JP6872592B2 - Electrolytes for electrochemical cells and electrochemical cells - Google Patents

Description

The present invention relates to an electrolyte for an electrochemical cell and an electrochemical cell.

The electrochemical cell has a pair of electrodes and an electrolyte. The electrolyte is located between the pair of electrodes. Specifically, a pair of electrodes are arranged in the central portion of the electrolyte. On the other hand, no electrode is arranged on the outer peripheral portion of the electrolyte. Alternatively, only one electrode is arranged on the outer peripheral portion of the electrolyte, and the other electrode is not arranged.

Japanese Unexamined Patent Publication No. 2018-206572

There is a demand for improved output in the electrochemical cell having the above configuration. Therefore, an object of the present invention is to improve the output of the electrochemical cell.

The electrolyte for an electrochemical cell according to the first aspect of the present invention is used for an electrochemical cell. The electrolyte for the electrochemical cell is in the form of a film. The electrolyte for an electrochemical cell has an ionic conductor and a support. The ionic conductor has ionic conductivity. The support supports the ionic conductor. The area ratio of the ionic conductor in the cross section of the outer peripheral portion of the electrolyte is smaller than the area ratio of the ionic conductor in the cross section of the central portion of the electrolyte.

In the conventional electrolyte, the area ratio of the ionic conductor in the cross section of the outer peripheral portion and the area ratio of the ionic conductor in the cross section of the central portion are the same. On the other hand, in the present invention, the area ratio of the ionic conductor in the cross section of the outer peripheral portion of the electrolyte is made smaller than the area ratio of the ionic conductor in the cross section of the central portion of the electrolyte. Therefore, the central portion can be preferentially ion-conducted as compared with the conventional electrolyte, and as a result, the output of the electrochemical cell using this electrolyte can be improved.

Further, according to the above configuration, the thermal stress generated in the electrolyte can be relaxed. Specifically, since the joint in which electrodes are formed on both sides of the electrolyte is restrained by a frame-shaped member or the like, thermal stress is generated in the electrolyte due to thermal expansion or contraction. On the other hand, the thermal stress generated in the electrolyte can be relaxed by making the area ratio of the ionic conductor in the cross section of the outer peripheral portion of the electrolyte smaller than the area ratio of the ionic conductor in the cross section of the central portion of the electrolyte. it can.

Preferably, the ratio (B / A) of the area ratio (B) of the ion conductor in the cross section of the outer peripheral portion to the area ratio (A) of the ion conductor in the cross section of the central portion is 0.99 or less. is there.

Preferably, the area ratio of the ionic conductor in the cross section of the outer peripheral portion is 20% or more. According to this configuration, ionic conduction in the outer peripheral portion can also be utilized.

Preferably, the support is made of resin.

Preferably, the support is a porous substrate.

Preferably, the support is a binder.

Preferably, the ionic conductor is made of a ceramic material.

The electrochemical cell according to the second aspect of the present invention includes a first electrode, a second electrode, and any of the above electrolytes. The electrolyte is arranged between the first electrode and the second electrode.

According to the present invention, the output of the electrochemical cell can be improved.

Sectional drawing of solid alkaline fuel cell. Top view of the electrolyte. An enlarged cross-sectional view of a fuel cell joint. FIG. 3 is a cross-sectional view of a fuel cell joint according to a modified example. An enlarged cross-sectional view of the electrolyte according to the modified example. An enlarged cross-sectional view of a fuel cell joint according to a modified example.

Hereinafter, an embodiment of the solid alkaline fuel cell 100, which is an example of an electrochemical cell using the electrolyte according to the present invention, will be described with reference to the drawings. The solid alkaline fuel cell 100 is a type of alkaline fuel cell (AFC) having a hydroxide ion as a carrier.

(Solid alkaline fuel cell 100)
FIG. 1 is a cross-sectional view showing the configuration of the solid alkaline fuel cell 100 according to the embodiment. The solid alkaline fuel cell 100 includes a cathode 2 (an example of a first electrode), an anode 3 (an example of a second electrode), and an electrolyte 4. Further, the solid alkaline fuel cell 100 includes a first separator 11 and a second separator 12. The cathode 2, the anode 3, and the electrolyte 4 constitute the fuel cell junction 10. In actual use, a plurality of solid alkaline fuel cells 100 are stacked. Specifically, a plurality of fuel cell joints 10 are stacked via the first and second separators 11 and 12.

(1st and 2nd separators 11 and 12)
The first and second separators 11 and 12 are arranged so as to sandwich the fuel cell joint 10 from both sides in the thickness direction (z-axis direction). The first separator 11 is configured to supply an oxidizing agent containing _{oxygen (O 2) to the cathode 2.} The first separator 11 has a first flow path 111. The first flow path 111 faces the cathode 2. _{An oxidizing agent containing oxygen (O 2} ) is supplied to the first flow path 111.

The second separator 12 is configured to supply fuel containing a hydrogen atom (H) to the anode 3. The second separator 12 has a second flow path 121. The second flow path 121 faces the anode 3. Fuel containing a hydrogen atom (H) is supplied to the second flow path 121. For example, methanol is supplied to the second flow path 121.

When a plurality of fuel cell joints 10 are stacked via the first and second separators 11 and 12, the first separator 11 is a surface opposite to the surface on which the first flow path 111 is formed. A second flow path is formed in. Further, in the second separator 12, the first flow path is formed on the surface opposite to the surface on which the second flow path 121 is formed.

A first seal member 13a is arranged between the first separator 11 and the fuel cell joint 10. The first seal member 13a improves the adhesion between the first separator 11 and the fuel cell joint 10 to prevent the oxidant from leaking to the outside. A second seal member 13b is arranged between the second separator 12 and the fuel cell joint 10. The second seal member 13b improves the adhesion between the second separator 12 and the fuel cell joint 10 to prevent fuel from leaking to the outside.

The first and second seal members 13a and 13b are annular and are in contact with the outer peripheral portion 44 of the electrolyte 4 of the fuel cell joint 10. Examples of the first and second seal members 13a and 13b include an O-ring and a rubber sheet. The first seal member 13a may be integrally formed with the first separator 11. The second seal member 13b may be integrally configured with the second separator 12.

(Fuel cell junction 10)
The fuel cell junction 10 includes a cathode 2, an anode 3, and an electrolyte 4. The fuel cell junction 10 generates electricity at a relatively low temperature (for example, 50 ° C. to 250 ° C.) based on the following electrochemical reaction formula. However, in the following electrochemical reaction formula, methanol is used as an example of fuel.

・ Cathode 2: 3 / 2O ₂ + 3H ₂ O + 6e ⁻ → 6OH ⁻
・ Anode 3: CH ₃ OH + 6OH ⁻ → 6e ⁻ + CO ₂ + 5H ₂ O
・ Overall: CH ₃ OH + 3 / 2O ₂ → CO ₂ + 2H ₂ O

(Cathode 2)
The cathode 2 is arranged on the first surface 41 side (upper surface side in FIG. 1) of the electrolyte 4. Specifically, the cathode 2 is arranged on the first surface 41 of the central portion 43 of the electrolyte 4. The cathode 2 is an anode generally called an air electrode.

During power generation of the solid alkaline fuel cell 100, an oxidizing agent containing _{oxygen (O 2} ) is supplied to the cathode 2 via the first flow path 111 of the first separator 11. As the oxidizing agent, it is preferable to use air, and it is more preferable that the air is humidified. The cathode 2 is a porous body capable of diffusing an oxidizing agent inside. The porosity of the cathode 2 is not particularly limited. The thickness of the cathode 2 is not particularly limited, but can be, for example, 10 to 200 μm.

The cathode 2 is not particularly limited as long as it contains a known air electrode catalyst used for AFC. As an example of the cathode catalyst, in the periodic table of Group 8 to 10 elements (IUPAC format) such as platinum group elements (Ru, Rh, Pd, Os, Ir, Pt) and iron group elements (Fe, Co, Ni). Group 8-10 elements), Group 11 elements such as Cu, Ag, Au (elements belonging to Group 11 in the periodic table in the IUPAC format), rhodium phthalocyanine, tetraphenylporphyrin, Co-salen, Ni-salen (elements belonging to Group 11), Cu, Ag, Au, etc. Salen = N, N'-bis (salicylidene) ethylenediamine), silver nitrate, and any combination thereof. The amount of the catalyst supported on the cathode 2 is not particularly limited, but is preferably 0.1 to 10 mg / cm ² , more preferably 0.1 to 5 mg / cm ² . The cathode catalyst is preferably supported on carbon. Preferred examples of the cathode 2 or the catalyst constituting the cathode 2 are platinum-supported carbon (Pt / C), palladium-supported carbon (Pd / C), rhodium-supported carbon (Rh / C), nickel-supported carbon (Ni / C), and the like. Examples thereof include copper-supported carbon (Cu / C) and silver-supported carbon (Ag / C).

The method for producing the cathode 2 is not particularly limited, but for example, the cathode catalyst and, if desired, the carrier are mixed with a binder to form a paste. Then, this paste-like mixture can be formed by applying it on the first surface 41 of the central portion 43 of the electrolyte 4.

(Anode 3)
The anode 3 is arranged on the second surface 42 side (lower surface side in FIG. 1) of the electrolyte 4. Specifically, the anode 3 is located on the second surface 42 of the central portion 43 of the electrolyte 4. The anode 3 is a cathode generally called a fuel electrode.

During power generation of the solid alkaline fuel cell 100, fuel containing a hydrogen atom (H) is supplied to the anode 3 via the second flow path 121 of the second separator 12. As the fuel, it is preferable to use methanol. The anode 3 is a porous body capable of diffusing fuel inside. The porosity of the anode 3 is not particularly limited. The thickness of the anode 3 is not particularly limited, but can be, for example, 10 to 500 μm.

The fuel may contain a fuel compound capable of reacting with hydroxide ions (OH ⁻ ) at the anode 3, and may be in the form of either a liquid fuel or a gaseous fuel.

Examples of the fuel compound include (i) hydrazine (NH ₂ NH ₂ ), hydrated hydrazine (NH ₂ NH ₂ · H ₂ O), hydrazine carbonate ((NH ₂ NH ₂ ) ₂ CO ₂ ), and hydrazine sulfate (NH). ₂ NH ₂ · H ₂ SO ₄ ), monomethylhydrazine (CH ₃ NHNH ₂ ), dimethylhydrazine ((CH ₃ ) ₂ NNH ₂ , CH ₃ NHNHCH ₃ ), and hydrazines such as _{carboxylic hydrazine ((NHNH 2} ) _{2 CO).} Class, (ii) urea (NH ₂ CONH ₂ ), (iii) ammonia (NH ₃ ), (iv) imidazole, 1,3,5-triazine, 3-amino-1,2,4-triazole and other heterocycles. Examples thereof include compounds such as (v) hydroxylamines such as hydroxylamine (NH ₂ OH) and hydroxylamine sulfate (NH ₂ OH · H ₂ SO ₄ ), and combinations thereof. Of these fuel compounds, carbon-free compounds (ie, hydrazine, hydrated hydrazine, hydrazine sulfate, ammonia, hydroxylamine, hydroxylamine sulfate, etc.) are particularly suitable because they do not have the problem of catalytic poisoning by carbon monoxide. is there.

The fuel compound may be used as a fuel as it is, or may be used as a solution dissolved in water and / or an alcohol (for example, a lower alcohol such as methanol, ethanol, propanol or isopropanol). For example, among the above fuel compounds, hydrazine, hydrated hydrazine, monomethylhydrazine and dimethylhydrazine are liquids and can be used as they are as liquid fuels. In addition, hydrazine carbonate, hydrazine sulfate, carboxylic hydrazine, urea, imidazole, and 3-amino-1,2,4-triazole, and hydroxylamine sulfate are solid but soluble in water. 1,3,5-triazine and hydroxylamine are solid but soluble in alcohol. Ammonia is a gas but is soluble in water. As described above, the solid fuel compound can be dissolved in water or alcohol and used as a liquid fuel. When the fuel compound is dissolved in water and / or alcohol and used, the concentration of the fuel compound in the solution is, for example, 1 to 90% by weight, preferably 1 to 30% by weight.

Further, a hydrocarbon-based liquid fuel containing alcohols such as methanol and ethanol and ethers, a hydrocarbon-based gas such as methane, or pure hydrogen can be used as it is as a fuel. In particular, methanol is preferable as the fuel used in the solid alkaline fuel cell 100 according to the present embodiment. Methanol may be in a gaseous state, a liquid state, or a gas-liquid mixed state.

The anode 3 is not particularly limited as long as it contains a known anode catalyst used for AFC. Examples of anode catalysts include metal catalysts such as Pt, Ni, Co, Fe, Ru, Sn, and Pd. The metal catalyst is preferably supported on a carrier such as carbon, but may be in the form of an organic metal complex having a metal atom of the metal catalyst as a central metal, or the organic metal complex may be supported as a carrier. Further, a diffusion layer made of a porous material or the like may be arranged on the surface of the anode catalyst. Preferred examples of the anode 3 and the catalysts constituting the anode 3 are nickel, cobalt, silver, platinum-supported carbon (Pt / C), palladium-supported carbon (Pd / C), rhodium-supported carbon (Rh / C), and nickel-supported carbon. (Ni / C), copper-supported carbon (Cu / C), and silver-supported carbon (Ag / C) can be mentioned.

The method for producing the anode 3 is not particularly limited, but for example, the anode catalyst and, if desired, the carrier are mixed with a binder to form a paste. Then, this paste-like mixture can be formed by applying it on the second surface 42 of the central portion 43 of the electrolyte 4.

(Electrolyte 4)
The electrolyte 4 is arranged between the cathode 2 and the anode 3. The electrolyte 4 is connected to each of the cathode 2 and the anode 3. Electrolyte 4 has ionic conductivity. The electrolyte 4 is in the form of a film and has a first surface 41 and a second surface 42. The first surface 41 and the second surface 42 face opposite to each other. The cathode 2 is arranged on the first surface 41 side of the electrolyte 4, and the anode 3 is arranged on the second surface 42 side.

FIG. 2 is a plan view of the electrolyte 4. The alternate long and short dash line in FIG. 2 represents the region where the cathode 2 is arranged. As shown in FIG. 2, the electrolyte 4 has a central portion 43 and an outer peripheral portion 44. The central portion 43 is a region that overlaps with both the cathode 2 and the anode 3 in the thickness direction view (z-axis direction view). The outer peripheral portion 44 is a region that does not overlap with at least one of the cathode 2 and the anode 3 in the thickness direction. The outer peripheral portion 44 is a region on the outer peripheral side of the central portion 43. The outer peripheral portion 44 has a frame shape. The first and second seal members 13a and 13b are arranged on the outer peripheral portion 44 of the electrolyte 4.

FIG. 3 is a schematic view showing an enlarged cross section of the electrolyte 4. The electrolyte 4 has a porous base material 5 (an example of a support) and an ionic conductor 6.

The porous substrate 5 is configured to support the ionic conductor 6. Specifically, the porous substrate 5 has a three-dimensional network structure. The "three-dimensional network structure" is a structure in which the constituent substances of the base material are three-dimensionally and network-likely connected. The porous base material 5 forms continuous pores 5a. The continuous pores 5a are formed by connecting the pores in a three-dimensional and mesh-like manner, and are exposed on the outer surface of the porous base material 5. The continuous hole 5a is impregnated with the ionic conductor 6.

The porous base material 5 can be composed of at least one selected from a metal material, a ceramic material, and a polymer material.

As the metal material constituting the porous base material 5, stainless steel (Fe—Cr alloy, Fe—Ni—Cr alloy, etc.), aluminum, zinc, nickel, titanium, or the like can be used. Since such a metal material has higher thermal conductivity than a ceramic material or a polymer material, it is possible to improve the heat dissipation efficiency of the porous base material 5 and reduce the temperature distribution in the porous base material 5. Can be made to. As long as it has a three-dimensional network structure, the form of the porous base material 5 is not particularly limited, and even a cell-like or monolithic structure made of a porous metal material (for example, a foamed metal material) may be used. It may be a mesh-like mass composed of a fine wire metal material.

When the porous base material 5 is made of a metal material, an insulating film may be formed on the surface of the porous base material 5. The insulating film can be composed of Cr ₂ O ₃ , Al ₂ O ₃ , ZrO ₂ , MgO, Mg _{Al 2} O _{4, and the} like. When the porous base material 5 is made of stainless steel, a Cr ₂ O ₃ film as an insulating film can be easily formed by oxidizing the stainless steel. However, in the present embodiment, since the first and second film-like portions 62 and 63, which will be described later, function as an insulating film, the insulating film may not be formed on the surface of the porous base material 5.

Examples of the ceramic material constituting the porous base material 5 include alumina, zirconia, titania, magnesia, calcia, cordierite, zeolite, mullite, zinc oxide, silicon carbide, and any combination thereof.

Examples of the polymer material constituting the porous base material 5 include polystyrene, polyether sulfone, polypropylene, epoxy resin, polyphenylene sulfide, hydrophilic fluororesin (tetrafluororesin: PTFE, etc., polyvinylidene fluoride). Examples include polystyrene, nylon, polyethylene and any combination thereof. When the porous base material 5 is made of a flexible polymer material, the thickness can be easily reduced while increasing the porosity, so that the hydroxide ion conductivity can be improved. As the porous base material 5 made of a polymer material, a microporous membrane as commercially available as a separator for a lithium battery can be used.

The thickness of the porous substrate 5 is not particularly limited, but can be, for example, 200 μm or less, preferably 100 μm or less, more preferably 75 μm or less, still more preferably 50 μm or less, particularly preferably 25 μm or less, and 5 μm. The following are the most preferable. The lower limit of the thickness of the porous base material 5 may be appropriately set according to the intended use, but is preferably 1 μm or more, more preferably 2 μm or more in order to secure a certain degree of hardness.

The average inner diameter of the continuous holes 5a in the cross section of the porous substrate 5 is not particularly limited, but can be, for example, 0.001 to 1.5 μm, preferably 0.001 to 1.25 μm, and more preferably 0. It is 001 to 1.0 μm, more preferably 0.001 to 0.75 μm, and particularly preferably 0.001 to 0.5 μm. Within these ranges, the density of the ionic conductor 6 can be improved while imparting strength as a support to the porous base material 5. The average inner diameter of the continuous holes 5a is obtained by arithmetically averaging the equivalent circle diameters of the continuous holes 5a at 20 randomly selected locations on the observation image when the cross section of the porous substrate 5 is observed with an electron microscope. can get. The circle-equivalent diameter of the continuous hole 5a is the diameter of a circle having the same area as the cross-sectional area of the continuous hole 5a in the observation image. The magnification of the electron microscope may be appropriately set according to the cross-sectional size of the continuous hole 5a.

The volume fraction of the continuous hole 5a is not particularly limited, but can be, for example, 10 to 60%, preferably 15 to 55%, and more preferably 20 to 50%. Within these ranges, the density of the ionic conductor 6 can be improved while ensuring the strength of the porous base material 5 as a support. The volume fraction of the continuous hole 5a can be measured by the Archimedes method.

Further, although not shown in FIG. 3, the porous base material 5 preferably has a plurality of pores inside itself. The plurality of pores may be connected to each other inside the porous base material 5. It is more preferable that each pore is an open pore that opens on the surface of the porous base material 5, and each pore is impregnated with the ionic conductor 6. As a result, a short-distance ion conduction path of continuous pores 5a → pores in the porous substrate 5 → continuous pores 5a, continuous pores 5a → pores in the porous substrate 5, → second film-like portion 63, or , The long-distance ion conduction path of the first film-like portion 62 → the pores in the porous substrate 5 → the second film-like portion 63 can be formed. As a result, the ionic conductive region in the composite portion 61 is widened, so that the ionic conductivity of the electrolyte 4 as a whole can be improved.

The ionic conductor 6 has hydroxide ionic conductivity. During power generation of the solid alkaline fuel cell 100, the ion conductor 6 conducts hydroxide ions (OH ⁻ ) from the cathode 2 side to the anode 3 side. The hydroxide ion conductivity of the ion conductor 6 is not particularly limited, but is preferably 0.1 mS / cm or more, more preferably 0.5 mS / cm or more, and further preferably 1.0 mS / cm or more. The higher the hydroxide ion conductivity of the ionic conductor 6, the more preferable it is, and the upper limit thereof is not particularly limited, but is, for example, 10 mS / cm.

The ionic conductor 6 can be made of a ceramic material having hydroxide ionic conductivity. As such a ceramic material, layered double hydroxide (LDH) is suitable.

LDH is M ²⁺ _1-x M ³⁺ _x (OH) ₂ A ⁿ⁻ x / n · mH ₂ O (in the formula, M ²⁺ is a divalent cation, M ³⁺ is a trivalent cation, and A ^The basic composition represented by the general formula of n− is an n-valent anion, n is an integer of 1 or more, x is 0.1 to 0.4, and m is an arbitrary integer meaning the number of moles of water). Have. Examples of M ^{2+ include Mg 2+} , Ca ²⁺ , Sr ²⁺ , Ni ²⁺ , Co ²⁺ , Fe ²⁺ , Mn ²⁺ , and Zn ²⁺ , and examples of M ^{3+ include Al 3+} , Fe ³⁺ , Ti ³⁺ , ^{Y 3+, Ce 3+, Mo 3+} , and ^{Cr 3+, and} examples of ^{a n-} is _CO ^{3 2-} and OH ^- are exemplified. As M ²⁺ and M ³⁺ , one type may be used alone or two or more types may be used in combination.

LDH is composed of a plurality of hydroxide basic layers and an intermediate layer interposed between the plurality of hydroxide basic layers. Intermediate layer is composed of an anion and _{H 2} O. The hydroxide basic layer contains, for example, Ni, Al, Ti and OH groups when the metal M is Ni, Al, Ti. Hereinafter, a case where the hydroxide basic layer of LDH contains Ni, Al, Ti and OH groups will be described.

Ni in LDH can take the form of nickel ions. Nickel ions in LDH are typically considered to be Ni ²⁺ , but are not particularly limited as other valences such as ^{Ni 3+ are possible.} Al in LDH can take the form of aluminum ions. Aluminum ions in LDH are typically considered to be Al ³⁺ , but are not particularly limited as other valences are possible. Ti in LDH can take the form of titanium ions. Titanium ions in LDH are typically considered to be Ti ⁴⁺ , but are not particularly limited as other valences such as ^{Ti 3+ are possible.} The hydroxide basic layer preferably contains Ni, Al, Ti and OH groups as main components, but may contain other elements or ions, or may contain unavoidable impurities. The unavoidable impurity is an arbitrary element that can be unavoidably mixed in the production method, and can be mixed in LDH, for example, derived from a raw material or a base material.

Intermediate layer of LDH is composed of anionic and _{H 2} O. The anion is a monovalent or higher anion, preferably a monovalent or divalent ion. Preferably, the anions in LDH contain OH ⁻ and / or CO ₃ ^2- .

As described above, since the valences of Ni, Al and Ti are not always fixed, it is impractical or impossible to specify LDH strictly by a general formula. Assuming that the basic hydroxide layer is mainly composed of Ni ²⁺ , Al ³⁺ , Ti ⁴⁺ and OH groups, LDH is expressed by the general formula: Ni ²⁺ _1-xy Al ³⁺ _x Ti ⁴⁺ _y (OH). _{^{) 2 a n- (x + 2y}} ) / n · mH 2 O ( ^{wherein, a n-n-valent} anion, n is an integer of 1 or more, preferably 1 or 2, 0 <x <1, preferably 0.01 ≦ x ≦ 0.5, 0 <y <1, preferably 0.01 ≦ y ≦ 0.5, 0 <x + y <1, m is 0 or more, typically more than 0 or 1 or more It can be expressed by the basic composition (which is a real number of). However, the above general formula should be understood as "basic composition" to the ^{extent that elements such as Ni 2+} , Al ³⁺ , and Ti ⁴⁺ do not impair the basic characteristics of LDH, and other elements or ions (of the same element). It should be understood as replaceable with other valence elements or ions or elements or ions that can be unavoidably mixed in the process.

The area ratio B of the ionic conductor 6 in the cross section of the outer peripheral portion 44 of the electrolyte 4 is smaller than the area ratio A of the ionic conductor 6 in the cross section of the central portion 43 of the electrolyte 4. In this way, the output of the fuel cell 100 can be improved by making the area ratio B of the ion conductor 6 in the cross section of the outer peripheral portion 44 smaller than the area ratio A of the ion conductor 6 in the cross section of the central portion 43. it can.

Here, the area ratio A of the ionic conductor 6 in the cross section of the central portion 43 of the electrolyte 4 can be obtained as follows. First, a cut surface of the electrolyte 4 as shown in FIG. 3 is formed by a plane that passes near the center of the electrolyte 4 and is orthogonal to the in-plane direction (xy plane direction), for example, the xz plane. The image data obtained by photographing the central portion 43 of the cut surface with an SEM, FE-SEM, TEM, cryo SEM, or the like is binarized. The ratio of the area occupied by the ionic conductor 6 to the data obtained by this binarization process is calculated as the area ratio of the ionic conductor 6. The area ratio of the ionic conductor 6 is calculated at the central portion of each region of the central portion 43 divided into five in the x direction of FIG. 3, and the average value is the area ratio of the ionic conductor 6 in the cross section of the central portion 43. Let it be A.

Further, the area ratio of the ionic conductor 6 in the cross section of the outer peripheral portion 44 of the electrolyte 4 can be obtained as follows. Of the cut surfaces formed as described above, the outer peripheral portion 44 is photographed with an SEM, FE-SEM, TEM, cryo SEM, or the like, and the obtained image data is binarized. The ratio of the area occupied by the ionic conductor 6 to the data obtained by this binarization process is calculated as the area ratio of the ionic conductor 6. The area ratio of the ionic conductor 6 is calculated at the central portion of each region in which the outer peripheral portion 44 is divided into five in the x direction of FIG. 3, and the average value thereof is the area ratio B of the ionic conductor 6 in the cross section of the outer peripheral portion 44. And.

The ratio (B / A) of the area ratio B of the ionic conductor 6 in the cross section of the outer peripheral portion 44 to the area ratio A of the ionic conductor 6 in the cross section of the central portion 43 is preferably less than 0.99. Further, the area ratio B of the ion conductor 6 in the cross section of the outer peripheral portion 44 is preferably 1% or more.

The ionic conductor 6 has a composite portion 61, a first membrane-like portion 62, and a second membrane-like portion 63. The area ratios A and B of the ionic conductor 6 described above are measured in the composite portion 61.

The composite portion 61 is arranged between the first film-like portion 62 and the second film-like portion 63. The composite portion 61 is supported by the porous base material 5 in the porous base material 5. Specifically, the composite portion 61 is arranged in the continuous pores 5a of the porous base material 5. The composite portion 61 is impregnated in the continuous pores 5a of the porous base material 5 and is integrated with the porous base material 5. By supporting the ionic conductor 6 with the porous base material 5 in this way, the strength of the ionic conductor 6 can be improved, so that the ionic conductor 6 can be made thinner. As a result, the resistance of the electrolyte 4 can be reduced.

In the present embodiment, the composite portion 61 extends over substantially the entire area of the continuous pores 5a of the porous base material 5. However, when the ionic conductor 6 does not have at least one of the first film-like portion 62 and the second film-like portion 63, the composite portion 61 may be impregnated only in a part of the porous base material 5. ..

Here, the composite portion 61 has a plurality of closed pores 611 formed inside the composite portion 61. Since such closed pores 611 are formed inside the composite portion 61, it is possible to alleviate the volume change of the electrolyte 4 due to the change in the water content of the composite portion 61 during the operation of the solid alkaline fuel cell 100. .. As a result, it is possible to suppress the generation of stress at the interface between the electrolyte 4 and the cathode 2 and / and the interface between the electrolyte 4 and the anode 3. As a result, it is possible to prevent the electrolyte 4 from peeling off from the cathode 2 and / and the anode 3 and the electrolyte 4 itself from being deformed.

Further, since the closed pores 611 are formed inside the composite portion 61, the composite portion 61 can be provided with flexibility. Therefore, due to the temperature distribution in the solid alkaline fuel cell 100, the cathode 2 and the cathode 2 It is possible to suppress the generation of thermal stress at the interface with the electrolyte 4 and / and the interface between the anode 3 and the electrolyte 4. Therefore, it is possible to prevent the electrolyte 4 from peeling off from the cathode 2 and / and the anode 3 or the electrolyte 4 itself from being deformed.

The closed pores 611 are separated from the porous substrate 5. That is, the closed air hole 611 is confined inside the composite portion 61 and does not come into direct contact with the inner surface of the continuous hole 5a. As a result, when the electrolyte 4 undergoes a volume change or deformation as compared with the case where the closed pores 611 come into direct contact with the porous base material 5, the porous base material 5, the composite portion 61, and the closed pores 611 are ternary. It is possible to prevent the composite portion 61 from peeling from the porous base material 5 starting from the corner portion made of.

The average circle-equivalent diameter of each closed hole 611 is not particularly limited, but can be, for example, 0.001 to 1.0 μm. The average circle-equivalent diameter of each closed hole 611 is preferably 0.001 μm or more, more preferably 0.002 μm or more. Thereby, the flexibility of the composite portion 61 can be further improved. The average circle-equivalent diameter of each closed hole 611 is preferably 1.0 μm or less, more preferably 0.8 μm or less.

For the average circle-equivalent diameter of each closed pore 611, the cross section of the electrolyte 4 was observed with an electron microscope at a magnification of 20,000 to 1,500,000 times, and the circle-equivalent diameter of 20 randomly selected pores 611 was calculated. Obtained by averaging. The circle-equivalent diameter of the closed pores 611 is the diameter of a circle having the same area as the closed pores 611 in the cross section of the electrolyte 4. However, since the closed pores 611 having a diameter equivalent to a circle of 0.001 μm or less have an extremely small contribution to improving the flexibility of the composite portion 61, they should be excluded when determining the average diameter equivalent to a circle of each closed hole 611. To do.

The first film-like portion 62 is connected to the cathode 2 side of the composite portion 61. The first film-like portion 62 is formed in a film-like shape. The first film-like portion 62 is formed integrally with the composite portion 61. The second film-like portion 63 is connected to the anode 3 side of the composite portion 61. The second film-like portion 63 is formed in a film-like shape. The second film-like portion 63 is integrally formed with the composite portion 61. Each of the first film-shaped portion 62 and the second film-shaped portion 63 can be made of a ceramic material having hydroxide ion conductivity. Each of the first film-like portion 62 and the second film-like portion 63 may be formed in a uniform planar shape, or may be patterned into a desired planar shape such as a striped shape. The thickness of each of the first film-like portion 62 and the second film-like portion 63 is not particularly limited, but can be, for example, 10 μm or less, preferably 7 μm or less, and more preferably 5 μm or less.

(Manufacturing method of ionic conductor 6)
The method for producing the ionic conductor 6 is not particularly limited, but when the ionic conductor 6 is composed of LDH and the hydroxide basic layer of LDH contains Ni, Al, Ti and OH groups, the following steps are taken. It can be produced in (1) to (4).

(1) Prepare the porous base material 5.

(2) The entire porous base material 5 is impregnated with a mixed sol of alumina and titania and heat-treated to form an alumina-titania layer. As will be described later, in order to grow LDH from the entire surface of the porous base material 5, it is important to form an alumina-titania layer on the entire surface of the porous base material 5. Therefore, a mixed sol of alumina and titania. Is impregnated and heat-treated a plurality of times. As a result, the alumina-titania layer can be formed on the entire surface of the porous base material 5.

Here, for example, by masking only the outer peripheral portion 44 in all or a part of the heat treatment performed a plurality of times, the area ratio B of the ionic conductor 6 in the outer peripheral portion 44 is set to the central portion 43. It can be made smaller than the area ratio A of the ion conductor 6 in.

(3) The porous base material 5 is immersed in an aqueous solution of a raw material containing ^{nickel ions (Ni 2+) and urea.}

(4) By hydrothermally treating the porous base material 5 in the raw material aqueous solution to form LDH on the porous base material 5 and in the porous base material 5, the composite portion 61, the first film-like portion 62, And an ionic conductor 6 having a second film-like portion 63 is formed. At this time, by appropriately adjusting the hydrothermal treatment time and the solution concentration, the closed pores 611 can be formed in the composite portion 61 by stopping the reaction before the pores are closed. Since LDH grows around the alumina-titania layer formed on the surface of the porous base material 5, when the alumina-titania layer is formed on the entire surface of the porous base material 5, the porous base material 5 is used. LDH will grow from the entire surface of the. As a result, the closed pores 611 can be separated from the porous substrate 5.

(Modified example of the embodiment)
Although the embodiments of the present invention have been described above, the present invention is not limited thereto, and various modifications can be made without departing from the spirit of the present invention.

Modification 1
In the above embodiment, the electrolyte 4 is a support, but the configuration of the fuel cell junction 10 is not limited to this. For example, as shown in FIG. 4, the anode 3 may be a support. In this case, the electrolyte 4 is formed on the upper surface of the anode 3. The electrolyte 4 is the same size as the anode 3 or one size smaller than the anode 3. The cathode 2 formed on the upper surface of the electrolyte 4 has the same size as the electrolyte 4 or one size smaller than the electrolyte 4.

In this modification, the cathode 2 is one size smaller than the electrolyte 4. In this modification, the central portion 43 of the electrolyte 4 is a portion that overlaps with the cathode 2 in the thickness direction view (z-axis direction view). The outer peripheral portion 44 of the electrolyte 4 is a portion that does not overlap with the cathode 2 in the thickness direction. The outer peripheral portion 44 of the electrolyte 4 overlaps with the anode 3 in the thickness direction.

The cathode 2 may be a support. Further, the fuel cell 100 may separately have a member serving as a support.

Modification 2
The electrolyte 4 does not have to have the porous base material 5. For example, as shown in FIG. 5, the electrolyte 4 has an ionic conductor 6 and a binder 7. The binder 7 functions as a support for the ionic conductor 6. Specifically, the binder 7 is arranged between the constituent particles of the ionic conductor 6. The binder 7 binds the constituent particles of the ionic conductor 6 to each other. For example, the binder 7 maintains the shape of the electrolyte 4 by binding LDH particles to each other. Examples of such a binder include polyethylene, polypropylene, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), styrene-butadiene rubber, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, and vinylidene fluoride-hexa. Fluoropropylene copolymer, vinylidene fluoride-chlorotrifluoroethylene copolymer, ethylene-tetrafluoroethylene copolymer, polychlorotrifluoroethylene, vinylidene fluoride-pentafluoropropylene copolymer, propylene-tetrafluoroethylene copolymer Polymer, ethylene-chlorotrifluoroethylene copolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer, vinylidene fluoride-perfluoromethylvinyl ether-tetrafluoroethylene copolymer, or ethylene-acrylic acid copolymer Examples thereof include copolymers.

Modification 3
In the above embodiment, the closed pores 611 are separated from the porous base material 5, but as shown in FIG. 6, the closed pores 611 may be in contact with the porous base material 5. That is, the closed air hole 611 may be in direct contact with the inner surface of the continuous hole 5a. As a result, the constrained area of the porous base material 5 due to the presence of the closed pores 611 can be reduced as compared with the case where the closed pores 611 are separated from the porous base material 5, so that the flexibility of the porous base material 5 itself can be reduced. Can be improved. Therefore, when the volume of the electrolyte 4 is changed or deformed, it is possible to further suppress the generation of stress at the interface between the cathode 2 and the electrolyte 4 and / or the interface between the anode 3 and the electrolyte 4.

Modification 4
In the above embodiment, the electrolyte 4 has a plurality of closed pores 611, but if it has at least one closed pore 611, it has a composite portion as compared with the case where it does not have any closed pores 611. Since flexibility can be imparted to 61, peeling of the electrolyte 4 can be suppressed.

Modification 5
In the above embodiment, the shape of the closed hole 611 has a circular cross section, but the shape of the closed hole 611 is not limited to this. For example, the closed air hole 611 may have an elliptical cross section or may have another shape.

Modification 6
In the above embodiment, the ionic conductor 6 has the composite portion 61, the first film-shaped portion 62, and the second film-shaped portion 63, but may have only the composite portion 61. That is, the ionic conductor 6 does not have to include at least one of the first film-shaped portion 62 and the second film-shaped portion 63.

Modification 7
In the above embodiment, the electrolyte 4 is configured as a single layer, but the electrolyte 4 may be a plurality of layers.

Modification 8
In the above embodiment, the embodiment in which the fuel cell according to the present invention is applied to the polymer electrolyte fuel cell has been described, but the object to which the fuel cell according to the present invention is applied is not limited to the polymer electrolyte fuel cell, for example. It can also be applied to other fuel cells such as polymer electrolyte fuel cells.

Hereinafter, examples of the present invention will be described. However, the present invention is not limited to the examples described below.

(Manufacture of solid alkaline fuel cell 100)
First, a porous base material 5 composed of polyvinylidene fluoride and having continuous pores 5a was prepared.

Next, the entire surface of the porous base material 5 is impregnated with a mixed sol of alumina and titania, and the heat treatment step at 120 ° C. for a predetermined time is repeated a plurality of times to cover the entire surface of the porous base material 5 with an alumina-titania layer. Was formed.

Next, the ^{porous base material 5 was immersed in a raw material aqueous solution containing Ni 2+} and urea, and the porous base material 5 was hydrothermally treated in the raw material aqueous solution to form an ion conductor 6 made of LDH. As a result, the electrolyte 4 having the ionic conductor 6 and the porous base material 5 was formed. By polishing this electrolyte 4, the thickness was adjusted to about 50 μm.

In each of Examples 1 to 8 and Comparative Examples 1 to 5, the area ratio A of the ionic conductor 6 in the central portion 43 and the area ratio B of the ionic conductor 6 in the outer peripheral portion 44 are as shown in Table 1. .. The area ratios A and B of each of the ion conductors 6 are determined in Examples 1 to 8 and Comparative Examples 1 to 8 by adjusting the presence / absence of masking of the outer peripheral portion 44, the number of heat treatments, and the heat treatment time in the heat treatment step described above. Electrolyte 4 of 5 was formed.

Next, the cathode 2 is coated by applying a paste-like mixture of a carbon-supported cathode catalyst (Pt / C) and a binder (polyvinylidene fluoride) on the first surface 41 of the central portion 43 of the electrolyte 4. Was formed.

Next, a paste-like mixture of a carbon-supported anode catalyst (Pt-Ru / C) and a binder (polyvinylidene fluoride) is applied onto the second surface 42 of the central portion 43 of the electrolyte 4. Anode 3 was formed.

As described above, the fuel cell junctions 10 of Examples 1 to 8 and Comparative Examples 1 to 5 were produced. Then, the solid alkaline fuel cell 100 was produced by sandwiching the fuel cell joints 10 of Examples 1 to 8 and Comparative Examples 1 to 5 between the first separator 11 and the second separator 12. In each of the examples and the comparative examples, the configuration is basically the same except for the area ratios A and B of the ionic conductor 6.

(Evaluation method)
First, the solid alkaline fuel cell 100 was heated to 120 ° C. Next, using a compressor, air appropriately humidified with dry air having a dew point of 0 ° C. or lower was supplied to the cathode 2, and the air utilization rate at the cathode 2 was adjusted to 50%. Further, vaporized methanol was supplied to the anode 3 and adjusted so that the fuel utilization rate at the anode 3 was 50%.

Then, the output of the solid alkaline fuel cell 100 was measured while generating electricity at a rated load (100 mA / cm ^2). The measurement results are shown in Table 1. In Table 1, the evaluation of the output was based on the output values of Comparative Examples 3, 5 and 7 in which the area ratio A and the area ratio B were equal. Then, in Comparative Examples 1 to 3 and Examples 1 to 4, based on the output value of Comparative Example 3, the case where the value is more than 110% with respect to the standard is evaluated as ⊚, and more than 105% and 110% or less. When it was, it was evaluated as ◯, when it was more than 100% and 105% or less, it was evaluated as Δ, and when it was 100% or less, it was evaluated as ×. Further, in Comparative Examples 4 to 5 and Examples 5 to 8, based on the output value of Comparative Example 5, a case where the output value is more than 110% with respect to the standard is evaluated as ⊚, and more than 105% and 110% or less. When it was, it was evaluated as ◯, when it was more than 100% and 105% or less, it was evaluated as Δ, and when it was 100% or less, it was evaluated as ×. Further, in Comparative Examples 6 to 7 and Examples 9 to 11, based on the output value of Comparative Example 7, a case where the output value is more than 110% with respect to the standard is evaluated as ⊚, and more than 105% and 110% or less. When it was, it was evaluated as ◯, when it was more than 100% and 105% or less, it was evaluated as Δ, and when it was 100% or less, it was evaluated as ×.

As shown in Table 1, the output of the fuel cell 100 can be improved by making the area ratio B of the ion conductor 6 in the outer peripheral portion 44 smaller than the area ratio A of the ion conductor 6 in the central portion 43. Do you get it. Specifically, it was found that the output of the fuel cell 100 is improved by setting the ratio (B / A) of the area ratio B to the area ratio A to 0.99 or less. This is because the central portion 43 of the electrolyte 4 is easier for ions to flow than the outer peripheral portion 44, and as a result, the central portion 43 having a short path is prioritized and the ions are conducted to improve the ionic conductivity. Is considered to be.

Further, as can be seen from the comparison between Example 2 and Example 3, the comparison between Example 6 and Example 7, and the comparison between Example 9 and Example 10, the area of the ionic conductor 6 in the outer peripheral portion 44. It was found that the output of the fuel cell 100 was improved by setting the ratio to 20% or more. It is considered that the output of the fuel cell 100 is improved because the outer peripheral portion 44 sufficiently functions as an ion conduction path.

2 Cathode 3 Anode 4 Electrolyte 43 Central part 44 Peripheral part 5 Porous base material 6 Ion conductor 7 Binder 100 Fuel cell

Claims (6)

A film-like electrolyte used in electrochemical cells.
Ion conductors with ionic conductivity and
A support that supports the ionic conductor and
With
Area ratio of the ion conductor in the cross section of the outer peripheral portion of the electrolyte rather smaller than the area ratio of the ion conductor in the cross section of the central portion of the electrolyte,
The ionic conductor is made of a ceramic material and is made of a ceramic material.
The support is made of resin.
Electrolyte for electrochemical cell.
The ratio (B / A) of the area ratio (B / A) of the ion conductor in the cross section of the outer peripheral portion to the area ratio (A) of the ion conductor in the cross section of the central portion is 0.99 or less.
The electrolyte for an electrochemical cell according to claim 1.
The area ratio of the ionic conductor in the cross section of the outer peripheral portion is 20% or more.
The electrolyte for an electrochemical cell according to claim 1 or 2.
The support is a porous base material,
The electrolyte for an electrochemical cell according to any one of claims 1 to 3.
The support is a binder,
The electrolyte for an electrochemical cell according to any one of claims 1 to 3.
With the first electrode
With the second electrode
The electrolyte according to any one of claims 1 to 5 , which is arranged between the first electrode and the second electrode.
The electrochemical cell.

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