JP2021150070A - Electrochemical cell - Google Patents

Abstract

To provide an electrochemical cell which can increase the initial conductivity of an electrolyte and suppress the degradation resulting from being dried.SOLUTION: An alkali type fuel cell 10 comprises an electrolyte 16 containing a layered composite hydroxide containing Ni ions and Al ions, and a hydroxide of at least one transition metal selected from Fe, Co and Mn. To Ni ions that the layered composite hydroxide contains, the ion total concentration of transition metal included in the hydroxide is 50 ppm or more and 20000 ppm or less.SELECTED DRAWING: Figure 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 reactions occur.

^{_{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 for further improving the initial conductivity of the electrolyte containing LDH.

Further, when an electrolyte containing LDH is used at the operating temperature of AFC, the electrolyte may be deteriorated and the conductivity may be lowered due to the lack of water in the LDH.

Therefore, it is desired to develop an electrolyte that can achieve both improvement of initial conductivity and suppression of deterioration due to drying.

Such electrolytes are not limited to alkaline fuel cells, but are also used in 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.

An object of the present invention is to provide an electrochemical cell capable of both improving the initial conductivity of an electrolyte and suppressing deterioration due to drying.

The electrochemical cell according to the present invention includes a cathode to which an oxidant is supplied, an anode to which fuel is supplied, and an electrolyte arranged between the cathode and the anode. The electrolyte contains a layered double hydroxide containing Ni and Al ions and a hydroxide of at least one transition metal selected from Fe, Co and Mn. The total ion concentration of the transition metal contained in the hydroxide with respect to Ni ions contained in the layered double hydroxide is 50 ppm or more and 20000 ppm or less.

According to the present invention, it is possible to provide an electrochemical cell capable of both improving the initial conductivity of the electrolyte and suppressing deterioration due to drying.

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 using hydroxide ions as a carrier (zinc air secondary battery or the like) or an electrolytic cell that generates hydrogen and oxygen from water vapor. Is suitable as.

The electrolyte material according to the present invention is a layered double hydroxide (LDH) containing Ni ions and Al ions, and a hydroxide of at least one transition metal selected from Fe, Co and Mn (LDH: Layered Double Hydroxide). Hereinafter, it is referred to as “transition metal hydroxide”).

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 can be expressed by, for example, the following general formula (1).

[Ni ²⁺ _1-pr-s Al ³⁺ _p M ²⁺ _r M ³⁺ _s (OH) ₂ ] [An ^- _{p + s / n} · mH ₂ O] ... Equation (1)
In the general formula (1), the Ni ²⁺ / Al ³⁺ ratio is 2 or more and 4 or less. A ^{stable layered structure can be formed by setting the Ni 2+} / Al ³⁺ ratio to 2 or more and 4 or less. Ni ²⁺ and Al ³⁺ are contained in each hydroxide basic layer. The Ni ²⁺ / Al ³⁺ ratio can be measured by inductively coupled plasma emission spectroscopy (ICP-AES) techniques.

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

In the formula (1), ^{the subscript 1-pr-s of Ni 2+} is 0.67 or more and 0.80 or less, ^{the subscript p of Al 3+} is 0.2 or more and 0.33 or less, and M. ^{The subscript r of 2+} is 0 or more and 0.10 or less, and ^{the subscript s of M 3+} is 0 or more and 0.10 or less.

In formula (1), ^An− is an n-valent anion. n is an integer having a valence of 1 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 from 0.2 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 an integer. 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 a "basic composition".

The particle size of LDH 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 0.01 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 10 μm or less, the moldability of the LDH powder can be improved, which is preferable.

The electrolyte material further comprises the transition metal hydroxides described above. Examples of Fe hydroxide include FeO (OH), Fe (OH) ₂ , Fe (OH) _{3, and the} like. Examples of the hydroxide of Co include CoO (OH), Co (OH) ₂ , Fe (OH) _{3 and the} like. Examples of the hydroxide of Mn include MnO (OH) and Mn (OH) ₂ .

In the electrolyte material according to the present invention, the total ion concentration of the transition metal contained in the transition metal hydroxide with respect to the Ni ion contained in LDH (hereinafter, abbreviated as "transition metal ion total concentration") is 50 ppm or more and 20000 ppm or less. It is characterized by being.

By setting the total concentration of transition metal ions to 50 ppm or more, when an electrolyte is constructed using the electrolyte material, water can be supplemented from the transition metal hydroxide to LDH at the operating temperature of the alkaline fuel cell. As a result, the deterioration of the electrolyte can be suppressed, so that the decrease in the conductivity of the electrolyte can be suppressed. The total metal ion concentration of the transition metal hydroxide with respect to Ni ions is preferably 100 ppm or more, more preferably 500 ppm or more.

Further, by setting the total concentration of transition metal ions to 20000 ppm or less, it is possible to prevent the transition metal oxide / hydroxide from coarsely agglomerating and blocking the grain boundaries between LDHs. When configured, the hydroxide ion conductivity of the electrolyte can be sufficiently secured, so that the initial conductivity of the electrolyte can be sufficiently secured. The total transition metal ion concentration is preferably 10,000 ppm or less, more preferably 5000 ppm or less.

When the electrolyte material contains two or more transition metal hydroxides selected from Fe, Co and Mn, the total transition metal ion concentration is the sum of the ion concentrations of each transition metal hydroxide with respect to Ni ions. .. The total transition metal ion concentration can be measured by inductively coupled plasma emission spectroscopy. In addition, hydroxide species can be identified by XRD measurement using synchrotron radiation.

The particle size of the transition metal hydroxide is not particularly limited, but for example, the volume-based D50 average particle size can be 0.01 μm or more and 2 μm or less. When the average particle size of D50 is 0.01 μm or more, it is possible to suppress the agglomeration of the transition metal hydroxide powders, so that the transition metal hydroxide powder can be uniformly dispersed in the LDH powder. .. When the average particle size of D50 is 2 μm or less, the moldability of the electrolyte material can be improved, which is preferable.

(Manufacturing method of electrolyte material)
First, the LDH powder represented by the above general formula (1) is prepared. Such LDH powder may be a commercially available product, or may be produced by a known method such as a liquid phase synthesis method using nitrate or chloride.

Next, a transition metal hydroxide powder is prepared. The transition metal hydroxide powder may be a commercially available product or may be produced by a known method such as a coprecipitation method.

Next, the LDH powder and the transition metal hydroxide powder are mixed. This completes the electrolyte material.

(Alkaline fuel cell 10)
Hereinafter, as an example of the alkaline fuel cell (AFC) according to the present invention, ^{the 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 group 11 elements (Ru, Rh, Pd, Ir, Pt) and group 11 elements (Fe, Co, Ni). Group 10 elements), Group 11 elements such as Cu, Ag, and 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, gaseous 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 ), 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).} Classes, (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. In the electrolyte 16, the total concentration of transition metal ions is 50 ppm or more and 20000 ppm or less. Therefore, since the initial conductivity of the electrolyte can be sufficiently secured, the initial output of the cell can be improved, and the conductivity of the electrolyte is lowered by supplementing the LDH with water from the transition metal hydroxide at the operating temperature of the alkaline fuel cell. Can be suppressed, so that the decrease in cell output can be suppressed.

When the electrolyte 16 contains two or more of the above-mentioned transition metal hydroxides, the total transition metal ion concentration is the total ion concentration of each transition metal hydroxide with respect to Ni ions. The total transition metal ion concentration can be measured by sampling the surface of the electrolyte 16 as a powder and then performing inductively coupled plasma emission spectroscopy. In addition, hydroxide species can be identified and analyzed by XRD measurement.

In the electrolyte 16, the transition metal hydroxide is preferably located in the gap between the secondary particles composed of LDH. As a result, it is possible to suppress the aggregation of the secondary particles of LDH, so that the output of the alkaline fuel cell 10 can be improved.

The method for producing the electrolyte 16 is not particularly limited, but the electrolyte 16 can be formed by compacting the electrolyte material by a known method such as a die uniaxial press or cold isotropic pressurization (CIP). can. Alternatively, the electrolyte 16 is also 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 then filling the porous base material with the electrolyte material. can do.

(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 the electrochemical cell according to the present invention, but the present invention is not limited to this. 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.

First, ^{LDH powder having a Ni 2+} / Al ³⁺ ratio (ratio of Ni ions to Al ions) of 2 or more and 4 or less, and a transition metal hydroxide powder were prepared. The transition metal hydroxide powder includes FeOOH powder (High Purity Chemical Laboratory Co., Ltd., α-ferrous hydroxide hydroxide) and Co (OH) ₂ powder (Fuji Film Wako Pure Chemical Industries, Ltd., cobalt hydroxide). , MnOOH powder prepared according to the method described in JP-A-2011-105538.

Next, the LDH powder and the transition metal hydroxide powder are mixed so that the ion concentration of each transition metal (Fe, Co and Mn) and the total transition metal ion concentration with respect to the Ni ions contained in the LDH are the values shown in Table 1. It was mixed to prepare an electrolyte material powder. The total ion concentration of the transition metal was measured by identifying the hydroxide species by XRD measurement on the surface of the electrolyte, which will be described later, and then performing inductively coupled plasma emission spectroscopic analysis on the surface of the electrolyte as a powder.

As shown in Table 1, FeOOH powder was used as the transition metal hydroxide powder in Comparative Examples 1 to 4 and Examples 1 to 6, and transition metal water was used in Comparative Examples 5 to 8 and Examples 7 to 12. Co (OH) ₂ powder was used as the oxide powder, and MnOOH powder was used as the transition metal hydroxide powder in Comparative Examples 9 to 12 and Examples 13 to 18. Further, as shown in Table 1, in Comparative Examples 13 to 18 and Examples 19 to _{27, FeOOH powder, Co (OH) 2} powder and MnOOH powder were used as the transition metal hydroxide powder.

Next, the electrolytes of Comparative Examples 1 to 18 and Examples 1 to 27 were prepared by forming the electrolyte material powder with a cold isotropic press (CIP) at ^{a pressure of 3000 kgf / cm 2.} ..

Next, the initial conductivity of the produced electrolyte was measured according to JISR1661 (method for measuring the conductivity of fine ceramic ion conductors). 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 initial conductivity of each of the electrolytes of Comparative Examples 1 to 18 and Examples 1 to 27 and their determination. 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.}

Next, the electrolyte whose initial conductivity was measured was exposed to air at 80 ° C. and a relative humidity of 20% for 10 minutes to dry, and then the conductivity of the electrolyte was measured again by the above method. Then, the deterioration rate due to drying was measured by dividing the conductivity after drying by the initial conductivity. Table 1 summarizes the deterioration rates of Comparative Examples 1 to 18 and Examples 1 to 27 due to drying and their determination. The deterioration rate was evaluated as ◯ when it was less than 3% and as x when it was 3% or more.

In Comparative Examples 1 to 2, 5 to 6, 9 to 10, 13 to 15 in which the total ion concentration of the transition metal (Fe, Co and Mn) with respect to the Ni ion contained in LDH was less than 50 ppm, the deterioration rate due to drying of the electrolyte was obtained. Was big. Further, in Comparative Examples 3 to 4, 7 to 8, 11 to 12, 16 to 18 in which the total ion concentration of the transition metal with respect to Ni ions contained in LDH was more than 20000 ppm, the initial conductivity of the electrolyte was low.

On the other hand, in Examples 1 to 27 in which the total ion concentration of the transition metal with respect to Ni ions contained in LDH was 50 ppm or more and 20000 ppm or less, it was possible to achieve both a reduction in the deterioration rate due to drying of the electrolyte and a high initial conductivity. .. Such a result was obtained because the total ion concentration of the transition metal was 50 ppm or more to supplement the water content from the transition metal hydroxide to the LDH, and the total ion concentration of the transition metal was 20000 ppm or less. This is because the hydroxide ion conductivity of LDH could be sufficiently ensured.

Further, it was confirmed that the deterioration rate due to drying of the electrolyte can be further reduced by setting the total ion concentration of the transition metal to 100 ppm or more and further increasing it to 500 ppm or more.

It was also confirmed that the initial conductivity can be further improved by setting the total ion concentration of the transition metal to 5000 ppm or less.

When the cross section of the electrolyte of Examples 1 to 24 was observed with a field emission scanning electron microscope (FE-SEM), the transition metal hydroxide was located in the gap between the secondary particles composed of LDH. rice field.

10 Alkaline fuel cell 12 Cathode 14 Anode 16 Electrolyte

Claims (2)

The cathode to which the oxidant is supplied and
With the anode where the fuel is supplied,
An electrolyte disposed between the cathode and the anode,
With
The electrolyte is
Layered double hydroxides containing Ni and Al ions,
Hydroxides of at least one transition metal selected from Fe, Co and Mn, and
Including
The total ion concentration of the transition metal contained in the hydroxide with respect to Ni ions contained in the layered double hydroxide is 50 ppm or more and 20000 ppm or less.
Electrochemical cell. In the electrolyte, the hydroxide is located in the gap between the secondary particles composed of the layered double hydroxide.
The electrochemical cell according to claim 1.

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