JP2015147990A - Electrode, method of producing electrode, electrochemical reduction method and method of producing electrochemical reduction product - Google Patents
Electrode, method of producing electrode, electrochemical reduction method and method of producing electrochemical reduction product Download PDFInfo
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Abstract
Description
本発明は、電極、電極の製造方法、電気化学還元方法及び電気化学還元生成物の製造方法に関する。 The present invention relates to an electrode, an electrode manufacturing method, an electrochemical reduction method, and an electrochemical reduction product manufacturing method.
金属を作用電極として二酸化炭素、水等の電気化学還元を行うと、産業上有用な種々の物質を生成することができる。例えば、水銀、カドミウム、インジウム等を作用電極として電気化学還元を行うとギ酸を主成分として生成し、金、銀等を作用電極として電気化学還元を行うと一酸化炭素及び水素を主成分として生成し、白金、鉄等を作用電極として電気化学還元を行うと、二酸化炭素に由来する還元生成物は殆ど生成しないが水の電気分解により水素が生成する（例えば、非特許文献１参照）。 When an electrochemical reduction of carbon dioxide, water or the like is performed using a metal as a working electrode, various industrially useful substances can be generated. For example, when electrochemical reduction is performed using mercury, cadmium, indium, etc. as the working electrode, formic acid is generated as the main component, and when electrochemical reduction is performed using gold, silver, etc. as the working electrode, carbon monoxide and hydrogen are generated as the main components. However, when electrochemical reduction is performed using platinum, iron, or the like as a working electrode, hydrogen is generated by electrolysis of water although almost no reduction product derived from carbon dioxide is generated (see, for example, Non-Patent Document 1).
銅を作用電極として電気化学還元を行うと、上記の金属とは異なり、水素及び一酸化炭素、メタン、ギ酸等の炭素原子が１個である分子の他にエチレン、エタノール、プロパノール等の炭素原子が２個以上である分子も生成させることができる。従って、銅を用いた電気化学還元によれば二酸化炭素、水等の豊富に存在する資源から産業上有用な種々の物質を生成させることができる。さらに、銅自体も比較的安価で生産量が豊富であり、高価な希少金属を使用する場合に比べて経済的にも有利である。 When electrochemical reduction is performed using copper as the working electrode, unlike the above metals, in addition to hydrogen and carbon monoxide, methane, formic acid, and other molecules having one carbon atom, carbon atoms such as ethylene, ethanol, propanol, etc. Molecules with 2 or more can also be generated. Therefore, according to electrochemical reduction using copper, various industrially useful substances can be generated from abundant resources such as carbon dioxide and water. Furthermore, copper itself is relatively inexpensive and abundant in production, which is economically advantageous compared to the case where expensive rare metals are used.
上述のように銅は電気化学還元用の触媒として有用であるが、一般に市販されている銅板を作用電極として用いる場合の触媒過電圧が可逆水素電極（ＲＨＥ）に対して０．７Ｖ以上（ｐＨ７）であり、白金等を作用電極として用いる場合と比べて大きい。このため、高い電圧を印加する必要がある。従って、銅を用いる場合の触媒過電圧を低減することができれば電気化学還元のエネルギー効率を向上させることができる。 As described above, copper is useful as a catalyst for electrochemical reduction. However, when a commercially available copper plate is used as a working electrode, the catalyst overvoltage is 0.7 V or more (pH 7) relative to the reversible hydrogen electrode (RHE). It is larger than the case where platinum or the like is used as the working electrode. For this reason, it is necessary to apply a high voltage. Therefore, if the catalyst overvoltage in the case of using copper can be reduced, the energy efficiency of electrochemical reduction can be improved.
本発明は上記課題に鑑み、電気化学還元のエネルギー効率に優れる電極、電極の製造方法、電気化学還元方法及び電気化学還元生成物の製造方法を提供することを目的とする。 An object of this invention is to provide the electrode excellent in the energy efficiency of electrochemical reduction, the manufacturing method of an electrode, the electrochemical reduction method, and the manufacturing method of an electrochemical reduction product in view of the said subject.
上記課題を解決するための手段は、以下のとおりである。
＜１＞基体と、前記基体の表面の少なくとも一部に存在し、粒子径が５０ｎｍ〜５００ｎｍの範囲内である銅含有粒子を含む触媒部と、を有する電極。
Means for solving the above problems are as follows.
<1> An electrode having a substrate and a catalyst part containing copper-containing particles which are present on at least a part of the surface of the substrate and have a particle diameter in the range of 50 nm to 500 nm.
＜２＞前記銅含有粒子が部分的に他の銅含有粒子と結合している、＜１＞に記載の電極。 <2> The electrode according to <1>, wherein the copper-containing particles are partially bonded to other copper-containing particles.
＜３＞前記銅含有粒子は、粒子径が５ｎｍ〜２００ｎｍの範囲内である銅含有粒子が融着して得られたものである＜１＞又は＜２＞に記載の電極。 <3> The electrode according to <1> or <2>, wherein the copper-containing particles are obtained by fusing copper-containing particles having a particle diameter in the range of 5 nm to 200 nm.
＜４＞前記基体が銅を含む、＜１＞〜＜３＞のいずれか１項に記載の電極。 <4> The electrode according to any one of <1> to <3>, wherein the substrate includes copper.
＜５＞基体の表面の少なくとも一部に粒子径が５ｎｍ〜２００ｎｍの範囲内である銅含有粒子を配置する工程と、前記銅含有粒子が表面の少なくとも一部に配置された基体を熱処理して粒子径が５０ｎｍ〜５００ｎｍの範囲内である銅含有粒子を含む触媒部を形成する工程と、を有する電極の製造方法。 <5> A step of arranging copper-containing particles having a particle diameter in the range of 5 nm to 200 nm on at least a part of the surface of the substrate, and a heat treatment of the substrate on which the copper-containing particles are arranged on at least a part of the surface Forming a catalyst part including copper-containing particles having a particle diameter in the range of 50 nm to 500 nm.
＜６＞前記銅含有粒子を配置する工程が、粒子径が５ｎｍ〜２００ｎｍの範囲内である銅含有粒子を含む触媒形成組成物を前記基体の表面の少なくとも一部に付与する工程である、＜５＞に記載の電極の製造方法。 <6> The step of arranging the copper-containing particles is a step of applying a catalyst-forming composition containing copper-containing particles having a particle diameter in the range of 5 nm to 200 nm to at least a part of the surface of the substrate. The manufacturing method of the electrode as described in 5>.
＜７＞前記銅含有粒子を配置する工程が、粒子径が５ｎｍ〜２００ｎｍの範囲内である銅含有粒子を含む分散液又はペーストを前記基体の表面の少なくとも一部に塗布する工程である、＜５＞又は＜６＞に記載の電極の製造方法。 <7> The step of arranging the copper-containing particles is a step of applying a dispersion or paste containing copper-containing particles having a particle diameter in the range of 5 nm to 200 nm on at least a part of the surface of the substrate. The manufacturing method of the electrode as described in 5> or <6>.
＜８＞前記粒子径が５ｎｍ〜２００ｎｍの範囲内である銅含有粒子が、銅を含む化合物、還元性化合物及びアルキルアミンを含む組成物を加熱する工程を含む方法によって製造される、＜５＞〜＜７＞のいずれか１項に記載の電極の製造方法。 <8> The copper-containing particles having a particle diameter in the range of 5 nm to 200 nm are produced by a method including a step of heating a composition containing copper, a reducing compound, and an alkylamine, <5> The manufacturing method of the electrode of any one of-<7>.
＜９＞＜１＞〜＜４＞のいずれか１項に記載の電極を用いて水及び二酸化炭素からなる群より選択される少なくとも一方を分解する工程を有する、電気化学還元方法。 <9> An electrochemical reduction method comprising a step of decomposing at least one selected from the group consisting of water and carbon dioxide using the electrode according to any one of <1> to <4>.
＜１０＞前記分解により水素及び炭素原子数が１個〜３個である化合物からなる群より選択される少なくとも一つが生成される、＜９＞に記載の電気化学還元方法。 <10> The electrochemical reduction method according to <9>, wherein at least one selected from the group consisting of hydrogen and a compound having 1 to 3 carbon atoms is generated by the decomposition.
＜１１＞＜１＞〜＜４＞のいずれか１項に記載の電極を用いて水及び二酸化炭素からなる群より選択される少なくとも一方を分解する工程を有する、電気化学還元生成物の製造方法。 <11> A method for producing an electrochemical reduction product, comprising the step of decomposing at least one selected from the group consisting of water and carbon dioxide using the electrode according to any one of <1> to <4>. .
＜１２＞前記電気化学還元生成物が水素及び炭素原子数が１個〜３個である化合物からなる群より選択される少なくとも一つである、＜１１＞に記載の電気化学還元生成物の製造方法。 <12> The production of the electrochemical reduction product according to <11>, wherein the electrochemical reduction product is at least one selected from the group consisting of hydrogen and a compound having 1 to 3 carbon atoms. Method.
本発明によれば、電気化学還元のエネルギー効率に優れる電極、電極の製造方法、電気化学還元方法及び電気化学還元生成物の製造方法を提供することができる。 ADVANTAGE OF THE INVENTION According to this invention, the electrode excellent in the energy efficiency of electrochemical reduction, the manufacturing method of an electrode, the electrochemical reduction method, and the manufacturing method of an electrochemical reduction product can be provided.
本明細書において「〜」を用いて示された数値範囲は、「〜」の前後に記載される数値をそれぞれ最小値及び最大値として含む範囲を示す。さらに本明細書において組成物中の各成分の含有量は、組成物中に各成分に該当する物質が複数存在する場合、特に断らない限り、組成物中に存在する当該複数の物質の合計量を意味する。 In the present specification, a numerical range indicated using “to” indicates a range including the numerical values described before and after “to” as the minimum value and the maximum value, respectively. Further, in the present specification, the content of each component in the composition is the total amount of the plurality of substances present in the composition unless there is a specific notice when there are a plurality of substances corresponding to each component in the composition. Means.
＜電極＞
本発明の電極は、基体と、前記基体の表面の少なくとも一部に存在し、粒子径が５０ｎｍ〜５００ｎｍの範囲内である銅含有粒子を含む触媒部と、を有する。本発明の電極は、電気化学還元に使用した場合の触媒過電圧が、触媒部を有しない銅板を作用電極として使用した場合の触媒過電圧よりも低い。従って、本発明の電極は、触媒部を有しない銅板を作用電極として使用した場合よりもエネルギー効率に優れている。
<Electrode>
The electrode of the present invention has a substrate and a catalyst part containing copper-containing particles that are present on at least a part of the surface of the substrate and have a particle diameter in the range of 50 nm to 500 nm. In the electrode of the present invention, the catalyst overvoltage when used for electrochemical reduction is lower than the catalyst overvoltage when a copper plate having no catalyst portion is used as a working electrode. Therefore, the electrode of the present invention is more energy efficient than the case where a copper plate having no catalyst portion is used as the working electrode.
本発明の電極を電気化学還元に使用すると触媒部を有しない銅板を使用した場合よりも触媒過電圧が低減する理由は明らかではないが、粒子径が５０ｎｍ〜５００ｎｍの範囲内である銅含有粒子を含む触媒部が表面に存在することにより、触媒部が存在しない平滑な面よりも比表面積が大きく、電解液と接触する面積が大きくなること、及び粒子径が５０ｎｍ〜５００ｎｍの範囲内である場合は、銅含有粒子の結晶表面エネルギーにより、特に、水や二酸化炭素を還元する活性触媒サイトが露出しやすくなるためと考えられる。 When the electrode of the present invention is used for electrochemical reduction, it is not clear why the catalyst overvoltage is lower than when a copper plate having no catalyst portion is used, but the copper-containing particles having a particle diameter in the range of 50 nm to 500 nm are not used. When the catalyst part is present on the surface, the specific surface area is larger than the smooth surface without the catalyst part, the area in contact with the electrolyte is increased, and the particle diameter is in the range of 50 nm to 500 nm This is presumably because the active catalyst sites that reduce water and carbon dioxide are likely to be exposed due to the crystal surface energy of the copper-containing particles.
（触媒部）
本発明の電極は、粒子径が５０ｎｍ〜５００ｎｍの範囲内である銅含有粒子を含む触媒部を有する。触媒部が「銅含有粒子を含む」とは、触媒部が、粒子径が５０ｎｍ〜５００ｎｍの範囲内であり、部分的に他の銅含有粒子と結合している銅含有粒子を含むことを意味する。結合の態様としては、銅含有粒子を加熱することにより生じる融着が挙げられる。
(Catalyst part)
The electrode of the present invention has a catalyst portion containing copper-containing particles having a particle diameter in the range of 50 nm to 500 nm. The catalyst part includes “copper-containing particles” means that the catalyst part includes copper-containing particles having a particle diameter in the range of 50 nm to 500 nm and partially bonded to other copper-containing particles. To do. Examples of the bonding include fusion produced by heating the copper-containing particles.
触媒部に粒子径が５０ｎｍ〜５００ｎｍの範囲内である銅含有粒子が含まれるか否かは、触媒部を走査電子顕微鏡や原子間力顕微鏡等で観察した際に、粒子径が５０ｎｍ〜５００ｎｍの範囲内である銅含有粒子が存在する部分があるか否かによって確認することができる。本発明では、他の銅含有粒子と部分的に結合して境界の一部が明確でないが、全体としては１個の粒子として確認できる場合も銅含有粒子に含まれるものとする。 Whether or not the catalyst part contains copper-containing particles having a particle diameter in the range of 50 nm to 500 nm is determined when the catalyst part is observed with a scanning electron microscope, an atomic force microscope, or the like. It can be confirmed by whether or not there is a portion where copper-containing particles within the range exist. In this invention, although it couple | bonds with other copper containing particle | grains and a part of boundary is not clear, the case where it can confirm as one particle as a whole shall be contained in copper containing particle | grains.
本発明では、触媒部を観察した際に、粒子径が５０ｎｍ〜５００ｎｍの範囲内である銅含有粒子が２０μｍ×２０μｍの領域中に５０個以上存在する部分がある場合は、触媒部が「粒子径が５０ｎｍ〜５００ｎｍの範囲内である銅含有粒子を含む」と判断する。 In the present invention, when the catalyst portion is observed, if there are 50 or more portions of copper-containing particles having a particle diameter in the range of 50 nm to 500 nm in a 20 μm × 20 μm region, the catalyst portion is “particle”. It includes a copper-containing particle having a diameter in the range of 50 nm to 500 nm ”.
本発明では、触媒部を観察した際に、粒子径が５０ｎｍ〜５００ｎｍの範囲内である銅含有粒子が２０μｍ×２０μｍの領域中に１００個以上存在する部分があることが好ましく、２０μｍ×２０μｍの領域を２μｍ×２μｍの領域に分割した場合、２μｍ×２μｍの領域のそれぞれにおいて粒子径が５０ｎｍ〜５００ｎｍの範囲内である銅含有粒子が１個以上存在する部分があることがより好ましい。 In the present invention, when the catalyst portion is observed, it is preferable that there are portions where 100 or more copper-containing particles having a particle diameter in the range of 50 nm to 500 nm are present in a region of 20 μm × 20 μm, and 20 μm × 20 μm When the region is divided into 2 μm × 2 μm regions, it is more preferable that each of the 2 μm × 2 μm regions has a portion where one or more copper-containing particles having a particle diameter in the range of 50 nm to 500 nm exist.
触媒部に含まれる銅含有粒子はその粒子径が５０ｎｍ〜５００ｎｍの範囲内である。銅含有粒子の粒子径が上記の範囲外であると、触媒過電圧の低減効果が充分に得られない場合がある。充分に低い触媒過電圧を得る観点からは、触媒部に含まれる銅含有粒子の粒子径は、５０ｎｍ〜５００ｎｍの範囲内であることが好ましく、５０ｎｍ〜３００ｎｍの範囲内であることがより好ましく、５０ｎｍ〜１００ｎｍの範囲内であることが更に好ましい。 The copper-containing particles contained in the catalyst part have a particle diameter in the range of 50 nm to 500 nm. If the particle size of the copper-containing particles is outside the above range, the catalyst overvoltage reduction effect may not be sufficiently obtained. From the viewpoint of obtaining a sufficiently low catalyst overvoltage, the particle size of the copper-containing particles contained in the catalyst part is preferably in the range of 50 nm to 500 nm, more preferably in the range of 50 nm to 300 nm, and 50 nm. More preferably, it is in the range of ˜100 nm.
触媒部に含まれる銅含有粒子の材質は特に制限されず、銅のみを含んでいても、銅以外の元素を含んでいてもよい。二酸化炭素を電気化学的に還元し有機物資源を生成する観点からは、銅含有粒子中の銅元素の含有率は５０物質量（モル）％以上であることが好ましく、７０物質量（モル）％以上であることがより好ましく、９０物質量（モル）％以上であることがさらに好ましい。銅含有粒子が銅以外の元素を含む場合、前記元素としてはＨ、Ｌｉ、Ｎａ、Ｋ、Ｃａ、Ｍｇ、Ｚｎ、Ｎｉ、Ｃｏ、Ｆｅ、Ｍｎ、Ｃｒ、Ａｇ、Ｓｎ、Ａｌ、Ｐｔ、Ａｕ、Ｓｉ、Ｐ、Ｓ、Ｃ、Ｎ、Ｏ、Ｃｌ、Ｂｒ、Ｉ等を挙げることができる。電極の製造コスト低減の観点からは、前記元素はＰｔ、Ａｕ等の高価な金属元素以外の元素であることが好ましい。触媒部に含まれる銅含有粒子は、材質が異なるコアとシェルとを有していてもよい。触媒部に含まれる銅含有粒子は１種のみであっても、材質が異なる２種以上の組み合わせであってもよい。 The material of the copper-containing particles contained in the catalyst part is not particularly limited, and may contain only copper or may contain elements other than copper. From the viewpoint of electrochemically reducing carbon dioxide to produce an organic resource, the content of copper element in the copper-containing particles is preferably 50 mass (mol)% or more, and 70 mass (mol)%. More preferably, it is more preferably 90 substance amount (mol)% or more. When the copper-containing particles contain an element other than copper, the elements include H, Li, Na, K, Ca, Mg, Zn, Ni, Co, Fe, Mn, Cr, Ag, Sn, Al, Pt, Au, Si, P, S, C, N, O, Cl, Br, I, etc. can be mentioned. From the viewpoint of reducing the manufacturing cost of the electrode, the element is preferably an element other than an expensive metal element such as Pt or Au. The copper-containing particles contained in the catalyst part may have a core and a shell made of different materials. The copper-containing particles contained in the catalyst portion may be only one type or a combination of two or more types having different materials.
触媒部は、粒子径が５０ｎｍ〜５００ｎｍの範囲内である銅含有粒子が部分的に他の銅含有粒子と結合している構造を有する。このような構造は、例えば原料となる銅含有粒子を加熱して互いに融着させることで得ることができる。銅含有粒子同士の融着が進むと、より粒子径の大きい銅含有粒子が形成される。従って、銅含有粒子の融着の度合いを制御することにより、触媒部を形成している銅含有粒子の粒子径を所望の範囲に制御することができる。銅含有粒子の融着の度合いは、例えば後述する電極の製造方法における熱処理の温度、時間、雰囲気等の条件、原料となる銅含有粒子の粒子径、銅含有粒子中の銅元素の含有率などを変更することにより制御することができる。 The catalyst portion has a structure in which copper-containing particles having a particle diameter in the range of 50 nm to 500 nm are partially bonded to other copper-containing particles. Such a structure can be obtained by, for example, heating and fusing the copper-containing particles as raw materials together. As the fusion of the copper-containing particles proceeds, copper-containing particles having a larger particle diameter are formed. Therefore, by controlling the degree of fusion of the copper-containing particles, the particle diameter of the copper-containing particles forming the catalyst portion can be controlled within a desired range. The degree of fusion of the copper-containing particles is, for example, the conditions of the heat treatment temperature, time, atmosphere, etc. in the electrode manufacturing method described later, the particle diameter of the copper-containing particles as the raw material, the content of the copper element in the copper-containing particles, etc. It is possible to control by changing.
（基体）
本発明の電極は、基体を有する。基体の材質は特に制限されず、導電性を有していても有していなくてもよい。例えば、Ｃｕ、Ａｕ、Ｐｔ、Ｐｄ，Ａｇ、Ｚｎ、Ｎｉ、Ｃｏ、Ｆｅ、Ａｌ、Ｓｎ等の金属、前記金属の合金、ＩＴＯ、ＺｎＯ、ＳｎＯ、Ｓｉ等の半導体、ガラス、黒鉛やグラファイト等のカーボン材料、樹脂などを挙げることができる。銅含有粒子の基体への付着性の観点からは、基体は銅を含むことが好ましい。基体が銅を含む場合の銅の含有率は特に制限されない。基体の導電性の観点からは５０物質量（モル）％以上であることが好ましく、７０物質量（モル）％以上であることがより好ましく、９０物質量（モル）％以上であることがさらに好ましい。
(Substrate)
The electrode of the present invention has a substrate. The material of the substrate is not particularly limited and may or may not have conductivity. For example, metals such as Cu, Au, Pt, Pd, Ag, Zn, Ni, Co, Fe, Al, and Sn, alloys of the metals, semiconductors such as ITO, ZnO, SnO, and Si, glass, graphite, graphite, etc. Examples thereof include carbon materials and resins. From the viewpoint of adhesion of the copper-containing particles to the substrate, the substrate preferably contains copper. The copper content is not particularly limited when the substrate contains copper. From the viewpoint of the conductivity of the substrate, the amount is preferably 50 substance amount (mol)% or more, more preferably 70 substance amount (mol)% or more, and further preferably 90 substance amount (mol)% or more. preferable.
基体の形状は特に制限されず、板状、棒状、ロール状等であってよい。基体の表面に対する触媒部が存在する部分の割合は特に制限されず、基体の表面全体に触媒部が存在していても、一部に触媒部が存在していてもよい。ある実施態様では、基体の表面全体の面積に対する触媒部が存在する面積の割合が５０％〜１００％である。 The shape of the substrate is not particularly limited, and may be a plate shape, a rod shape, a roll shape, or the like. The ratio of the portion where the catalyst portion is present relative to the surface of the substrate is not particularly limited, and the catalyst portion may be present on the entire surface of the substrate or may be partially present. In one embodiment, the ratio of the area where the catalyst portion is present to the area of the entire surface of the substrate is 50% to 100%.
本発明の電極は、触媒部及び基体以外の要素を含んでもよい。触媒部及び基体以外の要素としては、保護材、修飾剤、触媒改質剤等を挙げることができる。 The electrode of the present invention may include elements other than the catalyst portion and the substrate. Examples of elements other than the catalyst portion and the substrate include a protective material, a modifier, and a catalyst modifier.
＜電極の製造方法＞
本発明の電極の製造方法は、基体の表面の少なくとも一部に粒子径が５ｎｍ〜２００ｎｍの範囲内である銅含有粒子を配置する工程（以下、銅含有粒子配置工程ともいう）と、前記銅含有粒子が表面の少なくとも一部に配置された基体を熱処理して粒子径が５０ｎｍ〜５００ｎｍの範囲内である銅含有粒子を含む触媒部を形成する工程（以下、触媒部形成工程ともいう）と、を有する。本発明の電極の製造方法によれば、電気化学還元のエネルギー効率に優れる電極を製造することができる。また、蒸着等の比較的高価な装置を用いる方法によらずに簡便かつ経済的に大面積で電極を製造することができる。本発明の電極の製造方法は、必要に応じてその他の工程を含んでもよい。
<Method for producing electrode>
The method for producing an electrode of the present invention includes a step of arranging copper-containing particles having a particle diameter in the range of 5 nm to 200 nm on at least a part of the surface of the substrate (hereinafter also referred to as a copper-containing particle arranging step), and the copper A step of heat-treating a substrate on which at least a part of the contained particles is arranged to form a catalyst part containing copper-containing particles having a particle diameter in the range of 50 nm to 500 nm (hereinafter also referred to as a catalyst part forming step); Have. According to the method for producing an electrode of the present invention, an electrode excellent in energy efficiency of electrochemical reduction can be produced. In addition, an electrode can be manufactured in a large area simply and economically without using a relatively expensive apparatus such as vapor deposition. The electrode manufacturing method of the present invention may include other steps as necessary.
（銅含有粒子配置工程）
銅含有粒子配置工程では、基体の表面の少なくとも一部に粒子径が５ｎｍ〜２００ｎｍの範囲内である銅含有粒子を配置する。配置の方法は特に制限されない。例えば、銅含有粒子を含む組成物（以下、触媒形成組成物ともいう）を基体の表面の少なくとも一部に付与する方法、電解により銅含有粒子を基体の表面に析出させる方法、電解研磨により基体の表面に銅含有粒子を形成させる方法、イオン化傾向を利用して銅含有粒子を基体の表面に析出させる方法等を挙げることができる。
(Copper-containing particle placement process)
In the copper-containing particle arrangement step, copper-containing particles having a particle diameter in the range of 5 nm to 200 nm are arranged on at least a part of the surface of the substrate. The arrangement method is not particularly limited. For example, a method of applying a composition containing copper-containing particles (hereinafter also referred to as a catalyst-forming composition) to at least a part of the surface of the substrate, a method of depositing copper-containing particles on the surface of the substrate by electrolysis, and a substrate by electrolytic polishing Examples thereof include a method of forming copper-containing particles on the surface of the metal, a method of depositing copper-containing particles on the surface of the substrate by utilizing an ionization tendency, and the like.
触媒形成組成物を基体の表面の少なくとも一部に付与することによって銅含有粒子を配置する場合の付与の方法は特に制限されず、塗布法、印刷法、浸漬法、スプレー法等を目的に応じて適用することができる。適用する方法に応じて触媒形成組成物の粘度を調節してもよい。触媒形成組成物の状態は特に制限されず、用途に応じて選択できる。例えば、インク状分散液、ペースト等の状態を挙げることができる。 The method of application in the case of disposing the copper-containing particles by applying the catalyst-forming composition to at least a part of the surface of the substrate is not particularly limited, depending on the purpose such as coating method, printing method, dipping method, spray method, etc. Can be applied. Depending on the method applied, the viscosity of the catalyst-forming composition may be adjusted. The state of the catalyst-forming composition is not particularly limited and can be selected according to the application. For example, the state of ink-like dispersion liquid, paste, etc. can be mentioned.
触媒形成組成物は、粒子径が５ｎｍ〜２００ｎｍの範囲内である銅含有粒子の他に、必要に応じてその他の成分を含んでもよい。その他の成分としては有機溶剤、樹脂等の分散媒、分散剤、粘度調整剤、粒子の表面保護剤等を挙げることができる。触媒形成組成物中に含まれる銅含有粒子は、表面の少なくとも一部に有機物や無機物が付着していてもよい。 In addition to the copper-containing particles having a particle size in the range of 5 nm to 200 nm, the catalyst-forming composition may contain other components as necessary. Examples of other components include organic solvents, dispersion media such as resins, dispersants, viscosity modifiers, particle surface protective agents, and the like. The copper-containing particles contained in the catalyst-forming composition may have an organic substance or an inorganic substance attached to at least a part of the surface.
触媒形成組成物に含まれる銅含有粒子の粒子径は、電子顕微鏡、原子間力顕微鏡等によって測定することができる。銅含有粒子の粒子径が５０ｎｍ以下であると独立して溶剤に分散する傾向が高く、低粘度かつ流動性の高いインク状分散液を容易に調製することができるため、スピンコート法等で基体に塗布する場合に適する。銅含有粒子の粒子径が５０ｎｍを超えていると、溶剤への独立分散は難しいが、バーコート法、スクリーン印刷法、グラビヤオフセット印刷法等に使用される、銅含有粒子の濃度が高い（例えば、７０質量％以上）ペーストの作製に適する。また、銅含有粒子はその粒子径が小さいほど、より低温で粒子同士が融着する傾向が高い。従って、後述する電極の製造方法における熱処理での銅含有粒子同士の融着度合いの制御のし易さの観点からは、銅含有粒子の粒子径が５ｎｍ〜２００ｎｍの範囲内であることが好ましく、５ｎｍ〜１５０ｎｍの範囲内であることがより好ましく、５ｎｍ〜１００ｎｍの範囲内であることが更に好ましい。 The particle diameter of the copper-containing particles contained in the catalyst-forming composition can be measured with an electron microscope, an atomic force microscope, or the like. When the particle size of the copper-containing particles is 50 nm or less, the ink-like dispersion liquid having a high tendency to be dispersed in a solvent independently and having a low viscosity and a high fluidity can be easily prepared. Suitable when applied to. If the particle diameter of the copper-containing particles exceeds 50 nm, independent dispersion in a solvent is difficult, but the concentration of copper-containing particles used in bar coating methods, screen printing methods, gravure offset printing methods, etc. is high (for example, , 70% by mass or more) suitable for producing a paste. Moreover, the copper-containing particles have a higher tendency to fuse particles at a lower temperature as the particle size is smaller. Therefore, from the viewpoint of easy control of the degree of fusion between the copper-containing particles in the heat treatment in the electrode manufacturing method described later, the particle diameter of the copper-containing particles is preferably in the range of 5 nm to 200 nm. It is more preferably in the range of 5 nm to 150 nm, and still more preferably in the range of 5 nm to 100 nm.
触媒形成組成物に含まれる銅含有粒子の材質は特に制限されず、銅のみを含んでいても、銅以外の元素を含んでいてもよい。二酸化炭素を電気化学的に還元して有機物資源を生成する観点からは、銅含有粒子中の銅の含有率は５０物質量（モル）％以上であることが好ましく、７０物質量（モル）％以上であることがより好ましく、９０物質量（モル）％以上であることがさらに好ましい。銅含有粒子が銅以外の元素を含む場合、前記元素としてはＨ、Ｌｉ、Ｎａ、Ｋ、Ｃａ、Ｍｇ、Ｚｎ、Ｎｉ、Ｃｏ、Ｆｅ、Ｍｎ、Ｃｒ、Ａｇ、Ｓｎ、Ａｌ、Ｐｔ、Ａｕ、Ｓｉ、Ｐ、Ｓ、Ｃ、Ｎ、Ｏ、Ｃｌ、Ｂｒ、Ｉ等を挙げることができる。電極の製造コスト低減の観点からは、前記元素はＰｔ、Ａｕ等の高価な金属元素以外の元素であることが好ましい。触媒形成組成物に含まれる銅含有粒子は、材質が異なるコアとシェルとを有していてもよい。触媒形成組成物に含まれる銅含有粒子は１種のみであっても、材質が異なる２種以上の組み合わせであってもよい。 The material of the copper-containing particles contained in the catalyst-forming composition is not particularly limited, and may contain only copper or an element other than copper. From the viewpoint of electrochemically reducing carbon dioxide to produce an organic resource, the copper content in the copper-containing particles is preferably 50 mass (mol)% or more, and 70 mass (mol)%. More preferably, it is more preferably 90 substance amount (mol)% or more. When the copper-containing particles contain an element other than copper, the elements include H, Li, Na, K, Ca, Mg, Zn, Ni, Co, Fe, Mn, Cr, Ag, Sn, Al, Pt, Au, Si, P, S, C, N, O, Cl, Br, I, etc. can be mentioned. From the viewpoint of reducing the manufacturing cost of the electrode, the element is preferably an element other than an expensive metal element such as Pt or Au. The copper-containing particles contained in the catalyst-forming composition may have a core and a shell made of different materials. The copper-containing particles contained in the catalyst-forming composition may be only one type or a combination of two or more types having different materials.
触媒形成組成物に含まれる銅含有粒子は市販品であっても、製造したものであってもよい。銅含有粒子の製造方法は特に制限されず、通常の方法で作製することができる。例えば、特開２００８−５７０４１号公報、特開２００８−９５１９５号公報、特開２０１２−７２４１８号公報等に記載されている方法で製造することができる。 The copper-containing particles contained in the catalyst-forming composition may be commercially available or manufactured. The manufacturing method in particular of copper containing particle | grains is not restrict | limited, It can produce with a normal method. For example, it can be produced by the methods described in JP 2008-57041 A, JP 2008-95195 A, JP 2012-72418 A, and the like.
触媒形成組成物に含まれる銅含有粒子の製造方法の好ましい例としては、銅を含む化合物、還元性化合物及びアルキルアミンを含む組成物を加熱する工程を含む方法を挙げることができる。この方法によれば、アルキルアミン等に由来する被覆を有することで大気中での長期保存にも耐えうる銅含有粒子を製造することができる。 Preferable examples of the method for producing copper-containing particles contained in the catalyst-forming composition include a method including a step of heating a composition containing copper, a reducing compound and an alkylamine. According to this method, it is possible to produce copper-containing particles that can withstand long-term storage in the air by having a coating derived from alkylamine or the like.
上記の方法において、銅を含む化合物としては酢酸銅、シュウ酸銅、プロピオン酸銅、酪酸銅、吉草酸銅、カプロン酸銅、エナント酸銅、ノナン酸銅等のカルボン酸銅を挙げることができる。還元性化合物としてはヒドラジン、ヒドロキシルアミン、これらの誘導体等を挙げることができる。アルキルアミンとしては、分子内に一つのアミノ基を有するアルキルアミン、分子内に二つのアミノ基を有するアルキルアミン等を挙げることができる。これらの化合物は１種を単独で用いても、２種以上を組み合わせて用いてもよい。 In the above method, examples of the copper-containing compound include copper carboxylates such as copper acetate, copper oxalate, copper propionate, copper butyrate, copper valerate, copper caproate, copper enanthate, and copper nonanoate. . Examples of the reducing compound include hydrazine, hydroxylamine, and derivatives thereof. Examples of the alkylamine include an alkylamine having one amino group in the molecule, an alkylamine having two amino groups in the molecule, and the like. These compounds may be used alone or in combination of two or more.
上記の方法において、銅を含む化合物として炭素原子数が９以下であるカルボン酸銅を用いると加熱工程をより低温で実施することができる。さらに、得られる銅含有粒子の粒子径が小さくなり、粒子同士の融着が生じる温度が低くなる傾向にある。従って、触媒部を形成する際の熱処理をより低温で実施することが可能となる。 In the above method, when copper carboxylate having 9 or less carbon atoms is used as the compound containing copper, the heating step can be performed at a lower temperature. Further, the particle diameter of the obtained copper-containing particles tends to be small, and the temperature at which the particles are fused tends to be low. Accordingly, the heat treatment for forming the catalyst portion can be performed at a lower temperature.
（触媒部形成工程）
触媒部形成工程では、粒子径が５ｎｍ〜２００ｎｍの範囲内である銅含有粒子が表面の少なくとも一部に配置された基体を熱処理して粒子径が５０ｎｍ〜５００ｎｍの範囲内である銅含有粒子を含む触媒部を形成する。熱処理の条件は、所望の構造を有する触媒部が形成されるように選択できる。熱処理の際の温度、時間、圧力、雰囲気等の条件を制御することで、銅含有粒子の融着の度合いを制御することができ、所望の構造を有する（例えば、所望の粒子径の銅含有粒子を含む）触媒部を形成することができる。熱処理は、銅の酸化を抑制できる雰囲気中で行うことが好ましい。例えば、水素と窒素の混合気体、アルゴン等の雰囲気中で行うことが好ましい。
(Catalyst part formation process)
In the catalyst portion forming step, a copper-containing particle having a particle diameter in the range of 50 nm to 500 nm is obtained by heat-treating a substrate on which copper-containing particles having a particle diameter in the range of 5 nm to 200 nm are disposed on at least a part of the surface. A catalyst part containing is formed. The heat treatment conditions can be selected so that a catalyst portion having a desired structure is formed. By controlling the conditions such as temperature, time, pressure, atmosphere, etc. during the heat treatment, the degree of fusion of the copper-containing particles can be controlled and has a desired structure (for example, containing copper having a desired particle diameter) A catalyst part (including particles) can be formed. The heat treatment is preferably performed in an atmosphere capable of suppressing copper oxidation. For example, it is preferably performed in an atmosphere of a mixed gas of hydrogen and nitrogen, argon, or the like.
熱処理の温度は、例えば１００℃〜５００℃の範囲から選択することができ、１００℃〜３００℃の範囲から選択することができ、１００℃〜２００℃の範囲から選択することができる。熱処理の温度は熱処理工程を通じて一定であっても、異なっていてもよい。 The temperature of heat processing can be selected, for example from the range of 100 to 500 degreeC, can be selected from the range of 100 to 300 degreeC, and can be selected from the range of 100 to 200 degreeC. The temperature of the heat treatment may be constant or different throughout the heat treatment process.
熱処理の時間は、例えば５分〜１２０分の範囲から選択することができ、５分〜６０分の範囲から選択することができ、５分〜３０分の範囲から選択することができる。熱処理の時間は、熱処理の温度に達している間の時間を意味する。 The heat treatment time can be selected, for example, from a range of 5 minutes to 120 minutes, can be selected from a range of 5 minutes to 60 minutes, and can be selected from a range of 5 minutes to 30 minutes. The heat treatment time means the time during which the heat treatment temperature is reached.
＜電気化学還元方法＞
本発明の電気化学還元方法は、本発明の電極を用いて水及び二酸化炭素からなる群より選択される少なくとも一方を分解する工程を有する。本発明の方法によれば、平滑な銅板を電極として用いる場合よりも低い触媒過電圧で水又は二酸化炭素の電気化学還元を行うことができ、エネルギー効率に優れている。また、銅を含む電極を用いることにより、他の金属を用いる場合よりも多種類の物質を生成することができる。生成可能な物質としては、水素の他に、一酸化炭素、メタン、ホルムアルデヒド、ギ酸、メタノール等の炭素原子数が１個である化合物、エタン、エチレン、エタノール、アセトアルデヒド、酢酸、エチレングリコール、グリコールアルデヒド、グリコール酸、グリオキサール、シュウ酸等の炭素原子数が２個である化合物、アセトン、アリルアルコール、ヒドロキシアセトン、プロパノール、プロピオンアルデヒド等の炭素原子数が３個である化合物などを挙げることができる。もっとも、本発明の電気化学還元方法により得られる物質はこれらに制限されない。
<Electrochemical reduction method>
The electrochemical reduction method of the present invention includes a step of decomposing at least one selected from the group consisting of water and carbon dioxide using the electrode of the present invention. According to the method of the present invention, the electrochemical reduction of water or carbon dioxide can be performed with a lower catalyst overvoltage than when a smooth copper plate is used as an electrode, and the energy efficiency is excellent. In addition, by using an electrode containing copper, more types of substances can be generated than when other metals are used. Substances that can be generated include, in addition to hydrogen, compounds having one carbon atom such as carbon monoxide, methane, formaldehyde, formic acid, methanol, ethane, ethylene, ethanol, acetaldehyde, acetic acid, ethylene glycol, glycol aldehyde And compounds having 2 carbon atoms such as glycolic acid, glyoxal and oxalic acid, and compounds having 3 carbon atoms such as acetone, allyl alcohol, hydroxyacetone, propanol and propionaldehyde. However, substances obtained by the electrochemical reduction method of the present invention are not limited thereto.
＜電気化学還元生成物の製造方法＞
本発明の電気化学還元生成物の製造方法は、本発明の電極を用いて水及び二酸化炭素からなる群より選択される少なくとも一方を分解する工程を有する。本発明の方法によれば、平滑な銅板を電極として用いる場合よりも低い触媒過電圧で水又は二酸化炭素の電気化学還元生成物を製造することができ、エネルギー効率に優れている。また、銅を含む電極を用いることにより、他の金属を用いる場合よりも多種類の電気化学還元生成物を製造することができる。製造可能な電気化学還元生成物としては水素の他に、一酸化炭素、メタン、ホルムアルデヒド、ギ酸、メタノール等の炭素原子数が１個である化合物、エタン、エチレン、エタノール、アセトアルデヒド、酢酸、エチレングリコール、グリコールアルデヒド、グリコール酸、グリオキサール、シュウ酸等の炭素原子数が２個である化合物、アセトン、アリルアルコール、ヒドロキシアセトン、プロパノール、プロピオンアルデヒド等の炭素原子数が３個である化合物などを挙げることができる。もっとも、本発明の電気化学還元生成物の製造方法により得られる物質はこれらに制限されない。
<Method for producing electrochemical reduction product>
The method for producing an electrochemical reduction product of the present invention includes a step of decomposing at least one selected from the group consisting of water and carbon dioxide using the electrode of the present invention. According to the method of the present invention, an electrochemical reduction product of water or carbon dioxide can be produced with a lower catalyst overvoltage than when a smooth copper plate is used as an electrode, which is excellent in energy efficiency. In addition, by using an electrode containing copper, more types of electrochemical reduction products can be produced than when other metals are used. Electrochemical reduction products that can be produced include hydrogen, compounds with one carbon atom such as carbon monoxide, methane, formaldehyde, formic acid, methanol, ethane, ethylene, ethanol, acetaldehyde, acetic acid, ethylene glycol And compounds having 2 carbon atoms such as glycol aldehyde, glycolic acid, glyoxal and oxalic acid, and compounds having 3 carbon atoms such as acetone, allyl alcohol, hydroxyacetone, propanol and propionaldehyde. Can do. But the substance obtained by the manufacturing method of the electrochemical reduction product of this invention is not restrict | limited to these.
本発明の電気化学還元方法及び電気化学還元生成物の製造方法の条件は特に制限されず、通常の条件を適用することができる。本発明の電気化学還元方法及び電気化学還元生成物の製造方法によれば、生産量が実質的に無限である水又は二酸化炭素を原料として産業上有用な物質を製造することができる。さらに、夜間に発生する余剰電気等の利用されない電気エネルギーの有効活用、大気中の二酸化炭素の削減等の観点からも有益である。また、本発明での電極を用いれば、水又は二酸化炭素の電気化学還元において消費される電力を、ＴｉＯ２、ＳｒＴｉＯ３、ＺｒＯ２、ＺｎＯ、ＳｎＯ２、ＷＯ３、ＫＴａＯ３、Ｆｅ２Ｏ３、ＧａＮ、ＧａＰ、ＣｕＯ、Ｃｕ２Ｏ、ＣｄＳ、ＳｉＣ、ｇ−Ｃ３Ｎ４等の半導体からなる光触媒電極に太陽光等の光を照射することで得た電力を直接供給することもできる。 The conditions of the electrochemical reduction method and the method for producing the electrochemical reduction product of the present invention are not particularly limited, and normal conditions can be applied. According to the electrochemical reduction method and the method for producing an electrochemical reduction product of the present invention, industrially useful substances can be produced using water or carbon dioxide whose production amount is substantially infinite as a raw material. Furthermore, it is useful from the viewpoints of effective utilization of unused electric energy such as surplus electricity generated at night and reduction of carbon dioxide in the atmosphere. Moreover, if the electrode in this invention is used, the electric power consumed in the electrochemical reduction of water or carbon dioxide will be converted into TiO 2 , SrTiO 3 , ZrO 2 , ZnO, SnO 2 , WO 3 , KTaO 3 , Fe 2 O 3. , GaN, GaP, CuO, Cu 2 O, CdS, SiC, g—C 3 N 4, etc., can be directly supplied with electric power obtained by irradiating light such as sunlight onto a photocatalytic electrode made of a semiconductor.
以下、本発明を実施例に基づきより詳細に説明するが、本発明はこれらの実施例に何ら制限されるものではない。 EXAMPLES Hereinafter, although this invention is demonstrated in detail based on an Example, this invention is not restrict | limited to these Examples at all.
＜合成例１：銅粒子の合成＞
ノナン酸（関東化学株式会社、純度９０％以上）１．００ｇ（６．３５ｍｍｏｌ）及び酢酸（関東化学株式会社、特級）０．３８１ｇ（６．３５ｍｍｏｌ）を１−プロパノール（関東化学株式会社、特級）０．８ｍＬと混合した溶液を、水酸化銅（ＩＩ）（和光純薬工業株式会社、一級）０．６２０ｇ（６．３５ｍｍｏｌ）に加え、１１０℃で１０分間加熱撹拌した。得られた青色溶液を水冷しながら、ヘキシルアミン（東京化成工業株式会社、特級）２．５７ｇ（２５．４ｍｍｏｌ）及びヒドラジン一水和物（関東化学株式会社、特級）０．６３１ｍＬ（１２．７ｍｍｏｌ）を加え、１１０℃で６分間加熱撹拌した。その際、窒素の発生を伴いながら、青色溶液が赤褐色の懸濁液に変化した。加熱撹拌後、常温まで放冷し、ヘキサン（関東化学株式会社、特級）５ｍＬを加えてさらに撹拌した。その後、遠心分離により銅光沢を有する銅粒子の固体物（０．４００ｇ、ヘキシルアミン、ノナン酸等に由来する保護分子の重量を差し引いた銅基準の収率は物質量比で９８．８％）を得た。
<Synthesis Example 1: Synthesis of copper particles>
Nonanoic acid (Kanto Chemical Co., Inc., purity 90% or more) 1.00 g (6.35 mmol) and acetic acid (Kanto Chemical Co., special grade) 0.381 g (6.35 mmol) were added to 1-propanol (Kanto Chemical Co., Ltd., special grade). ) The solution mixed with 0.8 mL was added to 0.620 g (6.35 mmol) of copper hydroxide (II) (Wako Pure Chemical Industries, Ltd., first grade), and heated and stirred at 110 ° C. for 10 minutes. While cooling the obtained blue solution with water, hexylamine (Tokyo Chemical Industry Co., Ltd., special grade) 2.57 g (25.4 mmol) and hydrazine monohydrate (Kanto Chemical Co., Ltd., special grade) 0.631 mL (12.7 mmol) ) And heated and stirred at 110 ° C. for 6 minutes. At that time, the blue solution changed to a reddish brown suspension with generation of nitrogen. After heating and stirring, the mixture was allowed to cool to room temperature, and 5 mL of hexane (Kanto Chemical Co., Ltd., special grade) was added and further stirred. Thereafter, a solid product of copper particles having a copper luster by centrifugation (0.400 g, the yield based on copper after subtracting the weight of protective molecules derived from hexylamine, nonanoic acid, etc. is 98.8% by mass) Got.
（銅粒子の解析）
得られた銅光沢を有する固体物を粉末Ｘ線回折装置（株式会社リガク、ＭｉｎｉＦｌｅｘ ＩＩ）により解析を行ったところ、その粉末Ｘ線回折パターン（図１）から金属銅が生成していることが確認された。また、得られた銅粒子をカーボン製水平試料載台に付着させて電界放出型走査電子顕微鏡像（日本電子株式会社、ＪＥＭ−７６００Ｆ）で観察した。粒子径が１０ｎｍ〜１００ｎｍの範囲内である銅粒子が観察された（図２）。
(Analysis of copper particles)
When the obtained solid object having copper luster was analyzed by a powder X-ray diffractometer (Rigaku Corporation, MiniFlex II), it was found that metallic copper was generated from the powder X-ray diffraction pattern (FIG. 1). confirmed. Moreover, the obtained copper particle was made to adhere to the horizontal sample mounting stand made from carbon, and it observed with the field emission type | mold scanning electron microscope image (JEOL Co., Ltd., JEM-7600F). Copper particles having a particle diameter in the range of 10 nm to 100 nm were observed (FIG. 2).
（銅粒子分散液の調製）
得られた銅粒子をトルエン（関東化学株式会社、特級）に分散させ、５０質量％の分散液を調製した。
(Preparation of copper particle dispersion)
The obtained copper particles were dispersed in toluene (Kanto Chemical Co., Ltd., special grade) to prepare a 50 mass% dispersion.
（銅板上への銅粒子分散液の塗布）
２．０ｃｍ×２．５ｃｍ（厚み０．３ｍｍ）の銅板（株式会社ニラコ、純度９９．９６％）の片面に、バーコーターを用いて銅粒子のトルエン分散液を塗布し、トルエンが揮発するまで放置した。銅板上に存在する銅粒子を、電界放出型走査電子顕微鏡で観察した。粒子径が１０ｎｍ〜１００ｎｍの範囲内である銅粒子が積層及び凝集している様子が観察された（図３）。
(Application of copper particle dispersion on copper plate)
Apply a toluene dispersion of copper particles to one side of a 2.0 cm x 2.5 cm (thickness 0.3 mm) copper plate (Niraco Corporation, purity 99.96%) using a bar coater until the toluene volatilizes. I left it alone. The copper particles present on the copper plate were observed with a field emission scanning electron microscope. It was observed that copper particles having a particle diameter in the range of 10 nm to 100 nm were laminated and aggregated (FIG. 3).
＜合成例２：コアシェル型銅銀粒子の合成＞
（銀コア粒子の合成）
Ｎ，Ｎ−ジメチル−１，３−ジアミノプロパン（東京化成工業株式会社、特級）０．６２０ｇ（６．０７ｍｍｏｌ）、ｎ−ヘキシルアミン０．４２０ｇ（４．１５ｍｍｏｌ）、ｎ−ドデシルアミン（関東化学株式会社、特級）０．１２０ｇ（０．６４７ｍｍｏｌ）及びオレイン酸（東京化成工業株式会社、＞８５．０％）０．１００ｇ（０．３５４ｍｍｏｌ）を混合して溶液を得た。この混合溶液にシュウ酸銀（硝酸銀（関東化学株式会社、一級）とシュウ酸・二水和物（関東化学株式会社、特級）とから合成したもの）１．００ｇ（３．２９ｍｍｏｌ）を加え、室温で１時間撹拌した。撹拌している間に、シュウ酸イオン・アルキルアミン・アルキルジアミン・銀錯化合物が生成し、粘性のある固体物へと変化した。これを１１０℃で１０分間加熱撹拌すると、二酸化炭素の発泡を伴う反応が完結し、青色光沢を呈する懸濁液へと変化した。これにメタノール（関東化学株式会社、一級）５ｍＬを加え、遠心分離により得られた沈殿物を分離した。さらにもう一度、メタノール５ｍＬを加え、沈殿物を撹拌し、遠心分離により銀コア粒子の固形物（０．７４３ｇ、保護分子等の重量を差し引いた銀基準の収率は物質量比で９４．０％）を得た。
<Synthesis Example 2: Synthesis of core-shell type copper silver particles>
(Synthesis of silver core particles)
N, N-dimethyl-1,3-diaminopropane (Tokyo Chemical Industry Co., Ltd., special grade) 0.620 g (6.07 mmol), n-hexylamine 0.420 g (4.15 mmol), n-dodecylamine (Kanto Chemical) 0.120 g (0.647 mmol), special grade) and 0.100 g (0.354 mmol) of oleic acid (Tokyo Chemical Industry Co., Ltd.,> 85.0%) were mixed to obtain a solution. To this mixed solution is added 1.00 g (3.29 mmol) of silver oxalate (synthesized from silver nitrate (Kanto Chemical Co., Ltd., first grade) and oxalic acid dihydrate (Kanto Chemical Co., Ltd., special grade)). Stir at room temperature for 1 hour. During the stirring, oxalate ions, alkylamines, alkyldiamines, and silver complex compounds were formed and changed to viscous solids. When this was heated and stirred at 110 ° C. for 10 minutes, the reaction involving the foaming of carbon dioxide was completed, and the suspension changed to a blue glossy suspension. To this was added 5 mL of methanol (Kanto Chemical Co., Ltd., first grade), and the precipitate obtained by centrifugation was separated. Further, 5 mL of methanol was added again, the precipitate was stirred, and the yield based on the silver based on the weight of the solid matter of silver core particles (0.743 g, protective molecules, etc. was removed by centrifugation, and the mass ratio was 94.0%. )
（コアシェル型銅銀粒子の合成）
得られた銀コア粒子０．７７０ｇにｎ−オクタン（関東化学株式会社、特級）とｎ−ブタノール（関東化学株式会社、特級）の混合溶媒（体積比４：１ｖ／ｖ）５．０ｍＬ、酢酸銅・一水和物（和光純薬工業株式会社、特級）１．３１ｇ（６．５６ｍｍｏｌ）、オレイルアミン（アクロスオルガニクス株式会社、８０％〜９０％）５．３０ｇ（１９．８ｍｍｏｌ）及びオレイン酸０．１００ｇ（０．３５４ｍｍｏｌ）を加え、８０℃で３０分間加熱撹拌した。ここに、２−ヒドラジノエタノール（東京化成株式会社、特級）６７１μＬ（９．９０ｍｍｏｌ）を滴下し、さらに８０℃で１時間加熱撹拌した。室温まで放冷した反応混合物に、ヘキサン２ｍＬを加え、遠心分離により得られた沈殿物を分離した。さらにもう一度、ヘキサン２ｍＬを加え、沈殿物を攪拌し、遠心分離によりコアシェル型銅銀粒子を得た（１．１６ｇ、オレイルアミン等に由来する保護分子の重量を差し引いた銅基準の収率は物質量比で９６．２％）。得られたコアシェル型銅銀粒子の銅と銀の組成比（物質量（モル）比）は１：１である。
(Synthesis of core-shell type copper silver particles)
To 0.770 g of the obtained silver core particles, 5.0 mL of a mixed solvent (volume ratio 4: 1 v / v) of n-octane (Kanto Chemical Co., Ltd., special grade) and n-butanol (Kanto Chemical Co., Ltd.), acetic acid Copper monohydrate (Wako Pure Chemical Industries, Ltd., special grade) 1.31 g (6.56 mmol), oleylamine (Across Organics Co., Ltd., 80% to 90%) 5.30 g (19.8 mmol) and oleic acid 0.100 g (0.354 mmol) was added, and the mixture was heated and stirred at 80 ° C. for 30 minutes. To this was added dropwise 671 μL (9.90 mmol) of 2-hydrazinoethanol (Tokyo Chemical Industry Co., Ltd., special grade), and the mixture was further heated and stirred at 80 ° C. for 1 hour. To the reaction mixture allowed to cool to room temperature, 2 mL of hexane was added, and the precipitate obtained by centrifugation was separated. Furthermore, 2 mL of hexane was added again, the precipitate was stirred, and core-shell type copper silver particles were obtained by centrifugation (1.16 g, the yield based on copper minus the weight of protective molecules derived from oleylamine etc. 96.2% in ratio). The composition ratio (substance (molar) ratio) of copper and silver in the obtained core-shell type copper silver particles is 1: 1.
（コアシェル型銅銀粒子分散液の調製）
得られたコアシェル型銅銀粒子をトルエン（関東化学株式会社、特級）に分散させ、４０質量％の分散液を調製した。
(Preparation of core-shell type copper silver particle dispersion)
The obtained core-shell type copper silver particles were dispersed in toluene (Kanto Chemical Co., Ltd., special grade) to prepare a 40 mass% dispersion.
（コアシェル型銅銀粒子の解析）
得られたコアシェル型銅銀粒子のトルエン分散液を電子顕微鏡用カーボン支持膜（イーエムジャパン株式会社、モリブデン２００メッシュ）に塗布し、コアシェル型銅銀粒子の電界放出型透過電子顕微鏡像（日本電子株式会社、ＪＥＭ−２１００Ｆ）で観察した。その結果、粒子の表面と中心部分でコントラストの異なる、コアシェル型の構造が確認された（図４Ａ）。また、粒子径は１０ｎｍから３０ｎｍであった。エネルギー分散型蛍光Ｘ線測定分析（ＥＤＳ）により、明るいコントラストのコアには銀が多く含まれることが確認され（図４Ｂ）、暗いコントラストのシェルには銅が多く含まれることが確認された（図４Ｃ）。
(Analysis of core-shell type copper silver particles)
The obtained core shell type copper silver particle toluene dispersion was applied to a carbon support film for electron microscope (EM Japan Co., Ltd., molybdenum 200 mesh), and field emission type transmission electron microscope image of the core shell type copper silver particle (JEOL shares) Observed with company JEM-2100F). As a result, a core-shell type structure with different contrast between the particle surface and the central portion was confirmed (FIG. 4A). The particle diameter was 10 nm to 30 nm. Energy dispersive X-ray fluorescence analysis (EDS) confirmed that the bright contrast core was rich in silver (FIG. 4B) and the dark contrast shell was rich in copper ( FIG. 4C).
（銅板上へのコアシェル型銅銀粒子分散液の塗布）
２．０ｃｍ×２．５ｃｍ（厚み０．３ｍｍ）の銅板（株式会社ニラコ、純度９９．９６％）の片面に、スピンコーター（株式会社共和理研、Ｋ−３５９Ｓ１）を用いてコアシェル型銅銀粒子のトルエン分散液を塗布し、トルエンが揮発するまで放置した。
(Coating of core-shell type copper silver particle dispersion on copper plate)
Core-shell type copper silver particles using a spin coater (Kyowa Riken Co., Ltd., K-359S1) on one side of a 2.0 cm × 2.5 cm (thickness 0.3 mm) copper plate (Nilaco Corporation, purity 99.96%) The toluene dispersion was applied and allowed to stand until the toluene was volatilized.
＜実施例１＞
合成例１で得た銅粒子のトルエン分散液を塗布し、乾燥した後の銅板を赤外炉（アルバック理工株式会社、ＭＩＬＡ−５０００）で熱処理した。熱処理は、２２０℃で４５分間行った。銅粒子の酸化を抑制するため、炉内に水素発生機（ＹＭＣテクノス株式会社、ＹＨ−５００）から発生した水素を体積換算で４．８％となるように窒素と混合した気流を導入した。
<Example 1>
The copper dispersion obtained by applying the toluene dispersion of copper particles obtained in Synthesis Example 1 was dried and heat-treated in an infrared furnace (ULVAC RIKO, MILA-5000). The heat treatment was performed at 220 ° C. for 45 minutes. In order to suppress the oxidation of copper particles, an air stream mixed with nitrogen was introduced into the furnace so that hydrogen generated from a hydrogen generator (YMC Technos Co., Ltd., YH-500) was 4.8% in terms of volume.
＜実施例２＞
合成例１で得た銅粒子のトルエン分散液を塗布し、乾燥した後の銅板を熱処理した。熱処理は、加熱温度を３００℃とした以外は実施例１と同じ条件で行った。
<Example 2>
The copper plate obtained by the synthesis example 1 was coated with the toluene dispersion and dried, and then the copper plate was heat-treated. The heat treatment was performed under the same conditions as in Example 1 except that the heating temperature was 300 ° C.
＜実施例３＞
合成例１で得た銅粒子のトルエン分散液を塗布し、乾燥した後の銅板を熱処理した。熱処理は、加熱温度を４００℃とした以外は実施例１と同じ条件で行った。
<Example 3>
The copper plate obtained by the synthesis example 1 was coated with the toluene dispersion and dried, and then the copper plate was heat-treated. The heat treatment was performed under the same conditions as in Example 1 except that the heating temperature was 400 ° C.
＜実施例４＞
合成例１で得た銅粒子のトルエン分散液を塗布し、乾燥した後の銅板を熱処理した。熱処理は、銅粒子の酸化を抑制するための雰囲気をアルゴン気流とした以外は実施例１と同じ条件で行った。
<Example 4>
The copper plate obtained by the synthesis example 1 was coated with the toluene dispersion and dried, and then the copper plate was heat-treated. The heat treatment was performed under the same conditions as in Example 1 except that the atmosphere for suppressing the oxidation of the copper particles was an argon stream.
＜実施例５＞
合成例１で得た銅粒子のトルエン分散液を塗布し、乾燥した後の銅板を熱処理した。熱処理は、加熱温度を３００℃とした以外は実施例４と同じ条件で行った。
<Example 5>
The copper plate obtained by the synthesis example 1 was coated with the toluene dispersion and dried, and then the copper plate was heat-treated. The heat treatment was performed under the same conditions as in Example 4 except that the heating temperature was 300 ° C.
＜実施例６＞
合成例２で得たコアシェル型銅銀粒子のトルエン分散液を塗布し、乾燥した後の銅板を赤外炉（アルバック理工株式会社、ＭＩＬＡ−５０００）で熱処理した。熱処理は、２２０℃で４５分間行った。銅シェル層の酸化を抑制するため、炉内に水素発生機（ＹＭＣテクノス株式会社、ＹＨ−５００）から発生した水素を体積換算で４．８％となるように窒素と混合した気流を導入した。
<Example 6>
The copper dispersion obtained by applying the toluene dispersion of the core-shell type copper silver particles obtained in Synthesis Example 2 and drying was heat-treated in an infrared furnace (ULVAC RIKO, Inc., MILA-5000). The heat treatment was performed at 220 ° C. for 45 minutes. In order to suppress the oxidation of the copper shell layer, an air stream mixed with nitrogen so that hydrogen generated from a hydrogen generator (YMC Technos Co., Ltd., YH-500) was 4.8% in terms of volume was introduced into the furnace. .
＜比較例１＞
合成例１で得た銅粒子のトルエン分散液を塗布し、乾燥した後の銅板を熱処理した。熱処理は、加熱温度を４００℃とした以外は実施例４と同じ条件で行った。
<Comparative Example 1>
The copper plate obtained by the synthesis example 1 was coated with the toluene dispersion and dried, and then the copper plate was heat-treated. The heat treatment was performed under the same conditions as in Example 4 except that the heating temperature was 400 ° C.
＜比較例２＞
２．０ｃｍ×２．５ｃｍ（厚み０．３ｍｍ）の銅板（株式会社ニラコ、純度９９．９６％）の片面に、真空蒸着装置（株式会社アルバック、ＶＰＣ−２６０Ｆ）を用いて銅の蒸着膜を形成した。
<Comparative Example 2>
On one side of a 2.0 cm × 2.5 cm (thickness 0.3 mm) copper plate (Niraco Co., Ltd., purity 99.96%), a copper deposition film was formed using a vacuum deposition apparatus (ULVAC, Inc., VPC-260F). Formed.
（銅板表面の観察）
実施例１〜６及び比較例１、２で得た銅板の表面を電界放出型走査電子顕微鏡で観察した。銅粒子等のトルエン分散液の塗布及び熱処理を行っていない銅板の表面（図５）と比較すると、実施例１〜６及び比較例１で得た銅板の表面には銅粒子又は銅含有粒子が部分的に他の粒子と結合した構造が確認された。
(Observation of copper plate surface)
The surface of the copper plate obtained in Examples 1 to 6 and Comparative Examples 1 and 2 was observed with a field emission scanning electron microscope. When compared with the surface of the copper plate not subjected to the application of the toluene dispersion liquid such as copper particles and the heat treatment (FIG. 5), copper particles or copper-containing particles are present on the surfaces of the copper plates obtained in Examples 1 to 6 and Comparative Example 1. A structure partially bound to other particles was confirmed.
実施例１で得た銅板では、粒子径が５０ｎｍ〜２５０ｎｍの範囲内である銅粒子が観察された（図６）。 In the copper plate obtained in Example 1, copper particles having a particle diameter in the range of 50 nm to 250 nm were observed (FIG. 6).
熱処理の温度が実施例１よりも高い実施例２、３で得た銅板では、実施例１よりも銅粒子の融着が進んでおり、粒子径が１００ｎｍ〜３００ｎｍの範囲内である銅粒子が観察された（図７、８）。 In the copper plates obtained in Examples 2 and 3 in which the temperature of the heat treatment is higher than that of Example 1, the fusion of the copper particles has proceeded more than in Example 1, and the copper particles having a particle diameter in the range of 100 nm to 300 nm are obtained. Observed (FIGS. 7 and 8).
熱処理の温度が実施例１と同じであるがアルゴン気流下で熱処理を行った実施例４で得た銅板では、水素及び窒素の混合気体雰囲気下で熱処理を行った実施例１よりも銅粒子の融着が進んでおり、粒子径が１００ｎｍ〜２５０ｎｍの範囲内である銅粒子が観察された（図９）。 In the copper plate obtained in Example 4 in which the heat treatment temperature was the same as that in Example 1 but heat treatment was performed under an argon stream, the copper particles contained more than in Example 1 in which heat treatment was performed in a mixed gas atmosphere of hydrogen and nitrogen. The fusion progressed, and copper particles having a particle diameter in the range of 100 nm to 250 nm were observed (FIG. 9).
熱処理の温度が実施例４よりも高い実施例５で得た銅板では、実施例４よりも銅粒子の融着が進んでおり、粒子径が１００ｎｍ〜３００ｎｍの範囲内である銅粒子が観察された（図１０）。 In the copper plate obtained in Example 5 in which the temperature of the heat treatment is higher than that in Example 4, the fusion of the copper particles proceeds more than in Example 4, and copper particles having a particle diameter in the range of 100 nm to 300 nm are observed. (FIG. 10).
実施例６で得た銅板では、粒子径が５０ｎｍ〜１００ｎｍである銅含有粒子が観察された（図１１）。 In the copper plate obtained in Example 6, copper-containing particles having a particle diameter of 50 nm to 100 nm were observed (FIG. 11).
熱処理の温度が実施例５よりも高い比較例１で得た銅板では、銅粒子の融着が過度に進んでおり、粒子径が５０ｎｍ〜５００ｎｍの範囲内である銅粒子が観察されなかった（図１２）。 In the copper plate obtained in Comparative Example 1 in which the temperature of the heat treatment was higher than that in Example 5, the fusion of the copper particles proceeded excessively, and copper particles having a particle diameter in the range of 50 nm to 500 nm were not observed ( FIG. 12).
比較例２で得た銅板では、粒子径が２０ｎｍ〜４０ｎｍの範囲内である銅粒子が一様に銅板上に存在している様子が観察された（図１３）。 In the copper plate obtained in Comparative Example 2, it was observed that copper particles having a particle diameter in the range of 20 nm to 40 nm were uniformly present on the copper plate (FIG. 13).
（電気化学還元における触媒触媒過電圧の測定）
実施例１〜６及び比較例１、２で得た銅板を作用電極として触媒過電圧の測定を行った。測定は、電解セルとしてＥＣフロンティア製のＨ型セル、参照電極としてＡｇ／ＡｇＣｌ電極、対極として白金メッシュ電極、隔膜としてガラスフィルター、電解液として二酸化炭素をバブリングし飽和させた０．５Ｍの ＫＨＣＯ３水溶液（ｐＨ ７．２）をそれぞれ使用した。ポテンショスタットとして北斗電工製のＨＳＶ−１１０を用い、作用電極に印加する電位幅を−０．３Ｖ〜−２．０Ｖ（対 Ａｇ／ＡｇＣｌ電極）、掃引速度は１０ｍＶ／秒で制御し、流れる電流値を調べた。測定温度は２０℃〜２３℃とした。評価を１ｃｍ２の面積で実施するため、カプトンテープと瞬間接着剤を用いて作用電極に対してマスキングを行った。
(Measurement of catalyst overvoltage in electrochemical reduction)
The catalyst overvoltage was measured using the copper plates obtained in Examples 1 to 6 and Comparative Examples 1 and 2 as the working electrode. The measurement was performed using an EC frontier H-type cell as an electrolysis cell, an Ag / AgCl electrode as a reference electrode, a platinum mesh electrode as a counter electrode, a glass filter as a diaphragm, and 0.5 M KHCO 3 saturated by bubbling carbon dioxide as an electrolyte. An aqueous solution (pH 7.2) was used. Using a HSV-110 manufactured by Hokuto Denko as a potentiostat, the potential width applied to the working electrode is -0.3 V to -2.0 V (vs. Ag / AgCl electrode), the sweep speed is controlled at 10 mV / sec, and the flowing current The value was examined. The measurement temperature was 20 ° C to 23 ° C. In order to carry out the evaluation with an area of 1 cm 2 , masking was performed on the working electrode using a Kapton tape and an instantaneous adhesive.
比較対象として、銅粒子分散液の塗布及び熱処理を行っていない銅板（株式会社ニラコ、純度９９．９６％、厚み０．３ｍｍ）及び白金板（ニラコ、 純度９９.９８％、厚み０．１ｍｍ）を作用電極として用いた以外は上記と同じ条件で触媒過電圧の測定を行った。 For comparison, a copper plate (Nilaco Co., Ltd., purity 99.96%, thickness 0.3 mm) and a platinum plate (Nilaco, purity 99.98%, thickness 0.1 mm) not subjected to the application of the copper particle dispersion and heat treatment The catalyst overvoltage was measured under the same conditions as above except that was used as the working electrode.
（触媒過電圧の評価）
実施例１で得た銅板と、比較対象としての銅板及び白金板を作用電極として用いた場合の触媒過電圧の測定結果を図１４に示す。いずれの場合も、−０．３Ｖ〜−２．０Ｖの電位幅で電圧を印加すると、負の印加電圧が小さい場合は、二酸化炭素又は水の電気化学還元に伴う電流は流れないが、ある一定の負電位を超えると、急激に電流（触媒電流）が流れることが分かる。この急激な電流が流れ始める開始電圧を比較すると、例えば、比較対象の銅板に比べて、実施例１で得た銅板を作用電極とした場合の開始電圧（絶対値）が小さいことが分かる。
(Evaluation of catalyst overvoltage)
FIG. 14 shows the measurement results of the catalyst overvoltage when the copper plate obtained in Example 1 and the copper plate and the platinum plate as comparison objects are used as the working electrode. In either case, when a voltage is applied with a potential range of −0.3 V to −2.0 V, if the negative applied voltage is small, the current accompanying the electrochemical reduction of carbon dioxide or water does not flow, but a certain constant It can be seen that the current (catalyst current) suddenly flows when the negative potential is exceeded. Comparing the starting voltage at which this sudden current starts to flow, for example, it can be seen that the starting voltage (absolute value) is smaller when the copper plate obtained in Example 1 is used as the working electrode than the copper plate to be compared.
実施例１〜６及び比較例１、２で得た銅板と、比較対象としての銅板及び白金板を作用電極として用いた場合の電圧−電流曲線から求めた開始電圧を表１に示す。開始電圧は、触媒電流が流れ始める−１０ｍＡｃｍ−２から−５ｍＡｃｍ−２を結んだ直線を外挿し、電流が０ｍＡｃｍ−２になる電位として求めた。 Table 1 shows the starting voltages obtained from the voltage-current curves when the copper plates obtained in Examples 1 to 6 and Comparative Examples 1 and 2 and the copper plate and the platinum plate as comparison targets were used as the working electrodes. The starting voltage was obtained as a potential at which the current became 0 mAcm −2 by extrapolating a straight line connecting −10 mAcm −2 to −5 mAcm −2 at which the catalyst current began to flow.
表１に示した開始電圧の絶対値は、それぞれの作用電極上での、二酸化炭素又は水の電気化学還元反応に対する触媒過電圧の大きさの目安となる。つまり、開始電圧の絶対値が小さいほど触媒過電圧（印加電圧）が小さいため、二酸化炭素又は水の電気化学還元におけるエネルギー効率に優れることになる。表１に示すように、実施例１〜６で得た銅板を作用電極とした場合の開始電圧は比較対象の白金板に匹敵するほど小さく、比較対象の銅板に比べると大幅に小さかった。一方、比較例１で得た銅板を作用電極とした場合の開始電圧は実施例１〜６の場合よりも大きかった。比較例２で得た銅板を作用電極とした場合の開始電圧は、比較対象の銅板と同程度であった。 The absolute value of the starting voltage shown in Table 1 is a measure of the magnitude of the catalyst overvoltage for the electrochemical reduction reaction of carbon dioxide or water on each working electrode. That is, since the catalyst overvoltage (applied voltage) is smaller as the absolute value of the starting voltage is smaller, the energy efficiency in the electrochemical reduction of carbon dioxide or water is better. As shown in Table 1, the starting voltage when the copper plate obtained in Examples 1 to 6 was used as a working electrode was small enough to be comparable to the platinum plate to be compared, and was much smaller than the copper plate to be compared. On the other hand, the starting voltage when the copper plate obtained in Comparative Example 1 was used as the working electrode was larger than those in Examples 1-6. The starting voltage when the copper plate obtained in Comparative Example 2 was used as the working electrode was about the same as the copper plate to be compared.
上記の評価結果より、表面に粒子径が５０ｎｍ〜５００ｎｍの範囲内である銅粒子が存在する銅板は、表面に粒子径が５０ｎｍ〜５００ｎｍの範囲内である銅粒子が存在しない銅板と比較して、電気化学還元におけるエネルギー効率に優れることが分かった。 From the above evaluation results, the copper plate having a particle size in the range of 50 nm to 500 nm on the surface is compared with the copper plate having no copper particle in the range of the particle size of 50 nm to 500 nm on the surface. It was found to be excellent in energy efficiency in electrochemical reduction.
（電気化学還元による還元生成物）
実施例１で得た銅板を作用電極として用いて、その開始電圧に近い電位である−１．２Ｖ（対 Ａｇ／ＡｇＣｌ電極）で電気分解を行った。電気分解は、対極として白金メッシュ電極、隔膜としてナフィオン膜、電解液として０．５ＭのＫＨＣＯ３水溶液を使用し、二酸化炭素（５ｍＬ／分）でバブリングしながら行った。作用電極から発生した気体は、ガスクロマトグラフ（島津製作所、Ｔｒａｃｅｒａ）で分析カラム（信和加工株式会社、マイクロパックドＳＴ）を用いて分析した。また、電解質水溶液中の還元生成物は、同じガスクロマトグラフで分析カラム（アジレントテクノロジー株式会社、ＤＢ−ＷＡＸＥＴＲ）を用いて分析した。その結果、発生した気体は、主として水素及び一酸化炭素であった。電解質水溶液中の還元生成物は、主としてメタノール、エタノール及び酢酸であった。
(Reduction products from electrochemical reduction)
Using the copper plate obtained in Example 1 as a working electrode, electrolysis was performed at −1.2 V (vs. Ag / AgCl electrode) which is a potential close to the starting voltage. The electrolysis was performed while bubbling with carbon dioxide (5 mL / min) using a platinum mesh electrode as the counter electrode, a Nafion membrane as the diaphragm, and a 0.5 M aqueous KHCO 3 solution as the electrolyte. The gas generated from the working electrode was analyzed with a gas chromatograph (Shimadzu Corporation, Tracera) using an analysis column (Shinwa Processing Co., Ltd., Micropacked ST). Moreover, the reduction product in electrolyte aqueous solution was analyzed with the same gas chromatograph using the analytical column (Agilent Technology Co., Ltd., DB-WAXETR). As a result, the generated gas was mainly hydrogen and carbon monoxide. The reduction products in the aqueous electrolyte solution were mainly methanol, ethanol and acetic acid.
以上より、本発明の電極によれば、エネルギー効率よく二酸化炭素及び水を電気化学還元できることが分かった。 From the above, it was found that according to the electrode of the present invention, carbon dioxide and water can be electrochemically reduced efficiently.
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