Porous metal sheet, electrode for electrochemical device, current collector for electrochemical device, and electrochemical device

Abstract

This porous metal sheet comprises a first sheet and a second sheet. This porous metal sheet has, in a plan view, a first end and a second end, which are ends in a first direction, and a third end and a fourth end, which are ends in a second direction that is perpendicular to the first direction. Each of the first sheet and the second sheet is formed of a porous metal body which has a skeleton of a three-dimensional network structure and pores that are defined by the skeleton. The first sheet has a first end part that is located at an end of the first sheet in the second direction. The second sheet has a second end part that is located at an end of the second sheet in the second direction. The first sheet and the second sheet are arranged along the second direction so that the first end part and the second end part overlap each other between the first end and the second end so as to form a joint part.

Description

Metal porous sheet, electrode for electrochemical device, current collector for electrochemical device, and electrochemical device

[0001] The present disclosure relates to a metal porous sheet, an electrode for an electrochemical device, a current collector for an electrochemical device, and an electrochemical device. This application claims priority based on Japanese Patent Application No. 2024-199847, a Japanese patent application filed on November 15, 2024. All the descriptions contained in the Japanese patent application are incorporated herein by reference.

[0002] WO 2020 / 044776 (Patent Document 1) describes a metal porous sheet. The metal porous sheet described in Patent Document 1 has a first sheet and a second sheet. The first sheet and the second sheet each have a three-dimensional network structure skeleton and pores defined by the skeleton. The first sheet has a first end in a first direction, and the second sheet has a second end in the first direction. The first sheet and the second sheet are arranged along the first direction such that the first end and the second end overlap each other to form a joint. A concave portion is formed on one main surface of the metal porous sheet so as to overlap the joint in a plan view.

[0003] WO 2020 / 044776

[0004] The metal porous sheet of the present disclosure includes a first sheet and a second sheet. The metal porous sheet has, in a plan view, a first end and a second end which are ends in a first direction, and a third end and a fourth end which are ends in a second direction perpendicular to the first direction. Each of the first sheet and the second sheet is formed of a metal porous body having a three-dimensional network structure skeleton and pores defined by the skeleton. The first sheet has a first end portion located at the end of the first sheet in the second direction. The second sheet has a second end portion located at the end of the second sheet in the second direction. The first sheet and the second sheet are arranged along the second direction such that the first end portion and the second end portion overlap each other to form a joint between the first end and the second end. The width of the pores in a third direction perpendicular to the first direction and the second direction is smaller than the width of the pores in the first direction and the width of the pores in the second direction over the distance between the third end and the fourth end.

[0005] Figure 1 is a plan view of the porous metal sheet 100. Figure 2 is a cross-sectional view taken along line II-II in Figure 1. Figure 3A is a perspective view of the first sheet 10. Figure 3B is a schematic cross-sectional view of the first sheet 10. Figure 4 is a cross-sectional view of an electrochemical device 200 using the porous metal sheet 100. Figure 5 is a manufacturing process diagram of the porous metal sheet 100. Figure 6 is a perspective view illustrating the preparation process S1. Figure 7A is a plan view illustrating the roll press process S2. Figure 7B is a side view illustrating the roll press process S2. Figure 8 is a plan view of the porous metal sheet 400. Figure 9 is a cross-sectional view taken along line IX-IX in Figure 8.

[0006] The porous metal sheet described in Patent Document 1 does not have sufficient gas venting properties when used as an electrode in an electrochemical device. This disclosure provides a porous metal sheet that can ensure gas venting properties when used as an electrode in an electrochemical device while ensuring bonding properties between sheets.

[0007] The porous metal sheet of this disclosure ensures good bonding between the first sheet and the second sheet while also ensuring gas escape when used as an electrode in an electrochemical device.

[0008] (1) A porous metal sheet according to one embodiment comprises a first sheet and a second sheet. In a plan view, the porous metal sheet has a first end and a second end which are the ends in a first direction, and a third end and a fourth end which are the ends in a second direction perpendicular to the first direction. Each of the first and second sheets is formed of a porous metal having a three-dimensional network structure skeleton and voids defined by the skeleton. The first sheet has a first end located at the end of the first sheet in a second direction. The second sheet has a second end located at the end of the second sheet in a second direction. The first and second sheets are aligned along the second direction such that the first and second ends overlap each other and form a joint between the first and second ends. The width of the voids in the third direction perpendicular to the first and second directions is smaller than the width of the voids in the first direction and the width of the voids in the second direction, between the third and fourth ends.

[0009] According to the porous metal sheet described in (1) above, it is possible to ensure gas venting while securing bonding strength between the first sheet and the second sheet.

[0010] (2) The porous metal sheet described in (1) above may have a first main surface and a second main surface which are end faces in the third direction. The first main surface and the second main surface may be flat between the third end and the fourth end.

[0011] (3) In the case of the porous metal sheet described in (1) or (2) above, the maximum thickness and minimum thickness of the porous metal sheet may be 0.7 times or more and 1.3 times or less the average thickness of the porous metal sheet, respectively.

[0012] (4) In the porous metal sheets described in (1) to (3) above, the average diameter of the voids in the first sheet may be the same as the average diameter of the voids in the second sheet.

[0013] (5) In the porous metal sheets described in (1) to (3) above, the average diameter of the pores in the first sheet may be different from the average diameter of the pores in the second sheet.

[0014] (6) In the porous metal sheets described in (1) to (4) above, the width of the joint in the second direction may be 3 mm or more.

[0015] According to the porous metal sheet described in (6) above, a bonding area can be secured between the first sheet and the second sheet.

[0016] (7) In the porous metal sheet described in (1) to (6) above, the width of the joint in the second direction may be 0.5 times or less the distance between the third end and the fourth end in the second direction.

[0017] According to the porous metal sheet described in (7) above, it is possible to ensure the performance of the porous metal as an electrode while securing the bonding area between the first sheet and the second sheet.

[0018] (8) In the porous metal sheet described in (1) to (7) above, the width of the joint in the second direction may be 0.005 times or more the product of the distance between the third end and the fourth end in the second direction and the aspect ratio of the pores in the joint.

[0019] According to the porous metal sheet described in (8) above, it is possible to ensure the performance of the porous metal as an electrode while securing the bonding area between the first sheet and the second sheet.

[0020] (9) The electrode for the electrochemical device according to the embodiment comprises a porous metal sheet. It comprises the porous metal sheet described in (1) to (8) above.

[0021] (10) A current collector for an electrochemical device according to one embodiment comprises a porous metal sheet. The porous metal sheet is one of the porous metal sheets described in (1) to (8) above.

[0022] (11) The gas diffusion layer for the electrochemical device according to the embodiment comprises a porous metal sheet. The porous metal sheet is one of the porous metal sheets described in (1) to (8) above.

[0023] (12) An electrochemical device according to one embodiment comprises a diaphragm and a porous metal sheet. The porous metal sheet is the porous metal sheet described in (1) above. The porous metal sheet has a first main surface and a second main surface, which are end faces in the third direction. The first main surface and the second main surface are flat between the third end and the fourth end. One of the first main surface and the second main surface is in contact with the diaphragm.

[0024] The details of the embodiments of this disclosure will be described with reference to the drawings. In the following drawings, the same or corresponding parts are denoted by the same reference numerals, and redundant descriptions will not be repeated. The porous metal sheet according to the embodiment will be referred to as the porous metal sheet 100.

[0025] (Structure of the porous metal sheet 100) The structure of the porous metal sheet 100 is described below.

[0026] As shown in Figures 1 and 2, the shape of the porous metal sheet 100 is, for example, rectangular in plan view. A pair of parallel sides forming this rectangle are aligned along a first direction DR1, and another pair of parallel sides forming this rectangle are aligned along a second direction DR2. The second direction DR2 is perpendicular to the first direction DR1 in plan view. The porous metal sheet 100 has ends 100a and 100b in the first direction DR1, and ends 100c and 100d in the second direction DR2.

[0027] The width of the porous metal sheet 100 in the second direction DR2 is defined as width W1. Width W2 is the distance between the ends 100c and 100d in the second direction DR2. Width W1 is, for example, 50 mm or more. Width W1 is, for example, 1500 mm or less.

[0028] The porous metal sheet 100 has a main surface 100e and a main surface 100f. The main surfaces 100e and 100f are the end faces of the porous metal sheet 100 in the third direction DR3. The third direction DR3 is perpendicular to the first direction DR1 and the second direction DR2. The main surfaces 100e and 100f are flat. The thickness of the porous metal sheet 100 is denoted as thickness T. Thickness T is the distance between the main surfaces 100e and 100f in the third direction DR3. The maximum and minimum values ​​of thickness T are 1.3 times or less and 0.7 times or more the average value of thickness T, respectively. In this case, the main surfaces 100e and 100f are considered to be parallel and flat to each other.

[0029] The porous metal sheet 100 comprises a first sheet 10 and a second sheet 20. The first sheet 10 and the second sheet 20 are, for example, rectangular in plan view. A pair of parallel sides forming this rectangle are aligned along a first direction DR1, and another pair of parallel sides forming this rectangle are aligned along a second direction DR2.

[0030] The first sheet 10 has an end 11 and an end 12 in the second direction DR2. End 11 is located at end 100c. End 12 is located opposite to end 11 in the second direction DR2. The second sheet 20 has an end 21 and an end 22 in the second direction DR2. End 21 is located at end 100d. End 22 is located opposite to end 21 in the second direction DR2.

[0031] As shown in Figures 3A and 3B, the first sheet 10 is formed of a porous metal 30. The porous metal 30 has a framework 31. The framework 31 is made of a metallic material. For example, the framework 31 is made of nickel. The inside of the framework 31 is hollow. The porous metal 30 has voids 32 inside. The voids 32 are defined by the framework 31.

[0032] In forming the porous metal body 30, firstly, a foam made of resin material is prepared. The foam contains a large number of air bubbles inside. Secondly, the foam is subjected to a plating treatment. This forms a metal film on the surface of the air bubbles. Thirdly, the foam is removed using a chemical solution or the like, leaving only the metal film behind. This remaining metal film becomes the framework 31, and the locations where the air bubbles were contained within the foam become voids 32 defined in the framework 31.

[0033] The second sheet 20 is also formed of a porous metal 30. However, the average pore diameter of the porous metal 30 used in the second sheet 20 may be different from or the same as the average pore diameter of the porous metal 30 used in the first sheet 10.

[0034] The first sheet 10 and the second sheet 20 are arranged along the second direction DR2 such that their ends 12 and 22 overlap each other between ends 100a and 100b. Ends 12 and 22 form a joint 40. At the joint 40, the porous metal 30 forming the first sheet 10 and the porous metal 30 forming the second sheet 20 are intertwined with each other, and the first sheet 10 and the second sheet 20 are joined together. As described above, the thickness T is constant between ends 100c and 100d, so the thickness of the first sheet 10 at end 12 is smaller than the thickness of the first sheet 10 at other ends, and the thickness of the second sheet 20 at end 22 is smaller than the thickness of the second sheet 20 at other ends.

[0035] The porous metal sheet 100 is rolled so that its thickness T is constant between the end 100c and the end 100d. When rolling is performed, the width of the voids 32 in the third direction DR3 becomes smaller than the width of the voids 32 in the first direction DR1 and the width of the voids 32 in the second direction DR2. Therefore, in the porous metal sheet 100, the width of the voids 32 in the third direction DR3 is smaller than the width of the voids 32 in the first direction DR1 and the width of the voids 32 in the second direction DR2, across the distance between the end 100c and the end 100d.

[0036] The width of the joint 40 in the second direction DR2 is denoted as width W2. Width W2 is, for example, 3 mm or more. Width W2 is, for example, 0.5 times or less of width W1. As the rolling ratio when forming the porous metal sheet 100 increases, the aspect ratio of the voids in the joint 40 decreases. Width W2 is, for example, 0.005 times or more the product of width W1 and the aspect ratio of the voids in the joint 40. Note that the aspect ratio of the voids is the value obtained by dividing the width of the voids in the third direction DR3 by the width of the voids in the second direction DR2.

[0037] As shown in Figure 4, the porous metal sheet 100 is used in the electrochemical device 200. In the example shown in Figure 4, the electrochemical device 200 is an alkaline water electrolysis apparatus. Figure 4 shows one electrolytic cell of the alkaline water electrolysis apparatus. The electrolytic cell of the electrochemical device 200 (alkaline water electrolysis apparatus) has a case 210, a diaphragm 220, electrodes 231 and 232, and supports 241 and 242.

[0038] The diaphragm 220 is made of a material that does not allow oxygen or hydrogen gas to pass through, but does allow water to pass through. The diaphragm 220 is placed inside the case 210. The diaphragm 220 divides the internal space of the case 210 into a first space 211 and a second space 212.

[0039] Each of electrodes 231 and 232 has a porous metal sheet 100. The porous metal sheet 100 used in electrodes 231 and 232 supports a catalyst inside. One of the main surfaces of the porous metal sheet 100 used in electrodes 231 and 232 is in contact with the diaphragm 220. Each of supports 241 and 242 is made of a conductive material. Support 241 is in contact with the other main surface of the porous metal sheet 100 used in electrode 231. Support 242 is in contact with the other main surface of the porous metal sheet 100 used in electrode 232.

[0040] The anode and cathode of the power supply 250 are electrically connected to the support 241 and support 242, respectively. Therefore, electrodes 231 and 232 function as the anode and cathode of the electrolytic cell, respectively.

[0041] In the case 210, an inlet 213a and an outlet 213b, and an inlet 214a and an outlet 214b are formed. The inlet 213a and the outlet 213b communicate with the first space of the case 210, and the inlet 214a and the outlet 214b communicate with the second space of the case 210. An alkaline aqueous solution flows into the first space of the case 210 from the inlet 213a, and after flowing through the first space of the case 210, the alkaline aqueous solution flows out from the outlet 213b. Similarly, an alkaline aqueous solution flows into the second space of the case 210 from the inlet 214a, and after flowing through the second space of the case 210, the alkaline aqueous solution flows out from the outlet 214b. The above alkaline aqueous solution is, for example, an aqueous potassium hydroxide solution.

[0042] When the alkaline aqueous solution flows through the internal space of the case 210 as described above, oxygen gas is generated from the electrode 231 and hydrogen gas is generated from the electrode 232 due to the electrolysis of the alkaline aqueous solution by applying a voltage from the power source 250 between the electrode 231 and the electrode 232. The generated oxygen gas flows out from the outlet 213b, and the generated hydrogen gas flows out from the outlet 214b.

[0043] In the above, an alkaline water electrolyzer has been described as an example of the electrochemical device 200, but the electrochemical device 200 is not limited thereto. The electrochemical device 200 may be, for example, an AEM (Anion Exchange Membrane) electrolyzer or a fuel cell. Further, the metal porous sheet 100 may be used not only as an electrode for an alkaline water electrolyzer but also as an electrode for an AEM electrolyzer or a current collector or a gas diffusion layer for a fuel cell.

[0044] (Manufacturing method of the metal porous sheet 100) The manufacturing method of the metal porous sheet 100 will be described below.

[0045] As shown in FIG. 5, the manufacturing method of the metal porous sheet 100 has a preparation step S1 and a roll pressing step S2. As shown in FIG. 6, in the preparation step S1, the first sheet 10 and the second sheet 20 are arranged along the second direction DR2 such that the end portion 12 and the end portion 22 overlap each other.

[0046] As shown in FIGS. 7A and 7B, in the roll press process S2, roll pressing is performed on the first sheet 10 and the second sheet 20 arranged as described above. The roll pressing is performed using a roll press machine 300. The roll press machine 300 has a roll 311 and a roll 312. The roll 311 and the roll 312 are arranged at intervals along the third direction DR3.

[0047] Each of the roll 311 and the roll 312 extends along the second direction DR2. The roll 311 rotates around the central axis of the roll 311, and the roll 312 rotates around the central axis of the roll 312 in a direction opposite to that of the roll 311. By rotating the roll 311 and the roll 312 with the first sheet 10 and the second sheet 20 arranged as described above sandwiched between the roll 311 and the roll 312, the first sheet 10 and the second sheet 20 are sent along the first direction DR1 while being rolled. Since the length of the roll 311 in the second direction DR2 and the length of the roll 312 in the second direction DR2 are larger than the width W1, the metal porous body sheet 100 is rolled over between the end 100c and the end 100d.

[0048] In the above manner, the metal porous body sheet 100 is manufactured. Since the metal porous body sheet 100 is manufactured by the roll pressing as described above, the main surface 100e and the main surface 100f are flat over between the end 100c and the end 100d (the thickness T is constant over between the end 100c and the end 100d).

[0049] (Effect of the metal porous body sheet 100) Hereinafter, the effect of the metal porous body sheet 100 will be described while comparing it with the metal porous body sheet according to the comparative example. The metal porous body sheet according to the comparative example is referred to as a metal porous body sheet 400.

[0050] As shown in Figures 8 and 9, in the porous metal sheet 400, rolling is performed by the rollers only at the positions where the ends 12 and 22 overlap each other. That is, in the porous metal sheet 400, a recess 100g is formed on the main surface 100e so as to overlap with the joint 40 in a plan view. Therefore, in the porous metal sheet 400, the main surface 100e is not flat and the thickness T is not constant between the end 100c and the end 100d. In this respect, the structure of the porous metal sheet 400 differs from the structure of the porous metal sheet 100.

[0051] As described above, gases (oxygen gas and hydrogen gas) are generated at electrodes 231 and 232. When the porous metal sheets used for electrodes 231 and 232 are being rolled, these gases are more easily released from electrodes 231 and 232. In the porous metal sheet 400, rolling is performed only at the position that overlaps with the joint 40 in a plan view; therefore, the first sheet 10 and the second sheet 20 located outside the joint 40 are not subjected to rolling.

[0052] When a porous metal sheet 400 is used for electrodes 231 and 232, and the main surface 100e is brought into contact with the diaphragm 220, oxygen gas and hydrogen gas generated in the space demarcated by the recess 100g and the diaphragm 220 accumulate. On the other hand, the porous metal sheet 100 is rolled across the area between the end 100c and the end 100d. Furthermore, even when the main surface 100e of the porous metal sheet 100 is brought into contact with the diaphragm 220, gas does not easily accumulate because the main surface 100e is flat, unlike the porous metal sheet 400. Thus, the porous metal sheet 100 ensures gas venting.

[0053] When the porous metal sheet 400 is used for electrodes 231 and 232, and the main surface 100f is brought into contact with the diaphragm, the main surface 100e comes into contact with the support 241 and support 242. In the recess 100g, there is no contact with the support 241 and support 242, so in this case, the contact resistance between the support 241 and support 242 increases. On the other hand, with the porous metal sheet 100, both the main surface 100e and the main surface 100f are flat, so unlike the porous metal sheet 400, the contact resistance between the support 241 and support 242 does not increase. Thus, the porous metal sheet 100 also improves the electrical characteristics.

[0054] In the porous metal sheet 400, in order to improve gas venting, it is conceivable to pre-roll the first sheet 10 and the second sheet 20, and then further roll them to form a recess 100g and join the first sheet 10 and the second sheet 20. However, in this case, the porous metal 30 located at the joint 40 is rolled and then further rolled, resulting in insufficient joint strength at the joint 40. On the other hand, in the porous metal sheet 100, the rolling for joining and the rolling of the first sheet 10 and the second sheet 20 outside the joint 40 are carried out simultaneously, so both gas venting and joint strength can be achieved.

[0055] If the width W2 of the porous metal sheet 100 is 3 mm or more, a sufficient bonding area can be secured between the first sheet 10 and the second sheet 20. At the bonding portion 40, the rolling ratio of the porous metal 30 is greater than at the bonding portion 40. Therefore, if the width W2 is too large, the porosity of the porous metal sheet 100 as a whole will decrease too much, and the performance as an electrode 231 (electrode 232) will deteriorate. Therefore, if the width W2 is 0.5 times or less of the width W1, the bonding area between the first sheet 10 and the second sheet 20 can be secured while ensuring the performance as an electrode 231 (electrode 232).

[0056] Furthermore, as the rolling ratio of the porous metal sheet 100 increases, the aspect ratio of the pores in the joint 40 decreases. Therefore, by making the width W2 at least 0.005 times the product of the width W1 and the aspect ratio of the pores in the joint 40, it is possible to secure the bonding area between the first sheet 10 and the second sheet 20 while ensuring the performance as an electrode 231 (electrode 232).

[0057] (Examples) Samples 1 to 20 were prepared to confirm the effect of the porous metal sheet 100. In each sample, the width W1, width W2, aspect ratio of the pores at the joint 40, and the value obtained by dividing width W2 by the product of width W1 and the aspect ratio of the pores at the joint 40 were changed. However, in samples 1 and 14, the porous metal sheet was made up of a single sheet and did not have a joint 40. Details of each sample are shown in Table 1. In samples 7 to 10, three sheets were used.

[0058]

[0059] Tensile tests and electrolytic voltage measurements were performed on each sample. In the tensile tests, each sample was pulled along the second direction DR2, and the stress at which fracture occurred was used for evaluation. The tensile test result was evaluated as A if the difference between the tensile strength of sample 1 (sample 14) and the sample strength was -5 MPa or more; the tensile test result was evaluated as B if the difference between the tensile strength of sample 1 (sample 14) and the sample strength was -10 MPa or more but less than -5 MPa; and the tensile test result was evaluated as C if the difference between the tensile strength of sample 1 (sample 14) and the sample strength was less than -10 MPa.

[0060] In the measurement of electrolytic voltage, the measurement result was evaluated as A if the difference from the electrolytic voltage of Sample 1 (Sample 14) was less than -30 mV, the measurement result was evaluated as B if the difference from the electrolytic voltage of Sample 1 (Sample 14) was between -30 mV and 20 mV, and the measurement result was evaluated as C if the difference from the electrolytic voltage of Sample 1 (Sample 14) was 20 mV or more. The results of the tensile test and the electrolytic voltage measurement are shown in Table 2.

[0061]

[0062] As shown in Table 2, samples with a width W2 of 3 mm or more received a rating of B or higher in the tensile test. This indicates that the bonding strength between sheets is improved by setting the width W2 to 3 mm or more. Samples with a width W2 of 0.5 times or less of the width W1 received an A rating in the electrolytic voltage measurement results. This indicates that gas venting is ensured and the electrolytic voltage is improved by setting the width W2 to 0.5 times or less of the width W1. Furthermore, in samples where the width W2 is 0.005 times or more the product of the aspect ratio of the width W1 and the pores in the bonding portion 40, both the tensile test results and the electrolytic voltage measurement results were rated A. This indicates that both bonding strength between sheets and gas venting are possible by setting the width W2 to 0.005 times or more the product of the aspect ratio of the width W1 and the pores in the bonding portion 40.

[0063] It should be understood that at least one configuration or feature described in each embodiment and example can be combined with or modified in various ways in other embodiments and examples. Furthermore, the embodiments disclosed herein should be considered in all respects to be illustrative and not restrictive. The scope of the present invention is indicated by the claims rather than the embodiments described above, and all modifications within the meaning and scope of the claims are intended to be included.

[0064] 10 First sheet, 11, 12 Ends, 20 Second sheet, 21, 22 Ends, 30 Porous metal, 31 Skeleton, 32 Holes, 40 Joint, 100, 400 Porous metal sheet, 100a, 100b, 100c, 100d Ends, 100e, 100f Main surface, 100g Recess, 200 Electrochemical device, 210 Case, 211 First space, 212 Second space, 213a Inlet, 214a Inlet, 213b, 214b Outlet, 220 Diaphragm, 231, 232 Electrodes, 241, 242 Support, 250 Power supply, 300 Roll press machine, 311, 312 Rolls, DR1 First direction, DR2 Second direction, DR3 Third direction, S1 Preparation process, S2 Roll press process, T thickness, W1, W2 width.

Claims

1. A porous metal sheet comprising a first sheet and a second sheet, wherein the porous metal sheet has, in a plan view, a first end and a second end which are the ends in a first direction, and a third end and a fourth end which are the ends in a second direction perpendicular to the first direction, and each of the first sheet and the second sheet is formed of a porous metal having a three-dimensional mesh structure skeleton and voids defined by the skeleton, the first sheet has a first end located at the end of the first sheet in the second direction, the second sheet has a second end located at the end of the second sheet in the second direction, the first sheet and the second sheet are arranged along the second direction such that the first end and the second end overlap each other and form a joint between the first end and the second end, and the width of the voids in a third direction perpendicular to the first and second directions is smaller than the width of the voids in the first direction and the width of the voids in the second direction between the third end and the fourth end.

2. The porous metal sheet according to claim 1, wherein the porous metal sheet has a first main surface and a second main surface which are end faces in the third direction, and the first main surface and the second main surface are flat between the third end and the fourth end.

3. The metal porous sheet according to claim 1 or claim 2, wherein the maximum thickness and minimum thickness of the metal porous sheet are 0.7 times or more and 1.3 times or less of the average thickness of the metal porous sheet, respectively.

4. The porous metal sheet according to any one of claims 1 to 3, wherein the average diameter of the voids in the first sheet is the same as the average diameter of the voids in the second sheet.

5. The porous metal sheet according to any one of claims 1 to 3, wherein the average diameter of the voids in the first sheet is different from the average diameter of the voids in the second sheet.

6. The porous metal sheet according to any one of claims 1 to 4, wherein the width of the joint in the second direction is 3 mm or more.

7. The porous metal sheet according to any one of claims 1 to 6, wherein the width of the joint in the second direction is 0.5 times or less the distance between the third end and the fourth end in the second direction.

8. The porous metal sheet according to any one of claims 1 to 7, wherein the width of the joint in the second direction is 0.005 times or more the product of the distance between the third end and the fourth end in the second direction and the aspect ratio of the voids in the joint.

9. An electrode for an electrochemical device comprising the porous metal sheet described in any one of claims 1 to 8.

10. A current collector for an electrochemical device comprising the porous metal sheet described in any one of claims 1 to 8.

11. A gas diffusion layer for an electrochemical device comprising the porous metal sheet described in any one of claims 1 to 8.

12. An electrochemical device comprising a diaphragm and the porous metal sheet described in claim 1, wherein the porous metal sheet has a first main surface and a second main surface which are end faces in the third direction, the first main surface and the second main surface are flat between the third end and the fourth end, and one of the first main surface and the second main surface is in contact with the diaphragm.

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