A fabrication method for surface patterned microtubular solid oxide fuel cell

Abstract

This invention is about a fabrication method for surface patterned microtubular solid oxide fuel cell, which is fabricated by winding a thin and continuous anode support strip manufactured by tape casting method on a patterned rod followed by co-pressing in order to obtain a higher efficiency from solid oxide fuel cells producing electrical energy.

Description

[0001] A FABRICATION METHOD FOR SURFACE PATTERNED MICROTUBULAR SOLID OXIDE FUEL CELL

[0002] TECHNICAL FIELD

[0003] The invention is related to a fabrication method for surface patterned microtubular solid oxide fuel cells produced by wrapping a thin and continuous anode support strip manufactured by tape casting method on a patterned rod followed by copressing in order to increase the surface area and get a higher efficiency from solid oxide fuel cells that produce electrical energy.

[0004] BACKGROUND

[0005] A solid oxide fuel cell (SOFC) is an electrochemical conversion device that generates electricity directly from fuel. The electrolyte material of a SOFC is solid oxide or ceramic. These ceramic fuel cells operate at much higher temperatures than polymer-based ones.

[0006] SOFCs are mostly designed for stationary applications, operate at temperatures between 700-1000°C and provide power in desired capacities due to their modular structure. The high-temperature exhaust gases can also be directed to a gas turbine to increase the electrical efficiency. Efficiency in such hybrid systems can be as high as 70%. In these cells, oxygen ionizes at the cathode, passes through the solid oxide electrolyte and reacts with the hydrogen fed to the anode.

[0007] The fact that SOFCs are made of solid materials makes it possible to manufacture SOFCs in different geometries, but SOFCs are commonly manufactured in planar or tubular shapes (Figure 1 ). In tubular SOFCs, the structure generally consisting of anode (3), electrolyte (4) and cathode (2) generates electrical energy with the fuel flow (1 ) and air / oxygen flow (6) provided and the generated current is collected by the interconnection (5). Other relatively complex geometries are considered as modifications of tube and / or planar geometry and each has different advantages and disadvantages. Tubular SOFCs with a diameter of less than 5 mm, on the other hand, are called microtubular SOFCs. Similar to other SOFC geometries, the membrane electrode assembly (MEA), which consists of anode-electrolyte-cathode components and is the unit where the electrical energy conversion takes place, is built on the anode support to achieve relatively high power by reducing the electrolyte thickness. This support structure is commonly manufactured by extrusion method in microtubular SOFCs. In addition to its low manufacturing cost and flexible operation, this method attracts attention as a feasible production method even for both brittle and ductile materials with a complex cross-section. Basically, this technique is based on the preparation of a slurry by mixing the relevant powders with appropriate additives followed by forcing the slurry to pass through the cavity of a mold with the desired geometry. Although extrusion is a suitable method for mass production, it can lead to some problems such as structural defects in the thin walls, warping or twisting along with high initial costs. More importantly, since a fixed cross-section is mandatory in the extrusion method, it is not possible to produce complex geometries by this method. This specifically restricts the fabrication of microtubular SOFC geometries designed to increase the electrolyte-electrode interface areas and thus the SOFC electrochemical reaction zones through surface patterning to improve the cell performance. Although these patterns can be created with an additional process, this is not preferred because it brings an additional cost.

[0008] As known in the literature, the anode and cathode electrochemical reactions (H2+O2“>H2O+2e_and Vi O2+2e_->O2) taking place during SOFC operation occur in the so-called triple phase boundaries, where the catalyst, electrolyte and pore phases meet. Since these regions determine the number of electrochemical reactions that take place, the cell performance is directly related to the density of these regions (pm / pm3). Therefore, a typical SOFC anode or cathode electrode contains some electrolyte material besides the corresponding catalyst material, allowing electrochemical reactions to take place in a larger volume rather than at the electrode-electrolyte interface. However, the studies have revealed that anode and cathode electrochemical reactions take place near the electrode-electrolyte interfaces. This makes the anode and cathode microstructure as well as the anode-electrolyte and cathode-electrolyte interfaces very important in terms of active triple phase boundaries and thus the cell performance. In this context, there are various studies in the literature on increasing the interfacial surface area of planar SOFCs by creating patterns on the electrolyte or anode support surfaces with different methods such as micro powder imprinting, sandblasting, lithography, laser machining and spray. Although the performance increases obtained vary depending on the method and surface patterns, it is seen that surface patterning is highly effective on the cell performance. For example, Konno et al. (2011 ) created 200 pm wide channels with a distance of 250 pm on 8YSZ electrolyte via blasting. At an operating voltage of 0.5 V and an operating temperature of 800 °C, the cell with the channeled electrolyte exhibited 25% higher performance than the reference cell with the unmodified electrolyte. Masciandaro et al. (2019) created honeycomb patterns on 3YSZ electrolyte with a stereolithography 3D printer. The honeycomb electrolyte cell exhibited 15% higher maximum performance values than the flat electrolyte design. Larrea et al. (2011 ) produced similar honeycomb patterns on 8YSZ electrolyte with the help of laser processing technique. At 0.55 V operating voltage and 800 °C operating temperature, the cell with patterned electrolyte showed 25% higher performance values than the reference cell with un-patterned electrolyte. Xu et al. (2013) patterned 8YSZ electrolyte with millimeter-scale square patterns and circular cone microhole arrays by micro powder printing. The cell built on electrolyte containing micro-holes outperformed the flat electrolyte cell by a factor of 2 at 800 °C operating temperature due to partially reduced electrolyte thickness and increased surface areas of electrolyte-electrode interface.

[0009] Although the extrusion method, which is frequently used in microtube SOFC production, allows the production of parts with complex cross-sections, it does not allow the formation of different patterns (variable cross-sectional area) in the longitudinal direction. Therefore, as in planar SOFCs, the patterning process in microtubular SOFCs also requires extra devices, equipment, molds or a process for manufacturing or material preparation. Moreover, to the best of our knowledge, there is no study on microtubular SOFC patterning in the literature except the one by our team (Altan et al., 2023). Although the bolt-microtubular SOFC proposed in that study has significant advantages such as high performance and efficient current collection, the patterns formed after the patterning process are just uniform due to the need to remove the anode support from the bolt by rotating. Although it is possible to create different patterns by changing the thread geometry, this results in again patterns in the form of a uniform thread only.

[0010] SUMMARY OF THE INVENTION

[0011] The object of the invention relates to a fabrication method for surface patterned microtubular solid oxide fuel cells produced by winding a thin and continuous anode support strip manufactured by tape casting method on a patterned rod followed by copressing. After lamination by isostatic pressing, the patterns on the patterned rod are formed both on the inner wall of the anode support and on the outer wall of the anode support due to the moment effect created during the pressing. The surface patterned anode support is then obtained by removing the patterned rod before sintering. After the coating of the other cell layers on this support, microtubular SOFCs, called surface patterned microtubular SOFCs, are obtained.

[0012] Another aim of the invention is that the cells produced provide performance enhancement by offering higher electrochemical reaction zones due to the increased electrolyte-electrode interface areas obtained by patterning, unlike conventional microtubular cells with flat surface produced by extrusion.

[0013] Current collection in the anode region of conventional microtubular SOFCs is generally achieved by winding a conductive wire on the tube. Due to circular cell and current collection wire geometry in microtubular SOFCs, such strategy results in line contacts rather than large surface area as in planar SOFCs. Loss of contact between current collector wires and electrodes due to thermal expansion mismatch during the cell operation can be also seen. In this regard, another advantage of the invention is to provide a much more efficient current collection by increasing the current collection surface by winding the current collector wire in the spaces between the suitable patterns formed on the anode support. In this way, higher powers can be obtained from surface patterned microtubular SOFCs due to reduced current collection losses.

[0014] FIGURES

[0015] Figure 1. Conventional microtubular SOFCs

[0016] Figure 2. An isometric view of surface patterned microtubular anode support on a patterned rod

[0017] Figure3. A side view of surface patterned microtubular anode support on a patterned rod

[0018] Figure4. The surface patterned microtubular anode support

[0019] Figures. An isometric view of the invention

[0020] Figure 6a. An illustration of the layer structure of the invention

[0021] Figure 6b. A detailed illustration of the layer structure of the invention

[0022] Figure?. A performance comparison of surface patterned microtubular and standard microtubular SOFCs at 800 °C Equivalents of the numbers given in the figures:

[0023] 1 . Fuel flow

[0024] 2. Cathode

[0025] 3. Anode

[0026] 4. Electrolyte

[0027] 5. Interconnector

[0028] 6. Air / oxygen flow

[0029] 7. Anode support layer

[0030] 8. Anode functional layer

[0031] 9. Electrolyte

[0032] 10. Cathode functional layer

[0033] 11. Cathode current collection layer

[0034] 100. Patterned rod

[0035] 200. Surface patterned microtubular solid oxide fuel cell

[0036] DETAILED DESCRIPTION OF THE INVENTION

[0037] The invention relates to a fabrication method for surface patterned microtubular solid oxide fuel cell (200) produced by winding a thin and continuous anode support strip manufactured by tape casting on a patterned rod (100) and co-pressing. In this regard, the thin and continuous anode support strip manufactured by tape casting is wound on the patterned rod (100) with the desired thickness and pressed under isostatic press for lamination. Unlike conventional extrusion method, the product produced by this method eliminates the need for a high-cost mold and significantly reduces the production cost by employing the patterned rod (100) that can be easily fabricated.

[0038] The main object and main technical impact of the invention is a fabrication method for microtubular SOFC with increased surface area (200). In this regard, a method is introduced to eliminate the removal of the anode support from the threaded rod acting as a mold by rotating in the previous method.

[0039] In the inventive method here, a rod (100), which can be manufactured by different methods from different materials with patterns on it, is used and can be removed without damaging the anode support before sintering. In this way, patterns designed in any format can be transferred to the anode support and the limitations of a uniform thread pattern are eliminated. Representative drawings can be seen in Figures 2 and Figure 3. The examples given in these figures are not intended to be restrictive but are given for a better understanding of the invention. Furthermore, it is possible to achieve much higher performances with pattern optimization and to produce current collection regions in different patterns for efficient current collection. In other words, since there is no periodic patterning requirement, different regions of the microtube supports can have different patterns. A representative drawing showing the surface patterned microtubular anode support (7) after removed from the patterned rod (100) can be seen in Figures 4 and Figure 5. The figures given there are used to match the example mentioned above. There is no limitation for the inventive method here. In summary, any geometric form can be used in the inventive method.

[0040] As expected in the product, not only on the inner part of the anode support layer in contact with the patterned rod (100), but also on the surface of the anode support, the patterns can be formed with the proposed method without the need for an additional mold / process. In this way, the electrode-electrolyte surface area is increased with increasing anode support surface area, thus improving the active triple phase boundaries and thereby the cell performance.

[0041] The surface patterned microtubular cell (200) produced within the scope of this invention comprises five different layers, namely surface patterned microtubular anode support (7), anode functional layer (AFL) (8), electrolyte layer (9), cathode functional layer (CFL) (10) and cathode current collector layer (CCL) (11) from anode to cathode side (Figure 6a and 6b). The anode support layer (7) is produced using tape casting and isostatic press methods, while all other layers are produced by dip coating method.

[0042] The production of the surface patterned anode support layer (7), which forms the basis of the invention, is realized by winding continuous and thin anode support strips produced by tape casting on the patterned rod (100). The patterned rod (100) is fabricated on a 3D printer using liquid-soluble Polyvinyl Alcohol (PVA) or Acrylonitrile Butadiene Styrene (ABS) or High Impact Polystyrene (HIPS) or Butanediol vinyl alcohol copolymer (BVOH) filament. The liquid is at least one of water, caustic, ester, ketone, acetone. After winding, the anode support microtube (7) with the patterned rod (100) is placed in a vacuum bag and vacuumed. The lamination process is carried out by isostatic pressing method. After lamination, the structure is soaked in liquid to remove the patterned rod (100) and the surface patterned microtube anode support layer (7) is obtained. Following pre-sintering, four different layers, namely anode functional layer (AFL) (8), electrolyte (9), cathode functional layer (CFL) (10) and cathode current collector layer (CCL) (11), are coated by dip coating method and sintered at appropriate temperatures in the order in which they are listed, and finally the fabrication of surface patterned microtube cell (200) is completed.

Claims

CLAIMS1. A surface patterned microtubular solid oxide fuel cell with increased surface area without pre-sintering process, characterized in that comprising an anode support layer (7) wound on a patterned rod (100) fabricated in a 3D printer using a liquid fusible filament.

2. A surface patterned microtubular solid oxide fuel cell with increased surface area, characterized by comprising an anode support layer (7), which is shaped by a patterned rod (100) produced from a liquid-soluble filament prior to presintering and removed by decomposing in liquid, and an anode functional / functional layer (AFL) (8), electrolyte (9), cathode functional / functional layer (CFL) (10) and cathode current collector layer (CCL) (11 ) coated on this layer, respectively.

3. A fabrication method for surface patterned microtubular solid oxide fuel cell with increased surface area characterized by comprising the steps below;- Producing a patterned rod using a liquid-soluble filament in a 3D printer,- Winding of the anode support layer on the fabricated patterned rod (100),- Vacuuming the binary structure by placing it in a vacuum bag,- Pressing under isostatic press for lamination,- Decomposing the patterned rod (100) by soaking in liquid,- Performing pre-sintering process for surface patterned anode support (7),- Coating of four different layers, namely anode functional / functional layer (AFL) (8), electrolyte (9), cathode functional / functional layer (CFL) (10) and cathode current collector layer (CCL) (11), in the order in which they are listed, by dip coating method,- Sintering steps.

4. The liquid-soluble filament according to Claim 1 , characterized in that by being a Polyvinyl Alcohol (PVA) or Acrylonitrile Butadiene Styrene (ABS) or High Impact Polystyrene (HIPS) or Butanediol vinyl alcohol copolymer (BVOH) Filament.

5. The liquid-soluble filament according to Claim 2, characterized in that by being a Polyvinyl Alcohol (PVA) or Acrylonitrile Butadiene Styrene (ABS) or HighImpact Polystyrene (HIPS) or Butanediol vinyl alcohol copolymer (BVOH) Filament.

6. The liquid-soluble filament according to Claim 3, characterized in that by being a Polyvinyl Alcohol (PVA) or Acrylonitrile Butadiene Styrene (ABS) or High Impact Polystyrene (HIPS) or Butanediol vinyl alcohol copolymer (BVOH) Filament.

7. The liquid according to Claim 1, characterized in that by being at least one of water, caustic, ester, ketone, acetone.

8. The liquid according to Claim 2, characterized in that by being at least one of water, caustic, ester, ketone, acetone.

9. The liquid according to Claim 3, characterized in that by being at least one of water, caustic, ester, ketone, acetone.

10. The patterned rod according to Claim 1 , characterized in that it can be of any geometry.

11. The patterned rod according to Claim 2, characterized in that it can be of any geometry.

12. The patterned rod according to Claim 3, characterized in that it can be of any geometry.

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