JP2007117810A - Hydrogen permeable membrane and fuel cell using the same - Google Patents

Hydrogen permeable membrane and fuel cell using the same Download PDF

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JP2007117810A
JP2007117810A JP2005310225A JP2005310225A JP2007117810A JP 2007117810 A JP2007117810 A JP 2007117810A JP 2005310225 A JP2005310225 A JP 2005310225A JP 2005310225 A JP2005310225 A JP 2005310225A JP 2007117810 A JP2007117810 A JP 2007117810A
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hydrogen
hydrogen permeable
membrane
intermediate layer
film
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Osamu Mizuno
修 水野
Masahiko Iijima
昌彦 飯島
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Sumitomo Electric Industries Ltd
Toyota Motor Corp
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Toyota Motor Corp
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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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Abstract

<P>PROBLEM TO BE SOLVED: To provide a hydrogen permeable membrane which is composed of a Pd membrane, a hydrogen permeable base material using V or a V alloy and an intermediate layer containing other elements of the group V, and can suppress the degradation of hydrogen permeability with time by oxidation, and to provide a fuel cell which uses the hydrogen permeable membrane and is improved the problem that the hydrogen permeability is degraded with time. <P>SOLUTION: The hydrogen permeable membraneis composed of the hydrogen permeable base material using V or a V alloy, hydrogen permeable Pd membrane containing Pd, and the intermediate layer provided between the hydrogen permeable base material and Pd membrane. The intermediate layer contains elements of the group V other than V, and has a dense structure. The fuel cell uses the hydrogen permeable membrane. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

本発明は、高い水素透過性及び水素選択性を有し、しかも水素透過性の経時的劣化が小さい水素透過膜、及びこの水素透過膜を用いた燃料電池に関する。   The present invention relates to a hydrogen permeable membrane having high hydrogen permeability and hydrogen selectivity, and having little deterioration over time in hydrogen permeability, and a fuel cell using the hydrogen permeable membrane.

水素透過膜は、水素と他の気体の混合ガスから、水素のみを選択的に透過する水素透過性及び水素選択性を有する膜であり、水素含有ガスからの水素の抽出や、燃料電池等に広く用いられている。   A hydrogen permeable membrane is a membrane having hydrogen permeability and hydrogen selectivity that selectively permeates only hydrogen from a mixed gas of hydrogen and other gases, and is suitable for extraction of hydrogen from hydrogen-containing gas, fuel cells, etc. Widely used.

水素透過膜としては、水素透過性に優れるバナジウム（Ｖ）、ニオブ（Ｎｂ）、タンタル（Ｔａ）等の５族元素やパラジウム（Ｐｄ）を含む膜が種々提案されている。しかし、５族元素は酸化物生成エネルギーが低く、水素還元雰囲気でも水素中に含まれる水蒸気等により容易に酸化される。   As the hydrogen permeable membrane, various membranes containing a group 5 element such as vanadium (V), niobium (Nb), tantalum (Ta) and palladium (Pd) having excellent hydrogen permeability have been proposed. However, Group 5 elements have low oxide formation energy and are easily oxidized by water vapor or the like contained in hydrogen even in a hydrogen reduction atmosphere.

一方、Ｐｄは、水素透過性はＶ、Ｎｂ、Ｔａ等の５族元素より劣るものの、耐酸化性は、Ｖ、Ｎｂ、Ｔａ等の５族元素よりは優れる。又燃料電池に用いられる場合に求められる原子状水素を膜表面で生成する能力も優れる。しかし、Ｐｄは非常に高価である。また、５族の中でもＴａも埋蔵量が少ないことから高価である。ＮｂはＶに比較し水素膨張量が大きく、固く割れやすい。   On the other hand, although Pd is inferior to Group 5 elements such as V, Nb, and Ta in hydrogen permeability, its oxidation resistance is superior to Group 5 elements such as V, Nb, and Ta. In addition, the ability to generate atomic hydrogen required on the membrane surface when used in a fuel cell is also excellent. However, Pd is very expensive. Of the five groups, Ta is also expensive because it has a small reserve. Nb has a larger amount of hydrogen expansion than V and is hard and easily cracked.

そこで、Ｖ又はＶの合金を主体とする水素透過性基材の表面に、Ｐｄの薄膜（被覆層）を蒸着、スパッタリング、めっき等により形成した水素透過膜が提案されている（特開平７−１８５２７７号公報（特許文献１）、特開２００４−３４４７３１号公報（特許文献２）等、）。   Therefore, a hydrogen permeable membrane is proposed in which a Pd thin film (coating layer) is formed on the surface of a hydrogen permeable substrate mainly composed of V or V alloy by vapor deposition, sputtering, plating, etc. No. 185277 (Patent Document 1), Japanese Patent Application Laid-Open No. 2004-344731 (Patent Document 2), etc.).

前記のように、Ｐｄは貴金属であり耐酸化性はＶ、Ｎｂ、Ｔａ等の５族元素よりは優れるが、それでもＡｇ等よりも酸化物生成エネルギーが低く、近年の耐酸化性に対する要請を考慮すると、充分とは言えない。例えば、従来のＰｄの被覆層（Ｐｄ膜）、５族元素を含む水素透過性基材、及び他の５族元素を含む中間層からなる水素透過膜を、ガソリンなどの改質ガスから水素を抽出する分離膜として使用すると、改質ガスに含まれる水蒸気によりＰｄ膜、中間層、そして水素透過基材と酸化劣化を起こし、経時的に水素透過性能が低下する問題があった。
特開平７−１８５２７７号公報 特開２００４−３４４７３１号公報 As described above, Pd is a noble metal and its oxidation resistance is superior to that of Group 5 elements such as V, Nb, and Ta. However, it still has a lower oxide formation energy than Ag and the like, and the recent demand for oxidation resistance is taken into consideration. That's not enough. For example, a conventional Pd coating layer (Pd film), a hydrogen permeable base material including a hydrogen permeable substrate containing a Group 5 element, and an intermediate layer containing another Group 5 element can be used to remove hydrogen from a reformed gas such as gasoline. When used as a separation membrane for extraction, the water vapor contained in the reformed gas causes oxidative degradation with the Pd membrane, the intermediate layer, and the hydrogen permeable substrate, resulting in a problem that the hydrogen permeation performance deteriorates over time.
JP-A-7-185277 JP 2004-344731 A

本発明は、前記のような酸化による経時的な水素透過性能の低下が、従来の水素透過膜よりもさらに抑制された水素透過膜を提供することを課題とする。本発明は、又、この水素透過膜を用い、経時的な水素透過性能の低下の問題が改善された燃料電池を提供することも課題とする。   An object of the present invention is to provide a hydrogen permeable membrane in which the decrease in hydrogen permeation performance over time due to oxidation as described above is further suppressed as compared with a conventional hydrogen permeable membrane. Another object of the present invention is to provide a fuel cell using this hydrogen permeable membrane, in which the problem of deterioration in hydrogen permeation performance over time is improved.

本発明者は、鋭意検討の結果、中間層を、水素透過性基材とは異なる５族元素を含む緻密な組織とすることにより、前記の問題が解決できることを見出し、本発明を完成した。   As a result of intensive studies, the present inventor has found that the above problem can be solved by making the intermediate layer a dense structure containing a Group 5 element different from the hydrogen permeable substrate, and has completed the present invention.

本発明は、その請求項１において、Ｖ又はＶ合金を用いた水素透過性基材、Ｐｄを含む水素透過性のＰｄ膜、並びに、前記水素透過性基材及び前記Ｐｄ膜間に設けられた中間層からなり、この中間層が、Ｖ以外の５族元素を含み、かつ緻密な組織であることを特徴とする水素透過膜を提供する。   The present invention is the hydrogen permeable base material using V or V alloy, the hydrogen permeable Pd film containing Pd, and the hydrogen permeable base material and the Pd film. Provided is a hydrogen permeable membrane comprising an intermediate layer, wherein the intermediate layer contains a Group 5 element other than V and has a dense structure.

水素透過性基材とＰｄ膜間に設けられる中間層を構成する元素は、Ｖ以外の５族元素から選ばれる。５族元素とは、長周期表の５族に含まれる元素であり、Ｎｂ、Ｔａが例示される。中間層は、これらの５族元素の単体により構成されてもよいし、これらの５族元素の合金により構成されてもよい。この５族元素の合金としては、Ｔａ又はＮｂと、Ｎｉ、Ｔｉ、Ｃｏ、Ｃｒ等との合金が例示される。   The element constituting the intermediate layer provided between the hydrogen permeable substrate and the Pd film is selected from Group 5 elements other than V. The Group 5 element is an element included in Group 5 of the long periodic table, and Nb and Ta are exemplified. An intermediate | middle layer may be comprised with the simple substance of these Group 5 elements, and may be comprised with the alloy of these Group 5 elements. Examples of the group 5 element alloy include an alloy of Ta or Nb and Ni, Ti, Co, Cr, or the like.

この中間層は水素透過性が優れるものであり、従って水素透過膜全体の水素透過性を損なうことはない。又この中間層により、水素透過性基材とＰｄ膜間の相互拡散が抑制される。   This intermediate layer has excellent hydrogen permeability, and therefore does not impair the hydrogen permeability of the entire hydrogen permeable membrane. Further, the intermediate layer suppresses mutual diffusion between the hydrogen permeable substrate and the Pd film.

本発明の水素透過膜は、この中間層が、緻密な組織であることを特徴とする。ここで緻密な組織とは、さまざまな多数の結晶方位を持った、金属又は合金の微細結晶から形成され、この微細結晶粒間の隙間が小さく、かつピンホールを有しない組織を言う。   The hydrogen permeable membrane of the present invention is characterized in that the intermediate layer has a dense structure. Here, the dense structure refers to a structure formed from fine crystals of metal or alloy having various crystal orientations, with a small gap between the fine crystal grains and no pinholes.

図２は、一般的な蒸着やスパッタにより得られた膜組織を模式的に表した模式拡大図である。このような組織は柱状組織と呼ばれ、柱状結晶が多数並んだ形をとり、結晶粒間に直線的な１〜１０ｎｍの隙間が生じている。   FIG. 2 is a schematic enlarged view schematically showing a film structure obtained by general vapor deposition or sputtering. Such a structure is called a columnar structure, and has a shape in which a large number of columnar crystals are arranged, and linear gaps of 1 to 10 nm are generated between crystal grains.

一方図３は、緻密な組織を模式的に表わした模式拡大図である。この組織は粒径０．１μｍ〜１０μｍの微細結晶粒から形成され、さまざまな多数の結晶方位、形状を有するものである。微細結晶粒間には１ｎｍを超える隙間はなく、又ピンホールもない。   On the other hand, FIG. 3 is a schematic enlarged view schematically showing a dense structure. This structure is formed from fine crystal grains having a grain size of 0.1 μm to 10 μm and has various crystal orientations and shapes. There are no gaps exceeding 1 nm between fine crystal grains, and there are no pinholes.

従来のＰｄ膜、５族元素を含む水素透過性基材、及び他の５族元素を含む中間層からなる水素透過膜では、中間層は、真空蒸着、スパッタリング、めっき等により形成されており、図２に示すような柱状組織である。その結果、酸化劣化による、経時的な水素透過性能の低下を充分抑制することができなかったが、本発明は、中間層を図３に示すような緻密な組織とすることにより、この問題を解決するものである。すなわち、緻密な組織とすることにより、水素中に含まれる水蒸気の侵入が抑制され、その結果、酸化物の生成が減少し水素透過性能の経時的な低下が抑制されるものと思われる。   In the conventional Pd film, a hydrogen permeable film comprising a hydrogen permeable substrate containing a group 5 element, and an intermediate layer containing another group 5 element, the intermediate layer is formed by vacuum deposition, sputtering, plating, etc. It is a columnar structure as shown in FIG. As a result, the deterioration of hydrogen permeation performance over time due to oxidative degradation could not be sufficiently suppressed, but the present invention can solve this problem by making the intermediate layer a dense structure as shown in FIG. It is a solution. That is, by forming a dense structure, it is considered that invasion of water vapor contained in hydrogen is suppressed, and as a result, generation of oxides is reduced and deterioration of hydrogen permeation performance with time is suppressed.

中間層を緻密な組織とすることにより、さらに、水素透過性基材、中間層、及びＰｄ膜間の、相互熱拡散も抑制される。その結果、相互拡散により生成される金属間化合物の生成が抑制され、又水素透過性基材を構成するＶの水素透過膜最表層への表出も抑制されるので、これらの作用によっても、水素透過性能の経時的な低下が抑制される。   By making the intermediate layer a dense structure, mutual thermal diffusion between the hydrogen permeable substrate, the intermediate layer, and the Pd film is further suppressed. As a result, the production of intermetallic compounds produced by interdiffusion is suppressed, and the expression of V constituting the hydrogen permeable base material to the outermost layer of the hydrogen permeable membrane is also suppressed. A decrease in the hydrogen permeation performance over time is suppressed.

緻密な組織を有する中間層は、中間層を構成する材料を、イオンプレーティング法により、水素透過性基材の表面上に、蒸着する方法により形成することができる。請求項２は、この好ましい態様に該当し、前記の水素透過膜であって、前記中間層が、イオンプレーティング法により形成されたものであることを特徴とする水素透過膜を提供するものである。   The intermediate layer having a dense structure can be formed by a method of evaporating the material constituting the intermediate layer on the surface of the hydrogen permeable substrate by an ion plating method. Claim 2 corresponds to this preferred embodiment, and provides the hydrogen permeable membrane, characterized in that the intermediate layer is formed by an ion plating method. is there.

イオンプレーティング法には、アークイオンプレーティング法、高周波イオンプレーティング法などあり、いずれも有効に適用出来る。図４に高周波イオンプレーティング装置の概要を示す。   The ion plating method includes an arc ion plating method and a high frequency ion plating method, and any of them can be effectively applied. FIG. 4 shows an outline of the high-frequency ion plating apparatus.

この例の装置では、ベルジャ内で、ＥＢ（電子ビーム）により蒸発源を原子レベルに分解、蒸発させた後、蒸発源と基板との間にあるアンテナ部に印加されたＲＦ（高周波）により正イオン化する。基板側にはＤＣ（直流）のマイナスバイアスを印加することにより、正イオン化した蒸発物質が高エネルギーで基板に蒸着する。この高エネルギーにより基板と蒸着物質との密着強度が向上するとともに、蒸着粒子間の結合も強くピンホールなどの欠陥が少ない膜を得ることが出来る。   In the apparatus of this example, the evaporation source is decomposed to the atomic level by EB (electron beam) in the bell jar and evaporated, and then positive by RF (high frequency) applied to the antenna portion between the evaporation source and the substrate. Ionize. By applying a DC (direct current) negative bias to the substrate side, the positive ionized evaporation substance is deposited on the substrate with high energy. With this high energy, the adhesion strength between the substrate and the vapor deposition material can be improved, and a film with strong bonds between the vapor deposition particles and few defects such as pinholes can be obtained.

水素透過性基材とＰｄ膜間の相互拡散を抑制する効果をより充分にするためには、中間層の厚みは１０ｎｍ以上が好ましい。又、５族元素から構成される水素透過性基材及び中間層は、水素透過時に水素化物の生成による水素膨張を生じる場合があるが、水素透過性基材及び中間層は、異なった５族元素から形成されているので、水素膨張に差違を生じ、このミスマッチにより膜破損が生じる場合がある。そこで、膜破損をさけるため、中間層の厚みは、５００ｎｍ以下が好ましい。   In order to make the effect of suppressing interdiffusion between the hydrogen permeable substrate and the Pd film more satisfactory, the thickness of the intermediate layer is preferably 10 nm or more. In addition, hydrogen permeable base materials and intermediate layers composed of Group 5 elements may cause hydrogen expansion due to the formation of hydrides during hydrogen permeation, but hydrogen permeable base materials and intermediate layers are different Group 5 Since it is formed from elements, there is a difference in hydrogen expansion, and this mismatch may cause film breakage. Therefore, in order to avoid film breakage, the thickness of the intermediate layer is preferably 500 nm or less.

すなわち、中間層の厚みは、１０ｎｍ以上、５００ｎｍ以下であることが好ましく、請求項３は、この好ましい態様に該当する水素透過膜を提供するものである。   That is, the thickness of the intermediate layer is preferably 10 nm or more and 500 nm or less, and claim 3 provides a hydrogen permeable membrane corresponding to this preferred embodiment.

Ｖ又はＶ合金を用いた水素透過性基材は、Ｖ単体により構成されてもよいし、Ｖの合金により構成されてもよい。Ｖ合金としては、Ｔａ又はＮｂと、Ｎｉ、Ｔｉ、Ｃｏ、Ｃｒ等との合金が例示される。   The hydrogen-permeable base material using V or V alloy may be composed of V alone or may be composed of V alloy. Examples of the V alloy include an alloy of Ta or Nb and Ni, Ti, Co, Cr or the like.

水素透過膜の厚みは、通常、１０〜５００μｍ程度が好ましい。１０μｍ未満の場合は、膜の強度が不足し膜が破壊する場合がある。一方、５００μｍを越える場合は、膜の水素透過性が低下する可能性がある。中間層の厚みや、後述のようにＰｄ膜の厚みは、水素透過性基材の厚みに比べればはるかに薄いので、水素透過性基材の厚みとしても、通常、１０〜５００μｍ程度が好ましい。   The thickness of the hydrogen permeable membrane is usually preferably about 10 to 500 μm. When the thickness is less than 10 μm, the strength of the film is insufficient and the film may be broken. On the other hand, if it exceeds 500 μm, the hydrogen permeability of the membrane may be lowered. Since the thickness of the intermediate layer and the thickness of the Pd film as described later are much thinner than the thickness of the hydrogen permeable substrate, the thickness of the hydrogen permeable substrate is usually preferably about 10 to 500 μm.

この水素透過性基材の表面上に、イオンプレーティング法等により、緻密な組織を有する中間層が形成されるが、この場合、緻密な組織は水素透過性基材の表面の粗度が小さい程形成されやすい。特に、水素透過性基材の表面粗さＲａがＲａ＜０．０３μｍである場合が好ましい。請求項４は、この好ましい態様に該当する。なおここでいう表面粗さＲａとは、ＪＩＳ Ｂ０６０１ ’９４、ＪＩＳ Ｂ００３１ ’９４で定義される算術平均粗さである。   An intermediate layer having a dense structure is formed on the surface of the hydrogen permeable substrate by ion plating or the like. In this case, the dense structure has a low surface roughness of the hydrogen permeable substrate. It is easy to form. In particular, it is preferable that the surface roughness Ra of the hydrogen permeable substrate is Ra <0.03 μm. Claim 4 corresponds to this preferred embodiment. Here, the surface roughness Ra is an arithmetic average roughness defined by JIS B0601 '94 and JIS B0031 '94.

本発明の水素透過膜を構成するＰｄ膜は、Ｐｄを含み、水素透過性を有する膜である。この膜は、Ｐｄ単独からなる膜であってもよいし、Ｐｄ−Ａｇ、Ｐｄ−ＰｔやＰｄ−Ｃｕ等のＰｄ合金の膜であってもよい。   The Pd membrane constituting the hydrogen permeable membrane of the present invention is a membrane containing Pd and having hydrogen permeability. This film may be a film made of Pd alone or a film of a Pd alloy such as Pd—Ag, Pd—Pt, or Pd—Cu.

Ｐｄ膜の厚みは、０．０１〜２．０μｍ程度が通常好ましい。０．０１μｍ未満の場合は、中間層を充分被覆できず、中間層や水素透過性基材を構成する５族元素を含む材質が酸化して劣化する可能性がある。一方、２．０μｍを超えると高価なＰｄ使用量が増えコストアップが問題となる。   The thickness of the Pd film is usually preferably about 0.01 to 2.0 μm. When the thickness is less than 0.01 μm, the intermediate layer cannot be sufficiently covered, and the material containing the group 5 element constituting the intermediate layer or the hydrogen permeable substrate may be oxidized and deteriorated. On the other hand, if it exceeds 2.0 μm, the amount of expensive Pd used increases and there is a problem of cost increase.

Ｐｄ膜は、Ｐｄ箔を中間層の表面上に貼り合せる方法や、中間層の表面上に、蒸着、スパッタリング、めっき等を施す方法により形成することができる。しかし、Ｐｄ膜をイオンプレーティング法により形成すると、緻密な組織であるＰｄ膜を得ることができる。   The Pd film can be formed by a method of bonding a Pd foil on the surface of the intermediate layer or a method of performing vapor deposition, sputtering, plating, or the like on the surface of the intermediate layer. However, when the Pd film is formed by the ion plating method, a Pd film having a dense structure can be obtained.

Ｐｄ膜が、緻密な組織であると、Ｐｄ膜を構成する材質、すなわちＰｄやＰｄ合金の酸化を抑制できるし、又Ｐｄ膜と中間層間の相互拡散が抑制され、中間層や水素透過性基材を構成する５族元素が、Ｐｄ膜の外表面（すなわち、水素透過膜の最表面）へ表出し酸化することによる水素透過性能の経時劣化をさらに抑制することができるので、好ましい。   When the Pd film has a dense structure, the material constituting the Pd film, that is, the oxidation of Pd and Pd alloy can be suppressed, and the mutual diffusion between the Pd film and the intermediate layer can be suppressed. It is preferable because the group 5 element constituting the material can be further exposed to the outer surface of the Pd film (that is, the outermost surface of the hydrogen permeable film) and oxidized, thereby further suppressing deterioration with time of the hydrogen permeation performance.

又後述のように、本発明の水素透過膜を燃料電池に用いる場合、高い起電力を得るためには、Ｐｄ膜上にペロブスカイト膜の形成が望まれるが、その形成を容易にするためには、Ｐｄ膜がピンホールのない緻密質であることが望まれる。請求項５は、この好ましい態様に該当する。   As will be described later, when the hydrogen permeable membrane of the present invention is used in a fuel cell, in order to obtain a high electromotive force, it is desired to form a perovskite film on the Pd film. It is desirable that the Pd film be dense with no pinholes. Claim 5 corresponds to this preferable mode.

本発明の水素透過膜は、水素透過性が高く、酸化による経時劣化も低いことから、水素含有ガスから水素を抽出する水素抽出器や、水素センサー、燃料電池等に好適に用いることができる。例えば、この水素透過膜のＰｄ膜上にプロトン導電性膜を設けた燃料電池は、優れた起電力を示し、又起電力の経時的な低下もないとの特徴を有する。   Since the hydrogen permeable membrane of the present invention has high hydrogen permeability and low deterioration with time due to oxidation, it can be suitably used for a hydrogen extractor that extracts hydrogen from a hydrogen-containing gas, a hydrogen sensor, a fuel cell, or the like. For example, a fuel cell in which a proton conductive membrane is provided on a Pd membrane of the hydrogen permeable membrane has an excellent electromotive force and has no characteristic that the electromotive force does not decrease with time.

そこで本発明は、その請求項６において、前記の本発明の水素透過膜のＰｄ膜上にプロトン導電性膜が設けられていることを特徴とする燃料電池を提供する。   Accordingly, the present invention provides a fuel cell according to claim 6, wherein a proton conductive membrane is provided on the Pd membrane of the hydrogen permeable membrane of the present invention.

ここで、プロトン導電性膜とは、その中をプロトン（Ｈ＋、陽子）が伝播する性質を有する固体電解質の膜である。例えば、アルカリ土類金属及びＣｅ、Ｚｒ等の金属を含む酸化物からなる膜が挙げられ、特に、化学式ＡｘＭｙＬｚＯ３（ここで、Ａはアルカリ土類金属、ＭはＣｅ、Ｚｒ等の金属、Ｌは、３族と１３族の元素、ｘは１〜２程度、ｙ＋ｚは１程度、ｚ／（ｙ＋ｚ）は０〜０．８程度）で表わされる酸化物の膜が挙げられる。中でも、ペロブスカイト型の結晶構造を有する酸化物の膜はプロトン導電性が高く、高い起電力が得られるので好ましい。Ｌで表わされる元素には、ランタノイド系列の元素も含まれ、具体的には、Ｇａ、Ａｌ、Ｙ、Ｙｂ、Ｉｎ、Ｎｄ及びＳｃが例示される。 Here, the proton conductive membrane is a solid electrolyte membrane having the property of propagating protons (H + , protons). For example, alkaline earth metal and Ce, include film made of an oxide containing a metal such as Zr, in particular, the formula A x M y L z O 3 ( wherein, A represents an alkaline earth metal, M is Ce, A metal such as Zr, L is an element of Group 3 and Group 13, x is about 1 to 2, y + z is about 1, and z / (y + z) is about 0 to 0.8). It is done. Among these, an oxide film having a perovskite crystal structure is preferable because it has high proton conductivity and high electromotive force. The element represented by L includes lanthanoid series elements, and specifically, Ga, Al, Y, Yb, In, Nd, and Sc are exemplified.

プロトン導電性膜の厚みが２０μｍを越えると、プロトンの透過性能が低下し電池の出力が低下する等の問題が生じる。一方、膜の厚みは薄いほどプロトン導電性は高いが、厚みが０．１μｍ未満では、膜欠陥（ピンホール）が多く、水素がイオン化（プロトン化）することなく透過しやすくなり、固体電解質として充分機能しない場合がある。従って、これらの観点から、プロトン導電性膜の厚みとしては、０．１μｍ〜２０μｍの範囲が好ましい。さらに、この範囲内で、水素透過膜とのより高い密着力が達成される。   If the thickness of the proton conductive membrane exceeds 20 μm, problems such as a decrease in proton permeation performance and a decrease in battery output occur. On the other hand, the thinner the membrane, the higher the proton conductivity. However, when the thickness is less than 0.1 μm, there are many membrane defects (pinholes), and hydrogen easily permeates without being ionized (protonated). It may not function well. Therefore, from these viewpoints, the thickness of the proton conductive membrane is preferably in the range of 0.1 μm to 20 μm. Further, within this range, higher adhesion with the hydrogen permeable membrane is achieved.

本発明の燃料電池は、本発明の水素透過膜上に、前記のようなプロトン導電性膜を形成（成膜）する方法により得ることができる。酸化物プロトン導電性膜を形成する方法としては、スパッタリング法、電子ビーム蒸着法、レーザーアブレーション法、ＣＶＤ法等が挙げられ、又ゾルゲル法等ウェットプロセスによる方法（湿式法）も採用可能である。   The fuel cell of the present invention can be obtained by the method of forming (depositing) the proton conductive membrane as described above on the hydrogen permeable membrane of the present invention. Examples of the method for forming the oxide proton conductive film include a sputtering method, an electron beam evaporation method, a laser ablation method, a CVD method, and the like, and a method using a wet process such as a sol-gel method (wet method) can also be employed.

成膜は、４００℃以上の温度、酸化性雰囲気で行うことが好ましい。又は、４００℃以下で成膜し、その後４００℃以上の温度、非酸化性雰囲気での焼成を行う方法が好ましい。このような条件で成膜すると、ペロブスカイト構造となる。   The film formation is preferably performed at a temperature of 400 ° C. or higher and in an oxidizing atmosphere. Alternatively, a method of forming a film at 400 ° C. or lower and then baking at a temperature of 400 ° C. or higher in a non-oxidizing atmosphere is preferable. When a film is formed under such conditions, a perovskite structure is obtained.

本発明の水素透過膜は、高い水素透過性を有するとともに、水蒸気等によるＰｄ膜、中間層、水素透過基材の酸化劣化が小さく、水素透過性能の経時的低下が抑制されたものである。そして、水素透過性が高く、経時的劣化も小さいことから、水素含有ガスから水素を抽出する水素抽出器（水素分離膜）や、水素センサー、燃料電池等に好適に用いることができる。又、この水素透過膜のＰｄ膜上にプロトン導電性膜を設けた本発明の燃料電池は、優れた起電力を示し、又起電力の経時的な低下も小さいとの特徴を有する。   The hydrogen permeable membrane of the present invention has high hydrogen permeability, is less susceptible to oxidative degradation of the Pd membrane, intermediate layer, and hydrogen permeable substrate due to water vapor and the like, and suppresses a decrease in hydrogen permeation performance over time. Since hydrogen permeability is high and deterioration with time is small, it can be suitably used for a hydrogen extractor (hydrogen separation membrane) that extracts hydrogen from a hydrogen-containing gas, a hydrogen sensor, a fuel cell, or the like. In addition, the fuel cell of the present invention in which a proton conductive membrane is provided on the Pd membrane of the hydrogen permeable membrane has an excellent electromotive force, and has a feature that a decrease in electromotive force with time is small.

次の本発明を実施するための形態を、実施例により具体的に説明するが、本発明の範囲はこの実施例により限定されるものではない。   The following modes for carrying out the present invention will be specifically described with reference to examples, but the scope of the present invention is not limited to these examples.

実施例１
［水素透過膜の形成］
厚さ０．１ｍｍの市販Ｖ箔（水素透過性基材）を表面粗さＲａ＜０．０３μｍとなるように研磨し、その表面に、下記の条件のイオンプレーティング法によりＴａを被覆し、厚さ０．０３μｍ（３０ｎｍ）のＴａ層（中間層）を形成した。更に同様のイオンプレーティング法によりＰｄを被覆し、厚さ０．１μｍのＰｄ膜を形成して、水素透過膜を得た。 Example 1
[Formation of hydrogen permeable membrane]
A commercially available V foil (hydrogen permeable substrate) having a thickness of 0.1 mm was polished so that the surface roughness Ra <0.03 μm, and the surface was coated with Ta by an ion plating method under the following conditions: A Ta layer (intermediate layer) having a thickness of 0.03 μm (30 nm) was formed. Further, Pd was coated by the same ion plating method to form a Pd film having a thickness of 0.1 μm, thereby obtaining a hydrogen permeable film.

［イオンプレーティング法の条件］
高周波イオンプレーティング
真空度： ２×１０−１Ｐａ以下
基板加熱温度： 常温
ＲＦ： １３．５６ＭＨｚ ４００Ｗ
ＤＣバイアス： −１５０Ｖ [Conditions for ion plating method]
High frequency ion plating Vacuum degree: 2 × 10 −1 Pa or less Substrate heating temperature: room temperature RF: 13.56 MHz 400 W
DC bias: -150V

図１は、この水素透過膜の断面を模式的に示した模式断面図である。図に示されるように、Ｖからなる層の両表面上に、Ｔａ層（中間層）が形成され、両側のＴａ層のそれぞれの表面上に、Ｐｄ膜が形成されている。Ｔａ層の組織をＨＲ（Ｈｉｇｈ−Ｒｅｓｏｌｕｔｉｏｎ）−ＳＥＭにより観察したところ、緻密な組織であることが確認された。   FIG. 1 is a schematic cross-sectional view schematically showing a cross section of the hydrogen permeable membrane. As shown in the figure, Ta layers (intermediate layers) are formed on both surfaces of the layer made of V, and Pd films are formed on the surfaces of the Ta layers on both sides. When the structure of the Ta layer was observed by HR (High-Resolution) -SEM, it was confirmed to be a dense structure.

［水素透過性の経時変化の測定］
温度６００℃、両側の水素差圧Δが０．４気圧の条件で、得られた水素透過膜のφ１０ｍｍの円板を、単位時間当り透過する水素透過量を経時的に測定した。この測定を継続的に行ったところ、膜の劣化により水素透過量は低下して行くが、初期の水素透過量より３０％低下したのは、開始より１２００分後であった。 [Measurement of change in hydrogen permeability over time]
Under the conditions of a temperature of 600 ° C. and a hydrogen differential pressure Δ of both sides of 0.4 atm, the hydrogen permeation amount per unit time permeated through the φ10 mm disk of the obtained hydrogen permeable membrane was measured over time. When this measurement was continuously performed, the hydrogen permeation amount decreased due to the deterioration of the membrane, but it was 1200 minutes after the start that the hydrogen permeation amount decreased by 30% from the initial hydrogen permeation amount.

実施例２
Ｔａの代りにＮｂを用いた以外は、実施例１と同様にして水素透過膜を製造し、中間層の組織の観察を行ったところ、緻密な組織であることが確認された。又、初期の水素透過量より水素透過量が３０％低下する迄の時間を求めたところ、この時間は、開始より１５００分後であった。 Example 2
A hydrogen permeable membrane was produced in the same manner as in Example 1 except that Nb was used instead of Ta, and the structure of the intermediate layer was observed. As a result, a dense structure was confirmed. Further, when the time until the hydrogen permeation amount decreased by 30% from the initial hydrogen permeation amount was determined, this time was 1500 minutes after the start.

比較例１
実施例１で用いたＶ箔を研磨せずに表面粗さＲａ＝０．１μｍで使用した以外は、実施例１と同様にして水素透過膜を製造し、中間層の組織の観察を行ったところ、柱状組織であることが確認された。又、初期の水素透過量より水素透過量が３０％低下する迄の時間を求めたところ、この時間は開始より５００分後であった。 Comparative Example 1
A hydrogen permeable membrane was produced in the same manner as in Example 1 except that the V foil used in Example 1 was used without polishing and having a surface roughness Ra = 0.1 μm, and the structure of the intermediate layer was observed. However, it was confirmed to be a columnar structure. Further, when the time until the hydrogen permeation amount decreased by 30% from the initial hydrogen permeation amount was determined, this time was 500 minutes after the start.

比較例２
実施例１で用いたＶ箔と同じＶ箔の表面に、真空度２×１０−３Ｐａ以下、基板加熱なしの条件の真空蒸着法により、Ｔａを被覆して厚さ０．０３μｍ（３０ｎｍ）のＴａ層を得、更にＰｄを被覆して厚さ０．１μｍのＰｄ膜を形成して、水素透過膜を得た。得られた水素透過膜を用い、実施例１と同様にして、中間層の組織の観察を行ったところ、柱状組織であった。又、初期の水素透過量より水素透過量が３０％低下する迄の時間を求めたところ、この時間は開始より９００分後であった。 Comparative Example 2
The surface of the same V foil as the V foil used in Example 1 was coated with Ta by a vacuum deposition method with a vacuum degree of 2 × 10 −3 Pa or less and no substrate heating, and a thickness of 0.03 μm (30 nm). And a Pd film having a thickness of 0.1 μm was formed by coating with Pd to obtain a hydrogen permeable film. When the structure of the intermediate layer was observed in the same manner as in Example 1 using the obtained hydrogen permeable membrane, it was a columnar structure. Further, when the time until the hydrogen permeation amount decreased by 30% from the initial hydrogen permeation amount was determined, this time was 900 minutes after the start.

以上の、実施例１、２及び比較例１、２の条件及び結果を表１に示す。   The conditions and results of Examples 1 and 2 and Comparative Examples 1 and 2 are shown in Table 1.

Figure 2007117810
Figure 2007117810

中間層が、柱状組織である比較例１、２の水素透過膜では、水素透過量が、開始時より３０％低下する迄の時間は５００〜９００分であり、水素透過性の経時的な低下が大きい。一方、中間層が、緻密な組織である本発明例（実施例１、２）では、水素透過量が、開始時より３０％低下する迄の時間は１２００〜１５００分であり、比較例１、２と比べはるかに長く、中間層を緻密な組織とすることにより、水素透過性の経時的な低下が大きく抑制されることが示されている。   In the hydrogen permeable membranes of Comparative Examples 1 and 2 in which the intermediate layer has a columnar structure, the time until the hydrogen permeation amount is reduced by 30% from the start is 500 to 900 minutes, and the hydrogen permeability decreases with time. Is big. On the other hand, in the present invention examples (Examples 1 and 2) in which the intermediate layer has a dense structure, the time required for the hydrogen permeation amount to decrease by 30% from the start is 1200 to 1500 minutes. It is shown that the deterioration of the hydrogen permeability over time is greatly suppressed by making the intermediate layer a dense structure much longer than 2.

本発明の水素透過膜の一例を示す模式断面図である。It is a schematic cross section which shows an example of the hydrogen permeable film of this invention. 柱状組織を模式的に示す模式拡大図である。It is a model enlarged view which shows a columnar structure typically. 緻密な組織を模式的に示す模式拡大図である。It is a model enlarged view which shows a dense structure typically. 高周波イオンプレーティング装置の模式図である。It is a schematic diagram of a high frequency ion plating apparatus.

Claims (6)

Ｖ又はＶ合金を用いた水素透過性基材、Ｐｄを含む水素透過性のＰｄ膜、並びに、前記水素透過性基材及び前記Ｐｄ膜間に設けられた中間層からなり、この中間層が、Ｖ以外の５族元素を含み、かつ緻密な組織であることを特徴とする水素透過膜。   A hydrogen permeable base material using V or V alloy, a hydrogen permeable Pd film containing Pd, and an intermediate layer provided between the hydrogen permeable base material and the Pd film. A hydrogen permeable membrane comprising a Group 5 element other than V and having a dense structure. 前記中間層が、イオンプレーティング法により形成されたものであることを特徴とする請求項１に記載の水素透過膜。   The hydrogen permeable membrane according to claim 1, wherein the intermediate layer is formed by an ion plating method. 前記中間層の厚みが、１０ｎｍ以上、５００ｎｍ以下であることを特徴とする請求項１又は請求項２に記載の水素透過膜。   The hydrogen permeable membrane according to claim 1 or 2, wherein the thickness of the intermediate layer is 10 nm or more and 500 nm or less. 前記水素透過性基材の表面粗さＲａが、Ｒａ＜０．０３μｍであることを特徴とする請求項１ないし請求項３のいずれかに記載の水素透過膜。   4. The hydrogen permeable membrane according to claim 1, wherein the surface roughness Ra of the hydrogen permeable substrate is Ra <0.03 μm. 5. 前記Ｐｄ膜が、緻密な組織であることを特徴とする請求項１ないし請求項４のいずれかに記載の水素透過膜。   The hydrogen permeable membrane according to any one of claims 1 to 4, wherein the Pd membrane has a dense structure. 請求項１ないし請求項５のいずれかに記載の水素透過膜の前記Ｐｄ膜上に、プロトン導電性膜が設けられていることを特徴とする燃料電池。
A fuel cell, wherein a proton conductive membrane is provided on the Pd membrane of the hydrogen permeable membrane according to any one of claims 1 to 5.
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