JP4399586B2 - POLYMER ELECTROLYTE MEMBRANE, MEMBRANE ELECTRODE STRUCTURE PROVIDED WITH THE POLYMER ELECTROLYTE MEMBRANE, AND SOLID POLYMER TYPE FUEL CELL HAVING THE MEMBRANE ELECTRODE STRUCTURE - Google Patents

Description

【００３５】
前記重合体のスルホン化物は、前記重合体に濃硫酸を加え、スルホン酸基を０．５〜３．０ミリグラム当量／ｇの範囲で含むようにスルホン化することにより得ることができる。前記スルホン化物は、含有するスルホン酸基の量が０．５ミリグラム当量／ｇ未満であるときには十分なイオン導伝性を得ることができない。また、含有するスルホン酸基の量が３．０ミリグラム当量／ｇを超えると十分な靱性が得られず、後述の膜電極構造体を構成する際に取り扱いが難しくなる。
【００３６】
前記酸化防止剤は、複数のフェノール基を有し、かつフェノール基の酸素原子を除いて炭素原子及び水素原子のみから構成される化合物である。前記酸化防止剤としては、例えば、次式（５）で表される１，１，３−トリス（２−メチル−４−ヒドロキシ−５−ｔ−ブチルフェニル）ブタン、次式（６）で表される４，４’−ブチリデンビス（６−ｔ−ブチル−３−メチルフェノール）、次式（７）で表される１，３，５−トリメチル−２，４，６−トリス（３，５−ｔ−ブチル−４−ヒドロキシベンジル）ベンゼン等を挙げることができる。
【００３７】
【化２】

【００３８】
高分子電解質膜１を製造するときは、まず、前式（１）または（４）で表される重合体のスルホン化物を、Ｎ−メチルピロリドン等の溶媒に溶解して高分子電解質溶液とする。次に、前記高分子電解質溶液に、前記重合体のスルホン化物１００重量部に対し、前式（５）〜（７）で表される酸化防止剤のいずれか１種を０．１〜１０重量部の範囲で溶解する。そして、得られた溶液からキャスト法により成膜し、オーブンにて乾燥する。このようにすることにより、例えば、乾燥膜厚５０μｍの高分子電解質膜１を得ることができる。
【００３９】
電極触媒層２は、触媒粒子と含フッ素イオン導伝性高分子バインダーとからなる触媒ペーストを拡散層３上に触媒含有量が所定の量（例えば、０．５ｍｇ／ｃｍ²）となるようにスクリーン印刷し、乾燥させることにより形成される。前記触媒粒子は、カーボンブラック（ファーネスブラック）に白金粒子を所定の重量比（例えば、カーボンブラック：白金＝１：１）で担持させることにより作成される。また、前記触媒ペーストは、パーフルオロアルキレンスルホン酸高分子化合物（例えば、デュポン社製ナフィオン（商品名））等の含フッ素イオン導伝性高分子バインダー溶液に、前記触媒粒子を所定の重量比（例えば、触媒粒子：バインダー溶液＝１：１）で均一に分散させることにより調製される。
【００４０】
前記拡散層３は、下地層とカーボンペーパーとからなる。前記下地層は、カーボンブラックとポリテトラフルオロエチレン（ＰＴＦＥ）粒子とを所定の重量比（例えば、カーボンブラック：ＰＴＦＥ粒子＝４：６）で混合し、得られた混合物をエチレングリコール等の溶媒に均一に分散させたスラリーを前記カーボンペーパーの片面に塗布、乾燥させることにより形成される。
【００４１】
拡散層３上にスクリーン印刷された前記触媒ペーストは、例えば６０℃で１０分間の乾燥を行い、次いで１２０℃で６０分間の減圧乾燥を行うことにより乾燥される。
【００４２】
図１示の膜電極構造体は、前記１対の電極触媒層２と拡散層３とにより、電極触媒層２側で高分子電解質膜１を挟持し、ホットプレスを行うことにより得ることができる。前記ホットプレスは、例えば８０℃、５ＭＰａで２分間の一次ホットプレスを行い、次いで１６０℃、４ＭＰａで１分間の二次ホットプレスを行う。
【００４３】
次に、本発明の第２の実施形態の膜電極構造体は、図１示の高分子電解質膜１に替えて、図２示のように、高分子電解質膜４が１対の緩衝層５，５に挟持された複合高分子膜５を備えること以外は、第１の実施形態の膜電極構造体と全く同一の構成を備えている。
【００４４】
高分子電解質膜４は、主鎖及び／または側鎖に芳香族基を有する重合体のスルホン化物からなり、酸化防止剤を含んでいない。前記主鎖及び／または側鎖に芳香族基を有する重合体としては、例えば、第１の実施形態の膜電極構造体と同一の前式（１）で表されるポリエーテルエーテルケトン、または前式（４）で表される含フッ素共重合体等を挙げることができる。前記重合体のスルホン化物は、第１の実施形態の場合と全く同一にして得ることができる。
【００４５】
また、高分子電解質膜４は、前記重合体のスルホン化物を、Ｎ−メチルピロリドン等の溶媒に溶解して高分子電解質溶液とし、該高分子電解質溶液からキャスト法により成膜し、オーブンにて乾燥することにより、例えば、乾燥膜厚５０μｍの膜として得ることができる。
【００４６】
緩衝層５は、イオン導伝性物質と酸化防止剤とからなる。前記イオン導伝性物質としては、高分子電解質膜４と同一の主鎖及び／または側鎖に芳香族基を有する重合体のスルホン化物を用いてもよく、パーフルオロアルキレンスルホン酸高分子化合物（例えば、デュポン社製ナフィオン（商品名））を用いてもよい。また、前記酸化防止剤としては、第１の実施形態に用いたものと同一の前式（５）〜（７）で表される化合物のいずれか１種を用いることができる。
【００４７】
前記緩衝層５を製造するときは、まず、前記イオン導伝性物質を、Ｎ−メチルピロリドン等の溶媒に溶解する。次に、前記イオン導伝性物質の溶液に、前記イオン導伝性物質１００重量部に対し、前式（５）〜（７）で表される酸化防止剤のいずれか１種を０．０１〜６重量部の範囲で溶解する。そして、得られた溶液からキャスト法により成膜し、オーブンにて乾燥する。このようにすることにより、例えば、乾燥膜厚３μｍの緩衝層５を得ることができる。
【００４８】
前記複合高分子電解質膜６は、前記１対の緩衝層５により、高分子電解質膜４を挟持し、例えば、１５０℃、２．５ＭＰａで１分間のホットプレスを行うことにより得ることができる。
【００４９】
尚、緩衝層５は、高分子電解質膜４の両面から、前記酸化防止剤を所定の厚さに浸透させることにより形成するようにしてもよい。
【００５０】
また、図２示の膜電極構造体は、前記１対の電極触媒層２と拡散層３とにより、電極触媒層２側で複合高分子電解質膜６を挟持し、第１の実施形態の場合と全く同一にしてホットプレスを行うことにより得ることができる。
【００５１】
図１または図２に示す膜電極構造体は、拡散層３，３の上にさらにガス通路を兼ねるセパレータを積層することにより、固体高分子型燃料電池を構成することができる。
【００５２】
次に、本実施形態の実施例と比較例とを示す。
【００５３】
【実施例１】
本実施例では、まず、前式（１）で表されるポリエーテルエーテルケトン（ＶＩＣＴＲＥＸ社製、３８０Ｐ（グレード名））に濃硫酸を加え、スルホン酸基を１．９ミリグラム当量／ｇの範囲で含むようにスルホン化して、該ポリエーテルエーテルケトンのスルホン化物を調製した。次に、前記ポリエーテルエーテルケトンのスルホン化物を、Ｎ−メチルピロリドンに溶解して高分子電解質溶液とした。次に、該高分子電解質溶液に、前記ポリエーテルエーテルケトンのスルホン化物１００重量部に対し、酸化防止剤として前式（５）で表される１，１，３−トリス（２−メチル−４−ヒドロキシ−５−ｔ−ブチルフェニル）ブタン（ｍ．ｐ．１８６℃）を１重量部溶解した。そして、前記酸化防止剤を溶解した高分子電解質溶液からキャスト法により成膜し、オーブンにて乾燥することにより、乾燥膜厚５０μｍの高分子電解質膜を得た。
【００５４】
次に、本実施例の高分子電解質膜について、酸化防止剤の溶出の有無、耐酸化性、耐熱性を評価した。
【００５５】
前記高分子電解質膜は、酸化防止剤が溶出すると表面に白斑が現れるので、膜の外観を目視で観察し、酸化防止剤溶出の有無を確認した。
【００５６】
前記耐酸化性は、Ｈ₂Ｏ₂３％、Ｆｅ２０ｐｐｍを含む水溶液（フェントン試薬）を液温５０℃とし、該水溶液中に前記高分子電解質膜を８時間浸漬した後の該高分子電解質膜の重量低下率（％）として測定した。該重量低下率は、前記高分子電解質膜がフェントン試薬に酸化されて前記水溶液中に溶解した量を示し、数値が小さいほど耐酸化性が高いことを意味する。
【００５７】
前記耐熱性は、前記高分子電解質膜を１５０℃の雰囲気下に５時間放置し、さらに２３℃、相対湿度５０％の環境下に２時間放置する処理を行った後の引張試験による破断伸びの低下率（％）として算出した。前記引張試験は、ＪＩＳ Ｋ７１２７に準じて行った。
【００５８】
前記高分子電解質膜は、加熱されると高分子鎖間に架橋が形成され、脆くなる。従って、前記破断伸びの低下率（％）は、数値が小さいほど耐熱性が高いことを意味する。
【００５９】
また、前記高分子電解質膜は加熱により劣化が進むと色が変化するので、該高分子電解質膜の色の変化を目視で観察し、劣化の有無を判定した。
【００６０】
結果を表１に示す。また、重量低下率（％）と破断伸びの低下率（％）とを図３に示す。
【００６１】
【比較例１】
本比較例では、前記酸化防止剤を全く用いなかった以外は、実施例１と全く同一にして乾燥膜厚５０μｍの高分子電解質膜を得た。
【００６２】
次に、本比較例の高分子電解質膜について、実施例１と全く同一にして酸化防止剤の溶出の有無、耐酸化性、耐熱性を評価した。結果を表１に示す。また、重量低下率（％）と破断伸びの低下率（％）とを図３に示す。
【００６３】
【実施例２】
本実施例では、実施例１のポリエーテルエーテルケトンのスルホン化物に替えて、式（４）で表される含フッ素共重合体（ｎ：ｍ＝１：１）のスルホン化物を用いた以外は、実施例１と全く同一にして乾燥膜厚５０μｍの高分子電解質膜を得た。
【００６４】
次に、本実施例の高分子電解質膜について、実施例１と全く同一にして酸化防止剤の溶出の有無、耐酸化性、耐熱性を評価した。結果を表１に示す。また、重量低下率（％）と破断伸びの低下率（％）とを図３に示す。
【００６５】
次に、本実施例の高分子電解質膜の導電率を測定した。前記導電率は、前記高分子電解質膜を２枚の白金電極で挟持し、温度８５℃、相対湿度９０％の条件下、交流２端子法（周波数１０ｋＨｚ）で測定した。前記酸化防止剤の添加量と、前記導電率との関係を図４に示す。
【００６６】
【比較例２】
本比較例では、前記酸化防止剤を全く用いなかった以外は、実施例２と全く同一にして乾燥膜厚５０μｍの高分子電解質膜を得た。
【００６７】
次に、本比較例の高分子電解質膜について、実施例１と全く同一にして酸化防止剤の溶出の有無、耐酸化性、耐熱性を評価した。結果を表１に示す。また、重量低下率（％）と破断伸びの低下率（％）とを図３に示す。また、前記酸化防止剤の添加量と、重量低下率（％）との関係を図５に示す。
【００６８】
【表１】

【００６９】
表１、図３から、式（５）で表される酸化防止剤を用いる実施例１，２の高分子電解質膜は、前記酸化防止剤を全く用いない場合（比較例１，２）に比較して、重量低下率が小さく、優れた耐酸化性を示すことが明らかである。また、式（５）で表される酸化防止剤を用いる実施例１，２の高分子電解質膜は、前記酸化防止剤を全く用いない場合（比較例１，２）と略同等の耐熱性を備えていることが明らかである。
【００７０】
尚、実施例１の高分子電解質膜は、比較例２の高分子電解質膜に比較して、重量低下率が大きく、耐酸化性に劣るように見える。しかし、これは、実施例１、比較例１の高分子電解質膜が前式（１）で表されるポリエーテルエーテルケトンのスルホン化物であるのに対し、実施例２、比較例２の高分子電解質膜が前式（４）で表される含フッ素共重合体のスルホン化物であるという、高分子電解質の化学種の相違によるものである。
【００７１】
【実施例３】
本実施例では、前式（４）で表される含フッ素共重合体（ｎ：ｍ＝１：１）のスルホン化物１００重量部に対し、酸化防止剤として前式（５）で表される１，１，３−トリス（２−メチル−４−ヒドロキシ−５−ｔ−ブチルフェニル）ブタン６重量部を用いた以外は、実施例２と全く同一にして乾燥膜厚５０μｍの高分子電解質膜を得た。
【００７２】
次に、本実施例の高分子電解質膜について、実施例１と全く同一にして酸化防止剤の溶出の有無、耐酸化性、耐熱性を評価した。結果を表２に示す。また、前記酸化防止剤の添加量と、重量低下率（％）との関係を図５に示す。
【００７３】
また、本実施例の高分子電解質膜について、実施例２と全く同一にして導電率を測定した。前記酸化防止剤の添加量と、前記導電率との関係を図４に示す。
【００７４】
【実施例４】
本実施例では、前式（４）で表される含フッ素共重合体（ｎ：ｍ＝１：１）のスルホン化物１００重量部に対し、酸化防止剤として前式（５）で表される１，１，３−トリス（２−メチル−４−ヒドロキシ−５−ｔ−ブチルフェニル）ブタン０．４重量部を用いた以外は、実施例２と全く同一にして乾燥膜厚５０μｍの高分子電解質膜を得た。
【００７５】
次に、本実施例の高分子電解質膜について、実施例１と全く同一にして酸化防止剤の溶出の有無、耐酸化性、耐熱性を評価した。結果を表２に示す。また、前記酸化防止剤の添加量と、重量低下率（％）との関係を図５に示す。
【００７６】
また、本実施例の高分子電解質膜について、実施例２と全く同一にして導電率を測定した。前記酸化防止剤の添加量と、前記導電率との関係を図４に示す。
【００７７】
【比較例３】
本比較例では、前式（４）で表される含フッ素共重合体（ｎ：ｍ＝１：１）のスルホン化物１００重量部に対し、酸化防止剤として前式（５）で表される１，１，３−トリス（２−メチル−４−ヒドロキシ−５−ｔ−ブチルフェニル）ブタン０．００５重量部を用いた以外は、実施例２と全く同一にして乾燥膜厚５０μｍの高分子電解質膜を得た。
【００７８】
次に、本実施例の高分子電解質膜について、実施例１と全く同一にして酸化防止剤の溶出の有無、耐酸化性、耐熱性を評価した。結果を表２に示す。また、前記酸化防止剤の添加量と、重量低下率（％）との関係を図５に示す。
【００７９】
【比較例４】
本比較例では、前式（４）で表される含フッ素共重合体（ｎ：ｍ＝１：１）のスルホン化物１００重量部に対し、酸化防止剤として前式（５）で表される１，１，３−トリス（２−メチル−４−ヒドロキシ−５−ｔ−ブチルフェニル）ブタン２０重量部を用いた以外は、実施例２と全く同一にして乾燥膜厚５０μｍの高分子電解質膜を得た。
【００８０】
次に、本実施例の高分子電解質膜について、実施例１と全く同一にして酸化防止剤の溶出の有無、耐酸化性、耐熱性を評価した。結果を表２に示す。また、前記酸化防止剤の添加量と、重量低下率（％）との関係を図５に示す。
【００８１】
また、本実施例の高分子電解質膜について、実施例２と全く同一にして導電率を測定した。前記酸化防止剤の添加量と、前記導電率との関係を図４に示す。
【００８２】
【表２】

【００８３】
表２、図４，５から、前式（４）で表される含フッ素共重合体のスルホン化物１００重量部に対し、式（５）で表される酸化防止剤を０．１〜１０重量部の範囲で含む実施例２（表２に再掲した），３，４の高分子電解質膜は、耐酸化性、導電率に優れ、前記酸化防止剤を全く用いない場合（比較例２）と略同等の耐熱性を備えており、しかも前記酸化防止剤の溶出もないことが明らかである。
【００８４】
かかる実施例２〜４の高分子電解質膜に対し、前式（４）で表される含フッ素共重合体のスルホン化物１００重量部に対し、式（５）で表される酸化防止剤を０．１重量部未満の０．００５重量部含む比較例３の高分子電解質膜は、表２、図５から耐酸化性が酸化防止剤を全く含まない比較例２（表２に再掲した）の場合と略同等であり、殆ど耐酸化性を得ることができないことが明らかである。
【００８５】
また、前式（４）で表される含フッ素共重合体のスルホン化物１００重量部に対し、式（５）で表される酸化防止剤を１０重量部を超えて２０重量部含む比較例４の高分子電解質膜は、表２から、耐酸化性には優れているものの、前記酸化防止剤が溶出することが明らかである。かかる比較例４の高分子電解質膜は、図４から、実施例２〜４の高分子電解質膜に対し、著しく導電率が劣ることが明らかである。
【００８６】
【実施例５】
本実施例では、酸化防止剤として、実施例２で用いた前式（５）で表される１，１，３−トリス（２−メチル−４−ヒドロキシ−５−ｔ−ブチルフェニル）ブタンに替えて、前式（６）で表される４，４’−ブチリデンビス（６−ｔ−ブチル−３−メチルフェノール）（ｍ．ｐ．２１０℃）を用いた以外は、実施例２と全く同一にして乾燥膜厚５０μｍの高分子電解質膜を得た。
【００８７】
次に、本実施例の高分子電解質膜について、実施例１と全く同一にして酸化防止剤の溶出の有無、耐酸化性、耐熱性を評価した。結果を表３に示す。
【００８８】
【実施例６】
本実施例では、酸化防止剤として、実施例２で用いた前式（５）で表される１，１，３−トリス（２−メチル−４−ヒドロキシ−５−ｔ−ブチルフェニル）ブタンに替えて、前式（７）で表される１，３，５−トリメチル−２，４，６−トリス（３，５−ｔ−ブチル−４−ヒドロキシベンジル）ベンゼン（ｍ．ｐ．２４４℃）を用いた以外は、実施例２と全く同一にして乾燥膜厚５０μｍの高分子電解質膜を得た。
【００８９】
次に、本実施例の高分子電解質膜について、実施例１と全く同一にして酸化防止剤の溶出の有無、耐酸化性、耐熱性を評価した。結果を表３に示す。
【００９０】
【表３】

【００９１】
前式（６）で表される４，４’−ブチリデンビス（６−ｔ−ブチル−３−メチルフェノール）、前式（７）で表される１，３，５−トリメチル−２，４，６−トリス（３，５−ｔ−ブチル−４−ヒドロキシベンジル）ベンゼンは、前式（５）で表される１，１，３−トリス（２−メチル−４−ヒドロキシ−５−ｔ−ブチルフェニル）ブタンと同様に、複数のフェノール基を有し、かつフェノール基の酸素原子を除いて炭素原子及び水素原子のみから構成される化合物である。
【００９２】
この結果、表３から明らかなように、酸化防止剤として前式（６）、（７）の化合物を用いる実施例５，６の高分子電解質膜によれば、酸化防止剤として前式（５）の化合物を用いる実施例２の高分子電解質膜（表３に再掲する）と略同等の耐酸化性、耐熱性を得ることができることが明らかである。
【００９３】
【比較例５】
本比較例では、酸化防止剤として、実施例２で用いた前式（５）で表される１，１，３−トリス（２−メチル−４−ヒドロキシ−５−ｔ−ブチルフェニル）ブタンに替えて、次式（８）で表されるビス（２，２，６，６−テトラメチル−４−ピペリジル）セバケート（ｍ．ｐ．８６℃）を用いた以外は、実施例２と全く同一にして乾燥膜厚５０μｍの高分子電解質膜を得た。次式（８）で表される酸化防止剤は、分子構造中に全くフェノール基を含まず、しかもＮ原子、Ｏ原子を含んでいる。
【００９４】
【化３】

【００９５】
次に、本比較例の高分子電解質膜について、実施例１と全く同一にして酸化防止剤の溶出の有無、耐酸化性、耐熱性を評価した。結果を表４に示す。また、重量低下率（％）と破断伸びの低下率（％）とを図６に示す。
【００９６】
【比較例６】
本比較例では、酸化防止剤として、実施例２で用いた前式（５）で表される１，１，３−トリス（２−メチル−４−ヒドロキシ−５−ｔ−ブチルフェニル）ブタンに替えて、次式（９）で表される含イオウ化合物（ｍ．ｐ．２３℃以下）を用いた以外は、実施例２と全く同一にして乾燥膜厚５０μｍの高分子電解質膜を得た。次式（９）で表される酸化防止剤は、分子構造中に全くフェノール基を含まず、しかもＳ原子、Ｏ原子を含んでいる。
【００９７】
【化４】

【００９８】
次に、本比較例の高分子電解質膜について、実施例１と全く同一にして酸化防止剤の溶出の有無、耐酸化性、耐熱性を評価した。結果を表４に示す。また、重量低下率（％）と破断伸びの低下率（％）とを図６に示す。
【００９９】
【比較例７】
本比較例では、酸化防止剤として、実施例２で用いた前式（５）で表される１，１，３−トリス（２−メチル−４−ヒドロキシ−５−ｔ−ブチルフェニル）ブタンに替えて、次式（１０）で表される含リン化合物（ｍ．ｐ．１６５℃）を用いた以外は、実施例２と全く同一にして乾燥膜厚５０μｍの高分子電解質膜を得た。次式（１０）で表される酸化防止剤は、分子構造中に全くフェノール基を含まず、しかもＰ原子、Ｏ原子を含んでいる。
【０１００】
【化５】

【０１０１】
次に、本比較例の高分子電解質膜について、実施例１と全く同一にして酸化防止剤の溶出の有無、耐酸化性、耐熱性を評価した。結果を表４に示す。また、重量低下率（％）と破断伸びの低下率（％）とを図６に示す。
【０１０２】
【比較例８】
本比較例では、酸化防止剤として、実施例２で用いた前式（５）で表される１，１，３−トリス（２−メチル−４−ヒドロキシ−５−ｔ−ブチルフェニル）ブタンに替えて、次式（１１）で表されるトリス−（３，５−ジ−ｔ−ブチル−４−ヒドロキシベンジル）−イソシアヌレート（ｍ．ｐ．２２１℃）を用いた以外は、実施例２と全く同一にして乾燥膜厚５０μｍの高分子電解質膜を得た。次式（１１）で表される酸化防止剤は、分子構造中に複数のフェノール基を含むが、フェノール基以外にもＯ原子を含み、さらにＮ原子を含んでいる。
【０１０３】
【化６】

【０１０４】
次に、本比較例の高分子電解質膜について、実施例１と全く同一にして酸化防止剤の溶出の有無、耐酸化性、耐熱性を評価した。結果を表４に示す。また、重量低下率（％）と破断伸びの低下率（％）とを図６に示す。
【０１０５】
【比較例９】
本比較例では、酸化防止剤として、実施例２で用いた前式（５）で表される１，１，３−トリス（２−メチル−４−ヒドロキシ−５−ｔ−ブチルフェニル）ブタンに替えて、次式（１２）で表されるテトラキス〔メチレン−３−（３’，５’−ジ−ｔ−ブチル−４’−ヒドロキシフェニル）−プロピオネート〕メタン（ｍ．ｐ．１１５℃）を用いた以外は、実施例２と全く同一にして乾燥膜厚５０μｍの高分子電解質膜を得た。次式（１２）で表される酸化防止剤は、分子構造中に複数のフェノール基を含むが、フェノール基以外にもＯ原子を含んでいる。
【０１０６】
【化７】

【０１０７】
次に、本比較例の高分子電解質膜について、実施例１と全く同一にして酸化防止剤の溶出の有無、耐酸化性、耐熱性を評価した。結果を表４に示す。また、重量低下率（％）と破断伸びの低下率（％）とを図６に示す。
【０１０８】
【表４】

【０１０９】
表４、図６から、分子構造中に全くフェノール基を含まず、しかもＮ原子、Ｏ原子を含む酸化防止剤を用いる比較例５の高分子電解質膜、分子構造中に複数のフェノール基を含むが、フェノール基以外にもＯ原子を含み、さらにＮ原子を含む酸化防止剤を用いる比較例８の高分子電解質膜、分子構造中に複数のフェノール基を含むが、フェノール基以外にもＯ原子を含む比較例９の高分子電解質膜によれば、実施例２の高分子電解質膜（表４に再掲する）に対し、耐酸化性については略同等であるが、耐熱性について著しく劣ることが明らかである。
【０１１０】
また、表４、図６から、分子構造中に全くフェノール基を含まず、しかもＳ原子、Ｏ原子を含む比較例６の高分子電解質膜によれば、実施例２の高分子電解質膜に対し、耐酸化性、耐熱性について著しく劣ることが明らかである。
【０１１１】
さらに、表４、図６から、分子構造中に全くフェノール基を含まず、しかもＰ原子、Ｏ原子を含む比較例７の高分子電解質膜によれば、実施例２の高分子電解質膜に対し、耐熱性については略同等であるが、耐酸化性について著しく劣ることが明らかである。
【０１１２】
【比較例１０】
本比較例では、前式（４）で表される含フッ素共重合体（ｎ：ｍ＝１：１）のスルホン化物１００重量部に対し、酸化防止剤として前式（１１）で表されるトリス−（３，５−ジ−ｔ−ブチル−４−ヒドロキシベンジル）−イソシアヌレート６重量部を用いた以外は、実施例２と全く同一にして乾燥膜厚５０μｍの高分子電解質膜を得た。
【０１１３】
次に、本比較例の高分子電解質膜について、実施例１と全く同一にして酸化防止剤の溶出の有無、耐酸化性、耐熱性を評価した。結果を表５に示す。また、重量低下率（％）と破断伸びの低下率（％）とを図７に示す。
【０１１４】
【表５】

【０１１５】
表５、図７から、前式（４）で表される含フッ素共重合体（ｎ：ｍ＝１：１）のスルホン化物１００重量部に対し、酸化防止剤として前式（１１）で表されるトリス−（３，５−ジ−ｔ−ブチル−４−ヒドロキシベンジル）−イソシアヌレート６重量部を用いた本比較例の高分子電解質膜は、酸化防止剤として前式（５）で表される１，１，３−トリス（２−メチル−４−ヒドロキシ−５−ｔ−ブチルフェニル）ブタン６重量部を用いた実施例３の高分子電解質膜（表５に再掲する）に対して、耐酸化性については略同等であるが、耐熱性について著しく劣ることが明らかである。
【０１１６】
【実施例７】
本実施例では、まず、実施例で用いたものと同一の前式（４）で表される含フッ素共重合体（ｎ：ｍ＝１：１）のスルホン化物を、Ｎ−メチルピロリドンに溶解して高分子電解質溶液とし、該高分子電解質溶液からキャスト法により成膜し、オーブンにて乾燥することにより、乾燥膜厚５０μｍの第１の高分子電解質膜を得た。
【０１１７】
次に、前記高分子電解質溶液に、前記含フッ素共重合体のスルホン化物１００重量部に対し、酸化防止剤として前式（５）で表される１，１，３−トリス（２−メチル−４−ヒドロキシ−５−ｔ−ブチルフェニル）ブタン１重量部を溶解した。そして、前記酸化防止剤を溶解した高分子電解質溶液からキャスト法により成膜し、オーブンにて乾燥することにより、乾燥膜厚３μｍの第２の高分子電解質膜を２枚得た。
【０１１８】
次に、前記第２の高分子電解質膜を緩衝層とし、該緩衝層で前記第１の高分子電解質膜で挟持し、１５０℃、２．５ＭＰａで１分間のホットプレスを行うことにより複合高分子電解質膜Ａを得た。
【０１１９】
次に、本実施例の複合高分子電解質膜Ａについて、実施例１と全く同一にして酸化防止剤の溶出の有無、耐酸化性、耐熱性を評価した。結果を表６に示す。また、前記緩衝層（第２の高分子電解質膜）に対する前記酸化防止剤の添加量と、重量低下率（％）との関係を図８に示す。
【０１２０】
【実施例８】
本実施例では、前式（４）で表される含フッ素共重合体（ｎ：ｍ＝１：１）のスルホン化物１００重量部に対し、酸化防止剤として前式（５）で表される１，１，３−トリス（２−メチル−４−ヒドロキシ−５−ｔ−ブチルフェニル）ブタン０．４重量部を用いて乾燥膜厚３μｍの第２の高分子電解質膜２枚を得たた以外は、実施例７と全く同一にして、前記第１の高分子電解質膜が前記緩衝層（第２の高分子電解質膜）で挟持された複合高分子電解質膜Ａを得た。
【０１２１】
次に、本実施例の複合高分子電解質膜Ａについて、実施例１と全く同一にして酸化防止剤の溶出の有無、耐酸化性、耐熱性を評価した。結果を表６に示す。また、前記緩衝層（第２の高分子電解質膜）に対する前記酸化防止剤の添加量と、重量低下率（％）との関係を図８に示す。
【０１２２】
【実施例９】
本実施例では、前式（４）で表される含フッ素共重合体（ｎ：ｍ＝１：１）のスルホン化物１００重量部に対し、酸化防止剤として前式（５）で表される１，１，３−トリス（２−メチル−４−ヒドロキシ−５−ｔ−ブチルフェニル）ブタン６重量部を用いて乾燥膜厚３μｍの第２の高分子電解質膜２枚を得たた以外は、実施例７と全く同一にして、前記第１の高分子電解質膜が前記緩衝層（第２の高分子電解質膜）で挟持された複合高分子電解質膜Ａを得た。
【０１２３】
次に、本実施例の複合高分子電解質膜Ａについて、実施例１と全く同一にして酸化防止剤の溶出の有無、耐酸化性、耐熱性を評価した。結果を表６に示す。また、前記緩衝層（第２の高分子電解質膜）に対する前記酸化防止剤の添加量と、重量低下率（％）との関係を図８に示す。
【０１２４】
【比較例１１】
本比較例では、前式（４）で表される含フッ素共重合体（ｎ：ｍ＝１：１）のスルホン化物１００重量部に対し、酸化防止剤として前式（５）で表される１，１，３−トリス（２−メチル−４−ヒドロキシ−５−ｔ−ブチルフェニル）ブタン０．００５重量部を用いて乾燥膜厚３μｍの第２の高分子電解質膜２枚を得たた以外は、実施例７と全く同一にして、前記第１の高分子電解質膜が前記緩衝層（第２の高分子電解質膜）で挟持された複合高分子電解質膜Ａを得た。
【０１２５】
次に、本比較例の複合高分子電解質膜Ａについて、実施例１と全く同一にして酸化防止剤の溶出の有無、耐酸化性、耐熱性を評価した。結果を表６に示す。また、前記緩衝層（第２の高分子電解質膜）に対する前記酸化防止剤の添加量と、重量低下率（％）との関係を図８に示す。
【０１２６】
【実施例１０】
本実施例では、前式（４）で表される含フッ素共重合体（ｎ：ｍ＝１：１）のスルホン化物に替えて、パーフルオロアルキレンスルホン酸高分子化合物（デュポン社製ナフィオン（商品名））を用いて、乾燥膜厚３μｍの第２の高分子電解質膜２枚を得たた以外は、実施例７と全く同一にして、前記第１の高分子電解質膜が前記緩衝層（第２の高分子電解質膜）で挟持された複合高分子電解質膜Ｂを得た。
【０１２７】
次に、本実施例の複合高分子電解質膜Ｂについて、実施例１と全く同一にして酸化防止剤の溶出の有無、耐酸化性、耐熱性を評価した。結果を表６に示す。また、前記緩衝層（第２の高分子電解質膜）に対する前記酸化防止剤の添加量と、重量低下率（％）との関係を図８に示す。
【０１２８】
【実施例１１】
本実施例では、前記パーフルオロアルキレンスルホン酸高分子化合物１００重量部に対し、酸化防止剤として前式（５）で表される１，１，３−トリス（２−メチル−４−ヒドロキシ−５−ｔ−ブチルフェニル）ブタン０．０３重量部を用いて乾燥膜厚３μｍの第２の高分子電解質膜２枚を得たた以外は、実施例７と全く同一にして、前記第１の高分子電解質膜が前記緩衝層（第２の高分子電解質膜）で挟持された複合高分子電解質膜Ｂを得た。
【０１２９】
次に、本実施例の複合高分子電解質膜Ｂについて、実施例１と全く同一にして酸化防止剤の溶出の有無、耐酸化性、耐熱性を評価した。結果を表６に示す。また、前記緩衝層（第２の高分子電解質膜）に対する前記酸化防止剤の添加量と、重量低下率（％）との関係を図８に示す。
【０１３０】
【表６】

【０１３１】
表６、図８から、緩衝層（第２の高分子電解質膜）を構成するイオン導伝性物質が第１の高分子電解質膜と同一の前式（４）で表される含フッ素共重合体のスルホン化物であり、該緩衝層が前式（４）で表される含フッ素共重合体のスルホン化物１００重量部に対し前式（５）で表される酸化防止剤を０．４〜６重量部の範囲で含む実施例７〜９の複合高分子電解質膜Ａは、耐酸化性、導電率に優れ、しかも前記酸化防止剤の溶出もないことが明らかであり、実施例２〜４の高分子電解質膜（図８に再掲する）と同等の耐酸化性を備えていることが明らかである。
【０１３２】
かかる実施例７〜９の複合高分子電解質膜Ａに対し、前記緩衝層が前式（４）で表される含フッ素共重合体のスルホン化物１００重量部に対し式（５）で表される酸化防止剤を０．１重量部未満の０．００５重量部含む比較例１１の複合高分子電解質膜Ａは、耐酸化性において著しく劣ることが明らかである。
【０１３３】
また、前記実施例７〜９の複合高分子電解質膜Ａでは、酸化防止剤を全く含まない第１の高分子電解質膜の膜厚が５０μｍであることに対し、酸化防止剤を含む緩衝層（第２の高分子電解質膜）の膜厚が３μｍであることから、実施例２〜４の高分子電解質膜に対して、前記酸化防止剤の含有量が著しく低減されていることが明らかである。
【０１３４】
また、表６、図８から、緩衝層（第２の高分子電解質膜）を構成するイオン導伝性物質が前記パーフルオロアルキレンスルホン酸高分子化合物である実施例１０，１１の複合高分子電解質膜Ｂによれば、前記実施例７〜９の複合高分子電解質膜Ａに対してさらに優れた耐酸化性を得ることができることが明らかである。
【図面の簡単な説明】
【図１】本発明の第１の実施形態の膜電極構造体の構成を示す説明的断面図。
【図２】本発明の第２の実施形態の膜電極構造体の構成を示す説明的断面図。
【図３】本発明の第１の実施形態に用いる高分子電解質膜の重量低下率と破断伸び低下率とを酸化防止剤を含まない高分子電解質膜と比較するヒストグラム。
【図４】本発明の第１の実施形態に用いる高分子電解質膜における酸化防止剤の添加量と導電率との関係を示すグラフ。
【図５】本発明の第１の実施形態に用いる高分子電解質膜における酸化防止剤の添加量と重量低下率との関係を示すグラフ。
【図６】本発明の第１の実施形態に用いる高分子電解質膜の重量低下率と破断伸び低下率とを他の酸化防止剤を含む高分子電解質膜と比較するヒストグラム。
【図７】本発明の第１の実施形態に用いる高分子電解質膜の重量低下率と破断伸び低下率とを他の酸化防止剤を含む高分子電解質膜と比較するヒストグラム。
【図８】本発明の第２の実施形態に用いる高分子電解質膜における酸化防止剤の添加量と重量低下率との関係を第１の実施形態に用いる高分子電解質膜と比較するグラフ。
【符号の説明】
１，４…高分子電解質膜、 ２…電極、 ５…緩衝層、 ６…複合高分子電解質膜。[0001]
BACKGROUND OF THE INVENTION
The present invention Proton conductivity for polymer electrolyte fuel cells Polymer electrolyte membrane, Proton conductivity for polymer electrolyte fuel cells The present invention relates to a membrane electrode structure including a polymer electrolyte membrane and a polymer electrolyte fuel cell including the membrane electrode structure.
[0002]
[Prior art]
While oil resources are depleted, environmental problems such as global warming due to consumption of fossil fuels are becoming more serious. Therefore, fuel cells have attracted attention as a clean power source for electric motors that does not generate carbon dioxide, and have been widely developed. In some cases, the fuel cell has been put into practical use. When the fuel cell is mounted on an automobile or the like, a solid polymer fuel cell using a polymer electrolyte membrane is preferably used because a high voltage and a large current can be easily obtained.
[0003]
As a membrane electrode structure used in the polymer electrolyte fuel cell, a pair of electrodes formed by a catalyst such as platinum supported on a catalyst carrier such as carbon black and integrated by an ion conductive polymer binder A structure having a catalyst layer and having a polymer electrolyte membrane capable of conducting ions between both electrode catalyst layers is known. The membrane electrode structure can constitute a solid polymer fuel cell by laminating a diffusion layer on each electrode catalyst layer and further laminating a separator also serving as a gas passage.
[0004]
In the polymer electrolyte fuel cell, a reducing gas such as hydrogen or methanol is introduced through the diffusion layer using one electrode catalyst layer as a fuel electrode, and the diffusion layer is formed using the other electrode catalyst layer as an oxygen electrode. An oxidizing gas such as air or oxygen is introduced. In this way, on the fuel electrode side, protons and electrons are generated from the reducing gas by the action of the catalyst contained in the electrode catalyst layer, and the protons pass through the polymer electrolyte membrane to the oxygen electrode side. To the electrode catalyst layer. The protons react with the oxidizing gas and electrons introduced into the oxygen electrode by the action of the catalyst contained in the electrode catalyst layer in the electrode catalyst layer on the oxygen electrode side to generate water. Therefore, by connecting the fuel electrode and the oxygen electrode with a conducting wire, a circuit for sending electrons generated at the fuel electrode to the oxygen electrode is formed, and a current can be taken out.
[0005]
Conventionally, a perfluoroalkylenesulfonic acid polymer compound (for example, Nafion (trade name) manufactured by DuPont) has been widely used as the polymer electrolyte membrane. The perfluoroalkylene sulfonic acid polymer compound has excellent proton conductivity due to being sulfonated, and also has chemical resistance as a fluororesin, but is very expensive. There is.
[0006]
Therefore, as a low-cost polymer electrolyte membrane material replacing the perfluoroalkylene sulfonic acid polymer compound, for example, the use of a sulfonated polymer having an aromatic group in the main chain and / or side chain has been studied. . However, the polymer sulfonated product has a problem that sufficient oxidation resistance cannot be obtained when used in the polymer electrolyte fuel cell.
[0007]
The reason why sufficient oxidation resistance cannot be obtained is that water is generated in the electrode catalyst layer on the oxygen electrode side of the polymer electrolyte fuel cell. ₂ The action of radicals such as radicals and .OH radicals can be considered. When the radical is generated, the radical attacks a polymer electrolyte membrane made of a sulfonated polymer having an aromatic group in the main chain and / or side chain, and causes a chain reaction that breaks the polymer chain. As a result, it is considered that the polymer electrolyte membrane is deteriorated and the oxidation resistance is lowered.
[0008]
In order to prevent the polymer electrolyte membrane from being deteriorated by the radicals, it is conceivable to add an antioxidant having an action of trapping the radicals to the polymer electrolyte membrane. As said antioxidant, the compound provided with a some phenol group can be mentioned, for example.
[0009]
However, even if the antioxidant is added to the polymer electrolyte membrane, depending on the type of the antioxidant, deterioration of the polymer electrolyte membrane may not be prevented, and more than when no antioxidant is added. There is an inconvenience that heat resistance may decrease.
[0010]
[Problems to be solved by the invention]
The present invention eliminates such inconvenience and has excellent oxidation resistance and heat resistance equivalent to the conventional one. Proton conductivity for polymer electrolyte fuel cells Polymer electrolyte membrane, Proton conductivity for polymer electrolyte fuel cells It is an object of the present invention to provide a membrane electrode structure including a polymer electrolyte membrane and a solid polymer fuel cell including the membrane electrode structure.
[0011]
[Means for Solving the Problems]
When the present inventors added an antioxidant having an action of scavenging the radicals to the polymer electrolyte membrane made of a sulfonated polymer having an aromatic group in the main chain and / or side chain, The inventors have intensively studied why the polymer electrolyte membrane cannot be prevented from being deteriorated or the heat resistance may be lowered.
[0012]
As a result, the antioxidant has an O atom other than that contained in the phenol group in the molecular structure, or an atom having an unshared electron pair such as N, S, P, etc., and the sulfonated product of the polymer is electron withdrawing. It has been found that the polymer electrolyte membrane made of a sulfonated product of the polymer is deteriorated or the heat resistance is lowered when a portion that easily reacts with the unshared electron pair such as a functional group is provided. That is, in this case, although the radical is trapped by the antioxidant, it is considered that the antioxidant itself reacts with the sulfonated product of the polymer to cause deterioration of the sulfonated product of the polymer. .
[0013]
Therefore, the present inventors, as an antioxidant having the action of scavenging the radicals, a compound having a plurality of phenol groups and composed only of carbon atoms and hydrogen atoms excluding the oxygen atoms of the phenol group The present invention has been reached.
[0014]
In order to achieve the above object, the first aspect of the present invention Proton conductivity for polymer electrolyte fuel cells The polymer electrolyte membrane is a polymer electrolyte membrane containing a sulfonated polymer having an aromatic group in the main chain and / or side chain, and an antioxidant, and the antioxidant has a plurality of phenol groups. And 1,1,3-tris (2-methyl-4-hydroxy-5-tert-butylphenyl), which is a compound composed of only carbon atoms and hydrogen atoms excluding the oxygen atom of the phenol group It is one compound selected from the group consisting of butane and 4,4′-butylidenebis (6-t-butyl-3-methylphenol).
[0015]
Since the polymer electrolyte membrane contains the antioxidant, it is produced in the electrode catalyst layer on the oxygen electrode side of the fuel cell when used in a solid polymer fuel cell. ₂ The antioxidant captures radicals such as radicals and .OH radicals. Therefore, deterioration of the polymer electrolyte membrane due to reaction with the radicals can be prevented.
[0016]
Further, the antioxidant is composed of only carbon atoms and hydrogen atoms excluding the oxygen atom of the phenol group, and O atoms other than those contained in the phenol group in the molecular structure or N, S, P, etc. It does not have an atom with a shared electron pair. Therefore, even if the polymer electrolyte membrane includes a portion that easily reacts with the unshared electron pair, deterioration due to reaction with the antioxidant and reduction in heat resistance can be prevented.
[0017]
As a result, according to the polymer electrolyte membrane, excellent oxidation resistance and heat resistance equivalent to the conventional one can be obtained.
[0018]
The sulfonated polymer that forms the polymer electrolyte membrane has an aromatic group in the main chain and / or side chain, and the antioxidant also has a phenol group that is an aromatic group. Therefore, the antioxidant has an excellent affinity for the sulfonated product of the polymer, and can be blended in a relatively large amount with respect to the sulfonated product of the polymer.
[0019]
Therefore, the polymer electrolyte membrane includes the antioxidant in a range of 0.1 to 10 parts by weight with respect to 100 parts by weight of the sulfonated product. If the content of the antioxidant is less than 0.1 parts by weight, the effect of scavenging the radicals cannot be obtained. Further, when the content of the antioxidant exceeds 10 parts by weight, the antioxidant elutes from the polymer electrolyte membrane, and the conductivity is obtained when the polymer electrolyte membrane is used in a solid polymer fuel cell. Decreases.
[0020]
In the polymer electrolyte membrane, the antioxidant has a melting point of 150 ° C. or higher. When the melting point of the antioxidant is less than 150 ° C., when the polymer electrolyte membrane is used in a polymer electrolyte fuel cell, the antioxidant is eluted under a high temperature environment during operation of the fuel cell. There are things to do.
[0021]
Further, the second aspect of the present invention Proton conductivity for polymer electrolyte fuel cells The polymer electrolyte membrane is a composite high membrane composed of a polymer electrolyte membrane made of a sulfonated polymer having an aromatic group in the main chain and / or side chain, and a pair of buffer layers sandwiching the polymer electrolyte membrane. A molecular electrolyte membrane, wherein the buffer layer includes an ion conductive substance and an antioxidant, the antioxidant having a plurality of phenol groups, and excluding oxygen atoms of the phenol groups, A compound composed of only hydrogen atoms, 1,1,3-tris (2-methyl-4-hydroxy-5-tert-butylphenyl) butane, 4,4′-butylidenebis (6-tert-butyl-3) -A compound selected from the group consisting of (methylphenol), wherein the total thickness of the pair of buffer layers is smaller than the thickness of the polymer electrolyte membrane.
[0022]
In the present invention, the second aspect having the above-described configuration is provided. Proton conductivity for polymer electrolyte fuel cells Also according to the first aspect of the polymer electrolyte membrane Proton conductivity for polymer electrolyte fuel cells An effect equivalent to that of the polymer electrolyte membrane can be obtained, and deterioration of the polymer electrolyte membrane made of a sulfonated product of the polymer due to a reaction with the radical can be prevented. At this time, since the total thickness of the pair of buffer layers is smaller than the thickness of the polymer electrolyte membrane, the first aspect of the present invention Proton conductivity for polymer electrolyte fuel cells Compared to the polymer electrolyte membrane, the content of the antioxidant can be reduced.
[0023]
The ion conductive material used for the buffer layer may be a polymer sulfonated product having an aromatic group in the main chain and / or side chain, or a perfluoroalkylenesulfonic acid polymer compound.
[0024]
In the case where the ion conductive material is a sulfonated polymer having an aromatic group in the main chain and / or side chain, the buffer layer is added in an amount of 0.1% by weight with respect to 100 parts by weight of the ion conductive material. The antioxidant is contained in the range of 1 to 10 parts by weight. If the content of the antioxidant is less than 0.1 parts by weight, the effect of scavenging the radicals cannot be obtained. In addition, when the content of the antioxidant exceeds 10 parts by weight, the antioxidant is eluted from the buffer layer, and the conductivity is increased when the composite polymer electrolyte membrane is used in a solid polymer fuel cell. descend.
[0025]
Further, when the ion conductive material is the perfluoroalkylenesulfonic acid polymer compound, the perfluoroalkylenesulfonic acid polymer compound itself has excellent chemical stability, and the polymer electrolyte The effect | action which protects a film | membrane can be acquired. Therefore, in this case, the amount of the antioxidant contained in the buffer layer can be reduced, and the buffer layer is 0.01 to 5 parts by weight with respect to 100 parts by weight of the ion conductive material. In a range, the antioxidant is included.
[0026]
In the composite polymer electrolyte membrane, the content of the antioxidant is further reduced as compared with the polymer electrolyte membrane of the first aspect of the present invention by the buffer layer containing the antioxidant. Can do. When the content of the antioxidant is less than 0.01 parts by weight, the effect of scavenging the radicals cannot be obtained. Moreover, even if it contains the said antioxidant exceeding 5 weight part, the effect beyond it cannot be expected.
[0027]
On the other hand, since the perfluoroalkylene sulfonic acid polymer compound has excellent chemical stability as described above, even if it contains any antioxidant, deterioration due to reaction with the antioxidant, Does not cause deterioration of heat resistance. However, the antioxidant may migrate from the buffer layer to a polymer electrolyte membrane made of a sulfonated polymer having an aromatic group in the main chain and / or side chain. Therefore, even when the perfluoroalkylene sulfonic acid polymer compound is used as the ion conductive substance, the antioxidant has a plurality of phenol groups, and carbon atoms and oxygen atoms other than the phenol groups are excluded. It is preferable to use one composed only of hydrogen atoms.
[0029]
The membrane electrode structure of the present invention has any one of the above aspects. Proton conductivity for polymer electrolyte fuel cells A polymer electrolyte membrane; and Proton conductivity for polymer electrolyte fuel cells And an electrode sandwiching the polymer electrolyte membrane. The solid polymer fuel cell of the present invention is characterized by comprising the membrane electrode structure.
[0030]
The membrane electrode structure or the polymer electrolyte fuel cell of the present invention has any one of the above aspects. Proton conductivity for polymer electrolyte fuel cells Since the polymer electrolyte membrane is provided, excellent oxidation resistance and heat resistance equivalent to the conventional one can be obtained.
[0031]
DETAILED DESCRIPTION OF THE INVENTION
Next, embodiments of the present invention will be described in more detail with reference to the accompanying drawings. FIG. 1 is an explanatory sectional view showing the configuration of the membrane electrode structure according to the first embodiment of the present invention, and FIG. 2 is an explanatory sectional view showing the configuration of the membrane electrode structure according to the second embodiment. 3 is a histogram comparing the weight reduction rate and the breaking elongation reduction rate of the polymer electrolyte membrane used in the first embodiment with a polymer electrolyte membrane not containing an antioxidant, and FIG. 4 is a high histogram used in the first embodiment. FIG. 5 is a graph showing the relationship between the added amount of the antioxidant and the electrical conductivity in the molecular electrolyte membrane, and FIG. 5 shows the relationship between the added amount of the antioxidant and the weight reduction rate in the polymer electrolyte membrane used in the first embodiment. Graphs, FIGS. 6 and 7 are histograms comparing the weight reduction rate and the breaking elongation reduction rate of the polymer electrolyte membrane used in the first embodiment with polymer electrolyte membranes containing other antioxidants, and FIG. Of the antioxidant in the polymer electrolyte membrane used in the second embodiment The relationship between the pressure volume and weight reduction rate is a graph comparing the polymer electrolyte membrane used in the first embodiment.
[0032]
As shown in FIG. 1, a membrane electrode structure according to a first embodiment of the present invention includes a polymer electrolyte membrane 1, a pair of electrode catalyst layers 2 and 2 sandwiching the polymer electrolyte membrane 1, and both electrodes. It consists of a pair of diffusion layers 3 and 3 laminated on the catalyst layers 2 and 2.
[0033]
The polymer electrolyte membrane 1 comprises a polymer sulfonated product having an aromatic group in the main chain and / or side chain, and an antioxidant. Examples of the polymer having an aromatic group in the main chain and / or side chain include polyether ether ketone represented by the following formula (1) or 2,5-dichloro- represented by the following formula (2). 4 ′-(4-phenoxyphenoxy) benzophenone and 2,2-bis [4- {4- (4-chlorobenzoyl) phenoxy} phenyl] -1,1,1,3 represented by the following formula (3) Examples thereof include a fluorine-containing copolymer represented by the following formula (4) obtained by polymerizing 3,3-hexafluoropropane at a predetermined polymerization ratio.
[0034]
[Chemical 1]

[0035]
The sulfonated product of the polymer can be obtained by adding concentrated sulfuric acid to the polymer and sulfonated so as to contain sulfonic acid groups in the range of 0.5 to 3.0 milligram equivalent / g. The sulfonated product cannot obtain sufficient ion conductivity when the amount of the sulfonic acid group contained is less than 0.5 milligram equivalent / g. Further, if the amount of the sulfonic acid group contained exceeds 3.0 milligram equivalent / g, sufficient toughness cannot be obtained, and handling becomes difficult when constituting a membrane electrode structure described later.
[0036]
The antioxidant is a compound having a plurality of phenol groups and composed only of carbon atoms and hydrogen atoms excluding oxygen atoms of the phenol groups. Examples of the antioxidant include 1,1,3-tris (2-methyl-4-hydroxy-5-t-butylphenyl) butane represented by the following formula (5), and represented by the following formula (6). 4,4′-butylidenebis (6-tert-butyl-3-methylphenol), 1,3,5-trimethyl-2,4,6-tris (3,5- and t-butyl-4-hydroxybenzyl) benzene.
[0037]
[Chemical formula 2]

[0038]
When producing the polymer electrolyte membrane 1, first, the polymer sulfonated product represented by the above formula (1) or (4) is dissolved in a solvent such as N-methylpyrrolidone to obtain a polymer electrolyte solution. . Next, 0.1 to 10 weight percent of any one of the antioxidants represented by the above formulas (5) to (7) is added to the polymer electrolyte solution with respect to 100 weight parts of the sulfonated product of the polymer. Dissolves in the range of parts. Then, a film is formed from the obtained solution by a casting method and dried in an oven. By doing so, for example, the polymer electrolyte membrane 1 having a dry film thickness of 50 μm can be obtained.
[0039]
In the electrode catalyst layer 2, a catalyst paste comprising catalyst particles and a fluorine-containing ion conductive polymer binder is placed on the diffusion layer 3 with a predetermined catalyst content (for example, 0.5 mg / cm2). ² It is formed by screen-printing and drying. The catalyst particles are prepared by supporting platinum particles on carbon black (furnace black) at a predetermined weight ratio (for example, carbon black: platinum = 1: 1). Further, the catalyst paste is prepared by adding the catalyst particles to a fluorine-containing ion conductive polymer binder solution such as a perfluoroalkylenesulfonic acid polymer compound (for example, Nafion (trade name) manufactured by DuPont) in a predetermined weight ratio ( For example, it is prepared by uniformly dispersing with catalyst particles: binder solution = 1: 1).
[0040]
The diffusion layer 3 is composed of an underlayer and carbon paper. The undercoat layer is a mixture of carbon black and polytetrafluoroethylene (PTFE) particles at a predetermined weight ratio (for example, carbon black: PTFE particles = 4: 6), and the resulting mixture is mixed with a solvent such as ethylene glycol. It is formed by applying and drying a uniformly dispersed slurry on one side of the carbon paper.
[0041]
The catalyst paste screen-printed on the diffusion layer 3 is dried by, for example, drying at 60 ° C. for 10 minutes and then drying at 120 ° C. for 60 minutes under reduced pressure.
[0042]
The membrane electrode structure shown in FIG. 1 can be obtained by sandwiching the polymer electrolyte membrane 1 on the side of the electrode catalyst layer 2 between the pair of electrode catalyst layers 2 and the diffusion layer 3 and performing hot pressing. . The hot press is, for example, a primary hot press at 80 ° C. and 5 MPa for 2 minutes, and then a secondary hot press at 160 ° C. and 4 MPa for 1 minute.
[0043]
Next, in the membrane electrode structure of the second embodiment of the present invention, instead of the polymer electrolyte membrane 1 shown in FIG. 1, a polymer electrolyte membrane 4 is a pair of buffer layers 5 as shown in FIG. , 5 except that the composite polymer membrane 5 is sandwiched between the membrane electrode structures of the first embodiment.
[0044]
The polymer electrolyte membrane 4 is made of a sulfonated polymer having an aromatic group in the main chain and / or side chain, and does not contain an antioxidant. Examples of the polymer having an aromatic group in the main chain and / or side chain include polyether ether ketone represented by the same formula (1) as in the membrane electrode structure of the first embodiment, The fluorine-containing copolymer represented by Formula (4) can be mentioned. The sulfonated product of the polymer can be obtained in exactly the same way as in the first embodiment.
[0045]
The polymer electrolyte membrane 4 is prepared by dissolving the sulfonated polymer in a solvent such as N-methylpyrrolidone to form a polymer electrolyte solution, and forming the polymer electrolyte solution by a casting method in an oven. By drying, for example, a film having a dry film thickness of 50 μm can be obtained.
[0046]
The buffer layer 5 is made of an ion conductive material and an antioxidant. As the ion conductive material, a polymer sulfonated product having an aromatic group in the same main chain and / or side chain as the polymer electrolyte membrane 4 may be used, and a perfluoroalkylenesulfonic acid polymer compound ( For example, DuPont Nafion (trade name) may be used. In addition, as the antioxidant, any one of the compounds represented by the previous formulas (5) to (7) which are the same as those used in the first embodiment can be used.
[0047]
When the buffer layer 5 is manufactured, first, the ion conductive material is dissolved in a solvent such as N-methylpyrrolidone. Next, 0.01% of any one of the antioxidants represented by the previous formulas (5) to (7) is added to the solution of the ion conductive material with respect to 100 parts by weight of the ion conductive material. Dissolves in the range of ~ 6 parts by weight. Then, a film is formed from the obtained solution by a casting method and dried in an oven. In this way, for example, the buffer layer 5 having a dry film thickness of 3 μm Get Can.
[0048]
The composite polymer electrolyte membrane 6 can be obtained by sandwiching the polymer electrolyte membrane 4 between the pair of buffer layers 5 and performing hot pressing at 150 ° C. and 2.5 MPa for 1 minute, for example.
[0049]
The buffer layer 5 may be formed by infiltrating the antioxidant to a predetermined thickness from both sides of the polymer electrolyte membrane 4.
[0050]
In the case of the first embodiment, the membrane electrode structure shown in FIG. 2 sandwiches the composite polymer electrolyte membrane 6 on the electrode catalyst layer 2 side by the pair of electrode catalyst layers 2 and the diffusion layer 3. It can be obtained by performing hot pressing in exactly the same way.
[0051]
The membrane electrode structure shown in FIG. 1 or 2 can constitute a solid polymer fuel cell by further laminating a separator that also serves as a gas passage on the diffusion layers 3 and 3.
[0052]
Next, examples of the present embodiment and comparative examples will be described.
[0053]
[Example 1]
In this example, first, concentrated sulfuric acid was added to the polyether ether ketone represented by the above formula (1) (manufactured by VICTREX, 380P (grade name)), and the sulfonic acid group was within a range of 1.9 milligram equivalent / g. The polyether ether ketone sulfonated product was prepared by sulfonation to include Next, the sulfonated product of the polyether ether ketone was dissolved in N-methylpyrrolidone to obtain a polymer electrolyte solution. Next, 1,1,3-tris (2-methyl-4) represented by the above formula (5) as an antioxidant is added to the polymer electrolyte solution with respect to 100 parts by weight of the sulfonated product of the polyether ether ketone. 1 part by weight of -hydroxy-5-t-butylphenyl) butane (mp 186 ° C.) was dissolved. And it formed into a film by the casting method from the polymer electrolyte solution which melt | dissolved the said antioxidant, and the polymer electrolyte membrane with a dry film thickness of 50 micrometers was obtained by drying in oven.
[0054]
Next, the presence / absence of elution of the antioxidant, oxidation resistance, and heat resistance of the polymer electrolyte membrane of this example were evaluated.
[0055]
Since the polymer electrolyte membrane had white spots appearing on the surface when the antioxidant was eluted, the appearance of the membrane was visually observed to confirm whether the antioxidant was eluted.
[0056]
The oxidation resistance is H ₂ O ₂ An aqueous solution containing 3% Fe20 ppm (Fenton reagent) was set at a liquid temperature of 50 ° C., and the weight reduction rate (%) of the polymer electrolyte membrane after the polymer electrolyte membrane was immersed in the aqueous solution for 8 hours was measured. The weight reduction rate indicates the amount of the polymer electrolyte membrane oxidized by the Fenton reagent and dissolved in the aqueous solution, and the smaller the value, the higher the oxidation resistance.
[0057]
The heat resistance is determined by the elongation at break according to a tensile test after the polymer electrolyte membrane was left in an atmosphere of 150 ° C. for 5 hours and further left in an environment of 23 ° C. and 50% relative humidity for 2 hours. It was calculated as a reduction rate (%). The tensile test was performed according to JIS K7127.
[0058]
When the polymer electrolyte membrane is heated, crosslinks are formed between the polymer chains and become brittle. Therefore, the decreasing rate (%) of the elongation at break means that the smaller the value, the higher the heat resistance.
[0059]
Moreover, since the color of the polymer electrolyte membrane changes as the deterioration proceeds by heating, the color change of the polymer electrolyte membrane was visually observed to determine the presence or absence of deterioration.
[0060]
The results are shown in Table 1. Moreover, the weight reduction rate (%) and the elongation reduction rate (%) are shown in FIG.
[0061]
[Comparative Example 1]
In this comparative example, a polymer electrolyte membrane having a dry film thickness of 50 μm was obtained in the same manner as in Example 1 except that the antioxidant was not used at all.
[0062]
Next, the presence / absence of dissolution of the antioxidant, oxidation resistance, and heat resistance of the polymer electrolyte membrane of this comparative example were evaluated in exactly the same manner as in Example 1. The results are shown in Table 1. Moreover, the weight reduction rate (%) and the elongation reduction rate (%) are shown in FIG.
[0063]
[Example 2]
In this example, the sulfonated product of the fluorine-containing copolymer (n: m = 1: 1) represented by the formula (4) was used in place of the sulfonated product of the polyether ether ketone of Example 1. A polymer electrolyte membrane having a dry film thickness of 50 μm was obtained in exactly the same manner as in Example 1.
[0064]
Next, for the polymer electrolyte membrane of this example, the presence / absence of elution of the antioxidant, oxidation resistance, and heat resistance were evaluated in exactly the same manner as in Example 1. The results are shown in Table 1. Moreover, the weight reduction rate (%) and the elongation reduction rate (%) are shown in FIG.
[0065]
Next, the electrical conductivity of the polymer electrolyte membrane of this example was measured. The conductivity was measured by the AC two-terminal method (frequency 10 kHz) under the conditions of a temperature of 85 ° C. and a relative humidity of 90%, with the polymer electrolyte membrane sandwiched between two platinum electrodes. FIG. 4 shows the relationship between the added amount of the antioxidant and the conductivity.
[0066]
[Comparative Example 2]
In this comparative example, a polymer electrolyte membrane having a dry film thickness of 50 μm was obtained in the same manner as in Example 2 except that the antioxidant was not used at all.
[0067]
Next, the presence / absence of dissolution of the antioxidant, oxidation resistance, and heat resistance of the polymer electrolyte membrane of this comparative example were evaluated in exactly the same manner as in Example 1. The results are shown in Table 1. Moreover, the weight reduction rate (%) and the elongation reduction rate (%) are shown in FIG. Moreover, the relationship between the addition amount of the said antioxidant and a weight decreasing rate (%) is shown in FIG.
[0068]
[Table 1]

[0069]
From Table 1 and FIG. 3, the polymer electrolyte membranes of Examples 1 and 2 using the antioxidant represented by Formula (5) are compared with the case where the antioxidant is not used at all (Comparative Examples 1 and 2). Thus, it is apparent that the weight reduction rate is small and excellent oxidation resistance is exhibited. Further, the polymer electrolyte membranes of Examples 1 and 2 using the antioxidant represented by the formula (5) have substantially the same heat resistance as the case where the antioxidant is not used at all (Comparative Examples 1 and 2). It is clear that it has.
[0070]
It should be noted that the polymer electrolyte membrane of Example 1 has a larger weight reduction rate than the polymer electrolyte membrane of Comparative Example 2, and appears to be inferior in oxidation resistance. However, this is because the polymer electrolyte membranes of Example 1 and Comparative Example 1 are sulfonated products of polyetheretherketone represented by the above formula (1), whereas the polymers of Example 2 and Comparative Example 2 are used. This is due to the difference in the chemical species of the polymer electrolyte, in which the electrolyte membrane is a sulfonated product of the fluorine-containing copolymer represented by the above formula (4).
[0071]
[Example 3]
In this example, 100 parts by weight of the sulfonated product of the fluorine-containing copolymer (n: m = 1: 1) represented by the above formula (4) is represented by the above formula (5) as an antioxidant. A polymer electrolyte membrane having a dry film thickness of 50 μm exactly as in Example 2 except that 6 parts by weight of 1,1,3-tris (2-methyl-4-hydroxy-5-tert-butylphenyl) butane was used. Got.
[0072]
Next, for the polymer electrolyte membrane of this example, the presence / absence of elution of the antioxidant, oxidation resistance, and heat resistance were evaluated in exactly the same manner as in Example 1. The results are shown in Table 2. Moreover, the relationship between the addition amount of the said antioxidant and a weight decreasing rate (%) is shown in FIG.
[0073]
Further, the conductivity of the polymer electrolyte membrane of this example was measured in the same manner as in Example 2. FIG. 4 shows the relationship between the added amount of the antioxidant and the conductivity.
[0074]
[Example 4]
In this example, 100 parts by weight of the sulfonated product of the fluorine-containing copolymer (n: m = 1: 1) represented by the above formula (4) is represented by the above formula (5) as an antioxidant. A polymer having a dry film thickness of 50 μm exactly the same as in Example 2 except that 0.4 parts by weight of 1,1,3-tris (2-methyl-4-hydroxy-5-tert-butylphenyl) butane was used. An electrolyte membrane was obtained.
[0075]
Next, for the polymer electrolyte membrane of this example, the presence / absence of elution of the antioxidant, oxidation resistance, and heat resistance were evaluated in exactly the same manner as in Example 1. The results are shown in Table 2. Moreover, the relationship between the addition amount of the said antioxidant and a weight decreasing rate (%) is shown in FIG.
[0076]
Further, the conductivity of the polymer electrolyte membrane of this example was measured in the same manner as in Example 2. FIG. 4 shows the relationship between the added amount of the antioxidant and the conductivity.
[0077]
[Comparative Example 3]
In this comparative example, with respect to 100 parts by weight of the sulfonated product of the fluorine-containing copolymer (n: m = 1: 1) represented by the above formula (4), the antioxidant is represented by the above formula (5). A polymer having a dry film thickness of 50 μm exactly the same as Example 2 except that 0.005 part by weight of 1,1,3-tris (2-methyl-4-hydroxy-5-tert-butylphenyl) butane was used. An electrolyte membrane was obtained.
[0078]
Next, for the polymer electrolyte membrane of this example, the presence / absence of elution of the antioxidant, oxidation resistance, and heat resistance were evaluated in exactly the same manner as in Example 1. The results are shown in Table 2. Moreover, the relationship between the addition amount of the said antioxidant and a weight decreasing rate (%) is shown in FIG.
[0079]
[Comparative Example 4]
In this comparative example, with respect to 100 parts by weight of the sulfonated product of the fluorine-containing copolymer (n: m = 1: 1) represented by the above formula (4), the antioxidant is represented by the above formula (5). A polymer electrolyte membrane having a dry film thickness of 50 μm exactly as in Example 2 except that 20 parts by weight of 1,1,3-tris (2-methyl-4-hydroxy-5-tert-butylphenyl) butane was used. Got.
[0080]
Next, for the polymer electrolyte membrane of this example, the presence / absence of elution of the antioxidant, oxidation resistance, and heat resistance were evaluated in exactly the same manner as in Example 1. The results are shown in Table 2. Moreover, the relationship between the addition amount of the said antioxidant and a weight decreasing rate (%) is shown in FIG.
[0081]
Further, the conductivity of the polymer electrolyte membrane of this example was measured in the same manner as in Example 2. FIG. 4 shows the relationship between the added amount of the antioxidant and the conductivity.
[0082]
[Table 2]

[0083]
From Table 2 and FIGS. 4 and 5, 0.1 to 10 weight of the antioxidant represented by the formula (5) with respect to 100 parts by weight of the sulfonated fluorinated copolymer represented by the previous formula (4). The polymer electrolyte membranes of Example 2 (reprinted in Table 2), 3 and 4 included in the range of parts are excellent in oxidation resistance and electrical conductivity, and when no antioxidant is used (Comparative Example 2). It is apparent that they have substantially the same heat resistance and that the antioxidant is not eluted.
[0084]
For the polymer electrolyte membranes of Examples 2 to 4, the antioxidant represented by Formula (5) was added to 100 parts by weight of the sulfonated fluorinated copolymer represented by Formula (4). The polymer electrolyte membrane of Comparative Example 3 containing 0.005 parts by weight of less than 1 part by weight is that of Comparative Example 2 (reproduced in Table 2) whose oxidation resistance does not contain any antioxidant from Table 2 and FIG. It is clear that the oxidation resistance is almost the same as that of the case and almost no oxidation resistance can be obtained.
[0085]
Further, Comparative Example 4 containing 20 parts by weight of the antioxidant represented by formula (5) in excess of 10 parts by weight with respect to 100 parts by weight of the sulfonated fluorinated copolymer represented by formula (4). From Table 2, it is clear that the above-mentioned antioxidant elutes, although the polymer electrolyte membrane is excellent in oxidation resistance. It is clear from FIG. 4 that the polymer electrolyte membrane of Comparative Example 4 is significantly inferior in conductivity to the polymer electrolyte membranes of Examples 2 to 4.
[0086]
[Example 5]
In this example, as an antioxidant, 1,1,3-tris (2-methyl-4-hydroxy-5-t-butylphenyl) butane represented by the formula (5) used in Example 2 was used. Instead, it was exactly the same as Example 2 except that 4,4′-butylidenebis (6-tert-butyl-3-methylphenol) (mp 210 ° C.) represented by the formula (6) was used. Thus, a polymer electrolyte membrane having a dry film thickness of 50 μm was obtained.
[0087]
Next, for the polymer electrolyte membrane of this example, the presence / absence of elution of the antioxidant, oxidation resistance, and heat resistance were evaluated in exactly the same manner as in Example 1. The results are shown in Table 3.
[0088]
[Example 6]
In this example, as an antioxidant, 1,1,3-tris (2-methyl-4-hydroxy-5-t-butylphenyl) butane represented by the formula (5) used in Example 2 was used. Instead, 1,3,5-trimethyl-2,4,6-tris (3,5-t-butyl-4-hydroxybenzyl) benzene represented by the above formula (7) (mp 244 ° C.) A polymer electrolyte membrane having a dry film thickness of 50 μm was obtained in the same manner as in Example 2 except that was used.
[0089]
Next, for the polymer electrolyte membrane of this example, the presence / absence of elution of the antioxidant, oxidation resistance, and heat resistance were evaluated in exactly the same manner as in Example 1. The results are shown in Table 3.
[0090]
[Table 3]

[0091]
4,4′-butylidenebis (6-tert-butyl-3-methylphenol) represented by the formula (6), 1,3,5-trimethyl-2,4,6 represented by the formula (7) -Tris (3,5-t-butyl-4-hydroxybenzyl) benzene is 1,1,3-tris (2-methyl-4-hydroxy-5-t-butylphenyl) represented by the formula (5) ) Similar to butane, it is a compound having a plurality of phenol groups and composed only of carbon atoms and hydrogen atoms excluding the oxygen atoms of the phenol groups.
[0092]
As a result, as is apparent from Table 3, according to the polymer electrolyte membranes of Examples 5 and 6 using the compounds of the formulas (6) and (7) as the antioxidant, the formula (5) It is apparent that oxidation resistance and heat resistance substantially equivalent to those of the polymer electrolyte membrane of Example 2 using the compound (1) (reproduced in Table 3) can be obtained.
[0093]
[Comparative Example 5]
In this comparative example, 1,1,3-tris (2-methyl-4-hydroxy-5-t-butylphenyl) butane represented by the above formula (5) used in Example 2 was used as an antioxidant. Instead, it was exactly the same as Example 2 except that bis (2,2,6,6-tetramethyl-4-piperidyl) sebacate (mp 86 ° C.) represented by the following formula (8) was used. Thus, a polymer electrolyte membrane having a dry film thickness of 50 μm was obtained. The antioxidant represented by the following formula (8) does not contain any phenol group in the molecular structure, and further contains N atoms and O atoms.
[0094]
[Chemical 3]

[0095]
Next, the presence / absence of dissolution of the antioxidant, oxidation resistance, and heat resistance of the polymer electrolyte membrane of this comparative example were evaluated in exactly the same manner as in Example 1. The results are shown in Table 4. Moreover, the weight reduction rate (%) and the elongation reduction rate (%) are shown in FIG.
[0096]
[Comparative Example 6]
In this comparative example, 1,1,3-tris (2-methyl-4-hydroxy-5-t-butylphenyl) butane represented by the above formula (5) used in Example 2 was used as an antioxidant. Instead, a polymer electrolyte membrane having a dry film thickness of 50 μm was obtained in exactly the same manner as in Example 2 except that the sulfur-containing compound (mp 23 ° C. or lower) represented by the following formula (9) was used. . The antioxidant represented by the following formula (9) does not contain any phenol group in the molecular structure, and further contains S atoms and O atoms.
[0097]
[Formula 4]

[0098]
Next, for the polymer electrolyte membrane of this comparative example, the presence / absence of antioxidant dissolution, oxidation resistance, and heat resistance were evaluated in exactly the same manner as in Example 1. The results are shown in Table 4. Moreover, the weight reduction rate (%) and the elongation reduction rate (%) are shown in FIG.
[0099]
[Comparative Example 7]
In this comparative example, 1,1,3-tris (2-methyl-4-hydroxy-5-t-butylphenyl) butane represented by the above formula (5) used in Example 2 was used as an antioxidant. Instead, a polymer electrolyte membrane having a dry film thickness of 50 μm was obtained in exactly the same manner as in Example 2 except that the phosphorus-containing compound (mp 165 ° C.) represented by the following formula (10) was used. The antioxidant represented by the following formula (10) does not contain any phenol group in the molecular structure, and further contains P atoms and O atoms.
[0100]
[Chemical formula 5]

[0101]
Next, for the polymer electrolyte membrane of this comparative example, the presence / absence of antioxidant dissolution, oxidation resistance, and heat resistance were evaluated in exactly the same manner as in Example 1. The results are shown in Table 4. Moreover, the weight reduction rate (%) and the elongation reduction rate (%) are shown in FIG.
[0102]
[Comparative Example 8]
In this comparative example, 1,1,3-tris (2-methyl-4-hydroxy-5-t-butylphenyl) butane represented by the above formula (5) used in Example 2 was used as an antioxidant. Instead, Example 2 was used except that tris- (3,5-di-t-butyl-4-hydroxybenzyl) -isocyanurate (mp 221 ° C.) represented by the following formula (11) was used. And a polymer electrolyte membrane having a dry film thickness of 50 μm was obtained. The antioxidant represented by the following formula (11) contains a plurality of phenol groups in the molecular structure, but contains O atoms in addition to the phenol groups, and further contains N atoms.
[0103]
[Chemical 6]

[0104]
Next, for the polymer electrolyte membrane of this comparative example, the presence / absence of antioxidant dissolution, oxidation resistance, and heat resistance were evaluated in exactly the same manner as in Example 1. The results are shown in Table 4. Moreover, the weight reduction rate (%) and the elongation reduction rate (%) are shown in FIG.
[0105]
[Comparative Example 9]
In this comparative example, 1,1,3-tris (2-methyl-4-hydroxy-5-t-butylphenyl) butane represented by the above formula (5) used in Example 2 was used as an antioxidant. Instead, tetrakis [methylene-3- (3 ′, 5′-di-t-butyl-4′-hydroxyphenyl) -propionate] methane represented by the following formula (12) (mp 115 ° C.) is used. A polymer electrolyte membrane having a dry film thickness of 50 μm was obtained in exactly the same manner as in Example 2 except that it was used. The antioxidant represented by the following formula (12) contains a plurality of phenol groups in the molecular structure, but also contains O atoms in addition to the phenol groups.
[0106]
[Chemical 7]

[0107]
Next, for the polymer electrolyte membrane of this comparative example, the presence / absence of antioxidant dissolution, oxidation resistance, and heat resistance were evaluated in exactly the same manner as in Example 1. The results are shown in Table 4. Moreover, the weight reduction rate (%) and the elongation reduction rate (%) are shown in FIG.
[0108]
[Table 4]

[0109]
From Table 4 and FIG. 6, the polymer electrolyte membrane of the comparative example 5 which uses the antioxidant which does not contain a phenol group at all in a molecular structure and also contains an N atom and an O atom, and contains a plurality of phenol groups in the molecular structure However, the polymer electrolyte membrane of Comparative Example 8 containing an O atom in addition to the phenol group and further containing an N atom contains a plurality of phenol groups in the molecular structure. According to the polymer electrolyte membrane of Comparative Example 9 containing, the oxidation resistance of the polymer electrolyte membrane of Example 2 (reproduced in Table 4) is substantially equivalent, but the heat resistance may be significantly inferior. it is obvious.
[0110]
Further, from Table 4 and FIG. 6, according to the polymer electrolyte membrane of Comparative Example 6 containing no phenol group in the molecular structure and containing S atoms and O atoms, the polymer electrolyte membrane of Example 2 was compared with that of Example 2. It is apparent that the oxidation resistance and heat resistance are significantly inferior.
[0111]
Furthermore, from Table 4 and FIG. 6, according to the polymer electrolyte membrane of Comparative Example 7 which does not contain any phenol group in the molecular structure and also contains P atoms and O atoms, the polymer electrolyte membrane of Example 2 It is clear that the heat resistance is almost the same, but the oxidation resistance is remarkably inferior.
[0112]
[Comparative Example 10]
In this comparative example, with respect to 100 parts by weight of the sulfonated product of the fluorine-containing copolymer (n: m = 1: 1) represented by the above formula (4), the antioxidant is represented by the above formula (11). Except for using 6 parts by weight of tris- (3,5-di-t-butyl-4-hydroxybenzyl) -isocyanurate, a polymer electrolyte membrane having a dry film thickness of 50 μm was obtained in the same manner as in Example 2. .
[0113]
Next, for the polymer electrolyte membrane of this comparative example, the presence / absence of antioxidant dissolution, oxidation resistance, and heat resistance were evaluated in exactly the same manner as in Example 1. The results are shown in Table 5. Further, the weight reduction rate (%) and the elongation reduction rate (%) are shown in FIG.
[0114]
[Table 5]

[0115]
From Table 5 and FIG. 7, with respect to 100 parts by weight of the sulfonated product of the fluorine-containing copolymer (n: m = 1: 1) represented by the above formula (4), the antioxidant is represented by the above formula (11). The polymer electrolyte membrane of this comparative example using 6 parts by weight of tris- (3,5-di-t-butyl-4-hydroxybenzyl) -isocyanurate is represented by the formula (5) as an antioxidant. For the polymer electrolyte membrane of Example 3 using 6 parts by weight of 1,1,3-tris (2-methyl-4-hydroxy-5-t-butylphenyl) butane as described above (reproduced in Table 5) It is clear that the oxidation resistance is substantially the same, but the heat resistance is remarkably inferior.
[0116]
[Example 7]
In this example, first, a sulfonated product of a fluorine-containing copolymer (n: m = 1: 1) represented by the same formula (4) as that used in the example was dissolved in N-methylpyrrolidone. Thus, a polymer electrolyte solution was formed, and a film was formed from the polymer electrolyte solution by a casting method, followed by drying in an oven to obtain a first polymer electrolyte membrane having a dry film thickness of 50 μm.
[0117]
Next, in the polymer electrolyte solution, 1,1,3-tris (2-methyl-) represented by the above formula (5) as an antioxidant with respect to 100 parts by weight of the sulfonated product of the fluorine-containing copolymer. 1 part by weight of 4-hydroxy-5-tert-butylphenyl) butane was dissolved. And it formed into a film from the polymer electrolyte solution which melt | dissolved the said antioxidant by the casting method, and dried in oven, and obtained two 2nd polymer electrolyte membranes with a dry film thickness of 3 micrometers.
[0118]
Next, the second polymer electrolyte membrane is used as a buffer layer, and the buffer layer is sandwiched between the first polymer electrolyte membranes, and hot pressing is performed at 150 ° C. and 2.5 MPa for 1 minute. A molecular electrolyte membrane A was obtained.
[0119]
Next, the composite polymer electrolyte membrane A of this example was evaluated in the same manner as in Example 1 for the presence or absence of antioxidant dissolution, oxidation resistance, and heat resistance. The results are shown in Table 6. FIG. 8 shows the relationship between the amount of the antioxidant added to the buffer layer (second polymer electrolyte membrane) and the weight reduction rate (%).
[0120]
[Example 8]
In this example, 100 parts by weight of the sulfonated product of the fluorine-containing copolymer (n: m = 1: 1) represented by the above formula (4) is represented by the above formula (5) as an antioxidant. Two second polymer electrolyte membranes having a dry film thickness of 3 μm were obtained using 0.4 parts by weight of 1,1,3-tris (2-methyl-4-hydroxy-5-tert-butylphenyl) butane. Except for the above, a composite polymer electrolyte membrane A in which the first polymer electrolyte membrane was sandwiched between the buffer layers (second polymer electrolyte membrane) was obtained in the same manner as in Example 7.
[0121]
Next, the composite polymer electrolyte membrane A of this example was evaluated in the same manner as in Example 1 for the presence or absence of antioxidant dissolution, oxidation resistance, and heat resistance. The results are shown in Table 6. FIG. 8 shows the relationship between the amount of the antioxidant added to the buffer layer (second polymer electrolyte membrane) and the weight reduction rate (%).
[0122]
[Example 9]
In this example, 100 parts by weight of the sulfonated product of the fluorine-containing copolymer (n: m = 1: 1) represented by the above formula (4) is represented by the above formula (5) as an antioxidant. Except that two second polymer electrolyte membranes having a dry film thickness of 3 μm were obtained using 6 parts by weight of 1,1,3-tris (2-methyl-4-hydroxy-5-t-butylphenyl) butane. In the same manner as in Example 7, a composite polymer electrolyte membrane A in which the first polymer electrolyte membrane was sandwiched between the buffer layers (second polymer electrolyte membrane) was obtained.
[0123]
Next, the composite polymer electrolyte membrane A of this example was evaluated in the same manner as in Example 1 for the presence or absence of antioxidant dissolution, oxidation resistance, and heat resistance. The results are shown in Table 6. FIG. 8 shows the relationship between the amount of the antioxidant added to the buffer layer (second polymer electrolyte membrane) and the weight reduction rate (%).
[0124]
[Comparative Example 11]
In this comparative example, with respect to 100 parts by weight of the sulfonated product of the fluorine-containing copolymer (n: m = 1: 1) represented by the above formula (4), the antioxidant is represented by the above formula (5). Two second polymer electrolyte membranes having a dry film thickness of 3 μm were obtained using 0.005 parts by weight of 1,1,3-tris (2-methyl-4-hydroxy-5-tert-butylphenyl) butane. Except for the above, a composite polymer electrolyte membrane A in which the first polymer electrolyte membrane was sandwiched between the buffer layers (second polymer electrolyte membrane) was obtained in the same manner as in Example 7.
[0125]
Next, the composite polymer electrolyte membrane A of this comparative example was evaluated in the same manner as in Example 1 for the presence or absence of antioxidant dissolution, oxidation resistance, and heat resistance. The results are shown in Table 6. FIG. 8 shows the relationship between the amount of the antioxidant added to the buffer layer (second polymer electrolyte membrane) and the weight reduction rate (%).
[0126]
[Example 10]
In this example, perfluoroalkylenesulfonic acid polymer compound (Dafon Nafion (commercial product) was used instead of the sulfonated fluorinated copolymer (n: m = 1: 1) represented by the above formula (4). The first polymer electrolyte membrane is the same as in Example 7 except that two second polymer electrolyte membranes having a dry film thickness of 3 μm were obtained using A composite polymer electrolyte membrane B sandwiched between the second polymer electrolyte membranes) was obtained.
[0127]
Next, the composite polymer electrolyte membrane B of this example was evaluated in the same manner as in Example 1 for the presence or absence of antioxidant dissolution, oxidation resistance, and heat resistance. The results are shown in Table 6. FIG. 8 shows the relationship between the amount of the antioxidant added to the buffer layer (second polymer electrolyte membrane) and the weight reduction rate (%).
[0128]
Example 11
In this example, 1,1,3-tris (2-methyl-4-hydroxy-5) represented by the above formula (5) as an antioxidant with respect to 100 parts by weight of the perfluoroalkylenesulfonic acid polymer compound. Except that two second polymer electrolyte membranes having a dry film thickness of 3 μm were obtained using 0.03 part by weight of (t-butylphenyl) butane, the same procedure as in Example 7 was carried out. A composite polymer electrolyte membrane B in which a molecular electrolyte membrane was sandwiched between the buffer layers (second polymer electrolyte membrane) was obtained.
[0129]
Next, the composite polymer electrolyte membrane B of this example was evaluated in the same manner as in Example 1 for the presence or absence of antioxidant dissolution, oxidation resistance, and heat resistance. The results are shown in Table 6. FIG. 8 shows the relationship between the amount of the antioxidant added to the buffer layer (second polymer electrolyte membrane) and the weight reduction rate (%).
[0130]
[Table 6]

[0131]
From Table 6 and FIG. 8, the fluorine-containing copolymer represented by the same formula (4) as that of the first polymer electrolyte membrane is used as the ion conductive material constituting the buffer layer (second polymer electrolyte membrane). It is a sulfonated product of a combination, and the buffer layer has an antioxidant represented by the formula (5) of 0.4 to 100 parts by weight based on 100 parts by weight of the sulfonated fluorinated copolymer represented by the formula (4) It is clear that the composite polymer electrolyte membranes A of Examples 7 to 9 contained in the range of 6 parts by weight are excellent in oxidation resistance and electrical conductivity, and are free from elution of the antioxidant. It is apparent that the polymer electrolyte membrane (reproduced in FIG. 8) has the same oxidation resistance.
[0132]
For the composite polymer electrolyte membrane A of Examples 7 to 9, the buffer layer is represented by the formula (5) with respect to 100 parts by weight of the sulfonated fluorinated copolymer represented by the formula (4). It is apparent that the composite polymer electrolyte membrane A of Comparative Example 11 containing 0.005 parts by weight of antioxidant less than 0.1 parts by weight is remarkably inferior in oxidation resistance.
[0133]
In the composite polymer electrolyte membranes A of Examples 7 to 9, the first polymer electrolyte membrane containing no antioxidant is 50 μm in thickness, whereas the buffer layer containing the antioxidant ( Since the film thickness of the second polymer electrolyte membrane) is 3 μm, it is clear that the content of the antioxidant is remarkably reduced with respect to the polymer electrolyte membranes of Examples 2 to 4. .
[0134]
Further, from Table 6 and FIG. 8, the composite polymer electrolytes of Examples 10 and 11 in which the ion conductive material constituting the buffer layer (second polymer electrolyte membrane) is the perfluoroalkylenesulfonic acid polymer compound. According to the membrane B, it is clear that further excellent oxidation resistance can be obtained with respect to the composite polymer electrolyte membrane A of Examples 7-9.
[Brief description of the drawings]
FIG. 1 is an explanatory sectional view showing a configuration of a membrane electrode structure according to a first embodiment of the present invention.
FIG. 2 is an explanatory sectional view showing a configuration of a membrane electrode structure according to a second embodiment of the present invention.
FIG. 3 is a histogram comparing the weight reduction rate and the breaking elongation reduction rate of the polymer electrolyte membrane used in the first embodiment of the present invention with a polymer electrolyte membrane not containing an antioxidant.
FIG. 4 is a graph showing the relationship between the addition amount of an antioxidant and the electrical conductivity in the polymer electrolyte membrane used in the first embodiment of the present invention.
FIG. 5 is a graph showing the relationship between the amount of antioxidant added and the weight reduction rate in the polymer electrolyte membrane used in the first embodiment of the present invention.
FIG. 6 is a histogram comparing the weight reduction rate and the breaking elongation reduction rate of the polymer electrolyte membrane used in the first embodiment of the present invention with a polymer electrolyte membrane containing other antioxidants.
FIG. 7 is a histogram comparing the weight reduction rate and the breaking elongation reduction rate of the polymer electrolyte membrane used in the first embodiment of the present invention with a polymer electrolyte membrane containing other antioxidants.
FIG. 8 is a graph comparing the relationship between the amount of antioxidant added and the weight reduction rate in the polymer electrolyte membrane used in the second embodiment of the present invention, compared to the polymer electrolyte membrane used in the first embodiment.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1,4 ... Polymer electrolyte membrane, 2 ... Electrode, 5 ... Buffer layer, 6 ... Composite polymer electrolyte membrane.

Claims (10)

A polymer electrolyte membrane comprising a sulfonated polymer having an aromatic group in the main chain and / or side chain, and an antioxidant,
The antioxidant is a compound having a plurality of phenol groups and composed only of carbon atoms and hydrogen atoms excluding the oxygen atoms of the phenol group, and 1,1,3-tris (2-methyl-4 - solid high, which is a hydroxy -5-t-butylphenyl) butane, one compound selected from the group consisting of 4,4'-butylidenebis (6-t-butyl-3-methylphenol) Proton conducting polymer electrolyte membrane for molecular fuel cell . 2. The proton conducting polymer electrolyte for a polymer electrolyte fuel cell according to claim 1, wherein the antioxidant is contained in an amount of 0.1 to 10 parts by weight with respect to 100 parts by weight of the sulfonated product. film. The proton conductive polymer electrolyte membrane for a polymer electrolyte fuel cell according to claim 1 or 2, wherein the antioxidant has a melting point of 150 ° C or higher. A polymer sulfonated product having an aromatic group in the main chain and / or side chain, and an antioxidant, the antioxidant having a plurality of phenol groups, and excluding an oxygen atom of the phenol group; A compound composed of only carbon and hydrogen atoms, 1,1,3-tris (2-methyl-4-hydroxy-5-t-butylphenyl) butane, 4,4′-butylidenebis (6-t- butyl-3-methylphenol) one proton conducting polymer electrolyte membrane for a polymer electrolyte fuel cell is a compound selected from the group consisting of, the polymer electrolyte fuel cell proton-conductive high A membrane electrode structure comprising a pair of electrodes sandwiching a molecular electrolyte membrane. A polymer sulfonated product having an aromatic group in the main chain and / or side chain, and an antioxidant, the antioxidant having a plurality of phenol groups, and excluding an oxygen atom of the phenol group; A compound composed of only carbon and hydrogen atoms, 1,1,3-tris (2-methyl-4-hydroxy-5-t-butylphenyl) butane, 4,4′-butylidenebis (6-t- butyl-3-methylphenol) one proton conducting polymer electrolyte membrane for a polymer electrolyte fuel cell is a compound selected from the group consisting of, the polymer electrolyte fuel cell proton-conductive high A solid polymer fuel cell comprising a membrane electrode structure including a pair of electrodes sandwiching a molecular electrolyte membrane. A composite polymer electrolyte membrane comprising a polymer electrolyte membrane comprising a sulfonated polymer having an aromatic group in the main chain and / or side chain, and a pair of buffer layers sandwiching the polymer electrolyte membrane. ,
The buffer layer includes an ion conductive material and an antioxidant, and the antioxidant has a plurality of phenol groups, and is composed of only carbon atoms and hydrogen atoms excluding oxygen atoms of the phenol groups. A compound comprising 1,1,3-tris (2-methyl-4-hydroxy-5-tert-butylphenyl) butane and 4,4′-butylidenebis (6-tert-butyl-3-methylphenol) A proton compound for a polymer electrolyte fuel cell , wherein the total thickness of the pair of buffer layers is smaller than the thickness of the polymer electrolyte membrane. Conductive composite polymer electrolyte membrane. The buffer layer is a polymer sulfonated product in which the ion conductive material has an aromatic group in the main chain and / or side chain, and the antioxidant is used with respect to 100 parts by weight of the ion conductive material. The proton conductive composite polymer electrolyte membrane for a polymer electrolyte fuel cell according to claim 6, comprising 0.1 to 10 parts by weight. In the buffer layer, the ion conductive material is a perfluoroalkylenesulfonic acid polymer compound, and the antioxidant is in a range of 0.01 to 5 parts by weight with respect to 100 parts by weight of the ion conductive material. The proton-conducting composite polymer electrolyte membrane for a polymer electrolyte fuel cell according to claim 6, comprising: It comprises a polymer electrolyte membrane made of a sulfonated polymer having an aromatic group in the main chain and / or side chain, and a pair of buffer layers sandwiching the polymer electrolyte membrane. A compound having a plurality of phenol groups and composed only of carbon atoms and hydrogen atoms excluding oxygen atoms of the phenol group, and 1,1 , 3-tris (2-methyl-4-hydroxy-5-tert-butylphenyl) butane, 4,4′-butylidenebis (6-tert-butyl-3-methylphenol) a compound, a proton-conductive polymer electrolyte composite membrane for a polymer electrolyte fuel cell is smaller than the thickness of the pair of the total thickness of the buffer layer is the polymer electrolyte membrane, the solid high Proton conductive composite for molecular fuel cells A membrane electrode structure comprising a pair of electrodes sandwiching a molecular electrolyte membrane. It comprises a polymer electrolyte membrane made of a sulfonated polymer having an aromatic group in the main chain and / or side chain, and a pair of buffer layers sandwiching the polymer electrolyte membrane. A compound having a plurality of phenol groups and composed only of carbon atoms and hydrogen atoms excluding oxygen atoms of the phenol group, and 1,1 , 3-tris (2-methyl-4-hydroxy-5-tert-butylphenyl) butane, 4,4′-butylidenebis (6-tert-butyl-3-methylphenol) a compound, a proton-conductive polymer electrolyte composite membrane for a polymer electrolyte fuel cell is smaller than the thickness of the pair of the total thickness of the buffer layer is the polymer electrolyte membrane, the solid high Proton conductive composite for molecular fuel cells A solid polymer fuel cell comprising a membrane electrode structure comprising a pair of electrodes sandwiching a molecular electrolyte membrane.

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