Porous transport layer

Abstract

A porous transport layer for an electrolytic cell or a fuel cell, A first non-woven fabric layer of metal fibers provided for contact with a proton exchange membrane, comprising metal fibers of a first equivalent diameter, A first non-woven fabric layer of metal fibers having a first surface roughness and a first porosity, A second non-woven fabric layer of metal fibers, comprising metal fibers of a second equivalent diameter, A second non-woven fabric layer of metal fibers having a second surface roughness and a second porosity, and The first surface has a material ratio of less than 5% of the material at a height of 5 μm and a material ratio of more than 70% of the material at a depth of -5 μm, The first equivalent diameter is smaller than the second equivalent diameter, The first surface roughness is at least 20% smaller than the second surface roughness, for example, in the range of 20% to 120% smaller, The first porosity is at least 10% smaller than the second porosity, for example, in the range of 10% to 50% smaller, The first non-woven fabric layer is metallurgically bonded to the second non-woven fabric layer.

Description

[Technical Field]

[0001] The present invention relates to the field of porous transport layers, such as those used in electrolytic cells and fuel cells. [Background technology]

[0002] Proton exchange membrane (PEM) electrolytic cells can be used to convert water into separate hydrogen and oxygen streams. Such a PEM electrolytic cell contains a polymer electrolyte located between the anode and cathode electrodes. The anode-side porous transport layer and the cathode-side gas diffusion layer are located adjacent to the anode and cathode electrodes, respectively. Porous metals, such as titanium or titanium alloys, can be used as the anode-side porous transport layer.

[0003] International Publication No. 03 / 059556A2 discloses a stack for use as a porous transport layer in a fuel cell or electrolytic cell. The stack comprises an impermeable metal structure, a first metal fiber layer, and a second metal fiber layer. The impermeable metal structure is sintered on one side of the first metal fiber layer, and the second metal fiber layer is sintered on the other side of the first metal fiber layer. The second metal fiber layer is provided as a contact layer to the PEM in the fuel cell or electrolytic cell. The planar air permeability of the stack is greater than 0.02 l / min*cm.

[0004] A further modified porous transport layer is published in International Publication No. 2018 / 189005. The porous transport layer comprises a first nonwoven layer of metal fibers, a second nonwoven layer of metal fibers, and a third porous metal layer, all provided for contact with a proton exchange membrane. The first nonwoven layer contains metal fibers of a first equivalent diameter. The second nonwoven layer contains metal fibers of a second equivalent diameter, the second equivalent diameter being greater than the first equivalent diameter. The third porous metal layer contains open pores, the open pores of the third porous metal layer being larger than the open pores of the second nonwoven layer of metal fibers. The second nonwoven layer is provided between the first nonwoven layer and the third porous metal layer and is in contact with both the first and third porous metal layers. The second nonwoven layer is metallurgically bonded to the first and third porous metal layers.

[0005] The efficiency of fuel cell systems or electrolytic cell systems is greatly influenced by the properties of the porous transport layer. International Publication No. 2020 / 151997 discloses a porous transport layer based on multiple micro and nano-sintered porous layers. The sintered porous layer is permeable to gaseous and liquid substances in electrochemical cells, and the multilayer porous transport layer is suitable for integration between the bipolar plate and catalyst layer of an electrochemical cell. Multiple micro and nano-sintered porous layers are fabricated from irregularly shaped particles of conductive material. Micro-sintered porous layers are fabricated from particles having a larger diameter than the particles in nano-sintered porous layers. The multilayer structure is achieved by coaxial pressing of multiple irregularly sputtered powders, where the average particle diameter decreases from layer to layer. The mechanical integrity and specific bulk properties of the porous transport layer are obtained by the sintering process.

[0006] Another improved porous transport layer is a single-layer titanium sheet, as disclosed in U.S. Patent Application No. 2022 / 0023946. The porous titanium layer used as the anode-side porous transport layer is formed by a powder process, e.g., by tape casting, or by powder metallurgy techniques in which titanium powder is pressed into a porous titanium sheet using a compression process. The cast or compressed sheet is then sintered to produce a porous transport layer with established metallurgical joints. The porous titanium sheet may have a porosity of 40–60 percent. [Overview of the project]

[0007] A first aspect of the present invention is a porous transport layer for an electrolytic cell or fuel cell, A nonwoven fabric layer of first metal fibers provided for contact with a proton exchange membrane, comprising metal fibers of first equivalent diameter, A nonwoven fabric layer of first metal fibers having a first surface roughness and a first porosity, A second nonwoven fabric layer of metal fibers, comprising metal fibers of a second equivalent diameter, It comprises a second nonwoven fabric layer of metal fibers having a second surface roughness and a second porosity, The material ratio of the first surface is less than 5% of the material at a height of 5 μm, more than 70% of the material at a depth of -5 μm, preferably more than 75% of the material at a depth of -5 μm, and the zero level is the average line of the profile resulting from subtracting the best file line through the measurement from the surface roughness measurement. The first equivalent diameter is smaller than the second equivalent diameter. The first porosity is at least 10% smaller than the second porosity, for example, in the range of 10% to 50%. The first nonwoven fabric layer is metallurgically bonded to the second nonwoven fabric layer.

[0008] The first nonwoven layer is provided to act as a contact layer toward the anode electrode. It is beneficial that the porosity of the first layer is at least 10% lower than that of the second layer. The side of the porous transport layer with higher porosity, i.e., the second metal fiber nonwoven layer, will be oriented toward the flow plate side of the electrolytic cell or fuel cell. Therefore, higher porosity allows more water to enter the pores. On the other hand, the side of the porous transport layer with lower porosity, i.e., the first metal fiber nonwoven layer, will be oriented toward the anode electrode side of the electrolytic cell or fuel cell. Therefore, lower porosity provides improved electrical contact with the anode electrode. According to the present invention, the porous transport layer comprises two layers having different porosities. Importantly, the first nonwoven layer is metallurgically bonded to the second nonwoven layer. Therefore, the porous transport layer made from the first and second nonwoven layers behaves like an assembly. Therefore, the porosity of each side and the overall porosity of the porous transport layer can be well controlled by the assembly of two separate layers. This is advantageous compared to a single-layer porous transport layer, such as the one described in U.S. Patent Application No. 2022 / 0023946, in which the first main surface of the porous titanium sheet has at least 10 percent higher porosity than the second surface opposite the second main surface. This is also advantageous compared to International Publications No. 2018 / 189005 and 2020 / 151997, which disclose porous transport layers based on multiple sintered porous layers, because the porosity of each layer in those multiple sintered porous layers is quite similar as a result of a single sintering process.

[0009] Furthermore, the first surface roughness is at least 20% smaller than the second surface roughness, for example, in the range of 20% to 120%. The first and second surface roughnesses are mean surface roughness (Ra) and are measured according to the standard ASME B46.1. PEM electrolytic cells typically have a catalyst coating film. The catalyst coated on the film is platinum (Pt) on the cathode side and iridium (Ir) on the anode side. The deficiency of Ir is very relevant to the development of PEM. The global Ir production rate is approximately 7 tons / year. Current catalyst packing rate (2 mg / cm³) 2Under these conditions, the annual installation of PEM electrolytic cells is limited to 2 GW. Unfortunately, due to its high stability and efficiency, there are no alternative catalysts for the oxygen evolution reaction (anode side) that can compete with Ir. As there are no competing alternatives, research is focused on significantly reducing the amount of Ir catalyst packed in while maintaining the same performance. To maintain acceptable performance, the catalyst needs to be in close contact with the porous transport layer (electron pathway) and the ionomer (hydrogen ion pathway). A lower amount of Ir packing means a thinner catalyst layer, reducing contact with the porous transport layer. Furthermore, Ir particles tend to aggregate, which also negatively affects contact with the porous transport layer, and therefore reduces performance due to poor catalyst utilization.

[0010] In addition to reducing the amount of catalyst packed, the trend in PEM electrolytic cells is to reduce membrane thickness, decrease overvoltage, and improve overall performance. This trend presents several challenges regarding the mechanical properties at the porous transport layer / anode / membrane interface. In fact, the membrane is a fragile component of PEM batteries, and poor contact with the porous transport layer / anode can lead to membrane rupture, increasing the risk of short circuits within the battery.

[0011] According to the present invention, the material ratio of the first surface is characterized. The material ratio (MR) is the ratio of material in a profile to a perfectly flat and smooth profile at a given height above the mean plane, or in other words, the ratio of the area of ​​intersection of planes (i.e., parallel to the mean plane) passing through the surface at a given height to the cross-sectional area of ​​the evaluation region. The material ratio curve (MRC) (also known as the support area curve or Abbott-Firestone curve) is established by evaluating the MR at various levels from the highest peak to the lowest valley. For each profile, it is generated by simulating a horizontal line moving from top to bottom across the profile and evaluating the proportion of time the line is in contact with the surface at each level. MR and MRC are referenced and described in the standard ISO_21920-2_EN.

[0012] To solve the above problems, the porous transport layer of the present invention, in which the material ratio of the first surface is less than 5% of the material at a height of 5 μm, i.e., 5 μm above the reference zero level or mean plane, can be used to enhance contact with Ir particles and prevent film rupture. In addition, the material ratio of the first surface is more than 70% of the material at a depth of -5 μm (minus 5 μm), i.e., 5 μm below the reference zero level, preferably more than 75% of the material at a depth of -5 μm, where the zero level is the mean line of the profile resulting from subtracting the best file line through measurement from the surface roughness measurement. The microstructure of this first nonwoven layer should be finer and denser than that of the second nonwoven layer, and the interparticle distance should be smaller, in order to ensure close contact with the catalyst layer. This also provides a more uniform redistribution of the force applied to the film, preventing its mechanical degradation. The first surface roughness of the first layer is at least 20% smaller than the second surface roughness of the second layer, for example, in the range of 20% to 120%.

[0013] The second nonwoven fabric layer is metallurgically bonded to the first nonwoven fabric layer. The metallurgical bonding can be carried out, for example, by sintering or by welding (for example, by capacitive discharge welding, CDW). Preferably, the metal fibers in the first nonwoven fabric layer are metallurgically bonded to each other. Preferably, the metal fibers in the second nonwoven fabric layer are metallurgically bonded to each other.

[0014] The presence of a first nonwoven layer of metal fibers negatively affects the inflow and outflow of molecules through the plane, and as a result, the reduced flow increases the required overvoltage of the electrolytic cell, thus negatively impacting the functionality of the electrolytic cell or fuel cell. Interlayer metallurgical bonding is important because such bonding provides low electrical resistance between layers. It is desirable to provide a reliable metallurgical bonding between the first and second nonwoven layers. The advantages are that the ohmic resistance of the porous transport layer is reduced, the overvoltage of the electrolytic cell is reduced, and the mechanical stability of the porous transport layer is improved. Both nonwoven surfaces inevitably have some degree of fuzziness. As a result, fibers from the first nonwoven fabric penetrate to some extent into the second nonwoven fabric, and metal fibers from the second nonwoven fabric penetrate to some extent into the first nonwoven fabric. Penetration strengthens metal-to-metal contact and metallurgical bonding, both of which are beneficial in reducing the ohmic resistance of the porous transport layer, reducing the overvoltage of the electrolytic cell, and improving the mechanical stability of the porous transport layer.

[0015] The equivalent diameter of a fiber refers to the diameter of a circle that has the same surface area as the cross-section of a fiber, even if that fiber does not necessarily have a circular cross-section.

[0016] The pore size of the nonwoven fabric layer can be observed in several ways. A cross-section can be prepared through the thickness of the porous transport layer, and the cross-section can be analyzed under a microscope where the pores and their size are visible. A more advanced method is X-ray tomography of the porous transport layer. Alternatively, the pore size can be measured by mercury porosimetry.

[0017] According to the present invention, the first equivalent diameter may be less than 20 μm, preferably less than 15 μm. The use of fine fibers is beneficial because it provides a large contact area with the PEM for electrochemical reactions, and the fine pores present due to the use of fine fibers in the first nonwoven layer enable capillary action for efficient transport of mass to and from the reaction site in the PEM. The second equivalent diameter is preferably less than 50 μm, more preferably less than 30 μm. The second equivalent diameter is preferably larger than the first equivalent diameter. As an example, the first equivalent diameter is 14 μm and the second equivalent diameter is 22 μm. The second nonwoven layer of metal fibers has a larger diameter, and therefore the pores in the second nonwoven layer are larger than the pores in the first nonwoven layer. As an example, the first nonwoven fabric layer has a porosity in the range of 35-50%, preferably 40-50%, and the second nonwoven fabric layer has a porosity in the range of 51-90%, with the overall porosity of the porous transport layer being in the range of 50-80%. As a result, efficient planar mass inflow and outflow are obtained. Preferably, the thickness of the first nonwoven fabric layer is less than 100 μm. Such embodiments provide a particularly beneficial porous transport layer because the first nonwoven fabric layer providing the contact layer with the PEM is thin, and as a result, a second nonwoven fabric layer of greater thickness can be provided in the space available to provide a porous transport layer in the electrolytic cell, and the second nonwoven fabric layer provides planar inflow and outflow of water and reaction products.

[0018] Preferably, the thickness of the second nonwoven layer is at least twice the thickness of the first nonwoven layer. Thus, thanks to the thickness of the second nonwoven layer, planar flow is further improved, thereby providing a larger cross-section for planar mass flow. The second layer has a higher porosity and thus has a positive effect on planar permeability because the mass limit is controlled. The high porosity of the second layer allows more water to enter the pores, while the low porosity of the first layer on the anode side provides improved electrical contact with the anode. Furthermore, this structure has a cost advantage because the application of coarser fibers in the second layer, which has a higher sintered porosity, maintains the low cost of the transport layer.

[0019] Preferably, the first non-woven fabric layer and the second non-woven fabric layer contain titanium fibers, and more preferably consist of titanium fibers. Alternatively, the first and second non-woven fabric layers can be made of titanium alloy fibers, nickel fibers, nickel alloy fibers, or stainless steel fibers.

[0020] In a preferred embodiment, the metal fibers of the first non-woven fabric layer and / or the second non-woven fabric layer have a discontinuous length and a cross-section, and the cross-section has two adjacent straight sides with an included angle of less than 90 degrees and one or more irregularly shaped curved sides. The first non-woven fabric layer of metal fibers has a large surface area due to the irregular shape of its cross-section. As a result, when the surface of the first non-woven fabric layer is coated with a catalyst, or when the proton exchange membrane is coated with a catalyst, the surface area in contact with the proton exchange membrane where an electrochemical reaction can occur is increased. Such fibers can be produced as described in International Publication No. WO 2014 / 048738 A1. Another technique for producing such fibers is described in U.S. Patent No. 4,640,156.

[0021] Alternatively, the second non-woven fabric layer of metal fibers has a square, preferably rectangular cross-section. The technique for manufacturing such fibers is disclosed in U.S. Patent No. 4,930,199. This provides the advantage that the second non-woven fabric layer of metal fibers has a more compact cross-section, which does not create an obstacle to the planar inflow and outflow of gas in an electrolytic cell or fuel cell where a porous transport layer is used.

[0022] As an example, the second non-woven fabric layer may further include one or more expanded metal sheets or wire meshes, and the expanded metal sheets or wire meshes are metallurgically joined to each other, for example, by sintering or by welding, such as capacitive discharge welding (CDW). It is beneficial for the expanded metal sheet to have higher rigidity than the sintered non-woven fabric. The porous transport layer of the present invention may further include a third porous metal layer having a larger pore diameter and / or porosity adjacent to the second non-woven fabric layer of metal fibers. The multi-layer porous transport layer including one or more expanded metal sheets enables a large surface area on the PEM side, while the rigidity prevents sagging when compressed against the profiled surface provided by the machined bipolar plate in the flow path.

[0023] A second aspect of the present invention is a method for producing a porous transport layer for an electrolytic cell or a fuel cell according to any one of the preceding claims, preferably in the following order: (a) a step of producing a non-sintered layer of a non-woven fabric of first metal fibers; (b) a step of compressing the non-sintered layer of the non-woven fabric of first metal fibers to obtain a compressed non-woven fabric layer of first metal fibers; (c) a step of producing a non-sintered layer of a non-woven fabric of second metal fibers; (d) a step of stacking the compressed non-sintered layer of the non-woven fabric of first metal fibers on the non-sintered layer of the non-woven fabric of second metal fibers to form a double-layer structure; (e) a step of sintering the double-layer structure, for example, in an oxygen-free or low-oxygen atmosphere at 1000 to 1200 °C for 1 to 2 hours, preferably under a load of 70 kg / m 2 ~200 kg / m 2 ; (f) optionally, a step of compressing the sintered double-layer structure to a predetermined thickness, and the method includes these steps.

[0024] To obtain a durable compressed nonwoven fabric layer, compression can be applied under a load of 30-80 kN / mm², for example, 60 kN / mm². Such applied forces can result in a nonwoven fabric layer with a porosity of 30-50%. The applied force is selected according to the desired porosity. This force applied according to the present invention is significantly greater than the usual force applied for calendering of fiber webs. The fibers intertwine better in the nonwoven fabric layer after compression.

[0025] The porous transport layer of the present invention is manufactured by a single sintering process. Compared to a double-layer porous transport layer manufactured by two sintering steps, the porous transport layer of the present invention is less expensive because one sintering step is omitted. Surprisingly, the porous transport layer of the present invention exhibits a smoother surface and better performance than a similar double-layer porous transport layer manufactured by two sintering steps.

[0026] A third aspect of the present invention is a stack for an electrolytic cell or fuel cell, comprising a porous transport layer and a bipolar plate according to the first aspect of the present invention. The bipolar plate is in contact with a second nonwoven fabric layer. Preferably, the bipolar plate is metallurgically bonded to the second nonwoven fabric layer, for example, by sintering or welding. Preferably, the bipolar plate is flat across the entire surface in contact with the second nonwoven fabric layer, meaning that no flow field is provided on the bipolar plate.

[0027] A fourth aspect of the present invention is an assembly of a porous transport layer and a proton exchange membrane according to the first aspect of the present invention. The first nonwoven layer is in contact with the proton exchange membrane. Preferably, the catalyst is provided on the first nonwoven layer on the side in contact with the proton exchange membrane, or the catalyst is provided on the proton exchange membrane on the side in contact with the first nonwoven layer.

[0028] A fifth aspect of the present invention is an assembly of a stack according to the third aspect of the present invention and a proton exchange membrane. A first nonwoven layer is in contact with the proton exchange membrane. Preferably, the catalyst is provided on the first nonwoven layer on the side in contact with the proton exchange membrane, or the catalyst is provided on the proton exchange membrane on the side in contact with the first nonwoven layer. [Brief explanation of the drawing]

[0029] [Figure 1] A schematic cross-section of the porous transport layer according to the present invention is shown. [Figure 2] The material ratio curve of the porous transport layer (I) according to the present invention is compared with several reference porous transport layers (a, b, c, d, e). [Figure 3] The change in porosity (P) over the thickness (d) of the porous transport layer (I) of the present invention is compared with that of a reference porous transport layer (R). [Figure 4] The voltage (IV curve) at the measured cell current density of a proton exchange membrane water electrolysis (PEMWE) cell to which the porous transport layer (I) of the present invention is applied is illustrated and compared with reference porous transport layers (d) and (e). [Modes for carrying out the invention]

[0030] An exemplary porous transport layer 10 according to the present invention is schematically shown in Figure 1. The exemplary porous transport layer 10 consists of a first titanium fiber nonwoven fabric layer 12 and a second titanium fiber nonwoven fabric layer 22. The first titanium fiber nonwoven fabric layer is provided to be in contact with the proton exchange membrane in the electrolytic cell. The first titanium fiber nonwoven fabric layer contains, preferably, titanium fibers having an equivalent diameter of 14 μm. The titanium fibers of the first nonwoven fabric layer have a length of 10 mm and a cross-section, the cross-section having two adjacent straight sides with an angle of less than 90 degrees and one or more irregularly shaped curved sides. The first nonwoven fabric layer 12 has a thickness d1 of about 40 μm. The first nonwoven fabric layer 12 has a porosity of about 43%.

[0031] The second nonwoven fabric layer 22 has an equivalent diameter of 22 μm and weighs 400 g / m².2 It contains, and preferably consists of, titanium fibers. The thickness d2 of the second nonwoven layer 22 is about 160 μm to 200 μm. The second nonwoven layer 22 has a porosity of about 58%. Therefore, the overall porosity of the porous transport layer consisting of the first and second nonwoven layers is about 56%. Because the equivalent diameter of the fibers in the second nonwoven layer 22 is larger than that of the first nonwoven layer 12, the open pores are larger in the second nonwoven layer 22 than in the first nonwoven layer 12. The surface roughness of the first nonwoven layer 12 is at least 20% less than the surface roughness of the second nonwoven layer 32. As shown in Figure 2 of the material ratio (%) at different given depths (-30 μm to +30 μm) of the porous transport layer (I) of the present invention, the first surface has a material ratio of less than 5% of the material at a height of 5 μm and more than 70% of the material at a depth of -5 μm.

[0032] Such a porous transport layer 10 is preferably manufactured according to the following sequence of steps. (a) A step of producing a first nonwoven fabric layer of titanium fibers, (b) A step of compressing a first metal fiber nonwoven fabric layer under a load of preferably 30 to 80 kN / mm², for example 60 kN / mm², to obtain a compressed first metal fiber nonwoven fabric layer. (c) A process for producing a second nonwoven fabric layer of metal fibers, (d) A step of stacking a compression-sintered first titanium fiber nonwoven fabric layer with a second titanium fiber nonwoven fabric layer to form a double-layer structure. (e) The double-layer structure is subjected to a load of 70 kg / m³, preferably in an oxygen-free or low-oxygen atmosphere at 1000-1200°C for 1-2 hours. 2 ~200kg / m 2 A process of sintering under a load, (f) Optionally, a step of compressing the sintered double-layer structure to a predetermined thickness.

[0033] A similar double-layer porous transport layer (R) was prepared as a reference for comparison, following the above process except for the waste disposal step (b). Therefore, for the equivalent double-layer porous transport layer (R), the fiber diameter of the first layer is smaller than the fiber diameter of the second layer. For example, here, the first layer consists of titanium fibers with an equivalent diameter of 14 μm, and the second layer consists of titanium fibers with an equivalent diameter of 22 μm. Without performing the pre-compression step (b) during the production of the reference porous transport layer (R), a double-layer structure was formed by stacking the nonwoven fabric layer of the first titanium fibers with the nonwoven fabric layer of the second titanium fibers, and then this was sintered under equivalent conditions. Figure 3 compares the change in porosity throughout the thickness of the porous transport layer (I) and the reference porous transport layer (R) of the present invention. As shown in Figure 3, the porous transport layer (I) of the present invention has two porosities as described above, while the reference porous transport layer (R) has a uniform porosity throughout the entire thickness of the porous transport layer. The porosity of the reference transport layer (R) is approximately 56% for both the first and second nonwoven layers, which is similar to the porosity of the second nonwoven layer of the porous transport layer (I) of the present invention. The pre-sintering pre-compression step (b) has provided significant advantages in forming a double-layer structure with different porosities. The double-layer porous transport layer formed according to the present invention has a top surface with low porosity and roughness and a back layer with high porosity, which is desirable for its application.

[0034] An exemplary porous transport layer (I) according to the present invention was compared with several reference porous transport layers: (a) comparable double-layer porous transport layers having a similar structure to the porous transport layer of the present invention but produced by a different process; (b) a porous transport layer with 40% porosity produced from titanium powder; (c) a porous transport layer with 56% porosity produced from titanium fibers with an equivalent diameter of 14 μm; (d) a porous transport layer with 56% porosity produced from titanium fibers with an equivalent diameter of 22 μm; and (e) a porous transport layer with 77% porosity produced from titanium fibers with an equivalent diameter of 22 μm.

[0035] A reference porous transport layer (a) having a double layer is fabricated by the following process in the following order. (a) To produce a non-woven fabric layer of the first titanium fiber, (b) The non-woven fabric layer of the first titanium fiber is sintered at 1000 - 1200 °C for 1 - 2 hours, preferably under a load of 70 kg / m 2 ~200 kg / m 2 in, for example, an oxygen-free or low-oxygen atmosphere to obtain a sintered non-woven fabric layer of the first titanium fiber, (c) Compressing the sintered non-woven fabric layer of the first titanium fiber to obtain a compressed and sintered non-woven fabric layer of the first titanium fiber, (d) To produce a non-woven fabric layer of the second titanium fiber, (e) Stacking the compressed and sintered non-woven fabric layer of the first titanium fiber with the non-woven fabric layer of the second titanium fiber to form a double-layer structure, (f) Sintering the double-layer structure at 1000 - 1200 °C for 1 - 2 hours, preferably under a load of 70 kg / m2 - 200 kg / m 2 in, for example, an oxygen-free or low-oxygen atmosphere, and (g) Optionally, compressing the sintered double-layer structure to a predetermined thickness.

[0036] The roughness of the porous transport layer and the reference porous transport layer of the present invention as described above was measured. The first surface of the porous transport layer of the present invention, that is, the surface of the first layer made of 14-μm titanium fibers, was measured. For the reference porous transport layer (a), the surface made of 14-μm titanium fibers was also measured. The material ratio at a given depth was calculated using the roughness measurement data and OmniSurf software compliant with the ISO_21920-2_EN standard. The mean line of the profile is the zero level / line resulting from subtracting the best-fit file line through the measurement from the surface roughness measurement. Figure 2 shows the material ratio curve of the porous transport layer according to the present invention compared with the material ratio curves of several reference porous transport layers, showing the material ratio (%) in the profile on the horizontal axis or X-axis at a given depth on the vertical axis or Y-axis (μm). The distribution of the material ratios of the porous transport layer (I) of the present invention and the reference porous transport layers (a, b, c, d, e) at a given depth level is summarized in Table 1.

[0037] [Table 1]

[0038] As shown in Figure 2, the highest peak in the material ratio curve of the porous transport layer (I) of the present invention is the lowest at approximately 6 μm. Table 1 shows that the material ratio of the porous transport layer (I) of the present invention is 1.00% at a given depth of 5 μm, which is significantly lower than the rest of the reference porous transport layer. Furthermore, the material ratio of the porous transport layer of the present invention is over 75% at a depth of -5 μm. The zero level is the average line of the profile resulting from subtracting the best file line through measurement from the surface roughness measurement value. The reference porous transport layers (a, c) made from titanium fibers with an equivalent diameter of 14 μm also have a smaller material ratio peak compared to the reference porous transport layers (d, e) made from titanium fibers with an equivalent diameter of 22 μm, demonstrating that the material ratio peak decreases as the fiber diameter becomes finer. On the other hand, the material ratio peak of the reference porous transport layer (d) is smaller than that of the reference porous transport layer (e) made from the same fibers but with a different (higher) porosity, and the material ratio peak of the reference porous transport layer (a) is smaller than that of the reference porous transport layer (c) made from the same fibers but with a different (higher) porosity, demonstrating that the material ratio peak decreases as the porosity decreases. Furthermore, the core roughness and troughs of the porous transport layer (I) and the reference porous transport layers (a, b) of the present invention are considerably equivalent. The trough of the material ratio curve of the porous transport layer (I) of the present invention is much higher than that of the reference porous transport layers (d, e).

[0039] Surprisingly, although the reference porous transport layer (a) is fabricated from a double-layer porous transport layer having a similar structure to the porous transport layer of the present invention, the material ratio at the peak of the porous transport layer of the present invention is smaller than that of the reference porous transport layer (a). At a given depth of 5 μm, the material ratio of the porous transport layer (I) of the present invention is 1.00%, while that of the reference porous transport layer (a) is 6.84%. At a given depth of -5 μm, the material ratio of the porous transport layer (I) of the present invention is 76.56%, while that of the reference porous transport layer (a) is 71.96%. Overall, the porous transport layer of the present invention exhibits the best desired properties, namely, low material ratio values ​​in the peak region and high material ratio values ​​in the valley region. This provides better support for proton exchange membranes in electrolytic cells and fuel cells. Thus, by using the porous transport layer of the present invention, the opportunity for membrane elongation and rupture is reduced. This also ensures better contact with the catalyst and better reaction at the anode. Furthermore, it should be noted that while the porous transport layer of the present invention is manufactured in a single sintering step, the reference porous transport layer (a) is manufactured in two sintering steps, and these are more expensive. Low cost is another advantage of the porous transport layer of the present invention.

[0040] On the other hand, the porous transport layer should have the necessary permeability. The permeability of the porous transport layer (I) and the reference porous transport layers (a, b, c, d, e) of the present invention was evaluated by a standardized method and is shown in Table 2.

[0041] As shown in Table 2, the permeability of the porous transport layer of the present invention is 150 l / dm² / min. This meets the requirements for a high-quality porous transport layer for planar gas inflow and outflow in electrolytic cells or fuel cells in which the porous transport layer is used. The permeability of the reference powder porous transport layer (type b: 26 l / dm² / min in Table 2) is considerably low and undesirable. In this respect, the fibrous porous transport layer is more advanced than the powder porous transport layer due to its higher permeability.

[0042] [Table 2]

[0043] The porous transport layer (I) and reference porous transport layers (d) and (e) of the present invention were tested in situ in a proton exchange membrane water electrolysis (PEMWE) cell. Given the measured cell current density (A / cm²), 2 The cell voltage (volts) (IV curve) at ) is shown in Figure 4 for comparison. Note that the cell voltage obtained from the porous transport layer (I) of the present invention is lower than the cell voltage obtained from the reference porous transport layer at the same cell current density. 4A / cm 2 At a given current density, there is a 120 mV difference between the porous transport layer (I) of the present invention and the reference porous transport layer (d). The IV curve shows a lower cell voltage at a given current density obtained with the porous transport layer (I) of the present invention, and therefore demonstrates better performance of the porous transport layer (I) of the present invention. Furthermore, thanks to the low porosity and surface roughness of the porous transport layer (I) of the present invention, the anode catalyst packing amount is 0.7~0.8 mgIrOx / cm 2 This can be within a certain range, which is less than the fill amount in conventional technologies. This is a further advantage of PEMWE batteries to which the porous transport layer (I) of the present invention is applied, which reduces the amount of expensive iridium catalyst that needs to be filled.

Claims

1. A porous transport layer for electrolytic cells or fuel cells, A nonwoven fabric layer of first metal fibers provided for contact with a proton exchange membrane, comprising metal fibers of first equivalent diameter, A nonwoven fabric layer of first metal fibers having a first surface roughness and a first porosity, A second nonwoven fabric layer of metal fibers, comprising metal fibers of a second equivalent diameter, It comprises a second nonwoven fabric layer of metal fibers having a second surface roughness and a second porosity, The first surface has a material ratio of less than 5% of the material at a height of 5 μm and a material ratio of more than 70% of the material at a depth of -5 μm. The first equivalent diameter is smaller than the second equivalent diameter. The first surface roughness is at least 20% smaller than the second surface roughness, for example, in the range of 20% to 120%. The first porosity is at least 10% smaller than the second porosity, for example, in the range of 10% to 50%. The first nonwoven fabric layer is a porous transport layer that is metallurgically bonded to the second nonwoven fabric layer.

2. The porous transport layer according to claim 1, wherein the thickness of the second nonwoven fabric layer is at least twice the thickness of the first nonwoven fabric layer.

3. The porous transport layer according to claim 1 or 2, wherein the first equivalent diameter is less than 20 μm.

4. The porous transport layer according to any one of claims 1 to 3, wherein the second equivalent diameter is greater than the first equivalent diameter and less than 50 μm, preferably less than 30 μm.

5. The porous transport layer according to any one of claims 1 to 4, wherein the first equivalent diameter is 14 μm and the second equivalent diameter is 22 μm.

6. The porous transport layer according to any one of claims 1 to 5, wherein the thickness of the first nonwoven fabric layer is less than 100 μm.

7. The porous transport layer according to any one of claims 1 to 6, wherein the first nonwoven fabric layer and the second nonwoven fabric layer contain, preferably consist of, one of titanium fibers, nickel fibers, or stainless steel fibers.

8. The porous transport layer according to any one of claims 1 to 7, wherein the first nonwoven metal fiber layer has a discontinuous length and a cross-section, the cross-section having two adjacent straight sides having an angle of less than 90 degrees and one or more irregularly shaped curved sides.

9. The porous transport layer according to any one of claims 1 to 8, wherein the first nonwoven fabric layer has a porosity in the range of 30 to 50%, the second nonwoven fabric layer has a porosity in the range of 51 to 90%, and the overall porosity of the porous transport layer is in the range of 50 to 80%.

10. The porous transport layer according to any one of claims 1 to 9, further comprising a third porous metal layer adjacent to the second nonwoven metal fiber layer, having a larger pore diameter and / or porosity.

11. A method for producing a porous transport layer for an electrolytic cell or fuel cell according to any one of claims 1 to 10, (a) A step of producing a first nonwoven nonsintered layer of metal fibers, (b) A step of compressing the first nonwoven non-sintered layer of metal fibers to obtain a compressed first nonwoven layer of metal fibers, (c) A step of producing a second nonwoven nonsintered layer of metal fibers, (d) A step of stacking a compressed first nonwoven nonsintered layer of metal fibers with the second nonwoven nonsintered layer of metal fibers to form a double layer structure, (e) The double layer structure is subjected to, for example, an oxygen-free or low-oxygen atmosphere at 1000 to 1200°C for 1 to 2 hours, preferably at a load of 70 kg / m³. ２ ~200 kg / m ２ The process of sintering under a load, (f) A method comprising the optional step of compressing the sintered double-layer structure to a predetermined thickness.

12. A method for producing a porous transport layer according to claim 11, wherein in step (b), compression is applied under a load of 30 to 80 kN / mm2.

13. A stack for an electrolytic cell or fuel cell, A porous transport layer according to any one of claims 1 to 10, Bipolar plates and The bipolar plate is in contact with the second nonwoven fabric layer, Preferably, the bipolar plate is metallurgically bonded to the second nonwoven fabric layer, forming a stack.

14. An assembly of a porous transport layer and a proton exchange membrane according to any one of claims 1 to 10, or an assembly of a stack and a proton exchange membrane according to claim 13, The first nonwoven fabric layer is in contact with the proton exchange membrane. Preferably, the catalyst is provided on the first nonwoven fabric layer on the side where the first nonwoven fabric layer is in contact with the proton exchange membrane in the assembly.

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