JP5375152B2 - Fuel cell catalyst layer - Google Patents
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- JP5375152B2 JP5375152B2 JP2009031001A JP2009031001A JP5375152B2 JP 5375152 B2 JP5375152 B2 JP 5375152B2 JP 2009031001 A JP2009031001 A JP 2009031001A JP 2009031001 A JP2009031001 A JP 2009031001A JP 5375152 B2 JP5375152 B2 JP 5375152B2
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- 239000003054 catalyst Substances 0.000 title claims abstract description 178
- 239000000446 fuel Substances 0.000 title claims abstract description 24
- 239000011148 porous material Substances 0.000 claims abstract description 70
- 239000010419 fine particle Substances 0.000 claims abstract description 69
- 239000005518 polymer electrolyte Substances 0.000 claims abstract description 32
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims abstract description 24
- 229910052799 carbon Inorganic materials 0.000 claims abstract description 23
- 239000002245 particle Substances 0.000 claims description 10
- BASFCYQUMIYNBI-UHFFFAOYSA-N platinum Chemical compound [Pt] BASFCYQUMIYNBI-UHFFFAOYSA-N 0.000 abstract description 71
- 229910052697 platinum Inorganic materials 0.000 abstract description 32
- 230000000052 comparative effect Effects 0.000 description 25
- 238000012360 testing method Methods 0.000 description 13
- 239000007789 gas Substances 0.000 description 6
- 230000001590 oxidative effect Effects 0.000 description 6
- 239000006229 carbon black Substances 0.000 description 5
- 230000000694 effects Effects 0.000 description 5
- 239000000463 material Substances 0.000 description 5
- 239000003792 electrolyte Substances 0.000 description 4
- MYMOFIZGZYHOMD-UHFFFAOYSA-N Dioxygen Chemical compound O=O MYMOFIZGZYHOMD-UHFFFAOYSA-N 0.000 description 3
- 230000007423 decrease Effects 0.000 description 3
- 238000010586 diagram Methods 0.000 description 3
- 229910001882 dioxygen Inorganic materials 0.000 description 3
- 239000003273 ketjen black Substances 0.000 description 3
- 238000010248 power generation Methods 0.000 description 3
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 description 2
- 229910006404 SnO 2 Inorganic materials 0.000 description 2
- XLOMVQKBTHCTTD-UHFFFAOYSA-N Zinc monoxide Chemical compound [Zn]=O XLOMVQKBTHCTTD-UHFFFAOYSA-N 0.000 description 2
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 2
- 239000006185 dispersion Substances 0.000 description 2
- 239000012528 membrane Substances 0.000 description 2
- 238000000034 method Methods 0.000 description 2
- 238000002429 nitrogen sorption measurement Methods 0.000 description 2
- 239000001301 oxygen Substances 0.000 description 2
- 229910052760 oxygen Inorganic materials 0.000 description 2
- 230000036647 reaction Effects 0.000 description 2
- XOLBLPGZBRYERU-UHFFFAOYSA-N tin dioxide Chemical compound O=[Sn]=O XOLBLPGZBRYERU-UHFFFAOYSA-N 0.000 description 2
- 229910001887 tin oxide Inorganic materials 0.000 description 2
- 229920000557 Nafion® Polymers 0.000 description 1
- 229910001260 Pt alloy Inorganic materials 0.000 description 1
- 229910003114 SrVO Inorganic materials 0.000 description 1
- 238000003917 TEM image Methods 0.000 description 1
- GWEVSGVZZGPLCZ-UHFFFAOYSA-N Titan oxide Chemical compound O=[Ti]=O GWEVSGVZZGPLCZ-UHFFFAOYSA-N 0.000 description 1
- 229910045601 alloy Inorganic materials 0.000 description 1
- 239000000956 alloy Substances 0.000 description 1
- 239000000969 carrier Substances 0.000 description 1
- 238000012937 correction Methods 0.000 description 1
- 238000005260 corrosion Methods 0.000 description 1
- 230000007797 corrosion Effects 0.000 description 1
- 238000002484 cyclic voltammetry Methods 0.000 description 1
- 238000007599 discharging Methods 0.000 description 1
- 238000001035 drying Methods 0.000 description 1
- 239000008151 electrolyte solution Substances 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
- 238000002474 experimental method Methods 0.000 description 1
- 239000004744 fabric Substances 0.000 description 1
- 238000004519 manufacturing process Methods 0.000 description 1
- 229910052751 metal Inorganic materials 0.000 description 1
- 239000002184 metal Substances 0.000 description 1
- 229910044991 metal oxide Inorganic materials 0.000 description 1
- 150000004706 metal oxides Chemical class 0.000 description 1
- 150000002739 metals Chemical class 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 238000007650 screen-printing Methods 0.000 description 1
- 239000007787 solid Substances 0.000 description 1
- OGIDPMRJRNCKJF-UHFFFAOYSA-N titanium oxide Inorganic materials [Ti]=O OGIDPMRJRNCKJF-UHFFFAOYSA-N 0.000 description 1
- 238000012546 transfer Methods 0.000 description 1
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 1
- 239000011787 zinc oxide Substances 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
Abstract
Description
本発明は燃料電池用触媒層の改良に関する。更に詳しくは、触媒層の触媒を構成する担体の改良に関する。 The present invention relates to an improvement in a catalyst layer for a fuel cell. More specifically, the present invention relates to an improvement of the carrier constituting the catalyst of the catalyst layer.
燃料電池の電極の触媒層は、白金触媒微粒子を担体に担持させてなる触媒と高分子電解質とを混合して形成していた。燃料電池の性能を向上させるには、反応の活性点の密度の向上が必要と考え、担体の比表面積を大きくするとともに、これへより多くの白金触媒微粒子を高い分散率で担持させることを目指してきた。
例えば担体として比表面積が８００ｍ２／ｇ以上のカーボンブラックを採用し、これに白金触媒微粒子を５０ｗｔ％以上担持させることにより白金触媒微粒子の比表面積を１００ｍ２／ｇ−Ｐｔ以上とすることができた。かかるカーボンブラックとして、ケッチェンブラックＥＣ（ケッチェン・ブラック・インターナショナル社製の商品名、以下同じ）及びケッチェンブラックＥＣ−６００ＪＤ（ケッチェン・ブラック・インターナショナル社製の商品名以下同じ、この明細書においてＫＢ６００ＪＤと略することがある。）を挙げることができる。
The catalyst layer of the electrode of the fuel cell is formed by mixing a catalyst in which platinum catalyst fine particles are supported on a carrier and a polymer electrolyte. In order to improve the performance of the fuel cell, it is necessary to improve the density of active sites of the reaction, aiming to increase the specific surface area of the support and to support more platinum catalyst fine particles on this with a high dispersion rate. I came.
For example, carbon black having a specific surface area of 800 m 2 / g or more is used as a carrier, and the platinum catalyst fine particles can be supported by 50 wt% or more on the carbon black so that the specific surface area of the platinum catalyst fine particles can be 100 m 2 / g-Pt or more. It was. As such carbon black, Ketjen Black EC (trade name made by Ketjen Black International Co., Ltd., hereinafter the same) and Ketjen Black EC-600JD (trade name made by Ketjen Black International Co., Ltd., the same below, KB600JD in this specification) May be abbreviated.).
白金触媒微粒子の担持量を多くすることで触媒層の薄膜化が可能となり、高活性でかつ濃度過電圧の低いＭＥＡ（Membrane Electrode Assembly、膜電極接合体）を提供できる。
本件に関連する技術を開示する文献として非特許文献１がある。この非特許文献１には０．０４μｍ及び０．１μｍ径の細孔を有するカーボン担体が開示されている。
By increasing the amount of platinum catalyst fine particles supported, the catalyst layer can be made thin, and a highly active MEA (Membrane Electrode Assembly) with a low concentration overvoltage can be provided.
There is Non-Patent Document 1 as a document disclosing the technology related to the present case. Non-Patent Document 1 discloses a carbon support having pores having a diameter of 0.04 μm and 0.1 μm.
白金触媒微粒子は高価であるので、これを高濃度かつ高分散させると触媒層ひいてはＭＥＡの製造コストを増大させることとなる。
本発明者らは白金触媒微粒子の使用量を削減すべく鋭意検討を重ねてきた。その結果、下記の知見を見出した。
図１はカーボン担体としてのＫＢ６００ＪＤにＰｔ６０ｗｔ％担持した触媒の３Ｄ−ＴＥＭ観察結果を示す。図１の３方向スライス像から担体内部に白金触媒微粒子が存在することが確認される。観察対象のＰｔ６０％／ＫＢ６００ＪＤでは白金触媒微粒子数の約６割が担体内部に存在し、その結果、活性点となる白金触媒微粒子の表面の約５割の面積が担体の内部にあることとなる。
この担体内部に存在している白金触媒微粒子が発電に寄与していないのなら、担持した白金触媒微粒子のうちのかなりの割合が無駄に存在していることになる。
触媒微粒子担持量が十分に多ければ、担体外表面に存在する白金触媒微粒子のみで充分な性能を得られるが、触媒微粒子量低減のために触媒微粒子担持量を減らして、かつ、性能を維持するためには白金触媒微粒子が担体内部に存在する比率をできるだけ少なくして、触媒微粒子利用率を上げる必要がある。
Since the platinum catalyst fine particles are expensive, if they are dispersed at a high concentration and high concentration, the production cost of the catalyst layer and thus the MEA is increased.
The present inventors have intensively studied to reduce the amount of platinum catalyst fine particles used. As a result, the following knowledge was found.
FIG. 1 shows a 3D-TEM observation result of a catalyst in which Pt 60 wt% is supported on KB600JD as a carbon support. It is confirmed from the three-directional slice image of FIG. 1 that platinum catalyst fine particles are present inside the carrier. In the Pt 60% / KB600JD to be observed, about 60% of the number of platinum catalyst fine particles is present inside the carrier, and as a result, about 50% of the surface of the platinum catalyst fine particles serving as active sites is inside the carrier. .
If the platinum catalyst fine particles present inside the carrier do not contribute to power generation, a considerable proportion of the supported platinum catalyst fine particles exists in vain.
If the amount of catalyst fine particles supported is sufficiently large, sufficient performance can be obtained with only the platinum catalyst fine particles present on the outer surface of the carrier, but the amount of catalyst fine particles supported is reduced and the performance is maintained to reduce the amount of catalyst fine particles. For this purpose, it is necessary to increase the utilization ratio of the catalyst fine particles by reducing the ratio of the platinum catalyst fine particles present inside the carrier as much as possible.
図２はＮ／Ｃ比を変えて作製した触媒層のＮ２吸着測定結果である。N/C比を大きくしたとき減少する細孔容積は主に細孔径4nm以上の細孔径によるもので、担体内部の細孔に由来する約３．５nmの細孔による細孔容積はほとんど変化しない。このことから、担体内部の細孔は高分子電解質によって殆どふさがれていないことがわかる。
図３は、図２の結果に基づき、担体の細孔容積と電解質添加量（N/C比）との関係をグラフ化したものである。図３より、N/C比を大きくしたとき減少する細孔容積は主に細孔径4nm以上のもので、4nm未満の細孔による細孔容積はほとんど変化しないという結果が得られた。
FIG. 2 shows N 2 adsorption measurement results of catalyst layers produced by changing the N / C ratio. The pore volume that decreases when the N / C ratio is increased is mainly due to the pore diameter of 4 nm or more, and the pore volume due to pores of about 3.5 nm derived from the pores inside the carrier hardly changes. . This shows that the pores inside the carrier are hardly blocked by the polymer electrolyte.
FIG. 3 is a graph showing the relationship between the pore volume of the support and the amount of electrolyte added (N / C ratio) based on the results of FIG. FIG. 3 shows that the pore volume that decreases when the N / C ratio is increased is mainly those with a pore diameter of 4 nm or more, and the pore volume due to pores of less than 4 nm hardly changes.
以上から、高分子電解質は触媒層における4nm未満の細孔には入らず、4nm未満の細孔に存在する白金触媒微粒子は電解質に接することができない。このような白金触媒微粒子の周囲には三相界面が形成されず、発電に寄与することができなくなる。
かかる白金触媒微粒子に対して電解質を接触させる方策として、高分子電解質を微細化、あるいは低分子化して、細孔内部まで高分子電解質が入り込めるようにするということが考えられる。
しかし、プロトン導電性の確保のためには高分子電解質の連続性が必要であり、細孔内部での高分子電解質の構造制御は難しい。さらには、４nm未満のような極めて小径な細孔内部において、そもそも白金触媒微粒子に酸素を十分供給し、かつ生成水を排出するといった物質移動が円滑に実行されるか否か疑問のところもある。
From the above, the polymer electrolyte does not enter the pores of less than 4 nm in the catalyst layer, and the platinum catalyst fine particles existing in the pores of less than 4 nm cannot contact the electrolyte. A three-phase interface is not formed around such platinum catalyst fine particles, and cannot contribute to power generation.
As a measure for bringing the electrolyte into contact with the platinum catalyst fine particles, it is conceivable that the polymer electrolyte is made fine or low in molecular weight so that the polymer electrolyte can enter the pores.
However, in order to ensure proton conductivity, the continuity of the polymer electrolyte is necessary, and it is difficult to control the structure of the polymer electrolyte inside the pores. Furthermore, there is a question as to whether mass transfer such as supplying oxygen sufficiently to the platinum catalyst fine particles and discharging generated water in the extremely small pores of less than 4 nm is performed. .
本発明者らの上記の知見に基づき、燃料電池用の触媒として、細孔径が４ｎｍ以上の細孔のみを有する担体に触媒微粒子を担持させてなるものが好適なことに気がついた。
かかる触媒によれば、高分子電解質が入り込めない細孔に白金触媒微粒子が入ることを防ぐため、4nm未満の細孔を持たない担体を用いることで白金触媒微粒子利用率を高めることができ、結果として白金の使用量削減が可能になるからである。
かかる触媒は汎用的なものと比べてその物理的特性が異なるため、これを従来の条件にしたがって高分子電解質と混合して触媒層としても、その触媒層はベストパフォーマンスを奏するものとはならない。
Based on the above findings of the present inventors, it has been found that a catalyst having fine catalyst particles supported on a carrier having only pores having a pore diameter of 4 nm or more is suitable as a fuel cell catalyst.
According to such a catalyst, in order to prevent the platinum catalyst fine particles from entering the pores into which the polymer electrolyte cannot enter, the utilization rate of the platinum catalyst fine particles can be increased by using a carrier having no pores of less than 4 nm, As a result, the amount of platinum used can be reduced.
Since such catalysts have different physical characteristics compared to general-purpose catalysts, even if they are mixed with a polymer electrolyte according to conventional conditions to form a catalyst layer, the catalyst layer does not exhibit the best performance.
本発明者らは上記の触媒を用いて触媒層を構成するため、カーボンブラック等のカーボン製の担体に注目し、かかる担体へ触媒微粒子を担持してなる触媒と高分子電解質とを混合する好適な条件につき検討を重ねてきた。その結果、触媒と高分子電解質との混合比に好適な範囲があること、及び触媒を構成する担体にも備えるべき好適な物理的特性があることを見出し、下記に規定する発明に想到した。
即ち、この発明の第１の局面は次のように規定される。
開口部の直径が４ｎｍ以上の細孔のみを有する担体に触媒微粒子を担持させてなる触媒と高分子電解質とが混合されている燃料電池用触媒層であって、
前記担体（Ａ）と前記高分子電解質（Ｂ）との重量比（Ｂ）／（Ａ）が、カーボンの真密度（Ｃ）と前記担体の真密度（Ｄ）の比（Ｃ）／（Ｄ）に０．５を乗じた値以下である、燃料電池用触媒層。
Since the present inventors configure the catalyst layer using the above-mentioned catalyst, it is preferable to pay attention to a carbon carrier such as carbon black and to mix a catalyst in which catalyst fine particles are supported on the carrier and a polymer electrolyte. We have repeatedly examined various conditions. As a result, the inventors have found that there is a suitable range for the mixing ratio of the catalyst and the polymer electrolyte, and that there are suitable physical characteristics that should also be provided for the carrier constituting the catalyst, and the inventors have arrived at the invention defined below.
That is, the first aspect of the present invention is defined as follows.
A catalyst layer for a fuel cell in which a catalyst in which catalyst fine particles are supported on a support having only pores having a diameter of 4 nm or more in an opening and a polymer electrolyte are mixed,
The weight ratio (B) / (A) between the carrier (A) and the polymer electrolyte (B) is the ratio of the true density (C) of carbon to the true density (D) of the carrier (C) / (D ) And a value equal to or less than 0.5 multiplied by 0.5.
このように規定される第１の局面の燃料電池用触媒層によれば、4nm未満の細孔を持たない担体を採用することで、高分子電解質が入り込めないような微細孔に触媒微粒子が入り込むことが防止される。換言すれば、担体の有する細孔にはすべて高分子電解質が充填され、細孔内面に担持された触媒微粒子を被覆する。これにより、触媒微粒子利用率を高めることができ、結果として触媒微粒子の使用量削減が可能になる。
そして、触媒と高分子電解質との混合比（高分子電解質／触媒）を０．５以下とすることにより、触媒層における燃料電池反応が円滑に進行し、燃料電池触媒層はその機能を充分に発揮できる。
According to the fuel cell catalyst layer of the first aspect defined as described above, by adopting a carrier having no pores of less than 4 nm, the catalyst fine particles are placed in the fine pores where the polymer electrolyte cannot enter. Intrusion is prevented. In other words, all the pores of the carrier are filled with the polymer electrolyte, and the catalyst fine particles supported on the inner surfaces of the pores are coated. Thereby, the utilization rate of catalyst fine particles can be increased, and as a result, the amount of catalyst fine particles used can be reduced.
By setting the mixing ratio of the catalyst and the polymer electrolyte (polymer electrolyte / catalyst) to 0.5 or less, the fuel cell reaction in the catalyst layer proceeds smoothly, and the fuel cell catalyst layer has sufficient function. Can demonstrate.
この発明の第２の局面は次のように規定される。即ち、
第１の局面に規定される燃料電池用触媒層であって、前記担体における１μｍ以下の細孔容積は、カーボンの真密度（Ｃ）と前記担体の真密度（Ｄ）の比（Ｃ）／（Ｄ）に０．７を乗じた値以下である。
このように規定された燃料電池用触媒層は、第１の局面で説明した作用に加えて、無加湿特性に優れる。
The second aspect of the present invention is defined as follows. That is,
The catalyst layer for a fuel cell defined in the first aspect, wherein the pore volume of 1 μm or less in the carrier is a ratio of the true carbon density (C) to the true density (D) of the carrier (C) / It is below the value which multiplied (D) by 0.7.
The fuel cell catalyst layer thus defined is excellent in non-humidifying properties in addition to the action described in the first aspect.
この発明の第３の局面は次のように規定される。即ち、
開口部の直径が４ｎｍ以上の細孔のみを有する担体に触媒微粒子を担持させてなる触媒と高分子電解質とが混合されている燃料電池用触媒層であって、
前記担体における１μｍ以下の細孔容積は、カーボンの真密度（Ｃ）と前記担体の真密度（Ｄ）の比（Ｃ）／（Ｄ）に０．７を乗じた値以下である、燃料電池用触媒層。
このように規定された第３の局面の発明によれば、4nm未満の細孔を持たない担体を採用することで、高分子電解質が入り込めないような微細孔に触媒微粒子が入り込むことが防止される。それにより、触媒微粒子利用率を高めることができ、結果として白金の使用量削減が可能になる。
そして、担体における１μｍ以下の細孔容積をカーボンの真密度（Ｃ）と前記担体の真密度（Ｄ）の比（Ｃ）／（Ｄ）に０．７を乗じた値以下とすることにより、無加湿特性に優れた燃料電池用触媒層となる。
The third aspect of the present invention is defined as follows. That is,
A catalyst layer for a fuel cell in which a catalyst in which catalyst fine particles are supported on a support having only pores having a diameter of 4 nm or more in an opening and a polymer electrolyte are mixed,
The pore volume of 1 μm or less in the carrier is not more than a value obtained by multiplying the ratio (C) / (D) of the true density (C) of carbon to the true density (D) of the carrier by 0.7. Catalyst layer.
According to the invention of the third aspect defined as described above, by adopting a carrier having no pores of less than 4 nm, it is possible to prevent catalyst fine particles from entering into fine pores where polymer electrolyte cannot enter. Is done. Thereby, the utilization rate of catalyst fine particles can be increased, and as a result, the amount of platinum used can be reduced.
And by setting the pore volume of 1 μm or less in the carrier to a value obtained by multiplying the ratio (C) / (D) of the true density of carbon (C) and the true density of the carrier (D) by 0.7, The fuel cell catalyst layer is excellent in non-humidification characteristics.
この発明の第４の局面は次のように規定される。即ち、
第１〜第３の局面で規定される燃料電池用触媒層において前記触媒微粒子の平均粒径が４ｎｍ未満である。
このように規定された第４の局面の燃料電池用触媒層によれば、触媒微粒子の平均粒径が、担体の細孔の開口部径より小さくされているので、触媒微粒子は担体の、その細孔内面も含めて、全表面に行渡り、そこに担持される。
The fourth aspect of the present invention is defined as follows. That is,
In the fuel cell catalyst layer defined in the first to third aspects, the catalyst fine particles have an average particle size of less than 4 nm.
According to the fuel cell catalyst layer of the fourth aspect defined as described above, since the average particle diameter of the catalyst fine particles is made smaller than the opening diameter of the pores of the carrier, the catalyst fine particles are those of the carrier. The entire surface, including the inner surface of the pores, is distributed and supported thereon.
まずは、触媒について説明する。
上記において、4nm未満の細孔を持たない担体の比表面積は小さく、従来の高性能触媒のような高い担持率にすると触媒微粒子径が大きくて、触媒微粒子比表面積が小さい重量比活性の低い触媒になってしまい、触媒微粒子使用量の低減をすることができない。
そこで、（高比表面積担体に高担持・高分散担持することで、大きい触媒微粒子表面積を確保した高性能触媒とは逆に）、低触媒微粒子担持率にすることで触媒微粒子径を小さくし、もって触媒微粒子表面積を確保しつつ重量比活性の低下を回避する対策をとる。触媒微粒子使用量の削減、即ち触媒層中の触媒微粒子量（担持量あるいは目付量）を少なくする場合には、低担持率触媒でも触媒層の厚さを高性能触媒と同等に抑えれば濃度過電圧増加の懸念はない。
First, the catalyst will be described.
In the above, the specific surface area of the support having no pores smaller than 4 nm is small, and the catalyst fine particle diameter is large and the catalyst fine particle specific surface area is small when the loading ratio is high as in the case of a conventional high performance catalyst. As a result, the amount of catalyst fine particles used cannot be reduced.
Therefore, (as opposed to a high performance catalyst that ensures a large catalyst fine particle surface area by carrying a high specific surface area carrier with high loading and high dispersion), by making the catalyst fine particle loading ratio low, the catalyst fine particle diameter is reduced, Therefore, measures are taken to avoid a decrease in the weight specific activity while ensuring the catalyst fine particle surface area. To reduce the amount of catalyst fine particles used, that is, to reduce the amount of catalyst fine particles (supported amount or basis weight) in the catalyst layer, the concentration can be reduced even if the catalyst layer thickness is suppressed to the same level as the high performance catalyst even with a low supported catalyst. There is no concern about an increase in overvoltage.
図４に、実施例の担体として用いるカーボンブラックのＮ２吸着測定結果を示す。BJH法によって求めた細孔径1.7nm〜300nmのメソ細孔の比表面積と細孔径4nm〜300nmの比表面積とをそれぞれ棒グラフで示している。実施例の担体では、細孔径1.7nm〜300nmのメソ細孔の比表面積と細孔径4nm〜300nmの比表面積とがほぼ等しい。その結果、４nm未満の細孔が殆ど存在しないことがわかる。
比較例として示したＫＢ６００ＪＤでは、４nm未満の細孔が全比表面積の半分以上を占めている。
実施例の担体としてＣＡＢＯＴ社製のＢＰ８８０（商品名）を用いることができる。
FIG. 4 shows the N 2 adsorption measurement result of carbon black used as the carrier of the example. The specific surface area of mesopores having a pore diameter of 1.7 nm to 300 nm and the specific surface area of pore diameters of 4 nm to 300 nm determined by the BJH method are respectively shown by bar graphs. In the carrier of the example, the specific surface area of mesopores having a pore diameter of 1.7 nm to 300 nm and the specific surface area of pore diameters of 4 nm to 300 nm are substantially equal. As a result, it can be seen that there are almost no pores of less than 4 nm.
In KB600JD shown as a comparative example, pores of less than 4 nm account for more than half of the total specific surface area.
BP880 (trade name) manufactured by CABOT can be used as the carrier of the examples.
実施例の担体の比表面積に対する触媒微粒子重量と触媒微粒子径の関係から、触媒微粒子表面積を維持できる触媒微粒子担持率を決める。実施例のカーボン担体の細孔径4nm以上の細孔からなる比表面積は185m2/g-Cで、触媒微粒子担持率を20wt%にすれば、比較例であるKB600JD60wt%担持触媒と同等の触媒微粒子径にすることができる。
実際に作製した触媒微粒子の粒径は表１のようになり、発電前後ともに60wt%担持KB600JD触媒(比較例)とほぼ同等の触媒微粒子比表面積を確保できた。
The particle diameters of the actually produced catalyst fine particles are as shown in Table 1, and the specific surface area of the catalyst fine particles was almost the same as that of the 60 wt% supported KB600JD catalyst (comparative example) before and after power generation.
表１に示した比較例の触媒（白金触媒微粒子／担体）と実施例１の触媒（白金触媒微粒子／担体）とでそれぞれ作製した触媒層を有するMEAの50℃フル加湿での性能比較を行う。
実施例の触媒と電解質溶液とを混合してペーストを作製し、これをカーボン布等へスクリーン印刷法で塗布して実施例１の触媒層を形成し、これをカソード電極とする。このカソード電極、電解質膜（Nafion（商標名）製）、アノード電極を接合してMEAを作製する。本試験に使用したカソード電極の白金触媒微粒子担持量は0.1mg/cm２である。
比較例の触媒についても上記と同様にして触媒層を形成し、更にMEAを作製する。比較例のカソード電極の白金触媒微粒子担持量は同じく0.1mg/cm2である。
50℃フル加湿の空気性能の比較を図５に示す。同じ白金触媒微粒子担持量（重量ベース）の比較では全電流域で実施例の触媒層を備えたＭＥＡの性能が高かった。
また、低電流領域の性能比較（表2）では、面積比活性、重量比活性ともに実施例の触媒層を備えたＭＥＡが比較例の触媒層を備えたＭＥＡを上回った。
The catalyst of the example and the electrolyte solution are mixed to prepare a paste, and this is applied to a carbon cloth or the like by screen printing to form the catalyst layer of Example 1, which is used as a cathode electrode. The cathode electrode, the electrolyte membrane (manufactured by Nafion (trade name)), and the anode electrode are joined to produce an MEA. The amount of platinum catalyst fine particles supported on the cathode electrode used in this test is 0.1 mg / cm 2 .
For the catalyst of the comparative example, a catalyst layer is formed in the same manner as described above, and an MEA is further produced. The amount of platinum catalyst fine particles supported on the cathode electrode of the comparative example is also 0.1 mg / cm 2 .
FIG. 5 shows a comparison of air performance at 50 ° C. full humidification. In the comparison of the same platinum catalyst fine particle carrying amount (weight basis), the performance of the MEA including the catalyst layer of the example was high in the entire current range.
Further, in the performance comparison in the low current region (Table 2), the MEA including the catalyst layer of the example exceeded the MEA including the catalyst layer of the comparative example in both area specific activity and weight specific activity.
実施例の触媒と比較例の触媒を用いてそれぞれ作製した触媒層のフル加湿での電気化学的比表面積をCV測定で求め、Pt利用率を計算した。結果は表３に示す。
上記において、この発明における触媒微粒子とは、白金微粒子自体に限定されず、白金合金からなる粒子及びその他の金属及び合金からなる粒子など、燃料電池反応に利用できる全ての材料からなる微粒子粒子を含むものとする。
なお、上記明細書の記載において、４nm以上の細孔、４nm未満の細孔、３．５nmの細孔とは、それぞれ担体の細孔の開口部の直径が４nm以上の細孔、４nm未満の細孔、３．５nmの細孔を指す。
この発明を規定するにあたり、担体の細孔の開口部の直径を４nm以上と規定しているが、これは高分子電解質が入り込めない細孔の開口部の直径を規定せんがために発明者らが自らの実験に基づき特定した値である。
したがって、この発明の担体を用いた触媒層においては、担体における実質的に全ての細孔内に触媒粒子が担持されるとともに、当該細孔は高分子電解質で充填されている。
担体には高い電導性と耐蝕性を有し、触媒微粒子を担持できる物理的特性を有する材料を使用することができる。かかる材料として、実施例で使用したカーボン担体の他、酸化スズ、酸化チタン、酸化亜鉛等の金属酸化物、ＳｒＶＯ３等のペロブスカイト型酸化物などを挙げることができる。
In the above, the catalyst fine particles in the present invention are not limited to platinum fine particles per se, but include fine particles made of all materials that can be used for the fuel cell reaction, such as particles made of platinum alloys and particles made of other metals and alloys. Shall be.
In the description of the above specification, the pores of 4 nm or more, the pores of less than 4 nm, and the pores of 3.5 nm are pores having pore diameters of 4 nm or more and pores of less than 4 nm, respectively. Pore, refers to a pore of 3.5 nm.
In defining this invention, the diameter of the pore opening of the support is defined as 4 nm or more. This is because the diameter of the opening of the pore into which the polymer electrolyte cannot enter is defined by the inventor. This is the value that they identified based on their own experiments.
Therefore, in the catalyst layer using the carrier of the present invention, catalyst particles are supported in substantially all the pores in the carrier, and the pores are filled with the polymer electrolyte.
As the carrier, a material having high electrical conductivity and corrosion resistance and having physical characteristics capable of supporting catalyst fine particles can be used. Examples of such materials include the carbon support used in the examples, metal oxides such as tin oxide, titanium oxide, and zinc oxide, and perovskite oxides such as SrVO 3 .
以上説明してきた触媒を高分子電解質と混合させるときの態様について説明する。
実施例２の触媒層は、カーボン製の担体と高分子電解質の重量比（高分子電解質の質量／担体の質量＝Ｎ／Ｃ、以下同じ）が０．２５ｇ−高分子電解質／ｇ−Ｃとなるよう、実施例１の場合と同様な方法で形成されている。なお、実施例２の触媒層では、担体として、実施例１と同様の低比表面積カーボン担体であるＢＰ８００を用いた。
実施例３の触媒層では、担体として東海カーボン製トーカブラック＃３８８５を用いた。
実施例２、３の触媒層及び比較例２、試験例１の触媒層の特性を表４に示す。各実施例及び比較例、試験例とも同一条件でＭＥＡを構成するものとする。
担体としてこれらの材料を用いる場合、カーボン担体の真密度（Ｃ）と各材料の真密度（Ｄ）の比（Ｃ）／（Ｄ）を第１〜第３の局面で述べた「触媒担体と高分子電解質の混合比」、および、「触媒担体の１μｍ以下の細孔容積」に乗じて得た補正値を用いることで対応できる。
例えば、担体として酸化スズ（ＳｎＯ２）を用いる場合、カーボン担体の密度２ｇ／ｃｍ３、ＳｎＯ２の密度７ｇ／ｃｍ３より、
Ｎ／Ｃは、 ０．５×２／７＝０．１４
細孔容積は、０．７×２／７＝０．２［ｃｃ／ｇ−担体］ となる。
In the catalyst layer of Example 2, the weight ratio of the carbon support to the polymer electrolyte (the weight of the polymer electrolyte / the weight of the support = N / C, the same applies hereinafter) is 0.25 g-polymer electrolyte / g-C. In this way, it is formed by the same method as in the first embodiment. In the catalyst layer of Example 2, BP800, which is the same low specific surface area carbon support as in Example 1, was used as the support.
In the catalyst layer of Example 3, Toka Black # 3885 made by Tokai Carbon was used as a carrier.
Table 4 shows the characteristics of the catalyst layers of Examples 2 and 3, and the catalyst layers of Comparative Example 2 and Test Example 1. Each example, comparative example, and test example shall constitute MEA under the same conditions.
When these materials are used as the carrier, the ratio (C) / (D) of the true density (C) of the carbon carrier and the true density (D) of each material is described in “Catalyst carrier and This can be dealt with by using a correction value obtained by multiplying the “mixing ratio of the polymer electrolyte” and the “pore volume of 1 μm or less of the catalyst carrier”.
For example, when using tin oxide (SnO 2 ) as the carrier, the density of the carbon carrier is 2 g / cm 3 and the density of SnO 2 is 7 g / cm 3 .
N / C is 0.5 × 2/7 = 0.14
The pore volume is 0.7 × 2/7 = 0.2 [cc / g-carrier].
各触媒層を備えたＭＥＡを５０℃フル加湿したときの電流電圧特性を図６に示す。図６において「空気」とあるのは酸化ガスとして空気を使用したときの特性であり、「酸素」とあるのは酸化ガスとして酸素ガスを使用したときの特性である。なお、酸化ガスの流量は３．３７ＮＬＭで充分に加湿されている。他方、水素ガスの流量は０．５ＮＬＭであり充分に加湿されている。
酸化ガスとして空気を採用したとき、実施例２と試験例１との比較により、実施例２の触媒層を備えたＭＥＡが高Ｎ／Ｃとした試験例１の触媒層を備えたＭＥＡを上回る結果が得られた。
酸化ガスとして酸素ガスを採用したとき、同じ白金触媒担持量（重量ベース）の比較では全電流域で実施例２の触媒層を備えたＭＥＡの性能が比較例２及び試験例１の触媒層を備えたＭＥＡに比べ高かった。
また図７に示すように、実施例２の触媒層の触媒のＰｔ比表面積と比較例２の触媒層の触媒のＰｔ比表面積がほぼ同じであることを考慮し、酸素ガス供給時における面積比活性を比較すると、実施例２の触媒層では比較例２の触媒層に比べ約１５％のＰｔ量の削減が可能であることが示される結果が得られた。
FIG. 6 shows current-voltage characteristics when the MEA provided with each catalyst layer is fully humidified at 50 ° C. In FIG. 6, “air” is a characteristic when air is used as the oxidizing gas, and “oxygen” is a characteristic when oxygen gas is used as the oxidizing gas. Note that the flow rate of the oxidizing gas is sufficiently humidified at 3.37 NLM. On the other hand, the flow rate of hydrogen gas is 0.5 NLM and is sufficiently humidified.
When air is employed as the oxidizing gas, the comparison between Example 2 and Test Example 1 shows that the MEA with the catalyst layer of Example 2 exceeds the MEA with the catalyst layer of Test Example 1 with high N / C. Results were obtained.
When oxygen gas is used as the oxidizing gas, the performance of the MEA having the catalyst layer of Example 2 in the entire current range is the same as that of the catalyst layer of Comparative Example 2 and Test Example 1 in the same platinum catalyst loading (weight basis). It was higher than MEA provided.
Further, as shown in FIG. 7, considering that the Pt specific surface area of the catalyst of the catalyst layer of Example 2 and the Pt specific surface area of the catalyst of the catalyst layer of Comparative Example 2 are substantially the same, the area ratio at the time of supplying oxygen gas When the activities were compared, the results showed that the catalyst layer of Example 2 can reduce the Pt amount by about 15% compared to the catalyst layer of Comparative Example 2.
一方、酸化ガスとして無加湿の空気を用いたときの電流電圧特性を図８に示す（水素ガスは加湿、セル温度：７０℃）。無加湿の空気を用いる場合、実施例２の触媒層は比較例２の触媒層とほぼ同じかあるいはやや悪い特性となり、試験例１の触媒層が最も良い特性であった。表４に示すように、各実施例及び比較例、試験例の触媒層に含まれる担体においてカーボン製の担体１ｇあたりの開口径が１μｍ以下の細孔容積は、実施例２が約０．９［ｃｃ／ｇ−Ｃ］、比較例２が約１．０［ｃｃ／ｇ−Ｃ］とほぼ同じであるのに対し、試験例１は約０．６［ｃｃ／ｇ−Ｃ］と低い。これは、各担体において開口径が１μｍ以下（かつ４ｎｍ以上）の細孔が触媒層の空隙を構成し、このように規定される空隙のボリュームが実施例２及び比較例２の触媒層に対し試験例１の触媒層では少ないため、後者の触媒層は乾燥に強い結果が得られたと考えられる。このように得られた結果から、触媒層に含まれる担体の細孔容積は固体差を考慮の上、０．７［ｃｃ／ｇ−Ｃ］以下が適正と考えられる。 On the other hand, FIG. 8 shows current-voltage characteristics when non-humidified air is used as the oxidizing gas (hydrogen gas is humidified, cell temperature: 70 ° C.). When non-humidified air was used, the catalyst layer of Example 2 had almost the same or slightly worse characteristics as the catalyst layer of Comparative Example 2, and the catalyst layer of Test Example 1 had the best characteristics. As shown in Table 4, in the supports included in the catalyst layers of Examples, Comparative Examples, and Test Examples, the pore volume having an opening diameter of 1 μm or less per 1 g of the carbon support is about 0.9 in Example 2. [Cc / g-C], Comparative Example 2 is almost the same as about 1.0 [cc / g-C], whereas Test Example 1 is as low as about 0.6 [cc / g-C]. This is because pores having an opening diameter of 1 μm or less (and 4 nm or more) in each carrier constitute the voids of the catalyst layer, and the volume of voids defined in this way is larger than that of the catalyst layers of Example 2 and Comparative Example 2. Since the number of catalyst layers in Test Example 1 is small, it is considered that the latter catalyst layer obtained a strong result in drying. From the results thus obtained, it is considered that the pore volume of the support contained in the catalyst layer is appropriately 0.7 [cc / g-C] or less in consideration of the solid difference.
本発明は、上記発明の実施の形態及び実施例の説明に何ら限定されるものではない。特許請求の範囲の記載を逸脱せず、当業者が容易に想到できる範囲で種々の変形態様も本発明に含まれる。 The present invention is not limited to the description of the embodiments and examples of the invention described above. Various modifications are also included in the present invention as long as those skilled in the art can easily conceive without departing from the scope of the claims.
Claims (4)
前記担体（Ａ）と前記高分子電解質（Ｂ）との重量比（Ｂ）／（Ａ）が、カーボンの真密度（Ｃ）と前記担体の真密度（Ｄ）の比（Ｃ）／（Ｄ）に０．５を乗じた値以下である、燃料電池用触媒層。 A catalyst layer for a fuel cell in which a catalyst in which catalyst fine particles are supported on a support having only pores having a diameter of 4 nm or more in an opening and a polymer electrolyte are mixed,
The weight ratio (B) / (A) between the carrier (A) and the polymer electrolyte (B) is the ratio of the true density (C) of carbon to the true density (D) of the carrier (C) / (D ) And a value equal to or less than 0.5 multiplied by 0.5.
前記担体における１μｍ以下の細孔容積（ｃｍ ３ ／ｇ−Ｃ）は、カーボンの真密度（Ｃ）と前記担体の真密度（Ｄ）の比（Ｃ）／（Ｄ）に０．７を乗じた値以下である、燃料電池用触媒層。 A catalyst layer for a fuel cell in which a catalyst in which catalyst fine particles are supported on a support having only pores having a diameter of 4 nm or more in an opening and a polymer electrolyte are mixed,
The pore volume (cm 3 / g-C) of 1 μm or less in the carrier is obtained by multiplying 0.7 by the ratio (C) / (D) of the true density (C) of carbon and the true density (D) of the carrier. The fuel cell catalyst layer is less than or equal to the above value.
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