JP5109214B2

JP5109214B2 - Method for producing membrane electrode assembly for polymer electrolyte fuel cell

Info

Publication number: JP5109214B2
Application number: JP2001196589A
Authority: JP
Inventors: 伸二木下; 純向山
Original assignee: Asahi Glass Co Ltd
Current assignee: AGC Inc
Priority date: 2001-06-28
Filing date: 2001-06-28
Publication date: 2012-12-26
Anticipated expiration: 2021-06-28
Also published as: JP2003017086A

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用膜電極接合体の製造方法に関する。
【０００２】
【従来の技術】
燃料電池は発電効率が高く、環境への負荷も小さいことから今後の普及が見込まれている。なかでも固体高分子型燃料電池は、出力密度が高く作動温度が低いために小型化や低コスト化が他の燃料電池よりも容易なことから、自動車などの移動体用や分散発電システム、家庭用のコージェネレーションシステムとして広く普及することが期待されている。
【０００３】
一般に固体高分子型燃料電池は、固体高分子電解質膜の両面に金属触媒を含む触媒層を接合させ、その外側にガス拡散層としてカーボンペーパーやカーボンクロス等が配置されてなる膜電極接合体を備える。さらにガス拡散層の外側には、ガス流路が形成された導電性のセパレータが配置され、燃料ガスや酸化剤ガスを通過させると同時に、集電体の機能を有するガス拡散層から電流を外部に伝え、電気エネルギーを取り出す役割を担う。
【０００４】
上記触媒層の形成にあたっては、通常、金属触媒を担持したカーボンと固体高分子電解質樹脂（イオン交換樹脂）とを主要固形成分とした触媒層形成用塗工液を固体高分子電解質膜に直接塗布するか、別途用意した基材上にあらかじめシート状に触媒層を成形した後固体高分子電解質膜にホットプレス等により転写することによって作製される。固体高分子電解質膜に触媒層形成用塗工液を塗工する方法で膜と触媒層の接合体を得る場合、膜の片面のみに触媒層を形成したものを２枚作製し、その２枚の膜どうしを熱ロールプレス等によって接合し、接合された膜を固体高分子電解質膜とする方法が知られている。また、基板上に上記塗工液により触媒層を形成し、その上に電解質膜を構成する樹脂の溶液又は分散液を塗工したものを２枚作製し、この２枚の塗工面を熱ロールプレス等によって接合して膜と触媒層の接合体を得る方法も知られている。
【０００５】
触媒層中に固体高分子電解質樹脂を含有させるのは、電池反応が起こるために必要な電解質と触媒との接触面積を増大させ、電池出力を高める目的がある。そして、固体高分子電解質膜と触媒層の接合においてホットプレスなどの加熱処理を行わない場合には、固体高分子電解質樹脂の高次構造の変化による機械的強度の向上を目的として加熱処理を行うことにより、長期にわたって安定した電池反応を行わせられることが知られている。
【０００６】
【発明が解決しようとする課題】
従来は、作業の簡便性のため上記の固体高分子電解質膜と触媒層との接合体の加熱処理の工程は、通常、空気中で行われている。そのため、本発明者等が検討したところ、本来の目的である固体高分子電解質樹脂の機械的強度の向上以外に、空気中の酸素の影響により、触媒層中の固体高分子電解質樹脂の一部が酸化反応によって変質しており、電池性能の劣化を引き起こしていることがわかった。
【０００７】
そこで本発明は、固体高分子電解質樹脂を酸化させることなく機械的強度を向上させることにより、起動初期から長期にわたって安定した出力が得られる固体高分子型燃料電池を得るための膜電極接合体の製造方法を提供することを目的とする。
【０００８】
【課題を解決するための手段】
本発明は、イオン交換膜からなる固体高分子電解質膜の両面に触媒とイオン交換樹脂を含む触媒層を有するアノード及びカソードがそれぞれ接合されてなる固体高分子型燃料電池用膜電極接合体の製造方法であって、前記イオン交換膜の両面に前記触媒層を配設して接合し、得られた接合体を２枚のガス拡散層で挟んだ後、前記イオン交換膜と前記触媒層との接合体を２枚のガス拡散層で挟んだものの両面に酸素ガス不透過性のフィルムを配置することにより、前記接合体から酸素が遮断された環境下で６０〜２４０℃にて５秒以上加熱処理することを特徴とする固体高分子型燃料電池用膜電極接合体の製造方法を提供する。
また、本発明は、イオン交換膜からなる高分子電解質膜の両面に触媒とイオン交換樹脂を含む触媒層を有するアノード及びカソードがそれぞれ接合されてなる固体高分子型燃料電池用膜電極接合体の製造方法であって、前記イオン交換膜の両面に前記触媒層を配設して接合し、得られた接合体を２枚のガス拡散層で挟んだ後、前記イオン交換膜と前記触媒層との接合体を２枚のガス拡散層で挟んだものを、不活性ガス雰囲気中において、前記接合体から酸素が遮断された環境下で６０〜２４０℃にて５秒以上加熱処理することを特徴とする固体高分子型燃料電池用膜電極接合体の製造方法を提供する。
【０００９】
上記方法では、触媒層とイオン交換膜との接合体（以下、膜・触媒層接合体という。）を酸素が存在しない雰囲気で熱処理するので、触媒層中のイオン交換樹脂やイオン交換膜が部分的に酸化反応することがなく、イオン交換樹脂の機械的強度を向上させることができる。そのため、上記方法で得られた膜電極接合体を備える固体高分子型燃料電池は、起動初期から長期にわたって安定して高出力が得られる。
【００１０】
【発明の実施の形態】
本発明において、膜・触媒層接合体を酸素が遮断された環境下で加熱処理する方法は特に限定されないが、以下の２つの方法が好ましく採用される。（１）膜・触媒層接合体を不活性ガス雰囲気中で加熱処理する方法。（２）膜・触媒層接合体の両面に酸素ガス不透過性のフィルムを配置する方法。
【００１１】
（１）の方法をより具体的に説明すると、例えば以下の方法が挙げられる。膜・触媒層接合体をガス置換が可能な電気炉等に入れてから当該電気炉内を真空にした後、窒素ガスやアルゴンガス等の不活性ガスを導入する方法。電気炉内にガスを導入せずに真空にして加熱処理する方法。膜・触媒層接合体をガス置換が可能な電気炉等に入れてから不活性ガスを当該電気炉内で充分にオーバーフローさせた上で加熱処理する方法。
【００１２】
また、（２）の方法において、酸素ガス不透過性のフィルムとは、例えばガス透過係数が１．０×１０^−１０（ｍ^３・ｍ／ｍ^２・ｓ・ＭＰａ）程度以下（ＡＳＴＭＤ１４３４に準拠して２５℃にて測定）であり、実質的に空気中の酸素が膜電極接合体へ触れる量が充分に少なくできるものをいう。
【００１３】
このようなフィルムの素材としては例えば以下のものが挙げられる。ポリエチレンテレフタレート（以下、ＰＥＴという。）、ポリエチレン、ポリプロピレン、ポリイミド、ポリアミド等の非フッ素系ポリマー。ポリテトラフルオロエチレン、エチレン／テトラフルオロエチレン共重合体、エチレン／ヘキサフルオロプロピレン共重合体、テトラフルオロエチレン／パーフルオロ（アルキルビニルエーテル）共重合体、ポリフッ化ビニリデン等のフッ素系ポリマー。
【００１４】
本発明において、加熱処理の温度が６０℃未満では、イオン交換樹脂の高次構造の変化により機械的強度が向上するという効果を得るのに長時間の加熱処理が必要とされるので、生産効率の点から好ましくない。また、酸素が存在しなくも２４０℃より高温で熱処理を行うと、スルホン酸基が分解してイオン交換容量が低下する。機械的強度の向上、熱処理時間の短縮を行いながらイオン交換容量を維持するという観点から、特に１２０〜１６０℃で加熱処理することが好ましい。また、加熱時間は短すぎると高分子電解質樹脂の機械的強度向上の効果が充分に得られないので、５秒以上としている。
【００１５】
本発明において、高分子電解質膜であるイオン交換膜を構成するイオン交換樹脂及び触媒層に含まれるイオン交換樹脂としては、含フッ素イオン交換樹脂も非フッ素系イオン交換樹脂も使用でき、単一のイオン交換樹脂からなってもよく、２種以上のイオン交換樹脂を混合したものでもよい。また、触媒層に含まれるイオン交換樹脂はアノード側とカソード側で同じであっても異なっていてもよい。
【００１６】
しかし、耐久性の観点から、触媒層に含まれるイオン交換樹脂もイオン交換膜を構成する樹脂もスルホン酸基を有するパーフルオロカーボン重合体からなることが好ましい。特にテトラフルオロエチレンに基づく繰り返し単位とスルホン酸基を有するパーフルオロビニル化合物に基づく繰り返し単位とからなる共重合体が好ましい。
【００１７】
上記パーフルオロビニル化合物としては、ＣＦ_２＝ＣＦ（ＯＣＦ_２ＣＸ）_ｍＯ_ｐ（ＣＦ_２）_ｎＳＯ_３Ｈで表される化合物（Ｘはフッ素原子又はトリフルオロメチル基であり、ｍは０〜３の整数であり、ｎは１〜１２の整数であり、ｐは０又は１である。）が好ましく、特に式１、２又は３で表される化合物が好ましい。ただし式１〜３においてｑは１〜８の整数であり、ｒは１〜８の整数であり、ｔは２又は３である。
【００１８】
【化１】

【００１９】
イオン交換膜を構成するイオン交換樹脂及び触媒層に含まれるイオン交換樹脂のイオン交換容量は、０．５〜４．０ミリ当量／ｇ乾燥樹脂、特に０．７〜２．０ミリ当量／ｇ乾燥樹脂であることが好ましい。イオン交換容量が低すぎるとイオン交換膜及び触媒層のイオン導電性が低下する。
【００２０】
一方、イオン交換容量が高すぎると、イオン交換膜は強度が弱くなり、触媒層は含水率が高くなる。触媒層の含水率が高くなると、電池の反応により生じる水や反応を促進させるために燃料ガスとともに送られる水が触媒層の外部に排出されにくくなって触媒層内部に留まるおそれがある。その結果、触媒層の細孔は水で閉塞され、燃料ガスが触媒層に供給されにくくなり発電電圧が低下するというフラッディング現象が起こるおそれがある。
【００２１】
本発明において、カソード及びアノードはそれぞれ触媒層のみからなっていてもよいが、触媒層に隣接してカーボンクロスやカーボンペーパー等からなるガス拡散層を配置し、触媒層とガス拡散層とから構成されてもよい。ここでガス拡散層は、ガスの流路と触媒層との間に配置される多孔質層であり、触媒層にガスを均一に充分に供給する機能を有し、集電体としても機能する。この場合、触媒層−膜−触媒層の接合体を２枚のガス拡散層で挟むことにより、膜電極接合体を構成できる。なお、触媒層とガス拡散層とは、ホットプレス等により接合されていてもよい。
【００２２】
本発明において酸素が遮断された環境下で加熱処理する際の膜・触媒層接合体は、高分子電解質膜を構成するイオン交換膜の少なくとも片面に触媒層が配設されて接合されたものであるが、両面に触媒層が配設されている場合は加熱処理した後に必要に応じて２枚のガス拡散層で膜・触媒層接合体を挟むことにより膜電極接合体を形成できる。また、加熱処理は、２枚のガス拡散層で膜・触媒層接合体を挟んだ後に行ってもよい。一方、触媒層がイオン交換膜の片面のみに接合されている場合は、アノード側の膜・触媒層接合体とカソード側の膜・触媒層接合体とをそれぞれ加熱処理した後に、それぞれのイオン交換膜を対向させて積層し、熱ロールプレス等によりイオン交換膜どうしを接合させ、必要に応じて２枚のガス拡散層で挟むことにより膜電極接合体が得られる。すなわち、高分子電解質膜は、積層、接合された２枚のイオン交換膜により構成される。
【００２３】
膜電極接合体の外側には、通常、表面にガスの流路となる溝が形成されているセパレータを配置して固体高分子型燃料電池を構成する。そして、セパレータを介して膜電極接合体を積層すると、スタック構造の固体高分子型燃料電池が得られる。なお、セパレータのガス流路の実質的な流路幅が充分に狭い（例えば０．０５〜０．５ｍｍ程度）場合は、上述のガス拡散層は必ずしも存在しなくても、触媒層にガスを充分に拡散、供給することが可能である。
【００２４】
【実施例】
以下、本発明を実施例（例１〜３）及び比較例（例４、５）により具体的に説明するが、本発明はこれらに限定されない。なお、図１は、例１及び例５で得られた膜電極接合体を電流密度０．２Ａ／ｃｍ^２で連続運転した時の経時変化を示す図である。
【００２５】
［例１］
ＣＦ_２＝ＣＦ_２に基づく繰り返し単位とＣＦ_２＝ＣＦ−ＯＣＦ_２ＣＦ（ＣＦ_３）−ＯＣＦ_２ＣＦ_２ＳＯ_３Ｈに基づく繰り返し単位とからなる共重合体（イオン交換容量：１．１ミリ当量／グラム乾燥樹脂）と、白金ルテニウム合金をカーボン上に５０質量％担持させた担持触媒とを、エタノールと水の混合分散媒（質量比で１：１）に分散させ、得られた固形分濃度７質量％の液をアノード触媒層形成用の塗工液とした。このとき、上記共重合体と触媒は質量比で６：４とした。この塗工液を、シリコーン系離型剤で表面を処理した厚さ５０μｍのＰＥＴフィルムの上にダイコート法で塗工し、８０℃で乾燥して厚さ約１０μｍ、白金ルテニウム量が約０．４ｍｇ／ｃｍ^２であるアノード触媒層を形成した。
【００２６】
上記アノード触媒層の上に、上記共重合体を１４質量％含みエタノールを溶媒とする塗工液（以下、イオン交換膜形成用塗工液という。）をダイコート法で塗工し、８０℃で乾燥して厚さ約１５μｍのイオン交換層を形成した。得られた膜・触媒層接合体１を電気炉に入れ、内部を真空にしてから窒素ガスを導入した後、１２０℃で３０分の加熱処理を行った。
【００２７】
次に、上記共重合体と白金をカーボン上に５５質量％担持させた担持触媒とをエタノールと水の混合分散媒（質量比で１：１）に分散させ、得られた固形分濃度１４質量％の液をカソード触媒層形成用の塗工液とした。このとき、上記共重合体と触媒は質量比で７：３とした。この塗工液をシリコーン系離型剤で表面を処理したＰＥＴフィルム上にダイコート法で塗工し、８０℃で乾燥して厚さ１０μｍ、白金担持量が約０．４ｍｇ／ｃｍ^２のカソード触媒層を形成した。
【００２８】
上記カソード触媒層の上に、上記イオン交換膜形成用塗工液をダイコート法で塗工し、８０℃で乾燥して厚さ約１５μｍのイオン交換層を形成した。得られた膜・触媒層接合体２を電気炉に入れ、内部を真空にした後、窒素ガスを導入した後、１２０℃で３０分の加熱処理を行った。
【００２９】
上記工程で得られた膜・触媒層接合体１と膜・触媒層接合体２を、それぞれイオン交換層どうしが隣接するように積層し、２００℃に維持した金属ロールと１３０℃に維持したゴムロールの間を面圧０．４ＭＰａで通し、イオン交換層どうしを接合させ膜・触媒層接合体を作製した。得られた膜・触媒層接合体を７ｃｍ角に切り抜き、両面のＰＥＴフィルムを剥離した。次に、中心部に５ｃｍ角の切り抜きがあり、外形寸法が５．６ｃｍ×７ｃｍである額縁状の厚さ２０μｍのポリイミドフィルムを２枚用意し、２枚のフィルムの間に上記膜・触媒層接合体を中央部に位置するようにして挟み、２枚のフィルムと上記接合体とをシリコン系の粘着材を用いて貼り合わせた。
【００３０】
カーボンブラック（商品名：バルカンＸＣ−７２、キャボット社製）とポリテトラフルオロエチレン粒子とからなる厚さ約１０μｍの導電層が表面に形成された、厚さ約３００μｍのカーボンペーパーを２枚用意してガス拡散層とし、上記接合体を挟んで膜電極接合体を得た。これを電池性能測定用セルに組み込み、有効電極面積が２５ｃｍ^２である電池とした。この電池のアノードに水素ガス、カソードに空気をそれぞれ供給し、セル温度８０℃にて発電試験を行い、発電初期の電流密度０．２Ａ／ｃｍ^２及び０．７Ａ／ｃｍ^２における出力電圧を測定した。結果を表１に示す。また、電流密度０．２Ａ／ｃｍ^２で連続運転した時の経時変化を図１に示す。
【００３１】
［例２］
アノード、カソードそれぞれの膜・触媒層接合体の加熱処理の温度を１２０℃から１６０℃に変更した以外は例１と同様にして膜電極接合体を作製し、例１と同様に評価した。結果を表１に示す。
【００３２】
［例３］
例１と同様にしてアノード、カソードそれぞれの膜・触媒層接合体（加熱処理前のもの）を作製した後、それぞれのイオン交換膜側（ＰＥＴフィルムが付いていない面）に厚さ５０μｍのＰＥＴフィルムをかぶせて、ゴムローラでそれぞれ膜面に密着させた。これらを電気炉に入れて１２０℃で３０分の加熱処理を行った後、膜面に密着させたＰＥＴフィルムを取り除いた。得られた２枚の膜・触媒層接合体を、膜面どうしを対向させて積層し、２００℃に温度管理した金属ロールと１３０℃に温度管理したゴムロールの間を面圧０．４ＭＰａで通し、膜どうしを接合させて膜電極接合体を作製した。
得られた膜電極接合体を用いて例１と同様に電池性能測定用セルに組み込み、例１と同様に評価した。結果を表１に示す。
【００３３】
［例４］
アノード、カソードそれぞれの膜・触媒層接合体の加熱処理を窒素ガス雰囲気中ではなく空気中で行った以外は例１と同様にして膜電極接合体を作製し、例１と同様に評価した。結果を表１に示す。また、電流密度０．２Ａ／ｃｍ^２で連続運転したときの経時変化を図１に例１の結果とともに示す。
【００３４】
［例５］
加熱処理の温度を１２０℃から１６０℃に変更した以外は例４と同様にして膜電極接合体を作製し、例１と同様に評価した。結果を表１に示す。
【００３５】
【表１】

【００３６】
【発明の効果】
本発明の方法によれば、従来より高い電池出力を起動初期から長期にわたって安定して得られる固体高分子型燃料電池が提供できる。
【図面の簡単な説明】
【図１】例１及び例５で得られた膜電極接合体を電流密度０．２Ａ／ｃｍ^２で連続運転した時の経時変化を示す図。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing a membrane electrode assembly for a polymer electrolyte fuel cell.
[0002]
[Prior art]
Fuel cells are expected to become popular in the future because of their high power generation efficiency and low environmental impact. In particular, polymer electrolyte fuel cells are easier to reduce in size and cost than other fuel cells because of their high output density and low operating temperature. It is expected to spread widely as a cogeneration system.
[0003]
In general, a polymer electrolyte fuel cell has a membrane electrode assembly in which a catalyst layer containing a metal catalyst is bonded to both sides of a solid polymer electrolyte membrane, and carbon paper, carbon cloth, or the like is disposed as a gas diffusion layer on the outside. Prepare. In addition, a conductive separator having a gas flow path is disposed outside the gas diffusion layer, allowing the fuel gas and the oxidant gas to pass therethrough, and at the same time, the current is externally supplied from the gas diffusion layer having the function of a current collector. And take the role of extracting electrical energy.
[0004]
In forming the catalyst layer, a catalyst layer forming coating solution containing carbon carrying a metal catalyst and a solid polymer electrolyte resin (ion exchange resin) as main solid components is usually applied directly to the solid polymer electrolyte membrane. Alternatively, a catalyst layer is formed in advance on a separately prepared substrate and then transferred to a solid polymer electrolyte membrane by hot pressing or the like. When a membrane / catalyst layer assembly is obtained by applying a coating solution for forming a catalyst layer on a solid polymer electrolyte membrane, two sheets having a catalyst layer formed on only one side of the membrane are prepared. There is known a method in which these films are joined by a hot roll press or the like, and the joined film is used as a solid polymer electrolyte membrane. Moreover, a catalyst layer is formed on the substrate with the above-mentioned coating liquid, and two sheets of the resin solution or dispersion liquid constituting the electrolyte membrane are coated thereon, and the two coated surfaces are heated with a roll. A method of obtaining a joined body of a membrane and a catalyst layer by joining by pressing or the like is also known.
[0005]
The inclusion of the solid polymer electrolyte resin in the catalyst layer has the purpose of increasing the battery output by increasing the contact area between the electrolyte and the catalyst necessary for the battery reaction to occur. When heat treatment such as hot pressing is not performed in the joining of the solid polymer electrolyte membrane and the catalyst layer, heat treatment is performed for the purpose of improving the mechanical strength due to the change in the higher order structure of the solid polymer electrolyte resin. Thus, it is known that a stable battery reaction can be performed over a long period of time.
[0006]
[Problems to be solved by the invention]
Conventionally, for the convenience of work, the heat treatment process for the joined body of the solid polymer electrolyte membrane and the catalyst layer is usually performed in air. Therefore, when the present inventors examined, in addition to the improvement of the mechanical strength of the solid polymer electrolyte resin, which is the original purpose, a part of the solid polymer electrolyte resin in the catalyst layer due to the influence of oxygen in the air. Has been altered by oxidation reaction, and it was found that the battery performance deteriorated.
[0007]
Accordingly, the present invention provides a membrane electrode assembly for obtaining a polymer electrolyte fuel cell that can obtain a stable output over a long period from the initial start-up by improving the mechanical strength without oxidizing the polymer electrolyte resin. An object is to provide a manufacturing method.
[0008]
[Means for Solving the Problems]
The present invention provides a membrane electrode assembly for a polymer electrolyte fuel cell, in which an anode and a cathode each having a catalyst layer containing a catalyst and an ion exchange resin are bonded to both surfaces of a solid polymer electrolyte membrane made of an ion exchange membrane. In the method, the catalyst layer is disposed and bonded to both surfaces of the ion exchange membrane, and the obtained bonded body is sandwiched between two gas diffusion layers, and then the ion exchange membrane and the catalyst layer are bonded to each other. Heating at 60-240 ° C. for 5 seconds or more in an environment in which oxygen is blocked from the joined body by disposing oxygen gas-impermeable films on both sides of the joined body sandwiched between two gas diffusion layers Provided is a method for producing a membrane electrode assembly for a polymer electrolyte fuel cell, characterized by being treated.
The present invention also relates to a membrane electrode assembly for a polymer electrolyte fuel cell in which an anode and a cathode each having a catalyst layer containing a catalyst and an ion exchange resin are joined to both surfaces of a polymer electrolyte membrane comprising an ion exchange membrane. In the manufacturing method, the catalyst layers are disposed and bonded to both surfaces of the ion exchange membrane, and the obtained bonded body is sandwiched between two gas diffusion layers, and then the ion exchange membrane, the catalyst layer, A structure in which the joined body is sandwiched between two gas diffusion layers is heated in an inert gas atmosphere at 60 to 240 ° C. for 5 seconds or more in an environment in which oxygen is blocked from the joined body. A method for producing a membrane electrode assembly for a polymer electrolyte fuel cell is provided.
[0009]
In the above method, since the joined body of the catalyst layer and the ion exchange membrane (hereinafter referred to as a membrane / catalyst layer joined body) is heat-treated in an atmosphere in which oxygen does not exist, the ion exchange resin or ion exchange membrane in the catalyst layer is partially Therefore, the mechanical strength of the ion exchange resin can be improved. Therefore, the polymer electrolyte fuel cell provided with the membrane electrode assembly obtained by the above method can stably obtain a high output over a long period from the initial start-up.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
In the present invention, the method for heat-treating the membrane / catalyst layer assembly in an environment where oxygen is blocked is not particularly limited, but the following two methods are preferably employed. (1) A method of heat-treating the membrane / catalyst layer assembly in an inert gas atmosphere. (2) A method of disposing oxygen gas impermeable films on both surfaces of the membrane / catalyst layer assembly.
[0011]
The method (1) will be described more specifically. For example, the following method may be mentioned. A method of introducing an inert gas such as nitrogen gas or argon gas after putting the membrane / catalyst layer assembly into an electric furnace or the like capable of gas replacement and then evacuating the electric furnace. A method of heat-treating a vacuum without introducing gas into the electric furnace. A method in which the membrane / catalyst layer assembly is placed in an electric furnace or the like capable of gas replacement, and then the inert gas is sufficiently overflowed in the electric furnace and then heat-treated.
[0012]
In the method (2), the oxygen gas-impermeable film is, for example, a gas permeability coefficient of about 1.0 × 10 ⁻¹⁰ (m ³ · m / m ² · s · MPa) or less (according to ASTM D1434). (Measured at 25 ° C. in conformity), and means that the amount of oxygen in the air that touches the membrane / electrode assembly can be sufficiently reduced.
[0013]
Examples of such a film material include the following. Non-fluorine polymers such as polyethylene terephthalate (hereinafter referred to as PET), polyethylene, polypropylene, polyimide, and polyamide. Fluoropolymers such as polytetrafluoroethylene, ethylene / tetrafluoroethylene copolymer, ethylene / hexafluoropropylene copolymer, tetrafluoroethylene / perfluoro (alkyl vinyl ether) copolymer, and polyvinylidene fluoride.
[0014]
In the present invention, if the temperature of the heat treatment is less than 60 ° C., a long time heat treatment is required to obtain the effect of improving the mechanical strength due to the change in the higher order structure of the ion exchange resin, so that the production efficiency From the point of view, it is not preferable. In addition, when heat treatment is performed at a temperature higher than 240 ° C. even in the absence of oxygen, the sulfonic acid group is decomposed and the ion exchange capacity is reduced. From the viewpoint of maintaining the ion exchange capacity while improving the mechanical strength and shortening the heat treatment time, it is particularly preferable to perform the heat treatment at 120 to 160 ° C. Further, if the heating time is too short, the effect of improving the mechanical strength of the polymer electrolyte resin cannot be obtained sufficiently, so that it is set to 5 seconds or more.
[0015]
In the present invention, as the ion exchange resin constituting the ion exchange membrane that is a polymer electrolyte membrane and the ion exchange resin contained in the catalyst layer, a fluorine-containing ion exchange resin or a non-fluorine ion exchange resin can be used. It may be made of an ion exchange resin or a mixture of two or more ion exchange resins. Further, the ion exchange resin contained in the catalyst layer may be the same or different on the anode side and the cathode side.
[0016]
However, from the viewpoint of durability, the ion exchange resin contained in the catalyst layer and the resin constituting the ion exchange membrane are preferably made of a perfluorocarbon polymer having a sulfonic acid group. Particularly preferred is a copolymer comprising a repeating unit based on tetrafluoroethylene and a repeating unit based on a perfluorovinyl compound having a sulfonic acid group.
[0017]
As the perfluorovinyl compound _is _{_{_{CF 2 = CF (OCF 2 CX}}} ) m O p (CF 2) n SO 3 compound represented by H (X is fluorine atom or a trifluoromethyl group, m is 0 3 is an integer, n is an integer of 1 to 12, and p is 0 or 1. In particular, a compound represented by Formula 1, 2, or 3 is preferable. However, in Formulas 1-3, q is an integer of 1-8, r is an integer of 1-8, and t is 2 or 3.
[0018]
[Chemical 1]

[0019]
The ion exchange capacity of the ion exchange resin constituting the ion exchange membrane and the ion exchange resin contained in the catalyst layer is 0.5 to 4.0 meq / g dry resin, particularly 0.7 to 2.0 meq / g. A dry resin is preferred. If the ion exchange capacity is too low, the ion conductivity of the ion exchange membrane and the catalyst layer is lowered.
[0020]
On the other hand, if the ion exchange capacity is too high, the strength of the ion exchange membrane becomes weak, and the moisture content of the catalyst layer becomes high. When the moisture content of the catalyst layer becomes high, there is a possibility that the water generated by the reaction of the battery and the water sent together with the fuel gas to promote the reaction are not easily discharged to the outside of the catalyst layer and stay inside the catalyst layer. As a result, the pores of the catalyst layer are clogged with water, which may cause a flooding phenomenon in which the fuel gas is hardly supplied to the catalyst layer and the generated voltage decreases.
[0021]
In the present invention, each of the cathode and the anode may be composed of only a catalyst layer, but a gas diffusion layer made of carbon cloth, carbon paper, or the like is disposed adjacent to the catalyst layer, and is composed of the catalyst layer and the gas diffusion layer. May be. Here, the gas diffusion layer is a porous layer disposed between the gas flow path and the catalyst layer, and has a function of supplying the catalyst layer uniformly and sufficiently, and also functions as a current collector. . In this case, a membrane / electrode assembly can be formed by sandwiching a catalyst layer / membrane / catalyst layer assembly between two gas diffusion layers. The catalyst layer and the gas diffusion layer may be joined by hot pressing or the like.
[0022]
In the present invention, the membrane / catalyst layer assembly when heat-treating in an environment where oxygen is blocked is a membrane / catalyst layer assembly in which a catalyst layer is disposed on at least one side of the ion exchange membrane constituting the polymer electrolyte membrane. However, when catalyst layers are provided on both surfaces, a membrane / electrode assembly can be formed by sandwiching the membrane / catalyst layer assembly between two gas diffusion layers as necessary after heat treatment. The heat treatment may be performed after the membrane / catalyst layer assembly is sandwiched between two gas diffusion layers. On the other hand, when the catalyst layer is bonded to only one surface of the ion exchange membrane, the anode-side membrane / catalyst layer assembly and the cathode-side membrane / catalyst layer assembly are respectively heat-treated, and then each ion exchange is performed. A membrane electrode assembly is obtained by laminating the membranes facing each other, joining the ion exchange membranes by a hot roll press or the like, and sandwiching them between two gas diffusion layers as necessary. That is, the polymer electrolyte membrane is composed of two ion exchange membranes laminated and joined.
[0023]
In general, a polymer electrolyte fuel cell is configured by disposing a separator having grooves formed on the surface as gas flow paths on the outside of the membrane electrode assembly. Then, when the membrane electrode assembly is laminated via the separator, a polymer electrolyte fuel cell having a stack structure is obtained. In addition, when the substantial flow path width of the gas flow path of the separator is sufficiently narrow (for example, about 0.05 to 0.5 mm), the gas is not supplied to the catalyst layer even if the above gas diffusion layer is not necessarily present. It can be sufficiently diffused and supplied.
[0024]
【Example】
EXAMPLES Hereinafter, although an Example (Examples 1-3) and a comparative example (Examples 4 and 5) demonstrate this invention concretely, this invention is not limited to these. FIG. 1 is a graph showing a change with time when the membrane electrode assemblies obtained in Examples 1 and 5 were continuously operated at a current density of 0.2 A / cm ² .
[0025]
[Example 1]
Copolymer comprising a repeating unit based on CF ₂ ═CF ₂ and a repeating unit based on CF ₂ ═CF—OCF ₂ CF (CF ₃ ) —OCF ₂ CF ₂ SO ₃ H (ion exchange capacity: 1.1 milliequivalents) / Gram dry resin) and a supported catalyst in which a platinum ruthenium alloy is supported on carbon by 50 mass% are dispersed in a mixed dispersion medium (1: 1 by mass) of ethanol and water, and the resulting solid content concentration is obtained. 7% by mass of the liquid was used as a coating liquid for forming the anode catalyst layer. At this time, the copolymer and the catalyst were in a mass ratio of 6: 4. This coating solution was applied by die coating on a 50 μm thick PET film whose surface was treated with a silicone release agent, dried at 80 ° C. and about 10 μm in thickness, and the amount of platinum ruthenium was about 0.1. An anode catalyst layer that was 4 mg / cm ² was formed.
[0026]
On the anode catalyst layer, a coating solution containing 14% by mass of the copolymer and ethanol as a solvent (hereinafter referred to as an ion exchange membrane forming coating solution) was applied by a die coating method at 80 ° C. An ion exchange layer having a thickness of about 15 μm was formed by drying. The obtained membrane / catalyst layer assembly 1 was placed in an electric furnace, the inside was evacuated, nitrogen gas was introduced, and then heat treatment was performed at 120 ° C. for 30 minutes.
[0027]
Next, the copolymer and a supported catalyst in which platinum is supported by 55% by mass on carbon are dispersed in a mixed dispersion medium (mass ratio of 1: 1) of ethanol and water, and the resulting solid content concentration is 14% by mass. % Solution was used as a coating solution for forming the cathode catalyst layer. At this time, the copolymer and the catalyst were in a mass ratio of 7: 3. This coating solution is coated on a PET film whose surface has been treated with a silicone release agent by a die coating method, dried at 80 ° C., 10 μm thick, and a cathode catalyst having a platinum loading of about 0.4 mg / cm ² . A layer was formed.
[0028]
On the cathode catalyst layer, the ion exchange membrane-forming coating solution was applied by a die coating method and dried at 80 ° C. to form an ion exchange layer having a thickness of about 15 μm. The obtained membrane / catalyst layer assembly 2 was placed in an electric furnace, the inside was evacuated, nitrogen gas was introduced, and a heat treatment was performed at 120 ° C. for 30 minutes.
[0029]
The membrane / catalyst layer assembly 1 and the membrane / catalyst layer assembly 2 obtained in the above process are laminated so that the ion exchange layers are adjacent to each other, and a metal roll maintained at 200 ° C. and a rubber roll maintained at 130 ° C. The membrane was passed at a surface pressure of 0.4 MPa, and the ion exchange layers were joined together to produce a membrane / catalyst layer assembly. The obtained membrane / catalyst layer assembly was cut into a 7 cm square, and the PET films on both sides were peeled off. Next, two polyimide films having a frame thickness of 20 μm with a 5 cm square cutout at the center and an outer dimension of 5.6 cm × 7 cm are prepared, and the membrane / catalyst layer is interposed between the two films. The joined body was sandwiched so as to be positioned at the center, and the two films and the joined body were bonded together using a silicon-based adhesive material.
[0030]
Prepare two sheets of carbon paper with a thickness of about 300 μm, with a conductive layer of carbon black (trade name: Vulcan XC-72, manufactured by Cabot) and polytetrafluoroethylene particles formed on the surface. Thus, a gas diffusion layer was formed, and a membrane electrode assembly was obtained with the assembly interposed therebetween. This was incorporated into a battery performance measurement cell to obtain a battery having an effective electrode area of 25 cm ² . Supply hydrogen gas to the anode and air to the cathode of the battery, conduct a power generation test at a cell temperature of 80 ° C., and measure the output voltage at a current density of 0.2 A / cm ² and 0.7 A / cm ^{2 at the} initial stage of power generation. did. The results are shown in Table 1. Further, FIG. 1 shows a change with time when continuously operated at a current density of 0.2 A / cm ² .
[0031]
[Example 2]
A membrane / electrode assembly was prepared in the same manner as in Example 1 except that the temperature of the heat treatment of the anode / cathode membrane / catalyst layer assembly was changed from 120 ° C. to 160 ° C., and evaluated in the same manner as in Example 1. The results are shown in Table 1.
[0032]
[Example 3]
After preparing membrane / catalyst layer assemblies (before heat treatment) for each of the anode and cathode in the same manner as in Example 1, each ion exchange membrane side (side without the PET film) had a thickness of 50 μm. The film was covered and adhered to the film surface with a rubber roller. These were placed in an electric furnace and subjected to a heat treatment at 120 ° C. for 30 minutes, and then the PET film adhered to the film surface was removed. The obtained two membrane / catalyst layer assemblies were laminated with their membrane surfaces facing each other, and a metal roll temperature-controlled at 200 ° C. and a rubber roll temperature-controlled at 130 ° C. were passed at a surface pressure of 0.4 MPa. The membrane electrode assembly was produced by joining the membranes together.
The obtained membrane / electrode assembly was incorporated into a battery performance measurement cell in the same manner as in Example 1 and evaluated in the same manner as in Example 1. The results are shown in Table 1.
[0033]
[Example 4]
A membrane / electrode assembly was prepared in the same manner as in Example 1 except that the heat treatment of the membrane / catalyst layer assembly of each of the anode and cathode was performed in air instead of in a nitrogen gas atmosphere, and evaluation was performed in the same manner as in Example 1. The results are shown in Table 1. FIG. 1 shows the change with time when continuously operated at a current density of 0.2 A / cm ² together with the result of Example 1.
[0034]
[Example 5]
A membrane / electrode assembly was prepared in the same manner as in Example 4 except that the temperature of the heat treatment was changed from 120 ° C. to 160 ° C., and evaluated in the same manner as in Example 1. The results are shown in Table 1.
[0035]
[Table 1]

[0036]
【Effect of the invention】
According to the method of the present invention, it is possible to provide a polymer electrolyte fuel cell that can stably obtain a battery output higher than that in the prior art from the beginning of startup for a long period of time.
[Brief description of the drawings]
FIG. 1 is a graph showing changes with time when membrane electrode assemblies obtained in Examples 1 and 5 are continuously operated at a current density of 0.2 A / cm ² .

Claims

A method for producing a membrane electrode assembly for a polymer electrolyte fuel cell in which an anode and a cathode each having a catalyst layer containing a catalyst and an ion exchange resin are joined to both surfaces of a polymer electrolyte membrane comprising an ion exchange membrane, After the catalyst layers are disposed and bonded to both surfaces of the ion exchange membrane, the obtained bonded body is sandwiched between two gas diffusion layers, and then two bonded bodies of the ion exchange membrane and the catalyst layer are bonded. of by placing an oxygen gas-impermeable film on both surfaces but sandwiched by gas diffusion layer, characterized in that the heat treatment at least 5 seconds at 60 to 240 ° C. in an environment where oxygen from the conjugate is blocked A method for producing a membrane electrode assembly for a polymer electrolyte fuel cell.

A method for producing a membrane electrode assembly for a polymer electrolyte fuel cell in which an anode and a cathode each having a catalyst layer containing a catalyst and an ion exchange resin are joined to both surfaces of a polymer electrolyte membrane comprising an ion exchange membrane, After the catalyst layers are disposed and bonded to both surfaces of the ion exchange membrane, the obtained bonded body is sandwiched between two gas diffusion layers, and then two bonded bodies of the ion exchange membrane and the catalyst layer are bonded. of which is sandwiched by gas diffusion layer, in an inert gas atmosphere, a polymer electrolyte, characterized in that oxygen from the conjugate is heated more than 5 seconds at 60 to 240 ° C. in an environment that is cut off Manufacturing method of fuel cell membrane electrode assembly.

The method for producing a membrane / electrode assembly for a polymer electrolyte fuel cell according to claim 1 or 2 , wherein the ion exchange membrane and / or the ion exchange resin comprises a perfluorocarbon polymer having a sulfonic acid group.

After producing the membrane electrode assembly by a method according to any one of claims 1 to 3 polymer disposed adjacent the separator flow path of gas is formed on the surface of the membrane electrode assembly Type fuel cell manufacturing method.