JP3978663B2 - Electrolyte membrane-electrode assembly - Google Patents

Description

【００１３】
ここで、Ａｒ₁，Ａｒ₂，Ａｒ₃は、芳香族単位を示し、各種脂肪族基、芳香族基、ハロゲン基、水酸基、ニトロ基、シアノ基、トリフルオロメチル基等の置換基を有していても良い。これら芳香族単位は、ベンゼン環などの単環系単位、ナフタレン、アントラセン、ピレンなどの縮合環系単位、それらの芳香族単位が２個以上任意の結合を介してつながった多環系芳香族単位でも良い。また、芳香族単位におけるＮおよびＸの位置はベンザゾール環を形成できる配置であれば特に限定されるものではない。さらに、これらは炭化水素系芳香族単位だけでなく、芳香環内にＮ，Ｏ，Ｓ等を含んだヘテロ環系芳香族単位でも良い。ＸはＯ，Ｓ，ＮＨを示す。
上記Ａｒ₁は、下記一般式で表されるものが好ましい。
【００１４】
【化２】

【００１５】
ここで、Ｙ₁、Ｙ₂はＣＨまたはＮを示し、Ｚは直接結合、−Ｏ−，−Ｓ−，−ＳＯ₂−，−Ｃ（ＣＨ₃）₂−，−Ｃ（ＣＦ₃）₂−，−ＣＯ−を示す。
Ａｒ₂は、下記一般式で表されるものが好ましい。
【００１６】
【化３】

【００１７】
ここで、Ｗは−Ｏ−，−Ｓ−，−ＳＯ₂−，−Ｃ（ＣＨ₃）₂−，−Ｃ（ＣＨ₃）₂−，−ＣＯ−を示す。
Ａｒ₃は、下記一般式で表されるものが好ましい。
【００１８】
【化４】

【００１９】
これらポリベンザゾール系ポリマーは、上述の繰り返し単位を有するホモポリマーであっても良いが、上記構造単位を組み合わせたランダム、交互あるいはブロック共重合体であっても良く、例えば米国特許第４７０３１０３号、米国特許第４５３３６９２号、米国特許第４５３３７２４号、米国特許第４５３３６９３号、米国特許第４５３９５６７号、米国特許第４５７８４３２号等に記載されたものなども例示される。
【００２０】
これらポリベンザゾール系構成単位の具体例としては、下記構造式で表すものを例示することができる。
【００２１】
【化５】

【００２２】
【化６】

【００２３】
【化７】

【００２４】
【化８】

【００２５】
【化９】

【００２６】
【化１０】

【００２７】
【化１１】

【００２８】
さらに、これらポリベンザゾール系構成単位だけでなく、他のポリマー構成単位とのランダム、交互あるいはブロック共重合体であっても良い。この時、他のポリマー構成単位としては耐熱性に優れた芳香族系ポリマー構成単位から選ばれることが好ましい。具体的には、ポリイミド系構成単位、ポリアミド系構成単位、ポリアミドイミド系構成単位、ポリオキシジアゾール系構成単位、ポリアゾメチン系構成単位、ポリベンザゾールイミド系構成単位、ポリエーテルケトン系構成単位、ポリエーテルスルホン系構成単位などを挙げることができる。
【００２９】
ポリイミド系構成単位の例としては、下記一般式で表されるものが挙げられる。
【００３０】
【化１２】

【００３１】
ここで、Ａｒ₄は４価の芳香族単位で表されるが、下記構造で表されるものが好ましい。
【００３２】
【化１３】

【００３３】
また、Ａｒ₅は二価の芳香族単位であり、下記構造で表されるものが好ましい。ここで示される芳香環上には、メチル基、メトキシ基、ハロゲン基、トリフルオロメチル基、水酸基、ニトロ基、シアノ基等の各種置換基が存在していても良い。
【００３４】
【化１４】

【００３５】
これらポリイミド系構成単位の具体例としては、下記構造式で表すものを例示することができる。
【００３６】
【化１５】

【００３７】
【化１６】

【００３８】
ポリアミド系構成単位の例としては、下記構造式で表されるのもが挙げられる。
【００３９】
【化１７】

【００４０】
ここで、Ａｒ₆，Ａｒ₇，Ａｒ₈はそれぞれ独立に下記構造から選ばれるものが好ましい。ここで示される芳香環上には、メチル基、メトキシ基、ハロゲン基、トリフルオロメチル基、水酸基、ニトロ基、シアノ基等の各種置換基が存在していても良い。
【００４１】
【化１８】

【００４２】
これらポリアミド系構成単位の具体例としては、下記構造式で表すものを例示することができる。
【００４３】
【化１９】

【００４４】
ポリアミドイミド系構成単位の例としては、下記構造で表されるものが挙げられる。
【００４５】
【化２０】

【００４６】
ここで、Ａｒ₉は上記Ａｒ₅の具体例として示される構造から選ばれるものが好ましい。
【００４７】
これらポリアミドイミド構成単位の具体例としては、下記構造式で表すものを例示することができる。
【００４８】
【化２１】

【００４９】
ポリオキシジアゾール系構成単位の例としては、下記構造式で表されるものが挙げられる。
【００５０】
【化２２】

【００５１】
ここで、Ａｒ₁₀は上記Ａｒ₅の具体例として示される構造から選ばれるものが好ましい。
【００５２】
これらポリオキシジアゾール系構成単位の具体例としては、下記構造式で表すものを例示することができる。
【００５３】
【化２３】

【００５４】
ポリアゾメチン系構成単位の例としては、下記構造で表されるものが挙げられる。
【００５５】
【化２４】

【００５６】
ここで、Ａｒ₁₁，Ａｒ₁₂は、上記Ａｒ₆の具体例として示される構造から選ばれるものが好ましい。
【００５７】
これらポリアゾメチン系構成単位の具体例としては、下記構造式で表すものを例示することができる。
【００５８】
【化２５】

【００５９】
ポリベンザゾールイミド系構成単位の例としては、下記構造式で表されるものが挙げられる。
【００６０】
【化２６】

【００６１】
ここで、Ａｒ₁₃、Ａｒ₁₄は上記Ａｒ₄の具体例として示される構造から選ばれるものが好ましい。
【００６２】
これらポリベンザゾールイミド系構成単位の具体例としては、下記構造式で表すものを例示することができる。
【００６３】
【化２７】

【００６４】
ポリエーテルケトン系構成単位、ポリエーテルスルホン系構成単位は、一般に芳香族ユニットをエーテル結合とともにケトン結合やスルホン結合で連結した構造を有するものであり、下記構造式から選択される構造成分を含む。
【００６５】
【化２８】

【００６６】
ここで、Ａｒ₁₅〜Ａｒ₂₃はそれぞれ独立に下記構造で表されるものが好ましい。ここで示される芳香環上には、メチル基、メトキシ基、ハロゲン基、トリフルオロメチル基、水酸基、ニトロ基、シアノ基等の各種置換基が存在していても良い。
【００６７】
【化２９】

【００６８】
これらポリエーテルケトン系構成単位の具体例としては、下記構造式で表すものを例示することができる。
【００６９】
【化３０】

【００７０】
これらポリベンザゾール系ポリマー構成単位と共に共重合できる芳香族ポリマー構成単位は、厳密にポリマー鎖内の繰り返し単位を指しているのではなく、ポリマー主鎖中にポリベンザゾール系構成単位と共に存在できる構成単位を示しているものである。これら共重合できる芳香族ポリマー構成単位は一種だけでなく二種以上を組み合わせて共重合することもできる。このような共重合体を合成するには、ポリベンザゾール系ポリマー構成単位からなるユニット末端にアミノ基、カルボキシル基、水酸基、ハロゲン基等を導入して、これらの芳香族系ポリマーの合成における反応成分として重合しても良いし、これらの芳香族系ポリマー構成単位を含むユニット末端にカルボキシル基を導入してポリベンザゾール系ポリマーの合成における反応成分として重合しても良い。
【００７１】
前記ポリベンザゾール系ポリマーは、ポリ燐酸溶媒中で縮合重合されポリマーが得られる。ポリマーの重合度は極限粘度で表され、１５ｄＬ／ｇ以上が好ましく、より好ましくは２０ｄＬ／ｇ以上である。この範囲を下回った場合、得られる支持体膜の強度が低く好ましくない。また極限粘度は、３５ｄＬ／ｇ以下が好ましく、２６ｄＬ／ｇ以下がより好ましい。この範囲を上回った場合、等方性の溶液が得られるポリベンザゾール系ポリマー溶液の濃度範囲が限られ、等方性の条件での製膜が困難となるため好ましくない。
【００７２】
ポリベンザゾール系ポリマー溶液の製膜方法としては、ドクターブレード等を用いてポリマー溶液を基体上にキャスティングする流延法と呼ばれる製膜方法のほかにも、直線状スリットダイから押し出す方法や円周状スリットダイからブロー押し出しする方法、二枚の基体に挟んだポリマー溶液をローラーでプレスするサンドイッチ法、スピンコート法など、溶液を膜状に成型するあらゆる方法が使用できる。本発明の目的に適した好ましい製膜方法は流延法、サンドイッチ法である。流延法の基板やサンドイッチ法の基体にはガラス板や金属板、樹脂フィルム等の他、凝固時の支持体膜の空隙構造を制御する等の目的で種々の多孔質材料を基板、基体として好ましく用いることができる。
【００７３】
本発明で用いるポリベンザゾール系ポリマー溶液は、均一でかつ空隙率の大きな支持体膜を得るために等方性条件の組成で製膜することが重要であり、ポリベンザゾール系ポリマー溶液の好ましい濃度範囲は、０．３％以上であり、より好ましくは０．５％以上、さらに好ましくは０．８％以上である。この範囲よりも濃度が低いとポリマー溶液の粘度が小さくなり、適用できる製膜方法が限られるほか、得られる支持体膜の強度が小さくなるため好ましくない。またさらに、濃度範囲は、３％以下が好ましく、より好ましくは２％以下、さらに好ましくは１．５％以下である。この範囲よりも濃度が高いと空隙率の大きな支持体膜が得られないばかりか、ポリベンザゾール系ポリマーのポリマー組成や重合度によっては溶液が異方性を示すため好ましくない。
【００７４】
ポリベンザゾール系ポリマー溶液の濃度を上記で示したような範囲に調整するには次に示すような方法をとる事ができる。すなわち、重合されたポリベンザゾール系ポリマー溶液から一旦ポリマー固体を分離し、再度溶媒を加えて溶解することで濃度調整を行なう方法。さらには、ポリ燐酸中で縮合重合されたままのポリマー溶液からポリマー固体を分離することなく、そのポリマー溶液に溶媒を加えて希釈し、濃度調整を行なう方法。さらにはポリマーの重合組成を調整することで上記濃度範囲のポリマー溶液を直接得る方法などである。
【００７５】
ポリマー溶液の濃度調整に用いるのに好ましい溶媒としては、メタンスルホン酸、ジメチル硫酸、ポリ燐酸、硫酸、トリフルオロ酢酸などがあげられ、あるいはこれらの溶媒を組み合わせた混合溶媒を用いることもできる。中でも特にメタンスルホン酸、ポリリン酸が好ましい。
【００７６】
支持体膜の多孔質構造を実現する手段としては、製膜された等方性のポリベンザゾール系ポリマー溶液を、貧溶媒と接触させて凝固する方法を用いる。貧溶媒はポリマー溶液の溶媒と混和できる溶媒であって、液相状態であっても気相状態であっても良い。さらに、気相状態の貧溶媒による凝固と液相状態の貧溶媒による凝固を組み合わせることも好ましく用いることができる。凝固に用いる貧溶媒としては、水、酸水溶液や無機塩水溶液の他、アルコール類、グリコール類、グリセリンなどの有機溶媒等を利用することができるが、使用するポリベンザゾール系ポリマー溶液との組み合わせによっては、支持体膜の表面開孔率や空隙率が小さくなったり、支持体膜の内部に不連続な空洞ができたりするなどの問題が生じるため、凝固に用いる貧溶媒の選択には特に注意が必要である。本発明における等方性のポリベンザゾール系ポリマー溶液の凝固においては、水蒸気、メタンスルホン酸水溶液、リン酸水溶液、グリセリン水溶液の他、塩化マグネシウム水溶液などの無機塩水溶液などの中から貧溶媒と凝固条件を選択することにより支持体膜表面および内部の構造、空隙率を制御するに至った。特に好ましい凝固の手段は水蒸気と接触させて凝固する方法や、凝固の初期において水蒸気に短時間接触させた後に水に接触させて凝固する方法、メタンスルホン酸水溶液に接触させて凝固する方法などである。
【００７７】
ポリマーの凝固が進むと、支持体膜は収縮しようとする。凝固が進行する間は支持体膜の不均一な収縮によるシワの発生などを抑制する目的でテンターや固定枠を用いる場合もある。また、ガラス板などの基板上に成型したポリマー溶液を凝固する場合には、基板面の粗さを制御することで基板上での収縮を制御する場合もある。
【００７８】
上記のようにして凝固された支持体膜は、残留する溶媒によるポリマーの分解の促進や、複合電解質膜を使用する際に残留溶媒が流出するなどの問題を避ける目的で、十分に洗浄することが望ましい。洗浄は支持体膜を洗浄液に浸漬することで行なうことができる。特に好ましい洗浄液は水である。水による洗浄は、支持体膜を水中に浸漬したときの洗液のｐＨが５〜８の範囲になるまで行なうことが好ましく、さらに好ましくはｐＨが６．５〜７．５の範囲である。
【００７９】
上記に述べた特定の濃度範囲のポリベンザゾール系ポリマー等方性溶液を用い、上記に述べたような方法から選ばれた適当な凝固手段を用いることにより本発明の目的に適した構造を有するポリベンザゾール系ポリマーよりなる支持体膜が得られる。すなわち、支持体膜の少なくとも一方の表面に開口部を持つ連続した空隙を有する多孔質の支持体膜である。支持体膜はポリベンザゾール系ポリマーのフィブリル状繊維から形成される立体網目構造からなり、三次元的に連続した空隙を有することを、実施例に示したような原子間力顕微鏡を用いる水中での支持体膜表面の観察、および、エポキシ包埋−脱エポキシにより水中の構造を保持した支持体膜の透過型電子顕微鏡観察による断面観察から確認した。特開２００２−２０３５７６には膜の厚さ方向に貫通する連通孔を有する膜支持体にイオン伝導性物質が導入された電解質膜が記載されているが、これに記載されているような連通孔の方向性が主に膜の厚さ方向に限定されている支持体を燃料電池の電解質膜に用いた場合、膜の面方向のイオン伝導性物質の連続性が小さいために燃料電池のイオン交換膜に用いた場合に燃料ガスの濃度分布や電極触媒の付着量など面方向に不均一な状態が生じるとイオン交換膜の局所的な劣化が生じやすいなどの問題があるため好ましくない。
【００８０】
本発明の支持体膜の空隙率は９０体積％以上であることが好ましく、さらに好ましくは９５体積％以上である。空隙率がこの範囲よりも小さいと、イオン交換樹脂を複合化させた場合のイオン交換樹脂の含有率が小さく、イオン導電性が低下するため好ましくない。
【００８１】
本発明の支持体膜は、少なくとも一方の面の開孔率が４０％以上であることが好ましく、さらに好ましくは５０％以上、特に好ましくは６０％以上である。少なくとも一方の面の開孔率がこの範囲よりも小さいと、支持体膜とイオン交換樹脂を複合化させる際に支持体膜の空隙内部にイオン交換樹脂が含浸されにくくなるため好ましくない。
【００８２】
上述のような方法で得られたポリベンザゾール系ポリマーよりなる多孔質の該支持体膜にイオン交換樹脂を複合化させ、複合イオン交換膜を得る方法について説明する。即ち、該支持体膜を乾燥させずに、イオン交換樹脂溶液に浸漬し、該支持体膜内部の液をイオン交換樹脂溶液に置換してから乾燥させる方法により複合イオン交換膜を得る方法である。支持体膜内部の液がイオン交換樹脂溶液の溶媒組成と異なる場合には、その溶媒組成にあわせてあらかじめ内部の液を置換しておく方法も採られる。
【００８３】
本発明の支持体膜は乾燥により空隙内部の液体の体積が減少するのにしたがって空隙構造が収縮し、支持体膜の見かけの体積が大幅に減少するという特徴を有する。該支持体膜の内部にイオン交換樹脂を含浸することなく金属の枠などに固定して面方向の収縮を制限して乾燥させた場合には、収縮は膜厚方向に起こり、該支持体膜の乾燥後の見かけの膜厚は、乾燥前の膜厚の０．５％から１０％の範囲である。本発明の支持体膜以外の多孔質支持体膜、例えば、延伸ポリテトラフルオロエチレンポリマー多孔質膜からなる支持体膜ではこのような大幅な収縮は起こらない。
【００８４】
該支持体膜のこのような特徴により、該支持体膜の空隙内部の液をイオン交換樹脂溶液に置換してから乾燥させた場合、空隙内部に含浸された該イオン交換樹脂溶液の溶媒が蒸発して、該イオン交換樹脂溶液の体積が減少するにつれて該支持体膜も収縮するので、該支持体膜内部の空隙が析出したイオン交換樹脂によって満たされた緻密な複合膜構造を容易に得ることができる。この複合膜構造により、本発明の複合イオン交換膜は優れた燃料透過抑止性を示す。本発明の支持体膜以外の多孔質支持体膜、例えば、延伸ポリテトラフルオロエチレンポリマー多孔質膜からなる支持体膜では空隙内部に含浸されたイオン交換樹脂溶液の溶媒が蒸発して該イオン交換樹脂溶液の体積が減少しても、それに伴う支持体膜の収縮が少ないため、乾燥後の複合膜内部にはイオン交換樹脂で満たされていない空隙が多数できるばかりでなく、支持体膜の両面に支持体を含まないイオン交換樹脂の表面層が形成されないため好ましくない。
【００８５】
該複合イオン交換膜はまた、該支持体膜が大幅に収縮するため、該イオン交換樹脂溶液の濃度や粘度、溶媒の揮発性などの物性と、該支持体膜の膜厚や空隙率等の組み合わせを調整することで、該イオン交換樹脂が該支持体膜の内部空隙を満たした複合層を形成するのと並行して該支持体膜の両面に付着していた過剰なイオン交換樹脂溶液や、該支持体膜の収縮に伴って該支持体膜内部から排出されたイオン交換樹脂溶液が該支持体膜の表面外部で乾燥して該支持体を含まないイオン交換樹脂層を形成することにより、結果として該複合層を挟む形で該複合層の両面に支持体膜を含まないイオン交換樹脂の表面層を形成した構造を容易に実現することができる。
【００８６】
本発明の支持体膜以外の膜、例えばポリテトラフルオロエチレンポリマーからなる多孔質支持体膜は上記で述べたように、大幅な収縮が起こらないため、イオン交換樹脂溶液を含浸して乾燥する際に支持体膜内部にイオン交換樹脂が析出しても空隙が残ったままの状態となり、また、支持体膜複合層を挟む形のイオン交換樹脂層も形成されない。この状態を解消するためにはイオン交換樹脂溶液の含浸、乾燥を複数回繰り返す必要があり、工程が複雑になるため好ましくない。
【００８７】
本発明の複合イオン交換膜に使用されるイオン交換樹脂は特に限定されるものではなく、前述のパーフルオロカーボンスルホン酸ポリマー以外にも、例えばポリスチレンスルホン酸、ポリ（トリフルオロスチレン）スルホン酸、ポリビニルホスホン酸、ポリビニルカルボン酸、ポリビニルスルホン酸ポリマーの少なくとも一つのアイオノマー、ポリスルホン、ポリフェニレンオキシド、ポリフェニレンスルホキシド、ポリフェニレンスルフィド、ポリフェニレンスルフィドスルホン、ポリパラフェニレン、ポリフェニルキノキサリン、ポリアリールケトン、ポリエーテルケトン、ポリベンザゾール及びポリアラミドポリマーなどの芳香族ポリマーの少なくとも一つがスルホン化、ホスホン化またはカルボキシル化されたアイオノマー等が適用できる。ここでいうポリスルホンポリマーにはポリエーテルスルホン、ポリアリールスルホン、ポリアリールエーテルスルホン、ポリフェニルスルホン及びポリフェニレンスルホンポリマーの少なくとも一つが含まれる。また、ここでいうポリエーテルケトンポリマーにはポリエーテルエーテルケトン、ポリエーテルケトン−ケトン、ポリエーテルエーテルケトン−ケトンおよびポリエーテルケトンエーテル−ケトンポリマーの少なくとも一つが含まれる。
【００８８】
上記に記述したイオン交換樹脂溶液の溶媒はポリベンザゾール系ポリマー支持体膜を溶解、分解あるいは極端に膨潤させず、かつイオン交換樹脂を溶解できる溶媒の中から選ぶことができる。ただし、イオン交換樹脂溶液を支持体膜に含浸させた後に溶媒を除去してイオン交換樹脂を析出させる為、溶媒は加熱や減圧などの手段を用いて蒸発させるなどして除去することができるものであることが好ましい。ここで、本発明のポリベンザゾール系ポリマー支持体膜は高い耐熱性を有することから、１００℃程度の温度からクリープを生じるポリテトラフルオロエチレン製の支持体膜を用いる複合イオン交換膜の作製では使用できない高沸点の溶媒を含むイオン交換樹脂溶液を使用して複合イオン交換膜を作製できることも、多くの種類のイオン交換樹脂が選択できるという観点から優れた特徴である。
【００８９】
上記に記述したイオン交換樹脂溶液の濃度および、イオン交換樹脂の分子量は特に限定されるものではないが、イオン交換樹脂の種類や得ようとする複合イオン交換膜の膜厚などに応じて適宜選択される。
【００９０】
上記のようにして得られる複合イオン交換膜に占めるイオン交換樹脂の含有率は８０重量％以上である。この範囲より小さい含有率の場合、膜の導電抵抗が大きくなったり、膜の保水性が低下したりして、十分な発電性能が得られないため好ましくない。
【００９１】
また、本発明の複合イオン交換膜は、上記で記述したように複合層を挟む形で複合層の両面に支持体を含まないイオン交換樹脂からなる表面層を有することを特徴とする。複合イオン交換膜が該複合層と該表面層を有することにより、該複合イオン交換膜は高い機械的強度を有し、かつ、表面に電極層を形成させた場合の電極層との密着性に優れるという特長を有する。該表面層の厚みはそれぞれ２μｍ以上３０μｍ以下であり、かつ、それぞれが該複合イオン交換膜の全厚みの半分を超えない範囲であることが好ましい。該表面層の厚みが上記範囲よりも小さいと電極層との密着性が悪くなり、イオン伝導性が低下するなどするため好ましくない。また該表面層の厚みが上記範囲よりも大きいと、複合層による補強の効果が複合イオン交換膜の最外表面まで及ばず、複合イオン交換膜が吸湿した場合に表面層のみが大きく膨潤して表面層が複合層から剥離するなどするため好ましくない。
【００９２】
複合イオン交換膜は機械的強度やイオン伝導性、表面に形成されるイオン交換樹脂層の耐剥離性などの特性をさらに向上させる目的で、複合イオン交換膜を適当な条件で熱処理する方法も好ましく用いることができる。また、表面に形成されるイオン交換樹脂の表面層の厚みを調整するために、該複合イオン交換膜をさらにイオン交換樹脂溶液に浸漬したり、該複合イオン交換膜にイオン交換樹脂溶液を塗布したりしてから乾燥することによりイオン交換樹脂層の付着量を増加させたり、あるいは、イオン交換樹脂溶液に浸漬した後に支持体膜の表面に付着したイオン交換樹脂溶液の一部をスクレーパー、エアナイフ、ローラーなどで掻き落としたり、ろ紙やスポンジのような溶液吸収性のある材料で吸収したりすることにより、イオン交換樹脂層の付着量を減少させたりする方法も用いることができる。あるいは、熱プレスをかけることによりイオン交換樹脂層の密着性をさらに向上させるなどの方法を併せて用いることもできる。
【００９３】
本発明の複合イオン交換膜は高いイオン伝導性を有しながら、機械的強度に優れる。また、その特性を生かして、複合イオン交換膜特に固体高分子形燃料電池の高分子固体電解質膜として利用することができる。
【００９４】
本発明に用いられる電極に関しては特に限定されるものではないが、燃料電池の形状や、用途などに応じて適宜選択される。例えばカーボンペーパー、カーボンクロスなどが選択される。また、ＰＴＦＥなどで撥水加工したものも用いられる。電極の厚みに関しては特に限定されるものではないが、４００μｍ以下のものが好ましい。さらに好ましくは３００μｍ以下のものである。
【００９５】
本発明に用いられる触媒層とは、白金などの触媒を有する層である。触媒は固体高分子型燃料電池に用いられるものであれば特に限定されるものではない。白金などの金属、または合金の触媒をカーボンブラックに担持した状態で触媒層に含有されることが好ましい。また触媒層にはイオン交換樹脂を含有する。このイオン交換樹脂は該複合イオン交換膜に含まれるものと同一ものでもよいし、異なっていてもよいが、好ましくは同一ものである。また、２種類以上のイオン交換樹脂を含有していてもよい。触媒層内にはイオン交換樹脂以外にもフッ素樹脂など別の樹脂を含有していてもよい。また、触媒を担持していない単体のカーボンブラックを含有していてもよい。
【００９６】
本発明の電解質膜−電極接合体作成する方法については特に限定されるものではないが、燃料電池の形状や、用途などに応じて適宜選択される。例えば、白金などの触媒を担持したカーボンブラックをイオン交換樹脂の溶液またはイオン交換樹脂と結着剤を含む溶液に分散して作成したインクまたはペーストを電極上に、噴霧または塗布し、乾燥させたものを電解質膜と触媒層が接触するように重ね合わせ、ホットプレスする方法、白金などの触媒を担持したカーボンブラックをイオン交換樹脂の溶液またはイオン交換樹脂と結着剤を含む溶液に分散して作成したインクまたはペーストを電解質膜上に、噴霧または塗布し、乾燥させたものを電極と触媒層が接触するように重ね合わせ、ホットプレスする方法、白金などの触媒を担持したカーボンブラックをイオン交換樹脂の溶液またはイオン交換樹脂と結着剤を含む溶液に分散して作成したインクまたはペーストを離型材上に、噴霧または塗布し、乾燥させたものを電解質膜と触媒層が接触するように重ね合わせ、ホットプレスすることにより触媒層を電解質膜上に転写し、この膜を電極と触媒層が接触するように重ね合わせ、ホットプレスする方法、白金などの触媒を担持したカーボンブラックをイオン交換樹脂の溶液またはイオン交換樹脂と結着剤を含む溶液に分散して作成したインクまたはペーストをバインダーとして電解質膜と電極をはり合わせる方法、白金などの触媒を担持したカーボンブラックをフッ素樹脂などの結着剤を含む溶液に分散して電極に塗布、乾燥、焼成したものにイオン交換樹脂を塗布したものを乾燥し、電極と触媒層が接触するように重ね合わせ、ホットプレスする方法などどのような方法を用いてもかまわない。またホットプレスする際、膜または／および電極は水、アルコールなどの有機溶剤、酸水溶液などを含有していてもかまわない。
【００９７】
本発明の複合イオン交換膜を用いると電解質膜−電極接合体を作成する際、膜の膨潤や変形が少なく容易に行うことができる。
【００９８】
イオン交換膜の表層に支持体膜を含む複合イオン交換膜は電極との接合性がイオン交換樹脂単独のイオン交換膜と比較して劣ることが多いが、本発明の複合イオン交換膜は両面に支持体膜を含まないイオン交換樹脂からなる表面層を有するため、イオン交換樹脂単独のイオン交換膜と同様に電極との接合を容易に行うことができる。
【００９９】
本発明の電解質膜−電極接合体は高いイオン伝導性を有しながら、機械的強度に優れる。また、その特性を生かして、特に固体高分子形燃料電池の高分子固体電解質膜−電極接合体として利用することができる。
【０１００】
実施例
以下に本発明の実施例を示すが本発明はこれらの実施例に限定されるものではない。
評価法・測定法
【０１０１】
＜極限粘度＞
メタンスルホン酸を溶媒として、０．５ｇ／Ｌの濃度に調整したポリマー溶液の粘度をウベローデ型粘度計を用いて２５℃恒温槽中で測定し、算出した。
【０１０２】
＜支持体膜厚み＞
未乾燥の支持体膜の厚みは次に示す方法により測定した。測定荷重を変更可能なマイクロメータを用い、各荷重における水中での支持体膜の厚みを測定した。測定した厚みを荷重に対してプロットし、直線部分を荷重０に外挿したときの切片の値を厚みとし、一つの試料について５ヶ所で測定した厚みの平均値を支持体膜の厚みとした。
【０１０３】
＜複合イオン交換膜の厚さおよび、それを構成する層の厚さ＞
該複合イオン交換膜を構成する複合層および該複合層を挟む形で複合層の両面に形成された支持体膜を含まないイオン交換樹脂からなる表面層の厚さは、幅３００μｍ×長さ５ｍｍに切り出した複合膜片を、ルベアック８１２（ナカライテスク製）／ルベアックＮＭＡ（ナカライテスク製）／ＤＭＰ３０（ＴＡＡＢ製）＝１００／８９／４の組成とした樹脂で包埋し、６０℃で１２時間硬化させて試料ブロックを作製した。ウルトラミクロトーム（ＬＫＢ製２０８８ＵＬＴＲＯＴＯＭＥ ５）を用いて平滑な断面が露出するようブロックの先端をダイヤモンドナイフ（住友電工製ＳＫ２０４５）で切削した。このようにして露出させた複合膜の断面を光学顕微鏡で写真撮影し、既知の長さのスケールを同倍率で撮影したものと比較することで測定した。支持体の空隙率が大きい場合等で、少なくとも一方の面の表面層とその内側の複合層とが明確な界面を形成せずに界面付近の構造が連続的に変化している場合があるが、その場合は光学顕微鏡で連続的な構造の変化が確認できる部分のうち、複合イオン交換膜の外表面に最も近い部分を複合層の最外表面として、そこから複合イオン交換膜の外表面までの距離を該表面層の厚みとした。
【０１０４】
＜複合イオン交換膜のイオン交換樹脂（ＩＣＰ）含有率＞
複合イオン交換膜のイオン交換樹脂含有率は以下の方法により測定した。１１０℃で６時間真空乾燥させた複合イオン交換膜の目付けＤｃ［ｇ／ｍ²］を測定し、複合イオン交換膜の作製に用いたのと同じ製造条件の支持体膜をイオン交換樹脂を複合化させずに乾燥させて測定した乾燥支持体膜の目付けＤｓ［ｇ／ｍ²］とから、以下の計算によりイオン交換樹脂含有率を求めた。
イオン交換樹脂含有率［重量％］＝（Ｄｃ−Ｄｓ）／Ｄｃ×１００
また、複合イオン交換膜のイオン交換樹脂含有率は以下の方法によって測定することもできる。すなわち、複合イオン交換膜を複合イオン交換膜中の支持体膜成分あるいは、イオン交換樹脂成分のいずれかのみを溶解可能な溶剤に浸漬して一方の成分を抽出、除去した後、元の複合イオン交換膜との重量変化を測定することでイオン交換樹脂の含有率を求めることができる。
【０１０５】
＜強度・引張弾性率＞
イオン交換膜の強度特性は、気温２５℃、相対湿度５０％の雰囲気で、オリエンテック社製テンシロンを用いて測定した。試料は幅１０ｍｍの短冊状とし、支間長４０ｍｍ、引っ張り速度２０ｍｍ／ｓｅｃで測定した応力歪み曲線から算出した。
【０１０６】
＜イオン導電率＞
イオン導電率σは次のようにして測定した。自作測定用プローブ（ポリテトラフルオロエチレン製）上で幅１０ｍｍの短冊状膜試料の表面に白金線（直径：０．２ｍｍ）を押しあて、８０℃、相対湿度９５％の恒温恒湿槽中に試料を保持し、白金線間の１０ｋＨｚにおける交流インピーダンスをＳＯＬＡＲＴＲＯＮ社１２５０ＦＲＥＱＵＥＮＣＹ ＲＥＳＰＯＮＳＥ ＡＮＡＬＹＳＥＲにより測定した。極間距離を１０ｍｍから４０ｍｍまで１０ｍｍ間隔で変化させて測定し、極間距離と抵抗測定値をプロットした直線の勾配Ｄ_r［Ω／ｃｍ］から下記の式により膜と白金線間の接触抵抗をキャンセルして算出した。
σ［Ｓ／ｃｍ］＝１／（膜幅×膜厚［ｃｍ］×Ｄ_r）
【０１０７】
＜ガス透過率＞
イオン交換膜のガス透過率は以下の方法で測定した。イオン交換膜をメッシュ状のステンレス製サポート上に置き、ホルダーに固定した後、イオン交換膜の一方の面に室温にて水蒸気で飽和したヘリウムガスをゲージ圧が０．０９ＭＰａとなるようにして流通させ、イオン交換膜の他方の面に透過してくるヘリウムガスの量を石鹸膜流量計を用いて測定し算出した。
【０１０８】
＜発電特性＞
電解質膜−電極接合体をＥｌｅｃｔｒｏｃｈｅｍ社製評価用燃料電池セルＦＣ２５−０２ＳＰに組み込んでセル温度８０℃、ガス加湿温度８０℃、燃料ガスとして水素３００ｍL／ｍｉｎ、酸化ガスとして空気１０００ｍL／ｍｉｎのガス流量において発電特性評価を行った。
【０１０９】
実施例１
ポリ燐酸中にＩＶ＝２４ｄＬ／ｇのポリパラフェニレンシスベンゾビスオキサゾールポリマーを１４重量％含んだドープにメタンスルホン酸を加えて希釈し、ポリパラフェニレンシスベンゾビスオキサゾール濃度１重量％の等方性溶液を調製した。この溶液を、９０℃に加熱したガラス板上にクリアランス３００μｍのアプリケータを用いて製膜速度２０ｍｍ／秒で製膜した。このようにしてガラス板上に製膜したドープ膜をそのまま２５℃、相対湿度８０％の恒温恒湿槽中に置いて１時間凝固し、生成した膜を洗液がｐＨ７±０．５を示すまで水洗を行って支持体膜を作成した。この支持体膜を水中でステンレス製のフレームに固定し、支持体膜の内部の水をイオン交換樹脂溶液であるデュポン社製２０％ナフィオン（商品名）溶液（品番：ＳＥ−２０１９２）の溶媒組成とほぼ同じ水：エタノール：１−プロパノール＝２６：２６：４８（重量比）の混合溶媒で置換した。この支持体膜を２０％ナフィオン（商品名）溶液に２５℃で１５時間浸漬した後溶液から取り出し、膜の内部に含浸および膜表面に付着したナフィオン（商品名）溶液の溶媒を風乾により揮発させ乾燥させた。乾燥させた膜は６０℃のオーブン中で１時間予備熱処理して残留した溶媒を除いた後、窒素雰囲気下、１５０℃で１時間熱処理を行なうことにより複合イオン交換膜を調製した。デュポン社製２０％ナフィオン（商品名）溶液（品番：ＳＥ−２０１９２）に、白金担持カーボン（カーボン：Ｃａｂｏｔ社製ＶａｌｃａｎＸＣ−７２、白金担持量：４０重量％）を、白金とナフィオンの重量比が２．７：１になるように加え、撹拌して触媒ペーストを調製した。この触媒ペーストを、東レ製カーボンペーパーＴＧＰＨ−０６０に白金の付着量が１ｍｇ／ｃｍ²になるように塗布、乾燥して、電極触媒層付きガス拡散層を作成した。２枚の電極触媒層付きガス拡散層の間に、上記複合イオン交換膜を、電極触媒層が膜試料に接するように挟み、ホットプレス法により１２０℃、２ＭＰａにて３分間加圧、加熱することにより、実施例１の電解質膜−電極接合体とした。
【０１１０】
実施例２
デュポン社製２０％ナフィオン（商品名）溶液（品番：ＳＥ−２０１９２）に、白金担持カーボン（カーボン：Ｃａｂｏｔ社製ＶａｌｃａｎＸＣ−７２、白金担持量：４０重量％）を、白金とナフィオンの重量比が２．７：１になるように加え、撹拌して触媒ペーストを調製した。この触媒ペーストを実施例１で示したのと同じ複合イオン交換膜に白金の付着量が１ｍｇ／ｃｍ²になるように塗布、乾燥して、電極触媒層付きイオン交換膜を作成した。２枚の東レ製カーボンペーパーＴＧＰＨ−０６０の間に、上記イオン交換膜を挟み、ホットプレス法により１２０℃、２ＭＰａにて３分間加圧、加熱することにより、実施例２の電解質膜−電極接合体とした。
【０１１１】
実施例３
ポリ燐酸中に極限粘度１８ｄＬ／ｇのポリ｛２，６−ジイミダゾ［４，５−ｂ：４’，５’−ｅ］ピリジニレン−１，４（２，５−ジヒドロキシ）フェニレン｝（以下ＰＩＰＤと略）ポリマーを１９重量％含んだドープにメタンスルホン酸を加えて希釈し、ＰＩＰＤポリマー濃度１．５重量％の等方性溶液を調製し、支持体膜製膜用のドープとしたことを除き、実施例１に示したのと同じ方法で実施例３の電解質膜−電極接合体とした。
【０１１２】
比較例１
市販されているデュポン社製ナフィオン１１２（商品名）膜をイオン交換膜として用いた。この膜は実施例１で用いた２０％ナフィオン溶液や実施例２で用いた１０％ナフィオン水溶液に含まれるナフィオンポリマーと同じパーフルオロカーボンスルホン酸ポリマーからなるイオン交換膜であり、固体高分子形燃料電池用の電解質膜として広く用いられているものである。デュポン社製２０％ナフィオン（商品名）溶液（品番：ＳＥ−２０１９２）に、白金担持カーボン（カーボン：Ｃａｂｏｔ社製ＶａｌｃａｎＸＣ−７２、白金担持量：４０重量％）を、白金とナフィオンの重量比が２．７：１になるように加え、撹拌して触媒ペーストを調製した。この触媒ペーストをイオン交換膜に白金の付着量が１ｍｇ／ｃｍ²になるように塗布、乾燥して、電極触媒層付きイオン交換膜を作成した。この電極触媒層付きイオン交換膜は膨潤し膜が波打ったように変形した。２枚の東レ製カーボンペーパーＴＧＰＨ−０６０の間に、上記イオン交換膜を挟み、ホットプレス法により１２０℃、２ＭＰａにて３分間加圧、加熱することにより、比較例１の電解質膜−電極接合体とした。この接合体は膜が変形し波打っていたために接合が不完全であった。
【０１１３】
比較例２
ナフィオン溶液に浸漬した支持体膜をナフィオン溶液から取り出す際に、支持体膜の表面が露出するように支持体膜の両面に付着したナフィオン溶液をポリテトラフルオロエチレン製のスクレーパーで掻き取ったことを除き、実施例１で示したのと同じ方法で比較例２の電解質膜−電極接合体を調製した。
【０１１４】
実施例１、２、比較例１、２の物性値を表１に示す。
【０１１５】
【表１】

【０１１６】
実施例１から２の複合イオン交換膜は比較例１である市販のナフィオン１１２膜と対比して破断強度ならびに引張弾性率の大きなイオン交換膜であることがわかる。また実施例１から２の複合イオン交換膜は内部に支持体を有するにもかかわらず、支持体を含まない比較例１に比べてイオン導電率、発電性能ともに大幅な低下を起こすことなく、ガス透過率は半分以下の小さい値に抑えられており、燃料電池の高分子固体電解質膜として優れた特性を備えていることがわかる。
【０１１７】
実施例２の電解質膜−電極接合体では触媒ペーストを直接塗布しても膨潤変形が少なく、電極と良好に接合できたが、比較例２の電解質膜−電極接合体では触媒ペーストを直接塗布すると膨潤変形がおこり、ホットプレスによる接合が良好に行えなかった。また、発電評価後に評価後に燃料電池から電解質膜−電極接合体をとりだすと電解質膜から電極接合体が剥離した。このことから、本発明の電解質膜−電極接合体は電解質膜と電極との接合性が良好であることがわかる。
【０１１８】
実施例１の電解質膜−電極接合体では発電評価後も電解質膜と電極との剥離等は起こらなかったが、比較例１の電解質膜−電極接合体では発電評価後、電解質膜と電極との剥離が生じた。このことから、イオン交換膜の表層に支持体膜を含む複合イオン交換膜は電極との接合性がイオン交換樹脂単独のイオン交換膜と比較して劣ることが多いが、本発明に用いた複合イオン交換膜は両面に支持体膜を含まないイオン交換樹脂からなる表面層を有するため、本発明の電解質膜−電極接合体はイオン交換樹脂単独のイオン交換膜を用いた電解質膜−電極接合体と同様に電極との接合性が良好であることがわかる。
【０１１９】
【発明の効果】
機械的強度が高く、イオン伝導性、発電特性、ガスバリヤー性に優れた高分子固体電解質膜を有し、電解質膜と電極接合体接合性の良好な電解質膜−電極接合体を提供することができる。
【図面の簡単な説明】
【図１】複合イオン交換膜の断面構造の模式図である。
【符号の説明】
１ 表面層Ａ、 ２ 複合層、 ３ 表面層Ｂ、 ４ 触媒層、 ５ ガス拡散層[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a composite ion exchange membrane excellent in mechanical strength and ion conductivity, and particularly to an electrolyte membrane-electrode assembly using a polymer solid electrolyte membrane.
[0002]
[Prior art]
In recent years, new power generation technologies with excellent energy efficiency and environmental friendliness have attracted attention. Among them, polymer electrolyte fuel cells using polymer electrolyte membranes have high energy density, and have features such as easy startup and shutdown because of lower operating temperatures than other types of fuel cells. Developments as power supply devices for electric vehicles and distributed power generation are advancing. In addition, direct methanol fuel cells that use a solid polymer electrolyte membrane and directly supply methanol as a fuel are also being developed for applications such as power sources for portable devices. As the polymer solid electrolyte membrane, a proton conductive ion exchange resin membrane is usually used. In addition to proton conductivity, the polymer solid electrolyte membrane must have characteristics such as fuel permeation deterrence and mechanical strength to prevent the permeation of fuel hydrogen and the like. As such a polymer solid electrolyte membrane, for example, a perfluorocarbon sulfonic acid polymer membrane into which a sulfonic acid group is introduced as represented by Nafion (trade name) manufactured by DuPont, USA is known.
[0003]
In order to increase the output and efficiency of the polymer electrolyte fuel cell, it is effective to reduce the ionic conduction resistance of the polymer solid electrolyte membrane, and one of the measures is to reduce the film thickness. Attempts have also been made to reduce the film thickness of solid polymer electrolyte membranes such as Nafion. However, when the film thickness is reduced, the mechanical strength is reduced, and the polymer solid electrolyte is liable to break when the polymer solid electrolyte membrane and the electrode are joined by hot pressing, or due to fluctuations in the dimensions of the membrane. There have been problems such as the electrode bonded to the film being peeled off and the power generation characteristics being deteriorated. Furthermore, the fuel permeation deterrence is lowered by reducing the film thickness, which causes problems such as a reduction in electromotive force and a decrease in fuel utilization efficiency.
[0004]
Furthermore, the polymer solid electrolyte membrane is not only used as an ion exchange resin membrane for fuel cells as described above, but also for various electrolysis uses such as alkaline electrolysis and hydrogen production from water, and lithium batteries and nickel metal hydride batteries. Applied to a wide range of applications in the field of electrochemistry such as electrolyte applications, mechanical functional materials such as microactuators and artificial muscles, functional materials for recognition and response of ions and molecules, and functional materials for separation and purification It is considered that an excellent function that has never been achieved can be provided by achieving high strength and thinning of the polymer solid electrolyte membrane in each application.
[0005]
As a method for improving the mechanical strength of the polymer solid electrolyte membrane and suppressing dimensional changes, a composite polymer solid electrolyte membrane in which various reinforcing materials are combined with the polymer solid electrolyte membrane has been proposed. In a conventional composite polymer solid electrolyte membrane, a void portion of a stretched porous polytetrafluoroethylene membrane is impregnated with a perfluorocarbon sulfonic acid polymer that is an ion exchange resin and integrated (for example, see Patent Document 1). However, since these composite polymer solid electrolyte membranes are made of polytetrafluoroethylene, the reinforcing material is softened by heat during power generation and is likely to undergo dimensional changes due to creep. When the acid polymer solution is impregnated and dried, the volume of the void portion of the reinforcing material hardly changes. Therefore, the perfluorocarbon sulfonic acid polymer precipitated inside the reinforcing material void tends to be unevenly distributed, and the void is formed by the polymer. In order to be completely filled, a complicated process such as the impregnation and drying process of the ion exchange resin solution must be repeated several times, and since a void is likely to remain, a membrane with excellent fuel permeation deterrence can be obtained. There was a problem that it was difficult to be done. In addition, there are some in which fibrillated polytetrafluoroethylene is dispersed as a reinforcing material in a perfluorocarbon sulfonic acid polymer film (for example, see Patent Document 2). However, such a composite polymer solid electrolyte membrane has problems such as electrode peeling due to insufficient mechanical strength due to the discontinuous structure of the reinforcing material, and deformation of the membrane cannot be suppressed. Had.
[0006]
Polybenzazole polymers such as polybenzoxazole (PBO) and polybenzimidazole (PBI) are excellent in terms of high heat resistance, high strength, and high elastic modulus, and are therefore suitable for reinforcing materials for polymer solid electrolyte membranes. Expected to be. Conventionally, a PBO porous membrane and various ion exchange resins are combined (for example, refer to Patent Document 3). However, the porosity of the PBO porous membrane obtained by the method of directly coagulating the PBO solution thus formed in a water bath is 90% by volume or less, and when the ion exchange resin is combined, The content of the ion exchange resin becomes low, and the characteristics such as ion conductivity inherent to the ion exchange resin are greatly deteriorated. In addition, the composite ion exchange membrane described therein does not particularly define the formation of the surface ion exchange resin layer or the thickness thereof, but the presence or thickness of the surface layer in the composite ion exchange membrane is When forming an electrode on the surface, it is important to influence the adhesiveness between the ion exchange resin as a binder and the ion exchange resin to form a polymer solid electrolyte membrane, and to control them optimally.
[0007]
There is also a method for producing a polymer film for a fuel cell in which an acid is trapped in the voids of the PBI porous membrane (see, for example, Patent Document 4). However, the film trapped with a free acid obtained by such a method has low ionic conductivity in a low temperature region such as 100 ° C. or lower as compared with the above-described ion exchange membrane such as Nafion, and acid is likely to leak. It had problems such as. Furthermore, there is a method in which a polybenzazole film is obtained by forming an optically anisotropic polybenzazole-based polymer solution and then coagulating through an isotropic process by moisture absorption (see, for example, Patent Document 5). However, the polybenzazole film obtained by the method described therein is a transparent and dense film, and is not suitable for the purpose of impregnating an ion exchange resin to form an ion exchange membrane.
[0008]
Prior art document information related to the invention of this application includes the following.
[Patent Document 1]
JP-A-8-162132 (page 2-3)
[Patent Document 2]
JP 2001-35508 A (page 2-4)
[Patent Document 3]
International Publication No. 00/22684 (page 9-35, Table 2-7, Fig. 1)
[Patent Document 4]
International Publication No. 98/14505 Pamphlet (Pages 2-9)
[Patent Document 5]
JP 2000-273214 A (page 2-7)
[0009]
[Problems to be solved by the invention]
The present invention provides an electrolyte membrane-electrode assembly having a high polymer strength, a polymer solid electrolyte membrane excellent in ion conductivity, power generation characteristics, and gas barrier properties, and having good bondability between the electrolyte membrane and the electrode assembly. is there.
[0010]
[Means for Solving the Problems]
That is, the present invention It is obtained by solidifying an isotropic solution containing 0.3 to 3% by weight of a polybenzazole-based polymer into a film, Has continuous voids The porosity is 90% by volume or more, and the aperture ratio of at least one surface is 40% or more. A composite layer formed by impregnating a support membrane made of a polybenzazole-based polymer with an ion exchange resin, and an ion exchange resin that does not include the support membrane formed on both sides of the composite layer with the composite layer interposed therebetween Has a surface layer And the content of the ion exchange resin in the composite ion exchange membrane is 80% by weight or more. An electrolyte membrane-electrode assembly in which a catalyst layer and a gas diffusion layer are arranged on both sides of a composite ion exchange membrane. Furthermore, in the present invention, each thickness of the surface layer made of an ion exchange resin not including a support film formed on both surfaces is 2 μm or more and 30 μm or less And the electrolyte membrane-electrode assembly is in a range not exceeding half of the total thickness of the composite ion exchange membrane. The present invention also provides a fuel cell using the above electrolyte membrane-electrode assembly.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
The polybenzazole-based polymer used as the support membrane of the present invention is an oxazol in the polymer chain. Le A polymer having a structure containing a ring, a thiazole ring, and an imidazole ring, and a polymer chain containing a repeating unit represented by the following general formula.
[0012]
[Chemical 1]

[0013]
Where Ar ₁ , Ar ₂ , Ar _Three Represents an aromatic unit and may have various aliphatic groups, aromatic groups, halogen groups, hydroxyl groups, nitro groups, cyano groups, trifluoromethyl groups and other substituents. These aromatic units are monocyclic units such as benzene rings, condensed ring units such as naphthalene, anthracene, and pyrene, and polycyclic aromatic units in which two or more of these aromatic units are connected via an arbitrary bond. But it ’s okay. Moreover, the position of N and X in an aromatic unit will not be specifically limited if it is the arrangement | positioning which can form a benzazole ring. Furthermore, these may be not only hydrocarbon aromatic units but also heterocyclic aromatic units containing N, O, S, etc. in the aromatic ring. X represents O, S, NH.
Ar ₁ Are preferably those represented by the following general formula.
[0014]
[Chemical formula 2]

[0015]
Where Y ₁ , Y ₂ Represents CH or N, Z represents a direct bond, —O—, —S—, —SO. ₂ -, -C (CH _Three ) ₂ -, -C (CF _Three ) ₂ -, -CO-.
Ar ₂ Are preferably those represented by the following general formula.
[0016]
[Chemical 3]

[0017]
Here, W is -O-, -S-, -SO. ₂ -, -C (CH _Three ) ₂ -, -C (CH _Three ) ₂ -, -CO-.
Ar _Three Are preferably those represented by the following general formula.
[0018]
[Formula 4]

[0019]
These polybenzazole-based polymers may be homopolymers having the above-mentioned repeating units, but may be random, alternating or block copolymers in which the above structural units are combined. For example, US Pat. No. 4,703,103, Examples thereof include those described in US Pat. No. 4,533,692, US Pat. No. 4,533,724, US Pat. No. 4,533,693, US Pat. No. 4,359,567, US Pat. No. 4,578,432, and the like.
[0020]
Specific examples of these polybenzazole-based structural units include those represented by the following structural formulas.
[0021]
[Chemical formula 5]

[0022]
[Chemical 6]

[0023]
[Chemical 7]

[0024]
[Chemical 8]

[0025]
[Chemical 9]

[0026]
[Chemical Formula 10]

[0027]
Embedded image

[0028]
Furthermore, not only these polybenzazole-based structural units, but also random, alternating or block copolymers with other polymer structural units may be used. At this time, the other polymer constituent unit is preferably selected from aromatic polymer constituent units having excellent heat resistance. Specifically, polyimide structural unit, polyamide structural unit, polyamideimide structural unit, polyoxydiazole structural unit, polyazomethine structural unit, polybenzazoleimide structural unit, polyether ketone structural unit, Examples thereof include polyethersulfone structural units.
[0029]
As an example of a polyimide-type structural unit, what is represented by the following general formula is mentioned.
[0030]
Embedded image

[0031]
Where Ar _Four Is represented by a tetravalent aromatic unit, but is preferably represented by the following structure.
[0032]
Embedded image

[0033]
Ar _Five Is a divalent aromatic unit, preferably represented by the following structure. Various substituents such as a methyl group, a methoxy group, a halogen group, a trifluoromethyl group, a hydroxyl group, a nitro group, and a cyano group may be present on the aromatic ring shown here.
[0034]
Embedded image

[0035]
Specific examples of these polyimide-based structural units include those represented by the following structural formulas.
[0036]
Embedded image

[0037]
Embedded image

[0038]
Examples of the polyamide-based structural unit include those represented by the following structural formula.
[0039]
Embedded image

[0040]
Where Ar ₆ , Ar ₇ , Ar ₈ Are preferably independently selected from the following structures. Various substituents such as a methyl group, a methoxy group, a halogen group, a trifluoromethyl group, a hydroxyl group, a nitro group, and a cyano group may be present on the aromatic ring shown here.
[0041]
Embedded image

[0042]
Specific examples of these polyamide-based structural units include those represented by the following structural formulas.
[0043]
Embedded image

[0044]
Examples of the polyamideimide-based structural unit include those represented by the following structure.
[0045]
Embedded image

[0046]
Where Ar ₉ Is the above Ar _Five Those selected from the structures shown as specific examples are preferred.
[0047]
Specific examples of these polyamideimide structural units include those represented by the following structural formulas.
[0048]
Embedded image

[0049]
Examples of the polyoxydiazole-based structural unit include those represented by the following structural formula.
[0050]
Embedded image

[0051]
Where Ar _Ten Is the above Ar _Five Those selected from the structures shown as specific examples are preferred.
[0052]
Specific examples of these polyoxydiazole structural units include those represented by the following structural formulas.
[0053]
Embedded image

[0054]
Examples of polyazomethine structural units include those represented by the following structure.
[0055]
Embedded image

[0056]
Where Ar ₁₁ , Ar ₁₂ Is the above Ar ₆ Those selected from the structures shown as specific examples are preferred.
[0057]
Specific examples of these polyazomethine structural units include those represented by the following structural formulas.
[0058]
Embedded image

[0059]
Examples of the polybenzazole imide-based structural unit include those represented by the following structural formula.
[0060]
Embedded image

[0061]
Where Ar ₁₃ , Ar ₁₄ Is the above Ar _Four Those selected from the structures shown as specific examples are preferred.
[0062]
Specific examples of these polybenzazole imide-based structural units include those represented by the following structural formulas.
[0063]
Embedded image

[0064]
The polyether ketone structural unit and the polyether sulfone structural unit generally have a structure in which an aromatic unit is connected with an ether bond by a ketone bond or a sulfone bond, and includes a structural component selected from the following structural formula.
[0065]
Embedded image

[0066]
Where Ar ₁₅ ~ Ar _{twenty three} Are preferably independently represented by the following structures. Various substituents such as a methyl group, a methoxy group, a halogen group, a trifluoromethyl group, a hydroxyl group, a nitro group, and a cyano group may be present on the aromatic ring shown here.
[0067]
Embedded image

[0068]
Specific examples of these polyetherketone structural units include those represented by the following structural formula.
[0069]
Embedded image

[0070]
The aromatic polymer structural unit that can be copolymerized with these polybenzazole-based polymer structural units does not strictly indicate a repeating unit in the polymer chain, but can be present together with the polybenzazole-based structural units in the polymer main chain. Indicates the unit. These copolymerizable aromatic polymer structural units can be copolymerized not only alone but also in combination of two or more. In order to synthesize such a copolymer, an amino group, a carboxyl group, a hydroxyl group, a halogen group, etc. are introduced at the end of a unit consisting of a polybenzazole polymer constituent unit, and the reaction in the synthesis of these aromatic polymers. It may be polymerized as a component, or may be polymerized as a reaction component in the synthesis of a polybenzazole-based polymer by introducing a carboxyl group into the terminal of a unit containing these aromatic polymer constituent units.
[0071]
The polybenzazole-based polymer is subjected to condensation polymerization in a polyphosphoric acid solvent to obtain a polymer. The degree of polymerization of the polymer is expressed by intrinsic viscosity, preferably 15 dL / g or more, and more preferably 20 dL / g or more. If it falls below this range, the strength of the resulting support membrane is low, which is not preferred. The intrinsic viscosity is preferably 35 dL / g or less, and more preferably 26 dL / g or less. Exceeding this range is not preferable because the concentration range of the polybenzazole polymer solution from which an isotropic solution is obtained is limited, and film formation under isotropic conditions becomes difficult.
[0072]
As a method for forming a polybenzazole polymer solution, in addition to a casting method called casting method in which a polymer solution is cast on a substrate using a doctor blade or the like, a method of extruding from a linear slit die or a circumference Any method for forming a solution into a film, such as a method of blow-extrusion from a slit slit die, a sandwich method in which a polymer solution sandwiched between two substrates is pressed with a roller, or a spin coating method can be used. Preferred film forming methods suitable for the purpose of the present invention are the casting method and the sandwich method. As a substrate for casting and a substrate for sandwich method, various porous materials are used as substrates and substrates for the purpose of controlling the void structure of the support film during solidification in addition to glass plates, metal plates, resin films, etc. It can be preferably used.
[0073]
It is important that the polybenzazole-based polymer solution used in the present invention is formed in a composition under isotropic conditions in order to obtain a support film having a uniform and high porosity, which is preferable for the polybenzazole-based polymer solution. The concentration range is 0.3% or more, more preferably 0.5% or more, and further preferably 0.8% or more. If the concentration is lower than this range, the viscosity of the polymer solution becomes small, and the applicable film forming method is limited, and the strength of the obtained support film is small, which is not preferable. Furthermore, the concentration range is preferably 3% or less, more preferably 2% or less, and still more preferably 1.5% or less. If the concentration is higher than this range, a support film having a large porosity cannot be obtained, and the solution exhibits anisotropy depending on the polymer composition and degree of polymerization of the polybenzazole polymer, which is not preferable.
[0074]
In order to adjust the concentration of the polybenzazole polymer solution to the range shown above, the following method can be used. That is, a method in which a polymer solid is once separated from a polymerized polybenzazole-based polymer solution, and the concentration is adjusted by adding a solvent again and dissolving. Furthermore, a method of adjusting the concentration by adding a solvent to the polymer solution and diluting the polymer solution without separating the polymer solid from the polymer solution that has been subjected to condensation polymerization in polyphosphoric acid. Furthermore, there is a method of directly obtaining a polymer solution in the above concentration range by adjusting the polymerization composition of the polymer.
[0075]
Preferred solvents for use in adjusting the concentration of the polymer solution include methanesulfonic acid, dimethylsulfuric acid, polyphosphoric acid, sulfuric acid, trifluoroacetic acid, and the like, or a mixed solvent combining these solvents can also be used. Of these, methanesulfonic acid and polyphosphoric acid are particularly preferable.
[0076]
As a means for realizing the porous structure of the support membrane, a method of coagulating the formed isotropic polybenzazole polymer solution in contact with a poor solvent is used. The poor solvent is a solvent miscible with the solvent of the polymer solution, and may be in a liquid phase state or a gas phase state. Further, a combination of coagulation with a poor solvent in a gas phase and coagulation with a poor solvent in a liquid phase can be preferably used. As a poor solvent used for coagulation, water, acid aqueous solution, inorganic salt aqueous solution, alcohols, glycols, organic solvents such as glycerin, etc. can be used, but the combination with polybenzazole polymer solution to be used Depending on the problem, the surface porosity and porosity of the support membrane may be reduced, or discontinuous cavities may be formed inside the support membrane. Caution must be taken. In the coagulation of the isotropic polybenzazole-based polymer solution in the present invention, coagulation with a poor solvent from among water vapor, methanesulfonic acid aqueous solution, phosphoric acid aqueous solution, glycerin aqueous solution and inorganic salt aqueous solution such as magnesium chloride aqueous solution. By selecting the conditions, the surface and internal structure of the support film and the porosity were controlled. Particularly preferred solidification means are a method of solidifying by contacting with water vapor, a method of solidifying by contacting water vapor for a short time in the initial stage of solidification, then a method of solidifying by contacting with water, a method of solidifying by contacting with an aqueous methanesulfonic acid solution, etc. is there.
[0077]
As the polymer solidifies, the support membrane tends to shrink. While solidification proceeds, a tenter or a fixed frame may be used for the purpose of suppressing generation of wrinkles due to uneven shrinkage of the support film. Further, when solidifying a polymer solution molded on a substrate such as a glass plate, the shrinkage on the substrate may be controlled by controlling the roughness of the substrate surface.
[0078]
The support membrane solidified as described above should be thoroughly washed for the purpose of avoiding problems such as acceleration of polymer degradation by the residual solvent and outflow of residual solvent when using the composite electrolyte membrane. Is desirable. Cleaning can be performed by immersing the support membrane in a cleaning solution. A particularly preferred cleaning solution is water. Washing with water is preferably carried out until the pH of the washing solution when the support membrane is immersed in water is in the range of 5 to 8, more preferably in the range of 6.5 to 7.5.
[0079]
Using a polybenzazole-based polymer isotropic solution having a specific concentration range as described above, and having a structure suitable for the purpose of the present invention by using an appropriate coagulation means selected from the methods as described above. A support film made of a polybenzazole-based polymer is obtained. That is, it is a porous support film having continuous voids having openings on at least one surface of the support film. The support membrane consists of a three-dimensional network formed from fibrillar fibers of a polybenzazole-based polymer and has three-dimensional continuous voids in water using an atomic force microscope as shown in the examples. This was confirmed by observation of the surface of the support film and cross-sectional observation of the support film that retained the structure in water by epoxy embedding-deepoxidation by transmission electron microscope observation. Japanese Patent Application Laid-Open No. 2002-203576 describes an electrolyte membrane in which an ion conductive material is introduced into a membrane support having a communication hole penetrating in the thickness direction of the membrane. When a support whose orientation is mainly limited to the thickness direction of the membrane is used for the electrolyte membrane of a fuel cell, the continuity of the ion conductive material in the surface direction of the membrane is small, so the ion exchange of the fuel cell When used in a membrane, if a non-uniform state occurs in the surface direction, such as the concentration distribution of fuel gas or the amount of electrode catalyst attached, there is a problem that local deterioration of the ion exchange membrane tends to occur, which is not preferable.
[0080]
The porosity of the support film of the present invention is preferably 90% by volume or more, and more preferably 95% by volume or more. When the porosity is smaller than this range, the content of the ion exchange resin when the ion exchange resin is combined is small, and the ionic conductivity is lowered, which is not preferable.
[0081]
The support membrane of the present invention preferably has a porosity of at least one surface of 40% or more, more preferably 50% or more, and particularly preferably 60% or more. If the open area ratio of at least one surface is smaller than this range, it is not preferable because the ion exchange resin is hardly impregnated in the voids of the support membrane when the support membrane and the ion exchange resin are combined.
[0082]
A method of obtaining a composite ion exchange membrane by combining an ion exchange resin with a porous support membrane made of a polybenzazole-based polymer obtained by the above method will be described. That is, a method of obtaining a composite ion exchange membrane by immersing the support membrane in an ion exchange resin solution without drying, replacing the liquid inside the support membrane with an ion exchange resin solution, and drying. . When the liquid inside the support membrane is different from the solvent composition of the ion exchange resin solution, a method in which the liquid inside is replaced in advance according to the solvent composition is also employed.
[0083]
The support membrane of the present invention is characterized in that the void structure shrinks as the volume of the liquid inside the void decreases due to drying, and the apparent volume of the support membrane is greatly reduced. When the inside of the support film is fixed to a metal frame without impregnating the ion exchange resin and dried by limiting the shrinkage in the surface direction, the shrinkage occurs in the film thickness direction. The apparent film thickness after drying ranges from 0.5% to 10% of the film thickness before drying. Such a significant shrinkage does not occur in a porous support film other than the support film of the present invention, for example, a support film made of a stretched polytetrafluoroethylene polymer porous film.
[0084]
Due to such characteristics of the support membrane, when the liquid inside the voids of the support membrane is replaced with an ion exchange resin solution and then dried, the solvent of the ion exchange resin solution impregnated inside the voids evaporates. As the volume of the ion exchange resin solution decreases, the support membrane also shrinks, so that a dense composite membrane structure filled with the ion exchange resin in which voids inside the support membrane are deposited can be easily obtained. Can do. With this composite membrane structure, the composite ion exchange membrane of the present invention exhibits excellent fuel permeation deterrence. In a porous support film other than the support film of the present invention, for example, a support film made of a stretched polytetrafluoroethylene polymer porous film, the solvent of the ion exchange resin solution impregnated in the voids is evaporated and the ion exchange is performed. Even if the volume of the resin solution is reduced, the shrinkage of the support film is small, so that not only a large number of voids not filled with the ion exchange resin are formed inside the composite film after drying, but both sides of the support film are formed. Since the surface layer of the ion exchange resin which does not contain a support is not formed, it is not preferable.
[0085]
The composite ion exchange membrane also shrinks the support membrane significantly, so that the physical properties such as the concentration and viscosity of the ion exchange resin solution, the volatility of the solvent, the thickness and porosity of the support membrane, etc. By adjusting the combination, an excess of the ion exchange resin solution adhered to both surfaces of the support film in parallel with the formation of a composite layer in which the ion exchange resin filled the internal voids of the support film, The ion exchange resin solution discharged from the inside of the support membrane with the shrinkage of the support membrane is dried outside the surface of the support membrane to form an ion exchange resin layer that does not contain the support. As a result, it is possible to easily realize a structure in which a surface layer of an ion exchange resin not including a support film is formed on both sides of the composite layer with the composite layer interposed therebetween.
[0086]
Since the membrane other than the support membrane of the present invention, for example, the porous support membrane made of polytetrafluoroethylene polymer does not cause significant shrinkage as described above, when impregnated with an ion exchange resin solution and dried. Even if the ion exchange resin is deposited inside the support membrane, the voids remain, and the ion exchange resin layer sandwiching the support membrane composite layer is not formed. In order to eliminate this state, it is necessary to repeat the impregnation and drying of the ion exchange resin solution a plurality of times, which is not preferable because the process becomes complicated.
[0087]
The ion exchange resin used for the composite ion exchange membrane of the present invention is not particularly limited, and other than the above-mentioned perfluorocarbon sulfonic acid polymer, for example, polystyrene sulfonic acid, poly (trifluorostyrene) sulfonic acid, polyvinyl phosphone. Acid, polyvinyl carboxylic acid, at least one ionomer of polyvinyl sulfonic acid polymer, polysulfone, polyphenylene oxide, polyphenylene sulfoxide, polyphenylene sulfide, polyphenylene sulfide sulfone, polyparaphenylene, polyphenylquinoxaline, polyaryl ketone, polyether ketone, polybenzazole And ionomers in which at least one of aromatic polymers such as polyaramid polymer is sulfonated, phosphonated or carboxylated Kill. The polysulfone polymer here includes at least one of polyethersulfone, polyarylsulfone, polyarylethersulfone, polyphenylsulfone, and polyphenylenesulfone polymer. The polyether ketone polymer referred to here includes at least one of polyether ether ketone, polyether ketone-ketone, polyether ether ketone-ketone and polyether ketone ether-ketone polymer.
[0088]
The solvent for the ion exchange resin solution described above can be selected from solvents that do not dissolve, decompose or swell the polybenzazole polymer support membrane and can dissolve the ion exchange resin. However, since the solvent is removed after the support membrane is impregnated with the ion exchange resin solution to deposit the ion exchange resin, the solvent can be removed by evaporating using means such as heating or decompression. It is preferable that Here, since the polybenzazole-based polymer support membrane of the present invention has high heat resistance, in the production of a composite ion exchange membrane using a support membrane made of polytetrafluoroethylene that generates creep from a temperature of about 100 ° C. The ability to produce a composite ion exchange membrane using an ion exchange resin solution containing an unusable high boiling point solvent is also an excellent feature from the viewpoint that many types of ion exchange resins can be selected.
[0089]
The concentration of the ion exchange resin solution described above and the molecular weight of the ion exchange resin are not particularly limited, but are appropriately selected according to the type of ion exchange resin and the thickness of the composite ion exchange membrane to be obtained. Is done.
[0090]
Of the ion exchange resin in the composite ion exchange membrane obtained as described above. The content is 80% by weight or more. When the content is smaller than this range, the conductive resistance of the film increases or the water retention of the film decreases, so that sufficient power generation performance cannot be obtained.
[0091]
In addition, the composite ion exchange membrane of the present invention is characterized in that it has a surface layer made of an ion exchange resin not including a support on both sides of the composite layer so as to sandwich the composite layer as described above. Since the composite ion exchange membrane has the composite layer and the surface layer, the composite ion exchange membrane has high mechanical strength and has good adhesion with the electrode layer when the electrode layer is formed on the surface. It has the feature of being excellent. The thickness of the surface layer is 2 μm or more and 30 μm or less And each is preferably in a range not exceeding half of the total thickness of the composite ion exchange membrane. If the thickness of the surface layer is smaller than the above range, the adhesion with the electrode layer is deteriorated, and the ionic conductivity is lowered. If the thickness of the surface layer is larger than the above range, the reinforcing effect of the composite layer does not reach the outermost surface of the composite ion exchange membrane, and when the composite ion exchange membrane absorbs moisture, only the surface layer is greatly swollen. It is not preferable because the surface layer peels off from the composite layer.
[0092]
For the purpose of further improving properties such as mechanical strength, ion conductivity, and peel resistance of the ion exchange resin layer formed on the surface of the composite ion exchange membrane, a method of heat-treating the composite ion exchange membrane under appropriate conditions is also preferable. Can be used. Further, in order to adjust the thickness of the surface layer of the ion exchange resin formed on the surface, the composite ion exchange membrane is further immersed in an ion exchange resin solution, or an ion exchange resin solution is applied to the composite ion exchange membrane. Or by increasing the adhesion amount of the ion exchange resin layer by drying, or removing a part of the ion exchange resin solution adhering to the surface of the support film after being immersed in the ion exchange resin solution by a scraper, an air knife, It is also possible to use a method of reducing the amount of the ion exchange resin layer deposited by scraping it off with a roller or by absorbing it with a solution-absorbing material such as filter paper or sponge. Alternatively, a method of further improving the adhesion of the ion exchange resin layer by applying a hot press can be used together.
[0093]
The composite ion exchange membrane of the present invention is excellent in mechanical strength while having high ion conductivity. Moreover, it can be utilized as a composite ion exchange membrane, particularly as a polymer solid electrolyte membrane of a polymer electrolyte fuel cell, taking advantage of its characteristics.
[0094]
The electrode used in the present invention is not particularly limited, but is appropriately selected according to the shape and application of the fuel cell. For example, carbon paper or carbon cloth is selected. In addition, a water repellent processed with PTFE or the like is also used. The thickness of the electrode is not particularly limited, but is preferably 400 μm or less. More preferably, it is 300 μm or less.
[0095]
The catalyst layer used in the present invention is a layer having a catalyst such as platinum. The catalyst is not particularly limited as long as it is used for a polymer electrolyte fuel cell. It is preferable that a catalyst of a metal such as platinum or an alloy is contained in the catalyst layer in a state of being supported on carbon black. The catalyst layer contains an ion exchange resin. This ion exchange resin may be the same as or different from that contained in the composite ion exchange membrane, but is preferably the same. Two or more kinds of ion exchange resins may be contained. In addition to the ion exchange resin, the catalyst layer may contain another resin such as a fluororesin. Moreover, you may contain the single carbon black which does not carry | support a catalyst.
[0096]
The method for producing the electrolyte membrane-electrode assembly of the present invention is not particularly limited, but is appropriately selected according to the shape of the fuel cell, the use, and the like. For example, an ink or paste prepared by dispersing carbon black supporting a catalyst such as platinum in an ion exchange resin solution or a solution containing an ion exchange resin and a binder is sprayed or applied onto an electrode and dried. A method in which the electrolyte membrane and the catalyst layer are brought into contact with each other and hot pressed, and carbon black carrying a catalyst such as platinum is dispersed in an ion exchange resin solution or a solution containing an ion exchange resin and a binder. A method of spraying or applying the prepared ink or paste on the electrolyte membrane and overlaying the dried ink or paste so that the electrode and catalyst layer are in contact with each other and hot pressing, ion exchange of carbon black carrying a catalyst such as platinum Ink or paste prepared by dispersing in a resin solution or a solution containing an ion exchange resin and a binder is sprayed onto the release material. Is applied and dried so that the electrolyte membrane and the catalyst layer are in contact with each other, and the catalyst layer is transferred onto the electrolyte membrane by hot pressing, and this membrane is overlaid so that the electrode and the catalyst layer are in contact with each other. Combined and hot-pressed, the electrolyte membrane and electrode are bonded using an ink or paste created by dispersing carbon black carrying a catalyst such as platinum in an ion exchange resin solution or a solution containing an ion exchange resin and a binder. A method of bonding, carbon black supporting a catalyst such as platinum is dispersed in a solution containing a binder such as a fluororesin, applied to an electrode, dried and fired, and an ion exchange resin applied to the electrode, and then dried. Any method may be used such as a method of superposing and hot pressing so that the catalyst layer is in contact with the catalyst layer. In hot pressing, the film or / and the electrode may contain water, an organic solvent such as alcohol, an acid aqueous solution, or the like.
[0097]
When the composite ion exchange membrane of the present invention is used, when an electrolyte membrane-electrode assembly is produced, the membrane can be easily swelled or deformed.
[0098]
Composite ion exchange membranes that include a support membrane on the surface of the ion exchange membrane are often inferior in bondability to the electrodes compared to ion exchange membranes made solely of ion exchange resin, but the composite ion exchange membrane of the present invention is on both sides. Since it has the surface layer which consists of ion exchange resin which does not contain a support body film | membrane, it can join easily with an electrode similarly to the ion exchange membrane of ion exchange resin alone.
[0099]
The electrolyte membrane-electrode assembly of the present invention is excellent in mechanical strength while having high ionic conductivity. Further, taking advantage of the characteristics, it can be used as a polymer solid electrolyte membrane-electrode assembly particularly for a polymer electrolyte fuel cell.
[0100]
Example
Examples of the present invention are shown below, but the present invention is not limited to these Examples.
Evaluation and measurement methods
[0101]
<Intrinsic viscosity>
Using methanesulfonic acid as a solvent, the viscosity of the polymer solution adjusted to a concentration of 0.5 g / L was measured and calculated using a Ubbelohde viscometer in a 25 ° C. constant temperature bath.
[0102]
<Support film thickness>
The thickness of the undried support membrane was measured by the following method. Using a micrometer capable of changing the measurement load, the thickness of the support membrane in water at each load was measured. The measured thickness is plotted against the load, the value of the intercept when the linear portion is extrapolated to a load of 0 is taken as the thickness, and the average value of the thicknesses measured at five locations for one sample is taken as the thickness of the support membrane. .
[0103]
<Thickness of composite ion exchange membrane and thickness of layers constituting it>
The thickness of the composite layer constituting the composite ion exchange membrane and the surface layer made of an ion exchange resin not including a support membrane formed on both sides of the composite layer with the composite layer interposed therebetween is 300 μm wide × 5 mm long The composite membrane pieces cut out in the above are embedded with a resin having a composition of Lebeak 812 (manufactured by Nacalai Tesque) / rubeac NMA (manufactured by Nacalai Tesque) / DMP30 (manufactured by TAAB) = 100/89/4, and at 60 ° C. for 12 hours. A sample block was prepared by curing. The tip of the block was cut with a diamond knife (SK2045, manufactured by Sumitomo Electric) so that a smooth cross-section was exposed using an ultramicrotome (LKB 2088ULTROTOME 5). The cross section of the composite film thus exposed was photographed with an optical microscope and measured by comparing a scale with a known length with a photograph taken at the same magnification. In some cases, such as when the porosity of the support is large, the surface layer on at least one surface and the inner composite layer do not form a clear interface, and the structure near the interface may change continuously. In that case, the part that can be confirmed with the optical microscope with the continuous structural change is the part closest to the outer surface of the composite ion exchange membrane as the outermost surface of the composite layer, from there to the outer surface of the composite ion exchange membrane. Was the thickness of the surface layer.
[0104]
<Ion exchange resin (ICP) content of composite ion exchange membrane>
The ion exchange resin content of the composite ion exchange membrane was measured by the following method. Dc [g / m] of composite ion exchange membrane dried in vacuum at 110 ° C. for 6 hours ² ], And the basis weight Ds [g / m] of the dried support membrane measured by drying the support membrane under the same production conditions as used for the production of the composite ion exchange membrane without drying the ion exchange resin. ² From the above, the ion exchange resin content was determined by the following calculation.
Ion exchange resin content [wt%] = (Dc−Ds) / Dc × 100
Moreover, the ion exchange resin content rate of a composite ion exchange membrane can also be measured with the following method. That is, after the composite ion exchange membrane is immersed in a solvent capable of dissolving only the support membrane component or the ion exchange resin component in the composite ion exchange membrane, one component is extracted and removed, and then the original composite ion By measuring the weight change with the exchange membrane, the content of the ion exchange resin can be determined.
[0105]
<Strength and tensile modulus>
The strength characteristics of the ion exchange membrane were measured using Tensilon manufactured by Orientec Co., Ltd. in an atmosphere at a temperature of 25 ° C. and a relative humidity of 50%. The sample was a strip with a width of 10 mm, and was calculated from a stress strain curve measured at a span length of 40 mm and a pulling speed of 20 mm / sec.
[0106]
<Ionic conductivity>
The ionic conductivity σ was measured as follows. A platinum wire (diameter: 0.2 mm) is pressed against the surface of a strip-shaped film sample having a width of 10 mm on a self-made measuring probe (made of polytetrafluoroethylene) and placed in a constant temperature and humidity chamber at 80 ° C. and a relative humidity of 95%. The sample was held, and the AC impedance at 10 kHz between the platinum wires was measured by SOLARTRON 1250 FREQUENCY RESPONSE ANALYSER. Measured by changing the distance between the electrodes from 10 mm to 40 mm at 10 mm intervals, and the slope D of the straight line plotting the distance between the electrodes and the measured resistance value _r The contact resistance between the membrane and the platinum wire was canceled from [Ω / cm] by the following formula.
σ [S / cm] = 1 / (film width × film thickness [cm] × D _r )
[0107]
<Gas permeability>
The gas permeability of the ion exchange membrane was measured by the following method. After placing the ion exchange membrane on a mesh-like stainless steel support and fixing it to the holder, helium gas saturated with water vapor at room temperature is distributed on one side of the ion exchange membrane at a gauge pressure of 0.09 MPa. The amount of helium gas permeating the other surface of the ion exchange membrane was measured and calculated using a soap membrane flow meter.
[0108]
<Power generation characteristics>
The electrolyte membrane-electrode assembly is assembled in an evaluation fuel cell FC25-02SP manufactured by Electrochem, and the cell temperature is 80 ° C., the gas humidification temperature is 80 ° C., the fuel gas is 300 mL / min, the oxidizing gas is 1000 mL / min. The power generation characteristics were evaluated.
[0109]
Example 1
Isotropic with polyparaphenylene cis bisbisoxazole concentration of 1% by weight by adding methane sulfonic acid to a dope containing 14% by weight of polyparaphenylene cis benzobisoxazole polymer with IV = 24 dL / g in polyphosphoric acid A solution was prepared. This solution was formed on a glass plate heated to 90 ° C. using an applicator having a clearance of 300 μm at a film forming rate of 20 mm / second. The dope film thus formed on the glass plate was placed in a constant temperature and humidity chamber at 25 ° C. and 80% relative humidity to solidify for 1 hour, and the resulting film had a pH of 7 ± 0.5. The substrate film was prepared by washing with water. This support membrane is fixed to a stainless steel frame in water, and the water composition inside the support membrane is a solvent composition of a DuPont 20% Nafion (trade name) solution (product number: SE-20192) which is an ion exchange resin solution. And a mixed solvent of water: ethanol: 1-propanol = 26: 26: 48 (weight ratio). This support membrane was immersed in a 20% Nafion (trade name) solution at 25 ° C. for 15 hours and then removed from the solution. The solvent of the Nafion (trade name) solution impregnated inside the membrane and adhered to the membrane surface was volatilized by air drying. Dried. The dried membrane was preheated in an oven at 60 ° C. for 1 hour to remove the remaining solvent, and then heat treated at 150 ° C. for 1 hour in a nitrogen atmosphere to prepare a composite ion exchange membrane. DuPont 20% Nafion (trade name) solution (product number: SE-20192), platinum-supported carbon (carbon: Valbot XC-72, Cabot Co., platinum supported amount: 40 wt%), platinum and Nafion weight ratio The catalyst paste was prepared by adding 2.7: 1 and stirring. With this catalyst paste, the amount of platinum deposited on Toray carbon paper TGPH-060 is 1 mg / cm. ² It applied and dried so that it might become, and the gas diffusion layer with an electrode catalyst layer was created. The composite ion exchange membrane is sandwiched between two gas diffusion layers with an electrode catalyst layer so that the electrode catalyst layer is in contact with the membrane sample, and pressurized and heated at 120 ° C. and 2 MPa for 3 minutes by a hot press method. Thus, an electrolyte membrane-electrode assembly of Example 1 was obtained.
[0110]
Example 2
DuPont 20% Nafion (trade name) solution (product number: SE-20192), platinum-supported carbon (carbon: Valbot XC-72, Cabot Co., platinum supported amount: 40 wt%), platinum and Nafion weight ratio The catalyst paste was prepared by adding 2.7: 1 and stirring. This catalyst paste had an adhesion amount of platinum of 1 mg / cm on the same composite ion exchange membrane as shown in Example 1. ² It was applied and dried so that an ion exchange membrane with an electrode catalyst layer was formed. The ion exchange membrane was sandwiched between two Toray carbon papers TGPH-060, and the membrane-electrode junction of Example 2 was heated and pressurized at 120 ° C. and 2 MPa for 3 minutes by a hot press method. The body.
[0111]
Example 3
Poly {2,6-diimidazo [4,5-b: 4 ′, 5′-e] pyridinylene-1,4 (2,5-dihydroxy) phenylene} (hereinafter referred to as PIPD) having an intrinsic viscosity of 18 dL / g in polyphosphoric acid Except that the dope containing 19% by weight of polymer was diluted by adding methanesulfonic acid to prepare an isotropic solution with a PIPD polymer concentration of 1.5% by weight, which was used as a dope for forming a support membrane. The electrolyte membrane-electrode assembly of Example 3 was obtained in the same manner as shown in Example 1.
[0112]
Comparative Example 1
A commercially available Nafion 112 (trade name) membrane manufactured by DuPont was used as the ion exchange membrane. This membrane is an ion exchange membrane made of the same perfluorocarbon sulfonic acid polymer as the Nafion polymer contained in the 20% Nafion solution used in Example 1 and the 10% Nafion aqueous solution used in Example 2, and is a polymer electrolyte fuel cell It is widely used as an electrolyte membrane. DuPont 20% Nafion (trade name) solution (product number: SE-20192), platinum-supported carbon (carbon: Valbot XC-72, Cabot Co., platinum supported amount: 40 wt%), platinum and Nafion weight ratio The catalyst paste was prepared by adding 2.7: 1 and stirring. The amount of platinum deposited on this ion exchange membrane is 1 mg / cm. ² It was applied and dried so that an ion exchange membrane with an electrode catalyst layer was formed. This ion exchange membrane with an electrode catalyst layer swelled and deformed as if the membrane was wavy. The above-mentioned ion exchange membrane is sandwiched between two Toray carbon papers TGPH-060, and the electrolyte membrane-electrode joint of Comparative Example 1 is heated and heated at 120 ° C. and 2 MPa for 3 minutes by a hot press method. The body. This joined body was incompletely joined because the film was deformed and wavy.
[0113]
Comparative Example 2
When the support membrane immersed in the Nafion solution was removed from the Nafion solution, the Nafion solution adhered to both sides of the support membrane was scraped with a polytetrafluoroethylene scraper so that the surface of the support membrane was exposed. Except for the above, an electrolyte membrane-electrode assembly of Comparative Example 2 was prepared in the same manner as shown in Example 1.
[0114]
The physical property values of Examples 1 and 2 and Comparative Examples 1 and 2 are shown in Table 1.
[0115]
[Table 1]

[0116]
It can be seen that the composite ion exchange membranes of Examples 1 and 2 are ion exchange membranes having a large breaking strength and tensile modulus as compared with the commercially available Nafion 112 membrane of Comparative Example 1. In addition, the composite ion exchange membranes of Examples 1 and 2 have a support therein, but the ionic conductivity and power generation performance are not significantly reduced as compared with Comparative Example 1 that does not include a support. The transmittance is suppressed to a small value of half or less, and it can be seen that it has excellent characteristics as a polymer solid electrolyte membrane of a fuel cell.
[0117]
In the electrolyte membrane-electrode assembly of Example 2, even when the catalyst paste was directly applied, swelling deformation was small and the electrode could be bonded well. However, in the electrolyte membrane-electrode assembly of Comparative Example 2, when the catalyst paste was applied directly, Swelling deformation occurred and bonding by hot pressing could not be performed satisfactorily. Further, when the electrolyte membrane-electrode assembly was taken out from the fuel cell after evaluation after power generation evaluation, the electrode assembly was peeled off from the electrolyte membrane. This shows that the electrolyte membrane-electrode assembly of the present invention has good bondability between the electrolyte membrane and the electrode.
[0118]
In the electrolyte membrane-electrode assembly of Example 1, peeling between the electrolyte membrane and the electrode did not occur even after the power generation evaluation, but in the electrolyte membrane-electrode assembly of Comparative Example 1, after the power generation evaluation, the electrolyte membrane-electrode assembly Peeling occurred. Therefore, the composite ion exchange membrane including the support membrane on the surface layer of the ion exchange membrane is often inferior in bondability with the electrode to the ion exchange membrane of the ion exchange resin alone, but the composite used in the present invention Since the ion exchange membrane has a surface layer made of an ion exchange resin that does not include a support membrane on both sides, the electrolyte membrane-electrode assembly of the present invention is an electrolyte membrane-electrode assembly using an ion exchange membrane of an ion exchange resin alone. It can be seen that the bonding property with the electrode is good as with the above.
[0119]
【The invention's effect】
It is possible to provide an electrolyte membrane-electrode assembly having a high polymer strength, a solid polymer electrolyte membrane excellent in ion conductivity, power generation characteristics, and gas barrier properties, and having good bondability between the electrolyte membrane and the electrode assembly. it can.
[Brief description of the drawings]
FIG. 1 is a schematic diagram of a cross-sectional structure of a composite ion exchange membrane.
[Explanation of symbols]
1 surface layer A, 2 composite layer, 3 surface layer B, 4 catalyst layer, 5 gas diffusion layer

Claims (3)

In obtained by coagulating the isotropic solution containing 0.3 wt% to 3 wt% of polybenzazole polymer after molding into a film, have a continuous void, the void ratio is 90% or more by volume A composite layer in which an ion exchange resin is impregnated with a support membrane made of a polybenzazole-based polymer having an aperture ratio of at least 40% on at least one surface , and the composite layer sandwiched between the composite layers have a surface layer comprising an ion exchange resin containing no support membrane formed on both surfaces, the catalyst layer on both surfaces of the composite ion exchange membrane content of the ion-exchange resin which occupies the composite ion-exchange membrane is 80 wt% or more And an electrolyte membrane-electrode assembly provided with a gas diffusion layer. The thickness of each surface layer made of an ion exchange resin not including a support membrane formed on both sides is 2 μm or more and 30 μm or less, and does not exceed half of the total thickness of the composite ion exchange membrane. The electrolyte membrane-electrode assembly according to claim 1.   A fuel cell comprising the electrolyte membrane-electrode assembly according to claim 1.

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