JP6779470B2 - Electrode material for water electrolysis and its manufacturing method, electrode for water electrolysis and solid polymer type water electrolysis cell - Google Patents

Electrode material for water electrolysis and its manufacturing method, electrode for water electrolysis and solid polymer type water electrolysis cell Download PDF

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JP6779470B2
JP6779470B2 JP2016064542A JP2016064542A JP6779470B2 JP 6779470 B2 JP6779470 B2 JP 6779470B2 JP 2016064542 A JP2016064542 A JP 2016064542A JP 2016064542 A JP2016064542 A JP 2016064542A JP 6779470 B2 JP6779470 B2 JP 6779470B2
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裕喜 穴井
裕喜 穴井
志云 野田
志云 野田
潤子 松田
潤子 松田
雄也 立川
雄也 立川
灯 林
灯 林
衡平 伊藤
衡平 伊藤
一成 佐々木
一成 佐々木
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    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
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    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/30—Hydrogen technology
    • Y02E60/36—Hydrogen production from non-carbon containing sources, e.g. by water electrolysis
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/30—Hydrogen technology
    • Y02E60/50—Fuel cells

Description

本発明は、固体高分子形水電解セルに好適に用いられる水電解用電極材料及びその製造方法、並びに水電解用電極に関する。 The present invention relates to an electrode material for water electrolysis preferably used for a solid polymer type water electrolysis cell, a method for producing the same, and an electrode for water electrolysis.

固体高分子形燃料電池（ＰＥＦＣ）はすでに家庭用として市販されており、燃料電池自動車の市販も開始されている。燃料電池において性能を決める最も重要な部材は電極触媒を含む電極材料である。第一世代の燃料電池自動車にはカーボンブラックの表面に微細な白金系微粒子を担持した材料が使用されるが、カーボン担体は酸化し、担持された白金粒子が脱離して電池性能が劣化してしまうことが課題となっていた。
これまでに本発明者らは、炭素系材料の代わりに酸化スズ担体に貴金属粒子を分散させた電極材料を開発している（特許文献１）。当該電極材料はＰＥＦＣのカソードでの運転条件で熱力学的に安定であるため、当該電極材料を用いて製造したカソードは酸化腐食されることなく、燃料電池自動車の寿命に相当する６万回の電位サイクルに耐えることができる。さらに、本発明者らは、特許文献２で開示した燃料電池用電極材料の製造方法において、導電補助材である気相成長炭素繊維を含むカーボンナノチューブ系材料を高導電性パスとして使うことによって、炭素系担体材料と比較して電子を通しにくい導電性酸化物担体の欠点を改善して、電極全体の導電性を向上させ、ＰＥＦＣ用電極として優れた性能を得ることに成功している（特許文献２）。 Polymer electrolyte fuel cells (PEFCs) are already on the market for home use, and fuel cell vehicles are also on the market. The most important member that determines the performance of a fuel cell is an electrode material containing an electrode catalyst. In the first generation fuel cell vehicle, a material in which fine platinum-based fine particles are supported on the surface of carbon black is used, but the carbon carrier is oxidized and the supported platinum particles are desorbed, resulting in deterioration of battery performance. It was a problem to put it away.
So far, the present inventors have developed an electrode material in which noble metal particles are dispersed in a tin oxide carrier instead of a carbon-based material (Patent Document 1). Since the electrode material is thermodynamically stable under the operating conditions of the PEFC cathode, the cathode manufactured using the electrode material is not oxidatively corroded and is 60,000 times equivalent to the life of the fuel cell vehicle. Can withstand potential cycles. Further, in the method for producing an electrode material for a fuel cell disclosed in Patent Document 2, the present inventors use a carbon nanotube-based material containing a vapor-grown carbon fiber as a conductive auxiliary material as a highly conductive path. We have succeeded in improving the conductivity of the entire electrode by improving the drawbacks of the conductive oxide carrier, which is difficult for electrons to pass through compared to carbon-based carrier materials, and obtaining excellent performance as an electrode for PEFC (patented). Document 2).

一方、ＰＥＦＣと同様に固体高分子膜を使用した固体高分子形水電解セル（以下、単に「水電解セル」と記載する場合がある。）が知られている。図１に示すように水電解セルでは、水の電気分解によりアノード側で酸素が発生し、カソード側で水素が発生する。水の電気分解反応には、標準状態（２５℃、１気圧）で１．２３Ｖ以上の電圧が理論的に必要となる。 On the other hand, a solid polymer type water electrolysis cell (hereinafter, may be simply referred to as "water electrolysis cell") using a solid polymer membrane similar to PEFC is known. As shown in FIG. 1, in the water electrolysis cell, oxygen is generated on the anode side and hydrogen is generated on the cathode side by electrolysis of water. The electrolysis reaction of water theoretically requires a voltage of 1.23 V or higher under standard conditions (25 ° C., 1 atm).

水電解セルは燃料電池セル（０．６Ｖ〜１．０Ｖ程度）よりも更に高い電位下で使用される。水電解セルを特に再生可能エネルギーの貯蔵を目的に利用する際には高い電位（１．５Ｖ〜２．０Ｖ程度）で電位変動の激しい状況下で用いられるため、水電解セル用電極には、ＰＥＦＣ用電極材料より高電位における高い耐久性が求められる。例えば、ＰＥＦＣ用電極材料で用いられる白金系電極触媒は水電解セルにおける電位条件(１．５Ｖ以上)の高電位では触媒活性の低いＰｔ酸化物になったり、溶解して電解質膜に析出したりするため、そのまま水電解セル用電極材料に転用しても長期間の使用はできない。 The water electrolysis cell is used under a higher potential than the fuel cell (about 0.6V to 1.0V). When the water electrolysis cell is used especially for the purpose of storing renewable energy, it is used at a high potential (about 1.5V to 2.0V) under a situation where the potential fluctuates sharply. Higher durability at high potentials is required than electrode materials for PEFC. For example, the platinum-based electrode catalyst used in the electrode material for PEFC becomes a Pt oxide having low catalytic activity at a high potential under potential conditions (1.5 V or more) in the water electrolysis cell, or dissolves and precipitates on the electrolyte membrane. Therefore, even if it is directly used as an electrode material for a water electrolysis cell, it cannot be used for a long period of time.

そのため、水電解用電極材料に用いられる電極触媒として、Ｐｔの代わりにより高価なイリジウム（Ｉｒ）を酸化物で用いることが多い。酸化イリジウム（ＩｒＯ2）は、１．５Ｖ〜２．０Ｖの高電位でも安定であり、水電解におけるアノード反応に高い触媒活性を有する。水電解用電極材料の実用化のためには、高価なイリジウム貴金属材料の使用量をできるだけ少なくする必要があるが、現在、一般的に市販・使用されている水電解用の電極触媒は、数ミクロン径の酸化イリジウム（ＩｒＯ2）粉末をそのまま用いることが多い。 Therefore, as an electrode catalyst used for an electrode material for water electrolysis, more expensive iridium (Ir) is often used as an oxide instead of Pt. Iridium oxide (IrO 2 ) is stable even at a high potential of 1.5V to 2.0V and has high catalytic activity for the anodic reaction in water electrolysis. In order to put the electrode material for water electrolysis into practical use, it is necessary to reduce the amount of expensive iridium noble metal material used as much as possible. However, there are a number of electrode catalysts for water electrolysis currently commercially available and used. Iridium oxide (IrO 2 ) powder having a micron diameter is often used as it is.

一方、イリジウムの使用量の低減やイリジウムの代替となる触媒の開発が行われている。例えば、特許文献３には、酸化イリジウムと、無機酸化物とを複合化した水電解用電極材料が開示されており、ＴｉＯ2、ＳｉＯ2、Ａｌ2Ｏ3等の無機酸化物を触媒の全質量に対して２０質量％未満複合化することにより、酸化イリジウムだけの場合よりも高い触媒活性を示すことが開示されている。この電極材料では、電子伝導性を確保するために、無機酸化物の量を２０質量％未満に抑えなければならず、無機酸化物との複合化による酸化イリジウム使用量の低減効果は限定的である。
また、特許文献４には、酸素欠陥を設けた金属酸化物触媒を、Ｓｎ、Ｓｂ、Ｎｂ、Ｔａ及びＴｉから電子伝導性を有する酸化物を含む担体に担持した水電解用電極材料が開示されている。当該電極材料では、非貴金属の金属酸化物を電極触媒としているため、イリジウム等の貴金属を使用するものではないが、触媒活性の面では改善の余地がある。 On the other hand, the amount of iridium used has been reduced and catalysts that can replace iridium have been developed. For example, Patent Document 3 discloses an electrode material for water electrolysis in which iridium oxide and an inorganic oxide are composited, and all of the catalysts are inorganic oxides such as TiO 2 , SiO 2 , and Al 2 O 3. It is disclosed that the composite of less than 20% by mass with respect to the mass exhibits higher catalytic activity than the case of iridium oxide alone. In this electrode material, the amount of inorganic oxide must be suppressed to less than 20% by mass in order to ensure electron conductivity, and the effect of reducing the amount of iridium oxide used by compounding with the inorganic oxide is limited. is there.
Further, Patent Document 4 discloses an electrode material for water electrolysis in which a metal oxide catalyst provided with an oxygen defect is supported on a carrier containing an oxide having electron conductivity from Sn, Sb, Nb, Ta and Ti. ing. Since the electrode material uses a metal oxide of a non-precious metal as an electrode catalyst, no precious metal such as iridium is used, but there is room for improvement in terms of catalytic activity.

特許第５３２２１１０号公報Japanese Patent No. 5322110 国際公開第２０１５/１４１５９５号パンフレットInternational Publication No. 2015/141595 Pamphlet 国際公開第２００６/０１９１２８号パンフレットInternational Publication No. 2006/019128 Pamphlet 特開２０１５−１２９３４７号公報JP 2015-129347

このようにイリジウム等の貴金属使用量をできるだけ少なくし、水電解における高電位（１．５Ｖ以上）でも安定であり、十分な触媒活性を示す水電解用電極材料の開発が求められている。
かかる状況下、本発明の目的は、Ｉｒ使用量を低減でき、かつ、水電解における電位下でも安定であり、十分な触媒活性を示すことが可能な水電解用電極材料及びその製造方法を提供することである。 As described above, it is required to develop an electrode material for water electrolysis that uses as little precious metal as possible, is stable even at a high potential (1.5 V or more) in water electrolysis, and exhibits sufficient catalytic activity.
Under such circumstances, an object of the present invention is to provide an electrode material for water electrolysis capable of reducing the amount of Ir used, being stable even under a potential in water electrolysis, and exhibiting sufficient catalytic activity, and a method for producing the same. It is to be.

本発明者は、上記課題を解決すべく鋭意研究を重ねた結果、下記の発明が上記目的に合致することを見出し、本発明に至った。 As a result of diligent research to solve the above problems, the present inventor has found that the following invention meets the above object, and has reached the present invention.

すなわち、本発明は、以下の発明に係るものである。
＜１＞ 炭素系導電補助材と、前記炭素系導電補助材に担持された電子伝導性酸化物と、前記電子伝導性酸化物に分散担持された、平均粒子径１０ｎｍ以下の酸化イリジウム粒子とを含む水電解用電極材料。
＜２＞ 炭素系導電補助材が、表面がグラファイト構造である繊維状炭素からなる導電補助材である＜１＞に記載の水電解用電極材料。
＜３＞ 電子伝導性酸化物担体が、酸化スズを主体とする電子伝導性酸化物からなる＜１＞または＜２＞に記載の水電解用電極材料。
＜４＞ 以下の工程を有する水電解用電極材料の製造方法。
（１）表面がグラファイト構造である繊維状炭素からなる導電補助材に、電子伝導性酸化物を担持する工程
（２）電子伝導性酸化物担体を担持した前記導電補助材を、酸化イリジウム前駆体を含む溶液に浸漬し、前記電子伝導性酸化物担体の表面上に酸化イリジウム前駆体を担持する工程
（３）電子伝導性酸化物担体に担持された酸化イリジウム前駆体を、酸化雰囲気下、３００℃以上５００℃以下で熱処理し、酸化イリジウムに変換する工程
＜５＞ 工程（２）における担持が、蒸発乾固法による＜４＞に記載の水電解用電極材料の製造方法。
＜６＞ 電子伝導性酸化物担体が、酸化スズを主体とする電子伝導性酸化物からなる＜４＞または＜５＞に記載の水電解用電極材料の製造方法。
＜７＞ ＜１＞から＜３＞のいずれかに記載の水電解用電極材料とプロトン伝導性電解質材料とを含む水電解用電極。 That is, the present invention relates to the following invention.
<1> A carbon-based conductive auxiliary material, an electron conductive oxide supported on the carbon-based conductive auxiliary material, and iridium oxide particles having an average particle diameter of 10 nm or less dispersed and supported on the electron conductive oxide. Electrode material for water electrolysis including.
<2> The electrode material for water electrolysis according to <1>, wherein the carbon-based conductive auxiliary material is a conductive auxiliary material made of fibrous carbon having a graphite structure on the surface.
<3> The electrode material for water electrolysis according to <1> or <2>, wherein the electron conductive oxide carrier is composed of an electron conductive oxide mainly composed of tin oxide.
<4> A method for producing an electrode material for water electrolysis having the following steps.
(1) Step of supporting an electron conductive oxide on a conductive auxiliary material made of fibrous carbon having a graphite structure on the surface (2) The conductive auxiliary material supporting an electron conductive oxide carrier is a precursor of iridium oxide. Step of immersing the iridium oxide precursor on the surface of the electron conductive oxide carrier by immersing it in a solution containing (3) The iridium oxide precursor supported on the electron conductive oxide carrier is 300 in an oxidizing atmosphere. Step of heat-treating at ° C. or higher and 500 ° C. or lower to convert to iridium oxide <5> The method for producing an electrode material for water electrolysis according to <4>, wherein the carrier in step (2) is supported by an evaporation-drying method.
<6> The method for producing an electrode material for water electrolysis according to <4> or <5>, wherein the electron conductive oxide carrier is composed of an electron conductive oxide mainly composed of tin oxide.
<7> An electrode for water electrolysis containing the electrode material for water electrolysis according to any one of <1> to <3> and a proton conductive electrolyte material.

＜１ａ＞ 固体高分子電解質膜と、前記固体高分子電解質膜の一方面に接合されたカソードと、前記固体高分子電解質膜の他方面に接合されたアノードと、を有する膜電極接合体であって、前記アノードが、上記＜７＞に記載の水電解用電極である膜電極接合体。
＜２ａ＞ ＜１ａ＞に記載の膜電極接合体を備えてなることを特徴とする固体高分子形水電解セル。 <1a> A membrane electrode assembly having a solid polymer electrolyte membrane, a cathode bonded to one surface of the solid polymer electrolyte membrane, and an anode bonded to the other surface of the solid polymer electrolyte membrane. The membrane electrode assembly in which the anode is the water electrolyte electrode according to <7>.
<2a> A solid polymer electrolyzed cell comprising the membrane electrode assembly according to <1a>.

本発明によれば、酸化イリジウム微粒子が電子伝導性酸化物の上に高分散担持されて、水電解における電位下でも安定であり、十分な触媒活性を示すことが可能な水電解用電極材料が提供される。 According to the present invention, an electrode material for water electrolysis in which iridium oxide fine particles are highly dispersed and supported on an electron conductive oxide, is stable even under a potential in water electrolysis, and can exhibit sufficient catalytic activity. Provided.

固体高分子形水電解セルの代表的な構成を示す概念図である。It is a conceptual diagram which shows the typical structure of the solid polymer type water electrolysis cell. 本発明の水電解用電極材料の模式図である。It is a schematic diagram of the electrode material for water electrolysis of this invention. 本発明の膜電極接合体の断面模式図である。It is sectional drawing of the membrane electrode assembly of this invention. 実施例１の電極材料のＸＲＤプロファイルである。5 is an XRD profile of the electrode material of Example 1. 参考例１の電極材料のＸＲＤプロファイルである。It is an XRD profile of the electrode material of Reference Example 1. 電極材料のＦＥ−ＳＥＭ像であり、（ａ）は実施例１、（ｂ）は参考例１の電極材料である。It is an FE-SEM image of an electrode material, (a) is an electrode material of Example 1, and (b) is an electrode material of Reference Example 1. 実施例１の電極材料のＳＴＥＭ像及びＥＤＳマッピングである。It is a STEM image and EDS mapping of the electrode material of Example 1. FIG. 実施例１の電極材料のＳＴＥＭ像（高倍率）である。It is a STEM image (high magnification) of the electrode material of Example 1. 参考例１の電極材料のＳＴＥＭ像及びＥＤＳマッピングである。It is a STEM image and EDS mapping of the electrode material of Reference Example 1. ＸＰＳによる電極材料のＩｒ（４ｆ）スペクトルであり、（ａ）は実施例１、（ｂ）は参考例１の電極材料である。It is the Ir (4f) spectrum of the electrode material by XPS, (a) is the electrode material of Example 1, and (b) is the electrode material of Reference Example 1. 比較例１の電極のＦＥ−ＳＥＭ像である。It is an FE-SEM image of the electrode of Comparative Example 1. 実施例１、及び比較例１の水電解用電極のクロノアンペロメトリー（ＣＡ）による評価結果である。It is an evaluation result by chronoamperometry (CA) of the electrode for water electrolysis of Example 1 and Comparative Example 1.

以下、本発明について例示物等を示して詳細に説明するが、本発明は以下の例示物等に限定されるものではなく、本発明の要旨を逸脱しない範囲において任意に変更して実施できる。なお、本明細書において、「〜」とはその前後の数値又は物理量を含む表現として用いるものとする。 Hereinafter, the present invention will be described in detail by showing examples and the like, but the present invention is not limited to the following examples and the like, and can be arbitrarily modified and implemented without departing from the gist of the present invention. In addition, in this specification, "~" shall be used as an expression including numerical values or physical quantities before and after it.

＜１．水電解用電極材料＞
本発明は、炭素系導電補助材と、前記炭素系導電補助材に担持された電子伝導性酸化物と、前記電子伝導性酸化物に分散担持された、平均粒子径１０ｎｍ以下の酸化イリジウム粒子とを含む水電解用電極材料（以下、「本発明の電極材料」と記載する場合がある。）に関する。 <1. Electrode material for water electrolysis ＞
The present invention includes a carbon-based conductive auxiliary material, an electron conductive oxide supported on the carbon-based conductive auxiliary material, and iridium oxide particles having an average particle diameter of 10 nm or less dispersed and supported on the electron conductive oxide. The present invention relates to an electrode material for water electrolysis containing the above (hereinafter, may be referred to as “electrode material of the present invention”).

本発明の電極材料では、電子伝導性酸化物に担持された電極触媒粒子（酸化イリジウム微粒子）は炭素系材料である導電補助材とほとんど接触しないため、従来の炭素系担体に電極触媒粒子を担持した際に生じる電気化学的酸化による炭素系担体の腐食に起因する電極性能の低下を回避できる。そして、本発明の電極材料を構成する導電補助材は相互接触性がよく、優れた電子伝導性を有する炭素系導電補助材であるため、当該電極材料を用いて、燃料電池用電極を構成した際に、前記導電補助材が互いに接触して低抵抗の導電パスが形成され、電子伝導性に優れた電極となる。
このように、本発明の電極材料は、電子伝導性酸化物に起因する電気化学的酸化への優れた耐久性と、炭素系導電補助材に起因する優れた電子伝導性を併せ持つ。そのため、当該電極材料で形成された水電解用電極は、優れた電極性能を示すと共に、耐久性が高く、水電解反応を長期間継続することができる。 In the electrode material of the present invention, the electrode catalyst particles (iridium oxide fine particles) supported on the electron conductive oxide hardly come into contact with the conductive auxiliary material which is a carbon-based material, so that the electrode catalyst particles are supported on a conventional carbon-based carrier. It is possible to avoid the deterioration of the electrode performance due to the corrosion of the carbon-based carrier due to the electrochemical oxidation that occurs at that time. Since the conductive auxiliary material constituting the electrode material of the present invention is a carbon-based conductive auxiliary material having good mutual contact and excellent electron conductivity, the electrode material is used to form an electrode for a fuel cell. At that time, the conductive auxiliary materials come into contact with each other to form a low-resistance conductive path, resulting in an electrode having excellent electronic conductivity.
As described above, the electrode material of the present invention has both excellent durability against electrochemical oxidation caused by an electron conductive oxide and excellent electron conductivity caused by a carbon-based conductive auxiliary material. Therefore, the electrode for water electrolysis formed of the electrode material exhibits excellent electrode performance, has high durability, and can continue the water electrolysis reaction for a long period of time.

また、本願発明の水電解用電極材料では、電極の骨格としての役割を、炭素系導電補助材が担うため、電極触媒粒子（酸化イリジウム微粒子）が担持される電子伝導性酸化物担体の粒径（薄膜の場合は厚み）を小さくすることができる。そのため、本願発明の水電解用電極材料を用いて形成した水電解用電極では、電子伝導性酸化物に起因する電気抵抗を低減できる。 Further, in the electrode material for water electrolysis of the present invention, since the carbon-based conductive auxiliary material plays a role as the skeleton of the electrode, the particle size of the electron conductive oxide carrier on which the electrode catalyst particles (iridium oxide fine particles) are supported. (Thickness in the case of a thin film) can be reduced. Therefore, in the electrode for water electrolysis formed by using the electrode material for water electrolysis of the present invention, the electric resistance caused by the electron conductive oxide can be reduced.

また、電子伝導性酸化物に起因する電気抵抗を低減できるため、耐久性が高いが電子伝導性に乏しく、従来の水電解用電極材料では実用が困難であった電子伝導性酸化物（例えば、酸化チタン等）についても、本発明の電極材料として使用できる。 Further, since the electric resistance caused by the electron conductive oxide can be reduced, the durability is high but the electron conductivity is poor, and the electron conductive oxide (for example, which is difficult to put into practical use with the conventional electrode material for water electrolysis). (Titanium oxide, etc.) can also be used as the electrode material of the present invention.

以下、図面に基づいて本発明の好適な実施形態について詳細に説明する。 Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings.

図２は本発明の電極材料の代表的な構成を示す模式図である。図１に示すように、本発明に係る水電解用電極材料１は、（炭素系）導電補助材２と、導電補助材２に担持された粒子状の電子伝導性酸化物３ａと、電子伝導性酸化物３ａに分散担持された電極触媒粒子３ｂによって構成される。 FIG. 2 is a schematic view showing a typical configuration of the electrode material of the present invention. As shown in FIG. 1, the electrode material 1 for water electrolysis according to the present invention includes a (carbon-based) conductive auxiliary material 2, a particulate electron conductive oxide 3a supported on the conductive auxiliary material 2, and electron conduction. It is composed of electrode catalyst particles 3b dispersedly supported on the sex oxide 3a.

導電補助材２は、好適には表面がグラファイト構造である繊維状炭素からなる炭素系導電補助材である。なお、本明細書において、「導電補助材」とは、水電解用電極材料に含まれ、水電解用電極を形成した際に電子伝導性を向上させる役割を有するものを意味する。導電補助材２は、炭素系材料由来の優れた電子伝導性を有し、電子伝導性酸化物３ａを担持できる。水電解用電極材料１は、このような導電補助材２を用いているため、水電解用電極を形成した際に、隣接する導電補助材２が連続的に接触でき、かつ水電解用電極内の水素や酸素などのガス拡散及び水（蒸気）の排出がスムーズに行える程度の空間を形成できる。 The conductive auxiliary material 2 is preferably a carbon-based conductive auxiliary material made of fibrous carbon having a graphite structure on the surface. In the present specification, the "conductive auxiliary material" means a material contained in the electrode material for water electrolysis and having a role of improving electron conductivity when the electrode for water electrolysis is formed. The conductive auxiliary material 2 has excellent electron conductivity derived from a carbon-based material and can support the electron conductive oxide 3a. Since the electrode material 1 for water electrolysis uses such a conductive auxiliary material 2, when the electrode for water electrolysis is formed, the adjacent conductive auxiliary material 2 can be continuously contacted, and the inside of the electrode for water electrolysis It is possible to form a space that allows smooth diffusion of gases such as hydrogen and oxygen and discharge of water (steam).

炭素系導電補助材として、表面がグラファイト構造である繊維状炭素は相互接触性がよく、電子伝導性に優れるため、水電解用電極材料１を用いて水電解用電極を形成した際に導電パスが形成される As a carbon-based conductive auxiliary material, fibrous carbon having a graphite structure on the surface has good mutual contact and excellent electron conductivity. Therefore, when an electrode for water electrolysis is formed using the electrode material 1 for water electrolysis, a conductive path is obtained. Is formed

繊維状炭素は、中空状あるいは繊維状の炭素材料であり、具体的にはカーボンナノチューブ（ＣＮＴ）やカーボンナノファイバーが挙げられる。なお、本発明において、「カーボンナノチューブ」とは、単層ＣＮＴ、２層ＣＮＴ、複層ＣＮＴ及びこれらの混合物を含む。 The fibrous carbon is a hollow or fibrous carbon material, and specific examples thereof include carbon nanotubes (CNTs) and carbon nanofibers. In the present invention, the "carbon nanotube" includes a single-walled CNT, a two-walled CNT, a multi-walled CNT, and a mixture thereof.

ここで、水電解用電極を形成した際の電極内の電気伝導性とガス拡散性を両立させるためには、繊維状炭素は直径２ｎｍ〜１０μｍ、全長０．０３〜５００μｍであることが好適である。
なお、中空状あるいは繊維状の炭素材料のうち、カーボンナノチューブに代表されるように、直径が１００ｎｍ以下のもの、または、気相成長炭素繊維（Vaper Grown Carbon Fiber，ＶＧＣＦ）のような直径が１００〜１０００ｎｍ程度のもの、炭素繊維のような直径が１μｍ〜２０μｍのものを指すことが多いが、これらの炭素材料の長さと呼称についての明確な規定はないため、本明細書内ではこれらを合わせて繊維状炭素と称する。 Here, in order to achieve both electrical conductivity and gas diffusivity in the electrode when the electrode for water electrolysis is formed, it is preferable that the fibrous carbon has a diameter of 2 nm to 10 μm and a total length of 0.03 to 500 μm. is there.
Among the hollow or fibrous carbon materials, those having a diameter of 100 nm or less, as typified by carbon nanotubes, or those having a diameter of 100 such as vapor-grown carbon fiber (VGCF) are 100. It often refers to those with a diameter of about 1000 nm and those with a diameter of 1 μm to 20 μm such as carbon fibers, but since there is no clear specification regarding the length and name of these carbon materials, these are combined in this specification. Is called fibrous carbon.

また、表面がグラファイト構造である繊維状炭素であれば、化学的に安定で、表面積も小さいために電極触媒粒子が担持されにくく、大部分の電極触媒粒子が電子伝導性酸化物に選択的に担持される。そのため、全ての電極触媒粒子のうち、繊維状炭素と直接的に接触する電極触媒粒子の割合が小さくなり、水電解用電極として使用する際に繊維状炭素が電気化学的酸化腐食することが抑制される。表面がグラファイト構造である繊維状炭素としては、カーボンナノチューブ（単層ＣＮＴ、２層ＣＮＴ、複層ＣＮＴの何れも含む）、気相成長炭素繊維（ＶＧＣＦ）が挙げられ、高結晶性、高純度のものが好ましい。 Further, if the surface is fibrous carbon having a graphite structure, the electrode catalyst particles are difficult to be supported because it is chemically stable and the surface area is small, and most of the electrode catalyst particles are selectively selected as electron conductive oxides. Be carried. Therefore, the proportion of the electrode catalyst particles in direct contact with the fibrous carbon among all the electrode catalyst particles is reduced, and the fibrous carbon is suppressed from electrochemical oxidative corrosion when used as an electrode for water electrolysis. Will be done. Examples of fibrous carbon having a graphite structure on the surface include carbon nanotubes (including single-walled CNTs, double-walled CNTs, and multi-walled CNTs) and vapor-grown carbon fibers (VGCF), which have high crystallinity and high purity. Is preferable.

（電子伝導性酸化物）
電子伝導性酸化物３ａを構成する電子伝導性酸化物としては、固体高分子形水分解セルのアノード条件で十分な耐久性と電子伝導性を併せ持つものであればよい。
なお、アノード条件とは、固体高分子形水分解セルの通常運転時のアノードにおける条件であり、温度が室温〜１５０℃、水素を含む燃料ガスが供給される条件（還元雰囲気）であって、アノード-カソード間の電圧が１．５Ｖ以上２．０Ｖ以下を意味する。 (Electronic conductive oxide)
The electron-conductive oxide constituting the electron-conductive oxide 3a may be any one having sufficient durability and electron conductivity under the anode conditions of the solid polymer-type electrolysis cell.
The anode condition is a condition at the anode during normal operation of the solid polymer electrolysis cell, which is a condition where the temperature is room temperature to 150 ° C. and a fuel gas containing hydrogen is supplied (reducing atmosphere). It means that the voltage between the anode and the cathode is 1.5V or more and 2.0V or less.

電子伝導性酸化物として具体的には、酸化スズ、酸化モリブデン、酸化ニオブ、酸化タンタル、酸化チタン及び酸化タングステンから選択される１種を主体とする電子伝導性酸化物が挙げられる。ここで、本発明において「主体とする電子伝導性酸化物」とは、（Ａ）母体酸化物のみからなるもの、及び（Ｂ）他元素をドープされた酸化物であって、母体酸化物が５０ｍｏｌ％以上含まれるもの、を意味する。 Specific examples of the electron conductive oxide include an electron conductive oxide mainly composed of one selected from tin oxide, molybdenum oxide, niobium oxide, tantalum oxide, titanium oxide and tungsten oxide. Here, in the present invention, the "mainly electron-conducting oxide" is (A) an oxide composed only of a matrix oxide and (B) an oxide doped with another element, wherein the matrix oxide is It means that it is contained in an amount of 50 mol% or more.

ドープされる元素として、具体的には、Ｓｎ，Ｔｉ，Ｓｂ，Ｎｂ，Ｔａ，Ｗ，Ｃｏ，Ｖ，Ｃｒ，Ｍｎ，Ｍｏなどが挙げられる（但し、母体酸化物と異なる元素である。）。ドープされる元素は、母体酸化物より価数が高い元素であり、例えば、母体酸化物が酸化チタンの場合で例示すると、上記ドープ種元素のうち、Ｔｉ以外の元素（例えば、Ｎｂ）が選択される。 Specific examples of the element to be doped include Sn, Ti, Sb, Nb, Ta, W, Co, V, Cr, Mn, Mo and the like (however, the element is different from the parent oxide). The element to be doped is an element having a higher valence than the matrix oxide. For example, in the case where the matrix oxide is titanium oxide, an element other than Ti (for example, Nb) is selected from the above-mentioned doped seed elements. Will be done.

この中でも、電子伝導性酸化物３ａが、酸化スズを主体とする酸化物であることが好ましい。ここで、「主体とする酸化物」とは、対象となる酸化物を５０ｍｏｌ％以上含む酸化物をいう。 Among these, the electron conductive oxide 3a is preferably an oxide mainly composed of tin oxide. Here, the "mainly oxide" means an oxide containing 50 mol% or more of the target oxide.

また、電子伝導性酸化物３ａとして、ＳｒＴｉＯ3等高い導電率を有する電子伝導性酸化物をコアとし、その表面に水電解セルのアノード条件での優れた耐久性を有する酸化物（ＴｉＯ2等）からなるスキン層（層厚：数原子層〜数十原子層）で被覆したコアシェル構造を有する担体を使用することもできる。 Further, as the electron conductive oxide 3a, an electron conductive oxide having a high conductivity such as SrTiO 3 is used as a core, and an oxide having excellent durability under the anode condition of the water electrolysis cell (TiO 2 etc.) on the surface thereof. It is also possible to use a carrier having a core-shell structure coated with a skin layer (layer thickness: several atomic layers to several tens of atomic layers) composed of).

本発明の水電解用電極材料１において、水電解用電極の骨格としての役割は導電補助材２が担うことから、電子伝導性が炭素系材料と比較して小さい電子伝導性酸化物３ａは、電極触媒粒子３ｂが分散担持することができる範囲内で、粒径が小さい方が好ましい。電子伝導性酸化物３ａは、一次粒子、二次粒子のいずれでもよい。但し、電子伝導性酸化物３ａが一次粒子であることが好ましい。これは、電子伝導性酸化物３ａが二次粒子の場合には二次粒子を構成する一次粒子間の粒界抵抗により電気抵抗が大きくなるためである。
電子伝導性酸化物３ａは、好適には平均粒径１〜２００ｎｍの粒子状電子伝導性酸化物であり、より好適には実質的に一次粒子となる平均粒径１〜４０ｎｍの粒子状電子伝導性酸化物である。そして、水電解用電極材料１の導電性の観点からは、粒子状の電子伝導性酸化物３ａが密集せずに、導電補助材２の一部が露出され、導電補助材２と他の導電補助材２との直接的な接触を阻害しない程度に電子伝導性酸化物３ａが分散して担持されていることが好ましい。 In the electrode material 1 for water electrolysis of the present invention, since the conductive auxiliary material 2 plays a role as a skeleton of the electrode for water electrolysis, the electron conductive oxide 3a having a smaller electron conductivity than the carbon-based material can be used. It is preferable that the particle size is small within the range in which the electrode catalyst particles 3b can be dispersed and supported. The electron conductive oxide 3a may be either a primary particle or a secondary particle. However, it is preferable that the electron conductive oxide 3a is a primary particle. This is because when the electron conductive oxide 3a is a secondary particle, the electrical resistance increases due to the grain boundary resistance between the primary particles constituting the secondary particle.
The electron conductive oxide 3a is preferably a particulate electron conductive oxide having an average particle size of 1 to 200 nm, and more preferably a particulate electron conduction oxide having an average particle size of 1 to 40 nm, which is substantially primary particles. It is a sex oxide. Then, from the viewpoint of the conductivity of the electrode material 1 for water electrolysis, a part of the conductive auxiliary material 2 is exposed without the particulate electron conductive oxide 3a being densely packed, and the conductive auxiliary material 2 and other conductive materials 2 are exposed. It is preferable that the electron conductive oxide 3a is dispersed and supported so as not to hinder the direct contact with the auxiliary material 2.

すなわち、本発明の水電解用電極材料における電子伝導性酸化物の好適な態様の一つは、前記導電補助材２の表面の一部が露出するように、粒子状電子伝導性酸化物が前記導電補助材２に担持されている態様である。導電補助材の露出部分は、当該露出部分のそれぞれが互いに接触できる程度であればよい。そして、粒子状電子伝導性酸化物の平均粒径が、１〜２００ｎｍが好適であり、平均粒径１〜４０ｎｍがより好適である。
なお、「粒子状電子伝導性酸化物の平均粒径」は、電子顕微鏡像より調べられる任意の粒子状電子伝導性酸化物（２０個）の粒子径の平均値により得ることができる。 That is, one of the preferred embodiments of the electron conductive oxide in the electrode material for water electrolysis of the present invention is that the particulate electron conductive oxide is used so that a part of the surface of the conductive auxiliary material 2 is exposed. This is an embodiment supported on the conductive auxiliary material 2. The exposed portions of the conductive auxiliary material may be such that the exposed portions can come into contact with each other. The average particle size of the particulate electron conductive oxide is preferably 1 to 200 nm, and more preferably 1 to 40 nm.
The "average particle size of the particulate electron conductive oxides" can be obtained from the average value of the particle sizes of any particulate electron conductive oxides (20 pieces) examined from the electron microscope image.

なお、図２では、電子伝導性酸化物３ａは、導電補助材２に分散担持された粒子状電子伝導性酸化物であるがこれに限定されず、電子伝導性酸化物３ａは導電補助材２に担持されていればよい。例えば、導電補助材２を薄膜状の電子伝導性酸化物が被覆する形態であってもよい。薄膜状電子伝導性酸化物は、例えば、蒸着などの乾式法で導電補助材に対し、電子伝導性酸化物を被覆することで形成できる。
水電解用電極材料１の導電性の観点からは、薄膜状電子伝導性酸化物の膜厚は、形成できる範囲でできるだけ薄い方が好ましい。すなわち、本発明の水電解用電極材料における電子伝導性酸化物の好適な態様の一つは、電子伝導性酸化物が平均膜厚１〜５０ｎｍの薄膜状電子伝導性酸化物であって、当該薄膜状電子伝導性酸化物の一部又は全部が前記導電補助材を被覆するように担持されてなる態様である。電子伝導性酸化物が平均膜厚１〜５０ｎｍであれば、電子伝導性酸化物に起因する電気抵抗が実質的に問題にならないため、導電補助材の露出部分が互いに接触する必要がない。なお、「薄膜状電子伝導性酸化物の平均膜厚」は、薄膜状電子伝導性酸化物の厚み方向の断面電子顕微鏡像より調べられる任意位置の厚み（５点）の平均値により得ることができる。 In FIG. 2, the electron conductive oxide 3a is a particulate electron conductive oxide dispersed and supported on the conductive auxiliary material 2, but the present invention is not limited to this, and the electronic conductive oxide 3a is the conductive auxiliary material 2. It suffices if it is carried on. For example, the conductive auxiliary material 2 may be coated with a thin-film electron conductive oxide. The thin-film electron conductive oxide can be formed by coating the conductive auxiliary material with the electron conductive oxide by, for example, a dry method such as thin film deposition.
From the viewpoint of conductivity of the electrode material 1 for water electrolysis, the film thickness of the thin-film electron conductive oxide is preferably as thin as possible within the range in which it can be formed. That is, one of the preferred embodiments of the electron conductive oxide in the electrode material for water electrolysis of the present invention is that the electron conductive oxide is a thin film electronic conductive oxide having an average thickness of 1 to 50 nm. In this embodiment, a part or all of the thin-film electron conductive oxide is supported so as to cover the conductive auxiliary material. When the electron conductive oxide has an average thickness of 1 to 50 nm, the electric resistance caused by the electron conductive oxide does not substantially matter, so that the exposed portions of the conductive auxiliary materials do not need to come into contact with each other. The "average film thickness of the thin film electron conductive oxide" can be obtained from the average value of the thicknesses (5 points) at arbitrary positions examined from the cross-sectional electron microscope image in the thickness direction of the thin film electron conductive oxide. it can.

電子伝導性酸化物は、電極触媒の担持量を高めるために、機械的強度が保てる範囲で、表面積が大きい方が好ましい。 The electron conductive oxide preferably has a large surface area as long as the mechanical strength can be maintained in order to increase the amount of the electrode catalyst supported.

また、電子伝導性酸化物の担持量は、粒径（薄膜状の場合は膜厚）や表面積等の電子伝導性酸化物の物性、電子伝導性酸化物の製造方法によっても最適値がかわるため、十分な量の電極触媒粒子が担持できる範囲で適宜決定される。
酸化スズの場合を例示すると、導電補助材と電子伝導性酸化物の合計を１００重量％としたときに、通常、５〜９５重量％であり、好ましくは４５〜９５重量％である。電子伝導性酸化物の担持量が少なすぎると、水電解用電極材料として十分な量の電極触媒粒子が担持できなくなる。電子伝導性酸化物の担持量が多すぎると電子伝導性酸化物の粒径（薄膜状の場合は膜厚）が大きくなりすぎて水電解用電極材料の電気抵抗が高くなる場合がある。 In addition, the optimum value of the amount of the electron conductive oxide supported varies depending on the physical properties of the electron conductive oxide such as particle size (thickness in the case of a thin film) and surface area, and the method for producing the electron conductive oxide. , Is appropriately determined within a range in which a sufficient amount of electrode catalyst particles can be supported.
Taking the case of tin oxide as an example, when the total of the conductive auxiliary material and the electron conductive oxide is 100% by weight, it is usually 5 to 95% by weight, preferably 45 to 95% by weight. If the amount of the electron conductive oxide supported is too small, a sufficient amount of electrode catalyst particles as an electrode material for water electrolysis cannot be supported. If the amount of the electron conductive oxide carried is too large, the particle size of the electron conductive oxide (thickness in the case of a thin film) becomes too large, and the electric resistance of the electrode material for water electrolysis may increase.

ここで、電子伝導性酸化物が、酸化スズを主体とする酸化物である場合には、本発明の水電解用電極をアノードとして使用することが好ましい。
元素としてスズ（Ｓｎ）は、水電解セルのアノード条件で、酸化物であるＳｎＯ2が熱力学的に安定であり酸化分解が起こらない。また、酸化スズは、十分な電子伝導性を有し、電極触媒粒子（ＩｒＯ2微粒子）を高分散で担持が可能な担体となる。 Here, when the electron conductive oxide is an oxide mainly composed of tin oxide, it is preferable to use the electrode for water electrolysis of the present invention as an anode.
Tin (Sn) as the element is in the anode conditions of water electrolysis cell, SnO 2 does not occur is thermodynamically stable oxidative degradation is an oxide. In addition, tin oxide is a carrier that has sufficient electron conductivity and can support electrode catalyst particles (IrO 2 fine particles) with high dispersion.

酸化スズを主体とする酸化物の中でも、より優れた電極性能を有する水電解用電極が形成できる点で、ニオブ（Ｎｂ）を０．１〜２０ｍｏｌ％ドープしたニオブドープ酸化スズが特に好ましい。 Among the oxides mainly composed of tin oxide, niobium-doped tin oxide doped with niobium (Nb) in an amount of 0.1 to 20 mol% is particularly preferable in that an electrode for water electrolysis having better electrode performance can be formed.

（電極触媒粒子）
電極触媒粒子３ｂは、酸化イリジウムからなり、電子伝導性酸化物３ａに分散担持されている。電極触媒粒子３ｂは、電子伝導性酸化物に選択的に分散担持されていることが好ましい。ここで「電子伝導性酸化物に選択的に分散担持」とは、全ての電極触媒粒子（個数）のうち、８０％以上、好適には９０％以上、より好適には９５％以上（１００％を含む）が、電子伝導性酸化物に担持されていることを意味する。電子伝導性酸化物に担持された電極触媒粒子の割合は、評価対象となる水電解用電極材料を電磁顕微鏡で観察した任意の電極触媒粒子（１００個以上）を選出し、そのうち、電子伝導性酸化物に担持された個数と、炭素系導電補助材に担持された個数とをカウントすることにより、評価することができる。 (Electrode catalyst particles)
The electrode catalyst particles 3b are made of iridium oxide and are dispersed and supported on the electron conductive oxide 3a. It is preferable that the electrode catalyst particles 3b are selectively dispersed and supported on the electron conductive oxide. Here, "selectively dispersed and supported on an electron conductive oxide" means 80% or more, preferably 90% or more, more preferably 95% or more (100%) of all the electrode catalyst particles (number). Includes), which means that it is supported on an electron conductive oxide. For the ratio of the electrode catalyst particles supported on the electron conductive oxide, arbitrary electrode catalyst particles (100 or more) obtained by observing the electrode material for water electrolysis to be evaluated with an electromagnetic microscope were selected, and among them, the electron conductivity It can be evaluated by counting the number supported on the oxide and the number supported on the carbon-based conductive auxiliary material.

電極触媒粒子３ｂを構成する酸化イリジウムは、水の電気分解反応（Ｈ2Ｏ→２Ｈ+＋１／２Ｏ2＋２ｅ-）に対する優れた電気化学的触媒活性を有する。なお、電極触媒粒子３ｂは、その性能を損なわない範囲でＩｒ以外の他の金属元素を含んでいてもよい。また、金属Ｉｒ粒子の表面を酸化して表面層が酸化イリジウム層である粒子でもよい。 The iridium oxide constituting the electrode catalyst particles 3b has excellent electrochemical catalytic activity for the electrolysis reaction of water (H 2 O → 2H + + 1 / 2O 2 + 2e − ). The electrode catalyst particles 3b may contain a metal element other than Ir as long as the performance is not impaired. Further, the particles may be particles in which the surface of the metal Ir particles is oxidized and the surface layer is an iridium oxide layer.

電極触媒粒子３ｂの形状は、特に制限されず公知の電極触媒粒子と同様の形状のものが使用できる。具体的な形状として球形、楕円形、多面体、コアシェル構造等が挙げられる。また、電極触媒粒子３ｂの構造は、結晶に限定されず、非晶質であってよく、結晶と非晶質の混合体であってもよい。 The shape of the electrode catalyst particles 3b is not particularly limited, and those having the same shape as the known electrode catalyst particles can be used. Specific shapes include spheres, ellipses, polyhedra, core-shell structures and the like. Further, the structure of the electrode catalyst particles 3b is not limited to crystals, and may be amorphous, or may be a mixture of crystals and amorphous.

電極触媒粒子３ｂの大きさは、小さいほど電気化学反応が進行する有効表面積が増加するため、電気化学的触媒活性が高くなる傾向がある。しかし、その大きさが小さすぎると、電気化学的反応活性が低下する。従って、電極触媒粒子３ｂの大きさは、平均粒子径として１０ｎｍ以下であり、好ましくは０．５ｎｍ〜５ｎｍである。
なお、本発明における「電極触媒粒子の平均粒径」は、電子顕微鏡像より調べられる電極触媒粒子（２０個）の粒子径の平均値により得ることができる。電子顕微鏡像による平均粒径算出時は、微粒子の形状が、球形以外の場合は、粒子における最大長を示す方向の長さをその粒径とする。 As the size of the electrode catalyst particles 3b increases, the effective surface area through which the electrochemical reaction proceeds increases, so that the electrochemical catalytic activity tends to increase. However, if the size is too small, the electrochemical reaction activity is reduced. Therefore, the size of the electrode catalyst particles 3b is 10 nm or less as an average particle diameter, preferably 0.5 nm to 5 nm.
The "average particle size of the electrode catalyst particles" in the present invention can be obtained from the average value of the particle sizes of the electrode catalyst particles (20 particles) examined from the electron microscope image. When calculating the average particle size from an electron microscope image, if the shape of the fine particles is other than spherical, the length in the direction indicating the maximum length of the particles is taken as the particle size.

電極触媒粒子の担持量は、触媒の種類、担体である電子伝導性酸化物の大きさ（厚み）等の条件を考慮して適宜決定される。触媒担持量が少なすぎると電極性能が不十分となり、多すぎると電極触媒粒子が凝集して性能が低下する場合がある。 The amount of the electrode catalyst particles supported is appropriately determined in consideration of conditions such as the type of catalyst and the size (thickness) of the electron conductive oxide as the carrier. If the amount of catalyst supported is too small, the electrode performance may be insufficient, and if it is too large, the electrode catalyst particles may aggregate and the performance may deteriorate.

電極触媒粒子の担持量は、水電解用電極材料の全重量に対して、好ましくは１〜６０質量％、より好ましくは１０〜５０質量％とすると、単位質量あたりの触媒活性に優れ、担持量に応じた所望の電極反応活性を得ることができる。
電極材料単位重量当たりの電極触媒粒子の担持量を増やすことによって、電極における電極触媒層の厚みを低減することができるため、電極全体としての水素や酸素などのガス拡散性や及び水（蒸気）の拡散性が向上する。 When the amount of the electrode catalyst particles carried is preferably 1 to 60% by mass, more preferably 10 to 50% by mass with respect to the total weight of the electrode material for water electrolysis, the catalytic activity per unit mass is excellent and the amount of the electrode catalyst particles carried is excellent. It is possible to obtain a desired electrode reaction activity according to the above.
By increasing the amount of electrode catalyst particles carried per unit weight of the electrode material, the thickness of the electrode catalyst layer on the electrode can be reduced, so that the electrode as a whole has gas diffusivity such as hydrogen and oxygen, and water (steam). Diffusivity is improved.

また、電極触媒粒子の担持量は、電子伝導性酸化物に対して、好ましくは１０〜５０質量％である。このような範囲であれば、単位質量あたりの触媒活性に優れ、担持量に応じた所望の電気化学的触媒活性を得ることができる。前記担持量が少なすぎる場合は、電極反応活性が不十分であり、多すぎる場合は電極触媒粒子の凝集が起こりやすく、有効表面積が低下するという問題がある。なお、電極触媒粒子の担持量は、例えば、誘導結合プラズマ発光分析（ＩＣＰ）によって調べることができる。 The amount of the electrode catalyst particles supported is preferably 10 to 50% by mass with respect to the electron conductive oxide. Within such a range, the catalytic activity per unit mass is excellent, and a desired electrochemical catalytic activity can be obtained according to the amount carried. If the amount supported is too small, the electrode reaction activity is insufficient, and if it is too large, the electrode catalyst particles are likely to aggregate, and the effective surface area is lowered. The amount of the electrode catalyst particles supported can be examined by, for example, inductively coupled plasma emission spectrometry (ICP).

＜２．水電解用電極材料の製造方法＞
上述した本発明の水電解用電極材料は、以下に説明する製造方法（以下、「本発明の製造方法」と称す。）によって好適に製造することができる。
すなわち、本発明の水電解用電極材料の製造方法は、以下の工程を含む。
（１）表面がグラファイト構造である繊維状炭素からなる導電補助材に、電子伝導性酸化物を担持する工程
（２）電子伝導性酸化物担体を担持した前記導電補助材を、酸化イリジウム前駆体を含む溶液に浸漬し、前記電子伝導性酸化物担体の表面上に酸化イリジウム前駆体を担持する工程
（３）電子伝導性酸化物担体に担持された酸化イリジウム前駆体を、酸化雰囲気下、３００℃以上５００℃以下で熱処理し、酸化イリジウムに変換する工程 <2. Manufacturing method of electrode material for water electrolysis>
The above-described electrode material for water electrolysis of the present invention can be suitably produced by the production method described below (hereinafter, referred to as "the production method of the present invention").
That is, the method for producing an electrode material for water electrolysis of the present invention includes the following steps.
(1) Step of supporting an electron conductive oxide on a conductive auxiliary material made of fibrous carbon having a graphite structure on the surface (2) The conductive auxiliary material supporting an electron conductive oxide carrier is a precursor of iridium oxide. Step of immersing the iridium oxide precursor on the surface of the electron conductive oxide carrier by immersing it in a solution containing (3) The iridium oxide precursor supported on the electron conductive oxide carrier is 300 in an oxidizing atmosphere. Step of heat treatment at ℃ or more and 500 ℃ or less to convert to iridium oxide

以下、本発明の製造方法における各工程を詳細に説明する。 Hereinafter, each step in the production method of the present invention will be described in detail.

「工程（１）」
工程（１）は、表面がグラファイト構造である繊維状炭素からなる導電補助材に、電子伝導性酸化物を担持する工程である。
導電補助材および電子伝導性酸化物は、＜１．本発明の燃料電池用電極材料＞で上述した通りであり、ここでは詳しい説明を省略する。本発明の製造方法の工程（１）は、電子伝導性酸化物として、特に酸化スズを主体とする電子伝導性酸化物を、表面がグラファイト構造である繊維状炭素に担持するのに適した方法である。酸化スズを主体とする電子伝導性酸化物については上述の通りであるため、説明を省略する。 "Process (1)"
The step (1) is a step of supporting an electron conductive oxide on a conductive auxiliary material made of fibrous carbon whose surface has a graphite structure.
The conductive auxiliary material and the electronically conductive oxide are <1. As described above in Electrode Material for Fuel Cell> of the present invention, detailed description thereof will be omitted here. The step (1) of the production method of the present invention is a method suitable for supporting an electron conductive oxide mainly composed of tin oxide on fibrous carbon having a graphite structure on the surface. Is. Since the electron conductive oxide mainly composed of tin oxide is as described above, the description thereof will be omitted.

導電補助材としては、表面がグラファイト構造である繊維状炭素が好ましい。導電補助材は、表面改質により表面の一部を酸化してもよい。このようにすることにより、電子伝導性酸化物の担持性が向上する可能性がある。導電補助材の表面改質の方法は特に制限はないが、０．５〜３０％水（水蒸気）を含む不活性ガス（例えば、Ｎ2）で２００〜４００℃の温度で処理する方法が挙げられる。 As the conductive auxiliary material, fibrous carbon having a graphite structure on the surface is preferable. A part of the surface of the conductive auxiliary material may be oxidized by surface modification. By doing so, the supportability of the electron conductive oxide may be improved. The method of surface modification of the conductive auxiliary material is not particularly limited, but a method of treating with an inert gas (for example, N 2 ) containing 0.5 to 30% water (water vapor) at a temperature of 200 to 400 ° C. is mentioned. Be done.

本発明の製造方法では、表面がグラファイト構造である繊維状炭素からなる導電補助材に電子伝導性酸化物を担持したのちに、酸化イリジウム前駆体（ＩｒＯ2前駆体）を担持させる。
すなわち、表面がグラファイト構造である繊維状炭素は、電子伝導性酸化物を担持することができるが、ＩｒＯ2前駆体が担持されにくいという性質を有する。
導電補助材に電子伝導性酸化物を担持した後に、電極触媒前駆体（ＩｒＯ2前駆体）を含む溶液に浸漬すると、電極触媒前駆体（ＩｒＯ2前駆体）が選択的に電子伝導性酸化物に担持され、これを所定の条件で熱処理することによりＩｒＯ2微粒子に変換される。そのため、本発明の製造方法によれば、大部分の電極触媒粒子（ＩｒＯ2微粒子）が選択的に電子伝導性酸化物に分散担持された水電解用電極材料を得ることができる。 In the production method of the present invention, an electron conductive oxide is supported on a conductive auxiliary material whose surface is made of fibrous carbon having a graphite structure, and then an iridium oxide precursor (IrO 2 precursor) is supported.
That is, the fibrous carbon having a graphite structure on the surface can support an electron conductive oxide, but has a property that it is difficult to support an IrO 2 precursor.
After carrying an electron conductive oxide to conductive auxiliary material, when immersed in a solution containing the electrode catalyst precursor (IrO 2 precursor), the electrode catalyst precursor (IrO 2 precursor) is selectively electronically conducting oxide It is supported on the surface and converted into IrO 2 fine particles by heat treatment under predetermined conditions. Therefore, according to the production method of the present invention, it is possible to obtain an electrode material for water electrolysis in which most of the electrode catalyst particles (IrO 2 fine particles) are selectively dispersed and supported on an electron conductive oxide.

電子伝導性酸化物を担持する方法としては、導電補助材に電子伝導性酸化物を担持できる方法であればいかなる方法も採用できる。その中でも以下に説明する電子伝導性酸化物の前駆体にアンモニアを直接反応させる「アンモニア沈殿法」や、尿素等のアンモニア発生化合物を分解して発生するアンモニアを反応させる「均一沈殿法」が好適である。
なお、均一沈殿法は詳しくは後述するように、アンモニア発生化合物の分解生成物としてのアンモニアを利用する点で、アンモニア沈殿法の一種でもあるが、本明細書においてはアンモニアそのものを直接利用する方法のみを「アンモニア沈殿法」と称し、アンモニア発生化合物を分解してアンモニアを生成する方法は除外して、両者を区別するものとする。 As a method for supporting the electron conductive oxide, any method can be adopted as long as it can support the electron conductive oxide on the conductive auxiliary material. Among them, the "ammonia precipitation method" in which ammonia is directly reacted with the precursor of the electron conductive oxide described below and the "uniform precipitation method" in which ammonia generated by decomposing an ammonia-generating compound such as urea is reacted are preferable. Is.
As will be described in detail later, the homogeneous precipitation method is also a kind of ammonia precipitation method in that ammonia is used as a decomposition product of an ammonia-generating compound, but in the present specification, the method of directly using ammonia itself. Only the method is referred to as the "ammonia precipitation method", and the method of decomposing an ammonia-generating compound to produce ammonia is excluded, and the two are distinguished from each other.

アンモニア沈殿法は、溶媒中で電子伝導性酸化物の前駆体とアンモニアとを直接反応させて生成する電子伝導性酸化物を導電補助材に担持する方法である。
この方法の利点として、アンモニア溶液を滴下しながら順次反応させ、アンモニア溶液の濃度や滴下スピードを変えることによって反応速度を制御できることが挙げられる。なお、アンモニア沈殿法における電子伝導性酸化物の前駆体としては、特に制限はなく、電子伝導性酸化物の構成金属元素（例えば、スズ）の硫酸塩、オキシ硝酸塩、オキシ硫酸塩、酢酸塩、塩化物、アンモニウム錯体、リン酸塩、カルボン酸塩などを使用することができる。電子伝導性酸化物が酸化スズの場合の好適な前駆体として、塩化スズ（水和物含む）が挙げられる。 The ammonia precipitation method is a method of supporting an electron conductive oxide produced by directly reacting a precursor of an electron conductive oxide with ammonia in a solvent on a conductive auxiliary material.
An advantage of this method is that the reaction rate can be controlled by sequentially reacting while dropping the ammonia solution and changing the concentration and dropping speed of the ammonia solution. The precursor of the electron conductive oxide in the ammonia precipitation method is not particularly limited, and the sulfate, oxynitrate, oxysulfate, acetate, etc. of the constituent metal elements (for example, tin) of the electron conductive oxide are not particularly limited. Chlorides, ammonium complexes, phosphates, carboxylates and the like can be used. A suitable precursor when the electron conductive oxide is tin oxide includes tin chloride (including hydrate).

溶媒としては電子伝導性酸化物の前駆体を溶解できる溶媒であればよく、例えば、水、メタノール、エタノール等の低級アルコールが挙げられる。
詳細な理由は現時点では完全に明らかではないが、溶媒として無水エタノールを使用すると、導電補助材に対する電子伝導性酸化物の担持量が増加するため好ましい。 The solvent may be any solvent that can dissolve the precursor of the electron conductive oxide, and examples thereof include lower alcohols such as water, methanol, and ethanol.
Although the detailed reason is not completely clear at this time, it is preferable to use absolute ethanol as a solvent because the amount of the electron conductive oxide supported on the conductive auxiliary material increases.

アンモニア沈殿法によって、導電補助材に担持された電子伝導性酸化物は、非晶質状態であるものを含むため、これを乾燥、焼成することで結晶性が高い電子伝導性酸化物を得ることができる。
乾燥方法は、特に制限がなく、加熱・減圧・自然乾燥などの方法で上述の水、エタノールなどの溶媒を蒸発させればよい。また、乾燥時の雰囲気は特に限定されるものではなく、酸素を含有する酸化性雰囲気中や大気雰囲気、窒素やアルゴンなどを含有する不活性雰囲気、水素を含有する還元性雰囲気などの雰囲気条件を任意に選ぶことができるが、通常、大気雰囲気である。 Since the electron conductive oxide supported on the conductive auxiliary material by the ammonia precipitation method includes one in an amorphous state, the electron conductive oxide having high crystallinity can be obtained by drying and firing the oxide. Can be done.
The drying method is not particularly limited, and the above-mentioned solvent such as water and ethanol may be evaporated by a method such as heating, depressurization, or natural drying. The atmosphere at the time of drying is not particularly limited, and atmospheric conditions such as an oxidizing atmosphere containing oxygen, an atmospheric atmosphere, an inert atmosphere containing nitrogen and argon, and a reducing atmosphere containing hydrogen can be used. It can be chosen arbitrarily, but it is usually an atmospheric atmosphere.

導電補助材の上にアンモニア沈殿法で形成して担持した電子伝導性酸化物を、酸素を含有する酸化性雰囲気（例えば、大気雰囲気下）で、３００〜８００℃、好適には、４００〜７００℃、特に好適には４５０〜６５０℃で熱処理することで、結晶性及び電子伝導性の高い電子伝導性酸化物を得ることができる。熱処理温度が低すぎる場合には、結晶性が低くなり、十分な電子伝導性が得られない場合があり、８００℃を超える場合には、電子伝導性酸化物が凝集し、表面積が小さくなりすぎる場合や、導電補助材から電子伝導性酸化物が脱離する場合がある。 An electron conductive oxide formed and supported on a conductive auxiliary material by an ammonia precipitation method is placed at 300 to 800 ° C., preferably 400 to 700 in an oxygen-containing oxidizing atmosphere (for example, in an atmospheric atmosphere). By heat treatment at ° C., particularly preferably 450 to 650 ° C., an electron conductive oxide having high crystallinity and electron conductivity can be obtained. If the heat treatment temperature is too low, the crystallinity will be low and sufficient electron conductivity may not be obtained, and if it exceeds 800 ° C., the electron conductive oxide will aggregate and the surface area will be too small. In some cases, the electron conductive oxide may be desorbed from the conductive auxiliary material.

なお、炭素材料は、酸化雰囲気において高温（例えば、５００℃）を超えると酸化（燃焼）するおそれがあるが、本発明で導電補助材として使用される、表面がグラファイト構造である繊維状炭素は高温耐久性が高い。そのため、上記温度範囲の中で実質的に燃焼せず、電子伝導性酸化物が脱離しない範囲で熱処理温度を決定すればよい。 The carbon material may be oxidized (combusted) when the temperature exceeds a high temperature (for example, 500 ° C.) in an oxidizing atmosphere. However, the fibrous carbon having a graphite structure on the surface, which is used as a conductive auxiliary material in the present invention, is used. High high temperature durability. Therefore, the heat treatment temperature may be determined within the above temperature range in which combustion does not occur substantially and the electron conductive oxide does not desorb.

また、均一沈殿法は、電子伝導性酸化物の前駆体と、アンモニア発生化合物を分解して発生するアンモニアとを反応させて生成する電子伝導性酸化物を導電補助材に担持する方法である。均一沈殿法では、溶液中において、分子レベルでアンモニア発生化合物からアンモニアが生成されることで一様に反応が起こるために、均質な電子伝導性酸化物の沈殿物が生成し、導電補助材に担持される。
アンモニア発生化合物としては均一沈殿法を行う温度において分解し、アンモニアを発生する化合物であればよく、溶媒が水の場合には、１００℃以下で分解する尿素や尿素誘導体が用いられる。 Further, the homogeneous precipitation method is a method of supporting an electron conductive oxide produced by reacting a precursor of an electron conductive oxide with ammonia generated by decomposing an ammonia generating compound on a conductive auxiliary material. In the uniform precipitation method, ammonia is generated from the ammonia-generating compound at the molecular level in the solution to cause a uniform reaction, so that a homogeneous electron-conducting oxide precipitate is formed and used as a conductive auxiliary material. Be carried.
The ammonia-generating compound may be a compound that decomposes at a temperature at which a homogeneous precipitation method is performed to generate ammonia, and when the solvent is water, urea or a urea derivative that decomposes at 100 ° C. or lower is used.

なお、均一沈殿法における電子伝導性酸化物の前駆体や溶媒は、アンモニア沈殿法と同様であるため、説明を省略する。なお、電子伝導性酸化物が酸化スズの場合の好適な前駆体として、塩化スズ（水和物含む）が挙げられる。 Since the precursor and solvent of the electron conductive oxide in the homogeneous precipitation method are the same as those in the ammonia precipitation method, the description thereof will be omitted. In addition, as a suitable precursor when the electron conductive oxide is tin oxide, tin chloride (including hydrate) can be mentioned.

均一沈殿法におけるアンモニア発生化合物を分解する方法としては、アンモニア発生化合物を含む溶液を、熱伝導を利用して直接加熱する方法（以下、均一沈殿法（加熱式）と記載する場合がある）でもよいが、より比表面積が大きい沈殿物（電子伝導性酸化物）を導電補助材に担持させることができる点で、以下に説明するマイクロ波加熱均一沈殿法が好適である。 As a method of decomposing the ammonia-generating compound in the homogeneous precipitation method, a method of directly heating the solution containing the ammonia-generating compound by utilizing heat conduction (hereinafter, may be referred to as a homogeneous precipitation method (heating type)) is also used. However, the microwave heating uniform precipitation method described below is preferable in that a precipitate (electron conductive oxide) having a larger specific surface area can be supported on the conductive auxiliary material.

マイクロ波加熱均一沈殿法は、電子伝導性酸化物の前駆体と、アンモニア発生化合物を分解して発生するアンモニアとを反応させて生成する電子伝導性酸化物を導電補助材に担持する均一沈殿法において、マイクロ波照射によって加熱を行って、当該溶液中のアンモニア発生化合物を分解する方法である。電子伝導性酸化物が酸化スズを主体とする場合、マイクロ波加熱均一沈殿法では、粒径１０ｎｍ以下（特には５ｎｍ以下）の粒状電子伝導性酸化物を製造することができる。また、製造条件によっては生成する電子伝導性酸化物を薄膜状とすることができ、薄膜状の電子伝導性酸化物が導電補助材の一部または全部を被覆するように担持された構造を製造することができる。 The microwave heating uniform precipitation method is a homogeneous precipitation method in which an electron conductive oxide produced by reacting a precursor of an electron conductive oxide with ammonia generated by decomposing an ammonia-generating compound is supported on a conductive auxiliary material. In this method, the ammonia-generating compound in the solution is decomposed by heating by microwave irradiation. When the electron conductive oxide is mainly tin oxide, a granular electron conductive oxide having a particle size of 10 nm or less (particularly 5 nm or less) can be produced by the microwave heating uniform precipitation method. Further, depending on the production conditions, the generated electron conductive oxide can be made into a thin film, and a structure in which the thin film electron conductive oxide is supported so as to cover a part or all of the conductive auxiliary material is manufactured. can do.

マイクロ波加熱均一沈殿法では、アンモニア沈殿法よりも表面積が大きく、粒径（薄膜の場合は膜厚）の小さい電子伝導性酸化物を得ることができることに利点の一つがある。そのため、表面積が大きいため、多量の電極触媒粒子を担持でき、かつ、粒径（薄膜の場合は膜厚）の小さいため、電子伝導性酸化物に起因する電気抵抗を低減できる。 One of the advantages of the microwave heating uniform precipitation method is that an electron conductive oxide having a larger surface area and a smaller particle size (thickness in the case of a thin film) can be obtained as compared with the ammonia precipitation method. Therefore, since the surface area is large, a large amount of electrode catalyst particles can be supported, and the particle size (thickness in the case of a thin film) is small, so that the electric resistance caused by the electron conductive oxide can be reduced.

マイクロ波加熱均一沈殿法においても、電子伝導性酸化物を導電補助材に担持したのちに熱処理を行うこともできる。熱処理を行う場合の条件はアンモニア沈殿法と同様の条件である。 Also in the microwave heating uniform precipitation method, heat treatment can be performed after supporting the electron conductive oxide on the conductive auxiliary material. The conditions for performing the heat treatment are the same as those for the ammonia precipitation method.

また、マイクロ波加熱均一沈殿法は、マイクロ波照射によって、溶液中での導電補助材の分散性を高めることができる点でも好適である。 Further, the microwave heating uniform precipitation method is also suitable in that the dispersibility of the conductive auxiliary material in the solution can be enhanced by microwave irradiation.

溶媒としては電子伝導性酸化物の前駆体を溶解できる溶媒であればよく、例えば、水、メタノール、エタノール等の低級アルコールが挙げられる。 The solvent may be any solvent that can dissolve the precursor of the electron conductive oxide, and examples thereof include lower alcohols such as water, methanol, and ethanol.

マイクロ波加熱均一沈殿法の例を、電子伝導性酸化物が酸化スズである場合で具体的に説明すると、例えば、塩化スズ（ＳｎＣｌ4・５Ｈ2Ｏ）等の酸化スズ前駆体と、アンモニア発生化合物である尿素を含む溶液に導電補助材を添加し、マイクロ波照射した状態で目的の温度まで加熱し、その後所定の時間保持することによって、溶液中で尿素が分解されて発生するアンモニアによって酸化スズ前駆体から酸化スズ粒子が生成し、導電補助材に均一に分散担持される。
マイクロ波照射の強度は、溶液の量、アンモニア発生化合物の分解性や導電補助材の分散性等を考慮して適宜決定される。反応温度は、電子伝導性酸化物の種類、アンモニア発生化合物の分解性等の諸条件を考慮して決定されるが、均一な品質の電子伝導性酸化物が形成される点で９０〜１００℃が好ましい。 An example of the microwave heating homogeneous precipitation method, the electron conducting oxide is specifically described the case of tin oxide, e.g., a tin oxide precursor, such as tin chloride (SnCl 4 · 5H 2 O) , ammonia-generating By adding a conductive auxiliary material to a solution containing urea, which is a compound, heating it to a target temperature in a microwave-irradiated state, and then holding it for a predetermined time, urea is decomposed in the solution and oxidized by ammonia generated. Tin oxide particles are generated from the tin precursor and are uniformly dispersed and supported on the conductive auxiliary material.
The intensity of microwave irradiation is appropriately determined in consideration of the amount of the solution, the decomposability of the ammonia-generating compound, the dispersibility of the conductive auxiliary material, and the like. The reaction temperature is determined in consideration of various conditions such as the type of the electron conductive oxide and the decomposability of the ammonia-generating compound, but is 90 to 100 ° C. in that an electron conductive oxide of uniform quality is formed. Is preferable.

「工程（２）」
工程（２）は、電子伝導性酸化物担体を担持した前記導電補助材を、酸化イリジウム前駆体を含む溶液に浸漬し、前記電子伝導性酸化物担体の表面上に酸化イリジウム前駆体を担持する工程である。 "Process (2)"
In the step (2), the conductive auxiliary material carrying the electron conductive oxide carrier is immersed in a solution containing the iridium oxide precursor, and the iridium oxide precursor is supported on the surface of the electron conductive oxide carrier. It is a process.

酸化イリジウム粒子は、高活性を保ったまま高分散担持することが技術的に難しく、これまでに有効に１０ｎｍ以下（特には５ｎｍ以下）の微粒子を担持することができなかった。
本発明の製造方法の特徴のひとつは、工程（２）において、表面がグラファイト構造である繊維状炭素からなる導電補助材に担持された電子伝導性酸化物担体に対し、酸化イリジウム前駆体を選択的に担持するに当たり、酸化イリジウム前駆体を含む溶液に浸漬し、溶媒を留去する、いわゆる蒸発乾固法が適していることを見出したことにある。 It is technically difficult for the iridium oxide particles to be highly dispersed and supported while maintaining high activity, and so far it has not been possible to effectively support fine particles of 10 nm or less (particularly 5 nm or less).
One of the features of the production method of the present invention is that in step (2), an iridium oxide precursor is selected for an electron conductive oxide carrier supported on a conductive auxiliary material whose surface is made of fibrous carbon having a graphite structure. It has been found that the so-called evaporation-drying method, in which the solvent is distilled off by immersing the material in a solution containing an iridium oxide precursor, is suitable for carrying the material.

また、本発明者が特許文献２で報告した、Ｐｔ系貴金属触媒前駆体の担持方法である、貴金属アセチルアセトナート法も、酸化イリジウム前駆体の電子伝導性酸化物担体の表面上への担持方法に成り得る。 Further, the noble metal acetylacetonate method, which is a method for supporting a Pt-based noble metal catalyst precursor reported by the present inventor in Patent Document 2, is also a method for supporting an electron conductive oxide carrier of an iridium oxide precursor on the surface. Can be.

以下、蒸発乾固法の場合について説明する。
酸化イリジウム前駆体として、Ｉｒを含む無機化合物、有機化合物が選択できるが、好適な一例は、塩化イリジウム酸（Ｈ2ＩｒＣｌ6・nＨ2Ｏ）である。 Hereinafter, the case of the evaporation-drying method will be described.
As the iridium oxide precursor, an inorganic compound containing Ir or an organic compound can be selected, and a preferable example is iridium chloride (H 2 IrCl 6 · nH 2 O).

工程（２）における蒸発乾固法による、酸化イリジウム前駆体を例示すると、まず、酸化イリジウム前駆体を含む溶液を、溶媒の蒸発後に、目的とする酸化イリジウム担持量となる濃度に調整する。
次いで、この溶液に、工程（１）で得た所定量の電子伝導性酸化物を担持した導電補助材を、撹拌及び溶媒の留去を行うことにより、電極触媒前駆体（ＩｒＯ2前駆体）の担持が行う。
この方法であれば、複雑な化学反応を伴わずとも、酸化イリジウム前駆体を、電子伝導性酸化物に高分散に担持することができる。また、溶液中に強い酸化剤や還元剤を用いることがないため、電子伝導性酸化物や炭素系の導電補助材が劣化することを回避できるという利点がある。 To exemplify the iridium oxide precursor by the evaporation to dryness method in the step (2), first, the solution containing the iridium oxide precursor is adjusted to a concentration that becomes the target iridium oxide carrying amount after the solvent is evaporated.
Next, the electrode catalyst precursor (IrO 2 precursor) was prepared by stirring and distilling off the solvent of the conductive auxiliary material carrying a predetermined amount of the electron conductive oxide obtained in the step (1) in this solution. Is carried.
With this method, the iridium oxide precursor can be supported on the electron conductive oxide in a highly dispersed manner without involving a complicated chemical reaction. Further, since a strong oxidizing agent or reducing agent is not used in the solution, there is an advantage that deterioration of the electron conductive oxide or the carbon-based conductive auxiliary material can be avoided.

また、蒸発乾固法では、水溶媒を使用することができることも利点の一つである。溶媒に水を使用しているため、酸化イリジウム前駆体が、疎水性である表面がグラファイトの炭素材料へは特に担持されづらいため、電子伝導性酸化物の表面に選択的に担持されやすい。 Another advantage of the evaporation-drying method is that an aqueous solvent can be used. Since water is used as the solvent, the iridium oxide precursor is likely to be selectively supported on the surface of the electron conductive oxide because the hydrophobic surface is particularly difficult to be supported on the carbon material of graphite.

なお、水溶媒には、蒸発速度を制御するなどの目的で、他の溶媒（エタノール等）を含んでいてもよい。 The aqueous solvent may contain another solvent (ethanol or the like) for the purpose of controlling the evaporation rate.

「工程（３）」
工程（３）は、工程（２）において、電子伝導性酸化物担体に担持された酸化イリジウム前駆体を、酸化雰囲気下、３００℃以上５００℃以下で熱処理し、酸化イリジウムに変換する工程である。工程（２）において、電子伝導性酸化物に担持された酸化イリジウム前駆体は、そのままでは活性が低いため、酸化雰囲気下で熱処理することで酸化イリジウムに変換して活性化する。
本発明の製造方法の特徴のひとつは、工程（３）において、熱処理条件を、酸化雰囲気下、３００℃以上５００℃以下の温度範囲と規定することで、導電補助材や電子伝導性酸化物担体を劣化させることなく、酸化イリジウム本来の優れた電気化学的触媒活性を有する酸化イリジウム微粒子とすることができることにある。このような特定の担持方法、活性化方法を経る製造方法により、ＩｒＯ2微粒子は、平均粒子径１０ｎｍ以下の微粒子となり、高い触媒活性を有するため、担持量が少なくとも、優れた電極触媒となる。 "Process (3)"
The step (3) is a step of heat-treating the iridium oxide precursor supported on the electron-conductive oxide carrier at 300 ° C. or higher and 500 ° C. or lower in an oxidizing atmosphere to convert it into iridium oxide. .. In the step (2), since the iridium oxide precursor supported on the electron conductive oxide has low activity as it is, it is converted to iridium oxide and activated by heat treatment in an oxidizing atmosphere.
One of the features of the production method of the present invention is that in the step (3), the heat treatment conditions are defined as a temperature range of 300 ° C. or higher and 500 ° C. or lower in an oxidizing atmosphere, whereby a conductive auxiliary material or an electron conductive oxide carrier is used. It is possible to obtain iridium oxide fine particles having the original excellent electrochemical catalytic activity of iridium oxide without deteriorating. By the production method through such a specific supporting method and activation method, the IrO 2 fine particles become fine particles having an average particle diameter of 10 nm or less and have high catalytic activity, so that the carrying amount is at least an excellent electrode catalyst.

熱処理条件は、電子伝導性酸化物や、前駆体の種類にもよっても変わり得るが、高活性なＩｒＯ2微粒子が得られ、かつ、電子伝導性酸化物や炭素系導電補助材への影響がない条件として、酸化雰囲気下、３００℃以上５００℃以下（好適には４００℃以上４５０℃以下）の温度範囲である。温度が低すぎると高活性なＩｒＯ2微粒子が得られず、高すぎるとＩｒＯ2微粒子が凝集し、有効反応表面積が小さかったり、炭素系導電補助材が酸化（燃焼）分解するおそれがある。
なお、酸化雰囲気は、通常、大気雰囲気であるが、酸素のみ、酸素と不活性ガスの混合ガスを用いてもよい。雰囲気には必要に応じて水蒸気を加えてもよく、また、不活性ガスと水蒸気の混合ガスも酸化雰囲気となる。 The heat treatment conditions may vary depending on the type of electron conductive oxide and precursor, but highly active IrO 2 fine particles can be obtained, and the effect on the electron conductive oxide and carbon-based conductive auxiliary material is affected. As a condition, the temperature range is 300 ° C. or higher and 500 ° C. or lower (preferably 400 ° C. or higher and 450 ° C. or lower) under an oxidizing atmosphere. If the temperature is too low, highly active IrO 2 fine particles cannot be obtained, and if the temperature is too high, IrO 2 fine particles may aggregate, the effective reaction surface area may be small, or the carbon-based conductive auxiliary material may be oxidized (combusted) and decomposed.
The oxidizing atmosphere is usually an atmospheric atmosphere, but only oxygen or a mixed gas of oxygen and an inert gas may be used. Water vapor may be added to the atmosphere as needed, and the mixed gas of the inert gas and water vapor also becomes an oxidizing atmosphere.

＜３．水電解用電極＞
本発明の水電解用電極は、上述の水電解用電極材料とプロトン伝導性電解質材料とを含むことを特徴とする。当該水電解用電極では、前記炭素系導電補助材が互いに接触して導電パスを形成する。 <3. Electrode for water electrolysis ＞
The electrode for water electrolysis of the present invention is characterized by containing the above-mentioned electrode material for water electrolysis and a proton conductive electrolyte material. In the water electrolysis electrode, the carbon-based conductive auxiliary materials come into contact with each other to form a conductive path.

このような構成であれば、上述した本発明の電極材料を構成する導電補助材が、長径で優れた電子伝導性を有する繊維状炭素であるため、水電解用電極全体として、電子伝導性に優れる。さらに、長径の導電補助材の隙間は、少なくとも通気性を発現する程度に空隙を作ることができるため、水素、酸素、水蒸気等の電極反応に関与するガスの拡散性に優れると共に、プロトン伝導性電解質材料を十分に保持できる。そのため、当該電極材料で形成された水電解用電極は、優れた電極性能を示すと共に、耐久性が高く、長期間水の電気分解を行うことができる。 With such a configuration, since the conductive auxiliary material constituting the electrode material of the present invention described above is fibrous carbon having a long diameter and excellent electron conductivity, the entire electrode for water electrolysis has an electron conductivity. Excellent. Further, since the gaps between the long-diameter conductive auxiliary materials can be formed at least to the extent that air permeability is exhibited, the diffusivity of gases involved in the electrode reaction such as hydrogen, oxygen, and water vapor is excellent, and the proton conductivity is excellent. Sufficient retention of electrolyte material. Therefore, the electrode for water electrolysis formed of the electrode material exhibits excellent electrode performance, has high durability, and can electrolyze water for a long period of time.

以下に、本発明の水電解用電極材料を用いて形成した水電解用電極について説明する。 The water electrolysis electrode formed by using the water electrolysis electrode material of the present invention will be described below.

本発明の水電解用電極は、上述の水電解用電極材料のみから構成されていてもよいが、通常、水電解の電解質に使用されるプロトン伝導性電解質材料（以下、「プロトン伝導性電解質材料」、または単に「電解質材料」と記載する場合がある。）を含む。水電解用電極材料と共に電極に含まれる電解質材料は、水電解用電解質膜に使用される電解質材料と同じであってもよく、異なってもよい。水電解用電極と電解質膜の密着性を向上させる観点から、同じものを用いることが好ましい。 The electrode for water electrolysis of the present invention may be composed of only the above-mentioned electrode material for water electrolysis, but is usually a proton conductive electrolyte material used as an electrolyte for water electrolysis (hereinafter, "proton conductive electrolyte material"). , Or simply referred to as "electrolyte material"). The electrolyte material contained in the electrode together with the electrode material for water electrolysis may be the same as or different from the electrolyte material used for the electrolyte membrane for water electrolysis. From the viewpoint of improving the adhesion between the water electrolysis electrode and the electrolyte membrane, it is preferable to use the same one.

水電解用電極と電解質膜とに使用される電解質材料としては、プロトン伝導性電解質材料が挙げられる。このプロトン伝導性電解質材料は、ポリマー骨格の全部または一部にフッ素原子を含むフッ素系電解質材料と、ポリマー骨格にフッ素原子を含まない炭化水素系電解質材料に大別され、この両者を電解質材料として使用することができる。 Examples of the electrolyte material used for the electrode for water electrolysis and the electrolyte membrane include a proton conductive electrolyte material. This proton conductive electrolyte material is roughly classified into a fluorine-based electrolyte material in which all or part of the polymer skeleton contains fluorine atoms and a hydrocarbon-based electrolyte material in which the polymer skeleton does not contain fluorine atoms, and both of them are used as electrolyte materials. Can be used.

フッ素系電解質材料としては、具体的には、ナフィオン（登録商標、デュポン社製）、アシプレックス（登録商標、旭化成株式会社製）、フレミオン（登録商標、旭硝子株式会社製）などが好適な一例として挙げられる。 Specific preferred examples of the fluorine-based electrolyte material include Nafion (registered trademark, manufactured by DuPont), Aciplex (registered trademark, manufactured by Asahi Kasei Corporation), and Flemion (registered trademark, manufactured by Asahi Glass Co., Ltd.). Can be mentioned.

炭化水素系電解質材料としては、具体的には、ポリスルホン酸、ポリスチレンスルホン酸、ポリアリールエーテルケトンスルホン酸、ポリフェニルスルホン酸、ポリベンズイミダゾールスルホン酸、ポリベンズイミダゾールホスホン酸、ポリイミドスルホン酸等のポリマーや、これらにアルキル基等の側鎖を有するポリマーが好適な一例として挙げられる。 Specific examples of the hydrocarbon-based electrolyte material include polymers such as polysulfonic acid, polystyrene sulfonic acid, polyarylether ketone sulfonic acid, polyphenylsulfonic acid, polybenzimidazole sulfonic acid, polybenzimidazole phosphonic acid, and polyimide sulfonic acid. Alternatively, polymers having side chains such as alkyl groups are preferred examples.

上記水電解用電極材料と水電解用電極材料と混合する電解質材料との質量比は、これらの材料を用いて形成される電極内の良好なプロトン伝導性を付与し、かつ電極内のガス拡散及び水蒸気の排出をスムーズに行えるように適宜決定すればよい。ただし、水電解用電極材料に混合する電解質材料の量が多すぎるとプロトン伝導性はよくなるが、ガスの拡散性は低下する。逆に混合する電解質材料の量が少なすぎるとガス拡散性はよくなるが、プロトン伝導性は低下する。そのため、上記水電解用電極材料に対する電解質材料の質量比率は、１０〜５０質量％が好適な範囲である。この質量比率が１０質量％より小さい場合は、プロトン伝導性を有する材料の連続性が悪くなり、水電解用電極として十分なプロトン伝導性が確保できない。逆に５０質量％より大きい場合は水電解用電極材料の連続性が悪くなり、水電解用電極として十分な電子伝導性を有することができなくなる場合がある。さらには電極内部でのガス（酸素、水素、水蒸気）や水の拡散性が低下する場合がある。 The mass ratio of the electrode material for water electrolysis to the electrolyte material mixed with the electrode material for water electrolysis imparts good proton conductivity in the electrode formed by using these materials, and gas diffusion in the electrode. And, it may be decided appropriately so that the discharge of water vapor can be carried out smoothly. However, if the amount of the electrolyte material mixed with the electrode material for water electrolysis is too large, the proton conductivity is improved, but the diffusivity of the gas is lowered. On the contrary, if the amount of the electrolyte material to be mixed is too small, the gas diffusivity is improved, but the proton conductivity is lowered. Therefore, the mass ratio of the electrolyte material to the electrode material for water electrolysis is preferably in the range of 10 to 50% by mass. If this mass ratio is less than 10% by mass, the continuity of the material having proton conductivity is deteriorated, and sufficient proton conductivity cannot be secured as an electrode for water electrolysis. On the contrary, if it is larger than 50% by mass, the continuity of the electrode material for water electrolysis is deteriorated, and it may not be possible to have sufficient electron conductivity as the electrode for water electrolysis. Furthermore, the diffusivity of gas (oxygen, hydrogen, water vapor) and water inside the electrode may decrease.

本発明の水電解用電極は、本発明の目的を損なわない範囲で、上述の水電解用電極材料やプロトン伝導性材料以外の成分を含んでいてもよい。 The electrode for water electrolysis of the present invention may contain components other than the above-mentioned electrode material for water electrolysis and the proton conductive material as long as the object of the present invention is not impaired.

＜４．膜電極接合体（ＭＥＡ）＞
本発明の膜電極接合体は、固体高分子電解質膜と、前記固体高分子電解質膜の一方面に接合されたカソードと、前記固体高分子電解質膜の他方面に接合されたアノードと、を有する膜電極接合体であって、前記アノードが、上記本発明の水電解用電極であることを特徴とする。 <4. Membrane electrode assembly (MEA)>
The membrane electrode assembly of the present invention has a solid polymer electrolyte membrane, a cathode bonded to one surface of the solid polymer electrolyte membrane, and an anode bonded to the other surface of the solid polymer electrolyte membrane. It is a membrane electrode assembly, and the anode is the electrode for water electrolysis of the present invention.

本発明の好適な実施形態として、電子伝導性酸化物に酸化スズを主体とする酸化物を用いた電極材料を含む水電解用電極を本発明の水電解用電極をアノードに使用した膜電極接合体について説明する。
図３は本発明の実施形態に係る膜電極接合体の断面構造を模式的に示したものである。図３に示すように膜電極接合体１０は、カソード４及びアノード５が固体高分子電解質膜６に対面して配置された構造を有する。 As a preferred embodiment of the present invention, a membrane electrode assembly using an electrode for water electrolysis containing an electrode material containing an oxide mainly composed of tin oxide as an electron conductive oxide and the electrode for water electrolysis of the present invention as an anode. Explain the body.
FIG. 3 schematically shows the cross-sectional structure of the membrane electrode assembly according to the embodiment of the present invention. As shown in FIG. 3, the membrane electrode assembly 10 has a structure in which the cathode 4 and the anode 5 are arranged so as to face the solid polymer electrolyte membrane 6.

カソード４は、電極触媒層４ａとガス拡散層４ｂで構成され、その構成に特に制限はなく、それぞれ水電解用セルのカソードとして従来公知の電極触媒層、ガス拡散層を使用することができる。 The cathode 4 is composed of an electrode catalyst layer 4a and a gas diffusion layer 4b, and the configuration thereof is not particularly limited, and conventionally known electrode catalyst layers and gas diffusion layers can be used as the cathode of the water electrolysis cell, respectively.

アノード５は、電極触媒層５ａとガス拡散層５ｂで構成され、電極触媒層５ａは、上述の通り、本発明の水電解用電極（電子伝導性酸化物：酸化スズを主体とする酸化物）を用いているため、詳細な説明は省略する。
アノード５のガス拡散層５ｂは、カソード４で説明したガス拡散層４ｂと同様に、水電解用セルの従来公知のガス拡散層が使用できる。 The anode 5 is composed of an electrode catalyst layer 5a and a gas diffusion layer 5b, and the electrode catalyst layer 5a is the electrode for water electrolysis of the present invention (electron conductive oxide: an oxide mainly composed of tin oxide) as described above. Since the above is used, detailed description thereof will be omitted.
As the gas diffusion layer 5b of the anode 5, a conventionally known gas diffusion layer of a water electrolysis cell can be used in the same manner as the gas diffusion layer 4b described in the cathode 4.

固体高分子電解質膜６としては、プロトン伝導性を有し、化学的安定性及び熱的安定性を有するものであれば公知の固体高分子形水電解セル用電解質膜を用いればよい。なお、図３では厚みを強調して図示しているが、電気抵抗を低くするため固体高分子電解質膜６の厚みは破損が発生しない程度で薄膜であることが好ましい。 As the solid polymer electrolyte membrane 6, a known electrolyte membrane for a solid polymer electrolyte cell may be used as long as it has proton conductivity, chemical stability and thermal stability. Although the thickness is emphasized in FIG. 3, the thickness of the solid polymer electrolyte membrane 6 is preferably a thin film so as not to cause damage in order to reduce the electric resistance.

固体高分子電解質膜６を構成する電解質材料としては、水電解用セルの運転条件で分解が起こらないものを使用すればよく、水電解用セルの電解質材料として従来公知の材料が使用され、例えば、フッ素系電解質材料、炭化水素系電解質材料が挙げられる。特にフッ素系電解質材料で形成されている電解質膜が、耐熱性、化学的安定性などに優れているため好ましい。具体的には、ナフィオン（登録商標、デュポン社製）、アシプレックス（登録商標、旭化成株式会社製）、フレミオン（登録商標、旭硝子株式会社製）などが好適例として挙げられる。
炭化水素系高分子電解質材料としては、例えば、ポリスルホン酸、ポリスチレンスルホン酸、ポリアリールエーテルケトンスルホン酸、ポリフェニルスルホン酸、ポリベンズイミダゾールスルホン酸、ポリベンズイミダゾールホスホン酸、ポリイミドスルホン酸等のポリマーや、これらにアルキル基等の側鎖を有するポリマー等が挙げられる。また、電解質膜として、無機系プロトン伝導体であるリン酸塩、硫酸塩などからなる電解質膜を使用することもできる。 As the electrolyte material constituting the solid polymer electrolyte membrane 6, a material that does not decompose under the operating conditions of the water electrolysis cell may be used, and a conventionally known material is used as the electrolyte material of the water electrolysis cell, for example. , Fluorine-based electrolyte material, and hydrocarbon-based electrolyte material. In particular, an electrolyte membrane formed of a fluorine-based electrolyte material is preferable because it is excellent in heat resistance, chemical stability, and the like. Specific examples thereof include Nafion (registered trademark, manufactured by DuPont), Aciplex (registered trademark, manufactured by Asahi Kasei Corporation), Flemion (registered trademark, manufactured by Asahi Glass Co., Ltd.) and the like.
Examples of the hydrocarbon-based polymer electrolyte material include polymers such as polysulfonic acid, polystyrene sulfonic acid, polyarylether ketone sulfonic acid, polyphenylsulfonic acid, polybenzimidazole sulfonic acid, polybenzimidazole phosphonic acid, and polyimide sulfonic acid. , Polymers having side chains such as alkyl groups, and the like. Further, as the electrolyte membrane, an electrolyte membrane made of an inorganic proton conductor such as phosphate or sulfate can also be used.

以上、図面を参照して本発明のＭＥＡの実施形態について述べたが、これらは本発明のＭＥＡの例示であり、アノードとして本発明の水電解用電極を採用する限り、上記以外の様々な構成を採用することもできる。 The embodiments of the MEA of the present invention have been described above with reference to the drawings. These are examples of the MEA of the present invention, and various configurations other than the above are provided as long as the electrode for water electrolysis of the present invention is adopted as the anode. Can also be adopted.

以下に実施例を挙げて本発明をより具体的に説明するが、本発明はこれらに限定されるものではない。 Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited thereto.

使用した原料化合物、導電補助材は以下の通りである。
（Ｓｎ前駆体）
塩化スズ水和物（ＳｎＣｌ2・２Ｈ2Ｏ）（キシダ化学株式会社）
（Ｎｂ前駆体）
塩化ニオブ（ＮｂＣｌ5）（三津和化学薬品株式会社）
（Ｉｒ前駆体）
塩化イリジウム酸（Ｈ2ＩｒＣｌ6・nＨ2Ｏ）（和光純薬工業株式会社）
（導電補助材）
以下の物性を有する繊維状炭素（昭和電工株式会社製、気相法炭素繊維、ＶＧＣＦ−Ｈ（登録商標））を使用した。
繊維径：１５０ｎｍ
真密度：２．１ｇ/ｃｍ3
比表面積：１１．４ｍ2/ｇ
熱伝導率：１２００Ｗ/（ｍ・Ｋ）
導電率：１×１０-4Ωｃｍ
The raw material compounds and conductive auxiliary materials used are as follows.
(Sn precursor)
Tin chloride hydrate (SnCl 2 · 2H 2 O) ( Kishida Chemical Co., Ltd.)
(Nb precursor)
Niobium Chloride (NbCl 5 ) (Mitsuwa Chemical Co., Ltd.)
(Ir precursor)
Iridium Chloride (H 2 IrCl 6・ nH 2 O) (Wako Pure Chemical Industries, Ltd.)
(Conductive auxiliary material)
Fibrous carbon having the following physical properties (manufactured by Showa Denko KK, vapor phase carbon fiber, VGCF-H (registered trademark)) was used.
Fiber diameter: 150 nm
True density: 2.1 g / cm 3
Specific surface area: 11.4m 2 / g
Thermal conductivity: 1200 W / (m · K)
Conductivity: 1 x 10 -4 Ωcm

１．電極触媒材料の製造
＜実施例１＞
工程（１）
工程（１−１）：ニオブドープ酸化スズ担持繊維状炭素の製造
実施例１においては、アンモニア沈殿法でニオブドープ酸化スズ（Ｎｂ-ＳｎＯ2）粒子を担持した繊維状炭素を製造した。
まず、上記繊維状炭素（０．２５１９ｇ）に超純水を加え、超音波ホモジナイザーで攪拌し、繊維状炭素の分散液を得た。この分散液に塩化スズ水和物（ＳｎＣｌ2・２Ｈ2Ｏ）（０．７６９８ｇ）を入れ、さらに塩化ニオブ（ＮｂＣｌ5）を、Ｓｎ：Ｎｂ＝９８：２（ｍｏｌ比）の割合で添加し、ホットスターラーで５０℃に保持して、攪拌しながらアンモニア水（ＮＨ3２８重量％）をビュレットで滴下した（５ｃｃ/分）。アンモニア水の滴下後、１時間攪拌を続けたのちに、分散液の濾過、洗浄を行い、１００℃で１０時間乾燥させた。乾燥後大気雰囲気下、６００℃で２時間の熱処理を行い、実施例１の酸化スズ粒子を担持した繊維状炭素を得た。
また、熱分析装置（株式会社リガク製、ThermoPlus TG8120）を用いて、酸化スズ粒子を担持した繊維状炭素を、大気雰囲気下で８００℃まで昇温し、昇温前後の質量差を重量減少分を燃焼した繊維状炭素の重量として、酸化スズ粒子の担持率を求めたところ、７５重量％であった。 1. 1. Production of Electrode Catalyst Material <Example 1>
Process (1)
Step (1-1): Production of Niobope Tin Oxide-Supported Fibrous Carbon In Example 1, fibrous carbon supporting niob-doped tin oxide (Nb-SnO 2 ) particles was produced by an ammonia precipitation method.
First, ultrapure water was added to the fibrous carbon (0.2519 g) and stirred with an ultrasonic homogenizer to obtain a dispersion of fibrous carbon. This dispersion was charged with tin chloride hydrate (SnCl 2 · 2H 2 O) (0.7698g), further of niobium chloride (NbCl 5), Sn: Nb = 98: was added at a ratio of 2 (mol ratio) , The temperature was maintained at 50 ° C. with a hot stirrer, and aqueous ammonia (NH 3 28% by weight) was added dropwise with a burette while stirring (5 cc / min). After dropping the ammonia water, stirring was continued for 1 hour, then the dispersion was filtered and washed, and dried at 100 ° C. for 10 hours. After drying, heat treatment was performed at 600 ° C. for 2 hours in an air atmosphere to obtain fibrous carbon carrying tin oxide particles of Example 1.
In addition, using a thermal analyzer (ThermoPlus TG8120, manufactured by Rigaku Co., Ltd.), the fibrous carbon carrying tin oxide particles was heated to 800 ° C. in an air atmosphere, and the mass difference before and after the temperature increase was reduced by weight. The supported ratio of tin oxide particles was determined as the weight of the fibrous carbon burned in, and it was 75% by mass.

工程（１−２）：蒸発乾固法によるＩｒＯ2前駆体の担持
工程（１）で得られた、酸化スズ粒子を担持した繊維状炭素（以下、「担体粉末」と記載する場合がある）に、蒸発乾固法により、電極触媒粒子であるＩｒＯ2前駆体を担持した。蒸発乾固法は、蒸発皿に所定量の担体粉末、純水、ＩｒＯ2前駆体（Ｈ2ＩｒＣｌ6・nＨ2Ｏ）を加え、それを撹拌しながら液体が蒸発するまで加熱することにより、担体粉末にＩｒＯ2前駆体を担持した。 Step (1-2): Supporting IrO 2 precursor by evaporation dry method Fibrous carbon carrying tin oxide particles obtained in step (1) (hereinafter, may be referred to as “carrier powder”). The IrO 2 precursor, which is an electrode catalyst particle, was supported on the surface by the evaporation dry method. In the evaporation-drying method, a predetermined amount of carrier powder, pure water, and IrO 2 precursor (H 2 IrCl 6 · nH 2 O) are added to an evaporating dish, and the mixture is heated while stirring until the liquid evaporates. The IrO 2 precursor was supported on the carrier powder.

工程（２）
工程（１−２）で得られた粉末を、Ａｉｒ雰囲気中で４４０℃、１時間保持（昇温速度：２℃/分）の条件で熱処理を施すことで、実施例１の電極材料（IrO2/Nb-SnO2/VGCF）を得た。なお、実施例１の電極材料のＩｒＯ2担持量は２３ｗｔ％であった。ＩｒＯ2担持量は、ＴＧ−ＤＴＡから求めた繊維状炭素の燃焼前後の重量変化、及びニオブドープ酸化スズと繊維状炭素の重量比（仕込み）から算出した値である。 Process (2)
The electrode material (IrO) of Example 1 was obtained by heat-treating the powder obtained in the step (1-2) under the conditions of holding at 440 ° C. for 1 hour (heating rate: 2 ° C./min) in an Air atmosphere. 2 / Nb-SnO 2 / VGCF) was obtained. The amount of IrO 2 supported on the electrode material of Example 1 was 23 wt%. The IrO 2 supported amount is a value calculated from the weight change of fibrous carbon before and after combustion obtained from TG-DTA and the weight ratio (preparation) of niobium-doped tin oxide to fibrous carbon.

＜参考例１＞
工程（２）において、熱処理条件を、５％Ｈ2-Ｎ2雰囲気中で１５０℃、１時間とした以外は、実施例１と同様にして、参考例１の電極材料（Ir/Nb-SnO2/VGCF）を得た。 <Reference example 1>
In step (2), heat treatment conditions, 0.99 ° C. in 5% H 2 -N 2 atmosphere, except for using 1 hour, in the same manner as in Example 1, Reference Example 1 of an electrode material (Ir / Nb-SnO 2 / VGCF) was obtained.

２．評価
２−１：ＸＲＤによる評価
実施例１及び参考例１の電極触媒材料をＸ線回折法にて評価した。
図４に示すように実施例１の電極触媒材料では、ＳｎやＳｎＯのシグナルは確認されず、ＳｎＯ2のシグナルのみが確認された。また、実施例１におけるＳｎＯ2は、純粋なＳｎＯ2と比較してシグナルがシフトしていることから、Ｎｂがドープされていることが確認された。一方、ＩｒＯ2についてはＸＲＤでは明確なシグナルは確認されなかった。
一方、図５に示すように参考例１の電極触媒材料では、ＳｎＯ2と共にＳｎＯのシグナルが確認された。また、Ｉｒについては、Ｉｒのシグナルのみが確認された。 2. Evaluation 2-1: Evaluation by XRD The electrode catalyst materials of Example 1 and Reference Example 1 were evaluated by X-ray diffraction.
As shown in FIG. 4, in the electrode catalyst material of Example 1, no Sn or SnO signal was confirmed, but only the SnO 2 signal was confirmed. Further, since the signal of SnO 2 in Example 1 was shifted as compared with that of pure SnO 2 , it was confirmed that Nb was doped. On the other hand, no clear signal was confirmed by XRD for IrO 2 .
On the other hand, as shown in FIG. 5, in the electrode catalyst material of Reference Example 1, a SnO signal was confirmed together with SnO 2 . Regarding Ir, only the signal of Ir was confirmed.

２−２：電子顕微鏡による評価
（１）走査型電子顕微鏡（ＦＥ−ＳＥＭ）による評価
実施例１及び参考例１の電極触媒材料の微細構造観察を行った。図６（ａ）に実施例１の電極触媒材料、図６（ｂ）に参考例１の電極触媒材料のＦＥ−ＳＥＭ像をそれぞれ示す。図６（ａ）に示す実施例１の電極触媒材料のＦＥ−ＳＥＭ像では、導電補助材である繊維状炭素の表面上にＳｎＯ2が担持されていることが確認されるが、ＩｒＯ2微粒子単独では確認されなかった。一方、図６（ｂ）から参考例１の電極触媒材料では、繊維状炭素の表面上にＳｎＯ2（ＳｎＯ）が担持されていることが確認され、Ｉｒ粒子も単独では確認された。 2-2: Evaluation by electron microscope (1) Evaluation by scanning electron microscope (FE-SEM) The microstructure of the electrode catalyst materials of Example 1 and Reference Example 1 was observed. FIG. 6A shows an FE-SEM image of the electrode catalyst material of Example 1, and FIG. 6B shows an FE-SEM image of the electrode catalyst material of Reference Example 1. In the FE-SEM image of the electrode catalyst material of Example 1 shown in FIG. 6A, it is confirmed that SnO 2 is supported on the surface of the fibrous carbon which is the conductive auxiliary material, but the IrO 2 fine particles are confirmed. It was not confirmed alone. On the other hand, from FIG. 6B, it was confirmed that SnO 2 (SnO) was supported on the surface of the fibrous carbon in the electrode catalyst material of Reference Example 1, and Ir particles were also confirmed alone.

（２）走査型透過電子顕微鏡(ＳＴＥＭ)及びＥＤＳマッピングによる評価
実施例１及び参考例１の電極触媒材料の走査型透過電子顕微鏡(ＳＴＥＭ) 及びＥＤＳマッピングを用いてさらに詳細に微細構造の評価を行った。実施例１の電極触媒材料について図７にＳＴＥＭ像及びＥＤＳマッピング、図８にＳＴＥＭ像（高倍率）、図８に参考例１の電極触媒材料のＳＴＥＭ像及びＥＤＳマッピングをそれぞれ示す。
図７から実施例１の電極触媒材料では、ＥＤＳマッピングにおけるＩｒ原子の分布は担体粉末（ＳｎＯ2を担持した繊維状炭素）のＳｎＯ2部分に広がっており、図８に示すＳＴＥＭ像（高倍率）から、約１０〜数十ｎｍ径のＳｎＯ2粒子表面上に直径１０ｎｍ以下のＩｒＯ2が担持されていることが確認された。そのため、ＩｒＯ2はＳｎＯ2に表面担持した状態で存在すると考えられる。
また、図９に示すように、参考例１の電極触媒材料では、ＳｎＯ2（ＳｎＯ）表面上に直径１０ｎｍ以下のＩｒ粒子が存在することが確認された。 (2) Evaluation by Scanning Transmission Electron Microscopy (STEM) and EDS Mapping In more detailed evaluation of the microstructure using the scanning transmission electron microscope (STEM) and EDS mapping of the electrode catalyst materials of Example 1 and Reference Example 1. went. Regarding the electrode catalyst material of Example 1, STEM image and EDS mapping are shown in FIG. 7, STEM image (high magnification) is shown in FIG. 8, and STEM image and EDS mapping of the electrode catalyst material of Reference Example 1 are shown in FIG. 8, respectively.
The electrode catalyst material of Example 1 from 7, the distribution of Ir atoms in the EDS mapping is spread SnO 2 portions of support powder (fibrous carrying SnO 2 carbon), STEM images (high magnification shown in FIG. 8 ), It was confirmed that IrO 2 having a diameter of 10 nm or less is supported on the surface of SnO 2 particles having a diameter of about 10 to several tens of nm. Therefore, it is considered that IrO 2 exists in a state of being surface-supported on SnO 2 .
Further, as shown in FIG. 9, in the electrode catalyst material of Reference Example 1, it was confirmed that Ir particles having a diameter of 10 nm or less were present on the surface of SnO 2 (SnO).

２−３：ＸＰＳによる評価
試料表面の成分構成を確認するため、ＸＰＳによる評価を行った。図１０（ａ）に実施例１の電極触媒材料、図１０（ｂ）に参考例１の電極触媒材料のＩｒ（４ｆ）スペクトルをそれぞれ示す。
図１０（ａ）と図１０（ｂ）を対比すると、６２ｅＶ付近のピークと６５ｅＶ付近のピークの比が異なっており、実施例１の電極触媒材料における表面成分から、ＩｒＯ2であるといえる。すなわち、実施例１の電極触媒材料の表面にはＩｒＯ2微粒子が存在していることがＸＰＳによる評価で確認された。 2-3: Evaluation by XPS In order to confirm the composition of the sample surface, evaluation by XPS was performed. FIG. 10 (a) shows the Ir (4f) spectrum of the electrode catalyst material of Example 1, and FIG. 10 (b) shows the Ir (4f) spectrum of the electrode catalyst material of Reference Example 1.
Comparing FIGS. 10 (a) and 10 (b), the ratio of the peak near 62 eV to the peak near 65 eV is different, and it can be said that it is IrO 2 from the surface component in the electrode catalyst material of Example 1. That is, it was confirmed by XPS evaluation that IrO 2 fine particles were present on the surface of the electrode catalyst material of Example 1.

２−４．電気化学的評価（ハーフセル）
以下の電極触媒材料を用いて評価用電極を作製し、電位ステップ法（クロノアンペロメトリー（ＣＡ）)により、それぞれの性能を比較した。
実施例１の電極触媒材料（IrO2/Nb-SnO2/VGCF）
比較例１の電極触媒材料（市販のIrO2粉末、株式会社徳力本店製） 2-4. Electrochemical evaluation (half cell)
Evaluation electrodes were prepared using the following electrode catalyst materials, and their performances were compared by the potential step method (chronoamperometry (CA)).
Electrode catalyst material of Example 1 (IrO 2 / Nb-SnO 2 / VGCF)
Electrode catalyst material of Comparative Example 1 (commercially available IrO 2 powder, manufactured by Tokuriki Honten Co., Ltd.)

評価用の電極として、直径５ｍｍのＧＣ（グラッシーカーボン、北斗電工（株）、ＨＲ２−Ｄ１−ＧＣ５）上に、電極触媒材料と２−プロパノール、５％ナフィオン分散液をＦＣＣＪの評価プロトコル（固体高分子形燃料電池の目標・研究開発課題と評価方法の提案、平成２３年１月発行）に則った割合で混合したものを、ＩｒＯ2担持量が１７．３μｇ／ｃｍ2になるように塗布し電極を使用した。
図１１に比較例１の電極触媒材料（μｍオーダーのIrO2粉末）を用いた電極のＦＥ−ＳＥＭ像を示す。 As an electrode for evaluation, an electrode catalyst material and 2-propanol, 5% Nafion dispersion are placed on a GC (Glassy Carbon, Hokuto Denko Co., Ltd., HR2-D1-GC5) with a diameter of 5 mm according to the FCCJ evaluation protocol (solid height). A mixture of molecular fuel cells in a ratio according to the goals / research and development issues and evaluation method proposals (issued in January 2011) was applied so that the IrO 2 carrying amount was 17.3 μg / cm 2. Electrodes were used.
FIG. 11 shows an FE-SEM image of an electrode using the electrode catalyst material of Comparative Example 1 (IrO 2 powder on the order of μm).

ＣＡの測定条件は以下の通りである。
測定：三電極式セル（作用極：電極触媒材料／ＧＣ，対極：Ｐｔ，参照極：Ａｇ／ＡｇＣｌ）
電解液：０．１Ｍ ＨＣｌＯ4（ｐＨ：約１）
印加電圧：１．６Ｖ
回転数：１６００ｒｐｍ
電圧保持時間：３０ｍｉｎ
測定は、測定開始(０ｍｉｎ時)に０Ｖから１．６Ｖまでステップ的に電圧変化させてその後３０ｍｉｎ保持することによって行った。 The measurement conditions for CA are as follows.
Measurement: Three-electrode cell (working electrode: electrode catalyst material / GC, counter electrode: Pt, reference electrode: Ag / AgCl)
Electrolyte: 0.1M HClO 4 (pH: about 1)
Applied voltage: 1.6V
Rotation speed: 1600 rpm
Voltage holding time: 30 min
The measurement was performed by changing the voltage stepwise from 0 V to 1.6 V at the start of measurement (at 0 min) and then holding the voltage for 30 min.

図１２に実施例１、比較例１のＣＡの結果を示す。なお、図１２において、縦軸は電流密度であり、数値が大きいほど水電解反応が進むことを意味する。
図１２からわかるように、ＩｒＯ2粉末を用いた比較例１の電極に比べて、ＩｒＯ2微粒子が担持された実施例１の電極の方が、一定電圧値(１．６Ｖ)における電流密度が高いことが確認された。この結果より、本発明の電極触媒材料からなる電極は、少ないＩｒＯ2量でも高性能の電極を与えることができることが示唆される。 FIG. 12 shows the results of CA of Example 1 and Comparative Example 1. In FIG. 12, the vertical axis represents the current density, and the larger the value, the more the water electrolysis reaction proceeds.
As can be seen from FIG. 12, the electrode of Example 1 on which IrO 2 fine particles are supported has a higher current density at a constant voltage value (1.6 V) than the electrode of Comparative Example 1 using IrO 2 powder. It was confirmed that it was high. From this result, it is suggested that the electrode made of the electrode catalyst material of the present invention can provide a high-performance electrode even with a small amount of IrO 2 .

本発明によれば、Ｉｒ使用量を低減でき、かつ、水電解における電位下でも安定であり、十分な触媒活性を示すことが可能な水電解用電極材料の低コストでの生産が可能となり、余剰が電力を水素にして蓄えるシステムの中核となる水電解システムの高コストの問題を、根本的に解決できるブレイクスルーとなり得るため、産業的に有望である。 According to the present invention, it is possible to produce an electrode material for water electrolysis at low cost, which can reduce the amount of Ir used, is stable even under a potential in water electrolysis, and can exhibit sufficient catalytic activity. It is industrially promising because it can be a breakthrough that can fundamentally solve the high cost problem of the water electrolysis system, which is the core of the system in which the surplus stores electricity as hydrogen.

１ 水分解用電極材料
２ 導電補助材
３ａ （粒子状の）電子伝導性酸化物
３ｂ 電極触媒粒子
４ 水分解セル用電極（カソード）
４ａ カソード電極層
４ｂ ガス拡散層
５ 水分解セル用電極（アノード）
５ａ カソード電極層
５ｂ ガス拡散層
６ 固体高分子電解質膜
１０ 膜電極接合体（ＭＥＡ） 1 Electrode material for water splitting 2 Conductive auxiliary material 3a (particle-like) electron conductive oxide 3b Electrode catalyst particles 4 Electrode for water splitting cell (cathode)
4a Cathode electrode layer 4b Gas diffusion layer 5 Electrode for water splitting cell (anode)
5a Cathode electrode layer 5b Gas diffusion layer 6 Solid polymer electrolyte membrane 10 Membrane electrode assembly (MEA)

Claims (7)

表面がグラファイト構造である繊維状炭素からなる炭素系導電補助材と、
前記炭素系導電補助材に担持された酸化スズを主体とする粒子状電子伝導性酸化物からなる電子伝導性酸化物担体と、
前記電子伝導性酸化物担体に分散担持された、平均粒子径１０ｎｍ以下の酸化イリジウム粒子とを含み、前記炭素系導電補助材の上に酸化イリジウム粒子を有さないことを特徴とする水電解用電極材料。 A carbon-based conductive auxiliary material made of fibrous carbon whose surface has a graphite structure ,
An electron conductive oxide carrier made of particulate electron conductive oxide mainly composed of tin oxide supported on the carbon-based conductive auxiliary material.
Said dispersed supported electron conductivity oxide support, viewed including the iridium oxide particles of less than or equal to the average particle diameter of 10 nm, water electrolysis, characterized in that no iridium oxide particles on the carbon-based conductive auxiliary material For electrode material. 前記電子伝導性酸化物担体に分散担持された酸化イリジウム粒子の粒径が０．５ｎｍ以上５ｎｍ以下である請求項１に記載の水電解用電極材料。 The electrode material for water electrolysis according to claim 1, wherein the iridium oxide particles dispersed and supported on the electron conductive oxide carrier have a particle size of 0.5 nm or more and 5 nm or less . 前記酸化スズを主体とする粒子状電子伝導性酸化物の平均粒径が１ｎｍ以上４０ｎｍ以下である請求項１または２に記載の水電解用電極材料。 The electrode material for water electrolysis according to claim 1 or 2, wherein the average particle size of the particulate electron conductive oxide mainly composed of tin oxide is 1 nm or more and 40 nm or less . 請求項１から３のいずれかに記載の水電解用電極材料の製造方法であって、以下の工程を有することを特徴とする水電解用電極材料の製造方法。
（１）表面がグラファイト構造である繊維状炭素からなる導電補助材に、酸化スズを主体とする粒子状電子伝導性酸化物からなる電子伝導性酸化物担体を担持する工程
（２）電子伝導性酸化物担体を担持した前記導電補助材を、水を溶媒とした酸化イリジウム前駆体を含む溶液に浸漬し、蒸発乾固法によって前記電子伝導性酸化物の表面上に酸化イリジウム前駆体を担持する工程
（３）電子伝導性酸化物担体に担持された酸化イリジウム前駆体を、酸化雰囲気下、３００℃以上５００℃以下で熱処理し、酸化イリジウムに変換する工程 The method for producing an electrode material for water electrolysis according to any one of claims 1 to 3, wherein the method for producing an electrode material for water electrolysis includes the following steps.
(1) A step of supporting an electron conductive oxide carrier made of particulate electron conductive oxide mainly composed of tin oxide on a conductive auxiliary material made of fibrous carbon having a graphite structure on the surface (2) Electron conductivity The conductive auxiliary material carrying an oxide carrier is immersed in a solution containing an iridium oxide precursor using water as a solvent, and the iridium oxide precursor is supported on the surface of the electron conductive oxide by an evaporative drying method. Step (3) A step of heat-treating an iridium oxide precursor supported on an electron-conducting oxide carrier at 300 ° C. or higher and 500 ° C. or lower in an oxidizing atmosphere to convert it into iridium oxide. 工程（１）において、酸化スズを主体とする粒子状電子伝導性酸化物からなる電子伝導性酸化物担体を担持する方法が、マイクロ波加熱均一沈殿法である請求項４に記載の水電解用電極材料の製造方法。The method for supporting an electron conductive oxide carrier made of particulate electron conductive oxide mainly composed of tin oxide in the step (1) is a microwave heating uniform precipitation method for water electrolysis according to claim 4. Method of manufacturing electrode material. 請求項１から３のいずれかに記載の水電解用電極材料とプロトン伝導性電解質材料を含み、前記導電補助材が互いに接触して導電パスを形成している水電解用電極。A water electrolysis electrode containing the water electrolysis electrode material and the proton conductive electrolyte material according to any one of claims 1 to 3, wherein the conductive auxiliary materials are in contact with each other to form a conductive path. 固体高分子電解質膜と、前記固体高分子電解質膜の一方面に接合されたカソードと、前記固体高分子電解質膜の他方面に接合されたアノードと、を有する膜電極接合体であって、前記アノードが、請求項６に記載の水電解用電極である膜電極接合体を備えてなることを特徴とする固体高分子形水電解セル。A film electrode junction having a solid polymer electrolyte membrane, a cathode bonded to one surface of the solid polymer electrolyte membrane, and an anode bonded to the other surface of the solid polymer electrolyte membrane. A polymer electrolyte hydroelectrolyte cell, wherein the anode includes a membrane electrode joint which is the electrode for water electrolysis according to claim 6.
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