A method for preparing a ni-al intermetallic compound negative contact layer

Abstract

The application relates to the field of electrochemical energy materials, in particular to a preparation method of a Ni-Al intermetallic compound negative contact layer, which comprises the following steps: S1, powder mixing: nickel powder and aluminum powder are weighed according to an atomic ratio of 1.5:1, and then grinding is carried out to prepare mixed powder; S2, preparation of an adhesive: ethyl cellulose and terpineol are mixed, and then stirring is carried out to prepare transparent viscous gelatinous substances, so that the adhesive is prepared; S3, preparation of a sintered sample; and S4, atmosphere sintering: after the dried sample is calcined, cooling is carried out to room temperature, so that the Ni-Al intermetallic compound negative contact layer is prepared. The application provides a new negative contact layer material, the Ni-Al intermetallic compound, and the material has excellent electric conductivity and high-temperature oxidation resistance.

Description

Technical Field

[0001] This invention relates to the field of chemical coating preparation, specifically to a method for preparing a Ni-Al intermetallic compound cathode contact layer. Background Technology

[0002] The contact between the single-cell electrode and the metal connector is a "hard" contact between ceramic or cermet and metal. To reduce interfacial contact resistance (ASR, area-specific resistance) and voltage drop, a relatively "soft," compressible conductive contact material is typically used at this interface during fuel cell assembly. This material collects and conducts electrons (current collector layer) and enhances interfacial contact, thus reducing interfacial resistance. Therefore, at the fuel cell operating temperature, the contact material should possess compressibility, adhesion to the cathode / anode, good electronic conductivity, resistance to high-temperature oxidation, and maintain a porous structure (appropriate sintering activity and porosity) to facilitate the diffusion of reactive gases into the electrode and their participation in electrochemical reactions. Considering that the anode and cathode of each cell in the fuel cell stack are exposed to a reducing fuel atmosphere and an air atmosphere, respectively, nickel foam (Ni) is usually used as the gas diffusion layer material on the anode side, and Ni paste is used as the contact material between the nickel foam and the anode. On the cathode side, the commonly used diffusion layer material is ferritic stainless steel, and its structure is a channel or fin integrated with the metal connector. The contact material is often a compressible porous noble metal or conductive ceramic powder material.

[0003] The contact resistance at the cathode / metal connector interface is significantly higher than that at the anode, differing by orders of magnitude. Therefore, the performance of the cathode / metal connector interface is one of the bottlenecks restricting the development of intermediate-temperature solid oxide fuel cell (SOFC) technology. Cathode contact materials need to meet conditions such as high electronic conductivity, chemical stability, mechanical stability, a coefficient of thermal expansion (CTE) that matches the cathode and connector materials, and low cost. Common materials include perovskite, noble metals, and spinel coatings. Noble metals offer good conductivity but are relatively expensive. The main problem with perovskite materials as contact layers is the inability to perfectly balance conductivity, CTE, and sinterability. For example, lanthanum-strontium-cobalt has good conductivity, but its CTE is much higher than other components; lanthanum-strontium-manganese has a CTE compatible with other components, but its conductivity is low. Therefore, balancing the various properties of the material is a challenge. Spinel materials require high sintering temperatures to obtain the spinel phase, which may lead to severe oxidation of the connector during sintering. Summary of the Invention

[0004] To address the existing technical problems, this invention proposes a method for preparing a Ni-Al intermetallic compound cathode contact layer.

[0005] A method for preparing a Ni-Al intermetallic compound cathode contact layer includes the following steps:

[0006] S1, Powder mixing: Weigh nickel powder and aluminum powder at an atomic ratio of 1.5:1, grind them, and obtain a mixed powder;

[0007] S2, Preparation of adhesive: Ethyl cellulose and terpineol are mixed and stirred into a transparent and viscous gel-like substance to obtain an adhesive;

[0008] S3, Preparation of sintered samples: Weigh the mixed powder obtained in S1 and the binder obtained in S2 according to the proportion, mix them, grind them to obtain Ni-Al slurry, then coat the Ni-Al slurry onto the surface of the ferritic stainless steel connector and dry it.

[0009] S4, Atmosphere sintering: After calcining the dried sample, cool it to room temperature to obtain the Ni-Al intermetallic compound cathode contact layer.

[0010] Furthermore, in S1, the grinding process is as follows: nickel powder, aluminum powder and grinding media are mixed and mixed at a speed of 200 r / min for 8 hours to obtain mixed powder.

[0011] Furthermore, the grinding media is a mixture of φ10mm and φ5mm zirconia balls in a 1:1 mass ratio, and the mass of the grinding media is three times the total mass of nickel powder and aluminum powder.

[0012] Furthermore, in S2, the weight percentages are ethyl cellulose: terpineol = 96 wt.% : 4 wt.%.

[0013] Furthermore, in S2, the stirring temperature is 80°C and the stirring time is 5 hours.

[0014] Further, in S3, the powder and binder are mixed in a weight percentage ratio of 65 wt.% to 35 wt.%, and the grinding time is 30 min. The Ni-Al paste is then applied to the surface of the ferritic stainless steel connector using a screen printing method.

[0015] Furthermore, in S3, the drying temperature is 80°C and the drying time is 3 hours.

[0016] Furthermore, in S4, the specific calcination process is as follows: the dried sample is placed in a tube furnace, pure argon gas is introduced, the temperature is raised to 550°C at a heating rate of 5°C / min and held at that temperature for 30 min, and then the temperature is raised to 900°C and held at that temperature for 2 h.

[0017] The Ni-Al intermetallic compound cathode contact layer prepared by the above method.

[0018] The above-mentioned Ni-Al intermetallic compound anodizing contact layer is used in the electrocatalytic production of carbon monoxide from carbon dioxide.

[0019] Compared with the prior art, the present invention has the following advantages:

[0020] 1. This invention provides a novel cathode contact layer material, a Ni-Al intermetallic compound, which possesses excellent electrical conductivity and high-temperature oxidation resistance.

[0021] 2. The Ni-Al intermetallic compound cathode contact layer provided by this invention can maximize the service life and electrical performance of SOFC stacks when applied.

[0022] 3. The method for preparing the Ni-Al intermetallic compound cathode contact layer provided by this invention has a small process flow, requires simple equipment, and is easy to control, making it suitable for large-scale industrial production. Attached Figure Description

[0023] Figure 1 This is a flowchart illustrating the preparation process of a Ni-Al intermetallic compound cathode contact layer according to the present invention.

[0024] Figure 2 The figure shows the experimental results of the surface resistivity (ASR) of the Ni-Al intermetallic compound cathode contact layer prepared in Example 1.

[0025] Figure 3 The graph shows the variation of ASR (Al-Synthetic Ratio) of the Ni-Al intermetallic compound cathode contact layer prepared in Example 1 at different temperatures.

[0026] Figure 4 The image shows the oxidation XRD pattern of the Ni-Al intermetallic compound cathode contact layer prepared in Example 1, as measured by ASR.

[0027] Figure 5 (a) is a SEM image of the surface morphology of the Ni-Al intermetallic compound cathode contact layer prepared in Example 1 under a 500x microscope.

[0028] Figure 5 (b) is a SEM image of the surface morphology of the Ni-Al intermetallic compound cathode contact layer prepared in Example 1 under a 10k magnification microscope.

[0029] Figure 5 (c) is Figure 5 (b) EDS point scan map of point A.

[0030] Figure 5 (d) is Figure 5 (b) EDS point scan map of point B.

[0031] Figure 6 (a) is a cross-sectional view of the Ni-Al intermetallic compound cathode contact layer prepared in Example 1 after oxidation and ASR test.

[0032] Figure 6 (b) is Figure 6 (a) EDS surface scan pattern.

[0033] Figure 6 (c) is Figure 6 (a) EDS spot scan map.

[0034] Figure 6 (d) is Figure 6 (a) EDS spot scan map.

[0035] Figure 7 The XRD patterns of the Ni-Al intermetallic compound cathode contact layer prepared in Example 1 and the Ni-Al intermetallic compound cathode contact layer prepared in Comparative Example 1 are shown. Detailed Implementation

[0036] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Unless otherwise specified, the equipment and reagents used in the present invention are commercially available products conventional in this technical field.

[0037] Porous intermetallic compounds are a novel type of inorganic porous material that lies between porous ceramics and porous metals. Due to their excellent performance and promising development prospects, they have attracted considerable attention in recent years. Ni-Al based intermetallic compounds are a new generation of porous intermetallic compound materials, possessing good electrical conductivity and high-temperature oxidation resistance. They can be used as high-temperature structural and functional materials and have been widely applied in the field of porous materials. In the Ni-Al binary system, high-melting-point Ni3Al and NiAl not only possess the good electrical and thermal conductivity and high-temperature plasticity (compressibility) of metallic materials, but also the excellent properties of ceramic materials such as high-temperature resistance, corrosion resistance, and oxidation resistance; their superior physicochemical properties make them promising candidates for SOFC cathode contact materials. Therefore, this invention proposes porous Ni-Al intermetallic compounds as cathode / metal interface contact materials, providing a novel approach to the research and development of SOFC cathode contact materials and laying the foundation for solving the bottleneck technologies of SOFC stacks.

[0038] <Example 1>

[0039] Please refer to Figure 1The present invention provides a method for preparing a Ni-Al intermetallic compound cathode contact layer, comprising the following steps:

[0040] S1, Powder mixing: Weigh nickel powder and aluminum powder at an atomic ratio of 1.5:1, and put them into a mixing tank along with three times the mass of grinding media. Place the tank on a V-type mixer and mix at a speed of 200 r / min for 8 hours. The grinding media is a mixture of φ10mm and φ5mm zirconia balls with a mass ratio of 1:1.

[0041] S2, Preparation of adhesive: Pour 96wt.% ethyl cellulose and 4wt.% terpineol into a beaker, and heat in a water bath at 80°C for 5 hours with a magnetic stirrer until the two are completely mixed into a transparent and viscous colloid.

[0042] S3, Preparation of sintered samples: Weigh 65wt.% of mixed powder and 35wt.% of binder into a natural agate grinding body, grind at a uniform speed for 30min to obtain Ni-Al slurry, apply Ni-Al slurry to the surface of SUS430 ferritic stainless steel connector by screen printing, and dry in a drying oven at 80℃ for 3h.

[0043] S4, Atmosphere sintering: The dried sample is placed in a tube furnace and high-purity argon gas (99.9%) is introduced. The temperature is raised to 550°C at a rate of 5°C / min and held at that temperature for 30 min. Then the temperature is raised to 900°C and held at that temperature for 2 h. After the sample is cooled to room temperature, the Ni-Al intermetallic compound cathode contact layer can be obtained.

[0044] The Ni-Al intermetallic compound cathode contact layer prepared by this invention is different from traditional noble metal or conductive oxide cathode contact materials. The Ni-Al intermetallic compound not only has good electrical conductivity and high-temperature oxidation resistance, meeting the performance requirements of cathode contact materials, but also can form a porous contact layer through in-situ reaction sintering of Ni and Al mixed powders, and form a good interface bond with the cathode and metal connector.

[0045] The preparation method of this invention differs from conventional conductive oxide cathode contact materials, which are typically applied between the cathode and the metal connector via screen printing after phase formation. Under SOFC operating conditions, the interface between them is physically bonded and easily damaged. This patent, however, applies a Ni-Al mixed powder between the cathode and the metal connector, and holds it at a temperature above the melting point of Al during the SOFC stack heating process. A porous Ni-Al intermetallic compound contact layer is formed through in-situ reaction sintering. The heat released by the transient liquid (Al)-solid (Ni) reaction causes interdiffusion at the interface, forming a chemical bond, thereby increasing the bonding strength and reducing the contact resistance.

[0046] Figure 2This is an experimental result graph showing the areal resistivity (ASR) of the Ni-Al intermetallic compound cathode contact layer prepared by the method of this embodiment after continuous exposure to air at 750°C for 300 hours. Figure 2 As can be seen, although the graph appears to show large fluctuations, the ASR value actually fluctuates very little, with an overall value ranging from 8.4 to 9.2 mΩ·cm. 2 Within this range, the ASR value did not stabilize during the first 250 hours, but a plateau appeared between 250 and 300 hours, with the ASR stabilizing at 8.67 mΩ·cm. 2 The low ASR value indicates that the Ni-Al intermetallic compound contact layer has good conductivity, fully meeting the practical requirements for cathode contact layers.

[0047] Figure 3 This is a graph showing the ASR (Average Saturation Rate) of the Ni-Al intermetallic compound cathode contact layer prepared using the method of this embodiment at different temperatures ranging from 550 to 850°C. Figure 3 It can be seen that the ASR value increases with increasing temperature, reaching 1.51 mΩ·cm at 550℃. 2 It then continued to increase until it reached 4.50 mΩ·cm at 850℃. 2 Furthermore, the growth is relatively uniform, with the graph approximating a straight line. The characteristic of the Ni-Al contact layer's ASR value increasing with temperature is similar to that of metals. While the conductivity of metallic materials decreases with increasing temperature, the ASR increases, indicating that the conductivity of the Ni-Al intermetallic compound is also similar to that of metals. Although the ASR value of the Ni-Al cathode contact layer continuously increases with temperature, its overall value is very small, with even the maximum value at 850℃ below 5 mΩ·cm. 2 This indicates that the contact layer has good electrical properties at different temperatures.

[0048] Figure 4The XRD pattern of the Ni-Al intermetallic compound cathode contact layer prepared by the method of this embodiment after oxidation at 750℃ for 300 hours is shown in the figure. As can be seen from the figure, the main components of the Ni-Al cathode contact layer before oxidation are NiAl, NiFe, and a small amount of single-phase Ni, with NiAl being the most abundant phase. The newly generated NiFe is likely produced by interdiffusion between Fe in the Fe-Cr alloy linker and Ni in the Ni-Al contact layer. The XRD pattern after 300 hours of oxidation at 750℃ shows that the main components are NiAl, NiFe, a small amount of single-phase Ni, and very little NiO. The strongest peak is still NiAl, followed by NiFe, while the contents of Ni and NiO are very small. The diffraction peaks of the patterns before and after oxidation are very similar; the only difference is the appearance of a very small amount of NiO after oxidation. This also indicates that the cathode contact layer has good oxidation resistance, and no large amount of oxides were formed after 300 hours of oxidation.

[0049] Figure 5 This is a SEM image of the surface morphology of the Ni-Al intermetallic compound cathode contact layer prepared by the method of this embodiment, with point scans of energy dispersive spectroscopy performed at points A and B. Figure 5 As shown in (a), the Ni-Al cathode contact layer has a porous structure, and the spherical material with uniform surface distribution is formed by the aggregation of many small particles. Figure 5 (b) is a magnified image of the Ni-Al cathode contact layer surface at 10kx, with EDS point scanning performed on points A and B. The results are as follows: Figure 5 As shown in (c) and (d). According to Figure 5 (c) Energy dispersive spectroscopy (EDS) analysis revealed three elements at point A: Pt, Ni, and Al. The presence of platinum is due to the platinum coating applied to the sample surface before SEM imaging to increase conductivity and improve image clarity. The atomic percentage of Pt is negligible; the main elements are Ni and Al. Ni accounts for 70.04% by weight and 52.99% by atomic weight, while Al accounts for 28.33% by weight and 46.64% by atomic weight. The Ni / Al atomic ratio is close to 1:1, suggesting that point A is likely NiAl. Figure 5 (d) It can be seen that the elements detected at point B are Pt, Ni and Al, where Pt can be ignored. The weight ratio of Ni to Al is 50.17:46.40 and the atomic ratio is 32.97:66.37. The substance may be Ni2Al3.

[0050] Figure 6 This is a cross-sectional view of the Ni-Al intermetallic compound cathode contact layer prepared by the method in this embodiment after 300 hours of ASR oxidation. Figure 6In (a), the left side is the connector and the right side is the contact layer. The contact layer has a porous structure, but due to the fabrication of the mosaic sample, the pores of the contact layer are filled with acrylic resin. It can be seen that the thickness of the contact layer is more than 50 μm and it is tightly bonded to the connector. No obvious cracks or oxide layers are visible to the naked eye. However, the elemental analysis of O shows that the oxygen content at the interface position of 20-25 μm is exceptionally high. Therefore, it can be inferred that oxides are generated at this position, and an oxide layer may have formed. Figure 6 (b) is Figure 6 (a) EDS surface scan pattern, where red dots represent Fe particles, green dots represent Al particles, and yellow dots represent Ni particles. Figure 6 (c) and Figure 6 (d) are all Figure 6 (a) EDS line scan at the position indicated by the white line in the middle. Figure 6 (b) shows the elements and their content along the line. (d) The graph shows the distribution and content of elements at different locations along this line. From... Figure 6 (c) shows that the line contains C, O, Al, Cr, Mn, Fe, and Ni. Due to the presence of acrylic resin, C has the highest atomic percentage, followed by Ni and Al, with atomic percentages of 14.83% and 14.08% respectively, approximately in a 1:1 ratio. This suggests that the majority of the particles formed are NiAl particles, with lower levels of Cr, Mn, and Fe. Figure 6 The elemental spectra of Fe, Cr, O, Ni, and Al in (d) also suggest that the high Fe and Cr content in the first 20 μm indicates the presence of the connecting body. The presence of small amounts of O and Ni in the 20–25 μm range suggests the possible formation of a 5 μm oxide layer, likely NiO. The exceptionally high Ni and Al content beyond 25 μm indicates the presence of the contact layer. The absence of Cr aggregation in this contact layer suggests its effective ability to prevent Cr volatilization.

[0051] <Comparative Example 1>

[0052] A method for preparing a Ni-Al intermetallic compound cathode contact layer includes the following steps:

[0053] S1, Powder mixing: Weigh nickel powder and aluminum powder at an atomic ratio of 3:1, and load them into a mixing tank along with three times the mass of grinding media. Place the tank on a V-type mixer and mix at a speed of 200 r / min for 8 hours. The grinding media is a mixture of φ10 mm and φ5 mm zirconia balls with a mass ratio of 1:1.

[0054] S2, Preparation of adhesive: Pour 96wt.% ethyl cellulose and 4wt.% terpineol into a beaker, and heat in a water bath at 80°C for 5 hours with a magnetic stirrer until the two are completely mixed into a transparent and viscous colloid.

[0055] S3, Preparation of sintered samples: Weigh 65wt.% of mixed powder and 35wt.% of binder into a natural agate grinding body, grind at a uniform speed for 30min to obtain Ni-Al slurry, apply Ni-Al slurry to the surface of SUS430 ferritic stainless steel connector by screen printing, and dry in a drying oven at 80℃ for 3h.

[0056] S4, Atmosphere sintering: The dried sample is placed in a tube furnace and high-purity argon gas (99.9%) is introduced. The temperature is raised to 550°C at a rate of 5°C / min and held at that temperature for 30 min. Then the temperature is raised to 900°C and held at that temperature for 2 h. After the sample is cooled to room temperature, the Ni-Al intermetallic compound cathode contact layer (Ni3Al cathode contact layer) can be obtained.

[0057] A material comparison was made between the Ni1.5Al cathode contact layer prepared in Example 1 and the Ni3Al cathode contact layer prepared in Comparative Example 1, and the results are as follows: Figure 7 As shown in the figure, the main phase of the Ni3Al contact layer is Ni with only a very small amount of NiAl. This indicates that when the Ni:Al atomic ratio becomes 3:1, the Ni atomic ratio is too high, leading to the overflow of individual Ni atoms. The main components of the N1.5Al contact layer are NiAl and NiFe. From a phase perspective, the N1.5Al cathode contact layer has a better phase composition.

[0058] The above description of the embodiments is only for the purpose of helping to understand the technical solution and core idea of ​​the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made to the present invention without departing from the principle of the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

Claims

1. A method for producing a Ni-Al intermetallic compound cathode contact layer, characterized by, It comprises the following steps: S1, powder mixing: weighing nickel powder and aluminum powder in an atomic ratio of 1.5:1, grinding to obtain a mixed powder; S2, preparing a binder: mixing ethyl cellulose and terpineol, stirring to obtain a transparent viscous gel, and then preparing the binder; S3, preparing a sintered sample: weighing and mixing the mixed powder prepared in S1 and the binder prepared in S2 according to the proportion, grinding to obtain a Ni-Al slurry, coating the Ni-Al slurry on the surface of a ferritic stainless steel connector, and drying; wherein the weight percentage is used as the proportion, the mixed powder:binder=65wt.%:35wt.%, the grinding time is 30min, and the Ni-Al slurry is coated on the surface of the ferritic stainless steel connector by screen printing; S4, atmosphere sintering: calcining the dried sample, cooling to room temperature, and then obtaining a Ni-Al intermetallic compound cathode contact layer; wherein the specific process of calcination is as follows: placing the dried sample into a tube furnace, introducing pure argon, increasing the temperature to 550℃ at a rate of 5℃ / min and maintaining at this temperature for 30min, then continuing to increase the temperature to 900℃ and maintaining at this temperature for 2h.

2. The method for preparing a Ni-Al intermetallic compound cathode contact layer according to claim 1, characterized in that, In S1, the grinding process is as follows: mixing nickel powder, aluminum powder and grinding medium, mixing at a speed of 200r / min for 8h to obtain a mixed powder.

3. The method for preparing a Ni-Al intermetallic compound cathode contact layer according to claim 2, characterized in that, The grinding medium is a mixture of zirconia balls with a mass ratio of 1:1, φ10mm and φ5mm, and the mass of the grinding medium is three times the total mass of the nickel powder and the aluminum powder.

4. The method for preparing a Ni-Al intermetallic compound cathode contact layer according to claim 1, characterized in that, In S2, the weight percentage of ethyl cellulose:terpineol is 96wt.%:4wt.%.

5. The method for preparing a Ni-Al intermetallic compound cathode contact layer according to claim 1, characterized in that, In S2, the stirring temperature is 80℃ and the stirring time is 5h.

6. The method for preparing a Ni-Al intermetallic compound cathode contact layer according to claim 1, characterized in that, In S3, the drying temperature is 80℃ and the drying time is 3h.

7. The Ni-Al intermetallic compound cathode contact layer prepared by the preparation method according to any one of claims 1-6.

8. The use of the Ni-Al intermetallic compound cathode contact layer according to claim 7 in electrocatalytic carbon dioxide to carbon monoxide.

Images