JP3055350B2 - Operating method of barium-cerium type solid electrolyte fuel cell - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for starting and operating a barium-cerium solid electrolyte fuel cell.

[0002]

2. Description of the Related Art A barium-cerium type solid electrolyte fuel cell has features such as higher output discharge and long-term reliability than other solid electrolyte type fuel cells, especially zirconia-based solid electrolytes. Further, in barium-cerium type solid electrolyte fuel cells, the development of solid electrolytes having high ionic conductivity and the development of electrodes optimal for these electrolytes have been actively conducted. In the barium-cerium type solid electrolyte fuel cell, the elemental technology is currently in the stage of establishment, and no study has been made on how to start or operate the cell. On the other hand, in a zirconia-based solid electrolyte, as a general start-up method (start-up method), a fuel gas and an oxidizing gas are supplied to each pole, the temperature is raised to 1000 ° C., and then discharge is performed. Humidified hydrogen is generally used as the fuel gas at the time of startup, and after the temperature is raised, the gas is switched to a gas obtained by reforming city gas.

[0003]

However, as described above, the barium-cerium type solid electrolyte fuel cell is currently in the stage of establishing the elemental technology, and the method of starting and operating the cell has not been studied. At the time of starting the battery, it is preferable to start up with the same gas composition as at the time of discharging, for the sake of simplification of the process.However, the barium-cerium type solid electrolyte reacts with carbon dioxide gas under certain conditions, and Performance will be reduced. In a pure reducing atmosphere, the barium-cerium type solid electrolyte is reduced,
Decompose. Therefore, in a barium-cerium type solid electrolyte fuel cell, there is a need for a startup method and an operation method that do not degrade the cell performance.

[0004] In view of the above problems, the present invention clarifies the reactivity between carbon dioxide and barium-cerium type solid electrolyte,
It is an object of the present invention to propose a method of stably starting a battery and an operation method of operating stably for a long period of time.

[0005]

According to the present invention, there is provided an operation method characterized in that the concentration of carbon dioxide in a gas composition supplied to both fuel and air is reduced to 10% or less. Desirably, there are provided a battery start-up method and an operation method, wherein the supplied gas composition does not contain water vapor. Further, an operation method is characterized in that when a fuel gas or an oxidizing gas containing 10% or more of carbon dioxide gas is supplied to the battery, the operating temperature of the battery is maintained at 800 ° C. or more.

[0006]

In the above means, when the concentration of carbon dioxide is reduced to a predetermined value or less in the course of the temperature rise, the barium-cerium-based oxide forms a cubic crystal. Once a cubic crystal is formed, the structure becomes extremely stable, so that it is not affected by the atmosphere and stable battery discharge is possible.

[0007]

EXAMPLES The reactivity between barium-cerium-based solid electrolyte and carbon dioxide gas was clarified by atmosphere controlled high-temperature X-ray diffraction and differential thermogravimetric analysis. From the results, the starting method and operating conditions of the fuel cell were found. In addition, the battery was actually activated under the conditions, and the operation was verified.

(Example 1) The reactivity between barium-cerium-based solid electrolyte and carbon dioxide gas was analyzed. Using a solid electrolyte in which 20% of cerium of barium / cerium oxide was replaced with gadolinium, reactivity with a helium mixed gas having a carbon dioxide gas concentration of 0% to 100% was examined. In X-ray diffraction measurement, the reaction product and phase change were examined every 200 ° C. in the temperature range from room temperature to 1100 ° C., and differential thermogravimetric analysis revealed the relationship between the phase change temperature and the concentration of carbon dioxide and the reaction temperature. did. FIG. 1 shows an X-ray diffraction diagram of heating and cooling in air, and FIG.
FIG. 3 shows a diffraction diagram when the temperature was raised in 100% carbon dioxide gas.
FIG. 4 shows a diffraction diagram when the temperature is raised in 0% carbon dioxide gas. FIG. 4 shows the results of differential thermal analysis, and FIG. 5 shows the results of thermogravimetric analysis. When the temperature was raised, it was found that when the carbon dioxide concentration was 10% or less, the solid electrolyte and the carbon dioxide did not react. In addition, it was also confirmed that the reaction occurred when the carbon dioxide gas concentration was 20%.
In air, the temperature changes from orthorhombic to tetragonal at around 550 ° C.
The phase changed to cubic at around 0 ° C. Once in air, 1100
FIG. 6 shows a diffraction diagram when the temperature was raised to 100 ° C. and the temperature was lowered in a 100% carbon dioxide gas atmosphere. It was found that when the electrolyte became stable cubic by heating in air, it did not react even with 100% carbon dioxide gas. The above results are shown in FIG. 7 as a phase diagram. In the figure, the solid electrolyte is described as BCG. When the carbon dioxide gas concentration is in the range of 10% or less, the solid electrolyte undergoes a reversible phase change depending on the temperature. When the carbon dioxide gas concentration is 20% or more, the carbon electrolyte and the solid electrolyte react irreversibly.

Example 2 As in the above example, as a barium-cerium-based solid electrolyte, an oxide to which 25% of dispronium was added was examined. It has been found that the oxide undergoes a reversible phase change depending on the temperature, and irreversibly reacts with the carbon dioxide gas at a carbon dioxide gas concentration of 20% or more. (Table 1)
Fig. 3 shows the reaction concentration limit of barium-cerium-based oxide and carbon dioxide gas. In a barium-cerium-based oxide, ionic conductivity can be increased by substituting a part of cerium with a rare earth element. However, when the replacement amount is 30
%, The reactivity is not so different from the reactivity of barium-cerium oxide serving as a skeleton. When the concentration of carbon dioxide is 10% or less, the barium-cerium-based oxide undergoes a reversible phase change depending on the temperature and is stably present at around 800 ° C. Reacts and degrades electrolyte performance.

[0010]

[Table 1] (Example 3) A fuel cell was constructed using a platinum electrolyte and a solid electrolyte in which 20% of cerium of barium cerium oxide was replaced with gadolinium, as in the above-described example, and 800 in air at a rate of 20 ° C / min. The temperature was raised to 0 ° C. and started. After startup, air was supplied as an oxidizing gas, and a methane reforming simulation gas (20% carbon dioxide gas and 80% hydrogen gas) was supplied as a fuel gas, and the temperature was maintained at 800 ° C. Current density 100 mA / cm
FIG. 8 shows the change with time in the voltage when the battery was continuously discharged at ² .
Also, after 500 hours of discharge, the heater was heated down and restarted. At that time, air was supplied to both electrodes and the temperature was raised to 800 ° C. Thereafter, a reforming simulation gas was introduced into the fuel electrode and discharged. It turned out to be stable even after restarting.
It was confirmed that the operation method of the present invention was effective and the battery operated stably.

(Example 4) The operation method of the present invention was demonstrated by actual fuel cell operation. A fuel cell is constructed using a solid electrolyte in which 20% of cerium of barium cerium oxide is replaced with europium and a platinum electrode, and air is supplied to the air electrode, and methane reforming gas containing 8% carbon dioxide is supplied to the fuel electrode. The temperature was raised to 800 ° C. at a rate of 20 ° C./min to start up. After starting, hold at 800 ° C, current density 150mA
/ Cm ² . FIG. 9 shows a temporal change of the voltage at that time. Also, after the discharge was performed for 1100 hours, the apparatus was heated down and restarted. At that time, when a reforming simulated gas containing 20% carbon dioxide gas humidified (water vapor 2%) was introduced into the fuel electrode and the temperature was raised to 800 ° C., the electrolyte was deteriorated and discharge continued.

In the above embodiment, the temperature at the time of starting and operating is 800 ° C., but the starting temperature and operating temperature may be other temperatures as long as the battery operates. In the embodiment, the fuel gas composition at the time of operation is such that the carbon dioxide gas concentration is up to 20%. A gas, for example, a mixed gas containing 50% carbon dioxide may be introduced. Further, the barium-cerium-based oxide is not limited to the barium-cerium-based oxide shown in Table 1, and may be another barium-cerium-based oxide. Further, the operating state refers to a state in which the average temperature is substantially constant although the temperature fluctuates at a predetermined temperature. The process of shifting from one operating temperature to a different operating temperature is considered to be a restart.

[0013]

As described above, the operation method of the present invention enables stable discharge of a solid electrolyte fuel cell using a barium cerium type solid electrolyte and long-term battery operation by suppressing deterioration of the electrolyte. Can be.

[Brief description of the drawings]

FIG. 1 is a high-temperature X-ray diffraction diagram of a solid electrolyte when the temperature is raised and lowered in air.

FIG. 2 is a high-temperature X-ray diffraction diagram of a solid electrolyte when heated in 100% carbon dioxide gas.

FIG. 3 is a high-temperature X-ray diffraction diagram of the solid electrolyte when heated in 10% carbon dioxide gas.

FIG. 4 is a diagram showing the results of differential thermal analysis of a solid electrolyte.

FIG. 5 is a diagram showing the results of thermogravimetric analysis of a solid electrolyte.

FIG. 6 is an X-ray diffraction diagram of the solid electrolyte when the temperature is raised to 1100 ° C. in air and then lowered in a 100% carbon dioxide gas atmosphere.

FIG. 7 is a schematic phase diagram of a solid electrolyte.

FIG. 8 is a characteristic diagram of a temporal change in voltage when a continuous discharge is performed at a current density of 100 mA / cm ² .

FIG. 9 is a characteristic diagram of a temporal change in voltage when a continuous discharge is performed at a current density of 150 mA / cm ² .

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H01M 8/12 H01M 8/04

Claims (4)

(57) [Claims] 1. A barium-cerium-type solid electrolyte fuel cell, characterized in that the carbon dioxide concentration of the gas composition supplied to the fuel and air electrodes at the time of temperature rise in a starting state, an operating state or a restarting state is 10% or less. how to drive. 2. A method for operating a barium-cerium type solid electrolyte fuel cell according to claim 1, wherein water vapor is not contained in a gas composition supplied to both fuel and air electrodes. 3. The method for operating a barium-cerium type solid electrolyte fuel cell according to claim 1, wherein the gas supplied to both the fuel and air electrodes is air. 4. When a fuel gas or an oxidizing gas containing 10% or more of carbon dioxide gas is supplied to a battery, the operating temperature of the battery is set to 8%.
A method for operating a barium-cerium type solid electrolyte fuel cell, wherein the temperature is maintained at 00 ° C or higher.