TWI642228B - Electrolyte preparation method of solid oxide fuel cell - Google Patents

Abstract

A method for preparing an electrolyte for a solid oxide fuel cell, comprising: a solid oxidation mixture; and a solid state reaction, the process comprising: ball milling, drying, calcining, repeating, forming, sintering; The solid state oxidation treatment of the solid oxidation mixture will become a perovskite oxide, and the surface of the perovskite oxide is formed with a distribution of cerium oxide (CeO ₂ ).

Description

Electrolyte preparation method of solid oxide fuel cell

The present invention relates to a method for producing an electrolyte of a battery, and more particularly to a method for preparing an electrolyte of a solid oxide fuel cell.

Today, the world's energy is more focused on fossil fuels. In recent years, the average annual mining life of crude oil in the world is only about 40 years, while natural gas is only 60 years old. In the future, in addition to the international market facing high oil prices, it will face a crisis of energy shortage. Based on energy conservation and environmental protection considerations, fuel cells are one of the most promising power generation technologies because they provide clean energy.

A solid oxide fuel cell (SOFC) using proton-conducting electrolytes, mainly composed of perovskite oxide as protonic conductors, calcium and titanium The mineral oxides include: BaCeO3, BaZrO3, SrCeO3, and SiZrO3. In addition to the advantages of clean energy, the solid oxide fuel cell has the following advantages: 1. It is an all-solid battery, and there is no problem of electrolyte leakage. 2. The electrode reacts quickly and is not susceptible to the environment. 3. Thermodynamic efficiency. 4. No need to use precious metals as a catalyst.

Please refer to Patent No. I481109 of the Republic of China for providing an electrolyte preparation method for a solid oxide fuel cell. After mixing and compressing different solid oxide powders, the smaller solid oxide powder can be filled into another The pores of the solid oxide powder are sintered Thereafter, the density of the obtained product can be increased, and the obtained solid oxide product can be used as an excellent electrolyte for a proton-conducting fuel cell.

However, BaCeO3 oxides have poor chemical stability when the solid oxide fuel cell of the proton conducting electrolyte is exposed to high temperatures and carbon dioxide, and water or hydrogen sulfide. Among them, the problem encountered is that when the solid oxide fuel cell composed of BaCeO3 is in contact with carbon dioxide during operation, the perovskite structure on the surface of the solid oxide fuel cell will poison with carbon dioxide. After the poisoning of carbon dioxide for a long time, the surface of the perovskite structure will be covered by the heterophase (such as: BaCO3), causing the proton conduction path to be blocked, causing a large decline in proton conductivity or even a loss of proton conduction.

The main object of the present invention is to provide a method for preparing an electrolyte of a solid oxide fuel cell, which can form cerium oxide (CeO ₂ ) on the surface of a perovskite structure without additional processing. Stabilize the conductivity of protons to improve chemical stability.

In order to achieve the above object, the present invention provides a method for preparing an electrolyte for a solid oxide fuel cell, comprising: a solid oxidation mixture; and a solid state reaction, the process comprising: a. oxidizing the solid state The mixture is ball milled in isopropanol for 1 to 12 hours; b. the ball-milled solid oxidation mixture is dried at 60 to 180 ° C; c. the dried solid mixture is dried at 800 to 1500 ° C. 1~15 hours; d. repeating the a~c step for 1~5 times; e. dry pressing the solid oxidation mixture after calcination; f. sintering the solid pressed mixture of the dry press at at least 1600 ° C 1 to 24 hours; wherein the solid oxidation mixture is treated by the solid state reaction to form a perovskite oxide, and the surface of the perovskite oxide is formed with a distribution of cerium oxide (CeO ₂ ).

Thereby, the electrolyte preparation method of the solid oxide fuel cell of the invention can form cerium oxide on the surface of the perovskite oxide without additional processing methods, thereby stabilizing the conductivity of the proton and improving the chemical stability. efficacy.

10‧‧‧ Electrolyte preparation method for solid oxide fuel cell

11‧‧‧Solid oxidizing mixture

21‧‧‧ Solid state reaction method

31‧‧‧Perovskite oxide

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a block diagram of a preferred embodiment of the present invention.

Figure 2 is a flow chart of a preferred embodiment of the present invention.

Figure 3 is a first XRD pattern of a preferred embodiment of the invention; showing the formation of CeO ₂ at different sintering temperatures.

Figure 4 is a second XRD pattern of a preferred embodiment of the invention; showing the formation of CeO ₂ at different sintering times.

Figure 5 is a third XRD pattern of a preferred embodiment of the invention; showing the amount of BCY-CeO ₂ present on the surface of the BCY at different degrees of polishing.

6A and 6B are fourth XRD patterns of a preferred embodiment of the present invention; respectively, showing the condition of BCYZ-CeO ₂ before and after polishing.

7A and 7B are first conductivity of a preferred embodiment of the present invention; respectively, showing the condition of BCYZ-CeO ₂ before and after polishing.

Figure 8 is a second conductivity diagram of a preferred embodiment of the present invention; showing a comparison between before and after carbon dioxide poisoning when BCY and BCZY do not form CeO ₂ .

Figure 9 is a seventh XRD pattern of a preferred embodiment of the present invention; showing a comparison between before and after carbon dioxide poisoning when BCY and BCZY form CeO ₂ .

In order to describe the technical features of the present invention in detail, the following preferred embodiments are described with reference to the accompanying drawings, wherein, as shown in FIGS. 1 and 2, a solid oxide according to a preferred embodiment of the present invention is provided. The fuel cell electrolyte preparation method 10 is characterized in that a solid oxidation mixture 11 is treated by a solid state reaction.

The solid oxidation mixture 11 comprises barium carbonate (BaCO ₃ ), cerium oxide (CeO ₂ ) and zirconium oxide (ZrO ₂ ), and cerium carbonate (BaCO ₃ ), cerium oxide (CeO ₂ ) and zirconium oxide (ZrO ₂ ) are The respective Moire specific gravity is calculated and mixed; wherein the solid oxidation mixture 11 is treated by the solid state reaction method 21 to become a perovskite oxide 31, and the surface of the perovskite oxide 31 has cerium oxide (CeO ₂ ). distributed. In the preferred embodiment, the perovskite oxide 31 is a cerium oxide (BaCe _0.8 Y _0.2 O ₃ , BCY) (hereinafter referred to as cerium oxide (BCY)).

The solid state reaction method 21, the steps of which include:

a. The solid oxidation mixture 11 was ball milled in isopropanol for 6 hours. The ball milling is mainly for the purpose of sufficiently mixing the solid oxidation mixture 11 . Therefore, as long as the purpose of sufficient mixing is achieved, for example, 4, 8 and 12 hours can be used as the ball milling time, the ball milling time should not be only the preferred embodiment. The example is limited.

b. The ball-milled solid oxidation mixture 11 is dried at a temperature of 110 ° C; wherein, in addition to the drying temperature used in the preferred embodiment, only the temperature at which the drying purpose can be achieved is The application can be used as the drying temperature, for example, 60, 80, 130, and 180 ° C can be used as the drying temperature, so the drying temperature should not be limited to the preferred embodiment.

c. The dried solid oxidation mixture 11 is calcined at 1250 ° C for 8 hours; wherein, in addition to the calcination temperature of the preferred embodiment, the calcination temperature can also be applied at 1000, 1300, and 1500 ° C. Therefore, the calcination temperature should not be limited to the preferred embodiment.

d. Repeat steps a~c three times. Wherein, the steps a~c are repeated to ensure sufficient reaction of the solid oxidation mixture 11 at each step, and therefore, if only a step a~c is required, the solid mixture can be fully reacted, that is, without Repeat steps a~c to directly perform the subsequent steps d~f, or only 2 times; however, if it is not enough to repeat the steps (a) to (c) 3 times to achieve sufficient reaction, then The number of repetitions of steps (a) to (c) is increased, such as 4 or 5 times. Therefore, the number of repetitions of steps (a) to (c) should not be limited to the preferred embodiment.

(e) The solid oxidation mixture 11 after calcination was dry-pressed into a pellet and uniaxially pressed (a cylinder having a diameter of 1 cm/thickness of 1 mm was pressed at 250 MPa).

(f) sintering the solid-state oxidation mixture 11 after dry pressing at 1600 ° C for 12 hours; wherein, in the preferred embodiment, the sintering temperature and time are taken as an example, mainly based on the results of subsequent descriptions, and Consider the best conditions set by production costs (such as time and energy consumption). Therefore, if higher sintering temperatures are used, such as 1700, 1800, 1900, 2000 °C; sintering time is 1, 4, 8, 10, 14 The hour can be applied to this, so the sintering temperature and time should not be limited to the preferred embodiment.

Accordingly, the preferred embodiment of the present invention can cause the solid oxide mixture 11 to form cerium oxide (CeO ₂ ) on the surface without additional processing by the solid state reaction method 21 to oxidize the perovskite. The substance 31 can stabilize the conductivity of the proton and achieve the effect of improving chemical stability.

In addition, the solid oxidation mixture 11 may further contain yttrium oxide (Y ₂ O ₃ ), which is treated by the solid state reaction method 21 to be cerium zirconium lanthanum oxide (BaCe _0.6 Zr _0.2 Y _0.2 O ₃ , BCZY) (below) It is abbreviated as cerium zirconium lanthanum oxide (BCZY), and can also form cerium oxide (CeO ₂ ) on its surface to achieve stable proton conductivity and improve chemical stability. Therefore, the composition of the solid oxidation mixture 11 It should not be limited to the preferred embodiment.

Experimental data relating to the present invention will be described below.

Sintering temperature test: Please refer to Figure 3 for different sintering temperature tests for bismuth oxide (BCY). The bismuth oxide (BCY) is sintered at 1400~1600 °C for 12 hours, then X. X-ray Diffraction (XRD) shows the results. It can be seen that cerium oxide (CeO ₂ ) is formed only when the sintering temperature is 1600 ° C. It is known that cerium oxide (CeO _{2 ) is required.} ) Formation requires a sintering environment above 1600 °C.

Sintering time test: Please refer to Figure 4 for the observation of cerium oxide (CeO ₂ ) at 1600 ° C at three time points of sintering at 4, 8 and 12 hours by XRD pattern. From the results, it can be seen that the cerium oxide (BCY) has the highest amount of cerium oxide (CeO ₂ ) formed during sintering for 12 hours. Therefore, we believe that as the sintering time increases, the formation of cerium oxide (CeO ₂ ) also increases. Considering that the longer the sintering time, the production cost increases, so the present invention takes 12 hours as an example.

This proves that bismuth oxide (BCY) naturally forms cerium oxide (CeO ₂ ) on the surface of cerium oxide (BCY) as long as it can be sintered at 1600 ° C for a sufficient period of time, and step (f) The longer the sintering time is, the higher the amount of cerium oxide (CeO ₂ ) is formed.

Polishing test: Please refer to Figure 5 for the XRD analysis of the polishing thickness of 0, 10, 20, 30 μm by sintering the tantalum oxide (BCY) at a temperature of 1600 °C from the above sintering temperature and time test, according to the XRD pattern. As a result, it can be seen that when the polishing thickness is 0, 10, 20 μm, the signal of cerium oxide (CeO ₂ ) is detected, but the signal which can be detected by polishing the thickness of 20 μm is already quite weak, and when the polishing thickness is 30 μm. At the time, no signal was detected. From this, it can be confirmed that the formation of cerium oxide (CeO ₂ ) is limited to the surface of cerium oxide (BCY).

In addition, please refer to the drawings of Figs. 6A and 6B, and also the polishing test after sintering of lanthanum zirconium lanthanum oxide (BCZY). It can be seen from the pattern of Fig. 6A that there is indeed yttrium oxide after sintering at a temperature of 1600 ° C ( The formation of CeO ₂ ), and then, as can be seen from Fig. 6B, cerium oxide (CeO ₂ ) is also formed only on the surface of lanthanum zirconium lanthanum oxide (BCZY).

Chemical stability test: As shown in Figures 7A and 7B, Figure 7A shows the formation of cerium oxide (CeO ₂ ) cerium oxide (BCY) and cerium zirconium lanthanum oxide (BCZY), Figure 7B A cerium oxide (BCY) and cerium zirconium lanthanum oxide (BCZY) which do not form cerium oxide (CeO ₂ ) are shown. Among them, after being poisoned by exposure to carbon dioxide at 600 ° C for 8 hours, it can be seen from Fig. 7A that the cerium oxide (CeO ₂ ) cerium oxide (BCY) and cerium are formed by the method provided by the present invention. Zirconium lanthanum oxide (BCZY), after carbon dioxide poisoning, the formation of heterophases (such as BaCO ₃ ) is still quite low, and it is known from the results that cerium oxide (CeO ₂ ) is still present in cesium The surface of cerium oxide (BCY) and cerium zirconium lanthanum oxide (BCZY). However, as shown in Fig. 7B, no cerium oxide (CeO ₂ )-forming cerium oxide (BCY) and cerium zirconium lanthanum oxide (BCZY) are formed for the formation of hetero phases (e.g., BaCO ₃ ). It is quite serious; it can be confirmed that when cerium oxide (CeO ₂ ) is formed on the surface of cerium oxide (BCY) and cerium zirconium lanthanum oxide (BCZY), it is true for cerium oxide (BCY). And cerium zirconium lanthanum oxide (BCZY) has a protective effect, thereby improving the chemical stability of cerium oxide (BCY) and cerium zirconium lanthanum oxide (BCZY).

Conductivity test: Please refer to Figures 8 and 9. As can be seen from Figure 8, cerium oxide (BCY) and cerium-zirconium-cerium oxide (BCZY) without cerium oxide (CeO ₂ ) are not carbon dioxide. At the time of poisoning, the conductivity of bismuth oxide (BCY) is better than that of lanthanum zirconium lanthanum oxide (BCZY) (nearly 0.018 S/cm), but after carbon dioxide poisoning, 钡The conductivity of bismuth oxide (BCY) and lanthanum zirconium lanthanum oxide (BCZY) deteriorated rapidly from 0.0285 S/cm and 0.018 S/cm before the original poisoning to 0.016 S/cm and 0.009 S/ after poisoning. Cm, the decay of carbon dioxide before and after poisoning is as high as 50%; then, together with Figure 9, it can be seen that the formation of cerium oxide (CeO ₂ ) cerium oxide (BCY) and cerium zirconium lanthanum oxide (BCZY) The conductivity (0.020 S/cm) of cerium oxide (CeO 2 ) cerium oxide (BCY) and the conductivity of cerium zirconium lanthanum oxide (BCZY) (0.017 S/cm) are not formed when carbon dioxide is poisoned. The conductivity is slightly lower than the conductivity of the cerium oxide (BCY) without cerium oxide (CeO2) (0.285 S/cm) and the conductivity of lanthanum zirconium lanthanum oxide (BCZY) (0.018 S/cm), but Poisoning in carbon dioxide , the conductivity of cerium oxide (CeO2) cerium oxide (BCY) and cerium zirconium lanthanum oxide (BCZY) is formed, which only slightly decays from 0.020 S/cm and 0.017 S/cm to 0.0186 S/cm and 0.0153, respectively. S/cm, the decay rate is less than 10%; and the conductivity of cerium oxide (Be) which forms cerium oxide (CeO2) and cerium zirconium lanthanum oxide (BCZY) are poisoned by carbon dioxide (0.0186 respectively) S/cm and 0.0153 S/cm) are higher than those of cerium oxide (BCY) and cerium-zirconium-cerium oxide (BCZY) which do not form cerium oxide (CeO2) (0.0126 S/cm, respectively) And 0.009 s/cm).

It can be confirmed from the above results that the electrolyte preparation method 10 of the solid oxide fuel cell of the present invention can form the perovskite oxide 31 to form cerium oxide (CeO ₂ ) on the surface, thereby stabilizing the conductivity of the proton and improving the chemistry. The effect of stability.

Claims (8)

A method for preparing an electrolyte for a solid oxide fuel cell, comprising: a solid oxidation mixture; and a solid state reaction, the process comprising: (a) ball milling the solid oxidation mixture in isopropanol 4~ 12 hours; (b) drying the ball-milled solid oxidation mixture at 60-180 ° C; (c) drying the solid oxidation mixture at 1000-1500 ° C for 1 to 15 hours; (a) to (c) repeating the process 1 to 5 times; (e) dry-forming the solid oxidation mixture after calcination; (f) at least 1600 ° C for the solid-state oxidation mixture after dry pressing, Sintering for 1 to 24 hours; wherein the solid oxidation mixture is treated by the solid state reaction to form a perovskite type oxide, and the surface of the perovskite type oxide is formed with cerium oxide (CeO _{2 )} The distribution of ). The method for preparing an electrolyte for a solid oxide fuel cell according to claim 1, wherein the ball milling time of the process step (a) is 4 to 8 hours. The method for preparing an electrolyte for a solid oxide fuel cell according to the first aspect of the invention, wherein the step (b) of drying the solid oxidation mixture is carried out at a temperature of 80 to 130 °C. The method for preparing an electrolyte for a solid oxide fuel cell according to claim 1, wherein the solid mixture of the step (c) has a calcination temperature of 1000 to 1400 ° C for 6 to 10 hours. The method for preparing an electrolyte for a solid oxide fuel cell according to the first aspect of the invention, wherein the solid oxidation mixture after the calcination in the step (e) is dry pressed into a tablet shape. The method for preparing an electrolyte for a solid oxide fuel cell according to the first aspect of the invention, wherein the step (f) of the dry pressing of the solid oxidation mixture has a sintering temperature of 1600 to 2000 ° C and a sintering time of 8 to 14 hours. An electrolyte preparation method of a solid oxide fuel cell according to the first aspect of the invention, wherein the solid oxidation mixture comprises barium carbonate (BaCO ₃ ), cerium oxide (CeO ₂ ), and zirconium oxide (ZrO ₂ ). The method for preparing an electrolyte for a solid oxide fuel cell according to claim 7, wherein the solid oxidation mixture further comprises yttrium oxide (Y ₂ O ₃ ).