JP2007257888A - Oxygen pole catalyst for solid polymer fuel cell, oxygen reduction electrode using it, and manufacturing method of those - Google Patents
Oxygen pole catalyst for solid polymer fuel cell, oxygen reduction electrode using it, and manufacturing method of those Download PDFInfo
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Abstract
Description
本発明は固体高分子形燃料電池の電極として用いるのに好適な酸素還元電極に関する。 The present invention relates to an oxygen reduction electrode suitable for use as an electrode of a polymer electrolyte fuel cell.
従来、白金等の貴金属は高い電位においても安定でかつ高い触媒能を有するため各種の電気化学システムの電極用触媒に用いられている。しかし、白金の価格が高いことや資源的に限りがあることから、白金を代替できる高活性の触媒が要望され、種々の提案がなされている(例えば、特許文献1、2、3、及び4参照)。
Conventionally, noble metals such as platinum are stable and have high catalytic ability even at high potentials, and are therefore used as catalysts for electrodes in various electrochemical systems. However, since platinum is expensive and limited in terms of resources, a highly active catalyst that can replace platinum has been demanded and various proposals have been made (for example,
まず、特許文献1ではAl,Cu,第VIII族元素,La系列元素を含む面心立方体若しくは菱面体結晶の触媒に、ホウ素、酸素、窒素のうち少なくとも1種を添加し、次に炭素、珪素、ジルコニウム、チタニウム、ハフニウムのうち少なくとも1種を添加し、白金及び鉄、更にパラジウム、ルテニウム、ロジウムおよび金から選択される合金から成り、次にクロム、モリブデン、タングステンのうち少なくとも1種を添加し、次にバナジウム、ニオブ、タンタルのうち少なくとも1種を添加し、更に白金を添加した触媒が開示されている。
First, in
また、特許文献2では白金を含む合金からなる貴金属成分(Pm)と、遷移金属成分(Me、例えばFe)の合金からなる触媒物質(PmXMeY)を窒化処理により、触媒物質の表面に遷移金属四窒化物構造(Me−N4)を形成した電極触媒が開示されている。
Further, in
更に、特許文献3では酸化ルテニウム、酸化チタン、酸化バナジウム、酸化マンガン、酸化コバルト、酸化ニッケル、酸化タングステンから選ばれる少なくとも1種、又はモリブデンの窒化物の金属酸化物又は金属窒化物の電極触媒と白金、パラジウム、ルテニウム、ロジウム、銀、ニッケル、鉄、銅、コバルト、及びモリブデンから選ばれる少なくとも1種の無機酸化物の混合物の触媒が提案されている。
Further, in
上記のように、高価な白金を含まない技術は開発されていない。 As mentioned above, no technology that does not contain expensive platinum has been developed.
また、特許文献4には水に対して親和力の高いメタノールなどの有機液体燃料を用いる場合、有機液体燃料が水分を含んだ固体電解質膜に拡散して酸素還元電極まで到達するクロスオーバーによる燃料電池の効率低下を解決する技術として、燃料極又は酸素還元電極と固体電解質膜の間に水素含有ヘテロポリ酸塩を含む層を形成することが開示されている。
Further, in
このような従来の触媒は、白金を含むもので高価で資源的制約がある。さらに、白金含有量の低下に伴って触媒活性も減退し、固体高分子形燃料電池用酸素極触媒として満足するものはなかった。 Such conventional catalysts contain platinum and are expensive and resource-constrained. Furthermore, as the platinum content decreased, the catalytic activity also decreased, and there was no satisfactory oxygen electrode catalyst for polymer electrolyte fuel cells.
また白金を含むため、クロスオーバーによる燃料電池の効率が低下する問題点を有していた。 In addition, since platinum is contained, there is a problem that the efficiency of the fuel cell is reduced due to crossover.
本発明は上記の問題点を解決するもので、その技術的課題は、白金などの貴金属を全く含まない酸素還元の触媒活性が優れる固体高分子形燃料電池用酸素極触媒であって、クロスオーバーによる燃料電池の効率低下を起こさない固体高分子形燃料電池用酸素極触媒およびそれを用いた固体高分子形燃料電池用酸素還元電極およびそれらの製造方法を提供することにある。 The present invention solves the above-mentioned problems, and its technical problem is an oxygen electrode catalyst for a polymer electrolyte fuel cell that does not contain any precious metal such as platinum and has excellent catalytic activity for oxygen reduction. It is an object of the present invention to provide an oxygen electrode catalyst for a polymer electrolyte fuel cell that does not cause a decrease in the efficiency of the fuel cell due to the above, an oxygen reduction electrode for a polymer electrolyte fuel cell using the same, and a method for producing them.
この課題に対する本発明の解決手段は燃料電池酸素極の触媒において、高性能の燃料電池を実現するために炭窒化チタン粉末および複合炭窒化チタン粉末に窒素と炭素の含有量および処理条件により結晶性を制御するものである。また、導電性のカーボンブラック粉末との混合物を炭素系基体上に塗布しナフィオン(登録商標、以下単に、ナフィオンと呼ぶ)の電解質膜を形成した固体高分子形燃料電池用酸素還元電極において、クロスオーバーによる燃料電池の効率低下を防止するために、燃料の分解反応を触媒する作用を持たない炭窒化チタン粉末および複合炭窒化チタン粉末の触媒を用いることで課題の解決を図ったものである。 In order to realize a high-performance fuel cell, the solution according to the present invention for solving this problem is that the titanium carbonitride powder and the composite titanium carbonitride powder have crystallinity depending on the contents of nitrogen and carbon and the processing conditions. Is to control. Further, in an oxygen reduction electrode for a polymer electrolyte fuel cell in which a mixture of conductive carbon black powder is coated on a carbon-based substrate to form an electrolyte membrane of Nafion (registered trademark, hereinafter simply referred to as Nafion), In order to prevent the efficiency of the fuel cell from being reduced due to over, the problem is solved by using a catalyst of titanium carbonitride powder and composite titanium carbonitride powder that do not have an action of catalyzing the decomposition reaction of fuel.
即ち、本発明によれば、1対の電極間にイオン交換膜を配置した固体高分子形燃料電池に用いられる酸素還元電極の触媒であって、前記酸素還元電極の触媒は窒素を2.0〜15.5質量%、炭素を6.0〜19.0質量%および遊離炭素を0.1〜5.9質量%含有する立方晶の炭窒化チタン粉末であることを特徴とする固体高分子形燃料電池用酸素極触媒が得られる。 That is, according to the present invention, there is provided a catalyst for an oxygen reduction electrode used in a polymer electrolyte fuel cell in which an ion exchange membrane is disposed between a pair of electrodes. Solid polymer characterized in that it is a cubic titanium carbonitride powder containing -15.5% by mass, carbon 6.0-19.0% by mass and free carbon 0.1-5.9% by mass An oxygen electrode catalyst for a fuel cell is obtained.
また、本発明によれば、前記触媒固体高分子形燃料電池用酸素極触媒において、炭窒化チタン粉末はJCPDSファイルの42−1489(C0.7N0.3Ti)又は42−1488(C0.3N0.7Ti)に合致する立方晶系であって、ミラーの指数(hkl)511で測定した格子定数が4.260〜4.317Åを満たすことを特徴とする固体高分子形燃料電池用酸素極触媒が得られる。 Further, according to the present invention, in the oxygen electrode catalyst for a catalyst solid polymer fuel cell, the titanium carbonitride powder is JCPDS file 42-1489 (C 0.7 N 0.3 Ti) or 42-1488 (C 0.3 N 0.7 Ti), a solid polymer having a lattice constant measured by Miller's index (hkl) 511 of 4.260 to 4.317Å An oxygen electrode catalyst for a fuel cell is obtained.
また、本発明によれば、前記触媒固体高分子形燃料電池用酸素極触媒において、前記触媒は、さらにIVa族のジルコニウム、ハフニウム、Va族のバナジウム、ニオブ、タンタル、およびVIa族のクロム、モリブデン、タングステンのうちの少なくとも一種の元素を0.1〜20質量%添加した複合炭窒化チタン粉末であることを特徴とする固体高分子形燃料電池用酸素極触媒が得られる。ここで、本発明において、IVa族元素、Va族元素、及びVIa族元素とは、IUPAC無機化学命名法改訂版(1989)による4族、5族、及び6族元素に夫々相当する。
Further, according to the present invention, in the above-mentioned catalytic oxygen electrode catalyst for a polymer electrolyte fuel cell, the catalyst is further divided into group IVa zirconium, hafnium, group Va vanadium, niobium, tantalum, group VIa chromium, molybdenum. Thus, an oxygen electrode catalyst for a polymer electrolyte fuel cell is obtained, which is a composite titanium carbonitride powder to which 0.1 to 20% by mass of at least one element of tungsten is added. Here, in the present invention, the IVa group element, the Va group element, and the VIa group element respectively correspond to the
また、本発明によれば、クロスオーバーによる効率の低下を生じない固体高分子形燃料電池用酸素還元電極であって、請求項1又は2に記載の触媒と、導電性のカーボンブラック粉末との混合物を炭素系基体上のグラッシーカーボン基体上に塗布し、前記塗布膜上に高分子電解質のナフィオンの電解質膜を形成したことを特徴とする固体高分子形燃料電池用酸素還元電極が得られる。
Moreover, according to the present invention, there is provided an oxygen reduction electrode for a polymer electrolyte fuel cell that does not cause a decrease in efficiency due to crossover, comprising: the catalyst according to
また、本発明によれば、前記固体高分子形燃料電池用酸素還元電極において、対極に白金箔を用い、30℃の0.1mol/L硫酸水溶液中で、走査速度5mV/sで電位走査したとき、可逆水素電極電位基準で0.4Vにおいて両電極間に測定される酸素雰囲気での電流値をIO2とし、窒素雰囲気での電流値をIN2としたとき、R=(IO2−IN2)/IN2で表される値が0.5以上を有することを特徴とする固体高分子形燃料電池用酸素還元電極が得られる。 Further, according to the present invention, in the oxygen reduction electrode for a polymer electrolyte fuel cell, a potential is scanned at a scanning speed of 5 mV / s in a 0.1 mol / L sulfuric acid aqueous solution at 30 ° C. using a platinum foil as a counter electrode. When the current value in the oxygen atmosphere measured between the two electrodes at 0.4 V on the basis of the reversible hydrogen electrode potential is I O2 and the current value in the nitrogen atmosphere is I N2 , R = (I O2 −I A value represented by N2 ) / IN2 is 0.5 or more, and an oxygen reduction electrode for a polymer electrolyte fuel cell is obtained.
また、本発明によれば、前記固体高分子形燃料電池用酸素還元電極において、対極に白金箔を用い、30℃の0.1mol/L硫酸水溶液中で、走査速度5mV/sで電位走査したとき、酸素還元電流が流れ始める時の両電極間の電位が前記可逆水素電極電位基準で0.5V以上を有することを特徴とする固体高分子形燃料電池用酸素還元電極が得られる。 Further, according to the present invention, in the oxygen reduction electrode for a polymer electrolyte fuel cell, a potential is scanned at a scanning speed of 5 mV / s in a 0.1 mol / L sulfuric acid aqueous solution at 30 ° C. using a platinum foil as a counter electrode. In this case, an oxygen reduction electrode for a polymer electrolyte fuel cell is obtained in which the potential between both electrodes when the oxygen reduction current starts to flow is 0.5 V or more on the basis of the reversible hydrogen electrode potential.
また、本発明によれば、前記固体高分子形燃料電池用酸素極触媒に用いる炭窒化チタン粉末の製造方法であって、前記炭窒化チタン粉末の炭素量が6.0〜19.0質量%になるようにチタン原料としての酸化チタン、水素化チタン、及び金属チタンのうちの少なくとも一種と、カーボンブラック粉末とを混合する混合工程と、前記の混合粉末の窒素量が15.5〜2.0質量%になるように1400〜1800℃の窒素又は窒素と水素の混合雰囲気中で加熱処理を施す第一の加熱処理工程と、前記第一の加熱処理が施された炭窒化チタン粉末を1200〜1600℃の前記それぞれの雰囲気又は真空中でさらに加熱処理を施す第二の加熱処理工程と、前記第一の加熱処理が施された炭窒化チタン粉末、若しくは第二の加熱処理が施された炭窒化チタン粉末をボールミル又は衝撃粉砕機又はジェットミルで粉砕する粉砕工程とを備えていることを特徴とする固体高分子形燃料電池用酸素極触媒の製造方法が得られる。 Moreover, according to the present invention, there is provided a method for producing a titanium carbonitride powder used for the oxygen electrode catalyst for a polymer electrolyte fuel cell, wherein the carbon content of the titanium carbonitride powder is 6.0 to 19.0% by mass. So that at least one of titanium oxide, titanium hydride, and metal titanium as a titanium raw material is mixed with carbon black powder, and the amount of nitrogen in the mixed powder is 15.5-2. A first heat treatment step in which heat treatment is performed in nitrogen or a mixed atmosphere of nitrogen and hydrogen at 1400 to 1800 ° C. so as to be 0% by mass, and titanium carbonitride powder subjected to the first heat treatment is 1200 A second heat treatment step in which heat treatment is further performed in each of the above-described atmospheres or vacuum at ˜1600 ° C., and a titanium carbonitride powder subjected to the first heat treatment, or a second heat treatment was performed. Charcoal Method for producing a polymer electrolyte fuel cell oxygen electrode catalyst, characterized in that the titanium powder and a grinding step of grinding in a ball mill or an impact pulverizer or a jet mill can be obtained.
また、本発明によれば、固体高分子形燃料電池用酸素極触媒に用いる複合炭窒化チタン粉末の製造方法であって、チタン原料としての酸化チタン、水素化チタン、金属チタンのうちの少なくとも一種と、ジルコニウム、ハフニウム、バナジウム、ニオブ、タンタル、クロム、モリブデン、タングステンのうちの少なくとも一種の元素が0.1〜20質量%になるような酸化物粉末又は金属粉末又は炭化物粉末と、6.0〜19.0質量%の含有炭素および0.1〜5.9質量%の遊離炭素を含有するようにカーボンブラック粉末とを混合する混合工程と、前記複合炭窒化チタン粉末の窒素量が15.5〜2.0質量%になるように1400〜1800℃の窒素又は窒素と水素の混合雰囲気中で前記混合粉末に加熱処理を施す第一の加熱処理工程と、前記第一の加熱処理が施された複合炭窒化チタン粉末を1200〜1600℃の前記のそれぞれの雰囲気又は真空中でさらに熱処理を施す第二の加熱処理工程と、前記第一の加熱処理が施された複合炭窒化チタン粉末、若しくは第二の加熱処理が施された複合炭窒化チタン粉末をボールミル、衝撃粉砕機、及びジェットミルの内の少なくとも一種の粉砕手段で粉砕する粉砕工程とを備えてなることを特徴とする固体高分子形燃料電池用酸素極触媒の製造方法が得られる。 According to the present invention, there is also provided a method for producing a composite titanium carbonitride powder used for an oxygen electrode catalyst for a polymer electrolyte fuel cell, wherein at least one of titanium oxide, titanium hydride, and titanium metal as a titanium raw material. An oxide powder, a metal powder, or a carbide powder in which at least one element of zirconium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum, and tungsten is 0.1 to 20% by mass; and 6.0 A mixing step of mixing carbon black powder so as to contain ˜19.0% by mass of carbon and 0.1 to 5.9% by mass of free carbon, and the amount of nitrogen in the composite titanium carbonitride powder is 15. 1st heat processing process which heat-processes the said mixed powder in 1400-1800 degreeC nitrogen or the mixed atmosphere of nitrogen and hydrogen so that it may become 5-2.0 mass% A second heat treatment step of further heat-treating the composite titanium carbonitride powder subjected to the first heat treatment in the respective atmosphere or vacuum at 1200 to 1600 ° C., and the first heat treatment A pulverizing step of pulverizing the composite titanium carbonitride powder subjected to the above or the composite titanium carbonitride powder subjected to the second heat treatment with at least one pulverizing means of a ball mill, an impact pulverizer, and a jet mill. A method for producing an oxygen electrode catalyst for a polymer electrolyte fuel cell is provided.
また、本発明によれば、前記固体高分子形燃料電池用酸素還元電極を製造する方法であって、請求項1又は請求項3に記載の触媒と導電性のカーボンブラック粉末とを混合する工程と、前記混合粉末に結着剤テフロンを混合してペースト状とし、前記ペーストをグラッシーカーボン基体表面に塗布し乾燥して触媒と導電性物質からなる塗布膜を炭素系基体上に形成する工程と、前記塗布膜上に高分子電解質のナフィオンでコーティングする工程とを備えていることを特徴とする固体高分子形燃料電池用酸素還元電極の製造方法が得られる。
Moreover, according to this invention, it is a method of manufacturing the said oxygen reduction electrode for polymer electrolyte fuel cells, Comprising: The process of mixing the catalyst of
本発明によれば、高価で資源的制約がある白金を用いた触媒に代替できる固体高分子形燃料電池用酸素極触媒を提供することができる。 ADVANTAGE OF THE INVENTION According to this invention, the oxygen electrode catalyst for polymer electrolyte fuel cells which can substitute for the catalyst using platinum with an expensive and resource restrictions can be provided.
また、本発明によれば、白金を全く含まない炭窒化チタン粉末および複合炭窒化チタン粉末触媒であるため、クロスオーバーによる燃料電池の効率低下を起こさないという利点を有し、酸性電解質中において酸素を還元する優れた固体高分子形燃料電池用の酸素極触媒および酸素還元電極およびそれらの製造方法が提供できる。 Further, according to the present invention, the titanium carbonitride powder and the composite titanium carbonitride powder catalyst containing no platinum have the advantage that the efficiency of the fuel cell is not reduced by crossover, and oxygen in the acidic electrolyte. An oxygen electrode catalyst and an oxygen reduction electrode for a polymer electrolyte fuel cell excellent in reducing oxygen can be provided.
本発明についてさらに詳しく説明する。 The present invention will be described in more detail.
本発明の固体高分子形燃料電池用酸素極触媒は、1対の電極間にイオン交換膜を配置した固体高分子形燃料電池に用いられる酸素還元電極の触媒であって、前記酸素還元電極の触媒は窒素を2.0〜15.5質量%、炭素を6.0〜19.0質量%および遊離炭素を0.1〜5.9質量%含有する立方晶の炭窒化チタン粉末である構成を有する。 The oxygen electrode catalyst for a polymer electrolyte fuel cell of the present invention is a catalyst for an oxygen reduction electrode used in a polymer electrolyte fuel cell in which an ion exchange membrane is disposed between a pair of electrodes, The catalyst is a cubic titanium carbonitride powder containing 2.0 to 15.5% by mass of nitrogen, 6.0 to 19.0% by mass of carbon and 0.1 to 5.9% by mass of free carbon. Have
この固体高分子形燃料電池用酸素極触媒において、炭窒化チタン粉末はJCPDSファイルの42−1489(C0.7N0.3Ti)又は42−1488(C0.3N0.7Ti)に合致する立方晶系であって、ミラーの指数(hkl)511で測定した格子定数が4.260〜4.317Åを満たすことが好ましい。 In this polymer electrolyte fuel cell oxygen electrode catalyst, titanium carbonitride powder is either JCPDS file 42-1489 (C 0.7 N 0.3 Ti) or 42-1488 (C 0.3 N 0.7 Ti). It is preferable that the lattice constant measured by the Miller index (hkl) 511 satisfies 4.260 to 4.3174.
また、本発明では、この固体高分子形燃料電池用酸素極触媒に、さらにIVa族のジルコニウム(Zr)、ハフニウム(Hf)、Va族のバナジウム(V)、ニオブ(Nb)、タンタル(Ta)、およびVIa族のクロム(Cr)、モリブデン(Mo)、タングステン(W)うちの少なくとも一種の元素を0.1〜20質量%添加した複合炭窒化チタン粉末であることが好ましい。ここで、IVa族元素、Va族元素、及びVIa族元素とは、IUPAC無機化学命名法改訂版(1989)による4族、5族、及び6族元素に夫々相当する。
In the present invention, the oxygen electrode catalyst for a polymer electrolyte fuel cell is further added to group IVa zirconium (Zr), hafnium (Hf), group Va vanadium (V), niobium (Nb), tantalum (Ta). , And VIa group chromium (Cr), molybdenum (Mo), tungsten (W) is preferably a composite titanium carbonitride powder to which at least one element of at least one element is added. Here, the IVa group element, the Va group element, and the VIa group element respectively correspond to the
また、本発明の固体高分子形燃料電池用酸素還元電極は、クロスオーバーによる効率の低下を生じない固体高分子形燃料電池用酸素還元電極であって、前記のいずれかの触媒と、導電性のカーボンブラック粉末との混合物を炭素系基体上のグラッシーカーボン基体上に塗布し、前記塗布膜上に高分子電解質のナフィオンの電解質膜を形成したものである。 An oxygen reduction electrode for a polymer electrolyte fuel cell according to the present invention is an oxygen reduction electrode for a polymer electrolyte fuel cell that does not cause a decrease in efficiency due to crossover, and is provided with any one of the above-described catalyst and a conductive material. A carbon black powder mixture was applied onto a glassy carbon substrate on a carbon-based substrate, and a polymer electrolyte Nafion electrolyte membrane was formed on the coating membrane.
ここで、この固体高分子形燃料電池用酸素還元電極において、対極に白金箔を用い、30℃の0.1mol/L硫酸水溶液中で、走査速度5mV/sで電位走査したとき、可逆水素電極電位基準で0.4Vにおいて両電極間に測定される酸素雰囲気での電流値をIO2とし、窒素雰囲気での電流値をIN2としたとき、R=(IO2−IN2)/IN2で表される値が0.5以上を有することが好ましい。 Here, in this oxygen reduction electrode for a polymer electrolyte fuel cell, a reversible hydrogen electrode was obtained when a platinum foil was used as a counter electrode and a potential scan was performed at a scanning speed of 5 mV / s in a 0.1 mol / L sulfuric acid aqueous solution at 30 ° C. When the current value in an oxygen atmosphere measured between both electrodes at 0.4 V with reference to the potential is I O2 and the current value in a nitrogen atmosphere is I N2 , R = (I O2 −I N2 ) / I N2 It is preferable that the value represented by is 0.5 or more.
また、この固体高分子形燃料電池用酸素還元電極において、対極に白金箔を用い、30℃の0.1mol/L硫酸水溶液中で、走査速度5mV/sで電位走査したとき、酸素還元電流が流れ始める時の両電極間の電位が前記可逆水素電極電位基準で0.5V以上を有することが好ましい。 Further, in this oxygen reduction electrode for polymer electrolyte fuel cell, when a platinum foil was used as the counter electrode and the potential was scanned at a scanning speed of 5 mV / s in a 0.1 mol / L sulfuric acid aqueous solution at 30 ° C., the oxygen reduction current was It is preferable that the potential between both electrodes when starting to flow has 0.5 V or more based on the reversible hydrogen electrode potential.
また、本発明の固体高分子形燃料電池用酸素極触媒に用いる炭窒化チタン粉末の一製造方法は、前記炭窒化チタン粉末の炭素量が6.0〜19.0質量%になるようにチタン原料としての酸化チタン、水素化チタン、金属チタンのうちの一種と、カーボンブラック粉末とを混合する混合工程と、前記の混合粉末の窒素量が15.5〜2.0質量%になるように1400〜1800℃の窒素又は窒素と水素の混合雰囲気中で加熱処理を施す第一の加熱処理工程と、前記第一の加熱処理が施された炭窒化チタン粉末を1200〜1600℃の前記それぞれの雰囲気又は真空中でさらに加熱処理を施す第二の加熱処理工程と、前記第一の加熱処理が施された炭窒化チタン粉末、若しくは第二の加熱処理が施された炭窒化チタン粉末をボールミル又は衝撃粉砕機又はジェットミルで粉砕する粉砕工程とを備えている。 In addition, in one production method of the titanium carbonitride powder used for the oxygen electrode catalyst for the polymer electrolyte fuel cell of the present invention, the titanium carbonitride powder has a titanium content such that the carbon content is 6.0 to 19.0% by mass. A mixing step of mixing one of titanium oxide, titanium hydride, and titanium metal as a raw material with carbon black powder, and so that the nitrogen content of the mixed powder is 15.5 to 2.0% by mass. 1st heat processing process which heat-processes in 1400-1800 degreeC nitrogen or the mixed atmosphere of nitrogen and hydrogen, and said 1st-1600 degreeC said titanium carbonitride powder which performed said 1st heat processing A second heat treatment step for further heat treatment in an atmosphere or a vacuum, and a titanium carbonitride powder subjected to the first heat treatment, or a titanium carbonitride powder subjected to the second heat treatment in a ball mill or And a pulverizing step of pulverizing in a hammer crusher or a jet mill.
また、本発明の固体高分子形燃料電池用酸素極触媒に用いる複合炭窒化チタン粉末のもう一つの製造方法は、チタン原料としての酸化チタン、水素化チタン、金属チタンのうちの一種と、ジルコニウム、ハフニウム、バナジウム、ニオブ、タンタル、クロム、モリブデン、タングステンのうちの少なくとも一種の元素が0.1〜20質量%になるような酸化物粉末又は金属粉末又は炭化物粉末と、前記請求項1の炭素量になるようにカーボンブラック粉末とを混合する混合工程と、前記複合炭窒化チタン粉末の窒素量が15.5〜2.0質量%になるように1400〜1800℃の窒素又は窒素と水素の混合雰囲気中で前記混合粉末に加熱処理を施す第一の加熱処理工程と、前記第一の加熱処理が施された複合炭窒化チタン粉末を1200〜1600℃の前記のそれぞれの雰囲気又は真空中でさらに熱処理を施す第二の加熱処理工程と、前記第一の加熱処理が施された複合炭窒化チタン粉末、若しくは第二の加熱処理が施された複合炭窒化チタン粉末をボールミル又は衝撃粉砕機又はジェットミルで粉砕する粉砕工程とを備えている。
Further, another method for producing a composite titanium carbonitride powder used for the oxygen electrode catalyst for a polymer electrolyte fuel cell of the present invention includes titanium oxide, titanium hydride, titanium metal as a titanium raw material, zirconium , Hafnium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten, an oxide powder, a metal powder, or a carbide powder in which at least one element is 0.1 to 20% by mass; and carbon of
また、本発明の固体高分子形燃料電池用酸素還元電極の製造方法は、前記いずれかの触媒と導電性のカーボンブラック粉末とを混合する工程と、前記混合粉末に結着剤テフロンを混合してペースト状とし、前記ペーストをグラッシーカーボン基体表面に塗布し乾燥して触媒と導電性物質からなる塗布膜を炭素系基体上に形成する工程と、前記塗布膜上に高分子電解質のナフィオンでコーティングする工程とを備えている。 Further, the method for producing an oxygen reduction electrode for a polymer electrolyte fuel cell according to the present invention comprises a step of mixing any one of the catalyst and conductive carbon black powder, and a binder Teflon mixed with the mixed powder. Coating the paste onto the glassy carbon substrate surface and drying to form a coating film comprising a catalyst and a conductive material on the carbon-based substrate, and coating the coating film with Nafion, a polymer electrolyte. And a process of performing.
次に、本発明における数値限定の理由について説明する。 Next, the reason for the numerical limitation in the present invention will be described.
本発明において、窒素量を2.0〜15.5質量%と限定したのは、0.08〜18.4%の窒素量に変化させた炭窒化チタン粉末から作製した酸素還元電極と白金箔を用いた対極の両電極間でR値を測定した結果、実用可能な燃料電池が得られる0.5以上のR値の炭窒化チタン粉末の窒素は2.0〜15.5質量%であるからである。 In the present invention, the amount of nitrogen was limited to 2.0 to 15.5% by mass because the oxygen reduction electrode and the platinum foil were made from titanium carbonitride powder changed to 0.08 to 18.4% nitrogen. As a result of measuring the R value between the two electrodes of the counter electrode using N, the nitrogen content of the titanium carbonitride powder having an R value of 0.5 or more that gives a practical fuel cell is 2.0 to 15.5% by mass Because.
また、本発明において、炭素量を6.0〜19.0質量%と限定したのは、5.2〜21.0%の炭素量に変化させた炭窒化チタン粉末から作製した酸素還元電極と白金箔を用いた対極の両電極間でR値を測定した結果、実用可能な燃料電池が得られる0.5以上のR値の炭窒化チタン粉末の炭素は6.0〜19.0質量%であるからである。 In the present invention, the carbon content was limited to 6.0 to 19.0 mass% because the oxygen reduction electrode made from titanium carbonitride powder changed to 5.2 to 21.0% carbon content, As a result of measuring the R value between both electrodes of the counter electrode using the platinum foil, the carbon content of the titanium carbonitride powder having an R value of 0.5 or more that gives a practical fuel cell is 6.0 to 19.0% by mass. Because.
本発明において、遊離炭素を0.1〜5.9質量%と限定したのは、
0.08〜7.9%の遊離炭素量に変化させた炭窒化チタン粉末から作製した酸素還元電極と白金箔を用いた対極の両電極間でR値を測定した結果、実用可能な燃料電池が得られる0.5以上のR値の炭窒化チタン粉末の遊離炭素は0.1〜5.9質量%であるからである。
In the present invention, free carbon was limited to 0.1 to 5.9% by mass,
As a result of measuring the R value between both electrodes of an oxygen reduction electrode made of titanium carbonitride powder changed to 0.08 to 7.9% free carbon and a counter electrode using platinum foil, a practical fuel cell was obtained. This is because the free carbon of the titanium carbonitride powder having an R value of 0.5 or more obtained from 0.1 to 5.9% by mass.
また、本発明において、立方晶炭窒化チタン粉末の格子定数を260〜4.317Åと限定したのは、4.247〜4.324Åの格子定数に変化させた炭窒化チタン粉末から作製した酸素還元電極と白金箔を用いた対極の両電極間でR値を測定した結果、実用可能な燃料電池が得られる0.5以上のR値の立方晶炭窒化チタン粉末の格子定数は4.260〜4.317Åであるからである。 In the present invention, the lattice constant of the cubic titanium carbonitride powder was limited to 260 to 4.317%, and the oxygen reduction produced from the titanium carbonitride powder changed to 4.247 to 4.324%. As a result of measuring the R value between the electrode and the counter electrode using the platinum foil, the lattice constant of the cubic titanium carbonitride powder having an R value of 0.5 or more that gives a practical fuel cell is 4.260. This is because it is 4.317 mm.
また、本発明において、原料チタンに添加して使用される元素として、ジルコニウム、ハフニウム、バナジウム、ニオブ、タンタル、クロム、モリブデン、タングステンのうちの少なくとも一種の元素を0.1〜20質量%添加している。 Further, in the present invention, 0.1 to 20% by mass of at least one element selected from zirconium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum, and tungsten is added as an element to be used in addition to the raw material titanium. ing.
その理由は、作製された複合炭窒化チタン粉末から作製した酸素還元電極と白金箔を用いた対極の両電極間でR値を測定し、実用可能な燃料電池が得られる0.5以上のR値を得たからである。 The reason is that the R value is measured between the oxygen reduction electrode produced from the produced composite titanium carbonitride powder and the counter electrode using the platinum foil, and a practical fuel cell of 0.5 or more can be obtained. This is because the value was obtained.
次に、電極の電気化学的特性について説明する。 Next, the electrochemical characteristics of the electrode will be described.
本発明においては、上記炭窒化物を用いた電極の電気化学的特性が以下のようになっていることが好ましい。この規定は、触媒単位量当りの酸素還元電流を評価するものであり、この値が所定値以上であれば、充分な酸素還元能を有することになる。つまり、本発明の炭窒化チタン粉末を用い、以下の電気化学的特性を有する電極は、酸性電解質中での酸素還元能及び安定性がより一層優れている。 In the present invention, it is preferable that the electrochemical characteristics of the electrode using the carbonitride are as follows. This rule is for evaluating the oxygen reduction current per unit amount of the catalyst. If this value is equal to or greater than a predetermined value, the oxygen reduction current is sufficient. That is, an electrode having the following electrochemical characteristics using the titanium carbonitride powder of the present invention is further excellent in oxygen reducing ability and stability in an acidic electrolyte.
上記電極の電気化学的特性として、30℃の0.1mol/L硫酸水溶液中で、走査速度5mV/sで電位走査したとき、可逆水素電極電位基準で0.4Vにおいて測定される酸素雰囲気での電流値をIO2とし、窒素雰囲気での電流値をIN2としたとき、R=(IO2−IN2)/IN2で表される値が0.5以上となることが好ましい。 As an electrochemical characteristic of the above electrode, in an 0.1 mol / L sulfuric acid aqueous solution at 30 ° C., when an electric potential scan was performed at a scanning speed of 5 mV / s, the current value and I O2, when the current value in a nitrogen atmosphere was I N2, it is preferable that the value represented by R = (I O2 -I N2) / I N2 is 0.5 or more.
ここで、本発明において、R値を0.5以上に限定した理由について説明する。 Here, the reason why the R value is limited to 0.5 or more in the present invention will be described.
不活性で反応物のない状態で電位走査を行った場合でも、電極触媒と電解質の界面に電気二重層が生じるため、電位を走査すると電流が流れる。これはいわゆるコンデンサの充放電電流に相当する。従って、酸素還元電流(酸素の還元反応に伴う電流)を評価する際には、このコンデンサの充放電電流分を除く必要がある。そこで、不活性な状態として窒素雰囲気で電解電流IN2を測定し、これを酸素雰囲気での電流IO2から差引くことで、正味の酸素還元電流(IO2−IN2)を求める。次に、得られた酸素還元電流を触媒単位量当りの値に変換する必要がある。ここで、実際に電極触媒として作用しているのは電極表面であるので、触媒の絶対量でなく、反応面積で規格化する必要がある。しかし、気相法で求められる吸着面積は必ずしも電解質と接している電気化学的面積とは一致しない。そこで、上記した電気二重層の充放電電流(IN2)が電極の電気化学的な反応面積に比例することを利用し、正味の酸素還元電流をIN2で割ることによって、電極の実表面積あたりの触媒能の指標とすることができる。このようにすると、触媒が粉体であっても、窒素雰囲気と酸素雰囲気で電流を測定することで、容易に触媒能を評価できる。 Even when the potential scan is performed in an inert and reaction-free state, an electric double layer is generated at the interface between the electrode catalyst and the electrolyte, so that a current flows when the potential is scanned. This corresponds to a so-called charging / discharging current of the capacitor. Therefore, when evaluating the oxygen reduction current (current associated with the oxygen reduction reaction), it is necessary to exclude the charge / discharge current of this capacitor. Therefore, the electrolysis current I N2 is measured in a nitrogen atmosphere as an inactive state, and this is subtracted from the current I O2 in the oxygen atmosphere, thereby obtaining a net oxygen reduction current (I O2 −I N2 ). Next, it is necessary to convert the obtained oxygen reduction current into a value per unit amount of catalyst. Here, since it is the electrode surface that actually acts as an electrode catalyst, it is necessary to normalize the reaction area rather than the absolute amount of the catalyst. However, the adsorption area required by the gas phase method does not necessarily match the electrochemical area in contact with the electrolyte. Therefore, by utilizing the fact that the charge / discharge current (I N2 ) of the electric double layer is proportional to the electrochemical reaction area of the electrode, and dividing the net oxygen reduction current by I N2 , It can be used as an index of the catalytic ability. In this way, even if the catalyst is a powder, the catalytic ability can be easily evaluated by measuring the current in a nitrogen atmosphere and an oxygen atmosphere.
ここで、0.4Vにおける電流値を採用する理由は、実際の燃料電池では0.4Vより低い電位では空気極として使用しないため、0.4V以上の電位で、ある程度の酸素還元触媒能がないと、電極として実用的でないからである。 Here, the reason why the current value at 0.4 V is adopted is that an actual fuel cell is not used as an air electrode at a potential lower than 0.4 V, and therefore there is no oxygen reduction catalytic ability at a potential of 0.4 V or higher. This is because it is not practical as an electrode.
R値が大きいほど、単位電極表面積あたりの酸素還元電流が大きく、触媒能が高いことになる。R=0.5とは、酸素還元電流が二重層の充放電電流の1/2以上であることを示す。Rが0.5未満であると触媒能がなく、酸素還元電極として実用に適さないからである。 The larger the R value, the larger the oxygen reduction current per unit electrode surface area and the higher the catalytic ability. R = 0.5 indicates that the oxygen reduction current is ½ or more of the charge / discharge current of the double layer. This is because if R is less than 0.5, there is no catalytic ability and it is not suitable for practical use as an oxygen reduction electrode.
ところで、触媒能を評価する方法としては、所定の電位における還元電流値を指標とする上記方法の他に酸素還元電流が流れ始める時の電位(酸素還元電流開始電位)の大きさを指標とする方法がある。 By the way, as a method for evaluating catalytic ability, in addition to the above method using the reduction current value at a predetermined potential as an index, the magnitude of the potential (oxygen reduction current start potential) when the oxygen reduction current starts to flow is used as an index. There is a way.
酸素還元電流がより高電位から流れ始める程、反応の活性化エネルギーが小さい可能性があり、この場合は触媒の表面積を増大させるという工学的な改良によって還元電流値を増加させることができる。酸素還元電流開始電位は、可逆水素電極基準で0.5V以上であることが実用上から好ましい。固体高分子形燃料電池用酸素還元電極において、対極に白金箔を用い、30℃の0.1mol/L硫酸水溶液中で、走査速度5mV/sで電位走査したとき、酸素還元電流が流れ始める時の両電極間の電位が前記可逆水素電極電位基準で0.5V以上が実用上から好ましいからである。 As the oxygen reduction current starts to flow from a higher potential, the activation energy of the reaction may be smaller, and in this case, the reduction current value can be increased by engineering improvement that increases the surface area of the catalyst. In practice, the oxygen reduction current starting potential is preferably 0.5 V or more based on the reversible hydrogen electrode. In an oxygen reduction electrode for a polymer electrolyte fuel cell, when a platinum foil is used as a counter electrode and an oxygen reduction current starts to flow when a potential scan is performed at a scanning speed of 5 mV / s in a 0.1 mol / L sulfuric acid aqueous solution at 30 ° C. This is because the potential between the two electrodes is preferably 0.5 V or more on the basis of the reversible hydrogen electrode potential.
上記したR値による酸素還元電流値と、酸素還元開始電位のいずれか又は双方を触媒能を評価する指標として採用することが好ましい。 It is preferable to employ either or both of the oxygen reduction current value based on the R value and the oxygen reduction starting potential as an index for evaluating catalytic ability.
次に本発明に係わる固体高分子形燃料電池用酸素極触媒、固体高分子形燃料電池用酸素還元電極、及びその製造方法に関する実施例を説明するが、これらに本発明は限定されるものではないことは勿論である。 Next, examples relating to an oxygen electrode catalyst for a polymer electrolyte fuel cell, an oxygen reduction electrode for a polymer electrolyte fuel cell, and a method for producing the same according to the present invention will be described, but the present invention is not limited thereto. Of course not.
本発明の実施例1〜9では、炭窒化粉末の作製について説明する。 In Examples 1 to 9 of the present invention, preparation of carbonitrided powder will be described.
(実施例1)
平均粒径が0.5μmの酸化チタンとアセチレンブラックを炭窒化チタン粉末の窒素と炭素の比が72:28になるように調合した後、攪拌羽根が高速で回転するヘンシェルミキサーで混合し、これにエチルアルコールを加えて1〜2mmの顆粒状にした。この顆粒状の混合粉末を回転式の黒鉛管炉を用いて1600℃に保持された窒素雰囲気中を2回通過させて第一および第二の加熱処理を施した後、ジェットミルで粉砕し炭窒化チタン粉末を得た。
Example 1
After mixing titanium oxide with an average particle size of 0.5 μm and acetylene black so that the ratio of nitrogen to carbon in the titanium carbonitride powder is 72:28, this is mixed with a Henschel mixer whose stirring blades rotate at high speed. Ethyl alcohol was added to 1 to 2 mm granules. The granular mixed powder was passed through a nitrogen atmosphere maintained at 1600 ° C. twice using a rotary graphite tube furnace and subjected to first and second heat treatments. A titanium nitride powder was obtained.
得られた炭窒化チタン粉末の窒素および炭素はLECO社の測定装置(窒素量はTC600型、炭素量はWR112型)を用いて、遊離炭素は強酸で溶解されない残分をLECO社の測定装置を用いて、結晶系および格子定数は理学電機株式会社のガイガーフレックスを用いて、比表面積をユアサアイオニクス株式会社製MONOSOBを用いてそれぞれ測定した。その結果は、下記表1の実施例1に示す通り、窒素量が15.5質量%、炭素量が6.0質量%、遊離炭素量が1.9質量%、結晶系が立方晶、格子定数が4.260Å、比表面積が3.29m2/gであった。 Nitrogen and carbon of the obtained titanium carbonitride powder are measured by LECO measuring device (nitrogen amount is TC600 type, carbon amount is WR112 type), and free carbon is not dissolved by strong acid. The crystal system and the lattice constant were measured using Geiger Flex manufactured by Rigaku Corporation, and the specific surface area was measured using MONOSOB manufactured by Yuasa Ionics Co., Ltd. As a result, as shown in Example 1 of Table 1 below, the amount of nitrogen was 15.5% by mass, the amount of carbon was 6.0% by mass, the amount of free carbon was 1.9% by mass, the crystal system was cubic, the lattice The constant was 4.260 Å and the specific surface area was 3.29 m 2 / g.
(実施例2)
粒状の水素化チタンとアセチレンブラックを炭窒化チタン粉末の窒素と炭素の比が39:61になるように調合した後、ボールミルで混合した。混合粉末を黒鉛製のトレーに充填し、トンネル炉を用いて1400℃の窒素雰囲気中を通過させて第一の加熱処理を施し、その熱処理物をボールミルで粉砕した。
(Example 2)
Granular titanium hydride and acetylene black were mixed so that the ratio of nitrogen to carbon in the titanium carbonitride powder was 39:61, and then mixed in a ball mill. The mixed powder was filled in a graphite tray, passed through a nitrogen atmosphere at 1400 ° C. using a tunnel furnace, subjected to a first heat treatment, and the heat-treated product was pulverized with a ball mill.
粉砕された粉末を黒鉛製のトレーに充填し、トンネル炉を用いて1500℃の窒素雰囲気中を通過させて第二の加熱処理を施して炭窒化チタン粉末を得た。得られた炭窒化チタン粉末の窒素、炭素、および遊離炭素を実施例1と同様に測定した。その結果は、下記表1の実施例2に示す通り、窒素量が8.8質量%、炭素量が13.9質量%、遊離炭素量が2.8質量%、結晶系が立方晶、格子定数が4.290Å、比表面積が2.68m2/gであった。 The pulverized powder was filled in a graphite tray, passed through a nitrogen atmosphere at 1500 ° C. using a tunnel furnace, and subjected to a second heat treatment to obtain a titanium carbonitride powder. Nitrogen, carbon, and free carbon of the obtained titanium carbonitride powder were measured in the same manner as in Example 1. As a result, as shown in Example 2 in Table 1 below, the amount of nitrogen was 8.8% by mass, the amount of carbon was 13.9% by mass, the amount of free carbon was 2.8% by mass, the crystal system was cubic, the lattice The constant was 4.290 Å and the specific surface area was 2.68 m 2 / g.
(実施例3)
金属チタン粉末とアセチレンブラックを炭窒化チタン粉末の窒素と炭素の比が28:72になるように調合した後、ボールミルで混合した。混合粉末を黒鉛製のトレーに充填し、トンネル炉を用いて1600℃の窒素雰囲気中を通過させて第一の加熱処理を施し、その熱処理物をボールミルで粉砕した。
(Example 3)
Metal titanium powder and acetylene black were prepared so that the ratio of nitrogen to carbon in the titanium carbonitride powder was 28:72, and then mixed by a ball mill. The mixed powder was filled in a graphite tray, passed through a nitrogen atmosphere at 1600 ° C. using a tunnel furnace, subjected to a first heat treatment, and the heat-treated product was pulverized with a ball mill.
粉砕された粉末を黒鉛製のトレーに充填し、トンネル炉を用いて1200℃の窒素雰囲気中を通過させて第二の加熱処理を施して炭窒化チタン粉末を得た。 The pulverized powder was filled in a graphite tray, passed through a nitrogen atmosphere at 1200 ° C. using a tunnel furnace, and subjected to a second heat treatment to obtain a titanium carbonitride powder.
得られた炭窒化チタン粉末の窒素、炭素、および遊離炭素を実施例1と同様に測定した。その結果は、下記表1の実施例3に示す通り、窒素量が5.4質量%、炭素量が14.1質量%、遊離炭素量が0.10質量%、結晶系が立方晶、格子定数が4.304Å、比表面積が1.14m2/gであった。 Nitrogen, carbon, and free carbon of the obtained titanium carbonitride powder were measured in the same manner as in Example 1. As a result, as shown in Example 3 in Table 1 below, the amount of nitrogen was 5.4% by mass, the amount of carbon was 14.1% by mass, the amount of free carbon was 0.10% by mass, the crystal system was cubic, and the lattice The constant was 4.304 Å and the specific surface area was 1.14 m 2 / g.
(実施例4〜9)
上記実施例1〜3と同様にして、目的とする窒素、炭素、遊離炭素を含む炭窒化チタン粉末が得られるように、チタン原料とアセチレンブラックの調合割合、熱処理温度、熱処理の雰囲気を変えて下記表1に示す実施例4〜9の炭窒化チタン粉末を作製した。
(Examples 4 to 9)
In the same manner as in Examples 1 to 3, the mixing ratio of the titanium raw material and acetylene black, the heat treatment temperature, and the heat treatment atmosphere were changed so that the target titanium carbonitride powder containing nitrogen, carbon, and free carbon was obtained. Titanium carbonitride powders of Examples 4 to 9 shown in Table 1 below were produced.
下記表1の炭窒化チタン粉末の比表面積は1.1〜8.1m2/gの範囲で得られた。実施例1〜9の炭窒化チタン粉末をX線回折で調べたところ、何れも立方晶の炭窒化チタン粉末で、その一例として、実施例7による粉末のX線回折の結果を図に示す。 The specific surface area of the titanium carbonitride powder shown in Table 1 below was obtained in the range of 1.1 to 8.1 m 2 / g. When the titanium carbonitride powders of Examples 1 to 9 were examined by X-ray diffraction, all of them were cubic titanium carbonitride powders. As an example, the results of X-ray diffraction of the powders of Example 7 are shown in the figure.
また、目標とする炭窒化チタン粉末の特性に対して、窒素が高く炭素が低い場合を比較例1に、窒素が高く遊離炭素が高い場合を比較例2に、窒素が低く遊離炭素が低い場合を比較例3に、窒素が低く炭素が高い場合を比較例4に、炭素が高く遊離炭素が高い場合を比較例5として下記表1に示す。
次に、複合炭窒化チタン粉末の作製について説明する。 Next, preparation of composite titanium carbonitride powder will be described.
上記本発明の実施例7で得られた炭窒化チタン粉末の条件で、炭窒化チタンに対し、ジルコニウム、ハフニウム、バナジウム、ニオブ、タンタル、クロム、モリブデン、タングステンのうちの少なくとも一種の元素が0.1〜20質量%になるように前記元素の酸化物粉末、金属粉末、炭化物粉末のうちの少なくとも一種の元素をアセチレンブラックとの混合の際に添加し、作製した複合炭窒化チタン粉末を下記表2に示す。上記の添加物による複合化の触媒活性が期待できる組み合わせは数多く考えられ、これらに本発明は限定されるものではない。
次に、炭窒化チタン粉末の特性の実施例1〜9および複合炭窒化チタン粉末の実施例10〜19と比較例1〜5について酸素極電極を作製して酸素還元電流を測定した。なお、上記電解において、アノードとなる対極は何であってもよく、例えば、カーボン、Pt等を用いることができるが、Ptは微量に溶解することもあるので、カーボンが好ましい。 Next, oxygen electrode electrodes were prepared for Examples 1 to 9 of the characteristics of the titanium carbonitride powder and Examples 10 to 19 and Comparative Examples 1 to 5 of the composite titanium carbonitride powder, and the oxygen reduction current was measured. In the above electrolysis, any anode may be used as the counter electrode. For example, carbon, Pt, or the like can be used. However, carbon is preferable because Pt may be dissolved in a minute amount.
次に電極の製造について説明する。 Next, manufacture of an electrode is demonstrated.
上記の酸素還元電極は、例えば次のようにして製造することができる。まず、上記した炭窒化チタン粉末を、例えば酸化タングステン、酸化イリジウム等、炭素等の導電性物質の粉末と混合し、公知の結着剤と混合してペーストとし、このペーストを担体表面に塗布、乾燥させて電極を製造する。炭窒化チタン粉末および複合炭窒化チタン粉末触媒に対しては導電性粉末としてカーボンブラックを用いるのが好ましく、炭窒化チタン粉末および複合炭窒化チタン粉末は微粒子程好ましく、その比表面積は作製条件に依存し1.1〜8.1m2/gの範囲のものが得られ、微細な炭窒化チタン粉末ほど触媒量が少量でも触媒能を発揮できるので好ましい。 Said oxygen reduction electrode can be manufactured as follows, for example. First, the above-described titanium carbonitride powder is mixed with a powder of a conductive substance such as tungsten oxide, iridium oxide, etc., and mixed with a known binder to form a paste, and this paste is applied to the surface of the carrier. An electrode is manufactured by drying. For the titanium carbonitride powder and composite titanium carbonitride powder catalyst, it is preferable to use carbon black as the conductive powder. The titanium carbonitride powder and composite titanium carbonitride powder are more preferable for fine particles, and the specific surface area depends on the preparation conditions. In the range of 1.1 to 8.1 m 2 / g, a fine titanium carbonitride powder is preferable because the catalytic ability can be exhibited even with a small amount of catalyst.
以下の説明及び図及び表に用いる電位は可逆水素電極電位基準とし、これをRHEと表示した。また直径5.2mmの円柱状グラッシーカーボン製の炭素系基体にナフィオンをコーティングした比較電極をGCと表示した。 The potentials used in the following description, figures, and tables were based on the reversible hydrogen electrode potential reference, and this was indicated as RHE. A reference electrode obtained by coating Nafion on a carbon-based substrate made of cylindrical glassy carbon having a diameter of 5.2 mm was designated as GC.
本発明の炭窒化チタン粉末を酸素還元電極に用いると、酸性電解質中で使用しても0.8V以下であれば、電極が溶解せず安定であった。又、本発明者らの研究により、酸性電解質中で安定な電極は触媒活性(酸素還元触媒能)を持つことが判明した。以下に、炭窒化チタン粉末を固体高分子形燃料電池用触媒に用いることの優位性を説明する。 When the titanium carbonitride powder of the present invention was used for an oxygen reduction electrode, the electrode did not dissolve and was stable if it was 0.8 V or less even when used in an acidic electrolyte. Further, the inventors' research has revealed that a stable electrode in an acidic electrolyte has catalytic activity (oxygen reduction catalytic ability). Below, the advantage of using titanium carbonitride powder as a catalyst for a polymer electrolyte fuel cell will be described.
まず、実施例5の炭窒化チタン粉末を用いて、電極の作製について説明する。電極は直径5.2mmの円柱状グラッシーカーボンを基材とし、その底面に触媒を塗布、ナフィオンをコーティングし作成した。触媒塗布の際には、等量で塗布できるように水5ml中に0.1g秤量した触媒を混合した。その後、超音波で攪拌・懸濁して作製した溶液から30μl塗布し、触媒が均一に分散するようにした。 First, production of an electrode will be described using the titanium carbonitride powder of Example 5. The electrode was prepared by using cylindrical glassy carbon having a diameter of 5.2 mm as a base material, applying a catalyst to the bottom surface, and coating Nafion. When applying the catalyst, 0.1 g of the catalyst was mixed in 5 ml of water so that it could be applied in an equal amount. Thereafter, 30 μl of the solution prepared by stirring and suspending with ultrasonic waves was applied to uniformly disperse the catalyst.
0.1mol/dm3の硫酸溶液に触媒を塗布したグラッシーカーボン電極を浸漬し、30℃、大気圧で実験を行った。ガス雰囲気は窒素及び酸素とした。参照電極として同濃度硫酸溶液中での可逆水素電極を用いた。電流密度の表示は幾何面積当たりとした。 A glassy carbon electrode coated with a catalyst was immersed in a 0.1 mol / dm 3 sulfuric acid solution, and an experiment was conducted at 30 ° C. and atmospheric pressure. The gas atmosphere was nitrogen and oxygen. A reversible hydrogen electrode in the same concentration sulfuric acid solution was used as a reference electrode. The display of current density was per geometric area.
上記電極をカソードとして用い、対極に白金箔を用い、窒素雰囲気下、30℃の0.1mol/L硫酸水溶液を電解液として電解セルを用意した。参照電極としては、硫酸濃度が上記と同一の可逆水素電極を用いた。この電解セルを用い、電位走査速度50mV/sでサイクリックボルタモグラム(CV)を測定した。電位範囲は0.05〜0.8Vとした。このことを、酸性電解質中での電極のサイクリックボルタモグラム(CV)を示す図2を用いて説明する。 An electrolytic cell was prepared using the above electrode as a cathode, a platinum foil as a counter electrode, and a 0.1 mol / L sulfuric acid aqueous solution at 30 ° C. as an electrolytic solution in a nitrogen atmosphere. As the reference electrode, a reversible hydrogen electrode having the same sulfuric acid concentration as described above was used. Using this electrolytic cell, a cyclic voltammogram (CV) was measured at a potential scanning speed of 50 mV / s. The potential range was 0.05 to 0.8V. This will be described with reference to FIG. 2 showing a cyclic voltammogram (CV) of an electrode in an acidic electrolyte.
図2は本発明の実施例5の炭窒化チタン粉末を用いた本発明に係る電極のCVを示す図である。図2を参照すると、本発明に係る電極の場合、電位走査を数10回繰り返しても、CV曲線の形状がほとんど変化せず、酸性電解質中で炭窒化物が安定であることが分かる。 FIG. 2 is a diagram showing the CV of the electrode according to the present invention using the titanium carbonitride powder of Example 5 of the present invention. Referring to FIG. 2, in the case of the electrode according to the present invention, it can be seen that the shape of the CV curve hardly changes even when the potential scan is repeated several tens of times, and the carbonitride is stable in the acidic electrolyte.
酸素還元電流は前記電解セルを用い、30℃の0.1mol/L硫酸水溶液中で、走査速度5mV/sで電位走査したとき、可逆水素電極電位基準で0.4Vにおいて測定される酸素雰囲気での電流値IO2、窒素雰囲気での電流値IN2を測定した。次に、上記数式 R=(IO2−IN2)/IN2 で表される値を求めた。還元電流が高いほど、触媒能が高い。 The oxygen reduction current was measured in an oxygen atmosphere measured at 0.4 V on the basis of the reversible hydrogen electrode potential when the potential scan was performed at a scanning speed of 5 mV / s in a 0.1 mol / L sulfuric acid aqueous solution at 30 ° C. using the electrolytic cell. Current value I O2 and current value I N2 in a nitrogen atmosphere were measured. Next, to determine the value represented by the equation R = (I O2 -I N2) / I N2. The higher the reduction current, the higher the catalytic ability.
図3及び図4は、実施例7の炭窒化チタン粉末を用いた電極の還元電流の測定結果及び上記指標Rの計算結果を示す図である。図3より、窒素雰囲気でわずかに還元電流が流れ、酸素雰囲気では還元電流が大きいことが分かる。又、図4より、0.55V以下の電位で上記指標Rが0.5以上となっていることが分かる。 3 and 4 are diagrams showing measurement results of the reduction current of the electrode using the titanium carbonitride powder of Example 7 and calculation results of the index R. FIG. FIG. 3 shows that a slight reduction current flows in the nitrogen atmosphere and that the reduction current is large in the oxygen atmosphere. Further, FIG. 4 shows that the index R is 0.5 or more at a potential of 0.55 V or less.
実施例5の炭窒化チタン粉末と同様の方法で上記表1及び上記表2の炭窒化チタン及び複合炭窒化チタン粉から電極を作製して、還元電流及び酸素還元開始電位の測定を行い下記表3の結果を得た。
実施例1及び6、比較例1及び4に対して還元電流から求めるR指標を図5に示す。 FIG. 5 shows the R index obtained from the reduction current for Examples 1 and 6 and Comparative Examples 1 and 4.
次に、酸素還元開始電位の測定について説明する。上記電解セルを用い、上記還元電流の測定時におけるIO2が流れ始めた時の電位として、IO2=−1μA/cm2となる電位を酸素還元開始電位とし、可逆水素電極電位基準で求めた。酸素還元開始電位が高いほど、触媒能が高い。実施例7の炭窒化チタン粉末を用いた電極の酸素還元開始電位は0.66Vであった。 Next, measurement of the oxygen reduction start potential will be described. Using the above electrolytic cell, the potential at which I O2 started flowing at the time of measurement of the reduction current was determined on the basis of the reversible hydrogen electrode potential, with the potential of I O2 = -1 μA / cm 2 being the oxygen reduction start potential. . The higher the oxygen reduction starting potential, the higher the catalytic ability. The oxygen reduction starting potential of the electrode using the titanium carbonitride powder of Example 7 was 0.66V.
窒素を2.0〜15.5質量%、炭素を6.0〜19.0質量%および遊離炭素を0.1〜5.9質量%有する立方晶の炭窒化チタン粉末およびジルコニウム、ハフニウム、バナジウム、ニオブ、タンタル、クロム、モリブデン、タングステンのうちの少なくとも一種の元素を20質量%を上限に添加した前記元素と炭窒化チタンの複合炭窒化チタン粉末を触媒として、導電性のカーボンブラック粉末と混合し、結着剤テフロンと混合してペースト状とし、前記ペーストを担体(カーボンペーパー)表面に塗布し乾燥して触媒と導電性物質の塗布膜を炭素系基体上に形成し、上記の塗布膜上に高分子電解質のナフィオンでコーティングした固体高分子形燃料電池用酸素極電極を用いて、30℃の0.1mol/L硫酸水溶液中で、走査速度5mV/sで電位走査したとき、可逆水素電極電位基準で0.4Vにおいて測定される酸素雰囲気での電流値をIO2とし、窒素雰囲気での電流値をIN2としたとき、R=(IO2−IN2)/IN2で表される値が0.5以上の性能および酸素還元電流が流れ始める時の電位が可逆水素電極電位基準で0.5V以上の性能を有することが明らかになった。 Cubic titanium carbonitride powder having 2.0 to 15.5% by mass of nitrogen, 6.0 to 19.0% by mass of carbon and 0.1 to 5.9% by mass of free carbon, and zirconium, hafnium, vanadium , Niobium, Tantalum, Chromium, Molybdenum, Tungsten and mixed with conductive carbon black powder using titanium carbonitride powder composed of titanium carbonitride and the above-mentioned element added with up to 20% by mass of at least one element The paste is mixed with a binder Teflon to form a paste, and the paste is applied to the surface of a carrier (carbon paper) and dried to form a coating film of a catalyst and a conductive material on the carbon-based substrate. Using an oxygen electrode for a polymer electrolyte fuel cell coated with Nafion, a polymer electrolyte, in a 0.1 mol / L sulfuric acid aqueous solution at 30 ° C., a scanning speed of 5 When the potential scan at V / s, when the current value in an oxygen atmosphere to be measured at 0.4V with a reversible hydrogen electrode potential reference and I O2, a current value in a nitrogen atmosphere was I N2, R = (I O2- I N2 ) / I N2 has a value of 0.5 or more and a potential when the oxygen reduction current starts to flow is 0.5 V or more on the basis of the reversible hydrogen electrode potential. It was.
図6は実施例7の炭窒化チタン粉末を用いて、酸素雰囲気で30℃の0.1mol/L硫酸水溶液中および0.1mol/L硫酸+0.1mol/Lメタノール水溶液中で、走査速度5mV/sで電位走査したときのCV曲線示す図である。図6に示すように、炭窒化チタン粉末にはメタノールの分解触媒の活性は認められず、硫酸水溶液中も硫酸+メタノール水溶液中も全く同じ酸素還元電流を示した。従って、炭窒化チタン粉末は燃料極からクロスオーバーする燃料の反応を触媒する作用を持たないことから、燃料のクロスオーバーによる燃料電池の効率低下を起こさない固体高分子形燃料電池用酸素極触媒であることが判明した。 FIG. 6 shows a case where the titanium carbonitride powder of Example 7 was used, in a 0.1 mol / L sulfuric acid aqueous solution at 30 ° C. in an oxygen atmosphere and in a 0.1 mol / L sulfuric acid + 0.1 mol / L methanol aqueous solution, at a scanning speed of 5 mV / It is a figure which shows the CV curve when the electric potential scan is carried out by s. As shown in FIG. 6, the activity of methanol decomposition catalyst was not recognized in the titanium carbonitride powder, and the same oxygen reduction current was exhibited both in the sulfuric acid aqueous solution and in the sulfuric acid + methanol aqueous solution. Therefore, the titanium carbonitride powder does not have the action of catalyzing the reaction of the fuel that crosses over from the fuel electrode. Therefore, the titanium carbonitride powder is an oxygen electrode catalyst for a polymer electrolyte fuel cell that does not cause a decrease in fuel cell efficiency due to fuel crossover It turned out to be.
さらに、本発明の酸素還元電極は、水、無機物質、有機物質の電気分解、燃料電池等の酸性電解質を用いる電気化学システムのカソード用電極として好適に使用できる。 Furthermore, the oxygen reduction electrode of the present invention can be suitably used as a cathode electrode for an electrochemical system using an acidic electrolyte such as water, an inorganic substance, an organic substance, or a fuel cell.
また、本発明の酸素還元電極は、りん酸形燃料電池や高分子電解質形燃料電池等、酸性電解質を用いる際の酸化剤極として適する。従って、本発明は上記の実施例によって限定されるものではない。 The oxygen reduction electrode of the present invention is suitable as an oxidizer electrode when an acidic electrolyte is used, such as a phosphoric acid fuel cell or a polymer electrolyte fuel cell. Accordingly, the present invention is not limited to the above-described embodiments.
以上の説明の通り、本発明による酸素極触媒およびそれを用いた酸素還元電極は、酸性電解質中において酸素を還元する優れた固体高分子形燃料電池用の酸素極触媒および酸素還元電極に最適である。 As described above, the oxygen electrode catalyst and the oxygen reduction electrode using the same according to the present invention are most suitable as an oxygen electrode catalyst and an oxygen reduction electrode for excellent polymer electrolyte fuel cells that reduce oxygen in an acidic electrolyte. is there.
Claims (9)
前記の混合粉末の窒素量が15.5〜2.0質量%になるように1400〜1800℃の窒素又は窒素と水素の混合雰囲気中で加熱処理を施す第一の加熱処理工程と、
前記第一の加熱処理が施された炭窒化チタン粉末を1200〜1600℃の前記それぞれの雰囲気又は真空中でさらに加熱処理を施す第二の加熱処理工程と、
前記第一の加熱処理が施された炭窒化チタン粉末、若しくは第二の加熱処理が施された炭窒化チタン粉末をボールミル又は衝撃粉砕機又はジェットミルで粉砕する粉砕工程とを備えていることを特徴とする固体高分子形燃料電池用酸素極触媒の製造方法。 It is a manufacturing method of the titanium carbonitride powder used for the oxygen electrode catalyst for polymer electrolyte fuel cells of Claim 1, Comprising: The carbon amount of the said titanium carbonitride powder is set to 6.0-19.0 mass%. A mixing step of mixing carbon black powder with at least one of titanium oxide, titanium hydride, and titanium metal as a titanium raw material;
A first heat treatment step in which heat treatment is performed in a mixed atmosphere of nitrogen or nitrogen and hydrogen at 1400 to 1800 ° C. so that the amount of nitrogen in the mixed powder is 15.5 to 2.0% by mass;
A second heat treatment step of further heat-treating the titanium carbonitride powder subjected to the first heat treatment in the respective atmosphere or vacuum at 1200 to 1600 ° C .;
A pulverizing step of pulverizing the titanium carbonitride powder subjected to the first heat treatment or the titanium carbonitride powder subjected to the second heat treatment with a ball mill, an impact pulverizer, or a jet mill. A method for producing an oxygen electrode catalyst for a polymer electrolyte fuel cell.
前記複合炭窒化チタン粉末の窒素量が15.5〜2.0質量%になるように1400〜1800℃の窒素又は窒素と水素の混合雰囲気中で前記混合粉末に加熱処理を施す第一の加熱処理工程と、
前記第一の加熱処理が施された複合炭窒化チタン粉末を1200〜1600℃の前記のそれぞれの雰囲気又は真空中でさらに熱処理を施す第二の加熱処理工程と、
前記第一の加熱処理が施された複合炭窒化チタン粉末、若しくは第二の加熱処理が施された複合炭窒化チタン粉末をボールミル、衝撃粉砕機、及びジェットミルの内の少なくとも一種の粉砕手段で粉砕する粉砕工程とを備えてなることを特徴とする固体高分子形燃料電池用酸素極触媒の製造方法。 A method for producing a composite titanium carbonitride powder used for an oxygen electrode catalyst for a polymer electrolyte fuel cell, comprising at least one of titanium oxide, titanium hydride, and titanium metal as a titanium raw material, zirconium, hafnium, vanadium, Oxide powder or metal powder or carbide powder in which at least one element of niobium, tantalum, chromium, molybdenum, and tungsten is 0.1 to 20% by mass, and 6.0 to 19.0% by mass Mixing the carbon black powder so as to contain carbon and 0.1-5.9 mass% free carbon;
1st heating which heat-processes the said mixed powder in 1400-1800 degreeC nitrogen or the mixed atmosphere of nitrogen and hydrogen so that the nitrogen amount of the said composite titanium carbonitride powder may be 15.5-2.0 mass% Processing steps;
A second heat treatment step of further subjecting the composite titanium carbonitride powder subjected to the first heat treatment to heat treatment in the respective atmosphere or vacuum at 1200 to 1600 ° C .;
The composite titanium carbonitride powder subjected to the first heat treatment or the composite titanium carbonitride powder subjected to the second heat treatment is subjected to at least one kind of pulverization means among a ball mill, an impact pulverizer, and a jet mill. A method for producing an oxygen electrode catalyst for a polymer electrolyte fuel cell, comprising a pulverizing step.
A method for producing an oxygen reducing electrode for a polymer electrolyte fuel cell according to claim 5, wherein the catalyst according to claim 1 or 3 and a conductive carbon black powder are mixed, A step of forming a coating film composed of a catalyst and a conductive material on a carbon-based substrate by coating the mixed powder with a binder Teflon to form a paste, applying the paste to a glassy carbon substrate surface, and drying the coating; And a step of coating the membrane with Nafion (registered trademark) as a polymer electrolyte. A method for producing an oxygen reduction electrode for a polymer electrolyte fuel cell, comprising:
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