JP2004330181A - Catalyst, its production method and electrochemical device - Google Patents
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- 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、高分子電解質型燃料電池やリン酸型燃料電池の酸素還元触媒等に用いて好適な、活性炭化物からなる触媒及びその製造方法、並びにこの触媒を用いた電気化学デバイスに関するものである。 The present invention relates to a catalyst comprising an activated carbide, which is suitable for use as an oxygen reduction catalyst for a polymer electrolyte fuel cell or a phosphoric acid fuel cell, a method for producing the same, and an electrochemical device using the catalyst. .
燃料電池は、燃料が酸化される際に発生する燃焼熱を高い効率で電気エネルギーに変換することを可能にする装置である。 A fuel cell is a device that enables highly efficient conversion of combustion heat generated when fuel is oxidized into electric energy.
例えば、高分子電解質型燃料電池（以下、ＰＥＦＣと略記する。）は、主として燃料極、酸素極、及び両電極間に挟持された水素イオン（プロトン）伝導膜で構成され、燃料と酸素との反応による起電力が燃料極と酸素極との間に発生する。また、リン酸型燃料電池（以下、ＰＡＦＣと略記する。）では、電解質としてリン酸からなる電解液が用いられる。 For example, a polymer electrolyte fuel cell (hereinafter abbreviated as PEFC) is mainly composed of a fuel electrode, an oxygen electrode, and a hydrogen ion (proton) conductive film sandwiched between both electrodes. An electromotive force due to the reaction is generated between the fuel electrode and the oxygen electrode. In a phosphoric acid fuel cell (hereinafter abbreviated as PAFC), an electrolytic solution composed of phosphoric acid is used as an electrolyte.
燃料が水素である場合には、燃料極に供給された水素は、下記（式１）
２Ｈ2 → ４Ｈ+ ＋ ４ｅ- （式１）
の反応により燃料極上で酸化され、燃料極に電子を与える。生じた水素イオンＨ＋は、ＰＥＦＣであれば水素イオン伝導膜を介して、また、ＰＡＦＣであれば電解液を通じて酸素極へ移動する。
When the fuel is hydrogen, the hydrogen supplied to the fuel electrode is represented by the following (Equation 1)
2H 2 → 4H + + 4e - ( Equation 1)
Is oxidized on the fuel electrode by the reaction, and gives electrons to the fuel electrode. The generated hydrogen ions H + move to the oxygen electrode through the hydrogen ion conductive membrane in the case of PEFC, and to the oxygen electrode through the electrolyte in the case of PAFC.
酸素極へ移動した水素イオンは、酸素極に供給される酸素と下記（式２）
Ｏ2 ＋ ４Ｈ+ ＋ ４ｅ- → ２Ｈ2Ｏ （式２）
のように反応し、水を生成する。このとき、酸素は、酸素極から電子を取り込み、還元される。
The hydrogen ions transferred to the oxygen electrode are the same as the oxygen supplied to the oxygen electrode and
O 2 + 4H + + 4e − → 2H 2 O (formula 2)
To produce water. At this time, oxygen takes in electrons from the oxygen electrode and is reduced.
このようにして、燃料極では水素が酸化され、酸素極では酸素が還元され、燃料電池全体では下記（式３）
２Ｈ2 ＋ Ｏ2 → ２Ｈ2Ｏ （式３）
の水素の燃焼反応が進行する。このとき、電流が酸素極から燃料極へ流れ、燃料電池から電気エネルギーを取り出すことができる。
In this manner, hydrogen is oxidized at the fuel electrode, oxygen is reduced at the oxygen electrode, and the following formula (3) is obtained for the entire fuel cell.
2H 2 + O 2 → 2H 2 O (Formula 3)
The hydrogen combustion reaction proceeds. At this time, current flows from the oxygen electrode to the fuel electrode, and electric energy can be extracted from the fuel cell.
（式１）及び（式２）の反応は、自発的に進む反応ではあるが、活性化エネルギーが大きい。このため、一般的なＰＥＦＣやＰＡＦＣの動作温度で十分な反応速度を実現するには、白金等の触媒の助けが必要になる。そこで、多くのＰＥＦＣやＰＡＦＣでは、触媒である白金又は白金合金等をアセチレンブラックや活性炭などに担持し、これをカーボンシートやカーボンクロスなどの炭素系の導電性多孔質支持体の表面に塗布したものを、燃料極及び酸素極として用いている。 The reactions of (Equation 1) and (Equation 2) are reactions that proceed spontaneously, but have a large activation energy. For this reason, in order to achieve a sufficient reaction rate at the operating temperature of a general PEFC or PAFC, the aid of a catalyst such as platinum is required. Therefore, in many PEFCs and PAFCs, platinum or a platinum alloy, which is a catalyst, is supported on acetylene black, activated carbon, or the like, and this is applied to the surface of a carbon-based conductive porous support such as a carbon sheet or carbon cloth. It is used as a fuel electrode and an oxygen electrode.
現在、ＰＥＦＣは、自動車、屋外発電システム及び携帯機器などの電源として、精力的に開発が進められている。しかしながら現在のＰＥＦＣの製造コストは非常に高く、同じ出力を生み出すのに要する製造コストは、内燃機関に比べて２桁以上高い。このコスト高の主な原因は、電極触媒、水素イオン伝導膜及びバーポーラプレート（いわゆるセパレータ）の３つのコストが高いことにある。 Currently, PEFCs are being vigorously developed as power sources for automobiles, outdoor power generation systems, portable devices, and the like. However, the production costs of current PEFCs are very high, and the production costs required to produce the same output are more than two orders of magnitude higher than for internal combustion engines. The main cause of the high cost is that the three costs of the electrode catalyst, the hydrogen ion conductive membrane, and the bipolar plate (so-called separator) are high.
このうち、水素イオン伝導膜及びバーポーラプレートは、量産化やメーカー間の価格競争などの効果で、将来的には大幅にコストが低下する可能性が高いが、電極触媒に関しては量産化の効果によるコストダウンは見込めない。その理由は、ほとんどのＰＥＦＣで、高価な白金を電極触媒として用いているためである。 Of these, the hydrogen ion conductive membrane and the bar polar plate are likely to have a significant cost reduction in the future due to the effects of mass production and price competition among manufacturers, but the effect of mass production of electrode catalysts is high. Cost reduction is not expected. The reason is that most of the PEFCs use expensive platinum as an electrode catalyst.
また、自然界における白金の産出量は、年間１６８ｔ（１９９８年の数値）程度にすぎない。これに対し、仮に出力５０ｋＷ程度のＰＥＦＣを積載する電気自動車を年間２００万台製造したとすると、電極触媒として４０〜８０ｔの白金が必要になるとの試算もあり、将来的にはこのような燃料電池用の需要により、白金価格が高騰することも懸念されている。 Further, the amount of platinum produced in the natural world is only about 168 t / year (a numerical value in 1998). On the other hand, if 2 million electric vehicles loaded with PEFC with an output of about 50 kW were manufactured annually, there is a trial calculation that 40 to 80 t of platinum would be required as an electrode catalyst. It is feared that platinum prices will rise due to demand for batteries.
よって、燃料電池の電極触媒として用いる白金量を低減すること、もしくは白金等の貴金属を用いない電極触媒を開発することは、ＰＥＦＣを実用化するために極めて重要な課題である。 Therefore, reducing the amount of platinum used as an electrode catalyst for a fuel cell or developing an electrode catalyst that does not use a noble metal such as platinum is a very important issue for putting a PEFC into practical use.
さて、炭素材料は、導電性を有するものは電極材料として広く用いられているばかりでなく、活性炭のように多孔質のものは、触媒又は触媒の担体としても用いられている。例えば、ＰＥＦＣでは、上述したように、白金等をアセチレンブラックや活性炭などに担持した電極触媒が用いられている。活性炭は、水素の還元に対しては触媒作用をもたないが、酸素の還元に対しては中位程度の触媒作用を有することが知られている。しかも、活性炭等の炭化物そのものよりも、窒素を含有させた炭化物の方が良好な触媒活性を示す例も広く知られている。これらの事実に注目して、窒素を含有させて触媒活性を高めた活性炭を合成し、燃料電池の酸素極における酸素還元触媒として応用する提案がなされている（特許文献１参照。）。 Incidentally, carbon materials having conductivity are not only widely used as electrode materials, but porous materials such as activated carbon are also used as catalysts or catalyst carriers. For example, in PEFC, as described above, an electrode catalyst in which platinum or the like is supported on acetylene black or activated carbon is used. Activated carbon is known to have no catalytic action on the reduction of hydrogen, but has a moderate catalytic action on the reduction of oxygen. Moreover, it is widely known that carbides containing nitrogen exhibit better catalytic activity than carbides themselves such as activated carbon. In view of these facts, a proposal has been made for synthesizing an activated carbon containing nitrogen to enhance the catalytic activity and applying it as an oxygen reduction catalyst in an oxygen electrode of a fuel cell (see Patent Document 1).
特許文献１の実施例では、炭化できる含窒素有機重合体としてポリアクリロニトリルを用い、これを塩化亜鉛の濃厚な溶液に加熱溶解し、得られた粘性の高い溶液を窒素気流中で一定の昇温速度２℃／ｍｉｎで徐々に加熱し、１０００℃に達したところで一定温度に１時間保って焼成し、窒素を含む炭化物を合成した。そして、この炭化物を粉砕して得た炭化物粉末を用いて燃料電池の酸素極を作製したところ、良好な特性を示した例が記載されている。
In the example of
一般に、活性炭の触媒作用に対する窒素の効果は、表面の化学的性質の改変によるとされるが、酸素還元に対する活性炭の触媒作用に関しては、表面のどのような構造が触媒作用に寄与しているのか、具体的なことは何もわかっていない。 In general, the effect of nitrogen on the catalysis of activated carbon is attributed to the modification of the surface chemistry, but with regard to the catalysis of activated carbon on oxygen reduction, what structure of the surface contributes to the catalysis? I don't know anything concrete.
特許文献１には、塩化亜鉛の濃度や量を変更すると特性が変化する例、及び、原料をポリアクリロニトリルとメラミンとの混合物に変えたり、合成後の粉末状炭化物をアンモニアで処理したりすると特性が向上する例等が示されていて、様々な要因が複雑に粉末状炭化物の触媒作用に関わっていることを示している。また、特許文献１の方法で合成される粉末状炭化物では、塩化亜鉛などの塩の残渣がどのように影響しているのかということも不明である。
本発明の目的は、上記のような実情に鑑み、高分子電解質型燃料電池やリン酸型燃料電池の酸素還元触媒等に用いて好適な、活性炭化物からなる触媒及びその製造方法、並びに、この触媒を用いた電気化学デバイスを提供することにある。 In view of the above circumstances, an object of the present invention is a catalyst composed of activated carbide, which is suitable for use as an oxygen reduction catalyst for a polymer electrolyte fuel cell or a phosphoric acid fuel cell, and a method for producing the same. An object of the present invention is to provide an electrochemical device using a catalyst.
本発明者は上述の目的を達成せんものと種々の検討を重ねてきた。その結果、ある種の炭素材料に酸素還元触媒等として有効な触媒活性があることを発見した。 The inventor has made various studies to achieve the above object. As a result, they have found that certain carbon materials have an effective catalytic activity as an oxygen reduction catalyst or the like.
即ち、本発明は、炭素及び窒素を含有し、シェイクアップ過程に関与する炭素の存在比率が制御された材料からなる触媒に係わり、また、電子スピン共鳴測定においてｇ値が１．９９８０〜２．００００である第１の不対電子が、３．１×１０19／ｇ以下のスピン密度で含まれ、且つ、ｇ値が２．００２０〜２．００２６である第２の不対電子が、６．０×１０14／ｇ以上のスピン密度で含まれるように制御された活性炭からなる触媒に係わるものである。 That is, the present invention relates to a catalyst comprising a material containing carbon and nitrogen and having a controlled ratio of carbon involved in a shake-up process, and a g value of 1.9980 to 2.80 in electron spin resonance measurement. The first unpaired electron having a spin density of 3.1 × 10 19 / g or less and the second unpaired electron having a g value of 2.0020 to 2.0026 are 6 The present invention relates to a catalyst comprising activated carbon controlled to be contained at a spin density of 0.0 × 10 14 / g or more.
また、炭素及び窒素を構成元素とする材料を焼成する工程と、これによって得られた焼成物を水蒸気賦活する工程とを有し、シェイクアップ過程に関与する炭素の存在比率、及び／又は、ｇ値が１．９９８０〜２．００００である第１の不対電子のスピン密度と、ｇ値が２．００２０〜２．００２６である第２の不対電子のスピン密度とを制御する、触媒の製造方法に係わるものである。 In addition, the method includes a step of firing a material containing carbon and nitrogen as constituent elements, and a step of activating a fired product obtained by the steam, and an abundance ratio of carbon involved in a shake-up process, and / or g. A catalyst for controlling the spin density of a first unpaired electron having a value of 1.9980 to 2.0000 and the spin density of a second unpaired electron having a g value of 2.0020 to 2.0026. It relates to a manufacturing method.
また、複数の電極と、前記複数の電極に挟持されたイオン伝導体とからなり、前記複数の電極の少なくとも１つに前期触媒を含む電気化学デバイスに係わるものである。 In addition, the present invention relates to an electrochemical device including a plurality of electrodes and an ion conductor sandwiched between the plurality of electrodes, wherein at least one of the plurality of electrodes includes a catalyst.
前記シェイクアップ過程に関与する炭素とは、炭素原子の1s電子のＸＰＳ（X-ray Photoelectron Spectroscopy:Ｘ線励起光電子分光法）測定において、２９１．８±０．５ｅＶにピークをもつスペクトルを与える炭素のことである。シェイクアップ過程とは、ＸＰＳ測定などで内殻電子が放出される際に、それに伴って起こる有効核電荷の急激な変化によるポテンシャルエネルギーの変化を感じて、外殻電子が励起エネルギー準位に遷移する現象であり、見かけ上、この遷移に要するエネルギーの分だけ高エネルギー側にＸＰＳスペクトルが観察される。 The carbon involved in the shake-up process is defined as carbon that gives a spectrum having a peak at 291.8 ± 0.5 eV in XPS (X-ray Photoelectron Spectroscopy) of 1s electron of carbon atom. That is. In the shake-up process, when inner core electrons are emitted by XPS measurement or the like, the potential energy changes due to a sudden change in the effective nuclear charge that accompanies it, and the outer shell electrons transition to the excitation energy level. The XPS spectrum is apparently observed on the high energy side by the energy required for this transition.
２９１．８ｅＶ付近の領域にスペクトルを与える炭素に関わるシェイクアップ過程は、いわゆるπ−π＊シェイクアップと呼ばれる過程で、π結合を形成する電子が励起π準位に遷移する現象であり、黒鉛のように価電子帯と非占有帯のギャップが狭い材料で観察される。従って、前記シェイクアップ過程に関与し、２９１．８ｅＶ付近のＸＰＳスペクトルを与える炭素の割合が大きいほど、グラフェン構造がよく発達した炭素材料と言うことができる。 The shake-up process relating to carbon that gives a spectrum to a region around 291.8 eV is a phenomenon in which electrons forming a π bond transition to an excited π level in a so-called π-π * shake-up process. Thus, the gap between the valence band and the non-occupied band is observed in a narrow material. Therefore, it can be said that the higher the proportion of carbon that participates in the shake-up process and gives an XPS spectrum around 291.8 eV, the better the graphene structure of the carbon material.
本発明は、窒素を含有する活性炭化物の触媒作用が、表面における窒素の存在率およびＸＰＳ測定において前記シェイクアップ過程に関与し、２９１．８±０．５ｅＶにピークをもつスペクトルを与える炭素（以下、適宜シェイクアップ炭素と略称する。）の存在率が高いほど、また、ｇ値が２．００２０〜２．００２６である前記第２の不対電子のスピン密度が高いほど、向上するという実験上の発見に基づいている。 In the present invention, the catalytic action of activated carbon containing nitrogen is involved in the shake-up process in the abundance of nitrogen on the surface and XPS measurement, and the carbon (hereinafter referred to as carbon) which gives a spectrum having a peak at 291.8 ± 0.5 eV. The abundance of the second unpaired electron having a g-value of 2.0020 to 2.0026 increases with an increase in the abundance of the second unpaired electron. Based on the discovery of
前記シェイクアップ炭素の存在によって前記窒素含有活性炭化物の前記触媒作用が向上する理由は不明であるが、前記触媒作用が電子の授受を伴う反応に対するものであることを考慮すると、前記シェイクアップ炭素が炭素材料の電子伝導性に関与していることと何らかの関係があると考えられる。 The reason why the catalytic action of the nitrogen-containing activated carbide is improved by the presence of the shake-up carbon is unknown, but considering that the catalytic action is for a reaction involving the transfer of electrons, the shake-up carbon is It is considered that there is some relationship with the fact that the carbon material is involved in the electronic conductivity.
また、後に実施例において詳述するように、ｇ値が２．００２０〜２．００２６である前記第２の不対電子は、窒素を含まない炭素材料では観察されない特異的な電子であり、キュリー常磁性を示し、分子の一定箇所に局在化した不対電子である。分子軌道法計算によれば、キュリー常磁性を示す不対電子は、窒素を含む炭素材料の中でも、３個の炭素原子と結合した、ｓｐ2混成軌道の電子配置をもつ窒素を含有する材料のみが有し得る特殊な電子であることが判明した。この様な、窒素含有活性炭化物以外の炭素材料では見られない、局在化した不対電子が、触媒活性に大きな役割を果たしているものと考えられる。 Further, as described later in detail in Examples, the second unpaired electron having a g value of 2.0020 to 2.0026 is a specific electron not observed in a carbon material containing no nitrogen, and It is an unpaired electron that exhibits paramagnetism and is localized at a certain position in a molecule. According to molecular orbital calculations, the unpaired electrons exhibiting Curie paramagnetism are the only nitrogen-containing carbon-containing materials that have an electron configuration of sp 2 hybrid orbitals bonded to three carbon atoms. Has been found to be a special electron that can be possessed. It is considered that such localized unpaired electrons, which are not found in carbon materials other than nitrogen-containing activated carbides, play a large role in catalytic activity.
本発明の触媒及びその製造方法によれば、炭素及び窒素を構成元素とする材料を焼成し、これによって得られた焼成物を水蒸気賦活し、シェイクアップ過程に関与する炭素の存在比率、また、ｇ値が１．９９８０〜２．００００である前記第１の不対電子のスピン密度と、ｇ値が２．００２０〜２．００２６である前記第２の不対電子のスピン密度とを制御するので、窒素の作用によって高められた前記窒素含有活性炭化物の前記触媒作用が、更に一層高められた触媒及びその製造方法を提供することができる。 According to the catalyst of the present invention and the method for producing the same, a material containing carbon and nitrogen as constituent elements is calcined, and the calcined material obtained thereby is steam-activated, and the abundance ratio of carbon involved in the shake-up process, The spin density of the first unpaired electron having a g value of 1.9980 to 2.0000 and the spin density of the second unpaired electron having a g value of 2.0020 to 2.0026 are controlled. Therefore, it is possible to provide a catalyst in which the catalytic action of the nitrogen-containing activated carbide enhanced by the action of nitrogen is further enhanced and a method for producing the same.
また、本発明の電気化学デバイスは、前記シェイクアップ過程に関与する炭素の存在比率、また、ｇ値が１．９９８０〜２．００００である第１の不対電子のスピン密度と、ｇ値が２．００２０〜２．００２６である第２の不対電子のスピン密度とが制御された前記触媒を含有するので、電極上等での電子の授受がすみやかにおこり、分極等が起こりにくい。 Further, in the electrochemical device of the present invention, the abundance ratio of carbon involved in the shake-up process, the spin density of a first unpaired electron having a g value of 1.9980 to 2.0000, and a g value of Since the catalyst containing the second unpaired electron having a controlled spin density of 2.0020 to 2.0026 is contained, the transfer of electrons on the electrode or the like occurs promptly, and polarization and the like hardly occur.
本発明の触媒において、酸素を還元する次式の反応：
Ｏ2 ＋ ４Ｈ+ ＋ ４ｅ- → ２Ｈ2Ｏ
を促進する触媒であって、少なくとも炭素及び窒素を必須の構成元素とし、且つ表面における、シェイクアップ過程に関与する炭素の存在比率が制御された材料からなる酸素還元触媒であるのがよい。
In the catalyst of the present invention, a reaction of the following formula for reducing oxygen:
O 2 + 4H + + 4e - → 2H 2 O
It is preferable to use an oxygen reduction catalyst composed of a material in which at least carbon and nitrogen are indispensable constituent elements and whose surface has a controlled proportion of carbon involved in the shake-up process.
また、電子スピン共鳴測定において、前記第１の不対電子がパウリ常磁性を示し、且つ前記第２の不対電子がキュリー常磁性を示すのがよい。後に実施例において詳述するように、パウリ常磁性を示す不対電子は、伝導帯を占めていて非局在化している不対電子であり、キュリー常磁性を示す不対電子は、分子の一定箇所に局在化した不対電子である。本発明の触媒では、パウリ常磁性を示す不対電子を含む炭素材料に、キュリー常磁性を示す不対電子を、そのスピン濃度を制御しながら添加したため、電子伝導性が良好で、かつ酸素還元触媒性が備わった機能性炭素材料が実現されたものと考えられる。 In the electron spin resonance measurement, it is preferable that the first unpaired electron shows Pauli paramagnetism and the second unpaired electron shows Curie paramagnetism. As will be described later in detail in Examples, the unpaired electron exhibiting Pauli paramagnetism is an unpaired electron which occupies the conduction band and is delocalized, and the unpaired electron exhibiting Curie paramagnetism is a molecular unpaired electron. Unpaired electrons localized at a certain location. In the catalyst of the present invention, since unpaired electrons exhibiting Curie paramagnetism are added to the carbon material containing unpaired electrons exhibiting Pauli paramagnetism while controlling the spin concentration thereof, the electron conductivity is good and oxygen reduction is achieved. It is considered that a functional carbon material having catalytic properties was realized.
また、前記酸素還元触媒の表面における原子数百分率で、窒素原子が０．９６mol％以上含まれるのがよい。その中に、Ｎ1s電子の結合エネルギーが３９８．５±０．５ｅＶである第１の窒素原子が含まれ、その原子数百分率が０．２２mol％以上であり、また、Ｎ1s電子の結合エネルギーが４０１±０．５ｅＶである第２の窒素原子が含まれ、その原子数百分率が０．５３mol％以上であり、また、Ｎ1s電子の結合エネルギーが４０３．５±０．５ｅＶである第３の窒素原子が含まれ、その原子数百分率が０．２１mol％以上であるのがよい。これらは、前記シェイクアップ過程に関与する炭素の存在比率を高め、また、ｇ値が２．００２０〜２．００２６である前記第２の不対電子のスピン密度を高めるための条件である。 Further, it is preferable that nitrogen atoms are contained in an amount of 0.96 mol% or more in terms of atomic percentage on the surface of the oxygen reduction catalyst. Among them, a first nitrogen atom having a binding energy of N1s electrons of 398.5 ± 0.5 eV is included, the atomic percentage of which is 0.22 mol% or more, and the binding energy of N1s electrons is 401 A third nitrogen atom containing a second nitrogen atom of ± 0.5 eV, the atomic percentage of which is 0.53 mol% or more, and a binding energy of N1s electron of 403.5 ± 0.5 eV; And its atomic percentage is preferably 0.21 mol% or more. These are conditions for increasing the abundance ratio of carbon involved in the shake-up process and increasing the spin density of the second unpaired electron having a g value of 2.0020 to 2.0026.
本発明において、前記触媒を、少なくとも炭素及び窒素を構成元素とする非金属系材料を材料として、その原料を粉末状にして焼成し、得られた窒素含有炭化物粉末を水蒸気賦活処理して、前記触媒を製造するのがよい。この方法によれば、粉末状の原料を用い、気相と固相との界面で前記焼成や前記水蒸気賦活処理を行うので、前記触媒も粉末状で得られる。粉末状の形状は、電極上に付着させて触媒層を形成させたり、或いは利用に適した形状を有する成形体を形成させたりするのに、好都合である。 In the present invention, the catalyst is made of a non-metallic material having carbon and nitrogen as constituent elements, and the raw material is powdered and fired, and the obtained nitrogen-containing carbide powder is subjected to a steam activation treatment. A catalyst may be prepared. According to this method, since the baking and the steam activation treatment are performed at the interface between the gas phase and the solid phase using a powdery raw material, the catalyst is also obtained in a powdery form. The powdery shape is advantageous for forming a catalyst layer by being attached to an electrode or forming a molded product having a shape suitable for use.
より具体的には、前記原料として、炭素質固体原料と窒素含有有機化合物との混合物、又は窒素含有有機高分子化合物を粉末状にして焼成し、得られた前記窒素含有炭化物粉末を水蒸気賦活して、窒素含有活性炭化物からなる酸素還元触媒を製造するのがよい。ここで、前記炭素質固体原料として、石炭系バインダーピッチを用い、前記窒素含有有機化合物として、メラミン又はヒドラジンを用いるのがよい。また、前記窒素含有有機高分子化合物としては、ポリアクリロニトリル、メラミン樹脂、ナイロン、ゼラチン又はコラーゲンを用いるのがよい。このように、本方法は、大量に入手でき、安価で多様な物質を原料とすることができる。 More specifically, as the raw material, a mixture of a carbonaceous solid raw material and a nitrogen-containing organic compound, or a nitrogen-containing organic polymer compound is powdered and fired, and the obtained nitrogen-containing carbide powder is steam-activated. Thus, it is preferable to produce an oxygen reduction catalyst comprising a nitrogen-containing activated carbide. Here, coal-based binder pitch is preferably used as the carbonaceous solid raw material, and melamine or hydrazine is preferably used as the nitrogen-containing organic compound. Further, as the nitrogen-containing organic polymer compound, it is preferable to use polyacrylonitrile, melamine resin, nylon, gelatin or collagen. As described above, the present method can be obtained in large quantities, and can use inexpensive and various materials as raw materials.
この際、表面における、前記シェイクアップ過程に関与する炭素の存在比率、及び／又は、ｇ値が１．９９８０〜２．００００である第１の不対電子のスピン密度と、ｇ値が２．００２０〜２．００２６である第２の不対電子のスピン密度とを、前記焼成を行う温度、前記炭素質固体原料と前記窒素含有有機化合物との混合比率、又は用いられる前記窒素含有有機高分子化合物材料の選択によって制御するのがよい。例えば、前記焼成と前記水蒸気賦活とを、高純度窒素気流中、温度１０００℃で行うのがよい。 At this time, the abundance ratio of carbon involved in the shake-up process and / or the spin density of the first unpaired electron having a g value of 1.9980 to 2.000 on the surface and the g value of 2. The spin density of the second unpaired electron in the range of 0020 to 2.0026, the temperature at which the baking is performed, the mixing ratio of the carbonaceous solid material and the nitrogen-containing organic compound, or the nitrogen-containing organic polymer used It is better to control by selecting the compound material. For example, the baking and the steam activation are preferably performed at a temperature of 1000 ° C. in a high-purity nitrogen stream.
本発明において、複数の電極と、前記複数の電極に挟持されたイオン伝導体とからなる電気化学デバイスを形成し、前記複数の電極の少なくとも１つに前記触媒を含有させるのがよい。この電気化学デバイスは、電池、とりわけ燃料電池として構成するのがよい。 In the present invention, it is preferable that an electrochemical device including a plurality of electrodes and an ion conductor sandwiched between the plurality of electrodes is formed, and at least one of the plurality of electrodes contains the catalyst. The electrochemical device may be configured as a battery, especially a fuel cell.
この際、前記触媒は、イオン伝導性高分子と混合して、前記複数の電極の表面層を形成するようにするのがよい。また、前記複数の電極の間にイオン伝導性膜を挟持して膜−電極接合体（ＭＥＡ）を作製し、これを電気化学反応部に用いて電気化学デバイスを作製するのがよい。これにより、３相界面における水素イオンや電子の移動がスムーズに行われ、分極が抑制される。 At this time, it is preferable that the catalyst is mixed with the ion conductive polymer to form a surface layer of the plurality of electrodes. Further, it is preferable that an ion conductive membrane is sandwiched between the plurality of electrodes to produce a membrane-electrode assembly (MEA), and this is used for an electrochemical reaction section to produce an electrochemical device. This allows smooth movement of hydrogen ions and electrons at the three-phase interface, and suppresses polarization.
また、前記電気化学デバイスが、前記触媒を酸素極触媒として含む燃料電池であるのがよい。 Further, the electrochemical device may be a fuel cell including the catalyst as an oxygen electrode catalyst.
以下、本発明に基づく好ましい実施の形態による、窒素含有活性炭化物触媒の合成とその触媒を用いた燃料電池について、図面参照下、詳細に説明する。 Hereinafter, a synthesis of a nitrogen-containing active carbide catalyst and a fuel cell using the catalyst according to a preferred embodiment of the present invention will be described in detail with reference to the drawings.
＜窒素含有活性炭化物触媒の合成＞
図１は、窒素含有活性炭化物触媒の合成装置の概略断面図である。試料は、試料管２１に入れて試料支持台２２の上に置き、これら全体を電気炉２３の電気炉炉心管２４の内部に設置して、試料が電気炉２３の加熱温度域２５によって取り囲まれるように、その位置を調節する。電気炉２３は、電気炉ヒーター部２６への通電によって電気炉炉心管２４の内部のガスを加熱し、このガスを通じて試料を所望の温度に加熱できるように構成されている。電気炉炉心管２４の上部にはガス導入口２７が設けられ、また、炉心管２４の下部にはガス排出口２８が設けられている。
<Synthesis of nitrogen-containing active carbide catalyst>
FIG. 1 is a schematic sectional view of an apparatus for synthesizing a nitrogen-containing active carbide catalyst. The sample is placed in a sample tube 21 and placed on a sample support base 22, and the whole is placed inside an electric furnace core tube 24 of an electric furnace 23, and the sample is surrounded by a heating temperature range 25 of the electric furnace 23. Adjust its position as described. The electric furnace 23 is configured to heat the gas inside the electric furnace core tube 24 by energizing the electric furnace heater section 26 and heat the sample to a desired temperature through the gas. A gas inlet 27 is provided in an upper part of the electric furnace furnace tube 24, and a gas outlet 28 is provided in a lower part of the furnace tube 24.
試料の焼成に際しては、ガス導入口２７から高純度窒素ガス２９を導入し、反応後の排出ガス３０をガス排出口２８から排出する。試料管２１は試料の間を高温に加熱された窒素ガス２９が流通するように構成されていて、試料は無酸素の高純度窒素ガス雰囲気下で加熱乾留され、炭化物に変化する。 In firing the sample, a high-purity nitrogen gas 29 is introduced from a gas inlet 27 and an exhaust gas 30 after the reaction is exhausted from a gas outlet 28. The sample tube 21 is configured such that a nitrogen gas 29 heated to a high temperature flows between the samples, and the sample is heat-distilled in an oxygen-free high-purity nitrogen gas atmosphere to change into a carbide.
試料管２１の上部には水導入管３１が設けられており、水蒸気賦活の際には、この管を通じて電気炉炉心管２４の中に水が供給される。供給された水は、水導入管３１の出口付近で蒸発し、試料管２１に入れられた試料の所まで高純度窒素ガス気流によって運ばれ、ここで炭化物と水熱反応、例えば下記の反応
Ｃ ＋ Ｈ2Ｏ → ＣＯ ＋ Ｈ2
によって反応する。この結果、炭化物は多孔質に変化し、その表面積が著しく増大するので、ガス吸着性能や触媒作用が著しく活性化される。
A water inlet tube 31 is provided above the sample tube 21, and water is supplied into the electric furnace core tube 24 through this tube during steam activation. The supplied water evaporates near the outlet of the water inlet tube 31 and is carried by the high-purity nitrogen gas stream to the sample placed in the sample tube 21, where it undergoes a hydrothermal reaction with the carbide, for example, the following reaction C + H 2 O → CO + H 2
React by. As a result, the carbide changes into porous and the surface area thereof is significantly increased, so that the gas adsorption performance and the catalytic action are significantly activated.
＜燃料電池及びＭＥＡの作製＞
図２は、燃料電池の構成を示す概略断面図である。図３（ａ）は、図１の装置を少し分解して、その構成を見やすくした概略断面図であり、図３（ｂ）は、膜−電極接合体(ＭＥＡ)４の拡大断面図である。膜−電極接合体（ＭＥＡ）４は、水素イオン伝導性を有する高分子電解質膜２の両面に燃料極３と酸素極１とが接合されて形成されている。
<Fabrication of fuel cell and MEA>
FIG. 2 is a schematic sectional view showing the configuration of the fuel cell. FIG. 3A is a schematic cross-sectional view of the device of FIG. 1 which is slightly disassembled to make its configuration easier to see, and FIG. 3B is an enlarged cross-sectional view of the membrane-electrode assembly (MEA) 4. . The membrane-electrode assembly (MEA) 4 is formed by joining a fuel electrode 3 and an
図２の装置で、膜−電極接合体（ＭＥＡ）４はセル上半部７及びおよびセル下半部８の間に挟持され、燃料電池に組み込まれる。セル上半部７及びセル下半部８には、それぞれガス供給管９及び１０が設けられており、ガス供給管９からは水素、またガス供給管１０からは空気もしくは酸素が送気される。各ガスは図示省略した通気孔を有するガス供給部５及び６を通過して燃料極３および酸素極１に供給される。ガス供給部５は燃料極３とセル上半部７を電気的に接続し、ガス供給部６は酸素極１とセル下半部８を電気的に接続する。また、セル上半部７には水素ガスの漏洩を防ぐためにＯリング１１が配置されている。
In the apparatus of FIG. 2, the membrane-electrode assembly (MEA) 4 is sandwiched between the upper cell half 7 and the
発電は、上記のガスを供給しながら、セル上半部７及びセル下半部８に接続されている外部回路１２を閉じることで行うことができる。この時、燃料極３の表面上では下記（式１）
２Ｈ2 → ４Ｈ+ ＋ ４ｅ- （式１）
の反応により水素が酸化され、燃料極３に電子を与える。生じた水素イオンＨ＋は水素イオン伝導膜を介して酸素極１へ移動する。ここで、燃料極３には、いわゆるダイレクトメタノール方式の場合、燃料としてメタノールを供給することも可能である。
Power generation can be performed by closing the external circuit 12 connected to the cell upper half 7 and the cell
2H 2 → 4H + + 4e - ( Equation 1)
Hydrogen is oxidized by the reaction, and electrons are given to the fuel electrode 3. The generated hydrogen ions H + move to the
酸素極１へ移動した水素イオンは、酸素極１に供給される酸素と下記（式２）
Ｏ2 ＋ ４Ｈ+ ＋ ４ｅ- → ２Ｈ2Ｏ （式２）
のように反応し、水を生成する。このとき、酸素は、酸素極１から電子を取り込み、還元される。
The hydrogen ions transferred to the
O 2 + 4H + + 4e − → 2H 2 O (formula 2)
To produce water. At this time, oxygen takes in electrons from the
上記高分子電解質膜２は、水素イオン伝導性を有するものであれば、任意のものを使用することができる。例えば、セパレータに水素イオン伝導性を有する高分子材料を塗布したもの等が使用可能である。具体的に、この高分子電解質膜２に使用可能な材料としては、先ず、パーフルオロスルホン酸系樹脂（例えばデュポン社製、商品名 Nafion(R) 等）のような水素イオン伝導性の高分子材料を挙げることができ、またその他の水素イオン伝導体として、ポリスチレンスルホン酸、スルホン化ポリビニルアルコールなどの高分子材料やフラーレン誘導体が使用可能である。
As the
以下、本実施の形態の膜−電極接合体(ＭＥＡ)について、図３（ｂ）参照下に詳述する。 Hereinafter, the membrane-electrode assembly (MEA) of the present embodiment will be described in detail with reference to FIG.
酸素極１では、カーボンシートやカーボンクロスなどの導電性多孔質支持体１ｂの表面に、本発明による窒素含有活性炭化物からなる酸素還元触媒とNafion(R)などの水素イオン伝導体との混合物からなる酸素還元触媒層１ａが形成されている。
In the
また、燃料極３では、従来と同様、カーボンシートやカーボンクロスなどの導電性多孔質支持体３ｂの表面に、触媒能を有する金属として白金、若しくは白金合金等とNafion(R)などの水素イオン伝導体との混合物からなる水素酸化触媒層３ａが形成されている。 Further, in the fuel electrode 3, as in the conventional case, platinum or a platinum alloy or the like and a hydrogen ion such as Nafion (R) are formed on the surface of a conductive porous support 3 b such as a carbon sheet or a carbon cloth as a metal having catalytic activity. A hydrogen oxidation catalyst layer 3a made of a mixture with a conductor is formed.
このように、電極反応に直接曝される膜の両表面層には、化学的安定性に優れた材料からなる層、例えばNafion(R)などのパーフルオロスルホン酸系樹脂等からなる層が配置され、しかも、電極側にも同種の材料からなる層が形成され、膜−電極接合体(ＭＥＡ)が形成されているので、化学的に安定で、しかも水素イオンや電子の移動がスムーズに行われる、良好な接合面が形成される。 Thus, on both surface layers of the film directly exposed to the electrode reaction, a layer made of a material having excellent chemical stability, for example, a layer made of a perfluorosulfonic acid resin such as Nafion (R) is arranged. In addition, since a layer made of the same material is formed on the electrode side and a membrane-electrode assembly (MEA) is formed, it is chemically stable, and hydrogen ions and electrons can move smoothly. A good bonding surface is formed.
以下、本発明の好ましい実施例を詳しく具体的に説明する。 Hereinafter, preferred embodiments of the present invention will be described in detail.
以下の例においては、炭素質固体原料として石炭系バインダーピッチを用い、窒素含有有機化合物としてメラミンを用いて、窒素含有活性炭化物触媒を合成し、この触媒を用いて燃料電池を作製した例を説明する。 In the following examples, an example is described in which a coal-based binder pitch is used as a carbonaceous solid raw material, a melamine is used as a nitrogen-containing organic compound, a nitrogen-containing active carbide catalyst is synthesized, and a fuel cell is manufactured using this catalyst. I do.
＜窒素含有活性炭化物触媒の合成と、酸素極及びＭＥＡの作製＞
例１
本例では、石炭系バインダーピッチとメラミンを質量比９５：５ではかり取り、乳鉢を用いて粉砕して混合した粉末４ｇを試料管２１に入れ、上記の合成装置内にセットした。焼成は高純度窒素ガス気流中で行い、温度を常温から始めて５℃／ｍｉｎの昇温速度で１０００℃まで上昇させ、その後１時間１０００℃のまま保持した。この１時間の間に水蒸気賦活も行った。水の滴下速度は０．５ｍｌ／ｈで、用いた水の量は０．５ｍｌであった。この後、室温まで放冷した。粉末試料は焼成によって窒素含有炭化物粉末に変化し、水蒸気賦活により窒素含有活性炭化物に変化した。処理後、バインダーピッチの質量は約半分に減少し、メラミン分はほとんど残らなかった。本例では、約２ｇ（１．９７５ｇ）の窒素含有活性炭化物が得られた。
<Synthesis of nitrogen-containing active carbide catalyst and preparation of oxygen electrode and MEA>
Example 1
In this example, the coal-based binder pitch and melamine were weighed at a mass ratio of 95: 5, crushed using a mortar, and 4 g of the mixed powder was placed in the sample tube 21 and set in the above-described synthesis apparatus. The firing was performed in a high-purity nitrogen gas stream, and the temperature was increased from room temperature to 1000 ° C. at a rate of 5 ° C./min, and then maintained at 1000 ° C. for 1 hour. During this hour, steam activation was also performed. The dropping rate of water was 0.5 ml / h, and the amount of water used was 0.5 ml. Then, it was left to cool to room temperature. The powder sample was changed to a nitrogen-containing carbide powder by firing, and changed to a nitrogen-containing activated carbide by steam activation. After the treatment, the mass of the binder pitch was reduced to about half, and almost no melamine content remained. In this example, about 2 g (1.975 g) of nitrogen-containing activated carbide was obtained.
この窒素含有活性炭化物と、水素イオン伝導体であるNafion(R)溶液とを混ぜ合わせ、窒素含有活性炭化物とNafion(R)溶液の固形分との質量比が８：２の割合になっている、エタノールを溶媒とするスラリー状の混合物とした。このスラリー状の混合物をカーボンシートに塗布し、溶媒を蒸発させた後、カーボンシートを直径１５ｍｍの円盤状に打ち抜いて、酸素極を作製した。 This nitrogen-containing active carbide is mixed with a Nafion (R) solution which is a hydrogen ion conductor, and the mass ratio of the nitrogen-containing active carbide to the solid content of the Nafion (R) solution is 8: 2. And a slurry mixture using ethanol as a solvent. This slurry-like mixture was applied to a carbon sheet, and after evaporating the solvent, the carbon sheet was punched into a disk having a diameter of 15 mm to produce an oxygen electrode.
一方、市販の白金担持カーボン触媒を塗布したカーボンシートを直径１０ｍｍの円盤状に打ち抜いて、燃料極を作製した。更に、これら２つの電極の間に直径１５ｍｍの円盤状に打ち抜いたNafion(R)112を挟み、１５０℃で熱融着して膜−電極接合体（ＭＥＡ）を作製した。 On the other hand, a carbon sheet coated with a commercially available platinum-supported carbon catalyst was punched into a disk having a diameter of 10 mm to prepare a fuel electrode. Further, a Nafion (R) 112 punched into a disk having a diameter of 15 mm was sandwiched between these two electrodes, and was thermally fused at 150 ° C. to produce a membrane-electrode assembly (MEA).
例２
石炭系バインダーピッチとメラミンを質量比７５：２５ではかり取った以外は、例１と同様である。
Example 2
Same as Example 1 except that the coal-based binder pitch and melamine were weighed at a mass ratio of 75:25.
例３
石炭系バインダーピッチとメラミンを質量比５０：５０ではかり取った以外は、例１と同様である。
Example 3
Same as Example 1 except that the coal-based binder pitch and melamine were weighed out at a mass ratio of 50:50.
例４
石炭系バインダーピッチとメラミンを質量比２５：７５ではかり取った以外は、例１と同様である。
Example 4
Same as Example 1 except that the coal-based binder pitch and melamine were weighed at a mass ratio of 25:75.
例５
石炭系バインダーピッチとメラミンを質量比５：９５ではかり取った以外は、例１と同様である。処理後、バインダーピッチの質量は約半分に減少し、メラミン分はほとんど残らないので、本例では、０．０７７ｇの窒素含有活性炭化物が得られたのみであった。
Example 5
Same as Example 1 except that the coal-based binder pitch and melamine were weighed at a mass ratio of 5:95. After the treatment, the mass of the binder pitch was reduced to about half and almost no melamine content remained, so in this example, only 0.077 g of nitrogen-containing activated carbide was obtained.
例６
メラミンを混合せずにバインダーピッチのみを焼成して窒素含有炭化物粉末を形成した以外は、例１と同様である。
Example 6
The same as Example 1 except that only the binder pitch was fired without mixing melamine to form a nitrogen-containing carbide powder.
例７
石炭系バインダーピッチとメラミンから焼成した窒素含有炭化物粉末の代わりに、黒鉛粉末を用いた以外は、例１と同様である。
Example 7
Example 1 is the same as Example 1 except that graphite powder was used instead of the nitrogen-containing carbide powder fired from coal-based binder pitch and melamine.
例８
石炭系バインダーピッチとメラミンから焼成した窒素含有炭化物粉末の代わりに、アセチレンブラックを用いた以外は、例１と同様である。
Example 8
Example 1 is the same as Example 1 except that acetylene black was used instead of the nitrogen-containing carbide powder fired from coal-based binder pitch and melamine.
＜炭化物表面の元素組成＞
表１は、例１〜５で得られた窒素含有活性炭化物及び例６〜８で生成した炭化物の表面の元素組成を、ＸＰＳ（X-ray Photoelectron Spectroscopy:Ｘ線励起光電子分光法）測定によって定量した結果である。いずれの炭素材料においても、検出された元素は炭素、酸素及び窒素のみで、金属等の元素はいっさい含まれていなかった。なお、元素組成は、原子数百分率で表している。また、シェイクアップ炭素の比率は、炭素C1s電子のスペクトル全体に対する２９１．８±０．５ｅＶにピークをもつスペクトルの割合として求めたもので、全炭素中でのシェイクアップ炭素の存在比率と見なせるものである（以下、同様。）。
<Element composition on carbide surface>
Table 1 shows that the elemental compositions of the surfaces of the nitrogen-containing activated carbides obtained in Examples 1 to 5 and the carbides formed in Examples 6 to 8 were quantified by XPS (X-ray Photoelectron Spectroscopy). This is the result. In all the carbon materials, the detected elements were only carbon, oxygen, and nitrogen, and did not include any elements such as metals. Note that the element composition is represented by the atomic percentage. The ratio of the shake-up carbon was determined as the ratio of the spectrum having a peak at 291.8 ± 0.5 eV to the entire spectrum of the carbon C1s electron, which can be regarded as the abundance ratio of the shake-up carbon in all the carbons. (The same applies hereinafter).
例１〜５を比較すると、窒素含有活性炭化物を合成する原料としてメラミンの比率を高めた例ほど、窒素の存在率が高く、シェイクアップ炭素の比率も高くなっている。 Comparing Examples 1 to 5, the higher the ratio of melamine as a raw material for synthesizing the nitrogen-containing activated carbide, the higher the nitrogen abundance and the higher the shake-up carbon ratio.
例６の、メラミンを加えず、石炭系バインダーピッチのみから合成した炭化物においても０．８６mol％の窒素が含まれていた。これは、石炭系バインダーピッチ自身が含有していた窒素である。他方、例７及び例８で使用した炭素原料であるグラファイト及びアセチレンブラックには窒素が含まれておらず、その結果、水蒸気賦活処理後の炭素材料においても窒素は検出されなかった。 The carbide of Example 6 synthesized only from coal-based binder pitch without adding melamine also contained 0.86 mol% of nitrogen. This is the nitrogen contained in the coal-based binder pitch itself. On the other hand, graphite and acetylene black as the carbon raw materials used in Examples 7 and 8 did not contain nitrogen, and as a result, nitrogen was not detected in the carbon material after the steam activation treatment.
なお、グラファイト及びアセチレンブラックには酸素も含まれていないが、例７及び例８で得られた炭素材料には、２〜３mol％の酸素が含まれていた。これは水蒸気賦活処理によって導入されたものと考えられる。 Note that graphite and acetylene black did not contain oxygen, but the carbon materials obtained in Examples 7 and 8 contained 2-3 mol% of oxygen. This is considered to have been introduced by the steam activation treatment.
＜窒素の結合状態＞
ＸＰＳスペクトルの解析から、表面近傍にある窒素原子にはN1s電子の結合エネルギーが異なる３種の窒素原子Ｎ１〜Ｎ３が含まれていることがわかった。表２は、ＸＰＳスペクトルの解析から得られた、表面近傍におけるＮ１〜Ｎ３の原子数百分率で表した存在率（mol％）である。
<Nitrogen bonding state>
From the analysis of the XPS spectrum, it was found that the nitrogen atoms near the surface contained three types of nitrogen atoms N1 to N3 having different binding energies of N1s electrons. Table 2 shows the abundances (mol%) expressed as the number percentage of N1 to N3 in the vicinity of the surface, obtained from the analysis of the XPS spectrum.
N1s電子の結合エネルギーの違いは、窒素原子の結合状態の違いを反映している。窒素原子Ｎ１〜Ｎ３の帰属は、Energy & Fuels，第１２号(１９９８年)，ｐ.672-681、或いはCarbon，第４０号，ｐ.597-608 に記載されているデータを参考にして行った。第１の窒素原子Ｎ１は、N1s電子の結合エネルギーが３９８．５±０．５ｅＶの窒素原子で、ピリジン型窒素である。第２の窒素原子Ｎ２は、N1s電子の結合エネルギーが４０１±０．５ｅＶの窒素原子である。これは、４級窒素であり、水素化したピリジン型窒素、若しくはグラフェン層内の窒素と言われている。第３の窒素原子Ｎ３は、N1s電子の結合エネルギーが４０３．５±０．５ｅＶの窒素原子で、酸化したピリジン型窒素とされている。 The difference in the binding energy of the N1s electron reflects the difference in the bonding state of the nitrogen atom. The assignment of the nitrogen atoms N1 to N3 is performed with reference to the data described in Energy & Fuels, No. 12, (1998), pp. 672-681, or Carbon, No. 40, pp. 597-608. Was. The first nitrogen atom N1 is a pyridine type nitrogen having a binding energy of N1s electrons of 398.5 ± 0.5 eV. The second nitrogen atom N2 is a nitrogen atom having a binding energy of N1s electrons of 401 ± 0.5 eV. This is quaternary nitrogen, which is called hydrogenated pyridine-type nitrogen or nitrogen in the graphene layer. The third nitrogen atom N3 is a nitrogen atom having a binding energy of N1s electrons of 403.5 ± 0.5 eV and is oxidized pyridine type nitrogen.
例１〜５の窒素含有活性炭化物では、Ｎ１〜Ｎ３のどの窒素の存在率も、メラミンの混合比の増加に伴い増加する傾向がある。 In the nitrogen-containing activated carbides of Examples 1 to 5, the abundance of any of N1 to N3 tends to increase as the mixing ratio of melamine increases.
＜燃料電池特性＞
図２に示した燃料電池に、例１〜５及び例６〜８等で作製された膜−電極接合体（ＭＥＡ）を組み込み、燃料極に加湿した水素を流速３０ｍｌ／ｍｉｎで供給し、酸素極には空気を流速２０ｍｌ／ｍｉｎで供給し、例１〜５で得られた窒素含有活性炭化物触媒および例６〜８で生成した炭化物の、燃料電池の酸素極触媒としての特性を調べた。ここで、水素は酸素に比べて大過剰に加えられており、酸素の供給量も得られた出力電流に比して十分過剰である。
<Fuel cell characteristics>
The membrane-electrode assemblies (MEAs) produced in Examples 1 to 5 and Examples 6 to 8 are incorporated into the fuel cell shown in FIG. 2, and humidified hydrogen is supplied to the fuel electrode at a flow rate of 30 ml / min. Air was supplied to the poles at a flow rate of 20 ml / min, and the characteristics of the nitrogen-containing active carbide catalyst obtained in Examples 1 to 5 and the carbide generated in Examples 6 to 8 as an oxygen electrode catalyst of a fuel cell were examined. Here, hydrogen is added in a large excess in comparison with oxygen, and the supply amount of oxygen is sufficiently excessive in comparison with the obtained output current.
表３は、本実験において測定された開回路電圧と、０．４Ｖの出力電圧で発電している時の出力密度とである。また、図４は、この出力電圧と出力密度との関係を示すグラフである。 Table 3 shows the open circuit voltage measured in the present experiment and the output density when power was generated at an output voltage of 0.4 V. FIG. 4 is a graph showing the relationship between the output voltage and the output density.
各炭素材料の示す開回路電圧はどれも異なる値を示した。メラミンを混合して窒素の存在率を高めた例１〜５では、開回路電圧はいずれも０．８Ｖを越えており、更にメラミンの混合量の増加に伴い開回路電圧も上昇した。例１〜５において、出力密度もメラミンの混合量の増加に伴い増大した。これらの傾向は、表１に示した、例１〜５における窒素の存在率の増加及びシェイクアップ炭素の存在比率の増加と対応している。 The open circuit voltage of each carbon material showed different values. In Examples 1 to 5 in which the presence ratio of nitrogen was increased by mixing melamine, the open circuit voltage exceeded 0.8 V, and the open circuit voltage also increased with an increase in the amount of melamine mixed. In Examples 1 to 5, the power density also increased with an increase in the amount of melamine mixed. These tendencies correspond to the increase in the nitrogen content and the increase in the shake-up carbon content in Examples 1 to 5 shown in Table 1.
一方、例６のように窒素の存在率が０．８６％と小さい窒素含有活性炭化物を用いた燃料電池では開回路電圧が低く、また出力密度は極めて小さく、発電性能はほとんど得られなかった。例７及び８のように窒素を含まない炭化物を炭素材料として用いた燃料電池では、開回路電圧が低く、発電性能はほとんど得られず、これらの炭素材料には酸素還元触媒としての特性がほとんどないことがわかった。 On the other hand, in the fuel cell using the nitrogen-containing activated carbide having a low nitrogen content of 0.86% as in Example 6, the open circuit voltage was low, the output density was extremely low, and almost no power generation performance was obtained. In the fuel cell using a nitrogen-free carbide as a carbon material as in Examples 7 and 8, the open circuit voltage is low, the power generation performance is hardly obtained, and these carbon materials have almost no characteristics as an oxygen reduction catalyst. I knew it wasn't.
以上のごとく、活性炭化物中の窒素の存在率及びシェイクアップ炭素の存在比率と、活性炭化物の酸素還元触媒としての特性との間には相関があることは明白であり、燃料電池の酸素極の電極触媒として必要な特性を持つためには、活性炭化物の表面における窒素の存在率が０．９６％以上であることが重要といえる。 As described above, it is clear that there is a correlation between the abundance of nitrogen and the abundance of shake-up carbon in the activated carbide, and the properties of the activated carbide as an oxygen reduction catalyst. In order to have the characteristics required as an electrode catalyst, it can be said that it is important that the abundance of nitrogen on the surface of the activated carbide is 0.96% or more.
また、表２の結果を鑑みると、酸素極触媒として機能するには、各結合エネルギーの窒素の表面における存在率が例１を上回ることが必須であり、すなわち結合エネルギーが３９８．５±０．５ｅＶ付近である窒素の存在率が原子百分率で０．２２％以上、あるいは結合エネルギーが４０１±０．５ｅＶ付近である窒素の存在率が０．５３％以上、あるいは結合エネルギーが４０３．５±０．５ｅＶ付近である窒素の存在率が０．２１％以上であることが重要である。 Also, in view of the results in Table 2, in order to function as an oxygen electrode catalyst, it is essential that the abundance of each binding energy on the surface of nitrogen exceeds that of Example 1, that is, the binding energy is 398.5 ± 0. The abundance of nitrogen near 5 eV is 0.22% or more in atomic percentage, or the abundance of nitrogen near 401 ± 0.5 eV is 0.53% or more, or the binding energy is 403.5 ± 0. It is important that the abundance of nitrogen near 0.5 eV is 0.21% or more.
＜電子スピン共鳴（ＥＳＲ）測定＞
黒鉛をはじめとする炭素材料中には様々な結合構造を有する炭素原子が含まれ、その中には全電子数が奇数個である炭素も存在する。奇数個の電子を持つ場合、対を作らず１つの軌道を単独で占有する電子、即ち不対電子が必然的に存在する。不対電子は１／２の電子スピンを有するため、磁場中におかれると、電子スピンの向きの異なる２つのエネルギー状態にゼーマン***し、次の関係式1を満たす振動数νをもつ電磁波に対して共鳴吸収を示すようになる。
ｈν＝ｇβＨ
<Electron spin resonance (ESR) measurement>
Carbon materials having various bonding structures are included in carbon materials such as graphite, and among them, carbon having an odd number of total electrons also exists. When having an odd number of electrons, there is necessarily an electron that occupies one orbit independently without forming a pair, that is, an unpaired electron. Since an unpaired electron has a half electron spin, when it is placed in a magnetic field, it undergoes Zeeman splitting into two energy states with different electron spin directions, forming an electromagnetic wave having a frequency ν that satisfies the following
hν = gβH
ここで、ｇはｇ因子または磁気回転比と言われ、不対電子をもつ物質固有の値である。また、ｈはプランク定数６．６２５５×１０-34Ｊｓであり、βはボーア磁子９．２７４×１０-24ＪＴ-1であり、Ｈは単位Tで表した磁場の強さである。電子スピン共鳴（ＥＳＲ）測定法は上記の原理に基づく測定法で、不対電子を有する物質の結合構造を調べるのに有効な測定方法である。 Here, g is called a g-factor or a gyromagnetic ratio, and is a value specific to a substance having unpaired electrons. H is Planck's constant 6.6255 × 10 −34 Js, β is Bohr magneton 9.274 × 10 −24 JT −1 , and H is the strength of the magnetic field expressed in unit T. The electron spin resonance (ESR) measurement method is a measurement method based on the above principle, and is an effective measurement method for examining the bonding structure of a substance having an unpaired electron.
表４は、例１〜５で得られた窒素含有活性炭化物、および例６と７で生成した炭化物についてＥＳＲスペクトルの測定を行い、その吸収強度から不対電子の密度であるスピン密度を求めた結果である。例１〜例５の窒素含有活性炭化物、並びに例６の炭化物は、ＥＳＲスペクトルから求まるｇ値が１．９９８０〜２．００００である不対電子と、ｇ値が２．００２０〜２．００２６である不対電子との２種類の不対電子を有していた。それに対し、窒素を含有していない例７の炭化物は、ｇ値が２．００７５である１種類の不対電子を有するのみであった。 Table 4 shows that the nitrogen-containing activated carbide obtained in Examples 1 to 5 and the carbide generated in Examples 6 and 7 were measured for ESR spectra, and the spin density, which is the density of unpaired electrons, was determined from the absorption intensity. The result. The nitrogen-containing activated carbides of Examples 1 to 5 and the carbide of Example 6 had unpaired electrons having a g value of 1.9980 to 2.000 determined from the ESR spectrum and a g value of 2.0020 to 2.0026. It had two types of unpaired electrons with a certain unpaired electron. In contrast, the carbide of Example 7 containing no nitrogen had only one type of unpaired electron having a g-value of 2.0075.
図５は、例１〜例５の窒素含有活性炭化物および例６の炭化物における２種類の不対電子のスピン密度と、表１に示した表面における窒素の存在率との関係を示すグラフである。図５によると、ｇ値が１．９９８０〜２．００００である不対電子のスピン密度は、窒素の存在率の増加とともに減少するのに対し、ｇ値が２．００２０〜２．００２６である不対電子のスピン密度は、窒素の存在率の増加とともに増加しており、不対電子のスピン密度と窒素の存在率との間には明らかに相関関係が認められる。 FIG. 5 is a graph showing the relationship between the spin density of two types of unpaired electrons in the nitrogen-containing active carbides of Examples 1 to 5 and the carbide of Example 6, and the nitrogen abundance on the surface shown in Table 1. . According to FIG. 5, the spin density of an unpaired electron having a g value of 1.9980 to 2.000 decreases with an increase in the abundance of nitrogen, whereas the g value is 2.0020 to 2.0026. The spin density of unpaired electrons increases with increasing nitrogen abundance, and there is a clear correlation between the spin density of unpaired electrons and the abundance of nitrogen.
通常の炭素材料で観察される不対電子は、伝導帯を占めている不対電子であり、分子の電子構造に対し非局在化して、分子全体に均一に分布している。この電子はパウリ常磁性を示し、その磁化率は、比較的高い温度まで温度によらず一定である。常磁性を示す電子スピンには、この他に、磁化率が絶対温度に反比例するというキュリーの法則に従うものが存在し、キュリー常磁性スピンと呼ばれる。キュリー常磁性は、分子の電子構造の一定箇所に集中した存在確率分布を有する局在化した電子のスピンによるものである。不対電子がパウリ常磁性であるか、キュリー常磁性であるかは、ＥＳＲ吸収スペクトル強度の温度依存性を調べれば容易に判定することができる。 Unpaired electrons observed in ordinary carbon materials are unpaired electrons occupying the conduction band, are delocalized with respect to the electronic structure of the molecule, and are uniformly distributed throughout the molecule. These electrons exhibit Pauli paramagnetism, and their susceptibility is constant regardless of temperature up to a relatively high temperature. There are other electron spins exhibiting paramagnetism that follow Curie's law that the magnetic susceptibility is inversely proportional to the absolute temperature, and are called Curie paramagnetic spins. Curie paramagnetism is due to localized electron spins that have a distribution of existence probability concentrated at certain locations in the electronic structure of the molecule. Whether the unpaired electron is Pauli paramagnetic or Curie paramagnetic can be easily determined by examining the temperature dependence of the ESR absorption spectrum intensity.
表５および図６は、ＥＳＲ吸収スペクトル強度を異なる温度で測定し、例５の窒素含有活性炭化物に含まれる２種の不対電子、および例７の炭化物に含まれる不対電子のスピン密度の温度依存性を調べた結果である。測定は、２９６Ｋ、２００Ｋ、１２０Ｋ、および８０Ｋの４つの温度で行った。 Table 5 and FIG. 6 show that the ESR absorption spectrum intensity was measured at different temperatures, and the spin densities of two unpaired electrons contained in the nitrogen-containing activated carbide of Example 5 and unpaired electrons contained in the carbide of Example 7 were measured. It is the result of having investigated the temperature dependence. Measurements were taken at four temperatures: 296K, 200K, 120K, and 80K.
例５の窒素含有活性炭化物に含まれるｇ値が２．００００である不対電子、および例７の炭化物に含まれるｇ値が２．００７５である不対電子のスピン密度は、温度に対する依存性が見られず、このことからこれらの不対電子は、通常の炭素材料でも確認されるパウリ常磁性を示す伝導電子であることがわかる。 The spin density of the unpaired electron having a g value of 2.000 contained in the nitrogen-containing active carbide of Example 5 and the unpaired electron having a g value of 2.0075 contained in the carbide of Example 7 is dependent on temperature. , Which indicates that these unpaired electrons are conduction electrons exhibiting Pauli paramagnetism, which are also observed in ordinary carbon materials.
これに対し、例５の窒素含有活性炭化物に含まれるｇ値が２．００２６である不対電子のスピン密度は、温度の低下につれて増加しており、キュリー常磁性を示す不対電子であることがわかる。先述したように、キュリー常磁性を示す不対電子は分子の電子構造に対し局在化しており、例７の炭化物がそうであるように、窒素を含まない通常の炭素材料では観察されない特異的な電子である。 On the other hand, the spin density of the unpaired electron having a g value of 2.0026 contained in the nitrogen-containing active carbide of Example 5 increases with decreasing temperature, and is an unpaired electron exhibiting Curie paramagnetism. I understand. As previously mentioned, the unpaired electrons exhibiting Curie paramagnetism are localized to the electronic structure of the molecule and, as in the carbide of Example 7, are not observed in ordinary nitrogen-free carbon materials. Electron.
図８は、窒素含有活性炭化物中に存在が予想される窒素種を示す化学式である（Carbon，第４０号（２００２年），ｐ.597-608）。分子軌道法計算ソフト「Spartan '04 for Windows」を用い、様々な窒素含有黒鉛構造の半占有軌道（ＳＯＭＯ；Single Occupied Molecular Orbital ）を計算したところ、図中、「三炭素結合型」と記した、３個の炭素原子と結合したｓｐ2混成軌道の電子配置をもつ窒素（three-carbon bonding sp2 nitrogen；あるいは、quaternary nitrogenまたはcarbon substituted nitrogenとも呼ばれている。）を有する炭素材料のみが、不対電子が局在化した構造をとることがわかった。従って、キュリー常磁性を示す不対電子は、窒素を含む炭素材料のなかでも、特別な結合構造をもつ窒素含有炭素材料のみが有し得る特殊な電子であることが判明した。この様な、窒素含有活性炭化物以外の炭素材料では見られない、局在化した不対電子が、触媒活性に大きな役割を果たしているものと考えられる。 FIG. 8 is a chemical formula showing the nitrogen species expected to be present in the nitrogen-containing activated carbide (Carbon, No. 40 (2002), pp. 597-608). Using the molecular orbital calculation software "Spartan '04 for Windows", the half occupied orbitals (SOMOs) of various nitrogen-containing graphite structures were calculated. Only a carbon material having three-carbon bonding sp 2 nitrogen (also called quaternary nitrogen or carbon substitution nitrogen) having an electron configuration of sp 2 hybrid orbital bonded to three carbon atoms, It turned out that the unpaired electron takes a localized structure. Therefore, it was found that unpaired electrons exhibiting Curie paramagnetism are special electrons that can be possessed only by a nitrogen-containing carbon material having a special bonding structure among nitrogen-containing carbon materials. It is considered that such localized unpaired electrons, which are not found in carbon materials other than nitrogen-containing activated carbides, play a large role in catalytic activity.
以上のように、本発明に基づく窒素含有活性炭化物触媒では、パウリ常磁性を示す不対電子を含む炭素材料に、キュリー常磁性を示す不対電子を、そのスピン濃度を制御しながら添加したため、電子伝導性が良好で、かつ酸素還元触媒性が備わった機能性炭素材料が実現されたものと考えられる。 As described above, in the nitrogen-containing active carbide catalyst according to the present invention, an unpaired electron exhibiting Curie paramagnetism was added to a carbon material containing an unpaired electron exhibiting Pauli paramagnetism while controlling its spin concentration. It is considered that a functional carbon material having good electron conductivity and having oxygen reduction catalytic properties has been realized.
例１〜５においては、炭素源として石炭系バインダーピッチを用い、窒素源としてメラミンを用い、両者の混合物の焼成を行ったが、本発明の効果を得る方法は、この材料に限定されるものではない。例えば、Energy & Fuels，第１２号（１９９８年），ｐ.672-681 に記載されているように、窒素源としてメラミンの代わりにヒドラジンを使用することでも、窒素の存在率を高めることができる。また、アンモニア雰囲気下で焼成を行ってもよい。また、ポリアクリロニトリル、ナイロンやメラミン樹脂などの窒素含有合成高分子化合物、或いはゼラチンやコラーゲンなどのたんぱく質等の窒素含有天然有機高分子化合物を原料として、例１〜５と同様の触媒活性をもつ窒素含有活性炭化物を得ることもできる。次に、ポリアクリロニトリル又はメラミン樹脂を原料とした例を示す。 In Examples 1 to 5, the coal-based binder pitch was used as the carbon source, melamine was used as the nitrogen source, and the mixture of both was fired. However, the method of obtaining the effect of the present invention is limited to this material. is not. For example, as described in Energy & Fuels, No. 12, (1998), pp. 672-681, the use of hydrazine instead of melamine as a nitrogen source can increase the nitrogen abundance. . Further, the firing may be performed in an ammonia atmosphere. Further, a nitrogen-containing synthetic polymer compound such as polyacrylonitrile, nylon or melamine resin, or a nitrogen-containing natural organic polymer compound such as a protein such as gelatin or collagen is used as a raw material. It is also possible to obtain a contained active carbide. Next, an example using polyacrylonitrile or melamine resin as a raw material will be described.
例９
石炭系バインダーピッチとメラミンの混合物粉末の代わりに、ポリアクリロニトリルの粉末を焼成する以外は、例１と同様である。
Example 9
It is the same as Example 1 except that the powder of polyacrylonitrile is fired instead of the powder mixture of coal-based binder pitch and melamine.
例１０
焼成温度を１０００℃ではなく６００℃にした以外は、例９と同様である。
Example 10
It is the same as Example 9 except that the firing temperature was changed to 600 ° C. instead of 1000 ° C.
例１１
メラミン、市販ホルマリン液及び水を質量比１：２：２に混合し、ｐＨ ９ の弱塩基性下で加熱煮沸した。その後析出した白色固形物（メラミン樹脂）を回収した。この樹脂の粉末を、石炭系バインダーピッチとメラミンの混合物粉末の代わりに焼成した以外は、例１と同様である。
Example 11
Melamine, a commercially available formalin solution and water were mixed at a mass ratio of 1: 2: 2, and the mixture was heated and boiled under weakly
表６は、表２と同様、ＸＰＳで調べた、例９〜１１で得られた窒素含有活性炭化物の表面における第１〜第３の窒素原子Ｎ１〜Ｎ３の在在率及びシェイクアップ炭素の存在比率である。いずれの窒素含有活性炭化物も、先述したN1s電子の結合エネルギーで特徴づけられる第１〜第３の窒素原子Ｎ１〜Ｎ３を含んでいることが判明した。 Table 6 shows the abundance ratios of the first to third nitrogen atoms N1 to N3 and the presence of shake-up carbon on the surface of the nitrogen-containing activated carbide obtained in Examples 9 to 11, which were examined by XPS as in Table 2. It is a ratio. All of the nitrogen-containing activated carbides were found to contain the first to third nitrogen atoms N1 to N3 characterized by the binding energy of the N1s electron described above.
電極に加湿した水素を流速３０ｍｌ／ｍｉｎで供給し、酸素極には空気を流速２０ｍｌ／ｍｉｎで供給した。例９と例１１における出力電圧と出力密度との関係を図５に示す。例９と例１１の発電性能は、例５につぎ、例４と同程度であった。例９〜例１１の燃料電池を０．４Ｖの出力電圧で発電させている時の出力密度を測定した結果を表４に示す。 Humidified hydrogen was supplied to the electrode at a flow rate of 30 ml / min, and air was supplied to the oxygen electrode at a flow rate of 20 ml / min. FIG. 5 shows the relationship between the output voltage and the output density in Examples 9 and 11. The power generation performance of Examples 9 and 11 was similar to that of Example 4 after that of Example 5. Table 4 shows the results of measuring the output density when the fuel cells of Examples 9 to 11 were generated at an output voltage of 0.4 V.
１０００℃でポリアクリロニトリルの焼成を行った例９と、６００℃でポリアクリロニトリルの焼成を行った例１０とを比べると、焼成温度が低く活性化が不十分な例１０ではシェイクアップ炭素の存在比率が小さく、その結果、触媒性能が不十分で、燃料電池を構成した場合の出力密度が低いことがわかる。 When Example 9 in which polyacrylonitrile was fired at 1000 ° C. and Example 10 in which polyacrylonitrile was fired at 600 ° C., the ratio of shake-up carbon was present in Example 10 in which the firing temperature was low and activation was insufficient. It can be seen that the power density was low, and as a result, the catalyst performance was insufficient, and the power density when a fuel cell was configured was low.
また、例９と例１１とを比べると、材料の選択によっても窒素の存在率及びシェイクアップ炭素の存在比率を変化させることができること、また、ポリアクリロニトリルを焼成した場合は窒素の存在率は大きいがシェイクアップ炭素の存在比率が小さく、メラミン樹脂を焼成した場合にはシェイクアップ炭素の存在比率は大きいが窒素の存在率が小さく、結果として両者の燃料電池の出力密度は同程度であること、言い換えれば触媒性能を高くして、燃料電池を構成した場合の出力密度を大きくするには、窒素の存在率とシェイクアップ炭素の存在比率とを共に大きくする必要があることがわかる。 Further, comparing Example 9 with Example 11, it can be seen that the abundance of nitrogen and the abundance of shake-up carbon can be changed by selecting the material, and the abundance of nitrogen is large when polyacrylonitrile is fired. When the presence ratio of shake-up carbon is small, and when melamine resin is calcined, the presence ratio of shake-up carbon is large but the presence ratio of nitrogen is small, and as a result, the output densities of both fuel cells are approximately the same, In other words, it can be seen that in order to enhance the catalyst performance and increase the output density when a fuel cell is constructed, it is necessary to increase both the abundance of nitrogen and the abundance of shake-up carbon.
例１２
以上は、電解質に高分子膜を使用した高分子電解質型燃料電池への応用例であったが、本発明の酸素還元触媒はこれに限定されるものでなく、リン酸型燃料電池へも応用できる。ここではリン酸型燃料電池へ応用した例を示す。
Example 12
Although the above is an example of application to a polymer electrolyte fuel cell using a polymer membrane as an electrolyte, the oxygen reduction catalyst of the present invention is not limited to this, and is also applicable to a phosphoric acid fuel cell. it can. Here, an example in which the present invention is applied to a phosphoric acid fuel cell is shown.
炭化ケイ素粉末にポリテトラフルオロエチレンを質量比８：２で混練後、圧延した膜状成形物をマトリックスとして、これにリン酸を真空含浸させたものを電解質とした。一方、例４で合成した窒素含有活性炭化物にポリテトラフルオロエチレンを質量比８：２で混練し、圧延した。これを乾燥した後、直径１５ｍｍの円盤状に打ち抜き、酸素極を作製した。 After kneading silicon carbide powder with polytetrafluoroethylene at a mass ratio of 8: 2, a rolled film-shaped molded product was used as a matrix, which was impregnated with phosphoric acid under vacuum to obtain an electrolyte. On the other hand, polytetrafluoroethylene was kneaded with the nitrogen-containing activated carbide synthesized in Example 4 at a mass ratio of 8: 2 and rolled. After drying this, it was punched into a disk having a diameter of 15 mm to produce an oxygen electrode.
一方、市販の白金担持カーボン触媒を塗布したカーボンシートを直径１０ｍｍの円盤状に打ち抜き、燃料極とした。更に、これら２つの電極の間に電解質を挟み、これを例１などと同様、図２に示した燃料電池に組み込み、燃料極に加湿した水素を流速３０ｍｌ／ｍｉｎで供給し、酸素極には空気を流速２０ｍｌ／ｍｉｎで供給し、発電特性を評価した。 On the other hand, a carbon sheet coated with a commercially available platinum-supported carbon catalyst was punched into a disk having a diameter of 10 mm to obtain a fuel electrode. Further, an electrolyte is sandwiched between these two electrodes, and this is incorporated in the fuel cell shown in FIG. 2 as in Example 1 and the like, and humidified hydrogen is supplied to the fuel electrode at a flow rate of 30 ml / min. Air was supplied at a flow rate of 20 ml / min to evaluate the power generation characteristics.
本例による開回路電圧、及び０．４Ｖの出力電圧で発電している時の出力密度を表７に示す。 Table 7 shows the open circuit voltage according to the present example and the output density when power is generated at an output voltage of 0.4 V.
以上のように、本発明に基づく例１〜５、９及び１１による窒素含有活性炭化物触媒は、リン酸型燃料電池でも酸素極用触媒としての使用が可能である。 As described above, the nitrogen-containing active carbide catalysts according to Examples 1 to 5, 9 and 11 according to the present invention can be used as a catalyst for an oxygen electrode even in a phosphoric acid fuel cell.
上記のように、実験結果に基づき、炭素及び窒素を構成元素とする材料を焼成し、これによって得られた焼成物を水蒸気賦活することで、表面における窒素の存在率とシェイクアップ炭素の存在比率とが共に高くなるように制御し、また、キュリー常磁性を示す不対電子のスピン濃度が高くなるように制御した窒素含有活性炭化物を合成することができること、およびこの材料が酸素還元触媒として有効な特性を示すこととを発見し、燃料電池の酸素極に応用することに成功した。本実施例によれば、酸素極の原料コストを極めて低く低減することができ、従来白金を酸素極の電極触媒として使用してきた燃料電池の低コスト化に寄与することが可能である。 As described above, based on the experimental results, the material containing carbon and nitrogen as the constituent elements is fired, and the fired material obtained by this is activated with steam, so that the nitrogen abundance ratio and the shake-up carbon abundance ratio on the surface are obtained. Can be synthesized to increase the spin concentration of unpaired electrons exhibiting Curie paramagnetism, and the nitrogen-containing active carbide can be synthesized, and this material is effective as an oxygen reduction catalyst. It has been found that it exhibits excellent characteristics, and has been successfully applied to the oxygen electrode of a fuel cell. According to the present embodiment, the raw material cost of the oxygen electrode can be reduced extremely low, and it is possible to contribute to the cost reduction of a fuel cell that has conventionally used platinum as an electrode catalyst of the oxygen electrode.
以上、本発明を実施の形態および実施例に基づいて説明したが、本発明はこれらの例に何ら限定されるものではなく、本発明の技術的思想に基づいて適宜変更可能であることは言うまでもない。 As described above, the present invention has been described based on the embodiment and the examples. However, it is needless to say that the present invention is not limited to these examples at all and can be appropriately changed based on the technical idea of the present invention. No.
本発明は、次世代の発電装置として期待される、高分子電解質型燃料電池やリン酸型燃料電池の酸素極電極触媒などに好適に用いられ、白金使用量の少ない低コストの上記燃料電池を実現し、その普及に寄与することができる。 The present invention is expected to be used as a power generation device of the next generation, and is suitably used for an oxygen electrode electrode catalyst of a polymer electrolyte fuel cell or a phosphoric acid fuel cell, and uses the low-cost fuel cell with a small amount of platinum. It can be realized and contribute to its spread.
１…酸素極、１ａ…酸素還元触媒層、１ｂ…導電性多孔質支持体、
２…水素イオン伝導性高分子電解質膜、３…燃料極、３ａ…水素酸化触媒層、
３ｂ…導電性多孔質支持体、４…膜−電極接合体（ＭＥＡ）、
５、６…ガス供給部、５ａ、６ａ…ガス供給溝、７…セル上半部、
８…セル下半部、９、１０…ガス供給管、１１…Ｏリング、１２…外部回路、
２１…試料管、２２…試料支持台、２３…電気炉、２４…電気炉炉心管、
２５…電気炉の加熱領域、２６…電気炉ヒーター部、２７…ガス導入口、
２８…ガス排出口、２９…高純度窒素ガス、３０…排出ガス、３１…水導入管
DESCRIPTION OF
2 ... hydrogen ion conductive polymer electrolyte membrane, 3 ... fuel electrode, 3a ... hydrogen oxidation catalyst layer,
3b: conductive porous support, 4: membrane-electrode assembly (MEA),
5, 6: gas supply unit, 5a, 6a: gas supply groove, 7: upper half of the cell,
8: lower half of the cell, 9, 10: gas supply pipe, 11: O-ring, 12: external circuit,
21 ... sample tube, 22 ... sample support stand, 23 ... electric furnace, 24 ... electric furnace core tube,
25: electric furnace heating area, 26: electric furnace heater section, 27: gas inlet,
28 gas exhaust port, 29 high-purity nitrogen gas, 30 exhaust gas, 31 water introduction pipe
Claims (19)
Ｏ2 ＋ ４Ｈ+ ＋ ４ｅ- → ２Ｈ2Ｏ
を促進する触媒であって、炭素及び窒素を必須の構成元素とし、且つ表面における、シェイクアップ過程に関与する炭素の存在比率が制御された材料からなる酸素還元触媒である、請求項１に記載した触媒。 Reaction of the following formula to reduce oxygen:
O 2 + 4H + + 4e - → 2H 2 O
2. The oxygen reduction catalyst according to claim 1, wherein the catalyst is a catalyst for promoting carbon dioxide, wherein carbon and nitrogen are indispensable constituent elements, and an oxygen reduction catalyst made of a material whose surface has a controlled proportion of carbon involved in a shake-up process. Catalyst.
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| PCT/JP2004/005492 WO2004091781A1 (en) | 2003-04-17 | 2004-04-16 | Catalyst and process for producing the same, catalytic electrode and process for producing the same, membrane/electrode union, and electrochemical device |
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