JP5755124B2 - Method for producing cathode catalyst for polymer electrolyte fuel cell - Google Patents
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Description
本発明は、新規な固体高分子形燃料電池用カソード触媒及びその製造方法に関する。 The present invention relates to a novel cathode catalyst for a polymer electrolyte fuel cell and a method for producing the same.
固体高分子形燃料電池（PEFC）は、電解質としての役割を果たす固体高分子電解質膜の性質に起因して、他の燃料電池と比較して低い８０℃以下の温度域で作動するという特徴を有している。作動温度が低いため、固体高分子形燃料電池の起動は迅速である。また、作動温度が低いことで、概して高価である耐熱性の構成材料を使用する必要もない。固体高分子形燃料電池は、その他にも出力密度が高い等の利点を有していることから、自動車用、家庭用の燃料電池として現在急速に開発が進められている。 The polymer electrolyte fuel cell (PEFC) is characterized by operating in a temperature range of 80 ° C. or lower, which is lower than other fuel cells, due to the properties of the polymer electrolyte membrane that plays a role as an electrolyte. Have. Since the operating temperature is low, the start-up of the polymer electrolyte fuel cell is quick. Also, the low operating temperature eliminates the need for heat-resistant components that are generally expensive. Since the polymer electrolyte fuel cell has other advantages such as high output density, it is currently being rapidly developed as a fuel cell for automobiles and households.
固体高分子形燃料電池は、固体高分子電解質膜の両側に、それぞれ、水素が発生する燃料極（アノード（負極））、空気が反応する空気極（カソード（陽極））を貼りつけた一体構造（膜−電極接合体（MEA））をその構成として有している。このMEAと、ガス流路及び集電体としての機能を兼ねたセパレータとを組み合わせることで単セルが構成される。 The polymer electrolyte fuel cell has an integrated structure in which a fuel electrode (anode (anode)) that generates hydrogen and an air electrode (cathode (anode)) that reacts with air are attached to both sides of the polymer electrolyte membrane. (Membrane-electrode assembly (MEA)). A single cell is configured by combining this MEA and a separator that also functions as a gas flow path and a current collector.
固体高分子電解質膜として最も一般的に使用されているのはペルフルオロスルホン酸系のイオン交換膜である。当該イオン交換膜は化学的に安定であるものの、非常に強い酸性を示すため、電極材料として使用可能なものは限られている。このような耐酸性の要求を満たす必要から、通常、カーボン材料が電極触媒の担体として選択されている。カーボン材料の中でも、２０００℃以上の高温で処理することによってカーボンの結晶化度が高められたカーボン（以下、「高結晶化カーボン」と称する）は、耐酸化性が高いため好ましい担体である（特許文献１）。 The most commonly used solid polymer electrolyte membrane is a perfluorosulfonic acid ion exchange membrane. Although the ion exchange membrane is chemically stable, it exhibits very strong acidity, so that there are only a limited number of materials that can be used as electrode materials. Since it is necessary to satisfy such acid resistance requirements, a carbon material is usually selected as an electrode catalyst support. Among carbon materials, carbon whose crystallinity of carbon has been increased by treatment at a high temperature of 2000 ° C. or higher (hereinafter referred to as “highly crystallized carbon”) is a preferred carrier because of its high oxidation resistance ( Patent Document 1).
電極触媒は、貴金属や卑金属などの触媒金属をカーボン担体上に担持させることで形成される。例えば、触媒金属塩が溶解した溶液中にカーボン担体を含浸させ、触媒貴金属を担体上に吸着担持させた後、加熱還元することで電極触媒が得られる。しかしながら、高結晶化カーボンを担体として用いた場合、担持される触媒金属の粒子分布にばらつきが生じるという問題があった。このような金属粒子のばらつきを抑制する手段として、例えば、ポリビニルピロリドン、ポリアクリル酸、ギ酸、酢酸、プロピオン酸、乳酸などの有機保護剤がある（特許文献２）。触媒金属を含む溶液中にこのような有機保護剤を添加することでコロイドが形成され、触媒金属を均一に担体に担持することが可能になる。 The electrode catalyst is formed by supporting a catalyst metal such as a noble metal or a base metal on a carbon support. For example, an electrode catalyst can be obtained by impregnating a carbon support in a solution in which the catalyst metal salt is dissolved, adsorbing and supporting the catalyst noble metal on the support, and then reducing by heating. However, when highly crystallized carbon is used as a carrier, there is a problem that the particle distribution of the supported catalyst metal varies. Examples of means for suppressing such dispersion of metal particles include organic protective agents such as polyvinylpyrrolidone, polyacrylic acid, formic acid, acetic acid, propionic acid, and lactic acid (Patent Document 2). By adding such an organic protective agent to the solution containing the catalyst metal, a colloid is formed, and the catalyst metal can be uniformly supported on the support.
しかしながら、有機保護剤を使用した場合、高結晶化カーボンのような比表面積の小さいカーボン担体では触媒金属の担持効率が低下し、延いては電圧が低下し易いという別の問題が生じていた。従って、高結晶化カーボンに触媒金属が効率良く均一に担持されたカソード触媒を備えた、電圧が低下し難い固体高分子形燃料電池に対する需要が高まっている。 However, when an organic protective agent is used, a carbon support having a small specific surface area such as highly crystallized carbon has another problem that the catalyst metal loading efficiency is lowered and the voltage is likely to be lowered. Accordingly, there is an increasing demand for a polymer electrolyte fuel cell having a cathode catalyst in which a catalytic metal is efficiently and uniformly supported on highly crystallized carbon and in which the voltage is hardly lowered.
従って、本発明は、新規な固体高分子形燃料電池用カソード触媒及びその製造方法に関する。 Accordingly, the present invention relates to a novel cathode catalyst for a polymer electrolyte fuel cell and a method for producing the same.
本発明者が高結晶化カーボンを担体として使用する際の問題について検討したところ、高結晶化カーボンは比表面積が小さいため、担持工程において触媒金属塩が十分に含浸吸着されないことが原因であるとの結論に至った。吸着されなかった金属塩は担持工程後の加熱還元工程において急速に還元されてしまい、触媒金属としての役割を果たすことはできない。 The present inventor examined the problem when using highly crystallized carbon as a support, and because high crystallized carbon has a small specific surface area, the catalyst metal salt is not sufficiently impregnated and adsorbed in the supporting process. The conclusion was reached. The metal salt that has not been adsorbed is rapidly reduced in the heat reduction step after the supporting step, and cannot serve as a catalyst metal.
触媒金属塩はカーボン表面のエッジ部に吸着するため、触媒金属の吸着箇所の増大は、例えば、エッジ部に存在する酸性官能基を高温で熱処理することで除去することにより達成可能であるとも考えられる。しかしながら、高温で熱処理を行うとカーボン凝集により比表面積自体が減少するという問題があった。 Since the catalytic metal salt is adsorbed on the edge portion of the carbon surface, it is considered that the increase of the catalytic metal adsorption site can be achieved by removing the acidic functional group present on the edge portion by heat treatment at high temperature, for example. It is done. However, when heat treatment is performed at a high temperature, there is a problem in that the specific surface area itself decreases due to carbon aggregation.
そこで、本発明者が鋭意検討した結果、特定の条件下で炭素材料を熱処理することで触媒金属を高担持可能な性質が付与されることを見出し、本発明を完成させるに至った。 Thus, as a result of intensive studies by the present inventors, it has been found that a property capable of highly supporting a catalytic metal is imparted by heat-treating a carbon material under specific conditions, and the present invention has been completed.
即ち、本発明は、以下の発明を包含する。
［１］高結晶化カーボン担体に触媒金属が担持された固体高分子形燃料電池用カソード触媒であって、当該カーボン担体に担持された当該触媒金属の規格化分散度が３０％以下であり、担持前の当該カーボンのBET比表面積が５０〜６００ｍ2／ｇである、カソード触媒。
［２］前記触媒金属が白金である、［１］のカソード触媒。
［３］前記高結晶化カーボンがカーボンブラックである、［１］又は［２］のカソード触媒。
［４］［１］〜［３］のいずれかのカソード触媒を製造する方法であって、高結晶化カーボンを、水素雰囲気のもと１０００〜１６００℃の温度で熱処理する工程、及び当該高結晶化カーボンに触媒金属を担持する工程、を含んで成る、方法。
［５］前記熱処理が１〜５０％の水素濃度のもと実施される、［４］の方法。
That is, the present invention includes the following inventions.
[1] A cathode catalyst for a polymer electrolyte fuel cell in which a catalyst metal is supported on a highly crystallized carbon support, wherein the normalized dispersion degree of the catalyst metal supported on the carbon support is 30% or less, The cathode catalyst whose BET specific surface area of the said carbon before carrying | support is 50-600 m < 2 > / g.
[2] The cathode catalyst according to [1], wherein the catalytic metal is platinum.
[3] The cathode catalyst according to [1] or [2], wherein the highly crystallized carbon is carbon black.
[4] A method for producing a cathode catalyst according to any one of [1] to [3], comprising a step of heat-treating highly crystallized carbon at a temperature of 1000 to 1600 ° C. in a hydrogen atmosphere, and the high crystal Supporting a catalytic metal on activated carbon.
[5] The method according to [4], wherein the heat treatment is performed under a hydrogen concentration of 1 to 50%.
従来、高結晶化カーボン自体を調製するのにアルゴンガス等の不活性化ガス雰囲気下で熱処理されることは知られていた（例えば、特開２０１０−１０２９１１号公報）。本発明は、水素雰囲気で熱処理した高結晶化カーボンを担体として使用した点で異なり、その結果、担体上に触媒金属、例えば白金を均一に高担持することが初めて可能となった。このような担持効率の高さは、薬液が高濃度である場合に顕著である。 Conventionally, it has been known that a highly crystallized carbon itself is heat-treated in an atmosphere of an inert gas such as argon gas (for example, Japanese Patent Application Laid-Open No. 2010-102911). The present invention is different in that highly crystallized carbon heat-treated in a hydrogen atmosphere is used as a support. As a result, it has become possible for the first time to uniformly and highly support a catalytic metal such as platinum on the support. Such high loading efficiency is remarkable when the chemical solution has a high concentration.
本発明のカソード触媒によれば、従来のものと比較してより多くの触媒金属が均一に分散担持されているため、電圧が低下しにくく、耐久性が高い固体高分子形燃料電池が得られる。 According to the cathode catalyst of the present invention, a larger amount of catalytic metal is uniformly dispersed and supported as compared with the conventional one, so that a solid polymer fuel cell with high voltage resistance and high durability can be obtained. .
固体高分子形燃料電池用カソード触媒
本発明は第一の観点において、高結晶化カーボン担体に触媒金属が担持された固体高分子形燃料電池用カソード触媒、を提供する。本発明において担体として使用される「高結晶化カーボン」とは、Ｘ線回折解析により測定した場合、カーボンの結晶子の六員環面方向の長さＬａが４．０ｎｍ以上、例えば６．０ｎｍ前後のカーボンを意味する。ここで、結晶子の六員環面方向の長さＬａとは、カーボン担体を構成する炭素の黒鉛構造に基づく六員環面のＡ、Ｂ軸方向の長さを示し、カーボン担体のＸ線回折パターンから算出される値である。高結晶化カーボンは、例えば、カーボンブラックなどのカーボン担体を熱処理などによりグラファイト化することで調製することができる。
In the first aspect, the present invention provides a cathode catalyst for a polymer electrolyte fuel cell in which a catalyst metal is supported on a highly crystallized carbon support. The “highly crystallized carbon” used as a carrier in the present invention has a length La in the six-membered ring plane direction of the carbon crystallites of 4.0 nm or more, for example 6.0 nm, as measured by X-ray diffraction analysis. Means front and back carbon. Here, the length La in the six-membered ring plane direction of the crystallite indicates the length in the A and B axis directions of the six-membered ring plane based on the graphite structure of carbon constituting the carbon support. It is a value calculated from the diffraction pattern. The highly crystallized carbon can be prepared, for example, by graphitizing a carbon carrier such as carbon black by heat treatment or the like.
触媒金属を担持する前の高結晶化カーボンは、BET比表面積が５０〜６００ｍ2／ｇ、好ましくは１００〜５００ｍ2／ｇ、より好ましくは２００〜４００ｍ2／ｇ、より更に好ましくは２００〜２５０ｍ2／ｇである。本発明で使用する場合の「BET比表面積」とは、窒素(N2)ガスを吸着させるBET法によって求めた値を指す。 Highly crystallized carbon before carrying the catalyst metal, BET specific surface area of 50 to 600 m 2 / g, preferably from 100 to 500 m 2 / g, more preferably 200 to 400 m 2 / g, even more preferably 200~250m 2 / g. The “BET specific surface area” used in the present invention refers to a value obtained by a BET method in which nitrogen (N 2 ) gas is adsorbed.
担体に担持される触媒金属は、カソード触媒として使用されている貴金属や卑金属であればいずれでもよい。カソード側では電極から供給される電子を酸素分子が取り込んでイオン化するという還元反応が起こっているが、当該還元反応は過電圧が高く電圧ロスが大きいため、他の金属との比較では白金が好ましい。その他、必要に応じて合金を触媒金属として使用することもできる。 The catalyst metal supported on the carrier may be any noble metal or base metal used as a cathode catalyst. On the cathode side, a reduction reaction occurs in which oxygen molecules are taken in and ionized by electrons from the electrode. However, since the reduction reaction has a high overvoltage and a large voltage loss, platinum is preferable in comparison with other metals. In addition, an alloy can be used as a catalyst metal as necessary.
当該カーボン担体に担持された当該触媒金属の粒径分布は、エックス線小角散乱法（Small Angle X−ray Scattering：SAXS）により評価した場合、規格化分散度３０％以下、好ましくは２５％以下である。SAXSは、X線を物質に照射して散乱したX線のうち、2θ＜10°以下の低角領域に現れるものを測定し、物質の構造を評価する分析手法である。SAXSを用いることで、触媒金属の平均粒径と粒径分布を測定することができる。 The particle size distribution of the catalyst metal supported on the carbon support is 30% or less, preferably 25% or less, when evaluated by a small angle X-ray scattering (SAXS) method. . SAXS is an analytical method for measuring the structure of a substance by measuring the X-rays scattered by irradiating the substance with X-rays that appear in a low angle region of 2θ <10 ° or less. By using SAXS, the average particle size and particle size distribution of the catalyst metal can be measured.
本発明で使用する場合の「規格化分散度」とは、Ｘ線小角散乱の測定ピークから算出される触媒金属の平均粒子径で、粒度分布の半価幅（ピークの半分の値）を除した値を百分率で表したものである。規格化分散度の算出は解析ソフトを用いて行うことができ、例えばnano-solver（リガク社製）が使用可能である。規格化分散度の算出について一例を挙げると、白金を触媒金属として使用する場合、その平均粒径は２〜８ｎｍであるが、平均粒径が５ｎｍであり、その半価幅が１．５ｎｍであるとすると（５±１．５）、平均値から±３０％の広がりを持つため（１．５／５×１００＝３０）、規格化分散度は３０％と表される。 “Normalized dispersion” as used in the present invention is the average particle diameter of the catalyst metal calculated from the measurement peak of X-ray small angle scattering, and excludes the half width of the particle size distribution (half the value of the peak). The value obtained is expressed as a percentage. The normalization degree of dispersion can be calculated using analysis software. For example, nano-solver (manufactured by Rigaku Corporation) can be used. As an example of the calculation of the normalized dispersion, when platinum is used as the catalyst metal, the average particle diameter is 2 to 8 nm, the average particle diameter is 5 nm, and the half width is 1.5 nm. If there is (5 ± 1.5), since it has a spread of ± 30% from the average value (1.5 / 5 × 100 = 30), the normalized dispersion is expressed as 30%.
製造方法
本発明は第二の観点において、前記カソード触媒を製造する方法、を提供する。本発明のカソード触媒は、高結晶化カーボンを水素雰囲気のもと１０００〜１６００℃の温度で熱処理する工程、及び当該高結晶化カーボンに触媒金属を担持する工程を経て調製される。高結晶化カーボンはカーボンの結晶子の六員環面方向の長さＬａが４．０ｎｍ以上のものが使用される。
Manufacturing Method In a second aspect, the present invention provides a method for manufacturing the cathode catalyst. The cathode catalyst of the present invention is prepared through a step of heat-treating highly crystallized carbon under a hydrogen atmosphere at a temperature of 1000 to 1600 ° C. and a step of supporting a catalyst metal on the highly crystallized carbon. As the highly crystallized carbon, carbon crystallites having a length La in the six-membered ring plane direction of 4.0 nm or more are used.
上記熱処理工程における水素濃度は１〜５０％、好ましくは１〜４０％、より好ましくは２〜３０％である。水素雰囲気で使用するガスは、水素の他、例えばアルゴン等の不活性化ガスを含んでもよい。 The hydrogen concentration in the heat treatment step is 1 to 50%, preferably 1 to 40%, more preferably 2 to 30%. The gas used in the hydrogen atmosphere may include an inert gas such as argon in addition to hydrogen.
熱処理の温度は１０００〜１６００℃、好ましくは１０００〜１４００℃、より好ましくは１０００〜１２００℃である。熱処理の時間は特に限定されないが、例えば、６時間程度であれば所望の担体を調製することができる。 The temperature of heat processing is 1000-1600 degreeC, Preferably it is 1000-1400 degreeC, More preferably, it is 1000-1200 degreeC. Although the heat treatment time is not particularly limited, for example, a desired carrier can be prepared for about 6 hours.
触媒金属の担持は、触媒金属塩が溶解した溶液中にカーボン担体を含浸させ、触媒貴金属を担体上に吸着担持させることで実施され得るが、本発明の製造方法はこのような方法に限定されない。また、担持工程後の工程、例えば焼成工程等は、当業者であれば適宜その条件等を決定することができる。 The catalyst metal can be supported by impregnating the carbon support in a solution in which the catalyst metal salt is dissolved and adsorbing and supporting the catalyst noble metal on the support, but the production method of the present invention is not limited to such a method. . Further, those skilled in the art can appropriately determine the conditions and the like of the steps after the supporting step, for example, the firing step.
以下の実施例を用いて、本発明の発明を更に具体的に説明する。尚、本発明はこれらの実施例に限定されるものではない。 The invention of the present invention will be described more specifically with reference to the following examples. The present invention is not limited to these examples.
（実施例１）
カーボンの結晶子の六員環面方向の長さＬａが６ｎｍ、そしてBET比表面積が２５０ｍ2／ｇの高結晶化カーボンを準備した。六員環の面方向の長さはリガク社製の粉末Ｘ線回折装置（RINT-TTRIII）を用いて測定した。当該高結晶化カーボンを１０％水素及び９０％アルゴン中において、昇温速度５℃／分で１０００℃まで昇温し、６時間熱処理を行った。N2ガス吸着法で測定した場合のBET比表面積は、熱処理前と略同様の２４４ｍ2／ｇであった。
Example 1
A highly crystallized carbon was prepared in which the length La of the crystallites of the carbon was 6 nm and the BET specific surface area was 250 m 2 / g. The length in the surface direction of the six-membered ring was measured using a powder X-ray diffractometer (RINT-TTRIII) manufactured by Rigaku Corporation. The highly crystallized carbon was heated to 1000 ° C. at a temperature rising rate of 5 ° C./min in 10% hydrogen and 90% argon, and heat-treated for 6 hours. The BET specific surface area when measured by the N 2 gas adsorption method was 244 m 2 / g, which was substantially the same as that before the heat treatment.
かかる熱処理で得られた担体カーボン粉末７．５ｇに０．１Ｎ硝酸水溶液７００ｇを加えて分散させた。この分散液に、担体の重量当たりの白金量が５０重量％となるよう、７．５ｇの白金を含むジニトロジアミン白金硝酸溶液、９９．５％エタノール１００ｇの順に加え、十分に馴染ませた後加熱した。加熱条件は６０〜９０℃、２〜８時間の範囲で行った。 700 g of 0.1N nitric acid aqueous solution was added to and dispersed in 7.5 g of the carrier carbon powder obtained by the heat treatment. To this dispersion, 7.5 g of platinum-containing dinitrodiamine platinum nitric acid solution and 99.5% ethanol 100 g are added in this order so that the amount of platinum per weight of the carrier is 50% by weight. did. The heating conditions were 60 to 90 ° C. and 2 to 8 hours.
加熱後の分散液を、ろ過廃液の導電率が５０μＳ／ｃｍ以下になるまで繰り返しろ過し、ろ過洗浄して得られた粉末ケーキを送風しながら８０℃で１５時間乾燥させた。このようにして得られた触媒粉末をアルゴンガス中で熱処理した。熱処理は、６００〜９００℃の範囲で、昇温５℃／分を２時間保持して行った。当該熱処理の結果、実施例１のカソード触媒粉末が得られた。 The dispersion after heating was repeatedly filtered until the conductivity of the filtered waste liquid became 50 μS / cm or less, and dried at 80 ° C. for 15 hours while blowing a powder cake obtained by filtration and washing. The catalyst powder thus obtained was heat-treated in argon gas. The heat treatment was performed in the range of 600 to 900 ° C. while maintaining a temperature increase of 5 ° C./min for 2 hours. As a result of the heat treatment, the cathode catalyst powder of Example 1 was obtained.
（実施例２〜８）
実施例１に記載した高結晶化カーボンの熱処理工程の水素濃度（１０％水素及び９０％アルゴン）及び温度（１０００℃）を以下のとおり変更した点を除き、実施例１と同様の手順及び条件により実施例２〜８のカソード触媒を調製した。
実施例２ 熱処理温度：１２００℃；水素濃度：１０％水素及び９０％アルゴン
実施例３ 熱処理温度：１４００℃；水素濃度：１０％水素及び９０％アルゴン
実施例４ 熱処理温度：１２００℃；水素濃度：２％水素及び９８％アルゴン
実施例５ 熱処理温度：１２００℃；水素濃度：５％水素及び９５％アルゴン
実施例６ 熱処理温度：１２００℃；水素濃度：２０％水素及び８０％アルゴン
実施例７ 熱処理温度：１２００℃；水素濃度：３０％水素及び７０％アルゴン
実施例８ 熱処理温度：１２００℃；水素濃度：５０％水素及び５０％アルゴン
(Examples 2 to 8)
The same procedures and conditions as in Example 1 except that the hydrogen concentration (10% hydrogen and 90% argon) and temperature (1000 ° C.) in the heat treatment step of highly crystallized carbon described in Example 1 were changed as follows. Thus, cathode catalysts of Examples 2 to 8 were prepared.
Example 2 Heat treatment temperature: 1200 ° C .; Hydrogen concentration: 10% hydrogen and 90% argon Example 3 Heat treatment temperature: 1400 ° C .; Hydrogen concentration: 10% hydrogen and 90% argon Example 4 Heat treatment temperature: 1200 ° C .; Hydrogen concentration: 2% hydrogen and 98% argon Example 5 heat treatment temperature: 1200 ° C .; hydrogen concentration: 5% hydrogen and 95% argon Example 6 heat treatment temperature: 1200 ° C .; hydrogen concentration: 20% hydrogen and 80% argon Example 7 heat treatment temperature Hydrogen concentration: 30% hydrogen and 70% argon Example 8 Heat treatment temperature: 1200 ° C .; hydrogen concentration: 50% hydrogen and 50% argon
（比較例１〜４）
実施例１に記載した高結晶化カーボンの熱処理工程の水素濃度（１０％水素及び９０％アルゴン）及び温度（１０００℃）を以下のとおり変更した点を除き、実施例１と同様の手順及び条件により比較例１〜４のカソード触媒を調製した。
比較例１ 熱処理温度：熱処理なし；水素濃度：１０％水素及び９０％アルゴン
比較例２ 熱処理温度：７００℃ ；水素濃度：１０％水素及び９０％アルゴン
比較例３ 熱処理温度：２０００℃；水素濃度：１０％水素及び９０％アルゴン
比較例４ 熱処理温度：２０００℃；水素濃度：１００％アルゴン
(Comparative Examples 1-4)
The same procedures and conditions as in Example 1 except that the hydrogen concentration (10% hydrogen and 90% argon) and temperature (1000 ° C.) in the heat treatment step of highly crystallized carbon described in Example 1 were changed as follows. Thus, cathode catalysts of Comparative Examples 1 to 4 were prepared.
Comparative Example 1 Heat Treatment Temperature: No Heat Treatment; Hydrogen Concentration: 10% Hydrogen and 90% Argon Comparative Example 2 Heat Treatment Temperature: 700 ° C .; Hydrogen Concentration: 10% Hydrogen and 90% Argon Comparative Example 3 Heat Treatment Temperature: 2000 ° C .; Hydrogen Concentration: 10% hydrogen and 90% argon Comparative Example 4 Heat treatment temperature: 2000 ° C .; hydrogen concentration: 100% argon
（白金粒径分布測定）
実施例１〜８及び比較例１〜４の触媒粉末中の白金粒径分布（規格化分散度（％））を小角Ｘ線散乱法を用いて評価した。解析ソフトとして解析ソフトnano-solver（リガク社製）を用いた。１０％水素、９０％アルゴンのガス雰囲気のもと熱処理された触媒粉末の結果を図１に示す。図１の結果から、１０％水素下で一定の温度範囲で高結晶化カーボンを熱処理をすることで、規格化分散度（％）が低下することが分かる。また、１２００℃で熱処理した触媒粉末の規格化分散度（％）を図２にまとめるが、この図が示すとおり、水素雰囲気で高結晶化カーボンを熱処理することで規格化分散度が低下した。規格化分散度が低いということは、白金の粒径のばらつきが小さくなり、より白金粒径分布が均一になることを意味する。更に、結果は示さないが、本発明の触媒粉末は走査型電子顕微鏡で観察した場合、約５０ｎｍ以上の白金粒子が減少していることも明らかになった。
(Measurement of platinum particle size distribution)
The platinum particle size distribution (normalized dispersity (%)) in the catalyst powders of Examples 1 to 8 and Comparative Examples 1 to 4 was evaluated using a small angle X-ray scattering method. Analysis software nano-solver (manufactured by Rigaku Corporation) was used as the analysis software. FIG. 1 shows the result of the catalyst powder heat-treated in a gas atmosphere of 10% hydrogen and 90% argon. From the results of FIG. 1, it can be seen that the normalized dispersity (%) decreases by heat-treating highly crystallized carbon in a certain temperature range under 10% hydrogen. Moreover, the normalized dispersion degree (%) of the catalyst powder heat-treated at 1200 ° C. is summarized in FIG. 2. As shown in this figure, the normalized dispersion degree was lowered by heat-treating highly crystallized carbon in a hydrogen atmosphere. A low normalized dispersion means that the variation in the particle size of platinum is reduced, and the platinum particle size distribution is more uniform. Furthermore, although the results are not shown, it has also been clarified that platinum particles of about 50 nm or more are reduced when the catalyst powder of the present invention is observed with a scanning electron microscope.
（BET比表面積測定）
実施例１〜８及び比較例１〜４の触媒粉末中のカーボンについてN2吸着法によりBET比表面積を測定した。１０％水素、９０％アルゴンで熱処理された触媒粉末の結果を図３に示す。図３の結果から、１５００℃以上の熱処理温度の場合、比表面積が著しく低下することが分かる。理論に拘束されることを意図するものではないが、図３の結果を考慮すると、図１の結果は、比表面積の低下により白金が担持（吸着）される場所が減少し、その結果１５００℃以降の白金粒径分布にばらつきが生じたことを表していると考えられる。
(BET specific surface area measurement)
The BET specific surface area of the carbon in the catalyst powders of Examples 1 to 8 and Comparative Examples 1 to 4 was measured by the N 2 adsorption method. FIG. 3 shows the result of the catalyst powder heat-treated with 10% hydrogen and 90% argon. From the results of FIG. 3, it can be seen that the specific surface area is significantly reduced at a heat treatment temperature of 1500 ° C. or higher. While not intending to be bound by theory, considering the results of FIG. 3, the results of FIG. 1 show that the number of places where platinum is supported (adsorbed) decreases due to a decrease in specific surface area, resulting in 1500 ° C. It is considered that this represents a variation in the subsequent platinum particle size distribution.
（単セルの作製）
実施例１〜８及び比較例１〜４の触媒粉末をエタノール及びイソプロパノールの混合溶液中に分散させ、この分散液をテフロン（登録商標）シートへ塗布して触媒層を形成した。電極面積１ｃｍ2当たりに担持されている触媒中の白金量は０．２ｍｇとなるよう調節した。各触媒粉末から形成した電極をそれぞれ高分子電解質膜（デュポン社製ナフィオン（登録商標））を介してホットプレスにより貼りあわせ、その両側に拡散層を設置して単セル電極を形成した。
(Production of single cell)
The catalyst powders of Examples 1 to 8 and Comparative Examples 1 to 4 were dispersed in a mixed solution of ethanol and isopropanol, and this dispersion was applied to a Teflon (registered trademark) sheet to form a catalyst layer. The amount of platinum in the catalyst supported per 1 cm 2 of electrode area was adjusted to 0.2 mg. The electrodes formed from the respective catalyst powders were bonded together by hot pressing through polymer electrolyte membranes (Nafion (registered trademark) manufactured by DuPont), and diffusion layers were installed on both sides to form single cell electrodes.
（電位サイクル耐久評価試験）
実施例１〜８及び比較例１〜４の触媒粉末で作製した上記単セルについて電位サイクル耐久試験を行った。試験の電位サイクルは０．６０〜１．０V、８０，０００回とし、耐久前及び耐久後の電圧を１．０Ａ／ｃｍ2の電流密度で測定した。電圧維持率（耐久後電圧／耐久前電圧の百分率）を以下の表に示す。
A potential cycle endurance test was performed on the single cells prepared using the catalyst powders of Examples 1 to 8 and Comparative Examples 1 to 4. The potential cycle of the test was 0.60 to 1.0 V, 80,000 times, and the voltage before and after endurance was measured at a current density of 1.0 A / cm 2 . The following table shows the voltage maintenance ratio (voltage after durability / percentage of voltage before durability).
更に、１０％水素、９０％アルゴンで熱処理された触媒粉末、そして１２００度で熱処理された触媒粉末の耐久後電圧維持率を図４及び５にまとめる。これらの結果に示されているとおり、水素雰囲気のもと一定の熱処理温度で高結晶化カーボンを熱処理することで、得られたカソード触媒を備えた単セルの電圧の耐久性が著しく向上した。 Furthermore, the post-endurance voltage retention rates of the catalyst powder heat-treated with 10% hydrogen and 90% argon and the catalyst powder heat-treated at 1200 degrees are summarized in FIGS. As shown in these results, the heat resistance of the highly crystallized carbon at a constant heat treatment temperature in a hydrogen atmosphere significantly improved the voltage durability of the single cell provided with the obtained cathode catalyst.
本発明の固体高分子形燃料電池用カソード触媒は、高結晶化カーボンに触媒金属が効率良く均一に担持されている。本発明のカソード触媒は、耐久性の更なる向上が必要とされる固体高分子形燃料電池に好適に使用することができる。 In the cathode catalyst for a polymer electrolyte fuel cell of the present invention, a catalytic metal is efficiently and uniformly supported on highly crystallized carbon. The cathode catalyst of the present invention can be suitably used for a polymer electrolyte fuel cell that requires further improvement in durability.
Claims (5)
前記カソード触媒が、高結晶化カーボン担体に触媒金属が担持された固体高分子形燃料電池用カソード触媒であって、当該高結晶化カーボン担体に担持された当該触媒金属の規格化分散度が３０％以下であり、担持前の当該高結晶化カーボンのBET比表面積が５０〜６００ｍ2／ｇである、カソード触媒を製造する方法。 A method for producing a cathode catalyst, comprising: a step of heat-treating highly crystallized carbon at a temperature of 1000 to 1600 ° C. under a hydrogen atmosphere; and a step of supporting a catalyst metal on the highly crystallized carbon. ,
The cathode catalyst is a cathode catalyst for a polymer electrolyte fuel cell in which a catalyst metal is supported on a highly crystallized carbon support, and the normalized dispersion degree of the catalyst metal supported on the highly crystallized carbon support is 30. % or less, and the the high BET specific surface area of the crystallized carbon before carrying is 50 to 600 m 2 / g, a method of manufacturing a cathode catalyst.
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