JP2008047472A - Electrode catalyst - Google Patents
Electrode catalyst Download PDFInfo
- Publication number
- JP2008047472A JP2008047472A JP2006223566A JP2006223566A JP2008047472A JP 2008047472 A JP2008047472 A JP 2008047472A JP 2006223566 A JP2006223566 A JP 2006223566A JP 2006223566 A JP2006223566 A JP 2006223566A JP 2008047472 A JP2008047472 A JP 2008047472A
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- JP
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- Prior art keywords
- carbon
- catalyst
- conductive material
- catalyst component
- electrode catalyst
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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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
Abstract
Description
本発明は、電池に使用される電極触媒、特に固体高分子型燃料電池に使用される電極触媒に関する。 The present invention relates to an electrode catalyst used for a battery, and more particularly to an electrode catalyst used for a polymer electrolyte fuel cell.
化石燃料の有効利用、および環境問題と関連し、燃料電池の持つ高いエネルギー交換効率と排ガスのクリーンさや、自動車への搭載が注目されている現在において、ガソリン車と比べて、これら燃料電池を搭載した車がエネルギー交換効率的にどれだけ優位で、かつ低料金で実現するかは、ひとえに電池がどれだけ安価な材料で、かつ高性能化できるかにかかっている。なかでも固体高分子型燃料電池（ＰＥＦＣ）は、常温で起動でき、電解質の散逸の問題が少なく、高電流密度などの利点を有する。 In relation to effective use of fossil fuels and environmental problems, fuel cells have high energy exchange efficiency and clean exhaust gas, and these fuel cells are installed in comparison with gasoline vehicles. The superiority of the energy saving efficiency of a car that can be realized at low cost depends on how inexpensive the battery can be and the high performance. Among them, the polymer electrolyte fuel cell (PEFC) can be activated at room temperature, has few problems of electrolyte dissipation, and has advantages such as high current density.
しかし、現在のＰＥＦＣでは電極触媒として活性に優れた白金系触媒を用いるが、量産化を前提とした場合、白金の資源供給量の問題があるため、活性に優れ、かつ高効率の触媒開発が必要とされる。そのため電極触媒は触媒金属質量あたりの表面積を高める目的で、表面積の大きなカーボン含有導電性材料担体上にナノメートルオーダーの超微粒子の状態で分散担持されている。この担体上の触媒金属超微粒子やカーボン含有導電性材料に起こる不可逆な変化としては、（１）触媒粒子の凝集、（２）白金粒子の溶解ならびに再析出、（３）カーボン含有導電性材料の腐食（カーボン含有導電性材料にカーボン材料を使用した場合は、担体カーボンの腐食）、（４）カーボン含有導電性材料の腐食による白金粒子の脱落などが考えられる。これらの不可逆な変化の中で上記（２）の白金粒子の溶解ならびに再析出の問題は、上記の量産化を前提とした場合、白金の資源供給量の問題と直結する問題であり、かかる問題を解決する方法には例えば以下のような従来例が存在する。 However, the current PEFC uses a platinum-based catalyst with excellent activity as an electrode catalyst. However, if mass production is premised, there is a problem in the supply of platinum resources. Needed. Therefore, the electrode catalyst is dispersed and supported on the carbon-containing conductive material carrier having a large surface area in the form of ultrafine particles of nanometer order for the purpose of increasing the surface area per mass of the catalyst metal. Irreversible changes that occur in the catalyst metal ultrafine particles and the carbon-containing conductive material on the carrier include (1) agglomeration of catalyst particles, (2) dissolution and reprecipitation of platinum particles, and (3) the carbon-containing conductive material. Corrosion (corrosion of carrier carbon when a carbon material is used for the carbon-containing conductive material), (4) platinum particles falling off due to corrosion of the carbon-containing conductive material, and the like can be considered. Among these irreversible changes, the problem of dissolution and reprecipitation of platinum particles in (2) above is a problem directly related to the problem of platinum resource supply, assuming the above-mentioned mass production. For example, the following conventional examples exist.
特許文献１には、６００℃以上８００℃未満の温度で加熱することにより規則性構造を有する白金−ニッケル−コバルト３元合金粒子を含んでなる白金合金を利用した電極触媒について記載している。さらに、前記規則性構造は、（１００）又は（００１）及び（１１０）又は（１００）のピークが（１１１）又は（１０１）の主回折ピークより低回折角２θ側に現れることにより確認し（特許文献１ 表１、図１）、面心立方晶系規則構造または面心正方晶系規則構造を有する前記白金合金は、比較的高温で使用しても性能劣化が殆どなく長期間に亘って高活性を維持することができることについても記載している。
しかし、上記の特許文献１の合金触媒を実際に使用すると規則合金化していても第２成分以下の金属成分が多量に溶出し、経時的に触媒金属組成が大幅に変化し、実使用条件においては高い溶出耐性を長期間維持できない上、溶出金属が電解質やカーボン担体の劣化を促進する傾向が見られている。特に発電負荷変動の振幅が大きく、変動頻度が高い自動車用燃料電池用途に対する触媒金属としては溶出耐性が不十分であることがわかってきた。さらに溶出した触媒金属が電解質膜やカーボン担体などの他の要素材の劣化も促進する。 However, when the alloy catalyst of the above-mentioned Patent Document 1 is actually used, even if the alloy catalyst is made into a regular alloy, a large amount of the metal component below the second component elutes, and the catalyst metal composition changes significantly over time. In addition, high elution resistance cannot be maintained for a long time, and the elution metal tends to promote deterioration of the electrolyte and the carbon support. In particular, it has been found that elution resistance is insufficient as a catalyst metal for automotive fuel cell applications where the amplitude of power generation load fluctuation is large and the fluctuation frequency is high. Further, the eluted catalyst metal promotes the deterioration of other element materials such as the electrolyte membrane and the carbon support.
したがって、本発明は、上記事情を鑑みてなされたものであり、Ｐｔの溶出を有効に抑制・防止でき、さらに電極触媒活性に優れた電極体を提供することを目的とする。 Therefore, the present invention has been made in view of the above circumstances, and an object of the present invention is to provide an electrode body that can effectively suppress and prevent elution of Pt and is excellent in electrocatalytic activity.
一般には粒径が大きくなるほどＯｓｔｗａｌｄ成長理論によれば体積エネルギーの低下により溶出に対して安定になるが、粒径を大きくすると触媒金属使用量が多くなるためコスト高になる。しかし、本発明においては、カーボン担体の物性を最適化し、熱処理を加えることによって同じ触媒成分の粒径でもＰｔ溶出耐性が大幅に向上する。さらに本発明の電極触媒における触媒成分の一つである純Ｐｔが最も溶出耐性が高い。しかしながら、１０ ａｔ．％以下程度ならば第２成分を含んでいても顕著な溶出耐性の低下は見られない。したがって、触媒成分の溶出耐性の高い電極触媒を提供することができる。 In general, the larger the particle size, the more stable the elution is due to the decrease in volume energy according to the Ostwald growth theory, but the larger the particle size, the higher the cost because the amount of catalyst metal used increases. However, in the present invention, by optimizing the physical properties of the carbon support and applying heat treatment, the Pt elution resistance is greatly improved even with the same catalyst component particle size. Furthermore, pure Pt, which is one of the catalyst components in the electrode catalyst of the present invention, has the highest elution resistance. However, 10 at. If it is about% or less, even if the second component is contained, no significant decrease in elution resistance is observed. Therefore, it is possible to provide an electrode catalyst with high elution resistance of the catalyst component.
すなわち、上記目的は、触媒成分とカーボン含有導電性材料とを含む電極触媒において、前記触媒成分は少なくともＰｔを含んでおり、かつ前記カーボン含有導電性材料のＮ２−ＢＥＴ比表面積とＣＴＡＢ吸着比表面積の差が１００ｍ２／ｇ以下であることを特徴とする電極触媒によって達成される。 That is, the above object is an electrode catalyst including a catalyst component and a carbon-containing conductive material, wherein the catalyst component includes at least Pt, and the N 2 -BET specific surface area and CTAB adsorption ratio of the carbon-containing conductive material. It is achieved by an electrocatalyst characterized by a difference in surface area of 100 m 2 / g or less.
（電極触媒）
本発明の第一は、触媒成分とカーボン含有導電性材料とを含む電極触媒において、前記触媒成分は少なくともＰｔを含んでおり、かつ前記カーボン含有導電性材料のＮ２−ＢＥＴ比表面積とＣＴＡＢ吸着比表面積の差が１００ｍ２／ｇ以下であることを特徴とする電極触媒である。
(Electrode catalyst)
The first of the present invention is an electrode catalyst comprising a catalyst component and a carbon-containing conductive material, wherein the catalyst component contains at least Pt, and the N 2 -BET specific surface area and CTAB adsorption of the carbon-containing conductive material The electrode catalyst is characterized in that the difference in specific surface area is 100 m 2 / g or less.
Ｎ２とＣＴＡＢとでは吸着占有面積が異なるため、カーボン含有導電性材料表面の微細構造に起因して両比表面積の差が生じる。換言すると、窒素吸着比表面積の数値はカーボン含有導電性材料表面の微細な凹凸部分の表面積をも含む。一方、セチルトリメチルアンモニウムブロミド（ＣＴＡＢ）の吸着断面積は窒素分子よりもかなり大きいため、ＣＴＡＢ吸着比表面積の数値にはＣＴＡＢ分子が侵入できないような微小な凹凸部分による表面積は反映されない。このことから、両吸着比表面積の差は、カーボン含有導電性材料表面の微小な凹凸の起伏の数をあらわすものであるといえる。 Since N 2 and CTAB have different adsorption occupation areas, a difference in both specific surface areas occurs due to the fine structure of the surface of the carbon-containing conductive material. In other words, the numerical value of the nitrogen adsorption specific surface area includes the surface area of the fine irregularities on the surface of the carbon-containing conductive material. On the other hand, since the adsorption cross-sectional area of cetyltrimethylammonium bromide (CTAB) is considerably larger than that of nitrogen molecules, the surface area due to minute irregularities that cannot be penetrated by CTAB molecules is not reflected in the numerical value of CTAB adsorption specific surface area. From this, it can be said that the difference between both adsorption specific surface areas represents the number of undulations of minute irregularities on the surface of the carbon-containing conductive material.
したがって、両吸着比表面積の差が、１００ｍ２／ｇ以下であると、カーボン含有導電性材料表面の微小な凹凸に担持される小さな触媒成分の数が適度に少ないため、担持される触媒成分の粒径ばらつきが小さくなる効果ばかりでなく、詳細な機構は明らかではないがこのような物性値を有するような担体表面は表面エネルギーがより均一化されて安定であり、触媒成分と担体の相互作用により触媒成分がより安定化すると考えられる。以上の理由から、Ｐｔなどの触媒成分が溶出するような高い電位や大幅な電位振動が印加されたとしても触媒成分、特にＰｔの溶出が抑制・防止されると考えられる。 Therefore, when the difference between the adsorption specific surface areas is 100 m 2 / g or less, the number of small catalyst components supported on the minute irregularities on the surface of the carbon-containing conductive material is moderately small. Not only the effect of reducing the particle size variation but also the detailed mechanism is not clear, but the surface of the support having such physical property values is more uniform and stable, and the interaction between the catalyst component and the support This is considered to stabilize the catalyst component. For the above reasons, it is considered that elution of the catalyst component, particularly Pt, is suppressed / prevented even when a high potential at which the catalyst component such as Pt is eluted or a large potential oscillation is applied.
なお、Ｎ２−ＢＥＴ比表面積とＣＴＡＢ吸着比表面積の差は、１〜１００ｍ２／ｇであることが好ましく、２〜８０ｍ２／ｇであることがより好ましく、５〜５０ｍ２／ｇであることがさらに好ましい。 Incidentally, the difference between the N 2 BET specific surface area and the CTAB adsorption specific surface area is preferably 1 to 100 m 2 / g, more preferably 2~80m 2 / g, is 5 to 50 m 2 / g More preferably.
上記のような物性値範囲のカーボン含有導電性材料を担体として用いた触媒は、本発明の製造法によって十分な溶出耐性を有する電極触媒を得ることが出来る。 A catalyst using a carbon-containing conductive material having a physical property value range as described above as a carrier can provide an electrode catalyst having sufficient elution resistance by the production method of the present invention.
なお、本発明に係る電極触媒を例えば高分子型燃料電池に用いた場合、電極触媒には触媒成分、カーボン含有導電性材料を含み、その他必要に応じて添加剤などを含まれても良い。さらに、当然のことながら、本発明に係る電極触媒は、カソード電極触媒および／またはアノード電極触媒を含む概念である。また、本発明に係る電極触媒は、カーボン含有導電性材料に触媒成分が担持されていることが好ましく、さらにカーボン含有導電性材料に触媒成分が分散担持されていることがより好ましい。 When the electrode catalyst according to the present invention is used in, for example, a polymer fuel cell, the electrode catalyst contains a catalyst component and a carbon-containing conductive material, and may contain additives as necessary. Furthermore, as a matter of course, the electrode catalyst according to the present invention is a concept including a cathode electrode catalyst and / or an anode electrode catalyst. In the electrode catalyst according to the present invention, the catalyst component is preferably supported on the carbon-containing conductive material, and more preferably the catalyst component is dispersedly supported on the carbon-containing conductive material.
本発明に係るカーボン含有導電性材料のＮ２−ＢＥＴ比表面積は、公知の窒素を用いたＢＥＴ比表面積測定方法に従って測定した値を用いることができるが、具体的にはまず試料を試料管に入れ２５０〜３５０℃で加熱しながら真空排気し表面の清浄処理を行い、その後の試料重量を測定する。再び装置に吸着セルを取りつけ、試料を液体窒素温度にまで冷却しセル内に窒素ガスを送り込む。試料表面に窒素ガスが吸着し、吹きこむガスの量を増やしていくと試料表面はガス分子で覆われていく。そしてガス分子が多重に吸着していく様子を圧力の変化に対する吸着量の変化としてプロットする。このグラフから試料表面にだけ吸着したガス分子吸着量をＢＥＴ吸着等温式より求める。窒素分子はあらかじめ吸着占有面積がわかっているのでガス吸着量より試料の表面積を測定することができる。実際に本発明については、Ｑｕａｎｔａｃｈｒｏｍｅ社のＣｈｅｍＢＥＴ３０００を用いて装置の標準的な測定法に従って求めている。 As the N 2 -BET specific surface area of the carbon-containing conductive material according to the present invention, a value measured according to a known BET specific surface area measurement method using nitrogen can be used. Specifically, first, a sample is placed in a sample tube. While heating at 250 to 350 ° C., the surface is evacuated to clean the surface, and the weight of the sample after that is measured. The adsorption cell is attached to the apparatus again, the sample is cooled to the liquid nitrogen temperature, and nitrogen gas is sent into the cell. When nitrogen gas is adsorbed on the sample surface and the amount of gas blown is increased, the sample surface is covered with gas molecules. The state in which the gas molecules are adsorbed in a multiple manner is plotted as a change in the adsorption amount with respect to a change in pressure. From this graph, the adsorption amount of gas molecules adsorbed only on the sample surface is obtained from the BET adsorption isotherm. The surface area of the sample can be measured from the amount of adsorbed gas because the adsorption occupation area of nitrogen molecules is known in advance. Actually, the present invention is obtained according to the standard measurement method of the apparatus using ChemBET 3000 of Quantachrome.
本発明に係るＣＴＡＢ吸着比表面積は、ＣＴＡＢ（セチルトリメチルアンモニウムブロミド）を吸着媒に用いた比表面積の測定法であり、具体的にはＡＳＴＭ Ｄ３７６５−８０に従い測定することにより得られた結果を用いた。 The CTAB adsorption specific surface area according to the present invention is a specific surface area measurement method using CTAB (cetyltrimethylammonium bromide) as an adsorbent, and specifically uses the results obtained by measuring according to ASTM D3765-80. It was.
本発明に係るＮ２−ＢＥＴ比表面積は、１０〜１０００ ｍ２／ｇであることが好ましく、２０〜５００ ｍ２／ｇであることがより好ましく、５０〜３００ ｍ２／ｇであることがさらに好ましい。 N 2 BET specific surface area according to the present invention is preferably from 10 to 1000 m 2 / g, more preferably 20 to 500 m 2 / g, it is 50 to 300 m 2 / g Further preferred.
Ｎ２−ＢＥＴ比表面積が１０００ ｍ２／ｇを超えるような担体の表面は微細な凹凸が大部分を占めるため、Ｐｔ溶出耐性の高い電極触媒を得られなくなり、１０ ｍ２／ｇ未満だと十分な触媒担持面積が得られないので十分な触媒活性を得ることができない。 Since the surface of the support having a N 2 -BET specific surface area of more than 1000 m 2 / g is mainly composed of fine irregularities, an electrode catalyst having a high resistance to Pt elution cannot be obtained, and is less than 10 m 2 / g. Since a sufficient catalyst supporting area cannot be obtained, sufficient catalyst activity cannot be obtained.
本発明に係るＣＴＢＡ比表面積は、１〜１０００ ｍ２／ｇであることが好ましく、５〜５００ ｍ２／ｇであることがより好ましく、１０〜２００ ｍ２／ｇであることがさらに好ましい。 The CTBA specific surface area according to the present invention is preferably 1 to 1000 m 2 / g, more preferably 5 to 500 m 2 / g, and still more preferably 10 to 200 m 2 / g.
ＣＴＢＡ比表面積が１０００ ｍ２／ｇを超えなければ担体は実質、１次粒子径が小さすぎることがないので、担持する触媒成分が必要以上に小さくなることはない。よって、Ｐｔ溶出耐性の高い電極触媒が得られる。また、１ ｍ２／ｇ以上であれば、十分な触媒担持面積が得られるので、十分な触媒活性を得ることができる。 If the CTBA specific surface area does not exceed 1000 m 2 / g, the primary particle diameter will not be too small, and the supported catalyst component will not be unnecessarily small. Therefore, an electrode catalyst having high resistance to Pt elution can be obtained. Moreover, if it is 1 m < 2 > / g or more, since sufficient catalyst supporting area is obtained, sufficient catalyst activity can be obtained.
本発明に係るカーボン含有導電性材料は、触媒成分を所望の分散状態で担持させるための比表面積を有し、集電体として十分な電子導電性を有しているものであれば本発明に使用することができ、主成分がカーボン含有導電性材料であるのが好ましい。本発明に係るカーボン含有導電性材料にカーボン含有導電性材料を用いることで、電気抵抗ロス、物質拡散ロスの少ない高性能アノード極を得ることが出来る。具体的には、カーボンブラック、活性炭、コークス、天然黒鉛、人造黒鉛などからなるカーボン粒子が挙げられる。また、かようなカーボン材料として、より具体的には、アセチレンブラック、バルカン、ケッチェンブラック、ブラックパール、黒鉛化アセチレンブラック、黒鉛化バルカン、黒鉛化ケッチェンブラック、黒鉛化カーボン、黒鉛化ブラックパール、カーボンナノチューブ、カーボンナノファイバー、カーボンナノホーン、及びカーボンフィブリルから選ばれる少なくとも一種を主成分として含むものなどが挙げられる。 The carbon-containing conductive material according to the present invention has a specific surface area for supporting the catalyst component in a desired dispersed state and has sufficient electronic conductivity as a current collector. It can be used, and the main component is preferably a carbon-containing conductive material. By using a carbon-containing conductive material for the carbon-containing conductive material according to the present invention, a high-performance anode electrode with little electrical resistance loss and substance diffusion loss can be obtained. Specific examples include carbon particles made of carbon black, activated carbon, coke, natural graphite, artificial graphite and the like. Further, as such carbon materials, more specifically, acetylene black, Vulcan, Ketjen black, black pearl, graphitized acetylene black, graphitized Vulcan, graphitized Ketjen black, graphitized carbon, graphitized black pearl , Carbon nanotubes, carbon nanofibers, carbon nanohorns, and carbon fibrils as main components.
なお、本発明において「主成分がカーボンである」とは、主成分として炭素原子を含むことをいい、炭素原子のみからなる、実質的に炭素原子からなる、の双方を含む概念である。場合によっては、燃料電池の特性を向上させるために、炭素原子以外の元素が含まれていてもよい。なお、実質的に炭素原子からなるとは、２〜３質量％程度以下の不純物の混入が許容されることを意味する。 In the present invention, “the main component is carbon” refers to containing a carbon atom as a main component, and is a concept including both a carbon atom only and a substantially carbon atom. In some cases, elements other than carbon atoms may be included in order to improve the characteristics of the fuel cell. In addition, being substantially composed of carbon atoms means that mixing of impurities of about 2 to 3% by mass or less is allowed.
また、前記カーボン含有導電性材料の大きさは、特に限定されないが、担持の容易さ、触媒利用率、電極触媒（層）の厚みを適切な範囲で制御するなどの観点からは、１次粒子径が２〜１００ｎｍ、好ましくは１０〜８０ｎｍ、より好ましくは２０〜５０ｎｍ程度とするのがよい。 The size of the carbon-containing conductive material is not particularly limited. However, from the viewpoint of controlling the ease of loading, the catalyst utilization, and the thickness of the electrode catalyst (layer) within an appropriate range, the primary particles The diameter is 2 to 100 nm, preferably 10 to 80 nm, more preferably about 20 to 50 nm.
本発明に係る導電性材料１次粒子径が２ｎｍ以上であれば、触媒成分粒子径に対して小さすぎることなく、高分散担持を維持することが容易になり、１００ｎｍ以下だと担体として十分な比表面積が得られるため触媒成分の凝集が生じることなく十分な電極性能が得られる。 If the primary particle diameter of the conductive material according to the present invention is 2 nm or more, it becomes easy to maintain highly dispersed support without being too small with respect to the catalyst component particle diameter. Since the specific surface area is obtained, sufficient electrode performance can be obtained without aggregation of the catalyst components.
なお、本明細書において「１次粒子」とは、カーボン含有導電性材料、例えば上記のカーボンブラックなどの炭素材は、一般的に複数凝集しているが、その個々の粒子をいい、凝集体を構成する個々の粒子をいう。 In the present specification, the “primary particle” means a carbon-containing conductive material, for example, a carbon material such as the above-mentioned carbon black is generally agglomerated, but means individual particles. The individual particles that make up
また、本発明に係るカーボン含有導電性材料の空孔率は、５〜８０体積％が好ましく、１０〜７０体積％がより好ましい。 Moreover, 5-80 volume% is preferable and, as for the porosity of the carbon containing electroconductive material which concerns on this invention, 10-70 volume% is more preferable.
本発明に係るカーボン含有導電性材料の１次粒子径の測定方法としては、透過型電子顕微鏡像の任意の８視野中に観察される導電性材料の１次粒子の粒径をすべて測定し(総計Ｎ＞６０)、その粒径の中央値を１次粒子径とする条件で行なった。しかし、この測定方法に限らず公知の方法で１次粒子径を算出することができる。 As a measuring method of the primary particle diameter of the carbon-containing conductive material according to the present invention, all the particle diameters of the primary particles of the conductive material observed in any eight fields of the transmission electron microscope image are measured ( The total was N> 60), and the median value of the particle diameters was the primary particle diameter. However, the primary particle diameter can be calculated not only by this measuring method but also by a known method.
なお、上記のような本発明に係るカーボン含有導電性材料の製造方法は、後述の（電極触媒の製造方法）の欄で詳説する。 The method for producing the carbon-containing conductive material according to the present invention as described above will be described in detail in the section (Method for producing electrode catalyst) described later.
本発明に係る電極触媒に用いられる触媒成分として、カソード触媒では、酸素の還元反応に触媒作用を有するものであれば特に制限はなく公知の触媒が同様にして使用できる。また、アノード触媒に用いられる触媒成分もまた、水素の酸化反応に触媒作用を有するものであれば特に制限はなく公知の触媒が同様にして使用できる。具体的には、白金、ルテニウム、イリジウム、ロジウム、パラジウム、オスミウム、タングステン、鉛、鉄、クロム、金（Ａｕ）、銀（Ａｇ）、コバルト、ニッケル、マンガン、バナジウム、モリブデン、ガリウム、アルミニウム等の金属、及びそれらの合金等などから選択される。これらのうち、触媒活性、一酸化炭素等に対する耐被毒性、耐熱性などを向上させるために、少なくとも白金を含むものが好ましく用いられる。 As the catalyst component used in the electrode catalyst according to the present invention, the cathode catalyst is not particularly limited as long as it has a catalytic action for the oxygen reduction reaction, and a known catalyst can be used in the same manner. The catalyst component used for the anode catalyst is not particularly limited as long as it has a catalytic action for the oxidation reaction of hydrogen, and a known catalyst can be used in the same manner. Specifically, platinum, ruthenium, iridium, rhodium, palladium, osmium, tungsten, lead, iron, chromium, gold (Au), silver (Ag), cobalt, nickel, manganese, vanadium, molybdenum, gallium, aluminum, etc. It is selected from metals and their alloys. Among these, those containing at least platinum are preferably used in order to improve catalyst activity, poisoning resistance to carbon monoxide and the like, heat resistance, and the like.
本発明に係る触媒成分は、組成式ＰｔａＭｂ（ａ＋ｂ＝１００）で表され、ＭはＣｏ、Ｃｒ、Ｆｅ、Ｎｉ、Ｉｒ、Ｒｈ、Ｐｄ、Ａｇ及びＡｕからなる群から選択される１種以上の元素であり、ａ＝９０〜１００、ｂ＝０〜１０であることが好ましい。 The catalyst component according to the present invention is represented by a composition formula PtaMb (a + b = 100), and M is one or more selected from the group consisting of Co, Cr, Fe, Ni, Ir, Rh, Pd, Ag, and Au. It is an element, and it is preferable that a = 90-100 and b = 0-10.
電極触媒活性に優れることからＰｔ金属単独あるいはＰｔ基合金あるいはＰｔと他の金属、金属組成物を混合した電極触媒が望ましい。他の金属成分を加える目的は主に電極触媒活性を高めるためである。具体的には式 ＰｔａＭｂ で配合を表すことができ、Ｍは、Ｃｏ、Ｃｒ、Ｆｅ、Ｎｉ、Ｉｒ、Ｒｈ、Ｐｄ、Ａｇ及びＡｕから選ばれた１種以上の元素であり、ａ＝９０〜１００、ｂ＝０〜１０が良い。ｂが１０以下であれば、第２成分が占める金属が多くなりすぎることなく、Ｐｔ溶出耐性が低下しにくい。また、第２成分溶出による電解質やカーボン担体の劣化も起こりにくくなる。ｂは好ましくは０〜８、さらに好ましくは０〜６である。また、ａが９０以上であれば、Ｐｔ溶出耐性が低下しにくい。ａは好ましくは９２〜１００、さらに好ましくは９４〜１００である。 An electrode catalyst in which Pt metal alone, a Pt-based alloy, or Pt, another metal, or a metal composition is mixed is desirable because of its excellent electrode catalyst activity. The purpose of adding other metal components is mainly to increase the electrocatalytic activity. Specifically, the formula can be represented by the formula Pt a M b , where M is one or more elements selected from Co, Cr, Fe, Ni, Ir, Rh, Pd, Ag, and Au, and a = 90-100 and b = 0-10 are good. If b is 10 or less, the metal which a 2nd component occupies does not increase too much, and Pt elution tolerance does not fall easily. In addition, the electrolyte and the carbon support are less likely to deteriorate due to elution of the second component. b is preferably 0 to 8, more preferably 0 to 6. Moreover, if a is 90 or more, Pt elution tolerance is hard to fall. a is preferably 92 to 100, more preferably 94 to 100.
なお、合金とは、一般に金属元素に１種以上の金属元素または非金属元素を加えたものであって、金属的性質をもっているものの総称である。 In general, an alloy is a generic term for a metal element having one or more metal elements or non-metal elements added and having metallic properties.
合金の組織には、成分元素が別個の結晶となるいわば混合物である共晶合金、成分元素が完全に溶け合い固溶体となっているもの、成分元素が金属間化合物または金属と非金属との化合物を形成しているものなどがあり、本願ではいずれであってもよい。この際、カソード触媒（層）に用いられる触媒成分及びアノード触媒（層）に用いられる触媒成分は、上記の中から適宜選択できる。以下の説明では、特記しない限り、カソード触媒（層）及びアノード触媒（層）用の触媒成分についての説明は、両者について同様の定義であり、一括して、「触媒成分」と称する。しかしながら、カソード触媒（層）及びアノード触媒（層）用の触媒成分は同一である必要はなく、上記したような所望の作用を奏するように、適宜選択される。 The alloy structure consists of a eutectic alloy, which is a mixture of the component elements as separate crystals, a component element completely melted into a solid solution, and a component element composed of an intermetallic compound or a compound of a metal and a nonmetal. There is what is formed, and any may be used in the present application. At this time, the catalyst component used for the cathode catalyst (layer) and the catalyst component used for the anode catalyst (layer) can be appropriately selected from the above. In the following description, unless otherwise specified, the descriptions of the catalyst components for the cathode catalyst (layer) and the anode catalyst (layer) are the same definitions for both, and are collectively referred to as “catalyst components”. However, the catalyst components for the cathode catalyst (layer) and the anode catalyst (layer) do not have to be the same, and are appropriately selected so as to exhibit the desired action as described above.
触媒成分の形状や大きさは、特に制限されず公知の触媒成分と同様の形状及び大きさが使用できるが、触媒成分は、粒状であることが好ましい。この際、電極触媒に用いられる触媒成分の平均粒子径は、小さいほど電気化学反応が進行する有効電極面積が増加するため酸素還元活性も高くなり好ましいが、実際には平均粒子径が小さすぎると却って酸素還元活性が低下する現象が見られる。従って、本発明に係る触媒成分の平均粒子径は、２〜２０ｎｍであることが好ましく、３〜１５ｎｍであることがより好ましく、４〜１０ｎｍであることがさらに好ましい。平均粒子径が２ｎｍ以上であれば、比表面積が大き過ぎず高い質量活性もえられ、本発明の触媒製造方法などによって十分なＰｔの溶出耐性も得られる。２０ｎｍ以下であれば、溶出耐性も得られ、比表面積も小さすぎず十分な質量活性が得られると考えられる。 The shape and size of the catalyst component are not particularly limited, and the same shape and size as known catalyst components can be used, but the catalyst component is preferably granular. At this time, the smaller the average particle size of the catalyst component used in the electrode catalyst, the higher the effective electrode area where the electrochemical reaction proceeds, which is preferable because the oxygen reduction activity is also high, but actually the average particle size is too small On the other hand, a phenomenon in which the oxygen reduction activity decreases is observed. Therefore, the average particle size of the catalyst component according to the present invention is preferably 2 to 20 nm, more preferably 3 to 15 nm, and further preferably 4 to 10 nm. If the average particle diameter is 2 nm or more, the specific surface area is not too large and high mass activity can be obtained, and sufficient elution resistance of Pt can be obtained by the catalyst production method of the present invention. If it is 20 nm or less, it is considered that elution resistance is obtained, and the specific surface area is not too small so that sufficient mass activity can be obtained.
本発明に係る触媒成分の平均粒子径の測定方法としては、透過型電子顕微鏡像から代表サンプルについて数〜数１０視野中に観察される粒子の粒径を測定する方法が挙げられる。なお、この測定方法では観察するサンプルや視野によって平均粒子径に有意差が生じる。より簡易的にはＸ線回折プロファイルからある特定の反射ピークの半値幅から求められる結晶子径を触媒成分の平均粒子径として用いることも出来る。 Examples of the method for measuring the average particle diameter of the catalyst component according to the present invention include a method of measuring the particle diameter of particles observed in several to several tens of fields for a representative sample from a transmission electron microscope image. In this measurement method, there is a significant difference in the average particle diameter depending on the sample to be observed and the visual field. More simply, the crystallite diameter determined from the half width of a specific reflection peak from the X-ray diffraction profile can be used as the average particle diameter of the catalyst component.
本発明の触媒成分の平均粒子径は透過型電子顕微鏡像の任意の８視野中に観察される導電性材料の１次粒子の粒径をすべて測定し(総計Ｎ＞１２０)、その粒径の中央値を触媒成分の平均粒子径とする条件で行なった。 The average particle size of the catalyst component of the present invention was determined by measuring all the primary particle sizes of the conductive material observed in any 8 fields of the transmission electron microscope image (total N> 120). The test was carried out under the condition that the median was the average particle diameter of the catalyst component.
本発明に係る触媒成分の粒径標準偏差と前記触媒成分の平均粒径との比が０．３以下であることが好ましい。 The ratio of the particle size standard deviation of the catalyst component according to the present invention to the average particle size of the catalyst component is preferably 0.3 or less.
本発明に係る粒径標準偏差とは、以下の式で表すことができ、触媒成分を粒子と仮定した場合における粒径の散らばりを表す値をいい、分散の平方根である。 The particle size standard deviation according to the present invention can be expressed by the following equation, and is a value representing the dispersion of the particle size when the catalyst component is assumed to be a particle, and is a square root of dispersion.
本発明に係る触媒成分の粒径標準偏差は、透過型電子顕微鏡像から代表サンプルについて数〜数１０視野中に観察される粒子の粒径を統計処理する方法が挙げられる。すなわち、透過型電子顕微鏡像から代表サンプルについて数〜数１０視野中に観察される触媒成分の粒径の値と、各々の触媒成分の粒径の値をとる確率とを算出し、粒径標準偏差を求めることができる。 Examples of the particle size standard deviation of the catalyst component according to the present invention include a method of statistically processing the particle size of particles observed in several to several tens of fields for a representative sample from a transmission electron microscope image. That is, the value of the particle size of the catalyst component observed in several to several tens of fields for the representative sample from the transmission electron microscope image and the probability of taking the value of the particle size of each catalyst component are calculated, and the particle size standard is calculated. Deviation can be obtained.
上記触媒成分の粒径標準偏差と前記触媒成分の平均粒径との比（＝触媒成分の平均粒径に対する触媒成分の粒径標準偏差の比）が０．３超の場合、小さい粒径の触媒金属粒子の割合が増加し、溶出触媒成分量が多くなってしまう。したがって、上記触媒成分の粒径標準偏差と前記触媒成分の平均粒径との比は、０．３以下が好ましく、０．２５以下がより好ましく、０．２以下がさらに好ましい。 When the ratio of the particle size standard deviation of the catalyst component to the average particle size of the catalyst component (= ratio of the particle size standard deviation of the catalyst component to the average particle size of the catalyst component) exceeds 0.3, the small particle size The proportion of catalyst metal particles increases and the amount of the eluted catalyst component increases. Therefore, the ratio between the particle size standard deviation of the catalyst component and the average particle size of the catalyst component is preferably 0.3 or less, more preferably 0.25 or less, and further preferably 0.2 or less.
本発明に係るカーボン含有導電性材料の１次粒子径は、走査型や透過型などの電子顕微鏡、Ｘ線回折法を用いた公知な方法を用いることにより測定することが可能である。例えば、ＴＥＭにより撮影した画像から算出したカーボン含有導電性材料の１次粒子径に対する触媒成分との平均粒子径の比については好ましくは１〜５０、さらに好ましくは１．５〜１５、より好ましくは２〜１０である。 The primary particle diameter of the carbon-containing conductive material according to the present invention can be measured by using a known method using an electron microscope such as a scanning type or a transmission type, or an X-ray diffraction method. For example, the ratio of the average particle diameter with the catalyst component to the primary particle diameter of the carbon-containing conductive material calculated from the image taken by TEM is preferably 1 to 50, more preferably 1.5 to 15, and more preferably 2-10.
カーボン含有導電性材料の１次粒子径と触媒成分との平均粒子径の比が、１以上であれば担体の１次粒子径よりも触媒成分粒子の方が大きくなり過ぎず、触媒成分粒子の凝集が起こりにくく高分散担持が維持しやすい。このため、使用Ｐｔ量に対して十分な電極性能を得られることになる。またカーボン含有導電性材料の１次粒子径と触媒成分との平均粒子径の比が５０以下であれば、担体比表面積が小さくなり過ぎず、触媒成分が担持される面積が十分に存在する。このため、上記と同様に担持触媒成分粒子の凝集が起こりにくくなり、使用Ｐｔ量に対して十分な電極性能を得られる。 If the ratio of the average particle size between the primary particle size of the carbon-containing conductive material and the catalyst component is 1 or more, the catalyst component particles will not be too large compared to the primary particle size of the carrier. Aggregation is unlikely to occur and high dispersion support is easy to maintain. For this reason, sufficient electrode performance can be obtained with respect to the amount of Pt used. If the ratio of the average particle size of the primary particle size of the carbon-containing conductive material to the catalyst component is 50 or less, the specific surface area of the carrier does not become too small and there is a sufficient area for supporting the catalyst component. For this reason, the agglomeration of the supported catalyst component particles hardly occurs as described above, and sufficient electrode performance can be obtained with respect to the used Pt amount.
前記カーボン含有導電性材料に触媒成分が担持された電極触媒において、触媒成分の担持量は、カーボン含有導電性材料に対して、好ましくは１０〜８０質量％、より好ましくは３０〜６０質量％とするのがよい。なお、触媒成分の担持量は、誘導結合プラズマ発光分光法（ＩＣＰ）によって調べることができる。 In the electrode catalyst in which the catalyst component is supported on the carbon-containing conductive material, the supported amount of the catalyst component is preferably 10 to 80% by mass, more preferably 30 to 60% by mass with respect to the carbon-containing conductive material. It is good to do. The amount of the catalyst component supported can be examined by inductively coupled plasma emission spectroscopy (ICP).
Ｐｔの溶出をより抑制するためには触媒成分担持量をある一定の範囲にしたほうがよい。１０質量％以上であれば、触媒層が厚くなり過ぎず、かつ高い電極性能も得られる。また、８０質量％以下ではＰｔの溶出はより抑制され、かつ、触媒成分は高分散になるため触媒成分量に対して得られる性能が十分になる。 In order to further suppress the elution of Pt, it is better to set the catalyst component loading in a certain range. If it is 10 mass% or more, the catalyst layer does not become too thick, and high electrode performance can be obtained. Further, when the content is 80% by mass or less, the elution of Pt is further suppressed, and the catalyst component becomes highly dispersed, so that the performance obtained with respect to the amount of the catalyst component becomes sufficient.
本発明に係るカーボン含有導電性材料は８５質量％〜１００質量％の炭素により構成される粉末または多孔質構造体であることが好ましく、９０質量％〜１００質量％がより好ましく、９５質量％〜１００質量％がさらに好ましい。 The carbon-containing conductive material according to the present invention is preferably a powder or a porous structure composed of 85% by mass to 100% by mass of carbon, more preferably 90% by mass to 100% by mass, and more preferably 95% by mass to 100 mass% is more preferable.
カーボン含有導電性材料における炭素の割合が、８５質量％〜１００質量％だと十分な比表面積と電子導電性を両立可能で高性能な電極を得ることが可能になる。 When the proportion of carbon in the carbon-containing conductive material is 85% by mass to 100% by mass, it is possible to obtain a high-performance electrode that can achieve both a sufficient specific surface area and electronic conductivity.
触媒成分を担持する炭素より構成される材料は十分な電子導電性を有し、かつ触媒成分を容易に高分散させることが必要であることから、炭素質の材料が好適に用いられる。炭素以外に含まれる元素としては例えば撥水性を付与するためのフッ素や珪素などのほかにカーボン含有導電性材料の耐腐食性を向上させるためのホウ素や表面官能基に含まれる水素、酸素や窒素のほかに不純金属分などが挙げられる。 A material composed of carbon carrying the catalyst component has sufficient electronic conductivity, and since it is necessary to easily disperse the catalyst component easily, a carbonaceous material is preferably used. Examples of elements other than carbon include, for example, fluorine and silicon for imparting water repellency, boron for improving the corrosion resistance of carbon-containing conductive materials, and hydrogen, oxygen and nitrogen contained in surface functional groups. In addition to the above, impurities such as impure metals are listed.
（電極触媒の製造方法）
本発明の第二は、触媒成分を担持したカーボン含有導電性材料を含む電極触媒の製造方法において、触媒成分をカーボン含有導電性材料に担持する前に、前記カーボン含有導電性材料に対して表面処理工程を行うことを特徴とする電極触媒の製造方法である。
(Electrocatalyst production method)
The second aspect of the present invention is a method for producing an electrode catalyst comprising a carbon-containing conductive material carrying a catalyst component, and before the catalyst component is carried on the carbon-containing conductive material, the surface of the carbon-containing conductive material is surfaced. It is a manufacturing method of the electrode catalyst characterized by performing a processing process.
この製造方法により従来の電極触媒よりもＰｔ溶出耐性が大幅に向上する。詳細な溶出抑制機構は明らかではないが、例えば上記したようにカーボン含有導電性材料表面の微小な凹凸に担持される小さな触媒成分の数が適度に少ないため、担持される触媒成分の粒径ばらつきが小さくなる効果ばかりでなく、詳細な機構は明らかではないがこのような物性値を有するような担体表面は表面エネルギーがより均一化されて安定であり、触媒成分と担体の相互作用により触媒成分がより安定化すると考えられる。以上の理由から、Ｐｔなどの触媒成分が溶出するような高い電位や大幅な電位振動が印加されたとしても触媒成分、特にＰｔの溶出が抑制・防止されると考えられる。 By this production method, the Pt elution resistance is greatly improved as compared with the conventional electrode catalyst. Although the detailed elution suppression mechanism is not clear, for example, as described above, since the number of small catalyst components supported on the minute irregularities on the surface of the carbon-containing conductive material is moderately small, the particle size variation of the supported catalyst components Although the detailed mechanism is not clear, the surface of the support having such physical property values is more uniform and stable, and the catalyst component is supported by the interaction between the catalyst component and the support. Is considered to be more stable. For the above reasons, it is considered that elution of the catalyst component, particularly Pt, is suppressed / prevented even when a high potential at which the catalyst component such as Pt is eluted or a large potential oscillation is applied.
本発明に係る電極触媒の製造方法における表面処理工程としては、カーボン含有導電性材料自体に物理的または化学的に負荷を与えてカーボン含有導電性材料の微細構造を調節する方法であれば限定されないが、例えば、本発明に係る表面処理工程の一部分として酸処理、アルカリ処理、および水蒸気焼成などがカーボン含有導電性材料自体に物理的または化学的に負荷を与える手段として挙げられ、上記の酸処理、アルカリ処理、および水蒸気焼成などのカーボン含有導電性材料自体に物理的または化学的に負荷を与えてカーボン含有導電性材料の微細構造を調節する工程において、必要に応じて熱処理工程を加えることがより好ましく、特に酸処理、アルカリ処理、および水蒸気焼成をした後に熱処理をすることが好ましい。また、本発明に係る表面処理工程の一部分としての酸処理、アルカリ処理、および水蒸気焼成は、それぞれ１つの工程を行なっても、複数の工程を行なっても良く、本発明に係る表面処理工程の一部分としての熱処理も１回でも複数回でもよく、熱処理を行なう場合の雰囲気は不活性ガス雰囲気または還元性ガス雰囲気などが好ましい。 The surface treatment step in the method for producing an electrode catalyst according to the present invention is not limited as long as it is a method of physically or chemically applying a load to the carbon-containing conductive material itself to adjust the microstructure of the carbon-containing conductive material. However, as a part of the surface treatment process according to the present invention, acid treatment, alkali treatment, and steam firing are listed as means for physically or chemically loading the carbon-containing conductive material itself. In the process of adjusting the microstructure of the carbon-containing conductive material by physically or chemically applying a load to the carbon-containing conductive material itself, such as alkali treatment and steam baking, a heat treatment step may be added as necessary. More preferably, heat treatment is particularly preferred after acid treatment, alkali treatment, and water vapor firing. In addition, the acid treatment, the alkali treatment, and the steam baking as part of the surface treatment process according to the present invention may be performed in one step or a plurality of steps, respectively. The heat treatment as a part may be performed once or a plurality of times, and the atmosphere in the heat treatment is preferably an inert gas atmosphere or a reducing gas atmosphere.
上記不活性ガス、還元性ガスは、下記に使用する不活性ガス、還元性ガスと同様であり、詳説するのでここでの説明は省略する。 The inert gas and reducing gas are the same as the inert gas and reducing gas used below, and will not be described here because they will be described in detail.
なお、本明細書における「表面処理工程」とは、カーボン含有導電性材料自体に物理的または化学的に負荷を与えてカーボン含有導電性材料の微細構造を調節する工程をいい、いわゆる腐食処理工程および熱処理工程を含む概念である。 The “surface treatment step” in this specification refers to a step of physically or chemically applying a load to the carbon-containing conductive material itself to adjust the fine structure of the carbon-containing conductive material, so-called corrosion treatment step. And a concept including a heat treatment step.
本発明に係る表面処理工程の一部分である酸処理は、酢酸、塩酸、硫酸、硝酸、硫酸、亜硝酸、亜硫酸リン酸、弗酸やこれらの混酸などの公知の酸溶液にカーボン含有導電性材料を含浸する方法、前記酸水溶液をスプレーでカーボン含有導電性材料に吹きつける方法、などが挙げられる。 The acid treatment which is a part of the surface treatment process according to the present invention is carried out by using a carbon-containing conductive material in a known acid solution such as acetic acid, hydrochloric acid, sulfuric acid, nitric acid, sulfuric acid, nitrous acid, phosphorous acid, hydrofluoric acid, and mixed acids thereof. And a method of spraying the acid aqueous solution onto the carbon-containing conductive material by spraying.
また、上記の酸溶液に用いられる溶媒は主に水であるが、カーボン含有導電性材料を分散させやすくする目的でアセトン、アルコール類などの極性有機溶媒を含んでいても良い。上記酸溶液の濃度は、溶媒に対して１〜８０質量％が好ましく、１０〜７０質量％がより好ましく、１５〜６５質量％がさらに好ましい。 Moreover, although the solvent used for said acid solution is mainly water, polar organic solvents, such as acetone and alcohol, may be included in order to make it easy to disperse | distribute a carbon containing electroconductive material. The concentration of the acid solution is preferably 1 to 80% by mass, more preferably 10 to 70% by mass, and still more preferably 15 to 65% by mass with respect to the solvent.
上記の含浸する方法により本発明に係るカーボン含有導電性材料に微細構造を形成させる場合の含浸時間は特に限定されず酸溶液のｐＨやカーボン含有導電性材料の大きさなどに合わせて適宜選択されるものであるが、例えば所定の量の酸溶液に５〜１００時間程度含浸させるとよい。なお、上記熱処理、焼成の時間は、酸溶液のｐＨやカーボン含有導電性材料の大きさなど種々の条件に応じて適宜決定されるものである。 The impregnation time in the case of forming a microstructure in the carbon-containing conductive material according to the present invention by the above-described impregnation method is not particularly limited, and is appropriately selected according to the pH of the acid solution, the size of the carbon-containing conductive material, and the like. For example, it is preferable to impregnate a predetermined amount of acid solution for about 5 to 100 hours. The heat treatment and firing time are appropriately determined according to various conditions such as the pH of the acid solution and the size of the carbon-containing conductive material.
本発明に係る表面処理工程の一部分である酸処理をした後に必要に応じて、熱処理、焼成、洗浄などすることにより酸を除去してもよい。なお、この場合の熱処理、焼成の温度は、１００〜５００℃が好ましい。 After the acid treatment which is a part of the surface treatment process according to the present invention, the acid may be removed by heat treatment, baking, washing or the like, if necessary. In this case, the heat treatment and firing temperature is preferably 100 to 500 ° C.
本発明に係る表面処理工程の一部分であるアルカリ処理は、公知のアルカリ溶液にカーボン含有導電性材料を含浸する方法、前記酸水溶液をスプレーでカーボン含有導電性材料に吹きつける方法、などが挙げられる。 Examples of the alkali treatment that is a part of the surface treatment process according to the present invention include a method of impregnating a known alkaline solution with a carbon-containing conductive material, a method of spraying the acid aqueous solution onto the carbon-containing conductive material by spraying, and the like. .
上記アルカリ処理に用いられるアルカリ溶液は、特に限定されず公知のアルカリ溶液であれば好ましく用いられるが、アルカリ金属（水素を含む）、アルカリ土類金属を含むアルカリ溶液がより好ましく、なかでもナトリウム、カリウムを含むアルカリ溶液がさらに好ましく、ＮａＯＨ、ＫＯＨが特に好ましい。 The alkali solution used for the alkali treatment is not particularly limited and is preferably used as long as it is a known alkali solution. However, an alkali solution (including hydrogen) and an alkali solution containing an alkaline earth metal are more preferable, and sodium, An alkaline solution containing potassium is more preferable, and NaOH and KOH are particularly preferable.
上記のアルカリ溶液に用いられる溶媒は、主に水であるが、カーボン含有導電性材料を分散させやすくする目的でアセトン、アルコール類などの極性有機溶媒を含んでいても良い。上記アルカリ溶液の濃度は、溶媒に対して１〜８０質量％が好ましく、１０〜７０質量％がより好ましく、１５〜６５質量％がさらに好ましい。 The solvent used in the alkaline solution is mainly water, but may contain a polar organic solvent such as acetone or alcohols for the purpose of easily dispersing the carbon-containing conductive material. The concentration of the alkaline solution is preferably 1 to 80% by mass, more preferably 10 to 70% by mass, and still more preferably 15 to 65% by mass with respect to the solvent.
上記の含浸する方法により本発明に係るカーボン含有導電性材料に微細構造を形成させる場合の含浸時間は特に限定されずアルカリ溶液のｐＨやカーボン含有導電性材料の大きさなどに合わせて適宜選択されるものであるが、例えば所定の量のアルカリ溶液に５〜１００時間程度含浸させるとよい。 The impregnation time in the case of forming a microstructure in the carbon-containing conductive material according to the present invention by the above-described impregnation method is not particularly limited, and is appropriately selected according to the pH of the alkaline solution, the size of the carbon-containing conductive material, and the like. For example, it may be impregnated with a predetermined amount of alkaline solution for about 5 to 100 hours.
本発明に係る表面処理工程の一部分であるアルカリ処理をした後に必要に応じて、熱処理、焼成、洗浄などすることにより酸を除去してもよい。なお、この場合の熱処理、焼成の温度は、１００〜５００℃が好ましい。なお、上記熱処理、焼成の時間は、アルカリ溶液のｐＨやカーボン含有導電性材料の大きさなど種々の条件に応じて適宜決定されるものである。 After the alkali treatment which is a part of the surface treatment step according to the present invention, the acid may be removed by heat treatment, baking, washing or the like, if necessary. In this case, the heat treatment and firing temperature is preferably 100 to 500 ° C. The heat treatment and firing time are appropriately determined according to various conditions such as the pH of the alkaline solution and the size of the carbon-containing conductive material.
本発明に係る表面処理工程の一部分である水蒸気焼成は、公知の方法により行なうことができるが、例えば、好ましくは水蒸気濃度２０〜１００％、より好ましくは相対湿度５０〜９５％、さらに好ましくは相対湿度６０〜９０％の雰囲気下で、好ましくは６００〜１２００℃、より好ましくは７００〜１１００℃、さらに好ましくは８００〜１０００℃の温度条件の下、１〜６時間程度焼成することが好ましい。水蒸気に加えるバランスガスは不活性ガスあるいは二酸化炭素を用いることができる。 The steam baking which is a part of the surface treatment process according to the present invention can be performed by a known method. For example, the steam concentration is preferably 20 to 100%, more preferably relative humidity 50 to 95%, and still more preferably relative. Baking is preferably performed for about 1 to 6 hours under a temperature condition of 600 to 1200 ° C., more preferably 700 to 1100 ° C., and even more preferably 800 to 1000 ° C. in an atmosphere with a humidity of 60 to 90%. As the balance gas added to the water vapor, an inert gas or carbon dioxide can be used.
上記の表面処理工程において熱処理を行なった後、さらに担体の表面構造を適宜調節し、表面処理工程により不安定化した一部の表面を安定化させるために高温熱処理工程を行っても良く、また高温熱処理工程は、上記熱処理や焼成に代えて行なってもよい。このような目的を達成するための高温熱処理工程は不活性ガス雰囲気または還元性ガス雰囲気中で１５００〜３０００℃、より好ましくは１６００〜２８００℃、さらに好ましくは１８００〜２６００℃の温度条件下で０．１〜４時間程度焼成することが好ましい。 After performing the heat treatment in the surface treatment step, a high-temperature heat treatment step may be performed to further adjust the surface structure of the carrier as appropriate and stabilize a part of the surface destabilized by the surface treatment step. The high temperature heat treatment step may be performed in place of the heat treatment or firing. The high-temperature heat treatment step for achieving such an object is performed under a temperature condition of 1500 to 3000 ° C., more preferably 1600 to 2800 ° C., and further preferably 1800 to 2600 ° C. in an inert gas atmosphere or a reducing gas atmosphere. It is preferable to bake for about 1 to 4 hours.
なお、本明細書における（電極触媒の製造方法）以下に用いられる触媒成分、カーボン含有導電性材料については、上述の（電極触媒）中に用いられる「触媒成分」、「カーボン含有導電性材料」と同様の物質、物性であるためここでの説明は省略する。 In addition, regarding the catalyst component and carbon-containing conductive material used in the following (Electrocatalyst production method) in this specification, the “catalyst component” and “carbon-containing conductive material” used in the above-mentioned (electrode catalyst). The description is omitted here because of the same materials and physical properties.
本発明に係る電極触媒の製造方法は、触媒成分をカーボン含有導電性材料に担持した後に熱処理を加える工程（Ａ）をさらに含むことが好ましい。 The method for producing an electrode catalyst according to the present invention preferably further includes a step (A) of applying a heat treatment after supporting the catalyst component on the carbon-containing conductive material.
この製造方法により従来の電極触媒よりもＰｔ溶出耐性が大幅に向上する。詳細な溶出抑制機構は明らかではないが、本発明に示すような物性を有するカーボン担体種や触媒金属種および触媒担持方法の組み合わせが熱処理時における溶出耐性の高い触媒金属構造形成に寄与していると考えられる。 By this production method, the Pt elution resistance is greatly improved as compared with the conventional electrode catalyst. Although the detailed elution suppression mechanism is not clear, the combination of carbon support species and catalyst metal species having physical properties as shown in the present invention and the catalyst loading method contributes to the formation of a catalyst metal structure with high elution resistance during heat treatment. it is conceivable that.
本発明に係るカーボン含有導電性材料への触媒成分の担持は公知の方法で行うことができる。例えば、含浸法、液相還元担持法、蒸発乾固法、コロイド吸着法、噴霧熱分解法、逆ミセル（マイクロエマルジョン法）などの公知の方法が使用できる。 The catalyst component can be supported on the carbon-containing conductive material according to the present invention by a known method. For example, known methods such as impregnation method, liquid phase reduction support method, evaporation to dryness method, colloid adsorption method, spray pyrolysis method, reverse micelle (microemulsion method) can be used.
なかでも本発明に係る触媒成分の原料は、液相に溶解または分散された状態で還元されることにより前記カーボン含有導電性材料に担持されることがより好ましい。 In particular, the raw material of the catalyst component according to the present invention is more preferably supported on the carbon-containing conductive material by being reduced in a state dissolved or dispersed in the liquid phase.
本発明に係るカーボン含有導電性材料への触媒成分の担持は、金属塩を液相に溶解あるいは分散させた状態で、金属塩が還元剤により還元された状態でカーボン含有導電性材料に担持される製造方法がより好ましい。そのため、液相還元担持法、コロイド吸着法、逆ミセル法が特に好ましい。 The catalyst component is supported on the carbon-containing conductive material according to the present invention when the metal salt is dissolved or dispersed in the liquid phase and the metal salt is reduced by the reducing agent. The manufacturing method is more preferable. Therefore, a liquid phase reduction support method, a colloid adsorption method, and a reverse micelle method are particularly preferable.
例えば含浸法によりカーボン含有導電性材料表面に触媒成分を担持させるには、カーボン含有導電性材料を、触媒成分を含む溶液（以下、触媒溶液とも称する）に添加する段階と、前記カーボン含有導電性材料表面に前記触媒溶液を含浸させる段階と、により前記カーボン含有導電性材料に触媒成分を担持させる触媒成分担持工程を含む方法が用いられる。これにより、カーボン含有導電性材料表面に触媒成分を高分散担持することができ、十分な初期性能と優れた耐久性を有する電極触媒を得ることができる。 For example, in order to support the catalyst component on the surface of the carbon-containing conductive material by an impregnation method, a step of adding the carbon-containing conductive material to a solution containing the catalyst component (hereinafter also referred to as catalyst solution), and the carbon-containing conductive material The method includes a step of impregnating the surface of the material with the catalyst solution, and a catalyst component supporting step of supporting the catalyst component on the carbon-containing conductive material. Thereby, the catalyst component can be highly dispersed and supported on the surface of the carbon-containing conductive material, and an electrode catalyst having sufficient initial performance and excellent durability can be obtained.
なお、触媒成分を含む溶液とは、カーボン含有導電性材料に担持させる触媒成分の元素を含む溶液のことであり、前記触媒成分としては、高い触媒活性を示すことから、上記の本発明に係る電極触媒（層）に用いられる触媒成分と同様の元素が挙げられる。 The solution containing the catalyst component is a solution containing an element of the catalyst component to be supported on the carbon-containing conductive material. Since the catalyst component exhibits high catalytic activity, the solution according to the present invention described above is used. The same elements as the catalyst component used for the electrode catalyst (layer) can be mentioned.
また本発明に係る触媒成分の原料は、Ｐｔの塩化物、Ｐｔの硝酸塩、またはＰｔのジニトロジアンミン錯体塩であることが好ましい。 The raw material of the catalyst component according to the present invention is preferably Pt chloride, Pt nitrate, or Pt dinitrodiammine complex salt.
触媒成分原料として用いる金属塩の還元方法は、適度な還元速度を持つものがよく、本用途におけるカーボン含有導電性材料にＰｔなど上記の触媒成分の説明の際に列挙した触媒成分を担持する製造方法においては、塩化物、硝酸塩、ジニトロジアンミン錯体塩などが好適に用いられる。これにより、カーボン含有導電性材料表面に高分散に触媒成分を担持することができる。 The method for reducing the metal salt used as the catalyst component raw material should have an appropriate reduction rate, and the carbon-containing conductive material in this application is supported by carrying the catalyst components listed in the description of the above catalyst components such as Pt. In the method, chloride, nitrate, dinitrodiammine complex salt and the like are preferably used. Thereby, the catalyst component can be supported in a highly dispersed manner on the surface of the carbon-containing conductive material.
なお、前記触媒成分の原料として具体的には、例えば、触媒成分としてＰｔを用いる場合には、塩化白金酸、塩化アンミン白金、ジニトロジアンミン白金；イリジウムを用いる場合には、塩化イリジウムなど；パラジウムを用いる場合には、塩化パラジウムなど所望の触媒成分の元素を含む化合物（以下、単に「触媒化合物」とも記載する。）を、水および／または有機溶媒などに所定濃度に溶解させた溶液などのことである。有機溶媒としては、特に限定されず、水、メタノール、エタノール、プロパノール、イソプロピルアルコールなどのアルコール類や、アセトンなどのケトン類などが挙げられ、これらは１種単独で使用してもよいし２種以上を混合して使用してもよい。 Specifically, as the raw material of the catalyst component, for example, when Pt is used as the catalyst component, chloroplatinic acid, platinum chloride, dinitrodiammine platinum; when iridium is used, iridium chloride, etc .; palladium When used, such as a solution in which a compound containing an element of a desired catalyst component such as palladium chloride (hereinafter also simply referred to as “catalyst compound”) is dissolved in water and / or an organic solvent at a predetermined concentration. It is. It does not specifically limit as an organic solvent, Alcohols, such as water, methanol, ethanol, propanol, isopropyl alcohol, ketones, such as acetone, etc. are mentioned, These may be used individually by 1 type, or 2 types. You may mix and use the above.
触媒溶液における触媒化合物の濃度としては特に限定されず、所望の電極触媒が得られるように適宜決定すればよいが、溶媒に対して０．０１〜５質量％、好ましくは０．０５〜１質量％程度とすればよい。 It does not specifically limit as a density | concentration of the catalyst compound in a catalyst solution, What is necessary is just to determine suitably so that a desired electrode catalyst may be obtained, but 0.01-5 mass% with respect to a solvent, Preferably it is 0.05-1 mass. It may be about%.
前記触媒溶液にカーボン含有導電性材料を添加した後、前記カーボン含有導電性材料が粉末の場合には、前記触媒溶液にカーボン含有導電性材料をホモジナイザ、超音波分散装置等の適当な分散手段により十分に分散させてもよく、これらの分散手段は適宜組み合わせてもよい。前記カーボン含有導電性材料が多孔質構造体の場合には、溶液に添加した後、必要に応じて超音波照射や減圧脱泡により触媒溶液を細部にまで浸透させる手段を加えても良い。これらの手段により、カーボン含有導電性材料表面に触媒溶液を含浸させることができる。 After the carbon-containing conductive material is added to the catalyst solution, when the carbon-containing conductive material is a powder, the carbon-containing conductive material is added to the catalyst solution by an appropriate dispersing means such as a homogenizer or an ultrasonic dispersing device. It may be sufficiently dispersed, and these dispersing means may be appropriately combined. When the carbon-containing conductive material is a porous structure, it may be added to the solution, and then a means for penetrating the catalyst solution in detail by ultrasonic irradiation or vacuum degassing may be added as necessary. By these means, the surface of the carbon-containing conductive material can be impregnated with the catalyst solution.
本発明に係る触媒溶液に添加するカーボン含有導電性材料の添加量としては特に限定されず、所望の電極触媒が得られるように適宜決定すればよいが、触媒化合物溶液に対して０．０５〜１５質量％、好ましくは０．１〜１０質量％程度とすればよい。 The addition amount of the carbon-containing conductive material to be added to the catalyst solution according to the present invention is not particularly limited, and may be appropriately determined so that a desired electrode catalyst is obtained. It may be about 15% by mass, preferably about 0.1 to 10% by mass.
次に、触媒溶液が含浸された前記カーボン含有導電性材料を、吸引瀘過などの瀘別手段などの公知の手段を用いて、濾取し、乾燥する。その後、前記混合液をろ過して、得られた沈殿物を乾燥することにより、本発明の電極触媒を得ることができる。 Next, the carbon-containing conductive material impregnated with the catalyst solution is filtered and dried using a known means such as a separating means such as suction filtration. Thereafter, the electrode mixture of the present invention can be obtained by filtering the mixed solution and drying the resulting precipitate.
本発明の電極触媒の乾燥方法としては、真空乾燥、自然乾燥、ロータリーエバポレータ、沿送風乾燥機による乾燥など、公知の方法を用いればよく、特に限定されない。乾燥時間などは、使用する方法に応じて適宜決定すればよい。 The method for drying the electrode catalyst of the present invention may be any known method such as vacuum drying, natural drying, rotary evaporator, and drying by a blower dryer, and is not particularly limited. What is necessary is just to determine drying time etc. suitably according to the method to be used.
またたとえば、液相還元担持法によりカーボン含有導電性材料表面に触媒成分を担持させるには、カーボン含有導電性材料を、触媒溶液に添加する段階と、得られる混合液に還元剤を添加する段階と、により前記カーボン含有導電性材料に触媒成分を担持させる触媒担持工程を含む方法を用いてもよい。なお、前記カーボン含有導電性材料を触媒溶液に添加する段階としては、上記した含浸法においてした説明と同様にして行えばよい。 Further, for example, in order to support the catalyst component on the surface of the carbon-containing conductive material by the liquid phase reduction support method, a step of adding the carbon-containing conductive material to the catalyst solution and a step of adding a reducing agent to the resulting mixed solution A method including a catalyst supporting step of supporting a catalyst component on the carbon-containing conductive material may be used. The step of adding the carbon-containing conductive material to the catalyst solution may be performed in the same manner as described in the impregnation method.
次に、得られる混合液に還元剤を添加する段階において、前記還元剤としては、触媒化合物を還元できるものであり、適度な還元速度を持つものがよく、特に限定されない。例えば、還元剤としては、チオ硫酸ナトリウム、クエン酸、クエン酸ナトリウム、Ｌ−アスコルビン酸、水素化ホウ素ナトリウム、ヒドラジン、ホルムアルデヒド、メタノール、エタノール、水素、エチレン、一酸化炭素などが挙げられる。触媒溶液に添加する前記還元剤の添加量などは特に限定されず、適宜調整して決定すればよい。 Next, in the step of adding a reducing agent to the resulting mixed liquid, the reducing agent is capable of reducing the catalyst compound and has an appropriate reduction rate, and is not particularly limited. Examples of the reducing agent include sodium thiosulfate, citric acid, sodium citrate, L-ascorbic acid, sodium borohydride, hydrazine, formaldehyde, methanol, ethanol, hydrogen, ethylene, carbon monoxide and the like. The amount of the reducing agent added to the catalyst solution is not particularly limited, and may be determined as appropriate.
前記混合液に還元剤を添加した後は、還流反応装置などを用いて３０〜１００℃に加熱して、白金などの触媒粒子の還元担持を行えばよい。その後、必要に応じて室温まで放冷した後、触媒成分が担持されたカーボン含有導電性材料を吸引瀘過などの瀘別手段により濾取および乾燥すればよく、乾燥方法や、濾過方法は公知の方法や、上記の方法と同様でもよい。 After the reducing agent is added to the mixed solution, it may be heated to 30 to 100 ° C. using a reflux reactor or the like to carry out reduction loading of catalyst particles such as platinum. Then, after allowing to cool to room temperature if necessary, the carbon-containing conductive material carrying the catalyst component may be filtered and dried by a separating means such as suction filtration. The drying method and the filtration method are publicly known. This method may be the same as the above method.
たとえば、コロイド吸着法によりカーボン含有導電性材料表面に触媒成分を担持させるには、カーボン含有導電性材料を、触媒コロイド溶液に添加する段階と、前記カーボン含有導電性材料に触媒コロイドを吸着させる段階と、により前記カーボン含有導電性材料に触媒成分を担持させる触媒担持工程を含む方法を用いればよい。 For example, to support the catalyst component on the surface of the carbon-containing conductive material by the colloid adsorption method, a step of adding the carbon-containing conductive material to the catalyst colloid solution and a step of adsorbing the catalyst colloid to the carbon-containing conductive material Thus, a method including a catalyst supporting step of supporting a catalyst component on the carbon-containing conductive material may be used.
本発明に係る液相に用いる溶媒としては水、メタノール、エタノール、プロパノール、イソプロピルアルコールなどのアルコール類や、アセトンなどのケトン類が例示できるが、本用途においては水が最も好適に用いられる。 Examples of the solvent used in the liquid phase according to the present invention include water, alcohols such as methanol, ethanol, propanol, and isopropyl alcohol, and ketones such as acetone. In this application, water is most preferably used.
前記還元剤としては使用する金属塩の種類や金属種、還元条件によって種々の還元剤が適用可能であるが、例えばアルコール類、蟻酸、アルデヒド類などの有機還元剤や水素化ホウ素塩のような無機還元剤や水素、一酸化炭素のような還元ガスなどが適用可能である。その他具体的には、前記還元剤として、分子状水素、黄燐、ヒドラジン、テトラヒドロホウ酸ナトリウム、クエン酸ナトリウム、タンニン酸、亜硫酸水素ナトリウム等が挙げられる。前記還元剤による還元の代わりに、光照射または超音波照射による還元なども可能である。 Various reducing agents can be applied as the reducing agent depending on the type of metal salt used, the metal species, and the reducing conditions. For example, organic reducing agents such as alcohols, formic acid, aldehydes, and borohydride salts. An inorganic reducing agent, hydrogen, a reducing gas such as carbon monoxide, or the like is applicable. Other specific examples of the reducing agent include molecular hydrogen, yellow phosphorus, hydrazine, sodium tetrahydroborate, sodium citrate, tannic acid, sodium bisulfite, and the like. Instead of reduction with the reducing agent, reduction by light irradiation or ultrasonic irradiation is also possible.
また、還元剤により還元する方法のほかに電気化学的に還元する方法も用いることが出来る。すなわち、金属塩を液相に溶解あるいは分散させた状態で金属塩の還元電位以下で電解あるいは荷電触媒成分前駆体を泳動させることにより担体表面に担持させる方法も例示される。 In addition to the method of reducing with a reducing agent, a method of electrochemical reduction can also be used. That is, a method of supporting the carrier surface by electrolysis or migration of the charged catalyst component precursor at a potential lower than the reduction potential of the metal salt in a state where the metal salt is dissolved or dispersed in the liquid phase is also exemplified.
触媒コロイド溶液とは、ナノサイズの触媒成分が溶液中に均一に分散した溶液である。触媒コロイド溶液の調整方法としては公知技術を適宜用いればよいが、例えば、還元されてコロイド粒子となる触媒成分の元素を含む塩（以下、単に「触媒塩」ともいう。）を含む溶液に、還元剤などを添加することにより得られる。 The catalyst colloid solution is a solution in which nano-sized catalyst components are uniformly dispersed in the solution. As a method for preparing the catalyst colloid solution, a known technique may be used as appropriate. For example, in a solution containing a salt containing an element of a catalyst component that is reduced to become colloidal particles (hereinafter also simply referred to as “catalyst salt”) It can be obtained by adding a reducing agent or the like.
なお、触媒塩を含む溶液中の触媒塩の濃度は、特に制限されるべきものではなく、飽和濃度以下であればよい。ただし、低濃度では所望の担持量になるまでに上記段階を繰り返して調製する必要があることから、必要な濃度を適宜決定すればよい。また、触媒塩を含む溶液中に添加するカーボン含有導電性材料の添加量としても、所望する電極触媒が得られるように、適宜決定すればよい。 Note that the concentration of the catalyst salt in the solution containing the catalyst salt is not particularly limited and may be any saturation concentration or less. However, since it is necessary to repeat the above steps until the desired loading is achieved at low concentrations, the necessary concentration may be determined as appropriate. Moreover, what is necessary is just to determine suitably as addition amount of the carbon containing electroconductive material added to the solution containing a catalyst salt so that a desired electrode catalyst may be obtained.
前記触媒コロイド溶液には、前記還元剤の他、コロイド安定化剤などが添加されていてもよい。前記コロイド安定化剤としては、保護コロイド作用を有するものであれば特に限定されないが、その好ましい例として、ポリ（Ｎ−ビニル−２−ピロリドン）、ポリビニルアルコール、Ｎ−ビニル−２−ピロリドンとアクリルアミド又はアクリル酸メチルとの共重合体、ポリ（メチルビニルエーテル）、ゼラチン、カゼインナトリウムおよびアラビアゴム等を挙げることができる。 In addition to the reducing agent, a colloid stabilizer or the like may be added to the catalyst colloid solution. The colloid stabilizer is not particularly limited as long as it has a protective colloid action. Preferred examples thereof include poly (N-vinyl-2-pyrrolidone), polyvinyl alcohol, N-vinyl-2-pyrrolidone and acrylamide. Alternatively, a copolymer with methyl acrylate, poly (methyl vinyl ether), gelatin, sodium caseinate, gum arabic, and the like can be given.
前記触媒成分コロイド溶液にカーボン含有導電性材料を加え、適切な温度およびｐＨを設定することにより、触媒成分をカーボン含有導電性材料表面に吸着担持させることができる。条件は使用する触媒成分種、カーボン含有導電性材料種、溶液種によって変わるが、温度は１０〜４０℃、ｐＨは２〜１０の範囲で適宜調整するのが好ましい。この範囲の温度であれば、高すぎて吸着が促進される心配や、低すぎて溶液の凍結する恐れもなく望ましい範囲となる。また、ｐＨについても前記範囲であれば、触媒成分の担体への吸着も起こりやすく、溶液の触媒成分の分散性低下・凝集などが起こりにくい。 By adding a carbon-containing conductive material to the catalyst component colloid solution and setting an appropriate temperature and pH, the catalyst component can be adsorbed and supported on the surface of the carbon-containing conductive material. The conditions vary depending on the type of catalyst component used, the type of carbon-containing conductive material, and the type of solution, but it is preferable to adjust the temperature appropriately in the range of 10 to 40 ° C. and the pH of 2 to 10. If it is the temperature of this range, it will become a desirable range, without worrying that adsorption | suction is accelerated | stimulated because it is too high, and there is no fear that the solution will freeze. Further, if the pH is within the above range, the catalyst component is likely to be adsorbed on the carrier, and the catalyst component in the solution is less likely to be degraded or aggregated.
また、カーボン含有導電性材料表面に担持される触媒成分の形態としては、特に限定されず、カーボン含有導電性材料表面に触媒成分の水酸化物などの触媒成分前駆体が担持されてもよい。 The form of the catalyst component supported on the surface of the carbon-containing conductive material is not particularly limited, and a catalyst component precursor such as a hydroxide of the catalyst component may be supported on the surface of the carbon-containing conductive material.
触媒塩を含む溶液に添加する還元剤およびコロイド安定化剤などの添加量、ならびに、触媒成分コロイド溶液に添加するカーボン含有導電性材料の添加量などは、所望する電極触媒が得られるように適宜決定すればよい。 The amount of the reducing agent and colloid stabilizer added to the solution containing the catalyst salt and the amount of the carbon-containing conductive material added to the catalyst component colloid solution are appropriately determined so that the desired electrode catalyst can be obtained. Just decide.
このようにして触媒成分の吸着担持を行った後は、触媒コロイド溶液に触媒活性を阻害するような物質が含まれていなければ、ろ過および乾燥工程を経るだけで、本発明の電極触媒を得ることが出来る。乾燥方法としては、上述した含浸法においてした説明と同様にして行えばよい。 After the catalyst component is adsorbed and supported in this manner, if the catalyst colloid solution does not contain a substance that inhibits the catalytic activity, the electrode catalyst of the present invention can be obtained only through the filtration and drying steps. I can do it. The drying method may be performed in the same manner as described in the impregnation method described above.
本発明に係る電極触媒の製造方法は、前記触媒成分をカーボン含有導電性材料に担持した後に熱処理を加える工程（Ａ）の際に、不活性ガス雰囲気下で熱処理する工程（Ｉ）、還元性ガス雰囲気下で熱処理する工程（ＩＩ）、および酸化性ガス雰囲気下で熱処理する工程（ＩＩＩ）からなる群から選択された少なくとも一つの段階を含むことが好ましい。 The method for producing an electrode catalyst according to the present invention comprises a step (I) of heat-treating in an inert gas atmosphere during the step (A) of applying a heat treatment after supporting the catalyst component on a carbon-containing conductive material, a reducing property. It is preferable to include at least one stage selected from the group consisting of the step (II) of heat treatment under a gas atmosphere and the step (III) of heat treatment under an oxidizing gas atmosphere.
上記の種々のカーボン含有導電性材料に触媒成分を担持する方法だけでは触媒成分の粒径と平均粒径との比率を０．３以下にすることが困難であるばかりでなく、実際に高い溶出耐性を得ることが出来ない。不活性ガス中、酸化性ガス中、または還元性ガス中で所定の熱処理を加えることによって平均に対して小さすぎる粒子はシンタリングにより粒子サイズを調節し、かつ高い溶出耐性を得ることが出来る。 Not only is it difficult to reduce the ratio between the particle size of the catalyst component and the average particle size to 0.3 or less by only the method of supporting the catalyst component on the above-mentioned various carbon-containing conductive materials, but it is also practically high elution. I cannot gain resistance. By applying a predetermined heat treatment in an inert gas, an oxidizing gas, or a reducing gas, particles that are too small relative to the average can be adjusted in particle size by sintering, and high elution resistance can be obtained.
本発明に係る不活性ガス雰囲気下で熱処理する工程（Ｉ）および還元性ガス雰囲気下で熱処理する工程（ＩＩ）の温度は、３００〜１２００℃であることが好ましい。
３００℃より熱処理が低いと触媒金属の焼成が進まず、高い溶出耐性実現する触媒金属が得られない。また１２００℃より熱処理が高いと粒子のシンタリングが過剰に進み所望の触媒金属粒径が得られない。なお、本発明に係る不活性ガス雰囲気下で熱処理する工程（Ｉ）および還元性ガス雰囲気下で熱処理する工程（ＩＩ）の温度は、より好ましくは４００〜１０００℃、さらに好ましくは５００〜９００℃である。
It is preferable that the temperature of the process (I) heat-processed in the inert gas atmosphere which concerns on this invention, and the process (II) heat-processed in a reducing gas atmosphere is 300-1200 degreeC.
If the heat treatment is lower than 300 ° C., the catalyst metal does not calcinate and a catalyst metal that realizes high elution resistance cannot be obtained. On the other hand, if the heat treatment is higher than 1200 ° C., the sintering of the particles is excessive and the desired catalyst metal particle size cannot be obtained. In addition, the temperature of the process (I) heat-processed in the inert gas atmosphere which concerns on this invention, and the process (II) heat-processed in a reducing gas atmosphere becomes like this. More preferably, it is 400-1000 degreeC, More preferably, it is 500-900 degreeC. It is.
本発明に係る不活性ガスは、ヘリウム（Ｈｅ）、ネオン（Ｎｅ）、アルゴン（Ａｒ）、クリプトン（Ｋｒ）、キセノン（Ｘｅ）、および窒素（Ｎ２）からなる群から選ばれた１種以上であることが好ましい。 The inert gas according to the present invention is one or more selected from the group consisting of helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), and nitrogen (N 2 ). It is preferable that
本発明に係る還元性ガスの還元性成分が水素であり、水素濃度が１〜１００体積％であり、バランスガスがヘリウム（Ｈｅ）、ネオン（Ｎｅ）、アルゴン（Ａｒ）、クリプトン（Ｋｒ）、キセノン（Ｘｅ）、および窒素（Ｎ２）からなる群から選ばれた１種以上であることが好ましい。 The reducing component of the reducing gas according to the present invention is hydrogen, the hydrogen concentration is 1 to 100% by volume, and the balance gas is helium (He), neon (Ne), argon (Ar), krypton (Kr), One or more selected from the group consisting of xenon (Xe) and nitrogen (N 2 ) are preferred.
本発明に係る酸化性ガス雰囲気下で熱処理する工程（ＩＩＩ）の温度が、５００℃〜１５０℃であることが好ましく、より好ましくは４００℃〜１８０℃、さらに好ましくは３００℃〜２００℃である。 It is preferable that the temperature of the process (III) heat-processed in the oxidizing gas atmosphere which concerns on this invention is 500 to 150 degreeC, More preferably, it is 400 to 180 degreeC, More preferably, it is 300 to 200 degreeC .
酸化性ガス雰囲気下で熱処理する温度が、５００℃以下であれば、担体であるカーボン含有導電性材料の酸化（燃焼）が進行せず、触媒が劣化しにくい。また、１５０℃以上であれば、Ｐｔ溶出耐性が向上する効果が十分得られる。 If the temperature of the heat treatment in an oxidizing gas atmosphere is 500 ° C. or lower, oxidation (combustion) of the carbon-containing conductive material as a carrier does not proceed, and the catalyst is unlikely to deteriorate. Moreover, if it is 150 degreeC or more, the effect which Pt elution tolerance improves is fully acquired.
本発明に係る酸化性ガスの酸化性成分は酸素であり、酸素濃度が０．１〜３０体積％であり、バランスガスがヘリウム（Ｈｅ）、ネオン（Ｎｅ）、アルゴン（Ａｒ）、クリプトン（Ｋｒ）、キセノン（Ｘｅ）、および窒素（Ｎ２）から選ばれた１種以上であることが好ましい。 The oxidizing component of the oxidizing gas according to the present invention is oxygen, the oxygen concentration is 0.1 to 30% by volume, and the balance gas is helium (He), neon (Ne), argon (Ar), krypton (Kr). ), Xenon (Xe), and nitrogen (N 2 ).
第三の発明は、上記の本発明の第二によって製造された電極触媒、および本発明の第一の電極触媒を有する膜−電極接合体である。本明細書における「膜−電極接合体」は、高分子電解質膜の片面にアノード触媒層が配置され、他方の面にカソード触媒層が配置されているものをいう。 3rd invention is the membrane-electrode assembly which has the electrode catalyst manufactured by said 2nd of this invention, and the 1st electrode catalyst of this invention. The “membrane-electrode assembly” in the present specification refers to a polymer electrolyte membrane in which an anode catalyst layer is disposed on one side and a cathode catalyst layer is disposed on the other side.
本発明の膜−電極接合体に用いられる高分子電解質膜としては、特に限定されず、電極触媒層に用いたものと同様の高分子電解質からなる膜が挙げられる。また、デュポン社製の各種のＮａｆｉｏｎ（デュポン社登録商標）やフレミオンに代表されるパーフルオロスルホン酸膜、ダウケミカル社製のイオン交換樹脂、エチレン−四フッ化エチレン共重合体樹脂膜、トリフルオロスチレンをベース高分子とする樹脂膜などのフッ素系高分子電解質や、スルホン酸基を有する炭化水素系樹脂系膜など、一般的に市販されている高分子型電解質膜、高分子微多孔膜に液体電解質を含浸させた膜、多孔質体に高分子電解質を充填させた膜などを用いてもよい。前記高分子電解質膜に用いられる高分子電解質と、各電極触媒層に用いられる高分子電解質とは、同じであっても異なっていてもよいが、各電極触媒層と高分子電解質膜との密着性を向上させる観点から、同じものを用いるのが好ましい。 The polymer electrolyte membrane used for the membrane-electrode assembly of the present invention is not particularly limited, and examples thereof include a membrane made of the same polymer electrolyte as that used for the electrode catalyst layer. In addition, various Nafion (registered trademark of DuPont) manufactured by DuPont and perfluorosulfonic acid membranes represented by Flemion, ion exchange resins manufactured by Dow Chemical, ethylene-tetrafluoroethylene copolymer resin membrane, trifluoro Fluorine polymer electrolytes such as styrene-based polymer membranes, hydrocarbon-based resin membranes with sulfonic acid groups, etc. A membrane impregnated with a liquid electrolyte, a membrane in which a porous body is filled with a polymer electrolyte, or the like may be used. The polymer electrolyte used for the polymer electrolyte membrane and the polymer electrolyte used for each electrode catalyst layer may be the same or different, but the adhesion between each electrode catalyst layer and the polymer electrolyte membrane From the viewpoint of improving the properties, it is preferable to use the same one.
前記高分子電解質膜の厚みとしては、得られる膜電極接合体の特性を考慮して適宜決定すればよいが、好ましくは１０〜７５μｍ、より好ましくは１５〜７０μｍ、特に好ましくは２０〜６０μｍである。製膜時の強度や膜電極接合体作動時の耐久性の観点から１０μｍ以上であることが好ましく、膜電極接合体作動時の出力特性の観点から７５μｍ以下であることが好ましい。 The thickness of the polymer electrolyte membrane may be appropriately determined in consideration of the characteristics of the obtained membrane / electrode assembly, but is preferably 10 to 75 μm, more preferably 15 to 70 μm, and particularly preferably 20 to 60 μm. . The thickness is preferably 10 μm or more from the viewpoint of strength during film formation and durability during operation of the membrane electrode assembly, and is preferably 75 μm or less from the viewpoint of output characteristics during operation of the membrane electrode assembly.
また、上記高分子電解質膜としては、上記したようなフッ素系高分子電解質や、スルホン酸基を有する炭化水素系樹脂による膜に加えて、ポリテトラフルオロエチレン（ＰＴＦＥ）、ポリフッ化ビニリデン（ＰＶＤＦ）などから形成された多孔質状の薄膜に、リン酸やイオン性液体等の電解質成分を含浸したものを使用してもよい。 The polymer electrolyte membrane includes polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF) in addition to the above-described fluorine-based polymer electrolyte and membranes made of hydrocarbon resins having sulfonic acid groups. For example, a porous thin film formed from a material impregnated with an electrolyte component such as phosphoric acid or ionic liquid may be used.
次に、以下、本発明の膜電極接合体の製造方法の好ましい態様を説明して、上記の膜電極接合体を説明する。なお、以下の態様は、本発明の好ましい態様を示したものであり、本発明の膜電極接合体の製造方法が下記方法に限定されるものではない。 Next, a preferred embodiment of the method for producing a membrane electrode assembly of the present invention will be described below, and the above membrane electrode assembly will be described. In addition, the following aspects show the preferable aspect of this invention, and the manufacturing method of the membrane electrode assembly of this invention is not limited to the following method.
本発明の電極触媒は、上記に詳説しているが、例えばカーボンブラックなどの導電性担体に、白金などの触媒成分イオン水溶液に加えて、ホモジナイザなどで分散させた後還元担持させる。次いで、加熱および乾燥さ成分を担持したカーボン含有導電性材料を得た後、不活性ガス、酸性ガス、または還元性ガス雰囲気下で熱処理を行って作製する。その後、導電性担体に触媒成分を担持させた電極触媒、ならびにナフィオンなどのプロトン伝導性高分子を、を必要に応じて水またはアルコールなどの溶剤に添加して、触媒スラリーを調整する。 The electrode catalyst of the present invention has been described in detail above. For example, in addition to an aqueous catalyst component ion solution such as platinum, a conductive carrier such as carbon black is dispersed with a homogenizer and then reduced and supported. Next, after obtaining a carbon-containing conductive material carrying a heated and dried component, heat treatment is performed in an inert gas, acidic gas, or reducing gas atmosphere. Thereafter, an electrode catalyst in which a catalyst component is supported on a conductive carrier and a proton conductive polymer such as Nafion are added to a solvent such as water or alcohol as necessary to prepare a catalyst slurry.
本発明の触媒スラリーを転写用台紙上に塗布・乾燥して、電極触媒層を形成する。この際、転写用台紙としては、ＰＴＦＥ（ポリテトラフルオロエチレン）シート、ＰＥＴ（ポリエチレンテレフタレート）シート、ポリエステルシートなどの公知のシートが使用できる。なお、転写用台紙は、使用する触媒スラリー（特にインク中のカーボン等の導電性担体）の種類に応じて適宜選択される。また、上記工程において、電極触媒層の厚みは、水素の酸化反応（アノード側）及び酸素の還元反応（カソード側）の触媒作用が十分発揮できる厚みであれば特に制限されず、従来と同様の厚みが使用できる。具体的には、電極触媒層の厚みは、１〜５０μｍ、より好ましくは５〜２０μｍである。 The catalyst slurry of the present invention is applied to a transfer mount and dried to form an electrode catalyst layer. In this case, as the transfer mount, a known sheet such as a PTFE (polytetrafluoroethylene) sheet, a PET (polyethylene terephthalate) sheet, or a polyester sheet can be used. The transfer mount is appropriately selected according to the type of catalyst slurry used (particularly, a conductive carrier such as carbon in ink). In the above process, the thickness of the electrode catalyst layer is not particularly limited as long as it can sufficiently exhibit the catalytic action of the hydrogen oxidation reaction (anode side) and the oxygen reduction reaction (cathode side). Thickness can be used. Specifically, the thickness of the electrode catalyst layer is 1 to 50 μm, more preferably 5 to 20 μm.
転写用台紙上への触媒スラリーは、特に制限されず、スクリーン印刷法、沈積法、あるいはスプレー法などの公知の方法が同様にして適用できる。また、塗布された電極触媒層乾燥条件もまた、電極触媒層から極性溶剤を完全に除去できる条件であれば特に制限されない。具体的には、触媒スラリーの塗布層（電極触媒層）を真空乾燥機内にて、室温〜１００℃、より好ましくは５０〜８０℃で、３０〜６０分間、乾燥する。この際、触媒層の厚みが十分でない場合には、所望の厚みになるまで、上記塗布・乾燥工程を繰り返す。次に下記の工程に進む。 The catalyst slurry on the transfer mount is not particularly limited, and a known method such as a screen printing method, a deposition method, or a spray method can be similarly applied. The applied electrode catalyst layer drying conditions are not particularly limited as long as the polar solvent can be completely removed from the electrode catalyst layer. Specifically, the coating layer (electrode catalyst layer) of the catalyst slurry is dried at room temperature to 100 ° C., more preferably 50 to 80 ° C. for 30 to 60 minutes in a vacuum dryer. At this time, if the thickness of the catalyst layer is not sufficient, the coating and drying process is repeated until a desired thickness is obtained. Next, the process proceeds to the following steps.
すなわち、このようにして作製された固体高分子電解質膜を挟持した後、当該積層についてホットプレスを行なう。この際、ホットプレス条件は、電極触媒層及び固体高分子電解質膜が十分密接に接合できる条件であれば特に制限されないが、１１０〜１５０℃、より好ましくは１２０〜１４０℃で、電極面に対して１〜５ＭＰａのプレス圧力で行なうのが好ましい。これにより固体高分子電解質膜および電極触媒層との接合性を高めることができる。 That is, after sandwiching the solid polymer electrolyte membrane thus produced, hot pressing is performed on the laminate. At this time, the hot press conditions are not particularly limited as long as the electrode catalyst layer and the solid polymer electrolyte membrane can be joined sufficiently closely, but are 110 to 150 ° C., more preferably 120 to 140 ° C., with respect to the electrode surface. The press pressure is preferably 1 to 5 MPa. Thereby, bondability with a solid polymer electrolyte membrane and an electrode catalyst layer can be improved.
ホットプレスを行なった後、転写用台紙を剥がすことにより、電極触媒層および固体高分子電解質膜を含む膜−電極接合体を得ることができる。 After hot pressing, the transfer mount is peeled off to obtain a membrane-electrode assembly including the electrode catalyst layer and the solid polymer electrolyte membrane.
以下に説明するが、本発明に係る膜−電極接合体を用いた燃料電池の作成方法については、膜−電極接合体の両側に一対のガス拡散層を設ける必要がある。このガス拡散層の作製は、必要に応じてカーボンペーパまたはカーボン不織布またはカーボンクロスを、ポリテトラフルオロエチレン（ＰＴＦＥ）などのフッ素系樹脂を含む溶液中含浸させ、大気中または窒素などの不活性ガス中に乾燥させた後、ガス拡散層作製する。 As will be described below, in the method for producing a fuel cell using the membrane-electrode assembly according to the present invention, it is necessary to provide a pair of gas diffusion layers on both sides of the membrane-electrode assembly. This gas diffusion layer is produced by impregnating carbon paper, carbon non-woven fabric or carbon cloth in a solution containing a fluorine-based resin such as polytetrafluoroethylene (PTFE) as necessary, and in the atmosphere or an inert gas such as nitrogen. After drying inside, a gas diffusion layer is prepared.
そして、上記に作製したガス拡散層２枚を用いて電極触媒層および固体高分子電解質膜を含む電極を挟持することにより膜電極接合体を作製する。 Then, the membrane electrode assembly is produced by sandwiching the electrode including the electrode catalyst layer and the solid polymer electrolyte membrane using the two gas diffusion layers produced above.
本発明の触媒スラリーにおいて、電極触媒は、所望の作用、即ち、水素の酸化反応（アノード側）及び酸素の還元反応（カソード側）を触媒する作用を十分発揮できる量であればいずれの量で、使用されてもよい。電極触媒が、触媒スラリー中、５〜７５質量％、より好ましくは１０〜６０質量％となるような量で存在することが好ましい。 In the catalyst slurry of the present invention, the electrode catalyst may be used in any amount as long as it can sufficiently exhibit the desired action, that is, the action of catalyzing the hydrogen oxidation reaction (anode side) and the oxygen reduction reaction (cathode side). , May be used. It is preferable that the electrode catalyst is present in the catalyst slurry in an amount of 5 to 75% by mass, more preferably 10 to 60% by mass.
本発明の触媒スラリーには、電極触媒、イオン伝導性高分子、及び溶剤に加えて、必要があればポリテトラフルオロエチレン、ポリヘキサフルオロプロピレン、テトラフルオロエチレン−ヘキサフルオロプロピレン共重合体といった撥水性高分子、増粘剤などが含まれてもよい。これにより、得られる電極触媒層の撥水性を高めることができ、発電時に生成した水などを速やかに排出することができる。 The catalyst slurry of the present invention includes a water repellency such as polytetrafluoroethylene, polyhexafluoropropylene, and tetrafluoroethylene-hexafluoropropylene copolymer, if necessary, in addition to the electrode catalyst, the ion conductive polymer, and the solvent. Polymers, thickeners and the like may be included. Thereby, the water repellency of the obtained electrode catalyst layer can be increased, and water generated at the time of power generation can be quickly discharged.
本発明に係る電極触媒層におけるイオン導電性高分子は、特に限定されず公知のものを用いることができるが、高分子電解質膜に用いられたものと同様の材料が挙げられ、少なくとも高いプロトン伝導性を有する材料であればよい。本発明のカソード触媒（層）／アノード触媒（層）（以下、単に「触媒（層）」とも称する）には、電極触媒の他に、高分子電解質が含まれる。この際使用できる高分子電解質は、高分子骨格の全部又は一部にフッ素原子を含むフッ素系電解質と、高分子骨格にフッ素原子を含まない炭化水素系電解質とに大別される。 The ion conductive polymer in the electrode catalyst layer according to the present invention is not particularly limited, and a known one can be used. Examples thereof include the same materials as those used for the polymer electrolyte membrane, and at least high proton conductivity. Any material can be used. The cathode catalyst (layer) / anode catalyst (layer) (hereinafter, also simply referred to as “catalyst (layer)”) of the present invention includes a polymer electrolyte in addition to the electrode catalyst. The polymer electrolyte that can be used in this case is roughly classified into a fluorine-based electrolyte containing fluorine atoms in the whole or a part of the polymer skeleton and a hydrocarbon-based electrolyte not containing fluorine atoms in the polymer skeleton.
前記フッ素系電解質として、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）等のパーフルオロカーボンスルホン酸系高分子、ポリトリフルオロスチレンスルフォン酸系高分子、パーフルオロカーボンホスホン酸系高分子、トリフルオロスチレンスルホン酸系高分子、エチレンテトラフルオロエチレン−ｇ−スチレンスルホン酸系高分子、エチレン−テトラフルオロエチレン共重合体、ポリビニリデンフルオリド−パーフルオロカーボンスルホン酸系高分子などが好適な一例として挙げられる。 Specific examples of the fluorine electrolyte include perfluorocarbon sulfonic acids such as Nafion (registered trademark, manufactured by DuPont), Aciplex (registered trademark, manufactured by Asahi Kasei Co., Ltd.), and Flemion (registered trademark, manufactured by Asahi Glass Co., Ltd.). Polymer, polytrifluorostyrene sulfonic acid polymer, perfluorocarbon phosphonic acid polymer, trifluorostyrene sulfonic acid polymer, ethylene tetrafluoroethylene-g-styrene sulfonic acid polymer, ethylene-tetrafluoroethylene Preferred examples include polymers and polyvinylidene fluoride-perfluorocarbon sulfonic acid polymers.
前記炭化水素系電解質として、具体的には、ポリスルホンスルホン酸、ポリアリールエーテルケトンスルホン酸、ポリベンズイミダゾールアルキルスルホン酸、ポリベンズイミダゾールアルキルホスホン酸、ポリスチレンスルホン酸、ポリエーテルエーテルケトンスルホン酸、ポリフェニルスルホン酸等が好適な一例として挙げられる。 Specific examples of the hydrocarbon electrolyte include polysulfone sulfonic acid, polyaryl ether ketone sulfonic acid, polybenzimidazole alkyl sulfonic acid, polybenzimidazole alkyl phosphonic acid, polystyrene sulfonic acid, polyether ether ketone sulfonic acid, polyphenyl. A suitable example is sulfonic acid.
高分子電解質は、耐熱性、化学的安定性などに優れることから、フッ素原子を含むのが好ましく、なかでも、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）などのフッ素系電解質が好ましく挙げられる。 The polymer electrolyte preferably contains a fluorine atom because of its excellent heat resistance and chemical stability. Among them, Nafion (registered trademark, manufactured by DuPont), Aciplex (registered trademark, manufactured by Asahi Kasei Co., Ltd.) Fluorine electrolytes such as Flemion (registered trademark, manufactured by Asahi Glass Co., Ltd.) are preferred.
また、カーボン含有導電性材料への触媒成分の担持は公知の方法で行うことができる。以下の（電極触媒の製造方法）の欄でも説明するが、例えば、含浸法、液相還元担持法、蒸発乾固法、コロイド吸着法、噴霧熱分解法、逆ミセル（マイクロエマルジョン法）などの公知の方法が使用できる。 The catalyst component can be supported on the carbon-containing conductive material by a known method. As will be described in the following (Electrocatalyst production method) column, for example, impregnation method, liquid phase reduction support method, evaporation to dryness method, colloid adsorption method, spray pyrolysis method, reverse micelle (microemulsion method), etc. Known methods can be used.
尚、本発明に係る電極を膜−電極接合体（ＭＥＡ）として用いる場合において、高分子電解質膜と電極層とで用いる高分子電解質は、異なってもよいが、膜と電極の接触抵抗などを考慮すると同じものを用いるのが好ましい。また、本発明に係る電極触媒を膜−電極接合体（ＭＥＡ）として用いる場合の電極触媒層の厚さは、好ましくは１〜５０μｍ、より好ましくは５〜２０μｍ程度とするのがよい。 In the case where the electrode according to the present invention is used as a membrane-electrode assembly (MEA), the polymer electrolyte used in the polymer electrolyte membrane and the electrode layer may be different, but the contact resistance between the membrane and the electrode, etc. In consideration, it is preferable to use the same one. In addition, when the electrode catalyst according to the present invention is used as a membrane-electrode assembly (MEA), the thickness of the electrode catalyst layer is preferably 1 to 50 μm, more preferably about 5 to 20 μm.
前記高分子電解質は、接着の役割をする高分子として電極触媒を被覆しているのが好ましい。これにより、電極の構造を安定に維持できるとともに、電極反応が進行する三相界面を十分に確保して、高い触媒活性を得ることができる。電極中に含まれる前記イオン導電性高分子の含有量は、特に限定されないが、触媒成分の全量に対して２０〜６０質量％とするのがよい。 The polymer electrolyte is preferably coated with an electrode catalyst as a polymer that functions as an adhesive. Thereby, while being able to maintain the structure of an electrode stably, the sufficient three-phase interface where an electrode reaction advances can be ensured, and high catalyst activity can be obtained. Although content of the said ion conductive polymer contained in an electrode is not specifically limited, It is good to set it as 20-60 mass% with respect to the whole quantity of a catalyst component.
増粘剤の使用は、触媒スラリーなどが転写用台紙上にうまく塗布できない場合などに有効である。この際使用できる増粘剤は、特に制限されず、公知の増粘剤が使用できるが、例えば、グリセリン、（ＥＧ（エチレングリコール）、ＰＶＡ（ポリビニルアルコール））などが挙げられる。増粘剤を使用する際の、増粘剤の添加量は、本発明の上記効果を妨げない程度の量であれば特に制限されないが、触媒スラリーの全質量に対して、好ましくは０〜１０質量％である。さらに、本発明で使用される触媒スラリーを構成する溶剤としては、特に制限されず、触媒層を形成するのに使用される通常の溶剤が同様にして使用できる。具体的には、水、シクロヘキサノールやエタノールや２−プロパノール等の低級アルコールが使用できる。 The use of a thickener is effective when the catalyst slurry or the like cannot be successfully applied onto the transfer mount. The thickener that can be used in this case is not particularly limited, and a known thickener can be used. Examples thereof include glycerin, (EG (ethylene glycol), PVA (polyvinyl alcohol)), and the like. The amount of the thickener added when using the thickener is not particularly limited as long as it does not interfere with the above effect of the present invention, but is preferably 0 to 10 with respect to the total mass of the catalyst slurry. % By mass. Furthermore, the solvent constituting the catalyst slurry used in the present invention is not particularly limited, and ordinary solvents used for forming the catalyst layer can be used in the same manner. Specifically, water, lower alcohols such as cyclohexanol, ethanol and 2-propanol can be used.
本発明で使用される溶剤の量は、電解質を完全に溶解できる量であれば特に制限されないが、電解質が、溶剤中、好ましくは０．１〜２０質量％、より好ましくは０．５〜１０質量％の濃度になるような量である。この際、電解質の濃度が２０質量％以下であれば、電解質を完全には溶解し、コロイドが形成される可能性が低い。また、０．１質量％以上であると、含まれる電界質量が適量であるため、電解質高分子の分子鎖がよく絡まりあう。このため、形成される電極触媒層の機械的強度が優れる。また、触媒スラリーにおいて、電極触媒および固体高分子電解質などを合わせた固形分の濃度は、触媒スラリー中、５〜５０質量％、より好ましくは１０〜４０質量％程度とするのがよい。 The amount of the solvent used in the present invention is not particularly limited as long as the electrolyte can be completely dissolved, but the electrolyte is preferably 0.1 to 20% by mass, more preferably 0.5 to 10% in the solvent. The amount is such that the concentration becomes mass%. At this time, if the concentration of the electrolyte is 20% by mass or less, it is unlikely that the electrolyte is completely dissolved and colloid is formed. Moreover, since the electric field mass contained in it being 0.1 mass% or more is an appropriate amount, the molecular chains of the electrolyte polymer are entangled well. For this reason, the mechanical strength of the electrode catalyst layer formed is excellent. Moreover, in the catalyst slurry, the concentration of the solid content including the electrode catalyst and the solid polymer electrolyte is preferably 5 to 50% by mass, more preferably about 10 to 40% by mass in the catalyst slurry.
本発明の触媒スラリーは、カソード側電極触媒層またはアノード側電極触媒層のいずれか一方のみに使用されてもあるいは双方に使用されてもよいが、カソード側は特に出力変動による生成水量の変化により乾湿の変化を受けて、初期状態における電極触媒層の多孔構造が崩れ、空隙率が低下して、電極触媒層への反応ガス供給量が低下する危険性が高いため、少なくともアノード側電極触媒層に使用されることが好ましい。 The catalyst slurry of the present invention may be used for only one or both of the cathode side electrode catalyst layer and the anode side electrode catalyst layer, but the cathode side is particularly affected by changes in the amount of water produced due to output fluctuations. At least the anode-side electrode catalyst layer because there is a high risk that the porous structure of the electrode catalyst layer in the initial state collapses due to changes in dryness and moisture, the porosity decreases, and the amount of reaction gas supplied to the electrode catalyst layer decreases. It is preferable to be used for.
第４の発明は、第３の発明の膜電極接合体を用いたことを特徴とする燃料電池である。 A fourth invention is a fuel cell using the membrane electrode assembly of the third invention.
本発明に係る膜電極接合体を、用いた前記燃料電池は、下記に詳述されるように、一般的にガス拡散層をさらに有しており、この際、ガス拡散層は、上記方法において、転写用台紙を剥がし、得られた接合体をさらにガス拡散層で挟持することによって、電極触媒層と固体高分子電解質膜との接合後にさらに各電極触媒層に接合することが好ましい。または、電極触媒層を予めガス拡散層表面上に形成して電極触媒層−ガス拡散層接合体を製造した後、上記したのと同様にして、この電極触媒層−ガス拡散層接合体で固体高分子電解質膜をホットプレスにより挟持・接合することもまた好ましい。
前記のホットプレス方法以外に、ガス拡散層上に逐次塗布により電極触媒層−高分子電解質膜−電極触媒層−ガス拡散層を積層する方法を用いても良い。
The fuel cell using the membrane electrode assembly according to the present invention generally further has a gas diffusion layer as described in detail below. At this time, the gas diffusion layer is It is preferable that the transfer mount is peeled off, and the obtained joined body is further sandwiched between gas diffusion layers so that the electrode catalyst layer and the solid polymer electrolyte membrane are further joined to each electrode catalyst layer. Alternatively, after an electrode catalyst layer is formed on the surface of the gas diffusion layer in advance to produce an electrode catalyst layer-gas diffusion layer assembly, the electrode catalyst layer-gas diffusion layer assembly is solid as described above. It is also preferable to sandwich and bond the polymer electrolyte membrane by hot pressing.
In addition to the hot pressing method, a method of laminating an electrode catalyst layer, a polymer electrolyte membrane, an electrode catalyst layer, and a gas diffusion layer on the gas diffusion layer by sequential coating may be used.
本発明に係るガス拡散層（以下ＧＤＬと称する）に用いられる材料としては、カーボンペーパー、不織布、炭素製の織物、紙状抄紙体、フェルトなどからなるシート状材料が提案されている。ＧＤＬが優れた電子伝導性を有していると、発電反応により生じた電子の効率的な運搬が達成され、燃料電池の性能が向上する。またＧＤＬが優れた撥水性を有していると、生成した水が効率的に排出される。 As a material used for the gas diffusion layer (hereinafter referred to as GDL) according to the present invention, a sheet-like material made of carbon paper, non-woven fabric, carbon woven fabric, paper-like paper body, felt or the like has been proposed. When GDL has excellent electron conductivity, efficient transport of electrons generated by a power generation reaction is achieved, and the performance of the fuel cell is improved. Further, if the GDL has an excellent water repellency, the generated water is efficiently discharged.
高い撥水性を確保するために、ＧＤＬを構成する材料を撥水処理する技術も提案されている。例えば、ポリテトラフルオロエチレン（ＰＴＦＥ）などのフッ素系樹脂を含む溶液中にカーボンペーパーなどのＧＤＬを構成する材料を含浸させ、大気中または窒素などの不活性ガス中に乾燥させる。場合によっては、親水化処理がＧＤＬを構成する材料に施されてもよい。 In order to ensure high water repellency, a technique for water repellency treatment of a material constituting the GDL has also been proposed. For example, a solution containing a fluorine-based resin such as polytetrafluoroethylene (PTFE) is impregnated with a material constituting GDL such as carbon paper, and dried in the air or an inert gas such as nitrogen. Depending on the case, the hydrophilization treatment may be performed on the material constituting the GDL.
その他に、カーボンペーパー、不織布、炭素製の織物、紙状抄紙体、フェルトなどからなるシート状ＧＤＬ上に、カーボン粒子およびバインダーを配置して、両者をガス拡散層として使用してもよく、カーボン粒子およびバインダーからなるフィルム自体をガス拡散層として使用してもよい。この結果、フィルム自体に均一に撥水材料、カーボン粒子が形成されているため、上記の塗布に比較して撥水効率の上昇がみられる。 In addition, carbon particles and a binder may be disposed on a sheet-like GDL made of carbon paper, nonwoven fabric, carbon fabric, paper-like paper body, felt, etc., and both may be used as a gas diffusion layer. You may use the film itself which consists of particle | grains and a binder as a gas diffusion layer. As a result, since the water repellent material and the carbon particles are uniformly formed on the film itself, the water repellent efficiency is increased as compared with the above application.
前記撥水材料としては、ポリテトラフルオロエチレン（ＰＴＦＥ）、ポリフッ化ビニリデン（ＰＶＤＦ）、ポリヘキサフルオロプロピレン、テトラフルオロエチレン−ヘキサフルオロプロピレン共重合体（ＦＥＰ）などのフッ素系樹脂、ポリプロピレン、ポリエチレンなどが挙げられる。なかでも、撥水性、電極反応時の耐食性などに優れることから、フッ素系樹脂が好ましい。
尚、「バインダー」とは接着の役割を有する物質をいい、本発明に係る実施例では、バインダーの役割および撥水性の役割を兼ね備えたフッ素系樹脂を使用しているが、必ずしもこれに限定されず、バインダーおよび撥水材料を個々独立した物質で混合して使用しても良い。
Examples of the water repellent material include fluorine resins such as polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyhexafluoropropylene, and tetrafluoroethylene-hexafluoropropylene copolymer (FEP), polypropylene, polyethylene, and the like. Is mentioned. Of these, fluororesins are preferred because they are excellent in water repellency and corrosion resistance during electrode reaction.
Incidentally, the “binder” refers to a substance having a role of adhesion, and in the examples according to the present invention, a fluororesin having both a role of a binder and a role of water repellency is used, but it is not necessarily limited thereto. Alternatively, the binder and the water repellent material may be mixed and used as independent substances.
本発明に係るアノード側電極触媒層およびカソード側電極触媒層は、触媒成分、イオン伝導性高分子、撥水材料を含む。 The anode side electrode catalyst layer and the cathode side electrode catalyst layer according to the present invention include a catalyst component, an ion conductive polymer, and a water repellent material.
前記電極触媒層の空孔率は、３０〜７０％が好ましく、より好ましくは３５〜５０％である。空孔率が３０％以上であれば、ガスの拡散が良くなり、高電流域でのセル電圧が低下しない。また、空孔率が７０％以下であれば、電極触媒層の強度が高くなり、転写プロセスで空孔率が低下しにくい。 The porosity of the electrode catalyst layer is preferably 30 to 70%, more preferably 35 to 50%. If the porosity is 30% or more, gas diffusion is improved, and the cell voltage in the high current region does not decrease. In addition, when the porosity is 70% or less, the strength of the electrode catalyst layer is increased, and the porosity is not easily lowered in the transfer process.
前記燃料電池の種類としては、特に限定されず、上記した説明中では高分子電解質型燃料電池を例に挙げて説明したが、この他にも、アルカリ型燃料電池、リン酸型燃料電池に代表される酸型電解質の燃料電池、ダイレクトメタノール型燃料電池、マイクロ燃料電池などが挙げられる。なかでも小型かつ高密度・高出力化が可能であるから、固体高分子電解質型燃料電池が好ましく挙げられる。また、前記燃料電池は、搭載スペースが限定される車両などの移動体用電源の他、定置用電源などとして有用であるが、特にシステムの起動／停止や出力変動が頻繁に発生する自動車用途で特に好適に使用できる。 The type of the fuel cell is not particularly limited. In the above description, the polymer electrolyte fuel cell has been described as an example, but in addition to this, a representative example is an alkaline fuel cell and a phosphoric acid fuel cell. Examples thereof include an acid electrolyte fuel cell, a direct methanol fuel cell, and a micro fuel cell. Among them, a solid polymer electrolyte fuel cell is preferable because it is small in size and can achieve high density and high output. The fuel cell is useful as a stationary power source in addition to a power source for a moving body such as a vehicle in which a mounting space is limited. However, the fuel cell is particularly useful for an automobile application in which system start / stop and output fluctuation frequently occur. It can be particularly preferably used.
前記高分子電解質型燃料電池は、定置用電源の他、搭載スペースが限定される自動車などの移動体用電源などとして有用である。なかでも、比較的長時間の運転停止後に高い出力電圧が要求されることによるカーボン担体の腐食、および、運転時に高い出力電圧が取り出されることにより高分子電解質の劣化が生じやすい自動車などの移動体用電源として用いられるのが特に好ましい。 The polymer electrolyte fuel cell is useful not only as a stationary power source but also as a power source for a moving body such as an automobile having a limited mounting space. In particular, moving bodies such as automobiles that are susceptible to corrosion of the carbon support due to the high output voltage required after a relatively long shutdown, and deterioration of the polymer electrolyte due to the high output voltage being taken out during operation. It is particularly preferred to be used as a power source.
前記燃料電池の構成としては、特に限定されず、従来公知の技術を適宜利用すればよいが、一般的には膜電極接合体をセパレータで挟持した構造を有する。 The configuration of the fuel cell is not particularly limited, and a conventionally known technique may be appropriately used. Generally, the fuel cell has a structure in which a membrane electrode assembly is sandwiched between separators.
前記セパレータとしては、緻密カーボングラファイト、炭素板等のカーボン製や、ステンレス等の金属製のものなど、従来公知のものであれば制限なく用いることができる。セパレータは、空気と燃料ガスとを分離する機能を有するものであり、それらの流路を確保するための流路溝が形成されてもよい。セパレータの厚さや大きさ、流路溝の形状などについては、特に限定されず、得られる燃料電池の出力特性などを考慮して適宜決定すればよい。 The separator can be used without limitation as long as it is conventionally known, such as those made of carbon such as dense carbon graphite and a carbon plate, and those made of metal such as stainless steel. The separator has a function of separating air and fuel gas, and a channel groove for securing the channel may be formed. The thickness and size of the separator, the shape of the flow channel, and the like are not particularly limited, and may be appropriately determined in consideration of the output characteristics of the obtained fuel cell.
また、各触媒層に供給されるガスが外部にリークするのを防止するために、ガスケット層上の触媒層が形成されていない部位にさらにガスシール部が設けられてもよい。前記ガスシール部を構成する材料としては、フッ素ゴム、シリコンゴム、エチレンプロピレンゴム（ＥＰＤＭ）、ポリイソブチレンゴム等のゴム材料、ポリテトラフルオロエチレン（ＰＴＦＥ）、ポリフッ化ビニリデン（ＰＶＤＦ）、ポリヘキサフルオロプロピレン、テトラフルオロエチレン−ヘキサフルオロプロピレン共重合体（ＦＥＰ）等のフッ素系の高分子材料、ポリオレフィンやポリエステル等の熱可塑性樹脂などが挙げられる。また、ガスシール部の厚さとしては、２ｍｍ〜５０μｍ、望ましくは１ｍｍ〜１００μｍ程度とすればよい。 Further, in order to prevent the gas supplied to each catalyst layer from leaking to the outside, a gas seal portion may be further provided at a portion where the catalyst layer is not formed on the gasket layer. Examples of the material constituting the gas seal portion include rubber materials such as fluoro rubber, silicon rubber, ethylene propylene rubber (EPDM), polyisobutylene rubber, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyhexafluoro. Fluorine polymer materials such as propylene, tetrafluoroethylene-hexafluoropropylene copolymer (FEP), and thermoplastic resins such as polyolefin and polyester. The thickness of the gas seal portion may be 2 mm to 50 μm, preferably about 1 mm to 100 μm.
さらに、燃料電池が所望する電圧等を得られるように、セパレータを介して膜電極接合体を複数積層して直列に繋いだスタックを形成してもよい。燃料電池の形状などは、特に限定されず、所望する電圧などの電池特性が得られるように適宜決定すればよい。 Furthermore, a stack in which a plurality of membrane electrode assemblies are stacked via a separator and connected in series may be formed so that the fuel cell can obtain a desired voltage or the like. The shape of the fuel cell is not particularly limited, and may be determined as appropriate so that desired battery characteristics such as voltage can be obtained.
以下、本発明を実施例に基づいて具体的に説明する。なお、本発明は、これらの実施例のみに限定されることはない。また、当該実施例において、「％」は特記しない限り質量百分率を表わすものとする。 Hereinafter, the present invention will be specifically described based on examples. In addition, this invention is not limited only to these Examples. In the examples, “%” represents a mass percentage unless otherwise specified.
（電極触媒の作製）
（Ａ）カーボン含有導電性材料の前処理
カーボンブラックの前処理（表面処理工程）は以下のような各種腐食処理と熱処理工程を適宜組み合わせることによって行った。実施例に適用した腐食処理および熱処理工程は以下の通りである。
(Production of electrode catalyst)
(A) Pretreatment of carbon-containing conductive material The pretreatment (surface treatment step) of carbon black was performed by appropriately combining the following various corrosion treatments and heat treatment steps. The corrosion treatment and heat treatment steps applied to the examples are as follows.
表面処理（Ｉ）
４０％硝酸水溶液にカーボンブラックを浸漬し、６０℃に加熱して２４時間撹拌した。加熱撹拌後カーボンを濾取し、濾液のｐＨが５以上になるまで純水で洗浄した。
Surface treatment (I)
Carbon black was immersed in a 40% nitric acid aqueous solution, heated to 60 ° C., and stirred for 24 hours. After heating and stirring, carbon was collected by filtration and washed with pure water until the pH of the filtrate reached 5 or higher.
腐食処理（ＩＩ）
４２％水酸化カリウム水溶液にカーボンブラックを浸漬し、４０℃に加熱して２４時間撹拌した。加熱撹拌後カーボンを濾取し、濾液のｐＨが１０以下になるまで純水で洗浄した。
Corrosion treatment (II)
Carbon black was immersed in a 42% aqueous potassium hydroxide solution, heated to 40 ° C. and stirred for 24 hours. After heating and stirring, carbon was collected by filtration and washed with pure water until the pH of the filtrate was 10 or less.
表面処理（ＩＩＩ）
カーボンブラックを固定床流通式の電気炉内に入れて、流通ガスとして２００ｍｌ／ｍｉｎの高純度アルゴンに０．５ｇ／ｍｉｎの水を加えて炉心手前の加熱部で蒸発させることにより水蒸気含有ガスを用いた。昇温速度は３℃／ｍｉｎ、保持温度９００℃、保持時間２時間とした。
Surface treatment (III)
Carbon black is placed in a fixed-bed flow type electric furnace, 0.5 g / min water is added to 200 ml / min high-purity argon as a flow gas, and evaporated in the heating section in front of the core, thereby changing the steam-containing gas. Using. The heating rate was 3 ° C./min, the holding temperature was 900 ° C., and the holding time was 2 hours.
表面処理（熱処理（Ｉ））
高純度アルゴンガス流通下１８００℃で３０分熱処理を行った。
Surface treatment (heat treatment (I))
Heat treatment was performed at 1800 ° C. for 30 minutes under a flow of high purity argon gas.
表面処理（熱処理（ＩＩ））
高純度アルゴンガス流通下２４００℃で３０分熱処理を行った。
以上の各種腐食処理と熱処理を組み合わせて以下に示すカーボンブラック１〜４を調製した。
Surface treatment (heat treatment (II))
Heat treatment was performed at 2400 ° C. for 30 minutes under a high purity argon gas flow.
Carbon blacks 1 to 4 shown below were prepared by combining the above various corrosion treatments and heat treatments.
カーボンブラック１の表面処理工程
バルカンＸＣ−７２（キャボット社製：比表面積約２５０ｍ２／ｇ）に表面処理（Ｉ）を行った。（表面処理（熱処理（Ｉ）および（ＩＩ）は不実施）
カーボンブラック２の表面処理工程
バルカンＸＣ−７２（キャボット社製：比表面積約２５０ｍ２／ｇ）に表面処理（ＩＩ）を行った後、表面処理（熱処理（Ｉ））を行った。
Surface treatment (I) was performed on the surface treatment step Vulcan XC-72 (manufactured by Cabot Corporation: specific surface area of about 250 m 2 / g) of carbon black 1. (Surface treatment (heat treatment (I) and (II) are not implemented))
Surface treatment step of carbon black 2 Vulcan XC-72 (manufactured by Cabot: specific surface area of about 250 m 2 / g) was subjected to surface treatment (II) and then surface treatment (heat treatment (I)).
カーボンブラック３の表面処理工程
バルカンＸＣ−７２（キャボット社製：比表面積約２５０ｍ２／ｇ）腐食処理（ＩＩＩ）を行った後、表面処理（熱処理（ＩＩ））を行った。
Surface treatment process of carbon black 3 Vulcan XC-72 (manufactured by Cabot: specific surface area of about 250 m 2 / g) After performing corrosion treatment (III), surface treatment (heat treatment (II)) was performed.
カーボンブラック４の表面処理工程
ケッチェンブラックＥＣ（ケッチェンブラックインターナショナル社製：比表面積約８００ｍ２／ｇ）に表面処理（Ｉ）を行った後、さらに表面処理（熱処理（ＩＩ））を行った。
（Ｂ）触媒成分のカーボン含有導電性材料への担持
上記（Ａ）で作製したカーボンブラックへの触媒金属成分の担持は以下のような方法を用いて行った。
Surface treatment process of carbon black 4 After surface treatment (I) was performed on ketjen black EC (manufactured by ketjen black international Co., Ltd .: specific surface area of about 800 m 2 / g), surface treatment (heat treatment (II)) was further performed. .
(B) Loading of catalyst component on carbon-containing conductive material Loading of the catalyst metal component on the carbon black produced in (A) was performed using the following method.
各カーボンブラック粉末１．０ｇに対して０．４％の白金を含有する塩化白金酸水溶液２５０ｇ中にホモジナイザを用いて十分に分散させた後、これにクエン酸ナトリウム３ｇを加え、還流反応装置を使用して８５℃、６時間加熱し、白金の還元担持を行った。そして、室温まで放冷した後、白金が担持されたカーボンを濾別し、純水で十分に洗浄することにより、Ｐｔ担持カーボン粉末を得た。Ｐｔ−Ｃｏ合金担持カーボンは上記の方法で調製したＰｔ担持カーボンに所定量の硝酸コバルト水溶液を用いてコバルト成分を含浸させ、窒素雰囲気中８００℃で４時間焼成（合金化熱処理）を行うことによって得た。 After thoroughly dispersing in 250 g of chloroplatinic acid aqueous solution containing 0.4% platinum with respect to 1.0 g of each carbon black powder using a homogenizer, 3 g of sodium citrate was added thereto, and the reflux reactor was It was used and heated at 85 ° C. for 6 hours to carry out reduction loading of platinum. And after standing to cool to room temperature, platinum carrying | supported carbon was separated by filtration, and Pt carrying | support carbon powder was obtained by fully wash | cleaning with a pure water. Pt—Co alloy-supported carbon is obtained by impregnating a Pt-supported carbon prepared by the above method with a cobalt component using a predetermined amount of cobalt nitrate aqueous solution and firing (alloying heat treatment) at 800 ° C. for 4 hours in a nitrogen atmosphere. Obtained.
（電極触媒層の作製）
電極触媒層の作製については以下のように行った。
各触媒金属担持炭素材粉末の重量に対して５倍量の精製水を加えた後、０．５倍量のイソプロピルアルコールを加え、さらにはＮａｆｉｏｎの重量が０．８倍量になるようにＮａｆｉｏｎ溶液（Ａｌｄｒｉｃｈ社製５ｗｔ．％Ｎａｆｉｏｎ含有）を加えた。混合スラリーを超音波ホモジナイザでよく分散させ、それに続いて減圧脱泡操作を加えることによって触媒インクを作製した。これをガス拡散層（ＧＤＬ）であるカーボンペーパー（東レ製ＴＧＰ−Ｈ−０６０）の片面にスクリーン印刷法によって所定量の触媒インクを印刷し、６０℃で２４時間乾燥させることにより電極層を作製した。
(Production of electrode catalyst layer)
The production of the electrode catalyst layer was performed as follows.
After adding 5 times the amount of purified water to the weight of each catalyst metal-supported carbon material powder, 0.5 times the amount of isopropyl alcohol is added, and further, the Nafion is 0.8 times the weight of Nafion. A solution (containing 5 wt.% Nafion manufactured by Aldrich) was added. The mixed slurry was well dispersed with an ultrasonic homogenizer, followed by addition of a vacuum degassing operation to prepare a catalyst ink. A predetermined amount of catalyst ink is printed on one side of carbon paper (TGP-H-060 manufactured by Toray Industries, Inc.), which is a gas diffusion layer (GDL), and dried at 60 ° C. for 24 hours to produce an electrode layer. did.
（ＭＥＡの作製）
ＭＥＡ（膜―電極接合体）の作製については触媒を塗布した面を電解質膜に合わせて１２０℃、１．２ＭＰａで１０分間ホットプレスを行うことによりＭＥＡを作製した。すべてについてアノード触媒としては比較例１触媒を用いた。
比較例、実施例ともに使用したＭＥＡはＰｔ使用量を見かけの電極面積１ｃｍ２あたりアノードでは０．３ｍｇ、カソードでは０．５ｍｇとし、電極面積は２５ｃｍ２とした。また、電解質膜としてＮａｆｉｏｎ１１２（厚さ：約５０μｍ）を用いた。
(Production of MEA)
For the production of MEA (membrane-electrode assembly), MEA was produced by performing hot pressing at 120 ° C. and 1.2 MPa for 10 minutes with the surface coated with the catalyst aligned with the electrolyte membrane. In all cases, the catalyst of Comparative Example 1 was used as the anode catalyst.
The MEA used in both the comparative example and the example was 0.3 mg for the anode and 0.5 mg for the cathode per 1 cm 2 of the apparent electrode area, and the electrode area was 25 cm 2 . In addition, Nafion 112 (thickness: about 50 μm) was used as the electrolyte membrane.
（単セル評価）
作製したＭＥＡを用いて燃料電池単セルを構成し、発電負荷変動を模擬した電位サイクル印加試験を以下のような方法で行った。
燃料電池単セルのアノード側には水素を供給し、カソード側には窒素を供給した。両ガスとも供給圧力は大気圧とし、燃料電池本体の温度は７０℃に設定し、ガスはいずれも露点７０℃に加湿して水素流量は５００ ｍｌ／ｍｉｎ、窒素流量は１００ ｍｌ／ｍｉｎとした。この状態でカソードの電位を電位範囲０．９５Ｖから０．６０Ｖの矩形波を１サイクル１０秒の間隔で印加し、５０００サイクル印加前後のＰｔの電気化学的有効表面積（ＥＣＡ）を比較した。電位サイクル印加によりＰｔの溶出と再析出が繰り返し起こることにより印加電位サイクル数が増えるほどＰｔ平均粒径が増大する。このことから、ＰｔのＥＣＡ減少率が大きいものほどＰｔ溶出耐性が低く、電極性能の劣化速度が速いと言える。カソードのＥＣＡの測定はサイクリックボルタンメトリにより水素吸着波面積から見積もった。
(Single cell evaluation)
A fuel cell single cell was constructed using the produced MEA, and a potential cycle application test simulating power generation load fluctuation was performed by the following method.
Hydrogen was supplied to the anode side of the single fuel cell and nitrogen was supplied to the cathode side. The supply pressure for both gases was atmospheric pressure, the temperature of the fuel cell body was set to 70 ° C., and both gases were humidified to a dew point of 70 ° C., the hydrogen flow rate was 500 ml / min, and the nitrogen flow rate was 100 ml / min. . In this state, a rectangular wave with a potential range of 0.95 V to 0.60 V was applied at intervals of 10 seconds per cycle, and the electrochemical effective surface area (ECA) of Pt before and after 5000 cycles was compared. The Pt average particle size increases as the number of applied potential cycles increases due to repeated elution and reprecipitation of Pt by applying potential cycles. From this, it can be said that the larger the Pt ECA reduction rate, the lower the resistance to Pt elution and the faster the deterioration rate of the electrode performance. The ECA of the cathode was estimated from the hydrogen adsorption wave area by cyclic voltammetry.
表１は、その結果を示すグラフであって、実施例１および２の担体カーボンはカーボンブラック１、実施例３の担体カーボンはカーボンブラック２、実施例４および６〜９の担体カーボンはカーボンブラック３、実施例５の担体カーボンはカーボンブラック４、比較例１の担体カーボンは表面処理を施していないケッチェンブラックＥＣ、比較例２の担体カーボンは表面処理を施していないバルカンＸＣ−７２を用いている。比較例に比べ、実施例の方がＥＣＡの低下率が大きく実施例触媒を用いた方がＰｔ溶出耐性を著しく改善することが可能であり、電極性能を長く保つことが出来ることがわかった。
さらに表１に上記起動停止試験を行う前と２０００サイクル試験を行った後のサイクリックボルタンメトリにより求めたカソードのＰｔ有効電極面積の比較を示したが、実施例の方が試験後のＰｔ有効電極面積の低下量がかなり小さい事がわかる。これは図１の結果とも一致している。
以上のことから、起動時にカソードのＰｔを完全に還元することにより運転時のＰｔ溶出が抑制されたため、有効触媒表面積の低下を抑制出来たことによるものだと考えられる。
Table 1 is a graph showing the results. The carrier carbon of Examples 1 and 2 is carbon black 1, the carrier carbon of Example 3 is carbon black 2, and the carrier carbons of Examples 4 and 6-9 are carbon black. 3. The carrier carbon of Example 5 is carbon black 4, the carrier carbon of Comparative Example 1 is Ketjen Black EC without surface treatment, and the carrier carbon of Comparative Example 2 is Vulcan XC-72 without surface treatment. ing. Compared with the comparative example, it was found that the example had a larger ECA reduction rate, and that the use of the example catalyst can significantly improve the Pt elution resistance, and the electrode performance can be maintained for a long time.
Further, Table 1 shows a comparison of the cathode Pt effective electrode area obtained by cyclic voltammetry before the start / stop test and after the 2000 cycle test. It can be seen that the amount of decrease in the effective electrode area is considerably small. This is consistent with the result of FIG.
From the above, it is considered that the decrease in the effective catalyst surface area could be suppressed because the Pt elution during operation was suppressed by completely reducing the Pt of the cathode at the start-up.
Claims (16)
前記触媒成分は少なくともＰｔを含んでおり、かつ前記カーボン含有導電性材料のＮ２−ＢＥＴ比表面積とＣＴＡＢ吸着比表面積の差が１００ｍ２／ｇ以下であることを特徴とする電極触媒。 In an electrode catalyst comprising a catalyst component and a carbon-containing conductive material,
The catalyst component contains at least Pt, and the difference between the N 2 -BET specific surface area and the CTAB adsorption specific surface area of the carbon-containing conductive material is 100 m 2 / g or less.
触媒成分をカーボン含有導電性材料に担持する前に、前記カーボン含有導電性材料に対して表面処理工程を行うことを特徴とする電極触媒の製造方法。 In a method for producing an electrode catalyst comprising a carbon-containing conductive material carrying a catalyst component,
Before carrying | supporting a catalyst component on a carbon containing conductive material, the surface treatment process is performed with respect to the said carbon containing conductive material, The manufacturing method of the electrode catalyst characterized by the above-mentioned.
前記触媒成分をカーボン含有導電性材料に担持した後に熱処理を加える工程（Ａ）の際に、
不活性ガス雰囲気下で熱処理する工程（Ｉ）、
還元性ガス雰囲気下で熱処理する工程（ＩＩ）、および
酸化性ガス雰囲気下で熱処理する工程（ＩＩＩ）からなる群から選択された少なくとも一つの工程を含む、請求項５〜８のいずれか１項に記載の電極触媒の製造方法。 In a method for producing an electrode catalyst comprising a carbon-containing conductive material carrying a catalyst component,
During the step (A) of applying a heat treatment after supporting the catalyst component on the carbon-containing conductive material,
Heat treatment under an inert gas atmosphere (I),
9. The method according to claim 5, comprising at least one step selected from the group consisting of a step (II) of heat-treating in a reducing gas atmosphere and a step (III) of heat-treating in an oxidizing gas atmosphere. A method for producing the electrode catalyst according to 1.
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| JP2006223566A JP2008047472A (en) | 2006-08-18 | 2006-08-18 | Electrode catalyst |
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Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2010102911A (en) * | 2008-10-23 | 2010-05-06 | Toyota Motor Corp | Electrode catalyst for solid polymer fuel cell |
| JP2010150094A (en) * | 2008-12-25 | 2010-07-08 | Okayama Univ | Porous carbon material and method for producing the same, and fuel cell |
| US20120129686A1 (en) * | 2009-08-03 | 2012-05-24 | Basf Se | Catalyst for electrochemical reactions |
| KR101327537B1 (en) * | 2012-01-27 | 2013-11-13 | 한국과학기술연구원 | A process of preparing electrocatalysts for oxygen reduction reaction by using stabilizers |
-
2006
- 2006-08-18 JP JP2006223566A patent/JP2008047472A/en active Pending
Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2010102911A (en) * | 2008-10-23 | 2010-05-06 | Toyota Motor Corp | Electrode catalyst for solid polymer fuel cell |
| JP2010150094A (en) * | 2008-12-25 | 2010-07-08 | Okayama Univ | Porous carbon material and method for producing the same, and fuel cell |
| US20120129686A1 (en) * | 2009-08-03 | 2012-05-24 | Basf Se | Catalyst for electrochemical reactions |
| KR101327537B1 (en) * | 2012-01-27 | 2013-11-13 | 한국과학기술연구원 | A process of preparing electrocatalysts for oxygen reduction reaction by using stabilizers |
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