JP2004235051A - High polymer solid electrolyte and polymer electrolyte fuel cell using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a high polymer solid electrolyte having high ionic conductivity stable for a long time and little methanol cross over, and capable of attaining high output constantly for a long time, and to provide a polymer electrolyte fuel cell using it etc. <P>SOLUTION: In the polymer solid electrolyte, a polymer solid electrolyte is prepared using a mixture comprising at least a polymer having an anion group and a polymer having a -CONH-group or a -CONR-group (where R is an alkoxy group) in a main chain. By using the solid polymer solid electrolyte, the high performance polymer electrolyte fuel cell using methanol as fuel can be obtained. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

【００２１】
式（２）
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【化３】

【００２３】
式（３）
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【化４】

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式（４）
【００２６】
【化５】

【００２７】
（ここで、Ｚは芳香環を含む有機基、ｎは繰返し単位の数である、Ｒ１，Ｒ２は有機基を指し、Ｒ１，Ｒ２は同じでも異なっていても良い。
【００２８】
主鎖に−ＣＯＮＨ−基あるいは−ＣＯＮＲ−基（Ｒはアルコキシ基）を有するポリマとしては、かかる基を有するポリマが適用でき限定されないが、例えば、次の化学式で表される重合あるいはそれらの共重合体や混合物が好ましく用いられる。また、アルコキシポリアミドあるいはそれらの混合物、前記重合体類との共重合体や混合物も好ましく用いられ、特には、前記例示のポリアミドとアルコキシポリアミドとの混合物が好ましい。
【００２９】
【化６】

【００３０】
（ｎは重合度）
−ＣＯＮＨ−基あるいは−ＣＯＮＲ−基（Ｒはアルコキシ基）を有するポリマは、アニオン性基との牽引性を高め、本発明の効果を高める観点からは、脂肪族系のものが芳香族系のものよりも好ましい。また、アニオン性基ポリマとの混合を容易にするためには、通常のポリアミドに比べて低重合度であることが好ましく、重合度はおおよそ２００以下であることが好ましく。１５０以下であることが特に好ましい。この範囲の重合度であれば、多くの該ポリマ種がペンタノール、ブタノール、プロパノール、エタノール、メタノールなどの溶剤類に溶解することが可能である。また、溶液として用いるには、共重合体として用いることが有効であり、カプロラクタムとＡＨ塩（へキサメチレンジアミンとアジピン酸を１：１で化合したものの略称）との共重合（ナイロン６／６６共重合体）や、ナイロン６／１２共重合体、ナイロン６６／６１０／６共重合体は好ましい例である。また、アルコシキポリアミドはアルコール類に易溶であり好ましく用いられる。特に限定されないがアルコキシポリアミドの好ましい一例としてはメトキシメチルポリアミドが挙げられる。
【００３１】
アニオン性基を有するポリマと主鎖に−ＣＯＮＨ−基あるいは−ＣＯＮＲ−基（Ｒはアルコキシ基）ポリマの混合割合は、両者のポリマ種、アニオン性基ポリマのイオン交換当量、−ＣＯＮＨ−基あるいは−ＣＯＮＲ−基（Ｒはアルコキシ基）ポリマにおいては該基の当量などにより異なるが、一般には固形分重量比で２〜２０％であることが好ましい。また、５〜１５％であることがより好ましい。この含有量が少なすぎると拘束性が不足し、また高すぎるとアニオン性基ポリマのイオン伝導性引いては出力を損なうことになり好ましくない。
【００３２】
また、本発明において、特筆すべきもう一つの発明としては、主鎖に−ＣＯＮＨ−基あるいは−ＣＯＮＲ−基（Ｒはアルコキシ基）を有するポリマとして、珪酸塩層状物を含有し、かつその層間に該ポリマが存在するようにせしめたものが好ましく（かかる状態を珪酸塩層状物ポリマ複合体と言う）、かかる要件を満足することで、本発明の効果をより高めることを可能にし、加えて高分子電解質に耐熱性、耐水性、機械的強度、寸法安定性を著しく改善できることである。これは、珪酸塩層状物の層間に主鎖に−ＣＯＮＨ−基あるいは−ＣＯＮＲ−基（Ｒはアルコキシ基）を有するポリマの一部を存在せしめた状態下に、該珪酸塩層状物をミクロ分散した珪酸塩層状物分散ポリマ複合体としたものである。かかる珪酸塩層状物としては、モンモリロナイト、バイデライト、ノントロナイト、サポナイト、ヘクトライト、ソーコナイトであり、中でもモンモリロナイトあるいはサポナイトが好ましく用いられる。かかる珪酸塩層状物ポリマ複合体を作製する好ましい方法の例を挙げるならば次のとおりである。もちろん、この方法に限定されるものではない。
【００３３】
（１）珪酸塩層状物に、例えば、１２−アミノドデカン酸や１４−アミノテトラデカン酸などのカルボキシル基を有する炭素数１０以上のアルキル鎖を有する有機化合物の陽イオンを作用させ、該珪酸塩層状物の層間に吸着させた後、所望のポリアミド形成モノマと混合し、少なくとも該モノマの一部を該珪酸塩層状物の層間内で重合析出させる方法。
【００３４】
（２）ε−カプトラクタムなどラクタムあるいは６−アミノ−ｎ−カプロン酸などのポリアミドモノマーの有機イオンを珪酸塩層状物に作用させ、該有機イオンでイオン交換せしめた後、所望のポリアミド形成モノマと混合し、少なくとも該モノマの一部を珪酸塩層状物の層間内で重合析出させる方法。
【００３５】
このような方法により、珪酸塩層状物をポリアミド中にミクロ分散することができる。ここで、珪酸塩層状物は層間が拡大し、一層毎に分散した状態となってよく、また、層間は拡大しているが複数層がまとまったものとして分散したものであってもよい。
【００３６】
かかる珪酸塩層状物分散ポリマ複合体におけるポリアミドに対する珪酸塩層状物の割合は、０．１〜５０重量％が好ましく、特に、１〜２０重量％が好ましい。珪酸塩層状物の割合が、上記範囲をあまりにも超えると、機械的強度、柔軟性の低下をきたす恐れがある。また、上記範囲より少ない場合は特徴が得にくい。
【００３７】
アニオン性基と有するポリマと主鎖に−ＣＯＮＨ−基あるいは−ＣＯＮＲ−基（Ｒはアルコキシ基）を有するポリマとを混合する方法は、両成分が均一に混合されることが好ましく、その性状に応じてスクリュ、ブレンダー、ミル、バンバリミキサー、ホモジナイザー、ニーダなどの従来公知の混合機により混合される。なお、高分子固体電解質中における両成分が形態は、両成分の組合せにより、界面をもって接触するもの、両成分が複合した層を有するもの、あるいは両成分が分子レベルオーダで相容したものとなるが、いずれの形態で存在しても構わない。
【００３８】
また、前記の混合物には、増量、安定化、可塑化、耐熱化などの目的で、更に他のポリマや有機あるいは無機のフィラーとして、炭酸カルシウム、シリカ粉末、マイカ、カリオン、けい藻土、クレー、タルク、白雲石などが含まれても構わない。
【００３９】
本発明の高分子固体電解質をそのものの膜状態（フィルム状のもの）で用いても著しい効果が得られるものであるが、固体高分子電解質を膜状の多孔基材に充填することも可能であり、この様にして得られた固体高分子電解質膜は膨潤による変形がさらに抑制でき、本発明の目的であるメタノールクロスオーバーの低減、長時間安定した性能保持に対し好ましい態様である。多孔基材の形状は特に限定されるものではなく、複数個の孔を有するものが例として挙げられるが、厚み方向に複数個の独立した貫通孔や三次元網目構造を有する多孔基材が好ましい。
【００４０】
また、多孔基材が、平面方向に整然と配列された貫通孔を有するものであることが、さらに好ましい。ここで、「平面方向に整然と配列された貫通孔」とは、貫通孔が略等間隔あるいは規則的に配列されている状態を示す。具体的には、隣り合った貫通孔の中心間隔同士を比較した場合に、それぞれの中心間隔の差が１００％以内の範囲に入る配列状態のことである。すなわち、多孔基材の表面において、貫通孔は二次元的に配列しているので、隣り合った貫通孔は上下左右に存在するが、隣り合う貫通孔の中心間隔の差が１００％以内の範囲に入り配列されていることが必要である。好ましくは５０％以内であり、さらに好ましくは３０％以内である。また、隣り合う貫通孔の中心間隔の差が１００％を超えるている場合でも、ある個数ごとの組み合わせが繰り返された規則的な配列であれば、各々の配列内部の隣り合う貫通孔の中心間隔の誤差が１００％以内であれば好ましく用いられる。
【００４１】
本発明に用いられる多孔基材の具体例として、図１の形状が挙げられる。図１は、本発明の高分子固体電解質膜の一例を示す斜視模式図である。図１の多孔基材は、中央に多数の孔の空いた多孔部１があり、多孔部の周囲は孔の無い非多孔部２を有している。図２に多孔部の拡大模式図を示す。本発明の高分子固体電解質膜は、多孔部の孔３が、図２のように平面方向に見た配列ピッチが整然と等間隔に配列されていることが好ましい。図２中のＬが、上述した「隣り合う貫通孔の中心間隔」である。Ｌは、０．５〜１００μｍの範囲が好ましく、１〜５０μｍの範囲が特に好ましい。また、孔の内径ｄとしては、０．５〜５０μｍの範囲が好ましく、１〜２０μｍの範囲が特に好ましい。
【００４２】
図１において、多孔部１に本発明の高分子固体電解質が充填されて高分子固体電解質膜としての機能を発現するのである。また、図２の孔３に充填されることによって、膨潤が抑制され、燃料のメタノールがアノードからカソードに透過するクロスオーバーを低減するのであるが、孔３が整然と配列されていれば、開孔率を高めることが可能となり、イオン伝導性が向上する。
【００４３】
本発明の高分子固体電解質膜に用いられる多孔基材の好ましい作製方法としては、例えばフォトリソグラフィーの加工方法を適用することができる。従来、多孔基材としては、貫通孔を有する濾過用フィルター素材などが用いられてきた。これは通常、高分子フィルムにイオンを照射してポリマ鎖を破断し、アルカリ溶液などを用いて化学エッチング法で孔を開けたもの（トラックエッチ法）である。これに対してフォトリソグラフィー法を用いた孔３は、その孔径、形状、孔の間隔、多孔化する部分などを任意に設定することができ、クロスオーバーの低減による燃料電池の性能向上を図ることができる。さらに、フォトリソグラフィーは微細加工に優れるため、多孔部１と非多孔部２との微細な区分けが可能となり、燃料電池の小型化に優れた結果をもたらす。また、従来のトラックエッチ法に比べて生産性向上による低コスト化を達成することができる。
【００４４】
ここで、フォトリソグラフィー法を用いて作製した多孔基材の走査型電子顕微鏡（ＳＥＭ）写真を図３に示した。図３のごとくフォトリソグラフィー法の多孔基材の孔は、整然と等間隔に配列されていることが明瞭である。
【００４５】
フォトリソグラフィー法により作製された多孔基材における孔の横断面形状としては、特に限定されるものではないが、円、楕円、正方形、長方形、菱形、台形などが好ましい。これらの中でも、高分子固体電解質の充填のしやすさ、膨潤抑制の点から、円あるいは楕円が好ましい。孔の大きさや間隔については特に限定されることはなく、高分子固体電解質の充填のしやすさ、電池性能などに基づき適宜決めればよい。
【００４６】
フォトリソグラフィー法を用いて製造する多孔基材における多孔部分全体の大きさは、用いられる電極触媒層や電極基材の大きさに合わせて決めればよい。また、多孔基材の厚さに関しても、求められる電池性能に基づいて決めればよいが、通常１〜５０μｍの範囲が好ましく、５〜３０μｍの範囲が特に好ましい。
【００４７】
本発明に使用するフォトリソグラフィー法の詳細な方法は特に限定されるものではないが、例えば、感光性ポリマを基板に塗工し、フォトマスクをかけて露光し、現像後にポリマを溶解して孔を形成し、基板から剥がして多孔性高分子フィルムを得る方法などが用いられる。感光性ポリマは、ネガ型あるいはポジ型どちらの方式でも構わないが、求められる孔の大きさ、孔の間隔、燃料電池性能等に応じて適宜選択できる。基板素材は、ポリマとの密着性や剥がしやすさの点から決められ、好ましくはシリコンウエハやアルミ板などが用いられるが、特に限定されるものではない。露光は、縮小露光、等倍露光どちらでも構わないが、作製される電解質の大きさ、孔の大きさ、形状、間隔などによって適宜決めればよい。また、現像、溶解、基板からの剥離等の条件についても、ポリマの性質によって適宜、条件を選択すればよい。また、予め基板上に非感光性ポリマを塗工し、その上にフォトレジストを塗工、露光、現像、ポリマ溶解による空隙作製を行うことも可能である。
【００４８】
本発明に使用するフォトリソグラフィー法に用いられる感光性あるいは非感光性ポリマとしては、特に限定されるものではないが、フォトリソグラフィーによる加工性、ポリマの耐酸化性、強度等からポリイミドが好ましく用いられる。
【００４９】
ポリイミドを用いたフォトリソグラフィー法による多孔作製の具体的方法としては、たとえば、前駆体のポリアミド酸溶液を基板に塗工し、約１００℃程度にて溶媒を乾燥除去した後、フォトマスクを用いた露光、現像、アルカリ処理等によるフォトリソグラフィー加工を行うことで孔を形成した後、約３００℃以上にてイミド閉環反応を行い、最後に基板から剥がして多孔性ポリイミドフィルムを得る方法が挙げられる。溶媒除去およびイミド閉環反応の温度や時間は、用いるポリイミドの種類により適宜決めることができる。ポリイミドフィルムを基板から剥がす際には、通常、酸への浸漬が行われるが、用いられる基板がシリコンウエハではフッ酸、アルミ板では塩酸が好ましく用いられる。
【００５０】
ここで、本発明に用いられるポリイミドとしては、ネガ型あるいはポジ型の感光性ポリイミド、あるいは非感光性ポリイミドのいずれでも構わないが、孔の大きさ、形状、間隔、フィルムの厚さ等から感光性ポリイミドが好ましく、ネガ型感光性ポリイミドがさらに好ましい。
【００５１】
本発明に用いられる多孔基材に用いられるポリマとしては特に限定されないが、好ましくは、ポリイミド（ＰＩ）、ポリビニリデンフルオライド（ＰＶＤＦ）、ポリフェニレンスルフィドスルフォン（ＰＰＳＳ）、ポリテトラフルオロエチレン（ＰＴＦＥ）、ポリスルフォン（ＰＳＦ）など、あるいはこれらの共重合体、他のモノマとの共重合体（ヘキサフルオロプロピレン−フッ化ビニリデン共重合体等）、さらには、ブレンドなども用いることができる。これらのポリマは、耐酸化性、強度、湿式凝固の容易性などから好ましいものである。
【００５２】
多孔基材に本発明高分子固体電解質を充填する方法は特に限定されるものではない。たとえば、アニオン性基を有するポリマを溶液として、多孔基材への塗工あるいは浸漬することにより空隙内への充填が可能となる。空隙内への充填を容易にするために超音波を使用したり、減圧にするのも好ましく、これらを塗工あるいは浸漬時に併用するとさらに充填効率が向上し好ましい。また、アニオン性基を有するポリマの前駆体であるモノマを空隙内に充填した後に空隙内で重合する、あるいはモノマを気化してプラズマ重合を行う、などの方法を行っても良い。
【００５３】
本発明において燃料電池の形態、燃料電池の作製方法は特に限定されるものではない。以下にｓｉｄｅ−ｂｙ−ｓｉｄｅ構造の燃料電池作製にフォトリソグラフィー法を用いる方法を例に詳述する。ここで、ｓｉｄｅ−ｂｙ−ｓｉｄｅ構造とは、単一の高分子固体電解質膜面の平面方向に、一組みの対向する電極からなるセルを２個以上配置する構造を指す。この構造によると、２個以上配置された隣り合ったセルのアノードとカソードを高分子固体電解質膜を貫通する電子伝導体で接続することによりセルが直列に接続されるため、ｓｉｄｅ−ｂｙ−ｓｉｄｅ構造の高分子固体電解質膜断面はプロトン伝導部と電子伝導部が交互に存在する構造となる。このような構造を作製するには、小型化および生産性の観点からフォトリソグラフィー法を用いるのが好ましい。
【００５４】
本発明により得られた高分子固体電解質膜のイオン伝導度はインピーダンス法により測定できる。具体的には電気化学会発行の「（続）電気化学測定法」などに記載の方法で測定する。また、高分子固体電解質膜のメタノール透過性は、メタノール水溶液と純水あるいは気体を高分子固体電解質膜を介して配置し、純水あるいは気体へのメタノールの移動速度を求めることにより求める。本発明では具体的に下記方法で測定を行った。膜をエレクトロケム社製セルにセットし、片面に１ｍｏｌ／ｌメタノール水溶液を０．２ｍｌ／ｍｉｎで供給し、もう片面に空気を５０ｍｌ／ｍｉｎで供給した。排気された空気中のメタノール濃度あるいはその分解物の濃度を測定し、メタノール透過速度、透過量を求めた。
【００５５】
ｓｉｄｅ−ｂｙ−ｓｉｄｅ構造の一例を図４および図５に示す。図４は、ｓｉｄｅ−ｂｙ−ｓｉｄｅ構造を持つ本発明の高分子固体電解質膜の斜視模式図であり、図５は、その製造プロセスの一部を示す断面模式図である。なお図４、図５においては、２個のセルを横に配置した例示をしたが、同様なｓｉｄｅ−ｂｙ−ｓｉｄｅ構造で、３個以上の複数個を平面方向に配置することも可能である。以下の説明は簡便のために２個のセルで行う。図５においてプロトン伝導部は多孔部１に図示しないプロトン伝導体が充填され、電子伝導部は膜導電部４に電子伝導体が充填されている。プロトン伝導部の多孔部１と電子伝導部の膜導電部４以外の部分はプロトンや電子が伝導しない非多孔部２であり、緻密な高分子フィルムとなっている。このように複雑かつ微細な構造の高分子フィルム作製には、本発明に述べるフォトリソグラフィー法が好適に用いられる。フォトリソグラフィー法により図４に示す多孔基材を作製し、これを図５に例示する方法で高分子固体電解質膜とする。図５では、予め膜貫通電子伝導部に電子伝導体を充填した後に、プロトン伝導部にプロトン伝導体を充填しているが、この順序は逆でも構わない。また、プロトン伝導体を充填してプロトン伝導部を作製し、次に電極を設け、最後に電子伝導部を作製成しても構わない。
【００５６】
前述のｓｉｄｅ−ｂｙ−ｓｉｄｅ構造の電子伝導部は、電解質膜を貫通した構造である。ここで電子伝導部として電解質膜を貫通した部分を膜導電部という。この膜導電部は、プロトン伝導体を充填するための多孔部とは異なる機能である。その膜導電部の、大きさ、形状などは特に限定されるものではない。膜導電部が大きいほどセルとセルの電気抵抗が低下し直列での電圧向上が期待できる。ただし、膜導電部が大きいほど、アノード側の水素あるいはメタノールなどの有機溶媒がカソード側にリークする可能性、あるいはカソード側の空気がアノード側にリークする可能性が高まり、性能低下を引き起こすことがある。このため、電子伝導部に用いられる電子伝導体の電気抵抗と耐リーク性とを考慮して、膜導電部の大きさや形状を決めることが好ましい。なお、電子伝導部は高分子固体電解質膜を貫通せず、外部を通しても良い。
【００５７】
前記膜導電部４の電子伝導体としては特に限定されるものではないが、導電ペーストが好ましく用いられる。導電ペーストとしては、カーボン、銀、ニッケル、銅、白金、パラジウムなどの導電剤がポリマに分散されいるものなどを好ましく用いることができ、電子抵抗の低下と耐リーク性の向上が両立できる。特にＤＭＦＣにおいては、メタノールのリークを防ぐことが重要であり、シリコーン樹脂、ポリエステル、エポキシ樹脂などにカーボンや銀を分散した汎用導電ペーストのほか、カーボンブラック、銀、白金などをＰＶＤＦやポリイミドに分散した導電ペーストも好ましく用いられる。電子伝導部５は、セルの電極基材あるいは電極触媒層と電気的に接続されるが、この接触抵抗低下のためにも導電ペーストが好ましく使用される。
【００５８】
また、電子伝導部５として、ニッケル、ステンレススチール、アルミニウム、銅などの金属箔や金属線を用いても良い。また、これらの金属箔や金属線と導電ペーストを組み合わせることも可能である。
【００５９】
本発明の高分子固体電解質は、電極基材と電極触媒層とから構成される電極７と組み合わせて膜−電極複合体（ＭＥＡ）として固体高分子型燃料電池に用いられる。
【００６０】
本発明の固体高分子型燃料電池における電極７における電極触媒層は、特に限定されることなく公知のものを利用することが可能である。電極触媒層とは、電極反応に必要な触媒や電極活物質（酸化あるいは還元する物質を言う）を含み、さらに電極反応を促進する電子伝導やイオン電導に寄与する物質を含む層を言う。また電極活物質が液体や気体の場合には、その液体や気体が透過しやすい構造を有していることが必要であり、電極反応に伴う生成物質の排出も促す構造が必要である。
【００６１】
本発明の固体高分子型燃料電池において、電極活物質としては、好ましくは水素、メタノールなどの有機溶媒あるいは酸素等が挙げられ、触媒は白金などの貴金属粒子が好適な例として挙げられる。また、電極触媒層の導電性を改善する材料を含むことが好ましく、形態は特に限定されるものではないが、例えば、導電性粒子を有することが好ましい。導電性粒子としてはカーボンブラック等が挙げられ、特に触媒を担持したカーボンブラックとして白金担持カーボンなどが好ましく用いられる。電極触媒層は、触媒、電子伝導体（たとえばカーボンブラック）、イオン伝導体（たとえばプロトン交換樹脂）が互いに接触して、電極活物質と反応生成物が効率よく出入りする構造が求められる。また、イオン伝導性を改善したり、材料の結着性を向上させたり、或いは撥水性を高めたりするのに、高分子化合物が有効である。したがって、電極触媒層に、少なくとも触媒粒子と導電性粒子と高分子化合物を含むことが好ましい。
【００６２】
本発明の固体高分子型燃料電池には、電極触媒層に含まれる触媒としては公知の触媒を用いることができ、特に限定されるものではないが、白金、パラジウム、ルテニウム、イリジウム、金などの貴金属触媒が好ましく用いられる。また、これらの貴金属触媒の合金、混合物など、２種以上の元素が含まれていても構わない。
【００６３】
電極触媒層に含まれる電子伝導体（導電材）としては、特に限定されるものではないが、電子伝導性と耐触性の点から無機導電性物質が好ましく用いられる。なかでも、カーボンブラック、黒鉛質や炭素質の炭素材、あるいは金属や半金属が挙げられる。ここで、炭素材としては、チャネルブラック、サーマルブラック、ファーネスブラック、アセチレンブラックなどのカーボンブラックが、電子伝導性と比表面積の大きさから好ましく用いられる。ファーネスブラックとしては、キャボット社製バルカンＸＣ−７２、バルカンＰ、ブラックパールズ８８０、ブラックパールズ１１００、ブラックパールズ１３００、ブラックパールズ２０００、リーガル４００、ケッチェンブラック・インターナショナル社製ケッチェンブラックＥＣ、三菱化学社製＃３１５０、＃３２５０などが挙げられ、アセチレンブラックとしては電気化学工業社製デンカブラックなどが挙げられる。またカーボンブラックのほか、天然の黒鉛、ピッチ、コークス、ポリアクリロニトリル、フェノール樹脂、フラン樹脂などの有機化合物から得られる人工黒鉛や炭素なども使用することができる。これらの炭素材の形態としては特に限定されず、粒子状のほか繊維状のものも用いることができる。また、これら炭素材を後処理加工した炭素材も用いることが可能である。このような炭素材の中でも、特に、キャボット社製のバルカンＸＣ−７２が電子伝導性の点から好ましく用いられる。
【００６４】
これら電子伝導体の添加量としては、要求される電極特性や用いられる物質の比表面積や電子抵抗などに応じて適宜決められるべきものであるが、電極触媒層中の重量比率として１〜８０％の範囲が好ましく、２０〜６０％の範囲がさらに好ましい。電子伝導体は、少ない場合は電子抵抗が高くなり、多い場合はガス透過性を阻害したり触媒利用率が低下するなど、いずれも電極性能を低下させる。
【００６５】
電子伝導体は、触媒粒子と均一に分散していることが電極性能の点で好ましいものである。このため、触媒粒子と電子伝導体は予め塗液として良く分散しておくことが好ましい。
【００６６】
電極触媒層として、触媒と電子伝導体とが一体化した触媒担持カーボンを用いることも好ましい実施態様である。この触媒担持カーボンを用いることにより、触媒の利用効率が向上し、低コスト化に寄与できる。ここで、電極触媒層に触媒担持カーボンを用いた場合においても、さらに導電剤を添加することも可能である。このような導電剤としては、上述のカーボンブラックが好ましく用いられる。
【００６７】
電極触媒層に用いられるイオン伝導体としては、公知のものを用いることが可能である。イオン伝導体としては、一般的に、種々の有機、無機材料が公知であるが、燃料電池に用いる場合には、プロトン伝導性を向上するスルホン酸基、カルボン酸基、リン酸基などのイオン交換基を有するポリマが好ましく用いられる。なかでも、フルオロアルキルエーテル側鎖とフルオロアルキル主鎖とから構成されるプロトン交換基を有するポリマが好ましく用いられる。たとえば、デュポン社製のナフィオン、旭化成社製のアシプレックス、旭硝子社製フレミオンなどが好ましく用いられる。これらのイオン交換ポリマは、溶液または分散液の状態で電極触媒層中に設ける。この際に、ポリマを溶解あるいは分散化する溶媒は特に限定されるものではないが、イオン交換ポリマの溶解性の点から極性溶媒が好ましい。
【００６８】
イオン伝導体は、電極触媒層を作製する際に電極触媒粒子と電子伝導体とを主たる構成物質とする塗液に予め添加し、均一に分散した状態で塗布することが電極性能の点から好ましいものであるが、電極触媒層を塗布した後にイオン導電体を塗布してもかまわない。ここで、電極触媒層にイオン導電体を塗布する方法としては、スプレーコート、刷毛塗り、ディップコート、ダイコート、カーテンコート、フローコートなどが挙げられ、特に限定されるものではない。
【００６９】
電極触媒層に含まれるイオン伝導体の量としては、要求される電極特性や用いられるイオン伝導体の電導度などに応じて適宜決められるべきものであり、特に限定されるものではないが、重量比で１〜８０％の範囲が好ましく、５〜５０％の範囲がさらに好ましい。イオン伝導体は、少な過ぎる場合はイオン伝導度が低く、多過ぎる場合はガス透過性を阻害する点で、いずれも電極性能を低下させることがある。
【００７０】
電極触媒層には、上記の触媒、電子伝導体、イオン伝導体の他に、種々の物質を含んでいてもかまわない。特に電極触媒層中に含まれる物質の結着性を高めるために、上述のプロトン交換樹脂以外のポリマを含むことが好ましい。このようなポリマとしては、フッ素原子を含むポリマが挙げられ、特に限定されるものではないが、たとえば、ポリフッ化ビニル（ＰＶＦ）、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（ＦＥＰ）、ポリテトラフルオロエチレン、ポリパーフルオロアルキルビニルエーテル（ＰＦＡ）など、あるいはこれらの共重合体、これらのポリマを構成するモノマ単位とエチレンやスチレンなどの他のモノマとの共重合体、さらには、ブレンドなども用いることができる。これらポリマの電極触媒層中の含有量としては、重量比で５〜４０％の範囲が好ましい。ポリマ含有量が多すぎる場合、電子およびイオン抵抗が増大し電極性能が低下する傾向がある。
【００７１】
電極触媒層は、触媒−ポリマ複合体が三次元網目構造を有することも好ましい実施態様である。触媒−ポリマ複合体は、触媒粒子を含んだポリマ複合体であって、この複合体が三次元網目構造となっている場合である。つまり、触媒−ポリマ複合体が立体的に繋がった三次元状の網目構造を有している状態である。
【００７２】
電極触媒層が三次元網目構造を有している場合、その孔径が０．０５〜５μｍの範囲であることが好ましく、より好ましくは、０．１〜１μｍの範囲である。孔径は、走査型電子顕微鏡（ＳＥＭ）などで、表面を撮影した写真から、２０個以上好ましくは１００個以上の平均から求めることができ、通常は１００個で測定する。湿式凝固法によって製造された多孔質構造の電極触媒層は、孔径の分布が広いのでできるだけ多く、好ましくは１００〜５００個の孔径の平均をとることが好ましい。
【００７３】
電極触媒層の三次元網目構造の空隙率は、１０〜９５％の範囲であることが好ましい。より好ましくは５０〜９０％の範囲である。ここで、空隙率とは、電極触媒層全体積から触媒−ポリマ複合体の占める体積を減じたものを、電極触媒層全体積で除した百分率（％）である。
【００７４】
三次元網目構造を有する電極触媒層の作製には、通常、触媒層を電極基材、プロトン交換膜、それ以外の基材に塗布した後に湿式凝固を行う。電極触媒層を単独で空隙率を求めることが困難な場合には、電極基材、プロトン交換膜、それ以外の基材の空隙率を予め求めておき、これら基材と電極触媒層とを含む空隙率を求めた後に、電極触媒層単独での空隙率を求めることも可能である。
【００７５】
三次元網目構造を有する電極触媒層は、空隙率が大きくガス拡散性や生成水の排出が良好であり、かつ電子伝導性やプロトン伝導性も良好である。従来の多孔化では、触媒粒子径や添加ポリマの粒子径を増大させたり、造孔剤を用いて空隙を形成するなどが行われているが、このような多孔化方式では触媒担持カーボン間やプロトン交換樹脂間の接触抵抗が電極触媒層に比べて大きくなってしまう。それに対して、湿式凝固法による三次元網目構造では、触媒担持カーボンを含んだポリマ複合体が三次元網目状になっているので、このポリマ複合体を電子やプロトンが伝導しやすく、さらに微多孔質構造のためガス拡散性や生成水の排出も良好な構造となっており、好ましいものである。
【００７６】
電極触媒層が三次元網目構造を有している場合においても、触媒や電子伝導体、イオン伝導体に用いられる物質は、従来と同様の物質を用いることが可能である。ただし、三次元網目構造を有する電極触媒層を作製する際には、湿式凝固法を用いることが好ましいため、この湿式凝固法に適したポリマの選択が好ましく、触媒粒子を良く分散し、かつ燃料電池内の酸化−還元雰囲気で劣化しないポリマが好ましい。このようなポリマとしては、フッ素原子を含むポリマが挙げられ、特に限定されるものではないが、たとえば、ポリフッ化ビニル（ＰＶＦ）、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（ＦＥＰ）、ポリパーフルオロアルキルビニルエーテル（ＰＦＡ）など、あるいはこれらの共重合体、これらのポリマを構成するモノマ単位とエチレンやスチレンなどの他のモノマとの共重合体（例えば、ヘキサフルオロプロピレン−フッ化ビニリデン共重合体等）、さらには、ブレンドなども好ましく用いることができる。
【００７７】
この中でも、ポリフッ化ビニリデン（ＰＶＤＦ）、ヘキサフルオロプロピレン−フッ化ビニリデン共重合体は、非プロトン性極性溶媒を溶解溶媒として用い、プロトン性極性溶媒などを凝固溶媒とする湿式凝固法により、三次元網目構造を有する触媒−ポリマ複合体が得られる点で、特に好ましいポリマである。
【００７８】
ポリマの溶媒としては、具体的には、Ｎ−メチルピロリドン（ＮＭＰ）、ジメチルホルムアミド（ＤＭＦ）、ジメチルアセトアミド（ＤＭＡＣ）、プロピレンカーボネート（ＰＣ）、ジメチルイミダゾリジノン（ＤＭＩ）などが挙げられ、凝固溶媒としては水や、メタノール、エタノール、イソプロパノールなどの低級アルコール類などのほか、酢酸エチルや酢酸ブチルなどのエステル類、芳香族系あるいはハロゲン系の種々の有機溶剤を挙げることができる。
【００７９】
触媒−ポリマ複合体のポリマとしては、上記のポリマに加えて、プロトン伝導性を向上させるためにプロトン交換基を有するポリマも好ましいものである。このようなポリマに含まれるプロトン交換基としては、スルホン酸基、カルボン酸基、リン酸基などがあるが特に限定されるものではない。また、このようなプロトン交換基を骨格中に含有するポリマも、特に限定されることなく用いられる。たとえば、フルオロアルキルエーテル側鎖とフルオロアルキル主鎖とから構成されるプロトン交換基を有するポリマが好ましく用いられる。具体的には、デュポン社製のナフィオンなどである。また、プロトン交換基を有する上述のフッ素原子を含むポリマや、エチレンやスチレンなどの他のポリマ、これらの共重合体やブレンドであっても構わない。
【００８０】
ナフィオンを用いた場合、市販のナフィオン膜を非プロトン性極性溶媒に溶かしても良いし、アルデリッチ社、デュポン社、あるいはイオンパワー社等から市販されている、水−メタノール−イソプロパノール、水−エタノール−イソプロパノール、水−エタノール−ｎプロパノールなどの含低級アルコール混合溶媒のナフィオン溶液を用いることも可能である。また、これらのナフィオン溶液を濃縮あるいは溶媒置換したものを用いても良い。この場合、湿式凝固の際の凝固溶媒は、ナフィオン溶液の溶媒種により適宜決められるべきものであるが、ナフィオン溶液の溶媒が非プロトン性極性溶媒である場合には、凝固溶媒としては水やアルコール類、エステル類のほか、種々の有機溶媒などが好ましく、水−メタノール−イソプロパノール混合溶媒などの低級アルコール溶媒の場合には、酢酸ブチルなどのエステル類、種々の有機溶媒が好ましく用いられる。
【００８１】
触媒−ポリマ複合体に用いられるポリマは、上記のフッ素原子を含むポリマやプロトン交換膜を含むポリマを共重合あるいはブレンドして用いることも好ましいものである。特にポリフッ化ビニリデン、ポリ（ヘキサフルオロプロピレン−フッ化ビニリデン）共重合体などと、プロトン交換基にフルオロアルキルエーテル側鎖とフルオロアルキル主鎖を有するナフィオンなどのポリマを、ブレンドすることは電極性能の点から好ましいものである。
【００８２】
触媒−ポリマ複合体の主たる成分は触媒担持カーボンとポリマであり、それらの比率は必要とされる電極特性に応じて適宜決められるべきもので特に限定されるものではないが、触媒担持カーボン／ポリマの重量比率で５／９５〜９５／５が好ましく用いられる。特に固体高分子型燃料電池用電極触媒層として用いる場合には、触媒担持カーボン／ポリマ重量比率で４０／６０〜８５／１５が好ましいものである。
【００８３】
触媒−ポリマ複合体には、種々の添加物を加えることもできる。たとえば、電子伝導性向上のための炭素などの導電剤や、結着性向上のためのポリマ、三次元網目構造の孔径を制御する添加物などがあるが、特に限定されることなく用いることができる。これら添加物の添加量としては、触媒−ポリマ複合体に対する重量比率として０．１〜５０％の範囲が好ましく、１〜２０％の範囲がさらに好ましい。
【００８４】
三次元網目構造を有する触媒−ポリマ複合体の製造方法としては、湿式凝固法によるものが好ましい。ここでは、触媒−ポリマ溶液組成物を塗布した後に、この塗布層をポリマに対する凝固溶媒と接触させて、触媒−ポリマ溶液組成物の凝固析出と溶媒抽出とを同時に行なうことができる。この触媒−ポリマ溶液組成物は、ポリマ溶液中に触媒担持カーボンが均一に分散したものである。触媒担持カーボンとポリマは前述のものが好ましく用いられる。ポリマを溶かす溶媒については、用いられるポリマに応じて適宜決められるべきもので、特に限定されるものではない。ポリマ溶液は触媒担持カーボンを良く分散していることが重要である。分散状態が悪い場合には、湿式凝固の際に、触媒担持カーボンとポリマとが複合体を形成することができず好ましくない。
【００８５】
触媒−ポリマ溶液組成物の塗布方法については、触媒−ポリマ溶液組成物の粘度や固形分などに応じた塗布方法が選択され、特に限定されるものではないが、ナイフコーター、バーコーター、スプレー、ディップコーター、スピンコーター、ロールコーター、ダイコーター、カーテンコーターなどの一般的な塗布方法が用いられる。
【００８６】
また、ポリマを湿式凝固させる凝固溶媒についても特に限定されるものではないが、用いられるポリマを凝固析出しやすく、かつポリマ溶液の溶媒と相溶性のある溶媒が好ましい。基材と凝固溶媒との接触方法についても、特に限定されるものではないが、凝固溶媒に基材ごと浸漬する、塗布層のみを凝固溶媒の液面に接触させる、凝固溶媒を塗布層にシャワリングあるいはスプレーする、などの方法を用いることができる。
【００８７】
この触媒−ポリマ溶液組成物が塗布される基材については、電極基材、あるいは高分子固体電解質の何れにおいても、塗布した後に湿式凝固を行うことが可能である。また、電極基材や高分子電解質以外の基材（たとえば転写基材）に塗布し、その後に湿式凝固を行い、三次元網目構造を作製した後に、この電極触媒層を電極基材や高分子固体電解質に転写あるいは挟持させても良い。この場合の転写基材としては、ポリテトラフルオロエチレン（ＰＴＦＥ）のシート、あるいは表面をフッ素やシリコーン系の離型剤処理したガラス板や金属板なども用いられる。
【００８８】
本発明の固体高分子型燃料電池においては、電極基材は特に限定されることなく公知のものを用いることが可能である。また、省スペース化のために電極基材が用いられない場合もある。
【００８９】
本発明に用いられる電極基材としては、電気抵抗が低く、集（給）電を行えるものであればとくに限定されることなく用いることが可能である。電極基材の構成材としては、たとえば、導電性無機物質を主とするものが挙げられ、この導電性無機物質としては、ポリアクリロニトリルからの焼成体、ピッチからの焼成体、黒鉛及び膨張黒鉛などの炭素材、ステンレススチール、モリブデン、チタンなどが例示される。
【００９０】
電極基材の導電性無機物質の形態は特に限定されず、たとえば繊維状あるいは粒子状で用いられるが、ガス透過性の点から繊維状導電性無機物質（無機導電性繊維）、特に炭素繊維が好ましい。無機導電性繊維を用いた電極基材としては、織布あるいは不織布いずれの構造も使用可能である。たとえば、東レ（株）製カーボンペーパーＴＧＰシリーズ、ＳＯシリーズ、Ｅ−ＴＥＫ社製カーボンクロスなどが用いられる。織布としては、平織、斜文織、朱子織、紋織、綴織など、特に限定されること無く用いられる。また、不織布としては、抄紙法、ニードルパンチ法、スパンボンド法、ウォータージェットパンチ法、メルトブロー法によるものなど特に限定されること無く用いられる。また編物であっても構わない。これらの布帛において、特に炭素繊維を用いた場合、耐炎化紡績糸を用いた平織物を炭化あるいは黒鉛化した織布、耐炎化糸をニードルパンチ法やウォータージェットパンチ法などによる不織布加工した後に炭化あるいは黒鉛化した不織布、耐炎化糸あるいは炭化糸あるいは黒鉛化糸を用いた抄紙法によるマット不織布などが好ましく用いられる。特に、薄く強度のある布帛が得られる点から不織布を用いるのが好ましい。
【００９１】
電極基材に炭素繊維からなる無機導電性繊維を用いた場合、炭素繊維としては、ポリアクリロニトリル（ＰＡＮ）系炭素繊維、フェノール系炭素繊維、ピッチ系炭素繊維、レーヨン系炭素繊維などが例示される。なかでも、ＰＡＮ系炭素繊維が好ましい。一般的に、ＰＡＮ系炭素繊維はピッチ系炭素繊維にくらべて圧縮強さ、引張破断伸度が大きく、折れにくいからである。折れにくい炭素繊維を得るためには、炭素繊維の炭化温度は２，５００℃以下が好ましく、２，０００℃以下がより好ましい。
【００９２】
本発明の固体高分子型燃料電池に用いられる電極基材に、水の滞留によるガス拡散・透過性の低下を防ぐために行う撥水処理、水の排出路を形成するための部分的撥水、親水処理や、抵抗を下げるために行われる炭素粉末の添加等を行うことも好ましい実施態様である。
【００９３】
本発明の固体高分子型燃料電池がｓｉｄｅ−ｂｙ−ｓｉｄｅ構造を有している場合、水素やメタノール水溶液などの燃料や空気の流入、水や二酸化炭素などの生成物の排出を促進するために、拡散層を設けることも好ましい実施態様である。このような拡散層は、前述の電極基材もその役割を持つが、非導電性布帛を拡散層として用いることがさらに好ましい。ここで、非導電性布帛の構成材としては、たとえば、非導電性繊維であれば特に限定されること無く用いられる。
【００９４】
拡散層の非導電性布帛を構成する非導電性繊維としては、たとえばポリテトラフルオロエチレン（ＰＴＦＥ）、テトラフルオロエチレン−ヘキサフルオロエチレン共重合体（ＦＥＰ）、テトラフルオロエチレン−パーフルオロアルキルビニルエーテル共重合体（ＰＦＡ）、テトラフルオロエチレン−エチレン共重合体（ＥＴＦＥ）、ポリフッ化ビニリデン（ＰＶＤＦ）、ポリフッ化ビニル（ＰＶＦ）、ポリクロロトリフルオロエチレン（ＣＴＦＥ）、塩素化ポリエチレン、耐炎化ポリアクリロニトリル、ポリアクリロニトリル、ポリエステル、ポリアミド、ポリエチレン、ポリプロピレンなどが使用可能である。これらの非導電性繊維の中でも、ＰＴＦＥ、ＦＥＰ、ＰＦＡ、ＥＴＦＥ、ＰＶＤＦ、ＰＶＦ、ＣＴＦＥなどのフッ素原子含有ポリマからなる繊維が、電極反応時の耐食性などの点から好ましいものである。
【００９５】
拡散層の非導電性布帛としては、織布あるいは不織布いずれの構造も使用可能である。織布としては、平織、斜文織、朱子織、紋織、綴織など、特に限定されること無く用いられる。また、不織布としては、抄紙法、ニードルパンチ法、スパンボンド法、ウォータージェットパンチ法、メルトブロー法など、特に限定されること無く用いられる。また編物であっても構わない。これらの布帛において、特に平織物、ニードルパンチ法やウォータージェットパンチ法などによる不織布、抄紙法によるマット不織布などが好ましく用いられる。特に多孔質で薄く強度のある布帛が得られる点から不織布が好ましく用いられる。
【００９６】
拡散層の非導電性布帛は、水の滞留によるガス拡散・透過性の低下を防ぐための撥水処理、水の排出路を形成するための部分的撥水あるいは親水処理等を行うことも好ましい実施態様である。さらには、熱処理、延伸、プレスなどの後処理を行うことも好ましい実施態様である。これらの後処理により、薄膜化、空隙率増加、強度増加などの効果が期待できる。
【００９７】
本発明の固体高分子型燃料電池においては、電極基材と電極触媒層の間に、少なくとも無機導電性物質と疎水性ポリマを含む導電性中間層を設けることが好ましい。特に、電極基材が空隙率の大きい炭素繊維織物や不織布である場合、導電性中間層を設けることで、電極触媒層が電極基材にしみ込むことによる性能低下を抑えることができる。
【００９８】
本発明の高分子固体電解質を、たとえば膜−電極複合体（ＭＥＡ）に用いる場合、高分子固体電解質膜に後加工した後にＭＥＡとすることが好ましい。例えば、燃料メタノールの透過をさらに低減するために、金属薄膜を高分子固体電解質に被覆することも好ましい態様である。このような金属薄膜の例としては、パラジウム、白金、銀などが挙げられる。
【００９９】
本発明の高分子固体電解質膜において、電極触媒層あるいは電極触媒層と電極基材を用いて膜−電極複合体（ＭＥＡ）とする際の作製方法は特に限定されるものではない。ホットプレスにより一体化することが好ましいが、その温度や圧力は、高分子固体電解質膜の厚さ、空隙率、電極触媒層や電極基材により適宜選択すればよい。通常、温度は４０℃〜１８０℃、圧力は１０ｋｇｆ／ｃｍ^２〜８０ｋｇｆ／ｃｍ^２が好ましい。
【０１００】
本発明の高分子固体電解質は、種々の電気化学装置に適用可能である。例えば、燃料電池、水電解装置、クロロアルカリ電解装置等が挙げられるが、中でも燃料電池がもっとも好ましい。さらに燃料電池のなかでも固体高分子型燃料電池に好適であり、これには水素を燃料とするものとメタノールなどの有機溶媒を燃料とするものがあり、特に限定されるものではないが、メタノールを燃料とするＤＭＦＣに特に好ましく用いられる。
【０１０１】
さらに、本発明の固体高分子型燃料電池の用途としては、特に限定されないが、移動体の電力供給源が好ましいものである。特に、携帯電話、パソコン、ＰＤＡなどの携帯機器、掃除機等の家電、乗用車、バス、トラックなどの自動車や船舶、鉄道などの移動体の電力供給源として好ましく用いられる。
【０１０２】
【実施例】
以下、本発明を実施例を用いて説明する。
【０１０３】
高分子固体電解質の評価方法および作製方法は次のとおりである。
【０１０４】
（１）高分子固体電解質膜の性能
高分子固体電解質膜のメタノール透過量、イオン伝導度を評価した。メタノール透過量は以下の方法で測定した。前記膜をエレクトロケム社製セルにセットし、片面に１ｍｏｌ／ｌメタノール水溶液を０．２ｍｌ／ｍｉｎで供給し、もう片面に空気を５０ｍｌ／ｍｉｎで供給した。排気された空気中のメタノール濃度を測定し、メタノール透過量を求めた。
【０１０５】
前記膜のイオン電導度は、インピーダンス法により測定した。まず一定の電極間距離を有するセルを用い、これに硫酸水溶液を満たし、電極間の硫酸水溶液の抵抗を求める。その後、電極間に前記膜を挟み、同様にして抵抗を求める。膜を介した時の抵抗値から硫酸水溶液のみの時の抵抗値を差し引き膜のみの抵抗が分かる。イオン伝導度は抵抗の逆数なるので先ほど求めた膜の抵抗から算出する。
【０１０６】
（２）電極の作製
炭素繊維クロス基材に２０％ＰＴＦＥ撥水処理を行ったのち、ＰＴＦＥを２０％含むカーボンブラック分散液を塗工、焼成して電極基材を作製した。この電極基材上に、Ｐｔ−Ｒｕ担持カーボンとＮａｆｉｏｎ溶液からなるアノード電極触媒塗液を塗工、乾燥してアノード電極を、また、Ｐｔ担持カーボンとＮａｆｉｏｎ溶液からなるカソード電極触媒塗液を塗工、乾燥してカソード電極を作製した。
【０１０７】
（３）固体高分子型燃料電池の作製及び評価
前記工程（１）の高分子電解質膜を、前記工程（２）で作製したアノード電極とカソード電極で夾持し加熱プレスすることで膜−電極複合体（ＭＥＡ）を作製した。このＭＥＡをセパレータに挟みアノード側に３％ＭｅＯＨ水溶液、カソード側に空気を流してＭＥＡ評価を行った。評価はＭＥＡに定電流を流し、その時の電圧を測定した。電流を順次増加させ電圧が１０ｍＶ以下になるまで測定を行った。各測定点での電流と電圧の積が出力となる。
【０１０８】
実施例１、比較例１、比較例２
実施例１として、アニオン性基を有するポリマとしてデュポン社製２０．５重量％ナフィオン（イオン交換当量：１．０ｍｅｑ）溶液（Ａ）と、−ＣＯＮＨ−基含有ポリマとしてナイロン６／ナイロン６６共重合体（カプロラクタム／ＡＨ塩＝４０／６０の共重合物）のエタノール１０％溶液（Ｂ）を重量比Ａ／Ｂ＝１０／１で混合しミキサーで撹拌した後、ポリエステルフィルム上に厚さ約１ｍｍコートした。次いで、熱風乾燥機中で１００℃で２０分間処理し溶媒を除去した後ポリエステルフィルムを剥がし厚さ１５０μｍの高分子固体電解質を作製した。
【０１０９】
比較例１として、アニオン性基を有するポリマとしてデュポン社製ナフィオン（イオン交換当量：１．０ｍｅｑ）２０．５％溶液（Ａ）のみを用いて、実施例１と同様の方法にてコート、乾燥を行い厚さ１４８μｍの高分子個体電解質膜を得た。
【０１１０】
比較例２として、アニオン性基を有するポリマとしてデュポン社製ナフィオン（イオン交換当量：１．０ｍｅｑ）２０．５％溶液（Ａ）と、ポリスチレン樹脂のジメチルホルムアミド１０％溶液（Ｂ２）を重量比Ａ／Ｂ２＝１０／１で混合し、実施例１と同様の方法にてコート、乾燥を行い厚さ１４５μｍの高分子個体電解質膜を得た。
【０１１１】
これらを用いて高分子固体電解質膜のＭＣＯ、イオン伝導度、およびＭＥＡでの出力を測定した。
【０１１２】
その結果、表１に示すように実施例１の高分子固体電解質膜は、ＭＣＯにおいて比較例１に比べて明らか低く、また、イオン伝導度は同程度を示した。ＭＥＡでの最高出力は８．３［ｍＷ／ｃｍ^２］を示した。また、３０日間その性能を追跡したところ、初期は実施例１および比較例１および比較例２とも上昇するが、実施例１が３０日間最高出力を維持するのに対して、比較例１および比較例２は２０日経過したころから明らかな低下が認められた。一方、実施例１はこの出力を安定して維持した。
【０１１３】
実施例２、比較例３
実施例２としてアニオン性基ポリマとしてスルホン化ポリフェニレンスルフィドスルホン（ＰＰＳＳ）（イオン交換当量：２．０ｍｅｑ）の２０％ＤＭＦ溶液（Ｃ）を使用し、−ＣＯＮＲ−含有ポリマとして帝国化学産業製のメトキシメチル化ポリアミドのエタノール２０％溶液（Ｄ）を重量比Ｃ／Ｄ＝９０／１０で混合しミキサーで撹拌した後、ポリエステルフィルム上に厚さ約１ｍｍコートした。次いで、熱風乾燥機中で１００℃で２０分間処理し溶媒を除去し、ポリエステルフィルムを剥がして厚さ１４１μｍの高分子固体電解質を作製した。実施例１と同様にして高分子固体電解質膜およびその膜を用いてＭＥＡを作製し評価した。
【０１１４】
比較例３として、（Ｃ）のみを用いて同様の方法にて１３５μｍの高分子固体電解質膜を作製した。その結果は表１に示すように、実施例２は比較例３に比べてＭＣＯが明らかに低く、イオン伝導度も若干高い性能を示した。
【０１１５】
実施例３
アニオン性基を有するポリマとしてデュポン社製２０．５重量％ナフィオン（イオン交換当量：１．０ｍｅｑ）ポリマー溶液（Ａ）と、−ＣＯＮＨ−含有ポリマには、珪酸塩層状物としてモンモリロナイトを用い、ＮＨ_２Ｃ_１１Ｈ_２２ＣＯＯＨを用いて、イオン交換されたモンモリロナイト有機複合物をε−カプロラクタム／ＡＨ塩＝４０／６０中に添加重合せしめる製造方法にて分散複合体（珪酸塩層状物含量１２重量％）を作り、そのエタノール２０％溶液（Ｅ）を重量比Ａ／Ｅ＝９０／１０で混合しミキサーで撹拌した後、ポリエステルフィルム上に厚さ約１ｍｍコートした。次いで、熱風乾燥機中で１００℃で２０分間処理し溶媒を除去し、ポリエステルフィルムを剥がして厚さ約１４３μｍの高分子固体電解質膜を作製した。かかる高分子固体電解質膜およびその膜を用いてＭＥＡを作製し評価した。その結果は、表１に示すように、実施例３の膜はＭＣＯが比較例１に比べて明らかに低く、また、ＭＥＡに組み込んでから３０日後にＭＥＡを解体して膜状態を調べたところ、実施例３の膜は脆化がほとんど認められなかったのに対し、比較例１の膜はかなりの脆化しており、両者間には耐久性の面で差が認められた。
【０１１６】
実施例４、比較例４
実施例４として、シリコンウエハ上にネガ型感光性ポリイミドをスピンコート法にて塗工、１１０℃にてプリベークした。これに、フォトマスクをかけて露光し、現像、水洗後、３５０℃にてフルベークを行った。これをフッ酸溶液に浸漬してシリコンウエハから剥がして多孔性ポリイミドフィルムを得た。得られた多孔性ポリイミドフィルムの外形寸法が８ｃｍ×８ｃｍ角、厚さが１０μｍで、中央の多孔部は外形寸法が２．２ｃｍ×２．２ｃｍ角であり、多孔部の周囲は非多孔部である。多孔部においては孔径ｄが約１２μｍの貫通した孔が空いており、貫通孔の中心間隔は約３３μｍ、開孔率は約１１％、貫通孔の個数は約４４２，０００個であった。
【０１１７】
該工程にて作成した多孔性フィルムを実施例１の高分子固体電解質溶液に浸漬、乾燥し、貫通孔内に実施例１の高分子固体電解質が充填された多孔性ポリイミドフィルムからなる高分子電解質膜を作製した。膜厚さは３３μｍであった。
【０１１８】
比較例４として、上記多孔性ポリイミドフィルムを比較例１の高分子固体電解質溶液に浸漬、乾燥し、貫通孔内に比較例１の高分子固体電解質を充填し、高分子固体電解質膜を作製した。また、実施例１と同様の工程および方法にてＭＥＡを作製し評価を行った。
【０１１９】
その結果、実施例４は比較例４に比べて、膜でのＭＣＯが低く、また、ＭＥＡでの出力は３０日間低下することなく安定していた。
【０１２０】
【表１】

【０１２１】
【発明の効果】
本発明によれば、クロスオーバーを抑制し、長時間安定した高出力を達成できる新規な高分子電解質およびそれを用いた高性能な固体高分子型燃料電池を提供でき、その実用性は高い。
【図面の簡単な説明】
【図１】本発明の高分子固体電解質膜の１例を示す斜視模式図である。
【図２】本発明の高分子固体電解質膜の１例において多孔部１を拡大した平面模式図である。
【図３】本発明の高分子固体電解質膜に好適に用いられる多孔が整然と配列された多孔基材の例を示す走査型電子顕微鏡写真である。
【図４】本発明の高分子固体電解質を用いたｓｉｄｅ−ｂｙ−ｓｉｄｅ構造の高分子固体電解質膜の斜視模式図である。
【図５】本発明の高分子固体電解質を用いたｓｉｄｅ−ｂｙ−ｓｉｄｅ構造の燃料電池の製造プロセスの一部を示す断面模式図である。
【符号の説明】
１：多孔部
２：非多孔部
３：孔
４：膜導電部
５：膜貫通電子伝導部
６：プロトン伝導部（高分子固体電解質部）
７：電極
ｄ：孔径
Ｌ：隣り合う貫通孔の中心間隔[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a solid polymer electrolyte and a solid polymer fuel cell using the same.
[0002]
[Prior art]
A fuel cell is a power generation device that emits little, has high energy efficiency, and has a low burden on the environment. For this reason, they have been spotlighted again in recent years as global environmental protection has increased. Compared with the conventional large-scale power generation facilities, the power generation apparatus is expected to be a relatively small-scale distributed power generation facility and a power generation apparatus for mobile objects such as automobiles and ships in the future. In addition, it is attracting attention as a power source for small mobile devices and portable devices, and is expected to be mounted on mobile phones and personal computers instead of secondary batteries such as nickel-metal hydride batteries and lithium ion batteries.
[0003]
In a polymer electrolyte fuel cell, in addition to a conventional polymer electrolyte fuel cell (hereinafter referred to as PEFC) using hydrogen gas as a fuel, a direct methanol fuel cell (hereinafter referred to as DMFC) directly supplying methanol is used. Have been noted. DMFCs have lower output than conventional PEFCs, but have the advantage of higher energy density and longer usage time of portable devices per charge because the fuel is liquid and no reformer is used. is there.
[0004]
In a fuel cell, an anode and a cathode, in which a reaction responsible for power generation takes place, and an electrolyte membrane serving as an ion conductor between the anode and the cathode constitute a membrane-electrode assembly (MEA). The sandwiched cell is configured as a unit. Here, the electrode is composed of an electrode base material (also referred to as a gas diffusion electrode or a current collector) for promoting gas diffusion and collecting (supplying) electricity, and an electrode catalyst layer which actually serves as an electrochemical reaction field. ing. For example, in the anode electrode of a polymer electrolyte fuel cell, a fuel such as hydrogen gas reacts in the catalyst layer of the anode electrode to generate protons and electrons, the electrons are conducted to the electrode substrate, and the protons are converted to the polymer solid electrolyte. Conduct. Therefore, the anode electrode is required to have good gas diffusivity, electron conductivity, and ion conductivity. On the other hand, in the cathode electrode, an oxidizing gas such as oxygen or air is reacted in a catalyst layer of the cathode electrode with a proton conducted from the polymer solid electrolyte and an electron conducted from the electrode substrate to produce water. For this reason, in the cathode electrode, it is necessary to efficiently discharge generated water in addition to gas diffusion, electron conductivity, and ion conductivity.
[0005]
Among solid polymer fuel cells, a DMFC using an organic solvent such as methanol as a fuel is required to have different performance from a conventional PEFC using hydrogen gas as a fuel. That is, in DMFC, at the anode electrode, a fuel such as an aqueous methanol solution reacts in the catalyst layer of the anode electrode to generate protons, electrons, and carbon dioxide, the electrons conduct to the electrode base material, and the protons conduct to the polymer solid electrolyte. Carbon dioxide passes through the electrode substrate and is released out of the system. For this reason, in addition to the required characteristics of the anode electrode of the conventional PEFC, fuel permeability such as an aqueous methanol solution and carbon dioxide emission are also required. Furthermore, in the cathode electrode of the DMFC, in addition to the same reaction as that of the conventional PEFC, a reaction in which oxidizing gas such as methanol and oxygen or air permeating the electrolyte membrane generates carbon dioxide and water in the catalyst layer of the cathode electrode. Occur. For this reason, the amount of generated water is larger than that of the conventional PEFC, and it is necessary to discharge water more efficiently.
[0006]
As described above, the DMFC has a problem that a fuel crossover occurs in which methanol as a fuel permeates the polymer solid electrolyte, and thus the battery output and energy efficiency are reduced. In order to prevent crossover of the polymer solid electrolyte, measures to reduce the methanol concentration supplied to the anode include a new polymer electrolyte that is different from the conventional perfluoro-based proton exchange membrane. Polymer solid electrolytes into which groups have been introduced are exemplified. Further, there may be mentioned a method of devising a polymer electrolyte membrane structure. As a countermeasure for crossover by devising a polymer electrolyte membrane structure, there is a polymer electrolyte membrane that suppresses swelling of the proton exchanger by filling a through-hole with a proton exchange resin as an ion conductor, thereby suppressing crossover ( Patent Documents 1 and 2), and an ion conductive polymer membrane for a fuel cell made of an aromatic polyamide containing a protonic acid group as an example using a polyamide (Patent Document 3).
[0007]
[Patent Document 1]
US Patent Specification No. 5,631,099
[0008]
[Patent Document 2]
U.S. Pat. No. 5,759,712
[0009]
[Patent Document 3]
JP 2002-280019 A
[0010]
[Problems to be solved by the invention]
Conventionally, a perfluoro-based proton exchange membrane has been used as a solid polymer electrolyte. However, this is environmentally unfavorable because fluorine is used, and the cost is extremely high. Further, as described above, the DMFC has a problem that fuel permeation of methanol is large and cell output and energy efficiency are reduced. Examples of the non-fluorinated polymer solid electrolyte include a polymer solid electrolyte obtained by introducing an ionic group into many engineering plastics such as polyetheretherketone and polysulfone. However, these polymer solid electrolytes easily take in free water into the inside, and large clusters of water were formed, and a sufficient methanol crossover suppressing effect could not be obtained. In addition, the amount of free water taken in varies every moment due to environmental changes such as temperature and humidity, fuel concentration, and aging, and the battery output becomes unstable, and there is also a problem in durability. On the other hand, the amount of ion-exchange groups may be reduced in order to suppress the incorporation of free water, but in this case, the ion conductivity is reduced.
[0011]
The present invention solves the above problems, has a high ionic conductivity, suppresses methanol crossover, and is capable of achieving a stable and high output for a long time, a novel polymer electrolyte and a high-performance solid electrolyte using the same. It is an object to provide a molecular fuel cell and the like.
[0012]
[Means for Solving the Problems]
The present invention has the following configuration to solve the above problems. That is, it is a mixture containing at least a polymer having an anionic group and a polymer having a -CONH- group or -CONR- (R is an alkoxy group) in a main chain. Further, a polymer electrolyte fuel cell of the present invention is characterized by being constituted by using the polymer solid electrolyte of the present invention or a polymer solid electrolyte membrane obtained by using the same.
[0013]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, preferred embodiments of the present invention will be described.
[0014]
In the polymer solid electrolyte of the present invention, the polymer chain having an anionic group is bound by a polymer having a -CONH- group or a -CONR- group (R is an alkoxy group) in the main chain, and It is possible to control the intake of free water into the water and suppress the swelling due to the aqueous methanol solution, reduce the methanol crossover, and suppress the decrease in membrane strength. In addition, it is possible to exhibit stable performance for a long time against environmental changes due to temperature, humidity and aging.
[0015]
Although such an effect is not necessarily clear, the inventors of the present invention depend on the strong traction existing between the anionic group of the solid polymer electrolyte and the -CONH- or -CONR- group (R is an alkoxy group). Estimated. That is, the present invention utilizes the intermolecular attraction between the two polymers, and a polymer having a -CONH- group or a -CONR- group (R is an alkoxy group) is used in the form of water or It acts on the anionic groups of the anionic group polymer to take in the aqueous methanol solution to restrict its movement. Further, a -CONH- group or a -CONR- group (R is an alkoxy group) is present in the main chain of the polymer, and restricts the movement of the anionic group and the molecular chain in a molecular chain unit. As described above, the present invention comprises a polymer having at least two or more different chains, one of which is a polymer having an anionic group that contributes to ion conductivity, and the other is a -CONH- group or -CONR- It has a group (R is an alkoxy group) and plays a role of restricting and controlling the movement of the anionic group. That is, a polymer in which a -CONH- or -CONR- group (R is an alkoxy group) is present in the molecule of the anionic group polymer, or an ion in the -CONH- or -CONR- group (R is an alkoxy group) polymer This is due to a mechanism different from the restriction due to so-called intramolecular attraction such as those having a functional group, and the restriction when other polymers are present in the side chain. It is very different. Accordingly, Japanese Patent Application Laid-Open No. 2002-280019 discloses an ion conductive polymer membrane for a fuel cell made of an aromatic polyamide containing a protonic acid group. However, this membrane has both groups in the molecule. The configuration and the effect are completely different from this proposal.
[0016]
The polymer having an anionic group in the solid polymer electrolyte of the present invention is not particularly limited, and a polymer having an anionic group such as a sulfonic acid group, a phosphonic acid group, a phosphoric acid group, and a carboxylic acid group is used. . Among them, those containing a sulfonic acid group which contributes to ion conductivity and has strong intermolecular attraction with a -CONH- group or -CONR- group (R is an alkoxy group) and an alkali metal salt thereof are preferably used. Can be
[0017]
Examples of the polymer having an anionic group in the present invention are obtained by introducing an anionic group into a general polymer, but are not particularly limited. Polytetrafluoroethylene (PTFE: abbreviations are described in parentheses below), polytetrafluoroethylene-perfluoroalkyl ether copolymer (PFA), polytetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoro Fluorine-containing resins such as ethylene-ethylene copolymer (ETFE), polyvinylidene fluoride (PVDF), polyimide (PI), polyphenylene sulfide sulfone (PPSS), polysulfone (PSF), polyphenylene sulfide (PPS), polyphenylene oxide ( Heat- and oxidation-resistant polymers such as PPO), polyetherketone (PEK), polyetheretherketone (PEEK), and polybenzimidazole (PBI), and polyphosphazene (PPho). Those with is preferably used. Further, Nafion (manufactured by DuPont) having a PTFE main chain and a side chain of polyperfluoroalkyl ether sulfonic acid is preferably used. The equivalent of the anionic group in the polymer has an ion exchange equivalent of at least 0.5 meq, preferably at least 0.8 meq, particularly preferably at least 1.0 meq in order to obtain high ionic conductivity.
[0018]
Examples of the anionic group include a carboxyl group, a sulfonyl group, a phosphonic acid group, and a phosphinic acid group. ₃ H group or SO ₃ Preferably, it is an X group (X is an alkali metal).
[0019]
Among the above polymers, polyphenylene sulfide sulfone represented by the following formula (1), polyphenylene sulfide represented by the following formula (2), polyphosphazene represented by the following formula (3), polyimide represented by the following formula (4), And polybenzimidazole, polysulfone and the like are particularly preferably used.
Equation (1)
[0020]
Embedded image

[0021]
Equation (2)
[0022]
Embedded image

[0023]
Equation (3)
[0024]
Embedded image

[0025]
Equation (4)
[0026]
Embedded image

[0027]
(Where Z is an organic group containing an aromatic ring, n is the number of repeating units, R1 and R2 indicate organic groups, and R1 and R2 may be the same or different.
[0028]
As the polymer having a —CONH— group or a —CONR— group (R is an alkoxy group) in the main chain, a polymer having such a group can be applied and is not limited. For example, polymerization represented by the following chemical formula or copolymerization thereof may be used. Polymers and mixtures are preferably used. In addition, alkoxy polyamides, mixtures thereof, and copolymers and mixtures with the above polymers are also preferably used, and particularly, a mixture of the above-described polyamide and alkoxy polyamide is preferable.
[0029]
Embedded image

[0030]
(N is the degree of polymerization)
The polymer having a -CONH- group or a -CONR- group (R is an alkoxy group) enhances the traction with an anionic group, and from the viewpoint of enhancing the effect of the present invention, an aliphatic group is an aromatic group. Preferred over those. Further, in order to facilitate the mixing with the anionic group polymer, the polymerization degree is preferably lower than that of a general polyamide, and the polymerization degree is preferably about 200 or less. It is particularly preferred that it is 150 or less. With a degree of polymerization in this range, many of the polymer species can be dissolved in solvents such as pentanol, butanol, propanol, ethanol, and methanol. It is effective to use the copolymer as a solution, and it is effective to use a copolymer of caprolactam and an AH salt (abbreviation of hexamethylenediamine and adipic acid in a ratio of 1: 1) (nylon 6/66). Copolymer), nylon 6/12 copolymer, and nylon 66/610/6 copolymer are preferred examples. Alkoxy polyamides are easily used because they are easily soluble in alcohols. Although not particularly limited, a preferred example of the alkoxy polyamide is methoxymethyl polyamide.
[0031]
The mixing ratio of the polymer having an anionic group and the polymer of -CONH- group or -CONR- group (R is an alkoxy group) in the main chain depends on the type of both polymers, the ion exchange equivalent of the anionic group polymer, the -CONH- group or In a -CONR- group (R is an alkoxy group) polymer, it is generally preferably 2 to 20% by weight on a solid basis, though it depends on the equivalent of the group and the like. Further, the content is more preferably 5 to 15%. If the content is too small, the binding property is insufficient, and if it is too high, the ionic conductivity of the anionic group polymer and the output are impaired, which is not preferable.
[0032]
In the present invention, another notable invention includes a silicate layered material as a polymer having a -CONH- group or a -CONR- group (R is an alkoxy group) in a main chain thereof, and a layer containing the silicate layer. It is preferable that the polymer be present so that the polymer is present (this condition is called a silicate layered polymer composite). By satisfying such requirements, it is possible to further enhance the effect of the present invention. The heat resistance, water resistance, mechanical strength and dimensional stability of the polymer electrolyte can be remarkably improved. This is because the silicate layer is micro-dispersed in a state where a part of a polymer having a -CONH- group or -CONR- group (R is an alkoxy group) in the main chain is present between the layers of the silicate layer. This is a silicate layered material-dispersed polymer composite. Examples of the silicate layered material include montmorillonite, beidellite, nontronite, saponite, hectorite, and sauconite. Among them, montmorillonite or saponite is preferably used. An example of a preferred method for producing such a silicate layered polymer composite is as follows. Of course, it is not limited to this method.
[0033]
(1) A cation of an organic compound having a carboxyl group and having an alkyl chain having 10 or more carbon atoms, such as 12-aminododecanoic acid and 14-aminotetradecanoic acid, is allowed to act on the silicate layered material, and After adsorbing between layers of the product, mixing with a desired polyamide-forming monomer, and polymerizing and precipitating at least a part of the monomer between the layers of the silicate layered product.
[0034]
(2) An organic ion of a lactam such as ε-captolactam or a polyamide monomer such as 6-amino-n-caproic acid is allowed to act on the silicate layered product, and the resulting mixture is ion-exchanged with the organic ions. A method of mixing and polymerizing and depositing at least a part of the monomer between layers of the silicate layered material.
[0035]
By such a method, the silicate layered material can be micro-dispersed in the polyamide. Here, the silicate layered material may be in a state in which the layers are expanded and dispersed one by one, or may be in a state where the layers are expanded but a plurality of layers are dispersed.
[0036]
The ratio of the silicate layer material to the polyamide in the silicate layer material-dispersed polymer composite is preferably 0.1 to 50% by weight, particularly preferably 1 to 20% by weight. If the proportion of the silicate layered material is too large, the mechanical strength and flexibility may be reduced. If the amount is less than the above range, it is difficult to obtain features.
[0037]
In a method of mixing a polymer having an anionic group and a polymer having a -CONH- group or a -CONR- group (R is an alkoxy group) in a main chain, it is preferable that both components are uniformly mixed. The mixture is mixed by a conventionally known mixer such as a screw, a blender, a mill, a Banbury mixer, a homogenizer, and a kneader. In addition, the form of both components in the polymer solid electrolyte is determined by the combination of the two components, such that the two components are in contact with each other at the interface, the two components have a composite layer, or the two components are compatible on a molecular level. May exist in any form.
[0038]
Further, in the above mixture, for the purpose of increasing the amount, stabilization, plasticization, heat resistance, etc., as further polymer or organic or inorganic filler, calcium carbonate, silica powder, mica, carion, diatomaceous earth, clay , Talc, dolomite, etc. may be included.
[0039]
Although a remarkable effect can be obtained by using the polymer solid electrolyte of the present invention in its own membrane state (film-like one), it is also possible to fill the solid polymer electrolyte into a membrane-like porous substrate. Yes, the solid polymer electrolyte membrane thus obtained can further suppress deformation due to swelling, and is a preferred embodiment for reducing methanol crossover and maintaining stable performance for a long time, which are the objects of the present invention. The shape of the porous substrate is not particularly limited, and one having a plurality of holes is exemplified, but a porous substrate having a plurality of independent through holes or a three-dimensional network structure in a thickness direction is preferable. .
[0040]
Further, it is more preferable that the porous substrate has through holes arranged in a planar direction. Here, "the through-holes which are arranged neatly in the plane direction" indicate a state in which the through-holes are arranged at substantially equal intervals or regularly. Specifically, when the center intervals of adjacent through holes are compared with each other, the arrangement state is such that the difference between the center intervals falls within a range of 100% or less. That is, since the through-holes are two-dimensionally arranged on the surface of the porous base material, adjacent through-holes exist in the upper, lower, left, and right directions, but the difference between the centers of the adjacent through-holes is within 100%. Must be arranged in It is preferably within 50%, more preferably within 30%. Further, even when the difference between the center distances of adjacent through holes exceeds 100%, the center distance between the adjacent through holes in each array is a regular arrangement in which a combination of a certain number is repeated. Is preferably used as long as the error is within 100%.
[0041]
As a specific example of the porous substrate used in the present invention, the shape shown in FIG. FIG. 1 is a schematic perspective view showing an example of the polymer solid electrolyte membrane of the present invention. The porous substrate of FIG. 1 has a porous portion 1 having a large number of holes at the center, and a non-porous portion 2 having no holes around the porous portion. FIG. 2 shows an enlarged schematic diagram of the porous portion. In the solid polymer electrolyte membrane of the present invention, it is preferable that the holes 3 of the porous portion are arranged at regular intervals at regular intervals as viewed in a plane direction as shown in FIG. L in FIG. 2 is the above-mentioned “center distance between adjacent through holes”. L is preferably in the range of 0.5 to 100 μm, and particularly preferably in the range of 1 to 50 μm. Further, the inner diameter d of the hole is preferably in the range of 0.5 to 50 μm, and particularly preferably in the range of 1 to 20 μm.
[0042]
In FIG. 1, the porous portion 1 is filled with the polymer solid electrolyte of the present invention to exhibit a function as a polymer solid electrolyte membrane. Further, by filling the holes 3 in FIG. 2, swelling is suppressed, and crossover in which methanol of fuel permeates from the anode to the cathode is reduced. However, if the holes 3 are arranged in an orderly manner, the holes are opened. Rate can be increased, and ionic conductivity is improved.
[0043]
As a preferable method for producing the porous substrate used in the polymer solid electrolyte membrane of the present invention, for example, a processing method of photolithography can be applied. Conventionally, as a porous substrate, a filter material for filtration having a through hole has been used. This is generally a method in which a polymer film is irradiated with ions to break a polymer chain, and holes are formed by a chemical etching method using an alkali solution or the like (track etching method). On the other hand, in the hole 3 using the photolithography method, the hole diameter, the shape, the space between the holes, the portion to be made porous, and the like can be arbitrarily set, and the performance of the fuel cell is improved by reducing the crossover. Can be. Furthermore, since photolithography is excellent in microfabrication, it is possible to finely separate the porous portion 1 and the non-porous portion 2, which results in excellent miniaturization of the fuel cell. Further, cost reduction can be achieved by improving productivity as compared with the conventional track etch method.
[0044]
Here, a scanning electron microscope (SEM) photograph of the porous substrate manufactured by using the photolithography method is shown in FIG. As shown in FIG. 3, it is clear that the holes of the porous substrate formed by the photolithography method are regularly arranged at equal intervals.
[0045]
The cross-sectional shape of the holes in the porous substrate produced by photolithography is not particularly limited, but is preferably a circle, an ellipse, a square, a rectangle, a rhombus, a trapezoid, or the like. Among them, a circle or an ellipse is preferable from the viewpoint of easy filling of the solid polymer electrolyte and suppression of swelling. The size and spacing of the holes are not particularly limited, and may be determined as appropriate based on the ease of filling the solid polymer electrolyte, battery performance, and the like.
[0046]
The size of the entire porous portion in the porous substrate manufactured using the photolithography method may be determined according to the size of the electrode catalyst layer or the electrode substrate to be used. Also, the thickness of the porous substrate may be determined based on the required battery performance, but is usually preferably in the range of 1 to 50 μm, and particularly preferably in the range of 5 to 30 μm.
[0047]
Although the detailed method of the photolithography method used in the present invention is not particularly limited, for example, a photosensitive polymer is coated on a substrate, exposed with a photomask, and after development, the polymer is dissolved to form a hole. And a method of peeling it from the substrate to obtain a porous polymer film is used. The photosensitive polymer may be either a negative type or a positive type, but can be appropriately selected according to the required pore size, pore interval, fuel cell performance, and the like. The substrate material is determined in terms of adhesion to the polymer and ease of peeling, and a silicon wafer or an aluminum plate is preferably used, but is not particularly limited. Exposure may be either reduction exposure or 1: 1 exposure, but may be determined as appropriate depending on the size of the electrolyte to be produced, the size, shape, interval, etc. of the holes. In addition, conditions such as development, dissolution, and peeling from the substrate may be appropriately selected depending on the properties of the polymer. It is also possible to apply a non-photosensitive polymer on the substrate in advance, apply a photoresist thereon, expose, develop, and create voids by dissolving the polymer.
[0048]
The photosensitive or non-photosensitive polymer used in the photolithography method used in the present invention is not particularly limited, but polyimide is preferably used in view of workability by photolithography, oxidation resistance of the polymer, strength, and the like. .
[0049]
As a specific method of forming a porous film by a photolithography method using polyimide, for example, a polyamic acid solution of a precursor is applied to a substrate, and after removing the solvent by drying at about 100 ° C., a photomask is used. After forming holes by performing photolithography processing such as exposure, development, and alkali treatment, an imide ring-closing reaction is performed at about 300 ° C. or higher, and finally, a method of obtaining a porous polyimide film by peeling off from the substrate. The temperature and time for the solvent removal and the imide ring closure reaction can be appropriately determined depending on the type of the polyimide used. When the polyimide film is peeled off from the substrate, the substrate is usually immersed in an acid. However, hydrofluoric acid is preferably used when the substrate used is a silicon wafer, and hydrochloric acid is preferably used when the substrate is an aluminum plate.
[0050]
Here, the polyimide used in the present invention may be either a negative type or a positive type photosensitive polyimide, or a non-photosensitive polyimide, but is sensitive to the pore size, shape, interval, film thickness, etc. Is preferred, and negative photosensitive polyimide is more preferred.
[0051]
The polymer used for the porous substrate used in the present invention is not particularly limited, but is preferably polyimide (PI), polyvinylidene fluoride (PVDF), polyphenylene sulfide sulfone (PPSS), polytetrafluoroethylene (PTFE), Polysulfone (PSF) or the like, or a copolymer thereof, a copolymer with another monomer (eg, a hexafluoropropylene-vinylidene fluoride copolymer), or a blend can also be used. These polymers are preferable from the viewpoints of oxidation resistance, strength, ease of wet solidification, and the like.
[0052]
The method for filling the porous solid substrate with the polymer solid electrolyte of the present invention is not particularly limited. For example, by filling or immersing a polymer having an anionic group into a solution as a solution on a porous base material, it becomes possible to fill the gap. It is also preferable to use ultrasonic waves or to reduce the pressure in order to facilitate the filling into the voids, and it is preferable to use them at the time of coating or immersion because the filling efficiency is further improved. Further, a method may be employed in which a monomer, which is a precursor of a polymer having an anionic group, is filled in the gap and then polymerized in the gap, or plasma polymerization is performed by vaporizing the monomer.
[0053]
In the present invention, the form of the fuel cell and the method for manufacturing the fuel cell are not particularly limited. Hereinafter, a method using a photolithography method for producing a fuel cell having a side-by-side structure will be described in detail. Here, the side-by-side structure refers to a structure in which two or more cells including a pair of opposed electrodes are arranged in a plane direction of a single solid polymer electrolyte membrane surface. According to this structure, the cells are connected in series by connecting the anodes and cathodes of two or more adjacent cells with an electron conductor penetrating the polymer solid electrolyte membrane, so that side-by-side The cross section of the solid polymer electrolyte membrane having the structure has a structure in which proton conducting parts and electron conducting parts are present alternately. In order to manufacture such a structure, it is preferable to use a photolithography method from the viewpoint of miniaturization and productivity.
[0054]
The ionic conductivity of the polymer solid electrolyte membrane obtained according to the present invention can be measured by an impedance method. Specifically, it is measured by a method described in “(Continued) Electrochemical Measurement Method” published by the Institute of Electrochemical Society. The methanol permeability of the polymer solid electrolyte membrane is determined by arranging an aqueous methanol solution and pure water or a gas through the polymer solid electrolyte membrane, and determining the moving speed of methanol to the pure water or the gas. In the present invention, the measurement was specifically performed by the following method. The membrane was set in a cell manufactured by Electrochem, and a 1 mol / l aqueous methanol solution was supplied at 0.2 ml / min to one side, and air was supplied at 50 ml / min to the other side. The methanol concentration in the exhausted air or the concentration of its decomposition product was measured, and the methanol permeation rate and permeation amount were determined.
[0055]
An example of the side-by-side structure is shown in FIGS. FIG. 4 is a schematic perspective view of the polymer solid electrolyte membrane of the present invention having a side-by-side structure, and FIG. 5 is a schematic cross-sectional view showing a part of the manufacturing process. Although FIGS. 4 and 5 illustrate an example in which two cells are arranged horizontally, three or more cells can be arranged in a planar direction with a similar side-by-side structure. . The following description is made with two cells for simplicity. In FIG. 5, in the proton conductive portion, the porous portion 1 is filled with a proton conductor (not shown), and in the electron conductive portion, the membrane conductive portion 4 is filled with an electron conductor. Portions other than the porous portion 1 of the proton conducting portion and the membrane conducting portion 4 of the electron conducting portion are non-porous portions 2 through which protons and electrons do not conduct, and are dense polymer films. For producing a polymer film having such a complicated and fine structure, the photolithography method described in the present invention is suitably used. The porous substrate shown in FIG. 4 is prepared by a photolithography method, and this is used as a polymer solid electrolyte membrane by the method illustrated in FIG. In FIG. 5, the proton conductor is filled with the proton conductor after the transmembrane electron conductor is filled with the electron conductor in advance. However, the order may be reversed. Alternatively, a proton conductor may be filled to form a proton conductor, then an electrode may be provided, and finally, an electron conductor may be formed.
[0056]
The above-described side-by-side structure of the electron conducting portion has a structure penetrating the electrolyte membrane. Here, a portion penetrating the electrolyte membrane as an electron conducting portion is referred to as a membrane conducting portion. The membrane conductive part has a function different from that of the porous part for filling the proton conductor. The size, shape, and the like of the film conductive portion are not particularly limited. The larger the film conductive part, the lower the electric resistance of the cells and the higher the voltage in series can be expected. However, the larger the membrane conductive part, the higher the possibility that an organic solvent such as hydrogen or methanol on the anode side leaks to the cathode side, or the possibility that air on the cathode side leaks to the anode side, which may cause performance degradation. is there. For this reason, it is preferable to determine the size and shape of the film conductive part in consideration of the electric resistance and leak resistance of the electron conductor used for the electron conductive part. Note that the electron conducting portion may pass through the outside without penetrating the polymer solid electrolyte membrane.
[0057]
The electron conductor of the film conductor 4 is not particularly limited, but a conductive paste is preferably used. As the conductive paste, one in which a conductive agent such as carbon, silver, nickel, copper, platinum, and palladium is dispersed in a polymer can be preferably used, and both a reduction in electronic resistance and an improvement in leak resistance can be achieved. In DMFCs in particular, it is important to prevent the leakage of methanol. In addition to general-purpose conductive pastes in which carbon or silver is dispersed in silicone resin, polyester, epoxy resin, etc., carbon black, silver, platinum, etc. are dispersed in PVDF or polyimide. The conductive paste is also preferably used. The electron conducting portion 5 is electrically connected to the electrode base material or the electrode catalyst layer of the cell, and a conductive paste is preferably used also for reducing the contact resistance.
[0058]
Further, a metal foil or a metal wire of nickel, stainless steel, aluminum, copper, or the like may be used as the electron conducting portion 5. It is also possible to combine these metal foils and metal wires with a conductive paste.
[0059]
The polymer solid electrolyte of the present invention is used in a polymer electrolyte fuel cell as a membrane-electrode composite (MEA) in combination with an electrode 7 composed of an electrode substrate and an electrode catalyst layer.
[0060]
The electrode catalyst layer of the electrode 7 in the polymer electrolyte fuel cell of the present invention is not particularly limited, and a known one can be used. The electrode catalyst layer refers to a layer that contains a catalyst and an electrode active material (refer to a substance that oxidizes or reduces) necessary for an electrode reaction, and further contains a substance that contributes to electron conduction and ion conduction that promotes the electrode reaction. Further, when the electrode active material is a liquid or gas, it is necessary that the electrode active material has a structure that allows the liquid or gas to easily pass therethrough, and it is necessary that the electrode active material has a structure that promotes discharge of a generated material accompanying the electrode reaction.
[0061]
In the polymer electrolyte fuel cell of the present invention, the electrode active material is preferably an organic solvent such as hydrogen or methanol, or oxygen, and the catalyst is preferably a noble metal particle such as platinum. Further, it is preferable to include a material for improving the conductivity of the electrode catalyst layer, and the form is not particularly limited, but for example, it is preferable to have conductive particles. Examples of the conductive particles include carbon black and the like. In particular, platinum-supported carbon and the like are preferably used as the carbon black supporting the catalyst. The electrode catalyst layer is required to have a structure in which a catalyst, an electron conductor (for example, carbon black), and an ion conductor (for example, a proton exchange resin) come into contact with each other, so that an electrode active material and a reaction product enter and exit efficiently. In addition, a polymer compound is effective for improving ionic conductivity, improving binding properties of a material, or increasing water repellency. Therefore, it is preferable that the electrode catalyst layer contains at least catalyst particles, conductive particles, and a polymer compound.
[0062]
In the polymer electrolyte fuel cell of the present invention, a known catalyst can be used as a catalyst contained in the electrode catalyst layer, and is not particularly limited, but may be platinum, palladium, ruthenium, iridium, or gold. Noble metal catalysts are preferably used. Further, two or more elements such as alloys and mixtures of these noble metal catalysts may be contained.
[0063]
The electron conductor (conductive material) contained in the electrode catalyst layer is not particularly limited, but an inorganic conductive substance is preferably used from the viewpoint of electron conductivity and contact resistance. Among them, carbon black, graphite or carbonaceous carbon materials, or metals and metalloids are exemplified. Here, as the carbon material, carbon black such as channel black, thermal black, furnace black, and acetylene black is preferably used from the viewpoint of electron conductivity and specific surface area. Furnace black includes Vulcan XC-72, Vulcan P, Black Pearls 880, Black Pearls 1100, Black Pearls 1300, Black Pearls 2000, Regal 400, Ketchen Black EC manufactured by Ketchen Black International, Mitsubishi Chemical Corporation # 3150 and # 3250 manufactured by Denki Kagaku Kogyo Kabushiki Kaisha as acetylene black. In addition to carbon black, artificial graphite or carbon obtained from organic compounds such as natural graphite, pitch, coke, polyacrylonitrile, phenol resin, and furan resin can also be used. The form of these carbon materials is not particularly limited, and fibrous materials in addition to particles can be used. It is also possible to use carbon materials obtained by post-processing these carbon materials. Among such carbon materials, Vulcan XC-72 manufactured by Cabot Corporation is particularly preferably used from the viewpoint of electron conductivity.
[0064]
The amount of addition of these electron conductors should be appropriately determined according to the required electrode characteristics, the specific surface area of the substance used, the electronic resistance, etc., but the weight ratio in the electrode catalyst layer is 1 to 80%. Is preferable, and the range of 20 to 60% is more preferable. When the amount of the electron conductor is small, the electronic resistance increases. When the amount of the electron conductor is large, the gas permeability is impaired or the catalyst utilization rate is reduced.
[0065]
It is preferable that the electron conductor is uniformly dispersed with the catalyst particles from the viewpoint of electrode performance. For this reason, it is preferable that the catalyst particles and the electron conductor are well dispersed in advance as a coating liquid.
[0066]
It is also a preferred embodiment to use, as the electrode catalyst layer, a catalyst-carrying carbon in which a catalyst and an electron conductor are integrated. By using the catalyst-carrying carbon, the utilization efficiency of the catalyst is improved, which can contribute to cost reduction. Here, even when the catalyst-supporting carbon is used for the electrode catalyst layer, a conductive agent can be further added. As such a conductive agent, the above-described carbon black is preferably used.
[0067]
As the ion conductor used for the electrode catalyst layer, a known ion conductor can be used. As the ion conductor, various organic and inorganic materials are generally known, but when used for a fuel cell, ions such as a sulfonic acid group, a carboxylic acid group, and a phosphate group that improve proton conductivity are used. Polymers having exchange groups are preferably used. Among them, a polymer having a proton exchange group composed of a fluoroalkyl ether side chain and a fluoroalkyl main chain is preferably used. For example, Nafion manufactured by DuPont, Aciplex manufactured by Asahi Kasei, Flemion manufactured by Asahi Glass, and the like are preferably used. These ion exchange polymers are provided in the electrode catalyst layer in the form of a solution or a dispersion. At this time, the solvent for dissolving or dispersing the polymer is not particularly limited, but a polar solvent is preferable in view of the solubility of the ion exchange polymer.
[0068]
The ionic conductor is preferably added in advance to a coating solution containing the electrode catalyst particles and the electron conductor as main constituents when preparing the electrode catalyst layer, and applied in a uniformly dispersed state from the viewpoint of electrode performance. However, the ion conductor may be applied after the application of the electrode catalyst layer. Here, the method for applying the ionic conductor to the electrode catalyst layer includes spray coating, brush coating, dip coating, die coating, curtain coating, flow coating, and the like, and is not particularly limited.
[0069]
The amount of the ion conductor contained in the electrode catalyst layer should be appropriately determined according to the required electrode characteristics and the conductivity of the ion conductor to be used, and is not particularly limited, but is not particularly limited. The ratio is preferably in the range of 1 to 80%, more preferably 5 to 50%. When the ion conductor is too small, the ion conductivity is low, and when the ion conductor is too large, the gas permeability is impaired, and all of them may lower the electrode performance.
[0070]
The electrode catalyst layer may contain various substances in addition to the above-mentioned catalyst, electron conductor, and ion conductor. In particular, it is preferable to include a polymer other than the above-mentioned proton exchange resin in order to enhance the binding property of a substance contained in the electrode catalyst layer. Examples of such a polymer include a polymer containing a fluorine atom, and are not particularly limited. For example, polyvinyl fluoride (PVF), polyvinylidene fluoride (PVDF), polyhexafluoropropylene (FEP), Tetrafluoroethylene, polyperfluoroalkyl vinyl ether (PFA), etc., or copolymers thereof, copolymers of monomer units constituting these polymers with other monomers such as ethylene and styrene, and blends, etc. Can be used. The content of these polymers in the electrode catalyst layer is preferably in the range of 5 to 40% by weight. If the polymer content is too large, the electron and ionic resistances tend to increase and the electrode performance tends to decrease.
[0071]
The electrode catalyst layer is also a preferred embodiment in which the catalyst-polymer composite has a three-dimensional network structure. The catalyst-polymer composite is a polymer composite containing catalyst particles, and this composite has a three-dimensional network structure. That is, the catalyst-polymer composite has a three-dimensional network structure that is three-dimensionally connected.
[0072]
When the electrode catalyst layer has a three-dimensional network structure, the pore size is preferably in the range of 0.05 to 5 μm, and more preferably in the range of 0.1 to 1 μm. The pore size can be determined from an average of 20 or more, preferably 100 or more, from a photograph of the surface taken with a scanning electron microscope (SEM) or the like. The pore size distribution of the electrode catalyst layer having a porous structure produced by the wet coagulation method is wide as much as possible, and it is preferable to take the average of 100 to 500 pore diameters.
[0073]
The porosity of the three-dimensional network structure of the electrode catalyst layer is preferably in the range of 10 to 95%. More preferably, it is in the range of 50 to 90%. Here, the porosity is a percentage (%) obtained by subtracting the volume occupied by the catalyst-polymer composite from the total volume of the electrode catalyst layer and dividing it by the total volume of the electrode catalyst layer.
[0074]
In order to produce an electrode catalyst layer having a three-dimensional network structure, usually, the catalyst layer is applied to an electrode substrate, a proton exchange membrane, and other substrates, and then wet coagulation is performed. When it is difficult to determine the porosity of the electrode catalyst layer alone, the electrode substrate, the proton exchange membrane, and the porosity of the other substrates are determined in advance, and these substrates and the electrode catalyst layer are included. After determining the porosity, it is also possible to determine the porosity of the electrode catalyst layer alone.
[0075]
The electrode catalyst layer having a three-dimensional network structure has a large porosity, good gas diffusivity, good discharge of generated water, and good electron conductivity and proton conductivity. In the conventional porous method, the catalyst particle size and the particle size of the added polymer are increased, or a pore is formed by using a pore-forming agent. The contact resistance between the proton exchange resins becomes larger than that of the electrode catalyst layer. On the other hand, in the three-dimensional network structure formed by the wet solidification method, the polymer composite containing the catalyst-supporting carbon is in a three-dimensional network. The gas structure has good gas diffusibility and discharge of generated water because of its quality structure, which is preferable.
[0076]
Even when the electrode catalyst layer has a three-dimensional network structure, the same materials as those used in the related art can be used for the catalyst, the electron conductor, and the ion conductor. However, when producing an electrode catalyst layer having a three-dimensional network structure, it is preferable to use a wet coagulation method. Therefore, it is preferable to select a polymer suitable for this wet coagulation method, and to disperse the catalyst particles well and obtain a fuel Polymers that do not degrade in an oxidizing-reducing atmosphere within the battery are preferred. Examples of such a polymer include a polymer containing a fluorine atom, and are not particularly limited. For example, polyvinyl fluoride (PVF), polyvinylidene fluoride (PVDF), polyhexafluoropropylene (FEP), Perfluoroalkyl vinyl ether (PFA), or a copolymer thereof, or a copolymer of a monomer unit constituting these polymers with another monomer such as ethylene or styrene (for example, hexafluoropropylene-vinylidene fluoride copolymer) Coalescence, etc.), and blends, etc. can also be preferably used.
[0077]
Among them, polyvinylidene fluoride (PVDF) and hexafluoropropylene-vinylidene fluoride copolymer are three-dimensionally formed by a wet coagulation method using an aprotic polar solvent as a dissolving solvent and a protic polar solvent as a coagulating solvent. It is a particularly preferred polymer in that a catalyst-polymer composite having a network structure is obtained.
[0078]
Specific examples of the polymer solvent include N-methylpyrrolidone (NMP), dimethylformamide (DMF), dimethylacetamide (DMAC), propylene carbonate (PC), and dimethylimidazolidinone (DMI). Examples of the solvent include water, lower alcohols such as methanol, ethanol and isopropanol, esters such as ethyl acetate and butyl acetate, and various aromatic or halogen-based organic solvents.
[0079]
As the polymer of the catalyst-polymer composite, in addition to the above-mentioned polymers, a polymer having a proton exchange group for improving proton conductivity is also preferable. Examples of the proton exchange group contained in such a polymer include a sulfonic acid group, a carboxylic acid group, and a phosphoric acid group, but are not particularly limited. Further, a polymer containing such a proton exchange group in the skeleton is also used without particular limitation. For example, a polymer having a proton exchange group composed of a fluoroalkyl ether side chain and a fluoroalkyl main chain is preferably used. Specifically, it is Nafion manufactured by DuPont. Further, a polymer containing the above-described fluorine atom having a proton exchange group, another polymer such as ethylene or styrene, a copolymer or a blend thereof may be used.
[0080]
When Nafion is used, a commercially available Nafion membrane may be dissolved in an aprotic polar solvent, or water-methanol-isopropanol, water-ethanol-, which are commercially available from Alderich, Dupont, or Ion Power. It is also possible to use a Nafion solution of a mixed solvent of lower alcohols such as isopropanol and water-ethanol-n-propanol. Further, those obtained by concentrating or solvent-exchanging these Nafion solutions may be used. In this case, the coagulation solvent in the wet coagulation should be appropriately determined according to the solvent type of the Nafion solution, but when the Nafion solution solvent is an aprotic polar solvent, water or alcohol is used as the coagulation solvent. In addition to esters and esters, various organic solvents are preferable. In the case of a lower alcohol solvent such as a mixed solvent of water-methanol-isopropanol, esters and various organic solvents such as butyl acetate are preferably used.
[0081]
As the polymer used in the catalyst-polymer composite, it is also preferable to use a polymer containing a fluorine atom or a polymer containing a proton exchange membrane by copolymerization or blending. In particular, blending polyvinylidene fluoride, poly (hexafluoropropylene-vinylidene fluoride) copolymer, and a polymer such as Nafion, which has a fluoroalkyl ether side chain and a fluoroalkyl main chain in the proton exchange group, can improve electrode performance. It is preferable from the viewpoint.
[0082]
The main components of the catalyst-polymer composite are a catalyst-supporting carbon and a polymer, and the ratio thereof is to be appropriately determined according to the required electrode characteristics, and is not particularly limited. Is preferably used in a weight ratio of 5/95 to 95/5. In particular, when used as an electrode catalyst layer for a polymer electrolyte fuel cell, the weight ratio of the catalyst-supporting carbon / polymer is preferably 40/60 to 85/15.
[0083]
Various additives can also be added to the catalyst-polymer composite. For example, there are a conductive agent such as carbon for improving the electron conductivity, a polymer for improving the binding property, an additive for controlling the pore size of the three-dimensional network structure, and the like. it can. The amount of these additives is preferably in the range of 0.1 to 50%, more preferably in the range of 1 to 20% by weight based on the catalyst-polymer composite.
[0084]
As a method for producing a catalyst-polymer composite having a three-dimensional network structure, a method based on a wet coagulation method is preferable. Here, after applying the catalyst-polymer solution composition, this coating layer is brought into contact with a coagulation solvent for the polymer, so that coagulation precipitation of the catalyst-polymer solution composition and solvent extraction can be performed simultaneously. This catalyst-polymer solution composition is obtained by uniformly dispersing the catalyst-supporting carbon in the polymer solution. The above-mentioned catalyst-supporting carbon and polymer are preferably used. The solvent for dissolving the polymer should be appropriately determined according to the polymer used, and is not particularly limited. It is important that the polymer solution disperse the catalyst-supporting carbon well. If the dispersion state is poor, it is not preferable because the catalyst-supporting carbon and the polymer cannot form a composite during wet coagulation.
[0085]
With respect to the method of applying the catalyst-polymer solution composition, an application method is selected according to the viscosity and the solid content of the catalyst-polymer solution composition, and is not particularly limited. However, a knife coater, a bar coater, a spray, General coating methods such as a dip coater, a spin coater, a roll coater, a die coater, and a curtain coater are used.
[0086]
Further, the coagulation solvent for wet coagulation of the polymer is not particularly limited, but a solvent which is easy to coagulate and precipitate the polymer to be used and which is compatible with the solvent of the polymer solution is preferable. The method of contacting the substrate with the coagulating solvent is not particularly limited, either, the substrate is immersed in the coagulating solvent, only the coating layer is brought into contact with the liquid surface of the coagulating solvent, and the coagulating solvent is applied to the coating layer. A method such as ring or spraying can be used.
[0087]
Regarding the substrate to which the catalyst-polymer solution composition is applied, it is possible to perform wet coagulation after application to either the electrode substrate or the solid polymer electrolyte. Also, after coating on a substrate other than the electrode substrate and the polymer electrolyte (for example, a transfer substrate), and then performing wet coagulation to produce a three-dimensional network structure, the electrode catalyst layer is applied to the electrode substrate or the polymer. It may be transferred or sandwiched on a solid electrolyte. In this case, as a transfer substrate, a polytetrafluoroethylene (PTFE) sheet, a glass plate or a metal plate whose surface is treated with a fluorine or silicone release agent, or the like is used.
[0088]
In the polymer electrolyte fuel cell of the present invention, the electrode substrate is not particularly limited, and a known electrode substrate can be used. In some cases, the electrode base material is not used to save space.
[0089]
The electrode substrate used in the present invention can be used without any particular limitation as long as it has low electric resistance and can collect (supply) power. Examples of the constituent material of the electrode substrate include, for example, those mainly containing a conductive inorganic substance. Examples of the conductive inorganic substance include a fired body from polyacrylonitrile, a fired body from pitch, graphite, and expanded graphite. Carbon material, stainless steel, molybdenum, titanium and the like.
[0090]
The form of the conductive inorganic material of the electrode base material is not particularly limited, and is used, for example, in a fibrous or particulate form. From the viewpoint of gas permeability, a fibrous conductive inorganic material (inorganic conductive fiber), particularly carbon fiber, is used. preferable. As the electrode substrate using the inorganic conductive fiber, any structure of a woven fabric or a nonwoven fabric can be used. For example, carbon paper TGP series and SO series manufactured by Toray Industries, Inc., carbon cloth manufactured by E-TEK, and the like are used. As the woven fabric, plain weave, oblique weave, satin weave, crest weave, binding weave, and the like are used without any particular limitation. As the nonwoven fabric, a papermaking method, a needle punch method, a spun bond method, a water jet punch method, a melt blow method, or the like is used without any particular limitation. It may be a knit. In these fabrics, particularly when carbon fibers are used, a woven fabric obtained by carbonizing or graphitizing a plain woven fabric using a spun-resistant spun yarn, and carbonizing a non-woven fabric obtained by processing a non-woven fabric by a needle punch method or a water jet punch method. Alternatively, a graphitized nonwoven fabric, a flame resistant yarn, a carbonized yarn, or a mat nonwoven fabric formed by a papermaking method using a graphitized yarn is preferably used. In particular, it is preferable to use a nonwoven fabric because a thin and strong fabric can be obtained.
[0091]
When an inorganic conductive fiber made of carbon fiber is used for the electrode substrate, examples of the carbon fiber include polyacrylonitrile (PAN) -based carbon fiber, phenol-based carbon fiber, pitch-based carbon fiber, rayon-based carbon fiber, and the like. . Among them, PAN-based carbon fibers are preferred. In general, PAN-based carbon fibers have higher compressive strength and tensile elongation at break than pitch-based carbon fibers, and are less likely to break. In order to obtain carbon fibers that are not easily broken, the carbonization temperature of the carbon fibers is preferably 2,500 ° C. or less, more preferably 2,000 ° C. or less.
[0092]
Electrode substrate used in the polymer electrolyte fuel cell of the present invention, a water repellent treatment performed to prevent a decrease in gas diffusion and permeability due to stagnation of water, partial water repellency to form a water discharge path, It is also a preferred embodiment to perform hydrophilic treatment or addition of carbon powder performed to reduce resistance.
[0093]
When the polymer electrolyte fuel cell of the present invention has a side-by-side structure, in order to promote the inflow of fuel such as hydrogen or methanol aqueous solution and air, and the discharge of products such as water and carbon dioxide. It is also a preferred embodiment to provide a diffusion layer. Such a diffusion layer also has the role of the above-mentioned electrode substrate, but it is more preferable to use a non-conductive cloth as the diffusion layer. Here, as a constituent material of the non-conductive cloth, for example, any non-conductive fiber can be used without particular limitation.
[0094]
Examples of the non-conductive fibers constituting the non-conductive cloth of the diffusion layer include polytetrafluoroethylene (PTFE), tetrafluoroethylene-hexafluoroethylene copolymer (FEP), and tetrafluoroethylene-perfluoroalkylvinyl ether copolymer. Coalescence (PFA), tetrafluoroethylene-ethylene copolymer (ETFE), polyvinylidene fluoride (PVDF), polyvinyl fluoride (PVF), polychlorotrifluoroethylene (CTFE), chlorinated polyethylene, flame-resistant polyacrylonitrile, poly Acrylonitrile, polyester, polyamide, polyethylene, polypropylene and the like can be used. Among these non-conductive fibers, fibers made of a fluorine atom-containing polymer such as PTFE, FEP, PFA, ETFE, PVDF, PVF, and CTFE are preferable from the viewpoint of corrosion resistance during an electrode reaction.
[0095]
As the non-conductive cloth of the diffusion layer, any structure of woven cloth or non-woven cloth can be used. As the woven fabric, plain weave, oblique weave, satin weave, crest weave, binding weave, and the like are used without any particular limitation. Further, as the nonwoven fabric, a papermaking method, a needle punch method, a spun bond method, a water jet punch method, a melt blow method, and the like are used without particular limitation. It may be a knit. In these fabrics, a plain woven fabric, a nonwoven fabric by a needle punch method or a water jet punch method, a mat nonwoven fabric by a papermaking method, and the like are particularly preferably used. In particular, a nonwoven fabric is preferably used because a porous, thin and strong fabric can be obtained.
[0096]
The non-conductive cloth of the diffusion layer is also preferably subjected to a water repellent treatment for preventing a gas diffusion and a decrease in permeability due to water retention, a partial water repellent or a hydrophilic treatment for forming a water discharge path, and the like. It is an embodiment. Further, it is also a preferred embodiment to perform post-treatments such as heat treatment, stretching, and pressing. By these post-treatments, effects such as thinning, increase in porosity, and increase in strength can be expected.
[0097]
In the polymer electrolyte fuel cell of the present invention, it is preferable to provide a conductive intermediate layer containing at least an inorganic conductive substance and a hydrophobic polymer between the electrode substrate and the electrode catalyst layer. In particular, when the electrode substrate is a carbon fiber woven fabric or nonwoven fabric having a large porosity, the provision of the conductive intermediate layer can suppress the performance deterioration due to the electrode catalyst layer penetrating into the electrode substrate.
[0098]
When the polymer solid electrolyte of the present invention is used for, for example, a membrane-electrode composite (MEA), it is preferable that the polymer solid electrolyte be processed into a polymer solid electrolyte membrane before the MEA is formed. For example, in order to further reduce permeation of fuel methanol, it is also a preferable embodiment to coat a metal thin film with a polymer solid electrolyte. Examples of such a metal thin film include palladium, platinum, silver and the like.
[0099]
In the polymer solid electrolyte membrane of the present invention, a method for producing a membrane-electrode composite (MEA) using an electrode catalyst layer or an electrode catalyst layer and an electrode substrate is not particularly limited. It is preferable to integrate by hot pressing, but the temperature and pressure may be appropriately selected depending on the thickness of the polymer solid electrolyte membrane, the porosity, the electrode catalyst layer and the electrode substrate. Normally, the temperature is 40 ° C. to 180 ° C., and the pressure is 10 kgf / cm ² ~ 80kgf / cm ² Is preferred.
[0100]
The solid polymer electrolyte of the present invention is applicable to various electrochemical devices. For example, a fuel cell, a water electrolyzer, a chloroalkali electrolyzer and the like can be mentioned, and among them, the fuel cell is most preferable. Further, among the fuel cells, it is suitable for a polymer electrolyte fuel cell, which includes a fuel using hydrogen and a fuel using an organic solvent such as methanol, and is not particularly limited. It is particularly preferably used for a DMFC using as fuel.
[0101]
Further, the application of the polymer electrolyte fuel cell of the present invention is not particularly limited, but a power supply source for a moving body is preferable. In particular, it is preferably used as a power supply source for mobile devices such as mobile phones, personal computers, PDAs and the like, home appliances such as vacuum cleaners, automobiles such as cars, buses and trucks, and vehicles such as ships and railways.
[0102]
【Example】
Hereinafter, the present invention will be described using examples.
[0103]
The evaluation method and the production method of the polymer solid electrolyte are as follows.
[0104]
(1) Performance of solid polymer electrolyte membrane
The methanol permeation amount and the ionic conductivity of the polymer solid electrolyte membrane were evaluated. The methanol permeation amount was measured by the following method. The membrane was set in a cell manufactured by Electrochem, and a 1 mol / l aqueous methanol solution was supplied at 0.2 ml / min to one side, and air was supplied at 50 ml / min to the other side. The methanol concentration in the exhausted air was measured, and the amount of methanol permeated was determined.
[0105]
The ionic conductivity of the membrane was measured by an impedance method. First, a cell having a certain distance between the electrodes is used, filled with a sulfuric acid aqueous solution, and the resistance of the sulfuric acid aqueous solution between the electrodes is determined. Thereafter, the film is interposed between the electrodes, and the resistance is determined in the same manner. From the resistance value through the membrane, the resistance value of only the sulfuric acid aqueous solution is subtracted to find the resistance of the membrane alone. Since the ionic conductivity is the reciprocal of the resistance, it is calculated from the resistance of the membrane obtained earlier.
[0106]
(2) Preparation of electrode
After performing a 20% PTFE water repellent treatment on the carbon fiber cloth base material, a carbon black dispersion containing 20% PTFE was applied and fired to prepare an electrode base material. On this electrode substrate, an anode electrode catalyst coating solution composed of Pt-Ru supported carbon and a Nafion solution is applied and dried to coat an anode electrode, and a cathode electrode catalyst coating solution composed of Pt-supported carbon and a Nafion solution is coated. After drying, a cathode electrode was prepared.
[0107]
(3) Fabrication and evaluation of polymer electrolyte fuel cell
The membrane-electrode composite (MEA) was produced by sandwiching the polymer electrolyte membrane of the above step (1) between the anode electrode and the cathode electrode produced in the above step (2) and hot pressing. This MEA was sandwiched between separators, and a 3% MeOH aqueous solution was flowed on the anode side, and air was flowed on the cathode side, to evaluate the MEA. For evaluation, a constant current was applied to the MEA, and the voltage at that time was measured. The current was sequentially increased and the measurement was performed until the voltage became 10 mV or less. The product of the current and voltage at each measurement point is output.
[0108]
Example 1, Comparative Example 1, Comparative Example 2
In Example 1, a 20.5% by weight Nafion (ion exchange equivalent: 1.0 meq) solution (A) manufactured by DuPont as a polymer having an anionic group and a nylon 6 / nylon 66 copolymer as a -CONH- group-containing polymer were used. A 10% ethanol solution (B) of the coalesced (caprolactam / AH salt = 40/60 copolymer) was mixed at a weight ratio of A / B = 10/1 and stirred with a mixer, and then about 1 mm thick on a polyester film. Coated. Next, the resultant was treated in a hot air dryer at 100 ° C. for 20 minutes to remove the solvent, and then the polyester film was peeled off to produce a polymer solid electrolyte having a thickness of 150 μm.
[0109]
As Comparative Example 1, coating and drying were performed in the same manner as in Example 1 using only 20.5% solution (A) of Nafion (ion exchange equivalent: 1.0 meq) manufactured by DuPont as a polymer having an anionic group. Was carried out to obtain a solid polymer electrolyte membrane having a thickness of 148 μm.
[0110]
As Comparative Example 2, a 20.5% solution (A) of Nafion (ion exchange equivalent: 1.0 meq) manufactured by DuPont as a polymer having an anionic group and a 10% solution of dimethylformamide (B2) of a polystyrene resin were used in a weight ratio A. / B2 = 10/1, coated and dried in the same manner as in Example 1 to obtain a solid polymer electrolyte membrane having a thickness of 145 μm.
[0111]
Using these, the MCO, ionic conductivity, and output at MEA of the polymer solid electrolyte membrane were measured.
[0112]
As a result, as shown in Table 1, the polymer solid electrolyte membrane of Example 1 was clearly lower in MCO than Comparative Example 1, and showed the same ionic conductivity. The maximum output of the MEA is 8.3 [mW / cm ² ]showed that. When the performance was tracked for 30 days, the initial output increased in both Example 1 and Comparative Examples 1 and 2. Initially, Example 1 maintained the maximum output for 30 days, whereas Comparative Example 1 and Comparative Example 1 maintained the maximum output. In Example 2, a clear decrease was observed from the lapse of 20 days. On the other hand, in Example 1, this output was stably maintained.
[0113]
Example 2, Comparative Example 3
In Example 2, a 20% DMF solution (C) of sulfonated polyphenylene sulfide sulfone (PPSS) (ion exchange equivalent: 2.0 meq) was used as the anionic group polymer, and methoxy manufactured by Teikoku Chemical Industry was used as the -CONR-containing polymer. A 20% solution of methylated polyamide in ethanol (D) was mixed at a weight ratio of C / D = 90/10, and the mixture was stirred with a mixer, and then coated on a polyester film to a thickness of about 1 mm. Then, the mixture was treated in a hot air drier at 100 ° C. for 20 minutes to remove the solvent, and the polyester film was peeled off to produce a 141 μm thick polymer solid electrolyte. In the same manner as in Example 1, a polymer solid electrolyte membrane and an MEA were produced using the membrane and evaluated.
[0114]
As Comparative Example 3, a polymer solid electrolyte membrane of 135 μm was produced in the same manner using only (C). As shown in Table 1, the results showed that Example 2 had a clearly lower MCO and slightly higher ionic conductivity than Comparative Example 3.
[0115]
Example 3
For a polymer having an anionic group, 20.5% by weight of Nafion (ion exchange equivalent: 1.0 meq) polymer solution (A) manufactured by DuPont, and -CONH-containing polymer, montmorillonite was used as a silicate layer material, and NH ₂ C ₁₁ H ₂₂ A dispersion composite (silicate layer content 12% by weight) was prepared by a production method in which the ion-exchanged montmorillonite organic composite was added and polymerized in ε-caprolactam / AH salt = 40/60 using COOH. A 20% solution of ethanol (E) was mixed at a weight ratio of A / E = 90/10 and stirred by a mixer, and then coated on a polyester film to a thickness of about 1 mm. Next, the mixture was treated in a hot air dryer at 100 ° C. for 20 minutes to remove the solvent, and the polyester film was peeled off to produce a polymer solid electrolyte membrane having a thickness of about 143 μm. An MEA was prepared and evaluated using the polymer solid electrolyte membrane and the membrane. The results show that, as shown in Table 1, the film of Example 3 had a clearly lower MCO than that of Comparative Example 1, and the MEA was disassembled 30 days after being incorporated into the MEA to examine the film state. While the film of Example 3 showed little embrittlement, the film of Comparative Example 1 was considerably embrittled, and a difference was observed between the two in terms of durability.
[0116]
Example 4, Comparative Example 4
In Example 4, a negative photosensitive polyimide was coated on a silicon wafer by a spin coating method and prebaked at 110 ° C. This was exposed with a photomask, developed, washed with water, and then full-baked at 350 ° C. This was immersed in a hydrofluoric acid solution and peeled off from the silicon wafer to obtain a porous polyimide film. The outer dimensions of the obtained porous polyimide film are 8 cm × 8 cm square, the thickness is 10 μm, the outer dimensions of the central porous part are 2.2 cm × 2.2 cm square, and the periphery of the porous part is a non-porous part. is there. In the porous portion, a through hole having a hole diameter d of about 12 μm was formed, the center interval between the through holes was about 33 μm, the opening ratio was about 11%, and the number of through holes was about 442,000.
[0117]
The porous film produced in this step is immersed in the polymer solid electrolyte solution of Example 1 and dried, and a polymer electrolyte comprising a porous polyimide film in which through holes are filled with the polymer solid electrolyte of Example 1 A film was prepared. The thickness was 33 μm.
[0118]
As Comparative Example 4, the porous polyimide film was immersed in the polymer solid electrolyte solution of Comparative Example 1 and dried, and the polymer solid electrolyte of Comparative Example 1 was filled in the through holes to produce a polymer solid electrolyte membrane. . Further, an MEA was manufactured and evaluated by the same process and method as in Example 1.
[0119]
As a result, in Example 4, the MCO in the film was lower than that in Comparative Example 4, and the output from the MEA was stable without lowering for 30 days.
[0120]
[Table 1]

[0121]
【The invention's effect】
According to the present invention, it is possible to provide a novel polymer electrolyte capable of suppressing crossover and achieving stable and high output for a long time, and a high-performance polymer electrolyte fuel cell using the same, and its practicality is high.
[Brief description of the drawings]
FIG. 1 is a schematic perspective view showing one example of a polymer solid electrolyte membrane of the present invention.
FIG. 2 is an enlarged schematic plan view of a porous portion 1 in one example of the polymer solid electrolyte membrane of the present invention.
FIG. 3 is a scanning electron micrograph showing an example of a porous substrate in which pores are used in an orderly manner, which is suitably used for the polymer solid electrolyte membrane of the present invention.
FIG. 4 is a schematic perspective view of a polymer solid electrolyte membrane having a side-by-side structure using the polymer solid electrolyte of the present invention.
FIG. 5 is a schematic cross-sectional view showing a part of a manufacturing process of a fuel cell having a side-by-side structure using the solid polymer electrolyte of the present invention.
[Explanation of symbols]
1: Porous part
2: Non-porous part
3: Hole
4: Membrane conductive part
5: Transmembrane electron conduction unit
6: Proton conducting part (polymer solid electrolyte part)
7: Electrode
d: hole diameter
L: Center distance between adjacent through holes

Claims (8)

A polymer solid electrolyte comprising a mixture containing at least a polymer having an anionic group and a polymer having a -CONH- group or -CONR- (R is an alkoxy group) in a main chain. The anionic group is -SO 3 _H or -SO 3 X _(X is an alkali metal) polymer solid electrolyte according to claim 1, characterized in that it comprises a polymer having a. 3. The polymer according to claim 1, wherein the polymer having a —CONH— group in the main chain is a polymer represented by the following chemical formula (n is a degree of polymerization), a copolymer thereof, or a mixture thereof. 4. Polymer solid electrolyte.

The polymer having a -CONH- group or -CONR- (R is an alkoxy group) in the main chain is a mixture of an alkoxy polyamide and the polyamide according to claim 3. 3. The polymer solid electrolyte according to item 1. The polymer having a -CONH- group or -CONR- (R is an alkoxy group) in the main chain contains a silicate layered product, and the polymer is present between the layers. Item 5. The polymer solid electrolyte according to any one of Items 1 to 4. A polymer solid electrolyte membrane, wherein the polymer solid electrolyte according to claim 1 is filled in a porous substrate. A polymer electrolyte fuel cell using the polymer solid electrolyte membrane according to claim 1. The polymer electrolyte fuel cell according to claim 7, wherein the fuel is an aqueous methanol solution.

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