JP2022077365A - Proton conductive solid electrolyte, its manufacturing method, and proton conductive fuel cell - Google Patents

Abstract

To provide a proton conductive solid electrolyte which exhibits a high proton conductivity in a wide temperature range from a room temperature to a high temperature of 300°C or more in the upper limit and can be manufactured at a lower baking temperature than before without using an expensive or highly toxic raw material.SOLUTION: A proton conductive solid electrolyte is represented by the compositional formula AM1-xH2x(PO3)3 yH2O, where an element A is K or Rb, and an element M is one or more elements selected from the group consisting of Ni, Zn, Co and Fe, or is the combination of Mg and one or more elements selected from the group consisting of Ni, Zn, Co and Fe, or where the element A is K and Rb, and the element M is one or more elements selected from the group consisting of Ni, Zn, Co, Fe and Mg, and where x is 0.05 or more and 0.30 or less, y is 0.3 or more and 3.0 or less, and has a predetermined structure including a tunnel type structure and has H3O+ or H+ in the tunnel type structure.SELECTED DRAWING: Figure 11

Description

Application for application of Article 30, Paragraph 2 of the Patent Law Document 1: Copy of the final result report of the 2017 Private University Research Branding Project of the Ministry of Education, Culture, Sports, Science and Technology Document 2: Outline of the 87th Annual Meeting of the Electrochemical Society of Japan (Meeting Lecture) Program) and a copy of the above-mentioned event outline (convention lecture program) release date on the website of the above-mentioned conference "Proton Conductive Tunnel Type Phosphate KNi ▲ 1-x ▼ H ▲ 2x ▼ (PO ▲ 3 ▼) ▲ 3 ▼ ・ yH ▲ 2 ▼ O Synthesis, Thermal Stability and Electrochemical Properties" Copy Document 4: Copy of the exhibition outline and exhibition outline of Innovation Japan 2020 University Trade Fair Online Document 5: Copy of handouts at the Innovation Japan 2020 University Trade Fair Online Exhibition Document 6: INNOVATION DAYS 2020 Exhibition of wisdom and technology trade fair Copy of materials presented in Document 7: Copy of RSC Advance 2020,10,7803-7811

The present invention relates to a proton-conducting solid electrolyte, a method for producing the same, and a proton-conducting fuel cell.

In order to popularize fuel cells, it is required to further improve the performance of fuel cells, improve long-term durability, and reduce costs. As the above fuel cell, the development of a proton conduction type fuel cell (PCFC) is underway, and as a part of the development, there are some materials suitable for the proton conduction type solid electrolyte used in the proton conduction type fuel cell (PCFC). Proposed. Examples of proton-conducting solid electrolytes that have already been put into practical use include Nafion® membranes made of perfluorocarbon materials. Although this film exhibits high proton electrical conductivity, it requires a large amount of water for operation and has a problem that the upper limit of the operating temperature is about 90 ° C. and it cannot be used in a higher temperature range.

As a proton conduction type solid electrolyte having an operating temperature in a higher temperature range, several ones containing a solid oxide have been proposed. For example, Patent Document 1 describes a first layer made of a proton-conducting solid electrolyte material selected from BaZrO ₃ series, SrZrO ₃ series, CaZrO ₃ series, LaScO ₃ series, and LaYbO ₃ series, and BaCeO ₃ series or BaCeZrO ₃ series. A proton-conducting solid electrolyte characterized by being bonded to a second layer made of a proton-conducting solid electrolyte material is shown.

In Patent Document 2, as a fuel cell system using a proton conduction type solid oxide, BaZrCeYXO _3-δ (provided that any one or more of X = Sc, Ga, In, Gd, and Yb) is used. A fuel cell body having a solid electrolyte containing the solid oxide shown, a temperature control unit for keeping the fuel cell body at 400 ° C. or higher and lower than 700 ° C., a thickness of the solid electrolyte, and a current density of the fuel cell body. A fuel cell system including a control unit that maintains a multiplication value of 12.5 μm · A / cm ² or more has been proposed.

In Patent Document 3, La _{1- y} My Yb _1-x In _x O _3-δ (M = Ba, Sr, Ca, Mg; δ is the amount of oxygen vacancies; 0 <x <1; 0 <y ≦ A proton conductive solid electrolyte material characterized by having the composition of 0.2) is shown.

Patent Document 4 contains a trivalent metal oxide element, a pentavalent metal oxide element, phosphorus (P) and oxygen (O) as inorganic ion conductors having improved conductivity in the medium temperature range. Inorganic ion conductors have been proposed.

Furthermore, the present inventors have described in Non-Patent Document 1 that KMg _1-x H _2x (PO ₃ ) ₃ · yH ₂ O and RbMg _1-x H _2x (PO), which are known proton solid electrolytes having a tunnel-type structure. ₃ ) ₃・ yH ₂ O is proposed.

Japanese Unexamined Patent Publication No. 2019-175733 Japanese Unexamined Patent Publication No. 2019-21578 Japanese Unexamined Patent Publication No. 2016-13107 Japanese Unexamined Patent Publication No. 2013-191558

Matsuda et al., Arrangement of water molecules and high proton conductivity of tunnel structure phosphates, KMg1-xH2x (PO3) 3 · yH2O, RSC Adv., 2020, 10, 7803-7811

Perovskite-type proton solid electrolytes such as those shown in Patent Documents 1 to 3, for example, BaZrO ₃ , achieve high proton conductivity of ^10-2 Scm ^-1 at 400 ° C., but the raw materials are expensive. , High temperature firing at a thousand and several hundred degrees Celsius is required. Further, when a battery is manufactured using this material, there is a problem that the overvoltage of the anode is large and it is difficult to put the fuel cell into practical use at 600 ° C. or lower. The above-mentioned Patent Document 4 discloses an inorganic ion conductor used for a fuel cell operated in a temperature range of 100 ° C. or higher, but in order to develop high proton conductivity up to a high temperature range of 300 ° C. or higher, further. It seems that improvement is needed. Further, the known proton solid electrolyte having the tunnel type structure of Non-Patent Document 1 is limited to a temperature range in which the operating temperature is from room temperature to 250 ° C.

The present invention has been made in view of the above circumstances, and an object thereof is to exhibit high proton conductivity in a wide temperature range from room temperature to a high temperature having an upper limit of 300 ° C. or higher, and it is expensive or toxic. A novel proton-conducting solid electrolyte, a method for producing the proton-conducting solid electrolyte, and protons using the proton-conducting solid electrolyte, which can be produced at a lower firing temperature than before without using high-quality raw materials. The purpose is to provide a conduction fuel cell.

Aspect 1 of the present invention is represented by the composition formula AM _1-x H _2x (PO ₃ ) ₃ · yH ₂ O.
The element A is K or Rb, and the element M is selected from one or more elements selected from the group consisting of Ni, Zn, Co and Fe, or the group consisting of Ni, Zn, Co and Fe. A combination of one or more elements and Mg, or
The element A is K and Rb, and the element M is a combination of one or more elements selected from the group consisting of Ni, Zn, Co, Fe and Mg.
The x is in the range of 0.05 or more and 0.30 or less.
The y is in the range of 0.3 or more and 3.0 or less.
The octahedron formed by combining the ion of the element A and oxygen and the octahedron formed by combining the ion and oxygen of the element M alternately share the oxygen of each other's octahedron. A plurality of formed first columnar bodies exist in parallel,
A plurality of second columnar bodies having a longitudinal direction parallel to the first columnar body, which are composed of PO ₄ chains in which a plurality of PO _4s share oxygen and are connected in a chain, are present in parallel.
It has a tunnel-type structure in which a tunnel-like space surrounded by three second columnar bodies exists.
A proton-conducting solid electrolyte having H ₃ O ⁺ or H ⁺ in the tunnel-like space.

In aspect 2 of the present invention, whether the element A is K or Rb and the element M is a combination of one or more elements selected from the group consisting of Ni, Zn and Co.
The proton conduction type solid electrolyte according to the first aspect, wherein the element A is K and Rb, and the element M is Mg.

Aspect 3 of the present invention is the proton conduction type solid electrolyte according to Aspect 1, wherein the element A is K and the element M is Ni.

Aspect 4 of the present invention is the method for producing the proton-conducting solid electrolyte according to any one of aspects 1 to 3.
A mixing step of mixing the compound containing the element A, the compound containing the element M, and the compound containing phosphoric acid to obtain a mixture.
A method for producing a proton-conducting solid electrolyte, which comprises a firing step of firing the mixture at a temperature of 250 ° C. or higher and 800 ° C. or lower.

Aspect 5 of the present invention is a proton conduction type fuel cell using the proton conduction type solid electrolyte according to any one of aspects 1 to 3 as an electrolyte.

According to the present invention, a novel proton-conducting solid electrolyte that exhibits high proton conductivity in a wide temperature range from room temperature to a high temperature of 300 ° C. or higher is used as an expensive or highly toxic raw material. Even if it is not, it can be manufactured at a lower firing temperature than before.

It is a figure which shows the powder X-ray diffraction measurement result of the conventional proton conduction type solid electrolyte. It is a graph which shows the relationship between the x value of the conventional proton conduction type solid electrolyte, and the proton conductivity. It is a schematic diagram which illustrates a part in the cross section in the longitudinal direction of the proton conduction type solid electrolyte of this embodiment. It is a schematic diagram which illustrates a part in the cross section perpendicular to the longitudinal direction of the proton conduction type solid electrolyte of this embodiment. It is a figure which shows the TG / DTA measurement result in an Example. It is a figure which shows the powder X-ray diffraction analysis result in an Example. It is a figure which shows the result of another powder X-ray diffraction analysis in an Example. It is a figure which shows the result of another powder X-ray diffraction analysis in an Example. It is a figure which shows the result of having obtained the relationship between x of a composition formula and proton conductivity in an Example. It is a figure which shows the result of another powder X-ray diffraction analysis in an Example. It is a figure which shows the relationship between the temperature and the proton conductivity in an Example.

First, the present inventors first calcined KMg _1-x H _2x (PO ₃ ) ₃ · yH ₂ O, which is a conventional proton-conducting solid electrolyte, at 250 ° C. for about 12 hours with sample a and 300. The structures of a total of 3 samples, a sample b obtained by firing at ° C. for about 12 hours and a sample c obtained by firing at 800 ° C. for about 1 hour, were confirmed.

In order to confirm the structure, powder X-ray diffraction analysis was performed under the conditions shown in the examples below. The results are shown in FIG. In FIG. 1, the sample a shown as “(a) tunnel type KMg _1-x H _2x (PO ₃ ) ₃ · yH ₂ O” is 2θ = 16.18 °, 17.46 °, 23.88 °, 29.72 °, 30.44 °, 32.66 °, 35 °, 28 °, 37.24 °, 38.52 °, 39.02 °, 42.62 °, 45.24 ° in space group R3 Belonged.

On the other hand, the sample b obtained by calcining at 300 ° C. (“(b) Benitoite type structure fired at 300 ° C.” in FIG. 1) and the sample c obtained by calcining at 800 ° C. (“(c)” in FIG. 1). ) 800 ° C firing Benitoite type structure ”), 2θ = 15.48, 18.18, 23.94, 28.52, 31.26, 32.72, 36.36, 36.76, 38.80, 40 It changed to a Benitoite-type structure with peaks assigned to .08, 41.74, 42.80 in the space group P-6c2. That is, it was found that the Benitoite-type structure of the above KMg _1-x H _2x (PO ₃ ) ₃ · yH ₂ O is stable at 300 ° C. or higher.

Further, for each of the sample in which the x value in the composition formula of sample a was changed and the sample in which the x value in the composition formula of sample c was changed, the proton conductivity at 150 ° C. was the same as in the examples described later. Was measured. The results are shown in FIG. In FIG. 2, logσ on the vertical axis indicates the logarithm of the conductivity, and the higher the value, the higher the proton conductivity. From FIG. 2, when KMg _1-x H _2x (PO ₃ ) ₃ · yH ₂ O changes from a tunnel type structure to a Benitoite type structure, the proton conductivity decreases even if the x value in the composition formula is the same. You can see that it does. It is considered that the Benitoite-type structure has a smaller allowance for introducing protons into the structure than the tunnel-type structure, which is the cause of the decrease in the conductivity of the sample of the Benitoite-type structure.

From the results of FIGS. 1 and 2 above, if the phase transition to the Benitoite type structure can be suppressed at 300 ° C or higher and the tunnel type structure can be maintained even at 300 ° C or higher, high proton conductivity can be exhibited and at a wider temperature. We thought that it would be possible to develop an operating proton conduction fuel cell.

The present inventors cannot maintain a tunnel-type structure that contributes to exhibiting high proton conductivity at a high temperature with a conventional substance, and the operation in a temperature range up to about 250 ° C. is the limit. A novel proton-conducting solid electrolyte that can maintain a tunnel-type structure in a wide temperature range from room temperature to a high temperature of 300 ° C or higher, without using expensive or highly toxic raw materials, and low firing. Diligent research was done to manufacture at temperature.

As a result, as a proton-conducting solid electrolyte,
The composition formula is expressed by AM _1-x H _2x (PO ₃ ) ₃ · yH ₂ O.
The element A is K or Rb, and the element M is selected from one or more elements selected from the group consisting of Ni, Zn, Co and Fe, or the group consisting of Ni, Zn, Co and Fe. A combination of one or more elements and Mg, or
The element A is K and Rb, and the element M is a combination of one or more elements selected from the group consisting of Ni, Zn, Co, Fe and Mg.
The x is 0.05 or more, 0.30 or less,
The y is in the range of 0.3 or more and 3.0 or less, has a predetermined structure including a tunnel type structure, and has _H3O ⁺ or H ⁺ in the tunnel type structure. I found that I should do it.

Hereinafter, the proton conduction type solid electrolyte and its production method, and the proton conduction type fuel cell according to the present embodiment will be described in detail.

(Proton conduction type solid electrolyte)
The proton conduction type solid electrolyte in this embodiment is
The composition formula is expressed by AM _1-x H _2x (PO ₃ ) ₃ · yH ₂ O.
The combination of the element A and the element M is
A combination of one or more elements in which the element A is K or Rb and the element M is selected from the group consisting of Ni, Zn, Co and Fe.
A combination in which the element A is K or Rb and the element M is one or more elements and Mg selected from the group consisting of Ni, Zn, Co and Fe.
The element A is K and Rb, and the element M is any combination of one or more elements selected from the group consisting of Ni, Zn, Co, Fe and Mg.

The element A and the element M each exist as ions (cations) forming the skeleton of the solid electrolyte in the proton-conducting solid electrolyte of the present embodiment. The element M is an element having an ionic radius of 0.61 to 0.74 Å as a divalent ion.

The conventional proton conduction type solid electrolyte is a combination of K or Rb as the element A and Mg as the element M, that is, KMg _1-x H _2x (PO ₃ ) ₃ · yH ₂ O and Rb Mg _1-x H _2x ( PO ₃ ) Although it is ₃ · yH ₂ O, the solid electrolyte changed from a tunnel-type crystal structure to a Benitoite-type (Benito stone-type) crystal structure at around 300 ° C. On the other hand, in the proton conduction type solid electrolyte according to the present embodiment, when the element A is K or Rb, one or more elements selected from the group consisting of Ni, Zn, Co and Fe as the element M. Is essential, and when the element A is K and Rb, the element M is one or more elements selected from the group consisting of Ni, Zn, Co, Fe and Mg, and the element constituting the skeleton of the solid electrolyte is used. By using an element different from the conventional proton conduction type solid electrolyte, it is possible to suppress the transition to the Benitoite type (Benito stone type) structure, and as a result, a wide temperature from room temperature to a high temperature of 300 ° C or higher. It was found that high proton conductivity can be expressed in the region.

The combination of the element A and the element M is preferable.
Whether the element A is K or Rb and the element M is a combination of one or more elements selected from the group consisting of Ni, Zn and Co.
The element A is K and Rb, and the element M is Mg.

The combination of the element A and the element M is more preferably that the element A is K and the element M is Ni.

Whereas the conventional proton conduction type solid electrolyte has an operating temperature of up to 250 ° C., according to the proton conduction type solid electrolyte of the present embodiment, by combining the element A and the element M in the above composition formula, the room temperature is reached. It is possible to achieve a wide operating temperature range from to a high temperature of 300 ° C or higher. As a preferable combination of the element A and the element M, if K is combined with one or more of Ni and Zn, the upper limit of the operating temperature exceeds 300 ° C. and 500 ° C. or higher can be achieved.

(About x value)
The x is in the range of 0.05 or more and 0.30 or less. Protons can be easily introduced into the proton-conducting solid electrolyte by setting x to 0.05 or more and deleting a part of the element M. The x is preferably 0.10 or more, more preferably 0.15 or more. Further, from the viewpoint of suppressing excessive water absorption, x is preferably 0.25 or less, more preferably 0.20 or less.

(About y value)
y can be in the range of 0.3 or more and 3.0 or less. It is considered that in the proton conduction type solid electrolyte of the present embodiment, water molecules (crystal water) are secured in the structure even after firing at the time of production, and a water molecule chain is formed. It is considered that protons diffuse at high speed through the water molecule chain formed in this solid electrolyte during the operation of the proton conduction type fuel cell. Therefore, the proton-conducting solid electrolyte of the present embodiment can exhibit high proton conductivity without installing a large-scale humidifying device when the fuel cell is operated. From this point of view, the more water molecules contained in the proton-conducting solid electrolyte of the present embodiment, the more preferable, and y is preferably 1.0 or more, more preferably 1.5 or more. On the other hand, the value of y is 3.0 or less as the amount of water molecules (water of crystallization) that can be structurally retained by the proton-conducting solid electrolyte of the present embodiment. y is preferably 2.5 or less, more preferably 2.0 or less.

Next, the structure of the proton conduction type solid electrolyte of the present embodiment will be described.
The proton conduction type solid electrolyte of this embodiment is
The octahedron formed by combining the ion of the element A and oxygen and the octahedron formed by combining the ion and oxygen of the element M alternately share the oxygen of each other's octahedron. A plurality of formed first columnar bodies exist in parallel,
A plurality of second columnar bodies having a longitudinal direction parallel to the first columnar body, which are composed of PO ₄ chains in which a plurality of PO _4s share oxygen and are connected in a chain, are present in parallel.
It has a tunnel-type structure in which a tunnel-like space surrounded by three second columnar bodies exists.
It has H ₃ O ⁺ or H ⁺ in the tunnel-like space.

The structure of the proton-conducting solid electrolyte of the present embodiment will be described in detail with reference to a schematic diagram, but the proton-conducting solid electrolyte of the present embodiment is not limited to such an embodiment.

FIG. 3 shows a schematic diagram illustrating a part of the longitudinal section of the proton-conducting solid electrolyte of the present embodiment, and FIG. 4 shows a sectional view perpendicular to the longitudinal direction of the proton-conducting solid electrolyte of the present embodiment. It is a schematic diagram which exemplifies a part.

The proton conduction type solid electrolyte 1 of the present embodiment contains an octahedron 4 formed by combining the ions of the element A (reference numeral 2, for example, K) and oxygen 3A, and the ions of the element M (reference numeral 5, for example, Ni). The octahedron 6 formed by combining oxygen 3B is alternately formed by sharing the oxygen of each other's octahedron, that is, alternately formed so that one side 7 of each other's octahedron overlaps. , Has a plurality of first columnar bodies 8. Further, it has a plurality of second columnar bodies 10 having a longitudinal direction parallel to the first columnar body 8 formed by PO ₄ (reference numeral 9) sharing the oxygen atom 3C and connecting them in a chain shape.

And one oxygen of continuous or every other PO ₄ constituting the PO ₄ chain shares oxygen with one first columnar body, and PO ₄ which does not share oxygen with one first columnar body is adjacent. Shares oxygen with other first columnar bodies. Specifically, as shown in FIG. 3, the octahedron 6A formed by combining the ion of the element M and oxygen is composed of two _consecutive PO 49A and 9B constituting the PO ₄ chain and oxygen 31D. It shares 32D. Further, the octahedron 4A formed by combining the ions of the element A and oxygen is the every other PO ₄ among the three consecutive PO 49B, 9C, and 9D constituting the PO ₄ chain, that is, the first PO ₄ . It shares oxygen 32D and 33D with the _first PO 49B and the _third PO 49D. And the _second PO 49C shares oxygen with other first columnar bodies not shown _in FIG.

Further, as illustrated in FIG. 3, the first columnar body 8 and the second columnar body 10 share oxygen 3D, so that the tunnel-shaped space 11 is parallel to the first columnar body 8 and the second columnar body 10. It has a tunnel-shaped structure in which water molecules 12 are formed, and water molecules 12 are present in a chain in the tunnel-shaped space 11.

FIG. 4 shows a part of the structure in the cross section perpendicular to the longitudinal direction of the first columnar body and the second columnar body of FIG. In FIG. 4, the second columnar body is located at each apex of the triangle in three directions at intervals of about 120 degrees with one first columnar body as the central axis. Further, the first columnar body is located at each apex of the triangle in three directions at intervals of about 120 degrees with one second columnar body as the central axis. Then, as illustrated in FIG. 4, it has a tunnel-type structure in which a tunnel-shaped space 11 surrounded by three second columnar bodies of the second columnar body 8A, the second columnar body 8B, and the second columnar body 8C exists. are doing. More specifically, in the tunnel type structure, the three first columnar bodies 10A, 10B and 10C and the three second columnar bodies 8A, 8B and 8C share oxygen constituting the adjacent columnar bodies. Formed by More specifically, in FIG. 4, the three said second columnar bodies, that is, the _three said PO4 chains, are further arranged in the triangular space formed by the three said first columnar bodies. A tunnel-like space surrounded by the _two PO4 chains is formed. FIG. 4 shows a part of the structure in the vertical cross section, and the proton conduction type solid electrolyte of the present embodiment has a structure in which the structure shown in FIG. 4 is continuous on the paper surface. ing.

The above structure can be identified by X-ray diffraction analysis as shown in Examples described later. In the structure of the proton conduction type solid electrolyte of the present embodiment, the "tunnel type structure" refers to a crystal structure attributed to the space group R3, which is determined based on the X-ray diffraction pattern obtained in the X-ray diffraction analysis. say. Since the size of the unit cell changes slightly depending on the composition and constituent elements, a slight deviation can be observed at the peak position, but if the crystal structure is the same, that is, the crystal structure attributed to the space group R3. A similar diffraction pattern is observed. If the peak of the diffraction pattern is assigned by the space group R3, it can be said that the tunnel type structure according to the present embodiment.

The fact that the proton-conducting solid electrolyte of the present embodiment contains water of crystallization can be confirmed from the TG / DTA measurement, which is a thermal measurement, as shown in FIG. 5 below. Further, the introduction of protons by deleting the element M can be confirmed from the FTIR measurement.

(Manufacturing method of proton conduction type solid electrolyte)
The method for producing the proton-conducting solid electrolyte of the present embodiment will be described. The method for producing a proton-conducting solid electrolyte of the present embodiment includes a mixing step of mixing a compound containing the element A, a compound containing the element M, and a compound containing a phosphoric acid to obtain a mixture, and the mixture. Includes a firing step of firing at a temperature of 250 ° C. or higher and 800 ° C. or lower. The proton conduction type solid electrolyte of the present embodiment can be produced by a coprecipitation method or a solid phase method.

Hereinafter, each step will be described.

[Step of mixing the compound containing the element A, the compound containing the element M, and the compound containing phosphoric acid to obtain a mixture]
A compound containing the element A, a compound containing the element M, and a compound containing phosphoric acid, which constitute the proton conduction type solid electrolyte of the present embodiment, are prepared as raw materials. The type of these compounds may be solid or liquid as long as it is a raw material that can obtain a predetermined composition after firing. As the solid raw material of these compounds, for example, salts such as carbonates, nitrates, ammonium salts and phosphates and hydroxides of each of element A and element M are preferably used. Sulfates, halides, carbides, and sulfides are not preferable because SO ₄ , halogen elements, C, and S tend to remain after synthesis. The solid raw material may be pre-ground. These may be dissolved in a solvent such as water. The compound containing phosphoric acid may be a solid powder such as ammonium phosphate or an aqueous solution of phosphoric acid. The raw materials are weighed so as to have the molar ratios of element A, element M, and phosphoric acid in the composition formula. According to this embodiment, it can be produced without using expensive raw materials such as rare earth elements and highly toxic raw materials as in the prior art.

The above raw materials are mixed to obtain a mixture. The presence or absence of a solvent does not matter when mixing. If it can be easily mixed, it may be mixed without a solvent. When a solvent is used, an aqueous solvent or an organic solvent such as hexane or acetone can be used as the solvent. When an organic solvent is used, for example, it may be pulverized with a wet ball mill, mixed and fired. Preferably, by mixing the raw material with the aqueous solution, the salts constituting the raw material are dissolved and can be sufficiently mixed. In the above mixing, the raw material may be completely dissolved or only a part thereof may be dissolved. For example, when nickel hydroxide is used, only a part of it is dissolved.

In the present embodiment, the obtained mixture may be calcined, but for example, when the mixture contains a solvent, a heating stirring step and a drying step may be provided between the mixing step and the calcining step.

When the heating and stirring step and the drying step are performed, for example, they can be carried out as follows. In the heating and stirring step, for example, the above mixture can be heated and stirred at preferably 80 ° C. or higher and 200 ° C. or lower to obtain a concentrated mixture. The stirring method is not particularly limited, and examples thereof include stirring using a magnetic stirrer, a mechanical stirrer, a homomixer, a homogenizer, and the like. The stirring speed and time may be appropriately determined according to the production amount and the like. The heating can be performed using, for example, a hot stirrer or the like.

The drying step can be carried out by a normal operation, for example, can be heated and dried at 100 ° C. or higher, and can be carried out at 100 to 200 ° C. in the atmosphere. The drying time may be determined as needed. By the drying step, a precursor which is solid but amorphous and does not have a tunnel-type structure can be obtained. If necessary, the precursor obtained by drying may be pulverized and then molded. Examples of the molding method include pressure molding, and for example, uniaxial pressure molding and molding by CIP (Cold Isostatic Pressing: cold isotropic pressing) can be performed.

The precursor can also be obtained by calcining the mixture at, for example, 100 to 230 ° C. instead of the drying step. In the case of tentative firing, the mixture may be tentatively fired to obtain a powder, then molded, and the following firing may be performed as the main firing.

[Baking step of firing the precursor at a temperature of 250 ° C or higher and 800 ° C or lower]
The precursor is calcined at a temperature of 250 ° C. or higher and 800 ° C. or lower. By firing at a crystallization temperature of 250 ° C. or higher, the proton conduction type solid electrolyte of the present embodiment having a tunnel type structure can be obtained. By raising the firing temperature, the solid electrolyte can be sufficiently densified. From this point of view, the firing temperature is more preferably 280 ° C. or higher, still more preferably 300 ° C. or higher. On the other hand, for example, from the viewpoint of sufficiently securing water of crystallization in the solid electrolyte, the firing temperature is preferably 600 ° C. or lower, more preferably 400 ° C. or lower.

(Proton conduction fuel cell)
The proton conduction type fuel cell of the present embodiment can adopt the conventional configuration except that the proton conduction type solid electrolyte of the present embodiment is used as the solid electrolyte. For example, as the shape of the solid electrolyte, for example, the thickness when formed into a layer, the oxygen electrode constituting the electrochemical cell, the material and thickness of the hydrogen electrode, and the method for producing these oxygen electrode and hydrogen electrode are known methods. Can be adopted.

According to the proton-conducting solid electrolyte of the present embodiment, structural changes at around 300 ° C. are suppressed, and high proton conductivity can be exhibited in a wide temperature range from room temperature to a high temperature of about 300 ° C. or higher. Depending on the elements constituting the proton conduction type solid electrolyte, it can be operated from room temperature to a temperature range of about 520 ° C. That is, the proton conduction type fuel cell provided with the proton conduction type solid electrolyte of the present embodiment has a wide temperature range in which high proton conductivity is exhibited as compared with the conventional proton conduction type fuel cell. It is possible to realize operation in the temperature range of 100 to 500 ° C., which has been coveted as the power generation temperature of the fuel cell. Furthermore, since it exhibits high proton conductivity without humidification, a large-scale humidifier is not essential when developing a fuel cell system. Further, it does not contain expensive elements such as precious metals and rare earths, and can be produced with inexpensive raw materials without using highly toxic raw materials. Furthermore, since it can be manufactured at a low temperature of less than 1000 ° C., the manufacturing cost can be suppressed.

Hereinafter, the present invention will be described in more detail with reference to examples. The present invention is not limited by the following examples, and can be carried out with appropriate modifications to the extent that it can meet the above-mentioned and later-described intent, and both of them are the technical scope of the present invention. Included in.

[Production of sample]
First, various samples were produced as shown in Production Examples 1 to 6 below.
(Manufacturing Example 1)
Sample 1: Production of KNi _1-x H _2x (PO ₃ ) ₃ · yH ₂ O (x = 0 to 0.18) Potassium carbonate and nickel hydroxide are weighed to a predetermined molar ratio and 0.5 molL. It was dissolved in 30 mL of a -1 phosphoric acid aqueous solution, and heated and stirred at 120 ° C. Then, the concentrated solution (about 5 mL) obtained by heating and stirring was transferred to a watch glass on which a Teflon (registered trademark) sheet was placed, and dried in a dryer at 120 ° C. for 24 hours. The obtained precursor was pulverized and mixed, and the powder was molded into a cylindrical shape having a diameter of 1 cm and a thickness of about 1 mm and calcined at 400 ° C. for 6 to 12 hours to obtain Sample 1.

(Manufacturing Example 2)
Sample 2: Production of KZn _1-x H _2x (PO ₃ ) _{3.yH 2} O (x = 0 to 0.20) Potassium carbonate and zinc nitrate hexahydrate were weighed to a predetermined molar ratio. It was dissolved in 30 mL of a 0.5 molL-1 phosphoric acid aqueous solution, and heated and stirred at 200 ° C. Then, the concentrated solution (about 5 mL) obtained by heating and stirring was transferred to a watch glass on which a Teflon (registered trademark) sheet was placed, and dried in a dryer at 200 ° C. for 24 hours. The obtained precursor was pulverized and mixed, and the powder was molded into a cylindrical shape having a diameter of 1 cm and a thickness of about 1 mm and calcined at 330 ° C. for 12 hours to obtain Sample 2.

(Manufacturing Example 3)
Sample 3: Production of KCo _1-x H _2x (PO ₃ ) ₃ · yH ₂ O (x = 0 to 0.20) Potassium carbonate and cobalt nitrate hexahydrate were weighed to a predetermined molar ratio. It was dissolved in 30 mL of a 0.5 molL-1 phosphoric acid aqueous solution, and heated and stirred at 120 ° C. Then, the concentrated solution (about 5 mL) obtained by heating and stirring was transferred to a watch glass on which a Teflon (registered trademark) sheet was placed, and dried in a dryer at 200 ° C. for 24 hours. The obtained precursor was pulverized and mixed, and the powder was molded into a cylindrical shape having a diameter of 1 cm and a thickness of about 1 mm and calcined at 250 to 270 ° C. for 12 hours to obtain Sample 3.

(Manufacturing Example 4)
Sample 4: Production of K (Ni _0.82-z Zn _z ) H _2x (PO ₃ ) ₃ · yH ₂ O (z = 0.01, 0.42) Potassium carbonate, nickel hydroxide, and zinc nitrate hexahydrate The Japanese product was weighed to a predetermined molar ratio, dissolved in 30 mL of a 0.5 molL-1 phosphoric acid aqueous solution, and heated and stirred at 120 ° C. Then, the concentrated solution (about 5 mL) obtained by heating and stirring was transferred to a watch glass on which a Teflon (registered trademark) sheet was placed, and dried in a dryer at 120 ° C. for 24 hours. The obtained precursor was pulverized and mixed, and the powder was molded into a cylindrical shape having a diameter of 1 cm and a thickness of about 1 mm and calcined at 370 to 400 ° C. for 6-12 hours to obtain Sample 4.

(Manufacturing Example 5)
Sample 5: (Rb _0.5 K _0.5 ) Mg _0.9 H _0.2 (PO ₃ ) Production of ₃ · yH ₂ O Potassium carbonate, rubidium carbonate and nickel hydroxide so as to have a predetermined molar ratio. Weighed, dissolved in 30 mL of 0.5 molL-1 phosphoric acid aqueous solution, heated and stirred at 120 ° C. Then, the concentrated solution (about 5 mL) obtained by heating and stirring was transferred to a watch glass on which a Teflon (registered trademark) sheet was placed, and dried in a dryer at 120 ° C. for 24 hours. The obtained precursor was pulverized and mixed, and the powder was molded into a cylindrical shape having a diameter of 1 cm and a thickness of about 1 mm and calcined at 270 ° C. for 15 hours to obtain Sample 5.

(Manufacturing Example 6)
Sample 6: RbNi _0.95 H _0.10 (PO ₃ ) ₃ · Production of yH ₂ O Rubidium carbonate and nickel hydroxide are weighed to a predetermined molar ratio and made into 30 mL of 0.5 mol L-1 phosphoric acid aqueous solution. It was dissolved and heated and stirred at 120 ° C. Then, the concentrated solution (about 5 mL) obtained by heating and stirring was transferred to a watch glass on which a Teflon (registered trademark) sheet was placed, and dried in a dryer at 120 ° C. for 24 hours. The obtained precursor was pulverized and mixed, and the powder was molded into a cylindrical shape having a diameter of 1 cm and a thickness of about 1 mm and calcined at 270 ° C. for 12 hours to obtain Sample 6.

[Sample measuring means]
Using the obtained sample, X-ray diffraction analysis, proton conductivity and the like were measured. In the measurement of the proton conductivity, the above sample was used as it was. In the X-ray diffraction analysis, a powder having a particle size in the range of about 0.5 to 20 μm, which was obtained by pulverizing the sample, was used.
(Powder X-ray diffraction)
The structure of the sample was confirmed by powder X-ray diffraction under the following conditions.
・ Equipment used: Rigaku Co., Ltd. Rint2000
・ Measurement conditions Light source: Cu tube Characteristic X-ray: CuKα = 1.54 Å
Measurement range: 15 degrees -60 degrees Step width: 0.02 / degree

(Measurement of proton conductivity)
The proton conductivity of the above sample was measured by the AC impedance method in an _N2 gas stream using an LCR meter (product number IM3536) manufactured by Hioki Electric Co., Ltd. The atmosphere at the time of measuring the proton conductivity may be an inert atmosphere, and may be in the _N2 gas airflow or in the Ar gas airflow.

(Other measurements)
The fact that the proton-conducting solid electrolyte of the present embodiment has a proton introduced due to a deficiency of the element M is that Production Example 1 (KNi _1-x H _2x (PO ₃ ) ₃ · yH ₂ O, x = 0. Using the sample of .18), FTIR measurement was performed using a Fourier transform infrared spectrophotometer (IRAffinity-1S) manufactured by Shimadzu Corporation.

Further, the fact that the proton conduction type solid electrolyte of the present embodiment contained crystalline water and the y value was 1.0 indicates that Production Example 1 (KNi _1-x H _2x (PO ₃ ) ₃ · yH ₂ O, x Using the sample of = 0.10), TG / DTA measurement, which is a thermal measurement, was confirmed using a differential thermal thermal weight simultaneous measurement device (TG / DTA) 6300 manufactured by SI Nanotechnology Co., Ltd. The results are shown in FIG. FIG. 5 is a TG / DTA curve measured at a heating rate of 10 ° C./min in an _N2 gas stream.

[Sample evaluation]
(Evaluation 1: Structure of various samples)
Composition formula AM _1-x H _2x (PO ₃ ) _3. The results of powder X-ray diffraction of various samples of element A and element M of yH ₂ O are shown in FIG. From FIG. 6, it was confirmed that the reflections (peaks) attributed to the space group R3 were observed in all the samples according to the present embodiment, and that a tunnel-type structure was formed.

(Evaluation 2: Change of x value)
Composition formula For each of KNi _1-x H _2x (PO ₃ ) ₃ · yH ₂ O and KZn _1-x H _2x (PO ₃ ) ₃ · yH ₂ O, powder X-ray diffraction for samples with various x values. The results of the above are shown in FIGS. 7 and 8. In all the samples of x = 0 to 0.18 in FIG. 7 and all the samples of x = 0 to 0.20 in FIG. 8, only the reflection (peak) attributed to the space group R3 was observed. A single phase (sample without impurities) with a tunnel-type structure was obtained. However, the substance with x = 0 is not preferable because it is inferior in proton conductivity as described above.

Further, FIG. 9 shows the results of measuring the conductivity of the composition formula KNi _1-x H _2x (PO ₃ ) ₃ · yH ₂ O when x = 0.10, 0.15 and 0.18. From FIG. 9, it can be seen that the proton conductivity increases as the value of x increases. This can be considered as follows. That is, when a part of Ni ²⁺ is deleted, two H ⁺ are introduced into the sample, so that the electrical neutrality (plus or minus balance) of the sample is maintained. By increasing the amount of the above defects, the amount of protons in the sample is increased, and it is considered that the proton conductivity is expected to be improved.

(Evaluation 3: Structure at high temperature)
The structure at high temperature was confirmed by changing the firing temperature at the time of manufacture. Specifically, KNi _1-x H _2x (PO ₃ ) ₃ · yH ₂ O (x = 0.18), which is a sample obtained by firing at a firing temperature of 400 ° C. in Production Example 1, and a firing temperature of 500. Powder X-ray diffraction analysis was performed on KNi _1-x H _2x (PO ₃ ) ₃ · yH ₂ O (x = 0.18) obtained in the same manner as in Production Example 1 except that the temperature was set to ° C. The results are shown in FIG.

From FIG. 10, even in the sample obtained by firing at 500 ° C., the reflection (peak) attributed to the space group R3 was observed, it was confirmed that it had a tunnel type structure, and the diffraction pattern of the Benitoite type structure was confirmed. Was not done. The firing temperature can be regarded as a temperature at which the tunnel type structure can be maintained. From this, it is considered that the phase transition observed at high temperature in the conventional KMg _1-x H _2x (PO ₃ ) ₃ · yH ₂ O is suppressed in the proton conduction type solid electrolyte according to the present embodiment.

(Evaluation 4: Temperature dependence of proton conductivity)
FIG. 11 shows the results of measuring the proton conductivity in the temperature range from room temperature to over 500 ° C. using various samples as described above. The horizontal axis of FIG. 11 shows the temperature at the time of conductivity measurement. From FIG. 11, as a sample according to the present embodiment, the combination of element A being K and element M being Ni, and the combination of element A being K and element M being Ni and Zn are from room temperature to a high temperature of 300 ° C. or higher. High proton conductivity was developed in a wide temperature range. In particular, the combination of the element A as K and the element M as Ni exhibited high proton conductivity in a wider temperature range from room temperature to an upper limit exceeding 520 ° C. Further, from FIG. 11, the proton conductivity of the sample in which the element M is Ni alone is higher than that in the sample in which a part of Ni as the element M is replaced with Zn. It is considered that this is because the grain boundary resistance is increased by substituting a part of Ni with Zn, which is the cause of the decrease in conductivity.

The proton conduction type solid electrolyte according to the present embodiment can be preferably used as, for example, a proton conduction type fuel cell. Since the proton conduction type solid electrolyte according to the present embodiment has a wider operating temperature range than the conventional proton conduction type solid electrolyte, when applied to the proton conduction type fuel cell, the selectivity of the power generation temperature range is expanded. Material and manufacturing costs can be reduced.

1 Proton conduction type solid electrolyte 2 Element A
3A, 3B, 3C, 3D, 31D, 32D, 33D Oxygen (atom)
4, 4A Octahedron formed by combining the ions of element A and oxygen 5 element M
6, 6A Eighthedron formed by combining the ions of element M and oxygen 7 The octahedron formed by combining the ions of element A and oxygen and the octahedron formed by combining the ions of element M and oxygen Overlapping sides of 8, 8A, 8B, 8C 1st columnar body 9, 9A, 9B, 9C, 9D PO ₄
10, 10A, 10B, 10C 2nd columnar body 11 Tunnel-like space 12 Water molecules

Claims (5)

The composition formula is expressed by AM _1-x H _2x (PO ₃ ) ₃ · yH ₂ O.
The element A is K or Rb, and the element M is selected from one or more elements selected from the group consisting of Ni, Zn, Co and Fe, or the group consisting of Ni, Zn, Co and Fe. A combination of one or more elements and Mg, or
The element A is K and Rb, and the element M is a combination of one or more elements selected from the group consisting of Ni, Zn, Co, Fe and Mg.
The x is in the range of 0.05 or more and 0.30 or less.
The y is in the range of 0.3 or more and 3.0 or less.
The octahedron formed by combining the ion of the element A and oxygen and the octahedron formed by combining the ion and oxygen of the element M alternately share the oxygen of each other's octahedron. A plurality of formed first columnar bodies exist in parallel,
A plurality of second columnar bodies having a longitudinal direction parallel to the first columnar body, which are composed of PO ₄ chains in which a plurality of PO _4s share oxygen and are connected in a chain, are present in parallel.
It has a tunnel-type structure in which a tunnel-like space surrounded by three second columnar bodies exists.
A proton-conducting solid electrolyte having H ₃ O ⁺ or H ⁺ in the tunnel-like space. Whether the element A is K or Rb and the element M is a combination of one or more elements selected from the group consisting of Ni, Zn and Co.
The proton conduction type solid electrolyte according to claim 1, wherein the element A is K and Rb, and the element M is Mg. The proton conduction type solid electrolyte according to claim 1, wherein the element A is K and the element M is Ni. The method for producing a proton-conducting solid electrolyte according to any one of claims 1 to 3.
A mixing step of mixing the compound containing the element A, the compound containing the element M, and the compound containing phosphoric acid to obtain a mixture.
A method for producing a proton-conducting solid electrolyte, which comprises a firing step of firing the mixture at a temperature of 250 ° C. or higher and 800 ° C. or lower. A proton conduction type fuel cell using the proton conduction type solid electrolyte according to any one of claims 1 to 3 as an electrolyte.

Images