JP2004158261A

JP2004158261A - Proton-conductive material, film/electrode joint body, and fuel cell

Info

Publication number: JP2004158261A
Application number: JP2002321630A
Authority: JP
Inventors: Atsushi Gamachi; 厚志蒲地; Yoichi Asano; 洋一浅野
Original assignee: Honda Motor Co Ltd
Current assignee: Honda Motor Co Ltd
Priority date: 2002-11-05
Filing date: 2002-11-05
Publication date: 2004-06-03

Abstract

<P>PROBLEM TO BE SOLVED: To provide a proton-conductive material excellent in proton conductivity, a film/electrode joint body excellent in proton conductivity and mechanical strength, and a fuel cell with a small voltage drop and is capable of reducing the catalyst metal quantity. <P>SOLUTION: A proton-conductive film having excellent proton conductivity and high mechanical strength is provided by combining a polymer compound having an ion exchange group with a sulfuric acid-supporting metal oxide. By using the proton-conductive film as an electrolyte film and by using the sulfuric acid-supporting metal oxide for a proton conducting constituent in an electrode, a fuel cell capable of reducing voltage drop and having high output power can be provided. The proton-conductive material contains the polymer compound having an ion exchange group and the sulfuric acid-supporting metal oxide. <P>COPYRIGHT: (C)2004,JPO

Description

【０００１】
【発明の属する技術分野】
本発明はプロトン伝導性材料、それを用いた膜・電極接合体及び燃料電池に関する。
【０００２】
【従来の技術】
石油資源の枯渇化と地球温暖化等の環境問題の深刻化により、クリーンな電動機用電力源として燃料電池が注目され、広範に開発されているとともに、一部実用化もされている。特に電解質としてイオン交換樹脂膜を用いた固体高分子型燃料電池は、自動車用燃料電池等として活発に研究されている。このイオン交換樹脂膜は、膜・電極接合体（ＭＥＡ）を構成し、燃料電池の性能を決める最も重要な部品の一つである。
【０００３】
燃料電池の最も重要な性能の一つとして出力電力が挙げられる。燃料電池の起電圧は発電時に生じる電圧降下により、実際には理論起電圧の５０〜６０％に低下するため、燃料電池の電圧としてはまだ不十分である。電圧降下の原因としては、触媒電極やその周辺部材の構造等による活性化過電圧、燃料電池の構成部材や電力を取り出す集電部の抵抗による抵抗過電圧、反応ガスの水素及び酸素の供給や反応により生成する水の影響による濃度過電圧等が挙げられる。これらの電圧降下を削減して出力電力を向上させること、さらに主要な触媒金属である白金の使用量を大幅に低減することが重要な課題となる。
【０００４】
このため、燃料電池の電解質膜のプロトン伝導性を高めることにより出力電力を向上させることが検討されている（例えば、特許文献１〜３参照。）。燃料電池の電解質膜としては、一般にナフィオンに代表されるパーフルオロアルキレンスルホン酸系高分子化合物等のフッ素系樹脂膜やスルホン化ポリエーテルエーテルケトンの非フッ素系樹脂膜が提案されている。また、電池内にはプロトン伝導ネットワークを形成するため電解質膜と同じプロトン伝導性材料が含まれている。これらのプロトン伝導性材料はイオン伝導性に優れ、特定の温度領域で１０^−３〜１０^−１Ｓ／ｃｍのプロトン伝導率を示すものが開発されている。しかしながら、室温から１００℃を超える広範囲にわたる温度領域で、安定して１０^−１Ｓ／ｃｍ以上の高プロトン伝導率を示す電解質膜はまだ開発されていない。
【０００５】
一般に無機材料は有機材料より耐熱性に優れ、無機材料の中にはリン酸縮合型のシリカガラスのように高伝導度を示すものが知られている。このような無機材料の特性を利用して、プロトン伝導性の高い材料が提案されている。例えば、金属水酸化物に硫酸を担持することにより室温から１００℃を超える広い温度範囲で高伝導率を示すプロトン伝導性材料が開示されている（特許文献４参照。）。しかし、このような無機材料からなるプロトン伝導性材料は極めて脆いため、燃料電池の膜・電極接合体（ＭＥＡ）として用いる場合、燃料電池に加わる応力等により容易に破損するという問題が生じる。
【０００６】
【特許文献１】
特開２００２−２０３５６８号公報
【特許文献２】
特開２００１−６４４１７号公報
【特許文献３】
特開平８−２６４１９０号公報
【特許文献４】
特開２００２−２１６５３７号公報
【０００７】
【発明が解決しようとする課題】
従って本発明の目的は、プロトン伝導性に優れたプロトン伝導性材料、プロトン伝導性及び機械的強度に優れた膜・電極接合体、及び電圧降下が少なく触媒金属量を低減することができる燃料電池を提供することである。
【０００８】
【課題を解決するための手段】
上記目的に鑑み鋭意研究の結果、本発明者らは、硫酸担持金属酸化物のプロトン伝導性に着目し、イオン交換基を有する高分子化合物と硫酸担持金属酸化物を複合化することによりプロトン伝導性に優れ、機械的強度の高いプロトン伝導性膜が得られること、このプロトン伝導性膜を電解質膜として用いるとともに、電極内のプロトン伝導成分に硫酸担持金属酸化物を用いることにより、電圧降下が低減され、出力電力の高い燃料電池が得られることを発見し、本発明に想到した。
【０００９】
すなわち、本発明のプロトン伝導性材料は、イオン交換基を有する高分子化合物と、硫酸担持金属酸化物とを含むことを特徴とする。
【００１０】
前記硫酸担持金属酸化物の硫酸分の硫黄（Ｓ）と、担体である金属水酸化物及び／又は金属酸化物を構成する金属元素（Ｍ）とのモル比Ｓ／Ｍが０．０００１〜１．５であるのが好ましく、０．０１〜１であるのが特に好ましい。前記硫酸担持金属酸化物は、ジルコニウム、チタン、鉄、錫、シリコン、アルミニウム、モリブデン、及びタングステンからなる群から選ばれた少なくとも１種の元素を含むのが好ましい。また、プロトン伝導性材料に含まれる硫酸担持金属酸化物の量は、プロトン伝導性材料の質量を１００質量％としたときに、０．５〜５０質量％であるのが好ましい。
【００１１】
電解質膜の両面に触媒電極が形成された本発明の膜・電極接合体は、電解質膜及び／又は触媒電極に上記プロトン伝導性材料を用いる。電解質膜に上記プロトン伝導性材料を用いる場合、硫酸担持金属酸化物は電解質膜の少なくとも一方の面に偏在している構造とすることができる。触媒電極に上記プロトン伝導性材料を用いる場合、触媒電極は触媒粒子、ガス拡散層、及び上記プロトン伝導性材料を含む。触媒電極に含まれる硫酸担持金属酸化物は、触媒電極の電解質膜と接する面に偏在している構造とすることができる。上記膜・電極接合体を用いた燃料電池は発電時の電圧降下が低減され、出力電力を向上させることが可能である。
【００１２】
【発明の実施の形態】
［１］プロトン伝導性材料
（１）硫酸担持金属酸化物
硫酸担持金属酸化物は金属水酸化物及び／又は金属酸化物からなる担体に硫酸が担持したものである。ここで、硫酸担持金属酸化物の硫酸（ＳＡ）とは、Ｈ_２ＳＯ_４及びその化合物に限られず、ＳＯ、Ｓ_２Ｏ_３、ＳＯ_２、ＳＯ_３、Ｓ_２Ｏ_７、ＳＯ_４、これらの酸化イオウを含む化合物（酸、塩等）、及びこれらの混合物を意味する。
【００１３】
担体となる金属水酸化物及び／又は金属酸化物は、硫酸を担持することにより固体酸となるものであればよい。中でも硫酸担持金属酸化物ＳＡ／ＭｘＯｙの酸強度が大きいジルコニウム、チタン、鉄、錫、シリコン、アルミニウム、モリブデン、及びタングステンの各酸化物を用いるのが好ましい。これらは単独で用いても２種以上を併用してもよい。
【００１４】
プロトンの解離度は酸強度として表現でき、固体酸の酸強度はＨａｍｍｅｔｔの酸度関数Ｈ_０として表され、硫酸の場合Ｈ_０は−１１．９３である。本発明において固体超強酸性とはＨ_０＜−１１．９３の範囲内となる性質のものをいう。高プロトン伝導率を示す硫酸担持金属酸化物は、固体超強酸性を発現する金属元素と硫酸との組み合わせが好ましく、金属元素としては、ジルコニウム、チタン、鉄、錫、シリコン及びアルミニウムからなる群から選ばれた金属元素が好ましい（Ｋ．Ａｒａｔａ等による「ジャーナル・オブ・ジ・アメリカン・ケミカル・ソサイエティ（ＪｏｕｒｎａｌｏｆｔｈｅＡｍｅｒｉｃａｎＣｈｅｍｉｃａｌＳｏｃｉｅｔｙ）」，１９７９年，第１０１巻，ｐ．６４３９〜。）。
【００１５】
本発明に用いる硫酸担持金属酸化物は、好ましくは金属酸化物及び／又は金属水酸化物と硫酸との反応により合成される化合物である。ただし、硫酸担持金属酸化物の合成法はこれに限るものではない。硫酸と金属酸化物又は金属水酸化物との反応を進行させるため３００℃以上、好ましくは５００℃以上で熱処理を施す。熱処理を施すことにより、その熱処理温度までは耐熱性が向上し、固体電解質の使用温度領域が広がる。
【００１６】
硫酸担持金属酸化物の硫酸分に由来する硫黄（Ｓ）と、担体である金属水酸化物及び／又は金属酸化物を構成する金属元素（Ｍ）とのモル比Ｓ／Ｍは、０．０００１〜１．５が好ましく、０．００１〜１がより好ましく、０．０１〜１の範囲内がさらに好ましい。０．０１以下では担持の効果が低くなる場合があり、また１を超えるとプロトン伝導率の向上が見られないおそれがある。
【００１７】
プロトン伝導性材料に用いる硫酸担持金属酸化物としては、２種以上の元素からなる硫酸担持金属酸化物であってよい。この場合複合金属酸化物の硫酸担持物、又は硫酸担持金属酸化物の混合物でもよい。
【００１８】
硫酸担持金属酸化物は金属酸化物粒子（セラミックス粒子）に硫酸を担持することにより製造することができる。例えば、酸化ジルコニウムＺｒＯ_２にＣａＯ、Ｙ_２Ｏ_３等を添加して作製したセラミックス粒子を硫酸処理することにより、靱性に優れたプロトン伝導性固体電解質粒子を製造することができる。
【００１９】
（２）高分子化合物
本発明で用いる高分子化合物はイオン交換基を有する高分子化合物であり、公知のプロトン伝導性高分子化合物であってよい。例えば、パーフルオロアルキレンスルホン酸系高分子化合物（ナフィオン等）、スルホン化ポリエーテルエーテルケトン系高分子化合物、スルホン化ポリアリーレン系高分子化合物、スルホン化ポリエーテル系高分子化合物、スルホン化ポリスルフィド系高分子化合物、スルホン化ポリエーテルスルホン系高分子化合物、スルホン化ポリスルホン系高分子化合物、スルホン化ポリエーテルイミド系高分子化合物、スルホン化ポリベンズイミダゾール系高分子化合物等が挙げられる。これらは２種以上の混合物であってもよい。
【００２０】
（３）製造方法
本発明のプロトン伝導性材料は、上記のイオン交換基を有する高分子化合物と硫酸担持金属酸化物をミキサー等で混合して作製する。プロトン伝導性膜とする場合には、イオン交換基を有する高分子化合物を適当な溶媒に溶解し、これに硫酸担持金属酸化物粒子を添加し、十分に撹拌して均一に分散させた後支持体等に塗布して製膜するか、イオン交換基を有する高分子化合物と硫酸担持金属酸化物粒子を均一に混合した後、加熱し、軟らかくなった状態でスリットから押し出すことにより製膜することができる。硫酸担持金属酸化物粒子の含有量は、プロトン伝導性材料１００質量％に対し０．５〜５０質量％であるのが好ましく、２〜１０質量％であるのがより好ましい。０．５質量％未満ではプロトン伝導性が向上せず、５０質量％を超えるとプロトン伝導性材料が脆くなる。硫酸担持金属酸化物粒子は平均粒子径が０．０１〜５μｍが好ましく、０．０５〜１μｍがより好ましい。０．０１μｍ未満では硫酸担持金属酸化物粒子の製造が困難であり、５μｍを超えると均一なプロトン伝導性が得られない。
【００２１】
［２］膜・電極接合体
図１に示すように膜・電極接合体１は、触媒電極（アノード極１２及びカソード極１３）と電解質膜１１から構成される。触媒電極は、ガス拡散層１２ａ，１３ａと触媒層１２ｂ，１３ｂとからなり、ガス拡散層１２ａ，１３ａ上に、カーボンブラックに白金粒子又は白金合金粒子を担持してなる触媒粒子が塗布され、触媒層１２ｂ，１３ｂが形成される。膜・電極接合体１は、電解質膜１１の両側に触媒層１２ｂ，１３ｂが対向するようにアノード極１２とカソード極１３をホットプレスして作製するか、適当な支持体に触媒層１２ｂ，１３ｂを塗設したものを電解質膜１１に転写しながら圧着した後、ガス拡散層（多孔質導電材料）１２ａ，１３ａで挟み込んで作製する。
【００２２】
膜・電極接合体１は、電解質膜１１及び／又は触媒電極１２，１３に本発明のプロトン伝導性材料を用いる。電解質膜１１に用いる場合、プロトン伝導性を向上させる観点からは、硫酸担持金属酸化物が電解質膜１１の少なくとも一方の面に偏在する構造であるのが好ましい。また、電解質膜１１は単層に限られず、異なる膜を積層した複層膜であってもよい。複層膜の場合、例えば硫酸担持金属酸化物を含有する膜を触媒電極１２，１３と接する面に用いた複層膜とすることができる。本発明のプロトン伝導性材料を電解質膜１１以外の触媒電極１２，１３に添加しても、電解質膜１１に用いた場合と同様にプロトン伝導性を向上させることができる。その場合、硫酸担持金属酸化物は、少なくとも触媒電極の電解質膜と接する面に偏在しているのが好ましい。
【００２３】
［３］燃料電池
図２は、膜・電極接合体をセパレータに組み付けた燃料電池の一例を示す。アノード極側のセパレータ２１には燃料ガス流路２１ａが形成され、カソード極側のセパレータ２３には酸化剤ガス流路２３ａが形成されている。またセパレータの裏側には燃料電池を冷却するための冷媒流路２１ｂ，２３ｂが形成されている。シール性を確保するため、電解質膜１１の外縁部をセパレータ２１，２３で挟圧して、各種供給ガスの混合が生じない構造になっている。各セパレータの周辺部には、シール性を有する枠材２２が取り付けられており、電解質膜外縁部はシール性を有する枠材２２により挟持され、これによりセパレータとの間で十分なガスシール性が確保される。燃料電池のアノード極１２に水素等のガス燃料が供給され、カソード極１３に酸素、空気等の酸化剤ガスが供給され、電気化学的反応の進行により電気エネルギーが発生する。燃料電池は、通常図２に示す単位燃料電池が複数積層され、燃料電池スタックとして使用される。
【００２４】
【実施例】
本発明を以下の実施例によりさらに詳細に説明するが、本発明はそれらに限定されるものではない。
【００２５】
実施例１
（１）硫酸担持金属酸化物の作製
濃硫酸（９６％）０．５ｇに蒸留水を加え、総質量１００ｇの硫酸水溶液を調製した。この硫酸水溶液に酸化ジルコニウムＺｒＯ_２を２０ｇ添加し、３時間撹拌しスラリーを作製した。このスラリーを室温から５℃／分の昇温速度で１００℃まで加熱し、１００℃で３時間保持することにより水を除去した。次に１℃／分の昇温速度で２００℃まで加熱し２００℃で３時間保持することにより、白色の粉末を得た。この段階での質量減少はほとんどが水の揮発によるものであった。この白色の粉末をさらに１℃／分の昇温速度で５００℃まで加熱し、５００℃で３時間保持することにより、硫酸分の硫黄（Ｓ）と担体の酸化ジルコニウムを構成する金属元素Ｚｒとのモル比Ｓ／Ｚｒが０．００５である硫酸担持ジルコニア（ＳＡ／ＺｒＯ_２）の白色粉末を得た。得られた白色粉末の平均粒径は０．０７μｍであった。
【００２６】
（２）電解質膜（プロトン伝導性膜）の作製
プロトン伝導性材料１００質量％に対し、（１）で得られた硫酸担持ジルコニア（ＳＡ／ＺｒＯ_２）の含有量が５質量％となるように、スルホン化ポリエーテルエーテルケトンの溶液に硫酸担持ジルコニア（ＳＡ／ＺｒＯ_２）を加え、均一に分散するまでスターラーを用いて十分に混合した。得られた分散液をアプリケータを用いてガラス板上に塗布し、乾燥して厚さ２３μｍの膜を作製した。
【００２７】
（３）膜・電極接合体の作製
質量比で４：６のカーボンブラック及びポリテトラフルオロエチレン（ＰＴＦＥ）粒子をエチレングリコールに均一に分散させてなるスラリーをカーボンペーパーの片面に塗布し、乾燥させて下地層を形成し、カーボンペーパーと下地層からなるガス拡散層を作製した。得られたガス拡散層の下地層上に触媒ペーストをスクリーン印刷し、減圧乾燥してアノード極とカソード極を作製した。触媒ペーストはカーボンブラック（ファーネスブラック）に白金粒子を白金／カーボンの質量比が１：１になるように担持して触媒粒子とし、プロトン伝導成分としてナフィオン（デュポン社製）を使用し、ナフィオンの溶液中に触媒粒子を均一に混合して作製した。次に（２）で得られた電解質膜をアノード極及びカソード極で挟んだ後、１５０℃で１０分間ホットプレスし、膜・電極接合体を作製した。
【００２８】
（４）燃料電池の作製
（１）で得られた膜・電極接合体を、外縁部にシリコン系液状シール材（枠材）が塗布された一対のセパレータで挟んで圧着した。セパレータのアノード極側に燃料ガス（水素ガス）を供給するための流路、及びカソード極側に酸化剤ガス（空気）を供給するための流路を設けた。
【００２９】
（５）評価
得られた燃料電池を用い、電流密度を変化させたときのセル電位及びＩＲロスの変化を測定した。発電条件はセル出口圧力を大気圧、相対湿度をアノード、カソードともに５０％ＲＨ、セル温度を８０℃とした。結果を図３及び表１に示す。
【００３０】
実施例２
カソード電極のプロトン伝導成分のナフィオンにＳ／Ｚｒモル比が０．００５の硫酸担持ジルコニアをプロトン伝導成分１００質量％に対して５質量％になるように添加した以外、実施例１と同様にして燃料電池を作製した。実施例１と同様にして評価した結果を図３に示す。
【００３１】
実施例３〜８
硫酸担持ジルコニア（ＳＡ／ＺｒＯ_２）のＳ／Ｚｒモル比をそれぞれ０．０３、０．１、０．５、０．９、１．４及び２とした以外、実施例１と同様にして燃料電池を作製した。実施例１と同様にして測定した電流密度６００ｍＡ／ｃｍ^２におけるセル電位及びＩＲロスを表１に示し、Ｓ／Ｍモル比（Ｓ／Ｚｒモル比）に対するセル電位の変化を図４に示す。
【００３２】
実施例９〜１５
硫酸担持金属酸化物をそれぞれＳＡ／ＴｉＯ_２、ＳＡ／Ｆｅ_２Ｏ_３、ＳＡ／ＳｎＯ_２、ＳＡ／ＳｉＯ_２、ＳＡ／Ａｌ_２Ｏ_３、ＳＡ／ＭｏＯ_３、及びＳＡ／ＷＯ_３とし、Ｓ／Ｍモル比を０．５とした以外実施例１と同様にして燃料電池を作製した。実施例１と同様にして測定した電流密度６００ｍＡ／ｃｍ^２におけるセル電位及びＩＲロスを表２に示し、硫酸担持金属酸化物の種類とセル電位との関係を図５に示す。
【００３３】
実施例１６〜２２
プロトン伝導性材料１００質量％に対し、硫酸担持ジルコニア（ＳＡ／ＺｒＯ_２）の含有量がそれぞれ０．５、１、２、１０、３０、４５及び５２質量％となるように、スルホン化ポリエーテルエーテルケトンに硫酸担持ジルコニア（ＳＡ／ＺｒＯ_２）を加えた以外、実施例１と同様にして燃料電池を作製した。実施例１と同様にして測定した電流密度６００ｍＡ／ｃｍ^２におけるセル電位及びＩＲロスを表３に示し、硫酸担持ジルコニア（ＳＡ／ＺｒＯ_２）の含有量に対するセル電位の変化を図６に示す。
【００３４】
実施例２３
実施例１と同様にして、厚さ５μｍのスルホン化ポリエーテルエーテルケトンと硫酸担持ジルコニア（ＳＡ／ＺｒＯ_２）からなる電解質膜を作製した。作製した電解質膜２枚の間に厚さ１５μｍのスルホン化ポリエーテルエーテルケトン膜を挟んで積層し、加熱ロールで加圧・加熱して厚さ２３μｍの複合膜を作製した。得られた複合膜を用い、実施例１と同様にして燃料電池を作製した。実施例１と同様にして測定した電流密度６００ｍＡ／ｃｍ^２におけるセル電位及びＩＲロスを表４に示す。
【００３５】
実施例２４
カソード電極のプロトン伝導成分のナフィオンにＳ／Ｚｒモル比が０．５の硫酸担持ジルコニア（ＳＡ／ＺｒＯ_２）をプロトン伝導成分１００質量％に対して５質量％になるように添加した以外、実施例５と同様にして燃料電池を作製した。実施例１と同様にして測定した電流密度６００ｍＡ／ｃｍ^２におけるセル電位及びＩＲロスを表４に示す。
【００３６】
実施例２５
電解質膜として厚さ２３μｍのスルホン化ポリエーテルエーテルケトン膜を用い、カソード電極のプロトン伝導成分のナフィオンにＳ／Ｚｒモル比が０．５の硫酸担持ジルコニアをプロトン伝導成分１００質量％に対して５質量％になるように添加した以外、実施例５と同様にして燃料電池を作製した。実施例１と同様にして測定した電流密度６００ｍＡ／ｃｍ^２におけるセル電位及びＩＲロスを表４に示す。
【００３７】
比較例１
電解質膜としてスルホン化ポリエーテルエーテルケトンを使用した以外、実施例１と同様にして燃料電池を作製した。実施例１と同様にして評価した結果を図３及び表１に示す。
【００３８】
比較例２
プロトン伝導性材料として、プロトン伝導性材料１００質量％に対して酸化ジルコニア（ＺｒＯ_２）が５質量％となるようにスルホン化ポリエーテルエーテルケトンに対して酸化ジルコニア（ＺｒＯ_２）を混合したものを用いた以外、実施例１と同様にして燃料電池を作製した。実施例１と同様にして測定した電流密度６００ｍＡ／ｃｍ^２におけるセル電位及びＩＲロスを表１に示す。
【００３９】
【表１】

【００４０】
【表２】

【００４１】
【表３】

【００４２】
【表４】

【００４３】
（評価）
図３に示すように、硫酸担持金属酸化物として硫酸担持ジルコニア（ＳＡ／ＺｒＯ_２）を電解質膜に用いた場合（実施例１）、及び硫酸担持ジルコニア（ＳＡ／ＺｒＯ_２）を電解質膜と触媒電極に用いた場合（実施例２）は、硫酸担持金属酸化物を添加しなかった場合（比較例１）に比較し、ＩＲロスがほぼ同じであるのに対し、セル電位は低電流域から高電流域まで高い値を示した。これは硫酸担持ジルコニアを添加した場合の活性化過電圧（膜と電極との界面での抵抗）が小さいことによる。また、表１に示すように硫酸担持ジルコニア（ＳＡ／ＺｒＯ_２）をＳ／Ｍモル比が０．００５〜２の範囲で用いた場合（実施例１〜８）、硫酸担持金属酸化物を添加しなかった場合（比較例１）や金属酸化物（ＺｒＯ_２）のみ（Ｓ／Ｍモル比０）を添加した場合（比較例２）に比較し、高いセル電位を示した。
【００４４】
表２に示すように硫酸担持金属酸化物の金属酸化物としてＺｒＯ_２、ＴｉＯ_２、Ｆｅ_２Ｏ_３、ＳｎＯ_２、ＳｉＯ_２、Ａｌ_２Ｏ_３、ＭｏＯ_３及びＷＯ_３を用いた場合、いずれも高いセル電位を示した。これらの金属酸化物を担体として用いることにより高いプロトン伝導性が得られることがわかる。
【００４５】
表３に示すようにプロトン伝導性材料の質量を１００質量％としたときに、硫酸担持ジルコニア（ＳＡ／ＺｒＯ_２）の含有量が０．５〜４５質量％の範囲で高いセル電位を示した（実施例１６〜２１）。なお、硫酸担持ジルコニア（ＳＡ／ＺｒＯ_２）の含有量が５０質量％を超えると成膜が困難になるため、実施例２２ではセル電圧を測定できなかった。
【００４６】
表４に示すように、膜・電極接合体は、電解質膜（単層膜又は複層膜）のみに硫酸担持金属酸化物を含有する構成（実施例２３）、触媒電極のみに硫酸担持金属酸化物を含有する構成（実施例２５）、及び電解質膜と触媒電極の両方に硫酸担持金属酸化物を含有する構成（実施例２４）のいずれも高いセル電圧を示した。
【００４７】
【発明の効果】
上記の通り、本発明のプロトン伝導性材料は、イオン交換基を有する高分子化合物と硫酸担持金属酸化物とを含むので、高いプロトン伝導性を有する。そのため燃料電池に用いた場合に、電圧降下を削減し出力電力を向上させることが可能である。
【図面の簡単な説明】
【図１】本発明の膜・電極接合体（ＭＥＡ）の一例を示す概略断面図である。
【図２】本発明の膜・電極接合体（ＭＥＡ）を一対のセパレータで挟持した状態を示す概略断面図である。
【図３】実施例１、２及び比較例１の燃料電池を用いたときの電流密度に対するセル電位及びＩＲロスの変化を示すグラフである。
【図４】実施例３〜８の燃料電池を用いたときの硫酸担持ジルコニア（ＳＡ／ＺｒＯ_２）のＳ／Ｚｒモル比に対するセル電位の変化を示すグラフである。
【図５】実施例９〜１５の燃料電池を用いたときの硫酸担持金属酸化物の種類とセル電位との関係を示すグラフである。
【図６】実施例１６〜２２の燃料電池を用いたときの硫酸担持ジルコニア（ＳＡ／ＺｒＯ_２）の含有量に対するセル電位の変化を示すグラフである。
【符号の説明】
１・・・膜・電極接合体（ＭＥＡ）
１１・・・電解質膜
１２・・・アノード電極
１２ａ・・・ガス拡散層
１２ｂ・・・触媒層
１３・・・カソード電極
１３ａ・・・ガス拡散層
１３ｂ・・・触媒層
２１，２３・・・セパレータ
２２・・・シール材（枠材）[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a proton conductive material, a membrane / electrode assembly using the same, and a fuel cell.
[0002]
[Prior art]
Due to the depletion of petroleum resources and the seriousness of environmental problems such as global warming, fuel cells have attracted attention as a clean electric power source for electric motors, and have been widely developed and partially put into practical use. In particular, polymer electrolyte fuel cells using an ion exchange resin membrane as an electrolyte are being actively studied as fuel cells for automobiles and the like. This ion exchange resin membrane constitutes a membrane-electrode assembly (MEA) and is one of the most important parts that determine the performance of the fuel cell.
[0003]
One of the most important performances of a fuel cell is output power. The electromotive voltage of the fuel cell is actually reduced to 50 to 60% of the theoretical electromotive voltage due to a voltage drop generated at the time of power generation. Therefore, the voltage of the fuel cell is still insufficient. Causes of the voltage drop include activation overvoltage due to the structure of the catalyst electrode and its surrounding members, etc., resistance overvoltage due to the resistance of the fuel cell components and the current collection unit that extracts power, and the supply and reaction of hydrogen and oxygen in the reaction gas. There is a concentration overpotential due to the effect of generated water. It is important to reduce these voltage drops to improve the output power and to significantly reduce the amount of platinum, which is a major catalyst metal, in use.
[0004]
Therefore, it has been studied to improve the output power by increasing the proton conductivity of the electrolyte membrane of the fuel cell (for example, refer to Patent Documents 1 to 3). As an electrolyte membrane for a fuel cell, a fluorine-based resin membrane such as a perfluoroalkylenesulfonic acid-based polymer compound represented by Nafion or a non-fluorine-based resin membrane of sulfonated polyetheretherketone has been proposed. In addition, the same proton conductive material as the electrolyte membrane is included in the battery to form a proton conductive network. These proton conductive materials have been developed which have excellent ion conductivity and exhibit a proton conductivity of 10 ^-3 to 10 ^-1 S / cm in a specific temperature range. However, an electrolyte membrane exhibiting a stable high proton conductivity of 10 ⁻¹ S / cm or more in a wide temperature range from room temperature to over 100 ° C. has not been developed yet.
[0005]
In general, inorganic materials have higher heat resistance than organic materials, and some inorganic materials having high conductivity such as phosphoric acid condensation type silica glass are known. A material having high proton conductivity has been proposed by utilizing such characteristics of the inorganic material. For example, a proton conductive material that exhibits high conductivity in a wide temperature range from room temperature to over 100 ° C. by supporting sulfuric acid on a metal hydroxide has been disclosed (see Patent Document 4). However, since the proton conductive material made of such an inorganic material is extremely brittle, when it is used as a membrane-electrode assembly (MEA) for a fuel cell, there is a problem that the material is easily damaged by stress applied to the fuel cell.
[0006]
[Patent Document 1]
Japanese Patent Application Laid-Open No. 2002-203568 [Patent Document 2]
JP 2001-64417 A [Patent Document 3]
JP-A-8-264190 [Patent Document 4]
Japanese Patent Application Laid-Open No. 2002-216537
[Problems to be solved by the invention]
Accordingly, an object of the present invention is to provide a proton conductive material having excellent proton conductivity, a membrane / electrode assembly having excellent proton conductivity and mechanical strength, and a fuel cell capable of reducing the amount of catalytic metal with a small voltage drop. It is to provide.
[0008]
[Means for Solving the Problems]
In light of the above-mentioned objects, as a result of intensive research, the present inventors focused on the proton conductivity of the sulfuric acid-supported metal oxide, and produced a proton conductive material by complexing the polymer compound having an ion exchange group with the sulfuric acid-supporting metal oxide. It is possible to obtain a proton conductive membrane with excellent mechanical properties and high mechanical strength, and by using this proton conductive membrane as an electrolyte membrane and using a metal oxide supporting sulfuric acid as the proton conductive component in the electrode, the voltage drop is reduced. The inventors have found that a fuel cell with reduced output power and high output power can be obtained, and have reached the present invention.
[0009]
That is, the proton conductive material of the present invention is characterized by containing a polymer compound having an ion exchange group and a metal oxide supporting sulfuric acid.
[0010]
The molar ratio S / M of sulfur (S) of the sulfuric acid content of the sulfuric acid-supporting metal oxide to the metal hydroxide and / or metal element (M) constituting the metal oxide is 0.0001 to 1 .5, particularly preferably 0.01-1. The sulfuric acid-supporting metal oxide preferably contains at least one element selected from the group consisting of zirconium, titanium, iron, tin, silicon, aluminum, molybdenum, and tungsten. Further, the amount of the sulfuric acid-supporting metal oxide contained in the proton conductive material is preferably 0.5 to 50% by mass when the mass of the proton conductive material is 100% by mass.
[0011]
The membrane-electrode assembly of the present invention in which the catalyst electrodes are formed on both sides of the electrolyte membrane uses the above-mentioned proton conductive material for the electrolyte membrane and / or the catalyst electrodes. When the above-mentioned proton conductive material is used for the electrolyte membrane, a structure in which the sulfuric acid-supporting metal oxide is unevenly distributed on at least one surface of the electrolyte membrane can be employed. When the above-mentioned proton conductive material is used for the catalyst electrode, the catalyst electrode contains catalyst particles, a gas diffusion layer, and the above-mentioned proton conductive material. The sulfuric acid-carrying metal oxide contained in the catalyst electrode may have a structure unevenly distributed on the surface of the catalyst electrode in contact with the electrolyte membrane. In a fuel cell using the above-mentioned membrane-electrode assembly, a voltage drop during power generation is reduced, and output power can be improved.
[0012]
BEST MODE FOR CARRYING OUT THE INVENTION
[1] Proton conductive material (1) Sulfuric acid-supported metal oxide Sulfuric acid-supported metal oxide is obtained by supporting sulfuric acid on a support made of metal hydroxide and / or metal oxide. Here, the sulfuric acid (SA) of the sulfuric acid-supporting metal oxide is not limited to H ₂ SO ₄ and its compounds, but may be SO, S ₂ O ₃ , SO ₂ , SO ₃ , S ₂ O ₇ , SO ₄ , Compounds containing sulfur oxides (acids, salts, etc.) and mixtures thereof.
[0013]
The metal hydroxide and / or metal oxide serving as a carrier may be any as long as it becomes a solid acid by supporting sulfuric acid. Among them, it is preferable to use zirconium, titanium, iron, tin, silicon, aluminum, molybdenum, and tungsten oxides each having a large acid strength of the sulfuric acid-supporting metal oxide SA / MxOy. These may be used alone or in combination of two or more.
[0014]
The degree of proton dissociation can be expressed as an acid strength, and the acid strength of a solid acid is expressed as Hammett's acidity function H ₀ , and in the case of sulfuric acid, H ₀ is −11.93. In the present invention, the solid superacidity refers to a material having a property of being in the range of H ₀ <-11.93. Sulfuric acid-supporting metal oxides exhibiting high proton conductivity are preferably a combination of a metal element exhibiting solid superacidity and sulfuric acid, and the metal element is selected from the group consisting of zirconium, titanium, iron, tin, silicon, and aluminum. Selected metal elements are preferred (K. Arata et al., "Journal of the American Chemical Society", 1979, vol. 101, p. 6439-).
[0015]
The sulfuric acid-supporting metal oxide used in the present invention is preferably a compound synthesized by the reaction of a metal oxide and / or a metal hydroxide with sulfuric acid. However, the method for synthesizing the sulfuric acid-supporting metal oxide is not limited to this. Heat treatment is performed at 300 ° C. or higher, preferably 500 ° C. or higher to promote the reaction between sulfuric acid and the metal oxide or metal hydroxide. By performing the heat treatment, the heat resistance is improved up to the heat treatment temperature, and the operating temperature range of the solid electrolyte is widened.
[0016]
The molar ratio S / M of sulfur (S) derived from the sulfuric acid content of the sulfuric acid-supporting metal oxide to the metal hydroxide and / or metal element (M) constituting the metal oxide is 0.0001. -1.5 is preferred, 0.001-1 is more preferred, and the range of 0.01-1 is still more preferred. If it is less than 0.01, the effect of the loading may be reduced, and if it exceeds 1, the proton conductivity may not be improved.
[0017]
The sulfuric acid-supporting metal oxide used for the proton conductive material may be a sulfuric acid-supporting metal oxide composed of two or more elements. In this case, a mixed metal oxide supporting sulfuric acid or a mixture of sulfuric acid supporting metal oxide may be used.
[0018]
The sulfuric acid-supporting metal oxide can be produced by supporting sulfuric acid on metal oxide particles (ceramic particles). For example, proton conductive solid electrolyte particles having excellent toughness can be produced by subjecting ceramic particles produced by adding CaO, Y ₂ O _3, etc. to zirconium oxide ZrO ₂ to sulfuric acid treatment.
[0019]
(2) Polymer compound The polymer compound used in the present invention is a polymer compound having an ion exchange group, and may be a known proton-conductive polymer compound. For example, perfluoroalkylenesulfonic acid polymer compounds (such as Nafion), sulfonated polyetheretherketone polymer compounds, sulfonated polyarylene polymer compounds, sulfonated polyether polymer compounds, and sulfonated polysulfide polymer compounds. Molecular compounds, sulfonated polyethersulfone polymer compounds, sulfonated polysulfone polymer compounds, sulfonated polyetherimide polymer compounds, sulfonated polybenzimidazole polymer compounds, and the like. These may be a mixture of two or more.
[0020]
(3) Production Method The proton conductive material of the present invention is produced by mixing the above-mentioned polymer compound having an ion exchange group and a metal oxide carrying sulfuric acid with a mixer or the like. In the case of a proton conductive membrane, a polymer compound having an ion exchange group is dissolved in an appropriate solvent, and the sulfuric acid-supporting metal oxide particles are added thereto, sufficiently stirred and uniformly dispersed, and then supported. To form a film by applying it to a body or by uniformly mixing a polymer compound having an ion-exchange group and sulfuric acid-carrying metal oxide particles, and then heating and extruding through a slit in a softened state. Can be. The content of the sulfuric acid-supporting metal oxide particles is preferably from 0.5 to 50% by mass, more preferably from 2 to 10% by mass, based on 100% by mass of the proton conductive material. If it is less than 0.5% by mass, the proton conductivity does not improve, and if it exceeds 50% by mass, the proton conductive material becomes brittle. The average particle diameter of the sulfuric acid-supporting metal oxide particles is preferably from 0.01 to 5 μm, more preferably from 0.05 to 1 μm. If it is less than 0.01 μm, it is difficult to produce sulfuric acid-supported metal oxide particles, and if it exceeds 5 μm, uniform proton conductivity cannot be obtained.
[0021]
[2] Membrane-electrode assembly As shown in FIG. 1, the membrane-electrode assembly 1 is composed of a catalyst electrode (anode 12 and cathode 13) and an electrolyte membrane 11. The catalyst electrode is composed of gas diffusion layers 12a and 13a and catalyst layers 12b and 13b. Catalyst particles obtained by supporting platinum particles or platinum alloy particles on carbon black are coated on the gas diffusion layers 12a and 13a. The layers 12b and 13b are formed. The membrane-electrode assembly 1 is manufactured by hot pressing the anode 12 and the cathode 13 so that the catalyst layers 12 b and 13 b are opposed to both sides of the electrolyte membrane 11, or the catalyst layers 12 b and 13 b Is pressed and transferred onto the electrolyte membrane 11, and then sandwiched between gas diffusion layers (porous conductive materials) 12a and 13a.
[0022]
The membrane-electrode assembly 1 uses the proton conductive material of the present invention for the electrolyte membrane 11 and / or the

catalyst electrodes

12 and 13. When used for the electrolyte membrane 11, from the viewpoint of improving proton conductivity, it is preferable that the sulfuric acid-supporting metal oxide is unevenly distributed on at least one surface of the electrolyte membrane 11. Further, the electrolyte membrane 11 is not limited to a single layer, and may be a multilayer film in which different membranes are stacked. In the case of a multi-layer film, for example, a film containing a sulfuric acid-supporting metal oxide can be used as a multi-layer film used on the surfaces in contact with the

catalyst electrodes

12 and 13. Even when the proton conductive material of the present invention is added to the

catalyst electrodes

12 and 13 other than the electrolyte membrane 11, the proton conductivity can be improved as in the case where the proton conductive material is used for the electrolyte membrane 11. In this case, the sulfuric acid-supporting metal oxide is preferably unevenly distributed at least on the surface of the catalyst electrode in contact with the electrolyte membrane.
[0023]
[3] Fuel Cell FIG. 2 shows an example of a fuel cell in which the membrane / electrode assembly is assembled on a separator. A fuel gas channel 21a is formed in the separator 21 on the anode side, and an oxidizing gas channel 23a is formed in the separator 23 on the cathode side. Coolant channels 21b and 23b for cooling the fuel cell are formed on the back side of the separator. In order to ensure the sealing property, the outer edge of the electrolyte membrane 11 is sandwiched between the

separators

21 and 23 so that various supply gases are not mixed. A frame member 22 having a sealing property is attached to a peripheral portion of each separator, and an outer edge portion of the electrolyte membrane is sandwiched by the frame material 22 having a sealing property, whereby sufficient gas sealing property with the separator is achieved. Secured. A gas fuel such as hydrogen is supplied to the anode 12 of the fuel cell, and an oxidizing gas such as oxygen and air is supplied to the cathode 13, and electric energy is generated by the progress of the electrochemical reaction. The fuel cell is generally used as a fuel cell stack by stacking a plurality of unit fuel cells shown in FIG.
[0024]
【Example】
The present invention will be described in more detail by the following examples, but the present invention is not limited thereto.
[0025]
Example 1
(1) Preparation of Sulfuric Acid-Supported Metal Oxide Distilled water was added to 0.5 g of concentrated sulfuric acid (96%) to prepare a sulfuric acid aqueous solution having a total mass of 100 g. 20 g of zirconium oxide ZrO ₂ was added to the aqueous sulfuric acid solution, and the mixture was stirred for 3 hours to prepare a slurry. The slurry was heated from room temperature to 100 ° C. at a rate of 5 ° C./min and kept at 100 ° C. for 3 hours to remove water. Next, the mixture was heated to 200 ° C. at a rate of 1 ° C./min and maintained at 200 ° C. for 3 hours to obtain a white powder. Most of the weight loss at this stage was due to water volatilization. This white powder is further heated to 500 ° C. at a rate of 1 ° C./min and maintained at 500 ° C. for 3 hours, so that sulfur (S) in the sulfuric acid content and the metal element Zr constituting zirconium oxide of the carrier are removed. A white powder of sulfuric acid-supported zirconia (SA / ZrO ₂ ) having a molar ratio S / Zr of 0.005 was obtained. The average particle size of the obtained white powder was 0.07 μm.
[0026]
(2) Preparation of Electrolyte Membrane (Proton Conductive Membrane) The content of the sulfuric acid-carrying zirconia (SA / ZrO ₂ ) obtained in (1) was 5% by mass with respect to 100% by mass of the proton conductive material. Then, sulfuric acid-supported zirconia (SA / ZrO ₂ ) was added to the solution of the sulfonated polyetheretherketone, and the mixture was thoroughly mixed using a stirrer until the mixture was uniformly dispersed. The obtained dispersion was applied on a glass plate using an applicator, and dried to form a film having a thickness of 23 μm.
[0027]
(3) Preparation of membrane / electrode assembly A slurry obtained by uniformly dispersing carbon black and polytetrafluoroethylene (PTFE) particles in a mass ratio of 4: 6 in ethylene glycol is applied to one surface of carbon paper, and dried. To form a gas diffusion layer composed of carbon paper and the underlayer. The catalyst paste was screen-printed on the underlayer of the obtained gas diffusion layer, and dried under reduced pressure to produce an anode electrode and a cathode electrode. The catalyst paste is prepared by supporting platinum particles on carbon black (furnace black) so that the mass ratio of platinum / carbon becomes 1: 1 to form catalyst particles, and using Nafion (manufactured by DuPont) as a proton conductive component. It was prepared by uniformly mixing catalyst particles in a solution. Next, after sandwiching the electrolyte membrane obtained in (2) between the anode and the cathode, hot pressing was performed at 150 ° C. for 10 minutes to produce a membrane-electrode assembly.
[0028]
(4) Fabrication of Fuel Cell The membrane / electrode assembly obtained in (1) was sandwiched and pressed by a pair of separators whose outer edges were coated with a silicon-based liquid sealing material (frame material). A flow path for supplying a fuel gas (hydrogen gas) to the anode side of the separator and a flow path for supplying an oxidizing gas (air) to the cathode side were provided.
[0029]
(5) Using the obtained fuel cell, changes in cell potential and IR loss when the current density was changed were measured. Power generation conditions were as follows: cell outlet pressure was atmospheric pressure, relative humidity was 50% RH for both anode and cathode, and cell temperature was 80 ° C. The results are shown in FIG.
[0030]
Example 2
Sulfuric acid-supported zirconia having an S / Zr molar ratio of 0.005 was added to Nafion, a proton conductive component of the cathode electrode, in an amount of 5% by mass with respect to 100% by mass of the proton conductive component, in the same manner as in Example 1. A fuel cell was manufactured. FIG. 3 shows the results of evaluation performed in the same manner as in Example 1.
[0031]
Examples 3 to 8
The fuel was prepared in the same manner as in Example 1, except that the S / Zr molar ratio of the sulfuric acid-supported zirconia (SA / ZrO ₂ ) was changed to 0.03, 0.1, 0.5, 0.9, 1.4 and 2, respectively. A battery was manufactured. Table 1 shows the cell potential and IR loss at a current density of 600 mA / cm ² measured in the same manner as in Example 1. FIG. 4 shows the change in the cell potential with respect to the S / M molar ratio (S / Zr molar ratio). .
[0032]
Examples 9 to 15
Sulfuric acid-supporting metal oxides are designated as SA / TiO ₂ , SA / Fe ₂ O ₃ , SA / SnO ₂ , SA / SiO ₂ , SA / Al ₂ O ₃ , SA / MoO ₃ , and SA / WO ₃ , respectively. A fuel cell was produced in the same manner as in Example 1 except that the M molar ratio was changed to 0.5. Table 2 shows the cell potential and IR loss at a current density of 600 mA / cm ² measured in the same manner as in Example 1, and FIG. 5 shows the relationship between the type of the sulfuric acid-supported metal oxide and the cell potential.
[0033]
Examples 16 to 22
The sulfonated polyether is adjusted so that the content of sulfuric acid-supported zirconia (SA / ZrO ₂ ) is 0.5, 1, _{2, 10, 30,} 45, and 52% by mass with respect to 100% by mass of the proton conductive material. A fuel cell was produced in the same manner as in Example 1, except that zirconia carrying sulfuric acid (SA / ZrO ₂ ) was added to ether ketone. Table 3 shows the cell potential and IR loss at a current density of 600 mA / cm ² measured in the same manner as in Example 1. FIG. 6 shows the change in the cell potential with respect to the content of zirconia (SA / ZrO ₂ ) carrying sulfuric acid. .
[0034]
Example 23
In the same manner as in Example 1, a 5 μm-thick electrolyte membrane made of sulfonated polyetheretherketone and sulfuric acid-supported zirconia (SA / ZrO ₂ ) was produced. A 15 μm-thick sulfonated polyetheretherketone film was laminated between two prepared electrolyte membranes, and pressed and heated with a heating roll to form a 23 μm-thick composite film. A fuel cell was manufactured in the same manner as in Example 1 using the obtained composite membrane. Table 4 shows the cell potential and IR loss at a current density of 600 mA / cm ² measured in the same manner as in Example 1.
[0035]
Example 24
Sulfuric acid-supported zirconia (SA / ZrO ₂ ) having an S / Zr molar ratio of 0.5 was added to Nafion, which is a proton conductive component of the cathode electrode, so that the molar ratio of S / Zr was 0.5% by mass with respect to 100% by mass of the proton conductive component. A fuel cell was produced in the same manner as in Example 5. Table 4 shows the cell potential and IR loss at a current density of 600 mA / cm ² measured in the same manner as in Example 1.
[0036]
Example 25
A sulfonated polyetheretherketone membrane having a thickness of 23 μm was used as an electrolyte membrane, and sulfuric acid-supporting zirconia having an S / Zr molar ratio of 0.5 was added to Nafion, which is a proton conductive component of the cathode electrode, at a ratio of 0.5 to 100% by mass of the proton conductive component. A fuel cell was manufactured in the same manner as in Example 5, except that the fuel cell was added so as to be in a mass%. Table 4 shows the cell potential and IR loss at a current density of 600 mA / cm ² measured in the same manner as in Example 1.
[0037]
Comparative Example 1
A fuel cell was manufactured in the same manner as in Example 1, except that sulfonated polyetheretherketone was used as the electrolyte membrane. The results of the evaluation performed in the same manner as in Example 1 are shown in FIG.
[0038]
Comparative Example 2
As the proton conductive material, a material obtained by mixing zirconia oxide (ZrO ₂ ) with sulfonated polyetheretherketone so that zirconia oxide (ZrO ₂ ) is 5 mass% with respect to 100 mass% of the proton conductive material. A fuel cell was produced in the same manner as in Example 1 except that the fuel cell was used. Table 1 shows the cell potential and IR loss at a current density of 600 mA / cm ² measured in the same manner as in Example 1.
[0039]
[Table 1]

[0040]
[Table 2]

[0041]
[Table 3]

[0042]
[Table 4]

[0043]
(Evaluation)
As shown in FIG. 3, the case where sulphate-supported zirconia (SA / ZrO ₂ ) was used for the electrolyte membrane as the sulfuric acid-supported metal oxide (Example 1) and the case where the sulphate-supported zirconia (SA / ZrO ₂ ) was used as the electrolyte membrane and the catalyst In the case where the electrode was used for the electrode (Example 2), the IR loss was almost the same as compared to the case where the metal oxide supporting sulfuric acid was not added (Comparative Example 1), whereas the cell potential was from the low current region. It showed a high value up to the high current range. This is because the activation overvoltage (resistance at the interface between the membrane and the electrode) when zirconia carrying sulfuric acid is added is small. Further, as shown in Table 1, when sulphate-supported zirconia (SA / ZrO2) was used in an S / M molar ratio in the range of 0.005 to ₂ (Examples 1 to 8), a sulfuric acid-supported metal oxide was added. The cell potential was higher than in the case of not performing (Comparative Example 1) or the case of adding only the metal oxide (ZrO ₂ ) (S / M molar ratio: 0) (Comparative Example 2).
[0044]
As shown in Table 2, when ZrO ₂ , TiO ₂ , Fe ₂ O ₃ , SnO ₂ , SiO ₂ , Al ₂ O ₃ , MoO ₃ and WO ₃ were used as the metal oxides of the sulfuric acid-supporting metal oxide, all of them were used. It showed a high cell potential. It can be seen that high proton conductivity is obtained by using these metal oxides as carriers.
[0045]
The mass of the proton conductive material as shown in Table 3 is 100 mass%, exhibited a high cell voltage in the range amount of from 0.5 to 45 mass% of sulfuric acid supported zirconia (SA / ZrO ₂₎ (Examples 16 to 21). When the content of the sulfuric acid-supported zirconia (SA / ZrO ₂ ) exceeds 50% by mass, it becomes difficult to form a film. Therefore, in Example 22, the cell voltage could not be measured.
[0046]
As shown in Table 4, the membrane-electrode assembly had a structure in which only the electrolyte membrane (single-layer film or multilayer film) contained the metal oxide supporting sulfuric acid (Example 23), and only the catalyst electrode had a metal oxide supporting sulfuric acid. In both the configuration containing the substance (Example 25) and the configuration containing the metal oxide supporting sulfuric acid in both the electrolyte membrane and the catalyst electrode (Example 24), a high cell voltage was exhibited.
[0047]
【The invention's effect】
As described above, the proton conductive material of the present invention has high proton conductivity because it includes the polymer compound having an ion exchange group and the metal oxide supporting sulfuric acid. Therefore, when used in a fuel cell, it is possible to reduce voltage drop and improve output power.
[Brief description of the drawings]
FIG. 1 is a schematic cross-sectional view showing one example of a membrane-electrode assembly (MEA) of the present invention.
FIG. 2 is a schematic cross-sectional view showing a state where the membrane-electrode assembly (MEA) of the present invention is sandwiched between a pair of separators.
FIG. 3 is a graph showing changes in cell potential and IR loss with respect to current density when the fuel cells of Examples 1 and 2 and Comparative Example 1 are used.
FIG. 4 is a graph showing a change in cell potential with respect to an S / Zr molar ratio of sulfuric acid-supported zirconia (SA / ZrO ₂ ) when the fuel cells of Examples 3 to 8 are used.
FIG. 5 is a graph showing the relationship between the type of metal oxide supporting sulfuric acid and the cell potential when the fuel cells of Examples 9 to 15 are used.
FIG. 6 is a graph showing a change in cell potential with respect to the content of zirconia supported on sulfuric acid (SA / ZrO ₂ ) when the fuel cells of Examples 16 to 22 are used.
[Explanation of symbols]
1 ... Membrane-electrode assembly (MEA)
Reference Signs List 11 electrolyte membrane 12 anode electrode 12a gas diffusion layer 12b catalyst layer 13 cathode electrode 13a gas diffusion layer 13b catalyst layers 21, 23 Separator 22 ... sealing material (frame material)

Claims

A proton conductive material comprising a polymer compound having an ion exchange group and a sulfuric acid-supported metal oxide.

2. The proton conductive material according to claim 1, wherein sulfur (S) in a sulfuric acid content of the metal oxide supporting sulfuric acid and a metal element (M) constituting a metal hydroxide and / or a metal oxide serving as a carrier. Is a molar ratio S / M of 0.0001 to 1.5.

3. The proton conductive material according to claim 1, wherein the molar ratio S / M is 0.01 to 1. 4.

4. The proton conductive material according to claim 1, wherein the metal oxide supporting sulfuric acid is at least one selected from the group consisting of zirconium, titanium, iron, tin, silicon, aluminum, molybdenum, and tungsten. A proton conductive material comprising a kind of element.

The proton conductive material according to any one of claims 1 to 4, wherein the sulfuric acid-supporting metal oxide is contained in an amount of 0.5 to 50% by mass when the mass of the proton conductive material is 100% by mass. Proton conductive material.

A membrane-electrode assembly in which a catalyst electrode is formed on both sides of an electrolyte membrane, wherein the electrolyte membrane is made of the proton conductive material according to any one of claims 1 to 5. .

The membrane-electrode assembly according to claim 6, wherein the sulfuric acid-supporting metal oxide is unevenly distributed on at least one surface of the electrolyte membrane.

The membrane / electrode assembly according to claim 6 or 7, wherein the catalyst electrode includes catalyst particles, a gas diffusion layer, and the proton conductive material according to any one of claims 1 to 5. Membrane / electrode assembly.

The membrane / electrode assembly according to any one of claims 6 to 8, wherein the sulfuric acid-supporting metal oxide contained in the catalyst electrode is unevenly distributed on a surface of the catalyst electrode that contacts the electrolyte membrane. Membrane / electrode assembly.

In a membrane-electrode assembly in which a catalyst electrode is formed on both sides of an electrolyte membrane, the catalyst electrode includes a catalyst particle, a gas diffusion layer, and the proton conductive material according to any one of claims 1 to 5. Characterized membrane / electrode assembly.

11. The membrane / electrode assembly according to claim 10, wherein the sulfuric acid-supporting metal oxide contained in the catalyst electrode is unevenly distributed on a surface of the catalyst electrode in contact with the electrolyte membrane. .

A fuel cell using the membrane / electrode assembly according to any one of claims 6 to 11.