Method for manufacturing multiscale structured metal support for low-temperature thin film solid oxide fuel cells and metal support manufactured thereby

Abstract

The present invention relates to a method for manufacturing a metal support having a multiscale structure for a low-temperature thin-film solid oxide fuel cell, comprising the steps of: (a) filling the pores on the surface of a porous metal support with a first metal powder having a relatively large particle size; (b) filling the pores on the surface of the porous metal support with a second metal powder having a relatively small particle size and applying pressure; (c) heat-treating the porous metal support, on which the surface pores are filled with the first metal powder and the second metal powder, in a reducing atmosphere; and (d) filling the pores on the surface of the heat-treated porous metal support with a ceramic powder and heat-treating it in a reducing atmosphere, and to a metal support manufactured thereby.

Description

Technology Field

[0001] The present invention relates to a method for manufacturing a metal support constituting a solid oxide fuel cell and a metal support manufactured thereby. Background Technology

[0002] Despite decades of global efforts to prevent global warming, the average global temperature continues to rise. To limit continuously increasing carbon dioxide emissions, the development of clean energy sources to replace them is essential, leading to growing interest in fuel cells as a potential alternative. Among these, solid oxide fuel cells (SOFCs) are gaining prominence as the most promising candidate to replace fossil fuels due to their high efficiency.

[0003] Solid oxide fuel cells have the advantages of high efficiency due to their high operating temperature of 800 to 1000°C, the ability to use various types of fuel, and the elimination of the need for precious metal catalysts. However, due to the high temperature, the system degrades easily and the materials that can be used are limited. These problems have made commercialization difficult.

[0004] Therefore, to advance the technological level of solid oxide fuel cells, it is necessary to develop cells that possess high electrochemical performance even in low-temperature regions. Under low-temperature operating conditions, both ohmic losses and polarization resistance increase compared to high-temperature operation. The required performance can only be achieved by reducing these losses.

[0005] One method to reduce ohmic losses is to use thin-film electrolytes. Unlike high-temperature sintering processes that produce thicknesses of tens of micrometers, thin-film electrodes and electrolytes can be fabricated using physical vapor deposition and chemical vapor deposition, which can significantly reduce ohmic resistance.

[0006] However, for thin-film processing to be applied, the pore size of the support must be less than a few micrometers, and the surface must also be uniform. Due to these limitations, thin-film processing could not be applied to metal supports that are advantageous for commercialization. Prior art literature

[0007] Korean Published Patent No. 10-2012-0074773 (Date of publication: July 6, 2012) The problem to be solved

[0008] The technical problem that the present invention aims to solve is to provide a method for manufacturing a metal support applicable to a thin film process by controlling the surface of the metal support through an easy and simple process, and to provide the metal support manufactured thereby. means of solving the problem

[0009] To achieve the technical problem described above, the present invention proposes a method for manufacturing a multiscale metal support having a surface functional layer having nanoscale pores and roughness by controlling the surface of a metal support having microscale pores and roughness, comprising the steps of: (a) filling the pores on the surface of a porous metal support with a first metal powder having a relatively large particle size; (b) filling the pores on the surface of the porous metal support with a second metal powder having a relatively small particle size and applying pressure; (c) heat-treating the porous metal support, in which the surface pores are filled with the first metal powder and the second metal powder, in a reducing atmosphere; and (d) filling the pores on the surface of the heat-treated porous metal support with a ceramic powder and heat-treating it in a reducing atmosphere.

[0010] In step (a) above, the pores present on the surface of one side of the porous metal support are filled with a first metal powder having a relatively large particle size compared to the second metal powder, thereby primarily reducing the pore size and surface roughness of the metal support surface.

[0011] In this step, the method of filling the surface pores of the metal support with the first metal powder is not particularly limited, but preferably, it is desirable to fill the pores with the first metal powder using a vacuum filtration process.

[0012] A method of filling metal powder or ceramic powder into pores on the surface of a metal support using a vacuum filtration process refers to a method in which the pressure on one side of the metal support is reduced using a device such as a vacuum pump to create a pressure difference between said one side and the other side of the metal support, thereby causing the metal powder or ceramic powder located near the surface of the other side of the metal support to be sucked into and filled into the pores present on the surface of the other side of the metal support.

[0013] Next, in step (b), the pores on the surface of the porous metal support are filled with a second metal powder having a relatively smaller particle size compared to the first metal powder to further reduce the pore size and surface roughness of the metal support surface, and the surface of the metal support is flattened by applying pressure using a pressing device or the like to further reduce the surface roughness.

[0014] In this step as well, it is preferable to fill the pores of the metal support surface that were not filled in step (a) using a vacuum filtration process, just as in step (a).

[0015] Meanwhile, the first metal powder and the second metal powder may be made of the same pure metal or alloy, or may be made of different pure metals or alloys.

[0016] For example, the first metal powder and the second metal powder may be composed of one metal or an alloy selected from the group consisting of Ni, Zr, Ce, Ti, Mg, Al, Si, Mn, Fe, Co, Ni, Cu, Zn, Mo, Y, Nb, Sn, La, Ta, V, and Nd, and preferably may be composed of Ni.

[0017] Ni possesses high electronic conductivity and can exhibit high electrode catalytic activity through the adsorption of hydrogen and hydrocarbon fuels, while also having the advantage of being inexpensive compared to platinum and the like.

[0018] Next, in step (c), a porous metal support with surface pores filled with the first metal powder and the second metal powder is heat-treated in a reducing atmosphere to aggregate the particles of the first metal powder and the second metal powder, thereby imparting mechanical rigidity to the metal support.

[0019] For example, a metal support with surface pores filled with a first metal powder and a second metal powder made of Ni is sintered at 700°C, which is higher than the target operating temperature (500°C or lower) of a solid oxide fuel cell and lower than the melting point of Ni, thereby intentionally agglomerating and connecting the Ni powder particles to secure the mechanical strength of the metal support and simultaneously forming an electrical connection between the Ni powder particles and the metal support.

[0020] Finally, in step (d), the pores and / or defects on the surface of the metal support, which are generated by inter-particle aggregation and connection during the heat treatment process in step (c), are filled with ceramic powder and heat-treated in a reducing atmosphere to more precisely control the surface condition of the metal support, thereby further reducing the pore size and surface roughness of the metal support surface.

[0021] In this step as well, it is preferable to fill the pores and / or defects generated by the heat treatment in step (c) with ceramic powder using a vacuum filtration process, just as in step (a) above.

[0022] Meanwhile, it is preferable that the ceramic powder is composed of an inorganic oxide having the oxygen ion conductivity.

[0023] For example, the ceramic powder may be composed of a ceramic material selected from gadolinium-doped ceria (GDC), gadolinium-doped zirconia (GDZ), samarium-doped ceria (SDC), samarium-doped zirconia (SDZ), yttrium-doped ceria (YDC), yttrium-doped zirconia (YDZ), yttrium-stabilized zirconia (YSZ), and scandia-stabilized zirconia (ScSZ), and more preferably, it may be composed of gadolinium-doped ceria (GDC).

[0024] In addition, in another aspect of the invention, the present invention proposes a metal support having a multiscale structure manufactured according to the above manufacturing method.

[0025] Furthermore, in another aspect of the invention, the present invention proposes a solid oxide fuel cell comprising a metal support having a multiscale structure according to the present invention, a metal support having a multiscale structure according to the present invention, a fuel electrode formed on the metal support, an electrolyte layer formed on the fuel electrode, and an air electrode formed on the electrolyte layer. Effects of the invention

[0026] According to the present invention, a porous metal support with a multiscale structure having characteristics suitable for processability and stacking can be manufactured by controlling the surface of a support having micro-scale pores and roughness using metal powder and ceramic powder with different particle sizes. Since the porous metal support with a multiscale structure satisfies the characteristics required for application in thin film processes, it can be usefully utilized in the fabrication of high-performance low-temperature thin film solid oxide fuel cells. Brief explanation of the drawing

[0027] FIG. 1 is a schematic diagram showing the process of manufacturing a multiscale structured metal support in sequence in an embodiment of the present invention. FIG. 2 is an FESEM image showing the microstructure of the surface of a metal support obtained at each step of manufacturing a multiscale structured metal support in the present embodiment. Figure 3 is an FESEM image showing the cross-sectional microstructure of a porous stainless steel metal support (Bare SS) before pores are filled with nickel powder and a metal support (Surface Modified SS) with pores filled with two types of nickel powder with different particle sizes. Figure 4 is an FESEM image showing the difference in surface microstructure between the NiO / GDC fuel electrode and the YSZ electrolyte layer deposited on a multiscale metal support depending on whether a compression process is performed in the present embodiment. Specific details for implementing the invention

[0028] In describing the present invention, if it is determined that a detailed description of related known functions or configurations could unnecessarily obscure the essence of the invention, such detailed description will be omitted.

[0029] Since embodiments according to the concept of the present invention may be subject to various modifications and may take various forms, specific embodiments are illustrated in the drawings and described in detail in this specification or application. However, this is not intended to limit embodiments according to the concept of the present invention to specific disclosed forms, and it should be understood that they include all modifications, equivalents, and substitutions that fall within the spirit and scope of the present invention.

[0030] The terms used herein are merely for describing specific embodiments and are not intended to limit the invention. Singular expressions include plural expressions unless the context clearly indicates otherwise. In this specification, terms such as “comprising” or “having” are intended to specify the existence of the described features, numbers, steps, actions, components, parts, or combinations thereof, and should be understood as not precluding the existence or addition of one or more other features, numbers, steps, actions, components, parts, or combinations thereof.

[0031] The present invention will be described in more detail below with reference to examples.

[0032] The embodiments according to this specification may be modified in various different forms, and the scope of this specification is not to be interpreted as being limited to the embodiments described below. The embodiments of this specification are provided to more fully explain this specification to those with average knowledge in the art.

[0033] <Examples >

[0034] In this embodiment, as shown in FIG. 1, nickel particles of different sizes (Large Ni particles and Small Ni particles) were sequentially filled into the pores of a porous metal support (porous SS) made of stainless steel using a vacuum filtration process, and finally, ceramic particles (GDC particles) were used to reduce surface porosity and roughness. After each vacuum filtration process using nickel particles and GDC particles, a hard nickel network was formed without degradation of the metal support by sintering in a hydrogen environment at 700°C. Through this, a metal support having a surface composed of pores of tens of nanometers in size was fabricated, and it was verified that the application of a thin film process is possible.

[0035] First, a 1 x 1 cm porous stainless steel (SS) 316L sheet 2 A metal support was prepared by laser cutting to the size of and washing in an ultrasonic treatment bath for 10 minutes with acetone, ethanol, and deionized water in sequence.

[0036] As shown in Fig. 2(a), the porous stainless steel metal support (Bare) before being filled with nickel powder has irregular pores of 20 to 30 μm in size. On such a substrate with large pores and a rough surface, a thin film cannot be deposited by physical vapor deposition (PVD) such as sputtering.

[0037] 200 mg of the larger nickel powder (< 50 μm size) among two types of nickel powders with different particle sizes (< 50 μm and < 1 μm size) was dispersed in ethanol and vacuum filtered twice using a vacuum filtration device to fill the pores of the metal support and carefully remove excess powder on the metal support. At this time, in order to use only the powder of an appropriate size among the larger nickel powders, the mixture was allowed to settle for 3 minutes after dispersion, and only the suspended particles were used.

[0038] During the vacuum filtration process, very small nickel particles pass through the metal support, particles larger than the pores of the metal support remain on the surface of the metal support, and only particles of an appropriate size fill the gaps between the pores. As a result, only particles of 2–3 μm in size remain between the pores of the metal support, as shown in Fig. 2(b). However, the surface pore structure of the substrate did not change even after the first step of the surface conditioning process.

[0039] Next, 10 mg of small Ni powder (< 1 μm size) is dispersed in ethanol by ultrasonic treatment for 10 minutes, vacuum filtered, and then a press plate (R) surface-treated with sandpaper (2000 grit) without removing excess powder. q The metal support was compressed by applying a pressure of 10 MPa (=127 nm). Then, the compressed metal support was subjected to reduction heat treatment at 700°C for 3 hours.

[0040] When examining the difference in the microstructure of the metal support surface depending on whether a compression process is performed after filling pores through a vacuum filtration process using small Ni powder, it can be seen that in the case where the compression process is not performed, the pore size on the upper surface of the metal support is reduced from tens of μm to several μm, as shown in Fig. 2(c). The surface roughness was also reduced to 1.45 μm. Additionally, by performing vacuum filtration and reduction heat treatment of GDC10 powder, the pores were reduced to a nano size and the surface roughness was reduced to less than 1 μm.

[0041] On the other hand, it can be seen that when a compression process is performed, the surface roughness and pore size are significantly reduced compared to when no compression process is performed (Fig. 2(d)). This is because the roughness is controlled according to the surface shape of the compression plate in contact with the metal support during the process of compressing the excess nickel powder layer. The surface shape of the substrate is influenced not only by the surface roughness of the compression plate but also by the pressure.

[0042] When a compression process is applied, nickel particles are packed more densely and more particles are connected, increasing structural stability and electronic conductivity after reduction sintering. This is illustrated in Fig. 3(b), which shows a nanoporous nickel layer with a thickness of about 10 μm formed on a microporous metal support.

[0043] Next, 5 mg of GDC10 (Gd 10 mol% doped) powder (< 500 nm size) was dispersed in the same manner as the small Ni powder above and vacuum filtered. After vacuum filtering the GDC10 powder, it was heat-treated under the same conditions as the reduction heat treatment of the nickel powder above, and the excess powder was carefully removed to obtain a metal support with a multiscale structure.

[0044] A NiO-GDC thin-film anode was deposited on a multiscale metal support prepared as described above by sputtering using a nickel and GDC20 target, and a YSZ electrolyte layer was deposited on the anode using a Y-Zr (16:84 at%) alloy target.

[0045] Figure 4 is a scanning electron microscope (SEM) image showing the difference in microstructure of the fuel electrode and electrolyte layer surfaces depending on whether a compression process is applied during the fabrication of a multiscale metal support structure.

[0046] In the case where the compression process was not performed, sputtered atoms grew irregularly due to the very rough and irregular surface structure of the metal support, as shown in Fig. 4(a). As a result, the fuel electrode could not be deposited to have a uniform surface necessary for the deposition of a dense electrolyte layer. Although the surface of the electrolyte layer deposited on this rough fuel electrode showed a reduction in irregular particles and a significant improvement in surface roughness due to the YSZ electrolyte, it was found that many pinholes were formed on the surface due to insufficient electrolyte density (Fig. 4(b)).

[0047] On the other hand, as can be seen in FIGS. 4(c) and 4(d), the surface of the sputtered electrode and electrolyte layer of the metal support subjected to the compression process is very uniform. This is because, during the compression process, an excess amount of Ni powder is more densely packed onto the surface, and the surface roughness is uniformly adjusted. Through this surface image analysis, it was confirmed that a dense electrolyte layer without pinholes with a thickness of 1 μm can be deposited on the metal support according to the present invention through a sputtering process. This implies that the metal support according to the present invention can be applied to thin-film solid oxide fuel cells.

[0048] The present invention is not limited to the above embodiments and can be manufactured in various different forms, and those skilled in the art will understand that the invention can be implemented in other specific forms without changing the technical concept or essential features of the invention. Therefore, the embodiments described above should be understood as illustrative in all respects and not restrictive.

Claims

Claim 1 (a) a step of filling the pores on the surface of a porous metal support with a first metal powder having a relatively large particle size; (b) a step of filling the pores on the surface of the porous metal support with a second metal powder having a relatively small particle size and applying pressure; (c) a step of heat-treating the porous metal support, on which the surface pores are filled with the first metal powder and the second metal powder, in a reducing atmosphere; and (d) a step of filling the pores on the surface of the heat-treated porous metal support with a ceramic powder and heat-treating it in a reducing atmosphere; a method for manufacturing a metal support having a multiscale structure. Claim 2 A method for manufacturing a multiscale structured metal support according to claim 1, characterized in that, in steps (a), (b), and (d), the pores on the surface of the porous metal support are filled with a first metal powder, a second metal powder, and a ceramic powder, respectively, using a vacuum filtration process. Claim 3 A method for manufacturing a multiscale structured metal support according to claim 1, wherein the first metal powder and the second metal powder are composed of one metal or an alloy selected from the group consisting of Ni, Zr, Ce, Ti, Mg, Al, Si, Mn, Fe, Co, Ni, Cu, Zn, Mo, Y, Nb, Sn, La, Ta, V, and Nd. Claim 4 A method for manufacturing a multiscale metal support, wherein, in claim 1, the ceramic powder is composed of one or more ceramics selected from the group consisting of gadolinium-doped ceria (GDC), gadolinium-doped zirconia (GDZ), samarium-doped ceria (SDC), samarium-doped zirconia (SDZ), yttrium-doped ceria (YDC), yttrium-doped zirconia (YDZ), yttrium-stabilized zirconia (YSZ), and scandia-stabilized zirconia (ScSZ). Claim 5 A method for manufacturing a multiscale structured metal support according to claim 1, comprising: (a) a step of filling the pores on the surface of a porous metal support made of stainless steel with a first nickel (Ni) powder having a relatively large particle size using a vacuum filtration process; (b) a step of filling the pores on the surface of the porous metal support with a second nickel (Ni) powder having a relatively small particle size using a vacuum filtration process and applying pressure; (c) a step of heat-treating the porous metal support, on which the surface pores are filled with the first nickel (Ni) powder and the second nickel (Ni) powder, at a temperature of 700°C in a reducing atmosphere; and (d) a step of filling the pores on the surface of the heat-treated porous metal support with gadolinium-doped ceria (GDC) powder and heat-treating at a temperature of 700°C in a reducing atmosphere. Claim 6 A multiscale structured metal support manufactured according to the method of any one of claims 1 to 5. Claim 7 A solid oxide fuel cell comprising: a metal support having a multiscale structure according to claim 6; a fuel electrode formed on the metal support; an electrolyte layer formed on the fuel electrode; and an air electrode formed on the electrolyte layer.

Images