Catalyst-supported electrode

Abstract

To provide a catalyst-supported electrode suitable for improving the performance retention rate of catalysts. [Solution] The catalyst-supported electrode 10 of the present invention is a catalyst-supported electrode for converting carbon dioxide into reaction products, comprising a substrate 1 and a catalyst layer 2 disposed on the substrate 1 and containing an element M1 that functions as a catalytically active species, wherein the surface porosity of the catalyst layer 2 is less than 20%.

Description

[Technical Field]

[0001] This invention relates to a catalyst-supported electrode. [Background technology]

[0002] There are high expectations for technologies that convert carbon dioxide into useful compounds as a means of solving the problems of global warming and the depletion of fossil fuels.

[0003] Formic acid is an excellent compound for storing hydrogen and carbon dioxide because it requires low energy for dehydrogenation reactions and is easy to handle, and can be used in the technologies described above. Typical technologies for producing formic acid from carbon dioxide include hydrogenation reactions and artificial photosynthesis. However, these technologies have challenges such as requiring high temperature and high pressure conditions, and the need for energy to concentrate the product due to its dilute concentration.

[0004] Therefore, electrolytic technology, which produces formic acid from carbon dioxide and water using electrical energy, has many advantages, such as the reaction proceeding under mild conditions, the ability to produce relatively high concentrations of formic acid, the elimination of hydrogen requirements, and the space-saving nature of the equipment, making its social implementation highly desirable.

[0005] For example, Patent Document 1 describes an electrolytic cell that includes a catalyst layer containing catalytically active elements dispersed in an ion-conducting polymer. The catalyst layer described in Patent Document 1 is formed by applying an ink containing catalytically active elements. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Patent No. 6568326 [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] Conventional catalyst-supported electrodes had room for improvement. In particular, conventional catalyst-supported electrodes had the problem of catalyst performance degrading with repeated use.

[0008] Therefore, the present invention aims to provide a catalyst-supported electrode suitable for improving the performance retention rate of catalysts. [Means for solving the problem]

[0009] The present invention A catalyst-supported electrode for converting carbon dioxide into reaction products, Substrate and A catalyst layer disposed on the substrate and containing element M1 which functions as a catalytically active species, Equipped with, The present invention provides a catalyst-supported electrode in which the surface porosity of the catalyst layer is less than 20%.

[0010] Furthermore, the present invention, A catalyst-supported electrode for converting carbon dioxide into reaction products, Substrate and A catalyst layer disposed on the substrate and containing element M1 which functions as a catalytically active species, Equipped with, The catalyst layer is a vapor-deposited layer, providing a catalyst-supported electrode.

[0011] Furthermore, the present invention, An electrolytic apparatus for converting carbon dioxide into reaction products, The present invention provides an electrolytic device equipped with the catalyst-supported electrode described above. [Effects of the Invention]

[0012] According to the present invention, a catalyst-supported electrode suitable for improving the performance retention rate of catalysts can be provided. [Brief explanation of the drawing]

[0013] [Figure 1] Figure 1 is a schematic cross-sectional view showing a first example of the catalyst-supported electrode of this embodiment. [Figure 2] Figure 2 is a cross-sectional view schematically showing a second example of the catalyst-supporting electrode of the present embodiment. [Figure 3] Figure 3 is a cross-sectional view schematically showing a third example of the catalyst-supporting electrode of the present embodiment. [Figure 4] Figure 4 is a cross-sectional view schematically showing a fourth example of the catalyst-supporting electrode of the present embodiment. [Figure 5] Figure 5 is a cross-sectional view schematically showing an example of the electrolyzer 100 of the present embodiment. [Figure 6] Figure 6 is a SEM image (magnification: 5000 times) and a binarized image of an arbitrary point on the surface of the catalyst layer of the electrode sample 1.

Mode for Carrying Out the Invention

[0014] The catalyst-supporting electrode according to the first aspect of the present invention is a catalyst-supporting electrode for converting carbon dioxide into a reaction product, a substrate, a catalyst layer disposed on the substrate and containing an element M1 that functions as a catalytic active species, and the surface porosity of the catalyst layer is less than 20%.

[0015] The catalyst-supporting electrode according to the second aspect of the present invention is a catalyst-supporting electrode for converting carbon dioxide into a reaction product, a substrate, a catalyst layer disposed on the substrate and containing an element M1 that functions as a catalytic active species, and the catalyst layer is a vapor deposition layer.

[0016] In the third aspect of the present invention, for example, in the catalyst-supporting electrode according to the first aspect, the surface porosity is less than 10%.

[0017] In the fourth aspect of the present invention, for example, in the catalyst-supporting electrode according to any one of the first to third aspects, the catalyst layer mainly contains the element M1.

[0018] In a fifth embodiment of the present invention, for example, in a catalyst-supported electrode according to any one of the first to fourth embodiments, the element M1 is Bi or Sn.

[0019] In a sixth embodiment of the present invention, for example, in a catalyst-supported electrode according to any one of the first to fifth embodiments, the catalyst layer further comprises an element M2 different from the element M1.

[0020] In a seventh embodiment of the present invention, for example, a catalyst-supported electrode according to any one of the first to sixth embodiments further comprises an intermediate layer disposed between the substrate and the catalyst layer, The aforementioned substrate contains element X, The intermediate layer contains the element M1 and the element X.

[0021] In the eighth aspect of the present invention, for example, a catalyst-supported electrode according to any one of the first to seventh aspects further comprises an underlayer disposed between the substrate and the catalyst layer and in contact with the surface of the substrate, The aforementioned substrate contains element X, The aforementioned underlayer contains the element X.

[0022] In the ninth aspect of the present invention, for example, in a catalyst-supported electrode according to any one of the first to sixth aspects, a base layer is disposed between the substrate and the catalyst layer and is in contact with the surface of the substrate, An intermediate layer disposed between the aforementioned base layer and the aforementioned catalyst layer, Furthermore, The aforementioned substrate contains element X as its main component, The catalyst layer contains the element M1 as its main component, The aforementioned intermediate layer comprises the element M1 and the element X, The aforementioned underlayer contains the element X.

[0023] In the tenth aspect of the present invention, for example, in the catalyst-supported electrode according to the ninth aspect, the value of y1 calculated by the following formula (I) is -5.0 or less. y1=(-0.1203)x1+(-0.0426)x2+(-0.0112)x5+(-0.0476)x6+0.1388x7+2.2919 (I) In the above formula (I), x1 is the volume ratio (%) of the element M1 in the catalyst layer, x2 is the volume ratio (%) of element M1 in the intermediate layer, x5 is the thickness (nm) of the catalyst layer, x6 is the thickness (nm) of the intermediate layer, x7 is the thickness (nm) of the aforementioned underlayer.

[0024] In the 11th aspect of the present invention, for example, in the catalyst-supported electrode according to the 10th aspect, the value of y3 calculated by the following formulas (II) and (III) is 0.5 or greater. y2=0.0260x1+(-0.0286)x2+0.1193x3+(-0.0384)x4+(-0.1413)x5+(-0.0247)x6+0.2141x7+5.5788 (II) y3 = y2 / y1(III) In formula (II) above, x1 is the volume ratio (%) of the element M1 in the catalyst layer, x2 is the volume ratio (%) of element M1 in the intermediate layer, x3 is the volume ratio (%) of element X in the intermediate layer, x4 is the volume ratio (%) of element X in the underlying layer, x5 is the thickness (nm) of the catalyst layer, x6 is the thickness (nm) of the intermediate layer, x7 is the thickness (nm) of the aforementioned underlayer.

[0025] In a twelfth aspect of the present invention, for example, in a catalyst-supported electrode according to any one of the seventh to eleventh aspects, the element X is carbon (C).

[0026] In a thirteenth aspect of the present invention, for example, in a catalyst-supported electrode according to any one of the first to twelfth aspects, the thickness of the catalyst layer is 1 nm or more and 5000 nm or less.

[0027] In a fourteenth aspect of the present invention, for example, in a catalyst-supported electrode according to any one of the first to thirteenth aspects, the substrate is porous.

[0028] In a 15th aspect of the present invention, for example, in a catalyst-supported electrode according to any one of the first to 14th aspects, the catalytically active species is a catalyst that reduces carbon dioxide.

[0029] The electrolytic apparatus according to the 16th aspect of the present invention is An electrolytic apparatus for converting carbon dioxide into reaction products, The device comprises a catalyst-supported electrode as described in any one of the first to fifteenth embodiments.

[0030] The details of the present invention will be described below, but the following description is not intended to limit the present invention to any particular embodiment.

[0031] <Catalyst-supported electrode> Figure 1 is a schematic cross-sectional view showing a first example of the catalyst-supported electrode of this embodiment. The catalyst-supported electrode 10 is an electrode having a catalyst for converting carbon dioxide into reaction products. The catalyst-supported electrode 10 comprises a substrate 1 and a catalyst layer 2 disposed on the substrate 1. The catalyst layer 2 contains element M1 which functions as a catalytically active species. The surface porosity of the catalyst layer 2 is less than 20%.

[0032] The surface porosity of catalyst layer 2 is the proportion of voids on the surface of catalyst layer 2. The surface of catalyst layer 2 is the surface of catalyst layer 2 opposite to the substrate 1, for example, the surface of the catalyst-supported electrode 10. The surface porosity of catalyst layer 2 can be measured by, for example, the following method: Using a scanning electron microscope (SEM), observe five or more arbitrary points on the surface of catalyst layer 2 from a direction perpendicular to the surface at a magnification of 5000x. From the obtained SEM image, identify the void portions present on the surface of catalyst layer 2, and determine the average value of the proportion occupied by these voids as the surface porosity.

[0033] The surface porosity of the catalyst layer 2 is preferably less than 10%, and is 8% or less, 6% or less, 5% or less, less than 5%, 4.5% or less, and even 4.3% or less. Catalyst layers 2 with a small surface porosity that satisfies the above numerical range are easily fabricated by the vapor deposition method described later. Catalyst-supported electrodes 10 with a small surface porosity of catalyst layer 2 are suitable for improving the performance retention rate compared to conventional catalyst-supported electrodes, as degradation of catalyst performance due to repeated use is reduced. The lower limit of the surface porosity of the catalyst layer 2 is not particularly limited, and is, for example, 0% or more, 0.5% or more, 1.0% or more, 1.5% or more, 2.0% or more, and even 2.1% or more.

[0034] The catalyst layer 2 has, for example, a vapor-deposited film containing element M1 that functions as a catalytically active species, and is typically the vapor-deposited film itself. The vapor-deposited layer makes it easy to adjust the surface porosity of the catalyst layer 2 to a small value.

[0035] From another aspect, the present invention A catalyst-supported electrode for converting carbon dioxide into reaction products, Base material 1, A catalyst layer 2 is placed on a substrate 1 and contains element M1 which functions as a catalytically active species, Equipped with, The catalyst layer 2 is a vapor-deposited layer, providing a catalyst-supported electrode 10.

[0036] The catalyst layer 2 is supported, for example, on the substrate 1 (more specifically, on one side of the substrate 1).

[0037] In catalyst layer 2, element M1 functions as a catalytically active species in a reaction that electrolyzes carbon dioxide and converts it into reaction products. The catalytically active species reduces carbon dioxide, for example. The catalyst-supported electrode 10 is typically a cathode. The reaction products obtained by conversion from carbon dioxide using the catalyst-supported electrode 10 are typically organic compounds. An example of an organic compound is formic acid. The catalyst-supported electrode 10 may be an electrode for converting carbon dioxide into one type of reaction product, or it may be an electrode for converting carbon dioxide into two or more types of reaction products.

[0038] In detail, catalyst layer 2 comprises a material containing element M1. Catalyst layer 2 may consist substantially of only a material containing element M1. This material is, for example, a metal catalyst. The metal catalyst may contain a pure metal or an alloy. The metal catalyst may also contain metal oxides or complex oxides. That is, the metal catalyst may contain element M1 as a pure metal or as an alloy of element M1 with other elements.

[0039] The catalyst layer 2 may contain element M1 as its main component. In this specification, "main component" means the component that is present in the highest volume. The content of element M1 in the catalyst layer 2 may be 50 volume% or more, 55 volume% or more, 60 volume% or more, 65 volume% or more, and even 70 volume% or more. The content of element M1 in the catalyst layer 2 may be 100 volume% or less. For example, the content of element M1 in the catalyst layer 2 is 50 volume% or more and 100 volume% or less. The catalyst layer 2 may consist substantially of element M1 alone.

[0040] The content of element M1 in catalyst layer 2 can be calculated, for example, by repeatedly etching the surface of catalyst layer 2 and performing X-ray photoelectron spectroscopy (XPS) analysis to measure the elemental distribution in the thickness direction of catalyst layer 2, or by elemental mapping using energy-dispersive X-ray spectroscopy (EDX) with a transmission electron microscope (TEM) on a cross-section of catalyst layer 2.

[0041] Element M1 is, for example, one element selected from the group consisting of Bi, Sn, V, Cr, Mn, Fe, Co, Ni, Cu, Zr, Nb, Mo, Ru, Rh, Pd, Ag, Cd, Hf, Ta, W, Re, Ir, Pt, Au, Hg, Al, Si, In, Tl, Pb, Sb, Te, U, Sm, Tb, La, Ce, and Nd. Element M1 may be Bi or Sn, or it may be Bi.

[0042] The catalyst layer 2 may contain an element M2 that is different from element M1. Element M2 may be an element that functions as a catalytically active species, for example, the element exemplified as element M1. With such a configuration, the catalyst-supported electrode 10 can further improve the maintenance rate of the catalyst performance. If the catalyst layer 2 contains two or more elements that function as catalytically active species, the element that is present in the largest quantity by volume is designated as element M1, and the others as element M2.

[0043] Element M2 may be Bi or Sn, or it may be Sn. Element M1 may be Bi and element M2 may be Sn.

[0044] The catalyst layer 2 may contain elements M1 and M2 as elemental metals, or it may contain an alloy of elements M1 and M2. The catalyst layer 2 may contain Bi and Sn as elemental metals, or it may contain an alloy of Bi and Sn.

[0045] The thickness of the catalyst layer 2 is not particularly limited, and is, for example, between 1 nm and 5000 nm. Preferably, the thickness of the catalyst layer 2 is 4000 nm or less, but may be 3000 nm or less, 2000 nm or less, 1000 nm or less, 800 nm or less, 500 nm or less, 300 nm or less, 200 nm or less, 150 nm or less, and even 110 nm or less. In some cases, the thickness of the catalyst layer 2 may be 100 nm or less, and may be 90 nm or less, 70 nm or less, and even 50 nm or less. For example, the thickness of the catalyst layer 2 is 10 nm or more. A catalyst layer 2 with a thickness small enough to satisfy the above numerical range is easily fabricated by the vapor deposition method described later. The small thickness of the catalyst layer 2 makes it possible to save space in the equipment.

[0046] The substrate 1 functions, for example, as a support for the catalyst layer 2. The substrate 1 is preferably electrically conductive. Furthermore, the substrate 1 is preferably gas-diffusive. The substrate 1 may also be porous.

[0047] Substrate 1 contains element X. Element X and element M1 are different elements from each other. Element X may be an element that does not function as a catalytically active species. Element X is one selected from, for example, carbon (C), Si, Ni, Pt, Cu, Ti, Cr, F, and Al, and is preferably C. Element X may, in some cases, be one of the elements exemplified by element M1. Substrate 1 may contain element X as its main component. The content of element X in substrate 1 may be, for example, 70 volume% or more, 80 volume% or more, 90 volume% or more, and even 95 volume% or more. The content of element X in substrate 1 may be 100 volume% or less. Substrate 1 may consist substantially of element X alone. The content of element X in substrate 1 can be measured in the same manner as the content of element M1 in the catalyst layer 2 described above.

[0048] The base material 1 may contain carbon as its main component. Known materials can be used as the base material 1, such as carbon paper and carbon cloth, which are carbon supports. The carbon support is preferably porous. The base material 1 may also be a glassy carbon (GC) electrode.

[0049] The substrate 1 may further comprise a microporous layer (MPL) formed on a carbon support. The microporous layer includes, for example, a binder such as Teflon® and carbon particles. Since the surface structure of the catalyst layer 2 tends to depend on the structure of the substrate 1, the surface of the catalyst layer 2 formed on a substrate 1 with an MPL may have a relatively flat structure and a small surface porosity.

[0050] The catalyst layer 2 may be in contact with the substrate 1.

[0051] The method for manufacturing the catalyst-supported electrode of this embodiment includes, for example, forming a catalyst layer 2 containing an element M1 that functions as a catalytically active species by a vapor deposition method. For example, the catalyst-supported electrode 10 can be manufactured by the following method. First, a substrate 1 is prepared. Next, a vapor deposition method is performed so that a catalyst layer 2 is formed on the substrate 1. Specifically, a vapor deposition layer containing element M1 is formed on the substrate 1 by a vapor deposition method. By doing so, a catalyst-supported electrode 10 comprising a substrate 1 and a catalyst layer 2 can be obtained.

[0052] In this specification, vapor deposition refers to vapor phase deposition. That is, vapor deposition method is synonymous with vapor phase deposition method. Vapor deposition methods are typically physical vapor deposition methods such as sputtering. In sputtering, for example, a target containing a metal is used to form a metal catalyst. The conditions of the vapor deposition method can be appropriately set according to the composition and thickness of the target catalyst layer 2.

[0053] According to the manufacturing method of this embodiment, the surface porosity of the catalyst layer 2 can be easily adjusted to a small value, and the catalyst-supported electrode of this embodiment can be easily manufactured. Furthermore, unlike conventional coating methods, the manufacturing method of this embodiment does not require the use of solvents such as organic solvents. Therefore, by adopting the manufacturing method of this embodiment, the amount of waste liquid can be reduced. In addition, since organic solvents are not used, there is the advantage that there is no risk of ignition due to organic solvents. Compared to conventional coating methods, the vapor deposition method not only allows for easy adjustment of the surface porosity of the catalyst layer 2 to a small value, but also allows for easy reduction of the thickness of the catalyst layer 2, and tends to suppress variations in thickness. The vapor deposition method is suitable for manufacturing catalyst layers 2 over a large area and can be said to have high productivity.

[0054] The method for manufacturing the catalyst-supported electrode 10 is not limited to those described above. For example, the catalyst layer 2 may be prepared by depositing metal particles of element M1 onto the substrate 1 using a spray method or the like. However, from the viewpoint of ensuring mass production and large area capacity, it is preferable to prepare the catalyst layer 2 by a vapor deposition method.

[0055] Figure 2 is a schematic cross-sectional view showing a second example of the catalyst-supported electrode of this embodiment. The catalyst-supported electrode 20 comprises a substrate 1, a catalyst layer 2, and an intermediate layer 3 disposed between the substrate 1 and the catalyst layer 2. The intermediate layer 3 contains elements M1 and X. Except for the presence of the intermediate layer 3, the configuration of the catalyst-supported electrode 20 is the same as that of the catalyst-supported electrode 10 of the first example. Therefore, elements common to the catalyst-supported electrode 10 of the first example and the catalyst-supported electrode 20 of the second example are given the same reference numerals, and their descriptions may be omitted. That is, the descriptions of each example below can be applied to each other as long as they do not technically contradict each other. Furthermore, each example can be combined with each other as long as they do not technically contradict each other.

[0056] Intermediate layer 3 may contain Bi as element M1 and C (carbon) as element X.

[0057] The intermediate layer 3 has, for example, a vapor-deposited film containing elements M1 and X, and is typically the vapor-deposited film itself.

[0058] The inclusion of an intermediate layer 3 in the catalyst-supported electrode 20 makes it less likely for the catalyst to detach from the catalyst-supported electrode 20. As a result, the catalyst-supported electrode 20 is more suitable for improving the performance retention rate of the catalyst.

[0059] Intermediate layer 3 may consist substantially of only elements M1 and X.

[0060] The content of element M1 in the intermediate layer 3 may be 60 volume% or more, 70 volume% or more, 80 volume% or more, or even 85 volume% or more. The content of element M1 in the intermediate layer 3 may be less than 100 volume%, or 98 volume% or less. For example, the content of element M1 in the intermediate layer 3 may be 70 volume% or more and 98 volume% or less.

[0061] The content of element X in the intermediate layer 3 is, for example, greater than 0 volume%, and preferably 2 volume% or more. The content of element X in the intermediate layer 3 may be 40 volume% or less, 30 volume% or less, 20 volume% or less, or even 15 volume% or less. The content of element X in the intermediate layer 3 is, for example, 2 volume% or more and 30 volume% or less.

[0062] The content of elements M1 and X in the intermediate layer 3 can be measured in the same manner as the content of element M1 in the catalyst layer 2 described above.

[0063] The thickness of the intermediate layer 3 is not particularly limited, and is, for example, between 1 nm and 3000 nm. The thickness of the intermediate layer 3 is preferably 2000 nm or less, 1000 nm or less, 800 nm or less, 500 nm or less, 300 nm or less, 200 nm or less, 100 nm or less, 50 nm or less, and even 45 nm or less. The thickness of the intermediate layer 3 may, in some cases, be 40 nm or less, 30 nm or less, and even 20 nm or less. The thickness of the intermediate layer 3 is, for example, 1 nm or more, 2 nm or more, or 5 nm or more. Intermediate layers 3 with a thickness small enough to satisfy the above numerical range are easily fabricated by vapor deposition.

[0064] The intermediate layer 3 may bond the substrate 1 and the catalyst layer 2. The intermediate layer 3 may be in contact with the catalyst layer 2, or in contact with the substrate 1 and the catalyst layer 2.

[0065] The catalyst-supported electrode 20 can be manufactured in the same manner as the catalyst-supported electrode 10 of the first example, except that an intermediate layer 3 is formed on the substrate 1 by a vapor deposition method, and then the catalyst layer 2 is formed on the intermediate layer 3. Specifically, a vapor deposition layer containing elements M1 and X is formed on the substrate 1 by a vapor deposition method, and then another vapor deposition layer containing element M1 is formed on the said vapor deposition layer. Thus, a catalyst-supported electrode 20 comprising a substrate 1, a catalyst layer 2, and an intermediate layer 3 can be obtained.

[0066] In the manufacturing method of this embodiment, co-sputtering may be performed using a target containing carbon along with a target containing metal. Co-sputtering tends to allow for the easy fabrication of an intermediate layer 3 containing elements M1 and X.

[0067] Figure 3 is a schematic cross-sectional view showing a third example of the catalyst-supported electrode of this embodiment. The catalyst-supported electrode 30 comprises a substrate 1, a catalyst layer 2, and an underlayer 4 disposed between the substrate 1 and the catalyst layer 2 and in contact with the surface of the substrate 1. The underlayer 4 contains element X. Except for the presence of the underlayer 4, the configuration of the catalyst-supported electrode 30 is the same as the configuration of the catalyst-supported electrode 10 of the first example.

[0068] The base layer 4 may contain C (carbon) as element X.

[0069] The underlayer 4 has, for example, a vapor-deposited film containing element X, and is typically the vapor-deposited film itself. When the underlayer 4 and the substrate 1 have the same composition, the vapor-deposited film is the underlayer 4, and the non-vapor-deposited structure (e.g., a porous body) is the substrate 1.

[0070] The catalyst-supported electrode 30 includes the underlayer 4, which makes it less likely for the catalyst to detach from the catalyst-supported electrode 30. As a result, the catalyst-supported electrode 30 is suitable for improving the performance retention rate of the catalyst.

[0071] The base layer 4 may contain element X as its main component. The content of element X in the base layer 4 may be 50 volume% or more, 60 volume% or more, 70 volume% or more, 80 volume% or more, 90 volume% or more, and even 95 volume% or more. The base layer 4 may consist substantially of only element M1 and element X. The content of element X in the base layer 4 can be measured in the same manner as the content of element M1 in the catalyst layer 2 described above.

[0072] The thickness of the underlayer 4 is not particularly limited, and is, for example, between 1 nm and 1000 nm. The thickness of the underlayer 4 is preferably 800 nm or less, 500 nm or less, 300 nm or less, 100 nm or less, 50 nm or less, 40 nm or less, and even 30 nm or less. In some cases, the thickness of the underlayer 4 may be 20 nm or less, and even 10 nm or less. The thickness of the underlayer 4 is, for example, 1 nm or more, 2 nm or more, or 5 nm or more. Underlayers 4 with a thickness small enough to satisfy the above numerical ranges are easily fabricated by vapor deposition.

[0073] The base layer 4 may be in contact with the catalyst layer 2.

[0074] The catalyst-supported electrode 30 can be manufactured in the same manner as the catalyst-supported electrode 10 of the first example, except that a vapor deposition method is used to form a base layer 4 on a substrate 1, and then a catalyst layer 2 is formed on the base layer 4. Specifically, a vapor deposition layer containing element X is formed on the substrate 1 by vapor deposition, and then a vapor deposition layer containing element M1 is formed on the said vapor deposition layer. Thus, a catalyst-supported electrode 30 comprising a substrate 1, a catalyst layer 2, and a base layer 4 can be obtained.

[0075] Figure 4 is a schematic cross-sectional view showing a fourth example of the catalyst-supported electrode of this embodiment. The catalyst-supported electrode 40 comprises a substrate 1, a catalyst layer 2, an underlayer 4 disposed between the substrate 1 and the catalyst layer 2 and in contact with the surface of the substrate 1, and an intermediate layer 3 disposed between the underlayer 4 and the catalyst layer 2. Except for the presence of the intermediate layer 3 and the underlayer 4, the configuration of the catalyst-supported electrode 40 is the same as that of the catalyst-supported electrode 10 of the first example. That is, except for the presence of the intermediate layer 3, the configuration of the catalyst-supported electrode 40 is the same as that of the catalyst-supported electrode 30 of the third example. Elements common to the catalyst-supported electrodes of the first to third examples and the catalyst-supported electrode 40 of the fourth example are given the same reference numerals, and their descriptions may be omitted.

[0076] In the catalyst-supported electrode 40, element X may be carbon (C). Element M1 may be Bi.

[0077] The intermediate layer 3 may bond the catalyst layer 2 and the base layer 4. The base layer 4 may bond the substrate 1 and the intermediate layer 3.

[0078] The total thickness of the catalyst layer 2, the intermediate layer 3, and the base layer 4 is, for example, 10 nm or more and 5000 nm or less. The total thickness of the catalyst layer 2, the intermediate layer 3, and the base layer 4 may be 25 nm or more, 40 nm or more, 50 nm or more, 65 nm, or even 80 nm or more. The total thickness of the catalyst layer 2, the intermediate layer 3, and the base layer 4 may be 3000 nm or less, 2000 nm or less, 1000 nm or less, 700 nm or less, 500 nm or less, 300 nm or less, or even 150 nm or less.

[0079] The catalyst-supported electrode of this embodiment may have a structure in which three or more layers are laminated on a substrate 1, as shown in the catalyst-supported electrode 40 in Figure 4. The three or more layers may have different compositions from each other.

[0080] The catalyst-supported electrode 40 may have a value of y1 calculated by the following formula (I) that is -5.0 or less. y1=(-0.1203)x1+(-0.0426)x2+(-0.0112)x5+(-0.0476)x6+0.1388x7+2.2919 (I)

[0081] x1 is the volume ratio (%) of element M1 in catalyst layer 2. The value of x1 is, for example, 50 or more, and may be 55 or more, 60 or more, 65 or more, or even 70 or more. There is no particular upper limit to x1, for example, 100. The value of x1 is, for example, between 50 and 100.

[0082] x2 is the volume ratio (%) of element M1 in the intermediate layer 3. The value of x2 may be, for example, 60 or more, and may be 70 or more, 80 or more, 85 or more, 90 or more, or even 95 or more. The value of x2 may be, for example, less than 100, and may be 99 or less, or even 98 or less. The value of x2 may be, for example, 70 or more and less than 100.

[0083] x5 is the thickness (nm) of the catalyst layer 2. The value of x5 is not particularly limited and may be, for example, 5000 or less, but also 4000 or less, 3000 or less, 2000 or less, 1000 or less, 800 or less, 500 or less, 300 or less, 200 or less, 150 or less, 110 or less, 100 or less, and even 90 or less. The value of x5 may be, for example, 1 or more, but also 5 or more, 10 or more, 20 or more, 30 or more, and even 40 or more. The value of x5 may be, for example, 1 or more and less than 2000.

[0084] x6 is the thickness (nm) of the intermediate layer 3. The value of x6 is not particularly limited and may be, for example, 3000 or less, 2000 or less, 1000 or less, 800 or less, 500 or less, 300 or less, 200 or less, 100 or less, 50 or less, 45 or less, or even 40 or less. The value of x6 may be, for example, 1 or more, 2 or more, or 5 or more. The value of x6 may be, for example, 1 or more and 1000 or less.

[0085] x7 is the thickness (nm) of the underlayer 4. The value of x7 is not particularly limited and may be, for example, 1000 or less, 800 or less, 500 or less, 300 or less, 100 or less, 50 or less, 40 or less, 30 or less, 20 or less, or even 10 or less. The value of x7 may be, for example, 1 or more, 2 or more, or 5 or more. The value of x7 may be, for example, 1 or more and 1000 or less.

[0086] The value of y1 calculated by formula (I) is preferably -6.0 or less, but may also be -7.0 or less, -8.0 or less, -9.0 or less, -10.0 or less, and even -10.8 or less. The lower limit of y1 is not particularly limited, for example, -200.0. The value of y1 may also be -180.0 or more, and may also be -150.0 or more, -100.0 or more, -80.0 or more, -50.0 or more, -40.0 or more, -30.0 or more, -20.0 or more, and even -17.0 or more. Note that the value of y1 is the CO2 reduction current density (1st CO2 reduction current density, unit: mA / cm²) when carbon dioxide is reduced by the first electrolysis using the catalyst-supported electrode 40 at a constant voltage of -1.8V (vs. Ag / AgCl reference electrode) and under specific conditions (1st CO2 reduction current density, unit: mA / cm²). 2This is an indicator of the reaction. The value of y1 tends to be in good agreement with the CO2 reduction current density of the first reaction. When the value of y1 is small, such as -5.0 or less, the conversion from carbon dioxide to reaction products proceeds better, and a sufficient amount of reaction products tends to be obtained.

[0087] The CO2 reduction current density is the current density at -1.8V (vs. Ag / AgCl reference electrode) during carbon dioxide electrolysis (mA / cm²). 2 )) × (Formic acid production Faraday efficiency FE HCOOH This value is calculated using (%). Here, the Faraday efficiency of formic acid production, FE, is used. HCOOH The formula is:FE HCOOH This value is calculated using the formula = 2nF / Q, where n is the amount of formic acid produced by the electrolysis of carbon dioxide (mol), F is the Faraday constant (C / mol), and Q is the total charge (C).

[0088] The catalyst-supported electrode 40 may have a y1 value of -5.0 or less, and a y3 value calculated by the following formulas (II) and (III) may be 0.5 or more. y2=0.0260x1+(-0.0286)x2+0.1193x3+(-0.0384)x4+(-0.1413)x5+(-0.0247)x6+0.2141x7+5.5788 (II) y3 = y2 / y1(III)

[0089] In equation (II), x1, x2, x5, x6, and x7 are the same as x1, x2, x5, x6, and x7 in equation (I) above, and their respective numerical ranges are also as described above.

[0090] x3 is the volume ratio (%) of element X in the intermediate layer 3. The value of x3 may be, for example, greater than 0, greater than or equal to 1, or even greater than or equal to 2. The value of x3 may be, for example, 40 or less, less than or equal to 30, less than or equal to 20, or even less than or equal to 15. The value of x3 may be, for example, between 2 and 30.

[0091] x4 is the volume ratio (%) of element X in the underlying layer 4. The value of x4 may be, for example, 50 or more, but could also be 60 or more, 70 or more, 80 or more, 90 or more, 95 or more, or even 98 or more. The value of x4 may be, for example, 100 or less, but could also be 99 or less, or even 98 or less. The value of x4 may be, for example, 70 or more and 100 or less, or even 100.

[0092] The value of y2 calculated by equation (II) is -2.5 or less, and may be -3.5 or less, -5.0 or less, -6.0 or less, -7.0 or less, -8.0 or less, -9.0 or less, and even -10.0 or less. The lower limit of y2 is not particularly limited, for example, -200.0. The value of y2 may be -180.0 or more, and may be -150.0 or more, -100.0 or more, -80.0 or more, -50.0 or more, -40.0 or more, -30.0 or more, -20.0 or more, and even -15.0 or more. Note that the value of y2 is the CO2 reduction current density (second CO2 reduction current density, unit: mA / cm²) obtained when carbon dioxide is reduced by a second electrolysis performed under the same conditions after the first electrolysis performed under a constant voltage of -1.8V (vs. Ag / AgCl reference electrode) using the catalyst-supported electrode 40. 2 This is an indicator of the CO2 reduction current density. The value of y2 tends to correspond well to the CO2 reduction current density of the second CO2 reduction. When the value of y2 is small, such as -2.5 or less, the catalyst performance retention rate tends to improve.

[0093] The value of y3 calculated by equation (III) is preferably 0.55 or higher, but may be 0.6 or higher, 0.65 or higher, 0.66 or higher, or even 0.67 or higher. The upper limit of y3 is not particularly limited, for example, 1.5. The value of y3 may be 1.4 or lower, 1.3 or lower, 1.2 or lower, or even 1.1 or lower. The value of y3 is an indicator of the catalyst performance retention rate when electrolysis of carbon dioxide is repeated twice using the catalyst-supported electrode 40 at a constant voltage of -1.8V (vs. Ag / AgCl reference electrode) and under specific conditions. The value of y3 tends to agree well with the value calculated by (second CO2 reduction current density) / (first CO2 reduction current density). Therefore, the larger the value of y3, the more likely it is that the catalyst performance retention rate of the catalyst-supported electrode 40 will improve.

[0094] Equations (I) and (II) were prepared by the following method. First, the composition of the catalyst-supported electrodes, including the volume ratio of element M1 in catalyst layer 2, the volume ratio of element M1 in intermediate layer 3, the volume ratio of element X in intermediate layer 3, the volume ratio of element X in base layer 4, the thickness of catalyst layer 2, the thickness of intermediate layer 3, and the thickness of base layer 4, was arbitrarily set, and the reduction reaction of carbon dioxide by electrolysis was carried out. As a result, more than 80 experimental data points were obtained that correlated the composition of the catalyst-supported electrodes with the CO2 reduction current density. Next, the obtained experimental data were analyzed by PLS (Partial Least Squares) regression, and equations (I) and (II) were obtained from experimental data with a generalizability of 0.7 or higher.

[0095] The thickness of the catalyst-supported electrode in this embodiment may be, for example, 1 μm or more and 500 μm or less, 20 μm or more and 400 μm or less, 40 μm or more and 300 μm or less, or even 50 μm or more and 200 μm or less.

[0096] The catalyst-supported electrode 40 can be manufactured, for example, by performing a vapor deposition method to form a base layer 4 on a substrate 1. Next, the vapor deposition method is performed to form an intermediate layer 3 on the base layer 4, and then the vapor deposition method is performed to form a catalyst layer 2 on the intermediate layer 3. Specifically, by vapor deposition, a vapor deposition layer containing element X is formed on the substrate 1, a vapor deposition layer containing element M1 and element X is formed on the said vapor deposition layer, and then a vapor deposition layer containing element M1 is formed on the said layer. In this way, a catalyst-supported electrode 40 comprising a substrate 1, a catalyst layer 2, an intermediate layer 3, and a base layer 4 can be obtained.

[0097] <Electrolyzer> The electrolytic apparatus of this embodiment includes the catalyst-supported electrode described above. The electrolytic apparatus converts carbon dioxide into reaction products by electrolysis.

[0098] Figure 5 is a schematic cross-sectional view showing an example of the electrolytic apparatus 100 of this embodiment. The electrolytic apparatus 100 comprises a current collector 70A, a cathode catalyst electrode 50, an anion exchange membrane 71, a central chamber 72, a cation exchange membrane 73, an anode catalyst electrode 60, and a current collector 70B.

[0099] The cathode catalyst electrode 50 may be the catalyst-supported electrode 10 of this embodiment, or it may be the catalyst-supported electrode 20, catalyst-supported electrode 30, or catalyst-supported electrode 40. The catalyst-supported electrode 10 as the cathode catalyst electrode 50 may be arranged such that the base material 1 is located on the current collector 70A side and the catalyst layer 2 is located on the anion exchange membrane side.

[0100] Current collector 70A is the cathode-side current collector that contacts the cathode catalyst electrode 50. Current collector 70B is the anode-side current collector that contacts the anode catalyst electrode 60. Current collectors 70A and 70B may have gas flow paths. Conventional current collectors commonly used in electrolytic devices can be used as current collectors 70A and 70B. Current collectors 70A and 70B are, for example, graphite current collectors.

[0101] The electrolytic device 100 may have one or more openings for supplying or discharging carbon dioxide into or out of the electrolytic device 100. For example, the electrolytic device 100 may have a supply port 6A for supplying carbon dioxide to the current collector 70A and an outlet 7A for discharging carbon dioxide. The electrolytic device 100 may further have one or more openings for supplying or discharging water and oxygen into or out of the electrolytic device 100. For example, the electrolytic device 100 may have a supply port 6B for supplying water to the current collector 70B and an outlet 7B for discharging water or oxygen.

[0102] The central chamber 72 is typically filled with ion-exchange resin beads and supplied with water. The central chamber 72 includes, for example, a supply port 8 for supplying water. The central chamber 72 also includes an outlet 9 through which reaction products are discharged.

[0103] The anion exchange membrane 71 is not particularly limited as long as it is a membrane made of a material that has ionic conductivity, can transport anionic components, and does not have cation conductivity; known materials can be used. The anion exchange membrane 71 may also be made of anion exchange resin. The anion exchange resin is not particularly limited as long as it has anion exchange properties. The anion exchange resin may be a solid polymer electrolyte (ionomer) in which a polymer having anionic conductive functional groups is introduced into a polymer substrate. Specific examples of anion exchange resins include Sustainion (registered trademark, Dioxide Materials Inc.) and Fumasep (registered trademark, FuMA-Tech Inc.). Specific examples of the anion exchange membrane 71 include Sustainion (registered trademark) 37-50.

[0104] The cation exchange membrane 73 is not particularly limited as long as it is a membrane that has ionic conductivity, can transport cationic components (e.g., hydrogen ions), and does not exhibit electronic conductivity; known membranes can be used. The cation exchange membrane 73 is preferably a membrane composed of a polymer, and may also be composed of a cation exchange resin.

[0105] The cation exchange resin is not particularly limited as long as it has cation exchangeability. The cation exchange resin may be a solid polymer electrolyte (ionomer) having a cationic group, in which a polymer having a cation-conductive functional group (cationic group) is introduced into a polymer substrate. Specific examples of the cation exchange resin include perfluoroalkylsulfonic acid resins such as Nafion (registered trademark, DuPont), Flemion (registered trademark, AGC), and Aciplex (registered trademark, Asahi Kasei). Specific examples of the cation exchange membrane 73 include Nafion NR-211, NR-212, and the like.

[0106] The anode catalyst electrode 60 is not particularly limited as long as it can cause an oxidation reaction, and a conductive material can be used. For example, the anode catalyst electrode 60 contains iridium, platinum, gold, copper, iron, and the like.

[0107] The electrolysis device 100 may further include known members constituting the electrolysis device. For example, the electrolysis device 100 includes a power source that applies a voltage between the cathode catalyst electrode 50 and the anode catalyst electrode 60.

[0108] By supplying carbon dioxide to the cathode catalyst electrode 50 and applying a voltage to the electrolysis device 100, reactions proceed at the cathode catalyst electrode 50 and the anode catalyst electrode 60, whereby carbon dioxide can be electrolyzed. Carbon dioxide is electrolyzed and converted into a reaction product. The reaction product is typically an organic compound, such as formic acid.

[0109] According to the electrochemical reaction at the cathode catalyst electrode 50, carbon dioxide is reduced to generate HCOO - ions. The generated HCOO - ions are supplied to the central chamber 72 through the anion exchange membrane 7l. When carbon dioxide is supplied to the cathode catalyst electrode 50 and water is supplied to the anode catalyst electrode 60, hydrogen ions are generated, for example, by the electrochemical reaction at the anode catalyst electrode 60. The generated hydrogen ions are supplied to the central chamber 72 through the cation exchange membrane 73. HCOO -Formic acid is produced when hydrogen ions are added. For example, formic acid is produced in the central chamber 72, and the produced formic acid is discharged from the outlet 9.

[0110] The temperature during electrolysis by the electrolytic device 100 is not particularly limited and can be, for example, room temperature. Since the electrolytic device 100 can convert carbon dioxide into reaction products under mild conditions, it is possible to obtain reaction products with energy savings.

[0111] The electrolytic apparatus 100 is an example of a device that converts carbon dioxide into reaction products by electrolysis, and the electrolytic apparatus of this embodiment is not limited to the above configuration. Another configuration of the electrolytic apparatus is one in which an electrolyte is filled inside the electrolytic cell, and a first electrode and a second electrode are arranged in contact with the electrolyte. The first electrode or the second electrode is the catalyst-supported electrode of the present invention. The first electrode and the second electrode may be immersed in the electrolyte. A reference electrode in contact with the electrolyte may also be provided.

[0112] The electrolyte can be one of the conventionally known solutions commonly used in electrolytic devices. Examples of electrolytes include aqueous potassium bicarbonate solution, aqueous sodium bicarbonate solution, and aqueous sodium hydroxide solution. [Examples]

[0113] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited thereto.

[0114] (Example 1) First, a target made of Bi was set in the target mounting section of the sputtering apparatus. Next, a well-polished glassy carbon (GC) electrode (L-type, GC-3L, EC Frontier Co., Ltd.) was set in the sample introduction section of the sputtering apparatus. Then, sputtering was performed using the above target to fabricate a catalyst layer composed solely of Bi on the GC electrode. The thickness of the catalyst layer was 102 nm.

[0115] As described above, the catalyst-supported electrode of Example 1 was fabricated.

[0116] (Example 2) First, a target made of Bi and a target made of carbon (C) were set in the target mounting section of the sputtering apparatus. Next, a well-polished glassy carbon (GC) electrode (L-type, GC-3L, EC Frontier Co., Ltd.) was set in the sample introduction section of the sputtering apparatus. Then, co-sputtering was performed using the two targets to create an intermediate layer composed only of Bi and C on the GC electrode. In the co-sputtering method, the power output was controlled so that the Bi content in the intermediate layer was 85 volume percent. The thickness of the intermediate layer was 5 nm.

[0117] Next, a sputtering method was performed using only a Bi-based target to fabricate a catalyst layer composed solely of Bi on the intermediate layer. The thickness of the catalyst layer was 46 nm.

[0118] As described above, the catalyst-supported electrode of Example 2 was fabricated.

[0119] (Example 3) First, a target made of Bi and a target made of carbon (C) were set in the target mounting section of the sputtering apparatus. Next, a well-polished glassy carbon (GC) electrode (L-type, GC-3L, EC Frontier Co., Ltd.) was set in the sample introduction section of the sputtering apparatus. Then, a co-sputtering method was performed using the two targets to create an intermediate layer composed only of Bi and C on the GC electrode. In the co-sputtering method, the power output was controlled so that the Bi content in the intermediate layer was 85 volume%. The thickness of the intermediate layer was 20 nm.

[0120] Next, a target made of Bi and a target made of Sn were set in the target mounting section of the sputtering apparatus, and a co-sputtering method using the two targets was performed to fabricate a catalyst layer composed only of Bi and Sn on the intermediate layer. In this co-sputtering method, the power output was controlled so that the Bi content in the catalyst layer was 70 volume percent. The thickness of the catalyst layer was 66 nm.

[0121] As described above, the catalyst-supported electrode of Example 3 was fabricated.

[0122] (Example 4) First, a target made of carbon (C) was set in the target mounting section of the sputtering apparatus. Next, a well-polished carbon-glassy-carbon (GC) electrode (L-type, GC-3L, EC Frontier Co., Ltd.) was set in the sample introduction section of the sputtering apparatus. Then, the sputtering method using the above C target was performed to create a base layer composed solely of C on the GC electrode. The thickness of the base layer was 10 nm.

[0123] Next, a target made of Bi and a target made of Sn were set in the target mounting section of the sputtering apparatus, and a co-sputtering method using the two targets was performed to create a catalyst layer composed only of Bi and Sn on the substrate. In this co-sputtering method, the power output was controlled so that the Bi content in the catalyst layer was 70 volume percent. The thickness of the catalyst layer was 66 nm.

[0124] As described above, the catalyst-supported electrode of Example 4 was fabricated.

[0125] (Example 5) First, a target made of carbon (C) was set in the target mounting section of the sputtering apparatus. Next, a well-polished glassy carbon (GC) electrode (L-type, GC-3L, EC Frontier Co., Ltd.) was set in the sample introduction section of the sputtering apparatus. Then, the sputtering method using the above C target was performed to create a base layer composed solely of C on the GC electrode. The thickness of the base layer was 5 nm.

[0126] Next, a target made of Bi and a target made of carbon (C) were set in the target mounting section of the sputtering apparatus, and a co-sputtering method using the two targets was performed to create an intermediate layer composed only of Bi and C on the substrate. In this co-sputtering method, the power output was controlled so that the Bi content in the intermediate layer was 98 volume percent. The thickness of the intermediate layer was 40 nm.

[0127] Next, a catalyst layer composed solely of Bi was fabricated on the intermediate layer using a sputtering method with a Bi-based target. The thickness of the catalyst layer was 90 nm.

[0128] As described above, the catalyst-supported electrode of Example 5 was fabricated.

[0129] (Example 6) A base layer and an intermediate layer were fabricated on the GC electrode in the same manner as in Example 5. Next, a target made of Bi and a target made of Sn were set in the target mounting section of the sputtering apparatus, and a co-sputtering method using the two targets was performed to fabricate a catalyst layer composed only of Bi and Sn on the intermediate layer. In this co-sputtering method, the power output was controlled so that the Bi content in the catalyst layer was 56 volume percent. The thickness of the catalyst layer was 90 nm.

[0130] As described above, the catalyst-supported electrode of Example 6 was fabricated.

[0131] (Comparative Example 1) A catalyst ink was prepared by thoroughly mixing 10 mg of Bi2O3 powder (US Research Nanomaterials), 180 μL of ultrapure water, 4700 μL of ethanol, and 4 μL of alkaline ionomer (Sustainion® XA-9 5% in EtOH, Dioxide Materials) in an ultrasonic cleaner for 30 minutes.

[0132] Next, 1.5 μL of catalyst ink was dropped onto the surface of a well-polished glassy carbon (GC) electrode (L-type, GC-3L, EC Frontier Co., Ltd.) and dried for 60 minutes to prepare a catalyst layer. In this manner, the catalyst-supported electrode of Comparative Example 1 was prepared.

[0133] <Evaluation of surface porosity> The surface porosity of the catalyst layer was determined for the catalyst-supported electrodes prepared in Examples 1-6 by the following method. First, a carbon paper substrate (TGP-H-120, Toray Industries, Inc.) was used instead of a GC electrode, and the amount of catalytic active species supported per unit area (Bi support) was 2 mg / cm². 2 Electrode samples 1-6 corresponding to the catalyst-supported electrodes of Examples 1-6 were prepared by the same method as in each example, except that the catalyst layer was formed in such a manner.

[0134] Next, the surface porosity of the catalyst layer was determined for the obtained electrode samples 1-6. Specifically, five arbitrary points on the surface of the catalyst layer of each electrode sample were observed using a SEM from a direction perpendicular to the surface at a magnification of 5000x. For each obtained SEM image, a binarized image was obtained using image analysis software (ImageJ) to separate the structural portion and the void portion of the catalyst layer within a 10 μm × 10 μm area. By analyzing the binarized image, the proportion occupied by the void portion was determined, and the average value of these five points was calculated to determine the surface porosity of the catalyst layer of electrode samples 1-6. The surface porosity of the catalyst layer in electrode samples 1-6 was considered to be the surface porosity of the catalyst layer of the catalyst-supported electrode in Example 1-6.

[0135] Figure 6 shows an SEM image (magnification 5000x) and a binarized image of an arbitrary point on the surface of the catalyst layer of electrode sample 1. Figure 6(a) is the SEM image. Figure 6(b) is the binarized image of Figure 6(a). In Figure 6(b), the black areas represent voids.

[0136] The surface porosity of the catalyst layer was determined for the catalyst-supported electrode prepared in Comparative Example 1 by the following method. First, a carbon paper substrate (TGP-H-120, Toray Industries, Inc.) was used instead of a GC electrode, and the amount of catalytic active species supported per unit area (Bi2O3 supported) was 4 mg / cm². 2 Except for forming the catalyst layer in such a manner, electrode sample C1 corresponding to the catalyst-supported electrode of Comparative Example 1 was prepared by the same method as in Comparative Example 1. The surface porosity of the catalyst layer in electrode sample C1 was determined by the method described above, and this was considered to be the surface porosity of the catalyst layer of the catalyst-supported electrode in Comparative Example 1.

[0137] <Evaluation of performance retention rate> Using the catalyst-supported electrodes prepared in the examples and comparative examples, electrolysis of carbon dioxide was performed by the following method, and the performance retention rate of the catalyst was evaluated.

[0138] First, the working electrode, counter electrode, and reference electrode were set in a compact analytical cell (VB2, EC Frontier). The catalyst-supported electrodes from Examples 1-6 and Comparative Example 1 were used as the working electrode. A platinum electrode (CE-200, EC Frontier) was used as the counter electrode. A silver / silver chloride electrode (RE-1A, EC Frontier) was used as the reference electrode. 15 g of 0.1 M potassium bicarbonate aqueous solution was added to the cell as the electrolyte. In this way, the test electrolytic cell was assembled.

[0139] Next, the aqueous solution in the cell was replaced with CO2 gas by bubbling it at a flow rate of 30 mL / min for 30 minutes. Then, while continuously supplying CO2 gas to the cell, an electrolytic test was performed by applying a voltage of -1.8 V (vs Ag / AgCl) for 60 minutes.

[0140] The electrolyte solution was collected after the test, and the concentration of formic acid produced was quantified by analyzing the electrolyte solution using high-performance liquid chromatography (HPLC). From the formic acid concentration, the Faraday efficiency (FE) of formic acid production was calculated. HCOOH The Faraday efficiency (FE) formic acid production was calculated, and the current density for the first CO2 reduction in the catalyst was determined. As mentioned above, the Faraday efficiency (FE) formic acid production was calculated. HCOOH The CO2 reduction current density was calculated using the following formula. FE HCOOH = 2nF / Q (n is the amount of formic acid produced by the electrolysis of carbon dioxide (mol), F is the Faraday constant (C / mol), and Q is the total charge (C).) CO2 reduction current density = (current density at -1.8V (vs. Ag / AgCl)) × FE HCOOH

[0141] After cleaning and thoroughly drying each electrode following the test, the test electrolytic cell was reassembled, and the second electrolysis test was performed in the same manner. The formic acid concentration produced in the second electrolysis test was quantified using HPLC, and the CO2 reduction current density for the second test was determined.

[0142] The catalyst's performance retention rate was calculated from the values ​​of the CO2 reduction current density during the first and second CO2 reduction cycles. The performance retention rate was calculated using the following formula. Performance retention rate (%) = 100 × (CO2 reduction current density in the second cycle) / (CO2 reduction current density in the first cycle)

[0143] Table 1 shows the configurations of Examples 1-6 and Comparative Example 1. Table 2 shows the evaluation results of the performance retention rate. In Table 2, y1 is the value obtained by formula (I) above, and y3 is the value obtained by formulas (II) and (III). Regarding the amount of catalytic active species loaded in Table 2, Examples 1-6 are the amount of Bi loaded, and Comparative Example 1 is the amount of Bi2O3 loaded.

[0144] [Table 1]

[0145] [Table 2]

[0146] Examples 1-6, in which the surface porosity of the catalyst layer was less than 20%, showed improved catalyst performance retention compared to Comparative Example 1. The performance retention was further improved when the catalyst-supported electrode had an intermediate layer. The performance retention was further improved when the catalyst-supported electrode had a base layer. The performance retention was further improved when the catalyst layer contained another element in addition to element M1. The performance retention was further improved when the catalyst-supported electrode contained three layers: a catalyst layer, an intermediate layer, and a base layer. [Industrial applicability]

[0147] The catalyst-supported electrode of this embodiment is suitable for electrolytic devices that convert carbon dioxide into reaction products. [Explanation of Symbols]

[0148] 1 Base material 2 Catalyst layer 3. Middle Class 4 Base layer 10, 20, 30, 40 Catalyst-supported electrodes 50 Cathode Catalyst Electrodes 60 Anode catalyst electrodes 70A, 70B current collectors 6A, 6B, 8 supply ports 7A, 7B, 9 outlet 71 Anion exchange membrane 72 Central room 73 Cation exchange membrane 100 Electrolyzer

Claims

1. A catalyst-supported electrode for converting carbon dioxide into reaction products, Substrate and A catalyst layer disposed on the substrate and containing element M1 which functions as a catalytically active species, Equipped with, A catalyst-supported electrode having a surface porosity of less than 20% in the catalyst layer.

2. A catalyst-supported electrode for converting carbon dioxide into reaction products, Substrate and A catalyst layer disposed on the substrate and containing element M1 which functions as a catalytically active species, Equipped with, The catalyst layer is a vapor-deposited layer, which is a catalyst-supported electrode.

3. The catalyst-supported electrode according to claim 1, wherein the surface porosity is less than 10%.

4. The catalyst-supported electrode according to claim 1 or 2, wherein the catalyst layer mainly contains the element M1.

5. The catalyst-supported electrode according to claim 1 or 2, wherein the element M1 is Bi or Sn.

6. The catalyst-supported electrode according to claim 1 or 2, wherein the catalyst layer further comprises an element M2 different from the element M1.

7. The system further comprises an intermediate layer disposed between the substrate and the catalyst layer, The aforementioned substrate contains element X, The catalyst-supported electrode according to claim 1 or 2, wherein the intermediate layer comprises the element M1 and the element X.

8. The substrate and the catalyst layer are further provided with an underlayer that is placed between them and is in contact with the surface of the substrate, The aforementioned substrate contains element X, The catalyst-supported electrode according to claim 1 or 2, wherein the underlying layer contains the element X.

9. Displaced between the substrate and the catalyst layer, and a base layer in contact with the surface of the substrate, An intermediate layer disposed between the aforementioned base layer and the aforementioned catalyst layer, Furthermore, The aforementioned substrate contains element X as its main component, The catalyst layer contains the element M1 as its main component, The aforementioned intermediate layer comprises the element M1 and the element X, The aforementioned underlayer contains the element X, The catalyst-supported electrode according to claim 1 or 2.

10. y calculated by the following formula (I) 1 The catalyst-supported electrode according to claim 9, wherein the value of is -5.0 or less. y 1 =(-0.1203)x 1 +(-0.0426)x 2 +(-0.0112)x 5 +(-0.0476)x 6 +0.1388x 7 +2.2919 (I) In the above formula (I), x 1 This is the volume ratio (%) of the element M1 in the catalyst layer, x 2 is the volume ratio (%) of the element M1 in the intermediate layer, x 5 This is the thickness (nm) of the catalyst layer, x 6 This is the thickness (nm) of the intermediate layer, x 7 This is the thickness (nm) of the aforementioned underlayer.

11. y calculated by the following equations (II) and (III) 3 The catalyst-supported electrode according to claim 10, wherein the value of is 0.5 or greater. y 2 =0.0260x 1 +(-0.0286)x 2 +0.1193x 3 +(-0.0384)x 4 +(-0.1413)x 5 +(-0.0247)x 6 +0.2141x 7 +5.5788 (II) y 3  2 y 1 (_=) In the above formula (II), x 1 This is the volume ratio (%) of the element M1 in the catalyst layer, x 2 This is the volume ratio (%) of element M1 in the intermediate layer, x 3 This is the volume ratio (%) of element X in the intermediate layer, x 4 This is the volume ratio (%) of element X in the underlying layer, x 5 This is the thickness (nm) of the catalyst layer, x 6 This is the thickness (nm) of the intermediate layer, x 7 This is the thickness (nm) of the aforementioned underlayer.

12. The catalyst-supported electrode according to claim 7, wherein the element X is carbon (C).

13. The catalyst-supported electrode according to claim 1 or 2, wherein the thickness of the catalyst layer is 1 nm or more and 5000 nm or less.

14. The catalyst-supported electrode according to claim 1 or 2, wherein the substrate is porous.

15. The catalyst-supported electrode according to claim 1 or 2, wherein the catalytic active species is a catalyst that reduces carbon dioxide.

16. An electrolytic apparatus for converting carbon dioxide into reaction products, An electrolytic apparatus comprising a catalyst-supported electrode according to claim 1 or 2.

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