JP7543189B2 - Solid electrolyte electrolyzer - Google Patents

Description

This disclosure relates to a solid electrolyte electrolysis device.

Research into carbon dioxide reduction using electrical energy is being conducted widely around the world. In solid electrolyte electrolysis devices that reduce carbon dioxide, carbon dioxide is generally dissolved in an aqueous solution containing an electrolyte that is supplied to the negative electrode (hereinafter sometimes referred to as the cathode), and an aqueous solution containing the electrolyte is supplied to the positive electrode (hereinafter sometimes referred to as the anode). Generally, an electrolyte for exchanging ions is provided between the negative electrode and the anode, and an ion exchange membrane may be used as a material for this. An example of such a solid electrolyte electrolysis device is the carbon dioxide electrolysis device disclosed in Patent Document 1 (Patent Document 1).

JP 2018-154901 A

In the carbon dioxide electrolysis device disclosed in Patent Document 1, the ion exchange membrane used as a separator (solid electrolyte) is disposed between the anode and the cathode. In the anode of such a carbon dioxide electrolysis device, a reaction occurs in which water in an aqueous solution is oxidized to oxygen. However, water is not easily oxidized, and a catalyst with high oxidation performance is used in the anode to promote the oxidation reaction. In addition, in order to obtain high electrolysis performance in a carbon dioxide electrolysis device, the anode needs to be in contact with the separator, and there is a risk of oxidation of the solid electrolyte by the anode. As a result, the solid electrolyte is deteriorated by oxidation, and there is a possibility that problems such as a decrease in the electrolysis efficiency of the carbon dioxide electrolysis device (electrolysis efficiency of carbon dioxide, generation efficiency of carbon monoxide) or damage to the solid electrolyte may occur. Therefore, the present disclosure aims to provide a solid electrolyte electrolysis device that suppresses deterioration due to oxidation of the solid electrolyte in a solid electrolyte electrolysis device and can extend the life of the device.

As a result of intensive research aimed at achieving the above object, the inventors discovered that by providing a protective layer including a specific porous layer between an anode having a specific electrode material (A) and a solid electrolyte, and isolating the anode from the solid electrolyte, it is possible to suppress oxidative deterioration of the solid electrolyte, and thus completed the disclosed technology. That is, the disclosed technology is as follows.

According to one aspect of the disclosed technique,
A cathode for carrying out a reduction reaction;
an anode that forms a pair of electrodes with the cathode and has an electrode material (A) that promotes an oxygen generation reaction using water or an aqueous solution;
a solid electrolyte layer disposed in contact with the cathode;
a protective layer disposed between the anode and the solid electrolyte layer in contact therewith to separate the anode and the solid electrolyte;
A solid electrolyte electrolysis device having
the electrode material (A) contains one or more of Ir, IrO _x , Ru, RuO _x , and IrRuO _x ;
the protective layer is porous and has a plurality of continuous pores;
It is possible to provide a solid electrolyte electrolysis device, characterized in that the porous material is a metal having an oxidation potential of M ⁺ /M that is more noble than 1 V vs. NHE; an alloy containing one or more of Fe, Ni, Co, Mn, Cr, V, Ti, Ta, Nb, Zr, W, and Mo; or an electrically conductive compound.

This disclosure makes it possible to provide a solid electrolyte electrolysis device that suppresses oxidative degradation of the solid electrolyte and has an excellent device life.

1 is a solid electrolyte electrolysis device preferably used in an embodiment of the present disclosure. FIG. 1 is a conceptual diagram showing how CO ₂ can be locally and efficiently adsorbed by adding a solid base to the cathode surface in a solid electrolyte electrolysis device suitably used in an embodiment of the present disclosure. 1 is a flowchart showing a method for producing synthetic gas using a solid electrolyte electrolysis device preferably used in an embodiment of the present disclosure. 1 is an example of an application of a solid electrolyte electrolysis device preferably used in an embodiment of the present disclosure. 1 shows evaluation results showing electrode performance maintenance rates of examples and comparative examples in the present disclosure.

The solid electrolyte electrolysis device in this disclosure will be specifically described below with reference to Figures 1 and 2. Note that the technology in this disclosure is not limited to the form described below. In addition, in this disclosure, the term "~" in describing a numerical value indicates a value equal to or greater than the lower limit and equal to or less than the upper limit.

<<Solid electrolyte electrolyzer 100>>
A solid electrolyte electrolysis device (also called an electrolysis cell or an electrolysis module) according to this embodiment will be described with reference to FIG. As shown in FIG. 1, the solid electrolyte electrolysis device 100 according to this embodiment includes a cathode 101, an anode 102 which constitutes a pair of electrodes together with the cathode 101, and a cathode 102 which is in contact with the anode 102. a protective layer 108 that is applied in a state in which the cathode 101 and the protective layer 108 are in contact with each other; a solid electrolyte 103 that is applied between the cathode 101 and the protective layer 108 in a state in which at least a part of the solid electrolyte 103 is in contact with the cathode 101; A current collector 104 is in contact with the anode 102 at a surface 101-2 opposite to a contact surface 101-1 with the protective layer 108 of the anode 102. A support plate 105 contacting the collector plate 104 at −1 and a voltage application unit 106 for applying a voltage between the collector plate 104 and the support plate 105 (i.e., between the cathode and the anode). is doing. The anode 102 and the solid electrolyte 103 are separated by a protective layer 108. Furthermore, a supply source and a supply device (not shown) can be used to supply _CO2 in a gaseous state and an aqueous solution containing a supporting electrolyte. In addition, the solid electrolyte electrolysis device 100 shown in FIG. 1 is illustrated in a state in which each component such as the cathode 101 and the anode 102 is separated for the sake of explanation. The cathode 101, the solid electrolyte 103, the protective layer 108, the anode 102, and the support plate 105 are each bonded by a predetermined method and integrated into one body. The electrolysis device 100 may be configured as a refrigerant-type electrolysis device 100. Each of the components will be described in detail below.

<Cathode 101>
(Reduction reaction at cathode 101)
The reduction reaction in the cathode 101 varies depending on the type of solid electrolyte 103 used in the solid electrolyte electrolysis device 100. When a cation exchange membrane is used as the solid electrolyte 103, the reduction reactions of the following formulas (1) and (2) occur, and when an anion exchange membrane is used as the solid electrolyte, the reduction reactions of the following formulas (3) and (4) occur.

(Basic structure and materials of cathode 101)
The cathode 101 is a gas diffusion electrode including a gas diffusion layer. The gas diffusion layer includes a material having conductivity or porosity, such as carbon paper or nonwoven fabric, or a metal mesh. Examples of the electrode material (B) of the cathode 101 include graphite carbon, glassy carbon, titanium, and SUS. The catalyst of the cathode 101 capable of reducing carbon dioxide (hereinafter, may be referred to as CO ₂ ) to carbon monoxide (hereinafter, may be referred to as CO) includes, for example, a metal selected from silver, gold, copper, or a combination thereof. More specifically, the catalyst includes, for example, gold, gold alloy, silver, silver alloy, copper, copper alloy, or a mixed metal including any one or more of them. The type of catalyst is not particularly limited as long as it has a catalytic function, and can be determined in consideration of corrosion resistance and the like. For example, the catalyst does not include amphoteric metals such as Al, Sn, and Zn, thereby improving corrosion resistance. The catalyst can be supported on the cathode 101 (or the electrode material (B)) by carrying out a known method such as vapor deposition, deposition, adsorption, accumulation, adhesion, welding, physical mixing, spraying, or the like.

(Solid Base 107)
Here, as shown in FIG. 2, the cathode 101 has a solid base 107 . The solid base 107 is not particularly limited as long as it is a base that is solid at room temperature (25° C.), and examples thereof include potassium bicarbonate (KHCO ₃ ), sodium hydroxide (NaOH), an oxide of an alkaline earth metal, a hydroxide of an alkaline earth metal, or a carbonate of an alkaline earth metal {e.g., magnesium oxide (MgO), magnesium hydroxide (Mg(OH) ₂ ), magnesium carbonate (MgCO ₃ ), calcium oxide (CaO), calcium hydroxide (Ca(OH) ₂ ), calcium carbonate (CaCO ₃ ), strontium oxide (SrO), strontium hydroxide (Sr(OH) ₂ ), strontium carbonate (SrCO ₃ ), barium oxide (BaO), barium hydroxide (Ba(OH) ₂ ), barium carbonate (BaCO ₃ ), etc.}, an oxide of a rare earth metal, a hydroxide of a rare earth metal, or a carbonate of a rare earth metal {e.g., yttrium oxide (Y ₂ O ₃ ), lanthanum oxide (La ₂ O ₃ ), etc.}, hydrotalcite (e.g., metal complex hydroxide, carbonate, LDH, HT-CO ₃ , HT-OH, etc.), surface-treated zeolite, base-treated molecular sieve, surface-treated porous alumina (KF-Al ₂ O ₃ ), etc. are preferably used. In particular, weakly basic solid bases with small atomic numbers are more preferable. Furthermore, it is even more preferable to use water-insoluble solid bases such as alkaline earth metal oxides, alkaline earth metal hydroxides or alkaline earth metal carbonates, rare earth metal oxides, rare earth metal hydroxides or rare earth metal carbonates, because they are not washed away by water in the gas or water generated by the reaction, and the durability of the cathode having the solid base 107 is not reduced. Here, "water-insoluble" refers to a material that does not dissolve in 100 mL of water at 20°C per 10 mg. The solid base 107 is preferably present on the contact surface 101-1 side of the cathode 101 with the solid electrolyte 103. The reason for this configuration is that the interface between the cathode 101 and the solid electrolyte 103 is a reaction site. The solid base 107 may be present as a mixture with the material of the cathode 101, or may be present in an integrated state as a compound. The solid base 107 can be supported on the cathode 101 (or the electrode material (B)) by carrying out a known method such as coating, vapor deposition, precipitation, physical mixing, etc. The mass per unit area of the solid base is not particularly limited, but is, for example, 0.1 to 10 mg/cm ² , preferably 0.1 to 6 mg/cm ² .

Here, the reason why the efficiency is improved by using the solid base 107 is presumed to be the following mechanism of action. First, when a low-concentration CO ₂ gas with a content concentration of 10 to 20%, such as exhaust gas from a factory, is supplied to the solid electrolyte electrolysis device 100, the CO ₂ is not easily adsorbed on the surface of the cathode 101 due to its low concentration. Therefore, as shown in FIG. 2, it is understood that by adding the solid base 107 to the surface of the cathode 101, CO ₂ can be locally and efficiently adsorbed to the area where the solid base exists, and CO ₂ reduction can be promoted. In addition, when a cation exchange membrane is adopted as the solid electrolyte 103, it is understood that if there is a lot of H ⁺ on the surface of the cathode 101, CO ₂ cannot be sufficiently adsorbed. At this time, it is considered that the reaction proceeds when the solid base 107 is present (for example, when the above-mentioned water-insoluble solid base is used, it is preferable to control the pH so that pH>2). On the other hand, when an anion exchange membrane is adopted as the solid electrolyte, OH ^- exists on the cathode surface, so that CO ₂ is adsorbed, which is suitable for CO ₂ reduction. However, if there is too much ^OH- , it is adsorbed as stable _CO3 ^2- , and it is understood that the _CO2 reduction reaction does not proceed sufficiently. In this case, it is considered that the _CO2 reduction reaction proceeds more when a weakly basic solid base 107 is present than a strongly basic solid base (for example, when the above-mentioned water-insoluble solid base is used, it is preferable to control the pH so that the pH is less than 12). In the present disclosure, an electrode having such a solid base and catalyst can be expressed as "an electrode having a catalyst, an electrode material having a catalyst, and at least a solid base provided on the electrode material" (in other words, an electrode having an electrode material having a catalyst and a solid base), or "a cathode having a catalyst and further having a solid base", etc.

<Anode 102>
(Oxygen Evolution Reaction at the Anode 102)
The oxygen generation reaction using water or an aqueous solution at the anode 102 varies depending on the type of solid electrolyte 103 used in the solid electrolyte electrolysis device 100. When a cation exchange membrane is used as the solid electrolyte 103, the oxidation reaction of the following formula (5) occurs, and when an anion exchange membrane is used as the solid electrolyte 103, the oxidation reaction of the following formula (6) occurs.

(Basic structure and material of anode 102)
The anode 102 is a porous electrode including a porous substrate. The porous substrate includes, for example, a metal or carbon mesh or a nonwoven fabric. The electrode material (A) of the anode 102 includes, for example, any one of Ir, IrO _x , Ru, RuO _x , and IrRuO _x . These electrode materials can promote an oxygen production reaction in the anode 102 using water or an aqueous solution.

<Protective Layer 108>
The protective layer 108 is interposed between the anode 102 and the solid electrolyte 103 in contact with each other. The protective layer 108 separates the anode 102 and the solid electrolyte 103. The protective layer 108 is porous and has a plurality of continuous pores. The continuous pores may be holes that connect one surface of the protective layer 108 to the other surface, and include through holes such as punch holes, meshes, and ventilation structures of nonwoven fabrics. The porosity of the protective layer 108 is not particularly limited, but may be, for example, 40 to 95%, and preferably 50 to 80%. This allows the protective layer 108 to pass hydroxide ions, raw gases, liquids, and the like. The porosity is calculated by photographing the surface of the protective layer with a scanning electron microscope, and calculating the ratio of the area of all holes on the surface of the image to the observation area of the image using commercially available software.
By providing such a protective layer 108, it is possible to suppress oxidation deterioration of the solid electrolyte 103 due to the influence of the oxygen generation reaction in the anode 102, and it is possible to provide a solid electrolyte electrolysis device 100 having a long device life. In addition, since deterioration in the performance of the solid electrolyte 103 can be suppressed, it is possible to provide a solid electrolyte electrolysis device 100 that can suppress deterioration in electrolysis efficiency and improve the operation rate by shortening the maintenance time.

The material of the protective layer 108 is (1) a metal whose oxidation potential of M ⁺ /M is more noble than 1 V vs. NHE, (2) an alloy containing one or more of Fe, Ni, Co, Mn, Cr, V, Ti, Ta, Nb, Zr, W, and Mo, or (3) an electrically conductive compound.
Here, (1) a metal having an oxidation potential of M ⁺ /M more noble than 1V vs. NHE indicates a metal that is difficult to oxidize, and examples thereof include metals such as Pt, Au, Ru, Pd, Rh, Ti, Ta, Nb, Zr, W, and Mo. Here, M ⁺ indicates a metal ion, M indicates a metal, and M ⁺ /M indicates an electrode potential under a state in which the oxidation-reduction reaction between the metal ion and the metal reaches equilibrium. 1V vs. NHE indicates that the electrode potential measured using a hydrogen standard electrode is 1V.
In addition, (2) an alloy containing one or more of Fe, Ni, Co, Mn, Cr, V, Ti, Ta, Nb, Zr, W, or Mo is an alloy that is likely to form a passive state, and after the surface layer of these alloys is easily oxidized, a passive state is formed on the surface and the alloy is difficult to oxidize further.
In addition, (3) the electrically conductive compound includes electrically conductive glass, ceramic, and carbon materials, and examples thereof include electrically conductive ceramics such as ITO, FTO, AZO, and IGZO; electrically conductive glass; and electrically conductive carbon materials such as graphite carbon, glassy carbon, graphene, and carbon nanotubes. Here, the term "electrically conductive" in the present disclosure refers to a conductivity of 1×10 ⁻⁹ S/cm or more.

The thickness of the protective layer 108 is not particularly limited, but is, for example, 0.5 to 500 μm, and preferably 1 to 100 μm. When the thickness of the protective layer is within this range, oxidation deterioration of the solid electrolyte 103 can be suppressed.

<Solid electrolyte 103>
The solid electrolyte 103 is interposed between the cathode 101 and the protective layer 108 in a contact state. The solid electrolyte 103 is not particularly limited to a polymer membrane, but may be a cation exchange membrane or an anion exchange membrane. Anion exchange membranes are preferred, and anion exchange membranes are more preferred. Examples of cation exchange membranes include strongly acidic cation exchange membranes in which sulfonic groups are introduced into a fluororesin matrix, such as Nafion 117, Nafion 115, Nafion 212, and Nafion 350 ( As an anion exchange membrane, a strong acid cation exchange membrane having a sulfone group introduced into a styrene-divinylbenzene copolymer matrix, or NeoSepta CMX (Tokuyama Soda Co., Ltd.) can be used. Examples of the anion exchange membrane include a membrane having a quaternary ammonium group, a primary amino group, a secondary amino group, a tertiary amino group, and further an anion exchange membrane having a mixture of a plurality of these ion exchange groups. Specific examples include Neocepta (registered trademark) ASE, AHA, AMX, ACS, AFN, and AFX (manufactured by Tokuyama Corporation), Selemion (registered trademark) AMV, AMT, DSV, AAV, ASV, AHO, AHT, and APS4 ( (manufactured by Asahi Glass Co., Ltd.) can be used.

<Current collector plate 104>
Examples of the current collector 104 include metal materials such as copper (Cu), nickel (Ni), stainless steel (SUS), nickel-plated steel, and brass, and among these, copper is preferred from the viewpoints of ease of processing and cost. When the current collector 104 is made of a metal material, examples of the shape of the negative electrode current collector include metal foil, metal plate, metal thin film, expanded metal, punched metal, and foamed metal.

As shown in FIG. 1, the current collector 104 is provided with a gas supply hole 104-1 and a gas recovery hole 104-2 for supplying and recovering gas (raw material gas and generated gas) to the cathode 101. The gas supply hole 104-1 and the gas recovery hole 104-2 make it possible to uniformly and efficiently feed raw material gas to the cathode 101 and discharge generated gas (including unreacted raw material gas). In the figure, one gas supply hole and one gas recovery hole are provided, but the number, location, and size are not limited and are set appropriately. In addition, if the current collector 104 is breathable, the gas supply hole and the gas recovery hole are not necessarily required.

If the cathode 101 has the role of transmitting electrons, the current collector 104 is not necessarily required.

<Support Plate 105>
The support plate 105 plays a role in supporting the anode 102. Therefore, the required rigidity of the support plate 105 varies depending on the thickness, rigidity, etc. of the anode 102. In addition, the support plate 105 needs to have electrical conductivity so as to receive electrons from the anode 102. Examples of materials for the support plate 105 include Ti, SUS, and Ni.

1, the support plate 105 is provided with a flow path 105-1 for feeding raw materials (H ₂ O, etc.) for the oxidation reaction to the anode 102. This flow path makes it possible to feed raw materials (gas or liquid) for the oxidation reaction uniformly and efficiently to the anode 102. Note that, in this figure, nine flow paths are provided, but the number, locations, and sizes of the flow paths are not limited and may be set appropriately.

In this embodiment, the anode 102 and the support plate 105 are described as separate entities, but the anode 102 and the support plate 105 may be integral (i.e., may be configured as an integrated anode with a support function).

<Voltage application unit 106>
1, the voltage application unit 106 applies a voltage between the cathode 101 and the anode 102 by applying a voltage to the current collector 104 and the support plate 105. As described above, the current collector 104 is a conductor and therefore supplies electrons to the cathode 101, while the support plate 105 is also a conductor and therefore receives electrons from the anode 102. In addition, in the case where the current collector 104 is not required as described above, a voltage is applied between the cathode 101 and the support plate 105. In addition, a control unit (not shown) may be electrically connected to the voltage application unit 106 in order to apply an appropriate voltage.

<Reaction gas supply unit>
The solid electrolyte electrolysis device 100 in the present disclosure may be provided with a reaction gas supply unit (not shown) outside the solid electrolyte electrolysis device 100. That is, it is sufficient that CO ₂ , which is a reaction gas, is supplied to the surface 101-2, and the reaction gas may be supplied from the reaction gas supply unit to the gas supply hole 104-1 via a pipe (not shown) or the like, or the reaction gas may be sprayed onto the surface 104-A of the current collector 104 opposite to the contact surface 104-B with the cathode 101. From an environmental perspective, it is preferable to use factory exhaust gas discharged from a factory as the reaction gas.

<CO generation method>
Next, a method for producing CO using the above-mentioned solid electrolyte electrolysis device 100 will be described with reference to FIG.

<Reaction gas supply step S301>
First, _CO2 , which is a reactant gas serving as a raw material, is supplied in a gas phase state by a reactant gas supply unit (not shown) to the solid electrolyte electrolysis device 100. At this time, _CO2 is supplied to the cathode 101 through the gas supply hole 104-1 provided in the current collector plate 104 (S301).

<CO, H ₂ generation step S302>
Next, the CO ₂ supplied to the cathode 101 undergoes a reduction reaction on the surface of the cathode 101. When a cation exchange membrane is used as the solid electrolyte 103, the reduction reactions represented by the above formulas (1) and (2) are carried out. When an anion exchange membrane is used as the solid electrolyte, the reduction reactions of the above-mentioned formulas (3) and (4) occur, producing a synthesis gas containing at least CO and _H2. (S302).

<Produced gas recovery step S303>
Next, the synthesis gas containing the generated CO and _H2 is sent to a gas recovery device (not shown) through gas recovery holes 104-2 provided in the current collector 104, and is recovered in predetermined gas fractions (S303).

<Application>
As shown in Fig. 4, for the solid electrolyte electrolysis device according to the present disclosure as described above, it is possible to generate a synthesis gas containing at least CO and _H2 in a desired production ratio by using, for example, _CO2 gas discharged from a factory as a raw material and utilizing renewable energy such as a solar cell for the voltage application unit 106. The synthesis gas thus generated can be used to produce a fuel base material or a chemical raw material by a method such as FT synthesis or methanation.

The following provides a detailed explanation of the above-described embodiment using examples and comparative examples.

The solid electrolyte electrolysis device was assembled using the following components. The cathode was a mixture of conductive carbon black and silver nano catalyst attached to carbon paper and used as the cathode. The anode was a titanium mesh carrying iridium oxide. The solid electrolyte was an anion exchange membrane of fluorine resin-based ionomer (primary amino group) made of ionomer with a base point density of 1.0 mmol/cm ^3. In addition, a 0.5 M KHCO ₃ aqueous solution was used as the electrolyte solution (electrolyte). In addition, a titanium mesh (thickness 100 μm, aperture ratio 83%) was used as the protective layer as an example, and an evaluation was performed without using a protective layer as a comparative example. For the evaluation, the applied voltage of the cathode was set to -3.5 V with respect to the anode electrode, and the solid electrolyte electrolysis device was operated to generate a CO ₂ reduction reaction. The CO ₂ reduction reaction was continued, and the change over time in the amount of CO generated was measured. The initial amount of CO generation was taken as 100%, and the value obtained by dividing the amount of CO generation during measurement by the initial amount of CO generation was evaluated as the electrode performance maintenance rate. The measurement results of the electrode performance maintenance rates of the example and the comparative example are shown in Figure 5. As a result, in the solid electrolyte electrolysis device of the comparative example, the electrode performance rapidly deteriorated, and after about 20 hours, oxidation deterioration was severe and the solid electrolyte was broken, making it impossible to obtain data, whereas in the example, only very slight deterioration was observed in the electrode performance, and it can be seen that the effect of the disclosed technology, which is to extend the life of the device, was obtained.

100 Solid electrolyte electrolytic device 101 Cathode
101-1: Surface of cathode in contact with solid electrolyte 101-2: Surface of cathode in contact with current collector 102: Anode
102-1: Anode surface in contact with support plate 102-2: Anode surface in contact with solid electrolyte 103: Solid electrolyte 104: Current collector plate 104-1: Gas supply hole in current collector plate 104-2: Gas recovery hole in current collector plate 105: Support plate 105-1: Raw material flow path in support plate 106: Voltage application section 107: Solid base 108: Protective layer

Claims (3)

A cathode for carrying out a reduction reaction;
an anode that forms a pair of electrodes with the cathode and has an electrode material (A) that promotes an oxygen generation reaction using water or an aqueous solution;
a solid electrolyte layer disposed in contact with the cathode;
a protective layer disposed between the anode and the solid electrolyte layer in contact therewith to separate the anode and the solid electrolyte;
A solid electrolyte electrolysis device having
The electrode material (A) contains one or more of Ir, IrOx, Ru, RuOx, and IrRuOx,
The solid electrolyte layer has an anion exchange membrane,
the protective layer is porous and has a plurality of continuous pores;
The porous material is a metal having an oxidation potential of M+/M that is more noble than 1 V vs. NHE; an alloy containing one or more of Fe, Ni, Co, Mn, Cr, V, Ti, Ta, Nb, Zr, W, and Mo; or an electrically conductive compound. The solid electrolyte electrolytic device according to claim 1, characterized in that the porosity of the porous material is 40 to 95%. 3. The solid electrolyte electrolytic device according to claim 1, wherein the protective layer has a thickness of 0.5 to 500 μm.

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