JP6916332B1 - Electrochemical cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrolyte material and an electrochemical cell capable of both improving the initial conductivity and suppressing the decrease rate of the conductivity. An electrolyte material is composed of a layered double hydroxide containing Ni ions, Al ions, and at least one transition metal selected from Fe, Co and Mn. The total concentration of the transition metal with respect to Ni ions is 10 ppm or more and 10000 ppm or less. [Selection diagram] Fig. 1

Description

The present invention relates to an electrochemical cell.

Conventionally, as a fuel cell that operates at a relatively low temperature (for example, 250 ° C. or lower), an alkaline fuel cell (AFC) having ^{a hydroxide ion (OH −) as a carrier is known.} In AFC, various liquid fuels or gaseous fuels can be used. For example, when methanol is used as a fuel, the following electrochemical reaction occurs.

^{_{Anode: CH 3 OH + 6OH - →}} 6e - + CO 2 + 5H 2 O
・ Cathode: 3 / 2O ₂ + 3H ₂ O + 6e ⁻ → 6OH ⁻
・ Overall: CH ₃ OH + 3 / 2O ₂ → CO ₂ + 2H ₂ O

Here, Patent Document 1 proposes to use a layered double hydroxide (LDH: Layered Double Hydroxide) having hydroxide ion conductivity as an electrolyte in AFC.

Japanese Unexamined Patent Publication No. 2016-071948

By the way, there is a demand to further improve the initial conductivity of the electrolyte containing LDH.

Further, if the electrolyte containing LDH is used for a long time at the operating temperature of AFC, the hydroxide ion retention function in the hydroxide basic layer in LDH may deteriorate, and the conductivity of the electrolyte may decrease.

Therefore, it is desired to develop an electrolyte material capable of both improving the initial conductivity and suppressing the decrease rate of the conductivity.

Such electrolyte materials are not limited to alkaline fuel cells, but are electrochemical cells such as secondary batteries using hydroxide ions as carriers (zinc air secondary batteries, etc.) and electrolytic cells that generate hydrogen and oxygen from water vapor. It is useful for.

An object of the present invention is to provide an electrolyte material and an electrochemical cell capable of both improving the initial conductivity and suppressing the decrease rate of the conductivity.

The electrolyte material according to the present invention is composed of a layered double hydroxide containing Ni ions, Al ions, and at least one transition metal selected from Fe, Co and Mn. In the electrolyte material, the total concentration of the transition metal with respect to Ni ions is 10 ppm or more and 10000 ppm or less.

According to the present invention, it is possible to provide an electrolyte material and an electrochemical cell capable of both improving the initial conductivity and suppressing the decrease rate of the conductivity.

Cross-sectional view schematically showing the configuration of an alkaline fuel cell

(Electrolyte material)
The electrolyte material according to the present invention is a constituent material of an electrolyte used in an electrochemical cell such as a secondary battery (zinc-air secondary battery or the like) using hydroxide ions as a carrier or an electrolytic cell that generates hydrogen and oxygen from water vapor. Is suitable as. In the present embodiment, a case where the electrolyte material according to the present invention is applied as a constituent material of an electrolyte for an alkaline fuel cell (AFC) using ^{a hydroxide ion (OH −) as a carrier will be described.}

The electrolyte material according to the present invention is composed of a layered double hydroxide (LDH: Layered Double Hydroxide) containing Ni ions, Al ions, and at least one transition metal selected from Fe, Co, and Mn. NS. This LDH is composed of a plurality of hydroxide basic layers and an intermediate layer interposed between the plurality of hydroxide basic layers.

The basic composition of LDH constituting the electrolyte material according to the present invention can be represented by, for example, the following general formula (1).

[Ni ²⁺ _1-p-q-r-s Al ³⁺ _p E _q M 2 ⁺ _r M ³⁺ _s (OH) ₂ ] [An ^- _{p + s / n} · mH ₂ O] ... Equation (1)

In formula (1), E is at least one transition metal selected from Fe, Co and Mn. E is contained in each hydroxide basic layer.

In the formula (1), M ²⁺ is at least one selected from ^{Mg 2+} , Ca ²⁺ , Sr ²⁺ and Zn ^{2+ , and M 3+} is at least one selected from ^{Y 3+} , Ce ^{3+, and} be. M ²⁺ and M ³⁺ are contained in each hydroxide base layer.

In the formula (1), the subscript 1-p-q-r-s of ^{Ni 2+ is 0.67 or more and 0.80 or less, and the subscript p of Al 3+} is 0.20 or more and 0.33 or less. , E subscript q is 6.7 × 10 ^-6 or more and 8.0 × 10 ^-3 or less, M ²⁺ subscript r is 0 or more and 0.10 or less, and M ³⁺ subscript s is 0. It is 0.10 or less.

In formula (1), ^An− is an n-valent anion. n is an integer of one valence or more. A ^n- is preferably a monovalent or divalent anion. A ^n- is, OH ^- and / or _CO preferably comprises ^{3 2-.} P + s contained in A ^n- subscript is 0.20 to 0.43 or ^less, n included in the ^{A n-} subscript is an integer of 1 or more, the _{H 2} O factor m is any It is a number. A ^n- and _{H 2} O is contained in the intermediate layer of hydroxide base layers.

However, the valences of Ni ion, Al ion and M shown in the general formula (1) are not always fixed. For example, the valence of Ni ions can be 3+, and the valence of Al ions can be other than 3+. Therefore, it is impractical or impossible to strictly specify LDH by a general formula, and the above general formula (1) should be understood as an example showing the "basic composition".

The electrolyte material according to the present invention is characterized in that the total concentration of E (that is, at least one transition metal selected from Fe, Co and Mn) with respect to Ni ions is 10 ppm or more and 10000 ppm or less.

By setting the total concentration of E with respect to Ni ions to 10 ppm or more, at least one of Fe, Co, and Mn can be deteriorated preferentially over Ni. Therefore, the electrolyte itself deteriorates in the hydroxide basic layer. It is possible to suppress deterioration of the hydroxide ion retention function over time. Therefore, when the electrolyte is constructed using the electrolyte material, it is possible to prevent the hydroxide ion conductivity of the alkaline fuel cell from deteriorating with time. The total concentration of E with respect to Ni ions is preferably 50 ppm or more, more preferably 100 ppm or more, and even more preferably 500 ppm or more.

Further, by setting the total concentration of E with respect to Ni ions to 10000 ppm or less, the strain of the mother crystal can be minimized, so that the hydroxide ion conductivity of LDH can be sufficiently ensured. Therefore, when the electrolyte is constructed using the electrolyte material, the output of the alkaline fuel cell can be sufficiently secured. The total concentration of E with respect to Ni ions is preferably 8000 ppm or less, more preferably 5000 ppm or less.

When the electrolyte material contains two or more transition metals selected from Fe, Co and Mn, the total concentration of E with respect to Ni ions is the sum of the concentrations of each transition metal with respect to Ni ions.

The concentration of E with respect to Ni ions can be measured by inductively coupled plasma atomic emission spectroscopy (ICP-AES). When measuring the concentration of E with respect to Ni ions, the electrolyte material is dissolved in hydrochloric acid of the standard for high-purity analysis, sampled as an aqueous solution, and measured using an ICP emission spectrometer.

The particle size of the electrolyte material according to the present invention is not particularly limited, but for example, the volume-based D50 average particle size can be 0.01 μm or more and 10 μm or less. When the average particle size of D50 is 0.05 μm or more, LDH powders can be prevented from agglomerating with each other and leaving pores during molding, which is preferable. When the average particle size of D50 is 2 μm or less, the moldability of the electrolyte material can be improved, which is preferable.

(Method for Manufacturing Electrolyte Material) An example of the method for manufacturing the electrolyte material will be described.

First, a raw material serving as a metal ion source constituting LDH, a raw material serving as an anion source, a precipitant, and ion-exchanged water are mixed.

Next, the electrolyte material (LDH powder) can be produced by reacting while controlling the temperature of the mixture to 20 to 200 ° C. and controlling the pH value of the mixture to 5 to 11.

Examples of the raw material serving as a metal ion source constituting LDH include metal chloride, metal nitrate, metal sulfate, metal hydroxide, and metal oxide. By adding chloride, nitrate, sulfate, hydroxide, oxide, or the like of at least one of Fe, Co, and Mn to this metal ion source, the LDH mainly containing Ni and Al can be treated. Fe, Co and Mn can be doped.

As the anion source, a carbonate ion _(CO ^{3 2-),} sulfate ion _(SO ^{4 2-),} chloride ion (Cl ^-), phosphate ion _(PO ^{4 3-),} nitrate ion (NO ₃ ^-) Examples thereof include sodium salt and potassium salt, which are water-soluble salts such as. Examples of the precipitant include sodium hydroxide, potassium hydroxide, ammonia, urea and the like.

Further, as the reaction method, a coprecipitation method, a sol-gel method, a uniform precipitation method, an inverse uniform precipitation method or the like can be used.

(Alkaline fuel cell 10)
Hereinafter, as an example of the electrochemical cell according to the present invention, ^{an alkaline fuel cell 10 having a hydroxide ion (OH −} ) as a carrier will be described with reference to the drawings. FIG. 1 is a cross-sectional view showing the configuration of the alkaline fuel cell 10.

The alkaline fuel cell 10 includes a cathode 12, an anode 14, and an electrolyte 16. The alkaline fuel cell 10 generates electricity at a relatively low temperature (for example, 50 ° C. to 250 ° C.) based on the following electrochemical reaction formula. In the electrochemical reaction formula below, the case where methanol is used as an example of fuel is exemplified.

・ Cathode 12: 3 / 2O ₂ + 3H ₂ O + 6e ⁻ → 6OH ⁻
・ Anode 14: CH ₃ OH + 6OH ⁻ → 6e ⁻ + CO ₂ + 5H ₂ O
・ Overall: CH ₃ OH + 3 / 2O ₂ → CO ₂ + 2H ₂ O

1. 1. Cathode 12
The cathode 12 is an anode generally called an air electrode. During power generation of the alkaline fuel cell 10, an oxidizing agent _{containing oxygen (O 2} ) is supplied to the cathode 12 via the oxidizing agent supplying means 13. As the oxidizing agent, it is preferable to use air, and it is more preferable that the air is humidified. The cathode 12 is a porous body capable of diffusing an oxidizing agent inside. The porosity of the cathode 12 is not particularly limited.

The cathode 12 is not particularly limited as long as it contains a known air electrode catalyst used for AFC. Examples of cathode catalysts include Group 8-10 elements (IUPAC format periodic table) such as platinum group elements (Ru, Rh, Pd, Ir, Pt) and iron group elements (Fe, Co, Ni). Group 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 (salen =) N, N'-bis (salicylidene) ethylenediamine), silver nitrate, and any combination thereof. The amount of the catalyst supported on the cathode 12 is not particularly limited, but is preferably 0.05 to 10 mg / cm ² , more preferably 0.05 to 5 mg / cm ² . The cathode catalyst is preferably supported on carbon. Preferred examples of the cathode 12 or the catalyst constituting the cathode 12 are platinum-supported carbon (Pt / C), platinum-cobalt-supported carbon (PtCo / C), palladium-supported carbon (Pd / C), and rhodium-supported carbon (Rh / C). , Nickel-supported carbon (Ni / C), copper-supported carbon (Cu / C), and silver-supported carbon (Ag / C).

2. Anode 14
The anode 14 is a cathode generally called a fuel electrode. During power generation of the alkaline fuel cell 10, fuel containing a hydrogen atom (H) is supplied to the anode 14 via the fuel supply means 15.

The fuel may contain a fuel compound capable of reacting with hydroxide ions (OH ⁻ ) at the anode 14, and may be in any form of liquid fuel, gas fuel, or gas-liquid mixed 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 ), monomethyl hydrazine (CH ₃ NHNH ₂ ), dimethyl hydrazine ((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 catalyst poisoning by carbon monoxide. be.

The fuel compound may be used as it is as a fuel, 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, 30 to 99.9% by weight, preferably 66 to 99.9% by weight.

Hydrocarbon-based liquid fuels containing alcohols such as methanol and ethanol and ethers, hydrocarbon-based gases such as methane, and pure hydrogen can be used as they are as fuels. In particular, methanol is preferable as the fuel used in the alkaline fuel cell 10 according to the present embodiment. Methanol may be in a gaseous state, a liquid state, or a gas-liquid mixed state.

The anode 14 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 14 and the catalysts constituting the anode 14 are nickel, cobalt, silver, platinum-supported carbon (Pt / C), platinum-luthenium-supported carbon (PtRu / C), palladium-supported carbon (Pd / C), and rhodium-supported. Examples thereof include carbon (Rh / C), nickel-supported carbon (Ni / C), copper-supported carbon (Cu / C), and silver-supported carbon (Ag / C).

The method for producing the anode 14 is not particularly limited, but for example, the anode catalyst and, if desired, the carrier may be mixed with a binder to form a paste, and the paste-like mixture may be applied to the anode-side surface 16T of the electrolyte 16. can.

3. 3. Electrolyte 16
The electrolyte 16 is arranged between the cathode 12 and the anode 14. The electrolyte 16 is connected to each of the cathode 12 and the anode 14. The electrolyte 16 is formed in the form of a film, a layer, or a sheet. The thickness of the electrolyte 16 is not particularly limited, but can be, for example, 1 μm or more and 200 μm or less.

The electrolyte 16 contains the above-mentioned electrolyte material. As described above, in the electrolyte material, the total concentration of E with respect to Ni ions is 10 ppm or more and 10000 ppm or less. Therefore, it is possible to prevent the hydroxide ion conductivity of the alkaline fuel cell 10 from deteriorating with time, and it is possible to sufficiently secure the output of the alkaline fuel cell 10.

The method for producing the electrolyte 16 is not particularly limited, but for example, a paste obtained by mixing an electrolyte material and an organic binder is formed into a sheet by a printing method, and the sheet is heat-treated (80 to 200 hours, 80 to 150 ° C.). The electrolyte 16 can be formed. Further, the electrolyte 16 can also be formed by powder forming the electrolyte material by a known method such as a die uniaxial press or cold isotropic pressurization (CIP). Further, it can be formed by impregnating a slurry in which an electrolyte material and a dispersion medium are mixed with a porous base material, subjecting it to a drying treatment (80 to 150 ° C.), and filling the porous base material with the electrolyte material.

(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.

In the above embodiment, an alkaline fuel cell having a hydroxide ion as a carrier has been described as an example of an electrochemical cell to which the electrolyte material according to the present invention is applied. However, the electrolyte material according to the present invention has various electrochemicals. Applicable to cells. Examples of the electrochemical cell include a secondary battery using hydroxide ions as a carrier (such as a zinc-air secondary battery) and an electrolytic cell that generates hydrogen and oxygen from water vapor.

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

(Preparation of electrolyte)
Electrolytes according to Examples 1 to 30 and Comparative Examples 1 to 18 were prepared as follows, and their conductivity was evaluated.

First, raw materials that are the metal ion sources that make up LDH (specifically, special grade reagents manufactured by Kanto Chemical Co., Inc., nickel (II) nitrate hexahydrate and aluminum nitrate hexahydrate), and anion sources. Raw materials (specifically, special grade sodium carbonate manufactured by Kanto Chemical Co., Inc.), a precipitant (specifically, special grade sodium hydroxide manufactured by Kanto Chemical Co., Inc.), and ion-exchanged water were mixed. At this time, as shown in Table 1, in order to dope LDH with Fe, Co, and Mn, Fe nitrate (specifically, special grade iron (III) nitrate hydrate manufactured by Kanto Chemical Co., Ltd.). (Specifically), Co nitrate (specifically, special grade cobalt nitrate (II) hexahydrate manufactured by Kanto Chemical Co., Ltd.) and Mn nitrate (specifically, special grade manganese nitrate manufactured by Kanto Chemical Co., Ltd.) (II) Hexahydrate) was appropriately added to the raw material as a metal ion source.

Next, the LDH powder is powdered using the coprecipitation method while controlling the temperature of the mixture to 20 to 100 ° C. and controlling the pH value of the mixture to 6 to 10 by controlling the concentration of the raw material and the precipitant. (Electrolyte material) was prepared.

Next, an aqueous solution was prepared by dissolving the prepared LDH powder in hydrochloric acid (manufactured by Kanto Chemical Co., Inc.), which is a standard for high-purity analysis. Then, using the prepared aqueous solution, the total concentration of E (that is, at least one transition metal selected from Fe, Co and Mn) with respect to Ni ions in the LDH powder was measured. Specifically, using an ICP emission spectrometer, the concentration of Fe with respect to Ni ions, the concentration of Co with respect to Ni ions, and the concentration of Mn with respect to Ni ions were measured, and the total of them was calculated as E for Ni ions. It was taken as the total concentration. Table 1 summarizes each concentration. In Table 1, when the concentration is less than the detection limit (0.01 ppm), it is displayed as “−”.

In addition, the Ni ²⁺ / Al ³⁺ ratio (ratio of Ni ions to Al ions) in the LDH powder was measured using the prepared aqueous solution. Although not shown in Table 1, in all of Examples 1 to 30 and Comparative Examples 1 to 18, the Ni ²⁺ / Al ³⁺ ratio in the LDH powder was 2 or more and 4 or less.

Next, an electrolyte was prepared by forming a green compact from the prepared LDH powder at a pressure of 3000 kgf / cm ^{2 by a cold isotropic press.}

Next, according to JISR1661 (method for measuring the conductivity of fine ceramic ion conductors), the initial conductivity of the produced electrolyte and the conductivity after 400 hours were measured. The measurement was carried out in an environment of 80 ° C. in the air and 80% relative humidity. The conductivity is an index showing the hydroxide ion conductivity of the electrolyte.

Table 1 summarizes the rate of decrease in conductivity and the initial conductivity after 400 hours have passed. The rate of decrease in conductivity after the lapse of 400 hr is a value obtained by dividing the conductivity after the lapse of 400 hr by the initial conductivity.

In Table 1, the rate of decrease in conductivity after 400 hours was evaluated as ◯ when it was 10% or less, and evaluated as x when it was more than 10%. Further, in Table 1, the initial conductivity ^{was evaluated as ◯ when it was 5 × 10 -3} S / cm or more, and evaluated as × when it was less than ^{5 × 10 -3 S / cm.}

As shown in Table 1, Comparative Examples 1, 2, 5, 6, 9, in which the total concentration of E (that is, at least one transition metal selected from Fe, Co, and Mn) with respect to Ni ions was less than 10 ppm, In 10, 13 to 15, the rate of decrease in conductivity was large after 400 hours had passed. Further, in Comparative Examples 3, 4, 7, 8, 11, 12, 16 to 18 in which the total concentration of E with respect to Ni ions was more than 10,000 ppm, the initial conductivity was low.

On the other hand, in Examples 1 to 30 in which the total concentration of E with respect to Ni ions was 10 ppm or more and 10000 ppm or less, the rate of decrease in conductivity after the lapse of 400 hr was small and the initial conductivity was high. Such a result was obtained because at least one of Fe, Co and Mn was preferentially deteriorated over Ni and the deterioration of the electrolyte itself could be suppressed, so that the hydroxide ion retention in the hydroxide basic layer was obtained. This is because the deterioration of the function with time is suppressed, and the hydroxide ion conductivity of LDH can be sufficiently ensured by minimizing the strain of the mother crystal by minimizing the addition amount of at least one of Fe, Co and Mn. Is.

Further, it was confirmed that by setting the total concentration of E with respect to Ni ions to 100 ppm or more, and further by setting it to 500 ppm or more, the rate of decrease in conductivity after the lapse of 400 hours can be further reduced.

10 Alkaline fuel cell 12 Cathode 14 Anode 16 Electrolyte

Claims (2)

It is composed of a layered double hydroxide containing Ni ions, Al ions, and at least one transition metal selected from Fe, Co, and Mn.
The total concentration of the transition metal to Ni ion state, and are more 10000ppm or less 10 ppm,
The layered hydroxide is represented by the following formula (1).
Electrolyte material.
[Ni ²⁺ _1-p-q-r-s Al ³⁺ _p E _q M 2 ⁺ _r M ³⁺ _s (OH) ₂ ] [An ^- _{p + s / n} · mH ₂ O] ... Equation (1)
(In the formula (1), E is the transition metal, M ²⁺ is at least one selected from ^{Mg 2+} , Ca ²⁺ , Sr ²⁺ and Zn ^{2+ , and M 3+} is selected from ^{Y 3+} and Ce ^3+. that is at least ^{one, a n-is} the n-valent anion, 0.67 ≦ 1-p-q -r-s ≦ 0.80,0.20 ≦ p ≦ 0.33,6.7 × ^10-6 ≦ q ≦ 8.0 × 10 ^-3 , 0 ≦ r ≦ 0.10, 0 ≦ s ≦ 0.10, 0.20 ≦ p + s ≦ 0.43, n is an integer of 1 or more. m is an arbitrary number.) The cathode to which the oxidant is supplied and
With the anode where the fuel is supplied,
An electrolyte that is arranged between the cathode and the anode and contains the electrolyte material according to claim 1,
An electrochemical cell equipped with.

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