JP2597730B2 - Method for producing bottomed porous support tube for solid oxide fuel cell - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing a bottomed porous support tube for a solid oxide fuel cell.

(Prior Art) Recently, fuel cells have attracted attention as power generation devices. This is a device that can directly convert the chemical energy of fuel into electric energy. It is not restricted by the Carnot cycle, so it has an inherently high energy conversion efficiency and is capable of diversifying fuels (naphtha, natural gas, (Methanol, coal reformed gas, heavy oil, etc.), low pollution, and power generation efficiency is not affected by the scale of the equipment.

In particular, solid oxide fuel cells (SOFCs) operate at a high temperature of 1000 ° C, so the electrode reaction is extremely active, does not require expensive precious metal catalysts such as platinum, has low polarization, and has a relatively high output voltage. The energy conversion efficiency is significantly higher than other fuel cells. Further, since all the structural materials are composed of solids, they have a stable and long life.

FIG. 3 is a schematic sectional view showing an example of such a SOFC.

In FIG. 3, 1 is an oxidizing gas supply pipe for introducing an oxidizing gas such as air, 4 is a bottomed porous support pipe, 5 is an air electrode, 6 is a solid electrolyte, 7 is a fuel electrode, and 8 is an oxidizing gas. An upper plate that holds the supply pipe 1 and separates the oxidizing gas chamber 18 from the exhaust gas 19. A fuel inlet 10 that holds the SOFC element 40 and separates the battery reaction chamber 20 and the fuel chamber 30.
The bottom plate 9a has a gas outlet 9a which separates the exhaust gas chamber 19 and the battery reaction chamber 20 from each other.

In this state, when an oxidizing gas such as air is supplied from the oxidizing gas chamber 18 to the oxidizing gas supply pipe 1 as shown by an arrow A, the oxidizing gas flowing out of the oxidizing gas supply port 1a is inverted at the bottomed portion 4a, and is turned on. It flows in the space 29 inside the cylinder of the bottom porous support tube 4, and an arrow B
Flows out into the exhaust gas chamber 19 as shown in FIG. Meanwhile, the bottom plate
Fuel gas such as H ₂ or CH _{4 is} passed through SOFC
By flowing along the outer surface of the element 40, the fuel gas and oxygen ions diffused in the solid electrolyte react on the surface of the fuel electrode 7, and as a result, the air electrode 5 and the fuel electrode 7
A current flows between them, and the battery can be used as a battery. Since this fuel cell is used at a high temperature of about 1000 ° C., the configuration shown in FIG. 3, which can be configured without a seal portion, can be said to be a preferable configuration.

(Problems to be Solved by the Invention) In practical use of SOFC, it is necessary to reduce cost and improve power density. For this reason, it is required to increase the length of the SOFC element 40 and increase the power generation output per one.

However, the amount of power generated by the SOFC largely depends on the amount of oxygen passing through the bottomed porous support tube 4.

That is, since the oxygen content is still large near the oxidizing gas supply port 1a, the amount of oxygen ions reaching the fuel electrode 7 in the vicinity increases, and the reaction amount with the fuel on the surface of the fuel electrode 7 increases. , The temperature rises. Due to this temperature increase, the electrode reaction between oxygen ions and fuel gas at the fuel electrode surface becomes more active. On the other hand, as the gas flowing out from the oxygen gas supply port 1a approaches the gas outlet 9a, the oxygen concentration in the gas decreases, and as a result, the amount of oxygen ions reaching the fuel electrode 7 near the gas outlet 9a decreases. However, the reaction amount with the fuel on the surface of the fuel electrode 7 is small, and the temperature rise is small. As a result, the reaction becomes increasingly inactive due to this low temperature. This tendency becomes greater as the tubular SOFC element becomes longer.

In addition, with the recent improvement in the performance of fuel electrodes, support tubes having excellent oxygen diffusivity are required.

A similar problem also occurs in a SOFC in which a fuel electrode is provided inside the solid electrolyte 6 and a fuel gas is supplied to the in-cylinder space 29 to generate power. Moreover, in this case, the fuel gas having a reduced concentration contains a considerable amount of CO ₂ and water vapor, etc., which adhere to the electrode surface and inhibit the reaction. The temperature unevenness in the longitudinal direction of the SOFC element is remarkable.

An object of the present invention is to provide a solid electrolyte fuel cell having an air electrode, a solid electrolyte, and a fuel electrode on a bottomed cylindrical porous support, in which the amount of permeation of oxygen is controlled by the bottomed porous support. This is to make it possible to equalize each part of the tube, thereby making it possible to equalize the power generation efficiency in the longitudinal direction of the bottomed cylindrical solid electrolyte fuel cell, and to mass-produce such a solid electrolyte fuel cell. Is to be able to do it.

(Means for Solving the Problems) The present invention includes a bottomed porous support tube, and an air electrode, a solid electrolyte, and a fuel electrode which are sequentially formed on the outer peripheral surface of the bottomed porous support tube. When manufacturing a bottomed porous support tube for a solid oxide fuel cell that generates an electric power by supplying an oxidizing gas flow to the space inside the bottomed porous support tube, a bottomed cylindrical molded body of ceramics Holding the opening end side of, the bottomed cylindrical molded body is hung down so that the bottomed part faces downward, and fired in a state where the bottomed cylindrical molded body is suspended with a weight attached to the bottomed part, The open porosity of the open end of the bottomed porous support tube is made larger than the open porosity of the bottomed portion.

(Example) FIG. 1 is a sectional view showing a preferred example of a SOFC manufactured according to the present invention. The same reference numerals are given to the same functional members as those of the SOFC shown in FIG. 3, and the description is omitted.

What is characteristic in the present embodiment is that the distribution of oxygen gas permeability in the longitudinal direction of the bottomed porous support tube 4 is particularly focused on.

Specifically, conventionally, no particular attention has been paid to the porosity of the bottomed porous support tube 4, and the porosity has been substantially uniform throughout. For this reason, the oxidizing gas flowing in the in-cylinder space 29 almost uniformly permeated the bottomed porous support tube 4 at any point and reached the air electrode 5. On the other hand, the oxygen concentration in the oxygen gas decreases as it goes to the downstream side, that is, as it gets farther away from the bottomed portion 4a, the oxygen actually permeating the solid electrolyte 6 and used for power generation is As shown in FIG. 5, the number increased as approaching the bottomed portion 4a, and decreased as approaching the open end.

On the contrary, in the SOFC of this embodiment, the in-cylinder space
The open porosity of the bottomed porous support tube 4 was reduced on the upstream side of the oxidizing gas flowing through the inside 29, and the open porosity of the bottomed porous support tube 4 was increased on the downstream side. That is, the openness ratio at the bottomed portion 4a is smaller than the open porosity at the end 4b on the opening end side of the power generation portion. As a result, the amount of oxygen gas passing through the bottomed portion 4a is smaller than the amount of oxygen gas passing through the end 4b of the power generation part. On the other hand, since the oxygen concentration in the oxidizing gas passing through the bottomed portion 4a is higher than the oxygen concentration in the oxidizing gas passing through the end portion 4b, as shown in FIG. Since the amount of oxygen passing through the porous support tube 4 is made uniform as a whole, the non-uniformity of the electrode reaction in the longitudinal direction of the SOFC element 40 can be corrected. Further, as a result, the heat generation is made uniform throughout the bottomed porous support tube 4 to reduce thermal strain stress, prevent cracks, and improve the SOFC element.
It is possible to achieve a longer service life of 40 and to improve the power generation efficiency.

As described above, in the present embodiment, the difference in the open porosity of the bottomed porous support tube 4 is provided between the bottomed portion 4a and the end 4b of the power generation portion. It is preferable to gradually increase the open porosity as approaching the end 4b.

The open porosity of the bottomed porous support tube 4 is 20 to
Preferably it is 50%. The pore diameter is 1 to
It is preferably 10 μm.

When the open porosity of the bottomed porous support tube 4 is set to 50% or more,
The strength of the support tube 4 is remarkably reduced, and the reliability for long-term use is lacking. If the open porosity is set to 20% or less, the power generation efficiency of the SOFC element decreases. When the pore diameter of the support tube 4 is 10 μm or more, the strength of the support tube 4 decreases, and the fuel electrode contributing to power generation is localized. If it is 1 μm or less, the amount of gas permeation decreases.

The difference between the open porosity at the bottomed portion 4a and the open porosity at the end 4b of the power generation portion may be 4 to 6% when the distance between the bottomed portion 4a and the end 4b of the power generation portion is 1500 mm. Preferably, when it is 2 m, the content is preferably 8 to 12%.

In the present invention, in order to reduce the open porosity of the bottomed portion 4a of the bottomed porous support tube 4 and increase the open porosity of the open end portion, the bottomed porous support tube 4 is manufactured by firing. Then, holding the open end side of the bottomed tubular molded body of ceramics, the bottomed tubular molded body is hung down with the bottomed part down, and a weight is attached to the bottomed part and suspended. As a result, a load is applied to the side close to the open end of the bottomed tubular molded product, and the tube is slightly stretched. be able to.

The bottomed porous support tube 4 is assembled with a ceramic kiln fixture as described above and fired in the kiln.

Appropriately according to the predetermined porosity of the support tube 4 within the conditions of a heating rate of 20 to 100 ° C / h, a firing strength of 1400 to 1600 ° C, a firing temperature holding time of 30 minutes to 4 hours, and a cooling rate of 20 to 100 ° C / h. Set.

The air electrode 5 can be made of doped or undoped LaMnO ₃ , CaMnO ₃ , LaNiO ₃ , LaCoO ₃ , LaCrO _3, etc., and is preferably LaMnO ₃ to which strontium is added. The solid electrolyte 6 can generally be manufactured from yttria-stabilized zirconia or the like. The fuel electrode 7 is generally a nickel-zirconia cermet or a cobalt-zirconia cermet.

Of course, the present invention is also applicable to a so-called multi-cell type SOFC. In a multi-cell type SOFC, air electrodes are provided at a plurality of locations at predetermined intervals on the surface of a porous cylindrical support, a solid electrolyte and a fuel electrode are sequentially provided on each air electrode, and adjacent to each fuel electrode. Are electrically connected to each other by an interconnector.

 The above example can be variously modified.

Although the SOFC element 40 is supported vertically in FIG. 1, the entire power generator may be horizontal or may be inclined at a predetermined angle.

The bottomed porous support tube may be a square cylinder, a hexagonal cylinder, or the like, in addition to the bottomed cylinder.

 Hereinafter, more specific examples will be described.

First, a calibration curve showing the relationship between the average open porosity of the bottomed porous support tube and the oxidizing gas permeation amount is shown in FIG.

However, in the graph of FIG. 2, the oxidizing gas permeation amount when the average open porosity of the bottomed porous support tube was 35% was set to 100.0, and expressed as a relative ratio. As can be seen from FIG. 2, both were in a substantially linear relationship.

Then, as shown in FIG. 1 and FIG.
And an air electrode, a solid electrolyte, and a fuel electrode were formed thereon to produce a SOFC as shown in FIGS. 1 and 3. And according to the invention
The SOFC element and the conventional SOFC element are respectively installed in the battery reaction chamber 20, the inside of the battery reaction chamber 20 is heated to 1000 ° C., then air is supplied to the oxidizing gas supply pipe 1 and methane is supplied from the fuel inlet 10a. , And oxygen ions and methane were reacted on the surface of each SOFC element fuel electrode.

Then, at the measurement positions P1, P2, P3, P4, and P5 obtained by dividing the linear portion of each SOFC element shown in FIGS. 1 and 3 into four equal parts, the surface temperature of the fuel electrode during the reaction was measured with a thermocouple. And at the same time P
1, P2, P3, P4, the oxygen concentration at each position of the cylinder space 29 corresponding to the position of P5 was respectively measured by O ₂ meters. After cooling to room temperature and removing the fuel electrode, solid electrolyte and air electrode,
The open porosity of P1, P2, P3, P4, P5 was measured.

Then, the oxidized gas permeation amount at each position is calculated from the measured value of the open porosity at each position and the calibration curve in FIG. 2, and further, as the product of the oxidized gas permeation amount at each position and the oxygen concentration. The oxygen permeation amount at each position was determined. The results are shown in Tables 1 and 2 below.
Shown in

In Table 1, the amount of oxygen ions supplied to the fuel electrode surface near P5 is large, and the amount of reaction with the fuel gas methane is increased. Therefore, the fuel electrode surface temperature is significantly higher than the ambient temperature (1000 ° C.) of the cell reaction chamber 20. At high temperatures. On the other hand, the fuel electrode surface temperature near P1 is close to the ambient temperature of the cell reaction chamber 20, indicating that the cell reaction is inactive.

On the other hand, as shown in Table 2, the SOFC element using the support tube 4 manufactured according to the present invention has a temperature of the fuel electrode surface of the cell reaction chamber.
Since the oxygen transmission rate at each position of P1, P2, P3, P4, and P5 is almost the same according to the present invention since the temperature is substantially equal at a temperature higher than the ambient temperature of 20, the battery reaction at each position is uniform. It shows what is happening.

As is clear from the above results, according to the present invention, it is possible to make the amount of oxygen supplied to power generation permeated through the bottomed porous support tube uniform at each position of the bottomed porous support tube. It is possible to impart excellent oxygen permeability to the support tube. As a result, the battery reaction in the longitudinal direction of the SOFC element can be made uniform, and the temperature distribution in the longitudinal direction can be made uniform, so that the occurrence of cracks can be prevented.

(Effect of the Invention) According to the present invention, when manufacturing a solid oxide fuel cell having an air electrode, a solid electrolyte and a fuel electrode on a bottomed cylindrical porous support, the amount of permeated oxygen is reduced. The uniformity can be achieved in each part of the bottomed porous support tube, thereby making it possible to equalize the power generation efficiency in the longitudinal direction of the bottomed cylindrical solid electrolyte fuel cell, and to mass-produce such a solid electrolyte fuel cell. it can.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an SOFC according to an embodiment of the present invention, FIG. 2 is a graph showing a relationship between an average porosity of a bottomed porous support tube and an oxidizing gas permeation amount, and FIG. FIG. 1 ... Oxidizing gas supply pipe, 4 ... Bottomed porous support tube 4a ... Bottomed part, 4b ... End of power generation part 5,15 ... Air electrode, 6,16 ... Solid electrolyte 7,17 ... ... Fuel electrode, 11,29 ... Cylinder space 12 ... Interconnector 14 ... Cylindrical porous ceramic support 14a ... Upstream end, 14b ... Downstream end 40,50 ... SOFC Elements A, B, F: Oxidizing gas flow C, E: Fuel gas flow

Claims (1)

(57) [Claims] 1. A bottomed porous support tube comprising: a bottomed porous support tube; and an air electrode, a solid electrolyte, and a fuel electrode which are sequentially formed on an outer peripheral surface of the bottomed porous support tube. When manufacturing a bottomed porous support tube for a solid oxide fuel cell that supplies power by supplying an oxidizing gas flow to the inside space of the cylinder, it holds the open end side of the bottomed cylindrical molded body of ceramics And
The bottomed cylindrical molded body is hung downward so that the bottomed portion faces downward, the bottomed cylindrical molded body is fired with a weight attached to the bottomed portion, and the bottomed porous support is fired. A method for producing a bottomed porous support tube for a solid oxide fuel cell, wherein the open porosity of the open end of the tube is made larger than the open porosity of the bottomed portion.