Flat tube type SOFC anode with gradient pores and preparation method of flat tube type SOFC anode

Abstract

The invention relates to a flat tube type SOFC anode with gradient pores and a preparation method of the flat tube type SOFC anode, and belongs to the technical field of solid oxide fuel cells. Comprising an anode substrate, an anode diffusion layer and an anode functional layer which are sequentially arranged from bottom to top, wherein fuel pore channels with pore diameters of 1-1.5 mm are uniformly distributed on the anode substrate; the porosity of each layer of structure is different, so that a gradient pore anode structure is formed; the problem of low discharge power caused by too large gas mass transfer resistance due to too low porosity in a flat tube type solid oxide fuel cell due to single porosity is solved. In the preparation process, in order to better compound the three layers of anodes, a multi-platform-slow sintering procedure is adopted, and finally, the three-layer anode structure with gradient pores is successfully prepared.

Description

Technical Field

[0001] The present invention relates to a flat-tube SOFC anode with gradient pores and a preparation method thereof, belonging to the technical field of solid oxide fuel cells. Background Art

[0002] As a new generation of efficient and environmentally friendly energy conversion device, the anode, one of the core components of the flat-tube solid oxide fuel cell, plays a crucial role in the electrochemical reaction. The anode is not only responsible for catalyzing the oxidation reaction of the fuel gas, but also needs to have high conductivity, good anti-carbon deposition performance and long-term stability. Existing solutions usually adopt a single-layer anode matrix structure or a double-layer anode matrix and reaction layer structure, use NiO-YSZ composite material as the anode composition, and use Ni-based metal salts or oxides, as well as other organic substances as pore-forming agents to make the anode have a loose and porous structure.

[0003] In the existing anode materials, yttria-stabilized zirconia (YSZ) is relatively expensive. At the same time, due to the single porosity of the flat-tube solid oxide fuel cell anode, when the porosity is too low, the gas mass transfer resistance is too large, reducing the discharge power; when the porosity is too high, problems such as poor mechanical strength of the anode, large thermal stress, and poor bonding with the electrolyte layer and easy air leakage will occur, resulting in product failure. Therefore, it is necessary to design and prepare a flat-tube SOFC anode with low cost and gradient pores and a preparation method thereof. Summary of the Invention

[0004] In view of this, the purpose of the present invention is to provide a flat-tube SOFC anode with gradient pores and a preparation method thereof. In this anode, the porosity of each layer structure is different, forming a gradient pore anode structure.

[0005] To achieve the above purpose, the technical solution of the present invention is as follows.

[0006] A flat-tube SOFC anode with gradient pores includes an anode matrix, an anode diffusion layer and an anode functional layer arranged in sequence from bottom to top; wherein, fuel channels with a pore diameter of 1-1.5 mm are evenly distributed on the anode matrix;

[0007] The main body of the anode matrix is NiO and Y2O3, which is prepared by extrusion molding-sintering; the porosity of the anode matrix is 40%-50%, and the thickness is 400-500 μm;

[0008] The main body of the anode diffusion layer is NiO and YSZ, which is prepared by impregnation-sintering; the porosity of the anode diffusion layer is 20%-35%, and the thickness is 5-10 μm;

[0009] The main body of the anode functional layer is NiO and YSZ, which is prepared by plasma spraying-sintering; the porosity of the anode diffusion layer is 10% - 15%, and the thickness is 1 - 5 μm.

[0010] A preparation method of a flat tube type SOFC anode with gradient pores according to the present invention, the method steps include:

[0011] (1) Mix NiO powder, Y2O3 powder, the first pore former and the first binder evenly in ethanol to obtain a slurry; ball mill and dry to obtain anode powder; add water and a plasticizer to the anode powder, mix to obtain NiO - Y2O3 ceramic mud, knead, and extrude to form a green body with a uniformly distributed gas channel structure, air dry for 3 - 5 days, after debinding and drying, first sinter at T1 for 10 - 12 h, and then sinter at T2 for 4 - 5 h to obtain an anode substrate; the particle size of the first pore former is 2 - 5 μm;

[0012] (2) After mixing and dry grinding NiO powder and YSZ powder, add the second pore former, the second binder and the first dispersant, and disperse evenly in ethanol to obtain a diffusion layer slurry; place the anode substrate in the diffusion layer slurry, soak for 10 - 20 s, dry, repeat the soaking - drying 1 - 3 times, first sinter at T3 for 8 h - 10 h, and then sinter at T4 for 2 - 3 h to obtain an anode diffusion layer on the surface of the anode substrate; the particle size of the second pore former is 0.5 - 1 μm;

[0013] (3) After mixing and dry grinding NiO powder and YSZ powder, add the third pore former, the second binder and the second dispersant, and disperse evenly in ethanol, sand mill to obtain a functional layer slurry; spray the functional layer slurry on the surface of the anode diffusion layer by plasma spraying, the spraying pressure is 0.3 - 0.5 MPa, dry, repeat the spraying - drying 1 - 3 times, first sinter at T5 for 8 h - 10 h, and then sinter at T4 for 2 - 3 h to obtain an anode functional layer on the surface of the anode diffusion layer; the particle size of the third pore former is 50 - 100 nm;

[0014] Wherein, T1, T3 and T5 are respectively 450 - 550 °C, T2 is 1050 - 1150 °C, and T4 is 50 - 100 °C lower than T2.

[0015] Preferably, in step (1), the particle sizes of the NiO powder and the Y2O3 powder are respectively 0.1 - 2 μm.

[0016] Preferably, in step (1), the mass ratio of the NiO powder to the Y2O3 powder is 7:3 - 6:4.

[0017] Preferably, in step (1), the first binder is one or more of YB-167, methyl cellulose, and ethyl cellulose; more preferably, the addition amount of the first binder is 5% to 10% of the total mass of the NiO powder and the Y2O3 powder.

[0018] Preferably, in step (1), the first pore-forming agent is carbon powder and / or starch; more preferably, the addition amount of the first pore-forming agent is 10% to 20% of the total mass of the NiO powder and the Y2O3 powder.

[0019] Preferably, in step (1), the plasticizer is polyethylene glycol; more preferably, the addition amount of the plasticizer is 6% to 8% of the total mass of the NiO powder and the Y2O3 powder.

[0020] Preferably, in step (1), the mass ratio of the anode powder to water is 10:3 to 4, and the water content after kneading is 15% to 20%.

[0021] Preferably, in step (1), the pressure for extrusion molding is 5 to 10 MPa.

[0022] Preferably, in step (1), the debinding and drying temperature is 250 to 300 °C, and the time is 2 to 3 h.

[0023] Preferably, in step (1), the heating rate during sintering is 1 to 2 °C / min.

[0024] Preferably, in steps (2) and (3), the particle sizes of the NiO powder and the YSZ powder are 0.1 to 2 μm respectively.

[0025] Preferably, in steps (2) and (3), the mass ratio of the NiO powder to the YSZ powder is 1:1 to 3:2.

[0026] Preferably, in steps (2) and (3), the second binder is PVB (polyvinyl butyral) and / or polyethylene glycol; more preferably, the addition amount of the second binder is 5% to 10% of the total mass of the NiO powder and the YSZ powder.

[0027] Preferably, in step (2) and step (3), the first dispersant is triethylamine and / or dibutyl phthalate; more preferably, the addition amount of the first dispersant is 5% to 7% of the total mass of the NiO powder and the YSZ powder.

[0028] Preferably, in steps (2) and (3), the drying temperature is 50 to 60 °C, and the time is 10 to 15 min.

[0029] Preferably, in steps (2) and (3), the heating rate during sintering is 0.5 to 1 °C / min.

[0030] Preferably, in step (2), the second pore former is carbon powder and / or starch; more preferably, the addition amount of the second pore former is 5% - 10% of the total mass of the NiO powder and the YSZ powder.

[0031] Preferably, in step (3), the third pore former is nano-carbon powder; more preferably, the addition amount of the third pore former is 5% - 10% of the total mass of the NiO powder and the YSZ powder.

[0032] Advantageous Effects

[0033] In the present invention, the flat-tube SOFC anode with gradient pores includes an anode substrate, an anode diffusion layer, and an anode functional layer arranged in sequence from bottom to top; the pore rate and structure of each layer are precisely controlled by the extrusion molding method, the impregnation method, and the plasma spraying method for the three-layer structure. Among them, the pore rate of the anode substrate is 40% - 50%, and the thickness is 400 - 500 μm; the pore rate of the anode diffusion layer is 20% - 35%, and the thickness is 5 - 10 μm; the pore rate of the anode functional layer is 10% - 15%, and the thickness is 1 - 5 μm. The anode substrate plays a role in supporting and transporting gases, so it has a relatively large pore rate and thickness. The anode diffusion layer has a relatively large pore rate and a small thickness, which is beneficial to the diffusion of fuel gases. The anode functional layer, as the place where the electrochemical reaction occurs, has a low thickness and pore rate, which can reduce the interface resistance and prevent air leakage at the same time. The present invention solves the problems in the prior art of flat-tube solid oxide fuel cells due to a single pore rate. When the pore rate is too low, the gas mass transfer resistance is too large, resulting in low discharge power; when the pore rate is too high, there are problems such as poor mechanical strength, large thermal stress, and poor bonding with the electrolyte layer, which is likely to cause air leakage, resulting in product failure. During the preparation process, in order to better composite the three-layer anode, a sintering procedure of multi-platform - slow sintering is adopted, and finally a three-layer anode structure with gradient pores is successfully prepared. Description of the Drawings

[0034] Figure 1 It is a schematic cross-sectional view of the gradient anode structure described in the present invention.

[0035] Figure 2 It is a test result diagram of the pore size distribution of the gradient anode prepared in Example 1.

[0036] Figure 3 It is a three-point bending test result diagram of the gradient anode prepared in Example 1.

[0037] Figure 4 It is a partial electron microscope image of the gradient anode prepared in Example 1.

[0038] Figure 5 It is a partial electron microscope image of the anode prepared in Comparative Example 1.

[0039] Figure 6 It is a comparison chart of the anode discharge performance prepared in Example 1 and Comparative Example 2. Specific Embodiments

[0040] The present invention will be further described in detail below in conjunction with specific embodiments.

[0041] As Figure 1 shown, the present invention provides a flat-tubular SOFC anode structure with gradient porosity, including: an anode substrate, fuel gas channels, an anode diffusion layer, and an anode functional layer. The anode substrate has a porous structure and is prepared by the mud extrusion molding method. The main raw materials are NiO and Y2O3, which play a role in the preliminary radial diffusion of fuel gas and also have a supporting role; the fuel gas channels are arranged inside the anode substrate and play a role in transporting fuel gas; the anode diffusion layer has a porous structure and is coated on the surface of the anode substrate by the impregnation method. The main raw materials are NiO and YSZ, which play a role in fuel gas diffusion; the anode functional layer has a certain porosity and is coated on the surface of the anode diffusion layer by the spraying method. The main raw materials are NiO and YSZ, and its main function is to catalyze the electrochemical reaction and reduce the interfacial resistance at the same time. The SOFC anode prepared by the present invention has a gradient porosity on the basis of ensuring good mechanical strength, which not only facilitates the transmission of fuel gas, but also reduces the interfacial resistance between the functional layer and the electrolyte, greatly enhancing the output power of the battery.

[0042] Further, taking H2 fuel as an example, the reaction process is that H2 radially diffuses from the fuel gas channels, passes through the anode substrate and the anode diffusion layer to reach the anode functional layer, where H2 undergoes an oxidation reaction after reaching the anode functional layer. Specifically, two molecules of H2 react with one O 2- reaction, while losing two electrons, generating two molecules of water; on the cathode side, O2 undergoes a reduction reaction after reaching the cathode surface. O2 obtains electrons from the anode and is reduced to O 2- , and is conducted through the YSZ electrolyte layer to supply the anode for oxidation reaction, so that the reaction can proceed continuously.

[0043] Example 1

[0044] This example provides a flat-tubular SOFC anode with gradient porosity and its preparation method, including the following steps:

[0045] S1: Anode substrate preparation process

[0046] Mix NiO powder, Y2O3 powder, pore former (carbon powder with a particle size of 2 - 5 μm), and ethyl cellulose in an ethanol solution. After ball milling the obtained slurry for 24 h, dry it to obtain uniform anode powder. Then, add water and the plasticizer polyethylene glycol to the anode powder and mix well to obtain NiO - Y2O3 ceramic mud. Among them, the particle size of the NiO - Y2O3 powder is 0.5 μm - 1.0 μm, and the mass ratio of the two is 7:3. The addition amount of the anode matrix binder is 8% of the total mass of the main raw materials (NiO powder and Y2O3 powder); the addition amount of the anode matrix is 15% of the total mass of the main raw materials; the addition amount of the plasticizer of the anode matrix is 7% of the total mass of the main raw materials.

[0047] The additives for preparing the anode also include water retention agents, such as glycerol and / or ammonium chloride.

[0048] When mixing, the mass ratio of the powder to pure water is 10:4, and the mixing time is 1 h; the anode matrix mud needs to be kneaded 3 times before extrusion molding. After kneading, the water content should be controlled at 15%. The anode matrix mud is extruded using a single - screw extruder to obtain a wet blank with a uniformly distributed gas channel structure with a diameter of 1.2 mm, and the extrusion pressure is between 8 MPa. Then, air - dry the anode matrix wet blank for 4 days to obtain a dry blank. Set the debinding and drying temperature of the anode matrix dry blank to 250 °C for 2 h; immediately transfer the dry blank to a muffle furnace for sintering after drying and debinding. Set the first - stage sintering temperature to 500 °C with a holding time of 10 h, the second - stage temperature to 1100 °C with a holding time of 4 h, and the heating rate to 1 °C / min to finally obtain the anode matrix.

[0049] S2: Preparation process of the anode diffusion layer

[0050] Mix NiO and YSZ powders according to a mass ratio of 6:4, put them into a ball - mill jar and dry - mill for 12 h. Then, put 7.5% of the carbon powder / starch pore former (carbon powder with a particle size of 0.5 - 1 μm), 3% PVB, 6% polyethylene glycol, 3% triethylamine, and 5% dibutyl phthalate based on the mass of the main raw materials into the ball - milled powder, and add an appropriate amount of ethanol for dispersion. Put the above slurry into the ball - mill jar and ball - mill for another 12 h to obtain the anode diffusion layer slurry.

[0051] Immerse the anode matrix in the diffusion layer slurry for 15 s, then dry it at a temperature of 50 °C - 60 °C for 10 min. Repeat the above operation twice. Transfer the anode impregnated with the diffusion layer to a muffle furnace for sintering at a sintering temperature of 1000 °C for 2 h with a heating rate of 0.5 °C / min. After sintering, an anode diffusion layer is obtained on the surface of the anode matrix.

[0052] S3: Preparation Process of Anode Functional Layer

[0053] Mix NiO and YSZ powders in proportion and put them into a sand mill for sanding for 12 h to obtain mixed fine powders of NiO and YSZ. Then, put 7.5% nano-carbon powder pore former with a particle size of 50 - 100 nm, 3% PVB, 6% polyethylene glycol, 3% triethylamine, and 5% dibutyl phthalate into the sanded powders, and add an appropriate amount of ethanol for dispersion. Put the above slurry into the sand mill for sanding again for 12 h to obtain the anode functional layer slurry. Use a plasma spraying machine to spray the slurry on the surface of the anode diffusion layer, with a spraying pressure of 0.4 MPa. After each spraying, dry it, set the temperature to 50℃ - 60℃, set the drying time to 10 min, spray-dry 2 times. Transfer the anode with the sprayed functional layer to a muffle furnace for sintering, with a sintering temperature of 1000℃, a sintering time of 2 h, and a heating rate of 0.5℃ / min. After sintering, an anode functional layer is obtained on the surface of the anode diffusion layer.

[0054] In this anode, the pore size distribution results of the anode substrate, anode diffusion layer, and anode functional layer are as Figure 2 shown.

[0055] The three-point bending test results of this anode are as Figure 3 shown.

[0056] The local electron microscope structure of this anode is as Figure 4 shown.

[0057] Comparative Example 1

[0058] After impregnating and drying the anode diffusion layer, directly use a plasma spraying machine to spray the slurry on the surface of the anode diffusion layer to spray the anode functional layer, with a spraying pressure of 0.4 MPa. After each spraying, dry it, set the temperature to 50℃ - 60℃, set the drying time to 10 min, spray-dry 2 times. Transfer the anode with the sprayed functional layer to a muffle furnace for sintering, with a sintering temperature of 1000℃, a sintering time of 2 h, and a heating rate of 0.5℃ / min. After sintering, an anode functional layer is obtained on the surface of the anode diffusion layer, and the rest is the same as in Example 1.

[0059] The local electron microscope results of this anode are as Figure 5 shown.

[0060] Comparative Example 2

[0061] Using NiO and YSZ as the main raw materials for the anode substrate, adding additives according to the content described in Example 1. After obtaining the dry green body of the anode substrate, set the debinding and drying temperature of the dry green body of the anode substrate to 250 °C and the time to 2 h; immediately transfer the dry green body to a muffle furnace for sintering after debinding and drying. Set the first sintering temperature platform to 350 °C, the holding time to 6 h, the second temperature platform to 1100 °C, the holding time to 4 h, and the heating rate to 2 °C / min to finally obtain the anode substrate.

[0062] Then, mix NiO and YSZ powders in a mass ratio of 55:45, put them into a ball mill jar and dry mill for 12 h. Then, put 7.5% of the carbon powder / starch pore former (carbon powder with a particle size of 2 - 5 μm), 3% PVB, 6% polyethylene glycol, 3% triethylamine, and 5% dibutyl phthalate based on the mass of the main material into the ball-milled powder, and add an appropriate amount of ethanol for dispersion. Put the above slurry into the ball mill jar and ball mill for another 12 h to obtain the anode diffusion layer slurry.

[0063] Immerse the anode substrate in the diffusion layer slurry for 20 s, then dry it at a temperature of 50 °C - 60 °C for 10 min. Repeat the above operation twice. Transfer the anode impregnated with the diffusion layer to a muffle furnace for sintering at a sintering temperature of 1000 °C for 2 h and a heating rate of 0.5 °C / min. After sintering, an anode diffusion layer is obtained on the surface of the anode substrate.

[0064] The comparison results of the discharge performance of this anode and the anode prepared in Example 1 are as Figure 6 shown.

[0065] In summary, the invention includes but is not limited to the above embodiments. Any equivalent replacement or partial improvement made under the spirit and principle of the present invention will be regarded as within the protection scope of the present invention.

Claims

1. A flat-tubular SOFC anode with gradient pores, characterized in that: It includes an anode substrate, an anode diffusion layer, and an anode functional layer that are sequentially arranged from bottom to top; among them, fuel channels with a pore diameter of 1 - 1.5 mm are uniformly distributed on the anode substrate; The main body of the anode substrate is NiO and Y2O3, which is prepared by extrusion molding - sintering; the porosity of the anode substrate is 40% - 50%, and the thickness is 400 - 500 μm; The main body of the anode diffusion layer is NiO and YSZ, which is prepared by impregnation - sintering; the porosity of the anode diffusion layer is 20% - 35%, and the thickness is 5 - 10 μm; The main body of the anode functional layer is NiO and YSZ, which is prepared by plasma spraying - sintering; the porosity of the anode diffusion layer is 10% - 55%, and the thickness is 1 - 5 μm.

2. A preparation method of a flat-tube SOFC anode with gradient pores as described in claim 1, characterized in that: The method steps include: (1) Mix NiO powder, Y2O3 powder, a first pore - forming agent, and a first binder evenly in ethanol to obtain a slurry; ball - mill and dry to obtain anode powder; add water and a plasticizer to the anode powder, mix to obtain NiO - Y2O3 ceramic mud, knead, and extrude to form a green body with a uniformly distributed gas channel structure, air - dry for 3 - 5 days, after debinding and drying, first sinter at T1 for 10 - 12 h, and then sinter at T2 for 4 - 5 h to obtain the anode substrate; the particle size of the first pore - forming agent is 2 - 5 μm; (2) After mixing and dry - grinding NiO powder and YSZ powder, add a second pore - forming agent, a second binder, and a first dispersant, and disperse evenly in ethanol to obtain a diffusion layer slurry; place the anode substrate in the diffusion layer slurry, impregnate for 10 - 20 s, dry, repeat the impregnation - drying 1 - 3 times, first sinter at T3 for 8 h - 10 h, and then sinter at T4 for 2 - 3 h to obtain the anode diffusion layer on the surface of the anode substrate; the particle size of the second pore - forming agent is 0.5 - 1 μm; (3) After mixing and dry - grinding NiO powder and YSZ powder, add a third pore - forming agent, a second binder, and a second dispersant, and disperse evenly in ethanol, sand - mill to obtain a functional layer slurry; use plasma spraying to spray the functional layer slurry on the surface of the anode diffusion layer, the spraying pressure is 0.3 - 0.5 MPa, dry, repeat the spraying - drying 1 - 3 times, first sinter at T5 for 8 h - 10 h, and then sinter at T4 for 2 - 3 h to obtain the anode functional layer on the surface of the anode diffusion layer; the particle size of the third pore - forming agent is 50 - 100 nm; Among them, T1, T3, and T5 are respectively 450 - 550 °C, T2 is 1050 - 1150 °C, and T4 is 50 - 100 °C lower than T2.

3. The preparation method of a flat-tube SOFC anode with gradient pores according to claim 2, characterized in that: In step (1), the particle sizes of the NiO powder and the Y2O3 powder are respectively 0.1 - 2 μm; And / or, the mass ratio of the NiO powder and the Y2O3 powder is 7:3 - 6:

4.

4. The preparation method of a flat-tubular SOFC anode with gradient pores as described in claim 2, characterized in that: In step (1), the first binder is one or more of YB - 167, methyl cellulose, and ethyl cellulose; preferably, the addition amount of the first binder is 5% - 10% of the total mass of the NiO powder and the Y2O3 powder; And / or, the first pore former is carbon powder and / or starch; preferably, the addition amount of the first pore former is 10% - 20% of the total mass of the NiO powder and the Y2O3 powder; And / or, the plasticizer is polyethylene glycol; preferably, the addition amount of the plasticizer is 6% - 8% of the total mass of the NiO powder and the Y2O3 powder; And / or, the mass ratio of the anode powder to water is 10:3 - 4, and the water content after kneading is 15% - 20%.

5. The preparation method of a flat tube type SOFC anode with gradient pores as described in claim 2, characterized in that: In step (1), the pressure for extrusion molding is 5 - 10 MPa; And / or, the debinding and drying temperature is 250 - 300 °C, and the time is 2 - 3 h; And / or, the heating rate during sintering is 1 - 2 °C / min.

6. The preparation method of a flat-tube SOFC anode with gradient pores as described in claim 2, characterized in that: In steps (2) and (3), the particle sizes of the NiO powder and the YSZ powder are respectively 0.1 - 2 μm; And / or, the mass ratio of the NiO powder to the YSZ powder is 1:1 - 3:

2.

7. The preparation method of a flat-tube SOFC anode with gradient pores as claimed in claim 2, characterized in that: In steps (2) and (3), the second binder is PVB (polyvinyl butyral) and / or polyethylene glycol; preferably, the addition amount of the second binder is 5% - 10% of the total mass of the NiO powder and the YSZ powder; Preferably, in steps (2) and (3), the first dispersant is triethylamine and / or dibutyl phthalate; preferably, the addition amount of the first dispersant is 5% - 7% of the total mass of the NiO powder and the YSZ powder.

8. The preparation method of a flat tube type SOFC anode with gradient pores as described in claim 2, characterized in that: In steps (2) and (3), the drying temperature is 50 - 60 °C, and the time is 10 - 15 min. And / or, the heating rate during sintering is 0.5 - 1 °C / min.

9. The preparation method of a flat tube type SOFC anode with gradient pores as described in claim 2, characterized in that: In step (2), the second pore former is carbon powder and / or starch; more preferably, the addition amount of the second pore former is 5% - 10% of the total mass of the NiO powder and the YSZ powder.

10. The preparation method of a flat-tube SOFC anode with gradient pores as described in claim 2, characterized in that: In step (3), the third pore former is nano carbon powder; preferably, the addition amount of the third pore former is 5% - 10% of the total mass of the NiO powder and the YSZ powder.

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