JP2019175733A - Proton-conducting solid electrolyte and proton-conducting fuel cell - Google Patents

Abstract

To provide: a proton-conducting solid electrolyte having a high proton conductivity; and a proton-conducting fuel cell which shows high power generation characteristic and endurance when a methane-containing fuel gas is used.SOLUTION: A proton-conducting solid electrolyte 1 comprises a first layer 1a made of a proton-conducting solid electrolytic material selected from BaZrObased material, SrZrObased material, CaZrObased material, LaScObased material and LaYbObased material, and a second layer 2a made of a proton-conducting solid electrolytic material of BaCeOor BaCeZrObased material, in which the first and second layers are joined to each other. A proton-conducting fuel cell 10 comprises an anode 2 provided on the proton-conducting solid electrolyte 1 on a side of the first layer 1a thereof, and a cathode 3 provided on a side of the second layer 1b.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a proton conductive solid electrolyte and a proton conductive fuel cell using the same.

Development of a proton conductive fuel cell (PCFC) and a proton conductive solid electrolyte material used therefor is underway. Among these, a proton conductor obtained by adding another metal element to a BaCeO ₃ perovskite oxide is known as a material having good proton conductivity.

However, BaCeO ₃ -based and BaCeZrO ₃ -based proton conductive solid electrolyte materials have high proton conductivity, but have low resistance to methane, so that they can be put to practical use in applications such as fuel cells using methane as fuel gas. Is difficult. As a proton conductive solid electrolyte material composed of a LaYbO ₃ perovskite oxide having high carbon dioxide resistance and high proton conductivity, the present inventors have disclosed La _1-y M _y Yb as disclosed in Patent Document 1. _1-x In _x O _3-δ (M = Ba, Sr, Ca, Mg; δ is oxygen vacancy amount; 0 <x <1; 0 <y ≦ 0.2) We have developed materials and proton conducting fuel cells using them. Subsequent research by the present inventors revealed that the proton conductive solid electrolyte material has high resistance not only to carbon dioxide but also to methane.

JP 2016-1331075 A

_Above, the use of _{La 1-y M y Yb 1} -x In x O proton conductive solid electrolyte material having a composition of _3-[delta], high proton conductivity and a proton conductive solid electrolyte having a methane resistant, Methane There is a possibility that a proton-conducting fuel cell exhibiting high power generation characteristics and long-term durability can be constructed when power is generated using the fuel gas. _{Moreover, La 1-y M y Yb} 1-x In x O 3-δ Besides, the use of the excellent proton-conducting solid electrolyte material into methane-resistant proton conductive solid having a high proton conductivity and methane resistant There is a possibility that the electrolyte can be constructed.

  Provided is a proton conductive solid electrolyte having high resistance to methane and having high proton conductivity, and a proton conductive fuel cell exhibiting high power generation characteristics and durability when a fuel gas containing methane is used. There is.

In order to solve the above problems, a proton conductive solid electrolyte according to the present invention is made of a proton conductive solid electrolyte material selected from a BaZrO ₃ system, a SrZrO ₃ system, a CaZrO ₃ system, a LaScO ₃ system, and a LaYbO ₃ system. A first layer and a second layer made of a BaCeO ₃ -based or BaCeZrO ₃ -based proton conductive solid electrolyte material are joined.

Here, the first layer may be made of a proton conductive solid electrolyte material selected from a BaZrO ₃ system, a SrZrO ₃ system, and a CaZrO ₃ system. In particular, the first layer may be made of a CaZrO ₃ -based proton conductive solid electrolyte material.

The second layer may be made of a BaCeO ₃ -based proton conductive solid electrolyte material.

The BaZrO ₃ -based, SrZrO ₃ -based, CaZrO ₃ -based, LaScO ₃ -based, LaYbO ₃ -based proton conductive solid electrolyte materials are BaZr _1-x Yb _x O _3-δ , SrZr _1-x Y _x O _{3, respectively. -δ, CaZr 1-x In x} O 3-δ, La 1-x Sr x ScO 3-δ, La 1-x Sr x Yb 1-y In y O 3-δ may made of. However, 0 <x ≦ 0.2, 0 <y <1, and δ is the amount of oxygen vacancies.

  The second layer may be thicker than the first layer.

  A proton conductive fuel cell according to the present invention includes a proton conductive solid electrolyte as described above, an anode provided on the first layer side of the proton conductive solid electrolyte, and the second of the proton conductive solid electrolyte. And a cathode provided on the layer side.

  Here, the anode may be made of a material containing Ni. In the proton conductive fuel cell, the anode is used as a substrate, and the first layer, the second layer, and the cathode are provided on the surface of the substrate in this order as layers thinner than the substrate. Good.

  In the proton conductive solid electrolyte according to the above invention, all of the proton conductive solid electrolyte materials constituting the first layer exhibit high methane resistance. On the other hand, the proton conductive solid electrolyte material constituting the second layer is inferior in methane resistance, but exhibits high proton conductivity. As described above, the proton conductive solid electrolyte is configured as a composite material in which the first layer having high methane resistance and the second layer having high proton conductivity are joined. As a whole, the conductive solid electrolyte has both high methane resistance and proton conductivity. That is, when the proton conduction fuel cell is configured with the first layer as the anode side in contact with the fuel gas and the second layer as the cathode side not in contact with the fuel gas, and power is generated using methane as the fuel gas, Due to the high methane resistance of one layer and the high proton conductivity of the second layer, it can be used as a proton conductive solid electrolyte that achieves both high resistance to methane and high proton conductivity.

  In the proton conductive solid electrolyte material according to the above invention, when the anode made of a material containing Ni is provided on the first layer side to constitute a fuel cell, the Ni in the anode becomes the proton conductive solid electrolyte. As the solid solution dissolves, the rate of hole conduction increases and the electromotive force decreases. As a result, in the proton conduction fuel cell, a high electromotive force can be obtained and voltage efficiency can be improved.

Here, when the first layer is made of a proton conductive solid electrolyte material selected from the BaZrO ₃ system, SrZrO ₃ system, and CaZrO ₃ system, the material constituting the first layer has high proton conductivity and In particular, by having a high resistance to methane, it is possible to maintain high power generation characteristics even after a long period of power generation using methane as fuel in a proton conduction fuel cell.

In particular, when the first layer is made of a CaZrO ₃ -based proton conductive solid electrolyte material, the first layer from the second layer is used even after long-time power generation using methane as a fuel in a proton conductive fuel cell. Ce diffusion is difficult to occur, so that it is particularly excellent in maintaining high power generation characteristics. Further, even when power generation using methane as a fuel is performed, an increase in the rate of hole conduction accompanying solid solution of Ni is suppressed, and this is excellent in that a state having a high electromotive force can be maintained at a high level.

Further, when the second layer is made of a BaCeO ₃ -based proton conductive solid electrolyte material, high proton conductivity can be obtained as a whole proton conductive solid electrolyte due to its high proton conductivity.

BaZrO ₃ system, SrZrO ₃ based, CaZrO ₃ based, LASCO ₃ based proton-conducting solid electrolyte material LaYbO ₃ system, _{respectively, BaZr 1-x Yb x O} 3-δ, SrZr 1-x Y x O 3- _{In the case of δ} , CaZr _1-x In _x O _3-δ , La _1-x Sr _x ScO _3-δ , La _1-x Sr _x Yb _1-y In _y O _3-δ , It is easy to construct an excellent proton conductive solid electrolyte.

  When the second layer is thicker than the first layer, the second layer made of the solid electrolyte material having high proton conductivity and low electric resistance is formed thicker, so that the entire proton conductive solid electrolyte is formed. As a result, the electrical resistance can be kept low.

  The proton conducting fuel cell according to the invention uses a proton conducting solid electrolyte composed of the first layer and the second layer as described above, and is provided with an anode on the side of the first layer excellent in methane resistance. . Therefore, both the high methane resistance of the first layer and the high proton conductivity of the second layer can be used, and when conducting power generation using methane as the fuel gas, proton conduction that combines high power generation characteristics and durability. It becomes a fuel cell.

  Here, when the anode is made of a material containing Ni, the proton conductive solid electrolyte is in contact with the anode in the first layer, so that the first layer is not provided. It is possible to suppress a decrease in voltage efficiency of the proton conductive solid electrolyte due to an increase in contribution of proton conduction due to solid solution of Ni contained in the anode into the proton conductive solid electrolyte.

  When the proton conductive fuel cell is provided with the anode as a substrate and the surface of the substrate is provided with the first layer, the second layer, and the cathode as layers thinner than the substrate in this order, the electrolyte layer A high output density can be achieved by forming a thin film and keeping the electric resistance low.

It is the schematic explaining the structure of the proton conductive solid electrolyte and proton conductive fuel cell concerning one Embodiment of this invention. It is a figure which shows the continuous electric power generation characteristic of a single cell for every constituent material of electrolyte. It is a figure which shows a scanning electron microscope (SEM) image (left), and Ce distribution (right). The results of (a) BZYb / BCY, (b) SZY / BCY, and (c) CZI / BCY are shown, respectively. It is a figure which shows a scanning electron microscope (SEM) image (left), and Ce distribution (right). The results of (a) LSYbIn / BCY and (b) LSSc / BCY are shown, respectively. It is a figure which shows the open circuit voltage (OCV) after the electric power generation using an initial state and methane for every constituent material of electrolyte.

  Hereinafter, a proton conductive solid electrolyte and a proton conductive fuel cell according to an embodiment of the present invention will be described. As shown in FIG. 1, a proton conducting fuel cell 10 according to an embodiment of the present invention is configured by providing an anode 2 and a cathode 3 in a proton conducting solid electrolyte 1 according to an embodiment of the present invention. Can do.

[Proton conductive solid electrolyte]
First, the proton conductive solid electrolyte 1 according to one embodiment of the present invention will be described.

  The proton conductive solid electrolyte 1 is made of a composite material in which a first layer 1a made of a first solid electrolyte material and a second layer 1b made of a second solid electrolyte material are joined. Hereinafter, the proton conductive solid electrolyte 1 may be referred to as a composite solid electrolyte 1.

The first solid electrolyte material constituting the first layer 1a is made of any one of the proton-conducting solid electrolyte materials of BaZrO ₃ , SrZrO ₃ , CaZrO ₃ , LaScO ₃ , and LaYbO ₃ . These proton conductive solid electrolyte material, _{respectively,} the _{BaZrO 3, SrZrO 3, CaZrO 3} , LaScO 3, LaYbO 3 as a base material, as long as the proton conductivity is imparted by substitution of the cationic species composition However, the following composition can be exemplified as a suitable one. In the following, 0 <x ≦ 0.2; 0 <y <1, and δ is the amount of oxygen vacancies.
BaZrO ₃ series material: BaZr _1-x Yb _x O _{3 -δ} (BZYb); for example, x = 0.2
SrZrO ₃ -based material: SrZr _1-x Y _x O _3-δ (SZY); for example, x = 0.1
CaZrO ₃ -based material: CaZr _1-x In _x O _3-δ (CZI); for example, x = 0.04
LaScO ₃ series material: La _1-x Sr _x ScO _3-δ (LSSSc); for example, x = 0.1
LaYbO ₃ -based material: La _1-x Sr _x Yb _1-y In _y O _{3 -δ} (LSYbIn); for example, x = 0.1, y = 0.2
Comparison of characteristics between these materials will be described later.

The second solid electrolyte material constituting the second layer 1b is made of either a BaCeO ₃ -based or BaZrCeO ₃ -based proton conductive solid electrolyte material. These proton-conducting solid electrolyte materials are not limited in composition as long as they are based on BaCeO ₃ and BaZrCeO ₃ and are provided with proton conductivity by substitution of cation species. The following composition can be illustrated as a suitable thing. In the following, 0 <x ≦ 1; 0 <y ≦ 0.2, and δ is the amount of oxygen vacancies.
BaCeO ₃ -based material: BaCe _1-x Y _x O _3-δ (BCY); for example, x = 0.2
BaZrCeO ₃ -based material: BaZr _x Ce _1-xy Y _y O _3-δ (BZCY); for example x = 0.6, y = 0.2
Of the two types, BaCeO ₃ -based materials having particularly high proton conductivity can be used particularly preferably.

  As described above, the first layer 1a and the second layer 1b are made of different proton conductive solid electrolyte materials. The solid electrolyte material constituting the first layer 1a has higher resistance to methane (the degree of deterioration due to methane) than the solid electrolyte material constituting the second layer 1b. On the other hand, the solid electrolyte material constituting the second layer 1b has higher proton conductivity than the solid electrolyte material constituting the first layer 1a.

  Thus, by composing the first layer 1a made of a solid electrolyte material excellent in methane resistance and the second layer 1b made of a solid electrolyte material excellent in proton conductivity to constitute the composite solid electrolyte 1, Both the high methane resistance of the first layer 1a and the high proton conductivity of the second layer 1b can be utilized. In particular, as will be described later, if the fuel cell 10 is configured by providing the anode 2 on the first layer 1a side and the cathode 3 on the second layer 1b side, and generating power by the fuel cell 10 using methane as the fuel gas, the methane resistance The first layer 1a having a high level functions as a blocking layer for methane gas, and the second layer 1b having a low methane resistance is not brought into direct contact with methane, and the high proton conductivity of the second layer 1b is used to achieve high power generation characteristics. Can be obtained. And the high methane tolerance of the 1st layer 1a can maintain the high power generation characteristic over a long period of time.

The first layer 1a not only functions as a blocking layer for protecting the second layer 1b from methane gas in the fuel cell 10, but also prevents the material constituting the anode 2 from dissolving in the second layer 1b. Also plays a role. When Ni is dissolved in the BaCeO ₃ -based or BaZrCeO ₃ -based proton conductive solid electrolyte constituting the second layer 1b, the hole conduction ratio increases and the proton transport number decreases. As a result, the electromotive force of the fuel cell 10 is lowered and the voltage efficiency is lowered. On the other hand, even if Ni is brought into contact with each material constituting the first layer 1a, the hole conduction ratio does not increase significantly. Therefore, in the composite solid electrolyte 1, the fuel cell 10 is manufactured by including the first layer 1 a between the second layer 1 b and the anode 2 containing Ni to include a process requiring high temperature such as firing. It is possible to prevent Ni constituting the anode 2 from forming a solid solution in the second layer 1b and reducing the voltage efficiency of the fuel cell 10 when performing power generation at a high temperature. Thus, the 1st layer 1a functions as a blocking layer of the 2nd layer 1b with respect to both methane and Ni.

  The thicknesses of the first layer 1a and the second layer 1b may be determined arbitrarily, but it is preferable that the second layer 1b is thicker than the first layer 1a. This is because the solid electrolyte material constituting the second layer 1b has a lower proton resistance by having higher proton conductivity than the solid electrolyte material constituting the first layer 1a. By forming the first layer 1a having a higher electric resistance than the second layer 1b to be thin, the electric resistance of the composite solid electrolyte 1 as a whole can be kept low, and high power generation characteristics can be obtained. The areas of the first layer 1a and the second layer 1b may be arbitrarily determined. From the viewpoint of avoiding direct contact of methane and Ni with the second layer 1b, the first layer 1a It is preferable to form the same area as the area of the layer 1b or a larger area than that. In particular, the first layer 1a and the second layer 1b may have the same area from the viewpoint of the simplicity of the configuration and the efficient use of the proton conductivity of the second layer 1b.

  The composite solid electrolyte 1 can be manufactured by forming the first layer 1a and the second layer 1b by a liquid phase method, a solid phase method, or the like, respectively. In the case where the first layer 1a is formed by the liquid phase method, a nitrate containing each component element constituting the electrolyte material is used as a starting material, blended at a predetermined ratio, dissolved in distilled water, citric acid and EDTA. To produce a precursor. The powder obtained by calcining the precursor may be appropriately shaped and fired.

  In order to laminate and bond the first layer 1a and the second layer 1b, the material constituting one layer is appropriately formed, and the material constituting the other layer is superimposed on the surface of the formed body by coating or the like. What is necessary is just to shape. And the composite type solid electrolyte 1 can be formed by baking. Firing may be performed on the first layer 1a and the second layer 1b at a time, or once the one layer is formed, the other layer may be formed after firing once. .

  From the viewpoint of the simplicity of the configuration, the composite solid electrolyte 1 is preferably composed of only the first layer 1a and the second layer 1b as described above, but outside the first layer 1a and / or the second layer 1b. Or the layer which consists of another solid electrolyte material may be provided in the site | part between the 1st layer 1a and the 2nd layer 1b. Moreover, within the range in which each of the first layer 1a and the second layer 1b has the composition listed above, a mixture of two or more kinds of materials having different compositions, or a joined body of two or more kinds of layers having different compositions. It may be better. Furthermore, in the 1st layer 1a and the 2nd layer 1b, in addition to the material which has the composition enumerated above, if it is the 1st layer 1a, the methane tolerance of those materials, if it is the 2nd layer 1b As long as the proton conductivity of these materials is not impaired, another solid electrolyte material may be mixed.

[Proton conduction fuel cell]
Next, the proton conduction fuel cell 10 according to one embodiment of the present invention will be described.

  As shown in FIG. 1, a proton conducting fuel cell (hereinafter, simply referred to as a fuel cell) 10 according to an embodiment of the present invention is a composite having a first layer 1a and a second layer 1b as described above. A solid electrolyte 1 is provided. The composite solid electrolyte 1 has a single cell structure having an anode (fuel electrode) 2 on the surface on the first layer 1a side and a cathode (air electrode) 3 on the surface on the second layer 1b side. When the composite solid electrolyte 1 has proton conductivity, the single cell 10 functions as a proton conduction fuel cell.

  In the single cell 10, each of the anode 2 and the cathode 3 may be directly joined to the composite solid electrolyte 1, or any intermediate layer between the electrodes 2, 3 and the composite solid electrolyte 1. May be interposed. Moreover, the single cell 10 is normally used as a fuel cell in a state where a plurality of single cells 10 are appropriately stacked through separators. A current collector may be appropriately disposed between the separator and each of the electrodes 2 and 3.

  In the single cell 10, when power generation is performed while supplying methane as a fuel gas to the anode 2, the first layer 1 a of the composite solid electrolyte 1 comes into direct contact with methane. However, since the first layer 1a has high resistance to methane, the first layer 1a is not easily deteriorated even if power generation is performed using methane for a long time. On the other hand, the first layer 1a functions as a blocking layer of the second layer 1b against methane, and the second layer 1b does not substantially contact with methane. Therefore, even though the second layer 1b has low resistance to methane, the second layer 1b is unlikely to deteriorate even if long-time power generation using methane is performed in the single cell 10. On the other hand, since the second layer 1b has high proton conductivity, high power generation performance, that is, high electromotive force and high output density can be obtained in the single cell 10. And such high power generation performance is maintained over a long period of time by the blocking function with respect to methane by the first layer 1a. In particular, when the second layer 1b is formed thicker than the first layer 1a, high power generation performance is easily obtained. In addition, as fuel gas, what consists only of methane may be used, or gas which has methane as a main component and contains another component suitably, such as city gas, may be used.

  In addition, the first layer 1a plays a role of suppressing dissolution of Ni constituting the anode 2 in the second layer 1b. The anode 2 is in direct contact with the first layer 1a, not the second layer 1b, which causes a decrease in proton conduction due to solid solution of Ni. It functions as a blocking layer that prevents diffusion and reaching the second layer 1b. For this reason, the high proton conductivity of the second layer 1b is not hindered by the solid solution of Ni, and the relative increase in hole conduction is suppressed. Here, even if Ni is dissolved in the first layer 1a and the hole conduction of the first layer 1a is relatively increased, the increase in hole conduction is significant on the cathode side where the oxygen partial pressure is high. If the hole conduction of the second layer 1b on the side is suppressed, a high electromotive force can be obtained in the single cell 10 and the voltage efficiency can be increased.

  The degree of decrease in the voltage efficiency of the single cell 10 due to the increase in the percentage of hole conduction can be evaluated by, for example, an open circuit voltage (OCV). When the hole conduction ratio increases due to the solid solution of Ni in the composite solid electrolyte 1, the hole conduction acts as an electron leak, so the OCV decreases. It can be evaluated that the higher the OCV, the more the increase in the hole conduction ratio due to the solid solution of Ni is suppressed, and the higher the voltage efficiency.

  In the single cell 10, materials constituting the anode 2 and the cathode 3 are not particularly specified, and materials that can be used as an anode and a cathode of a general solid oxide fuel cell may be appropriately selected. Examples of the anode material and cathode material that can provide high power generation characteristics in combination with the material constituting the composite solid electrolyte 1 include the following.

  It is preferable to use a material containing Ni as the anode 2 bonded to the first layer 1a. As described above, the increase in the rate of hole conduction due to the solid solution of Ni in the composite solid electrolyte 1 is reduced by bonding the first layer 1a to the anode side surface of the second layer 1b. Can do. In particular, it is preferable to use Ni or a cermet of Ni as the anode 2 in that the anode overvoltage can be lowered. Ni constituting the cermet may be an alloy containing Ni as a main component in addition to pure Ni. Further, by adopting as the anode 2 a cermet using the first solid electrolyte material mentioned above as the solid electrolyte material constituting the first layer 1a as the ceramic material constituting the cermet, a particularly low anode overvoltage is obtained. Obtainable. This is considered to be because the electrode reaction at the anode 2 is likely to occur due to an increase in the number of three-phase interfaces where Ni, the first solid electrolyte material, and the fuel contact each other. Note that the material type and x, y values of the first solid electrolyte material constituting the cermet of the anode 2 and the first solid electrolyte material constituting the first layer 1a of the composite solid electrolyte 1 were the same. Or different. From the viewpoint of simplification of the configuration and prevention of reaction between the first solid electrolyte material and the anode 2, it is preferable to make them the same. The ratio of Ni to the electrolyte material constituting the cermet is preferably in the range of 4: 6 to 6: 4 by volume ratio.

The material is not particularly limited constituting the cathode 3 as cathode materials that provide excellent power generation characteristics (high power density, low cathodic _{overvoltage), Ba 0.5 Sr 0.5 Co 0.8} Fe 0. ₂ O _3-δ (BSCF; δ is the amount of oxygen vacancies). In BSCF, carbonate formation by methane cannot be ignored. However, here, since BSCF is used as the cathode 3 that does not come into contact with the fuel gas containing high-concentration methane, deterioration due to methane does not substantially occur. For the cathode 3, La _0.6 Sr _0.4 Co _0.2 Fe _0.8 O ₃ (LSCF) or LaCoO ₃ (LSC) -based materials often used in solid oxide fuel cells are also suitable. Can be used. The cathode 3 may be composed only of these materials, but in addition to these materials, a composite electrode in which about 20% by volume of a second solid electrolyte material constituting the second layer 1b of the proton conductive solid electrolyte 1 is mixed. Then, avoidance of peeling due to mismatch of thermal expansion coefficients of the second layer 1b and the cathode 3, and reduction of cathode overvoltage due to increase of the three-phase interface can be expected.

  In the fuel cell unit cell 10, even if the electrolyte layer is of a self-supporting membrane type, the anode 2 or the cathode 3 is used as a substrate, and the thin-film composite solid electrolyte 1 layer formed thinner than the thickness of the substrate is used. It may be a support film type supported by a substrate. From the viewpoint of reducing the electric resistance of the electrolyte layer, it is preferable to use a support membrane type that can thin the layer of the composite solid electrolyte 1. The anode is better than the cathode 3 because of its low electrical resistance, low current collection loss when it is made into a cell, close to optimum firing temperature, easy co-firing with electrolyte layer, high mechanical strength, etc. 2 is preferably the substrate. In this case, as shown in FIG. 1, the anode 2 is a substrate, and the first layer 1a and the second layer 1b of the composite solid electrolyte 1 and the cathode 3 are thinner on the surface than the anode 2 as the substrate. The layers may be stacked in this order.

  Proton conduction is dominant on the anode 2 side of the solid electrolyte material constituting the first layer 1a of the composite solid electrolyte 1 even in the temperature range exceeding 800 ° C. Therefore, the single cell 10 is preferably used at an operating temperature of 800 ° C. or lower at which hole conductivity is generated with a general proton conductor. On the other hand, even if the first layer 1a is a thin film even in a temperature range below 600 ° C., the resistance is small and sufficient power generation characteristics can be obtained. Thus, the single cell 10 can be used at an operating temperature of less than 600 ° C. In general, the single cell 10 is preferably used at a temperature of 400 ° C to 800 ° C.

[Comparison of solid electrolyte materials constituting the first layer]
The BaZrO ₃ -based materials (BZYb, etc.), SrZrO ₃ -based materials (SZY, etc.), CaZrO ₃ -based materials (CZI, etc.), LaScO ₃ -based materials (LSSc, etc.) listed above as the solid electrolyte materials constituting the first layer 1a ), LaYbO ₃ -based materials (LSYbIn, etc.) all have high methane resistance and high proton conductivity to some extent. Therefore, by joining the second layer 1b to form the composite solid electrolyte 1, high methane A solid electrolyte having both resistance and proton conductivity can be obtained. Further, by forming the proton conductive fuel cell single cell 10 using such a composite solid electrolyte 1, protons having excellent power generation characteristics and durability when generating power using methane as a fuel gas. It becomes a conduction fuel cell.

Among these materials, in particular, when BaZrO ₃ -based material, SrZrO ₃ -based material, CaZrO ₃ -based material, and LaYbO ₃ -based material are used as the first layer 1a, high methane resistance can be obtained. That is, in the single fuel cell 10, when power generation is performed for a long time using methane as a fuel gas, a high output voltage can be obtained even after long-time power generation.

Of the above four types, when BaZrO ₃ -based material, SrZrO ₃ -based material, and LaYbO ₃ -based material are used, the degree of decrease in output voltage with the passage of time during power generation using methane (output in the initial state) The amount of decrease in output voltage as a percentage of voltage) is high to a certain extent, but even if the output drops to some extent through power generation using methane due to the high electromotive force in the initial state before use for power generation, High output voltage can be maintained. Of these three types, BaZrO ₃ -based materials and SrZrO ₃ -based materials can be suitably used because the degree of decrease in output voltage due to power generation using methane is relatively small compared to LaYbO ₃ -based materials.

On the other hand, among the above four types, when a CaZrO ₃ system material is used, the value of electromotive force in the initial state is very low compared to BaZrO ₃ material, SrZrO ₃ system material, and LaYbO ₃ system material. Since it has high methane resistance, the degree of decrease in output voltage with the passage of time during power generation using methane is very small. Therefore, an output voltage close to the value in the initial state can be maintained over a long period during power generation. Therefore, when continuing the power generation over a particularly long time, the output voltage in the case of using CaZrO ₃ based material, compared with the output voltage in the case of using BaZrO ₃ based material, SrZrO ₃ based materials, the LaYbO ₃ based material Thus, even if the initial value is low, a reversal phenomenon that exceeds the output voltage of these three types may occur with time. Therefore, from the viewpoint of long-term durability, CaZrO ₃ -based material is most preferable among the four types.

It is considered that the high methane resistance of the CaZrO ₃ based material is due to the difficulty of diffusion of Ce atoms from the second layer 1b. As will be shown later as an example, in the composite solid electrolyte 1 after power generation using methane, when the distribution of Ce at the junction interface between the first layer 1a and the second layer 1b is confirmed, the first layer 1a is , BaZrO ₃ based material, SrZrO ₃ based material, if made of LASCO ₃ based materials, Ce atoms BaCeO ₃ based material or BaZrCeO ₃ based material constituting the second layer 1b is diffused into the first layer 1a, It is also distributed in the first layer 1a. Further, CeO ₂ is generated as a decomposition product. In contrast, when the first layer 1a is made of a CaZrO ₃ -based material, diffusion of Ce atoms from the second layer 1b hardly occurs. No formation of CeO ₂ occurs. Due to the diffusion of Ce atoms into the first layer 1a and the formation of CeO ₂ , the materials constituting the first layer 1a and the second layer 1b are denatured, causing the proton conductivity of the composite solid electrolyte 1 to decrease. By using a CaZrO ₃ -based material that is unlikely to cause these phenomena as the first layer 1a, even if power generation using methane is continued for a long time in the single cell 10, the output voltage decreases from the initial state. Hardly occurs, and high methane resistance is exhibited.

The reason why it is difficult for Ce atoms to diffuse from the second layer 1b when the CaZrO ₃ -based material is the first layer 1a can be explained as follows. As for Ba and Sr, both ZrO ₃ -based compounds (zirconate) and CeO ₃ -based compounds (selate) exist as stable compounds. Therefore, when a ZrO ₃ -based compound of Ba or Sr is present in the first layer 1a, if Ce diffuses from the second layer 1b, a CeO ₃ -based compound can be formed in the first layer 1a. it can. Therefore, the diffusion of Ce atoms from the second layer 1b to the first layer 1a easily proceeds. On the other hand, although Ca forms a stable ZrO ₃ -based compound, it does not exist stably as a CeO ₃ -based compound. Therefore, when a Ca ZrO ₃ -based compound is present in the first layer 1a, a stable compound cannot be formed even if Ce diffuses from the second layer 1b. Therefore, diffusion of Ce to the first layer 1a made of the CaZrO ₃ system material hardly occurs.

Next, paying attention to an increase in the rate of hole conduction due to Ni solid solution, as shown in a later example, in an initial state before use for power generation, BaZrO ₃ -based material, SrZrO ₃ -based material, LaScO ₃ When a system material, LaYbO ₃ system material is used as the first layer 1a, a significantly higher OCV value is obtained compared to the case where the first layer 1a is not provided. In other words, an increase in the rate of hole conduction due to solid solution of Ni from the anode 2 is suppressed to a small level. Even when a CaZrO ₃ -based material is used as the first layer 1a, the OCV value in the initial state is improved, although it is inferior to the above four types. The improvement in the OCV value is considered to be because the solid solution of Ni in the anode 2 in the solid electrolyte constituting the second layer 1b is suppressed by the presence of the first layer 1a as a blocking layer.

However, if power generation using methane as a fuel is performed for a long time, the OCV value decreases in the case of BaZrO ₃ -based materials, LaScO ₃ -based materials, and LaYbO ₃ -based materials. In particular, the decrease in the case of LaYbO ₃ -based material is remarkable. On the other hand, in the case of SrZrO ₃ -based materials and CaZrO ₃ -based materials, the degree of decrease in the OCV value can be suppressed even after power generation using methane as fuel. In particular, in the case of a CaZrO ₃ -based material, the decrease in the OCV value from the initial state is very small. This is considered to be due to the fact that the first layer 1a maintains a state in which solid solution of Ni into the second layer 1b can be highly suppressed even after power generation using methane as fuel.

As described above, when a CaZrO ₃ -based material is used as the material constituting the first layer 1a, even if long-term power generation using methane as fuel is performed, the second layer 1b is changed to the first layer 1a. The output voltage due to the diffusion of Ce atoms is unlikely to decrease, and the increase in the rate of hole conduction due to the solid solution of Ni from the anode 2 that appears as a decrease in OCV is unlikely to occur. Therefore, it is most preferable to use a CaZrO ₃ -based material among the groups listed above as the material constituting the first layer 1a.

  Hereinafter, the present invention will be described in detail using examples. The present invention is not limited to the following examples.

[Experiment 1: Evaluation of continuous power generation characteristics using methane]
First, in order to evaluate the methane resistance of the composite solid electrolyte, power generation using methane was performed in a single fuel cell, and the continuous power generation characteristics were evaluated.

(Sample preparation)
A composite solid electrolyte was produced by laminating the first layer and the second layer. First, BaCe _0.8 Y _0.2 O _3-δ (BCY) serving as the second layer was synthesized by a solid phase reaction method. Then, after calcination at 1300 ° C. for 10 hours and pulverization with a ball mill, BCY powder was obtained. The BCY powder was molded into a disk shape of φ20 and calcined at 1200 ° C. for 5 hours.

On the other hand, using the liquid phase method, BaZr _0.8 Yb _0.2 O _3-δ (BZYb), SrZr _0.9 Y _0.1 O _3-δ (SZY), CaZr _0.96 to be the first layer. In _0.04 O _3-δ (CZI), La _0.9 Sr _0.1 ScO _3-δ (LSSS), La _0.9 Sr _0.1 Yb _0.8 In _0.2 O _3-δ (LSYbIn ) Were synthesized respectively. Specifically, nitrates containing each component element were blended at a predetermined ratio and dissolved in distilled water. While stirring this at 300 ° C., citric acid and EDTA were added to synthesize a precursor. The obtained precursor was calcined at 900 ° C. for 10 hours to obtain each electrolyte material. The obtained electrolyte material was pulverized, and ethyl cellulose and diethylene glycol monobutyl ether were added to obtain a paste.

  Using a screen printing apparatus, the paste of the electrolyte material to be the first layer was applied to the BCY disk to be the second layer obtained above with a thickness of 5 μm. And sintering was performed at 1600 degreeC for 10 hours, and the composite type solid electrolyte which co-sintered the 2nd layer which consists of BCY and the 1st layer which consists of each electrolyte material was obtained. Hereinafter, the material configuration of the composite solid electrolyte is displayed in the form of “constituent material of the first layer / constituent material of the second layer” as “BZYb / BCY”. As a comparative example, a solid electrolyte was prepared in which only the second layer made of a BCY disk was formed without forming the first layer. This solid electrolyte is denoted as “BCY”.

Then, Ba _0.5 Sr _0.5 Co _0.8 Fe _0.2 O _3-δ (BSCF) is laminated as a cathode material on the surface on the second layer (BCY) side of the disk-shaped solid electrolyte, and 1150 Baked at ℃. Also, NiO and the same solid electrolyte material that constitutes the first layer of each composite solid electrolyte (BCY material for the “BCY” sample) are mixed at a volume ratio of 6: 4 to form a cermet, The anode material was laminated on the surface of the disk-shaped solid electrolyte on the first layer side. Then, Ni at the anode was reduced by hydrogen treatment at 600 ° C. In this way, a stack of fuel cell single cells was formed.

(Evaluation of power generation characteristics)
Electric power was generated using the single fuel cell formed as described above. At this time, 1.9% H ₂ O—CH ₄ was supplied to the anode, and 1.9% H ₂ O-21% O ₂ —N ₂ was supplied to the cathode. Under such conditions, the single fuel cell was held at 700 ° C. with a current of 2 mA applied, and the change in output voltage with time was observed.

(result)
FIG. 2 shows continuous power generation characteristics in power generation using methane, that is, changes with time in output voltage, for a fuel cell single cell using a solid electrolyte having each material structure. The discontinuities in the figure are due to the temporary interruption of power generation for detailed evaluation of fuel cell characteristics.

  In FIG. 2, first, attention is focused on the output voltage as an initial value when power generation is started. In the case where the first layer made of any material is provided, a voltage value close to or higher than the case where the solid electrolyte layer is made only of BCY is obtained. From this, it can be seen that each solid electrolyte material constituting the first layer has sufficient proton conductivity to constitute a proton conducting fuel cell.

  Moreover, in FIG. 2, when paying attention to the output voltage in the final stage of continuous power generation using each material configuration, in the case where the first layer made of any material is provided, the solid electrolyte is made only of BCY. High output voltage is maintained. This is because the solid electrolyte material constituting the first layer has high resistance to methane, and such a material having high resistance to methane is formed on the surface of the second layer made of BCY having low resistance to methane. By providing the first layer, it is shown that the first layer functions as a blocking layer for methane and protects the BCY of the second layer from contact with methane. In other words, the provision of the first layer makes it difficult for the BCY of the second layer to be deteriorated by methane, and the situation in which the high power generation characteristics exhibited by the BCY are drastically reduced by contact with methane is avoided.

Furthermore, when the output voltage in the end stage is compared for each material constituting the solid electrolyte, the voltage values are from the highest to the lowest in the following order.
BZYb / BCY → SZY / BCY → CZI / BCY → LSYbIn / BCY → LSSS / BCY → BCY

  In BZYb / BCY and SZY / BCY, a particularly high output voltage is obtained even after power generation using methane for a long time. This is because the initial value of the output voltage at the start of power generation is high. The contribution is large, and when attention is paid to the degree of decrease in the output voltage with respect to the initial value, it is not necessarily small as compared with other material configurations. On the other hand, CZI / BCY is inferior to BZYb / BCY and SZY / BCY as output values at the end of power generation (146 hours) in FIG. 2, but almost no decrease in output voltage from the initial value occurs. However, it is excellent in the degree of decrease in the output voltage with respect to the initial value. Therefore, if power generation is continued for a longer time than the time during which power generation is performed in FIG. 2 (146 hours), a reverse phenomenon occurs in which the output voltage of CZI / BCY exceeds the output voltage of BZYb / BCY or SZY / BCY. Probability is high. That is, it can be said that CZI / BCY is a material particularly excellent in long-term durability in power generation using methane.

[Experiment 2: Evaluation of the state of the layer interface]
Next, in order to clarify the origin of the difference in methane resistance for each constituent material of the first layer observed in Experiment 1, the state of the layer interface was evaluated for the composite solid electrolyte after power generation.

(Sample preparation)
In the above experiment 1, the solid electrolyte was cut in the vicinity of the center of the disk for each fuel cell after the power generation using the long-term methane shown in FIG.

(Observation of layer interface)
About each cross-section sample, the structure and element distribution of the interface of the 1st layer and the 2nd layer were observed. That is, the structure of the layer interface was observed using a scanning electron microscope (SEM). Moreover, the distribution at the interface of each element constituting the first layer and the second layer was observed by energy dispersive X-ray spectroscopy (SEM-EDX) using SEM. And distribution was evaluated especially paying attention to Ce.

  In addition, for each sample of BZYb / BCY, SZY / BCY, CZI / BCY, and LSSc / BCY, X-ray diffraction (with respect to the solid electrolyte after power generation using methane for a long time shown in FIG. XRD) measurements were made.

(result)
3 and 4 show the state of the interface after power generation using methane for the composite solid electrolyte of each material configuration. In each figure, the SEM image (left) and the Ce distribution (right) are shown for the same region. In the SEM image, the range occupied by each layer is displayed.

  In each sample of BZYb / BCY, SZY / BCY, CZI / BCY, and LSYbIn / BCY shown in FIGS. 3A to 3C and FIG. 4A, in the SEM image, the first layer and the second layer A clear boundary is observed between them. In other words, after sintering, a composite solid electrolyte having a laminated structure in which the first layer and the second layer are joined at a clear interface has been obtained, and even after a long period of power generation using methane, It is confirmed that such an interface structure is maintained.

On the other hand, paying attention to the distribution of Ce in each sample, in the case of BZYb / BCY in FIG. 3A and SZY / BCY in FIG. 3B, Ce is confirmed not only in the BCY layer but also in the SEM. Beyond the interface, the BZYb and SZY of the first layer are also widely distributed at substantially the same concentration as in the BCY layer. That is, through power generation using methane, Ce in BCY constituting the second layer is diffused into the first layer made of BZYb or SZY. For BZYb / BCY and SZY / BCY, the formation of CeO ₂ phase was confirmed in the results of XRD measurement. The LSYbIn / BCY in FIG. 4 (a) is not as remarkable as in the case of BZYb / BCY and SZY / BCY, but in the Ce distribution image, the distribution of Ce is observed in the first layer, and from the second layer. It is confirmed that the diffusion of Ce is occurring.

On the other hand, in the case of CZI / BCY in FIG. 3C, Ce is distributed at a high concentration in the region on the BCY layer side of the interface confirmed by SEM. Ce is also distributed in the CZI layer, but its concentration is lower than in the BCY layer. That is, it can be seen that the diffusion of Ce across the layer interface is suppressed as compared with the cases of BZYb / BCY and SZY / BCY. In the case of CZI / BCY, no CeO ₂ phase was observed in the XRD measurement.

From the above results, in BZYb / BCY, SZY / BCY, and LSYbIn / BCY, due to the remarkable diffusion of Ce at the layer interface and the generation of CeO ₂ as a decomposition product, the durability of FIG. As seen in the test, when the power generation using methane is performed for a long time, the deterioration and the output voltage drop are significantly suppressed as compared with the case of using BCY alone, but the entire composite solid electrolyte is deteriorated. However, the output voltage is considered to decrease. On the other hand, in CZI / BCY, since the diffusion of Ce from BCY to CZI and the generation of CeO ₂ phase are suppressed, power generation using methane for a long time as seen in the endurance test of FIG. Even if it passes through, it is thought that a composite type solid electrolyte is easy to maintain an initial state, and the fall of an output voltage hardly arises. Thus, the difficulty of Ce diffusion is considered to be the origin of the high methane resistance of CZI / BCY. The reason why Ce does not easily diffuse at the CZI / BCY interface is presumed to be because Ca does not form a stable CeO ₃ -based compound unlike Ba and Sr as described above.

In the case of LSSc / BCY in FIG. 4B, a flat boundary surface is not formed between the BCY layer and the LSSc layer in the SEM image, and the boundary between both layers is not clear. Such a structure having no clear interface is seen from the initial state in which power generation is performed, and the interdiffusion has already occurred between the BCY layer and the LSSc layer due to the firing in forming the composite solid electrolyte. It is thought that there is. Corresponding to such disturbance of the interface structure, the Ce distribution does not have a clear boundary. As shown in the measurement result of the continuous power generation characteristic in FIG. 2, the disturbance of the structure and element distribution at the interface is such that the output voltage is low from the initial state, and further, the output voltage is decreased from the initial state while the power generation is continued. Can be associated with the behavior that the degree of is higher than in the case of other composite solid electrolytes. Also in XRD, the formation of CeO ₂ phase was confirmed.

[Experiment 3: Evaluation of contribution of proton conduction]
Finally, in order to evaluate the degree of decrease in proton conductivity and relative increase in hole conductivity due to solid solution of Ni in the composite solid electrolyte, OCV measurement was performed in a single fuel cell.

(Sample preparation)
Each fuel cell single cell whose continuous power generation characteristics were evaluated in Experiment 1 was also used as a sample for OCV measurement.

(OCV measurement)
For each sample, OCV measurement was performed in the initial state before the evaluation of the continuous power generation characteristics shown in FIG. 2 and in the state after long-time power generation using methane. The duration of power generation was 96 hours for BCY, 144 hours for LSYbIn / BCY, and 168 hours for the other samples.

In the OCV measurement, 1.9% H ₂ O—CH ₄ was supplied to the anode and 1.9% H ₂ O-21% O ₂ —N ₂ was supplied to the cathode at 700 ° C. The current-voltage characteristics were measured. The voltage value when no current was flowing was recorded as OCV.

(result)
FIG. 5 shows OCV values in the initial state and the state after power generation in the case of using a solid electrolyte having each material structure.

  According to FIG. 5, in any of the composite type solid electrolytes, the OCV value is increased in the initial state as compared with the case where the solid electrolyte consisting only of BCY is used. This is because Ni contained in the anode is dissolved in BCY at the time of heating for forming the anode, and a decrease in proton transport number due to an increase in the hole conduction ratio is caused on the surface of the second layer made of BCY. It shows that it is suppressed by providing a first layer made of various solid electrolyte materials and contacting the anode with the first layer. In particular, in the case of LSSc / BCY, BZYb / BCY, SZY / BCY, such an effect is remarkable.

  On the other hand, when the OCV value after long-time power generation using methane is compared with the value in the initial state, the value is lowered after power generation in any of the composite solid electrolytes. In particular, the decrease is significant in LSYbIn / BCY. On the other hand, in SZY / BCY and CZI / BCY, the degree of decrease in the OCV value upon power generation is small. In these two types of composite solid electrolytes, it is interpreted that the state in which the solid solution of Ni in BCY is suppressed is highly maintained even after power generation. In particular, in CZI / BCY, the degree of decrease in the OCV value is very small, and in addition to the high methane resistance confirmed in the methane resistance test of Experiment 1, a material that can be particularly suitably used for power generation using methane. It can be said that.

  The present invention is not limited to the above-described embodiments and examples, and various modifications can be made without departing from the spirit of the present invention.

1 Proton conductive solid electrolyte (composite solid electrolyte)
1a 1st layer 1b 2nd layer 2 Anode 3 Cathode 10 Proton conduction fuel cell (single cell)

Claims (9)

A first layer made of a proton conductive solid electrolyte material selected from a BaZrO ₃ system, a SrZrO ₃ system, a CaZrO ₃ system, a LaScO ₃ system, and a LaYbO ₃ system;
A proton conductive solid electrolyte, characterized in that a second layer made of a BaCeO ₃ -based or BaCeZrO ₃ -based proton conductive solid electrolyte material is joined. 2. The proton conductive solid electrolyte according to claim 1, wherein the first layer is made of a proton conductive solid electrolyte material selected from a BaZrO ₃ system, a SrZrO ₃ system, and a CaZrO ₃ system. The proton conductive solid electrolyte according to claim 1, wherein the first layer is made of a CaZrO ₃ -based proton conductive solid electrolyte material. 4. The proton conductive solid electrolyte according to claim 1, wherein the second layer is made of a BaCeO ₃ -based proton conductive solid electrolyte material. 5. The BaZrO ₃ -based, SrZrO ₃ -based, CaZrO ₃ -based, LaScO ₃ -based, LaYbO ₃ -based proton conductive solid electrolyte materials are BaZr _1-x Yb _x O _3-δ , SrZr _1-x Y _x O _{3, respectively. -δ, CaZr 1-x In x} O 3-δ, La 1-x Sr x ScO 3-δ, La 1-x Sr x Yb 1-y In y O 3-δ claims, characterized in that consisting of 5. The proton conductive solid electrolyte according to any one of 1 to 4.
However, 0 <x ≦ 0.2, 0 <y <1, and δ is the amount of oxygen vacancies.   The proton conductive solid electrolyte according to any one of claims 1 to 5, wherein the second layer is thicker than the first layer. The proton conductive solid electrolyte according to any one of claims 1 to 6,
An anode provided on the first layer side of the proton conductive solid electrolyte;
And a cathode provided on the second layer side of the proton conductive solid electrolyte.   The proton conductive fuel cell according to claim 7, wherein the anode is made of a material containing Ni. The anode as a substrate,
The proton conduction according to claim 7 or 8, wherein the first layer, the second layer, and the cathode are provided on the surface of the substrate in this order as layers thinner than the substrate, respectively. Fuel cell.