JP4478009B2 - Fuel cell - Google Patents
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- JP4478009B2 JP4478009B2 JP2004370644A JP2004370644A JP4478009B2 JP 4478009 B2 JP4478009 B2 JP 4478009B2 JP 2004370644 A JP2004370644 A JP 2004370644A JP 2004370644 A JP2004370644 A JP 2004370644A JP 4478009 B2 JP4478009 B2 JP 4478009B2
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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
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/30—Hydrogen technology
- Y02E60/50—Fuel cells
Description
本発明は、固体高分子型燃料電池に関し、詳しくは、電極触媒として、白金とルテニウムとからなる合金（以下、白金／ルテニウム合金と記載する。）を担持させたアノードを有し、このアノードに供給する燃料として、一酸化炭素を含む改質水素を用いながら、一酸化炭素による上記電極触媒の被毒を抑制して、高い出力を発現することができる固体高分子型燃料電池に関する。 The present invention relates to a polymer electrolyte fuel cell. More specifically, the present invention has an anode supporting an alloy composed of platinum and ruthenium (hereinafter referred to as platinum / ruthenium alloy) as an electrode catalyst. The present invention relates to a solid polymer fuel cell capable of expressing high output by suppressing poisoning of the electrode catalyst by carbon monoxide while using reformed hydrogen containing carbon monoxide as a fuel to be supplied.
近年、固体高分子電解質膜を挟んで、白金を担持させたアノードとカソードとを配設して、電極／固体電解質膜／電極構造とし、内側に流路を形成した一対の集電体にて上記電極／固体電解質膜／電極構造の両側を挟み、上記集電体の二つの流路にそれぞれ燃料及び酸素（又は空気）を供給して発電するようにした燃料電池が開発されている。更に、このような燃料電池を積層したり、又は平面的に接続して、電圧、出力を向上させて、システムに組み込むことについても研究されている。 In recent years, a pair of current collectors having an electrode / solid electrolyte membrane / electrode structure in which an anode and a cathode supporting platinum are disposed with a solid polymer electrolyte membrane sandwiched therebetween, and a flow path is formed inside. A fuel cell has been developed in which both sides of the electrode / solid electrolyte membrane / electrode structure are sandwiched to generate power by supplying fuel and oxygen (or air) to the two flow paths of the current collector, respectively. Furthermore, research is also being conducted into stacking such fuel cells or connecting them in a planar manner to improve the voltage and output and incorporate them into the system.
このような燃料電池は、クリーンで且つ高効率であり、更に、従来の二次電池のように長時間の充電が不要であって、燃料を供給し続ければ、実質的に連続して用いることができるという特徴から、種々の用途、特に、電気自動車用電源、家庭用分散型電源、携帯機器用電源等として注目されている。 Such a fuel cell is clean and highly efficient. Further, unlike a conventional secondary battery, it does not require charging for a long time and can be used substantially continuously if fuel is continuously supplied. Therefore, it has been attracting attention as a power source for electric vehicles, a distributed power source for home use, a power source for portable devices, and the like.
一方、アノードに供給する燃料としては、代表的なものとして、純水素や、改質触媒を用いてアルコール類や炭化水素類等の燃料から生成させた水素（以後、改質水素ということがある。）等の気体燃料、メタノール、ジメチルエーテル、エチレングリコール、多価アルコール等と水との混合液体燃料等が検討されているが、課題も残されている。即ち、一般に、液体燃料を用いる燃料電池は出力が低く、一方、気体燃料を用いる燃料電池は、貯蔵、運搬の点で体積エネルギー密度が低い。 On the other hand, as a typical fuel to be supplied to the anode, pure hydrogen or hydrogen generated from a fuel such as alcohols or hydrocarbons using a reforming catalyst (hereinafter referred to as reformed hydrogen may be used). Gas fuels such as methanol, dimethyl ether, ethylene glycol, polyhydric alcohols, etc. and water, etc. are being studied, but problems remain. That is, in general, a fuel cell using liquid fuel has a low output, while a fuel cell using gaseous fuel has a low volumetric energy density in terms of storage and transportation.
そこで、燃料電池本体だけでなく、改質器をもシステムに搭載して、液体燃料から改質水素を発生させながら、同時に発電する方法が提案されている。しかし、改質水素には、改質反応によって発生する一酸化炭素が残留しており、これが白金触媒を被毒して、燃料電池の出力を低下させるという問題がある。このため、一酸化炭素を除去する装置を改質器に付加する方策もあるが、しかし、このような方策によれば、システム全体が大型化するので、スペースの限られた携帯機器用途や車載用途では問題となり、かくして、被毒の影響がなくなるレベルまで、一酸化炭素の含量を減らすことができないのが現状である。 Therefore, a method has been proposed in which not only the fuel cell main body but also a reformer is mounted in the system, and reformed hydrogen is generated from the liquid fuel while simultaneously generating power. However, carbon monoxide generated by the reforming reaction remains in the reformed hydrogen, which has a problem that the platinum catalyst is poisoned to reduce the output of the fuel cell. For this reason, there is a measure to add a device for removing carbon monoxide to the reformer. However, according to such a measure, the entire system is enlarged, so that it can be used for portable devices with limited space and in-vehicle use. The current situation is that the content of carbon monoxide cannot be reduced to such a level that it becomes a problem in use, and thus the level of the influence of poisoning is eliminated.
そこで、別の方法として、白金よりも被毒を受け難い電極触媒として、白金とルテニウム合金に代表される種々の白金合金触媒が提案されているが、しかし、未だにその効果は十分でない。 Thus, as another method, various platinum alloy catalysts represented by platinum and ruthenium alloys have been proposed as electrode catalysts that are less susceptible to poisoning than platinum, but the effect is still not sufficient.
本発明は、電極触媒として、白金又は白金合金を担持させたアノードを有し、このアノードに改質水素を燃料として供給する固体高分子型燃料電池料における上述した問題を解決するためになされたものであって、改質水素に含まれる一酸化炭素による電極触媒の被毒を抑制して、高い出力を発現することができる固体高分子型燃料電池を提供することを目的とする。 The present invention has been made to solve the above-described problems in a polymer electrolyte fuel cell material having an anode supporting platinum or a platinum alloy as an electrode catalyst and supplying reformed hydrogen as a fuel to the anode. An object of the present invention is to provide a polymer electrolyte fuel cell capable of suppressing the poisoning of the electrode catalyst by carbon monoxide contained in the reformed hydrogen and exhibiting high output.
本発明によれば、プロトン伝導性イオン交換電解質膜を挟んで、カソードとアノードとを配設し、上記カソードに酸素を供給し、上記アノードに一酸化炭素を含む水素を供給する燃料電池において、カソードが導電性多孔質基材上に白金又は白金合金とプロトン伝導性イオン交換電解質ポリマーとを含んでなる電極触媒層を担持させてなり、アノードが導電性多孔質基材上に吸水性ポリマーと導電性炭素粉末とを含んでなる厚み２０μｍ〜１００μｍの導電性保水層とこの導電性保水層上に白金／ルテニウム合金とプロトン伝導性イオン交換電解質ポリマーとを含んでなる電極触媒層とを担持させてなることを特徴とする燃料電池が提供される。 According to the present invention, in a fuel cell in which a cathode and an anode are disposed with a proton conducting ion exchange electrolyte membrane interposed therebetween, oxygen is supplied to the cathode, and hydrogen containing carbon monoxide is supplied to the anode. The cathode has an electrocatalyst layer comprising platinum or a platinum alloy and a proton conducting ion exchange electrolyte polymer supported on a conductive porous substrate, and the anode has a water absorbing polymer on the conductive porous substrate. A conductive water retaining layer having a thickness of 20 μm to 100 μm comprising conductive carbon powder and an electrode catalyst layer comprising a platinum / ruthenium alloy and a proton conductive ion exchange electrolyte polymer are supported on the conductive water retaining layer. A fuel cell is provided.
本発明によれば、導電性多孔質基材上に吸水性ポリマーと導電性炭素粉末とを含んでなる厚み２０μｍ〜１００μｍの導電性保水層とこの導電性保水層上に白金／ルテニウム合金とプロトン伝導性イオン交換電解質ポリマーとを含んでなる電極触媒層を担持させてアノードとすることによって、そのようなアノードに一酸化炭素を含む水素を燃料として供給しても、アノードの電極触媒は被毒が抑制されて、高い出力を有する燃料電池を得ることができる。 According to the present invention, a conductive water retaining layer having a thickness of 20 μm to 100 μm comprising a water-absorbing polymer and a conductive carbon powder on a conductive porous substrate, and a platinum / ruthenium alloy and proton on the conductive water retaining layer. By supporting an electrode catalyst layer containing a conductive ion-exchange electrolyte polymer as an anode, even if hydrogen containing carbon monoxide is supplied as a fuel to such an anode, the electrode catalyst of the anode is poisoned. Is suppressed, and a fuel cell having a high output can be obtained.
本発明による燃料電池は、導電性多孔質基材上に白金又は白金合金とプロトン伝導性イオン交換電解質ポリマーとを含んでなる電極触媒層を担持させてなるカソードと、導電性多孔質基材上に吸水性ポリマーと導電性炭素粉末とを含んでなる厚み２０μｍ〜１００μｍの導電性保水層とこの導電性保水層上に白金／ルテニウム合金とプロトン伝導性イオン交換電解質ポリマーとを含んでなる電極触媒層とを担持させてなるものである。 A fuel cell according to the present invention comprises a cathode on which an electrode catalyst layer comprising platinum or a platinum alloy and a proton conductive ion exchange electrolyte polymer is supported on a conductive porous substrate, and a conductive porous substrate. An electrocatalyst comprising a water-absorbing polymer and a conductive carbon powder having a thickness of 20 μm to 100 μm and a platinum / ruthenium alloy and a proton-conducting ion-exchange electrolyte polymer on the electroconductive water-retaining layer A layer is supported.
本発明において、カソードとアノードは、一般的には、導電性多孔質基材上に電極触媒層を形成してなるものであり、電極触媒層は、例えば、白金や白金合金のような貴金属微粒子を担持させたカーボンブラック粉末又は貴金属触媒の微粒子と、必要に応じて、導電助剤としてのカーボンブラック粉末と、これらを結着させる結着剤と、電気化学反応によって発生するプロトンの伝導体となるプロトン伝導性イオン交換電解質ポリマーとからなる。ここに、プロトン伝導性イオン交換電解質ポリマーを上記結着剤として用いることもできる。 In the present invention, the cathode and the anode are generally formed by forming an electrode catalyst layer on a conductive porous substrate, and the electrode catalyst layer includes, for example, noble metal fine particles such as platinum and a platinum alloy. Carbon black powder or noble metal catalyst fine particles supporting carbon, if necessary, carbon black powder as a conductive auxiliary agent, a binder for binding them, and a conductor for protons generated by an electrochemical reaction; And a proton conducting ion exchange electrolyte polymer. Here, a proton conductive ion exchange electrolyte polymer can also be used as the binder.
より詳しくは、カソードは、導電性多孔質基材上に白金又は白金合金（例えば、白金／ルテニウム合金）とプロトン伝導性イオン交換電解質ポリマーを含んでなる電極触媒層を担持させてなるものであって、例えば、次のようにして製造される。即ち、白金微粒子を担持させた導電性カーボンブラック粉末又は貴金属触媒の微粒子と、必要に応じて、導電助剤としてのカーボンブラックとを適宜の結着剤（例えば、ポリフッ化ビニリデン樹脂のＮ−メチル−２−ピロリドン溶液やデュポン社製のナフィオン（登録商標）のようなパーフルオロスルホン酸樹脂溶液）を用いてペーストとし、これを導電性多孔質基材（例えば、東レ（株）製カーボンペーパー）上に塗布し、加熱、乾燥させた後、、更に、その上にプロトン伝導性イオン交換電解質ポリマー（例えば、デュポン社製のナフィオン）の溶液を塗布し、、加熱、乾燥させることによって、カソードを得ることができる。しかし、本発明において、カソードの製造方法は、特に限定されるものではない。 More specifically, the cathode is formed by supporting an electrocatalyst layer containing platinum or a platinum alloy (for example, platinum / ruthenium alloy) and a proton conductive ion exchange electrolyte polymer on a conductive porous substrate. For example, it is manufactured as follows. That is, a conductive carbon black powder or precious metal catalyst fine particles supporting platinum fine particles and, if necessary, carbon black as a conductive auxiliary agent are combined with an appropriate binder (for example, N-methyl of polyvinylidene fluoride resin). 2-Pyrrolidone solution or a perfluorosulfonic acid resin solution such as Nafion (registered trademark) manufactured by DuPont, which is used as a paste, and this is made into a conductive porous substrate (for example, carbon paper manufactured by Toray Industries, Inc.) After coating on, heating and drying, a cathode conductive ion exchange electrolyte polymer (for example, Nafion manufactured by DuPont) is further coated thereon, and the cathode is heated and dried. Obtainable. However, in the present invention, the method for producing the cathode is not particularly limited.
アノードは、導電性多孔質基材上に吸水性ポリマーと導電性炭素粉末とを含んでなる厚み２０μｍ〜１００μｍの導電性保水層を有すると共に、この導電性保水層上に白金／ルテニウム合金とプロトン伝導性イオン交換電解質ポリマーとを含んでなる電極触媒層を担持させてなるものである。 The anode has a conductive water retention layer having a thickness of 20 μm to 100 μm comprising a water-absorbing polymer and a conductive carbon powder on a conductive porous substrate, and a platinum / ruthenium alloy and a proton on the conductive water retention layer. An electrode catalyst layer comprising a conductive ion exchange electrolyte polymer is supported.
上述したように、アノードは、導電性多孔質基材上に導電性保水層を有し、この導電性保水層上に電極触媒層を形成した層構造を有するが、ここに、本発明によれば、導電性多孔質基材の表面層のある深さまで、基材の多孔質構造中に導電性保水層の一部が形成されている態様をも上記層構造は含むものとする。即ち、本発明によれば、導電性保水層は、その一部が導電性多孔質基材の表面層のある深さまで、基材の表面層内に形成されていてもよい。従って、本発明によれば、導電性保水層は、少なくとも一部が導電性多孔質基材の表面上にある。 As described above, the anode has a layer structure in which a conductive water retention layer is provided on a conductive porous substrate and an electrode catalyst layer is formed on the conductive water retention layer. For example, the layer structure includes an aspect in which a part of the conductive water retention layer is formed in the porous structure of the substrate up to a certain depth of the surface layer of the conductive porous substrate. That is, according to the present invention, the conductive water retention layer may be partially formed in the surface layer of the substrate to a certain depth of the surface layer of the conductive porous substrate. Therefore, according to the present invention, the conductive water retention layer is at least partially on the surface of the conductive porous substrate.
本発明において、上記吸水性ポリマーは、特に限定されるものではないが、一例として分子中にカルボキシル基、スルホン酸基、ホスホン酸基、ホスフィン酸基及びリン酸基よりなる群から選ばれる少なくとも１種の酸基を有するポリマーが好ましく用いられる。上記酸基は、エステル又はアルカリ金属塩の形であってもよい。従って、例えば、分子中にスルホン酸基を有するプロトン伝導性イオン交換電解質ポリマー（例えば、デュポン社製のナフィオン）は、本発明において、吸水性ポリマーとして好ましく用いられる。 In the present invention, the water-absorbing polymer is not particularly limited, but as an example, at least one selected from the group consisting of a carboxyl group, a sulfonic acid group, a phosphonic acid group, a phosphinic acid group, and a phosphoric acid group in the molecule. Polymers having seed acid groups are preferably used. The acid group may be in the form of an ester or an alkali metal salt. Therefore, for example, a proton conductive ion exchange electrolyte polymer having a sulfonic acid group in the molecule (for example, Nafion manufactured by DuPont) is preferably used as the water absorbing polymer in the present invention.
このように、アノードは、導電性多孔質基材上に上記導電性保水層と白金／ルテニウム合金とを含んでなる電極触媒層とを有するものであるので、アノードは、導電性多孔質基材上に導電性保水層を形成し、この上に電極触媒層を形成する以外は、カソードと同様にして調製することができる。 Thus, since the anode has the electroconductive water retention layer and the electrode catalyst layer comprising the platinum / ruthenium alloy on the conductive porous substrate, the anode is formed of the conductive porous substrate. It can be prepared in the same manner as the cathode except that a conductive water retention layer is formed thereon and an electrode catalyst layer is formed thereon.
例えば、導電性カーボンブラック粉末と吸水性ポリマーとしてのプロトン伝導性イオン交換電解質ポリマーの溶液（例えば、デュポン社製ナフィオン）とを混合してペーストとし、このペーストを導電性多孔質基材（例えば、東レ（株）製カーボンペーパー）上に塗布し、加熱、乾燥させることによって、導電性多孔質基材上に導電性保水層を形成する。この場合において、例えば、プロトン伝導性イオン交換電解質ポリマー溶液に対する導電性カーボンブラック粉末の割合を低減して、得られるペーストの粘度を小さくし、そのようなペーストを導電性多孔質基材の表面に塗布して、ペーストを基材の表面層のある深さまで浸透させ、含浸させた後、加熱、乾燥させることによって、前述したように、導電性多孔質基材の表面層の多孔質構造中に導電性保水層を形成することができる。 For example, a conductive carbon black powder and a proton conductive ion exchange electrolyte polymer solution (for example, Nafion manufactured by DuPont) as a water-absorbing polymer are mixed to form a paste, and this paste is formed into a conductive porous substrate (for example, A conductive water-retaining layer is formed on the conductive porous substrate by coating on carbon paper manufactured by Toray Industries, Inc., heating and drying. In this case, for example, the ratio of the conductive carbon black powder to the proton conductive ion exchange electrolyte polymer solution is reduced to reduce the viscosity of the obtained paste, and such paste is applied to the surface of the conductive porous substrate. After applying and infiltrating the paste to a certain depth of the surface layer of the substrate, impregnating it, heating and drying, as described above, into the porous structure of the surface layer of the conductive porous substrate A conductive water retention layer can be formed.
このようにして、導電性多孔質基材上に導電性保水層を形成した後、白金／ルテニウム合金の微粒子を担持させた導電性カーボンブラック粉末と、必要に応じて、導電助剤としてのカーボンブラックとを適宜の結着剤（例えば、ポリフッ化ビニリデン樹脂のＮ−メチル−２−ピロリドン溶液やデュポン社製のナフィオン（登録商標）のようなパーフルオロスルホン酸樹脂溶液）を用いてペーストとし、これを上記導電性保水層に塗布し、乾燥させて、電極触媒層を形成し、更に、プロトン伝導性樹脂以外のポリマーを結着剤として用いた場合には、触媒層にプロトン伝導性を付与するために、更に、その上にプロトン伝導性イオン交換電解質ポリマー（例えば、デュポン社製のナフィオン）の溶液を塗布し、次いで、加熱、乾燥させることによって、アノードを得ることができる。しかし、本発明において、アノードの製造方法は、特に限定されるものではない。 Thus, after forming a conductive water retention layer on the conductive porous substrate, conductive carbon black powder carrying platinum / ruthenium alloy fine particles, and, if necessary, carbon as a conductive aid. Black and paste with an appropriate binder (for example, N-methyl-2-pyrrolidone solution of polyvinylidene fluoride resin and perfluorosulfonic acid resin solution such as Nafion (registered trademark) manufactured by DuPont), This is applied to the conductive water retention layer and dried to form an electrode catalyst layer. When a polymer other than the proton conductive resin is used as a binder, proton conductivity is imparted to the catalyst layer. In addition, a solution of a proton conductive ion exchange electrolyte polymer (for example, Nafion manufactured by DuPont) is applied thereon, and then heated and dried. It, it is possible to obtain the anode. However, in the present invention, the anode manufacturing method is not particularly limited.
本発明によれば、上記導電性保水層は、その厚みが２０μｍ〜１００μｍの範囲にあることが必要である。導電性保水層の厚みが２０μｍよりも小さいときは、電極触媒の一酸化炭素による被毒を抑制するには、導電性保水層の保水性が不十分である。他方、導電性保水層の厚みが１００μｍを越えるときは、燃料ガスの電極触媒層への拡散が遅くなって、得られる燃料電池の出力密度が却って低下する。 According to the present invention, the conductive water retention layer needs to have a thickness in the range of 20 μm to 100 μm. When the thickness of the conductive water retention layer is smaller than 20 μm, the water retention property of the conductive water retention layer is insufficient to suppress poisoning by carbon monoxide of the electrode catalyst. On the other hand, when the thickness of the conductive water retention layer exceeds 100 μm, the diffusion of the fuel gas into the electrode catalyst layer is delayed, and the output density of the obtained fuel cell is decreased.
白金を電極触媒とする燃料電池が電極触媒の一酸化炭素被毒によって出力が低下するのは、電極触媒表面に一酸化炭素が吸着し、燃料である水素分子の電極触媒への吸着を妨げて、燃料の酸化反応を阻害するからである。これに対して、白金／ルテニウム合金を電極触媒とする燃料電池においては、ルテニウムと水分子とから形成される化学種が白金表面に吸着した一酸化炭素を二酸化炭素に酸化するので、一酸化炭素は二酸化炭素として白金表面から除去され、かくして、電極触媒の一酸化炭素被毒が改善される。 The output of a fuel cell using platinum as an electrode catalyst decreases due to the carbon monoxide poisoning of the electrode catalyst because carbon monoxide is adsorbed on the surface of the electrode catalyst, preventing the adsorption of hydrogen molecules as fuel to the electrode catalyst. This is because the oxidation reaction of the fuel is inhibited. In contrast, in a fuel cell using a platinum / ruthenium alloy as an electrode catalyst, chemical species formed from ruthenium and water molecules oxidize carbon monoxide adsorbed on the platinum surface to carbon dioxide, so carbon monoxide. Is removed from the platinum surface as carbon dioxide, thus improving the carbon monoxide poisoning of the electrocatalyst.
ここに、本発明によれば、アノードにおいて、導電性多孔質基材と白金／ルテニウム合金からなる電極触媒層との間に導電性保水層を形成し、電極触媒領域の水分濃度を高めて、上記白金表面における一酸化炭素の二酸化炭素への酸化を促進するので、アノードにおける電極触媒の一酸化炭素被毒が一層抑制されるものとみられる。但し、本発明は、アノードにおける電極触媒の一酸化炭素被毒が抑制される機構によって何ら制約を受けるものではない。
本発明による燃料電池においては、プロトン伝導性イオン交換電解質膜には、従来の固体高分子膜型電池に用いられているようなパーフルオロスルホン酸樹脂からなる陽イオン交換膜、例えば、ナフィオン（登録商標）が好適に用いられるが、しかし、これに限定されるものではない。従って、例えば、ポリテトラフルオロエチレン等のフッ素樹脂からなる多孔質膜に上記ナフィオンや他のプロトン伝導性物質を含浸させたものや、ポリエチレンやポリプロピレン等のポリオレフィン樹脂からなる多孔質膜や不織布に上記ナフィオンや他のプロトン伝導性物質を担持させたものでもよい。
Here, according to the present invention, in the anode, a conductive water retention layer is formed between the conductive porous substrate and the electrode catalyst layer made of a platinum / ruthenium alloy, and the moisture concentration in the electrode catalyst region is increased. Since the oxidation of carbon monoxide to carbon dioxide on the platinum surface is promoted, it is considered that the carbon monoxide poisoning of the electrode catalyst at the anode is further suppressed. However, the present invention is not limited by the mechanism by which carbon monoxide poisoning of the electrode catalyst at the anode is suppressed.
In the fuel cell according to the present invention, the proton conductive ion exchange electrolyte membrane includes a cation exchange membrane made of a perfluorosulfonic acid resin, such as Nafion (registered), as used in a conventional polymer electrolyte membrane battery. (Trademark) is preferably used, but is not limited thereto. Therefore, for example, a porous membrane made of a fluororesin such as polytetrafluoroethylene impregnated with the above Nafion or other proton conductive material, or a porous membrane or nonwoven fabric made of a polyolefin resin such as polyethylene or polypropylene A material carrying Nafion or another proton conductive material may be used.
本発明による燃料電池においては、カソードに酸素が気体で供給され、アノードに一酸化炭素を含む水素が気体で供給される。上記酸素は、空気であってもよい。また、一酸化炭素を含む水素としては、例えば、改質触媒を用いてアルコール類や炭化水素類等の燃料から生成させた改質水素が好ましく用いられる。特に、本発明による燃料電池においては、一酸化炭素を１０〜５０００ｐｐｍの範囲で含む改質水素を燃料としても、アノードの電極触媒の被毒をよく抑制して、長期間にわたって、高い出力を得ることができる。 In the fuel cell according to the present invention, oxygen is supplied as a gas to the cathode, and hydrogen containing carbon monoxide is supplied as a gas to the anode. The oxygen may be air. Moreover, as hydrogen containing carbon monoxide, for example, reformed hydrogen generated from a fuel such as alcohols or hydrocarbons using a reforming catalyst is preferably used. In particular, in the fuel cell according to the present invention, even when reformed hydrogen containing carbon monoxide in the range of 10 to 5000 ppm is used as a fuel, poisoning of the anode electrode catalyst is well suppressed, and high output is obtained over a long period of time. be able to.
改質水素を製造する方法は、既によく知られており、例えば、メタノールの改質であれば、改質触媒を用いてメタノールを水蒸気改質すると共に、一酸化炭素改質を行って、水素と二酸化炭素を得ることができる。このようなメタノールの改質による改質水素は、尚、多くの一酸化炭素を含むので、一酸化炭素を選択的に二酸化炭素に接触酸化すれば、一酸化炭素を数百ｐｐｍまで低減することができる。しかし、本発明において、燃料として用いる一酸化炭素を含む水素の由来は、特に限定されるものではない。 A method for producing reformed hydrogen is already well known. For example, in the case of reforming of methanol, methanol is steam reformed using a reforming catalyst and carbon monoxide reforming is performed. And get carbon dioxide. Such reformed hydrogen produced by reforming methanol still contains a large amount of carbon monoxide, so that carbon monoxide can be reduced to several hundred ppm by selectively oxidizing carbon monoxide to carbon dioxide. Can do. However, in the present invention, the origin of hydrogen containing carbon monoxide used as fuel is not particularly limited.
また、本発明による燃料電池の作動温度は、通常、０℃以上であり、１５〜１２０℃の範囲が好ましく、特に、３０〜１００℃の範囲が好ましい。作動温度が高すぎるときは用いる材料の劣化や剥離等が起こるおそれがある。 Moreover, the operating temperature of the fuel cell according to the present invention is usually 0 ° C. or higher, preferably in the range of 15 to 120 ° C., particularly preferably in the range of 30 to 100 ° C. When the operating temperature is too high, the material used may be deteriorated or peeled off.
以下に実施例を挙げて本発明を説明するが、本発明はこれら実施例により何ら限定されるものではない。 EXAMPLES The present invention will be described below with reference to examples, but the present invention is not limited to these examples.
実施例１
（カソードの調製）
白金を２０重量％担持させた導電性カーボンブラック粉末１８０ｍｇ、導電性カーボンブラック３６ｍｇ、ポリフッ化ビニリデン２４ｍｇ及びＮ−メチル−２−ピロリドン９４０ｍｇを乳鉢にて混合して、ペーストとした。このペーストを２．３ｃｍ角のカーボンペーパー（東レ（株）製ＴＧＰ−Ｈ−９０、膜厚２６０μｍ）の片面上に塗布し、８０℃で６０分間加熱して、乾燥させた。このようにして調製した白金担持カーボンペーパーにおいて、固形分担持量は２０ｍｇであり、そのうち、白金の担持量は３ｍｇ（電極触媒単位面積当たりの担持量は０．５７ｍｇ／ｃｍ2）であった。次いで、この白金担持カーボンペーパーの白金担持表面の上にプロトン伝導性イオン交換電解質ポリマーであるナフィオン（登録商標）の５重量％アルコール系溶液（アルドリッチ社製）を塗布し、８０℃で３０分間、加熱し、乾燥させて、カーボンペーパー上に電極触媒層を有するカソードを得た。
Example 1
(Preparation of cathode)
180 mg of conductive carbon black powder carrying 20% by weight of platinum, 36 mg of conductive carbon black, 24 mg of polyvinylidene fluoride and 940 mg of N-methyl-2-pyrrolidone were mixed in a mortar to obtain a paste. This paste was applied onto one side of a 2.3 cm square carbon paper (TGP-H-90 manufactured by Toray Industries, Inc., film thickness 260 μm), heated at 80 ° C. for 60 minutes, and dried. In the thus-prepared platinum-supported carbon paper, the solid content was 20 mg, of which the platinum load was 3 mg (the supported amount per electrode catalyst unit area was 0.57 mg / cm 2 ). Next, a 5% by weight alcohol-based solution (manufactured by Aldrich) of Nafion (registered trademark), which is a proton-conductive ion exchange electrolyte polymer, is applied onto the platinum-supporting surface of the platinum-supporting carbon paper. It heated and dried and obtained the cathode which has an electrode catalyst layer on carbon paper.
（アノードの調製）
ナフィオンの２０重量％アルコール溶液２５ｇと導電性カーボンブラック（キャボット・スペシャルティ・ケミカルズ社製バルカンＸＣ７２Ｒ）５ｇとをボールミルて混合し、ペーストとした。このペーストをカーボンペーパー（上記と同じ。）の片面上に塗布し、８０℃で３０分間加熱し、乾燥させて、カーボンペーパー上に導電性保水層を形成した。この導電性保水層の厚みは、電子顕微鏡観察の結果、３０μｍであった。
(Preparation of anode)
25 g of Nafion 20 wt% alcohol solution and 5 g of conductive carbon black (Vulcan XC72R manufactured by Cabot Specialty Chemicals) were mixed by a ball mill to obtain a paste. This paste was applied on one side of carbon paper (same as above), heated at 80 ° C. for 30 minutes, and dried to form a conductive water retention layer on the carbon paper. The thickness of this electroconductive water retention layer was 30 micrometers as a result of electron microscope observation.
次いで、白金／ルテニウム合金（白金／ルテニウム重量比２／１）３０重量％担持させた導電性カーボンブラック粉末１２０ｍｇ、導電性カーボンブラック９６ｍｇ、ポリフッ化ビニリデン２４ｍｇ及びＮ−メチル−２−ピロリドン９４０ｍｇを乳鉢にて混合して、ペーストとした。このペーストを上記導電性保水層上に塗布し、８０℃で６０分間加熱して、乾燥させ、電極触媒層を形成した。このようにして調製した電極触媒層において、固形分担持量は１０ｍｇであり、そのうち、白金／ルテニウム合金の担持量は１．５ｍｇ（電極触媒単位面積当たりの担持量は０．２８ｍｇ／ｃｍ2）であった。 Next, 120 mg of conductive carbon black powder loaded with 30% by weight of a platinum / ruthenium alloy (platinum / ruthenium weight ratio 2/1), 96 mg of conductive carbon black, 24 mg of polyvinylidene fluoride and 940 mg of N-methyl-2-pyrrolidone were used in a mortar. To make a paste. This paste was applied onto the conductive water retention layer, heated at 80 ° C. for 60 minutes, and dried to form an electrode catalyst layer. In the electrode catalyst layer thus prepared, the solid content loading was 10 mg, of which the platinum / ruthenium alloy loading was 1.5 mg (the loading per electrode catalyst unit area was 0.28 mg / cm 2 ). Met.
次いで、この白金／ルテニウム合金担持カーボンペーパーの白金／ルテニウム合金担持表面の上にプロトン伝導性イオン交換電解質ポリマーであるナフィオン（登録商標）の５重量％アルコール系溶液（アルドリッチ社製）を塗布し、８０℃で３０分間、加熱し、乾燥させて、カーボンペーパー上に電極触媒層を有するアノードを得た。 Next, a 5% by weight alcohol-based solution (manufactured by Aldrich) of Nafion (registered trademark), which is a proton-conductive ion exchange electrolyte polymer, is applied onto the platinum / ruthenium alloy-supported surface of the platinum / ruthenium alloy-supported carbon paper. It was heated at 80 ° C. for 30 minutes and dried to obtain an anode having an electrode catalyst layer on carbon paper.
（燃料電池の特性の評価）
このようにして得られたカソードとアノードとの間にプロトン伝導性イオン交換電解質膜として酸型ナフィオン膜（デュボン社製ナフィオン１１２）を置き、金型を用いて、窒素雰囲気中、温度１３５℃の条件下、ホットプレスにて加熱加圧して、電極／プロトン伝導膜接合体を得、これを用いて試験用の単層の燃料電池セルを組み立てた。
(Evaluation of fuel cell characteristics)
An acid type Nafion membrane (Dubon Nafion 112) was placed as a proton conductive ion exchange electrolyte membrane between the cathode and the anode thus obtained, and the temperature was 135 ° C. in a nitrogen atmosphere using a mold. Under conditions, heating / pressurization was performed by a hot press to obtain an electrode / proton conductive membrane assembly, and a single-layer fuel cell for testing was assembled using this.
この燃料電池セルを燃料電池評価装置（東陽テクニカ（株）製、以下、同じ）に組み込み、セル温度３０℃とし、加湿器温度３０℃で酸素ガスを５００ｍＬ／分の割合でカソードに供給すると共に、加湿器温度３０℃で水素／二酸化炭素混合ガス（水素／二酸化炭素モル比７５／２５、一酸化炭素を２００ｐｐｍ含む。）を５００ｍＬ／分の割合でアノードに供給した。供給ガス圧力は常圧とした。この条件下に電流電圧特性（Ｉ−Ｖ）特性を求め、これより電池の出力密度を求めたところ、電圧０．６Ｖにおいて３５ｍＷ／ｃｍ2 であった。 This fuel cell is incorporated into a fuel cell evaluation apparatus (manufactured by Toyo Technica Co., Ltd., hereinafter the same), the cell temperature is set to 30 ° C., and oxygen gas is supplied to the cathode at a humidifier temperature of 30 ° C. at a rate of 500 mL / min. Then, a hydrogen / carbon dioxide mixed gas (hydrogen / carbon dioxide molar ratio 75/25, containing 200 ppm of carbon monoxide) was supplied to the anode at a rate of 500 mL / min at a humidifier temperature of 30 ° C. The supply gas pressure was normal pressure. Under this condition, the current-voltage characteristic (IV) characteristic was determined, and the output density of the battery was determined from this, and it was 35 mW / cm 2 at a voltage of 0.6V.
実施例２
アノードの調製に際して、プロトン伝導性保水層の厚みを１００μｍとした以外は、実施例１と同様にして、アノードを調製した。実施例１と同様にして、試験用の単層の燃料電池セルを組み立て、その電池の出力密度を求めたところ、電圧０．６Ｖにおいて３０ｍＷ／ｃｍ2 であった。
Example 2
In preparing the anode, an anode was prepared in the same manner as in Example 1 except that the thickness of the proton conductive water retention layer was changed to 100 μm. A single-layer fuel cell for test was assembled in the same manner as in Example 1, and the output density of the battery was determined. As a result, it was 30 mW / cm 2 at a voltage of 0.6V.
実施例３
実施例１において、アノードの調製に際して、ナフィオンの２０重量％アルコール溶液２５ｇと導電性カーボンブラック（キャボット・スペシャルティ・ケミカルズ社製バルカンＸＣ７２Ｒ）２ｇとをボールミルにて混合し、ペーストとし、このペーストをカーボンペーパー（上記と同じ。）の片面上に塗布し、カーボンペーパーの表面からある深さまで浸透、含浸させた後、８０℃で３０分間加熱し、乾燥させて、導電性保水層をその一部がカーボンペーパーの表面層内にあるように形成した。この導電性保水層の厚みは、電子顕微鏡観察の結果、５０μｍであった。
Example 3
In Example 1, when preparing the anode, 25 g of a 20% by weight alcohol solution of Nafion and 2 g of conductive carbon black (Vulcan XC72R manufactured by Cabot Specialty Chemicals) were mixed in a ball mill to obtain a paste. After coating on one side of the paper (same as above), penetrating and impregnating from the surface of the carbon paper to a certain depth, heating at 80 ° C. for 30 minutes and drying to make a part of the conductive water retention layer. It formed so that it might exist in the surface layer of carbon paper. The thickness of this electroconductive water retention layer was 50 micrometers as a result of electron microscope observation.
このようにして、導電性保水層を形成した以外は、実施例１と同様にして、試験用の単層の燃料電池セルを組み立て、その電池の出力密度を求めたところ、電圧０．６Ｖにおいて３４ｍＷ／ｃｍ2 であった。 In this way, a single layer fuel cell for test was assembled and the output density of the battery was determined in the same manner as in Example 1 except that the conductive water retention layer was formed. It was 34 mW / cm 2 .
比較例１
実施例１において、カーボンペーパー上にプロトン伝導性保水層を形成しなかった以外は同様にして、アノードを調製し、実施例１と同様にして、試験用の単層の燃料電池セルを組み立て、その電池の出力密度を求めたところ、電圧０．６Ｖにおいて１５ｍＷ／ｃｍ2 であった。
Comparative Example 1
In Example 1, an anode was prepared in the same manner except that the proton-conductive water-retaining layer was not formed on the carbon paper, and a test single-layer fuel cell was assembled in the same manner as in Example 1. When the output density of the battery was determined, it was 15 mW / cm 2 at a voltage of 0.6V.
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