JP3833898B2 - Method for producing electrode for fuel cell - Google Patents

Description

【００２４】
このスラリー状の第１液状物に対して抄紙処理を行い、第１液状物に含まれている固形物（カーボン繊維、パルプ、グラファイト粉末の粒子）を網状部材等の分離部材により分離させた。これにより厚さ０．３ｍｍの成形シートを製造した。抄紙処理は、水平に沿って配置した網状部材の上面に第１液状物を流し、第１液状物に含まれている水（分散媒）を固形分から分離し、固形分を網状部材の上面に堆積させるという方法で行った。
【００２５】
上記した成形シートを所定のサイズ（１６０ｍｍ×１６０ｍｍ）に切断し、実施例１〜５に係る電極用シート素材を作成した。
【００２６】
なお、第１液状物に分散されている薄片状のグラファイト粉末は、微小径であるため、本来的には、抄紙処理の際にスラリー状の第１液状物からは捕獲されにくい性質を有する。しかし本実施形態によれば、薄片状のグラファイト粉末は、抄紙処理の際にカーボン繊維やパルプ等に付着してスラリー状の第１液状物から捕獲される。ちなみに、第１液状物に含まれている薄片状のグラファイト粉末がシート素材に捕獲される歩留まりは、本発明者の試験によれば、約８０〜９０％程度であり、高かった。
【００２７】
また、カーボンブラック（導電物質）を界面活性剤で湿潤させると共にイオン交換水で希釈し、カーボンブラックを２０質量％含む水溶液を作成した。更に、ポリテトラフルオロエチレン（以下ＰＴＦＥともいう）粒子を分散させた懸濁分散液（ダイキン工業社製、Ｄー１、ＰＴＦＥ粒子６０質量％含有）と上記水溶液とを混ぜて第２液状物を形成した。第２液状物では、カーボンブラックとＰＴＦＥの固形分との質量比としては２０：１５となるよう混合した。
【００２８】
上記した実施例１〜実施例５に係る各電極用シート素材を第２液状物に浸漬させた。これにより第２液状物のＰＴＦＥを電極用シート素材の空隙に含浸させた。その後、電極用シート素材を大気中において１００℃で２０分間乾燥し、その後、大気中において３８０℃で１時間加熱保持した。これにより電極用シート素材に含まれていたパルプを酸化してガス化して消失除去すると共に、ＰＴＦＥをカーボン繊維に固着させ、以てシート状の燃料電池用電極を製造した。
【００２９】
従って、シート状の燃料電池用電極は、カーボン繊維及びアスペクト比が大きなグラファイト粉末の他に、カーボンブラックと撥水材であるＰＴＦＥとを含有している。前記したＰＴＦＥは、燃料電池用電極に撥水性を付与するとともに、消失除去されたパルプに替わってカーボン繊維、グラファイト粉末、カーボンブラックを保持する結合剤としての役割を果たしている。
【００３０】
上記したように製造した燃料電池用電極の単位面積当たりの電気抵抗を測定した。即ち、金メッキした２個１組の鋼板の間にこの電極を挟み、１．９６ＭＰａの荷重をかけた状態で電極の単位面積当たりの厚み方向の電気抵抗（平均値）を測定した。単位面積当たりの電気抵抗の測定結果を表２及び図１に示す。
【００３１】
表２及び図１に示す試験結果によれば、電極の電気抵抗を低減させるためには、アスペクト比が大きな薄片状のグラファイト粉末の量は、第１液状物におけるカーボン繊維及びパルプの合計を１００質量部としたとき、１〜３０質量部が良い。アスペクト比が大きな薄片状のグラファイト粉末の量が多すぎると、コストアップを誘発し易いし、成形性が低下するおそれがある。
【００３２】
また比較例２と実施例３は共に第１液状物にグラファイトを１０質量部配合しているが、アスペクト比が１．５のグラファイト粉末を配合した比較例２よりも、アスペクト比が２０のグラファイト粉末を配合した実施例３の方が、電極の電気抵抗は低減されていた。これによりアスペクト比が大きい薄片状のグラファイト粉末の使用が有効であることがわかる。
【００３３】
【表２】

【００３４】
（適用形態）上記した製造方法に基づいて製造した電極を燃料電池のセルに組み込んだ状態を図２に模式的に示す。図２は模式図であるため、厚みの大小関係まで特定するものではない。この燃料電池のセルは固体高分子電解質型の燃料電池である。図２に示すように、燃料電池のセルは、固体高分子膜型の固体電解質膜１０（米国デュポン社製 ナフィオン）を挟む燃料極２０と酸化剤極３０とを備えている。上記したセルを多数積層して燃料電池を形成する。
【００３５】
燃料極２０及び酸化剤極３０は、上記した製造方法により製造された電極に基づいて形成されている。燃料極２０と固体電解質膜１０との間には、触媒金属を有する触媒層２２が固体電解質膜１０に対面するように設けられている。酸化剤極３０と固体電解質膜１０との間にも、触媒金属を有する触媒層３２が固体電解質膜１０に対面するように設けられている。なお触媒層２２は燃料極２０に積層され、触媒層３２は酸化剤極３０に積層されていても良い。あるいは、触媒層２２、３２は固体電解質膜１０に積層されていても良い。触媒層２２を燃料極２０に積層し、触媒層３２を酸化剤極３０に積層する場合には、触媒を担持したカーボン粉末と水とイオン交換溶液とイソプロピルアルコールを所定の割合で配合した触媒ペーストを用い、電極用シートの片面にドクターブレード法により所定の厚みで塗布して形成することができる。
【００３６】
燃料極２０は、負極活物質としての水素を含む水素含有ガス（純水素ガスでも良い）が流れるガス通路２５を形成するセパレータとも呼ばれる通路形成部材２６に対面する。酸化剤極３０は、正極活物質としての酸素を含む酸素含有ガス（純酸素ガスでも良い）が流れるガス通路３５を形成するセパレータとも呼ばれる通路形成部材３６に対面する。上記した燃料電池によれば、水素を含む水素含有ガス（種類：純水素,水素利用率８０％）をガス通路２５に供給すると共に、酸素含有ガス（種類：空気,空気利用率２５％）をガス通路３５に供給して試験を行ったところ、燃料電池の発電性能は良好であった。
【００３７】
ところで燃料電池によれば、固体電解質膜１０の過剰乾燥は好ましくない。使用の際に固体電解質膜１０のプロトン伝導度が低下するためである。このため、従来より、燃料電池に送給する水素含有ガスや酸素含有ガスを加湿することが多い。これを考慮すると、燃料電池の用途や種類等に応じて、燃料極２０、酸化剤極３０の厚み方向のガス透過度をかなりの範囲で調整できることが好ましい。この点、アスペクト比が大きな２次元的性質が大きい薄片状のグラファイト粉末は、アスペクト比が１に近い通常のグラファイ粉末に比較して、カバー作用を期待できる。従って、２次元的な広がりを有するアスペクト比が大きな２次元的性質が大きい薄片状のグラファイト粉末がカーボン繊維と共に配合されている電極で形成された燃料極２０及び酸化剤極３０においては、燃料電池の用途や種類等に応じて、燃料極２０及び酸化剤極３０の厚み方向のガス透過度を調整するのに有利である。従って、固体電解質膜１０の含水率の調整、固体電解質膜１０のプロトン伝導度の調整を図るのに有利である。殊に、固体電解質膜１０の過剰乾燥の抑制、固体電解質膜１０のプロトン伝導度の向上、燃料電池の出力の向上に有利である。
【００３８】
更に上記した薄片状のグラファイト粉末がカーボン繊維と共に配合されている電極で形成された燃料極２０及び酸化剤極３０においては、薄片状のグラファイト粉末によって燃料極２０及び酸化剤極３０の面方向におけるガス拡散性の調整も期待することができる。
【００３９】
なお上記した適用形態によれば、燃料極２０及び酸化剤極３０は、上記した製造方法により製造された共通の電極に基づいて形成されているが、燃料極２０を構成する電極、酸化剤極３０を構成する電極において、カーボン繊維、アスペクト比が大きい薄片状のグラファイト粉末等の物理的特性、含有量を必要に応じて変えることにしても良い。
【００４０】
（その他）上記した実施形態によれば、第２液状物では、導電物質であるカーボンブラックとＰＴＦＥの固形分との質量比としては２０：１５となるよう混合しているが、これに限らず、必要に応じて変更させることがでる。第２液状物では、カーボンブラックとＰＴＦＥの固形分との質量比としては、例えば、２０：（２〜６０）までの範囲で調整することができる。混合割合が２より小さいと、シートの強度を確保しにくくなる。６０よりも大きいと、シートの電気抵抗が大きくなる。
【００４１】
更に上記した実施形態によれば、ＰＴＦＥ及びカーボンブラックを主要成分とする第２液状物を電極用シート素材の空隙に含浸させることにより、ＰＴＦＥ及びカーボンブラックを同時にシートに保持することにしているが、これに限らず、個別に保持することにしても良い。本発明は上記し且つ図面に示した実施例のみに限定されるものではなく、要旨を逸脱しない範囲内で適宜変更して実施できるものである。実施の形態に記載した事項は、一部であっても請求項に記載できるものである。
【００４２】
（付記）上記した記載から次の技術的思想も把握できる。
（付記項）導電性をもつ基材繊維と、アスペクト比が大きい薄片状のグラファイト粉末と、これらを結合する結合材（一般的にはフッ素樹脂）とを主要成分としていることを特徴とする燃料電池用電極。電極の導電性が確保される。
（付記項）導電性をもつ基材繊維と、アスペクト比が大きい薄片状のグラファイト粉末と、これらを結合する結合材（例えば、パルプ等の消失可能な結合材、または、フッ素樹脂）とを主要成分としている燃料電池電極用シート。
（付記項）導電性をもつ基材繊維と、アスペクト比が大きい薄片状のグラファイト粉末と、これらを結合する結合材（一般的にはフッ素樹脂）とを主要成分としており、導電性をもつ基材繊維同士は薄片状のグラファイト粉末の粒子を介して接触している頻度が高いことを特徴とする燃料電池用電極。電極の導電性が確保される。
（付記項）導電性をもつ基材繊維と、アスペクト比が大きい薄片状のグラファイト粉末と、これらを結合する結合材（パルプ等の消失可能な結合材、または、フッ素樹脂）とを主要成分としており、導電性をもつ基材繊維同士は薄片状のグラファイト粉末の粒子を介して接触している頻度が高いことを特徴とする燃料電池電極用シート。
（付記項）水素含有ガスが送給される燃料極と、酸素含有ガスが送給される酸化剤極と、燃料極及び酸化剤極で挟持された固体高分子電解質膜型の固体電解質膜とを有する燃料電池において、燃料極及び酸化剤極のうちの一方または双方は、導電性をもつ基材繊維と、アスペクト比が大きい薄片状のグラファイト粉末と、これらを結合する結合材とを主要成分としていることを特徴とする燃料電池。
【００４３】
【発明の効果】
以上説明したように、アスペクト比が大きな２次元的な形状を有する薄片状のグラファイト粉末の粒子が燃料電池用電極に添加されているため、カーボン繊維などの導電性をもつ基材繊維同士の導電接触点の増加、導電接触面積の増加を期待することができる。よって、燃料電池用電極の電気抵抗を低減させるのに有利であり、集電性の向上を図り得、燃料電池の性能を向上させるのに有利である。
【００４４】
更に、第１液状物に含まれている固形物と分散媒とを分離させて紙状のシートを得る抄紙処理を経て、電極となるシートを形成する場合には、抄紙処理の際に、第１液状物に含まれているアスペクト比が大きな薄片状のグラファイト粉末の粒子は、導電性をもつ基材繊維や結合材等に付着し易い傾向がある。このため、薄片状のグラファイト粉末の粒子によって、カーボン繊維などの導電性をもつ基材繊維同士の導電接触点の増加、導電接触面積の増加を図るのに一層有利となる。
【図面の簡単な説明】
【図１】電気抵抗の測定データを示すグラフである。
【図２】燃料電池の模式図である。
【図３】カーボン繊維等の導電性をもつ基材繊維同士の接触形態をモデル化した模式図である。
【符号の説明】
図中、１０は固体電解質膜、２０は燃料極、３０は酸化剤極、２２及び３２は触媒層を示す。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing an electrode for a fuel cell comprising a base fiber having conductivity as a main component. The present invention can be used for an electrode of a solid polymer electrolyte type fuel cell.
[0002]
[Prior art]
The main requirement for fuel cell electrodes is high electrical conductivity. As prior art 1, JP-A-7-130374 uses a commercially available carbon paper having a porosity of 80% and a commercially available carbon paper in which PTFE-based dispersion liquid in which PTFE particles capable of functioning as a water repellent material are dispersed. A technique for producing an electrode used in a solid polymer electrolyte type fuel cell is disclosed, which includes a step of immersing the substrate in a PTFE-based dispersion, followed by a step of firing carbon paper.
[0003]
Moreover, as prior art 2, JP 2000-136493 A uses a molded sheet that is molded into a sheet using conductive carbon fibers and a binder and dried, and this molded sheet is made into a PTFE dispersion. A technique for manufacturing an electrode used in a solid polymer electrolyte fuel cell is disclosed in which the PTFE particles are fixed to a molded sheet after being immersed, and at the same time the binder is oxidized and removed.
[0004]
[Problems to be solved by the invention]
The electrode manufactured by the above-described prior art has a limit in improving the conductivity. In addition, the carbon paper used in the prior art 1 is manufactured by hot pressing carbon fibers bonded with a thermosetting resin in an inert gas at a considerably high temperature of 1000 ° C. or higher. It was. Therefore, the fuel cell using the electrode manufactured in this way is expensive and has a problem that impedes its practical use.
[0005]
Moreover, the contact frequency of the contact point between the carbon fibers having conductivity is not always sufficient in the molded sheet used in the conventional technique 2.
[0006]
The present invention has been made in view of the above-described circumstances, and an object of the present invention is to provide a method for producing an electrode for a fuel cell that is advantageous for reducing electric resistance.
[0007]
[Means for Solving the Problems]
The inventor has been eagerly developing a method for manufacturing a fuel cell electrode. Then, using a material mixed with carbon fiber or other conductive base fiber, flaky graphite powder having a large aspect ratio, and a binder, this material is formed into a sheet shape based on a sheet forming process. It was found that forming an electrode for a fuel cell is advantageous in improving the conductivity of the electrode for a fuel cell, and it was confirmed by a test for measuring electric resistance, and the manufacturing method according to the present invention was completed.
[0008]
The reason for improving the conductivity of the fuel cell electrode is not necessarily clear, but is presumed as follows. In the case where flaky graphite powder having a large aspect ratio is not added, conductive base fibers such as carbon fibers are intertwined in a point contact or a state close to point contact. Thus, if it is a point contact or the state close | similar to a point contact, since the contact conductive area of base fibers with conductivity, such as carbon fiber, is small, there exists a limit in improvement of electroconductivity. However, if flaky graphite powder close to two dimensions with a large aspect ratio is added, the conductive base fibers such as carbon fibers will form particles of flaky two dimensional graphite powder with a large aspect ratio. The frequency of touching through increases.
[0009]
FIG. 3 shows a model of a contact form between base fibers 100 having conductivity such as carbon fibers. A hatching area | region shows the contact area between the base fibers 100 which have electroconductivity. As shown in FIG. 3A, even if the base fibers 100 having conductivity are entangled with each other, the base fibers 100 are long and thin, so that the contact area between the base fibers 100 having conductivity is small. . FIG. 3B shows an ideal contact form between the base fibers 100 having conductivity in the presence of flaky graphite powder particles. As shown in FIG. 3 (B), if the flaky graphite powder particles 200 having a two-dimensional shape are present between the conductive substrate fibers 100, the conductive substrate. The contact area between the fibers 100 is significantly increased. Accordingly, it is presumed that the conductivity between the base fibers 100 having conductivity is improved, and as a result, the conductivity and current collection of the fuel cell electrode are improved. FIG. 3B shows an ideal conductive contact form.
[0010]
A fuel cell electrode manufacturing method according to the present invention includes a sheet forming step of forming a sheet to be a fuel cell electrode from the material using a material obtained by mixing a base fiber having conductivity and a binder. In the method for manufacturing a battery electrode,
The material includes flaky graphite powder having an aspect ratio of 2 or more .
[0011]
The sheet produced by the production method according to the present invention includes flaky graphite powder having a large aspect ratio, in addition to conductive base fibers such as carbon fibers. If it is such a sheet | seat, the base fiber which has electroconductivity, such as a carbon fiber, will increase the frequency which contacts through the particle | grains of the flaky graphite powder which has a two-dimensional expansion with a large aspect ratio. It is assumed that this increases the conductive contact point or conductive contact area between the base fibers having conductivity such as carbon fibers. According to the present invention, at least one of the following modes can be adopted.
[0012]
-As the base fiber having conductivity, carbon fiber is preferable in consideration of thermal stability and chemical stability. The base fiber having conductivity such as carbon fiber is preferably a short fiber in consideration of dispersibility in the first liquid material, but may be a long fiber. The length and diameter of the base fiber having conductivity such as carbon fiber can be appropriately selected. However, considering the base fiber of the electrode and the dispersibility in the first liquid material, the length is A diameter of 0.2 to 30 mm, particularly 0.5 to 10 mm, and a diameter of 1 to 60 μm, particularly 3 to 30 μm can be employed.
[0013]
・ Graphite powder is flake shaped. A typical flaky shape is, for example, a scale shape. When the aspect ratio of the flaky graphite powder is excessively small, the effect of increasing the conductive contact point and conductive contact area between conductive base fibers such as carbon fibers cannot be sufficiently exhibited. If the aspect ratio of the flaky graphite powder is excessively large, the graphite powder particles tend to crack when the conductive base fiber, the binder, and the graphite powder are mixed. On the other hand, the aspect ratio may be decreased, and the particle size of the graphite powder may be difficult to control, and the dispersibility in the first liquid may be reduced, making it difficult to perform papermaking. In consideration of such circumstances and cost, the aspect ratio of the flaky graphite powder particles can be 2 to 300. The aspect ratio of the flake graphite powder particles is preferably 2 to 250, particularly 3 to 100, especially considering paper processing, securing of conductivity, cost, etc. and considering the case of paper processing. 10 to 40 are also preferable. However, it is not limited to this. The aspect ratio means the projected diameter / thickness of the flaky graphite powder particles.
[0014]
-Although it can select suitably as an average particle diameter of the particle | grains of flaky graphite powder, it can be set to 5-250 micrometers, and can be 10-100 micrometers, especially 15-40 micrometers. However, it is not limited to this.
[0015]
In the sheet forming step of the manufacturing method according to the present invention, a first liquid material including conductive base fiber such as carbon fiber, flaky graphite powder having a large aspect ratio, a binder, and a dispersion medium is prepared. A form including a process and a papermaking process for forming a sheet to be a fuel cell electrode by performing papermaking on the first liquid material can be adopted. Furthermore, according to the papermaking process, productivity can be improved, which is advantageous for cost reduction, and can further contribute to reduction of the thickness of the electrode. In this case, the first liquid material includes base fiber having conductivity such as carbon fiber, flaky graphite powder having a large aspect ratio, a binder, and a dispersion medium. As the binding material, organic substances such as fibers such as pulp can be used. In some cases, vegetable fibers such as cotton, animal fibers such as wool, and the like can also be used. Generally, water can be used as the dispersion medium, and in some cases, an organic solvent such as toluene, xylene, or cyclohexane may be used. The first liquid material may contain an organic dispersion material and other organic binders in addition to fibers such as pulp.
[0016]
As a typical papermaking process, there is a process in which a solid material and a dispersion medium in the first liquid material are separated and a paper-like sheet is formed by a collection of solid materials. In separating the solid material and the dispersion medium in the first liquid material, the first liquid material is rinsed with a separating member such as a mesh member, and the solid material contained in the first liquid material is separated from the dispersion medium. Examples of a form to obtain a paper-like thin sheet, or a form to obtain a paper-like thin sheet by separating the solid and dispersion medium in the first liquid by vacuum suction or drying to collect the solid The Examples of the solid material in the first liquid material include base fiber, binder, and particles of flaky graphite powder.
[0017]
The papermaking process is advantageous for attaching flaky graphite powder particles to conductive base fibers such as carbon fibers. During the papermaking process, the flaky graphite powder contained in the first liquid together with the base fiber having conductivity such as carbon fiber adheres to the base fiber or binder having conductivity and becomes first. This is because it is separated from the liquid material.
[0018]
-It is preferable that the binder contained in the above-mentioned first liquid material is a binder that can be lost. Organic materials such as fibers such as pulp can be used as the binder that can be lost. In some cases, vegetable fibers such as cotton, animal fibers such as wool, and the like can be used. In the first liquid material, when the base fiber having conductivity and the binder that can be lost are 100 parts by mass , the flake graphite powder having a large aspect ratio is contained in an amount of 0.5 to 60 parts by mass. can be employed, in particular 1 to 50 parts by weight, it is possible to employ 1 to 30 parts by weight.
[0019]
-In the sheet forming step according to the present invention, after the paper making step, the second liquid material containing a binder having water repellency as a main component and the sheet after the paper making step are brought into contact with each other to have a water repellent binding. Adopting a form including an impregnation step of impregnating a gap in the sheet with a material, and a disappearance step of heating the sheet after the impregnation step to fix the water-repellent binding material and at the same time disappear the disappearable binding material be able to. The water-repellent binding material ensures the retention of the conductive base fiber such as carbon fiber and the flaky graphite powder in the electrode. As described above, organic materials such as fibers such as pulp, vegetable fibers such as cotton, and animal fibers such as wool can be used as the binder that can be lost. Since the voids that can disappear can become voids after disappearing, it is possible to expect an effect that can contribute to an improvement in gas diffusibility during use of the fuel cell, and impregnation of the water-repellent binder is ensured.
[0020]
As the binder having water repellency, it is preferable to adopt a fluororesin system in consideration of ensuring water repellency and ensuring chemical stability. As the fluororesin system, polytetrafluoroethylene (PTFE) can be employed. In some cases, tetrafluoroethylene / ethylene copolymer (ETFE), tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer (PFA). Alternatively, at least one of tetrafluoroethylene / hexafluoropropylene copolymer (FEP) and the like may be employed. In the impregnation step, a suspension dispersion in which the above-mentioned fluororesin particles are dispersed can be employed as the second liquid material. The above-mentioned second liquid material preferably contains a fine powder conductive material such as carbon black. Thereby, the electroconductivity of an electrode can further be improved.
[0021]
-A catalyst layer may be laminated | stacked on an electrode, and it is not necessary to laminate | stack. The catalyst layer contains a catalyst metal such as platinum as a main component.
[0022]
DETAILED DESCRIPTION OF THE INVENTION
An embodiment of the present invention will be specifically described based on test examples. In the present embodiment, papermaking processing is performed. A short carbon fiber was used as the base fiber having conductivity. The size of the carbon fiber was 13 μm in diameter and 3 mm in length. Using the above-described carbon fiber, flaky graphite powder having a large aspect ratio, water (dispersion medium) and pulp (disappearable binder), these were dispersed in water as shown in Table 1. As a result, the first liquid material for slurry papermaking according to Examples 1 to 5 was formed. In this case, the total of carbon fiber and pulp was 100 parts by mass , and the flake-like graphite powder having a large aspect ratio was changed to 2 to 30 parts by mass . As the flaky graphite powder, one having an average particle diameter of 20 μm, an average thickness of 1 μm and an aspect ratio of 20 was used.
[0023]
[Table 1]

[0024]
The slurry-like first liquid material was subjected to papermaking, and solids (carbon fiber, pulp, graphite powder particles) contained in the first liquid material were separated by a separating member such as a net-like member. As a result, a molded sheet having a thickness of 0.3 mm was produced. In the papermaking process, the first liquid material is caused to flow on the upper surface of the mesh member arranged horizontally, the water (dispersion medium) contained in the first liquid material is separated from the solid content, and the solid content is applied to the upper surface of the mesh member. It was done by the method of depositing.
[0025]
The above-described molded sheet was cut into a predetermined size (160 mm × 160 mm), and electrode sheet materials according to Examples 1 to 5 were created.
[0026]
In addition, since the flaky graphite powder dispersed in the first liquid material has a small diameter, it inherently has a property that it is difficult to be captured from the slurry-like first liquid material during the papermaking process. However, according to the present embodiment, the flaky graphite powder adheres to carbon fibers, pulp, and the like during the papermaking process and is captured from the slurry-like first liquid material. Incidentally, the yield at which the flaky graphite powder contained in the first liquid material is captured by the sheet material is about 80 to 90%, which is high according to the test by the present inventors.
[0027]
In addition, carbon black (conductive substance) was wetted with a surfactant and diluted with ion-exchanged water to prepare an aqueous solution containing 20% by mass of carbon black. Furthermore, a suspension dispersion liquid (manufactured by Daikin Industries, Ltd., D-1, containing 60% by mass of PTFE particles) in which polytetrafluoroethylene (hereinafter also referred to as PTFE) particles are dispersed and the above aqueous solution are mixed to form a second liquid material. Formed. In the second liquid material, the mass ratio of carbon black and the solid content of PTFE was 20:15.
[0028]
Each electrode sheet material according to Examples 1 to 5 described above was immersed in the second liquid material. As a result, the voids of the electrode sheet material were impregnated with the second liquid PTFE. Thereafter, the electrode sheet material was dried at 100 ° C. for 20 minutes in the air, and then heated and held at 380 ° C. for 1 hour in the air. Thus, the pulp contained in the electrode sheet material was oxidized and gasified to disappear and removed, and PTFE was fixed to the carbon fiber, whereby a sheet-like fuel cell electrode was produced.
[0029]
Therefore, the sheet-like fuel cell electrode contains carbon black and PTFE which is a water repellent material, in addition to the carbon fiber and the graphite powder having a large aspect ratio. The PTFE described above imparts water repellency to the fuel cell electrode and plays a role as a binder for holding carbon fiber, graphite powder, and carbon black in place of the pulp that has been eliminated.
[0030]
The electric resistance per unit area of the fuel cell electrode manufactured as described above was measured. That is, the electrode was sandwiched between a pair of two steel plates plated with gold, and the electric resistance (average value) in the thickness direction per unit area of the electrode was measured under a load of 1.96 MPa. The measurement results of electrical resistance per unit area are shown in Table 2 and FIG.
[0031]
According to the test results shown in Table 2 and FIG. 1, in order to reduce the electrical resistance of the electrode, the amount of the flaky graphite powder having a large aspect ratio is 100% of the total of carbon fibers and pulp in the first liquid. when the mass portion, it is 1 to 30 parts by weight. If the amount of the flaky graphite powder having a large aspect ratio is too large, it is easy to induce an increase in cost and the moldability may be lowered.
[0032]
In both Comparative Example 2 and Example 3, 10 parts by mass of graphite was blended in the first liquid, but graphite having an aspect ratio of 20 was higher than that of Comparative Example 2 in which graphite powder having an aspect ratio of 1.5 was blended. In Example 3 in which powder was blended, the electrical resistance of the electrode was reduced. This shows that the use of flaky graphite powder having a large aspect ratio is effective.
[0033]
[Table 2]

[0034]
(Application Mode) FIG. 2 schematically shows a state in which an electrode manufactured based on the manufacturing method described above is incorporated in a cell of a fuel cell. Since FIG. 2 is a schematic diagram, it does not specify the thickness relationship. The cell of this fuel cell is a solid polymer electrolyte type fuel cell. As shown in FIG. 2, the fuel cell includes a fuel electrode 20 and an oxidizer electrode 30 that sandwich a solid polymer membrane type solid electrolyte membrane 10 (Nafion manufactured by DuPont, USA). A fuel cell is formed by stacking a large number of the above-described cells.
[0035]
The fuel electrode 20 and the oxidant electrode 30 are formed based on the electrodes manufactured by the above-described manufacturing method. A catalyst layer 22 having a catalyst metal is provided between the fuel electrode 20 and the solid electrolyte membrane 10 so as to face the solid electrolyte membrane 10. A catalyst layer 32 having a catalyst metal is also provided between the oxidant electrode 30 and the solid electrolyte membrane 10 so as to face the solid electrolyte membrane 10. The catalyst layer 22 may be stacked on the fuel electrode 20, and the catalyst layer 32 may be stacked on the oxidant electrode 30. Alternatively, the catalyst layers 22 and 32 may be laminated on the solid electrolyte membrane 10. When the catalyst layer 22 is laminated on the fuel electrode 20 and the catalyst layer 32 is laminated on the oxidant electrode 30, a catalyst paste in which carbon powder supporting the catalyst, water, an ion exchange solution, and isopropyl alcohol are blended at a predetermined ratio. Can be formed by applying a predetermined thickness on one side of the electrode sheet by a doctor blade method.
[0036]
The fuel electrode 20 faces a passage forming member 26 called a separator that forms a gas passage 25 through which a hydrogen-containing gas containing hydrogen as a negative electrode active material (which may be pure hydrogen gas) flows. The oxidant electrode 30 faces a passage forming member 36 called a separator that forms a gas passage 35 through which an oxygen-containing gas containing oxygen as a positive electrode active material (which may be pure oxygen gas) flows. According to the fuel cell described above, a hydrogen-containing gas containing hydrogen (type: pure hydrogen, hydrogen utilization rate of 80%) is supplied to the gas passage 25, and an oxygen-containing gas (type: air, air utilization rate of 25%) is supplied. When the gas passage 35 was supplied and tested, the power generation performance of the fuel cell was good.
[0037]
By the way, according to the fuel cell, excessive drying of the solid electrolyte membrane 10 is not preferable. This is because the proton conductivity of the solid electrolyte membrane 10 decreases during use. For this reason, conventionally, the hydrogen-containing gas and the oxygen-containing gas supplied to the fuel cell are often humidified. In consideration of this, it is preferable that the gas permeability in the thickness direction of the fuel electrode 20 and the oxidant electrode 30 can be adjusted in a considerable range according to the use and type of the fuel cell. In this respect, the flaky graphite powder having a large two-dimensional property with a large aspect ratio can be expected to have a cover action as compared with a normal graphite powder having an aspect ratio close to 1. Accordingly, in the fuel electrode 20 and the oxidant electrode 30 formed of electrodes in which flaky graphite powder having a two-dimensional spread and a large aspect ratio and a large two-dimensional property are blended with carbon fibers, a fuel cell is used. It is advantageous to adjust the gas permeability in the thickness direction of the fuel electrode 20 and the oxidant electrode 30 according to the use and type of the gas. Therefore, it is advantageous for adjusting the moisture content of the solid electrolyte membrane 10 and adjusting the proton conductivity of the solid electrolyte membrane 10. In particular, it is advantageous for suppressing excessive drying of the solid electrolyte membrane 10, improving the proton conductivity of the solid electrolyte membrane 10, and improving the output of the fuel cell.
[0038]
Further, in the fuel electrode 20 and the oxidant electrode 30 formed of electrodes in which the above-described flaky graphite powder is mixed with carbon fibers, the flaky graphite powder is used in the plane direction of the fuel electrode 20 and the oxidant electrode 30. Adjustment of gas diffusivity can also be expected.
[0039]
According to the application mode described above, the fuel electrode 20 and the oxidant electrode 30 are formed based on the common electrode manufactured by the above-described manufacturing method. In the electrode constituting 30, the physical properties and content of carbon fiber, flaky graphite powder having a large aspect ratio, and the like may be changed as necessary.
[0040]
(Others) According to the above-described embodiment, the second liquid material is mixed so that the mass ratio of carbon black as the conductive material and the solid content of PTFE is 20:15, but is not limited thereto. It can be changed as necessary. In the second liquid material, the mass ratio between the carbon black and the solid content of PTFE can be adjusted within a range of, for example, 20: (2 to 60). And the mixing ratio is less than 2, the phrase difficulty ensuring the strength of the sheet. When it is larger than 60, the electric resistance of the sheet becomes large.
[0041]
Furthermore, according to the above-described embodiment, the second liquid material containing PTFE and carbon black as main components is impregnated in the gaps of the electrode sheet material, so that PTFE and carbon black are simultaneously held on the sheet. However, the present invention is not limited to this and may be held individually. The present invention is not limited to the embodiments described above and shown in the drawings, and can be implemented with appropriate modifications within the scope not departing from the gist. Some of the matters described in the embodiment can be described in the claims.
[0042]
(Supplementary note) The following technical idea can be grasped from the above description.
(Additional Item) A fuel characterized in that the main components are conductive base fiber, flaky graphite powder having a large aspect ratio, and a binder (generally a fluororesin) that bonds them. Battery electrode. The conductivity of the electrode is ensured.
(Additional Notes) Mainly composed of conductive base fibers, flaky graphite powder having a large aspect ratio, and a binder (for example, a binder that can be lost such as pulp or a fluororesin) that binds these. A fuel cell electrode sheet as a component.
(Additional Notes) Main components are conductive base fiber, flaky graphite powder having a large aspect ratio, and a binder (generally a fluororesin) that binds these, and the conductive base fiber. An electrode for a fuel cell, characterized in that the material fibers are frequently in contact with each other through particles of flaky graphite powder. The conductivity of the electrode is ensured.
(Additional Notes) Main components are conductive base fiber, flaky graphite powder having a large aspect ratio, and a binder (bondable material such as pulp, or fluororesin) that binds them. The fuel cell electrode sheet is characterized in that the base fibers having conductivity are frequently in contact with each other through particles of flaky graphite powder.
(Additional Item) A fuel electrode to which a hydrogen-containing gas is supplied, an oxidant electrode to which an oxygen-containing gas is supplied, and a solid polymer electrolyte membrane type solid electrolyte membrane sandwiched between the fuel electrode and the oxidant electrode; In one or both of the fuel electrode and the oxidizer electrode, the main component is a conductive base fiber, a flaky graphite powder having a large aspect ratio, and a binder for bonding them. A fuel cell characterized by that.
[0043]
【The invention's effect】
As described above, since particles of flaky graphite powder having a two-dimensional shape with a large aspect ratio are added to the electrode for the fuel cell, the conductivity between the base fibers having conductivity such as carbon fibers can be reduced. An increase in contact points and an increase in conductive contact area can be expected. Therefore, it is advantageous for reducing the electric resistance of the electrode for the fuel cell, which can improve the current collecting performance, and is advantageous for improving the performance of the fuel cell.
[0044]
Further, in the case of forming a sheet to be an electrode through papermaking processing for separating the solid contained in the first liquid material and the dispersion medium to obtain a paper-like sheet, Particles of flaky graphite powder having a large aspect ratio contained in one liquid material tend to adhere to conductive base fibers or binders. For this reason, the particles of flaky graphite powder are more advantageous for increasing the number of conductive contact points between conductive base fibers such as carbon fibers and increasing the conductive contact area.
[Brief description of the drawings]
FIG. 1 is a graph showing measurement data of electrical resistance.
FIG. 2 is a schematic view of a fuel cell.
FIG. 3 is a schematic diagram modeling a contact form between conductive base fibers such as carbon fibers.
[Explanation of symbols]
In the figure, 10 is a solid electrolyte membrane, 20 is a fuel electrode, 30 is an oxidizer electrode, and 22 and 32 are catalyst layers.

Claims (7)

In a method for producing a fuel cell electrode, comprising a sheet molding step of forming a sheet to be a fuel cell electrode from the material using a material obtained by mixing a base fiber having a conductivity and a binder,
The method for producing a fuel cell electrode, wherein the material includes flaky graphite powder having an aspect ratio of 2 or more. The sheet forming step according to claim 1 comprises:
Preparing a first liquid material including the base fiber having conductivity, the flaky graphite powder having an aspect ratio of 2 or more, the binder, and a dispersion medium;
A method of manufacturing a fuel cell electrode, comprising: a papermaking step of forming a sheet to be a fuel cell electrode by performing paper processing on the first liquid material. 3. The method for producing an electrode for a fuel cell according to claim 1, wherein the flaky graphite powder has an aspect ratio of 2 to 300. In any one of claims 1 to 3, method for manufacturing a fuel cell electrode, wherein the average particle size of the flaky graphite powder is 10 to 250 .mu.m. In the material according to claim 1 or the first liquid material according to claim 2, when the base fiber and the binder having conductivity are 100 parts by mass , the flaky graphite powder is 0. The manufacturing method of the electrode for fuel cells characterized by being 5-60 mass parts. In any one of claims 1 to 5, the fuel cell electrode manufacturing method, wherein the base fiber having conductivity is carbon fiber. In any one of claims 2 to 5, the binder contained in the first liquid was a loss linkage member,
In the sheet forming step, after the paper making step, the second liquid material containing a binder having water repellency as a main component and the sheet after the paper making step are brought into contact with the sheet having the water repellency. An impregnation step of impregnating the void portion of the sheet;
A method for producing an electrode for a fuel cell, comprising: a step of heating the sheet after the impregnation step to fix the water-repellent binding material and at the same time to disappear the disappearable binding material.

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