JP7190602B1 - Electrochemical cell and its use - Google Patents

Abstract

A technique for suppressing deterioration of a hydrogen electrode in an electrochemical cell having a hydrogen electrode containing nickel particles is provided. An electrochemical cell disclosed herein includes a hydrogen electrode, an air electrode, and a solid electrolyte layer disposed between the hydrogen electrode and the air electrode. The hydrogen electrode contains nickel particles and oxide ion-conducting ceramic particles. Here, the average particle size of the nickel particles based on electron microscope observation is 30 nm to 80 nm. In the hydrogen electrode, the nickel particles and the ceramic particles exist in a mutually dispersed state. [Selection drawing] Fig. 4

Description

The present disclosure relates to electrochemical cells and their uses.

An example of an electrochemical cell is a Solid Oxide Electrolysis Cell (SOEC). The SOEC has, for example, a hydrogen electrode (fuel electrode), an air electrode, and a solid electrolyte layer arranged between the hydrogen electrode and the air electrode. The hydrogen electrode, the solid electrolyte layer, and the air electrode constitute a laminated structure that produces an electrochemical reaction. In SOEC, for example, the hydrogen electrode can function as the cathode and the air electrode as the anode. According to SOEC, for example, hydrogen gas can be generated from water (steam). For example, when water vapor is supplied to the hydrogen electrode having the laminated structure that produces the above-described electrochemical reaction and electricity is supplied in this state, the supplied water vapor is decomposed. At this time, oxygen gas can be generated at the air electrode and hydrogen gas can be generated at the hydrogen electrode. In addition, the reverse reaction of SOEC can be used for power generation, for example. The reverse reaction of SOEC can be used, for example, in Solid Oxide Fuel Cells (SOFCs).

Regarding the SOEC, Patent Documents 1 and 2 disclose a hydrogen electrode containing nickel particles. The hydrogen electrode (fuel electrode) disclosed in Patent Document 1 includes an electrode layer, mesh-like wiring formed on the surface layer of the electrode layer, and a current collector. It has been proposed that the electrode layer be formed of a mixed layer of a mixed conductive oxide and an aluminum-based oxide carrying nickel particles on its surface. According to this document, the catalytic activity and durability of the hydrogen electrode are improved, and it is said that the output performance of the electrochemical cell can be improved. On the other hand, the hydrogen electrode disclosed in Patent Literature 2 includes a current collection layer and a catalyst layer having mutually different structures. This document proposes a structure in which Ni-containing particles are dispersed and supported in a porous body of an electron-ion mixed conductive oxide for a catalyst layer. It is described that deterioration of the hydrogen electrode is suppressed with such a configuration.

As a method for producing nickel particles, for example, a vapor phase method and a liquid phase method (eg, wet reduction method) can be used. An example of a method for producing nickel particles using a liquid phase method is the production method of Patent Document 3. It is stated that this method can be used to produce metal nanoparticles (for example, nickel nanoparticles) with reduced variation in particle size.

JP-A-2009-64640 WO2020/196236 JP 2021-155836 A

By the way, in an electrochemical cell including a hydrogen electrode, an air electrode, and a solid electrolyte layer, it is required to improve the durability of the hydrogen electrode against energization.

Accordingly, the present invention has been made in view of the above circumstances, and an object thereof is to provide a technique for suppressing deterioration of a hydrogen electrode in an electrochemical cell having a hydrogen electrode containing nickel particles.

An electrochemical cell disclosed herein includes a hydrogen electrode, a cathode, and a solid electrolyte layer disposed between the hydrogen electrode and the cathode. The hydrogen electrode contains nickel particles and oxide ion-conducting ceramic particles. Here, the average particle size of the nickel particles based on electron microscope observation is 30 nm to 80 nm. In the hydrogen electrode, the nickel particles and the ceramic particles exist in a mutually dispersed state.

In the electrochemical cell having such a configuration, the nickel particles have an average particle size of 30 nm to 80 nm. By having an average particle size within this range, aggregation of the nickel particles can be suppressed during energization. Also, in the hydrogen electrode of such an electric cell, nickel particles and ceramic particles are present in a mutually dispersed state. In other words, the hydrogen electrode is in a state in which aggregation of nickel particles is suppressed. In the electrochemical cell disclosed herein, deterioration of the hydrogen electrode is suppressed.

In a preferred embodiment of the electrochemical cell disclosed herein, the mixing ratio of the nickel particles and the ceramic particles (nickel particles: ceramic particles) is 30:70 to 70:30. With such a configuration, both particles are easily dispersed in each other. Therefore, the effect of suppressing deterioration of the hydrogen electrode can be improved.

In another preferred embodiment of the electrochemical cell disclosed herein, the ceramic particles are zirconium oxide. According to such a configuration, the effect of the technology disclosed herein can be favorably exhibited in an electrochemical cell containing zirconium oxide as ceramic particles in the hydrogen electrode. In this case, the zirconium oxide may be yttria-stabilized zirconia.

In another preferred aspect of the electrochemical cell disclosed herein, the nickel particles have an average particle size of 30 nm to 50 nm. With such a configuration, the effect of suppressing deterioration of the hydrogen electrode can be better achieved. The nickel particles may be nickel particles produced using a liquid phase method.

In another preferred embodiment of the electrochemical cell disclosed herein, the hydrogen electrode is the cathode and the air electrode is the anode. In this case the electrochemical cell can operate as an SOEC. Therefore, with such a configuration, it is possible to provide an SOEC in which deterioration of the hydrogen electrode is suppressed.

Also provided herein is a hydrogen production apparatus. A hydrogen production apparatus disclosed herein includes the electrochemical cell described above. In the electrochemical cell, deterioration of the hydrogen electrode is suppressed. Therefore, a hydrogen production apparatus with improved hydrogen production efficiency can be provided.

Also provided herein is a method for producing hydrogen. In the production method disclosed herein, hydrogen is produced using the above-described hydrogen production apparatus. Hydrogen can be efficiently produced by using the hydrogen production apparatus.

1 is a cross-sectional view of an electrochemical cell 1; FIG. 2 is a schematic cross-sectional view of the hydrogen electrode 10. FIG. 1 is a schematic diagram of a hydrogen production device 100. FIG. It is a cross-sectional SEM observation image of the hydrogen electrode in the test example. It is a cross-sectional SEM observation image of the hydrogen electrode in the test example.

Preferred embodiments of the technology disclosed herein are described below. Matters other than those specifically referred to in this specification, and matters necessary for implementing the technology disclosed herein, can be grasped as design matters by those skilled in the art based on the prior art in the relevant field. The content of the technology disclosed here can be implemented based on the content disclosed in this specification and common general knowledge in the field. Further, in the drawings below, members and portions having the same function are denoted by the same reference numerals, and redundant description may be omitted or simplified. Also, in this specification, when the numerical range is described as "A to B (A and B are arbitrary numbers)", "A or more and B or less (including the range above A but below B)" shall mean.

As used herein, the term "electrochemical cell" refers to a device that can convert chemical energy into electrical energy, and a device that can convert electrical energy into chemical energy, and includes an anode, a cathode, and an electrolyte. As used herein, the term "anode" refers to an electrode from which electrons flow to an external circuit. As used herein, the term "cathode" refers to an electrode into which electrons flow from an external circuit. An example of an electrochemical cell is an electrolytic cell. In an electrolytic cell, for example, electrical energy can be applied to water (eg, water vapor) to cause a chemical reaction to form hydrogen and oxygen from the water. The electrolyte includes, for example, a SOEC (Solid Oxide Electrolysis Cell) having a solid electrolyte as the electrolyte. The following embodiments will be described by taking as an example the case where the technique disclosed here is applied to an SOEC.

1. Electrochemical Cell FIG. 1 is a cross-sectional view of an electrochemical cell 1 . FIG. 1 shows the laminated structure of an electrochemical cell 1 . As shown in FIG. 1, the electrochemical cell 1 includes a hydrogen electrode 10, an air electrode 14, and a solid electrolyte layer 12. In this embodiment the electrochemical cell 1 is a SOEC. Here, the hydrogen electrode 10 is the cathode and the air electrode 14 is the anode.

<Hydrogen electrode 10>
The hydrogen electrode 10 can have the function of supplying relatively high concentrations of oxide ions to one surface of the solid electrolyte layer 12 . The hydrogen electrode 10 can, for example, generate oxide ions and hydrogen gas from high-temperature water vapor and conduct the oxide ions toward the solid electrolyte layer 12 . Therefore, in the electrochemical cell 1, the hydrogen electrode 10 is supplied with a gas (for example, water vapor) that is a source of oxide ions. Considering the efficient supply of such gas, the hydrogen electrode 10 is preferably a porous body. The porosity of the hydrogen electrode 10 is preferably set to, for example, 5% to 40% by volume (preferably 20% to 30% by volume). In this embodiment, the hydrogen electrode 10 has a single layer structure with uniform porosity, but in other embodiments, it may have a multi-layer structure with two or more layers having mutually different porosities. Although the thickness of the hydrogen electrode 10 is not particularly limited, it is preferably 1 μm to 100 μm (eg, 5 μm to 50 μm).

The hydrogen electrode 10 contains nickel particles and oxygen ion conductive ceramic particles. Nickel particles are, for example, particles containing at least 95% or more, preferably 97% or more, more preferably 99% or more of nickel element. Elements other than nickel that can be contained in the nickel particles are unavoidable impurities that can be mixed in the production of the nickel particles, and are not particularly limited.

By the way, nickel is less expensive than other metals and can exhibit high reaction activity, so it can be preferably used as a constituent material for the hydrogen electrode of an electrochemical cell. The present inventor wanted to suppress deterioration of the hydrogen electrode in an electrochemical cell having a hydrogen electrode containing nickel particles. For example, in SOEC, nickel particles tend to agglomerate and be unevenly distributed, or to move in the direction opposite to the solid electrolyte layer as the energization time elapses. The inventor of the present invention has studied a configuration of the hydrogen electrode that suppresses such a tendency, and has wished to suppress the deterioration of the hydrogen electrode.

The nickel particles have an average particle size of 30 nm to 80 nm. As a result, it is possible to realize a preferable reaction area in the nickel particles, and to suppress aggregation of the particles due to energization. Therefore, the effect of suppressing deterioration of the hydrogen electrode 10 can be realized. The smaller the average particle size of the nickel particles, the larger the reaction area during energization. However, if the average particle size is too small, it tends to be difficult to produce nickel particles. From this point of view as well, the average particle size is preferably set within the above range. On the other hand, the larger the average particle size, the easier it is for the nickel particles to agglomerate during energization. From this point of view, the average particle size of the nickel particles is more preferably 70 nm or less, and even more preferably 60 nm or less. From the viewpoint of better realizing the effects of the technology disclosed herein, it is particularly preferable that the nickel particles have an average particle size of 30 nm to 50 nm.

As used herein, "average particle size" refers to the average particle size (SEM size) based on electron microscopic observation. For example, using a field emission-scanning electron microscope (FE-SEM), a predetermined number (eg, 50 or more) particles contained in the particles to be measured (eg, nickel particles) Observe and draw a minimum area rectangle that circumscribes each particle image. Then, the length of the long side of the rectangle drawn for each particle image is obtained, and the arithmetic mean value thereof is taken as the average particle diameter of the particles. Commercially available image analysis software can be used to obtain the average particle size.

Nickel particles having an average particle diameter of 30 nm to 80 nm may be used, and the production method is not particularly limited. Although not particularly limited, it is preferable to use nickel particles produced using a liquid phase method (wet reduction method) from the viewpoint of suitably realizing the effects of the technology disclosed herein. Nickel particles produced using a liquid phase method are preferred because they can have a smaller variation in average particle size than nickel particles produced using other production methods (eg, vapor phase method, etc.). As the nickel particles, commercially available nickel particles having the above average particle size may be used.

Ceramic particles can be, for example, metal oxides used in this type of application. Examples of such metal oxides include zirconium oxide and cerium oxide. Zirconium oxides can include, for example, zirconia and stabilized zirconia. Stabilized zirconia includes _one or _more stabilizers selected from the group consisting of _Y2O3 , _{Sc2O3 ,} Yb2O3 _{, Gd2O3 ,} CaO _, MgO, and CeO2. Solid solution zirconia is mentioned. Among them, yttria-stabilized zirconia in which Y ₂ O ₃ is solid-dissolved can be preferably used. Cerium oxides can include, for example, ceria and doped ceria. Doped ceria includes ceria in which one or more oxides selected from the group consisting of Sm ₂ O ₃ , Gd ₂ O ₃ , Y ₂ O ₃ and the like are solid-dissolved. The average particle size of the ceramic particles is not particularly limited as long as the effects of the technology disclosed herein are exhibited. The average particle size can be, for example, 0.1 μm to 5 μm (preferably about 0.2 μm to 2 μm).

The mixing ratio of the nickel particles and the ceramic particles can be one factor that affects the function of the hydrogen electrode and the dispersibility of the nickel particles in the hydrogen electrode. Here, the mixing ratio (nickel particles: ceramic particles) is preferably 30:70 to 70:30. This facilitates mutual dispersion of both particles. Therefore, the effect of suppressing deterioration of the hydrogen electrode can be improved. If the mixed amount of the nickel particles is too large, for example, the nickel particles cannot be sufficiently dispersed, and the nickel particles tend to agglomerate with each other during energization. On the other hand, if the mixed amount of nickel particles is too small, for example, the electrical conductivity may decrease, and the function of the hydrogen electrode may deteriorate. From this point of view, the mixing ratio (nickel particles: ceramic particles) is preferably set within the above range, or preferably set to 35:65 to 65:35 (for example, about 60:40).

FIG. 2 is a schematic cross-sectional view of the hydrogen electrode 10. As shown in FIG. FIG. 2 shows the cross-sectional structure of the hydrogen electrode 10 and part of the solid electrolyte layer 12 . As shown in FIG. 2, in the hydrogen electrode 10, the nickel particles 10a and the ceramic particles 10b exist in a mutually dispersed state. In this specification, "a state in which the nickel particles and the ceramic particles are mutually dispersed" means, for example, that the nickel particles and the ceramic particles are not agglomerated. The dispersed state of the nickel particles and the ceramic particles can be checked, for example, by scanning a cross section along the thickness direction of the hydrogen electrode 10 (the direction indicated by arrow Y in FIGS. 1 and 2) with a scanning electron microscope (SEM). It can be evaluated using an image obtained by observation. For example, SEM observation images are acquired in a plurality of (for example, 10 or more, preferably 20 or more, more preferably 30 or more) fields of view randomly selected from the cross section of the hydrogen electrode. The cross-sectional SEM observation image is binarized to distinguish between nickel particles and ceramic particles, and the number of each particle is counted. When neither nickel particle aggregates nor ceramic particle aggregates are observed in each cross-sectional SEM observation image, it is evaluated that the nickel particles and the ceramic particles are mutually dispersed. Aggregates can be, for example, aggregates of 20 or more (preferably 10 or more, more preferably 5 or more) nickel particles or ceramic particles.

<Solid electrolyte layer 12>
The solid electrolyte layer 12 may have a function of conducting oxide ions. As shown in FIG. 1, the solid electrolyte layer 12 is formed on the top surface of the hydrogen electrode 10 . The solid electrolyte layer 12 can, for example, conduct oxide ions generated at the hydrogen electrode 10 to the air electrode 14 . Further, the solid electrolyte layer 12 can function as a separator separating the hydrogen electrode 10 and the air electrode 14 from each other. From this point of view, the solid electrolyte layer 12 is preferably a dense layer. The thickness of the solid electrolyte layer 12 is not particularly limited, and is preferably 1 μm to 30 μm.

Solid electrolyte layer 12 may be composed of a solid electrolyte. The solid electrolyte can be, for example, a ceramic material with oxide ion conductivity. As such a solid electrolyte, any solid electrolyte used for this type of application can be used without particular limitation. For example, zirconium (Zr), cerium (Ce), magnesium (Mg), scandium (Sc), titanium (Ti), aluminum (Al), yttrium (Y), calcium (Ca), gadolinium (Gd), samarium (Sm ), barium (Ba), lanthanum (La), strontium (Sr), gallium (Ga), bismuth (Bi), niobium (Nb), and tungsten (W). Among them, zirconium oxides such as zirconia and stabilized zirconia; cerium oxides such as ceria and doped ceria; are preferably used. The solid electrolyte can be composed of one or two or more solid electrolytes. Stabilized zirconia and doped ceria are as described above.

<Air electrode 14>
The air electrode 14 may have the function of oxidizing oxide ions. The air electrode 14 receives, for example, oxide ions generated at the hydrogen electrode 10 through the solid electrolyte layer 12 . This oxide ion can be oxidized at the air electrode 14 to become oxygen gas. Considering the efficient release of such gas, the air electrode 14 is preferably a porous body. The porosity of the air electrode 14 is preferably set to, for example, 5% to 40% by volume (preferably 20% to 30% by volume). Although the thickness of the air electrode 14 is not particularly limited, it is preferably 5 μm to 100 μm.

As a constituent material of the air electrode 14, a material used for this type of application can be used without particular limitation. Perovskite-type oxides containing La, Sr, and Mn, such as (La, Sr) MnO ₃ (for example, La _0.8 Sr _0.2 MnO ₃ ; hereinafter referred to as LSM); (La, Sr) CoO ₃ (for example, La _0.6 Sr _0.4 CoO ₃ ; hereinafter referred to as LSC), (La, Sr) (Co, Fe) O ₃ (for example, La _0.6 Sr _0.4 Co _0.2 Fe ₀ and perovskite oxides containing La, Sr, and Co, such as _{.8O 3} (hereinafter referred to as LSCF). Cathode 14 may comprise one or more materials.

[Other forms]
The electrochemical cell 1 in the above embodiment was an SOEC comprising a hydrogen electrode 10, an air electrode 14, and a solid electrolyte layer 12. However, it is not limited to this. The technology disclosed here can also be applied to an aspect in which a plurality of electrochemical cells 1 are stacked. Moreover, a reaction inhibiting layer may be provided between the solid electrolyte layer 12 and the air electrode 14 as necessary. As a material for forming the reaction inhibiting layer, the same materials as those used in conventionally known SOEC reaction inhibiting layers can be used without particular limitation.

<Manufacturing method of electrochemical cell 1>
The manufacturing method of the electrochemical cell 1 can include, for example, a green sheet preparation process (step 1), a green sheet lamination process (step 2), and a firing process (step 3).

In the green sheet production process (step 1), for example, green sheets for each layer (hydrogen electrode 10, solid electrolyte layer 12, air electrode 14) constituting the electrochemical cell 1 are produced. This process will be described below by taking as an example the case of producing the green sheet of the hydrogen electrode 10 . As a method for producing the green sheets of the layers other than the hydrogen electrode 10, any method used in the production of this type of electrochemical cell can be used without particular limitation. Therefore, the description may be omitted.

In the production of the green sheet of the hydrogen electrode 10, first, for example, a slurry (including ink and paste) containing nickel particles and ceramic particles as described above, and optionally a binder and a dispersion medium is prepared. ) is prepared. The combined amount of nickel particles and ceramic particles may be, for example, 50% by mass to 70% by mass when the entire composition is 100% by mass.

A dispersion medium is not particularly limited. Dispersion media used in this type of application can be appropriately selected and used. Examples of dispersion media include alcohol-based dispersion media such as methanol, ethanol, m-propanol, i-propanol, and n-butanol; petroleum-based dispersion media such as toluene, coal, and xylene; terpineol (α-terpineol, etc.); Tolls; methyl ethyl ketone; water; and the like. A mixed dispersion medium of these may be used. The content of the dispersion medium is, for example, 20% by mass to 50% by mass when the entire composition is 100% by mass.

The binder is not particularly limited, but may be, for example, a resin material that has thermoplasticity and is burnt off by a firing process (for example, heating and firing at 200° C. or higher). By adding a binder, the formability of the green sheet can be improved. Binders include, for example, natural polymer compounds such as polyvinyl butyral, carrageenan and xanthan gum; cellulose polymer compounds such as ethyl cellulose and carboxymethyl cellulose; acrylic resins; epoxy resins; phenol resins; amine resins; ; and the like. The blending amount of the binder may be, for example, 1% by mass to 20% by mass when the entire composition is 100% by mass.

Additives used in this type of application may be added to the composition as long as they do not impair the effects of the technology disclosed herein. Examples of additives include dispersants, plasticizers, antifoaming agents, release agents, antioxidants, thickeners, pore-forming materials (pore-forming materials), and the like. The amount of the additive compounded may be, for example, 1% by mass to 10% by mass when the composition as a whole is 100% by mass.

A stirring and mixing device such as a ball mill, mixer, disper, or kneader may be used to prepare the composition. For example, nickel particles, ceramic particles, a binder, a dispersion medium, and an additive are put into an arbitrary stirring and mixing device, and stirred and mixed for a predetermined time (for example, 1 hour to 2 hours) to homogenize. compositions can be prepared. Although not particularly limited, the viscosity of the composition is, for example, 5 Pa s to 100 Pa s (25° C.-20 rpm), preferably 10 Pa s to 50 Pa s, in consideration of the blade coating method described later. . Viscosity can be measured, for example, using a commercially available viscometer.

Then, for example, using the composition prepared as described above, a hydrogen electrode green sheet is produced. The hydrogen electrode green sheet can be produced by conventionally known methods such as blade coating method, screen printing method, roll compaction molding method, injection molding method, and dip coating method.

In the green sheet lamination step (step 2), for example, each layer of green sheets is laminated. For example, by stacking the green sheets of the hydrogen electrode 10, the solid electrolyte layer 12, and the air electrode 14 in this order, a laminate that serves as a precursor of the electrochemical cell 1 is produced. The lamination method is not particularly limited. For example, green sheets for each layer can be prepared in advance and laminated.

Alternatively, a paste made of a composition for forming a solid electrolyte layer is applied onto the hydrogen electrode green sheet by screen printing or the like, and dried to form a laminate of the hydrogen electrode green sheet and the solid electrolyte layer green sheet ( 1st laminated body) is produced. Next, a composition for forming an air electrode is applied onto the solid electrolyte layer green sheet of the first laminate and dried to form a second laminate of the hydrogen electrode green sheet, the solid electrolyte layer green sheet, and the air electrode green sheet. A laminate (that is, a laminate serving as the precursor) may be produced. In this case, the first laminate may be fired before applying the composition for forming the air electrode. Such firing may be performed, for example, under a temperature condition of 1000° C. to 1500° C. in a reducing atmosphere. Also, the firing time can be, for example, 1 hour to 5 hours.

In the firing step (step 3), for example, the laminate that is the precursor of the electrochemical cell 1 is fired. For example, the second laminate produced in the green sheet lamination step (step 2) is fired. Such firing may be performed, for example, under a temperature condition of 1000° C. to 1500° C. in a reducing atmosphere. Also, the firing time can be, for example, 1 hour to 5 hours.

<Hydrogen production device 100>
The electrochemical cell 1 produced as described above can be used in a hydrogen production apparatus. FIG. 3 is a schematic diagram of the hydrogen production device 100. As shown in FIG. As shown, the hydrogen production device 100 includes a power supply 30 and a main body 40. As shown in FIG. In this embodiment, the body portion 40 includes an electrochemical cell 1 , a hydrogen electrode side channel 42 and an air electrode side channel 44 . Power supply 30 may be a DC power supply. As shown in FIG. 3, the positive terminal of power supply 30 is electrically connected to hydrogen electrode 10 (cathode). A negative terminal of the power supply 30 is electrically connected to the air electrode 14 (anode). It should be noted that the hydrogen production device 100 can be manufactured by a conventional method for constructing a hydrogen production device. Since such a manufacturing method does not characterize the technology disclosed herein, the description thereof is omitted here.

[Other forms]
In the above embodiment, the hydrogen production apparatus provided with one set of electrochemical cells 1 has been described. However, it is not limited to this. In another embodiment, for example, the hydrogen production device may comprise a plurality of electrochemical cells 1 in the form of a stack. Moreover, a separator may be appropriately provided as necessary.

<Method for producing hydrogen>
Hydrogen can be produced using the hydrogen production apparatus 100 shown in FIG. Such a method for producing hydrogen can include, for example, an electrolysis step (step 11) and a hydrogen recovery step (step 12). In the electrolysis step (step 11), for example, the raw material gas is electrolyzed. The source gas may be hot water vapor. In this embodiment, first, the power supply 30 is turned on to start the hydrogen production device 100 . As a result, current flows in the direction from the air electrode 14 to the hydrogen electrode 10 . Next, the raw material gas is injected from the introduction port 41 in the hydrogen electrode side channel 42 . This raw material gas is electrolyzed at the hydrogen electrode 10 into hydrogen (H ₂ ) and oxide ions (O ²⁻ ). In the hydrogen recovery step (step 12), for example, hydrogen is recovered. Hydrogen may be a decomposition product of the feed gas in the electrolysis step (step 11). In this embodiment, hydrogen is recovered at recovery port 43 shown in FIG. The oxide ions pass through the solid electrolyte layer 12 and are oxidized at the air electrode 14 to become oxygen (O ₂ ) and electrons (e ⁻ ). This oxygen can be discharged to the outside from the discharge port 45 in the air electrode side channel 44 .

[Test example]
Test examples relating to the technology disclosed herein will be described below. It should be noted that the following test examples are not intended to limit the technology disclosed herein. Unless otherwise specified, "%" in the following test examples is based on mass.

<<Preparation of hydrogen electrode>>
- Example 1 to Example 5 -
In an environment of 25 ° C., 10 kg to 20 kg of nickel acetate tetrahydrate as a raw material compound and 40 L to 60 L of oleylamine as a reducing agent are put into a manufacturing apparatus (IH reactor manufactured by Nippon Electric Heat Co., Ltd.), A solution was obtained by stirring at a stirring speed of 300 rpm. In order to obtain nickel particles having mutually different average particle sizes in each example, the blending amount of nickel acetate tetrahydrate and the blending amount of oleylamine were appropriately changed within the above ranges. The solution was heated while nitrogen gas was blown into the solution. Once the temperature of the solution reached about 140°C, this temperature was held for about 120 minutes. The solution was then heated until the temperature was about 200°C. The heating rate of such heating was 3° C./min to 10° C./min. Once the solution reached about 200°C, this temperature was maintained for 30-120 minutes. The solution was then heated further until the temperature reached 230°C-250°C. The heating rate of such heating was 3° C./min to 5° C./min. Once the solution reached the desired temperature, this temperature was maintained for about 10 minutes. Blowing of nitrogen gas was stopped while this temperature was maintained, and oxygen gas was blown into the solution for about 10 minutes.

Blowing of oxygen gas was stopped and nitrogen gas was started to be blown into the solution. The flow rate of nitrogen gas at this time was 40 L/min to 60 L/min. Heating of the solution was then stopped, and cooling water was supplied to the cooling pipe of the manufacturing apparatus. The solution was collected when the temperature of the solution reached about 50°C. The average quench rate was between 2°C/min and 7°C/min. In order to obtain nickel particles having mutually different average particle diameters in each example, various conditions such as the above temperature conditions, time conditions, and speed conditions were appropriately changed within the above ranges. Then, the collected solution was allowed to stand, and the precipitate was collected. The precipitate was washed with hexane and dried to obtain the nickel particles of Examples 1-5. It was confirmed by X-ray diffraction that the obtained particles were metallic nickel. Using FE-SEM, the average particle size of the resulting nickel particles was measured. The results are shown in the corresponding columns of Table 1.

The nickel particles obtained as described above and 8% yttria-stabilized zirconia particles (8% YSZ, average particle size: 0.5 μm) were mixed at a mass ratio of 60:40. Next, the mixture, a pore-forming material (carbon component), a binder (polyvinyl butyral; PVB), a plasticizer, and a dispersion medium (a mixture of coal and toluene) were mixed in order at 100:10:15:5:1. A paste-like composition for forming a hydrogen electrode was prepared by kneading at a mass ratio of . Next, this composition was applied onto a carrier sheet by a doctor blade method (see the X direction in FIG. 1) and dried repeatedly to produce a hydrogen electrode green sheet with a thickness of 0.3 mm to 0.5 mm.

Next, a solid electrolyte layer was formed. Here, 8% YSZ particles, a binder (ethyl cellulose; EC), and a dispersion medium (terpineol; TE) are kneaded at a mass ratio of 100:5:50 to obtain a composition for forming a solid electrolyte layer. rice field. Then, this composition was screen-printed on the hydrogen electrode green sheet and dried to form a solid electrolyte layer having a thickness of about 10 μm.

Next, a reaction inhibiting layer was formed. Here, first, 10% gadolinium-doped ceria particles (10% GDC, average particle diameter: 0.5 μm) as a reaction inhibiting material, a binder (EC), and a dispersion medium (TE) were mixed at a ratio of 100:5:60. A composition for forming a reaction inhibiting layer was prepared by kneading at a mass ratio of . This composition was screen-printed on the solid electrolyte layer and dried to form a reaction inhibiting layer having a thickness of about 10 μm.

A circular green sheet was cut out from the laminated green sheet thus prepared, and fired in a reducing atmosphere of 97% nitrogen and 3% hydrogen at a temperature of about 1350°C.

Next, an air electrode was formed on the fired body obtained as described above. Here, first, La _0.6 Sr _0.4 Co _0.2 Fe _0.8 O ₃ particles (LSCF, average particle size: 0.5 μm) as an air electrode material, a binder (EC), a dispersion medium (TE) were kneaded at a mass ratio of 100:5:50 to prepare a paste-like composition for forming an air electrode. This composition was then screen-printed onto the reaction inhibiting layer of the fired body and dried to form a dry film. An electrochemical cell of Example 1 was obtained by sintering the dry film together with the sintered body in the above reducing atmosphere at a temperature of 1000°C.

-Example 6-
8% YSZ particles (average particle size: 0.5 μm) were calcined in the air at a temperature of 1200 to 1300° C. for 2 hours. Thus, a zirconia porous body was produced. Next, the zirconia porous body was impregnated with an aqueous solution of nickel nitrate. Next, the zirconia porous body was sintered in the air at a temperature of 800° C. for 1 hour to support nickel oxide on the zirconia porous body. Next, the nickel oxide-supported zirconia porous body is fired at a temperature of 800° C. in the reducing atmosphere for 1 hour, thereby reducing the nickel oxide, allowing the nickel particles to be supported on the zirconia porous body, and producing a hydrogen electrode. got An electrochemical cell of this example was obtained in the same manner as in Example 1, except that the hydrogen electrode produced as described above was used. The average particle size of the nickel particles supported on the zirconia porous body is shown in the corresponding column of Table 1. This average particle size is measured by SEM observation of the zirconia porous body supporting nickel particles.

-Example 7-
A hydrogen electrode was obtained by supporting nickel particles on a zirconia porous body. First, a slurry was prepared by mixing nickel particles, alcohol, and a dispersant. A zirconia porous body was impregnated with this slurry. After that, the zirconia porous body was dried, and after drying, it was calcined at 900° C. for 1 hour to support it. An electrochemical cell of this example was obtained in the same manner as in Example 1, except that this hydrogen electrode was used. The nickel particles of this example were prepared using the same materials and procedures as in Example 1. The zirconia porous body of this example was produced using the same materials and procedures as in Example 6.

-Example 8-
As the nickel particles, nickel particles (average particle size: 120 nm) produced using a vapor phase method were used. The electrochemical cell of this example was obtained in the same manner as in Example 1 except for the above.

-Example 9-
Nickel oxide particles (average particle size: 200 nm) were used instead of nickel particles. The electrochemical cell of this example was obtained in the same manner as in Example 1 except for the above. In this example, nickel oxide particles were reduced to nickel particles by firing in a reducing atmosphere.

<<Dispersion evaluation with nickel particles>>
Here, the state of dispersion with nickel particles in the hydrogen electrode of the electrochemical cell of each example was evaluated. First, an SEM observation image (observation magnification: 20,000 times) of a cross section along the thickness direction of the hydrogen electrode was obtained for the electrochemical cell of each example. 4 and 5 show examples of cross-sectional SEM observation images of the hydrogen electrode. 4 is a cross-sectional SEM observation image of the hydrogen electrode of Example 3. FIG. 5 is a cross-sectional SEM observation image of the hydrogen electrode of Example 4. FIG. Note that the scale bar in the figure indicates 2 μm.

Next, nickel particles were extracted from the cross-sectional SEM observation image using image software, and the state of dispersion in the hydrogen electrode was evaluated. The results are shown in the corresponding columns of Table 1. Evaluation of the state of dispersion is as follows.
"Y (dispersed (no aggregates))": Aggregates of 20 or more nickel particles (primary particles) and aggregates of 20 or more ceramic particles (primary particles) are both observed. it wasn't.
"N (Not in a dispersed state (with aggregates))": Aggregates of 20 or more nickel particles (primary particles) or aggregates of 20 or more ceramic particles (primary particles) were observed. In Examples 6 and 7, the zirconia porous bodies were used as described above. Therefore, no evaluation was performed here. "-" in the corresponding column of Table 1 indicates non-implementation of evaluation.

《Degradation evaluation》
Here, the electrochemical cell of each example was operated under the following conditions to evaluate the degree of deterioration of the hydrogen electrode.
Cathode: Hydrogen electrode Anode: Air electrode Hydrogen electrode supply gas: Water vapor Operating temperature: 700°C
Operating time: 1000 hours After operation, the voltage V1 (V) was measured at a current density of 0.5 A/cm ² . The resistance increase rate (%) of the electrochemical cell was obtained based on the voltage V1 (V) and the voltage V0 (V) of the electrochemical cell previously obtained before operation. This resistance increase rate (%) was used as an indicator of the degree of deterioration of the hydrogen electrode of the electrochemical cell. The evaluation results are shown in the corresponding column of Table 1.

Evaluation of the degree of deterioration of the hydrogen electrode is as follows.
"E (excellent deterioration suppression ability)" ... resistance increase rate of 0.3% or less "G (good deterioration prevention ability)" ... resistance increase rate of over 0.3% and 0.5% or less "P ( Poor ability to suppress deterioration)” … Resistance increase rate exceeding 0.5% In this evaluation test, deterioration of the hydrogen electrode is suppressed when the resistance increase rate of the electrochemical cell is 0.5% or less. is evaluated. It is evaluated that the hydrogen electrode is degraded when the resistance increase rate is greater than 0.5%.

As noted above, the hydrogen electrodes of the electrochemical cells of Examples 1-9 included nickel particles and oxide ion conductive ceramic particles. Of these, in the electrochemical cells of Examples 1 to 3, the average particle size of the nickel particles based on electron microscope observation is 30 nm to 80 nm. In the hydrogen electrodes of these electrochemical cells, nickel particles and ceramic particles are present in a mutually dispersed state. As representatively shown in FIGS. 4 and 5, in Example 3, nickel particles and ceramic particles are observed to be mutually dispersed, but in Example 4, aggregation of nickel particles is observed. . As shown in Table 1, in the electrochemical cells of Examples 1 to 3, deterioration of the hydrogen electrodes containing nickel particles was suppressed.

Specific examples of the technology disclosed herein have been described above, but these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and changes of the specific examples illustrated above.

REFERENCE SIGNS LIST 1 electrochemical cell 10 hydrogen electrode 12 solid electrolyte layer 14 air electrode 30 power supply 40 main body 41 inlet 42 hydrogen electrode side channel 43 recovery port 44 air electrode side channel 45 outlet 100 hydrogen production device

Claims (9)

An electrochemical cell comprising a hydrogen electrode, an air electrode, and a solid electrolyte layer conducting oxide ions disposed between the hydrogen electrode and the air electrode,
The hydrogen electrode contains nickel particles and oxide ion conductive ceramic particles having an average particle size of 0.1 μm to 2 μm based on electron microscope observation ,
Here, the average particle size of the nickel particles based on electron microscope observation is 30 nm to 80 nm,
At the hydrogen electrode,
The nickel particles and the ceramic particles are present in a mutually dispersed state ,
An electrochemical cell , wherein the mixing ratio of the nickel particles and the ceramic particles (nickel particles: ceramic particles) is 30:70 to 70:30 . An electrochemical cell comprising a hydrogen electrode, an air electrode, and a solid electrolyte layer conducting oxide ions disposed between the hydrogen electrode and the air electrode,
The hydrogen electrode contains nickel particles and oxide ion conductive ceramic particles having an average particle size of 0.1 μm to 2 μm based on electron microscope observation,
Here, the average particle size of the nickel particles based on electron microscope observation is 30 nm to 80 nm,
In the hydrogen electrode, the nickel particles and the ceramic particles are present in a mutually dispersed state, and the electron microscope images in ten or more fields randomly sampled from the cross section of the hydrogen electrode show that the nickel particles are An electrochemical cell in which neither an aggregate of 20 or more nickel particles nor an aggregate of 20 or more ceramic particles is observed. An electrochemical cell comprising a hydrogen electrode, an air electrode, and a solid electrolyte layer conducting oxide ions disposed between the hydrogen electrode and the air electrode,
The hydrogen electrode contains nickel particles and oxide ion conductive ceramic particles having an average particle size of 0.1 μm to 2 μm based on electron microscope observation,
Here, the average particle size of the nickel particles based on electron microscope observation is 30 nm to 80 nm,
In the hydrogen electrode, the nickel particles and the ceramic particles are present in a mutually dispersed state,
The ceramic particles are cerium oxide or Y ₂ O. ₃ , Yb ₂ O. ₃ , Gd ₂ O. ₃ , CaO, MgO, or CeO ₂ is a zirconium oxide in which is dissolved zirconia. An electrochemical cell according to any preceding claim, wherein the ceramic particles are zirconium oxide. 5. The electrochemical cell of claim 4 , wherein said zirconium oxide is yttria stabilized zirconia. The electrochemical cell according to any one of claims 1 to 5 , wherein the nickel particles have an average particle size of 30 nm to 50 nm. An electrochemical cell according to any preceding claim, wherein the hydrogen electrode is the cathode and the air electrode is the anode. A hydrogen production apparatus comprising the electrochemical cell according to claim 7 . A method for producing hydrogen, comprising producing hydrogen using the hydrogen production apparatus according to claim 8 .

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