JP7508139B2 - Electrode catalyst for fuel cell and fuel cell - Google Patents
Electrode catalyst for fuel cell and fuel cell Download PDFInfo
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- JP7508139B2 JP7508139B2 JP2022541592A JP2022541592A JP7508139B2 JP 7508139 B2 JP7508139 B2 JP 7508139B2 JP 2022541592 A JP2022541592 A JP 2022541592A JP 2022541592 A JP2022541592 A JP 2022541592A JP 7508139 B2 JP7508139 B2 JP 7508139B2
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- 239000000446 fuel Substances 0.000 title claims description 90
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- 229910021389 graphene Inorganic materials 0.000 claims description 90
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 claims description 67
- 229910052697 platinum Inorganic materials 0.000 claims description 34
- 229910052757 nitrogen Inorganic materials 0.000 claims description 33
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Images
Description
本発明は、燃料電池用電極触媒及びそれを用いてなる燃料電池に関する。
本願は、２０２０年８月５日に、日本に出願された特願２０２０－１３３３５０号に基づき優先権を主張し、その内容をここに援用する。
The present invention relates to an electrode catalyst for a fuel cell and a fuel cell using the same.
This application claims priority based on Japanese Patent Application No. 2020-133350, filed on August 5, 2020, the contents of which are incorporated herein by reference.
従来、家庭用や自動車用に用いられている燃料電池の作動温度は、室温から８０℃程度に限定されている。燃料電池は、より高い温度で作動させることで発電効率が向上し、燃料ガス中のＣＯ濃度の許容範囲も大きくなる。燃料電池用触媒としては、一般に、白金及び白金合金の微粒子が炭素粒子上に担持されたものが用いられている。このような燃料電池用触媒は、温度の上昇と共に劣化が早まり、触媒活性が大きく低下する。したがって、１００℃以上の高温で作動する燃料電池は、未だ実用化されていない。燃料電池用触媒における温度の上昇に伴う共に触媒活性の低下は、酸素極と燃料極とに共通する課題である。前記課題は、白金及び白金合金の微粒子の溶解による劣化に起因するものである。溶解した白金類は、再度析出する。しかしながら、再度析出した白金及び白金合金の微粒子は、表面積が減少し、触媒活性が低下する。また、高温で作動させないとしても、規定の燃料電池性能を長期間維持するためには、電極触媒にある程度過剰の白金を用いる必要がある。このような過剰の白金が燃料電池の価格が高くなる要因となっている。また、酸素極については、上記炭素粒子自体が酸化され、電極としての特性が低下するという課題もある。Conventionally, the operating temperature of fuel cells used for home and automobile use is limited to about room temperature to 80°C. By operating a fuel cell at a higher temperature, the power generation efficiency improves and the allowable range of CO concentration in the fuel gas also becomes wider. Generally, catalysts for fuel cells are made of platinum and platinum alloy particles supported on carbon particles. Such catalysts for fuel cells deteriorate faster with increasing temperature, and their catalytic activity decreases significantly. Therefore, fuel cells that operate at high temperatures of 100°C or higher have not yet been put into practical use. The decrease in catalytic activity of fuel cell catalysts with increasing temperature is a common issue for both the oxygen electrode and the fuel electrode. The above issue is due to deterioration caused by the dissolution of platinum and platinum alloy particles. The dissolved platinum is precipitated again. However, the surface area of the precipitated platinum and platinum alloy particles is reduced, and the catalytic activity decreases. Even if the fuel cell is not operated at high temperatures, it is necessary to use a certain amount of excess platinum in the electrode catalyst in order to maintain the specified fuel cell performance for a long period of time. Such excess platinum is a factor in the high price of fuel cells. Furthermore, with respect to the oxygen electrode, there is a problem in that the carbon particles themselves are oxidized, deteriorating the properties as an electrode.
そこで、このような課題を解消すべく、種々の提案がなされている。
例えば、特許文献１には、白金を使用せずに良好な特性を有する燃料電池用カソード触媒を提供することが提案されている。具体的には、特許文献１には、ハードテンプレート法により作製される窒素ドープメソポーラスカーボンを、プロトン交換膜燃料電池などのカソード触媒として使用することが提案されている。
Therefore, various proposals have been made to solve such problems.
For example,
また、特許文献２には、電荷キャリア移動度が非常に高いグラフェンとして、下記の工程（ａ）、工程（ｂ）、工程（ｃ）、工程（ｄ）及び工程（ｅ）を有する方法で得られるグラフェン膜が提案されている。工程（ａ）基板を準備する工程。工程（ｂ）上記基板の表面上に金属層をエピタキシャル成長させる工程。工程（ｃ）必要に応じて、エピタキシャル成長させた金属層上に金属を成長させることにより、工程（ｂ）で得られた金属層の厚さを大きくする工程。工程（ｄ）工程（ｂ）又は必要に応じて実施した工程（ｃ）で得られた金属層を上記基板から剥離する工程。工程（ｅ）工程（ｄ）で剥離されるまでは上記基板と接触していた工程（ｄ）で得られた金属層の表面の少なくとも一部にグラフェンを積層する工程。
また、特許文献３には、ピリジン型窒素をドープまたはピリジン型窒素含有分子を付着した炭素材料からなる酸素還元触媒が提案されている。この酸素還元触媒は、高い二酸化炭素吸蔵機能と酸素還元反応に対する高い触媒性能とを有し、白金を代替する。具体的には、この酸素還元触媒は、二酸化炭素吸蔵材料としての機能を有する。この酸素還元触媒は、炭素材料と、そのエッジ部にドープされたピリジン型窒素または炭素材料に吸着されたピリジン型窒素含有分子とを有し、ピリジン型窒素の含有率が、０．０４ａｔ％以上１０．００ａｔ％以下である。
更に、特許文献４には、アノードと、カソードと、非貴金属触媒と、電解質とを含む、燃料電池が提案されている。非貴金属触媒は、カソードと接触している。電解質は、非貴金属触媒と接触しているプロトン性イオン液体を含む。Furthermore,
燃料電池では、より高い温度で安定に動作すること、エネルギー変換効率を向上すること、及び燃料ガスのＣＯ濃度許容値を高めることが求められている。Fuel cells are required to operate stably at higher temperatures, to improve energy conversion efficiency, and to increase the allowable CO concentration in the fuel gas.
本発明は、上記事情に鑑みてなされたものであり、白金等の貴金属の使用量を低減しつつ、高い酸素還元活性、ＣＯ耐性及び酸化耐性を実現する燃料電池用電極触媒、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。The present invention has been made in consideration of the above circumstances, and aims to provide an electrode catalyst for fuel cells that achieves high oxygen reduction activity, CO resistance and oxidation resistance while reducing the amount of precious metals such as platinum used, and a fuel cell using the same.
本発明者らは、上記課題を解消すべく鋭意検討した結果、特定の導電性担体上に金属及び金属化合物の少なくとも一方を担持した場合に、１００℃以上で燃料電池触媒反応を安定に行うことができることを知見し、本発明を完成するに至った。
すなわち、本発明は以下の態様を有する。
［１］導電性担体と、前記導電性担体上に担持された金属および金属化合物の少なくとも一方と、を具備し、１００℃以上の温度で動作する燃料電池用である、燃料電池用電極触媒。
［２］前記導電性担体が、グラフェン及び異種元素ドープグラフェンの少なくとも一方である、［１］に記載の燃料電池用電極触媒。
［３］前記異種元素ドープグラフェンが窒素ドープされており、窒素のドープ量が前記異種元素ドープグラフェンの表面の炭素に対して原子比で４ａｔｏｍ％以上であり、好ましくは４ａｔｏｍ％以上１０ａｔｏｍ％以下であり、より好ましくは６ａｔｏｍ％以上１０ａｔｏｍ％以下である、［２］に記載の燃料電池用電極触媒。
［４］前記金属および金属化合物の少なくとも一方の担持量が、１質量％～４０質量％であり、前記金属が白金の場合には、好ましくは１．５質量％～５質量％である、［１］～［３］のいずれかに記載の燃料電池用電極触媒。
［５］前記金属が、白金、パラジウム及び鉄からなる群より選択される少なくとも１種である、［１］～［４］のいずれかに記載の燃料電池用電極触媒。
［６］［１］～［５］のいずれかに記載の燃料電池用電極触媒を備えた１００℃以上で動作する、燃料電池。
［７］［１］～［５］のいずれかに記載の燃料電池用電極触媒を備え、ＣＯ濃度が１０ｐｐｍ以上の燃料ガスを許容可能に構成される、燃料電池。
［８］電解質としてイオン液体を備える、［６］又は［７］に記載の燃料電池。
［９］前記イオン液体が、ｔｒｉｆｌｕｒｏｍｅｔｈａｎｅｓｕｌｆｏｎｉｃ ａｃｉｄとＮ，Ｎ－ｄｉｅｔｈｙｌｍｅｔｈｙｌａｍｉｎｅとの等モル混合物であるｄｅｍａ－ＴｆＯである、［８］に記載の燃料電池。
［１０］前記電解質がさらにリン酸を含む、［８］又は［９］に記載の燃料電池。
As a result of intensive research aimed at solving the above problems, the inventors discovered that when at least one of a metal and a metal compound is supported on a specific conductive support, a fuel cell catalytic reaction can be stably carried out at 100°C or higher, and thus completed the present invention.
That is, the present invention has the following aspects.
[1] An electrode catalyst for a fuel cell, comprising a conductive support and at least one of a metal and a metal compound supported on the conductive support, the electrode catalyst being for use in a fuel cell operating at a temperature of 100° C. or higher.
[2] The fuel cell electrode catalyst according to [1], wherein the conductive support is at least one of graphene and graphene doped with a different element.
[3] The fuel cell electrode catalyst according to [2], wherein the hetero-element-doped graphene is doped with nitrogen, and the amount of nitrogen doped is 4 atom % or more, preferably 4 atom % or more and 10 atom % or less, and more preferably 6 atom % or more and 10 atom % or less, in terms of atomic ratio relative to carbon on a surface of the hetero-element-doped graphene.
[4] The fuel cell electrode catalyst according to any one of [1] to [3], wherein the amount of at least one of the metal and the metal compound supported is 1 mass % to 40 mass %, and when the metal is platinum, preferably 1.5 mass % to 5 mass %.
[5] The fuel cell electrode catalyst according to any one of [1] to [4], wherein the metal is at least one selected from the group consisting of platinum, palladium, and iron.
[6] A fuel cell comprising the fuel cell electrode catalyst according to any one of [1] to [5], which operates at 100° C. or higher.
[7] A fuel cell comprising the fuel cell electrode catalyst according to any one of [1] to [5], and configured to be capable of accepting a fuel gas having a CO concentration of 10 ppm or more.
[8] The fuel cell according to [6] or [7], comprising an ionic liquid as an electrolyte.
[9] The fuel cell according to [8], wherein the ionic liquid is dema-TfO, which is an equimolar mixture of trifluoromethanesulfonic acid and N,N-dimethylmethylamine.
[10] The fuel cell according to [8] or [9], wherein the electrolyte further contains phosphoric acid.
本発明の燃料電池用電極触媒によれば、白金等の貴金属の使用量を低減しつつ、高い酸素還元活性、ＣＯ耐性及び酸化耐性を実現することができる。
また、本発明の燃料電池は、白金等の貴金属の使用量を低減しつつ、高い酸素還元活性、ＣＯ耐性及び酸化耐性を有するものである。
According to the fuel cell electrode catalyst of the present invention, it is possible to realize high oxygen reduction activity, CO resistance, and oxidation resistance while reducing the amount of precious metal such as platinum used.
Furthermore, the fuel cell of the present invention has high oxygen reduction activity, CO resistance and oxidation resistance while reducing the amount of precious metals such as platinum used.
以下、本発明をさらに詳細に説明する。
本発明の一実施形態に係る燃料電池用電極触媒（以下、単に「触媒」という場合もある。）は、導電性担体と、前記導電性担体上に担持された金属及び金属化合物の少なくとも一方と、を具備してなる。本発明の一実施形態に係る触媒は、１００℃以上の温度で動作する燃料電池用である。
以下、本発明の一実施形態に係る触媒について、更に詳細に説明する。
The present invention will now be described in further detail.
An electrode catalyst for a fuel cell according to one embodiment of the present invention (hereinafter, sometimes simply referred to as a "catalyst") comprises a conductive support and at least one of a metal and a metal compound supported on the conductive support. The catalyst according to one embodiment of the present invention is for a fuel cell that operates at a temperature of 100° C. or higher.
The catalyst according to one embodiment of the present invention will be described in more detail below.
＜導電性担体＞
本発明の一実施形態に係る燃料電池用電極触媒に用いられる上記導電性担体としては、グラフェン及び異種元素ドープグラフェンの少なくとも一方を好ましく用いることができる。
上記グラフェンは、市販のものを特に制限なく用いることができる。上記グラフェンとしては、例えば、単相グラフェン膜、酸化グラフェン、還元型酸化グラフェン等を用いることができる。異種元素をドープさせるためには、酸化グラフェンを好ましく用いることができる。
<Conductive support>
As the conductive support used in the fuel cell electrode catalyst according to one embodiment of the present invention, at least one of graphene and graphene doped with a different element can be preferably used.
The graphene may be any commercially available one without any particular limitation. As the graphene, for example, a single-phase graphene film, graphene oxide, reduced graphene oxide, etc. may be used. In order to dope a different element, graphene oxide may be preferably used.
上記異種元素ドープグラフェンは、炭素以外の元素（異種元素）がドープされてなるグラフェンである。グラフェンにドープされる上記異種元素としては、例えば、窒素、酸素、ホウ素、リン、硫黄等を用いることができる。これらの異種元素のなかでも、窒素が特に好ましい。The heterogeneous element-doped graphene is graphene doped with an element (heterogeneous element) other than carbon. Examples of the heterogeneous element doped into graphene include nitrogen, oxygen, boron, phosphorus, and sulfur. Among these heterogeneous elements, nitrogen is particularly preferred.
ここで、上記異種元素のドープ量は、ドープ前のグラフェン表面に存在する炭素量に対して原子比で２．５ａｔｏｍ％（原子１００のうち２．５原子が置換されていることを意味する）以上であるのが好ましく、４ａｔｏｍ％以上であるのがさらに好ましく、６ａｔｏｍ％以上であるのが最も好ましい。上記異種元素のドープ量の上限は１０ａｔｏｍ％であるのが好ましい。上記異種元素のドープ量が上記下限未満であると、触媒活性が不十分である。上記異種元素のドープ量が１０ａｔｏｍ％を超えると、グラフェン構造が維持されない場合が生じる。
なお、この異種元素ドープグラフェンにおいて、窒素原子およびその他のドープ元素はグラフェンの炭素を置換した状態で存在している。
また、上記導電性担体としては、異種元素ドープグラフェンを用いることが好ましいが、上記導電性担体全体としての異種元素のドープ量が上記範囲内であれば、ドープされていないグラフェンが含まれていても良い。この場合のドープされていないグラフェンの量は、上記導電性担体全体の量の５ｗｔ％以下であることが好ましい。
Here, the doping amount of the different element is preferably 2.5 atom% or more (meaning that 2.5 atoms out of 100 atoms are substituted) in atomic ratio with respect to the amount of carbon present on the graphene surface before doping, more preferably 4 atom% or more, and most preferably 6 atom% or more. The upper limit of the doping amount of the different element is preferably 10 atom%. If the doping amount of the different element is less than the lower limit, the catalytic activity is insufficient. If the doping amount of the different element exceeds 10 atom%, the graphene structure may not be maintained.
In this hetero-element-doped graphene, nitrogen atoms and other doping elements are present in a state of substituting carbon in the graphene.
Although it is preferable to use graphene doped with a different element as the conductive support, the conductive support may contain undoped graphene as long as the doping amount of the different element as a whole is within the above range. In this case, the amount of undoped graphene is preferably 5 wt % or less of the total amount of the conductive support.
＜金属、金属化合物＞
上記導電性担体に担持される上記金属としては、例えば、白金（Ｐｔ）、パラジウム（Ｐｄ）、鉄（Ｆｅ）、ルテニウム（Ｒｕ）、コバルト（Ｃｏ）、ニッケル（Ｎｉ）、チタン（Ｔｉ）、タングステン（Ｗ）、モリブデン（Ｍｏ）、オスニウム（Ｏｓ）、ロジウム（Ｒｈ）、イリジウム（Ｉｒ）、クロム（Ｃｒ）、マンガン（Ｍｎ）、ニオブ（Ｎｂ）等を挙げることができる。中でも上記金属としては、白金、パラジウム及び鉄からなる群より選択される少なくとも１種を好ましく用いることができる。
また、上記金属化合物としては、上記金属を少なくとも１種含む化合物であり、例えば、合金化合物、酸化物、窒化物、酸窒化物、炭化物、リン化物、フッ化物、ポルフィリン化合物、フタロシアニン化合物等を挙げることができる。
<Metals and metal compounds>
Examples of the metal supported on the conductive support include platinum (Pt), palladium (Pd), iron (Fe), ruthenium (Ru), cobalt (Co), nickel (Ni), titanium (Ti), tungsten (W), molybdenum (Mo), osmium (Os), rhodium (Rh), iridium (Ir), chromium (Cr), manganese (Mn), niobium (Nb), etc. Among them, at least one selected from the group consisting of platinum, palladium, and iron can be preferably used as the metal.
The metal compound is a compound containing at least one of the above metals, and examples thereof include alloy compounds, oxides, nitrides, oxynitrides, carbides, phosphides, fluorides, porphyrin compounds, and phthalocyanine compounds.
上記導電性担体に担持される金属又は金属化合物の粒子形状は、半球状あるいは球状であるのが好ましい。
また、上記導電性担体に担持された上記金属又は上記金属化合物の平均粒子径は、２ｎｍ～２０ｎｍであるのが好ましく、２ｎｍ～１０ｎｍであるのが更に好ましい。なお、平均粒子径の測定方法は実施例の欄において説明する。
上記金属又は上記金属化合物の担持量は、金属又は金属化合物の種類に応じて変動するが、最終に得られる本発明の一実施形態に係る触媒中１質量％（ｗｔ％）～４０質量％（ｗｔ％）であるのが好ましい。また、例えば、金属が白金の場合には、１．５ｗｔ％～５ｗｔ％であるのがより好ましい。また、金属又は金属化合物の担持位置は異種元素ドープグラフェン中の異種元素近傍（例えば、窒素ドープグラフェンであればドープされた窒素元素の近傍）が好ましい。
The particle shape of the metal or metal compound supported on the conductive carrier is preferably hemispherical or spherical.
The average particle size of the metal or metal compound supported on the conductive carrier is preferably 2 nm to 20 nm, more preferably 2 nm to 10 nm. The method for measuring the average particle size will be described in the Examples section.
The amount of the metal or metal compound supported varies depending on the type of metal or metal compound, but is preferably 1% by mass (wt%) to 40% by mass (wt%) in the finally obtained catalyst according to one embodiment of the present invention. Furthermore, for example, when the metal is platinum, it is more preferably 1.5% by mass to 5% by mass. Furthermore, the position of the metal or metal compound supported is preferably in the vicinity of the heterogeneous element in the heterogeneous element-doped graphene (for example, in the vicinity of the doped nitrogen element in the case of nitrogen-doped graphene).
＜製造方法＞
本発明の一実施形態に係る触媒の製造方法を説明する。
まず、例えば、導電性担体として異種元素ドープグラフェンを得る。
酸化グラフェンに尿素など窒素付与のための異種元素導入剤を導入した後、異種元素導入剤を導入した酸化グラフェンを乾燥させる。その後、５００℃～１０００℃で０．５時間～５時間、異種元素導入剤を導入した酸化グラフェンの加熱処理を行い、異種元素ドープグラフェンを得る。
<Production Method>
A method for producing a catalyst according to one embodiment of the present invention will be described.
First, for example, graphene doped with a different element is obtained as a conductive support.
A different element introduction agent for adding nitrogen, such as urea, is introduced into the graphene oxide, and the graphene oxide into which the different element introduction agent is introduced is dried. Then, the graphene oxide into which the different element introduction agent is introduced is subjected to a heat treatment at 500° C. to 1000° C. for 0.5 hours to 5 hours to obtain graphene doped with a different element.
ついで、得られた異種元素ドープグラフェンを、水などの溶媒中に分散させ、異種元素ドープグラフェンの分散液を調製する。前記分散液に、金属又は金属化合物を導入するための金属導入剤を添加して、十分に分散させる。その後、金属導入剤の分散状態を保ちながら、前記分散液を５０℃～３００℃で１時間～１５時間加熱する。これにより、本発明の一実施形態に係る触媒を得ることができる。
また、異種元素ドープグラフェンに担持させる金属によっては、次のように加熱処理を行うこともできる。金属導入剤を添加した前記分散液を乾燥させて粉末とする。その後、不活性ガス中、５００℃～１０００℃で０．５～５時間、前記粉末の加熱処理を行う。
Next, the obtained hetero-element-doped graphene is dispersed in a solvent such as water to prepare a dispersion of hetero-element-doped graphene. A metal introduction agent for introducing a metal or metal compound is added to the dispersion and thoroughly dispersed. Thereafter, while maintaining the dispersed state of the metal introduction agent, the dispersion is heated at 50°C to 300°C for 1 hour to 15 hours. In this manner, a catalyst according to one embodiment of the present invention can be obtained.
Depending on the metal to be supported on the hetero-element-doped graphene, a heat treatment can be performed as follows: The dispersion liquid to which the metal introduction agent is added is dried to obtain a powder, and then the powder is heat-treated in an inert gas at 500° C. to 1000° C. for 0.5 to 5 hours.
＜電極の構造（触媒の用い方、他の成分）＞
本発明の一実施形態に係る触媒は、燃料電池の電極用触媒として使用することができる。本発明の一実施形態に係る触媒は、電解質としてイオン液体を用いた燃料電池用であることが好ましい。また、本発明の一実施形態に係る触媒は、１００℃以上の温度で動作する燃料電池用であることが好ましい。燃料電池については後述する。
<Electrode structure (catalyst use, other components)>
The catalyst according to one embodiment of the present invention can be used as an electrode catalyst for a fuel cell. The catalyst according to one embodiment of the present invention is preferably for a fuel cell using an ionic liquid as an electrolyte. The catalyst according to one embodiment of the present invention is preferably for a fuel cell that operates at a temperature of 100° C. or higher. Fuel cells will be described later.
また、本発明の一実施形態に係る触媒は、燃料電池の電極であれば、どの電極にも使用可能である。本発明の一実施形態に係る触媒は、カソード電極用の触媒として特に有用である。In addition, the catalyst according to one embodiment of the present invention can be used in any electrode of a fuel cell. The catalyst according to one embodiment of the present invention is particularly useful as a catalyst for a cathode electrode.
本発明の一実施形態に係る触媒は、次のようにして使用に供することができる。水などの分散媒中に燃料電池用電極触媒を分散し、電極インクを調製する。得られた電極インクをグラッシーカーボン電極などの通常燃料電池に用いられる電極に塗工し、乾燥させる。燃料電池用電極触媒の使用量は、使用する触媒全体における担持されている金属又は金属化合物における金属量で０．３ｍｇｃｍ－２以下であるのが好ましく、０．１ｍｇｃｍ－２以下であるのがより好ましい。
そして、本発明の一実施形態に係る触媒は、上記電極インクを電極に塗工して形成された膜に含まれる。本発明の一実施形態に係る触媒を有する電極は、通常の燃料電池の電極と同様に使用することができる。
The catalyst according to one embodiment of the present invention can be used as follows. An electrode catalyst for fuel cells is dispersed in a dispersion medium such as water to prepare an electrode ink. The obtained electrode ink is applied to an electrode typically used in fuel cells, such as a glassy carbon electrode, and dried. The amount of the electrode catalyst for fuel cells used is preferably 0.3 mg cm -2 or less, more preferably 0.1 mg cm -2 or less, in terms of the amount of metal in the metal or metal compound supported in the entire catalyst used.
The catalyst according to one embodiment of the present invention is contained in a film formed by applying the electrode ink to the electrode. The electrode having the catalyst according to one embodiment of the present invention can be used in the same manner as an electrode for a normal fuel cell.
本発明の一実施形態に係る触媒は、１００℃以上で燃料電池触媒反応を安定に行うことができる。その結果、燃料電池のエネルギー変換効率と燃料ガスのＣＯ濃度許容値を向上できるとともに、白金等の貴金属の使用量を低減することができる。また、本発明の一実施形態に係る触媒は、上述のように構成されているため、イオン液体を電解質に用いた場合に特に有用である。しかも、本発明の一実施形態に係る触媒は、上述のように少ない金属含有量で十分に高い触媒活性を発揮することができる。また、本発明の一実施形態に係る触媒は、耐久性も高く、長期間の使用でも高い触媒活性を保持することができる。The catalyst according to one embodiment of the present invention can stably carry out a fuel cell catalytic reaction at 100°C or higher. As a result, the energy conversion efficiency of the fuel cell and the allowable CO concentration value of the fuel gas can be improved, and the amount of precious metals such as platinum used can be reduced. Furthermore, since the catalyst according to one embodiment of the present invention is configured as described above, it is particularly useful when an ionic liquid is used as the electrolyte. Moreover, the catalyst according to one embodiment of the present invention can exhibit sufficiently high catalytic activity with a small metal content as described above. Furthermore, the catalyst according to one embodiment of the present invention is highly durable and can maintain high catalytic activity even when used for a long period of time.
＜燃料電池＞
本発明の一実施形態に係る燃料電池は、上述の本発明の一実施形態に係る燃料電池用電極触媒を備える。本発明の一実施形態に係る燃料電池は、上述のように本発明の一実施形態に係る触媒を有する電極を具備する以外は、通常の燃料電池と同様に構成することが可能である。本発明の一実施形態に係る燃料電池は、好ましくは１００℃以上で動作する燃料電池である。本発明の一実施形態に係る燃料電池は、ＣＯ濃度が１０ｐｐｍ以上の燃料ガスを許容可能に構成される燃料電池である。このような高温、高ＣＯ濃度で作動させる燃料電池としては、リン酸形燃料電池が該当する。通常、このような高温、高ＣＯ濃度で燃料電池を作動させると触媒の劣化が顕著になる。そのため、従来、このような高温、高ＣＯ濃度で作動させる燃料電池としては、リン酸形燃料電池のみが提案されていた。
<Fuel Cell>
The fuel cell according to one embodiment of the present invention comprises the fuel cell electrode catalyst according to one embodiment of the present invention described above. The fuel cell according to one embodiment of the present invention can be configured in the same manner as a normal fuel cell, except that it comprises an electrode having a catalyst according to one embodiment of the present invention as described above. The fuel cell according to one embodiment of the present invention is preferably a fuel cell that operates at 100° C. or higher. The fuel cell according to one embodiment of the present invention is a fuel cell that is configured to be able to tolerate a fuel gas with a CO concentration of 10 ppm or more. A phosphoric acid fuel cell corresponds to a fuel cell that operates at such high temperatures and high CO concentrations. Usually, when a fuel cell is operated at such high temperatures and high CO concentrations, catalyst deterioration becomes significant. Therefore, only phosphoric acid fuel cells have been proposed as fuel cells that operate at such high temperatures and high CO concentrations.
本発明においては、上述の構成の本発明の一実施形態に係る触媒を用いることにより、上述の高温高ＣＯ濃度でも、触媒の劣化が抑えられ、長期的に安定して動作する燃料電池とすることができる。なお、「１００℃以上の温度で動作する」という意味は、１００℃以上の温度となっても良好に動作するという意味であって、１００℃以下では動作しないという意味ではない。すなわち、従来の触媒では１００℃以上の温度条件下又はＣＯ濃度が１０ｐｐｍ以上の燃料ガスとなる燃料電池においては、良好な触媒活性を示すことができなかった。しかし、本発明の一実施形態に係る触媒を用いた場合には、燃料電池は、１００℃未満の条件下又はＣＯ濃度が１０ｐｐｍ未満の燃料ガス条件下においても十分な触媒活性を示す。また、本発明の一実施形態に係る触媒を用いた場合には、燃料電池は、１００℃以上の条件下又はＣＯ濃度が１０ｐｐｍ以上の燃料ガス条件下においても良好な触媒活性を示す。In the present invention, by using the catalyst according to one embodiment of the present invention having the above-mentioned configuration, the deterioration of the catalyst can be suppressed even at the above-mentioned high temperature and high CO concentration, and a fuel cell that operates stably for a long time can be obtained. Note that the meaning of "operating at a temperature of 100°C or higher" is that it operates well even at a temperature of 100°C or higher, and does not mean that it does not operate at a temperature of 100°C or lower. That is, conventional catalysts could not exhibit good catalytic activity under temperature conditions of 100°C or higher or in fuel cells with a fuel gas having a CO concentration of 10 ppm or higher. However, when the catalyst according to one embodiment of the present invention is used, the fuel cell exhibits sufficient catalytic activity even under conditions of less than 100°C or under fuel gas conditions with a CO concentration of less than 10 ppm. Furthermore, when the catalyst according to one embodiment of the present invention is used, the fuel cell exhibits good catalytic activity even under conditions of 100°C or higher or under fuel gas conditions with a CO concentration of 10 ppm or higher.
また、本発明の一実施形態に係る燃料電池においては、上述の本発明の一実施形態に係る燃料電池用電極触媒を用いたカソード電極を有する他は、通常の燃料電池と同様に構成することが可能である。本発明の一実施形態に係る燃料電池においては、電解質にイオン液体を用いるのが好ましい。In addition, the fuel cell according to one embodiment of the present invention can be configured in the same manner as a normal fuel cell, except that it has a cathode electrode using the fuel cell electrode catalyst according to one embodiment of the present invention described above. In the fuel cell according to one embodiment of the present invention, it is preferable to use an ionic liquid as the electrolyte.
イオン液体としては、例えば、ｔｒｉｆｌｕｒｏｍｅｔｈａｎｅｓｕｌｆｏｎｉｃ ａｃｉｄとＮ，Ｎ－ｄｉｅｔｈｙｌｍｅｔｈｙｌａｍｉｎｅとを等モル混合して得られるｄｅｍａ－ＴｆＯ、ｐｅｎｔａｆｌｕｏｒｏｍｅｔｈａｎｅｓｕｌｆｏｎｉｃ ａｃｉｄとＮ，Ｎ－ｄｉｅｔｈｙｌｍｅｔｈｙｌａｍｉｎｅとを等モル混合して得られるｄｅｍａ－ＰｆＯ、ｈｅｐｔａｆｌｕｏｒｏｍｅｔｈａｎｅｓｕｌｆｏｎｉｃ ａｃｉｄとＮ，Ｎ－ｄｉｅｔｈｙｌｍｅｔｈｙｌａｍｉｎｅとを等モル混合して得られるｄｅｍａ－ＨｆＯ、あるいはｂｉｓ（ｆｌｕｏｒｏｓｕｌｆｏｎｙｌ）ａｍｉｄｅとＮ，Ｎ－ｄｉｅｔｈｙｌｍｅｔｈｙｌａｍｉｎｅとを等モル混合して得られるｄｅｍａ－ＦＳＩ、ｄｅｍａ－ｂｉｓ（ｔｒｉｆｌｕｏｒｏｍｅｔｈｙｌｓｕｌｆｏｎｙｌ）ａｍｉｄｅとＮ，Ｎ－ｄｉｅｔｈｙｌｍｅｔｈｙｌａｍｉｎｅとを等モル混合して得られるｄｅｍａ－ＴＦＳＩ、ｂｉｓ（ｐｅｎｔａｆｌｕｏｒｏｅｔｈａｎｅｓｕｌｆｏｎｙｌ）ａｍｉｄｅとＮ，Ｎ－ｄｉｅｔｈｙｌｍｅｔｈｙｌａｍｉｎｅとを等モル混合して得られるｄｅｍａ－ＢＥＴＩ等を挙げることができる。Examples of ionic liquids include dema-TfO, which is obtained by mixing trifluoromethanesulfonic acid and N,N-dimethylmethylamine in equimolar amounts; dema-PfO, which is obtained by mixing pentafluoromethanesulfonic acid and N,N-dimethylmethylamine in equimolar amounts; Examples of such a dema-HfO include dema-HfO obtained by equimolar mixing of bis(fluorosulfonyl)amide and N,N-dimethylmethylamine, dema-FSI obtained by equimolar mixing of dema-bis(trifluoromethylsulfonyl)amide and N,N-dimethylmethylamine, dema-TFSI obtained by equimolar mixing of dema-bis(trifluoromethylsulfonyl)amide and N,N-dimethylmethylamine, and dema-BETI obtained by equimolar mixing of bis(pentafluoroethanesulfonyl)amide and N,N-dimethylmethylamine.
イオン液体としては、更に１－ｅｔｈｙｌ－３－ｍｅｔｈｙｌｉｍｉｄａｚｏｌｉｕｍ ｍｅｔｈａｎｅｓｕｌｆｏｎａｔｅ（ＥＭＩｍ－ＭｓＯ）、１－ｂｕｔｙｌ－３－ｍｅｔｈｙｌｉｍｉｄａｚｏｌｉｕｍ ｍｅｔｈａｎｅｓｕｌｆｏｎａｔｅ（ＢＭＩｍ－ＭｓＯ）、１－ｈｅｘｙｌ－３－ｍｅｔｈｙｌｉｍｉｄａｚｏｌｉｕｍ ｍｅｔｈａｎｅｓｕｌｆｏｎａｔｅ（ＨＭＩｍ－ＭｓＯ）、１－ｅｔｈｙｌ－３－ｍｅｔｈｙｌｉｍｉｄａｚｏｌｉｕｍ ｔｒｉｆｌｕｒｏｍｅｔｈａｎｅｓｕｌｆｏｎａｔｅ（ＥＭＩｍ－ＴｆＯ）、１－ｂｕｔｙｌ－３－ｍｅｔｈｙｌｉｍｉｄａｚｏｌｉｕｍ ｔｒｉｆｌｕｒｏｍｅｔｈａｎｅｓｕｌｆｏｎａｔｅ（ＢＭＩｍ－ＴｆＯ）、１－ｈｅｘｙｌ－３－ｍｅｔｈｙｌｉｍｉｄａｚｏｌｉｕｍ ｔｒｉｆｌｕｒｏｍｅｔｈａｎｅｓｕｌｆｏｎａｔｅ（ＨＭＩｍ－ＴｆＯ）、１－ｅｔｈｙｌ－３－ｍｅｔｈｙｌｉｍｉｄａｚｏｌｉｕｍ ｐｅｎｔａｆｌｕｒｏｍｅｔｈａｎｅｓｕｌｆｏｎａｔｅ（ＥＭＩｍ－ＰｆＯ）、１－ｂｕｔｙｌ－３－ｍｅｔｈｙｌｉｍｉｄａｚｏｌｉｕｍ ｐｅｎｔａｆｌｕｒｏｍｅｔｈａｎｅｓｕｌｆｏｎａｔｅ（ＢＭＩｍ－ＰｆＯ）、１－ｈｅｘｙｌ－３－ｍｅｔｈｙｌｉｍｉｄａｚｏｌｉｕｍ ｐｅｎｔａｌｕｒｏｍｅｔｈａｎｅｓｕｌｆｏｎａｔｅ（ＨＭＩｍ－ＰｆＯ）、１－ｅｔｈｙｌ－３－ｍｅｔｈｙｌｉｍｉｄａｚｏｌｉｕｍ ｈｅｐｔａｆｌｕｒｏｍｅｔｈａｎｅｓｕｌｆｏｎａｔｅ（ＥＭＩｍ－ＨｆＯ）、１－ｂｕｔｙｌ－３－ｍｅｔｈｙｌｉｍｉｄａｚｏｌｉｕｍ ｈｅｐｔａｆｌｕｒｏｍｅｔｈａｎｅｓｕｌｆｏｎａｔｅ（ＢＭＩｍ－ＨｆＯ）、１－ｈｅｘｙｌ－３－ｍｅｔｈｙｌｉｍｉｄａｚｏｌｉｕｍ ｈｅｐｔａｌｕｒｏｍｅｔｈａｎｅｓｕｌｆｏｎａｔｅ（ＨＭＩｍ－ＨｆＯ）などの非プロトン性イオン液体にリン酸を添加したイオン液体等を用いることができる。ここで、非プロトン性イオン液体とリン酸の混合比は、モル比で、１０：１～１：１０であることが好ましく、５：１～１：５であることがより好ましく、２：１～１：２であることが特に好ましい。Further examples of ionic liquids include 1-ethyl-3-methylimidazolium methanesulfonate (EMIm-MsO), 1-butyl-3-methylimidazolium methanesulfonate (BMIm-MsO), 1-hexyl-3-methylimidazolium methanesulfonate (HMIm-MsO), 1-ethyl-3-methylimidazolium trifluoromethanesulfonate (EMIm-TfO), 1-butyl-3-methylimidazolium trifluoromethanesulfonate (BMIm-TfO), 1-hexyl-3-methylimidazolium trifluoromethanesulfonate (HMIm-TfO), 1-ethyl-3-methylimidazolium pentafluoromethanesulfonate (EMIm-PfO), 1-butyl-3-methylimidazolium pentafluoromethanesulfonate (BMIm-PfO), 1-hexyl-3-methylimidazolium Ionic liquids in which phosphoric acid is added to aprotic ionic liquids such as pentaluromethanesulfonate (HMIm-PfO), 1-ethyl-3-methylimidazolium heptafluoromethanesulfonate (EMIm-HfO), 1-butyl-3-methylimidazolium heptafluoromethanesulfonate (BMIm-HfO), and 1-hexyl-3-methylimidazolium heptafluoromethanesulfonate (HMIm-HfO) can be used. Here, the mixing ratio of the aprotic ionic liquid to phosphoric acid is preferably 10:1 to 1:10, more preferably 5:1 to 1:5, and particularly preferably 2:1 to 1:2, in molar ratio.
本発明の一実施形態に係る燃料電池は、上述の本発明の一実施形態に係る触媒を備えるため、コストパフォーマンスに優れ、白金等の貴金属の使用量を低減しつつ、高い触媒活性を有すると共に、耐久性に優れる。The fuel cell of one embodiment of the present invention is equipped with the catalyst of one embodiment of the present invention described above, and therefore has excellent cost performance, high catalytic activity while reducing the amount of precious metals such as platinum used, and excellent durability.
以下、実施例および比較例により本発明を具体的に説明するが、本発明はこれらになんら制限されるものではない。The present invention will be explained in detail below with reference to examples and comparative examples, but the present invention is not limited to these in any way.
〔製造例１〕
（種々の窒素ドープ量を有する窒素ドープグラフェンの合成）
１０ｍＬの超純水に尿素（和光純薬社製）０ｇ～１．６ｇを溶解した水溶液を得た。その水溶液に、濃度４ｍｇｍＬ－１の酸化グラフェン水分散液（Ｓｉｇｍａ Ａｌｄｒｉｃｈ社製）１０ｍＬを添加し、６０℃で１日攪拌して溶液を蒸発乾固し、粉末を得た。得られた粉末をアルミナボートへ載せて、アルゴン雰囲気下９００℃の条件で１時間熱処理を行い、窒素ドープグラフェン（ＮＧ）を得た。
[Production Example 1]
(Synthesis of nitrogen-doped graphene with various nitrogen doping amounts)
An aqueous solution was obtained by dissolving 0 g to 1.6 g of urea (manufactured by Wako Pure Chemical Industries, Ltd.) in 10 mL of ultrapure water. 10 mL of a graphene oxide aqueous dispersion (manufactured by Sigma Aldrich) with a concentration of 4 mgmL was added to the aqueous solution, and the solution was evaporated to dryness by stirring at 60°C for one day to obtain a powder. The obtained powder was placed on an alumina boat and heat-treated at 900°C for one hour in an argon atmosphere to obtain nitrogen-doped graphene (NG).
Ｘ線光電子分光分析法（ＸＰＳ）により、得られた窒素ドープグラフェンの窒素のドープ量を確認した。その結果、窒素ドープ量が２．９ａｔｏｍ％，４．０ａｔｏｍ％，６．５ａｔｏｍ％および７．０ａｔｏｍ％の４種類の窒素ドープグラフェンが得られていることが確認された。得られた窒素ドープグラフェンを模式的に図１に示す。図１に示すように、窒素ドープグラフェン１は、グラフェン２に窒素１０がドープされている。
Ｘ線光電子分光分析法（ＸＰＳ）の使用装置及び測定条件は以下の通りである。
島津製作所社製のＸ線光電子分光分析装置Ｋｒａｔｏｓ ＡＸＩＳ－ＮＯＶＡ（商品名）を用い、窒素ドープグラフェンの組成を分析した。その際、炭素の１ｓ結合エネルギーを２８４．６ｅＶとして補正を行った。Ｃａｓａ Ｓｏｆｔｗａｒｅ社のフィッティングソフトウェアＣＡＳＡＸＰＳを用いてＸＰＳスペクトルの詳細な成分解析を行い、炭素：窒素：酸素の元素比を確認した。
The nitrogen doping amount of the obtained nitrogen-doped graphene was confirmed by X-ray photoelectron spectroscopy (XPS). As a result, it was confirmed that four types of nitrogen-doped graphene with nitrogen doping amounts of 2.9 atom%, 4.0 atom%, 6.5 atom%, and 7.0 atom% were obtained. The obtained nitrogen-doped graphene is shown in FIG. 1. As shown in FIG. 1, the nitrogen-doped
The apparatus and measurement conditions used for X-ray photoelectron spectroscopy (XPS) are as follows.
The composition of the nitrogen-doped graphene was analyzed using an X-ray photoelectron spectrometer Kratos AXIS-NOVA (product name) manufactured by Shimadzu Corporation. At that time, the carbon 1s binding energy was set to 284.6 eV for correction. Detailed component analysis of the XPS spectrum was performed using fitting software CASAXPS from Casa Software Inc., and the element ratio of carbon:nitrogen:oxygen was confirmed.
〔実施例１〕
（還元法で各窒素ドープグラフェン上に白金を担持した（白金担持量２．６ｗｔ％）白金担持窒素ドープグラフェンの合成）
製造例１で得られた４種の窒素ドープグラフェンのそれぞれの上に白金を担持させた（白金担持量２．６ｗｔ％）。超音波攪拌を１５分間行うことで、１０ｍｇの窒素ドープグラフェンを１０ｍＬの超純水へそれぞれ分散させて、分散液を得た。この分散液へ２０ｍＬのエチレングリコール（和光純薬社製）と１０ｍｇのヘキサクロロ白金（ＩＶ）酸六水和物（Ｓｉｇｍａ Ａｌｄｒｉｃｈ社製）を添加し、超音波攪拌を３０分間行った。この混合物を１３０℃に加熱したオイルバスへ入れて、３時間マグネティックスターラーで攪拌した。その後、固形分を超純水とエタノールで良く洗浄し、６０℃で１２時間乾燥を行い、窒素ドープ量が異なる４種類の白金担持窒素ドープグラフェン（Ｐｔ－ＮＧ）を得た。窒素ドープ量が２．９ａｔｏｍ％のＰｔ－ＮＧを実施例１－１、窒素ドープ量が４．０ａｔｏｍ％のＰｔ－ＮＧを実施例１－２、窒素ドープ量が６．５ａｔｏｍ％のＰｔ－ＮＧを実施例１－３、窒素ドープ量が７．０ａｔｏｍ％のＰｔ－ＮＧを実施例１－４とする。
Example 1
(Synthesis of platinum-loaded nitrogen-doped graphene in which platinum was loaded on each nitrogen-doped graphene by reduction method (platinum loading amount 2.6 wt%))
Platinum was supported on each of the four types of nitrogen-doped graphene obtained in Production Example 1 (platinum support amount 2.6 wt%). By performing ultrasonic stirring for 15 minutes, 10 mg of nitrogen-doped graphene was dispersed in 10 mL of ultrapure water to obtain a dispersion. 20 mL of ethylene glycol (manufactured by Wako Pure Chemical Industries, Ltd.) and 10 mg of hexachloroplatinic (IV) acid hexahydrate (manufactured by Sigma Aldrich Co., Ltd.) were added to this dispersion, and ultrasonic stirring was performed for 30 minutes. This mixture was placed in an oil bath heated to 130 ° C. and stirred with a magnetic stirrer for 3 hours. Thereafter, the solid content was thoroughly washed with ultrapure water and ethanol, and dried at 60 ° C. for 12 hours to obtain four types of platinum-supported nitrogen-doped graphene (Pt-NG) with different nitrogen doping amounts. Pt-NG with a nitrogen doping amount of 2.9 atom% is Example 1-1, Pt-NG with a nitrogen doping amount of 4.0 atom% is Example 1-2, Pt-NG with a nitrogen doping amount of 6.5 atom% is Example 1-3, and Pt-NG with a nitrogen doping amount of 7.0 atom% is Example 1-4.
得られた実施例１－４のＰｔ－ＮＧについて、透過型電子顕微鏡（ＪＥＯＬ社製，ＪＥＭ－ＡＲＭ２００Ｆ）を用いて窒素ドープグラフェン上の白金粒子の担持状態を観察した。Ｐｔ－ＮＧ上の白金粒子の粒子径分布を示すグラフを図２Ａに示す。Ｐｔ－ＮＧの透過型電子顕微鏡写真を図２Ｂ～図２Ｅに示す。図２Ｂから図２Ｅへと順に透過型電子顕微鏡写真を拡大して示す。Ｐｔ－ＮＧを構成する各元素の電子顕微鏡写真を図２Ｆに示す。図２Ａに示すように、数ｎｍの大きさの白金粒子（平均粒子径３．３ｎｍ）が窒素ドープグラフェン上に均一に担持されていることが分かる。
なお、平均粒子径は以下のようにして求めた。透過型電子顕微鏡観察で確認された白金粒子３００個についてそれぞれ直径を計測し、その平均値を求め平均粒子径とした。
The state of platinum particles supported on the nitrogen-doped graphene of the obtained Pt-NG of Example 1-4 was observed using a transmission electron microscope (JEM-ARM200F, manufactured by JEOL). A graph showing the particle size distribution of platinum particles on Pt-NG is shown in FIG. 2A. Transmission electron microscope photographs of Pt-NG are shown in FIG. 2B to FIG. 2E. The transmission electron microscope photographs are enlarged in order from FIG. 2B to FIG. 2E. An electron microscope photograph of each element constituting Pt-NG is shown in FIG. 2F. As shown in FIG. 2A, it can be seen that platinum particles of a few nm in size (average particle size 3.3 nm) are uniformly supported on the nitrogen-doped graphene.
The average particle size was determined as follows: The diameters of 300 platinum particles confirmed by observation under a transmission electron microscope were measured, and the average value was calculated to determine the average particle size.
〔実施例２〕
（還元法で窒素ドープグラフェン上にパラジウムを担持した（パラジウム担持量は、仕込んだパラジウム全量が担持されたと仮定して２４．６ｗｔ％）パラジウム担持窒素ドープグラフェンの合成）
還元法で得られた窒素ドープ量が７．０ａｔｏｍ％の窒素ドープグラフェン上にパラジウムを担持した。超音波攪拌を１５分間行うことで、１０ｍｇの窒素ドープグラフェンを１０ｍＬの超純水へ分散させて、分散液を得た。この分散液へ２０ｍＬのエチレングリコール（和光純薬社製）と１０ｍｇのテトラクロロパラジウム（ＩＩ）酸カリウム（Ｓｉｇｍａ Ａｌｄｒｉｃｈ社製）を添加し、超音波攪拌を３０分間行った。この混合物を１３０℃に加熱したオイルバスへ入れて、３時間マグネティックスターラーで攪拌した。その後、固形分を超純水とエタノールで良く洗浄し、６０℃で１２時間乾燥を行い、パラジウム担持窒素ドープグラフェン（Ｐｄ－ＮＧ）を得た。
Example 2
(Palladium was supported on nitrogen-doped graphene by reduction (the amount of supported palladium was 24.6 wt %, assuming that the entire amount of palladium charged was supported). Synthesis of palladium-supported nitrogen-doped graphene)
Palladium was supported on nitrogen-doped graphene with a nitrogen doping amount of 7.0 atom% obtained by reduction method. By performing ultrasonic stirring for 15 minutes, 10 mg of nitrogen-doped graphene was dispersed in 10 mL of ultrapure water to obtain a dispersion. 20 mL of ethylene glycol (manufactured by Wako Pure Chemical Industries, Ltd.) and 10 mg of potassium tetrachloropalladate (II) (manufactured by Sigma Aldrich) were added to this dispersion, and ultrasonic stirring was performed for 30 minutes. This mixture was placed in an oil bath heated to 130 ° C. and stirred with a magnetic stirrer for 3 hours. Thereafter, the solid content was thoroughly washed with ultrapure water and ethanol, and dried at 60 ° C. for 12 hours to obtain palladium-supported nitrogen-doped graphene (Pd-NG).
得られたＰｄ－ＮＧについて、透過型電子顕微鏡（ＪＥＯＬ社製，商品名「ＪＥＭ－ＡＲＭ２００Ｆ」）を用いて窒素ドープグラフェン上のパラジウム粒子の担持状態を実施例１と同様に観察した。Ｐｄ－ＮＧ上のパラジウム粒子の粒子径分布を示すグラフを図３Ａに示す。Ｐｄ－ＮＧの透過型電子顕微鏡写真を図３Ｂ～図３Ｄに示す。Ｐｄ－ＮＧを構成する各元素の電子顕微鏡写真を図３Ｅに示す。図３Ａに示す結果から明らかなように、数ｎｍの大きさのパラジウム粒子（平均粒子径３．６ｎｍ）が窒素ドープグラフェン上に均一に担持されていることが分かる。The state of palladium particle loading on the nitrogen-doped graphene of the obtained Pd-NG was observed in the same manner as in Example 1 using a transmission electron microscope (manufactured by JEOL, product name "JEM-ARM200F"). A graph showing the particle size distribution of palladium particles on Pd-NG is shown in Figure 3A. Transmission electron microscope photographs of Pd-NG are shown in Figures 3B to 3D. An electron microscope photograph of each element constituting Pd-NG is shown in Figure 3E. As is clear from the results shown in Figure 3A, palladium particles of a few nm in size (average particle size 3.6 nm) are uniformly loaded on the nitrogen-doped graphene.
〔実施例３〕
（還元法で窒素ドープグラフェン上に鉄を担持した（鉄担持量は、仕込んだ鉄全量が担持されたと仮定して３６．５ｗｔ％）鉄担持窒素ドープグラフェンの合成）
還元法で得られた窒素ドープ量が７．０ａｔｏｍ％の窒素ドープグラフェン上に鉄を担持した。超音波攪拌を３０分間行うことで、５０ｍｇの窒素ドープグラフェンを１５ｍＬの超純水へ分散させて、分散液を得た。この分散液へ１００ｍｇの酢酸鉄（ＩＩ）（Ｓｉｇｍａ Ａｌｄｒｉｃｈ社製）を添加し、終夜攪拌した。その後、２ｇの尿素（和光純薬社製）を添加し、６０℃で攪拌しながら乾燥させ、粉末を得た。得られた粉末をアルミナボートへ載せて、アルゴン雰囲気下９００℃の条件で１時間熱処理を行い、アルゴンガスを流しながら冷却した。その後、粉末に０．５ｍｏｌｄｍ－３の硫酸水溶液を添加し、８０℃で８時間攪拌した。これを濾過して超純水で洗浄後、再びアルゴン雰囲気下９００℃の条件で１時間熱処理を行い、鉄担持窒素ドープグラフェン（Ｆｅ－ＮＧ）を得た。
Example 3
(Iron was supported on nitrogen-doped graphene by reduction method (the amount of supported iron was 36.5 wt %, assuming that the entire amount of iron was supported). Synthesis of iron-supported nitrogen-doped graphene)
Iron was supported on nitrogen-doped graphene with a nitrogen doping amount of 7.0 atom% obtained by reduction method. 50 mg of nitrogen-doped graphene was dispersed in 15 mL of ultrapure water by performing ultrasonic stirring for 30 minutes to obtain a dispersion. 100 mg of iron acetate (II) (Sigma Aldrich) was added to this dispersion and stirred overnight. Then, 2 g of urea (Wako Pure Chemical Industries) was added and dried while stirring at 60 ° C. to obtain a powder. The obtained powder was placed on an alumina boat and heat-treated for 1 hour under an argon atmosphere at 900 ° C., and cooled while flowing argon gas. Then, 0.5 moldm -3 of sulfuric acid aqueous solution was added to the powder and stirred at 80 ° C. for 8 hours. This was filtered and washed with ultrapure water, and then heat-treated again for 1 hour under an argon atmosphere at 900 ° C. to obtain iron-supported nitrogen-doped graphene (Fe-NG).
得られたＦｅ－ＮＧについて、透過型電子顕微鏡（ＪＥＯＬ社製，商品名「ＪＥＭ－ＡＲＭ２００Ｆ」）を用いて窒素ドープグラフェン上の鉄粒子の担持状態を実施例１と同様に観察した。Ｆｅ－ＮＧ上の鉄粒子の粒子径分布を示すグラフを図４Ａに示す。Ｆｅ－ＮＧの透過型電子顕微鏡写真を図４Ｂ～図４Ｄに示す。Ｆｅ－ＮＧを構成する各元素の電子顕微鏡写真を図４Ｅに示す。図４Ａに示す結果から明らかなように、数ｎｍの大きさの鉄粒子（平均粒子径１５ｎｍ）が窒素ドープグラフェン上に均一に担持されていることが分かる。The state of iron particle loading on the nitrogen-doped graphene of the obtained Fe-NG was observed in the same manner as in Example 1 using a transmission electron microscope (manufactured by JEOL, product name "JEM-ARM200F"). A graph showing the particle size distribution of iron particles on Fe-NG is shown in Figure 4A. Transmission electron microscope photographs of Fe-NG are shown in Figures 4B to 4D. An electron microscope photograph of each element constituting Fe-NG is shown in Figure 4E. As is clear from the results shown in Figure 4A, it can be seen that iron particles of a few nm in size (average particle size 15 nm) are uniformly loaded on the nitrogen-doped graphene.
〔製造例４〕
（電解液の調製）
プロトン性イオン液体（電解液）として、Ｔｒｉｆｌｕｒｏｍｅｔｈａｎｅｓｕｌｆｏｎｉｃ ａｃｉｄ（以下「ＴｆＯ」という。東京化成社製）とＮ，Ｎ－ｄｉｅｔｈｙｌｍｅｔｈｙｌａｍｉｎｅ（以下「ｄｅｍａ」という。東京化成社製）を等モル混合して得たｄｅｍａ－ＴｆＯを、次のようにして調製した。
１４．５ｇのｄｅｍａを氷浴内に設置された１００ｍＬの超純水へ攪拌しながら添加した後、２５．０ｇのＴｆＯをゆっくりと加え水溶液を得た。ついで、ロータリーエバポレーターを用いて、この水溶液をある程度脱水した後、この水溶液を１００℃で４８時間、真空乾燥することにより、ｄｅｍａ－ＴｆＯを得た。
ｄｅｍａ－ＴｆＯを電気化学測定に使用する際には、窒素雰囲気下あるいは酸素飽和溶解下となるように、事前に窒素あるいは酸素ガスで、ｄｅｍａ－ＴｆＯに対して十分にバブリングを行った。
[Production Example 4]
(Preparation of Electrolyte)
As a protic ionic liquid (electrolyte), dema-TfO was prepared by mixing equimolar amounts of trifluoromethanesulfonic acid (hereinafter referred to as "TfO" manufactured by Tokyo Chemical Industry Co., Ltd.) and N,N-dimethylmethylamine (hereinafter referred to as "dema" manufactured by Tokyo Chemical Industry Co., Ltd.), as follows.
14.5 g of dema was added to 100 mL of ultrapure water placed in an ice bath while stirring, and then 25.0 g of TfO was slowly added to obtain an aqueous solution. Then, the aqueous solution was dehydrated to a certain extent using a rotary evaporator, and then vacuum-dried at 100° C. for 48 hours to obtain dema-TfO.
When dema-TfO was used for electrochemical measurement, nitrogen or oxygen gas was sufficiently bubbled through the dema-TfO in advance so that the dema-TfO was in a nitrogen atmosphere or in an oxygen-saturated dissolved state.
〔試験例１〕
（電気化学特性（酸素還元触媒能）の評価）
電気化学アナライザー（ＢＡＳ Ｉｎｃ．製，商品名「ＡＬＳ－６６０Ａ」）を用いて各触媒の電気化学活性を評価した。
評価に際して、直径５ｍｍのグラッシーカーボン電極上に各触媒を担持したものを作用極（電極）として用いた。対極には白金メッシュ電極を用い、参照極には可逆水素電極（ＲＨＥ）を用いた。粒子径０．０５μｍのアルミナ粒子による表面研磨とその後１０分間の超純水中での超音波洗浄を、グラッシーカーボン電極の前処理として行った。
触媒の担持は、超純水とナフィオン分散液（市販品，Ｓｉｇｍａ Ａｌｄｒｉｃｈ社製）を９：１（質量比）の比率で含む混合液１ｍＬに実施例１～実施例３で得られた各触媒１ｍｇを添加して２０分間の超音波分散を行い、電極インクを得た。この電極インク１０μＬをグラッシーカーボン電極上へ滴下し、乾燥させることにより、試験用の作用極（電極）を得た。
得られた電極、電解液を用いて試験用の燃料電池を作製した。
また、市販の白金担持カーボン触媒（Ｐｔ／Ｃ，Ｐｔ担持量３７．５ｗｔ％）を用いた以外は上述と同様にして電極インクを得た。この電極インクを、グラッシーカーボン電極上に滴下し、乾燥させることにより、比較品としての電極を得た。この電極（比較品）を用い、上述と同様にして、燃料電池を作製した。
[Test Example 1]
(Evaluation of electrochemical properties (oxygen reduction catalytic activity))
The electrochemical activity of each catalyst was evaluated using an electrochemical analyzer (manufactured by BAS Inc., trade name "ALS-660A").
In the evaluation, a glassy carbon electrode with a diameter of 5 mm on which each catalyst was supported was used as the working electrode (electrode). A platinum mesh electrode was used as the counter electrode, and a reversible hydrogen electrode (RHE) was used as the reference electrode. Surface polishing with alumina particles with a particle diameter of 0.05 μm and then ultrasonic cleaning in ultrapure water for 10 minutes were performed as pretreatment of the glassy carbon electrode.
The catalyst was supported by adding 1 mg of each of the catalysts obtained in Examples 1 to 3 to 1 mL of a mixed solution containing ultrapure water and Nafion dispersion (commercially available, manufactured by Sigma Aldrich) in a ratio of 9:1 (mass ratio), and ultrasonically dispersing the mixture for 20 minutes to obtain an electrode ink. 10 μL of this electrode ink was dropped onto a glassy carbon electrode and dried to obtain a working electrode (electrode) for testing.
A test fuel cell was fabricated using the obtained electrodes and electrolyte.
In addition, an electrode ink was obtained in the same manner as described above, except that a commercially available platinum-supported carbon catalyst (Pt/C, Pt loading 37.5 wt%) was used. This electrode ink was dropped onto a glassy carbon electrode and dried to obtain an electrode as a comparison product. Using this electrode (comparison product), a fuel cell was fabricated in the same manner as described above.
電極電位を規定の範囲で掃引し、そのときに得られる電流値から触媒活性を評価した。また、反応種の拡散の影響を低減して触媒活性を詳しく評価するために、各触媒を堆積したグラッシーカーボン電極を１６００ｒｐｍの速度で回転させ、電気化学試験を行った。これらの試験では、電極電位の掃引速度を５ｍＶｓ－１とした。
また、各触媒の劣化耐久試験を、燃料電池実用化推進協議会（ＪＦＣＣ）で規定されている手法により実施した。電位掃引速度を０．５Ｖｓ－１、電位掃引範囲を１．０Ｖｖｓ．ＲＨＥ～１．５Ｖｖｓ．ＲＨＥとし、サイクリックボルタンメトリー法により２０００サイクルの電位掃引を行った。
試験溶液として室温（２５℃）の０．５ｍｏｌｄｍ－３硫酸水溶液および１２０℃のイオン液体ｄｅｍａ－ＴｆＯの２種類を用いた。劣化耐久試験の第１サイクルおよび第２０００サイクル終了後に電極回転速度を１６００ｒｐｍに設定して、５ｍＶｓ－１の速度で電位を掃引し、得られた酸素還元電流から触媒活性（酸素還元反応活性）を評価した。
プロトン性イオン液体ｄｅｍａ－ＴｆＯ中における各白金担持窒素ドープグラフェンの酸素還元反応活性について、図５Ａ～図５Ｅに示す。
The electrode potential was swept in a specified range, and the catalytic activity was evaluated from the current value obtained at that time. In order to reduce the influence of diffusion of reactive species and to evaluate the catalytic activity in detail, the glassy carbon electrode on which each catalyst was deposited was rotated at a speed of 1600 rpm and electrochemical tests were performed. In these tests, the sweep speed of the electrode potential was set to 5 mVs -1 .
In addition, a degradation durability test of each catalyst was performed according to the method specified by the Japan Fuel Cell Commercialization Council (JFCC). A potential sweep was performed for 2000 cycles by cyclic voltammetry at a potential sweep rate of 0.5 Vs −1 in the potential sweep range of 1.0 V vs. RHE to 1.5 V vs. RHE.
Two types of test solutions were used: a 0.5 mol dm -3 aqueous sulfuric acid solution at room temperature (25 ° C.) and the ionic liquid dema-TfO at 120 ° C. After the first and 2000th cycles of the degradation durability test, the electrode rotation speed was set to 1600 rpm, the potential was swept at a rate of 5 mV s -1 , and the catalytic activity (oxygen reduction reaction activity) was evaluated from the obtained oxygen reduction current.
The oxygen reduction reaction activity of each platinum-supported nitrogen-doped graphene in the protic ionic liquid dema-TfO is shown in FIGS. 5A to 5E.
図５Ａ～図５Ｅに示す結果から明らかなように、いずれの触媒においても電位を負に掃引することで酸素還元反応に伴う還元電流が認められた。窒素ドープ量が増加すると酸素還元反応がより貴な電位から進行することが認められた。窒素ドープ量が４．０ａｔｏｍ％を超える触媒では、いずれも約１．０Ｖｖｓ．ＲＨＥから酸素還元反応の進行が認められた。本結果より、白金担持窒素ドープグラフェンにおいて、４．０ａｔｏｍ％以上の窒素ドープ量が好適であることが分かる。実施例１－１～実施例１－４の白金担持窒素ドープグラフェンの酸素還元反応の開始電位は、市販のＰｔ／Ｃ触媒（Ｐｔ担持量３７．５ｗｔ％）に比べて貴である。また、実施例１－１～実施例１－４の白金担持窒素ドープグラフェンは、市販のＰｔ／Ｃ触媒に比べて優れた酸素還元触媒能を有している。 As is clear from the results shown in Figures 5A to 5E, a reduction current associated with the oxygen reduction reaction was observed in all catalysts by sweeping the potential negatively. It was observed that the oxygen reduction reaction proceeds from a more noble potential as the amount of nitrogen doping increases. In all catalysts with a nitrogen doping amount of more than 4.0 atom%, the oxygen reduction reaction proceeds from about 1.0 V vs. RHE. From these results, it can be seen that a nitrogen doping amount of 4.0 atom% or more is suitable for platinum-supported nitrogen-doped graphene. The starting potential of the oxygen reduction reaction of the platinum-supported nitrogen-doped graphene of Examples 1-1 to 1-4 is more noble than that of a commercially available Pt/C catalyst (Pt loading amount 37.5 wt%). In addition, the platinum-supported nitrogen-doped graphene of Examples 1-1 to 1-4 has superior oxygen reduction catalytic ability compared to a commercially available Pt/C catalyst.
白金担持窒素ドープグラフェン又は市販のＰｔ／Ｃ触媒において、単位面積あたりの酸素還元電流密度の窒素ドープ量毎の比較を図６に示す。図６に示すように、窒素ドープ量の増加に伴って、単位面積あたりの酸素還元電流密度の増加が認められた。この結果は、窒素ドープ量の増加に伴い、触媒活性サイトが増加していることを示唆している。また、それぞれの白金担持窒素ドープグラフェンの酸素還元電流密度は、市販のＰｔ／Ｃ触媒に比べて大きい。耐久性試験後も、それぞれの白金担持窒素ドープグラフェンの酸素還元電流密度は、市販のＰｔ／Ｃ触媒に比べて大きい。一方、Ｐｔ／Ｃ触媒は、耐久性試験後に酸素還元電流が大きく減少した。例えば、０．１Ｖｖｓ．ＲＨＥにおける電流値は１．１８ｍＡｃｍ－２から約半分の０．５２ｍＡｃｍ－２へ低下した。 FIG. 6 shows a comparison of the oxygen reduction current density per unit area for each nitrogen doping amount in platinum-supported nitrogen-doped graphene or a commercially available Pt/C catalyst. As shown in FIG. 6, an increase in the oxygen reduction current density per unit area was observed with an increase in the nitrogen doping amount. This result suggests that the catalytic activity sites increase with an increase in the nitrogen doping amount. In addition, the oxygen reduction current density of each platinum-supported nitrogen-doped graphene is larger than that of the commercially available Pt/C catalyst. Even after the durability test, the oxygen reduction current density of each platinum-supported nitrogen-doped graphene is larger than that of the commercially available Pt/C catalyst. On the other hand, the oxygen reduction current of the Pt/C catalyst was greatly reduced after the durability test. For example, the current value at 0.1 V vs. RHE decreased from 1.18 mA cm −2 to about half, 0.52 mA cm −2 .
〔試験例２〕
（単位量あたりの触媒活性の比較）
上記製造例４で得られた各電解液中における窒素ドープ量が７．０ａｔｏｍ％のＰｔ－ＮＧ触媒（実施例１－４）の触媒活性を図７に示す。図７Ａは、実施例１－４の触媒の触媒活性を示すチャートであり、触媒単位面積あたりの活性を示す。図７Ｂは、実施例１－４の触媒の触媒活性を示すチャートであり、単位白金質量あたりの触媒活性を示す。
図７Ａと図７Ｂに示す結果から、Ｐｔ－ＮＧ触媒のＰｔ担持量は誘導結合プラズマ（ＩＣＰ）発光分光分析から求められ、その値は２．６ｗｔ％であった。これにより単位量あたりのＰｔ－ＮＧ触媒の触媒活性は、Ｐｔ／Ｃ触媒より優れていることが分かる。白金質量当たりの触媒活性が高いことは、燃料電池の白金使用量を低減できることを意味しており、Ｐｔ－ＮＧ触媒の優位性を顕著に表している。また、電解液を硫酸水溶液からプロトン性イオン液体ｄｅｍａ－ＴｆＯに置き換えた場合、従来のＰｔ／Ｃ触媒では触媒活性が低下するが、Ｐｔ－ＮＧ触媒では逆に触媒活性が増加する傾向が認められた。このことは、１００℃以上の高温域で作動する燃料電池用電極触媒としては、Ｐｔ－ＮＧ触媒がより適していることを示している。
[Test Example 2]
(Comparison of catalytic activity per unit amount)
The catalytic activity of the Pt-NG catalyst (Examples 1-4) with a nitrogen doping amount of 7.0 atom% in each electrolyte solution obtained in Production Example 4 is shown in Figure 7. Figure 7A is a chart showing the catalytic activity of the catalyst of Examples 1-4, showing the activity per unit area of the catalyst. Figure 7B is a chart showing the catalytic activity of the catalyst of Examples 1-4, showing the catalytic activity per unit platinum mass.
From the results shown in FIG. 7A and FIG. 7B, the amount of Pt supported on the Pt-NG catalyst was determined by inductively coupled plasma (ICP) emission spectroscopy, and the value was 2.6 wt%. This shows that the catalytic activity of the Pt-NG catalyst per unit amount is superior to that of the Pt/C catalyst. High catalytic activity per platinum mass means that the amount of platinum used in the fuel cell can be reduced, and the superiority of the Pt-NG catalyst is clearly shown. In addition, when the electrolyte is replaced from the sulfuric acid aqueous solution to the protic ionic liquid dema-TfO, the catalytic activity of the conventional Pt/C catalyst decreases, but the catalytic activity of the Pt-NG catalyst tends to increase. This shows that the Pt-NG catalyst is more suitable as an electrode catalyst for fuel cells operating in a high temperature range of 100°C or higher.
〔試験例３〕
（プロトン性イオン液体ｄｅｍａ－ＴｆＯ中におけるパラジウム担持窒素ドープグラフェン（Ｐｄ－ＮＧ）触媒および鉄担持窒素ドープグラフェン（Ｆｅ－ＮＧ）触媒の酸素還元反応活性）
１２０℃におけるプロトン性イオン液体ｄｅｍａ－ＴｆＯ中のＰｄ－ＮＧ触媒の酸素還元反応活性を図８Ａに示す。１２０℃におけるプロトン性イオン液体ｄｅｍａ－ＴｆＯ中のＦｅ－ＮＧ触媒の酸素還元反応活性を図８Ｂに示す。Ｐｄ－ＮＧ触媒は、耐久性試験後も触媒活性を維持した。Ｆｅ－ＮＧ触媒は、その触媒活性が半分程度に低下した。実施例１～実施例３で得られた各触媒（全て窒素ドープ量は７ａｔｏｍ％）について、耐久性試験前後の酸素還元開始電位および０．１Ｖｖｓ．ＲＨＥにおける電流密度を測定した。劣化耐久試験の第１サイクルおよび第２０００サイクル終了後に電極回転速度を１６００ｒｐｍに設定して、５ｍＶｓ－１の速度で電位を掃引し、得られた酸素還元電流から触媒活性を評価した。結果を表１に示す。
[Test Example 3]
(Oxygen reduction reaction activity of palladium-supported nitrogen-doped graphene (Pd-NG) catalyst and iron-supported nitrogen-doped graphene (Fe-NG) catalyst in protic ionic liquid dema-TfO)
FIG. 8A shows the oxygen reduction reaction activity of the Pd-NG catalyst in the protic ionic liquid dema-TfO at 120° C. FIG. 8B shows the oxygen reduction reaction activity of the Fe-NG catalyst in the protic ionic liquid dema-TfO at 120° C. The Pd-NG catalyst maintained its catalytic activity even after the durability test. The catalytic activity of the Fe-NG catalyst decreased to about half. For each catalyst obtained in Examples 1 to 3 (all nitrogen doped at 7 atom%), the oxygen reduction onset potential and the current density at 0.1 V vs. RHE before and after the durability test were measured. After the first and 2000th cycles of the deterioration durability test, the electrode rotation speed was set to 1600 rpm, the potential was swept at a rate of 5 mVs −1 , and the catalytic activity was evaluated from the obtained oxygen reduction current. The results are shown in Table 1.
〔試験例４〕
（劣化耐久試験に伴う触媒構造の変化）
耐久性試験前のＰｔ／Ｃ触媒の透過型電子顕微鏡写真を図９Ａに示す。耐久性試験後のＰｔ／Ｃ触媒の透過型電子顕微鏡写真を図９Ｂに示す。
図９Ａと図９Ｂに示す結果から、耐久性試験前にカーボン担体上に担持されたＰｔ粒子（図９Ａに示す黒いスポット）が、耐久試験後（図９Ｂに示す）には認められなかった。すなわち、耐久性試験によって、Ｐｔ／Ｃ触媒において、一般的に知られているＰｔ粒子の溶出が起こっていることが分かる。
[Test Example 4]
(Changes in catalyst structure due to deterioration durability test)
A transmission electron microscope image of the Pt/C catalyst before the durability test is shown in Figure 9A. A transmission electron microscope image of the Pt/C catalyst after the durability test is shown in Figure 9B.
9A and 9B, the Pt particles (black spots shown in FIG. 9A) supported on the carbon support before the durability test were not observed after the durability test (shown in FIG. 9B). In other words, it is understood that the durability test causes the commonly known elution of Pt particles in the Pt/C catalyst.
また、ラマン分光測定から、耐久性試験前後のＰｔ／Ｃ触媒のカーボン担体の状態を調べた。結果を図１０に示す。図１０に示す結果から、耐久性試験前後において、カーボン担体自体も構造が変化していることが分かった。また、図１０に示す結果から、耐久試験後の試料では、カーボン担体の構造に起因するピークが消失し、構造規則性が失われていることが分かる。 Additionally, the state of the carbon support of the Pt/C catalyst was examined before and after the durability test using Raman spectroscopy. The results are shown in Figure 10. From the results shown in Figure 10, it was found that the structure of the carbon support itself also changed before and after the durability test. Furthermore, from the results shown in Figure 10, it can be seen that in the sample after the durability test, the peaks due to the structure of the carbon support have disappeared, and structural regularity has been lost.
窒素ドープグラフェンを担体に用いた、実施例１－４、実施例２－４及び実施例３－４で得られた各触媒の耐久試験後の透過型電子顕微鏡写真を図１１Ａ～図１１Ｉに示す。図１１Ａ～図１１Ｉに示す結果から、図２Ｂ～図２Ｆおよび図４Ｂ～図４Ｅに示す耐久試験前の構造がほぼ維持されていることが分かる。
また、ラマン分光測定から、担体である窒素ドープグラフェンの状態を調べた。結果を図１２Ａおよび図１２Ｂに示す。図１２Ａおよび図１２Ｂに示す結果から明らかなように、耐久性試験前後において、担体である窒素ドープグラフェンの構造変化も殆どなかった。
11A to 11I show transmission electron microscope photographs of the catalysts obtained in Examples 1-4, 2-4, and 3-4 using nitrogen-doped graphene as a carrier after the durability test. From the results shown in Fig. 11A to 11I, it can be seen that the structures before the durability test shown in Fig. 2B to 2F and Fig. 4B to 4E are almost maintained.
In addition, the state of the nitrogen-doped graphene carrier was examined by Raman spectroscopy. The results are shown in Figures 12A and 12B. As is clear from the results shown in Figures 12A and 12B, there was almost no structural change in the nitrogen-doped graphene carrier before and after the durability test.
〔試験例５〕
（プロトン性イオン液体ｄｅｍａ－ＴｆＯ／ＰＡ混合電解質中における白金担持窒素ドープグラフェン（Ｐｔ－ＮＧ）触媒の酸素還元反応活性）
プロトン性イオン液体ｄｅｍａ－ＴｆＯを製造例４に従い調製した。得られたｄｅｍａ－ＴｆＯへ、リン酸（ＰＡ，純度：９９．９９９％，Ｓｉｇｍａ Ａｌｄｒｉｃｈ社製）を添加し、６０℃で加熱しながら混合することで均一な混合電解質を調製した。なお、モル比でｄｅｍａ－ＴｆＯ：ＰＡが２：１、１：１および１：２となるように混合比率を変えて、３種類の混合電解質を調製した。
試験例１に従い、調製したｄｅｍａ－ＴｆＯ／ＰＡ混合電解質中で実施例１－４の白金担持窒素ドープグラフェンの酸素還元反応活性を評価した。モル比でｄｅｍａ－ＴｆＯ：ＰＡが１：２の場合、ｄｅｍａ－ＴｆＯ／ＰＡ混合電解質中における白金担持窒素ドープグラフェンの酸素還元反応活性を図１３Ａに示す。モル比でｄｅｍａ－ＴｆＯ：ＰＡが１：１の場合、ｄｅｍａ－ＴｆＯ／ＰＡ混合電解質中における白金担持窒素ドープグラフェンの酸素還元反応活性を図１３Ｂに示す。モル比でｄｅｍａ－ＴｆＯ：ＰＡが２：１の場合、ｄｅｍａ－ＴｆＯ／ＰＡ混合電解質中における白金担持窒素ドープグラフェンの酸素還元反応活性を図１３Ｃに示す。
Test Example 5
(Oxygen reduction reaction activity of platinum-supported nitrogen-doped graphene (Pt-NG) catalyst in protic ionic liquid dema-TfO/PA mixed electrolyte)
Protic ionic liquid dema-TfO was prepared according to Production Example 4. Phosphoric acid (PA, purity: 99.999%, manufactured by Sigma Aldrich) was added to the obtained dema-TfO, and mixed while heating at 60° C. to prepare a homogeneous mixed electrolyte. Note that the mixing ratio was changed so that the molar ratio of dema-TfO:PA was 2:1, 1:1, and 1:2, and three types of mixed electrolytes were prepared.
According to Test Example 1, the oxygen reduction reaction activity of the platinum-supported nitrogen-doped graphene of Example 1-4 was evaluated in the prepared dema-TfO/PA mixed electrolyte. When the molar ratio of dema-TfO:PA is 1:2, the oxygen reduction reaction activity of the platinum-supported nitrogen-doped graphene in the dema-TfO/PA mixed electrolyte is shown in FIG. 13A. When the molar ratio of dema-TfO:PA is 1:1, the oxygen reduction reaction activity of the platinum-supported nitrogen-doped graphene in the dema-TfO/PA mixed electrolyte is shown in FIG. 13B. When the molar ratio of dema-TfO:PA is 2:1, the oxygen reduction reaction activity of the platinum-supported nitrogen-doped graphene in the dema-TfO/PA mixed electrolyte is shown in FIG. 13C.
図１３Ａ～図１３Ｃに示す結果から、プロトン性イオン液体として、ｄｅｍａ－ＴｆＯ／ＰＡ混合電解質を用いることより、Ｐｔ－ＮＧ触媒の耐久性がさらに向上することが分かる。すなわち、ｄｅｍａ－ＴｆＯ／ＰＡ混合電解質を用いた場合、耐久性試験後の酸素還元電流の減少がｄｅｍａ－ＴｆＯを単独で用いた場合に比べて大幅に抑制されることが分かる。 The results shown in Figures 13A to 13C show that the durability of the Pt-NG catalyst is further improved by using a dema-TfO/PA mixed electrolyte as the protic ionic liquid. In other words, when the dema-TfO/PA mixed electrolyte is used, the decrease in oxygen reduction current after the durability test is significantly suppressed compared to when dema-TfO is used alone.
Claims (9)
１００℃以上の温度で動作する燃料電池用である、燃料電池用電極触媒。 A method for manufacturing a semiconductor device comprising the steps of: providing a semiconductor device comprising: a semiconductor substrate ; and a semiconductor material having a first insulating layer and a second insulating layer, the first insulating layer being formed on the semiconductor substrate ;
A fuel cell electrode catalyst for a fuel cell operating at a temperature of 100° C. or higher.
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| JP2020133350 | 2020-08-05 | ||
| PCT/JP2021/028967 WO2022030552A1 (en) | 2020-08-05 | 2021-08-04 | Electrode catalyst for fuel cells, and fuel cell |
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