JP3853193B2 - Polymer electrolyte fuel cell - Google Patents

Description

【００３０】
次に、比表面積が８００ｍ²／ｇ、ＤＢＰ吸油量が３６０ｍｌ／１００ｇのケッチェンブラックＥＣ（ケッチェンブラック・インターナショナル社製ファーネスブラック）に、白金を重量比１：１の割合で担持させた。この触媒粉末１０ｇに、水３５ｇおよび水素イオン伝導性高分子電解質のアルコール分散液（旭硝子（株）製、商品名：９％ＦＦＳ）５９ｇを混合し、超音波攪拌機を用いて分散させて、触媒層インクを作製した。この触媒層インクを、ポリプロピレンフィルム（東レ（株）製、商品名：トレファン５０−２５００）上に塗工し、乾燥して触媒層を作製した。得られた触媒層を所定のサイズ６ｃｍ×６ｃｍにカットした。こうして作製した触媒層を、サイズ１２ｃｍ×１２ｃｍの高分子電解質膜（米国デュポン社のＮａｆｉｏｎ１１２膜）の両面に転写した。
ポリテトラフルオロエチレン微粉末（ダイキン工業（株）製）とアセチレンブラック（電気化学工業（株）製）とを重量比１：４の比率で含む水性インクを調製した。このインクを上記の撥水性電極の一方の面に塗布し、３５０℃で２０分間焼成して撥水層を形成した。焼成後の撥水層密度は、電極の単位面積当たり２．０ｍｇ／ｃｍ²であった。これらの撥水層を形成した一対の電極をそれらの撥水層が電解質膜側となるように、前記の触媒層を接合した電解質膜に温度１３０℃、圧力１５ｋｇ／ｃｍ²でホットプレスにより接合してＭＥＡを作製した。これに上記のガス流路を有する親水性電極であるアノードおよびカソードをそれらの溝の開放部が撥水性電極に接するように組み合わせて試験用セルを組み立てた。
ここに用いたセルは、上で説明した図２１に示す構造のものである。
【００３１】
上記の電池を７５℃に保持し、アノードに各種の露点となるように加湿・加温した純水素ガスを、カソードに６５℃の露点となるように加湿・加温した空気をそれぞれ供給し、燃料ガス利用率７０％、空気利用率４０％の条件で電池の放電試験を行った。
比較例として、図２３に示す構造のセル、すなわち、ガス流路を有する親水性電極シート１０５に代えて、当該親水性電極と同じ溝幅、ピッチおよび溝深さの流路加工を施した導電性セパレータ板を用い、これで上記のＭＥＡを挟み込んだ構造の単セルを組み立て、同じ条件で電池放電試験を行った。
【００３２】
図２４にアノードのバブラー温度と電流密度２００ｍＡ／ｃｍ²における電池の単セル当たりの電圧との関係を示す。本実施例の電池は、比較例に比して、低加湿状態での電池電圧が向上している。これは電極の保湿特性の向上によって供給水の利用率が向上したことによるものと推測される。
図２５は、燃料ガスの間欠的な増減に伴う電池電圧の挙動を示す。図中ＵＰは燃料ガス供給開始を表し、ＤＮは燃料ガスの供給停止を表す。実施例の電池は、負荷増大に伴い燃料ガスを増加した場合の立ち上がり特性が比較例に比してよく、負荷減少に伴い燃料ガスを絞った場合の応答は比較例より鈍いことがわかる。一般に、どのような加湿装置を用いた場合にも、燃料ガスと供給水では供給速度のタイムラグがあり、これが立ち上がり特性の悪化要因となる。実施例の電池では、供給水の燃料ガス供給に対する遅れを、電極滞留水が補償し、上記タイムラグを短縮する効果が認められる。特に、車載用燃料電池では、負荷増大時のレスポンスが負荷減少時のそれよりも重視されるため、実施例の電池は、比較例に比べて優れていると判断される。
【００３３】
上記の実施例および比較例のセル構成でそれぞれ１０セルを積層した積層電池を組み立て、上記と同じ条件で運転した。通常、単セルでは電池温度を維持するために加熱が必要であるが、積層電池では、自己発熱のために過熱するので冷却が必要である。
図２６は、出力電流密度と、電池温度を７５℃に維持するために必要であった冷却水量との関係を示す。実施例の電池は、比較例に比べて特に高出力電流密度における所要冷却水量が少ない。その理由は、高電流密度で多量に発生する生成水が電極に一時滞留した後、気化潜熱を奪って電池外へ排出されるためと推定される。これは特に廃熱を直接利用する必要がなく、かつ高電流密度で運転される車載用燃料電池に好適な特性である。
【００３４】
《実施例２》
メソフェーズピッチ系炭素繊維原糸（紡糸し、安定化前のもの）を１５０μｍ厚に織布し、これにフェノール系炭素繊維原糸を６００μｍ厚になるよう縫込んだ。これを安定化および炭化工程を経てグラファイト化し、図６に示すような電極を製作した。その後連続炉において８００℃、２４０秒の条件で水蒸気酸化して賦活した。このときの、ガス流路の底を構成する部分および側壁部分の、賦活前および賦活後の比表面積および親水性の評価結果を表２に示す。表２に示すように、賦活により、特にフェノール系からなる流路側壁部分の表面積および親水性に著しい増大が見られた。
【００３５】
【表２】

【００３６】
この電極を用いて、ガス流路を有しない方の面に、実施例１と同様の撥水層を形成した。そして、その撥水層を有する面が電解質膜側となるように電解質膜に接合してＭＥＡを作製し、実施例１と同じセパレータ板を用いて図８に示す断面構造の試験用単セルを組み立てた。この電池も実施例１とほぼ同様の特性を示した。
【００３７】
《参考例》
炭化まで終了したＰＡＮ系炭素繊維を、繊維長２ｍｍに裁断し、それを抄紙して、厚み５０μｍ、目付け０．１２ｇ／ｃｍ²のシートを作製した。
その後、図３および図４に示すように、型抜きを行わないシートの３枚と、型抜きしたシートの８枚とを、位置決めしながらカルボキシメチルセルロースの水溶液のバインダーを用いて貼り合わせた。これを２４００℃でグラファイト化して、単一電極を作製した。シートＢの型抜き形状は溝幅１．５ｍｍ、ピッチ３ｍｍとした。
この単一電極に対し、図１１に示す手法により、側壁部に親水処理を行った。すなわち、コロイダルシリカ（日産化学（株）製、ＩＰＡ−ＳＴシリカゾル）６０重量部に、アセチレンブラック（電気化学工業（株）製）２５重量部、シリカゲル（粒子径：１０〜３０μｍ、ＪＩＳ Ａ級）１５重量部および熱硬化型エポキシ樹脂（９０％架橋点７５℃ １分）５重量部を加えて混練してインクを調製した。このインクを前記電極のガス流路を形成する側壁部にスクリーン印刷によって印刷（３度塗り）し、へらで押さえて圧入した。その後、１２０℃で溶媒を除去した後、２００℃でエポキシ樹脂を架橋させ、さらに３２０℃で２時間熱処理してコロイダルシリカを脱水縮合し、側壁部のみに親水性を付与した電極を得た。本実施例の電極は、実施例１および２と同様の効果を有することが確認された。また、適当なインク組成によって、側壁部の親水性を任意に制御することが可能であり、上記の効果を容易に加減することができた。
【００３８】
《実施例３》
図１５に示す装置により、以下の炭化抄紙原反をピッチ系バインダーで結着した後、不活性ガス雰囲気下で２４５０℃、３時間の黒鉛化を行い、４層からなる電極シートＸ１を作製した。
第１層：メソフェーズピッチ系炭化抄紙（繊維径１２μｍ、繊維長５ｍｍ、厚み１５０μｍ）
第２層：高弾性ＰＡＮ系炭化抄紙（繊維径６．５μｍ、繊維長５ｍｍ、厚み１５０μｍ）
第３層：等方性ピッチ系炭化抄紙（繊維径１３μｍ、繊維長２ｍｍ、厚み８０μｍ）
第４層：フェノール系炭化抄紙（繊維径１１μｍ、繊維長２ｍｍ、厚み８０μｍ）。
【００３９】
上記のシート８０を固定用ガラスに接着した後研摩し、図２７に示すように、第１層８０ａ、第２層８０ｂ、第３層８０ｃおよび第４層８０ｄの各層の研摩面を露出させた。この研摩面に対し、図２８に９０で示すように、様々な濡れ指数標準液を滴下して各層の撥水性を評価した。撥水性の評価は、しみ込んだ標準液のうちで最も大きな表面張力を有する液の表面張力をその層の撥水性の指標とした。撥水性の指標は、値が小さいほど撥水性であることを示す。濡れ指数標準液は、表面張力が２３ｍＮ／ｃｍ〜７２ｍＮ／ｃｍのものを使用した。
撥水性の評価結果、および各層のＸ線回折パターンを図２９に示す。図２９の（ａ）、（ｂ）、（ｃ）および（ｄ）は、それぞれ第１層、第２層、第３層および第４層の特性を表す。図２９から明らかなように、配向度、黒鉛化度の高いメソフェーズピッチ系、およびＰＡＮ系の炭化抄紙由来の層は、高い撥水性を持っている。一方、配向度、黒鉛化度の低い等方性ピッチ系およびフェノール系の炭化抄紙由来の層は、撥水性が低い。つまり、上記のシート８０は、配向度、黒鉛化度由来の撥水勾配を有する。
上記のシートをＸ１とする。次に、シートＸ１を２％硝酸で３０分間還流して表面に水酸基を付加した。これをシートＸ２とする。シートＸ２の水酸基を撥水処理剤ヘプタデカフルオロデシルトリクロロシランで撥水処理した。これをシートＸ３とする。シートＸ１を１０％硝酸で２時間還流して表面に水酸基を付加したシートをＸ４、シートＸ４の水酸基を撥水処理剤ヘプタデカフルオロデシルトリクロロシランで撥水処理したシートをＸ５とする。これらのシートについて、前記と同様にして撥水性を評価した。その結果を表３に示す。
【００４０】
【表３】

【００４１】
表３から明らかなように、シートＸ２及びＸ４は、シートＸ１の撥水勾配序列に従って、その勾配量が増強されており、その程度は処理プロセスに応じて制御可能であった。逆にシートＸ３及びＸ５では、シートＸ１の撥水勾配序列とは逆方向の撥水序列を持ち、かつその撥水能はシートＸ１の撥水能を上回り、その程度はシートＸ２及びＸ４の親水性に依存していた。
このように、前述の電極シート製作プロセスと、化学修飾プロセスの組み合わせによって、任意の序列および強度の撥水能力を有する単一のシートを作ることが可能となる。また、シートの内部抵抗は、通常用いられるＰＡＮ系、ピッチ系の単一シートとほぼ同等であった。
【００４２】
【発明の効果】
以上のように本発明によれば、ガス透過を犠牲にせず、電極に保水性を与えることができるため、電池特性を犠牲にせず、供給水の低減、負荷変動に対する応答性の向上、蒸発潜熱による冷却効果等の副次特性を付与することができる。
【図面の簡単な説明】
【図１】本発明の実施例における多孔質電極の原料の炭素繊維原糸からなる織物の平面図である。
【図２】同織物の断面図である。
【図３】本発明の他の実施例における多孔質電極の原料となる２枚の炭素繊維シートの平面図である。
【図４】前記２枚のシートを重ね合わせた状態の平面図である。
【図５】同シートの断面図である。
【図６】本発明のさらに他の実施例における多孔質電極の原料となる織物に別の炭素繊維を織り込んだシートの断面図である。
【図７】ＭＥＡの構成例を示す断面図である。
【図８】ＭＥＡの別の構成例を示す断面図である。
【図９】ＭＥＡのさらに別の構成例を示す断面図である。
【図１０】本発明のさらに他の実施例において電極に局部的に親水性を付与する工程を示す断面図である。
【図１１】本発明の他の実施例における多孔質電極の製造工程を示す断面図である。
【図１２】同製造工程により得られた多孔質電極の断面図である。
【図１３】同様の電極を構成するシートの組合せ例を示す断面図である。
【図１４】本発明のさらに他の実施例において電極に局部的に親水性を付与する工程を示す断面図である。
【図１５】４層の炭素繊維シートから単一の電極シートを作製する工程を示す図である。
【図１６】他の実施例におけるＭＥＡのアノード側の正面図である。
【図１７】同ＭＥＡの上面図である。
【図１８】カソード側セパレータ板の正面図である。
【図１９】同カソード側セパレータ板の背面図である。
【図２０】図１８のＡ−Ａ’線断面図である。
【図２１】アノード側セパレータ板の正面図である。
【図２２】本発明の実施例における燃料電池の要部の断面図である。
【図２３】従来の燃料電池の要部の断面図である。
【図２４】本発明の実施例および比較例の燃料電池のアノードのバブラー温度と電流密度２００ｍＡ／ｃｍ²における電池電圧との関係を示す図である。
【図２５】本発明の実施例および比較例の燃料電池の燃料ガスの増減に伴う電池電圧の挙動を示す図である。
【図２６】本発明の実施例および比較例の燃料電池の出力電流密度と、電池温度を７５℃に維持するために必要であった冷却水量との関係を示す図である。
【図２７】複数のシートからなる電極シートから各層を露出させた状態を示す平面図である。
【図２８】同電極シートの各層の撥水性を評価する様子を示す平面図である。
【図２９】同電極シートの各層のＸ線回折パターンと撥水性の指標を示す図である。
【符号の説明】
３２ 水素イオン伝導性高分子電解質膜
３３ 導電性セパレータ板
３４ ガス流路
３５ 炭素繊維シート
３６ 別の炭素繊維からなる側壁部分[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a polymer electrolyte fuel cell, and more particularly to improvement of a porous electrode thereof.
[0002]
[Prior art]
A solid polymer electrolyte fuel cell exposes one surface of a hydrogen ion conductive polymer electrolyte membrane to a fuel gas such as hydrogen and the other to oxygen, and synthesizes water through a chemical reaction through the electrolyte membrane, The basic principle is to electrically extract the reaction energy generated thereby. The structure of this type of fuel cell is shown in FIG.
The hydrogen ion conductive polymer electrolyte membrane 1 and the porous electrode 2 having a pair of catalysts sandwiching the electrolyte membrane 1 are joined together by hot pressing or the like. This is called an electrolyte membrane-electrode assembly (MEA) and can be handled independently. A pair of conductive separator plates 3 having gas flow paths 4 for supplying fuel gas or oxidant gas to the respective electrodes are disposed outside the electrodes 2. Between the periphery of the electrolyte membrane 1 protruding from the electrode 2 and the conductive separator plate, a gasket 5 for preventing leakage of gas to the outside is disposed. The reaction gas introduced from the gas flow path 4 of the separator plate 3 causes an electrochemical reaction in the porous electrode 2 through the electrolyte membrane 1, and the generated electric power is recovered outside through the separator plate 3.
[0003]
The porous electrode is required to have good electrical conductivity, air permeability, water permeability and corrosion resistance. Therefore, carbon fibers (fibers fired at about 1000 ° C. through a stabilization process and having a degree of graphitization of about 50%, hereinafter referred to as carbon fibers) are made paper or woven to make structurally breathable. After making it a sheet (hereinafter referred to as carbonized paper or carbonized woven fabric), this is heat-treated at 2000 ° C. or higher to obtain a graphite paper or graphite woven fabric having a graphitization degree of 80% or higher. A method of utilizing good electrical conductivity, corrosion resistance, and water repellency is used.
In principle, the polymer electrolyte fuel cell needs to supply water for ion conduction to the anode, and water is generated at one cathode. Therefore, basically, the porous electrode on the anode side quickly passes the supplied water to the polymer electrolyte membrane, and conversely, the porous electrode on the cathode side quickly removes the generated water from the polymer electrolyte membrane. It is necessary. For this reason, the porous electrode is desirably water-repellent. However, when water supply reduction, temporary accumulation of supply water / produced water accompanying rapid increase / decrease in load, cooling effect due to latent heat of evaporation, etc. are expected, moderate water retention may be required. .
[0004]
[Problems to be solved by the invention]
In order to satisfy this contradictory demand, it has been proposed that the porous electrode is composed of a water-repellent porous electrode and a hydrophilic porous electrode, and is made partially hydrophilic while maintaining water repellency as a whole. However, when the entire surface is covered with a hydrophilic porous electrode, there is a problem that the hydrophilic porous electrode is clogged with water and easily causes a phenomenon (flooding) that inhibits gas permeation.
[0005]
[Means for Solving the Problems]
  In the present invention, the gas diffusion layer, which is a porous electrode made of a conductive carbon fiber sheet, has a structure having a gas flow path with the electrolyte membrane side as a bottom surface, or the electrolyte membrane side as a bottom surface and the opposite side as a top surface. The structure has a gas flow path. And the bottom of the gas flow pathsurface, Carbon fiber of the part constituting the side wall of the gas flow path and / or the part constituting the top surface of the gas flow pathHydrophilic group density of sheetAre different.
  The polymer electrolyte fuel cell of the present invention comprises a hydrogen ion conductive polymer electrolyte membrane, an electrolyte membrane / electrode assembly comprising a pair of electrodes sandwiching the hydrogen ion conductive polymer electrolyte membrane, and the electrolyte membrane / electrode junction. A polymer electrolyte fuel cell comprising a pair of conductive separator plates sandwiching a body, wherein the electrode comprises a catalyst layer in contact with the electrolyte membrane and a gas diffusion layer comprising a conductive carbon fiber sheet in contact with the catalyst layer A carbon fiber having a gas flow path with the gas diffusion layer having a bottom surface on the electrolyte membrane side, and constituting the bottom surface of the gas flow pathHydrophilic group density of sheetIs a carbon fiber constituting the side wall of the gas flow pathLess than the hydrophilic group density of the sheetIt is characterized byThe
[0006]
  The present invention relates to an electrolyte membrane / electrode assembly comprising a hydrogen ion conductive polymer electrolyte membrane and a pair of electrodes sandwiching the hydrogen ion conductive polymer electrolyte membrane, and a pair of electrical conductivity sandwiching the electrolyte membrane / electrode assembly. A polymer electrolyte fuel cell comprising a separator plate, wherein the electrode has a catalyst layer in contact with the electrolyte membrane and a gas diffusion layer made of a conductive carbon fiber sheet in contact with the catalyst layer, and the gas diffusion layer Has a gas flow path having the electrolyte membrane side as a bottom surface and the opposite side as a top surface, and constitutes a bottom surface of the gas flow pathHydrophilic group density of sheetIs a carbon fiber constituting the top surface of the gas flow pathSheetAnd carbon fiber constituting the side wall of the gas flow pathSheetAt least one ofLess than hydrophilic group densityA polymer electrolyte fuel cell is provided.
[0007]
  put it here,The hydrophilic group density of the carbon fiber sheet that constitutes the bottom surface of the gas flow path, the hydrophilic group density of at least one of the carbon fiber sheet that constitutes the top surface of the gas flow path and the carbon fiber sheet that constitutes the side wall of the gas flow path In order to make it smaller, it is preferable to vary at least one of the degree of graphitization and the degree of graphite orientation of the carbon fiber sheet. That is, the degree of graphitization and / or the degree of graphite orientation of the carbon fiber sheet that constitutes the bottom surface of the gas flow path, the carbon fiber sheet that constitutes the top face of the gas flow path, and the carbon fiber that constitutes the side wall of the gas flow path Preferably lower than that of at least one of the sheets.
  The degree of graphitizationAnd graphite orientationThis difference can be derived from a difference between different carbon fiber materials selected from a group of carbon fiber materials composed of PAN, pitch, cellulose, and phenol.
  A porous electrode can be comprised from the composite_body | complex of the carbon fiber sheet which has the groove | channel which comprises a gas flow path in one surface, and a flat carbon fiber sheet.
  The carbon fiber sheet having the groove and the flat carbon fiber sheet are different in at least one property of fiber density, pore density, graphitization degree, degree of graphite orientation, fiber microstructure and hydrophilic group density. Preferably.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
  As described above, the gas diffusion layer used in the polymer electrolyte fuel cell of the present invention has a gas flow path having a bottom surface on the electrolyte membrane side, and the carbon fiber constituting the bottom surface of the flow pathHydrophilic group density of sheetIs the carbon fiber of the part constituting the side wall of the gas flow pathSmaller than that of the sheet.
  In another aspect, the gas diffusion layer of the present invention has a gas flow path having the electrolyte membrane side as a bottom surface and the opposite side as a top surface, and constitutes a bottom surface of the gas flow path.Hydrophilic group density of sheetIs a carbon fiber constituting the top surface of the gas flow pathSheetAnd carbon fiber constituting the side wall of the gas flow pathSheetAt least one of itLess than.
[0009]
Typical conductive carbon fibers are PAN-based, pitch-based, rayon-based (cellulose-based), and phenol-based (Kinol-based) graphite fibers, which are derived from the properties of their starting materials, The degree of graphitization that can be reached is different. For example, with PAN and mesophase pitch systems (also called liquid crystal pitch or anisotropic pitch), long fibers with a high degree of orientation can be obtained at the spinning stage, and the structure of the starting material is simple and benzene rings can be easily formed. It is. Accordingly, when carbonized and graphitized, carbon fibers having a high degree of crystal orientation and a high degree of graphitization can be obtained. On the other hand, in the rayon system and the phenol system, both the degree of crystal orientation and the degree of graphitization are low due to the difficulty of forming a benzene ring due to the complexity of the starting materials and the low degree of crystal orientation derived from the raw materials. .
[0010]
Even with graphite fibers belonging to the same system, it is possible to obtain electrodes having different degrees of orientation and graphitization by changing production conditions such as temperature and time. For example, in the pitch system, decant oil (bottom oil of a petroleum refining distillation column) is treated at about 400 ° C. to partially polycondensate the benzene ring to make it anisotropic. Then, a mixture (mesophase pitch or liquid crystal pitch) with an isotropic portion is spun and oriented. The mixture is then subjected to stabilization, carbonization, and graphitization steps to obtain graphite fibers. At this time, the ratio of the anisotropic portion to the isotropic portion and the degree of polymerization of the anisotropic portion can be controlled by adjusting the treatment temperature or treatment time in the mesophase pitch production stage. Further, by adjusting the spinning temperature, yarns having different degrees of orientation can be obtained. By taking such a preparation means, it is reflected in the crystal orientation degree and graphitization degree of the finally obtained graphite fiber.
For example, a PAN-based graphite fiber is roughly manufactured by the following process, and a fiber with a high degree of graphitization cannot be obtained even if any process is incomplete.
[0011]
1) PAN fiber production process (polymerization and spinning of monomers)
2) Oxidation step (stabilization of fibers by air oxidation at 200 ° C to 300 ° C)
3) Pre-carbonization step (ring condensation with dehydrating acid in nitrogen at 400 ° C to 900 ° C)
4) Carbonization step (900-1500 ° C. in nitrogen, ring condensation by denitrification and graphite structure formation)
5) Graphitization process (2000 ° C or higher, development of graphite crystals)
[0012]
Therefore, for example, by reducing the processing temperature in the carbonization process and controlling the processing time, a plurality of carbon fibers having different orientation characteristics and graphite structures are produced, and a plurality of carbon fiber sheets obtained by papermaking or woven are bonded together with a binder. After that, by graphitizing under the same conditions, it is possible to easily produce a multi-layer carbon sheet having a different degree of crystal orientation and graphitization in each layer, and thus having a water-repellent gradient.
[0013]
It is possible to adjust the amount of water-repellent gradient and the order by chemically modifying a plurality of carbon sheets having different degrees of orientation and graphitization obtained as described above by an appropriate method. That is, a sheet having a high degree of orientation and graphitization is difficult to chemically modify because graphite crystals are chemically inert and there is no room for modification groups to enter because the degree of orientation is high. . On the other hand, a sheet with a low degree of orientation and graphitization is vice versa and can be easily chemically modified. Therefore, when the above-described carbon sheet is subjected to a hydrophilic treatment by a technique such as nitric acid oxidation, electrolytic oxidation (anodic oxidation), or steam oxidation, the amount of the gradient is enhanced according to the original water-repellent gradient sequence. On the contrary, after the hydrophilic treatment, for example, when the water repellent treatment is performed with a fluorocarbon-based water repellent treatment agent, the hydrophilic group is modified with the fluorocarbon. Thus, the water repellency is higher than the original water repellency. As described above, it is possible to produce a sheet having a desired order and strength and a hydrophilic / water-repellent function by combining the carbon sheet manufacturing process and the chemical modification process.
Considering the above, it is possible to select the constituent material of each part of the electrode made of a carbon sheet having a gas flow path. Moreover, the sheet | seat which comprises the bottom face of a gas flow path, and / or the sheet | seat which comprises the top | upper surface of a gas flow path can also be comprised with several sheets from which a crystal orientation degree and a graphitization degree differ.
[0014]
Several embodiments will be described below with reference to the drawings.
In a porous electrode having a gas flow path, the part that requires gas permeation is the part that constitutes the bottom of the flow path, and the part that does not require gas permeation is the part that constitutes the side wall of the flow path and the top of the flow path. It is the part which comprises a surface. Therefore, the portion corresponding to the bottom of the flow path is made of water-repellent carbon fiber, and the side wall portion of the flow path and / or the top surface portion of the flow path is made of hydrophilic carbon fiber, thereby sacrificing gas permeability. Without imparting hydrophilicity.
The carbon fiber yarn at the spinning stage before stabilization by oxygen crosslinking is flexible and can be knitted into an arbitrary shape. Therefore, as shown in FIGS. 1 and 2, a fiber cloth 10 having grooves 12 is prepared by providing a large number of protrusions 11 in parallel, and this is stabilized, carbonized, and graphitized. Thus, a porous electrode having a gas flow path in the groove 12 can be easily obtained. Moreover, since the short fiber of a carbon fiber can also be formed in the mat | matte shape and felt shape of arbitrary shapes, the porous electrode which has a gas flow path similarly can be obtained.
FIG. 6 shows an example in which the side wall portion 24 forming the groove 25 is integrally formed by weaving another carbon fiber yarn into the raw fabric 23.
The examples shown above are suitable methods for pitch-based and rayon-based carbon fibers that do not generate a large amount of heat when stabilizing. It is not suitable for PAN-based carbon fibers that have a large heat generation amount for stabilization and are difficult to stabilize unless they are single yarns.
[0015]
Next, a method applicable to PAN-based carbon fibers will be shown.
First, as shown in FIG. 3, a carbonized sheet 20a obtained by cutting long fibers into an appropriate length and making a paper, and a sheet 20b in which slits 22 are formed by punching the same carbonized sheet into a flow path shape are bonded to a binder. (Fig. 4). Next, the binder and the carbonized sheets 20a and 20b are graphitized in a lump, and this is cut off at a dotted line portion shown in FIG. In this way, as shown in FIG. 5, a carbon fiber sheet having a groove formed by the slit 22 is obtained. FIG. 5 shows an example in which two carbonized sheets 20a and 20b are used. A side wall portion is formed by the portion 21 of the sheet 20b.
By forming the gas flow path in this way, the PAN-based carbon fiber having poor flexibility, for example, the process up to the carbonization process and partially progressing the crystallization of graphite is the same as shown in FIG. It can be shaped. In other words, the gas flow path can be formed using any carbon fiber according to an appropriate processing method.
[0016]
FIG. 7 shows an example of an electrolyte membrane-electrode assembly (MEA) provided with a porous electrode made of a carbon fiber sheet obtained as described above. 32 represents a hydrogen ion conductive polymer electrolyte membrane. A pair of water-repellent porous electrodes 31 formed by a conventional method are disposed with the electrolyte membrane 32 interposed therebetween. The porous electrode 30 arranged on the outside of the electrode 31 is formed by hydrophilizing the electrode in which the groove 34 is formed by the above-described method using, for example, nitric acid oxidation, electrolytic oxidation (anodic oxidation), steam oxidation, or the like. This is a hydrophilic porous electrode. Therefore, the electrode composed of the water repellent porous electrode 31 and the hydrophilic porous electrode 30 has water repellency at the bottom of the gas flow path 34 on the electrolyte membrane side, and the side wall portion and the ceiling of the gas flow path 34 The surface portion has hydrophilicity. That is, with such a configuration, a porous electrode imparted with hydrophilicity without sacrificing gas permeability can be realized. 33 represents a conductive separator plate.
[0017]
In FIG. 6, a carbon fiber having a high crystal orientation and a small surface area, such as a PAN-based or mesophase pitch-based carbon fiber, is used for the raw fabric 23 and in FIG. . On the other hand, in FIG. 6, carbon fiber yarns woven into the raw fabric 23, and in FIG. 3, a carbon fiber having a low crystal orientation (glassy) and a large surface area, such as phenol, is applied to a woven fabric or papermaking sheet 20 b to be die-cut. System activated carbon fiber or the like is used. Then, by forming the structure shown in FIGS. 6 and 5 and performing a light hydrophilic treatment, the carbon fibers with a high degree of crystal orientation are hardly hydrophilically modified, and the carbon fibers with a low degree of crystal orientation are preferentially subjected to a hydrophilic treatment. A single electrode having a water repellent part and a hydrophilic part can be produced.
[0018]
Examples of the MEA provided with the porous electrode thus obtained are shown in FIGS.
FIG. 8 uses an electrode made of a carbon fiber sheet having the structure shown in FIG. That is, an electrode is used in which a side wall portion 36 of the gas flow path 34 is formed by weaving a carbon fiber having a low crystal orientation and a large surface area into a sheet 35 made of carbon fibers having a high crystal orientation and a small surface area. The MEA is configured by sandwiching the electrolyte membrane 32 on the sheet 35 side of the electrode.
FIG. 9 uses a carbon fiber sheet configured as shown in FIG. That is, an electrode in which three sheets 38 made of carbon fibers having a low crystal orientation and a large surface area are joined to a sheet 37 made of carbon fibers having a high degree of crystal orientation and a small surface area to form a side wall portion of the gas flow path 34. Used.
Even when the same carbon fiber is used, it is possible to form the water-repellent part and the hydrophilic part by adjusting the fiber density. This is because the capillary phenomenon can be used by increasing the density. Since the water repellent part has a low density, the gas permeability is not sacrificed, and the high density hydrophilic part wetted with water functions sufficiently as a gas partition between the flow paths.
[0019]
A hydrophilic part can be formed by embedding a hydrophilic agent, for example, silica gel, in the side wall part of the gas flow path by utilizing the porosity of the electrode. FIG. 10 shows the manufacturing process of such an electrode.
First, the side wall part 42 which forms the gas flow path 43 by bonding three sheets made of the same carbon fiber to the sheet 41 made of carbon fiber is provided (FIG. 10A). Next, the screen 45 is set on the side wall portion 42 (FIG. 10B), the ink containing the silica gel powder 47 is printed (FIG. 10C), and then the ink is pushed into the side wall portion 42 by the pressure plate 46. (FIG. 10 (d)). Thus, an electrode is formed in which the side wall portion 42 is composed of a portion 42a made of the original carbon fiber and a portion 42b filled with silica gel (FIG. 10E).
By appropriately combining the above methods, desired hydrophilicity can be imparted to the hydrophilic portion while sufficiently ensuring gas permeability in the water repellent portion.
[0020]
Next, another method for manufacturing an electrode having a gas flow path with the electrolyte membrane side as the bottom surface and the opposite side as the top surface will be described.
First, as shown in FIG. 11, carbonized sheets 50a and 50d obtained by cutting long fibers into an appropriate length and making paper, and sheets 50b and 50c formed by slitting the same carbonized sheet into a channel shape to form slits 52. Are bonded together with a binder in the order of the sheets 50a, 50b, 50c and 50d. Next, the binder and the carbonized sheet are graphitized in a lump and cut at a dotted line portion in FIG. In this way, as shown in FIG. 12, an electrode is obtained in which the sheet 50a is the bottom surface, the sheet 50d is the top surface, and the gas flow path is formed at the slit 52 portion. Here, an example is shown in which four sheets of the same material are used, but it goes without saying that the number of sheets and the material can be changed as necessary.
[0021]
FIG. 13 shows a combination example of the respective sheets constituting the electrode manufactured as described above. FIG. 13A shows a sheet 50a constituting the bottom surface of the gas flow path 52, sheets 50b and 50c constituting the side walls of the flow path, and a PAN-based or pitch-based water-repellent carbon sheet and the top surface of the flow path. This is an example in which a cellulose-based or phenol-based hydrophilic carbon sheet is used for each of the constituent sheets 50d. In FIG. 13B, the sheet 50a constituting the bottom surface of the gas flow path 52 is hydrophilic to the water repellent carbon sheet, the sheets 50b and 50c constituting the side wall portion of the flow path, and the sheet 50d constituting the top surface of the flow path. Carbon sheets are used. In FIG. 13C, the sheet 50a constituting the bottom surface of the gas flow path 52 and the sheet 50d constituting the top surface of the flow path are hydrophilic to the water-repellent carbon sheet, and the sheets 50b and 50c constituting the side wall portions of the flow path are hydrophilic. Carbon sheets are used. In any case, a water-repellent layer 53 is formed on the electrolyte membrane side of the sheet 50a constituting the bottom surface of the flow path.
[0022]
FIG. 14 shows an example in which a specific portion of an electrode sheet manufactured by the method described with reference to FIG. 11 is subjected to hydrophilic treatment and the other specific portion is subjected to water repellency treatment.
The mask 65 is positioned on the sheet 60d of the electrode sheet composed of the sheet 60a constituting the bottom surface of the flow path 62, the sheet 60d constituting the top surface, and the sheets 60b and 60c constituting the side walls (FIG. 14B). Next, the hydrophilic material 64 is printed on the surface on which the mask 65 is set (FIG. 14C), and this is impregnated into the sheet 60d (FIG. 14D). Next, the entire sheet is turned upside down, the water repellent 63 is printed on the sheet 60a (FIG. 14E), and heat treatment is performed. Thus, an electrode is obtained in which the top surface of the flow path 62 is made of the hydrophilic sheet 60d and the bottom surface is made of the sheet 60a having the water repellent layer 63 (FIG. 14F). The hydrophilic agent used here is, for example, silica gel, the water repellent is polytetrafluoroethylene, and the heat treatment temperature is about 340 ° C. By this heat treatment, moderate hydrophilicity and water repellency are imparted.
[0023]
Next, two or three of the carbon fiber sheet that forms the bottom surface of the gas flow path, the carbon fiber sheet that forms the side wall of the gas flow path, and the carbon fiber sheet that forms the top surface of the gas flow path are connected by graphitized material. A method in the case of wearing, or binding a sheet of each part with a graphitized material to form a multilayer sheet will be described.
The apparatus of FIG. 15 will be described. From the rolls 71a, 71b, 71c and 71d, the first layer carbonized paper original fabric 72a, the second layer carbonized paper original fabric 72b, the third layer carbonized paper original fabric 72c, and the fourth layer carbonized paper original fabric 72d, respectively. Is paid out. The carbonized paper 72b, 72c and 72d are coated with binders by coating rolls 73b, 73c and 73d, respectively, and these are joined to the carbonized paper 72a by the rolls 75a and 75b via the rolls 74b, 74c and 74d. . The carbonized paper 76 that is integrally bonded to the four layers is then graphitized in a firing furnace 77, passes through rolls 78 a and 78 b, and is cut into individual electrode sizes by a cutter 79. Thus, a single conductive carbon fiber sheet 80 composed of four layers is obtained.
[0024]
The structure of the fuel cell using the gas diffusion layer or porous electrode according to the present invention described above will be described below.
16 and 17 show the MEA, FIGS. 18 to 20 show the cathode side separator plate, FIG. 21 shows the anode side separator plate, and FIG. 22 shows the fuel cell.
The MEA 100 includes a polymer electrolyte membrane 101, an anode 102 and a cathode 103 bonded to both surfaces thereof, and a gasket 110 that covers the periphery of the electrolyte membrane. The gasket 110 is provided with a pair of fuel gas manifold holes 112, an oxidant gas manifold hole 113, and a cooling water manifold hole 114. These manifold holes communicate with respective manifold holes of the separator plate described below. In this example, as shown in FIG. 22, the anode 102 and the cathode 103 are hydrophilic having a water repellent electrode sheet 104 disposed on the electrolyte membrane side and a gas flow path 106 formed by a groove opened on the sheet 104 side. A combination of the conductive electrode sheets 105.
[0025]
The anode-side separator plate 120 has a pair of fuel gas manifold holes 122, an oxidant gas manifold hole 123, and a cooling water manifold hole 124. Further, the anode-side separator plate 120 has a recess 121 for receiving the anode 102 in the center on the surface facing the anode of the MEA, and on both sides of the recess by a combination with the gas flow path 106 of the anode 102. , And a groove 125 for constituting a gas flow path communicating from one fuel gas manifold hole 122 to the other manifold hole 122. Similarly, the cathode separator plate 130 has a pair of fuel gas manifold holes 132, an oxidant gas manifold hole 133, and a cooling water manifold hole 134. The cathode-side separator plate 130 further has a recess 131 that receives the cathode 103 in the center on the surface facing the cathode of the MEA, and a combination with the gas flow path 106 of the cathode 103 on both sides of the recess. , And a groove 135 for constituting a gas flow path communicating from one oxidant gas manifold hole 133 to the other manifold hole 133.
The cathode-side separator plate 130 has a groove 136 for forming a cooling water flow path so as to communicate with the pair of cooling water manifold holes 134 on the back surface thereof. A cooling unit for cooling the cell is configured by combining with the anode separator plate 120 provided with the same cooling water flow channel groove 126. In a portion where the cooling part is not formed, one separator plate 140 having one surface as the anode side separator plate and the other surface as the cathode side separator plate is inserted between the cells.
[0026]
In the cell having the above structure, the fuel gas supplied from the manifold hole 122 of the separator plate 120 is supplied from the groove 125 of the separator plate 120 to the anode through the gas flow path 106 of the anode 102. Excess fuel gas and moisture generated by the electrode reaction are discharged from the gas flow path 106 of the anode 102 to the manifold hole 122 through the groove 125 of the separator plate. Similarly, the oxidant gas supplied from the manifold hole 133 of the separator plate 130 is supplied from the groove 135 of the separator plate 130 to the anode via the gas flow path 106 of the cathode 103, and excess gas and moisture are supplied to the groove of the separator plate. 135 is discharged to the manifold hole 133.
[0027]
【Example】
Examples of the present invention will be described below.
Example 1
A continuous woven fabric in which mesophase pitch-based carbon fiber yarns were knitted into the shape shown in FIGS. 1 and 2 was produced, and this was stabilized at 250 ° C. by a continuous heating device, and then cut into an appropriate size. This was carbonized at 1200 ° C. in a batch furnace and then graphitized at 2400 ° C. to produce a porous electrode. As shown in FIG. 2A, the anode has a groove for forming a gas flow path and a side wall having a width of 1.5 mm, a pitch of 3.0 mm, a groove depth of 0.4 mm, and a groove bottom thickness of 0.1 mm. It was 15 mm. As shown in FIG. 2B, the cathode was the same as the anode except that the groove depth was 0.6 mm. A flat electrode having a thickness of 0.36 mm without forming a gas flow path was manufactured under the same conditions.
[0028]
These porous electrodes exhibit water repellency. Next, the porous electrode having the gas flow path was refluxed with 2% nitric acid for 1 hour for hydrophilic treatment to prepare a hydrophilic electrode. The flat electrode is not subjected to hydrophilic treatment and is called a water repellent electrode. Table 1 shows the results of evaluating the hydrophilicity of these electrodes. For the evaluation of hydrophilicity, wetting index standard solutions having various surface tensions were dropped, and the surface tension of the liquid having the largest surface tension among the soaked standard solutions was used as the hydrophilicity index of the layer. The hydrophilicity index indicates that the larger the value is, the more hydrophilic it is. A wetting index standard solution having a surface tension of 23 mN / cm to 72 mN / cm was used.
[0029]
[Table 1]

[0030]
Next, the specific surface area is 800m²Platinum was supported on Ketjen Black EC (furnace black manufactured by Ketjen Black International Co., Ltd.) having a DBP oil absorption of 360 ml / 100 g at a weight ratio of 1: 1. To 10 g of this catalyst powder, 35 g of water and 59 g of an alcohol dispersion of a hydrogen ion conductive polymer electrolyte (Asahi Glass Co., Ltd., trade name: 9% FFS) are mixed and dispersed using an ultrasonic stirrer. A layer ink was prepared. This catalyst layer ink was applied onto a polypropylene film (trade name: Treffan 50-2500, manufactured by Toray Industries, Inc.) and dried to prepare a catalyst layer. The obtained catalyst layer was cut into a predetermined size of 6 cm × 6 cm. The catalyst layer thus prepared was transferred onto both sides of a polymer electrolyte membrane (Nafion 112 membrane manufactured by DuPont, USA) having a size of 12 cm × 12 cm.
A water-based ink containing polytetrafluoroethylene fine powder (manufactured by Daikin Industries, Ltd.) and acetylene black (manufactured by Denki Kagaku Kogyo Co., Ltd.) in a weight ratio of 1: 4 was prepared. This ink was applied to one surface of the water-repellent electrode and baked at 350 ° C. for 20 minutes to form a water-repellent layer. The density of the water-repellent layer after firing is 2.0 mg / cm per unit area of the electrode.²Met. A pair of electrodes on which these water repellent layers are formed have a temperature of 130 ° C. and a pressure of 15 kg / cm on the electrolyte membrane joined with the catalyst layer so that the water repellent layer is on the electrolyte membrane side.²Then, an MEA was manufactured by hot pressing. A test cell was assembled by combining the anode and cathode, which are hydrophilic electrodes having the gas flow path, with the groove open portions in contact with the water-repellent electrode.
The cell used here has the structure shown in FIG. 21 described above.
[0031]
The above battery is held at 75 ° C., pure hydrogen gas humidified and heated to various dew points is supplied to the anode, and air humidified and heated to 65 ° C. dew point is supplied to the cathode, respectively. The discharge test of the battery was performed under conditions of a fuel gas utilization factor of 70% and an air utilization factor of 40%.
As a comparative example, instead of the cell having the structure shown in FIG. 23, that is, the hydrophilic electrode sheet 105 having a gas flow path, a conductive material subjected to flow path processing having the same groove width, pitch, and groove depth as the hydrophilic electrode. A unit cell having a structure in which the above MEA was sandwiched was assembled using a conductive separator plate, and a battery discharge test was performed under the same conditions.
[0032]
FIG. 24 shows the anode bubbler temperature and the current density of 200 mA / cm.²The relationship with the voltage per unit cell of the battery in is shown. In the battery of this example, the battery voltage in a low humidified state is improved as compared with the comparative example. This is presumably because the utilization rate of the supplied water has been improved by improving the moisture retention characteristics of the electrode.
FIG. 25 shows the behavior of the battery voltage as the fuel gas is intermittently increased or decreased. In the figure, UP represents the start of fuel gas supply, and DN represents the stop of fuel gas supply. It can be seen that the battery of the example may have a rising characteristic when the fuel gas is increased as the load increases, as compared with the comparative example, and the response when the fuel gas is reduced as the load decreases is slower than the comparative example. In general, no matter what type of humidifier is used, there is a time lag in the supply speed between the fuel gas and the supply water, and this is a factor that deteriorates the start-up characteristics. In the battery of the example, the electrode stagnant water compensates for the delay of the supplied water with respect to the fuel gas supply, and the effect of shortening the time lag is recognized. In particular, in an in-vehicle fuel cell, since the response at the time of load increase is more important than that at the time of load decrease, the battery of the example is judged to be superior to the comparative example.
[0033]
A laminated battery in which 10 cells were laminated in the cell configurations of the above examples and comparative examples was assembled and operated under the same conditions as described above. Usually, heating is necessary to maintain the battery temperature in a single cell, but in a laminated battery, cooling is necessary because it overheats due to self-heating.
FIG. 26 shows the relationship between the output current density and the amount of cooling water required to maintain the battery temperature at 75 ° C. The batteries of the examples require a smaller amount of cooling water especially at high output current densities than the comparative examples. The reason is presumed that the generated water generated in a large amount at a high current density temporarily stays in the electrode, then takes away the latent heat of vaporization and is discharged out of the battery. This is a characteristic suitable for an on-vehicle fuel cell that does not need to directly use waste heat and operates at a high current density.
[0034]
Example 2
Mesophase pitch-based carbon fiber yarn (spun and unstabilized) was woven to a thickness of 150 μm, and phenol-based carbon fiber yarn was sewn to a thickness of 600 μm. This was graphitized through a stabilization and carbonization process to produce an electrode as shown in FIG. Thereafter, it was activated by steam oxidation under conditions of 800 ° C. and 240 seconds in a continuous furnace. Table 2 shows the evaluation results of specific surface area and hydrophilicity before activation and after activation of the portion constituting the bottom of the gas flow path and the side wall portion at this time. As shown in Table 2, a significant increase was observed in the surface area and hydrophilicity of the channel side wall portion made of phenol in particular due to the activation.
[0035]
[Table 2]

[0036]
Using this electrode, a water repellent layer similar to that of Example 1 was formed on the side having no gas flow path. Then, the MEA was fabricated by bonding to the electrolyte membrane so that the surface having the water repellent layer was on the electrolyte membrane side, and the test single cell having the cross-sectional structure shown in FIG. Assembled. This battery also exhibited substantially the same characteristics as in Example 1.
[0037]
《Reference example>>
  The PAN-based carbon fiber that has been carbonized is cut into a fiber length of 2 mm, paper-made, and has a thickness of 50 μm and a basis weight of 0.12 g / cm.²A sheet of was prepared.
  Thereafter, as shown in FIG. 3 and FIG. 4, three sheets that were not subjected to die cutting and eight sheets that were subjected to die cutting were bonded together using a binder of an aqueous solution of carboxymethyl cellulose while positioning. This was graphitized at 2400 ° C. to produce a single electrode. The punched shape of the sheet B was a groove width of 1.5 mm and a pitch of 3 mm.
  The single electrode was subjected to a hydrophilic treatment on the side wall by the method shown in FIG. That is, 60 parts by weight of colloidal silica (Nissan Chemical Co., Ltd., IPA-ST silica sol), 25 parts by weight of acetylene black (manufactured by Denki Kagaku Kogyo Co., Ltd.), silica gel (particle size: 10 to 30 μm, JIS A class) 15 parts by weight and 5 parts by weight of a thermosetting epoxy resin (90% crosslinking point, 75 ° C., 1 minute) were added and kneaded to prepare an ink. This ink was printed by screen printing (applied three times) on the side wall forming the gas flow path of the electrode, and pressed with a spatula. Then, after removing the solvent at 120 ° C., the epoxy resin was crosslinked at 200 ° C., and further heat treated at 320 ° C. for 2 hours to dehydrate and condense the colloidal silica to obtain an electrode having hydrophilicity only on the side wall portion. It was confirmed that the electrode of this example had the same effect as that of Examples 1 and 2. Further, the hydrophilicity of the side wall portion can be arbitrarily controlled by an appropriate ink composition, and the above effects can be easily adjusted.
[0038]
"Example3>>
  The following carbonized paper original fabric was bound with a pitch-based binder using the apparatus shown in FIG. 15, and then graphitized at 2450 ° C. for 3 hours in an inert gas atmosphere to produce a four-layer electrode sheet X1. .
  First layer: Mesophase pitch carbonized paper (fiber diameter 12 μm, fiber length 5 mm, thickness 150 μm)
  Second layer: highly elastic PAN-based carbonized paper (fiber diameter 6.5 μm, fiber length 5 mm, thickness 150 μm)
  Third layer: isotropic pitch-based carbonized paper (fiber diameter 13 μm, fiber length 2 mm, thickness 80 μm)
  Fourth layer: phenolic carbonized paper (fiber diameter 11 μm, fiber length 2 mm, thickness 80 μm).
[0039]
The sheet 80 was bonded to the fixing glass and then polished to expose the polished surfaces of the first layer 80a, the second layer 80b, the third layer 80c, and the fourth layer 80d, as shown in FIG. . As shown by 90 in FIG. 28, various wetness index standard solutions were dropped on this polished surface to evaluate the water repellency of each layer. In the evaluation of water repellency, the surface tension of a liquid having the largest surface tension among the soaked standard liquids was used as an index of water repellency of the layer. The smaller the value of the water repellency index, the more water repellent. A wetting index standard solution having a surface tension of 23 mN / cm to 72 mN / cm was used.
The evaluation results of water repellency and the X-ray diffraction pattern of each layer are shown in FIG. (A), (b), (c), and (d) of FIG. 29 represent the characteristics of the first layer, the second layer, the third layer, and the fourth layer, respectively. As is clear from FIG. 29, the layer derived from the mesophase pitch-based and PAN-based carbonized paper having a high degree of orientation and graphitization has high water repellency. On the other hand, isotropic pitch-based and phenol-based carbonized paper-derived layers having a low degree of orientation and graphitization have low water repellency. That is, the sheet 80 has a water repellent gradient derived from the degree of orientation and the degree of graphitization.
The sheet is X1. Next, the sheet X1 was refluxed with 2% nitric acid for 30 minutes to add hydroxyl groups to the surface. This is a sheet X2. The hydroxyl group of the sheet X2 was water repellent treated with the water repellent treatment agent heptadecafluorodecyltrichlorosilane. This is a sheet X3. The sheet X1 is refluxed with 10% nitric acid for 2 hours to add a hydroxyl group to the surface, and the sheet X4 is X4. The sheet X4 has a hydroxyl group treated with a water repellent treatment agent heptadecafluorodecyltrichlorosilane. These sheets were evaluated for water repellency in the same manner as described above. The results are shown in Table 3.
[0040]
[Table 3]

[0041]
As is apparent from Table 3, the amount of the gradients of the sheets X2 and X4 were enhanced according to the order of the water repellent gradient of the sheet X1, and the degree thereof could be controlled according to the treatment process. Conversely, the sheets X3 and X5 have a water repellency order opposite to the water repellency gradient order of the sheet X1, and the water repellency exceeds the water repellency of the sheet X1, and the degree thereof is hydrophilic in the sheets X2 and X4. Dependent on gender.
As described above, a combination of the above-described electrode sheet manufacturing process and the chemical modification process makes it possible to produce a single sheet having an arbitrary order and strength of water repellency. Further, the internal resistance of the sheet was almost the same as that of a commonly used PAN-based or pitch-based single sheet.
[0042]
【The invention's effect】
As described above, according to the present invention, water permeability can be imparted to the electrode without sacrificing gas permeation, so that battery characteristics are not sacrificed, supply water is reduced, load response is improved, and latent heat of vaporization is obtained. It is possible to impart secondary characteristics such as a cooling effect due to.
[Brief description of the drawings]
FIG. 1 is a plan view of a woven fabric made of carbon fiber yarns as a raw material for a porous electrode in an embodiment of the present invention.
FIG. 2 is a cross-sectional view of the fabric.
FIG. 3 is a plan view of two carbon fiber sheets as raw materials for a porous electrode in another embodiment of the present invention.
FIG. 4 is a plan view showing a state in which the two sheets are overlapped.
FIG. 5 is a sectional view of the sheet.
FIG. 6 is a cross-sectional view of a sheet in which another carbon fiber is woven into a woven fabric that is a raw material for a porous electrode according to still another embodiment of the present invention.
FIG. 7 is a cross-sectional view showing a configuration example of an MEA.
FIG. 8 is a cross-sectional view showing another configuration example of the MEA.
FIG. 9 is a cross-sectional view showing still another configuration example of the MEA.
FIG. 10 is a cross-sectional view showing a step of locally imparting hydrophilicity to an electrode in still another embodiment of the present invention.
FIG. 11 is a cross-sectional view showing a manufacturing process of a porous electrode according to another embodiment of the present invention.
FIG. 12 is a cross-sectional view of a porous electrode obtained by the same manufacturing process.
FIG. 13 is a cross-sectional view showing a combination example of sheets constituting the same electrode.
FIG. 14 is a cross-sectional view showing a step of locally imparting hydrophilicity to an electrode in still another embodiment of the present invention.
FIG. 15 is a diagram showing a process of producing a single electrode sheet from a four-layer carbon fiber sheet.
FIG. 16 is a front view of the MEA on the anode side according to another embodiment.
FIG. 17 is a top view of the MEA.
FIG. 18 is a front view of a cathode side separator plate.
FIG. 19 is a rear view of the cathode separator plate.
20 is a cross-sectional view taken along line A-A ′ of FIG. 18;
FIG. 21 is a front view of an anode separator plate.
FIG. 22 is a cross-sectional view of a main part of a fuel cell in an example of the present invention.
FIG. 23 is a cross-sectional view of a main part of a conventional fuel cell.
FIG. 24 shows the bubbler temperature and current density of 200 mA / cm at the anodes of the fuel cells of Examples and Comparative Examples of the present invention.²It is a figure which shows the relationship with the battery voltage in.
FIG. 25 is a graph showing the behavior of the cell voltage accompanying the increase / decrease of the fuel gas in the fuel cells of Examples and Comparative Examples of the present invention.
FIG. 26 is a graph showing the relationship between the output current density of the fuel cells of Examples and Comparative Examples of the present invention and the amount of cooling water required to maintain the cell temperature at 75 ° C.
FIG. 27 is a plan view showing a state in which each layer is exposed from an electrode sheet composed of a plurality of sheets.
FIG. 28 is a plan view showing how water repellency of each layer of the electrode sheet is evaluated.
FIG. 29 is a diagram showing an X-ray diffraction pattern and a water repellency index of each layer of the electrode sheet.
[Explanation of symbols]
32 Hydrogen ion conductive polymer electrolyte membrane
33 Conductive separator plate
34 Gas flow path
35 Carbon fiber sheet
36 Side wall portion made of another carbon fiber

Claims (14)

An electrolyte membrane / electrode assembly comprising a hydrogen ion conductive polymer electrolyte membrane and a pair of electrodes sandwiching the hydrogen ion conductive polymer electrolyte membrane, and a pair of conductive separator plates sandwiching the electrolyte membrane / electrode assembly A polymer electrolyte fuel cell, wherein the electrode has a catalyst layer in contact with the electrolyte membrane and a gas diffusion layer made of a conductive carbon fiber sheet in contact with the catalyst layer, and the gas diffusion layer is the electrolyte membrane A gas channel having a bottom surface on the side, wherein the hydrophilic group density of the carbon fiber sheet constituting the bottom surface of the gas channel is smaller than the hydrophilic group density of the carbon fiber sheet constituting the side wall of the gas channel A polymer electrolyte fuel cell. 2. The polymer according to claim 1 , wherein the carbon fiber sheet constituting the bottom surface of the gas flow path has at least one of a degree of graphitization and a degree of graphite orientation higher than that of the carbon fiber sheet constituting the side wall of the gas flow path. Electrolytic fuel cell. The at least one difference between the degree of graphitization and the degree of graphite orientation is derived from a difference between different carbon fiber materials selected from a carbon fiber material group consisting of PAN, pitch, cellulose, and phenol. 2. The polymer electrolyte fuel cell according to 2.   2. The polymer electrolyte fuel cell according to claim 1, wherein the carbon fiber sheet comprises a plurality of sheets and a graphitized material binding them. 2. The polymer electrolyte fuel cell according to claim 1, wherein the carbon fiber sheet comprises a plurality of sheets having at least one of a degree of graphitization and a degree of graphite orientation , and a graphitized material binding them. An electrolyte membrane / electrode assembly comprising a hydrogen ion conductive polymer electrolyte membrane and a pair of electrodes sandwiching the hydrogen ion conductive polymer electrolyte membrane, and a pair of conductive separator plates sandwiching the electrolyte membrane / electrode assembly A polymer electrolyte fuel cell, wherein the electrode has a catalyst layer in contact with the electrolyte membrane and a gas diffusion layer made of a conductive carbon fiber sheet in contact with the catalyst layer, and the gas diffusion layer is the electrolyte membrane the side and bottom, having a gas flow path to the opposite top, the carbon fiber sheets hydrophilic group density of the carbon fiber sheet constituting the bottom surface of the gas passage, which forms the ceiling of the gas flow path And a density of hydrophilic groups of at least one of the carbon fiber sheets constituting the side walls of the gas flow path. The polymer electrolyte according to claim 6 , wherein the hydrophilic group density of the carbon fiber sheet constituting the bottom surface of the gas flow path in the gas diffusion layer is the same as the hydrophilic group density of the carbon fiber sheet constituting the side wall of the gas flow path. Type fuel cell. The polymer according to claim 6 , wherein the hydrophilic group density of the carbon fiber sheet constituting the bottom surface of the gas flow path in the gas diffusion layer is the same as the hydrophilic group density of the carbon fiber sheet constituting the top surface of the gas flow path. Electrolytic fuel cell. The carbon fiber sheet constituting the bottom surface of the gas flow path is such that at least one of the degree of graphitization and the degree of graphite orientation is the carbon fiber sheet constituting the top face of the gas flow path and the carbon constituting the side wall of the gas flow path. The polymer electrolyte fuel cell according to claim 6 , which is higher than that of at least one of the fiber sheets . The at least one difference between the degree of graphitization and the degree of graphite orientation is derived from a difference between different carbon fiber materials selected from a carbon fiber material group consisting of PAN, pitch, cellulose, and phenol. 9. The polymer electrolyte fuel cell according to 9 . The gas diffusion layer according to claim 6 consisting of a carbon fiber sheet having grooves constituting the gas flow path has been released on a flat carbon fiber sheet and the plate-shaped carbon fiber sheet side positioned in the polymer electrolyte membrane side The polymer electrolyte fuel cell as described. A carbon fiber sheet having a groove that constitutes a gas flow path in which the gas diffusion layer is released on the side opposite to the polymer electrolyte membrane, and a flat carbon fiber bonded to the carbon fiber sheet so as to close the groove The polymer electrolyte fuel cell according to claim 6, comprising a sheet. The polymer electrolyte fuel cell according to claim 6 , wherein the carbon fiber sheet comprises a plurality of sheets and a graphitized material binding them. The polymer electrolyte fuel cell according to claim 6 , wherein the carbon fiber sheet comprises a plurality of sheets having at least one of a degree of graphitization and a degree of graphite orientation , and a graphitized material binding them.

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