JP5644277B2 - Method for observing the reaction layer of a fuel cell - Google Patents

Method for observing the reaction layer of a fuel cell Download PDF

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JP5644277B2
JP5644277B2 JP2010195090A JP2010195090A JP5644277B2 JP 5644277 B2 JP5644277 B2 JP 5644277B2 JP 2010195090 A JP2010195090 A JP 2010195090A JP 2010195090 A JP2010195090 A JP 2010195090A JP 5644277 B2 JP5644277 B2 JP 5644277B2
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山本　泰三
泰三 山本
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Equos Research Co Ltd
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Description

本発明は、燃料電池の反応層の観察方法に関する。   The present invention relates to a method for observing a reaction layer of a fuel cell.

燃料電池に用いられる膜電極接合体は固体高分子電解質膜を水素極と空気極とで挟んだ構成であり、水素極及び空気極はそれぞれ固体高分子電解質膜側から反応層と拡散層とを順次積層してなる。
反応層は触媒と電解質との混合物からなり、電子及びプロトンの伝導性と通気性が求められる。ここにプロトンは水を伴ってＨ３Ｏ＋のかたちで移動するので、反応層を湿潤状態に維持する必要がある。勿論、反応層に水分が過剰に存在すると通気性を阻害するので（いわゆるフラッディング現象）、反応層の水分は常に適当量に維持されなければならない。
かかる要求を満足すべく、本出願人は、特許文献１及び特許文献２において触媒と電解質との間に薄い水の膜を備える触媒ペーストを提案している。かかる触媒ペーストは、触媒と水とを予め混合したプレペーストを準備し、このプレペーストと電解質溶液とを混合し、適切な撹拌方法を採用することにより得られる。このように形成される触媒ペーストでは、電解質の親水基が触媒を覆う水膜に引き寄せられて対向し、電解質と触媒と間に親水性の領域が形成され、この親水性領域が水の膜となる。以下、触媒と電解質との混合物において触媒と電解質との間に親水性の領域を有する構造を「ＰＦＦ構造」ということがある。
電解質と触媒との間の親水性の領域を連続させることにより（即ち、当該親水性の領域を斑状としないことにより）、反応層における水の偏在が防止される。また、燃料電池を低加湿環境下で運転するときにおいても、この親水性の領域に水がまとまって存在するので、過乾燥を防止できる。また、高加湿環境下での運転では、過剰な水がこの親水性の領域を介して外部（拡散層側）へ排出されるので、フラッティングを防止できる。
なお、本件発明に関連する技術を開示する文献として特許文献３及び非特許文献１〜３を参照されたい。 A membrane electrode assembly used in a fuel cell has a structure in which a solid polymer electrolyte membrane is sandwiched between a hydrogen electrode and an air electrode. The hydrogen electrode and the air electrode are each provided with a reaction layer and a diffusion layer from the solid polymer electrolyte membrane side. It is laminated sequentially.
The reaction layer is composed of a mixture of a catalyst and an electrolyte, and is required to have electron and proton conductivity and air permeability. Here, since protons move in the form of H 3 O + with water, it is necessary to maintain the reaction layer in a wet state. Of course, excessive moisture in the reaction layer inhibits air permeability (so-called flooding phenomenon), so the moisture in the reaction layer must always be maintained at an appropriate amount.
In order to satisfy this requirement, the present applicant has proposed a catalyst paste including a thin water film between the catalyst and the electrolyte in Patent Document 1 and Patent Document 2. Such a catalyst paste can be obtained by preparing a pre-paste in which a catalyst and water are mixed in advance, mixing the pre-paste and the electrolyte solution, and employing an appropriate stirring method. In the catalyst paste formed in this way, the hydrophilic group of the electrolyte is attracted to and opposed to the water film covering the catalyst, and a hydrophilic region is formed between the electrolyte and the catalyst. Become. Hereinafter, a structure having a hydrophilic region between the catalyst and the electrolyte in the mixture of the catalyst and the electrolyte may be referred to as a “PFF structure”.
By making the hydrophilic region between the electrolyte and the catalyst continuous (that is, by making the hydrophilic region not patchy), uneven distribution of water in the reaction layer is prevented. Further, even when the fuel cell is operated in a low humidified environment, water is present in this hydrophilic region, so that overdrying can be prevented. Further, in operation in a highly humidified environment, excess water is discharged to the outside (diffusion layer side) through this hydrophilic region, so that flatting can be prevented.
In addition, please refer to patent document 3 and nonpatent literatures 1-3 as literature which discloses the technique relevant to this invention.

特開２００６−１４００６１号公報JP 2006-140061 A 特開２００６−１４００６２号公報JP 2006-140062 JP 特開２００９−１０４９０５号公報JP 2009-104905 A

Journal of Electrochemical Society 2005, vol.152,No.5,PP.A970-A977 MAKHARIA Rohit ; MATHIAS Mark F. ; BAKER Daniel R. “Measurement of catalyst layer electrolyte resistance in PEFCs using electrochemicalimpedance spectroscopy”Journal of Electrochemical Society 2005, vol.152, No.5, PP.A970-A977 MAKHARIA Rohit; MATHIAS Mark F.; BAKER Daniel R. “Measurement of catalyst layer electrolyte resistance in PEFCs using electrochemicalimpedance spectroscopy” Journal of Electroanalytical Chemistry 475, 107-123(1999) M.Eikerling and A.A.kornyshev “electrochemical impedance of Cathode Catalyst Layer of Polymer Electrolyte Fuel Cells”Journal of Electroanalytical Chemistry 475, 107-123 (1999) M.Eikerling and A.A.kornyshev “electrochemical impedance of Cathode Catalyst Layer of Polymer Electrolyte Fuel Cells” 「電気化学インピーダンス法」（丸善 板垣 昌幸） ８ 分布定数型等価回路を用いた電気化学インピーダンス解析(pp133〜146)"Electrochemical Impedance Method" (Maruzen, Masayuki Itagaki) 8 Electrochemical Impedance Analysis Using Distributed Constant Type Equivalent Circuit (pp133-146)

ＰＦＦ構造に限らず、プロトンの伝導性を確保するには水のパスが形成されていなければならない。反応層を構成する物質において本質的に親水性であるのは、電解質の親水基（例えばスルホン基）であり、反応層において水のパスを形成するにはこの親水基が凝集し、かつその凝集体が連続していることが必要である。
なお、既述のＰＦＦ構造は触媒の表面に親水基の凝集体を集め、当該触媒表面に水のパスを形成したものである。
例えば、親水基が分散していると、当該親水基に吸着された水が相互に離隔して水のパスが形成されない。よって、外部から供給されるプロトンを受け渡しすることができない。また、過剰な生成水を排水する観点からも好ましくない。
このように、燃料電池の反応層の特性を知る上で、電解質の親水基の分布状態を把握することは重要である。しかしながら、従来技術において、これを把握する方法は何ら提供されていない。 Not only the PFF structure but also a water path must be formed to ensure proton conductivity. It is the hydrophilic group (for example, sulfone group) of the electrolyte that is essentially hydrophilic in the material constituting the reaction layer, and this hydrophilic group aggregates and forms the aggregate in order to form a water path in the reaction layer. The collection must be continuous.
The PFF structure described above is one in which aggregates of hydrophilic groups are collected on the surface of the catalyst and a water path is formed on the surface of the catalyst.
For example, when hydrophilic groups are dispersed, water adsorbed on the hydrophilic groups is separated from each other, and a water path is not formed. Therefore, protons supplied from outside cannot be delivered. Moreover, it is not preferable also from a viewpoint of draining excess generated water.
Thus, in order to know the characteristics of the reaction layer of the fuel cell, it is important to grasp the distribution state of the hydrophilic group of the electrolyte. However, the conventional technology does not provide any method for grasping this.

本発明者は反応層中の電解質の親水基の分布状態について検討を重ね、電解質の親水基に官能基を親和させ、この官能基を金属イオンで染色することにより親水基の分布状態を顕微鏡で観察可能であることに気づき、この発明を完成するに至った。
即ち、この発明の第１の局面は次のように規定される。
燃料電池の反応層を構成する電解質の親水基に官能基を親和させるステップと、
前記官能基と錯体を形成可能な金属イオンを前記反応層へ導入し、該金属イオンにより前記官能基を染色するステップと、を含むことを特徴とする燃料電池反応層の観察方法。
かかる観察方法によれば、電解質の親水基が、官能基を介しての間接的にではあるが、金属イオンで染色されるので、当該親水基の分布状態を顕微鏡により目視観察可能となる。 The present inventor has repeatedly investigated the distribution state of hydrophilic groups of the electrolyte in the reaction layer, and made the functional group affinity to the hydrophilic group of the electrolyte, and stained the functional group with a metal ion to observe the distribution state of the hydrophilic group with a microscope. It was noticed that it was observable, and the present invention was completed.
That is, the first aspect of the present invention is defined as follows.
A step of making the functional group affinity with the hydrophilic group of the electrolyte constituting the reaction layer of the fuel cell;
Introducing a metal ion capable of forming a complex with the functional group into the reaction layer, and staining the functional group with the metal ion.
According to such an observation method, since the hydrophilic group of the electrolyte is dyed with the metal ion indirectly through the functional group, the distribution state of the hydrophilic group can be visually observed with a microscope.

燃料電池の反応層に用いられる電解質は高分子化合物からなり、例えばナフィオン（デュポン社商標名、以下同じ）等のフッ素系ポリマーが一般的に用いられる。この高分子化合物は、図１に示すように、疎水性の主鎖１００と親水性のイオン交換基を持つ側鎖１０１を有する。親水性のイオン交換基は、例えばスルホン基（ＳＯ３ -）からなる。
かかる電解質は溶媒に溶解される。この溶媒は水と有機溶剤との混合物からなる。電解質溶液は触媒と混合され触媒ペーストとなる。
電解質溶液において電解質と水分量との間には次の関係がある。
電解質溶液中の水分の濃度を低減させると、電解質溶液における電解質の濃度が同じ場合においても電解質溶液の粘度が高くなり、逆に水分の濃度を高くすると電解質溶液の粘度が低くなる。この理由は次のように推定される。
即ち、電解質溶液の水分の濃度が高い場合、図１（Ａ）に示す通り、電解質８２の側鎖１０１に水が吸着し電解質溶液中で電解質８２の固形分が凝集した状態となり、電解質溶液の粘度が低下する。また、電解質溶液の水分濃度がやや低くなれば、電解質溶液に含有されている有機溶媒の作用によって、図１の（Ｂ）に示すように、電解質溶液中で電解質８２の固形分が開き、相互に絡むため電解質溶液の粘度が上昇する。 The electrolyte used for the reaction layer of the fuel cell is made of a polymer compound, and for example, a fluorine-based polymer such as Nafion (trade name of DuPont, the same shall apply hereinafter) is generally used. As shown in FIG. 1, the polymer compound has a hydrophobic main chain 100 and a side chain 101 having a hydrophilic ion exchange group. The hydrophilic ion exchange group is composed of, for example, a sulfone group (SO 3 − ).
Such an electrolyte is dissolved in a solvent. This solvent consists of a mixture of water and an organic solvent. The electrolyte solution is mixed with a catalyst to form a catalyst paste.
There is the following relationship between the electrolyte and the amount of water in the electrolyte solution.
When the concentration of water in the electrolyte solution is reduced, the viscosity of the electrolyte solution increases even when the concentration of the electrolyte in the electrolyte solution is the same. Conversely, when the concentration of water is increased, the viscosity of the electrolyte solution decreases. The reason for this is estimated as follows.
That is, when the concentration of water in the electrolyte solution is high, as shown in FIG. 1A, water is adsorbed on the side chain 101 of the electrolyte 82 and the solid content of the electrolyte 82 is aggregated in the electrolyte solution. Viscosity decreases. Further, when the water concentration of the electrolyte solution is slightly lowered, the solid content of the electrolyte 82 is opened in the electrolyte solution by the action of the organic solvent contained in the electrolyte solution, as shown in FIG. As a result, the viscosity of the electrolyte solution increases.

凝集が進行した電解質８２（図１Ａ）の固形分を含む電解質溶液を混合して反応層を形成した場合、この反応層では、図２に示すような状態となっていると考えられる。すなわち、電解質８２の固形分が凝集していることから、側鎖１０１が多方向に向かって延びることとなる。そして、この側鎖１０１と反応層中の水とが吸着することにより、反応層中で親水性の領域８３が分散して形成されることとなる。このため、この反応層において電解質８２の固形分が凝集している箇所では、反応層中のイオン抵抗により、プロトン及び水が反応層内を移動し難い。このため、低加湿状態では、電解質膜及び各触媒層中の電解質８２の乾燥による性能低下を引き起こし、過加湿状態では、フラッディングによる性能低下が生じる要因となる。
換言すれば、電解質の親水基（側鎖１０１）を触媒へ対向させて両者の間に親水性の領域を確実に形成するためには、電解質溶液中において電解質は図１（Ｂ）の状態にすることが好ましい。そのためには、既述のとおり、電解質溶液に含まれる水分量を電解質溶液の１０重量％以下とする。 When the reaction solution is formed by mixing the electrolyte solution containing the solid content of the electrolyte 82 (FIG. 1A) in which the aggregation has progressed, it is considered that the reaction layer is in a state as shown in FIG. That is, since the solid content of the electrolyte 82 is aggregated, the side chain 101 extends in multiple directions. Then, the side chains 101 and the water in the reaction layer are adsorbed, so that hydrophilic regions 83 are dispersed and formed in the reaction layer. For this reason, in the reaction layer where the solid content of the electrolyte 82 is aggregated, protons and water hardly move in the reaction layer due to ionic resistance in the reaction layer. For this reason, in a low humidification state, the performance degradation by drying of the electrolyte membrane and the electrolyte 82 in each catalyst layer is caused, and in the excessive humidification state, a performance degradation by flooding is caused.
In other words, in order to make the hydrophilic region (side chain 101) of the electrolyte face the catalyst and to reliably form a hydrophilic region between the two, the electrolyte is in the state of FIG. It is preferable to do. For this purpose, as described above, the amount of water contained in the electrolyte solution is set to 10% by weight or less of the electrolyte solution.

図１（Ｂ）の状態の電解質を用いたときのカソード触媒層は図３の状態になると考えられる。
電解質８２の側鎖１０１は、一方向に延びた状態にあり、このため、触媒ペースト、すなわち燃料電池用反応層では、親水性のイオン交換基（スルホン基）がプレペースト中の水を吸着することとなる。このため、図３に示すように、この反応層では、触媒８１の表面に電解質８２の親水基１０１が対向した状態となり、電解質８２と触媒８１との間に親水性の領域８３が形成される。そして、上記のようにスルホン基がプレペースト中の水と吸着することで、触媒８１周りに親水領域８３が連続して形成され、かつ互いに連通した状態で形成されると考えられる。このため、この触媒ペーストを用いた反応層では、図３に示すように、プロトン及び水が移動し易く、電気化学的反応が円滑に進行される。かかる反応層を有する燃料電池は低加湿状態及び過加湿状態のいずれであっても、発電能力を高くすること可能となる。
詳細は特願２０１０−００２３６２号を参照されたい。 The cathode catalyst layer when the electrolyte in the state of FIG. 1B is used is considered to be in the state of FIG.
The side chain 101 of the electrolyte 82 extends in one direction. Therefore, in the catalyst paste, that is, the fuel cell reaction layer, hydrophilic ion exchange groups (sulfone groups) adsorb water in the pre-paste. It will be. For this reason, as shown in FIG. 3, in this reaction layer, the hydrophilic group 101 of the electrolyte 82 faces the surface of the catalyst 81, and a hydrophilic region 83 is formed between the electrolyte 82 and the catalyst 81. . Then, it is considered that the hydrophilic region 83 is continuously formed around the catalyst 81 and is in a state of communicating with each other as the sulfone group adsorbs with the water in the pre-paste as described above. For this reason, in the reaction layer using this catalyst paste, as shown in FIG. 3, protons and water easily move, and the electrochemical reaction proceeds smoothly. A fuel cell having such a reaction layer can have a high power generation capacity regardless of whether it is in a low humidified state or an excessively humidified state.
For details, refer to Japanese Patent Application No. 2010-002362.

電解質の親水基に親和する官能基として、硝酸基、アミノ基、スルホン酸基、水酸基及びハロゲン基から選ばれる少なくとも１種を選択できる。電解質の親水基がスルホン基の場合、好ましい官能基は硝酸基、アミノ基若しくはスルホン酸基であり、更に好ましくは硝酸基である。
電解質の親水基へかかる官能基を親和させる方法は特に限定されないが、予め触媒側に官能基を付与しておくことが好ましい。ここに、親和とは、親水基へ官能基が化学的に吸着された状態をいう。 As the functional group having an affinity for the hydrophilic group of the electrolyte, at least one selected from a nitric acid group, an amino group, a sulfonic acid group, a hydroxyl group, and a halogen group can be selected. When the hydrophilic group of the electrolyte is a sulfone group, the preferred functional group is a nitrate group, an amino group or a sulfonic acid group, and more preferably a nitrate group.
A method for making the functional group affinity to the hydrophilic group of the electrolyte is not particularly limited, but it is preferable to give the functional group to the catalyst side in advance. Here, affinity means a state in which a functional group is chemically adsorbed to a hydrophilic group.

触媒へ官能基を導入する際には、触媒の触媒金属粒子へ当該官能基を集中しておくことが好ましい。電解質溶液と触媒とを混合するときに、官能基が分散していると電解質の親水基に干渉し、電解質を開いた状態（図１（Ｂ）参照）に維持できないおそれがあるからである。
触媒金属粒子へ官能基を集中しておくには、触媒金属粒子と同一若しくは同種の金属の錯体であって当該官能基を含むものを当該触媒金属粒子へ結合する。
触媒金属粒子に白金粒子若しくは白金合金粒子を採用したときには、次の溶液を用いることにより触媒金属（Ｐｔ）粒子を官能基で修飾できる。
（１）官能基：硝酸基の例
ジニトロジアンミン白金（II）硝酸溶液（cis-[Pt(NH3)2(NO2)2]/HNO3 sln.）
同エージング処理品（cis-[Pt(NO2)4]/HNO3 sln.）
ヘキサヒドロキソ白金（IV）酸硝酸溶液（(H2Pt(OH)6)/HNO3 sol.）
（２）官能基：スルホン酸基の例
ヘキサヒドロキソ白金（IV）酸硫酸溶液（(H2Pt(OH)6)/H2SO4 sol.）
（３）官能基：アミノ基の例
テトラアンミン白金（II）水酸化物水溶液（[Pt(NH3)4(OH)2]/H2O sln.） When introducing the functional group into the catalyst, it is preferable to concentrate the functional group on the catalyst metal particles of the catalyst. This is because, when the electrolyte solution and the catalyst are mixed, if the functional group is dispersed, the electrolyte may interfere with the hydrophilic group of the electrolyte, and the electrolyte may not be kept open (see FIG. 1B).
In order to concentrate the functional groups on the catalyst metal particles, the same or the same kind of metal complex as the catalyst metal particles and containing the functional group is bonded to the catalyst metal particles.
When platinum particles or platinum alloy particles are employed as the catalyst metal particles, the catalyst metal (Pt) particles can be modified with functional groups by using the following solution.
(1) the functional groups: Examples of a nitrate group Jinitoroji ammine platinum (II) nitrate solution (cis- [Pt (NH3) 2 (NO2) 2] / HNO3 sln.)
Aged product (cis- [Pt (NO2) 4] / HNO3 sln.)
Hexahydroxoplatinum (IV) acid nitric acid solution ((H2Pt (OH) 6) / HNO3 sol.)
(2) Functional groups: Examples of sulfonic acid groups Hexahydroxoplatinum (IV) acid sulfuric acid solution ((H2Pt (OH) 6) / H2SO4 sol.)
(3) Functional group: Example of amino group Tetraammineplatinum (II) hydroxide aqueous solution ([Pt (NH3) 4 (OH) 2] / H2O sln.)

反応層において燃料電池反応が進行すると、生成水の生成及び移動に伴い、触媒金属粒子に集中していた官能基はこれから離れて反応層中に分散する。これにより、反応層中の電解質の親水基に官能基が結合する。
予め触媒側へ官能基を導入することなく、触媒ペースト若しくは反応層に対して後から官能基を導入してもよい。
反応層の全体へ官能基を行き渡らせるには、反応層へ官能基を導入後、燃料電池反応を実行し生成水を発生させてこれを移動させることが好ましい。このとき燃料電池反応は高加湿条件とし、生成水リッチとすることが好ましい。
導入する官能基の量はその当量を親水基の当量以上とすべきものであるが、燃料電池反応を実行させる見地から、官能基の導入量は０．０５〜０．６当量とすることが好ましい。
勿論、大量の官能基を反応層へ浸潤させることにより、反応層全体の電解質の親水基へ感応層を均一に親和させることができる。 As the fuel cell reaction proceeds in the reaction layer, the functional groups concentrated on the catalyst metal particles are dispersed in the reaction layer away from the catalyst metal particles as the produced water is generated and moved. Thereby, a functional group couple | bonds with the hydrophilic group of the electrolyte in a reaction layer.
The functional group may be introduced later to the catalyst paste or the reaction layer without previously introducing the functional group to the catalyst side.
In order to spread the functional group throughout the reaction layer, it is preferable to introduce the functional group into the reaction layer and then perform a fuel cell reaction to generate generated water and move it. At this time, it is preferable that the fuel cell reaction is performed under high humidification conditions and is rich in generated water.
The amount of the functional group to be introduced should be equal to or more than the equivalent of the hydrophilic group, but from the viewpoint of executing the fuel cell reaction, the amount of the functional group introduced is preferably 0.05 to 0.6 equivalent. .
Of course, by infiltrating a large amount of functional groups into the reaction layer, the sensitive layer can be made to have a uniform affinity to the hydrophilic groups of the electrolyte in the entire reaction layer.

電解質の親水基に官能基を親和させた後、官能基と錯体を形成可能な金属イオンを反応層へ導入する。
金属イオンの導入方法は特に限定されるものではないが、当該金属イオンの水溶液へ反応層を浸漬する方法を採用できる。
官能基として硝酸基を採用したときには、ルテニウムイオン、オスミウムイオンを用いることができ、それぞれニトロシル錯体を形成する。
他の官能基の場合もそれぞれ適切な金属イオンを採用する。
金属イオンの導入量はその当量を、反応層に含まれる電解質の親水基の当量以上とする。
電解質の親水基に親和した官能基と未反応の金属イオンを除去するため、反応層を洗浄する。金属イオン導入後も燃料電池反応が可能であれば、生成水により余分な金属イオンを除去することができる。 After the functional group is made to affinity with the hydrophilic group of the electrolyte, a metal ion capable of forming a complex with the functional group is introduced into the reaction layer.
The method for introducing metal ions is not particularly limited, but a method of immersing the reaction layer in an aqueous solution of the metal ions can be employed.
When a nitrate group is employed as a functional group, ruthenium ions and osmium ions can be used, and each form a nitrosyl complex.
In the case of other functional groups, an appropriate metal ion is adopted.
The amount of metal ions introduced is equal to or greater than the equivalent of the hydrophilic group of the electrolyte contained in the reaction layer.
The reaction layer is washed in order to remove the functional group having an affinity for the hydrophilic group of the electrolyte and unreacted metal ions. If the fuel cell reaction is possible even after the introduction of metal ions, excess metal ions can be removed with the produced water.

図１は電解質溶液中の電解質の形態を示す模式図である。FIG. 1 is a schematic diagram showing the form of the electrolyte in the electrolyte solution. 図２は図１（Ａ）に対応したＰＦＦ構造を説明する模式図である。FIG. 2 is a schematic diagram for explaining a PFF structure corresponding to FIG. 図３は図１（Ｂ）に対応したＰＦＦ構造を説明する模式図である。FIG. 3 is a schematic diagram for explaining the PFF structure corresponding to FIG. 図４は実施形態における製造直後の反応層の構成を示す模式図である。FIG. 4 is a schematic diagram showing the structure of the reaction layer immediately after production in the embodiment. 図５は燃料電池反応を実行後の反応層の構成を示す模式図である。FIG. 5 is a schematic diagram showing the structure of the reaction layer after the fuel cell reaction is performed. 図６はルテニウムイオンによる染色を示す模式図である。FIG. 6 is a schematic diagram showing staining with ruthenium ions. 図７はルテニウム染色した反応層の３Ｄ−ＴＥＭ写真である。FIG. 7 is a 3D-TEM photograph of the reaction layer stained with ruthenium.

原料触媒としてカーボン担持触媒を準備した。この原料触媒はカーボンブラック粒子を担体として、これに触媒白金粒子を周知の方法で担持させたものである（担持量：５０％）。
フルヤ金属(株)の提供するジニトロジアンミン白金の硝酸水溶液（Pt0.05/150ml）,硝酸濃度０．０７％（０．０１Ｍ）に原料触媒１ｇを投入し、室内温度で５時間スターラー撹拌する。その後濾過し、大気雰囲気で６０℃２時間乾燥する。更に、窒素雰囲気下で１５０℃２時間熱処理する。得られた試料の最終重量は１．０１２ｇであり、ろ液のＰｔ残留量から求められたＰｔ収率は８４．３％であった。
これにより、原料触媒の触媒白金粒子に錯体の白金が吸着し、もって触媒白金粒子の周囲に硝酸基が存在することとなる。 A carbon supported catalyst was prepared as a raw material catalyst. This raw material catalyst has carbon black particles as a carrier and catalyst platinum particles supported thereon by a well-known method (supported amount: 50%).
Furuya aqueous nitric acid Jinitoroji ammine platinum to provide a metal (strain) (Pt0.05 / 150ml), a raw material catalyst 1g was added to a nitric acid concentration 0.07% (0.01 M), for 5 hours stirrer stirring at room temperature. Then, it is filtered and dried in an air atmosphere at 60 ° C. for 2 hours. Further, heat treatment is performed at 150 ° C. for 2 hours in a nitrogen atmosphere. The final weight of the obtained sample was 1.012 g, and the Pt yield determined from the residual amount of Pt in the filtrate was 84.3%.
As a result, the complex platinum is adsorbed on the catalyst platinum particles of the raw material catalyst, so that nitrate groups exist around the catalyst platinum particles.

次に、得られた触媒を粉砕した。粉砕した触媒を水１００ｍＬとともに容器へ投入し、ハイブリッドミキサー（キーエンス社製、型番ＨＭ−５００）を用いて脱泡処理をおこなった。脱泡処理の時間は４分とした。
脱泡処理を行なった後、一晩放置し、上澄み液を捨て、電解質（ナフィオンの５％水溶液）を１０ｇ添加し、撹拌（ハイブリッドミキサーにより遠心撹拌（４分））した。 Next, the obtained catalyst was pulverized. The pulverized catalyst was put into a container together with 100 mL of water, and defoamed using a hybrid mixer (manufactured by Keyence Corporation, model number HM-500). The defoaming time was 4 minutes.
After carrying out the defoaming treatment, the mixture was left overnight, the supernatant was discarded, 10 g of electrolyte (5% aqueous solution of Nafion) was added, and the mixture was stirred (centrifugated with a hybrid mixer (4 minutes)).

このようにして得られたペーストを水素極側、酸素極側のそれぞれの拡散層へ塗布し、乾燥して反応層とした。この反応層を固体高分子電解質膜へホットプレスにより張り合わせた。
このようにして得られた反応層は、図４に示すように、ＰＦＦ構造をとり、触媒白金粒子の周囲に硝酸基が存在している。
図５において、電解質層と触媒との間に形成される親水性領域がＰＦＦ構造の本体であるが、電解質層中にも触媒側に配向しきれなかったスルホン基が固まって、クラスターを形成していると考えられる。 The paste thus obtained was applied to each diffusion layer on the hydrogen electrode side and oxygen electrode side, and dried to obtain a reaction layer. This reaction layer was bonded to the solid polymer electrolyte membrane by hot pressing.
The reaction layer thus obtained has a PFF structure as shown in FIG. 4, and nitrate groups exist around the catalyst platinum particles.
In FIG. 5, the hydrophilic region formed between the electrolyte layer and the catalyst is the main body of the PFF structure, but the sulfone groups that could not be fully oriented to the catalyst side in the electrolyte layer are solidified to form clusters. It is thought that.

このようにして得られた膜電極接合体を用いて燃料電池反応を実行した。
燃料電池反応を実行すると触媒白金粒子の表面が活性化されて硝酸基が離脱しやすくなり、更に生成水の生成及び移動に伴い、硝酸基は反応層全体に拡散する。
なお、燃料電池反応の実行時間は１〜４時間（高加湿条件）とすることが好ましい。
次に、膜電極接合体から反応層を切り出して、酸化ルテニウム溶液へ浸漬し、図６に示すように、硝酸基（硝酸イオン）をルテニウムで染色する。
このとき、親水基であるスルホン基が凝集していると（ＰＦＦ構造やクラスター等）、硝酸基も凝集する。従って、ルテニウムイオンで染色された硝酸基を顕微鏡（電子顕微鏡）で観察可能となる。
３Ｄ−ＴＥＭ観察像を図７に示す。図７に示す写真は一つの断層像であり、図中の大きい黒丸は白金粒子を示し、小さな黒点がルテニウムである。無地の部分は触媒又は親水基が存在しない若しくは親水基が高分散した電解質を示し、何れもプロトンの移動に実質的に寄与しない。 A fuel cell reaction was performed using the membrane electrode assembly thus obtained.
When the fuel cell reaction is performed, the surface of the catalyst platinum particles is activated and the nitrate groups are easily released, and the nitrate groups diffuse throughout the reaction layer as the produced water is generated and moved.
The fuel cell reaction is preferably performed for 1 to 4 hours (highly humidified condition).
Next, the reaction layer is cut out from the membrane electrode assembly, immersed in a ruthenium oxide solution, and nitrate groups (nitrate ions) are stained with ruthenium as shown in FIG.
At this time, if the sulfone group which is a hydrophilic group is aggregated (PFF structure, cluster, etc.), the nitrate group is also aggregated. Accordingly, the nitrate group stained with ruthenium ions can be observed with a microscope (electron microscope).
A 3D-TEM observation image is shown in FIG. The photograph shown in FIG. 7 is a tomographic image. Large black circles in the figure indicate platinum particles, and small black dots are ruthenium. The solid portion indicates a catalyst or an electrolyte in which a hydrophilic group does not exist or a hydrophilic group is highly dispersed, and any of them does not substantially contribute to proton transfer .

本発明は、上記発明の実施の形態及び実施例の説明に何ら限定されるものではない。特許請求の範囲の記載を逸脱せず、当業者が容易に想到できる範囲で種々の変形態様も本発明に含まれる。   The present invention is not limited to the description of the embodiments and examples of the invention described above. Various modifications are also included in the present invention as long as those skilled in the art can easily conceive without departing from the scope of the claims.

８１ 触媒
８１ａ 担体
８１ｂ 白金触媒微粒子
８２ 電解質
８３ 親水性領域 81 catalyst 81a carrier 81b platinum catalyst fine particle 82 electrolyte 83 hydrophilic region

Claims (4)

燃料電池の反応層を構成する電解質の親水基に官能基を親和させるステップと、
前記官能基と錯体を形成可能な金属イオンを前記反応層へ導入し、該金属イオンにより前記官能基を染色するステップと、を含むことを特徴とする燃料電池反応層の観察方法。 A step of making the functional group affinity with the hydrophilic group of the electrolyte constituting the reaction layer of the fuel cell;
Introducing a metal ion capable of forming a complex with the functional group into the reaction layer, and staining the functional group with the metal ion. 前記官能基は硝酸基であり、前記金属イオンはニトロシル錯体を形成可能な金属イオンである、ことを特徴とする請求項１に記載の観察方法。   The observation method according to claim 1, wherein the functional group is a nitrate group, and the metal ion is a metal ion capable of forming a nitrosyl complex. 前記金属イオンはルテニウムイオン及び又はオスミウムイオンである、ことを特徴とする請求項２に記載の観察方法。   The observation method according to claim 2, wherein the metal ions are ruthenium ions and / or osmium ions. 白金系の触媒金属粒子を有する触媒と電解質との混合物からなる燃料電池の反応層を観察する方法であって、
硝酸基を有する白金錯体の水溶液中で前記触媒を撹拌し、前記触媒の触媒金属粒子を前記硝酸基で修飾するとともに、前記触媒を親水化するステップと、
親水化された前記触媒と前記電解質の溶液と混合し、触媒ペーストを形成するステップと、
該触媒ペーストを用いて燃料電池の反応層を形成するステップと、
該反応層の前記電解質の親水基へ前記硝酸基を親和させるステップと、
前記硝酸基をルテニウムイオンで染色するステップと、
を含む燃料電池反応層の観察方法。 A method for observing a reaction layer of a fuel cell comprising a mixture of a catalyst having platinum-based catalytic metal particles and an electrolyte,
Stirring the catalyst in an aqueous solution of a platinum complex having a nitrate group, modifying the catalyst metal particles of the catalyst with the nitrate group, and hydrophilizing the catalyst;
Mixing the hydrophilized catalyst and the electrolyte solution to form a catalyst paste;
Forming a reaction layer of the fuel cell using the catalyst paste;
Affinity of the nitrate group to the hydrophilic group of the electrolyte of the reaction layer;
Staining the nitrate group with ruthenium ions;
Method for observing a fuel cell reaction layer containing
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