JP2004349034A - Electrolyte film and fuel cell using the electrolyte film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrolyte film with high productivity, low cost, and excellent durability in the case of operation as a fuel cell, by solving the problem of permeation of methanol or swelling when used as a direct methanol type fuel cell (DMFC). <P>SOLUTION: The electrolyte film is formed by filling cross-linked polymers having an epoxy-group-containing compound or an oxetanyl-group-containing compound as a component substance into pores of a porous base material. The cross-linked polymers contains an ion-exchange group. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

ここで、Ａは酸素原子を含むエポキシ基またはオキセタニル基を有する基であり、Ａはベンゼン環に１ないし複数個有しており、複数ある場合は同じでも違っていてもよい。Ｘは水素またはメチル基、Ｙは水素、メチル基またはエチル基である。Ｒのうち少なくとも１つは水素であるが、他は水素または官能基を示し、またＲの内の一つは、直接または他の原子もしくは原子鎖を介しての他のベンゼン環との結合でも良い。なお複数のＲは同じでも違っていてもよい。ｎは１〜５の整数である。
Ｒの内の一つが、直接または他の原子もしくは原子鎖を介しての他のベンゼン環と結合している場合は、化学式（ａ）で示される化合物は、ベンゼン環が２つ以上有することとなる。
【００２１】
本発明で使用することができるエポキシ基含有化合物の具体例のうち、ベンゼン環含有エポキシ化合物としては、化合物（ａ）に該当するフェニルグリシジルエーテル、クレジルグリシジルエーテル、イソプロピルフェニルグリシジルエーテル、ｔ―ブチルグリシジルエーテル、ビスフェノールＡジグリシジルエーテル、ビスフェノールＦジグリシジルエーテル、ビスフェノールＳジグリシジルエーテル、ナフタレンジグリシジルエーテル、ビフェニルジグリシジルエーテル、テトラメチルビスフェノールＡジグリシジルエーテル、テトラブロモビスフェノールＡジグリシジルエーテル、テトラメチルビフェニルジグリシジルエーテル、ハイドロキノンジグリシジルエーテル、レゾルシノールジグリシジルエーテル、フェノールノボラック型グリシジルエーテル、クレゾールノボラック型グリシジルエーテル、トリフェニルメタントリグリシジルエーテル、テトラフェニルエタンテトラグリシジルエーテル、トリグリシジルアミノフェノール、トリグリシジルアミノクレゾール、ビスフェノールヘキサフルオロアセトンジグリシジルエーテル、１，３−ビス〔１−（２，３−エポキシプロポキシ）−１−トリフルオロメチル−２，２，２−トリフルオロエチル〕ベンゼン、１，４−ビス〔１−（２，３−エポキシプロポキシ）−１−トリフルオロメチル−２，２，２−トリフルオロエチル〕ベンゼン等が挙げられる。
また、化合物（ａ）に該当しないものとして、スチレンオキサイド、テトラグリシジルジアミノジフェニルメタン、テトラグリシジルジアミノキシレン、ジグリシジルアニリン等が挙げられる。
これらの中ではスルホン化等イオン交換基を導入し易い点でグリシジルエーテル型の化合物が好ましい。
【００２２】
ベンゼン環を含有しないエポキシ含有化合物はイオン交換基の導入には適さないが、架橋重合体の弾性率、吸水率の調整等の目的でポリマー前駆体に配合することができる。そのような化合物としてはエチレングリコールジグリシジルエーテル、プロピレングリコールジグリシジルエーテル、ポリエチレングリコールジグリシジルエーテル、ポリプロピレングリコールジグリシジルエーテル、ポリテトラメチレングリコールジグリシジルエーテル、ブタンジオールジグリシジルエーテル、ヘキサンジオールジグリシジルエーテル、ネオペンチルグリコールジグリシジルエーテル、トリグリシジルイソシアヌレート、水添ビスフェノールＡジグリシジルエーテル、テトラグリシジル−１，３−ビスアミノメチルシクロヘキサン、２−エチルヘキシルグリシジルエーテル、ペンタエリスリトールポリグリシジルエーテル等が挙げられる。
【００２３】
本発明で用いるエポキシ基含有化合物を重合させる際の触媒としては、３フッ化ホウ素誘導体や３級アミン、４級アンモニウム塩等が使用できる。このような化合物の具体例としては３フッ化ホウ素、３フッ化ホウ素エチルアミン塩、３フッ化ホウ素ジエチルアミン塩、３フッ化ホウ素トリエチルアミン塩、３フッ化ホウ素ヘキシルアミン塩、３フッ化ホウ素ベンジルアミン塩、３フッ化ホウ素ベンジルアミン塩、３フッ化ホウ素ピペリジン塩、３フッ化ホウ素アニリン塩、ジメチルベンジルアミン、４−ジメチルアミノピリジン、１，８−ジアザビシクロ［５，４，０］ウンデセン−７、２−（ジメチルアミノメチル）フェノール、２，４，６−トリス（ジメチルアミノメチル）フェノール、トリエチレンジアミン、ピペリジン、Ｎ，Ｎ’−ジメチルピペラジン、イミダゾール、２−メチルイミダゾール、２−エチル−４−メチルイミダゾール、２−ウンデシルイミダゾール、２−ヘプタデシルイミダゾール、２−フェニルイミダゾール、１−シアノエチル−２−エチル−４−メチルイミダゾール等のイミダゾール化合物やその塩が挙げられる。
この中で好ましいものはイミダゾール化合物である。さらに好ましくは２−メチルイミダゾール、２−エチル−４−メチルイミダゾール、１−シアノエチル−２−エチル−４−メチルイミダゾールである。好ましい理由としては本発明で用いる多孔性基材がポリオレフィン等である場合、硬化温度が高いと基材が収縮する等の問題があるため、硬化温度を１５０℃以下、より好ましくは１３０℃以下で行う必要があるが、イミダゾール化合物以外の触媒では重合反応が遅いため生産性が悪くなるからである。
【００２４】
これらの触媒の使用量は、エポキシ基含有化合物を含んでなるポリマー前駆体の総質量に対して０．００１〜１０質量％が好ましく、さらに好ましくは０．００１〜５質量％、特に好ましくは０．０１〜３質量％である。
【００２５】
本発明で使用することができるオキセタニル基含有化合物としては化合物（ａ）に該当するものが好ましく、具体的には、３−エチル−３−（フェノキシメチル）オキセタン、１，４−ビス｛〔（３−エチルオキセタン−３−イル）メトキシ〕メチル｝ベンゼン、１，３−ビス｛〔（３−エチルオキセタン−３−イル）メトキシ〕メチル｝ベンゼン、フェノールノボラックオキセタン、４，４’−ビス〔（３−エチルオキセタン−３−イル）メトキシ〕ビフェニル等が挙げられる。これら化合物はいずれも好ましく使用することができるがフェノールノボラックやビフェニル骨格のものは重合物が硬すぎるため、単官能化合物等で希釈して用いると良い。
【００２６】
ベンゼン環を有していないオキセタニル基含有化合物の具体例としては３−エチル−３−ヒドロキシオキセタン、ビス〔１−エチル（３−オキセタニル）〕メチルエーテル、３−エチル−３−（２−エチルヘキシロキシメチル）オキセタン等が挙げられる。これらはイオン交換基の導入には適さないが何れも低粘度であるため、ポリマー前駆体の粘度を下げ多孔性基材への充填を容易にさせる目的や重合体の膨潤性を調製する等の目的で使用することができる。
【００２７】
イオン交換基の導入に適さないエポキシ基含有化合物またはオキセタニル基含有化合物を使用する場合、または得られる架橋重合体のイオン交換容量を増す目的で、イオン交換基を導入可能な部位を有しているこれら化合物の硬化剤を用いることができる。当該硬化剤の内、エポキシ基含有化合物用硬化剤の例としては、ベンゼン環を有し、かつカルボキシル基、水酸基若しくはチオール基等を２個以上有するかまたはアミノ基を１個以上有する化合物が挙げられ、オキセタニル基含有化合物用硬化剤の例としては、ベンゼン環を有し、かつカルボキシル基を２個以上有する化合物等が挙げられる。
【００２８】
またオキセタニル基含有化合物とエポキシ基含有化合物はカチオン重合において共重合性があることが確認されており、オキセタニル基含有化合物を後述の光や加熱により酸を発生する化合物を用いて重合する際はオキセタニル基含有化合物にエポキシ基含有化合物を混合して用いることができる。オキセタニル基含有化合物にエポキシ基含有化合物を少量添加すると、重合速度が大きく向上するため本発明の電解質膜を連続的に生産する場合に好ましい。
【００２９】
オキセタニル基含有化合物を重合させるためのカチオン重合触媒としては、光酸発生剤、すなわち光や加熱により酸を発生する化合物が用いられる。そのような化合物としてはスルホニウム塩やヨードニウム塩が挙げられ、具体的にはサートマー社製、商品名ＣＤ−１０１１、商品名ＣＤ−１０１０、商品名ＣＤ−１０１２；旭電化（株）製、アデカオプトマーＳＰ−１５０、同ＳＰ−１５２、同ＳＰ−１７０、同ＳＰ−１７２；ローディア社製、商品名フォトイニシエイター２０７４、チバスペシャリティーケミカル社製、商品名イルガキュアー２６１；日本曹達（株）製、商品名ＣＩ−１３７０、同２３９７、同２６２４、同２６３９、同２０６４；三新化学（株）製サンエードＳＩ−６０Ｌ、同８０Ｌ、同１００Ｌ等がある。
【００３０】
これらカチオン重合触媒の使用量は、オキセタニル基含有化合物あるいは必要に応じて一部エポキシ基含有化合物を添加してなるポリマー前駆体の総質量に対して０．００１〜１０質量％が好ましく、さらに好ましくは０．００１〜５質量％、特に好ましくは０．０１〜３質量％である。
【００３１】
オキセタニル基含有化合物を含んでなるポリマー前駆体の重合を紫外線または可視光線で行う場合は照射量を１〜５０００ｍＪ／ｃｍ^２、好ましくは１００〜２０００ｍＪ／ｃｍ^２で行う。照射量がこれ以下の場合は重合が不十分となりやすく、これ以上照射してもそれ以前に充分な重合が起っているためエネルギーの無駄である。
【００３２】
本発明において多孔性基材にポリマー前駆体を含浸する際は、エポキシ基含有化合物またはオキセタニル基含有化合物に重合触媒等を混合し液状にしてポリマー前駆体液とすることが好ましい。ポリマー前駆体だけの混合物が低粘度の液体である場合はそのまま含浸に用いることもできる。溶液として用いる場合の溶剤はアニオン重合やカチオン重合を阻害しないものが好ましく、不純物としての水分等もできるだけ取り除いて使用し、水分は５００ｐｐｍより好ましくは１００ｐｐｍ以下にするのが良い。
【００３３】
また含浸作業をより行い易くする目的で含浸中に超音波の照射を行ったり振動を与えたりするのが好ましい。
【００３４】
本発明においてイオン交換基は燃料電池用電解質膜とした場合に内部抵抗が低いという点で陽イオン交換基であるのが好ましく、その例としてはカルボキシル基、スルホン酸基、ホスホン酸基、硫酸基等が挙げられる。このうちスルホン酸基はプロトン移動抵抗が小さく燃料電池性能が高くなるため好ましい。
【００３５】
このような基を導入するには、公知の方法を採用することができる。このうちスルホン酸基を導入する方法としては、濃硫酸による方法、発煙硫酸による方法、クロロスルホン酸による方法、三酸化硫黄による方法等が挙げられる。このような方法を記した文献としては例えば高分子学会編「高分子化学実験法」東京化学同人ｐ７１〜７５、日本化学会編「新実験科学講座１４（ＩＩＩ）」丸善、ｐ１７７６〜１７８４（１９７８）等がある。
【００３６】
上記の方法はいずれも強酸を使用するが、エポキシ基含有化合物やオキセタニル基含有化合物に由来する重合体は強い酸によって結合が切れ易いエーテル結合を有しているため、５０℃以下、好ましくは２０℃以下、より好ましくは５℃以下でスルホン化を行う必要がある。これ以上の温度でスルホン化を行うと基材の細孔に充填した重合体がスルホン化工程中に分解してしまい電解質膜として機能しなくなるため好ましくない。またスルホン化の際はパークロロエチレン、トリクロロエチレン、クロロホルム、ジクロロメタン、四塩化炭素、ジクロロエチレン等のハロゲン系溶剤を使用することができる。
【００３７】
具体的なスルホン化方法の例としてクロロスルホン酸による方法を挙げる。この方法は、多孔性基材にエポキシ基含有化合物またはオキセタニル基含有化合物からなるポリマー前駆体を充填し重合した後に、上述の塩素系溶剤に膜を浸し、膜を浸している容器の外側から氷浴等で冷却しながらクロロスルホン酸またはその塩素系溶剤で希釈した溶液を少しずつ添加していき、添加後は必要な反応が進むまで攪拌することで、まずクロロスルホン化する。これを一旦乾燥し水酸化ナトリウム水溶液、水酸化カリウム水溶液等で分解してスルホン酸塩とし、最後に塩酸等の酸でプロトン酸型に変換することでスルホン化を行うことができる。
【００３８】
本発明の電解質膜は固体高分子形燃料電池、特に直接メタノール形燃料電池に好ましく用いることができる。このような燃料電池に電解質膜を用いる際は白金に代表される触媒を付与した２枚の電極間に電解質膜を挟んで加熱プレス等によって一体化した電解質膜電極接合体（ＭＥＡ）とし、燃料電池セルに組み込んで使用することは広く知られており、本発明による電解質膜も同様の方法によってＭＥＡを作成し、燃料電池セルに組み込んで使用することができる。
【００３９】
【作用】
本発明の電解質膜は、外力に対して変形し難い材質でできた多孔性基材にプロトン伝導性を有する重合体を充填しているため、充填された重合体が水やメタノールによって膨潤しようとしても物理的にそれを抑えることができ、メタノールの透過を抑制することができる。またポリマー前駆体の重合反応がラジカル反応ではないため、空気中の酸素やポリマー前駆体中に溶存する酸素の影響で重合性が変化することがなく生産性が高い。また、充填された重合体が架橋点を多く有しているため、重合体内でフリーラジカルが生じても全体が溶出するまでには到らずまたラジカルによる解重合等も起らないことからゲル形状を保持することができるため耐久性が高く、固体高分子形燃料電池、特に直接メタノール形燃料電池に好ましく用いることができる。
【００４０】
【実施例】
（実施例１）
多孔性基材として架橋ポリエチレン膜（大きさ５ｃｍ×６ｃｍ、厚さ１６μｍ、空孔率４０％、平均孔径約０．１μｍ）を用いた。エポキシ基含有化合物として、フェニルグリシジルエーテル４．５ｇおよびエチレングリコールジグリシジルエーテル３．４ｇを用い、これに２−エチル−４−メチルイミダゾール０．６ｇを混合したポリマー前駆体液に前記膜を浸漬させ、当該前駆体液を充填した。次いで、膜を液から引き上げた後、ポリ４フッ化エチレン製シートで膜を挟んで１２０℃に加熱したオーブンで２時間放置して細孔内部のポリマー前駆体を重合させた。重合工程が終了後、膜を取出して１，２−ジクロロエタン３０ｍｌに浸して氷浴により約１℃に冷却した。膜を浸した容器を攪拌しながら、ここへ１体積％に希釈したクロロスルホン酸の１，２−ジクロロエタン溶液７１ｍｌを１０分かけて滴下し、滴下終了後２０分攪拌を続けた。次に攪拌を止めて、膜を取出し、１，２−ジクロロエタンで３回洗浄し自然乾燥させた。次にこの膜を１Ｎ水酸化カリウム水溶液に室温下で２０時間浸漬し、これを水洗した。最後に１Ｎの塩酸水溶液に２時間浸漬してから表面に付着している余分な重合体をプラスチック製ヘラで掻き取り蒸留水で洗浄して乾燥して電解質膜を得た。得られた電解質膜の評価結果を表１にまとめた。
【００４１】
（実施例２）
エポキシ基含有化合物を、フェニルグリシジルエーテル４．５ｇおよびビスフェノールＦジグリシジルエーテル（油化シェルエポキシ（株）製、商品名エピコート８０７）６．１ｇとしたこと以外は実施例１に準じて電解質膜を作成し、評価を行った。その結果を表１に示す。
【００４２】
（実施例３）
実施例１で使用した多孔性基材を用い、ポリマー前駆体として、３−エチル−３−（フェノキシメチル）オキセタン（東亞合成（株）製、商品名アロンオキセタンＯＸＴ−２１１）５．８ｇ、１，３−ビス〔（３−エチルオキセタン−３−イル）メトキシ〕ベンゼン（東亞合成（株）製、商品名アロンオキセタンＲＳＯＸ）６．０ｇおよび光酸発生剤（旭電化（株）製、商品名アデカオプトマーＳＰ１５０）０．１２ｇからなる混合液を用い、実施例１と同様にポリマー前駆体を充填した。ポリマー前駆体充填後、厚さ２５μｍのＰＥＴフィルムで挟んで、高圧水銀ランプで紫外線を１０００ｍＪ／ｃｍ^２照射して重合を行った。重合工程の後は実施例１に準じて電解質膜を作成し、評価を行った。その結果を表１に示す。
【００４３】
（実施例４）
実施例１で使用した多孔性基材を用い、ポリマー前駆体として、３−エチル−３−（フェノキシメチル）オキセタン（東亞合成（株）製、商品名アロンオキセタンＯＸＴ−２１１）５．８ｇ、１，４−ビス｛〔（３−エチルオキセタン−３−イル）メトキシ〕メチル｝ベンゼン（東亞合成（株）製、商品名アロンオキセタンＯＸＴ−１２１）６．５ｇおよび光酸発生剤（旭電化（株）製、商品名アデカオプトマーＳＰ１５０）０．１２ｇからなる混合液を用い実施例１と同様にポリマー前駆体を充填した。ポリマー前駆体充填後厚さ２５μｍのＰＥＴフィルムで挟んで、高圧水銀ランプで紫外線を１０００ｍＪ／ｃｍ^２照射して重合を行った。重合工程の後は実施例１に準じて電解質膜を作成し、評価を行った。その結果を表１に示す。
【００４４】
（実施例５）化学式（ａ）の化合物の効果確認
エポキシ基含有化合物を、スチレンオキサイド３．６ｇおよびエチレングリコールジグリシジルエーテル３．４ｇとしたこと以外は実施例１に準じて電解質膜を作成し、評価を行ったところ、イオン交換容量は０．１ｍｅｑ／ｇであり電解質膜としての機能は極めて低いものであった。このためエチレングリコールジグリシジルエーテルの代わりにビスフェノールＦジグリシジルエーテル（油化シェルエポキシ（株）製、商品名エピコート８０７）６．１ｇとしたところスルホン酸が導入され電解質膜として機能することがわかった。このため化学式（ａ）の構造を有する化合物にはスルホン酸基の導入が容易に起こることが判明した。化学式（ａ）の構造を有さないスチレンオキサイドはスルホン酸導入には適さないが共重合成分としては好ましく使用することができる。本実施例で作成した膜の内、後者のものについての評価結果を表１に示す。
【００４５】
（比較例１）
実施例１で使用した多孔性基材（膜）を用い、２−アクリルアミド−２−メチルプロパンスルホン酸１０ｇ、Ｎ，Ｎ’−メチレンビスアクリルアミド０．１ｇ、ノニオン性界面活性剤０．００１ｇ、過硫酸アンモニウム（水素引き抜き型光重合開始剤）０．００１ｇおよび水１０ｇからなるポリマー前駆体水溶液に窒素ガスを吹き込んで酸素を除去した後、前記膜を浸漬させ当該水溶液を充填させた。次いで、当該膜を溶液から引き上げた後、ガラスで挟んで８０℃に加熱したオーブンで２時間放置して細孔内部のポリマー前駆体を重合させた。得られた膜について評価を行った結果を表１に示す。
【００４６】
（比較例２）
市販のパーフルオロアルキルスルホン酸製の電解質膜（デュポン社製、商品名ナフィオン１１５）について評価を行った結果を表１に示す。
【００４７】
【表１】

【００４８】
（電解質膜の評価方法）
▲１▼イオン交換容量
得られた電解質膜を０．０１Ｎ水酸化ナトリウム水溶液２０ｍｌに浸して密栓し、５０℃で２時間放置後室温まで冷却した後に膜を取出した。膜を取出す際、蒸留水で数回膜を洗浄し残りの水酸化ナトリウム水溶液に加えた。この液を０．０１Ｎの塩酸水溶液で滴定し、消費された塩酸のモル数を電解質膜の乾燥重量で割ってイオン交換容量とした。
▲２▼プロトン伝導性
２５℃における膨潤試料の伝導度測定を行なった。純水に１時間浸して膨潤させた電解質膜を２枚の白金板で挟み込み測定用試料とした。その後、１００Ｈｚから４０ＭＨｚの交流インピーダンス測定を実施して、伝導率を測定した。
▲３▼メタノール透過性
２５℃における浸透実験を以下のように行なった。電解質膜を透析用ガラス製セルに挟み、一方のセルに１０％メタノール水溶液を入れ、もう一方のセルに純水を入れた。純水側に浸透するメタノール量をガスクロマトグラフ分析により経時的に測定し、定常状態になった時の透過係数を測定した。透過係数が低い（（透過係数）^−１が大きい）ほど、電解質膜中をメタノールが透過し難く、燃料電池用途に適していることを示す。
▲４▼耐久性（強制劣化試験）
電池内で発生する過酸化水素によるポリマーの劣化現象を確認する代わりに強制劣化により評価するため、０．５％過酸化水素および０．００５％硫酸第二鉄７水和物を含む水溶液を調整し、その中に電解質膜を浸し、７０℃で２時間放置した後、電解質膜を引き上げた。試験前後の重量変化から電解質膜中の充填ポリマーの残存率を求めた。残存率が小さいほど、電池として運転した時の劣化が早く、大きいほど劣化し難いことを示す。実施例はいずれも比較例１より劣化が少ないことを確認した。
▲５▼メタノール水溶液中での面積変化率
電解質膜を７０℃で２時間真空乾燥して面積を測定後、２５℃の１０％メタノール水溶液に１時間浸漬して面積を測定。下記式により面積変化率を求めた。
面積変化率＝１００×（メタノール水溶液膨潤後の面積−乾燥時面積）／乾燥時面積
【００４９】
（実施例６）
得られた膜が燃料電池として機能することを確認するため実施例１で作成した膜をＤＭＦＣセルに組み込んで評価を行った。
酸素極用に白金担持カーボン（田中貴金属工業（株）製：ＴＥＣ１０Ｅ５０Ｅ）、および燃料極用に白金ルテニウム合金担持カーボン（田中貴金属工業（株）製：ＴＥＣ６１Ｅ５４）をそれぞれ用い、これらの触媒粉末に高分子電解質溶液（デュポン社製：ナフィオン５％溶液）とポリテトラフルオロエチレンディスパージョンを配合し、水を適宜加えて攪拌して反応層用塗料を得た。これをスクリーン印刷法でカーボンペーパー（東レ（株）製：ＴＧＰ−Ｈ−０６０）の片面に印刷し乾燥して電極とした。その際酸素極側は白金量が１ｍｇ／ｃｍ^２、燃料極側は白金とルテニウムの総量が３ｍｇ／ｃｍ^２とした。これらを実施例１で得られた電解質膜の中央部に塗料面を内側にして重ね合せ、１２０℃で加熱プレスし燃料電池用膜電極接合体（ＭＥＡ）を作成した。これをＤＭＦＣ単セルに組み込んで運転し、性能を確認した。ＤＭＦＣ運転条件はセル温度を５０℃とし、燃料極へ濃度２ｍｏｌ／ｌのメタノール水溶液を１０ｍｌ／分で供給し、酸素極には純酸素を１００ｍｌ／分で供給した。電流値を上げながら電圧を読み取り図１の電流密度−電圧曲線を得た。
【００５０】
【発明の効果】
本発明の電解質膜は、従来燃料電池用電解質膜に用いられてきたポリパーフルオロスルホン酸系電解質膜をＤＭＦＣに用いる場合に問題とされていたメタノール透過の問題を克服し、さらに炭化水素系電解質重合体を使用することによって問題となっていた膜作成時の酸素による重合阻害の影響がないため生産性が良好になる。また耐久性も向上させることができる。
これは充分な強度と弾性率を有する多孔性基材の細孔にプロトン導電性を有する架橋重合体を充填したことによって、水やメタノールが透過し難くなるためと、架橋重合体の高度な架橋構造によって燃料電池運転中に充填した重合体が分解して細孔から脱落するのを防止するためである。
これらのため、本発明の電解質膜は燃料電池としての出力特性と耐久性を併せ持ち、燃料電池等用途として極めて有用である。
【図面の簡単な説明】
【図１】実施例６の燃料電池における電流密度−電圧曲線を示したグラフである。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an electrolyte membrane, and the electrolyte membrane is suitable for use in an electrochemical device, particularly a fuel cell, and more specifically, a direct alcohol fuel cell.
[0002]
[Prior art]
The performance of polymer electrolyte fuel cells, a type of electrochemical device using polymer electrolyte membranes, has been remarkably improved due to the development of electrolyte membranes and catalyst technology in recent years, and has attracted attention as a power source for low-emission vehicles and a high-efficiency power generation method. Are gathering. A polymer electrolyte fuel cell has a structure in which a reaction layer having an oxidation and reduction catalyst is formed on the surface of a membrane. In a polymer electrolyte fuel cell, a reaction occurs in which hydrogen molecules are decomposed into protons and electrons at the fuel electrode, and the generated electrons are transported to the oxygen electrode side by operating electrical components through a conducting wire. In water, water is generated from oxygen, protons, and electrons transported from the anode through a conductor. In a direct methanol fuel cell (DMFC), methanol and water are supplied to a fuel electrode, and a catalyst near the membrane reacts methanol and water to extract protons. In these fuel cells, an electrolyte membrane made of polyperfluorosulfonic acid is usually used.
[0003]
However, when the electrolyte membrane made of polyperfluorosulfonic acid is used in a direct methanol fuel cell, methanol passes through the membrane and energy loss occurs. However, there is a problem in that a problem such as peeling of the joint portion easily occurs, and the fuel concentration cannot be increased. Further, there is an economical problem that the material itself is expensive due to having a fluorine atom, and it is very expensive due to a complicated manufacturing process and low productivity.
[0004]
For this reason, there has been a demand for a polymer electrolyte membrane comprising a hydrocarbon skeleton, which suppresses methanol permeation in a direct methanol fuel cell and is inexpensive. The electrolyte membrane for a fuel cell disclosed in Patent Document 1 by the present inventors comprises a porous substrate filled with an inexpensive polymer electrolyte, and has a structure in which the polymer electrolyte is filled in pores. Excessive swelling of the polymer electrolyte by the aqueous methanol solution can be prevented, and as a result, permeation of methanol can be suppressed. However, durability in continuous operation as a direct methanol fuel cell was not sufficient.
[0005]
Further, the above-mentioned polymer electrolyte membrane is obtained by filling a porous substrate with a mixture containing a monomer having a carbon-carbon double bond such as an acrylic acid derivative, and subjecting the mixture to radical polymerization. Since the polymerization is inhibited by oxygen present in the air, it is necessary to shut off the air by performing the polymerization step in an atmosphere of an inert gas such as nitrogen or by sandwiching the glass plate or the like. For this reason, if the replacement with the inert gas in the polymerization atmosphere is insufficient or if the mixture contains a large amount of dissolved oxygen, air bubbles enter between the glass plate or the like and the porous substrate filled with the mixture. In some cases, insufficient polymerization occurs in some places, causing defects such as pinholes in the film. If a defect such as a pinhole exists in the formed film, the fuel and the oxidizing agent are directly mixed in the fuel cell, and as a result, there is a possibility that the cell performance may be reduced or the cell may be damaged. Is not preferred. In addition, depending on radicals derived from hydrogen peroxide generated during operation of the fuel cell and on the materials used, the polymer electrolyte is decomposed by hydrolysis, so that the durability was insufficient.
[0006]
It is known that such a radical polymerization-based polymer undergoes depolymerization due to the presence of a radical, and the molecular weight decreases in a chain reaction. Further, it has an amide bond such as 2-acrylamido-2-methylpropanesulfonic acid used by the present inventors in Japanese Patent Application No. 2002-311929 and N, N'-methylenebisacrylamide used as a crosslinking agent. It is also known that some polymers undergo gradual hydrolysis.
[0007]
[Patent Document 1]
JP-A-2002-83612
[0008]
[Problems to be solved by the invention]
The present invention solves the problems of permeation and swelling of methanol in the fuel cell electrolyte membrane as described above, and provides an electrolyte membrane having high productivity, low cost, and excellent durability when operated as a fuel cell. The study was conducted in order to do so.
[0009]
[Means for Solving the Problems]
The present inventors have conducted intensive studies in order to solve the above-mentioned problems, and as a result, a mixture obtained by adding a monomer composed of an epoxy group-containing compound or an oxetanyl group-containing compound and, if necessary, a curing catalyst, a solvent, etc. ) Is filled into the pores of the porous substrate, and then cured and cross-linked to form a cross-linked polymer, and further a step of introducing an ion-conductive group into the cross-linked polymer. The inventors have found that the prepared electrolyte membrane has both output characteristics and durability as a fuel cell, and have completed the present invention.
[0010]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the present invention will be described in detail.
The electrolyte membrane of the present invention is filled with a crosslinked polymer having an ion-exchange group in the pores of a porous substrate, has durability, and suppresses methanol permeability as compared with a conventional fluorine-based electrolyte membrane. You can do it.
[0011]
The porous base material used in the present invention is preferably a material that does not substantially swell with methanol and water, and it is particularly desirable that the area change when wet with water is small or little compared to when dry. The area increase rate varies depending on the immersion time and temperature, but it is preferable that the area increase rate when immersed in pure water is 20% or less at the maximum as compared with the time of drying.
[0012]
The porous substrate of the present invention also preferably has a tensile modulus of 500 to 5000 MPa, more preferably 1000 to 5000 MPa, and preferably has a breaking strength of 50 to 500 MPa, more preferably 100 to 500 MPa. 500 MPa.
If these ranges are deviated to the lower side, the filled polymer tends to be deformed by the force of swelling with methanol or water, and if deviated to the higher side, the base material becomes too brittle and press molding at the time of electrode bonding and The membrane is likely to crack due to tightening or the like when assembled in the battery. The porous substrate preferably has heat resistance to the temperature at which the fuel cell is operated, and preferably does not easily expand even when an external force is applied.
Examples of materials having such properties include inorganic materials such as glass and ceramics such as alumina and silica. Examples of the organic materials include engineering plastics such as aromatic polyimides, and those in which polyolefins are hardly deformed by elongation against external force by a method such as irradiation or irradiation with a cross-linking agent, cross-linking or stretching. These materials may be used alone or may be used as a composite by laminating two or more kinds.
[0013]
Among these porous substrates, those comprising stretched polyolefin, cross-linked polyolefin, cross-linked polyolefin after stretching, and polyimides have good workability in the filling step, and have cracks in the battery due to their flexibility. It is preferable to use the above-mentioned polyolefin from the viewpoint of low cost.
[0014]
The porosity of the porous substrate is preferably from 5 to 95%, more preferably from 5 to 90%, and particularly preferably from 20 to 80%. Further, the average pore size is preferably in the range of 0.001 to 100 μm, and more preferably in the range of 0.01 to 1 μm. If the porosity is too small, the proton acid group, which is a proton conductive group per area, is too small, resulting in a low output for a fuel cell. If the porosity is too large, the membrane strength is undesirably reduced. The thickness of the substrate is preferably 200 μm or less. It is more preferably from 1 to 150 μm, further preferably from 5 to 100 μm, particularly preferably from 5 to 50 μm. If the film thickness is too small, the membrane strength is reduced and the amount of permeation of methanol is increased. If the film thickness is too large, the membrane resistance becomes too large and the output of the fuel cell is low.
[0015]
Further, it is preferable that a crosslinked polymer having an ion exchange group is chemically bonded to the surface of the porous substrate, particularly to the inner surface of the pores. As a means for forming the bond, the porous substrate is subjected to oxidation treatment. A method of introducing a hydroxyl group, a carboxyl group, etc., which can react with an epoxy group or an oxetanyl group, or irradiating an electron beam or a gamma ray after the step of polymerizing a filled polymer precursor, thereby obtaining a substrate or a crosslinked polymer. Once radicals are generated in the inside, and when they are recombined, a bond is formed between the substrate and the crosslinked polymer. These may be performed alone or in combination of a plurality of methods.
[0016]
The electrolyte membrane of the present invention is obtained by filling the pores of a porous substrate with an ion-exchange group-containing crosslinked polymer derived from an epoxy group-containing compound or an oxetanyl group-containing compound. The method for filling the polymer can be obtained by impregnating a porous substrate with a polymer precursor, polymerizing the porous substrate, and subsequently introducing an ion exchange group into the polymer. At that time, the polymer precursor to be filled may contain a catalyst, a curing agent, a surfactant, and the like, if necessary.
[0017]
Among the polymer precursors used in the present invention, the epoxy group-containing compound or oxetanyl group-containing compound is a compound having one or more epoxy groups or oxetanyl groups in one molecule. In this case, if only a monofunctional compound is used alone, a crosslinked structure can hardly be formed, and therefore it is necessary to mix bifunctional or more compounds. In the case of an epoxy group-containing compound, the number of epoxy groups derived from a compound having two or more functional groups is preferably 10% or more, and more preferably 20% or more, based on the total number of epoxy groups. is there. When this ratio is less than 10%, a crosslinked structure is hardly formed, and since it has fluidity even after polymerization, it does not easily function as an electrolyte membrane. In the case of the oxetanyl group-containing compound, the oxetanyl group derived from a compound having two or more functional groups is preferably 3% or more, more preferably 5% or more, based on all oxetanyl groups. The reason that the oxetanyl group-containing compound may have less bifunctional or more functional components than the epoxy group-containing compound is that the oxetanyl group-containing compound has higher polymerization reactivity.
[0018]
In order to provide a crosslinked structure, it is possible to use a specific crosslinking agent in addition to using a polyfunctional epoxy group-containing compound or an oxetanyl group-containing compound as described above. For example, when a hydroxyl group is formed in the epoxy group-containing compound after the curing reaction, it can be crosslinked with a methylol compound. However, in this case, it is not a very preferable method because an acid catalyst is required or a step is required to introduce an ion exchange group, which complicates the process.
[0019]
In order to obtain a crosslinked polymer having ion exchange groups in the pores of the porous substrate, at least a part of the epoxy group-containing compound and the oxetanyl group-containing compound of the polymer precursor can introduce an ion exchange group. It is preferable to have a unique site. As such a site into which an ion exchange group can be introduced, a benzene ring which can be directly sulfonated is preferable, and a compound having 1 to 5 oxygen atoms bonded to 6 carbon atoms of the benzene ring is preferably a sulfone. It is more preferable because a reaction such as conversion is more likely to occur. The compounding amount of the compound having a site into which the ion exchange group can be introduced is 10% by mass or more, preferably 30% by mass or more of the polymer precursor. If it is less than this, the ion exchange capacity becomes too small, and the performance of an electrochemical device such as a fuel cell may be deteriorated.
[0020]
Preferred epoxy group-containing compounds and oxetanyl group-containing compounds are those represented by the chemical formula (a).
Embedded image

Here, A is a group having an epoxy group or an oxetanyl group containing an oxygen atom, and A has one or more benzene rings, and when there are a plurality of them, they may be the same or different. X is hydrogen or a methyl group, and Y is hydrogen, a methyl group or an ethyl group. At least one of R is hydrogen, the other represents hydrogen or a functional group, and one of R is bonded to another benzene ring directly or through another atom or an atom chain. good. A plurality of Rs may be the same or different. n is an integer of 1 to 5.
When one of R is bonded to another benzene ring directly or via another atom or an atomic chain, the compound represented by the chemical formula (a) has two or more benzene rings. Become.
[0021]
Among the specific examples of the epoxy group-containing compound that can be used in the present invention, the benzene ring-containing epoxy compound includes phenyl glycidyl ether, cresyl glycidyl ether, isopropylphenyl glycidyl ether, t-butyl corresponding to compound (a). Glycidyl ether, bisphenol A diglycidyl ether, bisphenol F diglycidyl ether, bisphenol S diglycidyl ether, naphthalenediglycidyl ether, biphenyl diglycidyl ether, tetramethylbisphenol A diglycidyl ether, tetrabromobisphenol A diglycidyl ether, tetramethylbiphenyl Diglycidyl ether, hydroquinone diglycidyl ether, resorcinol diglycidyl ether, phenol novolak type Lysidyl ether, cresol novolak glycidyl ether, triphenylmethane triglycidyl ether, tetraphenylethane tetraglycidyl ether, triglycidylaminophenol, triglycidylaminocresol, bisphenol hexafluoroacetone diglycidyl ether, 1,3-bis [1- (2,3-epoxypropoxy) -1-trifluoromethyl-2,2,2-trifluoroethyl] benzene, 1,4-bis [1- (2,3-epoxypropoxy) -1-trifluoromethyl- 2,2,2-trifluoroethyl] benzene and the like.
In addition, styrene oxide, tetraglycidyldiaminodiphenylmethane, tetraglycidyldiaminoxylene, diglycidylaniline, and the like are not included in the compound (a).
Among these, a glycidyl ether type compound is preferable because an ion exchange group such as sulfonation can be easily introduced.
[0022]
Epoxy-containing compounds that do not contain a benzene ring are not suitable for introducing ion-exchange groups, but can be added to the polymer precursor for the purpose of adjusting the elastic modulus and water absorption of the crosslinked polymer. Such compounds include ethylene glycol diglycidyl ether, propylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, polytetramethylene glycol diglycidyl ether, butanediol diglycidyl ether, hexanediol diglycidyl ether, Neopentyl glycol diglycidyl ether, triglycidyl isocyanurate, hydrogenated bisphenol A diglycidyl ether, tetraglycidyl-1,3-bisaminomethylcyclohexane, 2-ethylhexyl glycidyl ether, pentaerythritol polyglycidyl ether, and the like.
[0023]
As a catalyst for polymerizing the epoxy group-containing compound used in the present invention, boron trifluoride derivatives, tertiary amines, quaternary ammonium salts, and the like can be used. Specific examples of such compounds include boron trifluoride, boron trifluoride ethylamine, boron trifluoride diethylamine, boron trifluoride triethylamine, boron trifluoride hexylamine, boron trifluoride benzylamine, and the like. Boron trifluoride benzylamine salt, boron trifluoride piperidine salt, boron trifluoride aniline salt, dimethylbenzylamine, 4-dimethylaminopyridine, 1,8-diazabicyclo [5,4,0] undecene-7,2 -(Dimethylaminomethyl) phenol, 2,4,6-tris (dimethylaminomethyl) phenol, triethylenediamine, piperidine, N, N'-dimethylpiperazine, imidazole, 2-methylimidazole, 2-ethyl-4-methylimidazole , 2-undecylimidazole, 2-hepta Examples thereof include imidazole compounds such as decyl imidazole, 2-phenylimidazole, 1-cyanoethyl-2-ethyl-4-methylimidazole and salts thereof.
Preferred among these are imidazole compounds. More preferred are 2-methylimidazole, 2-ethyl-4-methylimidazole and 1-cyanoethyl-2-ethyl-4-methylimidazole. As a preferable reason, when the porous substrate used in the present invention is a polyolefin or the like, there is a problem such as shrinkage of the substrate when the curing temperature is high, so that the curing temperature is 150 ° C. or lower, more preferably 130 ° C. or lower. This is because the polymerization reaction is slow with a catalyst other than the imidazole compound, so that productivity is deteriorated.
[0024]
The use amount of these catalysts is preferably 0.001 to 10% by mass, more preferably 0.001 to 5% by mass, and particularly preferably 0 to 10% by mass with respect to the total mass of the polymer precursor containing the epoxy group-containing compound. 0.01 to 3% by mass.
[0025]
As the oxetanyl group-containing compound that can be used in the present invention, those corresponding to compound (a) are preferable, and specifically, 3-ethyl-3- (phenoxymethyl) oxetane, 1,4-bis} [( 3-ethyloxetane-3-yl) methoxy] methyl} benzene, 1,3-bis {[(3-ethyloxetane-3-yl) methoxy] methyl} benzene, phenol novolak oxetane, 4,4′-bis [( 3-ethyloxetane-3-yl) methoxy] biphenyl and the like. Any of these compounds can be preferably used, but those having a phenol novolak or a biphenyl skeleton are preferably used after dilution with a monofunctional compound or the like because the polymer is too hard.
[0026]
Specific examples of the oxetanyl group-containing compound having no benzene ring include 3-ethyl-3-hydroxyoxetane, bis [1-ethyl (3-oxetanyl)] methyl ether, and 3-ethyl-3- (2-ethylhexane). (Siloxymethyl) oxetane and the like. These are not suitable for introducing ion-exchange groups, but all have a low viscosity, so that the viscosity of the polymer precursor is lowered and the purpose of facilitating the filling of the porous substrate or the swelling property of the polymer is adjusted. Can be used for purpose.
[0027]
When using an epoxy group-containing compound or an oxetanyl group-containing compound that is not suitable for introducing an ion-exchange group, or for the purpose of increasing the ion-exchange capacity of the obtained crosslinked polymer, it has a site where an ion-exchange group can be introduced. Curing agents of these compounds can be used. Among the curing agents, examples of the curing agent for an epoxy group-containing compound include compounds having a benzene ring and having two or more carboxyl groups, hydroxyl groups or thiol groups, or having one or more amino groups. Examples of the curing agent for the oxetanyl group-containing compound include compounds having a benzene ring and having two or more carboxyl groups.
[0028]
In addition, it has been confirmed that the oxetanyl group-containing compound and the epoxy group-containing compound have copolymerizability in cationic polymerization, and when the oxetanyl group-containing compound is polymerized using a compound that generates an acid by light or heating as described below, oxetanyl is used. An epoxy group-containing compound can be used as a mixture with the group-containing compound. The addition of a small amount of the epoxy group-containing compound to the oxetanyl group-containing compound is preferable when the electrolyte membrane of the present invention is continuously produced because the polymerization rate is greatly improved.
[0029]
As the cationic polymerization catalyst for polymerizing the oxetanyl group-containing compound, a photoacid generator, that is, a compound that generates an acid by light or heating is used. Examples of such a compound include a sulfonium salt and an iodonium salt, specifically, manufactured by Sartomer Co., Ltd., trade name CD-1011, trade name CD-1010, trade name CD-1012; Asahi Denka Co., Ltd., Adeka Opto Mer SP-150, SP-152, SP-170, SP-172; Rhodia Co., Ltd., trade name Photo Initiator 2074, Ciba Specialty Chemical Co., Ltd., trade name Irgacure 261; Nippon Soda Co., Ltd. CI-1370, 2397, 2624, 2639, and 2064 (trade names); Sanade SI-60L, 80L, and 100L manufactured by Sanshin Chemical Co., Ltd.
[0030]
The use amount of these cationic polymerization catalysts is preferably 0.001 to 10% by mass, more preferably 0.001 to 10% by mass, based on the total mass of the oxetanyl group-containing compound or the polymer precursor obtained by partially adding the epoxy group-containing compound as required. Is 0.001 to 5% by mass, particularly preferably 0.01 to 3% by mass.
[0031]
When the polymerization of the polymer precursor containing the oxetanyl group-containing compound is performed by ultraviolet light or visible light, the irradiation amount is 1 to 5000 mJ / cm. ² , Preferably 100 to 2000 mJ / cm ² Do with. If the irradiation amount is less than this, polymerization tends to be insufficient, and even if irradiation is performed further, sufficient polymerization has occurred before that, so that energy is wasted.
[0032]
When the porous substrate is impregnated with the polymer precursor in the present invention, it is preferable to mix the epoxy group-containing compound or the oxetanyl group-containing compound with a polymerization catalyst or the like to form a liquid, thereby obtaining a polymer precursor liquid. When a mixture of only the polymer precursor is a low-viscosity liquid, it can be used for impregnation as it is. When used as a solution, the solvent is preferably one that does not inhibit anionic polymerization or cationic polymerization, and water used as impurities is removed as much as possible. The water content is preferably 500 ppm, more preferably 100 ppm or less.
[0033]
It is preferable to irradiate ultrasonic waves or apply vibration during the impregnation for the purpose of making the impregnation work easier.
[0034]
In the present invention, the ion exchange group is preferably a cation exchange group in terms of low internal resistance when used as an electrolyte membrane for a fuel cell, and examples thereof include a carboxyl group, a sulfonic group, a phosphonic group, and a sulfate group. And the like. Among them, a sulfonic acid group is preferable because proton transfer resistance is small and fuel cell performance is high.
[0035]
In order to introduce such a group, a known method can be adopted. Among them, methods for introducing a sulfonic acid group include a method using concentrated sulfuric acid, a method using fuming sulfuric acid, a method using chlorosulfonic acid, a method using sulfur trioxide, and the like. Documents describing such a method include, for example, “Polymer Chemistry Experimental Method” edited by the Society of Polymer Science, Tokyo Chemical Doujins, p71-75, “New Experimental Science Course 14 (III)” edited by The Chemical Society of Japan, Maruzen, p1776-1784 (1978) ).
[0036]
All of the above methods use a strong acid, but a polymer derived from an epoxy group-containing compound or an oxetanyl group-containing compound has an ether bond that can be easily broken by a strong acid, and thus is 50 ° C. or lower, preferably 20 ° C. It is necessary to carry out the sulfonation at a temperature of not more than 5 ° C, more preferably at most 5 ° C. If the sulfonation is carried out at a temperature higher than this, the polymer filled in the pores of the substrate is decomposed during the sulfonation step, and the polymer does not function as an electrolyte membrane. In the case of sulfonation, halogen solvents such as perchlorethylene, trichloroethylene, chloroform, dichloromethane, carbon tetrachloride, and dichloroethylene can be used.
[0037]
An example of a specific sulfonation method is a method using chlorosulfonic acid. In this method, after filling and polymerizing a polymer precursor comprising an epoxy group-containing compound or an oxetanyl group-containing compound in a porous substrate, the film is immersed in the above-mentioned chlorinated solvent, and ice is applied from the outside of the vessel in which the film is immersed. While cooling in a bath or the like, chlorosulfonic acid or a solution thereof diluted with a chlorinated solvent is added little by little, and after the addition, the mixture is stirred until the required reaction proceeds, thereby first chlorosulfonating. This is once dried, decomposed with a sodium hydroxide aqueous solution, potassium hydroxide aqueous solution or the like to form a sulfonic acid salt, and finally converted to a proton acid form with an acid such as hydrochloric acid, whereby sulfonation can be performed.
[0038]
The electrolyte membrane of the present invention can be preferably used for a polymer electrolyte fuel cell, particularly for a direct methanol fuel cell. When an electrolyte membrane is used in such a fuel cell, an electrolyte membrane-electrode assembly (MEA) is formed by sandwiching the electrolyte membrane between two electrodes provided with a catalyst typified by platinum by a heat press, etc. It is widely known that the electrolyte membrane according to the present invention is used by incorporating it into a battery cell, and an MEA can be prepared in the same manner as the electrolyte membrane according to the present invention and used by incorporating it into a fuel cell.
[0039]
[Action]
Since the electrolyte membrane of the present invention is filled with a polymer having proton conductivity in a porous substrate made of a material that is not easily deformed by an external force, the filled polymer tends to swell with water or methanol. Can also be physically suppressed, and the permeation of methanol can be suppressed. Further, since the polymerization reaction of the polymer precursor is not a radical reaction, the polymerizability is not changed by the influence of oxygen in the air or oxygen dissolved in the polymer precursor, and the productivity is high. In addition, since the filled polymer has many cross-linking points, even if free radicals are generated in the polymer, the polymer does not reach the whole and does not depolymerize due to radicals. Since it can maintain its shape, it has high durability and can be preferably used for a polymer electrolyte fuel cell, particularly a direct methanol fuel cell.
[0040]
【Example】
(Example 1)
A cross-linked polyethylene membrane (size 5 cm × 6 cm, thickness 16 μm, porosity 40%, average pore diameter about 0.1 μm) was used as a porous substrate. As the epoxy group-containing compound, 4.5 g of phenyl glycidyl ether and 3.4 g of ethylene glycol diglycidyl ether were used, and the film was immersed in a polymer precursor solution obtained by mixing 0.6 g of 2-ethyl-4-methylimidazole, The precursor liquid was filled. Next, after the film was pulled out of the liquid, the film was sandwiched between polytetrafluoroethylene sheets and left in an oven heated to 120 ° C. for 2 hours to polymerize the polymer precursor inside the pores. After the completion of the polymerization step, the membrane was taken out, immersed in 30 ml of 1,2-dichloroethane, and cooled to about 1 ° C. with an ice bath. While stirring the container in which the membrane was immersed, 71 ml of a 1,2-dichloroethane solution of chlorosulfonic acid diluted to 1% by volume was added dropwise over 10 minutes, and stirring was continued for 20 minutes after completion of the dropwise addition. Next, the stirring was stopped, the membrane was taken out, washed three times with 1,2-dichloroethane, and air-dried. Next, this film was immersed in a 1N aqueous solution of potassium hydroxide at room temperature for 20 hours and washed with water. Finally, the polymer was immersed in a 1N aqueous hydrochloric acid solution for 2 hours, and the excess polymer adhering to the surface was scraped off with a plastic spatula, washed with distilled water, and dried to obtain an electrolyte membrane. Table 1 summarizes the evaluation results of the obtained electrolyte membranes.
[0041]
(Example 2)
The electrolyte membrane was prepared in the same manner as in Example 1 except that the epoxy group-containing compound was changed to 4.5 g of phenyl glycidyl ether and 6.1 g of bisphenol F diglycidyl ether (trade name: Epicoat 807, manufactured by Yuka Shell Epoxy Co., Ltd.). Created and evaluated. Table 1 shows the results.
[0042]
(Example 3)
Using the porous substrate used in Example 1, 5.8 g of 3-ethyl-3- (phenoxymethyl) oxetane (trade name: Alonoxetane OXT-211 manufactured by Toagosei Co., Ltd.) as a polymer precursor 6.0 g of 3,3-bis [(3-ethyloxetane-3-yl) methoxy] benzene (trade name: Alonoxetane RSOX, manufactured by Toagosei Co., Ltd.) and a photoacid generator (trade name, manufactured by Asahi Denka Co., Ltd.) A polymer precursor was filled in the same manner as in Example 1 using a mixed solution consisting of 0.12 g of Adeka Optomer SP150). After filling the polymer precursor, sandwiched by a PET film having a thickness of 25 μm, ultraviolet rays were irradiated with a high-pressure mercury lamp at 1000 mJ / cm. ² The polymerization was performed by irradiation. After the polymerization step, an electrolyte membrane was prepared according to Example 1 and evaluated. Table 1 shows the results.
[0043]
(Example 4)
Using the porous substrate used in Example 1, 5.8 g of 3-ethyl-3- (phenoxymethyl) oxetane (trade name: Alonoxetane OXT-211 manufactured by Toagosei Co., Ltd.) as a polymer precursor 6.5 g of 4,4-bis {[(3-ethyloxetane-3-yl) methoxy] methyl} benzene (produced by Toagosei Co., Ltd., trade name: Aronoxetane OXT-121) and a photoacid generator (Asahi Denka Co., Ltd.) The polymer precursor was filled in the same manner as in Example 1 using a mixed solution consisting of 0.12 g of Adeka Optomer SP150 (trade name). After filling the polymer precursor, sandwich it with a PET film having a thickness of 25 μm, and apply ultraviolet light with a high-pressure mercury lamp at 1000 mJ / cm. ² The polymerization was performed by irradiation. After the polymerization step, an electrolyte membrane was prepared according to Example 1 and evaluated. Table 1 shows the results.
[0044]
Example 5 Confirmation of Effect of Compound of Chemical Formula (a)
An electrolyte membrane was prepared and evaluated according to Example 1 except that the epoxy group-containing compound was changed to 3.6 g of styrene oxide and 3.4 g of ethylene glycol diglycidyl ether. The ion exchange capacity was 0.1 meq. / G, and the function as an electrolyte membrane was extremely low. For this reason, when 6.1 g of bisphenol F diglycidyl ether (trade name: Epicoat 807, manufactured by Yuka Shell Epoxy Co., Ltd.) was used instead of ethylene glycol diglycidyl ether, it was found that sulfonic acid was introduced and functioned as an electrolyte membrane. . For this reason, it was found that introduction of a sulfonic acid group easily occurs in a compound having the structure of the chemical formula (a). Styrene oxide having no structure represented by the chemical formula (a) is not suitable for sulfonic acid introduction, but can be preferably used as a copolymerization component. Table 1 shows the evaluation results of the latter film among the films prepared in this example.
[0045]
(Comparative Example 1)
Using the porous substrate (membrane) used in Example 1, 10 g of 2-acrylamido-2-methylpropanesulfonic acid, 0.1 g of N, N'-methylenebisacrylamide, 0.001 g of nonionic surfactant, After nitrogen gas was blown into an aqueous solution of a polymer precursor composed of 0.001 g of ammonium sulfate (hydrogen abstraction type photopolymerization initiator) and 10 g of water to remove oxygen, the film was immersed and filled with the aqueous solution. Then, after the film was pulled out of the solution, the film was sandwiched between glass and left in an oven heated to 80 ° C. for 2 hours to polymerize the polymer precursor inside the pores. Table 1 shows the results of evaluation of the obtained film.
[0046]
(Comparative Example 2)
Table 1 shows the results of evaluation of a commercially available electrolyte membrane made of perfluoroalkylsulfonic acid (manufactured by DuPont, trade name: Nafion 115).
[0047]
[Table 1]

[0048]
(Evaluation method of electrolyte membrane)
(1) Ion exchange capacity
The obtained electrolyte membrane was immersed in 20 ml of a 0.01N sodium hydroxide aqueous solution, sealed tightly, left at 50 ° C. for 2 hours, cooled to room temperature, and then taken out. When removing the membrane, the membrane was washed several times with distilled water and added to the remaining aqueous sodium hydroxide solution. This solution was titrated with a 0.01 N hydrochloric acid aqueous solution, and the number of moles of consumed hydrochloric acid was divided by the dry weight of the electrolyte membrane to obtain an ion exchange capacity.
(2) Proton conductivity
The conductivity of the swollen sample at 25 ° C. was measured. The electrolyte membrane swelled by immersion in pure water for 1 hour was sandwiched between two platinum plates to obtain a measurement sample. Thereafter, an alternating current impedance measurement from 100 Hz to 40 MHz was performed to measure the conductivity.
(3) Methanol permeability
A penetration experiment at 25 ° C. was performed as follows. The electrolyte membrane was sandwiched between dialysis glass cells, and one cell was charged with a 10% aqueous methanol solution, and the other cell was charged with pure water. The amount of methanol permeating into the pure water side was measured over time by gas chromatography analysis, and the permeation coefficient at the time of steady state was measured. Low transmission coefficient ((transmission coefficient) ^-1 The larger the value, the more difficult it is for methanol to permeate through the electrolyte membrane, indicating that it is more suitable for use in fuel cells.
4) Durability (compulsory deterioration test)
An aqueous solution containing 0.5% hydrogen peroxide and 0.005% ferric sulfate heptahydrate was prepared to evaluate by forced deterioration instead of confirming the polymer deterioration phenomenon due to hydrogen peroxide generated in the battery. Then, the electrolyte membrane was immersed therein, left at 70 ° C. for 2 hours, and then pulled up. From the weight change before and after the test, the residual ratio of the filled polymer in the electrolyte membrane was determined. The smaller the residual ratio, the quicker the deterioration when operating as a battery, and the larger the residual ratio, the less the deterioration. In each of the examples, it was confirmed that the deterioration was smaller than that of the comparative example 1.
(5) Area change rate in methanol aqueous solution
After vacuum drying the electrolyte membrane at 70 ° C. for 2 hours and measuring the area, it was immersed in a 10% aqueous methanol solution at 25 ° C. for 1 hour to measure the area. The area change rate was determined by the following equation.
Area change rate = 100 × (area after swelling of aqueous methanol solution−area when dried) / area when dried
[0049]
(Example 6)
In order to confirm that the obtained membrane functions as a fuel cell, the membrane prepared in Example 1 was incorporated into a DMFC cell and evaluated.
Platinum-supported carbon (Tanaka Kikinzoku Kogyo Co., Ltd .: TEC10E50E) is used for the oxygen electrode, and platinum-ruthenium alloy-carrying carbon (Tanaka Kikinzoku Kogyo Co., Ltd .: TEC61E54) is used for the fuel electrode. A molecular electrolyte solution (manufactured by DuPont: Nafion 5% solution) and polytetrafluoroethylene dispersion were blended, water was appropriately added and the mixture was stirred to obtain a coating for a reaction layer. This was printed on one side of carbon paper (TGP-H-060, manufactured by Toray Industries, Inc.) by screen printing and dried to form electrodes. At that time, the amount of platinum on the oxygen electrode side was 1 mg / cm. ² The total amount of platinum and ruthenium on the fuel electrode side is 3 mg / cm ² And These were superimposed on the central part of the electrolyte membrane obtained in Example 1 with the paint surface inside, and heated and pressed at 120 ° C. to produce a membrane electrode assembly (MEA) for a fuel cell. This was installed in a DMFC single cell and operated, and the performance was confirmed. The DMFC operation conditions were as follows: the cell temperature was 50 ° C., a 2 mol / l aqueous methanol solution was supplied to the fuel electrode at 10 ml / min, and pure oxygen was supplied to the oxygen electrode at 100 ml / min. The voltage was read while increasing the current value to obtain a current density-voltage curve of FIG.
[0050]
【The invention's effect】
The electrolyte membrane of the present invention overcomes the problem of methanol permeation, which has been a problem when a polyperfluorosulfonic acid-based electrolyte membrane conventionally used for fuel cell electrolyte membranes is used for DMFC, and furthermore, a hydrocarbon-based Use of the polymer improves productivity because there is no effect of polymerization inhibition due to oxygen at the time of film formation, which has been a problem. In addition, durability can be improved.
This is because the pores of a porous substrate having sufficient strength and elastic modulus are filled with a cross-linked polymer having proton conductivity, which makes it difficult for water and methanol to permeate. This is because the structure prevents the filled polymer from decomposing and dropping out of the pores during operation of the fuel cell.
For these reasons, the electrolyte membrane of the present invention has both output characteristics and durability as a fuel cell, and is extremely useful as a fuel cell or the like.
[Brief description of the drawings]
FIG. 1 is a graph showing a current density-voltage curve in a fuel cell of Example 6.

Claims (8)

An electrolyte characterized in that a crosslinked polymer containing an epoxy group-containing compound or an oxetanyl group-containing compound as a component is filled in pores of a porous substrate, and the crosslinked polymer has an ion exchange group. film. The electrolyte membrane according to claim 1, which is obtained by a manufacturing method including the following steps.
(1) A monomer or a mixture thereof containing an epoxy group-containing compound or an oxetanyl group-containing compound at least partially having a site into which an ion exchange group can be introduced, or an epoxy group-containing compound or an oxetanyl group A step of filling a mixture of a compound containing a compound and a curing agent of these compounds having a site into which an ion exchange group can be introduced into pores of a porous substrate (2) a step of polymerizing the monomer (3) Step of introducing ion exchange groups into polymer in pores 3. The electrolyte membrane according to claim 2, wherein the polymerization of the monomer is performed by heating at a temperature of 150 ° C. or less or by irradiation with active energy rays. 4. 4. The electrolyte membrane according to claim 1, wherein the porous substrate is made of a polyolefin. The electrolyte membrane according to any one of claims 1 to 4, wherein the crosslinked polymer is obtained using an epoxy group-containing compound as a constituent component and using an imidazole derivative as a polymerization catalyst. The electrolyte membrane according to any one of claims 1 to 4, wherein the crosslinked polymer is obtained using an oxetanyl group-containing compound as a constituent component and a photoacid generator as a polymerization catalyst. 7. The electrolyte membrane according to claim 1, wherein at least a part of the epoxy group-containing compound or the oxetanyl group-containing compound has a structure represented by the following chemical formula (a).

Here, A is a group having an epoxy group or an oxetanyl group containing an oxygen atom, and A has one or more benzene rings, and when there are a plurality of them, they may be the same or different. X is hydrogen or a methyl group, and Y is hydrogen, a methyl group or an ethyl group. At least one of R is hydrogen, the other represents hydrogen or a functional group, and one of R is bonded to another benzene ring directly or through another atom or an atom chain. good. A plurality of Rs may be the same or different. n is an integer of 1 to 5. A fuel cell using the electrolyte membrane according to claim 1.

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