JP2004169165A

JP2004169165A - Method for producing gas diffusion electrode

Info

Publication number: JP2004169165A
Application number: JP2002339443A
Authority: JP
Inventors: Choichi Furuya; 長一古屋
Original assignee: ASS FOR PROGRESS OF NEW CH; ASSOCIATION FOR PROGRESS OF NEW CHEMISTRY
Current assignee: ASS FOR PROGRESS OF NEW CH; ASSOCIATION FOR PROGRESS OF NEW CHEMISTRY
Priority date: 2002-11-22
Filing date: 2002-11-22
Publication date: 2004-06-17

Abstract

<P>PROBLEM TO BE SOLVED: To provide a production method by which an inexpensive gas diffusion electrode can be produced by shortening a production process. <P>SOLUTION: The method for producing a gas diffusion electrode is characterized in that fluid dispersion for a gas diffusion electrode having a solid content concentration of 30 to 60% and a viscosity of 20 to 100 mPa s is used . At this time, it is preferable that the fluid dispersion for the gas diffusion electrode is applied, impregnated or sprayed so as to be a film shape. After that, moisture is removed, a surfactant is extracted with alcohol, and heating treatment is performed at the melting point of a fluorinated carbon resin or above, so that the gas diffusion electrode is produced. <P>COPYRIGHT: (C)2004,JPO

Description

【０００１】
【発明の属する技術分野】
本発明は、ガス拡散電極の製造方法に関し、特にガス拡散電極用分散液を平板上あるいは基体上に塗布、含浸、あるいはスプレーすることにより膜状とするガス拡散電極の製造方法に関する。
【０００２】
【従来の技術】
ガス拡散電極の製造は以下のような工程で得られる。カーボンブラックを多量の界面活性剤含有水で分散させ、ポリテトラフルオロエチレン（ＰＴＦＥ）デイスパージョンを添加、分散させてガス拡散電極用分散液を得る。この際、分散液は、超音波分散、ジェットミル分散などで平均粒径４００ｎｍ程度に分散させる。
この分散液にアルコールを加えて分散物を凝集させ、濾過、乾燥して粉末状にした後、ソルベントナフサを添加し、粘土状にしてロールでシートを作製する。このシートに含まれる界面活性剤をエタノール等のアルコールで抽出除去した後、ホットプレスすることでガス拡散電極を得ていた。
【０００３】
【発明が解決しようとする課題】
従来のガス拡散電極を製造する工程は上記のように煩雑で、多くの装置を要するうえ、製造時間が長いので、その分製造コストは高いものになる。特に、製膜工程、ホットプレス工程が律速段階となる。安価な電極とするため、これらの工程を除去することが望まれていた。
【０００４】
【課題を解決するための手段】
本発明は、下記（１）〜（３）の手段により上記課題を解決した。
（１）固形分濃度が３０％以上６０％以下、粘度が２０ｍＰａ・ｓ以上１００ｍＰａ・ｓ以下のガス拡散電極用分散液を用いることを特徴とするガス拡散電極の製造方法。
（２）該ガス拡散電極用分散液を塗布、含浸又はスプレーすることで膜状にすることを特徴とする前記（１）記載のガス拡散電極の製造方法。
（３）該膜状にした後、水分を除き、アルコールで界面活性剤を抽出し、フッ素樹脂の融点以上で加熱処理することを特徴とする前記（２）記載のガス拡散電極の製造方法。
【０００５】
【発明の実施の形態】
従来のガス拡散電極用分散液は固形分１０％以下で希薄なため、直接塗布すると多量に含まれる水分の除去過程で大きく収縮し、大きなひび割れが生じ膜状にはならない。ところが、本発明者は、前記課題を解決するため鋭意検討の結果、少なくとも３０％以上６０％以下の固形分を含み、粘度が２０ｍＰａ・ｓ以上１００ｍＰａ・ｓ以下の分散液を使用すれば、その分散液を平板上に塗布、あるいは散布することにより、乾燥後に良好な膜状体が得られ、またカーボンペーパー、カーボンクロス、発泡ニッケル、網等の基体を使用し、それに塗布、含浸等の操作を行った場合でも、その空間に浸透するので、乾燥後も良好な膜状となることを見いだした。
【０００６】
上記分散液は、低粘度であって、カーボンブラックとＰＴＦＥの分散が維持されているので、膜となったときにカーボンブラックとＰＴＦＥの粒子が累積した状態となる。その為、この膜はホットプレスせずとも強度が高く、特に常温でロール、プレスした後、熱処理することで従来のホットプレス品に匹敵する性能が得られることを見いだし本発明が完成した。なお、ホットプレスをすれば一層強度が大きい膜状体が得られる。
【０００７】
本発明において用いられる高濃度、低粘度のカーボンブラック分散液は、単体又は触媒担持カーボンブラック（例えば、金、銀、白金属金属又はこれらの合金、金属酸化物などを担持）とポリオキシエチレン型非イオン性界面活性剤とで構成されている。
【０００８】
分散に用いる界面活性剤は、ポリオキシエチレン型非イオン性界面活性剤が好ましく、該界面活性剤は、種々あるが、そのなかでもトライトン（Ｔｒｉｔｏｎ−Ｘ１００）が好適に用いられる。なお、トライトンは、略号で「ＴＲ」で表すこともある。その他、ニューコール１３１０（日本乳化剤株式会社）、ディスパノールＴＯＣ（日本油脂株式会社）、ナロアクティーＮ−１００（三洋化成工業株式会社）、ニッコールＢＴ−９（日光ケミカルズ株式会社）等のＨＬＢが１３．５近辺のポリオキシエチレン型界面活性剤が好適に用いられる。
【０００９】
界面活性剤の含有量は、徴粒子が良好に分散される濃度であれば１％以下でもいいが、通常１％〜４％の範囲で適宜選択することができる。分散液中の構成微粒子の含有量は材料により分散性の良否によって１〜５％程度である。ＰＴＦＥデイスパージョンに分散剤として８％程度添加されているので、カーボンブラック分散液を濃縮するとほぼ同一濃度のＴＲとなるのが望ましい。カーボンブラックの種類にもよるが２％程度の低濃度界面活性剤分散液はジェットミルでの分散効率も良く、界面活性剤の使用量も少ないので分散液としては望ましい。
【００１０】
前記分散液から水を蒸発するのに用いる容器は熱伝導性がよく、耐食性を有することが望まれる。具体的な材料としてはガラス、ステンレス製が良い。容器の口は、なるべく広口の方が蒸発面積が大きいので望ましい。加熱は水浴が望ましいが、１００℃以上にならなければ直加熱でも良い。分散液は加熱蒸発時に攪拌するのが望ましい。また、蒸発を促すために乾燥気体を液面に流しても良い。さらに、脱泡装置を付けて減圧して蒸発を促進してもよい。蒸発乾燥する場合は静置しておいても良い。
【００１１】
加熱手段としては、例えば分散液を入れたガラス管を恒温槽で加熱するとか、ポリテトラフルオロエチレン加工したホットプレート内に入れて直加熱する手段が好適に用いられる。２０％以上に濃縮されたカーボンブラック分散液は、所定のＰＴＦＥディスパージョンを添加し、混合分散することで高濃度ガス拡散電極用分散液が得られる。また、カーボンブラック分散液乾燥物に水分を加え再液状にすることで高濃度カーボンブラック分散液が得られるので、所定のＰＴＦＥディスパージョンを添加し、混合分散することで高濃度、低粘度のガス拡散電極用分散液が得られる。得られる高濃度ガス拡散電極用分散液の固形分濃度は３０％以上であるが、その上限は実用上からある程度制約があり、６０％程度であり、容易に製造できる点から５０％程度である。また、その分散液の粘度は１００ｍＰａ・ｓ以下であるが、その下限は固形分濃度が３０％以上である関係からそれほど低くすることは難しく、実用上は２０ｍＰａ・ｓ程度である。
【００１２】
また、３〜１５％ＴＲ含む分散液を恒温水槽中で１日程度静置して置くと相分離して濃厚分散液となる。例えば、１０％ＴＲ含有ガス供給層分散液（１０％の固形分を含む）は７０℃で保持すると二層に分離し、１日程度の保持で下部に３８％分散液、上部に１２％ＴＲ溶液となる。これはＴＲ等のポリオキシエチレン型非イオン性界面活性剤の水溶液を加熟していくと水溶性が低下して溶液が白濁する（この温度を曇点という。）現象に基づくものである。非イオン系界面活性剤はその曇点温度以下では水に溶解し、界面活性を示すが、曇点温度以上では親水性基が脱水和し、分子が会合して界面活性を失い、液温がさらに高くなるとフロック状または液状の形で沈殿する。逆に、液温が曇点温度以下に下がると一度不溶性となった界面活性剤の親水性基が水和し、再び水に溶解し、界面活性を回復するという性質をもつ。
【００１３】
しかし、本発明のような高濃度の界面活性剤は低温ではミセルを形成して水中にコロイド状態で分散している。曇点以上になると界面活性剤同士が凝集し、濃厚相は下部に、低濃度相は上部にと２相に分離する。この界面活性剤水溶液中に曇点以下ではカーボンブラック等の微粒子は界面活性剤の作用で分散される。ところが曇点以上になると微粒子の周りに疎水性化した界面活性剤が沈着し疎水化し、比重は液相より大きいので沈降分離する。また、前記現象を利用した分散液の濃縮は分散安定性の高いまま濃縮される。ポリオキシエチレン型非イオン性界面活性剤の中でＨＢＬ＝１２〜１５の範囲のものが望ましく、特にＨＢＬ＝１３．５近辺の値を持つものが望ましい。三洋化成（株）のナロアクティー，Ｎ−１１０、日光ケミカルズのＢＴ−９、第一工業製薬（株）のＮＬ−９０、日本乳化剤（株）のニューコール１３１０、等が良好に使用できる。
【００１４】
以上の様に得られた高濃度分散液は高濃度であるにもかかわらず低粘度である。すなわち、カーボンブラックとＰＴＦＥの微粒子が界面活性剤で保護され分散状態が維持されるので、６ヶ月以上の長期保存でも固形化することはなかった。この分散液は粘度が低く、粒径も小さいので、多孔体のカーボンペーパー、カーボンクロス、５０ＰＰＩ以下の発泡ニッケルに浸透していき容易に充填される。また、分散が良好で個々の徴粒子の相互作用が少なく濃度が高いので、水分除去による収縮が少なく良好な膜になる。
【００１５】
前記分散物を塗布、含浸させたものから水分を除くには界面活性剤の曇点以上で加熱するのが望ましい。界面活性剤を除去する前に１５０℃以上２５０℃以下で加熱すると、アルコール抽出操作中にカーボンブラックの脱着が少ない。アルコール抽出はソックスレー型の抽出器が望ましく、高純度のエタノールに入れ替え、３時問程度、２回行うとほぼ完全に除去出来る。界面活性剤の除去後に１５０℃で乾燥し、３５０℃で１０分間熱処理することでガス拡散電極が得られる。冷間プレス、ロール等は適宣シートの平滑化、緻密化のために必要なら施してもよい。より強度の高い膜状体をを製造するためにはホットプレスをすることができる。
【００１６】
【実施例】
以下、本発明を実施例により具体的に説明するが、本発明はこれらの実施例により何等制限されるものではない。また、全実施例を通じて「％」及び「部」は全て重量表示によるものである。
【００１７】
実施例１
２％トライトン−Ｘ１００水溶液２２００ｇに、疎水性カーボンブラック（Ｎｏ．６、平均粒径５００オングストローム、試作品、電気化学工業社製）２００ｇを添加、攪拌分散した。このカーボンブラック分散液２４００ｇを、ジェットミル（ジーナス社、ノズル径０．２ｍｍ）で１５００ｋｇ／ｃｍ^２の圧力で５回通過させた。その結果、平均粒子径は０．３７ミクロンとなり、２ミクロン以上の大きな粒子がないシャープな分布になった。
【００１８】
この分散液２４００ｇを面積９６０ｃｍ^２深さ６ｃｍのポリテトラフルオロエチレンコートしたホットプレートに移し、約８０℃で攪拌しながら水分を２時問蒸発させたところ固形物濃度３６．１％、界面活性剤濃度７．４％の濃縮カーボンブラック分散液が得られた。この濃縮カーボンブラック分散液にＰＴＦＥディスパージョン（Ｄ−１、濃度６０ｗｔ％）をＰＴＦＥ濃度４０％となるように秤量し、添加、混合、分散させた。固形物４３．５％の濃厚ガス供給層分散液が得られた。粘度は４９．５ｍＰａ・ｓであった。
【００１９】
得られた固形物濃度４３．５％の濃厚ガス供給層分散液の固形分に対して０．６部の銀微粒子（平均粒径０．３ミクロン、三井金属社製）を混合、超音波で分散させた。水平に置いた常温の３０ｃｍ×２０ｃｍの熱板上にアルミニウム箔を引き、この銀入り高濃度分散液を厚さ０．１５ｍｍに塗布して、その塗布物の上にすぐに、厚さ１．８ｍｍ、大きさ１２ｃｍ角、５０ＰＰＩの銀メッキ発泡ニッケル板を載せた。その際、前記塗布物の液は銀メッキ発泡ニッケル板の下面からその内部に含浸する。熱板を加熱して８０℃とし２０分間乾燥した。熱板から下ろし冷却した反応層上の発泡ニッケル板内の空間に４３．５％の濃厚ガス供給層分散液を流し込み発泡ニッケル板からはみ出た余分な分散液をヘラで取り去り、８０℃熱板上に載せ１時間乾燥させた。ＴＲの曇点は６５℃であるから曇点以上にして乾燥するとＰＴＦＥの偏りが少ない。
【００２０】
１５０℃で１時間乾燥後、界面活性剤をソックスレー抽出器でエタノールを用いて３時間除去した。この操作を２回行った。１５０℃で１時間乾燥後、３５０℃で１０分間加熱処理することで厚さ１．６３ｍｍ、１２ｃｍ角のガス拡散電極を得た。この電極を酸素陰極としての性能を向上させるために、８０℃、３２％ＮａＯＨ、３０Ａ／ｄｍ^２で１０分間の水素発生処理を行った。その後、酸素を論理量の１．６倍流し、８０℃、３２％ＮａＯＨ、３０Ａ／ｄｍ^２の条件で電圧は０．８０６Ｖｖｓ．ＲＨＥを示した。この性能は従来の酸素陰極とほぼ同じであった。この電極はその製造においてホットプレスの作業を必要としないために、従来のガス拡散電極の作成方法に比べ、大幅な工程の短縮と時間の節約になった。
【００２１】
実施例２
３．６％トライトン−Ｘ１００水溶液２４００ｇに、疎水性カーボンブラック（Ｎｏ．６、平均粒径５００オングストローム、試作品、電気化学工業社製）２００ｇを添加、攪拌分散した。このカーボンブラック分散液２６００ｇを、ジェットミル（ジーナス社、ノズル径０．２ｍｍ）で１５００ｋｇ／ｃｍ^２の圧力で５回通過させた。その結果、平均粒子径は０．３７ミクロンとなり、２ミクロン以上の大きな粒子がないシャープな分布になった。
この分散液にＰＴＦＥディスパージョン（Ｄ−１、濃度６０ｗｔ％）をＰＴＦＥ濃度４０％となるように秤量し添加、混合、分散させた。固形物１０．２％のガス供給層分散液が得られた。
【００２２】
１リットルのガラス瓶に入れた前記ガス供給層分散液を７０℃の恒温水槽に１日保持すると相分離して瓶の下部に３６％の固形物濃度の濃厚分散液を分離した。その濃厚分散液の粘度は４１．５ｍＰａ・ｓであった。
得られた３６％の濃厚ガス供給層分散液の固形分に対して０．６部の銀微粒子（平均粒径０．３ミクロン、三井金属社製）を混合、超音波で分散させた。水平に置いた常温の３０ｃｍ×２０ｃｍの熱板上にアルミニウム箔を引き、この銀入り高濃度分散液を厚さ０．１５ｍｍ塗布してすぐに厚さ１．８ｍｍ、大きさ１２角、５０ｐｐＩの銀メッキ発泡ニッケル板を載せた。熱板を加熱して８０℃とし２０分間乾燥した。熱板から下ろし冷却した反応層上の発泡ニッケル板の空間に４２．９％の濃厚ガス供給層分散液を流し込み発泡ニッケル板からはみ出た余分な分散液をヘラで取り去り、８０℃の熱板上に載せ１時間乾燥させた。
【００２３】
ＴＲの曇点は６５℃であるから曇点以上にして乾燥すると、ＰＴＦＥの分布に偏りが少ない。乾燥後、界面活性剤をソックスレー抽出器でエタノールを用いて６時間除去した。１６０℃で１時間乾燥後、常温で５０ｋｇ／ｃｍ^２で１分間プレスして押し固めた。その後３５０℃、１０分間加熱処理を施した。厚さ１．０３ｍｍ、１２ｃｍ角の電極を得た。この電極を酸素陰極としての性能を向上させるために、８０℃、３２％ＮａＯＨ、３０Ａ／ｄｍ^２で１０分間の水素発生処理を行った。その後、酸索を論理量の１．６倍流し、８０℃、３２％ＮａＯＨ、３０Ａ／ｄｍ^２の条件で電圧は０．８１３Ｖｖｓ．ＲＨＥを示した。この性能は従来の性能の良い酸素陰極とほぼ同じである。この方法は、ホットプレスの作業を必要としないため、大幅な工程の短縮と時間の節約になり、安価な電極の製造を可能にする。
【００２４】
【発明の効果】
本発明によれば、固形分濃度が３０％以上６０％以下、粘度が２０ｍＰａ・ｓ以上１００ｍＰａ・ｓ以下のガス拡散電極用分散液はカーボンブラックとＰＴＦＥ微粒子の分散が良好なため、カーボンクロス等に含浸でき、水分除去後の膜はひび割れが少ないものであり、それを熱処理することで強度が大きく優れたガス拡散電極を製造することが可能になった。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for producing a gas diffusion electrode, and more particularly to a method for producing a gas diffusion electrode by applying, impregnating, or spraying a dispersion liquid for a gas diffusion electrode on a flat plate or a substrate.
[0002]
[Prior art]
The production of the gas diffusion electrode is obtained by the following steps. Carbon black is dispersed in a large amount of water containing a surfactant, and a polytetrafluoroethylene (PTFE) dispersion is added and dispersed to obtain a dispersion for a gas diffusion electrode. At this time, the dispersion is dispersed to an average particle size of about 400 nm by ultrasonic dispersion, jet mill dispersion, or the like.
Alcohol is added to this dispersion to coagulate the dispersion, which is then filtered and dried to form a powder. Then, solvent naphtha is added, and the dispersion is made into a clay to form a sheet with a roll. A gas diffusion electrode has been obtained by extracting and removing the surfactant contained in this sheet with alcohol such as ethanol and then hot pressing.
[0003]
[Problems to be solved by the invention]
The process of manufacturing a conventional gas diffusion electrode is complicated as described above, requires many devices, and requires a long manufacturing time, resulting in a high manufacturing cost. In particular, the film forming process and the hot pressing process are the rate-determining stages. It has been desired to eliminate these steps in order to provide an inexpensive electrode.
[0004]
[Means for Solving the Problems]
The present invention has solved the above problems by the following means (1) to (3).
(1) A method for producing a gas diffusion electrode, comprising using a dispersion liquid for a gas diffusion electrode having a solid content concentration of 30% to 60% and a viscosity of 20 mPa · s to 100 mPa · s.
(2) The method for producing a gas diffusion electrode according to the above (1), wherein the dispersion liquid for a gas diffusion electrode is coated, impregnated or sprayed to form a film.
(3) The method for producing a gas diffusion electrode according to (2), wherein after forming the film, remove water, extract a surfactant with alcohol, and heat-treat at a temperature equal to or higher than the melting point of the fluororesin.
[0005]
BEST MODE FOR CARRYING OUT THE INVENTION
Since the conventional dispersion liquid for gas diffusion electrodes is dilute with a solid content of 10% or less, if it is directly applied, it is greatly shrunk in the process of removing a large amount of water, and large cracks do not occur to form a film. However, the present inventor has conducted intensive studies in order to solve the above-mentioned problems. As a result, if a dispersion containing a solid content of at least 30% or more and 60% or less and having a viscosity of 20 mPa · s or more and 100 mPa · s or less is used, By coating or dispersing the dispersion on a flat plate, a good film is obtained after drying, and using a substrate such as carbon paper, carbon cloth, nickel foam, or a net, and applying and impregnating the substrate. It was found that even when drying was carried out, it permeated into the space, so that a good film was formed even after drying.
[0006]
Since the dispersion has a low viscosity and the dispersion of carbon black and PTFE is maintained, particles of carbon black and PTFE are accumulated when a film is formed. For this reason, it has been found that this film has high strength without hot pressing, and in particular, it is possible to obtain a performance comparable to that of a conventional hot-pressed product by rolling and pressing at room temperature, followed by heat treatment, and completed the present invention. In addition, if hot pressing is performed, a film having higher strength can be obtained.
[0007]
The high-concentration, low-viscosity carbon black dispersion used in the present invention may be a simple substance or a catalyst-supporting carbon black (for example, carrying gold, silver, a white metal or an alloy thereof, or a metal oxide) and a polyoxyethylene type. And a nonionic surfactant.
[0008]
The surfactant used for the dispersion is preferably a polyoxyethylene-type nonionic surfactant, and various surfactants are used. Among them, Triton (Triton-X100) is preferably used. The triton may be represented by an abbreviation “TR”. In addition, HLB of 13 such as Newcol 1310 (Nippon Emulsifier Co., Ltd.), Dispanol TOC (Nippon Yushi Co., Ltd.), NAROACTY N-100 (Sanyo Kasei Kogyo Co., Ltd.), Nikkor BT-9 (Nikko Chemicals Co., Ltd.), etc. A polyoxyethylene type surfactant around 0.5 is preferably used.
[0009]
The content of the surfactant may be 1% or less as long as it is a concentration at which the collected particles are well dispersed, but can be appropriately selected usually in the range of 1% to 4%. The content of the constituent fine particles in the dispersion is about 1 to 5% depending on the dispersibility of the material. Since about 8% is added to the PTFE dispersion as a dispersant, it is desirable that the TR of the carbon black dispersion be substantially the same when concentrated. Although it depends on the type of carbon black, a surfactant dispersion having a low concentration of about 2% is desirable as a dispersion because the dispersion efficiency in a jet mill is good and the amount of surfactant used is small.
[0010]
It is desired that the container used for evaporating water from the dispersion has good thermal conductivity and has corrosion resistance. As a specific material, glass and stainless steel are good. As for the mouth of the container, a wide mouth is preferable because the evaporation area is large. Heating is desirably a water bath, but may be direct heating if the temperature does not reach 100 ° C. or higher. It is desirable that the dispersion be stirred during heating and evaporation. Also, a dry gas may be flowed over the liquid surface to promote evaporation. Further, a defoaming device may be provided to reduce the pressure and promote the evaporation. When evaporating and drying, it may be left still.
[0011]
As the heating means, for example, a means for heating a glass tube containing the dispersion liquid in a thermostat or a method for directly heating the glass tube in a hot plate processed with polytetrafluoroethylene is preferably used. The carbon black dispersion concentrated to 20% or more is added with a predetermined PTFE dispersion and mixed and dispersed to obtain a high concentration gas diffusion electrode dispersion. In addition, a high-concentration carbon black dispersion can be obtained by adding water to the dried carbon black dispersion to make it re-liquid, so that a predetermined PTFE dispersion is added and mixed and dispersed to obtain a high-concentration, low-viscosity gas. A dispersion for a diffusion electrode is obtained. The solid content concentration of the resulting dispersion for a high concentration gas diffusion electrode is 30% or more, but the upper limit is limited to some extent in practical use, is about 60%, and is about 50% from the viewpoint of easy production. . Further, the viscosity of the dispersion is 100 mPa · s or less, but it is difficult to lower the lower limit so much because the solid concentration is 30% or more, and practically about 20 mPa · s.
[0012]
When a dispersion containing 3 to 15% TR is allowed to stand for about one day in a thermostatic water bath, the dispersion separates into a concentrated dispersion. For example, a 10% TR-containing gas supply layer dispersion (containing 10% solids) separates into two layers when held at 70 ° C. and holds for about one day a 38% dispersion at the bottom and a 12% TR at the top. It becomes a solution. This is based on the phenomenon that when an aqueous solution of a polyoxyethylene type nonionic surfactant such as TR is ripened, the water solubility decreases and the solution becomes cloudy (this temperature is called a cloud point). Nonionic surfactants dissolve in water below their cloud point temperature and exhibit surface activity, but above the cloud point temperature, hydrophilic groups dehydrate, molecules associate and lose surface activity, and the liquid temperature decreases. As the temperature rises further, it precipitates in a floc or liquid form. Conversely, when the liquid temperature falls below the cloud point temperature, the hydrophilic group of the surfactant, which has become insoluble once, hydrates and dissolves in water again to recover the surface activity.
[0013]
However, a surfactant at a high concentration as in the present invention forms micelles at a low temperature and is dispersed in a colloidal state in water. When the cloud point is exceeded, the surfactants coagulate, and the concentrated phase is separated into two phases, ie, the lower phase and the lower concentration phase are separated into the upper phase. If the cloud point is lower than the cloud point, fine particles such as carbon black are dispersed in the aqueous surfactant solution by the action of the surfactant. However, when the cloud point is exceeded, the hydrophobicized surfactant is deposited around the fine particles and becomes hydrophobic. Since the specific gravity is larger than the liquid phase, sedimentation occurs. Further, the concentration of the dispersion using the above phenomenon is performed while the dispersion stability is high. Among the polyoxyethylene type nonionic surfactants, those having a range of HBL = 12 to 15 are desirable, and those having a value near HBL = 13.5 are particularly desirable. Narrowacty, N-110 from Sanyo Chemical Co., Ltd., BT-9 from Nikko Chemicals, NL-90 from Daiichi Kogyo Seiyaku Co., Ltd., and Newcol 1310 from Nippon Emulsifier Co., Ltd. can be used favorably.
[0014]
The high-concentration dispersion obtained as described above has a low viscosity despite its high concentration. That is, since the fine particles of carbon black and PTFE are protected by the surfactant and maintained in a dispersed state, they did not solidify even after long-term storage for 6 months or more. Since this dispersion has a low viscosity and a small particle size, it penetrates into porous carbon paper, carbon cloth, and foamed nickel of 50 PPI or less and is easily filled. In addition, since the dispersion is good, the interaction between the individual particles is small, and the concentration is high, a good film with little shrinkage due to water removal is obtained.
[0015]
In order to remove water from the coated and impregnated dispersion, it is desirable to heat the dispersion above the cloud point of the surfactant. Heating at 150 ° C. or higher and 250 ° C. or lower before removing the surfactant causes less desorption of carbon black during the alcohol extraction operation. Alcohol extraction is preferably a Soxhlet extractor, which can be almost completely removed by replacing it with high-purity ethanol and performing it twice for about three hours. After removing the surfactant, the substrate is dried at 150 ° C. and heat-treated at 350 ° C. for 10 minutes to obtain a gas diffusion electrode. Cold pressing, rolls and the like may be applied if necessary for smoothing and densification of the sheet. Hot pressing can be performed to produce a film having higher strength.
[0016]
【Example】
Hereinafter, the present invention will be described specifically with reference to examples, but the present invention is not limited to these examples. Further, “%” and “parts” are all expressed by weight throughout the examples.
[0017]
Example 1
To 2200 g of a 2% aqueous solution of Triton-X100, 200 g of hydrophobic carbon black (No. 6, average particle size 500 angstrom, prototype, manufactured by Denki Kagaku Kogyo Co., Ltd.) was added and stirred and dispersed. 2400 g of this carbon black dispersion was passed five times with a jet mill (Genus, nozzle diameter 0.2 mm) at a pressure of 1500 kg / cm ² . As a result, the average particle diameter was 0.37 μm, and a sharp distribution without large particles of 2 μm or more was obtained.
[0018]
2400 g of this dispersion was transferred to a polytetrafluoroethylene-coated hot plate having an area of 960 cm ^{2 and a} depth of 6 cm, and the water was evaporated for 2 hours while stirring at about 80 ° C. The solid content was 36.1%, and the surfactant was A concentrated carbon black dispersion having a concentration of 7.4% was obtained. A PTFE dispersion (D-1, concentration: 60% by weight) was weighed to this concentrated carbon black dispersion so as to have a PTFE concentration of 40%, added, mixed, and dispersed. A dense gas feed layer dispersion of 43.5% solids was obtained. The viscosity was 49.5 mPa · s.
[0019]
0.6 parts of silver fine particles (average particle size: 0.3 micron, manufactured by Mitsui Kinzoku Co., Ltd.) were mixed with the solid content of the obtained concentrated gas supply layer dispersion having a solid concentration of 43.5%, and the mixture was subjected to ultrasonication. Dispersed. An aluminum foil is drawn on a hot plate of 30 cm × 20 cm at a normal temperature placed horizontally, and this silver-containing high concentration dispersion is applied to a thickness of 0.15 mm. An 8 mm, 12 cm square, 50 PPI silver-plated foamed nickel plate was placed. At this time, the liquid of the coating material is impregnated into the inside of the silver-plated nickel foam plate from the lower surface. The hot plate was heated to 80 ° C. and dried for 20 minutes. A 43.5% concentrated gas supply layer dispersion is poured into the space inside the nickel foam plate on the reaction layer that has been cooled down from the hot plate and the excess dispersion liquid that has overflowed the nickel foam plate is removed with a spatula. And dried for 1 hour. Since the cloud point of TR is 65 ° C., if it is dried at the cloud point or higher, the unevenness of PTFE is small.
[0020]
After drying at 150 ° C. for 1 hour, the surfactant was removed with a Soxhlet extractor using ethanol for 3 hours. This operation was performed twice. After drying at 150 ° C. for 1 hour, a heat treatment was performed at 350 ° C. for 10 minutes to obtain a gas diffusion electrode having a thickness of 1.63 mm and a square of 12 cm. In order to improve the performance of this electrode as an oxygen cathode, a hydrogen generation treatment was performed at 80 ° C., 32% NaOH, and 30 A / dm ² for 10 minutes. Thereafter, oxygen was flowed 1.6 times the logical amount, and the voltage was 0.806 V vs. 80 ° C., 32% NaOH, and 30 A / dm ² . RHE was indicated. This performance was almost the same as the conventional oxygen cathode. Since this electrode does not require a hot press operation in its manufacture, the process is greatly shortened and time is saved as compared with the conventional method for producing a gas diffusion electrode.
[0021]
Example 2
200 g of hydrophobic carbon black (No. 6, average particle size 500 angstrom, prototype, manufactured by Denki Kagaku Kogyo Co., Ltd.) was added to 2,400 g of the 3.6% Triton-X100 aqueous solution, and the mixture was stirred and dispersed. 2600 g of this carbon black dispersion was passed five times with a jet mill (Genus, nozzle diameter 0.2 mm) at a pressure of 1500 kg / cm ² . As a result, the average particle diameter was 0.37 μm, and a sharp distribution without large particles of 2 μm or more was obtained.
A PTFE dispersion (D-1, concentration: 60 wt%) was weighed, added, mixed and dispersed to the dispersion so that the PTFE concentration became 40%. A gas supply layer dispersion of 10.2% solids was obtained.
[0022]
When the gas supply layer dispersion liquid contained in a 1-liter glass bottle was kept in a constant temperature water bath at 70 ° C. for 1 day, phase separation was performed to separate a concentrated dispersion liquid having a solid concentration of 36% at the lower part of the bottle. The viscosity of the concentrated dispersion was 41.5 mPa · s.
0.6 parts of silver fine particles (average particle diameter: 0.3 μm, manufactured by Mitsui Kinzoku Co., Ltd.) were mixed with the solid content of the obtained 36% concentrated gas supply layer dispersion and dispersed by ultrasonic waves. An aluminum foil was drawn on a hot plate of 30 cm × 20 cm at room temperature placed horizontally, and this high-concentration dispersion liquid containing silver was applied to a thickness of 0.15 mm. A silver-plated foamed nickel plate was placed. The hot plate was heated to 80 ° C. and dried for 20 minutes. A 42.9% concentrated gas supply layer dispersion is poured into the space of the nickel foam plate on the reaction layer which has been cooled down from the hot plate, and the excess dispersion liquid which has protruded from the nickel foam plate is removed with a spatula. And dried for 1 hour.
[0023]
Since the cloud point of TR is 65 ° C., if it is dried at the cloud point or higher, the distribution of PTFE is less biased. After drying, the surfactant was removed with a Soxhlet extractor using ethanol for 6 hours. After drying at 160 ° C. for 1 hour, the mixture was pressed at room temperature at 50 kg / cm ² for 1 minute and compacted. Thereafter, heat treatment was performed at 350 ° C. for 10 minutes. An electrode having a thickness of 1.03 mm and a square of 12 cm was obtained. In order to improve the performance of this electrode as an oxygen cathode, a hydrogen generation treatment was performed at 80 ° C., 32% NaOH, and 30 A / dm ² for 10 minutes. Thereafter, the acid cable was flowed 1.6 times the logical amount, and the voltage was 0.813 V vs. 80 ° C., 32% NaOH, and 30 A / dm ² . RHE was indicated. This performance is almost the same as the conventional high performance oxygen cathode. Since this method does not require a hot pressing operation, the process can be greatly shortened and time can be saved, so that an inexpensive electrode can be manufactured.
[0024]
【The invention's effect】
According to the present invention, the dispersion liquid for a gas diffusion electrode having a solid content concentration of 30% to 60% and a viscosity of 20 mPa · s to 100 mPa · s has a good dispersion of carbon black and PTFE fine particles. The film after moisture removal had few cracks, and heat treatment of the film made it possible to produce a gas diffusion electrode having high strength and excellent properties.

Claims

A method for producing a gas diffusion electrode, comprising using a dispersion for a gas diffusion electrode having a solid concentration of 30% or more and 60% or less and a viscosity of 20 mPa · s or more and 100 mPa · s or less.

The method for producing a gas diffusion electrode according to claim 1, wherein the dispersion liquid for a gas diffusion electrode is coated, impregnated or sprayed to form a film.

The method for producing a gas diffusion electrode according to claim 2, wherein after the formation of the film, a surfactant is extracted with an alcohol after removing water, and a heat treatment is performed at a temperature equal to or higher than the melting point of the fluororesin.