JP2004342480A

JP2004342480A - Direct methanol fuel cell

Info

Publication number: JP2004342480A
Application number: JP2003138392A
Authority: JP
Inventors: Yukio Fujita; 幸雄藤田; Ryoichi Okuyama; 良一奥山; Eiichi Nomura; 栄一野村
Original assignee: Yuasa Corp; Yuasa Battery Corp
Current assignee: Yuasa Corp
Priority date: 2003-05-16
Filing date: 2003-05-16
Publication date: 2004-12-02

Abstract

<P>PROBLEM TO BE SOLVED: To improve characteristics of a direct methanol fuel cell for supplying methanol solution to a negative electrode using capillarity, and supplying air to a positive electrode using natural diffusion or natural convection. <P>SOLUTION: A fuel cell comprises an electrode-membrane assembly having the negative electrode 2 and the positive electrode 3 bonded by an electrolyte 1 made of a proton conductive polymer membrane, and a negative electrode side collecting sheet 5 provided on the negative electrode side of the electrode-membrane assembly. For the negative electrode 2, wettability of a conductive porous material of a negative electrode base material is improved so that the methanol solution can be taken as fuel. For the positive electrode 3, water repellent treatment is performed on a conductive porous material of a positive electrode base material, so that air can be taken as oxidant gas. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

【０００１】
【発明の属する技術分野】
本発明は、電解質にプロトン導電性の高分子膜を用い、燃料にメタノール水溶液を、酸化剤ガスに空気を供給して発電する直接メタノール形燃料電池に関するものである。
【０００２】
【従来の技術】
直接メタノール形燃料電池は、燃料のメタノール水溶液をガス化または改質せずに直接供給して発電できるという特徴を持っているため、従来からの固体高分子形燃料電池と比べて、構造がシンプルであって、小型化、軽量化が容易であるということから、分散型電源やポータブル電源としての用途が注目されている。
【０００３】
このような直接メタノール形燃料電池は、電解質にプロトン導電性の高分子膜を用い、この電解質を介して負極と正極を接合し、負極の、電解質に接合されない側には負極側集電シートが設けられ、正極の、電解質に接合されない側には正極側集電シートが設けられた構造であり、負極にメタノール水溶液を供給し、正極に空気を供給すると、負極ではメタノールと水が反応して二酸化炭素を生成するとともに水素イオンと電子を放出し、正極では電解質を通過してきた前記水素イオンと空気中の酸素と電子が反応して水を生成し、外部回路に電気エネルギーを発生させる。
【０００４】
従来の直接メタノール形燃料電池では、カーボンペーパーやカーボンクロスのような導電性炭素材料にポリテトラフルオロエチレン等のフッ素系樹脂を含有させた分散液を含浸し、乾燥、焼成することによって撥水性を付与し、これを正極および負極の基材として用いていた。このようにするのは、負極側では反応生成物である二酸化炭素が円滑に排出でき、正極側では空気が円滑に供給できるようにするためであり、前記負極には、さらに負極側の集電と負極にメタノール水溶液を供給するための負極側セパレータを設け、前記正極には、さらに正極側の集電と正極に空気を供給するための正極側セパレータを設けている。
【０００５】
ところで、分散型電源やポータブル電源に直接メタノール形燃料電池を用いる場合、小型化することが不可欠であり、メタノール水溶液の供給はポンプ等を用いずに毛管現象を利用して燃料保持部から供給し、空気の供給も自然拡散または自然対流によって供給することが検討されている。
【０００６】
【特許文献１】
特開昭５９−６６０６６号公報
【０００７】
上記特許文献１には、負極の集電側（基材側）の面に毛細管作用を示す材料を接触させ、かつ該材料の一端を液体燃料に接するように配置し、この材料を介して負極に液体燃料を供給する方法が開示されている。
【０００８】
【発明が解決しようとする課題】
上記した特許文献１に開示されたものは、前述した負極側セパレータを設ける代わりに、負極の集電側（基材側）の面と負極側集電体との間の接触抵抗が小さく、かつ負極の集電側（基材側）の面と前述した毛細管作用を示す材料とが均一に接触するように、該材料の形状と負極側集電体の形状を櫛歯状にして、両者を互いに嵌合させて、これを負極の集電側（基材側）に設けていた。このため、ポンプ等を用いないで液体燃料を供給できる利点はあるものの、該材料の形状や負極側集電体の形状が複雑になるという問題があった。
【０００９】
【課題を解決するための手段】
本発明は、上記のような課題を解決することを目的とし、その請求項１記載の直接メタノール形燃料電池は、プロトン導電性の高分子膜からなる電解質を介して負極と正極とを接合した電極―膜接合体と、この電極―膜接合体の負極側に設けた負極側集電シートと、正極側に設けた正極側集電シートとを備えたセルからなる直接メタノール形燃料電池において、前記負極は、燃料としてのメタノール水溶液を毛細管現象によって取り入れることができるように濡れ性を向上させた導電性多孔質材料を負極基材とし、その電解質側表面に負極触媒を担持したものであり、前記正極は、酸化剤ガスとして空気を自然拡散または自然対流によって取り入れることができるように撥水処理が施された導電性多孔質材料を正極基材とし、その電解質側表面に正極触媒を担持したものであることを特徴とする。
【００１０】
また、請求項２記載の直接メタノール形燃料電池は、前記負極基材および正極基材の導電性多孔質材料が、カーボンまたはグラファイト繊維を原料にした不織布またはペーパー状もしくはクロス状のシートであることを特徴とする。
【００１１】
また、請求項３記載の直接メタノール形燃料電池は、前記負極基材が、酸性水溶液中で、負極基材の導電性多孔質材料を陽極として電圧を印加することによって濡れ性が向上されたことを特徴とする。
【００１２】
また、請求項４記載の直接メタノール形燃料電池は、前記正極基材が、フッ素系樹脂の分散液に、正極基材の導電性多孔質材料を浸漬し、乾燥、焼成することによって撥水処理が施されたことを特徴とする。
【００１３】
また、請求項５記載の直接メタノール形燃料電池は、前記請求項１〜４の少なくとも一項記載のものにおいて、電極―膜接合体、負極側集電シートおよび正極側集電シートを備えたセルが、負極側集電シートまたは正極側集電シートの少なくとも一方の表面に絶縁シートが配されて巻回されて円筒状にしたことを特徴とする。
【００１４】
上記した直接メタノール形燃料電池によれば、負極基材の導電性多孔質材料の濡れ性を向上しているため、毛細管現象によってメタノール水溶液を円滑に取り入れて負極触媒に供給することができるとともに、負極の、電解質に接触しない外側面の全面に負極側集電シートを配することができるので、負極側集電シートの形状を複雑にしなくても負極と負極側集電シートとの間の接触抵抗を小さくすることができる。なお、濡れ性が向上したかどうかは、濡れ性向上の処理をした負極基材の導電性多孔質材料が未処理の同材料に対して、２５℃の蒸留水を吸水したかどうかで判定した。このように判定したのは、濡れ性向上のメカニズムは明らかでないが、この処理によって表面粗さを含めた表面形態や表面状態が変化することが考えられるからである。また、正極基材の導電性多孔質材料に撥水処理を施し、パンチングメタルのような貫通穴を有する正極側集電シートを設けると、この貫通穴を介して空気を自然拡散または自然対流によって円滑に取り入れて正極触媒に供給することができる。
【００１５】
【発明の実施の形態】
以下、本発明を、その実施の形態に基づいて説明する。
【００１６】
図１は、本発明に係る直接メタノール形燃料電池の断面図である。
【００１７】
図１に示した直接メタノール形燃料電池は、プロトン導電性の高分子膜からなる電解質１を介して負極２と正極３とを接合した電極−膜接合体と、この電極−膜接合体の負極側に設けた負極側集電シート５と、正極側に設けた正極側集電シート６とを備えたセルからなる。前記負極２は、メタノール水溶液を毛細管現象によって取り入れることができるように濡れ性を向上させた導電性多孔質材料を負極基材とし、その電解質側表面（電解質１に接触する面）に負極触媒（炭素粉末に担持された白金−ルテニウム粉末）を担持し、その一端が取り入れられたメタノール水溶液を前記負極触媒に供給できるように燃料保持部４に到達させている。前記正極３は、空気を自然拡散または自然対流によって取り入れることができるように撥水処理が施された導電性多孔質材料を正極基材とし、その電解質側表面（電解質１に接触する面）に正極触媒（炭素粉末に担持された白金粉末）を担持している。前記負極側集電シート５と正極側集電シート６にはステンレスなどの金属板や炭素板のような導電性を有するものが用いられるが、空気が自然拡散または自然対流によって取り入れられるように、正極側集電シート６には貫通穴を設けている。なお、図１において、負極基材に負極触媒を担持させる範囲は電解質１を介して正極３に対向する範囲とするのがよい。
【００１８】
前記負極基材は、酸性水溶液中で、その導電性多孔質材料を陽極として電圧を印加することによって濡れ性を向上させ、前記正極基材は、フッ素樹脂の分散液に、その導電性多孔質材料を浸漬した後、乾燥、焼成することによって撥水処理を施している。
【００１９】
その結果、濡れ性を向上させた負極基材は、その一端を燃料保持部４に到達させてメタノール水溶液を毛管現象によって取り入れることができるから、負極２にメタノール水溶液を円滑に供給することができる。また、負極側集電シート５を、負極２の、電解質１に接触しない外側面の全面で接触させるようにできるから、前述した特許文献１のように、その形状を複雑にしなくても、負極２と負極側集電シート５との間の接触抵抗を小さくすることができる。
【００２０】
また、撥水性を付与した正極基材は、空気を自然拡散または自然対流で円滑に取り入れることができる。
【００２１】
上記した実施の形態では、負極基材を介してメタノール水溶液を直接供給する方式としたが、負極２と接触する部材を別に設け、この部材の濡れ性を向上させて、この部材を介してメタノール水溶液を供給するようにしてもよい。
【００２２】
また、上記した実施の形態では、負極側セパレータを設けて、これにメタノール水溶液を供給するための溝加工をしたり、正極側セパレータを設けて、これに空気を供給するための溝加工をする必要がないから、コスト面でも有利である。
【００２３】
また、上記した実施の形態では、燃料保持部４を負極２の下方に設けた場合を示しているが、この位置関係はこれに限られるものではない。
【００２４】
なお、燃料保持部４に与えるメタノール水溶液としては、１〜２モル／リットル程度のものが用いられてきたが、このように毛管現象によってメタノール水溶液を供給する方式の場合には、負極基材に対する浸透性の向上、電池の温度上昇による出力特性の向上、エネルギー密度の向上の観点から、１０モル／リットル程度までその濃度を高くすることができるが、その濃度を１０モル／リットル以上にすると、電池の温度上昇が大きくなり過ぎること、正極側へのメタノール水溶液のクロスオーバー量の増加によって出力特性が低下すること、により好ましくない。
【００２５】
図２は上記した実施の形態に係る直接メタノール形燃料電池を用いて組電池とした場合の斜視図である。
【００２６】
図２に示した組電池は、プロトン導電性の高分子膜からなる電解質を介して負極と正極を接合した電極−膜接合体、負極側集電シートとしての箔材および正極側集電シートとしての箔材を備えたセルを、負極側集電シートまたは正極側集電シートの少なくとも一方の表面に絶縁シートを配して巻回して円筒状の巻回体９にし、この巻回体９を５個、負極基材が燃料保持シート１０に接触し、各々を端子板１１によって相互に直列に接続したことを特徴とする。
【００２７】
すなわち、図２に示した実施の形態によれば、濡れ性を向上させた負極基材を通じて燃料保持シート１０からメタノール水溶液を毛管現象によって取り入れ、それを負極と電解質との接触面に円滑に供給することができるとともに、撥水処理を施された正極の基材を通じて空気を自然拡散または自然対流によって取り入れ、それを正極と電解質との接触面に円滑に供給することができる。また、負極基材は濡れ性が向上され、正極基材は撥水処理が施されているため、巻回されることによって円周上で隣接するセル間に隔壁を設けなくとも、負極は空気中の酸素の影響を受けることはなく、正極はメタノール水溶液の影響を受けることはなく、電池の特性に影響することもない。そのため、電池の出力特性を低下させることなく、このような巻回体９からなる組電池をシンプルでかつコンパクトに構成することができる。
【００２８】
【実施例】
以下、実施例について説明する。
【００２９】
（実施例）
厚さが２００μｍのカーボンクロスを陽極、白金箔を陰極として２５℃の温度下で、１モル／リットルの硫酸水溶液中で５ｍＡ／ｃｍ^２の電流密度で１時間通電し、取り出したカーボンクロスを湯洗、乾燥することによって濡れ性を向上した負極基材を得た。このカーボンクロスを前述した評価方法で評価したところ、濡れ性は７００であった。次に、同じカーボンクロスを濃度が５％のポリテトラフルオロエチレン分散液に浸漬して、乾燥し、３６０℃の温度で焼成することによって撥水処理を施した正極基材を得た。前記カーボンクロスは厚さを２００μｍとしたが、１００〜５００μｍの間で適宜選択できる。そして、活性炭微粒子に白金−ルテニウムを担持させた負極触媒を、ＰＴＦＥとナフィオン（登録商標）を含む溶液中に分散させてペースト化し、このペーストを前述した負極基材に塗布して乾燥させて負極２とした。前記負極触媒の白金とルテニウムの合計含有量は４０重量％のものを使用したが、１０〜７０重量％の間で適宜選択でき、白金：ルテニウムの重量比は２：１のものを使用したが、５：１〜１：２の間で適宜選択できる。また、負極触媒、ＰＴＦＥおよびナフィオン（登録商標）の重量比は、負極触媒５５重量％、ＰＴＦＥ１５重量％およびナフィオン（登録商標）３０重量％としたが、これに限るものではない。一方、活性炭微粒子に白金を担持させた正極触媒を、ＰＴＦＥとナフィオン（登録商標）を含む溶液中に分散させてペースト化し、このペーストを前述した正極基材に塗布して乾燥させたものを正極３とした。前記正極触媒の白金の含有量は４０重量％のものを使用したが、１０〜７０重量％の間で適宜選択できる。また、正極触媒、ＰＴＦＥおよびナフィオン（登録商標）の重量比は、正極触媒６５重量％、ＰＴＦＥ１５重量％およびナフィオン（登録商標）２０重量％としたが、これに限るものではない。こうして得た負極２と正極３をナフィオン１１７（登録商標）からなる高分子膜からなる電解質１の両面に１５０℃の温度下でプレスし、図１のような負極側集電シート５と、正極側集電シート６とで挟持し、前述した負極基材の一端を燃料保持部４に浸漬して実施例に係るセルを作製した。前記電解質１は厚さを１８０μｍとしたが、２０〜２００μｍの間で適宜選択できる。
【００３０】
（比較例１）
上記した実施例に係るセルに対し、前記特許文献１の第２図のように、アノードの外側面（電解質に接触しない面）に、櫛状の燃料供給部材９とアノード側集電体５とを、両者が互いに嵌合するように配置したセルを作製し、これを比較例１とした。なお、前記アノードには実施例のカーボンクロスと同じもので、濡れ性を向上させていないものを使用した。
【００３１】
（比較例２）
上記した実施例に係るセルに対し、濡れ性を向上させていないカーボンクロスを負極基材とし、負極基材の外側面（電解質に接触しない面）の全面に負極側集電シートを配置したセルを作製し、これを比較例２とした。
【００３２】
（比較例３）
上記した実施例に係るセルに対し、カーボンクロスを濃度が５％のＰＴＦＥ分散液に浸漬、乾燥し、３６０℃の温度で焼成することによって撥水処理を施して負極基材とした以外は実施例と同じセルを作製し、これを比較例３とした。
【００３３】
（実験１）
上記した実施例、比較例１，２，３に係るセルを用い、室温（２５℃）下で、負極基材に１０モル／リットルのメタノール水溶液を与え、各セルの電流−電圧特性を測定し、結果を図３に示す。
【００３４】
図３から明らかなように、実施例に係るセルは比較例１，２，３のセルに比べて、電流−電圧特性が良好であることがわかる。
【００３５】
（実験２）
上記した実施例、比較例１，２，３に係るセルを用い、室温（２５℃）下で、負極基材に１０モル／リットルのメタノール水溶液を１ミリリットル与え、５ｍＡ／ｃｍ^２の電流密度の定電流で運転し、その電圧変化を調査し、結果を図４に示す。
【００３６】
図４から明らかなように、実施例に係るセルは比較例１，２，３のセルに比べて、電圧が安定していることがわかる。
【００３７】
上記実験１、２の結果は、実施例に係るセルでは、負極基材の濡れ性を向上させたことにより、メタノール水溶液の供給が円滑に行えるようになったためであることによるものと考えられる。特に、実施例に係るセルは、比較例２に係るセルに比べて、負極基材であるカーボンクロスに濡れ性を向上させる処理をしたことによって特性が大きく向上したことがわかる。このことは、実施例に係るセルと比較例１，３のセルとの間でも言えることである。
【００３８】
【発明の効果】
本発明によれば、燃料としてのメタノール水溶液を毛管現象によって取り入れることができるように濡れ性を向上させた負極基材を用いているから、負極側集電シートを負極の全面に接触させるようにできる。また、空気を自然拡散または自然対流によって取り入れることができるように撥水処理を施した正極基材を用いているから、空気を円滑に正極触媒に供給することができる。従って、負極と負極側集電シートとの間の抵抗を高くすることなく、メタノール水溶液や空気を取り入れるためのポンプ等を不要にできるから、直接メタノール形燃料電池の小型化に寄与することができる。
【００３９】
また、本発明によれば、負極側セパレータを設け、これにメタノール水溶液を供給するための溝加工を施したり、正極側セパレータを設け、これに空気を供給するための溝加工を施す必要がないので、直接メタノール形燃料電池の小型化と低コスト化に寄与することができる。
【００４０】
また、負極基材は濡れ性を向上し、正極基材は撥水処理を施しているため、セルを巻回した場合、円周上で隣接するセル間に隔壁を設けなくとも、負極が空気中の酸素の影響を受けたり、正極がメタノール水溶液の影響を受けることはなく、電池の特性に影響することもない。そのため、電池の出力特性を低下させないで巻回体からなる組電池をシンプルでかつコンパクトに構成することができる。
【図面の簡単な説明】
【図１】本発明に係る直接メタノール形燃料電池の断面図である。
【図２】本発明に係る直接メタノール形燃料電池を用いた組電池の斜視図である。
【図３】電流−電圧特性を比較した図である。
【図４】定電流での運転時の電圧特性を比較した図である。
【符号の説明】
１電解質
２負極
３正極
４燃料保持部
５負極側集電シート
６正極側集電シート
９巻回体
１０燃料保持シート
１１端子板[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a direct methanol fuel cell that uses a proton conductive polymer membrane as an electrolyte and supplies an aqueous methanol solution as a fuel and air as an oxidizing gas to generate power.
[0002]
[Prior art]
Direct methanol fuel cells have the feature of being able to generate electricity by directly supplying an aqueous methanol solution of fuel without gasification or reforming, and therefore have a simpler structure than conventional polymer electrolyte fuel cells. However, since it is easy to reduce the size and weight, applications as a distributed power supply and a portable power supply are attracting attention.
[0003]
Such a direct methanol fuel cell uses a proton conductive polymer membrane as an electrolyte, and joins a negative electrode and a positive electrode through the electrolyte. A negative electrode-side current collecting sheet is provided on the side of the negative electrode that is not joined to the electrolyte. The positive electrode has a structure in which a positive electrode side current collecting sheet is provided on the side not joined to the electrolyte, and when a methanol aqueous solution is supplied to the negative electrode and air is supplied to the positive electrode, methanol and water react on the negative electrode. In addition to generating carbon dioxide, it emits hydrogen ions and electrons. At the positive electrode, the hydrogen ions passing through the electrolyte react with oxygen and electrons in the air to generate water and generate electric energy in an external circuit.
[0004]
In a conventional direct methanol fuel cell, water repellency is obtained by impregnating a conductive carbon material such as carbon paper or carbon cloth with a dispersion liquid containing a fluorine-based resin such as polytetrafluoroethylene, followed by drying and firing. This was used as a base material for the positive electrode and the negative electrode. The reason for this is that carbon dioxide as a reaction product can be smoothly discharged on the negative electrode side, and air can be smoothly supplied on the positive electrode side. The negative electrode is provided with a negative electrode side separator for supplying a methanol aqueous solution, and the positive electrode is further provided with a positive electrode side separator for collecting current on the positive electrode side and supplying air to the positive electrode.
[0005]
By the way, when a direct methanol fuel cell is used for a distributed power source or a portable power source, miniaturization is indispensable. The methanol aqueous solution is supplied from the fuel holding unit using a capillary phenomenon without using a pump or the like. It has been considered that the supply of air is also supplied by natural diffusion or natural convection.
[0006]
[Patent Document 1]
JP-A-59-66066
In Patent Document 1, a material exhibiting a capillary action is brought into contact with the current collecting side (substrate side) of the negative electrode, and one end of the material is arranged so as to be in contact with the liquid fuel. A method for supplying a liquid fuel to a fuel cell is disclosed.
[0008]
[Problems to be solved by the invention]
The one disclosed in the above-mentioned Patent Document 1 has a small contact resistance between the current collector side (base material side) of the negative electrode and the negative electrode current collector instead of providing the negative electrode separator described above, and The shape of the material and the shape of the negative electrode side current collector are comb-shaped so that the surface on the current collecting side (substrate side) of the negative electrode and the material exhibiting the above-mentioned capillary action are uniformly contacted. They were fitted to each other and provided on the current collecting side (base material side) of the negative electrode. For this reason, although there is an advantage that the liquid fuel can be supplied without using a pump or the like, there is a problem that the shape of the material and the shape of the negative electrode side current collector become complicated.
[0009]
[Means for Solving the Problems]
An object of the present invention is to solve the above-described problems, and the direct methanol fuel cell according to claim 1 has a structure in which a negative electrode and a positive electrode are joined via an electrolyte made of a proton conductive polymer membrane. In a direct methanol fuel cell comprising a cell having an electrode-membrane assembly, a negative electrode-side current collecting sheet provided on the negative electrode side of the electrode-membrane assembly, and a positive electrode-side current collecting sheet provided on the positive electrode side, The negative electrode has a conductive porous material having improved wettability so that a methanol aqueous solution as a fuel can be taken in by a capillary phenomenon as a negative electrode substrate, and a negative electrode catalyst is supported on an electrolyte side surface thereof, The positive electrode has a positive electrode substrate made of a conductive porous material that has been subjected to a water-repellent treatment so that air can be taken in by natural diffusion or natural convection as an oxidant gas, and an electrolyte side surface thereof is used. Characterized in that the positive electrode catalyst is obtained by carrying the.
[0010]
Further, in the direct methanol fuel cell according to claim 2, the conductive porous material of the negative electrode substrate and the positive electrode substrate is a nonwoven fabric or a paper-like or cloth-like sheet made of carbon or graphite fiber. It is characterized by.
[0011]
Further, in the direct methanol fuel cell according to claim 3, the negative electrode substrate has improved wettability by applying a voltage in an acidic aqueous solution using the conductive porous material of the negative electrode substrate as an anode. It is characterized by.
[0012]
Further, in the direct methanol fuel cell according to claim 4, the positive electrode substrate has a water-repellent treatment by immersing a conductive porous material of the positive electrode substrate in a fluororesin dispersion, followed by drying and firing. It is characterized by having been given.
[0013]
A direct methanol fuel cell according to claim 5 is the cell according to at least one of claims 1 to 4, comprising an electrode-membrane assembly, a negative electrode-side current collector sheet, and a positive electrode-side current collector sheet. Is characterized in that an insulating sheet is disposed on at least one surface of the negative electrode side current collecting sheet or the positive electrode side current collecting sheet and is wound into a cylindrical shape.
[0014]
According to the direct methanol fuel cell described above, since the wettability of the conductive porous material of the negative electrode substrate is improved, the methanol aqueous solution can be smoothly taken in by the capillary phenomenon and supplied to the negative electrode catalyst, Since the negative electrode current collector sheet can be disposed on the entire outer surface of the negative electrode that does not contact the electrolyte, the contact between the negative electrode and the negative electrode current collector sheet can be performed without complicating the shape of the negative electrode current collector sheet. Resistance can be reduced. In addition, whether the wettability was improved was determined by whether the conductive porous material of the negative electrode substrate treated with the wettability improvement absorbed 25 ° C. distilled water with respect to the untreated same material. . The reason for this determination is that although the mechanism of improving the wettability is not clear, it is conceivable that this treatment may change the surface morphology and surface condition including surface roughness. In addition, when a water-repellent treatment is performed on the conductive porous material of the positive electrode base material and a positive electrode side current collecting sheet having a through hole such as a punching metal is provided, air is naturally diffused or natural convection through the through hole. It can be taken in smoothly and supplied to the cathode catalyst.
[0015]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the present invention will be described based on the embodiments.
[0016]
FIG. 1 is a sectional view of a direct methanol fuel cell according to the present invention.
[0017]
The direct methanol fuel cell shown in FIG. 1 has an electrode-membrane assembly in which a negative electrode 2 and a positive electrode 3 are joined via an electrolyte 1 made of a proton conductive polymer membrane, and a negative electrode of the electrode-membrane assembly. The cell comprises a negative current collecting sheet 5 provided on the side and a positive current collecting sheet 6 provided on the positive electrode. The negative electrode 2 is made of a conductive porous material having improved wettability so that an aqueous methanol solution can be taken in by capillary action, and has a negative electrode base material, and a negative electrode catalyst ( Platinum-ruthenium powder supported on carbon powder) is supported, and one end of the methanol aqueous solution reaches the fuel holding unit 4 so that the aqueous methanol solution can be supplied to the negative electrode catalyst. The positive electrode 3 is made of a conductive porous material subjected to a water-repellent treatment so that air can be taken in by natural diffusion or natural convection as a positive electrode base material, and has an electrolyte-side surface (a surface in contact with the electrolyte 1). A positive electrode catalyst (platinum powder supported on carbon powder) is supported. The negative electrode-side current collecting sheet 5 and the positive electrode-side current collecting sheet 6 are made of a conductive material such as a metal plate such as stainless steel or a carbon plate, and are introduced such that air is taken in by natural diffusion or natural convection. The positive electrode side current collecting sheet 6 has a through hole. In FIG. 1, the range in which the negative electrode base material carries the negative electrode catalyst is preferably a range facing the positive electrode 3 via the electrolyte 1.
[0018]
The negative electrode substrate is improved in wettability by applying a voltage to the conductive porous material as an anode in an acidic aqueous solution, and the positive electrode substrate is coated with a conductive porous material in a fluororesin dispersion. After the material is immersed, it is subjected to a water-repellent treatment by drying and firing.
[0019]
As a result, the negative electrode base material with improved wettability can be supplied with the methanol aqueous solution to the negative electrode 2 smoothly because one end thereof can reach the fuel holding portion 4 and the methanol aqueous solution can be taken in by the capillary phenomenon. . Further, since the negative electrode-side current collecting sheet 5 can be brought into contact with the entire outer surface of the negative electrode 2 which does not come into contact with the electrolyte 1, the negative electrode current collecting sheet 5 can be formed without complicating the shape as in Patent Document 1 described above. 2 and the contact resistance between the negative electrode side current collecting sheet 5 can be reduced.
[0020]
In addition, the positive electrode substrate provided with water repellency can smoothly take in air by natural diffusion or natural convection.
[0021]
In the above-described embodiment, a method in which the aqueous methanol solution is directly supplied through the negative electrode base material is used. However, a member that comes into contact with the negative electrode 2 is separately provided, the wettability of this member is improved, and methanol is supplied through this member. An aqueous solution may be supplied.
[0022]
Further, in the above-described embodiment, the negative electrode side separator is provided, and the groove processing for supplying the aqueous methanol solution thereto or the positive electrode side separator is provided, and the groove processing for supplying air thereto is performed. Since there is no need, it is advantageous in terms of cost.
[0023]
Further, in the above-described embodiment, the case where the fuel holding unit 4 is provided below the negative electrode 2 is shown, but this positional relationship is not limited to this.
[0024]
As the aqueous methanol solution to be supplied to the fuel holding unit 4, an aqueous methanol solution of about 1 to 2 mol / liter has been used. The concentration can be increased to about 10 mol / l from the viewpoints of improvement in permeability, improvement in output characteristics due to increase in battery temperature, and improvement in energy density, but when the concentration is increased to 10 mol / l or more, It is not preferable because the temperature rise of the battery becomes too large, and the output characteristics decrease due to an increase in the crossover amount of the aqueous methanol solution to the positive electrode side.
[0025]
FIG. 2 is a perspective view in the case where the direct methanol fuel cell according to the above-described embodiment is used as an assembled battery.
[0026]
The battery assembly shown in FIG. 2 has an electrode-membrane assembly in which a negative electrode and a positive electrode are bonded via an electrolyte made of a proton-conductive polymer membrane, a foil material as a negative electrode-side current collecting sheet, and a positive electrode-side current collecting sheet. A cell provided with the above foil material is provided with an insulating sheet on at least one surface of the negative electrode side current collecting sheet or the positive electrode side current collecting sheet, and wound into a cylindrical wound body 9. It is characterized in that five pieces of the negative electrode base material are in contact with the fuel holding sheet 10 and are connected to each other in series by the terminal plate 11.
[0027]
That is, according to the embodiment shown in FIG. 2, the methanol aqueous solution is taken in from the fuel holding sheet 10 by capillary action through the negative electrode base material having improved wettability, and is smoothly supplied to the contact surface between the negative electrode and the electrolyte. In addition, air can be taken in by natural diffusion or natural convection through the water-repellent substrate of the positive electrode, and can be smoothly supplied to the contact surface between the positive electrode and the electrolyte. In addition, since the negative electrode substrate has improved wettability and the positive electrode substrate has been subjected to a water-repellent treatment, the negative electrode can be made into air without being provided with a partition wall between adjacent cells on the circumference by being wound. The positive electrode is not affected by the oxygen contained therein, the positive electrode is not affected by the aqueous methanol solution, and the characteristics of the battery are not affected. Therefore, the assembled battery including such a winding body 9 can be configured simply and compactly without lowering the output characteristics of the battery.
[0028]
【Example】
Hereinafter, examples will be described.
[0029]
(Example)
Using a 200 μm-thick carbon cloth as an anode and a platinum foil as a cathode, a current is applied at a current density of 5 mA / cm ² for 1 hour in a 1 mol / liter sulfuric acid aqueous solution at a temperature of 25 ° C. A negative electrode substrate with improved wettability was obtained by washing and drying. When this carbon cloth was evaluated by the above-described evaluation method, the wettability was 700. Next, the same carbon cloth was immersed in a polytetrafluoroethylene dispersion having a concentration of 5%, dried, and fired at a temperature of 360 ° C. to obtain a positive electrode substrate subjected to a water-repellent treatment. The carbon cloth has a thickness of 200 μm, but can be appropriately selected from 100 to 500 μm. Then, the negative electrode catalyst in which platinum-ruthenium is supported on activated carbon fine particles is dispersed in a solution containing PTFE and Nafion (registered trademark) to form a paste. And 2. Although the total content of platinum and ruthenium in the negative electrode catalyst was 40% by weight, it could be appropriately selected from 10 to 70% by weight, and a platinum: ruthenium weight ratio of 2: 1 was used. , 5: 1 to 1: 2. The weight ratio of the negative electrode catalyst, PTFE, and Nafion (registered trademark) was 55% by weight of the negative electrode catalyst, 15% by weight of PTFE, and 30% by weight of Nafion (registered trademark), but is not limited thereto. On the other hand, a positive electrode catalyst in which platinum is supported on activated carbon fine particles is dispersed in a solution containing PTFE and Nafion (registered trademark) to form a paste. It was set to 3. Although the platinum content of the positive electrode catalyst was 40% by weight, it can be appropriately selected from 10 to 70% by weight. The weight ratio of the positive electrode catalyst, PTFE, and Nafion (registered trademark) was 65% by weight of the positive electrode catalyst, 15% by weight of PTFE, and 20% by weight of Nafion (registered trademark), but is not limited thereto. The negative electrode 2 and the positive electrode 3 thus obtained were pressed at 150 ° C. on both sides of an electrolyte 1 composed of a polymer film made of Nafion 117 (registered trademark), and the negative electrode-side current collecting sheet 5 and the positive electrode as shown in FIG. One end of the above-described negative electrode substrate was sandwiched between the side current collecting sheets 6, and one end of the above-described negative electrode substrate was immersed in the fuel holding unit 4 to manufacture a cell according to an example. The electrolyte 1 has a thickness of 180 μm, but can be appropriately selected from 20 to 200 μm.
[0030]
(Comparative Example 1)
For the cell according to the above-described embodiment, as shown in FIG. 2 of Patent Document 1, the comb-shaped fuel supply member 9 and the anode-side current collector 5 are provided on the outer surface of the anode (the surface not in contact with the electrolyte). Was prepared in such a way that both were fitted to each other, and this was designated as Comparative Example 1. The anode used was the same as the carbon cloth of the example, but did not improve the wettability.
[0031]
(Comparative Example 2)
In contrast to the cell according to the above-described embodiment, a cell in which a carbon cloth whose wettability is not improved is used as a negative electrode substrate, and a negative electrode-side current collecting sheet is disposed on the entire outer surface (a surface not in contact with an electrolyte) of the negative electrode substrate. This was used as Comparative Example 2.
[0032]
(Comparative Example 3)
The cell according to the above example was immersed in a PTFE dispersion having a concentration of 5%, dried, and fired at a temperature of 360 ° C. to perform a water-repellent treatment to obtain a negative electrode substrate. The same cell as in the example was produced, and this was designated as Comparative Example 3.
[0033]
(Experiment 1)
Using the cells according to the above Examples and Comparative Examples 1, 2 and 3, a 10 mol / L aqueous methanol solution was applied to the negative electrode substrate at room temperature (25 ° C.), and the current-voltage characteristics of each cell were measured. The results are shown in FIG.
[0034]
As is clear from FIG. 3, the cell according to the example has better current-voltage characteristics than the cells of comparative examples 1, 2, and 3.
[0035]
(Experiment 2)
Using the cells according to the above Examples and Comparative Examples 1, 2, and 3, 1 ml of a 10 mol / l aqueous methanol solution was applied to the negative electrode substrate at room temperature (25 ° C.) to give a current density of 5 mA / cm ² . It was operated at a constant current, and its voltage change was investigated. The results are shown in FIG.
[0036]
As is clear from FIG. 4, the cell according to the example has a more stable voltage than the cells of Comparative Examples 1, 2, and 3.
[0037]
It is considered that the results of Experiments 1 and 2 are due to the fact that in the cell according to the example, the improvement of the wettability of the negative electrode base material allowed the supply of the methanol aqueous solution to be performed smoothly. In particular, it can be seen that the characteristics of the cell according to the example were significantly improved by performing the treatment for improving the wettability on the carbon cloth as the negative electrode substrate, as compared with the cell according to the comparative example 2. This can be said between the cell according to the example and the cells of Comparative Examples 1 and 3.
[0038]
【The invention's effect】
According to the present invention, since the negative electrode base material having improved wettability so that the methanol aqueous solution as a fuel can be taken in by capillary action is used, the negative electrode side current collector sheet is brought into contact with the entire surface of the negative electrode. it can. Further, since the positive electrode base material subjected to the water repellent treatment so that air can be taken in by natural diffusion or natural convection is used, the air can be smoothly supplied to the positive electrode catalyst. Therefore, it is possible to eliminate the need for a pump for taking in an aqueous methanol solution or air without increasing the resistance between the negative electrode and the negative electrode-side current collecting sheet, thereby directly contributing to downsizing of the methanol fuel cell. .
[0039]
Further, according to the present invention, it is not necessary to provide a negative electrode side separator and perform groove processing for supplying an aqueous methanol solution thereto, or provide a positive electrode side separator and perform groove processing for supplying air thereto. Therefore, the direct methanol fuel cell can be reduced in size and cost.
[0040]
In addition, since the negative electrode substrate has improved wettability and the positive electrode substrate has been subjected to a water-repellent treatment, when a cell is wound, the negative electrode can be air-flowed without providing a partition between adjacent cells on the circumference. Neither is it affected by the oxygen inside, nor is the positive electrode affected by the aqueous methanol solution, and it does not affect the characteristics of the battery. Therefore, the battery pack composed of the wound body can be simply and compactly formed without lowering the output characteristics of the battery.
[Brief description of the drawings]
FIG. 1 is a sectional view of a direct methanol fuel cell according to the present invention.
FIG. 2 is a perspective view of an assembled battery using the direct methanol fuel cell according to the present invention.
FIG. 3 is a diagram comparing current-voltage characteristics.
FIG. 4 is a diagram comparing voltage characteristics during operation at a constant current.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Electrolyte 2 Negative electrode 3 Positive electrode 4 Fuel holding part 5 Negative side current collecting sheet 6 Positive side current collecting sheet 9 Rolled body 10 Fuel holding sheet 11 Terminal plate

Claims

An electrode-membrane assembly in which a negative electrode and a positive electrode are joined via an electrolyte made of a proton-conductive polymer membrane, a negative-side current collecting sheet provided on the negative electrode side of the electrode-membrane assembly, and In a direct methanol fuel cell comprising a cell provided with a positive electrode-side current collecting sheet, the negative electrode is a conductive porous material having improved wettability so that an aqueous methanol solution as a fuel can be introduced by capillary action. Is a negative electrode base material, and a negative electrode catalyst is supported on the electrolyte side surface of the negative electrode substrate. A direct methanol fuel cell characterized in that a porous material is used as a positive electrode substrate and a positive electrode catalyst is supported on the electrolyte side surface thereof.

2. The direct methanol fuel cell according to claim 1, wherein the conductive porous material of the negative electrode substrate and the positive electrode substrate is a nonwoven fabric or a paper-like or cloth-like sheet made of carbon or graphite fibers. Direct methanol fuel cell.

3. The direct methanol fuel cell according to claim 1, wherein the negative electrode substrate has improved wettability by applying a voltage in an acidic aqueous solution using the conductive porous material of the negative electrode substrate as an anode. Features direct methanol fuel cell.

3. The direct methanol fuel cell according to claim 1, wherein the positive electrode substrate has a water-repellent treatment by immersing the conductive porous material of the positive electrode substrate in a dispersion of a fluororesin, followed by drying and firing. Direct methanol fuel cell characterized by being applied.

The direct methanol fuel cell according to at least one of claims 1 to 4, wherein the cell including the electrode-membrane assembly, the negative electrode-side current collector sheet, and the positive electrode-side current collector sheet comprises a negative electrode-side current collector sheet or a positive electrode-side current collector. A direct methanol fuel cell, wherein an insulating sheet is disposed on at least one surface of an electric sheet and wound to form a cylindrical shape.