JP4239461B2

JP4239461B2 - Manufacturing method of membrane electrode assembly

Info

Publication number: JP4239461B2
Application number: JP2002085272A
Authority: JP
Inventors: 昭彦吉田; 栄一安本; 安男武部; 誠内田; 純司森田; 靖菅原; 堀　　喜博; 慎也古佐小
Original assignee: Panasonic Corp; Matsushita Electric Industrial Co Ltd
Current assignee: Panasonic Corp; Panasonic Holdings Corp
Priority date: 2002-03-26
Filing date: 2002-03-26
Publication date: 2009-03-18
Anticipated expiration: 2022-03-26
Also published as: JP2003282094A

Description

【０００１】
【発明の属する技術分野】
本発明は、燃料として純水素、あるいはメタノールまたは化石燃料からの改質水素、もしくはメタノール、エタノール、ジメチルエーテルなどの液体燃料を直接用い、空気や酸素を酸化剤とする燃料電池に関するものであり、とくに固体高分子を電解質に用いた燃料電池に関し、その膜電極接合体の製造方法に関するものである。
【０００２】
【従来の技術】
一般的に高分子電解質形燃料電池の電極は、高分子電解質を中心としてその外側両面に触媒層を持ち、さらにその触媒層の外面にガス拡散電極を形成してなる。燃料電池は、アノード側電極へ水素を、カソード側電極へ酸素を供給し、アノード電極中の触媒上で水素が水素イオンと電子に別れる。アノード電極中触媒上で生成された水素イオンは高分子電解質中を移動しカソード電極中触媒上まで達する。カソード電極中触媒上でこの高分子電解質中を移動してきた水素イオンと外部から供給された酸素が反応し、水が生成される。この際、全体反応により電気と熱が作り出される。ここで、高分子電解質中を水素イオンが容易に移動するためには、高分子電解質膜中に十分な水が確保されていることが不可欠である。そのため、高分子電解質に求められる特性としては、水分を吸いやすく、また、長期に渡り水分を保持できる能力が高いことが重要である。
【０００３】
【発明が解決しようとする課題】
このため、高分子電解質は保水性に優れた特性を持つよう開発されているため、燃料電池用電極の作製上でも作業環境雰囲気中の水分を高分子電解質が吸着しやすく、高分子電解質中の含水率が変化し、これに比例し形状も大きく変化してしまう。また、触媒を担持した導電性炭素粒子と高分子電解質と溶媒からなる塗料を用いて形成した電極を高分子電解質膜の片面または両面に配置した膜電極接合体では、電極で高分子電解質膜を挟時されている部分と、高分子電解質膜の両側に電極が存在しない部分とでは、含水率に差が生じているため、膜電極接合体の雰囲気による吸水量にも差が生じ膜電極接合体面内で膨張・収縮率に差が生じ、変形を引き起こしてしまう。さらに、電極面内および高分子電解質膜面内でも微妙に吸水量のバラツキを持っているため、波うちやひずみが発生している。燃料電池は水素ガスを燃料として供給するため、ガスシール性も重要である。このように、膜電極接合体の寸法変化は、製造工程での寸法不良を誘発し、シール性の低下を引き起こし、出力特性の低下および信頼性の低下を生じている。
【０００４】
【課題を解決するための手段】
本発明はこれら上記従来の課題を解決するもので、触媒を担持した導電性炭素粒子と、高分子電解質と、溶媒と、を有する電極用塗料を用いて形成した電極を、高分子電解質膜の片面もしくは両面に配置した膜電極接合体の製造方法において、高分子電解質膜を中央部がくり貫かれたフィルム状弾性体で面方向に固定した状態で、電極用塗料を塗布する工程と、電極用塗料を塗布する工程ののちに、高分子電解質膜を前記フィルム状弾性体で固定した状態で、溶媒を除去する工程と、を備えている、膜電極接合体の製造方法である。また、膜電極接合体の製造工程において、水分の吸収放出を行う工程、特に水洗工程、乾燥工程では、膜電極接合体を面方向に挟みこみ固定してあげることで、含水量による寸法変化を厚み方向で行い、面方向での寸法変化を抑止することにより、寸法不良の大幅低減が可能となる。
【０００５】
これらの構成によって、膜電極接合体の変形や寸法不良を低減することにより、ガスシール性が確実に行え、放電性能および信頼性の高い膜電極接合体の製造方法を提供することができる。
【０００６】
【発明の実施の形態】
本発明は、触媒を担持した導電性炭素粒子と、高分子電解質と、溶媒と、を有する電極用塗料を用いて形成した電極を、高分子電解質膜の片面もしくは両面に配置した膜電極接合体の製造方法において、高分子電解質膜を中央部がくり貫かれたフィルム状弾性体で面方向に固定した状態で、電極用塗料を塗布する工程と、電極用塗料を塗布する工程ののちに、高分子電解質膜をフィルム状弾性体で固定した状態で、溶媒を除去する工程と、を備えている。高分子電解質膜の含水率変化の最も大きい工程で高分子電解質膜を面方向に固定した状態で膜電極接合体を製造することで、面方向での寸法変化を抑え、膜電極接合体のひずみを緩和し、かつ、寸法不良を低減させることで、平滑なたわみの無い膜電極接合体を提供することが可能となり、ガスシール性の高く、放電性能および信頼性の高い膜電極接合体を提供するという作用を有する。
【０００７】
さらに、本発明の溶媒を除去する工程は、溶媒を水洗により除去する工程である。高分子電解質膜の片面または両面へ電極を設けた際、膜電極接合体中のイオン交換基に吸着していた残存する溶媒を強制的に水洗により除去することで、イオン交換パスが十分確保され、高い放電性能を提供することが可能となる。また、この際、膜電極接合体は水分の吸収放出を行うため、高分子電解質膜を面方向に固定した状態で膜電極接合体を製造することで、面方向での寸法変化を抑え、膜電極接合体のひずみを緩和し、かつ、寸法不良を低減させることで、平滑なたわみの無い膜電極接合体を提供することが可能となり、ガスシール性の高く、放電性能および信頼性の高い膜電極接合体を提供するという作用を有する。
【０００８】
さらに、本発明の溶媒を除去する工程は、溶媒をオゾン酸化処理により除去する工程である。高分子電解質膜の片面または両面へ電極を設けた際、膜電極接合体中のイオン交換基に吸着していた残存する溶媒を強制的に酸化処理により除去することで、イオン交換パスが十分確保され、高い放電性能を提供することが可能となる。また、この際、膜電極接合体は残存溶媒の放出を行うため、高分子電解質膜を面方向に固定した状態で膜電極接合体を製造することで、面方向での寸法変化を抑え、膜電極接合体のひずみを緩和し、かつ、寸法不良を低減させることで、平滑なたわみの無い膜電極接合体を提供することが可能となり、ガスシール性の高く、放電性能および信頼性の高い膜電極接合体を提供するという作用を有する。
【０００９】
さらに、本発明の高分子電解質膜をフィルム状弾性体で面方向に固定した状態は、高分子電解質膜の両面を一対のフィルム状弾性体で挟み込むように固定した状態である。この際、膜電極接合体は水分の吸収放出を行うため、フィルム状弾性体で高分子電解質膜を面方向に固定した状態で膜電極接合体を製造することで、面方向での寸法変化を厚み方向に逃がすことにより、膜電極接合体のひずみを速やかに緩和し、かつ、寸法不良を低減させることで、平滑なたわみの無い膜電極接合体を提供することが可能となり、ガスシール性の高く、放電性能および信頼性の高い膜電極接合体を提供するという作用を有する。
【００１０】
以下、本発明の実施の形態について説明する。
【００１１】
図１に示すとおり、高分子電解質膜１の外面に２Ａ、２Ｂで示される触媒層電極が配置され、膜電極接合体を構成する。通常、燃料電池では、この膜電極接合体の外面に、ガス拡散電極３Ａおよび３Ｂを配置し、さらにその外面にガス供給・排出路をもつセパレータ４Ａおよび４Ｂを配置し、単セルを構成する。この、単セルを複数枚積層することで希望の発電能力を持つ燃料電池スタックを得る。ここで、発電のポイントとなる電極反応を以下に記す。アノード反応ガス（水素）は４Ａから供給され３Ａを通り２Ａへ、カソード反応ガス（酸素）は４Ｂから３Ｂを通り２Ｂへ供給される。アノード触媒層上２ＡではＨ_２→２Ｈ^＋＋２ｅ⁻の反応が起こり、カソード触媒層上２Ｂでは１／２Ｏ_２＋２Ｈ^＋＋２ｅ⁻→Ｈ_２Ｏの反応が起こり、全体としてＨ_２＋１／２Ｏ_２→Ｈ_２Ｏ＋Ｑとなる。この反応により起電力が得られ、この電気エネルギーにより発電がなされる。同時に水の生成がカソード触媒層２Ｂで起こる。また、起電反応の際、アノード触媒層２Ａで生じたＨ^＋は高分子電解質膜１中を移動しカソード触媒層２Ｂへ至る。この際１個のＨ^＋イオンが移動する際、５〜２０個のＨ_２Ｏ分子を同伴して移動する。高分子電解質膜は十分な水が存在し初めてＨ^＋イオンの高い導電性を発揮する性質がある。そのため、高分子電解質膜は高い水分吸着能力を持つよう開発が進められている。このため、膜電極接合体を製造する工程中で、空気中の水分を電解質が吸収してしまうため、膜の平滑性が損なわれる。このため、膜が水分を吸収し浪打が生じる部分、特に膜電極接合体の膜と電極が接していない部分、電極の外周部に位置する高分子電解質のみの部分に、あらかじめその表面を粗すことにより表面積を増してあげることで、面方向への伸びを緩和し、寸法変化の少ない、平滑な膜電極接合体を提供することが可能となり、シール性が高く、放電特性および信頼性の高い膜電極接合体を提供することが図れる。高分子電解質膜の表面をあらす方法としては、テフロンシートや、ポリエチレンシート、ポリプロピレンシート、他、あらかじめシートの表面が荒れているもので高分子電解質膜を挟み込み、１０ｋｇｆ／ｃｍ ^２以上の面圧で締め付けてあげることで達成できる。この際、高分子電解質を挟み込むシートは２層以上で成っていることが好ましく、１層は表面が荒れていて、耐熱性が高く、弾性の低いシートと残りの１層は耐熱性が高く弾性の高いシートであることが好ましい。高分子電解質膜の表面をより均一にかつ素早く粗すために、両面をフィルム状弾性体で挟み込み熱プレスを施す。この際、高分子電解質膜は雰囲気と同量の飽和水蒸気量を保持しているため、熱プレスによりこの水分が放出され、変形を起こす。このとき、高分子電解質膜に働く収縮しようとする力に負けない力で保持するだけのシートを用いなくてはならないためである。
【００１２】
また、高分子電解質膜の表面を粗す方法と同様に高分子電解質膜を固定した状態で製造する方法も必要である。高分子電解質膜へ電極を配置する方法として、高分子電解質膜へ直接電極を印刷または塗工する印刷法、シートへ一旦電極を形成し、出来上がった電極を高分子電解質膜へ転写させる転写法、等が考えられる。この膜電極接合体を作製するにはコピー機のように電極構成材料を粉体の状態で扱うことも可能であるが、一般的には溶媒を用いてインクとして電極構成材料を扱い、電極形成後に溶媒を除去する方法が採られている。この後者の方法では、電極中に溶媒が残存するため、溶媒除去を行うことが高い放電性能を確保するために重要である。その際、高分子電解質膜上に電極を形成する際および膜電極接合体中の電極分の溶媒除去に伴い高分子電解質膜の変形が発生するため、前述のシート等で膜電極接合体の製造工程中はこれを挟み込んでおくことで、平滑な膜電極接合体を提供することが可能となり、シール性が高く、放電特性および信頼性の高い膜電極接合体を提供することが図れる。
【００１３】
以上の本発明の方法により作成された膜電極接合体を用いることによって、シール性が高く、放電特性および信頼性の高い膜電極接合体およびその電極を用いた燃料電池を提供することができる。さらに詳しくは実施例において具体的に説明する。
【００１４】
【実施例】
（実施例１）
ジャパンゴアテックス社製ゴアセレクト高分子電解質膜の両面を、両面がシリコーンゴムでなり、中央部がＰＥＴフィルムでできた３層からなるクレハエラストマー社製高分子フィルムで挟み込み、１１５℃の温度で面圧２５ｋｇ／ｃｍ ^２の条件で３分間熱プレスすることで高分子電解質膜を固定した。この際、高分子フイルムは高分子電解質膜にあとから電極を構成できるよう中央部を電極寸法でくり貫いておいた。
【００１５】
また、ライオン社製の炭素微粉末ケッチェンブラックＥＣ上に、白金触媒を５０重量％担持した触媒を、旭硝子社製ＦＳＳ溶液を高分子電解質が３０重量％となるよう混合した電極用塗料を用いて、ポリプロピレンフィルムの上に電極を形成し、５０℃の温度で３０分間乾燥してシート状電極を得た。ついで、この高分子フィルムがくり貫かれ高分子電解質膜が出ている中央部分に、あらかじめ作製しておいた電極を両面から熱プレスし、膜電極接合体を作製した。さらにこの膜電極接合体を、片面に複数本の溝を切ったポリカーボネート製板で挟み込み、さらに、これらを両面からステンレス板で挟みこみ締結圧が１ｋｇ／ｃｍ ^２となるよう挟み込み、その状態を保持したまま水洗を１時間、その後、１００℃で３時間乾燥させ、室温まで冷却した。この後、締結をはずし、高分子フィルムをはがして膜電極接合体Ａを得た。このとき、膜電極接合体の電極部分の外周部に位置する高分子電解質膜部分のＪＩＳＢ０６０１評価法における表面粗さの算術平均粗さＲａは０
．３４μｍであり、最大高さＲｙは４．９４μｍであった。
【００１６】
（実施例２）
ジャパンゴアテックス社製ゴアセレクト高分子電解質膜の両面を、両面がシリコーンゴムでなり、中央部がＰＥＴフィルムでできた３層からなるクレハエラストマー社製高分子フィルムで挟み込み、１１５℃の温度で面圧２５ｋｇ／ｃｍ ^２の条件で３分間熱プレスすることで高分子電解質膜を固定した。この際、高分子フイルムは高分子電解質膜にあとから電極を構成できるよう中央部を電極寸法でくり貫いておいた。また、ライオン社製の炭素微粉末ケッチェンブラックＥＣ上に、白金触媒を５０重量％担持した触媒を、旭硝子社製ＦＳＳ溶液を高分子電解質が３０重量％となるよう混合した電極用塗料を用いて、ポリプロピレンフィルムの上に電極を形成し、５０℃の温度で３０分間乾燥してシート状電極を得た。ついで、この高分子フィルムがくり貫かれ高分子電解質膜が出ている中央部分に、あらかじめ作製しておいた電極を両面から熱プレスし、膜電極接合体を作製した。さらにこの膜電極接合体を、片面に複数本の溝を切ったポリカーボネート製板で挟み込み、さらに、これらを両面からステンレス板で挟みこみ締結圧が１ｋｇ／ｃｍ ^２となるよう挟み込み、その状態を保持したまま、オゾン洗浄装置で２０分間洗浄、室温まで冷却した後、締結をはずし、高分子フィルムをはがして膜電極接合体Ｂを得た。このとき、膜電極接合体の電極部分の外周部に位置する高分子電解質膜部分のＪＩＳＢ０６０１評価法における表面粗さの算術平均粗さＲａは０．４４μｍであり、最大高さＲｙは５．８２μｍであった。
【００１７】
（比較例１）
ジャパンゴアテックス社製ゴアセレクト高分子電解質膜の両面を、両面がシリコーンゴムでなり、中央部がＰＥＴフィルムでできた３層からなるクレハエラストマー社製高分子フィルムで挟み込み、１１５℃の温度で面圧２５ｋｇ／ｃｍ ^２の条件で３分間熱プレスすることで高分子電解質膜を固定した。この際、高分子フイルムは高分子電解質膜にあとから電極を構成できるよう中央部を電極寸法でくり貫いておいた。また、ライオン社製の炭素微粉末ケッチェンブラックＥＣ上に、白金触媒を５０重量％担持した触媒を、旭硝子社製ＦＳＳ溶液を高分子電解質が３０重量％となるよう混合した電極用塗料を用いて、ポリプロピレンフィルムの上に電極を形成し、５０℃の温度で３０分間乾燥してシート状電極を得た。ついで、この高分子フィルムがくり貫かれ高分子電解質膜が出ている中央部分に、あらかじめ作製しておいた電極を両面から熱プレスし、膜電極接合体Ｃを作製した。このとき、膜電極接合体の電極部分の外周部に位置する高分子電解質膜部分のＪＩＳＢ０６０１評価法における表面粗さの算術平均粗さＲａは０．１４μｍであり、最大高さＲｙは１．５５μｍであった。
【００１８】
（比較例２）
例えば、ライオン社製の炭素微粉末ケッチェンブラックＥＣ上に、白金触媒を５０重量％担持した触媒を、旭硝子社製ＦＳＳ溶液を高分子電解質が３０重量％となるよう混合した電極用塗料を用いて、ポリプロピレンフィルムの上に電極を形成し、５０℃の温度で３０分間乾燥してシート状電極を得た。ついで、ジャパンゴアテックス社製ゴアセレクト高分子電解質膜の両面に電極を配置し、両面から熱プレスして、膜電極接合体Ｄを作製した。このとき、膜電極接合体の電極部分の外周部に位置する高分子電解質膜部分のＪＩＳＢ０６０１評価法における表面粗さの算術平均粗さＲａは０．０４μｍであり、最大高さＲｙは０．２６μｍであった。膜電極接合体の波打ちがひどく、平滑性は確保されていなかった。
【００１９】
（比較例３）
例えば、ライオン社製の炭素微粉末ケッチェンブラックＥＣ上に、白金触媒を５０重量％担持した触媒を、旭硝子社製ＦＳＳ溶液を高分子電解質が３０重量％となるよう混合した電極用塗料を用いて、ポリプロピレンフィルムの上に電極を形成し、５０℃の温度で３０分間乾燥してシート状電極を得た。ついで、ジャパンゴアテックス社製ゴアセレクト高分子電解質膜の両面に電極を配置し、両面から熱プレスして、膜電極接合体を作製した。次いで、この膜電極接合体の４角を固定した状態で、水洗し、乾燥させた。このとき得られた、膜電極接合体Ｅは収縮による変形がひどく水洗条件、乾燥条件を変更しても膜電極接合体として使用可能な状態で得ることはできなかった。
【００２０】
以上のとおり作製した実施例１、２および比較例１、２の膜電極接合体にガス拡散電極およびシール材を定着し、単電池Ａ、ＢおよびＣ、Ｄを作製し、燃料極に純水素ガスを，空気極に空気をそれぞれ供給し、電池温度を７５℃、燃料ガス利用率を７０％、空気利用率（以下Ｕｏと略。）を４０％とした。ガス加湿は燃料ガスを７０℃、空気を７０℃のバブラーをそれぞれ通して供給し、水素―空気燃料電池としての単電池の放電試験を行った。
【００２１】
図２に，本発明の実施例１と２の単電池ＡとＢおよび比較例１と２の単電池ＣとＤの水素−空気型燃料電池としての放電特性試験結果を示した。電流密度２００ｍＡ／ｃｍ^２における単電池電圧で示すと、単電池Ａ、ＢおよびＣ、Ｄの電圧は、それぞれ順に、７７９ｍＶ、７７１ｍＶ、７４２ｍＶ、５７０ｍＶであった。図２からも分かるとおり電極中に残存している電極作製時の溶媒を除去することで、高い活性が得られ放電性能が高いことが分かる。また、比較例２の単電池Ｄではシール性が悪く、燃料ガスの漏れが発生してしまい、放電性能の低下を引き起こしてしまった。特に低電流密度側では供給ガスの絶対量が少ないため、放電特性の低下は顕著である。
【００２２】
図３に本発明の実施例１と２の単電池ＡとＢおよび比較例１と２の単電池ＣとＤの水素−空気型燃料電池としての耐久試験結果を示した。実施例１、２および比較例１、２の単電池Ａ、ＢおよびＣ、Ｄの燃料極に純水素ガスを，空気極に空気をそれぞれ供給し、電池温度を７５℃、燃料ガス利用率を７０％、空気利用率（以下Ｕｏと略。）を４０％、電流密度を３００ｍＡ／ｃｍ ^２とし、ガス加湿は燃料ガスを７０℃、空気を７０℃のバブラーをそれぞれ通して供給し、水素―空気燃料電池としての単電池の耐久試験を行った。この結果から分かる通り、溶媒除去を実施した膜電極接合体は信頼性も確保されているのに対し、溶媒除去を実施しなかったものは信頼性が確保できなかった。残存溶媒によるイオン導電パスが初期の段階では阻害されていて、運転により生成された水により一旦は溶媒除去と同等の効果を得られたが、初期の段階で電流密度が偏析し、局部的に発電を行ったため劣化を招き、長期信頼性が低下したものと考えられる。
【００２３】
高分子膜電解質を固定せずに製造したものは、変形が大きく製品として完成できないものが多く、完成しても結果として性能が悪いことが分かった。
【００２４】
このように、本発明の膜電極接合体およびその製造方法とそれを用いた燃料電池のように触媒を担持した導電性炭素粒子と高分子電解質と溶媒からなる塗料を用いて形成した電極を高分子電解質膜の片面または両面に配置した膜電極接合体において、電極の周縁部に位置する高分子電解質膜部分の表面を粗すことにより、電極の周縁部に位置する高分子電解質膜の表面積を増し、水分の吸収放出による膜の膨張収縮を低減させることで、変形によるシール性の低下を抑制するものである。また、膜電極接合体の製造工程において、水分の吸収放出を行う工程、特に水洗工程、乾燥工程では、膜電極接合体を面方向に挟みこみ固定してあげることで、含水量による寸法変化を厚み方向で行い、面方向での寸法変化を抑止することにより、寸法不良の大幅低減が可能となる。
【００２５】
これらの構成によって、膜電極接合体の変形や寸法不良を低減することにより、ガスシール性が確実に行え、放電性能および信頼性の高い膜電極接合体を提供することができる。
【００２６】
燃料電池は通常、複数の単電池を直列または並列に接続して用いられる。したがって、単電池での特性低下は燃料電池スタックの性能に大きく影響する。とくに、直列に接続された場合には、最も特性の低い単電池の限界電流値が燃料電池スタック全体の限界電流値となってしまうため、最も低い単電池の性能が燃料電池スタック全体の性能の限界値となる。つまり、単電池での性能を少しでも低減することが今後の重要な課題となる。従って、本発明の燃料電池用電極は、結果的に燃料電池スタックの放電性能が向上すると言える。
【００２７】
なお、本実施例において燃料の一例として、水素と空気を用いたが、水素は改質水素として炭酸ガスや窒素、一酸化炭素などの不純物を含む燃料においても同様の結果が得られ、水素の代わりにメタノール、エタノール、ジメチルエーテルなどの液体燃料およびその混合物を用いても同様の結果が得られた。また、液体燃料はあらかじめ蒸発させ、蒸気として供給してもよい。
【００２８】
さらに、本実施例の構成は、実施例の触媒層や膜の構成に限定されるものではなく種々の触媒層の構成にも効果があった。
【００２９】
さらに、本発明の固体高分子型電解質と電極との接合体を用いて、酸素、オゾン、水素などのガス発生機やガス精製機および酸素センサ、アルコールセンサなどの各種ガスセンサへの応用にも効果がある。
【００３０】
【発明の効果】
以上、実施例の説明から明らかなように、膜電極接合体の変形や寸法不良を低減することにより、ガスシール性が確実に行え、放電性能および信頼性の高い膜電極接合体およびその製造方法とそれを用いた燃料電池を実現することができた。
【図面の簡単な説明】
【図１】従来の燃料電池単セルの断面概略図
【図２】水素−空気型燃料電池の電圧−電流特性を示す図
【図３】水素−空気型燃料電池の信頼性を示す図
【符号の説明】
１高分子電解質膜
２Ａ，２Ｂ触媒層電極
３Ａ，３Ｂガス拡散電極
４Ａ，４Ｂセパレータ[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a fuel cell using pure hydrogen as a fuel, reformed hydrogen from methanol or fossil fuel, or liquid fuel such as methanol, ethanol, dimethyl ether, etc., and using air or oxygen as an oxidant. it relates to a fuel cell using a solid polymer as the electrolyte, a manufacturing method of that of the membrane electrode assembly.
[0002]
[Prior art]
In general, an electrode of a polymer electrolyte fuel cell is formed by having a catalyst layer on both outer sides of a polymer electrolyte, and further forming a gas diffusion electrode on the outer surface of the catalyst layer. The fuel cell supplies hydrogen to the anode side electrode and oxygen to the cathode side electrode, and hydrogen is separated into hydrogen ions and electrons on the catalyst in the anode electrode. Hydrogen ions generated on the catalyst in the anode electrode move in the polymer electrolyte and reach the catalyst in the cathode electrode. Hydrogen ions that have migrated in the polymer electrolyte on the catalyst in the cathode electrode react with oxygen supplied from the outside to produce water. At this time, electricity and heat are generated by the overall reaction. Here, in order for hydrogen ions to move easily in the polymer electrolyte, it is essential that sufficient water is secured in the polymer electrolyte membrane. For this reason, it is important that the polymer electrolyte has a high ability to easily absorb moisture and to retain moisture for a long period of time.
[0003]
[Problems to be solved by the invention]
For this reason, since the polymer electrolyte has been developed to have excellent water retention characteristics, it is easy for the polymer electrolyte to adsorb moisture in the working environment atmosphere even in the production of the fuel cell electrode. The moisture content changes, and the shape changes greatly in proportion to this. In addition, in a membrane electrode assembly in which an electrode formed using a coating composed of conductive carbon particles supporting a catalyst, a polymer electrolyte, and a solvent is disposed on one or both sides of the polymer electrolyte membrane, the polymer electrolyte membrane is attached with an electrode. Since there is a difference in moisture content between the sandwiched part and the part where no electrode is present on both sides of the polymer electrolyte membrane, there is also a difference in water absorption due to the atmosphere of the membrane electrode assembly. Differences in expansion / contraction rates occur within the body surface, causing deformation. Furthermore, since there is a slight variation in the amount of water absorption even within the electrode surface and the polymer electrolyte membrane surface, wave undulations and distortion occur. Since the fuel cell supplies hydrogen gas as fuel, gas sealing performance is also important. Thus, the dimensional change of the membrane electrode assembly induces a dimensional defect in the manufacturing process, causes a decrease in sealing performance, and causes a decrease in output characteristics and a decrease in reliability.
[0004]
[Means for Solving the Problems]
The present invention solves these aforementioned conventional problems, and conductive carbon particles carrying catalyst, and a polymer electrolyte, a solvent, an electrode formed using the electrode for coating having the polymer electrolyte membrane It sided Moshiku in the manufacturing method of the membrane electrode assembly arranged on both sides, while being fixed to the surface direction in the polymer electrolyte membrane central portion is hollowed film-like elastic body, a step of applying an electrode coating material And a step of removing the solvent after fixing the polymer electrolyte membrane with the film-like elastic body after the step of applying the electrode coating material . Also, in the process of manufacturing a membrane electrode assembly, in the process of absorbing and releasing moisture, especially in the water washing process and the drying process, the membrane electrode assembly is sandwiched and fixed in the surface direction, so that the dimensional change due to the water content is changed. By performing in the thickness direction and suppressing dimensional changes in the surface direction, dimensional defects can be greatly reduced.
[0005]
With these configurations, it is possible to provide a method of manufacturing a membrane / electrode assembly with high gas discharge performance and high discharge performance and reliability by reducing deformation and dimensional defects of the membrane / electrode assembly.
[0006]
DETAILED DESCRIPTION OF THE INVENTION
The present invention includes a conductive carbon particles carrying catalyst, and a polymer electrolyte, a solvent, an electrode formed using the electrode for coating having a film one side Moshiku of the polymer electrolyte membrane was disposed on both sides electrodes In the method of manufacturing the joined body , after the step of applying the electrode coating material and the step of applying the electrode coating material in a state where the polymer electrolyte membrane is fixed in the surface direction with a film-like elastic body having a central portion cut out, And a step of removing the solvent in a state where the polymer electrolyte membrane is fixed with a film-like elastic body. By manufacturing the membrane electrode assembly with the polymer electrolyte membrane fixed in the surface direction in the process with the largest change in the moisture content of the polymer electrolyte membrane, the dimensional change in the surface direction is suppressed, and the strain of the membrane electrode assembly is reduced. It is possible to provide a membrane electrode assembly that is smooth and free of deflection by reducing dimensional defects and providing a membrane electrode assembly that has high gas sealing performance, high discharge performance, and high reliability. Has the effect of
[0007]
Furthermore, the step of removing the solvent of the present invention is a step of removing the solvent by washing with water. When the electrode is provided on one or both sides of the polymer electrolyte membrane, the remaining solvent adsorbed on the ion exchange groups in the membrane / electrode assembly is forcibly removed by washing with water to ensure a sufficient ion exchange path. It is possible to provide high discharge performance. At this time, since the membrane / electrode assembly absorbs and releases moisture, the membrane / electrode assembly is manufactured with the polymer electrolyte membrane fixed in the plane direction, thereby suppressing the dimensional change in the plane direction. By reducing the distortion of the electrode assembly and reducing the dimensional defects, it becomes possible to provide a membrane electrode assembly that is smooth and free of deflection, and has a high gas sealing property, high discharge performance, and high reliability. It has the effect | action of providing an electrode assembly.
[0008]
Furthermore, the step of removing the solvent of the present invention is a step of removing the solvent by ozone oxidation treatment. When an electrode is provided on one or both sides of a polymer electrolyte membrane, the remaining solvent adsorbed on the ion exchange groups in the membrane electrode assembly is forcibly removed by oxidation treatment, ensuring a sufficient ion exchange path Therefore, it becomes possible to provide high discharge performance. At this time, since the membrane / electrode assembly releases the residual solvent, the membrane / electrode assembly is manufactured with the polymer electrolyte membrane fixed in the plane direction, thereby suppressing the dimensional change in the plane direction. By reducing the distortion of the electrode assembly and reducing the dimensional defects, it becomes possible to provide a membrane electrode assembly that is smooth and free of deflection, and has a high gas sealing property, high discharge performance, and high reliability. It has the effect | action of providing an electrode assembly.
[0009]
Furthermore, the state in which the polymer electrolyte membrane of the present invention is fixed in the plane direction with a film-like elastic body is a state in which both surfaces of the polymer electrolyte membrane are fixed so as to be sandwiched between a pair of film-like elastic bodies. At this time, since the membrane / electrode assembly absorbs and releases moisture, the dimensional change in the plane direction can be changed by manufacturing the membrane / electrode assembly with the polymer electrolyte membrane fixed in the plane direction with a film-like elastic body. By escaping in the thickness direction, the strain of the membrane electrode assembly can be quickly relieved, and the dimensional defects can be reduced, thereby providing a membrane electrode assembly that is smooth and free of deflection. It has the effect of providing a membrane electrode assembly that is high in discharge performance and reliability.
[0010]
Embodiments of the present invention will be described below.
[0011]
As shown in FIG. 1, catalyst layer electrodes indicated by 2A and 2B are arranged on the outer surface of the polymer electrolyte membrane 1 to constitute a membrane electrode assembly. Normally, in a fuel cell, gas diffusion electrodes 3A and 3B are disposed on the outer surface of the membrane electrode assembly, and separators 4A and 4B having gas supply / discharge paths are disposed on the outer surface to constitute a single cell. A fuel cell stack having a desired power generation capacity is obtained by laminating a plurality of single cells. Here, the electrode reaction that is the point of power generation is described below. The anode reaction gas (hydrogen) is supplied from 4A and passes through 3A to 2A, and the cathode reaction gas (oxygen) is supplied from 4B through 3B to 2B. A reaction of H ₂ → 2H ⁺ + 2e ⁻ occurs on the anode catalyst layer 2A, and a reaction of 1 / 2O ₂ + 2H ⁺ + 2e ⁻ → H ₂ O occurs on the cathode catalyst layer 2B. As a whole, H ₂ + 1 / 2O ₂ → H ₂ O + Q. An electromotive force is obtained by this reaction, and electric power is generated by this electric energy. At the same time, water is generated in the cathode catalyst layer 2B. Further, during the electromotive reaction, H ⁺ generated in the anode catalyst layer 2A moves through the polymer electrolyte membrane 1 and reaches the cathode catalyst layer 2B. At this time, when one H ⁺ ion moves, it moves with 5 to 20 H ₂ O molecules. The polymer electrolyte membrane has a property of exhibiting high conductivity of H ⁺ ions only when sufficient water is present. Therefore, the development of polymer electrolyte membranes is progressing to have a high moisture adsorption ability. For this reason, in the process of manufacturing a membrane electrode assembly, since the electrolyte absorbs moisture in the air, the smoothness of the membrane is impaired. For this reason, the surface of the membrane is preliminarily roughened in the portion where the membrane absorbs moisture and causes slap, particularly in the portion where the membrane and the electrode are not in contact with each other, or only in the portion of the polymer electrolyte located on the outer periphery of the electrode By increasing the surface area, it becomes possible to provide a smooth membrane electrode assembly that relaxes the elongation in the surface direction and has little dimensional change, and has high sealing performance, high discharge characteristics and high reliability. It is possible to provide a membrane electrode assembly. As a method for expressing the surface of the polymer electrolyte membrane, a Teflon sheet, a polyethylene sheet, a polypropylene sheet, or the like, in which the surface of the sheet is rough in advance, the polymer electrolyte membrane is sandwiched and the surface pressure is 10 kgf / cm ² or more. This can be achieved by tightening. In this case, the sheet sandwiching the polymer electrolyte is preferably composed of two or more layers, and one layer has a rough surface, high heat resistance, and a low elasticity sheet and the remaining one layer have high heat resistance and elasticity. The sheet is preferably high. In order to roughen the surface of the polymer electrolyte membrane more uniformly and quickly, both sides are sandwiched between film-like elastic bodies and subjected to hot press. At this time, since the polymer electrolyte membrane retains the same amount of saturated water vapor as the atmosphere, this moisture is released by hot pressing, causing deformation. This is because a sheet that can be held only by a force that does not lose the force of contracting acting on the polymer electrolyte membrane must be used.
[0012]
In addition, a method for producing a state in which the polymer electrolyte membrane is fixed is also required as in the method for roughening the surface of the polymer electrolyte membrane. As a method of placing the electrode on the polymer electrolyte membrane, a printing method in which the electrode is directly printed or coated on the polymer electrolyte membrane, a transfer method in which the electrode is once formed on the sheet, and the completed electrode is transferred to the polymer electrolyte membrane, Etc. are considered. In order to produce this membrane electrode assembly, it is possible to handle the electrode constituent material in a powder state as in a copying machine, but in general, the electrode constituent material is handled as ink using a solvent to form an electrode. method for removing the solvent are adopted after. In this latter method, since the solvent remains in the electrode, it is important to remove the solvent in order to ensure high discharge performance. At that time, since the polymer electrolyte membrane is deformed when the electrode is formed on the polymer electrolyte membrane and when the solvent in the membrane electrode assembly is removed, the membrane electrode assembly is manufactured using the above-mentioned sheet or the like. By sandwiching this during the process, it is possible to provide a smooth membrane / electrode assembly, and it is possible to provide a membrane / electrode assembly with high sealing performance and high discharge characteristics and reliability.
[0013]
By using the membrane electrode assembly produced by the above-described method of the present invention, it is possible to provide a membrane electrode assembly having high sealing properties and high discharge characteristics and reliability, and a fuel cell using the electrode. Further details will be specifically described in Examples.
[0014]
【Example】
Example 1
Japan Gore-Tex's Gore Select polymer electrolyte membrane is sandwiched between three layers of Kureha Elastomer's polymer film consisting of silicone rubber on both sides and PET film at the center, and the surface at a temperature of 115 ° C. The polymer electrolyte membrane was fixed by hot pressing for 3 minutes under a pressure of 25 kg / cm ² . At this time, the polymer film was cut through the central portion with the electrode dimensions so that the electrode could be formed later on the polymer electrolyte membrane.
[0015]
In addition, a paint for electrodes in which a catalyst supporting 50% by weight of a platinum catalyst on a carbon fine powder ketjen black EC manufactured by Lion Co., Ltd. and an FSS solution manufactured by Asahi Glass Co., Ltd. so that the polymer electrolyte is 30% by weight is used. Then, an electrode was formed on the polypropylene film and dried at a temperature of 50 ° C. for 30 minutes to obtain a sheet-like electrode. Next, the electrode prepared in advance was hot-pressed from both sides in the central portion where the polymer film was cut out and the polymer electrolyte membrane was protruding, to prepare a membrane electrode assembly. Further, the membrane electrode assembly is sandwiched between polycarbonate plates having a plurality of grooves cut on one side, and further sandwiched between both sides with a stainless steel plate so that the fastening pressure is 1 kg / cm ^2, and the state is maintained. Washing with water for 1 hour, followed by drying at 100 ° C. for 3 hours and cooling to room temperature. Thereafter, the fastening was removed, and the polymer film was peeled off to obtain a membrane electrode assembly A. At this time, the arithmetic average roughness Ra of the surface roughness in the JIS B 0601 evaluation method of the polymer electrolyte membrane portion located on the outer peripheral portion of the electrode portion of the membrane electrode assembly is 0.
. It was 34 μm, and the maximum height Ry was 4.94 μm.
[0016]
(Example 2)
Japan Gore-Tex's Gore Select polymer electrolyte membrane is sandwiched between three layers of Kureha Elastomer's polymer film consisting of silicone rubber on both sides and PET film at the center, and the surface at a temperature of 115 ° C. The polymer electrolyte membrane was fixed by hot pressing for 3 minutes under a pressure of 25 kg / cm ² . At this time, the polymer film was cut through the central portion with the electrode dimensions so that the electrode could be formed later on the polymer electrolyte membrane. In addition, a paint for electrodes in which a catalyst supporting 50% by weight of a platinum catalyst on a carbon fine powder ketjen black EC manufactured by Lion Co., Ltd. and an FSS solution manufactured by Asahi Glass Co., Ltd. so that the polymer electrolyte is 30% by weight is used. Then, an electrode was formed on the polypropylene film and dried at a temperature of 50 ° C. for 30 minutes to obtain a sheet-like electrode. Next, the electrode prepared in advance was hot-pressed from both sides in the central portion where the polymer film was cut out and the polymer electrolyte membrane was protruding, to prepare a membrane electrode assembly. Further, the membrane electrode assembly is sandwiched between polycarbonate plates having a plurality of grooves cut on one side, and further sandwiched between both sides with a stainless steel plate so that the fastening pressure is 1 kg / cm ^2, and the state is maintained. Then, after washing with an ozone cleaning device for 20 minutes and cooling to room temperature, the fastening was removed, and the polymer film was peeled off to obtain a membrane electrode assembly B. At this time, the arithmetic average roughness Ra of the surface roughness in the JIS B 0601 evaluation method of the polymer electrolyte membrane portion located on the outer peripheral portion of the electrode portion of the membrane electrode assembly is 0.44 μm, and the maximum height Ry is 5 0.82 μm.
[0017]
(Comparative Example 1)
Japan Gore-Tex's Gore Select polymer electrolyte membrane is sandwiched between three layers of Kureha Elastomer's polymer film consisting of silicone rubber on both sides and PET film at the center, and the surface at a temperature of 115 ° C. The polymer electrolyte membrane was fixed by hot pressing for 3 minutes under a pressure of 25 kg / cm ² . At this time, the polymer film was cut through the central portion with the electrode dimensions so that the electrode could be formed later on the polymer electrolyte membrane. In addition, a paint for electrodes in which a catalyst supporting 50% by weight of a platinum catalyst on a carbon fine powder ketjen black EC manufactured by Lion Co., Ltd. and an FSS solution manufactured by Asahi Glass Co., Ltd. so that the polymer electrolyte is 30% by weight is used. Then, an electrode was formed on the polypropylene film and dried at a temperature of 50 ° C. for 30 minutes to obtain a sheet-like electrode. Next, the electrode prepared in advance was hot-pressed from both sides in the central portion where the polymer film was cut out and the polymer electrolyte membrane was protruding, so that a membrane electrode assembly C was prepared. At this time, the arithmetic average roughness Ra of the surface roughness in the JIS B 0601 evaluation method of the polymer electrolyte membrane portion located on the outer peripheral portion of the electrode portion of the membrane electrode assembly is 0.14 μm, and the maximum height Ry is 1. 0.55 μm.
[0018]
(Comparative Example 2)
For example, a paint for electrodes in which a catalyst supporting 50% by weight of a platinum catalyst on a carbon fine powder ketjen black EC manufactured by Lion is mixed with an FSS solution manufactured by Asahi Glass Co., Ltd. so that the polymer electrolyte is 30% by weight is used. Then, an electrode was formed on the polypropylene film and dried at a temperature of 50 ° C. for 30 minutes to obtain a sheet-like electrode. Next, electrodes were placed on both sides of the Gore Select polymer electrolyte membrane manufactured by Japan Gore-Tex, and hot pressed from both sides to produce membrane electrode assembly D. At this time, the arithmetic average roughness Ra of the surface roughness in the JIS B 0601 evaluation method of the polymer electrolyte membrane portion located on the outer peripheral portion of the electrode portion of the membrane electrode assembly is 0.04 μm, and the maximum height Ry is 0. .26 μm. The corrugation of the membrane electrode assembly was severe, and smoothness was not ensured.
[0019]
(Comparative Example 3)
For example, a paint for electrodes in which a catalyst supporting 50% by weight of a platinum catalyst on a carbon fine powder ketjen black EC manufactured by Lion is mixed with an FSS solution manufactured by Asahi Glass Co., Ltd. so that the polymer electrolyte is 30% by weight is used. Then, an electrode was formed on the polypropylene film and dried at a temperature of 50 ° C. for 30 minutes to obtain a sheet-like electrode. Next, electrodes were placed on both sides of the Gore Select polymer electrolyte membrane manufactured by Japan Gore-Tex, and hot pressed from both sides to produce a membrane electrode assembly. Next, the membrane electrode assembly was washed with water and dried with the four corners fixed. The membrane electrode assembly E obtained at this time was severely deformed by shrinkage and could not be obtained in a usable state as a membrane electrode assembly even if the washing and drying conditions were changed.
[0020]
A gas diffusion electrode and a sealing material were fixed to the membrane electrode assemblies of Examples 1 and 2 and Comparative Examples 1 and 2 produced as described above, and single cells A, B, C, and D were produced. Gas and air were respectively supplied to the air electrode, the battery temperature was 75 ° C., the fuel gas utilization rate was 70%, and the air utilization rate (hereinafter abbreviated as Uo) was 40%. For gas humidification, a fuel cell was supplied through a bubbler at 70 ° C. and air was supplied at 70 ° C., and a discharge test of a unit cell as a hydrogen-air fuel cell was performed.
[0021]
FIG. 2 shows the discharge characteristics test results of unit cells A and B of Examples 1 and 2 of the present invention and unit cells C and D of Comparative Examples 1 and 2 as hydrogen-air fuel cells. In terms of cell voltage at a current density of 200 mA / cm ^2, the voltages of the cells A, B, C, and D were 779 mV, 771 mV, 742 mV, and 570 mV, respectively. As can be seen from FIG. 2, it can be seen that high activity is obtained and discharge performance is high by removing the solvent at the time of electrode preparation remaining in the electrode. In addition, the unit cell D of Comparative Example 2 has poor sealing properties, and fuel gas leaks, causing a reduction in discharge performance. In particular, on the low current density side, since the absolute amount of the supply gas is small, the deterioration of the discharge characteristics is remarkable.
[0022]
FIG. 3 shows the endurance test results of the unit cells A and B of Examples 1 and 2 of the present invention and the unit cells C and D of Comparative Examples 1 and 2 as hydrogen-air fuel cells. Pure hydrogen gas was supplied to the fuel electrode of each of the cells A, B, C, and D of Examples 1 and 2 and Comparative Examples 1 and 2, and air was supplied to the air electrode. The cell temperature was 75 ° C., and the fuel gas utilization rate was 70%, air utilization rate (hereinafter abbreviated as Uo) is 40%, current density is 300 mA / cm ^2, and gas humidification is performed by supplying fuel gas through a 70 ° C bubbler and air through a 70 ° C bubbler. The durability test of the unit cell as an air fuel cell was conducted. As can be seen from these results, the membrane / electrode assembly from which the solvent was removed was secured with reliability, whereas the one without the solvent removal could not be secured. The ionic conduction path due to the residual solvent is obstructed at the initial stage, and the water generated by the operation once obtained the same effect as the solvent removal, but the current density segregates at the initial stage, and locally. It is thought that the long-term reliability was lowered due to the deterioration caused by the power generation.
[0023]
Many of the products manufactured without fixing the polymer membrane electrolyte have a large deformation and cannot be completed as a product.
[0024]
As described above, a membrane electrode assembly of the present invention, a method for producing the same, and a fuel cell using the membrane, and an electrode formed using a coating composed of conductive carbon particles carrying a catalyst, a polymer electrolyte, and a solvent are highly developed. In a membrane / electrode assembly arranged on one or both sides of a molecular electrolyte membrane, the surface area of the polymer electrolyte membrane located on the peripheral edge of the electrode is roughened, thereby reducing the surface area of the polymer electrolyte membrane located on the peripheral edge of the electrode. In addition, the expansion and contraction of the film due to the absorption and release of moisture is reduced, thereby suppressing a decrease in sealing performance due to deformation. Also, in the process of manufacturing a membrane electrode assembly, in the process of absorbing and releasing moisture, especially in the water washing process and the drying process, the membrane electrode assembly is sandwiched and fixed in the surface direction, so that the dimensional change due to the water content is changed. By performing in the thickness direction and suppressing dimensional changes in the surface direction, dimensional defects can be greatly reduced.
[0025]
By reducing the deformation and dimensional defects of the membrane electrode assembly by these configurations, the gas seal performance can be surely achieved, and a membrane electrode assembly with high discharge performance and high reliability can be provided.
[0026]
A fuel cell is usually used by connecting a plurality of single cells in series or in parallel. Therefore, the characteristic deterioration in the single cell greatly affects the performance of the fuel cell stack. In particular, when connected in series, the limit current value of the unit cell with the lowest characteristics becomes the limit current value of the entire fuel cell stack, so the performance of the lowest unit cell is the performance of the entire fuel cell stack. Limit value. In other words, it will be an important issue in the future to reduce the performance of the single battery as much as possible. Therefore, it can be said that the fuel cell electrode of the present invention improves the discharge performance of the fuel cell stack as a result.
[0027]
In this example, hydrogen and air are used as an example of fuel. However, hydrogen is obtained as a reformed hydrogen in the case of a fuel containing impurities such as carbon dioxide, nitrogen, and carbon monoxide. methanol, ethanol, di-methyl ether, such as liquid fuels and similar results using the mixture is obtained instead. Further, the liquid fuel may be vaporized in advance and supplied as a vapor.
[0028]
Further, the configuration of the present example is not limited to the configuration of the catalyst layer and the membrane of the example, and the configuration of various catalyst layers was also effective.
[0029]
Furthermore, using the solid polymer electrolyte-electrode assembly of the present invention, it is also effective for application to various gas sensors such as oxygen, ozone, hydrogen and other gas generators, gas purifiers, oxygen sensors, and alcohol sensors. There is.
[0030]
【The invention's effect】
As described above, as is clear from the description of the embodiments, by reducing deformation and dimensional defects of the membrane electrode assembly, gas sealing performance can be surely achieved, and the membrane electrode assembly having high discharge performance and reliability, and a method for manufacturing the same And a fuel cell using the same.
[Brief description of the drawings]
FIG. 1 is a schematic cross-sectional view of a conventional fuel cell single cell. FIG. 2 is a diagram showing voltage-current characteristics of a hydrogen-air type fuel cell. FIG. 3 is a diagram showing reliability of a hydrogen-air type fuel cell. Explanation of]
1 Polymer Electrolyte Membrane 2A, 2B Catalyst Layer Electrode 3A, 3B Gas Diffusion Electrode 4A, 4B Separator

Claims

And conductive carbon particles carrying catalyst, and a polymer electrolyte, a manufacturing method of a solvent, the electrode formed using the electrode for paints having a membrane electrode assembly disposed on one or both sides of the polymer electrolyte membrane In
Applying the electrode coating material in a state where the polymer electrolyte membrane is fixed in a plane direction with a film-like elastic body having a central portion cut through;
After the step of applying the electrode paint, the step of removing the solvent in a state where the polymer electrolyte membrane is fixed with the elastic film,
A method for producing a membrane electrode assembly, comprising :

The method for producing a membrane / electrode assembly according to claim 1 , wherein the step of removing the solvent is a step of removing the solvent by washing with water .

The method for producing a membrane / electrode assembly according to claim 2 , further comprising a step of drying the polymer electrolyte membrane in a state where the polymer electrolyte membrane is fixed by the film-like elastic body after the step of removing the solvent .

The method for producing a membrane electrode assembly according to claim 1 , wherein the step of removing the solvent is a step of removing the solvent by ozone oxidation treatment .

State of the polymer electrolyte membrane was fixed in the surface direction in the film-like elastic body is a fixed state so as to sandwich both sides of the polymer electrolyte membrane with a pair of the film-like elastic body, according to claim 1 The manufacturing method of the membrane electrode assembly.