JP4407133B2 - Polymer solid electrolyte, method for producing the same, and polymer electrolyte fuel cell using the same - Google Patents

Description

【００３３】
（ここで、Ｘ：極性基、Ｉ₁、Ｉ₂：アニオン性基、Ｒ：有機基。）
構造式（１）にて表されるポリマー中の極性基Ｘはアニオン性基と異なるものであれば特に限定されるものではないが、極性基に水が配位できるものが好ましい。中でもスルホニル基（−ＳＯ₂−）、オキシ基（−Ｏ−）、チオ基（−Ｓ−）、カルボニル基（−ＣＯ−）、エステル基（−ＣＯＯ−）、アミド基（−ＮＲＣＯ−）およびイミド基並びに式（２）および式（３）で示される繰り返し単位を有するものが好ましく用いられる。極性基は高分子固体電解質中に２種類以上存在しても良く、組み合わせて使えば好ましい場合がある。
【００３４】
式（２）
【００３５】
【化２】

【００３６】
式（３）
【００３７】
【化３】

【００３８】
（Ｒ：有機基。）
また、前記極性基Ｘを含むようなポリマーは特に限定されるものではない。具体例として下式（４）で示されるポリフェニレンスルフィドスルホン、下式（５）で示されるポリフェニレンスルフィド、下式（６）で示されるポリフォスファゼン、下式（７）で示されるポリイミド、およびポリスルホン（ＰＳＦ）、ポリフェニレンオキシド（ＰＰＯ）、ポリエーテルケトン（ＰＥＫ）、ポリエーテルエーテルケトン（ＰＥＥＫ）、ポリベンゾイミダゾール（ＰＢＩ）、ポリエーテルスルホン（ＰＥＳ）などの耐熱・耐酸化性ポリマーが好ましく用いられる。中でもポリフェニレンスルフィドスルホン、ポリフェニレンスルフィド、ポリフォスファゼン、ポリイミド、ポリベンゾイミダゾール、ポリスルホンは水の配位やメタノールに対する親和性の点から特に好ましく用いられる。また、これらのポリマーは２種類以上、組み合わせて使用することもできる。
式（４）
【００３９】
【化４】

【００４０】
式（５）
【００４１】
【化５】

【００４２】
式（６）
【００４３】
【化６】

【００４４】
式（７）
【００４５】
【化７】

【００４６】
（ここで、Ｚは芳香環を含む有機基。ｎは正の整数であり、繰返しの数を表す。）
本発明において構造式（１）にて表されるポリマー中のアニオン性基（Ｉ₁、Ｉ₂）は特に限定されるものではないが、プロトン交換能を有するものが好ましい。このような官能基としては、スルホン酸基、硫酸基、リン酸基、カルボン酸基、ホスホン酸基等が好ましく用いられる。ここで、スルホン酸基とは−ＳＯ₂−（ＯＨ）、硫酸基は−ＯＳＯ₂（ＯＨ）、ホスホン酸基は−ＰＯ（ＯＨ）₂、リン酸基は−ＯＰＯ（ＯＨ）₂、カルボン酸基は−ＣＯ（ＯＨ）、およびこれらの塩のことを意味する。これらのアニオン性基は前記ポリマー中に２種類以上含むことができ、組み合わせることにより好ましくなる場合がある。組み合わせはポリマーの構造などにより適宜決められる。
【００４７】
本発明において構造式（１）にて表されるポリマー中の有機基Ｒは特に限定されるものではない。剛直性や、有機基へのイオン性基の導入などの点から芳香環を含んでいるのが好ましい。また、分子鎖を拘束するために架橋点を有することも好ましい。
【００４８】
本発明において拘束とはアニオン性基含有ポリマーが単独で存在する場合に比べて含水率が抑制された状態であることを意味する。
【００４９】
本発明において構造式（１）を有するポリマーの分子鎖を拘束する方法はアニオン性基含有ポリマーと三次元架橋体ポリマーが均一に混じり合って構成されることによる方法が挙げられる。アニオン性基を有するポリマーとその他のポリマーが、互いの分子鎖どうしが絡み合った状態で存在することがＭＣＯ抑制および膨潤抑制のために好ましい。分子鎖どうしが絡み合うことで、互いの動きを拘束しメタノール透過を妨げるものと考えられる。分子鎖の拘束は強いほど自由水の取り込みが抑制できるが、イオン伝導性が低下する可能性がある。このため、分子鎖の拘束度合いは必要特性に応じて適宜選ぶ必要がある。分子鎖を拘束する具体的方法は構造式（１）を有するポリマーとは別に架橋可能な高分子を用いて両者が均一に混じり合って構成される構造とする方法などがある。別に架橋可能な高分子を用いる方法としては、シロキサンなどの炭素以外の元素を架橋点とする３次元架橋体などが挙げられる。
【００５０】
本発明の高分子固体電解質において、アニオン性基を有するポリマーと三次元架橋体ポリマーが均一に混じり合って構成される構造を有する場合とは、３次元架橋体の網目内部にアニオン性基を有するポリマーが存在する状態を指す。本発明の高分子固体電解質は、アニオン性基を有するポリマーおよび炭素以外の元素を架橋点とする３次元架橋性重合体からなる部位を含んでいるが、これらの部位を含むと高分子固体電解質のプロトン伝導性低下やクロスオーバー抑制効果の低下を招くことがある。このため高分子固体電解質中においてアニオン性基を有するポリマーと三次元架橋体ポリマーが均一に混じり合い構成される部位の割合は高分子固体電解質全体の３０％以上が好ましく、５０％以上であればさらに好ましい。
【００５１】
これらの３次元架橋体はイオン伝導性、相溶性の点からイオン性基を有していれば好ましい。３次元架橋体の中でも耐酸化性、架橋密度の点から炭素以外の元素を架橋点とする３次元架橋体が用いられる。これらの中でもケイ素、チタン、ジルコニウム、アルミニウム、ホウ素、リン、鉄などを架橋点とする３次元架橋体はさらに好ましい。
【００５２】
本発明の高分子固体電解質において、アニオン性基を有するポリマーと三次元架橋体ポリマーが均一に混じり合い構成される構造を有する場合、炭素以外の元素を架橋点とする３次元架橋体の作製方法において、炭素以外の元素からなるアルコキシド化合物を用いて架橋体を作成することも好ましい実施態様である。このアルコキシド化合物は、加水分解可能であることが好ましく、さらにこの加水分解可能な化合物および／またはその加水分解物とアニオン性基を有するポリマーを含む溶液を用いると、アニオン性基を有するポリマーと三次元架橋体ポリマーが均一に混じり合い構成される構造を形成しやすくなり好ましい。特に、アルコキシド化合物の縮合反応を利用して、アニオン性基を有するポリマーと三次元架橋体ポリマーが均一に混じり合い構成される構造を作製することも好ましい作製方法である。また、混合する微粒子が表面官能基を有する場合には、アルコキシド化合物の縮合反応により、架橋体と微粒子とが化学結合を有し一体化され、ＭＣＯ低減やプロトン伝導度向上への効果が大なるものとなる。
【００５３】
本発明では固体高分子電解質を多孔質フィルムに充填することも可能であり、この様にして得られた固体高分子電解質は膨潤による変形が抑制され、好ましいものである。多孔質フィルムは、ランダム方向に開孔した三次元網目微多孔、膜厚方向に開孔した貫通孔など特に限定されるものではない。
【００５４】
また、多孔質フィルムが膜厚方向に貫通孔を有する場合には、平面方向に整然と配列された貫通孔を有するものであることが、さらに好ましい。ここで、「平面方向に整然と配列された貫通孔」とは、貫通孔が略等間隔あるいは規則的に配列されている状態を示す。具体的には、隣り合った貫通孔の中心間隔同士を比較した場合に、それぞれの中心間隔の差が１００％以内の範囲に入る配列状態のことである。すなわち、多孔質フィルムの表面において、貫通孔は二次元的に配列しているので、隣り合った貫通孔は上下左右に存在するが、隣り合う貫通孔の中心間隔の差が１００％以内の範囲に入り配列されていることが必要である。好ましくは５０％以内であり、さらに好ましくは３０％以内である。また、隣り合う貫通孔の中心間隔の差が１００％を越えている場合でも、ある個数ごとの組み合わせが繰り返された規則的な配列であれば、各々の配列内部の隣り合う貫通孔の中心間隔の誤差が１００％以内であれば好ましく用いられる。
【００５５】
本発明に用いられる多孔質フィルムの具体例として、図１の形状が挙げられる。図１は、本発明の高分子固体電解質の一例を示す斜視模式図である。図１の多孔質フィルムは、中央に多数の孔の空いた多孔部１があり、多孔部の周囲は孔の無い非多孔部２を有している。図２に多孔部の拡大模式図を示す。本発明の高分子固体電解質は、多孔部の孔３が、図２のように平面方向に見た配列ピッチが整然と等間隔に配列されていることが好ましい。図２中のＬが、上述した「隣り合う貫通孔の中心間隔」である。Ｌは、０．５〜１００μｍの範囲が好ましく、１〜５０μｍの範囲が特に好ましい。また、孔の内径ｄとしては、０．５〜５０μｍの範囲が好ましく、１〜３０μｍの範囲が特に好ましい。
【００５６】
図１において、多孔部１にプロトン伝導体が充填されて高分子固体電解質としての機能を発現するのである。また、図２の孔３にプロトン伝導体が充填されることによって、膨潤が抑制され、燃料のメタノールがアノードからカソードに透過するクロスオーバーを低減するのであるが、孔３が整然と配列されていれば、このクロスオーバー低減効果が一層向上するものである。
【００５７】
本発明の高分子固体電解質に用いられる多孔質フィルムの好ましい作製方法としては、例えばフォトリソグラフィーの加工方法を適用することができる。従来、多孔質フィルムとしては、貫通孔を有する濾過用フィルター素材などが用いられてきた。これは通常、高分子フィルムにイオンを照射してポリマー鎖を破断し、アルカリ溶液などを用いて化学エッチング法で孔を開けたもの（トラックエッチ法）である。これに対してフォトリソグラフィー法を用いた孔３は、その孔径、形状、孔の間隔、多孔化する部分などを任意に設定することができ、クロスオーバーの低減による燃料電池の性能向上を図ることができる。さらに、フォトリソグラフィーは微細加工に優れるため、多孔部１と非多孔部２との微細な区分けが可能となり、燃料電池の小型化に優れた結果をもたらす。また、従来のトラックエッチ法に比べて生産性向上による低コスト化を達成することができる。
【００５８】
ここで、フォトリソグラフィー法を用いて作製した多孔質フィルムの走査型電子顕微鏡（ＳＥＭ）写真を図３に示し、従来のトラックエッチ法で作製された多孔質フィルムの走査型電子顕微鏡（ＳＥＭ）写真を図４に示す。図３のフォトリソグラフィー法の多孔質フィルムの孔は、図４のトラックエッチ法に比べて整然と等間隔に配列されていることが明瞭である。
【００５９】
フォトリソグラフィー法により作製された多孔質フィルムにおける孔の横断面形状としては、特に限定されるものではないが、円、楕円、正方形、長方形、菱形、台形などが好ましい。これらの中でも、プロトン伝導体の充填のしやすさ、膨潤抑制の点から、円あるいは楕円が好ましい。孔の大きさや間隔については特に限定されることはなく、プロトン伝導体の充填のしやすさ、電池性能などに基づき適宜決めればよい。
【００６０】
フォトリソグラフィー法を用いて製造する多孔質フィルムにおける多孔部分全体の大きさは、用いられる電極触媒層や電極基材の大きさに合わせて決めればよい。また、多孔質フィルムの厚さに関しても、求められる電池性能に基づいて決めればよいが、通常１〜５０μｍの範囲が好ましく、５〜２０μｍの範囲が特に好ましい。
【００６１】
本発明に使用するフォトリソグラフィー法の詳細な方法は特に限定されるものではないが、例えば、感光性ポリマーを基板に塗工し、フォトマスクをかけて露光し、現像後にポリマーを溶解して孔を形成し、基板から剥がして多孔性高分子フィルムを得る方法などが用いられる。感光性ポリマーは、ネガ型あるいはポジ型どちらの方式でも構わないが、求められる孔の大きさ、孔の間隔、燃料電池性能等に応じて適宜選択できる。基板素材は、ポリマーとの密着性や剥がしやすさの点から決められ、好ましくはシリコンウエハやアルミ板などが用いられるが、特に限定されるものではない。露光は、縮小露光、等倍露光どちらでも構わないが、作製される電解質の大きさ、孔の大きさ、形状、間隔などによって適宜決めればよい。また、現像、溶解、基板からの剥離等の条件についても、ポリマーの性質によって適宜、条件を選択すればよい。また、予め基板上に非感光性ポリマーを塗工し、その上にフォトレジストを塗工、露光、現像、ポリマー溶解による空隙作製を行うことも可能である。
【００６２】
本発明に使用するフォトリソグラフィー法に用いられる感光性あるいは非感光性ポリマーとしては、特に限定されるものではないが、フォトリソグラフィーによる加工性、ポリマーの耐酸化性、強度等からポリイミドが好ましく用いられる。
【００６３】
ポリイミドを用いたフォトリソグラフィー法による多孔作製の具体的方法としては、たとえば、前駆体のポリアミド酸溶液を基板に塗工し、約１００℃程度にて溶媒を乾燥除去した後、フォトマスクを用いた露光、現像、アルカリ処理等によるフォトリソグラフィー加工を行うことで孔を形成した後、約３００℃以上にてイミド閉環反応を行い、最後に基板から剥がして多孔性ポリイミドフィルムを得る方法が挙げられる。溶媒除去およびイミド閉環反応の温度や時間は、用いるポリイミドの種類により適宜決めることができる。ポリイミドフィルムを基板から剥がす際には、通常、酸への浸漬が行われるが、用いられる基板がシリコンウエハではフッ酸、アルミ板では塩酸が好ましく用いられる。
【００６４】
ここで、本発明に用いられるポリイミドとしては、ネガ型あるいはポジ型の感光性ポリイミド、あるいは非感光性ポリイミドのいずれでも構わないが、孔の大きさ、形状、間隔、フィルムの厚さ等から感光性ポリイミドが好ましく、ネガ型感光性ポリイミドがさらに好ましい。
【００６５】
上記のフォトリソ法作製による多孔質フィルムの他に、三次元網目構造を有する多孔質フィルムも好ましい。「三次元網目構造」とは、多孔質フィルムを構成するポリマーが立体的に繋がった三次元状の網目構造を有している状態をいう。ここで、本発明に好ましく用いられる三次元網目構造を有する多孔質フィルムの走査型電子顕微鏡（ＳＥＭ）写真を図５に示す。
【００６６】
多孔質フィルムが三次元網目構造を有している場合、その孔径が０．０５〜５μｍの範囲であることが好ましく、より好ましくは、０．１〜１μｍの範囲である。孔径は、走査型電子顕微鏡（ＳＥＭ）などで、表面を撮影した写真から、２０個以上好ましくは１００個以上の孔の平均から求めることができ、通常は１００個で測定する。たとえば、湿式凝固法によって製造された三次元網目の多孔質フィルムは、孔径の分布が広いので、できるだけ多く、たとえば１００〜５００個の孔径の平均をとることが好ましい。
【００６７】
三次元網目構造の空隙率は、１０〜９５％の範囲であることが好ましい。より好ましくは５０〜９０％の範囲である。ここで、空隙率とは、多孔質フィルム全体積からポリマーの占める体積を減じたものを、多孔質フィルム全体積で除した百分率（％）である。
【００６８】
上記の三次元網目構造を有する多孔質フィルムの製造方法としては、湿式凝固法が好ましく用いられる。具体的には、良溶媒を含む溶解溶媒にポリマーを溶解したポリマー溶液を貧溶媒を含む凝固溶媒に浸漬することにより、三次元網目構造の微多孔を有する凝固ポリマーを得ることができる。多孔質フィルムをフィルム形状とする際には、基板上にポリマー溶液を塗工し、溶媒が乾燥除去される前に、凝固溶媒に浸漬することで微細な多孔を有する多孔質フィルムを得ることができる。ここで、溶解溶媒や凝固溶媒は、用いられるポリマーによって適宜選択することができ、また、所望する孔の大きさ、形状、燃料電池性能に応じて適宜選択することができるが、溶媒同士互いに相溶することが必要である。
【００６９】
湿式凝固法により作製された多孔質フィルムを高分子固体電解質に用いる場合においても、図１のように、中央が多孔部であり周辺を緻密な高分子フィルムとする形状が好ましい実施態様となる。このような形状とするには、たとえば以下の方法が好ましく用いられるが、これに限定されるものではない。
【００７０】
第一の方法としては、予め周辺部のみの緻密フィルムを作製し、その後に中央の多孔部を作製する方法が挙げられる。緻密なフィルムは、基板上にポリマー溶液を塗工、通常に乾燥して作製される。多孔とする中央部を後から切り取っても良いし、塗工時にマスキングを行うことで中央を未塗工とすることも可能である。その後、中央のみにポリマー溶液を塗工し、貧溶媒へ浸漬することで湿式凝固が行われる。
【００７１】
第二の方法としては、全体を湿式凝固法で多孔化したフィルムを作製し、周辺部の孔を閉塞するものである。孔の閉塞には、プレスで潰す方法、あるいは孔に非プロトン伝導性ポリマーを充填する方法などを用いることができるが、これらに限定されるものではない。
【００７２】
本発明に用いられる多孔質フィルムに用いられるポリマーとしては特に限定されないが、好ましくは、ポリイミド（ＰＩ）、ポリビニリデンフルオライド（ＰＶＤＦ）、ポリフェニレンスルフィドスルフォン（ＰＰＳＳ）、ポリテトラフルオロエチレン（ＰＴＦＥ）、ポリスルフォン（ＰＳＦ）など、あるいはこれらの共重合体、他のモノマとの共重合体（ヘキサフルオロプロピレン−フッ化ビニリデン共重合体等）、さらには、ブレンドなども用いることができる。これらのポリマーは、耐酸化性、強度、湿式凝固の容易性などから好ましいものである。
【００７３】
湿式凝固法を用いる場合、これらのポリマーの溶解溶媒としては、高誘電率の極性溶媒が用いられ、凝固溶媒としては、アルコール、エーテル、エステル、水などが用いられる。なかでも溶解溶媒としては、Ｎ−メチル−２−ピロリドン（ＮＭＰ）、ジメチルフォルムアミド（ＤＭＦ）、ジメチルアセトアミド（ＤＭＡＣ）が好ましく、凝固溶媒としてはメタノール、エタノール、イソプロパノール、水等が好ましい。また、孔径を制御するために開孔剤を添加しても良い。開孔剤には微粒子や塩、界面活性剤などが用いられる。
【００７４】
本発明に用いられる多孔質フィルムは、上記のフォトリソ法あるいは湿式凝固法に拘わらず、表面と裏面において、孔の形状や大きさが異なっていても良く、プロトン伝導体の充填のしやすさの点からは、表面と裏面の孔の大きさが異なっていることも好ましい実施態様である。これによりプロトン伝導体の充填が容易になることが期待される。その程度としては、表と裏の孔径ｄの比が５：１〜１：１の範囲であることが好ましい。さらには、同一平面内に大きさや形状の異なる孔が混在していても構わない。
【００７５】
多孔質フィルムに上記プロトン伝導体を充填する方法は特に限定されるものではない。たとえば、アニオン性基を有するポリマーを溶液として、多孔質フィルムへの塗工あるいは浸漬することにより空隙内への充填が可能となる。空隙内への充填を容易にするために超音波を使用したり、減圧にするのも好ましく、これらを塗工あるいは浸漬時に併用するとさらに充填効率が向上し好ましい。また、アニオン性基を有するポリマーの前駆体であるモノマを空隙内に充填した後に空隙内で重合する、あるいはモノマを気化してプラズマ重合を行う、などの方法を行っても良い。
【００７６】
本発明において燃料電池の形態、燃料電池の作製方法は特に限定されるものではない。以下にｓｉｄｅ−ｂｙ−ｓｉｄｅ構造の燃料電池作製にフォトリソグラフィー法を用いる方法を例に詳述する。ここで、ｓｉｄｅ−ｂｙ−ｓｉｄｅ構造とは、単一の高分子固体電解質面の平面方向に、一組みの対向する電極からなるセルを２個以上配置する構造を指す。この構造によると、２個以上配置された隣り合ったセルのアノードとカソードを高分子固体電解質を貫通する電子伝導体で接続することによりセルが直列に接続されるため、ｓｉｄｅ−ｂｙ−ｓｉｄｅ構造の高分子固体電解質断面はプロトン伝導部と電子伝導部が交互に存在する構造となる。このような構造を作製するには、小型化および生産性の観点からフォトリソグラフィー法を用いるのが好ましい。
【００７７】
Ｓｉｄｅ−ｂｙ−ｓｉｄｅ構造の一例を図６および図７に示す。図６は、ｓｉｄｅ−ｂｙ−ｓｉｄｅ構造を持つ本発明の高分子固体電解質の斜視模式図であり、図７は、その製造プロセスの一部を示す断面模式図である。なお図６、図７においては、２個のセルを横に配置した例示をしたが、同様なｓｉｄｅ−ｂｙ−ｓｉｄｅ構造で、３個以上の複数個を平面方向に配置することも可能である。以下の説明は簡便のために２個のセルで行う。図６においてプロトン伝導部は多孔部１に図示しないプロトン伝導体が充填され、電子伝導部は膜導電部４に電子伝導体が充填されている。プロトン伝導部の多孔部１と電子伝導部の膜導電部４以外の部分はプロトンや電子が伝導しない非多孔部２であり、緻密な高分子フィルムとなっている。このように複雑かつ微細な構造の高分子フィルム作製には、本発明に述べるフォトリソグラフィー法が好適に用いられる。フォトリソグラフィー法により図６に示す多孔質フィルムを作製し、これを図７に例示する方法で高分子固体電解質とする。図７では、予め膜貫通電子伝導部に電子伝導体を充填した後に、プロトン伝導部にプロトン伝導体を充填しているが、この順序は逆でも構わない。また、プロトン伝導体を充填してプロトン伝導部を作製し、次に電極を設け、最後に電子伝導部を作製成しても構わない。
【００７８】
前述のｓｉｄｅ−ｂｙ−ｓｉｄｅ構造の電子伝導部は、電解質膜を貫通した構造である。ここで電子伝導部として電解質膜を貫通した部分を膜導電部という。この膜導電部は、プロトン伝導体を充填するための多孔部とは異なる機能である。その膜導電部の、大きさ、形状などは特に限定されるものではない。膜導電部が大きいほどセルとセルの電気抵抗が低下し直列での電圧向上が期待できる。ただし、膜導電部が大きいほど、アノード側の水素あるいはメタノールなどの有機溶媒がカソード側にリークする可能性、あるいはカソード側の空気がアノード側にリークする可能性が高まり、性能低下を引き起こすことがある。このため、電子伝導部に用いられる電子伝導体の電気抵抗と耐リーク性とを考慮して、膜導電部の大きさや形状を決めることが好ましい。なお、電子伝導部は高分子固体電解質を貫通せず、外部を通しても良い。
【００７９】
前記膜導電部４の電子伝導体としては特に限定されるものではないが、導電ペーストが好ましく用いられる。導電ペーストとしては、カーボン、銀、ニッケル、銅、白金、パラジウムなどの導電剤がポリマーに分散されいるものなどを好ましく用いることができ、電子抵抗の低下と耐リーク性の向上が両立できる。特にＤＭＦＣにおいては、メタノールのリークを防ぐことが重要であり、シリコーン樹脂、ポリエステル、エポキシ樹脂などにカーボンや銀を分散した汎用導電ペーストのほか、カーボンブラック、銀、白金などをＰＶＤＦやポリイミドに分散した導電ペーストも好ましく用いられる。電子伝導部５は、セルの電極基材あるいは電極触媒層と電気的に接続されるが、この接触抵抗低下のためにも導電ペーストが好ましく使用される。
【００８０】
また、電子伝導部５として、ニッケル、ステンレススチール、アルミニウム、銅などの金属箔や金属線を用いても良い。また、これらの金属箔や金属線と導電ペーストを組み合わせることも可能である。
【００８１】
本発明の高分子固体電解質は、電極基材と電極触媒層とから構成される電極７と組み合わせて膜−電極複合体（ＭＥＡ）として固体高分子型燃料電池に用いられる。
【００８２】
本発明の固体高分子型燃料電池における電極７における電極触媒層は、特に限定されることなく公知のものを利用することが可能である。電極触媒層とは、電極反応に必要な触媒や電極活物質（酸化あるいは還元する物質を言う）を含み、さらに電極反応を促進する電子伝導やイオン電導に寄与する物質を含む層を言う。また電極活物質が液体や気体の場合には、その液体や気体が透過しやすい構造を有していることが必要であり、電極反応に伴う生成物質の排出も促す構造が必要である。
【００８３】
本発明の固体高分子型燃料電池において、電極活物質としては、好ましくは水素、メタノールなどの有機溶媒あるいは酸素等が挙げられ、触媒は白金などの貴金属粒子が好適な例として挙げられる。また、電極触媒層の導電性を改善する材料を含むことが好ましく、形態は特に限定されるものではないが、例えば、導電性粒子を有することが好ましい。導電性粒子としてはカーボンブラック等が挙げられ、特に触媒を担持したカーボンブラックとして白金担持カーボンなどが好ましく用いられる。電極触媒層は、触媒、電子伝導体（たとえばカーボンブラック）、イオン伝導体（たとえばプロトン交換樹脂）が互いに接触して、電極活物質と反応生成物が効率よく出入りする構造が求められる。また、イオン伝導性を改善したり、材料の結着性を向上させたり、或いは撥水性を高めたりするのに、高分子化合物が有効である。したがって、電極触媒層に、少なくとも触媒粒子と導電性粒子と高分子化合物を含むことが好ましい。
【００８４】
本発明の固体高分子型燃料電池には、電極触媒層に含まれる触媒としては公知の触媒を用いることができ、特に限定されるものではないが、白金、パラジウム、ルテニウム、イリジウム、金などの貴金属触媒が好ましく用いられる。また、これらの貴金属触媒の合金、混合物など、２種以上の元素が含まれていても構わない。
【００８５】
電極触媒層に含まれる電子伝導体（導電材）としては、特に限定されるものではないが、電子伝導性と耐触性の点から無機導電性物質が好ましく用いられる。なかでも、カーボンブラック、黒鉛質や炭素質の炭素材、あるいは金属や半金属が挙げられる。ここで、炭素材としては、チャネルブラック、サーマルブラック、ファーネスブラック、アセチレンブラックなどのカーボンブラックが、電子伝導性と比表面積の大きさから好ましく用いられる。ファーネスブラックとしては、キャボット社製バルカンＸＣ−７２、バルカンＰ、ブラックパールズ８８０、ブラックパールズ１１００、ブラックパールズ１３００、ブラックパールズ２０００、リーガル４００、ケッチェンブラック・インターナショナル社製ケッチェンブラックＥＣ、三菱化学社製＃３１５０、＃３２５０などが挙げられ、アセチレンブラックとしては電気化学工業社製デンカブラックなどが挙げられる。またカーボンブラックのほか、天然の黒鉛、ピッチ、コークス、ポリアクリロニトリル、フェノール樹脂、フラン樹脂などの有機化合物から得られる人工黒鉛や炭素なども使用することができる。これらの炭素材の形態としては特に限定されず、粒子状のほか繊維状のものも用いることができる。また、これら炭素材を後処理加工した炭素材も用いることが可能である。このような炭素材の中でも、特に、キャボット社製のバルカンＸＣ−７２が電子伝導性の点から好ましく用いられる。
【００８６】
これら電子伝導体の添加量としては、要求される電極特性や用いられる物質の比表面積や電子抵抗などに応じて適宜決められるべきものであるが、電極触媒層中の重量比率として１〜８０％の範囲が好ましく、２０〜６０％の範囲がさらに好ましい。電子伝導体は、少ない場合は電子抵抗が高くなり、多い場合はガス透過性を阻害したり触媒利用率が低下するなど、いずれも電極性能を低下させる。
【００８７】
電子伝導体は、触媒粒子と均一に分散していることが電極性能の点で好ましいものである。このため、触媒粒子と電子伝導体は予め塗液として良く分散しておくことが好ましい。
【００８８】
電極触媒層として、触媒と電子伝導体とが一体化した触媒担持カーボンを用いることも好ましい実施態様である。この触媒担持カーボンを用いることにより、触媒の利用効率が向上し、低コスト化に寄与できる。ここで、電極触媒層に触媒担持カーボンを用いた場合においても、さらに導電剤を添加することも可能である。このような導電剤としては、上述のカーボンブラックが好ましく用いられる。
【００８９】
電極触媒層に用いられるイオン伝導体としては、公知のものを用いることが可能である。イオン伝導体としては、一般的に、種々の有機、無機材料が公知であるが、燃料電池に用いる場合には、プロトン伝導性を向上するスルホン酸基、カルボン酸基、リン酸基などのイオン交換基を有するポリマーが好ましく用いられる。なかでも、フルオロアルキルエーテル側鎖とフルオロアルキル主鎖とから構成されるプロトン交換基を有するポリマーが好ましく用いられる。たとえば、ＤｕＰｏｎｔ社製のＮａｆｉｏｎ、旭化成社製のＡｃｉｐｌｅｘ、旭硝子社製Ｆｌｅｍｉｏｎなどが好ましく用いられる。これらのイオン交換ポリマーは、溶液または分散液の状態で電極触媒層中に設ける。この際に、ポリマーを溶解あるいは分散化する溶媒は特に限定されるものではないが、イオン交換ポリマーの溶解性の点から極性溶媒が好ましい。
【００９０】
イオン伝導体は、電極触媒層を作製する際に電極触媒粒子と電子伝導体とを主たる構成物質とする塗液に予め添加し、均一に分散した状態で塗布することが電極性能の点から好ましいものであるが、電極触媒層を塗布した後にイオン導電体を塗布してもかまわない。ここで、電極触媒層にイオン導電体を塗布する方法としては、スプレーコート、刷毛塗り、ディップコート、ダイコート、カーテンコート、フローコートなどが挙げられ、特に限定されるものではない。
【００９１】
電極触媒層に含まれるイオン伝導体の量としては、要求される電極特性や用いられるイオン伝導体の電導度などに応じて適宜決められるべきものであり、特に限定されるものではないが、重量比で１〜８０％の範囲が好ましく、５〜５０％の範囲がさらに好ましい。イオン伝導体は、少な過ぎる場合はイオン伝導度が低く、多過ぎる場合はガス透過性を阻害する点で、いずれも電極性能を低下させることがある。
【００９２】
電極触媒層には、上記の触媒、電子伝導体、イオン伝導体の他に、種々の物質を含んでいてもかまわない。特に電極触媒層中に含まれる物質の結着性を高めるために、上述のプロトン交換樹脂以外のポリマーを含むことが好ましい。このようなポリマーとしては、フッ素原子を含むポリマーが挙げられ、特に限定されるものではないが、たとえば、ポリフッ化ビニル（ＰＶＦ）、ポリフッ化ビニリデン（ＰＶＤＦ）、ポリヘキサフルオロプロピレン（ＦＥＰ）、ポリテトラフルオロエチレン、ポリパーフルオロアルキルビニルエーテル（ＰＦＡ）など、あるいはこれらの共重合体、これらのポリマーを構成するモノマ単位とエチレンやスチレンなどの他のモノマとの共重合体、さらには、ブレンドなども用いることができる。これらポリマーの電極触媒層中の含有量としては、重量比で５〜４０％の範囲が好ましい。ポリマー含有量が多すぎる場合、電子およびイオン抵抗が増大し電極性能が低下する傾向がある。
【００９３】
電極触媒層は、触媒−ポリマー複合体が三次元網目構造を有することも好ましい実施態様である。触媒−ポリマー複合体は、触媒粒子を含んだポリマー複合体であって、この複合体が三次元網目構造となっている場合である。つまり、触媒−ポリマー複合体が立体的に繋がった三次元状の網目構造を有している状態である。
【００９４】
電極触媒層が三次元網目構造を有している場合、その孔径が０．０５〜５μｍの範囲であることが好ましく、より好ましくは、０．１〜１μｍの範囲である。孔径は、走査型電子顕微鏡（ＳＥＭ）などで、表面を撮影した写真から、２０個以上好ましくは１００個以上の平均から求めることができ、通常は１００個で測定する。湿式凝固法によって製造された多孔質構造の電極触媒層は、孔径の分布が広いのでできるだけ多く、好ましくは１００〜５００個の孔径の平均をとることが好ましい。
【００９５】
電極触媒層の三次元網目構造の空隙率は、１０〜９５％の範囲であることが好ましい。より好ましくは５０〜９０％の範囲である。ここで、空隙率とは、電極触媒層全体積から触媒−ポリマー複合体の占める体積を減じたものを、電極触媒層全体積で除した百分率（％）である。
【００９６】
三次元網目構造を有する電極触媒層の作製には、通常、触媒層を電極基材、プロトン交換膜、それ以外の基材に塗布した後に湿式凝固を行う。電極触媒層を単独で空隙率を求めることが困難な場合には、電極基材、プロトン交換膜、それ以外の基材の空隙率を予め求めておき、これら基材と電極触媒層とを含む空隙率を求めた後に、電極触媒層単独での空隙率を求めることも可能である。
【００９７】
三次元網目構造を有する電極触媒層は、空隙率が大きくガス拡散性や生成水の排出が良好であり、かつ電子伝導性やプロトン伝導性も良好である。従来の多孔化では、触媒粒子径や添加ポリマーの粒子径を増大させたり、造孔剤を用いて空隙を形成するなどが行われているが、このような多孔化方式では触媒担持カーボン間やプロトン交換樹脂間の接触抵抗が電極触媒層に比べて大きくなってしまう。それに対して、湿式凝固法による三次元網目構造では、触媒担持カーボンを含んだポリマー複合体が三次元網目状になっているので、このポリマー複合体を電子やプロトンが伝導しやすく、さらに微多孔質構造のためガス拡散性や生成水の排出も良好な構造となっており、好ましいものである。
【００９８】
電極触媒層が三次元網目構造を有している場合においても、触媒や電子伝導体、イオン伝導体に用いられる物質は、従来と同様の物質を用いることが可能である。ただし、三次元網目構造を有する電極触媒層を作製する際には、湿式凝固法を用いることが好ましいため、この湿式凝固法に適したポリマーの選択が好ましく、触媒粒子を良く分散し、かつ燃料電池内の酸化−還元雰囲気で劣化しないポリマーが好ましい。このようなポリマーとしては、フッ素原子を含むポリマーが挙げられ、特に限定されるものではないが、たとえば、ポリフッ化ビニル（ＰＶＦ）、ポリフッ化ビニリデン（ＰＶＤＦ）、ポリヘキサフルオロプロピレン（ＦＥＰ）、ポリパーフルオロアルキルビニルエーテル（ＰＦＡ）など、あるいはこれらの共重合体、これらのポリマーを構成するモノマ単位とエチレンやスチレンなどの他のモノマとの共重合体（例えば、ヘキサフルオロプロピレン−フッ化ビニリデン共重合体等）、さらには、ブレンドなども好ましく用いることができる。
【００９９】
この中でも、ポリフッ化ビニリデン（ＰＶＤＦ）、ヘキサフルオロプロピレン−フッ化ビニリデン共重合体は、非プロトン性極性溶媒を溶解溶媒として用い、プロトン性極性溶媒などを凝固溶媒とする湿式凝固法により、三次元網目構造を有する触媒−ポリマー複合体が得られる点で、特に好ましいポリマーである。
【０１００】
ポリマーの溶媒としては、具体的には、Ｎ−メチルピロリドン（ＮＭＰ）、ジメチルホルムアミド（ＤＭＦ）、ジメチルアセトアミド（ＤＭＡＣ）、プロピレンカーボネート（ＰＣ）、ジメチルイミダゾリジノン（ＤＭＩ）などが挙げられ、凝固溶媒としては水や、メタノール、エタノール、イソプロパノールなどの低級アルコール類などのほか、酢酸エチルや酢酸ブチルなどのエステル類、芳香族系あるいはハロゲン系の種々の有機溶剤を挙げることができる。
【０１０１】
触媒−ポリマー複合体のポリマーとしては、上記のポリマーに加えて、プロトン伝導性を向上させるためにプロトン交換基を有するポリマーも好ましいものである。このようなポリマーに含まれるプロトン交換基としては、スルホン酸基、カルボン酸基、リン酸基などがあるが特に限定されるものではない。また、このようなプロトン交換基を骨格中に含有するポリマーも、特に限定されることなく用いられる。たとえば、フルオロアルキルエーテル側鎖とフルオロアルキル主鎖とから構成されるプロトン交換基を有するポリマーが好ましく用いられる。具体的には、ＤｕＰｏｎｔ社製のＮａｆｉｏｎなどである。また、プロトン交換基を有する上述のフッ素原子を含むポリマーや、エチレンやスチレンなどの他のポリマー、これらの共重合体やブレンドであっても構わない。
【０１０２】
Ｎａｆｉｏｎを用いた場合、市販のＮａｆｉｏｎ膜を非プロトン性極性溶媒に溶かしても良いし、Ａｌｄｒｉｃｈ社、ＤｕＰｏｎｔ社、あるいはＩｏｎＰｏｗｅｒ社等から市販されている、水−メタノール−ｉｓｏプロパノール、水−エタノール−ｉｓｏプロパノール、水−エタノール−ｎプロパノールなどの含低級アルコール混合溶媒のＮａｆｉｏｎ溶液を用いることも可能である。また、これらのＮａｆｉｏｎ溶液を濃縮あるいは溶媒置換したものを用いても良い。この場合、湿式凝固の際の凝固溶媒は、Ｎａｆｉｏｎ溶液の溶媒種により適宜決められるべきものであるが、Ｎａｆｉｏｎ溶液の溶媒が非プロトン性極性溶媒である場合には、凝固溶媒としては水やアルコール類、エステル類のほか、種々の有機溶媒などが好ましく、水−メタノール−イソプロパノール混合溶媒などの低級アルコール溶媒の場合には、酢酸ブチルなどのエステル類、種々の有機溶媒が好ましく用いられる。
【０１０３】
触媒−ポリマー複合体に用いられるポリマーは、上記のフッ素原子を含むポリマーやプロトン交換膜を含むポリマーを共重合あるいはブレンドして用いることも好ましいものである。特にポリフッ化ビニリデン、ポリ（ヘキサフルオロプロピレン−フッ化ビニリデン）共重合体などと、プロトン交換基にフルオロアルキルエーテル側鎖とフルオロアルキル主鎖を有するＮａｆｉｏｎなどのポリマーを、ブレンドすることは電極性能の点から好ましいものである。
【０１０４】
触媒−ポリマー複合体の主たる成分は触媒担持カーボンとポリマーであり、それらの比率は必要とされる電極特性に応じて適宜決められるべきもので特に限定されるものではないが、触媒担持カーボン／ポリマーの重量比率で５／９５〜９５／５が好ましく用いられる。特に固体高分子型燃料電池用電極触媒層として用いる場合には、触媒担持カーボン／ポリマー重量比率で４０／６０〜８５／１５が好ましいものである。
【０１０５】
触媒−ポリマー複合体には、種々の添加物を加えることもできる。たとえば、電子伝導性向上のための炭素などの導電剤や、結着性向上のためのポリマー、三次元網目構造の孔径を制御する添加物などがあるが、特に限定されることなく用いることができる。これら添加物の添加量としては、触媒−ポリマー複合体に対する重量比率として０．１〜５０％の範囲が好ましく、１〜２０％の範囲がさらに好ましい。
【０１０６】
三次元網目構造を有する触媒−ポリマー複合体の製造方法としては、湿式凝固法によるものが好ましい。ここでは、触媒−ポリマー溶液組成物を塗布した後に、この塗布層をポリマーに対する凝固溶媒と接触させて、触媒−ポリマー溶液組成物の凝固析出と溶媒抽出とを同時に行なうことができる。この触媒−ポリマー溶液組成物は、ポリマー溶液中に触媒担持カーボンが均一に分散したものである。触媒担持カーボンとポリマーは前述のものが好ましく用いられる。ポリマーを溶かす溶媒については、用いられるポリマーに応じて適宜決められるべきもので、特に限定されるものではない。ポリマー溶液は触媒担持カーボンを良く分散していることが重要である。分散状態が悪い場合には、湿式凝固の際に、触媒担持カーボンとポリマーとが複合体を形成することができず好ましくない。
【０１０７】
触媒−ポリマー溶液組成物の塗布方法については、触媒−ポリマー溶液組成物の粘度や固形分などに応じた塗布方法が選択され、特に限定されるものではないが、ナイフコーター、バーコーター、スプレー、ディップコーター、スピンコーター、ロールコーター、ダイコーター、カーテンコーターなどの一般的な塗布方法が用いられる。
【０１０８】
また、ポリマーを湿式凝固させる凝固溶媒についても特に限定されるものではないが、用いられるポリマーを凝固析出しやすく、かつポリマー溶液の溶媒と相溶性のある溶媒が好ましい。基材と凝固溶媒との接触方法についても、特に限定されるものではないが、凝固溶媒に基材ごと浸漬する、塗布層のみを凝固溶媒の液面に接触させる、凝固溶媒を塗布層にシャワリングあるいはスプレーする、などの方法を用いることができる。
【０１０９】
この触媒−ポリマー溶液組成物が塗布される基材については、電極基材、あるいは高分子固体電解質の何れにおいても、塗布した後に湿式凝固を行うことが可能である。また、電極基材や高分子電解質以外の基材（たとえば転写基材）に塗布し、その後に湿式凝固を行い、三次元網目構造を作製した後に、この電極触媒層を電極基材や高分子固体電解質に転写あるいは挟持させても良い。この場合の転写基材としては、ポリテトラフルオロエチレン（ＰＴＦＥ）のシート、あるいは表面をフッ素やシリコーン系の離型剤処理したガラス板や金属板なども用いられる。
【０１１０】
本発明の固体高分子型燃料電池においては、電極基材は特に限定されることなく公知のものを用いることが可能である。また、省スペース化のために電極基材が用いられない場合もある。
【０１１１】
本発明に用いられる電極基材としては、電気抵抗が低く、集（給）電を行えるものであればとくに限定されることなく用いることが可能である。電極基材の構成材としては、たとえば、導電性無機物質を主とするものが挙げられ、この導電性無機物質としては、ポリアクリロニトリルからの焼成体、ピッチからの焼成体、黒鉛及び膨張黒鉛などの炭素材、ステンレススチール、モリブデン、チタンなどが例示される。
【０１１２】
電極基材の導電性無機物質の形態は特に限定されず、たとえば繊維状あるいは粒子状で用いられるが、ガス透過性の点から繊維状導電性無機物質（無機導電性繊維）、特に炭素繊維が好ましい。無機導電性繊維を用いた電極基材としては、織布あるいは不織布いずれの構造も使用可能である。たとえば、東レ（株）製カーボンペーパーＴＧＰシリーズ、ＳＯシリーズ、Ｅ−ＴＥＫ社製カーボンクロスなどが用いられる。織布としては、平織、斜文織、朱子織、紋織、綴織など、特に限定されること無く用いられる。また、不織布としては、抄紙法、ニードルパンチ法、スパンボンド法、ウォータージェットパンチ法、メルトブロー法によるものなど特に限定されること無く用いられる。また編物であっても構わない。これらの布帛において、特に炭素繊維を用いた場合、耐炎化紡績糸を用いた平織物を炭化あるいは黒鉛化した織布、耐炎化糸をニードルパンチ法やウォータージェットパンチ法などによる不織布加工した後に炭化あるいは黒鉛化した不織布、耐炎化糸あるいは炭化糸あるいは黒鉛化糸を用いた抄紙法によるマット不織布などが好ましく用いられる。特に、薄く強度のある布帛が得られる点から不織布を用いるのが好ましい。
【０１１３】
電極基材に炭素繊維からなる無機導電性繊維を用いた場合、炭素繊維としては、ポリアクリロニトリル（ＰＡＮ）系炭素繊維、フェノール系炭素繊維、ピッチ系炭素繊維、レーヨン系炭素繊維などが例示される。なかでも、ＰＡＮ系炭素繊維が好ましい。一般的に、ＰＡＮ系炭素繊維はピッチ系炭素繊維にくらべて圧縮強さ、引張破断伸度が大きく、折れにくいからである。折れにくい炭素繊維を得るためには、炭素繊維の炭化温度は２，５００℃以下が好ましく、２，０００℃以下がより好ましい。
【０１１４】
本発明の固体高分子型燃料電池に用いられる電極基材に、水の滞留によるガス拡散・透過性の低下を防ぐために行う撥水処理、水の排出路を形成するための部分的撥水、親水処理や、抵抗を下げるために行われる炭素粉末の添加等を行うことも好ましい実施態様である。
【０１１５】
本発明の固体高分子型燃料電池がｓｉｄｅ−ｂｙ−ｓｉｄｅ構造を有している場合、水素やメタノール水溶液などの燃料や空気の流入、水や二酸化炭素などの生成物の排出を促進するために、拡散層を設けることも好ましい実施態様である。このような拡散層は、前述の電極基材もその役割を持つが、非導電性布帛を拡散層として用いることがさらに好ましい。ここで、非導電性布帛の構成材としては、たとえば、非導電性繊維であれば特に限定されること無く用いられる。
【０１１６】
拡散層の非導電性布帛を構成する非導電性繊維としては、たとえばポリテトラフルオロエチレン（ＰＴＦＥ）、テトラフルオロエチレン−ヘキサフルオロエチレン共重合体（ＦＥＰ）、テトラフルオロエチレン−パーフルオロアルキルビニルエーテル共重合体（ＰＦＡ）、テトラフルオロエチレン−エチレン共重合体（ＥＴＦＥ）、ポリフッ化ビニリデン（ＰＶＤＦ）、ポリフッ化ビニル（ＰＶＦ）、ポリクロロトリフルオロエチレン（ＣＴＦＥ）、塩素化ポリエチレン、耐炎化ポリアクリロニトリル、ポリアクリロニトリル、ポリエステル、ポリアミド、ポリエチレン、ポリプロピレンなどが使用可能である。これらの非導電性繊維の中でも、ＰＴＦＥ、ＦＥＰ、ＰＦＡ、ＥＴＦＥ、ＰＶＤＦ、ＰＶＦ、ＣＴＦＥなどのフッ素原子含有ポリマーからなる繊維が、電極反応時の耐食性などの点から好ましいものである。
【０１１７】
拡散層の非導電性布帛としては、織布あるいは不織布いずれの構造も使用可能である。織布としては、平織、斜文織、朱子織、紋織、綴織など、特に限定されること無く用いられる。また、不織布としては、抄紙法、ニードルパンチ法、スパンボンド法、ウォータージェットパンチ法、メルトブロー法など、特に限定されること無く用いられる。また編物であっても構わない。これらの布帛において、特に平織物、ニードルパンチ法やウォータージェットパンチ法などによる不織布、抄紙法によるマット不織布などが好ましく用いられる。特に多孔質で薄く強度のある布帛が得られる点から不織布が好ましく用いられる。
【０１１８】
拡散層の非導電性布帛は、水の滞留によるガス拡散・透過性の低下を防ぐための撥水処理、水の排出路を形成するための部分的撥水あるいは親水処理等を行うことも好ましい実施態様である。さらには、熱処理、延伸、プレスなどの後処理を行うことも好ましい実施態様である。これらの後処理により、薄膜化、空隙率増加、強度増加などの効果が期待できる。
【０１１９】
本発明の固体高分子型燃料電池においては、電極基材と電極触媒層の間に、少なくとも無機導電性物質と疎水性ポリマーを含む導電性中間層を設けることが好ましい。特に、電極基材が空隙率の大きい炭素繊維織物や不織布である場合、導電性中間層を設けることで、電極触媒層が電極基材にしみ込むことによる性能低下を抑えることができる。
【０１２０】
本発明の高分子固体電解質を、たとえば膜−電極複合体（ＭＥＡ）に用いる場合、高分子固体電解質に後加工した後にＭＥＡとすることが好ましい。例えば、燃料メタノールの透過をさらに低減するために、金属薄膜を高分子固体電解質に被覆することも好ましい態様である。このような金属薄膜の例としては、パラジウム、白金、銀などが挙げられる。
【０１２１】
本発明の高分子固体電解質において、電極触媒層あるいは電極触媒層と電極基材を用いて膜−電極複合体（ＭＥＡ）とする際の作製方法は特に限定されるものではない。ホットプレスにより一体化することが好ましいが、その温度や圧力は、高分子固体電解質の厚さ、空隙率、電極触媒層や電極基材により適宜選択すればよい。通常、温度は４０℃〜１８０℃、圧力は１０ｋｇｆ／ｃｍ²〜８０ｋｇｆ／ｃｍ²が好ましい。
【０１２２】
本発明の高分子固体電解質は、種々の電気化学装置に適用可能である。例えば、燃料電池、水電解装置、クロロアルカリ電解装置等が挙げられるが、中でも燃料電池がもっとも好ましい。さらに燃料電池のなかでも固体高分子型燃料電池に好適であり、これには水素を燃料とするものとメタノールなどの有機溶媒を燃料とするものがあり、特に限定されるものではないが、メタノールを燃料とするＤＭＦＣに特に好ましく用いられる。
【０１２３】
さらに、本発明の固体高分子型燃料電池の用途としては、特に限定されないが、移動体の電力供給源が好ましいものである。特に、携帯電話、パソコン、ＰＤＡなどの携帯機器、掃除機等の家電、乗用車、バス、トラックなどの自動車や船舶、鉄道などの移動体の電力供給源として好ましく用いられる。
【０１２４】
【実施例】
以下、本発明を実施例を用いて説明するが、本発明はこれらに限定されるものではない。なお、各物性の測定条件は次の通りである。
（１）粒径および数平均粒径の測定
走査型電子顕微鏡（ＳＥＭ）により撮影した写真から任意に選んだ１００個の粒子について個々の粒子の粒径（円相当平均径）を測定し、その数平均として算出した。
【０１２５】
参考例１
（１）炭素以外の元素を架橋点とする３次元架橋性化合物の加水分解
東レダウコーニングシリコーン社製テトラブトキシチタン５ｇに０．０１Ｎ塩酸水溶液を添加し、室温にて３０分間攪拌し、無色透明の加水分解物を得た。
（２）高分子固体電解質の作製
市販の２０％Ｎａｆｉｏｎ溶液（デュポン社製）１０ｇに、（１）で作製した加水分解物を０．２２ｇ、および無機微粒子として数平均粒径６００ｎｍのシリカゾルを加え、この溶液を１００℃で３０分間加熱し、高分子固体電解質を得た。
（３）高分子固体電解質の性能
（２）で得られた膜を比較例１と同様にしてメタノール透過量とイオン伝導性を評価した。膜をエレクトロケム社製セルにセットし、片面に１ｍｏｌ／ｌメタノール水溶液を０．２ｍｌ／ｍｉｎで供給し、もう片面に空気を５０ｍｌ／ｍｉｎで供給した。メタノール透過量は排気された空気中のメタノール濃度を測定し求めた。膜のイオン電導度は膜面に電流および電圧端子を接触させ抵抗を測定し求めた。この膜のメタノール透過量は１．０μｍｏｌ／ｃｍ²／ｍｉｎ、イオン伝導度は４．８Ｓ／ｃｍ²であった。
【０１２６】
比較例１
参考例１において、無機微粒子のシリカゾルを加えない他は、同様にして高分子固体電解質を得た。この膜のメタノール透過量は１．５μｍｏｌ／ｃｍ²／ｍｉｎ、イオン伝導度は４．８Ｓ／ｃｍ²であり、無機微粒子を加えた実施例１よりも性能が悪かった。
【０１２７】
比較例２
参考例１において、数平均粒径６００ｎｍのシリカゾルの代わりに数平均粒径２μｍのシリカゾルを用いる他は、同様にして高分子固体電解質を得た。この膜のメタノール透過量は１．８μｍｏｌ／ｃｍ²／ｍｉｎ、イオン伝導度は４．４Ｓ／ｃｍ²であり、数平均粒径が１μｍより小さい無機微粒子を加えた実施例１よりも性能が悪かった。
【０１３４】
実施例１
（１）炭素以外の元素を架橋点とする３次元架橋性化合物の加水分解
東レダウコーニングシリコーン社製γ−グリシドキシプロピルトリメトキシシラン５ｇに０．０１Ｎ塩酸水溶液を添加し、室温にて３０分間攪拌し、加水分解物を得た。
【０１３５】
該γ−グリシドキシプロピルトリメトキシシラン加水分解物をＮ，Ｎ−ジメチルアセトアミド（ＤＭＡｃ）に溶解し、１５重量％溶液とした。
（２）スルホン化ポリフェニレンオキシドの合成
室温、窒素雰囲気下で三菱エンジニアリングプラスチック社製ポリフェニレンオキシド（ＹＰＸ−１００Ｌ）（１００ｇ）をクロロホルム（１０００ｇ）に溶解させた後、撹拌しながらクロロスルホン酸（３４ｍＬ）をゆっくり滴下した。滴下終了後室温で３０分間撹拌を続けた。析出したポリマーを濾別後、ミルで粉砕し、水で十分に洗浄後、真空乾燥し、目的のスルホン化ポリフェニレンオキシドを得た。（イオン交換当量：３．０ｍｅｑ）
該スルホン化ポリフェニレンオキシドをＮ，Ｎ−ジメチルアセトアミド（ＤＭＡｃ）に溶解し、１５重量％溶液とした。
（３）スルホン化スチレン−ジビニルベンゼン微粒子の合成
還流冷却管、撹拌装置および窒素ガス導入管を備えた３００ｍＬ四ツ口フラスコに、スチレン（４．５ｇ）およびジビニルベンゼン（０．５ｇ）を入れた。フラスコに窒素ガスを導入し撹拌しながら、日本油脂製ノニオン系界面活性剤”ノニオンＨＳ−２１０”水溶液（９３．５ｇ）および過硫酸カリウム水溶液（２ｇ）を滴下した。反応の進行にともない、スチレン−ジビニルベンゼン微粒子が生成した。該スチレン−ジビニルベンゼン微粒子を遠心分離により固液分離した後、クロロスルホン酸の１，２−ジクロロエタン溶液中で撹拌した。反応終了後、透析チューブを用いて十分に洗浄を行い、目的のスルホン化スチレン−ジビニルベンゼンを得た。該スルホン化スチレン−ジビニルベンゼン微粒子の数平均粒径を測定したところ５００ｎｍであった。該スルホン化スチレン−ジビニルベンゼンの硫黄濃度をＳＴＥＭ−ＥＤＸ法で分析したところ、微粒子内部と表面の硫黄濃度比すなわちスルホン酸基濃度比は１：１で変わらなかった。
（４）高分子固体電解質膜の作製
前記（１）のγ−グリシドキシプロピルトリメトキシシラン加水分解物ＤＭＡｃ溶液０．５ｇおよび前記（２）のスルホン化ポリフェニレンオキシドＤＭＡｃ溶液４．５ｇおよび前記（３）のスルホン化スチレン−ジビニルベンゼン微粒子を混合した。この液をガラス板上にキャストし、１００℃、３時間加熱して高分子固体電解質膜を作製した。膜厚は９０μｍであった。
（５）高分子固体電解質膜のメタノール透過量測定法
Ｈ型セル間にサンプル膜を挟み、一方のセルには純水を入れ、他方のセルには１Ｍメタノール水溶液を入れた。セルの容量は各８０ｍＬであった。またセル間の開口部面積は１．７７ｃｍ２であった。２０℃において両方のセルを撹拌した。１時間，２時間および３時間経過時点で純水中に溶出したメタノール量を島津製作所製ガスクロマトグラフィ（ＧＣ−２０１０）で測定し定量した。グラフの傾きから単位時間、単位面積あたりのメタノール透過量を求めた。
（６）高分子固体電解質膜のイオン伝導度測定法
Ｓｏｌａｒｔｒｏｎ製電気化学測定システム（Ｓｏｌａｒｔｒｏｎ１２８７ Ｅｌｅｃｔｒｏｃｈｅｍｉｃａｌ ＩｎｔｅｒｆａｃｅおよびＳｏｌａｒｔｒｏｎ １２５５Ｂ Ｆｒｅｑｕｅｎｃｙ Ｒｅｓｐｏｎｓｅ Ａｎａｌｙｚｅｒ）を使用した。サンプルをφ２ｍｍおよびφ１０ｍｍの２枚の円形電極（ステンレス製）間に加重１ｋｇをかけて挟持した（有効電極面積０．０３１４ｃｍ２）。サンプルと電極の界面には、ポリ（２−アクリルアミド−２−メチルプロパンスルホン酸）の１５％水溶液を塗布した。２５℃において、定電位インピーダンス測定を行い、膜厚方向のイオン伝導度を求めた。交流振幅は５０ｍＶとした。
（７）高分子固体電解質膜の性能評価
前記（４）で得られた膜を前記（５）および前記（６）の方法でメタノール透過量とイオン伝導度を評価した。この膜のメタノール透過量は６．３μｍｏｌ／ｃｍ²・ｍｉｎ、イオン伝導度は６．７Ｓ／ｃｍ²であった。
【０１３６】
比較例３
実施例１において、スルホン化スチレン−ジビニルベンゼン微粒子を加えない他は、同様にして高分子固体電解質を得た。この膜のメタノール透過量は９．０μｍｏｌ／ｃｍ²／ｍｉｎ、イオン伝導度は６．７Ｓ／ｃｍ²であり、有機微粒子を加えた実施例１よりもメタノール透過量が多く、性能が悪かった。
【０１３７】
実施例２
γ−グリシドキシプロピルトリメトキシシラン加水分解物溶液の代わりにγ−グリシドキシプロピルメチルジエトキシシラン加水分解物溶液を用い、実施例１と同様にして高分子固体電解質を作製した。この膜の性能を実施例１と同様に評価したところ、メタノール透過量は７．６μｍｏｌ／ｃｍ²／ｍｉｎ、イオン伝導度は６．９Ｓ／ｃｍ²であった。比較例２と比較してメタノール透過量が小さかった。
【０１３８】
実施例３
γ−グリシドキシプロピルトリメトキシシラン加水分解物溶液の代わりにビス（トリメトキシシリル）ヘキサン加水分解物溶液を用い、実施例１と同様にして高分子固体電解質を作製した。この膜の性能を実施例１と同様に評価したところ、メタノール透過量は６．０μｍｏｌ／ｃｍ²／ｍｉｎ、イオン伝導度は６．７Ｓ／ｃｍ²であった。比較例２と比較してメタノール透過量が小さかった。
【０１３９】
実施例４
スルホン化ポリフェニレンオキシドＤＭＡｃ溶液の代わりに市販の２０％Ｎａｆｉｏｎ溶液（デュポン社製）を用い、実施例１と同様にして高分子固体電解質を作製した。この膜の性能を実施例１と同様に評価したところ、メタノール透過量は６．５μｍｏｌ／ｃｍ²／ｍｉｎ、イオン伝導度は６．７Ｓ／ｃｍ²であった。
【０１４０】
比較例４
実施例４において、市販の２０％Ｎａｆｉｏｎ溶液（デュポン社製）のみを用い、実施例１と同様にして高分子固体電解質を得た。この膜のメタノール透過量は８．０μｍｏｌ／ｃｍ²／ｍｉｎ、イオン伝導度は６．７Ｓ／ｃｍ²であり、有機微粒子および加水分解物を加えた実施例４よりも性能が悪かった。
【０１４１】
実施例５
（１）スルホン化スチレン−ジビニルベンゼン微粒子の合成
還流冷却管、撹拌装置および窒素ガス導入管を備えた３００ｍＬ四ツ口フラスコに、スチレン（３．２ｇ）およびジビニルベンゼン（１．８ｇ）を入れた。フラスコに窒素ガスを導入し撹拌しながら、日本油脂製ノニオン系界面活性剤”ノニオンＨＳ−２１０”水溶液（９３．５ｇ）および過硫酸カリウム水溶液（２ｇ）を滴下した。反応の進行にともない、スチレン−ジビニルベンゼン微粒子が生成した。該スチレン−ジビニルベンゼン微粒子を遠心分離により固液分離した後、濃硫酸中で加熱撹拌した。反応終了後、多量のメタノールで精製し、目的のスルホン化スチレン−ジビニルベンゼンを得た。該スルホン化スチレン−ジビニルベンゼン微粒子の数平均粒径を測定したところ４８０ｎｍであった。該スルホン化スチレン−ジビニルベンゼンの硫黄濃度をＳＴＥＭ−ＥＤＸ法で分析したところ、微粒子内部と表面の硫黄濃度比すなわちスルホン酸基濃度比は１：５であった。
（２）高分子固体電解質膜の性能評価
実施例１のスルホン化スチレン−ジビニルベンゼン微粒子の代わりに、前記（１）のスルホン化スチレン−ジビニルベンゼン微粒子を用い、実施例１と同様にして高分子固体電解質を作製した。この膜の性能を実施例１と同様に評価したところ、メタノール透過量は５．０μｍｏｌ／ｃｍ²／ｍｉｎ、イオン伝導度は９．０Ｓ／ｃｍ²であり、比較例２と比較してメタノール透過量が小さくかった。また、実施例１よりも性能が良かった。
【０１４２】
実施例６
スルホン化ポリフェニレンオキシドＤＭＡｃ溶液の代わりにＮａｆｉｏｎ溶液を用い、実施例５と同様にして高分子固体電解質を作製した。この膜の性能を実施例１と同様に評価したところ、メタノール透過量は６．６μｍｏｌ／ｃｍ²／ｍｉｎ、イオン伝導度は６．７Ｓ／ｃｍ²であった。比較例３と比較してメタノール透過量が小さかった。
【０１４３】
実施例７
（１）スルホン化フェニルマレイミド−スチレン−ジビニルベンゼン微粒子の合成
還流冷却管、撹拌装置および窒素ガス導入管を備えた３００ｍＬ四ツ口フラスコに、スチレン（３．０ｇ）、ジビニルベンゼン（０．５ｇ）およびフェニルマレイミド（１．５ｇ）を入れた。フラスコに窒素ガスを導入し撹拌しながら、日本油脂製ノニオン系界面活性剤”ノニオンＨＳ−２１０”水溶液（９３．５ｇ）および過硫酸カリウム水溶液（２ｇ）を滴下した。反応の進行にともない、フェニルマレイミド−スチレン−ジビニルベンゼン微粒子が生成した。該フェニルマレイミド−スチレン−ジビニルベンゼン微粒子を遠心分離により固液分離した後、濃硫酸中で撹拌した。反応終了後、多量のメタノールで精製し、目的のスルホン化フェニルマレイミド−スチレン−ジビニルベンゼンを得た。該スルホン化フェニルマレイミド−スチレン−ジビニルベンゼン微粒子の数平均粒径を測定したところ５５０ｎｍであった。該スルホン化フェニルマレイミド−スチレン−ジビニルベンゼンの硫黄濃度をＳＴＥＭ−ＥＤＸ法で分析したところ、微粒子内部と表面の硫黄濃度比すなわちスルホン酸基濃度比は１：９であった。
（２）高分子固体電解質膜の性能評価
実施例１２のスルホン化スチレン−ジビニルベンゼン微粒子の代わりに、前記（１）のスルホン化フェニルマレイミド−スチレン−ジビニルベンゼン微粒子を用い、実施例１と同様にして高分子固体電解質を作製した。この膜の性能を実施例１と同様に評価したところ、メタノール透過量は５．０μｍｏｌ／ｃｍ²／ｍｉｎ、イオン伝導度は８．０Ｓ／ｃｍ²であった。比較例２と比較してメタノール透過量が小さかった。
【０１４４】
実施例８
スルホン化ポリフェニレンオキシドＤＭＡｃ溶液の代わりにＮａｆｉｏｎ溶液を用い、実施例１と同様にして高分子固体電解質を作製した。この膜の性能を実施例１と同様に評価したところ、メタノール透過量は６．５μｍｏｌ／ｃｍ²／ｍｉｎ、イオン伝導度は６．７Ｓ／ｃｍ²であった。比較例２と比較してメタノール透過量が小さかった。
【０１４５】
【発明の効果】
本発明によれば、メタノールクロスオーバーを抑制し、イオン伝導性が高く、高出力を達成できる新規な高分子電解質およびその製造方法ならびにそれを用いた高性能な固体高分子型燃料電池を提供でき、その実用性は高い。
【図面の簡単な説明】
【図１】 本発明の高分子固体電解質の概略斜視図である。
【図２】 本発明の高分子固体電解質における多孔部１を拡大した平面模式図である。
【図３】 本発明の高分子固体電解質に用いられる多孔が整然と配列されている多孔基材の走査型電子顕微鏡写真である。
【図４】 従来の高分子固体電解質に用いられる多孔基材の走査型電子顕微鏡写真である。
【図５】 本発明の高分子固体電解質に用いられる三次元網目構造を有する多孔基材の走査型電子顕微鏡写真である。
【図６】 本発明のｓｉｄｅ−ｂｙ−ｓｉｄｅ構造の高分子固体電解質の概略斜視図である。
【図７】 本発明の高分子固体電解質を用いたｓｉｄｅ−ｂｙ−ｓｉｄｅ構造燃料電池の製造プロセスの一部を示す断面模式図である。
【符号の説明】
１：多孔部
２：非多孔部
３：孔
４：膜導電部
５：膜貫通電子伝導部
６：プロトン伝導部
７：電極
ｄ：孔径
Ｌ：隣り合う貫通孔の中心間隔[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a polymer solid electrolyte and a polymer electrolyte fuel cell using the same.
[0002]
[Prior art]
A fuel cell is a power generation device with low emissions, high energy efficiency, and low environmental burden. For this reason, it is in the spotlight again in recent years to the protection of the global environment. Compared to conventional large-scale power generation facilities, this is a power generation device expected in the future as a relatively small-scale distributed power generation facility, and as a power generation device for mobile objects such as automobiles and ships. It is also attracting attention as a power source for small mobile devices and portable devices, and is expected to be installed in mobile phones and personal computers in place of secondary batteries such as nickel metal hydride batteries and lithium ion batteries.
[0003]
In a polymer electrolyte fuel cell, in addition to a conventional polymer electrolyte fuel cell using hydrogen gas as a fuel (hereinafter also referred to as PEFC), a direct methanol fuel cell (hereinafter also referred to as DMFC) that directly supplies methanol. ) Is also attracting attention. Although the DMFC has a lower output than the conventional PEFC, the fuel is liquid and does not use a reformer. Therefore, the energy density is high, and the use time of the portable device per filling is long. is there.
[0004]
In a fuel cell, an anode electrode and a cathode electrode in which a reaction responsible for power generation occurs and an electrolyte membrane serving as an ion conductor between the anode and the cathode constitute a membrane-electrode complex (MEA), and this MEA is separated by a separator. The sandwiched cell is configured as a unit. Here, the electrode is composed of an electrode substrate (also referred to as a gas diffusion electrode or a current collector) that promotes gas diffusion and collects (supply) electricity, and an electrode catalyst layer that actually becomes an electrochemical reaction field. ing. For example, in an anode electrode of a solid polymer type fuel cell, a fuel such as hydrogen gas reacts with a catalyst layer of the anode electrode to generate protons and electrons, and the electrons are conducted to the electrode substrate, and the protons are transferred to the polymer solid electrolyte. Conduct. For this reason, the anode electrode is required to have good gas diffusibility, electron conductivity, and ion conductivity. On the other hand, in the cathode electrode, an oxidizing gas such as oxygen or air reacts with protons conducted from the polymer solid electrolyte and electrons conducted from the electrode base material in the cathode electrode catalyst layer to produce water. For this reason, in the cathode electrode, it is necessary to efficiently discharge the generated water in addition to gas diffusibility, electron conductivity, and ion conductivity.
[0005]
In particular, among solid polymer fuel cells, in an electrolyte membrane for DMFC using an organic solvent such as methanol as a fuel, in addition to the performance required for a conventional electrolyte membrane for PEFC using hydrogen gas as a fuel, Inhibition of methanol aqueous solution permeation is also required. Methanol permeation of the electrolyte membrane is also called methanol crossover (hereinafter also referred to as MCO) or chemical short, and causes a problem that battery output and energy efficiency are lowered.
[0006]
Until now, perfluoro polymers have been used in electrolyte membranes of polymer electrolyte fuel cells. Since this membrane swells in an aqueous methanol solution, there is a problem that methanol crossover is large and mechanical strength is also reduced. In order to prevent MCO, there are measures based on fuel cell operating conditions such as reducing the concentration of methanol supplied to the anode, improvements to conventional perfluoro-based electrolyte membranes, or material-based measures such as new polymer electrolytes.
[0007]
In the improvement of the conventional perfluoro-based electrolyte, there is a method in which MCO reduction and proton conductivity are improved by filling an electrolyte membrane with an inorganic proton conductor (Patent Document 1). Moreover, the electrolyte membrane comprised from an organic polymer and an inorganic proton conductor is disclosed (patent documents 2 and 3).
[0008]
On the other hand, Patent Document 4 and the like are known examples of novel polymer electrolytes.
[0009]
[Patent Document 1]
JP 2000-516014 A
[0010]
[Patent Document 2]
JP 2001-102071 A
[0011]
[Patent Document 3]
JP 2002-015742 A
[0012]
[Patent Document 4]
International Publication No. 98/22989 Pamphlet
[0013]
[Problems to be solved by the invention]
However, the organic polymer other than the inorganic proton conductor in the method described in Patent Document 1 uses a conventional perfluoro-based electrolyte polymer, so that it is essentially weak against methanol and has a low MCO reduction effect. Yes. Further, the method described in Patent Document 3 has a disadvantage that the organic polymer other than the inorganic proton conductor does not have proton conductivity, and the proton conductivity of the entire membrane is low. Furthermore, the method described in Patent Document 4 has a problem in that it is difficult to increase the crosslink density and there is a limit to the suppression of crossover.
[0014]
The present invention provides a novel polymer electrolyte capable of solving the above-mentioned problems, suppressing crossover and achieving high output, a method for producing the same, a high-performance solid polymer fuel cell using the same, and the like. Objective.
[0015]
[Means for Solving the Problems]
  The present invention has the following configuration in order to solve the above problems. That is, in the polymer solid electrolyte of the present invention, a polymer having an anionic group is uniformly mixed with a three-dimensional crosslinked polymer having an element other than carbon as a crosslinking point, and has a particle size of 1 μm or less.Does not dissolve or swell in methanolOrganic polymer fine particles are included. Furthermore, the polymer electrolyte fuel cell of the present invention is constituted by using the polymer solid electrolyte of the present invention.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, preferred embodiments of the present invention will be described.
[0017]
  In the polymer solid electrolyte of the present invention, a polymer having an anionic group is uniformly mixed with a three-dimensional crosslinked polymer having an element other than carbon as a crosslinking point, and has a particle size of 1 μm or less.Does not dissolve or swell in methanolOrganic polymer fine particles are included. By including the fine particles, the swelling of the methanol aqueous solution is suppressed, the MCO is reduced, and the reduction in the strength of the film is also suppressed.
[0018]
When a conventional polymer having an anionic group is used alone as a polymer solid electrolyte, if the content of the ionic group is increased in order to obtain high ionic conductivity, water having a large diameter is formed inside the polymer solid electrolyte. A cluster is formed, and free water increases in the polymer solid electrolyte. Since methanol easily moves in free water, a sufficient methanol crossover suppression effect cannot be obtained, and conventional ones cannot achieve both ion conductivity and methanol suppression effect. On the other hand, the polymer solid electrolyte of the present invention can reduce the cluster diameter of water existing inside by restraining the polymer molecular chain and adding fine particles, so that the ion conductivity and the methanol crossover suppression effect are reduced. Can be achieved. In addition, there is an effect of suppressing swelling deformation and the like.
[0019]
  The fine particles contained in the polymer solid electrolyte of the present invention are organic.Is a polymerThe number average particle size of the primary particles needs to be 1 μm or less. When the number average particle size is larger than 1 μm, it is difficult to disperse well in the polymer having an anionic group, and as a result, a high-quality solid polymer electrolyte cannot be obtained. About the calculation method of a number average particle diameter, the particle size (equivalent circle average diameter) of each particle | grain is measured from the photograph which image | photographed the electrolyte cross section with the scanning electron microscope (SEM), and it calculates | requires by the number average. If measurement is easy, a transmission electron microscope (TEM) may be used.
[0021]
  Specific examples of organic polymers include polymers that do not dissolve or swell in methanol, such as polystyrene, polyvinylidene fluoride, polytetrafluoroethylene, polysulfone, polyphenylene sulfide, polyphenylene sulfide sulfone, polyether sulfone, polyphenylene oxide, and polyimide.IfIt is not particularly limited.
[0022]
As the fine particles of the organic polymer, a copolymer obtained by polymerization of monomers may be used. Here, the monomer is a substance capable of undergoing a polymerization reaction that is a main component of the components constituting the fine particles to be finally produced, and is not particularly limited as long as polymerization is possible. Specific examples of the monomer include styrene monomers such as styrene, methylstyrene, ethylstyrene, chlorostyrene, styrenesulfonic acid, t-butoxystyrene, methyl (meth) acrylate, ethyl (meth) acrylate, (meth) acrylic. 2-ethylhexyl acid, lauryl (meth) acrylate, glycidyl (meth) acrylate, dimethylaminoethyl (meth) acrylate, hydroxyethyl (meth) acrylate, diethylene glycol mono (meth) acrylate, polyethylene glycol mono (meth) acrylate, butanediol (Meth) acrylic acid ester monomers such as mono (meth) acrylate, unsaturated carboxylic acid monomers such as (meth) acrylic acid and maleic acid, alkyl vinyl ethers such as methyl vinyl ether and ethyl vinyl ether Vinyl ether monomers, vinyl ester monomers such as vinyl acetate and vinyl butyrate, (meth) acrylamide, N-methyl (meth) acrylamide, N-ethyl (meth) acrylamide, 2-acrylamide 2-methylpropanesulfonic acid, etc. ) Nitrile monomers such as acrylamide monomers and (meth) acrylonitrile. The above monomers may be used alone or as a mixture of two or more. Of the monomers, styrene monomers are preferred.
[0023]
Furthermore, it is preferable to use a polyfunctional monomer as a crosslinking agent in order to introduce a crosslinked structure into the copolymer. The polyfunctional monomer is not particularly limited as long as it is a monomer having two or more unsaturated functional groups copolymerizable in the molecule. Specific examples include aromatic polyfunctional monomers such as o-divinylbenzene, m-divinylbenzene, and p-divinylbenzene, ethylene glycol di (meth) acrylate, diethylene glycol di (meth) acrylate, and triethylene glycol di (meth) acrylate. Di-, tri-, polyhydric alcohols such as glycerol (di / tri) (meth) acrylate, trimethylolpropane (di / tri) (meth) acrylate, pentaerythritol (di / tri / tetra) (meth) acrylate, Tetra- (meth) acrylate compounds, polyethylene glycol di (meth) acrylate, polyethylene glycol di (meth) acrylate, (meth) acrylate compounds such as methoxypolyethylene glycol mono (meth) acrylate, di (meth) acrylate (Meth) allyl compounds such as ruphthalate, di (meth) allyl (meth) acrylamide, tri (meth) allyl cyanurate, ester compounds such as (meth) acrylic acid vinyl ester, (meth) acrylic acid allyl ester, diethylene glycol bisallyl Examples thereof include diallyl compounds such as carbonate and diallyl phthalate, and diene compounds such as butadiene, hexadiene and pentadiene. The above polyfunctional monomers may be used alone or as a mixture of two or more. Among the polyfunctional monomers, aromatic polyfunctional monomers are preferable from the viewpoints of polymerizability with styrene monomers and particle size reduction, and divinylbenzenes are particularly preferable. Divinylbenzene may be mixed with various isomers.
[0024]
When the organic polymer fine particles contained in the polymer solid electrolyte of the present invention are polymerized from monomers, the monomers may be mixed in a homogeneous solution such as an organic solvent to produce, or consist of a phase containing monomers and an aqueous phase. It may be produced in a heterogeneous system. In this case, the monomer phase may be a monomer alone, or an appropriate solvent may be added for the purpose of controlling the reaction rate. Further, a catalyst such as a polymerization initiator and other additives may be contained. When producing fine particles in a heterogeneous system, it is preferably carried out by emulsifying with an emulsifier or the like in order to realize finer particle size and monodispersibility of the particle size distribution. Moreover, when manufacturing by a heterogeneous system, it exists in the tendency for a blocky polymerization product to generate | occur | produce at an interface only by leaving still without stirring at all. Conversely, if the stirring is too early, the reaction proceeds rapidly and the particle size distribution tends to be widened. The stirring speed can be experimentally determined by the scale of the reaction vessel, the shape of the stirring blade, the stirring method, and the like. For the solid-liquid separation of the obtained organic fine particles, generally known methods such as filtration, centrifugation, and evaporation can be used.
[0025]
In the present invention, the fine particles contained in the solid polymer electrolyte are subjected to surface treatment or the like on the surface for hydrophilicity such as hydroxyl groups, sulfonic acid groups, sulfonimide groups, sulfuric acid groups, phosphoric acid groups, phosphonic acid groups, and carboxylic acid groups. It is a preferred embodiment to be used with those provided with a sex group. Here, the sulfonic acid group is -SO₂-(OH), sulfonimide group is -SO2-NH-SO₂-R (R represents an arbitrary substituent), sulfate group is -OSO₂(OH), the phosphonic acid group is -PO (OH)₂The phosphate group is -OPO (OH)₂The carboxylic acid group means -CO (OH), and salts thereof. This is expected to improve the ionic conductivity of the polymer solid electrolyte. At this time, it is preferable from the viewpoint of MCO reduction that the fine particles have no hydrophilic group as much as possible. The ratio of the hydrophilic group concentration inside the fine particles (in the center) and the surface is preferably 1: 3 or less, more preferably 1: 5 or less, and most preferably 1:10 or less. If such fine particles are used, both high ion conductivity and low MCO can be achieved. In order to calculate the hydrophilic group concentration ratio between the inside and the surface of the fine particles, for example, STEM-EDX method (Scanning Transmission Electron Microscope-Energy Dispersion X-ray Spectroscopy; composition combining energy dispersive X-ray spectroscopy with scanning transmission electron microscope) Analysis method). In the STEM-EDX method, the atomic ratio of sample constituent elements can be measured, and the hydrophilic group concentration ratio can be calculated from the atomic ratio.
[0026]
The mixing amount of the fine particles contained in the polymer solid electrolyte of the present invention is preferably 30 to 80% in terms of volume fraction, but is appropriately selected depending on the required polymer species having MCO, ion conduction, membrane strength, or anionic group. It should be.
[0027]
The shape of the fine particles contained in the polymer solid electrolyte of the present invention is preferably spherical from the viewpoint of improving the packing density, but may be scale-like or flake-like, and is not particularly limited. Also, functional fine particles having a surface modification may be used by attaching functional fine particles having a smaller particle diameter to the fine particle surface, or chemically bonding a target functional substance to the fine particle surface.
[0028]
As a method for mixing fine particles into the solid polymer electrolyte of the present invention, a method in which fine particles are melted or dispersed in an anionic group-containing polymer, or a fine particle precursor is mixed in an anionic group-containing polymer in a molten or solution state. There is no particular limitation on the method of making the fine particles alone later. Further, in the case where the molecular chain constraint in the anionic group-containing polymer is configured by uniformly mixing the polymer and the three-dimensional crosslinked body, the fine particles or the crosslinked body precursor may have fine particles or There is also a method in which the fine particle precursor is mixed in a molten or solution state and then mixed with an anionic group-containing polymer.
[0029]
The anionic group-containing polymer in the polymer solid electrolyte of the present invention is not particularly limited, and a polymer having an anionic group such as a sulfonic acid group, a phosphonic acid group, a phosphoric acid group, or a carboxylic acid group is used. Nafion or the like can be used as a conventional perfluoro-based electrolyte.
[0030]
As the anionic group-containing polymer of the present invention, a polymer having bound water is preferably used in order to increase the effect of mixing fine particles. Here, the bound water is water that is present near the polymer main chain or near the anionic group and is considered to interact with the molecular chain. The melting point of such bound water has a melting temperature lower than the normal water melting temperature of 0 ° C. Therefore, the amount of bound water can be determined using a differential scanning calorimeter (DSC) method, and DSC measurement is performed by the following method. That is, after removing excessive surface adhering water from the water-containing sample, it is placed in a sealed container. After cooling this from room temperature to -30 ° C. at a rate of 10 ° C./min, the temperature is raised at 0.3 ° C./min, and the DSC curve of this temperature rising process is measured. Of the melting area obtained from the DSC curve in the temperature raising process, the melting area of 0 ° C. or higher is called free water, and bound water is obtained by subtracting free water from the total water content.
[0031]
Examples of the anionic group-containing polymer of the present invention include a polymer having a structure represented by the following formula (1).
Formula (1)
[0032]
[Chemical 1]

[0033]
(Where X: polar group, I₁, I₂: Anionic group, R: organic group. )
The polar group X in the polymer represented by the structural formula (1) is not particularly limited as long as it is different from the anionic group, but is preferably one capable of coordinating water to the polar group. Among them, a sulfonyl group (—SO₂-), Oxy group (-O-), thio group (-S-), carbonyl group (-CO-), ester group (-COO-), amide group (-NRCO-) and imide group and formula (2) And what has a repeating unit shown by Formula (3) is used preferably. Two or more types of polar groups may be present in the polymer solid electrolyte, and it may be preferable to use them in combination.
[0034]
Formula (2)
[0035]
[Chemical 2]

[0036]
Formula (3)
[0037]
[Chemical Formula 3]

[0038]
(R: organic group.)
The polymer containing the polar group X is not particularly limited. Specific examples include polyphenylene sulfide sulfone represented by the following formula (4), polyphenylene sulfide represented by the following formula (5), polyphosphazene represented by the following formula (6), polyimide represented by the following formula (7), and polysulfone. Heat- and oxidation-resistant polymers such as (PSF), polyphenylene oxide (PPO), polyether ketone (PEK), polyether ether ketone (PEEK), polybenzimidazole (PBI), polyether sulfone (PES) are preferably used. . Of these, polyphenylene sulfide sulfone, polyphenylene sulfide, polyphosphazene, polyimide, polybenzimidazole, and polysulfone are particularly preferably used from the viewpoint of water coordination and methanol affinity. These polymers can also be used in combination of two or more.
Formula (4)
[0039]
[Formula 4]

[0040]
Formula (5)
[0041]
[Chemical formula 5]

[0042]
Formula (6)
[0043]
[Chemical 6]

[0044]
Formula (7)
[0045]
[Chemical 7]

[0046]
(Here, Z is an organic group containing an aromatic ring. N is a positive integer and represents the number of repetitions.)
In the present invention, the anionic group (I in the polymer represented by the structural formula (1))₁, I₂) Is not particularly limited, but those having proton exchange ability are preferred. As such a functional group, a sulfonic acid group, a sulfuric acid group, a phosphoric acid group, a carboxylic acid group, a phosphonic acid group and the like are preferably used. Here, the sulfonic acid group is -SO₂-(OH), sulfate group is -OSO₂(OH), the phosphonic acid group is -PO (OH)₂The phosphate group is -OPO (OH)₂The carboxylic acid group means -CO (OH), and salts thereof. These anionic groups may be contained in the polymer in two or more types, and may be preferable by combining them. The combination is appropriately determined depending on the structure of the polymer.
[0047]
In the present invention, the organic group R in the polymer represented by the structural formula (1) is not particularly limited. An aromatic ring is preferably included from the viewpoints of rigidity and introduction of an ionic group into an organic group. It is also preferable to have a crosslinking point in order to constrain the molecular chain.
[0048]
In the present invention, “restraint” means that the water content is suppressed as compared with the case where the anionic group-containing polymer is present alone.
[0049]
  Method for restraining the molecular chain of a polymer having the structural formula (1) in the present inventionIs aExamples thereof include a method in which a nonionic group-containing polymer and a three-dimensional cross-linked polymer are uniformly mixed. The polymer having an anionic group and other polymer are preferably present in a state where their molecular chains are intertwined with each other in order to suppress MCO and swelling. It is thought that molecular chains are entangled with each other to restrain each other's movement and prevent methanol permeation. The stronger the constraint of the molecular chain, the lower the uptake of free water, but the ionic conductivity may be reduced. For this reason, it is necessary to select the degree of restriction of the molecular chain as appropriate according to the required characteristics. Specific methods for constraining molecular chainsIsThere is a method of using a crosslinkable polymer separately from the polymer having the formula (1) to form a structure in which both are uniformly mixed. As another method using a crosslinkable polymer,,Examples thereof include a three-dimensional crosslinked body having an element other than carbon such as loxane as a crosslinking point.
[0050]
  In the solid polymer electrolyte of the present invention, the case where the polymer having an anionic group and the three-dimensional cross-linked polymer are uniformly mixed has a structure having an anionic group inside the network of the three-dimensional cross-linked product. The state in which a polymer exists. The solid polymer electrolyte of the present invention is a polymer having an anionic group.andDoes not contain a site consisting of a three-dimensional cross-linkable polymer whose cross-linking point is an element other than carbonRuHowever, if these sites are included, the proton conductivity of the polymer solid electrolyte may be lowered and the crossover suppression effect may be lowered. For this reason, the proportion of the portion in which the polymer having an anionic group and the three-dimensional crosslinked polymer are uniformly mixed in the polymer solid electrolyte is preferably 30% or more of the whole polymer solid electrolyte, and if it is 50% or more Further preferred.
[0051]
  These three-dimensionally crosslinked products preferably have an ionic group from the viewpoint of ion conductivity and compatibility. Among three-dimensional cross-linked bodies, three-dimensional cross-linked bodies having elements other than carbon as cross-linking points in terms of oxidation resistance and cross-linking densityForI can. Among these, a three-dimensional crosslinked body having silicon, titanium, zirconium, aluminum, boron, phosphorus, iron, or the like as crosslinking points is more preferable.
[0052]
In the polymer solid electrolyte of the present invention, when the polymer having an anionic group and the three-dimensional crosslinked polymer are uniformly mixed, a method for producing a three-dimensional crosslinked product having an element other than carbon as a crosslinking point In the above, it is also a preferred embodiment to produce a crosslinked body using an alkoxide compound comprising an element other than carbon. The alkoxide compound is preferably hydrolyzable. Further, when a solution containing the hydrolyzable compound and / or a hydrolyzate thereof and a polymer having an anionic group is used, a polymer having an anionic group and a tertiary compound are used. A structure in which the original crosslinked polymer is uniformly mixed and formed is preferable. In particular, it is also a preferable production method to produce a structure in which a polymer having an anionic group and a three-dimensional crosslinked polymer are uniformly mixed using a condensation reaction of an alkoxide compound. Further, when the fine particles to be mixed have a surface functional group, the cross-linked product and the fine particles are integrated with a chemical bond by the condensation reaction of the alkoxide compound, and the effect of reducing MCO and improving proton conductivity is increased. It will be a thing.
[0053]
In the present invention, it is also possible to fill a solid polymer electrolyte into a porous film, and the solid polymer electrolyte obtained in this manner is preferable because deformation due to swelling is suppressed. The porous film is not particularly limited, such as a three-dimensional network micropore opened in a random direction and a through-hole opened in a film thickness direction.
[0054]
Moreover, when a porous film has a through-hole in a film thickness direction, it is still more preferable that it has a through-hole arranged in order in the plane direction. Here, the “through holes arranged in an orderly manner in the plane direction” indicates a state in which the through holes are arranged at regular intervals or regularly. Specifically, it is an arrangement state in which the difference between the center intervals is within a range of 100% when the center intervals of the adjacent through holes are compared. That is, since the through-holes are two-dimensionally arranged on the surface of the porous film, adjacent through-holes exist vertically and horizontally, but the difference in the center interval between the adjacent through-holes is within 100%. It is necessary to enter and arrange. Preferably it is within 50%, more preferably within 30%. In addition, even when the difference in the center interval between adjacent through holes exceeds 100%, the center interval between adjacent through holes in each array is a regular array in which a certain number of combinations are repeated. If the error is within 100%, it is preferably used.
[0055]
The shape of FIG. 1 is mentioned as a specific example of the porous film used for this invention. FIG. 1 is a schematic perspective view showing an example of a solid polymer electrolyte of the present invention. The porous film of FIG. 1 has a porous part 1 having a large number of holes in the center, and a non-porous part 2 having no holes around the porous part. FIG. 2 shows an enlarged schematic view of the porous portion. In the solid polymer electrolyte of the present invention, it is preferable that the pores 3 of the porous portion are regularly arranged at regular intervals with the arrangement pitch viewed in the plane direction as shown in FIG. L in FIG. 2 is the “center distance between adjacent through holes” described above. L is preferably in the range of 0.5 to 100 μm, particularly preferably in the range of 1 to 50 μm. Moreover, as the internal diameter d of a hole, the range of 0.5-50 micrometers is preferable, and the range of 1-30 micrometers is especially preferable.
[0056]
In FIG. 1, a porous conductor 1 is filled with a proton conductor to exhibit a function as a polymer solid electrolyte. In addition, filling the holes 3 in FIG. 2 with the proton conductor suppresses the swelling and reduces the crossover in which the fuel methanol permeates from the anode to the cathode. However, the holes 3 are arranged in an orderly manner. In this case, the crossover reduction effect is further improved.
[0057]
As a preferred method for producing a porous film used for the polymer solid electrolyte of the present invention, for example, a photolithography processing method can be applied. Conventionally, filter materials for filtration having through holes have been used as porous films. This is usually a film formed by irradiating a polymer film with ions to break the polymer chain, and using an alkaline solution or the like to make a hole by a chemical etching method (track etching method). On the other hand, the hole 3 using the photolithographic method can arbitrarily set the hole diameter, shape, hole interval, porous portion, etc., and improve the performance of the fuel cell by reducing the crossover. Can do. Furthermore, since photolithography is excellent in microfabrication, it is possible to finely divide the porous portion 1 and the non-porous portion 2, resulting in excellent results in downsizing of the fuel cell. Further, it is possible to achieve cost reduction by improving productivity as compared with the conventional track etching method.
[0058]
Here, the scanning electron microscope (SEM) photograph of the porous film produced using the photolithography method is shown in FIG. 3, and the scanning electron microscope (SEM) photograph of the porous film produced by the conventional track etch method. Is shown in FIG. It is clear that the holes of the porous film of the photolithography method of FIG. 3 are regularly arranged at equal intervals as compared with the track etching method of FIG.
[0059]
The cross-sectional shape of the holes in the porous film produced by the photolithography method is not particularly limited, but a circle, an ellipse, a square, a rectangle, a rhombus, a trapezoid, and the like are preferable. Among these, a circle or an ellipse is preferable from the viewpoint of easy filling of the proton conductor and suppression of swelling. The size and interval of the holes are not particularly limited, and may be appropriately determined based on ease of filling with the proton conductor, battery performance, and the like.
[0060]
What is necessary is just to determine the magnitude | size of the whole porous part in the porous film manufactured using a photolithographic method according to the magnitude | size of the electrode catalyst layer and electrode base material to be used. The thickness of the porous film may be determined based on the required battery performance, but is usually preferably in the range of 1 to 50 μm and particularly preferably in the range of 5 to 20 μm.
[0061]
Although the detailed method of the photolithography method used in the present invention is not particularly limited, for example, a photosensitive polymer is coated on a substrate, exposed with a photomask, and after development, the polymer is dissolved to form holes. And forming a porous polymer film by peeling from the substrate. The photosensitive polymer may be either a negative type or a positive type, but can be appropriately selected according to the required hole size, hole interval, fuel cell performance, and the like. The substrate material is determined in terms of adhesion to the polymer and ease of peeling, and a silicon wafer or an aluminum plate is preferably used, but is not particularly limited. The exposure may be either reduced exposure or equal magnification exposure, but may be determined as appropriate depending on the size of the electrolyte to be produced, the size, shape, interval, etc. of the holes. Further, the conditions such as development, dissolution, and peeling from the substrate may be appropriately selected depending on the properties of the polymer. It is also possible to apply a non-photosensitive polymer on the substrate in advance, and apply a photoresist on the substrate, expose, develop, and create voids by dissolving the polymer.
[0062]
The photosensitive or non-photosensitive polymer used in the photolithography method used in the present invention is not particularly limited, but polyimide is preferably used from the viewpoint of workability by photolithography, oxidation resistance of the polymer, strength, and the like. .
[0063]
As a specific method for producing a porous film by photolithography using polyimide, for example, a precursor polyamic acid solution was applied to a substrate, and the solvent was dried and removed at about 100 ° C., and then a photomask was used. Examples include a method of forming a hole by performing photolithography processing by exposure, development, alkali treatment, etc., then performing an imide ring-closing reaction at about 300 ° C. or higher, and finally peeling off from the substrate to obtain a porous polyimide film. The temperature and time of solvent removal and imide ring closure reaction can be determined appropriately depending on the type of polyimide used. When the polyimide film is peeled off from the substrate, it is usually immersed in an acid. However, hydrofluoric acid is preferably used for a silicon wafer and hydrochloric acid is preferably used for an aluminum plate.
[0064]
Here, the polyimide used in the present invention may be either a negative or positive photosensitive polyimide or non-photosensitive polyimide. However, the polyimide is sensitive to the size, shape, spacing, film thickness, etc. of the holes. Is preferred, and negative photosensitive polyimide is more preferred.
[0065]
In addition to the porous film produced by the photolithography method described above, a porous film having a three-dimensional network structure is also preferable. The “three-dimensional network structure” means a state having a three-dimensional network structure in which the polymers constituting the porous film are three-dimensionally connected. Here, a scanning electron microscope (SEM) photograph of a porous film having a three-dimensional network structure preferably used in the present invention is shown in FIG.
[0066]
When the porous film has a three-dimensional network structure, the pore diameter is preferably in the range of 0.05 to 5 μm, and more preferably in the range of 0.1 to 1 μm. The pore diameter can be determined from an average of 20 or more, preferably 100 or more, from a photograph of the surface taken with a scanning electron microscope (SEM) or the like, and is usually measured with 100. For example, a porous film of a three-dimensional network produced by a wet coagulation method has a wide pore size distribution, and therefore it is preferable to take as many as possible, for example, an average of 100 to 500 pore sizes.
[0067]
The porosity of the three-dimensional network structure is preferably in the range of 10 to 95%. More preferably, it is 50 to 90% of range. Here, the porosity is a percentage (%) obtained by dividing the total volume of the porous film by the volume occupied by the polymer by the total volume of the porous film.
[0068]
As a method for producing a porous film having the above three-dimensional network structure, a wet coagulation method is preferably used. Specifically, by immersing a polymer solution obtained by dissolving a polymer in a dissolving solvent containing a good solvent in a coagulating solvent containing a poor solvent, a coagulated polymer having a microporous structure of a three-dimensional network structure can be obtained. When making the porous film into a film shape, it is possible to obtain a porous film having fine porosity by applying a polymer solution on the substrate and immersing in a coagulation solvent before the solvent is removed by drying. it can. Here, the dissolving solvent and the coagulating solvent can be appropriately selected depending on the polymer used, and can be appropriately selected according to the desired pore size, shape, and fuel cell performance. It is necessary to dissolve.
[0069]
Even when a porous film produced by a wet coagulation method is used for a polymer solid electrolyte, a shape in which the center is a porous portion and the periphery is a dense polymer film as shown in FIG. 1 is a preferred embodiment. In order to obtain such a shape, for example, the following method is preferably used, but is not limited thereto.
[0070]
As the first method, there is a method in which a dense film having only a peripheral portion is prepared in advance and then a central porous portion is prepared. A dense film is produced by applying a polymer solution onto a substrate and usually drying it. The porous central portion may be cut off later, or the center may be uncoated by performing masking during coating. Thereafter, the polymer solution is applied only in the center and immersed in a poor solvent to perform wet coagulation.
[0071]
As a second method, a film having a whole made porous by a wet coagulation method is produced, and the holes in the peripheral portion are closed. For closing the hole, a method of crushing with a press or a method of filling the hole with an aprotic conductive polymer can be used, but the method is not limited thereto.
[0072]
Although it does not specifically limit as a polymer used for the porous film used for this invention, Preferably, a polyimide (PI), a polyvinylidene fluoride (PVDF), a polyphenylene sulfide sulfone (PPSS), a polytetrafluoroethylene (PTFE), Polysulfone (PSF) or the like, copolymers thereof, copolymers with other monomers (such as hexafluoropropylene-vinylidene fluoride copolymer), and blends can also be used. These polymers are preferable from the viewpoint of oxidation resistance, strength, ease of wet coagulation, and the like.
[0073]
When the wet coagulation method is used, a polar solvent having a high dielectric constant is used as a solvent for dissolving these polymers, and alcohol, ether, ester, water, or the like is used as the coagulation solvent. Of these, N-methyl-2-pyrrolidone (NMP), dimethylformamide (DMF), and dimethylacetamide (DMAC) are preferable as the dissolving solvent, and methanol, ethanol, isopropanol, water, and the like are preferable as the coagulation solvent. A pore opening agent may be added to control the pore diameter. As the pore-opening agent, fine particles, salts, surfactants and the like are used.
[0074]
Regardless of the photolithography method or wet coagulation method described above, the porous film used in the present invention may have different shapes and sizes of holes on the front surface and the back surface, and can be easily filled with a proton conductor. From a point of view, it is also a preferred embodiment that the sizes of the holes on the front surface and the back surface are different. This is expected to facilitate filling of the proton conductor. As the degree, the ratio of the front and back hole diameters d is preferably in the range of 5: 1 to 1: 1. Furthermore, holes having different sizes and shapes may be mixed in the same plane.
[0075]
The method for filling the porous film with the proton conductor is not particularly limited. For example, the space can be filled by applying or dipping the polymer having an anionic group as a solution to the porous film. In order to facilitate filling into the voids, it is also preferable to use ultrasonic waves or to reduce the pressure. When these are used together during coating or dipping, the filling efficiency is further improved, which is preferable. Alternatively, a method may be employed in which a monomer, which is a precursor of a polymer having an anionic group, is filled in the void and then polymerized in the void, or the monomer is vaporized and plasma polymerization is performed.
[0076]
In the present invention, the form of the fuel cell and the method for producing the fuel cell are not particularly limited. Hereinafter, a method using a photolithography method for producing a fuel cell having a side-by-side structure will be described in detail. Here, the side-by-side structure refers to a structure in which two or more cells composed of a pair of opposed electrodes are arranged in the plane direction of a single polymer solid electrolyte surface. According to this structure, since the cells are connected in series by connecting anodes and cathodes of two or more adjacent cells arranged with an electronic conductor penetrating the polymer solid electrolyte, a side-by-side structure is used. The cross section of the polymer solid electrolyte has a structure in which proton conducting portions and electron conducting portions exist alternately. In order to produce such a structure, it is preferable to use a photolithography method from the viewpoint of miniaturization and productivity.
[0077]
An example of the Side-by-side structure is shown in FIGS. FIG. 6 is a schematic perspective view of a polymer solid electrolyte of the present invention having a side-by-side structure, and FIG. 7 is a schematic cross-sectional view showing a part of the manufacturing process. 6 and 7 exemplify the arrangement of two cells horizontally, but it is also possible to arrange a plurality of three or more cells in the planar direction with a similar side-by-side structure. . The following description will be made with two cells for convenience. In FIG. 6, the proton conducting part is filled with a proton conductor (not shown) in the porous part 1, and the electron conducting part is filled with an electron conductor in the membrane conductive part 4. The portions other than the porous portion 1 of the proton conducting portion and the membrane conducting portion 4 of the electron conducting portion are non-porous portions 2 through which protons and electrons do not conduct, and are dense polymer films. The photolithographic method described in the present invention is preferably used for producing a polymer film having such a complicated and fine structure. A porous film shown in FIG. 6 is produced by photolithography, and this is made into a polymer solid electrolyte by the method illustrated in FIG. In FIG. 7, the transmembrane electron conducting portion is filled with the electron conductor in advance, and then the proton conducting portion is filled with the proton conductor, but this order may be reversed. Alternatively, a proton conductor may be filled to produce a proton conducting part, an electrode may be provided next, and finally an electron conducting part may be produced.
[0078]
The above-described side-by-side electron conducting portion has a structure that penetrates the electrolyte membrane. Here, a portion penetrating the electrolyte membrane as the electron conductive portion is referred to as a membrane conductive portion. This membrane conductive part has a function different from that of the porous part for filling the proton conductor. There are no particular limitations on the size, shape, and the like of the conductive film portion. The larger the membrane conductive portion, the lower the electrical resistance of the cell and the cell, and an improvement in voltage in series can be expected. However, the larger the membrane conductive part, the more likely the organic solvent such as hydrogen or methanol on the anode side to leak to the cathode side, or the possibility that air on the cathode side leaks to the anode side, leading to performance degradation. is there. For this reason, it is preferable to determine the size and shape of the film conductive portion in consideration of the electric resistance and leakage resistance of the electron conductor used in the electron conductive portion. Note that the electron conducting portion may not pass through the polymer solid electrolyte but may pass through the outside.
[0079]
Although it does not specifically limit as an electronic conductor of the said film | membrane conductive part 4, A conductive paste is used preferably. As the conductive paste, one in which a conductive agent such as carbon, silver, nickel, copper, platinum, or palladium is dispersed in a polymer can be preferably used, and both reduction in electronic resistance and improvement in leakage resistance can be achieved. Especially in DMFC, it is important to prevent methanol leakage. In addition to general-purpose conductive paste in which carbon or silver is dispersed in silicone resin, polyester, epoxy resin, etc., carbon black, silver, platinum, etc. are dispersed in PVDF or polyimide. The conductive paste is also preferably used. The electron conducting portion 5 is electrically connected to the electrode base material or electrode catalyst layer of the cell, and a conductive paste is preferably used for reducing the contact resistance.
[0080]
Further, a metal foil or a metal wire such as nickel, stainless steel, aluminum, or copper may be used as the electron conducting portion 5. It is also possible to combine these metal foils and metal wires with a conductive paste.
[0081]
The polymer solid electrolyte of the present invention is used in a polymer electrolyte fuel cell as a membrane-electrode assembly (MEA) in combination with an electrode 7 composed of an electrode substrate and an electrode catalyst layer.
[0082]
The electrode catalyst layer in the electrode 7 in the polymer electrolyte fuel cell of the present invention is not particularly limited, and a known one can be used. The electrode catalyst layer refers to a layer containing a catalyst necessary for electrode reaction and an electrode active material (referred to as a substance that oxidizes or reduces), and further includes a substance that contributes to electron conduction and ion conduction that promote the electrode reaction. In addition, when the electrode active material is a liquid or a gas, it is necessary to have a structure in which the liquid or gas can easily permeate, and a structure that facilitates the discharge of a generated material accompanying the electrode reaction is required.
[0083]
In the polymer electrolyte fuel cell of the present invention, the electrode active material is preferably an organic solvent such as hydrogen or methanol or oxygen, and the catalyst is preferably a noble metal particle such as platinum. Moreover, it is preferable that the material which improves the electroconductivity of an electrode catalyst layer is included, and although a form is not specifically limited, For example, it is preferable to have electroconductive particle. Examples of the conductive particles include carbon black, and platinum-supported carbon is particularly preferably used as the carbon black supporting the catalyst. The electrode catalyst layer is required to have a structure in which the catalyst, the electron conductor (for example, carbon black), and the ionic conductor (for example, proton exchange resin) come into contact with each other and the electrode active material and the reaction product efficiently enter and exit. In addition, a polymer compound is effective for improving ion conductivity, improving the binding property of a material, or increasing water repellency. Therefore, it is preferable that the electrode catalyst layer contains at least catalyst particles, conductive particles, and a polymer compound.
[0084]
In the polymer electrolyte fuel cell of the present invention, a known catalyst can be used as the catalyst contained in the electrode catalyst layer, and is not particularly limited, but platinum, palladium, ruthenium, iridium, gold, etc. A noble metal catalyst is preferably used. Two or more elements such as alloys and mixtures of these noble metal catalysts may be contained.
[0085]
The electron conductor (conductive material) contained in the electrode catalyst layer is not particularly limited, but an inorganic conductive material is preferably used from the viewpoint of electron conductivity and touch resistance. Among these, carbon black, graphite or carbonaceous carbon material, metal or metalloid can be mentioned. Here, as the carbon material, carbon black such as channel black, thermal black, furnace black, and acetylene black is preferably used in view of electron conductivity and specific surface area. Furnace Black includes Cabot Vulcan XC-72, Vulcan P, Black Pearls 880, Black Pearls 1100, Black Pearls 1300, Black Pearls 2000, Legal 400, Ketjen Black International Ketjen Black EC, Mitsubishi Chemical Examples of the acetylene black include Denka Black manufactured by Denki Kagaku Kogyo Co., Ltd. In addition to carbon black, artificial graphite or carbon obtained from organic compounds such as natural graphite, pitch, coke, polyacrylonitrile, phenol resin, and furan resin can also be used. The form of these carbon materials is not particularly limited, and fibrous and fibrous forms can also be used. It is also possible to use carbon materials obtained by post-processing these carbon materials. Among these carbon materials, in particular, Vulcan XC-72 manufactured by Cabot is preferably used from the viewpoint of electron conductivity.
[0086]
The amount of these electron conductors to be added should be appropriately determined according to required electrode characteristics, specific surface area of the substance used, electronic resistance, etc., but is 1 to 80% as a weight ratio in the electrode catalyst layer. Is preferable, and the range of 20 to 60% is more preferable. When the amount of the electron conductor is small, the electron resistance is high, and when the amount is large, the gas performance is hindered or the catalyst utilization rate is lowered.
[0087]
It is preferable in terms of electrode performance that the electron conductor is uniformly dispersed with the catalyst particles. For this reason, it is preferable that the catalyst particles and the electron conductor are well dispersed in advance as a coating liquid.
[0088]
It is also a preferred embodiment to use a catalyst-supporting carbon in which a catalyst and an electron conductor are integrated as an electrode catalyst layer. By using this catalyst-supported carbon, the utilization efficiency of the catalyst can be improved, and the cost can be reduced. Here, even when catalyst-supported carbon is used for the electrode catalyst layer, a conductive agent can be further added. As such a conductive agent, the above-described carbon black is preferably used.
[0089]
A well-known thing can be used as an ion conductor used for an electrode catalyst layer. As an ionic conductor, various organic and inorganic materials are generally known, but when used in a fuel cell, ions such as sulfonic acid groups, carboxylic acid groups, and phosphoric acid groups that improve proton conductivity are used. A polymer having an exchange group is preferably used. Among these, a polymer having a proton exchange group composed of a fluoroalkyl ether side chain and a fluoroalkyl main chain is preferably used. For example, Na Pontion manufactured by DuPont, Aciplex manufactured by Asahi Kasei Co., Ltd., Flemion manufactured by Asahi Glass Co., etc. are preferably used. These ion exchange polymers are provided in the electrode catalyst layer in the form of a solution or a dispersion. In this case, the solvent for dissolving or dispersing the polymer is not particularly limited, but a polar solvent is preferable from the viewpoint of the solubility of the ion exchange polymer.
[0090]
It is preferable from the viewpoint of electrode performance that the ionic conductor is added in advance to a coating liquid mainly composed of electrode catalyst particles and an electron conductor when the electrode catalyst layer is produced, and is applied in a uniformly dispersed state. However, the ionic conductor may be applied after the electrode catalyst layer is applied. Here, examples of the method of applying the ionic conductor to the electrode catalyst layer include spray coating, brush coating, dip coating, die coating, curtain coating, and flow coating, and are not particularly limited.
[0091]
The amount of the ionic conductor contained in the electrode catalyst layer should be appropriately determined according to the required electrode characteristics and the conductivity of the ionic conductor used, and is not particularly limited. The range of 1 to 80% is preferable, and the range of 5 to 50% is more preferable. When the ion conductor is too small, the ion conductivity is low, and when it is too much, the gas permeability may be hindered.
[0092]
The electrode catalyst layer may contain various substances in addition to the catalyst, the electronic conductor, and the ionic conductor. In particular, in order to enhance the binding property of the substance contained in the electrode catalyst layer, it is preferable to include a polymer other than the above-described proton exchange resin. Such a polymer includes a polymer containing a fluorine atom, and is not particularly limited. For example, polyvinyl fluoride (PVF), polyvinylidene fluoride (PVDF), polyhexafluoropropylene (FEP), poly Tetrafluoroethylene, polyperfluoroalkyl vinyl ether (PFA), etc., or their copolymers, copolymers of monomer units constituting these polymers with other monomers such as ethylene and styrene, and blends, etc. Can be used. The content of these polymers in the electrode catalyst layer is preferably in the range of 5 to 40% by weight. When there is too much polymer content, there exists a tendency for an electronic and ionic resistance to increase and for electrode performance to fall.
[0093]
In the electrocatalyst layer, it is also a preferable embodiment that the catalyst-polymer composite has a three-dimensional network structure. The catalyst-polymer composite is a polymer composite containing catalyst particles, and this composite has a three-dimensional network structure. That is, the catalyst-polymer complex has a three-dimensional network structure that is three-dimensionally connected.
[0094]
When the electrode catalyst layer has a three-dimensional network structure, the pore diameter is preferably in the range of 0.05 to 5 μm, more preferably in the range of 0.1 to 1 μm. The pore diameter can be determined from an average of 20 or more, preferably 100 or more, from a photograph of the surface taken with a scanning electron microscope (SEM) or the like, and is usually measured with 100. The electrode catalyst layer having a porous structure manufactured by the wet coagulation method has as many pore sizes as possible because of a wide pore size distribution, and preferably averages 100 to 500 pore sizes.
[0095]
The porosity of the three-dimensional network structure of the electrode catalyst layer is preferably in the range of 10 to 95%. More preferably, it is 50 to 90% of range. Here, the porosity is a percentage (%) obtained by dividing the total volume of the electrode catalyst layer from the volume occupied by the catalyst-polymer complex by the total volume of the electrode catalyst layer.
[0096]
In order to produce an electrode catalyst layer having a three-dimensional network structure, wet coagulation is usually performed after the catalyst layer is applied to an electrode substrate, a proton exchange membrane, and other substrates. When it is difficult to determine the porosity of the electrode catalyst layer alone, the porosity of the electrode substrate, the proton exchange membrane, and other substrates is determined in advance, and the substrate and the electrode catalyst layer are included. It is also possible to determine the porosity of the electrode catalyst layer alone after determining the porosity.
[0097]
The electrocatalyst layer having a three-dimensional network structure has a large porosity and good gas diffusibility and discharge of generated water, and also has good electron conductivity and proton conductivity. In the conventional porosification, the catalyst particle size and the particle size of the added polymer are increased, or voids are formed using a pore-forming agent. The contact resistance between the proton exchange resins is larger than that of the electrode catalyst layer. On the other hand, in the three-dimensional network structure by the wet coagulation method, the polymer composite containing the catalyst-supporting carbon has a three-dimensional network shape. Due to the quality structure, the gas diffusibility and the discharge of the generated water are also favorable, which is preferable.
[0098]
Even in the case where the electrode catalyst layer has a three-dimensional network structure, the same materials as those used in the past can be used for the catalyst, the electron conductor, and the ion conductor. However, since it is preferable to use a wet coagulation method when producing an electrode catalyst layer having a three-dimensional network structure, selection of a polymer suitable for this wet coagulation method is preferable, catalyst particles are well dispersed, and fuel is used. Polymers that do not deteriorate in the oxidation-reduction atmosphere in the battery are preferred. Such a polymer includes a polymer containing a fluorine atom, and is not particularly limited. For example, polyvinyl fluoride (PVF), polyvinylidene fluoride (PVDF), polyhexafluoropropylene (FEP), poly Perfluoroalkyl vinyl ether (PFA) or the like, copolymers thereof, copolymers of monomer units constituting these polymers and other monomers such as ethylene and styrene (for example, hexafluoropropylene-vinylidene fluoride copolymer) For example, blends and the like can also be preferably used.
[0099]
Among these, polyvinylidene fluoride (PVDF) and hexafluoropropylene-vinylidene fluoride copolymer are three-dimensionally obtained by a wet coagulation method using an aprotic polar solvent as a dissolving solvent and a protic polar solvent as a coagulating solvent. This is a particularly preferred polymer in that a catalyst-polymer complex having a network structure can be obtained.
[0100]
Specific examples of the polymer solvent include N-methylpyrrolidone (NMP), dimethylformamide (DMF), dimethylacetamide (DMAC), propylene carbonate (PC), dimethylimidazolidinone (DMI), and the like. Examples of the solvent include water, lower alcohols such as methanol, ethanol, and isopropanol, esters such as ethyl acetate and butyl acetate, and various organic solvents such as aromatic and halogen compounds.
[0101]
As the polymer of the catalyst-polymer complex, in addition to the above-mentioned polymer, a polymer having a proton exchange group for improving proton conductivity is also preferable. Proton exchange groups contained in such polymers include sulfonic acid groups, carboxylic acid groups, and phosphoric acid groups, but are not particularly limited. A polymer containing such a proton exchange group in the skeleton is also used without particular limitation. For example, a polymer having a proton exchange group composed of a fluoroalkyl ether side chain and a fluoroalkyl main chain is preferably used. Specifically, it is NaPotion made by DuPont. Moreover, the above-mentioned fluorine atom-containing polymer having a proton exchange group, other polymers such as ethylene and styrene, copolymers and blends thereof may be used.
[0102]
When Nafion is used, a commercially available Nafion membrane may be dissolved in an aprotic polar solvent, or commercially available from Aldrich, DuPont, or IonPower, water-methanol-isopropanol, water-ethanol- It is also possible to use a Nafion solution of a lower alcohol-containing mixed solvent such as isopropanol or water-ethanol-npropanol. Moreover, you may use what concentrated these Nafion solutions or substituted solvent. In this case, the coagulation solvent in the wet coagulation should be appropriately determined according to the solvent type of the Nafion solution. However, when the solvent of the Nafion solution is an aprotic polar solvent, the coagulation solvent is water or alcohol. In addition to esters and esters, various organic solvents are preferable. In the case of a lower alcohol solvent such as a water-methanol-isopropanol mixed solvent, esters such as butyl acetate and various organic solvents are preferably used.
[0103]
As the polymer used in the catalyst-polymer composite, it is also preferable to use a polymer containing the above-mentioned fluorine atom or a polymer containing a proton exchange membrane by copolymerization or blending. In particular, blending a polyvinylidene fluoride, a poly (hexafluoropropylene-vinylidene fluoride) copolymer, and a polymer such as Nafion having a fluoroalkyl ether side chain and a fluoroalkyl main chain in the proton exchange group can improve the electrode performance. From the point of view, it is preferable.
[0104]
The main components of the catalyst-polymer composite are catalyst-supported carbon and polymer, and the ratio thereof should be appropriately determined according to the required electrode characteristics and is not particularly limited. The weight ratio of 5/95 to 95/5 is preferably used. In particular, when used as an electrode catalyst layer for a polymer electrolyte fuel cell, the catalyst-supporting carbon / polymer weight ratio is preferably 40/60 to 85/15.
[0105]
Various additives can also be added to the catalyst-polymer composite. For example, there are conductive agents such as carbon for improving electronic conductivity, polymers for improving binding properties, additives for controlling the pore size of the three-dimensional network structure, etc. it can. The addition amount of these additives is preferably in the range of 0.1 to 50%, more preferably in the range of 1 to 20% as a weight ratio with respect to the catalyst-polymer composite.
[0106]
As a method for producing a catalyst-polymer composite having a three-dimensional network structure, a wet coagulation method is preferred. Here, after applying the catalyst-polymer solution composition, the coating layer is brought into contact with a coagulation solvent for the polymer, so that coagulation precipitation and solvent extraction of the catalyst-polymer solution composition can be performed simultaneously. In this catalyst-polymer solution composition, the catalyst-supporting carbon is uniformly dispersed in the polymer solution. As the catalyst-supporting carbon and polymer, those described above are preferably used. The solvent for dissolving the polymer should be appropriately determined according to the polymer used, and is not particularly limited. It is important that the polymer-supported carbon is well dispersed in the polymer solution. If the dispersion state is poor, the catalyst-carrying carbon and the polymer cannot form a composite during wet coagulation, which is not preferable.
[0107]
About the coating method of a catalyst-polymer solution composition, the coating method according to the viscosity, solid content, etc. of a catalyst-polymer solution composition is selected, although it does not specifically limit, a knife coater, a bar coater, a spray, A general coating method such as a dip coater, a spin coater, a roll coater, a die coater, or a curtain coater is used.
[0108]
The coagulation solvent for wet coagulation of the polymer is not particularly limited, but a solvent that is easy to coagulate and precipitate the polymer to be used and is compatible with the solvent of the polymer solution is preferable. The method for contacting the base material with the coagulation solvent is not particularly limited, but the whole base material is immersed in the coagulation solvent, only the coating layer is brought into contact with the liquid surface of the coagulation solvent, and the coagulation solvent is showered on the coating layer. Methods such as ringing or spraying can be used.
[0109]
As for the substrate on which the catalyst-polymer solution composition is applied, wet coagulation can be performed after the application on either the electrode substrate or the polymer solid electrolyte. In addition, the electrode catalyst layer is applied to a substrate other than the electrode substrate and the polymer electrolyte (for example, a transfer substrate), and then wet coagulated to form a three-dimensional network structure. It may be transferred or sandwiched between solid electrolytes. As the transfer substrate in this case, a polytetrafluoroethylene (PTFE) sheet, or a glass plate or a metal plate whose surface is treated with a fluorine or silicone release agent is also used.
[0110]
In the polymer electrolyte fuel cell of the present invention, a known electrode substrate can be used without any particular limitation. Moreover, an electrode base material may not be used for space saving.
[0111]
The electrode substrate used in the present invention is not particularly limited as long as it has a low electrical resistance and can collect (supply) electricity. Examples of the constituent material of the electrode base material include those mainly composed of a conductive inorganic substance. Examples of the conductive inorganic substance include a fired body from polyacrylonitrile, a fired body from pitch, graphite, and expanded graphite. Examples thereof include carbon materials, stainless steel, molybdenum, and titanium.
[0112]
The form of the conductive inorganic substance of the electrode substrate is not particularly limited, and for example, it is used in the form of fibers or particles. From the viewpoint of gas permeability, fibrous conductive inorganic substances (inorganic conductive fibers), particularly carbon fibers are used. preferable. As an electrode substrate using inorganic conductive fibers, either a woven fabric or non-woven fabric structure can be used. For example, carbon paper TGP series, SO series manufactured by Toray Industries, Inc., carbon cloth manufactured by E-TEK, etc. are used. As the woven fabric, a plain weave, a twill weave, a satin weave, a crest weave, a binding weave and the like are used without particular limitation. Moreover, as a nonwoven fabric, it does not specifically limit, such as a paper making method, a needle punch method, a spun bond method, a water jet punch method, and a melt blow method. It may be a knitted fabric. In these fabrics, especially when carbon fibers are used, a plain fabric using flame-resistant spun yarn is carbonized or graphitized woven fabric, and the flame-resistant yarn is carbonized after being processed into a nonwoven fabric by the needle punch method or water jet punch method. Alternatively, a graphitized nonwoven fabric, a flameproof yarn, a carbonized yarn, or a mat nonwoven fabric by a paper making method using a graphitized yarn is preferably used. In particular, it is preferable to use a non-woven fabric because a thin and strong fabric can be obtained.
[0113]
When inorganic conductive fibers made of carbon fibers are used for the electrode substrate, examples of the carbon fibers include polyacrylonitrile (PAN) -based carbon fibers, phenol-based carbon fibers, pitch-based carbon fibers, and rayon-based carbon fibers. . Of these, PAN-based carbon fibers are preferable. This is because PAN-based carbon fibers generally have higher compressive strength and tensile elongation at break than pitch-based carbon fibers, and are not easily broken. In order to obtain a carbon fiber that is not easily broken, the carbonization temperature of the carbon fiber is preferably 2,500 ° C. or less, and more preferably 2,000 ° C. or less.
[0114]
Water repellent treatment performed to prevent gas diffusion / permeability deterioration due to water retention on the electrode substrate used in the polymer electrolyte fuel cell of the present invention, partial water repellent for forming a water discharge path, It is also a preferred embodiment to perform hydrophilic treatment, addition of carbon powder or the like performed to reduce resistance.
[0115]
When the polymer electrolyte fuel cell of the present invention has a side-by-side structure, in order to promote the inflow of fuel such as hydrogen or aqueous methanol solution or air, and the discharge of products such as water or carbon dioxide It is also a preferred embodiment to provide a diffusion layer. Such a diffusion layer also has the role of the above-mentioned electrode base material, but it is more preferable to use a non-conductive fabric as the diffusion layer. Here, as a constituent material of the non-conductive fabric, for example, any non-conductive fiber can be used without any particular limitation.
[0116]
Non-conductive fibers constituting the non-conductive fabric of the diffusion layer include, for example, polytetrafluoroethylene (PTFE), tetrafluoroethylene-hexafluoroethylene copolymer (FEP), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer Polymer (PFA), tetrafluoroethylene-ethylene copolymer (ETFE), polyvinylidene fluoride (PVDF), polyvinyl fluoride (PVF), polychlorotrifluoroethylene (CTFE), chlorinated polyethylene, flame-resistant polyacrylonitrile, poly Acrylonitrile, polyester, polyamide, polyethylene, polypropylene and the like can be used. Among these non-conductive fibers, fibers made of fluorine atom-containing polymers such as PTFE, FEP, PFA, ETFE, PVDF, PVF, and CTFE are preferable from the viewpoint of corrosion resistance during electrode reaction.
[0117]
As the non-conductive fabric of the diffusion layer, either a woven fabric or a non-woven fabric structure can be used. As the woven fabric, a plain weave, a twill weave, a satin weave, a crest weave, a binding weave and the like are used without particular limitation. Moreover, as a nonwoven fabric, it does not specifically limit, such as a paper-making method, a needle punch method, a spun bond method, a water jet punch method, a melt blow method, and the like. It may be a knitted fabric. Of these fabrics, plain fabrics, nonwoven fabrics by needle punching or water jet punching, mat nonwoven fabrics by papermaking, etc. are particularly preferably used. In particular, a nonwoven fabric is preferably used because a porous, thin and strong fabric can be obtained.
[0118]
The non-conductive fabric of the diffusion layer is also preferably subjected to water repellency treatment for preventing gas diffusion / permeability deterioration due to water retention, partial water repellency or hydrophilic treatment for forming a water discharge path, and the like. This is an embodiment. Furthermore, it is also a preferred embodiment to perform post-treatment such as heat treatment, stretching, and pressing. By these post-treatments, effects such as thinning, increasing the porosity, and increasing the strength can be expected.
[0119]
In the polymer electrolyte fuel cell of the present invention, it is preferable to provide a conductive intermediate layer containing at least an inorganic conductive substance and a hydrophobic polymer between the electrode substrate and the electrode catalyst layer. In particular, when the electrode base material is a carbon fiber woven fabric or a nonwoven fabric having a large porosity, by providing the conductive intermediate layer, it is possible to suppress performance degradation due to the electrode catalyst layer permeating into the electrode base material.
[0120]
When the polymer solid electrolyte of the present invention is used for, for example, a membrane-electrode assembly (MEA), it is preferable to use MEA after post-processing to a polymer solid electrolyte. For example, in order to further reduce the permeation of fuel methanol, it is also a preferred embodiment to coat a metal thin film with a polymer solid electrolyte. Examples of such a metal thin film include palladium, platinum, silver and the like.
[0121]
In the polymer solid electrolyte of the present invention, the production method for forming a membrane-electrode assembly (MEA) using the electrode catalyst layer or the electrode catalyst layer and the electrode substrate is not particularly limited. It is preferable to integrate by hot pressing, but the temperature and pressure may be appropriately selected depending on the thickness of the polymer solid electrolyte, the porosity, the electrode catalyst layer and the electrode substrate. Usually, the temperature is 40 ° C to 180 ° C, and the pressure is 10 kgf / cm²~ 80kgf / cm²Is preferred.
[0122]
The polymer solid electrolyte of the present invention can be applied to various electrochemical devices. For example, a fuel cell, a water electrolysis device, a chloroalkali electrolysis device, and the like can be mentioned. Further, among fuel cells, it is suitable for a polymer electrolyte fuel cell, and there are those using hydrogen as a fuel and those using an organic solvent such as methanol as a fuel. It is particularly preferably used for DMFCs using as fuel.
[0123]
Furthermore, the application of the polymer electrolyte fuel cell of the present invention is not particularly limited, but a power supply source for a mobile body is preferable. In particular, it is preferably used as a power supply source for mobile devices such as mobile devices such as mobile phones, personal computers and PDAs, household appliances such as vacuum cleaners, automobiles such as passenger cars, buses and trucks, ships, and railways.
[0124]
【Example】
EXAMPLES Hereinafter, although this invention is demonstrated using an Example, this invention is not limited to these. In addition, the measurement conditions of each physical property are as follows.
(1) Measurement of particle size and number average particle size
For 100 particles arbitrarily selected from a photograph taken with a scanning electron microscope (SEM), the particle size (equivalent circle average diameter) of each particle was measured and calculated as the number average.
[0125]
  referenceExample 1
(1) Hydrolysis of a three-dimensional crosslinkable compound having an element other than carbon as a crosslinking point
  A 0.01N hydrochloric acid aqueous solution was added to 5 g of tetrabutoxy titanium manufactured by Toray Dow Corning Silicone Co., Ltd. and stirred at room temperature for 30 minutes to obtain a colorless and transparent hydrolyzate.
(2) Preparation of polymer solid electrolyte
  To 10 g of a commercially available 20% Nafion solution (manufactured by DuPont), 0.22 g of the hydrolyzate prepared in (1) and silica sol having a number average particle diameter of 600 nm as inorganic fine particles were added, and this solution was added at 100 ° C. for 30 minutes. The polymer solid electrolyte was obtained by heating.
(3) Performance of polymer solid electrolyte
  The membrane obtained in (2) was evaluated for methanol permeation and ionic conductivity in the same manner as in Comparative Example 1. The membrane was set in a cell manufactured by Electrochem, 1 mol / l methanol aqueous solution was supplied at 0.2 ml / min on one side, and air was supplied at 50 ml / min on the other side. The amount of methanol permeated was determined by measuring the methanol concentration in the exhausted air. The ionic conductivity of the membrane was determined by measuring the resistance by bringing current and voltage terminals into contact with the membrane surface. The methanol permeation amount of this membrane is 1.0 μmol / cm.²/ Min, ion conductivity is 4.8 S / cm²Met.
[0126]
  Comparative Example 1
  referenceA solid polymer electrolyte was obtained in the same manner as in Example 1 except that silica sol of inorganic fine particles was not added. The methanol permeation rate of this membrane is 1.5 μmol / cm²/ Min, ion conductivity is 4.8 S / cm²The performance was worse than that of Example 1 in which inorganic fine particles were added.
[0127]
  Comparative Example 2
  referenceA solid polymer electrolyte was obtained in the same manner as in Example 1 except that a silica sol having a number average particle diameter of 2 μm was used instead of the silica sol having a number average particle diameter of 600 nm. The methanol permeation rate of this membrane is 1.8 μmol / cm.²/ Min, ionic conductivity is 4.4 S / cm²The performance was worse than that of Example 1 in which inorganic fine particles having a number average particle diameter of less than 1 μm were added.
[0134]
  Example1
(1) Hydrolysis of a three-dimensional crosslinkable compound having an element other than carbon as a crosslinking point
  A 0.01N hydrochloric acid aqueous solution was added to 5 g of γ-glycidoxypropyltrimethoxysilane manufactured by Toray Dow Corning Silicone Co., and stirred at room temperature for 30 minutes to obtain a hydrolyzate.
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The γ-glycidoxypropyltrimethoxysilane hydrolyzate was dissolved in N, N-dimethylacetamide (DMAc) to give a 15% by weight solution.
(2) Synthesis of sulfonated polyphenylene oxide
After dissolving polyphenylene oxide (YPX-100L) (100 g) manufactured by Mitsubishi Engineering Plastics in chloroform (1000 g) under a nitrogen atmosphere at room temperature, chlorosulfonic acid (34 mL) was slowly added dropwise with stirring. After completion of the dropwise addition, stirring was continued for 30 minutes at room temperature. The precipitated polymer was separated by filtration, pulverized with a mill, thoroughly washed with water, and then vacuum dried to obtain the desired sulfonated polyphenylene oxide. (Ion exchange equivalent: 3.0 meq)
The sulfonated polyphenylene oxide was dissolved in N, N-dimethylacetamide (DMAc) to give a 15% by weight solution.
(3) Synthesis of sulfonated styrene-divinylbenzene fine particles
Styrene (4.5 g) and divinylbenzene (0.5 g) were placed in a 300 mL four-necked flask equipped with a reflux condenser, a stirrer, and a nitrogen gas inlet tube. While introducing nitrogen gas into the flask and stirring, a non-ionic surfactant “Nonion HS-210” aqueous solution (93.5 g) and a potassium persulfate aqueous solution (2 g) manufactured by NOF Corporation were added dropwise. As the reaction progressed, styrene-divinylbenzene fine particles were produced. The styrene-divinylbenzene fine particles were subjected to solid-liquid separation by centrifugation, and then stirred in a 1,2-dichloroethane solution of chlorosulfonic acid. After completion of the reaction, washing was sufficiently performed using a dialysis tube to obtain a target sulfonated styrene-divinylbenzene. The number average particle diameter of the sulfonated styrene-divinylbenzene fine particles was measured and found to be 500 nm. When the sulfur concentration of the sulfonated styrene-divinylbenzene was analyzed by the STEM-EDX method, the sulfur concentration ratio between the inside and the surface of the fine particles, that is, the sulfonic acid group concentration ratio was not changed at 1: 1.
(4) Production of polymer solid electrolyte membrane
0.5 g of the γ-glycidoxypropyltrimethoxysilane hydrolyzate DMAc solution (1) and 4.5 g of the sulfonated polyphenylene oxide DMAc solution (2) and the sulfonated styrene-divinylbenzene fine particles (3) Were mixed. This liquid was cast on a glass plate and heated at 100 ° C. for 3 hours to prepare a polymer solid electrolyte membrane. The film thickness was 90 μm.
(5) Methanol permeation measurement method of polymer solid electrolyte membrane
A sample membrane was sandwiched between the H-type cells, pure water was put into one cell, and 1M methanol aqueous solution was put into the other cell. The cell capacity was 80 mL each. The area of the opening between the cells was 1.77 cm2. Both cells were stirred at 20 ° C. The amount of methanol eluted in pure water at the time of 1 hour, 2 hours and 3 hours was measured and quantified with a gas chromatography (GC-2010) manufactured by Shimadzu Corporation. The methanol permeation amount per unit time and unit area was determined from the slope of the graph.
(6) Method for measuring ionic conductivity of polymer solid electrolyte membrane
A Solartron electrochemical measurement system (Solartron 1287 Electrochemical Interface and Solartron 1255B Frequency Response Analyzer) was used. The sample was sandwiched between two circular electrodes (made of stainless steel) of φ2 mm and φ10 mm with a weight of 1 kg (effective electrode area 0.0314 cm 2). A 15% aqueous solution of poly (2-acrylamido-2-methylpropanesulfonic acid) was applied to the interface between the sample and the electrode. A constant potential impedance measurement was performed at 25 ° C., and the ionic conductivity in the film thickness direction was determined. The AC amplitude was 50 mV.
(7) Performance evaluation of polymer electrolyte membrane
The amount of methanol permeation and ionic conductivity of the membrane obtained in (4) were evaluated by the methods (5) and (6). The methanol permeation rate of this membrane is 6.3 μmol / cm.²Min, ion conductivity is 6.7 S / cm²Met.
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  Comparative Example 3
  Example1In Example 1, a polymer solid electrolyte was obtained in the same manner except that sulfonated styrene-divinylbenzene fine particles were not added. The methanol permeation amount of this membrane is 9.0 μmol / cm.²/ Min, ionic conductivity is 6.7 S / cm²Example of adding organic fine particles1The amount of methanol permeation was larger than that of the above, and the performance was poor.
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  Example2
  Example using γ-glycidoxypropylmethyldiethoxysilane hydrolyzate solution instead of γ-glycidoxypropyltrimethoxysilane hydrolyzate solution1In the same manner, a polymer solid electrolyte was produced. Examples of performance of this membrane1The methanol permeation amount was 7.6 μmol / cm²/ Min, ionic conductivity is 6.9 S / cm²Met. Compared with Comparative Example 2, the methanol permeation amount was small.
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  Example3
  Example of using bis (trimethoxysilyl) hexane hydrolyzate solution instead of γ-glycidoxypropyltrimethoxysilane hydrolyzate solution1In the same manner, a polymer solid electrolyte was produced. Examples of performance of this membrane1The methanol permeation amount was 6.0 μmol / cm²/ Min, ionic conductivity is 6.7 S / cm²Met. Compared with Comparative Example 2, the methanol permeation amount was small.
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  Example4
  A commercially available 20% Nafion solution (manufactured by DuPont) was used in place of the sulfonated polyphenylene oxide DMAc solution.1In the same manner, a polymer solid electrolyte was produced. Examples of performance of this membrane1The methanol permeation amount was 6.5 μmol / cm.²/ Min, ionic conductivity is 6.7 S / cm²Met.
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  Comparative Example 4
  Example4In Example, using only a commercially available 20% Nafion solution (manufactured by DuPont)1In the same manner, a polymer solid electrolyte was obtained. The methanol permeation rate of this membrane is 8.0 μmol / cm.²/ Min, ionic conductivity is 6.7 S / cm²Example of adding organic fine particles and hydrolyzate4The performance was worse than.
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  Example5
(1) Synthesis of sulfonated styrene-divinylbenzene fine particles
  Styrene (3.2 g) and divinylbenzene (1.8 g) were placed in a 300 mL four-necked flask equipped with a reflux condenser, a stirrer, and a nitrogen gas inlet tube. While introducing nitrogen gas into the flask and stirring, a nonionic surfactant “Nonion HS-210” aqueous solution (93.5 g) and a potassium persulfate aqueous solution (2 g) manufactured by NOF Corporation were added dropwise. As the reaction progressed, styrene-divinylbenzene fine particles were produced. The styrene-divinylbenzene fine particles were subjected to solid-liquid separation by centrifugation, and then heated and stirred in concentrated sulfuric acid. After completion of the reaction, purification with a large amount of methanol gave the desired sulfonated styrene-divinylbenzene. The number average particle size of the sulfonated styrene-divinylbenzene fine particles was measured and found to be 480 nm. When the sulfur concentration of the sulfonated styrene-divinylbenzene was analyzed by the STEM-EDX method, the sulfur concentration ratio between the inside and the surface of the fine particles, that is, the sulfonic acid group concentration ratio was 1: 5.
(2) Performance evaluation of solid polymer electrolyte membrane
  Example1In place of the sulfonated styrene-divinylbenzene fine particles of Example 1, the sulfonated styrene-divinylbenzene fine particles of (1) were used.1In the same manner, a polymer solid electrolyte was produced. Examples of performance of this membrane1As evaluated in the same manner, the methanol permeation amount was 5.0 μmol / cm.²/ Min, ionic conductivity is 9.0 S / cm²Compared with Comparative Example 2, the methanol permeation amount was small. Examples1The performance was better than.
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  Example6
  Example of using Nafion solution instead of sulfonated polyphenylene oxide DMAc solution5In the same manner, a polymer solid electrolyte was produced. Examples of performance of this membrane1The methanol permeation amount was 6.6 μmol / cm²/ Min, ionic conductivity is 6.7 S / cm²Met. Compared with Comparative Example 3, the methanol permeation amount was small.
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  Example7
(1) Synthesis of sulfonated phenylmaleimide-styrene-divinylbenzene fine particles
  Styrene (3.0 g), divinylbenzene (0.5 g) and phenylmaleimide (1.5 g) were placed in a 300 mL four-necked flask equipped with a reflux condenser, a stirrer, and a nitrogen gas inlet tube. While introducing nitrogen gas into the flask and stirring, a non-ionic surfactant “Nonion HS-210” aqueous solution (93.5 g) and a potassium persulfate aqueous solution (2 g) manufactured by NOF Corporation were added dropwise. As the reaction progressed, phenylmaleimide-styrene-divinylbenzene fine particles were formed. The phenylmaleimide-styrene-divinylbenzene fine particles were solid-liquid separated by centrifugation and then stirred in concentrated sulfuric acid. After completion of the reaction, purification with a large amount of methanol gave the desired sulfonated phenylmaleimide-styrene-divinylbenzene. The number average particle diameter of the sulfonated phenylmaleimide-styrene-divinylbenzene fine particles was measured and found to be 550 nm. When the sulfur concentration of the sulfonated phenylmaleimide-styrene-divinylbenzene was analyzed by the STEM-EDX method, the sulfur concentration ratio between the inside and the surface of the fine particles, that is, the sulfonic acid group concentration ratio was 1: 9.
(2) Performance evaluation of solid polymer electrolyte membrane
  Instead of the sulfonated styrene-divinylbenzene fine particles of Example 12, the sulfonated phenylmaleimide-styrene-divinylbenzene fine particles of (1) were used.1In the same manner, a polymer solid electrolyte was produced. Examples of performance of this membrane1As evaluated in the same manner, the methanol permeation amount was 5.0 μmol / cm.²/ Min, ionic conductivity is 8.0 S / cm²Met. Compared with Comparative Example 2, the methanol permeation amount was small.
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  Example8
  Example of using Nafion solution instead of sulfonated polyphenylene oxide DMAc solution1In the same manner, a polymer solid electrolyte was produced. Examples of performance of this membrane1The methanol permeation amount was 6.5 μmol / cm.²/ Min, ionic conductivity is 6.7 S / cm²Met. Compared with Comparative Example 2, the methanol permeation amount was small.
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【The invention's effect】
According to the present invention, it is possible to provide a novel polymer electrolyte that suppresses methanol crossover, has high ionic conductivity, and can achieve high output, a method for producing the same, and a high-performance solid polymer fuel cell using the same. , Its practicality is high.
[Brief description of the drawings]
FIG. 1 is a schematic perspective view of a solid polymer electrolyte of the present invention.
FIG. 2 is an enlarged schematic plan view of a porous portion 1 in a polymer solid electrolyte of the present invention.
FIG. 3 is a scanning electron micrograph of a porous substrate in which pores used in the solid polymer electrolyte of the present invention are arranged in an orderly manner.
FIG. 4 is a scanning electron micrograph of a porous substrate used in a conventional polymer solid electrolyte.
FIG. 5 is a scanning electron micrograph of a porous substrate having a three-dimensional network structure used in the polymer solid electrolyte of the present invention.
FIG. 6 is a schematic perspective view of a polymer solid electrolyte having a side-by-side structure of the present invention.
FIG. 7 is a schematic cross-sectional view showing a part of a manufacturing process of a side-by-side structure fuel cell using the solid polymer electrolyte of the present invention.
[Explanation of symbols]
1: Porous part
2: Non-porous part
3: Hole
4: Membrane conductive part
5: Transmembrane electron conduction part
6: Proton conduction part
7: Electrode
d: Hole diameter
L: Center distance between adjacent through holes

Claims (5)

Contains organic polymer fine particles that are uniformly mixed with a three-dimensional cross-linked polymer having an anionic group as a cross-linking point other than carbon and that do not dissolve or swell in methanol with a primary particle number average particle size of 1 μm or less A solid polymer electrolyte characterized by the above.   The polymer solid electrolyte according to claim 1, wherein the fine particles have a hydrophilic group on a surface thereof.   A polymer electrolyte fuel cell using the polymer solid electrolyte according to claim 1 as an electrolyte membrane.   4. The polymer electrolyte fuel cell according to claim 3, wherein a fuel containing an organic solvent is used.   A mobile power source using the polymer electrolyte fuel cell according to claim 3.

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