JP2005317289A - Low platinum sulfide fuel cell catalyst, and manufacturing method of the same - Google Patents
Low platinum sulfide fuel cell catalyst, and manufacturing method of the same Download PDFInfo
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Abstract
Description
本発明は、白金含有量の低い低白金硫化物系燃料電池触媒とその製造方法に関する。詳しくは、イオン交換膜形燃料電池（ＰＥＦＣ）、直接メタノール形燃料電池（ＤＭＦＣ）に使用する、白金担持量の少ないシェブレル相硫化物触媒とその製造方法に関する。 The present invention relates to a low platinum sulfide fuel cell catalyst having a low platinum content and a method for producing the same. More specifically, the present invention relates to a chevrel phase sulfide catalyst with a small amount of supported platinum used for an ion exchange membrane fuel cell (PEFC) and a direct methanol fuel cell (DMFC) and a method for producing the same.
近年、新しい発電システムとして燃料電池に関する研究が盛んに行われている。その理由は、環境問題やエネルギー資源の有効活用を図ることが急務となっていることによる。環境に対して負荷要因となっている化石燃料の有効利用を図ること、さらには化石燃料に代わるクリーンで効率のいいエネルギーシステムの確立を図ることはいまや時代の要請するところであり、その有力な解決手段として燃料電池に対する期待が高まっている。特に、イオン交換膜形燃料電池（ＰＥＦＣ）は、高効率な電源として電気自動車や家庭据置用として注目されている。また、メタノール形燃料電池（ＤＭＦＣ）も、二次電池に変わる充電不要の携帯用電子機器の電源として位置づけられ、開発されている。これらに関し様々な提案や報告が各種論文、技術報文等に多数発表され、この分野の活発な研究動向は特許文献においても反映し、燃料電池の開発に係る活発な提案は、最近に限ってもかなりの数にのぼる（例えば、特許文献１ないし４を参照のこと）。 In recent years, research on fuel cells as a new power generation system has been actively conducted. The reason is that there is an urgent need to make effective use of environmental issues and energy resources. Efficient use of fossil fuels, which are a burden factor for the environment, and the establishment of a clean and efficient energy system to replace fossil fuels are now demanded by the times, and a promising solution. As a means, expectations for fuel cells are increasing. In particular, ion-exchange membrane fuel cells (PEFC) are attracting attention as electric vehicles and household stationary devices as highly efficient power supplies. A methanol fuel cell (DMFC) is also positioned and developed as a power source for portable electronic devices that do not require charging, instead of secondary batteries. Many proposals and reports on these issues have been published in various papers, technical reports, etc., and active research trends in this field are also reflected in the patent literature. (See, for example, Patent Documents 1 to 4).
しかしながら、これまでに提案されている燃料電池システムは、白金ないしは白金系合金を使用する燃料極触媒によるものであった。しかし、白金は資源的に希少であり且つ高価であること、さらに、燃料として純水素以外の炭化水素改質ガス、メタノール改質ガスを使用する場合、ガス中に僅かに含まれる一酸化炭素によっても燃料極の白金触媒が被毒され、その触媒性能は著しい低下をきたす、といった点で資源的に、技術的に問題のあるものであった。すなわち、白金の担持量の少ない設計とすること、好ましくは白金を使用することのない白金フリー触媒を設計すること、ＣＯガスに対しても被毒されることのない、耐性のある白金フリー触媒の設計、開発が求められている。このような要求に対して従来提案されている白金フリー触媒設計は、酸化物系をベースとしたものが提案され、報告されている（非特許文献１、２参照）。しかし、酸化物は酸性条件下では劣化、溶解等の現象が生じ、不安定であることから酸化物系触媒設計は、実用的には問題があった。 However, the fuel cell systems proposed so far have been based on a fuel electrode catalyst using platinum or a platinum-based alloy. However, platinum is scarce and expensive in terms of resources. Furthermore, when a hydrocarbon reformed gas other than pure hydrogen or a methanol reformed gas is used as a fuel, the carbon monoxide slightly contained in the gas However, there was a problem in terms of resources and technology in that the platinum catalyst of the fuel electrode was poisoned and the catalyst performance was significantly reduced. That is, design with a small amount of platinum supported, preferably design a platinum-free catalyst that does not use platinum, and is a platinum-free catalyst that is resistant to CO gas and is resistant to poisoning Design and development is required. Conventionally proposed platinum-free catalyst designs for such requirements have been proposed and reported based on oxide systems (see Non-Patent Documents 1 and 2). However, oxides are unstable due to deterioration and dissolution under acidic conditions, and oxide-based catalyst design has a problem in practical use.
そこで本発明の第１の目的は、白金担持量の低い、低白金型燃料電池触媒を開発し、提供しようというものである。さらに、第２の目的は、酸性雰囲気下で不安定な酸化物を用いることのない、非酸化物系燃料電池触媒を開発し、提供しようというものである。さらにまた第３の目的は、電子導電性の高い非酸化物系燃料電池触媒を開発し、提供しようというものである。 Accordingly, a first object of the present invention is to develop and provide a low platinum type fuel cell catalyst having a low platinum loading. Furthermore, the second object is to develop and provide a non-oxide fuel cell catalyst that does not use an unstable oxide in an acidic atmosphere. A third object is to develop and provide a non-oxide fuel cell catalyst having high electronic conductivity.
本発明者らにおいては、上記目的を達成する条件に合致する触媒を開発すべく鋭意研究した結果、銅シェブレル相硫化物に着目し、これを触媒担体として選定し、この硫化物に白金を担持させて触媒設計を試みた。そして、さらに銅以外の金属を含むシュブレル相硫化物についても同様の研究を進めた結果、Ｃｕを含めた各種金属のシュブレル相硫化物、すなわち、Ｃｕ、Ｔｉ、Ｚｒ、Ｈｆ、Ｓｎ、Ｐｂ、Ｖ、Ｎｂ、Ｔａ、Ｍｏ、Ｗ、Ｔｃ、Ｒｅ、Ｆｅ、Ｃｏ、Ｎｉ、Ｐｔ、Ｃｅ、Ｐｒ、Ｎｄ、Ｓｍ、Ｅｕ、Ｇｄ、Ｔｂ、Ｄｒ、Ｈｏ、Ｅｒ、Ｔｍ、Ｙｂ、Ｌｕから選ばれる一種または２種以上の遷移金属元素を含むシュブレル相硫化物であって、一般式ＭxＭｏ6Ｓ8-yで（ただし、０＜ｘ≦４、０＜ｙ≦１）表されるシュブレル相硫化物が酸性雰囲気でも安定で、電子伝導性に優れていることを見いだしたものである。そして、さらに研究を進めた結果、前記シュブレル相硫化物に白金を担持することによって高い酸素還元能が発現し、白金使用量の少ない燃料電池触媒として機能することを知見したものである。 As a result of diligent research to develop a catalyst that meets the conditions for achieving the above-mentioned objectives, the inventors of the present invention focused on copper chevrel phase sulfide, selected it as a catalyst carrier, and supported platinum on this sulfide. I tried to design the catalyst. Further, as a result of conducting the same research on the subrel phase sulfide containing a metal other than copper, as a result of the research on the subrel phase sulfide of various metals including Cu, that is, Cu, Ti, Zr, Hf, Sn, Pb, V Nb, Ta, Mo, W, Tc, Re, Fe, Co, Ni, Pt, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dr, Ho, Er, Tm, Yb, Lu Or a subrel phase sulfide containing two or more transition metal elements, represented by the general formula M x Mo 6 S 8-y (where 0 <x ≦ 4, 0 <y ≦ 1) It was found that the product is stable even in an acidic atmosphere and has excellent electron conductivity. As a result of further research, it has been found that by supporting platinum on the subrel phase sulfide, a high oxygen reduction ability is expressed and it functions as a fuel cell catalyst with a small amount of platinum used.
すなわち、銅シュブレル相硫化物、及び上記一般式で表される特定の遷移金属を含むシュブレル相硫化物に白金を担持させ、Ｘ線吸収端構造（Ｘ−ｒａｙ Ａｂｓｏｒｐｔｉｏｎ Ｎｅａｒ Ｅｄｇｅ Ｓｔｒｕｃｔｕｒｅ；ＸＡＮＥＳ）を測定した。すなわち、Ｃｕ（ないしＭ） Ｋ-ｅｄｇｅ ＸＡＮＥＳ スペクトル、Ｐｔ Ｌiii-ｅｄｇｅ ＸＡＮＥＳ スペクトルを求め、銅（ないし他の金属Ｍ）シュブレル相硫化物と白金との関係を電子構造的に観察し、これに基づいて電子導電性特性を評価した。その結果、電子伝導性を有していることが明らかにされた。 That is, X-ray absorption near edge structure (XANES) is measured by supporting platinum on a subrel phase sulfide containing a specific transition metal represented by the above-described general formula and copper subrel phase sulfide. did. That is, Cu (or M) K-edge XANES spectrum, Pt L iii -edge XANES spectrum is obtained, and the relationship between copper (or other metal M) schulerel phase sulfide and platinum is observed electronically. Based on this, the electronic conductivity characteristics were evaluated. As a result, it was clarified that it has electronic conductivity.
さらに、白金担持シュブレル相を回転電極に塗布し、回転電極法によって電位−電流密度を求め、活性化支配電流に基づいて触媒特性すなわち、酸素還元特性の有無等を評価した。 Further, a platinum-supporting chevrel phase was applied to the rotating electrode, the potential-current density was determined by the rotating electrode method, and the presence or absence of catalytic characteristics, that is, oxygen reduction characteristics, etc. were evaluated based on the activation dominant current.
その結果、銅あるいは銅以外の遷移金属Ｍのシェブレル相硫化物を担持体として選定し、これに白金を担持せしめたことによって、燃料電池触媒に必要な要件を備えていることを示す有意な特性のデータが観察された。すなわち上記触媒設計によって、電子導電性、酸素還元能が求められる燃料電池用の触媒に必要な要件を充分に備えていることを知見したものである。本発明は、この知見に基づいてなされたものであり、その講じてなる構成は、以下（１）ないし（８）に記載の通りである。 As a result, significant characteristics indicating that the fuel cell catalyst has the necessary requirements by selecting a chevrel-phase sulfide of transition metal M other than copper or copper as the support and supporting platinum on this support. Data were observed. In other words, it has been found that the above catalyst design has sufficient requirements for a fuel cell catalyst that requires electronic conductivity and oxygen reducing ability. The present invention has been made on the basis of this finding, and the configuration taken is as described in (1) to (8) below.
（１） 金属M、モリブデン、硫黄を含み、一般式MxＭｏ6Ｓ8-yで表されるシュブレル相硫化物に白金を担持したことを特徴とする、酸素還元能を有する燃料電池用触媒。ただし、式中、金属ＭはＣｕ、Ｔｉ、Ｚｒ、Ｈｆ、Ｓｎ、Ｐｂ、Ｖ、Ｎｂ、Ｔａ、Ｍｏ、Ｗ、Ｔｃ、Ｒｅ、Ｆｅ、Ｃｏ、Ｎｉ、Ｐｔ、Ｃｅ、Ｐｒ、Ｎｄ、Ｓｍ、Ｅｕ、Ｇｄ、Ｔｂ、Ｄｒ、Ｈｏ、Ｅｒ、Ｔｍ、Ｙｂ、Ｌｕから選ばれる一種または２種以上の遷移金属元素であり、金属Mの組成比ｘは０を超え４以下、硫黄の組成比yは０以上１以下である。
（２） 該ｘの値を０を超え２．９４に設定したことを特徴とする、請求項１記載の酸素還元能を有する燃料電池用触媒。
（３） 金属Ｍが、特に銅元素を含む請求項１または２記載の酸素還元能を有する燃料電池用触媒。
（４） 金属Ｍ、金属モリブデンＭｏ、硫黄Ｓを含む反応混合物を調整し、反応混合物を真空焼成し、一般式ＭxＭｏ6Ｓ8-yで表されるシュブレル相硫化物を生成し、回収し、次いで回収したシュブレル相硫化物に白金を含む水溶液を含浸し、乾燥することを特徴とした、酸素還元能を有する燃料電池用触媒の製造方法。ただし、式中、金属ＭはＣｕ、Ｔｉ、Ｚｒ、Ｈｆ、Ｓｎ、Ｐｂ、Ｖ、Ｎｂ、Ｔａ、Ｍｏ、Ｗ、Ｔｃ、Ｒｅ、Ｆｅ、Ｃｏ、Ｎｉ、Ｐｔ、Ｃｅ、Ｐｒ、Ｎｄ、Ｓｍ、Ｅｕ、Ｇｄ、Ｔｂ、Ｄｒ、Ｈｏ、Ｅｒ、Ｔｍ、Ｙｂ、Ｌｕから選ばれる一種または２種以上の遷移金属元素であり、金属Mの組成比ｘは０を超え４以下、硫黄の組成比yは０以上１以下である。
（５） 該金属Ｍの値ｘを、好ましくは０を超え２．９４以下に設定したことを特徴とする、前記（４）項に記載の酸素還元能を有する燃料電池用触媒の製造方法。
（６） 該金属Ｍが銅Ｃｕ元素を含む、前記（４）または（５）項に記載の酸素還元能を有する燃料電池用触媒の製造方法。
（７） 該反応混合物をペレット化し、ペレット化した反応混合物を石英管内に真空封入し、次いで真空焼成することを特徴とする、前記（４）ないし（６）の何れか１項記載に記載の酸素還元能を有する燃料電池用触媒の製造方法。
（８） 該真空焼成は、４００℃で低温予備焼成する工程、引き続き１０００℃で高温焼成する工程の２段階焼成工程からなることを特徴とする、前記（４）または（７）項に記載の酸素還元能を有する燃料電池用触媒の製造方法。
(1) A catalyst for a fuel cell having an oxygen reducing ability, comprising metal M, molybdenum, sulfur, and platinum supported on a subrel phase sulfide represented by the general formula M x Mo 6 S 8-y . However, in the formula, the metal M is Cu, Ti, Zr, Hf, Sn, Pb, V, Nb, Ta, Mo, W, Tc, Re, Fe, Co, Ni, Pt, Ce, Pr, Nd, Sm, It is one or more transition metal elements selected from Eu, Gd, Tb, Dr, Ho, Er, Tm, Yb, and Lu, and the composition ratio x of the metal M exceeds 0 and 4 or less, the composition ratio y of sulfur Is 0 or more and 1 or less.
(2) The fuel cell catalyst having oxygen reducing ability according to claim 1, wherein the value of x exceeds 0 and is set to 2.94.
(3) The fuel cell catalyst having oxygen reducing ability according to claim 1 or 2, wherein the metal M contains a copper element.
(4) A reaction mixture containing metal M, metal molybdenum Mo, and sulfur S is prepared, and the reaction mixture is baked in vacuum to produce and recover a subrel phase sulfide represented by the general formula M x Mo 6 S 8-y. A method for producing a catalyst for a fuel cell having an oxygen reducing ability, comprising: impregnating an aqueous solution containing platinum into the recovered schrebrel phase sulfide and then drying the solution. However, in the formula, the metal M is Cu, Ti, Zr, Hf, Sn, Pb, V, Nb, Ta, Mo, W, Tc, Re, Fe, Co, Ni, Pt, Ce, Pr, Nd, Sm, It is one or more transition metal elements selected from Eu, Gd, Tb, Dr, Ho, Er, Tm, Yb, and Lu, and the composition ratio x of the metal M exceeds 0 and 4 or less, the composition ratio y of sulfur Is 0 or more and 1 or less.
(5) The method for producing a fuel cell catalyst having oxygen reducing ability according to the above (4), wherein the value x of the metal M is preferably set to be greater than 0 and less than or equal to 2.94.
(6) The method for producing a fuel cell catalyst having oxygen reducing ability according to (4) or (5), wherein the metal M contains a copper Cu element.
(7) The reaction mixture according to any one of (4) to (6), wherein the reaction mixture is pelletized, the pelletized reaction mixture is vacuum sealed in a quartz tube, and then vacuum fired. A method for producing a fuel cell catalyst having oxygen reduction ability.
(8) The vacuum firing is a two-stage firing step including a step of low-temperature pre-baking at 400 ° C. and a step of baking at a high temperature of 1000 ° C. Subsequently, as described in (4) or (7) above A method for producing a fuel cell catalyst having oxygen reduction ability.
本発明は、上記構成を講ずることによって、酸素還元能を有する非酸化物系燃料電池用触媒を提供することに成功したものである。すなわち、銅、モリブデン、硫黄を含み、組成式ＣｕxＭｏ6Ｓ8-yで表される銅シュブレル相硫化物を始め、銅サイトに他の遷移金属元素が置換ないし固溶されてなる、一般式ＭxＭｏ6Ｓ8-yで示される各種金属のシュブレル相硫化物に白金を担持することによって、酸性雰囲気でも安定で、高い電子伝導性、酸素還元能を有する新規な非酸化物系燃料電池触媒を提供することに成功したものであり、産業上有用な発明をなしたものであり、その意義は極めて大きいと言える。しかも、これによって、稀少かつ高価な白金への依存度を減らすことが出来、その点でも評価される。今後、燃料電池の重要性がますます高まることを考慮すると、本発明の意義は極めて大であり、燃料電池の発展に大いに寄与するものと期待される。 The present invention has succeeded in providing a non-oxide fuel cell catalyst having oxygen reduction ability by adopting the above-described configuration. In other words, it contains copper, molybdenum, and sulfur, including copper subrel phase sulfide represented by the composition formula Cu x Mo 6 S 8-y , and other transition metal elements at the copper site. A novel non-oxide fuel that is stable even in an acidic atmosphere and has high electron conductivity and oxygen reduction ability by supporting platinum on the various kinds of metal schevrel phase sulfides represented by the formula M x Mo 6 S 8-y The present invention has succeeded in providing a battery catalyst, and has made an industrially useful invention, and it can be said that its significance is extremely great. In addition, this makes it possible to reduce the dependence on rare and expensive platinum, which is also highly evaluated. In view of the increasing importance of fuel cells in the future, the significance of the present invention is extremely great and is expected to contribute greatly to the development of fuel cells.
本発明の燃料電池触媒は、銅、モリブデン、硫黄を含み、一般式ＣｕxＭｏ6Ｓ8-yで表されるシュブレル相硫化物を担体とし、これに白金を担持せしめて成るものであるが、この担体と白金との組み合わせにより触媒活性の向上を図ることができ、また、ｘの値は０を超え４以下に設定することが出来るが、その中でも低めの０を超え２．９４以下に設定するほうが、高い酸素還元能が発現され、発明の実施態様としては好ましい。本発明の触媒は、基本的には上記組成で構成されるが、電子電導性及び酸素還元性を有し、燃料電池触媒としての触媒機能を奏し得る限りは、白金以外にも他の活性金属を担持し、含むことは差し支えなく、本発明は、この態様を制限するものではない。 The fuel cell catalyst of the present invention, copper, molybdenum, including sulfur, a general formula Cu x Mo 6 Shubureru phase sulfide represented by S 8-y as a carrier, but those formed by allowed loading platinum on this The combination of the carrier and platinum can improve the catalytic activity, and the value of x can be set to more than 0 and 4 or less, but more than 0 and less than 2.94. Higher oxygen reducing ability is expressed when the setting is made, and it is preferable as an embodiment of the invention. The catalyst of the present invention is basically composed of the above composition, but other active metals other than platinum as long as it has electronic conductivity and oxygen reducing property and can function as a fuel cell catalyst. However, the present invention is not limited to this embodiment.
このＭ、Ｍｏ、Ｓを含む組成式ＭxＭｏ6Ｓ8-yで表されるシュブレル相硫化物からなる触媒担体は、触媒担体と同じ組成比を有する反応混合物を調製し、加圧成形手段によってペレット化して反応容器に真空封入し、１０００℃前後の温度で焼成することによって得ることができる。この焼成は、一段階で高温焼成するプロセスによってもいいが、反応混合物を充分に反応せしめるには、始めは４００℃の比較的低い温度領域で予備的に焼成し、引き続き１０００℃高温で焼成する２段階焼成を実施するのが好ましい。 A catalyst carrier comprising a subrel phase sulfide represented by the composition formula M x Mo 6 S 8-y containing M, Mo, S is prepared by preparing a reaction mixture having the same composition ratio as the catalyst carrier, Can be obtained by pelletizing by vacuum sealing in a reaction vessel and baking at a temperature of about 1000 ° C. This firing may be performed by a high-temperature firing process in one step, but in order to sufficiently react the reaction mixture, first, preliminary firing is performed in a relatively low temperature range of 400 ° C., and then firing is performed at a high temperature of 1000 ° C. It is preferable to carry out a two-stage firing.
焼成は、ペレット化した反応混合物を好ましくは石英管を使用し、石英管に真空封入し、石英管ごと高温焼成することができる。石英管に真空封入した状態で焼成することによって、反応混合物は大気から遮断され、酸化反応が阻止されると共に、原料成分の蒸発、揮散による配合組成比の崩れが阻止される。これによって、当初設定した配合比が反応終了まで維持され、銅シュブレル相硫化物担体を安定して合成することができる。 For the firing, the pelletized reaction mixture is preferably sealed in a quartz tube using a quartz tube, and the quartz tube can be fired at a high temperature. By firing in a vacuum sealed state in the quartz tube, the reaction mixture is shut off from the atmosphere, preventing the oxidation reaction and preventing the composition ratio from being lost due to evaporation and volatilization of the raw material components. Thereby, the initially set compounding ratio is maintained until the end of the reaction, and the copper chevrel phase sulfide support can be stably synthesized.
この担体を合成するには、使用する材料としては各金属元素粉末、すなわち金属元素粉末Ｍ、モリブデン金属粉末Ｍｏ、及び硫黄Ｓの各粉末を所定の混合比に混合したものを用いることができるが、これらの金属元素からなる合金、あるいは硫化物を用いることもできる。何れにしても、不純物の混入は、電子伝導性や、触媒性能に重大な影響を与えることから、反応混合物には不純物の混入は避けることが好ましい。したがって、使用する原料には、該成分以外の不純物は含まない材料を使用することが好ましい。 In order to synthesize this carrier, the metal element powder, that is, the metal element powder M, the molybdenum metal powder Mo, and the sulfur S powder mixed at a predetermined mixing ratio can be used. Further, alloys made of these metal elements or sulfides can also be used. In any case, it is preferable to avoid mixing impurities in the reaction mixture because mixing impurities has a significant effect on electronic conductivity and catalytic performance. Therefore, it is preferable to use a material that does not contain impurities other than the component as the raw material to be used.
高温焼成によって合成された銅シェブレル相硫化物は、これを粉砕し、この粉末に所定濃度に調製した塩化白金溶液を混合し、乾燥するまでグラインドし、得られた粉末を水素気流中で還元焼成することによって白金を担持する。 The copper chevrel phase sulfide synthesized by high-temperature firing is pulverized, mixed with this powder with a platinum chloride solution prepared to a predetermined concentration, ground to dryness, and the resulting powder is reduced and fired in a hydrogen stream To carry platinum.
以下、本発明を、実施例及び図面に基づいて説明する。ただし、これらは本発明を容易に理解するための一助として開示するものであって、本発明はこれらによって限定されるものではない。 Hereinafter, the present invention will be described based on examples and drawings. However, these are disclosed as an aid for easily understanding the present invention, and the present invention is not limited thereto.
実施例１；
Ｃｕ金属粉末、Ｍｏ金属粉末、及び硫黄粉末をそれぞれ用意し、Ｃｕ／Ｍｏ／Ｓ原子比が１．７３〜４／６／８の割合になるように秤量し、混合した。反応混合物を、加圧成形してペレットにした後、これを石英管に真空封印した。これを石英管に封入した状態で４５０℃で２日間予備焼成し、次いで、１０００℃で１〜２日間電気炉で焼成することにより合成した。黒色粉末である反応生成物を急冷して取り出し、Ｘ線回折法によって結晶構造を同定した結果、図１に示す模式構造を有する銅シュブレル相構造であることが確認された。合成された銅シュブレル相硫化物のペレットを粉末化し、これに所定濃度の塩化白金溶液を混合し、乾燥するまでグラインドし、得られた粉末を２５０℃の水素気流中で還元焼成し該硫化物に白金金属を析出担持せしめた。得られた粉末をＸ線回折によって同定した結果、銅シュブレル相と白金が確認され、銅シュブレル相粉末の表面に白金金属が担持されていることが確認された。
Example 1;
A Cu metal powder, a Mo metal powder, and a sulfur powder were prepared, and weighed and mixed so that the Cu / Mo / S atomic ratio was 1.73 to 4/6/8. The reaction mixture was pressed into pellets and then vacuum sealed to a quartz tube. This was preliminarily fired at 450 ° C. for 2 days in a state enclosed in a quartz tube, and then synthesized in an electric furnace at 1000 ° C. for 1-2 days. The reaction product, which is a black powder, was rapidly cooled and taken out, and the crystal structure was identified by X-ray diffraction. As a result, it was confirmed that the reaction product had a copper shuffle phase structure having the schematic structure shown in FIG. The synthesized copper subrel phase sulfide pellets are pulverized, mixed with a platinum chloride solution of a predetermined concentration and ground until dry, and the resulting powder is reduced and fired in a hydrogen stream at 250 ° C. The platinum metal was deposited and supported. As a result of identifying the obtained powder by X-ray diffraction, it was confirmed that the copper schrerel phase and platinum were supported, and that the platinum metal was supported on the surface of the copper schevrel phase powder.
白金を担持した試料を、Ｘ線吸収端構造測定手段（Ｘ−ｒａｙ Ａｂｓｏｒｐｔｉｏｎ Ｎｅａｒ Ｅｄｇｅ Ｓｔｒｕｃｔｕｒｅ；ＸＡＮＥＳ）によって物質の状態を観察した。具体的にはＣｕ Ｋ−ｅｄｇｅ ＸＡＮＥＳ スペクトルを求め、Ｃｕによる電子的特性を評価した。図２は、この観察によって得られた銅シュブレル相硫化物のＣｕ Ｋ−ｅｄｇｅ ＸＡＮＥＳ スペクトルである。この図から、合成された試料は、Ｃｕは０価と２価の間の酸化数をとること、Ｃｕの組成が変化してもＣｕの価数にはほとんど影響なくＣｕの価数は変化しないことが明らかにされた。 The state of the substance of the sample carrying platinum was observed by means of X-ray absorption near edge structure measuring means (XANES). Specifically, a Cu K-edge XANES spectrum was obtained, and the electronic characteristics of Cu were evaluated. FIG. 2 is a Cu K-edge XANES spectrum of the copper subrel phase sulfide obtained by this observation. From this figure, the synthesized sample shows that Cu has an oxidation number between zero and divalent, and even if the composition of Cu changes, the valence of Cu hardly changes without affecting the valence of Cu. It was revealed.
図３は、銅シュブレル相硫化物のＰｔによる電子的特性を求めたものであり、Ｐｔ ＬIII-ｅｇｄｅ ＸＡＮＥＳ スペクトルを示すものである。この図からは吸収端の立ち上がり部分のエネルギーシフトは銅の組成を変化させても、またＰｔの担持量を変化させても大きな変化がみられず、Ｐｔの価数の大きな変化は観察されなかった。Ｐｔの吸収端位置から、Ｐｔは０価の状態で存在すると考えられる。ただ、白金単身のものに比しシェブレル相に担持することによりピーク強度が増加していることわかり、Ｐｔ ５ｄ軌道にホールが導入されていることが示唆されているものと思料される。このことは触媒活性の向上を図る上で有利であると思料される。これは、酸素分子の反結合軌道にd電子が逆供与され、酸素―酸素結合の開裂に有利であるからである。 FIG. 3 shows the Pt L III -egde XANES spectrum obtained from the electronic characteristics of copper subrel phase sulfide by Pt. From this figure, the energy shift at the rising edge of the absorption edge does not change greatly even when the copper composition is changed or the amount of supported Pt is changed, and no significant change in the valence of Pt is observed. It was. From the absorption edge position of Pt, Pt is considered to exist in a zero-valent state. However, it can be seen that the peak intensity is increased by supporting it in the chevrel phase as compared with the platinum single substance, suggesting that holes are introduced into the Pt 5d orbit. This is considered to be advantageous in improving the catalytic activity. This is because d electrons are reversely donated to the antibonding orbitals of oxygen molecules, which is advantageous for the cleavage of the oxygen-oxygen bond.
次に、上記作製された触媒、すなわち、銅シュブレル相硫化物ＣｕxＭｏ6Ｓ8に白金を担持してなる触媒について、この触媒を塗布した電極を作用極、Ａｇ／ＡｇＣｌを参照極としてセルを組み立て、電位掃引して電位−電流密度曲線を求め、触媒の活性化支配電流を評価した。触媒の活性を評価するためには、物質供給が律速にならない条件下で測定し、触媒上での反応速度のみを抽出する必要がある。回転電極を用い、酸素の拡散速度を制御して、回転数無限大の条件に外挿して、触媒上での反応速度（活性化支配電流）を求めた。この図から、ｖｕｌｃａｎ（炭素）に比し、シュブレル相硫化物に白金を担持してなるものは、酸素還元の活性化支配電流値が増加していることから、飛躍的に触媒能が上昇することがわかった。また、活性化電流は銅組成ｘに依存し、触媒中のｘが４．０よりは、１．７３とした方が酸素還元能が高く、Ｐｔを担持させた銅シュブレル相硫化物は、銅の組成が低い方が酸素還元能が高いことを示唆している。 Next, with respect to the prepared catalyst, that is, a catalyst in which platinum is supported on copper subrel phase sulfide Cu x Mo 6 S 8 , the cell coated with this catalyst is used as a working electrode, and Ag / AgCl as a reference electrode. Were assembled, and the potential was swept to obtain a potential-current density curve, and the activation-dominated current of the catalyst was evaluated. In order to evaluate the activity of the catalyst, it is necessary to measure under conditions where the material supply is not rate-limiting and extract only the reaction rate on the catalyst. Using a rotating electrode, the oxygen diffusion rate was controlled and extrapolated to the condition of infinite number of rotations to obtain the reaction rate (activation dominant current) on the catalyst. From this figure, as compared with vulcan (carbon), the one in which platinum is supported on the subrel phase sulfide has an increased activation dominant current value for oxygen reduction, so that the catalytic ability is dramatically increased. I understood it. In addition, the activation current depends on the copper composition x, and the oxygen reducing ability is higher when x in the catalyst is set to 1.73 than 4.0, and the copper schrerel phase sulfide carrying Pt is copper. It is suggested that the lower the composition, the higher the oxygen reducing ability.
以上の実験の結果、本発明の実施態様である一般式ＣｕxＭｏ6Ｓ8-yで表される銅シュブレル相硫化物に白金を担持してなる触媒設計を講じたことにより、この組み合わせによる触媒は、電子伝導性を有し、高い酸素還元能を有することが明らかとなった。これは、銅シュブレル相が白金触媒の触媒担体として機能することを示唆しているものである。また、その触媒活性はシェブレル相の銅組成に依存し、銅組成の減少に伴い触媒特性の向上が認められた。すなわち、燃料電池触媒として機能することが明らかにされた。以上の例は、金属元素Ｍが銅元素である、銅シュブレル相に基づいてその触媒性能を明らかにしたが、本発明者らにおいては、銅以外にも、Ｔｉ、Ｚｒ、Ｈｆ、Ｓｎ、Ｐｂ、Ｖ、Ｎｂ、Ｔａ、Ｍｏ、Ｗ、Ｔｃ、Ｒｅ、Ｆｅ、Ｃｏ、Ｎｉ、Ｐｔ、Ｃｅ、Ｐｒ、Ｎｄ、Ｓｍ、Ｅｕ、Ｇｄ、Ｔｂ、Ｄｒ、Ｈｏ、Ｅｒ、Ｔｍ、Ｙｂ、Ｌｕから選ばれる一種または２種以上の遷移金属元素においてもシュブレル相構造が生成し、同様の作用効果があることを確認した。 As a result of the above experiment, the catalyst design comprising platinum supported on the copper schrebrel phase sulfide represented by the general formula Cu x Mo 6 S 8-y , which is an embodiment of the present invention, has been achieved. It was revealed that the catalyst has electronic conductivity and high oxygen reducing ability. This suggests that the copper subrel phase functions as a catalyst support for the platinum catalyst. Moreover, the catalytic activity was dependent on the copper composition of the chevrel phase, and it was confirmed that the catalytic properties were improved as the copper composition decreased. That is, it was clarified that it functions as a fuel cell catalyst. Although the above example clarified the catalytic performance based on the copper schrerel phase in which the metal element M is a copper element, in the present inventors, besides copper, Ti, Zr, Hf, Sn, Pb Select from V, Nb, Ta, Mo, W, Tc, Re, Fe, Co, Ni, Pt, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dr, Ho, Er, Tm, Yb, Lu It was confirmed that a single or two or more kinds of transition metal elements formed a schbrell phase structure and had similar effects.
本発明は、酸化性雰囲気の下でも安定で、電子伝導性の高い銅を始め各種金属のシュブレル相硫化物に白金を担持することにより、高い酸素還元能が発現する触媒設計を可能としたもので、白金の触媒機能は特定の担体、すなわち、シュブレル相硫化物を選定したことにより、大きく向上することから、通常の担体、すなわちシュブレル相以外のものを用いた場合に比し、白金の低減に大きく寄与し、希少かつ高価な白金のより高い有効活用が図られることによって、コスト的、資源的に有利である。また、酸化物系によって設計された触媒に比し、酸性雰囲気下での安定性の点でも有利である。燃料電池の開発は地球的規模での急を要する一大重要プロジェクトの一つであり、本発明は、上記した特有な構成により、極めて安価であり、また、優れた作用効果が奏せられるものであることから、今後、燃料電池に大いに使用され、その発展に寄与するものと期待される。 The present invention makes it possible to design a catalyst that exhibits high oxygen reduction ability by supporting platinum on a subrel phase sulfide of various metals including copper, which is stable under an oxidizing atmosphere and has high electron conductivity. Therefore, the catalytic function of platinum is greatly improved by selecting a specific carrier, that is, a subrel phase sulfide, so that platinum is reduced compared to the case of using a normal carrier, that is, a material other than the subrel phase. It is advantageous in terms of cost and resources because it contributes greatly to the use of rare and expensive platinum. It is also advantageous in terms of stability in an acidic atmosphere as compared to a catalyst designed by an oxide system. The development of fuel cells is one of the most important projects that need to be urgent on a global scale, and the present invention is extremely inexpensive and has excellent operational effects due to the above-described unique configuration. Therefore, it is expected that it will be greatly used in fuel cells and contribute to its development.
Claims (8)
The oxygen-reducing ability fuel according to claim 4 or 7, wherein the vacuum firing comprises a two-stage firing step of a low-temperature pre-baking step at 400 ° C and a subsequent high-temperature firing step at 1000 ° C. A method for producing a battery catalyst.
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| KR101735132B1 (en) | 2009-07-17 | 2017-05-12 | 덴마크스 텍니스케 유니버시테트 | Platinum and palladium alloys suitable as fuel cell electrodes |
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| CN103007935A (en) * | 2012-12-13 | 2013-04-03 | 北京化工大学常州先进材料研究院 | Preparation method of Pt/antimony-doped tin oxide-graphene catalyst |
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