Electrochemical cell

Abstract

This electrochemical cell (10) comprises: a support layer (11); an intermediate layer (12) located on the support layer (11); a hydrogen electrode (13) located on the intermediate layer (12); an electrolyte (14); and an oxygen electrode (16). The support layer (11) is composed of YSZ and Ni. The hydrogen electrode (13) is composed of a ceria oxide having a rare earth element added thereto, and Ni. The intermediate layer (12) is composed of a solid solution of YSZ and a ceria oxide having a rare earth element added thereto, and Ni.

Description

electrochemical cell

[0001] The present invention relates to electrochemical cells.

[0002] An anode-supported fuel cell is known as an example of an electrochemical cell (see, for example, Patent Document 1). The anode-supported fuel cell includes a support layer, a hydrogen electrode disposed on the support layer, an oxygen electrode, and an electrolyte disposed between the hydrogen electrode and the oxygen electrode.

[0003] The support layer can be made of YSZ (yttria-stabilized zirconia) and Ni (nickel), and the hydrogen electrode can be made of a ceria-based oxide containing a rare earth element and Ni. The Ni contained in the hydrogen electrode and the support layer exists in the form of NiO in an oxidizing atmosphere.

[0004] JP 2017-123231 A

[0005] When the support layer and the hydrogen electrode are exposed to a reducing atmosphere, the NiO contained in the support layer and the hydrogen electrode is reduced to Ni, causing a volume change in each of the support layer and the hydrogen electrode. ２ ) has a large expansion amount in a reducing atmosphere, whereas the zirconia (ZrO ２ ) has a relatively small expansion rate in a reducing atmosphere, so a difference in expansion rate occurs between the hydrogen electrode and the support layer in a reducing atmosphere. When the operation is repeatedly started and stopped under this condition, stress accumulates in the hydrogen electrode, causing cracks.

[0006] An object of the present invention is to provide an electrochemical cell capable of suppressing cracks in the hydrogen electrode.

[0007] The electrochemical cell according to the present invention includes a support layer, an intermediate layer disposed on the support layer, a hydrogen electrode disposed on the intermediate layer, an oxygen electrode, and an electrolyte disposed between the hydrogen electrode and the oxygen electrode. The support layer is composed of yttria-stabilized zirconia and nickel. The hydrogen electrode is composed of a ceria-based oxide doped with a rare earth element and nickel. The intermediate layer is composed of a solid solution of yttria-stabilized zirconia and a ceria-based oxide doped with a rare earth element and nickel.

[0008] According to the present invention, it is possible to provide an electrochemical cell that can suppress cracks in the hydrogen electrode.

[0009] FIG. 1 is a cross-sectional view of a fuel cell.

[0010] (Fuel Cell 10) The fuel cell 10 is a so-called anode-supported fuel cell, and includes a support layer 11, an intermediate layer 12, a hydrogen electrode 13, an electrolyte 14, a reaction prevention layer 15, and an oxygen electrode 16.

[0011] [Support Layer 11] The support layer 11 supports the intermediate layer 12. The shape of the support layer 11 is not particularly limited, and it can be formed into, for example, a plate shape, a hollow plate shape, a cylinder shape, or the like.

[0012] The support layer 11 is made of a porous material having electron conductivity. Specifically, the support layer 11 contains YSZ (yttria-stabilized zirconia) and Ni (nickel). The YSZ contains 3 mol % to 10 mol % of Y. ２ O ３ (Yttria) stabilized ZrO ２ Ni becomes metallic Ni in a reducing atmosphere to which fuel gas is supplied, and becomes NiO in an oxidizing atmosphere to which no fuel gas is supplied.

[0013] The YSZ content in the support layer 11 may be 25 mol % or more and 55 mol % or less, and the Ni content in the support layer 11 may be 45 mol % or more and 75 mol % or less in terms of NiO.

[0014] The respective contents of YSZ and Ni in the support layer 11 are obtained by line analysis using atomic concentration profiles, i.e., element mapping using an EPMA (Electron Probe Micro Analyzer). Specifically, concentration distribution data for each element is obtained by performing line analysis in the thickness direction using an EPMA on a cross section along the thickness direction. Note that EPMA is a concept that includes EDS (Energy Dispersive x-ray spectroscopy).

[0015] The porosity of the support layer 11 can be, for example, 10% to 50%. In this specification, the porosity is the ratio of the area of ​​the gas phase to the total area of ​​the solid phase and the gas phase when a cross section is observed using a scanning electron microscope (SEM). The thickness of the support layer 11 can be, for example, 50 μm to 1 mm.

[0016] [Intermediate Layer 12] The intermediate layer 12 is disposed on the support layer 11. The intermediate layer 12 is disposed between the support layer 11 and the hydrogen electrode 13.

[0017] The intermediate layer 12 is made of a porous material having electronic and ionic conductivity. Specifically, the intermediate layer 12 contains a solid solution of YSZ and a ceria-based oxide to which a rare earth element has been added, and Ni. The solid solution refers to a state in which the YSZ and the ceria-based oxide to which a rare earth element has been added are dissolved together to form a uniform solid phase.

[0018] When the support layer 11 and the hydrogen electrode 13 are exposed to a reducing atmosphere, the NiO contained in the support layer 11 and the hydrogen electrode 13 is reduced to Ni, causing a volume change in each of the support layer 11 and the hydrogen electrode 13. In addition, the CeO ２ The expansion amount of ZrO in the support layer 11 is large in a reducing atmosphere. ２ Since the expansion amount of the hydrogen electrode 13 is relatively small in a reducing atmosphere, a difference in the amount of expansion occurs between the hydrogen electrode 13 and the support layer 11 in a reducing atmosphere. If the fuel cell 10 is repeatedly started and stopped under this condition, stress accumulated in the hydrogen electrode 13 is likely to cause cracks.

[0019] Therefore, the intermediate layer 12 according to this embodiment contains both YSZ, which is the constituent material of the support layer 11, and a ceria-based oxide to which a rare earth element has been added, which is the constituent material of the hydrogen electrode 13 described below. The intermediate layer 12 functions as a buffer layer that buffers the difference in the amount of expansion between the hydrogen electrode 13 and the support layer 11, thereby suppressing the accumulation of stress in the hydrogen electrode 13 compared to when the support layer 11 and the hydrogen electrode 13 are directly connected. This makes it possible to suppress the occurrence of cracks in the hydrogen electrode 13.

[0020] The intermediate layer 12 is a region between the support layer 11 and the hydrogen electrode 13, in which a solid solution of YSZ and a ceria-based oxide to which a rare earth element is added exists. Examples of ceria-based oxides to which a rare earth element is added include, but are not limited to, gadolinium-doped ceria (GDC), samarium-doped ceria (SDC), and yttrium-doped ceria (YDC). GDC is CeO doped with 5 mol % to 20 mol % of Gd (gadolinium) oxide. ２ Ni becomes metallic Ni in a reducing atmosphere to which a fuel gas is supplied, and becomes NiO in an oxidizing atmosphere to which no fuel gas is supplied.

[0021] The YSZ content in the intermediate layer 12 can be 15 mol % or more and 35 mol % or less. The rare earth element-doped ceria-based oxide content in the intermediate layer 12 can be 15 mol % or more and 35 mol % or less. The Ni content in the intermediate layer 12 can be 35 mol % or more and 65 mol % or less in terms of NiO. The respective contents of YSZ, rare earth element-doped ceria-based oxide, and Ni in the support layer 11 are obtained by line analysis using the above-mentioned atomic concentration profile.

[0022] The thickness of the intermediate layer 12 can be, for example, 1 μm or more and 50 μm or less. The thickness of the intermediate layer 12 is preferably 20 μm or less. This can prevent the ion conduction paths in the intermediate layer 12 from being broken, thereby preventing a decrease in the initial performance of the fuel cell 10. The thickness of the intermediate layer 12 is also preferably 3 μm or more. This can further prevent cracks from occurring in the hydrogen electrode 13. Therefore, by setting the thickness of the intermediate layer 12 to 3 μm or more and 20 μm or less, it is possible to ensure the initial performance of the fuel cell 10 while further preventing cracks.

[0023] The thickness of the intermediate layer 12 is obtained by observing a cross section of the intermediate layer 12 along the thickness direction at 1000x magnification using an FE-SEM and arithmetically averaging the thicknesses of the intermediate layer 12 at five points randomly selected from the observed image. The thickness direction is the direction perpendicular to the hydrogen electrode side surface of the electrolyte 14.

[0024] The porosity of the intermediate layer 12 can be, for example, 10% or more and 50% or less.

[0025] [Hydrogen electrode 13] The hydrogen electrode 13 is disposed on the intermediate layer 12. The hydrogen electrode 13 is disposed between the intermediate layer 12 and the electrolyte 14. A fuel gas is supplied to the hydrogen electrode 13 via the support layer 11 and the intermediate layer 12. An electrode reaction represented by the following formula (1) occurs in the hydrogen electrode 13.

[0026] H ２ +O ２－ →H ２ O + 2e － …(1)

[0027] The hydrogen electrode 13 is made of a porous material having electronic and ionic conductivity. Specifically, the hydrogen electrode 13 contains a ceria-based oxide doped with a rare earth element and Ni. Examples of ceria-based oxides doped with a rare earth element include, but are not limited to, GDC, SDC, and YDC. GDC is CeO doped with 5 mol % to 20 mol % of Gd (gadolinium) oxide. ２ Ceria (ceria) can be used. The rare earth element-doped ceria-based oxide contained in the hydrogen electrode 13 may be the same as or different from the rare earth element-doped ceria-based oxide contained in the intermediate layer 12. Ni becomes metallic Ni in a reducing atmosphere where fuel gas is supplied, and becomes NiO in an oxidizing atmosphere where fuel gas is not supplied. As described above, the hydrogen electrode 13 contracts and expands in response to the reduction and oxidation of Ni. However, as described above, the volume change of the hydrogen electrode 13 is absorbed by the intermediate layer 12, thereby suppressing the occurrence of cracks in the hydrogen electrode 13.

[0028] The content of the ceria-based oxide to which a rare earth element has been added in the hydrogen electrode 13 can be 35 mol % or more and 65 mol % or less. The content of Ni in the hydrogen electrode 13 can be 35 mol % or more and 65 mol % or less in terms of NiO. The contents of the ceria-based oxide to which a rare earth element has been added and Ni in the hydrogen electrode 13 can be obtained by line analysis using the above-mentioned atomic concentration profile.

[0029] The porosity of the hydrogen electrode 13 can be, for example, 10% to 50%. The thickness of the hydrogen electrode 13 can be, for example, 5 μm to 0.1 mm.

[0030] [Electrolyte 14] The electrolyte 14 is disposed on the hydrogen electrode 13. The electrolyte 14 is disposed between the hydrogen electrode 13 and the oxygen electrode 16. In this embodiment, since the fuel cell 10 is provided with a reaction prevention layer 15, the electrolyte 14 is sandwiched between the hydrogen electrode 13 and the reaction prevention layer 15.

[0031] The electrolyte 14 is made of a dense material that has ionic conductivity but no electronic conductivity. ２ O ３ , CeO ２ , Sc ２ O ３ , Yb ２ O ３ ZrO stabilized with ２ Ya, Y ２ O ３ , Sm ２ O ３ , Gd ２ O ３ etc. doped CeO ２ Alternatively, the electrolyte 14 may be made of lanthanum gallate or a lanthanum gallate-type perovskite structure oxide in which part of the lanthanum or gallium in lanthanum gallate is substituted with strontium, calcium, barium, magnesium, aluminum, indium, cobalt, iron, nickel, copper, or the like. The electrolyte 14 may be made of one type of electrolyte material, or may be made of two or more types of electrolyte materials.

[0032] The porosity of the electrolyte 14 may be, for example, 0% or more and 7% or less. The thickness of the electrolyte 14 may be, for example, 3 μm or more and 50 μm or less. The electrolyte 14 may have a single-layer structure or a multi-layer structure.

[0033] [Reaction prevention layer 15] The reaction prevention layer 15 is disposed on the electrolyte 14. The reaction prevention layer 15 is disposed between the electrolyte 14 and the oxygen electrode 16. The reaction prevention layer 15 is provided to prevent the constituent materials of the electrolyte 14 and the oxygen electrode 16 from reacting with each other to form a reaction layer with high electrical resistance.

[0034] The reaction prevention layer 15 is made of an ion-conductive material, such as ceria doped with an oxide of a rare earth element such as Gd, Sm, or Y.

[0035] The porosity of the reaction prevention layer 15 can be, for example, 0.1% or more and 50% or less, and the thickness of the reaction prevention layer 15 can be, for example, 1 μm or more and 50 μm or less.

[0036] [Oxygen Electrode 16] The oxygen electrode 16 is disposed on the reaction prevention layer 15. A gas containing oxygen (e.g., air) is supplied to the oxygen electrode 16. In the oxygen electrode 16, an electrode reaction represented by the following formula (2) occurs.

[0037] (1 / 2)・O ２ +2e － →O ２－ …(2)

[0038] The oxygen electrode 16 is made of a porous material having electron conductivity, for example, LSCF=(La, Sr)(Co, Fe)O ３ (lanthanum strontium cobalt ferrite), LSF = (La,Sr)FeO ３ (lanthanum strontium ferrite), LNF = La(Ni,Fe)O ３ (lanthanum nickel ferrite), LSC = (La,Sr)CoO ３ (lanthanum strontium cobaltite), etc.

[0039] The porosity of the oxygen electrode 16 can be, for example, 10% to 50%. The thickness of the oxygen electrode 16 can be, for example, 10 μm to 100 μm.

[0040] (Modifications of the Embodiment) Although the embodiment of the present invention has been described above, the present invention is not limited to these, and various modifications are possible without departing from the spirit of the present invention.

[0041] [Modification 1] In the above embodiment, a so-called anode-supported fuel cell has been described as an example of a fuel cell, but the electrochemical cell is not limited to this. The present invention can also be applied to an electrochemical cell in which a hydrogen electrode and an oxygen electrode are disposed on either side of an electrolyte layer.

[0042] An electrochemical cell is a general term for an element in which a pair of electrodes is arranged so that an electromotive force is generated from an overall oxidation-reduction reaction in order to convert electrical energy into chemical energy, and an element for converting chemical energy into electrical energy.

[0043] Examples of electrochemical cells include anode-supported fuel cells, horizontally striped fuel cells, vertically striped fuel cells, flat plate fuel cells, cylindrical fuel cells, and electrolysis cells that generate hydrogen by utilizing the electrolysis reaction of water. ２－ (oxygen ion) was used as the carrier, but OH － (hydroxide ions) or protons may be used as carriers.

[0044] [Modification 2] In the above embodiment, the fuel cell 10 is provided with the reaction prevention layer 15, but the reaction prevention layer 15 may not be provided.

[0045] Examples of the electrolytic cell according to the present invention will be described below, but the present invention is not limited to the examples described below.

[0046] (Preparation of Examples 1 to 7) Electrolytic cells according to Examples 1 to 7 were prepared as follows.

[0047] First, a support layer slurry, which was a mixture of YSZ powder, NiO powder, a binder, a pore-forming agent, a plasticizer, a dispersion medium, and a solvent, was formed into a sheet to prepare a support layer compact.

[0048] Next, an intermediate layer paste prepared by mixing YSZ powder, GDC powder, NiO powder, binder, pore-forming agent, plasticizer, dispersion medium, and solvent was printed on the support layer molded body to form an intermediate layer molded body. In this case, the thickness of the intermediate layer for each of Examples 1 to 7 was adjusted by changing the printing thickness of the intermediate layer paste, as shown in Table 1.

[0049] Next, a hydrogen electrode paste prepared by mixing GDC powder, NiO powder, a binder, a pore-forming agent, a plasticizer, a dispersion medium, and a solvent was printed on the intermediate layer compact to form a hydrogen electrode compact.

[0050] Next, an electrolyte paste prepared by mixing YSZ powder, a binder, a plasticizer, a dispersion medium, and a solvent was printed on the hydrogen electrode compact to form an electrolyte compact.

[0051] Next, a paste for the reaction prevention layer, which was prepared by mixing GDC powder, a binder, and a solvent, was printed on the electrolyte compact to form a reaction prevention layer compact.

[0052] A laminate of the support layer compact, intermediate layer compact, hydrogen electrode compact, electrolyte compact, and reaction prevention layer compact was fired (1300°C, 5 hours) to produce a fired body consisting of the support layer, intermediate layer, hydrogen electrode, electrolyte, and reaction prevention layer.

[0053] An oxygen electrode paste prepared by mixing LSCF powder, a binder, and a solvent was printed on the reaction prevention layer to form an oxygen electrode compact.

[0054] Next, the cathode molded body was fired (1050° C., 2 hours) to obtain the electrolytic cells according to Examples 1 to 7.

[0055] (Preparation of Comparative Example 1) An electrolytic cell according to Comparative Example 1 was prepared by the same steps as those of Examples 1 to 7, except that no intermediate layer was formed.

[0056] (Thermal Cycle Test) A first thermal cycle test was conducted on the electrolytic cells according to Examples 1 to 7 and Comparative Example 1. Specifically, while supplying Ar gas and hydrogen gas (4% relative to Ar gas) to the hydrogen electrode, one cycle was repeated 10 times, where one cycle consisted of increasing the temperature from room temperature to 750°C over 2 hours and then decreasing the temperature from 750°C to room temperature over 4 hours.

[0057] Thereafter, the cross section of the hydrogen electrode was observed with a FE-SEM (field emission scanning electron microscope) to check for the presence or absence of cracks.

[0058] Subsequently, a second thermal cycle test was carried out on the electrolytic cells according to Examples 1 to 7 and Comparative Example 1. Specifically, while supplying Ar gas and hydrogen gas (4% relative to Ar gas) to the hydrogen electrode, one cycle was repeated 10 times, in which the temperature was increased from room temperature to 850°C over 2 hours and then decreased from 850°C to room temperature over 4 hours.

[0059] Thereafter, the cross section of the hydrogen electrode was observed with an FE-SEM to check for the presence or absence of cracks.

[0060] In Table 1, samples that developed cracks in the first thermal cycle test were evaluated as "x", samples that developed cracks for the first time in the second thermal cycle test were evaluated as "◯", and samples that did not develop cracks in the second thermal cycle test were evaluated as "◎".

[0061] (Initial Performance Evaluation Test) An initial performance evaluation test was carried out on the electrolytic cells according to Examples 1 to 7 and Comparative Example 1. Specifically, a mixed gas of water vapor and hydrogen gas (mixing ratio 50:50) was supplied to the hydrogen electrode, and air was supplied to the oxygen electrode, while a current of 0.5 A / cm ２ The electrolysis voltage was measured when the current value was swept.

[0062] The increase rates of the electrolysis voltages of Examples 1 to 7 were calculated relative to the electrolysis voltage of Comparative Example 1. In Table 1, the increase rate of the electrolysis voltage of less than 1% was evaluated as "Good", and the increase rate of the electrolysis voltage of 1% or more was evaluated as "Good".

[0063] As shown in Table 1, in Examples 1 to 7, in which an intermediate layer was provided between the support layer and the hydrogen electrode, the occurrence of cracks in the hydrogen electrode was suppressed. This result was obtained because the intermediate layer contained both YSZ, which was the constituent material of the support layer, and ceria-based oxide with added rare earth elements, which was the constituent material of the hydrogen electrode, and thus the intermediate layer was able to buffer the difference in the amount of expansion between the hydrogen electrode and the support layer during thermal cycling.

[0064] Furthermore, in Examples 1 to 6, in which the thickness of the intermediate layer was set to 20 μm or less, it was possible to prevent the initial performance from decreasing compared to Example 7. Such results were obtained because it was possible to prevent the ion conduction paths in the intermediate layer from being broken.

[0065] Furthermore, in Examples 2 to 7, in which the thickness of the intermediate layer was set to 3 μm or more, the occurrence of cracks in the hydrogen electrode was further suppressed compared to Example 1.

[0066] REFERENCE SIGNS LIST 10 Fuel cell 11 Support layer 12 Intermediate layer 13 Hydrogen electrode 14 Electrolyte 15 Reaction prevention layer 16 Oxygen electrode

Claims

1. A support layer having electronic conductivity; an intermediate layer disposed on the support layer; a hydrogen electrode disposed on the intermediate layer; An oxygen electrode; an electrolyte disposed between the hydrogen electrode and the oxygen electrode; Equipped with The support layer comprises yttria-stabilized zirconia and nickel; The hydrogen electrode contains a ceria-based oxide to which a rare earth element is added and nickel, The intermediate layer contains a solid solution of yttria-stabilized zirconia and a ceria-based oxide to which a rare earth element is added, and nickel. Electrochemical cell.

2. The thickness of the intermediate layer is 20 μm or less.

10. The electrochemical cell of claim 1.

3. The thickness of the intermediate layer is 3 μm or more.

3. An electrochemical cell according to claim 1 or 2.