78 being the anode. In this case, the electrode chamber indicated by the reference numeral 16 is the cathode chamber, and the electrode chamber indicated by the reference numeral 18 is the anode chamber.

[0058] 1, 2, and 9, the membrane assembly 6 includes a membrane 80, a membrane support frame 82 that supports the peripheral edge of the membrane 80, and a gasket 84 that seals the anode chamber 16 and the cathode chamber 18. Note that the illustration of the gasket 84 is omitted in FIG.

[0059] (Membrane 80) In the case of electrolysis of an alkali metal hydroxide aqueous solution, the membrane 80 is configured as a membrane having ion permeability (for example, a diaphragm or an ion exchange membrane), and in the case of electrolysis of an alkali metal chloride aqueous solution, the membrane 80 is configured as an ion exchange membrane. As shown in Fig. 9, the membrane 80 is formed in a circular shape, similar to the partition wall 8.

[0060] (Membrane Support Frame 82) The membrane support frame 82 is formed in an annular shape corresponding to the partition wall support frame 10. The membrane support frame 82 is disposed radially outside the circular membrane 80, and supports the membrane 80 by sandwiching the outer periphery of the membrane 80 with the inner periphery of the membrane support frame 82. The material of the membrane support frame 82 may be a conductive material (e.g., a metal material such as a steel plate) or an insulating material (e.g., a resin or an elastomer). If the membrane support frame 82 is made of a conductive material, the surface of the membrane support frame 82 may be subjected to a surface treatment such as nickel plating. Note that the membrane support frame 82 may be provided with a bracket (not shown) extending radially outward from the outer periphery of the membrane support frame 82.

[0061] 9 , first and second supply openings 86, 88 penetrating the membrane support frame 82 are formed in the lower part of the membrane support frame 82. Furthermore, first and second discharge openings 90, 92 penetrating the membrane support frame 82 are formed in the upper part of the membrane support frame 82. The position of the first supply opening 86 of the membrane support frame 82 corresponds to the position of the first supply opening 56 of the partition wall support frame 10, and the position of the second supply opening 88 of the membrane support frame 82 corresponds to the position of the second supply opening 60 of the partition wall support frame 10. Furthermore, the position of the first discharge opening 90 of the membrane support frame 82 corresponds to the position of the first discharge opening 68 of the partition wall support frame 10, and the position of the second discharge opening 92 of the membrane support frame 82 corresponds to the position of the second discharge opening 72 of the partition wall support frame 10.

[0062] 1 and 2, the gaskets 84 are attached to both sides of the membrane support frame 82 in the X direction. The gaskets 84 may be attached to the membrane support frame 82 with adhesive, double-sided adhesive tape, or the like. The gaskets 84 are formed in an annular shape extending along the entire periphery of the membrane support frame 82. However, although not shown in detail, the gaskets 84 are not present in positions corresponding to the first and second supply openings 86, 88 and the first and second discharge openings 90, 92 of the membrane support frame 82. The material of the gaskets 84 may be an appropriate known material, such as an elastomer.

[0063] The gasket 84 can also serve as the membrane support frame 82. That is, the inner peripheral portion of the annular gasket 84 formed to correspond to the partition wall support frame 10 can sandwich and support the outer peripheral edge of the membrane 80. In this case, the gasket 84 functions as the membrane support frame 82, and, like the membrane support frame 82, is provided with first and second supply openings 86, 88 and first and second discharge openings 90, 92.

[0064] When assembling the electrolytic cell 2 as described above, a plurality of partition wall assemblies 4 and membrane assemblies 6 are prepared and arranged alternately. At this time, the first and second supply openings 56, 60 of the partition wall support frame 10 are aligned with the first and second supply openings 86, 88 of the membrane support frame 82. Furthermore, the first and second discharge openings 68, 72 of the partition wall support frame 10 are aligned with the first and second discharge openings 90, 92 of the membrane support frame 82. Furthermore, an electrode 78 is arranged, via a cushion material 76, on the surface of the current collector 14 opposite to the surface that is joined to the partition wall 8.

[0065] Next, the alternatingly arranged partition wall assemblies 4 and the alternatingly arranged membrane assemblies 6 are sandwiched and pressed by a fixed head (not shown) and a movable head (not shown). Specifically, the fixed head and the movable head are connected by a plurality of tie rods (not shown), so that the alternatingly arranged partition wall assemblies 4 and the membrane assemblies 6 are sandwiched and pressed by the fixed head and the movable head.

[0066] Although not shown, the movable head and the fixed head are connected to the following flow path members: an anode liquid supply flow path member that communicates with the first supply opening 56 of the partition wall support frame 10 and the first supply opening 86 of the membrane support frame 82; a cathode liquid supply flow path member that communicates with the second supply opening 60 of the partition wall support frame 10 and the second supply opening 88 of the membrane support frame 82; an anode liquid discharge flow path member that communicates with the first discharge opening 68 of the partition wall support frame 10 and the first discharge opening 90 of the membrane support frame 82; and a cathode liquid discharge flow path member that communicates with the second discharge opening 72 of the partition wall support frame 10 and the second discharge opening 92 of the membrane support frame 82.

[0067] (Electrolysis) When electrolysis is performed in the electrolytic cell 2, first, an anolyte pump (not shown) supplies anolyte to the anolyte supply flow path member, and a catholyte pump (not shown) supplies catholyte to the catholyte supply flow path member. The pressure within the electrolytic cell 2 during electrolysis can be set to any pressure value within a range of approximately 10 kPa to 10 MPa. It is more preferable that the pressure within the electrolytic cell 2 during electrolysis be within a range of 300 kPa to 5 MPa, as this enables the electrolytic cell 2 to be made smaller and the electrolysis efficiency to be improved.

[0068] The anolyte supplied to the anolyte supply flow path member passes through the first supply opening 56 of the partition wall support frame 10 and the first supply opening 86 of the membrane support frame 82, and then passes through the first supply recess 58 of the partition wall support frame 10, to be supplied to the anode chamber 16. Furthermore, the catholyte supplied to the catholyte supply flow path member passes through the second supply opening 60 of the partition wall support frame 10 and the second supply opening 88 of the membrane support frame 82, and then passes through the second supply recess 62 of the partition wall support frame 10, to be supplied to the cathode chamber 18.

[0069] After the anolyte is supplied to the anode chamber 16 and the cathode liquid is supplied to the cathode chamber 18, a required voltage is applied to the electrode 12 (anode in this embodiment) and the electrode 78 (cathode in this embodiment). This causes gas to be generated from both the electrodes 12 and 78. The gas generated at the electrode 12 is discharged from the anode chamber 16 together with the anolyte through the first discharge recess 70 in the partition wall support frame 10, and then passes through the first discharge opening 68 in the partition wall support frame 10 and the first discharge opening 90 in the membrane support frame 82, and is delivered to the flow path member for discharging the anolyte. The gas generated at the electrode 78 is discharged from the cathode chamber 18 together with the cathode liquid through the second discharge recess 74 in the partition wall support frame 10, and then passes through the second discharge opening 72 in the partition wall support frame 10 and the second discharge opening 92 in the membrane support frame 82, and is delivered to the flow path member for discharging the cathode liquid.

[0070] As described above, in this embodiment, the edges 40, 46 of the first and second recesses 36, 42 are rounded, so that gas generated at the electrode 12 flows without accumulating inside the first recess 36, and gas generated at the electrode 78 flows without accumulating inside the second recess 42. As a result, gas accumulation inside the first and second recesses 36, 42 can be suppressed. Therefore, the flow of the electrode solution inside the electrode chambers (anode chamber 16 and cathode chamber 18) is made uniform, preventing excessively large differences in concentration of the electrode solution inside the electrode chambers. As a result, the current distribution is made uniform, preventing a decrease in electrolysis efficiency.

[0071] Furthermore, when the bottoms 28, 34 of the first and second protrusions 26, 32 are also rounded as in this embodiment, gas accumulation near the first and second protrusions 26, 32 is suppressed, thereby making the flow of the electrode solution in the electrode chamber more uniform.

[0072] However, when the operation of the electrolytic cell 2 is stopped, gas dissolved in the electrode solution may be released from the electrode solution, potentially reducing the purity of the gas produced by electrolysis. Therefore, when the operation of the electrolytic cell 2 is stopped, it is preferable to quickly replace or drain the electrode solution in the electrode chambers. In particular, in a high-pressure electrolytic cell 2 operating at a relatively high pressure (e.g., an electrolytic cell operated at a pressure in the range of 300 kPa to 5 MPa), the amount of dissolved gas in the electrode solution is large, making it necessary to quickly replace or drain the electrode solution in the electrode chambers. In this regard, in the electrolytic cell 2 of this embodiment, the edges 40, 46 of the first and second recesses 36, 42 are rounded, thereby reducing the retention of electrode solution in the first and second recesses 36, 42. This allows the electrode solution in the electrode chambers to be quickly replaced or drained, thereby preventing a reduction in the purity of the gas produced by electrolysis.

[0073] (First Modification) In the above embodiment, the first and second protrusions 26, 32 and the first and second recesses 36, 42 are described as being hemispherical. However, other shapes are also possible. For example, as shown in Figures 10(a) and 10(b), the first and second protrusions 26, 32 and the first and second recesses 36, 42 may be conical. The tops 26a, 32a of the first and second protrusions 26, 32 are rounded. The bottoms 36a, 42a of the first and second recesses 36, 42 are also rounded. The diameters of the first protrusions 26 and the first recesses 36 gradually decrease with increasing distance from the first flat portion 24. The diameters of the second protrusions 32 and the second recesses 42 gradually decrease with increasing distance from the second flat portion 30.

[0074] The radius of curvature of the tops 26a, 32a of the first and second protrusions 26, 32 in the first modified example may be, for example, approximately 3 mm to 200 mm, but is preferably 3 mm to 200 mm, and more preferably 5 mm to 50 mm. The radius of curvature of the bottoms 36a, 42a of the first and second recesses 36, 42 may be, for example, approximately 1 mm to 190 mm, but is preferably 1 mm to 190 mm, more preferably 2 mm to 50 mm, and even more preferably 3 mm to 20 mm. The height H of the first and second protrusions 26, 32 and the depth D of the first and second recesses 36, 42 in the first modified example may be, for example, 3 mm to 20 mm, more preferably 5 mm to 15 mm, and even more preferably 7 mm to 10 mm.

[0075] In the first modified example, the edges 40, 46 of the first and second recesses 36, 42 are also rounded. If the radius of curvature of the edge 40 of the first recess 36 is R7 and the radius of curvature of the bottom 36a of the first recess 36 is R8, the ratio of the radii of curvature R8 / R7 is preferably 0.05 to 190, more preferably 0.2 to 17, and even more preferably 0.3 to 7. Furthermore, the base 28 of the first protrusion 26 may also be rounded. For example, if the radius of curvature of the base 28 of the first protrusion 26 is R5 and the radius of curvature of the top 26a of the first protrusion 26 is R6, the ratio of the radii of curvature R6 / R5 is preferably 0.6 to 400.

[0076] The radius of curvature R5 of the base 28 of the first protrusion 26 may be, for example, 0.5 mm or more and 5 mm or less, but preferably 0.7 mm or more and 3 mm or less. The radius of curvature R7 of the edge 40 of the first recess 36 may be, for example, 1 mm or more and 20 mm or less, but preferably 3 mm or more and 10 mm or less. In the example shown in Fig. 10, the dimensions of the second protrusion 32 (including the radii of curvature of the top 32a and base 34) are the same as those of the first protrusion 26, and the dimensions of the second recess 42 (including the radii of curvature of the bottom 42a and edge 46) are the same as those of the first recess 36, but may be different.

[0077] The radii of curvature R5 to R8 in the first modified example correspond to the radii of curvature R1 to R4 described above, respectively, and are defined in the same manner as the radii of curvature R1 to R4, and can be calculated in the same manner as the radii of curvature R1 to R4.

[0078] In the first modified example as described above, the gas generated at the electrode 12 flows without stagnating inside the first recess 36, and the gas generated at the electrode 78 flows without stagnating inside the second recess 42, so gas accumulation is suppressed inside the first and second recesses 36, 42. Furthermore, if the skirts 28, 34 of the first and second protrusions 26, 32 are also rounded, the gas generated at the electrode 12 flows without stagnating near the first protrusion 26, and the gas generated at the electrode 78 flows without stagnating near the second protrusion 32, so gas accumulation near the first and second protrusions 26, 32 can be further suppressed.

[0079] In the first modified example, the first recess 36 and the first protrusion 26 may also be connected via the first flat portion 24, and the second recess 42 and the second protrusion 32 may also be connected via the second flat portion 30 (see FIG. 10( a)). Alternatively, as shown in FIG. 10( b), a first inclined portion 38 may be provided between the first recess 36 and the first protrusion 26, and a second inclined portion 44 may be provided between the second recess 42 and the second protrusion 32.

[0080] 11( a) and 11(b), the first and second protrusions 26, 32 and the first and second recesses 36, 42 may be frustoconical. The diameters of the first protrusions 26 and the first recesses 36 gradually decrease with increasing distance from the first flat portion 24. The diameters of the second protrusions 32 and the second recesses 42 gradually decrease with increasing distance from the second flat portion 30. In the second modification, the height H of the first and second protrusions 26, 32 and the depth D of the first and second recesses 36, 42 may be, for example, 3 mm or more and 20 mm or less, more preferably 5 mm or more and 15 mm or less, and even more preferably 7 mm or more and 10 mm or less.

[0081] In the second modification, the tops 26 a, 32 a of the first and second protrusions 26, 32 are circular or approximately circular when viewed from a direction perpendicular to the first main surface 20 and the second main surface 22, respectively. As shown in FIG. 11 , the diameter d1 of the tops 26 a, 32 a of the first and second protrusions 26, 32 is the diameter of a portion parallel or approximately parallel to the first flat portion 24 of the first main surface 20 (excluding the portion subjected to rounding), and is smaller than the diameter d of the first and second depressions 36, 42. In the second modification, electrodes or current collectors are joined to the tops 26 a, 32 a of the first and second protrusions 26, 32 by welding, and current passes through them during electrolysis. From the viewpoint of reducing electrical resistance during electrolysis and increasing electrolysis efficiency, the diameter d1 of the tops 26 a, 32 a of the first and second protrusions 26, 32 is, for example, preferably 5 mm or more, more preferably 10 mm or more, and even more preferably 15 mm or more. In the second modified example as well, the electrodes or current collectors may be joined to the tops 26a, 32a of the first and second projections 26, 32 by a method other than welding.

[0082] In the second modified example, the edges 40, 46 of the first and second recesses 36, 42 are also rounded. Furthermore, the bottom portions 28, 34 of the first and second protrusions 26, 32 may also be rounded. In the second modified example, it is preferable that the top edges 26b, 32b of the first and second protrusions 26, 32 are also rounded, and that the bottom edges 36b, 42b of the first and second recesses 36, 42 are also rounded.

[0083] If the radius of curvature of the base 28 of the first projection 26 is R9 and the radius of curvature of the top periphery 26b of the first projection 26 is R10, the ratio of the radii of curvature R10 / R9 is preferably 0.1 or more and 100 or less, and more preferably 0.4 or more and 40 or less. Furthermore, if the radius of curvature of the edge 40 of the first recess 36 is R11 and the radius of curvature of the bottom periphery 36b of the first recess 36 is R12, the ratio of the radii of curvature R12 / R11 is preferably 0.05 or more and 50 or less, more preferably 0.1 or more and 10 or less, and even more preferably 0.2 or more and 5 or less.

[0084] The radius of curvature R9 of the base 28 of the first projection 26 may be, for example, 0.5 mm or more and 5 mm or less, and the radius of curvature R11 of the edge 40 of the first recess 36 may be, for example, 1 mm or more and 20 mm or less, but preferably 3 mm or more and 15 mm or less. The radius of curvature R10 of the top peripheral edge 26b of the first projection 26 may be, for example, 0.5 mm or more and 50 mm or less, but preferably 2 mm or more and 20 mm or less. The radius of curvature R12 of the bottom peripheral edge 36b of the first recess 36 may be, for example, 1 mm or more and 50 mm or less, but preferably 2 mm or more and 20 mm or less, and more preferably 3 mm or more and 10 mm or less. In the example shown in Figure 11, the dimensions of the second protrusion 32 (including the radius of curvature of the top periphery 32b and the bottom 34) are the same as the dimensions of the first protrusion 26, and the dimensions of the second recess 42 (including the radius of curvature of the bottom periphery 42b and the edge 46) are the same as the dimensions of the first recess 36, but they may be different.

[0085] The radius of curvature R9 of the bottom 28 of the first protrusion 26 and the radius of curvature R9 of the bottom 34 of the second protrusion 32 in the second modified example are defined in the same way as the radius of curvature R1 described above, and can be determined in the same way as the method for determining the radius of curvature R1. Furthermore, the radius of curvature R11 of the edge 40 of the first recess 36 and the radius of curvature R11 of the edge 46 of the second recess 42 in the second modified example are defined in the same way as the radius of curvature R3 described above, and can be determined in the same way as the method for determining the radius of curvature R3.

[0086] The radius of curvature R10 of the top periphery 26b of the first protrusion 26 in the second modified example will be described with reference to FIG. 12 . The intersection point P3 between a straight line L8 extending along the top 26a of the first protrusion 26 and a tangent line L9 to the first protrusion 26 passing through the top periphery 26b is defined as P3. An auxiliary line L10 is defined that passes through the intersection point P3 and bisects the angle θ3 between the line L8 and the tangent line L9. A virtual circle C5 having a center O5 on the auxiliary line L10 is assumed. The radius of the virtual circle C5 when its circumference passes through the intersection point Q3 between the top periphery 26b of the first protrusion 26 and the auxiliary line L10 and is tangent to both the straight line L8 and the tangent line L9 is defined as the radius of curvature R10 in the present invention.

[0087] The radius of curvature R12 of the bottom periphery 36b of the first recess 36 in the second modified example will be described with reference to FIG. 13 . The intersection point P4 between a straight line L11 extending along the bottom 36a of the first recess 36 and a tangent line L12 to the first recess 36 passing through the bottom periphery 36b is defined as P4. An auxiliary line L13 is defined that passes through the intersection point P4 and bisects the angle θ4 between the line L11 and the tangent line L12. An imaginary circle C6 having a center O6 on the auxiliary line L13 is assumed. The radius of the imaginary circle C6, which passes through the intersection point Q4 between the bottom periphery 36b of the first recess 36 and the auxiliary line L13 and is tangent to both the line L11 and the tangent line L12, is defined as the radius of curvature R12 in the present invention.

[0088] In the second modified example as described above, the gas generated at the electrode 12 flows without stagnation inside the first recess 36, and the gas generated at the electrode 78 flows without stagnation inside the second recess 42, so that it is possible to prevent gas from pooling inside the first and second recesses 36, 42. Furthermore, if the skirts 28, 34 of the first and second protrusions 26, 32 are also rounded, the gas generated at the electrode 12 flows without stagnation near the first protrusion 26, and the gas generated at the electrode 78 flows without stagnation near the second protrusion 32, so that it is possible to further prevent gas from pooling near the first and second protrusions 26, 32.

[0089] Furthermore, in the second modified example, the first and second protrusions 26, 32 have a truncated cone shape, so the contact area between the first protrusions 26 and the electrode 12 and the contact area between the second protrusions 32 and the current collector 14 are larger than in the above-described embodiment and the first modified example. Therefore, electrical resistance during electrolysis is reduced, improving the efficiency of electrolysis.

[0090] In the second modified example, the first recess 36 and the first protrusion 26 may also be connected via the first flat portion 24, and the second recess 42 and the second protrusion 32 may also be connected via the second flat portion 30 (see FIG. 11( a)). Alternatively, as shown in FIG. 11( b), a first inclined portion 38 may be provided between the first recess 36 and the first protrusion 26, and a second inclined portion 44 may be provided between the second recess 42 and the second protrusion 32.

[0091] 2: Electrolytic cell 4: Partition wall assembly 6: Membrane assembly 8: Partition wall 10: Partition wall support frame 12: Electrode 14: Current collector 16: Anode chamber 18: Cathode chamber 20: First main surface of partition wall 22: Second main surface of partition wall 24: First flat portion 26: First projection 26a: Top of first projection 26b: Top periphery of first projection (second modified example) 28: Bottom of first projection 30: Second flat portion 32: Second projection 32a: Top of second projection 32b: Top periphery of second projection (second modified example) 34: Bottom of second projection 36: First recess 36a: Bottom of first recess 36b: Bottom periphery of first recess (second modified example) 40: Edge of first recess 42: Second recess 42a: Bottom of second recess 42b: Bottom rim of second recess (second modified example) 46: Edge of second recess 76: Cushion material 78: Electrode 80: Membrane 82: Membrane support frame 84: Gasket

Claims

1. A partition wall of an electrolytic cell that separates an anode chamber and a cathode chamber, the partition wall having a first main surface and a second main surface located opposite the first main surface, the first main surface including a first flat portion and a plurality of first depressions recessed from the first flat portion, the edges of the first depressions being rounded, and the second main surface including a second flat portion and a plurality of second depressions recessed from the second flat portion, the edges of the second depressions being rounded.

2. A partition wall for an electrolytic cell according to claim 1, wherein the first main surface includes a plurality of first mountain-shaped projections that protrude beyond the first flat portion, and the second main surface includes a plurality of second mountain-shaped projections that protrude beyond the second flat portion.

3. A partition wall for an electrolytic cell as described in claim 2, wherein a first inclined portion inclined with respect to the first flat portion is provided between the first protrusion and the first recess on the first main surface, and a second inclined portion inclined with respect to the second flat portion is provided between the second protrusion and the second recess on the second main surface.

4. A partition wall for an electrolytic cell according to claim 2, wherein the positions of the plurality of first depressions correspond to the positions of the plurality of second projections, and the positions of the plurality of second depressions correspond to the positions of the plurality of first projections.

5. The partition wall of an electrolytic cell according to claim 2, wherein the first protrusion, the second protrusion, the first recess and the second recess are hemispherical.

6. A partition wall for an electrolytic cell according to claim 5, wherein, when the radius of curvature of the edges of the first recess and the second recess is R3 and the radius of curvature of the bottoms of the first recess and the second recess is R4, the ratio of the radii of curvature R4 / R3 is 0.1 or more and 19 or less.

7. A partition wall for an electrolytic cell according to claim 5, wherein the bottoms of the first projections and the second projections are rounded.

8. A partition wall for an electrolytic cell according to claim 7, wherein, when the radius of curvature of the base of the first projection and the second projection is R1 and the radius of curvature of the top of the first projection and the second projection is R2, the ratio of the radii of curvature R2 / R1 is 0.6 or more and 40 or less; and when the radius of curvature of the edges of the first depression and the second depression is R3 and the radius of curvature of the bottom of the first depression and the second depression is R4, the ratio of the radii of curvature R4 / R3 is 0.1 or more and 19 or less.

9. A partition wall for an electrolytic cell as described in claim 2, wherein the first protrusion, the second protrusion, the first depression and the second depression are conical in shape, and the tops of the first protrusion and the second protrusion and the bottoms of the first depression and the second depression are rounded.

10. A partition wall for an electrolytic cell according to claim 9, wherein when the radius of curvature of the edges of the first recess and the second recess is R7 and the radius of curvature of the bottoms of the first recess and the second recess is R8, the ratio of the radii of curvature R8 / R7 is 0.05 or more and 190 or less.

11. The partition wall of an electrolytic cell according to claim 9, wherein the bottoms of the first projections and the second projections are rounded.

12. A partition wall for an electrolytic cell according to claim 11, wherein, when the radius of curvature of the base of the first projection and the second projection is R5 and the radius of curvature of the top of the first projection and the second projection is R6, the ratio of the radii of curvature R6 / R5 is 0.6 or more and 400 or less; and when the radius of curvature of the edges of the first depression and the second depression is R7 and the radius of curvature of the bottom of the first depression and the second depression is R8, the ratio of the radii of curvature R8 / R7 is 0.05 or more and 190 or less.

13. A partition wall for an electrolytic cell according to claim 2, wherein the first protrusion, the second protrusion, the first recess and the second recess are frustoconical in shape, and the bottom periphery of the first recess and the bottom periphery of the second recess are rounded.

14. A partition wall for an electrolytic cell according to claim 13, wherein, when the radius of curvature of the edges of the first recess and the second recess is R11 and the radius of curvature of the bottom peripheral edges of the first recess and the second recess is R12, the ratio of the radii of curvature R12 / R11 is 0.05 or more and 50 or less.

15. A partition wall for an electrolytic cell according to claim 13, wherein the bottoms of the first projections and the second projections and the top periphery of the first projections and the top periphery of the second projections are rounded.

16. A partition wall for an electrolytic cell according to claim 15, wherein, when the radius of curvature of the base of the first projection and the second projection is R9 and the radius of curvature of the top peripheral edges of the first projection and the second projection is R10, the ratio of the radii of curvature R10 / R9 is 0.1 or more and 100 or less; and when the radius of curvature of the edges of the first depression and the second depression is R11 and the radius of curvature of the bottom peripheral edges of the first depression and the second depression is R12, the ratio of the radii of curvature R12 / R11 is 0.05 or more and 50 or less.

17. A bulkhead assembly comprising a bulkhead according to any one of claims 1 to 16 and a bulkhead support frame that supports the peripheral edge of the bulkhead.

18. The bulkhead assembly of claim 17, wherein the bulkhead is circular and the bulkhead support frame is annular.

19. The bulkhead assembly of claim 17, comprising an electrode or current collector bonded to the top of each of the plurality of first projections, and a current collector or electrode bonded to the top of each of the plurality of second projections.

20. The bulkhead assembly of claim 17, comprising an electrode or current collector joined by welding to the top of each of the plurality of first projections, and a current collector or electrode joined to the top of each of the plurality of second projections.

21. The bulkhead assembly of claim 17, comprising an electrode or current collector joined by welding to the top of each of the plurality of first projections, and a current collector or electrode joined by welding to the top of each of the plurality of second projections.

22. An electrolytic cell in which a plurality of partition wall assemblies and a plurality of membrane assemblies according to claim 19 are alternately arranged, wherein the membrane assembly includes a membrane and a membrane support frame that supports the peripheral edge of the membrane.

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