CN100426576C - Connecting material of solid oxide fuel battery and its preparation method - Google Patents

Abstract

The molecular formula of the connection material of a solid oxide fuel cell of the present invention is: Nd _1-x Ca _x Cr _1-δ O ₃ , where 0<X≤0.30, 0<δ≤0.1. Its preparation adopts the method of solid phase reaction: 1. Weigh the following raw materials in proportion: Nd ₂ O ₃ , CaCO ₃ and Cr ₂ O ₃ ; 2. Put the weighed raw materials together to grind and press them into shape; 3. After Pre-fired twice at 1000°C and 1200°C and repeatedly crushed and ground before pressing; 4. Finally, sintered at 1550°C-1700°C for 10-20 hours to obtain the desired sample. The connecting material of the present invention has the advantages of high electrical conductivity, good sintering performance, and compact bonding between crystal grains; at the same time, it also solves the problem of price change of Pr in the PrCrO ₃ -based material, and has good chemical stability. The preparation method of the invention has the advantages of simple process and low production cost.

Description

A connection material for a solid oxide fuel cell and its preparation method

technical field

The invention relates to a solid oxide fuel cell connection material, in particular to a novel intermediate temperature solid oxide fuel cell connection material.

Background technique

The prior art closest to the present invention is a Chinese invention patent application, the title of the invention is "Connecting material for solid oxide fuel cell and its preparation method and application", and the publication number is CN1503389A. The molecular formula of the connection material of the solid oxide fuel cell is Pr _1-x Ca _x Cr _1-δ O ₃ , where 0.1≤X≤0.5, 0<δ≤0.06. The preparation method of the connection material adopts the method of solid phase reaction, and the technological process includes batching, grinding, pressing and forming, and sintering. Wherein, the pressing pressure is 10-20 MPa; during the sintering process, the sintering temperature is 1000-1500° C., and the sintering time is 10-40 hours. However, Pr has two valence states of Pr ³⁺ and Pr ⁴⁺ , so there is a problem of price change, resulting in poor chemical stability of the connection material during use, resulting in a mismatch between the connection material and other materials of the fuel cell, causing the fuel cell to fail when it is working. Gas leak.

Contents of the invention

The technical problem to be solved in the present invention is to replace the Pr ³⁺ in the background technology Pr _1-x Ca _x Cr _1-δ O ₃ with Nd ³⁺ , which can not only solve the price change problem of rare earth ions, but also because the raw materials in the present invention Neodymium oxides are cheaper than praseodymium oxides, and can further reduce the cost of connecting materials. At the same time, the problems of low electrical conductivity and poor density of sintered ceramics existing in existing battery connection materials are solved.

The invention prepares a novel solid oxide fuel cell connection material by a solid phase method, and its molecular formula is: Nd _1-x Ca _x Cr _1-δ O ₃ , where 0<X≤0.30, 0<δ≤0.1.

The optimal molecular formula of the connecting material is: Nd _1-x Ca _x Cr _1-δ O ₃ , where 0.2≤X≤0.25, δ=0.02.

The preparation method of the connection material of the solid oxide fuel cell of the present invention is as follows: 1. Three raw materials are mixed in molar ratio Nd ₂ O ₃ : CaCO ₃ : Cr ₂ O ₃ =(1-X): 2X: (1-δ ), wherein, 0<X≤0.30, 0<δ≤0.1, mixing and grinding for 30 minutes; 2. Compress the ground powder at 180-200MPa, and pre-calcine for the first time at 950-1050°C for 9- 12h; 3. Re-grind for 30min, press-form at 180-200MPa, pre-fire for the second time at 1150-1250℃ for 9-12h; 4. Finally grind for 30min, press-form at 220-230MPa, press-form at 1550-1700℃ Sinter for 10-15 hours to obtain the connecting material.

Said press forming can be disc shape, cylindrical shape etc., such as pressing a disc with a diameter of 13 mm and a thickness of 0.8 mm, and pressing a cylinder with a diameter of 6 mm and a height of 5 mm.

The application of the present invention is: use Nd _1-x Ca _x Cr _1-δ O ₃ as the connection material of solid oxide fuel cell, where 0<X≤0.30, 0<δ≤0.1.

The present invention makes the Cr element in the connecting material deviate from the stoichiometric ratio, and still uses a simple solid-phase preparation method to suppress the volatilization of the chromium element during the sintering process, thereby obtaining a denser connecting material and further improving the electrical conductivity. improve. The connection material of the present invention has the advantages of high electrical conductivity, high sintering density, and compact bonding between grains. The electrical conductivity of the Pr _0.7 Ca _0.3 Cr _0.98 O ₃ material prepared in the background technology is 21.8S.cm ^-1 at 800°C ; The electrical conductivity of the sample Nd _0.75 Ca _0.25 Cr _1-δ O ₃ obtained in the present invention reaches 37.6S.cm ^-1 at 800°C; the relative density reaches 96.3%, which can meet the requirements of connecting materials in terms of compactness; Its thermal expansion coefficient is 9.24×10 ^-6 K ^-1 , which matches that of YSZ electrolyte. It can be seen that Nd _0.75 Ca _0.25 Cr _1-δ O ₃ is a connection material with great application potential. At the same time, the connection material of the present invention also avoids the problem of Pr price change in the PrCrO ₃ -based connection material, and has better chemical stability. The preparation method of the invention has the advantages of simple process and low production cost.

Description of drawings

Fig. 1 is the SEM photo of the connection material Nd _1-x Ca _x CrO ₃ (x=0.05, 0.15, 0.25) of the present invention compared with NdCrO ₃ .

Fig. 2 is the SEM photo of Nd _0.75 Ca _0.2 5Cr _1-δ O ₃ (δ=0.02, 0.04, 0.06) of the present invention.

Detailed ways

Embodiment 1 The best composition of the connecting material of the present invention

A series of NdCrO ₃ -based materials doped with Ca at the A site were prepared according to different molar ratios, and the performance of the resulting product Nd _1-x Ca _x CrO ₃ (x=0.00, 0.05, 0.10, 0.15, 0.20, 0.25) was compared, see Figure 1, Table 1, Table 2.

Fig. 1 is a SEM photo of Nd _1-x Ca _x CrO ₃ (x=0, 0.05, 0.15, 0.25) at a magnification of 2000 times. In Figure 1, a is the SEM photo of NdCrO ₃ (x=0), b is the SEM photo of Nd _0.85 Ca _0.15 CrO ₃ , c is the SEM photo of Nd _0.80 Ca _0.20 CrO ₃ , d is the SEM photo of Nd _0.75 Ca _0.25 CrO ₃ photo. It can be seen from Figure 1 that with the increase of Ca doping amount, the density of the sample is also increasing, the grains are more closely bonded, and the pores between grains are reduced, which also reflects the Ca doping microscopically. It can significantly improve the sintering performance of the sample, which is also one of the reasons for the increase in electrical conductivity.

Table 1 Conductivity of Ca-doped materials at different temperatures in A-site

It can be seen from Table 1 that the conductivity of pure NdCrO ₃ is very low, only 0.16S.cm ^-1 at 850°C, which is far from meeting the electrical performance requirements of the connecting material. Ca doping makes the conductivity of the sample better. The electrical properties of the Nd _0.75 Ca _0.25 CrO ₃ sample are the best, and the electrical conductivity reaches 28.79S.cm ^-1 at 850℃.

Table 2 The thermal expansion coefficient of Ca-doped materials at 30-1000°C in A-site

It can be seen from Table 2 that the thermal expansion coefficient of Nd _0.75 Ca _0.25 CrO ₃ reaches 9.19×10 ^-6 K ^-1 , which is 10.3×10 -1 higher than that of YSZ (8% mol Y ₂ O ₃ stabilized zirconia) electrolyte ^{. 6} K ^-1 is slightly smaller, but the thermal expansion of the connecting material and the material being connected is basically matched.

Conclusion: When Nd _1-x Ca _x CrO ₃ (x=0.20～0.25), the compactness, electrical properties and thermal expansion properties of the material are the best.

A series of Nd _0.75 Ca _0.25 Cr _1-δ O ₃ samples are prepared according to different molar ratios, and the connecting materials Nd _0.75 Ca _0.25 Cr _0.98 O ₃ , Nd _0.75 Ca _0.25 Cr _0.96 O ₃ and Nd The performance comparison of _0.75 Ca _0.25 Cr _0.94 O ₃ is shown in Figure 2, Table 3, Table 4, and Table 5.

Fig. 2 is an SEM photo of the sample Nd _0.75 Ca _0.25 Cr _1-δ O ₃ (δ=0.02, 0.04, 0.06) at a magnification of 2000 times. In Fig. 2, a is the SEM photo of Nd _0.75 Ca _0.25 Cr _0.98 O ₃ , b is the SEM photo of Nd _0.75 Ca _0.25 Cr _0.96 O ₃ , and c is the SEM photo of Nd _0.75 Ca _0.25 Cr _0.94 O ₃ . It can be seen from Figure 2 that the sample Nd _0.75 Ca _0.25 Cr _0.98 O ₃ not only has the largest grain size, but also the highest degree of compactness, and the least porosity between grains, which also reflects that the sample Nd _0.75 Ca _0.25 Cr _0.98 O ₃ has the highest sintering performance and is also one of the reasons for the higher conductivity of the Nd _0.75 Ca _0.25 Cr _0.98 O ₃ samples

Table 3 Sintered density and relative density of _{Nd 0.75} Ca _0.25 Cr _1-δ O ₃ (δ=0.02, 0.04, 0.06) samples

It can be seen from Table 3 that the sample Nd _0.75 Ca _0.25 Cr _0.98 O ₃ has the highest sintered density, and its relative density reaches 96.3%, which meets the requirements of connecting materials in terms of compactness.

Table 4 Conductivity of Nd _0.75 Ca _0.25 Cr _1-δ O ₃ (δ=0.02, 0.04, 0.06) samples in the temperature range of 300-850°C

It can be seen from Table 4 that Nd _0.75 Ca _0.25 Cr _0.98 O ₃ has the best conductivity, and this sample also has the lowest conduction activation energy.

Table 5 Thermal expansion coefficients of samples Nd _0.75 Ca _0.25 Cr _1-δ O ₃ (δ=0.02, 0.04, 0.06)

It can be seen from Table 5 that the thermal expansion coefficient of Nd _0.75 Ca _0.25 Cr _0.98 O ₃ is 9.24×10 ^-6 K ^-1 , which is closer to the thermal expansion coefficient of YSZ electrolyte, so the thermal expansion coefficient also meets the requirements for connecting materials.

Conclusion: when δ=0.02, the connection material of the present invention has the best compactness, electrical properties and thermal expansion properties.

Embodiment 2 The preparation method of the connecting material of the present invention adopting solid phase reaction

Weigh the three raw materials according to the molar ratio of Nd ₂ O ₃ : CaCO ₃ : Cr ₂ O ₃ =0.75:0.5:0.98, put the weighed raw materials in an agate mortar and grind them with alcohol for 30 minutes; then press down at 200MPa Tablet forming, first calcined at 1000°C for 10 hours; crushed and ground for 30 minutes after pre-calcined, pressed at 200MPa, and calcined for the second time at 1200°C for 10 hours; second calcined and then crushed and ground After 30 minutes, press molding at 220MPa, and sintering at 1600°C for 10 hours, a highly conductive Nd _0.75 Ca _0.25 Cr _0.98 O ₃ connection material was obtained.

Changing the ratio of raw materials to Nd ₂ O ₃ :CaCO ₃ :Cr ₂ O ₃ =0.75:0.5:0.94, according to the above process, can produce Nd _0.75 Ca _0.25 Cr _0.94 O ₃ connecting material.

Changing the ratio of raw materials to Nd ₂ O ₃ :CaCO ₃ :Cr ₂ O ₃ =0.85:0.3:0.98, according to the above process, can produce Nd _0.85 Ca _0.15 Cr _0.98 O ₃ connecting material.

The connecting material Nd _1-x Ca _x Cr _1-δ O ₃ provided by the present invention, where 0<X≤0.30, 0<δ≤0.1, as long as the appropriate raw material ratio is selected, can be used according to the process of this embodiment Process made.

Embodiment 3 The preparation method of connecting material of the present invention

Change the pre-sintering and sintering temperature in Example 2 and reduce it by no more than 50°C, or use a higher temperature, such as increasing 100°C; the pre-sintering and sintering time is less than 1 hour, or use more time, such as 15 hours, The process and other process conditions remain unchanged, and the properties of the obtained connecting materials are basically the same.

Claims (3)

1, a kind of connection material of Solid Oxide Fuel Cell is characterized in that, its composition is: Nd _1-xCa _xCr _1-δO ₃, 0＜X in the formula≤0.3,0＜δ≤0.1.

According to the connection material of the described a kind of Solid Oxide Fuel Cell of claim 1, it is characterized in that 2, its composition is: Nd _1-xCa _xCr _1-δO ₃, 0.2≤X in the formula≤0.25, δ=0.02.

3, a kind of Solid Oxide Fuel Cell of claim 1 connects preparation methods, it is characterized in that 1, with three kinds of raw materials Nd in molar ratio ₂O ₃: CaCO ₃: Cr ₂O ₃=(1-X): 2X: (1-δ), and wherein, 0＜X≤0.30,0＜δ≤0.1, batch mixing grinds 30min; 2, the powder after will grinding, press forming under 180～200MPa is at 950～1050 ℃ of 9～12h of pre-burning for the first time down; 3, grind 30min again, press forming under 180～200MPa, the 9～12h of pre-burning for the second time under 1150～1250 ℃; 4, grind 30min at last, press forming under 220～230MPa is at 1550～1700 ℃ of sintering 10～15h.

Images