JP2023171007A - Solid oxide fuel battery cell - Google Patents

Abstract

To provide a solid oxide fuel battery cells with which it is possible to control the reactivity of power generation reaction and equalize the power generation distribution in the cell plane.SOLUTION: Provided is a solid oxide fuel battery cell comprising an electrolyte layer 20 that has ion conductivity to pass oxide ions through, an anode layer 22 that is provided to one side of the electrolyte layer 20, and a cathode layer that is provided to the other side of the electrolyte layer 20. The anode layer 22 includes an electron conduction phase 32 that conducts electrons, an ion conduction phase 34 that conducts ions, and a void phase 36 that diffuses a fuel gas. The degree of flexion of one of the electron conduction phase 32, the ion conduction phase 34, and the void phase 36 in the upstream region of the anode layer 22 is larger than the degree of flexion of one of the electron conduction phase 32, the ion conduction phase 34, and the void phase 36 in the downstream region of the anode layer 22, which composition makes it possible to equalize the power generation distribution of the anode layer 22.SELECTED DRAWING: Figure 4

Description

The present invention relates to a solid oxide fuel cell comprising an electrolyte layer, an anode layer and a cathode layer.

A solid oxide fuel cell (hereinafter sometimes referred to as a "fuel cell") includes an electrolyte layer having ionic conductivity that allows oxide ions to pass through, and an anode layer provided on one side of this electrolyte layer. A device having a fuel electrode (fuel electrode) and a cathode layer (air electrode) provided on the other side of the electrolyte layer is known. In such a fuel cell, fuel gas (for example, hydrogen) is supplied to the anode layer side, and oxidizing gas (for example, air) is supplied to the cathode layer side.

In this solid oxide fuel cell, in the cathode layer,
Reaction on the cathode layer (air electrode) side: 1/20 ₂ +2e ^- → O ^2-... (1)
The reaction occurs, and the oxide ions generated on the cathode layer side flow to the anode layer side through the electrolyte layer, and in the anode layer,
Reaction on the anode layer (fuel electrode) side: H ₂ + O ^2- → H ₂ O+2e ^- (2)
The following reaction occurs, and power generation is performed by such a power generation reaction.

Such a power generation reaction in a fuel cell is concentrated on the inflow side where the concentration of fuel gas (for example, hydrogen) is high, and resistance heat generation (ohmic heat generation) occurs at the power generation point where the power generation current flows. The temperature on the inflow side tends to increase locally. When the temperature gradient locally increases on the inflow side of the fuel cell, thermal stress is generated in that region, and there is a risk that the fuel cell (electrolyte layer, anode layer, or cathode layer) will be damaged.

Therefore, in order to suppress the rise in the local temperature gradient on the inflow side of the fuel cell, it has been proposed that the porosity of the outflow side of the anode layer of the fuel cell is greater than that of the inflow side. (See Patent Document 1). In this fuel cell, the porosity of the anode layer is small at the inflow side portion of the anode layer, and the porosity is large at the outflow side portion of the anode layer. The resistance in the layer to the movement of hydrogen to the reaction interface and the release of water vapor (H ₂ O gas) generated by the power generation reaction is reduced. This increases the diffusivity of the fuel gas in the downstream part of the anode layer, increases the reactivity of the outflow side part of the anode layer where the concentration of fuel gas is low, and makes the power generation distribution in the anode layer more uniform. There is.

Furthermore, instead of changing the porosity of the anode layer in the flow direction of fuel gas, it has been proposed to change the thickness of the anode layer of the fuel cell (for example, see Patent Document 2). In this fuel cell, the thickness of the anode layer is thick at the inflow side part, and the thickness is thin at the outflow side part of the anode layer, which increases the diffusivity of the fuel gas at this outflow side part, and the anode layer The aim is to equalize the distribution of power generation.

JP2012-94427A Patent No. 6118694

In conventional solid oxide fuel cells, the porosity or thickness of the anode layer in the flow direction of the fuel gas is changed in order to equalize the power generation distribution in the anode layer. It has been desired to realize a fuel cell in which the reactivity of the power generation reaction can be controlled by other factors.

An object of the present invention is to provide a solid oxide fuel cell that can control the reactivity of the power generation reaction and make the power generation distribution uniform within the cell surface (anode layer and/or cathode layer). It is.

The solid oxide fuel cell according to claim 1 of the present invention includes an electrolyte layer having ionic conductivity that allows oxide ions to pass through, an anode layer provided on one side of the electrolyte layer, and an anode layer provided on one side of the electrolyte layer. A solid oxide fuel cell having a cathode layer provided on the other side,
The anode layer includes an electron conductive phase that conducts electrons, an ion conductive phase that conducts ions, and a void phase that diffuses fuel gas,
The degree of curvature of at least one of the electron conductive phase, the ion conductive phase, and the void phase in the upstream region of the anode layer located upstream in the flow direction of the fuel gas depends on the direction of flow of the fuel gas. The degree of curvature is greater than the degree of curvature of the electron conductive phase, the ion conductive phase, and the void phase in a downstream region of the anode layer located downstream.

In the solid oxide fuel cell according to claim 2 of the present invention, the degree of curvature of the void phase in the upstream portion of the anode layer is equal to the degree of curvature of the void phase in the downstream portion of the anode layer. It is characterized by a greater degree of curvature.

Further, in the solid oxide fuel cell according to claim 3 of the present invention, the cathode layer includes an electron conductive phase that conducts electrons, an ion conductive phase that conducts ions, and a void phase that diffuses gas. The degree of curvature of at least one of the electron conductive phase, the ion conductive phase, and the void phase in the upstream portion of the cathode layer located upstream in the flow direction of the oxidant gas The degree of curvature is greater than the degree of curvature of the electron conductive phase, the ion conductive phase, and the void phase in the downstream portion of the cathode layer located downstream in the gas flow direction.

Further, in the solid oxide fuel cell according to claim 4 of the present invention, the electron conductive phase, the ion conductive phase, and the void phase of the anode layer are formed at a portion where these three phases contact each other. An anode three-phase interface is formed, and the density of the anode three-phase interface in the downstream part of the anode layer is higher than the density of the anode three-phase interface in the upstream part of the anode layer. .

Further, in the solid oxide fuel cell according to claim 5 of the present invention, in the downstream region of the anode layer, the ion conductive phase and the electron conductive phase have a high reactivity ratio. In the upstream portion of the anode layer, the ion conductive phase and the electron conductive phase have a low reactivity ratio.

Further, the solid oxide fuel cell according to claim 6 of the present invention includes an electrolyte layer having ionic conductivity that allows oxide ions to pass through, an anode layer provided on one side of the electrolyte layer, and an anode layer provided on one side of the electrolyte layer. A solid oxide fuel cell having a cathode layer provided on the other side of the layer,
The anode layer includes an electron conductive phase that conducts electrons, an ion conductive phase that conducts ions, and a void phase that diffuses fuel gas. The anode three-phase interface is formed at the part where the three phases contact each other.
The density of the anode three-phase interface in the downstream part of the anode layer located downstream in the flow direction of the fuel gas is equal to the density of the anode three-phase interface in the upstream part of the anode layer located upstream in the flow direction of the fuel gas. It is characterized by a density greater than that of the phase interface.

Further, in the solid oxide fuel cell according to claim 7 of the present invention, the cathode layer includes an electron conductive phase that conducts electrons, an ion conductive phase that conducts ions, and voids that diffuse oxidant gas. The electron conductive phase, the ion conductive phase, and the void phase constitute a cathode three-phase interface at a portion where these three phases come into contact, and is located on the downstream side in the flow direction of the oxidant gas. The density of the cathode three-phase interface in the downstream region of the cathode layer is greater than the density of the cathode three-phase interface in the upstream region of the cathode layer located upstream in the flow direction of the oxidant gas. shall be.

Further, in the solid oxide fuel cell according to claim 8 of the present invention, the cathode layer includes an electron/ion conductive phase that conducts electrons and ions, and a void phase that diffuses oxidant gas. The electron/ion conduction phase and the void phase constitute a cathode two-phase interface at a portion where these two phases contact each other, and the cathode layer is located downstream of the cathode layer on the downstream side in the flow direction of the oxidant gas. The density of the cathode two-phase interface in the side portion is higher than the density of the cathode two-phase interface in the upstream portion of the cathode layer located upstream in the flow direction of the oxidant gas.

Further, the solid oxide fuel cell according to claim 9 of the present invention includes an electrolyte layer having ionic conductivity that allows oxide ions to pass through, an anode layer provided on one side of the electrolyte layer, and an anode layer provided on one side of the electrolyte layer. A solid oxide fuel cell having a cathode layer provided on the other side of the layer,
The anode layer includes an electron conductive phase that conducts electrons, an ion conductive phase that conducts ions, and a void phase that diffuses fuel gas,
In the downstream part of the anode layer located downstream in the flow direction of the fuel gas, the ion conductive phase and the electron conductive phase have a high reactivity ratio, and in the upstream part of the anode layer is characterized in that the ion conductive phase and the electronic conductive phase have a low reactivity ratio.

Furthermore, in the solid oxide fuel cell according to claim 10 of the present invention, the cathode layer includes an electron conductive phase that conducts electrons, an ion conductive phase that conducts ions, and voids that diffuse oxidant gas. In the downstream portion of the cathode layer located downstream in the flow direction of the oxidant gas, the ionic conductive phase and the electronic conductive phase have a high reactivity ratio, and the cathode layer The ion conductive phase and the electronic conductive phase have a low reactivity ratio in the upstream region.

According to the solid oxide fuel cell according to claim 1 of the present invention, the anode layer includes an electron conductive phase that conducts electrons, an ion conductive phase that conducts ions, and a void phase that diffuses fuel gas. The degree of curvature of at least one of the electron conductive phase, ion conductive phase, and void phase in the upstream portion of the anode layer located on the upstream side in the flow direction of the fuel gas is Since the degree of tortuosity of the electron-conducting phase, ion-conducting phase and void phase is greater than that of the downstream region of the anode layer, the reactivity in this downstream region is enhanced, thereby increasing the anode layer in the flow direction of the fuel gas. power generation distribution can be made uniform.

For example, if the degree of curvature of the void phase in the upstream part of the anode layer is greater than the degree of curvature in the downstream part, the fuel gas will flow into the power generation reaction field (i.e., between the anode layer and the electrolyte) in this downstream part. As a result, the gas diffusivity in this downstream region is increased, and the power generation distribution of the anode layer in the flow direction of the fuel gas can be made uniform.

Further, for example, if the degree of curvature of the electron conductive phase in the upstream region of the anode layer is configured to be greater than the degree of curvature of the electron conductive phase in the downstream region, the electrical conductivity will be high in this downstream region. As a result, the power generation performance of this downstream portion is improved, and as a result, the power generation distribution of the anode layer in the flow direction of the fuel gas can be made uniform.

Furthermore, for example, if the degree of curvature of the ion conductive phase in the upstream part of the anode layer is configured to be greater than the degree of curvature of the ion conductive phase in the downstream part, the ion conductivity will be high in this downstream part. As a result, the power generation performance of this downstream portion is improved, and as a result, the power generation distribution of the anode layer in the flow direction of the fuel gas can be made uniform.

The power generation distribution in the anode layer can be made uniform by changing the degree of curvature of at least one of the electron conductive phase, ion conductive phase, and void phase. By changing the degree of curvature of any two or all three phases, the power generation distribution of the anode layer can be made more uniform.

Further, according to the solid oxide fuel cell according to claim 2 of the present invention, the degree of curvature of the void phase in the upstream portion of the anode layer is greater than the degree of curvature of the void phase in the downstream portion thereof. , it is possible to improve the gas diffusivity in this downstream region and to equalize the power generation distribution of the anode layer in the flow direction of the fuel gas.

Further, according to the solid oxide fuel cell according to claim 3 of the present invention, at least the electron conductive phase, the ion conductive phase, and the void phase in the upstream portion of the cathode layer on the upstream side in the flow direction of the oxidant gas. The degree of curvature of any one phase is larger than the degree of curvature of the electron conductive phase, the ion conductive phase, and the void phase in the downstream part of the cathode layer on the downstream side in the flow direction of the oxidant gas. The reactivity of the cathode layer in the flow direction of the oxidizing gas can be made uniform.

Further, according to the solid oxide fuel cell according to claims 4 and 6 of the present invention, the electron conductive phase, the ion conductive phase, and the void phase of the anode layer are formed at a portion where these three phases contact each other. The density of the anode three-phase interface in the downstream part of the anode layer is higher than the density of the anode three-phase interface in the upstream part of the anode layer. Since the power generation performance is also large, the power generation performance in this downstream region is improved, and as a result, the power generation distribution of the anode layer in the flow direction of the fuel gas can be made uniform.

Further, according to the solid oxide fuel cell according to claims 5 and 9 of the present invention, the ion conductive phase and the electron conductive phase have a high reactivity ratio in the downstream region of the anode layer, and the anode layer has a high reactivity ratio. Since the ion-conducting phase and the electron-conducting phase have a low reactivity ratio in the upstream region of the layer, the reactivity in the downstream region of the anode layer is increased, and as a result, the anode in the direction of fuel gas flow is increased. It is possible to make the power generation distribution of the layer uniform.

Further, according to the solid oxide fuel cell according to claim 7 of the present invention, the electron conductive phase, the ion conductive phase, and the void phase of the cathode layer form a cathode layer at a portion where these three phases contact each other. The density of the cathode three-phase interface in the downstream part of the cathode layer, which constitutes a phase interface, is greater than the density of the cathode three-phase interface in the upstream part, so it is possible to increase the reactivity in the downstream part of the cathode layer. As a result, the reaction distribution of the anode layer in the flow direction of the oxidant gas can be made uniform.

Further, according to the solid oxide fuel cell according to claim 8 of the present invention, the electron/ion conductive phase and the void phase of the cathode layer form a cathode two-phase interface at a portion where these two phases contact each other. Since the density of the cathode two-phase interface in the downstream part of the cathode layer is greater than the density of the cathode two-phase interface in the upstream part, the reactivity in the downstream part of the cathode layer is increased, and the oxidant gas The reaction distribution of the anode layer in the flow direction can be made uniform.

Furthermore, according to the solid oxide fuel cell according to claim 10 of the present invention, the cathode layer includes an electron conductive phase that conducts electrons, an ion conductive phase that conducts ions, and an oxidant gas that diffuses. In the downstream part of the cathode layer, the ion-conducting phase and the electron-conducting phase have a high reactivity, and in the upstream part of the cathode layer, the ion-conducting phase and the electron-conducting phase have a high reactivity. Since the proportion is low, the reactivity in the downstream portion of the cathode layer can be increased, and the reaction distribution in the anode layer in the flow direction of the oxidizing gas can be made uniform.

FIG. 1 is a perspective view showing an example of a cell stack using a first embodiment of a solid oxide fuel cell according to the present invention. FIG. 2 is a cross-sectional view schematically showing the cell stack of FIG. 1. FIG. FIG. 3 is an enlarged cross-sectional view of the solid oxide fuel cell shown in FIG. 2; FIG. 2 is an enlarged cross-sectional view schematically showing a part of the anode layer. FIG. 3 is an explanatory diagram for explaining the degree of curvature of an electron conductive phase, an ion conductive phase, and a void phase of an anode layer. FIG. 2 is an enlarged cross-sectional view schematically showing a part of the anode layer in a second embodiment of the solid oxide fuel cell according to the present invention. FIG. 3 is a diagram showing the relationship between the anode three-phase interface length ratio in the anode layer and the power generation performance of the fuel cell. FIG. 3 is a diagram showing the relationship between the volume fraction of the ion conductive phase in the anode layer and the overvoltage of the anode layer. FIG. 3 is a diagram showing changes in temperature and generated current from the inflow side to the outflow side in a solid oxide fuel cell according to an example. FIG. 3 is a diagram showing changes in temperature and generated current from the inflow side to the outflow side in a solid oxide fuel cell of a comparative example.

EMBODIMENT OF THE INVENTION Hereinafter, various embodiments of the solid oxide fuel cell according to the present invention will be described with reference to the accompanying drawings.

First, a first embodiment of a solid oxide fuel cell according to the present invention will be described with reference to FIGS. 1 to 5. 1 and 2 show a cell stack using the solid oxide fuel cell of the first embodiment. In FIGS. 1 and 2, the illustrated cell stack 2 includes a stack main body 4 having a rectangular outer shape, and a plurality of solid oxide fuel cells 6 are assembled into the stack main body 4 in a stacked state. The stack body 4 is provided with a first inlet manifold 8 and a first outlet manifold 10, and after the fuel gas (for example, hydrogen) from the fuel supply flow path is distributed by the first inlet manifold 8, it is distributed to a plurality of fuels. The fuel off-gas is supplied to the anode chamber 12 of the battery cell 6 , and the fuel off-gas from the anode chamber 12 is discharged through the first outflow side manifold 10 .
The stack body 4 is further provided with a second inlet manifold 14 and a second outlet manifold 16, and the oxidizing gas (for example, air) from the oxidizing gas supply channel is distributed by the second inlet manifold 14. The oxidizing agent off-gas is then fed to the cathode chambers 18 of the plurality of fuel cells 6, and the oxidant off-gas from the cathode chambers 18 is discharged through the second outlet manifold 16.

Next, the illustrated solid oxide fuel cell 6 will be explained. The plurality of solid oxide fuel cells 6 have substantially the same configuration, and one of them will be explained below. Mainly referring to FIG. 3, the illustrated solid oxide fuel cell 6 includes an electrolyte layer 20 and an anode layer 22 disposed on one side of the electrolyte layer 20 (lower side in FIGS. 2 and 3). (fuel electrode), and a cathode layer 24 (air electrode) disposed on the other surface side (upper surface side in FIGS. 2 and 3) of this electrolyte layer 20. In this embodiment, an electrolyte layer 20 is provided on the surface side of the anode layer 22 as a support base, and a cathode layer 24 is provided on the surface side of this electrolyte layer 20.

Interconnectors 26 are disposed between adjacent fuel cells 6 among the plurality of fuel cells 6 (see also FIG. 2), and these interconnectors 26 connect the anode layer 22 and cathode layer 24 of the adjacent fuel cells 6. electrically connected to. Each anode chamber 12 is formed between the anode layer 22 of the fuel cell 6 and the interconnector 26, and the cathode chamber 18 is formed between the cathode layer 24 of the fuel cell 6 and the interconnector 26. .

The electrolyte layer 20 is formed of, for example, yttria-stabilized zirconia (also referred to as "YSZ"), scandia-stabilized zirconia (ScSZ), or the like. This electrolyte layer 20 has ionic conductivity and has the function of passing oxide ions generated on the cathode layer 24 (air electrode) side to the anode layer 22 side. The anode layer 22 (fuel electrode) is formed of, for example, nickel-yttria stabilized zirconia (also referred to as "Ni-YSZ"), and the reaction of formula (2) above takes place in this anode layer 22. The cathode layer 24 (air electrode) is made of, for example, lanthanum strontium manganite-yttria stabilized zirconia (La _0.6 Sr _0.4 MnO) (also referred to as "LSM-YSZ"), lanthanum strontium cobaltite ferrite [( La, Sr) (Co, Fe) O ₃ ] (LSCF), lanthanum strontium cobaltite (La _0.6 Sr _0.4 CoO ₃ ) (LSC), etc., and the cathode layer 24 has the above formula (1). reaction takes place. As will be described in detail later, LSM-YSZ is a material having a cathode three-phase interface, and LSCF and LSC are materials having a cathode two-phase interface.

This solid oxide fuel cell 6 is further configured as follows so that the power generation distribution of the anode layer 22 in the flow direction of the fuel gas is made uniform. Mainly referring to FIGS. 4 and 5, when the anode layer 22 (fuel electrode) is formed of, for example, Ni-YSZ, the Ni phase 32 functions as an electron-conducting phase that conducts electrons, and the YSZ phase 34 functions as an ion-conducting phase. The void phase 36 functions as a gas diffusion phase that diffuses fuel gas (for example, hydrogen).

In this embodiment, attention is paid to the degree of curvature of the void phase 36, and the power generation distribution of the anode layer 22 in the flow direction of the fuel gas is made uniform. In such a fuel cell 6, the concentration of fuel gas (for example, hydrogen) on the inflow side is high, and the power generation distribution tends to be large on the inflow side where the concentration is high and small on the outflow side where the concentration is low. For this reason, the degree of curvature of the void phase 36 in the upstream portion 22a of the anode layer 22 located on the upstream side as seen in the flow direction of fuel gas is different from that in the anode located on the downstream side as seen in the flow direction of fuel gas. The degree of curvature of the void phase 36 in the downstream region 22b of the layer 22 is greater than that of the void phase 36 in the downstream region 22b of the layer 22.

To explain the degree of tortuosity (τ) here, this degree of tortuosity (τ) is an index that indicates the degree to which conduction and diffusion of a substance is suppressed, and the relationship between this degree of tortuosity (τ) and the phase structure is as follows. For example, as shown in FIG. In a structure that extends linearly as shown in Figure 5(a), the degree of curvature (τ) is "1" (τ = 1), and in a structure that extends at an angle of 45 degrees as shown in Figure 5(b), the degree of curvature (τ) is "1" (τ = 1). , the degree of tortuosity (τ) is “1.4” (τ = 1.4), and in the structure where the particles are connected in a straight line as shown in Figure 5(c), the degree of tortuosity (τ) is greater than “1”. is a relatively small value (τ = small), and in the structure where the particles are bent and connected as shown in Figure 5(d), the degree of tortuosity (τ) is a relatively large value (τ = large). As shown in 5(e), in a structure that is not continuously connected (in other words, a disconnected structure), the degree of curvature (τ) is infinite (τ=∞).

The relationship between the degree of curvature (τ ₁ ) of the void phase 36 and the effective diffusion coefficient (De ₁ ) of the fuel gas considering its structure is as follows:
Effective diffusion coefficient De ₁ = (ε ₁ /τ ₁ )×D ₁ (3)
ε ₁ : Volume fraction of the void phase τ ₁ : Degree of curvature of the void phase D ₁ : Expressed by the theoretical diffusion coefficient of the fuel gas, and as understood from this equation (3), the degree of curvature of the void phase 36 The smaller (τ ₁ ) is, the larger the effective diffusion coefficient (De ₁ ) of the fuel gas becomes.

In this embodiment, the degree of tortuosity (τ _1a ) of the void phase 36 in the upstream region 22a of the anode layer 22 is configured to be greater than the degree of tortuosity (τ _1b ) of the void phase 36 in the downstream region 22b thereof. (τ _1a >τ _1b ), the degree of curvature (τ _1a ) of the upstream portion 22a is, for example, about 5 to 20, and the degree of curvature (τ _1b ) of the downstream portion 22b is, for example, about 1 to 15. It is configured so that

With this structure, the effective diffusion coefficient of the downstream part 22b of the anode layer 22 is larger than the effective diffusion coefficient of the upstream part 22a, and the gas diffusivity of this downstream part 22b is high, so that the fuel gas easily flows into the reaction field (near the interface between the anode layer 22 and the electrolyte layer 20). Therefore, the power generation reactivity (that is, power generation performance) of the downstream portion 22b of the anode layer 22 (fuel electrode) increases, and as a result, it is possible to equalize the power generation distribution of the anode phase 22 in the flow direction of the fuel gas. This makes it possible to suppress a local temperature rise in the anode layer 22.

In the embodiment described above, the degree of curvature (τ ₁ ) of the void phase 36 of the anode layer 22 is changed, but instead of this air phase 36, the degree of curvature ( τ ₂ ) or the degree of curvature (τ ₃ ) of the ion conductive phase (YSZ phase 34) may be changed.

To explain the case where the degree of curvature (τ ₂ ) of the electron conductive phase (Ni phase 32) of the anode layer 22 is changed, in this case, the degree of curvature (τ ₂ ) of this electron conduction phase and the effective electronic conductivity in consideration of its structure. The relationship with (σe ₂ ) is
Effective electronic conductivity σe ₂ = (ε ₂ /τ ₂ )×σ ₂ (4)
ε ₂ : Volume fraction of the electron conduction phase τ ₂ : Curvature degree of the electron conduction phase σ ₂ : Expressed by the electronic conductivity of the electron conduction phase, and as understood from this equation (4), the The smaller the tortuosity (τ ₂ ), the larger the effective electronic conductivity (σe ₂ ).

In this case, as described above, the degree of curvature (τ _2a ) of the electron conductive phase 32 at the upstream portion 22a of the anode layer 22 is greater than the degree of curvature (τ _2b ) of the electron conductive phase 36 at the downstream portion 22b. (τ _2a >τ _2b ). With this configuration, the effective electronic conductivity of the downstream portion 22b of the anode layer 22 is greater than the effective electronic conductivity of the upstream portion 22a, and electrons flow more easily in the downstream portion 22b. Therefore, even with this configuration, the power generation reactivity (power generation performance) of the downstream portion 22b of the anode layer 22 (fuel electrode) is increased, and the power generation distribution of the anode layer 22 in the flow direction of the fuel gas is made uniform. can be achieved.

Also, to explain the case where the degree of curvature (τ ₃ ) of the ion-conducting phase (YSZ phase 34) of the anode layer 22 is changed, in this case, the degree of curvature (τ ₃ ) of the ion-conducting phase and the effective ion The relationship with electrical conductivity (σe ₃ ) is
Effective ionic conductivity σe ₃ = (ε ₃ /τ ₃ )×σ ₃ (5)
ε ₃ : Volume fraction of the ion-conducting phase τ ₃ : Curvature of the ion-conducting phase σ ₃ : Expressed by the ionic conductivity of the ion-conducting phase, and as understood from this equation (5), the The smaller the tortuosity (τ ₂ ), the larger the effective electronic conductivity (σe ₃ ).

In this case, as described above, the degree of curvature (τ _3a ) of the ion conductive phase 34 at the upstream portion 22a of the anode layer 22 is greater than the degree of curvature (τ _3b ) of the ion conductive phase 32 at the downstream portion 22b. (τ _3a >τ _3b ). With this configuration, the effective ionic conductivity of the downstream region 22b of the anode layer 22 is greater than the effective ionic conductivity of its upstream region 22a, and ions easily flow in this downstream region 22b. Therefore, even with this configuration, the power generation reactivity (power generation performance) of the downstream portion 22b of the anode layer 22 (fuel electrode) is increased, and the power generation distribution of the anode layer 22 in the flow direction of the fuel gas is made uniform. can be achieved.

In the embodiment described above, the degree of curvature of any one of the electron conductive phase 32 (Ni phase), the ion conductive phase 34 (YSZ phase), and the void phase 36 in the anode layer 22 is determined based on the upstream region 22a and the downstream region thereof. Although the bending degree of any two phases of the electron conductive phase 32, the ion conductive phase 34, and the void phase 36 may be changed, The tortuosity of all three phases of the void phase 36 may be varied.

In the embodiment described above, the degree of curvature of the electron conductive phase 32 (Ni phase), the ion conductive phase 34 (YSZ phase), and the void phase 36 in the anode layer 22 is changed between the upstream region 22a and the downstream region 22b. However, in addition to the anode layer 22, the degree of curvature of the cathode layer 24 may be changed.

For example, when the cathode layer 24 is formed from LSM-YSZ, this LSM-YSZ has a cathode three-phase interface, the LSM phase functions as an electron-conducting phase, the YSZ phase functions as an ion-conducting phase, and these electron-conducting phase and an ion-conducting phase as well as a void phase. In order to equalize the reaction of the cathode layer 24 in the flow direction of the oxidant gas (for example, air), similarly to the anode layer 22, the cathode layer 24 located on the upstream side in the flow direction of the oxidant gas is The degree of curvature of the void phase (or electron conductive phase, ion conductive phase) in the upstream region 24a is the same as that of the void phase (or electron conductive phase, ion conductive phase) in the downstream region 24b of the cathode layer 24 located downstream in the flow direction of the oxidant gas. conduction phase, ionic conduction phase).

With this configuration, the effective diffusion coefficient (or effective electronic conductivity, effective ionic conductivity) of the downstream portion 24b of the cathode layer 24 is the same as the effective diffusion coefficient (or effective electronic conductivity, effective ionic conductivity) of the upstream portion 24b. The gas diffusivity (or electronic conductivity, ionic conductivity) of this downstream region 24b is higher than that of its upstream region 24a. Therefore, the reactivity of the downstream portion 24b of the cathode layer 24 (air electrode) becomes high, and as a result, the reaction distribution of the cathode phase 24 in the flow direction of the oxidant gas can be made uniform.

In the embodiment described above, the degree of curvature of any one of the void phase, electron conduction phase, and ion conduction phase in the upstream region 24a of the cathode layer 24 is determined by the degree of curvature of any one of the void phase, electron conduction phase, and ion conduction phase in the downstream region 24b. Although the degree of tortuosity is greater than the degree of tortuosity of the phase, the degree of tortuosity of any two phases of the void phase, the electron conduction phase, and the ion conduction phase in this upstream region 24a may be made larger, or , the electronic conduction phase, and the ion conduction phase, the tortuosity of all three phases may be increased.

Further, for example, when the cathode layer 24 is formed from LSCF (LSC), this LSCF (LSC) has an anode two-phase interface, and the LSCF phase (LSC phase) conducts electrons and ions. It functions as a conductive phase (having the functions of both an electron conductive phase and an ion conductive phase), and contains a void phase in addition to this electron/ion conductive phase. In this case, in order to uniformize the reaction of the cathode layer 24, the degree of curvature of the void phase (or electron/ion conductive phase) in the upstream region 24a of the cathode layer 24 is such that the voids in the downstream region 24b of the cathode layer 24 The degree of curvature of the cathode layer 24 is larger than that of the phase (or the electron/ion conduction phase), and by configuring it in this way, similar to the structure having a three-phase interface, the effective The diffusion coefficient (or effective electronic conductivity/effective ionic conductivity) becomes larger than the effective diffusion coefficient (or effective electronic conductivity/effective ionic conductivity) of the upstream portion 24b, and the gas diffusivity of this downstream portion 24b increases. (or electronic conductivity/ion conductivity) increases. Therefore, the reactivity of the downstream portion 24b of the cathode layer 24 (air electrode) becomes high, and as a result, the reaction distribution of the cathode layer 24 in the flow direction of the oxidant gas can be made uniform.

In the above-described embodiment, the degree of curvature of either the void phase or the electron/ion conduction phase in the upstream portion 24a of the cathode layer 24 is the degree of curvature of the void phase or the electron/ion conduction phase in the downstream portion 24b. However, the degree of curvature of both the void phase and the electron/ion conductive phase in this upstream region 24a may be increased.

Next, a second embodiment of the solid oxide fuel cell according to the present invention will be described. In the first embodiment described above, attention is paid to the degree of curvature of the void phase, electron conduction phase, and ion conduction phase of the anode layer, but in this second embodiment, the density of the anode three-phase interface of the anode layer is We are aiming to equalize the power generation distribution. In the following embodiments, members that are substantially the same as those in the above-described first embodiment are given the same numbers, and their explanations will be omitted.

In this second embodiment, the basic configuration of the solid oxide fuel cell is the same as that of the first embodiment described above, but the structure of the anode layer and cathode layer is different from the first embodiment. . In this second embodiment, the anode layer 22A of the solid oxide fuel cell 2A is formed of, for example, Ni-YSZ, as in the first embodiment, and the Ni phase 32 functions as an electron conductive phase. The YSZ phase 34 functions as an ion conductive phase, the void phase 36 functions as a gas diffusion phase that diffuses fuel gas (for example, hydrogen), and the electron conductive layer 32 (Ni phase), the ion conductive phase 34 (YSZ phase), and The location where the three phases of the void phase 36 come into contact becomes an anode three-phase interface 38, and a power generation reaction takes place at this anode three-phase interface 38.

The length ratio of this anode three-phase interface 38 and the maximum output density (W/cm ² ) have a relationship as shown in FIG. 7, for example (cited from JP 2015-176774 as a reference), As the length ratio of the anode three-phase interface 38 of the anode layer 22A increases, its maximum output density also increases.In other words, as the density of the anode three-phase interface 38 increases, the generated current of the anode layer 22A also increases. Note that 40 μm, 20 μm, 10 μm, and 5 μm in FIG. 7 are the sizes of the ion conductive phase 34 (YSZ layer), and the maximum output density can be further improved by further reducing the size of the ion conductive phase 34. .

The density of the anode three-phase interface of this anode layer 22A can be determined, for example, by changing the particle size of the electron conductive phase 32 (Ni), the particle size of the ion conductive phase 34 (YSZ), the pore-forming material (void size), or by changing the electrode ( The density of the anode three-phase interface can be adjusted by changing the firing time and/or firing temperature when producing the anode layer (anode layer), and in general, the smaller the particle size of the material used, the more the anode three-phase interface density tends to increase.

For this reason, in the second embodiment, the density of the anode three-phase interface 38 is changed so that the density of the anode three-phase interface 38 in the downstream region of the anode layer 22A is the same as that in the upstream region. The density of the anode three-phase interface 38 in the upstream region is, for example, about 2 to 4 μm/μm3, and the density of the anode three-phase interface ³⁸ in the downstream region is higher than that of the anode three-phase interface 38. The density of 38 is, for example, about 3 to 5 μm/μm ³ .

With this configuration, the density of the anode three-phase interface 38 in the downstream part of the anode layer 22A is greater than that in the upstream part, and the power generation reactivity (power generation performance) of this downstream part is increased. As a result, it is possible to make the power generation distribution of the anode layer 22A uniform in the flow direction of the fuel gas.

In the embodiment described above, the density of the anode three-phase interface 38 in the anode layer 22A is different between the upstream region and the downstream region, but in addition to the anode layer 22A, the cathode three-phase interface or two-phase It is also possible to change the density of the interface.

For example, when the cathode layer is formed from LSM-YSZ, this LSM-YSZ includes an LSM phase as an electron conductive layer, a YSZ phase as an ion conductive layer, and a void phase as a gas diffusion phase, as described above. The location where these three phases, the electron conductive phase, the ion conductive phase, and the void phase, come into contact constitutes a cathode three-phase interface, and a reaction on the cathode layer side takes place at this cathode three-phase interface. In such a cathode layer, in order to equalize the reaction in the flow direction of the oxidant gas (for example, air), the density of the cathode three-phase interface in the downstream region of the cathode layer is The density is greater than the density of the cathode three-phase interface in the upstream region.

With this configuration, the reactivity in the downstream portion of the cathode layer is higher than that in the upstream portion, and it is possible to make the reaction distribution of the cathode layer uniform in the flow direction of the oxidant gas.

Further, for example, when the cathode layer is formed from LSCF (LSC), this LSCF (LSC) includes an LSCF phase (LSC phase) as an electron/ion conductive phase and a void phase as a gas diffusion phase, and - The location where the ion conductive phase and the void phase come into contact constitutes a cathode two-phase interface, and a reaction on the cathode layer side takes place at this cathode two-phase interface. In this case, the density of the cathode two-phase interface in the downstream region of the cathode layer is greater than the density of the cathode two-phase interface in the upstream region.

With this configuration, similar to the cathode having a three-phase interface, the reactivity of the downstream part of the cathode layer is increased, and the reaction distribution of the cathode layer in the flow direction of the oxidizing gas is made uniform. Can be done.

Next, a third embodiment of the solid oxide fuel cell according to the present invention will be described. The first embodiment focuses on the degree of curvature of the void phase, electronic conduction phase, and ion conduction phase of the anode layer, and the second embodiment focuses on the density of the anode three-phase interface of the anode layer. In the third embodiment, the distribution of power generation in the anode layer is made uniform by focusing on the reactivity ratio between the ion conductive phase and the electron conductive phase of the anode layer.

In this third embodiment, the basic configuration of the solid oxide fuel cell is the same as in the first and second embodiments described above, and the ion conductive phase (YSZ phase) and the electron conductive phase of the anode layer are the same. (Ni phase) is different from the first and second embodiments in terms of the reactivity ratio.

In this third embodiment, although not shown, the anode layer of the solid oxide fuel cell is formed of, for example, Ni-YSZ, and includes a Ni phase as an electron conductive phase and a YSZ phase as an ion conductive phase. and a void phase as a gas diffusion phase.

The volume fraction (Vaε) of the ion conductive phase (YSZ phase) in this anode layer is
Volume fraction Vaε=V _YSZ /(V _Ni +V _YSZ ) ...(6)
V _Ni : Volume of electronic conduction phase V _YSZ : Volume of ionic conduction phase.

The relationship between the volume ratio of the ion-conducting phase of the anode layer and the overvoltage (Arb.unit) of the anode layer is, for example, as shown in FIG. 8 (cited from JP 2015-176774 as a reference), When the volume ratio of the ion conductive phase (Vaε) is in the range of 0.2 to 0.8, as the volume ratio of the ion conductive phase increases, the overvoltage (voltage loss) of the anode layer decreases, and the power generation reactivity (power generation performance) of the anode layer decreases. ) becomes higher.

Since there is such a relationship regarding the volume ratio (Vaε) of the ion conductive phase, in this third embodiment, the overvoltage (voltage loss) depending on the volume ratio of the ion conductive phase (YSZ phase) of the anode phase is changed. In other words, the composition ratio regarding the reactivity between the ion conductive phase (YSZ phase) and the electron conductive phase (Ni phase) is changed, and in the downstream part of the anode layer, the ion conductive phase (YSZ phase) and the electron conductive phase The layer (Ni phase) is configured to have a high reactivity ratio, and the upstream portion thereof is configured such that the ion conductive phase (YSZ phase) and the electron conductive phase (Ni phase) have a low reactivity ratio. Ru. For example, the ratio of the ion conductive phase to the electronic conductive phase in the upstream part of the anode layer is, for example, about 0.2 to 0.6:0.8 to 0.4, and in the downstream part The ratio of the ion conductive phase to the electron conductive phase is, for example, about 0.4 to 0.8:0.6 to 0.2.

With this configuration, the overvoltage (voltage loss) in the downstream part of the anode layer is smaller than that in the upstream part, and the power generation reactivity (power generation performance) is increased. It is possible to equalize the power generation distribution.

In this third embodiment as well, in addition to changing the composition ratio regarding the reactivity between the ion conductive phase and the electron conductive phase of the anode layer between the upstream region and the downstream region, the ion conductive phase of the cathode layer The composition ratio regarding the reactivity between the phase and the electron conductive phase may be changed.

For example, when the cathode layer is formed from LSM-YSZ, this LSM-YSZ includes an LSM phase as an electron conductive layer, a YSZ phase as an ion conductive layer, and a void phase as a gas diffusion phase. In this case, similarly to the anode layer, in this cathode layer, the composition ratio regarding reactivity between the ion conductive phase (YSZ phase) and the electronic conductive phase (LSM phase) is changed, and in the downstream part of the cathode layer, The ion-conducting phase and the electron-conducting phase are configured to have a high reactivity ratio, and the ion-conducting phase and the electron-conducting phase are configured to have a low reactivity ratio in the upstream region.

With this configuration, the overvoltage (voltage loss) at the downstream side of the cathode layer is reduced, the reactivity is increased, and the reaction distribution of the cathode layer in the flow direction of the oxidant gas can be made uniform. .

Although various embodiments of the solid oxide fuel cell according to the present invention have been described above, the present invention is not limited to these embodiments, and various changes and modifications can be made without departing from the scope of the present invention. .

For example, in the first embodiment described above, a technique is applied to change the degree of curvature of the electron conductive phase (ion conductive phase, void phase) between the upstream region and the downstream region of the anode layer, and the second embodiment described above In the embodiment described above, a technique is applied to change the density of the anode three-phase interface between the upstream side and the downstream side of the anode layer. Although the description has been made by applying a technique of changing the composition ratio regarding the reactivity of the ion conductive phase and the electron conductive phase depending on the region, the present invention does not require the application of these three techniques separately, and the degree of curvature of the anode layer can be changed. It is also possible to apply any two of the following techniques in combination: a technique related to the anode three-phase interface of the anode layer, and a technique related to the composition ratio related to the reactivity of the anode layer, or even a combination of all three techniques. You can also.

For example, a solid oxide fuel cell is constructed in which the degree of curvature of the void phase in the upstream part of the anode layer located on the upstream side as seen in the flow direction of fuel gas is greater than the degree of curvature of the void phase in the downstream part. As an example, the temperature and current density states from the inflow side (inlet side) of the fuel gas to the outflow side (outlet side) of the fuel gas in this example are shown in FIG.

On the other hand, a conventional solid oxide fuel cell in which the degree of curvature of the void phase of the anode layer is constant when viewed in the flow direction of the fuel gas is used as a comparative example. ) to the outflow side (exit side) of the temperature and current density as shown in FIG.

As can be easily understood by comparing FIG. 9 and FIG. 10, in the embodiment in which the degree of curvature of the void phase in the downstream region of the anode layer is smaller than that of the void phase in the upstream region, the anode layer Since it is possible to increase the power generation reaction in the downstream region, it is possible to suppress the power generation current on the inflow side (inlet side) and increase the power generation current on the outflow side (outlet side).In this way, the power generation current in the anode layer By making the distribution uniform, the gradient of temperature rise on the inflow side can be kept small, and the generation of thermal stress can also be made small.

In contrast, in a comparative example in which the degree of curvature of the void phase is constant in the flow direction of the fuel gas, the power generation reaction is concentrated on the inflow side (inlet side) where the concentration of fuel gas is high, and the power generation current is large on the inflow side. , the generated current is lower on the outflow side (outlet side), which causes the temperature to rise locally on the inflow side, and the temperature increase gradient becomes large. Such a large temperature increase gradient leads to damage due to thermal stress. There is a risk.

2 Cell stack 6 Solid oxide fuel cell 20 Electrolyte 22, 22A Anode layer (fuel electrode)
24 Cathode layer (air electrode)
32 Ni phase (electronic conduction phase)
34 YSZ phase (ion conductive phase)
36 Vocal phase (gas diffusion phase)
38 Anode three-phase interface

Claims (10)

A solid oxide fuel cell comprising an electrolyte layer having ionic conductivity that allows oxide ions to pass through, an anode layer provided on one side of the electrolyte layer, and a cathode layer provided on the other side of the electrolyte layer. A cell,
The anode layer includes an electron conductive phase that conducts electrons, an ion conductive phase that conducts ions, and a void phase that diffuses fuel gas,
The degree of curvature of at least one of the electron conductive phase, the ion conductive phase, and the void phase in the upstream region of the anode layer located upstream in the flow direction of the fuel gas depends on the direction of flow of the fuel gas. A solid oxide fuel cell characterized in that the degree of curvature is greater than the degree of curvature of the electron conductive phase, the ion conductive phase, and the void phase in a downstream region of the anode layer located on the downstream side. The solid oxide form of claim 1, wherein the degree of tortuosity of the void phase in the upstream region of the anode layer is greater than the degree of tortuosity of the void phase in the downstream region of the anode layer. fuel cell. The cathode layer includes an electron conductive phase that conducts electrons, an ion conductive phase that conducts ions, and a void phase that diffuses gas, and is located on the upstream side of the cathode layer in the flow direction of the oxidizing gas. The degree of curvature of at least one of the electron-conducting phase, the ion-conducting phase, and the void phase of the region is determined by the electron-conducting degree of the downstream region of the cathode layer located downstream in the flow direction of the oxidant gas. 2. The solid oxide fuel cell according to claim 1, wherein the degree of tortuosity is greater than that of the ion conductive phase and the void phase. The electron conductive phase, the ion conductive phase, and the void phase of the anode layer constitute an anode three-phase interface at a portion where these three phases contact each other, and the anode three phase interface in the downstream portion of the anode layer The solid oxide fuel cell according to claim 1, wherein the density of the phase interface is greater than the density of the anode three-phase interface in the upstream portion of the anode layer. In the downstream part of the anode layer, the ion conductive phase and the electron conductive phase have a high reactivity, and in the upstream part of the anode layer, the ion conductive phase and the electron conductive phase have high reactivity. 2. The solid oxide fuel cell according to claim 1, wherein the solid oxide fuel cell has a low reactivity. A solid oxide fuel cell comprising an electrolyte layer having ionic conductivity that allows oxide ions to pass through, an anode layer provided on one side of the electrolyte layer, and a cathode layer provided on the other side of the electrolyte layer. A cell,
The anode layer includes an electron conductive phase that conducts electrons, an ion conductive phase that conducts ions, and a void phase that diffuses fuel gas. The anode three-phase interface is formed at the part where the three phases contact each other.
The density of the anode three-phase interface in the downstream part of the anode layer located downstream in the flow direction of the fuel gas is equal to the density of the anode three-phase interface in the upstream part of the anode layer located upstream in the flow direction of the fuel gas. A solid oxide fuel cell characterized by having a density greater than that of a phase interface. The cathode layer includes an electron conductive phase that conducts electrons, an ion conductive phase that conducts ions, and a void phase that diffuses an oxidant gas, and the electron conductive phase, the ion conductive phase, and the void phase include: A cathode three-phase interface is formed at a portion where these three phases contact, and the density of the cathode three-phase interface in the downstream portion of the cathode layer located downstream in the flow direction of the oxidant gas is 7. The solid oxide fuel cell according to claim 6, wherein the density is greater than the density of the cathode three-phase interface in an upstream portion of the cathode layer located upstream in the gas flow direction. The cathode layer includes an electron/ion conductive phase that conducts electrons and ions, and a void phase that diffuses an oxidant gas, and the electron/ion conduction phase and the void phase are composed of these two phases. The density of the cathode two-phase interface in the downstream part of the cathode layer that is located downstream in the flow direction of the oxidant gas is equal to the density of the cathode two-phase interface in the region where the oxidant gas 7. The solid oxide fuel cell according to claim 6, wherein the density is higher than the density of the cathode two-phase interface at the upstream side of the cathode layer located on the side. A solid oxide fuel cell comprising an electrolyte layer having ionic conductivity that allows oxide ions to pass through, an anode layer provided on one side of the electrolyte layer, and a cathode layer provided on the other side of the electrolyte layer. A cell,
The anode layer includes an electron conductive phase that conducts electrons, an ion conductive phase that conducts ions, and a void phase that diffuses fuel gas,
In the downstream part of the anode layer located downstream in the flow direction of the fuel gas, the ion conductive phase and the electron conductive phase have a high reactivity ratio, and in the upstream part of the anode layer The solid oxide fuel cell is characterized in that the ion conductive phase and the electron conductive phase have a low reactivity ratio. The cathode layer includes an electron conductive phase that conducts electrons, an ion conductive phase that conducts ions, and a void phase that diffuses oxidizing gas, and the cathode layer is located downstream in the flow direction of the oxidizing gas. In the downstream region of the anode layer, the ion conductive phase and the electron conductive phase have a high reactivity, and in the upstream region of the anode layer, the ion conductive phase and the electron conductive phase have a high reactivity. The solid oxide fuel cell according to claim 9, wherein the solid oxide fuel cell has a low ratio.

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