JP5110836B2 - Catalyst electrode for fuel cell, membrane / electrode assembly using the same, and fuel cell - Google Patents
Catalyst electrode for fuel cell, membrane / electrode assembly using the same, and fuel cell Download PDFInfo
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- 239000003054 catalyst Substances 0.000 title claims description 281
- 239000000446 fuel Substances 0.000 title claims description 131
- 239000012528 membrane Substances 0.000 title claims description 36
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims description 143
- 210000004027 cell Anatomy 0.000 claims description 135
- 239000002041 carbon nanotube Substances 0.000 claims description 111
- 229910021393 carbon nanotube Inorganic materials 0.000 claims description 111
- BASFCYQUMIYNBI-UHFFFAOYSA-N platinum Chemical group [Pt] BASFCYQUMIYNBI-UHFFFAOYSA-N 0.000 claims description 66
- 239000000758 substrate Substances 0.000 claims description 61
- 239000007788 liquid Substances 0.000 claims description 33
- 239000002245 particle Substances 0.000 claims description 31
- 239000005518 polymer electrolyte Substances 0.000 claims description 17
- GPRLSGONYQIRFK-UHFFFAOYSA-N hydron Chemical compound [H+] GPRLSGONYQIRFK-UHFFFAOYSA-N 0.000 claims description 13
- 210000000170 cell membrane Anatomy 0.000 claims description 9
- 229910017052 cobalt Inorganic materials 0.000 claims description 6
- 239000010941 cobalt Substances 0.000 claims description 6
- GUTLYIVDDKVIGB-UHFFFAOYSA-N cobalt atom Chemical compound [Co] GUTLYIVDDKVIGB-UHFFFAOYSA-N 0.000 claims description 6
- 239000007787 solid Substances 0.000 claims description 6
- 238000010438 heat treatment Methods 0.000 claims description 3
- 239000002904 solvent Substances 0.000 claims description 3
- 239000011852 carbon nanoparticle Substances 0.000 claims 1
- OKKJLVBELUTLKV-UHFFFAOYSA-N Methanol Chemical compound OC OKKJLVBELUTLKV-UHFFFAOYSA-N 0.000 description 36
- 239000007789 gas Substances 0.000 description 35
- 238000010248 power generation Methods 0.000 description 29
- 229910052799 carbon Inorganic materials 0.000 description 26
- 238000003411 electrode reaction Methods 0.000 description 21
- 238000000034 method Methods 0.000 description 21
- 239000010419 fine particle Substances 0.000 description 18
- 238000009792 diffusion process Methods 0.000 description 17
- 239000001257 hydrogen Substances 0.000 description 12
- 229910052739 hydrogen Inorganic materials 0.000 description 12
- 239000000463 material Substances 0.000 description 12
- 239000000969 carrier Substances 0.000 description 10
- 239000010409 thin film Substances 0.000 description 10
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 description 9
- 229910000428 cobalt oxide Inorganic materials 0.000 description 9
- IVMYJDGYRUAWML-UHFFFAOYSA-N cobalt(ii) oxide Chemical compound [Co]=O IVMYJDGYRUAWML-UHFFFAOYSA-N 0.000 description 9
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 9
- 238000003421 catalytic decomposition reaction Methods 0.000 description 8
- 239000007784 solid electrolyte Substances 0.000 description 8
- 230000015572 biosynthetic process Effects 0.000 description 7
- 238000006243 chemical reaction Methods 0.000 description 7
- 229920001940 conductive polymer Polymers 0.000 description 7
- 238000001816 cooling Methods 0.000 description 7
- -1 hydrogen ions Chemical class 0.000 description 7
- 239000000843 powder Substances 0.000 description 7
- 238000003786 synthesis reaction Methods 0.000 description 7
- UGFAIRIUMAVXCW-UHFFFAOYSA-N Carbon monoxide Chemical compound [O+]#[C-] UGFAIRIUMAVXCW-UHFFFAOYSA-N 0.000 description 6
- 229910002091 carbon monoxide Inorganic materials 0.000 description 6
- 238000006555 catalytic reaction Methods 0.000 description 5
- 239000002105 nanoparticle Substances 0.000 description 5
- 239000011148 porous material Substances 0.000 description 5
- CIWBSHSKHKDKBQ-JLAZNSOCSA-N Ascorbic acid Chemical compound OC[C@H](O)[C@H]1OC(=O)C(O)=C1O CIWBSHSKHKDKBQ-JLAZNSOCSA-N 0.000 description 4
- KFZMGEQAYNKOFK-UHFFFAOYSA-N Isopropanol Chemical compound CC(C)O KFZMGEQAYNKOFK-UHFFFAOYSA-N 0.000 description 4
- 229920000557 Nafion® Polymers 0.000 description 4
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 4
- 230000003647 oxidation Effects 0.000 description 4
- 238000007254 oxidation reaction Methods 0.000 description 4
- 239000001301 oxygen Substances 0.000 description 4
- 229910052760 oxygen Inorganic materials 0.000 description 4
- 229910052697 platinum Inorganic materials 0.000 description 4
- 239000000047 product Substances 0.000 description 4
- 239000012495 reaction gas Substances 0.000 description 4
- 230000003197 catalytic effect Effects 0.000 description 3
- 238000010586 diagram Methods 0.000 description 3
- 239000004744 fabric Substances 0.000 description 3
- 238000005470 impregnation Methods 0.000 description 3
- 238000004519 manufacturing process Methods 0.000 description 3
- 238000005259 measurement Methods 0.000 description 3
- 229910052751 metal Inorganic materials 0.000 description 3
- 239000002184 metal Substances 0.000 description 3
- 230000002194 synthesizing effect Effects 0.000 description 3
- 238000007740 vapor deposition Methods 0.000 description 3
- 239000012808 vapor phase Substances 0.000 description 3
- CURLTUGMZLYLDI-UHFFFAOYSA-N Carbon dioxide Chemical compound O=C=O CURLTUGMZLYLDI-UHFFFAOYSA-N 0.000 description 2
- MYMOFIZGZYHOMD-UHFFFAOYSA-N Dioxygen Chemical compound O=O MYMOFIZGZYHOMD-UHFFFAOYSA-N 0.000 description 2
- 238000001241 arc-discharge method Methods 0.000 description 2
- 238000009835 boiling Methods 0.000 description 2
- 239000006229 carbon black Substances 0.000 description 2
- 238000005229 chemical vapour deposition Methods 0.000 description 2
- 229910001882 dioxygen Inorganic materials 0.000 description 2
- 238000004880 explosion Methods 0.000 description 2
- VNWKTOKETHGBQD-UHFFFAOYSA-N methane Chemical compound C VNWKTOKETHGBQD-UHFFFAOYSA-N 0.000 description 2
- 238000001000 micrograph Methods 0.000 description 2
- 239000012046 mixed solvent Substances 0.000 description 2
- 238000002156 mixing Methods 0.000 description 2
- 230000009467 reduction Effects 0.000 description 2
- 238000004544 sputter deposition Methods 0.000 description 2
- 238000003756 stirring Methods 0.000 description 2
- 239000011800 void material Substances 0.000 description 2
- 229910017518 Cu Zn Inorganic materials 0.000 description 1
- 229910017752 Cu-Zn Inorganic materials 0.000 description 1
- 229910017943 Cu—Zn Inorganic materials 0.000 description 1
- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical compound CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 description 1
- 206010067482 No adverse event Diseases 0.000 description 1
- 239000011230 binding agent Substances 0.000 description 1
- 150000001721 carbon Chemical class 0.000 description 1
- 239000001569 carbon dioxide Substances 0.000 description 1
- 229910002092 carbon dioxide Inorganic materials 0.000 description 1
- 238000001628 carbon nanotube synthesis method Methods 0.000 description 1
- 238000004523 catalytic cracking Methods 0.000 description 1
- 230000008859 change Effects 0.000 description 1
- 239000007795 chemical reaction product Substances 0.000 description 1
- 230000000052 comparative effect Effects 0.000 description 1
- TVZPLCNGKSPOJA-UHFFFAOYSA-N copper zinc Chemical compound [Cu].[Zn] TVZPLCNGKSPOJA-UHFFFAOYSA-N 0.000 description 1
- 238000000354 decomposition reaction Methods 0.000 description 1
- 230000007423 decrease Effects 0.000 description 1
- 238000000151 deposition Methods 0.000 description 1
- 230000008021 deposition Effects 0.000 description 1
- 238000009826 distribution Methods 0.000 description 1
- 238000007772 electroless plating Methods 0.000 description 1
- 239000003792 electrolyte Substances 0.000 description 1
- 239000010408 film Substances 0.000 description 1
- 230000004907 flux Effects 0.000 description 1
- 239000002737 fuel gas Substances 0.000 description 1
- 238000007731 hot pressing Methods 0.000 description 1
- 239000011261 inert gas Substances 0.000 description 1
- 239000003014 ion exchange membrane Substances 0.000 description 1
- 238000005304 joining Methods 0.000 description 1
- 238000010030 laminating Methods 0.000 description 1
- 239000002071 nanotube Substances 0.000 description 1
- 239000012071 phase Substances 0.000 description 1
- 230000008569 process Effects 0.000 description 1
- 238000000629 steam reforming Methods 0.000 description 1
- 229910052723 transition metal Inorganic materials 0.000 description 1
- 150000003624 transition metals Chemical class 0.000 description 1
- 238000002525 ultrasonication Methods 0.000 description 1
Classifications
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- 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、車載用、家庭据え置き用、あるいは携帯機器用のバッテリーとして有用な、燃料電池用触媒電極、それを用いた膜・電極接合体、及び燃料電池に関する。 The present invention relates to a catalyst electrode for a fuel cell, a membrane / electrode assembly using the catalyst electrode, and a fuel cell, which are useful as a battery for in-vehicle use, household use or portable equipment.
水素と酸素を使用する燃料電池は、その反応生成物が原理的に水のみであり、環境への悪影響がほとんどない発電システムとして注目されている。近年、燃料電池のなかでも、水素イオン伝導性を有するイオン交換膜を電解質として使用する固体高分子型燃料電池は、作動温度が低く、出力密度が高く、かつ、小型化が容易なため、車載用電源や家庭据置用電源などへの使用が有望視されている。 A fuel cell using hydrogen and oxygen has been attracting attention as a power generation system in which the reaction product is in principle only water and has almost no adverse effects on the environment. In recent years, a polymer electrolyte fuel cell using an ion exchange membrane having hydrogen ion conductivity as an electrolyte among fuel cells has a low operating temperature, a high output density, and is easy to downsize. It is considered promising for use as a power supply for home use or a power supply for home use.
図７は固体高分子型燃料電池の単セルの構成例を示す分解斜視図である。固体高分子型燃料電池は、単セル６０が多数積層されて構成されている。単セル６０は、アノード側のセパレータ６１、アノード側触媒電極６２、水素イオンを伝導する固体高分子電解質膜６３、カソード側の触媒電極６４、及びカソード側のセパレータ６５を、この順に積層して構成されている。アノード側の触媒電極６２は、電極基材６２ａと、電極基材６２ａの表面に積層された触媒層６２ｂとで構成されており、カソード側の触媒電極６４は電極基材６４ａと、電極基材６４ａの表面に積層された触媒層６４ｂとで構成されている。アノード側電極基材６２ａとカソード側電極基材６４ａとは、いずれも、ガス拡散能力と、電子導電性と、機械的強度とを有する部材から構成されており、例えば、カーボンペーパーあるいはカーボンクロス等が利用されている。また、アノード側触媒層６２ｂとカソード側触媒層６４ｂは、白金族触媒を担持したカーボン微粒子や多孔質活性炭で構成されており、水素イオンを伝導する固体高分子電解質膜６３の上下面にそれぞれ接続されている。
アノード側のセパレータ６１には反応ガス流路６１ａが設けられており水素ガスを供給する。他方、カソード側のセパレータ６５には反応ガス流路６５ａが設けられており酸素ガスを供給する。水素ガスはアノード側触媒層６２ｂの白金族触媒の触媒作用により水素イオンと電子に分解し（アノード電極反応）、水素イオンは固体高分子電解質膜６３を伝導して、また、電子は負荷回路を含む外部電気回路を伝導してカソード側触媒層６４ｂに到る。カソード側電極触媒層６４ｂの白金族触媒の触媒作用により酸素と水素イオンと電子とが反応して水を生じ（カソード電極反応）、この際、アノード側触媒電極６２とカソード側の触媒電極６４間に流れる電子流によって電力が生成される。
FIG. 7 is an exploded perspective view showing a configuration example of a single cell of the polymer electrolyte fuel cell. The polymer electrolyte fuel cell is configured by stacking a large number of single cells 60. The single cell 60 is configured by laminating an anode-side separator 61, an anode-side catalyst electrode 62, a solid polymer electrolyte membrane 63 that conducts hydrogen ions, a cathode-side catalyst electrode 64, and a cathode-side separator 65 in this order. Has been. The anode-side catalyst electrode 62 includes an electrode base material 62a and a catalyst layer 62b laminated on the surface of the electrode base material 62a. The cathode-side catalyst electrode 64 includes an electrode base material 64a and an electrode base material. And a catalyst layer 64b laminated on the surface of 64a. Each of the anode side electrode base material 62a and the cathode side electrode base material 64a is composed of a member having gas diffusion capacity, electronic conductivity, and mechanical strength, such as carbon paper or carbon cloth. Is being used. The anode side catalyst layer 62b and the cathode side catalyst layer 64b are composed of carbon fine particles carrying a platinum group catalyst or porous activated carbon, and are connected to the upper and lower surfaces of the solid polymer electrolyte membrane 63 that conducts hydrogen ions, respectively. Has been.
The anode-side separator 61 is provided with a reaction gas channel 61a to supply hydrogen gas. On the other hand, the cathode-side separator 65 is provided with a reaction gas channel 65a for supplying oxygen gas. The hydrogen gas is decomposed into hydrogen ions and electrons by the catalytic action of the platinum group catalyst of the anode side catalyst layer 62b (anode electrode reaction), the hydrogen ions are conducted through the solid polymer electrolyte membrane 63, and the electrons pass through the load circuit. The external electric circuit is conducted to reach the cathode side catalyst layer 64b. Oxygen, hydrogen ions, and electrons react to generate water (cathode electrode reaction) by the catalytic action of the platinum group catalyst of the cathode side electrode catalyst layer 64b (cathode electrode reaction). At this time, between the anode side catalyst electrode 62 and the cathode side catalyst electrode 64 Electric power is generated by the electron flow flowing through the.
アノードに供給する水素ガスとしては、メタンやメタノール等を水蒸気改質して得られる改質ガスを使用することも可能である。例えば、メタノールを使用する場合、２５０〜３００℃の温度でＣｕ-Ｚｎ系等の触媒を使用して、下記（１）、（２）式のようにメタノールを段階的に反応させる。
ＣＨ3ＯＨ＝２Ｈ2＋ＣＯ-９０ｋＪ／ｍｏｌ （１）
ＣＯ＋Ｈ2Ｏ＝Ｈ2＋ＣＯ2＋４０ｋＪ／ｍｏｌ （２）
すなわち、改質装置でメタノールを水素と一酸化炭素（ＣＯ）に分解すると共に、生成したＣＯを水蒸気と反応させて、水素ガスと二酸化炭素（ＣＯ２）からなる改質ガスを生成し、この改質ガスをアノードに燃料ガスとして供給する。
As the hydrogen gas supplied to the anode, it is also possible to use a reformed gas obtained by steam reforming methane, methanol or the like. For example, when methanol is used, methanol is reacted stepwise as shown in the following formulas (1) and (2) using a catalyst such as a Cu—Zn system at a temperature of 250 to 300 ° C.
CH 3 OH = 2H 2 + CO-90 kJ / mol (1)
CO + H 2 O = H 2 + CO 2 +40 kJ / mol (2)
That is, methanol is decomposed into hydrogen and carbon monoxide (CO) in a reformer, and the produced CO is reacted with water vapor to produce a reformed gas composed of hydrogen gas and carbon dioxide (CO 2 ). The reformed gas is supplied to the anode as a fuel gas.
燃料電池の発電能力を高くするには、触媒層の単位表面積当たりの電極反応速度を大きくすることが必要である。すなわち、触媒層は、十分なガスが拡散できること、ガスに接触する触媒表面積が大きく、触媒反応速度が大きいことが必要である。また、触媒層は、電子が伝導できること、及び、生成した水素イオンが容易に高分子電解質膜に取り込まれるために、あるいは、固体高分子電解質膜中の水素イオンを容易に取り込めるために、厚さが一定値以下であることが必要である。
また、触媒層が、触媒担体と触媒担体の表面に担持された触媒とからなる構成である場合には、ガス拡散能力及び触媒表面積の大きさの観点から、比表面積が大きい触媒担体を用いることが好ましい。
また、白金族元素の埋蔵量は限られており、燃料電池を低コストで供給するためには、白金族触媒の使用量の低減が必要不可欠である。白金族触媒の単位量あたりの触媒反応速度は担持された白金族触媒の粒径に依存し、その最適のサイズはナノメーター（ｎｍ）オーダー、すなわち、クラスターサイズである（特許文献１参照）ことが知られており、白金族触媒の使用量の低減には、白金族触媒の粒径を小さくすること、好ましくはナノメーターオーダーにすることが必要である。
In order to increase the power generation capacity of the fuel cell, it is necessary to increase the electrode reaction rate per unit surface area of the catalyst layer. That is, the catalyst layer needs to be able to diffuse a sufficient gas, have a large catalyst surface area in contact with the gas, and have a high catalyst reaction rate. In addition, the catalyst layer has a thickness that allows electrons to conduct, and that the generated hydrogen ions are easily taken into the polymer electrolyte membrane, or that the hydrogen ions in the solid polymer electrolyte membrane can be easily taken in. Must be below a certain value.
If the catalyst layer is composed of a catalyst carrier and a catalyst supported on the surface of the catalyst carrier, a catalyst carrier having a large specific surface area should be used from the viewpoint of gas diffusion capacity and catalyst surface area. Is preferred.
In addition, the reserves of platinum group elements are limited, and in order to supply fuel cells at low cost, it is essential to reduce the amount of platinum group catalysts used. The catalytic reaction rate per unit amount of the platinum group catalyst depends on the particle size of the supported platinum group catalyst, and the optimum size is in the order of nanometers (nm), that is, the cluster size (see Patent Document 1). In order to reduce the amount of platinum group catalyst used, it is necessary to reduce the particle size of the platinum group catalyst, preferably to the nanometer order.
従来、燃料電池の触媒層として、カーボンブラック等の導電性球状のカーボン粒子を触媒担体とするものがある。この触媒層は、蒸着法、含浸法、無電界メッキ法、あるいはアルコール還元法等により白金族元素をカーボン粒子の表面に担持させ、このカーボン粒子を積層して触媒層としている。積層したカーボン粒子間の空隙を介してガスが拡散し、このガスがカーボン粒子の表面に担持された白金族触媒に接触して触媒反応が生じる。触媒層の電極反応速度を高めるためには、カーボン粒子の粒径を小さくして比表面積を大きくし、ガスに接触する白金族触媒の表面積を大きくすることが有効である。
しかしながら、カーボン粒子の形状は球であるため、粒径を小さくすると、積層されたカーボン粒子間の空隙が急激に小さくなり、十分な量のガスが拡散できなくなる。十分な量のガスが拡散できるためには、カーボン粒子の粒径が一定値以上である必要があり、このため、ガスに接触する白金族触媒の表面積の増大には限界があり、この構成の触媒層の更なる電極反応速度の向上は困難である。
また、白金族触媒の使用量の低減には、白金族触媒の単位量あたりの触媒反応速度を高めること、すなわち、白金族触媒の粒径を小さくすること、好ましくはナノメーターオーダーにすることが必要である。ところが、カーボン担体に白金族触媒を担持した場合の白金族触媒の粒径は、カーボン担体の曲率に反比例する、すなわち、カーボン担体がカーボン粒子である場合にはその粒径に比例する。従って、白金族触媒の粒径を小さくするためには粒径の小さなカーボン粒子上に担持する必要があるが、上記のように、ガス拡散能力の点から一定値以上の粒径のカーボン粒子を用いる必要があり、このため、白金族触媒の粒径を小さくできず、白金族触媒の使用量の低減ができない。
すなわち、カーボン粒子を用いる燃料電池の触媒層では、更なる発電能力の向上、及び、白金族触媒の使用量を低減することが困難ある。
Conventionally, as a catalyst layer of a fuel cell, there is a layer using conductive spherical carbon particles such as carbon black as a catalyst carrier. In this catalyst layer, a platinum group element is supported on the surface of carbon particles by vapor deposition, impregnation, electroless plating, alcohol reduction, or the like, and the carbon particles are laminated to form a catalyst layer. Gas diffuses through voids between the laminated carbon particles, and this gas comes into contact with the platinum group catalyst supported on the surface of the carbon particles to cause a catalytic reaction. In order to increase the electrode reaction rate of the catalyst layer, it is effective to increase the specific surface area by reducing the particle size of the carbon particles and to increase the surface area of the platinum group catalyst in contact with the gas.
However, since the shape of the carbon particles is a sphere, if the particle size is reduced, the gaps between the stacked carbon particles are rapidly reduced, and a sufficient amount of gas cannot be diffused. In order for a sufficient amount of gas to be diffused, the particle size of the carbon particles needs to be a certain value or more. For this reason, there is a limit in increasing the surface area of the platinum group catalyst in contact with the gas. It is difficult to further improve the electrode reaction rate of the catalyst layer.
In order to reduce the amount of platinum group catalyst used, it is necessary to increase the catalyst reaction rate per unit amount of the platinum group catalyst, that is, to reduce the particle size of the platinum group catalyst, preferably to the nanometer order. is necessary. However, the particle size of the platinum group catalyst when the platinum group catalyst is supported on the carbon carrier is inversely proportional to the curvature of the carbon carrier, that is, when the carbon carrier is carbon particles, it is proportional to the particle size. Therefore, in order to reduce the particle size of the platinum group catalyst, it is necessary to carry it on carbon particles having a small particle size. Therefore, the particle size of the platinum group catalyst cannot be reduced, and the amount of the platinum group catalyst used cannot be reduced.
That is, in the catalyst layer of the fuel cell using carbon particles, it is difficult to further improve the power generation capability and reduce the amount of platinum group catalyst used.
また、従来、上記のカーボン粒子の替わりに活性炭を使用した触媒層がある。活性炭は微細な細孔を有しているので、これらの細孔を介してガスを拡散させることができる。しかしながら、これらの細孔は相互の連結姓が十分でないためにガス拡散能力が低く、発電能力が低いことが知られており（例えば特許文献２参照）、また、白金族触媒を担持させる際、細孔内にも白金族触媒が担持されてしまい、細孔内に担持された白金族触媒は触媒として十分働かないという現象があり、この構成の触媒層では、更なる発電能力の向上、及び、白金族触媒の使用量の低減が困難である。 Conventionally, there is a catalyst layer using activated carbon instead of the carbon particles. Since activated carbon has fine pores, gas can be diffused through these pores. However, these pores are known to have low gas diffusion capacity due to insufficient interconnected surname and low power generation capacity (see, for example, Patent Document 2), and when supporting a platinum group catalyst, There is a phenomenon in which the platinum group catalyst is also supported in the pores, and the platinum group catalyst supported in the pores does not sufficiently function as a catalyst, and in the catalyst layer of this configuration, the power generation capacity is further improved, and It is difficult to reduce the amount of platinum group catalyst used.
また近年、上記の課題を解決する触媒層として、アーク放電法や化学気相成長法でカーボンナノチューブ粉末を合成し、この粉末に白金族触媒を担持し、この粉末を電極基体に積層する燃料電池用触媒層（特許文献３参照）が知られている。カーボンナノチューブは電子導電性を有しており、また、ナノサイズの細長い形状を有するので比表面積が極めて大きく、触媒担体として用いれば、触媒層の触媒表面積を大きくできる。また、カーボンナノチューブに担持した白金族触媒の粒径はカーボンナノチューブの径に比例したナノサイズになるので白金族触媒の単位量あたりの触媒反応速度も大きくなり、白金族触媒の使用量を低減できる。
ところで、触媒粒子を表面に担持した多数の触媒担体を空間的に配列して構成される一定膜厚の触媒層において、触媒担体間の空隙を大きくすると、ガス拡散能力は大きくなるが、一方、触媒担体の密度は減少するので触媒表面積が減少して触媒反応速度が小さくなる。逆に、触媒担体間の空隙を小さくすると、触媒担体の密度が大きくなるので、触媒層の触媒表面積が増大して触媒反応速度が大きくなるが、一方、ガス拡散能力は小さくなる。すなわち、ガス拡散能力は触媒担体間の空隙に比例し、触媒表面積は触媒担体間の空隙に反比例し、また、触媒層の電極反応速度の大きさはガス拡散能力と触媒表面積の積に比例するので、触媒層の電極反応速度を最大とする触媒担体間の空隙が存在する。従って、カーボンナノチューブを触媒担体とする触媒層においても、カーボンナノチューブ間の空隙は、ガス拡散能力と触媒表面積の積が最大となる、すなわち、触媒層の電極反応速度が最大となる空隙であることが好ましい。
しかしながら一般に、アーク放電法や化学気相成長法でカーボンナノチューブを合成すると、種々の曲率半径で種々の方向に曲がりくねった様々な形状のカーボンナノチューブが無秩序に配列・積層したカーボンナノチューブ粉末として合成されるので、カーボンナノチューブの径の数十倍から数百倍の大きさの空隙が無秩序に分布して形成される。カーボンナノチューブの径は数ｎｍから数十ｎｍであり、水素分子や酸素分子の大きさが０．１ｎｍオーダーであることからしても、これらの空隙は触媒層の電極反応速度を最大とする空隙よりも極めて大きい。
それ故、このカーボンナノチューブ粉末に白金族触媒を担持し、この粉末を電極基体に積層した従来の触媒層は、カーボンナノチューブ間の空隙が触媒層の電極反応速度を最大とする空隙よりも大きいために、ガス拡散能力は十分大きいが、触媒反応速度が小さく、発電能力が触媒反応速度によって律速されてしまい、発電能力が低いという課題がある。
また、この触媒層は、触媒担体間の空隙が触媒層全体にわたって不均一であるので、同一の空隙率を有する、触媒担体間の空隙が均一である触媒層と比べて、ガス拡散能力が低く、発電能力が低いという課題がある。
By the way, in a catalyst layer having a constant film thickness configured by spatially arranging a large number of catalyst carriers carrying catalyst particles on the surface, increasing the gap between the catalyst carriers increases the gas diffusion ability, Since the density of the catalyst support is reduced, the catalyst surface area is reduced and the catalyst reaction rate is reduced. Conversely, if the gap between the catalyst carriers is reduced, the density of the catalyst carriers increases, so that the catalyst surface area of the catalyst layer increases and the catalyst reaction rate increases, while the gas diffusion capacity decreases. That is, the gas diffusion capacity is proportional to the gap between the catalyst supports, the catalyst surface area is inversely proportional to the gap between the catalyst supports, and the electrode reaction rate of the catalyst layer is proportional to the product of the gas diffusion capacity and the catalyst surface area. Therefore, there is a gap between the catalyst supports that maximizes the electrode reaction rate of the catalyst layer. Therefore, even in a catalyst layer using carbon nanotubes as a catalyst support, the gap between the carbon nanotubes is the gap where the product of the gas diffusion capacity and the catalyst surface area is maximized, that is, the electrode reaction rate of the catalyst layer is maximized. Is preferred.
However, generally, when carbon nanotubes are synthesized by the arc discharge method or chemical vapor deposition method, carbon nanotube powders are synthesized as a carbon nanotube powder in which various shapes of carbon nanotubes with various radii of curvature are randomly arranged and stacked. Therefore, voids having a size of several tens to several hundred times the diameter of the carbon nanotubes are randomly distributed. Even though the diameter of the carbon nanotube is from several nanometers to several tens of nanometers and the size of hydrogen molecules and oxygen molecules is on the order of 0.1 nm, these voids are voids that maximize the electrode reaction rate of the catalyst layer. Is much larger than.
Therefore, in the conventional catalyst layer in which a platinum group catalyst is supported on this carbon nanotube powder and this powder is laminated on the electrode substrate, the gap between the carbon nanotubes is larger than the gap that maximizes the electrode reaction rate of the catalyst layer. In addition, although the gas diffusion capacity is sufficiently large, there is a problem that the catalytic reaction rate is low, the power generation capability is limited by the catalyst reaction rate, and the power generation capability is low.
In addition, since the gap between the catalyst carriers is non-uniform throughout the catalyst layer, the catalyst layer has a lower gas diffusion capacity than a catalyst layer having the same porosity and a uniform gap between the catalyst carriers. There is a problem that power generation capacity is low.
上記課題に鑑み本発明は、発電能力が向上し、且つ、白金族触媒の使用量を低減できる新規な構成の燃料電池用触媒電極、それを用いた膜・電極接合体、及び、それを用いた燃料電池を提供することを目的とする。 In view of the above problems, the present invention provides a fuel cell catalyst electrode having a novel configuration capable of improving power generation capacity and reducing the amount of platinum group catalyst used, a membrane / electrode assembly using the same, and a method for using the same. An object of the present invention is to provide a fuel cell.
上記目的を達成するために、本発明の燃料電池用触媒電極は、電極基材と電極基材面に積層した白金族触媒層とからなる燃料電池用触媒電極において、白金族触媒層を構成する触媒担体に、略同一の径と長さを有する直線形状のカーボンナノチューブが略等間隔で同一方向に配列した高密度・高配向カーボンナノチューブを用いることを特徴とする。
また、上記触媒担体間の空隙は、ガス拡散能力と触媒表面積の積が最大となる空隙であれば好ましい。
In order to achieve the above object, the fuel cell catalyst electrode of the present invention comprises a platinum group catalyst layer in a fuel cell catalyst electrode comprising an electrode substrate and a platinum group catalyst layer laminated on the electrode substrate surface. The catalyst carrier is characterized by using high-density and highly-oriented carbon nanotubes in which linear carbon nanotubes having substantially the same diameter and length are arranged in the same direction at substantially equal intervals.
The gap between the catalyst carriers is preferably a gap that maximizes the product of gas diffusion capacity and catalyst surface area.
この構成によれば以下のように作用する。すなわち、上記高密度・高配向カーボンナノチューブのカーボンナノチューブは、同一の径と長さを有する直線形状のカーボンナノチューブが等間隔で同一方向に配列しているので、上記触媒担体間の空隙は、触媒層全体にわたって均一であり、その結果、ガス拡散能力が高くなり、発電能力を向上させることができる。
また、上記カーボンナノチューブ間の空隙は、高密度・高配向カーボンナノチューブを合成する際の合成条件を選択して、触媒層の電極反応速度が最大となる空隙とすることできる。
また、カーボンナノチューブは比表面積が極めて大きいので、カーボンナノチューブに担持した白金族触媒の表面積も極めて大きくなり触媒層の電極反応速度が増大する。
また、カーボンナノチューブはナノサイズの細長い形状を有するので、カーボンナノチューブに担持された白金族触媒のサイズもナノサイズとなり、白金族触媒の単位量あたりの触媒反応速度が大きくなり、従って、白金族触媒の使用量を低減できる。
従って、高密度・高配向カーボンナノチューブを触媒担体に用いた本発明の燃料電池用触媒電極は、発電能力が向上でき、且つ、白金族触媒の使用量を低減できる。
According to this structure, it acts as follows. That is, since the carbon nanotubes of the high-density and highly-oriented carbon nanotubes are linear carbon nanotubes having the same diameter and length arranged in the same direction at equal intervals, the gap between the catalyst carriers It is uniform throughout the layer, and as a result, the gas diffusion capacity is increased and the power generation capacity can be improved.
Moreover, the space | gap between the said carbon nanotubes can be made into the space | gap which maximizes the electrode reaction rate of a catalyst layer by selecting the synthesis conditions at the time of synthesize | combining a high density and highly oriented carbon nanotube.
Further, since the carbon nanotube has an extremely large specific surface area, the surface area of the platinum group catalyst supported on the carbon nanotube is also extremely increased, and the electrode reaction rate of the catalyst layer is increased.
In addition, since the carbon nanotube has a nano-sized elongated shape, the size of the platinum group catalyst supported on the carbon nanotube is also nano-sized, and the catalytic reaction rate per unit amount of the platinum group catalyst is increased. Can be reduced.
Therefore, the fuel cell catalyst electrode of the present invention using high-density, highly-oriented carbon nanotubes as a catalyst carrier can improve the power generation capability and reduce the amount of platinum group catalyst used.
また、上記の高密度・高配向カーボンナノチューブには、基板上に触媒微粒子を担持し、この基板を有機液体中で加熱して、基板上に同一の径と長さを有する直線形状のカーボンナノチューブが等間隔で同一方向に配列した高密度・高配向カーボンナノチューブを合成し、このカーボンナノチューブを基板から束状に剥離したものを用いることができる。このカーボンナノチューブの合成方法は、固液界面接触分解法（特許文献４参照）と呼ばれており、この方法によれば、基板表面から有機液体に向かう、基板表面に垂直に且つ基板表面全面にわたって均一に形成される急激な温度勾配によって、有機液体が分解されてカーボンナノチューブが成長するので、基板上に同一の径と長さを有する直線形状のカーボンナノチューブが等間隔で同一方向に配列した高密度・高配向カーボンナノチューブを合成できる。 Further, the above-mentioned high-density and highly-oriented carbon nanotubes support catalyst fine particles on a substrate, and the substrate is heated in an organic liquid so that the linear carbon nanotubes having the same diameter and length on the substrate. Can be used by synthesizing high-density and highly-oriented carbon nanotubes arranged in the same direction at equal intervals, and separating the carbon nanotubes from the substrate in a bundle shape. This carbon nanotube synthesis method is called a solid-liquid interface catalytic decomposition method (see Patent Document 4). According to this method, the substrate surface is directed to an organic liquid, perpendicular to the substrate surface and over the entire surface of the substrate. Since the organic liquid is decomposed and carbon nanotubes grow due to the suddenly formed temperature gradient, the carbon nanotubes with the same diameter and length on the substrate are arranged at equal intervals in the same direction. Density and highly oriented carbon nanotubes can be synthesized.
さらに、上記の触媒微粒子は、コバルトの結合エネルギーが正方向に１ｅＶから３ｅＶの範囲でシフトする酸化度で酸化された酸化コバルト微粒子（特願２００５−３４１１８１）であれば好ましい。この微粒子を用いれば、カーボンナノチューブの径が極めて小さく、且つカーボンナノチューブが極めて高密度に配列した上記高密度・高配向カーボンナノチューブを合成できる。この高密度・高配向カーボンナノチューブを用いれば、触媒層の電極反応速度をさらに大きくできる。 The catalyst fine particles are preferably cobalt oxide fine particles (Japanese Patent Application No. 2005-341181) oxidized with an oxidation degree in which the binding energy of cobalt is shifted in the positive direction in the range of 1 eV to 3 eV. By using these fine particles, the above-mentioned high-density and highly-oriented carbon nanotubes in which the diameters of the carbon nanotubes are extremely small and the carbon nanotubes are arranged at a very high density can be synthesized. If this high density and highly oriented carbon nanotube is used, the electrode reaction rate of the catalyst layer can be further increased.
また、本発明の燃料電池用膜・電極接合体は、上記の燃料電池用触媒電極と、燃料電池用触媒電極に接合した水素イオン導電性高分子電解質膜とからなることを特徴とする。
この構成の燃料電池用膜・電極接合体を、アノード側電極、カソード側電極、又はその両方に用いることによって、発電能力が向上した、且つ、白金族触媒の使用量を低減した燃料電池を実現できる。
The fuel cell membrane / electrode assembly of the present invention comprises the above fuel cell catalyst electrode and a hydrogen ion conductive polymer electrolyte membrane joined to the fuel cell catalyst electrode.
Using the fuel cell membrane / electrode assembly with this configuration for the anode side electrode, cathode side electrode, or both, a fuel cell with improved power generation capability and reduced platinum group catalyst usage is realized. it can.
また、本発明の燃料電池は上記の燃料電池用触媒電極を、アノード側電極、又は、カソード側電極、又はその両方に用いたことを特徴としており、発電能力が向上した、且つ、白金族触媒の使用量を低減した燃料電池である。 The fuel cell of the present invention is characterized in that the above-described catalyst electrode for a fuel cell is used as an anode side electrode, a cathode side electrode, or both, and the power generation capacity is improved, and a platinum group catalyst. This is a fuel cell with a reduced amount of use.
以下、本発明を実施するための最良の形態を図を用いて詳細に説明する。
初めに、本発明の燃料電池用触媒電極を説明する。
図１は、本発明の燃料電池用触媒電極の構成を示す図であり、(a)図は燃料電池用触媒電極の模式断面図であり、（ｂ）図は触媒層を構成する高密度・高配向カーボンナノチューブを詳細に示す図である。
（ａ）図に示すように、本発明の燃料電池用触媒電極１は、電極基材２と電極基材２の表面に積層した触媒層３とからなる。触媒層３は、白金族触媒を担持した、カーボンナノチューブの束４が積層されて構成される。電極基材２は、ガス拡散能力と、電子導電性と、機械的強度とを有する部材であればよく、例えば、カーボンペーパーあるいはカーボンクロスである。
（ｂ）図に示すように、カーボンナノチューブの束４は、白金族触媒６が担持された、同一の径と長さを有する直線形状のカーボンナノチューブ５が等間隔で、すなわち、等しい空隙５ａを有して同一方向に配列した構成、すなわち、高密度・高配向カーボンナノチューブからなる。カーボンナノチューブの束４は、下記に説明する固液界面接触分解法を用いて、高密度・高配向カーボンナノチューブを基板上に合成し、このカーボンナノチューブを、先端が尖った、あるいは辺が刃状になった金属等の硬い部材で擦ることによって、束状に剥離して作製することができる。カーボンナノチューブの束４のカーボンナノチューブ５は、互いに平行に、且つ、基板上に合成した際の空隙にほぼ等しい空隙５ａを有して配列している。このカーボンナノチューブの束４が、電極基材２上に積層されて、触媒層３が構成されている。尚、図示を省略しているが、カーボンナノチューブの束４同士を結合する少量のバインダーを含んでいてもよい。
カーボンナノチューブ５の径は、ナノメーターオーダーから数百ナノメーターオーダーのいずれであってよいが、好ましくはナノメーターオーダーである。また、カーボンナノチューブ５間の空隙５ａは、ナノメーターオーダーから数百ナノメーターオーダーのいずれであってよいが、好ましくはナノメーターオーダーである。
Hereinafter, the best mode for carrying out the present invention will be described in detail with reference to the drawings.
First, the catalyst electrode for a fuel cell of the present invention will be described.
FIG. 1 is a diagram showing a configuration of a catalyst electrode for a fuel cell according to the present invention, (a) a schematic cross-sectional view of the catalyst electrode for a fuel cell, and (b) a high-density It is a figure which shows a highly oriented carbon nanotube in detail.
(A) As shown to a figure, the catalyst electrode 1 for fuel cells of this invention consists of the catalyst layer 3 laminated | stacked on the surface of the electrode base material 2 and the electrode base material 2. FIG. The catalyst layer 3 is configured by stacking a bundle 4 of carbon nanotubes carrying a platinum group catalyst. The electrode base material 2 may be a member having gas diffusion capacity, electronic conductivity, and mechanical strength, and is, for example, carbon paper or carbon cloth.
(B) As shown in the figure, the bundle 4 of carbon nanotubes is composed of linear carbon nanotubes 5 carrying the platinum group catalyst 6 and having the same diameter and length at equal intervals, that is, equal gaps 5a. And having a structure arranged in the same direction, that is, a high-density, highly-oriented carbon nanotube. The bundle 4 of carbon nanotubes was synthesized on a substrate using a solid-liquid interfacial catalytic decomposition method described below, and the carbon nanotubes were sharpened at the tip or edged. By rubbing with a hard member such as a metal, it can be peeled off into a bundle. The carbon nanotubes 5 of the bundle 4 of carbon nanotubes are arranged in parallel with each other and having gaps 5a substantially equal to the gaps when synthesized on the substrate. The bundle 4 of carbon nanotubes is laminated on the electrode substrate 2 to form a catalyst layer 3. In addition, although illustration is abbreviate | omitted, the small amount of binder which couple | bonds the bundles 4 of carbon nanotubes may be included.
The diameter of the carbon nanotube 5 may be in the order of nanometers to several hundreds of nanometers, but is preferably in the order of nanometers. Further, the gap 5a between the carbon nanotubes 5 may be in the order of nanometers to several hundreds of nanometers, but preferably in the order of nanometers.
次に、本発明の燃料電池用触媒電極の作用を説明する。
触媒層３の触媒担体は、同一の径と長さを有する直線形状のカーボンナノチューブ５であり、触媒担体間の空隙は、カーボンナノチューブ５が等間隔で、すなわち、等しい空隙５ａを有して同一方向に配列して形成される空隙５ａであるので、触媒層３の触媒担体間の空隙は、触媒層３全体にわたって均一に分布しており、その結果、ガス拡散能力が高くなり、発電能力を向上させることができる。
また、触媒層３はカーボンナノチューブの束４が積層されてなるので、触媒層３のガス拡散能力は、カーボンナノチューブの束４を構成するカーボンナノチューブ５間の空隙５ａによって定まる。従って、触媒層３のガス拡散能力と触媒表面積の積が最大となる空隙５ａ、すなわち、電極反応速度を最大とする空隙５ａを有するカーボンナノチューブの束４を用いることによって、触媒層３の電極反応速度を最大にすることができる。
また、カーボンナノチューブ５は比表面積が極めて大きいので、カーボンナノチューブ５からなる触媒層３の白金族触媒の表面積も極めて大きくなり触媒層３の電極反応速度が増大する。
また、カーボンナノチューブ５はナノサイズの細長い形状を有するので、カーボンナノチューブ５に担持された白金族触媒６のサイズもナノサイズとなり、白金族触媒６の単位量あたりの触媒反応速度が大きくなるので、白金族触媒の使用量を低減できる。
従って、高密度・高配向カーボンナノチューブを白金族触媒層の触媒担体とした本発明の燃料電池用触媒電極は、発電能力が向上でき、且つ、白金族触媒の使用量を低減できる。
Next, the operation of the fuel cell catalyst electrode of the present invention will be described.
The catalyst carrier of the catalyst layer 3 is linear carbon nanotubes 5 having the same diameter and length, and the gaps between the catalyst carriers are the same with the carbon nanotubes 5 being equidistant, that is, having the same gaps 5a. Since the gaps 5a are formed so as to be arranged in the direction, the gaps between the catalyst carriers of the catalyst layer 3 are uniformly distributed over the entire catalyst layer 3, and as a result, the gas diffusion capacity is increased and the power generation capacity is increased. Can be improved.
Further, since the catalyst layer 3 is formed by stacking the bundles 4 of carbon nanotubes, the gas diffusion ability of the catalyst layer 3 is determined by the gaps 5 a between the carbon nanotubes 5 constituting the bundle 4 of carbon nanotubes. Therefore, the electrode reaction of the catalyst layer 3 is achieved by using the gap 5a having the maximum product of the gas diffusion capacity and the catalyst surface area of the catalyst layer 3, that is, the bundle 4 of carbon nanotubes having the gap 5a that maximizes the electrode reaction rate. Speed can be maximized.
Moreover, since the carbon nanotube 5 has a very large specific surface area, the surface area of the platinum group catalyst of the catalyst layer 3 made of the carbon nanotube 5 is also extremely increased, and the electrode reaction rate of the catalyst layer 3 is increased.
Further, since the carbon nanotube 5 has a nano-sized elongated shape, the size of the platinum group catalyst 6 supported on the carbon nanotube 5 is also nano-sized, and the catalytic reaction rate per unit amount of the platinum group catalyst 6 is increased. The amount of platinum group catalyst used can be reduced.
Therefore, the fuel cell catalyst electrode of the present invention using high-density, highly oriented carbon nanotubes as the catalyst carrier of the platinum group catalyst layer can improve the power generation capacity and reduce the amount of platinum group catalyst used.
次に、固液界面接触分解法による、上記の高密度・高配向カーボンナノチューブの合成方法を説明する。
図２は、固液界面接触分解法に用いる合成装置の構成を示す断面模式図である。
この合成装置は、液体槽２１の外側に液体槽２１を冷却するための水冷手段２２と、基板２３を保持し、かつ、基板２３に電流を流すための電極２４を有する基板ホルダー２５と、液体槽２１から蒸発する有機液体蒸気を冷却凝縮して液体槽２１に戻す水冷パイプ２６からなる凝縮手段２７と、基板ホルダー２５と凝縮手段２７とＮ2 ガスを導入するバルブ２８とを保持する蓋２９を有し、液体槽２１と蓋２９で有機液体３０を密閉して保持する構成である。
Next, a method for synthesizing the above-mentioned high-density and highly-oriented carbon nanotubes by the solid-liquid interface catalytic decomposition method will be described.
FIG. 2 is a schematic cross-sectional view showing a configuration of a synthesis apparatus used in the solid-liquid interface catalytic decomposition method.
This synthesizer includes a water cooling means 22 for cooling the liquid tank 21 outside the liquid tank 21, a substrate holder 25 having an electrode 24 for holding the substrate 23 and flowing current to the substrate 23, and a liquid A lid 29 for holding a condensing means 27 comprising a water-cooled pipe 26 for cooling and condensing the organic liquid vapor evaporated from the tank 21 and returning it to the liquid tank 21, a substrate holder 25, the condensing means 27, and a valve 28 for introducing N 2 gas. The organic liquid 30 is sealed and held by the liquid tank 21 and the lid 29.
この装置によれば、有機液体３０の温度を沸点未満に保持することができると共に、基板２３の温度を高温の成長温度に保持でき、カーボンナノチューブの合成が可能になる。 また、有機液体３０の気相が凝縮手段２７によって凝縮されて液体にもどるため原料の有機液体３０を無駄にすることがなく、さらに有機気相と空気との混合による爆発、炎上の危険がない。また、Ｎ2 ガスからなる不活性ガス導入手段を有するから、液体槽中での有機気相と空気との混合による爆発、炎上の危険がない。 According to this apparatus, the temperature of the organic liquid 30 can be kept below the boiling point, the temperature of the substrate 23 can be kept at a high growth temperature, and carbon nanotubes can be synthesized. Further, since the vapor phase of the organic liquid 30 is condensed by the condensing means 27 and returned to the liquid, the raw organic liquid 30 is not wasted, and there is no risk of explosion or flame due to mixing of the organic vapor phase and air. . Further, since the inert gas introducing means made of N 2 gas is provided, there is no danger of explosion and flame due to mixing of the organic gas phase and air in the liquid tank.
この装置を用いて、高密度・高配向カーボンナノチューブを合成する方法を、基板２３がＳｉであり、有機液体３０がメタノールの場合を例にとって説明する。導電性を有するＳｉ基板２３を洗浄し、Ｆｅ薄膜を堆積する。堆積手段は、例えば、Ａｒ中のスパッターでもよい。堆積するＦｅ薄膜の厚さは、合成するナノチューブの径と密度を決定するので目的に合わせてＦｅ薄膜の厚さを選択する。次に、Ｆｅ薄膜を堆積したＳｉ基板２３を、８５０℃に加熱する。この加熱処理によって、Ｆｅ薄膜が触媒微粒子となってＳｉ基板２３上に島状に分布すると共に、Ｓｉ基板２３に結合する。 A method for synthesizing high-density, highly-oriented carbon nanotubes using this apparatus will be described by taking the case where the substrate 23 is Si and the organic liquid 30 is methanol as an example. The conductive Si substrate 23 is cleaned, and an Fe thin film is deposited. The deposition means may be, for example, sputtering in Ar. The thickness of the Fe thin film to be deposited determines the diameter and density of the nanotube to be synthesized, so the thickness of the Fe thin film is selected according to the purpose. Next, the Si substrate 23 on which the Fe thin film is deposited is heated to 850 ° C. By this heat treatment, the Fe thin film becomes catalyst fine particles and is distributed in an island shape on the Si substrate 23 and is bonded to the Si substrate 23.
続いて、上記のＳｉ基板２３を、図２で示した合成装置の基板ホルダー２５に配置し、メタノール３０を満たし、Ｎ2 ガスを、バルブ２８を介して導入し、合成装置内の残留空気をＮ2 ガスで置換する。そして、電極２４を介してＳｉ基板２３に電流を流して加熱する。基板温度が９３０℃になる電流を流し、合成中もこの電流値に保つ。Ｓｉ基板２３の表面からメタノールのガスからなる気泡が発生すると共に、Ｓｉ基板２３の表面がこの気泡によって覆われる。この際、メタノール３０の温度をメタノールの沸点以下に保つことが必要であり、水冷手段２２を用いて冷却する。また気相のメタノールを凝縮手段２７により液体に戻し、液体槽２１に戻す。所望のカーボンナノチューブの長さに応じた一定時間、合成装置を上記の状態に保つことにより、Ｓｉ基板２３上に、高密度、且つ、高配向に整列した直線形状のカーボンナノチューブが合成できる。 Subsequently, the Si substrate 23 is placed on the substrate holder 25 of the synthesizer shown in FIG. 2, filled with methanol 30, and N 2 gas is introduced through the valve 28, and residual air in the synthesizer is removed. Replace with N 2 gas. Then, a current is passed through the Si substrate 23 through the electrode 24 to heat it. A current that causes the substrate temperature to reach 930 ° C. is passed, and this current value is maintained during the synthesis. Bubbles made of methanol gas are generated from the surface of the Si substrate 23, and the surface of the Si substrate 23 is covered with the bubbles. At this time, it is necessary to keep the temperature of the methanol 30 below the boiling point of methanol, and the water cooling means 22 is used for cooling. The vapor phase methanol is returned to the liquid by the condensing means 27 and returned to the liquid tank 21. By maintaining the synthesis apparatus in the above state for a certain period of time according to the length of the desired carbon nanotubes, linear carbon nanotubes aligned in a high density and high orientation can be synthesized on the Si substrate 23.
さらに、上記のＦｅ薄膜の替わりに、コバルトの結合エネルギーが正方向に１ｅＶから３ｅＶの範囲でシフトする酸化度で酸化された酸化コバルト薄膜を用いれば、極めて径が小さい直線形状のカーボンナノチューブを基板上に極めて高い密度で成長させることができる。すなわち、基板上に島状に分布したＦｅ等の遷移金属からなる触媒微粒子は、有機液体中で基板を加熱する際の高温によって、互いに結合して大きな径の触媒微粒子になる粒成長が起きやすく、また、成長するカーボンナノチューブの径は触媒微粒子の径に比例するので、成長した、高密度・高配向カーボンナノチューブのカーボンナノチューブは、径が比較的大きく、また、密度が比較的小さくなりやすい。一方、酸化コバルト触媒微粒子は、有機液体中で基板を加熱する際の高温によって粒成長が生じず、酸化コバルト薄膜を加熱処理して基板上に触媒微粒子を島状に分布させた際の粒径、密度が変化しない。このため、極めて径の小さいカーボンナノチューブを極めて高密度に成長できる。コバルトの結合エネルギーのシフトが、正方向に１ｅＶ未満の低い酸化度では、粒成長がおきやすくなり、３ｅＶを超える高い酸化度では、触媒作用を失ってカーボンナノチューブが成長しなくなる。以下に、酸化コバルト触媒微粒子を用いて固液界面接触分解法により合成した高密度・高配向カーボンナノチューブの例を示す。 Furthermore, instead of the above-described Fe thin film, if a cobalt oxide thin film oxidized with an oxidation degree in which the binding energy of cobalt is shifted in the range of 1 eV to 3 eV in the positive direction is used, a linear carbon nanotube having a very small diameter is used as the substrate. It can be grown at a very high density. That is, catalyst fine particles composed of transition metals such as Fe distributed in islands on the substrate are likely to grow together to become large-sized catalyst fine particles due to high temperatures when the substrate is heated in an organic liquid. Further, since the diameter of the growing carbon nanotube is proportional to the diameter of the catalyst fine particles, the grown carbon nanotube of the high-density / highly oriented carbon nanotube has a relatively large diameter and is likely to have a relatively small density. On the other hand, the cobalt oxide catalyst fine particle does not grow due to the high temperature when the substrate is heated in the organic liquid, and the particle size when the catalyst fine particle is distributed in islands on the substrate by heat treatment of the cobalt oxide thin film. The density does not change. For this reason, carbon nanotubes having a very small diameter can be grown at a very high density. When the shift of the binding energy of cobalt is low and the degree of oxidation is less than 1 eV, grain growth tends to occur. When the degree of oxidation exceeds 3 eV, the catalytic action is lost and carbon nanotubes do not grow. Examples of high density and highly oriented carbon nanotubes synthesized by solid-liquid interface catalytic cracking using cobalt oxide catalyst fine particles are shown below.
導電性ｎ型Ｓｉ（１００）基板上に、厚さ５ｎｍのコバルト薄膜を堆積し、空気中で９００℃、１０分加熱して、酸化コバルト触媒微粒子を担持した。この基板を、メタノール中で９００℃、３０分間加熱して、高密度・高配向カーボンナノチューブを合成した。
図３は、酸化コバルト触媒微粒子を用いた固液界面接触分解法により合成した、高密度・高配向カーボンナノチューブの走査電子顕微鏡像を示す図である。
図は、高密度・高配向カーボンナノチューブが合成された基板を、基板表面に垂直に壁開し、表面に対し斜め上方より観測した走査電子顕微鏡像である。
図から、基板面に、径が約１０ｎｍの直線状のカーボンナノチューブが、約１０ｎｍの等間隔で配列して成長していることがわかる。直線状のカーボンナノチューブが、平行に同一方向に配列しているのでガス拡散能力大きく、径が小さいので触媒表面積が大きく、また、空隙が触媒層の電極反応速度を最大とする最適な触媒担体間の空隙に近いので、触媒層の電極反応速度を大きくできる。
A cobalt thin film having a thickness of 5 nm was deposited on a conductive n-type Si (100) substrate and heated in air at 900 ° C. for 10 minutes to carry cobalt oxide catalyst fine particles. This substrate was heated in methanol at 900 ° C. for 30 minutes to synthesize high density and highly oriented carbon nanotubes.
FIG. 3 is a view showing a scanning electron microscope image of high-density and highly-oriented carbon nanotubes synthesized by a solid-liquid interface catalytic decomposition method using cobalt oxide catalyst fine particles.
The figure shows a scanning electron microscope image of a substrate on which high-density and highly-oriented carbon nanotubes were synthesized, opened from a wall perpendicular to the substrate surface and observed obliquely from above the surface.
From the figure, it can be seen that linear carbon nanotubes having a diameter of about 10 nm are grown on the substrate surface at regular intervals of about 10 nm. Linear carbon nanotubes are arranged in parallel in the same direction, so the gas diffusion capacity is large, the diameter is small, the catalyst surface area is large, and the gap between the optimal catalyst supports maximizes the electrode reaction rate of the catalyst layer. Therefore, the electrode reaction rate of the catalyst layer can be increased.
次に、本発明の燃料電池用膜・電極接合体を説明する。
図４は、本発明の燃料電池用膜・電極接合体の構成を示す模式断面図である。
（ａ）図に示すように、本発明の燃料電池用膜・電極接合体４１は、図1に示した本発明の燃料電池用触媒電極１と、燃料電池用触媒電極１に接合した水素イオン伝導性固体電解質膜４２とからなる。水素イオン伝導性固体電解質膜４２は例えば、ナフィオン膜（デュポン社製、登録商標）であれば好ましい。燃料電池用膜・電極接合体４１はアノード側のみに用いてもよく、また、カソード側のみに用いてもよく、また、（ｂ）図に示すように、水素イオン伝導性固体電解質膜４２の両面にそれぞれ、触媒層３を接合し、それぞれの触媒層３にそれぞれ、電極基材２を接合し、アノード側及びカソード側の両方に用いる構成の燃料電池用膜・電極接合体４３であってもよい。
Next, the membrane / electrode assembly for a fuel cell of the present invention will be described.
FIG. 4 is a schematic cross-sectional view showing the configuration of the fuel cell membrane-electrode assembly of the present invention.
(A) As shown in the figure, the fuel cell membrane / electrode assembly 41 of the present invention comprises the fuel cell catalyst electrode 1 of the present invention shown in FIG. 1 and hydrogen ions bonded to the fuel cell catalyst electrode 1. It consists of a conductive solid electrolyte membrane 42. The hydrogen ion conductive solid electrolyte membrane 42 is preferably, for example, a Nafion membrane (manufactured by DuPont, registered trademark). The fuel cell membrane / electrode assembly 41 may be used only on the anode side, or may be used only on the cathode side. Also, as shown in FIG. A fuel cell membrane / electrode assembly 43 having a structure in which a catalyst layer 3 is bonded to each of both surfaces, an electrode base material 2 is bonded to each of the catalyst layers 3 and used on both the anode side and the cathode side. Also good.
次に、本発明の燃料電池用触媒電極を用いた燃料電池を説明する。
図５は、本発明の燃料電池の単セルの構成を示す模式断面図であり、（ａ）図は本発明の燃料電池用触媒電極１をアノード側に用いた本発明の燃料電池の単セル５１、（ｂ）図は本発明の燃料電池用触媒電極１をカソード側に用いた本発明の燃料電池の単セル５２、及び、（ｃ）図は本発明の燃料電池用触媒電極１をアノード側及びカソード側に用いた本発明の燃料電池の単セル５３を示す。
本発明の燃料電池の単セル５１、５２、及び５３は、図７に示した従来技術の燃料電池と比べて、燃料電池用触媒電極に、図１示した本発明の燃料電池用触媒電極１を用いることのみ異なり、他の構成は同じであるので、説明を省略する。
この構成によれば、発電能力が向上し、且つ、白金族触媒の使用量を低減した燃料電池が実現できる。
Next, a fuel cell using the fuel cell catalyst electrode of the present invention will be described.
FIG. 5 is a schematic cross-sectional view showing the configuration of a single cell of the fuel cell of the present invention. FIG. 5A is a single cell of the fuel cell of the present invention using the fuel cell catalyst electrode 1 of the present invention on the anode side. 51, (b) shows the single cell 52 of the fuel cell of the present invention using the fuel cell catalyst electrode 1 of the present invention on the cathode side, and (c) shows the anode of the fuel cell catalyst electrode 1 of the present invention as the anode. The single cell 53 of the fuel cell of the present invention used on the side and the cathode side is shown.
Compared with the prior art fuel cell shown in FIG. 7, the single cells 51, 52, and 53 of the fuel cell of the present invention are different from the fuel cell catalyst electrode shown in FIG. Since the other configurations are the same except for the use of, the description is omitted.
According to this configuration, it is possible to realize a fuel cell with improved power generation capacity and a reduced amount of platinum group catalyst used.
次に、本発明の燃料電池用触媒電極の製造方法を説明する。
はじめに、図２に示した合成装置を用いて固液界面接触分解法により、基板上に、高密度、且つ、高配向に整列した直線形状のカーボンナノチューブを合成する。
次に、このカーボンナノチューブに白金族触媒を担持する。担持方法は一般的な含浸法が使用できる。例えば、白金族塩を溶媒に溶解又は分散させてコロイド状とし、このコロイド溶液中に上記カーボンナノチューブを浸し、還元処理をしてカーボンナノチューブ上に白金族触媒を担持する。また、白金族金属をスパッタリングして蒸着する等の蒸着法でもよい。
Next, the manufacturing method of the catalyst electrode for fuel cells of this invention is demonstrated.
First, linear carbon nanotubes aligned with high density and high orientation are synthesized on a substrate by a solid-liquid interface catalytic decomposition method using the synthesis apparatus shown in FIG.
Next, a platinum group catalyst is supported on the carbon nanotubes. As a supporting method, a general impregnation method can be used. For example, a platinum group salt is dissolved or dispersed in a solvent to form a colloidal form, the carbon nanotubes are immersed in the colloidal solution, and subjected to a reduction treatment to support the platinum group catalyst on the carbon nanotubes. Alternatively, a vapor deposition method such as sputtering and vapor deposition of a platinum group metal may be used.
次に、白金族触媒を担持したカーボンナノチューブを基板上から剥離する。剥離方法は、先端が尖った、あるいは辺が刃状になった金属等の硬い部材で擦ることによって、基板からカーボンナノチューブを束状に剥離できる。カーボンナノチューブの束のカーボンナノチューブは、互いに平行に、且つ、基板上に合成した際の空隙にほぼ等しい空隙を有して配列している。このカーボンナノチューブの束を、溶媒に分散させてペースト状とし、これをカーボンペーパーやカーボンクロス等の多孔質電極基材に塗布し、焼成することによって、本発明の燃料電池用触媒電極を製造する。 Next, the carbon nanotube carrying the platinum group catalyst is peeled from the substrate. In the peeling method, the carbon nanotubes can be peeled from the substrate in a bundle by rubbing with a hard member such as a metal having a sharp tip or a blade-like edge. The carbon nanotubes in the bundle of carbon nanotubes are arranged in parallel to each other and having a void substantially equal to the void when synthesized on the substrate. The bundle of carbon nanotubes is dispersed in a solvent to form a paste, which is applied to a porous electrode substrate such as carbon paper or carbon cloth, and fired to produce the fuel cell catalyst electrode of the present invention. .
次に、本発明の燃料電池用膜・電極接合体の製造方法を説明する。
本発明の燃料電池用膜・電極接合体は、図１に示した本発明の燃料電池用触媒電極と水素イオン伝導性高分子電解質膜とを重ねあわせ、熱プレスして接合し、製造する。
また、図４（ｂ）に示したように、本発明の燃料電池用触媒電極をアノード側触媒電極及びカソード側触媒電極として用いる場合には、水素イオン伝導性固体電解質膜の両面にそれぞれ、本発明の燃料電池用触媒電極の触媒層面を重ねあわせ、熱プレスして接合し、製造する。
Next, the manufacturing method of the membrane-electrode assembly for fuel cells of this invention is demonstrated.
The fuel cell membrane / electrode assembly of the present invention is produced by superposing the fuel cell catalyst electrode of the present invention and the hydrogen ion conductive polymer electrolyte membrane shown in FIG.
Further, as shown in FIG. 4B, when the fuel cell catalyst electrode of the present invention is used as an anode side catalyst electrode and a cathode side catalyst electrode, the present invention is provided on both sides of the hydrogen ion conductive solid electrolyte membrane, respectively. The catalyst layer surfaces of the catalyst electrode for a fuel cell of the invention are overlapped and joined by hot pressing.
次に、本発明の燃料電池の製造方法を説明する。
図５（ａ）に示したように、本発明の燃料電池用触媒電極をアノード側触媒電極として用いる場合は、本発明の燃料電池用膜・電極接合体の水素イオン伝導性高分子電解質膜側に従来技術のカソード側触媒電極を接合し、この接合体の上下面にセパレータを接合して単セルとし、この単セルを複数、直列に接合して本発明の燃料電池を製造する。
また、図５（ｂ）に示したように、本発明の燃料電池用触媒電極をカソード側触媒電極として用いる場合は、本発明の燃料電池用膜・電極接合体の水素イオン伝導性高分子電解質膜に従来技術のアノード側触媒電極を接合し、この接合体の上下面にセパレータを接合して単セルとし、この単セルを複数、直列に接合して本発明の燃料電池を製造する。
また、図５（ｃ）に示したように、本発明の燃料電池用触媒電極をアノード側触媒電極及びカソード側触媒電極として用いる場合は、図４（ｂ）に示した本発明の燃料電池用膜・電極接合体の上下面にそれぞれ、セパレータを接合して単セルとし、この単セルを複数、直列に接合して本発明の燃料電池を製造する。
Next, the manufacturing method of the fuel cell of this invention is demonstrated.
As shown in FIG. 5A, when the fuel cell catalyst electrode of the present invention is used as an anode side catalyst electrode, the hydrogen ion conductive polymer electrolyte membrane side of the fuel cell membrane / electrode assembly of the present invention is used. The cathode-side catalyst electrode of the prior art is joined, separators are joined to the upper and lower surfaces of the joined body to form a single cell, and a plurality of the single cells are joined in series to produce the fuel cell of the present invention.
Further, as shown in FIG. 5B, when the fuel cell catalyst electrode of the present invention is used as a cathode side catalyst electrode, the hydrogen ion conductive polymer electrolyte of the fuel cell membrane / electrode assembly of the present invention is used. A conventional anode-side catalyst electrode is joined to the membrane, separators are joined to the upper and lower surfaces of the joined body to form a single cell, and a plurality of the single cells are joined in series to produce the fuel cell of the present invention.
As shown in FIG. 5 (c), when the fuel cell catalyst electrode of the present invention is used as an anode side catalyst electrode and a cathode side catalyst electrode, it is used for the fuel cell of the present invention shown in FIG. 4 (b). A separator is joined to the upper and lower surfaces of the membrane / electrode assembly to form a single cell, and a plurality of single cells are joined in series to produce the fuel cell of the present invention.
（実施例１）
導電性ｎ型Ｓｉ（１００）基板上に、厚さ５ｎｍのコバルト薄膜を堆積し、空気中で９００℃、１０分加熱して、酸化コバルト触媒微粒子を担持した基板を作成した。この基板を、メタノール中で６００℃、５分間加熱し、引き続き、９００℃、５分間加熱する固液界面接触分解法により、径が約１０ｎｍ、長さが約１μｍの直線状のカーボンナノチューブが約１０ｎｍの等間隔で配列した高密度・高配向カーボンナノチューブを合成した。尚、合成過程を６００℃と９００℃の２段階に分けて合成することによってカーボンナノチューブの導電性を向上させることができる（特願２００６−０７００３０参照）。
次に、含浸法により、上記カーボンナノチューブに白金触媒を５ｗ％担持した。このカーボンナノチューブを基板から剥離して、約１０μｍ径のカーボンナノチューブの束を作成した。このカーボンナノチューブの束４．８ｇ、市販の水素イオン伝導性高分子電解質２１ｗｔ％ナフィオン溶液（登録商標）１１．４ｇ、水６．４ｇ、及び、イソプロパノール１０．０ｇとからなる混合溶媒中で超音波ホモジナイザーを使用して３０分間攪拌して触媒ペーストを調製した。この触媒ペーストを触媒ペーストＡとする。
また、従来技術による触媒ペーストを次のようにして作製した。すなわち、粒径約１０ｎｍのカーボンブラック微粒子に白金触媒を３０ｗｔ％担持した市販の白金担持カーボン触媒２．０ｇ、市販の水素イオン伝導性高分子電解質２１ｗｔ％溶液ナフィオン溶液（登録商標）５．０ｇ、水１１．０ｇ、及び、イソプロパノール１６．０ｇとからなる混合溶媒中で超音波ホモジナイザーを使用して３０分間攪拌して触媒ペーストを調製した。この触媒ペーストを触媒ペーストＢとする。
次に、調整した触媒ペーストＡをカーボンペーパー（Ｅ―Ｔｅｋ社製）上へ厚さ３μｍで塗布して焼成し、本発明の燃料電池用触媒電極を作製した。この燃料電池用触媒電極を触媒電極Ａとする。また、調整した触媒ペーストＢをカーボンペーパー（Ｅ―Ｔｅｋ社製）上へ厚さ３μｍで塗布して焼成し、従来技術の比較用燃料電池用触媒電極を作製した。この燃料電池用触媒電極を触媒電極Ｂとする。
次に、触媒電極Ａ、及び、触媒電極Ｂを同一の面積に切断し、これらの触媒電極をそれぞれ、水素イオン伝導性高分子電解質膜（デュポン社製ナフィオン膜、登録商標）に接合し、燃料電池用膜・電極接合体を作製した。接合には熱プレスを用いて、１４０℃、５０ｋｇ／ｃｍ2、５分の条件で行った。触媒電極Ａを用いた燃料電池用膜・電極接合体を膜・電極接合体Ａ、触媒電極Ｂを用いた燃料電池用膜・電極接合体を膜・電極接合体Ｂとする。
次に、膜・電極接合体Ａの固体電解質膜側に触媒電極Ｂを接合し、この接合体の上下面にセパレータを接合し、本発明の燃料電池用触媒電極Ａをアノード側に用い、カソード側には従来技術の触媒電極Ｂを用いた構成の燃料電池を作成した。この燃料電池を燃料電池Ａとする。
Example 1
A cobalt thin film having a thickness of 5 nm was deposited on a conductive n-type Si (100) substrate and heated in air at 900 ° C. for 10 minutes to prepare a substrate carrying cobalt oxide catalyst fine particles. This substrate was heated in methanol at 600 ° C. for 5 minutes, and subsequently heated at 900 ° C. for 5 minutes, so that the solid carbon nanotubes having a diameter of about 10 nm and a length of about 1 μm were obtained. High density and highly oriented carbon nanotubes arrayed at equal intervals of 10 nm were synthesized. Note that the conductivity of the carbon nanotube can be improved by dividing the synthesis process into two steps of 600 ° C. and 900 ° C. (see Japanese Patent Application No. 2006-070030).
Next, 5% by weight of a platinum catalyst was supported on the carbon nanotubes by an impregnation method. The carbon nanotubes were peeled from the substrate to produce a bundle of carbon nanotubes having a diameter of about 10 μm. Ultrasonication was performed in a mixed solvent consisting of 4.8 g of this carbon nanotube bundle, 11.4 g of a commercially available hydrogen ion conductive polymer electrolyte 21 wt% Nafion solution (registered trademark) 11.4 g, water 6.4 g, and 10.0 g of isopropanol. A catalyst paste was prepared by stirring for 30 minutes using a homogenizer. This catalyst paste is referred to as catalyst paste A.
Moreover, the catalyst paste by a prior art was produced as follows. That is, 2.0 g of a commercially available platinum-supported carbon catalyst in which 30 wt% of a platinum catalyst is supported on carbon black fine particles having a particle diameter of about 10 nm, 5.0 g of a commercially available hydrogen ion conductive polymer electrolyte 21 wt% solution Nafion solution (registered trademark), A catalyst paste was prepared by stirring for 30 minutes using an ultrasonic homogenizer in a mixed solvent consisting of 11.0 g of water and 16.0 g of isopropanol. This catalyst paste is referred to as catalyst paste B.
Next, the prepared catalyst paste A was applied onto carbon paper (manufactured by E-Tek) at a thickness of 3 μm and fired to produce a fuel cell catalyst electrode of the present invention. This catalyst electrode for a fuel cell is referred to as catalyst electrode A. Further, the prepared catalyst paste B was applied onto carbon paper (manufactured by E-Tek) at a thickness of 3 μm and fired to produce a catalyst electrode for a comparative fuel cell of the prior art. This catalyst electrode for a fuel cell is referred to as catalyst electrode B.
Next, the catalyst electrode A and the catalyst electrode B are cut into the same area, and each of these catalyst electrodes is joined to a hydrogen ion conductive polymer electrolyte membrane (Nafion membrane, registered trademark) manufactured by DuPont. A battery membrane / electrode assembly was prepared. The joining was performed using a hot press under conditions of 140 ° C., 50 kg / cm 2 , and 5 minutes. The membrane / electrode assembly for fuel cell using the catalyst electrode A is referred to as membrane / electrode assembly A, and the membrane / electrode assembly for fuel cell using the catalyst electrode B is referred to as membrane / electrode assembly B.
Next, the catalyst electrode B is joined to the solid electrolyte membrane side of the membrane / electrode assembly A, separators are joined to the upper and lower surfaces of the joined body, the fuel cell catalyst electrode A of the present invention is used on the anode side, and the cathode On the side, a fuel cell having a configuration using the catalyst electrode B of the prior art was prepared. This fuel cell is referred to as a fuel cell A.
（実施例２）
膜・電極接合体Ｂの固体電解質膜側に触媒電極Ａを接合し、本発明の燃料電池用触媒電極Ａをカソード側に用い、アノード側には従来技術の触媒電極Ｂを用いたことのみ実施例１と異なる構成の燃料電池を作成した。この燃料電池を燃料電池Ｂとする。
(Example 2)
Only the catalyst electrode A was joined to the solid electrolyte membrane side of the membrane-electrode assembly B, the catalyst electrode A for the fuel cell of the present invention was used on the cathode side, and the conventional catalyst electrode B was used on the anode side. A fuel cell having a configuration different from that of Example 1 was prepared. This fuel cell is referred to as a fuel cell B.
（実施例３）
膜・電極接合体Ａの固体電解質膜側に触媒電極Ａを接合し、本発明の燃料電池用触媒電極Ａをアノード側及びカソード側の両方に用いたことのみ実施例１と異なる構成の燃料電池を作成した。この燃料電池を燃料電池Ｃとする。
(Example 3)
A fuel cell having a configuration different from that of Example 1 only in that the catalyst electrode A is joined to the solid electrolyte membrane side of the membrane-electrode assembly A, and the catalyst electrode A for the fuel cell of the present invention is used on both the anode side and the cathode side. It was created. This fuel cell is referred to as a fuel cell C.
次に、上記燃料電池Ａ、Ｂ、及び、Ｃの発電能力を測定した。水素流量が１０００ｍｌ／分、酸素流量が１０００ｍｌ／分となるようにして８０℃で加湿・加熱した水素ガスと、酸素ガスを供給して反応を行わせて発電能力を測定した。測定は、起電力が０．５ｖｏｌｔになるように負荷抵抗を選択したときの、触媒層単位表面積当たりの発電電流、すなわち、発電電流密度で比較した。
図６は、燃料電池Ａ、Ｂ、及び、Ｃの発電能力の測定結果を示す図である。
図から、本発明の燃料電池用触媒電極Ａをアノード側及びカソード側の両方に用いた燃料電池Ｃは、１２００ｍＡ／ｃｍ２の発電電流密度を有することがわかり、また、燃料電池の発電電流密度は、アノード側、又はカソード側のいずれか小さい方の発電電流密度によって制限されるので、本発明のアノード側燃料電池用触媒電極Ａ、又は、本発明のカソード側燃料電池用触媒電極Ａはそれぞれ、少なくとも１２００ｍＡ／ｃｍ２の発電電流密度を有することがわかる。
また、図から、本発明の燃料電池用触媒電極Ａをアノード側及び従来技術の触媒電極Ｂをカソード側に用いた燃料電池Ａの発電電流密度は、燃料電池Ｃの発電電流密度よりも低いことがわかり、従って、燃料電池Ａの発電電流密度は従来技術のカソード側触媒電極Ｂの発電電流密度によって制限されており、その大きさは６００ｍＡ／ｃｍ２であることがわかる。
また、図から、本発明の燃料電池用触媒電極Ａをカソード側及び従来技術の触媒電極Ｂをアノード側に用いた燃料電池Ｂの発電電流密度は、燃料電池Ｃの発電電流密度よりも低いことがわかり、従って、燃料電池Ｂの発電電流密度は従来技術のアノード側触媒電極Ｂの発電電流密度によって制限されており、その大きさは６２０ｍＡ／ｃｍ２であることがわかる。
このように、本発明の燃料電池用触媒電極は、アノード側及びカソード側とも、カーボン微粒子を用いる従来技術の燃料電池用触媒電極に比べて、白金使用量が少ないにもかかわらず、約２倍の発電能力を有することがわかる。この結果は、高密度・高配向カーボンナノチューブの空隙分布が均一であること、その空隙の大きさが触媒層の電極反応速度を最大とする空隙に近いこと、また、径の小さいカーボンナノチューブを触媒担体とするので、触媒表面積が大きく、且つ白金触媒単位量あたりの電極反応速度が大きいためと考えられる。
Next, the power generation capacities of the fuel cells A, B, and C were measured. The power generation capacity was measured by supplying hydrogen gas that was humidified and heated at 80 ° C. so that the hydrogen flow rate was 1000 ml / min and the oxygen flow rate was 1000 ml / min, and the reaction was performed by supplying oxygen gas. The measurement was made by comparing the generated current per unit surface area of the catalyst layer when the load resistance was selected so that the electromotive force was 0.5 volt, that is, the generated current density.
FIG. 6 is a diagram illustrating measurement results of the power generation capacities of the fuel cells A, B, and C.
From the figure, it can be seen that the fuel cell C using the fuel cell catalyst electrode A of the present invention on both the anode side and the cathode side has a power generation current density of 1200 mA / cm 2 , and the power generation current density of the fuel cell. Is limited by the smaller power generation current density on the anode side or on the cathode side, the anode side fuel cell catalyst electrode A of the present invention or the cathode side fuel cell catalyst electrode A of the present invention is respectively It can be seen that it has a generated current density of at least 1200 mA / cm 2 .
Also, from the figure, the power generation current density of the fuel cell A using the fuel cell catalyst electrode A of the present invention on the anode side and the prior art catalyst electrode B on the cathode side is lower than the power generation current density of the fuel cell C. Therefore, it can be seen that the generated current density of the fuel cell A is limited by the generated current density of the cathode-side catalyst electrode B of the prior art, and the magnitude is 600 mA / cm 2 .
Also, from the figure, the power generation current density of the fuel cell B using the catalyst electrode A for the fuel cell of the present invention on the cathode side and the catalyst electrode B of the prior art on the anode side is lower than the power generation current density of the fuel cell C. Therefore, it can be seen that the generated current density of the fuel cell B is limited by the generated current density of the anode-side catalyst electrode B of the prior art, and the size thereof is 620 mA / cm 2 .
Thus, the fuel cell catalyst electrode of the present invention is about twice as large on both the anode side and the cathode side as compared with the prior art fuel cell catalyst electrode using carbon fine particles, although the amount of platinum used is small. It can be seen that it has the power generation capacity. This result shows that the distribution of voids in the high density and highly oriented carbon nanotubes is uniform, that the size of the voids is close to the voids that maximize the electrode reaction rate of the catalyst layer, and that carbon nanotubes with small diameters are catalyzed. Since it is a support, the catalyst surface area is large and the electrode reaction rate per unit amount of platinum catalyst is high.
上記説明から理解されるように、本発明の燃料電池用触媒電極、膜・電極接合体、及び、燃料電池は、電極の触媒層に、高密度・高配向カーボンナノチューブを用いるので、発電能力が高く、且つ、白金族触媒の使用量が少ない。
また、高密度・高配向カーボンナノチューブは、固液界面接触分解法により、再現性よく、且つ、大量に製造できるので、低コストで本発明の燃料電池を供給できる。
As understood from the above description, the catalyst electrode for fuel cells, the membrane / electrode assembly, and the fuel cell of the present invention use high-density and highly-oriented carbon nanotubes in the electrode catalyst layer, so that the power generation capacity is high. High and the amount of platinum group catalyst used is small.
In addition, since the high-density and highly-oriented carbon nanotubes can be produced in large quantities with good reproducibility by the solid-liquid interface catalytic decomposition method, the fuel cell of the present invention can be supplied at low cost.
１ 本発明の燃料電池用触媒電極
２ 電極基材
３ 触媒層
４ カーボンナノチューブの束
５ カーボンナノチューブ
５ａ カーボンナノチューブの間隔
６ 白金族触媒
２１ 液体槽
２２ 水冷手段
２３ 基板
２４ 電極
２５ 基板ホルダー
２６ 水冷パイプ
２７ 凝縮手段
２８ バルブ
２９ 蓋
３０ 有機液体
４１ 本発明の燃料電池用触媒電極・膜接合体
４２ 水素イオン伝導性固体電解質膜
４３ 本発明の燃料電池用触媒電極・膜接合体
５１ 本発明の燃料電池
５２ 本発明の燃料電池
５３ 本発明の燃料電池
６０ 燃料電池単セル
６１ アノード側セパレータ
６１ａ 反応ガス流路
６２ アノード側触媒電極
６２ａ 電極基材
６２ｂ 触媒層
６３ 水素イオン伝導性固体電解質膜
６４ カソード側触媒電極
６４ａ 電極基材
６４ｂ 触媒層
６５ カソード側セパレータ
６５ａ 反応ガス流路
DESCRIPTION OF SYMBOLS 1 Catalyst electrode for fuel cells 2 Electrode base material 3 Catalyst layer 4 Carbon nanotube bundle 5 Carbon nanotube 5a Interval between carbon nanotubes 6 Platinum group catalyst 21 Liquid tank 22 Water cooling means 23 Substrate 24 Electrode 25 Substrate holder 26 Water cooling pipe 27 Condensing means 28 Valve 29 Lid 30 Organic liquid 41 Fuel cell catalyst electrode / membrane assembly 42 of the present invention Hydrogen ion conductive solid electrolyte membrane 43 Fuel cell catalyst electrode / membrane assembly 51 of the present invention Fuel cell 52 of the present invention Fuel cell 53 of the present invention Fuel cell 60 of the present invention Fuel cell single cell 61 Anode-side separator 61a Reaction gas flow path 62 Anode-side catalyst electrode 62a Electrode base material 62b Catalyst layer 63 Hydrogen ion conductive solid electrolyte membrane 64 Cathode-side catalyst electrode 64a Electrode substrate 64b Catalyst layer 65 Cathode side separator 65a Reaction gas A road
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| CN101635362B (en) * | 2008-07-25 | 2012-03-28 | 清华大学 | Membrane electrode and fuel cell adopting same |
| JP5476753B2 (en) * | 2009-03-16 | 2014-04-23 | トヨタ自動車株式会社 | Fuel cell |
| JP5686988B2 (en) | 2009-05-04 | 2015-03-18 | シャープ株式会社 | Catalyst layer used for membrane electrode assembly for fuel cell, membrane electrode assembly for fuel cell using the same, fuel cell, and production method thereof |
| JP5476883B2 (en) * | 2009-09-15 | 2014-04-23 | 独立行政法人物質・材料研究機構 | Nanocarbon material composite and method for producing the same |
| JP5558087B2 (en) * | 2009-12-08 | 2014-07-23 | ニッタ株式会社 | CNT network structure |
| JP5402662B2 (en) * | 2010-01-18 | 2014-01-29 | トヨタ自動車株式会社 | Membrane electrode assembly and method for producing membrane electrode assembly |
| JP6387300B2 (en) * | 2011-06-20 | 2018-09-05 | 矢崎総業株式会社 | Carbon agglomeration assembly and its applications |
| JP5831009B2 (en) * | 2011-07-25 | 2015-12-09 | 株式会社豊田中央研究所 | MICROSTRUCTURE MATERIAL, PROCESS FOR PRODUCING THE SAME, AND MEMBRANE ELECTRODE ASSEMBLY FOR FUEL CELL |
| JP5655802B2 (en) * | 2012-03-01 | 2015-01-21 | トヨタ自動車株式会社 | Membrane electrode assembly manufacturing method, membrane electrode assembly, and fuel cell |
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