JP5433147B2 - Porous electrode substrate, method for producing the same, membrane-electrode assembly, and polymer electrolyte fuel cell - Google Patents
Porous electrode substrate, method for producing the same, membrane-electrode assembly, and polymer electrolyte fuel cell Download PDFInfo
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
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- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
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- Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
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Description
本発明は、液体燃料を用いた固体高分子型燃料電池に用いられる多孔質電極基材およびその製造方法、ならびにその多孔質電極基材を用いた膜−電極接合体および固体高分子型燃料電池に関するものである。 The present invention relates to a porous electrode substrate used for a polymer electrolyte fuel cell using a liquid fuel, a method for producing the same, and a membrane-electrode assembly and a polymer electrolyte fuel cell using the porous electrode substrate. It is about.
固体高分子型燃料電池はプロトン伝導性の高分子電解質膜を用いることを特徴としており、水素等の燃料ガスと酸素等の酸化ガスを電気化学的に反応させることにより起電力を得る装置である。固体高分子型燃料電池は、自家発電装置や、自動車等の移動体用の発電装置として利用可能である。 A polymer electrolyte fuel cell is characterized by using a proton-conducting polymer electrolyte membrane, and is an apparatus for obtaining an electromotive force by electrochemically reacting a fuel gas such as hydrogen and an oxidizing gas such as oxygen. . The polymer electrolyte fuel cell can be used as a self-power generation device or a power generation device for a moving body such as an automobile.
このような固体高分子型燃料電池は、水素イオン（プロトン）を選択的に伝導する高分子電解質膜を有する。また、貴金属系触媒を担持したカーボン粉末を主成分とする触媒層とガス拡散電極基材とを有するガス拡散電極が、触媒層側を内側にして、高分子電解質膜の両面に接合された構造となっている。 Such a polymer electrolyte fuel cell has a polymer electrolyte membrane that selectively conducts hydrogen ions (protons). Also, a structure in which a gas diffusion electrode having a catalyst layer mainly composed of carbon powder supporting a noble metal catalyst and a gas diffusion electrode base material is bonded to both surfaces of the polymer electrolyte membrane with the catalyst layer side inside It has become.
このような高分子電解質膜と２枚のガス拡散電極からなる接合体は膜−電極接合体（ＭＥＡ： Ｍｅｍｂｒａｎｅ Ｅｌｅｃｔｒｏｄｅ Ａｓｓｅｍｂｌｙ）と呼ばれている。またＭＥＡの両外側には燃料ガスまたは酸化ガスを供給し、かつ生成ガスおよび過剰ガスを排出することを目的としたガス流路を形成したセパレーターが設置されている。 Such a joined body composed of a polymer electrolyte membrane and two gas diffusion electrodes is called a membrane-electrode assembly (MEA: Membrane Electrode Assembly). In addition, separators are provided on both outer sides of the MEA so as to supply a fuel gas or an oxidizing gas and to form a gas flow path for the purpose of discharging generated gas and excess gas.
多孔質電極基材は電気的な接触抵抗を低減し、かつ、セパレーターより供給される燃料ガスまたは酸化ガスがセル外へ漏出することを抑制することを目的として、セパレーターによって数ＭＰａの荷重で締結されるため、機械的強度が必要となる。 The porous electrode substrate is fastened by a separator with a load of several MPa for the purpose of reducing electrical contact resistance and suppressing leakage of fuel gas or oxidizing gas supplied from the separator to the outside of the cell. Therefore, mechanical strength is required.
さらに、多孔質電極基材は主に次の３つの機能を持つ必要がある。第１に多孔質電極基材の外側に配置されたセパレーターに形成されたガス流路より触媒層中の貴金属系触媒に均一に燃料ガスまたは酸化ガスを供給する機能である。第２に触媒層で反応により生成した水を排出する機能である。第３に触媒層での反応に必要な電子または生成される電子をセパレーターへ導電する機能である。これらの機能を付与するため、多孔質電極基材は一般的に炭素質材料を用いることが有効とされている。 Furthermore, the porous electrode substrate mainly needs to have the following three functions. The first function is to supply the fuel gas or the oxidizing gas uniformly to the noble metal catalyst in the catalyst layer from the gas flow path formed in the separator disposed outside the porous electrode substrate. The second function is to discharge water generated by the reaction in the catalyst layer. The third function is to conduct electrons necessary for the reaction in the catalyst layer or generated electrons to the separator. In order to impart these functions, it is generally effective to use a carbonaceous material for the porous electrode substrate.
従来は、機械強度を強くするために、炭素短繊維を抄造後有機高分子で結着させ、高温で焼成し有機高分子を炭素化させたペーパー状の炭素／炭素複合体か成る多孔質電極基材を得ていたが、製造プロセスが複雑であり、高コストであるという問題があった。また、低コスト化を目的として、酸化短繊維を抄造後有機高分子で結着させずに、高温で焼成し酸化短繊維を炭素化させた多孔質電極基材が提案されているが、焼成時の酸化短繊維の収縮により寸法安定性、表面精度に問題があった。さらに低コスト化を目的として、炭素化可能なアクリルパルプを炭素短繊維と混合後、硬化、炭素化する多孔質電極基材が提案されているが、硬化時間が十分でなく、炭素化した後のアクリルパルプ炭素化率が低くなってしまうという問題があった。 Conventionally, in order to increase the mechanical strength, a porous electrode composed of a paper-like carbon / carbon composite in which short carbon fibers are made with paper, bound with an organic polymer, and baked at a high temperature to carbonize the organic polymer. Although the base material was obtained, there existed a problem that a manufacturing process was complicated and it was expensive. For the purpose of cost reduction, porous electrode base materials have been proposed in which oxidized short fibers are baked at high temperature and carbonized oxidized short fibers without binding with organic polymer after paper making. There was a problem in dimensional stability and surface accuracy due to shrinkage of oxidized short fibers. For the purpose of further cost reduction, a porous electrode base material has been proposed in which carbonized acrylic pulp is mixed with short carbon fibers and then cured and carbonized. There was a problem that the carbonization rate of acrylic pulp was low.
特許文献１には、厚みが０．０５〜０．５ｍｍで嵩密度が０．３〜０．８ｇ／ｃｍであり、かつ、歪み速度１０ｍｍ／ｍｉｎ、支点間距離２ｃｍおよび試験片幅１ｃｍの条件での３点曲げ試験において曲げ強度が１０ＭＰａ以上でかつ曲げの際のたわみが１．５ｍｍ以上であることを特徴とする燃料電池用多孔質炭素電極基材が記載されている。しかし、この多孔質電極基材は、機械的強度、表面平滑性が高く、十分なガス透気度、導電性は有しているもの、高コストであるという問題があった。 In Patent Document 1, the thickness is 0.05 to 0.5 mm, the bulk density is 0.3 to 0.8 g / cm, the strain rate is 10 mm / min, the distance between fulcrums is 2 cm, and the specimen width is 1 cm. Describes a porous carbon electrode substrate for a fuel cell, characterized in that the bending strength is 10 MPa or more and the bending deflection is 1.5 mm or more. However, this porous electrode base material has a problem of high mechanical strength and surface smoothness, sufficient gas permeability and conductivity, and high cost.
特許文献２には、厚さ０．１５〜１．０ｍｍ、嵩密度０．１５〜０．４５ｇ／ｃｍ、炭素繊維含有率９５質量％以上、圧縮変形率１０〜３５％、電気抵抗値６ｍΩ以下、風合度５〜７０ｇの炭素繊維シートが記載されている。この多孔質電極基材は、低コスト化は可能であるものの、焼成時の収縮が大きく厚みムラが大きいことや表面精度が低いといった問題があった。 In Patent Document 2, the thickness is 0.15 to 1.0 mm, the bulk density is 0.15 to 0.45 g / cm, the carbon fiber content is 95% by mass or more, the compression deformation rate is 10 to 35%, and the electric resistance is 6 mΩ or less. A carbon fiber sheet having a texture of 5 to 70 g is described. Although this porous electrode substrate can be reduced in cost, there are problems such as large shrinkage during firing and large thickness unevenness and low surface accuracy.
特許文献３には、複数の炭素繊維を含んで成るマット；及び該炭素繊維マットに組み込まれた複数のアクリルパルプ繊維を含んでなり、該アクリルパルプ繊維は、炭素繊維マットに組み込まれた後に硬化され炭化される燃料電池用ガス拡散層が記載されている。この多孔質電極基材は低コスト化は可能であるが、硬化時間が十分でなく、炭素化した後のアクリルパルプ炭素化率が低くなり、炭素短繊維をより強固に接着させるためには多くのアクリルパルプ繊維を用いなければならないという問題があった。
本発明は、上記のような問題点を克服し、安価でありながら、機械的強度、厚み精度、表面平滑性が高く、かつ十分なガス透気度、導電性を持った多孔質電極基材およびその製造方法を提供することを目的とする。 The present invention overcomes the problems as described above, and is a porous electrode substrate that is inexpensive but has high mechanical strength, thickness accuracy, and surface smoothness, and has sufficient gas permeability and conductivity. And it aims at providing the manufacturing method.
本発明は以下のとおりである。
（１）炭素短繊維と、炭素化可能なフィブリル状繊維とを二次元平面内において分散させて、前駆体シートを作製する工程；前記前駆体シートを２００℃以上３００℃未満の温度で１０分〜２時間酸化処理する工程；および酸化処理した前記前駆体シートを１０００℃以上の温度で炭素化処理する工程；を有する多孔質電極基材の製造方法。但し、前記前駆体シートに熱硬化性樹脂の含浸処理を行う場合を除く。
（２）炭素短繊維と、炭素化可能なフィブリル状繊維とを二次元平面内において分散させて、前駆体シートを作製する工程；前記前駆体シートを２００℃未満の温度で加熱加圧成型する工程；加熱加圧成型した前記前駆体シートを２００℃以上３００℃未満の温度で１０分〜２時間酸化処理する工程；および酸化処理した前記前駆体シートを１０００℃以上の温度で炭素化処理する工程；を有する多孔質電極基材の製造方法。但し、前記前駆体シートに熱硬化性樹脂の含浸処理を行う場合を除く。
（３）前記（１）または（２）に記載の多孔質電極基材の製造方法で製造される多孔質電極基材。
（４）２次元平面内において分散した炭素短繊維同士が、フィブリル状炭素のみによって接合されている前記（３）に記載の多孔質電極基材。
（５）前記（３）または（４）に記載の多孔質電極基材を用いた膜−電極接合体。
（６）前記（５）に記載の膜−電極接合体を用いた固体高分子型燃料電池。
The present invention is as follows.
(1) A step of producing a precursor sheet by dispersing short carbon fibers and carbonizable fibrillar fibers in a two-dimensional plane; the precursor sheet is heated at a temperature of 200 ° C. or higher and lower than 300 ° C. for 10 minutes. A method for producing a porous electrode substrate, comprising: a step of oxidizing for 2 hours; and a step of carbonizing the oxidized precursor sheet at a temperature of 1000 ° C. or higher. However, the case where the precursor sheet is impregnated with a thermosetting resin is excluded.
(2) A step of producing a precursor sheet by dispersing short carbon fibers and carbonizable fibrillar fibers in a two-dimensional plane; the precursor sheet is heated and pressed at a temperature of less than 200 ° C. A step; a step of oxidizing the precursor sheet subjected to heat and pressure molding at a temperature of 200 ° C. or higher and lower than 300 ° C. for 10 minutes to 2 hours; and a carbonization treatment of the oxidized precursor sheet at a temperature of 1000 ° C. or higher. A method for producing a porous electrode substrate. However, the case where the precursor sheet is impregnated with a thermosetting resin is excluded.
(3) (1) or porous electrode substrate produced by the production method of the porous electrode substrate according to (2).
(4) short carbon fibers dispersed in a 2-dimensional plane, the porous electrode substrate according to the which are joined only by the fibrillated carbon (3).
(5) A membrane-electrode assembly using the porous electrode substrate according to (3) or (4) .
(6) A polymer electrolyte fuel cell using the membrane-electrode assembly according to (5) .
本発明によれば、安価でありながら、機械的強度、厚み精度、表面平滑性が高く、かつ十分なガス透気度、導電性を持った多孔質電極基材を得ることができる。また、本発明の多孔質電極基材の製造方法によれば、前記多孔質電極基材を低コストで生産することができる。 According to the present invention, it is possible to obtain a porous electrode substrate that is inexpensive but has high mechanical strength, thickness accuracy, and surface smoothness, and has sufficient gas permeability and conductivity. Moreover, according to the manufacturing method of the porous electrode base material of this invention, the said porous electrode base material can be produced at low cost.
＜炭素短繊維＞
本発明で用いる炭素短繊維の原料である炭素繊維は、ポリアクリロニトリル系炭素繊維、ピッチ系炭素繊維、レーヨン系炭素繊維などいずれであっても良いが、ポリアクリロニトリル系炭素繊維が好ましい。特に、多孔質炭素電極基材の機械的強度を比較的高くすることができることから、用いる炭素繊維がポリアクリロニトリル（ＰＡＮ）系炭素繊維のみからなることが好ましい。
<Short carbon fiber>
The carbon fiber that is a raw material of the short carbon fiber used in the present invention may be any of polyacrylonitrile-based carbon fiber, pitch-based carbon fiber, rayon-based carbon fiber, etc., but polyacrylonitrile-based carbon fiber is preferable. In particular, since the mechanical strength of the porous carbon electrode base material can be made relatively high, it is preferable that the carbon fiber to be used consists only of polyacrylonitrile (PAN) based carbon fiber.
炭素短繊維の直径は、炭素短繊維の生産コスト、分散性の面から、３〜９μｍであることが好ましい。最終的に得られる多孔質電極基材の平滑性の面から、４μｍ以上、８μｍ以下であることがさらに好ましい。 The diameter of the short carbon fiber is preferably 3 to 9 μm from the viewpoint of production cost and dispersibility of the short carbon fiber. From the aspect of smoothness of the finally obtained porous electrode substrate, it is more preferably 4 μm or more and 8 μm or less.
炭素短繊維の繊維長は、分散性の点から、２〜１２ｍｍが好ましい。 The fiber length of the short carbon fiber is preferably 2 to 12 mm from the viewpoint of dispersibility.
＜フィブリル状炭素＞
本発明では、多孔質電極基材中の炭素短繊維同士は、直接接合しておらず、フィブリル状炭素によって接合している。フィブリル状炭素とは、フィブリル状繊維を炭素化してできた、炭素短繊維同士を接合する物質である。このフィブリル状繊維としては、ポリアクリロニトリル（ＰＡＮ）系フィブリル状繊維、セルロース系フィブリル状繊維などいずれであっても良いが、低温から高温にかけて炭素短繊維同士を接合させることができ、炭素化した際の残存質量が大きいポリアクリロニトリル（ＰＡＮ）系フィブリル状繊維がより好ましい。ポリアクリロニトリル（ＰＡＮ）系フィブリル状繊維、セルロース系フィブリル状繊維などのフィブリル状繊維は、その種類や炭素短繊維との混合比、２００℃以上３００℃未満の温度での酸化処理の有無によって、最終的に得られる多孔質電極基材中にフィブリル状炭素として残る割合が異なる。
<Fibrous carbon>
In the present invention, the short carbon fibers in the porous electrode base material are not directly joined but joined by fibrillar carbon. Fibril-like carbon is a substance that joins short carbon fibers that are made by carbonizing fibril-like fibers. This fibrillar fiber may be any of polyacrylonitrile (PAN) fibrillar fiber, cellulose fibrillar fiber, etc., but carbon short fibers can be joined from low to high temperature, and when carbonized A polyacrylonitrile (PAN) fibrillar fiber having a large residual mass is more preferred. Fibril fibers such as polyacrylonitrile (PAN) fibril-like fibers and cellulosic fibril-like fibers, the final ratio depends on the type and mixing ratio with short carbon fibers and whether or not oxidation treatment is performed at a temperature of 200 ° C. or more and less than 300 ° C. The remaining ratio of fibrillar carbon in the porous electrode base material obtained in a different manner is different.
多孔質電極基材を１００質量％としたときに、その中に含まれるフィブリル状炭素の量は、１０〜９０質量％であることが好ましい。多孔質電極基材の機械的強度を十分なものに保つため、３０質量％以上、６０質量％以下がさらに好ましい。 When the porous electrode substrate is 100% by mass, the amount of fibrillar carbon contained therein is preferably 10 to 90% by mass. In order to keep the mechanical strength of the porous electrode substrate at a sufficient level, it is more preferably 30% by mass or more and 60% by mass or less.
＜分散＞
本発明において、「二次元平面内において分散」とは、炭素短繊維がおおむね一つの面を形成するように横たわっているという意味である。これにより炭素短繊維による短絡や炭素短繊維の折損を防止することができる。二次元平面内での炭素短繊維の配向方向は実質的にランダムであっても、特定方向への配向性が高くなっていても良い。
<Dispersion>
In the present invention, “dispersion in a two-dimensional plane” means that the carbon short fibers lie so as to form a single plane. Thereby, the short circuit by carbon short fiber and the breakage of carbon short fiber can be prevented. The orientation direction of the short carbon fibers in the two-dimensional plane may be substantially random, or the orientation in a specific direction may be high.
＜製造方法＞
本発明の多孔質電極基材の製造方法は、以下に示す方法である。上記の多孔質電極基材は、例えば以下の方法により好適に製造することができる。
（１）炭素短繊維と、炭素化可能なフィブリル状繊維とを二次元平面内において分散させて、前駆体シートを作製し、その前駆体シートを２００℃以上３００℃未満の温度で１０分〜２時間酸化処理した後、酸化処理した前駆体シートを１０００℃以上の温度で炭素化処理する。
（２）炭素短繊維と、炭素化可能なフィブリル状繊維とを二次元平面内において分散させて、前駆体シートを作製し、その前駆体シートを２００℃未満の温度で加熱加圧成型し、加熱加圧成型した前駆体シートを２００℃以上３００℃未満の温度で１０分〜２時間酸化処理した後、酸化処理した前駆体シートを１０００℃以上の温度で炭素化処理する。
<Manufacturing method>
The manufacturing method of the porous electrode base material of this invention is the method shown below. Said porous electrode base material can be suitably manufactured, for example with the following method.
(1) Carbon short fibers and carbonizable fibrillar fibers are dispersed in a two-dimensional plane to prepare a precursor sheet, and the precursor sheet is heated at a temperature of 200 ° C. or higher and lower than 300 ° C. for 10 minutes to After oxidizing for 2 hours, the oxidized precursor sheet is carbonized at a temperature of 1000 ° C. or higher.
(2) A short carbon fiber and a carbonizable fibrillar fiber are dispersed in a two-dimensional plane to produce a precursor sheet, and the precursor sheet is heated and pressed at a temperature of less than 200 ° C., The precursor sheet subjected to heat and pressure molding is oxidized at a temperature of 200 ° C. or higher and lower than 300 ° C. for 10 minutes to 2 hours, and then the oxidized precursor sheet is carbonized at a temperature of 1000 ° C. or higher.
＜フィブリル状繊維＞
本発明の製造方法では、炭素化可能なフィブリル状繊維を用いることが必要である。フィブリル状繊維とは、繊維状の幹より直径が数μｍ以下（例えば０．１〜３μｍ）のフィブリルが多数分岐した構造を有する。このフィブリル状繊維を用いることにより、前駆体シート中で炭素短繊維とフィブリル状繊維が良く絡み合い、機械的強度の優れた前駆体シートを得ることが容易となる。フィブリル状繊維の濾水度は特に限定されないが、一般的に濾水度が高いフィブリル状繊維を用いると機械的強度が向上するが、多孔質電極基材のガス透気度が低下する。
<Fibrous fiber>
In the production method of the present invention, it is necessary to use carbonizable fibrillar fibers. A fibrillar fiber has a structure in which a large number of fibrils having a diameter of several μm or less (for example, 0.1 to 3 μm) are branched from a fibrous trunk. By using this fibrillar fiber, the short carbon fiber and the fibrillar fiber are entangled well in the precursor sheet, and it becomes easy to obtain a precursor sheet having excellent mechanical strength. The freeness of the fibrillar fibers is not particularly limited, but generally, when fibrillar fibers having a high freeness are used, the mechanical strength is improved, but the gas permeability of the porous electrode substrate is lowered.
＜有機高分子化合物＞
有機高分子化合物は、炭素短繊維と、炭素化可能なフィブリル状繊維とを含む前駆体シート中で各成分をつなぎとめるバインダー（糊剤）として使用される。有機高分子化合物としては、ポリビニルアルコール（ＰＶＡ）、ポリ酢酸ビニルなどを用いることができる。特にポリビニルアルコールは前駆体シートの作製工程での結着力に優れるため、炭素短繊維の脱落が少なくバインダーとして好ましい。本発明では、有機高分子化合物を繊維状として用いることも可能である。
<Organic polymer compound>
The organic polymer compound is used as a binder (glue agent) that holds each component in a precursor sheet containing short carbon fibers and carbonizable fibrillar fibers. As the organic polymer compound, polyvinyl alcohol (PVA), polyvinyl acetate, or the like can be used. In particular, polyvinyl alcohol is preferable as a binder because it has excellent binding power in the precursor sheet production process, and the short carbon fibers are not dropped off. In the present invention, it is also possible to use an organic polymer compound as a fiber.
炭素短繊維と、炭素化可能なフィブリル状繊維とを含む前駆体シートでは、フィブリル状繊維が、炭素短繊維またはフィブリル状繊維同士と絡み合うことによって、前駆体シート中の各成分をつなぎとめるバインダーとしても機能するため、一般的な炭素繊維前駆体シートで用いられるバインダーとしての有機高分子化合物を使用の有無は特に限定されないが、低コスト化の観点からは、有機高分子化合物を使用しないことが好ましい。 In the precursor sheet containing carbon short fibers and carbonizable fibrillar fibers, the fibrillar fibers can be used as a binder to connect the components in the precursor sheet by tangling the carbon short fibers or the fibrillar fibers with each other. In order to function, whether or not to use an organic polymer compound as a binder used in a general carbon fiber precursor sheet is not particularly limited, but from the viewpoint of cost reduction, it is preferable not to use an organic polymer compound .
＜前駆体シートを作製する工程＞
炭素短繊維と、炭素化可能なフィブリル状繊維とを二次元平面内において分散させて、前駆体シートを作製する方法としては、液体の媒体中に炭素短繊維およびフィブリル状繊維を分散させて抄造する湿式法や、空気中に炭素短繊維およびフィブリル状繊維を分散させて降り積もらせる乾式法などの抄紙方法が適用できるが、中でも湿式法が好ましい。炭素短繊維が単繊維に分散するのを助け、分散した単繊維が再び収束を防止するのを防ぐためにも、適切な量のフィブリル状繊維を、必要に応じてバインダーとして適切な量の有機高分子化合物と共に、湿式抄紙することが好ましい。
<Process for producing precursor sheet>
A method for producing a precursor sheet by dispersing short carbon fibers and carbonizable fibrillar fibers in a two-dimensional plane is to make paper by dispersing short carbon fibers and fibrillar fibers in a liquid medium. A paper making method such as a wet method or a dry method in which short carbon fibers and fibrillar fibers are dispersed in the air to be deposited can be applied. Among these, a wet method is preferable. To help the short carbon fibers disperse into the single fibers and to prevent the dispersed single fibers from rebounding again, an appropriate amount of fibrillar fibers can be used as a binder with an appropriate amount of organic high as needed. It is preferable to perform wet papermaking together with the molecular compound.
炭素短繊維と、フィブリル状繊維と、必要に応じて有機高分子化合物とを混合する方法としては、水中で攪拌分散させる方法と、直接混ぜ込む方法があるが、均一に分散させるためには水中で攪拌分散させる方法が好ましい。炭素短繊維と、フィブリル状繊維と、必要に応じて有機高分子化合物とを同時に抄紙して前駆体シートを作製することにより、前駆体シートの強度が向上し、その製造途中で前駆体シートから炭素短繊維が剥離したり、炭素短繊維の配向が変化したりするのを防止することができる。 As a method of mixing the short carbon fiber, the fibrillar fiber, and the organic polymer compound as necessary, there are a method of stirring and dispersing in water and a method of directly mixing, but in order to uniformly disperse, The method of stirring and dispersing with is preferable. By making a precursor sheet by simultaneously making short carbon fibers, fibrillar fibers, and if necessary, an organic polymer compound, the strength of the precursor sheet is improved. It is possible to prevent the short carbon fibers from peeling off or the orientation of the short carbon fibers from changing.
また、前駆体シートの作製は連続で行う方法やバッチ式で行う方法があるが、本発明では特に限定されない。生産性および機械的強度の観点からは連続で行うことが好ましい。 Moreover, although the preparation of the precursor sheet includes a continuous method and a batch method, it is not particularly limited in the present invention. From the viewpoint of productivity and mechanical strength, it is preferable to carry out continuously.
前駆体シートの目付けは、１０〜２００ｇ／ｍとすることが好ましい。 The basis weight of the precursor sheet is preferably 10 to 200 g / m.
＜酸化処理＞
炭素短繊維と、炭素化可能なフィブリル状繊維とを含む前駆体シートは、２００℃以上３００℃未満の温度で１０分〜２時間酸化処理することが、炭素短繊維をフィブリル状繊維でより融着させ、かつ、フィブリル状繊維の炭素化率を向上させるという点で好ましい。
<Oxidation treatment>
Precursor sheets containing carbon short fibers and carbonizable fibrillar fibers are oxidized at a temperature of 200 ° C. or higher and lower than 300 ° C. for 10 minutes to 2 hours. It is preferable in that it is applied and the carbonization rate of the fibrillar fibers is improved.
酸化処理は、２００℃以上３００℃未満の温度範囲で行うことが好ましく、２４０〜２７０℃で行うことがより好ましい。酸化処理は、大気雰囲気下で行うことが好ましい。 The oxidation treatment is preferably performed in a temperature range of 200 ° C. or higher and lower than 300 ° C., and more preferably performed at 240 to 270 ° C. The oxidation treatment is preferably performed in an air atmosphere.
炭素化可能なフィブリル状繊維の酸化処理を行い、フィブリル状繊維の炭素化率を向上させるため、酸化処理の時間は１０分〜２時間とすることが好ましく、１０分〜９０分とすることがさらに好ましい。 In order to oxidize carbonizable fibrillar fibers and improve the carbonization rate of the fibrillar fibers, the oxidation treatment time is preferably 10 minutes to 2 hours, preferably 10 minutes to 90 minutes. Further preferred.
連続的に作製された前駆体シートを酸化処理する場合は、前駆体シートの全長にわたって連続で酸化処理を行うことが低コスト化という観点で好ましい。多孔質電極基材が長尺であれば、多孔質電極基材の生産性が高くなるだけでなく、その後のＭＥＡ製造も連続で行うことができ、燃料電池のコスト低減に大きく寄与することができる。また本発明の多孔質電極基材は、連続的に巻き取ることも可能で、多孔質電極基材や燃料電池の生産性、コストの観点から好ましい。 When oxidizing the precursor sheet produced continuously, it is preferable from the viewpoint of cost reduction that the oxidation process is continuously performed over the entire length of the precursor sheet. If the porous electrode substrate is long, not only the productivity of the porous electrode substrate is increased, but also the subsequent MEA production can be performed continuously, which can greatly contribute to the cost reduction of the fuel cell. it can. Further, the porous electrode substrate of the present invention can be continuously wound, and is preferable from the viewpoints of productivity and cost of the porous electrode substrate and the fuel cell.
＜炭素化処理＞
炭素短繊維と、炭素化可能なフィブリル状繊維を含む前駆体シートは、そのまま酸化処理した後に炭素化処理することができる。その他、前駆体シートを加熱加圧成型し、その加熱加圧成型後の前駆体シートを酸化処理した後に炭素化処理することが可能である。前駆体シートの炭素化処理は、炭素短繊維をフィブリル状繊維で融着させ、かつフィブリル状繊維を炭素化することより、多孔質電極基材の機械的強度と導電性を発現させることを目的に行う。
<Carbonization treatment>
The precursor sheet containing short carbon fibers and carbonizable fibrillar fibers can be subjected to carbonization treatment after being directly oxidized. In addition, the precursor sheet can be heat-press molded, and the precursor sheet after the heat-press molding can be oxidized and then carbonized. The carbonization treatment of the precursor sheet aims to develop the mechanical strength and conductivity of the porous electrode substrate by fusing short carbon fibers with fibrillar fibers and carbonizing the fibrillar fibers. To do.
炭素化処理は、多孔質電極基材の導電性を高めるために、不活性ガス中で行うことが好ましい。炭素化処理は、１０００℃以上の温度で行う。１０００〜３０００℃の温度範囲で炭素化処理することが好ましく、１０００〜２２００℃の温度範囲がより好ましい。１０００℃未満の温度で炭素化処理して得られた多孔質電極基材は、導電性が十分ではない。炭素化処理の前に３００〜８００℃の程度の不活性雰囲気での焼成による前処理を行っても良い。 The carbonization treatment is preferably performed in an inert gas in order to increase the conductivity of the porous electrode substrate. The carbonization treatment is performed at a temperature of 1000 ° C. or higher. Carbonization treatment is preferably performed in a temperature range of 1000 to 3000 ° C, and a temperature range of 1000 to 2200 ° C is more preferable. A porous electrode substrate obtained by carbonization treatment at a temperature of less than 1000 ° C. does not have sufficient conductivity. Before the carbonization treatment, a pretreatment by firing in an inert atmosphere of about 300 to 800 ° C. may be performed.
炭素化処理の時間は、例えば１０分〜１時間とすることができる。 The time for the carbonization treatment can be, for example, 10 minutes to 1 hour.
連続的に作製された前駆体シートを炭素化処理する場合は、前駆体シートの全長にわたって連続で炭素化処理を行うことが、低コスト化という観点で好ましい。多孔質電極基材が長尺であれば、多孔質電極基材の生産性が高くなるだけでなく、その後のＭＥＡ製造も連続で行うことができ、燃料電池のコスト低減に大きく寄与することができる。また、本発明の多孔質電極基材は、連続的に巻き取ることも可能で、多孔質電極基材や燃料電池の生産性、コストの観点から好ましい。 When carbonizing the continuously produced precursor sheet, it is preferable to perform the carbonizing process continuously over the entire length of the precursor sheet from the viewpoint of cost reduction. If the porous electrode substrate is long, not only the productivity of the porous electrode substrate is increased, but also the subsequent MEA production can be performed continuously, which can greatly contribute to the cost reduction of the fuel cell. it can. Moreover, the porous electrode base material of the present invention can be continuously wound, and is preferable from the viewpoint of productivity and cost of the porous electrode base material and the fuel cell.
＜加熱加圧成型＞
炭素短繊維と、炭素化可能なフィブリル状繊維を含む前駆体シートは、酸化処理の前に、２００℃未満の温度で加熱加圧成型することが、炭素短繊維をフィブリル状繊維で融着させ、かつ、多孔質電極基材の厚みムラを低減できるという点で好ましい。加熱加圧成型は、前駆体シートを均等に加熱加圧成型できる技術であれば、いかなる技術も適用できる。その例としては、上下両面から平滑な剛板にて熱プレスする方法や連続ベルトプレス装置を用いて行う方法がある。
<Heat and pressure molding>
Precursor sheets containing carbon short fibers and carbonizable fibrillar fibers can be heat-pressed at a temperature of less than 200 ° C. before the oxidation treatment to fuse the carbon short fibers with the fibrillar fibers. And it is preferable at the point which can reduce the thickness nonuniformity of a porous electrode base material. Any technique can be applied to the heat and pressure molding as long as the technique can uniformly heat and mold the precursor sheet. As an example, there are a method of performing hot pressing with smooth rigid plates from both upper and lower surfaces, and a method of performing using a continuous belt press apparatus.
連続的に作製された前駆体シートを加熱加圧成型する場合は、連続ベルトプレス装置を用いて行う方法が、長尺の多孔質電極基材ができるという点で好ましい。多孔質電極基材が長尺であれば、多孔質電極基材の生産性が高くなるだけでなく、その後のＭＥＡ製造も連続で行うことができ、燃料電池のコスト低減化に大きく寄与することができる。また、本発明の多孔質電極基材は、連続的に巻き取ることも可能で、多孔質電極基材や燃料電池の生産性、コストの観点から好ましい。連続ベルト装置におけるプレス方法としては、ロールプレスによりベルトに線圧で圧力を加える方法と液圧ヘッドプレスにより面圧でプレスする方法があるが、後者の方がより平滑な多孔質電極基材が得られるという点で好ましい。 In the case of heating and press-molding a continuously produced precursor sheet, a method of using a continuous belt press apparatus is preferable in that a long porous electrode substrate can be formed. If the porous electrode substrate is long, not only the productivity of the porous electrode substrate is increased, but also the subsequent MEA production can be performed continuously, which greatly contributes to the cost reduction of the fuel cell. Can do. Moreover, the porous electrode base material of the present invention can be continuously wound, and is preferable from the viewpoint of productivity and cost of the porous electrode base material and the fuel cell. As a pressing method in the continuous belt device, there are a method of applying pressure to the belt by a roll press by a linear pressure and a method of pressing by a surface pressure by a hydraulic head press, but the latter is a smoother porous electrode substrate. It is preferable in that it is obtained.
加熱温度は、効果的に表面を平滑にするために、２００℃未満が好ましく、１２０〜１９０℃がより好ましい。 In order to effectively smooth the surface, the heating temperature is preferably less than 200 ° C, more preferably 120 to 190 ° C.
成型圧力は特に限定されないが、フィブリル状繊維の比率が多い場合は、成型圧力が低くても前駆体シートの表面を平滑にすることが容易である。このとき必要以上にプレス圧を高くすることは、成型時に炭素短繊維を破壊する、多孔質電極基材としたときその組織が緻密になりすぎるなどの問題が生じる場合がある。例えば、２０ｋＰａ〜１０ＭＰａの圧力で加圧することができる。 The molding pressure is not particularly limited, but when the ratio of fibrillar fibers is large, it is easy to smooth the surface of the precursor sheet even if the molding pressure is low. If the press pressure is increased more than necessary at this time, problems such as destruction of short carbon fibers during molding and excessively dense structure when used as a porous electrode substrate may occur. For example, pressurization can be performed at a pressure of 20 kPa to 10 MPa.
加熱加圧成型の時間は、例えば３０秒〜１０分とすることができる。 The time for heat and pressure molding can be, for example, 30 seconds to 10 minutes.
剛板に挟んで、又連続ベルト装置で前駆体シートの加熱加圧成型を行う時は、剛板やベルトにフィブリル状繊維などが付着しないようにあらかじめ剥離剤を塗っておくか、前駆体シートと剛板やベルトとの間に離型紙を挟んで行うことが好ましい。 When the precursor sheet is sandwiched between rigid plates or heated and pressed with a continuous belt device, a release agent is applied beforehand to prevent the fibrillar fibers from adhering to the rigid plate or belt, or the precursor sheet. It is preferable that the release paper is sandwiched between the belt and the rigid plate or belt.
＜多孔質電極基材＞
本発明の多孔質電極基材の厚みは、５０〜３００μｍであることが好ましい。
<Porous electrode substrate>
The thickness of the porous electrode substrate of the present invention is preferably 50 to 300 μm.
＜膜−電極接合体（ＭＥＡ）、固体高分子型燃料電池＞
以上のような本発明の多孔質電極基材は、膜−電極接合体に好適に用いることができる。そして、本発明の多孔質電極基材を用いた膜−電極接合体は、固体高分子型燃料電池に好適に用いることができる。
<Membrane-electrode assembly (MEA), polymer electrolyte fuel cell>
The porous electrode substrate of the present invention as described above can be suitably used for a membrane-electrode assembly. The membrane-electrode assembly using the porous electrode substrate of the present invention can be suitably used for a polymer electrolyte fuel cell.
以下、本発明を実施例により、さらに具体的に説明する。実施例中の各物性値等は以下の方法で測定した。 Hereinafter, the present invention will be described more specifically with reference to examples. Each physical property value in the examples was measured by the following method.
（１）ガス透気度
ＪＩＳ規格Ｐ−８１１７に準拠し、ガーレーデンソメーターを使用して２００ｍＬの空気が透過するのにかかった時間を測定し、ガス透気度を算出した。
(1) Gas air permeability Based on JIS standard P-8117, the time required for 200 mL of air to permeate was measured using a Gurley densometer, and the gas air permeability was calculated.
（２）厚み
多孔質電極基材の厚みは、厚み測定装置ダイヤルシックネスゲージ７３２１（商品名、ミツトヨ製）を使用して測定した。測定子の大きさは直径１０ｍｍで、測定圧力は１．５ｋＰａとした。
(2) Thickness The thickness of the porous electrode substrate was measured using a thickness measuring device dial thickness gauge 7321 (trade name, manufactured by Mitutoyo Corporation). The size of the probe was 10 mm in diameter, and the measurement pressure was 1.5 kPa.
（３）貫通方向抵抗
多孔質電極基材の厚さ方向の電気抵抗（貫通方向抵抗）は、試料を金メッキした銅板に挟み、金メッキした銅板の上下から１ＭＰａで加圧し、１０ｍＡ／ｃｍ2の電流密度で電流を流したときの抵抗値を測定し、次式より求めた。
(3) Through-direction resistance The thickness-direction electrical resistance (through-direction resistance) of the porous electrode substrate is 10 mA / cm 2 when a sample is sandwiched between gold-plated copper plates and pressed from above and below the gold-plated copper plate at 1 MPa. The resistance value when a current was passed at a density was measured and obtained from the following equation.
貫通抵抗（ｍΩ・ｃｍ2）＝測定抵抗値（Ω）×試料面積（ｃｍ2）
（４）フィブリル状炭素の質量比
フィブリル状炭素の質量比は、得られた多孔質電極基材の目付と、使用した炭素短繊維の目付とから、次式より算出した。
Penetration resistance (mΩ · cm 2 ) = Measurement resistance value (Ω) × Sample area (cm 2 )
(4) Mass ratio of fibrillar carbon The mass ratio of fibrillar carbon was calculated from the following formula using the basis weight of the obtained porous electrode substrate and the basis weight of the carbon short fibers used.
フィブリル状炭素の質量比（質量％）＝［多孔質電極基材目付（ｇ／ｍ）−炭素短繊維目付（ｇ／ｍ）］÷多孔質電極基材目付（ｇ／ｍ）×１００
（実施例１）
炭素短繊維として、平均繊維径が７μｍ、平均繊維長が３ｍｍのポリアクリロニトリル（ＰＡＮ）系炭素繊維を用意した。また、炭素化可能なフィブリル状繊維として、噴射凝固によって作製したポリアクリロニトリル系パルプを用意した。
Fibrous carbon mass ratio (% by mass) = [Porous electrode substrate basis weight (g / m) −carbon short fiber basis weight (g / m)] ÷ Porous electrode substrate basis weight (g / m) × 100
Example 1
As short carbon fibers, polyacrylonitrile (PAN) carbon fibers having an average fiber diameter of 7 μm and an average fiber length of 3 mm were prepared. Moreover, the polyacrylonitrile-type pulp produced by the injection coagulation was prepared as a carbonizable fibrillar fiber.
炭素短繊維１００質量部を水中に均一に分散して単繊維に解繊し、十分に分散したところに、ポリアクリロニトリル系パルプ７０質量部を均一に分散し、標準角型シートマシン（熊谷理機工業（株）製、商品名：Ｎｏ．２５５５ 標準角型シートマシン）を用いてＪＩＳ Ｐ−８２０９法に準拠して手動で抄紙を行い、乾燥させて、目付けが２６ｇ／ｍの前駆体シートを得た。炭素短繊維およびポリアクリロニトリル系パルプの分散状態は良好であった。 100 parts by mass of short carbon fibers are uniformly dispersed in water, fibrillated into single fibers, and 70 parts by mass of polyacrylonitrile-based pulp are uniformly dispersed in a sufficiently dispersed state. A paper sheet is manually made according to JIS P-8209 method using a trade name manufactured by Kogyo Co., Ltd., trade name: No. 2555 standard square sheet machine, and dried to obtain a precursor sheet having a basis weight of 26 g / m. Obtained. The dispersion state of the short carbon fiber and the polyacrylonitrile pulp was good.
次に、この前駆体シートを２枚重ね合わせ、その両面をシリコーン系離型剤をコートした紙で挟んだ後、バッチプレス装置にて１８０℃、３ＭＰａの条件下で３分間加熱加圧成型した。さらに、この加熱加圧成型した前駆体シートをバッチ熱風炉で、空気中、２５０℃の条件下で１時間酸化処理した。その後、酸化処理した抄紙体をバッチ炭素化炉にて、窒素ガス雰囲気中、２０００℃の条件下で１時間炭素化処理することで、多孔質電極基材を得た。 Next, two sheets of this precursor sheet were overlapped, and both surfaces thereof were sandwiched between papers coated with a silicone-based release agent, and then heated and pressed for 3 minutes under conditions of 180 ° C. and 3 MPa in a batch press apparatus. . Further, the precursor sheet formed by heating and pressing was subjected to an oxidation treatment in a batch hot air oven in air at 250 ° C. for 1 hour. Thereafter, the oxidized papermaking body was carbonized in a batch carbonization furnace in a nitrogen gas atmosphere at 2000 ° C. for 1 hour to obtain a porous electrode substrate.
得られた多孔質電極基材は、炭素化処理時における面内の収縮がほとんどなく、ガス透気度、厚み、貫通方向抵抗がそれぞれ良好な結果であった。また、フィブリル状炭素の質量比は３２質量％であった。結果を表１に示した。なお、多孔質電極基材の表面ＳＥＭ写真を図１に示す。２次元平面内に分散した炭素短繊維同士が、フィブリル状炭素によって接合されていることが確認できた。 The obtained porous electrode base material had almost no in-plane shrinkage during the carbonization treatment, and the gas permeability, thickness, and penetration direction resistance were favorable. The mass ratio of fibrillar carbon was 32% by mass. The results are shown in Table 1. In addition, the surface SEM photograph of a porous electrode base material is shown in FIG. It was confirmed that the short carbon fibers dispersed in the two-dimensional plane were joined by the fibrillar carbon.
（実施例２）
（１）ＭＥＡの作製
実施例１で得られた多孔質炭素電極基材をカソード用、アノード用に２組用意した。両面に触媒担持カーボン（触媒：Ｐｔ、触媒担持量：５０質量％）からなる触媒層（触媒層面積：２５ｃｍ2、Ｐｔ付着量：０．３ｍｇ／ｃｍ2）を形成したパーフルオロスルホン酸系の高分子電解質膜（膜厚：３０μｍ）を、カソード用、アノード用の多孔質炭素電極基材で挟持し、これらを接合してＭＥＡを得た。
(Example 2)
(1) Production of MEA Two sets of the porous carbon electrode base material obtained in Example 1 were prepared for the cathode and the anode. Perfluorosulfonic acid based catalyst in which a catalyst layer (catalyst layer area: 25 cm 2 , Pt adhesion amount: 0.3 mg / cm 2 ) made of catalyst-supported carbon (catalyst: Pt, catalyst support amount: 50 mass%) is formed on both surfaces A polymer electrolyte membrane (film thickness: 30 μm) was sandwiched between porous carbon electrode substrates for cathode and anode, and these were joined to obtain MEA.
（２）ＭＥＡの燃料電池特性評価
前記（１）で作製したＭＥＡを、蛇腹状のガス流路を有する２枚のカーボンセパレーターによって挟み、固体高分子型燃料電池（単セル）を形成した。
(2) Evaluation of MEA Fuel Cell Characteristics The MEA produced in (1) was sandwiched between two carbon separators having bellows-like gas flow paths to form a polymer electrolyte fuel cell (single cell).
この単セルの電流密度−電圧特性を測定することによって、燃料電池特性評価を行った。燃料ガスとしては水素ガスを用い、酸化ガスとしては空気を用いた。セル温度を８０℃、燃料ガス利用率を６０％、酸化ガス利用率を４０％とした。また、ガス加湿は８０℃のバブラーにそれぞれ燃料ガスと酸化ガスを通すことによって行った。その結果、電流密度が０．８Ａ／ｃｍ2のときの燃料電池セルのセル電圧が０．６０５Ｖ、セルの内部抵抗が３．７ｍΩであり、良好な特性を示した。 The fuel cell characteristics were evaluated by measuring the current density-voltage characteristics of this single cell. Hydrogen gas was used as the fuel gas, and air was used as the oxidizing gas. The cell temperature was 80 ° C., the fuel gas utilization rate was 60%, and the oxidizing gas utilization rate was 40%. Gas humidification was performed by passing fuel gas and oxidizing gas through a bubbler at 80 ° C., respectively. As a result, when the current density was 0.8 A / cm 2 , the cell voltage of the fuel cell was 0.605 V, and the internal resistance of the cell was 3.7 mΩ, which showed good characteristics.
（比較例１）
ポリアクリロニトリル系パルプの代わりに、有機高分子化合物としてポリビニルアルコール（ＰＶＡ）（商品名：ＶＢＰ１０５−１、クラレ株式会社製）３５質量部を用い、得られる前駆体シートの目付けが２７ｇ／ｍとなるようにした以外は、実施例１と同様にして多孔質電極基材を得た。得られた多孔質電極基材は、ＰＶＡがほとんど炭素化しないため炭素短繊維同士が接合されておらず、シート状の多孔質電極基材として構造を維持することができなかった。
(Comparative Example 1)
Instead of polyacrylonitrile-based pulp, 35 parts by mass of polyvinyl alcohol (PVA) (trade name: VBP105-1, manufactured by Kuraray Co., Ltd.) is used as the organic polymer compound, and the basis weight of the resulting precursor sheet is 27 g / m. A porous electrode substrate was obtained in the same manner as in Example 1 except for the above. The obtained porous electrode base material was not carbonized because PVA hardly carbonized, and the structure could not be maintained as a sheet-like porous electrode base material.
（比較例２）
炭素短繊維を用いず、ポリアクリロニトリル系パルプのみを用いて、得られる前駆体シートの目付けが４０ｇ／ｍとなるようにした以外は、実施例１と同様にして多孔質電極基材を得た。得られた多孔質電極基材は、ポリアクリロニトリル系パルプが炭素化する際の収縮により、シート状の多孔質電極基材として構造を維持することができなかった。
(Comparative Example 2)
A porous electrode substrate was obtained in the same manner as in Example 1 except that only the polyacrylonitrile pulp was used and the basis weight of the obtained precursor sheet was 40 g / m without using carbon short fibers. . The resulting porous electrode base material could not maintain its structure as a sheet-like porous electrode base material due to shrinkage when the polyacrylonitrile pulp was carbonized.
（比較例３）
比較例１で得られた前駆体シートに、フェノール樹脂（商品名：フェノライトＪ−３２５、大日本インキ化学株式会社製）のメタノール溶液を含浸させ、室温でメタノールを十分に乾燥させ、炭素短繊維１００質量部に対しフェノール樹脂の不揮発分を１００質量部付着させたフェノール樹脂含浸前駆体シートを得た。
(Comparative Example 3)
The precursor sheet obtained in Comparative Example 1 was impregnated with a methanol solution of a phenol resin (trade name: Phenolite J-325, manufactured by Dainippon Ink & Chemicals, Inc.), and the methanol was sufficiently dried at room temperature. A phenol resin-impregnated precursor sheet in which 100 parts by mass of the nonvolatile content of the phenol resin was adhered to 100 parts by mass of the fiber was obtained.
このフェノール樹脂含浸前駆体シートを２枚重ね合わせ、その両面をシリコーン系離型剤をコートした紙で挟み、バッチプレス装置にて１８０℃、３ＭＰａの条件下で３分間加熱加圧成型してフェノール樹脂を硬化させた後、実施例１と同様の条件で炭素化処理することで多孔質電極基材を得た。得られた多孔質電極基材は、炭素化処理時における面内の収縮がほとんどなく、ガス透気度、厚み、貫通方向抵抗がそれぞれ良好な結果であったが、製造プロセスが複雑であり高コストとなった。結果を表１に示した。 Two of these phenolic resin impregnated precursor sheets are overlapped, and both sides are sandwiched between papers coated with a silicone-based release agent, and heated and pressure-molded under conditions of 180 ° C. and 3 MPa for 3 minutes in a batch press apparatus. After curing the resin, a carbonization treatment was performed under the same conditions as in Example 1 to obtain a porous electrode substrate. The obtained porous electrode substrate had almost no in-plane shrinkage during the carbonization treatment, and the gas permeability, thickness, and penetration direction resistance were favorable, but the manufacturing process was complicated and high. It became cost. The results are shown in Table 1.
（比較例４）
加熱加圧成型した前駆体シートをバッチ熱風炉で、空気中、２５０℃の条件下で２分間酸化処理した以外は、実施例１と同様にして多孔質電極基材を得た。得られた多孔質電極基材は、炭素化処理時における面内の収縮がほとんどなく、ガス透気度、厚み、貫通方向抵抗がそれぞれ良好な結果であったが、フィブリル状炭素の質量比は２８質量％であり、実施例１で得られた多孔質電極基材と比較して、低い炭素化率であり、ハンドリング性に劣るものとなった。
(Comparative Example 4)
A porous electrode base material was obtained in the same manner as in Example 1 except that the heat-pressed precursor sheet was oxidized in a batch hot air oven in air at 250 ° C. for 2 minutes. The obtained porous electrode base material had almost no in-plane shrinkage during the carbonization treatment, and the gas permeability, thickness, and penetration direction resistance were good results, respectively, but the mass ratio of fibrillar carbon was Compared with the porous electrode base material obtained in Example 1, the carbonization rate was low and the handling property was inferior.
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