JP2020161272A - Electrode material, electrode, membrane electrode assembly, and polymer electrolyte fuel cell - Google Patents
Electrode material, electrode, membrane electrode assembly, and polymer electrolyte fuel cell Download PDFInfo
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Classifications
-
- 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
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- Fuel Cell (AREA)
- Catalysts (AREA)
- Inert Electrodes (AREA)
Abstract
Description
本発明は、固体高分子形燃料電池の電極に好適な電極材料及びこれを使用した電極、膜電極接合体及び固体高分子形燃料電池に関する。 The present invention relates to an electrode material suitable for an electrode of a polymer electrolyte fuel cell, an electrode using the same, a membrane electrode assembly, and a polymer electrolyte fuel cell.
電解質に固体高分子膜を使用した固体高分子形燃料電池（ＰＥＦＣ）は、作動温度が８０℃付近と比較的低温であるため、例えば、車載用電源、家庭用等の小規模な固定電源として導入されている。ＰＥＦＣでは、以下の電気化学反応によって電力を取り出すことができる。
アノード反応：２Ｈ2 → ４Ｈ+＋４ｅ- （反応１）
カソード反応：Ｏ2＋４Ｈ+＋４ｅ-→２Ｈ2Ｏ （反応２）
全反応 ：２Ｈ2＋Ｏ2→２Ｈ2Ｏ
A polymer electrolyte fuel cell (PEFC) using a solid polymer membrane as an electrolyte has a relatively low operating temperature of around 80 ° C. Therefore, for example, it can be used as a small-scale fixed power source for automobiles, households, etc. Has been introduced. In PEFC, electric power can be extracted by the following electrochemical reaction.
Anode reaction: 2H 2 → 4H + + 4e - ( Reaction 1)
Cathode reaction: O 2 + 4H + + 4e - → 2H 2 O ( Reaction 2)
Total reaction: 2H 2 + O 2 → 2H 2 O
ＰＥＦＣは、電解質膜と前記電解質膜の両面に積層された電極（アノード及びカソード）とを含む膜電極接合体（ＭＥＡ）と、前記膜電極接合体の両面に積層されたガス拡散層（ＧＤＬ）とからなる発電モジュールを、ガス流路が形成された２つのセパレータで挟んだ構造のセルを基本単位として構成されている。ＰＥＦＣの構成部材は、一般的に、セパレータは金属材料で形成されており、ガス拡散層は多孔質の炭素材料が使用されている。また、電極触媒層（アノード及びカソード）は、担体の表面にＰｔ等の貴金属からなる電極触媒粒子が担持された構造を有し、担体には一般的に炭素材料が使用されている（例えば、特許文献１，２）。 PEFCs are a membrane electrode assembly (MEA) including an electrolyte membrane and electrodes (anode and cathode) laminated on both sides of the electrolyte membrane, and a gas diffusion layer (GDL) laminated on both sides of the membrane electrode assembly. The power generation module composed of the above is configured with a cell having a structure sandwiched between two separators having a gas flow path as a basic unit. In the PEFC constituent members, the separator is generally made of a metal material, and the gas diffusion layer is made of a porous carbon material. Further, the electrode catalyst layer (anode and cathode) has a structure in which electrode catalyst particles made of a noble metal such as Pt are supported on the surface of the carrier, and a carbon material is generally used for the carrier (for example,). Patent Documents 1 and 2).
一方、ＰＥＦＣの膜電極接合体（ＭＥＡ）の電解質膜で使用されるナフィオン（Nafion）は酸性（ｐＨ＝０〜３）であるため、ＰＥＦＣの電極材料は超強酸性条件で使用されることになる。また、通常運転しているときのセル電圧は０．４〜１．０Ｖであるが、起動停止時にはセル電圧が１．５Ｖまで上昇するため、カソードでは、炭素系担体が電気化学的に酸化されてＣＯ2に分解する反応が起こり、炭素系担体が腐食されて触媒活性成分である電極触媒粒子が脱落するという問題があり、アノードにおいても運転初期などに燃料ガスが不足すると、その部分での電圧低下、あるいは濃度分極が生じて局部的に通常と反対の電位となり、炭素系担体の電気化学的酸化分解反応が起こることがある。 On the other hand, since Nafion used in the electrolyte membrane of the PEFC membrane electrode assembly (MEA) is acidic (pH = 0 to 3), the PEFC electrode material will be used under superacidic conditions. Become. In addition, the cell voltage during normal operation is 0.4 to 1.0 V, but the cell voltage rises to 1.5 V when starting and stopping, so the carbon-based carrier is electrochemically oxidized at the cathode. There is a problem that the carbon-based carrier is corroded and the electrode catalyst particles, which are the catalytically active components, fall off due to the reaction of decomposition into CO 2 , and if the fuel gas is insufficient at the beginning of operation even at the anode, that part A voltage drop or concentration polarization may occur and the potential may be locally opposite to the normal potential, resulting in an electrochemical oxidative decomposition reaction of the carbon-based carrier.
上述した炭素系担体の腐食の問題に対し、特許文献３において、ＰＥＦＣ作動条件（強酸性、高電位）で熱力学的に安定な電子伝導性酸化物である酸化チタン（ＴｉＯ２）を担体として利用した電極材料が報告されている。この電極材料は、酸化チタン担体に起因する電気抵抗を低減させるために、繊維状炭素材料表面上に微粒子状の酸化チタン担体を高分散に担持し、当該粒子状の酸化チタン担体に電極触媒粒子が選択的に担持された構造を有している。 In response to the above-mentioned problem of corrosion of carbon-based carriers, in Patent Document 3, titanium oxide (TiO 2 ), which is a thermodynamically stable electron-conducting oxide under PEFC operating conditions (strong acidity, high potential), is used as a carrier. The electrode materials used have been reported. In this electrode material, in order to reduce the electrical resistance caused by the titanium oxide carrier, fine particles of the titanium oxide carrier are supported on the surface of the fibrous carbon material in a highly dispersed manner, and the electrode catalyst particles are mounted on the particulate titanium oxide carrier. Has a structure that is selectively supported.
上述の通り、特許文献３の電極材料は、酸化チタン担体がＰＥＦＣ作動条件（強酸性、高電位）で熱力学的に安定であるため酸化腐食されることなく長期間安定であり、酸化チタン担体に担持された電極触媒粒子は実質的に炭素系導電補助材と直接接触しないため、上述した炭素腐食によって電極触媒粒子が脱落することが回避されるという利点がある。
しかしながら、ＰＥＦＣ作動条件で長期間使用されると酸化チタン担体に担持させた電極触媒粒子が凝集し、肥大化する場合があるという課題があり、この点においては改善の余地があった。
As described above, the electrode material of Patent Document 3 is stable for a long period of time without being oxidatively corroded because the titanium oxide carrier is thermodynamically stable under PEFC operating conditions (strong acidity, high potential), and the titanium oxide carrier. Since the electrode catalyst particles supported on the surface do not substantially come into direct contact with the carbon-based conductive auxiliary material, there is an advantage that the electrode catalyst particles are prevented from falling off due to the carbon corrosion described above.
However, there is a problem that the electrode catalyst particles supported on the titanium oxide carrier may aggregate and become enlarged when used for a long period of time under PEFC operating conditions, and there is room for improvement in this respect.
かかる状況下、本発明の目的は、電極触媒粒子の凝集による肥大化が抑制され、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、炭素系材料に起因する優れた電子伝導性を併せ持つ電極材料、及びこれを利用した応用技術を提供することである。 Under such circumstances, an object of the present invention is that enlargement due to aggregation of electrode catalyst particles is suppressed, excellent durability against electrochemical oxidation due to electron conductive oxides, and excellent due to carbon-based materials. It is to provide an electrode material having electron conductivity and an applied technique using the electrode material.
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極触媒複合体とを含み、
前記電極触媒複合体は、電極触媒粒子と、電子伝導性酸化物とを含み、
前記電子伝導性酸化物は、前記電極触媒粒子の間に存在する電極材料。
＜２＞ 前記電極触媒粒子が、粒径１ｎｍ以上１０ｎｍ以下の貴金属からなる粒子である＜１＞に記載の電極材料。
＜３＞ 前記電極触媒粒子が、ＰｔまたはＰｔを含む合金からなる粒子である＜１＞または＜２＞に記載の電極材料。
＜４＞ 前記電子伝導性酸化物が、Ｔｉ酸化物である＜１＞から＜３＞のいずれかに記載の電極材料。
＜５＞ 前記Ｔｉ酸化物が、粒子状である＜４＞に記載の電極材料。
＜６＞ 前記電極触媒複合体が、前記炭素系導電補助材の表面の少なくとも一部が露出するように前記炭素系導電補助材に担持されてなる＜１＞から＜５＞のいずれかに記載の電極材料。
＜７＞ 前記炭素系導電補助材が、高黒鉛化カーボンブラックである＜１＞から＜６＞のいずれかに記載の電極材料。
That is, the present invention relates to the following invention.
<1> A carbon-based conductive auxiliary material and an electrode catalyst composite supported on the carbon-based conductive auxiliary material are included.
The electrode catalyst composite contains electrode catalyst particles and an electron conductive oxide.
The electron conductive oxide is an electrode material existing between the electrode catalyst particles.
<2> The electrode material according to <1>, wherein the electrode catalyst particles are particles made of a noble metal having a particle size of 1 nm or more and 10 nm or less.
<3> The electrode material according to <1> or <2>, wherein the electrode catalyst particles are particles made of Pt or an alloy containing Pt.
<4> The electrode material according to any one of <1> to <3>, wherein the electron conductive oxide is a Ti oxide.
<5> The electrode material according to <4>, wherein the Ti oxide is in the form of particles.
<6> The method according to any one of <1> to <5>, wherein the electrode catalyst composite is supported on the carbon-based conductive auxiliary material so that at least a part of the surface of the carbon-based conductive auxiliary material is exposed. Electrode material.
<7> The electrode material according to any one of <1> to <6>, wherein the carbon-based conductive auxiliary material is highly graphitized carbon black.
また、本発明は、上記本発明の電極材料を利用した以下の発明に係るものである。
＜８＞ ＜１＞から＜７＞のいずれかに記載の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電極。
＜９＞ 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、前記アノードまたはカソードのいずれか一方又は両方が、＜８＞に記載の電極である膜電極接合体。
＜１０＞ ＜９＞に記載の膜電極接合体を備えてなる固体高分子形燃料電池。
＜１１＞ ＜９＞に記載の膜電極接合体を備えてなる固体高分子形水電解装置。
The present invention also relates to the following invention using the electrode material of the present invention.
<8> An electrode containing the electrode material according to any one of <1> to <7> and a proton conductive electrolyte material, and the conductive auxiliary materials are in contact with each other to form a conductive path.
<9> 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. A membrane electrode assembly in which either one or both of the anode and the cathode are the electrodes according to <8>.
<10> A polymer electrolyte fuel cell comprising the membrane electrode assembly according to <9>.
<11> A solid polymer water electrolyzer comprising the membrane electrode assembly according to <9>.
また、本発明は、以下の上記本発明の電極材料の製造方法に係るものである。
＜Ａ１＞ ＜１＞から＜７＞に記載の電極材料の製造方法であって、以下の工程（１）及び（２）を含む製造方法。
工程（１）：疎水性有機溶媒に、炭素系導電補助材を分散させた分散液に、電極触媒粒子前駆体のアセチルアセトナート化合物と、電子伝導性酸化物前駆体のアセチルアセトナート化合物とを溶解させ、撹拌及び溶媒の留去を行うことにより、電極触媒粒子前駆体と電子伝導性酸化物前駆体とが担持された炭素系導電補助材を得る工程
工程（２）：工程（１）で得らえた電極触媒粒子前駆体と電子伝導性酸化物前駆体とが担持された炭素系導電補助材を、不活性ガス雰囲気で熱処理することによって、電極触媒複合体を形成する工程
＜Ａ２＞ 前記炭素系導電補助材が、高黒鉛化カーボンブラックである＜Ａ１＞に記載の製造方法。
＜Ａ３＞ 工程（２）において、熱処理を異なる温度で２段階に分けて行う＜Ａ１＞または＜Ａ２＞に記載の製造方法。
＜Ａ４＞ 工程（２）において、水蒸気共存下で熱処理を行う工程を含む＜Ａ１＞から＜Ａ３＞のいずれかに記載の製造方法。
The present invention also relates to the following method for producing the electrode material of the present invention.
<A1> The method for producing an electrode material according to <1> to <7>, which comprises the following steps (1) and (2).
Step (1): An acetylacetonate compound as an electrode catalyst particle precursor and an acetylacetonate compound as an electron conductive oxide precursor are mixed in a dispersion liquid in which a carbon-based conductive auxiliary material is dispersed in a hydrophobic organic solvent. Steps to obtain a carbon-based conductive auxiliary material on which the electrode catalyst particle precursor and the electron conductive oxide precursor are supported by dissolving, stirring and distilling off the solvent Step (2): In step (1). Step of forming an electrode catalyst composite by heat-treating the obtained carbon-based conductive auxiliary material on which the electrode catalyst particle precursor and the electron conductive oxide precursor are supported in an inert gas atmosphere <A2> The production method according to <A1>, wherein the carbon-based conductive auxiliary material is a highly graphitized carbon black.
<A3> The production method according to <A1> or <A2>, wherein the heat treatment is performed in two stages at different temperatures in the step (2).
<A4> The production method according to any one of <A1> to <A3>, which comprises a step of performing heat treatment in the coexistence of steam in step (2).
本発明によれば、電極触媒粒子の凝集による肥大化が抑制され、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、炭素系材料に起因する優れた電子伝導性を併せ持つ電極材料が提供される。 According to the present invention, bloating due to aggregation of electrode catalyst particles is suppressed, excellent durability against electrochemical oxidation caused by electron conductive oxides, and excellent electron conductivity caused by carbon-based materials can be obtained. An electrode material to be combined is provided.
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．本発明の電極材料＞
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極触媒複合体とを含み、前記電極触媒複合体は、電極触媒粒子と、電子伝導性酸化物とを含み、前記電子伝導性酸化物は、前記電極触媒粒子の間に存在する電極材料（本明細書において、単に「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 of the present invention>
The present invention includes a carbon-based conductive auxiliary material and an electrode catalyst composite supported on the carbon-based conductive auxiliary material, and the electrode catalyst composite contains electrode catalyst particles and an electron conductive oxide. The electron conductive oxide relates to an electrode material existing between the electrode catalyst particles (sometimes referred to simply as "the electrode material of the present invention" in the present specification).
図１に本発明の電極材料の模式図（好適な一形態）を示す。図１に示す本発明の電極材料は、炭素系導電補助材と、これに担持された電極触媒複合体とからなる。電極触媒複合体は、微細な電極触媒粒子と、当該電極触媒粒子の間に存在する電子伝導性酸化物とからなる。このように電極触媒粒子の間の間隙を埋めるように電子伝導性酸化物が存在することによって、電極触媒粒子が凝集して肥大化することを抑制することができる。電極触媒複合体の粒子は分散して炭素系導電補助材に担持されており、炭素系導電補助材の表面の一部は露出してため、当該電極材料を用いて電極を構成した際に、前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。 FIG. 1 shows a schematic view (a suitable form) of the electrode material of the present invention. The electrode material of the present invention shown in FIG. 1 is composed of a carbon-based conductive auxiliary material and an electrode catalyst composite supported on the carbon-based conductive auxiliary material. The electrode catalyst composite is composed of fine electrode catalyst particles and an electron conductive oxide existing between the electrode catalyst particles. The presence of the electron-conducting oxide so as to fill the gaps between the electrode catalyst particles in this way can prevent the electrode catalyst particles from aggregating and enlarging. The particles of the electrode catalyst composite are dispersed and supported on the carbon-based conductive auxiliary material, and a part of the surface of the carbon-based conductive auxiliary material is exposed. Therefore, when the electrode is constructed using the electrode material, the electrode is formed. The pre-conductive auxiliary materials come into contact with each other to form a low-resistance conductive path, resulting in an electrode having excellent electron conductivity.
なお、図１においては、電極触媒粒子の間に存在する電子伝導性酸化物の形態は粒子であるが、電子伝導性酸化物の形態は電極触媒粒子の間に存在するのであれば粒子に限定されず、不定形であってもよい。また、電子伝導性酸化物は、結晶であっても非晶質体であってもよい。 In FIG. 1, the form of the electron conductive oxide existing between the electrode catalyst particles is a particle, but the form of the electron conductive oxide is limited to the particle if it exists between the electrode catalyst particles. However, it may be indefinite. Further, the electron conductive oxide may be a crystal or an amorphous substance.
本発明の電極材料では、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、電極触媒複合体の粒径を小さくすることができる。そのため、本発明の電極材料を用いて形成した電極では、電極触媒複合体に含まれる電子伝導性酸化物に起因する電気抵抗を低減できる。 In the electrode material 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 electrode catalyst composite can be reduced. Therefore, in the electrode formed by using the electrode material of the present invention, the electric resistance caused by the electron conductive oxide contained in the electrode catalyst composite can be reduced.
このように、本発明の電極材料は、電極触媒粒子の間に存在する電子伝導性酸化物によって電極触媒粒子の凝集が抑制され、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を有し、かつ、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、長期間発電することができる。 As described above, the electrode material of the present invention is excellent in the electrochemical oxidation caused by the electron conductive oxide by suppressing the aggregation of the electrode catalyst particles by the electron conductive oxide existing between the electrode catalyst particles. It has durability and also has excellent electron conductivity due to the carbon-based conductive auxiliary material. Therefore, the electrode formed of the electrode material exhibits excellent electrode performance, has high durability, and can generate electricity for a long period of time.
本発明の電極材料の用途は限定されないが、固体高分子形燃料電池用電極や固体高分子形水電解用電極に用いる電極材料として好適である。 The use of the electrode material of the present invention is not limited, but it is suitable as an electrode material used for an electrode for a polymer electrolyte fuel cell or an electrode for solid polymer water electrolysis.
以下、本発明の電極材料の構成要素について詳細に説明する。なお、以下において、本発明の電極材料を固定高分子形燃料電池（ＰＥＦＣ）用電極に使用することを想定して説明するが、本発明の電極材料はこの用途に限定されない。 Hereinafter, the components of the electrode material of the present invention will be described in detail. In the following description, it is assumed that the electrode material of the present invention is used for an electrode for a polymer electrolyte fuel cell (PEFC), but the electrode material of the present invention is not limited to this application.
［炭素系導電補助材］
本発明の電極材料において、炭素系導電補助材（以下、単に「導電補助材」と記載する場合がある。）は、本発明の電極材料に含まれ、電極を形成した際に電子伝導性を向上させる役割を有し、かつ、電極の骨格としての役割を有する。
[Carbon-based conductive auxiliary material]
In the electrode material of the present invention, the carbon-based conductive auxiliary material (hereinafter, may be simply referred to as “conductive auxiliary material”) is included in the electrode material of the present invention, and when the electrode is formed, the electron conductivity is improved. It has a role of improving and also has a role of a skeleton of an electrode.
本発明の電極材料における炭素系導電補助材は、二次電池や燃料電池に使用される任意の炭素系導電補助材を使用することができる。その形状や大きさは、電極の使用目的等を考慮して適宜選択できるが、燃料電池用電極等のガス拡散電極用途では、電極を形成した際の電極内の電気伝導性とガス拡散性が求められる。そのため、電気伝導性とガス拡散性とを両立させるために、炭素系導電補助材が粒子状である場合には、粒径０．０３〜５００μｍであり、繊維状である場合、直径２ｎｍ〜２０μｍ、全長０．０３〜５００μｍ程度であることが好適である。 As the carbon-based conductive auxiliary material in the electrode material of the present invention, any carbon-based conductive auxiliary material used in a secondary battery or a fuel cell can be used. The shape and size can be appropriately selected in consideration of the purpose of use of the electrode, but in the case of gas diffusion electrode applications such as fuel cell electrodes, the electrical conductivity and gas diffusivity inside the electrode when the electrode is formed are Desired. Therefore, in order to achieve both electrical conductivity and gas diffusivity, the carbon-based conductive auxiliary material has a particle size of 0.03 to 500 μm when it is in the form of particles, and a diameter of 2 nm to 20 μm when it is in the form of fibers. It is preferable that the total length is about 0.03 to 500 μm.
炭素系導電補助材は、特に結晶性の高い炭素材料を好適に使用することができる。当該導電補助材は、結晶性の高い炭素材料は、結晶性が低い炭素材料と比較して疎水性有機溶媒に対する分散性がよく、電極触媒複合体の前駆体化合物を固着しやすい傾向にある。 As the carbon-based conductive auxiliary material, a carbon material having particularly high crystallinity can be preferably used. In the conductive auxiliary material, a carbon material having high crystallinity has better dispersibility in a hydrophobic organic solvent than a carbon material having low crystallinity, and tends to easily adhere a precursor compound of an electrode catalyst composite.
結晶性の高い炭素材料として、カーボンナノチューブや気相成長炭素繊維等の繊維状炭素も使用できるが、特に高黒鉛化カーボンブラック（Graphitized Carbon Black, ＧＣＢ）を好適に使用できる。 As the highly crystalline carbon material, fibrous carbon such as carbon nanotubes and vapor-grown carbon fibers can be used, but highly graphitized carbon black (GCB) can be particularly preferably used.
高黒鉛化カーボンブラックは、カーボンブラックを高温黒鉛化炉で熱処理（例えば、２５００℃以上）して黒鉛化（結晶化）したものである。黒鉛化の程度は、例えば、ラマン分光法で評価することができ、例えば、ラマン分光法により求めたＲ値が１．１０以下であるものが好適に使用される。Ｒ値は、黒鉛の結晶化度を示す指標であり、１３６０ｃｍ-1及び１５８０ｃｍ-1のラマンバンドの相対強度比(I1360/I1580)である。 The highly graphitized carbon black is obtained by heat-treating (for example, 2500 ° C. or higher) carbon black in a high-temperature graphitization furnace to graphitize (crystallize) it. The degree of graphitization can be evaluated by, for example, Raman spectroscopy, and for example, those having an R value of 1.10 or less determined by Raman spectroscopy are preferably used. R value is an index representing the crystallinity of the graphite, the relative intensity ratio of the Raman band at 1360 cm -1 and 1580cm -1 (I 1360 / I 1580 ).
高黒鉛化カーボンブラックは、二次粒子の粒径で０．０３〜５００μｍ（一次粒子径１０ｎｍ〜１００ｎｍ程度）である。 The highly graphitized carbon black has a particle size of secondary particles of 0.03 to 500 μm (primary particle size of about 10 nm to 100 nm).
高黒鉛化カーボンブラックは自作品、市販品のいずれでも使用できる。好適な市販品を例示すると、キャボット社の「ＧＣＢ」シリーズ（品番：ＧＣＢ２００等）や、東海カーボン社製の「トーカブラック」シリーズ（品番：トーカブラック＃３８００等）などが挙げられる。 Highly graphitized carbon black can be used either as a self-made product or as a commercial product. Examples of suitable commercially available products include Cabot's "GCB" series (product number: GCB200, etc.) and Tokai Carbon's "Talker Black" series (product number: Talker Black # 3800, etc.).
本発明で使用される炭素系導電補助材は、１種類でもよいし、または大きさ（粒径、繊維径及び繊維長さ）や結晶性等の異なる２種以上の炭素材料を任意の割合で使用してもよい。 The carbon-based conductive auxiliary material used in the present invention may be one kind, or two or more kinds of carbon materials having different sizes (particle size, fiber diameter and fiber length), crystallinity, etc. may be used in an arbitrary ratio. You may use it.
［電極触媒複合体］
本発明の電極材料は、電極触媒粒子と、電子伝導性酸化物とを含む電極触媒複合体を含み、当該電極触媒複合体において、電子伝導性酸化物は、前記電極触媒粒子の間に存在することに特徴がある。
[Electrode catalyst complex]
The electrode material of the present invention contains an electrode catalyst composite containing electrode catalyst particles and an electron conductive oxide, and in the electrode catalyst composite, the electron conductive oxide is present between the electrode catalyst particles. It is unique in that.
上述の通り、従来の電子伝導性酸化物に貴金属触媒粒子が担持された電極材料では、電極として長期間使用した際に電極触媒である貴金属触媒粒子が凝集して肥大化する問題があるが、本発明の電極材料では、電極触媒粒子の間を埋めるように電子伝導性酸化物が存在する構造を有することによって電極として使用する際に電極触媒粒子が凝集して肥大化することを抑制することができる。 As described above, the conventional electrode material in which the noble metal catalyst particles are supported on the electron conductive oxide has a problem that the noble metal catalyst particles, which are the electrode catalysts, aggregate and enlarge when used as an electrode for a long period of time. In the electrode material of the present invention, by having a structure in which an electron conductive oxide exists so as to fill the space between the electrode catalyst particles, it is possible to suppress the aggregation and enlargement of the electrode catalyst particles when used as an electrode. Can be done.
炭素系導電補助材に担持される電極触媒複合体の形態は、本発明の目的を損なわない限り、任意であり、例えば、粒子状、島状、膜状等が挙げられる。
電極を形成した際の導電性の観点からは、電極触媒複合体が粒子状であって、当該粒子状の電極触媒複合体が導電補助材表面を完全に被覆せずに、導電補助材の表面の一部が露出され、導電補助材と他の導電補助材とが接触の直接的な接触を阻害しない程度に分散して担持されていることが好ましい。粒子状である場合の電極触媒複合体の大きさは特に限定はなく、好適には平均粒径１０〜５００ｎｍである。「電極触媒複合体の平均粒径」は、電子顕微鏡像より調べられる任意の電極触媒複合体（２０個）の粒子径の平均値により得ることができる。
The form of the electrode catalyst composite supported on the carbon-based conductive auxiliary material is arbitrary as long as the object of the present invention is not impaired, and examples thereof include particulate, island-like, and film-like.
From the viewpoint of conductivity when the electrode is formed, the electrode catalyst composite is in the form of particles, and the particle-shaped electrode catalyst composite does not completely cover the surface of the conductive auxiliary material, but the surface of the conductive auxiliary material. It is preferable that a part of the conductive auxiliary material is exposed and the conductive auxiliary material and the other conductive auxiliary material are dispersed and supported so as not to hinder the direct contact of the contact. The size of the electrode catalyst composite in the form of particles is not particularly limited, and the average particle size is preferably 10 to 500 nm. The "average particle size of the electrode catalyst composite" can be obtained from the average value of the particle diameters of any of the electrode catalyst composites (20 pieces) examined from the electron microscope image.
また、電極触媒複合体の担持量は、電極として十分な量の電極触媒粒子が含まれるような範囲で適宜決定される。電極触媒粒子の活性は、電極触媒金属の種類、結晶性、粒径等及び複合化させる電子伝導性酸化物の種類、結晶性、粒径等に依存するため、この点を考慮して電極触媒複合体の担持量が決定される。
電極触媒複合体の担持量は、例えば、導電補助材と電極触媒複合体の合計を１００重量％としたときに、通常、５〜５０重量％であり、好ましくは１０〜４０重量％である。
Further, the amount of the electrode catalyst composite supported is appropriately determined within a range in which a sufficient amount of electrode catalyst particles are contained as an electrode. Since the activity of the electrode catalyst particles depends on the type, crystallinity, particle size, etc. of the electrode catalyst metal and the type, crystallinity, particle size, etc. of the electron conductive oxide to be compounded, the electrode catalyst takes this point into consideration. The amount of the complex carried is determined.
The supported amount of the electrode catalyst composite is usually 5 to 50% by weight, preferably 10 to 40% by weight, when the total of the conductive auxiliary material and the electrode catalyst composite is 100% by weight, for example.
以下、電極触媒複合体を構成する電極触媒粒子及び電子伝導性酸化物について詳述する。 Hereinafter, the electrode catalyst particles and the electron conductive oxide constituting the electrode catalyst composite will be described in detail.
（電極触媒粒子）
電極触媒粒子は、酸素の還元（及び水素の酸化）に対する電気化学的触媒活性を有するものであれば、貴金属系触媒、非貴金属系触媒のいずれでもよいが、好適には、Ｐｔ，Ｒｕ，Ｉｒ，Ｐｄ，Ｒｈ，Ｏｓ，Ａｕ，Ａｇ等の貴金属、及びこれらの貴金属を含む合金から選択される。なお、「貴金属を含む合金」とは「上記の貴金属のみからなる合金」と、「上記の貴金属とそれ以外の金属からなる合金で上記の貴金属を１０質量％以上含む合金」を含む。貴金属と合金化させる上記「それ以外の金属」は、特に限定されないが、Ｃｏ，Ｎｉ，Ｗ，Ｔａ，Ｎｂ，Ｓｎを好適な例として挙げることができ、これらを１種類あるいは２種類以上を使用してもよい。また、分相した状態で２種類以上の上記貴金属及び貴金属を含む合金を使用してもよい。なお、上記貴金属、及びこれらの貴金属を含む合金を以下、「電極触媒金属」と呼ぶ場合がある。
(Electrode catalyst particles)
The electrode catalyst particles may be either a noble metal-based catalyst or a non-precious metal-based catalyst as long as they have electrochemical catalytic activity for the reduction of oxygen (and the oxidation of hydrogen), but Pt, Ru, Ir are preferable. , Pd, Rh, Os, Au, Ag and the like, and alloys containing these precious metals. The "alloy containing a noble metal" includes an "alloy composed only of the above noble metal" and an "alloy composed of the above noble metal and other metals and containing 10% by mass or more of the above noble metal". The above-mentioned "other metals" to be alloyed with a noble metal are not particularly limited, but Co, Ni, W, Ta, Nb, Sn can be mentioned as suitable examples, and one kind or two or more kinds thereof are used. You may. Further, an alloy containing two or more kinds of the precious metal and the precious metal may be used in a phase-separated state. The precious metals and alloys containing these precious metals may be hereinafter referred to as "electrode catalyst metals".
電極触媒金属の中でも、Ｐｔ及びＰｔを含む合金は、固体高分子形燃料電池の作動温度である８０℃付近の温度域において、酸素の還元（及び水素の酸化）に対する電気化学的触媒活性が高いため、特に好適に使用することができる。 Among the electrode catalyst metals, Pt and alloys containing Pt have high electrochemical catalytic activity for oxygen reduction (and hydrogen oxidation) in the temperature range of around 80 ° C., which is the operating temperature of polymer electrolyte fuel cells. Therefore, it can be used particularly preferably.
電極触媒粒子の形状は、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、電極触媒粒子は結晶があることが好ましいが、結晶と非晶質の混合体であってもよい。 The shape of the electrode catalyst particles 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 electrode catalyst particles preferably have crystals, but may be a mixture of crystals and amorphous.
電極触媒粒子の大きさは、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、電極触媒粒子の大きさは、平均粒径として、粒径１〜１０ｎｍであることが好ましく、より好ましくは１．５〜５ｎｍ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。
すなわち、本発明の電極材料における電極触媒粒子の好適な態様の一つは、前記電極触媒粒子が、平均粒子径１〜１０ｎｍのＰｔ及びＰｔを含む合金からなる電極触媒粒子である。
As the size of the electrode catalyst particles 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 is preferably 1 to 10 nm, more preferably 1.5 to 5 nm, as an average particle size.
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.
That is, one of the preferred embodiments of the electrode catalyst particles in the electrode material of the present invention is the electrode catalyst particles made of an alloy containing Pt and Pt having an average particle diameter of 1 to 10 nm.
電極触媒粒子の量は、目的とする電極触媒活性と、複合化させる電子伝導性酸化物の種類や量を考慮して決定される。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 is determined in consideration of the target electrode catalyst activity and the type and amount of the electron conductive oxide to be compounded. The amount of the electrode catalyst particles supported can be examined by, for example, inductively coupled plasma emission spectrometry (ICP).
電極触媒活性の観点からは、電極材料の全重量に対して、好ましくは０．１〜６０質量％、より好ましくは０．５〜３０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。 From the viewpoint of electrode catalytic activity, preferably 0.1 to 60% by mass, more preferably 0.5 to 30% by mass with respect to the total weight of the electrode material, the catalytic activity per unit mass is excellent and supported. The desired electrode reaction activity can be obtained according to the amount.
（電子伝導性酸化物）
電子伝導性酸化物としては、燃料電池（特には固体高分子形燃料電池）のアノード条件、カソード条件の少なくともいずれか一方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、ＰＥＦＣのカソード条件とは、ＰＥＦＣの通常運転時のカソードにおける条件であり、温度が室温〜１５０℃程度、空気等の酸素を含むガスが供給される条件（酸化雰囲気）を意味し、アノード条件とは、ＰＥＦＣ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℃程度、水素を含む燃料ガスが供給される条件（還元雰囲気）を意味する。
(Electronic conductive oxide)
The electron conductive oxide may be any one having sufficient durability and electron conductivity in at least one of the anode condition and the cathode condition of the fuel cell (particularly the polymer electrolyte fuel cell). The cathode condition of PEFC is a condition at the cathode during normal operation of PEFC, and means a condition (oxidizing atmosphere) in which a gas containing oxygen such as air is supplied at a temperature of about room temperature to 150 ° C., and an anode. The condition is a condition at the anode during normal operation of PEFC, and means a condition (reducing atmosphere) in which a fuel gas containing hydrogen is supplied at a temperature of about room temperature to 150 ° C.
電子伝導性酸化物の形態は、本発明の目的を損なわない限り、任意であり、例えば、粒子状、島状、膜状等が挙げられるが、粒子状であることが好ましい。また、電子伝導性酸化物は、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が、電子伝導性を高めるためには、電子伝導性酸化物は結晶であることが好ましい。
なお、本明細書において、「Ｍ酸化物」（但し、Ｍは金属元素である）と記載した場合には、Ｍ酸化物の形態は、結晶に限定されず、結晶、非晶質、結晶と非晶質の混合体のいずれも含まれる概念とする。例えば、Ｔｉ酸化物は、ＴｉＯ２結晶、酸素不定比の酸化物（「ＴｉＯｘ」と表記する）、及びこれらの混合物を含む。
The form of the electron-conducting oxide is arbitrary as long as the object of the present invention is not impaired, and examples thereof include particle-like, island-like, and film-like, but particle-like is preferable. Further, the electron conductive oxide is not limited to a crystal, and may be amorphous or a mixture of a crystal and an amorphous, but in order to enhance the electron conductivity, the electron conductivity is increased. The oxide is preferably crystalline.
In the present specification, when "M oxide" (however, M is a metal element) is described, the form of M oxide is not limited to crystals, and may be crystalline, amorphous, or crystalline. The concept includes any amorphous mixture. For example, Ti oxides include TiO 2 crystals, oxides of non-stoichiometric oxygen ratio (denoted as "TiOx"), and mixtures thereof.
電子伝導性酸化物として具体的には、スズ（Ｓｎ）、モリブデン（Ｍｏ）、ニオブ（Ｎｂ）、タンタル（Ｔａ）、チタン（Ｔｉ）及びタングステン（Ｗ）から選択される１種の金属元素の酸化物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８０ｍｏｌ％以上含まれるもの、を意味する。 Specifically, as the electron conductive oxide, one kind of metal element selected from tin (Sn), molybdenum (Mo), niobium (Nb), tantalum (Ta), titanium (Ti) and tungsten (W). Examples thereof include electron-conducting oxides mainly composed of oxides. Here, in the present invention, the "mainly electron-conducting oxide" is (A) an oxide composed of only a matrix oxide and (B) an oxide doped with another element, and the matrix oxide is It means that it is contained in an amount of 80 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，Ｉｎ，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Ｔｉ酸化物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、Ｓｂ，Ｎｂ，Ｔａ，Ｗ，Ｉｎ，Ｖ，Ｃｒ，Ｍｎ，Ｍｏなど）が選択される。この中でも、酸化チタンの電子導電性を特に高めることができる点で、ニオブ（Ｎｂ）を０．１〜２０ｍｏｌ％ドープしたニオブドープ酸化チタンが特に好ましい。 Specific examples of the element to be doped include Sn, Ti, Sb, Nb, Ta, W, In, 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 a Ti oxide, among the above-mentioned doped seed elements, elements other than Ti (for example, Sb, Nb) , Ta, W, In, V, Cr, Mn, Mo, etc.) are selected. Among these, niobium-doped titanium oxide doped with niobium (Nb) in an amount of 0.1 to 20 mol% is particularly preferable in that the electron conductivity of titanium oxide can be particularly enhanced.
なお、元素としてチタン（Ｔｉ）は、ＰＥＦＣのアノード条件で、酸化物であるＴｉＯ2が熱力学的に安定であり還元が起こらない。さらにＴｉ酸化物は、ＰＥＦＣのアノード条件のみならず、カソード条件でも、酸化物であるＴｉＯ2が熱力学的に安定であるため、カソードとしても使用できる。 As for titanium (Ti) as an element, under the anode conditions of PEFC, the oxide TiO 2 is thermodynamically stable and reduction does not occur. Further, the Ti oxide can be used as a cathode because the oxide TiO 2 is thermodynamically stable not only under the anode condition of PEFC but also under the cathode condition.
上述の通り、電極触媒複合体において、電子伝導酸化物は電極触媒粒子の間を埋めるように存在することによって、電極触媒粒子の凝集を阻害するものであり、電子伝導酸化物は、この目的を達成できるように形態で含まれていればよい。特に本発明の電極材料において、電極の骨格としての役割は導電補助材が担うことから、電子伝導性が炭素系材料と比較して小さい電子伝導酸化物は、電極触媒複合体においてできる範囲内で少量であることが好ましい。
電極触媒複合体における電子伝導酸化物の割合は、電子伝導酸化物の種類や大きさ、結晶性、並びに複合化される電極触媒粒子の種類、量や大きさに応じて適宜決定される。例えば、電極触媒粒子がＰｔ、電子伝導酸化物がＴｉ酸化物の場合では、Ｐｔ：Ｔｉ＝０．１〜１０：１（モル比）である。
As described above, in the electrode catalyst composite, the electron conductive oxide inhibits the aggregation of the electrode catalyst particles by being present so as to fill the space between the electrode catalyst particles, and the electron conductive oxide has this purpose. It may be included in the form so that it can be achieved. In particular, in the electrode material of the present invention, since the conductive auxiliary material plays a role as the skeleton of the electrode, the electron conductive oxide having a smaller electron conductivity than the carbon-based material can be produced within the range that can be produced in the electrode catalyst composite. A small amount is preferable.
The ratio of the electron conductive oxide in the electrode catalyst composite is appropriately determined according to the type and size of the electron conductive oxide, the crystallinity, and the type, amount and size of the electrode catalyst particles to be composited. For example, when the electrode catalyst particles are Pt and the electron conductive oxide is Ti oxide, Pt: Ti = 0.1 to 10: 1 (molar ratio).
なお、本発明の電極材料では、電子伝導性酸化物は、電極触媒複合体において電極触媒粒子の間を充填させるものであり電子伝導性酸化物を小さくできるので、これに起因する電気抵抗を小さくできる。そのため、電子伝導性酸化物が結晶である場合のみならず、非晶質体であってもよい。
但し、電気抵抗をより小さくするためには、電子伝導性酸化物は結晶であることが好ましい。Ｔｉ酸化物の場合では、より好適には平均粒径５〜４０ｎｍの結晶性のＴｉ酸化物（ＴｉＯ２）である。
In the electrode material of the present invention, the electron conductive oxide fills the space between the electrode catalyst particles in the electrode catalyst composite, and the electron conductive oxide can be reduced, so that the electric resistance caused by this can be reduced. it can. Therefore, the electron conductive oxide may be an amorphous substance as well as a crystal.
However, in order to reduce the electrical resistance, the electron conductive oxide is preferably crystalline. In the case of Ti oxide, a crystalline Ti oxide (TiO 2 ) having an average particle size of 5 to 40 nm is more preferable.
＜本発明の電極材料の製造方法＞
上述した本発明の電極材料の製造方法は特に限定されず、電極材料を構成する導電補助材、電子伝導性酸化物、電極触媒粒子の種類に応じて適宜好適な方法を選択すればよい。本発明の電極材料の製造方法の好適な一例は、以下に説明する製造方法（以下、「本発明の製造方法」と称す。）である。
<Manufacturing method of electrode material of the present invention>
The method for producing the electrode material of the present invention described above is not particularly limited, and a suitable method may be appropriately selected depending on the types of the conductive auxiliary material, the electron conductive oxide, and the electrode catalyst particles constituting the electrode material. A preferred example of the method for producing the electrode material of the present invention is the production method described below (hereinafter, referred to as "the production method of the present invention").
すなわち、本発明の製造方法は、以下の工程（１）及び（２）を含む。
工程（１）：疎水性有機溶媒に、炭素系導電補助材を分散させた分散液に、電極触媒粒子前駆体のアセチルアセトナート化合物と、電子伝導性酸化物前駆体のアセチルアセトナート化合物とを溶解させ、撹拌及び溶媒の留去を行うことにより、電極触媒粒子前駆体と電子伝導性酸化物前駆体とが担持された炭素系導電補助材を得る工程
工程（２）：工程（１）で得らえた電極触媒粒子前駆体と電子伝導性酸化物前駆体とが担持された炭素系導電補助材を、不活性ガス雰囲気で熱処理することによって、電極触媒複合体を形成する工程
That is, the production method of the present invention includes the following steps (1) and (2).
Step (1): An acetylacetonate compound as an electrode catalyst particle precursor and an acetylacetonate compound as an electron conductive oxide precursor are mixed in a dispersion liquid in which a carbon-based conductive auxiliary material is dispersed in a hydrophobic organic solvent. Steps to obtain a carbon-based conductive auxiliary material on which the electrode catalyst particle precursor and the electron conductive oxide precursor are supported by dissolving, stirring and distilling off the solvent Step (2): In step (1). A step of forming an electrode catalyst composite by heat-treating a carbon-based conductive auxiliary material on which the obtained electrode catalyst particle precursor and an electron conductive oxide precursor are supported in an inert gas atmosphere.
本発明の電極材料の製造方法の具体的な一例は後述する実施例で説明する方法である。 A specific example of the method for producing the electrode material of the present invention is the method described in Examples described later.
本発明の製造方法の特徴は、工程（１）において、疎水性有機溶媒を使用し、電極触媒粒子と電子伝導性酸化物の前駆体化合物としてそれぞれのアセチルアセトナート化合物を使用し、これを１ステップで炭素系導電補助材に担持することによって、電極触媒粒子と電子伝導性酸化物とが複合化（ナノコンポジット化）した電極触媒複合体前駆体を得ることができる。また、アセチルアセトナート化合物は、電極触媒の性能低下の一因となる塩素や硫黄といった不純物を含まないという利点がある。 The feature of the production method of the present invention is that in step (1), a hydrophobic organic solvent is used, and each acetylacetonate compound is used as a precursor compound of the electrode catalyst particles and the electron conductive oxide. By supporting the electrode catalyst particles on the carbon-based conductive auxiliary material in the step, an electrode catalyst composite precursor in which the electrode catalyst particles and the electron conductive oxide are compounded (nanocomposited) can be obtained. Further, the acetylacetonate compound has an advantage that it does not contain impurities such as chlorine and sulfur, which contribute to the deterioration of the performance of the electrode catalyst.
本発明の製造方法において、上述した結晶性の高い疎水性の炭素系導電補助材とすると、疎水性有機溶媒中での分散性が高まると共に、アセチルアセトナート化合物が付着しやすいため、電極触媒複合体が高分散に均等に担持される傾向にある。表面がグラファイト構造である炭素系導電補助材の具体例は上述した通りである。 In the production method of the present invention, when the above-mentioned highly crystalline hydrophobic carbon-based conductive auxiliary material is used, the dispersibility in the hydrophobic organic solvent is enhanced and the acetylacetonate compound easily adheres to the electrode catalyst composite. The body tends to be evenly supported with high dispersion. Specific examples of the carbon-based conductive auxiliary material having a graphite structure on the surface are as described above.
工程（２）は、工程（１）で得らえた電極触媒粒子前駆体と電子伝導性酸化物前駆体とが担持された炭素系導電補助材を、不活性ガス雰囲気で熱処理することによって、電極触媒複合体を形成する工程である。
工程（２）において、窒素やアルゴン等の不活性雰囲気で熱処理することで電極触媒前駆体や電子伝導性酸化物前駆体とからなる電極触媒複合体前駆体が分解され、電極触媒となる金属の有する電気化学触媒作用を活性化し、電子伝導性酸化物の結晶性を高め、電子伝導性を向上させる。
In the step (2), the electrode catalyst particle precursor obtained in the step (1) and the carbon-based conductive auxiliary material on which the electron conductive oxide precursor is supported are heat-treated in an inert gas atmosphere to obtain an electrode. This is a step of forming a catalyst complex.
In the step (2), the electrode catalyst complex precursor composed of the electrode catalyst precursor and the electron conductive oxide precursor is decomposed by heat treatment in an inert atmosphere such as nitrogen or argon, and the metal serving as the electrode catalyst is decomposed. It activates the electrochemical catalytic action of the electron conductive oxide, enhances the crystallinity of the electron conductive oxide, and improves the electron conductivity.
本発明の製造方法において、工程（２）における熱処理温度は、使用する原料アセチルアセトナート化合物の分解温度を考慮して適宜決定される。この際に、熱処理を異なる温度で２段階に分けて行うことが好ましい。
例えば、Ｔｉ酸化物の場合には、熱処理温度は電極触媒がＰｔやＰｔ合金の場合、通常、１８０〜４００℃、好適には２００〜２５０℃である。温度が低すぎると電極触媒となる金属の活性化が不十分となり、温度が高すぎると電極触媒粒子が凝集し、有効反応表面積が小さくなりすぎる問題がある。
In the production method of the present invention, the heat treatment temperature in the step (2) is appropriately determined in consideration of the decomposition temperature of the raw material acetylacetonate compound used. At this time, it is preferable that the heat treatment is performed in two stages at different temperatures.
For example, in the case of Ti oxide, the heat treatment temperature is usually 180 to 400 ° C., preferably 200 to 250 ° C. when the electrode catalyst is Pt or Pt alloy. If the temperature is too low, the activation of the metal serving as the electrode catalyst becomes insufficient, and if the temperature is too high, the electrode catalyst particles aggregate and the effective reaction surface area becomes too small.
また、Ｔｉ酸化物等の水素を含有する還元性雰囲気中でも安定な電子伝導性酸化物の場合には、水素の存在下で熱処理を行うことができる。水素は窒素、ヘリウム、アルゴンなどの不活性気体で０．１〜５０％（好適には１〜１０％）に希釈されて用いられる。 Further, in the case of an electron conductive oxide that is stable even in a reducing atmosphere containing hydrogen such as Ti oxide, the heat treatment can be performed in the presence of hydrogen. Hydrogen is used after being diluted to 0.1 to 50% (preferably 1 to 10%) with an inert gas such as nitrogen, helium, or argon.
また、工程（２）において、水蒸気共存下で熱処理を行う工程を含むことが好ましい。水蒸気共存下（加湿雰囲気）における熱処理によって、電子伝導性酸化物前駆体が十分に分解・酸化されるため、電極性能が向上する傾向にある。 Further, it is preferable that the step (2) includes a step of performing a heat treatment in the presence of steam. By heat treatment in the coexistence of water vapor (humidified atmosphere), the electron conductive oxide precursor is sufficiently decomposed and oxidized, so that the electrode performance tends to be improved.
＜２．本発明の電極材料の用途＞
（電極）
本発明の電極材料の用途は限定されないが、固体高分子形燃料電池用電極や、固体高分子形水電解装置用電極の構成材料として好適に使用できる。
本発明の電極材料のＰＥＦＣにおける電極として用いたケースについて説明すると、本発明の電極は、上述の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ことを特徴とする。
<2. Applications of the electrode material of the present invention>
(electrode)
The use of the electrode material of the present invention is not limited, but it can be suitably used as a constituent material of an electrode for a polymer electrolyte fuel cell and an electrode for a polymer electrolyte water electrolyzer.
Explaining the case where the electrode material of the present invention is used as an electrode in PEFC, the electrode of the present invention contains the above-mentioned electrode material and a proton conductive electrolyte material, and the conductive auxiliary materials come into contact with each other to form a conductive path. It is characterized by being.
本発明の電極は、上述の電極材料のみから構成されていてもよいが、通常、燃料電池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。電極材料と共に燃料電池の電極に含まれる電解質材料は、燃料電池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。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 of the present invention may be composed of only the above-mentioned electrode materials, but is usually a proton conductive electrolyte material used for an electrolyte of a fuel cell (hereinafter, “proton conductive electrolyte material”, or simply “electrolyte”. It may be described as "material"). The electrolyte material contained in the electrode of the fuel cell together with the electrode material may be the same as or different from the electrolyte material used for the electrolyte membrane for the fuel cell. From the viewpoint of improving the adhesion between the electrode and the electrolyte membrane, it is preferable to use the same one.
ＰＥＦＣの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 PEFC electrode 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.
上記電極材料と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、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、燃料電池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％より大きい場合は電極材料の連続性が悪くなり、燃料電池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）の拡散性が低下する場合がある。 The mass ratio of the electrode material to the electrolyte material is appropriately adjusted so as to impart good proton conductivity in the electrode formed by using these materials and to smoothly diffuse gas and discharge water vapor in the electrode. You just have to decide. However, if the amount of the electrolyte material mixed with the electrode material is too large, the proton conductivity is improved, but the gas diffusibility 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 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 ensured as an electrode for a fuel cell. On the contrary, if it is more than 50% by mass, the continuity of the electrode material is deteriorated, and it may not be possible to have sufficient electron conductivity as an electrode for a fuel cell. Furthermore, the diffusivity of gas (oxygen, hydrogen, water vapor) inside the electrode may decrease.
本発明の燃料電池用電極は、上述の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。例えば、上述の電極材料に含まれる導電補助材以外の導電補助材（以下、「他の導電補助材」と記載する。）を含んでいてもよい。他の導電補助材を含むことにより、電極材料をつなぐ導電パスが増加し、電極全体としての導電性が向上する場合がある。他の導電補助材としては、上述した導電補助材である繊維状炭素及び鎖状連結炭素粒子でもよいし（但し、電子伝導性酸化物や電極触媒粒子は担持されていないもの）、カーボンブラック、活性炭など通常の粒子状炭素でもよい。 The electrode for a fuel cell of the present invention may contain components other than the above-mentioned electrode material and proton conductive material. For example, a conductive auxiliary material other than the conductive auxiliary material contained in the above-mentioned electrode material (hereinafter, referred to as “another conductive auxiliary material”) may be included. By including the other conductive auxiliary material, the conductive path connecting the electrode materials may be increased, and the conductivity of the electrode as a whole may be improved. Other conductive auxiliary materials may be fibrous carbon and chain-connected carbon particles, which are the above-mentioned conductive auxiliary materials (however, electron conductive oxides and electrode catalyst particles are not supported), carbon black, and the like. Ordinary particulate carbon such as activated carbon may be used.
なお、本発明の電極材料を含む燃料電池用電極として、ＰＥＦＣ用電極について説明したが、ＰＥＦＣ以外にもアルカリ形燃料電池、リン酸形燃料電池などの各種燃料電池における電極として用いることができる。また、ＰＥＦＣと同様な高分子電解質膜を使用した水の電解装置用の電極としても好適に使用することができる。 Although the PEFC electrode has been described as the fuel cell electrode containing the electrode material of the present invention, it can be used as an electrode in various fuel cells such as an alkaline fuel cell and a phosphoric acid fuel cell in addition to PEFC. It can also be suitably used as an electrode for a water electrolyzer using a polymer electrolyte membrane similar to PEFC.
（膜電極接合体）
本発明の電極材料を用いた電極は、固体高分子形燃料電池や固体高分子形水電解装置に用いる膜電極接合体（ＭＥＡ）に好適に使用することができる。
すなわち、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、前記カソードとアノードの少なくとも一方が、上記本発明の電極であることを特徴とする。
本発明の膜電極接合体における本発明の電極以外の構成は、従来公知の構成を適用させることができる。
(Membrane electrode assembly)
The electrode using the electrode material of the present invention can be suitably used for a membrane electrode assembly (MEA) used in a polymer electrolyte fuel cell or a polymer electrolyte water electrolyzer.
That is, the membrane electrode assembly of the present invention includes 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 having the above, and at least one of the cathode and the anode is the electrode of the present invention.
Conventionally known configurations can be applied to the configurations other than the electrodes of the present invention in the membrane electrode assembly of the present invention.
（固体高分子形燃料電池）
本発明の固体高分子形燃料電池（単セル）は、本発明の膜電極接合体を備えてなり、通常、膜電極接合体をガス流路が形成されたセパレータで挟持した構造を有する。
本発明の固体高分子形燃料電池において、本発明の膜電極接合体以外の構成要素は、公知の固体高分子形燃料電池と同様であるため、詳細な説明を省略する。
実際には、本発明の固体高分子形燃料電池（単セル）が発電性能に応じた基数だけ積層された燃料電池スタックが形成され、ガス供給装置、冷却装置などその他付随する装置を組み立てることにより使用される。
(Proton electrolyte fuel cell)
The polymer electrolyte fuel cell (single cell) of the present invention comprises the membrane electrode assembly of the present invention, and usually has a structure in which the membrane electrode assembly is sandwiched between separators having a gas flow path formed therein.
In the polymer electrolyte fuel cell of the present invention, the components other than the membrane electrode assembly of the present invention are the same as those of the known polymer electrolyte fuel cell, and thus detailed description thereof will be omitted.
Actually, a fuel cell stack in which the polymer electrolyte fuel cells (single cells) of the present invention are stacked by the number of units according to the power generation performance is formed, and by assembling other accompanying devices such as a gas supply device and a cooling device. used.
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。なお、以下の実施例の説明において、高黒鉛化カーボンブラックを「ＧＣＢ」と表記し、Ｔｉ酸化物を「ＴｉＯｘ」と表記し、ＰｔとＴｉ酸化物とからなる電極触媒複合体を「Ｐｔ−ＴｉＯｘ」、Ｐｔ−ＴｉＯｘを担持したＧＣＢを「Ｐｔ−ＴｉＯｘ/ＧＣＢ」と記載する場合がある。
Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited thereto. In the description of the following examples, the highly graphitized carbon black is referred to as "GCB", the Ti oxide is referred to as "TiOx", and the electrode catalyst complex composed of Pt and Ti oxide is referred to as "Pt-". The GCB carrying "TiOx" and Pt-TiOx may be described as "Pt-TiOx / GCB".
１．電極材料の作製
実施例の電極材料として、以下の実施例１〜４の電極材料を製造した。
1. 1. Preparation of Electrode Material As the electrode material of the example, the following electrode materials of Examples 1 to 4 were manufactured.
使用した導電補助材、貴金属触媒前駆体、Ｔｉ前駆体は以下の通りである。
＜導電補助材＞
導電補助材として、高黒鉛化カーボンブラック（ＧＣＢ）（キャボット社製、ＧＣＢ２００）を使用した。
＜貴金属触媒前駆体＞
貴金属触媒前駆体として、Ｐｔアセチルアセトナート（Platinum(II) acetylacetonate，97%,Sigma Aldrich）（以下、「Pt（acac)2」と記載する場合がある。）を使用した。
＜電子伝導性酸化物前駆体＞
電子伝導性酸化物前駆体として、Ｔｉアセチルアセトナート（Titanium diisopropoxide bis(acetylacetonate)，75wt.% in isopropanol,Sigma Aldrich）（以下、「Ti（acac)2OiPr2」と記載する場合がある。）を使用した。
The conductive auxiliary materials, noble metal catalyst precursors, and Ti precursors used are as follows.
<Conductive auxiliary material>
Highly graphitized carbon black (GCB) (manufactured by Cabot Corporation, GCB200) was used as the conductive auxiliary material.
<Precious metal catalyst precursor>
As a noble metal catalyst precursor, Pt acetylacetonate (Platinum (II) acetylacetonate, 97%, Sigma Aldrich) (hereinafter, may be referred to as “Pt (acac) 2 ”) was used.
<Electronic conductive oxide precursor>
Ti acetylacetonate (Titanium diisopropoxide bis (acetylacetonate), 75wt.% In isopropanol, Sigma Aldrich) (hereinafter, may be referred to as "Ti (acac) 2 OiPr 2 ") as an electron conductive oxide precursor. It was used.
＜実施例１＞
工程（１）
まず、導電補助材であるＧＣＢ（２０１．５ｍｇ）をナスフラスコに入れ、これにアセトン（３０ｍＬ)を加え、超音波ホモジナイザーで撹拌し、ＧＣＢの分散液を得た。得られたＧＣＢ分散液に、Ｐｔアセチルアセトナート（９１．９ｍｇ）を加え、次いで、イソプロパノールに溶解されたＴｉアセチルアセトナート（１１４μＬ）とを加えて十分に撹拌し溶解させた。Ｐｔ前駆体とＴｉ酸化物前駆体の仕込み量は、電極材料全体に対する担持量としてＰｔを１７．７ｗｔ％、Ｔｉを４．３ｗｔ％となるようにした。なお、当該仕込み量でＰｔ：Ｔｉ（ｍｏｌ比）＝１：１である。
次いで、試料が入ったナスフラスコを減圧機能と回転機能が備わったロータリーエバポレータにセットし、氷冷しながら、溶媒が全て揮発するまで減圧しながら超音波撹拌を行い、粉末（Ｐｔ前駆体とＴｉ酸化物前駆体とを含む電極触媒複合体前駆体を担持したＧＣＢ）を得た。
<Example 1>
Process (1)
First, GCB (201.5 mg), which is a conductive auxiliary material, was placed in an eggplant flask, acetone (30 mL) was added thereto, and the mixture was stirred with an ultrasonic homogenizer to obtain a dispersion of GCB. Pt acetylacetonate (91.9 mg) was added to the obtained GCB dispersion, and then Ti acetylacetonate (114 μL) dissolved in isopropanol was added, and the mixture was thoroughly stirred and dissolved. The amount of the Pt precursor and the Ti oxide precursor charged was set so that Pt was 17.7 wt% and Ti was 4.3 wt% as the supported amount with respect to the entire electrode material. The amount charged is Pt: Ti (mol ratio) = 1: 1.
Next, the eggplant flask containing the sample was set in a rotary evaporator equipped with a depressurizing function and a rotating function, and ultrasonically stirred while cooling with ice until all the solvent was volatilized, and powder (Pt precursor and Ti). A GCB) carrying an electrode-catalyst complex precursor containing an oxide precursor was obtained.
工程（２）
工程（１）で得られた粉末を、Ｎ2雰囲気下で、昇温速度１℃/分、２１０℃で３時間保持、２４０℃で３時間保持の条件で熱処理（還元処理）を施すことで実施例１の電極材料を得た。
Process (2)
The powder obtained in step (1), under N 2, 1 ° C. / minute heating rate, 3 hour hold at 210 ° C., by heat treatment under the conditions of 3 hour hold at 240 ° C. (reduction treatment) The electrode material of Example 1 was obtained.
＜実施例２＞
実施例１の電極材料の製造方法の工程（２）において、Ｎ2雰囲気下で、２４０℃で３時間保持したのちに、０．６％加湿Ｎ２で３０分保持した以外は、実施例１と同様にして実施例２の電極材料を得た。
<Example 2>
In the step (2) of the method for producing the electrode material of Example 1, the electrode material was held at 240 ° C. for 3 hours in an N 2 atmosphere and then held at 0.6% humidified N 2 for 30 minutes. The electrode material of Example 2 was obtained in the same manner as in the above.
＜実施例３＞
実施例１の電極材料の製造方法の工程（２）において、Ｎ2雰囲気下で、２４０℃で３時間保持したのちに、３％加湿Ｎ２で３０分保持した以外は、実施例１と同様にして実施例３の電極材料を得た。
<Example 3>
Same as in Example 1 except that in step (2) of the method for producing an electrode material of Example 1, the electrode material was held at 240 ° C. for 3 hours in an N 2 atmosphere and then held in 3% humidified N 2 for 30 minutes. The electrode material of Example 3 was obtained.
＜実施例４＞
実施例１の電極材料の製造方法の工程（１）において、Ｐｔ前駆体とＴｉ酸化物前駆体の仕込み量を、電極材料形成後の担持量としてＰｔを２０．３ｗｔ％、Ｔｉを１．７ｗｔ％となるようにし（Ｐｔ：Ｔｉ（ｍｏｌ比）＝３：１）、工程（２）において、Ｎ2雰囲気下で、２４０℃で３時間保持したのちに、３％加湿Ｎ２で３０分保持した以外は、実施例１と同様にして実施例４の電極材料を得た。
<Example 4>
In the step (1) of the method for manufacturing the electrode material of Example 1, the amount of the Pt precursor and the Ti oxide precursor charged is 20.3 wt% for Pt and 1.7 wt% for Ti as the supported amount after the electrode material is formed. % (Pt: Ti (mol ratio) = 3: 1), and in step (2), hold at 240 ° C. for 3 hours in an N 2 atmosphere, and then hold for 30 minutes with 3% humidification N 2. The electrode material of Example 4 was obtained in the same manner as in Example 1.
また、実施例の電極材料と比較するための標準触媒として、田中貴金属工業株式会社製Ｐｔ担持カーボン（Ｐｔ/Ｃ、品番：ＴＥＣ１０Ｅ５０Ｅ、Ｐｔ担持率４６ｗｔ％）を使用した。 Further, as a standard catalyst for comparison with the electrode material of Examples, Pt-supported carbon (Pt / C, product number: TEC10E50E, Pt-supporting ratio 46 wt%) manufactured by Tanaka Kikinzoku Kogyo Co., Ltd. was used.
実施例１〜４及び比較例１として使用したＰｔ／Ｃ標準触媒の電極材料を表１にまとめて示す。なお、表１におけるＰｔ担持率は、ＩＣＰ測定での実測値（括弧は仕込み値）である。 Table 1 summarizes the electrode materials of the Pt / C standard catalyst used in Examples 1 to 4 and Comparative Example 1. The Pt loading ratio in Table 1 is an actually measured value (parentheses are the charged value) in ICP measurement.
２．物性評価
２−１．Ｘ線回折（ＸＲＤ）による解析
調製した各電極材料の結晶構造をＸＲＤによって評価した。図２に実施例１の電極材料、図３に実施例３の電極材料、図４に実施例４の電極材料のＸＲＤパターンを示す。なお、２θが約２７°のピークはＧＣＢに起因するピークである。
いずれの電極材料においても、Ｐtピークが確認され、Ｐtが結晶として存在していることが認められた。一方、いずれの電極材料においても、ＴｉＯ２のピークが確認できなかったことから、Ｔｉは非常に微小なＴｉＯ２結晶あるいは非晶質のＴｉ酸化物（ＴｉＯｘ）として存在していると判断できる。
また、ＰｔＴｉやＰｔ３Ｔｉなどの合金の明確なピークは確認されないことから、ＰｔとＴｉの合金はほとんど形成されていないと判断できる。
2. 2. Physical property evaluation 2-1. Analysis by X-ray diffraction (XRD) The crystal structure of each prepared electrode material was evaluated by XRD. FIG. 2 shows the electrode material of Example 1, FIG. 3 shows the electrode material of Example 3, and FIG. 4 shows the XRD pattern of the electrode material of Example 4. The peak with 2θ of about 27 ° is a peak caused by GCB.
A Pt peak was confirmed in each of the electrode materials, and it was confirmed that Pt was present as a crystal. On the other hand, since the peak of TiO 2 could not be confirmed in any of the electrode materials, it can be determined that Ti exists as a very fine TiO 2 crystal or an amorphous Ti oxide (TIOx).
Further, it can be determined that the fact that a clear peak of alloys such PtTi or Pt 3 Ti is not confirmed, an alloy of Pt and Ti are hardly formed.
また、Scherrer法により求めた実施例１，３，４の電極材料のＰｔ微粒子の結晶子径をそれぞれ表２に示す。いずれの条件で調製した電極材料についても、２ｎｍ程度の結晶子径を有するＰｔ微粒子が形成されていることが明らかになった。 Table 2 shows the crystallite diameters of the Pt fine particles of the electrode materials of Examples 1, 3 and 4 obtained by the Scherrer method, respectively. It was clarified that Pt fine particles having a crystallite diameter of about 2 nm were formed in the electrode material prepared under any of the conditions.
２−２．微細構造評価
実施例３の電極材料の微細構造評価を行った結果を図５及び図６に示す。
実施例３の電極材料のＦＥ−ＳＥＭ像（図５（ａ））及びＴＥＭ像（図５（ｂ））から、ＧＣＢに粒径１〜２ｎｍの粒子が高分散に担持されていることが確認された。
また、図６に実施例３の電極材料のＳＴＥＭ像及びＥＤＳ分析を示す。図６のＥＤＳ分析からわかるように、粒径１〜２ｎｍのＰｔ粒子の間に入り込むようにＴｉ酸化物が分布し、ＰｔとＴｉ酸化物とのコンポジット構造を形成していることがわかる。Ｐｔ粒子の間にＴｉ酸化物が入り込むことでＰｔの粒成長が抑えられ、粒径１〜２ｎｍ程度の微小なＰｔ粒子が保持できていると判断した。
上述の通り、ＸＲＤ測定の結果からはＴｉＯ２のピークは検出されず、ＴｉＯ２結晶の存在を確認できなかったが、ＥＤＳ分析結果からはＴｉの存在は確認できたことから、Ｔｉ酸化物は存在していると判断した。
2-2. Microstructure Evaluation The results of the microstructure evaluation of the electrode material of Example 3 are shown in FIGS. 5 and 6.
From the FE-SEM image (FIG. 5 (a)) and TEM image (FIG. 5 (b)) of the electrode material of Example 3, it was confirmed that particles having a particle size of 1 to 2 nm were supported on the GCB in a highly dispersed manner. Was done.
In addition, FIG. 6 shows a STEM image and EDS analysis of the electrode material of Example 3. As can be seen from the EDS analysis of FIG. 6, Ti oxides are distributed so as to enter between Pt particles having a particle size of 1 to 2 nm, and a composite structure of Pt and Ti oxides is formed. It was determined that the growth of Pt particles was suppressed by the inclusion of Ti oxide between the Pt particles, and that fine Pt particles having a particle size of about 1 to 2 nm could be retained.
As described above, the peak of TiO 2 was not detected from the XRD measurement results, and the presence of TiO 2 crystals could not be confirmed. However, since the presence of Ti could be confirmed from the EDS analysis results, the Ti oxide was found. Judged to exist.
実施例４の電極材料の微細構造評価を行った結果を図７に示す。
図３（ｂ）で示したＰｔ：Ｔｉ=１：１（ｍｏｌ比）で調製した実施例３の電極材料のＴＥＭ像と比較すると、Ｐｔ：Ｔｉ=３：１（ｍｏｌ比）で調製した実施例４の電極材料の方が、より微小な粒子が高分散に担持されていることが認められる一方で、一部で粒子が凝集している箇所も確認された。
The result of the microstructure evaluation of the electrode material of Example 4 is shown in FIG.
Compared with the TEM image of the electrode material of Example 3 prepared at Pt: Ti = 1: 1 (mol ratio) shown in FIG. 3 (b), the implementation prepared at Pt: Ti = 3: 1 (mol ratio). In the electrode material of Example 4, it was confirmed that finer particles were supported with higher dispersion, but some parts of the particles were agglomerated.
３．電気化学的評価（ハーフセル）
３−１．電気化学的表面積（ＥＣＳＡ）の評価
実施例１〜４及び比較例１の電極材料について、サイクリックボルタンメトリー（ＣＶ）を行い、ＣＶから求めた水素吸着量から電気化学的表面積（ＥＣＳＡ）を算出した。なお、ＥＣＳＡは、電極材料に含まれるＰｔの有効表面積に相当する。
3. 3. Electrochemical evaluation (half cell)
3-1. Evaluation of Electrochemical Surface Area (ECSA) Cyclic voltammetry (CV) was performed on the electrode materials of Examples 1 to 4 and Comparative Example 1, and the electrochemical surface area (ECSA) was calculated from the hydrogen adsorption amount obtained from the CV. .. ECSA corresponds to the effective surface area of Pt contained in the electrode material.
ＣＶの測定条件は以下の通りである。なお、１原子のＰｔに付き １原子のＨが吸着すると仮定すると２１０μＣ/ｃｍ2の電気量となる。
測定：三電極式セル（作用極：電極材料／ＧＣ、対極：Ｐｔ、参照極：Ａｇ／ＡｇＣｌ）
電解液：０．１Ｍ ＨＣｌＯ4（ｐＨ：約１）
測定電位範囲：０．０５〜１．２Ｖ（可逆水素電極基準）
走査速度 ：５０ ｍＶ／ｓ
水素吸着量：０．０５〜０．４Ｖの水素吸着を示すピーク面積から算出
電気化学的表面積（ＥＣＳＡ）：下記式より算出
ＥＣＳＡ＝（水素吸着量）[μＣ] / ２１０[μＣ/ｃｍ2]
The measurement conditions for CV are as follows. Assuming that 1 atom of H is adsorbed per 1 atom of Pt, the amount of electricity is 210 μC / cm 2 .
Measurement: Three-electrode cell (working electrode: electrode material / GC, counter electrode: Pt, reference electrode: Ag / AgCl)
Electrolyte: 0.1M HClO4 (pH: about 1)
Measurement potential range: 0.05 to 1.2 V (based on reversible hydrogen electrode)
Scanning speed: 50 mV / s
Hydrogen adsorption amount: Calculated from the peak area showing hydrogen adsorption of 0.05 to 0.4 V Electrochemical surface area (ECSA): Calculated from the following formula
ECSA = (hydrogen adsorption amount) [μC] / 210 [μC / cm 2 ]
実施例１〜４及び比較例１の電極材料のＣＶにおいて水素の吸脱着に由来するピークが観察された（図示せず）。ＣＶから求めた実施例１〜４及び比較例１の電極材料の電気化学的表面積（ＥＣＳＡ）の評価結果を図８に示す。
図８に示されるように、実施例１〜４の電極材料は、比較例１の電極材料（Ｐｔ／Ｃ、標準触媒）と比較していずれもＥＣＳＡが大きいことが分かる。この結果は、上述の通り、実施例の電極材料におけるＰｔ粒子の粒径は１〜２ｎｍ程度と非常に小さく、高分散担持され、Ｐｔ有効表面積が増大したことに起因していると判断した。
また、加湿処理を行っていない実施例１の電極材料よりも、加湿熱処理を行った実施例２（０．６％加湿）の方がＥＣＳＡが大きく、さらに水蒸気濃度を高めた実施例３（３％加湿）の方がＥＣＳＡがより大きいことが分かる。加湿雰囲気における熱処理によって、Ｔｉ前駆体（Ti(acac)2OiPr2）が十分に分解・酸化され、電極触媒複合体に含まれるＰｔ及びＴｉが、金属ＰｔとＴｉ酸化物（ＴｉＯｘ）に明確に相分離したことに起因していると判断した。
Ｐｔ：Ｔｉ=３：１（ｍｏｌ比）で調製した実施例４の電極材料の方が、Ｐｔ：Ｔｉ=１：１（ｍｏｌ比）で調製した実施例３の電極材料よりもＥＣＳＡが小さいが、上記微細構造評価の通り、実施例４の電極材料は、微小なＰｔ粒子が高分散に担持されているものの、一部で凝集している粒子が存在しているためと判断した。
Peaks derived from hydrogen adsorption and desorption were observed in the CVs of the electrode materials of Examples 1 to 4 and Comparative Example 1 (not shown). FIG. 8 shows the evaluation results of the electrochemical surface area (ECSA) of the electrode materials of Examples 1 to 4 and Comparative Example 1 obtained from CV.
As shown in FIG. 8, it can be seen that the electrode materials of Examples 1 to 4 all have a larger ECSA than the electrode materials of Comparative Example 1 (Pt / C, standard catalyst). As described above, it was judged that this result was caused by the fact that the particle size of the Pt particles in the electrode material of the example was very small, about 1 to 2 nm, was supported with high dispersion, and the effective surface area of Pt was increased.
Further, the ECSA of Example 2 (0.6% humidification) subjected to the humidification heat treatment was larger than that of the electrode material of Example 1 not subjected to the humidification treatment, and the water vapor concentration was further increased in Example 3 (3). It can be seen that the ECSA is larger for% humidification). By heat treatment in a humidified atmosphere, the Ti precursor (Ti (acac) 2 OiPr 2 ) is sufficiently decomposed and oxidized, and Pt and Ti contained in the electrode catalyst complex are clearly converted into metal Pt and Ti oxide (TIOx). It was judged that it was caused by the phase separation.
Although the electrode material of Example 4 prepared with Pt: Ti = 3: 1 (mol ratio) has a smaller ECSA than the electrode material of Example 3 prepared with Pt: Ti = 1: 1 (mol ratio). As described in the above microstructure evaluation, it was determined that the electrode material of Example 4 had fine Pt particles supported in a high dispersion, but some particles were agglomerated.
３−２．ＯＲＲ活性の評価
実施例１〜４及び比較例１の電極材料について、ＯＲＲ活性を評価した。
ＯＲＲ活性は、回転ディスク電極法（ＲＤＥ法）でリニアスイープボルタンメトリー（ＬＳＶ）を行い、得られる活性化支配電流（ik）を基に算出するMass activity（単位Ｐｔ質量当たりの活性）を指標とした。
Ｍａｓｓ ａｃｔｉｖｉｔｙ = ｉｋ / 電極上のＰｔ質量
活性化支配電流（ik）は、回転電極測定によって得られた電流−電位曲線について、任意の電位においてi-1とω-1/2でプロットして得られるKoutecky-Levichプロットを作成し、得られた直線を外挿することによって切片から求めた。
具体的な手順として、まず、Ｏ2を５０ｍＬ/分で３０分間バブリングした後、０．２ＶRHEから貴な方向に向けて１０ｍＶ/ｓで１．２０ＶRHEまで電位を走査し、測定を行なった。なお、測定中は常にＯ2を５０ｍＬ/分でパージした。なお、ＶRHEは可逆水素電極（ＲＨＥ）基準の電位である
3-2. Evaluation of ORR activity The ORR activity was evaluated for the electrode materials of Examples 1 to 4 and Comparative Example 1.
The ORR activity is indexed by Mass activity (activity per unit Pt mass) calculated based on the activation dominant current (i k ) obtained by performing linear sweep voltammetry (LSV) by the rotating disk electrode method (RDE method). did.
Pt mass on Mass activity = i k / electrode
For the activation dominant current (i k ), create a Koutecky-Levich plot obtained by plotting the current-potential curve obtained by rotating electrode measurement with i -1 and ω -1 / 2 at any potential. Obtained from the section by extrapolating the resulting straight line.
As a specific procedure, first, O 2 was bubbled at 50 mL / min for 30 minutes, and then the potential was scanned from 0.2 V RHE to 1.20 V RHE at 10 mV / s in a noble direction to perform measurement. During the measurement, O 2 was always purged at 50 mL / min. V RHE is a potential based on the reversible hydrogen electrode (RHE).
図９に実施例１〜３及び比較例１の電極材料のリニアスイープボルタモグラム(１６００ｒｐｍ)を示す。図９において、実施例１〜３の対比から、熱処理における水蒸気濃度を高くするほど酸素還元電位がポジティブシフトしていることから、水蒸気共存下での熱処理により電極性能が向上していることが示された。
図１０に、実施例１〜４及び比較例１の電極材料のMass activityの評価結果を示す。
図１０からわかるように、加湿なしの実施例１、または０．６％加湿の実施例２の電極材料は、比較例１の電極材料（Ｐ／Ｃ標準触媒）よりもMass activityが小さかった。一方、３％加湿の実施例３及び実施例４の電極材料は、比較例１の電極材料よりもMass activityが大きな値を示していた。３％加湿の実施例３の電極材料はではMass activityがはるかに大きくなっていることが確認された。これら結果から、Ｐｔ−ＴｉＯｘ/ＧＣＢからなる電極材料は、水蒸気共存下での熱処理により、Mass activityが増加すると判断した。なお、加湿なしの実施例１又は０．６％加湿の実施例２の電極材料はほとんどMass activityの値に差が見られなかったが、０．６％加湿窒素雰囲気での熱処理では不十分であったと判断した。
FIG. 9 shows a linear sweep voltammogram (1600 rpm) of the electrode materials of Examples 1 to 3 and Comparative Example 1. In FIG. 9, from the comparison of Examples 1 to 3, the oxygen reduction potential shifts positively as the water vapor concentration in the heat treatment increases, indicating that the electrode performance is improved by the heat treatment in the presence of water vapor. Was done.
FIG. 10 shows the evaluation results of the Mass activity of the electrode materials of Examples 1 to 4 and Comparative Example 1.
As can be seen from FIG. 10, the electrode material of Example 1 without humidification or Example 2 with 0.6% humidification had a smaller mass activity than the electrode material of Comparative Example 1 (P / C standard catalyst). On the other hand, the electrode materials of Examples 3 and 4 with 3% humidification showed a larger mass activity value than the electrode materials of Comparative Example 1. It was confirmed that the electrode material of Example 3 with 3% humidification had a much larger mass activity. From these results, it was judged that the mass activity of the electrode material made of Pt-TiOx / GCB was increased by the heat treatment in the coexistence of water vapor. The electrode materials of Example 1 without humidification or Example 2 with 0.6% humidification showed almost no difference in the mass activity value, but the heat treatment in a 0.6% humidified nitrogen atmosphere was insufficient. I decided it was there.
３−３．負荷変動サイクル試験
ＯＲＲ活性が最大となった実施例３の電極材料について、負荷変動サイクル耐久性試験を行った。負荷変動サイクル試験は、燃料電池実用化推進協議会（ＦＣＣＪ）が推奨する方法（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）にて、負荷変動を模擬した電位サイクルを負荷することによって行った。図１１に示す負荷変動サイクルは，触媒自体の溶解・再析出などを伴う劣化を促進させるサイクルであり、０．６〜１．０ ＶRHEの短形波を用いて１サイクル当たり３秒ずつの６秒負荷することで実験を行い、４０万サイクル後のＥＣＳＡを測定した。
3-3. Load Fluctuation Cycle Test A load fluctuation cycle durability test was conducted on the electrode material of Example 3 in which the ORR activity was maximized. The load fluctuation cycle test is performed by the method recommended by the Fuel Cell Practical Use Promotion Council (FCCJ) (Proposal of goals / R & D issues and evaluation methods for polymer electrolyte fuel cells, published in January 2011). This was done by loading a potential cycle that simulated fluctuations. The load fluctuation cycle shown in FIG. 11 is a cycle that promotes deterioration accompanied by dissolution / reprecipitation of the catalyst itself, and is a cycle of 3 seconds per cycle using a short wave of 0.6 to 1.0 V RHE . The experiment was carried out by loading for 6 seconds, and the ECSA after 400,000 cycles was measured.
図１２に負荷変動サイクル試験(４０万サイクル)における実施例３及び比較例１の電極材料のＥＣＳＡ変化を示す。
図１２からわかるように、ＥＣＳＡが初期値の５０％を切ったのは、比較例１の電極材料（Ｐｔ/Ｃ）で４万サイクルであり、実施例３の電極材料で６万サイクルであった。また、４０万サイクル後のＥＣＳＡ保持率は、比較例１の電極材料で１４．９％、実施例３の電極材料で２３．７ ％であった。また、負荷変動サイクル試験のＯＲＲ活性を評価したところ（図示せず）、負荷変動サイクル印加による酸素還元電位のネガティブシフトが小さいことが確認されたことから、実施例３の電極材料はＥＣＳＡとＯＲＲ活性の両面で、標準触媒である比較例１の電極材料（Ｐｔ/Ｃ）より高い負荷変動サイクル耐久性を有していることが確認された。
FIG. 12 shows the ECSA changes of the electrode materials of Example 3 and Comparative Example 1 in the load fluctuation cycle test (400,000 cycles).
As can be seen from FIG. 12, ECSA fell below 50% of the initial value in 40,000 cycles for the electrode material (Pt / C) of Comparative Example 1 and 60,000 cycles for the electrode material of Example 3. It was. The ECSA retention rate after 400,000 cycles was 14.9% for the electrode material of Comparative Example 1 and 23.7% for the electrode material of Example 3. Further, when the ORR activity of the load fluctuation cycle test was evaluated (not shown), it was confirmed that the negative shift of the oxygen reduction potential due to the application of the load fluctuation cycle was small. Therefore, the electrode materials of Example 3 were ECSA and ORR. In terms of both activity, it was confirmed that the electrode material (Pt / C) of Comparative Example 1 which is a standard catalyst has higher load fluctuation cycle durability.
本発明の電極材料によれば、優れた電極触媒活性、電子伝導性、ガス拡散性、及び優れた耐久性を有する電極を供することができる。当該電極は、長期運転が必要である固体高分子形燃料電池用の電極に好適である。 According to the electrode material of the present invention, it is possible to provide an electrode having excellent electrode catalytic activity, electron conductivity, gas diffusivity, and excellent durability. The electrode is suitable for an electrode for a polymer electrolyte fuel cell that requires long-term operation.
Claims (10)
前記電極触媒複合体は、電極触媒粒子と、電子伝導性酸化物とを含み、
前記電子伝導性酸化物は、前記電極触媒粒子の間に存在することを特徴とする電極材料。 It contains a carbon-based conductive auxiliary material and an electrode catalyst composite supported on the carbon-based conductive auxiliary material.
The electrode catalyst composite contains electrode catalyst particles and an electron conductive oxide.
An electrode material characterized in that the electron conductive oxide is present between the electrode catalyst particles.
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| WO2023037953A1 (en) * | 2021-09-08 | 2023-03-16 | 国立大学法人弘前大学 | Electroconductive titanium oxide, metal-supported electroconductive titanium oxide, membrane electrode assembly, solid polymer electrolyte fuel cell, method for producing electroconductive titanium oxide, and method for producing metal-supported electroconductive titanium oxide |
| WO2023132374A1 (en) * | 2022-01-10 | 2023-07-13 | 国立大学法人九州大学 | Electrode material, method for producing same, and electrode using same, membrane electrode assembly, and solid-state polymer fuel cell |
| JP2023134400A (en) * | 2022-03-14 | 2023-09-27 | 国立大学法人九州大学 | Electrode material, electrode using the same, membrane electrode assembly and polymer electrolyte fuel cell |
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