JP3563372B2 - Electrode structure for polymer electrolyte fuel cell - Google Patents
Electrode structure for polymer electrolyte fuel cell Download PDFInfo
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- JP3563372B2 JP3563372B2 JP2001176695A JP2001176695A JP3563372B2 JP 3563372 B2 JP3563372 B2 JP 3563372B2 JP 2001176695 A JP2001176695 A JP 2001176695A JP 2001176695 A JP2001176695 A JP 2001176695A JP 3563372 B2 JP3563372 B2 JP 3563372B2
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/30—Hydrogen technology
- Y02E60/50—Fuel cells
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
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- Polyoxymethylene Polymers And Polymers With Carbon-To-Carbon Bonds (AREA)
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Description
【０００１】
【発明の属する技術分野】
本発明は、固体高分子型燃料電池に用いられる電極構造体に関するものである。
【０００２】
【従来の技術】
石油資源が枯渇化する一方、化石燃料の消費による地球温暖化等の環境問題が深刻化しており、二酸化炭素の発生を伴わないクリーンな電動機用電力源として燃料電池が注目されて広範に開発されると共に、一部では実用化され始めている。前記燃料電池を自動車等に搭載する場合には、高電圧と大電流とが得やすいことから、高分子電解質膜を用いる固体高分子型燃料電池が好適に用いられる。
【０００３】
前記固体高分子型燃料電池に用いる電極構造体として、白金等の触媒がカーボンブラック等の触媒担体に担持されイオン導伝性高分子バインダーにより一体化されることにより形成されている一対の電極触媒層を備え、両電極触媒層の間にイオン導伝可能な高分子電解質膜を挟持すると共に、各電極触媒層の上に、拡散層を積層したものが知られている。前記電極構造体は、さらに各電極触媒層の上に、ガス通路を兼ねたセパレータを積層することにより、固体高分子型燃料電池を構成する。
【０００４】
前記固体高分子型燃料電池では、一方の電極触媒層を燃料極として前記拡散層を介して水素、メタノール等の還元性ガスを導入すると共に、他方の電極触媒層を酸素極として前記拡散層を介して空気、酸素等の酸化性ガスを導入する。このようにすると、燃料極側では、前記電極触媒層に含まれる触媒の作用により、前記還元性ガスからプロトンが生成し、前記プロトンは前記高分子電解質膜を介して、前記酸素極側の電極触媒層に移動する。そして、前記プロトンは、前記酸素極側の電極触媒層で、前記電極触媒層に含まれる触媒の作用により、該酸素極に導入される前記酸化性ガスと反応して水を生成する。従って、前記燃料極と酸素極とを導線により接続することにより電流を取り出すことができる。
【０００５】
従来、前記電極構造体では、前記高分子電解質膜としてパーフルオロアルキレンスルホン酸高分子化合物（例えば、デュポン社製ナフィオン（商品名））が広く利用されている。前記パーフルオロアルキレンスルホン酸高分子化合物は、スルホン化されていることにより優れたプロトン導伝性を備えると共に、フッ素樹脂としての耐薬品性とを併せ備えているが、非常に高価であるとの問題がある。
【０００６】
そこで、パーフルオロアルキレンスルホン酸高分子化合物に代わる廉価なイオン導伝性材料を用いて、固体高分子型燃料電池用電極構造体を構成することが検討されている。
【０００７】
前記廉価なイオン導伝性材料として、例えば、ポリエーテルケトンやポリベンゾイミダゾールをスルホン化したものがある。しかし、前記イオン導伝性材料はいずれもイオン導電性、機械的強度に劣るという問題がある。
【０００８】
一方、米国特許第５４０３６７５号明細書には、前記廉価なイオン導伝性材料として、剛直ポリフェニレンをスルホン化したものが提案されている。前記明細書記載の剛直ポリフェニレンのスルホン化物は、フェニレン連鎖を備える芳香族化合物を重合して得られるポリマーを主成分として、該ポリマーをスルホン化したものであり、イオン導電性に優れている。
【０００９】
しかしながら、前記剛直ポリフェニレンのスルホン化物は靱性が低く、該剛直ポリフェニレンのスルホン化物を高分子電解質膜として電極構造体を構成したときに該高分子電解質膜が割れやすくなるという不都合がある。
【００１０】
【発明が解決しようとする課題】
本発明は、かかる不都合を解消して、靱性に優れた高分子電解質膜を備え製造容易であると共に、優れた発電性能を備える固体高分子型燃料電池用電極構造体を提供することを目的とする。
【００１１】
【課題を解決するための手段】
かかる目的を達成するために、本発明者らは種々検討を重ねた結果、特定の分子構造を備える共重合体のスルホン化物により前記高分子電解質膜を構成すると共に、該スルホン化物を溶媒に溶解した溶液から成膜して乾燥する際に、乾燥後に所定の範囲の溶媒を残存させることにより、優れた靱性を備える高分子電解質膜が得られることを見出し、本発明を完成した。
【００１２】
そこで、本発明の固体高分子型燃料電池用電極構造体は、一対の電極触媒層と、両電極触媒層に挟持された高分子電解質膜とを備える固体高分子型燃料電池用電極構造体において、前記高分子電解質膜は一般式（１）で表される第１の繰返し単位と、一般式（２）で表される第２の繰返し単位との共重合体のスルホン化物を溶媒に溶解した溶液から成膜、乾燥してなり、乾燥後に前記溶媒を３〜１２重量％の範囲で含むことを特徴とする。
【００１３】
【化３】
前記高分子電解質膜を構成するスルホン化物は、一般式（１）で表される第１の繰返し単位と、一般式（２）で表される第２の繰返し単位との共重合体をスルホン化して得られる。尚、本明細書において、前記電子吸引性基とは、−ＣＯ−、−ＣＯＮＨ−、−（ＣＦ２）ｐ−（ｐは１〜１０の整数）、−Ｃ（ＣＦ３）２−、−ＣＯＯ−、−ＳＯ−、−ＳＯ２−等のハメット置換基常数がフェニル基のメタ位では０．０６以上、フェニル基のパラ位では０．０１以上の値となる２価の基をいう。また、本明細書において、前記電子供与性基とは、−Ｏ−、−Ｓ−、−ＣＨ＝ＣＨ−、−Ｃ≡Ｃ−等の２価の基をいう。
【００１５】
ここで、前記スルホン化は、電子吸引性基が結合していないベンゼン環、換言すれば電子供与性基のみが結合しているベンゼン環に対して起きる。従って、一般式（１）で表される第１の繰返し単位と、一般式（２）で表される第２の繰返し単位との共重合体をスルホン化すると、第１の繰返し単位の主鎖となるベンゼン環と、第２の繰返し単位の各ベンゼン環とにはスルホン酸基が導入されず、第１の繰返し単位の側鎖のベンゼン環にスルホン酸基が導入されることになる。そこで、前記共重合体では、第１の繰返し単位と第２の繰返し単位とのモル比を調整することにより、導入されるスルホン酸基の量を制御して、イオン導伝性と靱性とに優れた高分子電解質膜を得ることができる。
【００１６】
前記第１の繰返し単位に用いるモノマーとして、具体的には、次式（３）で示される２，５−ジクロロ−４’−（４−フェノキシフェノキシ）ベンゾフェノン等を挙げることができる。
【００１７】
【化４】
また、前記第１の繰返し単位に用いるモノマーとして、具体的には、次式（４）で示される２，２−ビス〔４−｛４−（４−クロロベンゾイル）フェノキシ｝フェニル〕−１，１，１，３，３，３−ヘキサフルオロプロパン、次式（５）で示される２，２−ビス〔４−｛４−（４−クロロベンゾイル）フェノキシ｝フェニル〕スルホン等を挙げることができる。
【００１９】
【化５】
前記高分子電解質膜は、前記共重合体のスルホン化物を溶媒に溶解した溶液からキャスト法等により成膜し、乾燥することにより作成される。このとき、前記高分子電解質膜は、乾燥後に前記溶媒を３〜１５重量％の範囲で含むことにより特に優れた靱性を得ることができる。
【００２１】
前記高分子電解質膜は、乾燥後の前記溶媒の含有量が３重量％未満であるときには十分な靱性が得られず、１５重量％を超えると十分な発電性能が得られない。
【００２２】
前記溶媒は、優れた発電性能を備える電極構造体を得るために、Ｎ−メチルピロリドンが適している。
【００２３】
本発明の電極構造体において、前記高分子電解質膜を構成する共重合体は、導入されるスルホン酸基の量を制御して、イオン導伝性と靱性とを好ましい範囲とするために、前記第１の繰返し単位１０〜８０モル％と、前記第２の繰返し単位９０〜２０モル％とからなることが好ましい。前記第１の繰返し単位が１０モル％未満で、前記第２の繰返し単位が９０モル％を超えると、前記共重合体に導入されるスルホン酸基の量が少なく、十分なイオン導伝性が得られないことがある。また、前記第１の繰返し単位が８０モル％を超え、前記第２の繰返し単位が２０モル％未満であると、前記共重合体に導入されるスルホン酸基の量が多くなり、十分な靱性が得られないことがある。
【００２４】
また、本発明の電極構造体において、前記高分子電解質膜を構成する共重合体は、イオン導伝性と靱性とを好ましい範囲とするために、スルホン酸基を０．５〜３．０ミリグラム当量／ｇの範囲で含有することが好ましい。前記共重合体が含有するスルホン酸基の量が０．５ミリグラム当量／ｇ未満では十分なイオン導伝性が得られないことがあり、３．０ミリグラム当量／ｇを超えると十分な靱性が得られないことがある。
【００２５】
本発明の電極構造体は、一方の面に酸化性ガスを供給すると共に、他方の面に還元性ガスを供給することにより発電する固体高分子型燃料電池を構成することができる。
【００２６】
【発明の実施の形態】
次に、添付の図面を参照しながら本発明の実施の形態についてさらに詳しく説明する。図１は本実施形態の電極構造体の構成を示す説明的断面図であり、図２は本実施形態の電極構造体に用いる高分子電解質膜の初期イオン導伝率と該高分子電解質膜が含有する溶媒の量との関係を示すグラフ、図３は本実施形態の電極構造体に用いる高分子電解質膜のイオン導伝率保持率と該高分子電解質膜が含有する溶媒の量との関係を示すグラフ、図４は本実施形態の電極構造体に用いる高分子電解質膜の靱性と該高分子電解質膜が含有する溶媒の量との関係を示すグラフである。
【００２７】
本実施形態の電極構造体は、図１示のように、一対の電極触媒層１，１と、両電極触媒層１，１に挟持された高分子電解質膜２と、各電極触媒層１，１の上に積層された拡散層３，３とからなる。
【００２８】
前記電極構造体は、次のようにして製造することができる。
【００２９】
まず、次式（３）で示される２，５−ジクロロ−４’−（４−フェノキシフェノキシ）ベンゾフェノンと、次式（４）で示される２，２−ビス〔４−｛４−（４−クロロベンゾイル）フェノキシ｝フェニル〕−１，１，１，３，３，３−ヘキサフルオロプロパンとを、５０：５０の重合比で重合させて次式（６）の共重合体を得る。
【００３０】
【化６】
前記共重合体は、ポリマー分子量がポリスチレン換算重量平均分子量で、１万〜１００万の範囲にあることが好ましい。前記ポリマー分子量が１万未満では高分子電解質膜として好適な機械的強度が得られないことがあり、１００万を超えると後述のように成膜のために溶媒に溶解する際に溶解性が低くなったり、溶液の粘度が高くなり、取り扱いが難しくなる。
【００３２】
次に、前記共重合体に濃硫酸を加えてスルホン化し、例えば、イオン交換容量が２．３ｍｅｑ／ｇのスルホン化物を得る。次に、前記共重合体のスルホン化物を、Ｎ−メチルピロリドンに溶解して高分子電解質溶液とし、該高分子電解質溶液からキャスト法により成膜し、オーブンにて乾燥することにより、例えば、乾燥膜厚５０μｍの高分子電解質膜２を作成する。
【００３３】
次に、カーボンブラック（ファーネスブラック）に白金粒子を所定の重量比（例えば、カーボンブラック：白金＝１：１）で担持させ、触媒粒子を作成する。次に、イオン導伝性バインダー溶液（例えば、パーフルオロアルキレンスルホン酸高分子化合物（デュポン社製ナフィオン（商品名））に、前記触媒粒子を所定の重量比（例えば、イオン導伝性バインダー：触媒粒子＝８：５）で均一に分散させ、触媒ペーストを調製する。
【００３４】
次に、カーボンブラックとポリテトラフルオロエチレン（ＰＴＦＥ）粒子とを所定の重量比（例えば、カーボンブラック：ＰＴＦＥ粒子＝４：６）で混合し、得られた混合物をエチレングリコール等の溶媒に均一に分散させたスラリーをカーボンペーパーの片面に塗布、乾燥させて下地層とし、該下地層とカーボンペーパーとからなる拡散層３を２つ作成する。
【００３５】
次に、各拡散層３上に、前記触媒ペーストを、白金含有量が所定の量（例えば、０．５ｍｇ／ｃｍ２）となるようにスクリーン印刷し、乾燥させることにより電極触媒層１とし、電極触媒層１と拡散層３とからなる一対の電極を作成する。前記乾燥は、例えば６０℃で１０分間の乾燥を行い、次いで１２０℃で６０分間の減圧乾燥を行う。
【００３６】
次に、高分子電解質膜２を前記電極の電極触媒層１側で挟持し、ホットプレスを行って図１示の電極構造体を得た。前記ホットプレスは、例えば８０℃、５ＭＰａで２分間の一次ホットプレスを行い、次いで１６０℃、４ＭＰａで１分間の二次ホットプレスを行う。
【００３７】
また、図１示の電極構造体は、拡散層３，３の上にさらにガス通路を兼ねるセパレータを積層することにより、固体高分子型燃料電池を構成することができる。
【００３８】
次に、前記高分子電解質膜２の乾燥後の溶媒の含有量を０〜３０重量％の範囲で変量して、９種の高分子電解質膜２（乾燥膜厚５０μｍ）を作成し、各高分子電解質膜２の初期イオン導伝率、イオン導伝率の保持率、靱性を測定した。
【００３９】
前記初期イオン導伝率は、前記高分子電解質膜２を２枚の白金電極で挟持し、温度８５℃、相対湿度９０％の条件下、交流２端子法（周波数１０ｋＨｚ）で測定した。結果を図２に示す。
【００４０】
また、前記イオン導伝率保持率は、前記初期イオン導伝率測定後、６０日間放置した前記高分子電解質膜２について、前記初期イオン導伝率と同一の方法によりイオン導伝率を測定し、該イオン導伝率の前記初期イオン導伝率に対する百分率として算出した。結果を図３に示す。
【００４１】
また、前記靱性は、前記高分子電解質膜２をＪＩＳ７号ダンベルに加工し、チャック間距離２０ｍｍ、クロスヘッドスピード５０ミリ／分、温度２５℃、相対湿度５０％の条件下、引張り破断伸びとして測定した。結果を図４に示す。
【００４２】
図２及び図３から、前記高分子電解質膜２は、乾燥後の溶媒の含有量が１５重量％を超えると、初期イオン導伝率、イオン導伝率保持率が急激に低下することが明らかであり、乾燥後の溶媒の含有量が３％未満では十分な引張り破断伸びが得られず、靱性が低いことが明らかである。
【００４３】
従って、本実施形態の電極構造体は、前記高分子電解質膜２の乾燥後の溶媒の含有量を３〜１５重量％の範囲とすることにより、前記イオン導伝率を備える高分子電解質膜２のために優れた発電性能が得られることが明らかであり、前記引張り破断伸び（靱性）を備える高分子電解質膜２のために容易に製造できることが明らかである。
【００４４】
次に、比較のために、前記共重合体のスルホン化物を、Ｎ−メチルピロリドンに替えてジメチルアセトアミドに溶解して高分子電解質溶液とし、該高分子電解質溶液からキャスト法により成膜した以外は、前記実施形態と全く同一にして、乾燥膜厚５０μｍ、乾燥後の溶媒の含有量が５重量％である高分子電解質膜を作成した。前記高分子電解質膜（比較例）について、前記実施形態と全く同一の方法により、初期イオン導伝率、イオン導伝率保持率、靱性を測定した。結果を、前記実施形態における乾燥後の溶媒の含有量が５重量％である高分子電解質膜２（実施例）と共に、表１に示す。
【００４５】
【表１】
表１から明らかなように、前記共重合体のスルホン化物をＮ−メチルピロリドンに溶解した高分子電解質溶液から成膜した前記高分子電解質膜（実施例）は、前記共重合体のスルホン化物をジメチルアセトアミドに溶解した高分子電解質溶液から成膜した前記高分子電解質膜（比較例）に対して、初期イオン導伝率と、引張り破断伸び（靱性）とはほぼ同等であるが、イオン導伝率保持率が格段に優れている。従って、前記実施例の高分子電解質膜を用いることにより、優れた発電性能を備える電極構造体を得ることができることが明らかである。
【図面の簡単な説明】
【図１】本発明の電極構造体の構成を示す説明的断面図。
【図２】本発明の電極構造体に用いる高分子電解質膜の初期イオン導伝率該高分子電解質膜が含有する溶媒の量との関係を示すグラフ。
【図３】本発明の電極構造体に用いる高分子電解質膜のイオン導伝率保持率と該高分子電解質膜が含有する溶媒の量との関係を示すグラフ。
【図４】本発明の電極構造体に用いる高分子電解質膜の靱性と該高分子電解質膜が含有する溶媒の量との関係を示すグラフ。
【符号の説明】
１…電極触媒層、 ２…高分子電解質膜。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an electrode structure used for a polymer electrolyte fuel cell.
[0002]
[Prior art]
While petroleum resources are being depleted, environmental issues such as global warming due to consumption of fossil fuels are becoming more serious, and fuel cells have been widely developed as a power source for clean electric motors that do not generate carbon dioxide. In addition, some have begun to be put into practical use. When the fuel cell is mounted on an automobile or the like, a solid polymer fuel cell using a polymer electrolyte membrane is preferably used because a high voltage and a large current are easily obtained.
[0003]
As the electrode structure used in the polymer electrolyte fuel cell, a pair of electrode catalysts formed by a catalyst such as platinum supported on a catalyst carrier such as carbon black and integrated with an ion-conductive polymer binder It is known that an electrode-conductive polymer electrolyte membrane is sandwiched between both electrode catalyst layers, and a diffusion layer is laminated on each electrode catalyst layer. The electrode structure further constitutes a polymer electrolyte fuel cell by laminating a separator also serving as a gas passage on each electrode catalyst layer.
[0004]
In the polymer electrolyte fuel cell, a reducing gas such as hydrogen or methanol is introduced through the diffusion layer using one electrode catalyst layer as a fuel electrode, and the diffusion layer is formed using the other electrode catalyst layer as an oxygen electrode. An oxidizing gas, such as air or oxygen, is introduced through the air. With this configuration, on the fuel electrode side, protons are generated from the reducing gas by the action of the catalyst contained in the electrode catalyst layer, and the protons pass through the polymer electrolyte membrane to the electrode on the oxygen electrode side. Move to the catalyst layer. Then, the protons react with the oxidizing gas introduced into the oxygen electrode in the electrode catalyst layer on the oxygen electrode side by the action of a catalyst contained in the electrode catalyst layer to generate water. Therefore, a current can be taken out by connecting the fuel electrode and the oxygen electrode with a conducting wire.
[0005]
Conventionally, in the electrode structure, a perfluoroalkylenesulfonic acid polymer compound (for example, Nafion (trade name) manufactured by DuPont) has been widely used as the polymer electrolyte membrane. The perfluoroalkylene sulfonic acid polymer compound has excellent proton conductivity due to being sulfonated, and also has chemical resistance as a fluororesin, but is very expensive. There's a problem.
[0006]
Therefore, it has been studied to construct an electrode structure for a polymer electrolyte fuel cell by using an inexpensive ion conductive material instead of a perfluoroalkylenesulfonic acid polymer compound.
[0007]
Examples of the inexpensive ion conductive material include those obtained by sulfonating polyetherketone or polybenzimidazole. However, there is a problem that all of the ion conductive materials are inferior in ionic conductivity and mechanical strength.
[0008]
On the other hand, US Pat. No. 5,403,675 proposes, as the inexpensive ion conductive material, a material obtained by sulfonating rigid polyphenylene. The sulfonated product of rigid polyphenylene described in the above specification is obtained by sulfonating a polymer obtained by polymerizing an aromatic compound having a phenylene chain as a main component, and has excellent ionic conductivity.
[0009]
However, the sulfonated product of the rigid polyphenylene has low toughness, and there is a disadvantage that the polymer electrolyte membrane is easily broken when an electrode structure is formed using the sulfonated product of the rigid polyphenylene as a polymer electrolyte membrane.
[0010]
[Problems to be solved by the invention]
An object of the present invention is to provide an electrode structure for a polymer electrolyte fuel cell, which eliminates such inconveniences, is easy to manufacture with a polymer electrolyte membrane having excellent toughness, and has excellent power generation performance. I do.
[0011]
[Means for Solving the Problems]
In order to achieve such an object, the present inventors have conducted various studies and found that the polymer electrolyte membrane was composed of a sulfonate of a copolymer having a specific molecular structure, and the sulfonate was dissolved in a solvent. It has been found that a polymer electrolyte membrane having excellent toughness can be obtained by leaving a solvent in a predetermined range after drying when forming a film from the prepared solution and drying, and completed the present invention.
[0012]
Therefore, an electrode structure for a polymer electrolyte fuel cell according to the present invention is an electrode structure for a polymer electrolyte fuel cell comprising a pair of electrode catalyst layers and a polymer electrolyte membrane sandwiched between both electrode catalyst layers. The polymer electrolyte membrane was prepared by dissolving a sulfonated product of a copolymer of a first repeating unit represented by the general formula (1) and a second repeating unit represented by the general formula (2) in a solvent. A film is formed from a solution and dried, and after drying, the solvent is contained in a range of 3 to 12% by weight.
[0013]
Embedded image
The sulfonate constituting the polymer electrolyte membrane is obtained by sulfonating a copolymer of a first repeating unit represented by the general formula (1) and a second repeating unit represented by the general formula (2). Obtained. In the present specification, the electron-withdrawing group, -CO -, - CONH -, - (CF 2) p - (p is an integer of from 1 to 10), - C (CF 3) 2 -, - COO -, - SO -, - SO 2 - Hammett substituent constant of 0.06 or more is in the meta position of the phenyl group such as in the para position of the phenyl group means a divalent group of 0.01 or more. In this specification, the electron donating group refers to a divalent group such as -O-, -S-, -CH = CH-, -C≡C-, and the like.
[0015]
Here, the sulfonation occurs on a benzene ring to which an electron-withdrawing group is not bonded, in other words, a benzene ring to which only an electron-donating group is bonded. Therefore, when a copolymer of the first repeating unit represented by the general formula (1) and the second repeating unit represented by the general formula (2) is sulfonated, the main chain of the first repeating unit is A sulfonic acid group is not introduced into the benzene ring to be used and each benzene ring of the second repeating unit, and a sulfonic acid group is introduced into the benzene ring of the side chain of the first repeating unit. Therefore, in the copolymer, by controlling the molar ratio of the first repeating unit and the second repeating unit, the amount of the sulfonic acid group to be introduced is controlled, and the ion conductivity and the toughness are improved. An excellent polymer electrolyte membrane can be obtained.
[0016]
Specific examples of the monomer used for the first repeating unit include 2,5-dichloro-4 ′-(4-phenoxyphenoxy) benzophenone represented by the following formula (3).
[0017]
Embedded image
Further, as the monomer used for the first repeating unit, specifically, 2,2-bis [4- {4- (4-chlorobenzoyl) phenoxy} phenyl] -1, represented by the following formula (4), Examples thereof include 1,1,3,3,3-hexafluoropropane and 2,2-bis [4- {4- (4-chlorobenzoyl) phenoxy} phenyl] sulfone represented by the following formula (5). .
[0019]
Embedded image
The polymer electrolyte membrane is formed by forming a film from a solution in which a sulfonated product of the copolymer is dissolved in a solvent by a casting method or the like, and drying the film. At this time, the polymer electrolyte membrane can obtain particularly excellent toughness by including the solvent in a range of 3 to 15% by weight after drying.
[0021]
When the content of the solvent after drying is less than 3% by weight, sufficient toughness cannot be obtained, and when it exceeds 15% by weight, sufficient power generation performance cannot be obtained.
[0022]
As the solvent, N-methylpyrrolidone is suitable in order to obtain an electrode structure having excellent power generation performance.
[0023]
In the electrode structure of the present invention, the copolymer constituting the polymer electrolyte membrane controls the amount of sulfonic acid groups to be introduced, so that the ion conductivity and the toughness are in a preferable range. It is preferable that the second repeating unit comprises 10 to 80 mol% of the first repeating unit and 90 to 20 mol% of the second repeating unit. When the amount of the first repeating unit is less than 10 mol% and the amount of the second repeating unit exceeds 90 mol%, the amount of sulfonic acid groups introduced into the copolymer is small, and sufficient ion conductivity is not obtained. May not be obtained. When the amount of the first repeating unit is more than 80 mol% and the amount of the second repeating unit is less than 20 mol%, the amount of sulfonic acid groups introduced into the copolymer increases, and sufficient toughness is obtained. May not be obtained.
[0024]
Further, in the electrode structure of the present invention, the copolymer constituting the polymer electrolyte membrane has a sulfonic acid group content of 0.5 to 3.0 milligrams in order to keep ion conductivity and toughness in a preferable range. It is preferable to contain it in the range of equivalent weight / g. If the amount of the sulfonic acid group contained in the copolymer is less than 0.5 milligram equivalent / g, sufficient ion conductivity may not be obtained, and if the amount exceeds 3.0 milligram equivalent / g, sufficient toughness is obtained. May not be obtained.
[0025]
The electrode structure of the present invention can constitute a polymer electrolyte fuel cell that generates electricity by supplying an oxidizing gas to one surface and a reducing gas to the other surface.
[0026]
BEST MODE FOR CARRYING OUT THE INVENTION
Next, embodiments of the present invention will be described in more detail with reference to the accompanying drawings. FIG. 1 is an explanatory cross-sectional view showing the configuration of the electrode structure of the present embodiment. FIG. 2 is a diagram showing the initial ionic conductivity of the polymer electrolyte membrane used in the electrode structure of the present embodiment. FIG. 3 is a graph showing a relationship between the amount of the solvent contained and FIG. 3 is a graph showing a relationship between the ion conductivity retention of the polymer electrolyte membrane used in the electrode structure of the present embodiment and the amount of the solvent contained in the polymer electrolyte membrane; FIG. 4 is a graph showing the relationship between the toughness of the polymer electrolyte membrane used in the electrode structure of the present embodiment and the amount of the solvent contained in the polymer electrolyte membrane.
[0027]
As shown in FIG. 1, the electrode structure of the present embodiment includes a pair of electrode catalyst layers 1, 1, a polymer electrolyte membrane 2 sandwiched between the two electrode catalyst layers 1, 1, and each
[0028]
The electrode structure can be manufactured as follows.
[0029]
First, 2,5-dichloro-4 '-(4-phenoxyphenoxy) benzophenone represented by the following formula (3) and 2,2-bis [4- {4- (4- Chlorobenzoyl) phenoxy {phenyl] -1,1,1,1,3,3,3-hexafluoropropane is polymerized at a polymerization ratio of 50:50 to obtain a copolymer of the following formula (6).
[0030]
Embedded image
The copolymer preferably has a polymer molecular weight in the range of 10,000 to 1,000,000 in terms of polystyrene equivalent weight average molecular weight. If the polymer molecular weight is less than 10,000, a suitable mechanical strength as a polymer electrolyte membrane may not be obtained, and if it exceeds 1,000,000, the solubility is low when dissolved in a solvent for film formation as described below. Or the viscosity of the solution increases, making handling difficult.
[0032]
Next, concentrated sulfuric acid is added to the copolymer to form a sulfonate, for example, to obtain a sulfonate having an ion exchange capacity of 2.3 meq / g. Next, a sulfonated product of the copolymer is dissolved in N-methylpyrrolidone to form a polymer electrolyte solution, and a film is formed from the polymer electrolyte solution by a casting method, and dried in an oven, for example, to be dried. A polymer electrolyte membrane 2 having a thickness of 50 μm is formed.
[0033]
Next, platinum particles are supported on carbon black (furnace black) at a predetermined weight ratio (for example, carbon black: platinum = 1: 1) to prepare catalyst particles. Next, the catalyst particles are added to an ion-conductive binder solution (for example, a perfluoroalkylenesulfonic acid polymer compound (Nafion (trade name) manufactured by DuPont)) in a predetermined weight ratio (for example, ion-conductive binder: catalyst). Particles = 8: 5) are uniformly dispersed to prepare a catalyst paste.
[0034]
Next, carbon black and polytetrafluoroethylene (PTFE) particles are mixed at a predetermined weight ratio (for example, carbon black: PTFE particles = 4: 6), and the resulting mixture is uniformly mixed with a solvent such as ethylene glycol. The dispersed slurry is applied to one side of carbon paper and dried to form an underlayer, and two
[0035]
Next, on each of the diffusion layers 3, the catalyst paste is screen-printed such that the platinum content is a predetermined amount (for example, 0.5 mg / cm 2 ), and dried to form the
[0036]
Next, the polymer electrolyte membrane 2 was sandwiched between the electrodes on the
[0037]
In addition, the electrode structure shown in FIG. 1 can constitute a polymer electrolyte fuel cell by further laminating a separator also serving as a gas passage on the diffusion layers 3 and 3.
[0038]
Next, the content of the dried solvent of the polymer electrolyte membrane 2 was varied in the range of 0 to 30% by weight to prepare nine kinds of polymer electrolyte membranes 2 (dry film thickness 50 μm). The initial ionic conductivity, the retention of ionic conductivity, and the toughness of the molecular electrolyte membrane 2 were measured.
[0039]
The initial ion conductivity was measured by sandwiching the polymer electrolyte membrane 2 between two platinum electrodes and using a two-terminal alternating current method (frequency: 10 kHz) at a temperature of 85 ° C. and a relative humidity of 90%. FIG. 2 shows the results.
[0040]
In addition, the ion conductivity retention rate is obtained by measuring the ion conductivity of the polymer electrolyte membrane 2 left for 60 days after the initial ion conductivity measurement by the same method as the initial ion conductivity. The ion conductivity was calculated as a percentage of the initial ion conductivity. The results are shown in FIG.
[0041]
The toughness is measured as a tensile elongation at break under the conditions that the polymer electrolyte membrane 2 is processed into a JIS No. 7 dumbbell, the chuck distance is 20 mm, the crosshead speed is 50 mm / min, the temperature is 25 ° C., and the relative humidity is 50%. did. FIG. 4 shows the results.
[0042]
From FIGS. 2 and 3, it is clear that, when the content of the solvent after drying exceeds 15% by weight, the initial ionic conductivity and the ionic conductivity retention of the polymer electrolyte membrane 2 rapidly decrease. When the content of the solvent after drying is less than 3%, it is apparent that sufficient tensile elongation at break cannot be obtained and the toughness is low.
[0043]
Therefore, the electrode structure according to the present embodiment provides the polymer electrolyte membrane 2 having the ionic conductivity by setting the content of the solvent after drying the polymer electrolyte membrane 2 in the range of 3 to 15% by weight. It is clear that excellent power generation performance can be obtained because of the above, and it can be easily produced for the polymer electrolyte membrane 2 having the tensile elongation at break (toughness).
[0044]
Next, for comparison, except that the sulfonated product of the copolymer was dissolved in dimethylacetamide instead of N-methylpyrrolidone to form a polymer electrolyte solution, and a film was formed from the polymer electrolyte solution by a casting method. A polymer electrolyte membrane having a dry film thickness of 50 μm and a solvent content of 5% by weight after drying was prepared in exactly the same manner as in the above embodiment. With respect to the polymer electrolyte membrane (Comparative Example), the initial ion conductivity, the ion conductivity retention, and the toughness were measured by exactly the same methods as in the above embodiment. The results are shown in Table 1 together with the polymer electrolyte membrane 2 (Example) in which the content of the solvent after drying in the above embodiment is 5% by weight.
[0045]
[Table 1]
As is clear from Table 1, the polymer electrolyte membrane (Example) formed from a polymer electrolyte solution obtained by dissolving a sulfonated product of the copolymer in N-methylpyrrolidone was obtained by using a sulfonated product of the copolymer. For the polymer electrolyte membrane (comparative example) formed from a polymer electrolyte solution dissolved in dimethylacetamide, the initial ionic conductivity and the tensile elongation at break (toughness) are almost the same, but the The rate retention is much better. Therefore, it is clear that an electrode structure having excellent power generation performance can be obtained by using the polymer electrolyte membrane of the above example.
[Brief description of the drawings]
FIG. 1 is an explanatory sectional view showing a configuration of an electrode structure of the present invention.
FIG. 2 is a graph showing the relationship between the initial ionic conductivity of a polymer electrolyte membrane used for an electrode structure of the present invention and the amount of a solvent contained in the polymer electrolyte membrane.
FIG. 3 is a graph showing the relationship between the ionic conductivity retention of a polymer electrolyte membrane used in the electrode structure of the present invention and the amount of a solvent contained in the polymer electrolyte membrane.
FIG. 4 is a graph showing the relationship between the toughness of a polymer electrolyte membrane used for the electrode structure of the present invention and the amount of a solvent contained in the polymer electrolyte membrane.
[Explanation of symbols]
1 ... electrode catalyst layer, 2 ... polymer electrolyte membrane.
Claims (5)
前記高分子電解質膜は一般式（１）で表される第１の繰返し単位と、一般式（２）で表される第２の繰返し単位との共重合体のスルホン化物を溶媒に溶解した溶液から成膜、乾燥してなり、乾燥後に前記溶媒を３〜１５重量％の範囲で含むことを特徴とする固体高分子型燃料電池用電極構造体。
The polymer electrolyte membrane is a solution in which a sulfonated copolymer of a first repeating unit represented by the general formula (1) and a second repeating unit represented by the general formula (2) is dissolved in a solvent. An electrode structure for a polymer electrolyte fuel cell, characterized in that the electrode structure is formed and dried, and after drying, the solvent is contained in the range of 3 to 15% by weight.
Priority Applications (6)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP2001176695A JP3563372B2 (en) | 2001-06-12 | 2001-06-12 | Electrode structure for polymer electrolyte fuel cell |
| PCT/JP2002/005728 WO2002101860A1 (en) | 2001-06-11 | 2002-06-10 | Electrode structure for solid polymer fuel cell, its production method, and solid polymer fuel cell |
| CA2450346A CA2450346C (en) | 2001-06-11 | 2002-06-10 | Electrode structure for solid polymer fuel cell, its production method, and solid polymer fuel cell |
| DE10296922T DE10296922T5 (en) | 2001-06-11 | 2002-06-10 | Electrode structure for polymer electrolyte fuel cells, method of manufacturing the same and polymer electrolyte fuel cell |
| CA2686279A CA2686279C (en) | 2001-06-11 | 2002-06-10 | Production method for an electrode structure for a solid polymer fuel cell |
| US10/480,375 US7494733B2 (en) | 2001-06-11 | 2002-06-10 | Electrode structure for solid polymer fuel cell, its production method, and solid polymer fuel cell |
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| JP2001176695A JP3563372B2 (en) | 2001-06-12 | 2001-06-12 | Electrode structure for polymer electrolyte fuel cell |
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